Implication of VEGF and aquaporin 4 mediating Müller cell swelling to diabetic retinal edema

Aquaporin 4 (AQP4), a water channel protein, is known to be expressed in retinal Müller cells. The purpose of this study was to determine the effects of VEGF and AQP4 channels on the volumetric changes in Müller cells.

Retinas from diabetic rats and a cultured Müller cell line, TR-MUL5, were used in this study. Intravitreal injections of VEGF or PBS were performed on either streptozotocin (STZ)-induced diabetic or normoglycemic rats. Retinal sections were immunostained for anti-glial fibrillary acidic protein (GFAP), anti-AQP4, and anti-VEGF. VEGF protein levels from collected retinas were determined by western blot analysis. Volumetric changes and nitric oxide (NO) levels in cultured Müller cells were determined using flow cytometry (FACS), in the presence or absence of VEGF and TGN-020, a selective AQP4 inhibitor.

In the diabetic rat retina, VEGF immunoreactivity was concentrated in the internal retinal layers, and AQP4 immunoreactivity was higher than controls. The expressions of AQP4 were colocalized with GFAP. Protein levels of VEGF in the hyperglycemic rat retina were significantly higher than controls. FACS analyses showed that exposure to VEGF enlarged Müller cells, while exposure to TGN-020 suppressed the enlargement. Intracellular levels of NO were increased after exposure to VEGF, which was suppressed following the addition of TGN-020.

The observed Müller cell swelling is mediated by VEGF and AQP4.