PAX6, modified by SUMOylation, plays a protective role in corneal endothelial injury

Fei Yu,Jie Zhou,Hao Sun,Huiqing Liu,Chenxi Yan,Meng Zhou,Yao Fu,Weijie Zhang,Xiangteng Zhao,Aoxue Zhu,Dan Yan,Junzhao Chen

doi:10.1038/s41419-020-02848-5

Abstract

Treating corneal endothelial diseases tends to be challenging as human corneal endothelial cells (CECs) do not proliferate in vivo. The pathogenesis or mechanisms underlying injured CECs need further studies. The abnormal expression of PAX6, which is an essential transcription factor for corneal homeostasis, exhibits corneal endothelial defects. However, the effects of PAX6 protein involved in corneal endothelial wound process are still unknown. Here, we found the upregulated protein levels of PAX6 in human corneal endothelial monolayer after injury; the expression of PAX6 also increased in murine and rat corneal endothelium injury models. Enforced PAX6 expression could alleviate the damages to CECs via regulating permeability by prompting cellular tight junction. In addition, SUMOylation mainly happened on both K53 and K89 residues of 48-kD PAX6 (the longest and main isoform expressed in cornea), and de-SUMOylation promoted the stability of PAX6 protein in vitro. In CECs of SENP1+/− mice, increased SUMOylation levels leading to instability and low expression of PAX6, delayed the repair of CECs after injury. Furthermore, overexpression of PAX6 accelerated the rate of corneal endothelial repair of SENP1+/− mice. Our findings indicate that SENP1-mediated de-SUMOylation improving the stability of PAX6, amplifies the protective effects of PAX6 on corneal endothelial injuries, highlighting potentials of PAX6 and/or SUMOylation to be used as a treatment target for corneal endothelial disorders.

Highlights

Corneal endothelial cells (CECs) locate at the innermost layer of the cornea, which are essential for corneal transparency due to its barrier and ionic “pump” function[1]
The expression of PAX6 protein increased in injured human corneal endothelium monolayer and B4G12 cells
The images of PAX6 staining showed that there was little PAX6 protein in relative normal corneal endothelial cells (CECs), which was identified by relatively regular nuclei, while the expression of PAX6 protein remarkably increased in injured human CECs (hCECs) with irregular nuclei (p < 0.01) (Fig. 1b, c)

Summary

Introduction

Corneal endothelial cells (CECs) locate at the innermost layer of the cornea, which are essential for corneal transparency due to its barrier and ionic “pump” function[1]. Extra traumas, corneal surgeries, and stresses from glaucoma or endothelial dystrophies may significantly reduce endothelial cell density, even leading to decompensation of residual CECs6. Corneal transplantation is the only definitive treatment for patients with corneal endothelial decompensation. The worldwide shortages of donor corneas, highly technology dependence of surgical procedures, and numerous postoperative complications, such as immunologic rejection, highlight the urgency of alternative treatments for corneal endothelial injuries and the importance of insights into corneal endothelial diseases[8,9]. Previous studies have shown that topical Rho kinase (ROCK) inhibitors can promote the healing process of cryoinjured corneal endothelium in animal models[10,11].

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Results

Conclusion