Association of endothelial nitric oxide synthase genotypes with bone mineral density, bone loss, hip structure, and risk of fracture in older women: the SOF study

A systematic review and cross-database analysis of single nucleotide polymorphisms underlying hip morphology and osteoarthritis reveals shared mechanisms

OBJECTIVE

Understanding the mechanisms of hip disease, such as osteoarthritis (OA), is crucial to advance their treatment. Such hip diseases often involve specific morphological changes. Genetic variations, called single nucleotide polymorphisms (SNPs), influence various hip morphological parameters. This study investigated the biological relevance of SNPs correlated to hip morphology in genome-wide association studies (GWAS). The SNP-associated genes were compared to genes associated with OA in other joints, aiming to see if the same genes play a role in both hip development and the risk of OA in other lower limb joints.

METHODOLOGY

A systematic literature review was conducted to identify SNPs correlated with hip morphology, based on the Population, Intervention, Comparison, Outcome, and Study (PICOS) framework. Afterwards, Gene Ontology (GO) analysis was performed, using EnrichR, on the SNP-associated genes and compared with non-hip OA-associated genes, across different databases.

RESULTS

Reviewing 49 GWAS identified 436 SNPs associated with hip joint morphology, encompassing variance in bone size, structure and shape. Among the SNP-associated genes, SOX9 plays a pivotal role in size, GDF5 impacts bone structure, and BMP7 affects shape. Overall, skeletal system development, regulation of cell differentiation, and chondrocyte differentiation emerged as crucial processes influencing hip morphology. Eighteen percent of GWAS-identified genes related to hip morphology were also associated with non-hip OA.

CONCLUSION

Our findings indicate the existence of multiple shared genetic mechanisms across hip morphology and OA, highlighting the necessity for more extensive research in this area, as in contrast to the hip, the genetic background on knee or foot morphology remains largely understudied.

Drug Delivery Systems Based on Titania Nanotubes and Active Agents for Enhanced Osseointegration of Bone Implants

TiO2 nanotubes (TNTs) are attractive nanostructures for localized drug delivery. Owing to their excellent biocompatibility and physicochemical properties, numerous functionalizations of TNTs have been attempted for their use as therapeutic agent delivery platforms. In this review, we discuss the current advances in the applications of TNT-based delivery systems with an emphasis on the various functionalizations of TNTs for enhancing osteogenesis at the bone-implant interface and for preventing implant-related infection. Innovation of therapies for enhancing osteogenesis still represents a critical challenge in regeneration of bone defects. The overall concept focuses on the use of osteoconductive materials in combination with the use of osteoinductive or osteopromotive factors. In this context, we highlight the strategies for improving the functionality of TNTs, using five classes of bioactive agents: growth factors (GFs), statins, plant derived molecules, inorganic therapeutic ions/nanoparticles (NPs) and antimicrobial compounds.

Molecular control of nitric oxide synthesis through eNOS and caveolin-1 interaction regulates osteogenic differentiation of adipose-derived stem cells by modulation of Wnt/β-catenin signaling

Background

Nitric oxide (NO) plays a role in a number of physiological processes including stem cell differentiation and osteogenesis. Endothelial nitric oxide synthase (eNOS), one of three NO-producing enzymes, is located in a close conformation with the caveolin-1 (CAV-1^WT) membrane protein which is inhibitory to NO production. Modification of this interaction through mutation of the caveolin scaffold domain can increase NO release. In this study, we genetically modified equine adipose-derived stem cells (eASCs) with eNOS, CAV-1^WT, and a CAV-1^F92A (CAV-1^WT mutant) and assessed NO-mediated osteogenic differentiation and the relationship with the Wnt signaling pathway.

Methods

NO production was enhanced by lentiviral vector co-delivery of eNOS and CAV-1^F92A to eASCs, and osteogenesis and Wnt signaling was assessed by gene expression analysis and activity of a novel Runx2-GFP reporter. Cells were also exposed to a NO donor (NONOate) and the eNOS inhibitor, l-NAME.

Results

NO production as measured by nitrite was significantly increased in eNOS and CAV-1^F92A transduced eASCs +(5.59 ± 0.22 μM) compared to eNOS alone (4.81 ± 0.59 μM) and un-transduced control cells (0.91 ± 0.23 μM) (p < 0.05). During osteogenic differentiation, higher NO correlated with increased calcium deposition, Runx2, and alkaline phosphatase (ALP) gene expression and the activity of a Runx2-eGFP reporter. Co-expression of eNOS and CAV-1^WT transgenes resulted in lower NO production. Canonical Wnt signaling pathway-associated Wnt3a and Wnt8a gene expressions were increased in eNOS-CAV-1^F92A cells undergoing osteogenesis whilst non-canonical Wnt5a was decreased and similar results were seen with NONOate treatment. Treatment of osteogenic cultures with 2 mM l-NAME resulted in reduced Runx2, ALP, and Wnt3a expressions, whilst Wnt5a expression was increased in eNOS-delivered cells. Co-transduction of eASCs with a Wnt pathway responsive lenti-TCF/LEF-dGFP reporter only showed activity in osteogenic cultures co-transduced with a doxycycline inducible eNOS. Lentiviral vector expression of canonical Wnt3a and non-canonical Wnt5a in eASCs was associated with induced and suppressed osteogenic differentiation, respectively, whilst treatment of eNOS-osteogenic cells with the Wnt inhibitor Dkk-1 significantly reduced expressions of Runx2 and ALP.

Conclusions

This study identifies NO as a regulator of canonical Wnt/β-catenin signaling to promote osteogenesis in eASCs which may contribute to novel bone regeneration strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0442-9) contains supplementary material, which is available to authorized users.

In situ plasma fabrication of ceramic-like structure on polymeric implant with enhanced surface hardness, cytocompatibility and antibacterial capability

Polymeric materials are commonly found in orthopedic implants due to their unique mechanical properties and biocompatibility but the poor surface hardness and bacterial infection hamper many biomedical applications. In this study, a ceramic-like surface structure doped with silver is produced by successive plasma implantation of silicon (Si) and silver (Ag) into the polyamine 66 (PA66) substrate. Not only the surface hardness and elastic modulus are greatly enhanced due to the partial surface carbonization and the ceramic-like structure produced by the reaction between energetic Si and the carbon chain of PA66, but also the antibacterial activity is improved because of the combined effects rendered by Ag and SiC structure. Furthermore, the modified materials which exhibit good cytocompatibility upregulate bone-related genes and proteins expressions of the contacted bone mesenchymal stem cells (BMSCs). For the first time, it explores out that BMSCs osteogenesis on the antibacterial ceramic-like structure is mediated via the iNOS and nNOS signal pathways. The results reveal that in situ plasma fabrication of an antibacterial ceramic-like structure can endow PA66 with excellent surface hardness, cytocompatibility, as well as antibacterial capability.

Upregulation of BMSCs osteogenesis by positively-charged tertiary amines on polymeric implants via charge/iNOS signaling pathway

Positively-charged surfaces on implants have a similar potential to upregulate osteogenesis of bone marrow-derived mesenchymal stem cells (BMSCs) as electromagnetic therapy approved for bone regeneration. Generally, their osteogenesis functions are generally considered to stem from the charge-induced adhesion of extracellular matrix (ECM) proteins without exploring the underlying surface charge/cell signaling molecule pathways. Herein, a positively-charged surface with controllable tertiary amines is produced on a polymer implant by plasma surface modification. In addition to inhibiting the TNF-α expression, the positively-charged surface with tertiary amines exhibits excellent cytocompatibility as well as remarkably upregulated osteogenesis-related gene/protein expressions and calcification of the contacted BMSCs. Stimulated by the charged surface, these BMSCs display high iNOS expressions among the three NOS isoforms. Meanwhile, downregulation of the iNOS by L-Can or siRNA inhibit osteogenic differentiation in the BMSCs. These findings suggest that a positively-charged surface with tertiary amines induces osteogenesis of BMSCs via the surface charge/iNOS signaling pathway in addition to elevated ECM protein adhesion. Therefore, creating a positively-charged surface with tertiary amines is a promising approach to promote osseointegration with bone tissues.

A susceptibility haplotype within the endothelial nitric oxide synthase gene influences bone mineral density in hypertensive women

The influence of the coordinated effect of various single-nucleotide polymorphisms (SNPs) within the endothelial nitric oxide synthase (eNOS) gene on the risk of osteoporosis in hypertension has remained undetermined. Four pertinent SNPs of the eNOS gene, rs2070774, rs1799983, rs1800780 and rs3918181, were examined for the risk of osteoporosis in 313 hypertensive postmenopausal women in Northwest India. All the hypertensive women were verified with dual energy X-ray absorptiometry and categorized as 150 with osteoporosis and 163 without osteoporosis. The minor allele (T) of rs1799983 exerts a statistically significant risk for osteoporosis both in dominant [odds ratio (OR) 3.71, 95 % confidence interval (CI) 2.12-6.49, P < 0.001] and recessive mode (OR 5.75, 95 % CI 1.24-26.69, P = 0.036) after Bonferroni correction. Bone mineral density (BMD) values (corrected for the effects of risk variables) according to eNOS SNP genotypes revealed a significant association with rs1799983 at both the lumbar spine (P = 0.001) and femoral neck (P = 0.023). Risk association analyses revealed a susceptibility haplotype TTAG which influences the risk of osteoporosis (OR 2.02, 95 % CI 1.05-3.39, P = 0.042) in hypertension after adjusting for the effects of risk factors. Furthermore, this haplotype was significantly associated with BMD at the lumbar spine (P = 0.029) and femoral neck (P = 0.021) in a dose-dependent manner. The results suggest that possession of the TTAG haplotype of the eNOS gene may increase the risk of osteoporosis two-fold in hypertensive postmenopausal women in Northwest India.

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.

Relationships between endothelial nitric oxide synthase gene polymorphisms and osteoporosis in postmenopausal women

OBJECTIVE

To investigate the relationships between endothelial nitric oxide synthases (eNOS) G894T and 27 bp-variable number tandem repeat (VNTR) gene polymorphisms and osteoporosis in the postmenopausal women of Chinese Han nationality.

METHODS

In the present study, 281 postmenopausal women from Xi'an urban area in West China were recruited, and divided into osteoporosis, osteopenia, and normal groups according to the diagnostic criteria of osteoporosis proposed by World Health Organization (WHO). The bone mineral density (BMD) values of lumbar vertebrae and left hips were determined by QDR-2000 dual energy X-ray absorptiometry. Blood samples were tested for plasma biochemical indicators including testosterone, estradiol, calcitonin, osteocalcin, and procollagen type I amino-terminal propeptide by enzyme-linked immunosorbent assay (ELISA), tartrate-resistant acid phosphatase by spectrophotometric method, and the content of nitric oxide by Griess method. Genome DNA was extracted from whole blood, and G894T polymorphism of eNOS gene was analyzed by using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method and 27 bp-VNTR polymorphism of eNOS gene was genotyped by PCR method. Then the relationships between genotypes and biochemical indicators, genotypes and osteoporosis, and haplotypes and osteoporosis were analyzed.

RESULTS

The average BMD values of the femoral neck, ward's triangle and lumbar vertebrae 1-4 (L1-L4) in the subjects with T/T genotype in eNOS G894T locus were significantly higher than those in the subjects with G/T and G/G genotypes (P<0.05). The average BMD of the femoral neck in the subjects with a/a genotype of eNOS 27 bp-VNTR locus was evidently higher than that in the subjects with b/b genotype (P<0.05). The plasma testosterone and osteocalcin concentrations in the subjects of eNOS G894T G/T genotype were evidently higher than those in the subjects of other genotypes (P<0.05); the plasma estradiol concentration in the subjects of eNOS 27 bp-VNTR a/a genotype was obviously higher than that in the subjects of b/b genotype (P<0.01). eNOS G/G homozygous frequencies in osteoporosis women, osteopenia women, and normal women were 85.37%, 76.38%, and 83.87%, respectively (P>0.05). 0% osteoporosis woman, 0.79% osteopenia women, and 3.23% normal women were eNOS a/a homozygous (P<0.05). The frequencies of eNOS 27 bp-VNTR a allele were 5.33% in the osteoporosis group, 10.24% in the osteopenia group, and 16.13% in the normal group (P<0.05, odds ratio (OR)=0.29, 95% confidence interval (CI)=0.11-0.77), suggesting that a/a genotype and a allele might have protective effects on osteoporosis. The haplotype analysis showed that G-b was 87.7% (214/244) in the osteoporosis group (P<0.05, OR=2.48, 95% CI=1.18-5.18). G-a was 5.3% (13/244) in the osteoporosis group (P<0.05, OR=0.29, 95% CI=0.11-0.77). G-b was a risk factor for osteoporosis, and G-a a protective factor.

CONCLUSION

eNOS G894T G/T genotype influenced the plasma testosterone and osteocalcin concentrations, and T/T genotype influenced BMD. eNOS 27 bp-VNTR a/a genotype increased plasma estradiol concentration to have a protective effect on osteoporosis.

Evaluation of eNOS gene polymorphisms in relation to BMD in postmenopausal women

OBJECTIVE

The aim of the present study was to evaluate the relations between T(-786)C and Glu298Asp polymorphisms of the endothelial nitric oxide synthase (eNOS) gene and BMD in postmenopausal Turkish women.

METHODS

The T(-786)C and Glu298Asp polymorphisms were genotyped by PCR-RFLP method in 311 postmenopausal osteoporotic women (OP) and in 305 age-matched postmenopausal females (CG) with normal BMD.

RESULTS

None of the SNPs of the eNOS gene was significantly associated with BMD at the lumbar spine, femoral neck, Ward's triangle and femoral trochanter in the combined group. Mean BMD values were therefore found to be similar across the genotypes in postmenopausal Turkish women. However, there was a significant association between the T(-786)C polymorphism and BMD values at the lumbar spine in the normal control group (P=0.005), and at the femoral trochanter in the osteoporotic patients (P=0.046). The mean value of the lumbar spine BMD in the normal controls was significantly higher in women with the TC genotype of the T(-786)C polymorphism than in women with the TT genotype (P=0.0012). Women with the CC genotype of the T(-786)C polymorphism in the osteoporotic patients had significantly higher BMD value at the femoral trochanter than those with the TC (P=0.018) and TT genotypes (P=0.024). Frequencies of the TC heterozygotes for T(-786)C polymorphism were significantly higher among osteoporotic subjects than normal controls. Also, the CC and TT genotype frequencies of control group were significantly higher than those of the osteoporotic group at the femoral neck.

CONCLUSIONS

We conclude that, although the biological role of the nitric oxide synthases is well established, our study does not suggest that eNOS gene polymorphisms, T(-786)C and Glu298Asp, are major contributors to adult bone mineral density in the postmenopausal Turkish women.

Isosorbide mononitrate versus alendronate for postmenopausal osteoporosis

OBJECTIVE

To compare the effectiveness, safety, and affordability of isosorbide mononitrate with alendronate for postmenopausal osteoporosis.

METHODS

A randomized controlled trial of 60 postmenopausal women with osteoporosis. Participants were randomly assigned to receive either 20 mg daily of isosorbide mononitrate or 70 mg weekly of alendronate for 12 months. Bone mineral density (BMD) was measured using dual X-ray absorptiometry (DXA) at baseline and after 12 months.

RESULTS

Both groups showed significant improvement in BMD. Isosorbide mononitrate yielded a comparable effect to alendronate for BMD and T-score at the end of the follow-up period. For BMD and T score the mean differences between the 2 groups were -0.005 (95% CI, -0.02 to 0.03) and 0.31 (95% CI, -0.03 to 0.64), respectively. A 10.8% and 12.1% change in BMD after 12 months was seen for isosorbide mononitrate and alendronate, respectively.

CONCLUSION

Isosorbide mononitrate is comparable to alendronate. Nitric oxide donors may be an effective and affordable therapy to improve bone mineral density.

Genetic variation in candidate osteoporosis genes, bone mineral density, and fracture risk: the study of osteoporotic fractures

Candidate osteoporosis gene variants were examined for associations with fracture risk and bone mineral density (BMD). A total of 9,704 white women were recruited at four U.S. clinical centers and enrolled into the Study of Osteoporotic Fractures, a longitudinal cohort study. Genotyping of 31 polymorphisms from 18 candidate osteoporosis genes was performed in 6,752 women. Incident radiographic fractures were identified at the third and eighth examinations compared with the baseline examination. BMD was measured at the total hip by dual-energy X-ray absorptiometry. Analyses were adjusted for age, clinic site, and self-reported ethnicity. During a mean follow-up of 14.5 years, a total of 849 hip, 658 vertebral, and 2,496 nonhip/nonvertebral fractures occurred in 6,752 women. Women carrying the ALOX15_G48924T T/T genotype had a higher rate of hip fracture (hazard ratio [HR] = 1.33;95% confidence interval [95% CI] = 1.00-1.77) compared with the G/G genotype. Compared with those carrying the PRL_T228C T/T genotype, women with either the C/C (HR = 0.80; 95% CI = 0.67-0.95) or C/T (HR = 0.81; 95% CI = 0.68-0.97) genotype had a lower rate of nonvertebral/nonhip fractures. Women carrying the BMP2_A125611G G/G genotype had a higher rate of vertebral fracture (odds ratio [OR] = 1.51; 95% CI = 1.03-2.23) compared with the A/A genotype. Women with the ESR1_C1335G G/G genotype had a higher rate of vertebral fracture (OR = 1.64; 95% CI = 1.07-2.50) compared with the C/C genotype. Compared with those with the MMP2_C595T C/C genotype, women with the C/T (OR = 0.79; 95% CI = 0.65-0.96) or T/T (OR = 0.44; 95% CI = 0.27-0.72) genotype had a lower rate of vertebral fracture. In conclusion, polymorphisms in several candidate genes were associated with hip, vertebral, and nonhip/nonvertebral fractures but not with total hip BMD in this large population based cohort study.

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.

Polymorphisms in the endothelial nitric oxide synthase gene and bone density/ultrasound and geometry in humans

Nitric oxide (NO), produced by endothelial cells, is a signaling molecule synthesized from l-arginine by nitric oxide synthases (NOS). NO is known to reduce the ratio of receptor activator of nuclear factor KappaB (RANKL)/osteoprotegerin (OPG), leading to decreased osteoclastogenesis and a reduction in bone resorption. Endothelial nitric oxide synthase (eNOS or NOS3) is the predominant constitutive isoform of nitric NOS within bone. Recently, a NOS3 polymorphism, Glu298Asp, previously implicated in osteoporosis, failed to demonstrate an association with bone mineral density (BMD), although there was some indication of an association with selected geometry indices. Since a single polymorphism does not capture all of the potential variants in a given gene, we investigated a broader coverage of the NOS3 gene with bone density/ultrasound and geometry indices in a sample of unrelated individuals from the Framingham Offspring Study. Our results indicated that the Glu298Asp polymorphism was not associated with BMD but suggested some haplotype-based associations in the linkage disequilibrium (LD) region that included the Glu298Asp polymorphism with several geometry indices. Although our findings exhibited several associations with selected bone density/ultrasound and geometry indices, the nominally significant associations are regarded as primarily hypothesis generating and suggest that replication in other samples is needed. Thus, NOS3 genetic variation does not appear to be a major contributor to adult bone density/ultrasound and geometry in our sample.

The effect of interleukin-1alpha polymorphisms on bone mineral density and the risk of vertebral fractures

Interleukin-1alpha (IL-1alpha) stimulates bone resorption via osteoclasts. Mononuclear cells from patients with osteoporosis show increased IL-1alpha production, and IL-1alpha mRNA is more often detected in bone biopsies from osteoporotic compared to normal postmenopausal women. Polymorphisms have been identified in the IL-1alpha gene; however, none of these has been examined for an effect on bone phenotypes in Caucasians. We investigated if the polymorphisms in the IL-1alpha gene affect the risk of osteoporotic fractures, bone mineral density (BMD), and bone turnover in 462 osteoporotic patients and 336 normal controls. Based on previous studies of polymorphisms in the gene and data from the International Hap-Map Project, four polymorphisms needed examination in order to investigate the effect of known polymorphisms in the IL-1alpha gene. We examined C(-1202)-T(rs1800794), C(-889)-T(rs1800587), T(155 + 209)-C(rs2071373), C(155 + 320)-T(rs2856838), and G(398)-T(rs 17561) by Taqman and restriction fragment-length polymorphism assays. BMD was examined by dual-energy X-ray absorptiometry. Bone turnover was evaluated by serum osteocalcin, serum carboxy-terminal propeptide of human type I procollagen, serum bone-specific alkaline phosphatase, serum carboxy-terminal telopeptide of type I collagen, and urinary hydroxyproline/creatinine. Genotype distributions were in Hardy-Weinberg equilibrium. All polymorphisms were in strong linkage disequilibrium. The C allele of the C(155 + 320)-T polymorphism tended to be more common among patients with vertebral fractures (P = 0.06) and patients with BMD T score <-2.5 (P = 0.05). Furthermore, haplotype 1 was associated with reduced risk of having BMD T score <-2.5 (P = 0.02). None of the other polymorphisms or haplotypes was associated with fracture risk or BMD T score <-2.5. BMD and bone turnover were not associated with any of the genetic variants. In conclusion, all the polymorphisms within the IL-1alpha gene are in strong linkage disequilibrium and not convincingly associated with fracture risk, BMD, or bone turnover.