Gene expression profiling of bone marrow stromal cells from juvenile, adult, aged and osteoporotic rats: with an emphasis on osteoporosis

CCN Proteins as Matricellular Regulators of Bone in Aging and Disease

PURPOSE OF REVIEW

This review explores the role of cell communication network (CCN) proteins in regulating skeletal physiology, aging, and disease, particularly within the context of balanced bone remodeling.

RECENT FINDINGS

Recent conceptualization of paracrine and endocrine networks in bone marrow as a form of osteoimmunological crosstalk suggests a significant role for matricellular signaling in regulating bone homeostasis. As multifunctional adapters of cell-matrix interactions, CCNs are emerging as a focal point for parathyroid hormone (PTH) signaling and regulation of the RANKL/RANK/OPG axis in skeletal aging. Altered bone marrow CCN expression creates a permissive environment for accelerated postmenopausal bone loss and may contribute to the pathogenesis of osteoporosis and other diseases related to skeletal aging. CCNs modulate fundamental signaling mechanisms in bone development, homeostasis and repair. During aging, dysregulation of CCNs may negatively affect skeletal health and contribute to disease progression. As a result, CCNs may constitute promising therapeutic targets for improving and maintaining aging bone health.

Mitochondria-specific antioxidant MitoTEMPO alleviates senescence of bone marrow mesenchymal stem cells in ovariectomized rats

Senescence in bone marrow mesenchymal stem cells (BMSCs), triggered by excessive oxidative stress, plays a crucial role in the onset of postmenopausal osteoporosis. Recent studies underscore the importance of mitochondrial rehabilitation and quality control as key determinants in the modulation of oxidative stress and cellular senescence. MitoTEMPO, a mitochondria-targeted antioxidant, has been shown to mitigate the heightened levels of reactive oxygen species (ROS). In our research, we observed that BMSCs from ovariectomized (OVX) rats displayed premature senescence, which was attributed to combined mitochondrial and lysosomal dysfunction, a condition that worsens with extended estrogen deprivation. Treatment with MitoTEMPO effectively reversed these effects, reinstating lysosomal functionality and suppressing the mitochondrial unfolded protein response (UPRmt). Subsequent in vivo experiments corroborated these observations, revealing that MitoTEMPO administration in OVX rats curtailed trabecular bone loss and reduced the expression of p53, HSP60, and CLPP in the trabecular bone region of the proximal tibia. Overall, our findings suggest that MitoTEMPO holds promise as a therapeutic agent to counteract senescence in OVX-BMSCs, offering a potential strategy for treating postmenopausal osteoporosis.

Osteoporotic Goat Spine Implantation Study Using a Synthetic, Resorbable Ca/P/S-Based Bone Substitute

One primary purpose of the present study is to clarify whether the highly porous, resorbable Ca/P/S-based bone substitute used in this study would still induce an osteoporotic bone when implanted into the osteoporotic vertebral defects of ovariectomized (OVX) goats, or the newly-grown bone would expectantly be rather healthy bone. The bone substitute material used for the study is a synthetic, 100% inorganic, highly porous and fast-resorbable Ca/P/S-based material (Ezechbone^® Granule CBS-400). The results show that the OVX procedure along with a low calcium diet and breeding away from light can successfully induce osteoporosis in the present female experimental goats. The histological examination reveals a newly-formed trabecular bone network within the surgically-created defect of the CBS-400-implanted (OVX_IP) goat. This new trabecular bone network in the OVX_IP goat appears much denser than the OVX goat and comparable to the healthy control goat. Histomorphometry show that, among all the experimental goats, the OVX_IP goat has the highest trabecular thickness and lowest trabecular bone packet prevalence. The differences in trabecular plate separation, trabecular number and trabecular bone tissue area ratio between the OVX_IP goat and the control goat are not significant, indicating that the trabecular bone architecture of the OVX_IP goat has substantially recovered to the normal level in about 6 months after implantation without signs of osteoporosis-related delay in the bone maturing process. The quick and nicely recovered trabecular architecture parameters observed in the OVX_IP goat indicate that the present Ca/P/S-based bone substitute material has a high potential to treat osteoporotic fractures.

Association of gut microbiota composition and function with an aged rat model of senile osteoporosis using 16S rRNA and metagenomic sequencing analysis

Recently, more interest has been paid to the association between bone mass and gut microecological dysbiosis. The results of clinical studies comparing gut microbiota (GM) in osteoporosis patients have been inconsistent due to different inclusion and exclusion criteria. To date, the association between the GM and senile osteoporosis remains poorly understood. Here, we utilized an aged rat model (22 months old) of senile osteoporosis to study the association of the composition and function of the GM with osteoporosis by 16S rRNA and metagenomic sequencing. The results showed that there was a significant reduction in alpha diversity and the F/B (Firmicutes/Bacteroidetes) ratio in aged rats. At the genus level, the enrichment of Helicobacter was potentially related to osteoporosis as a risk factor. Metagenomics results based on two databases indicated that shifts in the GM contribute to senile osteoporosis through metabolic pathways and subsequent immune disorders. In conclusion, our study reveals the association of gut microbiota composition and function with senile osteoporosis in an aged rat model in a brand new way, and variations in the GM might contribute to senile osteoporosis through metabolic pathways.

Specificity proteins 1 and 4 in peripheral blood mononuclear cells in postmenopausal women with schizophrenia: a 24-week double-blind, randomized, parallel, placebo-controlled trial

Accumulating evidence suggests that Specificity Protein 1 (SP1) and 4 (SP4) transcription factors are involved in the pathophysiology of schizophrenia. The therapeutic use of selective oestrogen modulators such as raloxifene added to antipsychotic drugs in the treatment of postmenopausal women with schizophrenia has been investigated in a few clinical trials, which reported an improvement in negative, positive, and general psychopathological symptoms. We aimed to investigate the possible association between peripheral SP protein levels and symptom improvement in postmenopausal women with schizophrenia treated with adjuvant raloxifene. In a subgroup of 14 postmenopausal women with schizophrenia from a 24-week, randomized, parallel, double-blind, placebo-controlled clinical trial (NCT015736370), we investigated changes in SP1 and SP4 protein levels in peripheral blood mononuclear cells. Participants were randomized to either 60 mg/day adjunctive raloxifene or placebo. Psychopathological symptoms were assessed at baseline and at week 24 with the Positive and Negative Syndrome Scale (PANSS). The expression of SP proteins was evaluated by immunoblot, and changes in PANSS scores and protein levels were compared at baseline and after 24 weeks of treatment. An improvement in symptoms was observed in the intervention group, but not in placebo group. Post-treatment protein levels of SP4, but not SP1, correlated with improvements in general and total PANSS subscales in the raloxifene intervention group. A reduction in SP4 levels was found after raloxifene treatment. These results suggest that SP4 may be involved in raloxifene symptom improvement in postmenopausal women and could be a potential candidate for future studies investigating blood-based biomarkers for raloxifene effectiveness.

The effect of quercetin delivery system on osteogenesis and angiogenesis under osteoporotic conditions

Bone regeneration under osteoporotic conditions with impaired angiogenesis, osteogenesis and remodeling represents a great challenge.

Flow perfusion culture of MC3T3-E1 osteogenic cells on gradient calcium polyphosphate scaffolds with different pore sizes

Calcium polyphosphate is a biodegradable bone substitute. It remains a challenge to prepare porous calcium polyphosphate with desired gradient porous structures. In this study, a modified one-step gravity sintering method was used to prepare calcium polyphosphate scaffolds with desired-gradient-pore-size distribution. The differences of porous structure, mechanical strength, and degradation rate between gradient and homogenous calcium polyphosphate scaffolds were evaluated by micro-computed tomography, scanning electron microscopy, and mechanical testing. Preosteoblastic MC3T3-E1 cells were seeded onto gradient and homogenous calcium polyphosphate scaffolds and cultured in a flow perfusion bioreactor. The distribution, proliferation, and differentiation of the MC3T3-E1 cells were compared to that of homogenous calcium polyphosphate scaffolds. Though no significant difference of cell proliferation was found between the gradient and the homogenous calcium polyphosphate scaffolds, a much higher cell differentiation and mineralization were observed in the gradient calcium polyphosphate scaffolds than that of the homogenous calcium polyphosphate scaffolds, as manifested by increased alkaline phosphatase activity ( p < 0.05). The improved distribution and differentiation of cultured cells within gradient scaffolds were further supported by both 18F-fluorine micro-positron emission tomography scanning and in vitro tetracycline labeling. We conclude that the calcium polyphosphate scaffold with gradient pore sizes enhances osteogenic cell differentiation as well as mineralization. The in vivo performance of gradient calcium polyphosphate scaffolds warrants further investigation in animal bone defect models.

Bone regeneration and gene expression in bone defects under healthy and osteoporotic bone conditions using two commercially available bone graft substitutes

Biosilicate(®) and Bio-Oss(®) are two commercially available bone substitutes, however, little is known regarding their efficacy in osteoporotic conditions. The purpose of this study was to evaluate the osteogenic properties of both materials, at tissue and molecular level. Thirty-six Wistar rats were submitted to ovariectomy (OVX) for inducing osteoporotic conditions and sham surgery (SHAM) as a control. Bone defects were created in both femurs, which were filled with Biosilicate(®) or Bio-Oss(®), and empty defects were used as control. For the healthy condition both Biosilicate(®) and Bio-Oss(®) did not improve bone formation after 4 weeks. Histomorphometric evaluation of osteoporotic bone defects with bone substitutes showed more bone formation, significant for Bio-Oss(®). Molecular biological evaluation was performed by gene-expression analysis (Runx-2, ALP, OC, OPG, RANKL). The relative gene expression was increased with Biosilicate(®) for all genes in OVX rats and for Runx-2, ALP, OC and RANKL in SHAM rats. In contrast, with Bio-Oss(®), the relative gene expression of OVX rats was similar for all three groups. For SHAM rats it was increased for Runx-2, ALP, OC and RANKL. Since both materials improved bone regeneration in osteoporotic conditions, our results suggest that bone defects in osteoporotic conditions can be efficiently treated with these two bone substitutes.

In vitro proliferation and differentiation potential of bone marrow-derived mesenchymal stem cells from ovariectomized rats

Bone marrow-derived mesenchymal stem cells (BMMSCs) from the patients suffering from age-related osteoporosis were found to have numerous degeneration, such as decreased growth rate, impaired capacity of differentiating into local tissue, and repressed telomerase activity. However, it is not clear whether post-menopausal osteoporotic bone is either subject to such decline in cellular function. In the present study, bone marrow cells were harvested from ovariectomized (OVX) and Sham rats and cultured in vitro at 3 months post-surgery. MTT assay indicated that the proliferation potential of (OVX)BMMSCs was always higher than that of (Sham)BMMSCs, no matter cultured in basic, osteoblastic or adipogenic medium. Alkaline phosphatase activity assay, Alizarin red S staining, Oil red O staining and real-time RT-PCR analysis further demonstrated that bilateral ovariectomization positively influenced the osteoblastic and adipogenic differentiation potential of BMMSCs, this action may be partly mediated through up-regulation of osteoblastic special markers core binding factor a1, collagen type I and low-density lipoprotein receptor-related protein 5, as well as adipogenic special markers peroxisome proliferators activated receptor gamma, CCAAT/enhancer binding protein alpha and adipocyte lipid-binding protein 2. These results may hold great promise for using post-menopausal osteoporotic bone as an attractive autologous marrow source for tissue engineering and cell-based therapies.

Gene expression profile induced by ovariectomy in bone marrow of mice: a functional approach to identify new candidate genes associated to osteoporosis risk in women

Osteoporosis is a multifactorial skeletal pathology with a main genetic component. To date, however, the majority of genes associated with this pathology remain unknown since genes cataloged to date only explain a part of the heritability of bone phenotypes. In the present study, we have used a genome-wide gene expression approach by means of microarrays to identify new candidate genes involved in the physiopathology of osteoporosis, using as a model the ovariectomized (OVX) mice by comparing global bone marrow gene expression of the OVX mice with those of SHAM operated mice. One hundred and eighty transcripts were found to be differentially expressed between groups. The analysis showed 23 significant regulatory networks, of which the top five canonical pathways included B-cell development, primary immunodeficiency signaling, PI3K signaling in B-cells, phospholipase C signaling, and FcgRIIB signaling in B-cells. Twelve differentially expressed genes were validated by MALDI-TOF mass spectrometry with good reproducibility. Finally, the association to bone phenotypes of SNPs in genes whose expression was increased (IL7R and CD79A) or decreased (GPX3 and IRAK3) by OVX in mice was analyzed in a cohort of 706 postmenopausal women. We detected an association of a SNP in a gene involved in the detoxification of free radicals like glutathione peroxidase 3 (GPX3) with femoral neck BMD (rs8177447, P=0.043) and two SNPs in the Ig-alpha protein of the B-cell antigen component gene (CD79A) with lumbar spine BMD (rs3810153 and rs1428922, P=0.016 and P=0.001, respectively). These results reinforce the role of antioxidant pathways and of B-cells in bone metabolism. Furthermore, it shows that a genome-wide gene expression approach in animal models is a useful method for detecting genes associated to BMD and osteoporosis risk in humans.

F-spondin deficient mice have a high bone mass phenotype

F-spondin is a pericellular matrix protein upregulated in developing growth plate cartilage and articular cartilage during osteoarthritis. To address its function in bone and cartilage in vivo, we generated mice that were deficient for the F-spondin gene, Spon1. Spon1^−/− mice were viable and developed normally to adulthood with no major skeletal abnormalities. At 6 months, femurs and tibiae of Spon1^−/− mice exhibited increased bone mass, evidenced by histological staining and micro CT analyses, which persisted up to 12 months. In contrast, no major abnormalities were observed in articular cartilage at any age group. Immunohistochemical staining of femurs and tibiae revealed increased levels of periostin, alkaline phosphate and tartrate resistant acid phosphatase (TRAP) activity in the growth plate region of Spon1^−/− mice, suggesting elevated bone synthesis and turnover. However, there were no differences in serum levels of TRAP, the bone resorption marker, CTX-1, or osteoclast differentiation potential between genotypes. Knockout mice also exhibited reduced levels of TGF-β1 in serum and cultured costal chondrocytes relative to wild type. This was accompanied by increased levels of the BMP-regulatory SMADs, P-SMAD1/5 in tibiae and chondrocytes. Our findings indicate a previously unrecognized role for Spon1 as a negative regulator of bone mass. We speculate that Spon1 deletion leads to a local and systemic reduction of TGF-β levels resulting in increased BMP signaling and increased bone deposition in adult mice.

NELL-1 injection maintains long-bone quantity and quality in an ovariectomy-induced osteoporotic senile rat model

Over 10 million Americans have osteoporosis, and is the predominant cause of fractures in the elderly. Treatment of fractures in the setting of osteoporosis is complicated by a suboptimal bone regenerative response due to a decline in the number of osteoblasts, their function, and survival. Consequently, an osteogenic therapeutic to prevent and treat fractures in patients with osteoporosis is needed. Nel-like molecule-1 (NELL-1), a novel osteoinductive growth factor, has been shown to promote bone regeneration. In this study, we aim to demonstrate the capacity of recombinant NELL-1 to prevent ovariectomy (OVX)-induced osteoporosis in a senile rat model. Ten-month-old female Sprague-Dawley rats underwent either sham surgery or OVX. Subsequently, 50 μL of 600 μg/mL NELL-1 lyophilized onto a 0-50-μm tricalcium phosphate (TCP) carrier was injected into the femoral bone marrow cavity while phosphate-buffered saline (PBS) control was injected into the contralateral femur. Our microcomputed tomography results showed that OVX+PBS/TCP control femurs showed a continuous decrease in the bone volume (BV) and bone mineral density (BMD) from 2 to 8 weeks post-OVX. In contrast, OVX+NELL-1/TCP femurs showed resistance to OVX-induced bone resorption showing BV and BMD levels similar to that of SHAM femurs at 8 weeks post-OVX. Histology showed increased endosteal-woven bone, as well as decreased adipocytes in the bone marrow of NELL-1-treated femurs compared to control. NELL-1-treated femurs also showed increased immunostaining for bone differentiation markers osteopontin and osteocalcin. These findings were validated in vitro, in which addition of NELL-1 in OVX bone marrow stem cells resulted in increased osteogenic differentiation. Thus, NELL-1 effectively enhances in situ osteogenesis in the bone marrow, making it potentially useful in the prevention and treatment of osteoporotic fractures.

Post-genomics of bone metabolic dysfunctions and neoplasias

Post-genomic research on osteoblastic and osteoclastic cells, in contrast to that on many other cell types, has only been undertaken recently. Nevertheless, important information has been gained from these investigations on the mechanisms involved in osteoblast differentiation and on markers relevant for tissue regeneration and therapeutic validation of drugs, hormones and growth factors. These protein indicators may also have a diagnostic and prognostic value for bone dysfunctions and tumors. Some reviews have already focused on the application of transcriptomics and/or proteomics for exploring skeletal biology and related disorders. The main goal of the present review is to systematically summarize the most relevant post-genomic studies on various metabolic bone diseases (osteoporosis, Paget's disease and osteonecrosis), neoplasias (osteosarcoma) and metabolic conditions that indirectly affect bone tissue, such as alkaptonuria.

Age-related biological characterization of mesenchymal progenitor cells in human articular cartilage

Adult articular cartilage has a low regeneration capacity due to lack of viable progenitor cells caused by limited blood supply to cartilage. However, recent studies have demonstrated the existence of chondroprogenitor cells in articular cartilage. A critical question is whether these mesenchymal progenitor cells are functionally viable for tissue renewal and cartilage repair to postpone cartilage degeneration. This study was designed to compare the number and function of mesenchymal progenitor cells in articular cartilage collected from human fetuses, healthy adults (aged 28-45 years), and elderly adults (aged 60-75 years) and cultured in vitro. We detected multipotent mesenchymal progenitor cells, defined as CD105+/CD166+ cells, in human articular cartilage of all ages. However, mesenchymal progenitor cells accounted for 94.69%±2.31%, 4.85%±2.62%, and 6.33%±3.05% of cells in articular cartilage obtained from fetuses, adults, and elderly patients, respectively (P<.001). Furthermore, fetal mesenchymal progenitor cells had the highest rates of proliferation measured by cell doubling times and chondrogenic differentiation as compared to those from adult and elderly patients. In contrast, alkaline phosphatase levels, which are indicative of osteogenic differentiation, did not show significant reduction with aging. However, spontaneous osteogenic differentiation was detected only in mesenchymal progenitor cells from elderly patients (with lower Markin scales). The lower chondrogenic and spontaneous osteogenic differentiation of mesenchymal progenitor cells derived from elderly patients may be associated with the development of primary osteoarthritis. These results suggest that measuring cartilage mesenchymal progenitor cells may not only identify underlying mechanisms but also offer new diagnostic and therapeutic potential for patients with osteoarthritis.

Maf promotes osteoblast differentiation in mice by mediating the age-related switch in mesenchymal cell differentiation

Aging leads to the disruption of the homeostatic balance of multiple biological systems. In bone marrow multipotent mesenchymal cells undergo differentiation into various anchorage-dependent cell types, including osteoblasts and adipocytes. With age as well as with treatment of antidiabetic drugs such as thiazolidinediones, mesenchymal cells favor differentiation into adipocytes, resulting in an increased number of adipocytes and a decreased number of osteoblasts, causing osteoporosis. The mechanism behind this differentiation switch is unknown. Here we show an age-related decrease in the expression of Maf in mouse mesenchymal cells, which regulated mesenchymal cell bifurcation into osteoblasts and adipocytes by cooperating with the osteogenic transcription factor Runx2 and inhibiting the expression of the adipogenic transcription factor Pparg. The crucial role of Maf in both osteogenesis and adipogenesis was underscored by in vivo observations of delayed bone formation in perinatal Maf(-/-) mice and an accelerated formation of fatty marrow associated with bone loss in aged Maf(+/-) mice. This study identifies a transcriptional mechanism for an age-related switch in cell fate determination and may provide a molecular basis for novel therapeutic strategies against age-related bone diseases.

Gene expression and distribution of key bone turnover markers in the callus of estrogen-deficient, vitamin D-depleted rats

An experimental rat model was used to test the hypothesis that in osteoporosis (OP) the molecular composition of the extracellular matrix in the fracture callus is disturbed. OP was induced at 10 weeks of age by ovariectomy and a vitamin D(3)-deficient diet, and sham-operated animals fed normal diet served as controls. Three months later a closed tibial fracture was made and stabilized with an intramedullary nail. After 3 and 6 weeks of healing, the animals were killed and the fracture calluses examined with global gene expression, in situ mRNA expression, and ultrastructural protein distribution of four bone turnover markers: osteopontin, bone sialoprotein, tartrate-resistant acid phosphatase, and cathepsin K. Global gene expression showed a relatively small number of differently regulated genes, mostly upregulated and at 3 weeks. The four chosen markers were not differently regulated, and only minor differences in the in situ mRNA expression and ultrastructural protein distribution were detected. Gene expression and composition of fracture calluses are not generally disturbed in experimental OP.

Structural and cellular features in metaphyseal and diaphyseal periosteum of osteoporotic rats

Despite the important physiological role of periosteum in the pathogenesis and treatment of osteoporosis, little is known about the structural and cellular characteristics of periosteum in osteoporosis. To study the structural and cellular differences in both diaphyseal and metaphyseal periosteum of osteoporotic rats, samples from the right femur of osteoporotic and normal female Lewis rats were collected and tissue sections were stained with hematoxylin and eosin, antibodies or staining kit against tartrate resistant acid phosphatase (TRAP), alkaline phosphatase (ALP), vascular endothelial growth factor (VEGF), von Willebrand (vWF), tyrosine hydroxylase (TH) and calcitonin gene-related peptide (CGRP). The results showed that the osteoporotic rats had much thicker and more cellular cambial layer of metaphyseal periosteum compared with other periosteal areas and normal rats (P < 0.001). The number of TRAP⁺ osteoclasts in bone resorption pits, VEGF⁺ cells and the degree of vascularization were found to be greater in the cambial layer of metaphyseal periosteum of osteoporotic rats (P < 0.05), while no significant difference was detected in the number of ALP⁺ cells between the two groups. Sympathetic nerve fibers identified by TH staining were predominantly located in the cambial layer of metaphyseal periosteum of osteoporotic rats. No obvious difference in the expression of CGRP between the two groups was found. In conclusion, periosteum may play an important role in the cortical bone resorption in osteoporotic rats and this pathological process may be regulated by the sympathetic nervous system.

Gene expression profile of the bone microenvironment in human fragility fracture bone

Osteoporosis (OP) is a common age-related systemic skeletal disease, with a strong genetic component, characterised by loss of bone mass and strength, which leads to increased bone fragility and susceptibility to fracture. Although some progress has been made in identifying genes that may contribute to OP disease, much of the genetic component of OP has yet to be accounted for. Therefore, to investigate the molecular basis for the changes in bone causally involved in OP and fragility fracture, we have used a microarray approach. We have analysed altered gene expression in human OP fracture bone by comparing mRNA in bone from individuals with fracture of the neck of the proximal femur (OP) with that from age-matched individuals with osteoarthritis (OA), and control (CTL) individuals with no known bone pathology. The OA sample set was included because an inverse association, with respect to bone density, has been reported between OA and the OP individuals. Compugen H19K oligo human microarray slides were used to compare the gene expression profiles of three sets of female samples comprising, 10 OP-CTL, 10 OP-OA, and 10 OA-CTL sample pairs. Using linear models for microarray analysis (Limma), 150 differentially expressed genes in OP bone with t scores >5 were identified. Differential expression of 32 genes in OP bone was confirmed by real time PCR analysis (p<0.01). Many of the genes identified have known or suspected roles in bone metabolism and in some cases have been implicated previously in OP pathogenesis. Three major sets of differentially expressed genes in OP bone were identified with known or suspected roles in either osteoblast maturation (PRRX1, ANXA2, ST14, CTSB, SPARC, FST, LGALS1, SPP1, ADM, and COL4A1), myelomonocytic differentiation and osteoclastogenesis (TREM2, ANXA2, IL10, CD14, CCR1, ADAM9, CCL2, CTGF, and KLF10), or adipogenesis, lipid and/or glucose metabolism (IL10, MARCO, CD14, AEBP1, FST, CCL2, CTGF, SLC14A1, ANGPTL4, ADM, TAZ, PEA15, and DOK4). Altered expression of these genes and others in these groups is consistent with previously suggested underlying molecular mechanisms for OP that include altered osteoblast and osteoclast differentiation and function, and an imbalance between osteoblastogenesis and adipogenesis.

Molecular genetic studies of gene identification for osteoporosis

This review comprehensively summarizes the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of September 2007. It is intended to constitute a sequential update of our previously published reviews covering the available data up to the end of 2004. Evidence from candidate gene-association studies, genome-wide linkage and association studies, as well as functional genomic studies (including gene-expression microarray and proteomics) on osteogenesis and osteoporosis, are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. The major results of all studies are tabulated for comparison and ease of reference. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Accelerated fracture healing in the geriatric, osteoporotic rat with recombinant human platelet-derived growth factor-BB and an injectable beta-tricalcium phosphate/collagen matrix

Aging and osteoporosis contribute to decreased bone mass and bone mineral density as well as compromised fracture healing rates and bone repair quality. Consequently, the purpose of this study was to determine if recombinant human platelet-derived growth factor-BB (rhPDGF-BB) delivered in an injectable beta-tricalcium phosphate/collagen matrix would enhance tibial fracture healing in geriatric (>2 years of age), osteoporotic rats. A total of 80 rats were divided equally among four groups: Fracture alone; Fracture plus matrix; Fracture plus matrix and either 0.3 mg/mL or 1.0 mg/mL rhPDGF-BB. At 3 and 5 weeks, rats were euthanized and treatment outcome was assessed histologically, radiographically, biomechanically, and by micro-CT. Results indicated rhPDGF-BB-treated fractures in osteoporotic, geriatric rats caused a statistically significant time-dependent increase in torsional strength 5 weeks after treatment. The healed fractures were equivalent in torsional strength to the contralateral, unoperated tibiae. Data from the study are the first, to our knowledge, to underscore rhPDGF-BB efficacy in an injectable beta-tricalcium phosphate/collagen matrix accelerated fracture repair in a geriatric, osteoporotic rat model.