Aquaporins enriched in endothelial vacuole membrane regulate the diameters of microvasculature in hyperglycemia

Abstract

In patients with diabetic microvascular complications, reduced vessel perfusion or vascular occlusion is a common characteristic which will cause the insufficient blood supply. However, identification of novel regulators involved in microvascular lumenization defects is hindered by the lacking of a model for imaging the blood vessels at high resolution in vivo. Taking advantage of the transparency of zebrafish, we observed the reduction of vascular diameter and compromised perfusion in high glucose treated embryos. RNA sequencing and whole-mount in situ hybridization analysis indicated that two aquaporins (aqp1a.1 and aqp8a.1) were significant down-regulated, which was further confirmed by endothelial specific Q-PCR. It was also shown that the two aqps were spatio-temporally enriched in the endothelial cells (ECs) of vascular system. Zebrafish with loss of aqp1a.1 or aqp8a.1 displayed lumenization defects in intersegmental vessels, recapitulating the phenotype in hyperglycemic zebrafish model. While overexpressing the aquaporins in zebrafish promoted the enlargement of the vascular diameter. Moreover, the defective vasculature induced by high-glucose treatment could be rescued by aqp1a.1 upregulation. In addition, both aqp1a.1 and apq8a.1 were localized in the intracellular vacuoles in cultured ECs as well as in the ECs of sprouting ISVs, and loss of Aqps caused the reduction of those vacuoles, which was required for lumenization. Finally, we found that the expression of human AQP1 was downregulated in diabetic human retina samples and high-glucose treated human retinal microvascular endothelial cells. All these results suggest that EC-enriched aquaporins have a role in developmental and pathological blood vessel lumenization, and they might be potential targets for gene therapy to cure diabetes-related vascular lumenization defects.