MiR-137 promotes TLR4/NF-κB pathway activity through targeting KDM4A, inhibits osteogenic differentiation of human bone marrow mesenchymal stem cells and aggravates osteoporosis

Abstract

Purpose As the global population ages rapidly, osteoporotic fractures have become an important public health problem. Previous studies have suggested that miR-137 is involved in the regulation of bone formation, but its specific regulatory mechanism remains unclear. In this study, we aimed to explore the expression, role, and regulatory mechanism of miR-137 in the osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs). Methods hBMSCs were induced into osteoblasts at first, and the expression level of miR-137 at different time points was detected. After knockdown and overexpression of miR-137, the effect of miR-137 on the osteogenic differentiation of hBMSCs was examined through alkaline phosphatase (ALP) staining and Alizarin Red staining. Western blotting was performed to detect the expression of runt-related transcription factor 2 (Runx2), osteocalcin (OCN), and toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) pathway. Bioinformatics websites were used to predict the target binding sites for miR-137 and KDM4A, and the results were validated using luciferase reporter gene experiments. Moreover, the ALP activity, calcium nodule formation, and activation of Runx2, OCN, and TLR4/NF-κB pathways were observed after knockdown of KDM4A. Results The expression of miR-137 decreased during osteogenic differentiation. Knockdown of miR-137 expression increased the osteogenic ability of hBMSCs, while overexpression of it weakened the ability. Through the activation of the TLR4/NF-κB pathway, miR-137 inhibited osteogenic differentiation. KDM4A was identified as a predicted target gene of miR-137. After knocking down KDM4A expression, the osteogenic ability of hBMSCs was diminished, and the TLR4/NF-κB pathway was activated. Furthermore, the osteogenic ability of hBMSCs was partially restored and the activation level of TLR4/NF-κB was reduced after miR-137 knockdown. Conclusion MiR-137 enhances the activity of the TLR4/NF-κB pathway by targeting KDM4A, thereby inhibiting the osteogenic differentiation of hBMSCs and exacerbating osteoporosis.

The critical role of toll-like receptor 4 in bone remodeling of osteoporosis: from inflammation recognition to immunity

“…Also, TLR4 can be activated by LPS and ovariectomized surgery. Mechanistically, overexpressed Zinc finer E-box binding homeobox 1 (ZEB1), down-regulated KDM4A, overexpressed miR-137, overexpression of circ_0134944, and inhibition of miR-630 ( 12 , 38 , 39 ). Rajpar et al.…”

“…As shown in Figure 1 with the flow diagram, thirty studies were finally included. Among them, six included studies ( 39 , 41 – 45 ) provided the clinical data from osteoporosis patients ( Table 1 ), 17 studies ( 12 , 37 , 38 , 40 , 46 – 58 ) reported the molecular mechanisms underlying the role of TLR4 in osteoporosis ( Table 2 ), and seven studies ( 59 – 65 ) provided the data of specific treatments-targeted TLR4 for osteoporosis ( Table 3 ). The key information of the 30 eligible studies included the study object, disease modeling method, the status of TLR4, effect on osteoblast or osteoclast, associated genes or pathways, and the main findings of the independent study.…”

“…In addition, the authors also found that oleate exerted a protective action on bone cells by inhibiting proinflammatory response and TLR-4 expression. A more recent study ( 12 ) showed that the miR−137/KDM4A axis suppressed the osteogenic differentiation of human BMSCs (promoted osteoclast) and exacerbated osteoporosis by activating the TLR4/NF−κB pathway.…”

“…Therefore, new targets for osteoporosis prevention and treatment have become an important endeavor. In recent years, increasing numbers of studies have demonstrated that the Toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) pathway plays a pivotal role in the development of osteoporosis ( 12 ).…”

“…It can be activated by specific exogenous substances (i.e., bacterial endotoxin), thus prompting the activation of NF-κB into the nucleus, releasing a variety of inflammatory factors, such as TNF-α, IL-1β, and IL-6 ( 17 ). Elevation of these inflammatory mediators inhibits osteogenic differentiation of BMSCs and accelerates the maturation of osteoclasts, and ultimately leads to the occurrence of osteoporosis ( 12 ). TLR4 is expressed on the surface of osteoclasts and osteoblasts, which regulates the immune response in patients with chronic inflammation, eventually causing the onset of osteoporosis.…”