The immune cell transcription factor T-bet: A novel metabolic regulator

Absence of T-box transcription factor 21 limits neuromuscular junction recovery after nerve injury in T-bet-knockout mice

Introduction

Terminal Schwann cells (tSCs), at the neuromuscular junction (NMJ), play critical roles in the repair of motor axon terminals at muscle, and rebuild neuronal signaling following nerve injury. Knowledge of mediators impacting tSCs post-nerve injury and in disease may guide beneficial therapies to improve motor outcomes. We previously found T-box transcription factor 21 (TBX21/TBET), classically associated with T-helper1 cells and immune cell recruitment, is expressed in tSCs at the mouse NMJ. The purpose of this study was to examine effects of Tbx21 absence during NMJ regeneration following peripheral nerve injury.

Methods

Wildtype (WT) and Tbet-knockout (Tbet-KO) mice underwent sciatic nerve transection and immediate repair. Functional muscle recovery assessment was performed with muscle force testing on mice at 2-, 3-, 4-, and 6-week (wks) and 6 months after nerve injury repair. Morphometric analyses of NMJ reinnervation, tSC number, and tSC processes were evaluated. Full NMJ reinnervation was defined as ≥75% coverage of endplates by axons. A minimum of three mice were evaluated in each group, and 50-100 NMJs were evaluated per mouse.

Results

Tbet-KO mice had significantly diminished muscle function compared to WT mice at every time point beyond 3 weeks. Tbet-KO mice showed just over half of the muscle force generated by WT mice at 4 weeks and 6 weeks post-injury and repair. By 6 months, Tbet-KO mice generated only 84.1% the muscle force of WT mice. Tbet-KO mice showed significantly decreased levels of fully reinnervated NMJs compared to WT mice at each time point tested. Tbet-KO mice also showed a lower number of tSCs with reduced cytoplasmic processes beyond NMJ area and lower number of immune cells during process of NMJ regeneration.

Discussion

Our findings show that the Tbx21 transcription factor promotes NMJ reinnervation to regain muscle function following nerve injury.

Depth-corrected multi-factor dissection of chromatin accessibility for scATAC-seq data with PACS

Single cell ATAC-seq (scATAC-seq) experimental designs have become increasingly complex, with multiple factors that might affect chromatin accessibility, including genotype, cell type, tissue of origin, sample location, batch, etc., whose compound effects are difficult to test by existing methods. In addition, current scATAC-seq data present statistical difficulties due to their sparsity and variations in individual sequence capture. To address these problems, we present a zero-adjusted statistical model, Probability model of Accessible Chromatin of Single cells (PACS), that allows complex hypothesis testing of accessibility-modulating factors while accounting for sparse and incomplete data. For differential accessibility analysis, PACS controls the false positive rate and achieves a 17% to 122% higher power on average than existing tools. We demonstrate the effectiveness of PACS through several analysis tasks, including supervised cell type annotation, compound hypothesis testing, batch effect correction, and spatiotemporal modeling. We apply PACS to datasets from various tissues and show its ability to reveal previously undiscovered insights in scATAC-seq data.

Tbx21 gene and its association with resistance against viral nervous necrosis (VNN) in Asian seabass, Lates calcarifer

Viral nervous necrosis (VNN) caused by a betanodavirus (NNV) is one of the major diseases in Asian seabass (Lates calcarifer) hatcheries. Our previous studies showed that the tbx21 gene was in a QTL for NNV resistance in linkage group 23 in Asian seabass. The expression of this gene was changed in tissues of Asian seabass challenged with NNV. However, the role of tbx21 in NNV resistance remains largely unknown. In this study, tbx21 of Asian seabass was characterized. This gene consists of an ORF of 1866 bp, a 5' UTR of 357 bp, and a 3' UTR of 4674 bp. The TBX21 protein showed substantial amino acid similarity (70-96%) with other fish but exhibited lower identity (47-52%) with mammals. One SNP identified in the first intron was significantly associated with NNV resistance. In healthy fish, tbx21 was expressed in all tissues examined, and was highly expressed in the kidney and liver. The expression of tbx21 increased in the eye, gills, heart, kidney and gut, but decreased in the brain and spleen at five days after NNV challenge. Overexpression of tbx21 reduced the replication of NNV, whereas knockdown increased viral expression and virus titers. These results suggest that tbx21 plays a key role in NNV resistance. The SNP in this gene could be used as a marker to facilitate marker-assisted selection for NNV resistance. Further investigation of polymorphisms in the 5' and 3' UTRs of tbx21 may provide additional insights into the gene's role in NNV resistance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00234-0.

Immunosenescence and inflammaging: Mechanisms and role in diseases

Age-related changes initiate a cascade of cellular and molecular alterations that lead to immune system dysfunction or abnormal activation, predisposing individuals to age-related diseases. This phenomenon, commonly referred to as immunosenescence, highlighting aging-associated progressive decline of the immune system. Moreover, mounting evidence suggests that immunosenescence contributes to a related pathological phenomenon known as inflammaging. Inflammaging refers to chronic, low-grade, and systemic inflammation associated with aging, occurring despite the absence of overt stimuli. In the body, inflammation is typically activated in response to overt stimuli such as bacterial/microbial invasion or a pathological state, however, inflammaging occurrence and its underpinning mechanisms seem to be independent and in the absence of such stimuli. Despite recent advancements in molecular characterization and the scrutiny of disease relevance, these two interconnected concepts have remained largely unexplored and unrecognized. In this comprehensive review, we aim to shed light on the mechanistic and cellular aspects of immunosenescence and inflammaging, as well as their pivotal roles in the pathogenesis of aging-related diseases, including cancer, infections, dementia, and neurodegenerative disorders.

Persistent transcriptional changes in cardiac adaptive immune cells following myocardial infarction: New evidence from the re-analysis of publicly available single cell and nuclei RNA-sequencing data sets

INTRODUCTION

Chronic immunopathology contributes to the development of heart failure after a myocardial infarction. Both T and B cells of the adaptive immune system are present in the myocardium and have been suggested to be involved in post-MI immunopathology.

METHODS

We analyzed the B and T cell populations isolated from previously published single cell RNA-sequencing data sets (PMID: 32130914, PMID: 35948637, PMID: 32971526 and PMID: 35926050), of the mouse and human heart, using differential expression analysis, functional enrichment analysis, gene regulatory inferences, and integration with autoimmune and cardiovascular GWAS.

RESULTS

Already at baseline, mature effector B and T cells are present in the human and mouse heart, having increased activity in transcription factors maintaining tolerance (e.g. DEAF1, JDP2, SPI-B). Following MI, T cells upregulate pro-inflammatory transcript levels (e.g. Cd11, Gzmk, Prf1), while B cells upregulate activation markers (e.g. Il6, Il1rn, Ccl6) and collagen (e.g. Col5a2, Col4a1, Col1a2). Importantly, pro-inflammatory and fibrotic transcription factors (e.g. NFKB1, CREM, REL) remain active in T cells, while B cells maintain elevated activity in transcription factors related to immunoglobulin production (e.g. ERG, REL) in both mouse and human post-MI hearts. Notably, genes differentially expressed in post-MI T and B cells are associated with cardiovascular and autoimmune disease.

CONCLUSION

These findings highlight the varied and time-dependent dynamic roles of post-MI T and B cells. They appear ready-to-go and are activated immediately after MI, thus participate in the acute wound healing response. However, they subsequently remain in a state of pro-inflammatory activation contributing to persistent immunopathology.

PACS allows comprehensive dissection of multiple factors governing chromatin accessibility from snATAC-seq data

Single nucleus ATAC-seq (snATAC-seq) experimental designs have become increasingly complex with multiple factors that might affect chromatin accessibility, including genotype, cell type, tissue of origin, sample location, batch, etc., whose compound effects are difficult to test by existing methods. In addition, current snATAC-seq data present statistical difficulties due to their sparsity and variations in individual sequence capture. To address these problems, we present a zero-adjusted statistical model, Probability model of Accessible Chromatin of Single cells (PACS), that can allow complex hypothesis testing of factors that affect accessibility while accounting for sparse and incomplete data. For differential accessibility analysis, PACS controls the false positive rate and achieves on average a 17% to 122% higher power than existing tools. We demonstrate the effectiveness of PACS through several analysis tasks including supervised cell type annotation, compound hypothesis testing, batch effect correction, and spatiotemporal modeling. We apply PACS to several datasets from a variety of tissues and show its ability to reveal previously undiscovered insights in snATAC-seq data.

Single-cell spatial multi-omics and deep learning dissect enhancer-driven gene regulatory networks in liver zonation

In the mammalian liver, hepatocytes exhibit diverse metabolic and functional profiles based on their location within the liver lobule. However, it is unclear whether this spatial variation, called zonation, is governed by a well-defined gene regulatory code. Here, using a combination of single-cell multiomics, spatial omics, massively parallel reporter assays and deep learning, we mapped enhancer-gene regulatory networks across mouse liver cell types. We found that zonation affects gene expression and chromatin accessibility in hepatocytes, among other cell types. These states are driven by the repressors TCF7L1 and TBX3, alongside other core hepatocyte transcription factors, such as HNF4A, CEBPA, FOXA1 and ONECUT1. To examine the architecture of the enhancers driving these cell states, we trained a hierarchical deep learning model called DeepLiver. Our study provides a multimodal understanding of the regulatory code underlying hepatocyte identity and their zonation state that can be used to engineer enhancers with specific activity levels and zonation patterns.

TBX21 attenuates colorectal cancer progression via an ARHGAP29/RSK/GSK3β dependent manner

PURPOSE

Previous studies have shown that TBX21 (T-Box Transcription Factor 21) plays a vital role in coordinating multiple aspects of the immune response especially type 1 immune response as well as tumor progression. However, the function of TBX21 in colorectal cancer (CRC) remains unclear.

METHODS

IHC to investigate TBX21 expression in CRC tissues. Cell proliferation and apoptosis assays to validate TBX21 function in vitro and in vivo. RNA-seq assay to explore target genes of TBX21. Human phospho-kinase array assay to explore down-stream signaling of TBX21.

RESULTS

We disclosed that the expression of TBX21 was marked decreased in CRC versus normal tissue, and negatively correlated with CRC TNM stages. Surprisingly, we found that the CRC and normal cell lines show no TBX21 expression levels. Ectopic expression of TBX21 inhibited cell proliferation and promoted cell apoptosis in vitro. Moreover, RNA-sequence data first time showed that ARHGAP29 acts as the target gene of TBX21 to mediate down-stream signaling activation. Human phospho-kinase array data first time displayed that ectopic expression of TBX21 reduced kinase RSK and GSK3β activation. In contrast, knocked down the expression of TBX21 or ARHGAP29 alternatively abolished TBX21 mediated cell proliferation suppression, cell apoptosis enhancement and RSK/GSK3β activation. In addition, xenograft model studies demonstrated that TBX21 inhibits colorectal tumor progression via ARHGAP29/ RSK/ GSK3β signaling in vivo.

CONCLUSIONS

In summary, the aforementioned findings suggest a model of TBX21 in suppressing CRC progression. This may provide a promising target for CRC therapy.

DISCERN: deep single-cell expression reconstruction for improved cell clustering and cell subtype and state detection

BACKGROUND

Single-cell sequencing provides detailed insights into biological processes including cell differentiation and identity. While providing deep cell-specific information, the method suffers from technical constraints, most notably a limited number of expressed genes per cell, which leads to suboptimal clustering and cell type identification.

RESULTS

Here, we present DISCERN, a novel deep generative network that precisely reconstructs missing single-cell gene expression using a reference dataset. DISCERN outperforms competing algorithms in expression inference resulting in greatly improved cell clustering, cell type and activity detection, and insights into the cellular regulation of disease. We show that DISCERN is robust against differences between batches and is able to keep biological differences between batches, which is a common problem for imputation and batch correction algorithms. We use DISCERN to detect two unseen COVID-19-associated T cell types, cytotoxic CD4+ and CD8+ Tc2 T helper cells, with a potential role in adverse disease outcome. We utilize T cell fraction information of patient blood to classify mild or severe COVID-19 with an AUROC of 80% that can serve as a biomarker of disease stage. DISCERN can be easily integrated into existing single-cell sequencing workflow.

CONCLUSIONS

Thus, DISCERN is a flexible tool for reconstructing missing single-cell gene expression using a reference dataset and can easily be applied to a variety of data sets yielding novel insights, e.g., into disease mechanisms.

Molecular Mechanisms for the Vicious Cycle between Insulin Resistance and the Inflammatory Response in Obesity

The comprehensive anabolic effects of insulin throughout the body, in addition to the control of glycemia, include ensuring lipid homeostasis and anti-inflammatory modulation, especially in adipose tissue (AT). The prevalence of obesity, defined as a body mass index (BMI) ≥ 30 kg/m², has been increasing worldwide on a pandemic scale with accompanying syndemic health problems, including glucose intolerance, insulin resistance (IR), and diabetes. Impaired tissue sensitivity to insulin or IR paradoxically leads to diseases with an inflammatory component despite hyperinsulinemia. Therefore, an excess of visceral AT in obesity initiates chronic low-grade inflammatory conditions that interfere with insulin signaling via insulin receptors (INSRs). Moreover, in response to IR, hyperglycemia itself stimulates a primarily defensive inflammatory response associated with the subsequent release of numerous inflammatory cytokines and a real threat of organ function deterioration. In this review, all components of this vicious cycle are characterized with particular emphasis on the interplay between insulin signaling and both the innate and adaptive immune responses related to obesity. Increased visceral AT accumulation in obesity should be considered the main environmental factor responsible for the disruption in the epigenetic regulatory mechanisms in the immune system, resulting in autoimmunity and inflammation.

Integrated omics analysis reveals the immunologic characteristics of cystic Peyer's patches in the cecum of Bactrian camels

Bactrian camels have specific mucosa-associated lymphoid tissue (MALT) throughout the large intestine, with species-unique cystic Peyer's patches (PPS) as the main type of tissue. However, detailed information about the molecular characteristics of PPS remains unclear. This study applied a transcriptomic analysis, untargeted metabolomics, and 16S rDNA sequencing to compare the significant differences between PPS and the adjacent normal intestine tissues (NPPS) during the healthy stage of three young Bactrian camels. The results showed that samples from PPS could be easily differentiated from the NPPS samples based on gene expression profile, metabolites, and microbial composition, separately indicated using dimension reduction methods. A total of 7,568 up-regulated and 1,266 down-regulated differentially expressed genes (DEGs) were detected, and an enrichment analysis found 994 DEGs that participated in immune-related functions, and a co-occurance network analysis identified nine hub genes (BTK, P2RX7, Pax5, DSG1, PTPN2, DOCK11, TBX21, IL10, and HLA-DOB) during multiple immunologic processes. Further, PPS and NPPS both had a similar pattern of most compounds among all profiles of metabolites, and only 113 differentially expressed metabolites (DEMs) were identified, with 101 of these being down-regulated. Deoxycholic acid (DCA; VIP = 37.96, log2FC = -2.97, P = 0), cholic acid (CA; VIP = 13.10, log2FC = -2.10, P = 0.01), and lithocholic acid (LCA; VIP = 12.94, log2FC = -1.63, P = 0.01) were the highest contributors to the significant dissimilarities between groups. PPS had significantly lower species richness (Chao1), while Firmicutes (35.92% ± 19.39%), Bacteroidetes (31.73% ± 6.24%), and Proteobacteria (13.96% ± 16.21%) were the main phyla across all samples. The LEfSe analysis showed that Lysinibacillus, Rikenellaceae_RC9_gut_group, Candidatus_Stoquefichus, Mailhella, Alistipes, and Ruminococcaceae_UCG_005 were biomarkers of the NPPS group, while Escherichia_Shigella, Synergistes, Pyramidobacter, Odoribacter, Methanobrevibacter, Cloacibacillus, Fusobacterium, and Parabacteroides were significantly higher in the PPS group. In the Procrustes analysis, the transcriptome changes between groups showed no significant correlations with metabolites or microbial communities, whereas the alteration of metabolites significantly correlated with the alteration of the microbial community. In the co-occurrence network, seven DEMs (M403T65-neg, M329T119-neg, M309T38-neg, M277T42-2-neg, M473T27-neg, M747T38-1-pos, and M482t187-pos) and 14 genera (e.g., Akkermansia, Candidatus-Stoquefichus, Caproiciproducens, and Erysipelatoclostridium) clustered much more tightly, suggesting dense interactions. The results of this study provide new insights into the understanding of the immune microenvironment of the cystic PPS in the cecum of Bactrian camels.

Apical periodontitis promotes insulin resistance and alters adaptive immunity markers in rats

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Periapical lesions promotes higher T-bet expression and lower GATA3 and FOXP3 expression.

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Periapical lesion promotes increased GATA3 and decreased FOXP3 expression in the group with 4 periapical lesions (4PL)

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The adaptive immune system, with a predominance of the Th1 polarization, may be involved in the development of insulin resistance in rats with Periapical lesions.

Objective

Apical periodontitis (AP) is a chronic or acute inflammatory disease usually developed from endodontic infections, predominantly due to gram-negative anaerobic bacteria invading the dental pulp. This study aimed to evaluate lymphocyte markers to assess the involvement of adaptive immunity in insulin resistance (IR) in a rat model of AP.

Design.

Forty-five male Wistar albino rats were divided into 3 groups (control, 1AP and 4AP). AP was induced in the upper right first molar (1AP), and in the first and second upper and lower right molars (4AP). The spleen was collected to evaluate the expression of transcription factors involved in lymphocyte polarization, including T-bet (Th1), GATA3 (Th2), and FOXP3 (Treg). Blood samples were assessed for serum cytokine levels transcribed by the respective lymphocyte polarizations, INF-γ (Th1), IL-4 (Th2) and TGF-β (Treg). In addition, glucose and insulin levels were measured to evaluate IR by the HOMA-IR method.

Results

The results showed higher T-bet expression on AP groups, along with lower GATA3 and FOXP3 expression in the 1AP, in addition to increased GATA3 and decreased FOXP3 expression in the 4AP group compared to the CN group. There was no difference in the INF-γ levels, while IL-4 was decreased in the AP groups. Taken together, these results suggest that the adaptive immune system, with a predominance of the Th1 polarization, may be involved in the development of IR in rats with AP.

Conclusions

AP promotes increase in the expression of T-bet (4AP) and decrease of FOXP3 expressions and IL-4 levels (1AP and 4AP). However, depending on the number of lesions (1 or 4 lesions), the expression of GATA3 appears differently. Thus, innate immunity and adaptive immunity may contribute to the IR observed in rats with AP.

GHR-/- Mice are protected from obesity-related white adipose tissue inflammation

Growth hormone (GH) excess in bovine (b)GH transgenic mice has been shown to alter white adipose tissue (WAT) immune cell populations. The present study aimed to evaluate the effects of GH resistance on WAT immune cell populations using GH receptor knockout (GHR^-/- ) mice. Eight- and 24-month-old, male GHR^-/- and wild-type mice were used. Body composition and tissue weights were determined, and systemic inflammation was assessed by measuring serum cytokine levels. The stromal vascular fraction (SVF) was isolated from three distinct WAT depots, and immune cell populations were quantified using flow cytometry. GHR^-/- mice at both ages had decreased body weight but were obese. Although no significant changes were observed in serum levels of the measured cytokines, SVF cell alterations were seen and differed from depot to depot. Total SVF cells were decreased in epidydimal (Epi) depots, whereas SVF cells per gram adipose tissue weight were increased in mesenteric (Mes) depots of GHR^-/- mice relative to controls. T cells and T helper cells were increased in Mes at 8 months old, whereas cytotoxic T cells were decreased in subcutaneous (SubQ) at 24 months old. Other cells were unchanged at both ages measured. The present study demonstrates that removal of GH action results in modest and depot-specific changes to several immune cell populations in WAT of intra-abdominal depots (Epi and Mes), which are somewhat surprising results because the SubQ has the largest change in size, whereas the Mes has no size change. Taken together with previous results from bovine GH transgenic mice, these data suggest that GH induces changes in the immune cell population of WAT in a depot-specific manner. Notably, GHR^-/- mice appear to be protected from age-related WAT inflammation and immune cell infiltration despite obesity.

Master regulator genes and their impact on major diseases

Master regulator genes (MRGs) have become a hot topic in recent decades. They not only affect the development of tissue and organ systems but also play a role in other signal pathways by regulating additional MRGs. Because a MRG can regulate the concurrent expression of several genes, its mutation often leads to major diseases. Moreover, the occurrence of many tumors and cardiovascular and nervous system diseases are closely related to MRG changes. With the development in omics technology, an increasing amount of investigations will be directed toward MRGs because their regulation involves all aspects of an organism’s development. This review focuses on the definition and classification of MRGs as well as their influence on disease regulation.

IL-21 in Homeostasis of Resident Memory and Exhausted CD8 T Cells during Persistent Infection

CD4 T cells guide the development of CD8 T cells into memory by elaborating mitogenic and differentiation factors and by licensing professional antigen-presenting cells. CD4 T cells also act to stave off CD8 T cell dysfunction during repetitive antigen stimulation in persistent infection and cancer by mitigating generation of exhausted T cells (T_EX). CD4 T cell help is also required for establishing and maintaining tissue-resident memory T cells (T_RM), the nonrecirculating memory T cell subset parked in nonlymphoid tissues to provide frontline defense against reinvading pathogens. Interleukin (IL)-21 is the signature cytokine secreted by follicular helper CD4 T cells (T_FH) to drive B cell expansion and differentiation in germinal centers to mount high-affinity, isotype class-switched antibodies. In several infection models, IL-21 has been identified as the CD4 T help needed for formation and survival of T_RM and T_EX. In this review, we will explore the different memory subsets of CD8 T cells in persistent infections, the metabolic profiles associated with each, and evidence documenting the importance of CD4 T cell-derived IL-21 in regulating CD8 T_RM and T_EX development, homeostasis, and function.

Downregulation of Transcription Factor T-Bet as a Protective Strategy in Monosodium Urate-Induced Gouty Inflammation

Gout is sterile joint inflammation triggered by the damaging effects of monosodium urate (MSU) crystals accumulation. Previous studies suggest transcription factor T-bet plays an important role in inflammatory arthritis. Notably, mice lacking T-bet markedly reduced joint inflammation of rheumatoid arthritis models, however, the involvement of T-bet in gouty inflammation has yet to be clarified. Here, we took advantage of T-bet knockout (KO) mice to investigate the role of T-bet in the pathogenesis of MSU-induced gout inflammation. T-bet KO and wild type (WT) mice were used for models of acute inflammation induced with MSU crystals, including footpad, air pouch and peritonitis models. Inflammatory cytokines and phagocytosis were detected in bone-marrow-derived macrophages (BMDMs) from T-bet KO and WT mice treated with MSU crystals in vitro. In addition, T-bet expression in peripheral blood mononuclear cells (PBMCs) from gout patients was measured, as well as plasma inflammatory cytokines. We found that the levels of interleukin (IL)-17, IL-23, and interferon-γ were reduced, but tumor necrosis factor-α was not, in BMDMs from T-bet KO compared with WT mice after MSU challenge in vitro, as well as MSU phagocytosis. In comparison with WT mice in vivo, the swelling index of T-bet KO mice was significantly decreased in the footpad model. T-bet deficiency also dramatically relieved MSU-induced inflammatory cell infiltration in peritonitis and air pouch models in vivo, and as well as the IL-1β levels of air pouch lavage fluid (APLF). In addition, plasma IL-17 and IL-23 levels were elevated in acute gout, whereas protein levels of T-bet were downregulated in PBMCs from acute gout patients and intercritical gout treated with MSU crystals in vitro as well. Transcription factor T-bet deficiency protects against MSU-induced gouty inflammation, suggesting that downregulation of T-bet could be a protective strategy and contribute to spontaneous remission of inflammation in acute gout.

PD-1 and its ligands are important immune checkpoints in cancer

Checkpoint programmed death-1 (PD-1)/programmed cell death ligands (PD-Ls) have been identified as negative immunoregulatory molecules that promote immune evasion of tumor cells. The interaction of PD-1 and PD-Ls inhibits the function of T cells and tumor-infiltrating lymphocytes (TIL) while increasing the function of immunosuppressive regulatory T cells (Tregs). This condition causes the tumor cells to evade immune response. Thus, the blockade of PD-1/PD-L1 enhances anti-tumor immunity by reducing the number and/or the suppressive activity of Tregs and by restoring the activity of effector T cells. Furthermore, some monoclonal antibodies blockading PD-1/PD-Ls axis have achieved good effect and received Food and Drug Administration approval. The role of PD-1/PD-Ls in tumors has been well studied, but little is known on the mechanism by which PD-1 blocks T-cell activation. In this study, we provide a brief overview on the discovery and regulatory mechanism of PD-1 and PD-L1 dysregulation in tumors, as well as the function and signaling pathway of PD-1 and its ligands; their roles in tumor evasion and clinical treatment were also studied.

Antigen Presentation and T-Cell Activation Are Critical for RBP4-Induced Insulin Resistance

Adipose tissue (AT) inflammation contributes to impaired insulin action, which is a major cause of type 2 diabetes. RBP4 is an adipocyte- and liver-derived protein with an important role in insulin resistance, metabolic syndrome, and AT inflammation. RBP4 elevation causes AT inflammation by activating innate immunity, which elicits an adaptive immune response. RBP4-overexpressing mice (RBP4-Ox) are insulin resistant and glucose intolerant and have increased AT macrophages and T-helper 1 cells. We show that high-fat diet-fed RBP4(-/-) mice have reduced AT inflammation and improved insulin sensitivity versus wild type. We also elucidate the mechanism for RBP4-induced macrophage antigen presentation and subsequent T-cell activation. In RBP4-Ox, AT macrophages display enhanced c-Jun N-terminal kinase, extracellular signal-related kinase, and p38 phosphorylation. Inhibition of these pathways and of NF-κB reduces activation of macrophages and CD4 T cells. MyD88 is an adaptor protein involved in proinflammatory signaling. In macrophages from MyD88(-/-) mice, RBP4 fails to stimulate secretion of tumor necrosis factor, IL-12, and IL-6 and CD4 T-cell activation. In vivo blockade of antigen presentation by treating RBP4-Ox mice with CTLA4-Ig, which blocks costimulation of T cells, is sufficient to reduce AT inflammation and improve insulin resistance. Thus, MyD88 and downstream mitogen-activated protein kinase and NF-κB pathways are necessary for RBP4-induced macrophage antigen presentation and subsequent T-cell activation. Also, blocking antigen presentation with CTLA4-Ig improves RBP4-induced insulin resistance and macrophage-induced T-cell activation.

Modulation of Cell-Mediated Immunity to Suppress High Fat Diet-Induced Obesity and Insulin Resistance

PURPOSE

To assess the effect of immune modulators, cyclosporin A and fingolimod, on high fat diet-induced obesity and insulin resistance.

METHODS

C57BL/6 mice were fed a high fat diet and injected intraperitoneally with cyclosporine A, fingolimod, or vehicle twice weekly for 15 weeks. Body weight and food intake were manually measured every other day. Glucose tolerance test, insulin sensitivity, and body composition were examined and compared between the control and the immune modulator treated animals. Tissue samples were collected at the end of the experiment and examined for serum biochemistry, histology, and mRNA levels of marker genes for inflammation, and glucose and lipid metabolism in white and brown adipose tissues and in the liver.

RESULTS

Cyclosporine A and fingolimod suppressed high fat diet-induced weight gain, reduced hepatic fat accumulation, and improved insulin sensitivity. The beneficial effects are associated with altered expression of F4/80, Cd68, Il-6, Tnf-α, and Mcp-1 genes, which are involved in macrophage-related chronic inflammation in adipose and hepatic tissues.

CONCLUSION

Immune modulation represents an important intervention for obesity and obesity-associated insulin resistance.

Differential Immunometabolic Phenotype in Th1 and Th2 Dominant Mouse Strains in Response to High-Fat Feeding

Immune reactivity plays an important role in obesity-associated metabolic disorders. We investigated immunometabolic phenotype of C57Bl/6 and BALB/c mice, prototypical Th1 and Th2-type strains, fed chow or high-fat diet (HFD) for 24 weeks. In comparison to C57Bl/6 mice, chow-fed BALB/c mice had higher body weight and weight gain, lower glycemia, more pronounced liver steatosis, but less inflammation and collagen deposition in liver. In response to HFD C57Bl/6 mice exhibited higher weight gain, higher glycemia, HbA1c and liver glycogen content, increased amount of visceral adipose tissue (VAT) and number of VAT associated CD3+CXCR3+ T cells, CD11c+ dendritic cells (DCs) and F4/80+ macrophages than BALB/c mice. More numerous CD3+ and CD8+ T lymphocytes, myeloid DCs, proinflammatory macrophages (F4/80+CD11b+CD11+ and F4/80+IL-1β+) and CD11b+Ly6Chigh monocytes and higher levels of proinflammatory IL-6, TNF-α and IFN-γ were present in liver in HFD-fed C57Bl/6 mice compared with diet-matched BALB/c mice. As opposed to C57Bl/6 mice, HFD induced marked liver steatosis and upregulated the hepatic LXRα and PPARγ genes in BALB/c mice. C57Bl/6 mice fed HFD developed liver fibrosis and increased hepatic procollagen and TGF-β mRNA expression, and IL-33, IL-13 and TGF-β levels in liver homogenates, while BALB/c mice fed HFD had scarce collagen deposition in liver. The obtained results suggest inherent immunometabolic differences in C57Bl/6 and BALB/c mice. Moreover, HFD Th1-type mice on high fat diet regimen are more susceptible to adiposity, liver inflammation and fibrosis, while Th2-type mice to liver steatosis, which is associated with differential immune cell composition in metabolic tissues. Strain-dependent differences in immunometabolic phenotype may be relevant for studies of obesity-associated metabolic diseases in humans.

Dysregulation of circulating CD4+CXCR5+ T cells in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is characterized by a chronic low-grade inflammatory state. Follicular helper T cells (Tfh) play critical roles in inducing B-cell activation and producing various cytokines, whereas circulating CD4+CXCR5+ T cells (CTfh) may act as a counterpart to measure Tfh cell disorders. In this study, we investigated whether Tfh could be involved in the development of T2DM by assessing CTfh in peripheral blood. CTfh and it subtypes were determined by measuring CD3, CD4, CXCR5, CXCR3, and CCR6 in 68 T2DM patients and 60 healthy controls using flow cytometry. Results showed that proportion of CTfh in the peripheral CD4+ T cells was significantly increased in T2DM patients (8.5 ± 0.5%) than in controls (4.5 ± 0.3%) (p < 0.001). Further study revealed that the balance of CTfh subtypes was greatly dysregulated, in which percentage of Th17 subtype was significantly increased in patients. Investigating the correlation between CTfh and risk factors of T2DM demonstrated that proportion of CTfh were significantly elevated in patients with body mass index (BMI) over 24.0 (p = 0.005). Interestingly, patients with abdominal obesity had further increase in CTfh than those without abdominal obesity. This study suggests the involvement of CTfh in T2DM, especially in T2DM-related obesity.

Role of T cells in malnutrition and obesity

Nutritional status is critically important for immune cell function. While obesity is characterized by inflammation that promotes metabolic syndrome including cardiovascular disease and insulin resistance, malnutrition can result in immune cell defects and increased risk of mortality from infectious diseases. T cells play an important role in the immune adaptation to both obesity and malnutrition. T cells in obesity have been shown to have an early and critical role in inducing inflammation, accompanying the accumulation of inflammatory macrophages in obese adipose tissue, which are known to promote insulin resistance. How T cells are recruited to adipose tissue and activated in obesity is a topic of considerable interest. Conversely, T cell number is decreased in malnourished individuals, and T cells in the setting of malnutrition have decreased effector function and proliferative capacity. The adipokine leptin, which is secreted in proportion to adipocyte mass, may have a key role in mediating adipocyte-T cell interactions in both obesity and malnutrition, and has been shown to promote effector T cell function and metabolism while inhibiting regulatory T cell proliferation. Additionally, key molecular signals are involved in T cell metabolic adaptation during nutrient stress; among them, the metabolic regulator AMP kinase and the mammalian target of rapamycin have critical roles in regulating T cell number, function, and metabolism. In summary, understanding how T cell number and function are altered in obesity and malnutrition will lead to better understanding of and treatment for diseases where nutritional status determines clinical outcome.