Mouse Skeleton Research Articles

OPG-Fc treatment partially rescues low bone mass phenotype in mature Bgn/Fmod deficient mice but is deleterious to the young mouse skeleton

Biglycan (Bgn) and Fibromodulin (Fmod) are small leucine rich proteoglycans (SLRPs) which are abundant in the extra-cellular matrix (ECM) of mineralized tissues. We have previously generated a Bgn/Fmod double knock-out (DKO) mouse model and found it has a 3-fold increase in osteoclastogenesis compared with Wild type (WT) controls, resulting in a markedly low bone mass (LBM) phenotype. To try and rescue/repair the LBM phenotype of Bgn/Fmod DKO mice by suppressing osteoclast formation and activity, 3- and 26-week-old Bgn/Fmod DKO mice and age/gender matched WT controls were treated with OPG-Fc for 6 weeks after which bone parameters were evaluated using DEXA, micro-computed tomography (μCT) and serum biomarkers analyses. In the appendicular skeleton, OPG-Fc treatment improved some morphometric and geometric parameters in both the trabecular and cortical compartments in Bgn/Fmod DKO female and male mice, especially in the repair module. For many of the skeletal parameters analyzed, the Bgn/Fmod DKO mice were more responsive to the treatment than their WT controls. In addition, we found that OPG-Fc treatment was not able to prevent or ameliorate the formation of ectopic ossification, which are common lesions seen in aged joints and are one of the phenotypical hallmarks of our Bgn/Fmod DKO model. Analysis of skull bones, specifically the occipital bone, showed the treatment recovered some parameters of LBM phenotype in the craniofacial skeleton, more so in the younger rescue module. Using OPG-Fc as treatment alleviated, yet did not completely restore, the severe osteopenia and mineralized tissue structural abnormalities that Bgn/Fmod DKO mice suffer from.

Crossfibrillar mineral tessellation in normal and Hyp mouse bone as revealed by 3D FIB-SEM microscopy

In bone, structural components such as mineral extend across length scales to provide essential biomechanical functions. Using X-ray micro-computed tomography (µCT), and focused ion beam scanning electron microscopy (FIB-SEM) in serial-surface-view mode, together with 3D reconstruction, entire mouse skeletons and small bone tissue volumes were examined in normal wildtype (WT) and mutant Hyp mice (an animal model for X-linked hypophosphatemia/XLH, a disease with severe hypomineralization of bone). 3D thickness maps of the skeletons showed pronounced irregular thickening and abnormalities of many skeletal elements in Hyp mice compared to WT mice. At the micro- and nanoscale, near the mineralization front in WT tibial bone volumes, mineralization foci grow as expanding prolate ellipsoids (tesselles) to abut and pack against one another to form a congruent and contiguous mineral tessellation pattern within collagen bundles that contributes to lamellar periodicity. In the osteomalacic Hyp mouse bone, mineralization foci form and begin initial ellipsoid growth within normally organized collagen assembly, but their growth trajectory aborts. Mineralization-inhibiting events in XLH/Hyp (low circulating serum phosphate, and increased matrix osteopontin) combine to result in decreased mineral ellipsoid tessellation – a defective mineral-packing organization that leaves discrete mineral volumes isolated in the extracellular matrix such that ellipsoid packing/tessellation is not achieved. Such a severely altered mineralization pattern invariably leads to abnormal compliance, other aberrant biomechanical properties, and altered remodeling of bone, all of which indubitably lead to macroscopic bone deformities and anomalous mechanical performance in XLH/Hyp. Also, we show the relationship of osteocytes and their cell processes to this mineralization pattern.

DDB1 promotes the proliferation and hypertrophy of chondrocytes during mouse skeleton development

The proliferation and hypertrophy of chondrocytes play important roles in endochondral ossification, which is tightly regulated during skeleton development. However, the regulation mechanism remains largely unknown. Here we show that DDB1 (Damaged DNA Binding Protein 1) has a critical function in the development of growth plates. Using chondrocyte-specific DDB1 knockout mice, we found that DDB1 deletion in chondrocytes results in dwarfism due to the aberrant skeleton development. The structure of growth plate in tibia becomes disordered at P21, not in femur. But at P70, the changes are severer in femur than tibia. Chondrocyte proliferation and differentiation are attenuated and asynchronous in both tibia and femur at P7 and P21. Furthermore, DDB1 deficiency induces p27 upregulation and subsequent cell cycle arrest in primary chondrocytes. Therefore, our data reveal that DDB1 is essential for the skeleton development by controlling chondrocyte proliferation and differentiation.

Expression of a Constitutively Active Form of Hck in Chondrocytes Activates Wnt and Hedgehog Signaling Pathways, and Induces Chondrocyte Proliferation in Mice.

Runx2 is required for chondrocyte proliferation and maturation. In the search of Runx2 target genes in chondrocytes, we found that Runx2 up-regulated the expression of hematopoietic cell kinase (Hck), which is a member of the Src tyrosine kinase family, in chondrocytes, that Hck expression was high in cartilaginous limb skeletons of wild-type mice but low in those of Runx2–/– mice, and that Runx2 bound the promoter region of Hck. To investigate the functions of Hck in chondrocytes, transgenic mice expressing a constitutively active form of Hck (HckCA) were generated using the Col2a1 promoter/enhancer. The hind limb skeletons were fused, the tibia became a large, round mass, and the growth plate was markedly disorganized. Chondrocyte maturation was delayed until E16.5 but accelerated thereafter. BrdU-labeled, but not terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive, chondrocytes were increased. Furthermore, Hck knock-down reduced the proliferation of primary chondrocytes. In microarray and real-time RT-PCR analyses using hind limb RNA from HckCA transgenic mice, the expression of Wnt (Wnt10b, Tcf7, Lef1, Dkk1) and hedgehog (Ihh, Ptch1, and Gli1) signaling pathway genes was upregulated. These findings indicated that Hck, whose expression is regulated by Runx2, is highly expressed in chondrocytes, and that HckCA activates Wnt and hedgehog signaling pathways, and promotes chondrocyte proliferation without increasing apoptosis.

Development of Craniofacial Biomineralization in Mice with Osteogenesis Imperfecta (OI)

Osteogenesis imperfecta (OI), or “brittle bone disease,” is a rare autosomal dominant disorder characterized by mutations in the genes that encode the alpha 1 (COL1A1) and alpha 2 (COL1A2) chains of type I collagen, a significant component of bone. Misfolding of the mutated collagen polypeptides interfere with proper assembly of collagen chains, or the triple helical structures, leading to extreme skeletal fragility. OI manifests in a variety of types, with type I being the most mild and most common, and type III, the subject of this study, being more severe and more rare. Clinical manifestations of OI type III generally include a short stature, low bone mineral density (BMD), dental problems, hearing loss, and blue sclerae. In this study, we use a mouse model of OI type III to examine how mutations in type I collagen synthesis impact craniofacial biomineralization during postnatal growth.The homozygous recessive osteogenesis imperfecta murine (OIM) is a model of OI type III and is characterized by increased skeletal fractures, low postcranial BMD, osteopenia, progressive skeletal deformities, and small body size. Wild type mice (WT) and OIM littermates (n≥3/genotype) were micro‐CT scanned at weaning (4 weeks) and adulthood (16 weeks). BMD at three regions of interest (ROI) within the mouse skull was measured using Bruker CTAnalyzer software. ROIs were chosen based on the amount of load during mastication, and included the temporomandibular joint (TMJ), the parietal bone (1mm from the sagittal suture), and the anterior maxilla at the incisal alveolus. Mann‐Whitney U‐tests (α=0.05) were used to compare BMD values between the genotypes for each ROI.At weaning, OIM mice had significantly lower BMD values (g.cm−3 CaHA) than their wild type littermates at the TMJ (0.39 vs 0.58), parietal bone (0.35 vs 0.64), and anterior maxilla (0.53 vs 0.85). These statistical differences persist into adulthood. This decrease in BMD reflects decreased deposition of CaHA due to an abnormal collagen framework in the craniofacial skeleton of OIM mice. Ongoing efforts will expand this analysis to quantify the development of BMD at additional regions within the craniofacial skeleton.Support or Funding InformationThis research was supported by an Indiana University Collaborative Research Grant and the Ralph W. and Grace Showalter Trust.

High-Phosphate Diet Improved the Skeletal Development of Fam20c-Deficient Mice

FAM20C (family with sequence similarity 20 – member C) is a protein kinase that phosphorylates secretory proteins, including the proteins that are essential to the formation and mineralization of calcified tissues. Previously, we reported that inactivation of Fam20c in mice led to hypophosphatemic rickets/osteomalacia along with increased circulating fibroblast growth factor 23 (FGF23) levels and dental defects. In this study, we examined whether a high-phosphate (hPi) diet could rescue the skeletal defects in Fam20c-deficient mice. Fam20c conditional knockout (cKO) mice were generated by crossing female Fam20c-floxed mice (Fam20cfl/fl) with male Sox2-Cre;Fam20cfl/+ mice. The pregnant female Fam20cfi/fl mice were fed either a normal or hPi diet until the litters were weaned. The cKO and control offspring were continuously given a normal or hPi diet for 4 weeks after weaning. Plain X-ray radiography, micro-CT, histology, immunohistochemistry (FGF23, DMP1, OPN, and SOX9), and in situ hybridization (type II and type X collagen) analyses were performed to evaluate the effects of an hPi diet on the mouse skeleton. Plain X-ray radiography and micro-CT radiography analyses showed that the hPi diet improved the shape and mineral density of the Fam20c-deficient femurs/tibiae, and rescued the growth plate defects in the long bone. Histology analyses further demonstrated that an hPi diet nearly completely rescued the growth plate-widening defects in the long bone and restored the expanded hypertrophic zone to nearly normal width. These results suggested that the hPi diet significantly improved the skeletal development of the Fam20c-deficient mice, implying that hypophosphatemia partially contributed to the skeletal defects in Fam20c-deficient subjects.

A study on the distribution of 85Sr and 134Cs radionuclides after total body irradiation

The kinetics of strontium, 85Sr, and cesium, 134Cs, were evaluated in a mouse experimental model to determine the impact of these radionuclides on a living organism concerning total body irradiation. Our study demonstrates that the elimination rate of 134Cs from the skeleton and teeth is influenced by total body irradiation and the presence of 85Sr. Higher accumulation and faster 134Cs elimination rates were observed in the skeleton and teeth of mice administrated with a mixture of 134Cs + 85Sr radionuclides. Regarding 85Sr, only a minimal effect was observed on its accumulation rate in skeleton, teeth, and muscle in total body irradiation mice. The effect of the 85Sr + 134Cs radionuclide mix on the accumulation of 85Sr was more apparent in teeth, showing a higher retention rate after 10-24 days of administration in non-irradiated mice. The evaluation of the kinetics of these radionuclides provided much-needed insight on their effects during the first two months after exposure, demonstrating that the accumulation rate of 85Sr is greater than that of 134Cs. Further, the elimination rate of the former is slower in comparison to the latter. Interestingly, total body irradiation has a greater effect on the hematological parameters of the mice blood than the radionuclides alone.

Megakaryocyte-Driven Myelofibrosis Leads to Progressive Osteosclerosis in G6b-B Knockout Mice

Bone and bone marrow are not only anatomically, but also functionally interdependent. In a systematic review, we examined bone health in patients with hematopoietic disorders and demonstrated that an increased hematopoietic cell proliferation, such as in patients with hemolytic anemias, was associated with bone loss, while bone marrow hypocellularity, such as in patients with chronic myelofibrosis (CMF), was associated with bone gain [Steer K et al. J Bone Miner Res 2017]. Since bone mass in CMF increases at the expense of bone marrow, it contributes to patients' morbidity as it is associated with bone pain, and mortality as it may lead to bone marrow failure. A mouse model with a global knockout of the megakaryocyte (MK) lineage specific inhibitory receptor G6b-B was shown to develop myelofibrosis secondary to aberrant platelet production and function [Mazharian A et al Sci Signal 2012]. Moreover, a group of patients with primary myelofibrosis was identified to have loss-of-function mutations in the G6b-B gene [Hofmann I et al Blood 2018]. The objective of this study was to characterize temporal changes in the skeleton of the G6b-B knockout mice. We examined age- and sex-related changes in 4, 8, 16, and 32 week-old G6b-B+/+, G6b-B-/- female and male mice. Starting from 8 weeks-of-age, spleen progressively increased in female G6b-B-/- mice compared to corresponding G6b-B+/+ mice, reaching 2.9-fold increase at 32 weeks (p < 0.001) (Fig.1A). Micro-computed tomography analysis of femur demonstrated that starting at 8 weeks of age female G6b-B-/- mice had a significantly higher proportion of cortical bone and a respectively lower proportion of marrow (Fig.1B). Starting at 16 weeks of age, female G6b-B-/- mice developed trabecula in the medullary cavity normally occupied by the bone marrow, which by 32 weeks led to a 38-fold increase (p < 0.001) in the proportion of bone to tissue volume compared to G6b-B+/+ (Fig.1C,D). At 32-weeks of age, female G6b-B-/- mice also demonstrated a 7-fold increase in BV/TV (p < 0.001) in the region of metaphysis. While some abnormalities were found in male G6b-B-/- mice, they were considerably less severe compared to females. To establish whether the observed bone phenotype is due to MK and platelet functional defects, we performed microcomputed tomography analysis on femurs of 22 week-old G6b-Bfl/fl;Gp1ba-Cre-/- mice with a MK/platelet-specific knockout of G6b-B. Changes in trabecular bone of G6b-Bfl/fl;Gp1ba-Cre-/- mice recapitulated changes of G6b-B-/- mice. However, periosteal perimeter in male G6b-Bfl/fl;Gp1ba-Cre-/- mice was significantly larger, and in female G6b-Bfl/fl;Gp1ba-Cre-/- mice - significantly smaller than in corresponding control mice, while in global G6b-B-/- mice periosteal perimeter was not affected. Female G6b-B-/- mice demonstrated severe splenomegaly as well as progressive osteosclerosis, which was confirmed in G6b-Bfl/fl;Gp1ba-Cre-/- mice, indicating that trabecular bone gain in G6b-B-/- mice is consequent to a MK disfunction. Dramatic sexual dimorphism suggests that sex-related factors play an important role in the development of osteosclerosis. The differences in cortical bone phenotype between the global and conditional knockout of G6b-B suggest the potential role of G6b-B signaling in osteoclasts or osteoblasts. This study demonstrates that MK-associated myelofibrosis is sufficient to induce osteosclerosis of bone marrow, and that sex hormones play an important role either in protecting male mice from osteosclerosis or in exacerbating osteosclerosis in female mice. Disclosures No relevant conflicts of interest to declare.

Genetically-achieved disturbances to the expression levels of TNFSF11 receptors modulate the effects of zoledronic acid on growing mouse skeletons

Zoledronic acid (ZOL), a nitrogen bisphosphonate (N-BP), is currently used to treat and control pediatric osteolytic diseases. Variations in the intensity of the effects and side effects of N-BPs have been reported with no clear explanations regarding their origins. We wonder if such variations could be associated with different levels of RANKL signaling activity in growing bone during and after the treatment with N-BPs. To answer this question, ZOL was injected into neonate C57BL/6J mice with different genetically-determined RANKL signaling activity levels (Opg+/+\\RankTg−, Opg+/+\\RankTg+, Opg+/−\\RankTg−, Opg+/−\\RankTg+, Opg−/−\\RankTg− and Opg−/−\\RankTg+ mice) following a protocol (4 injections from post-natal day 1 to 7 at the dose of 50 μg/kg) that mimics those used in onco-pediatric patients. At the end of pediatric growth (1 and half months) and at an adult age (10 months), the bone morphometric and mineral parameters were measured using μCT in the tibia and skull for the different mice. A histologic analysis of the dental and periodontal tissues was also performed. At the end of pediatric growth, a delay in long bone and skull bone growth, a blockage of tooth eruption, some molar root alterations and a neoplasia-like structure associated with incisor development were found. Interestingly, the magnitude of these side effects was reduced by Opg deficiency (Opg−/−) but increased by Rank overexpression (RankTg). Analysis of the skeletal phenotype at ten months confirmed respectively the beneficial and harmful effects of Opg deficiency and Rank overexpression.These results validated the hypothesis that the RANKL signaling activity level in the bone microenvironment is implicated in the modulation of the response to ZOL. Further studies will be necessary to understand the underlying molecular mechanisms, which will help decipher the variability in the effects of N-BPs reported in the human population. Significant statementsThe present study establishes that in mice the RANKL signaling activity level is a major modulator of the effects and side-effects of bisphosphonates on the individual skeleton during growth. However, the modulatory actions are dependent on the ways in which this level of activity is increased. A decrease in OPG expression is beneficial to the skeletal phenotype observed at the end of growth, while RANK overexpression deteriorates it. Far removed from pediatric treatment, in adults, the skeletal phenotypes initially observed at the end of growth for the different levels of RANKL signaling activity were maintained, although significant improvement was associated only with reductions in OPG expression.

Growth differentiation factor 11 (GDF11) has pronounced effects on skin biology.

Growth differentiation factor 11 (GDF11) belongs to the TGF-β superfamily of proteins and is closely related to myostatin. Recent findings show that GDF11 has rejuvenating properties with pronounced effects on the cardiovascular system, brain, skeletal muscle, and skeleton in mice. Several human studies were also conducted, some implicating decreasing levels of circulating GDF11 with age. To date, however, there have not been any reports on its role in human skin. This study examined the impact of GDF11 on human skin, specifically related to skin aging. The effect of recombinant GDF11 on the function of various skin cells was examined in human epidermal keratinocytes, dermal fibroblasts, melanocytes, dermal microvascular endothelial cells and 3D skin equivalents, as well as in ex vivo human skin explants. GDF11 had significant effects on the production of dermal matrix components in multiple skin models in vitro and ex vivo. In addition, it had a pronounced effect on expression of multiple skin related genes in full thickness 3D skin equivalents. This work, for the first time, demonstrates an important role for GDF11 in skin biology and a potential impact on skin health and aging.

Reduced bone formation in males and increased bone resorption in females drive bone loss in hemophilia A mice

AbstractHemophilia A (HA), a rare X-linked recessive genetic disorder caused by insufficient blood clotting factor VIII, leaves affected individuals susceptible to spontaneous and traumatic hemorrhage. Although males generally exhibit severe symptoms, due to variable X inactivation, females can also be severely impacted. Osteoporosis is a disease of the skeleton predisposing patients to fragility fracture, a cause of significant morbidity and mortality and a common comorbidity in HA. Because the causes of osteoporosis in HA are unclear and in humans confounded by other traditional risk factors for bone loss, in this study, we phenotyped the skeletons of F8 total knockout (F8TKO) mice, an animal model of severe HA. We found that trabecular bone accretion in the axial and appendicular skeletons of male F8TKO mice lagged significantly between 2 and 6 months of age, with more modest cortical bone decline. By contrast, in female mice, diminished bone accretion was mostly limited to the cortical compartment. Interestingly, bone loss was associated with a decline in bone formation in male mice but increased bone resorption in female mice, a possible result of sex steroid insufficiency. In conclusion, our studies reveal a sexual dimorphism in the mechanism driving bone loss in male and female F8TKO mice, preventing attainment of peak bone mass and strength. If validated in humans, therapies aimed at promoting bone formation in males but suppressing bone resorption in females may be indicated to facilitate attainment of peak mass in children with HA to reduce the risk for fracture later in life.

Multimodal Bioluminescent and Positronic-emission Tomography/Computational Tomography Imaging of Multiple Myeloma Bone Marrow Xenografts in NOG Mice

Multiple myeloma (MM) tumors engraft in the bone marrow (BM) and their survival and progression are dependent upon complex molecular and cellular interactions that exist within this microenvironment. Yet the BM microenvironment cannot be easily replicated in vitro, which potentially limits the physiologic relevance of many in vitro and ex vivo experimental models. These issues can be overcome by utilizing a xenograft model in which luciferase (LUC)-transfected 8226 MM cells will specifically engraft in the mouse skeleton. When these mice are given the appropriate substrate, D-luciferin, the effects of therapy on tumor growth and survival can be analyzed by measuring changes in the bioluminescent images (BLI) produced by the tumors in vivo. This BLI data combined with positronic-emission tomography/computational tomography (PET/CT) analysis using the metabolic marker 2-deoxy-2-(18F)fluoro-D-glucose (18F-FDG) is used to monitor changes in tumor metabolism over time. These imaging platforms allow for multiple noninvasive measurements within the tumor/BM microenvironment.

Androgen Receptor in Neurons Slows Age-Related Cortical Thinning in Male Mice.

Androgens via the androgen receptor (AR) are required for optimal male bone health. The target cell(s) for the effects of androgens on cortical bone remain(s) incompletely understood. In females, estrogen receptor alpha in neurons is a negative regulator of cortical and trabecular bone. Whether neuronal AR regulates bone mass in males remains unexplored. Here, we inactivated AR in neurons using a tamoxifen-inducible CreERT2 under the control of the neuronal promoter Thy1. Tamoxifen induced a 70% to 80% reduction of AR mRNA levels in Thy1-CreERT2-positive brain regions cerebral cortex and brainstem as well as in the peripheral nervous tissue of male neuronal AR knockout (N-ARKO) mice. Hypothalamic AR mRNA levels were only marginally reduced and the hypothalamic-pituitary-gonadal axis remained unaffected, as determined by normal levels of serum testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH). In contrast to orchidectomy, deletion of neuronal AR did not alter body weight, body composition, hindlimb muscle mass, grip strength, or wheel running. MicroCT analysis of the femur revealed no changes in bone accrual during growth in N-ARKO mice. However, 36- and 46-week-old N-ARKO mice displayed an accelerated age-related cortical involution, namely a more pronounced loss of cortical thickness and strength, which occurred in the setting of androgen sufficiency. Neuronal AR inactivation decreased the cancellous bone volume fraction in L5 vertebra but not in the appendicular skeleton of aging mice. MicroCT findings were corroborated in the tibia and after normalization of hormonal levels. Serum markers of bone turnover and histomorphometry parameters were comparable between genotypes, except for a 30% increase in osteoclast surface in the trabecular compartment of 36-week-old N-ARKO mice. Cortical bone loss in N-ARKO mice was associated with an upregulation of Ucp1 expression in brown adipose tissue, a widely used readout for sympathetic tone. We conclude that androgens preserve cortical integrity in aging male mice via AR in neurons. © 2018 American Society for Bone and Mineral Research.

A requirement for Fgfr2 in middle ear development.

The skeletal structure of the mammalian middle ear, which is composed of three endochondral ossicles suspended within a membranous air-filled capsule, plays a critical role in conducting sound. Gene mutations that alter skeletal development in the middle ear result in auditory impairment. Mutations in fibroblast growth factor receptor 2 (FGFR2), an important regulator of endochondral and intramembranous bone formation, cause a spectrum of congenital skeletal disorders featuring conductive hearing loss. Although the middle ear malformations in multiple FGFR2 gain-of-function disorders are clinically characterized, those in the FGFR2 loss-of-function disorder lacrimo-auriculo-dento-digital (LADD) syndrome are relatively undescribed. To better understand conductive hearing loss in LADD, we examined the middle ear skeleton of mice with conditional loss of Fgfr2. We find that decreased auditory function in Fgfr2 mutant mice correlates with hypoplasia of the auditory bulla and ectopic bone growth at sites of tendon/ligament attachment. We show that ectopic bone associated with the intra-articular ligaments of the incudomalleal joint is derived from Scx-expressing cells and preceded by decreased expression of the joint progenitor marker Gdf5. Together, these results identify a role for Fgfr2 in development of the middle ear skeletal tissues and suggest potential causes for conductive hearing loss in LADD syndrome.

Effects of Nutritional Deficiency of Boron on the Bones of the Appendicular Skeleton of Mice.

Scientific evidence has shown the nutritional importance of boron (B) in the remodeling and repair of cancellous bone tissue. However, the effects of the nutritional deficiency of B on the cortical bone tissue of the appendicular skeleton have not yet been described. Thus, a study was performed to histomorphometrically evaluate the density of osteocyte lacunae of cortical bone of mouse femora under conditions of nutritional deficiency of B and to analyze the effects of the deficiency on the biomechanical properties of mouse tibiae. Weaning, 21-day-old male Swiss mice were assigned to the following two groups: controls (B+; n = 10) and experimental (B-; n = 10). Control mice were fed a basal diet containing 3mg B/kg, whereas experimental mice were fed a B-deficient diet containing 0.07mg B/kg for 9weeks. The histological and histomorphometric evaluations of the mice fed a B-deficient diet showed a decrease in the density of osteocyte lacunae in the femoral cortical bone tissue and the evaluation of biomechanical properties showed lower bone rigidity in the tibia.

A comparative laboratory study of the preservation of different rodent bones in pellets of Strigiformes

Studies of variation in preservation of different skeletal elements in the pellets of birds of prey helps us understand which bones should be used for effective and reliable diet analyses. The preservation of cranial and postcranial elements of skeletons of laboratory mice was studied in owl pellets. The research was conducted with three male individuals of three species: Long-eared Owl, Tawny Owl and Pygmy Owl. The owls were fed with adult and immature mice in laboratory conditions. The preservation of bones was defined as the ratio of the number of whole specimens of a certain bone to the total number of bones which were contained in the body of one mouse. The largest and the most massive bones had a high preservation. The upper part of cranium and the large bones of limb girdles had the highest preservation in the owl pellets. The bones of immature mice had higher preservation in the pellets of Pygmy Owl compared to Long-eared and Tawny Owl. Age differences in bone size and thickness were explained the variation in preservation of immature and adult mouse bones.

Structural and functional properties of bone are compromised in amyotrophic lateral sclerosis mice

In addition to muscle weakness, amyotrophic lateral sclerosis (ALS) is associated with an increased incidence of skeletal fractures. The SOD1G93A mouse model recapitulates many features of human ALS. These mice also exhibit decreased bone mass. However, the functional, or biomechanical, behavior of the skeleton in SOD1G93A mice has not been investigated. To do so, we examined skeletal phenotypes in end-stage (16-week-old) SOD1G93A female mice and healthy littermate female controls (N = 9–10/group). Outcomes included trabecular and cortical bone microarchitecture by microcomputed tomography; stiffness and strength via three-point bending; resistance to crack growth by fracture toughness testing; and cortical bone matrix properties via cyclic reference point indentation. SOD1G93A mice had similar bone size, but significantly lower trabecular bone mass (–54%), thinner trabeculae (–41%) and decreased cortical bone thickness (–17%) and cortical area (–18%) compared to control mice (all p < 0.01). In line with these bone mass and microstructure deficits, SOD1G93A mice had significantly lower femoral bending stiffness (–27%) and failure moment (–41%), along with decreased fracture toughness (–18%) (all p < 0.001). This is the first study to demonstrate functional deficits in the skeleton of end-stage ALS mice, and imply multiple mechanisms for increased skeletal fragility and fracture risk in patients in ALS. Importantly, our results provide strong rationale for interventions to reduce fracture risk in ALS patients with advanced disease.

16. Physiological effects of IDH1 loss-of-function on Chondrocyte Differentiation through Hedgehog Pathway upregulation

Cartilage tumors are the most common and terminal primary neoplasms in bone. Physiologically, bones formed through endochondral ossification are regulated by the Hedgehog pathway and Parathyroid hormone-like hormone feedback loop. The upregulation of the infamous Hedgehog pathway has been demonstrated in several non-cartilaginous neoplasms. Recently, frequent mutational events of isocitrate dehydrogenase1 (IDH1) were identified in cartilage tumors. In other neoplasms, IDH mutations produces an oncometabolite that can promote HIF1a activation, contributing to tumorigenesis. Currently, the role of IDH1 mutations in cartilage tumors remain unknown. Investigating the physiological aspect of IDH1proves useful in identifying novel therapeutic targets for cartilage tumors. IDH1 deficient and wild-type littermates, were harvested for forelimbs and hindlimbs at various developmental stages for phenotypic analysis via hematoxylin and eosin staining. Histological analysis demonstrated IDH1 homozygous deficient mice at embryonic stages exhibited dwarfism and an elongated layer of hypertrophic chondrocytes. This was verified via immunohistochemistry Type 10 Collagen staining and Quantitative PCR (qPCR) using the chondrocyte terminal differentiation marker Col10a1. Whole skeletons of IDH1 deficient mice were subjected to skeletal double staining which demonstrated delayed mineralization of underdeveloped IDH1 deficient mice contrasted with wild-type littermates. qPCR was performed to examine the status of chondrocyte differentiation through the Hedgehog pathway in cultured primarymouse growth plate chondrocytes. Interestingly, IDH1 deficient non-neoplastic cells revealed significant upregulation of Hedgehog target molecules in IDH1 deficient chondrocytes. As a result, the loss-offunction of IDH1 was identified as a potential impairment of chondrocyte differentiation and a factor towards chondrocyte tumorgenisis.

Estrogen receptor α- (ERα), but not ERβ-signaling, is crucially involved in mechanostimulation of bone fracture healing by whole-body vibration.

Mechanostimulation by low-magnitude high frequency vibration (LMHFV) has been shown to provoke anabolic effects on the intact skeleton in both mice and humans. However, experimental studies revealed that, during bone fracture healing, the effect of whole-body vibration is profoundly influenced by the estrogen status. LMHFV significantly improved fracture healing in ovariectomized (OVX) mice being estrogen deficient, whereas bone regeneration was significantly reduced in non-OVX, estrogen-competent mice. Furthermore, estrogen receptors α (ERα) and β (ERβ) were differentially expressed in the fracture callus after whole-body vibration, depending on the estrogen status. Based on these data, we hypothesized that ERs may mediate vibration-induced effects on fracture healing. To prove this hypothesis, we investigated the effects of LMHFV on bone healing in mice lacking ERα or ERβ. To study the influence of the ER ligand estrogen, both non-OVX and OVX mice were used. All mice received a femur osteotomy stabilized by an external fixator. Half of the mice were sham-operated or subjected to OVX 4 weeks before osteotomy. Half of each group received LMHFV with 0.3 g and 45 Hz for 20 min per day, 5 days per week. After 21 days, fracture healing was evaluated by biomechanical testing, μCT analysis, histomorphometry and immunohistochemistry. Absence of ERα or ERβ did not affect fracture healing in sham-treated mice. Wildtype (WT) and ERβ-knockout mice similarly displayed impaired bone regeneration after OVX, whereas ERα-knockout mice did not. Confirming previous data, in WT mice, LMHFV negatively affected bone repair in non-OVX mice, whereas OVX-induced compromised healing was significantly improved by vibration. In contrast, vibrated ERα-knockout mice did not display significant differences in fracture healing compared to non-vibrated animals, both in non-OVX and OVX mice. Fracture healing in ERβ-knockout mice was similarly affected by LMHFV as in WT mice. These results suggest that ERα-signaling may be crucial for vibration-induced effects on fracture healing, whereas ERβ-signaling may play a minor role.

Regulation of bone mass by the gut microbiota is dependent on NOD1 and NOD2 signaling

Germ-free (GF) mice have increased bone mass that is normalized by colonization with gut microbiota (GM) from conventionally raised (CONV-R) mice. To determine if innate immune signaling pathways mediated the effect of the GM, we studied the skeleton of GF and CONV-R mice with targeted inactivation of MYD88, NOD1 or NOD2. In contrast to WT and Myd88−/− mice, cortical bone thickness in mice lacking Nod1 or Nod2 was not increased under GF conditions. The expression of Tnfα and the osteoclastogenic factor Rankl in bone was reduced in GF compared to CONV-R WT mice but not in Nod1−/− or Nod2−/− mice indicating that the effect of the GM to increase Tnfα and Rankl in bone and to reduce bone mass is dependent on both NOD1 and NOD2 signaling.