Genetic control of bone mass

Studies on the Role of MAP4K2, SPI1, and CTSD in Osteoporosis

Osteoporosis (OP) is a prevalent skeletal disorder characterized by an imbalance between bone resorption and bone formation, resulting in a significant global burden. Previous research utilizing bioinformatics analysis has identified MAP4K2, SPI1, and CTSD as hub genes associated with OP. In this current investigation, we have successfully established a differential expression system of MAP4K2, SPI1, and CTSD in rat bone marrow mesenchymal stem cells (BMSCs) through transfection techniques. Additionally, the CCK-8 assay was employed to assess cell proliferation, while the alkaline phosphatase (ALP) activity assay and ALP staining assay were utilized to evaluate osteogenic differentiation. Alizarin red staining was employed to detect mineralization of BMSCs. Furthermore, the expression of relevant genes and molecules associated with the MAPK signaling pathway, autophagy, and apoptosis in the sera of rat BMSCs were examined using quantitative real-time polymerase chain reaction (qRT-PCR). The purpose of this study was to preliminarily investigate whether MAP4K2, SPI1, and CTSD have an effect on the osteogenic capacity of rat BMSCs and whether these genes, when differentially expressed, affect the expression of related genes in the MAPK, autophagy, and apoptosis signaling pathways and thus the osteogenic function of BMSCs. In summary, the findings of this study indicate that MAP4K2 and CTSD exert significant influence on the proliferation, osteogenic differentiation, and mineralization processes of rat BMSCs cells. Furthermore, these proteins may contribute to the development of OP through their involvement in the regulation of autophagy and apoptosis. Conversely, our investigation did not reveal any discernible impact of SPI1 on OP-related phenotypes. Consequently, this research serves as a fundamental basis for further exploration of potential therapeutic targets for the treatment of OP.

Menopause and gastrointestinal health and disease

Menopause has far-reaching effects on human physiology, including the gastrointestinal tract, and can negatively influence the quality of life of women who are affected. Menopause can have multiple effects on gastrointestinal function, including altering gut motility and changing the composition of the gut microbiota. As a result, some gastrointestinal and hepatic conditions are more common among individuals in peri- and postmenopause, and people with these conditions before menopause might also experience greater symptom severity and worse health-related quality of life during this time. The use of hormone replacement therapy to treat menopausal symptoms might also affect gastrointestinal health and well-being. Individuals in postmenopause are at risk for bone remodelling and osteoporosis due to ageing and loss of sex hormones. However, secondary osteoporosis can also occur due to medications used to treat gastrointestinal conditions (for example, glucocorticoids and other immunosuppressive medications) and the conditions themselves (for example, autoimmune disease or coeliac disease). Although all people who menstruate will eventually transition to menopause, there are relatively few studies evaluating the effect of menopause on gastrointestinal symptoms and quality of life. This Review aims to summarize available evidence and highlight areas where research is needed.

The effects of endurance trainability phenotype, sex, and interval running training on bone collagen synthesis in adult rats

Bone is influenced by many factors such as genetics and mechanical loading, but the short-term physiological effects of these factors on bone (re)modelling are not well characterised. This study investigated the effects of endurance trainability phenotype, sex, and interval running training (7-week intervention) on bone collagen formation in rats using a deuterium oxide stable isotope tracer method. Bone samples of the femur diaphysis, proximal tibia, mid-shaft tibia, and distal tibia were collected after necropsy from forty-six 9 ± 3-month male and female rats selectively bred for yielding low (LRT) or high (HRT) responses to endurance training. Bone collagen proteins were isolated and hydrolysed, and fractional synthetic rates (FSRs) were determined by the incorporation of deuterium into protein-bound alanine via GC-pyrolysis-IRMS. There was a significant large main effect of phenotype at the femur site (p < 0.001; η2g = 0.473) with HRT rats showing greater bone collagen FSRs than LRT rats. There was a significant large main effect of phenotype (p = 0.008; η2g = 0.178) and a significant large main effect of sex (p = 0.005; η2g = 0.196) at the proximal site of the tibia with HRT rats showing greater bone collagen FSRs than LRT rats, and male rats showing greater bone collagen FSRs compared to female rats. There was a significant large main effect of training at the mid-shaft site of the tibia (p = 0.012; η2g = 0.159), with rats that underwent interval running training having greater bone collagen FSRs than control rats. Similarly, there was a significant large main effect of training at the distal site of the tibia (p = 0.050; η2g = 0.156), with rats in the interval running training group having greater bone collagen FSRs compared to rats in the control group. Collectively, this evidence highlights that bone responses to physiological effects are site-specific, indicating that interval running training has positive effects on bone collagen synthesis at the tibial mid-shaft and distal sites, whilst genetic factors affect bone collagen synthesis at the femur diaphysis (phenotype) and proximal tibia (phenotype and sex) in rats.

The Cross-Sectional and Longitudinal Associations Between Adherence to 24-Hour Movement Behavior Guidelines and Bone Health in Young Children

BACKGROUND

Adherence to the World Health Organization's 24-hour movement behavior (24-HMB) guidelines is associated with various health outcomes. However, its relationship with bone mineral density (BMD) in young children has not been investigated. This study aimed to examine the cross-sectional and longitudinal associations between adherence to the 24-HMB guidelines and BMD in young children.

METHODS

A total of 120 children aged 3-5 years were recruited from three kindergartens in Changsha, Hunan, China. Physical activity (PA) was objectively measured using ActiGraph wGT3X-BT accelerometers, and BMD was assessed using the Sunlight Omnisense 7000P ultrasound device. Screen time (ST) and sleep duration (SD) were reported by parents. Logistic regression was used to analyze the associations between guideline adherence and BMD.

RESULTS

Only 5.5% of the participants met all three guidelines for PA, ST, and SD, while 16.5% did not meet any. In the cross-sectional analysis, young children who met both ST and SD guidelines (OR = 0.29, 95% CI: 0.09, 0.95) had a lower risk of insufficient BMD compared to those who met none. In the one-year cohort follow-up, young children who met the PA guideline at baseline (OR = 0.22, 95% CI: 0.07, 0.71), as well as those who met both the PA and ST guidelines (OR = 0.18, 95% CI: 0.04, 0.83) or all three (OR = 0.13, 95% CI: 0.03, 0.69), had a lower risk of insufficient BMD at one year.

CONCLUSIONS

Adherence to the 24-HMB guidelines may promote bone health in young children. Future research should prioritize achievable goals, such as limiting ST and ensuring adequate SD, while gradually increasing MVPA to optimize bone development.

Identification of osteoporosis genes using family studies

Osteoporosis is a multifactorial bone disease characterised by reduced bone mass and increased fracture risk. Family studies have made significant contribution in unravelling the genetics of osteoporosis. Yet, most of the underlying molecular and biological mechanisms remain unknown prompting the need for further studies. This review outlines the proper phenotyping and advanced genetic techniques in the form of high-throughput DNA sequencing used to identify genetic factors underlying monogenic osteoporosis in a family-based setting. The steps related to variant filtering prioritisation and curation are also described. From an evolutionary perspective, deleterious risk variants with higher penetrance tend to be rare as a result of negative selection. High-throughput sequencing (HTS) can identify rare variants with large effect sizes which are likely to be missed by candidate gene analysis or genome-wide association studies (GWAS) wherein common variants with small to moderate effect sizes are identified. We also describe the importance of replicating implicated genes, and possibly variants, identified following HTS to confirm their causality. Replication of the gene in other families, singletons or independent cohorts confirms that the shortlisted genes and/or variants are indeed causal. Furthermore, novel genes and/or variants implicated in monogenic osteoporosis require a thorough validation by means of in vitro and in vivo assessment. Therefore, analyses of families can continue to elucidate the genetic architecture of osteoporosis, paving the way for improved diagnostic and therapeutic strategies.

Complex interplay of neurodevelopmental disorders (NDDs), fractures, and osteoporosis: a mendelian randomization study

BACKGROUND

Neurodevelopmental disorders (NDDs), such as Attention-Deficit/Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD), and Tourette Syndrome (TS), have been extensively studied for their multifaceted impacts on social and emotional well-being. Recently, there has been growing interest in their potential relationship with fracture risks in adulthood. This study aims to explore the associations between these disorders and fracture rates, in order to facilitate better prevention and treatment.

METHODS

Employing a novel approach, this study utilized Mendelian randomization (MR) analysis to investigate the complex interplay between ADHD, ASD, TS, and fractures. The MR framework, leveraging extensive genomic datasets, facilitated a systematic examination of potential causal relationships and genetic predispositions.

RESULTS

The findings unveil intriguing bidirectional causal links between ADHD, ASD, and specific types of fractures. Notably, ADHD is identified as a risk factor for fractures, with pronounced associations in various anatomical regions, including the skull, trunk, and lower limbs. Conversely, individuals with specific fractures, notably those affecting the femur and lumbar spine, exhibit an increased genetic predisposition to ADHD and ASD. In this research, no correlation was found between TS and fractures, or osteoporosis.These results provide a genetic perspective on the complex relationships between NDDs and fractures, emphasizing the importance of early diagnosis, intervention, and a holistic approach to healthcare.

CONCLUSION

This research sheds new light on the intricate connections between NDDs and fractures, offering valuable insights into potential risk factors and causal links. The bidirectional causal relationships between ADHD, ASD, and specific fractures highlight the need for comprehensive clinical approaches that consider both NDDs and physical well-being.

Mechanism of action of gut microbiota and probiotic Lactobacillus rhamnosus GG on skeletal remodeling in mice

INTRODUCTION

Gut microbiota (GM) is the collection of small organisms such as bacteria, fungi, bacteriophages and protozoans living in the intestine in symbiotics relation within their host. GM regulates host metabolism by various mechanisms.

METHODS

This review aims to consolidate current information for physicians on the effect of GM on bone health. For this, an online search of the literature was conducted using the keywords gut microbiota, bone mass, osteoporosis, Lactobacillus and sex steroid.

RESULTS AND CONCLUSIONS

There is a considerable degree of variation in bone mineral density (BMD) within populations, and it is estimated that a significant component of BMD variability is due to genetics. However, the remaining causes of bone mass variance within populations remain largely unknown. A well-recognized cause of phenotypic variation in bone mass is the composition of the microbiome. Studies have shown that germ-free (GF) mice have higher bone mass compared to conventionally raised (CR) mice. Furthermore, GM dysbiosis, also called dysbacteriosis, is defined as any alteration in the composition of the microbial community that has been colonized in the host intestine and associated with the development of bone diseases. For instance, postmenopausal osteoporosis (PMO) and diabetes. GM can be modulated by several factors such as genetics, age, drugs, food habits and probiotics. Probiotics are defined as viable bacteria that confer health benefits by modulating GM when administered in adequate quantity. Lactobacillus rhamnosus GG (LGG) is a great example of such a probiotic. LGG has been shown to regulate bone mass in healthy mice as well as ovariectomized (OVX) mice via two different mechanisms. This review will focus on the literature regarding the mechanism by which GM and probiotic LGG regulate bone mass in healthy mice as well as in OVX mice, a model of PMO.

An FGFR2 mutation as the potential cause of a new phenotype including early-onset osteoporosis and bone fractures: a case report

Osteoporosis is a systemic, multifactorial disorder of bone mineralization. Many factors contributing to the development of osteoporosis have been identified so far, including gender, age, nutrition, lifestyle, exercise, drug use, as well as a range of comorbidities. In addition to environmental and lifestyle factors, molecular genetic factors account for 50-85% of osteoporosis cases. For example, the vitamin D receptor (VDR), collagen type I (COL1), estrogen receptor (ER), apolypoprotein Е (ApoE), bone morphogenetic protein (BMP), and Low-density lipoprotein receptor-related protein 5 (LRP5) are all involved in the pathogenesis of osteoporosis. Among the candidate genes, the pathogenic variants in which are involved in the pathogenesis of osteoporosis is FGFR2. Additionally, FGFs/FGFRs-dependent signaling has been shown to regulate skeletal development and has been linked to a plethora of heritable disorders of the musculoskeletal system. In this study we present the clinical, biochemical and radiological findings, as well as results of molecular genetic testing of a 13-year-old male proband with heritable osteoporosis, arthralgia and multiple fractures and a family history of abnormal bone mineralization and fractures. Whole exome sequencing found a heterozygous previously undescribed variant in the FGFR2 gene (NM_000141.5) (GRCh37.p13 ENSG00000066468.16: g.123298133dup; ENST00000358487.5:c.722dup; ENSP00000351276.5:p.Asn241LysfsTer43). The same variant was found in two affected relatives. These data lead us to believe that the variant in FGFR2 found in our proband and his relatives could be related to their phenotype. Therefore, modern methods of molecular genetic testing can allow us to differentiate between osteogenesis imperfecta and other bone mineralization disorders.

Bone Homeostasis and Physiology in Normal and Orthopaedic Disease Conditions

Some of the most common human systemic diseases-both benign and malignant-affect bone regulation, formation, and homeostasis (the cellular balance regulated by osteocytes, osteoblasts, and osteoclasts). This review discusses our current understanding of the molecular components and mechanisms that are responsible for homeostasis and interactions resulting in dysregulation (dysfunction due to the loss of the dynamic equilibrium of bone homeostasis). Knowledge of key pathways in bone biology can improve surgeon understanding, clinical recognition, and treatment of bone homeostasis-related diseases.

Understanding root fenestration: A systematic scoping review of prevalence and clinical factors

The aim of this systematic scoping review is to explore the literature on root fenestration prevalence and its possible etiologic, aggravating and predisposing clinical factors. A systematic search was conducted in 5 electronic databases, by two independent reviewers, without any language and date restrictions. Forty-six full-text records were included in the study, out of which 27 were used for prevalence analysis and 42 for clinical factor analysis. The results suggest that the literature is heterogenous, with major differences in the study protocols and results' presentation, providing limited information regarding root fenestration prevalence and possible racial distribution patterns. Further documentation is also required regarding clinical parameters that may affect root fenestration's presence and severity. Despite their few limitations, retrospective cone beam computed tomography studies with high-resolution protocols, as well as open flap studies for direct observation of possible root fenestration sites, seem the most reliable methods to better comprehend its presence and possible distribution patterns.

Copy Number Variation and Osteoporosis

PURPOSE OF REVIEW

The purpose of this review is to summarize recent findings on copy number variations and susceptibility to osteoporosis.

RECENT FINDINGS

Osteoporosis is highly influenced by genetic factors, including copy number variations (CNVs). The development and accessibility of whole genome sequencing methods has accelerated the study of CNVs and osteoporosis. Recent findings include mutations in novel genes and validation of previously known pathogenic CNVs in monogenic skeletal diseases. Identification of CNVs in genes previously associated with osteoporosis (e.g. RUNX2, COL1A2, and PLS3) has confirmed their importance in bone remodelling. This process has been associated also with the ETV1-DGKB, AGBL2, ATM, and GPR68 genes, identified by comparative genomic hybridisation microarray studies. Importantly, studies in patients with bone pathologies have associated bone disease with the long non-coding RNA LINC01260 and enhancer sequences residing in the HDAC9 gene. Further functional investigation of genetic loci harbouring CNVs associated with skeletal phenotypes will reveal their role as molecular drivers of osteoporosis.

Integrating genome-wide association study with regulatory SNP annotations identified novel candidate genes for osteoporosis

Osteoporosis (OP) is a metabolic bone disease, characterized by a decrease in bone mineral density (BMD). However, the research of regulatory variants has been limited for BMD. In this study, we aimed to explore novel regulatory genetic variants associated with BMD. We conducted an integrative analysis of BMD genome-wide association study (GWAS) and regulatory single nucleotide polymorphism (rSNP) annotation information. Firstly, the discovery GWAS dataset and replication GWAS dataset were integrated with rSNP annotation database to obtain BMD associated SNP regulatory elements and SNP regulatory element-target gene (E-G) pairs, respectively. Then, the common genes were further subjected to HumanNet v2 to explore the biological effects. Through discovery and replication integrative analysis for BMD GWAS and rSNP annotation database, we identified 36 common BMD-associated genes for BMD irrespective of regulatory elements, such as FAM3C (pdiscovery GWAS = 1.21 × 10-25, preplication GWAS = 1.80 × 10-12), CCDC170 (pdiscovery GWAS = 1.23 × 10-11, preplication GWAS = 3.22 × 10-9), and SOX6 (pdiscovery GWAS = 4.41 × 10-15, preplication GWAS = 6.57 × 10-14). Then, for the 36 common target genes, multiple gene ontology (GO) terms were detected for BMD such as positive regulation of cartilage development (p = 9.27 × 10-3) and positive regulation of chondrocyte differentiation (p = 9.27 × 10-3). We explored the potential roles of rSNP in the genetic mechanisms of BMD and identified multiple candidate genes. Our study results support the implication of regulatory genetic variants in the development of OP.

A case-control study coupling with meta-analysis elaborates decisive association between IGF-1 rs35767 and osteoporosis in Asian postmenopausal females

BACKGROUND

Osteoporosis (OP) is prevalent in postmenopausal women. Several studies investigated the association between IGF-1 polymorphisms and OP among postmenopausal females with conflicting outcomes.

OBJECTIVE

To investigate whether the IGF-1 (rs35767, rs2288377, rs5742612) were associated with OP in postmenopausal females.

METHODS

In case-control study, 95 OP cases and 222 healthy controls were recruited between March 2015 and July 2019. OP was diagnosed based on WHO criteria for diagnosis of OP as T score of bone mineral density (BMD) ≤-2.5; normal, as T score of BMD ≥-1. IGF-1 SNPs were genotyped by iPLEX Gold SNP genotyping. To be solid, related studies from PubMed, Embase, Cochrane, Web of science, and previous meta-analysis up until November 2020, along with our case-control study, were incorporated into a meta-analysis with criteria of significance using odds ratios (ORs) with corresponding 95% confidence intervals (CI) to evaluate risk factor of SNPs on OP. TSA was used to estimate the sample sizes required to achieve a conclusion.

RESULTS

In dominant model of our case-control study, we found nonsignificant association of rs35767 [Adj-OR: 0.95 (95% CI: 0.56-1.60)], rs2288377 [Adj-OR: 1.15 (95% CI: 0.67-1.97)], and rs5742612 [Adj-OR: 1.07 (95% CI: 0.62-1.83)] with OP in postmenopausal females. However, integration of our case-control study and 3 published studies, rs35767 [OR: 1.24 (95% CI: 1.05-1.47)] showed a conclusively risk association with OP in postmenopausal females judged by TSA with 2267 Asians.

CONCLUSIONS

This study demonstrates a crucial sample to conclude that IGF-1 rs35767 is significantly associated with OP in postmenopausal women.

Association between LEPR polymorphism and susceptibility of osteoporosis in Chinese Mulao people

To explore the association between the single nucleotide polymorphism (SNP) of leptin receptor (LEPR) gene and the susceptibility to osteoporosis (OP) among Chinese Mulao people. A total of 738 people were involved. Bone mineral density (BMD) was examined by calcaneus ultrasound attenuation measurement. Six SNPs of LEPR were detected. The genotypes, allele frequencies, linkage disequilibrium, and haplotype were analyzed. BMD decreased with age and males had higher BMD than women. The proportion of normal bone mass decreased with age, and morbidity of OP increased. Three out of six SNPs showed a difference between OP and normal group. Individuals with AA genotype of rs1137100 in OP group outnumber the normal group, AA increased the risk of OP. In rs2767485, CT increased the risk of OP, C allele may be susceptible to OP. TT genotype of rs465555 was susceptible genotype of OP, T locus may be associated with OP. Strong linkage disequilibrium was detected among rs1137100, rs1137101, and rs4655555. Four haplotypes were constructed, among which, AACGCT and GGTGTA increased the risk of OP by 3.9 and 4.2 times, respectively, whereas, GGCGTA reduced 74% of OP susceptibility. The rs1137100, rs2767485, and rs465555 of LEPR were associated with OP in Chinese Mulao people.

Associations of bone mass and polygenic risk of osteoporosis with indicators of arterial wall condition

Background: The identification of genetic factors that are simultaneously responsible for the predisposition to the development of cardiovascular diseases (CVD) and osteoporosis (OP) is important for the prevention of both conditions.

Aim: The aim of this study is to evaluate three genetic risk scales (GRS) that previously showed an association with bone mineral density (BMD) and fracture risk, as well as to study the associations of these GRS with vascular wall pathology.

Materials and methods: 250 female outpatients (aged 45 to 69) were enrolled into a cross-sectional study. The intima-media thickness (IMT), the presence and number of atherosclerotic plaques (AP) were studied using duplex scanning. Pulse wave velocity (PWV), augmentation index (AI) were measured by applanation tonometry. Coronary vessels calcium deposits were registered by multispiral computed tomography (MSCT) using the Agatston calcium index (CI). The BMD of the spine, hip neck (HN) and proximal hip (PH) was measured using double energy x-ray absorptiometry. Bone resorption marker type-1 collagen C-terminal telopeptide (CTx) was assessed solid-phase enzyme immunoassay. The genetic study included DNA extraction from whole blood samples. Targeted sequencing was performed on the Nextseq550 sequencer (Illumina, USA). Statistical analysis was carried out using the SAS software package for Windows, version 9.0 (SAS Institute Inc., USA).

Results: The chance of detecting low bone mass increased more than 4 times at values of IMT ≥0.9 mm (OR=4.17; 95%CI [1.2–14.4], p<0.02), 2.4 times in the presence of AP in the carotid arteries (OR=2.45; 95%CI [1.12–4.88], p><0.05), by 6.7 times with an Agatstone CI ≥ 100 units (OR=6.68; 95%CI [1.56–28.7], p><0.001), 1.4 times (OR=1.43; 95%CI [0.56–3.68], p><0.438) with a PWV ≥10 m/s, 1.2 times (OR=1.2; 95%CI [0.601–2.43], p><0.60) with increased AI ≥ 27%. According to multivariate linear regression analysis (adjusted for age, duration of postmenopause, marker of bone resorption CTx), a significant association of all GRS with BMD in all parts of the skeleton was revealed. Both univariate and multivariate regression models adjusted for several covariants (age, total cholesterol, systolic blood pressure) showed a reliable association of GRS62 with the presence of plaques and GRS63 — with coronary artery CI. Conclusion: The results of the study demonstrated the association of polygenic genetic risk of GRS-based OP with BMD and vascular wall status indicators in women in the peri and postmenopausal periods.>< 0.02), 2.4 times in the presence of AP in the carotid arteries (OR=2.45; 95%CI [1.12–4.88], p< 0.05), by 6.7 times with an Agatstone CI ≥ 100 units (OR=6.68; 95%CI [1.56–28.7], p< 0.001), 1.4 times (OR=1.43; 95%CI [0.56–3.68], p< 0.438) with a PWV ≥10 m/s, 1.2 times (OR=1.2; 95%CI [0.601–2.43], p<0.60) with increased AI ≥ 27%. According to multivariate linear regression analysis (adjusted for age, duration of postmenopause, marker of bone resorption CTx), a significant association of all GRS with BMD in all parts of the skeleton was revealed. Both univariate and multivariate regression models adjusted for several covariants (age, total cholesterol, systolic blood pressure) showed a reliable association of GRS62 with the presence of plaques and GRS63 — with coronary artery CI.>< 0.60) with increased AI ≥ 27%. According to multivariate linear regression analysis (adjusted for age, duration of postmenopause, marker of bone resorption CTx), a significant association of all GRS with BMD in all parts of the skeleton was revealed. Both univariate and multivariate regression models adjusted for several covariants (age, total cholesterol, systolic blood pressure) showed a reliable association of GRS62 with the presence of plaques and GRS63 — with coronary artery CI.

Conclusion: The results of the study demonstrated the association of polygenic genetic risk of GRS-based OP with BMD and vascular wall status indicators in women in the peri and postmenopausal periods.

Modifiable risk factors for bone health & fragility fractures

Osteoporosis is an ageing disorder characterised by poor microstructural architecture of the bone and an increase in the risk of fragility fractures, which often leads to hospitalisation and eventually a loss of mobility and independence. By 2050, it is estimated that more than 30 million people in Europe will be affected by bone diseases, and European hospitalisation alone can approximately cost up to 3.5 billion euros each year [1]. Although inherited variation in bone mineral density (BMD) is pre-determined by up to 85% [2], there is a window of opportunity to optimise BMD and reduce fracture risk through key modifiable lifestyle factors during the life course. An optimal diet rich in micronutrients, such as calcium, vitamin D, and potassium, has long been considered an important modifiable component of bone health, which is attributed to their direct roles within bone metabolism. Recently, there has been emerging evidence to suggest that protein and even an adequate intake of fruit and vegetables may also play an important role in improving BMD [3,4]. Maintaining a physically active lifestyle is not only protective from non-communicable diseases such as cardiovascular disease but it also has been shown to lessen the risk of fractures later in life, thereby making it an imperative modifiable factor for bone health, particularly as it also supports peak bone mass attainment during childhood/adolescence and can facilitate the maintenance of bone mass throughout adulthood [5]. Other key lifestyle factors that could be potentially modified to reduce the risk of osteoporosis or osteoporotic fractures later in life include smoking status, alcohol intake, and body composition [6]. Therefore, the principle aim of this review is to highlight the recent evidence pertaining to modifiable lifestyle factors that contribute to optimal bone health and the prevention of fragility fractures in later life.

Genetic variation in WNT16 and its association with bone mineral density, fractures and osteoporosis in children with bone fragility

Several genome-wide association studies (GWAS), GWAS meta-analyses, and mouse studies have demonstrated that wingless-related integration site 16 (WNT16) gene is associated with bone mineral density (BMD), cortical bone thickness, bone strength and fracture risk. Practically no data exist regarding the significance of WNT16 in childhood-onset osteoporosis and related fractures. We hypothesized that pathogenic variants and genetic variations in WNT16 could explain skeletal fragility in affected children. We screened the WNT16 gene by Sanger sequencing in three pediatric cohorts: 35 with primary osteoporosis, 59 with multiple fractures, and in 95 healthy controls. Altogether, we identified 12 variants in WNT16. Of them one was a rare 5′UTR variant rs1386898215 in genome aggregate and medical trans-omic databases (GnomAD, TOPMED; minor allele frequency (MAF) 0.00 and 0.000008, respectively). One variant rs1554366753, overrepresented in children with osteoporosis (MAF = 0.06 vs healthy controls MAF = 0.01), was significantly associated with lower BMD. This variant was found associated with increased WNT16 gene expression at mRNA level in fibroblast cultures. None of the other identified variants were rare (MAF < 0.001) or deemed pathogenic by predictor programs. WNT16 may play a role in childhood osteoporosis but genetic WNT16 variation is not a common cause of skeletal fragility in childhood.

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No pathogenic WNT16 variants were found associated with pediatric osteoporosis or fracture-prone patients

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Altogether, twelve WNT16 variants were found in pediatric osteoporosis or fracture-prone patients

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The genetic variation rs1554366753 in the WNT16 gene is associated with bone mineral density and primary osteoporosis

Osteoporosis in children and adolescents: when to suspect and how to diagnose it

Early recognition of osteoporosis in children and adolescents is important in order to establish an appropriate diagnosis of the underlying condition and to initiate treatment if necessary. In this review, we present the diagnostic work-up, and its pitfalls, of pediatric patients suspected of osteoporosis including a careful collection of the medical and personal history, a complete physical examination, biochemical data, molecular genetics, and imaging techniques. The most recent and relevant literature has been reviewed to offer a broad overview on the topic. Genetic and acquired pediatric bone disorders are relatively common and cause substantial morbidity. In recent years, there has been significant progress in the understanding of the genetic and molecular mechanistic basis of bone fragility and in the identification of acquired causes of osteoporosis in children. Specifically, drugs that can negatively impact bone health (e.g. steroids) and immobilization related to acute and chronic diseases (e.g. Duchenne muscular dystrophy) represent major risk factors for the development of secondary osteoporosis and therefore an indication to screen for bone mineral density and vertebral fractures. Long-term studies in children chronically treated with steroids have resulted in the development of systematic approaches to diagnose and manage pediatric osteoporosis.

CONCLUSIONS

Osteoporosis in children requires consultation with and/or referral to a pediatric bone specialist. This is particularly relevant since children possess the unique ability for spontaneous and medication-assisted recovery, including reshaping of vertebral fractures. As such, pediatricians have an opportunity to improve bone mass accrual and musculoskeletal health in osteoporotic children.

WHAT IS KNOWN

• Both genetic and acquired pediatric disorders can compromise bone health and predispose to fractures early in life. • The identification of children at risk of osteoporosis is essential to make a timely diagnosis and start the treatment, if necessary.

WHAT IS NEW

• Pediatricians have an opportunity to improve bone mass accrual and musculoskeletal health in osteoporotic children and children at risk of osteoporosis. • We offer an extensive but concise overview about the risk factors for osteoporosis and the diagnostic work-up (and its pitfalls) of pediatric patients suspected of osteoporosis.

Frequency of root fenestration in a Greek subpopulation: A cone beam computed tomography clinical study

This cone beam computed tomography (CBCT) study aimed to assess the root fenestration (RF) frequency in healthy, intact teeth and analyse their features in a Greek subpopulation. 432 CBCT scans were examined. 5486 teeth were evaluated for RF prevalence. RF prevalence and distribution were recorded for each jaw, tooth group, as well as patient age and sex. RF symmetry, distribution to the affected root surface and the effects of age and sex were evaluated. The prevalence of RF ranged from 0.57% (central incisors) to 7.18% (first premolars) and from 0.48% (second premolars) to 10.79% (lateral incisors) for the maxilla and the mandible, respectively. No symmetrical occurrence of RF was detected. Most RF patients presented one or two defects in both jaws. Types I and IV were the most prevalent in the maxilla, while Types III, II and V were the most prevalent in the mandible. No statistical difference was detected between different sexes and age groups (P > 0.05).

IL1R2 polymorphisms and their interaction are associated with osteoporosis susceptibility in the Chinese Han population

AIMS

Interleukin 1 (IL-1) inhibitory receptor type 2 (IL1R2) serves as a negative regulator of IL-1 signalling and is involved in the pathogenesis of osteoporosis. This study aimed to determine the correlation between IL1R2 polymorphism and osteoporosis susceptibility in the Chinese Han population.

METHODS

We recruited 594 osteoporosis patients and 599 healthy controls. Six single nucleotide polymorphisms (SNPs) in IL1R2 were selected for genotyping using the Agena MassARRAY platform. The odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using logistic regression analysis with adjustment for age and sex. Linkage disequilibrium analysis was plotted using Haploview v4.2. Multifactor dimension reduction (MDR) was performed to estimate the SNP-SNP interactions of IL1R2 variants.

RESULTS

Rs11674595 (OR = 1.86, p = 0.020), rs2072472 (OR = 1.26, p = 0.019) and rs4851527 (OR = 0.78, p = 0.007) were related to the risk of osteoporosis. Moreover, the contribution of IL1R2 polymorphisms to osteoporosis risk was associated with age, sex and body mass index. We found the relationships of T_rs11674595 A_rs4851527 (OR = 0.80, p = 0.015), C_rs11674595 G_rs4851527 (OR = 1.22, p = 0.043) and A_rs3218977 G_rs2072472 (OR = 1.25, p = 0.022) haplotypes to osteoporosis occurrence, and a potential accumulated effect of IL1R2 SNPs (testing accuracy = 0.5783 and cross validation consistency = 10/10) on osteoporosis susceptibility.

CONCLUSION

IL1R2 polymorphisms (rs11674595, rs4851527, rs2072472 and rs3218977) may contribute to osteoporosis risk in the Chinese Han population. Our findings may increase our understanding of the effects of IL1R2 polymorphisms on the predisposition to osteoporosis.

The Impact of Maternal High-Fat Diet on Bone Microarchitecture in Offspring

The incidence of obesity in women of reproductive age has significantly increased over the past 100 years. There is a well-established connection between maternal obesity during pregnancy and an increased risk of developing non-communicable cardiometabolic diseases in her offspring. This mini-review focuses on evidence examining the effect of maternal high-fat diet (HFD) on skeletal development and bone health in later life in offspring. The majority of rodent studies indicate that maternal HFD generally negatively affects both embryonic bone development and bone volume in adult animals. Details surrounding the mechanisms of action that drive changes in the skeleton in offspring remain unclear, although numerous studies suggest that some effects are sex-specific. Human studies in this area are limited but also suggest that HFD during pregnancy may impair bone formation and increase fracture risk during childhood. Given the consequences of low bone mass and deranged bone microarchitecture for offspring, advances in our understanding of the developmental origins of bone health is critical in the battle against osteoporosis.

Non-union bone fractures

The human skeleton has remarkable regenerative properties, being one of the few structures in the body that can heal by recreating its normal cellular composition, orientation and mechanical strength. When the healing process of a fractured bone fails owing to inadequate immobilization, failed surgical intervention, insufficient biological response or infection, the outcome after a prolonged period of no healing is defined as non-union. Non-union represents a chronic medical condition not only affecting function but also potentially impacting the individual's psychosocial and economic well-being. This Primer provides the reader with an in-depth understanding of our contemporary knowledge regarding the important features to be considered when faced with non-union. The normal mechanisms involved in bone healing and the factors that disrupt the normal signalling mechanisms are addressed. Epidemiological considerations and advances in the diagnosis and surgical therapy of non-union are highlighted and the need for greater efforts in basic, translational and clinical research are identified.

CD13 is a critical regulator of cell-cell fusion in osteoclastogenesis

The transmembrane aminopeptidase CD13 is highly expressed in cells of the myeloid lineage, regulates dynamin-dependent receptor endocytosis and recycling and is a necessary component of actin cytoskeletal organization. Here, we show that CD13-deficient mice present a low bone density phenotype with increased numbers of osteoclasts per bone surface, but display a normal distribution of osteoclast progenitor populations in the bone marrow and periphery. In addition, the bone formation and mineral apposition rates are similar between genotypes, indicating a defect in osteoclast-specific function in vivo. Lack of CD13 led to exaggerated in vitro osteoclastogenesis as indicated by significantly enhanced fusion of bone marrow-derived multinucleated osteoclasts in the presence of M-CSF and RANKL, resulting in abnormally large cells containing remarkably high numbers of nuclei. Mechanistically, while expression levels of the fusion-regulatory proteins dynamin and DC-STAMP1 must be downregulated for fusion to proceed, these are aberrantly sustained at high levels even in CD13-deficient mature multi-nucleated osteoclasts. Further, the stability of fusion-promoting proteins is maintained in the absence of CD13, implicating CD13 in protein turnover mechanisms. Together, we conclude that CD13 may regulate cell–cell fusion by controlling the expression and localization of key fusion regulatory proteins that are critical for osteoclast fusion.

Bone material properties and response to teriparatide in osteoporosis due to WNT1 and PLS3 mutations

CONTEXT

Patients with osteoporosis-associated WNT1 or PLS3 mutations have unique bone histomorphometric features and osteocyte-specific hormone expression patterns.

OBJECTIVE

To investigate the effects of WNT1 and PLS3 mutations on bone material properties.

DESIGN

Transiliac bone biopsies were evaluated by quantitative backscattered electron imaging, immunohistochemistry, and bone histomorphometry.

SETTING

Ambulatory patients.

PATIENTS

Three pediatric and eight adult patients with WNT1 or PLS3 mutations.

INTERVENTION

Bone mineralization density distribution and osteocyte protein expression was evaluated in 11 patients and repeated in six patients who underwent repeat biopsy after 24 months of teriparatide treatment.

MAIN OUTCOME MEASURE

Bone mineralization density distribution and protein expression.

RESULTS

Children with WNT1 or PLS3 mutations had heterogeneous bone matrix mineralization, consistent with bone modeling during growth. Bone matrix mineralization was homogenous in adults and increased throughout the age spectrum. Teriparatide had very little effect on matrix mineralization or bone formation in patients with WNT1 or PLS3 mutations. However, teriparatide decreased trabecular osteocyte lacunae size and increased trabecular bone FGF23 expression.

CONCLUSION

The contrast between preserved bone formation with heterogeneous mineralization in children and low bone turnover with homogenous bone mineral content in adults suggests that WNT1 and PLS3 have differential effects on bone modeling and remodeling. The lack of change in matrix mineralization in response to teriparatide, despite clear changes in osteocyte lacunae size and protein expression, suggests that altered WNT1 and PLS3 expression may interfere with coupling of osteocyte, osteoblast, and osteoclast function. Further studies are warranted to determine the mechanism of these changes.

Decompression of the internal auditory canal via the retrosigmoid approach in a patient with Camurati-Engelmann disease: illustrative case

BACKGROUND

Camurati-Engelmann disease (CED) is a rare condition characterized by hyperostosis of the long bones and skull base. Symptoms include contractures and pain in affected extremities but can also include manifestations of cranial hyperostosis such as intracranial hypertension, Chiari malformation, exophthalmia, frontal bossing, and several cranial neuropathies due to cranial foraminal stenosis.

OBSERVATIONS

This report describes a 27-year-old patient with suspected CED who developed progressive intermittent facial nerve paresis, hemifacial spasms, and a decrease in hearing. There were no symptoms of increased intracranial pressure or vertigo. Radiological evaluation showed a significant thickening of the skull base with serious bilateral internal auditory canal stenosis. Because of the progressive nature of the aforementioned cranial neuropathies in combination with the correlating severe radiological compression, a surgical decompression of the facial nerve and vestibulocochlear nerve was performed via a retrosigmoid approach with intraoperative monitoring. Postoperative facial nerve function was intact. Hearing and vestibular function were unchanged. There were no more episodes of facial nerve palsy or spasm.

LESSONS

To the authors' knowledge, this is the first report to describe decompression of the internal auditory canal via a retrosigmoid approach for symptomatic facial and cochlear nerve compression in a patient with CED.

The gut microbiota is a transmissible determinant of skeletal maturation

Genetic factors account for the majority of the variance of human bone mass, but the contribution of non-genetic factors remains largely unknown. By utilizing maternal/offspring transmission, cohabitation, or fecal material transplantation (FMT) studies, we investigated the influence of the gut microbiome on skeletal maturation. We show that the gut microbiome is a communicable regulator of bone structure and turnover in mice. In addition, we found that the acquisition of a specific bacterial strain, segmented filamentous bacteria (SFB), a gut microbe that induces intestinal Th17 cell expansion, was sufficient to negatively impact skeletal maturation. These findings have significant translational implications, as the identification of methods or timing of microbiome transfer may lead to the development of bacteriotherapeutic interventions to optimize skeletal maturation in humans. Moreover, the transfer of SFB-like microbes capable of triggering the expansion of human Th17 cells during therapeutic FMT procedures could lead to significant bone loss in fecal material recipients.

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.

A Novel Variant in CLCN7 Regulates the Coupling of Angiogenesis and Osteogenesis

Autosomal dominant osteopetrosis type II (ADO II), characterized by increased bone mass and density, is caused by mutations in the chloride channel 7 (CLCN7) gene. In this study, a novel missense variant in CLCN7 (c.1678A > G; p.Met560Val) was identified in three symptomatic subjects and one carrier of a Chinese family with ADO II. Notably, bone formation markers, including osteocalcin and total procollagen type N-terminal propeptide, have increased or presented at the upper limit of the normal range in the three patients. Serum factors secreted by osteoclast lineage cells and affecting the CD31^hiEMCN^hi vessel formation, such as tartrate-resistant acid phosphatase 5b, platelet-derived growth factor-BB, vascular endothelial growth factor, and SLIT3, had a higher expression in three ADO II subjects than in 15 healthy age-matched and sex-matched controls. Moreover, the conditioned medium was obtained from preosteoclast induced from the ADO II patients’ peripheral blood mononuclear cells. It was found to promote the CD31^hiEMCN^hi vessel formation of human microvascular endothelial cells and osteogenic differentiation of bone marrow-derived stem cells. Taken together, our finding revealed a novel CLCN7 variant associated with ADO II and suggested that the sclerotic bone was potentially associated with the increase of the CD31^hiEMCN^hi vessel formation and bone formation.

Genomic Medicine: Lessons Learned From Monogenic and Complex Bone Disorders

Current genetic studies of monogenic and complex bone diseases have broadened our understanding of disease pathophysiology, highlighting the need for medical interventions and treatments tailored to the characteristics of patients. As genomic research progresses, novel insights into the molecular mechanisms are starting to provide support to clinical decision-making; now offering ample opportunities for disease screening, diagnosis, prognosis and treatment. Drug targets holding mechanisms with genetic support are more likely to be successful. Therefore, implementing genetic information to the drug development process and a molecular redefinition of skeletal disease can help overcoming current shortcomings in pharmaceutical research, including failed attempts and appalling costs. This review summarizes the achievements of genetic studies in the bone field and their application to clinical care, illustrating the imminent advent of the genomic medicine era.

Rosamultin Attenuates Acute Hypobaric Hypoxia-Induced Bone Injuries by Regulation of Sclerostin and Its Downstream Signals

Wang, Xing-Min, Hui Liu, Jian-Yu Li, Jin-Xia Wei, Xia Li, Yong-Liang Zhang, Ling-Zhi Li, and Xi-Zheng Zhang. Rosamultin attenuates acute hypobaric hypoxia-induced bone injuries by regulation of sclerostin and its downstream signals. High Alt Med Biol. 21:273-286, 2020. Background: Rosamultin, one of the compounds extracted from Potentilla anserina L., exhibited significant pharmacological activity against oxidative stress and hypoxic injury in our previous study. However, the effect of rosamultin on bone damage induced by acute hypobaric hypoxia (HH) has not been thoroughly studied. Methods: In this study, we first investigated the protective effect of rosamultin against bone damage in rats following acute exposure to simulated high-altitude hypoxia. Furthermore, we explored the detailed mechanism involved in the regulation of rat bone remodeling by rosamultin in an acute HH environment through analysis of sclerostin expression and the regulation of downstream signaling pathways. Results: Pretreatment with rosamultin significantly reduced HH-induced oxidative stress and inflammation, improved bone metabolic abnormalities, and alleviated the imbalance in bone remodeling in rats exposed to acute HH. Rosamultin markedly downregulated the expression of sclerostin, activated the Wnt/β-catenin signaling pathway, and enhanced the ratio of osteoprotegerin/receptor activator of nuclear factor kappa B ligand to maintain the balance of bone formation and resorption. Conclusions: Rosamultin attenuates acute HH-induced bone damage and improves abnormal bone remodeling in rats by inhibition of sclerostin expression and activation of the Wnt/β-catenin signaling pathway.

Genetic analysis of osteoblast activity identifies Zbtb40 as a regulator of osteoblast activity and bone mass

Osteoporosis is a genetic disease characterized by progressive reductions in bone mineral density (BMD) leading to an increased risk of fracture. Over the last decade, genome-wide association studies (GWASs) have identified over 1000 associations for BMD. However, as a phenotype BMD is challenging as bone is a multicellular tissue affected by both local and systemic physiology. Here, we focused on a single component of BMD, osteoblast-mediated bone formation in mice, and identified associations influencing osteoblast activity on mouse Chromosomes (Chrs) 1, 4, and 17. The locus on Chr. 4 was in an intergenic region between Wnt4 and Zbtb40, homologous to a locus for BMD in humans. We tested both Wnt4 and Zbtb40 for a role in osteoblast activity and BMD. Knockdown of Zbtb40, but not Wnt4, in osteoblasts drastically reduced mineralization. Additionally, loss-of-function mouse models for both genes exhibited reduced BMD. Our results highlight that investigating the genetic basis of in vitro osteoblast mineralization can be used to identify genes impacting bone formation and BMD.

Genetic Burden Contributing to Extremely Low or High Bone Mineral Density in a Senior Male Population From the Osteoporotic Fractures in Men Study (MrOS)

Worldwide, one in five men aged over 50 years will experience osteoporosis or a clinical bone fracture, with a greater fracture-related mortality rate than women. However, the genetic etiology of osteoporosis in men is still poorly understood. We aimed to identify the genetic variants and candidate genes associated with extremely low or high BMD for a better understanding of the biology underlying low bone density that may point to potential therapeutic targets for increasing bone mass. Subjects from the Osteoporotic Fractures in Men Study (MrOS) cohort were evaluated by age and BMI-adjusted total hip BMD. Those with BMD values 3 SDs away from the mean were selected and the remaining individuals whose adjusted BMD ranked at the highest or lowest 100 were included. Men with the lowest adjusted BMD (N = 98) and highest adjusted BMD (N = 110) were chosen for exome sequencing. Controls (N = 82) were men of Northern and Western European descent from the US Utah population of the 1000 Genomes Project. Fisher's exact test was performed to compare low- or high-BMD subjects with controls for single-gene associations. Additionally, sets of candidate genes causative of heritable disorders of connective tissue, including osteogenesis imperfecta (OI) and Ehlers-Danlos syndrome (EDS), were grouped for multigene and mutation burden analyses. No single-gene associations with rare variants were found for either the low BMD group (33 genes) or high BMD group (18 genes). In the group of OI genes, we detected a significant threefold increased accumulation of rare variants in low-BMD subjects compared with controls (p = 0.009). Additionally, genes associated with EDS had a twofold increased frequency in low-BMD subjects compared with controls (p = 0.03). These findings reveal a rare variant burden in OI and EDS disease genes at low BMD, which suggests a potential gene-panel approach to screen for multivariant associations in larger cohorts. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

WNT16 Requires Gα Subunits as Intracellular Partners for Both Its Canonical and Non-Canonical WNT Signalling Activity in Osteoblasts

In the past years, WNT16 became an interesting target in the field of skeletal research, as it was identified as an essential regulator of the cortical bone compartment, with the ability to increase both cortical and trabecular bone mass and strength in vivo. Even though there are indications that these advantageous effects are coming from canonical and non-canonical WNT-signalling activity, a clear model of WNT signalling by WNT16 is not yet depicted. We, therefore, investigated the modulation of canonical (WNT/β-catenin) and non-canonical [WNT/calcium, WNT/planar cell polarity (PCP)] signalling in human embryonic kidney (HEK) 293 T and SaOS2 cells. Here, we demonstrated that WNT16 activates all WNT-signalling pathways in osteoblasts, whereas only WNT/calcium signalling was activated in HEK293T cells. In osteoblasts, we therefore, additionally investigated the role of Gα subunits as intracellular partners in WNT16's mechanism of action by performing knockdown of Gα12, Gα13 and Gαq. These studies point out that the above-mentioned Gα subunits might be involved in the WNT/β-catenin and WNT/calcium-signalling activity by WNT16 in osteoblasts, and for Gα12 in its WNT/PCP-signalling activity, illustrating a novel possible mechanism of interplay between the different WNT-signalling pathways in osteoblasts. Additional studies are needed to demonstrate whether this mechanism is specific for WNT16 signalling or relevant for all other WNT ligands as well. Altogether, we further defined WNT16's mechanism of action in osteoblasts that might underlie the well-known beneficial effects of WNT16 on skeletal homeostasis. These findings on WNT16 and the activity of specific Gα subunits in osteoblasts could definitely contribute to the development of novel therapeutic approaches for fragility fractures in the future.

Cross-Species RNA-Seq Study Comparing Transcriptomes of Enriched Osteocyte Populations in the Tibia and Skull

Local site-specific differences between bones in different regions of the skeleton account for their different properties and functions. To identify mechanisms behind these differences, we have performed a cross-species study comparing RNA transcriptomes of cranial and tibial osteocytes, from bones with very different primary functions and physiological responses, collected from the same individual mouse, rat, and rhesus macaque. Bioinformatic analysis was performed to identify 32 genes changed in the same direction between sites and shared across all three species. Several well-established key genes in bone growth and remodeling were upregulated in the tibias of all three species (BMP7, DKK1, FGF1, FRZB, SOST). Many of them associate or crosstalk with the Wnt signaling pathway. These results suggest Wnt signaling-related candidates for different control of regulatory mechanisms in bone homeostasis in the skull and tibia and indicate a different balance between genetically determined structure and feedback mechanisms to strains induced by mechanical loading at the different sites.

The Osteocyte as the New Discovery of Therapeutic Options in Rare Bone Diseases

Osteocytes are the most abundant (~95%) cells in bone with the longest half-life (~25 years) in humans. In the past osteocytes have been regarded as vestigial cells in bone, since they are buried inside the tough bone matrix. However, during the last 30 years it has become clear that osteocytes are as important as bone forming osteoblasts and bone resorbing osteoclasts in maintaining bone homeostasis. The osteocyte cell body and dendritic processes reside in bone in a complex lacuno-canalicular system, which allows the direct networking of osteocytes to their neighboring osteocytes, osteoblasts, osteoclasts, bone marrow, blood vessels, and nerves. Mechanosensing of osteocytes translates the applied mechanical force on bone to cellular signaling and regulation of bone adaptation. The osteocyte lacuno-canalicular system is highly efficient in transferring external mechanical force on bone to the osteocyte cell body and dendritic processes via displacement of fluid in the lacuno-canalicular space. Osteocyte mechanotransduction regulates the formation and function of the osteoblasts and osteoclasts to maintain bone homeostasis. Osteocytes produce a variety of proteins and signaling molecules such as sclerostin, cathepsin K, Wnts, DKK1, DMP1, IGF1, and RANKL/OPG to regulate osteoblast and osteoclast activity. Various genetic abnormality-associated rare bone diseases are related to disrupted osteocyte functions, including sclerosteosis, van Buchem disease, hypophosphatemic rickets, and WNT1 and plastin3 mutation-related disorders. Meticulous studies during the last 15 years on disrupted osteocyte function in rare bone diseases guided for the development of various novel therapeutic agents to treat bone diseases. Studies on genetic, molecular, and cellular mechanisms of sclerosteosis and van Buchem disease revealed a role for sclerostin in bone homeostasis, which led to the development of the sclerostin antibody to treat osteoporosis and other bone degenerative diseases. The mechanism of many other rare bone diseases and the role of the osteocyte in the development of such conditions still needs to be investigated. In this review, we mainly discuss the knowledge obtained during the last 30 years on the role of the osteocyte in rare bone diseases. We speculate about future research directions to develop novel therapeutic drugs targeting osteocyte functions to treat both common and rare bone diseases.

Integrating transcriptome-wide association study and mRNA expression profiling identifies novel genes associated with bone mineral density

To scan novel candidate genes associated with osteoporosis, a two-stage transcriptome-wide association study (TWAS) of bone mineral density (BMD) was conducted. The BMD-associated genes identified by TWAS were then compared with the gene expression profiling of BMD in bone cells, B cells, and mesenchymal stem cells. We identified multiple candidate genes and gene ontology (GO) terms associated with BMD.

INTRODUCTION

Osteoporosis (OP) is a metabolic bone disease characterized by decrease in BMD. Our objective is to scan novel candidate genes associated with OP.

METHODS

A transcriptome-wide association study (TWAS) was performed by integrating the genome-wide association study (GWAS) summary of bone mineral density (BMD) with two pre-computed mRNA expression weights of peripheral blood and muscle skeleton. Then, another independent GWAS data of BMD was used to verify the discovery results. The BMD-associated genes identified between discovery and replicate TWAS were further subjected to gene ontology (GO) analysis implemented by DAVID. Finally, the BMD-associated genes and GO terms were further compared with the mRNA expression profiling results of BMD to detect the common genes and GO terms shared by both DNA-level TWAS and mRNA expression profile analysis.

RESULTS

TWAS identified 95 common genes with permutation P value < 0.05 for peripheral blood and muscle skeleton, such as TMTC4 in muscle skeleton and DDX17 in peripheral blood. Further comparing the genes detected by discovery-replicate TWAS with the differentially expressed genes identified by mRNA expression profiling of OP patients found 18 overlapped genes, such as MUL1 in muscle skeleton and SPTBN1 in peripheral blood. GO analysis of the genes identified by discovery-replicate TWAS detected 12 BMD-associated GO terms, such as negative regulation of cell growth and regulation of glycogen catabolic process. Further comparing the GO results of discovery-replicate TWAS and mRNA expression profiles found 6 overlapped GO terms, such as membrane and cell adhesion.

CONCLUSION

Our study identified multiple candidate genes and GO terms for BMD, providing novel clues for understanding the genetic mechanism of OP.

The association of genetic variants in FGFR2 with osteoporosis susceptibility in Chinese Han population

Objective: The present study was conducted for exploring the influence of fibroblast growth factor 2 receptor (FGFR2) gene polymorphisms on osteoporosis occurrence risk in the Chinese population.

Methods: Polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) was conducted for the genotyping of polymorphism in 145 osteoporosis patients and 123 controls. The status of Hardy–Weinberg equilibrium was detected in the control group. Genotype and allele frequency comparison of polymorphism between the two groups was performed by χ² test, odds ratio (OR) with 95% confidence interval (95% CI) was used for the result expression about the association of FGFR2 polymorphisms with osteoporosis. Furthermore, the results were adjusted by clinical features via logistic regression analysis.

Results: AA genotype and A allele of rs2420946 were significantly associated with the increased risk of osteoporosis development adjusted by clinical features (OR = 2.238, 95% CI = 1.055–4.746; OR = 1.482, 95% CI = 1.042–2.019). Similarly, CC genotype and C allele frequencies of rs1219648 were detected the significant difference between the case and control groups (P<0.01); moreover, it was still significant by the adjustion of clinical features, which indicated that rs1219648 was significantly associated with the risk of osteoporosis occurrence (OR = 2.900, 95% CI = 1.341–6.271; OR = 1.602, 95% CI = 1.126–2.279). Haplotype T-A-C-T also obviously increased the occurrence risk of osteoporosis (OR = 1.844, 95% CI = 1.180–2.884). Besides, the significant interaction of FGFR2 polymorphisms with drinking status in osteoporosis was also found (P<0.05), especially rs2981579.

Conclusion:FGFR2 rs2420946 and rs1219648 polymorphisms may be the risk factor of osteoporosis in Chinese population. Furthermore, the interaction of FGFR2 polymorphisms with drinking may play an important role in osteoporosis etiology.

Gut microbiota composition and bone mineral loss-epidemiologic evidence from individuals in Wuhan, China

We explored the association between gut microbiota composition and bone mineral loss in Chinese elderly people by high-throughput 16S ribosomal RNA (rRNA) gene sequencing. Compared with controls, a smaller number of operational taxonomic units (OTUs), several taxa with altered abundance, and specific functional pathways were found in individuals with low-bone mineral density (BMD).

INTRODUCTION

Gut microbiota plays important roles in human health and associates with a number of diseases. However, few studies explored its association with bone mineral loss in human.

METHODS

We collected 102 fecal samples from each eligible individual belonging to low-BMD and control groups for high-throughput 16S rRNA gene sequencing.

RESULTS

The low-BMD individuals had a smaller number of OTUs and bacterial taxa at each level. At the phylum level, Bacteroidetes were more abundant in the low-BMD group; Firmicutes were enriched in the control group; Firmicutes and Actinobacteria positively correlated and Bacteroidetes negatively correlated with the BMD and T-score in all subjects. At the family level, the abundance of Lachnospiraceae in low-BMD individuals reduced and positively correlated with BMD and T-score; meanwhile, BMD increased with increasing Bifidobacteriaceae. At the genus level, low-BMD individuals had decreased proportions of Roseburia compared with control ones (P < 0.05). Roseburia, Bifidobacterium, and Lactobacillus positively correlated with BMD and T-score. Furthermore, BMD increased with rising abundance of Bifidobacterium. Functional prediction revealed that 93 metabolic pathways significantly differed between the two groups (FDR-corrected P < 0.05). Most pathways, especially pathways related to LPS biosynthesis, were more abundant in low-BMD individuals than in control ones.

CONCLUSIONS

Several taxa with altered abundance and specific functional pathways were discovered in low-BMD individuals. Our findings provide novel epidemiologic evidence to elucidate the underlying microbiota-relevant mechanism in bone mineral loss and osteoporosis.

Camurati-Engelmann Disease

Camurati-Engelmann disease or progressive diaphyseal dysplasia is a rare autosomal dominant sclerosing bone dysplasia. Mainly the skull and the diaphyses of the long tubular bones are affected. Clinically, the patients suffer from bone pain, easy fatigability, and decreased muscle mass and weakness in the proximal parts of the lower limbs resulting in gait disturbances. The disease-causing mutations are located within the TGFβ-1 gene and expected to or thought to disrupt the binding between TGFβ1 and its latency-associated peptide resulting in an increased signaling of the pathway and subsequently accelerated bone turnover. In preclinical studies, it was shown that targeting the type I receptor ameliorates the high bone turnover. In patients, treatment options are currently mostly limited to corticosteroids that may relieve the pain, and improve the muscle weakness and fatigue. In this review, the clinical and radiological characteristics as well as the molecular genetics of this condition are discussed.

Sclerosing bone dysplasias

The group of sclerosing bone dysplasia's is a clinically and genetically heterogeneous group of rare bone disorders which, according to the latest Nosology and classification of genetic skeletal disorders (2015), can be subdivided in three subgroups; the neonatal osteosclerotic dysplasias, the osteopetroses and related disorders and the other sclerosing bone disorders. Here, we give an overview of the most important radiographic and clinical symptoms, the underlying genetic defect and potential treatment options of the different sclerosing dysplasias included in these subgroups.

Evaluation of WISP1 as a candidate gene for bone mineral density in the Old Order Amish

Wnt1-inducible signaling pathway protein-1 (WISP1) is a novel target of the Wnt pathway for modulating osteogenesis and improving bone strength. However, it is not clear if genetic variants in the WISP1 region are associated with bone mineral density (BMD) in human. The aim of this study is to investigate the role of genetic variation in WISP1 gene as a determinant of BMD in 1,510 Old Order Amish (OOA). We performed regional association analysis of 58 tag variants within 5 kb upstream and downstream to WISP1 with BMD and found 5 variants that were associated with BMD at multiple skeletal sites (P values from 2.89 × 10⁻⁶ to 1.62 × 10⁻²), with some significant associations even after adjustment for multiple comparisons. To replicate these results in an independent dataset, we performed a look-up of BMD associations with these variants in European ancestry subjects from the large GEFOS Consortium and observed the nominal associations of two of these variants with BMD (P values: 0.031 to 0.048). In conclusion, we have demonstrated that genetic variants surrounding WISP1 are associated with BMD at multiple skeletal sites in the OOA, thus influencing osteoporosis risk. These results support a role for the WISP1 gene on influencing variation in BMD.

Genetically Determined Later Puberty Impacts Lowered Bone Mineral Density in Childhood and Adulthood

Later puberty associates with lower areal bone mineral density (aBMD), and both are risk factors for osteoporosis. However, the association between puberty timing-associated genetic variants and aBMD during development, and the causal relationship between puberty timing and aBMD, remain uncharacterized. We constructed sex-specific polygenic risk scores (GRS) consisting of 333 genetic variants associated with later puberty in European-descent children in the Bone Mineral Density in Childhood Study (BMDCS), consisting of a longitudinal cohort with up to seven assessments (n = 933) and a cross-sectional cohort (n = 486). These GRS were tested for associations with age- and sex-specific aBMD Z-scores at the lumbar spine (LS), femoral neck (FN), total hip, and distal radius, accounting for clinical covariates using sex-stratified linear mixed models. The causal relationship between puberty timing and aBMD was tested in the BMDCS and in publicly available adult data (GEFOS consortium) using two-sample Mendelian randomization (MR). The puberty-delaying GRS was associated with later puberty and lower LS-aBMD in the BMDCS in both sexes (combined beta ± SE = -0.078 ± 0.024; p = 0.0010). In the MR framework, the puberty-delaying genetic instrument also supported a causal association with lower LS-aBMD and FN-aBMD in adults of both sexes. Our results suggest that pubertal timing is causal for diminished aBMD in a skeletal site- and sex-specific manner that tracks throughout life, potentially impacting later risk for osteoporosis, which should be tested in future studies. © 2017 American Society for Bone and Mineral Research.

Interaction between LRP5 and periostin gene polymorphisms on serum periostin levels and cortical bone microstructure

We investigated the interaction between periostin SNPs and the SNPs of the genes assumed to modulate serum periostin levels and bone microstructure in a cohort of postmenopausal women. We identified an interaction between LRP5 SNP rs648438 and periostin SNP rs9547970 on serum periostin levels and on radial cortical porosity.

PURPOSE

The purpose of this study is to investigate the interaction between periostin gene polymorphisms (SNPs) and other genes potentially responsible for modulating serum periostin levels and bone microstructure in a cohort of postmenopausal women.

METHODS

In 648 postmenopausal women from the Geneva Retirees Cohort, we analyzed 6 periostin SNPs and another 149 SNPs in 14 genes, namely BMP2, CTNNB1, ESR1, ESR2, LRP5, LRP6, PTH, SPTBN1, SOST, TGFb1, TNFRSF11A, TNFSF11, TNFRSF11B and WNT16. Volumetric BMD and bone microstructure were measured by high-resolution peripheral quantitative computed tomography at the distal radius and tibia.

RESULTS

Serum periostin levels were associated with radial cortical porosity, including after adjustment for age, BMI, and years since menopause (p = 0.036). Sixteen SNPs in the ESR1, LRP5, TNFRSF11A, SOST, SPTBN1, TNFRSF11B and TNFSF11 genes were associated with serum periostin levels (p range 0.03-0.001) whereas 26 SNPs in 9 genes were associated with cortical porosity at the radius and/or at the tibia. WNT 16 was the gene with the highest number of SNPs associated with both trabecular and cortical microstructure. The periostin SNP rs9547970 was also associated with cortical porosity (p = 0.04). In particular, SNPs in LRP5, ESR1 and near the TNFRSF11A gene were associated with both cortical porosity and serum periostin levels. Eventually, we identified an interaction between LRP5 SNP rs648438 and periostin SNP rs9547970 on serum periostin levels (interaction p = 0.01) and on radial cortical porosity (interaction p = 0.005).

CONCLUSION

These results suggest that periostin expression is genetically modulated, particularly by polymorphisms in the Wnt pathway, and is thereby implicated in the genetic variation of bone microstructure.

MECHANISMS IN ENDOCRINOLOGY: Genetics of human bone formation

Throughout life, bone is continuously remodelled to be able to fulfil its multiple functions. The importance of strictly regulating the bone remodelling process, which is defined by the sequential actions of osteoclasts and osteoblasts, is shown by a variety of disorders with abnormalities in bone mass and strength. The best known and most common example of such a disorder is osteoporosis, which is marked by a decreased bone mass and strength that consequently results in an increased fracture risk. As osteoporosis is a serious health problem, a large number of studies focus on elucidating the aetiology of the disease as well as on the identification of novel therapeutic targets for the treatment of osteoporotic patients. These studies have demonstrated that a large amount of variation in bone mass and strength is often influenced by genetic variation in genes encoding important regulators of bone homeostasis. Throughout the years, studies into the genetic causes of osteoporosis as well as several rare monogenic disorders with abnormal high or low bone mass and strength have largely increased the knowledge on regulatory pathways important for bone resorption and formation. This review gives an overview of genes and pathways that are important for the regulation of bone formation and that are identified through their involvement in monogenic and complex disorders with abnormal bone mass. Furthermore, novel bone-forming strategies for the treatment of osteoporosis that resulted from these discoveries, such as antibodies against sclerostin, are discussed as well.

Osteocyte Protein Expression Is Altered in Low-Turnover Osteoporosis Caused by Mutations in WNT1 and PLS3

CONTEXT

Osteocytes express proteins that regulate bone remodeling and mineralization.

OBJECTIVE

To evaluate the relationship between osteocyte-specific protein expression and bone histology in patients with monogenic osteoporosis due to wingless integration site 1 (WNT1) or plastin 3 (PLS3) mutations.

DESIGN AND SETTING

Cross-sectional cohort study at a university hospital.

PARTICIPANTS

Six patients (four males; ages: 14 to 72 years) with a heterozygous WNT1 mutation and five patients (four males; ages: 9 to 70 years) with a heterozygous/hemizygous PLS3 mutation.

METHODS AND MAIN OUTCOME MEASURES

Immunohistochemistry was performed for fibroblast growth factor 23 (FGF23), dentin matrix protein 1 (DMP1), sclerostin, and phosphorylated (phospho-)β-catenin in iliac crest samples and compared with bone histomorphometry.

RESULTS

FGF23 expression in WNT1 patients was 243% that observed in PLS3 patients (P < 0.01). DMP1, sclerostin, and phospho-β-catenin expression did not differ between groups. Serum phosphate correlated inversely with FGF23 expression (r = -0.79, P = 0.01) and serum ionized calcium correlated inversely with sclerostin expression (r = -0.60, P = 0.05). Phospho-β-catenin expression correlated inversely with DMP1 expression (r = -0.88, P < 0.001), osteoid volume/bone volume (r = -0.68, P = 0.02), and bone formation rate (r = -0.78, P < 0.01). FGF23 expression did not correlate with DMP1 expression, sclerostin expression, or bone histomorphometry. Marrow adiposity was higher in WNT1 than in PLS3 patients (P = 0.04).

CONCLUSIONS

Mutations that disrupt WNT signaling and osteocytic mechanosensing affect osteocyte protein expression. Abnormal osteocyte function may play a role in the pathogenesis of monogenetic forms of osteoporosis.

FGF-2 Gene Polymorphism in Osteoporosis among Guangxi's Zhuang Chinese

Osteoporosis is a complex multifactorial disorder of gradual bone loss and increased fracture risk. While previous studies have shown the importance of many genetic factors in determining peak bone mass and fragility fractures and in suggesting involvement of fibroblast growth factor-2 (FGF-2) in bone metabolism and bone mass, the relationship of FGF-2 genetic diversity with bone mass/osteoporosis has not yet been revealed. The current study investigated the potential relevance of FGF-2 gene polymorphism in osteoporosis among a Zhuang ethnic Chinese cohort of 623, including 237 normal bone mass controls, 227 osteopenia, and 159 osteoporosis of different ages. Bone density was examined by calcaneus ultrasound attenuation measurement, and single nucleotide polymorphisms (SNPs) and linkage disequilibrium analyses were performed on five SNP loci of FGF-2 gene. Significant differences were found in bone mass in males between the 45-year-old and ≥70-year-old groups (p < 0.01), and in females among 55, 60, 65 and 70-year-old groups (p < 0.05). Males had higher bone mass values than females in the same age (over 55-year-old) (p < 0.05). The proportions of individuals with normal bone mass decreased with age (65.2% to 40% in males, and 50% to 0% in females), whereas prevalence of osteoporosis increased with age (15.4% to 30% in men, and 7.7% to 82% in women). Out of five FGF-2 SNP loci, the TA genotype of rs308442 in the osteoporosis group (40.2%) was higher than in the control group (29.5%) (p < 0.05). The TA genotype was significantly correlated with the risk of osteoporosis (odds ratio OR = 1.653), 95% confidence interval (CI): 1.968-1.441). Strong linkage disequilibrium in FGF-2 gene was also detected between rs12644427 and rs3747676, between rs12644427 and rs3789138, and between rs3747676 and rs3789138 (D' > 0.8, and r² > 0.33). Thus, the rs308442 locus of FGF-2 gene is closely correlated to osteoporosis in this Zhuang ethnic Chinese cohort, and the TA may be the risk genotype of osteoporosis.

Genetic Screening of WNT4 and WNT5B in Two Populations with Deviating Bone Mineral Densities

A role for WNT4 and WNT5B in bone metabolism was indicated by genome-wide association studies (GWAS) and a Wnt4 knockout mouse model. The aim of this study was therefore to replicate and further investigate the causality between genetic variation in WNT4 and WNT5B and deviating bone mineral density (BMD) values. A WNT4 and WNT5B mutation screening was performed in patients with craniotubular hyperostosis using Sanger sequencing. Here, no putative causal mutations were detected. Moreover, a high and low BMD cohort was selected from the Odense Androgen Study population for re-sequencing. In WNT4 we detected four variants (three rare, one common), while in WNT5B we detected five variants (two rare, three common). For the common variants, no significant difference in genotype frequencies between the high and low BMD cohorts was observed. The SNPs associated with the GWAS were genotyped in these cohorts, but again no significant difference in genotype frequencies was observed. Despite the findings of the GWAS, we were not able to replicate or further verify the genetic association of polymorphisms in WNT4 and WNT5B with BMD. In order to do so, the intronic regions of both genes could be investigated more thoroughly in more extended populations (or extremes) with greater power. Future genetic and functional studies toward adjacent genes of WNT4 and WNT5B can also be interesting to figure out whether the signal from GWAS could possibly be attributed to genetic variation in these genes.

Inherited diseases caused by mutations in cathepsin protease genes

Lysosomal cathepsins are proteolytic enzymes increasingly recognized as prognostic markers and potential therapeutic targets in a variety of diseases. In those conditions, the cathepsins are mostly overexpressed, thereby driving the respective pathogenic processes. Although less known, there are also diseases with a genetic deficiency of cathepsins. In fact, nowadays 6 of the 15 human proteases called 'cathepsins' have been linked to inherited syndromes. However, only three of these syndromes are typical lysosomal storage diseases, while the others are apparently caused by defective cleavage of specific protein substrates. Here, we will provide an introduction on lysosomal cathepsins, followed by a brief description of the clinical symptoms of the various genetic diseases. For each disease, we focus on the known mutations of which many have been only recently identified by modern genome sequencing approaches. We further discuss the effect of the respective mutation on protease structure and activity, the resulting pathogenesis, and possible therapeutic strategies.