Mitochondrial ACSS1-K635 acetylation knock-in mice exhibit altered liver lipid metabolism on a ketogenic diet

Acetyl-CoA Synthetase Short Chain Family Member-1 (ACSS1) catalyzes the ligation of acetate and coenzyme A to generate acetyl-CoA in the mitochondria to produce ATP through the tricarboxylic acid (TCA) cycle. We recently generated an ACSS1-acetylation (Ac) mimic knock-in mouse, where lysine 635 was mutated to glutamine (K635Q), which structurally and biochemically mimics an acetylated lysine. ACSS1 enzymatic activity is regulated, at least in part, through the acetylation of lysine 635 in mice (lysine 642 in humans), a Sirtuin 3 deacetylation target. We challenged our Acss1^K635Q knock-in mice with a three-week ketogenic diet. While both wild-type and Acss1^K635Q knock-in mice were in ketosis with similar blood glucose levels, the Acss1^K635Q mice exhibited elevated blood acetate and liver acetyl-CoA. In addition, and importantly, compared to wild-type mice, the liver in the Acss1^K635Q mice displayed a much more predominant liver steatosis morphology and accumulation of lipid drops, as measured by H&E and Oil Red O staining. RNAseq analysis identified that genes related to mitochondrial respiratory chain complexes and oxidative stress were significantly overexpressed in the Acss1^K635Q mice on a KD. Finally, lipidomics analysis revealed very different lipid profiles for these groups, including a dramatic increase in triacylglycerides (TAGs), phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), and cardiolipins in the Acss1^K635Q liver.