Recent reports have identified a phenomenon by which hypoxia shifts glutamine metabolism from oxidation to reductive carboxylation. We now identify the mechanism by which HIF-1 activation results in ...a dramatic reduction in the activity of the key mitochondrial enzyme complex α ketoglutarate dehydrogenase (αKGDH). HIF-1 activation promotes SIAH2 targeted ubiquitination and proteolysis of the 48 kDa splice variant of the E1 subunit of the αKGDH complex (OGDH2). Knockdown of SIAH2 or mutation of the ubiquitinated lysine residue on OGDH2 (336KA) reverses the hypoxic drop in αKGDH activity, stimulates glutamine oxidation, and reduces glutamine-dependent lipid synthesis. 336KA OGDH2-expressing cells require exogenous lipids or citrate for growth in hypoxia in vitro and fail to grow as model tumors in immunodeficient mice. Reversal of hypoxic mitochondrial function may provide a target for the development of next-generation anticancer agents targeting tumor metabolism.
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•HIF-1 activation reduces mitochondrial OCR while generating anabolic precursors•Hypoxia reduces glutamine oxidation through SIAH2-dependent proteolysis of OGDH2•Active OGDH2 makes cells dependent on exogenous lipids for hypoxic growth•Expression of nondegradable OGDH2 blocks the growth of model tumors
Sun and Denko identify a mechanism by which hypoxia redirects the metabolism of glutamine away from mitochondrial oxidation toward the synthesis of cellular fatty acids in order to support tumor cell proliferation. This work suggests that redirecting the intracellular fate of glutamine may be an effective anticancer therapy.
Nuclear glycogen was first documented in the early 1940s, but its role in cellular physiology remained elusive. In this study, we utilized pure nuclei preparations and stable isotope tracers to ...define the origin and metabolic fate of nuclear glycogen. Herein, we describe a key function for nuclear glycogen in epigenetic regulation through compartmentalized pyruvate production and histone acetylation. This pathway is altered in human non-small cell lung cancers, as surgical specimens accumulate glycogen in the nucleus. We demonstrate that the decreased abundance of malin, an E3 ubiquitin ligase, impaired nuclear glycogenolysis by preventing the nuclear translocation of glycogen phosphorylase and causing nuclear glycogen accumulation. Re-introduction of malin in lung cancer cells restored nuclear glycogenolysis, increased histone acetylation, and decreased growth of cancer cells transplanted into mice. This study uncovers a previously unknown role for glycogen metabolism in the nucleus and elucidates another mechanism by which cellular metabolites control epigenetic regulation.
The Apolipoprotein E (APOE) gene is a major genetic risk factor associated with Alzheimer's disease (AD). APOE encodes for three main isoforms in humans (E2, E3, and E4). Homozygous E4 individuals ...have more than a 10-fold higher risk for developing late-onset AD, while E2 carriers are protected. A hallmark of AD is a reduction in cerebral glucose metabolism, alluding to a strong metabolic component in disease onset and progression. Interestingly, E4 individuals display a similar regional pattern of cerebral glucose hypometabolism decades prior to disease onset. Mapping this metabolic landscape may help elucidate the underlying biological mechanism of APOE-associated risk for AD. Efficient metabolic coupling of neurons and glia is necessary for proper neuronal function, and disruption in glial energy distribution has been proposed to contribute to neuronal cell death and AD pathology. One important function of astrocytes – canonically the primary source of apolipoprotein E in the brain – is to provide metabolic substrates (lactate, lipids, amino acids and neurotransmitters) to neurons. Here we investigate the effects of APOE on astrocyte glucose metabolism in vitro utilizing scintillation proximity assays, stable isotope tracer metabolomics, and gene expression analyses. Glucose uptake is impaired in E4 astrocytes relative to E2 or E3 with specific alterations in central carbon metabolism. Using stable isotope labeled glucose U-13C allowed analyses of astrocyte-specific deep metabolic networks affected by APOE, and provided insight to the effects downstream of glucose uptake. Enrichment of 13C in early steps of glycolysis was lowest in E4 astrocytes (highest in E2), while synthesis of lactate from glucose was highest in E4 astrocytes (lowest in E2). We observed an increase in glucose flux through the pentose phosphate pathway (PPP), with downstream increases in gluconeogenesis, lipid, and de novo nucleotide biosynthesis in E4 astrocytes. There was also a marked increase in 13C enrichment in the TCA cycle of E4 astrocytes – whose substrates were also incorporated into biosynthetic pathways at a higher rate. Pyruvate carboxylase (PC) and pyruvate dehydrogenase (PDH) are the two main enzymes controlling pyruvate entry to the TCA cycle. PC gene expression is increased in E4 astrocytes and the activity relative to PDH was also increased, compared to E2 or E3. Decreased enrichment in the TCA cycle of E2 and E3 astrocytes is suggestive of increased oxidation and non-glucose derived anaplerosis, which could be fueling mitochondrial ATP production. Conversely, E4 astrocytes appear to increase carbon flux into the TCA cycle to fuel cataplerosis. Together, these data demonstrate clear APOE isoform-specific effects on glucose utilization in astrocytes, including E4-associated increases in lactate synthesis, PPP flux, and de novo biosynthesis pathways.
Glucose utilization in astrocytes expressing either human E2 (green arrows) or E4 (red arrows) relative to E3. E2 astrocytes display increased flux through glycolysis, a more oxidative TCA cycle, and decreased pentose phosphate pathway (PPP) flux. E4 astrocytes display increased glucose flux through PPP, in both re-entry into glycolysis (gluconeogenesis), increased biosynthesis, and increased lactate synthesis, with a less oxidative TCA cycle. Display omitted
•Stable isotope tracing reveals APOE-specific changes in astrocyte glucose utilization•APOE alters glucose entry into the TCA cycle•E4 astrocytes increase glucose flux into PPP and de novo biosynthesis pathways
Delivering isotopic tracers for metabolic studies in rodents without overt stress is challenging. Current methods achieve low label enrichment in proteins and lipids. Here, we report noninvasive ...introduction of
C
-glucose via a stress-free, ad libitum liquid diet. Using NMR and ion chromatography-mass spectrometry, we quantify extensive
C enrichment in products of glycolysis, the Krebs cycle, the pentose phosphate pathway, nucleobases, UDP-sugars, glycogen, lipids, and proteins in mouse tissues during 12 to 48 h of
C
-glucose feeding. Applying this approach to patient-derived lung tumor xenografts (PDTX), we show that the liver supplies glucose-derived Gln via the blood to the PDTX to fuel Glu and glutathione synthesis while gluconeogenesis occurs in the PDTX. Comparison of PDTX with ex vivo tumor cultures and arsenic-transformed lung cells versus xenografts reveals differential glucose metabolism that could reflect distinct tumor microenvironment. We further found differences in glucose metabolism between the primary PDTX and distant lymph node metastases.
Cancer cells have a different metabolic profile compared to normal cells. The Warburg effect (increased aerobic glycolysis) and glutaminolysis (increased mitochondrial activity from glutamine ...catabolism) are well known hallmarks of cancer and are accompanied by increased lactate production, hyperpolarized mitochondrial membrane and increased production of reactive oxygen species.
In this study we target the Warburg effect with dichloroacetate (DCA) and the increased mitochondrial activity of glutaminolysis with arsenic trioxide (ATO) in breast cancer cells, measuring cell proliferation, cell death and mitochondrial characteristics.
The combination of DCA and ATO was more effective at inhibiting cell proliferation and inducing cell death than either drug alone. We examined the effect of these treatments on mitochondrial membrane potential, reactive oxygen species production and ATP levels and have identified new molecular mechanisms within the mitochondria for both ATO and DCA: ATO reduces mitochondrial function through the inhibition of cytochrome C oxidase (complex IV of the electron transport chain) while DCA up-regulates ATP synthase β subunit expression. The potentiation of ATO cytotoxicity by DCA is correlated with strong suppression of the expression of c-Myc and HIF-1α, and decreased expression of the survival protein Bcl-2.
This study is the first to demonstrate that targeting two key metabolic hallmarks of cancer is an effective anti-cancer strategy with therapeutic potential.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The E4 allele of Apolipoprotein E (APOE) is associated with both metabolic dysfunction and a heightened pro-inflammatory response: two findings that may be intrinsically linked through the concept of ...immunometabolism. Here, we combined bulk, single-cell, and spatial transcriptomics with cell-specific and spatially resolved metabolic analyses in mice expressing human APOE to systematically address the role of APOE across age, neuroinflammation, and AD pathology. RNA sequencing (RNA-seq) highlighted immunometabolic changes across the APOE4 glial transcriptome, specifically in subsets of metabolically distinct microglia enriched in the E4 brain during aging or following an inflammatory challenge. E4 microglia display increased Hif1α expression and a disrupted tricarboxylic acid (TCA) cycle and are inherently pro-glycolytic, while spatial transcriptomics and mass spectrometry imaging highlight an E4-specific response to amyloid that is characterized by widespread alterations in lipid metabolism. Taken together, our findings emphasize a central role for APOE in regulating microglial immunometabolism and provide valuable, interactive resources for discovery and validation research.
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•APOE4 and age interact to drive DAM-like signatures in the absence of AD pathology•APOE4 microglia have increased aerobic glycolysis and higher Hif1α expression•APOE4 exacerbates plaque-induced microglial reactivity and lipid metabolism•Mass spectrometry imaging reveals distinct phospholipid distribution in E4FAD brains
Lee et al. integrate single-cell and spatially resolved -omics technologies to systematically characterize APOE4’s role in the brain’s response to aging, peripheral inflammatory challenge, and amyloid pathology. E4 microglia display a unique metabolic response to each of these paradigms, with increased aerobic glycolysis and altered expression of lipid metabolism pathways.
Histopathological detection and quantitation of glycogen in situ are important for the assessment of glycogen storage diseases and different types of cancer. The current standard method for defining ...the regionality of glycogen rely almost exclusively on Periodic Acid-Schiff (PAS) staining, a workflow that lacks specificity and sensitivity. Herein, we describe a new and much improved workflow to detect microenvironmental glycogen in situ using enzyme-assisted matrix-assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI). This method provides superior sensitivity and can elucidate the molecular features of glycogen structure, with 50 μm spatial resolution for a next-generation histopathological assessment of glycogen.
N-linked glycosylation is a complex, co- and post-translational series of events that connects metabolism to signaling in almost all cells. Metabolic assembly of N-linked glycans spans multiple ...cellular compartments, and early N-linked glycan biosynthesis is a central mediator of protein folding and the unfolded protein response (UPR). In the brain, N-linked glycosylated proteins participate in a myriad of processes, from electrical gradients to neurotransmission. However, it is less clear how perturbations in N-linked glycosylation impact and even potentially drive aspects of neurological disorders. In this review, we discuss our current understanding of the metabolic origins of N-linked glycans in the brain, their role in modulating neuronal function, and how aberrant N-linked glycosylation can drive neurological disorders.
At least ten unique monosaccharides are present in cells of the central nervous system, and they provide an essential repertoire of oligosaccharides critical for brain function.Monosaccharide and sugar-nucleotide biosynthesis exhibit metabolic plasticity and are channeled through multiple substrates.N-linked glycans impact nearly all neuronal functions, including maintenance of resting membrane potential, axon firing, and synaptic vesicle release.N-linked glycosylation is a central mediator of the unfolded protein response (UPR), which determines neuronal cell fate.Cytokines, nitric oxide synthase, and other protein/enzymes involved in the innate immune response are N-linked glycosylated, suggesting a central role for N-linked glycans in neuroinflammation.
The glycolytic phenotype is a widespread phenomenon in solid cancer forms, including breast cancer. Dichloroacetate (DCA) has recently been proposed as a novel and relatively non-toxic anti-cancer ...agent that can reverse the glycolytic phenotype in cancer cells through the inhibition of pyruvate dehydrogenase kinase. We have examined the effect of DCA against breast cancer cells, including in a highly metastatic in vivo model. The growth of several breast cancer cell lines was found to be inhibited by DCA in vitro. Further examination of 13762 MAT rat mammary adenocarcinoma cells found that reversal of the glycolytic phenotype by DCA correlated with the inhibition of proliferation without any increase in cell death. This was despite a small but significant increase in caspase 3/7 activity, which may sensitize cancer cells to other apoptotic triggers. In vivo, DCA caused a 58% reduction in the number of lung metastases observed macroscopically after injection of 13762 MAT cells into the tail vein of rats (P = 0.0001, n ≥ 9 per group). These results demonstrate that DCA has anti-proliferative properties in addition to pro-apoptotic properties, and can be effective against highly metastatic disease in vivo, highlighting its potential for clinical use.
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