Acetylation of Mitochondrial Trifunctional Protein α-Subunit Enhances Its Stability To Promote Fatty Acid Oxidation and Is Decreased in Nonalcoholic Fatty Liver Disease

Abstract

bNonalcoholic fatty liver disease (NAFLD) has become the most common liver disease, and decreased fatty acid oxidation is one of the important contributors to NAFLD. Mitochondrial trifunctional protein ␣-subunit (MTP␣) functions as a critical enzyme for fatty acid ␤-oxidation, but whether dysregulation of MTP␣ is pathogenically connected to NAFLD is poorly understood. We show that MTP␣ is acetylated at lysine residues 350, 383, and 406 (MTP␣-3K), which promotes its protein stability by antagonizing its ubiquitylation on the same three lysines (MTP␣-3K) and blocking its subsequent degradation. Sirtuin 4 (SIRT4) has been identified as the deacetylase, deacetylating and destabilizing MTP␣. Replacement of MTP␣-3K with either MTP␣-3KR or MTP␣-3KQ inhibits cellular lipid accumulation both in free fatty acid (FFA)-treated alpha mouse liver 12 (AML12) cells and primary hepatocytes and in the livers of high-fat/high-sucrose (HF/HS) diet-fed mice. Moreover, knockdown of SIRT4 could phenocopy the effects of MTP␣-3K mutant expression in mouse livers, and MTP␣-3K mutants more efficiently attenuate SIRT4-mediated hepatic steatosis in HF/HS diet-fed mice. Importantly, acetylation of both MTP␣ and MTP␣-3K is decreased while SIRT4 is increased in the livers of mice and humans with NAFLD. Our study reveals a novel mechanism of MTP␣ regulation by acetylation and ubiquitylation and a direct functional link of this regulation to NAFLD.

Time Course of Decrease in Skeletal Muscle Mitochondrial Biogenesis after Discontinuation of High-Fat Diet

“…These differences may explain, in part, the different rates of decline of mitochondrial components in the skeletal muscle after high-fat diet withdrawal. In addition, mitochondrial proteins, including LCAD, can be modified by posttranslational modifications that regulate their enzymatic activity or protein stability (19,20). These protein modifications might affect the reversal rates for different mitochondrial components after withdrawal of the high-fat diet.…”

Sirtuins in metabolism, DNA repair and cancer

“…In parallel, SIRT4 decreases PPARα and its target genes activities, consequently repressing fatty acid oxidation in liver [63]. A more recent study highlighted a novel mechanism that deacetylating and destabilizing MTPα, a key enzyme in β-oxidation by SIRT4 may contribute to the pathogenesis of Nonalcoholic fatty liver disease (NAFLD) [64]. …”

Hepatic neuregulin 4 signaling defines an endocrine checkpoint for steatosis-to-NASH progression

“…Hepa 1 cells were transfected with the plasmids encoding HA-tagged c-FLIP L and Flag-tagged ubiquitin by using polyethylenimine (Polysciences, catalog 23966). Ubiquitination assays were performed following a previously described protocol (46). Briefly, cells were lysed in 1% SDS buffer (Tris [pH 7.5], 0.5 mM EDTA, 1 mM DTT) and boiled for 10 minutes.…”