Abstract 71: AAV-Mediated Expression of Human IDOL in Mouse Liver Increases LDL Cholesterol in a Dose-Dependent Fashion

Abstract

IDOL (inducible degrader of the low-density lipoprotein receptor, LDLR), originally known as Mylip, is an E3 ubiquitin ligase that promotes the ubiquitination and degradation of the LDLR. Adenoviral overexpression of mouse IDOL was shown to increase LDL cholesterol by decreasing LDLR. Human genetics support a role for genetic variation in IDOL influencing LDL-C levels and support the concept that IDOL inhibition could be a novel strategy to reduce LDL-C levels. In this study we examined the effects of stable expression of human IDOL in mouse liver on LDLR protein and plasma lipids. Using an adeno-associated virus serotype 9 (AAV9)-mediated delivery, we expressed hIDOL (AAV-hIDOL) under the liver-specific TBG promoter to achieve liver-specific expression in adult mice. Five doses of AAV-hIDOL (1x10 10 , 3x10 10 , 1x10 11 , 3x10 11 , 1x10 12 GC) were administered by intra-peritoneal injection and compared to a group injected with AAV-Null as control. AAV-hIDOL produced a dose-dependent increase in hIDOL expression in liver as shown by RT-PCR. Analysis of liver LDLR protein by western blotting revealed a dose-dependent decrease of the LDLR that was completely abolished starting at the dose of 3x10 11 GC. A significant dose-dependent increase in total and LDL cholesterol was observed. At the highest vector dose, LDL-C levels increased more than two-fold. Plasma triglyceride (TG) levels were unchanged through the dose range except at the highest dose where they increased by about 75%. Finally, we used a “humanized” mouse model of heterozygous familial hypercholesterolemia (LDLR +/- /Apobec1 -/- /hApoB-Tg) and expressed hIDOL using AAV-hIDOL at 2x10 11 GC. In this model TC and LDL-C levels were increased by about 60% starting from one week and were sustainable for at least 4 weeks post-injection. In conclusion, our study demonstrates a dose-dependent physiological effect of human IDOL on LDL metabolism in mice and provides a potential model for preclinical testing of IDOL inhibitors for reduction of LDL-C levels.