Irisin alleviates oxidative stress and osteoblast apoptosis in glucocorticoid-induced rat osteonecrosis of the femoral head via the integrin αVβ5/Bach1/Nrf2 signaling pathway

Glucocorticoid (GC)‑induced osteonecrosis of the femoral head (ONFH) is associated with oxidative stress and osteoblast apoptosis. Irisin, the cleaved form of fibronectin type III domain‑containing protein 5, attenuates oxidative stress and apoptosis in numerous types of cells, including osteoblasts, osteocytes and cardiomyocytes. The present study aimed to investigate the role of irisin and the mechanism behind GC‑induced ONFH in vivo, as well as oxidative stress and osteoblast apoptosis in vitro. In the present study, GC‑induced ONFH was established in rats by intramuscular injection of methylprednisolone, with irisin administered by intraperitoneal injection; the FHs were then assessed by micro‑CT, histology, immunohistochemistry and TUNEL staining. In vitro, murine osteoblastic MC3T3‑E1 cells were treated with dexamethasone (DEX), and oxidative stress, apoptosis and Nrf2 signaling were evaluated by dihydroethidium/JC‑1 staining, flow cytometry, reverse transcription‑quantitative PCR and western blotting. Irisin prevented the development of GC‑induced ONFH in rats, and alleviated oxidative stress and apoptosis in DEX‑treated osteoblasts. To determine the underlying mechanisms by which irisin exerted beneficial effects on DEX‑treated osteoblasts, the present study investigated Nrf2 signaling cascades. Irisin induced Nrf2 signaling cascade activation in MC3T3‑E1 cells and Nrf2 silencing by targeted short hairpin RNA reversed the beneficial effects of irisin on DEX‑treated osteoblasts. Further mechanistic analysis revealed that irisin physically interacted with integrin (ITG) αVβ5 on osteoblasts, activating Erk1 signaling. This activation promoted nuclear export of Bach1, a competitive suppressor of Nrf2, thereby relieving Bach1‑mediated suppression of antioxidant response elements. Consequently, irisin enhanced Nrf2 nuclear accumulation and upregulated its target genes [heme oxygenase, NAD(P)H quinone oxidoreductase 1, glutamate‑cysteine ligase catalytic subunit], reducing reactive oxygen species and mitochondrial membrane potential loss. Pharmacological inhibition of ITG αVβ5 or Erk1/2 abolished irisin‑induced Bach1 export, Nrf2 activation and cytoprotective effects. Collectively, the present study indicated that irisin may mitigate GC‑induced ONFH and osteoblast apoptosis via the ITG αVβ5/Bach1/Nrf2 signaling pathway, highlighting its therapeutic potential.