Abstract Body: Background: Very-low-density lipoprotein receptor (VLDLR), a member of the LDL receptor family, binds and increases the catabolism of triglyceride–rich lipoproteins. Although VLDLR is highly expressed in the heart, its role in VLDLR in oxidative stress and insulin resistance is unclear. Here, we used lean (WT), genetically obese leptin-deficient (ob/ob), and leptin–VLDLR double-null (ob/ob-VLDLR-/-) mice to determine the role of VLDLR in VLDL-induced oxidative stress and insulin resistance in the heart.
Methods: Insulin resistance was investigated using glucose tolerance test and uptake of labeled deoxyglucose. Uptake VLDL was assessed in vivo and in isolated cardiomyocytes using double labeled ([3H]-TG, cholesteryl oleoyl ether ([14C])-VLDL. Oxidative stress was evaluated by the measurement of lipid peroxidation products (LPO) and hydrogen peroxides (HPO). NADPH-dependent superoxide production was measured in tissue homogenates and cardiomyocytes with the lucigenin chemiluminescent assay. Superoxide production in cardiomyocytes was investigated using fluorescent probe.
Results: While insulin sensitivity and glucose uptake were reduced in the hearts of ob/ob mice, VLDLR expression was upregulated and was associated with increased VLDL uptake and excess lipid deposition in the heart. This was accompanied by an upregulation of cardiac NADPH oxidase (Nox) expression (+100%), increased oxidative stress markers LPO and HPO (+300%) and Nox-dependent superoxide production (+300%). Silencing VLDLR in ob/ob mice had reduced VLDL uptake and prevented excess lipid deposition in the heart, in addition to a reduction of superoxide production and the normalization of insulin sensitivity and glucose uptake. In isolated cardiomyocytes, VLDLR deficiency had prevented VLDL-mediated induction of Nox activity and superoxide overproduction while improving insulin sensitivity and glucose uptake.
Conclusions: Our findings indicate that VLDLR deficiency prevents excess lipid accumulation and moderates oxidative stress and insulin resistance in the heart of obese mice. This effect is linked to the active role of VLDLR in VLDL uptake, which triggers a cascade of events leading to increased NOX activity, overproduction superoxide and insulin resistance.