ObjectiveTo investigate the pathogenic role and possible mechanism of NADPH oxidase 4 (Nox4) in type 1 diabetic keratopathy mouse models.

MethodsForty Nox4 knockout ( Nox4 ^-/-) heterozygous male mice were selected and 120 age- and sex-matched wild-type C57BL/6 ( Nox4 ^{+ /+} ) mice were selected as controls. Nox4 ^-/- and Nox4 ^{+ /+} mice were randomized into diabetic group (DM group) and non-DM group by random number method.Type 1 DM model was established in DM groups by intraperitoneal injection of streptozotocin.The DM and non-DM groups of Nox4 ^{+ /+} mice were randomized into regular feed group and Nox4 inhibitor GKT137831 (GKT) supplementary feed group by random number method.At 16 weeks after modeling, tear secretion of mice in different groups was measured by the phenol red thread test.Corneal epithelial integrity was evaluated by fluorescent staining.Changes in corneal never fiber density were observed by the in vivo laser scanning confocal microscopy.Reactive oxygen species (ROS) products in corneal epithelium were assayed by CellROX staining.The expressions of E-Cadherin and nuclear factor-κB (NF-κB) proteins were detected by immunofluorescence staining.Central corneal nerve fiber density was examined by flatmount staining with TUBB3 antibody.The use and care of laboratory animals complied with ARVO statement.The study protocol was approved by Laboratory Animal Care Committee of Xi'an Jiaotong University (No.XJTULAC201301).

ResultsIn Nox4 ^{+ /+} mice, the tear secretion was (2.40±1.18)mm/minute in DM group, which was significantly less than (5.30±1.02)mm/minute in non-DM group ( P<0.01).The tear secretion was (4.19±0.63)mm/minute in DM group of Nox4 ^-/- mice, which was significantly more than that in DM group of Nox4 ^{+ /+} mice ( P<0.05).Significant difference was found between (2.23±0.83)mm/minute of regular feed group and (4.02±0.71)mm/minute of GKT supplementary feed group ( P<0.01).In Nox4 ^{+ /+} mice, the DM group showed significantly increased corneal staining score, reduced corneal nerve fiber density, increased fluorescence intensity of ROS in corneal epithelium, weakened fluorescence intensity of E-Cadherin protein expression, and enhanced fluorescence of NF-κB protein expression compared with non-DM group.In Nox4 ^-/- mice and mice fed with GKT supplementary feed, the increased fluorescence of ROS and decreased fluorescence of E-Cadherin protein expression were seen in the corneal epithelium of the DM groups compared with non-DM groups.In Nox4 ^-/- mice and mice fed with GKT supplementary feed, NF-κB protein fluorescence was weak in corneal epithelial cells in DM groups, which was similar to that in non-DM groups.Immunofluorescence staining of corneal flatmount showed that the density of TUBB3-stained nerve fibers in DM group of Nox4 ^{+ /+} mice was significantly lower than that in non-DM group of Nox4 ^{+ /+} mice, and there was no significant reduction of nerve fibers in the corneal stromal layer in DM group of Nox4 ^-/- mice or mice fed with GKT supplementary feed.

ConclusionsNox4 is involved in the pathogenic process of diabetic keratopathy, and its mechanism may be related to oxidative stress-induced aggregation of ROS products and activation of NF-κB-mediated inflammatory responses.