Dietary fat overconsumption leads to myocardial lipid accumulation through mechanisms that are incompletely resolved. Previously, we identified increased translocation of the fatty acid transporter CD36 from its endosomal storage compartment to the sarcolemma as primary mechanism of excessive myocellular lipid import. Here, we show that increased CD36 translocation is caused by alkalinization of endosomes due to inhibition of proton pumping activity of vacuolar-type H+-ATPase (v-ATPase). Endosomal alkalinization was observed in hearts from rats fed a lard-based high fat-diet and in rodent and human cardiomyocytes upon palmitate overexposure, and appeared as early lipid-induced event preceding the onset of insulin resistance. Either genetic or pharmacological inhibition of v-ATPase in cardiomyocytes exposed to low palmitate concentrations reduced insulin sensitivity and cardiomyocyte contractility, which was rescued by CD36 silencing. The mechanism of palmitate-induced v-ATPase inhibition involved its dissociation into two parts: the cytosolic V1 and the integral membrane V0 sub-complex. Interestingly, also oleate inhibits v-ATPase function, yielding triacylglycerol accumulation but not insulin resistance. In conclusion, lipid oversupply increases CD36-mediated lipid uptake that directly impairs v-ATPase function. This feeds forward to enhanced CD36 translocation and further increased lipid uptake. In case of palmitate, its accelerated uptake ultimately precipitates into cardiac insulin resistance and contractile dysfunction.
This article contains Supplementary Data online at http://diabetes.diabetesjournals.org/lookup/suppl/doi:10.2337/db16-0727/-/DC1.
- Received June 10, 2016.
- Accepted March 13, 2017.
- © 2017 by the American Diabetes Association.