Metformin is a biguanide widely prescribed to treat Type II diabetes that has gained interest as an antineoplastic agent. Recent work suggests that metformin directly antagonizes cancer cell growth ...through its actions on complex I of the mitochondrial electron transport chain (ETC). However, the mechanisms by which metformin arrests cancer cell proliferation remain poorly defined. Here we demonstrate that the metabolic checkpoint kinases AMP-activated protein kinase (AMPK) and LKB1 are not required for the antiproliferative effects of metformin. Rather, metformin inhibits cancer cell proliferation by suppressing mitochondrial-dependent biosynthetic activity. We show that in vitro metformin decreases the flow of glucose- and glutamine-derived metabolic intermediates into the Tricarboxylic Acid (TCA) cycle, leading to reduced citrate production and de novo lipid biosynthesis. Tumor cells lacking functional mitochondria maintain lipid biosynthesis in the presence of metformin via glutamine-dependent reductive carboxylation, and display reduced sensitivity to metformin-induced proliferative arrest. Our data indicate that metformin inhibits cancer cell proliferation by suppressing the production of mitochondrial-dependent metabolic intermediates required for cell growth, and that metabolic adaptations that bypass mitochondrial-dependent biosynthesis may provide a mechanism of tumor cell resistance to biguanide activity.
Reactive oxygen species (ROS) are continuously produced as a by-product of mitochondrial metabolism and eliminated via antioxidant systems. Regulation of mitochondrially produced ROS is required for ...proper cellular function, adaptation to metabolic stress, and bypassing cellular senescence. Here, we report non-canonical regulation of the cellular energy sensor AMP-activated protein kinase (AMPK) by mitochondrial ROS (mROS) that functions to maintain cellular metabolic homeostasis. We demonstrate that mitochondrial ROS are a physiological activator of AMPK and that AMPK activation triggers a PGC-1α-dependent antioxidant response that limits mitochondrial ROS production. Cells lacking AMPK activity display increased mitochondrial ROS levels and undergo premature senescence. Finally, we show that AMPK-PGC-1α-dependent control of mitochondrial ROS regulates HIF-1α stabilization and that mitochondrial ROS promote the Warburg effect in cells lacking AMPK signaling. These data highlight a key function for AMPK in sensing and resolving mitochondrial ROS for stress resistance and maintaining cellular metabolic balance.
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•Mitochondrial ROS (mROS) are a non-canonical activator of AMPK•AMPK-deficient cells have elevated mROS and undergo premature senescence•AMPK activation promotes a PGC-1α-dependent antioxidant response•AMPK-PGC-1α control of mROS regulates Warburg metabolism
AMP-activated protein kinase (AMPK) regulates cellular metabolic balance in response to energy stress. This work by Rabinovitch et al. demonstrates that mitochondrial reactive oxygen species (mROS) are a physiological activator of AMPK and that AMPK couples mROS to an antioxidant program that regulates mitochondrial homeostasis and cellular metabolic balance.
How systemic metabolic alterations during acute infections impact immune cell function remains poorly understood. We found that acetate accumulates in the serum within hours of systemic bacterial ...infections and that these increased acetate concentrations are required for optimal memory CD8+ T cell function in vitro and in vivo. Mechanistically, upon uptake by memory CD8+ T cells, stress levels of acetate expanded the cellular acetyl-coenzyme A pool via ATP citrate lyase and promoted acetylation of the enzyme GAPDH. This context-dependent post-translational modification enhanced GAPDH activity, catalyzing glycolysis and thus boosting rapid memory CD8+ T cell responses. Accordingly, in a murine Listeria monocytogenes model, transfer of acetate-augmented memory CD8+ T cells exerted superior immune control compared to control cells. Our results demonstrate that increased systemic acetate concentrations are functionally integrated by CD8+ T cells and translate into increased glycolytic and functional capacity. The immune system thus directly relates systemic metabolism with immune alertness.
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•Serum acetate levels rapidly increase following systemic bacterial infection•Memory CD8+ T cells take up acetate and expand their acetyl-CoA pool•Increased acetyl-CoA levels catalyze functional activity of GAPDH by acetylation•Augmented glycolytic flux rates boost rapid recall responses of memory CD8+ T cells
How systemic metabolic alterations during acute infections impact immune-cell function remains poorly understood. Hess and colleagues demonstrate that acetate rapidly increases during infections, which drives acetylation of GAPDH in memory CD8+ T cells and thereby catalyzes the rapid recall response.
Dendritic cells (DCs) are first responders of the innate immune system that integrate signals from external stimuli to direct context-specific immune responses. Current models suggest that an active ...switch from mitochondrial metabolism to glycolysis accompanies DC activation to support the anabolic requirements of DC function. We show that early glycolytic activation is a common program for both strong and weak stimuli, but that weakly activated DCs lack long-term HIF-1α-dependent glycolytic reprogramming and retain mitochondrial oxidative metabolism. Early induction of glycolysis is associated with activation of AKT, TBK, and mTOR, and sustained activation of these pathways is associated with long-term glycolytic reprogramming. We show that inhibition of glycolysis impaired maintenance of elongated cell shape, DC motility, CCR7 oligomerization, and DC migration to draining lymph nodes. Together, our results indicate that early induction of glycolysis occurs independent of pro-inflammatory phenotype, and that glycolysis supports DC migratory ability regardless of mitochondrial bioenergetics.
Neutrophils are phenotypically heterogeneous and exert either anti- or pro-metastatic functions. We show that cancer-cell-derived G-CSF is necessary, but not sufficient, to mobilize immature ...low-density neutrophils (iLDNs) that promote liver metastasis. In contrast, mature high-density neutrophils inhibit the formation of liver metastases. Transcriptomic and metabolomic analyses of high- and low-density neutrophils reveal engagement of numerous metabolic pathways specifically in low-density neutrophils. iLDNs exhibit enhanced global bioenergetic capacity, through their ability to engage mitochondrial-dependent ATP production, and remain capable of executing pro-metastatic neutrophil functions, including NETosis, under nutrient-deprived conditions. We demonstrate that NETosis is an important neutrophil function that promotes breast cancer liver metastasis. iLDNs rely on the catabolism of glutamate and proline to support mitochondrial-dependent metabolism in the absence of glucose, which enables sustained NETosis. These data reveal that distinct pro-metastatic neutrophil populations exhibit a high degree of metabolic flexibility, which facilitates the formation of liver metastases.
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•G-CSF is required, but not sufficient, to mobilize immature low-density neutrophils•Immature low-density neutrophils are defined by a C/EBPε transcriptional signature•Immature low-density neutrophils promote the formation of liver metastases•Immature low-density neutrophils have a higher global bioenergetic capacity
Hsu et al. demonstrate that tumor-derived G-CSF, in concert with additional factors, mobilizes immature low-density neutrophils (iLDNs) that promote breast cancer liver metastasis. iLDNs are able to perform pro-metastatic functions under metabolically challenging conditions, such as low glucose, due to their enhanced global bioenergetic capacity.
TFEB and TFE3 are transcriptional regulators of the innate immune response, but the mechanisms regulating their activation upon pathogen infection are poorly elucidated. Using C. elegans and ...mammalian models, we report that the master metabolic modulator 5′-AMP-activated protein kinase (AMPK) and its negative regulator Folliculin (FLCN) act upstream of TFEB/TFE3 in the innate immune response, independently of the mTORC1 signaling pathway. In nematodes, loss of FLCN or overexpression of AMPK confers pathogen resistance via activation of TFEB/TFE3-dependent antimicrobial genes, whereas ablation of total AMPK activity abolishes this phenotype. Similarly, in mammalian cells, loss of FLCN or pharmacological activation of AMPK induces TFEB/TFE3-dependent pro-inflammatory cytokine expression. Importantly, a rapid reduction in cellular ATP levels in murine macrophages is observed upon lipopolysaccharide (LPS) treatment accompanied by an acute AMPK activation and TFEB nuclear localization. These results uncover an ancient, highly conserved, and pharmacologically actionable mechanism coupling energy status with innate immunity.
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•AMPK and FLCN regulate TFEB/TFE3-mediated innate immunity and pathogen resistance•Loss of FLCN or activation of AMPK induces TFEB/TFE3-dependent pro-inflammatory profile•FLCN depletion in macrophages enhances their energy metabolism and phagocytosis•LPS treatment induces acute ATP reduction followed by AMPK and TFEB activation
El-Houjeiri et al. show that loss of FLCN or pharmacological activation of AMPK induces TFEB/TFE3-dependent pro-inflammatory cytokine expression and phagocytosis in macrophages and confers pathogen resistance in C. elegans. These results uncover an ancient, highly conserved, and pharmacologically actionable mechanism coupling energy status to innate immunity.
CD73 is an ectonucleotidase overexpressed on tumor cells that suppresses anti-tumor immunity. Accordingly, several CD73 inhibitors are currently being evaluated in the clinic, including in large ...randomized clinical trials. Yet, the tumor cell-intrinsic impact of CD73 remain largely uncharacterized. Using metabolomics, we discovered that CD73 significantly enhances tumor cell mitochondrial respiration and aspartate biosynthesis. Importantly, rescuing aspartate biosynthesis was sufficient to restore proliferation of CD73-deficient tumors in immune deficient mice. Seahorse analysis of a large panel of mouse and human tumor cells demonstrated that CD73 enhanced oxidative phosphorylation (OXPHOS) and glycolytic reserve. Targeting CD73 decreased tumor cell metabolic fitness, increased genomic instability and suppressed poly ADP ribose polymerase (PARP) activity. Our study thus uncovered an important immune-independent function for CD73 in promoting tumor cell metabolism, and provides the rationale for previously unforeseen combination therapies incorporating CD73 inhibition.
Whether screening the metabolic activity of immune cells facilitates discovery of molecular pathology remains unknown. Here we prospectively screened the extracellular acidification rate as a measure ...of glycolysis and the oxygen consumption rate as a measure of mitochondrial respiration in B cells from patients with primary antibody deficiency. The highest oxygen consumption rate values were detected in three study participants with persistent polyclonal B cell lymphocytosis (PPBL). Exome sequencing identified germline mutations in SDHA, which encodes succinate dehydrogenase subunit A, in all three patients with PPBL. SDHA gain-of-function led to an accumulation of fumarate in PPBL B cells, which engaged the KEAP1-Nrf2 system to drive the transcription of genes encoding inflammatory cytokines. In a single patient trial, blocking the activity of the cytokine interleukin-6 in vivo prevented systemic inflammation and ameliorated clinical disease. Overall, our study has identified pathological mitochondrial retrograde signaling as a disease modifier in primary antibody deficiency.
A central hallmark of cancer cells is the reprogramming of cellular metabolism to meet the bioenergetic and biosynthetic demands of malignant growth. Here, we report that the miR-17∼92 microRNA ...(miRNA) cluster is an oncogenic driver of tumor metabolic reprogramming. Loss of miR-17∼92 in Myc+ tumor cells leads to a global decrease in tumor cell metabolism, affecting both glycolytic and mitochondrial metabolism, whereas increased miR-17∼92 expression is sufficient to drive increased nutrient usage by tumor cells. We mapped the metabolic control element of miR-17∼92 to the miR-17 seed family, which influences cellular metabolism and mammalian target of rapamycin complex 1 (mTORC1) signaling through negative regulation of the LKB1 tumor suppressor. miR-17-dependent tuning of LKB1 levels regulates both the metabolic potential of Myc+ lymphomas and tumor growth in vivo. Our results establish metabolic reprogramming as a central function of the oncogenic miR-17∼92 miRNA cluster that drives the progression of MYC-dependent tumors.
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•miR-17∼92 is required for metabolic reprogramming of Myc+ tumor cells•miR-17/20 is the primary metabolic regulatory element of miR-17∼92•miR-17 negatively regulates the tumor suppressor LKB1•miR-17-dependent silencing of LKB1 dictates metabolic and tumorigenic potential
Cancer cells re-wire cellular metabolic pathways to help fuel the increased bioenergetic and biosynthetic demands of malignant growth. Work by Izreig et al. demonstrate that this process is controlled in lymphoma cells by the miR-17∼92 microRNA cluster, which coordinates tumor metabolism by silencing the LKB1 tumor suppressor pathway.
Abstract
Metabolic programming of the innate immune cells known as dendritic cells (DCs) changes in response to different stimuli, influencing their function. While the mechanisms behind increased ...glycolytic metabolism in response to inflammatory stimuli are well-studied, less is known about the programming of mitochondrial metabolism in DCs. We used lipopolysaccharide (LPS) and interferon-β (IFN-β), which differentially stimulate the use of glycolysis and oxidative phosphorylation (OXPHOS), respectively, to identify factors important for mitochondrial metabolism. We found that the expression of peroxisome proliferator-activated receptor gamma co-activator 1β (PGC-1β), a transcriptional co-activator and known regulator of mitochondrial metabolism, decreases when DCs are activated with LPS, when OXPHOS is diminished, but not with IFN-β, when OXPHOS is maintained. We examined the role of PGC-1β in bioenergetic metabolism of DCs and found that PGC-1β deficiency indeed impairs their mitochondrial respiration. PGC-1β-deficient DCs are more glycolytic compared to controls, likely to compensate for reduced OXPHOS. PGC-1β deficiency also causes decreased capacity for ATP production at steady state and in response to IFN-β treatment. Loss of PGC-1β in DCs leads to increased expression of genes in inflammatory pathways, and reduced expression of genes encoding proteins important for mitochondrial metabolism and function. Collectively, these results demonstrate that PGC-1β is a key regulator of mitochondrial metabolism and negative regulator of inflammatory gene expression in DCs.
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