Loss of aquaporin 5 contributes to the corneal epithelial pathogenesis via Wnt/β‐catenin pathway

Abstract

AQP5 plays a crucial role in maintaining corneal transparency and the barrier function of the cornea. Here, we found that in the corneas of Aqp5−/− mice at older than 6 months, loss of AQP5 significantly increased corneal neovascularization, inflammatory cell infiltration, and corneal haze. The results of immunofluorescence staining showed that upregulation of K1, K10, and K14, and downregulation of K12 and Pax6 were detected in Aqp5−/− cornea and primary corneal epithelial cells. Loss of AQP5 aggravated wound‐induced corneal neovascularization, inflammation, and haze. mRNA sequencing, western blotting, and qRT‐PCR showed that Wnt2 and Wnt6 were significantly decreased in Aqp5−/− corneas and primary corneal epithelial cells, accompanied by decreased aggregation in the cytoplasm and nucleus of β‐catenin. IIIC3 significantly suppressed corneal neovascularization, inflammation, haze, and maintained corneal transparent epithelial in Aqp5−/− corneas. We also found that pre‐stimulated Aqp5−/− primary corneal epithelial cells with IIIC3 caused the decreased expression of K1, K10, and K14, the increased expression of K12, Pax6, and increased aggregation in the cytoplasm and nucleus of β‐catenin. These findings revealed that AQP5 may regulate corneal epithelial homeostasis and function through the Wnt/β‐catenin signaling pathway. Together, we uncovered a possible role of AQP5 in determining corneal epithelial cell fate and providing a potential therapeutic target for corneal epithelial dysfunction.

Aquaporins in the Cornea

“…AQP5 expression is also enriched in the cornea and localizes specifically to the corneal epithelium [25,27,40]. In global AQP5 knockout mice in vivo, the ablation of AQP5 leads to an increase in corneal thickness, which is further enhanced as the mice age, as well as a reduction in the extent of corneal swelling when a hypotonic solution is introduced [37,41]. Verkman's laboratory additionally showed that AQP5 is a principal route of water flux across the intact corneal epithelium: the deletion of APQ5 caused an approximate five-fold reduction in trans-corneal water flux through intact corneas, which could be restored via the removal of the epithelium [30].…”

“…Furthermore, when experiments were repeated in the presence of AKT inhibitors, NGF treatment is unable to restore corneal nerve fiber density and sensitivity in the AQP5 knockout mice [51]. In aged mice (older than 6 months), AQP5 knockout leads to significantly more corneal neovascularization, inflammatory cell infiltration, and corneal haze [41]. Aged AQP5 knockout mice show a reduction in Wnt signaling, which is important for differentiation and migration during development [41].…”

“…In aged mice (older than 6 months), AQP5 knockout leads to significantly more corneal neovascularization, inflammatory cell infiltration, and corneal haze [41]. Aged AQP5 knockout mice show a reduction in Wnt signaling, which is important for differentiation and migration during development [41]. The introduction of IIC3 (an inhibitor of the Wnt antagonist Dickkopf WNT Signaling Pathway Inhibitor 1, or DKK1) restores the wound healing rate of AQP5 knockout mice to that of the wild type, indicating that AQP5 plays an important role in activating Wnt signaling in the cornea, although the method of activation is still unknown [41].…”

“…Aged AQP5 knockout mice show a reduction in Wnt signaling, which is important for differentiation and migration during development [41]. The introduction of IIC3 (an inhibitor of the Wnt antagonist Dickkopf WNT Signaling Pathway Inhibitor 1, or DKK1) restores the wound healing rate of AQP5 knockout mice to that of the wild type, indicating that AQP5 plays an important role in activating Wnt signaling in the cornea, although the method of activation is still unknown [41]. AQP5 may also play a role in the differentiation of corneal epithelium cells, since aged AQP5 knockout mice show a reduction in the mRNA and protein levels of keratin 12, a marker of the differentiated corneal epithelium, as well as an increase in keratin 1, 10 and 14 mRNA and protein levels, which are keratins expressed by epidermal keratinocytes of the skin epithelium [41].…”

Reticulated Retinoic Acid Synthesis is Implicated in the Pathogenesis of Dry Eye in Aqp5 Deficiency Mice

“…Our earlier research has shown that the knockout of Aqp5 leads to defects in corneal epithelium 20 and abnormalities in homeostasis. 21 Studies have demonstrated that RA therapy maintains the integrity of the epithelial barrier, thereby regulating the proliferation and migration of CECs 22 and facilitating cell adhesion during corneal epithelium repair. 23 Furthermore, emerging evidence suggests that all trans-RA provides its anti-inflammatory actions by suppressing the production of pro-inflammatory chemicals (interleukin-1β [IL-1β], IL-12, and RANTES) associated with DE while enhancing the generation of IL-10, an anti-inflammatory cytokine.…”