Hepatic TM6SF2 Is Required for Lipidation of VLDL in a Pre-Golgi Compartment in Mice and Rats

Fei Luo; Eriks Smagris; Sarah A Martin; Goncalo Vale; Jeffrey G McDonald; Justin A Fletcher; Shawn C Burgess; Helen H Hobbs; Jonathan C Cohen

doi:10.1016/j.jcmgh.2021.12.008

Hepatic TM6SF2 Is Required for Lipidation of VLDL in a Pre-Golgi Compartment in Mice and Rats

Cell Mol Gastroenterol Hepatol. 2022;13(3):879-899. doi: 10.1016/j.jcmgh.2021.12.008. Epub 2021 Dec 16.

Authors

Fei Luo¹, Eriks Smagris², Sarah A Martin², Goncalo Vale³, Jeffrey G McDonald³, Justin A Fletcher⁴, Shawn C Burgess⁴, Helen H Hobbs⁵, Jonathan C Cohen⁶

Affiliations

¹ Department of Molecular Genetics, Dallas, Texas; Department of Cardiovascular Medicine, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China.
² Department of Molecular Genetics, Dallas, Texas.
³ Department of Molecular Genetics, Dallas, Texas; Center for Human Nutrition, Dallas, Texas.
⁴ Center for Human Nutrition, Dallas, Texas.
⁵ Department of Molecular Genetics, Dallas, Texas; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas. Electronic address: [email protected].
⁶ Center for Human Nutrition, Dallas, Texas. Electronic address: [email protected].

Abstract

Background & aims: Substitution of lysine for glutamic acid at residu 167 in Transmembrane 6 superfamily member 2 (TM6SF2) is associated with fatty liver disease and reduced plasma lipid levels. Tm6sf2^-/- mice replicate the human phenotype but were not suitable for detailed mechanistic studies. As an alternative model, we generated Tm6sf2^-/- rats to determine the subcellular location and function of TM6SF2.

Methods: Two lines of Tm6sf2^-/- rats were established using gene editing. Lipids from tissues and from newly secreted very low density lipoproteins (VLDLs) were quantified using enzymatic assays and mass spectrometry. Neutral lipids were visualized in tissue sections using Oil Red O staining. The rate of dietary triglyceride (TG) absorption and hepatic VLDL-TG secretion were compared in Tm6sf2^-/- mice and in their wild-type littermates. The intracellular location of TM6SF2 was determined by cell fractionation. Finally, TM6SF2 was immunoprecipitated from liver and enterocytes to identify interacting proteins.

Results: Tm6sf2^-/- rats had a 6-fold higher mean hepatic TG content (56.1 ± 28.9 9 vs 9.8 ± 3.9 mg/g; P < .0001) and lower plasma cholesterol levels (99.0 ± 10.5 vs 110.6 ± 14.0 mg/dL; P = .0294) than their wild-type littermates. Rates of appearance of dietary and hepatic TG into blood were reduced significantly in Tm6sf2^-/- rats (P < .001 and P < .01, respectively). Lipid content of newly secreted VLDLs isolated from perfused livers was reduced by 53% (TG) and 62% (cholesterol) (P = .005 and P = .01, respectively) in Tm6sf2^-/- mice. TM6SF2 was present predominantly in the smooth endoplasmic reticulum and endoplasmic reticulum-Golgi intermediate compartments, but not in Golgi. Both apolipoprotein B-48 and acyl-CoA synthetase long chain family member 5 physically interacted with TM6SF2.

Conclusions: TM6SF2 acts in the smooth endoplasmic reticulum to promote bulk lipidation of apolipoprotein B-containing lipoproteins, thus preventing fatty liver disease.

Keywords: Fatty Liver; Liver Perfusion; Triglycerides; VLDL.

Publication types

Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

MeSH terms

Animals
Membrane Proteins* / metabolism
Mice
Non-alcoholic Fatty Liver Disease* / metabolism
Rats

Substances

Membrane Proteins

Abstract

Publication types

MeSH terms

Substances

Grants and funding