Brain regulatory T cells suppress astrogliosis and potentiate neurological recovery.

In addition to maintaining immune tolerance, FOXP3+ regulatory T (Treg) cells perform specialized functions in tissue homeostasis and remodelling1,2. However, the characteristics and functions of brain Treg cells are not well understood because there is a low number of Treg cells in the brain under normal conditions. Here we show that there is massive accumulation of Treg cells in the mouse brain after ischaemic stroke, and this potentiates neurological recovery during the chronic phase of ischaemic brain injury. Although brain Treg cells are similar to Treg cells in other tissues such as visceral adipose tissue and muscle3-5, they are apparently distinct and express unique genes related to the nervous system including Htr7, which encodes the serotonin receptor 5-HT7. The amplification of brain Treg cells is dependent on interleukin (IL)-2, IL-33, serotonin and T cell receptor recognition, and infiltration into the brain is driven by the chemokines CCL1 and CCL20. Brain Treg cells suppress neurotoxic astrogliosis by producing amphiregulin, a low-affinity epidermal growth factor receptor (EGFR) ligand. Stroke is a leading cause of neurological disability, and there are currently few effective recovery methods other than rehabilitation during the chronic phase. Our findings suggest that Treg cells and their products may provide therapeutic opportunities for neuronal protection against stroke and neuroinflammatory diseases.

Reconstruction of Sjögren's syndrome-like sialadenitis by a defined disease specific gut-reactive single TCR and an autoantibody.

Lymphocytes such as CD4+ T cells and B cells mainly infiltrate the salivary glands; however, the precise roles and targets of autoreactive T cells and autoantibodies in the pathogenesis of Sjögren's Syndrome (SS) remain unclear. This study was designed to clarify the role of autoreactive T cells and autoantibodies at the single-cell level involved in the development of sialadenitis. Infiltrated CD4+ T and B cells in the salivary glands of a mouse model resembling SS were single-cell-sorted, and their T cell receptor (TCR) and B cell receptor (BCR) sequences were analyzed. The predominant TCR and BCR clonotypes were reconstituted in vitro, and their pathogenicity was evaluated by transferring reconstituted TCR-expressing CD4+ T cells into Rag2-/- mice and administering recombinant IgG in vivo. The reconstitution of Th17 cells expressing TCR (#G) in Rag2-/- mice resulted in the infiltration of T cells into the salivary glands and development of sialadenitis, while an autoantibody (IgGr22) was observed to promote the proliferation of pathogenic T cells. IgGr22 specifically recognizes double-stranded RNA (dsRNA) and induces the activation of dendritic cells, thereby enhancing the expression of IFN signature and inflammatory genes. TCR#G recognizes antigens related to the gut microbiota. Antibiotic treatment severely reduces the activation of TCR#G-expressing Th17 cells and suppresses sialadenitis development. These data suggest that the anti-dsRNA antibodies and, TCR recognizing the gut microbiota involved in the development of sialadenitis like SS. Thus, our model provides a novel strategy for defining the roles of autoreactive TCR and autoantibodies in the development and pathogenesis of SS.

Smad2 and Smad3 Inversely Regulate TGF-ß Autoinduction in Clostridium butyricum-Activated Dendritic Cells.

Colonization with a mixture of Clostridium species has been shown to induce accumulation of induced regulatory T (iTreg) cells in the colon. Transforming growth factor-ß (TGF-ß) is an essential factor for iTreg cell induction; however, the relationship between Clostridium species and TGF-ß remains to be clarified. Here we demonstrated that a gram-positive probiotic bacterial strain, Clostridium butyricum (C. butyricum), promoted iTreg cell generation in the intestine through induction of TGF-ß1 from lamina propria dendritic cells (LPDCs). C. butyricum-mediated TGF-ß1 induction was mainly Toll-like receptor 2 (TLR2) dependent, and the ERK-AP-1 kinase pathway played an important role. In addition, the autocrine TGF-ß-Smad3 transcription factor signal was necessary for robust TGF-ß expression in DCs, whereas Smad2 negatively regulated TGF-ß expression. Smad2-deficient DCs expressed higher concentrations of TGF-ß and were tolerogenic for colitis models. This study reveals a novel mechanism of TGF-ß induction by Clostridia through a cooperation between TLR2-AP-1 and TGF-ß-Smad signaling pathways.

Tissue regulatory T cells and neural repair.

Inflammation and immune responses after tissue injury play pivotal roles in the pathology, resolution of inflammation, tissue recovery, fibrosis and remodeling. Regulatory T cells (Tregs) are the cells responsible for suppressing immune responses and can be activated in secondary lymphatic tissues, where they subsequently regulate effector T cell and dendritic cell activation. Recently, Tregs that reside in non-lymphoid tissues, called tissue Tregs, have been shown to exhibit tissue-specific functions that contribute to the maintenance of tissue homeostasis and repair. Unlike other tissue Tregs, the role of Tregs in the brain has not been well elucidated because the number of brain Tregs is very small under normal conditions. However, we found that Tregs accumulate in the brain at the chronic phase of ischemic brain injury and control astrogliosis through secretion of a cytokine, amphiregulin (Areg). Brain Tregs resemble other tissue Tregs in many ways but, unlike the other tissue Tregs, brain Tregs express neural-cell-specific genes such as the serotonin receptor (Htr7) and respond to serotonin. Administering serotonin or selective serotonin reuptake inhibitors (SSRIs) in an experimental mouse model of stroke increases the number of brain Tregs and ameliorates neurological symptoms. Knowledge of brain Tregs will contribute to the understanding of various types of neuroinflammation.

Role of scavenger receptors as damage-associated molecular pattern receptors in Toll-like receptor activation.

Damage-associated molecular patterns (DAMPs) have been implicated in sterile inflammation in various tissue injuries. High-mobility group box 1 (HMGB1) is a representative DAMP, and has been shown to transmit signals through receptors for advanced glycation end products (RAGEs) and TLRs, including TLR2 and TLR4. HMGB1 does not, however, bind to TLRs with high affinity; therefore, the mechanism of HMGB1-mediated TLR activation remains unclear. In this study, we found that fluorescently labeled HMGB1 was efficiently internalized into macrophages through class A scavenger receptors. Although both M1- and M2-type macrophages internalized HMGB1, only M1-type macrophages secreted cytokines in response to HMGB1. The pan-class A scavenger receptor competitive inhibitor, maleylated bovine serum albumin (M-BSA), inhibited HMGB1 internalization and reduced cytokine production from macrophages in response to HMGB1 but not to LPS. The C-terminal acidic domain of HMGB1 is responsible for scavenger receptor-mediated internalization and cytokine production. HMGB1 and TLR4 co-localized in macrophages, and this interaction was disrupted by M-BSA, suggesting that class A scavenger receptors function as co-receptors of HMGB1 for TLR activation. M-BSA ameliorated LPS-induced sepsis and dextran sulfate sodium (DSS)-induced colitis models in which HMGB1 has been shown to play progressive roles. These data suggest that scavenger receptors function as co-receptors along with TLRs for HMGB1 in M1-type inflammatory macrophages.

The role of ferroptosis in cell-to-cell propagation of cell death initiated from focal injury in cardiomyocytes.

AIMS: Ferroptosis has grown in importance as a key factor in ischemia-reperfusion (I/R) injury. This study explores the mechanism underlying fibrotic scarring extending along myofibers in cardiac ischemic injury and demonstrates the integral role of ferroptosis in causing a unique cell death pattern linked to I/R injury. MAIN METHODS: Cadaveric hearts from individuals who had ischemic injury were examined by histological assays. We created a novel model of inducing cell death in H9c2 cells, and used it to demonstrate ferroptotic cell death extending in a cell-to-cell manner. Ex vivo Langendorff-perfused hearts were used alongside the model to replicate cell death extension along myofibers while also demonstrating protective effects of a ferroptosis inhibitor, ferrostatin-1 (Fer-1). KEY FINDINGS: Human hearts from individuals who had I/R injury demonstrated scarring along myofibers that was consistent with mouse models, suggesting that cell death extended from cell-to-cell. Treatment with Ras-selective lethal 3 (RSL3), a ferroptosis inducer, and exposure to excess iron exacerbated cell death propagation in in vitro models, and inhibition of ferroptosis by Fer-1 blunted this effect in both settings. In ex vivo models, Fer-1 was sufficient to reduce cell death along the myofibers caused by external injury. SIGNIFICANCE: The unique I/R injury-induced pattern of cell death along myofibers requires novel injury models that mimic this phenomenon, thus we established new methods to replicate it. Ferroptosis is important in propagating injury between cells and better understanding this mechanism may lead to therapeutic responses that limit I/R injury.

The Role of Ferroptosis in Adverse Left Ventricular Remodeling Following Acute Myocardial Infarction.

Ferroptosis is an iron-dependent form of regulated cell death and is distinct from other conventional forms of regulated cell death. It is often characterized by the dysfunction of the antioxidant selenoprotein glutathione peroxidase 4 (GPX4) antioxidant system. This loss of antioxidant capacity leads to the peroxidation of lipids and subsequent compromised plasma membrane structure. Disruption of the GPX4 antioxidant system has been associated with various conditions such as cardiomyopathy and ischemia-reperfusion (I/R) injury. GPX4 regulates lipid peroxidation, and chemical or genetic inhibition of GPX4 leads to reduced cardiac function. Iron chelators or antioxidants can be used for inhibiting ferroptosis, which restores functionality in in vivo and ex vivo experiments and confers overall cardioprotective effects against I/R injury. Moreover, suppression of ferroptosis also suppresses inflammation and limits the extent of left ventricle remodeling after I/R injury. Future research is necessary to understand the role of ferroptosis following an ischemic incident and can lead to the discovery of more potential therapeutics that prevent ferroptosis in the heart.

SOCS3 in T and NKT cells negatively regulates cytokine production and ameliorates ConA-induced hepatitis.

Suppressor of cytokine signaling 3 (SOCS3), a negative-feedback molecule for cytokine signaling, has been implicated in protection against liver injury. Previous studies have shown that overexpression of SOCS3 in the liver by adenovirus or membrane permeable recombinant protein protected the liver from various injuries. However it remained uncertain in which type of cells SOCS3 suppresses liver injury. In this study, we demonstrated that forced expression of SOCS3 in T and NKT cells suppressed ConA-induced hepatitis using T and NKT cell-specific SOCS3 transgenic (Lck-SOCS3 Tg) mice. IFN-gamma and IL-4 production was reduced in Lck-SOCS3 Tg mice as well as splenocytes treated with ConA. IFN-gamma and IL-4 levels were also reduced in Lck-SOCS3 Tg mice administrated with alpha-galactosylceramide, suggesting that SOCS3 in NKT cells has suppressive function. Sustained expression of SOCS3 in an NKT cell line also resulted in reduced expression of various cytokines and transcription factors. In contrast, T and NKT cell-specific SOCS3 conditional knockout (Lck-SOCS3 cKO) mice were hypersensitive to ConA-mediated hepatitis. Isolated SOCS3-deficient NKT cells produced higher levels of IFN-gamma and IL-4. These data indicate that SOCS3 plays a negative regulatory role in NKT cell activation and that forced expression of SOCS3 in NKT cells is effective in preventing hepatitis.

Single-Cell Analysis Revealed the Role of CD8+ Effector T Cells in Preventing Cardioprotective Macrophage Differentiation in the Early Phase of Heart Failure.

Heart failure is a complex clinical syndrome characterized by insufficient cardiac function. Heart-resident and infiltrated macrophages have been shown to play important roles in the cardiac remodeling that occurs in response to cardiac pressure overload. However, the possible roles of T cells in this process, have not been well characterized. Here we show that T cell depletion conferred late-stage heart protection but induced cardioprotective hypertrophy at an early stage of heart failure caused by cardiac pressure overload. Single-cell RNA sequencing analysis revealed that CD8+T cell depletion induced cardioprotective hypertrophy characterized with the expression of mitochondrial genes and growth factor receptor genes. CD8+T cells regulated the conversion of both cardiac-resident macrophages and infiltrated macrophages into cardioprotective macrophages expressing growth factor genes such as Areg, Osm, and Igf1, which have been shown to be essential for the myocardial adaptive response after cardiac pressure overload. Our results demonstrate a dynamic interplay between cardiac CD8+T cells and macrophages that is necessary for adaptation to cardiac stress, highlighting the homeostatic functions of resident and infiltrated macrophages in the heart.

Kidney GATA3+ regulatory T cells play roles in the convalescence stage after antibody-mediated renal injury.

FoxP3+ regulatory T cells (Tregs) play crucial roles in peripheral immune tolerance. In addition, Tregs that reside or accumulate in nonlymphoid tissues, called tissue Tregs, exhibit tissue-specific functions and contribute to the maintenance of tissue homeostasis and repair. In an experimental mouse model of crescentic glomerulonephritis induced by an anti-glomerular basement membrane antibody, Tregs started to accumulate in the kidney on day 10 of disease onset and remained at high levels (~30-35% of CD4+ T cells) during the late stage (days 21-90), which correlated with stable disease control. Treg depletion on day 21 resulted in the relapse of renal dysfunction and an increase in Th1 cells, suggesting that Tregs are essential for disease control during the convalescence stage. The Tregs that accumulated in the kidney showed tissue Treg phenotypes, including high expression of GATA3, ST2 (the IL33 receptor subunit), amphiregulin (Areg), and PPARγ. Although T-bet+ Tregs and RORγt+ Tregs were observed in the kidney, GATA3+ Tregs were predominant during the convalescence stage, and a PPARγ agonist enhanced the accumulation of GATA3+ Tregs in the kidney. To understand the function of specific genes in kidney Tregs, we developed a novel T cell transfer system to T cell-deficient mice. This experiment demonstrates that ST2, Areg, and CCR4 in Tregs play important roles in the accumulation of GATA3+ Tregs in the kidney and in the amelioration of renal injury. Our data suggest that GATA3 is important for the recruitment of Tregs into the kidney, which is necessary for convalescence after renal tissue destruction.

Gfi1 negatively regulates T(h)17 differentiation by inhibiting RORgammat activity.

T(h) cells have long been divided into two subsets, T(h)1 and T(h)2; however, recently, T(h)17 and inducible regulatory T (iTreg) cells were identified as new T(h) cell subsets. Although T(h)1- and T(h)2-polarizing cytokines have been shown to suppress T(h)17 and iTreg development, transcriptional regulation of T(h)17 and iTreg differentiation by cytokines remains to be clarified. In this study, we found that expression of the growth factor independent 1 (Gfi1) gene, which has been implicated in T(h)2 development, was repressed in T(h)17 and iTreg cells compared with T(h)1 and T(h)2 lineages. Gfi1 expression was enhanced by the IFN-gamma/STAT1 and IL-4/STAT6 pathways, whereas it was repressed by the transforming growth factor-beta1 stimulation at the promoter level. Over-expression of Gfi1 strongly reduced IL-17A transcription in the EL4 T cell line, as well as in primary T cells. This was due to the blockade of recruitment of retinoid-related orphan receptor gammat to the IL-17A promoter. In contrast, IL-17A expression was significantly enhanced in Gfi1-deficient T cells under T(h)17-promoting differentiation conditions as compared with wild-type T cells. In contrast, the impacts of Gfi1 in iTregs were not as strong as in T(h)17 cells. Taken together, these data strongly suggest that Gfi1 is a negative regulator of T(h)17 differentiation, which represents a novel mechanism for the regulation of T(h)17 development by cytokines.

Regulatory T Cells: Pathophysiological Roles and Clinical Applications.

Inflammation and immune responses after tissue injury play pivotal roles in the resolution of inflammation, tissue recovery, fibrosis, and remodeling. Regulatory T cells (Tregs) are responsible for immune tolerance and are usually activated in secondary lymphatic tissues. Activated Tregs subsequently regulate effector T cell and dendritic cell activation. For clinical applications such as the suppression of both autoimmune diseases and the rejection of transplanted organs, methods to generate stabilized antigen-specific Tregs are required. For this purpose, transcriptional and epigenetic regulation of Foxp3 expression has been investigated. In addition to conventional Tregs, there are some Tregs that reside in tissues and are called tissue Tregs. Tissue Tregs exhibit tissue-specific functions that contribute to the maintenance of tissue homeostasis and repair. Such tissue Tregs could also be useful for Treg-based cell therapy. We recently discovered brain Tregs that accumulate in the brain during the chronic phase of ischemic brain injury. Brain Tregs resemble other tissue Tregs, but are unique in expressing neural cell-specific genes such as the serotonin receptor (Htr7); consequently, brain Tregs respond to serotonin. Here, we describe our experiences in the use of Tregs to suppress graft-versus-host disease and to promote neural recovery after stroke.

The mTOR pathway is highly activated in diabetic nephropathy and rapamycin has a strong therapeutic potential.

Diabetic nephropathy (DN) associated with type 2 diabetes is the most common cause of end-stage renal disease (ESRD) and a serious health issue in the world. Currently, molecular basis for DN has not been established and only limited clinical treatments are effective in abating the progression to ESRD associated with DN. Here we found that diabetic db/db mice which lack the leptin receptor signaling can be used as a model of ESRD associated with DN. We demonstrated that p70S6-kinase was highly activated in mesangial cells in diabetic obese db/db mice. Furthermore, systemic administration of rapamycin, a specific and potent inhibitor of mTOR, markedly ameliorated pathological changes and renal dysfunctions. Moreover, rapamycin treatment shows a significant reduction in fat deposits and attenuates hyperinsulinemia with few side effects. These results indicate that mTOR activation plays a pivotal role in the development of ESRD and that rapamycin could be an effective therapeutic agent for DN.

MAFB prevents excess inflammation after ischemic stroke by accelerating clearance of damage signals through MSR1.

Damage-associated molecular patterns (DAMPs) trigger sterile inflammation after tissue injury, but the mechanisms underlying the resolution of inflammation remain unclear. In this study, we demonstrate that common DAMPs, such as high-mobility-group box 1 (HMGB1), peroxiredoxins (PRXs), and S100A8 and S100A9, were internalized through the class A scavenger receptors MSR1 and MARCO in vitro. In ischemic murine brain, DAMP internalization was largely mediated by MSR1. An elevation of MSR1 levels in infiltrating myeloid cells observed 3 d after experimental stroke was dependent on the transcription factor Mafb. Combined deficiency for Msr1 and Marco, or for Mafb alone, in infiltrating myeloid cells caused impaired clearance of DAMPs, more severe inflammation, and exacerbated neuronal injury in a murine model of ischemic stroke. The retinoic acid receptor (RAR) agonist Am80 increased the expression of Mafb, thereby enhancing MSR1 expression. Am80 exhibited therapeutic efficacy when administered, even at 24 h after the onset of experimental stroke. Our findings uncover cellular mechanisms contributing to DAMP clearance in resolution of the sterile inflammation triggered by tissue injury.

Prostaglandin E2 and SOCS1 have a role in intestinal immune tolerance.

Interleukin 10 (IL-10) and regulatory T cells (Tregs) maintain tolerance to intestinal microorganisms. However, Il10(-/-)Rag2(-/-) mice, which lack IL-10 and Tregs, remain healthy, suggesting the existence of other mechanisms of tolerance. Here, we identify suppressor of cytokine signalling 1 (SOCS1) as an essential mediator of immune tolerance in the intestine. Socs1(-/-)Rag2(-/-) mice develop severe colitis, which can be prevented by the reduction of microbiota and the transfer of IL-10-sufficient Tregs. Additionally, we find an essential role for prostaglandin E2 (PGE2) in the maintenance of tolerance within the intestine in the absence of Tregs. Socs1(-/-) dendritic cells are resistant to PGE2-mediated immunosuppression because of dysregulated cytokine signalling. Thus, we propose that SOCS1 and PGE2, potentially interacting together, act as an alternative intestinal tolerance mechanism distinct from IL-10 and Tregs.