Abstract Body: Background: Carnitine palmitoyltransferase 1 (CPT1) is the rate-limiting enzyme in mitochondrial fatty acid oxidation (FAO). Our laboratory and others have shown that CPT1a is the most abundant CPT1 enzyme in white adipose tissue (WAT) in mice and humans, prompting an investigation into its role in adipocyte biology.

Methods: CRISPR-Cas9N was used to delete endogenous CPT1a in murine 3T3-L1 fibroblasts. WT and CPT1a KO cells were used to study adipocyte differentiation and insulin responses in-vitro. For in-vivo studies, eight-week old male and female AKO (Cpt1a^ΔAdipo) and littermate controls (Cpt1a^F/F) were placed on a high-fat diet (HFD; 60% kcal fat) for 16 weeks. Glucose and insulin tolerance tests were completed after 11 and 13 weeks on diet. Mice were necropsied after a 16 hour fast, and tissues and serum were collected for insulin and C-peptide analysis, bulk RNA sequencing, and protein expression by immunoblotting.

Results: Murine 3T3L1 KO cells exhibited increased adipocyte differentiation, which was accompanied by a ~50% increase in triglycerides and a 4-5 fold increase in expression of known adipogenic markers (Cd36, Cidec). Despite comparable IRβ phosphorylation, fully differentiated KO adipocytes had reduced Akt and Erk phosphorylation in response to insulin treatment, as compared to controls. Deletion of CPT1a from adipose tissue of female mice resulted in increased body weight and subcutaneous adiposity in response to HFD, as compared to littermate controls. Further, female Cpt1a^ΔAdipo mice displayed a 2-fold increase in fasting insulin and insulin to C-peptide ratios, which coincided with glucose intolerance and insulin resistance in these mice. Notably, no changes were observed in male mice across all parameters tested.

Conclusions: Deletion of CPT1a in adipose tissue promotes sex-specific responses in adiposity and insulin resistance. Future research will determine mechanisms by which substrates (fatty acids) and products (acylcarnitines) of CPT1a impact insulin signaling in adipocytes.