PERK Regulates Epithelial-Mesenchymal Transition Through Autophagy and Lipid Metabolism in Lens Epithelial Cells

Pathological epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) plays a crucial role in the formation of lens fibrosis, particularly in fibrotic posterior capsular opacification and anterior subcapsular cataract (ASC). Here we investigated the potential roles of endoplasmic reticulum (ER) stress in the development of lens fibrosis.

RNA sequencing was performed to examine global gene expression changes in patients with ASC, as well as in TGFβ2-induced human lens explants and rabbit primary LECs. Rabbit LECs were treated with TGFβ2 in the presence or absence of the ER stress modulator, PERK inhibitor ISRIB, and autophagy inducer for in vitro studies. In vivo investigations were carried out using a mouse model of injury-induced capsular fibrosis, with ISRIB administration. To uncover the underlying mechanisms, we conducted lipidomics analysis, transmission electron microscopy, immunostaining, quantitative PCR, Western blot, and capillary Western immunoassay.

ER stress genes were upregulated in patients with ASC, TGFβ2-stimulated human explants and primary LECs. Pharmacologic ER stress induction promoted EMT, while its inhibition reduced TGFβ2-induced mesenchymal gene levels. Blocking the PERK axis of ER stress with ISRIB or targeting downstream factor ATF4 suppressed EMT, whereas the IRE1 axis showed no effect. Consistent with these in vitro observations, anterior chamber injection of ISRIB also reduced subcapsular plaque formation in a mouse model of lens fibrosis by suppressing SMAD2/3 activation. Mechanistically, ISRIB suppressed LC3-II conversion and P62 degradation, indicating autophagy suppression. Lipidomics revealed phosphatidylethanolamine (PE), essential for autophagosome formation, was downregulated in TGFβ2-treated LECs and upregulated with ISRIB cotreatment. Inducing autophagy with rapamycin significantly rescued the mesenchymal gene suppression by ISRIB, whereas autophagy inhibitor CQ produced opposite effects.

ER stress, particularly the PERK axis, promotes LECs' EMT through autophagy and PE metabolism, offering potential therapeutic targets for the treatment of lens fibrosis.