Insulin and IGF-1 Receptors Regulate Complex-I Dependent Mitochondrial Bioenergetics and Supercomplexes via FoxOs in Muscle

Decreased skeletal muscle strength and mitochondrial dysfunction are characteristic of diabetes. Action of insulin through insulin receptor (IR) and IGF-1 receptor (IGF1R) maintain muscle mass via suppression of FoxOs, but whether FoxO activation coordinates atrophy in concert with mitochondrial dysfunction is unknown. In the absence of systemic glucose or lipid abnormalities, muscle-specific IR knockout (MIRKO) or combined IR/IGF1R knockout (MIGIRKO) impaired mitochondrial respiration, decreased ATP production, and increased ROS. These mitochondrial abnormalities were not present in muscle-specific IR/IGF1R and FoxO1/3/4 quintuple knockout mice (QKO). Although autophagy was increased when IR/IGF1R were deleted in muscle, mitophagy was not increased. Mechanistically, RNA-seq revealed that complex-I core subunits were decreased in MIGIRKO muscle, and these were reversed with FoxO knockout. Thus, insulin-deficient diabetes or loss of insulin/IGF-1 action in muscle decreases complex-I driven mitochondrial respiration and supercomplex assembly, in part by FoxO-mediated repression of Complex-I subunit expression. Male mice were used in all animal studies unless stated otherwise. Muscle-specific IR knock-out (MIRKO), IGF1R knock-out (MIGF1RKO) combined IR/IGF1R knock-out (MIGIRKO), and combined IR/IGF1R with FoxO1/3/4 quintuple knock-out (QKO) mice were generated as previously described (PMID: 25981038, 27525440). Briefly, MIRKO, MIGIRKO, and QKO mice were generated using Acta1-Cre (stock 006149; Jackson Laboratory). Each mouse line was maintained in a separate colony and floxed littermates were used as controls in each experiment. All animals were on a mixed background containing C57Blk6, C57Blk6J, and 129 strains and as such may contain random mutations in the Nnt (Nicotinamide nucleotide transhydrogenase) gene. A post-hoc determination of Nnt genotype revealed that MIGIRKO and IRIGFRlox were heterozygous, whereas other strains (MIRKO, IRlox, QKO, and Qlox were mixed homozygous and heterozygous for Nnt gene (data not shown), but did not correlate with the mitochondrial differences demonstrated in our study.