Perturbation of TM6SF2 Expression Alters Lipid Metabolism in a Human Liver Cell Line

Abstract

Non-alcoholic fatty liver disease (NAFLD) is caused by excess lipid accumulation in hepatocytes. Genome-wide association studies have identified a strong association of NAFLD with non-synonymous E167K amino acid mutation in the transmembrane 6 superfamily member 2 (TM6SF2) protein. The E167K mutation reduces TM6SF2 stability, and its carriers display increased hepatic lipids and lower serum triglycerides. However, the effects of TM6SF2 on hepatic lipid metabolism are not completely understood. We overexpressed wild-type or E167K variant of TM6SF2 or knocked down TM6SF2 expression in lipid-treated Huh-7 cells and used untargeted lipidomic analysis, RNAseq transcriptome analysis, and fluorescent imaging to determine changes in hepatic lipid metabolism. Both TM6SF2 knockdown and E167K overexpression increased hepatic lipid accumulation, while wild-type overexpression decreased acylglyceride levels. We also observed lipid chain remodeling for acylglycerides by TM6SF2 knockdown, leading to a relative increase in species with shorter, more saturated side chains. RNA-sequencing revealed differential expression of several lipid metabolizing genes, including genes belonging to AKR1 family and lipases, primarily in cells with TM6SF2 knockdown. Taken together, our data show that overexpression of TM6SF2 gene or its loss-of-function changes hepatic lipid species composition and expression of lipid metabolizing genes. Additionally, our data further confirms a loss-of-function effect for the E167K variant.

Investigating the role of lipid genes in liver disease using fatty liver models of alcohol and high fat in zebrafish (Danio rerio)

“…Loss of TM6SF2 function modulates hepatic lipid metabolism to produce significant changes in intracellular lipid accumulation 42 . Depleting TM6SF 2, which assists secretion of lipids in TG‐rich lipoprotein from lipid droplets, increases intracellular lipid deposition and is accompanied by enhanced fatty acid synthesis and impaired fatty acid oxidation in mice 8,42 .…”

“…Loss of TM6SF2 function modulates hepatic lipid metabolism to produce significant changes in intracellular lipid accumulation. 42 Depleting TM6SF2, which assists secretion of lipids in TG-rich lipoprotein from lipid droplets, increases intracellular lipid deposition and is accompanied by enhanced fatty acid synthesis and impaired fatty acid oxidation in mice. 8,42 Our tm6sf2 gene depletion alone confirms this role by downregulating β-oxidation with increased TG accumulation and further by increasing lipid synthesis in the presence of EtOH and HFD.…”

Investigating the role of lipid genes in liver disease using fatty liver models of alcohol and high fat in zebrafish (Danio rerio)

“…Loss of TM6SF2 function modulates hepatic lipid metabolism to produce significant changes in intracellular lipid accumulation. [42] Knockdown of TM6SF2 which assists secretion of lipids in TG-rich lipoprotein from lipid droplets increases intracellular lipid deposition and is accompanied by enhanced fatty acid synthesis and impaired fatty acid oxidation in mice. [8,42] Our tm6sf2 knockdown alone confirms this role by downregulating b-oxidation with increased TG accumulation, and further by increasing lipid synthesis in the presence of EtOH and HFD.…”