Autophagy-related 7 (ATG7) regulates food intake and liver health during asparaginase exposure

Abstract

Amino acid starvation by the chemotherapy agent asparaginase is a potent activator of the integrated stress response (ISR) in the liver and can upregulate autophagy in some cell types. We hypothesized that autophagy-related 7 (ATG7), a protein that is essential for autophagy and an ISR target gene, was necessary during exposure to asparaginase to maintain liver health. We knocked down Atg7 systemically (Atg7^Δ/Δ) or in hepatocytes only (ls-Atg7KO) in mice before exposure to pegylated asparaginase for 5 days. Intact mice injected with asparaginase lost body weight due to reduced food intake and increased energy expenditure. Systemic Atg7 ablation reduced liver protein synthesis and increased liver injury in vehicle-injected mice but did not further reduce liver protein synthesis, exacerbate steatosis or liver injury, or alter energy expenditure following 5 days of asparaginase exposure. Atg7^Δ/Δ mice were unexpectantly protected from asparaginase-induced anorexia and weight loss. This protection corresponded with reduced phosphorylation of hepatic GCN2 and blunted increases in ISR gene targets including growth differentiation factor 15 (GDF15), a negative regulator of food intake. Interestingly, asparaginase elevated serum GDF15 and reduced food intake in ls-Atg7KO mice, similar to intact mice. Liver triglycerides and production of the hepatokine fibroblast growth factor 21, another ISR gene target, were suppressed in asparaginase-exposed Atg7^Δ/Δ and ls-Atg7KO mice. This work identifies a bidirectional relationship between autophagy and the ISR in the liver during asparaginase, affecting food intake and liver health.

Keywords: FGF21; GDF15; amino acid; body composition; eukaryotic initiation factor 2 (eIF2); gene expression; polysome profiling; protein synthesis; translation.