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Peripheral blood mononuclear cell- and cortical bone-derived transcriptional profiles

ABSTRACT: Large-scale transcriptional profiling has enormous potential for discovery of osteoporosis susceptibility genes and for identification of the molecular mechanisms by which these genes and associated pathways regulate bone maintenance and turnover. A potential challenge in the use of this method for the discovery of osteoporosis genes is the difficulty of obtaining bone tissue samples from large numbers of individuals. In this study, we tested the applicability of using peripheral blood mononuclear cell (PBMC)-derived transcriptional profiles as a surrogate to cortical bone transcriptional profiles to address questions of skeletal genetics. We used a well-established and genetically well-characterized nonhuman primate model for human bone maintenance and turnover. We determined that a high degree of overlap exists in gene expression of cortical bone and PBMCs and that genes in both the osteoporosis-associated RANK Osteoclast and Estrogen Receptor Signaling pathways are highly expressed in PBMCs. Genes within the Wnt Signaling pathway, also implicated in osteoporosis pathobiology, are expressed in PBMCs, albeit to a lesser extent. These results are the first in an effort to comprehensively characterize the relationship between the PBMC transcriptome and bone – knowledge that is essential for maximizing the use of PBMCs to identify genes and signaling pathways relevant to osteoporosis pathogenesis. It is also a first step in identifying genes that correlate in a predictable manner between PBMCs and cortical bone from healthy and osteoporotic individuals, potentially allowing us to identify genes that could be used to diagnose osteoporosis prior to detectible bone loss and with easily obtained PBMCs.

ORGANISM(S): Papio hamadryas Homo sapiens

PROVIDER: GSE51495 | GEO | 2013/10/22

SECONDARY ACCESSION(S): PRJNA223315

REPOSITORIES: GEO

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Project description:Large-scale transcriptional profiling has enormous potential for discovery of osteoporosis susceptibility genes and for identification of the molecular mechanisms by which these genes and associated pathways regulate bone maintenance and turnover. A potential challenge in the use of this method for the discovery of osteoporosis genes is the difficulty of obtaining bone tissue samples from large numbers of individuals. In this study, we tested the applicability of using peripheral blood mononuclear cell (PBMC)-derived transcriptional profiles as a surrogate to cortical bone transcriptional profiles to address questions of skeletal genetics. We used a well-established and genetically well-characterized nonhuman primate model for human bone maintenance and turnover. We determined that a high degree of overlap exists in gene expression of cortical bone and PBMCs and that genes in both the osteoporosis-associated RANK Osteoclast and Estrogen Receptor Signaling pathways are highly expressed in PBMCs. Genes within the Wnt Signaling pathway, also implicated in osteoporosis pathobiology, are expressed in PBMCs, albeit to a lesser extent. These results are the first in an effort to comprehensively characterize the relationship between the PBMC transcriptome and bone M-bM-^@M-^S knowledge that is essential for maximizing the use of PBMCs to identify genes and signaling pathways relevant to osteoporosis pathogenesis. It is also a first step in identifying genes that correlate in a predictable manner between PBMCs and cortical bone from healthy and osteoporotic individuals, potentially allowing us to identify genes that could be used to diagnose osteoporosis prior to detectible bone loss and with easily obtained PBMCs. Total RNA was isolated from peripheral blood mononuclear cells and cortical bone of a nonhuman primate model (Papio hamadryas ssp.) of bone maintenance and turnover. Both samples were taken from the same animal. Tissue from 15 animals was used for the study.

Project description:Osteoporosis affects over 200 million women worldwide, one third of whom are predicted to suffer from an osteoporotic fracture in their lifetime. The most promising anabolic drugs involve administration of expensive antibodies. Because mechanical loading stimulates bone formation, our current data, using a mouse model, replicates the anabolic effects of loading in humans and may identify novel pathways amenable to oral treatment. Murine tibial compression produces axially-varying deformations along the cortical bone, inducing highest strains at the mid-diaphysis and lowest at the metaphyseal shell. To test the hypothesis that load-induced transcriptomic responses at different axial locations of cortical bone would vary as a function of strain magnitude, we loaded the left tibiae of 10wk female C57Bl/6 mice in vivo in compression, with contralateral limbs as controls. Animals were euthanized at 1, 3 or 24 h post-loading or loaded for 1 wk (n=4-5/group). Bone marrow and cancellous bone were removed, cortical bone was segmented into the metaphyseal shell, proximal diaphysis and mid-diaphysis, and load-induced differential gene expression and enriched biological processes were examined for the three segments. At each time point, the mid-diaphysis (highest strain) had the greatest transcriptomic response. Similarly, biological processes regulating bone formation and turnover increased earlier and to the greatest extent at the mid-diaphysis. Higher strain induced greater levels of osteoblast and osteocyte genes, whereas expression was lower in osteoclasts. Among the top differentially-expressed genes at 24-hours post-loading, seventeen had known functions in bone biology, of which twelve were present only in osteoblasts, three exclusively in osteoclasts, and two were present in both cell types. Based on these results, we conclude that murine tibial loading induces spatially-unique transcriptomic responses correlating with strain magnitude in cortical bone.

Project description:Sparc null mutants have been generated independently via two targeted mutations in exons 4 and 6. Previous studies have identified low turnover osteopenia in the exon 4 knockout (on a mixed 129Sv/C57Bl/6 background). Since both Sparc null mutations have been shown to result in complete absence of Sparc protein, similar phenotypic outcomes are likely. However, genetic background and/or linkage disequilibrium effects can influence phenotype; abnormalities attributed to a given mutation have often been later found to be caused by closely linked genetic anomalies or strain effects. Ideally therefore, different inactivating mutations should be tested in various mouse strains; similar phenotypic outcomes can then confidently be assigned to the mutated gene. We have evaluated the bone phenotype in the Sparctm1cam exon 6 knockout on a purebred 129Sv/Ev background at 4 and 9 months, using physical measurement, mechanical strength tests and DXA scanning. We have also quantified bone marrow adiposity and circulating leptin levels to assess adipose tissue regulation anomalies in these mice. 129Sv/EvSparctm1cam null mice show decreased bone mineral density and bone mineral content. Increased mechanical fragility of bone was also evident, largely in line with previous studies. However, differences were also noted. Increased body weight and levels of bone marrow adiposity, but decreased circulating leptin concentrations were identified at 4 months, but not at 9 months. Circulating leptin concentrations were reportedly increased in Sparc exon 4 null animals, suggesting that leptin concentrations may be influenced more by genetic background than by the absence of Sparc. 129Sv/EvSparctm1cam null mice have shorter femurs; this difference was not noted in prior studies, possibly due to increased variation owing to use of a hybrid strain. Molecular phenotyping was carried out using mouse HGMP NIA microarrays with cortical femur samples at various ages, using semi-quantitative RT PCR validation. Array studies have identified 429 genes expressed in normal bone. Six genes (Sparc, Zfp162, Bysl, E2F4 and two ESTs) are differentially regulated in 129Sv/EvSparctm1cam cortical femur versus 129Sv/Ev controls. We confirm low turnover osteopenia as a feature of the Sparc null phenotype, identifying the usefulness of this mouse as a model for human osteoporosis. Keywords: disease state analysis, time course, genetic modification, osteoporosis, knockout mouse

Project description:Purpose: Using RNA-sequencing technology to screen the effect of moderate-intensity treadmill exercise on the key genes that affect bone mass in the peripheral blood mononuclear cells (PBMCs) of ovariectomized (OVX) rats. Methods: Three-month-old female Sprague–Dawley rats of Specific Pathogen Free (SPF) grade were randomly divided into the sham operation (SHAM) group, OVX group, and OVX combined exercise (OVX+EX) group. The OVX+EX group performed moderate-intensity treadmill exercise for 17 weeks. Upon completion of these exercises, the body composition and bone mineral density (BMD) were measured using dual-energy X-ray absorptiometry, and the bone microstructure of the femur was observed using micro-computed tomography scanning. PBMCs were collected from the abdominal aorta, and the differential genes were analyzed by transcriptome sequencing. The Metascape software was used for gene ontology and pathway enrichment analysis to further screen key genes. Results: 1. In the OVX group, the body weight and body fat content were significantly higher than in the SHAM group and the body muscle content and BMD were significantly lower. 2. The trabecular bone parameters in the OVX group were significantly lower than in the SHAM group, and they were significantly higher in the OVX+EX group than in the OVX group. When compared with the SHAM group, the microstructure of the distal femur trabecular in the OVX group was severely damaged, the trabecular bones were sparse, and there was a large gap between the trabecular bones. The number and continuity of the trabecular bones were higher in OVX+EX group than in the OVX group. 3. A Venn diagram showed that there were 58 common differential genes, with a fold change ≥2 and p value <0.05. and the differential genes were mainly enriched in the PI3K-Akt signaling pathway. Five key genes were screened including CCL2, Nos3, Tgfb3, ITGb4, and LpL. Conclusion: Moderate-intensity treadmill exercise may improve the body composition and bone mass of the OVX group by upregulating CCL2 and other genes of the PBMC. The results also showed that the PBMCs in the peripheral blood can be a useful tool for monitoring the effect of exercise on bone health in postmenopausal osteoporosis.

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Peripheral blood mononuclear cell- and cortical bone-derived transcriptional profiles

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