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Nature Reviews. Nephrology Sep 2022Cellular hypoxia occurs when the demand for sufficient molecular oxygen needed to produce the levels of ATP required to perform physiological functions exceeds the... (Review)
Review
Cellular hypoxia occurs when the demand for sufficient molecular oxygen needed to produce the levels of ATP required to perform physiological functions exceeds the vascular supply, thereby leading to a state of oxygen depletion with the associated risk of bioenergetic crisis. To protect against the threat of hypoxia, eukaryotic cells have evolved the capacity to elicit oxygen-sensitive adaptive transcriptional responses driven primarily (although not exclusively) by the hypoxia-inducible factor (HIF) pathway. In addition to the canonical regulation of HIF by oxygen-dependent hydroxylases, multiple other input signals, including gasotransmitters, non-coding RNAs, histone modifiers and post-translational modifications, modulate the nature of the HIF response in discreet cell types and contexts. Activation of HIF induces various effector pathways that mitigate the effects of hypoxia, including metabolic reprogramming and the production of erythropoietin. Drugs that target the HIF pathway to induce erythropoietin production are now approved for the treatment of chronic kidney disease-related anaemia. However, HIF-dependent changes in cell metabolism also have profound implications for functional responses in innate and adaptive immune cells, and thereby heavily influence immunity and the inflammatory response. Preclinical studies indicate a potential use of HIF therapeutics to treat inflammatory diseases, such as inflammatory bowel disease. Understanding the links between HIF, cellular metabolism and immunity is key to unlocking the full therapeutic potential of drugs that target the HIF pathway.
Topics: Cell Hypoxia; Erythropoietin; Humans; Hypoxia; Kidney; Oxygen
PubMed: 35726016
DOI: 10.1038/s41581-022-00587-8 -
Nature Reviews. Molecular Cell Biology May 2020Molecular oxygen (O) sustains intracellular bioenergetics and is consumed by numerous biochemical reactions, making it essential for most species on Earth. Accordingly,... (Review)
Review
Molecular oxygen (O) sustains intracellular bioenergetics and is consumed by numerous biochemical reactions, making it essential for most species on Earth. Accordingly, decreased oxygen concentration (hypoxia) is a major stressor that generally subverts life of aerobic species and is a prominent feature of pathological states encountered in bacterial infection, inflammation, wounds, cardiovascular defects and cancer. Therefore, key adaptive mechanisms to cope with hypoxia have evolved in mammals. Systemically, these adaptations include increased ventilation, cardiac output, blood vessel growth and circulating red blood cell numbers. On a cellular level, ATP-consuming reactions are suppressed, and metabolism is altered until oxygen homeostasis is restored. A critical question is how mammalian cells sense oxygen levels to coordinate diverse biological outputs during hypoxia. The best-studied mechanism of response to hypoxia involves hypoxia inducible factors (HIFs), which are stabilized by low oxygen availability and control the expression of a multitude of genes, including those involved in cell survival, angiogenesis, glycolysis and invasion/metastasis. Importantly, changes in oxygen can also be sensed via other stress pathways as well as changes in metabolite levels and the generation of reactive oxygen species by mitochondria. Collectively, this leads to cellular adaptations of protein synthesis, energy metabolism, mitochondrial respiration, lipid and carbon metabolism as well as nutrient acquisition. These mechanisms are integral inputs into fine-tuning the responses to hypoxic stress.
Topics: Adenosine Triphosphate; Cell Hypoxia; Energy Metabolism; Humans; Mitochondria; Oxidative Stress; Oxygen; Reactive Oxygen Species; Signal Transduction
PubMed: 32144406
DOI: 10.1038/s41580-020-0227-y -
European Review For Medical and... Feb 2020To investigate the roles and underlying mechanisms of melatonin in oxygen-glucose deprivation/reoxygenation (OGD/R)-insulted SH SY5Y cells.
OBJECTIVE
To investigate the roles and underlying mechanisms of melatonin in oxygen-glucose deprivation/reoxygenation (OGD/R)-insulted SH SY5Y cells.
MATERIALS AND METHODS
SH SY5Y cells were cultured for OGD/R stimulation. Cell viability and cytotoxicity were measured by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide, lactate dehydrogenase (LDH), and Hoechst 33258/propidium iodide (PI) staining assays. The mRNA levels of high mobility group box-1 (HMGB1), tumor necrosis factor α (TNF-α), and inducible nitric oxide synthase (iNOS) were analyzed by quantitative Real Time-PCR assays. Nitric oxide (NO) production was assessed by Griess reagent. Reactive oxygen species (ROS) production was detected by fluorescent probe. Malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were examined by commercial kits. Cell apoptosis was analyzed by flow cytometry and caspase-3 activity. The protein levels were detected by Western blot.
RESULTS
Melatonin enhanced the viability and reduced the death and LDH release of OGD/R exposed SH SY5Y cells. Melatonin repressed the HMGB1, TNF-α, and iNOS mRNA expression, NO production, and nuclear factor κB (NF-κB) activation in OGD/R challenged SH SY5Y cells. Melatonin reduced the ROS, MDA, 4-HNE, and 8-OHdG contents but further enhanced the levels of the nuclear factor E2-related factor-2 (Nrf2) and heme oxygenase (HO-1). Melatonin-increased viability and melatonin-decreased LDH release were also mediated by the blockage of NF-κB or reversed by Nrf2 or HO-1 knockdown. Melatonin exerted antiapoptotic effect on OGD/R treated SH SY5Y cells partly by activating Akt signaling. OGD/R challenged SH SY5Y cell autophagy was also repressed by melatonin, as evidenced by the decreased levels of LC-II and beclin-1 and the increased phosphorylation of mammalian target of rapamycin (mTOR), p70 ribosomal protein S6 kinase (p70S6K), and eukaryotic initiation factor 4E binding protein 1 (4E-BP-1).
CONCLUSIONS
Melatonin protected SH SY5Y cells from OGD/R induced oxidative stress, inflammation, apoptosis, and autophagy by blocking NF-κB signaling and activating Nrf2/HO-1, Akt, and mTOR/p70S6K/4E-BP-1 pathways, thereby indicating that melatonin is a potential and novel therapeutic drug for ischemic stroke.
Topics: Antioxidants; Apoptosis; Cell Hypoxia; Cell Line, Tumor; Cell Survival; Glucose; Humans; Inflammation Mediators; Melatonin; Neurons; Oxidation-Reduction; Oxidative Stress; Oxygen; Reactive Oxygen Species; Signal Transduction
PubMed: 32096202
DOI: 10.26355/eurrev_202002_20211 -
Cell Metabolism Apr 2020NADH provides electrons for aerobic ATP production. In cells deprived of oxygen or with impaired electron transport chain activity, NADH accumulation can be toxic. To...
NADH provides electrons for aerobic ATP production. In cells deprived of oxygen or with impaired electron transport chain activity, NADH accumulation can be toxic. To minimize such toxicity, elevated NADH inhibits the classical NADH-producing pathways: glucose, glutamine, and fat oxidation. Here, through deuterium-tracing studies in cultured cells and mice, we show that folate-dependent serine catabolism also produces substantial NADH. Strikingly, when respiration is impaired, serine catabolism through methylene tetrahydrofolate dehydrogenase (MTHFD2) becomes a major NADH source. In cells whose respiration is slowed by hypoxia, metformin, or genetic lesions, mitochondrial serine catabolism inhibition partially normalizes NADH levels and facilitates cell growth. In mice with engineered mitochondrial complex I deficiency (NDUSF4-/-), serine's contribution to NADH is elevated, and progression of spasticity is modestly slowed by pharmacological blockade of serine degradation. Thus, when respiration is impaired, serine catabolism contributes to toxic NADH accumulation.
Topics: Animals; Cell Hypoxia; Cell Line; Humans; Mice; Mice, Inbred C57BL; Mice, Nude; Mitochondria; NAD; Oxygen; Serine
PubMed: 32187526
DOI: 10.1016/j.cmet.2020.02.017 -
Plant Physiology Apr 2023
Topics: Respiration; Ecosystem; Cell Respiration
PubMed: 36703191
DOI: 10.1093/plphys/kiad041 -
Biomolecules Jun 2020Effective metabolism is highly dependent on a narrow therapeutic range of oxygen. Accordingly, low levels of oxygen, or hypoxia, are one of the most powerful inducers of... (Review)
Review
Effective metabolism is highly dependent on a narrow therapeutic range of oxygen. Accordingly, low levels of oxygen, or hypoxia, are one of the most powerful inducers of gene expression, metabolic changes, and regenerative processes, including angiogenesis and stimulation of stem cell proliferation, migration, and differentiation. The sensing of decreased oxygen levels (hypoxia) or increased oxygen levels (hyperoxia), occurs through specialized chemoreceptor cells and metabolic changes at the cellular level, which regulate the response. Interestingly, fluctuations in the free oxygen concentration rather than the absolute level of oxygen can be interpreted at the cellular level as a lack of oxygen. Thus, repeated intermittent hyperoxia can induce many of the mediators and cellular mechanisms that are usually induced during hypoxia. This is called the hyperoxic-hypoxic paradox (HHP). This article reviews oxygen physiology, the main cellular processes triggered by hypoxia, and the cascade of events triggered by the HHP.
Topics: Animals; Cell Hypoxia; Humans; Hyperoxia; Oxygen
PubMed: 32630465
DOI: 10.3390/biom10060958 -
Proceedings of the National Academy of... Aug 2022Dynamic regulation of mitochondrial morphology provides cells with the flexibility required to adapt and respond to electron transport chain (ETC) toxins and...
Dynamic regulation of mitochondrial morphology provides cells with the flexibility required to adapt and respond to electron transport chain (ETC) toxins and mitochondrial DNA-linked disease mutations, yet the mechanisms underpinning the regulation of mitochondrial dynamics machinery by these stimuli is poorly understood. Here, we show that pyruvate dehydrogenase kinase 4 (PDK4) is genetically required for cells to undergo rapid mitochondrial fragmentation when challenged with ETC toxins. Moreover, PDK4 overexpression was sufficient to promote mitochondrial fission even in the absence of mitochondrial stress. Importantly, we observed that the PDK4-mediated regulation of mitochondrial fission was independent of its canonical function, i.e., inhibitory phosphorylation of the pyruvate dehydrogenase complex (PDC). Phosphoproteomic screen for PDK4 substrates, followed by nonphosphorylatable and phosphomimetic mutations of the PDK4 site revealed cytoplasmic GTPase, Septin 2 (SEPT2), as the key effector molecule that acts as a receptor for DRP1 in the outer mitochondrial membrane to promote mitochondrial fission. Conversely, inhibition of the PDK4-SEPT2 axis could restore the balance in mitochondrial dynamics and reinvigorates cellular respiration in mitochondrial fusion factor, mitofusin 2-deficient cells. Furthermore, PDK4-mediated mitochondrial reshaping limits mitochondrial bioenergetics and supports cancer cell growth. Our results identify the PDK4-SEPT2-DRP1 axis as a regulator of mitochondrial function at the interface between cellular bioenergetics and mitochondrial dynamics.
Topics: Cell Respiration; GTP Phosphohydrolases; Gene Expression; Mitochondria; Mitochondrial Dynamics; Protein Kinases
PubMed: 35969774
DOI: 10.1073/pnas.2120157119 -
Cell Death & Disease Sep 2020Oxygen glucose deprivation/re-oxygenation (OGD/R) induces neuronal injury via mechanisms that are believed to mimic the pathways associated with brain ischemia. In...
Oxygen glucose deprivation/re-oxygenation (OGD/R) induces neuronal injury via mechanisms that are believed to mimic the pathways associated with brain ischemia. In SH-SY5Y cells and primary murine neurons, we report that OGD/R induces the accumulation of the microRNA miR-422a, leading to downregulation of miR-422a targets myocyte enhancer factor-2D (MEF2D) and mitogen-activated protein kinase kinase 6 (MAPKK6). Ectopic miR-422a inhibition attenuated OGD/R-induced cell death and apoptosis, whereas overexpression of miR-422a induced significant neuronal cell apoptosis. In addition, OGD/R decreased the expression of the long non-coding RNA D63785 (Lnc-D63785) to regulate miR-422a accumulation. Lnc-D63785 directly associated with miR-422a and overexpression of Lnc-D63785 reversed OGD/R-induced miR-422a accumulation and neuronal cell death. OGD/R downregulated Lnc-D63785 expression through increased methyltransferase-like protein 3 (METTL3)-dependent Lnc-D63785 m6A methylation. Conversely METTL3 shRNA reversed OGD/R-induced Lnc-D63785 m6A methylation to decrease miR-422a accumulation. Together, Lnc-D63785 m6A methylation by OGD/R causes miR-422a accumulation and neuronal cell apoptosis.
Topics: Animals; Cell Death; Cell Hypoxia; Cell Line, Tumor; DNA Methylation; Glucose; Humans; Mice; MicroRNAs; Neurons; Oxygen; RNA, Long Noncoding; Transfection
PubMed: 32999283
DOI: 10.1038/s41419-020-03021-8 -
The Journal of Biological Chemistry Sep 2023Ferredoxins are a family of iron-sulfur (Fe-S) cluster proteins that serve as essential electron donors in numerous cellular processes that are conserved through...
Ferredoxins are a family of iron-sulfur (Fe-S) cluster proteins that serve as essential electron donors in numerous cellular processes that are conserved through evolution. The promiscuous nature of ferredoxins as electron donors enables them to participate in many metabolic processes including steroid, heme, vitamin D, and Fe-S cluster biosynthesis in different organisms. However, the unique natural function(s) of each of the two human ferredoxins (FDX1 and FDX2) are still poorly characterized. We recently reported that FDX1 is both a crucial regulator of copper ionophore-induced cell death and serves as an upstream regulator of cellular protein lipoylation, a mitochondrial lipid-based post-translational modification naturally occurring on four mitochondrial enzymes that are crucial for TCA cycle function. Here we show that FDX1 directly regulates protein lipoylation by binding the lipoyl synthase (LIAS) enzyme promoting its functional binding to the lipoyl carrier protein GCSH and not through indirect regulation of cellular Fe-S cluster biosynthesis. Metabolite profiling revealed that the predominant cellular metabolic outcome of FDX1 loss of function is manifested through the regulation of the four lipoylation-dependent enzymes ultimately resulting in loss of cellular respiration and sensitivity to mild glucose starvation. Transcriptional profiling established that FDX1 loss-of-function results in the induction of both compensatory metabolism-related genes and the integrated stress response, consistent with our findings that FDX1 loss-of-function is conditionally lethal. Together, our findings establish that FDX1 directly engages with LIAS, promoting its role in cellular protein lipoylation, a process essential in maintaining cell viability under low glucose conditions.
Topics: Humans; Ferredoxins; Lipoylation; Protein Binding; Cell Respiration; Cell Proliferation; Metabolome; Sulfurtransferases
PubMed: 37453661
DOI: 10.1016/j.jbc.2023.105046 -
Clinical Oncology (Royal College of... Nov 2021Regions of reduced oxygenation (hypoxia) are a characteristic feature of virtually all animal and human solid tumours. Numerous preclinical studies, both in vitro and... (Review)
Review
Regions of reduced oxygenation (hypoxia) are a characteristic feature of virtually all animal and human solid tumours. Numerous preclinical studies, both in vitro and in vivo, have shown that decreasing oxygen concentration induces resistance to radiation. Importantly, hypoxia in human tumours is a negative indicator of radiotherapy outcome. Hypoxia also contributes to resistance to other cancer therapeutics, including immunotherapy, and increases malignant progression as well as cancer cell dissemination. Consequently, substantial effort has been made to detect hypoxia in human tumours and identify realistic approaches to overcome hypoxia and improve cancer therapy outcomes. Hypoxia-targeting strategies include improving oxygen availability, sensitising hypoxic cells to radiation, preferentially killing these cells, locating the hypoxic regions in tumours and increasing the radiation dose to those areas, or applying high energy transfer radiation, which is less affected by hypoxia. Despite numerous clinical studies with each of these hypoxia-modifying approaches, many of which improved both local tumour control and overall survival, hypoxic modification has not been established in routine clinical practice. Here we review the background and significance of hypoxia, how it can be imaged clinically and focus on the various hypoxia-modifying techniques that have undergone, or are currently in, clinical evaluation.
Topics: Animals; Cell Hypoxia; Humans; Hypoxia; Neoplasms; Oxygen
PubMed: 34535359
DOI: 10.1016/j.clon.2021.08.014