The PERK-p38 MAPK Axis Drives Endoplasmic Reticulum Stress-Induced Apoptosis in Fuchs Endothelial Corneal Dystrophy.

Purpose: To investigate the role of p38 mitogen-activated protein kinase (MAPK) in endoplasmic reticulum (ER) stress-induced corneal endothelial cell death in Fuchs endothelial corneal dystrophy (FECD) and to evaluate its potential as a therapeutic target. Methods: Three complementary ER stress models were utilized: (1) FECD patient-derived (iFECD) cells treated with TGF-β to mimic disease-specific conditions, (2) normal immortalized human corneal endothelial cells (iHCECs) treated with thapsigargin, and (3) iHCECs treated with MG-132 (a proteasome inhibitor). The p38 MAPK activity was modulated using three structurally distinct p38 MAPK-specific inhibitors (SB203580, PH-797804, and VX-702). Gene-specific siRNA knockdown of protein kinase RNA-like ER kinase (PERK) pathway components was performed to elucidate the signaling hierarchy. PERK-eukaryotic translation initiation factor 2α (eIF2α)-activating transcription factor 4 (ATF4)-CCAAT/enhancer-binding protein homologous protein (CHOP) pathway activation, p38 MAPK phosphorylation, aggresome formation, mitochondrial function, and apoptosis were evaluated by western blotting, immunofluorescence, and flow cytometry. Results: In all three models, p38 MAPK activation occurred downstream of PERK-eIF2α phosphorylation but upstream of ATF4-CHOP induction. In the iFECD/TGF-β model, p38 MAPK inhibition prevented CHOP upregulation, maintained mitochondrial membrane potential, and reduced apoptosis without affecting TGF-β-Smad signaling or aggresome formation. Similar protective effects were observed in iHCEC cells treated with thapsigargin or MG-132. Mechanistically, PERK knockdown prevented p38 MAPK activation, but p38 MAPK inhibition did not affect PERK activation, thereby establishing their hierarchical relationship. Conclusions: p38 MAPK serves as a critical mediator of ER stress-induced apoptosis in corneal endothelial cells, where it functions as a molecular switch between adaptive and pro-apoptotic UPR signaling. The cytoprotective efficacy of p38 MAPK inhibitors across multiple ER stress models suggests their potential for therapeutic repurposing in FECD.