| dc.description.abstract | Blood glucose homeostasis is essential for human growth, physical activities, and health. The present study proposes a possible mechanism for autophagy-mediated hepatic glucose production (HGP) during starvation, which is likely to be in a FoxO1-dependent manner. HGP assay showed that autophagy deficiency induced by either chloroquine (CQ) or siRNA-ATG7 significantly suppressed the HGP in wild type (WT), but not in liver-specific FoxO1 knockout (L-FKO) mouse hepatocytes. Similarly, the glucagon tolerance test and pyruvate tolerance test showed that upon inhibition of autophagy, only WT mice but not L-FKO mice exhibited a significant reduction in glucose production compared to the WT or L-FKO mice without autophagy deficiency. Western blot results further revealed that under autophagy deficiency, the protein amount of FoxO1 was remarkably reduced, accompanied with a significant decrease of FoxO1 nuclear localization. Notably, the reduction of FoxO1 protein amounts induced by autophagy deficiency was independent of FoxO1-S253 and FoxO1-S273 phosphorylation, as the reduction of FoxO1 persisted in hepatocytes isolated from FoxO1-S253A/A and FoxO1-S273D/D knock-in (KI) mice. Even proteasome inhibitor MG132 did not prevent FoxO1 from decreasing under autophagy deficiency, suggesting that the FoxO1 degradation was unlikely the major cause. In addition, autophagy deficiency did not change FoxO1 mRNA level, meaning that the reduction of FoxO1 was likely happening in post-transcriptional activities. The HPLC results unveiled that autophagy deficiency significantly altered hepatic amino acid pools and amino acid transportation including ATF4-LAT1 axis. With an addition of exogenous amino acid mixture, we successfully restored the FoxO1 protein amount and HGP even under autophagy deficiency. Meanwhile, amino acid supplementation-induced restoration of FoxO1 and HGP was abolished by protein synthesis inhibitor cycloheximide (CHX), suggesting that the alteration of amino acid pools caused by autophagy deficiency impaired FoxO1 protein synthesis. The present study highlights an important role of autophagy involved in glucose homeostasis, which is to maintain the hepatic amino acid pools under starvation, subsequently supporting the activity of FoxO1 in control of the HGP. | |
