VDR activation attenuates osteoblastic ferroptosis and senescence by stimulating the Nrf2/GPX4 pathway in age-related osteoporosis

Ferroptosis plays an essential role in the pathology of osteoporosis . This study investigated whether vitamin D receptor (VDR) activation could protect against age-related osteoporosis through an anti-ferroptosis mechanism. d -galactose (D-gal)-induced mice and VDR-knockout mice were used in the in-vivo study. The VDR activator (1,25(OH) 2 D 3 ) attenuated senescence and ferroptosis in the D-gal-induced bone, as illustrated by downregulated senescence-associated secretory phenotype genes, improved mitochondrial morphology, elevated glutathione , and decreased lipid peroxidation markers (malondialdehyde and 4-hydroxynonenal). The pre-osteoblast MC3T3-E1 cells and primary rat osteoblasts were applied in the in-vitro studies. 1,25(OH) 2 D 3 or ferroptosis inhibitor (ferrostatin-1) treatment downregulated the cellular senescence markers in D-gal-induced osteoblasts. Mechanistically, 1,25(OH) 2 D 3 activated the VDR and its downstream nuclear factor erythroid 2-related factor 2 (Nrf2)/glutathione peroxidase 4 (GPX4) signaling pathway , resulting in the downregulation of lipid peroxidation. Nrf2 knockdown or addition of GPX4 inhibitor (RSL-3) blocked the protective effect of 1,25(OH) 2 D 3 against D-gal-induced ferroptosis and senescence. VDR knockdown impeded the 1,25(OH) 2 D 3 -induced activation of Nrf2/GPX4 pathway in osteoblasts. Proteomics and immunofluorescence analysis confirmed that ferroptosis and suppression of the Nrf2/GPX4 pathway occurred in VDR-knockout mice. Our data demonstrated that ferroptosis played an essential role in age-related osteoporosis. The VDR activation attenuated osteoblast ferroptosis via stimulating the Nrf2/GPX4 signaling pathway.