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

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.

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.

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.

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.