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Dendritic cells (DCs) are important for adaptive immune responses through the activation of T cells. The molecular interplay between DCs and T cells determines the magnitude of T cell responses or outcomes of functional differentiation of T cells. In this study, we demonstrated that DCs in mice that are Rbpj deficient in CD11c+ cells (Rbpj−/− mice) promoted the differentiation of IL-17A–producing Th17 cells. Rbpj-deficient DCs expressed little Aldh1a2 protein that is required for generating retinoic acid. Those DCs exhibited a reduced ability for differentiating regulatory T cells induced by TGF-β. Rbpj protein directly regulated Aldh1a2 transcription by binding to its promoter region. The overexpression of Aldh1a2 in Rbpj-deficient DCs negated their Th17-promoting ability. Transfer of naive CD4+ T cells into Rag1-deficient Rbpj−/− mice enhanced colitis with increased Th17 and reduced induced regulatory T cells (iTreg) compared with control Rag1-deficient mice. The cotransfer of iTreg and naive CD4+ T cells into Rag1-deficient Rbpj−/− mice improved colitis compared with transfer of naive CD4+ T cell alone. Furthermore, cotransfer of DCs from Rbpj−/− mice that overexpressed Aldh1a2 or Notch-stimulated DCs together with naive CD4+ T cells into Rbpj−/− Rag1-deficient mice led to reduced colitis with increased iTreg numbers. Therefore, our studies identify Notch signaling in DCs as a crucial balancer of Th17/iTreg, which depends on the direct regulation of Aldh1a2 transcription in DCs.

MicroRNAs have broad roles in tumorigenesis and cell differentiation through regulation of target genes. Notch signaling also controls cell differentiation and tumorigenesis. However, the mechanisms through which Notch mediates microRNA expression are still unclear. In this study, we aimed to identify microRNAs regulated by Notch signaling. Our analysis found that microRNA-449a (miR-449a) was indirectly regulated by Notch signaling. Although miR-449a-deficient mice did not show any Notch-dependent defects in immune cell development, treatment of miR-449a-deficient mice with azoxymethane (AOM) or dextran sodium sulfate (DSS) increased the numbers and sizes of colon tumors. These effects were associated with an increase in intestinal epithelial cell proliferation following AOM/DSS treatment. In patients with colon cancer, miR-449a expression was inversely correlated with disease-free survival and histological scores and was positively correlated with the expression of MLH1 for which loss-of function mutations have been shown to be involved in colon cancer. Colon tissues of miR-449a-deficient mice showed reduced Mlh1 expression compared with those of wild-type mice. Thus, these data suggested that miR-449a acted as a key regulator of colon tumorigenesis by controlling the proliferation of intestinal epithelial cells. Additionally, activation of miR-449a may represent an effective therapeutic strategy and prognostic marker in colon cancer.

The gastrointestinal tract comes into direct contact with environmental agents, including bacteria, viruses, and foods. Intestine-specific subsets of immune cells maintain gut homeostasis by continuously sampling luminal antigens and maintaining immune tolerance. CD11c(+)CX3CR1(+) cells sample luminal antigens in the small intestine and contribute to the trafficking of bacteria to lymph nodes under dysbiotic conditions. The molecular mechanisms crucial for the differentiation of CD11c(+)CX3CR1(+) cells remain unclear. Here we demonstrate that the Notch1- or Notch2-Rbpj axis is essential for the development of CD11c(+)CX3CR1(+) cells. In mice in which Rbpj or Notch1 and Notch2 were deleted from CD11c(+) cells, there was a deficit of CD11c(+)CX3CR1(+) cells and an accumulation of CD11c(low)CX3CR1(+) cells. The CD11c(low)CX3CR1(+) cells could not differentiate to CD11c(+)CX3CR1(+) cells, suggesting that CD11c(low)CX3CR1(+) cells represent a lineage distinct from CD11c(+)CX3CR1(+) cells. These data indicate that Notch signaling is essential for lineage fixation of intestinal CD11c(+)CX3CR1(+) cells.

The myeloid cell population includes mononuclear phagocytes such as dendritic cells, macrophages, and monocytes. They have roles in phagocytosis, digestion, and presentation of antigens through the use of microbe pattern recognition receptors and secreting effector molecules such as cytokines and chemokines. Notch signaling strictly controls specific subsets in different tissues and developmental stages in both mice and humans. Here, we describe recent reports of Notch regulation in mononuclear phagocytes.

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.

Upon their recognition of antigens presented by the MHC, T cell proliferation is vital for clonal expansion and the acquisition of effector functions, which are essential for mounting adaptive immune responses. The CD98 heavy chain (CD98hc, Slc3a2) plays a crucial role in the proliferation of both CD4+ and CD8+ T cells, although it is unclear if CD98hc directly regulates the T cell effector functions that are not linked with T cell proliferation in vivo. Here, we demonstrate that CD98hc is required for both CD4+ T cell proliferation and Th1 functional differentiation. T cell-specific deletion of CD98hc did not affect T cell development in the thymus. CD98hc-deficient CD4+ T cells proliferated in vivo more slowly as compared with control T cells. C57BL/6 mice lacking CD98hc in their CD4+ T cells could not control Leishmania major infections due to lowered IFN-γ production, even with massive CD4+ T cell proliferation. CD98hc-deficient CD4+ T cells exhibited lower IFN-γ production compared with wild-type T cells, even when comparing IFN-γ expression in cells that underwent the same number of cell divisions. Therefore, these data indicate that CD98hc is required for CD4+ T cell expansion and functional Th1 differentiation in vivo, and suggest that CD98hc might be a good target for treating Th1-mediated immune disorders.

Nature Communications 7: Article number: 12597 (2016); Published: 31 August 2016; Updated: 3 May 2017 The authors inadvertently omitted Christine Häger, who was involved in the initial characterization of Notch mutant mice presented in this Article, from the author list and Author contributions statement.

Invariant natural killer T cells are a distinct subset of T cells that exert Janus-like functions. Moreover, Notch signaling is known to have critical roles in the development and functions of T cells. However, it is not known whether Notch signaling contributes to the development or functions of invariant natural killer T cells. Here, we found that CD4-specific gene ablation of Notch 1 and Notch 2 (N1N2−/−) increased the number of invariant natural killer T cells in the thymus but decreased them in the liver. N1N2−/− mice showed impaired thymic maturation of invariant natural killer T cells from the NK1.1−CD44+ to the NK1.1+CD44+ stage, resulting in accumulation of NK1.1−CD44+ invariant natural killer T cells in the thymus. Upon activation, hepatic invariant natural killer T cells from N1N2−/− mice produced lower cytokine levels and increased apoptosis versus wild-type invariant natural killer T cells. Furthermore, Notch 1/Notch 2-deficient, but not wild type, invariant natural killer T cells failed to promote antibody-induced arthritis in CD1d−/− mice. Unlike N1N2−/− mice, RBP-jlox/lox CD4-Cre mice showed similar percentages and numbers of thymic invariant natural killer T cells to wild-type mice but had defects in their homeostasis, maturation, and cytokine production in the liver. Taken together, our data indicate distinct effects of Notch signaling on invariant natural killer T cells in the thymus and liver, which are at least partly independent of RBP-j in the thymus.

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.

Experimental autoimmune uveoretinitis (EAU) is an organ-specific T cell-mediated disease induced by immunizing mice with interphotoreceptor retinoid binding protein (IRBP). Autoaggressive CD4(+) T cells are the major pathogenic population for EAU. We investigated the contribution of Notch signaling in T cells to EAU pathogenesis because Notch signaling regulates various aspects of CD4(+) T cell functions. Rbpj is required for Notch signaling, and Rbpj deficiency in T cells inhibited EAU disease severity. The amelioration of EAU in T cell-specific Rbpj-deficient mice correlated with low levels of IL-22 production from CD4(+) T cells, although IRBP-specific CD4(+) T cell proliferation and Th17 differentiation were unaffected. Administration of recombinant IL-22 during the late phase, but not the early phase, of EAU increased EAU clinical scores in T cell-specific Rbpj-deficient mice. Notch inhibition in mice immunized with IRBP with a γ-secretase inhibitor (GSI) suppressed EAU progression, even when GSI was administered as late as 13 days after IRBP immunization. Our data demonstrate that Rbpj/Notch-mediated IL-22 production in T cells has a key pathological role in the late phase of EAU, and suggest that Notch blockade might be a useful therapeutic approach for treating EAU.

Intestinal intraepithelial T cells contribute to the regulation of inflammatory responses in the intestine; however, the molecular basis for their development and maintenance is unknown. The aryl hydrocarbon receptor complexes with the aryl hydrocarbon receptor nuclear translocator (ARNT) and senses environmental factors, including gut microbiota. Here, we identify ARNT as a critical regulator of the differentiation of TCRαβ(+)CD8αα(+) intestinal intraepithelial T cells. Mice deficient in either ARNT or aryl hydrocarbon receptor show a greater than- eight-fold reduction in the number of TCRαβ(+)CD8αα(+) intestinal intraepithelial T cells. The number of TCRαβ(+)CD8αα(+) intestinal intraepithelial T cells is increased by treatment with an aryl hydrocarbon receptor agonist in germ-free mice and is decreased by antibiotic treatment. The Arnt-deficient precursors of TCRαβ(+)CD8αα(+) intestinal intraepithelial T cells express low amounts of STAT3 and fail to differentiate towards the TCRαβ(+)CD8αα(+) cell fate after IL-15 stimulation, a deficiency that is overcome by overexpression of Stat3. These data demonstrate that the ARNT-STAT3 axis is a critical regulator of TCRαβ(+)CD8αα(+) intestinal intraepithelial T-cell development and differentiation.

B cells are classified into several subsets depending on their functions, marker expression pattern and localization. Marginal zone B (MZB) cells are a distinct lineage from follicular B cells, and regulate host defenses against blood-borne pathogens. Notch2/RBP-J signaling regulates the development of MZB cells by interacting with delta-like 1 ligand, although the target genes for Notch2 signaling remain unclear. We identified Fos as an upregulated gene in LPS-stimulated B cells that received Notch2 signaling. Fos is expressed in CD21(high)CD23(low) MZB cells at a higher level compared to CD21(Int)CD23(high) follicular B cells. Deleting the Notch2 gene in CD19(+) B cells decreased Fos expression in B cells. Overexpression of Fos in Notch2-deficient B cells or bone marrow cells partially restored MZB development. Fos promoter activity was upregulated by Notch2 signaling, indicating that Notch2 directly controls Fos transcription associated with MZB development. These data identify Fos as one of the target genes for Notch2 signaling that is crucial for MZB development.

A population of monocytes, known as Ly6Clo monocytes, patrol blood vessels by crawling along the vascular endothelium. Here we show that endothelial cells control their origin through Notch signalling. Using combinations of conditional genetic deletion strategies and cell-fate tracking experiments we show that Notch2 regulates conversion of Ly6Chi monocytes into Ly6Clo monocytes in vivo and in vitro, thereby regulating monocyte cell fate under steady-state conditions. This process is controlled by Notch ligand delta-like 1 (Dll1) expressed by a population of endothelial cells that constitute distinct vascular niches in the bone marrow and spleen in vivo, while culture on recombinant DLL1 induces monocyte conversion in vitro. Thus, blood vessels regulate monocyte conversion, a form of committed myeloid cell fate regulation.