Nutrient Sensing Nuclear Receptors Coordinate Autophagy

Autophagy is an evolutionally conserved catabolic process that recycles nutrients upon starvation and maintains cellular energy homeostasis(1–3). Its acute regulation by nutrient sensing signaling pathways is well described, but its longer-term transcriptional regulation is not. The nuclear receptors PPARα and FXR are activated in the fasted or fed liver, respectively(4,5). Here we show that both regulate hepatic autophagy. Pharmacologic activation of PPARα reverses the normal suppression of autophagy in the fed state, inducing autophagic lipid degradation, or lipophagy. This response is lost in PPARα knockout (PPARα(−/−)) mice, which are partially defective in the induction of autophagy by fasting. Pharmacologic activation of the bile acid receptor FXR strongly suppresses the induction of autophagy in the fasting state, and this response is absent in FXR knockout (FXR(−/−)) mice, which show a partial defect in suppression of hepatic autophagy in the fed state. PPARα and FXR compete for binding to shared sites in autophagic gene promoters, with opposite transcriptional outputs. These results reveal complementary, interlocking mechanisms for regulation of autophagy by nutrient status.