Melatonin inhibits adipogenesis and enhances osteogenesis of BMSCs through increasing KLF5 expression.

Bone marrow-derived mesenchymal stem cells (BMSCs) maintain bone homeostasis by balancing adipogenesis and osteogenesis, with disruption of this balance favoring adipogenesis contributing to osteoporosis. Melatonin, known for regulating bone metabolism, promotes osteogenesis and inhibits adipogenesis, but the mechanisms remain unclear. This study investigates whether melatonin regulates BMSC differentiation by modulating the methylation of the Krüppel-like factor 5 (KLF5) promoter, a transcription factor involved in both adipogenesis and osteogenesis. Using an ovariectomy (OVX)-induced osteoporosis mouse model, we found that melatonin treatment significantly reversed OVX-induced bone loss, increased bone mineral density, and reduced bone marrow adiposity, accompanied by increased KLF5 expression in bone tissue. In vitro, melatonin promoted osteogenic differentiation and suppressed adipogenic differentiation in BMSCs, with decreased methylation of the KLF5 promoter. Knockdown of KLF5 suppressed osteogenesis and enhanced adipogenesis, while KLF5 overexpression promoted osteogenesis and inhibited adipogenesis. Melatonin-induced demethylation of the KLF5 promoter was associated with increased KLF5 expression, which in turn promoted osteogenic differentiation and inhibited adipogenic differentiation. These findings reveal a novel epigenetic mechanism underlying melatonin's bone-protective effects and suggest KLF5 promoter methylation as a potential therapeutic target for osteoporosis and related bone disorders.