The kinase PDK1 is critical for promoting T follicular helper cell differentiation

Curcumin enhances anti-tumor immunity in anaplastic thyroid carcinoma by elevating CD8+ T cell function and downregulating the AKT/mTORC1/STAT3/PD-L1 axis

Curcumin, a compound isolated from turmeric, has been found to have promising anti-tumor effects in various cancers, including anaplastic thyroid carcinoma (ATC). However, the molecular mechanism of curcumin in ATC remains largely unclear. CD8 +T cells could eliminate rapidly proliferating malignant cells, whereas interaction between programmed death-1 (PD-1) and programmed cell death ligand 1 (PD-L1) could inhibit the activation and functions of CD8 + T cells. Thus, we aimed to explore whether curcumin could inhibit ATC progression via regulating CD8 + T cells and PD-L1 expression. The protein expression of PD-L1 in ATC cells was detected by western blot assay. Additionally, a syngeneic mouse model was used to assess the effect of curcumin or/and anti-PD-1 treatment on tumorigenesis in vivo. The effect of curcumin on CD8 +T cell function was investigated by flow cytometry in vitro and in vivo. The results indicated curcumin notably suppressed ATC cell proliferation, migration and invasion and induced cell apoptosis. Additionally, curcumin could reduce PD-L1 level in ATC cells through inactivating AKT/mTORC1/STAT3 signaling. Meanwhile, curcumin obviously elevated CD8 + T cell function by elevating the number of IFN-γ producing CD8 + T cells. Furthermore, curcumin or anti-PD-L1 treatment could enhance anti-tumor immunity by increasing infiltration of CD8 + T cells in tumor tissues in vivo. As expected, compared to the single treatment, combination curcumin and anti-PD-1 treatment further elevated CD8 + T cell function in vivo, thereby potentiating anti-tumor immunity in ATC. Collectively, curcumin could enhance anti-tumor immunity in ATC by elevating CD8 + T cell function and inactivating the AKT/mTORC1/STAT3/PD-L1 axis. Our findings demonstrated a novel mechanism of the anti-tumor effects of curcumin in ATC.

The ultrafine powder of atractylodis macrocephalae rhizoma improves immune function in naturally aging rats by regulating the PI3K/Akt/NF-κB signaling pathway

Background

The phenomenon of population aging presents a significant global challenge, with the aging population in China steadily increasing. As individuals progress in age, there is a gradual deterioration of human organs and systems, as well as a decline in the immune system, referred to as immunosenescence. Atractylodis macrocephalae rhizoma (BZ) has been historically used in China for its medicinal properties, including gastrointestinal improvement, immunomodulation, anti-aging, antioxidant effects, and anti-tumor effects. Nevertheless, there remains a gap in understanding the pharmacological and molecular mechanisms underlying its anti-immunosenescence effects.

Methods

This study employed UPLC-ESI-MS and network pharmacology to create a network map of BZ ultrafine powder (BZU) and its aging targets. Enrichment analysis was then used to identify the primary mechanistic pathways underlying BZU's anti-immunosenescence effects. The primary components of BZU were quantitatively analyzed using high-performance liquid chromatography (HPLC). Naturally aging rats were used to examine the effects of different oral doses (0.25, 0.5, and 1 g/kg) of BZU over 5 weeks on aging performance, peripheral blood immunophenotyping and cell count, and splenic lymphocyte proliferation rate. To validate the findings of network pharmacology, quantitative RT-PCR, Western blotting, and immunofluorescence analyses were conducted.

Results

Our analyses demonstrated that BZU improved various indicators of aging in naturally aging rats, such as increasing the number of voluntary activities, enhance grip strength and fatigue resistance, increasing the microcirculatory blood flow and improving hematological levels. The BZU administration enhanced T and B lymphocyte proliferation and significantly improved the lymphocyte-to-T cell subpopulation ratio. It can elevate serum IL-2 and IL-4 levels while reducing IL-6, IFN-γ and TNF-α levels in naturally aging rats. Finally, it increased CD3 protein expression in the spleen while decreasing protein levels of PI3K, p-AKT, IKKα/β, and NF-κB. It also decreased the mRNA expression of Pik3cg, Akt1, Pdk1 and Nfκb1.

Conclusion

These findings suggest that BZU may enhance lymphocyte proliferation by inhibiting the PI3K/Akt/NF-κB signaling pathway, correcting immune cell imbalances, reducing inflammatory responses, and ultimately enhancing immune function and potentially delaying aging.

Aire attenuate collagen-induced arthritis by suppressing T follicular helper cells through ICOSL

OBJECTIVE

To assess the expression levels of autoimmune regulator (Aire) and inducible costimulator molecule ligand (ICOSL), as well as T follicular helper (Tfh) cell numbers in rheumatoid arthritis (RA) patients, and to explore their relationship with RA severity. We also aimed to investigate the effect of Aire on arthritis and its underlying mechanisms.

METHODS

The expression levels of Aire, ICOSL, and Tfh cell numbers were measured in RA patients. The relationship between these factors and the levels of anticyclic citrullinated peptide antibodies (Anti-CCP) as well as the Disease Activity Score in 28 joints (DAS28) was analyzed. To investigate the effect of Aire on arthritis, Aire-overexpressing bone marrow-derived dendritic cells (Aire-BMDCs) and recombinant ICOSL were transferred into collagen-induced arthritis (CIA) mice, the symptoms, clinical scores, anti-collagen type II antibodies (anti-CII Abs), rheumatoid factor (RF), proportions of Tfh cells, and percentages of germinal center (GC) B cells in CIA mice were examined.

RESULTS

The results showed that Aire levels were significantly decreased in CD14+ PBMCs from patients with RA, and there were negative correlations between ICOSL expression levels, Tfh cell numbers, and Aire expression. Additionally, these factors were correlated with Anti-CCP levels and DAS28. Aire-BMDCs could influence Tfh differentiation, GC B cell development, as well as the levels of anti-CII Abs and RF, which further alleviate the symptoms and reduce clinical scores partly through ICOSL in CIA mice.

CONCLUSIONS

The findings suggest that Aire may alleviate rheumatoid arthritis by inhibiting ICOSL, which further inhibits Tfh cell differentiation and autoantibody production.

The effect of PDK1 in maintaining immune cell development and function

3-phosphoinositide-dependent protein kinase 1 (PDK1) exhibits a substantial influence on immune cell development by establishing a vital connection between PI3K and downstream mTOR signaling cascades. However, it remains unclear whether PDK1 signaling affects the homeostasis and functionality of immune cells. To explore the impact of PDK1 on different immune cells within immune organs, transgenic mouse strains with lymphocyte-specific PDK1 knockout (PDK1fl/fl CD2-Cre) were generated. Unlike wild-type (WT) mice, lymphocyte-specific PDK1 knockout (KO) mice exhibited thymic atrophy, elevated percentages of CD8+ T cells and neutrophils, and reduced proportions of γδ T cells, B cells, and NK cells in the spleen. Functional analysis revealed elevated release of IFN-γ and IL-17A by T cells in PDK1 KO mice, contrasting with diminished levels observed in γδ T cells and Treg cells. Furthermore, the activation, cytotoxicity, and migratory potential of γδ T cells in PDK1 KO mice are heightened, indicating a potential association with the regulation of the mTOR signaling pathway. To conclude, the findings of this research demonstrated that specific knockout of PDK1 in lymphocytes hindered T cell development in the thymus and exhibited a substantial influence on immune cell homeostasis in the spleen and lymph nodes.

Abnormal energy metabolism in the pathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease with significant socioeconomic impact worldwide. Orderly energy metabolism is essential for normal immune function, and disordered energy metabolism is increasingly recognized as an important contributor to the pathogenesis of SLE. Disorders of energy metabolism are characterized by increased reactive oxygen species, ATP deficiency, and abnormal metabolic pathways. Oxygen and mitochondria are critical for the production of ATP, and both mitochondrial dysfunction and hypoxia affect the energy production processes. In addition, several signaling pathways, including mammalian target of rapamycin (mTOR)/adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling and the hypoxia-inducible factor (HIF) pathway also play important regulatory roles in energy metabolism. Furthermore, drugs with clear clinical effects on SLE, such as sirolimus, metformin, and tacrolimus, have been proven to improve the disordered energy metabolism of immune cells, suggesting the potential of targeting energy metabolism for the treatment of SLE. Moreover, several metabolic modulators under investigation are expected to have potential therapeutic effects in SLE. This review aimed to gain insights into the role and mechanism of abnormal energy metabolism in the pathogenesis of SLE, and summarizes the progression of metabolic modulator in the treatment of SLE.

ETV5 promotes lupus pathogenesis and follicular helper T cell differentiation by inducing osteopontin expression

Follicular helper T (TFH) cells mediate germinal center reactions to generate high affinity antibodies against specific pathogens, and their excessive production is associated with the pathogenesis of systemic autoimmune diseases such as systemic lupus erythematosus (SLE). ETV5, a member of the ETS transcription factor family, promotes TFH cell differentiation in mice. In this study, we examined the role of ETV5 in the pathogenesis of lupus in mice and humans. T cell-specific deletion of Etv5 alleles ameliorated TFH cell differentiation and autoimmune phenotypes in lupus mouse models. Further, we identified SPP1 as an ETV5 target that promotes TFH cell differentiation in both mice and humans. Notably, extracellular osteopontin (OPN) encoded by SPP1 enhances TFH cell differentiation by activating the CD44-AKT signaling pathway. Furthermore, ETV5 and SPP1 levels were increased in CD4+ T cells from patients with SLE and were positively correlated with disease activity. Taken together, our findings demonstrate that ETV5 is a lupus-promoting transcription factor, and secreted OPN promotes TFH cell differentiation.

The mTORC2 signaling network: targets and cross-talks

The mechanistic target of rapamycin, mTOR, controls cell metabolism in response to growth signals and stress stimuli. The cellular functions of mTOR are mediated by two distinct protein complexes, mTOR complex 1 (mTORC1) and mTORC2. Rapamycin and its analogs are currently used in the clinic to treat a variety of diseases and have been instrumental in delineating the functions of its direct target, mTORC1. Despite the lack of a specific mTORC2 inhibitor, genetic studies that disrupt mTORC2 expression unravel the functions of this more elusive mTOR complex. Like mTORC1 which responds to growth signals, mTORC2 is also activated by anabolic signals but is additionally triggered by stress. mTORC2 mediates signals from growth factor receptors and G-protein coupled receptors. How stress conditions such as nutrient limitation modulate mTORC2 activation to allow metabolic reprogramming and ensure cell survival remains poorly understood. A variety of downstream effectors of mTORC2 have been identified but the most well-characterized mTORC2 substrates include Akt, PKC, and SGK, which are members of the AGC protein kinase family. Here, we review how mTORC2 is regulated by cellular stimuli including how compartmentalization and modulation of complex components affect mTORC2 signaling. We elaborate on how phosphorylation of its substrates, particularly the AGC kinases, mediates its diverse functions in growth, proliferation, survival, and differentiation. We discuss other signaling and metabolic components that cross-talk with mTORC2 and the cellular output of these signals. Lastly, we consider how to more effectively target the mTORC2 pathway to treat diseases that have deregulated mTOR signaling.

Mettl3-dependent m6A modification is essential for effector differentiation and memory formation of CD8+ T cells

Efficient immune responses rely on the proper differentiation of CD8+ T cells into effector and memory cells. Here, we show a critical requirement of N6-Methyladenosine (m6A) methyltransferase Mettl3 during CD8+ T cell responses upon acute viral infection. Conditional deletion of Mettl3 in CD8+ T cells impairs effector expansion and terminal differentiation in an m6A-dependent manner, subsequently affecting memory formation and the secondary response of CD8+ T cells. Our combined RNA-seq and m6A-miCLIP-seq analyses reveal that Mettl3 deficiency broadly impacts the expression of cell cycle and transcriptional regulators. Remarkably, Mettl3 binds to the Tbx21 transcript and stabilizes it, promoting effector differentiation of CD8+ T cells. Moreover, ectopic expression of T-bet partially restores the defects in CD8+ T cell differentiation in the absence of Mettl3. Thus, our study highlights the role of Mettl3 in regulating multiple target genes in an m6A-dependent manner and underscores the importance of m6A modification during CD8+ T cell response.

Iguratimod suppresses Tfh cell differentiation in primary Sjögren's syndrome patients through inhibiting Akt/mTOR/STAT3 signaling

BACKGROUND

Iguratimod (IGU) reduces hypergammaglobulinemia and disease activity in pSS (primary Sjögren's syndrome) patients. However, the therapeutical mechanism of IGU for pSS remains largely unknown. This study aimed to investigate the regulation of Tfh cell differentiation by IGU in pSS patients.

METHODS

We prospectively enrolled 13 pSS patients treated with IGU for 3 months and examined circulating T cell and B cell subsets by flow cytometry. We measured Tfh cell differentiation treated by IGU in pSS patients and healthy controls. Transcriptome analysis combined with molecular docking were employed to identify potential therapeutical targets of IGU, which were verified by Western blot and Tfh cell differentiation.

RESULTS

Tfh, plasmablast, and plasma cells were suppressed by IGU treatment at 1 and 3 months. Tfh cell differentiation and function were significant inhibited by IGU in pSS patients and healthy controls in vitro. Pyruvate dehydrogenase kinase 1 (PDK1) was identified as a target of IGU during Tfh cell differentiation, and the downstream Akt phosphorylation was attenuated by IGU. Moreover, the activity of mTORC1 and phosphorylation of STAT3 were suppressed by IGU, with downregulation of BCL6 and upregulation of PRDM1. Finally, Akt activator restored IGU-suppressed Tfh cell differentiation.

CONCLUSIONS

IGU suppresses Tfh cell differentiation in pSS patients through interacting with PDK1 and suppressing Akt-mTOR-STAT3 signaling.

Short-Chain Fatty Acids Alleviate Vancomycin-Caused Humoral Immunity Attenuation in Rabies-Vaccinated Mice by Promoting the Generation of Plasma Cells via Akt-mTOR Pathway

Mounting evidence suggests that gut microbial composition and its metabolites, including short-chain fatty acids (SCFAs), have beneficial effects in regulating host immunogenicity to vaccines. However, it remains unknown whether and how SCFAs improve the immunogenicity of the rabies vaccine. In this study, we investigated the effect of SCFAs on the immune response to rabies vaccine in vancomycin (Vanco)-treated mice and found that oral gavage with butyrate-producing bacteria (C. butyricum) and butyrate supplementation elevated RABV-specific IgM, IgG, and virus-neutralizing antibodies (VNAs) in Vanco-treated mice. Supplementation with butyrate expanded antigen-specific CD4+ T cells and IFN-γ-secreting cells, augmented germinal center (GC) B cell recruitment, promoted plasma cells (PCs) and RABV-specific antibody-secreting cells (ASCs) generation in Vanco-treated mice. Mechanistically, butyrate enhanced mitochondrial function and activated the Akt-mTOR pathway in primary B cells isolated from Vanco-treated mice, ultimately promoting B lymphocyte-induced maturation protein-1 (Blimp-1) expression and CD138+ PCs generation. These results highlight the important role of butyrate in alleviating Vanco-caused humoral immunity attenuation in rabies-vaccinated mice and maintaining host immune homeostasis. IMPORTANCE The gut microbiome plays many crucial roles in the maintenance of immune homeostasis. Alteration of the gut microbiome and metabolites has been shown to impact vaccine efficacy. SCFAs can act as an energy source for B-cells, thereby promoting both mucosal and systemic immunity in the host by inhibiting HDACs and activation of GPR receptors. This study investigates the impact of orally administered butyrate, an SCFA, on the immunogenicity of rabies vaccines in Vanco-treated mice. The results showed that butyrate ameliorated humoral immunity by facilitating the generation of plasma cells via the Akt-mTOR in Vanco-treated mice. These findings unveil the impact of SCFAs on the immune response of the rabies vaccine and confirm the crucial role of butyrate in regulating immunogenicity to rabies vaccines in antibiotic-treated mice. This study provides a fresh insight into the relationship of microbial metabolites and rabies vaccination.

T follicular helper cells in autoimmune diseases

T follicular helper (Tfh) cells with the phenotype of mainly expressing surface molecules C-X-C motif chemokine receptor type 5 (CXCR5), inducible co-stimulator (ICOS), secreting cytokine interleukin-21 (IL-21) and requiring the transcription factor B cell lymphoma 6 (BCL-6) have been recently defined as a new subset of CD4⁺ T cells. They exist in germinal centers (GCs) of lymphoid organs and in peripheral blood. With the ability to promote B cell development, GC formation and antibody production, Tfh cells play critical roles in the pathogenesis of many autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), primary Sjögren's syndrome (pSS), etc. The aberrant proliferation and function of Tfh cells will cause the pathological process like autoantibody production and tissue injury. In this paper, we review the recent advances in Tfh cell biology and their roles in autoimmune diseases, with a mention of their use as therapeutic targets, which will shed more light on the pathogenesis and treatment of certain autoimmune diseases.

Obesity and metabolic dysfunction drive sex-associated differential disease profiles in hACE2-mice challenged with SARS-CoV-2

Severe outcomes from SARS-CoV-2 infection are highly associated with preexisting comorbid conditions like hypertension, diabetes, and obesity. We utilized the diet-induced obesity (DIO) model of metabolic dysfunction in K18-hACE2 transgenic mice to model obesity as a COVID-19 comorbidity. Female DIO, but not male DIO mice challenged with SARS-CoV-2 were observed to have shortened time to morbidity compared to controls. Increased susceptibility to SARS-CoV-2 in female DIO was associated with increased viral RNA burden and interferon production compared to males. Transcriptomic analysis of the lungs from all mouse cohorts revealed sex- and DIO-associated differential gene expression profiles. Male DIO mice after challenge had decreased expression of antibody-related genes compared to controls, suggesting antibody producing cell localization in the lung. Collectively, this study establishes a preclinical comorbidity model of COVID-19 in mice where we observed sex- and diet-specific responses that begin explaining the effects of obesity and metabolic disease on COVID-19 pathology.

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Transcriptomic analysis of infected lungs revealed unique sex-dependent differences

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Obese female mice have high viral RNA burden and interferon production in the lung

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Male mice have altered antibody and T cell response gene profiles after viral challenge

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Metabolic dysfunction comorbidity can be studied in the hACE2 mouse model of COVID-19

Regulation of immune cell metabolism in health and disease: Special focus on T and B cell subsets

Metabolism is a dynamic process and keeps changing from time to time according to the demand of a particular cell to meet its bio-energetic requirement. Different immune cells rely on distinct metabolic programs which allow the cell to balance its requirements for energy, molecular biosynthesis, and effector activity. In the aspect of infection and cancer immunology, effector T and B cells get exhausted and help tumor cells to evade immunosurveillance. On the other hand, T cells become hyperresponsive in the scenario of autoimmune diseases. In this article, we have explored the uniqueness and distinct metabolic features of key CD4⁺ T and B helper cell subsets, CD4⁺ T, B regulatory cell subsets and CD8⁺ T cells regarding health and disease. Th1 cells rely on glycolysis and glutaminolysis; inhibition of these metabolic pathways promotes Th1 cells in Treg population. However, Th2 cells are also dependent on glycolysis but an abundance of lactate within TME shifts their metabolic dependency to fatty acid metabolism. Th17 cells depend on HIF-1α mediated glycolysis, ablation of HIF-1α reduces Th17 cells but enhance Treg population. In contrast to effector T cells which are largely dependent on glycolysis for their differentiation and function, Treg cells mainly rely on FAO for their function. Therefore, it is of utmost importance to understand the metabolic fates of immune cells and how it facilitates their differentiation and function for different disease models. Targeting metabolic pathways to restore the functionality of immune cells in diseased conditions can lead to potent therapeutic measures.

The Differentiation and Maintenance of SARS-CoV-2-Specific Follicular Helper T Cells

Upon acute viral infection, virus-specific CD4+ T cells differentiate into either TH1 cells or follicular helper T (TFH) cells. The molecular pathways governing such bimodal cell fate commitment remain elusive. Additionally, effector virus-specific TFH cells further differentiate into corresponding memory population, which confer long-term protection against re-infection of same viruses by providing immediate help to virus-specific memory B cells. Currently, the molecular mechanisms underlying the long-term maintenance of memory TFH cells are largely unknown. In this review, we discuss current understanding of early differentiation of virus-specific effector TFH cells and long-term maintenance of virus-specific memory TFH cells in mouse models of viral infection and patients of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

SRSF1 Deficiency Impairs the Late Thymocyte Maturation and the CD8 Single-Positive Lineage Fate Decision

The underlying mechanisms of thymocyte development and lineage determination remain incompletely understood, and the emerging evidences demonstrated that RNA binding proteins (RBPs) are deeply involved in governing T cell fate in thymus. Serine/arginine-rich splicing factor 1 (SRSF1), as a classical splicing factor, is a pivotal RBP for gene expression in various biological processes. Our recent study demonstrated that SRSF1 plays essential roles in the development of late thymocytes by modulating the T cell regulatory gene networks post-transcriptionally, which are critical in response to type I interferon signaling for supporting thymocyte maturation. Here, we report SRSF1 also contributes to the determination of the CD8⁺ T cell fate. By specific ablation of SRSF1 in CD4⁺CD8⁺ double positive (DP) thymocytes, we found that SRSF1 deficiency impaired the maturation of late thymocytes and diminished the output of both CD4⁺ and CD8⁺ single positive T cells. Interestingly, the ratio of mature CD4⁺ to CD8⁺ cells was notably altered and more severe defects were exhibited in CD8⁺ lineage than those in CD4⁺ lineage, reflecting the specific function of SRSF1 in CD8⁺ T cell fate decision. Mechanistically, SRSF1-deficient cells downregulate their expression of Runx3, which is a crucial transcriptional regulator in sustaining CD8⁺ single positive (SP) thymocyte development and lineage choice. Moreover, forced expression of Runx3 partially rectified the defects in SRSF1-deficient CD8⁺ thymocyte maturation. Thus, our data uncovered the previous unknown role of SRSF1 in establishment of CD8⁺ cell identity.

Machine Learning Identifies Pan-Cancer Landscape of Nrf2 Oxidative Stress Response Pathway-Related Genes

BACKGROUND

Oxidative stress produced a large amount of reactive oxygen species (ROS), which played a pivotal role in balanced ability and determining cell fate. The activated Nrf2 signaling pathway that responds to the excessive ROS regulated the expressions of antiapoptotic proteins, antioxidative enzymes, drug transporters, and detoxifying factors.

METHODS

The Nrf2 signaling pathway-related genes that had a direct relationship with Nrf2, including ATF4, BACH1, CREBBP, CUL3, EIF2AK3, EP300, FOS, FOSL1, GSK3B, JUN, KEAP1, MAF, MAFF, MAFG, MAFK, MAPK1, MAPK3, MAPK7, MAPK8, MAPK9, PIK3CA, PRRT2, and RIT1, were selected to do a systematic pan-cancer analysis. The relationship of Nrf2 signaling pathway-related gene expressions with tumor mutation burden, microsatellite status, clinical characteristics, immune system, cancer stemness index, and drug sensitivity was calculated by the Spearson correlation analysis across 11,057 subjects representing 33 cancer types. The prognosis models in lung squamous carcinoma, breast cancer, and stomach cancer were constructed with the Cox multivariate regression analysis and least absolute shrinkage and selection operator (Lasso) regression.

RESULTS

Many Nrf2 signaling pathway-related genes were differently expressed between tumor and normal tissues. PIK3CA showed high mutation rate in pan-cancer. The expressions of Nrf2 signaling pathway-related genes were significantly related to tumor mutation burden, copy number variant, microsatellite instability score, survival rate, pathological stage, immune phenotype, immune score, immune cell, cancer stemness index, and drug sensitivity. The prognosis models were significantly associated with survival rate in lung squamous carcinoma, breast cancer, and stomach cancer; and the prognosis model-based riskscore was significantly associated with clinicopathological characteristics of each cancer.

CONCLUSIONS

The study provided a comprehensive pan-cancer landscape of Nrf2 pathway-related genes. Based on the same Nrf2 pathway-related genes, the different prognosis models were constructed for different types of cancers.

Metabolic adaptation of lymphocytes in immunity and disease

Adaptive immune responses mediated by T cells and B cells are crucial for protective immunity against pathogens and tumors. Differentiation and function of immune cells require dynamic reprogramming of cellular metabolism. Metabolic inputs, pathways, and enzymes display remarkable flexibility and heterogeneity, especially in vivo. How metabolic plasticity and adaptation dictate functional specialization of immune cells is fundamental to our understanding and therapeutic modulation of the immune system. Extensive progress has been made in characterizing the effects of metabolic networks on immune cell fate and function in discrete microenvironments or immunological contexts. In this review, we summarize how rewiring of cellular metabolism determines the outcome of adaptive immunity in vivo, with a focus on how metabolites, nutrients, and driver genes in immunometabolism instruct cellular programming and immune responses during infection, inflammation, and cancer in mice and humans. Understanding context-dependent metabolic remodeling will manifest legitimate opportunities for therapeutic intervention of human disease.

The kinase PDK1 regulates regulatory T cell survival via controlling redox homeostasis

Rationale: Regulatory T cells (Treg cells) play an important role in maintaining peripheral tolerance by suppressing over-activation of effector T cells. The kinase PDK1 plays a pivotal role in conventional T cell development. However, whether PDK1 signaling affects the homeostasis and function of Treg cells remains elusive. Methods: In order to evaluate the role of PDK1 in Treg cells from a genetic perspective, mice carrying the floxed PDK1 allele were crossbred with Foxp3Cre mice to efficiently deleted PDK1 in Foxp3+ Treg cells. Flow cytometry was used to detect the immune cell homeostasis of WT and PDK1fl/flFoxp3Cre mice. RNA-seq was used to assess the differences in transcriptional expression profile of WT and PDK1-deficient Treg cells. The metabolic profiles of WT and PDK1-deficient Treg cells were tested using the Glycolysis Stress Test and Mito Stress Test Kits by the Seahorse XFe96 Analyser. Results: PDK1 was essential for the establishment and maintenance of Treg cell homeostasis and function. Disruption of PDK1 in Treg cells led to a spontaneous fatal systemic autoimmune disorder and multi-tissue inflammatory damage, accompanied by a reduction in the number and function of Treg cells. The deletion of PDK1 in Treg cells destroyed the iron ion balance through regulating MEK-ERK signaling and CD71 expression, resulting in excessive production of intracellular ROS, which did not depend on the down-regulation of mTORC1 signaling. Inhibition of excessive ROS, activated MEK-Erk signaling or overload Fe2+ could partially rescue the survival of PDK1-deficient Treg cells. Conclusion: Our results defined a key finding on the mechanism by which PDK1 regulates Treg cell survival via controlling redox homeostasis.