Vitamin K₂ Protects Against Glucocorticoid-Induced Osteoporosis by Activating the NRF2/FSP1 Pathway to Inhibit Osteoblast Ferroptosis

Glucocorticoid-induced osteoporosis (GIOP) is the most common form of secondary osteoporosis, and its pathogenesis is closely associated with oxidative stress and impaired osteogenic differentiation. Vitamin K₂ (VK₂) has strong antioxidant properties and potent bone-forming effects, but its application in GIOP is still unclear. This study investigates the therapeutic potential of VK₂ in GIOP and elucidates its underlying molecular mechanisms.

Dexamethasone (DEX) was used to establish GIOP model within C57BL/6 mice. The bone mass was assessed using micro-computed tomography (micro-CT), hematoxylin and eosin (HE) staining, and Masson's trichrome staining in vivo. The osteoblast activity and the expression of osteogenic and ferroptosis-related markers were evaluated via immunohistochemistry (IHC), RT-qPCR, Western blotting, ALP and alizarin red staining. The mitochondrial function and lipid peroxidation of MC3T3-E1 cells were detected by flow cytometry, immunofluorescence and specific kits.

VK₂ partially prevented bone mass reduction and osteoblast activity inhibition in GIOP mice. VK₂ not only reversed the DEX-induced reductions in Tb.N, BV/TV, and Tb.Th, but also significantly increased the expression of osteogenic markers, including OCN and ALP (P<0.05). Moreover, VK₂ improved DEX-induced ferroptosis, oxidative stress and mitochondrial dysfunction in MC3T3-E1 cells and promoted osteogenic differentiation in vitro, which could be reversed by ferroptosis inducer (P<0.05). VK₂ also increased the expression of NRF2, HO-1 and FSP1 which inhibited by DEX in vivo and in vitro (P<0.05). The inhibition of FSP1 and NRF2 reversed the osteogenic differentiation promotion and ferroptosis inhibition by VK₂ (P<0.05).

VK₂ restores mitochondrial function and reduces lipid peroxidation and ferroptosis via the NRF2/FSP1 signaling pathway, thereby facilitating osteoblast differentiation and improving bone mass in GIOP mice. This finding not only provides a fresh perspective on the etiology of GIOP but also positions ferroptosis inhibition as a promising and innovative therapeutic strategy for this condition, with VK₂ emerging as a potential candidate for clinical translation.