Robust and comprehensive analysis of 20 osteoporosis candidate genes by very high-density single-nucleotide polymorphism screen among 405 white nuclear families identified significant association and gene-gene interaction

Association between Bone Morphogenetic Protein 2 Gene Polymorphisms and Skeletal Fluorosis of The Brick-tea Type Fluorosis in Tibetans and Kazakhs, China

To investigate the potential association between BMP2 single nucleotide polymorphisms (SNPs) and brick-tea-type skeletal fluorosis risk in cross-sectional case-control study conducted in Sinkiang and Qinghai, China, a total of 598 individuals, including 308 Tibetans and 290 Kazakhs, were enrolled. Using the standard WS/192-2008 (China), 221 skeletal fluorosis cases were diagnosed, including 123 Tibetans and 98 Kazakhs. Logistic regressions 2 analysis did not find the association between SNPs (Rs235764, Rs235739 and Rs996544) and skeletal fluorosis. Genetic models, linkage disequilibrium (LD) and haplotype analysis were not found to be associated with risk of skeletal fluorosis after adjustment by age and sex (P>0.05).Our data suggested that Rs 235764, Rs 235739 and Rs 996544 were not linked susceptibility for skeletal fluorosis in our cross-sectional case-control study.

Sexual differences in bone porosity, osteocyte density, and extracellular matrix organization due to osteoblastic-specific Bmp2 deficiency in mice

Clinical studies have come to conflicting conclusions regarding BMP2 deficiency's link to regulating bone mass and increasing fracture risk. This may be due to the signaling protein having sex- or age-dependent effects. Previous pre-clinical studies have supported a role, but have not adequately determined the physical mechanism causing altered bulk material properties. This study investigated the physical effects of Bmp2 ablation from osteogenic lineage cells (Osx-Cre; Bmp2^fl/fl) in 10- and 15-week-old male and female mice. Bones collected post-mortem were subjected to fracture toughness testing, reference point indentation testing, microCT, and histological analysis to determine the multi-scale relationships between mechanical/material behavior and collagen production, collagen organization, and bone architecture. BMP2-deficient bones were smaller, more brittle, and contained more lacunae-scale voids and cortical pores. The cellular density was significantly increased and there were material-level differences measured by reference point indentation, independently of collagen fiber alignment or organization. The disparities in bone size and in bone fracture toughness between genotypes were especially striking in males at 15-weeks-old. Together, this study suggests that there are sex- and age-dependent effects of BMP2 deficiency. The results from both sexes also warrant further investigation into BMP2 deficiency's role in osteoblasts' transition to osteocytes and overall bone porosity.

[Association between root abnormalities and related pathogenic genes in patients with generalized aggressive periodontitis]

OBJECTIVE

To explore the association between the abnormal root morphology and bone metabolism or root development related gene polymorphism in patients with generalized aggressive periodontitis.

METHODS

In the study, 179 patients with generalized aggressive periodontitis were enrolled, with an average age of (27.23±5.19) years, male / female = 67/112. The average number of teeth remaining in the mouth was (26.80±1.84). Thirteen single nucleotide polymorphisms (SNPs) of nine genes which related to bone metabolism and root development were detected by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). Root abnormalities were identified using periapical radiographs. The abnormal root morphology included cone-rooted teeth, slender-root teeth, short-rooted teeth, curved-rooted teeth, syncretic-rooted molars, and molar root abnormalities. The number of teeth and incidence of abnormal root morphology in different genotypes of 13 SNPs were analyzed.

RESULTS

The constituent ratio of root with root abnormality in GAgP patients was 14.49%(695/4 798). The average number of teeth with abnormal root morphology in GAgP was (3.88±3.84). The average number of teeth with abnormal root morphology in CC, CT and TT genotypes in vitamin D receptor (VDR) rs2228570 was (4.66±4.10), (3.71±3.93) and (2.68±2.68). There was significant difference between TT genotype and CC genotype (t = 2.62, P =0.01). The average number of root morphological abnormalities in CC, CT and TT genotypes of Calcitotin Receptor (CTR) gene rs2283002 was (5.02±3.70), (3.43±3.95), and (3.05±3.12). The incidence of root morphological abnormalities in CC genotype was higher than that in the patients with CT and TT, and the difference was statistically significant(87.86% vs. 65.26% & 63.64%, P=0.006, adjusted OR =3.71, 95%CI: 1.45-9.50). There was no significant difference in the incidence of abnormal root morphology between CT and TT genotypes.

CONCLUSION

VDR rs2228570 and CTR rs2283002 may be associated with the occurrence of abnormal root morphology in patients with generalized aggressive periodontitis, which is worthy of further research.

[Association between root abnormalities and related pathogenic genes in patients with generalized aggressive periodontitis]

OBJECTIVE

To explore the association between the abnormal root morphology and bone metabolism or root development related gene polymorphism in patients with generalized aggressive periodontitis.

METHODS

In the study, 179 patients with generalized aggressive periodontitis were enrolled, with an average age of (27.23±5.19) years, male / female = 67/112. The average number of teeth remaining in the mouth was (26.80±1.84). Thirteen single nucleotide polymorphisms (SNPs) of nine genes which related to bone metabolism and root development were detected by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). Root abnormalities were identified using periapical radiographs. The abnormal root morphology included cone-rooted teeth, slender-root teeth, short-rooted teeth, curved-rooted teeth, syncretic-rooted molars, and molar root abnormalities. The number of teeth and incidence of abnormal root morphology in different genotypes of 13 SNPs were analyzed.

RESULTS

The constituent ratio of root with root abnormality in GAgP patients was 14.49%(695/4 798). The average number of teeth with abnormal root morphology in GAgP was (3.88±3.84). The average number of teeth with abnormal root morphology in CC, CT and TT genotypes in vitamin D receptor (VDR) rs2228570 was (4.66±4.10), (3.71±3.93) and (2.68±2.68). There was significant difference between TT genotype and CC genotype (t = 2.62, P =0.01). The average number of root morphological abnormalities in CC, CT and TT genotypes of Calcitotin Receptor (CTR) gene rs2283002 was (5.02±3.70), (3.43±3.95), and (3.05±3.12). The incidence of root morphological abnormalities in CC genotype was higher than that in the patients with CT and TT, and the difference was statistically significant(87.86% vs. 65.26% & 63.64%, P=0.006, adjusted OR =3.71, 95%CI: 1.45-9.50). There was no significant difference in the incidence of abnormal root morphology between CT and TT genotypes.

CONCLUSION

VDR rs2228570 and CTR rs2283002 may be associated with the occurrence of abnormal root morphology in patients with generalized aggressive periodontitis, which is worthy of further research.

Bone Microvasculature: Stimulus for Tissue Function and Regeneration

Bone is a highly vascularized organ, providing structural support to the body, and its development, regeneration, and remodeling depend on the microvascular homeostasis. Loss or impairment of vascular function can develop diseases, such as large bone defects, avascular necrosis, osteoporosis, osteoarthritis, and osteopetrosis. In this review, we summarize how vasculature controls bone development and homeostasis in normal and disease cases. A better understanding of this process will facilitate the development of novel disease treatments that promote bone regeneration and remodeling. Specifically, approaches based on tissue engineering components, such as stem cells and growth factors, have demonstrated the capacity to induce bone microvasculature regeneration and mineralization. This knowledge will have relevant clinical implications for the treatment of bone disorders by developing novel pharmaceutical approaches and bone grafts. Finally, the tissue engineering approaches incorporating vascular components may widely be applied to treat other organ diseases by enhancing their regeneration capacity. Impact statement Bone vasculature is imperative in the process of bone development, regeneration, and remodeling. Alterations or disruption of the bone vasculature leads to loss of bone homeostasis and the development of bone diseases. In this study, we review the role of vasculature on bone diseases and how vascular tissue engineering strategies, with a detailed emphasis on the role of stem cells and growth factors, will contribute to bone therapeutics.

Associations of LRP5 Gene With Bone Mineral Density, Bone Turnover Markers, and Fractures in the Elderly With Osteoporosis

Objective: The study aimed to explore the associations of rs4988300 and rs634008 in the low-density lipoprotein receptor-related protein 5 (LRP5) gene with bone mineral density (BMD), bone turnover markers (BTM), and fractures in elderly patients with osteoporosis (OP). Methods: Our study included 328 unrelated OP patients with or without fractures. Genomic DNA was extracted for genotyping. BTM levels were assessed by electrochemiluminescence (ECL). Dual-energy X-ray absorptiometry (DXA) was employed to measure BMD in the lumbar spine (LS) and proximal femur. Basic features between the OP and fracture groups were analyzed using the t-test. The Chi-square test was performed to analyze the differences in allele and genotype frequencies. The associations of single-nucleotide polymorphisms (SNPs) with BMD and BTM in the subgroups were investigated by the analysis of covariance (ANCOVA) adjusted for confounding factors. Results: In both females and males, individuals with fractures exhibited higher BTM levels and lower BMD values than those with OP (P < 0.05). The allele and genotype frequencies of rs4988300 in the subgroups were significantly different (P < 0.05). In both females and males suffering from OP, participants with rs4988300 GG or rs634008 TT presented lower procollagen I N-terminal propeptide (PINP) levels (P < 0.05). Women with OP carrying rs4988300 GG exhibited lower BMD values at FN and TH (P < 0.05). In both females and males with fractures, individuals carrying rs4988300 GG genotype or rs634008 TT genotype exhibited lower PINP levels and BMD values at FN and TH than those with other genotypes (P < 0.05). Conclusions: Rs4988300 and rs634008 polymorphisms in the LRP5 gene are associated with bone phenotypes in the elderly with OP or fractures.

Association of clinical variables and polymorphisms in RANKL, RANK, and OPG genes with external apical root resorption

OBJECTIVES

The aim of this study was to investigate the association of clinical variables and polymorphisms in the RANKL, RANK, and OPG genes with external apical root resorption (EARR).

METHODS

The sample was composed of 338 unrelated patients of both sexes, average age 14.9 years (range 8-21) with Class II Division 1 malocclusion, orthodontically treated. Periapical radiographs of the maxillary central incisor with the longer root (reference tooth) were taken before treatment and 6 months after starting treatment. DNA was extracted from buccal epithelial cells with the use of 10 mol/L ammonium acetate and 1 mmol/L EDTA. The analysis of 42 polymorphisms in the RANKL, RANK, and OPG genes was performed by means of real-time polymerase chain reaction. Univariate and multivariate analyzes were performed to verify the association of clinical and genetic variables with EARR (P <0.05).

RESULTS

The initial root length and patient age were associated with EARR. Considering the study of polymorphisms of RANKL, no significant association was found of genetic polymorphisms with EARR. For RANK polymorphisms, only rs12455775 was associated with EARR. Regarding OPG polymorphisms, an association of rs3102724, rs2875845, rs1032128, and rs3102728 with EARR was found. After multivariate analysis, the initial root length, rapid maxillary expansion, and rs3102724 of the OPG gene were associated with EARR.

CONCLUSIONS

Longer roots of upper central incisors and rapid maxillary expansion, as well as allele A of the rs3102724 polymorphism of the OPG gene, were associated with EARR in the study population.

In vivo identification of Bmp2-correlation networks during fracture healing by means of a limb-specific conditional inactivation of Bmp2

Bmp2 is known to play an essential role in the initiation of fracture healing via periosteal activation. Specifically, activation and subsequent differentiation of periosteal progenitor cells requires Bmp2 signaling for activation of the osteo-chondrogenic pathway. Here, we explored the interactive transcriptional gene-gene interplays between Bmp2 and 150 known candidate genes during fracture repair. We constructed the interactive Bmp2 signaling pathways in vivo, by comparing gene expression levels prior and 24 h post femur fracture, in presence (wild type) and in absence of Bmp2 (Bmp2c/c;Prx1::cre limb-specific conditional knockout). Twenty-six differentially expressed genes (pre- vs. post-fracture), which demonstrated high correlations within each experimental condition, were used to construct the co-expression networks. Topological dynamic shifts across different co-expression networks characterized the 26 differentially expressed genes as non-redundant focal linking hubs, redundant connecting hubs, periphery genes, or non-existent. Top-ranked up- or down-regulated genes were identified and discussed. Protein-protein interactions in public databases support our findings. Thus, the co-expression networks from this study can be used for future experimental hypotheses.

Insights into the Role of Circadian Rhythms in Bone Metabolism: A Promising Intervention Target?

Numerous physiological processes of mammals, including bone metabolism, are regulated by the circadian clock system, which consists of a central regulator, the suprachiasmatic nucleus (SCN), and the peripheral oscillators of the BMAL1/CLOCK-PERs/CRYs system. Various bone turnover markers and bone metabolism-regulating hormones such as melatonin and parathyroid hormone (PTH) display diurnal rhythmicity. According to previous research, disruption of the circadian clock due to shift work, sleep restriction, or clock gene knockout is associated with osteoporosis or other abnormal bone metabolism, showing the importance of the circadian clock system for maintaining homeostasis of bone metabolism. Moreover, common causes of osteoporosis, including postmenopausal status and aging, are associated with changes in the circadian clock. In our previous research, we found that agonism of the circadian regulators REV-ERBs inhibits osteoclast differentiation and ameliorates ovariectomy-induced bone loss in mice, suggesting that clock genes may be promising intervention targets for abnormal bone metabolism. Moreover, osteoporosis interventions at different time points can provide varying degrees of bone protection, showing the importance of accounting for circadian rhythms for optimal curative effects in clinical treatment of osteoporosis. In this review, we summarize current knowledge about circadian rhythms and bone metabolism.

VDR, RANKL and OPG polymorphisms as possible predisposing cofactors of postmenopausal osteoporosis: explorative study in Italian population

Postmenopausal osteoporosis (PO) has a strong genetic component. Presently, the published evidence on the association between the main single-nucleotide polymorphisms (SNPs) of the receptor activator of nuclear factor-kb ligand (RANKL), osteoprotegerin (OPG) and vitamin D receptor (VDR) and bone mass density (BMD) are scarce, mostly considering Italian population. This study sought to determine whether OPG (rs2073618), RANKL (rs9525641) and the VDR (rs2228570) SNPs were associated with BMD in a sample of 139 North-Italian postmenopausal women. The allelic distribution of rs9525641 in women with PO or osteopenia (OP + OPE group) differed from controls (p < 0.05), suggesting that this allele might confer a greater susceptibility to bone resorption. Concerning rs2228570, CC genotype was associated with OP + OPE women, with a worst total hip BMD. Notably, the combined genotype RANK (CT)-VDR (TT) was significantly associated to spine BMD (p < 0.05). In conclusion, this pilot study showed that rs9525641 and rs2228570 polymorphisms might contribute, separately or in combination, in determining BMD phenotype in selected postmenopausal populations.

Immunohistochemical Analysis on Cortex-to-Cortex Healing After Mandibular Vertical Ramus Osteotomy: A Preliminary Study

PURPOSE

The present study analyzed the expression of specific cytokines in the transforming growth factor (TGF)-β superfamily postoperatively after mandibular vertical ramus osteotomy (VRO).

MATERIALS AND METHODS

Four beagle dogs were enrolled and euthanized at 1, 2, 4, and 8 weeks postoperatively for immunohistochemical analysis using 6 specific antibodies (bone morphogenetic protein [BMP]-2/4, BMP-7, TGF-β2, TGF-β3, matrix metalloproteinase-3, and vascular endothelial growth factor [VEGF]). The results from the surgical site and control (adjacent area) were compared.

RESULTS

Generalized upregulation of BMP-2/4 was observed in all healing periods, and the strongest expression of BMP-7 was observed at 1 week postoperatively. The strongest expression of TGF-β2 was observed at 8 weeks with increasing pattern. The strong expression of TGF-β3 was observed at 1 and 4 weeks, with the strongest expression of VEGF at 1 week, with a decreasing pattern. No notable uptake was detected with the 6 specific antibodies in the adjacent bone (control).

CONCLUSIONS

The absence of internal fixation after VRO led to dynamic healing with a specific expression pattern of BMP-7 and TGF-β2. The anatomic factors, including sufficient preexisting vascularity, led to the earlier expression pattern of VEGF.

Polymorphisms of Il-10 (-1082) and RANKL (-438) Genes and the Failure of Dental Implants

Background. Genetic polymorphisms in certain cytokines and chemokines have been investigated to understand why some individuals display implant flaws despite having few risk factors at the time of implant. Purpose. To investigate the association of genetic polymorphisms in interleukin- (IL-) 10 [-1082 region (A/G)] and RANKL [-438 region (A/G)] with the failure of dental implants. Materials and Methods. This study included 90 partially edentulous male and female patients who were rehabilitated with a total of 245 Straumann dental implants. An implant was considered a failure if any of the following occurred: mobility, persistent subjective complaint, recurrent peri-implant infection with suppuration, continuous radiolucency around the implant, probing depth ≥ 5 mm, and bleeding on probing. Buccal mucosal cells were collected for analysis of RANKL438 and IL-10. Results. The implant success rate in this population was 34.4%. The mutant allele (G) in RANKL had an incidence of 52.3% and mutant allele (A) in IL-10 was observed in 37.8%. No statistically significant difference was detected between the failure of the implant and the genotypes and allelic frequencies. Conclusion. No association was detected between the genetic polymorphisms of RANKL (-438) and IL-10 (-1082) and the failure of dental implants in the population studied.

Congenic Strains Confirm the Pleiotropic Effect of Chromosome 4 QTL on Mouse Femoral Geometry and Biomechanical Performance

A pleiotropic quantitative trait locus (QTL) for bone geometry and mechanical performance in mice was mapped to distal chromosome 4 via an intercross of recombinant congenic mice HcB-8 and HcB-23. To study the QTL in isolation, we have generated C3H.B10-(rs6355453-rs13478087) (C.B.4.3) and C3H.B10-(rs6369860-D4Mit170) (C.B.4.2) congenic strains that harbor ~20 Mb and ~3 Mb, respectively, of chromosome 4 overlapping segments from C57BL/10ScSnA (B10) within the locus on a C3H/DiSnA (C3H) background. Using 3-point bend testing and standard beam equations, we phenotyped these mice for femoral mid-diaphyseal geometry and biomechanical performance. We analyzed the results via 2-way ANOVA, using sex and genotype as factors. In the C.B.4.3 strain, we found that homozygous B10/B10 male mice had smaller cross sectional area (CSA) and reduced total displacement than homozygous C3H/C3H mice. Sex by genotype interaction was also observed for maximum load and stiffness for C3H/C3H and B10/B10 mice, respectively. In C.B.4.2 strain, we found that homozygous B10/B10 mice had lower total displacement, post-yield displacement (PYD), stiffness, yield load and maximum load than mice harboring C3H allele. Sex by genotype interaction was observed in B10/B10 mice for perimeter, outer minor axis (OMA) and CSA. There were no significant differences in tissue level mechanical performance, which suggest that the QTL acts primarily on circumferential bone size. These data confirm the prior QTL mapping data and support other work demonstrating the importance of chromosome 4 QTL on bone modeling and bone responses to mechanical loading.

GC Gene Polymorphisms and Vitamin D-Binding Protein Levels Are Related to the Risk of Generalized Aggressive Periodontitis

Objective. To explore whether GC (group-specific component) rs17467825, rs4588, and rs7041 polymorphisms are associated with generalized aggressive periodontitis. Methods. This case-control study recruited 372 patients with generalized aggressive periodontitis (group AgP) and 133 periodontal healthy subjects (group HP). GC rs17467825, rs4588, and rs7041 genotypes and plasmatic vitamin D-binding protein (DBP) were measured. Analysis of single SNP and multiple SNPs was performed and relevance between plasmatic DBP and haplotypes was analyzed. Results. GC rs17467825 GG genotype was statistically associated with lower risk for generalized aggressive periodontitis under the recessive model (OR = 0.52, 95% CI: 0.30-0.92, p = 0.028). GC rs17467825 and rs4588 had strong linkage disequilibrium with r² ≥ 0.8 and D' ≥ 0.8. Haplotype (GC rs17467825, rs4588) GC was associated with the less risk for generalized aggressive periodontitis (OR = 0.29, 95% CI: 0.09-0.96, p = 0.043). In group AgP, individuals with combined genotype (GC rs17467825, rs4588) AG+CA had significantly lower plasmatic DBP level than those with the other two combined genotypes (AG+CA versus AA+CC p = 0.007; AG+CA versus GG+AA p = 0.026). Conclusions. GC rs17467825 genotype GG and haplotype (GC rs17467825, rs4588) GC are associated with generalized aggressive periodontitis. The association may be acquired through regulating DBP levels. The functions of GC gene and DBP in inflammatory disease need to be further studied.

Strong effect of SNP rs4988300 of the LRP5 gene on bone phenotype of Caucasian postmenopausal women

The purpose of this study was to identify relationships between single nucleotide polymorphisms (SNPs) in the genes of the Wnt pathway and bone mineral density (BMD) of postmenopausal women. We chose this pathway due to its importance in bone metabolism that was underlined in several studies. DNA samples of 932 Hungarian postmenopausal women were studied. First, their BMD values at different sites (spine, total hip) were measured, using a Lunar Prodigy DXA scanner. Thereafter, T-score values and the patients' body mass indices (BMIs) were calculated, while information about the fracture history of the sample population was also collected. We genotyped nine SNPs of the following three genes: LRP5, GPR177, and SP7, using a Sequenom MassARRAY Analyzer 4 instrument. The genomic DNA samples used for genotyping were extracted from the buccal mucosa of the subjects. Statistical analyses were carried out using the SPSS 21 and R package. The results of this analysis showed a significant association between SNP rs4988300 of the LRP5 gene and total hip BMD values. We could not reveal any associations between the markers of GPR177, SP7, and bone phenotypes. We found no effect of these genotypes on fracture risk. We could demonstrate a significant gene-gene interaction between two SNPs of LRP5 (rs4988300 and rs634008, p = 0.009) which was lost after Bonferroni correction. We could firmly demonstrate a significant association between rs4988300 of the LRP5 gene and bone density of the hip on the largest homogeneous postmenopausal study group analyzed to date. Our finding corroborates the relationship between LRP5 genotype and bone phenotype in postmenopausal women, however, the complete mechanism of this relationship requires further investigations.

The role of lipoxygenases in pathophysiology; new insights and future perspectives

Lipoxygenases (LOXs) are dioxygenases that catalyze the formation of corresponding hydroperoxides from polyunsaturated fatty acids such as linoleic acid and arachidonic acid. LOX enzymes are expressed in immune, epithelial, and tumor cells that display a variety of physiological functions, including inflammation, skin disorder, and tumorigenesis. In the humans and mice, six LOX isoforms have been known. 15-LOX, a prototypical enzyme originally found in reticulocytes shares the similarity of amino acid sequence as well as the biochemical property to plant LOX enzymes. 15-LOX-2, which is expressed in epithelial cells and leukocytes, has different substrate specificity in the humans and mice, therefore, the role of them in mammals has not been established. 12-LOX is an isoform expressed in epithelial cells and myeloid cells including platelets. Many mutations in this isoform are found in epithelial cancers, suggesting a potential link between 12-LOX and tumorigenesis. 12R-LOX can be found in the epithelial cells of the skin. Defects in this gene result in ichthyosis, a cutaneous disorder characterized by pathophysiologically dried skin due to abnormal loss of water from its epithelial cell layer. Similarly, eLOX-3, which is also expressed in the skin epithelial cells acting downstream 12R-LOX, is another causative factor for ichthyosis. 5-LOX is a distinct isoform playing an important role in asthma and inflammation. This isoform causes the constriction of bronchioles in response to cysteinyl leukotrienes such as LTC4, thus leading to asthma. It also induces neutrophilic inflammation by its recruitment in response to LTB4. Importantly, 5-LOX activity is strictly regulated by 5-LOX activating protein (FLAP) though the distribution of 5-LOX in the nucleus. Currently, pharmacological drugs targeting FLAP are actively developing. This review summarized these functions of LOX enzymes under pathophysiological conditions in mammals.

Novel hedgehog agonists promote osteoblast differentiation in mesenchymal stem cells

Hedgehog (Hh) family members are involved in multiple cellular processes including proliferation, migration, differentiation, and cell fate determination. Recently, the novel Hh agonists Hh-Ag 1.3 and 1.7 were identified in a high-throughput screening of small molecule compounds that activate the expression of Gli1, a target of Hh signaling. This study demonstrates that Hh-Ag 1.3 and 1.7 strongly activate the expression of endogenous Gli1 and promote osteoblast differentiation in the mesenchymal stem cell line C3H10T1/2. Both compounds stimulated alkaline phosphatase activity in a dose-dependent manner, and induced osteoblast marker gene expression in C3H10T1/2 cells, which indicated that they had acquired an osteoblast identity. Of the markers, the expression of osterix/Sp7, a downstream target of runt-related transcription factor (Runx)2, was induced by Hh-Ag 1.7, which also rescued the osteoblast differentiation defect of RD-127, a mesenchymal cell line from Runx2-deficient mice. Hh-Ags also activated canonical Wnt signaling and synergized with low doses of BMP-2 to enhance osteoblastic potential. Thus, Hh-Ag 1.7 could be useful for bone healing in individuals with abnormalities in osteogenesis, such as osteoporosis patients and the elderly, and can contribute to the development of novel therapeutics for the treatment of bone fractures and defects.

Polymorphisms in genes in the RANKL/RANK/OPG pathway are associated with bone mineral density at different skeletal sites in post-menopausal women

Association between 22 single nucleotide polymorphisms (SNPs) in the TNFSF11, TNFRSF11A, and TNFRSF11B genes in the RANKL/RANK/OPG pathway with bone mineral density (BMD) in 881 post-menopausal women. Our results suggest that TNFSF11 and TNFRSF11A, but not TNFRSF11B, genetic polymorphisms influence BMD mainly in the femoral neck in post-menopausal Chinese women.

INTRODUCTION

The aim of this study was to assess the relationship of polymorphisms in the TNFSF11, TNFRSF11A, and TNFRSF11B genes in the RANKL/RANK/OPG pathway with bone mineral density (BMD) in a cohort of Chinese post-menopausal women.

METHODS

A cross-sectional study was conducted in 881 post-menopausal women aged 50-89 years. All participants underwent lumbar spinal (LS) and femoral neck (FN) BMD evaluation by dual-energy X-ray absorptiometry. Twenty-two TNFSF11, TNFRSF11A, and TNFRSF11B SNPs were genotyped. We tested whether a single SNP or a haplotype was associated with BMD variations.

RESULTS

Two SNPs in the TNFSF11 gene (rs2277439 and rs2324851) and one in the TNFRSF11A gene (rs7239261) were found to be significantly associated with FN BMD (p = 0.014, 0.013, and 0.047, respectively). Haplotype TGACGT of TNFSF11 rs9525641-rs2277439-rs2324851-rs2875459-rs2200287-rs9533166 was a genetic risk factor toward a lower FN BMD (beta = -0.1473; p = 0.01126). In contrary, haplotype TAGCGT of TNFSF11 rs9525641-rs2277439-rs2324851-rs2875459-rs2200287-rs9533166 was genetic protective factor for LS BMD (beta = 0.3923; p = 0.04917).

CONCLUSIONS

Our findings suggest that TNFSF11 and TNFRSF11A, but not TNFRSF11B, genetic polymorphisms influence BMD mainly in the femoral neck in post-menopausal Chinese women. This contributes to the understanding of the role of genetic variation in this pathway in determining bone health.

Pregnancy-associated osteoporosis with a heterozygous deactivating LDL receptor-related protein 5 (LRP5) mutation and a homozygous methylenetetrahydrofolate reductase (MTHFR) polymorphism

Pregnancy-associated osteoporosis (PAO) is a rare, idiopathic disorder that usually presents with vertebral compression fractures (VCFs) within 6 months of a first pregnancy and delivery. Spontaneous improvement is typical. There is no known genetic basis for PAO. A 26-year-old primagravida with a neonatal history of unilateral blindness attributable to hyperplastic primary vitreous sustained postpartum VCFs consistent with PAO. Her low bone mineral density (BMD) seemed to respond to vitamin D and calcium therapy, with no fractures after her next successful pregnancy. Investigation of subsequent fetal losses revealed homozygosity for the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism associated both with fetal loss and with osteoporosis (OP). Because her neonatal unilateral blindness and OP were suggestive of loss-of-function mutation(s) in the gene that encodes LDL receptor-related protein 5 (LRP5), LRP5 exon and splice site sequencing was also performed. This revealed a unique heterozygous 12-bp deletion in exon 21 (c.4454_4465del, p.1485_1488del SSSS) in the patient, her mother and sons, but not her father or brother. Her mother had a normal BMD, no history of fractures, PAO, ophthalmopathy, or fetal loss. Her two sons had no ophthalmopathy and no skeletal issues. Her osteoporotic father (with a family history of blindness) and brother had low BMDs first documented at ages ∼40 and 32 years, respectively. Serum biochemical and bone turnover studies were unremarkable in all subjects. We postulate that our patient's heterozygous LRP5 mutation together with her homozygous MTHFR polymorphism likely predisposed her to low peak BMD. However, OP did not cosegregate in her family with the LRP5 mutation, the homozygous MTHFR polymorphism, or even the combination of the two, implicating additional genetic or nongenetic factors in her PAO. Nevertheless, exploration for potential genetic contributions to PAO may explain part of the pathogenesis of this enigmatic disorder and identify some at-risk women.

Mesenchymal stem cells from osteoporotic patients feature impaired signal transduction but sustained osteoinduction in response to BMP-2 stimulation

Osteoporotic fractures show reduced callus formation and delayed bone healing. Cellular sources of fracture healing are mesenchymal stem cells (MSC) that differentiate into osteoblasts by stimulation with osteoinductive cytokines, such as BMP-2. We hypothesized that impaired signal transduction and reduced osteogenic differentiation capacity in response to BMP-2 may underlie the delayed fracture healing. Therefore, MSC were isolated from femoral heads of healthy and osteoporotic patients. Grouping was carried out by bone mineral densitometry in an age-matched manner. MSC were stimulated with BMP-2. Signal transduction was assessed by western blotting of pSMAD1/5/8 and pERK1/2 as well as by quantitative RT-PCR of Runx-2, Dlx5, and Osteocalcin. Osteogenic differentiation was assessed by quantifying Alizarin Red staining. Osteoporotic MSC featured an accurate phosphorylation pattern of SMAD1/5/8 but a significantly reduced activation of ERK1/2 by BMP-2 stimulation. Furthermore, osteoporotic MSC showed significantly reduced basal expression levels of Runx-2 and Dlx5. However, Runx-2, Dlx5, and Osteocalcin expression showed adequate up-regulation due to BMP-2 stimulation. The global osteogenic differentiation in standard osteogenic differentiation media was reduced in osteoporotic MSC. Nevertheless, osteoporotic MSC were shown to feature an adequate induction of osteogenic differentiation due to BMP-2 stimulation. Taken together, we here demonstrate osteoporosis associated alterations in BMP-2 signaling but sustained specific osteogenic differentiation capacity in response to BMP-2. Therefore, BMP-2 may represent a promising therapeutic agent for the treatment of fractures in osteoporotic patients.

Gene-gene interaction between RBMS3 and ZNF516 influences bone mineral density

Osteoporosis is characterized by low bone mineral density (BMD), a highly heritable trait that is determined, in part, by the actions and interactions of multiple genes. Although an increasing number of genes have been identified to have independent effects on BMD, few studies have been performed to identify genes that interact with one another to affect BMD. In this study, we performed gene-gene interaction analyses in selected candidate genes in individuals with extremely high versus low hip BMD (20% tails of the distributions), in two independent U.S. Caucasian samples. The first sample contained 916 unrelated subjects with extreme hip BMD Z-scores selected from a population composed of 2286 subjects. The second sample consisted of 400 unrelated subjects with extreme hip BMD Z-scores selected from a population composed of 1000 subjects. Combining results from these two samples, we found one interacting gene pair (RBMS3 versus ZNF516) which, even after Bonferroni correction for multiple testing, showed consistently significant effects on hip BMD. RMBS3 harbored two single-nucleotide polymorphisms (SNPs), rs6549904 and rs7640046, both of which had significant interactions with an SNP, rs4891159, located on ZNF516 (p = 7.04 × 10(-11) and 1.03 × 10(-10) ). We further validated these results in two additional samples of Caucasian and African descent. The gene pair, RBMS3 versus ZNF516, was successfully replicated in the Caucasian sample (p = 8.07 × 10(-3) and 2.91 × 10(-3) ). For the African sample, a significant interaction was also detected (p = 0.031 and 0.043), but the direction of the effect was opposite to that observed in the three Caucasian samples. By providing evidence for genetic interactions underlying BMD, this study further delineates the genetic architecture of osteoporosis.

Association of genetic polymorphisms of RANK, RANKL and OPG with bone mineral density in Chinese peri- and postmenopausal women

OBJECTIVES

To explore the influence of 14 single nucleotide polymorphisms (SNPs) in receptor activator of nuclear factor-kappa B (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) on bone mineral density (BMD) in a Chinese female population.

DESIGN AND METHODS

A cross-sectional study was conducted in 108 perimenopausal and 127 postmenopausal women aged 43-65 years. All participants underwent lumbar spinal and nondominant femoral BMD evaluation by dual energy X-ray absorptiometry. Fourteen RANK, RANKL and OPG genotypes were determined by chip-based MALDI-TOF mass spectrometry. The differences between the BMDs of the RANK genotypes were analyzed.

RESULTS

Five SNPs (rs6993813, rs4355801, rs1032129 and rs2073618 in OPG and rs3018362 in RANK) were significantly associated with BMD or with BMD adjusted for body weight or years since menopause, mostly at the femoral neck but also partly at the total hip (p<0.05). The risk allele frequencies observed in our sample were different from those found in Europeans but the effects of these risk alleles on BMD values had the same direction in our cohort as in Europeans, except for rs3018362 with G as the risk allele, which was contrary to other studies. None of the SNPs in RANKL were associated with BMD at any anatomical site.

CONCLUSIONS

Our findings suggest that OPG and RANK but not RANKL genetic polymorphisms influence BMD mainly in the femoral neck in peri- and postmenopausal Chinese women. This contributes to the understanding of the role of genetic variation in this pathway in determining bone health.

Low-density lipoprotein receptor-related protein 5 gene polymorphisms and genetic susceptibility to abdominal aortic aneurysm

BACKGROUND

Previous data showed decreased low-density lipoprotein receptor-related protein 5 (LRP5) gene expression in peripheral blood cells of abdominal aortic aneurysm (AAA) patients and an association between decreased expression of LRP5 and increased lipoprotein (a) [Lp(a)] levels in AAA. LRP5 gene is involved in bone, lipid, and glucose metabolism, and experimental studies showed that atherosclerotic lesions of ApoE:LRP5 double knockout mice were ~threefold greater than those in ApoE-knockout mice and were characterized by features of advanced atherosclerosis, with remarkable accumulation of foam cells and destruction of the internal elastic lamina. The aim of this study was to evaluate the role of polymorphisms in LRP5 gene in determining genetic susceptibility to AAA.

METHODS

A total of 423 AAA patients and 423 controls comparable for sex and age were genotyped for seven polymorphisms within the LRP5 (rs667126, rs3736228, rs4988300, rs3781590, rs312016, rs556442, rs627174) by TaqMan approach.

RESULTS

Two polymorphisms were significantly associated with AAA: rs4988300, carriers of the T allele in AAA (74.0% vs 65.3% in controls; P = .007); and rs3781590, carriers of the T allele in AAA (66.5% vs 57.4% in controls; P =.009). At the multiple logistic regression analysis, adjusted for age, sex, dyslipidemia, hypertension, smoking habit, and chronic obstructive pulmonary disease, rs4988300 and rs3781590 polymorphisms remained significant and independent determinants of AAA (OR, 1.62; 95% CI, 1.02-2.56; P = .040, and OR, 1.83; 95% CI, 1.17-2.85; P = .008, respectively). We confirmed that AAA patients had significantly higher Lp(a) levels than control subjects (180.0 mg/L vs 107.6 mg/L; P < .0001). The prevalence of patients with Lp(a) levels ≥ 300 mg/L was significantly higher in patient carriers of the rs4988300 T allele than in wild-type patients (42.6% vs 30.8%; P = .048).

CONCLUSIONS

Present data have identified rs4988300 and rs3781590 LPR5 polymorphisms as independent genetic markers of AAA and underlined the need to concentrate our effort in studying the role of these markers in AAA and of LRP5 gene in Lp(a) catabolism and AAA pathophysiology.

The genetic pleiotropy of musculoskeletal aging

Musculoskeletal aging is detrimental to multiple bodily functions and starts early, probably in the fourth decade of an individual's life. Sarcopenia is a health problem that is expected to only increase as a greater portion of the population lives longer; prevalence of the related musculoskeletal diseases is similarly expected to increase. Unraveling the biological and biomechanical associations and molecular mechanisms underlying these diseases represents a formidable challenge. There are two major problems making disentangling the biological complexity of musculoskeletal aging difficult: (a) it is a systemic, rather than "compartmental," problem, which should be approached accordingly, and (b) the aging per se is neither well defined nor reliably measurable. A unique challenge of studying any age-related condition is a need of distinguishing between the "norm" and "pathology," which are interwoven throughout the aging organism. We argue that detecting genes with pleiotropic functions in musculoskeletal aging is needed to provide insights into the potential biological mechanisms underlying inter-individual differences insusceptibility to the musculoskeletal diseases. However, exploring pleiotropic relationships among the system's components is challenging both methodologically and conceptually. We aimed to focus on genetic aspects of the cross-talk between muscle and its "neighboring" tissues and organs (tendon, bone, and cartilage), and to explore the role of genetics to find the new molecular links between skeletal muscle and other parts of the "musculoskeleton." Identification of significant genetic variants underlying the musculoskeletal system's aging is now possible more than ever due to the currently available advanced genomic technologies. In summary, a "holistic" genetic approach is needed to study the systems's normal functioning and the disease predisposition in order to improve musculoskeletal health.

Polymorphisms in the human ALOX12 and ALOX15 genes are associated with peak bone mineral density in Chinese nuclear families

SUMMARY

Association between ten single-nucleotide polymorphisms (SNPs) in the human ALOX12 and ALOX15 genes and variations in peak bone mineral density (BMD) in a large sample of Chinese nuclear families with female offspring using the quantitative transmission disequilibrium test (QTDT). Our results suggest that the genetic polymorphisms in both human ALOX12 and ALOX15 may contribute to variations in the peak BMD of Chinese women.

INTRODUCTION

The aim of this study was to investigate whether polymorphisms in the human ALOX12 and ALOX15 genes are associated with variations in peak BMD in Chinese nuclear families with female offspring.

METHODS

Each five SNPs in the ALOX12 and ALOX15 genes were genotyped in a total of 1,260 individuals from 401 Chinese nuclear families. The BMD of the lumbar spine, femoral neck and total hip was measured by dual-energy X-ray absorptiometry. We tested whether a single SNP or a haplotype was associated with peak BMD variations using the QTDT.

RESULTS

Using QTDT to measure within-family associations in ALOX15, we observed a significant association between rs916055 and BMD in the lumbar spine (p = 0.027 in the permutation 1,000 test). However, in ALOX12, rs312470 was significantly associated with BMD in the femoral neck (p = 0.029 and p = 0.036 in the permutation 1,000 test). The results of a haplotype analysis supported the findings of the single locus test for ALOX15.

CONCLUSIONS

Our results suggest that the genetic polymorphisms in both human ALOX12 and ALOX15 may contribute to variations in the peak BMD of Chinese women.

Multiple quantitative trait loci for cortical and trabecular bone regulation map to mid-distal mouse chromosome 4 that shares linkage homology to human chromosome 1p36

The mid-distal region of mouse chromosome 4 (Chr 4) is homologous with human Chr 1p36. Previously, we reported that mouse Chr 4 carries a quantitative trait locus (QTL) with strong regulatory effect on volumetric bone mineral density (vBMD). The intent of this study is to utilize nested congenic strains to decompose the genetic complexity of this gene-rich region. Adult females and males from 18 nested congenic strains carrying discrete C3H sequences were phenotyped for femoral mineral and volume by pQCT and for trabecular bone volume (BV), tissue volume (TV), trabecular number (Trab.no), and trabecular thickness (Trab.thk) by MicroCT 40. Our data show that the mouse Chr 4 region consists of at least 10 regulatory QTL regions that affected either or both pQCT and MicroCT 40 phenotypes. The pQCT phenotypes were typically similar between sexes, whereas the MicroCT 40 phenotypes were divergent. Individual congenic strains contained one to seven QTL regions. These regions conferred large positive or negative effects in some congenic strains, depending on the particular bone phenotype. The QTL regions II to X are syntenic with human 1p36, containing from 1 to 102 known genes. We identified 13 candidate genes that can be linked to bone within these regions. Six of these genes were linked to osteoblasts, three linked to osteoclasts, and two linked to skeletal development. Three of these genes have been identified in Genome Wide Association Studies (GWAS) linked to 1p36. In region III, there is only one gene, Lck, which conferred negative pQCT and MicroCT 40 phenotypes in both sexes. This gene is important to development and functioning of T cells, has been associated with osteoclast activity, and represents a novel bone regulatory gene that merits further experimental evaluation. In summary, congenic strains are powerful tools for identifying regulatory regions that influence bone biology and offer models for testing hypotheses about gene-gene and gene-environment interactions that are not available to experimental work in humans.

Identification of genes for bone mineral density variation by computational disease gene identification strategy

We previously used five freely available bioinformatics tools (Prioritizer, Geneseeker, PROSPECTR and SUSPECTS, Disease Gene Prediction, and Endeavour) to analyze the thirteen well-replicated osteoporosis susceptibility loci and identify a subset of most likely candidate osteoporosis susceptibility genes (Huang et al. in J Hum Genet 53:644-655, 2008). In the current study, we experimentally tested the association between bone mineral density (BMD) and the 9 most likely candidate genes [LAMC2(1q25-q31), MATN3(2p24-p23), ITGAV(2q31-q32), ACVR1(2q23-q24), TDGF1(3p21.31), EGF(4q25), IGF1(12q22-q23), ZIC2(13q32), BMP2(20p12)] which were pinpointed by 4 or more bioinformatics tools. Forty tag SNPs in nine candidate genes were genotyped in a southern Chinese female case-control cohort consisting of 1643 subjects. Single- and multi-marker association analyses were performed using logistic regression analysis implemented by PLINK. Potential transcription factor binding sites were predicted by MatInspector. The strongest association was observed between rs10178256 (MATN3) and trochanter (P < 0.001) and total hip BMD (P = 0.002). The SNP rs6214 (IGF1) showed consistent association with BMD at all the four measured skeletal sites (P = 0.005-0.044). Prediction of transcription factor binding suggested that the minor allele G of rs10178256 might abolish the binding of MESP1 and MESP2 which play vital roles in bone homeostasis, whereas the minor allele G of rs6214 might create an additional binding site for XBP1, a constitutive regulator of endoplasmic reticulum stress response. Our data suggested that variants in MATN3 and IGF1 were involved in BMD regulation in southern Chinese women.

The ESR2 AluI gene polymorphism is associated with bone mineral density in postmenopausal women

Multiple factors may contribute to the pathogenesis of postmenopausal osteoporosis including environmental, life-style and genetic factors. Common variants in ESR2 gene encoding for ER-beta, highly expressed in bone tissue, have recently been proposed as candidates for affecting bone phenotype at the population level, particularly in postmenopausal women. In this study, we examined the genetic background at ESR2 AluI (rs4986938, 1730G>A) locus in 89 osteopenic, postmenopausal women (age range 49-56 years) together with BMD at lumbar spine and femoral neck sites as well as variations in plasma levels of bone metabolism and turnover markers. Genotyping for ESR2 G1730A polymorphism showed that the frequency of A mutated allele accounted for 0.4 in our cohort of postmenopausal women; moreover, the GA1730 heterozygous individuals were the most represented (50.6%) compared with GG (37.8%) and AA homozygous ones (14.6%). A regression analysis showed that lumbar spine BMD values were significantly associated with both ESR2 AA1730 genotype (p=0.044) and time since the onset of menopause (p=0.031), while no significant association was detected between biochemical markers and genetic background. Interestingly, 85% of patients with AA1730 genotype presented the smallest lumbar spine BMD values. These findings first indicate a worsening effect of ESR2 AluI polymorphism on lumbar spine BMD reduction in postmenopause, suggesting that the detection of this ESR2 variant should be recommended in postmenopausal women, particularly in populations with a high prevalence of ESR2 AA1730 homozygous genotype.

Camurati-Engelmann disease: unique variant featuring a novel mutation in TGFβ1 encoding transforming growth factor beta 1 and a missense change in TNFSF11 encoding RANK ligand

We report a 32-year-old man and his 59-year-old mother with a unique and extensive variant of Camurati-Engelmann disease (CED) featuring histopathological changes of osteomalacia and alterations within TGFβ1 and TNFSF11 encoding TGFβ1 and RANKL, respectively. He suffered leg pain and weakness since childhood and reportedly grew until his late 20s, reaching 7 feet in height. He had deafness, perforated nasal septum, torus palatinus, disproportionately long limbs with knock-knees, low muscle mass, and pseudoclubbing. Radiographs revealed generalized skeletal abnormalities, including wide bones and cortical and trabecular bone thickening in keeping with CED, except that long bone ends were also affected. Lumbar spine and hip BMD Z-scores were + 7.7 and + 4.4, respectively. Biochemical markers of bone turnover were elevated. Hypocalciuria accompanied low serum 25-hydroxyvitamin D (25[OH]D) levels. Pituitary hypogonadism and low serum insulin-like growth factor (IGF)-1 were present. Karyotype was normal. Despite vitamin D repletion, iliac crest histology revealed severe osteomalacia. Exon 1 of TNFRSF11A (RANK), exons 2, 3, and 4 of LRP5, and all coding exons and adjacent mRNA splice junctions of TNFRSF11B (OPG), SQSTM1 (sequestosome 1), and TNSALP (tissue nonspecific alkaline phosphatase) were intact. His asymptomatic and less dysmorphic 5'11″ mother, also with low serum 25(OH)D, had milder clinical, radiological, biochemical, and histopathological findings. Both individuals were heterozygous for a novel 12-bp duplication (c.27_38dup, p.L10_L13dup) in exon 1 of TGFβ1, predicting four additional leucine residues in the latency-associated-peptide segment of TGFβ1, consistent with CED. The son was also homozygous for a single base transversion in TNFSF11, predicting a nonconservative amino acid change (c.107C > G, p.Pro36Arg) in the intracellular domain of RANKL that was heterozygous in his nonconsanguineous parents. This TNFSF11 variant was not found in the SNP Database, nor in published TNFSF11 association studies, but it occurred in four of the 134 TNFSF11 alleles (3.0%) we tested randomly among individuals without CED. Perhaps the unique phenotype of this CED family is conditioned by altered RANKL activity.

Lack of association of bone morphogenetic protein 2 gene haplotypes with bone mineral density, bone loss, or risk of fractures in men

Introduction. The association of bone morphogenetic protein 2 (BMP2) with BMD and risk of fracture was suggested by a recent linkage study, but subsequent studies have been contradictory. We report the results of a study of the relationship between BMP2 genotypes and BMD, annual change in BMD, and risk of fracture in male subjects. Materials and Methods. We tested three single-nucleotide polymorphisms (SNPs) across the BMP2 gene, including Ser37Ala SNP, in 342 Caucasian Englishmen, comprising 224 control and 118 osteoporotic subjects. Results. BMP2 SNP1 (Ser37Ala) genotypes were found to have similar low frequency in control subjects and men with osteoporosis. The major informative polymorphism, BMP2 SNP3 (Arg190Ser), showed no statistically significant association with weight, height, BMD, change in BMD at hip or lumbar spine, and risk of fracture. Conclusion. There were no genotypic or haplotypic effects of the BMP2 candidate gene on BMD, change in BMD, or fracture risk identified in this cohort.

Dysosteosclerosis presents as an "osteoclast-poor" form of osteopetrosis: comprehensive investigation of a 3-year-old girl and literature review

Dysosteosclerosis (DSS), an extremely rare dense bone disease, features short stature and fractures and sometimes optic atrophy, cranial nerve palsy, developmental delay, and failure of tooth eruption in infancy or early childhood consistent with osteopetrosis (OPT). Bone histology during childhood shows unresorbed primary spongiosa from deficient osteoclast action. Additionally, there is remarkable progressive flattening of all vertebrae and, by adolescence, paradoxical metaphyseal osteopenia with thin cortical bone. Reports of consanguinity indicate autosomal recessive inheritance, yet more affected males than females suggest X-linked recessive inheritance. We investigated a nonconsanguineous girl with DSS. Osteosclerosis was discovered at age 7 months. Our studies, spanning ages 11 to 44 months, showed weight at approximately 50th percentile, and length diminishing from approximately 30th percentile to -2.3 SD. Head circumference was +4 SD. The patient had frontal bossing, blue sclera, normal teeth, genu valgum, and unremarkable joints. Radiographs showed orbital and facial sclerosis, basilar thickening, bone-in-bone appearance of the pelvis, sclerotic long bone ends, and fractures of ribs and extremities. Progressive metaphyseal widening occurred as vertebrae changed from ovoid to flattened and became beaked anteriorly. A hemogram was normal. Consistent with OPT, serum parathyroid hormone (PTH) concentrations reflected dietary calcium levels. Serum bone alkaline phosphatase, osteocalcin, and TRACP-5b were subnormal. The iliac crest contained excessive primary spongiosa and no osteoclasts. No mutations were identified in the splice sites or exons for the genes encoding chloride channel 7, T-cell immune regulator 1, OPT-associated transmembrane protein 1, and monocyte colony-stimulating factor (M-CSF) and its receptor C-FMS, ANKH, OPG, RANK, and RANKL. Genomic copy-number microarray was unrevealing. Hence, DSS is a distinctive OPT of unknown etiology featuring osteoclast deficiency during early childhood. How osteopenia follows is an enigma of human skeletal pathobiology.

Genetics of osteoporosis: perspectives for personalized medicine

Osteoporosis is the most common metabolic bone disorder worldwide. At least 15 genes (e.g., ESR1, LRP5, SOST, OPG, RANK and RANKL) have been confirmed as osteoporosis susceptibility genes, and another 30 have been highlighted as promising susceptibility genes. Notably, these genes are clustered in three biological pathways: the estrogen endocrine pathway, the Wnt/β-catenin signaling pathway and the RANK/RANKL/osteoprotegerin (OPG) pathway. In this article, using data pertaining to these three biological pathways as examples, we illustrate possible principles of personalized therapy for osteoporosis. In particular, we propose to use inhibitors (e.g., denosumab) of the RANK/RANKL/OPG signaling pathway to circumvent resistance to estrogen-replacement therapy: a novel idea resulting from the consideration of a mechanistic link between the estrogen endocrine pathway and the RANK/RANKL/OPG signaling pathway. In addition, we call for more attention to be focused on rare variants of major effects in future studies.

Evaluation of compressive strength index of the femoral neck in Caucasians and chinese

Compressive strength index (CSI) of the femoral neck is a parameter that integrates the information of bone mineral density (BMD), femoral neck width (FNW), and body weight. CSI is considered to have the potential to improve the performance of assessment for hip fracture risk. However, studies on CSI have been rare. In particular, few studies have evaluated the performance of CSI, in comparison with BMD, FNW, and bending geometry, for assessment of hip fracture risk. We studied two large populations, including 1683 unrelated U.S. Caucasians and 2758 unrelated Chinese adults. For all the study subjects, CSI, femoral neck BMD (FN_BMD), FNW, and bending geometry (section modulus [Z]) of the samples were obtained from dual-energy X-ray absorptiometry scans. We investigated the age-related trends of these bone phenotypes and potential sex and ethnic differences. We further evaluated the performance of these four phenotypes for assessment of hip fracture risk by logistic regression models. Chinese had significantly lower FN_BMD, FNW, and Z, but higher CSI than sex-matched Caucasians. Logistic regression analysis showed that higher CSI was significantly associated with lower risk of hip fracture, and the significance remained after adjusting for covariates of age, sex, and height. Each standard deviation (SD) increment in CSI was associated with odds ratios of 0.765 (95% confidence interval, 0.634, 0.992) and 0.724 (95% confidence interval, 0.569, 0.921) for hip fracture risk in Caucasians and Chinese, respectively. The higher CSI in Chinese may partially help explain the lower incidence of hip fractures in this population compared to Caucasians. Further studies in larger cohorts and/or longitudinal observations are necessary to confirm our findings.

ALOX12 polymorphisms are associated with fat mass but not peak bone mineral density in Chinese nuclear families

OBJECTIVE

Arachidonate 12-lipoxygenase (ALOX12) is a member of the lipoxygenase superfamily, which catalyzes the incorporation of molecular oxygen into polyunsaturated fatty acids. The products of ALOX12 reactions serve as endogenous ligands for peroxisome proliferator-activated receptor γ (PPARG). The activation of the PPARG pathway in marrow-derived mesenchymal progenitors stimulates adipogenesis and inhibits osteoblastogenesis. Our objective was to determine whether polymorphisms in the ALOX12 gene were associated with variations in peak bone mineral density (BMD) and obesity phenotypes in young Chinese men.

METHODS

All six tagging single-nucleotide polymorphisms (SNPs) in the ALOX12 gene were genotyped in a total of 1215 subjects from 400 Chinese nuclear families by allele-specific polymerase chain reaction. The BMD at the lumbar spine and hip, total fat mass (TFM) and total lean mass (TLM) were measured using dual-energy X-ray absorptiometry. The pairwise linkage disequilibrium among SNPs was measured, and the haplotype blocks were inferred. Both the individual SNP markers and the haplotypes were tested for an association with the peak BMD, body mass index, TFM, TLM and percentage fat mass (PFM) using the quantitative transmission disequilibrium test (QTDT).

RESULTS

Using the QTDT, significant within-family association was found between the rs2073438 polymorphism in the ALOX12 gene and the TFM and PFM (P=0.007 and 0.012, respectively). Haplotype analyses were combined with our individual SNP results and remained significant even after correction for multiple testing. However, we failed to find significant within-family associations between ALOX12 SNPs and the BMD at any bone site in young Chinese men.

CONCLUSIONS

Our present results suggest that the rs2073438 polymorphism of ALOX12 contributes to the variation of obesity phenotypes in young Chinese men, although we failed to replicate the association with the peak BMD variation in this sample. Further independent studies are needed to confirm our findings.

Genetic variation in the RANKL/RANK/OPG signaling pathway is associated with bone turnover and bone mineral density in men

The aim of this study was to determine if single-nucleotide polymorphisms (SNPs) in RANKL, RANK, and OPG influence bone turnover and bone mineral density (BMD) in men. Pairwise tag SNPs (r(2) > or = 0.8) were selected for RANKL, RANK, and OPG and their 10-kb flanking regions. Selected tag SNPs plus five SNPs near RANKL and OPG, associated with BMD in published genome-wide association studies (GWAS), were genotyped in 2653 men aged 40 to 79 years of age recruited for participation in a population-based study of male aging, the European Male Ageing Study (EMAS). N-terminal propeptide of type I procollagen (PINP) and C-terminal cross-linked telopeptide of type I collagen (CTX-I) serum levels were measured in all men. BMD at the calcaneus was estimated by quantitative ultrasound (QUS) in all men. Lumbar spine and total-hip areal BMD (BMD(a)) was measured by dual-energy X-ray absorptiometry (DXA) in a subsample of 620 men. Multiple OPG, RANK, and RANKL SNPs were associated with bone turnover markers. We also identified a number of SNPs associated with BMD, including rs2073618 in OPG and rs9594759 near RANKL. The minor allele of rs2073618 (C) was associated with higher levels of both PINP (beta = 1.83, p = .004) and CTX-I (beta = 17.59, p = 4.74 x 10(-4)), and lower lumbar spine BMD(a) (beta = -0.02, p = .026). The minor allele of rs9594759 (C) was associated with lower PINP (beta = -1.84, p = .003) and CTX-I (beta = -27.02, p = 6.06 x 10(-8)) and higher ultrasound BMD at the calcaneus (beta = 0.01, p = .037). Our findings suggest that genetic variation in the RANKL/RANK/OPG signaling pathway influences bone turnover and BMD in European men.

Percent body fat, fractures and risk of osteoporosis in women

OBJECTIVES

Globally, in an aging population, osteoporosis and fractures are emerging as major public health problems; accessible and affordable recognition, prevention and treatment strategies are needed. Percent body fat is known to be associated with bone mineral density and fractures. This paper uses an innovative, virtually cost-free method to estimate percent body fat from age, height and weight, and assesses its validity by examining the association between percent body fat and fractures among women 39 and older.

DESIGN

An epidemiologic study.

PARTICIPANTS

3940 college alumnae, median age 53.6, participated by responding to a mailed questionnaire covering medical history, behavioral factors, birth date, weight and height.

STATISTICAL METHODS

T-tests, chi-square and multivariable logistic regression.

MEASUREMENTS

Percent body fat estimated from age, weight, height and gender.

RESULTS

Associations of fractures with percent body fat are expressed as odds ratios: for osteoporotic (wrist, hip and/or x-ray confirmed vertebral), the adjusted OR = 2.41, 95% CI (1.65, 3.54), P < 0.0001; for wrist fractures, the adjusted OR = 2.56, 95% CI (1.65, 3.96), P < 0.0001; for x-ray confirmed vertebral fractures the adjusted OR = 4.69, 95% CI (2.05, 10.77), P=0.0003).; and for non-osteoporotic, he adjusted OR= 1.00, 95% CI (0.76 1.32), P=0.999.

CONCLUSION

The findings are consistent with methods using DXA and/or other technologies that show percent body fat is associated with fractures of the wrist and vertebrae. Identification of risk factors is necessary for the prevention and treatment of osteoporosis and osteoporotic fractures. Estimation of percent body fat from age, height and weight may be a valid, cost-saving, and cost-effective alternative tool for screening and assessing risk of osteoporosis in settings where Dual x-ray absorptiometry (DXA) or other radiological techniques are too costly or unavailable.

Skeletal site-related variation in human trabecular bone transcriptome and signaling

Background

The skeletal site-specific influence of multiple genes on bone morphology is recognised, but the question as to how these influences may be exerted at the molecular and cellular level has not been explored.

Methodology

To address this question, we have compared global gene expression profiles of human trabecular bone from two different skeletal sites that experience vastly different degrees of mechanical loading, namely biopsies from iliac crest and lumbar spinal lamina.

Principal Findings

In the lumbar spine, compared to the iliac crest, the majority of the differentially expressed genes showed significantly increased levels of expression; 3406 transcripts were up- whilst 838 were down-regulated. Interestingly, all gene transcripts that have been recently demonstrated to be markers of osteocyte, as well as osteoblast and osteoclast-related genes, were markedly up-regulated in the spine. The transcriptome data is consistent with osteocyte numbers being almost identical at the two anatomical sites, but suggesting a relatively low osteocyte functional activity in the iliac crest. Similarly, osteoblast and osteoclast expression data suggested similar numbers of the cells, but presented with higher activity in the spine than iliac crest. This analysis has also led to the identification of expression of a number of transcripts, previously known and novel, which to our knowledge have never earlier been associated with bone growth and remodelling.

Conclusions and Significance

This study provides molecular evidence explaining anatomical and micro-architectural site-related changes in bone cell function, which is predominantly attributable to alteration in cell transcriptional activity. A number of novel signaling molecules in critical pathways, which have been hitherto not known to be expressed in bone cells of mature vertebrates, were identified.

Evidence for pleiotropic factors in genetics of the musculoskeletal system

There are both theoretical and empirical underpinnings that provide evidence that the musculoskeletal system develops, functions, and ages as a whole. Thus, the risk of osteoporotic fracture can be viewed as a function of loading conditions and the ability of the bone to withstand the load. Both bone loss (osteoporosis) and muscle wasting (sarcopenia) are the two sides of the same coin, an involution of the musculoskeletal system. Skeletal loads are dominated by muscle action; both bone and muscle share environmental, endocrine and paracrine influences. Muscle also has an endocrine function by producing bioactive molecules, which can contribute to homeostatic regulation of both bone and muscle. It also becomes clear that bone and muscle share genetic determinants; therefore the consideration of pleiotropy is an important aspect in the study of the genetics of osteoporosis and sarcopenia. The aim of this review is to provide an additional evidence for existence of the tight genetic co-regulation of muscles and bones, starting early in development and still evident in aging. Recently, important papers were published, including those dealing with the cellular mechanisms and anatomic substrate of bone mechanosensitivity. Further evidence has emerged suggesting that the relationship between skeletal muscle and bone parameters extends beyond the general paradigm of bone responses to mechanical loading. We provide insights into several pathways and single genes, which apparently have a biologically plausible pleiotropic effect on both bones and muscles; the list is continuing to grow. Understanding the crosstalk between muscles and bones will translate into a conceptual framework aimed at studying the pleiotropic genetic relationships in the etiology of complex musculoskeletal disease. We believe that further progress in understanding the common genetic etiology of osteoporosis and sarcopenia will provide valuable insight into important biological underpinnings for both musculoskeletal conditions. This may translate into new approaches to reduce the burden of both conditions, which are prevalent in the elderly population.

Genetics of osteoporosis: accelerating pace in gene identification and validation

Osteoporosis is characterized by low bone mineral density and structural deterioration of bone tissue, leading to an increased risk of fractures. It is the most common metabolic bone disorder worldwide, affecting one in three women and one in eight men over the age of 50. In the past 15 years, a large number of genes have been reported as being associated with osteoporosis. However, only in the past 4 years we have witnessed an accelerated pace in identifying and validating osteoporosis susceptibility loci. This increase in pace is mostly due to large-scale association studies, meta-analyses, and genome-wide association studies of both single nucleotide polymorphisms and copy number variations. A comprehensive review of these developments revealed that, to date, at least 15 genes (VDR, ESR1, ESR2, LRP5, LRP4, SOST, GRP177, OPG, RANK, RANKL, COLIA1, SPP1, ITGA1, SP7, and SOX6) can be reasonably assigned as confirmed osteoporosis susceptibility genes, whereas, another >30 genes are promising candidate genes. Notably, confirmed and promising genes are clustered in three biological pathways, the estrogen endocrine pathway, the Wnt/beta-catenin signaling pathway, and the RANKL/RANK/OPG pathway. New biological pathways will certainly emerge when more osteoporosis genes are identified and validated. These genetic findings may provide new routes toward improved therapeutic and preventive interventions of this complex disease.

Differences in fat and muscle mass associated with a functional human polymorphism in a post-transcriptional BMP2 gene regulatory element

A classic morphogen, bone morphogenetic protein 2 (BMP2) regulates the differentiation of pluripotent mesenchymal cells. High BMP2 levels promote osteogenesis or chondrogenesis and low levels promote adipogenesis. BMP2 inhibits myogenesis. Thus, BMP2 synthesis is tightly controlled. Several hundred nucleotides within the 3' untranslated regions of BMP2 genes are conserved from mammals to fishes indicating that the region is under stringent selective pressure. Our analyses indicate that this region controls BMP2 synthesis by post-transcriptional mechanisms. A common A to C single nucleotide polymorphism (SNP) in the BMP2 gene (rs15705, +A1123C) disrupts a putative post-transcriptional regulatory motif within the human ultra-conserved sequence. In vitro studies indicate that RNAs bearing the A or C alleles have different protein binding characteristics in extracts from mesenchymal cells. Reporter genes with the C allele of the ultra-conserved sequence were differentially expressed in mesenchymal cells. Finally, we analyzed MRI data from the upper arm of 517 healthy individuals aged 18-41 years. Individuals with the C/C genotype were associated with lower baseline subcutaneous fat volumes (P = 0.0030) and an increased gain in skeletal muscle volume (P = 0.0060) following resistance training in a cohort of young males. The rs15705 SNP explained 2-4% of inter-individual variability in the measured parameters. The rs15705 variant is one of the first genetic markers that may be exploited to facilitate early diagnosis, treatment, and/or prevention of diseases associated with poor fitness. Furthermore, understanding the mechanisms by which regulatory polymorphisms influence BMP2 synthesis will reveal novel pharmaceutical targets for these disabling conditions.

Powerful bivariate genome-wide association analyses suggest the SOX6 gene influencing both obesity and osteoporosis phenotypes in males

Background

Current genome-wide association studies (GWAS) are normally implemented in a univariate framework and analyze different phenotypes in isolation. This univariate approach ignores the potential genetic correlation between important disease traits. Hence this approach is difficult to detect pleiotropic genes, which may exist for obesity and osteoporosis, two common diseases of major public health importance that are closely correlated genetically.

Principal Findings

To identify such pleiotropic genes and the key mechanistic links between the two diseases, we here performed the first bivariate GWAS of obesity and osteoporosis. We searched for genes underlying co-variation of the obesity phenotype, body mass index (BMI), with the osteoporosis risk phenotype, hip bone mineral density (BMD), scanning ∼380,000 SNPs in 1,000 unrelated homogeneous Caucasians, including 499 males and 501 females. We identified in the male subjects two SNPs in intron 1 of the SOX6 (SRY-box 6) gene, rs297325 and rs4756846, which were bivariately associated with both BMI and hip BMD, achieving p values of 6.82×10⁻⁷ and 1.47×10⁻⁶, respectively. The two SNPs ranked at the top in significance for bivariate association with BMI and hip BMD in the male subjects among all the ∼380,000 SNPs examined genome-wide. The two SNPs were replicated in a Framingham Heart Study (FHS) cohort containing 3,355 Caucasians (1,370 males and 1,985 females) from 975 families. In the FHS male subjects, the two SNPs achieved p values of 0.03 and 0.02, respectively, for bivariate association with BMI and femoral neck BMD. Interestingly, SOX6 was previously found to be essential to both cartilage formation/chondrogenesis and obesity-related insulin resistance, suggesting the gene's dual role in both bone and fat.

Conclusions

Our findings, together with the prior biological evidence, suggest the SOX6 gene's importance in co-regulation of obesity and osteoporosis.

Identification and association analysis of single nucleotide polymorphisms in the human noggin (NOG) gene and osteoporosis phenotypes

Noggin, an extracellular bone morphogenic protein (BMP) antagonist, blocks BMP signaling and decreases osteoblastogenesis. The purpose of this study was to identify novel sequence variations in the human noggin gene and to perform association analyses of these variations with phenotypes related to osteoporosis. Novel single nucleotide polymorphisms (SNPs) were identified by resequencing 7 kb of the noggin gene region in 24 randomly selected Afro-Caribbean men without regard to their bone mineral density (BMD) level. We identified 22 SNPs in the 7 kb noggin gene region, only 2 of which were previously described in dbSNP (build 126). There were also 11 unvalidated SNPs from dbSNP that could not be verified in our sequence analysis. Ten of the 22 identified SNPs showed a minor allele frequency greater than 0.05. Seven of these common SNPs were genotyped in 2060 Afro-Caribbean men age 40 and older. None of the 7 SNPs were associated with BMD at the proximal femur or lumbar spine. Our analysis suggests that a common variation in the noggin gene is unlikely to have a major impact on BMD among older men of African ancestry.

Identifying hypothetical genetic influences on complex disease phenotypes

BACKGROUND

Statistical interactions between disease-associated loci of complex genetic diseases suggest that genes from these regions are involved in a common mechanism impacting, or impacted by, the disease. The computational problem we address is to discover relationships among genes from these interacting regions that may explain the observed statistical interaction and the role of these genes in the disease phenotype.

RESULTS

We describe a heuristic algorithm for generating hypothetical gene relationships from loci associated with a complex disease phenotype. This approach, called Prioritizing Disease Genes by Analysis of Common Elements (PDG-ACE), mines biomedical keywords from text descriptions of genes and uses them to relate genes close to disease-associated loci. A keyword common to, and significantly over-represented in, a pair of gene descriptions may represent a preliminary hypothesis about the biological relationship between the genes, and suggest the role the genes play in the disease phenotype.

CONCLUSION

Our experimentation shows that the approach finds previously published relationships, while failing to find relationships that don't exist. The results also indicate that the approach is robust to differences in keyword vocabulary. We outline a brief case study in which results from a recently published Type 2 Diabetes association study are used to identify potential hypotheses.

Large-scale association study for structural soundness and leg locomotion traits in the pig

BACKGROUND

Identification and culling of replacement gilts with poor skeletal conformation and feet and leg (FL) unsoundness is an approach used to reduce sow culling and mortality rates in breeding stock. Few candidate genes related to soundness traits have been identified in the pig.

METHODS

In this study, 2066 commercial females were scored for 17 traits describing body conformation and FL structure, and were used for association analyses. Genotyping of 121 SNPs derived from 95 genes was implemented using Sequenom's MassARRAY system.

RESULTS

Based on the association results from single trait and principal components using mixed linear model analyses and false discovery rate testing, it was observed that APOE, BMP8, CALCR, COL1A2, COL9A1, DKFZ, FBN1 and VDBP were very highly significantly (P < 0.001) associated with body conformation traits. The genes ALOX5, BMP8, CALCR, OPG, OXTR and WNT16 were very highly significantly (P < 0.001) associated with FL structures, and APOE, CALCR, COL1A2, GNRHR, IHH, MTHFR and WNT16 were highly significantly (P < 0.01) associated with overall leg action. Strong linkage disequilibrium between CALCR and COL1A2 on SSC9 was detected, and haplotype -ACGACC- was highly significantly (P < 0.01) associated with overall leg action and several important FL soundness traits.

CONCLUSION

The present findings provide a comprehensive list of candidate genes for further use in fine mapping and biological functional analyses.