Following diabetes, the heart has a singular reliance on fatty acid (FA) for energy production, which is achieved by increased coronary lipoprotein lipase (LPL) that breaks down circulating triglycerides. Coronary LPL originates from cardiomyocytes, and to translocate to the vascular lumen, the enzyme requires liberation from myocyte surface heparan sulfate proteoglycans (HSPGs), an activity that needs to be sustained following chronic hyperglycemia. We investigated the mechanism by which endothelial cells (EC) and cardiomyocytes operate together to enable continuous translocation of LPL following diabetes.
EC were co-cultured with myocytes, exposed to high glucose, and uptake of endothelial heparanase into myocytes determined. Upon uptake, the impact of nuclear entry of heparanase was also investigated. A streptozotocin model of diabetes was used to expand our in vitro observations.
In high glucose, EC-derived latent heparanase was taken up by cardiomyocytes via a caveolae-dependent pathway using HSPGs. This latent heparanase was converted into an active form in myocyte lysosomes, entered the nucleus, and upregulated gene expression of matrix metalloproteinase-9. The net effect was increased shedding of HSPGs from the myocyte surface, releasing LPL for its onwards translocation to the coronary lumen.
EC-derived heparanase regulates the ability of cardiomyocyte to send LPL to the coronary lumen. This adaptation, although beneficial acutely, could be catastrophic chronically as excess FA causes lipotoxicity. Inhibiting heparanase function could offer a new strategy for managing cardiomyopathy observed following diabetes.
- Received December 5, 2013.
- Accepted March 3, 2014.
- © 2014 by the American Diabetes Association.
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