LDL receptor deficiency unmasks altered VLDL triglyceride metabolism in VLDL receptor transgenic and knockout mice

The very low density lipoprotein receptor (VLDLR) has been proposed to play a role in the delivery of fatty acids to peripheral tissues. However, despite reduced adipose tissue mass in VLDLR-deficient (VLDLR-/-) mice, this has been difficult to substantiate. In the present study, VLDLR-deficient and VLDLR-overexpressing (PVL) mice were cross-bred onto a low density Lipoprotein receptor knockout (LDLR-/-) background to study the VLDLR under conditions of relatively high serum VLDL and triglyceride levels. Absence of the VLDLR resulted in a significant increase in serum triglyceride levels (1.9-fold) when mice were fed a high fat diet. In contrast, overexpression of the VLDLR resulted in a significant decrease in serum triglyceride levels (2.0-fold) under similar conditions. When kept on a chow diet, a period of prolonged fasting revealed a significant increase in serum triglyceride levels in VLDLR-/-; LDLR-/- mice (2.3-fold) as compared with LDLR-/- controls. This could not be attributed to altered apolipoprotein B and VLDL triglyceride production rates. Furthermore, no major differences in nascent VLDL triglyceride content were found between VLDLR-/-; LDLR-/- mice and LDLR-/- controls. However, the triglyceride content of circulating VLDL of VLDLR-/-; LDLR-/- mice (63%) was relatively high as compared with LDLR-/- controls (49%). These observations suggest that the VLDLR affects peripheral uptake of VLDL triglycerides. In conclusion, under conditions of LDLR deficiency in combination with high fat feeding or prolonged fasting, the effect of the VLDLR on VLDL triglyceride metabolism was revealed.