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Iron is retained in the duodenum of PrP KO mice. (A) Autoradiogram of upper gastrointestinal tract of Wt and PrP KO mice fed 20 mCi of 59 FeCl 3 by gastric gavage shows higher levels of 59 Fe in PrP KO samples after 1, 4, 24, and 48 hours of chase (lanes 1-10). The difference becomes more obvious after 11 days of chase (lanes 11 and 12). (Lanes 9 and 10 were exposed for 24 hours and lanes 11 and 12 for 6 days to observe the difference clearly). A representative experiment out of a total of three is shown. (B) Quantification of 59 Fe in the first 10 cm of the duodenum shows significantly higher 59 Fe in the PrP KO samples at all time points tested compared to matched Wt controls. Values are mean6SEM, n = 3. *p,0.01 as compared to Wt. doi:10.1371/journal.pone.0006115.g005
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Despite overwhelming evidence implicating the prion protein (PrP) in prion disease pathogenesis, the normal function of this cell surface glycoprotein remains unclear. In previous reports we demonstrated that PrP mediates cellular iron uptake and transport, and aggregation of PrP to the disease causing PrP-scrapie (PrP(Sc)) form results in imbalanc...
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... following organs were evaluated: 1) stomach with attached duodenum, jejunum, and a small piece of ileum, 2) liver, 3) spleen, 4) brain, 5) femurs, and 6) tibial bones. Washed upper gastrointestinal tract was vacuum-dried and exposed to X-ray film ( Figure 5A), and after obtaining adequate film exposures, 59 Fe incorporated in the upper 10 cm of the duodenum was quantified in a c-counter. Whole blood, washed red blood cells (RBCs), plasma, organs, and bones were counted in a c-counter to quantify 59 Fe incorporation. ...
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... of duodenum samples demonstrate significantly more 59 Fe in PrP KO samples at each time point compared to Wt controls ( Figure 5A, lanes 1-12). Surprisingly, the amount of 59 Fe in the duodenum of PrP KO mice is significantly higher than Wt samples even after 11 days of chase ( Figure 5A, lanes 11 and 12). ...
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... of duodenum samples demonstrate significantly more 59 Fe in PrP KO samples at each time point compared to Wt controls ( Figure 5A, lanes 1-12). Surprisingly, the amount of 59 Fe in the duodenum of PrP KO mice is significantly higher than Wt samples even after 11 days of chase ( Figure 5A, lanes 11 and 12). Samples in lanes 1-8 were exposed to X-ray film for 2 hours, lanes 9 and 10 for 24 hours, and lanes 11 and 12 for 6 days to highlight the difference in 59 Fe content between Wt and PrP KO samples ( Figure 5A, lanes 9-12). ...
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... the amount of 59 Fe in the duodenum of PrP KO mice is significantly higher than Wt samples even after 11 days of chase ( Figure 5A, lanes 11 and 12). Samples in lanes 1-8 were exposed to X-ray film for 2 hours, lanes 9 and 10 for 24 hours, and lanes 11 and 12 for 6 days to highlight the difference in 59 Fe content between Wt and PrP KO samples ( Figure 5A, lanes 9-12). Quantitative analysis of these results was performed by counting the first 10 cm of the duodenum from each sample in a c-counter. ...
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... expected, both samples show a gradual decline in 59 Fe counts with increasing chase time, falling to 0.1% of the initial value after 11 days of chase. However, PrP KO samples show higher retention of 59 Fe by 21, 60, 87, 32, and 57% relative to matched Wt controls after a chase of 1, 4, 24, and 48 hours and 11 days respectively ( Figure 5B). Mice ranging in age from 3-6 months and blinded to the person performing the experiment yielded similar results. ...
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... is retained within ferritin in the duodenal epithelium of PrP KO mice. (A) The 4 hour duodenum samples in Figure 5 above were homogenized and separated on a non-denaturing gel followed by autoradiography (lanes 1 and 2). The level of 59 Fe labeled ferritin is significantly higher in the PrP KO sample compared to matched Wt control (lanes 1 and 2). ...
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... bands of 59 Fe-ferritin and 59 Fe-Tf are detected in the PrP KO sample after 4 hours of chase revealing 59 Fe content several-fold higher than matched Wt controls (Figure 9, and 4). However, the signal is lost by 24 hours of chase, making it unlikely that reticulo-endothelial cells sequester the incorporated 59 Fe (Figure 9, lanes 5-8). At all other time points the Wt sample shows slightly higher 59 Fe-ferritin and 59 Fe-Tf compared to PrP KO samples (Figure 9, lanes 1, 2, and 5-8). ...
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... reduce variability, littermate PrP KO and PrP + mice were obtained by crossing PrP + and PrP KO breeding pairs. After confirming the genotype (data not shown), littermate PrP + and PrP KO , Wt, and PrP KO mice were evaluated for iron uptake and transport by introducing equal amounts of 59 FeCl 3 by gastric gavage as in Figures 5 and 7 above ( Figure 10B and C). Only the 4 hour chase time point was assessed since the maximum differences between Wt and PrP KO mice are observed at this time point (Figure 5 and 7 above). ...
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... confirming the genotype (data not shown), littermate PrP + and PrP KO , Wt, and PrP KO mice were evaluated for iron uptake and transport by introducing equal amounts of 59 FeCl 3 by gastric gavage as in Figures 5 and 7 above ( Figure 10B and C). Only the 4 hour chase time point was assessed since the maximum differences between Wt and PrP KO mice are observed at this time point (Figure 5 and 7 above). Autoradiography of duodenum samples shows significantly more 59 Fe in the PrP KO sample compared to the Wt control as noted in Figure 5 above ( Figure 10B, lanes 1 and 2). ...
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... the 4 hour chase time point was assessed since the maximum differences between Wt and PrP KO mice are observed at this time point (Figure 5 and 7 above). Autoradiography of duodenum samples shows significantly more 59 Fe in the PrP KO sample compared to the Wt control as noted in Figure 5 above ( Figure 10B, lanes 1 and 2). Notably, a similar difference is seen between PrP KO and PrP + littermates ( Figure 10B, lanes 3 and 4), indicating improved transport of 59 Fe from the duodenum of mice expressing PrP. ...
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Brain iron-dyshomeostasis is an important cause of neurotoxicity in prion disorders, a group of neurodegenerative conditions associated with the conversion of prion protein (PrPC) from its normal conformation to an aggregated, PrP-scrapie (PrPSc) isoform. Alteration of iron homeostasis is believed to result from impaired function of PrPC in neurona...
Citations
... Considering that ZIP14 transports Fe 2+ , but not Fe 3+ , reduction of Fe 3+ is required, which occurs, likely, with the help of specific reductase [61]. There is a possibility that the reductase activity is mediated by the cellular prion protein (PrPc) [62]. ...
... There is increasing evidence that PrP is involved in iron homeostasis. Mice lacking PrP gene show an altered iron metabolism and reduced brain iron levels [146]. PrP Sc and ferritin complex is of high redox activity and is highly cytotoxic unless rapidly degraded by cellular mechanisms [147,148]. ...
... Additionally, patients with CJD have altered levels of ferroxidase and transferrin in the CSF [150]. PrP c models cellular iron uptake and induces the conversion of Fe 3+ to Fe 2+ [146,151]. PrP c gene mRNAs contain IREs that control iron homeostasis. The binding of IRP proteins to IREs is influenced by changes in intracellular iron levels. ...
Iron is the micronutrient with the best-studied biological functions. It is widely distributed in nature, and its involvement in the main metabolic pathways determines the great importance of this metal for all organisms. Iron is required for cellular respiration and various biochemical processes that ensure the proper functioning of cells and organs in the human body, including the brain. Iron also plays an important role in the production of free radicals, which can be beneficial or harmful to cells under various conditions. Reviews of iron metabolism and its regulation can be found in the literature, and further advances in understanding the molecular basis of iron metabolism are being made every year. The aim of this review is to systematise the available data on the role of iron in the function of the nervous system, especially in the brain. The review summarises recent views on iron metabolism and its regulatory mechanisms in humans, including the essential action of hepcidin. Special attention is given to the mechanisms of iron absorption in the small intestine and the purpose of this small but critically important pool of iron in the brain.
... The regulation of these iron ion-containing molecules is tightly controlled as their dysregulation may be harmful to human health [12,[25][26][27][28][29][30], as heme also appears to have toxic properties [31]. Further evidence for the tight regulation of iron ions during pregnancy [32], exercise [33], and hypoxia [34] indicate that this ion is very important biologically. ...
Life on Earth evolved to accommodate the biochemical and biophysical boundary conditions of the planet millions of years ago. The former includes nutrients, water, and the ability to synthesize other needed chemicals. The latter includes the 1 g gravity of the planet, radiation, and the geomagnetic field (GMF) of the planet. How complex life forms have accommodated the GMF is not known in detail, considering that Homo sapiens evolved a neurological system, a neuromuscular system, and a cardiovascular system that developed electromagnetic fields as part of their functioning. Therefore, all of these could be impacted by magnetic fields. In addition, many proteins and physiologic processes utilize iron ions, which exhibit magnetic properties. Thus, complex organisms, such as humans, generate magnetic fields, contain significant quantities of iron ions, and respond to exogenous static and electromagnetic fields. Given the current body of literature, it remains somewhat unclear if Homo sapiens use exogenous magnetic fields to regulate function and what can happen if the boundary condition of the GMF no longer exerts an effect. Proposed deep space flights to destinations such as Mars will provide some insights, as space flight could not have been anticipated by evolution. The results of such space flight “experiments” will provide new insights into the role of magnetic fields on human functioning. This review will discuss the literature regarding the involvement of magnetic fields in various normal and disturbed processes in humans while on Earth and then further discuss potential outcomes when the GMF is no longer present to impact host systems, as well as the limitations in the current knowledge. The GMF has been present throughout evolution, but many details of its role in human functioning remain to be elucidated, and how humans have adapted to such fields in order to develop and retain function remains to be elucidated. Why this understudied area has not received the attention required to elucidate the critical information remains a conundrum for both health professionals and those embarking on space flight. However, proposed deep space flights to destinations such as Mars may provide the environments to test and assess the potential roles of magnetic fields in human functioning.
... The octarepeat domain was essential for this ferrireductase activity. Moreover, PrP-knockout mice exhibited altered Fe metabolism and reduced Fe levels in the brain [97]. Meanwhile, the Fe level controls the expression of PrP C because its mRNA possesses an IRE motif as well as the APP gene [98]. ...
Trace elements such as iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn) are absorbed from food via the gastrointestinal tract, transported into the brain, and play central roles in normal brain functions. An excess of these trace elements often produces reactive oxygen species and damages the brain. Moreover, increasing evidence suggests that the dyshomeostasis of these metals is involved in the pathogenesis of neurodegenerative diseases, including Alzheimer’s disease, prion diseases, and Lewy body diseases. The disease-related amyloidogenic proteins can regulate metal homeostasis at the synapses, and thus loss of the protective functions of these amyloidogenic proteins causes neurodegeneration. Meanwhile, metal-induced conformational changes of the amyloidogenic proteins contribute to enhancing their neurotoxicity. Moreover, excess Zn and Cu play central roles in the pathogenesis of vascular-type senile dementia. Here, we present an overview of the intake, absorption, and transport of four essential elements (Fe, Zn, Cu, Mn) and one non-essential element (aluminum: Al) in food and their connections with the pathogenesis of neurodegenerative diseases based on metal–protein, and metal–metal cross-talk.
... Rogers et al. [104] reported that a set of common-acting, iron-responsive 5 ′ -untranslated region (5 ′ UTR) motifs can be folded into RNA stem-loops that have a significant impact on AD. Iron is a positive regulator of amyloid precursor protein (APP) translation via the iron-responsive-like element (IRE-like) RNA stem-loops in the 5 ′ UTR of APP mRNA [104][105][106]. Studies have shown that Aβ plays an important role in the reduction of divalent iron, with this transformational process leading to excess free radical production and neuronal damage [107]. ...
Ferroptosis is distinct from other apoptotic forms of programmed cell death and is characterized by the accumulation of iron and lipid peroxidation. Iron plays a crucial role in the oxidation of lipids via the Fenton reaction with oxygen. Hence, iron accumulation causes phospholipid peroxidation which induces ferroptosis. Moreover, detoxification by glutathione is disrupted during ferroptosis. A growing number of studies have implicated ferroptosis in nervous system disorders such as depression, neurodegenerative disease, stroke, traumatic brain injury, and sepsis-associated encephalopathy. This review summarizes the pathogenesis of ferroptosis and its relationship with various nervous system disorders.
... It seems to facilitate iron transport across duodenal enterocytes, as shown in PrP KO mice whose systemic iron homeostasis is abnormal. Specifically, a functional role of PrP in iron metabolism has been reported, which might explain the imbalance of iron homeostasis in prion disease as a result of a loss of PrP function [20]. After reduction, DMT-1 channels Fe 2+ into the enterocyte thanks to an electrochemical gradient of H + (from outside to inside of the cell) [17,21] (Table 1, Figure 1). ...
Reactive Oxygen Species (ROS) play a key role in the neurodegeneration processes. Increased oxidative stress damages lipids, proteins, and nucleic acids in brain tissue, and it is tied to the loss of biometal homeostasis. For this reason, attention has been focused on transition metals involved in several biochemical reactions producing ROS. Even though a bulk of evidence has uncovered the role of metals in the generation of the toxic pathways at the base of Alzheimer’s disease (AD), this matter has been sidelined by the advent of the Amyloid Cascade Hypothesis. However, the link between metals and AD has been investigated in the last two decades, focusing on their local accumulation in brain areas known to be critical for AD. Recent evidence revealed a relation between iron and AD, particularly in relation to its capacity to increase the risk of the disease through ferroptosis. In this review, we briefly summarize the major points characterizing the function of iron in our body and highlight why, even though it is essential for our life, we have to monitor its dysfunction, particularly if we want to control our risk of AD.
... 124 The brains from transgenic mice expressing different levels of PrP ( wild-type, expressing normal level of PrP, a Tga20 over-expressing line, and a prion gene knockout line ) have been mapped with XFM, and these demonstrated significant differences in Fe, Cu, and Zn as a function of PrP expression level. 121 A line of FVB mice infected with the RML strain of infectious prion material ( a strain passaged in mice by inoculation with scrapie 125 and once deaths were identified to be imminent the animals were euthanized and their brains harvested. 126 Perls' stain is used to identify ferric iron in tissue and turns a vibrant blue color when Fe is present. ...
Synchrotron-based X-ray fluorescence microscopy is a flexible tool for identifying the distribution of trace elements in biological specimens across a broad range of sample sizes. The technique is not particularly limited by sample type and can be performed on ancient fossils, fixed or fresh tissue specimens, and in some cases even live tissue and live cells can be studied. The technique can also be expanded to provide chemical specificity to elemental maps, either at individual points of interest in a map or across a large field of view. While virtually any sample type can be characterized with X-ray fluorescence microscopy, common biological sample preparation methods (often borrowed from other fields, such as histology) can lead to unforeseen pitfalls, resulting in altered element distributions and concentrations. A general overview of sample preparation and data acquisition methods for X-ray fluorescence microscopy is presented, along with outlining the general approach for applying this technique to a new field of investigation for prospective new-users. Considerations for improving data acquisition and quality are reviewed as well as the effects of sample preparation, with a particular focus on soft tissues. The effects of common sample pre-treatment steps as well as the underlying factors that govern which, and to what extent, specific elements are likely to be altered are reviewed along with common artifacts observed in X-ray fluorescence microscopy data.
... It contains a short polybasic stretch ( 23 KKRPKPGGW 31 ), a series of four histidine-containing octapeptide repeats (residues 59-90), a second, positively charged cluster (residues [101][102][103][104][105][106][107][108][109], and a hydrophobic region (residues 112-129) [1,4]. The globular C-terminal domain (AA 128-230), consists of three α-helices (at AA 144-154; AA [175][176][177][178][179][180][181][182][183][184][185][186][187][188][189][190][191][192][193], and two short, antiparallel β-strands flanking helix 1 (S1: 128-131; and S2: 161-164) [1,[4][5][6]. The globular C-terminal domain also contains two variably occupied N-glycosylation sites at Asn181 and Asn197 and a disulfide bridge between Cys179 and Cys214 [7] (see Fig. 1). ...
... It would be interesting to clarify the role of the Cu-bound forms of PrP C in the reduction of Fe(III). The available evidence highlights an important role for PrP C in iron physiology and, fittingly, a role of iron imbalances in prion disease pathology [187][188][189]. Interestingly, Fe(III) seems to induce the conversion of PrP C to a proteinase-resistant form during vesicular trafficking [190]. ...
The prion protein is a multifunctional protein that exists in at least two different folding states. It is subject to diverse proteolytic processing steps that lead to prion protein fragments some of which are membrane-bound whereas others are soluble. A multitude of ligands bind to the prion protein and besides proteinaceous binding partners, interaction with metal ions and nucleic acids occurs. Although of great importance, information on structural and functional consequences of prion protein binding to its partners is limited. Here, we will reflect on the structure-function relationship of the prion protein and its binding partner considering the different folding states and prion proteins fragments.
... The symptom of prion protein infection was first described in 1732 when Merino sheep scraped pathologically against fences [1], but the term prion (PRoteinaceous Infective ONly particle) was not coined until 1982 by Prusiner who defined prions in 1998 as heritable, infectious, proteinaceous particles that are converted from the normal, cellular form (PrP C ) into the pathogenic form (PrP Sc ) that associates with amyloid plaques [2,3]. The full-length prion protein (PrP) [4] exists as a native, soluble cellular PrP C isoform with important physiological functions [5] including cellular differentiation [6][7][8], proliferation [9], and adhesion [10]; myelin maintenance [11]; circadian rhythm regulation [12,13]; signal transduction [14]; glucose homeostasis [15,16]; immune regulation [17,18]; as well as copper homeostasis, utilization [19,20]; iron uptake, transport, and metabolism [21][22][23]; and even facilitating the persistence and storage of memory [24,25]. In humans, quantitative transcriptomics analysis (RNA-Seq) of 27 different tissues obtained from 95 human individuals [26] found the prion gene PRNP to be ubiquitously expressed in all 27 human tissues examined in addition to mitochondria, with the highest expressions found in the brain, followed by the ovary, prostate, heart, gallbladder, endometrium, adrenal, urinary bladder, thyroid, testis, skin, esophagus, and lung [27]. ...
... Iron is required in essential metabolic processes [524], and PrP may perform important roles in iron uptake and transport [22]. Absence of PrP induces systemic iron deficiency in PrP KO mice caused by less efficient uptake by red blood cells (RBCs), liver, and brain as the result of impaired transport of iron from the duodenal enterocytes-a condition that can be easily reversed by expressing WT PrP [23]. Similarly, over-expression of PrP C increased intracellular iron, cellular labile iron pool, and iron content of ferritin leading to a decrease in total cellular content of transferrin (Tf) and transferrin receptor (TfR) proteins responsible for iron uptake, but an increase in ferritin responsible for iron storage [525]. ...
The unique ability to adapt and thrive in inhospitable, stressful tumor microenvironments (TME) also renders cancer cells resistant to traditional chemotherapeutic treatments and/or novel pharmaceuticals. Cancer cells exhibit extensive metabolic alterations involving hypoxia, accelerated glycolysis, oxidative stress, and increased extracellular ATP that may activate ancient, conserved prion adaptive response strategies that exacerbate multidrug resistance (MDR) by exploiting cellular stress to increase cancer metastatic potential and stemness, balance proliferation and differentiation, and amplify resistance to apoptosis. The regulation of prions in MDR is further complicated by important, putative physiological functions of ligand-binding and signal transduction. Melatonin is capable of both enhancing physiological functions and inhibiting oncogenic properties of prion proteins. Through regulation of phase separation of the prion N-terminal domain which targets and interacts with lipid rafts, melatonin may prevent conformational changes that can result in aggregation and/or conversion to pathological, infectious isoforms. As a cancer therapy adjuvant, melatonin could modulate TME oxidative stress levels and hypoxia, reverse pH gradient changes, reduce lipid peroxidation, and protect lipid raft compositions to suppress prion-mediated, non-Mendelian, heritable, but often reversible epigenetic adaptations that facilitate cancer heterogeneity, stemness, metastasis, and drug resistance. This review examines some of the mechanisms that may balance physiological and pathological effects of prions and prion-like proteins achieved through the synergistic use of melatonin to ameliorate MDR, which remains a challenge in cancer treatment.
... However, under pathological conditions of iron overload, excess iron circulates bound to a mixture of lowmolecular weight molecules, collectively referred to as nontransferrin-bound iron (NTBI). 71,72 NTBI is rapidly taken up by hepatocytes along the sinusoidal membrane; a reductase converts Fe 3+ of NTBI to Fe 2+ , possibly by prion protein, 73,74 which then translocates via the Zrt-and Irt-like protein 14 (ZIP14) transmembrane metal-ion transporter. 75−77 3.2. ...
