Inhibition of KDM7A/B histone demethylases restores H3K79 methylation and protects against osteoarthritis.

OBJECTIVES: In osteoarthritis, methylation of lysine 79 on histone H3 (H3K79me), a protective epigenetic mechanism, is reduced. Histone methylation levels are dynamically regulated by histone methyltransferases and demethylases. Here, we aimed to identify which histone demethylases regulate H3K79me in cartilage and investigate whether their targeting protects against osteoarthritis. METHODS: We determined histone demethylase expression in human non-osteoarthritis and osteoarthritis cartilage using qPCR. The role of histone demethylase families and subfamilies on H3K79me was interrogated by treatment of human C28/I2 chondrocytes with pharmacological inhibitors, followed by western blot and immunofluorescence. We performed C28/I2 micromasses to evaluate effects on glycosaminoglycans by Alcian blue staining. Changes in H3K79me after destabilisation of the medial meniscus (DMM) in mice were determined by immunohistochemistry. Daminozide, a KDM2/7 subfamily inhibitor, was intra-articularly injected in mice upon DMM. Histone demethylases targeted by daminozide were individually silenced in chondrocytes to dissect their role on H3K79me and osteoarthritis. RESULTS: We documented the expression signature of histone demethylases in human non-osteoarthritis and osteoarthritis articular cartilage. Inhibition of Jumonji-C demethylase family increased H3K79me in human chondrocytes. Blockade of KDM2/7 histone demethylases with daminozide increased H3K79me and glycosaminoglycans. In mouse articular cartilage, H3K79me decayed rapidly upon induction of joint injury. Early and sustained intra-articular treatment with daminozide enhanced H3K79me and exerted protective effects in mice upon DMM. Individual silencing of KDM7A/B demethylases in human chondrocytes demonstrated that KDM7A/B mediate protective effects of daminozide on H3K79me and osteoarthritis. CONCLUSION: Targeting KDM7A/B histone demethylases could be an attractive strategy to protect joints against osteoarthritis.

Fetal bovine serum-derived exosomes regulate the adipogenic differentiation of human bone marrow mesenchymal stromal cells in a cross-species manner.

Fetal bovine serum (FBS) contains a large number of exosomes which may disturb the analysis of exosomes derived from cultured cells. We investigated the effect of FBS-derived exosomes (FBS-Exos) on the adipogenic differentiation of human bone marrow mesenchymal stromal cells (hBM-MSCs) and the underlying molecular mechanism. The uptake of FBS-Exos by hBM-MSCs could be detected by the laser confocal microscopy, and the treatment of exosomes resulted in the decreased lipid droplet formation and reduced expression of genes associated with adipogenic differentiation of hBM-MSCs. miR-1246 was identified as an abundant microRNA in FBS-Exos by public sequencing data identification and RT-qPCR validation. Moreover, miR-1246 overexpression in hBM-MSCs led to decreased adipogenic differentiation level, while miR-1246 knockdown in FBS-Exos attenuated the inhibitory effect on the adipogenic differentiation. Our results indicate that FBS-Exos inhibit the adipogenic differentiation of hBM-MSCs in a cross-species manner and miR-1246 transferred by FBS-Exos partly contributes to this effect.

Serum exosomes from young rats improve the reduced osteogenic differentiation of BMSCs in aged rats with osteoporosis after fatigue loading in vivo.

BACKGROUND: Osteoporosis is a major public health concern for the elderly population and is characterized by fatigue load resulting in bone microdamage. The ability of bone mesenchymal stem cells (BMSCs) to repair bone microdamage diminishes with age, and the accumulation of bone microdamage increases the risk of osteoporotic fracture. There is a lack of effective means to promote the repair of bone microdamage in aged patients with osteoporosis. Exosomes have been shown to be related to the osteogenic differentiation of BMSCs. Here, we aimed to evaluate the changes in the osteogenic differentiation capacity of BMSCs in aged osteoporotic rats after fatigue loading and the treatment potential of serum exosomes from young rats. METHODS: The tibias of six aged osteoporotic rats were subjected to fatigue loading in vivo for 2 weeks, and the bone microdamage, microstructures, and mechanical properties were assessed. Subsequently, BMSCs were extracted to evaluate their proliferation and osteogenic differentiation abilities. In addition, the BMSCs of aged osteoporotic rats after fatigue loading were treated with serum exosomes from young rats under osteogenic induction conditions, and the expression of osteogenic-related miRNAs was quantified. The osteogenetic effects of miRNA-19b-3p in exosomes and the possible target protein PTEN was detected. RESULTS: Obvious bone microdamage at the fatigue load stress point, the bone microstructure and biomechanical properties were not obviously changed. A decreased osteogenic differentiation ability of BMSCs was observed after fatigue loading, while serum exosomes from young rats highly expressing miRNA-19b-3p improved the decreased osteogenic differentiation ability of BMSCs. Transfection with miRNA-19b-3p mimic could promote osteoblastic differentiation of BMSCs and decreased the expression of PTEN. After transfection of miRNA-19b-3p inhibitor, the promotional effect of exosomes on bone differentiation was weakened. Treatment with transfected exosomes increased the expression of PTEN. CONCLUSION: Serum exosomes derived from young rats can improve the decreased osteogenic differentiation ability of BMSCs in aged rats with osteoporosis after fatigue loading and can provide a new treatment strategy for the repair of bone microdamage and prevention of fractures.