The genetics of bone mass and susceptibility to bone diseases

Green space, genetic susceptibility, and risk of osteoporosis:a cohort study from the UK Biobank

OBJECTIVE

This study aimed to investigate the effect of residential exposure to green space on the incident osteoporosis and further explore the modification effect of genetic susceptibility.

METHODS

Participants from the UK Biobank were followed from 2006 to 2010 (baseline) to December 31st, 2022. Using land use coverage, we evaluated exposure to residential surrounding green space, natural environment, and domestic gardens. We used the Cox regression to examine the association between the residential environment and incident osteoporosis. The interactive effects between polygenic risk score (PRS) of osteoporosis and residential environments on incident osteoporosis were investigated.

RESULTS

This study included 292,662 participants. Over a median follow-up period of 13.65 years, we documented 9177 incidents of osteoporosis. Per interquartile (IQR) increase in greenness and natural environment at a 300 m buffer was associated with a 4% lower risk of incident osteoporosis [HR = 0.96 (95% CI: 0.93, 0.99)] and [HR = 0.96 (95% CI: 0.93, 0.98)], respectively. We did not identify any interactive effects between genetic risk and residential environment on incident osteoporosis.

CONCLUSIONS

This study found that public greenness and natural environments could reduce the risk of incident osteoporosis regardless of genetic predisposition. Developing sustainable and publicly accessible natural environments might benefit populations' bone health.

Transcriptomics reveals the molecular regulation of Chinese medicine formula on improving bone quality in broiler

Skeletal disorder is of concern to the poultry industry as it affects animal welfare and production performance. Traditional Chinese medicine could improve bone quality and reduce the incidence of bone disease, but the molecular regulation of Chinese medicine formula (CMF) on improving bone quality in broilers is still unclear. This study was performed to research the effects of CMF on skeletal performance of Cobb broilers and reveal the molecular regulation. A total of 120 one-day-old Cobb broilers were randomly allocated into 4 equal groups of 30 chickens, with 5 replicates and 6 chickens in each replicate. The control (CON) group was fed a diet without CMF, while the CMF1, CMF2, and CMF3 groups were supplemented with different CMF at 6,000 mg/kg diet, respectively. The broilers were raised to 60 d of age, then bone tissues were collected for biomechanical properties, micro-CT detection and transcriptomic sequencing analysis. The results showed that CMF3 improved the biomechanical properties of broiler tibia, via increasing the elastic modulus (P < 0.05), yield strength (P > 0.05), maximum stress (P < 0.05) and fracture stress (P < 0.05) of the tibia. Micro-CT analysis indicated that CMF3 increased the bone mineral density (BMD), bone volume/total volume (BV/TV), bone surface density (BS/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), and decreased the trabecular separation (Tb.Sp) of femur cancellous bone (P < 0.05). RNA-seq analysis revealed 2,177 differentially expressed genes (DEGs) (|log2FoldChange| ≥ 1, FDR < 0.05) between the CMF3 group and CON group. Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) analysis showed 13 pathways mostly associated with bone growth and development and bone metabolism, and we identified 39 bone-related DEGs. This study suggests that CMF3 could improve bone strength and bone microstructure of broilers, and showed a positive effect on bone performance. Our research could provide a theoretical reference for the development of pollution-free feed additives to improve the skeletal performance of broilers, which could help promote healthy farming of chickens.

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.

Application of Single-Cell and Spatial Omics in Musculoskeletal Disorder Research

Musculoskeletal disorders, including fractures, scoliosis, heterotopic ossification, osteoporosis, osteoarthritis, disc degeneration, and muscular injury, etc., can occur at any stage of human life. Understanding the occurrence and development mechanism of musculoskeletal disorders, as well as the changes in tissues and cells during therapy, might help us find targeted treatment methods. Single-cell techniques provide excellent tools for studying alterations at the cellular level of disorders. However, the application of these techniques in research on musculoskeletal disorders is still limited. This review summarizes the current single-cell and spatial omics used in musculoskeletal disorders. Cell isolation, experimental methods, and feasible experimental designs for single-cell studies of musculoskeletal system diseases have been reviewed based on tissue characteristics. Then, the paper summarizes the latest findings of single-cell studies in musculoskeletal disorders from three aspects: bone and ossification, joint, and muscle and tendon disorders. Recent discoveries about the cell populations involved in these diseases are highlighted. Furthermore, the therapeutic responses of musculoskeletal disorders, especially single-cell changes after the treatments of implants, stem cell therapies, and drugs are described. Finally, the application potential and future development directions of single-cell and spatial omics in research on musculoskeletal diseases are discussed.

Vitamin D Receptor Gene Polymorphisms Affect Osteoporosis-Related Traits and Response to Antiresorptive Therapy

The present study analyzed the effect of vitamin D receptor (VDR) gene polymorphisms (ApaI, TaqI, BsmI, FokI, and Cdx2) on bone mineral density (BMD), biochemical parameters and bone turnover markers, fracture prevalence, and response to three types of antiresorptive therapy (estrogen-progesterone, raloxifene, and ibandronate) in 356 postmenopausal women from Slovakia. Association analysis revealed a significant effect of BsmI polymorphism on lumbar spine BMD, serum osteocalcin (OC), and β-CrossLaps levels. While ApaI and Cdx2 polymorphisms were associated with OC and alkaline phosphatase, TaqI polymorphism affected all turnover markers. ApaI, TaqI, and BsmI genotypes increased the risk of spinal, radial, or total fractures with odds ratios ranging from 2.03 to 3.17. Each of therapy types evaluated had a beneficial effect on all osteoporosis-related traits; however, the VDR gene affected only ibandronate and raloxifene treatment. ApaI/aa, TaqI/TT, and BsmI/bb genotypes showed a weaker or no response to ibandronate therapy in femoral and spinal BMD. The impact of aforementioned polymorphisms on turnover markers was also genotype dependent. On the contrary, only TaqI and BsmI polymorphisms influenced raloxifene therapy, even only in lumbar spine BMD. These results point to the potential of using the VDR gene in personalized pharmacotherapy of osteoporosis.

Feature selection approaches identify potential plasma metabolites in postmenopausal osteoporosis patients

INTRODUCTION

Postmenopausal women with osteoporosis (PMOP) are prone to fragility fractures. Osteoporosis is associated with alterations in the levels of specific circulating metabolites.

OBJECTIVES

To analyze the metabolic profile of individuals with PMOP and identify novel metabolites associated with bone mineral density (BMD).

METHODS

We performed an unsupervised metabolomics analysis of plasma samples from participants with PMOP and of normal controls (NC) with normal bone mass. BMD values for the lumber spine and the proximal femur were determined using dual-energy X-ray absorptiometry. Principal component analysis (PCA) and supervised partial least squares discriminant analysis (PLS-DA) were performed for metabolomic profile analyses. Metabolites with P < 0.05 in the t-test, VIP > 1 in the PLS-DA model, and SNR > 0.3 between the PMOP and NC groups were defined as differential abundant metabolites (DAMs). The SHapley additive explanations (SHAP) method was utilized to determine the importance of permutation of each DAM in the predictive model between the two groups. ROC analysis and correlation analysis of metabolite relative abundance and BMD/T-scores were conducted. KEGG pathway analysis was used for functional annotation of the candidate metabolites.

RESULTS

Overall, 527 annotated molecular markers were extracted in the positive and negative total ion chromatogram (TIC) of each sample. The PMOP and NC groups could be differentiated using the PLS-DA model. Sixty-eight DAMs were identified, with most relative abundances decreasing in the PMOP samples. SHAP was used to identify 9 DAM metabolites as factors distinguishing PMOP from NC. The logistic regression model including Triethanolamine, Linoleic acid, and PC(18:1(9Z)/18:1(9Z)) metabolites demonstrated excellent discrimination performance (sensitivity = 97.0, specificity = 96.6, AUC = 0.993). The correlation analysis revealed that the abundances of Triethanolamine, PC(18:1(9Z)/18:1(9Z)), 16-Hydroxypalmitic acid, and Palmitic acid were significantly positively correlated with the BMD/T score (Pearson correlation coefficients > 0.5, P < 0.05). Most candidate metabolites were involved in lipid metabolism based on KEGG functional annotations.

CONCLUSION

The plasma metabolomic signature of PMOP patients differed from that of healthy controls. Marker metabolites may help provide information for the diagnosis, therapy, and prevention of PMOP. We highlight the application of feature selection approaches in the analysis of high-dimensional biological data.

Physiological Mineralization during In Vitro Osteogenesis in a Biomimetic Spheroid Culture Model

Bone health-targeting drug development strategies still largely rely on inferior 2D in vitro screenings. We aimed at developing a scaffold-free progenitor cell-based 3D biomineralization model for more physiological high-throughput screenings. MC3T3-E1 pre-osteoblasts were cultured in α-MEM with 10% FCS, at 37 °C and 5% CO₂ for up to 28 days, in non-adherent V-shaped plates to form uniformly sized 3D spheroids. Osteogenic differentiation was induced by 10 mM β-glycerophosphate and 50 µg/mL ascorbic acid. Mineralization stages were assessed through studying expression of marker genes, alkaline phosphatase activity, and calcium deposition by histochemistry. Mineralization quality was evaluated by Fourier transformed infrared (FTIR) and scanning electron microscopic (SEM) analyses and quantified by micro-CT analyses. Expression profiles of selected early- and late-stage osteoblast differentiation markers indicated a well-developed 3D biomineralization process with strongly upregulated Col1a1, Bglap and Alpl mRNA levels and type I collagen- and osteocalcin-positive immunohistochemistry (IHC). A dynamic biomineralization process with increasing mineral densities was observed during the second half of the culture period. SEM–Energy-Dispersive X-ray analyses (EDX) and FTIR ultimately confirmed a native bone-like hydroxyapatite mineral deposition ex vivo. We thus established a robust and versatile biomimetic, and high-throughput compatible, cost-efficient spheroid culture model with a native bone-like mineralization for improved pharmacological ex vivo screenings.

Functional Validation of Osteoporosis Genetic Findings Using Small Fish Models

The advancement of human genomics has revolutionized our understanding of the genetic architecture of many skeletal diseases, including osteoporosis. However, interpreting results from human association studies remains a challenge, since index variants often reside in non-coding regions of the genome and do not possess an obvious regulatory function. To bridge the gap between genetic association and causality, a systematic functional investigation is necessary, such as the one offered by animal models. These models enable us to identify causal mechanisms, clarify the underlying biology, and apply interventions. Over the past several decades, small teleost fishes, mostly zebrafish and medaka, have emerged as powerful systems for modeling the genetics of human diseases. Due to their amenability to genetic intervention and the highly conserved genetic and physiological features, fish have become indispensable for skeletal genomic studies. The goal of this review is to summarize the evidence supporting the utility of Zebrafish (Danio rerio) for accelerating our understanding of human skeletal genomics and outlining the remaining gaps in knowledge. We provide an overview of zebrafish skeletal morphophysiology and gene homology, shedding light on the advantages of human skeletal genomic exploration and validation. Knowledge of the biology underlying osteoporosis through animal models will lead to the translation into new, better and more effective therapeutic approaches.

Evolutionary Genetic Signatures of Selection on Bone-Related Variation within Human and Chimpanzee Populations

Bone strength and the incidence and severity of skeletal disorders vary significantly among human populations, due in part to underlying genetic differentiation. While clinical models predict that this variation is largely deleterious, natural population variation unrelated to disease can go unnoticed, altering our perception of how natural selection has shaped bone morphologies over deep and recent time periods. Here, we conduct the first comparative population-based genetic analysis of the main bone structural protein gene, collagen type I α 1 (COL1A1), in clinical and 1000 Genomes Project datasets in humans, and in natural populations of chimpanzees. Contrary to predictions from clinical studies, we reveal abundant COL1A1 amino acid variation, predicted to have little association with disease in the natural population. We also find signatures of positive selection associated with intron haplotype structure, linkage disequilibrium, and population differentiation in regions of known gene expression regulation in humans and chimpanzees. These results recall how recent and deep evolutionary regimes can be linked, in that bone morphology differences that developed among vertebrates over 450 million years of evolution are the result of positive selection on subtle type I collagen functional variation segregating within populations over time.

The "GEnomics of Musculo Skeletal Traits TranslatiOnal NEtwork": Origins, Rationale, Organization, and Prospects

Musculoskeletal research has been enriched in the past ten years with a great wealth of new discoveries arising from genome wide association studies (GWAS). In addition to the novel factors identified by GWAS, the advent of whole-genome and whole-exome sequencing efforts in family based studies has also identified new genes and pathways. However, the function and the mechanisms by which such genes influence clinical traits remain largely unknown. There is imperative need to bring multidisciplinary expertise together that will allow translating these genomic discoveries into useful clinical applications with the potential of improving patient care. Therefore "GEnomics of MusculoSkeletal traits TranslatiOnal NEtwork" (GEMSTONE) aims to set the ground for the: 1) functional characterization of discovered genes and pathways; 2) understanding of the correspondence between molecular and clinical assessments; and 3) implementation of novel methodological approaches. This research network is funded by The European Cooperation in Science and Technology (COST). GEMSTONE includes six working groups (WG), each with specific objectives: WG1-Study populations and expertise groups: creating, maintaining and updating an inventory of experts and resources (studies and datasets) participating in the network, helping to assemble focus groups defined by phenotype, functional and methodological expertise. WG2-Phenotyping: describe ways to decompose the phenotypes of the different functional studies into meaningful components that will aid the interpretation of identified biological pathways. WG3 Monogenic conditions - human KO models: makes an inventory of genes underlying musculoskeletal monogenic conditions that aids the assignment of genes to GWAS signals and prioritizing GWAS genes as candidates responsible for monogenic presentations, through biological plausibility. WG4 Functional investigations: creating a roadmap of genes and pathways to be prioritized for functional assessment in cell and organism models of the musculoskeletal system. WG5 Bioinformatics seeks the integration of the knowledge derived from the distinct efforts, with particular emphasis on systems biology and artificial intelligence applications. Finally, WG6 Translational outreach: makes a synopsis of the knowledge derived from the distinct efforts, allowing to prioritize factors within biological pathways, use refined disease trait definitions and/or improve study design of future investigations in a potential therapeutic context (e.g. clinical trials) for musculoskeletal diseases.

Identification and Functional Annotation of Genes Related to Bone Stability in Laying Hens Using Random Forests

Skeletal disorders, including fractures and osteoporosis, in laying hens cause major welfare and economic problems. Although genetics have been shown to play a key role in bone integrity, little is yet known about the underlying genetic architecture of the traits. This study aimed to identify genes associated with bone breaking strength and bone mineral density of the tibiotarsus and the humerus in laying hens. Potentially informative single nucleotide polymorphisms (SNP) were identified using Random Forests classification. We then searched for genes known to be related to bone stability in close proximity to the SNPs and identified 16 potential candidates. Some of them had human orthologues. Based on our findings, we can support the assumption that multiple genes determine bone strength, with each of them having a rather small effect, as illustrated by our SNP effect estimates. Furthermore, the enrichment analysis showed that some of these candidates are involved in metabolic pathways critical for bone integrity. In conclusion, the identified candidates represent genes that may play a role in the bone integrity of chickens. Although further studies are needed to determine causality, the genes reported here are promising in terms of alleviating bone disorders in laying hens.

Comprehensive Analysis of RNA-Seq Gene Expression Profiling of Brain Transcriptomes Reveals Novel Genes, Regulators, and Pathways in Autism Spectrum Disorder

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with deficits in social communication ability and repetitive behavior. The pathophysiological events involved in the brain of this complex disease are still unclear.

METHODS

In this study, we aimed to profile the gene expression signatures of brain cortex of ASD patients, by using two publicly available RNA-seq studies, in order to discover new ASD-related genes.

RESULTS

We detected 1567 differentially expressed genes (DEGs) by meta-analysis, where 1194 were upregulated and 373 were downregulated genes. Several ASD-related genes previously reported were also identified. Our meta-analysis identified 235 new DEGs that were not detected using the individual RNA-seq studies used. Some of those genes, including seven DEGs (PAK1, DNAH17, DOCK8, DAPP1, PCDHAC2, and ERBIN, SLC7A7), have been confirmed in previous reports to be associated with ASD. Gene Ontology (GO) and pathways analysis showed several molecular pathways enriched by the DEGs, namely, osteoclast differentiation, TNF signaling pathway, complement and coagulation cascade. Topological analysis of protein-protein interaction of the ASD brain cortex revealed proteomics hub gene signatures: MYC, TP53, HDAC1, CDK2, BAG3, CDKN1A, GABARAPL1, EZH2, VIM, and TRAF1. We also identified the transcriptional factors (TFs) regulating DEGs, namely, FOXC1, GATA2, YY1, FOXL1, USF2, NFIC, NFKB1, E2F1, TFAP2A, HINFP.

CONCLUSION

Novel core genes and molecular signatures involved with ASD were identified by our meta-analysis.

Discovery of ingenane and jatrophane diterpenoids from Euphorbia esula as inhibitors of RANKL-induced osteoclastogenesis

Two new ingenane diterpenoids (1-2), four new jatrophane diterpenoids (3-6), and seven known analogues (7-13), were isolated from the 95% ethanol extract of Euphorbia esula. Their structures were determined by extensive spectroscopic methods and ECD data analysis. These compounds were assayed for their anti-osteoporotic activity in a bone marrow-derived macrophage (BMM) cell line, and compounds 2, 4, 7, 8, 9, and 11 significantly inhibited the formation of osteoclasts with IC₅₀ values of 3.4, 4.3, 2.1, 0.5, 1.5, and 4.5 μM, respectively. These compounds also dose-dependently reduced the activity of nuclear factor activated T-cell cytoplasmic 1 (NFATc1). This study reveals the anti-osteoporotic effects of ingenane diterpenoids for the first time.

Epigenetic Regulation of Skeletal Tissue Integrity and Osteoporosis Development

Bone turnover is sophisticatedly balanced by a dynamic coupling of bone formation and resorption at various rates. The orchestration of this continuous remodeling of the skeleton further affects other skeletal tissues through organ crosstalk. Chronic excessive bone resorption compromises bone mass and its porous microstructure as well as proper biomechanics. This accelerates the development of osteoporotic disorders, a leading cause of skeletal degeneration-associated disability and premature death. Bone-forming cells play important roles in maintaining bone deposit and osteoclastic resorption. A poor organelle machinery, such as mitochondrial dysfunction, endoplasmic reticulum stress, and defective autophagy, etc., dysregulates growth factor secretion, mineralization matrix production, or osteoclast-regulatory capacity in osteoblastic cells. A plethora of epigenetic pathways regulate bone formation, skeletal integrity, and the development of osteoporosis. MicroRNAs inhibit protein translation by binding the 3'-untranslated region of mRNAs or promote translation through post-transcriptional pathways. DNA methylation and post-translational modification of histones alter the chromatin structure, hindering histone enrichment in promoter regions. MicroRNA-processing enzymes and DNA as well as histone modification enzymes catalyze these modifying reactions. Gain and loss of these epigenetic modifiers in bone-forming cells affect their epigenetic landscapes, influencing bone homeostasis, microarchitectural integrity, and osteoporotic changes. This article conveys productive insights into biological roles of DNA methylation, microRNA, and histone modification and highlights their interactions during skeletal development and bone loss under physiological and pathological conditions.

Genetics of Skeletal Disorders

Bone and mineral diseases encompass a variety of conditions that involve altered skeletal homeostasis and are frequently associated with changes in circulating calcium, phosphate, or vitamin D metabolites. These disorders often have a genetic etiology and comprise monogenic disorders caused by a single-gene mutation, which may be germline or somatic, or an oligogenic or polygenic condition involving multiple genetic variants. Single-gene mutations causing Mendelian diseases are usually highly penetrant, whereas the gene variants contributing to oligogenic or polygenic disorders are each associated with smaller effects with additional contributions from environmental factors. The detection of monogenic disorders is clinically important and facilitates timely assessment and management of the patient and their affected relatives. The diagnosis of monogenic metabolic bone disorders requires detailed clinical assessment of the wide variety of symptoms and signs associated with these diseases. Thus, clinicians should undertake a systematic approach commencing with careful history taking and physical examination, followed by appropriate laboratory and skeletal imaging investigations. Finally, clinicians should be familiar with the range of molecular genetic tests available to ensure their appropriate use and interpretation. These considerations are reviewed in this chapter.

Postmenopausal Osteoporosis reference genes for qPCR expression assays

Osteoporosis (OP) is a multifactorial disease influenced by genetic factors in more than half of the cases. In spite of the efforts to clarify the relationship among genetic factors and susceptibility to develop OP, many genetic associations need to be further functionally validated. Besides, some limitations as the choice of stably expressed reference genes (RG) should be overcome to ensure the quality and reproducibility of gene expression assays. To our knowledge, a validation study for RG in OP is still missing. We compared the expression levels, using polymerase chain reaction quantitative real time (qPCR) of 10 RG (G6PD, B2M, GUSB, HSP90, EF1A, RPLP0, GAPDH, ACTB, 18 S and HPRT1) to assess their suitability in OP analysis by using GeNorm, Normfinder, BestKeeper and RefFinder programs. A minimal number of two RG was recommended by GeNorm to obtain a reliable normalization. RPLP0 and B2M were identified as the most stable genes in OP studies while ACTB, 18 S and HPRT1 were inadequate for normalization in our data set. Moreover, we showed the dramatic effects of suboptimal RG choice on the quantification of a target gene, highlighting the importance in the identification of the most appropriate reference gene to specific diseases. We suggest the use of RPLP0 and B2M as the most stable reference genes while we do not recommend the use of the least stable reference genes HPRT1, 18 S and ACTB in OP expression assays using PBMC as biological source. Additionally, we emphasize the importance of individualized and careful choice in software and reference genes selection.

[An optimized method for embedding undecalcified mouse tibias in plastic blocks]

OBJECTIVE

To optimize the method for embedding multiple undecalcified mouse tibias in plastic blocks, improve the efficiency and stability of plastic embedding and reduce the detachment rate of plastic slides.

METHODS

Thirty undecalcified tibias from 15 B6 mice were used for plastic embedding after calcein labeling, fixation, dehydration and infiltration. The tibias were embedded in cylindrical plastic blocks with a diameter of 4 mm. For each bone, the 1/4 proximal tibia was cut off, and the remaining 3/4 was used for re-embedding. Five bones were embedded in a single block with each bone standing closely on the surface of a flat plate. The samples were randomized into control and experimental groups in all the processes of embedding, sectioning and staining. In the 3 groups with modified embedment, flowing CO2 was added into the embedding solution, embedding solution was applied to the section surface, and the slides were heated at 95 ℃ for 15 min. The polymerization time, slide detachment rate, bone formation and osteoblast parameters were analyzed.

RESULTS

We prepared 6 plastic blocks, each containing 5 tibias, whose cross sections were on the same plane. The blocks were completely polymerized and suitable for sectioning. Flowing CO2 into the embedding solution reduced the polymerization time and increased the rate of complete polymerization. Application of the embedding solution on the section surface significantly reduced the detachment rate of the sections (P < 0.05) without affecting bone formation analysis (P > 0.05). Heating the slides significantly lowered the detachment rate of the sections (P < 0.05) without affecting osteoblast analysis (P > 0.05).

CONCLUSIONS

The optimized method allows effective embedding of multiple undecalcified mice tibias in the same block and can be an ideal method for histological analysis of undecalcified bones.

WNT3A accelerates delayed alveolar bone repair in ovariectomized mice

Our goal was to evaluate alveolar bone healing in OVX mice, and to assess the functional utility of a WNT-based treatment to accelerate healing in mice with an osteoporotic-like bony phenotype.

INTRODUCTION

Is osteoporosis a risk factor for dental procedures? This relatively simple question is exceedingly difficult to answer in a clinical setting, for two reasons. First, as an age-related disease, osteoporosis is frequently accompanied by age-related co-morbidities that can contribute to slower tissue repair. Second, the intervals at which alveolar bone repair are assessed in a clinical study are often measured in months to years. This study aimed to evaluate alveolar bone repair in ovariectomized (OVX) mice and provide preclinical evidence to support a WNT-based treatment to accelerate alveolar bone formation.

METHODS

OVX was performed in young mice to produce an osteoporotic-like bone phenotype. Thereafter, the rate of extraction socket healing and osteotomy repair was assessed. A liposomal WNT3A treatment was tested for its ability to promote alveolar bone formation in this OVX-induced model of bone loss.

RESULTS

Bone loss was observed throughout the murine skeleton, including the maxilla, and mirrored the pattern of bone loss observed in aged mice. Injuries to the alveolar bone, including tooth extraction and osteotomy site preparation, both healed significantly slower than the same injuries produced in young controls. Given sufficient time, however, all injuries eventually healed. In OVX mice, osteotomies healed significantly faster if they were treated with L-WNT3A.

CONCLUSIONS

Alveolar bone injuries heal slower in OVX mice that exhibit an osteoporotic-like phenotype. The rate of alveolar bone repair in OVX mice can be significantly promoted with local delivery of L-WNT3A.

The Biomechanical Effect of the Sagittal Split Ramus Osteotomy on the Temporomandibular Joint: Current Perspectives on the Remodeling Spectrum

The sagittal split ramus osteotomy is a key approach for treating dentofacial deformities. Although it delivers excellent results, the sagittal split ramus osteotomy is believed to induce stress to the temporomandibular joint. Potential stress inducers could be classified as intra- and postoperative factors resulting in an inflammatory response and molecular cascades, which initiate physiological remodeling. Occasionally, this process exceeds its capacity and causes pathological remodeling, through either degenerative joint disease or condylar resorption. Hard evidence on how orthognathic surgery causes inflammation and how this inflammation is linked to the spectrum of remodeling remains scarce. Current concepts on this matter are mainly based on clinical observations and molecular mechanisms are extrapolated from fundamental research in other body parts or joints. This perspective study provides an overview of current knowledge on molecular pathways and biomechanical effects in temporomandibular joint remodeling. It provides research directions that could lead to acquiring fundamental evidence of the relation of orthognathic surgery and inflammation and its role in remodeling. Performing osteotomies in animal models and identifying inflammatory mediators as well as their effect on the joint seem promising. Patients affected by pathological remodeling can also provide samples for histological as well as molecular analysis. Individual susceptibility analysis by linking certain suspect phenotypes to genetic variation could identify the cause and molecular pathway responsible for degenerative joint disease and condylar resorption, ultimately leading to clinically applicable treatment and prevention strategies.

Mechanical Competence and Bone Quality Develop During Skeletal Growth

Bone fracture risk is influenced by bone quality, which encompasses bone's composition as well as its multiscale organization and architecture. Aging and disease deteriorate bone quality, leading to reduced mechanical properties and higher fracture incidence. Largely unexplored is how bone quality and mechanical competence progress during longitudinal bone growth. Human femoral cortical bone was acquired from fetal (n = 1), infantile (n = 3), and 2- to 14-year-old cases (n = 4) at the mid-diaphysis. Bone quality was assessed in terms of bone structure, osteocyte characteristics, mineralization, and collagen orientation. The mechanical properties were investigated by measuring tensile deformation at multiple length scales via synchrotron X-ray diffraction. We find dramatic differences in mechanical resistance with age. Specifically, cortical bone in 2- to 14-year-old cases exhibits a 160% greater stiffness and 83% higher strength than fetal/infantile cases. The higher mechanical resistance of the 2- to 14-year-old cases is associated with advantageous bone quality, specifically higher bone volume fraction, better micronscale organization (woven versus lamellar), and higher mean mineralization compared with fetal/infantile cases. Our study reveals that bone quality is superior after remodeling/modeling processes convert the primary woven bone structure to lamellar bone. In this cohort of female children, the microstructural differences at the femoral diaphysis were apparent between the 1- to 2-year-old cases. Indeed, the lamellar bone in 2- to 14-year-old cases had a superior structural organization (collagen and osteocyte characteristics) and composition for resisting deformation and fracture than fetal/infantile bone. Mechanistically, the changes in bone quality during longitudinal bone growth lead to higher fracture resistance because collagen fibrils are better aligned to resist tensile forces, while elevated mean mineralization reinforces the collagen scaffold. Thus, our results reveal inherent weaknesses of the fetal/infantile skeleton signifying its inferior bone quality. These results have implications for pediatric fracture risk, as bone produced at ossification centers during children's longitudinal bone growth could display similarly weak points. © 2019 American Society for Bone and Mineral Research.

Identification of pleiotropic genetic variants affecting osteoporosis risk in a Korean elderly cohort

Pleiotropy has important implications for understanding the genetic basis and risk assessment of osteoporosis. Our aim was to identify pleiotropic genetic variants associated with the development of osteoporosis and predict osteoporosis risk by leveraging pleiotropic variants. We evaluated the effects of 21 conventional risk factors and 185 single-nucleotide polymorphisms (SNPs) in 63 inflammation- and metabolism-related genes on osteoporosis risk in a community-based Korean cohort study of 1025 participants, the Hallym Aging Study. Ten nongenetic factors, including sex (female) and hematocrit level, and 12 SNPs across ten genes showed evidence of association with incident osteoporosis in 270 initially osteoporosis-free subjects who completed a 6-year follow up. Three gene variants, rs1801282 (PPARG-Pro12Ala, hazard ratio (HR) = 3.26, P = 0.008), rs1408282 (near EPHA7, HR = 1.87, P = 0.002), and rs2076212 (PNPLA3-Gly115Cys, HR = 2.24, P = 0.024), were associated with significant differences in survival among the three genotype groups (P_diff = 0.042, 0.003, and 0.048, respectively). Individuals in the highest polygenic risk score tertile were 27.9 fold more likely to develop osteoporosis than those in the lowest tertile (P = 0.004). The PPARG gene in particular was a hub pleiotropic gene in the epistasis network. Our findings highlight pleiotropic modulations of metabolism- and inflammation-related genes in the development of osteoporosis and demonstrate the contribution of pleiotropic genetic variants in prediction of osteoporosis risk.

WNT Signaling in Cancer Immunosurveillance

Deregulated WNT signaling has been shown to favor malignant transformation, tumor progression, and resistance to conventional cancer therapy in a variety of preclinical and clinical settings. Accumulating evidence suggests that aberrant WNT signaling may also subvert cancer immunosurveillance, hence promoting immunoevasion and resistance to multiple immunotherapeutics, including immune checkpoint blockers. Here, we discuss the molecular and cellular mechanisms through which WNT signaling influences cancer immunosurveillance and present potential therapeutic avenues to harness currently available WNT modulators for cancer immunotherapy.

Genetic approaches to metabolic bone diseases

Metabolic bone diseases comprise a diverse group of disorders characterized by alterations in skeletal homeostasis, and are often associated with abnormal circulating concentrations of calcium, phosphate or vitamin D metabolites. These diseases commonly have a genetic basis and represent either a monogenic disorder due to a germline or somatic single gene mutation, or an oligogenic or polygenic disorder that involves variants in more than one gene. Germline single gene mutations causing Mendelian diseases typically have a high penetrance, whereas the genetic variations causing oligogenic or polygenic disorders are each associated with smaller effects with additional contributions from environmental factors. Recognition of familial monogenic disorders is of clinical importance to facilitate timely investigations and management of the patient and any affected relatives. The diagnosis of monogenic metabolic bone disease requires careful clinical evaluation of the large diversity of symptoms and signs associated with these disorders. Thus, the clinician must pursue a systematic approach beginning with a detailed history and physical examination, followed by appropriate laboratory and skeletal imaging evaluations. Finally, the clinician must understand the increasing number and complexity of molecular genetic tests available to ensure their appropriate use and interpretation.

Impaired Wnt Signaling in the Prefrontal Cortex of Alzheimer's Disease

Wnt pathway is involved in synaptic plasticity and neuronal survival, and alterations in Wnt signaling have previously been reported both in aging and neurodegenerative diseases, including Alzheimer's disease (AD). This study sought to evaluate Wnt signaling pathway interplay integrity across prefrontal lobe structures in AD patients compared to normal aging. Using the open-access BrainCloud™ database, 84 gene expression profiles and clustering effect were analyzed in the dorsomedial prefrontal cortex (PFC) across a time span of 21-78 years of age. Next, expression levels of the selected genes were investigated in post-mortem brain tissue from 30 AD patients and 30 age-matched controls in three interdependent brain areas of the PFC. Results were assessed in relation to Braak stage and cognitive impairment of the patients. We found a general age-related factor in Wnt pathway genes with a group of genes being closely interrelated in their expression across the time span investigated in healthy individuals. This interrelation was altered in the AD brains studied, as several genes presented aberrant transcription, even though not always being altered at protein levels. Noteworthy, beta(β)-catenin and glycogen synthase kinase 3-beta (GSK3β) showed a dynamic switch in protein levels and activity, especially in the orbitofrontal cortex and the medial frontal gyrus. A significant decrease in β-catenin protein levels were inversely associated with increased GSK3β tyrosine activating phosphorylation, in addition to downstream effects associated with disease progression and cognitive decline. This study is the first that comprehensively evaluates Wnt signaling pathway in the prefrontal cortical lobe structures of AD brains, in relation to age-related coordinated Wnt signaling changes. Our findings further support that increased kinase activity of GSK3β is associated with AD pathology in the PFC.

Spina bifida-predisposing heterozygous mutations in Planar Cell Polarity genes and Zic2 reduce bone mass in young mice

Fractures are a common comorbidity in children with the neural tube defect (NTD) spina bifida. Mutations in the Wnt/planar cell polarity (PCP) pathway contribute to NTDs in humans and mice, but whether this pathway independently determines bone mass is poorly understood. Here, we first confirmed that core Wnt/PCP components are expressed in osteoblasts and osteoclasts in vitro. In vivo, we performed detailed µCT comparisons of bone structure in tibiae from young male mice heterozygous for NTD-associated mutations versus WT littermates. PCP signalling disruption caused by Vangl2 (Vangl2Lp/+) or Celsr1 (Celsr1Crsh/+) mutations significantly reduced trabecular bone mass and distal tibial cortical thickness. NTD-associated mutations in non-PCP transcription factors were also investigated. Pax3 mutation (Pax3Sp2H/+) had minimal effects on bone mass. Zic2 mutation (Zic2Ku/+) significantly altered the position of the tibia/fibula junction and diminished cortical bone in the proximal tibia. Beyond these genes, we bioinformatically documented the known extent of shared genetic networks between NTDs and bone properties. 46 genes involved in neural tube closure are annotated with bone-related ontologies. These findings document shared genetic networks between spina bifida risk and bone structure, including PCP components and Zic2. Genetic variants which predispose to spina bifida may therefore independently diminish bone mass.

Regulation of Bone Metabolism by microRNAs

PURPOSE OF REVIEW

The small non-coding microRNAs (miRNAs) have emerged as important post-transcriptional regulators of various physiological and pathological processes. The purpose of this article is to review the important recent advances on the role of miRNAs in bone remodeling and metabolic bone disorders.

RECENT FINDINGS

In a physiological context, miRNAs regulate bone formation and bone resorption, thereby contributing to the maintenance of bone homeostasis. Under pathological conditions, an aberrant miRNA signaling contributes to the onset and progression of skeletal disorders, such as osteoporosis. Furthermore, miRNAs can be secreted to circulation and have clinical potential as non-invasive biomarkers. In a therapeutic setting, miRNA delivery or antagonism has been reported to affect several diseases under pre-clinical conditions thereby emerging as novel pharmacological tools. miRNAs are key regulators of bone remodeling in health and disease. The future perspectives in the field include the role of secreted miRNAs in cell-cell communication in the bone environment. Furthermore, the clinical potential of using miRNAs as diagnostic tools and therapeutic targets to treat metabolic bone diseases provides an attractive future direction.

Exercise and bone health across the lifespan

With ageing, bone tissue undergoes significant compositional, architectural and metabolic alterations potentially leading to osteoporosis. Osteoporosis is the most prevalent bone disorder, which is characterised by progressive bone weakening and an increased risk of fragility fractures. Although this metabolic disease is conventionally associated with ageing and menopause, the predisposing factors are thought to be established during childhood and adolescence. In light of this, exercise interventions implemented during maturation are likely to be highly beneficial as part of a long-term strategy to maximise peak bone mass and hence delay the onset of age- or menopause-related osteoporosis. This notion is supported by data on exercise interventions implemented during childhood and adolescence, which confirmed that weight-bearing activity, particularly if undertaken during peripubertal development, is capable of generating a significant osteogenic response leading to bone anabolism. Recent work on human ageing and epigenetics suggests that undertaking exercise after the fourth decade of life is still important, given the anti-ageing effect and health benefits provided, potentially occurring via a delay in telomere shortening and modification of DNA methylation patterns associated with ageing. Exercise is among the primary modifiable factors capable of influencing bone health by preserving bone mass and strength, preventing the death of bone cells and anti-ageing action provided.

Epigenetics and Bone Remodeling

PURPOSE OF REVIEW

Bone remodeling is a diverse field of study with many direct clinical applications; past studies have implicated epigenetic alterations as key factors of both normal bone tissue development and function and diseases of pathologic bone remodeling. The purpose of this article is to review the most important recent advances that link epigenetic changes to the bone remodeling field.

RECENT FINDINGS

Epigenetics describes three major phenomena: DNA modification via methylation, histone side chain modifications, and short non-coding RNA sequences which work in concert to regulate gene transcription in a heritable fashion. Recent findings include the role of DNA methylation changes of Wnt, RANK/RANKL, and other key signaling pathways, epigenetic regulation of osteoblast and osteoclast differentiation, and others. Although much work has been done, much is still unknown. Future epigenome-wide studies should focus on extending the tissue coverage, integrating multiple epigenetic analyses with transcriptome data, and working to uncover epigenetic changes linked with early events in aberrant bone remodeling.

Dishevelled2 promotes apoptosis and inhibits inflammatory cytokine secretion in rheumatoid arthritis fibroblast-like synoviocytes through crosstalk with the NF-κB pathway

Dishevelled (Dvl) not only links the canonical Wnt and non-canonical Wnt pathways but can also crosstalk with other pathways. As there is no systematic study to date on Dvl in rheumatoid arthritis (RA), we explored the impact of Dvl2 on proliferation and inflammatory cytokine secretion in RA fibroblast-like synoviocytes (FLSs). Expression of Dvl2 in RA synovial tissue and RA-FLSs was measured. Dvl2 was overexpressed in collagen-induced arthritis rats and human RA-FLSs,. the apoptosis and secretion of inflammatory cytokines were observed. Genetic changes and corresponding mechanisms caused by overexpressing Dvl2 in RA-FLSs were assessed. Dvl2 was found to be overexpressed in RA synovial tissue and RA-FLSs. Overexpression of Dvl2 increased apoptosis and inhibited inflammatory cytokine secretion by RA-FLSs in vivo and in vitro, and Dvl2 inhibited expression of anti-apoptotic and inflammatory genes. One possible mechanism is that Dvl2 decreases the nuclear translocation of P65 and inhibits its ability to bind to the promoters of NF-κB target genes. Our findings reveal an underappreciated role of Dvl2 in regulating inflammation and RA-FLS apoptosis and provide insight into crosstalk between the Wnt and nuclear factor-κB (NF-κB) pathways.

Skeletal Site-specific Changes in Bone Mass in a Genetic Mouse Model for Human 15q11-13 Duplication Seen in Autism

Children suffering from autism have been reported to have low bone mineral density and increased risk for fracture, yet the cellular origin of the bone phenotype remains unknown. Here we have utilized a mouse model of autism that duplicates 6.3 Mb region of chromosome 7 (Dp/+) corresponding to a region of chromosome 15q11-13, duplication of which is recurrent in humans to characterize the bone phenotype. Paternally inherited Dp/+ (patDp/+) mice showed expected increases in the gene expression in bone, normal postnatal growth and body weight acquisition compared to the littermate controls. Four weeks-old patDp/+ mice develop a low bone mass phenotype in the appendicular but not the axial skeleton compared to the littermate controls. This low bone mass in the mutant mice was secondary to a decrease in the number of osteoblasts and bone formation rate while the osteoclasts remained relatively unaffected. Further in vitro cell culture experiments and gene expression analysis revealed a major defect in the proliferation, differentiation and mineralization abilities of patDp/+ osteoblasts while osteoclast differentiation remained unchanged compared to controls. This study therefore characterizes the structural and cellular bone phenotype in a mouse model of autism that can be further utilized to investigate therapeutic avenues to treat bone fractures in children with autism.

Gene-Hormone Therapy Interaction and Fracture Risk in Postmenopausal Women

CONTEXT

Evidence supports a protective effect of menopausal hormone therapy (HT) on bone. However, whether genetic susceptibility modifies the association of HT and fracture risk is not sufficiently explored.

OBJECTIVE

The objective was to test an interaction between genetic susceptibility and HT on fracture risk.

DESIGN

We constructed two weighted genetic risk scores (GRSs) based on 16 fracture-associated variants (Fx-GRSs) and 50 bone mineral density variants (BMD-GRSs). We used Cox regression to estimate the main effects of GRSs and their interactions with HT on fracture risk. We estimated the relative excess risk due to interaction (RERI) as a measure of additive interaction. We also used the case-only approach to test for a multiplicative interaction.

SETTING

Forty US clinical centers.

PARTICIPANTS

A total of 9922 genotyped white postmenopausal women (age, 50 to 79) from the Women's Health Initiative HT randomized trials.

MAIN OUTCOME MEASURES

Adjudicated fracture incidence.

RESULTS

Both GRSs were associated with fracture risk per 1-unit increment in GRS (hazard ratio, 1.04 [95% confidence interval, 1.02 to 1.06] for Fx-GRS and hazard ratio, 1.03 [95% confidence interval,1.02-1.04] for BMD-GRS). We found no evidence for multiplicative interaction for either of the GRS. However, we observed a substantial additive interaction, where the highest quartile of both GRSs and randomization to placebo have excess fracture risk: Fx-GRS P for RERI = 0.047, BMD-GRS P for RERI = 0.046.

CONCLUSIONS

These results suggest that HT reduces fracture risk in postmenopausal women, especially in those at highest genetic risk of fracture and low BMD.

Osteoporosis and Periodontitis

Osteoporosis and periodontitis are both diseases characterized by bone resorption. Osteoporosis features systemic degenerative bone loss that leads to loss of skeletal cancellous microstructure and subsequent fracture, whereas periodontitis involves local inflammatory bone loss, following an infectious breach of the alveolar cortical bone, and it may result in tooth loss. Most cross-sectional studies have confirmed the association of osteoporosis and periodontitis primarily on radiographic measurements and to a lesser degree on clinical parameters. Multiple shared risk factors include age, genetics, hormonal change, smoking, as well as calcium and vitamin D deficiency. Both diseases could also be risk factors for each other and have a mutual impact that requires concomitant management. Suggested mechanisms underlying the linkage are disruption of the homeostasis concerning bone remodeling, hormonal balance, and inflammation resolution. A mutual interventional approach is emerging with complex treatment interactions. Prevention and management of both diseases require interdisciplinary approaches and warrants future well-controlled longitudinal and interventional studies for evidence-based clinical guidelines.

Bioavailable 25(OH)D but Not Total 25(OH)D Is an Independent Determinant for Bone Mineral Density in Chinese Postmenopausal Women

Total 25(OH)D levels were determined to assess bone health in elderly populations; however, the bioavailability of 25(OH)D is regulated by the albumin and vitamin D binding protein (DBP) levels and DBP variations. Whether bioavailable 25(OH)D level is a superior biomarker for vitamin D than total 25(OH)D level regarding the BMD and the bone metabolism were not yet fully understood. With a community based cross-sectional study of 967 postmenopausal women, we found that the variant rs7041, but not rs4588, of DBP was significantly associated with the blood DBP level, which was positively correlated with the total 25(OH)D level but negatively associated with bioavailable 25(OH)D levels. Both total and bioavailable 25(OH)D levels were significantly correlated with the BMD value in postmenopausal women; however, only the bioavailable 25(OH)D level was an independent determinant of the BMD values when adjusted for age, body mass index and bone turnover biomarkers (OST and β-CTX). The bioavailable and total 25(OH)D were negatively correlated with bone formation biomarkers (OST, PINP and ALP) and PTH levels, while they were positively correlated with osteoprotegerin (OPG) level; however, the bone resorption biomarker (β-CTX) was not correlated with the 25(OH)D levels. An increment of PTH level, along with reduced bioavailable 25(OH)D levels, was evident when the bioavailable 25(OH)D level was < 5 ng/mL, which may be the optimal cutpoint for sufficient vitamin D in Chinese elderly women. The blood calcium, magnesium, ALP, TSH, FGF23, and phosphorus levels were not correlated with the total or the bioavailable 25(OH)D levels. These results suggested that high bioavailable 25(OH)D levels were correlated with reduced bone turnover processes and were a biomarker superior to total 25(OH)D for vitamin D in assessing the risks of bone-related diseases. The results indicate that the bioavailable 25(OH)D level should be determined in assessing the bone health.

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DBP levels and variants on DBP were associated with the total and bioavailable 25(OH)D levels in the elderly populations.

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Both the total and bioavailable 25(OH)D levels were correlated with the BMD in postmenopausal women.

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Multivariate analyses suggested that the bioavailable but not total 25(OH)D was an independent determinant for the BMD.

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Higher bioavailable 25(OH)D levels were correlated with reduced bone turnover and lower PTH in postmenopausal women.

With a cross-sectional community study, we found that the variant rs7041, but not rs4588, of DBP was significantly associated with the blood DBP level, which was positively correlated with the total 25(OH)D levels but negatively associated with the bioavailable 25(OH)D levels. The bioavailable 25(OH)D level was an independent determinant for BMD but not total 25(OH)D. Higher vitamin D levels were correlated with the reduced bone turnover process and lower PTH levels, which might lead to the higher BMD value in postmenopausal women. These results suggested that bioavailable 25(OH)D was a superior biomarker than total 25(OH)D regarding the bone metabolism, and that vitamin D intervention may improve the bone health in elderly populations.

A systems approach to renal inflammation in SLE

Lupus disease and its complications including lupus nephritis (LN) are very disabling and significantly impact the quality of life and longevity of patients. Broadly immunosuppressive treatments do not always provide the expected clinical benefits and have significant side effects that contribute to patient morbidity. In the era of systems biology, new strategies are being deployed integrating diverse sources of information (molecular and clinical) so as to identify individual disease specificities and select less aggressive treatments. In this review, we summarize integrative approaches linking molecular disease profiles (mainly tissue transcriptomics) and clinical phenotypes. The main goals are to better understand the pathogenesis of lupus nephritis, to identify the risk factors for renal flare and to find the predictors of both short and long-term clinical outcome. Identification of common key drivers and additional patient-specific key drivers can open the door to improved and individualized therapy to prevent and treat LN.

Osteoporosis: The Result of an 'Aged' Bone Microenvironment

Osteoporosis is an age-related progressive bone disease. Recent advances in epigenetics, cell biology, osteoimmunology, and genetic epidemiology have unraveled new mechanisms and players underlying the pathology of osteoporosis, supporting a model of age-related dysregulation and crosstalk in the bone microenvironment.

Regulation of local bone remodeling mediated by hybrid multilayer coating embedded with hyaluronan-alendronate/BMP-2 nanoparticles on Ti6Al7Nb implants

Hyaluronate-alendronate/BMP-2 nanoparticles were inserted into Gel/Chi multilayers on Ti6Al7Nb for enhancing BMP-2 stability and promoting local osteogenesis under osteoporosis.