Carnitine-acylcarnitine translocase is essential for liver long-chain fatty acid oxidation

Hepatic mitochondrial long-chain fatty acid oxidation (mLCFAO) is critical for maintaining systemic metabolism and carbon homeostasis. mLCFAO requires acyl-chains to be transported into the mitochondrial matrix in the form of acylcarnitines by carnitine-acylcarnitine translocase (CACT). Unlike long-chain, medium-chain fatty acids do not require the acylcarnitine transport system for mitochondrial oxidative metabolism. While CACT is known as an essential component of mLCFAO, it is unknown if it’s a redundant enzyme, its role in long- versus medium-chain fatty acid oxidation, and its requirement for liver health. To determine the role and requirement for CACT we generated a novel conditional deletion mouse model targeting CACT specifically in hepatocytes, CACT Liv-/- . Liver pathology, mitochondrial bioenergetics, and metabolite homeostasis were assessed under control low-fat diet conditions, and in response to ketogenic diets containing either long-chain or medium-chain fatty acids. The long-chain ketogenic diet increased circulating triglycerides and free fatty acids and caused severe hepatic steatosis in CACT Liv-/- mice within one week. Indicators of metabolic stress were evident by increased expression of liver Fgf21, Gdf15 and TGFb1 in CACT Liv-/- mice on the long-chain ketogenic diet. However, the medium-chain ketogenic diet failed to induce metabolic stress genes or severe hepatic steatosis in CACT Liv-/- mice. These data demonstrate that dietary medium-chain fatty acids are able to flux through hepatic oxidative metabolism in the absence of the acylcarnitine shuttle. R01: DK125812 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.