Metabolic pathways in T cell activation and lineage differentiation

Recent advances in the field of immunometabolism support the concept that fundamental processes in T cell biology, such as TCR-mediated activation and T helper lineage differentiation, are closely linked to changes in the cellular metabolic programs. Although the major task of the intermediate metabolism is to provide the cell with a constant supply of energy and molecular precursors for the production of biomolecules, the dynamic regulation of metabolic pathways also plays an active role in shaping T cell responses. Key metabolic processes such as glycolysis, fatty acid and mitochondrial metabolism are now recognized as crucial players in T cell activation and differentiation, and their modulation can differentially affect the development of T helper cell lineages. In this review, we describe the diverse metabolic processes that T cells engage during their life cycle from naïve towards effector and memory T cells. We consider in particular how the cellular metabolism may actively support the function of T cells in their different states. Moreover, we discuss how molecular regulators such as mTOR or AMPK link environmental changes to adaptations in the cellular metabolism and elucidate the consequences on T cell differentiation and function.     

Metabolism of murine TH17 cells: Impact on cell fate and function

An effective adaptive immune response relies on the ability of lymphocytes to rapidly act upon a variety of insults. In T lymphocytes, this response includes cell growth, clonal expansion, differentiation, and cytokine production, all of which place a significant energy burden on the cell. Recent evidence shows that T‐cell metabolic reprogramming is an essential component of the adaptive immune response and specific metabolic pathways dictate T‐cell fate decisions, including the development of T_H17 versus T regulatory (Treg) cells. T_H17 cells have garnered significant attention due to their roles in the pathology of immune‐mediated inflammatory diseases. Attempts to characterize T_H17 cells have demonstrated that they are highly dynamic, adjusting their function to environmental cues, which dictate their metabolic program. In this review, we highlight recent data demonstrating the impact of cellular metabolism on the T_H17/Treg balance and present factors that mediate T_H17‐cell metabolism. Some examples of these include the differential impact of the mTOR signaling complexes on T‐helper‐cell differentiation, hypoxia inducible factor 1 alpha (HIF1α) promotion of glycolysis to favor T_H17‐cell development, and ACC1‐dependent de novo fatty acid synthesis favoring T_H17‐cell development over Treg cells. Finally, we discuss the potential therapeutic options and the implications of modulating T_H17‐cell metabolism for the treatment of T_H17‐mediated diseases.     

Histone Deacetylase 6 Inhibition Exploits Selective Metabolic Vulnerabilities in LKB1 Mutant,KRAS Driven NSCLC

IntroductionIn KRAS-mutant NSCLC, co-occurring alterations in LKB1 confer a negative prognosis compared with other mutations such as TP53. LKB1 is a tumor suppressor that coordinates several signaling pathways in response to energetic stress. Our recent work on pharmacologic and genetic inhibition of histone deacetylase 6 (HDAC6) revealed the impaired activity of numerous enzymes involved in glycolysis. On the basis of these previous findings, we explored the therapeutic window for HDAC6 inhibition in metabolically-active KRAS-mutant lung tumors.MethodsUsing cell lines derived from mouse autochthonous tumors bearing the KRAS/LKB1 (KL) and KRAS/TP53 mutant genotypes to control for confounding germline and somatic mutations in human models, we characterize the metabolic phenotypes at baseline and in response to HDAC6 inhibition. The impact of HDAC6 inhibition was measured on cancer cell growth in vitro and on tumor growth in vivo.ResultsSurprisingly, KL-mutant cells revealed reduced levels of redox-sensitive cofactors at baseline. This is associated with increased sensitivity to pharmacologic HDAC6 inhibition with ACY-1215 and blunted ability to increase compensatory metabolism and buffer oxidative stress. Seeking synergistic metabolic combination treatments, we found enhanced cell killing and antitumor efficacy with glutaminase inhibition in KL lung cancer models in vitro and in vivo.ConclusionsExploring the differential metabolism of KL and KRAS/TP53-mutant NSCLC, we identified decreased metabolic reserve in KL-mutant tumors. HDAC6 inhibition exploited a therapeutic window in KL NSCLC on the basis of a diminished ability to compensate for impaired glycolysis, nominating a novel strategy for the treatment of KRAS-mutant NSCLC with co-occurring LKB1 mutations.     

1型糖尿病大鼠心肌对缺血再灌注损伤的耐受性及其机制

目的 研究1型糖尿病大鼠心肌对缺血再灌注损伤的耐受性及其可能机制。方法 健康雄性SD大鼠以链脲佐菌素腹腔注射制作1型糖尿病模型，血糖升高3～4周后取心脏在体外进行灌注，并进行缺血再灌注实验。依据心肌磷酸肌酸激酶(CPK)释放量、心脏收缩及舒张功能、再灌注心律失常判定心脏缺血再灌注损害程度。测定冠状动脉流出液中脂质过氧化产物丙二醛(MDA)及糖酵解产物乳酸盐含量。结果 与正常大鼠相比，糖尿病大鼠基础心脏收缩功能显著减弱，但缺血再灌注后心脏收缩及舒张功能恢复较对照组显著增强，心肌CPK释放量减少，心律失常严重程度减轻。糖尿病大鼠心脏冠状动脉流出液中的MDA含量显著升高，乳酸盐含量显著减少，提示糖尿病心肌脂质过氧化反应增强，糖酵解受抑制。结论 1型糖尿病大鼠心肌对缺血再灌注损伤的耐受性显著增强，心肌糖酵解抑制使酸性代谢产物减少可能是其机制之一。     

Lactate accumulation following concussive brain injury: the role of ionic fluxes induced by excitatory amino acids

During the first few minutes following traumatic brain injury, cells are exposed to an indiscriminate release of glutamate from nerve terminals resulting in a massive ionic flux (e.g., K⁺ efflux) via stimulation of excitatory amino acid (EAA)-coupled ion channels. The present study was undertaken to elucidate the causal relationship between these ionic shifts and lactate accumulation in the injured brain, by examining the effects of ouabain (an inhibitor of Na⁺/K⁺-ATPase), Ba²⁺ (an inhibitor of non-energy-dependent glial K⁺ uptake) and kynurenic acid (KYN; a broad-spectrum EAA antagonist) on lactate accumulation. Two microdialysis probes were placed bilaterally in the rat parietal cortex. One was perfused with a test drug (1.0 mM ouabain, 2.0 mM Ba²⁺ or 10 mM KYN) and the other with Ringer's solution (control) for 30 min prior to injury. Following a 2.2–2.7 atm fluid-percussion injury, lactate levels in the dialysate increased (up to 116.6% above baseline) for the first 16 min and returned to baseline levels within 20 min after injury. This lactate accumulation was attenuated by preinjury administration of ouabain and KYN and was prolonged by Ba²⁺ administration. These findings indicate that lactate accumulation following concussive brain injury is a result of increased glycolysis which supports ion-pumping mechanisms, thereby, restoring the ionic balance which was disrupted by stimulation of EAA-coupled ion channels.     

Lithium effects on rat brain glucose metabolism in vivo. Effects after administration of lithium by various routes

The effects of lithium on several brain energy metabolites were investigated in rats. Lithium was administered by three alternative routes: 1) in food, 2) via IP injection, or 3) intracisternally via the suboccipital route. Lithium given in food induced permanent changes, mainly in glycolytic processes and in glycogen content. Lithium injected IP induced, in addition, several changes which depended on the increase in brain lithium concentration following injection of lithium. These changes in brain metabolites disappeared as brain lithium concentration stabilized. Intracisternal injection of lithium produced brain lithium concentrations between 1 and 2 mmoles/kg wet wt., with a mean of about 1.6 mmoles/kg wet wt. Lithium concentrations below about 1.6 mmoles/kg wet wt. induced changes in brain metabolites which were similar to the changes seen after IP injection of lithium. Lithium concentrations above about 1.6 mmoles/kg wet wt. induced changes in several brain metabolites which were at variance with the changes induced by lower lithium concentrations. These changes were in many respects similar to changes in brain metabolites seen in rats exposed to convulsive treatment.It is hypothesized that such metabolic changes during lithium treatment, in discrete areas of the brain with higher concentration of lithium, e.g., hypothalamus, might be related to the prophylactic effect of lithium treatment in man.     

Uptake of the trypanocidal drug suramin by bloodstream forms of Trypanosoma brucei and its effect on respiration and growth rate in vivo

After a single intravenous injection of suramin the rate of removal of the drug from the plasma into other tissue compartments of the rat is independent of initial concentration. The data can be fitted to the sum of two exponential functions, consistent with a two-compartment, open model system. Trypanosomes take up only small amounts of suramin in vivo and do not actively concentrate the drug within the cell. Uptake is apparently by a non-saturable process that decreases with time and is dependent on the amount of suramin already taken up. Once within the cell, suramin progressively inhibits respiration and glycolysis, such that, for a given exposure in vivo, inhibition of oxygen consumption is proportional to the total amount of suramin absorbed. It can be calculated that only a fraction (4--9%) of this total is required to inhibit respiration to the extent found in broken cell preparations. The combined inhibition of two key enzymes in glycolysis--the sn-glycerol-3-phosphate oxidase (EC unassigned) and the glycerol-3-phosphate dehydrogenase (NAD+) (sn-glycerol-3-phosphate: NAD+ 2-oxidoreductase, EC 1.1.1.8)--are sufficient to account for the differential inhibition of glucose and oxygen consumption and of pyruvate production, together with the small, but significant, production of glycerol. Even at the highest dose of suramin tolerated by the rat, trypanosomes continue to increase exponentially in the bloodstream for at least 6 h. The mean doubling time is increased from 4.6 h to a maximum of about 12.5 h in rats treated with doses of suramin in the range 25--150 mg/kg. In the light of these and other findings, it is concluded that part of the trypanocidal action of suramin results from the inhibition of ATP production by glycolysis.     

Computer simulation of metabolism in palmitate-perfused rat heart. II. Behavior of complete model

Intermediary metabolism in rat hearts persfused with 11 mM glucose plus 1 mM palmitate was simulated by a computer model. Several enzyme submodels in a previous version of the isolated rat heart computer model wre improved, and a new fatty acid oxidation pathway model was added. Compartmentation of metabolites in a pseudostationary state was calculated, and its implications are discussed, e.g., citrate level may not regulate glycolysis because it is mostly mitochondrial. Citrate synthetase, controlled largely by its inhibitors, is of key importance in regulating fatty acid metabolism. The response of aconitase to the mitochondrial Mg²⁺ levels is of major importance in setting both the mitochondrial citrate and isocitrate levels. Pyruvate dehydrogenase is about 96% in the inactive phosphorylated form, and the active form is also 15% inhibited by products, severely limiting pyruvate oxidation and causing preferential utilization of palmitate as the metabolic fuel. The simulation is consistent with a creatine phosphate shuttle which delivers high energy phosphate to the site of its utilization for mechanical work.     

The effects of various fatty acids on action potential shortening during sequential periods of ischaemia and reperfusion

Intracellular potentials were recorded from Langendorff-perfused guinea-pig hearts. All fatty acids studied (palmitate, linoleate, octanoate and acetate) potentiated action potential (AP) shortening in an experimental protocol involving sequential periods of coronary flow reduction and reperfusion. Pyruvate and acetoacetate did not share this effect. The dose relation of the AP shortening effect was studied in the case of palmitate and found to saturate at a relatively low palmitate: albumin molar ratio. Palmitate-induced potentiation of ischaemic AP shortening was less marked in sustained ischaemia than in the protocol involving periods of reperfusion. Palmitate and acetate were shown to cause an excerbation of the decline in glycogen levels in the sequential low flow protocol. Ischaemic AP duration was closely correlated with glycogen content at low, but not at high glycogen levels. It seemed possible that part of the fatty acid induced potentiation of AP shortening in the sequential low flow protocol might be attributable to glycogen depletion. In the absence of a glycolytic substrate, acetate and octanoate potentiated ischaemic AP shortening, whereas palmitate was without effect. The degree of ischaemia studied was associated with a stimulation of exogenous glucose utilization, and fatty acids did not prevent this stimulation.