BACKGROUND: Postmenopausal osteoporosis (PMOP) is the predominant form of primary osteoporosis. Its etiology remains incompletely elucidated, and the senescence of bone marrow mesenchymal stem cells (BMSCs) is potentially a contributing factor. Kaempferol (Ka), a common flavonoid with antioxidant and anti-inflammatory effects, is a prospective candidate for therapeutic intervention in osteoporosis. However, its impact on BMSC senescence and the underlying mechanisms remains to be elucidated.
PURPOSE: This study sought to elucidate the impact of Ka on BMSCs and to ascertain its potential targets and regulatory mechanisms.
METHODS: BMSCs were extracted from ovariectomized (OVX) rats to observe the impact of Ka on cellular senescence, mitochondrial function, and mitophagy. Proteomics was utilized to investigate the potential mechanisms. Molecular docking, cellular thermal shift assay, small molecule pull-down assay, and surface plasmon resonance were employed to evaluate the relationship between Ka and its direct target Sp1. Dual-luciferase reporter gene assay and chromatin immunoprecipitation (ChIP) were used to investigate the transcriptional regulatory relationship between Sp1 and FUNDC1. Moreover, we performed detailed imaging and histological observations using micro-CT, hematoxylin and eosin (H&E) staining, Masson staining, immunofluorescence, and immunohistochemistry to assess the role of Ka in rat model of PMOP.
RESULTS: Our results indicated that Ka counteracts senescent BMSCs and osteogenic differentiation deficit caused by postmenopausal, which may be achieved by restoring the basal mitophagy level of OVX-BMSCs, mitochondrial function and reducing reactive oxygen species. Furthermore, Ka treatment enhanced bone density and strength, upregulated Sp1 and FUNDC1 expression in the distal femoral region, and the number of γH2AX positive BMSCs decreased. In terms of mechanism, Ka directly binds to Sp1, promoting its transcriptional activation of FUNDC1-mediated mitophagy. Inhibiting mitophagy or Sp1, or FUNDC1 eliminated the therapeutic effect of Ka.
CONCLUSIONS: Our findings suggest that Ka ameliorates the senescence of OVX-BMSCs by activating the Sp1/FUNDC1 signaling pathway, promoting mitophagy, and providing a new therapeutic strategy and molecular basis for PMOP.
