UBC Theses and Dissertations
Endothelial heparanase regulation of cardiac metabolism Wang, Fang
Following diabetes, the heart increases its lipoprotein lipase (LPL) at the coronary lumen by transferring LPL from the cardiomyocyte to the endothelial lumen. Heparanase is an endoglycosidase that specifically cleaves carbohydrate chains of heparan sulfate (HS). We examined the mechanisms behind endothelial heparanase control of cardiac LPL translocation. Using diazoxide (DZ) to decrease serum insulin, we observed that within 30 min of DZ, interstitial heparanase increased, an effect that closely mirrored an augmentation in interstitial LPL. In bovine coronary artery endothelial cells incubated with glucose or palmitic acid (PA), glucose dose-dependently increased heparanase secretion, a process that required ATP release, purinergic receptor activation, cortical actin disassembly and stress actin formation. Phosphorylation of filamin likely contributed towards the cortical actin disassembly, whereas Ca²⁺/calmodulin-dependent protein kinase II and p38 mitogen activated protein kinase/heat shock protein 25 phosphorylation mediated stress actin formation. The endothelial-secreted heparanase in response to HG demonstrated endoglycosidase activity, cleaved HS, and released attached proteins like lipoprotein lipase and basic fibroblast growth factor. Unlike glucose, PA increased intracellular heparanase and induced rapid nuclear accumulation of heparanase that was dependent on Bax activation and lysosome permeabilization. Heat shock protein 90 was an important mediator of PA-induced shuttling of heparanase to the nucleus. Nuclear heparanase promoted cleavage of HS, a potent inhibitor of histone acetyltransferase activity and gene transcription. A TaqMan gene expression assay revealed an increase in genes related to glucose metabolism and inflammation. In addition, glycolysis was uncoupled from glucose oxidation, resulting in accumulation of lactate. Our data suggest that following hyperglycemia, translocation of LPL from the cardiomyocyte cell surface to the apical side of endothelial cells is influenced by the ability of fatty acid to increase endothelial intracellular heparanase followed by rapid secretion of this enzyme by glucose. Given that both LPL and heparanase have been implicated in the progression of diabetes, our data may serve to reduce the associated cardiovascular complications by limiting the utilization of fatty acid after diabetes.
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