Ron Shahar

Hebrew University of Jerusalem | HUJI · Koret School of Veterinary Medicine

Understanding how living tissues respond to changes in their mechanical environment is a key question in evolutionary biology. Invasive species provide an ideal model for this as they are often transplanted between environments that differ drastically in their ecological and environmental context. Spatial sorting, the name given to the phenomenon d...

Bone material contains a hierarchical network of micro- and nano-cavities and channels, known as the lacuna-canalicular network (LCN), that is thought to play an important role in mechanobiology and turnover. The LCN comprises micrometer-sized lacunae, voids that house osteocytes, and submicrometer-sized canaliculi that connect bone cells. Characte...

Synopsis Teeth are composed of the hardest tissues in the vertebrate body and have been studied extensively to infer diet in vertebrates. The morphology and structure of enamel is thought to reflect feeding ecology. Snakes have a diversified diet, some species feed on armored lizards, others on soft invertebrates. Yet, little is known about how too...

The structure, composition, and shape of teeth have been related to dietary specialization in many vertebrate species, but comparative studies on snakes' teeth are lacking. Yet, snakes have diverse dietary habits that may impact the shape of their teeth. We hypothesize that prey properties, such as hardness and shape, as well as feeding behavior, s...

1. The structure, composition, and shape of teeth have been related to dietary specialization in many vertebrate species, except snakes. Yet, snakes have diverse dietary habits that may impact the shape of their teeth. We hypothesize that prey properties, such as hardness and shape, as well as feeding behavior, such as aquatic or arboreal predation...

Teeth are one of the most studied hard tissues in vertebrates. Their structure, composition and shape are related to dietary specialization in many species. At first glance, snake teeth all look similar; conical, sharp, curved. Yet, snakes, like other vertebrates, have very diverse diets that may have affected their shape. We compared the morpholog...

Introduction Sirtuin 1 (SIRT1) is a key player in aging and metabolism and regulates bone mass and architecture. Sexual dimorphism in skeletal effects of SIRT1 has been reported, with an unfavorable phenotype primarily in female mice. Methods To investigate the mechanisms of gender differences in SIRT1 skeletal effect, we investigated femoral and...

The gelatinases, a subgroup of the matrix metalloproteinases (MMPs) superfamily are composed of two members; MMP2 and MMP9. They are known to degrade gelatin among other components of the extracellular matrix. Recently, the two gelatinases were found to be necessary for neural crest cell migration and to compensate for each other loss in these cell...

Vertebrate bones are made of a nanocomposite consisting of water, mineral and organics. Water helps bone material withstand mechanical stress and participates in sensation of external loads. Water diffusion across vertebrae of medaka (bone material lacking osteocytes) and zebrafish (bone material containing osteocytes) was compared using neutron to...

Dietary protein is necessary throughout all life stages. Adequate intake of protein during juvenile years is essential to enable appropriate synthesis of bone matrix and achieve the full peak bone mass (PBM). Due to socio-demographic changes, accompanied by environmental damage and ethical problems, a transition to the consumption of different and...

Bone is a fascinating biomaterial comprised mostly of type-I collagen fibers as an organic phase, apatite as an inorganic phase, with water molecules residing at the interfaces between these phases. They are hierarchically organized with minor constituents such as non-collagenous proteins, citrate ions and glycosaminoglycans into a composite struct...

The severe impairment of bone development and quality was recently described as a new target for unbalanced ultra-processed food (UPF). Here, we describe nutritional approaches to repair this skeletal impairment in rats: supplementation with micro-nutrients and a rescue approach and switching the UPF to balanced nutrition during the growth period....

The teeth of actinopterygian fish, like those of mammals, consist of a thin outer hyper-mineralized layer (enamel or enameloid) that surrounds a core of dentin. While all mammalian species have a single type of dentin (called orthodentin), various dentin types have been reported in the teeth of actinopterygian fish. The most common type of actinopt...

Ultra processed foods (UPF) consumption is becoming dominant in the global food system, to the point of being the most recent cause of malnutrition. Health outcomes of this diet include obesity and metabolic syndrome; however, its effect on skeletal development has yet to be examined. This project studied the influence of UPF diet on the developmen...

Ultra-processed foods have known negative implications for health; however, their effect on skeletal development has never been explored. Here, we show that young rats fed ultra-processed food rich in fat and sugar suffer from growth retardation due to lesions in their tibial growth plates. The bone mineral density decreases significantly, and the...

Today’s eating patterns are characterized by the consumption of unbalanced diets (UBDs) resulting in a variety of health consequences on the one hand, and the consumption of dietary supplements in order to achieve overall health and wellness on the other. Balanced nutrition is especially crucial during childhood and adolescence as these time period...

With an exclusive diet of hard-shelled mollusks, the black drum fish (Pogonias Cromis) exhibits one of the highest bite forces among extant animals. Here we present a systematic microstructural, chemical, crystallographic, and mechanical analysis of the black drum teeth to understand the structural basis for achieving the molluscivorous requirement...

A thorough knowledge of the structures of healthy mineralized tissues, such as bone or cartilage, is key to understanding the pathological changes occurring during disease. Such knowledge enables the underlying mechanisms that are responsible for pathology to be pinpointed. One high-resolution 3D method in particular — focused ion beam-scanning ele...

Background Post-menopausal osteoporosis is a common health problem worldwide, most commonly caused by estrogen deficiency. Most of the information regarding the skeletal effects of this disease relates to trabecular bone, while cortical bone is less studied. The purpose of this study was to evaluate the influence of estrogen deficiency on the struc...

N-3 polyunsaturated fatty acids (PUFAs) are essential nutrients that must be obtained from the diet. We have previously showed that endogenous n-3 PUFAs contribute to skeletal development and bone quality in fat-1 mice. Unlike other mammals, these transgenic mice, carry the n-3 desaturase gene and thus can convert n-6 to n-3 PUFAs endogenously. Sin...

The mineralized collagen fibril is the basic building block of bone, and hence is the key to understanding bone structure and function. Here we report imaging of mineralized pig bone samples in 3D using the focused ion beam-scanning electron microscope (FIB-SEM) under conditions that reveal the 67 nm D-banding of mineralized collagen fibrils. We sh...

We examine the structure of the bone of the pharyngeal jaws of a large fish, the black drum (Pogonias cromis), that uses its tooth-jaw complex to crush hard-shelled bivalve mollusks. During mastication huge compressive forces are concentrated in a tiny zone at the tooth-bone interface. We report on the structure of this bone, with emphasis on its c...

Medaka (O. latipes) and zebrafish (D. rerio) are two teleost fish increasingly used as models to study human skeletal diseases. Although they are similar in size, swimming pattern and many other characteristics, these two species are very distant from an evolutionary point of view (by at least 100 million years). A prominent difference between the...

Durophagous fish consume a diet based primarily on hard-shelled animals, mainly mollusks. In order to successfully perform this task, they are equipped with an extra set of jaws located in their throat called pharyngeal jaws. Here we present the results of a study of the structure of the bony material of the exceptionally powerful lower pharyngeal...

Bones are nanocomposites of protein, mineral and water that form mineralized collagen fibrils arranged in a variety of layered lamellae. Bone material has a long evolutionary record and specific bones attain shapes and microstructures that have well stood the test of time such that they can be considered optimized to match their function. Further,...

The naked mole-rat (NMR) is a small rodent with a remarkable array of properties, such as unique physiology, extremely long life-span and unusual social life. However, very little is known regarding its skeleton. The aim of this study was to describe the structure, composition and mechanical properties in an ontogenetic series of naked mole-rat bon...

The bone material of almost all vertebrates contains the same cellular components. These comprise osteoblasts that produce bone, osteoclasts that resorb bone and osteocytes, which are the master regulators of bone metabolism, particularly bone modeling and remodeling. It is thus surprising that the largest group of extant vertebrates, neoteleost fi...

When describing the architecture and ultrastructure of animal skeletons, introductory biology, anatomy and histology textbooks typically focus on the few bone and cartilage types prevalent in humans. In reality, cartilage and bone are far more diverse in the animal kingdom, particularly within fishes, where cartilage and bone types exist that are c...

Teeth are subjected to compressive loads during mastication. Under small loads the soft tissue periodontal ligament (PDL) deforms most. However when the loads increase and the PDL is highly compressed, the tooth and the alveolar bone supporting the tooth, begin to deform. Here we report on the structure of this alveolar bone in the upper furcation...

One strategy evolved by teeth to avoid irreversible damage is to move and deform under the loads incurred during mastication. A key component in this regard is the periodontal ligament (PDL). The role of the bone underlying the PDL is less well defined. We study the interplay between the PDL and the underlying alveolar bone when loaded in the minip...

Osteocytes, cells forming an elaborate network within the bones of most vertebrate taxa, are thought to be the master regulators of bone modeling, a process of coordinated, local bone-tissue deposition and removal that keeps bone strains at safe levels throughout life. Neoteleost fish, however, lack osteocytes and yet are known to be capable of bon...

Young’s moduli derived from nanoindentation of the vertebral body of swim-trained and untrained medaka and zebrafish. N = 30–65 indents from 3 fish of each group. Quantitative data were compared between groups by the nonparametric Mann–Whitney test, with the level of significance set at P ≤ 0.05. All original measurements of Young’s moduli determin...

List of primers used. (DOCX)

Swim training. (a) Medaka swim trained against a water current with tightly controlled (26 cm/s) velocity. Note that fish are swimming against the current, station-holding, and not turning. (b) Untrained (control) medaka swimming in a similar-sized chamber as the swim-training chamber, with minimal speed water flow (only sufficient for maintaining...

Sequencing results of the MO-injected transcript compared with the medaka genome. The primer sequences used are shown in red letters. The exon parts are highlighted in blue, and the intron parts are highlighted in yellow. A stop codon present on the intron that was retained is highlighted in red. The sequencing shows that a significant portion of t...

Musculature and bone in the caudal region of medaka. Caudal is to the right in all images. (a) Sagittal section of a 3D reconstruction of contrast-enhanced (PTA) tomography showing the dense musculature surrounding the caudal vertebral column of medaka. One vertebra is segmented in white to show the full 3D muscle–vertebral relationship. The caudal...

Distribution of fish lengths (mm) in the first swimming experiment. No significant difference was found between untrained and trained fish of either species. There was a significant difference between medaka and zebrafish average lengths; as a result, higher swimming speeds were used for zebrafish in swimming experiments. (TIF)

ISH results for 2 vertebral regions in zebrafish. Top row: NS; bottom row: intervertebral J. Each row comprises (from left to right) a multichannel RGB double fluorescent ISH image, followed by isolated single-channel images: DAPI, collagen (col1a1 = top row, col2a1 = bottom row), SOST. The figure provides a deconstruction of the multichannel ISH i...

Underlying numeric data used in this work. (XLSX)

ISH results for 2 vertebral regions in medaka. Top row: NS and adjacent fin R; bottom row: intervertebral J. Each row comprises (from left to right) a multichannel RGB double fluorescent ISH image, followed by isolated single-channel images (DAPI, col1, col2, respectively) and a SOST ISH image. The figure provides a deconstruction of the multichann...

List of ages of medaka used in different experiments. All original measurements of the total length of the fish participating in the different experimental groups are presented in S1 Data. (DOCX)

Background: Chronic kidney disease (CKD) is common in companion animals. Secondary hyperparathyroidism is an inevitable consequence of the disease and may have deleterious effect on the bone; however, the information regarding CKD-associated bone abnormalities in companion animals is scarce. Hypothesis/objectives: Dogs with CKD have decreased bo...

Our current understanding of the structures of vertebrate mineralized tissues is largely based on light microscopy/histology and projections of 3D structures onto 2D planes using electron microscopy. We know little about the fine details of these structures in 3D at the length scales of their basic building blocks, the inherent variations of struct...

Cancellous bone is an intricate network of interconnected trabeculae, to which analysis of network topology can be applied. The inter-trabecular angle (ITA) analysis—an analysis of network topological parameters and regularity of network-forming nodes—was previously carried out on human proximal femora and showed that trabecular bone follows two ma...

The structural, compositional and mechanical properties of the spines of the dorsal fin in mature anosteocytic blue tilapia Oreochromis aureus and osteocytic common carp Cyprinus carpio are described, as well as their temporal growth pattern and regenerative capacities. The three-dimensional architecture of both spines, from macro to sub-micron lev...

We question two major tenets of bone biology: that the primary role of remodelling is to remove damage in the bone (so-called damage-driven remodelling) and that osteocytes are the only strain-sensing orchestrators of this process. These concepts are distilled largely from research on model mammal species, but in fact, there are a number of feature...

Statement of significance: The Inter-Trabecular Angle (ITA) is a new topological parameter of trabecular bone. The ITA characterizes the way trabeculae connect with each other at nodes, regardless of their thickness and shape. The mean ITA value of nodes with 3 trabeculae is close to 120°, of nodes with 4 trabeculae is just below 109°, and the mea...

Injuries to ligaments are common, painful and debilitating, causing joint instability and impaired protective proprioception sensation around the joint. Healing of torn ligaments usually fails to take place, and surgical replacement or reconstruction is required. Previously, we showed that in vivo application of the recombinant human amelogenin pro...

The bones of the skeleton of most advanced teleost fish do not contain osteocytes. Considering the pivotal role assigned to osteocytes in the process of modeling and remodeling (the adaptation of external and internal bone structure and morphology to external loads and the repair of areas with micro-damage accumulation, respectively) it is unclear...

One of the major challenges that developing organs face is scaling, that is, the adjustment of physical proportions during the massive increase in size. Although organ scaling is fundamental for development and function, little is known about the mechanisms that regulate it. Bone superstructures are projections that typically serve for tendon and l...

The lamellar unit is a critical component in defining the overall mechanical properties of bone. In this paper, micro-beams of bone with dimensions comparable to the lamellar unit were fabricated using focused ion beam (FIB) microscopy and mechanically tested in bending to failure using atomic force microscopy (AFM). A variation in the mechanical p...

Osteoporosis is a disease known to promote bone fragility but the effect on the mechanical properties of bone material, which is independent of geometric effects, is particularly unclear. To address this problem, micro-beams of osteoporotic bone were prepared using focused ion beam microscopy and mechanically tested in compression using an atomic f...

Fish represent the most diverse and numerous of the vertebrate clades. In contrast to the bones of all tetrapods and evolutionarily primitive fish, many of the evolutionarily more advanced fish have bones that do not contain osteocytes. Here we use a variety of imaging techniques to show that anosteocytic fish bone is composed of a sequence of plan...

Significance A fundamental paradigm of bone biology is that the remodeling process—by which bones detect and repair damage—is orchestrated by osteocytes. The bones of most extant fish, however, lack these cells and should be unable to repair damage in their bones. We provide evidence for intense remodeling in the anosteocytic bone of billfishes, su...

Chronic kidney disease (CKD) is a growing public health concern worldwide, and is associated with marked increase of bone fragility. Previous studies assessing the effect of CKD on bone quality were based on biopsies from human patients or on laboratory animal models. Such studies provide information of limited relevance due to the small size of th...

Growth stunting constitutes the most common effect of malnutrition. When the primary cause of malnutrition is resolved, catch-up (CU) growth usually occurs. In this study we wanted to explore the effect of food restriction (RES) and re-feeding on bone structure and mechanical properties. 24 days old SD male rats were subjected to 10 days of 40% RES...

Bone is a dynamic tissue which is continuously adapting not only to external mechanical stimuli but also to internal metabolic calcium demands. During normal bone remodeling, bone-resorbing osteoclasts release calcium from the bone and digest the collagenous bone matrix, after which bone-depositing osteoblasts form unmineralized collagen matrix, wh...

Here we describe the results of a preliminary study to evaluate the response of the cellular skeleton of the large African barb, Labeobarbus intermedius, to exposure to high levels of the thyroid hormone T3 for 1 and 3 months. We examined the effects in terms of mineral density and mechanical properties of the operculum bone, as well as evaluated a...

Estrogen deficiency leads to rapid bone loss and skeletal fragility. Sclerostin, encoded by the sost gene, and a product of the osteocyte, is a negative regulator of bone formation. Blocking sclerostin increases bone mass and strength in animals and humans. Sirtuin1 (Sirt1), a player in aging and metabolism, regulates bone mass and inhibits sost ex...

Bone is a complex hierarchically structured family of materials that includes a network of cells and their interconnected cell processes. New insights into the 3D structure of various bone materials (mainly rat and human lamellar bone and minipig fibrolamellar bone) were obtained using the focused ion beam electron microscope and the serial surface...

Fibrolamellar bone is transiently produced by large, fast growing mammals. The fibrolamellar bone unit is initially formed by elaboration of a network of blood vessels. This is followed by the deposition of a thin, porous and hypercalcified layer, then by the infilling of the vascular cavities by the sequential deposition of a relatively thick rapi...

Abstract The 3D imaging of soft tissues in their native state is challenging, especially when high resolution is required. An X-ray-based microCT is, to date, the best choice for high resolution 3D imaging of soft tissues. However, since X-ray attenuation of soft tissues is very low, contrasting enhancement using different staining materials is nee...

Lamellar bone is the most common bone type in humans. The predominant components of individual lamellae are plywood-like arrays of mineralized collagen fibrils aligned in different directions. Using a dual-beam electron microscope and the Serial Surface View (SSV) method we previously identified a small, but significantly different layer in rat lam...

Leptin's in-vivo effect on the rodent skeleton depends on the model used and the mode of administration. Superactive mouse leptin antagonist (SMLA) was produced and then pegylated (PEG) to prolong and enhance its in-vivo activity. We blocked leptin signaling by injecting this antagonist peripherally into normal mice at various time points, and stud...

[This corrects the article DOI: 10.1038/bonekey.2013.77.].

Bone includes cavities in various length scales, from nanoporosities occurring between the collagen fibrils and the mineral crystals all the way to macrocavities like the medullary cavity. In particular, bone is permeated by a vast number of channels (the lacunar-canalicular system), that reduce the stiffness and, more importantly, the strength of...

One of the hallmarks of tetrapod bone is the presence of numerous cells (osteocytes) within the matrix. Osteocytes are vital components of tetrapod bone, orchestrating the processes of bone building, reshaping and repairing (modeling and remodeling), and probably also participating in calcium-phosphorus homeostasis via both the local process of ost...

The laboratory rat is one of the most frequently-used animal models for studying bone biology and skeletal diseases. Here we show that a substantial portion of the cortical bone of mature rats is primary endochondral bone, consisting of a disorganized arrangement of mineralized collagen fibers which often include mineralized cartilage islands. We c...

The pro-inflammatory cytokine interleukin-1 (IL-1) signals through IL-1 receptor type I (IL-1RI) and induces osteoclastogenesis and bone resorption, mainly during pathological conditions. Little is known about the effect of excess or absence of IL-1 signaling on the physiological development of the growth plate and bone. In this study, we examine g...

The objective of this study was to examine the effect of embryonic nutritional enrichment on the development and properties of broiler leg bones (tibia and femur) from the pre-natal period until maturity. To accomplish the objective, 300 eggs were divided into 2 groups: a non-injected group (control) and a group injected in ovo with a solution cont...

The effect of hydration on the mechanical properties of osteonal bone, in directions parallel and perpendicular to the bone axis, was studied on three length scales: (i) the mineralized fibril level (∼100 nm), (ii) the lamellar level (∼6 µm); (iii) the osteon level (up to ∼30 µm).We used a number of techniques, namely atomic force microscopy (AFM),...

Fetal and postnatal bone development in humans is traditionally viewed as a process characterized by progressively increasing mineral density. Yet, a temporary decrease in mineral density has been described in the long bones of infants in the immediate postnatal period. The mechanism that underlies this phenomenon, as well as its causes and consequ...

The development of broilers is an extreme example of rapid growth, increasing in weight from 40 g at hatch to 2,000 g 5 to 6 wk later. Such rapid growth requires a correspondingly fast development of the skeleton. Bone development is a genetically programmed process that is modified by epigenetic factors, mainly muscle-induced stresses and strains....

In the darkness of the deep ocean a surprising diversity of organisms generate their own light to find food, communicate or avoid predation. The velvet belly lanternshark, Etmopterus spinax, from one of the few families of luminous sharks, emits a blue glow from thousands of tiny photophores embedded in its skin. Etmopterus, like most luminous and...

The histological diversity of the skeletal tissues of fishes is impressive compared with that of other vertebrate groups, yet our understanding of the functional consequences of this diversity is limited. In particular, although it has been known since the mid-1800s that a large number of fish species possess acellular bones, the mechanical advanta...

Designed peptides may generate molecular scaffolds in the form of hydrogels to support tissue regeneration. We studied the effect of hydrogels comprising β-sheet-forming peptides rich in aspartic amino acids and of tricalcium phosphate (β-TCP)-loaded hydrogels on calcium adsorption and cell culture in vitro, and on bone regeneration in vivo. The hy...

Although fish species represent probably about half of all vertebrate species, the structure and material properties of fish skeletons are poorly understood. Since osteocytes (cells within the bone tissue) are believed to orchestrate the modeling and remodeling responses in mammalian bone, the unique lack of these cells in the bones of the majority...

The mechanical properties of rat bone at micron length scales have been evaluated as a function of environmental conditions using an in situ atomic force microscope (AFM) setup while observing using scanning electron microscopy (SEM). Focused ion beam fabricated rat bone cantilever samples were tested in both low and high vacuum conditions in the S...

Teeth sustain high loads over a lifetime and yet intact tooth failure is rare. The different structures of the tooth, jaw bone and the intervening soft periodontal ligament enable the tooth to endure repeated loading during mastication. Although mechanical and functional properties of the different components are thoroughly investigated, the manner...