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Bone-forming cells in clinical conditions
... Bone contains over 98% of total body calcium. Bone metabolism is regulated by the functions of osteoblasts and osteoclasts, which are major cells in bone tissue [21][22][23]. Bone formation in adult cancellous bone takes place only at sites of bone remodeling. During this process, old bone is replaced with new at discrete sites by the basic multicellular unit (BMU), which comprises team of osteoclasts and osteoblasts. ...
... Remodeling of cancellous bone begins with the retraction of lining cells that cover the bone surface [21]. Osteoclasts, which develop from hematopoietic progenitors, are recruited to the site and excavate the calcified matrix. ...
Zinc is essential for the growth of the human and animals. Bone growth retardation is a common finding in various conditions associated with zinc deficiency, suggesting a physiologic role of zinc in the growth and mineralization of bone tissues. Bone zinc content is decreased by development with aging, skeletal unloading, and postmenopausal conditions. Zinc deficiency may play a pathophysiologic role in the deteriodation of bone metabolism. Zinc has been demonstrated to have a stimulatory effect on osteoblastic bone formation and mineralization; the metal directly activates aminoacyl-tRNA synthetase, a rate-limiting enzyme at translational process of protein synthesis, in osteoblastic cells, and it stimulates cellular protein synthesis. Zinc has been shown to stimulate gene expression of the transcription facter Runx2 that is related to differentiation into osteoblastic cells. Moreover, zinc inhibits osteoclastic bone resorption due to inhibiting osteoclast-like cell formation from bone marrow cells and stimulating apoptotic cell death of mature osteoclasts. Zinc has a suppressive effect on the receptor activator of nuclear factor(NF)-κB ligand(RANKL)-induced osteoclastogenesis, indicating that the metal inhibits RANKL signaling in pre-osteoclasts. Zinc may act on the process of bone resorbing factors-induced protein kinase C activation, which is involved in Ca²⁺ signaling in osteoclastic cells. Zinc plays a role in the preservation of bone mass. β-Alanyl-L-histidinato zinc(AHZ)is a zinc compound, in which zinc is chelated to β-alanyl-L-histidine. The stimulatory effect of AHZ on bone formation was more intensive than that of zinc sulfate. Also, zinc acexamate has a potent- anabolic effect on bone metabolism. The effect of AHZ or zinc acexamate on bone formation is equal in comparison with the effect of various bone-regulating hormones and other factors. The oral administration of AHZ or zinc acexamate has a fine restorative effect on bone loss with various pathophysiologic conditions(including aging, skeletal unloading, aluminium bone toxicity, calcium- and vitamin D-deficiency, adjuvant arthritis, estrogen deficiency, diabetes, and fracture healing). Zinc compounds may be designed as new drugs in the therapy of osteoporosis.
... Some of these osteoblasts show cytoplasmic processes towards the bone matrix and reach the osteocyte processes [46]. At this stage, the mature osteoblasts can undergo apoptosis or become osteocytes or bone lining cells [47] [48]. Interestingly, round/ ovoid structures containing dense bodies and TUNEL-positive structures have been observed inside osteoblast vacuoles . ...
... Some of these osteoblasts show cytoplasmic processes towards the bone matrix and reach the osteocyte processes [46]. At this stage, the mature osteoblasts can undergo apoptosis or become osteocytes or bone lining cells [47, 48]. Interestingly, round/ ovoid structures containing dense bodies and TUNEL-positive structures have been observed inside osteoblast vacuoles . ...
Bone tissue is continuously remodeled through the concerted actions of bone cells, which include bone resorption by osteoclasts and bone formation by osteoblasts, whereas osteocytes act as mechanosensors and orchestrators of the bone remodeling process. This process is under the control of local (e.g., growth factors and cytokines) and systemic (e.g., calcitonin and estrogens) factors that all together contribute for bone homeostasis. An imbalance between bone resorption and formation can result in bone diseases including osteoporosis. Recently, it has been recognized that, during bone remodeling, there are an intricate communication among bone cells. For instance, the coupling from bone resorption to bone formation is achieved by interaction between osteoclasts and osteoblasts. Moreover, osteocytes produce factors that influence osteoblast and osteoclast activities, whereas osteocyte apoptosis is followed by osteoclastic bone resorption. The increasing knowledge about the structure and functions of bone cells contributed to a better understanding of bone biology. It has been suggested that there is a complex communication between bone cells and other organs, indicating the dynamic nature of bone tissue. In this review, we discuss the current data about the structure and functions of bone cells and the factors that influence bone remodeling.
... Bone remodeling renews the bone matrix through a tightly regulated process starting with resorption of old bone by osteoclasts (OCs), then a " reversal phase " , followed by reconstruction of new bone by osteoblasts (OBs) [1] . It has been known for a long time that reconstruction of new bone during remodeling demands OB recruitment [1]. ...
... Bone remodeling renews the bone matrix through a tightly regulated process starting with resorption of old bone by osteoclasts (OCs), then a " reversal phase " , followed by reconstruction of new bone by osteoblasts (OBs) [1] . It has been known for a long time that reconstruction of new bone during remodeling demands OB recruitment [1]. A series of observations indicate that this recruitment is closely associated with osteoclast activity [2,3] , and is therefore likely to already occur during the resorption and reversal phase. ...
Osteoblast recruitment during bone remodeling is obligatory to re-construct the bone resorbed by the osteoclast. This recruitment is believed to be triggered by osteoclast products and is therefore likely to start early during the remodeling cycle. Several osteoclast products with osteoblast recruitment potential are already known. Here we draw the attention on the osteoblast recruitment potential of the collagen that is freshly demineralized by the osteoclast. Our evidence is based on observations on adult human cancellous bone, combined with in vitro assays. First, freshly eroded surfaces where osteoblasts have to be recruited show the presence of non-degraded demineralized collagen and close cell-collagen interactions, as revealed by electron microscopy, while surface-bound collagen strongly attracts osteoblast lineage cells in a transmembrane migration assay. Compared with other extracellular matrix molecules, collagen's potency was superior and only equaled by fibronectin. Next, the majority of the newly recruited osteoblast lineage cells positioned immediately next to the osteoclasts, exhibit uPARAP/Endo180, an endocytic collagen receptor reported to be involved in collagen internalization and cell migration in various cell types, and whose inactivation is reported to lead to lack of bone formation and skeletal deformities. In the present study, an antibody directed against this receptor inhibits collagen internalization in osteoblast lineage cells and decreases to some extent their migration to surface-bound collagen in the transmembrane migration assay. These complementary observations lead to a model where collagen demineralized by osteoclasts attracts surrounding osteoprogenitors onto eroded surfaces, and where the endocytic collagen receptor uPARAP/Endo180 contributes to this migration, probably together with other collagen receptors. This model fits recent knowledge on the position of osteoprogenitor cells immediately next to remodeling sites in adult human cancellous bone.
... The proportion of osteoblasts following each fate is not the same in all mammals and is not conserved among all taxa or all types of bone. Parfitt (1990) report that in human cancellous bone, 65% of the osteoblasts undergo apoptosis and only about 30% transform into osteocytes. Aubin and Liu (1996) give a figure of 10 –20% for the number of osteoblasts transforming into osteocytes. ...
... ). Nevertheless , during this (first) phase of intramembranous ossification, osteoblasts appear to undergo self-burial (Parfitt, 1990). ...
During osteogenesis, osteoblasts lay down osteoid and transform into osteocytes embedded in mineralized bone matrix. Despite the fact that osteocytes are the most abundant cellular component of bone, little is known about the process of osteoblast-to-osteocyte transformation. What is known is that osteoblasts undergo a number of changes during this transformation, yet retain their connections to preosteoblasts and osteocytes. This review explores the osteoblast-to-osteocyte transformation during intramembranous ossification from both morphological and molecular perspectives. We investigate how these data support five schemes that describe how an osteoblast could become entrapped in the bone matrix (in mammals) and suggest one of the five scenarios that best fits as a model. Those osteoblasts on the bone surface that are destined for burial and destined to become osteocytes slow down matrix production compared to neighbouring osteoblasts, which continue to produce bone matrix. That is, cells that continue to produce matrix actively bury cells producing less or no new bone matrix (passive burial). We summarize which morphological and molecular changes could be used as characters (or markers) to follow the transformation process. Developmental Dynamics 235:176 –190, 2006. © 2005 Wiley-Liss, Inc.
... Another more recent paper using a much higher number of cycles but with the same low strain rate reported in the first study also documented a loss of trabecular bone in the proximal tibia with loading (38). However, studies using an identical experimental protocol, but with a strain rate 10 times higher than that used in the first study, have consistently reported a robust increase in trabecular bone volume fraction, thickness, and even number (58,61,62,86,97,105). To the authors' knowledge, no studies have directly compared the influence of strain rate on the relative responses of cortical and trabecular bone. ...
... This period is 3-6 months in humans and only 6 weeks in rabbits. [16] Based on these data, in our study, recovery at the end of days 30 and 60 assessed bone healing in the rabbit tibia; at the end of this period, the animals were sacrificed. ...
Background:
Various materials and techniques have been developed to facilitate bone healing process and reduce its healing period. In recent studies, it is pointed out that, platelet-rich fibrin (PRF) which is derived autogenously from the own blood of the individuals, increase regeneration and accelerate the healing of the wound, due to the consisting various growing factors. The aim of the experimental study is to evaluate the efficiency of PRF and PRF/autogenous graft combination on bone healing in different time intervals.
Materials and methods:
A total of 24 skeletally mature New Zealand rabbits were used. Animals were divided randomly into two groups. Two bone defects with a diameter 3, 3 mm were created on the right and left tibia in all group animals. Only particulate autogeneous bone graft, only PRF, combination of PRF and autogeneous bone graft and empty bone cavity, were performed to all animals. The animals in the first experimental group were sacrificed after 30 days. The animals in the second experimental group were sacrificed after 60 days from the operation. Histomorphometrical and statistical analysis was performed. The data were analyzed using Tukey test (P < 0.05 for osteoblast number, P < 0.01 for osteoclast and new bone area values).
Results:
Histomorphometrical analyzes showed that either PRF used alone or used in conjuction with autogenous bone graft, PRF accelerated the healing of the bone defects. There were statistically significant differences in osteoblast, osteoblast and new bone area values in PRF alone and autogenous graft with PRF than the other groups.
Conclusion:
Our preliminary result demonstrated that PRF increase new bone formation and has a positive effect on early bone healing.
... Although a few reports have indicated that there is an interaction between PTH and estrogen in osteoblasts (Rao et al. 1994, Kudo et al. 1995), the mechanism has not been clearly defined. The rate of bone formation is largely determined by the number of osteoblasts (Parfitt 1990) and it was widely believed that the anabolic effect of PTH was the result of increased osteoblast differentiation (Dempster et al. 1993). We therefore examined the effects of the interaction between PTH and estrogen on osteoblast proliferation, alkaline phosphatase (ALP) activity and type-1 collagen synthesis, by using human osteoblastic SaOS-2 cells. ...
Although there is clinical evidence showing that combined therapy with parathyroid hormone (PTH) and estrogen is additively effective in increasing the bone mass of patients with osteoporosis, the mechanism of the interaction between these hormones remains unclear. The present study was performed to determine whether estrogen would affect osteoblast proliferation and function modulated by PTH in human osteoblastic SaOS-2 cells. Human PTH-(1-34) significantly inhibited [(3)H]thymidine (TdR) incorporation, which was attenuated by 24 h pretreatment with 10(-10) to 10(-7) M 17 beta-estradiol (17 beta-E(2)) in a concentration-dependent manner. PTH significantly stimulated alkaline phosphatase (ALP) activity, collagen synthesis and type-1 procollagen mRNA expression after pretreatment with 17 beta-E(2 )in these cells. Tamoxifen, an anti-estrogen, antagonized these 17 beta-E(2)-induced effects. Pretreatment with insulin-like growth factor-I (IGF-I) mimicked estrogen action, and coincubation of 3 microg/ml anti-IGF-I antibody antagonized the effects of 17 beta-E(2 )as well as those of IGF-I. In the presence of 17 beta-E(2 )pretreatment, PTH strongly stimulated IGF-binding protein (IGFBP)-5 mRNA expression in these cells, and recombinant IGFBP-5 increased type-1 procollagen mRNA expression and ALP activity. In conclusion, estrogen attenuates PTH-induced inhibition of osteoblast proliferation and PTH stimulates osteoblast function in the presence of estrogen pretreatment. IGF-I and/or IGFBP-5 seemed to be involved in the estrogen-induced modulation of PTH action on osteoblast proliferation and function.
... At the IBHS of the DECBM group, only a few areas expressed the fluorochromes, signifying that osteoblasts were scantly present and that there was low osteoblastic activity. According to the previous study by Parfitt et al., the total rate of bone formation was affected by the number of osteoblasts and the average volume of matrix secreted by the osteoblasts [42, 43].Figure 4: Fluorescence image of histological cross-section represented fluorochrome-labeled mineral deposition in defect (a), DECBM (b), HGCS with MAPCs (c), and HGCS (d). Calcein (green) and Alizarin Red (red) were administered in series. ...
Our laboratory utilized biomimicry to develop a synthetic bone scaffold based on hydroxyapatite-gelatin-calcium silicate (HGCS). Here, we evaluated the potential of HGCS scaffold in bone formation in vivo using the rat calvarial critical-sized defect (CSD). Twelve Sprague-Dawley rats were randomized to four groups: control (defect only), decellularized bone matrix (DECBM), and HGCS with and without multipotent adult progenitor cells (MAPCs). DECBM was prepared by removing all the cells using SDS and NH4OH. After 12 weeks, the CSD specimens were harvested to evaluate radiographical, histological, and histomorphometrical outcomes. The in vitro osteogenic effects of the materials were studied by focal adhesion, MTS, and alizarin red. Micro-CT analysis indicated that the DECBM and the HGCS scaffold groups developed greater radiopaque areas than the other groups. Bone regeneration, assessed using histological analysis and fluorochrome labeling, was the highest in the HGCS scaffold seeded with MAPCs. The DECBM group showed limited osteoinductivity, causing a gap between the implant and host tissue. The group grafted with HGCS+MAPCs resulting in twice as much new bone formation seems to indicate a role for effective bone regeneration. In conclusion, the novel HGCS scaffold could improve bone regeneration and is a promising carrier for stem cell-mediated bone regeneration.
... The molecular phenotype of OB cells is of clinical relevance. Osteoporosis is a disease characterized by decreased bone mass, caused by impaired bone formation due to defective osteoblastic functions [11]. ...
The phenotype of osteoblastic (OB) cells in culture is currently defined using a limited number of markers of low sensitivity and specificity. For the clinical use of human skeletal (stromal, mesenchymal) stem cells (hMSC) in therapy, there is also a need to identify a set of gene markers that predict in vivo bone forming capacity. Thus, we used RNA sequencing to examine changes in expression for a set of skeletally-related genes across 8 time points between 0-12 days of ex vivo OB differentiation of hMSC. We identified 123 genes showing significant temporal expression change. Hierarchical clustering and Pearson's correlation generated 4 groups of genes: early stage differentiation genes (peak expression: 0-24hrs, n=28) which were enriched for extracellular matrix organisation, e.g. COL1A1, LOX, SERPINH1; middle stage differentiating genes (peak expression days: 3 and 6, n=20) which were enriched for extracellular matrix/skeletal system development e.g. BMP4, CYP24A1, TGFBR2; and late stage differentiation genes (peak expression days: 9 and 12, n=27) which were enriched for bone development/osteoblast differentiation, e.g. BMP2, IGF2. In addition, we identified 13 genes with bimodal temporal expression (2 peaks of expression: day 0 and 12) including VEGFA, PDGFA and FGF2. We examined the specificity of the 123 genes' expression in skeletal tissues and thus propose a set of ex vivo differentiation-stage-specific markers (n=21). In an independent analysis, we identified a subset of genes (n=20, e.g. ELN, COL11A1, BMP4) to predict the bone forming capacity of hMSC and another set (n=20, e.g. IGF2, TGFB2, SMAD3) associated with the ex vivo phenotype of hMSC obtained from osteoporotic patients.
... Once differentiated osteoblasts have completed their boneforming function, they are entrapped in the matrix and become either osteocytes or bone lining cells. However, analysis of available data from histomorphometric examinations of human bone has revealed that 50–70% of osteoblasts at the remodeling site cannot be accounted for [15] . The " missing " osteoblasts appear to have died, possibly by apoptosis, and if apoptosis does occur in osteoblasts or their progenitors, osteoblastogenesis might be diminished [16]. ...
The purpose of the current study was to examine the effect of dexamethasone (Dex) at various concentrations on the apoptosis and mineralization of human periodontal ligament (hPDL) cells.
hPDL cells were obtained from the mid-third of premolars extracted for orthodontic reasons, and a primary culture of hPDL cells was prepared using an explant technique. Groups of cells were divided according to the concentration of Dex (0, 1, 10, 100, and 1,000 nM). A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was performed for evaluation of cellular viability, and alkaline phosphatase activity was examined for osteogenic differentiation of hPDL cells. Alizarin Red S staining was performed for observation of mineralization, and real-time polymerase chain reaction was performed for the evaluation of related genes.
Increasing the Dex concentration was found to reduce cellular viability, with an increase in alkaline phosphatase activity and mineralization. Within the range of Dex concentrations tested in this study, 100 nM of Dex was found to promote the most vigorous differentiation and mineralization of hPDL cells. Dex-induced osteogenic differentiation and mineralization was accompanied by an increase in the level of osteogenic and apoptosis-related genes and a reduction in the level of antiapoptotic genes. The decrease in hPDL cellular viability by glucocorticoid may be explained in part by the increased prevalence of cell apoptosis, as demonstrated by BAX expression and decreased expression of the antiapoptotic gene, Bcl-2.
An increase in hPDL cell differentiation rather than cellular viability at an early stage is likely to be a key factor in glucocorticoid induced mineralization. In addition, apoptosis might play an important role in Dex-induced tissue regeneration; however, further study is needed for investigation of the precise mechanism.
... MAR in antler primary osteons, shown for the first time, is high. The value of approximately 2 μm/d for early forming primary osteons is three times that of secondary osteons in humans (0.7 μm/d) [32] and twice that of trabecular bone in beagle dogs (0.9-1.3 μm/d) [33], although it is lower than the rates reported in growing small mammals (4-10 μm/d) [34]. The high MAR and the large mineralizing surface in antlers (particularly the large scaffold surface at the beginning of the infilling process) mean the mineralization of an enormous amount of bone in a short period. ...
... A previous study showed that defective bone formation during the process of bone remodeling seemed to be the principal pathophysiologi-cal mechanism responsible for age-related bone loss [15]. Bone marrow mesenchymal cells (BMSCs) in the marrow pool are the major source of osteogenitor cells that contribute to bone remodeling in adults. ...
Unlabelled:
Osteoporosis is a major health problem affecting the aging population, especially in patients 65 years of age and older. The imbalance between bone formation and bone resorption is generally accepted as the essential mechanism leading to osteoporosis. In addition to the abnormal activation of osteoclast-mediated bone resorption, the dysfunction of bone marrow stromal cells (BMSCs) in mediating bone formation has been accepted as a major contributor to the progression of senile osteoporosis.
Results:
In our study, senile osteoporotic hBMSCs displayed a decreasing capacity for proliferation and osteoblast differentiation, which was associated with the downregulation of integrin α2. Forced ectopic integrin α2 expression using a lentivirus vector reversed the dysfunction of senile osteoporotic hBMSCs. Additionally, the overexpression of integrin α2 upregulated the levels of Runx2 and Osterix. Mechanically, Western blot analyses revealed that integrin α2 phosphorylated ERK1/2 and the inactivation of ERK by PD98059 suppressed the osteoblastic differentiation of hBMSCs, suggesting that integrin α2 promotes osteoblast proliferation through the activation of ERK1/2 MAPK.
Conclusion:
Taken together, our results show that hBMSCs obtained from senile osteoporotic patients gradually lose their capability to differentiate along the osteogenic lineage and proliferate, which might be associated with the abnormal regulation of the integrin α2/ERK/Runx2 signaling pathway undergoing senile osteoporosis.
... ed in the matrix and become osteocytes or remain on the surface of the newly formed bone and become lining cells. Analysis of available data from histomorphometric examinations of human bone has revealed that 50 –70% of the osteoblasts initially present at the remodeling site cannot be accounted for after enumeration of lining cells and osteocytes. (13) Based on this evidence, we have hypothesized that the " missing " osteoblasts must have died, possibly by apoptosis. Furthermore, we have reasoned that if apoptosis does occur in osteoblasts or their progenitors, by analogy with the case of osteoclasts, the incidence of apoptosis in concert with osteoblastogenesis would determine the nu ...
Once osteoblasts have completed their bone-forming function, they are either entrapped in bone matrix and become osteocytes or remain on the surface as lining cells. Nonetheless, 50–70% of the osteoblasts initially present at the remodeling site cannot be accounted for after enumeration of lining cells and osteocytes. We hypothesized that the missing osteoblasts die by apoptosis and that growth factors and cytokines produced in the bone microenvironment influence this process. We report that murine osteoblastic MC3T3-E1 cells underwent apoptosis following removal of serum, or addition of tumor necrosis factor (TNF), as indicated by terminal deoxynucleotidyl transferase–mediated dUTP-nick end labeling and DNA fragmentation studies. Transforming growth factor-β and interleukin-6 (IL-6)–type cytokines had antiapoptotic effects because they were able to counteract the effect of serum starvation or TNF. In addition, anti-Fas antibody stimulated apoptosis of human osteoblastic MG-63 cells and IL-6–type cytokines prevented these changes. The induction of apoptosis in MG-63 cells was associated with an increase in the ratio of the proapoptotic protein bax to the antiapoptotic protein bcl-2, and oncostatin M prevented this change. Examination of undecalcified sections of murine cancellous bone revealed the presence of apoptotic cells, identified as osteoblasts by their proximity to osteoid seams and their juxtaposition to cuboidal osteoblasts. Assuming an osteoblast life span of 300 h and a prevalence of apoptosis of 0.6%, we calculated that the fraction that undergo this process in vivo can indeed account for the missing osteoblasts. These findings establish that osteoblasts undergo apoptosis and strongly suggest that the process can be modulated by growth factors and cytokines produced in the bone microenvironment.
... Besides the calcium and phosphorus balances in the serum and the urine, we also included two sub-compartments corresponding to the parathyroid glands and bone (bone forming osteoblasts and bone degrading osteoclasts). The rates of growth and degradation as well as the functional status of these compartments were subject to the regulatory factors (e.g., PTH, 1,25(OH) 2 D, calcium, and phosphorus)34567 . In interpreting clinical data, we used the procedure taken by Parfitt and co-workers8910111213. ...
Parathyroid hormone (PTH) plays a critical role in calcium and phosphorus metabolism. Interestingly, in two forms of hyperparathyroidism (excessive amount of PTH in the serum), the metabolic disturbances in patients with chronic kidney disease (CKD) significantly differ from those with primary hyperparathyroidism (PHP). Since an intuitive understanding of these PTH-linked regulatory mechanisms are hardly possible, we developed a mathematical model using clinical data (1586 CKD and 40 PHP patients). The model was composed of a set of ordinary differential equations, in which the regulatory mechanism of PTH together with other key factors such as 1,25-Dihydroxyvitamin D (1,25(OH)₂D) and calcium was described in the tissues including bone, the kidney, the serum, and the parathyroid glands. In this model, an increase in PTH was induced by its autonomous production in PHP, while PTH in CKD was elevated by a decrease in feedback inhibition of 1,25(OH)₂D in the serum, as well as an increase in stimulation by phosphorus in the serum. The model-based analysis revealed characteristic differences in the outcomes of hyperparathyroidism in CKD and PHP. The calcium exchange in bone, for instance, was predicted significantly higher in PHP than CKD. Furthermore, we evaluated the observed and predicted responses to the administration of calcimimetics, a recently developed synthetic drug that modulated efficacy of calcium-sensing receptors. The results herein support the notion that the described model would enable us to pose testable hypotheses about the actions of PTH, providing a quantitative analytical tool for evaluating treatment strategies of PHP and CKD.
... endothelial cells, nerve cells) are organized in specialized units called bone multicellular units (analogous to the organization of kidney cells into nephrons) [61]. The main function of the bone multicellular units in the adult skeleton is to mediate a bone 'rejuvenation' mechanism called 'bone remodelling' aimed at the maintenance of the integrity of the skeleton by removing old bone of high mineral density and high prevalence of fatigue micro-fractures through repetitive cycles of bone resorption and bone formation [61, 62]. During bone formation phase, the osteoblasts are recruited from MSC present in bone marrow [63]. ...
This invited review covers research areas of central importance for orthopaedic and maxillofacial bone tissue repair, including normal fracture healing and healing problems, biomaterial scaffolds for tissue engineering, mesenchymal and foetal stem cells, effects of sex steroids on mesenchymal stem cells, use of platelet-rich plasma for tissue repair, osteogenesis and its molecular markers. A variety of cells in addition to stem cells, as well as advances in materials science to meet specific requirements for bone and soft tissue regeneration by addition of bioactive molecules, are discussed.
Osteoporotic vertebral compression fractures (OVCFs) are the most common fragility fracture and significantly influence the quality of life in the elderly. Currently, the literature lacks a comprehensive narrative review of the management of OVCFs. The purpose of this study is to review background information, diagnosis, and surgical and non-surgical management of the OVCFs. A comprehensive search of PubMed and Google Scholar for articles in the English language between 1980 and 2021 was performed. Combinations of the following terms were used: compression fractures, vertebral compression fractures, osteoporosis, osteoporotic compression fractures, vertebroplasty, kyphoplasty, bisphosphonates, calcitonin, and osteoporosis treatments. Additional articles were also included by examining the reference list of articles found in the search. OVCFs, especially those that occur over long periods, can be asymptomatic. Symptoms of acute OVCFs include pain localized to the mid-line spine, a loss in height, and decreased mobility. The primary treatment regimens are pain control, medication management, vertebral augmentation, and anterior or posterior decompression and reconstructions. Pain control can be achieved with acetaminophen or nonsteroidal anti-inflammatory drugs for mild pain or opioids and/or calcitonin for moderate to severe pain. Bisphosphonates and denosumab are the first-line treatments for osteoporosis. Vertebroplasty and kyphoplasty are reserved for patients who have not found symptomatic relief through conservative methods and are effective in achieving pain relief. Vertebroplasty is less technical and cheaper than kyphoplasty but could have more complications. Calcium and vitamin D supplementation can have a protective and therapeutic effect. Management of OVCFs must be combined with multiple approaches. Appropriate exercises and activity modification are important in fracture prevention. Medication with different mechanisms of action is a critical long-term causal treatment strategy. The minimally invasive surgical interventions such as vertebroplasty and kyphoplasty are reserved for patients not responsive to conservative therapy and are recognized as efficient stopgap treatment methods. Posterior decompression and fixation or Anterior decompression and reconstruction may be required if neurological deficits are present. The detailed pathogenesis and related targeted treatment options still need to be developed for better clinical outcomes.
The efficiency of cloning and the content of multipotent stromal cells (MSC) in the femoral bone marrow of intact CBA mice was 1.5 times less in old mice (24-36 months) than in young ones (2-3 months). The concentration of osteogenic MSC was higher in old vs. young mice (42±3 vs. 22±2%, respectively). Changes in the total counts of MSC and concentrations of osteogenic MSC in response to osteogenic (curettage, BMP-2) and immunogenic stimuli (S. typhimurium antigenic complex) were similar in young and old mice in comparison with intact controls of respective age. The counts of the total pool of bone marrow MSC and pool of osteogenic MSC in response to osteogenic stimuli were 1.5-2 times less in old vs. young mice. This difference seemed to be a result of age-specific decrease of their bone marrow count but not of age-specific decrease of the MSC functional activity, this leading to a decrease in the transplantability of bone marrow stromal tissue of old mice. Comparison of transplantations “old donor — young recipient” vs. “young donor — young recipient” demonstrated a decrease in the count of nuclear cells (1.8 times), size of bone capsule (2-fold), efficiency of MSC cloning (1.6 times), count of MSC per transplant (2.9 times), and count of osteogenic MSC per transplant (3.3 times). The concentrations of osteogenic MSC in transplants from young and old donors leveled in young recipients, that is, seemed to be regulated by the host. Serum concentrations of IL-10 and TNF-α in intact old mice were at least 2.9 and 2 times higher than in young animals, while the concentrations of almost all the rest studied cytokines (IL-2, IL-5, GM-CSF, IFN-γ, IL-4, IL-12) were lower. Presumably, the decrease in the content of bone marrow MSC and in transplantability of bone marrow stromal tissue in old mice were caused by exhaustion of the MSC pool as a result of age-specific chronic inflammation. These data indicated a close relationship between age-specific changes in the stromal tissue and immune system.
Macrophages have established roles supporting bone formation. Despite their professional phagocytic nature, the role of macrophage phagocytosis in bone homeostasis is not well understood. Interestingly, apoptosis is a pivotal feature of cellular regulation and the primary fate of osteoblasts is apoptosis. Efferocytosis (phagocytosis of apoptotic cells) is a key physiologic process for the homeostasis of many tissues, and is associated with expression of osteoinductive factors. To test effects of macrophage depletion and compromised phagocytosis on bone, 16 wk old male C57BL/6J mice were treated with trabectedin - a chemotherapeutic with established anti-macrophage effects. Trabectedin treatment reduced F4/80+ and CD68+ macrophages in the bone marrow as assessed by flow cytometry, osteal macrophages near the bone surface, and macrophage viability in vitro. Trabectedin treatment significantly reduced marrow gene expression of key phagocytic factors (Mfge8, Mrc1), and macrophages from treated mice had a reduced ability to phagocytose apoptotic mimicry beads. Macrophages cultured in vitro and treated with trabectedin displayed reduced efferocytosis of apoptotic osteoblasts. Moreover, efferocytosis increased macrophage osteoinductive TGF-β production and this increase was inhibited by trabectedin. Long-term (6 wk) treatment of 16 wk C57BL/6J mice with trabectedin significantly reduced trabecular BV/TV and cortical BMD. Although trabectedin reduced osteoclast numbers in vitro, osteoclast surface in vivo was not altered. Trabectedin treatment reduced serum P1NP as well as MS/BS and BFR/BS, and inhibited mineralization and Runx2 gene expression of osteoblast cultures. Finally, intermittent PTH 1-34 (iPTH) treatment was administered in combination with trabectedin, and iPTH increased trabecular BV/TV in trabectedin treated mice. Collectively, the data support a model whereby trabectedin significantly reduces bone mass due to compromised macrophages and efferocytosis, but also due to direct effects on osteoblasts. This data has immediate clinical relevance in light of increasing use of trabectedin in oncology. This article is protected by copyright. All rights reserved.
Osteocytes play an integral role in bone by sensing mechanical stimuli and releasing signaling factors that direct bone formation. The importance of osteocytes in mechanotransduction suggests that regions of bone tissue with greater osteocyte populations are more responsive to mechanical stimuli. To determine the effects of osteocyte population on bone functional adaptation we applied mechanical loads to the 8(th) caudal vertebra of skeletally mature female Sprague Dawley rats (6 months of age, n = 8 loaded, n = 8 sham controls). The distribution of tissue stress/strain within cancellous bone was determined using high-resolution finite element models, osteocyte distribution was determined using nano-computed tomography, and locations of bone formation were determined using three-dimensional images of fluorescent bone formation markers. Loading increased bone formation (3D MS/BS 10.82 ± 2.09% in loaded v. 3.17 ± 2.05% in sham control, mean ± SD). Bone formation occurred at regions of cancellous bone experiencing greater tissue stress/strain, however stress/strain was only a modest predictor of bone formation; even at locations of greatest stress/strain the probability of observing bone formation did not exceed 41%. The local osteocyte population was not correlated with locations of new bone formation. The findings support the idea that local tissue stress/strain influence the locations of bone formation in cancellous bone, but suggest that the size of the osteocyte population itself is not influential. We conclude that other aspects of osteocytes such as osteocyte connectivity, lacunocanilicular nano-geometry and/or fluid pressure/shear distributions within the marrow space may be more influential in regulating bone mechanotransduction than the number of osteocytes. This article is protected by copyright. All rights reserved.
Human aging is associated with bone loss leading to bone fragility and increased risk for fractures, a disease known as osteoporosis. Osteoporosis is one of the most prevalent and serious diseases affecting the elderly population and constitutes a major public health problem. The cellular and molecular causes of age-related bone loss are current intensive topic of investigation with the aim of identifying new approaches to abolish its negative effects on the skeleton. The aim of this chapter is to give a review on the current understanding of the contribution of aging of the osteoblasts (the bone forming cells) to the phenomenon of age-related boneloss.
The cellular etiology of bone loss in osteoporosis is complex. At the tissue level it results from an imbalance between the activities of osteoclasts and osteoblasts such that, at the completion of each remodeling cycle, the amount of bone that remains is less than that originally present. The magnitude of the bone deficit and the precise mechanism responsible for its occurrence vary according to the underlying cause of the disease and its stage of progression. In the postmenopausal variant there is evidence that bone loss during the immediate perimenopausal period results from an increase in the number, activity and, possibly, functional life span of osteoclasts that is not matched by similar changes in the osteoblast population. During the later stages of the disease, however, there is evidence that the continuing loss of trabecular bone results from a decrease in bone formation that is due to a reduction in the number of osteoblasts. It has been proposed that this same mechanism is a major cause of bone loss in all other forms of osteoporosis (Parfitt 1990a, b, 1992; Cohen-Solal et al. 1991; Compston et al. 1989; Jilka et al. 1996).
For many years bone physiology has been thought of in terms of two opposing but otherwise unrelated kinds of cell, often depicted as sitting on either side of a seesaw. The assumption that osteoclasts and osteoblasts are independent still dominates the field, although it was demolished over 30 years ago by (1973), who recognized that the production and activity of these cells were coordinated in time and space in different modes for different biological purposes, the major modes being redistribution, repair, and replacement (Table 1.1). During growth, bone is formed in one location and soon after resorbed in a location that is different relative to the increased size and altered shape of the bone, not because there is anything wrong with it, but because it is no longer needed at that location. As bones grow in length, bone formed at the junction between the growth plate and the metaphysis is resorbed at the junction between the metaphysis and the diaphysis. As bones grow in width, bone formed beneath the periosteum is resorbed at the endosteum. At these various relative locations, resorption and formation continue with only brief interruptions for extended periods; the cells are operating in the modeling mode (Parfitt, 1997). In fracture healing, damaged bone is removed and callus in the form of woven bone is laid down; the prime consideration is speed of production while the quality of the bone is of lesser importance.
Sex steroids play an important role in skeletal growth and maintenance of bone mass in adults (Johnston 1985). Estrogen deficiency is important in the development of osteoporosis in women. Androgen deficiency may be as important in osteoporotic men (Foresta et al. 1985). The main effects of estrogen and androgen withdrawal are an increase in bone resorption with a smaller increase in bone formation and a consequent decrease in bone mass (osteopenia or osteoporosis; Jackson et al. 1987).
Condensation of pre-osteogenic, or pre-chondrogenic, cells is the first of a series of processes that initiate skeletal development. We present a validated, novel, three-dimensional agent-based model of in vitro intramembranous osteogenic condensation. The model, informed by system heterogeneity and relying on an interaction-reliant strategy, is shown to be sensitive to 'rules' capturing condensation growth and can be employed to track activity of individual cells to observe their macroscopic impact. It, therefore, makes available previously inaccessible data, offering new insights and providing a new context for exploring the emergence, as well as normal and abnormal development, of osteogenic structures. Of the several stages of condensation we investigate osteoblast 'burial' within the osteoid they deposit. The mechanisms underlying entrapment - required for osteoblasts to differentiate into osteocytes - remain a matter of conjecture with several hypotheses claiming to capture this important transition. Computational examination of this transition indicates that osteoblasts neither turn off nor slow down their matrix secreting genes - a widely held view; nor do they secrete matrix randomly. The model further reveals that osteoblasts display polarised behaviour to deposit osteoid. This is both an important addition to our understanding of condensation and an important validation of the model's utility.
This study assesses the usefulness of alkaline phosphatase (ALP) in predicting the radiologic osteopenia and rickets for very low birth weight infants (VLBWI) below 1,500 g of birth weight.
Mechanical loading, a potent stimulator of bone formation, is governed by osteocyte regulation of osteoblasts. We developed a three-dimensional (3D) in vitro co-culture system to investigate the effect of loading on osteocyte–osteoblast interactions. MLO-Y4 cells were embedded in type I collagen gels and MC3T3-E1(14) or MG63 cells layered on top. Ethidium homodimer staining of 3D co-cultures showed 100% osteoblasts and 86% osteocytes were viable after 7 days. Microscopy revealed osteoblasts and osteocytes maintain their respective ovoid/pyriform and dendritic morphologies in 3D co-cultures. Reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR) of messenger ribonucleic acid (mRNA) extracted separately from osteoblasts and osteocytes, showed that podoplanin (E11), osteocalcin, and runt-related transcription factor 2 mRNAs were expressed in both cell types. Type I collagen (Col1a1) mRNA expression was higher in osteoblasts (P < 0.001), whereas, alkaline phosphatase mRNA was higher in osteocytes (P = 0.001). Immunohistochemistry revealed osteoblasts and osteocytes express E11, type I pro-collagen, and connexin 43 proteins. In preliminary experiments to assess osteogenic responses, co-cultures were treated with human recombinant bone morphogenetic protein 2 (BMP-2) or mechanical loading using a custom built loading device. BMP-2 treatment significantly increased osteoblast Col1a1 mRNA synthesis (P = 0.031) in MLO-Y4/MG63 co-cultures after 5 days treatment. A 16-well silicone plate, loaded (5 min, 10 Hz, 2.5 N) to induce 4000–4500 με cyclic compression within gels increased prostaglandin E2 (PGE2) release 0.5 h post-load in MLO-Y4 cells pre-cultured in 3D collagen gels for 48, 72 h, or 7 days. Mechanical loading of 3D co-cultures increased type I pro-collagen release 1 and 5 days later. These methods reveal a new osteocyte–osteoblast co-culture model that may be useful for investigating mechanically induced osteocyte control of osteoblast bone formation.
Bone-forming osteoblasts recruited during bone remodeling might originate from bone marrow perivascular cells, bone-remodeling compartment canopy cells, or bone-lining cells. However, an assessment of osteoblast recruitment during adult human cancellous bone remodeling is lacking. We addressed this question by quantifying cell densities, cell proliferation, osteoblast differentiation markers, and capillaries in human iliac crest biopsy specimens. We found that recruitment occurs on both reversal and bone-forming surfaces, as shown by the cell density and osterix levels on these respective surfaces, and bone formation occurs only above a given cell density. Next, canopies represent an important source of osteoprogenitors, because canopy cells proved to be more proliferative and less differentiated than bone surface cells, as shown by the inverse levels of Ki-67 and procollagen-3 N-terminal peptide versus osterix; and canopy cell densities, which decline with age, and canopy-capillary contacts above eroded surfaces correlated positively with osteoblast density on bone-forming surfaces. Bone-remodeling compartment canopies also arise from a mesenchymal envelope surrounding the red bone marrow, which is lifted and hypertrophied on initiation of bone resorption. This study, together with earlier reports, led to a model in which canopies and nearby capillaries are critical for reaching the osteoblast density required for bone formation.
Bone tissue is characterized by a constant turnover in response to mechanical stimuli, and osteocytes play an essential role in bone mechanical adaptation. However, little to no information has been published regarding osteocyte density as a function of implantation time in vivo. The aim of this retrospective histological study was to evaluate the osteocyte density of the peri-implant bone in implants retrieved because of different reasons in a time period from 4 weeks to 27 years. A total of 18 samples were included in the present study. Specimens were divided into 3 groups depending on the loading history of the implants: loading between 4 weeks and 7 months (group 1); loading between 1 and 5 years (group 2); loading between 14 and 27 years (group 3). All the samples were histologically evaluated and osteocyte density was obtained using the ratio of the number of osteocytes to the bone-area (mm(2) ). The osteocyte density values significantly increased in the Group 2 (1-5 years) compared with Group 1 (4 weeks-7 months), and significantly decreased in the Group 3 (14-27 years) compared to Group 2. No significant differences were detected between Group 1 and Group 3. The decrease in osteocyte density observed in samples that were in vivo for long periods of time under loading is possibly because of the fact that once the bone structure is well aligned and biomechanically competent, a lower number of osteocytes are necessary to keep the tissue homeostasis under loading. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.
Estrogens preserve the adult skeleton by suppressing bone turnover and maintaining a focal balance between the rate of bone
resorption and formation. Slowing of bone remodeling is due to the attenuating effects of estrogens on the generation of osteoclast
and osteoblasts. Maintenance of a focal balance between formation and resorption apparently results from a pro-apoptotic effect
on osteoclasts and an anti-apoptotic effect on osteoblasts and osteocytes. Conversely, loss of estrogens leads to a decrease
in bone mass due to an increase in bone resorption and formation, with resorption exceeding formation. Bone cells are direct
targets of estrogens which bind, predominantly, to the ERα. Estrogens suppress the proliferation of osteoblast progenitors
and the apoptosis of osteoblasts and osteocytes and also modulate osteoblast differentiation. The anti-apoptotic actions of
estrogens on osteoblasts and osteocytes are mediated by extranuclear kinases and do not require the DNA-binding function of
the ER. In cells of the osteoclast lineage, estrogens inhibit the differentiation of osteoclast progenitors and promote the
apoptosis of mature osteoclasts. Moreover, estrogens can inhibit osteoclastogenesis indirectly, via the attenuation of the
production of osteoclastogenic cytokines by bone marrow mononuclear cells, T lymphocytes, or osteoblast-lineage cells. Importantly,
most of the effects of estrogens on bone cells are mediated via an anti-oxidant mechanism of action.
Wnt/β-catenin/TCF signaling stimulates bone formation and suppresses adipogenesis. The hallmarks of skeletal involution with age, on the other hand, are decreased bone formation and increased bone marrow adiposity. These changes are associated with increased oxidative stress and decreased growth factor production, which activates members of the FOXO family of transcription factors. FOXOs in turn attenuate Wnt/β-catenin signaling by diverting β-catenin from TCF- to FOXO-mediated transcription. We show herein that mice lacking Foxo1, -3, and -4 in bipotential progenitors of osteoblast and adipocytes (expressing Osterix1) exhibited increased osteoblast number and high bone mass that was maintained in old age as well as decreased adiposity in the aged bone marrow. The increased bone mass in the Foxo-deficient mice was accounted for by increased proliferation of osteoprogenitor cells and bone formation resulting from upregulation of Wnt/β-catenin signaling and cyclin D1 expression, but not changes in redox balance. Consistent with this mechanism, β-catenin deletion in Foxo null cells abrogated both the increased cyclin D1 expression and proliferation. The elucidation of a restraining effect of FOXOs on Wnt signaling in bipotential progenitors suggests that FOXO activation by accumulation of age-associated cellular stressors may be a seminal pathogenetic mechanism in the development of involutional osteoporosis.
Bone loss with aging induces osteoporosis. The most dramatic expression of the disease is represented by fractures of the proximal femur. Pharmacologic and nutritional factors may play a role in the prevention of bone loss with aging. beta-Cryptoxanthin, a kind of carotenoid, is abundant in Satsuma mandarin orange (Citrus unshiu MARC.). Amoung various carotenoids including beta-cryptoxanthin, lutein, lycopene, beta-carotene, astaxanthin, and rutin, beta-cryptoxanthin has been found to have a unique anabolic effect on bone calcification in vitro. Hesperidin, which is contained in Satsuma mandarin orange, did not have an anabolic effect on bone calcification in vitro. beta-Cryptoxanthin has stimulatory effects on osteoblastic bone formation and inhibitory effects on osteoclastic bone resorption in vitro, thereby increasing bone mass. beta-Cryptoxanthin has an effect on the gene expression of various proteins which are related to osteoblastic bone formation and mineralization in vitro. beta-Cryptoxanthin has inhibitory effects on enzyme activity which is related to osteoclastic bone resororption, and the carotenoid induces apoptosis of mature osteoclastic cells in vitro. Oral administration of beta-cryptoxanthin has been shown to have the anabolic effects on bone components in young and aged rats, and the administration has the preventive effects on bone loss in streptozotocin-diabetic rats and ovariectomized rats in vivo. Moreover, the intake of, beta-cryptoxanthin-reinforced juice for longer periods has been shown to have both stimulatory effects on bone formation and inhibitory effects on bone resorption in healthy human or postmenopausal women in evaluating with serum biochemical markers of bone metabolism in vivo. Thus the intake of dietary beta-cryptoxanthin may have a preventive effect on osteoporosis due to stimulating bone formation and due to inhibiting bone resorption. Moreover, epidemiological studies suggest the potential role of beta-cryptoxanthin as a sustainable nutritional approach to improving bone health of human subjects. beta-Cryptoxanthin is an important food factor in maintaining bone healthy and in preventing osteoporosis.
Although a decline in bone formation and loss of bone mass are common features of human aging, the molecular mechanisms mediating
these effects have remained unclear. Evidence from pharmacological and genetic studies in mice has provided support for a
deleterious effect of oxidative stress in bone and has strengthened the idea that an increase in reactive oxygen species (ROS)
with advancing age represents a pathophysiological mechanism underlying age-related bone loss. Mesenchymal stem cells and
osteocytes are long-lived cells and, therefore, are more susceptible than other types of bone cells to the molecular changes
caused by aging, including increased levels of ROS and decreased autophagy. However, short-lived cells like osteoblast progenitors
and mature osteoblasts and osteoclasts are also affected by the altered aged environment characterized by lower levels of
sex steroids, increased endogenous glucocorticoids, and higher oxidized lipids. This article reviews current knowledge on
the effects of the aging process on bone, with particular emphasis on the role of ROS and autophagy in cells of the osteoblast
lineage in mice.
Cysteine (C)-X-C chemokine receptor-4 (CXCR4) is the primary transmembrane receptor for stromal cell-derived factor-1 (SDF-1). We previously reported in mouse or human bone marrow-derived mesenchymal stromal stem cells (BMSCs) that deleting or antagonizing CXCR4 inhibits bone morphogenetic protein-2 (BMP2)-induced osteogenic differentiation. The goal of this study was to determine whether CXCR4-deficiency in BMSCs is an age-related effect in association with impaired osteogenic differentiation potency of aged BMSCs. Using BMSCs derived from C57BL/6J wild type mice at ages ranging from 3 to 23 months old, we detected decreased CXCR4 mRNA and protein expression as well as SDF-1 secretion with advancing aging. Moreover, CXCR4-deficient BMSCs from elderly versus young mice exhibited impaired osteogenic differentiation in response to BMP2 stimulation or when cultured in dexamethasone (Dex)-containing osteogenic medium, evidenced by decreased alkaline phosphatase activity, osteocalcin synthesis, and calcium deposition (markers for immature and mature osteoblasts). Mechanistically, impaired BMP2- or Dex-osteoinduction in BMSCs of elderly mice was mediated by inhibited phosphorylation of intracellular R-Smads and Erk1/2 or Erk1/2 and p38 proteins, and decreased Runx2 and Osx expression (osteogenesis "master" regulators) were also detected. Furthermore, adenovirus-mediated repair of CXCR4 expression in BMSCs of elderly mice restored their osteogenic differentiation potentials to both BMP2 treatment and osteogenic medium. Collectively, our results demonstrate for the first time that CXCR4 expression in mouse BMSCs declines with aging, and this CXCR4-deficiency impairs osteogenic differentiation potency of aged BMSCs. These findings provide novel insights into mechanisms underlying age-related changes in BMSC-osteogenesis, and will potentiate CXCR4 as a therapeutic target to improve BMSC-based bone repair and regeneration in broad orthopaedic situations.
Advancing age and loss of bone mass and strength are closely linked. Elevated osteoblast and osteocyte apoptosis and decreased osteoblast number characterize the age-related skeletal changes in humans and rodents. Similar to other tissues, oxidative stress increases in bone with age. This article reviews current knowledge on the effects of the aging process on bone and its cellular constituents, with particular emphasis on the role of reactive oxygen species (ROS). FoxOs, sirtuins and the p53/p66(shc) signaling cascade alter osteoblast number and bone formation via ROS-dependent and -independent mechanisms. Specifically, activation of the p53/p66(shc) signaling increases osteoblast/osteocyte apoptosis in the aged skeleton and decreases bone mass. FoxO activation in osteoblasts prevents oxidative stress to preserve skeletal homeostasis. However, while defending against stress FoxOs bind to β-catenin and attenuate Wnt/T-cell cell factor transcriptional activity and osteoblast generation. Thus, pathways that impact longevity and several diseases of ageing might also contribute to age-related osteoporosis.
Bmal1 is a transcription factor that plays a central role in the regulation of circadian rhythms. Recent study reported that Bmal1-/- mice displayed many known features of premature ageing, such as reduction of bone mass. Our previous study has found that both the proliferation of bone marrow mesenchymal stem cells (BMSCs) and Bmal1 expression decreased with advancing age. It seemed that a positive correlation existed between Bmal1 protein level and the proliferative activity of BMSCs. β-catenin, the core factor of the canonical Wnt pathway, also showed reduced expression in aged mice. In order to further confirm this, we constructed a lentiviral vector to over-express Bmal1 in NIH-3T3 cells; successful transfection was verified. The cell proliferation rate of infected cells was higher than the non-transfected NIH-3T3 cells, suggesting that circadian clock gene Bmal1 can promote proliferation. β-catenin showed an increased expression in NIH-3T3 cells after Bmal1 over-expression, indicating that activation of the canonical Wnt pathway might be the mechanism underlying the effect of circadian clock gene Bmal on promoting cell proliferation. Copyright © 2012 John Wiley & Sons, Ltd.
Idiopathic juvenile osteoporosis (IJO), a rare cause of osteoporosis in children, is characterized by the occurrence of vertebral and metaphyseal fractures. Little is known about the histopathogenesis of IJO. We analyzed by quantitative histomorphometry iliac crest biopsies from 9 IJO patients (age, 10.0–12.3 years; 7 girls) after tetracycline labeling. Results were compared with identically processed samples from 12 age-matched children without metabolic bone disease and 11 patients with osteogenesis imperfecta type I. Compared with healthy controls, cancellous bone volume (BV) was markedly decreased in IJO patients (mean [SD]: 10.0% [3.1%] vs. 24.4% [3.8%]), because of a 34% reduction in trabecular thickness (Tb.Th) and a 37% lower trabecular number (Tb.N; p < 0.0001 each; unpaired t-test). Bone formation rate (BFR) per bone surface was decreased to 38% of the level in controls (p = 0.0006). This was partly caused by decreased recruitment of remodeling units, as shown by a trend toward lower activation frequency (54% of the control value; p = 0.08). Importantly, osteoblast team performance also was impaired, as evidenced by a decreased wall thickness (W.Th; 70% of the control value; p < 0.0001). Reconstruction of the formative sites revealed that osteoblast team performance was abnormally low even before mineralization started at a given site. No evidence was found for increased bone resorption. Compared with children with osteogenesis imperfecta (OI), IJO patients had a similarly decreased cancellous BV but a much lower bone turnover. These results suggest a pathogenetic model for IJO, in which impaired osteoblast team performance decreases the ability of cancellous bone to adapt to the increasing mechanical needs during growth. This will finally result in load failure at sites where cancellous bone is essential for stability. (J Bone Miner Res 2000;15:957–963)
Bone densitometry has great potential to improve our understanding of bone development. However, densitometric data in children rarely are interpreted in light of the biological processes they reflect. To strengthen the link between bone densitometry and the physiology of bone development, we review the literature on physiological mechanisms and structural changes determining bone mineral density (BMD). BMD (defined as mass of mineral per unit volume) is analyzed in three levels: in bone material (BMDmaterial), in a bone's trabecular and cortical tissue compartments (BMDcompartment), and in the entire bone (BMDtotal). BMDmaterial of the femoral midshaft cortex decreases after birth to a nadir in the first year of life and thereafter increases. In iliac trabecular bone, BMDmaterial also increases from infancy to adulthood, reflecting the decrease in bone turnover. BMDmaterial cannot be determined with current noninvasive techniques because of insufficient spatial resolution. BMDcompartment of the femoral midshaft cortex decreases in the first months after birth followed by a rapid increase during the next 2 years and slower changes thereafter, reflecting changes in both relative bone volume and BMDmaterial. Trabecular BMDcompartment increases in vertebral bodies but not at the distal radius. Quantitative computed tomography (QCT) allows for the determination of both trabecular and cortical BMDcompartment, whereas projectional techniques such as dual-energy X-ray absorptiometry (DXA) can be used only to assess cortical BMDcompartment of long bone diaphyses. BMDtotal of long bones decreases by about 30% in the first months after birth, reflecting a redistribution of bone tissue from the endocortical to the periosteal surface. In children of school age and in adolescents, changes in BMDtotal are site-specific. There is a marked rise in BMDtotal at locations where relative cortical area increases (metacarpal bones, phalanges, and forearm), but little change at the femoral neck and midshaft. BMDtotal can be measured by QCT at any site of the skeleton, regardless of bone shape. DXA allows the estimation of BMDtotal at skeletal sites, which have an approximately circular cross-section. The system presented here may help to interpret densitometric results in growing subjects on a physiological basis.
A consistent observation in osteoporosis is bone volume reduction accompanied by increased marrow adipose tissue. No single
cause linking the two phenomena has yet been identified. In a human progenitor cell clone (hOP 7) derived from bone marrow,
however, we have demonstrated that rabbit serum can direct differentiation away from an osteoblast lineage to one of adipocytes.
We now report on whether human serum has a similar effect. Serum was collected from 10 pre- and 10 postmenopausal women and
from the 10 postmenopausal women before and following 6-week hormone replacement therapy (HRT). hOP 7 cells were cultured
with the various sera, and after 7-14 days adipocytogenesis was determined by oil red O staining and lipoprotein lipase (LPL)
and glycerol 3-phosphate dehydrogenase (G3PDH) expression. Incubation with 10% premenopausal serum led to labeling of 10.9%
of cells (P<0.05) with oil red O, whereas application of 10% postmenopausal serum led to a much larger effect, 43.5% labeling (P<0.001 with respect to premenopausal serum). Oil red O positivity was accompanied by loss of type I collagen expression
and increased LPL and G3PDH expression. HRT did not reverse the adipocytogenic effect of postmenopausal serum. In conclusion,
serum from postmenopausal women contains factors that steer hOP 7 bone progenitor cells toward an adipocytic phenotype, irrespective
of HRT. The study suggests a role for serum factors in the development of fatty marrow in postmenopausal osteoporosis.
The last decade has provided a virtual explosion of data on the molecular biology and function of osteocytes. Far from being the passive placeholder in bone, this cell has been found to have numerous functions, such as acting as an orchestrator of bone remodeling through regulation of both osteoclast and osteoblast activity and also functioning as an endocrine cell. The osteocyte is a source of soluble factors not only to target cells on the bone surface but also to target distant organs, such as kidney, muscle, and other tissues. This cell plays a role in both phosphate metabolism and calcium availability and can remodel its perilacunar matrix. Osteocytes compose 90% to 95% of all bone cells in adult bone and are the longest lived bone cell, up to decades within their mineralized environment. As we age, these cells die, leaving behind empty lacunae that frequently micropetrose. In aged bone such as osteonecrotic bone, empty lacunae are associated with reduced remodeling. Inflammatory factors such as
Bone homeostasis is regulated through osteoclasts and osteoblasts. Osteoporosis, which is induced with its accompanying decrease in bone mass with increasing age, is widely recognized as a major public health problem. Bone loss may be due to decreased osteoblastic bone formation and increased osteoclastic bone resorption. There is growing evidence that nutritional and food factors may play a part in the prevention of bone loss with aging and have been to be worthy of notice in the prevention of osteoporosis. Zinc, an essential trace element, or genistein, which are contained in soybeans, has been shown to have a stimulatory effect on osteoblastic bone formation and an inhibitory effect on osteoclastic bone resorption, thereby increasing bone mass. These factors have an effect on protein synthesis and gene expression, which are related to bone formation in osteoblastic cells and bone resorption in osteoclastic cells. The combination of zinc and genistein is found to reveal the synergistic effect on bone anabolic effect. The oral administration of those factors has been shown to prevent on bone loss in ovariectomized rats, an animal model for osteoporosis, indicating a role in the prevention of osteoporosis. Supplemental intake of ingredient with the combination of zinc and genistein has been shown to have a preventive effect on osteoporosis in human subjects, suggesting a role in the prevention of bone loss.
There are tremendous unmet clinical needs for effective strategies to enhance bone regeneration in vivo. The sustained presence of multipotent mesenchymal progenitors in the bone marrow in aged and osteoporotic individuals offers the potential for therapeutic interventions to induce osteoblast production from the resident progenitors. Recent advances in understanding the intercellular signals governing osteogenic decisions may provide targets for developing novel bone-enhancing therapeutics.
Marotti (Ital J Anat Embryol 1 01:25-79, 1996) described a theory of osteocyte differentiation from osteoblasts during bone formation. This theory postulates that, when a previously formed osteocyte is sufficiently covered by new bone and osteoid, it sends an inhibitory signal through its dendritic processes to the neighboring osteoblasts that reduces their individual apposition rates. The osteoblast most affected by this inhibition becomes buried by its neighbors, and becomes one of the next layer of osteocytes. By pursuing this concept, the present study develops a mathematical theory that predicts another observation about bone remodeling: the diminishment of the apposition rate during the refilling of basic multicellular units (BMUs). This decrease in apposition rate is different in osteonal and surface (e.g., trabecular) BMUs, and the theory shows that this result is consistent with the accrual of osteocyte inhibition throughout the refilling period, with the different ratios of bone volume to surface area in these two types of BMUs.
Le tissu osseux est en perpétuel renouvellement (processus désigné remodelage osseux) qui se caractérise par la dégradation (résorption) du tissu osseux par les ostéoclastes et la formation d'un nouveau tissu osseux par les ostéoblastes. L'équilibre entre ces deux processus permet le maintien et le renouvellement permanent de la matrice osseuse. Dans bien des cas où l'équilibre est perdu, il y a apparition d'ostéoporose (littéralement: la maladie des os poreux) qui est caractérisée par une masse osseuse réduite due à une dégradation osseuse supérieure à la fonnation osseuse, une fragilité osseuse et une susceptibilité accrue aux fractures. L'ostéoporose affecte plus de 1,4 million de Canadiens; ainsi 25% des femmes et 13% des hommes de plus de 50 ans souffrent de cette maladie. La réduction de la qualité de vie (diminution de l'estime de soi, réduction ou perte de mobilité et d'autonomie) pour les personnes atteintes d'ostéoporose est énorme. Les coûts pour traiter l'ostéoporose et les fractures qui en résultent sont supérieurs à 1,9 milliard chaque année au Canada. Ces impacts socioéconomiques militent en faveur d'une meilleure compréhension du remodelage osseux. Parmi les facteurs de risque, une diète déficiente en magnésium (Mg2+) a été identifiée comme une condition prédisposant à une réduction graduelle de la masse osseuse et au développement de l'ostéoporose. Des études indiquent qu'une diète réduite en Mg2+ entraîne une augmentation du nombre d'ostéoclastes, une diminution du nombre d'ostéoblastes et une perte de la masse osseuse. Les mécanismes assurant l'homéostasie du Mg2+ intracellulaire ne sont pas encore parfaitement élucidés. La présente étude vise à détenniner l'importance du Mg2+ et l'implication des canaux «melastatin related transient receptor potentiel 7» (TRPM7) au niveau de la prolifération, de la migration et de la différenciation des ostéoblastes ainsi que leur capacité à synthétiser et minéraliser la matrice osseuse. Nos travaux indiquent pour la première fois que les cellules ostéoblastiques expriment les canaux TRPM7 et qu'une réduction du Mg2+ extracellulaire est associée à une diminution de l'activité des ostéoblastes (prolifération, migration, différenciation, minéralisation). De plus, nos résultats indiquent que le canal TRPM7 assure l'homéostasie du Mg2 + intracellulaire, et que son expression est augmentée dans des conditions de prolifération cellulaire induite par le "platelet-derived growth factor" (PDGF), de différenciation et en présence d'un milieu de culture réduit en Mg2+, suggérant son implication dans les fonctions des ostéoblastes. Par ailleurs, une stratégie d'interférence à l'ARN ciblant le TRPM7 des ostéoblastes diminue la prolifération ainsi que la migration basale et induite par le PDGF, en plus de réduire la capacité des ostéoblastes à se différencier et par la suite à minéraliser la matrice osseuse. En conclusion, nos résultats indiquent que les fonctions des ostéoblastes sont favorisées par la présence de concentrations adéquates de Mg2+ extracellulaire et des canaux TRPM7. Cette étude souligne l'importance du Mg2+ au niveau des fonctions des cellules ostéoblastiques et nos résultats se veulent en accord avec la diminution de la formation osseuse et le développement de l'ostéoporose associés à une diète déficiente en Mg2+. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : TRPM7, ostéoblastes, prolifération, migration, différenciation, PDGF, ostéoporose
Although the search for the ideal bone substitute has been the focus of a large number of studies, autogenous bone is still the gold standard for the filling of defects caused by pathologies and traumas, and mainly, for alveolar ridge reconstruction, allowing the titanium implants installation.
The aim of this study was to evaluate the dynamics of autogenous bone graft incorporation process to surgically created defects in rat calvaria, using epifluorescence microscopy.
Five adult male rats weighing 200-300 g were used. The animals received two 5-mm-diameter bone defects bilaterally in each parietal bone with a trephine bur under general anesthesia. Two groups of defects were formed: a control group (n=5), in which the defects were filled with blood clot, and a graft group (n=5), in which the defects were filled with autogenous bone block, removed from the contralateral defect. The fluorochromes calcein and alizarin were applied at the 7th and 30th postoperative days, respectively. The animals were killed at 35 days.
The mineralization process was more intense in the graft group (32.09%) and occurred mainly between 7 and 30 days, the period labeled by calcein (24.66%).
The fluorochromes showed to be appropriate to label mineralization areas. The interfacial areas between fluorochrome labels are important sources of information about the bone regeneration dynamics.
Sex steroids are main regulators of skeletal growth, maturation and mass in both men and women. People with disorders of sex development (DSD) may experience problems in developing normal bone growth, structure and mass, because abnormal sex steroid secretion or action may be operative. In complete androgen insensitivity syndrome several reports documented reduced bone mineral density (BMD). Reduced BMD is evident in patients with not removed or removed gonads, but it is poorer in the latter, mainly when compliance with estrogen replacement therapy is not guaranteed. Large impairment of BMD does not seem to be present in patients with partial androgen insensitivity syndrome or 5alpha-reductase-2 deficiency, providing that gonads are not removed or that substitutive therapy is optimized. In congenital adrenal hyperplasia, BMD may be impaired as a result of not optimal glucocorticoid administration. In Turner syndrome, impaired BMD may result from the combined actions of estrogen deficiency, low bone dimensions, altered bone geometry, deficient cortical bone, and trabecular bone loss. Optimal estrogen administration seems to be important in preserving bone mass and enhancing trabecular bone volume. On the whole, bone health represents a main clinical issue for the management of persons with disorders of sex differentiation, and well designed longitudinal studies should be developed to improve their bone health and well-being.
The application of tetracycline-based iliac bone histomorphometry to the study of the pathogenesis of osteoporosis has given conflicting results. Accordingly, we performed this procedure in 78 postmenopausal white women with one or more vertebral fractures identified according to rigorous criteria that excluded other causes of vertebral deformity and 66 healthy postmenopausal white women recruited from the same geographic region; the groups did not differ in age or weight. In each subject, measurements were made separately on the cancellous (Cn), endocortical (Ec), and intracortical (Ct) subdivisions of the endosteal envelope. In the fracture patients, osteoblast surface was reduced substantially on each subdivision, most markedly on the Cn surface, where about 25% of the deficit was in cuboidal (type II) osteoblasts, suggesting impaired recruitment; the remaining 75% of the deficit was in intermediate (type III) cells, suggesting earlier transition from type III to type IV (flat) cells. On the Ec and Ct surfaces, the deficit was exclusively in type III cells. Mean bone formation rate was reduced by about 18% on the Cn but not on the Ec or Ct surfaces. The deficit was more significant in subjects matched for Cn BV/TV when adjusted for the inverse regression on osteocyte density and after logarithmic transformation. The difference in bone formation rate resulted from a corresponding reduction in wall thickness without a change in activation frequency. The frequency distribution of bone formation rate was more skewed to the left in the fracture patients than in the controls. Osteoclast surface was significantly lower on each subdivision. The variation in osteoblast surface, bone formation rate, and osteoclast surface was significantly greater in the fracture patients than in the controls, with more abnormally low and abnormally high values. The data suggest the following conclusions: (1) The histologic heterogeneity of postmenopausal osteoporosis is reaffirmed; (2) the different subdivisions of the endosteal envelope, although in continuity, behave differently in health and disease; (3) a combination of defective osteoblast recruitment and premature osteoblast apoptosis would account for the deficit in type II and III cells and the reductions in wall thickness and bone formation rate on the Cn surface and the previously reported osteocyte deficiency in Cn bone; (4) premature disaggregation of multinuclear to mononuclear resorbing cells could account for the osteoclast deficit; and (5) some patients with vertebral fracture have one or another disorder of bone remodeling that at present cannot be identified by noninvasive means.
In diesem Versuch wurden 30 trabekuläre, humane Knochenzylinder über einen Zeitraum von 29 Tagen kultiviert und an 26 Tagen belastet. Das Belastungssignal entsprach dem physiologischen Springen und wurde in ungefilterter Form und in gefilterter Form auf die Knochenproben appliziert. Die Knochenzylinder wurden per Randomisierung in 5 Gruppen mit je 6 Proben eingeteilt, mit einer weiteren Unterteilung in jeweils 3 männliche und 3 weibliche Proben. In zwei Gruppen erfolgte die Abtötung der Knochenzylinder mittels KCl-Lösung. Einer Kontrollgruppe wurden 4 Belastungsgruppen mit den Unterteilungen lebend und ungefiltertes Signal, lebend und gefiltertes Signal, tot und ungefiltertes Signal sowie tot und gefiltertes Signal gegenübergestellt. Das Belastungssignal wurde täglich mit 300 Zyklen bei einer Frequenz von 1Hz, mit einer Intensität von 3000µstrain auf die Knochenproben appliziert. Nach der eigentlichen Belastung wurde die Steifigkeit (E-Modul) der Knochenzylinder bestimmt. In der Kontrollgruppe wurde diese alle 48 Stunden bestimmt. Bei den regelmäßigen Wechseln des Nährmediums (alle 48 Stunden) wurde dieses sowohl auf Knochenstoffwechselmarker als auch auf knochenzellspezifische Marker untersucht. Die Vitalität und Aktivität der lebenden Knochenproben wurde über den gesamten Versuchszeitraum mittels der verwendeten Stoffwechselmarker – Alkalische Phosphatase, Laktat, Laktatdehydrogenase und pH- Wert – dokumentiert. In this experiment 30 trabecular human bone cores were cultivated over a period of 29 days and loaded during 26 days. The mechanical load-signal corresponded to that of physiological jumping and was applied in a unfiltrated as well as filtrated form onto the bone samples. The bone cores were randomly devided into five groups with six samples each and a further subdivision into three male and three female samples. Two groups were terminated using potassium chloride solution. A control-group was contrasted to four load-groups with the following subdivisions: live and unfiltrated signal, live and filtrated signal, dead and unfiltrated signal and dead and filtrated signal. The load signal was applied onto the bone samples with 300 cycles, with a frequency of 1 Hz and an intensity of 3000 μstrain daily. The stiffness (e-module) of each bone core was determined after the actual exposure to the mechanical load while the control-group was only measured every 48 hours. In addition the cultivating medium was exchanged and analysed to bone metabolism as well as to bone cell-specific markers on a 48hour basis. Vitality as well as the activity of the live bone samples were documented via the metabolismic markers, alkaline phosphatase,lactate, lactatedehydrogenase and ph-value, during the entire experiment period.
It is well established that scaffolds for applications in bone tissue engineering require interconnected pores on the order of 100 microm for bone in growth and nutrient and waste transport. As a result, most studies have focused on scaffold macroporosity (>100 microm). More recently researchers have investigated the role of microporosity in calcium phosphate -based scaffolds. Osteointegration into macropores improves when scaffold rods or struts contain micropores, typically defined as pores less than approximately 50 microm. We recently demonstrated multiscale osteointegration, or growth into both macropores and intra-red micropores (<10 microm), of biphasic calcium phosphate (BCP) scaffolds. The combined effect of BMP-2, a potent osteoinductive growth factor, and multiscale porosity has yet to be investigated. In this study we implanted BCP scaffolds into porcine mandibular defects for 3, 6, 12 and 24 weeks and evaluated the effect of BMP-2 on multiscale osteointegration. The results showed that given this in vivo model BMP-2 influences osteointegration at the microscale, but not at the macroscale, but not at the macroscale. Cell density was higher in the rod micropores for scaffolds containing BMP-2 compared with controls at all time points, but BMP-2 was not required for bone formation in micropores. In contrast, there was essentially no difference in the fraction of bone in macropores for scaffolds with BMP-2 compared with controls. Additionally, bone in macropores seemed to have reached steady-state by 3 weeks. Multiscale osteointegration results in bone-scaffold composites that are fully osteointegrated, with no 'dead space'. These composites are likely to contain a continuous cell network as well as the potential for enhanced load transfer and improved mechanical properties.
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