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.

Vacuolar ATPase as a potential therapeutic target and mediator of treatment resistance in cancer

“…Although AMPK is classically activated in response to rising AMP/ATP ratios, recent studies have demonstrated that V‐ATPase plays a role in AMP‐independent AMPK activation. Thus, binding of aldolase to V‐ATPase in the absence of the glycolytic intermediate fructose‐1,6‐bisphosphate results in AMPK activation 10, 11…”

“…PI3‐kinase‐dependent signaling appears to play a central role in inducing V‐ATPase assembly in response to increased glucose, but not amino‐acid deprivation 20, 21. V‐ATPase assembly is also promoted by interaction with aldolase or phosphofructokinase22, 23 and this may be important for AMPK activation 10…”

“…This results in production of lactic acid and H + , and plasma membrane V‐ATPase may be key under these conditions for maintaining intracellular pH homeostasis 68. In addition, via its action as a coordinator of regulators of opposing anabolic versus catabolic pathways (eg, mediated via mTORC1 or AMPK, respectively) 10. V‐ATPase may support “metabolic plasticity” allowing tumor cells to adapt to distinct and shifting tumor microenvironments (eg, nutrient/O 2 replete versus limited).…”

Control of Ribosomal RNA Transcription by Nutrients

“…In the fourth step, the hexose ring of fructose 1, 6-bisphosphate (FBP) is split by aldolase into two triose sugars: dihydroxyacetone phosphate (a ketose) and glyceraldehyde 3-phosphate (an aldose). When extracellular glucose is decreased, intracellular FBP is decreased, and aldolase unoccupied by FBP promotes the formation of a lysosomal complex containing v-ATPase axin, liver kinase B1 (LKB1), and AMPK, which regulates AMPK activity [78]. These results suggest that the decreased level of the metabolite in glycolysis controls AMPK before the reduction of ATP production just after changing environmental conditions, emphasizing that AMPK is a highly sensitive monitor of energy conditions.…”

Targeting AMPK Signaling as a Neuroprotective Strategy in Parkinson’s Disease

“…It is constitutively active, but its phosphorylation of AMPK can be modulated by both AMP, as discussed above, and through a mechanism independent from AMP [30]. In response to glucose deprivation, a complex forms between AMPK and LKB1 at the lysosomal surface that facilitates Thr172 phosphorylation [31,32]. CaMKK2, which may be the dominant AMPK activating kinase in neurons, is activated by increased intracellular calcium [18].…”