Bumetanide Rescues Aquaporin-4 Depolarization via Suppressing p-Dys-troglycan Cleavage and Provides Neuroprotection in Rat Retinal Ischemia-Reperfusion Injury

(AQP4) regulates retinal water homeostasis and participates in retinal oedema pathophys-iology. p-dystroglycan (p-DG) is responsible for AQP4 polarization and can be cleaved by matrix metalloproteinase-9 (MMP9). Retinal oedema induced by ischemia-reperfusion (I/R) injury is an early complica-tion. Bumetanide (BU) has potential efficacy against cytotoxic oedema. Our study investigated the effects of p -DG cleavage on AQP4 and the roles of BU in a rat retinal I/R injury model. The model was induced by applying 110 mm Hg intraocular pressure to the anterior eye chamber. BU and U0126 (a selective ERK inhibitor) were intraperitoneally administered 15 and 30 min, respectively, before I/R induction. Rhodamine isothiocyanate extravasation detection, quantitative real-time PCR, transmission electron microscopy, hematoxylin-eosin stain-ing, immunofluorescence staining, western blotting, and TUNEL staining were performed. AQP4 lost its polariza-tion in the retinal perivascular domain as a result of p-DG cleavage. BU rescued AQP4 depolarization, suppressed AQP4 protein expression, attenuated retinal cytotoxic oedema, and downregulated p-DG and AQP4 mRNA expres-sion. BU suppressed glial responses and mitochondria-mediated apoptotic protein expression, including that of Caspase-3 and Cyto C, raised the Bcl-2/Bax ratio, and lowered the number of apoptotic cells in the retina. Both BU and U0126 downregulated p-ERK and MMP9 expression. Thus, BU treatment suppressed p-DG cleavage, recov-ered AQP4 polarization partially via inhibiting ERK/MMP9 signaling pathway, and possess potential neuroprotec-tive efficacy in the rat retinal ischemia-reperfusion injury model.(c) 2022 IBRO. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the effects of p-DG cleavage on AQP4 and the roles of BU in a rat retinal I/R injury model. The results showed that p-DG cleavage led to the depolarization of AQP4, while BU could recover AQP4 polarization, suppress AQP4 protein expression, attenuate retinal cytotoxic edema, and regulate the expression of p-DG and AQP4 genes. Additionally, BU also inhibited glial responses and mitochondria-mediated apoptotic protein expression, showing potential neuroprotective efficacy.