SIRT3 negatively regulates TFH cell differentiation in cancer.

Follicular helper T (TFH) cells are essential for inducing germinal center (GC) reactions to mediate humoral adaptive immunity in tumors, but the mechanisms underlying TFH cell differentiation remain unclear. Here, we found that the metabolism sensor sirtuin 3 (SIRT3) is critical for TFH cell differentiation and GC formation during tumor and viral infection. SIRT3 deficiency in CD4+ T cells intrinsically enhanced TFH cell differentiation and GC reactions during tumor and virus infection. Mechanistically, damaged oxidative phosphorylation (OXPHOS) compensatively triggered the NAD+-glycolysis pathway to provide a cellular energy supply, which was necessary for SIRT3 deficiency-induced TFH cell differentiation. Blocking NAD+ synthesis-glycolysis signaling or recovering OXPHOS activities reversed the TFH cell differentiation induced by SIRT3 deficiency. Moreover, the mTOR and HIF1α signaling axis was found to be responsible for TFH cell differentiation induced by SIRT3 deficiency. HIF1α directly interacted with and regulated the activity of the transcription factor Bcl-6. Thus, our findings identify a cellular energy compensatory mechanism, regulated by the mitochondrial sensor SIRT3, that triggers NAD+-dependent glycolysis during mitochondrial OXPHOS injuries and a mTOR-HIF1α-Bcl-6 pathway to reprogram TFH cell differentiation. These data have implications for future cancer immunotherapy research targeting SIRT3 in T cells.

Deacetylase sirtuin 2 negatively regulates myeloid-derived suppressor cell functions in allograft rejection.

Although myeloid-derived suppressor cells (MDSCs) are critical for allograft survival, their regulatory mechanism remains unclear. Herein, our results showed that metabolism sensor sirtuin 2 (SIRT2) negatively regulates the functions of MDSCs in inducing allogeneic skin graft rejection. Genetic deletion of SIRT2 in myeloid cells (Sirt2Δmye) increased the number of CD11b+Gr1+ MDSCs in bone marrow, spleens, draining lymph nodes, and allografts, inhibited the production of proinflammatory cytokine tumor necrosis factor ɑ, enhanced the production of anti-inflammatory cytokine interleukin 10, and potentiated the suppressive activation of MDSCs in prolonging allograft skin survival. C-X-C motif chemokine receptor 2 is critical for mediating the recruitment and cytokine production of MDSCs induced by SIRT2. Mechanistically, Sirt2Δmye enhanced NAD+ levels, succinate dehydrogenase subunit A (SDHA) activities, and oxidative phosphorylation (OXPHOS) levels in MDSCs after transplantation. Pharmacologically blocking nicotinamide phosphoribosyltransferase effectively reverses the production of cytokines and suppressive activities of MDSC induced by Sirt2Δmye. Blocking OXPHOS with knockdown of SDHA or pharmacological blocking of SDHA significantly restores Sirt2Δmye-mediated stronger MDSC suppressive activity and inflammatory factor productions. Thus, our findings identify a previously unrecognized interplay between NAD+ and SDH-mediated OXPHOS metabolic pathways in regulating MDSC functions induced by the metabolic sensor SIRT2 in allogeneic transplantation.

New insights into follicular regulatory T cells in the intestinal and tumor microenvironments.

Follicular regulatory T (Tfr) cells are a novel and unique subset of effector regulatory T (Treg) cells that are located in germinal centers (GCs). Tfr cells express transcription profiles that are characteristic of both follicular helper T (Tfh) cells and Treg cells and negatively regulate GC reactions, including Tfh cell activation and cytokine production, class switch recombination and B cell activation. Evidence also shows that Tfr cells have specific characteristics in different local immune microenvironments. This review focuses on the regulation of Tfr cell differentiation and function in unique local immune microenvironments, including the intestine and tumor.

The hippo kinase MST1 negatively regulates the differentiation of follicular helper T cells.

Follicular helper T (TFH ) cells are essential for inducing germinal centre (GC) reactions to mediate humoral adaptive immunity and antiviral effects, but the mechanisms of TFH cell differentiation remain unclear. Here, we found that the hippo kinase MST1 is critical for TFH cell differentiation, GC formation, and antibody production under steady-state conditions and viral infection. MST1 deficiency intrinsically enhanced TFH cell differentiation and GC reactions in vivo and in vitro. Mechanistically, mTOR and HIF1α signalling is involved in glucose metabolism and increased glycolysis and decreased OXPHOS, which are critically required for MST1 deficiency-directed TFH cell differentiation. Moreover, upregulated Foxo3 expression is critically responsible for TFH cell differentiation induced by Mst1-/- . Thus, our findings identify a previously unrecognized relationship between hippo kinase MST1 signalling and mTOR-HIF1α-metabolic reprogramming coupled with Foxo3 signalling in reprogramming TFH cell differentiation.

Regulation of follicular T helper cell differentiation in antitumor immunity.

Follicular T helper (Tfh) cells are a subset of CD4+ T cells that play an important role in the formation of germinal centers and the maturation and differentiation of affinity-matured B cells. Recent studies have demonstrated important functions of Tfh cells in tertiary lymphoid structures of tumors, revealing great potential of Tfh cells in tumor immunity. However, Tfh development is incompletely understood. The differentiation of Tfh cells is a complex, multistage process regulated at the DNA, RNA and protein levels. This review just summarizes current research on the molecular mechanisms of Tfh cell differentiation to better understand the role of Tfh cells in antitumor immunity.

Dendritic cell Piezo1 directs the differentiation of TH1 and Treg cells in cancer.

Dendritic cells (DCs) play an important role in anti-tumor immunity by inducing T cell differentiation. Herein, we found that the DC mechanical sensor Piezo1 stimulated by mechanical stiffness or inflammatory signals directs the reciprocal differentiation of TH1 and regulatory T (Treg) cells in cancer. Genetic deletion of Piezo1 in DCs inhibited the generation of TH1 cells while driving the development of Treg cells in promoting cancer growth in mice. Mechanistically, Piezo1-deficient DCs regulated the secretion of the polarizing cytokines TGFß1 and IL-12, leading to increased TGFßR2-p-Smad3 activity and decreased IL-12Rß2-p-STAT4 activity while inducing the reciprocal differentiation of Treg and TH1 cells. In addition, Piezo1 integrated the SIRT1-hypoxia-inducible factor-1 alpha (HIF1α)-dependent metabolic pathway and calcium-calcineurin-NFAT signaling pathway to orchestrate reciprocal TH1 and Treg lineage commitment through DC-derived IL-12 and TGFß1. Our studies provide critical insight for understanding the role of the DC-based mechanical regulation of immunopathology in directing T cell lineage commitment in tumor microenvironments.

Protein Tyrosine Phosphatase PTPRO Signaling Couples Metabolic States to Control the Development of Granulocyte Progenitor Cells.

Protein tyrosine phosphatase (PTPase) is critically involved in the regulation of hematopoietic stem cell development and differentiation. Roles of novel isolated receptor PTPase PTPRO from bone marrow hematopoietic stem cells in granulopoiesis have not been investigated. PTPRO expression is correlated with granulocytic differentiation, and Ptpro -/- mice developed neutrophilia, with an expanded granulocytic compartment resulting from a cell-autonomous increase in the number of granulocyte progenitors under steady-state and potentiated innate immune responses against Listeria monocytogenes infection. Mechanistically, mTOR and HIF1α signaling engaged glucose metabolism and initiated a transcriptional program involving the lineage decision factor C/EBPα, which is critically required for the PTPRO deficiency-directed granulopoiesis. Genetic ablation of mTOR or HIF1α or perturbation of glucose metabolism suppresses progenitor expansion, neutrophilia, and higher glycolytic activities by Ptpro -/- In addition, Ptpro -/- upregulated HIF1α regulates the lineage decision factor C/EBPα promoter activities. Thus, our findings identify a previously unrecognized interplay between receptor PTPase PTPRO signaling and mTOR-HIF1α metabolic reprogramming in progenitor cells of granulocytes that underlies granulopoiesis.

Immunoregulatory Role of the Mechanosensitive Ion Channel Piezo1 in Inflammation and Cancer.

Piezo1 was originally identified as a mechanically activated, nonselective cation ion channel, with significant permeability to calcium ions, is evolutionally conserved, and is involved in the proliferation and development of various types of cells, in the context of various types of mechanical or innate stimuli. Recently, our study and work by others have reported that Piezo1 from all kinds of immune cells is involved in regulating many diseases, including infectious inflammation and cancer. This review summarizes the recent progress made in understanding the immunoregulatory role and mechanisms of the mechanical receptor Piezo1 in inflammation and cancer and provides new insight into the biological significance of Piezo1 in regulating immunity and tumors.

N6 -methyladenosine RNA methylation: A novel regulator of the development and function of immune cells.

N6 -methyladenosine (m6 A) RNA methylation is a reversible posttranscriptional modification in eukaryotes involving three types of functional proteins: "writers", "erasers", and "readers". m6 A regulates the metabolism of messenger RNAs and noncoding RNAs through RNA structure, splicing, stability, export, and translation, thereby participating in various physiological and pathological processes. Here, we summarize the current state of m6 A methylation researches, focusing on how these modifications modulate the fate decisions of innate and adaptive immune cells and regulate immune responses in immune-associated diseases, including viral infections and cancer. These studies showed that m6 A modifications and m6 A modifying proteins play a critical role in pathogen recognition, immune cell activation, immune cell fate decisions, and immune reactions. m6 A is a novel regulator of immune system homeostasis and activation.

The direct and indirect regulation of follicular T helper cell differentiation in inflammation and cancer.

Follicular T helper (Tfh) cells play important roles in facilitating B-cell differentiation and inducing the antibody response in humoral immunity and immune-associated inflammatory diseases, including infections, autoimmune diseases, and cancers. However, Tfh cell differentiation is mainly achieved through self-directed differentiation regulation and the indirect regulation mechanism of antigen-presenting cells (APCs). During the direct intrinsic differentiation of naïve CD4+ T cells into Tfh cells, Bcl-6, as the characteristic transcription factor, plays the core role of transcriptional regulation. APCs indirectly drive Tfh cell differentiation mainly by changing cytokine secretion mechanisms. Altered metabolic signaling is also critically involved in Tfh cell differentiation. This review summarizes the recent progress in understanding the direct and indirect regulatory signals and metabolic mechanisms of Tfh cell differentiation and function in immune-associated diseases.

Functional differentiation and regulation of follicular T helper cells in inflammation and autoimmunity.

Follicular T helper (TFH ) cells are specialized T cells that support B cells, which are essential for humoral immunity. TFH cells express the transcription factor B-cell lymphoma 6 (Bcl-6), chemokine (C-X-C motif) receptor (CXCR) 5, the surface receptors programmed cell death protein 1 (PD-1) and inducible T-cell costimulator (ICOS), the cytokine IL-21 and other molecules. The activation, proliferation and differentiation of TFH cells are closely related to dynamic changes in cellular metabolism. In this review, we summarize the progress made in understanding the development and functional differentiation of TFH cells. Specifically, we focus on the regulatory mechanisms of TFH cell functional differentiation, including regulatory signalling pathways and the metabolic regulatory mechanisms of TFH cells. In addition, TFH cells are closely related to immune-associated diseases, including infections, autoimmune diseases and cancers.

Targeting Myeloid-Derived Suppressor Cells in Cancer Immunotherapy.

Myeloid-derived suppressor cells (MDSCs), which are activated under pathological conditions, are a group of heterogeneous immature myeloid cells. MDSCs have potent capacities to support tumor growth via inhibition of the antitumoral immune response and/or the induction of immunosuppressive cells. In addition, multiple studies have demonstrated that MDSCs provide potential therapeutic targets for the elimination of immunosuppressive functions and the inhibition of tumor growth. The combination of targeting MDSCs and other therapeutic approaches has also demonstrated powerful antitumor effects. In this review, we summarize the characteristics of MDSCs in the tumor microenvironment (TME) and current strategies of cancer treatment by targeting MDSCs.

Regulations of Glycolytic Activities on Macrophages Functions in Tumor and Infectious Inflammation.

Macrophages differentiated into a classically activated (M1) or alternatively activated phenotype (M2) in infection and tumor, but the precise effects of glycolysis and oxidative phosphorylation (OXPHOS) metabolic pathway remain unclear. Herein, the effects of glycolysis or OXPHOS on macrophage polarizations were investigated using a pharmacological approach in mice. 2-Deoxy-D-glucose (2-DG) treatments, which blocks the key enzyme hexokinase of glycolysis, efficiently inhibits a specific switch to M1 lineage, decreasing the secretion of pro-inflammatory cytokines and expressions of co-stimulatory molecules associated with relieving infectious inflammation in vitro and in vivo. Glycolytic activation through the hypoxia-inducible factor-1α (HIF-1α) pathway was required for differentiation to the M1 phenotype, which conferred protection against infection. Dimethyl malonate (DMM) treatment, which blocks the key element succinate of OXPHOS, efficiently inhibits a specific switch to M2 lineage when macrophages receiving M2 stimulation, decreasing the secretion of anti-inflammatory cytokine and CD206 expressions. Mitochondrial dynamic alterations including mitochondrial mass, mitochondrial membrane potential (Dym) and ROS productions were critically for differentiation to the M2 phenotype, which conferred protection against anti-tumor immunity. Glycolysis is also required for macrophage M2 differentiation. Thus, these data provide a basis for a comprehensively understanding the role of glycolysis and OXPHOS in macrophage differentiation during anti-infection and anti-tumor inflammation.

Glucocorticoids Promote the Onset of Acute Experimental Colitis and Cancer by Upregulating mTOR Signaling in Intestinal Epithelial Cells.

The therapeutic effects of glucocorticoids on colitis and colitis-associated cancer are unclear. In this study, we investigated the therapeutic roles of glucocorticoids in acute experimental ulcerative colitis and colitis-associated cancer in mice and their immunoregulatory mechanisms. Murine acute ulcerative colitis was induced by dextran sulfate sodium (DSS) and treated with dexamethasone (Dex) at different doses. Dex significantly exacerbated the onset and severity of DSS-induced colitis and potentiated mucosal inflammatory macrophage and neutrophil infiltration, as well as cytokine production. Furthermore, under inflammatory conditions, the expression of the glucocorticoid receptor (GR) did not change significantly, while mammalian target of rapamycin (mTOR) signaling was higher in colonic epithelial cells than in colonic immune cells. The deletion of mTOR in intestinal epithelial cells, but not that in myeloid immune cells, in mice significantly ameliorated the severe course of colitis caused by Dex, including weight loss, clinical score, colon length, pathological damage, inflammatory cell infiltration and pro-inflammatory cytokine production. These data suggest that mTOR signaling in intestinal epithelial cells, mainly mTORC1, plays a critical role in the Dex-induced exacerbation of acute colitis and colitis-associated cancer. Thus, these pieces of evidence indicate that glucocorticoid-induced mTOR signaling in epithelial cells is required in the early stages of acute ulcerative colitis by modulating the dynamics of innate immune cell recruitment and activation.

IL-9 and Th9 Cells in Tumor Immunity.

T cells can be categorized into functionally diverse subpopulations, which include Th1, Th2, Th9, Th17, Th22, and Tfh cells and Foxp3+ Tregs, based on their role in maintaining normal immune homeostasis and affecting pathological immune-associated diseases. Among these subpopulations, Th9 cells are relatively new, and less is known about their signaling and effects on tumor immunity. Recently, some studies have focused on regulation of the IL-9/IL-9R signaling pathway and Th9 cell differentiation and their roles in tumor environments. Herein, we summarize recent progress in understanding the regulatory signaling of IL-9 and Th9 cells and their critical roles and mechanisms in antitumor immunity.

Hippo Kinases MST1/2 Regulate Immune Cell Functions in Cancer, Infection, and Autoimmune Diseases.

Mammalian STE20-like protein kinases (MST), including MST1, MST2, MST3, and MST4, belong to the germinal center kinase (GCK) family. Kinase MST1/2 is an important component of the Hippo pathway in regulating cell proliferation, tissue homeostasis, and organ development. Recent studies have shown that Hippo kinase MST1/2 plays a crucial role in immune-associated diseases, which has attracted extensive attention of researchers. This review summarizes recent research on Hippo kinases MST1/2 in regulating the function of immune cells in innate and adaptive immune systems, and also includes its regulatory role and significance in cancer, infection, and autoimmune diseases.

HIF1α-Dependent Metabolic Signals Control the Differentiation of Follicular Helper T Cells.

Follicular helper T (TFH) cells are critical for germinal center (GC) formation and are responsible for effective B cell-mediated immunity; metabolic signaling is an important regulatory mechanism for the differentiation of TFH cells. However, the precise roles of hypoxia inducible factor (HIF) 1α-dependent glycolysis and oxidative phosphorylation (OXPHOS) metabolic signaling remain unclear in TFH cell differentiation. Herein, we investigated the effects of glycolysis and OXPHOS on TFH cell differentiation and GC responses using a pharmacological approach in mice under a steady immune status or an activated immune status, which can be caused by foreign antigen stimulation and viral infection. GC and TFH cell responses are related to signals from glycolytic metabolism in mice of different ages. Foreign, specific antigen-induced GC, and TFH cell responses and metabolic signals are essential upon PR8 infection. Glycolysis and succinate-mediated OXPHOS are required for the GC response and TFH cell differentiation. Furthermore, HIF1α is responsible for glycolysis- and OXPHOS-induced alterations in the GC response and TFH cell differentiation under steady or activated conditions in vivo. Blocking glycolysis and upregulating OXPHOS signaling significantly recovered TFH cell differentiation upon PR8 infection and ameliorated inflammatory damage in mice. Thus, our data provide a comprehensive experimental basis for fully understanding the precise roles of HIF1α-mediated glycolysis and OXPHOS metabolic signaling in regulating the GC response and TFH cell differentiation during stable physiological conditions or an antiviral immune response.

Immune effects of glycolysis or oxidative phosphorylation metabolic pathway in protecting against bacterial infection.

The metabolism of immune cells reprograms inflammatory responses to protect against infection by pathogenic microorganisms, but the immune effects of glycolysis and the oxidative phosphorylation (OXPHOS) metabolic pathway remain unclear. Herein, the effects of glycolysis or OXPHOS on the neutrophils and T cells were investigated using a pharmacological approach in mice. 2-Deoxy-d-glucose (2-DG), which blocks the key enzyme hexokinase of glycolysis, and dimethyl malonate (DMM), which blocks the key element succinate of OXPHOS, both efficiently expanded the population of neutrophils, but significantly inhibited tumor necrosis factor a secretion and reactive oxygen species (ROS) production. These compounds also effectively inhibited the differentiation of type 1 T helper cells (Th1) but had no effects on the differentiation of type 2 T helper cells (Th2) and regulatory T cells. A study of the underlying mechanism showed that hypoxia-inducible factor 1-alpha (HIF1α) was an upstream signal in the regulation of glycolysis, but not OXPHOS. In thioglycolate broth-induced neutrophil peritonitis, blockade of glycolysis or OXPHOS efficiently expanded the population of neutrophils, but diminished their abilities to secrete proinflammatory factors, produce ROS, and phagocytose bacteria. In Listeria monocytogenes bacteria-infected mice, 2-DG or DMM treatment consistently inhibited antibacterial activity and Th1 function. Thus, our results provide a basis for comprehensively understanding the role of glycolysis and OXPHOS in anti-infectious immunity.