Lack of Elevated Expression of TGFβ3 Contributes to the Delay of Epithelial Wound Healing in Diabetic Corneas

PURPOSE. To investigate the mechanisms underlying the differential roles of TGF/31 and TGF/33 in accelerating corneal epithelial wound healing (CEWH) in diabetic (DM) corneas, with normoglycemia (NL) corneas as the control. METHODS. Two types of diabetic mice, human corneal organ cultures, mouse corneal epithelial progenitor cell lines, and bone marrow-derived macrophages (BMDMs) were employed to assess the effects of TGF/31 and TGF/33 on CEWH, utilizing quantitative PCR, western blotting, ELISA, and whole -mount confocal microscopy. RESULTS. Epithelial debridement led to an increased expression of TGF/31 and TGF/33 in cultured human NL corneas, but only TGF/31 in DM corneas. TGF/31 and TGF/33 inhibition was significantly impeded, but exogenous TGF/31 and, more potently, TGF/33 promoted CEWH in cultured TKE2 cells and in NL and DM C57BL6 mouse corneas. Wounding induced similar levels of p-SMAD2/SMAD3 in NL and DM corneas but weaker ERK1/2, Akt, and EGFR phosphorylation in DM corneas compared to NL corneas. Whereas TGF/31 augmented SMAD2/SMAD3 phosphorylation, TGF/33 preferentially activated ERK, PI3K, and EGFR in healing DM corneas. Furthermore, TGF/31 and TGF/33 differentially regulated the expression of S100a9, PAI-1, uPA/tPA, and CCL3 in healing NL and DM corneas. Finally, TGF/31 induced the expression of M1 macrophage markers iNOS, CD86, and CTGF, whereas TGF/33 promoted the expression of M2 markers CD206 and NGF in BMDMs from db/db or db/+ mice. CONCLUSIONS. Hyperglycemia disrupts the balanced expression of TGF/33/TGF/31, resulting in delayed CEWH, including impaired sensory nerve regeneration in the cornea. Supplementing TGF/33 in DM wounds may hold therapeutic potential for accelerating delayed wound healing in diabetic patients.