Peroxisome Proliferator-Activated Receptor-α (PPARα) Regulates Mitochondrial Metabolism and Wound Healing in the Cornea

Abstract

Purpose : Diabetic keratopathy is a common complication of diabetes and affects more than half of patients with diabetes worldwide, and the pathogenesis remains unclear. The present study aims to explore the molecular mechanism for wound healing impairment due to disturbed mitochondrial metabolism in the diabetic cornea.

Methods : PPARα RNAscope in situ hybridization and immunofluorescence staining was carried out with human donor eyes with type 1 and type 2 diabetes. Oxygen consumption rate (OCR) was measured using live cornea biopsy punches from wild-type (WT) C57BL/6J mice, Streptozotocin (STZ)-induced diabetic mice, Akita mice, db/db mice, corneal epithelium-specific PPARα conditional knockout (PPARα^CEKO) mice, and corneal epithelium-specific PPARα transgenic (PPARα^CETg) mice. The real-time ATP production rate assay and mitochondrial stress test were performed using primary human cornea epithelial cells (HCEC). 4-Hydroxy-2-nonenal (HNE), a lipid peroxidation product, was used as a diabetic stressor in vitro.

Results : Human diabetic corneas showed significant downregulation of PPARα mRNA expression relative to non-diabetic donors. Seahorse analysis showed that mitochondrial oxidative phosphorylation is a major source of ATP production in HCEC. Live cornea biopsy punches from type 1 and type 2 diabetic mouse models showed impaired mitochondrial functions compared to non-diabetic controls. Disturbed mitochondrial function along with delayed wound healing was observed in the corneas from PPARα^CEKO mice. In contrast, the treatment of fenofibrate, a PPARα agonist, upregulated PPARα expression, ameliorated mitochondrial dysfunction, and enhanced wound healing in the diabetic mouse cornea. PPARα^CETg mice also showed a mitochondrial protective effect in the cornea. Furthermore, fenofibric acid, an active metabolite of fenofibrate, ameliorated the mitochondrial dysfunction in primary human cornea epithelial cells exposed to HNE.

Conclusions : Downregulation of PPARα plays an important role in impaired mitochondrial function, contributing to delayed wound healing in the diabetic cornea.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.