Sodium hydrosulfide alleviates dexamethasone-induced cell senescence and dysfunction through targeting the miR-22/sirt1 pathway in osteoblastic MC3T3-E1 cells

BMSC-derived extracellular vesicles promoted osteogenesis via Axin2 inhibition by delivering MiR-16-5p

Osteoporosis (OP) is a systemic bone disease caused by an imbalance in osteogenesis and osteoclastic resorption. Extracellular vesicles (EVs)-encapsulated miRNAs from bone mesenchymal stem cells (BMSCs) have been reported to participate in osteogenesis. MiR-16-5p is one of the miRNAs that regulates osteogenic differentiation; however, studies have shown that its role in osteogenesis is controversial. Thus, this study aims to investigate the role of miR-16-5p from BMSC-derived extracellular vesicles (EVs) in osteogenic differentiation and uncover the underlying mechanisms. In this study, we used an ovariectomized (OVX) mouse model and an H₂O₂-treated BMSCs model to investigate the effects of BMSC-derived EVs and EV-encapsulated miR-16-5p on OP and the underlying mechanisms. Our results proved that the miR-16-5p level was significantly decreased in H₂O₂-treated BMSCs, bone tissues of OVX mice, and lumbar lamina tissues from osteoporotic women. EVs-encapsulated miR-16-5p from BMSCs could promote osteogenic differentiation. Moreover, the miR-16-5p mimics promoted osteogenic differentiation of H₂O₂-treated BMSCs, and the effects exerted by miR-16-5p were mediated by targeting Axin2, a scaffolding protein of GSK3β that negatively regulates the Wnt/β-catenin signaling pathway. This study provides evidence that EVs-encapsulated miR-16-5p from BMSCs could promote osteogenic differentiation by repressing Axin2.

Ablation of miRNA-22 protects against obesity-induced adipocyte senescence and ameliorates metabolic disorders in middle-aged mice

High-fat diet (HFD) promotes obesity-related metabolic complications by activating cellular senescence in white adipose tissue (WAT). Growing evidence supports the importance of microRNA-22 (miR-22) in metabolic disorders and cellular senescence. Recently, we showed that miR-22 deletion attenuates obesity-related metabolic abnormalities. However, whether miR-22 mediates HFD-induced cellular senescence of WAT remains unknown. Here, we uncovered that obese mice displayed increased pri-miR-22 levels and cellular senescence in WAT. However, miR-22 ablation protected mice against HFD-induced WAT senescence. In addition, in vitro studies showed that miR-22 deletion prevented preadipocyte senescence in response to Doxorubicin (Doxo). Loss-of-function studies in vitro and in vivo revealed that miR-22 increases H2ax mRNA and γH2ax levels in preadipocytes and WAT without inducing DNA damage. Intriguingly, miR-22 ablation prevented HFD-induced increase in γH2ax levels and DNA damage in WAT. Similarly, miR-22 deletion prevented Doxo-induced increase in γH2ax levels in preadipocytes. Adipose miR-22 levels were enhanced in middle-aged mice fed a HFD than those found in young mice. Furthermore, miR-22 deletion attenuated fat mass gain and glucose imbalance induced by HFD in middle-aged mice. Overall, our findings indicate that miR-22 is a key regulator of obesity-induced WAT senescence and metabolic disorders in middle-aged mice.

SIRT1 targeted by miR-211-5p regulated proliferation and apoptosis of Dex-treated growth plate chondrocytes via mediating SOX2

Dexamethasone (Dex) is reported to cause bone growth retardation in children, which is associated with the increased apoptosis and decreased proliferation of growth plate chondrocytes. Sirtuin 1 (SIRT1) plays an important role in chondrocyte function and homeostasis. Thus, we further explored the regulatory mechanism of SIRT1 in Dex-induced growth plate chondrocyte dysfunction. SIRT1 expression was detected in Dex-treated growth plate chondrocytes using RT-qPCR and western blot assay. The modulation of SIRT1 on SOX2 expression was evaluated. Besides, we identified that SIRT1 was targeted by miR-211-5p using TargetScan and RNA pull-down assay. A loss-of-function assay was performed to evaluate the effects of miR-211-5p on Dex-induced growth plate chondrocyte dysfunction in vitro and in vivo. We found that SIRT1 was downregulated in Dex-treated growth plate chondrocytes. The expression of SOX2 was upregulated by overexpression SIRT1. Meanwhile, downregulation of SOX2 weakened the positive function of SIRT1 overexpression on Dex-induced growth plate chondrocytes dysfunction. Subsequently, we confirmed that SIRT1 was targeted by miR-211-5p. MiR-211-5p inhibitor increased the expression levels of SIRT1 and SOX2, and restored the Dex-treated growth plate chondrocyte function. Animal assays further demonstrated that the effects of miR-211-5p on the growth plate chondrogenesis. In conclusion, our data suggest that SIRT1 exerts a protective effect on growth plate chondrocyte under Dex stimulation. MiR-211-5p/SIRT1/SOX2 axis regulates the process of Dex-inhibited growth plate chondrogenesis.

miR-27b attenuates dexamethasone-inhibited proliferation and osteoblastic differentiation in MC3T3-E1 cells by targeting PPARγ2

Osteoporosis is a metabolic bone illness characterized by low bone density and a high risk of fracture. It is estimated that there are >60 million individuals in China suffering from this disease, which highlights an urgent requirement for the development of novel and safe drugs for the long-term treatment of osteoporosis. MicroRNAs (miRNAs/miRs) have previously been identified as critical regulators in the progression of osteoporosis. As an intronic miRNA, miR-27b enhances the osteoblastic differentiation of stem cells from the bone marrow and the maxillary sinus membrane. However, the mechanism underlying miR-27b in osteoporosis remains to be elucidated. In the present study, MC3T3-E1 pre-osteoblasts were treated with dexamethasone (DEX) to establish an in vitro model of osteoporosis. The results of the present study demonstrated that DEX treatment markedly inhibited the viability of MC3T3-E1 cells, and downregulated the expression level of miR-27b. The results of reverse transcription-quantitative PCR, western blotting and dual-luciferase assays revealed that miR-27b directly regulated and suppressed the expression of peroxisome proliferator-activated receptor γ2 (PPARγ2) in MC3T3-E1 cells. Furthermore, overexpression of miR-27b by transfection of cells with miR-27b mimic attenuated DEX-mediated inhibition of cell viability, alkaline phosphatase (ALP) activity and the expression levels of bone morphogenetic protein-2 (BMP2), runt-related protein 2 (Runx2) and osteocalcin (OCN). The results of the present study indicated that miR-27b alleviated DEX-inhibited proliferation and osteoblastic differentiation. Moreover, miR-27b knockdown repressed MC3T3-E1 cell viability, ALP activity and protein levels of BMP2, Runx2 and OCN. However, these effects were abrogated by small interfering RNA-mediated PPARγ2 silencing. In conclusion, the results of the present study demonstrated that miR-27b attenuated DEX-inhibited proliferation and osteoblastic differentiation in MC3T3-E1 pre-osteoblasts by targeting PPARγ2.

Metformin attenuates H2O2-induced osteoblast apoptosis by regulating SIRT3 via the PI3K/AKT pathway

Osteoporosis is a common metabolic disease that has a high incidence in postmenopausal women. Studies have indicated that oxidative damage plays an important role in the development of postmenopausal osteoporosis. Metformin has been showed to have the ability to relieve excessive oxidation. The aim of the present was to determine the therapeutic effect and potential mechanism of metformin in postmenopausal osteoporosis. Oxidative damage was stimulated in vitro by the addition of H₂O₂ to MC3T3-E1 cells and a mouse menopausal model was also constructed. Cell viability and flow cytometry experiments were performed to determine the effects of H₂O₂ and metformin treatment on apoptosis. Mitochondrial membrane potential was tested by JC-1 assays. Western blotting was used to detect the expression of mitochondrial apoptosis markers and antioxidant enzymes. Small interfering RNA was used to knockdown sirtuin3 (SIRT3), which was verified at the mRNA and protein levels. Bilateral ovariectomy was used to prepare menopausal mice, which were analyzed using micro-computed tomography. The results indicated that metformin is able to repair mitochondrial damage and inhibit the apoptosis of osteoblasts induced by H₂O₂, and also reverse bone mass loss in ovariectomized mice. Western blotting results demonstrated the involvement of SIRT3 in the production of antioxidant enzymes that are essential in protecting against mitochondrial injury. In addition, experiments with SIRT3 knockdown indicated that metformin reverses H₂O₂-induced osteoblast apoptosis by upregulating the expression of SIRT3 via the PI3K/AKT pathway. The results of the present reveal the pathogenesis of oxidative damage and the therapeutic effect of metformin in postmenopausal osteoporosis. They also suggest that SIRT3 is a potential drug target in the treatment of osteoporosis, with metformin being a candidate drug for modification and/or clinical application.