Electron microscopic analysis of glucose-induced endothelial damage in primary culture: possible mechanism and prevention

Lysosome-membrane fusion mediated superoxide production in hyperglycaemia-induced endothelial dysfunction

Lysosomal exocytosis and fusion to cellular membrane is critical in the oxidative stress formation of endothelium under apoptotic stimulus. We investigated the role therein of it in hyperglycaemia-induced endothelial dysfunction. The lysosome-membrane fusion was shown by the expression of lamp1, the lysosomal membrane marker, on cellular membrane and the transportation of lysosomal symbolic enzymes into cultural medium. We also examined the ceramide production, lipid rafts (LRs) clustering, colocalization of gp91^phox, a NADPH oxidase subunit (NOX) to LRs clusters, superoxide (O₂^.-) formation and nitric oxide (NO) content in human umbilical vein endothelial cells (HUVEC) and the endothelium-dependent NO-mediated vasodilation in isolated rat aorta. As compared to normal glucose (5.6 mmol/l, Ctrl) incubation, high glucose (22 mmol/l, HG) exposure facilitated the lysosome-membrane fusion in HUVEC shown by significantly increased quantity of lamp1 protein on cellular membrane and enhanced activity of lysosomal symbolized enzymes in cultural medium. HG incubation also elicited ceramide generation, LRs clustering and gp91^phox colocalization to LRs clusters which were proved to mediate the HG induced O₂^.- formation and NO depletion in HUVEC. Functionally, the endothelium-dependent NO-mediated vasodilation in aorta was blunted substantially after HG incubation. Moreover, the HG-induced effect including ceramide production, LRs clustering, gp91^phox colocalization to LRs clusters, O₂^.- formation and endothelial dysfunction could be blocked significantly by the inhibition of lysosome-membrane fusion. We propose that hyperglycaemia-induced endothelial impairment is closely related to the lysosome-membrane fusion and the following LRs clustering, LRs-NOX platforms formation and O₂^.- production.

Angiotensin II mediates the high-glucose-induced endothelial-to-mesenchymal transition in human aortic endothelial cells

Background

Substantial evidence suggests that high glucose (HG) causes endothelial cell damage; however, the potential mechanism therein has yet to be clarified. The aim of this study was to investigate the influence of HG on the endothelial-to-mesenchymal transition (EndMT) and its relevance to the activation of the renin-angiotensin system.

Methods

Primary human aortic endothelial cells (HAECs) were divided into three groups: a normal glucose (NG) group, HG group, and irbesartan (1 μM)-treated (HG+irbesartan) group. The concentration of angiotensin II in the supernatant was detected by radioimmunoassay. Pathological changes were investigated using fluorescence microscopy and electron microscopy. Immunofluorescence staining was performed to detect the co-expression of CD31 and fibroblast markers, such as fibroblast-specific protein 1 (FSP1). The expressions of FSP1 and α-SMA were detected by RT-PCR and Western blot.

Results

The treatment of HAECs in the HG group resulted in significant increases in the expressions of FSP1 and angiotensin II in dose-and time-dependent manners. The incubation of HAECs exposure to HG resulted in a fibroblast-like phenotype, wherein increased microfilamentation and a roughened endoplasmic reticulum structure were observed in the cytoplasm. The expressions of FSP1 and α-SMA were significantly increased in the HG group, and these changes were inhibited by irbesartan treatment (P < 0.05). Double staining of the HAECs indicated a co-localization of CD31 and FSP1 and that some cells acquired spindle-shaped morphologies and a loss of CD31 staining; however, treatment with irbesartan attenuated the expression of EndMT (P < 0.05).

Conclusions

These findings suggest a novel mechanism in HG-induced endothelial damage via the mediation of the EndMT by angiotensin II, which was inhibited by Irbesartan.