PURPOSE: This study aimed to investigate the role of serum- and glucocorticoid-inducible kinase 1 (SGK1) in dry eye disease (DED) pathogenesis and its underlying molecular mechanisms.
METHODS: We established in vitro hyperosmotic models using human corneal epithelial cells (HCECs) and in vivo DED models induced by benzalkonium chloride in C57BL/6 mice. SGK1 was inhibited pharmacologically with GSK650394, and genetic knockdown of Forkhead box O3a (FoxO3a) was performed using small interfering RNA. Comprehensive assessments included western blot for apoptosis and autophagy markers, flow cytometry for apoptosis and reactive oxygen species (ROS) detection, mRFP-GFP-LC3 lentiviral transfection for autophagic flux monitoring, transmission electron microscopy for autophagic ultrastructure, co-immunoprecipitation for protein interactions, immunofluorescence staining for cellular localization, and histological examinations of ocular tissues.
RESULTS: SGK1 expression was significantly upregulated in both hyperosmotic-treated HCECs and the corneal epithelium of DED mice. SGK1 inhibition alleviated ocular surface damage, restored tear secretion, and reduced apoptosis and oxidative stress in vivo and in vitro. Mechanistically, SGK1 inhibition enhances autophagic flux by promoting FoxO3a nuclear translocation and activation, whereas FoxO3a knockdown abolishes the protective effects of SGK1 inhibition. Autophagy induction with rapamycin replicated the protective effects against DED-related damage.
CONCLUSIONS: Inhibition of SGK1 alleviates apoptosis and oxidative stress in DED by activating FoxO3a-mediated autophagy. Our findings suggest that the SGK1/FoxO3a/autophagy axis may play a critical role in the pathogenesis of DED, and SGK1 may represent a potential therapeutic target for this condition.
