Inhibition of GCN5 decreases skeletal muscle fat metabolism during high fat diet feeding

Abstract

AbstractIntroductionGCN5 (Kat2a) is a lysine acetyl transferase capable of acetylating and inhibiting PGC-1α activity. As such, it is described as a negative regulator of PGC-1α and subsequently restricts mitochondrial content. However, elimination of GCN5 in skeletal muscle does not increase mitochondrial content or alter lipid metabolism under normal metabolic conditions. GCN5 levels increase with high-fat diet (HFD) feeding in rodents. Additionally, the GCN5 homolog, PCAF, has previously been shown to also acetylate and inhibit PGC-1α and therefore may possibly compensate for loss of GCN5.ObjectiveThe objective of this study was to examine if with HFD feeding that elimination of GCN5 (Kat2agene) from skeletal muscle would elicit improvements in mitochondrial and metabolic markers.MethodsSkeletal muscle specific GCN5 knockouts (Gcn5 skm-/-) were fed an HFD. Body composition, cardio-metabolic and physical fitness outcomes were monitored. Additionally, cultured myotubes were treated with a pan-GCN5/PCAF inhibitor and examined for changes in mitochondrial markers.ResultsElimination of skeletal muscle GCN5 did not alter body composition, tissue masses, energy intake, or energy expenditure measurements of mice fed an HFD. Furthermore, whole body glucose homeostasis and cardiac measurements were not altered. There were few differences in lipid metabolism genes, relatively more glucose oxidation versusGcn5 skm+/+(wildtype) mice, and a reduction inPdk4expression. Exercise capacity and mitochondrial content levels were not altered inGcn5 skm-/-mice. Further, elimination of GCN5 in skeletal muscle increasedKat2b(PCAF) mRNA expression; however, inhibition of GCN5/PCAF bromodomains in cultured myotubes did not increase oxidative metabolism genes and decreased expression of some mitochondrial genes andPdk4mRNA.ConclusionsNeither elimination of GCN5, nor simultaneous inhibition of GCN5 and its homolog PCAF improved skeletal muscle mitochondrial content under normal or HFD-fed conditions. Despite this, GCN5 may play a role in regulating macronutrient preference by regulatingPdk4content. Thus, HFD/macronutrient excess revealed novel roles of GCN5 in skeletal muscle.Highlights– Skeletal muscle specific elimination ofGcn5/Kat2adecreases fat oxidation without 1) preventing high-fat diet induced weight gain, 2) improving whole body glucose handling, or 3) improving skeletal muscle mitochondrial content.– Inhibition of the GCN5 and PCAF bromodomains andGcn5ablation decreases expression ofPdk4.– Expression ofKat2bincreases withGcn5elimination in skeletal muscle.– Inhibition of the GCN5 and PCAF bromodomains do not result in increased skeletal muscle mitochondrial content.