Fisetin enhances osteoblast differentiation and bone formation under simulated microgravity

Osteoporosis is a systemic bone disease characterized by decreased bone density and mass, compromised bone microstructure, increased bone fragility, and susceptibility to fractures. In recent years, as space exploration activities have intensified, the health issues faced by astronauts during prolonged space missions have increasingly become a focal point in scientific research. In particular, the problem of bone loss resulting from astronauts' extended exposure to microgravity environments has emerged as a significant area of study within space medicine and biological sciences. Currently, small-natural product have become promising intervention strategies in this field. Previous studies have proved that cyclin-dependent kinase 12 (CDK12) is an effective screening target for the treatment strategy of osteoporosis. The purpose of this paper is to evaluate the preventive and therapeutic effects of a small-natural product, Fisetin, which was screened with targeting CDK12. In this study, based on the method of weighted set similarity (WES), the small-natural product Fisetin, was screened and obtained by targeting CDK12. The Alkaline Phosphatase (ALP) staining and Alizarin red S (ARS) staining, as well as the mRNA and protein expression levels of osteoblast-related markers, Runt-related Transcription Factor 2 (RUNX2) and Collagen Type I Alpha 1 (COL1A1), were used to detect the effect of Fisetin on osteoblast differentiation. The micro-CT and Dual-energy X-ray absorptiometry (DXA) analysis were used to evaluate the efficacy of Fisetin in preventing and treating osteoporosis in hindlimb-unloaded (HU) mice and ovariectomized (OVX) mice model. The findings revealed that Fisetin promotes osteoblast differentiation and further proved that Fisetin could alleviate the bone loss in HU mice and OVX mice. Additionally, the expression of CDK12 and phospho-RUNX2 (p-RUNX2) were significantly down-regulated in the process of promoting osteoblast differentiation and bone formation. Further research revealed the potential and preliminary molecular mechanism that Fisetin might release RUNX2 and reduce the phosphorylation of p-RUNX2 by down-regulating the expression of CDK12, thereby enhancing the transcription of osteoblast differentiation. In conclusion, Fisetin demonstrates efficacy in improving osteoporosis and holds promise as a potential small-natural product to prevent and treat osteoporosis.