Abstract 13164: Tm6sf2 is a Regulator of Liver Fat Metabolism in Smooth Er Influencing Vldl Lipidation

Abstract

Backgrounds: A variant in Transmembrane 6 Superfamily Member 2 [ TM6SF2 (E167K)] that is associated with a loss of function is strongly associated with both alcoholic and nonalcoholic fatty liver disease. TM6SF2 is a polytopic protein that is expressed predominantly in the liver and small intestines. Immunolocalization studies are consistent with the protein being present in the endoplasmic reticulum (ER) and the Golgi complex. Tm6sf2 -/- mice replicate the phenotype of individuals with TM6SF2 -167K variant: hepatic steatosis accompanied by hypocholesterolemia, and transaminitis. These mice have a reduced rate of secretion of VLDL-TG without any change in the rate of secretion of ApoB. Thus, TM6SF2 is required for normal lipidation of VLDL. To determine where in the secretory pathway TM6SF2 promotes lipid addition to nascent VLDL, we have generated Tm6sf2 -/- rats. Methods: Two lines of Tm6sf2 -/- rats with different frameshift mutations in exon 1 were generated using CRISPR/Cas9 technology. Rats were fasted 4 hours and tissues were collected and frozen at -80°C. Cell fractionation studies were performed to isolate the smooth and rough ER along with trans - and cis -Golgi membranes. Result: Both lines of rats were confirmed by immunoblotting to produce no TM6SF2 in the liver or intestines. The phenotype of the Tm6sf2 -/- rats resembles that of mice and humans. Cell fractionation studies revealed that TM6SF2 mainly localized to the smooth ER. Unlike what was observed previously by immunocytochemistry, no TM6SF2 was found in the Golgi fraction. Analysis of the lipid profile of the Golgi apparatus in the KO rat revealed that the majority triglyceride (TG) and fatty acids (FA) subclasses were decreased by one to two folds compared to WT in terms of TG or FA to ApoB48 ratios. Conclusions: TM6SF2 is localized predominantly in the smooth ER and regulates the lipidation of VLDL.