Maintenance of CD4 T cell fitness through regulation of Foxo1.

Foxo transcription factors play an essential role in regulating specialized lymphocyte functions and in maintaining T cell quiescence. Here, we used a system in which Foxo1 transcription-factor activity, which is normally terminated upon cell activation, cannot be silenced, and we show that enforcing Foxo1 activity disrupts homeostasis of CD4 conventional and regulatory T cells. Despite limiting cell metabolism, continued Foxo1 activity is associated with increased activation of the kinase Akt and a cell-intrinsic proliferative advantage; however, survival and cell division are decreased in a competitive setting or growth-factor-limiting conditions. Via control of expression of the transcription factor Myc and the IL-2 receptor ß-chain, termination of Foxo1 signaling couples the increase in cellular cholesterol to biomass accumulation after activation, thereby facilitating immunological synapse formation and mTORC1 activity. These data reveal that Foxo1 regulates the integration of metabolic and mitogenic signals essential for T cell competitive fitness and the coordination of cell growth with cell division.

Autophagy enforces functional integrity of regulatory T cells by coupling environmental cues and metabolic homeostasis.

Regulatory T (Treg) cells respond to immune and inflammatory signals to mediate immunosuppression, but how the functional integrity of Treg cells is maintained under activating environments is unclear. Here we show that autophagy is active in Treg cells and supports their lineage stability and survival fitness. Treg cell-specific deletion of Atg7 or Atg5, two essential genes in autophagy, leads to loss of Treg cells, greater tumor resistance and development of inflammatory disorders. Atg7-deficient Treg cells show increased apoptosis and readily lose expression of the transcription factor Foxp3, especially after activation. Mechanistically, autophagy deficiency upregulates metabolic regulators mTORC1 and c-Myc and glycolysis, which contribute to defective Treg function. Therefore, autophagy couples environmental signals and metabolic homeostasis to protect lineage and survival integrity of Treg cells in activating contexts.

Treg cells require the phosphatase PTEN to restrain TH1 and TFH cell responses.

The interplay between effector T cells and regulatory T cells (Treg cells) is crucial for adaptive immunity, but how Treg cells control diverse effector responses is elusive. We found that the phosphatase PTEN links Treg cell stability to repression of type 1 helper T cell (TH1 cell) and follicular helper T cell (TFH cell) responses. Depletion of PTEN in Treg cells resulted in excessive TFH cell and germinal center responses and spontaneous inflammatory disease. These defects were considerably blocked by deletion of interferon-γ, indicating coordinated control of TH1 and TFH responses. Mechanistically, PTEN maintained Treg cell stability and metabolic balance between glycolysis and mitochondrial fitness. Moreover, PTEN deficiency upregulates activity of the metabolic checkpoint kinase complex mTORC2 and the serine-threonine kinase Akt, and loss of this activity restores functioning of PTEN-deficient Treg cells. Our studies establish a PTEN-mTORC2 axis that maintains Treg cell stability and coordinates Treg cell-mediated control of effector responses.

mTORC1 and mTORC2 Kinase Signaling and Glucose Metabolism Drive Follicular Helper T Cell Differentiation.

Follicular helper T (Tfh) cells are crucial for germinal center (GC) formation and humoral adaptive immunity. Mechanisms underlying Tfh cell differentiation in peripheral and mucosal lymphoid organs are incompletely understood. We report here that mTOR kinase complexes 1 and 2 (mTORC1 and mTORC2) are essential for Tfh cell differentiation and GC reaction under steady state and after antigen immunization and viral infection. Loss of mTORC1 and mTORC2 in T cells exerted distinct effects on Tfh cell signature gene expression, whereas increased mTOR activity promoted Tfh responses. Deficiency of mTORC2 impaired CD4(+) T cell accumulation and immunoglobulin A production and aberrantly induced the transcription factor Foxo1. Mechanistically, the costimulatory molecule ICOS activated mTORC1 and mTORC2 to drive glycolysis and lipogenesis, and glucose transporter 1-mediated glucose metabolism promoted Tfh cell responses. Altogether, mTOR acts as a central node in Tfh cells by linking immune signals to anabolic metabolism and transcriptional activity.

Homeostatic control of metabolic and functional fitness of Treg cells by LKB1 signalling.

Regulatory T cells (Treg cells) have a pivotal role in the establishment and maintenance of immunological self-tolerance and homeostasis. Transcriptional programming of regulatory mechanisms facilitates the functional activation of Treg cells in the prevention of diverse types of inflammatory responses. It remains unclear how Treg cells orchestrate their homeostasis and interplay with environmental signals. Here we show that liver kinase B1 (LKB1) programs the metabolic and functional fitness of Treg cells in the control of immune tolerance and homeostasis. Mice with a Treg-specific deletion of LKB1 developed a fatal inflammatory disease characterized by excessive TH2-type-dominant responses. LKB1 deficiency disrupted Treg cell survival and mitochondrial fitness and metabolism, but also induced aberrant expression of immune regulatory molecules including the negative co-receptor PD-1 and the TNF receptor superfamily proteins GITR and OX40. Unexpectedly, LKB1 function in Treg cells was independent of conventional AMPK signalling or the mTORC1-HIF-1α axis, but contributed to the activation of ß-catenin signalling for the control of PD-1 and TNF receptor proteins. Blockade of PD-1 activity reinvigorated the ability of LKB1-deficient Treg cells to suppress TH2 responses and the interplay with dendritic cells primed by thymic stromal lymphopoietin. Thus, Treg cells use LKB1 signalling to coordinate their metabolic and immunological homeostasis and to prevent apoptotic and functional exhaustion, thereby orchestrating the balance between immunity and tolerance.

The S1P(1)-mTOR axis directs the reciprocal differentiation of T(H)1 and T(reg) cells.

Naive CD4(+) T cells differentiate into diverse effector and regulatory lineages to orchestrate immunity and tolerance. Here we found that the differentiation of proinflammatory T helper type 1 (T(H)1) cells and anti-inflammatory Foxp3(+) regulatory T cells (T(reg) cells) was reciprocally regulated by S1P(1), a receptor for the bioactive lipid sphingosine 1-phosphate (S1P). S1P(1) inhibited the generation of extrathymic and natural T(reg) cells while driving T(H)1 development in a reciprocal manner and disrupted immune homeostasis. S1P(1) signaled through the kinase mTOR and antagonized the function of transforming growth factor-ß mainly by attenuating sustained activity of the signal transducer Smad3. S1P(1) function was dependent on endogenous sphingosine kinase activity. Notably, two seemingly unrelated immunosuppressants, FTY720 and rapamycin, targeted the same S1P(1) and mTOR pathway to regulate the dichotomy between T(H)1 cells and T(reg) cells. Our studies establish an S1P(1)-mTOR axis that controls T cell lineage specification.

T cell exit from quiescence and differentiation into Th2 cells depend on Raptor-mTORC1-mediated metabolic reprogramming.

Naive T cells respond to antigen stimulation by exiting from quiescence and initiating clonal expansion and functional differentiation, but the control mechanism is elusive. Here we describe that Raptor-mTORC1-dependent metabolic reprogramming is a central determinant of this transitional process. Loss of Raptor abrogated T cell priming and T helper 2 (Th2) cell differentiation, although Raptor function is less important for continuous proliferation of actively cycling cells. mTORC1 coordinated multiple metabolic programs in T cells including glycolysis, lipid synthesis, and oxidative phosphorylation to mediate antigen-triggered exit from quiescence. mTORC1 further linked glucose metabolism to the initiation of Th2 cell differentiation by orchestrating cytokine receptor expression and cytokine responsiveness. Activation of Raptor-mTORC1 integrated T cell receptor and CD28 costimulatory signals in antigen-stimulated T cells. Our studies identify a Raptor-mTORC1-dependent pathway linking signal-dependent metabolic reprogramming to quiescence exit, and this in turn coordinates lymphocyte activation and fate decisions in adaptive immunity.

Metabolism in Immune Cell Differentiation and Function.

The immune system is a central determinant of organismal health. Functional immune responses require quiescent immune cells to rapidly grow, proliferate, and acquire effector functions when they sense infectious agents or other insults. Specialized metabolic programs are critical regulators of immune responses, and alterations in immune metabolism can cause immunological disorders. There has thus been growing interest in understanding how metabolic processes control immune cell functions under normal and pathophysiological conditions. In this chapter, we summarize how metabolic programs are tuned and what the physiological consequences of metabolic reprogramming are as they relate to immune cell homeostasis, differentiation, and function.

Tsc1 promotes the differentiation of memory CD8+ T cells via orchestrating the transcriptional and metabolic programs.

Memory CD8(+) T cells are an essential component of protective immunity. Signaling via mechanistic target of rapamycin (mTOR) has been implicated in the regulation of the differentiation of effector and memory T cells. However, little is understood about the mechanisms that control mTOR activity, or the effector pathways regulated by mTOR. We describe here that tuberous sclerosis 1 (Tsc1), a regulator of mTOR signaling, plays a crucial role in promoting the differentiation and function of memory CD8(+) T cells in response to Listeria monocytogenes infection. Mice with specific deletion of Tsc1 in antigen-experienced CD8(+) T cells evoked normal effector responses, but were markedly impaired in the generation of memory T cells and their recall responses to antigen reexposure in a cell-intrinsic manner. Tsc1 deficiency suppressed the generation of memory-precursor effector cells while promoting short-lived effector cell differentiation. Transcriptome analysis indicated that Tsc1 coordinated gene expression programs underlying immune function, transcriptional regulation, and cell metabolism. Furthermore, Tsc1 deletion led to excessive mTORC1 activity and dysregulated glycolytic and oxidative metabolism in response to IL-15 stimulation. These findings establish a Tsc1-mediated checkpoint in linking immune signaling and cell metabolism to orchestrate memory CD8(+) T-cell development and function.

Risk Assessment in Artisanal Fisheries in Developing Countries: A Systematic Review.

INTRODUCTION: Artisanal fisheries generally do not have injury prevention plans and safety or quality management systems on board, thus making them prone to more fatal and nonfatal injuries. The objective of the study is to systematically review and synthesize the literature to identify the risks of injuries (fatal and nonfatal) and health problems in artisanal fisheries in developing countries. METHODS: A systematic literature search was carried out from December 2019 to March 2020. Articles were included with at least 1 outcome of interest (fatal injuries, nonfatal injuries, health problems, causal factors). In all, 18 articles on occupational safety and health aspects in artisanal fisheries from developing countries were kept for final analysis. RESULTS: Of the 4 studies on fatal injuries, only 1 reported fatal incidence rates (14 per 1,000 person-years). Vessel disasters were the most common cause of fatal injuries, with 14.3%-81% drownings. The prevalence of nonfatal injuries was between 55% and 61%. The most common causes were falls on the deck or into the sea/river, blows from objects/tools, punctures and cuts by fishhooks/fish rays and fishing equipment, and animal attacks or bites. Health problems included eye, ear, cardiovascular (hypertension), respiratory (decompression sickness), dermatological, and musculoskeletal problems. DISCUSSION: There is a serious gap of health and safety information in artisanal fishery, which is more extensive in developing countries. Epidemiological studies are needed with comparable incidence and prevalence rates. For adequate prevention and compliance with the UN sustainable goals, there is an urgent need to establish a health information system in the countries to register the relevant demographic and epidemiologic characteristics of the population.

Elderly care in Nepal: Are existing health and community support systems enough.

In Nepal, a few governmental and community-based programmes for elderly care are in place; however, information about successful implementation and overall effectiveness of these programmes is not well understood. In this article, we introduced these programmes and discussed existing programmes' gaps and implementation problems in light of existing grey and peer-reviewed evidence. A few notable governmental programmes, such as providing monthly allowances, pensions and free health care, have targeted specifically the elderly individuals. Yet, most health care institutions and providers are privately owned and profit-oriented, and there is a general lack of proper governmental health as well as social security systems for the elderly in the country. Generally, Nepalese communities consist of neighbourhood-based and religious-based groups that provide emotional and spiritual support to elderly individuals as well as provide support for health care access when needed. However, the influence that these groups can have on health and social well-being of elderly remains not well understood. Traditional family-based support systems may be feasible only for some families, while for others it could impose financial and psychological burdens. The role of the state is important in the effective implementation of existing programmes as well as in the development and implementation of additional programmes to ensure health and social well-being of elderly individuals. Furthermore, there is a need to establish partnerships with existing community structures and to mobilize them in the implementation of community-based programmes.

Metabolic reprogramming of alloantigen-activated T cells after hematopoietic cell transplantation.

Alloreactive donor T cells are the driving force in the induction of graft-versus-host disease (GVHD), yet little is known about T cell metabolism in response to alloantigens after hematopoietic cell transplantation (HCT). Here, we have demonstrated that donor T cells undergo metabolic reprograming after allogeneic HCT. Specifically, we employed a murine allogeneic BM transplant model and determined that T cells switch from fatty acid ß-oxidation (FAO) and pyruvate oxidation via the tricarboxylic (TCA) cycle to aerobic glycolysis, thereby increasing dependence upon glutaminolysis and the pentose phosphate pathway. Glycolysis was required for optimal function of alloantigen-activated T cells and induction of GVHD, as inhibition of glycolysis by targeting mTORC1 or 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3) ameliorated GVHD mortality and morbidity. Together, our results indicate that donor T cells use glycolysis as the predominant metabolic process after allogeneic HCT and suggest that glycolysis has potential as a therapeutic target for the control of GVHD.