AMPK and mTOR play principal roles in governing metabolic programs; however, mechanisms underlying the coordination of the two inversely regulated kinases remain unclear. In this study we found, most ...surprisingly, that the late endosomal/lysosomal protein complex v-ATPase-Ragulator, essential for activation of mTORC1, is also required for AMPK activation. We also uncovered that AMPK is a residential protein of late endosome/lysosome. Under glucose starvation, the v-ATPase-Ragulator complex is accessible to AXIN/LKB1 for AMPK activation. Concurrently, the guanine nucleotide exchange factor (GEF) activity of Ragulator toward RAG is inhibited by AXIN, causing dissociation from endosome and inactivation of mTORC1. We have thus revealed that the v-ATPase-Ragulator complex is also an initiating sensor for energy stress and meanwhile serves as an endosomal docking site for LKB1-mediated AMPK activation by forming the v-ATPase-Ragulator-AXIN/LKB1-AMPK complex, thereby providing a switch between catabolism and anabolism. Our current study also emphasizes a general role of late endosome/lysosome in controlling metabolic programs.
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•Ragulator is essential for starvation-induced AMPK activation•LKB1-dependent activation of AMPK takes place on late endosome/lysosome•V-ATPase-Ragulator provides docking sites for AXIN/LKB1 endosomal translocation•V-ATPase-Ragulator is a switch between anabolism and catabolism
AMPK and mTOR regulate cellular balance between catabolism and anabolism. Zhang et al. show that the endosomal v-ATPase-Ragulator complex, required for mTORC1 activation when nutrients are abundant, is also essential in LKB1-mediated AMPK activation in response to energy stress, thus acting as a dual energy sensor.
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), but it is ...unclear whether this activation occurs solely via changes in AMP or ADP, the classical activators of AMPK. Here, we describe an AMP/ADP-independent mechanism that triggers AMPK activation by sensing the absence of fructose-1,6-bisphosphate (FBP), with AMPK being progressively activated as extracellular glucose and intracellular FBP decrease. When unoccupied by FBP, aldolases promote the formation of a lysosomal complex containing at least v-ATPase, ragulator, axin, liver kinase B1 (LKB1) and AMPK, which has previously been shown to be required for AMPK activation. Knockdown of aldolases activates AMPK even in cells with abundant glucose, whereas the catalysis-defective D34S aldolase mutant, which still binds FBP, blocks AMPK activation. Cell-free reconstitution assays show that addition of FBP disrupts the association of axin and LKB1 with v-ATPase and ragulator. Importantly, in some cell types AMP/ATP and 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 being a glycolytic enzyme, is a sensor of glucose availability that regulates AMPK.
Metformin, the most prescribed antidiabetic medicine, has shown other benefits such as anti-ageing and anticancer effects
. For clinical doses of metformin, AMP-activated protein kinase (AMPK) has a ...major role in its mechanism of action
; however, the direct molecular target of metformin remains unknown. Here we show that clinically relevant concentrations of metformin inhibit the lysosomal proton pump v-ATPase, which is a central node for AMPK activation following glucose starvation
. We synthesize a photoactive metformin probe and identify PEN2, a subunit of γ-secretase
, as a binding partner of metformin with a dissociation constant at micromolar levels. Metformin-bound PEN2 forms a complex with ATP6AP1, a subunit of the v-ATPase
, which leads to the inhibition of v-ATPase and the activation of AMPK without effects on cellular AMP levels. Knockout of PEN2 or re-introduction of a PEN2 mutant that does not bind ATP6AP1 blunts AMPK activation. In vivo, liver-specific knockout of Pen2 abolishes metformin-mediated reduction of hepatic fat content, whereas intestine-specific knockout of Pen2 impairs its glucose-lowering effects. Furthermore, knockdown of pen-2 in Caenorhabditis elegans abrogates metformin-induced extension of lifespan. Together, these findings reveal that metformin binds PEN2 and initiates a signalling route that intersects, through ATP6AP1, the lysosomal glucose-sensing pathway for AMPK activation. This ensures that metformin exerts its therapeutic benefits in patients without substantial adverse effects.
AMPK, a master regulator of metabolic homeostasis, is activated by both AMP-dependent and AMP-independent mechanisms. The conditions under which these different mechanisms operate, and their ...biological implications are unclear. Here, we show that, depending on the degree of elevation of cellular AMP, distinct compartmentalized pools of AMPK are activated, phosphorylating different sets of targets. Low glucose activates AMPK exclusively through the AMP-independent, AXIN-based pathway in lysosomes to phosphorylate targets such as ACC1 and SREBP1c, exerting early anti-anabolic and pro-catabolic roles. Moderate increases in AMP expand this to activate cytosolic AMPK also in an AXIN-dependent manner. In contrast, high concentrations of AMP, arising from severe nutrient stress, activate all pools of AMPK independently of AXIN. Surprisingly, mitochondrion-localized AMPK is activated to phosphorylate ACC2 and mitochondrial fission factor (MFF) only during severe nutrient stress. Our findings reveal a spatiotemporal basis for hierarchical activation of different pools of AMPK during differing degrees of stress severity.
Cancer cells are known for their capacity to rewire metabolic pathways to support survival and proliferation under various stress conditions. Ketone bodies, though produced in the liver, are not ...consumed in normal adult liver cells. We find here that ketone catabolism or ketolysis is re-activated in hepatocellular carcinoma （HCC） cells under nutrition deprivation conditions. Mechanistically, 3-oxoacid CoA-transferase 1 （OXCT1）, a rate-limiting ketolytic enzyme whose expression is suppressed in normal adult liver tissues, is re-induced by serum starvation-triggered mTORC2- AKT-SP1 signaling in HCC cells. Moreover, we observe that enhanced ketolysis in HCC is critical for repression of AMPK activation and protects HCC cells from excessive autophagy, thereby enhancing tumor growth. Importantly, analysis of clinical HCC samples reveals that increased OXCT1 expression predicts higher patient mortality. Taken together, we uncover here a novel metabolic adaptation by which nutrition-deprived HCC cells employ ketone bodies for energy supply and cancer progression.
In metazoans, cells depend on extracellular growth factors for energy homeostasis. We found that glycogen synthase kinase-3 (GSK3), when deinhibited by default in cells deprived of growth factors, ...activates acetyltransferase TIP60 through phosphorylating TIP60-Ser⁸⁶, which directly acetylates and stimulates the protein kinase ULK1, which is required for autophagy. Cells engineered to express TIP60 S86A that cannot be phosphorylated by GSK3 could not undergo serum deprivation-induced autophagy. An acetylation-defective mutant of ULK1 failed to rescue autophagy in ULK1 -/- mouse embryonic fibroblasts. Cells used signaling from GSK3 to TIP60 and ULK1 to regulate autophagy when deprived of serum but not glucose. These findings uncover an activating pathway that integrates protein phosphorylation and acetylation to connect growth factor deprivation to autophagy.
Necrosis can be induced by stimulating death receptors with tumor necrosis factor (TNF) or other agonists; however, the underlying mechanism differentiating necrosis from apoptosis is largely ...unknown. We identified the protein kinase receptor-interacting protein 3 (RIP3) as a molecular switch between TNF-induced apoptosis and necrosis in NIH 3T3 cells and found that RIP3 was required for necrosis in other cells. RIP3 did not affect RIP1-mediated apoptosis but was required for RIP1-mediated necrosis and the enhancement of necrosis by the caspase inhibitor zVAD. By activating key enzymes of metabolic pathways, RIP3 regulates TNF-induced reactive oxygen species production, which partially accounts for RIP3's ability to promote necrosis. Our data suggest that modulation of energy metabolism in response to death stimuli has an important role in the choice between apoptosis and necrosis.
Despite very different functions, studies increasingly report that there may be a potential central nervous anatomical connection between the heart and the small intestine. In this study, the central ...nervous anatomical relationship between the heart and small intestine was studied via a viral tracer. Pseudorabies virus (PRV) syngeneic strains with different fluorescent reporter genes (eGFP or mRFP) were microinjected into the heart walls and small intestinal walls of male C57BL/6J using glass microelectrode. The results showed that the co-labeled nuclei in the brain were lateral periaqueductal gray (LPAG) and ventrolateral periaqueductal gray (VLPAG) in the midbrain, mesencephalic trigeminal nucleus (Me5), and motor trigeminal nucleus anterior digastric Part (5Adi) in the pons. The co-labeled sites in the spinal cord were intermediolateral column (IML) in the second thoracic vertebra, IML and lamina 7 of the spinal gray (7SP) in the third thoracic vertebra, and IML in the fourth thoracic vertebra. Our data show that there is a neuroanatomical connection between the small intestine and the heart in the central nervous system (CNS). Neuroanatomical integration of the heart and small intestine may provide a basis for revealing the physiological and pathological interactions between the circulatory and digestive systems. The interactions may be mediated more effectively through sympathetic nerves.
The movement toward cobalt‐free cathode materials has served as a motivation for increased research in layered nickel‐rich cathodes for next generation metal batteries. Unfortunately, Ni‐rich cathode ...materials suffer from low capacity retention and poor thermal stability due to phase transition that results in issues such as the oxygen evolution reaction, hindering its extensive implementation. Herein, highly pliable separators with a 3D porous structure are prepared via a facile phase‐inversion method from an inorganic phosphorus‐based flame retardant and a thermally conductive graphene oxide additive. Benefiting from its 3D porous structure, in‐built radical scavenger, and uniform thermal distribution, the obtained separator enables a near‐single Li+ migration (tLi+ = 0.8) by blocking large‐size anions, driving the LiNi0.8Mn0.1Co0.1O2/Li metal batteries to 188.8 mAh g−1 at 0.2 C, and demonstrating a capacity retention of 82.2% versus 41.4% for commercial polyolefin separators after 200 cycles, as well as excellent dendrite‐suppressing capabilities by reducing localized temperature hotspots and enabling sufficient mass transfer. This work also suggests a new alternative pathway for stabilizing reactive electrode materials for other high‐energy battery systems.
A porous but highly thermal conductive membrane with an in‐built stabilizer and near‐single Li+ migration enables the quenching of highly reactive free radicals for the structural stablization of Ni‐rich cathodes, and restrains the uneven Li stripping/deposition caused by temperature variation induced changes in current density and Li+ supply.
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