ABSTRACT
Adult skeletal muscle is a dynamic, remarkably plastic tissue, which allows myofibers to switch from fast/glycolytic to slow/oxidative types and to increase mitochondrial fatty acid ...oxidation (mFAO) capacity and vascularization in response to exercise training. mFAO is the main muscle energy source during endurance exercise, with carnitine palmitoyltransferase 1 (CPT1) being the key regulatory enzyme. Whether increasing muscle mFAO affects skeletal muscle physiology in adulthood actually remains unknown. To investigate this, we used in vivo electrotransfer technology to express in mouse tibialis anterior (TA), a fast/glycolytic muscle, a mutated CPT1 form (CPT1mt) that is active but insensitive to malonyl‐CoA, its physiologic inhibitor. In young (2‐mo‐old) adult mice, muscle CPT1mt expression enhanced mFAO (+40%), but also increased the percentage of oxidative fibers (+28%), glycogen content, and capillary‐to‐fiber density (+45%). This CPT1mt‐induced muscle remodeling, which mimicked exercise‐induced oxidative phenotype, led to a greater resistance to muscle fatigue. In the context of aging, characterized by sarcopenia and reduced oxidative capacity, CPT1mt expression in TAs from aged (20‐mo‐old) mice partially reversed aging‐associated sarcopenia and fiber‐type transition, and increased muscle capillarity. These findings provide evidence that mFAO regulates muscle phenotype and may be a potential target to combat age‐related decline in muscle function.—Hénique, C., Mansouri, A., Vavrova, E., Lenoir, V., Ferry, A., Esnous, C., Ramond, E., Girard, J., Bouillaud, F., Prip‐Buus, C., Cohen, I. Increasing mitochondrial muscle fatty acid oxidation induces skeletal muscle remodeling toward an oxidative phenotype. FASEB J. 29, 2473‐2483 (2015). www.fasebj.org
Emerging work demonstrates the dual regulation of mitochondrial function by hydrogen sulfide (H2S), including, at lower concentrations, a stimulatory effect as an electron donor, and, at higher ...concentrations, an inhibitory effect on cytochrome C oxidase. In the current article, we overview the pathophysiological and therapeutic aspects of these processes. During cellular hypoxia/acidosis, the inhibitory effect of H2S on complex IV is enhanced, which may shift the balance of H2S from protective to deleterious. Several pathophysiological conditions are associated with an overproduction of H2S (e.g. sepsis), while in other disease states H2S levels and H2S bioavailability are reduced and its therapeutic replacement is warranted (e.g. diabetic vascular complications). Moreover, recent studies demonstrate that colorectal cancer cells up‐regulate the H2S‐producing enzyme cystathionine β‐synthase (CBS), and utilize its product, H2S, as a metabolic fuel and tumour‐cell survival factor; pharmacological CBS inhibition or genetic CBS silencing suppresses cancer cell bioenergetics and suppresses cell proliferation and cell chemotaxis. In the last chapter of the current article, we overview the field of H2S‐induced therapeutic ‘suspended animation’, a concept in which a temporary pharmacological reduction in cell metabolism is achieved, producing a decreased oxygen demand for the experimental therapy of critical illness and/or organ transplantation.
Linked Articles
This article is part of a themed issue on Mitochondrial Pharmacology: Energy, Injury & Beyond. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2014.171.issue‐8
Mitochondrial DNA (mtDNA) mutations frequently cause neurological diseases. Modeling of these defects has been difficult because of the challenges associated with engineering mtDNA. We show here that ...neural progenitor cells (NPCs) derived from human induced pluripotent stem cells (iPSCs) retain the parental mtDNA profile and exhibit a metabolic switch toward oxidative phosphorylation. NPCs derived in this way from patients carrying a deleterious homoplasmic mutation in the mitochondrial gene MT-ATP6 (m.9185T>C) showed defective ATP production and abnormally high mitochondrial membrane potential (MMP), plus altered calcium homeostasis, which represents a potential cause of neural impairment. High-content screening of FDA-approved drugs using the MMP phenotype highlighted avanafil, which we found was able to partially rescue the calcium defect in patient NPCs and differentiated neurons. Overall, our results show that iPSC-derived NPCs provide an effective model for drug screening to target mtDNA disorders that affect the nervous system.
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•iPSC-derived neural progenitors develop neuronal-like mitochondrial metabolism•Derived NPCs retain parental mtDNA sequences and model mutant phenotypes•Altered calcium homeostasis is a candidate pathological mechanism•Drug screening based on mitochondrial phenotypes rescues calcium defects
Prigione and colleagues show that neural progenitors differentiated from patient-derived iPSCs are an effective modeling tool for neuronal disease associated with mtDNA mutations and can be used for drug screening.
Protein fermentation by the gut microbiota releases in the large intestine lumen various amino-acid derived metabolites. Among them, hydrogen sulfide (H2S) in excess has been suspected to be ...detrimental for colonic epithelium energy metabolism and DNA integrity. The first objective of this study was to evaluate in rats the epithelial response to an increased exposure to H2S. Experiments from colonocyte incubation and intra-colonic instillation indicate that low millimolar concentrations of the sulfide donor NaHS reversibly inhibited colonocyte mitochondrial oxygen consumption and increased gene expression of hypoxia inducible factor 1α (Hif-1α) together with inflammation-related genes namely inducible nitric oxide synthase (iNos) and interleukin-6 (Il-6). Additionally, rat colonocyte H2S detoxification capacity was severely impaired in the presence of nitric oxide. Based on the γH2AX ICW technique, NaHS did not induce DNA damage in colonocytes. Since H2S is notably produced by the gut microbiota from sulfur containing amino acids, the second objective of the study was to investigate the effects of a high protein diet (HPD) on large intestine luminal sulfide content and on the expression of genes involved in H2S detoxification in colonocytes. We found that HPD markedly increased H2S content in the large intestine but the concomitant increase of the content mass maintained the luminal sulfide concentration. HPD also provoked an increase of sulfide quinone reductase (Sqr) gene expression in colonocytes, indicating an adaptive response to increased H2S bacterial production. In conclusion, low millimolar NaHS concentration severely affects colonocyte respiration in association with increased expression of genes associated with intestinal inflammation. Although HPD increases the sulfide content of the large intestine, the colonic adaptive responses to this modification limit the epithelial exposure to this deleterious bacterial metabolite.
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•H2S in excess reversibly inhibits colonocyte respiration and increases inflammatory genes expression.•H2S detoxification capacity in colonocytes is impaired in the presence of excessive nitric oxide concentration.•High-protein diet markedly increases sulfide content in the large intestine.•Increased luminal bulk and increased expression of SQR represent adaptive responses to excessive H2S exposition.
Theileria annulata infects bovine leukocytes, transforming them into invasive, cancer-like cells that cause the widespread disease called tropical theileriosis. We report that in ...Theileria-transformed leukocytes hexokinase-2 (HK2) binds to B cell lymphoma-2-associated death promoter (BAD) only when serine (S) 155 in BAD is phosphorylated. We show that HK2 recruitment to BAD is abolished by a cell-penetrating peptide that acts as a nonphosphorylatable BAD substrate that inhibits endogenous S155 phosphorylation, leading to complex dissociation and ubiquitination and degradation of HK2 by the proteasome. As HK2 is a critical enzyme involved in Warburg glycolysis, its loss forces Theileria-transformed macrophages to switch back to HK1-dependent oxidative glycolysis that down-regulates macrophage proliferation only when they are growing on glucose. When growing on galactose, degradation of HK2 has no effect on Theileria-infected leukocyte proliferation, because metabolism of this sugar is independent of hexokinases. Thus, targeted disruption of the phosphorylation-dependent HK2/BAD complex may represent a novel approach to control Theileria-transformed leukocyte proliferation.
Uncoupling proteins (UCPs) are specialized members of the mitochondrial transporter family. They allow passive proton transport through the mitochondrial inner membrane. This activity leads to ...uncoupling of mitochondrial respiration and to energy waste, which is well documented with UCP1 in brown adipose tissue. The uncoupling activity of the new UCPs (discovered after 1997), such as UCP2 and UCP3 in mammals or avUCP in birds, is more difficult to characterize. However, extensive data support the idea that the new UCPs are involved in the control of reactive oxygen species (ROS) generation. This fits with the hypothesis that mild uncoupling caused by the UCPs prevents ROS production. Activators and inhibitors regulate the proton transport activity of the UCPs. In the absence of activators of proton transport, the UCP allows the permeation of other ions. We suggest that this activity has physiological significance and, for example, UCP3 expressed in glycolytic muscle fibres may be a passive pyruvate transporter ensuring equilibrium between glycolysis and oxidative phosphorylation. Induction of UCP2 expression by glutamine strengthens the proposal that new UCPs could act to determine the choice of mitochondrial substrate. This would obviously have an impact on mitochondrial bioenergetics and ROS production.
Abstract
HIV-1 eradication is hindered by viral persistence in cell reservoirs, established not only in circulatory CD4
+
T-cells but also in tissue-resident macrophages. The nature of macrophage ...reservoirs and mechanisms of persistence despite combined anti-retroviral therapy (cART) remain unclear. Using genital mucosa from cART-suppressed HIV-1-infected individuals, we evaluated the implication of macrophage immunometabolic pathways in HIV-1 persistence. We demonstrate that ex vivo, macrophage tissue reservoirs contain transcriptionally active HIV-1 and viral particles accumulated in virus-containing compartments, and harbor an inflammatory IL-1R
+
S100A8
+
MMP7
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M4-phenotype prone to glycolysis. Reactivation of infectious virus production and release from these reservoirs in vitro are induced by the alarmin S100A8, an endogenous factor produced by M4-macrophages and implicated in “sterile” inflammation. This process metabolically depends on glycolysis. Altogether, inflammatory M4-macrophages form a major tissue reservoir of replication-competent HIV-1, which reactivate viral production upon autocrine/paracrine S100A8-mediated glycolytic stimulation. This HIV-1 persistence pathway needs to be targeted in future HIV eradication strategies.
Uncoupling protein 2 (UCP2) belongs to a family of transporters of the mitochondrial inner membrane and is reported to uncouple respiration from ATP synthesis. Our observation that the amino acid ...glutamine specifically induces UCP2 protein expression prompted us to investigate metabolic consequences of a UCP2 knockdown (
Ucp2-KO) when glutamine is offered as a substrate. We found that
Ucp2-KO macrophages incubated in the presence of glutamine exhibit a lower ammonium release, a decreased respiratory rate, and an intracellular accumulation of aspartate. Therefore, we conclude that UCP2 expression is required for efficient oxidation of glutamine in macrophages. This role of UCP2 in glutamine metabolism appears independent from the uncoupling activity of UCP2.
Colorectal cancer (CRC) is associated with metabolic and redox perturbation. The mitochondrial transporter uncoupling protein 2 (UCP2) controls cell proliferation in vitro through the modulation of ...cellular metabolism, but the underlying mechanism in tumors in vivo remains unexplored. Using murine intestinal cancer models and CRC patient samples, we find higher UCP2 protein levels in tumors compared to their non-tumoral counterparts. We reveal the tumor-suppressive role of UCP2 as its deletion enhances colon and small intestinal tumorigenesis in AOM/DSS-treated and ApcMin/+ mice, respectively, and correlates with poor survival in the latter model. Mechanistically, UCP2 loss increases levels of oxidized glutathione and proteins in tumors. UCP2 deficiency alters glycolytic pathways while promoting phospholipid synthesis, thereby limiting the availability of NADPH for buffering oxidative stress. We show that UCP2 loss renders colon cells more prone to malignant transformation through metabolic reprogramming and perturbation of redox homeostasis and could favor worse outcomes in CRC.
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•UCP2 protein expression, but not mRNA, is increased in CRC in both mice and humans•UCP2 loss promotes AOM/DSS-induced CAC and ApcMin-dependent intestinal cancer•UCP2 loss-induced oxidative stress contributes to increased colon tumorigenesis•UCP2 deficiency drives an imbalance between lipid metabolism and NADPH homeostasis
Aguilar et al. show that the inhibition of mitochondrial transporter UCP2 increases susceptibility to colon and intestinal tumorigenesis and correlates with poor prognosis. The underlying mechanisms involve deregulation of redox homeostasis through metabolic rewiring. Thus, UCP2 plays a key role in CRC, and its loss is potentially associated with worse outcomes.
The mechanisms underlying the protective effect of monounsaturated fatty acids (e.g. oleate) against the lipotoxic action of saturated fatty acids (e.g. palmitate) in skeletal muscle cells remain ...poorly understood. This study aimed to examine the role of mitochondrial long-chain fatty acid (LCFA) oxidation in mediating oleate's protective effect against palmitate-induced lipotoxicity. CPT1 (carnitine palmitoyltransferase 1), which is the key regulatory enzyme of mitochondrial LCFA oxidation, is inhibited by malonyl-CoA, an intermediate of lipogenesis. We showed that expression of a mutant form of CPT1 (CPT1mt), which is active but insensitive to malonyl-CoA inhibition, in C2C12 myotubes led to increased LCFA oxidation flux even in the presence of high concentrations of glucose and insulin. Furthermore, similar to preincubation with oleate, CPT1mt expression protected muscle cells from palmitate-induced apoptosis and insulin resistance by decreasing the content of deleterious palmitate derivates (i.e. diacylglycerols and ceramides). Oleate preincubation exerted its protective effect by two mechanisms: (i) in contrast to CPT1mt expression, oleate preincubation increased the channeling of palmitate toward triglycerides, as a result of enhanced diacylglycerol acyltransferase 2 expression, and (ii) oleate preincubation promoted palmitate oxidation through increasing CPT1 expression and modulating the activities of acetyl-CoA carboxylase and AMP-activated protein kinase. In conclusion, we demonstrated that targeting mitochondrial LCFA oxidation via CPT1mt expression leads to the same protective effect as oleate preincubation, providing strong evidence that redirecting palmitate metabolism toward oxidation is sufficient to protect against palmitate-induced lipotoxicity.
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