Mitochondrial arginase-2 is essential for IL-10 metabolic reprogramming of inflammatory macrophages

Mitochondria are important regulators of macrophage polarisation. Here, we show that arginase-2 (Arg2) is a microRNA-155 (miR-155) and interleukin-10 (IL-10) regulated protein localized at the mitochondria in inflammatory macrophages, and is critical for IL-10-induced modulation of mitochondrial dynamics and oxidative respiration. Mechanistically, the catalytic activity and presence of Arg2 at the mitochondria is crucial for oxidative phosphorylation. We further show that Arg2 mediates this process by increasing the activity of complex II (succinate dehydrogenase). Moreover, Arg2 is essential for IL-10-mediated downregulation of the inflammatory mediators succinate, hypoxia inducible factor 1α (HIF-1α) and IL-1β in vitro. Accordingly, HIF-1α and IL-1β are highly expressed in an LPS-induced in vivo model of acute inflammation using Arg2^-/- mice. These findings shed light on a new arm of IL-10-mediated metabolic regulation, working to resolve the inflammatory status of the cell.

De novo polyamine synthesis supports metabolic and functional responses in activated murine NK cells

Cellular metabolism is dynamically regulated in NK cells and strongly influences their responses. Metabolic dysfunction is linked to defective NK cell responses in diseases such as obesity and cancer. The transcription factors, sterol regulatory element binding protein (SREBP) and cMyc, are crucial for controlling NK cell metabolic and functional responses, though the mechanisms involved are not fully understood. This study reveals a new role for SREBP in NK cells in supporting de novo polyamine synthesis through facilitating elevated cMyc expression. Polyamines have diverse roles and their de novo synthesis is required for NK cell glycolytic and oxidative metabolism and to support optimal NK cell effector functions. When NK cells with impaired SREBP activity were supplemented with exogenous polyamines, NK cell metabolic defects were not rescued but these NK cells displayed significant improvement in some effector functions. One role for polyamines is in the control of protein translation where spermidine supports the posttranslational hypusination of translation factor eIF5a. Pharmacological inhibition of hypusination also impacts upon NK cell metabolism and effector function. Considering recent evidence that cholesterol-rich tumor microenvironments inhibit SREBP activation and drive lymphocyte dysfunction, this study provides key mechanistic insight into this tumor-evasion strategy.

Memory CD8+ T Cells Balance Pro- and Anti-inflammatory Activity by Reprogramming Cellular Acetate Handling at Sites of Infection

Serum acetate increases upon systemic infection. Acutely, assimilation of acetate expands the capacity of memory CD8⁺ T cells to produce IFN-γ. Whether acetate modulates memory CD8⁺ T cell metabolism and function during pathogen re-encounter remains unexplored. Here we show that at sites of infection, high acetate concentrations are being reached, yet memory CD8⁺ T cells shut down the acetate assimilating enzymes ACSS1 and ACSS2. Acetate, being thus largely excluded from incorporation into cellular metabolic pathways, now had different effects, namely (1) directly activating glutaminase, thereby augmenting glutaminolysis, cellular respiration, and survival, and (2) suppressing TCR-triggered calcium flux, and consequently cell activation and effector cell function. In vivo, high acetate abundance at sites of infection improved pathogen clearance while reducing immunopathology. This indicates that, during different stages of the immune response, the same metabolite-acetate-induces distinct immunometabolic programs within the same cell type.

Inhibitors of the NMDA-Nitric Oxide Signaling Pathway Protect Against Neuronal Atrophy and Synapse Loss Provoked by l-alpha Aminoadipic Acid-treated Astrocytes

The impact of treating astrocytes with the astrocytic toxin l-alpha amino adipic acid (L-AAA) on neuronal outgrowth, complexity and synapse formation was assessed, using a model of astrocyte-neuronal interaction. Treatment of rat primary cortical neurons with conditioned media (CM) derived from astrocytes treated with L-AAA reduced neuronal complexity and synapse formation. L-AAA provoked a reduction in the expression of glial fibrillary acid protein (GFAP) and a reduction in ATP-linked mitochondrial respiration in astrocytic cells. As the NMDA-R/PSD-95/NOS signaling pathway is implicated in regulating the structural plasticity of neurons, treatment of neuronal cultures with the neuronal nitric oxide synthase (nNOS) inhibitor 1-[2-(trifluoromethyl)phenyl] imidazole (TRIM) [100 nM] was assessed and observed to protect against L-AAA-treated astrocytic CM-induced reduction in neuronal complexity and synapse loss. Treatment with the NMDA-R antagonist ketamine protected against the CM-induced loss of synapse formation whereas the novel PSD-95/nNOS inhibitors 2-((1H-benzo[d] [1,2,3]triazol-5-ylamino) methyl)-4,6-dichlorophenol (IC87201) and 4-(3,5-dichloro-2-hydroxy-benzylamino)-2-hydroxybenzoic acid (ZL006) protected against synapse loss with partial protection against reduced neurite outgrowth. Furthermore, L-AAA delivery to the pre-limbic cortex (PLC) of mice was found to increase dendritic spine density and treatment with ZL006 reduced this effect. In summary, L-AAA-induced astrocyte impairment leads to a loss of neuronal complexity and synapse loss in vitro and increased dendritic spine density in vivo that may be reversed by inhibitors of the NMDA-R/PSD-95/NOS pathway. The results have implications for understanding astrocytic-neuronal interaction and the search for drug candidates that may provide therapeutic approaches for brain disorders associated with astrocytic histopathology.

Amino acid-dependent cMyc expression is essential for NK cell metabolic and functional responses in mice

Natural killer (NK) cells are lymphocytes with important anti-tumour functions. Cytokine activation of NK cell glycolysis and oxidative phosphorylation (OXPHOS) are essential for robust NK cell responses. However, the mechanisms leading to this metabolic phenotype are unclear. Here we show that the transcription factor cMyc is essential for IL-2/IL-12-induced metabolic and functional responses in mice. cMyc protein levels are acutely regulated by amino acids; cMyc protein is lost rapidly when glutamine is withdrawn or when system L-amino acid transport is blocked. We identify SLC7A5 as the predominant system L-amino acid transporter in activated NK cells. Unlike other lymphocyte subsets, glutaminolysis and the tricarboxylic acid cycle do not sustain OXPHOS in activated NK cells. Glutamine withdrawal, but not the inhibition of glutaminolysis, results in the loss of cMyc protein, reduced cell growth and impaired NK cell responses. These data identify an essential role for amino acid-controlled cMyc for NK cell metabolism and function.

Metabolic regulation of immune responses: therapeutic opportunities

Immune cell metabolism is dynamically regulated in parallel with the substantial changes in cellular function that accompany immune cell activation. While these changes in metabolism are important for facilitating the increased energetic and biosynthetic demands of activated cells, immune cell metabolism also has direct roles in controlling the functions of immune cells and shaping the immune response. A theme is emerging wherein nutrients, metabolic enzymes, and metabolites can act as an extension of the established immune signal transduction pathways, thereby adding an extra layer of complexity to the regulation of immunity. This Review will outline the metabolic configurations adopted by different immune cell subsets, describe the emerging roles for metabolic enzymes and metabolites in the control of immune cell function, and discuss the therapeutic implications of this emerging immune regulatory axis.

Renal Fanconi Syndrome Is Caused by a Mistargeting-Based Mitochondriopathy

We recently reported an autosomal dominant form of renal Fanconi syndrome caused by a missense mutation in the third codon of the peroxisomal protein EHHADH. The mutation mistargets EHHADH to mitochondria, thereby impairing mitochondrial energy production and, consequently, reabsorption of electrolytes and low-molecular-weight nutrients in the proximal tubule. Here, we further elucidate the molecular mechanism underlying this pathology. We find that mutated EHHADH is incorporated into mitochondrial trifunctional protein (MTP), thereby disturbing β-oxidation of long-chain fatty acids. The resulting MTP deficiency leads to a characteristic accumulation of hydroxyacyl- and acylcarnitines. Mutated EHHADH also limits respiratory complex I and corresponding supercomplex formation, leading to decreases in oxidative phosphorylation capacity, mitochondrial membrane potential maintenance, and ATP generation. Activity of the Na(+)/K(+)-ATPase is thereby diminished, ultimately decreasing the transport activity of the proximal tubule cells.

Melanocytes are more responsive to IFN-γ and produce higher amounts of kynurenine than melanoma cells

A key link between amino acid catabolism and immune regulation in cancer is the augmented tryptophan (Trp) catabolism through the kynurenine pathway (KP), a metabolic route induced by interferon-γ (IFN-γ) and related to poor prognosis in melanomas. Besides its role in cancer, IFN-γ plays a key role in the control of pigmentation homeostasis. Here we measured KP metabolites in human melanoma lines and skin melanocytes and fibroblasts in response to IFN-γ. In general, IFN-γ affected KP in skin cells more than in melanoma cells, supporting IFN-γ roles in skin physiology and that of stromal cells in modulating the tumor microenvironment.

Mistargeting of peroxisomal EHHADH and inherited renal Fanconi's syndrome

BACKGROUND

In renal Fanconi's syndrome, dysfunction in proximal tubular cells leads to renal losses of water, electrolytes, and low-molecular-weight nutrients. For most types of isolated Fanconi's syndrome, the genetic cause and underlying defect remain unknown.

METHODS

We clinically and genetically characterized members of a five-generation black family with isolated autosomal dominant Fanconi's syndrome. We performed genomewide linkage analysis, gene sequencing, biochemical and cell-biologic investigations of renal proximal tubular cells, studies in knockout mice, and functional evaluations of mitochondria. Urine was studied with the use of proton nuclear magnetic resonance ((1)H-NMR) spectroscopy.

RESULTS

We linked the phenotype of this family's Fanconi's syndrome to a single locus on chromosome 3q27, where a heterozygous missense mutation in EHHADH segregated with the disease. The p.E3K mutation created a new mitochondrial targeting motif in the N-terminal portion of EHHADH, an enzyme that is involved in peroxisomal oxidation of fatty acids and is expressed in the proximal tubule. Immunocytofluorescence studies showed mistargeting of the mutant EHHADH to mitochondria. Studies of proximal tubular cells revealed impaired mitochondrial oxidative phosphorylation and defects in the transport of fluids and a glucose analogue across the epithelium. (1)H-NMR spectroscopy showed elevated levels of mitochondrial metabolites in urine from affected family members. Ehhadh knockout mice showed no abnormalities in renal tubular cells, a finding that indicates a dominant negative nature of the mutation rather than haploinsufficiency.

CONCLUSIONS

Mistargeting of peroxisomal EHHADH disrupts mitochondrial metabolism and leads to renal Fanconi's syndrome; this indicates a central role of mitochondria in proximal tubular function. The dominant negative effect of the mistargeted protein adds to the spectrum of monogenic mechanisms of Fanconi's syndrome. (Funded by the European Commission Seventh Framework Programme and others.).

Direct detection of Pneumocysytis carinii in outdoor air: preliminary results of a field study

P. carinii causes pneumonia in immunocompromised patients. New studies are suggestive of the de novo infections. Although P. carinii is believed to be ubiquitous it has not been detected directly from outdoor air. Therefore, outdoor air samples (n = 20) of 5 m3 were collected onto gelatin filters (pore size: 3 microns) on a cemetery using a suction pump (Sartorius MD8). Five samples were silver-stained, five samples were stained with an indirect immunfluorescence test kit, the remaining ten samples were stained with the combinations of the two individual stains. In a total of 100 m3 outdoor air one cyst resembling P. carinii was detected by the methenamine silver stain. Other cells not resembling P. carinii were found with a silver stained cell wall and positive fluorescence. The natural reservoir of P. carinii remains unknown. The indirect immunfluoresence which is common in the clinical laboratory is probably not specific enough for environmental samples.

Genotoxic activity of important nitrobenzenes and nitroanilines in the Ames test and their structure-activity relationship

The most important commercially available nitro- and aminobenzenes and the explosive trinitrobenzene were tested for mutagenicity in the Salmonella typhymurium TA 98 and TA 100 both in the absence and presence of S 9. Ten of the 14 compounds tested (71%) were mutagenic. All the substances showed positive results in TA 98 and 4 substances were also mutagenic in TA 100. The three diaminobenzenes and 4-nitroaniline were mutagenic only with metabolic activation. All other compounds did not require the addition of S 9. Only nitrobenzene, 1,2-dinitrobenzene, aniline and 2-nitroaniline were negative in both strains. In summary, all substances that are derived from nitrobenzene or aniline by addition of a nitro group in the meta- or para-position were mutagenic, whereas nitrobenzene and aniline themselves and their ortho-derivates were nonmutagenic. The possible relationships between the position of the substituents and the mutagenicity are discussed.

Gait characteristics in multiple sclerosis: progressive changes and effects of exercise on parameters

This study determines the characteristics of the multiple sclerosis gait, identifies the progressive gait changes associated with this degenerative disease, and determines the effects of an aquatic exercise program on gait parameters. Eleven patients with multiple sclerosis volunteered to participate and were filmed three times during a 10 week period with a Locam camera at 100 frames/s. During the testing period, subjects participated in an aquatic exercise program. In addition, they were rated according to the Kurtzke Scale for Evaluating Disability in Multiple Sclerosis. Results indicated that these patients with MS have shorter stride lengths, slower free speed walking rates, and higher cadence than do persons without MS. Knee and ankle joint rotation were characterized by lower than normal excursion with less vertical lift of the center of gravity and greater trunk lean than normal. Significant correlations between the Kurtzke Scale and gait parameters were indicated for step length and hip and ankle joint excursion. The aquatic exercise program appeared to have had no effect on the studied gait parameters.