Amino acids fuel T cell-mediated inflammation.

Reprogramming cellular metabolism helps support T cell growth and effector function upon activation. In this issue of Immunity, Nakaya et al. (2014) report that the glutamine transporter ASCT2 regulates T cell metabolism and mTOR kinase signaling to shape inflammatory T helper cell responses.

The role of AMPK in T cell metabolism and function.

The AMP-activated protein kinase (AMPK) is a key metabolic regulator that both senses changes in cellular energy levels and activates pathways to maintain cellular energy balance. AMPK achieves this by stimulating catabolic pathways that generate ATP and inhibiting biological pathways that consume ATP consumption. Recent work has established that AMPK is activated in T cells by both immunological and environmental stimuli, and plays an important role in T cell metabolism, in part by controlling T cell 'metabolic plasticity'. Recent data have revealed distinct functions for AMPK in T cells, including effects on memory T cell development, cytokine production, and potentially anti-tumor responses. In this review, we discuss recent advances in our understanding of AMPK function in T cells, and discuss future research areas for this energy-sensing pathway in lymphocytes.

The miR-17∼92 microRNA Cluster Is a Global Regulator of Tumor Metabolism.

A central hallmark of cancer cells is the reprogramming of cellular metabolism to meet the bioenergetic and biosynthetic demands of malignant growth. Here, we report that the miR-17∼92 microRNA (miRNA) cluster is an oncogenic driver of tumor metabolic reprogramming. Loss of miR-17∼92 in Myc(+) tumor cells leads to a global decrease in tumor cell metabolism, affecting both glycolytic and mitochondrial metabolism, whereas increased miR-17∼92 expression is sufficient to drive increased nutrient usage by tumor cells. We mapped the metabolic control element of miR-17∼92 to the miR-17 seed family, which influences cellular metabolism and mammalian target of rapamycin complex 1 (mTORC1) signaling through negative regulation of the LKB1 tumor suppressor. miR-17-dependent tuning of LKB1 levels regulates both the metabolic potential of Myc(+) lymphomas and tumor growth in vivo. Our results establish metabolic reprogramming as a central function of the oncogenic miR-17∼92 miRNA cluster that drives the progression of MYC-dependent tumors.

The AMP-activated protein kinase (AMPK) and cancer: many faces of a metabolic regulator.

The AMP-activated protein kinase (AMPK) is a central regulator of cellular metabolism and energy homeostasis in mammalian tissues. Pertinent to cancer biology is the fact that AMPK is situated in the center of a signaling network involving established tumor suppressors including LKB1, TSC2 and p53. However, recent research suggests that AMPK can exert pro- or anti-tumorigenic roles in cancer depending on context. Loss of AMPK activity has been observed in several tumor types, and can cooperate with oncogenic drivers to reprogram tumor cell metabolism and enhance cell growth and proliferation. However, AMPK activation can also provide a growth advantage to tumor cells by regulating cellular metabolic plasticity, thus providing tumor cells the flexibility to adapt to metabolic stress. Here we discuss the contextual nature of the "two faces" of AMPK in cancer, and discuss the rationale and context for employing AMPK activators versus inhibitors for cancer therapy.

Oxidative metabolism enables Salmonella evasion of the NLRP3 inflammasome.

Microbial infection triggers assembly of inflammasome complexes that promote caspase-1-dependent antimicrobial responses. Inflammasome assembly is mediated by members of the nucleotide binding domain leucine-rich repeat (NLR) protein family that respond to cytosolic bacterial products or disruption of cellular processes. Flagellin injected into host cells by invading Salmonella induces inflammasome activation through NLRC4, whereas NLRP3 is required for inflammasome activation in response to multiple stimuli, including microbial infection, tissue damage, and metabolic dysregulation, through mechanisms that remain poorly understood. During systemic infection, Salmonella avoids NLRC4 inflammasome activation by down-regulating flagellin expression. Macrophages exhibit delayed NLRP3 inflammasome activation after Salmonella infection, suggesting that Salmonella may evade or prevent the rapid activation of the NLRP3 inflammasome. We therefore screened a Salmonella Typhimurium transposon library to identify bacterial factors that limit NLRP3 inflammasome activation. Surprisingly, absence of the Salmonella TCA enzyme aconitase induced rapid NLRP3 inflammasome activation. This inflammasome activation correlated with elevated levels of bacterial citrate, and required mitochondrial reactive oxygen species and bacterial citrate synthase. Importantly, Salmonella lacking aconitase displayed NLRP3- and caspase-1/11-dependent attenuation of virulence, and induced elevated serum IL-18 in wild-type mice. Together, our data link Salmonella genes controlling oxidative metabolism to inflammasome activation and suggest that NLRP3 inflammasome evasion promotes systemic Salmonella virulence.

Fueling immunity: insights into metabolism and lymphocyte function.

Lymphocytes face major metabolic challenges upon activation. They must meet the bioenergetic and biosynthetic demands of increased cell proliferation and also adapt to changing environmental conditions, in which nutrients and oxygen may be limiting. An emerging theme in immunology is that metabolic reprogramming and lymphocyte activation are intricately linked. However, why T cells adopt specific metabolic programs and the impact that these programs have on T cell function and, ultimately, immunological outcome remain unclear. Research on tumor cell metabolism has provided valuable insight into metabolic pathways important for cell proliferation and the influence of metabolites themselves on signal transduction and epigenetic programming. In this Review, we highlight emerging concepts regarding metabolic reprogramming in proliferating cells and discuss their potential impact on T cell fate and function.

Novel nonmajor histocompatibility complex-linked loci from mouse chromosome 17 confer susceptibility to viral-mediated chronic autoimmune myocarditis.

BACKGROUND: Development of viral-induced chronic myocarditis is thought to involve both environmental and genetic factors. However, to date, no susceptibility genes have been identified. METHODS AND RESULTS: We sought to identify loci that confer susceptibility to viral-induced chronic myocarditis with the use of chromosome substitution strain mice that are composed of 1 chromosome from the disease susceptible A/J strain on an otherwise resistant C57BL/6 background. By this method, we identified chromosome 17 to confer susceptibility. To further isolate the region of susceptibility, 8 strains of mice congenic for different portions of chromosome 17 were generated. Characterization of these strains identified at least 4 susceptibility loci on the chromosome. Three of these loci are located in the proximal 22.8 cM, whereas the fourth locus is located in the portion of the chromosome distal to 34.3 cM. CONCLUSIONS: We have identified 4 loci that confer susceptibility of viral-induced chronic myocarditis. Of these loci, 3 were distinct from the major histocompatibility complex locus and thus represent novel susceptibility loci. The close proximately of the 2 novel loci with susceptibility loci for other autoimmune diseases such as type 1 diabetes and chronic experimental autoimmune thyroiditis suggests the presence of global autoimmune susceptibility genes.

IL-6 during viral-induced chronic autoimmune myocarditis.

Interleukin (IL)-6 is a pleiotropic cytokine that plays a key role in a wide variety of diseases. Based on a number of adjuvant-induced experimental models, IL-6 is critical to the development of autoimmune diseases including experimental autoimmune encephalomyelitis, adjuvant-induced arthritis, and experimental autoimmune myocarditis. However, whether it plays a pathogenic role in viral-induced autoimmune myocarditis has been less well defined. While experimental models of myocarditis have clearly linked IL-6 to the generation of pathogenic autoreactive T cells, IL-6 has exhibited a protective role in autoimmune disease development in viral-induced disease models. As pathogen infection has been linked to the majority of myocarditis patients, treatments aimed at decreasing IL-6 levels in the hopes of limiting the autoimmune response run the risk of increasing disease severity.

Lack of IL-6 during coxsackievirus infection heightens the early immune response resulting in increased severity of chronic autoimmune myocarditis.

BACKGROUND: Chronic myocarditis is often initiated by viral infection, the most common of which is coxsackievirus infection. The precise mechanism by which viral infection leads to chronic autoimmune pathology is poorly understood, however it is clear that the early immune response plays a critical role. Previous results have shown that the inflammatory cytokine interleukin (IL)-6 is integral to the development of experimental-induced autoimmune myocarditis. However, the function of IL-6 during viral-mediated autoimmunity has yet to be elucidated. METHODS AND RESULTS: To address the requirement of IL-6 during disease induction, IL-6 deficient mice were infected with coxsackievirus B3 (CB3). Following infection, mice lacking IL-6 developed increased chronic autoimmune disease pathology compared to wild type controls without a corresponding change in the level of viral replication in the heart. This increase in disease severity was accompanied by elevated levels of TNF-alpha, MCP-1, IL-10, activated T cells and cardiac infiltrating macrophage/monocytes. Injection of recombinant IL-6 early following infection in the IL-6 deficient mice was sufficient to lower the serum cytokines TNF-alpha and IL-10 as well as the serum chemokines MCP-1, MIP-1beta, RANTES and MIG with a corresponding decrease in the chronic disease pathology strongly suggests an important regulatory role for IL-6 during the early response. CONCLUSIONS: While IL-6 plays a pathogenic role in experimental-induced autoimmune disease, its function following viral-induced autoimmunity is not reprised. By regulating the early immune response and thereby controlling the severity of chronic disease, IL-6 directs the outcome of chronic autoimmune myocarditis.

Intestinal phenotype of variable-weight cystic fibrosis knockout mice.

Cystic fibrosis (CF) transmembrane conductance regulator (Cftr) knockout mice present the clinical features of low body weight and intestinal disease permitting an assessment of the interrelatedness of these phenotypes in a controlled environment. To identify intestinal alterations that are affected by body weight in CF mice, the histological phenotypes of crypt-villus axis height, goblet cell hyperplasia, mast cell infiltrate, crypt cell proliferation, and apoptosis were measured in a population of 12-wk-old (C57BL/6 x BALB/cJ) F2 Cftr(tm1UNC) and non-CF mice presenting a range of body weight. In addition, cardiac blood samples were assessed, and gene expression profiling of the ileum was completed. Crypt-villus axis height decreased with increasing body weight in CF but not control mice. Intestinal crypts from CF mice had fewer apoptotic cells, per unit length, than did non-CF mice, and normalized cell proliferation was similar to control levels. Goblet cell hyperplasia and mast cell infiltration were increased in the CF intestine and identified to be independent of body weight. Blood triglyceride levels were found to be significantly lower in CF mice than in control mice but were not dependent on CF mouse weight. By expression profiling, genes of DNA replication and lipid metabolism were among those altered in CF mice relative to non-CF controls, and no differences in gene expression were measured between samples from CF mice in the 25th and 75th percentile for weight. In this CF mouse model, crypt elongation, due to an expanded proliferative zone and decreased apoptosis, was identified to be dependent on body weight.