Notch controls the magnitude of T helper cell responses by promoting cellular longevity

SARS-CoV-2 inflammation durably imprints memory CD4 T cells

Memory CD4 T cells are critical to human immunity, yet it is unclear whether viral inflammation during memory formation has long-term consequences. Here, we compared transcriptional and epigenetic landscapes of Spike (S)-specific memory CD4 T cells in 24 individuals whose first exposure to S was via SARS-CoV-2 infection or mRNA vaccination. Nearly 2 years after memory formation, S-specific CD4 T cells established by infection remained enriched for transcripts related to cytotoxicity and for interferon-stimulated genes, likely because of a chromatin accessibility landscape altered by inflammation. Moreover, S-specific CD4 T cells primed by infection had reduced proliferative capacity in vitro relative to vaccine-primed cells. Furthermore, the transcriptional state of S-specific memory CD4 T cells was minimally altered by booster immunization and/or breakthrough infection. Thus, infection-associated inflammation durably imprints CD4 T cell memory, which affects the function of these cells and may have consequences for long-term immunity.

Tissue-resident memory T cells: decoding intra-organ diversity with a gut perspective

Tissue-resident memory T cells (TRM) serve as the frontline of host defense, playing a critical role in protection against invading pathogens. This emphasizes their role in providing rapid on-site immune responses across various organs. The physiological significance of TRM is not just confined to infection control; accumulating evidence has revealed that TRM also determine the pathology of diseases such as autoimmune disorders, inflammatory bowel disease, and cancer. Intensive studies on the origin, mechanisms of formation and maintenance, and physiological significance of TRM have elucidated the transcriptional and functional diversity of these cells, which are often affected by local cues associated with their presence. These were further confirmed by the recent remarkable advancements of next-generation sequencing and single-cell technologies, which allow the transcriptional and phenotypic characterization of each TRM subset induced in different microenvironments. This review first overviews the current knowledge of the cell fate, molecular features, transcriptional and metabolic regulation, and biological importance of TRM in health and disease. Finally, this article presents a variety of recent studies on disease-associated TRM, particularly focusing and elaborating on the TRM in the gut, which constitute the largest and most intricate immune network in the body, and their pathological relevance to gut inflammation in humans.

Update on the role of T cells in cognitive impairment

The central nervous system (CNS) has long been considered an immune-privileged site, with minimal interaction between immune cells, particularly of the adaptive immune system. Previously, the presence of immune cells in this organ was primarily linked to events involving disruption of the blood-brain barrier (BBB) or inflammation. However, current research has shown that immune cells are found patrolling CNS under homeostatic conditions. Specifically, T cells of the adaptive immune system are able to cross the BBB and are associated with ageing and cognitive impairment. In addition, T-cell infiltration has been observed in pathological conditions, where inflammation correlates with poor prognosis. Despite ongoing research, the role of this population in the ageing brain under both physiological and pathological conditions is not yet fully understood. In this review, we provide an overview of the interactions between T cells and other immune and CNS parenchymal cells, and examine the molecular mechanisms by which these interactions may contribute to normal brain function and the scenarios in which disruption of these connections lead to cognitive impairment. A comprehensive understanding of the role of T cells in the ageing brain and the underlying molecular pathways under normal conditions could pave the way for new research to better understand brain disorders. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

Inflammation durably imprints memory CD4+ T cells

Adaptive immune responses are induced by vaccination and infection, yet little is known about how CD4+ T cell memory differs when primed in these two contexts. Notably, viral infection is generally associated with higher levels of systemic inflammation than is vaccination. To assess whether the inflammatory milieu at the time of CD4+ T cell priming has long-term effects on memory, we compared Spike-specific memory CD4+ T cells in 22 individuals around the time of the participants' third SARS-CoV-2 mRNA vaccination, with stratification by whether the participants' first exposure to Spike was via virus or mRNA vaccine. Multimodal single-cell profiling of Spike-specific CD4+ T cells revealed 755 differentially expressed genes that distinguished infection- and vaccine-primed memory CD4+ T cells. Spike-specific CD4+ T cells from infection-primed individuals had strong enrichment for cytotoxicity and interferon signaling genes, whereas Spike-specific CD4+ T cells from vaccine-primed individuals were enriched for proliferative pathways by gene set enrichment analysis. Moreover, Spike-specific memory CD4+ T cells established by infection had distinct epigenetic landscapes driven by enrichment of IRF-family transcription factors, relative to T cells established by mRNA vaccination. This transcriptional imprint was minimally altered following subsequent mRNA vaccination or breakthrough infection, reflecting the strong bias induced by the inflammatory environment during initial memory differentiation. Together, these data suggest that the inflammatory context during CD4+ T cell priming is durably imprinted in the memory state at transcriptional and epigenetic levels, which has implications for personalization of vaccination based on prior infection history.

Late-onset neonatal sepsis: genetic differences by sex and involvement of the NOTCH pathway

BACKGROUND

Late-Onset Neonatal Sepsis (LOS) is a rare condition, involving widespread infection, immune disruption, organ dysfunction, and often death. Because exposure to pathogens is not completely preventable, identifying susceptibility factors is critical to characterizing the pathophysiology and developing interventions. Prior studies demonstrated both genetics and infant sex influence susceptibility. Our study was designed to identify LOS associated genetic variants.

METHODS

We performed an exploratory genome wide association study (GWAS) with 224 LOS cases and 273 controls from six European countries. LOS was defined as sepsis presenting from 3 to 90 days of age; diagnosis was established by clinical criteria consensus guidelines. We tested for association with both autosomal and X-chromosome variants in the total sample and in sex-stratified analyses.

RESULTS

In total, 71 SNPs associated with neonatal sepsis at p < 1 × 10^-4 in at least one analysis. Most importantly, sex-stratified analyses revealed associations with multiple SNPs (28 in males and 16 in females), but no variants from single-sex analyses associated with sepsis in the other sex. Pathway analyses showed NOTCH signaling is over-represented among genes linked to these SNPS.

CONCLUSION

Our results indicate genetic susceptibility to LOS is sexually dimorphic and corroborate that NOTCH signaling plays a role in determining risk.

IMPACT

Genes associate with late onset neonatal sepsis. Notch pathway genes are overrepresented in associations with sepsis. Genes associating with sepsis do not overlap between males and females. Sexual dimorphism can lead to sex specific treatment of sepsis.

Genetic architecture of innate and adaptive immune cells in pigs

Pig industry is facing new challenges that make necessary to reorient breeding programs to produce more robust and resilient pig populations. The aim of the present work was to study the genetic determinism of lymphocyte subpopulations in the peripheral blood of pigs and identify genomic regions and biomarkers associated to them. For this purpose, we stained peripheral blood mononuclear cells to measure ten immune-cell-related traits including the relative abundance of different populations of lymphocytes, the proportions of CD4⁺ T cells and CD8⁺ T cells, and the ratio of CD4⁺/CD8⁺ T cells from 391 healthy Duroc piglets aged 8 weeks. Medium to high heritabilities were observed for the ten immune-cell-related traits and significant genetic correlations were obtained between the proportion of some lymphocytes populations. A genome-wide association study pointed out 32 SNPs located at four chromosomal regions on pig chromosomes SSC3, SSC5, SSC8, and SSCX as significantly associated to T-helper cells, memory T-helper cells and γδ T cells. Several genes previously identified in human association studies for the same or related traits were located in the associated regions, and were proposed as candidate genes to explain the variation of T cell populations such as CD4, CD8A, CD8B, KLRC2, RMND5A and VPS24. The transcriptome analysis of whole blood samples from animals with extreme proportions of γδ T, T-helper and memory T-helper cells identified differentially expressed genes (CAPG, TCF7L1, KLRD1 and CD4) located into the associated regions. In addition, differentially expressed genes specific of different T cells subpopulations were identified such as SOX13 and WC1 genes for γδ T cells. Our results enhance the knowledge about the genetic control of lymphocyte traits that could be considered to optimize the induction of immune responses to vaccines against pathogens. Furthermore, they open the possibility of applying effective selection programs for improving immunocompetence in pigs and support the use of the pig as a very reliable human biomedical model.

The role of A Disintegrin and Metalloproteinase (ADAM)-10 in T helper cell biology

A Disintegrin and Metalloproteinases (ADAM)-10 is a member of a family of membrane-anchored proteinases that regulate a broad range of cellular functions with central roles within the immune system. This has spurred the interest to modulate ADAM activity therapeutically in immunological diseases. CD4 T helper (Th) cells are the key regulators of adaptive immune responses. Their development and function is strongly dependent on Notch, a key ADAM-10 substrate. However, Th cells rely on a variety of additional ADAM-10 substrates regulating their functional activity at multiple levels. The complexity of both, the ADAM substrate expression as well as the functional consequences of ADAM-mediated cleavage of the various substrates complicates the analysis of cell type specific effects. Here we provide an overview on the major ADAM-10 substrates relevant for CD4 T cell biology and discuss the potential effects of ADAM-mediated cleavage exemplified for a selection of important substrates.

Critical Role of Notch-1 in Mechanistic Target of Rapamycin Hyperactivity and Vascular Inflammation in Patients With Takayasu Arteritis

OBJECTIVE

Takayasu arteritis (TA) is a major type of large vessel vasculitis characterized by progressive inflammation in vascular layers. In our recent study we identified a central role of mechanistic target of rapamycin (mTOR) hyperactivity in proinflammatory T cell differentiation in TA. This study was undertaken to explore potential mechanisms underpinning T cell-intrinsic mTOR hyperactivity and vascular inflammation in TA, with a focus on Notch-1.

METHODS

Notch-1 expression and activity was determined according to Notch-1, activated Notch-1, and HES-1 levels. We detected mTOR activity with intracellular expression of phosphorylated ribosomal protein S6. Differentiation of proinflammatory T cells was analyzed by detecting Th1 and Th17 lineage-determining transcription factors. The function of Notch-1 was evaluated using γ-secretase inhibitor DAPT and gene knockdown using a short hairpin RNA (shRNA) strategy. We performed our translational study using humanized NSG mouse chimeras in which human vasculitis was induced using immune cells from TA patients.

RESULTS

CD4+ T cells from TA patients exerted Notch-1^high , leading to mTOR hyperactivity and spontaneous maldifferentiation of Th1 cells and Th17 cells. Blockade of Notch-1 using DAPT and Notch-1 shRNA efficiently abrogated mTOR complex 1 (mTORC1) activation and proinflammatory T cell differentiation. Mechanistically, Notch-1 promoted mTOR expression, interacted with mTOR, and was associated with lysosomal localization of mTOR. Accordingly, systemic administration of DAPT and CD4+ T cell-specific gene knockdown of Notch-1 could alleviate vascular inflammation in humanized TA chimeras.

CONCLUSION

Expression of Notch-1 is elevated in CD4+ T cells from TA patients, resulting in mTORC1 hyperactivity and proinflammatory T cell differentiation. Targeting Notch-1 is a promising therapeutic strategy for the clinical management of TA.

Mucosal Vaccination with Cyclic Dinucleotide Adjuvants Induces Effective T Cell Homing and IL-17-Dependent Protection against Mycobacterium tuberculosis Infection

Tuberculosis consistently causes more deaths worldwide annually than any other single pathogen, making new effective vaccines an urgent priority for global public health. Among potential adjuvants, STING-activating cyclic dinucleotides (CDNs) uniquely stimulate a cytosolic sensing pathway activated only by pathogens. Recently, we demonstrated that a CDN-adjuvanted protein subunit vaccine robustly protects against tuberculosis infection in mice. In this study, we delineate the mechanistic basis underlying the efficacy of CDN vaccines for tuberculosis. CDN vaccines elicit CD4 T cells that home to lung parenchyma and penetrate into macrophage lesions in the lung. Although CDNs, like other mucosal vaccines, generate B cell-containing lymphoid structures in the lungs, protection is independent of B cells. Mucosal vaccination with a CDN vaccine induces Th1, Th17, and Th1-Th17 cells, and protection is dependent upon both IL-17 and IFN-γ. Single-cell RNA sequencing experiments reveal that vaccination enhances a metabolic state in Th17 cells reflective of activated effector function and implicate expression of Tnfsf8 (CD153) in vaccine-induced protection. Finally, we demonstrate that simply eliciting Th17 cells via mucosal vaccination with any adjuvant is not sufficient for protection. A vaccine adjuvanted with deacylated monophosphoryl lipid A (MPLA) failed to protect against tuberculosis infection when delivered mucosally, despite eliciting Th17 cells, highlighting the unique promise of CDNs as adjuvants for tuberculosis vaccines.

Insights into T-cell dysfunction in Alzheimer's disease

T cells, the critical immune cells of the adaptive immune system, are often dysfunctional in Alzheimer's disease (AD) and are involved in AD pathology. Reports highlight neuroinflammation as a crucial modulator of AD pathogenesis, and aberrant T cells indirectly contribute to neuroinflammation by secreting proinflammatory mediators via direct crosstalk with glial cells infiltrating the brain. However, the mechanisms underlying T‐cell abnormalities in AD appear multifactorial. Risk factors for AD and pathological hallmarks of AD have been tightly linked with immune responses, implying the potential regulatory effects of these factors on T cells. In this review, we discuss how the risk factors for AD, particularly Apolipoprotein E (ApoE), Aβ, α‐secretase, β‐secretase, γ‐secretase, Tau, and neuroinflammation, modulate T‐cell activation and the association between T cells and pathological AD hallmarks. Understanding these associations is critical to provide a comprehensive view of appropriate therapeutic strategies for AD.

Notch signalling in T cell homeostasis and differentiation

The evolutionarily conserved Notch signalling pathway regulates the differentiation and function of mature T lymphocytes with major context-dependent consequences in host defence, autoimmunity and alloimmunity. The emerging effects of Notch signalling in T cell responses build upon a more established role for Notch in T cell development. Here, we provide a critical review of this burgeoning literature to make sense of what has been learned so far and highlight the experimental strategies that have been most useful in gleaning physiologically relevant information. We outline the functional consequences of Notch signalling in mature T cells in addition to key specific Notch ligand–receptor interactions and downstream molecular signalling pathways. Our goal is to help clarify future directions for this expanding body of work and the best approaches to answer important open questions.

JAG2/Notch2 inhibits intervertebral disc degeneration by modulating cell proliferation, apoptosis, and extracellular matrix

Background

Intervertebral disc degeneration (IVDD)-related disorders are the major causes of low back pain. A previous study suggested that Notch activation serves as a protective mechanism and is a part of the compensatory response that maintains the necessary resident nucleus pulposus (NP) cell proliferation to replace lost or non-functional cells. However, the exact mechanism remains to be determined. In this study, we aimed to investigate the role of JAG2/Notch2 in NP cell proliferation and apoptosis.

Methods

Recombinant JAG2 or Notch2, Hes1, and Hey2 siRNAs were used to activate or inhibit Notch signaling. Cell proliferation, apoptosis, cell cycle regulatory factors, and pathways associated with Notch-mediated proliferation were examined. In vivo experiments involving an intradiscal injection of Sprague-Dawley rats were performed.

Results

Recombinant JAG2 induced Notch2 and Hes1/Hey2 expression together with NP cell proliferation. Downregulation of Notch2/Hes1/Hey2 induced G0/G1 phase cell cycle arrest in NP cells. Moreover, Notch2 mediated NP cell proliferation by regulating cyclin D1 and by activating PI3K/Akt and Wnt/β-catenin signaling. Furthermore, Notch signaling inhibited TNF-α-promoted NP cell apoptosis by suppressing the formation of the RIP1-FADD-caspase-8 complex. Finally, we found that intradiscal injection of JAG2 alleviated IVDD and that sh-Notch2 aggravated IVDD in a rat model. These results indicated that JAG2/Notch2 inhibited IVDD by modulating cell proliferation, apoptosis, and extracellular matrix. The JAG2/Notch2 axis regulated NP cell proliferation via PI3K/Akt and Wnt/β-catenin signaling and inhibited TNF-α-induced apoptosis by suppressing the formation of the RIP1-FADD-caspase-8 complex.

Conclusions

The current and previous results shed light on the therapeutic implications of targeting the JAG2/Notch2 axis to inhibit or reverse IVDD.

Notch Signaling Orchestrates Helminth-Induced Type 2 Inflammation

Infection with helminth parasites poses a significant challenge to the mammalian immune system. The type 2 immune response to helminth infection is critical in limiting worm-induced tissue damage and expelling parasites. Conversely, aberrant type 2 inflammation can cause debilitating allergic disease. Recent studies have revealed that key type 2 inflammation-associated immune and epithelial cell types respond to Notch signaling, broadly regulating gene expression programs in cell development and function. Here, we discuss new advances demonstrating that Notch is active in the development, recruitment, localization, and cytokine production of immune and epithelial effector cells during type 2 inflammation. Understanding how Notch signaling controls type 2 inflammatory processes could inform the development of Notch pathway modulators to treat helminth infections and allergies.

CD4+ Memory T Cells at Home in the Tissue: Mechanisms for Health and Disease

During the last 10 years, a population of clonally expanded T cells that take up permanent residence in non-lymphoid tissues has been identified. The localization of these tissue resident memory (TRM) cells allows them to rapidly respond at the site of antigen exposure, making them an attractive therapeutic target for various immune interventions. Although most studies have focused on understanding the biology underlying CD8 TRMs, CD4 T cells actually far outnumber CD8 T cells in barrier tissues such as lung and skin. Depending on the immune context, CD4 TRM can contribute to immune protection, pathology, or tissue remodeling. Although the ability of CD4 T cells to differentiate into heterogeneous effector and memory subsets has been well-established, how this heterogeneity manifests within the TRM compartment and within different tissues is just beginning to be elucidated. In this review we will discuss our current understanding of how CD4 TRMs are generated and maintained as well as a potential role for CD4 TRM plasticity in mediating the balance between beneficial and pathogenic immune responses.

NOTCH1 Represses MCL-1 Levels in GSI-resistant T-ALL, Making them Susceptible to ABT-263

PURPOSE

Effective targeted therapies are lacking for refractory and relapsed T-cell acute lymphoblastic leukemia (T-ALL). Suppression of the NOTCH pathway using gamma-secretase inhibitors (GSI) is toxic and clinically not effective. The goal of this study was to identify alternative therapeutic strategies for T-ALL.

EXPERIMENTAL DESIGN

We performed a comprehensive analysis of our high-throughput drug screen across hundreds of human cell lines including 15 T-ALL models. We validated and further studied the top hit, navitoclax (ABT-263). We used multiple human T-ALL cell lines as well as primary patient samples, and performed both in vitro experiments and in vivo studies on patient-derived xenograft models.

RESULTS

We found that T-ALL are hypersensitive to navitoclax, an inhibitor of BCL2 family of antiapoptotic proteins. Importantly, GSI-resistant T-ALL are also susceptible to navitoclax. Sensitivity to navitoclax is due to low levels of MCL-1 in T-ALL. We identify an unsuspected regulation of mTORC1 by the NOTCH pathway, resulting in increased MCL-1 upon GSI treatment. Finally, we show that pharmacologic inhibition of mTORC1 lowers MCL-1 levels and further sensitizes cells to navitoclax in vitro and leads to tumor regressions in vivo.

CONCLUSIONS

Our results support the development of navitoclax, as single agent and in combination with mTOR inhibitors, as a new therapeutic strategy for T-ALL, including in the setting of GSI resistance.

Notch signaling triggered via the ligand DLL4 impedes M2 macrophage differentiation and promotes their apoptosis

BACKGROUND

Notch signaling controls many cellular processes, including cell fate determination, cell differentiation, proliferation and apoptosis. In mammals, four Notch receptors (Notch 1-4) can interact with five distinct ligands [Jagged1, Jagged2, Delta-like 1 (DLL1), DLL3, and DLL4]. We previously reported that Notch activation is modulated in endothelial cells and monocytes during inflammation and showed that inflammation upregulates DLL4 on endothelial cells. DLL4 promotes differentiation of blood monocytes into proinflammatory M1 macrophages. Here, we further investigated the ability of DLL4 to interfere with the polarization of blood monocytes into immunosuppressive M2 macrophages.

METHODS

Human blood monocytes were differentiated in vitro into M0 macrophages and then polarized into M1 or M2 macrophages with LPS/IFNγ and IL-4, respectively. Polarization steps were performed in the presence of immobilized recombinant DLL4. Immune phenotype and apoptosis of macrophage subsets were analyzed and quantified by flow cytometry. Regulatory effects of DLL4 on gene expression, cell signaling and apoptotic pathways were investigated by QPCR and western blots.

RESULTS

The phenotype of M2 macrophages was subject to specific alterations in the presence of recombinant DLL4. DLL4 inhibits the upregulation of IL-4 induced M2 markers such as CD11b, CD206, and CD200R. Survival of macrophages upon M2 polarization was also strongly reduced in the presence of DLL4. DLL4 induces a caspase3/7-dependent apoptosis during M2 but not M1 macrophage polarization. The Notch ligand DLL1 has no apoptotic effect. Both DLL4 signaling via Notch1 as well as DLL4-mediated apoptosis are Notch-dependent. Fully differentiated M2 macrophages became resistant to DLL4 action. Mechanistically, DLL4 selectively upregulates gene expression in macrophages upon M2 polarization, thereby affecting the Notch pattern (Notch1, 3, Jag1), activity (HES1), and transcription (IRF5, STAT1). The pro-apoptotic effectors Bax and Bak and the BH3-only proteins Bid and Bim seem to convey DLL4 apoptotic signal.

CONCLUSION

Interplay between the DLL4/Notch and IL-4/IL-4R signaling pathways impairs M2 differentiation. Thus, DLL4 may drive a Notch-dependent selection process not only by promoting M1 macrophage differentiation but also by preventing M2 macrophage differentiation through inhibition of M2-specific gene expression and apoptotic cell death.

T Cell-Restricted Notch Signaling Contributes to Pulmonary Th1 and Th2 Immunity during Cryptococcus neoformans Infection

Cryptococcus neoformans is a ubiquitous, opportunistic fungal pathogen but the cell signaling pathways that drive T cell responses regulating antifungal immunity are incompletely understood. Notch is a key signaling pathway regulating T cell development, and differentiation and functional responses of mature T cells in the periphery. The targeting of Notch signaling within T cells has been proposed as a potential treatment for alloimmune and autoimmune disorders, but it is unknown whether disturbances to T cell immunity may render these patients vulnerable to fungal infections. To elucidate the role of Notch signaling during fungal infections, we infected mice expressing the pan-Notch inhibitor dominant negative mastermind-like within mature T cells with C. neoformans Inhibition of T cell-restricted Notch signaling increased fungal burdens in the lungs and CNS, diminished pulmonary leukocyte recruitment, and simultaneously impaired Th1 and Th2 responses. Pulmonary leukocyte cultures from T cell Notch-deprived mice produced less IFN-γ, IL-5, and IL-13 than wild-type cells. This correlated with lower frequencies of IFN-γ-, IL-5-, and IL-13-producing CD4⁺ T cells, reduced expression of Th1 and Th2 associated transcription factors, Tbet and GATA3, and reduced production of IFN-γ by CD8⁺ T cells. In contrast, Th17 responses were largely unaffected by Notch signaling. The changes in T cell responses corresponded with impaired macrophage activation and reduced leukocyte accumulation, leading to diminished fungal control. These results identify Notch signaling as a previously unappreciated regulator of Th1 and Th2 immunity and an important element of antifungal defenses against cryptococcal infection and CNS dissemination.

Notch Signaling in T Helper Cell Subsets: Instructor or Unbiased Amplifier?

For protection against pathogens, it is essential that naïve CD4⁺ T cells differentiate into specific effector T helper (Th) cell subsets following activation by antigen presented by dendritic cells (DCs). Next to T cell receptor and cytokine signals, membrane-bound Notch ligands have an important role in orchestrating Th cell differentiation. Several studies provided evidence that DC activation is accompanied by surface expression of Notch ligands. Intriguingly, DCs that express the delta-like or Jagged Notch ligands gain the capacity to instruct Th1 or Th2 cell polarization, respectively. However, in contrast to this model it has also been hypothesized that Notch signaling acts as a general amplifier of Th cell responses rather than an instructive director of specific T cell fates. In this alternative model, Notch enhances proliferation, cytokine production, and anti-apoptotic signals or promotes co-stimulatory signals in T cells. An instructive role for Notch ligand expressing DCs in the induction of Th cell differentiation is further challenged by evidence for the involvement of Notch signaling in differentiation of Th9, Th17, regulatory T cells, and follicular Th cells. In this review, we will discuss the two opposing models, referred to as the “instructive” and the “unbiased amplifier” model. We highlight both the function of different Notch receptors on CD4⁺ T cells and the impact of Notch ligands on antigen-presenting cells.

Notch signaling in T cells is essential for allergic airway inflammation, but expression of the Notch ligands Jagged 1 and Jagged 2 on dendritic cells is dispensable

BACKGROUND

Allergic asthma is characterized by a T_H2 response induced by dendritic cells (DCs) that present inhaled allergen. Although the mechanisms by which they instruct T_H2 differentiation are still poorly understood, expression of the Notch ligand Jagged on DCs has been implicated in this process.

OBJECTIVE

We sought to establish whether Notch signaling induced by DCs is critical for house dust mite (HDM)-driven allergic airway inflammation (AAI) in vivo.

METHODS

The induction of Notch ligand expression on DC subsets by HDM was quantified by using quantitative real-time PCR. We used an HDM-driven asthma mouse model to compare the capacity of Jagged 1 and Jagged 2 single- and double-deficient DCs to induce AAI. In addition, we studied AAI in mice with a T cell-specific deletion of recombination signal-binding protein for immunoglobulin Jκ region (RBPJκ), a downstream effector of Notch signaling.

RESULTS

HDM exposure promoted expression of Jagged 1, but not Jagged 2, on DCs. In agreement with published findings, in vitro-differentiated and HDM-pulsed Jagged 1 and Jagged 2 double-deficient DCs lacked the capacity to induce AAI. However, after in vivo intranasal sensitization and challenge with HDM, DC-specific Jagged 1 or Jagged 2 single- or double-deficient mice had eosinophilic airway inflammation and a T_H2 cell activation phenotype that was not different from that in control littermates. In contrast, RBPJκ-deficient mice did not experience AAI and airway hyperreactivity.

CONCLUSION

Our results show that the Notch signaling pathway in T cells is crucial for the induction of T_H2-mediated AAI in an HDM-driven asthma model but that expression of Jagged 1 or Jagged 2 on DCs is not required.

Systemic Expression of Notch Ligand Delta-Like 4 during Mycobacterial Infection Alters the T Cell Immune Response

The Notch ligand delta-like 4 (DLL4) is known to fine-tune the CD4⁺ T cell cytokine response. DLL4 is expressed on the surface of antigen-presenting cells (APCs) in a MyD88-dependent manner. We found that DLL4 expression was upregulated on bone marrow progenitor cells and APCs in mice infected with BCG Mycobacterium. Transfer of DLL4⁺ progenitor cells from infected hosts resulted in an increase DLL4⁺ myeloid cells in the spleen, indicating that expression of the dll4 gene is propagated throughout hematopoiesis. We also found an increase in DLL4⁺ monocytes from individuals who were infected with Mycobacterium tuberculosis. In latent individuals, DLL4 expression correlated with increased cytokine production from T cells in response to PPD stimulation. Finally, antibody blockade of DLL4 reduced T cell cytokine production from naïve T cells stimulated with antigen. These results demonstrate that the Notch ligand DLL4 can influence T cell cytokine production in both humans and mice, and further reveal that expression of DLL4 is upregulated on early hematopoietic progenitors in response to chronic mycobacterial infection. These data suggest that widespread DLL4 expression may occur as a result of mycobacterial infection, and that this expression may alter CD4⁺ T cell responses to both previously encountered and novel antigens.

Targeting the Notch Pathway to Prevent Rejection

Immune rejection is mediated by a complex interplay of cellular and humoral mechanisms. Current therapeutic strategies, which rely on global immunosuppression, can result in serious complications and are not completely effective. Notch signaling is a cell-to-cell communication pathway that plays an important role during T cell development and in the regulation of peripheral immune responses. Initial work, performed mainly through gain-of-function approaches, paradoxically identified Notch as an inducer of tolerance; however, recent studies using loss-of-function approaches in mouse models of transplant rejection and graft-versus-host disease have clarified an important role for Notch as a central mediator of T cell alloreactivity. Short-term inhibition of individual Notch ligands in the peritransplant period had long-lasting protective effects. In a vascularized heart allograft model, blockade of Delta-like Notch ligands dampened both cellular and humoral rejection. In this minireview, we summarize current knowledge about the role of Notch signaling during allograft rejection and provide an overarching mechanism through which Notch acts to promote T cell pathogenicity and allograft damage. We propose that targeting elements of the Notch pathway could provide a new therapeutic approach to prevent allograft rejection.

Transmission of survival signals through Delta-like 1 on activated CD4+ T cells

Notch expressed on CD4⁺ T cells transduces signals that mediate their effector functions and survival. Although Notch signaling is known to be cis-inhibited by Notch ligands expressed on the same cells, the role of Notch ligands on T cells remains unclear. In this report we demonstrate that the CD4⁺ T cell Notch ligand Dll1 transduces signals required for their survival. Co-transfer of CD4⁺ T cells from Dll1^−/− and control mice into recipient mice followed by immunization revealed a rapid decline of CD4⁺ T cells from Dll1^−/− mice compared with control cells. Dll1^−/− mice exhibited lower clinical scores of experimental autoimmune encephalitis than control mice. The expression of Notch target genes in CD4⁺ T cells from Dll1^−/− mice was not affected, suggesting that Dll1 deficiency in T cells does not affect cis Notch signaling. Overexpression of the intracellular domain of Dll1 in Dll1-deficient CD4⁺ T cells partially rescued impaired survival. Our data demonstrate that Dll1 is an independent regulator of Notch-signaling important for the survival of activated CD4⁺ T cells, and provide new insight into the physiological roles of Notch ligands as well as a regulatory mechanism important for maintaining adaptive immune responses.

RBPJ Controls Development of Pathogenic Th17 Cells by Regulating IL-23 Receptor Expression

Interleukin-17 (IL-17)-producing helper T cells (Th17 cells) play an important role in autoimmune diseases. However, not all Th17 cells induce tissue inflammation or autoimmunity. Th17 cells require IL-23 receptor (IL-23R) signaling to become pathogenic. The transcriptional mechanisms controlling the pathogenicity of Th17 cells and IL-23R expression are unknown. Here, we demonstrate that the canonical Notch signaling mediator RBPJ is a key driver of IL-23R expression. In the absence of RBPJ, Th17 cells fail to upregulate IL-23R, lack stability, and do not induce autoimmune tissue inflammation in vivo, whereas overexpression of IL-23R rescues this defect and promotes pathogenicity of RBPJ-deficient Th17 cells. RBPJ binds and trans-activates the Il23r promoter and induces IL-23R expression and represses anti-inflammatory IL-10 production in Th17 cells. We thus find that Notch signaling influences the development of pathogenic and non-pathogenic Th17 cells by reciprocally regulating IL-23R and IL-10 expression.

Transcription Factor KLF2 in Dendritic Cells Downregulates Th2 Programming via the HIF-1α/Jagged2/Notch Axis

The adaptive immune response is tightly regulated by complex signals in dendritic cells (DCs). Although Th2 polarization is dictated by defined functional DC subsets, the molecular factors that govern the amplitude of these responses are not well understood. Krüppel-like factor 2 (KLF2) is a transcription factor that negatively regulates the activation of numerous immune cells in response to stimuli. Here, we demonstrate that suppression of KLF2 in conditioned DCs preferentially amplifies Th2 responses in two model systems, one of which is a prototypical intracellular pathogen and the other an allergen. This elevation in Th2 responses was dependent on contact-mediated Notch signaling in vitro and in vivo. A deficiency of KLF2 increased the expression of Notch ligand Jagged2 via hypoxia-inducible factor 1α (HIF-1α), which led to Th2 amplification. Our results revealed a novel circuit in DCs for Th2 polarization that is governed by KLF2.

Dendritic cells are the key element that bridges innate and adaptive immunity. A complex and not-well-understood area in dendritic cell biology is the regulatory network that predetermines or moderates their function to shape the adaptive immune response. Our study for the first time demonstrates that KLF2, a transcription factor, conditions dendritic cells to regulate Th2 responses via a Jagged2/Notch axis. Downregulation of KLF2 expression in dendritic cells may provide a beneficial effect for treatment of diseases such as obesity or parasitic infections but may be deleterious in the case of invasion by intracellular pathogens. Strategies to tune KLF2 may be useful for future therapeutic approaches to particular diseases of mankind.

Notch in T Cell Differentiation: All Things Considered

Differentiation of naïve T cells into effector cells is required for optimal protection against different classes of microbial pathogen and for the development of immune memory. Recent findings have revealed important roles for the Notch signaling pathway in T cell differentiation into all known effector subsets, raising the question of how this pathway controls such diverse differentiation programs. Studies in preclinical models support the therapeutic potential of manipulating the Notch pathway to alleviate immune pathology, highlighting the importance of understanding the mechanisms through which Notch regulates T cell differentiation and function. We review these findings here, and outline both unifying principles involved in Notch-mediated T cell fate decisions and cell type- and context-specific differences that may present the most suitable points for therapeutic intervention.

Immune dysregulation in Alagille syndrome: A new feature of the evolving phenotype

Alagille syndrome (ALGS) is a rare autosomal dominant, multi-system disease caused by mutations in one of two NOTCH signaling pathway genes. Mutations in JAG1 are found in more than 94% of patients, with associated Jagged1 defects. We previously showed that CD46, which is a complement and immune regulator, regulates NOTCH expression during T cell activation after binding to C3b/C4b. We have identified 25% of our ALGS cohort with frequent infections and studied a subgroup of 4 in detail who were not showing current features of infections in order to show if Jagged1 abnormalities could affect immune function. We used cytometric bead arrays and FACS to measure cytokines and cell membrane expression. Resting and activated T cells were studied in both low and high IL-2 concentration to assess the TH1 ability to shift from INFγ to IL-10 production. In vitro initial PBMC cell population and subpopulation assessment were normal but further assessment of the lymphocytes revealed that while NOTCH1 expression and regulation was normal on resting TH1, Jagged1 expression was exaggerated. Resting TH1 cells from some patients exhibited high CD132 levels. Upon activating T cells, TH1 cells managed to produce TNF but failed to produce sufficient IFNγ levels (in two patients TH1 produced no IFNγ). TH2 exhibited exaggerated response with high IL-4 and IL-5 levels. TH1 were unable to down-regulate CD127, resulting in prolonged immune activation, and failed to shift from IFNγ to IL-10 production maintaining high IL-2 levels suggesting an impaired T cell response. Disturbed CD46-Jagged1 interaction may explain recurrent infections among ALGS patients, and could predispose to Th2-driven conditions such as asthma, eczema, food allergies and airway atopy and otitis media. The ALGS description could now be extended to include immune dysregulation.

Complexity and Controversies over the Cytokine Profiles of T Helper Cell Subpopulations in Tuberculosis

Tuberculosis (TB) is a contagious infectious disease caused by the TB-causing bacillus Mycobacterium tuberculosis and is considered a public health problem with enormous social impact. Disease progression is determined mainly by the balance between the microorganism and the host defense systems. Although the immune system controls the infection, this control does not necessarily lead to sterilization. Over recent decades, the patterns of CD4+ T cell responses have been studied with a goal of complete understanding of the immunological mechanisms involved in the maintenance of latent or active tuberculosis infection and of the clinical cure after treatment. Conflicting results have been suggested over the years, particularly in studies comparing experimental models and human disease. In recent years, in addition to Th1, Th2, and Th17 profiles, new standards of cellular immune responses, such as Th9, Th22, and IFN-γ-IL-10 double-producing Th cells, discussed here, have also been described. Additionally, many new roles and cellular sources have been described for IL-10, demonstrating a critical role for this cytokine as regulatory, rather than merely pathogenic cytokine, involved in the establishment of chronic latent infection, in the clinical cure after treatment and in keeping antibacillary effector mechanisms active to prevent immune-mediated damage.

Taking T cell priming down a Notch: signaling through Notch receptors enhances T cell sensitivity to antigen

Notch receptors are widely expressed and have recognized functions in thymocytes and mature T cells. In this issue, Laky et al. (2015) show that Notch interactions with Delta-like ligand 4 (DLL4) amplify priming of naive T cells.

Notch signaling regulates antigen sensitivity of naive CD4+ T cells by tuning co-stimulation

Adaptive immune responses begin when naive CD4(+) T cells engage peptide+major histocompatibility complex class II and co-stimulatory molecules on antigen-presenting cells (APCs). Notch signaling can influence effector functions in differentiated CD4(+) T helper and T regulatory cells. Whether and how ligand-induced Notch signaling influences the initial priming of CD4(+) T cells has not been addressed. We have found that Delta Like Ligand 4 (DLL4)-induced Notch signaling potentiates phosphatidylinositol 3-OH kinase (PI3K)-dependent signaling downstream of the T cell receptor+CD28, allowing naive CD4(+) T cells to respond to lower doses of antigen. In vitro, DLL4-deficient APCs were less efficient stimulators of CD4(+) T cell activation, metabolism, proliferation, and cytokine secretion. With deletion of DLL4 from CD11c(+) APCs in vivo, these deficits translated to an impaired ability to mount an effective CD4(+)-dependent anti-tumor response. These data implicate Notch signaling as an important regulator of adaptive immune responses.

Notch controls the survival of memory CD4+ T cells by regulating glucose uptake

CD4+ T cells differentiate into memory T cells that protect the host from subsequent infection. In contrast, autoreactive memory CD4+ T cells harm the body by persisting in the tissues. The underlying pathways controlling the maintenance of memory CD4+ T cells remain undefined. We show here that memory CD4+ T cell survival is impaired in the absence of the Notch signaling protein known as recombination signal binding protein for immunoglobulin κ J region (Rbpj). Treatment of mice with a Notch inhibitor reduced memory CD4+ T cell numbers and prevented the recurrent induction of experimental autoimmune encephalomyelitis. Rbpj-deficient CD4+ memory T cells exhibit reduced glucose uptake due to impaired AKT phosphorylation, resulting in low Glut1 expression. Treating mice with pyruvic acid, which bypasses glucose uptake and supplies the metabolite downstream of glucose uptake, inhibited the decrease of autoimmune memory CD4+ T cells in the absence of Notch signaling, suggesting memory CD4+ T cell survival relies on glucose metabolism. Together, these data define a central role for Notch signaling in maintaining memory CD4+ T cells through the regulation of glucose uptake.

Delta-like 1-mediated Notch signaling enhances the in vitro conversion of human memory CD4 T cells into FOXP3-expressing regulatory T cells

FOXP3-expressing regulatory T cells (Treg) are essential for the prevention of autoimmunity and were shown to be reduced and/or dysfunctional in several autoimmune diseases. Although Treg-based adoptive transfer represents a promising therapy, the large cell number required to achieve clinical efficacy constitutes an important limitation. Therefore, novel strategies to generate bona fide in vitro-induced Treg (iTreg) are critical. In this study, we report that human memory CD4 T cells can be efficiently converted into iTreg, and that Delta-like 1 (DL1)-mediated Notch signaling significantly enhances this process. The iTreg generated in the presence of DL1 featured higher levels of Treg function-associated molecules and were efficient suppressors. Importantly, these iTreg displayed a stable phenotype in long-term cultures, even in the presence of proinflammatory cytokines. Additionally, DL1 potentiated FOXP3 acquisition by memory CD4 cells through the modulation of the TGF-β signaling pathway and of Foxp3 transcription. Our data demonstrate that iTreg can be efficiently induced from memory CD4 cells, a subset enriched in relevant specificities for targeting in autoimmune diseases, and that DL1 enhances this process. DL1 also enhanced the proliferation and Treg function-associated marker expression of ex vivo-stimulated human circulating FOXP3(+) cells. Manipulation of the Notch signaling pathway constitutes a promising approach to boost the in vitro generation of iTreg and ex vivo Treg expansion, thus facilitating the establishment of effective Treg-based adoptive therapy in autoimmune diseases.

Specific fibroblastic niches in secondary lymphoid organs orchestrate distinct Notch-regulated immune responses

Fasnacht et al. now show that fibroblasts in secondary lymphoid organs are responsible for the production of Notch ligands regulating the differentiation of immune cells

Fibroblast-like cells of secondary lymphoid organs (SLO) are important for tissue architecture. In addition, they regulate lymphocyte compartmentalization through the secretion of chemokines, and participate in the orchestration of appropriate cell–cell interactions required for adaptive immunity. Here, we provide data demonstrating the functional importance of SLO fibroblasts during Notch-mediated lineage specification and immune response. Genetic ablation of the Notch ligand Delta-like (DL)1 identified splenic fibroblasts rather than hematopoietic or endothelial cells as niche cells, allowing Notch 2–driven differentiation of marginal zone B cells and of Esam⁺ dendritic cells. Moreover, conditional inactivation of DL4 in lymph node fibroblasts resulted in impaired follicular helper T cell differentiation and, consequently, in reduced numbers of germinal center B cells and absence of high-affinity antibodies. Our data demonstrate previously unknown roles for DL ligand-expressing fibroblasts in SLO niches as drivers of multiple Notch-mediated immune differentiation processes.

Notch signaling genes: myogenic DNA hypomethylation and 5-hydroxymethylcytosine

Notch intercellular signaling is critical for diverse developmental pathways and for homeostasis in various types of stem cells and progenitor cells. Because Notch gene products need to be precisely regulated spatially and temporally, epigenetics is likely to help control expression of Notch signaling genes. Reduced representation bisulfite sequencing (RRBS) indicated significant hypomethylation in myoblasts, myotubes, and skeletal muscle vs. many nonmuscle samples at intragenic or intergenic regions of the following Notch receptor or ligand genes: NOTCH1, NOTCH2, JAG2, and DLL1. An enzymatic assay of sites in or near these genes revealed unusually high enrichment of 5-hydroxymethylcytosine (up to 81%) in skeletal muscle, heart, and cerebellum. Epigenetics studies and gene expression profiles suggest that hypomethylation and/or hydroxymethylation help control expression of these genes in heart, brain, myoblasts, myotubes, and within skeletal muscle myofibers. Such regulation could promote cell renewal, cell maintenance, homeostasis, and a poised state for repair of tissue damage.

Rescue of notch-1 signaling in antigen-specific CD8+ T cells overcomes tumor-induced T-cell suppression and enhances immunotherapy in cancer

An impaired antitumor immunity is found in patients with cancer and represents a major obstacle in the successful development of different forms of immunotherapy. Signaling through Notch receptors regulates the differentiation and function of many cell types, including immune cells. However, the effect of Notch in CD8(+) T-cell responses in tumors remains unclear. Thus, we aimed to determine the role of Notch signaling in CD8(+) T cells in the induction of tumor-induced suppression. Our results using conditional knockout mice show that Notch-1 and Notch-2 were critical for the proliferation and IFNγ production of activated CD8(+) T cells and were significantly decreased in tumor-infiltrating T cells. Conditional transgenic expression of Notch-1 intracellular domain (N1IC) in antigen-specific CD8(+) T cells did not affect activation or proliferation of CD8(+) T cells, but induced a central memory phenotype and increased cytotoxicity effects and granzyme B levels. Consequently, a higher antitumor response and resistance to tumor-induced tolerance were found after adoptive transfer of N1IC-transgenic CD8(+) T cells into tumor-bearing mice. Additional results showed that myeloid-derived suppressor cells (MDSC) blocked the expression of Notch-1 and Notch-2 in T cells through nitric oxide-dependent mechanisms. Interestingly, N1IC overexpression rendered CD8(+) T cells resistant to the tolerogenic effect induced by MDSC in vivo. Together, the results suggest the key role of Notch in the suppression of CD8(+) T-cell responses in tumors and the therapeutic potential of N1IC in antigen-specific CD8(+) T cells to reverse T-cell suppression and increase the efficacy of T cell-based immunotherapies in cancer.

The immunological synapse: the gateway to the HIV reservoir

A major challenge in the development of a cure for human immunodeficiency virus (HIV) has been the incomplete understanding of the basic mechanisms underlying HIV persistence during antiretroviral therapy. It is now realized that the establishment of a latently infected reservoir refractory to immune system recognition has thus far hindered eradication efforts. Recent investigation into the innate immune response has shed light on signaling pathways downstream of the immunological synapse critical for T-cell activation and establishment of T-cell memory. This has led to the understanding that the cell-to-cell contacts observed in an immunological synapse that involve the CD4⁺ T cell and antigen-presenting cell or T-cell–T-cell interactions enhance efficient viral spread and facilitate the induction and maintenance of latency in HIV-infected memory T cells. This review focuses on recent work characterizing the immunological synapse and the signaling pathways involved in T-cell activation and gene regulation in the context of HIV persistence.

STAT5-induced lunatic fringe during Th2 development alters delta-like 4-mediated Th2 cytokine production in respiratory syncytial virus-exacerbated airway allergic disease

Notch activation plays an important role in T cell development and mature T cell differentiation. In this study, we investigated the role of Notch activation in a mouse model of respiratory syncytial virus (RSV)-exacerbated allergic airway disease. During RSV exacerbation, in vivo neutralization of a specific Notch ligand, Delta-like ligand (Dll)-4, significantly decreased airway hyperreactivity, mucus production, and Th2 cytokines. Lunatic Fringe (Lfng), a glycosyltransferase that enhances Notch activation by Dll4, was increased during RSV exacerbation. Lfng loss of function in Th2-skewed cells inhibited Dll4-Notch activation and subsequent IL-4 production. Further knockdown of Lfng in T cells in CD4Cre(+)Lfng(fl/fl) mice showed reduced Th2 response and disease pathology during RSV exacerbation. Finally, we identified STAT5-binding cis-acting regulatory element activation as a critical driver of Lfng transcriptional activation. These data demonstrate that STAT5-dependent amplification of Notch-modifying Lfng augments Th2 response via Dll4 and is critical for amplifying viral exacerbation during allergic airway disease.

Histone modifications of Notch1 promoter affect lung CD4+ T cell differentiation in asthmatic rats

Asthma is an inflammatory disease of the airways, and the current treatment in managing asthma is the control of inflammation. Notch signaling pathway has been linked to T-cell imbalance. The present study aimed to explore the histone modifications of Notch1 promoter in normal and asthmatic lung CD4+ T cells. Chromatin immunoprecipitation analysis showed that the acetylation levels of total H3, H4, site-specific H3K9, H3K14, H3K27, H3K18, H4K16, and the trimethylation levels of H3K4, H3K79 of Notch1 gene promoter were increased significantly in asthmatic lung CD4+ T cells compared to the control group, which correlated with increased P300, PCAF activity and decreased HDAC1, HDAC2 activity. After intervention of garcinol, a potent inhibitor of histone acetyltransferases, in asthmatic lung CD4+ T cells, HAT activity decreased significantly and the increased Notch1 and hes-1 expression was reversed. The total H3ac, H4ac, site-specific H3K9ac, H3K14ac, H3K27ac, H3K18ac, H4K16ac and H3K79me3 levels of Notch1 gene promoter decreased significantly, and the H3K4me3, H3K9me3, H4K20me3 levels had no significant difference. We further investigated the suppressive effects of GAR on asthmatic parameters. Results showed that the levels of IL-4, IL-5 and IL-13 were significantly reduced and a small reverse trend was found in the level of IFN-g after GAR treatment. Furthermore, the expression of NF-&#954;B and AP-1 reduced significantly. These results suggest that asthma is associated with changes in the epigenetic status of Notch1 promoter, including abnormal histone acetylation and methylation, and GAR may have applications in the treatment of asthma.

Notch simultaneously orchestrates multiple helper T cell programs independently of cytokine signals

Two models are proposed to explain Notch function during helper T (Th) cell differentiation. One argues that Notch instructs one Th cell fate over the other, whereas the other posits that Notch function is dictated by cytokines. Here we provide a detailed mechanistic study investigating the role of Notch in orchestrating Th cell differentiation. Notch neither instructed Th cell differentiation nor did cytokines direct Notch activity, but instead, Notch simultaneously regulated the Th1, Th2, and Th17 cell genetic programs independently of cytokine signals. In addition to regulating these programs in both polarized and nonpolarized Th cells, we identified Ifng as a direct Notch target. Notch bound the Ifng CNS-22 enhancer, where it synergized with Tbet at the promoter. Thus, Notch acts as an unbiased amplifier of Th cell differentiation. Our data provide a paradigm for Notch in hematopoiesis, with Notch simultaneously orchestrating multiple lineage programs, rather than restricting alternate outcomes.

Notch 1 signalling inhibits cardiomyocyte apoptosis in ischaemic postconditioning

AIM

Recent studies have demonstrated that Notch signalling pathway is an important mediator of cardiac repair and regeneration after myocardial infarction. However, the mechanism by which Notch signalling pathway is mediating cardioprotection after ischaemic postconditioning (IPost) is still not understood thoroughly. The aim of the present study was to investigate the mechanism by which Notch signalling pathway mediated the cardioprotection effect after IPost.

METHODS

Rat heart-derived H9c2 cells were randomly divided into six groups as follows: Control group, hypoxia/reoxygenation group (H/R), H/R+N1ICD group, H-post group, H-post+Notch-1miRNA group, and Mock group. We used pcDNA3.1-Myc-His plasmid and RNA interference (RNAi) to activate/inhibit the expression of Notch-1 in H9c2 cell lines. The Bcl-2, Bax genes and proteins were assessed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and Western blot analysis. The effects of Notch 1 signalling on cell survival, proliferation and apoptosis were detected by 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di-phenytetrazoliumromide (MTT) and flow cytometry analysis, respectively. Furthermore, Notch 1 signalling induced the disruption of mitochondrial membrane potential, thus leading to the activation of caspase-9/-3 measured using the colorimetric activity assay.

RESULTS

We found Notch 1 signalling reduced cardiomyocyte apoptosis in IPost through regulating the expression of Bcl-2, Bax and activation of caspase-9 and -3. We found that after transfected with pcDNA3.1-Myc-His plasmid, activation of the Notch 1 gene effectively promoted cell proliferation and inhibited apoptosis. The Notch 1 upregulation was accompanied by an upregulation of Bcl-2 and a downregulation of Bax. In addition, a paralled increase in caspase-9/-3 activities was observed. These effects were blunted by transfected with Notch-1 miRNA in the H9c2 cells.

CONCLUSION

Notch 1 signalling has a cardioprotection effect, which may result from cardiomyocyte apoptosis, by means of regulating the expression of cell apoptosis inhibiting proteins Bcl-2, Bax and the activation of caspase-9 and -3.

T cell-specific notch inhibition blocks graft-versus-host disease by inducing a hyporesponsive program in alloreactive CD4+ and CD8+ T cells

Graft-versus-host disease (GVHD) induced by donor-derived T cells remains the major limitation of allogeneic bone marrow transplantation (allo-BMT). We previously reported that the pan-Notch inhibitor dominant-negative form of Mastermind-like 1 (DNMAML) markedly decreased the severity and mortality of acute GVHD mediated by CD4(+) T cells in mice. To elucidate the mechanisms of Notch action in GVHD and its role in CD8(+) T cells, we studied the effects of Notch inhibition in alloreactive CD4(+) and CD8(+) T cells using mouse models of allo-BMT. DNMAML blocked GVHD induced by either CD4(+) or CD8(+) T cells. Both CD4(+) and CD8(+) Notch-deprived T cells had preserved expansion in lymphoid organs of recipients, but profoundly decreased IFN-γ production despite normal T-bet and enhanced Eomesodermin expression. Alloreactive DNMAML T cells exhibited decreased Ras/MAPK and NF-κB activity upon ex vivo restimulation through the TCR. In addition, alloreactive T cells primed in the absence of Notch signaling had increased expression of several negative regulators of T cell activation, including Dgka, Cblb, and Pdcd1. DNMAML expression had modest effects on in vivo proliferation but preserved overall alloreactive T cell expansion while enhancing accumulation of pre-existing natural regulatory T cells. Overall, DNMAML T cells acquired a hyporesponsive phenotype that blocked cytokine production but maintained their expansion in irradiated allo-BMT recipients, as well as their in vivo and ex vivo cytotoxic potential. Our results reveal parallel roles for Notch signaling in alloreactive CD4(+) and CD8(+) T cells that differ from past reports of Notch action and highlight the therapeutic potential of Notch inhibition in GVHD.

Diversity, function, and transcriptional regulation of gut innate lymphocytes

The innate immune system plays a critical early role in host defense against viruses, bacteria, and tumor cells. Until recently, natural killer (NK) cells and lymphoid tissue inducer (LTi) cells were the primary members of the innate lymphocyte family: NK cells form the front-line interface between the external environment and the adaptive immune system, while LTi cells are essential for secondary lymphoid tissue formation. More recently, it has become apparent that the composition of this family is much more diverse than previously appreciated and newly recognized populations play distinct and essential functions in tissue protection. Despite the importance of these cells, the developmental relationships between different innate lymphocyte populations remain unclear. Here we review recent advances in our understanding of the development of different innate immune cell subsets, the transcriptional programs that might be involved in driving fate decisions during development, and their relationship to NK cells.

IL-21-stimulated human plasmacytoid dendritic cells secrete granzyme B, which impairs their capacity to induce T-cell proliferation

Plasmacytoid dendritic cells (pDCs) play a crucial role during innate immunity by secreting bulk amounts of type I interferons (IFNs) in response to Toll-like receptor (TLR)-mediated pathogen recognition. In addition, pDCs can also contribute to adaptive immunity by activation of antigen-specific T cells. Furthermore, it is well established that pDCs contribute to the pathogenesis of autoimmune diseases, including lupus. Interleukin-21 (IL-21) is a cytokine produced by activated CD4(+) T and natural killer T (NKT) cells and has a pleiotropic role in immunity by controlling myeloid DC-, NKT-, T-, and B-cell functions. It has remained elusive whether IL-21 affects pDCs. Here we investigate the role of IL-21 in human pDC activation and function and observe that IL-21 activates signal transducer and activator of transcription 3 in line with the finding that pDCs express the IL-21 receptor. Although IL-21 did not affect TLR-induced type I IFNs, IL-6, and TNF-α nor expression of major-histocompatibility-complex class II or costimulatory molecules, IL-21 markedly increased expression of the serine protease granzyme B (GrB). We demonstrate that GrB induction was, in part, responsible for IL-21-mediated downmodulation of CD4(+) T-cell proliferation induced by TLR preactivated pDCs. Collectively, our data provide evidence that pDCs are important cells to consider when investigating the role of IL-21 in immunity or pathogenesis.

Notch controls generation and function of human effector CD8+ T cells

The generation of effector CD8(+) T cells with lytic capacity is crucial for tumor control. Dendritic cells (DCs) provide important signals to promote naive CD8(+) T cell priming and activation of effector T cells. Here, we report that the Notch pathway has an important role in both these processes in human CD8(+) T cells. Activated monocyte-derived DCs express Notch ligands Jagged1 and Delta-like4, whereas naive CD8(+) T cells express Notch2. The role for Notch signaling in CD8(+) T cell priming was determined using an ex-vivo model system in which tumor antigen-specific primary CD8(+) T cell responses were measured. Inhibition of Notch using γ-secretase inhibitors or soluble Delta-like4-Fc during activation reduced expansion of antigen-specific CD8(+) T cells, which was mirrored by decreased frequencies of interferon (IFN)γ-, tumor necrosis factor-α-, and granzymeB-producing CD8(+) T cells. Moreover, T cells primed when Notch signaling was prevented are functionally low-avidity T cells. In addition, Notch partially regulates established effector T cell function. Activation-induced Notch signaling is needed for IFNγ release but not for cytolytic activity. These data indicate that Notch signaling controls human CD8(+) T cell priming and also influences effector T cell functions. This may provide important information for designing new immunotherapies for treatment of cancer.

Relevance of long-lived CD8(+) T effector memory cells for protective immunity elicited by heterologous prime-boost vaccination

Owing to the importance of major histocompatibility complex class Ia-restricted CD8(+) T cells for host survival following viral, bacterial, fungal, or parasitic infection, it has become largely accepted that these cells should be considered in the design of a new generation of vaccines. For the past 20 years, solid evidence has been provided that the heterologous prime-boost regimen achieves the best results in terms of induction of long-lived protective CD8(+) T cells against a variety of experimental infections. Although this regimen has often been used experimentally, as is the case for many vaccines, the mechanism behind the efficacy of this vaccination regimen is still largely unknown. The main purpose of this review is to examine the characteristics of the protective CD8(+) T cells generated by this vaccination regimen. Part of its efficacy certainly relies on the generation and maintenance of large numbers of specific lymphocytes. Other specific characteristics may also be important, and studies on this direction have only recently been initiated. So far, the characterization of these protective, long-lived T cell populations suggests that there is a high frequency of polyfunctional T cells; these cells cover a large breadth and display a T effector memory (TEM) phenotype. These TEM cells are capable of proliferating after an infectious challenge and are highly refractory to apoptosis due to a control of the expression of pro-apoptotic receptors such as CD95. Also, they do not undergo significant long-term immunological erosion. Understanding the mechanisms that control the generation and maintenance of the protective activity of these long-lived TEM cells will certainly provide important insights into the physiology of CD8(+) T cells and pave the way for the design of new or improved vaccines.

Notch signaling regulates PD-1 expression during CD8(+) T-cell activation

Programmed cell death 1 (PD-1) is an inhibitory receptor involved in T-cell activation, tolerance and exhaustion. Little is known on how the expression of PD-1 is controlled during T-cell activation. Recent studies demonstrated that NFATc1 and IRF9 regulate Pdcd1 (PD-1) transcription and that T-bet acts as a transcriptional repressor. In this study, we have investigated the role of the Notch signaling pathway in PD-1 regulation. Using specific inhibitors of the Notch signaling pathway, we showed decreased PD-1 expression and inhibition of Pdcd1 transcription by activated CD8(+) T cells. Chromatin immunoprecipitation further showed occupancy of the Pdcd1 promoter with RBPJk and Notch1 intracellular domain at RBPJk-binding sites. Our results identify the Notch signaling pathway as an important regulator of PD-1 expression by activated CD8(+) T cells.