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

Introduction: GCN5 (Kat2a) is a lysine acetyl transferase capable of acetylating and inhibiting PGC-1ɑ activity. As such, it is described as a negative regulator of PGC-1ɑ 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-1ɑ and therefore may possibly compensate for loss of GCN5. Objective: The objective of this study was to examine if with HFD feeding that elimination of GCN5 (Kat2a gene) from skeletal muscle would elicit improvements in mitochondrial and metabolic markers. Methods: Skeletal 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. Results: Elimination 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 versus Gcn5 skm+/+ (wildtype) mice, and a reduction in Pdk4 expression. Exercise capacity and mitochondrial content levels were not altered in Gcn5 skm-/- mice. Further, elimination of GCN5 in skeletal muscle increased Kat2b (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 and Pdk4 mRNA. Conclusions: Neither 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 regulating Pdk4 content. Thus, HFD/macronutrient excess revealed novel roles of GCN5 in skeletal muscle. ### Competing Interest Statement The authors have declared no competing interest.