Novel insights into the complex architecture of osteoporosis molecular genetics

A homozygous SP7/OSX mutation causes osteogenesis and dentinogenesis imperfecta with craniofacial anomalies

Osteogenesis imperfecta (OI) is a heterogeneous spectrum of hereditary genetic disorders that cause bone fragility, through various quantitative and qualitative defects of type 1 collagen, a triple helix composed of two α1 and one α2 chains encoded by COL1A1 and COL1A2, respectively. The main extra-skeletal manifestations of OI include blue sclerae, opalescent teeth, and hearing impairment. Moreover, multiple genes involved in osteoblast maturation and type 1 collagen biosynthesis are now known to cause recessive forms of OI. In this study a multiplex consanguineous family of two affected males with OI was recruited for genetic screening. To determine the causative, pathogenic variant(s), genomic DNA from two affected family members were analyzed using whole exome sequencing, autozygosity mapping, and then validated with Sanger sequencing. The analysis led to the mapping of a homozygous variant previously reported in SP7/OSX, a gene encoding for Osterix, a transcription factor that activates a repertoire of genes involved in osteoblast and osteocyte differentiation and function. The identified variant (c.946C > T; p.Arg316Cys) in exon 2 of SP7/OSX results in a pathogenic amino acid change in two affected male siblings and develops OI, dentinogenesis imperfecta, and craniofacial anomaly. On the basis of the findings of the present study, SP7/OSX:c. 946C > T is a rare homozygous variant causing OI with extra-skeletal features in inbred Arab populations.

Associations of residential greenness with bone mineral density and osteoporosis: the modifying effect of genetic susceptibility

OBJECTIVES

To investigate the associations of residential greenness with bone mineral density and incident osteoporosis, and further evaluate the potential modifying effect of genetic susceptibility.

METHODS

We used the Normalised Difference Vegetation Index (NDVI) at various buffer distances, including 300 m (NDVI300m), 500 m (NDVI500m), 1000 m (NDVI1000m) and 1500 m (NDVI1500m), to serve as indicators of greenness. We fitted linear regression, logistic regression and Cox proportional hazard models to assess the associations of residential greenness with estimated bone mineral density (eBMD), prevalent osteoporosis and incident osteoporosis, respectively. With the Polygenic Risk Score (PRS) for osteoporosis, we further assessed the joint effects of genetic risk and greenness on the risk of osteoporosis. We conducted causal mediation analyses to explore potential mediators.

RESULTS

Each IQR increase in NDVI300m was associated with 0.0007 (95% CI 0.0002 to 0.0013) increase in eBMD, 6% lower risk of prevalent osteoporosis (OR 0.94; 95% CI 0.92 to 0.97) and 5% lower risk of incident osteoporosis (HR 0.95; 95% CI 0.93 to 0.98). The joint effects of greenness and PRS on the risk of osteoporosis displayed a clear dose-response pattern. Compared with individuals exposed to low NDVI levels and high genetic risk, those exposed to high NDVI levels and low genetic risk had a 56% (95% CI 51% to 61%) lower risk of osteoporosis. The primary mediators in the association between greenness and incident osteoporosis were identified as PM2.5 and NO2.

CONCLUSIONS

Residential greenness was associated with higher bone mineral density and decreased risk of incident osteoporosis.

Correlation between bone density, bone metabolism markers with lipid metabolism markers and body mass index

PURPOSE

We aimed to explore the relationship between bone mineral density (BMD), bone metabolism markers, and blood lipid-related indicators, body mass index (BMI) in elderly individuals.

METHODS

A retrospective analysis was conducted on 710 patients. Patients' gender, age, height, weight, bone density values, T-scores, bone metabolism markers (including serum N-terminal propeptide of type I collagen (s-PINP), serum C-terminal telopeptide of type I collagen (s-CTX) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and lipid-related indicators (including total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG) and Castelli index 1 (TC/HDL-C index) and Castelli index 2 (LDL-C/HDL-C index) were recorded. Correlations between variables were analyzed, and patients were grouped according to gender and T-score for intergroup comparisons.

RESULTS

HDL-C negatively correlates with BMD and s-CTX. TG, Castelli index, and BMI positively correlate with BMD. BMI negatively correlates with s-PINP. 1,25(OH)2D3 negatively correlates with TC, LDL-C, and Castelli index. LDL-C positively correlates with BMD in males, and TC negatively correlates with s-PINP. In females, HDL-C negatively correlates with BMD, and s-CTX positively correlates with Castelli index. 1,25(OH)2D3 negatively correlates with TC, LDL-C, and Castelli index. TG and Castelli index were higher in normal bone mass group, while HDL-C is higher in the osteoporosis group. TG and BMI positively predicted bone mass density, while HDL-C negatively predicted bone mass density.

CONCLUSIONS

HDL-C may have a predictive role in osteoporosis, particularly in women. The likelihood of osteoporosis is lower in individuals with high BMI or hyperlipidemia. Some lipid metabolism markers can be used to predict osteoporosis, and further research is needed.

Duchenne Muscular Dystrophy Gene Therapy

Duchenne and Becker muscular dystrophies are allelic X-linked recessive neuromuscular diseases affecting both skeletal and cardiac muscles. Therefore, owing to their single X chromosome, the affected boys receive pathogenic gene mutations from their unknowing carrier mothers. Current pharmacological drugs are palliative that address the symptoms of the disease rather than the genetic cause imbedded in the Dystrophin gene DNA sequence. Therefore, alternative therapies like gene drugs that could address the genetic cause of the disease at its root are crucial, which include gene transfer/implantation, exon skipping, and gene editing. Presently, it is possible through genetic reprogramming to engineer AAV vectors to deliver certain therapeutic cargos specifically to muscle or other organs regardless of their serotype. Similarly, it is possible to direct the biogenesis of exosomes to carry gene editing constituents or certain therapeutic cargos to specific tissue or cell type like brain and muscle. While autologous exosomes are immunologically inert, it is possible to camouflage AAV capsids, and lipid nanoparticles to evade the immune system recognition. In this review, we highlight current opportunities for Duchenne muscular dystrophy gene therapy, which has been known thus far as an incurable genetic disease. This article is a part of Gene Therapy of Rare Genetic Diseases thematic issue.

Demystifying the Risk Factors and Preventive Measures for Osteoporosis

Background

Osteoporosis is a major health problem, globally. It is characterized by structural bone weakness leading to an increased risk of fragility fractures. These fractures commonly affect the spine, hip and wrist bones. Consequently, Osteoporosis related proximal femur and vertebral fractures represent a substantial, growing social and economic burden on healthcare systems worldwide. Indentification of the risk factors, clinical risk assessment, utilization of risk assessment tools and appropriate management that play a crucial role in reducing the burden of Osteoporosis by tackling modifiable risk factors.

Methods

This chapter explores various risk factors that are associated with Osteoporosis and provides an overview of various clinical and diagnostic risk assessment tools with a particular emphasis on evidence-based strategies for their prevention.

Conclusion

The role of emerging technologies such as Artificial Intelligence (AI) and perspectives such as newer diagnostic modalities, monitoring and surveillance approaches in prevention of risk factors in the pathogenesis of Osteoporosis is highlighted.

Advances in Dystrophinopathy Diagnosis and Therapy

Dystrophinopathies are x-linked muscular disorders which emerge from mutations in the Dystrophin gene, including Duchenne and Becker muscular dystrophy, and dilated cardiomyopathy. However, Duchenne muscular dystrophy interconnects with bone loss and osteoporosis, which are exacerbated by glucocorticoids therapy. Procedures for diagnosing dystrophinopathies include creatine kinase assay, haplotype analysis, Southern blot analysis, immunological analysis, multiplex PCR, multiplex ligation-dependent probe amplification, Sanger DNA sequencing, and next generation DNA sequencing. Pharmacological therapy for dystrophinopathies comprises glucocorticoids (prednisone, prednisolone, and deflazacort), vamorolone, and ataluren. However, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and β-blockers are the first-line to prevent dilated cardiomyopathy in dystrophinopathy patients. Duchenne muscular dystrophy gene therapy strategies involve gene transfer, exon skipping, exon reframing, and CRISPR gene editing. Eteplirsen, an antisense-oligonucleotide drug for skipping exon 51 from the Dystrophin gene, is available on the market, which may help up to 14% of Duchenne muscular dystrophy patients. There are various FDA-approved exon skipping drugs including ExonDys-51 for exon 51, VyonDys-53 and Viltolarsen for exon 53 and AmonDys-45 for exon 45 skipping. Other antisense oligonucleotide drugs in the pipeline include casimersen for exon 45, suvodirsen for exon 51, and golodirsen for exon 53 skipping. Advances in the diagnosis and therapy of dystrophinopathies offer new perspectives for their early discovery and care.

Effects of E'Jiao on Skeletal Mineralisation, Osteocyte and WNT Signalling Inhibitors in Ovariectomised Rats

E'Jiao is a traditional Chinese medicine derived from donkey skin. E'Jiao is reported to suppress elevated bone remodelling in ovariectomised rats but its mechanism of action is not known. To bridge this research gap, the current study aims to investigate the effects of E'Jiao on skeletal mineralisation, osteocyte and WNT signalling inhibitors in ovariectomised rats. Female Sprague-Dawley rats (3 months old) were ovariectomised and supplemented with E'Jiao at 0.26 g/kg, 0.53 g/kg and 1.06 g/kg, or 1% calcium carbonate (w/v) in drinking water. The rats were euthanised after two months of supplementation and their bones were collected for Fourier-transform infrared spectroscopy, histomorphometry and protein analysis. Neither ovariectomy nor treatment affected the skeletal mineral/matrix ratio, osteocyte number, empty lacunar number, and Dickkopf-1 and sclerostin protein levels (p > 0.05). Rats treated with calcium carbonate had a higher Dickkopf-1 level than baseline (p = 0.002) and E'Jiao at 0.53 g/kg (p = 0.002). In conclusion, E'Jiao has no significant effect on skeletal mineralisation, osteocyte and WNT signalling inhibitors in ovariectomised rats. The skeletal effect of E'Jiao might not be mediated through osteocytes.

Association of osteoporosis and skeletal muscle loss with serum type I collagen carboxyl-terminal peptide β glypeptide: A cross-sectional study in elder Chinese population

Type I collagen carboxyl-terminal peptide β (β-CTX) increases in osteoporosis. The study aimed to explore the relationship between serum β-CTX and the risk of osteoporosis as well as sarcopenia in Chinese elderly inpatients. Around 228 patients whose age >65 years were recruited in this cross-sectional study. Dual-energy X-ray scanning was used to access skeletal muscle and bone mass. Serum concentration of β-CTX as well as the prevalence of osteoporosis were significantly higher in low skeletal muscle index (SMI) group than that in the normal SMI group (P < 0.05). Serum β-CTX levels negatively correlated with SMI and bone mass (P < 0.05). Total muscle mass, appendicular skeletal muscle mass, SMI, total bone mass, and bone mass at various sites including the limbs, spine, and pelvis decreased significantly, and the prevalence of low SMI increased with the increase of the quartiles of β-CTX. Higher serum β-CTX had an increased risk of low SMI and osteoporosis (P < 0.05). Summarily, with increasing serum β-CTX levels, both muscle and bone mass decreased in Chinese elderly inpatients. Serum β-CTX was positively associated with the risk of not only osteoporosis but also skeletal muscle loss.

Molecular basis and therapeutic potential of myostatin on bone formation and metabolism in orthopedic disease

Myostatin, a member of the transforming growth factor-β (TGF-β) superfamily, is a key autocrine/paracrine inhibitor of skeletal muscle growth. Recently, researchers have postulated that myostatin is a negative regulator of bone formation and metabolism. Reportedly, myostatin is highly expressed in the fracture area, affecting the endochondral ossification process during the early stages of fracture healing. Furthermore, myostatin is highly expressed in the synovium of patients with rheumatoid arthritis (RA) and is an effective therapeutic target for interfering with osteoclast formation and joint destruction in RA. Thus, myostatin is a potent anti-osteogenic factor and a direct modulator of osteoclast differentiation. Evaluation of the molecular pathway revealed that myostatin can activate SMAD and mitogen-activated protein kinase signaling pathways, inhibiting the Wnt/β-catenin pathway to synergistically regulate muscle and bone growth and metabolism. In summary, inhibition of myostatin or the myostatin signaling pathway has therapeutic potential in the treatment of orthopedic diseases. This review focused on the effects of myostatin on bone formation and metabolism and discussed the potential therapeutic effects of inhibiting myostatin and its pathways in related orthopedic diseases.

An Open-Label, Randomized Pharmacokinetic Study of 2 Formulations of Eldecalcitol Capsules Following Single Oral Administration in Healthy Chinese Volunteers Under Fasting and Fed Conditions

Eldecalcitol is an active vitamin D₃ derivative that is used for the prevention and treatment of osteoporosis. The objectives of this study were to evaluate the bioequivalence and safety of 2 formulations of eldecalcitol capsule (0.75 μg) in healthy Chinese male and female volunteers, as well as to investigate the food effect on the pharmacokinetics of this drug. An open label, randomized, 3-period, 3-sequence, reference replicated crossover clinical study was performed in 27 healthy Chinese volunteers under fasting conditions, while a 2-way crossover study was carried out in 28 healthy Chinese volunteers under fed conditions. Volunteers were administered a single oral dose of 0.75 μg eldecalcitol after fasting overnight. Blood samples were collected at scheduled time points from 0 to 168 hours after administration of eldecalcitol. The 90%CIs of the test/reference geometric mean ratio (area under the plasma concentration-time curve and maximum plasma concentration) of eldecalcitol after a single-dose administration were within the acceptance criteria based on the average bioequivalence method. The time to maximum concentration of the test and reference formulations were elevated by ≈2.3-fold and 1.7-fold, respectively, after a high-fat meal. Only mild and transient adverse events were reported in this study, and no severe adverse events occurred. These results indicated that the 2 formulations of eldecalcitol were bioequivalent under both fasting and fed conditions. Food intake prolonged the oral absorption of eldecalcitol but did not significantly influence systemic exposure.

Comprehensive ceRNA network for MACF1 regulates osteoblast proliferation

BACKGROUND

Previous studies have shown that microtubule actin crosslinking factor 1 (MACF1) can regulate osteoblast proliferation and differentiation through non-coding RNA (ncRNA) in bone-forming osteoblasts. However, the role of MACF1 in targeting the competing endogenous RNA (ceRNA) network to regulate osteoblast differentiation remains poorly understood. Here, we profiled messenger RNA (mRNA), microRNA (miRNA), and long ncRNA (lncRNA) expression in MACF1 knockdown MC3TC‑E1 pre‑osteoblast cells.

RESULTS

In total, 547 lncRNAs, 107 miRNAs, and 376 mRNAs were differentially expressed. Significantly altered lncRNAs, miRNAs, and mRNAs were primarily found on chromosome 2. A lncRNA-miRNA-mRNA network was constructed using a bioinformatics computational approach. The network indicated that mir-7063 and mir-7646 were the most potent ncRNA regulators and mef2c was the most potent target gene. Pathway enrichment analysis showed that the fluid shear stress and atherosclerosis, p53 signaling, and focal adhesion pathways were highly enriched and contributed to osteoblast proliferation. Importantly, the fluid shear stress and atherosclerosis pathway was co-regulated by lncRNAs and miRNAs. In this pathway, Dusp1 was regulated by AK079370, while Arhgef2 was regulated by mir-5101. Furthermore, Map3k5 was regulated by AK154638 and mir-466q simultaneously. AK003142 and mir-3082-5p as well as Ak141402 and mir-446 m-3p were identified as interacting pairs that regulate target genes.

CONCLUSION

This study revealed the global expression profile of ceRNAs involved in the differentiation of MC3TC‑E1 osteoblasts induced by MACF1 deletion. These results indicate that loss of MACF1 activates a comprehensive ceRNA network to regulate osteoblast proliferation.

The role of melatonin in bone regeneration: A review of involved signaling pathways

Increasing bone resorption followed by decreasing bone mineralization are hallmarks of bone degeneration, which mostly occurs in the elderly population and post-menopausal women. The use of mesenchymal stem cells (MSCs) has raised many promises in the field of bone regeneration due to their high osteoblastic differentiation capacity and easy availability from abundant sources. A variety of compounds, including growth factors, cytokines, and other internal factors, have been combined with MSCs to increase their osteoblastic differentiation capacity. One of these factors is melatonin, whose possible regulatory role in bone metabolism and formation has recently been suggested by many studies. Melatonin also is a potential signaling molecule and can affect many of the signaling pathways involved in MSCs osteoblastic differentiation, such as activation of PI3K/AKT, BMP/Smad, MAPK, NFkB, Nrf2/HO-1, Wnt, SIRT/SOD, PERK/ATF4. Furthermore, melatonin in combination with other components such as strontium, vitamin D3, and vitamin K2 has a synergistic effect on bone microstructure and improves bone mineral density (BMD). In this review article, we aim to summarize the regulatory mechanisms of melatonin in osteoblastic differentiation of MSCs and underling involved signaling pathways as well as the clinical potential of using melatonin in bone degenerative disorders.

CD137 Regulates Bone Loss via the p53 Wnt/β-Catenin Signaling Pathways in Aged Mice

Senile osteoporosis is a chronic skeletal disease, leading to increased bone brittleness and risk of fragile fractures. With the acceleration of population aging, osteoporosis has gradually become one of the most serious and prevalent problems worldwide. Bone formation is highly dependent on the proper osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in the bone marrow microenvironment, which is generated by the functional relationship among different cell types, including osteoblasts, adipogenic cells, and bone marrow stromal cells in the bone marrow. It is still not clear how osteoporosis is caused by its molecular mechanism. With aging, bone marrow is able to restrain osteogenesis. Discovering the underlying signals that oppose BMSC osteogenic differentiation from the bone marrow microenvironment and identifying the unusual changes in BMSCs with aging is important to elucidate possible mechanisms of senile osteoporosis. We used 3 gene expression profiles (GSE35956, GSE35957, and GSE35959) associated with osteoporosis. And a protein-protein interaction (PPI) network was also built to identify the promising gene CD137. After that, we performed in vivo experiments to verify its function and mechanism. In this experiment, we found that significant bone loss was observed in aged (18-month-old) mice compared with young (6-month-old) mice. The adipose tissue in bone marrow cavity from aged mice reached above 10 times more than young mice. Combining bioinformatics analysis and vivo experiments, we inferred that CD137 might be involved in the p53 and canonical Wnt/β-catenin signaling pathways and thereby influenced bone mass through regulation of marrow adipogenesis. Importantly, osteoporosis can be rescued by blocking CD137 signaling in vivo. Our research will contribute to our understanding not only of the pathogenesis of age-related bone loss but also to the identification of new targets for treating senile osteoporosis.

Polymorphisms in Genes Involved in Osteoblast Differentiation and Function Are Associated with Anthropometric Phenotypes in Spanish Women

Much of the genetic variance associated with osteoporosis is still unknown. Bone mineral density (BMD) is the main predictor of osteoporosis risk, although other anthropometric phenotypes have recently gained importance. The aim of this study was to analyze the association of SNPs in genes involved in osteoblast differentiation and function with BMD, body mass index (BMI), and waist (WC) and hip (HC) circumferences. Four genes that affect osteoblast differentiation and/or function were selected from among the differentially expressed genes in fragility hip fracture (FOXC1, CTNNB1, MEF2C, and EBF2), and an association study of four single-nucleotide polymorphisms (SNPs) was conducted in a cohort of 1001 women. Possible allelic imbalance was also studied for SNP rs87939 of the CTNNB1 gene. We found significant associations of SNP rs87939 of the CTNNB1 gene with LS-sBMD, and of SNP rs1366594 of the MEF2C gene with BMI, after adjustment for confounding variables. The SNP of the MEF2C gene also showed a significant trend to association with FN-sBMD (p = 0.009). A possible allelic imbalance was ruled out as no differences for each allele were detected in CTNNB1 expression in primary osteoblasts obtained from homozygous women. In conclusion, we demonstrated that two SNPs in the MEF2C and CTNNB1 genes, both implicated in osteoblast differentiation and/or function, are associated with BMI and LS-sBMD, respectively.

DANCR Mediates the Rescuing Effects of Sesamin on Postmenopausal Osteoporosis Treatment via Orchestrating Osteogenesis and Osteoclastogenesis

As one of the leading causes of bone fracture in postmenopausal women and in older men, osteoporosis worldwide is attracting more attention in recent decades. Osteoporosis is a common disease mainly resulting from an imbalance of bone formation and bone resorption. Pharmaceutically active compounds that both activate osteogenesis, while repressing osteoclastogenesis hold the potential of being therapeutic medications for osteoporosis treatment. In the present study, sesamin, a bioactive ingredient derived from the seed of Sesamum Indicum, was screened out from a bioactive compound library and shown to exhibit dual-regulating functions on these two processes. Sesamin was demonstrated to promote osteogenesis by upregulating Wnt/β-catenin, while repressing osteoclastogenesis via downregulating NF-κB signaling . Furthermore, DANCR was found to be the key regulator in sesamin-mediated bone formation and resorption . In an ovariectomy (OVX)-induced osteoporotic mouse model, sesamin could rescue OVX-induced bone loss and impairment. The increased serum level of DANCR caused by OVX was also downregulated upon sesamin treatment. In conclusion, our results demonstrate that sesamin plays a dual-functional role in both osteogenesis activation and osteoclastogenesis de-activation in a DANCR-dependent manner, suggesting that it may be a possible medication candidate for osteoporotic patients with elevated DNACR expression levels.

Cadmium exposure induces osteoporosis through cellular senescence, associated with activation of NF-κB pathway and mitochondrial dysfunction

Cadmium (Cd) is a heavy metal toxicant as a common pollutant derived from many agricultural and industrial sources. The absorption of Cd takes place primarily through Cd-contaminated food and water and, to a significant extent, via inhalation of Cd-contaminated air and cigarette smoking. Epidemiological data suggest that occupational or environmental exposure to Cd increases the health risk for osteoporosis and spontaneous fracture such as itai-itai disease. However, the direct effects and underlying mechanism(s) of Cd exposure on bone damage are largely unknown. We used primary bone marrow-derived mesenchymal stromal cells (BMMSCs) and found that Cd significantly induced BMMSC cellular senescence through over-activation of NF-κB signaling pathway. Increased cell senescence was determined by production of senescence-associated secretory phenotype (SASP), cell cycle arrest and upregulation of p21/p53/p16^INK4a protein expression. Additionally, Cd impaired osteogenic differentiation and increased adipogenesis of BMMSCs, and significantly induced cellular senescence-associated defects such as mitochondrial dysfunction and DNA damage. Sprague-Dawley (SD) rats were chronically exposed to Cd to verify that Cd significantly increased adipocyte number, and decreased mineralization tissues of bone marrow in vivo. Interestingly, we observed that Cd exposure remarkably retarded bone repair and regeneration after operation of skull defect. Notably, pretreatment of melatonin is able to partially prevent Cd-induced some senescence-associated defects of BMMSCs including mitochondrial dysfunction and DNA damage. Although Cd activated mammalian target of rapamycin (mTOR) pathway, rapamycin only partially ameliorated Cd-induced cell apoptosis rather than cellular senescence phenotypes of BMMSCs. In addition, a selective NF-κB inhibitor moderately alleviated Cd-caused the senescence-related defects of the BMMSCs. The study shed light on the action and mechanism of Cd on osteoporosis and bone ageing, and may provide a novel option to ameliorate the harmful effects of Cd exposure.

Targeting Filamin A alleviates ovariectomy-induced bone loss in mice via the WNT/β-catenin signaling pathway

Osteoporosis (OP) is a worldwide prevalent chronic metabolic bone disease, causing by a disruption of the balance between bone resorption and formation. Estrogen deficiency and aging are the main causes for disturbances in bone remodeling activity and bone loss, however, the mechanisms underlying bone remodeling regulation require clarification if novel targets for OP treatment are to be identified. In this investigation, we showed that filamin A (FLNA) accumulated in osteoblasts (OBs) and osteoclasts (OC) in bone from human OP samples, and mice with age-related and postmenopausal OP. FLNA negatively modulated in vitro osteogenic differentiation and positively promoted RANKL-induced osteoclastic differentiation. Mechanistically, FLNA interacted with low-density lipoprotein receptor-related proteins 6 (LRP6) to inhibit β-catenin expression, and enhanced nuclear factor of activated T cell c1 (NFATc1)-dependent osteoclastogenic gene expression to inhibit osteogenesis, and promote osteoclastogenesis. Inhibiting FLNA with calpeptin activated WNT/β-catenin signaling, resulting in prominent protective effects of bone loss in ovariectomy (OVX)-induced postmenopausal OP mice. Our findings revealed that FLNA not only participated in OP pathogenesis, but could be a new target to stimulate bone formation and inhibit bone resorption. Targeting FLNA with calpeptin may be a promising therapeutic approach for postmenopausal OP in the future.

Induction of osteoclast formation by LOX mutant (LOXG473A) through regulation of autophagy

Background

Lysyl oxidase (LOX) has been identified to modulate osteoclast activity, so we explored the role of LOX_G473A, the highest frequency single nucleotide polymorphism in LOX, in osteoclast formation and its potential relationship to autophagy.

Methods

The ability of the LOX mutant, LOX_G473A, to promote autophagy and osteoclast formation was evaluated in the pre-osteoclast cell line RAW264.7. Furthermore, autophagy-related protein expression and autophagosomes were detected by western blot and electron microscopy, respectively. Simultaneously, osteoclast formation and resorption ability were also detected using TRAP staining assay and bone resorption assay. In addition, the osteoclast-related proteins and mRNAs, as well as p-AMPKα and p-mTOR proteins, were further evaluated by western blot and qPCR assays.

Results

Autophagy inhibitor 3-MA suppressed the Beclin-1 and ATG5 protein levels and the ratio of LC3-II to LC3-I, as well as autophagosome formation in RAW264.7 transfected with the MUT plasmid and enhanced p62 protein expression. Simultaneously, 3-MA also reduced osteoclast formation and resorption, as well as the F-actin ring level of osteoclasts. In addition, 3-MA inhibited osteoclast-related protein and mRNA expression, including NFATC1, ACP5, CTSK. And the autophagy-related pathway protein p-AMPKα was increased and p-mTOR was reduced by 3-MA treatment. However, autophagy agonist RAPA reversed the effect of 3-MA on RAW264.7 with LOX_G473A mutation, indicating that promoting autophagy could enhance the ability of LOX_G473A to induce osteoclast formation.

Conclusions

LOX mutant (LOX_G473A) might promote osteoclast formation for RAW264.7 by enhancing autophagy via the AMPK/mTOR pathway, which is a new direction for bone disease research.

Vaccine of RANKL mutant conjugated with KLH effectively stabilizing bone metabolism and preventing trabecular microstructural degeneration in osteoporotic rats

Receptor activator of nuclear factor kappa-B ligand (RANKL) is one of the key factors regulating the maturation of osteoclasts and an important target for osteoporosis treatment. A monoclonal antibody against RANKL showed effective therapeutic activity against osteoporosis by inhibiting bone resorption by osteoclasts. However, being an exogenous protein, its efficacy decreases after long-term use, and its discontinuation increases the risk of vertebral fractures. Here, we aimed to design an active immunotherapeutic agent to induce a T-cell dependent primary response. The agent, a mutant RANKL vaccine (mRv), was produced by cross-linking mutant RANKL, lacking the ability to stimulate osteoclast maturation, with the carrier protein keyhole limpet hemocyanin, a neo-antigen with a large molecular mass. Subcutaneous injection of mRv stimulated rats with ovariectomy-induced osteoporosis to produce high titers of anti-RANKL antibodies. The mutant RANKL vaccine decreased serum CTX-1 and BALP levels and inhibited the microstructural degeneration of trabecular bone in osteoporotic rats. mRv overcame immune system tolerance, stimulated rats to produce therapeutic antibodies, stabilized bone metabolism, and inhibited trabecular microstructural degeneration. These findings confirm the potential of the mutant RANKL vaccine to be developed into an effective preventive and therapeutic agent for osteoporosis.

Vitamin D Receptor Gene Variants Susceptible to Osteoporosis in Arab Post-Menopausal Women

Post-menopausal osteoporosis (PMO) is a multifactorial bone disorder in elderly women. Various vitamin D receptor (VDR) gene variants have been studied and associated with osteoporosis in other populations, but not in a homogenous Arab ethnic group. Herein, the current study explores the association between VDR polymorphisms and susceptibility to osteoporosis in Saudi postmenopausal women. In total, 600 Saudi postmenopausal women (N = 300 osteoporosis; N = 300 control) were genotyped for VDR gene variants (rs7975232, rs1544410, rs731236) using TaqMan^® SNP genotyping assays. Bone mineral density (BMD) for the lumbar spine and femur was assessed using dual-energy X-ray absorptiometry (DEXA). The heterozygous frequency distributions AC of rs7975232, CT of rs1544410, and AG of rs731236 were significantly higher in the osteoporosis group than controls (p < 0.05). Heterozygous AC of rs7975232 (1.6; 95% CI 1.1–2.3; p < 0.023), CT of rs1544410 (1.6; 95% CI 1.1–2.4; p < 0.022), and AG of rs731236 (1.6; 95% CI 1.1–2.4; p < 0.024) were significantly associated with increased risk of osteoporosis, independent of age and BMI. In conclusion, VDR gene variants rs7975232, rs1544410, rs731236 had a significant effect on BMD and were associated with osteoporosis risk in Saudi postmenopausal women.

Analysis of potential genetic biomarkers and molecular mechanism of smoking-related postmenopausal osteoporosis using weighted gene co-expression network analysis and machine learning

OBJECTIVES

Smoking is a significant independent risk factor for postmenopausal osteoporosis, leading to genome variations in postmenopausal smokers. This study investigates potential biomarkers and molecular mechanisms of smoking-related postmenopausal osteoporosis (SRPO).

MATERIALS AND METHODS

The GSE13850 microarray dataset was downloaded from Gene Expression Omnibus (GEO). Gene modules associated with SRPO were identified using weighted gene co-expression network analysis (WGCNA), protein-protein interaction (PPI) analysis, and pathway and functional enrichment analyses. Feature genes were selected using two machine learning methods: support vector machine-recursive feature elimination (SVM-RFE) and random forest (RF). The diagnostic efficiency of the selected genes was assessed by gene expression analysis and receiver operating characteristic curve.

RESULTS

Eight highly conserved modules were detected in the WGCNA network, and the genes in the module that was strongly correlated with SRPO were used for constructing the PPI network. A total of 113 hub genes were identified in the core network using topological network analysis. Enrichment analysis results showed that hub genes were closely associated with the regulation of RNA transcription and translation, ATPase activity, and immune-related signaling. Six genes (HNRNPC, PFDN2, PSMC5, RPS16, TCEB2, and UBE2V2) were selected as genetic biomarkers for SRPO by integrating the feature selection of SVM-RFE and RF.

CONCLUSION

The present study identified potential genetic biomarkers and provided a novel insight into the underlying molecular mechanism of SRPO.

Insulin growth factor-1 promotes the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells through the Wnt/β-catenin pathway

Bone marrow mesenchymal stem cells (BMSCs) are stem cells that exist in bone marrow tissue and have osteogenic differentiation potential. Insulin growth factor-1 (IGF-1) plays a key role in the proliferation and osteogenic differentiation of BMSCs. However, the specific mechanism of IGF-1 in cell proliferation and osteogenic differentiation remains unclear. In the present study, BMSCs were transfected with lentivirus carrying the siRNA-Wnt3a gene, and the Wnt3a level in BMSCs was revealed to be reduced by western blotting, real-time quantitative polymerase chain reaction and immunofluorescence detection. Then, BMSCs were treated with 80 ng/ml IGF-1 in complete medium for 5 days. CCK-8 and cell cycle assays revealed that cell proliferation was significantly decreased in the siRNA-Wnt3a group than in the control group. The protein and mRNA levels of β-catenin and cyclin D1 were significantly downregulated in the siRNA-Wnt3a group compared with the control group. In addition, BMSCs were treated with IGF-1 in osteogenic differentiation medium for 7 and 21 days, and alkaline phosphatase staining and Alizarin Red staining demonstrated significantly reduced osteogenic differentiation ability in the siRNA-Wnt3a group compared with the control group. Furthermore, the protein and mRNA levels of β-catenin, RUNX2, and OPN were downregulated compared with the control group. Our findings revealed that IGF-1 promoted the proliferation and differentiation of BMSCs at least partially through the Wnt/β-catenin pathway. These findings provided new insight into the clinical treatment of bone disease.

DEC1 deficiency results in accelerated osteopenia through enhanced DKK1 activity and attenuated PI3KCA/Akt/GSK3β signaling

BACKGROUND

Human differentiated embryonic chondrocyte expressed gene 1 (DEC1) has been implicated in enhancing osteogenesis, a desirable outcome to counteract against deregulated bone formation such as retarded bone development, osteopenia and osteoporosis.

METHODS AND RESULTS

DEC1 knockout (KO) and the age-matched wild-type (WT) mice were tested for the impact of DEC1 deficiency on bone development and osteopenia as a function of age. DEC1 deficiency exhibited retarded bone development at the age of 4 weeks and osteopenic phenotype in both 4- and 24-week old mice. However, the osteopenia was more severe in the 24-week age groups. Mechanistically, DEC1 deficiency downregulated the expression of bone-enhancing genes such as Runx2 and β-catenin accompanied by upregulating DKK1, an inhibitor of the Wnt/β-catenin signaling pathway. Consistently, DEC1 deficiency favored the attenuation of the integrated PI3KCA/Akt/GSK3β signaling, a pathway targeting β-catenin for degradation. Likewise, the attenuation was greater in the 24-week age group. These changes, however, were reversed by in vivo treatment with lithium chloride, a stabilizer of β-catenin, and confirmed by gain-of-function study with DEC1 transfection into DEC1 KO bone marrow mesenchymal stem cells and loss-of-function study with siDEC1 lentiviral infection into the corresponding WT cells.

CONCLUSION

DEC1 is a positive regulator with a broad activity spectrum in both bone development and maintenance, and the osteopenic phenotype accelerated by DEC1 deficiency is achieved by enhanced DKK1 activity and attenuated PI3KCA/Akt/GSK3β signaling.

Effects of marathon race on selected myokines and sclerostin in middle-aged male amateur runners

In recent years, there has been increasing interest in the homeostatic response to extreme exercises, especially in the integrated function of muscle and bone. The aim of this study was to evaluate the effects of a marathon race on selected myokines and sclerostin in 10 male recreational runners (mean age 41 ± 7.7 years). Body composition, bone mineral density (BMD), and the serum concentration of myostatin, irisin, sclerostin, osteoprotegerin (OPG), 25-hydroxyvitamin D (25(OH)D), parathyroid hormone (PTH), high-sensitivity interleukin-6 (hsIL-6), tumor necrosis factor α (TNFα), high-sensitivity C-reactive protein (hsCRP) and myoglobin, were determined 24 h before and 24 h and 72 h after a marathon race. Post-marathon increases were observed in the levels of myostatin (1.2-fold), OPG (1.5-fold), and PTH (1.3-fold), hsIL-6 (1.9-fold), myoglobin (4.1-fold), hsCRP (fivefold), TNFα (2.6-fold), after 24 h; and in myostatin (1.2-fold), irisin (1.1-fold), sclerostin (1.3-fold), OPG (1.3-fold), and PTH (1.4-fold), hsIL-6 (1.4-fold), TNFα (1.9-fold), after 72 h compared to the baseline level. The results show that in response to the marathon run, a complex network of endocrine interactions is initiated. Further research is needed to fully elucidate the long-term impact of prolonged high intensity exercise on the human body.

MSTN is a key mediator for low-intensity pulsed ultrasound preventing bone loss in hindlimb-suspended rats

Low-intensity pulsed ultrasound (LIPUS) has been used to accelerate bone fracture healing. However, the issue whether LIPUS is effective in preventing osteoporosis has not been clarified, and if so, what possible mechanisms might be responsible. Myostatin (MSTN) is a negative regulator of muscle growth, and its absence will trigger a positive response to bone. In this study, we examined the effects of LIPUS on bone micro-structure, mechanical properties and damage healing of hindlimb-suspended rats, and investigated whether the inhibition of MSTN plays a role in this process. The rats were randomly divided into four groups: Normal control group (NC), Hind limb suspension group (HLS), Hind limb suspension and 80 mW/cm² LIPUS irradiation group (HLS+ 80 mW/cm²), Hind limb suspension and 30 mW/cm² LIPUS irradiation group (HLS+ 30 mW/cm²). The HLS+ 80 mW/cm² rats were treated with LIPUS (1 MHz, 80 mW/cm²) and the HLS+ 30 mW/cm² rats were treated with LIPUS (1 MHz, 30 mW/cm²) on the femur for 20 min/day for 28 days. MC3T3-E1 cells were respectively cultured with the serum of wild type mouse and MSTN knockout mouse at 1% concentration for 7 days. After 28 days, LIPUS effectively prevented the destruction of bone microstructure and the decline of mechanical properties, and promoted bone defect healing in the tail-suspended rats. In addition, LIPUS effectively reduced the MSTN content in the quadriceps and serum of the tail-suspended rats, inhibited its receptor and downstream signaling molecules and activated the Wnt signaling pathway in femurs. Growth of MC-3T3-E1 cell cultured with the serum of MSTN knockout mice was superior to that with wild mice serum on day 7. These results indicate that MSTN is a key mediator in LIPUS preventing bone loss caused by hindlimb-suspension.

Pharmacological inhibition of NF-κB-inducing kinase (NIK) with small molecules for the treatment of human diseases

NIK is a key kinase required for the activation of alternative NF-κB signaling pathways. Overactivation of NIK in patients has been observed and is implicated in the pathogenesis of inflammatory diseases, B-cell malignances, and solid tumors. Over the past decade, inhibition of NIK overactivation with small molecules has been pursued as an attractive strategy for drug discovery, where numerous potent and selective NIK inhibitors with novel pharmacophores have been identified. This review summarizes the structural features and key efficacy studies of the NIK inhibitors reported, which justify the mechanism of action of such inhibitors in animal models driven by NIK overactivation. Given the strong pathological associations between overactivation of NIK and human diseases, human clinical trials of NIK inhibitors as drug candidates are eagerly awaited. Information showcased in this review article might be helpful for the discovery and clinical development of the next generation of NIK inhibitors in the near future.

The Polymorphism at PLCB4 Promoter (rs6086746) Changes the Binding Affinity of RUNX2 and Affects Osteoporosis Susceptibility: An Analysis of Bioinformatics-Based Case-Control Study and Functional Validation

PURPOSE

Genome-wide association studies have identified numerous genetic variants that are associated with osteoporosis risk; however, most of them are present in the non-coding regions of the genome and the functional mechanisms are unknown. In this study, we aimed to investigate the potential variation in runt domain transcription factor 2 (RUNX2), which is an osteoblast-specific transcription factor that normally stimulates bone formation and osteoblast differentiation, regarding variants within RUNX2 binding sites and risk of osteoporosis in postmenopausal osteoporosis (PMOP).

METHODS

We performed bioinformatics-based prediction by combining whole genome sequencing and chromatin immunoprecipitation sequencing to screen functional SNPs in the RUNX2 binding site using data from the database of Taiwan Biobank; Case-control studies with 651 postmenopausal women comprising 107 osteoporosis patients, 290 osteopenia patients, and 254 controls at Tri-Service General Hospital between 2015 and 2019 were included. The subjects were examined for bone mass density and classified into normal and those with osteopenia or osteoporosis by T-scoring with dual-energy X-ray absorptiometry. Furthermore, mRNA expression and luciferase reporter assay were used to provide additional evidence regarding the associations identified in the association analyses. Chi-square tests and logistic regression were mainly used for statistical assessment.

RESULTS

Through candidate gene approaches, 3 SNPs in the RUNX2 binding site were selected. A novel SNP rs6086746 in the PLCB4 promoter was identified to be associated with osteoporosis in Chinese populations. Patients with AA allele had higher risk of osteoporosis than those with GG+AG (adjusted OR = 6.89; 95% confidence intervals: 2.23-21.31, p = 0.001). Moreover, the AA genotype exhibited lower bone mass density (p < 0.05). Regarding mRNA expression, there were large differences in the correlation between PLCB4 and different RUNX2 alleles (Cohen's q = 0.91). Functionally, the rs6086746 A allele reduces the RUNX2 binding affinity, thus enhancing the suppression of PLCB4 expression (p < 0.05).

CONCLUSIONS

Our results provide further evidence to support the important role of the SNP rs6086746 in the etiology of osteopenia/osteoporosis, thereby enhancing the current understanding of the susceptibility to osteoporosis. We further studied the mechanism underlying osteoporosis regulation by PLCB4.

Bone Mineral Density in Adolescent Boys: Cross-Sectional Observational Study

Physical inactivity of children can be a precursor of reduced bone mineral density, considered to be a typical problem only in old age. The aim of this study was to evaluate bone mineral density in 96 Polish boys aged 14–17 years with varied physical activity (swimmers, track and field athletes, non-athletes) and the effect of bone composition, birth weight and breastfeeding during infancy on bone parameters. Anthropometric and body composition measurements were performed according to the kinanthropometric standards. Bone parameters of the forearm were measured by means of dual-energy X-ray absorptiometry. Data on the infant’s birth weight and the length of breastfeeding were collected during direct interviews with mothers. The strongest links with bone parameters were found for the type of physical activity and birth weight. Regardless of birth weight, track and field athletes had the most advantageous bone parameters (mainly sT-score prox values). Swimmers with normal or low birth weight had less favourable sT-score prox values than non-athletes. The type of physical activity proved to be an important determinant of bone parameters. Childhood and adolescence are important periods of bone development and increasing the content of bone mineral components, and the bone status in later years of life depends to a large extent on this period. The perinatal period, especially the correct birth weight of the child, not only has a significant effect on general health, but also on bone status.

Obesity and Bone Health: A Complex Link

So far, the connections between obesity and skeleton have been extensively explored, but the results are inconsistent. Obesity is thought to affect bone health through a variety of mechanisms, including body weight, fat volume, bone formation/resorption, proinflammatory cytokines together with bone marrow microenvironment. In this review, we will mainly describe the effects of adipokines secreted by white adipose tissue on bone cells, as well as the interaction between brown adipose tissue, bone marrow adipose tissue, and bone metabolism. Meanwhile, this review also reviews the evidence for the effects of adipose tissue and its distribution on bone mass and bone-related diseases, along with the correlation between different populations with obesity and bone health. And we describe changes in bone metabolism in patients with anorexia nervosa or type 2 diabetes. In summary, all of these findings show that the response of skeleton to obesity is complex and depends on diversified factors, such as mechanical loading, obesity type, the location of adipose tissue, gender, age, bone sites, and secreted cytokines, and that these factors may exert a primary function in bone health.

Integrative Analysis of Genomics and Transcriptome Data to Identify Regulation Networks in Female Osteoporosis

Background: Osteoporosis is a highly heritable skeletal muscle disease. However, the genetic mechanisms mediating the pathogenesis of osteoporosis remain unclear. Accordingly, in this study, we aimed to clarify the transcriptional regulation and heritability underlying the onset of osteoporosis.

Methods: Transcriptome gene expression data were obtained from the Gene Expression Omnibus database. Microarray data from peripheral blood monocytes of 73 Caucasian women with high and low bone mineral density (BMD) were analyzed. Differentially expressed messenger RNAs (mRNAs) and long non-coding RNAs (lncRNAs) were identified. Differences in BMD were then attributed to several gene modules using weighted gene co-expression network analysis (WGCNA). LncRNA/mRNA regulatory networks were constructed based on the WGCNA and subjected to functional enrichment analysis.

Results: In total, 3,355 mRNAs and 999 lncRNAs were identified as differentially expressed genes between patients with high and low BMD. The WGCNA yielded three gene modules, including 26 lncRNAs and 55 mRNAs as hub genes in the blue module, 36 lncRNAs and 31 mRNAs as hub genes in the turquoise module, and 56 mRNAs and 30 lncRNAs as hub genes in the brown module. JUN and ACSL5 were subsequently identified in the modular gene network. After functional pathway enrichment, 40 lncRNAs and 16 mRNAs were found to be related to differences in BMD. All three modules were enriched in metabolic pathways. Finally, mRNA/lncRNA/pathway networks were constructed using the identified regulatory networks of lncRNAs/mRNAs and pathway enrichment relationships.

Conclusion: The mRNAs and lncRNAs identified in this WGCNA could be novel clinical targets in the diagnosis and management of osteoporosis. Our findings may help elucidate the complex interactions between transcripts and non-coding RNAs and provide novel perspectives on the regulatory mechanisms of osteoporosis.

A validated miRNA signature for the diagnosis of osteoporosis related fractures using SVM algorithm classification

The aim of the present study was to develop a circulating microRNA expression signature for early prediction of osteoporotic fractures and to validate the results using Gene Expression Omnibus (GEO) datasets. The GSE70318 dataset was downloaded from GEO and used to build an osteoporotic fracture prediction model based on the receiver operating characteristic curve and support vector machine (SVM) classification index. The GSE74209 dataset was used as a validation dataset. Additionally, in vitro, alkaline phosphatase (ALP) activity was measured in the presence or absence of microRNA (miRNA/miR) treatments in human osteoblast cells. The expression of two selected genes was detected by western blotting. miR-188-3p, miR-942-3p, miR-576-3p and miR-135a-5p were differentially expressed between controls and osteoporotic patients with fractures. SVM classification using these four miRNAs provided better dichotomization. It was further confirmed that miR-576-3p and 135a-5p in the GSE74209 dataset could also significantly discriminate between the controls and fracture patients, the area under the curve of SVM2 was 0.9722 with 95% CI 0.8885-1.056. Further analysis indicated that the target genes of the two miRNAs participated in the Wingless-related integration site, Hedgehog and transforming growth factor-β signaling pathways and osteoclast differentiation. miR-576-3p and miR-135-5p transfection decreased ALP activity and ALP activity was increased in the presence of blocking antisense oligonucleotides. Western blotting indicated miR-576-3p and miR-135-5p decreased CSNK1A1L and LRP6 levels, respectively. In conclusion, two miRNA signatures were developed and validated for the prediction of osteoporotic fractures.

Comprehensive Analysis of the Genetic and Epigenetic Mechanisms of Osteoporosis and Bone Mineral Density

Osteoporosis is a skeletal disorder characterized by a systemic impairment of bone mineral density (BMD). Genome-wide association studies (GWAS) have identified hundreds of susceptibility loci for osteoporosis and BMD. However, the vast majority of susceptibility loci are located in non-coding regions of the genome and provide limited information about the genetic mechanisms of osteoporosis. Herein we performed a comprehensive functional analysis to investigate the genetic and epigenetic mechanisms of osteoporosis and BMD. BMD and osteoporosis are found to share many common susceptibility loci, and the corresponding susceptibility genes are significantly enriched in bone-related biological pathways. The regulatory element enrichment analysis indicated that BMD and osteoporosis susceptibility loci are significantly enriched in 5′UTR and DNase I hypersensitive sites (DHSs) of peripheral blood immune cells. By integrating GWAS and expression Quantitative Trait Locus (eQTL) data, we found that 15 protein-coding genes are regulated by the osteoporosis and BMD susceptibility loci. Our analysis provides new clues for a better understanding of the pathogenic mechanisms and offers potential therapeutic targets for osteoporosis.

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.