Fructose-1,6-bisphosphate and aldolase mediate glucose sensing by AMPK

Abstract

The major energy source for most cells is glucose, from which ATP is generated via glycolysis and/or oxidative metabolism. Glucose deprivation activates AMP-activated protein kinase (AMPK)1, but it has been unclear whether this occurs solely via changes in AMP or ADP, the classical activators of AMPK2–5. Here, we uncover a mechanism that triggers AMPK activation via an AMP/ADP-independent mechanism sensing absence of FBP, with AMPK being progressively activated as extracellular glucose and intracellular FBP decrease. When unoccupied by FBP, aldolases promote the formation of lysosomal complexes containing the v-ATPase, Ragulator, AXIN, LKB1 and AMPK, previously shown to be required for AMPK activation6,7. Knockdown of aldolases activates AMPK even in cells with abundant glucose, while the catalysis-defective D34S aldolase mutant, which still binds FBP, blocks AMPK activation. Cell-free reconstitution assays show that addition of FBP disrupts association of AXIN/LKB1 with v-ATPase/Ragulator. Importantly, in some cell types AMP:ATP/ADP:ATP ratios remain unchanged during acute glucose starvation, and intact AMP-binding sites on AMPK are not required for AMPK activation. These results establish that aldolase, as well as a glycolytic enzyme, is a sensor of glucose availability that regulates AMPK.