Carnitine palmitoyltransferase 2 (CPT2) knockout potentiates palmitate-induced insulin resistance in C2C12 myotubes: Role of palmitoylcarnitine

Authors: BLACKBURN, MICHAEL - Arkansas Children'S Nutrition Research Center (ACNC); ONO-MOORE, KIKUMI - Arkansas Children'S Nutrition Research Center (ACNC); HOPPEL, CHARLES - Case Western Reserve University (CWRU); SOBHI, HANY - Coppin State University; Ferruzzi, Mario

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/12/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Saturated fatty acids (SFAs) are implicated in muscle inflammation/cell stress and insulin resistance ("lipotoxicity"), but the catalog of factors involved is incomplete. SFA derivatives that accumulate with mismatched FA availability and FA oxidation (FAO) are likely involved, and evidence has emerged that select acylcarnitines should be considered. To understand if excessive long-chain acylcarnitine renders cells more susceptible to lipotoxicity, carnitine palmitoyltransferase 2 knockout C2C12 cells were generated (CPT2 KO). CPT2 KO was confirmed by Western blot, increased palmitoylcarnitine accumulation and loss of long-chain FAO capacity. There was no effect of CPT2 KO on typical palmitic acid (PA) concentration-dependent increases in media IL-6 or adenylate kinase (markers of cell stress and permeability/cell death responses). PA at 200 or 500 uM did not trigger other cell stress responses (phospho-Erk, -JNK, or -p38) in either WT (wildtype) or CPT2 KO cells, above that of vehicle alone. In contrast, loss of CPT2 significantly exacerbated PA-induced insulin resistance (acute phospho-Akt; using 10 or 100 nM insulin) by as much as ~50-96% compared to WT. The CPT1 inhibitor etomoxir increased p-Akt, and growing cells in carnitine-free media abolished differences between WT and CPT2 KO. The results indicate that PA-induced insulin resistance stems in part from palmitoylcarnitine accumulation, which helps explain increased CPT2 KO susceptibility to PA. The data further support the hypothesis that select acylcarnitines participate in cell signaling and when in excess, compromise myocyte cell function. Since etomoxir and carnitine-free conditions could not fully rescue insulin signaling, and CPT2 KO did not alter PA-associated IL-6 or adenylate kinase release, the majority of PA-induced "lipotoxicity" in C2C12 myotubes cannot be attributed to palmitoylcarnitine alone. It remains to be established if these phenomena underlie the episodic cardiac and skeletal muscle myopathies typical of inherited disorders of FAO, and contribute to the insulin resistance accompanying type 2 diabetes.