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Mitochondria are signaling organelles that regulate a wide variety of cellular functions and can dictate cell fate. Multiple mechanisms contribute to communicate mitochondrial fitness to the rest of the cell. Recent evidence confers a new role for TCA cycle intermediates, generally thought to be important for biosynthetic purposes, as signaling molecules with functions controlling chromatin modifications, DNA methylation, the hypoxic response, and immunity. This review summarizes the mechanisms by which the abundance of different TCA cycle metabolites controls cellular function and fate in different contexts. We will focus on how these metabolites mediated signaling can affect physiology and disease. Mitochondrial metabolites contribute to more than biosynthesis, and it is clear that they influence multiple cellular functions in a variety of ways. Here, Martínez-Reyes and Chandel review key metabolites and describe their effects on processes involved in physiology and disease including chromatin dynamics, immunity, and hypoxia.

Glioblastoma (GBM) is a primary tumor of the brain defined by its uniform lethality and resistance to conventional therapies. There have been considerable efforts to untangle the metabolic underpinnings of this disease to find novel therapeutic avenues for treatment. An emerging focus in this field is fatty acid (FA) metabolism, which is critical for numerous diverse biological processes involved in GBM pathogenesis. These processes can be classified into four broad fates: anabolism, catabolism, regulation of ferroptosis, and the generation of signaling molecules. Each fate provides a unique perspective by which we can inspect GBM biology and gives us a road map to understanding this complicated field. This Review discusses the basic, translational, and clinical insights into each of these fates to provide a contemporary understanding of FA biology in GBM. It is clear, based on the literature, that there are far more questions than answers in the field of FA metabolism in GBM, and substantial efforts should be made to untangle these complex processes in this intractable disease.

Molecular oxygen (O2) 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.The transcriptional response to hypoxia and the role of hypoxia inducible factors have been extensively studied. Yet, hypoxic cells also adapt to hypoxia by modulating protein synthesis, metabolism and nutrient uptake. Understanding these processes could shed light on pathologies associated with hypoxia, including cardiovascular diseases and cancer, and disease mechanisms, such as inflammation and wound repair.

‘Reactive oxygen species’ (ROS) is a generic term that defines a wide variety of oxidant molecules with vastly different properties and biological functions that range from signalling to causing cell damage. Consequently, the description of oxidants needs to be chemically precise to translate research on their biological effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues associated with identifying the physiological roles of oxidants, focusing on H2O2 and O2.–. The generic term ROS should not be used to describe specific molecular agents. We also advocate for greater precision in measurement of H2O2, O2.– and other oxidants, along with more specific identification of their signalling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signalling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiological O2 levels should be maintained in cell culture to better mimic in vivo redox reactions associated with specific cell types. Use of precise definitions and analytical tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biology.Reactive oxygen species (ROS) comprise a wide variety of oxidant molecules with vastly different properties and biological functions in physiology and in disease. Approaches to characterize oxidants in the in vivo context and identify their specific cellular targets will be required to understand and control the pathophysiological activities of ROS.

The majority of cancer cells have a functional mitochondrial electron transport chain (ETC). Mitochondrial complex I is the primary entry point into the ETC, where oxidative phosphorylation occurs, generating ATP as an energy source for powering the cell. Electrons are transferred through a chain of mitochondrial protein complexes (complex I, II, III, and IV) to the final electron acceptor, molecular oxygen, while protons are pumped by complexes I, III, and IV to create an electrochemical proton gradient, ultimately driving ATP synthesis through complex V. The ETC can function optimally even in hypoxic conditions, allowing solid tumors, which often have limited oxygen availability, to maintain mitochondrial respiration. Mitochondrial ETC function is intrinsically linked to the oxidative tricyclic acid (TCA) cycle, which supports tumor growth by enabling macromolecule biosynthesis. Genetic and pharmacologic inhibition of the ETC prevents de novo pyrimidine synthesis and oxidative TCA cycle flux, supporting lipid, heme, aspartate, and asparagine production, all of which act together to decrease primary tumor growth and metastasis.

Key Points Different immune cell subsets use diverse metabolic pathways. In general, inflammatory and suppressive cells each utilize glycolysis and oxidative phosphorylation for distinct purposes. Mitochondrial metabolism produces a variety of signalling molecules (such as mitochondrial reactive oxygen species (mROS) and acetyl-CoA) that can drive changes in immune cell function through the regulation of transcription factors and epigenetics. mROS are produced by the mitochondrial electron transport chain as a signal to increase interleukin-2 (IL-2) production in T cells and IL-1β production in macrophages. Acetyl-CoA produced by fatty acid oxidation or pyruvate oxidation in mitochondria can be transported by the citrate shuttle into the cytoplasm, where it can be used for fatty acid synthesis or acetylation reactions. These pathways have crucial roles in immune cell function. M1 macrophages use an altered tricarboxylic acid (TCA) cycle and reverse electron transport to drive inflammation through increased succinate and mROS levels. M2 macrophages have an intact TCA cycle and require the function of the hexosamine branch of glycolysis. Cellular metabolism can be altered by drugs that target mitochondria, such as metformin and mitochondria-targeted antioxidants. Does mitochondrial metabolism simply support the bioenergetic and biosynthetic needs of committed immune cells, or does it also control their fate? In this Review, Chandel and colleagues explore variations in mitochondrial metabolism across different immune cells and discuss how mitochondria can act as important signalling organelles to dictate immune cell function. Mitochondria are important signalling organelles, and they dictate immunological fate. From T cells to macrophages, mitochondria form the nexus of the various metabolic pathways that define each immune cell subset. In this central position, mitochondria help to control the various metabolic decision points that determine immune cell function. In this Review, we discuss how mitochondrial metabolism varies across different immune cell subsets, how metabolic signalling dictates cell fate and how this signalling could potentially be targeted therapeutically.

The NLRP3 inflammasome is linked to sterile and pathogen-dependent inflammation, and its dysregulation underlies many chronic diseases. Mitochondria have been implicated as regulators of the NLRP3 inflammasome through several mechanisms including generation of mitochondrial reactive oxygen species (ROS). Here, we report that mitochondrial electron transport chain (ETC) complex I, II, III and V inhibitors all prevent NLRP3 inflammasome activation. Ectopic expression of Saccharomyces cerevisiae NADH dehydrogenase (NDI1) or Ciona intestinalis alternative oxidase, which can complement the functional loss of mitochondrial complex I or III, respectively, without generation of ROS, rescued NLRP3 inflammasome activation in the absence of endogenous mitochondrial complex I or complex III function. Metabolomics revealed phosphocreatine (PCr), which can sustain ATP levels, as a common metabolite that is diminished by mitochondrial ETC inhibitors. PCr depletion decreased ATP levels and NLRP3 inflammasome activation. Thus, the mitochondrial ETC sustains NLRP3 inflammasome activation through PCr-dependent generation of ATP, but via a ROS-independent mechanism.How the mitochondrial electron transport chain (ETC) interacts with the NLRP3 inflammasome is somewhat unclear. Here the authors use individual complex inhibitors and new genetic models to show that ETC is critical in providing ATP via the phosphocreatine shuttle to activate the NLRP3 inflammasome.

It has been proposed that reactive oxygen species (ROS) cause mutations, and thus cancer, and that antioxidants counter this effect, but studies suggest that antioxidants do not prevent cancer and may accelerate it. These findings may be due to the cellular location of ROS targeted by antioxidants. Reactive oxygen species (ROS) have been proposed to both accelerate and delay cancer initiation and progression. These conflicting outcomes may be explained by the multiple roles that ROS play during the evolution of cancer cells. ROS can promote cancer by oxidizing specific intracellular chemical moieties, resulting in genetic mutations and the activation of biochemical pathways that stimulate proliferation and neoplastic transformation. 1 These tumorigenic properties of ROS have prompted the evaluation of dietary antioxidants as potential preventive and therapeutic agents in animal models and humans. Although some early preclinical studies supported this concept, dietary antioxidants have consistently failed to reduce the . . .

Abstract Metabolism is essential for a living organism to sustain life. It provides energy to a cell by breaking down compounds (catabolism) and supplies building blocks for the synthesis of macromolecules (anabolism). Signal transduction pathways tightly regulate mammalian cellular metabolism. Simultaneously, metabolism itself serves as a signaling pathway to control many cellular processes, such as proliferation, differentiation, cell death, gene expression, and adaptation to stress. Considerable progress in the metabolism field has come from understanding how cancer cells co-opt metabolic pathways for growth and survival. Recent data also show that several metabolic pathways may participate in the pathogenesis of lung diseases, some of which could be promising therapeutic targets. In this translational review, we will outline the basic metabolic principles learned from the cancer metabolism field as they apply to the pathogenesis of pulmonary arterial hypertension and fibrosis and will place an emphasis on therapeutic potential.

Alveolar epithelial type 1 (AT1) cells are necessary to transfer oxygen and carbon dioxide between the blood and air. Alveolar epithelial type 2 (AT2) cells serve as a partially committed stem cell population, producing AT1 cells during postnatal alveolar development and repair after influenza A and SARS-CoV-2 pneumonia 1 – 6 . Little is known about the metabolic regulation of the fate of lung epithelial cells. Here we report that deleting the mitochondrial electron transport chain complex I subunit Ndufs2 in lung epithelial cells during mouse gestation led to death during postnatal alveolar development. Affected mice displayed hypertrophic cells with AT2 and AT1 cell features, known as transitional cells. Mammalian mitochondrial complex I, comprising 45 subunits, regenerates NAD + and pumps protons. Conditional expression of yeast NADH dehydrogenase (NDI1) protein that regenerates NAD + without proton pumping 7 , 8 was sufficient to correct abnormal alveolar development and avert lethality. Single-cell RNA sequencing revealed enrichment of integrated stress response (ISR) genes in transitional cells. Administering an ISR inhibitor 9 , 10 or NAD + precursor reduced ISR gene signatures in epithelial cells and partially rescued lethality in the absence of mitochondrial complex I function. Notably, lung epithelial-specific loss of mitochondrial electron transport chain complex II subunit Sdhd , which maintains NAD + regeneration, did not trigger high ISR activation or lethality. These findings highlight an unanticipated requirement for mitochondrial complex I-dependent NAD + regeneration in directing cell fate during postnatal alveolar development by preventing pathological ISR induction. This study highlights the role of mitochondrial complex I-dependent NAD + regeneration in directing lung epithelial cell fate during postnatal alveolar development by preventing pathological integrated stress response induction.