Leucine-rich α-2-glycoprotein-1 promotes diabetic corneal epithelial wound healing and nerve regeneration via regulation of matrix metalloproteinases

Abstract

Leucine-rich α-2-glycoprotein-1 (LRG1) is involved in several pathophysiological processes, including angiogenesis, cutaneous wound repair and cancer metastasis. In this study, we investigated the potential role and mechanism of LRG1 in corneal re-epithelialisation and nerve regeneration in streptozotocin-induced diabetic mice. We found decreased levels of LRG1 in the corneal epithelium after wounding in diabetic mice compared to normal controls. Hyperglycaemia downregulated the LRG1 expression in the corneal epithelium in vivo, as well as in vitro in a cultured mouse corneal epithelial stem/progenitor cell line (TKE2 cells) exposed to high glucose (HG; 30 mM) in the culture medium. Exogenous application of LRG1 accelerated corneal re-epithelialisation and nerve regeneration in normal mice and diabetic mice. LRG1 also overcame the suppression of wound healing in TKE2 cells by HG conditions, and it activated repair-related signalling by JAK2/STAT3, AKT, epidermal growth factor receptor (EGFR) and transforming growth factor (TGF)-β3. We also found that LRG1 treatment overcame the hyperglycaemia-suppressed expression of matrix metalloproteinase 3 (MMP3) and metalloproteinase 13 (MMP13) in the regenerated corneal epithelium. The promoted effects of LRG1 on corneal re-epithelialisation and nerve regeneration were blocked by inhibitors of MMP3 and MMP13. Subconjunctival injection of 0.5 μg MMP inhibitors did not cause any obvious toxic damage in corneal epithelial cells. Immunoprecipitation and proximity ligation assay experiments confirmed that endogenous LRG1 coprecipitated with MMP3 and MMP13 in TKE2 cells. These results indicate that LRG1 promoted wound repair and nerve regeneration in the diabetic corneal epithelium by regulation of MMPs. Our findings reveal a new function and mechanism for LRG1 in the cornea, and they provide new insights for a better understanding of diabetic keratopathy.