Microarray gene expression profiling of osteoarthritic bone suggests altered bone remodelling, WNT and transforming growth factor-beta/bone morphogenic protein signalling

PDZK1 protects against mechanical overload-induced chondrocyte senescence and osteoarthritis by targeting mitochondrial function

Mechanical overloading and aging are two essential factors for osteoarthritis (OA) development. Mitochondria have been identified as a mechano-transducer situated between extracellular mechanical signals and chondrocyte biology, but their roles and the associated mechanisms in mechanical stress-associated chondrocyte senescence and OA have not been elucidated. Herein, we found that PDZ domain containing 1 (PDZK1), one of the PDZ proteins, which belongs to the Na+/H+ Exchanger (NHE) regulatory factor family, is a key factor in biomechanically induced mitochondrial dysfunction and chondrocyte senescence during OA progression. PDZK1 is reduced by mechanical overload, and is diminished in the articular cartilage of OA patients, aged mice and OA mice. Pdzk1 knockout in chondrocytes exacerbates mechanical overload-induced cartilage degeneration, whereas intraarticular injection of adeno-associated virus-expressing PDZK1 had a therapeutic effect. Moreover, PDZK1 loss impaired chondrocyte mitochondrial function with accumulated damaged mitochondria, decreased mitochondrion DNA (mtDNA) content and increased reactive oxygen species (ROS) production. PDZK1 supplementation or mitoubiquinone (MitoQ) application alleviated chondrocyte senescence and cartilage degeneration and significantly protected chondrocyte mitochondrial functions. MRNA sequencing in articular cartilage from Pdzk1 knockout mice and controls showed that PDZK1 deficiency in chondrocytes interfered with mitochondrial function through inhibiting Hmgcs2 by increasing its ubiquitination. Our results suggested that PDZK1 deficiency plays a crucial role in mediating excessive mechanical load-induced chondrocyte senescence and is associated with mitochondrial dysfunction. PDZK1 overexpression or preservation of mitochondrial functions by MitoQ might present a new therapeutic approach for mechanical overload-induced OA.

Wnt/β-catenin signaling components and mechanisms in bone formation, homeostasis, and disease

Wnts are secreted, lipid-modified proteins that bind to different receptors on the cell surface to activate canonical or non-canonical Wnt signaling pathways, which control various biological processes throughout embryonic development and adult life. Aberrant Wnt signaling pathway underlies a wide range of human disease pathogeneses. In this review, we provide an update of Wnt/β-catenin signaling components and mechanisms in bone formation, homeostasis, and diseases. The Wnt proteins, receptors, activators, inhibitors, and the crosstalk of Wnt signaling pathways with other signaling pathways are summarized and discussed. We mainly review Wnt signaling functions in bone formation, homeostasis, and related diseases, and summarize mouse models carrying genetic modifications of Wnt signaling components. Moreover, the therapeutic strategies for treating bone diseases by targeting Wnt signaling, including the extracellular molecules, cytosol components, and nuclear components of Wnt signaling are reviewed. In summary, this paper reviews our current understanding of the mechanisms by which Wnt signaling regulates bone formation, homeostasis, and the efforts targeting Wnt signaling for treating bone diseases. Finally, the paper evaluates the important questions in Wnt signaling to be further explored based on the progress of new biological analytical technologies.

siRNA therapy in osteoarthritis: targeting cellular pathways for advanced treatment approaches

Osteoarthritis (OA) is a common joint disorder characterized by the degeneration of cartilage and inflammation, affecting millions worldwide. The disease's complex pathogenesis involves various cell types, such as chondrocytes, synovial cells, osteoblasts, and immune cells, contributing to the intricate interplay of factors leading to tissue degradation and pain. RNA interference (RNAi) therapy, particularly through the use of small interfering RNA (siRNA), emerges as a promising avenue for OA treatment due to its capacity for specific gene silencing. siRNA molecules can modulate post-transcriptional gene expression, targeting key pathways involved in cellular proliferation, apoptosis, senescence, autophagy, biomolecule secretion, inflammation, and bone remodeling. This review delves into the mechanisms by which siRNA targets various cell populations within the OA milieu, offering a comprehensive overview of the potential therapeutic benefits and challenges in clinical application. By summarizing the current advancements in siRNA delivery systems and therapeutic targets, we provide a solid theoretical foundation for the future development of novel siRNA-based strategies for OA diagnosis and treatment, paving the way for innovative and more effective approaches to managing this debilitating disease.

Three decades of advancements in osteoarthritis research: insights from transcriptomic, proteomic, and metabolomic studies

OBJECTIVE

Osteoarthritis (OA) is a complex disease involving contributions from both local joint tissues and systemic sources. Patient characteristics, encompassing sociodemographic and clinical variables, are intricately linked with OA rendering its understanding challenging. Technological advancements have allowed for a comprehensive analysis of transcripts, proteomes and metabolomes in OA tissues/fluids through omic analyses. The objective of this review is to highlight the advancements achieved by omic studies in enhancing our understanding of OA pathogenesis over the last three decades.

DESIGN

We conducted an extensive literature search focusing on transcriptomics, proteomics and metabolomics within the context of OA. Specifically, we explore how these technologies have identified individual transcripts, proteins, and metabolites, as well as distinctive endotype signatures from various body tissues or fluids of OA patients, including insights at the single-cell level, to advance our understanding of this highly complex disease.

RESULTS

Omic studies reveal the description of numerous individual molecules and molecular patterns within OA-associated tissues and fluids. This includes the identification of specific cell (sub)types and associated pathways that contribute to disease mechanisms. However, there remains a necessity to further advance these technologies to delineate the spatial organization of cellular subtypes and molecular patterns within OA-afflicted tissues.

CONCLUSIONS

Leveraging a multi-omics approach that integrates datasets from diverse molecular detection technologies, combined with patients' clinical and sociodemographic features, and molecular and regulatory networks, holds promise for identifying unique patient endophenotypes. This holistic approach can illuminate the heterogeneity among OA patients and, in turn, facilitate the development of tailored therapeutic interventions.

Osteoporosis and osteoarthritis: a bi-directional Mendelian randomization study

OBJECTIVE

To investigate the causal relationship between low bone mineral density (BMD) and osteoarthritis (OA) using Mendelian randomization (MR) design.

METHODS

Two-sample bi-directional MR analyses were performed using summary-level information on OA traits from UK Biobank and arcOGEN. Sensitivity analyses including MR-Egger, simple median, weighted median, MR pleiotropy residual sum, and outlier approaches were utilized in conjunction with inverse variance weighting (IVW). Gene ontology (GO) enrichment analyses and expression quantitative trait locus (eQTL) colocalization analyses were used to investigate the potential mechanism and shared genes between osteoporosis (OP) and OA.

RESULTS

The IVW method revealed that genetically predicted low femoral neck BMD was significantly linked with hip (β = 0.105, 95% CI: 0.023-0.188) and knee OA (β = 0.117, 95% CI: 0.049-0.184), but not with other site-specific OA. Genetically predicted low lumber spine BMD was significantly associated with OA at any sites (β = 0.048, 95% CI: 0.011-0.085), knee OA (β = 0.101, 95% CI: 0.045-0.156), and hip OA (β = 0.150, 95% CI: 0.077-0.224). Only hip OA was significantly linked with genetically predicted reduced total bone BMD (β = 0.092, 95% CI: 0.010-0.174). In the reverse MR analyses, no evidence for a causal effect of OA on BMD was found. GO enrichment analysis and eQTL analysis illustrated that DDN and SMAD-3 were the most prominent co-located genes.

CONCLUSIONS

These findings suggested that OP may be causally linked to an increased risk of OA, indicating that measures to raise BMD may be effective in preventing OA. More research is required to determine the underlying processes via which OP causes OA.

Molecular mechanism of a novel root-end filling material containing zirconium oxide on the osteogenic/odontogenic differentiation of human osteosarcoma MG-63 cells

Although the novel root-end filling material containing zirconium oxide (NRFM-Zr) which is hydroxyapatite-based may promote osteoblast differentiation, the molecular mechanism remains unclear. The aim of this study is to investigate it underlying the osteogenic/odontogenic differentiation of human osteosarcoma MG-63 cells induced by NRFM-Zr, compared with calcium silicate-based mineral trioxide aggregate (MTA), and glass ionomer cement (GIC). Firstly, three different types of root filling materials were co-cultured with MG-63 cells, and their cell toxicity, alkaline phosphatase (ALP) activity, and calcium ion concentration were evaluated. Next, gene expression profiling microarray was employed to analyze the impact of the materials on the gene expression profile of MG-63 cells. The results of cell viability revealed that NRFM-Zr group had no significant difference compared to the negative control group. After 5 and 7 days of cultivation, both the NRFM-Zr and MTA groups exhibited significantly higher ALP activity compared to the negative control (p < 0.05). Moreover, the NRFM-Zr group had the highest calcium ion concentration, while the GIC group was the lowest (p < 0.05). Gene expression profiling microarray analysis identified 2915 (NRFM-Zr), 2254 (MTA) and 392 (GIC) differentially expressed genes, respectively. GO functional and KEGG pathway analysis revealed that differentially expressed genes of NRFM-Zr, MTA and GIC participated in 8, 6 and 0 differentiation-related pathways, respectively. Comparing the molecular mechanisms of osteogenic/odontogenic differentiation induced by hydroxyapatite-based NRFM-Zr and calcium silicate-based MTA, it was found that they shared similarities in their molecular mechanisms of promoting osteogenic differentiation. NRFM-Zr primarily promotes differentiation and inhibits cell apoptosis, thereby enhancing osteogenic/odontogenic differentiation of MG-63 cells. Furthermore, the inducing efficacy of NRFM-Zr was found to be superior to MTA.

CC-Chemokine Receptor-2 Expression in Osteoblasts Contributes to Cartilage and Bone Damage during Post-Traumatic Osteoarthritis

In osteoarthritis (OA), bone changes are radiological hallmarks and are considered important for disease progression. The C-C chemokine receptor-2 (CCR2) has been shown to play an important role in bone physiology. In this study, we investigated whether Ccr2 osteoblast-specific inactivation at different times during post-traumatic OA (PTOA) progression improves joint structures, bone parameters, and pain. We used a tamoxifen-inducible Ccr2 inactivation in Collagen1α-expressing cells to obtain osteoblasts lacking Ccr2 (CCR2-Col1αKO). We stimulated PTOA changes in CCR2-Col1αKO and CCR2+/+ mice using the destabilization of the meniscus model (DMM), inducing recombination before or after DMM (early- vs. late-inactivation). Joint damage was evaluated at two, four, eight, and twelve weeks post-DMM using multiple scores: articular-cartilage structure (ACS), Safranin-O, histomorphometry, osteophyte size/maturity, subchondral bone thickness and synovial hyperplasia. Spontaneous and evoked pain were assessed for up to 20 weeks. We found that early osteoblast-Ccr2 inactivation delayed articular cartilage damage and matrix degeneration compared to CCR2+/+, as well as DMM-induced bone thickness. Osteophyte formation and maturation were only minimally affected. Late Collagen1α-Ccr2 deletion led to less evident improvements. Osteoblast-Ccr2 deletion also improved static measures of pain, while evoked pain did not change. Our study demonstrates that Ccr2 expression in osteoblasts contributes to PTOA disease progression and pain by affecting both cartilage and bone tissues.

Transcriptomic changes in porcine articular cartilage one year following disruption of the anterior cruciate ligament

To determine the transcriptomic changes seen in early- to mid-stage posttraumatic osteoarthritis (PTOA) development, 72 Yucatan minipigs underwent transection of the anterior cruciate ligament. Subjects were randomized to no further intervention, ligament reconstruction, or ligament repair, followed by articular cartilage harvesting and RNA-sequencing at three different postoperative timepoints (1, 4, and 52 weeks). Six additional subjects received no ligament transection and provided cartilage tissue to serve as controls. Differential gene expression analysis between post-transection cartilage and healthy cartilage revealed an initial increase in transcriptomic differences at 1 and 4 weeks followed by a stark reduction in transcriptomic differences at 52 weeks. This analysis also showed how different treatments genetically modulate the course of PTOA following ligament disruption. Specific genes (e.g., MMP1, POSTN, IGF1, PTGFR, HK1) were identified as being upregulated in the cartilage of injured subjects across all timepoints regardless of treatment. At the 52-week timepoint, 4 genes (e.g., A4GALT, EFS, NPTXR, ABCA3) that-as far as we know-have yet to be associated with PTOA were identified as being concordantly differentially expressed across all treatment groups when compared to controls. Functional pathway analysis of injured subject cartilage compared to control cartilage revealed overarching patterns of cellular proliferation at 1 week, angiogenesis, ECM interaction, focal adhesion, and cellular migration at 4 weeks, and calcium signaling, immune system activation, GABA signaling, and HIF-1 signaling at 52 weeks.

Expression and diagnostic significance of integrin beta-2 in synovial fluid of patients with osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is characterized by synovial cartilage degeneration and is the leading cause of disability and pain worldwide. This study sought to investigate the expression of integrin beta-2 (ITGB2) in synovial fluid of OA patients and its clinical significance.

METHODS

A total of 110 OA patients were enrolled, who were classified into grade I (N = 35), II (N = 42), and III (N = 33) according to the Kellgren-Lawrence classification, with 110 healthy subjects as controls, and their clinical data were compared. ITGB2 level was detected by RT-qPCR. The receiver operating characteristic curve was used to analyze the predictive value of ITGB2 on OA occurrence. The correlation between ITGB2 and bone metabolism indexes procollagen type I N-terminal peptide (PINP), bone glaprotein (BGP), bone alkaline phosphatase (BALP), and β-collagen I telopeptide (β-CTX) was analyzed by the Pearson method. Logistic regression model was performed to analyze the influencing factors of OA.

RESULTS

The content of red blood cells, white blood cells, PINP, BGP, and BALP was lowered in OA patients, while β-CTX was elevated. ITGB2 was highly-expressed in OA patients, negatively-correlated with PINP, BGP, and BALP, but positively-correlated with β-CTX. ITGB2 level increased with the elevation of OA grade. The ITGB2 level >1.375 had certain diagnostic values for OA. ITGB2 level is related to OA severity and may be a biomarker for OA classification. ITGB2 was an independent risk factor for OA.

CONCLUSION

High expression of ITGB2 in synovial fluid can assist OA diagnosis and may be a biomarker for OA grade.

Re-thinking osteoarthritis pathogenesis: what can we learn (and what do we need to unlearn) from mouse models about the mechanisms involved in disease development

Efforts to develop effective disease-modifying drugs to treat osteoarthritis have so far proved unsuccessful with a number of promising drug candidates from pre-clinical studies failing to show efficacy in clinical trials. It is therefore timely to re-evaluate our current understanding of osteoarthritis pathogenesis and the similarities and differences in disease development between commonly used pre-clinical mouse models and human patients. There is substantial heterogeneity between patients presenting with osteoarthritis and mounting evidence that the pathways involved in osteoarthritis (e.g. Wnt signalling) differ between patient sub-groups. There is also emerging evidence that the pathways involved in osteoarthritis differ between the STR/ort mouse model (the most extensively studied mouse model of spontaneously occurring osteoarthritis) and injury-induced osteoarthritis mouse models. For instance, while canonical Wnt signalling is upregulated in the synovium and cartilage at an early stage of disease in injury-induced osteoarthritis mouse models, this does not appear to be the case in the STR/ort mouse. Such findings may prove insightful for understanding the heterogeneity in mechanisms involved in osteoarthritis pathogenesis in human disease. However, it is important to recognise that there are differences between mice and humans in osteoarthritis pathogenesis. A much more extensive array of pathological changes are evident in osteoarthritic joints in individual mice with osteoarthritis compared to individual patients. There are also specified differences in the pathways involved in disease development. For instance, although increased TGF-β signalling is implicated in osteoarthritis development in both mouse models of osteoarthritis and human disease, in mice, this is mainly mediated through TGF-β3 whereas in humans, it is through TGF-β1. Studies in other tissues have shown TGF-β1 is more potent than TGF-β3 in inducing the switch to SMAD1/5 signalling that occurs in osteoarthritic cartilage and that TGF-β1 and TGF-β3 have opposing effects on fibrosis. It is therefore possible that the relative contribution of TGF-β signalling to joint pathology in osteoarthritis differs between murine models and humans. Understanding the similarities and differences in osteoarthritis pathogenesis between mouse models and humans is critical for understanding the translational potential of findings from pre-clinical studies.

Conditioned serum in vitro treatment of chondrocyte pellets and osteoarthritic explants

BACKGROUND

Autologous conditioned serum (ACS) is used to treat osteoarthritis in horses, although its effects are not fully investigated.

OBJECTIVES

To investigate the effects of equine serum and conditioned serum on chondrocytes stimulated with interleukin (IL)-1β and cartilage explants with mild osteoarthritis.

STUDY DESIGN

In vitro experimental study.

METHODS

The effect of three different serum preparations (unincubated control [PS], serum incubated 24 h [PS24h] and serum incubated 24 h in ACS containers [PCS]) pooled from lame horses were tested in two in vitro models. IL-1β and IL-1 receptor antagonist (IL-1Ra) concentrations were measured in all sera. In model 1, chondrocyte pellet cultures were stimulated with IL-1β prior to treatment with the serum preparations for 2 and 48 h. Microarray, polymerase chain reaction, and matrix metallopeptidase-13 analyses were performed. In model 2, cartilage explants from horses with structural osteoarthritis were treated with PS or PCS on days 0, 6 and 12, or left untreated, and evaluated at day 24 using the OARSI grading scale for histological evaluation of articular cartilage.

RESULTS

The IL-1Ra concentration in PS24h and PCS was significantly higher than in PS. In model 1, inflammation- and cartilage matrix degradation-related genes were upregulated after 48 h in all treatment groups versus untreated controls. Cartilage matrix molecules, aggrecan and collagens, were downregulated in PS24h- and PCS-treated pellets versus untreated controls. Growth factor signalling genes were upregulated-FGF7 in all treatment groups, BMP2 in PS24h-, and INHBA in PCS-treated-compared with untreated controls. In model 2, the OARSI score at day 24 was not significantly different between treatment groups.

MAIN LIMITATIONS

Results from in vitro models cannot be directly translated to in vivo situations.

CONCLUSIONS

In vitro treatment with conditioned serum did not alleviate IL-1β-induced responses in chondrocyte pellets or lead to morphological improvement in osteoarthritic cartilage explants.

Latest insights in disease-modifying osteoarthritis drugs development

Osteoarthritis (OA) is a prevalent and severely debilitating disease with an unmet medical need. In order to alleviate OA symptoms or prevent structural progression of OA, new drugs, particularly disease-modifying osteoarthritis drugs (DMOADs), are required. Several drugs have been reported to attenuate cartilage loss or reduce subchondral bone lesions in OA and thus potentially be DMOADs. Most biologics (including interleukin-1 (IL-1) and tumor necrosis factor (TNF) inhibitors), sprifermin, and bisphosphonates failed to yield satisfactory results when treating OA. OA clinical heterogeneity is one of the primary reasons for the failure of these clinical trials, which can require different therapeutic approaches based on different phenotypes. This review describes the latest insights into the development of DMOADs. We summarize in this review the efficacy and safety profiles of various DMOADs targeting cartilage, synovitis, and subchondral bone endotypes in phase 2 and 3 clinical trials. To conclude, we summarize the reasons for clinical trial failures in OA and suggest possible solutions.

At the Crux of Joint Crosstalk: TGFβ Signaling in the Synovial Joint

PURPOSE OF REVIEW

The effect of the transforming growth factor beta (TGFβ) signaling pathway on joint homeostasis is tissue-specific, non-linear, and context-dependent, representing a unique complexity in targeting TGFβ signaling in joint disease. Here we discuss the variety of mechanisms that TGFβ signaling employs in the synovial joint to maintain healthy joint crosstalk and the ways in which aberrant TGFβ signaling can result in joint degeneration.

RECENT FINDINGS

Osteoarthritis (OA) epitomizes a condition of disordered joint crosstalk in which multiple joint tissues degenerate leading to overall joint deterioration. Synovial joint tissues, such as subchondral bone, articular cartilage, and synovium, as well as mesenchymal stem cells, each demonstrate aberrant TGFβ signaling during joint disease, whether by excessive or suppressed signaling, imbalance of canonical and non-canonical signaling, a perturbed mechanical microenvironment, or a distorted response to TGFβ signaling during aging. The synovial joint relies upon a sophisticated alliance among each joint tissue to maintain joint homeostasis. The TGFβ signaling pathway is a key regulator of the health of individual joint tissues, and the subsequent interaction among these different joint tissues, also known as joint crosstalk. Dissecting the sophisticated function of TGFβ signaling in the synovial joint is key to therapeutically interrogating the pathway to optimize overall joint health.

Repurposed and investigational disease-modifying drugs in osteoarthritis (DMOADs)

In spite of a major public health burden with increasing prevalence, current osteoarthritis (OA) management is largely palliative with an unmet need for effective treatment. Both industry and academic researchers have invested a vast amount of time and financial expense to discover the first diseasing-modifying osteoarthritis drugs (DMOADs), with no regulatory success so far. In this narrative review, we discuss repurposed drugs as well as investigational agents which have progressed into phase II and III clinical trials based on three principal endotypes: bone-driven, synovitis-driven and cartilage-driven. Then, we will briefly describe the recent failures and lessons learned, promising findings from predefined post hoc analyses and insights gained, novel methodologies to enhance future success and steps underway to overcome regulatory hurdles.

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

The Wnt pathway is involved in several processes essential for bone development and homeostasis. For proper functioning, the Wnt pathway is tightly regulated by numerous extracellular elements that act by both activating and inhibiting the pathway at different moments. This review aims to describe, summarize and update the findings regarding the extracellular modulators of the Wnt pathway, including co-receptors, ligands and inhibitors, in relation to bone homeostasis, with an emphasis on the animal models generated, the diseases associated with each gene and the bone processes in which each member is involved. The precise knowledge of all these elements will help us to identify possible targets that can be used as a therapeutic target for the treatment of bone diseases such as osteoporosis.

Perspective of the GEMSTONE Consortium on Current and Future Approaches to Functional Validation for Skeletal Genetic Disease Using Cellular, Molecular and Animal-Modeling Techniques

The availability of large human datasets for genome-wide association studies (GWAS) and the advancement of sequencing technologies have boosted the identification of genetic variants in complex and rare diseases in the skeletal field. Yet, interpreting results from human association studies remains a challenge. To bridge the gap between genetic association and causality, a systematic functional investigation is necessary. Multiple unknowns exist for putative causal genes, including cellular localization of the molecular function. Intermediate traits ("endophenotypes"), e.g. molecular quantitative trait loci (molQTLs), are needed to identify mechanisms of underlying associations. Furthermore, index variants often reside in non-coding regions of the genome, therefore challenging for interpretation. Knowledge of non-coding variance (e.g. ncRNAs), repetitive sequences, and regulatory interactions between enhancers and their target genes is central for understanding causal genes in skeletal conditions. Animal models with deep skeletal phenotyping and cell culture models have already facilitated fine mapping of some association signals, elucidated gene mechanisms, and revealed disease-relevant biology. However, to accelerate research towards bridging the current gap between association and causality in skeletal diseases, alternative in vivo platforms need to be used and developed in parallel with the current -omics and traditional in vivo resources. Therefore, we argue that as a field we need to establish resource-sharing standards to collectively address complex research questions. These standards will promote data integration from various -omics technologies and functional dissection of human complex traits. In this mission statement, we review the current available resources and as a group propose a consensus to facilitate resource sharing using existing and future resources. Such coordination efforts will maximize the acquisition of knowledge from different approaches and thus reduce redundancy and duplication of resources. These measures will help to understand the pathogenesis of osteoporosis and other skeletal diseases towards defining new and more efficient therapeutic targets.

Study TPX-100-5: intra-articular TPX-100 significantly delays pathological bone shape change and stabilizes cartilage in moderate to severe bilateral knee OA

Background

TPX-100, a promotor of osteoblast and chondroblast differentiation, is a potential osteoarthritis (OA) therapy. This retrospective study compared MRI 3D femoral bone shape changes (B-scores) after intra-articular TPX-100 or placebo and analyzed the relationship between cartilage thickness and bone shape change over 12 months.

Methods

One hundred and four participants with bilateral moderate to severe knee cartilage defects were randomized to receive TPX-100 (200 mg) or placebo. Each subject’s contralateral placebo-treated knee served as a paired internal control. After MRI quality control, 78/93 subjects (84%; 156 knees) were analyzed for quantitative femoral B-score and cartilage thickness. All analyses were performed centrally, blind to treatment assignment and clinical data.

Results

TPX-100-treated knees (n = 78) demonstrated a statistically significant decrease in pathologic bone shape change compared with placebo-treated knees at 6 and 12 months: 0.0298 (95% C.I. − 0.037, 0.097) vs 0.1246 (95% C.I. 0.067, 0.182) (P = 0.02), and 0.0856 (95% C.I. 0.013, 0.158) vs. 0.1969 (95% C.I. 0.123, 0.271) (P = 0.01), respectively. The correlation between bone shape change and medial and total tibiofemoral cartilage thickness changes at 12 months was statistically significant in TPX-100-treated knees (P < 0.01).

Conclusions

This is the first report of a potential therapy demonstrating a significant effect on bone shape measured by B-score in knee OA. These data, in combination with previously reported statistically significant and clinically meaningful improvements in WOMAC physical function versus placebo, support TPX-100 as a candidate for disease modification in knee OA.

Trial registration

NIH ClinicalTrials.gov, NCT01925261. Registered 15 August 2013

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02622-8.

Hypertension meets osteoarthritis - revisiting the vascular aetiology hypothesis

Osteoarthritis (OA) is a whole-joint disease characterized by subchondral bone perfusion abnormalities and neovascular invasion into the synovium and articular cartilage. In addition to local vascular disturbance, mounting evidence suggests a pivotal role for systemic vascular pathology in the aetiology of OA. This Review outlines the current understanding of the close relationship between high blood pressure (hypertension) and OA at the crossroads of epidemiology and molecular biology. As one of the most common comorbidities in patients with OA, hypertension can disrupt joint homeostasis both biophysically and biochemically. High blood pressure can increase intraosseous pressure and cause hypoxia, which in turn triggers subchondral bone and osteochondral junction remodelling. Furthermore, systemic activation of the renin-angiotensin and endothelin systems can affect the Wnt-β-catenin signalling pathway locally to govern joint disease. The intimate relationship between hypertension and OA indicates that endothelium-targeted strategies, including re-purposed FDA-approved antihypertensive drugs, could be useful in the treatment of OA.

Evaluation of the cargo contents and potential role of extracellular vesicles in osteoporosis

Osteoporosis is a common aging-related disease diagnosed primarily using bone mineral density (BMD). Extracellular vesicles (EVs) remain unexplored in the context of osteoporosis. Towards this, EVs were isolated from plasma of a discovery cohort with 8 non-osteoporotic and 8 osteoporotic individuals, and nanoparticle tracking analysis (NTA) revealed a significantly higher EV concentration in osteoporotic individuals (P = 0.003). Moreover, EVs concentration showed a linear correlation with bone mineral density (BMD) values (linear correlation coefficient r = 0.9542, deviation from zero, p < 0.001). Results using a mouse model of osteoporosis confirmed that the number of EVs in mice from hindlimb unloading group was significantly higher than that from the age-matched control group (p = 0.015). TaqMan Real-Time PCR demonstrated that miR-335-5p, -320a, -483-5p, and miR-21-5p, were significantly higher expressed in osteoporotic patients compared with non-osteoporotic individuals. Quantitative real-time PCR shown that Wnt1, Wnt5a, Wnt7a, and Wnt9a mRNAs were lower expressed in osteoporosis derived EVs. In vitro functional assay indicated that osteoporosis derived EVs resulted in reduced mineralization in SaOS-2 cells. In conclusion, these results suggest that osteoporosis increased the secretion of EVs which carry higher expression of miRNAs and decreased expression of Wnt signals, further decreased the mineralization capacity in human osteoblasts.

The Development of Disease-Modifying Therapies for Osteoarthritis (DMOADs): The Evidence to Date

Osteoarthritis (OA) is a complex heterogeneous articular disease with multiple joint tissue involvement of varying severity and no regulatory-agency-approved disease-modifying drugs (DMOADs). In this review, we discuss the reasons necessitating the development of DMOADs for OA management, the classifications of clinical phenotypes or molecular/mechanistic endotypes from the viewpoint of targeted drug discovery, and then summarize the efficacy and safety profile of a range of targeted drugs in Phase 2 and 3 clinical trials directed to cartilage-driven, bone-driven, and inflammation-driven endotypes. Finally, we briefly put forward the reasons for failures in OA clinical trials and possible steps to overcome these barriers.

The hidden secrets of soluble RANKL in bone biology

The discovery of cytokine tumor necrosis factor (TNF) in the 20th century revealed numerous secrets about organ development. In particular, the functions identified for the receptor activator of nuclear factor kappa-β (NF-κβ) ligand (also known as the RANKL/osteoprotegerin ligand (OPGL) or RANK ligand/TNFSF11) in the homeostasis of skeletal structure, function and regulation were not anticipated. Empirical evidence established the receptor-ligand interaction of RANKL with RANK in osteoclast formation. Reverse signaling of RANKL triggers NF-κβ for the degradation of β-catenin to inhibit bone formation. There is also evidence that RANKL modifies the behavior of other cells in the bone microenvironment, including osteoblasts, chondrocytes, endothelial cells and lymphocytes during normal (homeostatic) and diseased (osteoimmune) states. Two forms of RANKL, i.e., soluble and membrane-bound RANKL, are produced by bone cells. Even though soluble RANKL (sRANKL) and membrane-bound RANKL (mRANKL) both stimulate osteoclast formation in vitro, their biological roles are different. mRANKL triggers osteoclastogenesis by binding to RANK through cell-cell interaction; however, sRANKL released from osteogenic cells binds to RANK without cell-cell interaction. This review attempts to hypothesize how sRANKL functions biologically in bone and explore how this hypothesis might influence future research.

WNT5B in Physiology and Disease

WNT5B, a member of the WNT family of proteins that is closely related to WNT5A, is required for cell migration, cell proliferation, or cell differentiation in many cell types. WNT5B signals through the non-canonical β-catenin-independent signaling pathway and often functions as an antagonist of canonical WNT signaling. Although WNT5B has a high amino acid identity with WNT5A and is often assumed to have similar activities, WNT5B often exhibits unique expression patterns and functions. Here, we describe the distinct effects and mechanisms of WNT5B on development, bone, adipose tissue, cardiac tissue, the nervous system, the mammary gland, the lung and hematopoietic cells, compared to WNT5A. We also highlight aberrances in non-canonical WNT5B signaling contributing to diseases such as osteoarthritis, osteoporosis, obesity, type 2 diabetes mellitus, neuropathology, and chronic diseases associated with aging, as well as various cancers.

The association of transforming growth factor beta 1 gene polymorphisms with arthritis: a systematic review and meta-analysis

The objective of this study was to explore the association between transformation growth factor beta 1 (TGF-β1) gene polymorphisms and different types of arthritis. PubMed, Medline, Web of Science, Cochrane Library, Biosis and four Chinese databases: China Biology Medicine, China National Knowledge Infrastructure, Wanfang and CQVIP, were searched. Studies that analyzed the association of the TGF-β1 polymorphisms with different types of arthritis were included. OR, 95% confidence interval and P value were calculated in three models including allele, dominant and recessive models, using D + L method. The Newcastle-Ottawa Scale was used to assess the quality of the included studies. TGF-β1 869T > C polymorphism was significantly associated with rheumatoid arthritis (RA) in allele and recessive models, but not in dominant model (allele model T vs. C: OR = 1.30, 95% CI = 1.13-1.49, P < 0.001; recessive model CC vs. TT + TC: OR = 0.57, 95% CI = 0.43-0.76, P < 0.001; dominant model TT vs. TC + CC: OR = 1.20, 95% CI = 0.99-1.45, P = 0.063). Additionally, allele and recessive models showed that TGF-β1 -509C > T was significantly correlated with RA susceptibility, while dominant model revealed nonsignificant correlation (allele model: C vs. T: OR = 1.51; 95% CI = 1.00-2.28; P = 0.049; recessive model: TT vs. CC + TC: OR = 0.52, 95% CI = 0.37-0.72, P = 0.000; dominant model: CC vs. TT + TC: OR = 1.48; 95% CI = 0.79-2.76; P = 0.223). However, no significant association was found between TGF-β1 polymorphisms and ankylosing spondylitis (AS) or osteoarthritis (OA) risk. This study demonstrated that 869T > C, -509 C > T polymorphisms of TGF-β1 gene were associated with increased susceptibility of RA, while polymorphisms of TGF-β1 gene were not associated with OA and AS. These findings suggest that studying TGF-β1 genotype may be useful in the prevention and management of RA. However, more studies are needed to evaluate the association of TGF-β1 gene polymorphisms with the susceptibility of OA and AS.

The effect of age on the microarchitecture and profile of gene expression in femoral head and neck bone from patients with osteoarthritis

Ageing of the skeleton is characterised by decreased bone mineral density, reduced strength, and increased risk of fracture. Although it is known that these changes are determined by the activities of bone cells through the processes of bone modelling and remodelling, details of the molecular mechanisms that underlie age-related changes in bone are still missing. Here, we analysed age-related changes in bone microarchitecture along with global gene expression in samples obtained from patients with osteoarthritis (OA). We hypothesised that changes would be evident in both microarchitecture and gene expression and aimed to identify novel molecular mechanisms that underlie ageing processes in bone. Samples of femoral head and neck were obtained from patients undergoing hip arthroplasty for OA, who were either ≤60 years or ≥70 years of age. Bone microarchitecture was analysed in cores of trabecular bone from the femoral head (17 from the younger group and 18 from the older), and cortical bone from the femoral neck (25 younger/22 older), using a Skyscan 1172 microCT scanner (Bruker). Gene expression was compared between the two age groups in 20 trabecular samples from each group, and 10 cortical samples from each group, using Clariom S Human microarrays (ThermoFisher Scientific). We found no significant changes between the two age groups in indices of trabecular or cortical bone microarchitecture. Gene expression analysis identified seven genes that had higher expression in the older group, including the transcription factor EGR1 and the glucose transporter SLC2A3 (GLUT3), and 21 differentially expressed genes in cortical bone samples (P<0.05, fold change>2). However, none of the comparisons of gene expression had false discovery rate-adjusted P<0.1. In contrast to our working hypothesis, we found only minor differences in gene expression and no differences in bone microarchitecture between the two age-groups. It is possible that pathological processes related to OA provide protection against age-related changes in bone. Our study suggests that in patients with OA, the bone properties measured here in femoral head and neck do not deteriorate significantly from the sixth to the eighth decade of life.

Gene Expression and RNA Splicing Imputation Identifies Novel Candidate Genes Associated with Osteoporosis

CONTEXT

Though genome-wide association studies (GWASs) have identified hundreds of genetic variants associated with osteoporosis related traits, such as bone mineral density (BMD) and fracture, it remains a challenge to interpret their biological functions and underlying biological mechanisms.

OBJECTIVE

Integrate diverse expression quantitative trait loci and splicing quantitative trait loci data with several powerful GWAS datasets to identify novel candidate genes associated with osteoporosis.

DESIGN, SETTING, AND PARTICIPANTS

Here, we conducted a transcriptome-wide association study (TWAS) for total body BMD (TB-BMD) (n = 66 628 for discovery and 7697 for validation) and fracture (53 184 fracture cases and 373 611 controls for discovery and 37 857 cases and 227 116 controls for validation), respectively. We also conducted multi-SNP-based summarized mendelian randomization analysis to further validate our findings.

RESULTS

In total, we detected 88 genes significantly associated with TB-BMD or fracture through expression or ribonucleic acid splicing. Summarized mendelian randomization analysis revealed that 78 of the significant genes may have potential causal effects on TB-BMD or fracture in at least 1 specific tissue. Among them, 64 genes have been reported in previous GWASs or TWASs for osteoporosis, such as ING3, CPED1, and WNT16, as well as 14 novel genes, such as DBF4B, GRN, TMUB2, and UNC93B1.

CONCLUSIONS

Overall, our findings provide novel insights into the pathogenesis mechanisms of osteoporosis and highlight the power of a TWAS to identify and prioritize potential causal genes.

Knee osteoarthritis in young growing rats is associated with widespread osteopenia and impaired bone mineralization

Osteoarthritis (OA) leads to joint pain from intraarticular inflammation with articular cartilage erosion, deterioration of joint function and abnormal subchondral bone structure. Besides aging, chronic repetitive joint injury is a common risk factor in young individuals. Nevertheless, whether OA is associated with bone loss at other skeletal sites is unclear. Since OA-associated proinflammatory cytokines-some of which are osteoclastogenic factors-are often detected in the circulation, we hypothesized that the injury-induced knee OA could result in widespread osteopenia at bone sites distant to the injured knee. Here we performed anterior cruciate ligament transection (ACLT) to induce knee OA in one limb of female Sprague-Dawley rats and determined bone changes post-OA induction by micro-computed tomography and computer-assisted bone histomorphometry. We found that although OA modestly altered bone density, histomorphometric analyses revealed increases in bone resorption and osteoid production with impaired mineralization. The bone formation rate was also reduced in OA rats. In conclusions, ACLT in young growing rats induced microstructural defects in the trabecular portion of weight-bearing (tibia) and non-weight-bearing bones (L5 vertebra), in part by enhancing bone resorption and suppressing bone formation. This finding supports the increasing concern regarding the repetitive sport-related ACL injuries and the consequent bone loss.

Arthritis and the role of endogenous glucocorticoids

Rheumatoid arthritis and osteoarthritis, the most common forms of arthritis, are chronic, painful, and disabling conditions. Although both diseases differ in etiology, they manifest in progressive joint destruction characterized by pathological changes in the articular cartilage, bone, and synovium. While the potent anti-inflammatory properties of therapeutic (i.e., exogenous) glucocorticoids have been heavily researched and are widely used in clinical practice, the role of endogenous glucocorticoids in arthritis susceptibility and disease progression remains poorly understood. Current evidence from mouse models suggests that local endogenous glucocorticoid signaling is upregulated by the pro-inflammatory microenvironment in rheumatoid arthritis and by aging-related mechanisms in osteoarthritis. Furthermore, these models indicate that endogenous glucocorticoid signaling in macrophages, mast cells, and chondrocytes has anti-inflammatory effects, while signaling in fibroblast-like synoviocytes, myocytes, osteoblasts, and osteocytes has pro-inflammatory actions in rheumatoid arthritis. Conversely, in osteoarthritis, endogenous glucocorticoid signaling in both osteoblasts and chondrocytes has destructive actions. Together these studies provide insights into the role of endogenous glucocorticoids in the pathogenesis of both inflammatory and degenerative joint disease.

The Function of Wnt Ligands on Osteocyte and Bone Remodeling

Bone homeostasis is continually maintained by the process of bone remodeling throughout life. Recent studies have demonstrated that Wnt signaling pathways play a fundamental role in the process of bone homeostasis and remodeling. Intracellular Wnt signaling cascades are initially triggered by a Wnt ligand-receptor complex formation. In previous studies, the blocking of Wnt ligands from different osteoblastic differentiation stages could cause defective bone development at an early stage. Osteocytes, the most abundant and long-lived type of bone cell, are a crucial orchestrator of bone remodeling. However, the role of Wnt ligands on osteocyte and bone remodeling remains unclear. In our present study, we found that, besides osteoblasts, osteocytes also express multiple Wnt ligands in the bone environment. Then, we used a Dmp1-Cre mouse line, in which there is expression in a subset of osteoblasts but mainly osteocytes, to study the function of Wnt ligands on osteocyte and bone remodeling in vivo. Furthermore, we explored the role of Wnt ligands on osteocytic mineralization ability, as well as the regulatory function of osteocytes on the process of osteoblastic differentiation and osteoclastic migration and maturity in vitro. We concluded that Wnt proteins play an important regulatory role in 1) the process of perilacunar/canalicular remodeling, as mediated by osteocytes, and 2) the balance of osteogenesis and bone resorption at the bone surface, as mediated by osteoblasts and osteoclasts, at least partly through the canonical Wnt/β-catenin signaling pathway and the OPG/RANKL signaling pathway.

Alterations in DNA methylation profiles in cancellous bone of postmenopausal women with osteoporosis

Osteoporosis is characterized by systemic microarchitecture impairment and bone loss, which ultimately lead to fragility fractures. This disease is most common in older people, especially in postmenopausal women. Cancellous bone is affected by osteoporosis earlier than cortical bone, and DNA methylation microarray analysis of the hip cancellous bone of patients with osteoarthritis revealed differential methylation. In view of the important role of cancellous bone in bone development, we examined genome‐wide DNA methylation profiles in the cancellous bone from patients with postmenopausal osteoporosis versus healthy postmenopausal women using Illumina 850K methylation microarray analysis. Under a threshold of P < 0.05, we obtained a total of 8973 differentially methylated genes, such as SOX6, ACE, SYK and TGFB3. Under a threshold of P < 0.05 and |△β| > 0.2, a total of 17 and 34 key differentially methylated genes were further identified at the promoter region and cytosine‐ phosphate‐ guanine (CpG) islands (such as PRKCZ, GNA11 and COL4A1), respectively. PLEKHA2, PLEKHB1, PNPLA7, SCD, MGST3 and TSNAX were the most common differentially methylated genes at both the promoter region and CpG islands. Five important signaling pathways, including the calcium signaling pathway, the cyclic guanosine phospho‐protein kinase G (cGMP‐PKG) signaling pathway, endocytosis, the Rap1 signaling pathway and the AMPK signaling pathway were identified. Our study may be suitable as a basis for exploring the mechanisms underlying osteoporosis in postmenopausal women.

Integration of transcriptome-wide association study and messenger RNA expression profile to identify genes associated with osteoarthritis

Aims

Osteoarthritis (OA) is the most prevalent joint disease. However, the specific and definitive genetic mechanisms of OA are still unclear.

Methods

Tissue-related transcriptome-wide association studies (TWAS) of hip OA and knee OA were performed utilizing the genome-wide association study (GWAS) data of hip OA and knee OA (including 2,396 hospital-diagnosed hip OA patients versus 9,593 controls, and 4,462 hospital-diagnosed knee OA patients versus 17,885 controls) and gene expression reference to skeletal muscle and blood. The OA-associated genes identified by TWAS were further compared with the differentially expressed genes detected by the messenger RNA (mRNA) expression profiles of hip OA and knee OA. Functional enrichment and annotation analysis of identified genes was performed by the DAVID and FUMAGWAS tools.

Results

We detected 33 common genes, eight common gene ontology (GO) terms, and one common pathway for hip OA, such as calcium and integrin-binding protein 1 (CIB1) (P_TWAS = 0.025, FC_mRNA = -1.575 for skeletal muscle), adrenomedullin (ADM) (P_TWAS = 0.022, FC_mRNA = -4.644 for blood), Golgi apparatus (P_TWAS <0.001, P_mRNA = 0.012 for blood), and phosphatidylinositol 3' -kinase-protein kinase B (PI3K-Akt) signalling pathway (P_TWAS = 0.033, P_mRNA = 0.005 for blood). For knee OA, we detected 24 common genes, eight common GO terms, and two common pathways, such as histocompatibility complex, class II, DR beta 1 (HLA-DRB1) (P_TWAS = 0.040, FC_mRNA = 4.062 for skeletal muscle), Follistatin-like 1 (FSTL1) (P_TWAS = 0.048, FC_mRNA = 3.000 for blood), cytoplasm (P_TWAS < 0.001, P_mRNA = 0.005 for blood), and complement and coagulation cascades (P_TWAS = 0.017, P_mRNA = 0.001 for skeletal muscle).

Conclusion

We identified a group of OA-associated genes and pathways, providing novel clues for understanding the genetic mechanism of OA.

Cite this article:Bone Joint Res. 2020;9(3):130–138.

Mechanobiological Mechanisms of Load-Induced Osteoarthritis in the Mouse Knee

Osteoarthritis (OA) is a degenerative joint disease that affects millions of people worldwide, yet its disease mechanism is not clearly understood. Animal models have been established to study disease progression by initiating OA through modified joint mechanics or altered biological activity within the joint. However, animal models often do not have the capability to directly relate the mechanical environment to joint damage. This review focuses on a novel in vivo approach based on controlled, cyclic tibial compression to induce OA in the mouse knee. First, we discuss the development of the load-induced OA model, its different loading configurations, and other techniques used by research laboratories around the world. Next, we review the lessons learned regarding the mechanobiological mechanisms of load-induced OA and relate these findings to the current understanding of the disease. Then, we discuss the role of specific genetic and cellular pathways involved in load-induced OA progression and the contribution of altered tissue properties to the joint response to mechanical loading. Finally, we propose using this approach to test the therapeutic efficacy of novel treatment strategies for OA. Ultimately, elucidating the mechanobiological mechanisms of load-induced OA will aid in developing targeted treatments for this disabling disease.

Proteomic and Transcriptomic Approaches for Studying Bone Regeneration in Health and Systemically Compromised Conditions

Bone regeneration is a complex biological process, where the molecular mechanisms are only partially understood. In an ageing population, where the prevalence of chronic diseases with an impact on bone metabolism is increasing, it becomes crucial to identify new strategies that would improve regenerative outcomes also in medically compromised patients. In this context, omics are demonstrating a great potential, as they offer new insights on the molecular mechanisms regulating physiologic/pathologic bone healing and, at the same time, allow the identification of new diagnostic and therapeutic targets. This review provides an overview on the current evidence on the use of transcriptomic and proteomic approaches in bone regeneration research, particularly in relation to type 1 diabetes and osteoporosis, and discusses future scenarios and potential benefits and limitations on the integration of multi-omics. It is suggested that future research will leverage the synergy of omics with statistical modeling and bioinformatics to prompt the understanding of the biology underpinning bone formation in health and medically compromised conditions. With an eye toward personalized medicine, new strategies combining the mining of large datasets and bioinformatic data with a detailed characterization of relevant phenotypes will need to be pursued to further the understanding of disease mechanisms.

Osteocyte dysfunction promotes osteoarthritis through MMP13-dependent suppression of subchondral bone homeostasis

Osteoarthritis (OA), long considered a primary disorder of articular cartilage, is commonly associated with subchondral bone sclerosis. However, the cellular mechanisms responsible for changes to subchondral bone in OA, and the extent to which these changes are drivers of or a secondary reaction to cartilage degeneration, remain unclear. In knee joints from human patients with end-stage OA, we found evidence of profound defects in osteocyte function. Suppression of osteocyte perilacunar/canalicular remodeling (PLR) was most severe in the medial compartment of OA subchondral bone, with lower protease expression, diminished canalicular networks, and disorganized and hypermineralized extracellular matrix. As a step toward evaluating the causality of PLR suppression in OA, we ablated the PLR enzyme MMP13 in osteocytes while leaving chondrocytic MMP13 intact, using Cre recombinase driven by the 9.6-kb DMP1 promoter. Not only did osteocytic MMP13 deficiency suppress PLR in cortical and subchondral bone, but it also compromised cartilage. Even in the absence of injury, osteocytic MMP13 deficiency was sufficient to reduce cartilage proteoglycan content, change chondrocyte production of collagen II, aggrecan, and MMP13, and increase the incidence of cartilage lesions, consistent with early OA. Thus, in humans and mice, defects in PLR coincide with cartilage defects. Osteocyte-derived MMP13 emerges as a critical regulator of cartilage homeostasis, likely via its effects on PLR. Together, these findings implicate osteocytes in bone-cartilage crosstalk in the joint and suggest a causal role for suppressed perilacunar/canalicular remodeling in osteoarthritis.

Evaluation of the association between a single-nucleotide polymorphism of bone morphogenetic proteins 5 gene and risk of knee osteoarthritis

Background:

Osteoarthritis (OA) is a chronic degenerative disorder probably affected by both genetic and environmental causes. Bone morphogenetic proteins (BMPs) are bone-derived factors that can induce new bone formation. Single-nucleotide polymorphisms (SNPs) of BMP5 gene alters the transcriptional activity of the BMP5 promoter that has been involved in OA susceptibility. This case–control study investigated the association of rs1470527 and rs9382564 SNP of BMP5 gene with susceptibility to knee OA (KOA).

Materials and Methods:

A total of 499 cases with radiographic KOA and 458 age- and sex-matched healthy controls were enrolled. Venous blood samples were obtained from all the cases as well as controls for polymerase chain reaction-restriction fragment length polymorphism.

Results:

The genotype distribution for rs1470527 and rs9382564 SNP was significantly different in cases and controls (P < 0.0001). Within both the SNPs of BMP5 gene, genotype CT and TT were significantly (P < 0.0001) associated with KOA as compared to the CC genotype. T allele of both the studied SNP was significantly associated with KOA (P < 0.0001). The allele frequencies of rs1470527 were 0.56(T) and 0.44(C) in cases and 0.33(T) and 0.67(C) in controls and in rs9382564 were 0.57(C) and 0.43(T) in cases and 0.71(C) and 0.29(T) in controls. Further in relation with clinical severity of OA, we observed signification association of TT genotype with both visual analog scale (P < 0.0001) and Western Ontario and McMaster Universities score (P < 0.05).

Conclusion:

Our results indicate significant association of rs1470527 and rs9382564 polymorphism of BMP5 gene with KOA.

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.

Wnt and RUNX2 mediate cartilage breakdown by osteoarthritis synovial fibroblast-derived ADAMTS-7 and -12

Failure of therapeutic approaches for the treatment of osteoarthritis (OA) based on the inhibition of metalloproteinases, might be because of their constitutive expression in homeostasis, together with their network complexity. The knowledge of this network would contribute to selective target pathological conditions. In this sense, blockade of mediators produced by neighbouring joint cells, such as synovial fibroblasts (SF), would prevent cartilage damage. Thus, we studied the contribution of ADAMTS-7 and -12 from SF to cartilage oligomeric matrix protein (COMP) degradation, and the signalling pathways involved in their expression. We report for the first time in SF, the involvement of ERK-Runx2 axis and Wnt/β-catenin signalling in ADAMTS-12 and ADAMTS-7 expressions, respectively, with the subsequent consequences in COMP degradation from cartilage extracellular matrix. After stimulation with IL-1β or fibronectin fragments, we showed that ERK inhibition decreased Runx2 activation and ADAMTS-12 expression in OA-SF, also reducing Fn-fs-induced COMP degradation. Blockage of Wnt signalling by DKK1 reduced ADAMTS-7 and COMP degradation in OA-SF as well. In addition, Wnt7B expression was induced by IL-1β and by itself, also increasing ADAMTS-7. Our results could contribute to the development of disease-modifying OA drugs targeting ADAMTS-7 and -12 for the prevention of extracellular matrix components degradation like COMP.

The commercial pig as a model of spontaneously-occurring osteoarthritis

BACKGROUND

Preclinical osteoarthritis models where damage occurs spontaneously may better reflect the initiation and development of human osteoarthritis. The aim was to assess the commercial pig as a model of spontaneous osteoarthritis development by examining pain-associated behaviour, joint cartilage integrity, as well as the use of porcine cartilage explants and isolated chondrocytes and osteoblasts for ex vivo and in vitro studies.

METHODS

Female pigs (Large white x Landrace x Duroc) were examined at different ages from 6 weeks to 3-4 years old. Lameness was assessed as a marker of pain-associated behaviour. Femorotibial joint cartilage integrity was determined by chondropathy scoring and histological staining of proteoglycan. IL-6 production and proteoglycan degradation was assessed in cartilage explants and primary porcine chondrocytes by ELISA and DMMB assay. Primary porcine osteoblasts from damaged and non-damaged joints, as determined by chondropathy scoring, were assessed for mineralisation, proliferative and mitochondrial function as a marker of metabolic capacity.

RESULTS

Pigs aged 80 weeks and older exhibited lameness. Osteoarthritic lesions in femoral condyle and tibial plateau cartilage were apparent from 40 weeks and increased in severity with age up to 3-4 years old. Cartilage from damaged joints exhibited proteoglycan loss, which positively correlated with chondropathy score. Stimulation of porcine cartilage explants and primary chondrocytes with either IL-1β or visfatin induced IL-6 production and proteoglycan degradation. Primary porcine osteoblasts from damaged joints exhibited reduced proliferative, mineralisation, and metabolic capacity.

CONCLUSION

In conclusion, the commercial pig represents an alternative model of spontaneous osteoarthritis and an excellent source of tissue for in vitro and ex vivo studies.

Disease-modifying drugs in osteoarthritis: current understanding and future therapeutics

INTRODUCTION

Osteoarthritis (OA) is a leading cause of pain and disability among adults with a current prevalence of around 15% and a predicted prevalence of 35% in 2030 for symptomatic OA. It is increasingly recognized as a heterogeneous multi-faceted joint disease with multi-tissue involvement of varying severity. Current therapeutic regimens for OA are only partially effective and often have significant associated toxicities. There are no disease-modifying drugs approved by the regulatory bodies. Areas covered: We reviewed the opportunities within key OA pathogenetic mechanism: cartilage catabolism/anabolism, pathological remodeling of subchondral bone and synovial inflammation to identify targeted disease-modifying osteoarthritis drugs, based on compounds currently in Phase II and III stages of clinical development in which x-ray and/or MRI was used as the structural outcome with/without symptomatic outcomes according to regulatory requirements. Expert opinion: Given the heterogeneity of the OA disease process and complex overlapping among these phenotypes, a 'one size fits all' approach used in most clinical trials would unlikely be practical and equally effective in all patients, as well as in all anatomical OA sites. On the other hand, it is a challenge to develop a targeted drug with high activity, specificity, potency, and bioavailability in the absence of toxicity for long-term use in this chronic disease of predominantly older adults. Further research and insight into evaluation methods for drug-targeted identification of early OA and specific characterization of phenotypes, improvement of methodological designs, and development/refinement of sensitive imaging and biomarkers will help pave the way to the successful discovery of disease-modifying drugs and the optimal administration strategies in clinical practice.

Associations between the chemokine biomarker CCL2 and knee osteoarthritis outcomes: the Johnston County Osteoarthritis Project

OBJECTIVE

Our study analyzes the association between chemokine-ligand-2 (CCL2) serum concentrations at baseline and knee radiographic osteoarthritis (OA) (knee-rOA), knee-rOA progression, individual radiographic features and knee symptomatic OA at 5-year follow-up.

DESIGN

OA outcomes were analyzed in a community-based cohort including a baseline enrollment and a 5-year follow-up. Baseline CCL2 serum concentrations were assessed by multiplex assay and associated with presence or progression of individual radiographic features at 5-year follow-up. Separate multiple logistic regression models were used to examine adjusted associations between baseline CCL2 and each of the knee OA variables at follow-up. CCL2 at baseline was modeled as an explanatory variable, whereas each of the knee OA variables at follow-up served as the response variables. Models were adjusted for age, BMI, race, and sex. Trend tests were conducted to assess any linear effect on outcomes across CCL2 tertiles.

RESULTS

Participants (n = 168) had a median age of 57-years and median BMI of 29 kg/m2. About 63% of all participants were women, and 58% Caucasian (42% African American). In adjusted logistic models, continuous log-CCL2 was significantly associated with knee-rOA. For each unit increase in log CCL2, the odds of having knee-rOA at follow-up was increased by 72%. CCL2 tertiles showed significant linear associations with presence and progression of knee-rOA and medial joint space narrowing (JSN), but not with presence or progression of osteophytes, bone sclerosis, knee symptoms, or symptomatic knee-rOA.

CONCLUSIONS

Serum CCL2 may help to elucidate some mechanisms of joint destruction and identify individuals with higher odds of structural knee changes.

Bone marrow lesions in osteoarthritis: What lies beneath

Osteoarthritis (OA) is the most common joint disease in the United States, affecting more than 30 million people, and is characterized by cartilage degeneration in articulating joints. OA can be viewed as a group of overlapping disorders, which result in functional joint failure. However, the precise cellular and molecular events within which lead to these clinically observable changes are neither well understood nor easily measurable. It is now clear that multiple factors, in multiple joint tissues, contribute to degeneration. Changes in subchondral bone are recognized as a hallmark of OA, but are normally associated with late-stage disease when degeneration is well established. However, early changes such as Bone Marrow Lesions (BMLs) in OA are a relatively recent discovery. BMLs are patterns from magnetic resonance images (MRI) that have been linked with pain and cartilage degeneration. Their potential utility in predicting progression, or as a target for therapy, is not yet fully understood. Here, we will review the current state-of-the-art in this field under three broad headings: (i) BMLs in symptomatic OA: malalignment, joint pain, and disease progression; (ii) biological considerations for bone-cartilage crosstalk in joint disease; and (iii) mechanical factors that may underlie BMLs and drive their communication with other joint tissues. Thus, this review will provide insights on this topic from a clinical, biological, and mechanical perspective. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1818-1825, 2018.

High-fat diet disrupts bone remodeling by inducing local and systemic alterations

A high-fat (HF) diet leads to detrimental effects on alveolar bone (AB); however, the mechanisms linking adiposity to bone loss are poorly understood. This study investigated if AB resorption induced by an HF diet is associated with the regulation of inflammatory gene expression and if adipocytes can directly interfere with osteoclastogenesis. We also evaluated the effects of diet restriction (DR) on bone phenotype. C57BL6/J mice were fed normal chow or an HF diet for 12 weeks. Samples of maxillae, femur, blood and white adipose tissue were analyzed. In vitro co-culture of bone marrow-derived osteoclasts and mature adipocytes was carried out. The results revealed an increased number of osteoclasts and fewer osteoblasts in animals fed the HF diet, which led to the disruption of trabecular bone and horizontal AB loss. Similar effects were observed in the femur. The metabolic parameters and the deleterious effects of the HF diet on AB and the femur were reversed after DR. The HF diet modulated the expression of 30 inflammatory genes in AB such as Fam3c, InhBa, Tnfs11, Ackr2, Pxmp2 and Chil3, which are related to the inflammatory response and bone remodeling. In vitro, mature adipocytes produced increased levels of adipokines, and co-culture with osteoclasts resulted in augmented osteoclastogenesis. The results indicate that the mechanisms by which an HF diet affects bone involve induction of osteoclastogenesis and inflammatory gene expression. Adipokines apparently are key molecules in this process. Strategies to control diet-induced bone loss might be beneficial in patients with preexisting bone inflammatory conditions.

Combined bioinformatics analysis reveals gene expression and DNA methylation patterns in osteoarthritis

Osteoarthritis (OA) is a common type of arthritis, which may cause pain and disability. Alterations in gene expression and DNA methylation have been proven to be associated with the development of OA. The aim of the present study was to identify potential therapeutic targets and associated processes for OA via the combined analysis of gene expression and DNA methylation datasets. The gene expression and DNA methylation profiles were obtained from the Gene Expression Omnibus, and differentially expressed genes (DEGs) and differentially methylated sites (DMSs) were identified in the present study, using R programming software. The enriched functions of DEGs and DMSs were obtained via the Database for Annotation, Visualization and Integrated Discovery. Finally, cross analysis of DEGs and DMSs was performed to identify genes that exhibited differential expression and methylation simultaneously. The protein‑protein interaction (PPI) network of overlaps between DEGs and DMSs was obtained using the Human Protein Reference Database; the topological properties of PPI network overlaps were additionally obtained. Hub genes in the PPI network were further confirmed via reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). The results of the present study revealed that the majority of DEGs and DMSs were upregulated and hypomethylated in patients with OA, respectively. DEGs and DMSs were primarily involved in inflammatory, immune and gene expression regulation‑associated processes and pathways. Cross analysis revealed 30 genes that exhibited differential expression and methylation in OA simultaneously. Topological analysis of the PPI network revealed that numerous genes, including G protein subunit α1 (GNAI1), runt related transcription factor 2 (RUNX2) and integrin subunit β2 (ITGB2), may be involved in the development of OA. Additionally, RT‑qPCR analysis of GNAI1, RUNX2 and ITGB2 provided further confirmation. Numerous known and novel therapeutic targets were obtained via network analysis. The results of the present study may be beneficial for the diagnosis and treatment of OA.

Interleukin-6 from subchondral bone mesenchymal stem cells contributes to the pathological phenotypes of experimental osteoarthritis

As a main cause of morbidity in the aged population, osteoarthritis (OA) is characterized by cartilage destruction, synovium inflammation, osteophytes, and subchondral bone sclerosis. To date its etiology remains elusive. Recent data highlight an important role of subchondral bone in the onset and progression of OA. Therefore, elucidating the mechanisms underlying abnormal subchondral bone could be of importance in the treatment of OA. Interleukin-6 is a proinflammatory cytokine involved in many physiological and pathological processes. Although in vitro and in vivo studies have indicated that IL-6 is an important cytokine in the physiopathogenesis of OA, its effects on subchondral bone have not been studied in OA animal models. In this study, we aimed to i) investigate the role of IL-6 in the pathological phenotypes of OA subchondral bone MSCs including increase in cell numbers, mineralization disorder and abnormal type I collagen production; ii) explore whether the systemic blockade of IL-6 signaling could alleviate the pathological phenotypes of experimental OA. We found that IL-6 was over-secreted by OA subchondral bone MSCs compared with normal MSCs and IL-6/STAT3 signaling was over-activated in subchondral bone MSCs, which contributed to the pathological phenotypes of OA subchondral bone MSCs. More importantly, systemic inhibition of IL-6/STAT3 signaling with IL-6 antibody or STAT3 inhibitor AG490 decreased the severity of pathological phenotypes of OA subchondral bone MSCs and cartilage lesions in OA. Our findings provide strong evidence for a pivotal role for IL-6 signaling in OA and open up new therapeutic perspectives.

MicroRNA-214-5p/TGF-β/Smad2 signaling alters adipogenic differentiation of bone marrow stem cells in postmenopausal osteoporosis

Postmenopausal osteoporosis (OPM) is a common type of osteoporosis in females. It is a systemic, chronic bone disease that presents as microstructure degradation of osseous tissue, decreased bone mineral density and increased osteopsathyrosis caused by hypoovarianism and reduced estrogen levels in the body following menopause. In the present study, the role of microRNA (miR)-214-5p in the regulation of the expression of bone marrow stem cells (BMSCs) was investigated, and its molecular mechanism of osteogenic induction in vitro was assessed. When dexamethasone-induced adipogenic differentiation was performed, miR-214-5p expression was increased compared with the control group, as determined by RT-qPCR. Furthermore, oil red O staining, RT-qPCR and western blot analysis demonstrated that overexpression of miR-214-5p promoted adipogenic differentiation, inhibited alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), osteocalcin (OC) and collagen α-1 (I) chain (COL1A1) mRNA expression, and suppressed transforming growth factor (TGF)-β, phosphorylated (p)-Smad2 and collagen type IV α1 chain (COL4A1) protein expression in BMSCs. Additionally, downregulation of miR-214-5p increased the ALP, Runx2, OC and COL1 mRNA expression and increased TGF-β, Smad2 and COL4A1 protein expression in BMSCs. Furthermore, a TGF-β inhibitor was employed to inhibit TGF-β expression in BMSCs following miR-214-5p downregulation, which led to reduced Smad2, TGF-β and COL4A1 protein expression, and ALP, Runx2, OC and COL1 mRNA expression was also reduced, compared with the miR-214-5p downregulation only group. It was demonstrated that miR-214-5p may weaken osteogenic differentiation of BMSCs through regulating COL4A1. In conclusion, the results of the present study indicated that miR-214-5p may promote the adipogenic differentiation of BMSCs through regulation of the TGF-β/Smad2/COL4A1 signaling pathway, and potentially may be used to develop a novel drug for postmenopausal osteoporosis.