let-7c-5p promotes fracture healing by downregulating CDK8

BACKGROUND: Previous studies have shown that let-7c-5p is significantly expressed at a lower level in the serum of fracture patients, suggesting that it may play a role in bone repair. Therefore, this study aims to explore how let-7c-5p regulates osteogenic differentiation in tibial fractures. METHODS: A total of 80 patients with tibial fractures and 83 healthy individuals were included in this study. The level of let-7c-5p in the serum were detected by RT-qPCR. Osteoblast cell line (MC3T3-E1) were cultured in vitro to induce osteogenic differentiation. RT-qPCR was used to detect the expression of let-7c-5p and osteogenic differentiation markers. The activity of alkaline phosphatase (ALP) was determined using an ALP assay kit. Dual-luciferase reporter gene assay and RNA immunoprecipitation were used to verify the targeting relationship between let-7c-5p and CDK8. RESULTS: In the early stage of tibial fractures, the level of let-7c-5p in the patient's serum was significantly lower than that of the control group, and as the healing processes progressed, its level gradually increased. In osteogenic induction, let-7c-5p, the activity of ALP, and the levels of osteogenic markers all increase. Increasing the level of let-7c-5p significantly enhanced the expression of osteogenic markers, while inhibiting its expression would weaken this effect. let-7c-5p directly targeted and negatively regulated the expression of cyclin-dependent kinase 8 (CDK8). Overexpression of CDK8 could reverse the osteogenic effect mediated by let-7c-5p. CONCLUSION: During the healing process of tibial fractures, let-7c-5p promotes osteogenic differentiation by inhibiting CDK8, thereby accelerating fracture healing.