Low RIP140 expression rescues insulin‐mediated FA oxidation via a rise in MCAD gene expression in skeletal muscle cells exposed to high palmitate availability

Abstract

We have shown that in L6 cells incubated with high palmitate, low Receptor Interacting Protein 140 (RIP140) expression alters the regulation of muscle fatty acid (FA) uptake and FA oxidation under insulin‐mediated conditions. To provide mechanistic insights for these metabolic changes, we measured mRNA and/or protein expression of several genes involved in the regulation of FA uptake and oxidation. Cells were incubated with insulin (1000 nM) ± palmitate (400 μM) and with siRNA sequences for either RIP140 or a negative control. Under insulin‐mediated conditions, short‐term incubation with palmitate decreased (P<0.05) FA uptake (24%) and oxidation (42%). Under these conditions, low RIP140 expression reduced (P<0.05) FA uptake (35%) and restored FA oxidation so that it was not different (P>;0.05) from the control rate. Incubation with palmitate increased (P<0.05) CD36 (70%) and FATP1 (224%) mRNA, decreased (P<0.05) CPT1 (45%) mRNA and did not change MCAD (P>;0.05) mRNA. High palmitate was accompanied by reductions (P<0.05) in protein content for FATP1 (68%) and total (59%) and plasma membrane (31%) CD36 but it did not affect (P>;0.05) CPT1. Under those same conditions, low RIP140 expression was accompanied by a rise in the mRNA expression of MCAD (83%; P<0.05) and FATP1 (38%; P=0.08) but no change (P>;0.05) in mRNA expression of CPT1 and CD36. Protein content of CPT1, FATP1, CD36 (total and plasma membrane) were not affected (P>;0.05) by low RIP140 expression. Our results indicate that low RIP140 expression in the context of high palmitate availability increases gene expression of MCAD and that this may in part explain the restoration of insulin‐mediated FA oxidation.USC Women in Science and Engineering, USC Integrative and Evolutionary Biology and USC Zumberge Research Innovation Fund