In this report we show that the adipocytokine leptin directly modulates autophagy in human CD4(+)CD25(-) conventional (Tconv) T cells.

Chronic obstructive pulmonary disease (COPD) is an inflammatory condition associated with abnormal immune responses, leading to airflow obstruction. Lungs of COPD subjects show accumulation of proinflammatory T helper (Th) 1 and Th17 cells resembling that of autoreactive immune responses. As regulatory T (Treg) cells play a central role in the control of autoimmune responses and their generation and function are controlled by the adipocytokine leptin, we herein investigated the association among systemic leptin overproduction, reduced engagement of glycolysis in T cells, and reduced peripheral frequency of Treg cells in different COPD stages. These phenomena were also associated with an impaired capacity to generate inducible Treg (iTreg) cells from conventional T (Tconv) cells. At the molecular level, we found that leptin inhibited the expression of forkhead-boxP3 (FoxP3) and its splicing variants containing the exon 2 (FoxP3-E2) that correlated inversely with inflammation and weakened lung function during COPD progression. Our data reveal that the immunometabolic pathomechanism leading to COPD progression is characterized by leptin overproduction, a decline in the expression of FoxP3 splicing forms, and an impairment in Treg cell generation and function. These results have potential implications for better understanding the autoimmune-like nature of COPD and the pathogenic events leading to lung damage.

MicroRNAs (miRNAs), small non-coding molecules targeting messenger RNAs and inhibiting protein translation, modulate key biological processes, including cell growth and development, energy utilization, and homeostasis. In particular, miRNAs control the differentiation, survival, and activation of CD4 + T conventional (Tconv) cells, key players of the adaptive immunity, and regulate the physiological response to infections and the pathological loss of immune homeostasis in autoimmunity. Upon T-cell receptor (TCR) stimulation, the described global miRNA quantitative decrease occurring in T cells is believed to promote the acquisition of effector functions by relaxing the post-transcriptional repression of genes associated with proliferation and cell activity. MiRNAs were initially thought to get downregulated uniquely by intracellular degradation; on the other hand, miRNA secretion via extracellular vesicles (EVs) represents an additional mechanism of rapid downregulation. By focusing on molecular interactions by means of graph theory, we have found that miRNAs released by TCR-stimulated Tconv cells are significantly enriched for targeting transcripts upregulated upon stimulation, including those encoding for crucial proteins associated with Tconv cell activation and function. Based on this computational approach, we present our perspective based on the following hypothesis: a stimulated Tconv cell will release miRNAs targeting genes associated with the effector function in the extracellular space in association with EVs, which will thus possess a suppressive potential toward other Tconv cells in the paracrine environment. We also propose possible future directions of investigation aimed at taking advantage of these phenomena to control Tconv cell effector function in health and autoimmunity.

Migration of activated regulatory T (Treg) cells to inflamed tissue is crucial for their immune-modulatory function. While metabolic reprogramming during Treg cell differentiation has been extensively studied, the bioenergetics of Treg cell trafficking remains undefined. We have investigated the metabolic demands of migrating Treg cells in vitro and in vivo. We show that glycolysis was instrumental for their migration and was initiated by pro-migratory stimuli via a PI3K-mTORC2-mediated pathway culminating in induction of the enzyme glucokinase (GCK). Subsequently, GCK promoted cytoskeletal rearrangements by associating with actin. Treg cells lacking this pathway were functionally suppressive but failed to migrate to skin allografts and inhibit rejection. Similarly, human carriers of a loss-of-function GCK regulatory protein gene-leading to increased GCK activity-had reduced numbers of circulating Treg cells. These cells displayed enhanced migratory activity but similar suppressive function, while conventional T cells were unaffected. Thus, GCK-dependent glycolysis regulates Treg cell migration.

We report here that leptin can act as a negative signal for the proliferation of human naturally occurring Foxp3(+)CD4(+)CD25(+) regulatory T (T(reg)) cells. Freshly isolated T(reg) cells produced leptin and expressed high amounts of leptin receptor (ObR). In vitro neutralization with leptin monoclonal antibody (mAb), during anti-CD3 and anti-CD28 stimulation, resulted in T(reg) cell proliferation, which was interleukin-2 (IL-2) dependent. T(reg) cells that proliferated in the presence of leptin mAb had increased expression of Foxp3 and remained suppressive. The phenomena appeared secondary to leptin signaling via ObR and, importantly, leptin neutralization reversed the anergic state of the T(reg) cells, as indicated by downmodulation of the cyclin-dependent kinase inhibitor p27 (p27(kip1)) and the phosphorylation of the extracellular-related kinases 1 (ERK1) and ERK2. Together with the finding of enhanced proliferation of T(reg) cells observed in leptin- and ObR-deficient mice, these results suggest a potential for therapeutic interventions in immune and autoimmune diseases.

There is a strong relationship between metabolic state and susceptibility to Mycobacterium tuberculosis (MTB) infection, with energy metabolism setting the basis for an exaggerated immuno-inflammatory response, which concurs with MTB pathogenesis. Herein, we show that controlled caloric restriction (CR), not leading to malnutrition, protects susceptible DBA/2 mice against pulmonary MTB infection by reducing bacterial load, lung immunopathology, and generation of foam cells, an MTB reservoir in lung granulomas. Mechanistically, CR induced a metabolic shift toward glycolysis, and decreased both fatty acid oxidation and mTOR activity associated with induction of autophagy in immune cells. An integrated multi-omics approach revealed a specific CR-induced metabolomic, transcriptomic, and proteomic signature leading to reduced lung damage and protective remodeling of lung interstitial tightness able to limit MTB spreading. Our data propose CR as a feasible immunometabolic manipulation to control MTB infection, and this approach offers an unexpected strategy to boost immunity against MTB.

Forkhead box P3 (FoxP3)+ regulatory T cells (Treg) are powerful mediators of immune regulation and immune homeostasis. In humans, Tregs are a heterogeneous population expressing surface markers which define phenotypically and functionally distinct subsets. Moreover, it is now clear that intracellular staining for FoxP3 does not unequivocally identify "true" suppressor cells, since several FoxP3 isoforms exist, and different reagents for FoxP3 detection are available. Here, we propose a strategy to identify potentially functional and suppressive Treg cells in an autoimmune disease like multiple sclerosis, and we suggest that in patients affected by this disease these cells are both reduced in number and functionally exhausted.

An unresolved issue in autoimmunity is the lack of surrogate biomarkers of immunological self-tolerance for disease monitoring. Here, we show that peripheral frequency of a regulatory T cell population, characterized by the co-expression of CD3 and CD56 molecules (TR3-56), is reduced in subjects with new-onset type 1 diabetes (T1D). In three independent T1D cohorts, we find that low frequency of circulating TR3-56 cells is associated with reduced β-cell function and with the presence of diabetic ketoacidosis. As autoreactive CD8+ T cells mediate disruption of insulin-producing β-cells1-3, we demonstrate that TR3-56 cells can suppress CD8+ T cell functions in vitro by reducing levels of intracellular reactive oxygen species. The suppressive function, phenotype and transcriptional signature of TR3-56 cells are also altered in T1D children. Together, our findings indicate that TR3-56 cells constitute a regulatory cell population that controls CD8+ effector functions, whose peripheral frequency may represent a traceable biomarker for monitoring immunological self-tolerance in T1D.

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) which involves a complex interaction between immune system and neural cells. Animal modeling has been critical for addressing MS pathogenesis. The three most characterized animal models of MS are (1) the experimental autoimmune/allergic encephalomyelitis (EAE); (2) the virally-induced chronic demyelinating disease, known as Theiler׳s murine encephalomyelitis virus (TMEV) infection and (3) the toxin-induced demyelination. All these models, in a complementary way, have allowed to reach a good knowledge of the pathogenesis of MS. Specifically, EAE is the model which better reflects the autoimmune pathogenesis of MS and is extremely useful to study potential experimental treatments. Furthermore, both TMEV and toxin-induced demyelination models are suitable for characterizing the role of the axonal injury/repair and the remyelination process in MS. In conclusion, animal models, despite their limitations, remain the most useful instrument for implementing the study of MS.

Human CD4(+)CD25(hi)Foxp3(+)CD127(-) Treg and CD4(+)CD25(-)Foxp3(-) Tconv cell functions are governed by their metabolic requirements. Here we report a comprehensive comparative analysis between ex vivo human Treg and Tconv cells that comprises analyses of the proteomic networks in subcellular compartments. We identified a dominant proteomic signature at the metabolic level that primarily impacted the highly-tuned balance between glucose and fatty-acid oxidation in the two cell types. Ex vivo Treg cells were highly glycolytic while Tconv cells used predominantly fatty-acid oxidation (FAO). When cultured in vitro, Treg cells engaged both glycolysis and FAO to proliferate, while Tconv cell proliferation mainly relied on glucose metabolism. Our unbiased proteomic analysis provides a molecular picture of the impact of metabolism on ex vivo human Treg versus Tconv cell functions that might be relevant for therapeutic manipulations of these cells.

There is a discrepancy between the in vitro anergic state of CD4(+)CD25(hi)FoxP3(+) regulatory T (Treg) cells and their in vivo proliferative capability. The underlying mechanism of this paradox is unknown. Here we show that the anergic state of Treg cells depends on the elevated activity of the mammalian target of rapamycin (mTOR) pathway induced by leptin: a transient inhibition of mTOR with rapamycin, before T cell receptor (TCR) stimulation, made Treg cells highly proliferative in the absence of exogenous interleukin-2 (IL-2). This was a dynamic and oscillatory phenomenon characterized by an early downregulation of the leptin-mTOR pathway followed by an increase in mTOR activation necessary for Treg cell expansion to occur. These data suggest that energy metabolism, through the leptin-mTOR-axis, sets responsiveness of Treg cells that use this information to control immune tolerance and autoimmunity.