NK1.1- CD4+ NKG2D+ T cells suppress DSS-induced colitis in mice through production of TGF-β

The Role of NKG2D and Its Ligands in Autoimmune Diseases: New Targets for Immunotherapy

Natural killer (NK) cells and CD8+ T cells can clear infected and transformed cells and generate tolerance to themselves, which also prevents autoimmune diseases. Natural killer group 2 member D (NKG2D) is an important activating immune receptor that is expressed on NK cells, CD8+ T cells, γδ T cells, and a very small percentage of CD4+ T cells. In contrast, the NKG2D ligand (NKG2D-L) is generally not expressed on normal cells but is overexpressed under stress. Thus, the inappropriate expression of NKG2D-L leads to the activation of self-reactive effector cells, which can trigger or exacerbate autoimmunity. In this review, we discuss the role of NKG2D and NKG2D-L in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis (MS), type I diabetes (T1DM), inflammatory bowel disease (IBD), and celiac disease (CeD). The data suggest that NKG2D and NKG2D-L play a pathogenic role in some autoimmune diseases. Therefore, the development of strategies to block the interaction of NKG2D and NKG2D-L may have therapeutic effects in some autoimmune diseases.

Low miR-16 expression induces regulatory CD4+NKG2D+ T cells involved in colorectal cancer progression

MiR-15a/16 is a member of the miRNA cluster that exhibits tumor suppression and immune modulation via targeting multiple genes. Decreased miR-15a/16 expression is involved in many cancer cells. Here, miR-16 had decreased expression in NK1.1^-CD4⁺NKG2D⁺ T cells and bound with the 3'-UTR of NKG2D gene. MiR-15a/16-deficient mice had many CD4⁺NKG2D⁺ T cells, which produced TGF-β1 and IL-10 and inhibited the IFN-γ production of CD8⁺ T cells. Adoptive transfer of NK1.1^-CD4⁺NKG2D⁺ T cells from miR-15a/16-deficient mice promoted tumor growth in vivo. However, no changes for NK1.1^-CD4⁺NKG2D⁺ T cells were found in the miR-15a/16-transgenic mice. Although the miR-15a/16 transgenic mice transplanted with B16BL6 or MC38 cells exhibited rapid growth, these tumor-bearing mice did not show changes in NK1.1^-CD4⁺NKG2D⁺ T cell distributions in either spleens or tumors. When NK1.1^-CD4⁺ T cells were stimulated by α-CD3/sRAE-1 ex vivo, the NKG2D expression was difficult to induce in the T cells of miR-15a/16-transgenic mice. Finally, increased frequencies of regulatory CD4⁺NKG2D⁺ T cells with low miR-16 levels were observed in patients with late-stage colorectal cancer (Duke's C, D). Thus, miR-16 modulates NK1.1^-CD4⁺NKG2D⁺ T cell functions via targeting NKG2D. Low miR-16 expression in CD4⁺ T cells induces the regulatory CD4⁺NKG2D⁺ T subpopulation, which promotes tumor evasion via the secretion of immune-suppressive molecules.

Deficiency of miR-15a/16 upregulates NKG2D in CD8+ T cells to exacerbate dextran sulfate sodium-induced colitis

The miR-15a/16 gene cluster is located in human chromosome 13 (13q14.3) and mouse chromosome 14 (14qC3). These genes are involved in cancer development and immune regulation. Our group has previously verified the binding of the 3'-untranslated region of NKG2D gene by miR-16 through dual-luciferase reporter assay. Herein, we found that miR-16 overexpression inhibited the NKG2D expression of CD8⁺ T cells, and that CD8⁺ NKG2D⁺ T cell frequency increased in miR-15/16^-/- mice. CD8⁺ NKG2D⁺ T cells derived of miR-15/16^-/- mice displayed activatory phenotype with enhanced IFN-γ production and cytotoxicity. The transfection of lentivirus containing antago-miR-16 sequences enhanced the NKG2D expression level of CD8⁺ T cells. However, no significant differences in CD8⁺ NKG2D⁺ T cell frequencies existed between wild-type and miR-15/16-transgenic mice because NKG2D was not expressed on the rest CD8⁺ T cells. When CD8⁺ T cells of miR-15/16-transgenic mice were treated with IL-2 in vitro, the magnitude of NKG2D expression and activation of CD8⁺ T cells was lower than that of wild-type mice. miR-15/16^-/- mice showed that the exacerbation of colitis induced by dextran sulfate sodium (DSS) with more CD8⁺ T cells accumulated in inflamed colons, whereas miR-15/16-transgenic mice ameliorated DSS-induced colitis with less infiltration of CD8⁺ T cells. When NKG2D⁺ cells were depleted with NKG2D antibody in miR-15/16^-/- mice, the aggravated colitis disappeared. All these results demonstrated that NKG2D could be upregulated by decreased miR-16 in CD8⁺ T cells to mediate inflammation. Thus, gene therapy based on the overexpression of miR-16 in CD8⁺ T cells can be used for patients with inflammatory diseases.

Early growth response genes 2 and 3 induced by AP-1 and NF-κB modulate TGF-β1 transcription in NK1.1- CD4+ NKG2D+ T cells

NK1.1^- CD4⁺ NKG2D⁺ T cells are a subpopulation of regulatory T cells that downregulate the functions of CD4⁺ T, CD8⁺ T, natural killer (NK) cells, and macrophages through TGF-β1 production. Early growth response genes 2 (Egr2) and 3 (Egr3) maintain immune homeostasis by modulating T lymphocyte development, inhibiting effector T cell function, and promoting the induction of regulatory T cells. Whether Egr2 and Egr3 directly regulate TGF-β1 transcription in NK1.1^- CD4⁺ NKG2D⁺ T cells remains elusive. The expression levels of Egr2 and Egr3 were higher in NK1.1^- CD4⁺ NKG2D⁺ T cells than in NK1.1^- CD4⁺ NKG2D^- T cells. Egr2 and Egr3 expression were remarkably increased after stimulating NK1.1^- CD4⁺ NKG2D⁺ T cells with sRAE or α-CD3/sRAE. The ectopic expression of Egr2 or Egr3 resulted in the enhancement of TGF-β1 expression, while knockdown of Egr2 or Egr3 led to the decreased expression of TGF-β1 in NK1.1^- CD4⁺ NKG2D⁺ T cells. Egr2 and Egr3 directly bound with the TGF-β1 promoter as demonstrated by the electrophoretic mobility shift assay and dual-luciferase gene reporter assay. Furthermore, the Egr2 and Egr3 expression of NK1.1^- CD4⁺ NKG2D⁺ T cells could be induced by the AP-1 and NF-κB transcriptional factors, but had no involvement with the activation of NF-AT and STAT3. In conclusion, Egr2 and Egr3 induced by AP-1 and NF-κB directly initiate TGF-β1 transcription in NK1.1^- CD4⁺ NKG2D⁺ T cells. This study indicates that manipulating Egr2 and Egr3 expression would potentiate or alleviate the regulatory function of NK1.1^- CD4⁺ NKG2D⁺ T cells and this strategy could be used in the therapy for patients with autoimmune diseases or tumor.

Astilbin promotes the induction of regulatory NK1.1- CD4+ NKG2D+ T cells through the PI3K, STAT3, and MAPK signaling pathways

Astilbin is a potential agent for autoimmune and inflammatory diseases and has a protective effect in mice with DSS-induced colitis. NK1.1^- CD4⁺ NKG2D⁺ T cells are a subpopulation of regulatory T cells that produce TGF-β1 and IL-10. Whether astilbin directly promotes the induction of NK1.1^- CD4⁺ NKG2D⁺ T cells and whether these astilbin-stimulated T cells exert an immune-regulatory role remain unclear. Here, we show that astilbin efficiently induces the production of NK1.1^- CD4⁺ NKG2D⁺ T cells with high expressions of TGF-β1, IL-10, CCR6, and CCR9 in a dose-dependent manner ex vivo. These regulatory T cells also substantially inhibit the activities of CD8⁺ T cells and macrophages. Intraperitoneal injection of astilbin ameliorates the severity of colitis with an increase in the frequency of NK1.1^- CD4⁺ NKG2D⁺ T cells in the colon tissue of DSS-treated mice. Moreover, adoptive transfer of NK1.1^- CD4⁺ NKG2D⁺ T cells induced by astilbin remarkably protects against the onset of DSS-induced colitis. Finally, the PI3K, STAT3, and MAPK signaling pathways are involved in the induction of NK1.1^- CD4⁺ NKG2D⁺ T cells by astilbin. Taken together, our study elucidates a new immune-regulatory mechanism of astilbin by inducing the regulatory NK1.1^- CD4⁺ NKG2D⁺ T cells and indicates a potential clinical use of astilbin for patients with inflammatory bowel diseases.

Regulatory NK1.1-CD4+NKG2D+ subset induced by NKG2DL+ cells promotes tumor evasion in mice

Regulatory T cells play critical roles in self-tolerance and tumor evasion. CD4+NKG2D+ cells with regulatory activity are present in patients with NKG2DL+ tumors and juvenile systemic lupus erythematosus. We previously showed that TGF-β-producing CD4+NKG2D+ T cells are present in pCD86-Rae-1ε transgenic mice. Here, we performed both ex vivo and in vivo studies on pCD86-Rae-1ε transgenic mice and an MC38 tumor-bearing mouse model and show that NK1.1-CD4+NKG2D+ T cells have regulatory activity in pCD86-Rae-1ε transgenic mice. Furthermore, this T-cell subset was induced in mice transplanted with NKG2DL+ tumor cells and produced TGF-β and FasL, and secreted low amounts of IFN-γ. This T-cell subset downregulated the function of effector T cells and dendritic cells, which were abolished by anti-TGF-β antibody. In vivo, adoptive transfer of NK1.1-CD4+NKG2D+ T cells promoted TGF-β-dependent tumor growth in mice. We further found that ex vivo induction of NK1.1-CD4+NKG2D+ T cells was dependent on both anti-CD3 and NKG2DL stimulation. Furthermore, regulatory NK1.1-CD4+NKG2D+ T cells did not express Foxp3 or CD25 and expressed intermediate levels of T-bet. Western-blotting showed that STAT3 signaling was activated in NK1.1-CD4+NKG2D+ T cells of MC38 tumor-bearing and pCD86-Rae-1ε transgenic mice. In conclusion, we describe a regulatory NK1.1-CD4+NKG2D+ T-cell population, different from other regulatory T cells and abnormally elevated in pCD86-Rae-1ε transgenic and MC38 tumor-bearing mice.

The Role of Natural Killer Group 2, Member D in Chronic Inflammation and Autoimmunity

Current medicine and medical science puts great effort into elucidating the basis of chronicity and finding appropriate treatments for inflammatory diseases; however, the mechanisms driving aberrant immune responses are mostly unknown and deserve further study. Of particular interest is the identification of checkpoints that regulate the function and differentiation of pro-inflammatory cells during pathogenesis, along with means of their modulation for therapeutic purposes. Natural killer group 2, member D (NKG2D) is a potent activator of the immune system, known as a sensor for “induced-self” ligands, i.e., cellular danger signals that, in the context of chronic inflammation and autoimmunity, can be presented by cells being exposed to an inflammatory cytokine milieu, endoplasmic reticulum stress, or cell death. Engagement by such ligands can be translated by NKG2D into activation or co-stimulation of NK cells and different subsets of T cells, respectively, thus contributing to the regulation of the inflammatory response. In this review, we discuss the current knowledge on the contribution of the NKG2D–NKG2DL signaling axis during intestinal inflammation, type 1 diabetes, multiple sclerosis, and rheumatoid arthritis, where the role of NKG2D has been associated either by aberrant expression of the receptor and its ligands and/or by functional data in corresponding mouse models.

TGF-β1 expression in regulatory NK1.1-CD4+NKG2D+ T cells dependents on the PI3K-p85α/JNK, NF-κB and STAT3 pathways

NK1.1^-CD4⁺NKG2D⁺ cells exert their immune-regulatory function in tumor as an unconventional regulatory T cell subset through the production of TGF-β1; however, the molecular mechanisms involving with the activation of nuclear factors for TGF-β1 transcription remain unclear. Here we determined that the PI3K-p85α subunit was specifically activated in NK1.1^-CD4⁺NKG2D⁺ cells following an 8-hour stimulation by sRAE-1 or α-CD3/sRAE-1, subsequently leading to the activation of PI3K-p110, Akt, and JNK. On the contrary, α-CD3/α-CD28 stimulation did not induce the activation of PI3K-p85 and JNK. Consequently, activation of the nuclear transcription factor AP-1 as a consequence of JNK activation regulated TGF-β1 expression in NK1.1^-CD4⁺NKG2D⁺ cells. Furthermore, activation of NF-κB in NK1.1^-CD4⁺NKG2D⁺ cells resulted from both protein kinase C activation downstream of TCR/CD3 signaling and PI3K activation induced by NKG2D engagement. The STAT3-Y705 phosphorylation, as activated by PI3K, under stimulations of the sRAE-1 or α-CD3/sRAE-1 also contributed to the TGF-β1 expression in NK1.1^-CD4⁺NKG2D⁺ cells. Moreover, ChIP assay confirmed that STAT3 was capable of binding with the promoter regions of TGF-β1. In conclusion, our data showed that the TGF-β1 transcription in NK1.1^-CD4⁺NKG2D⁺ cells induced by sRAE-1 or α-CD3/sRAE-1 was involved with the AP-1, NF-κB, and STAT3 signaling pathways; therefore, regulation of AP-1, NF-κB, and STAT3 activation may play important roles in the development and function of NK1.1^-CD4⁺NKG2D⁺ cells.

Formononetin Administration Ameliorates Dextran Sulfate Sodium-Induced Acute Colitis by Inhibiting NLRP3 Inflammasome Signaling Pathway

Formononetin is a kind of isoflavone compound and has been reported to possess anti-inflammatory properties. In this present study, we aimed to explore the protective effects of formononetin on dextran sulfate sodium- (DSS-) induced acute colitis. By intraperitoneal injection of formononetin in mice, the disease severity of colitis was attenuated in a dose-dependent manner, mainly manifesting as relieved clinical symptoms of colitis, mitigated colonic epithelial cell injury, and upregulations of colonic tight junction proteins levels (ZO-1, claudin-1, and occludin). Meanwhile, our study found that formononetin significantly prevented acute injury of colonic cells induced by TNF-α in vitro, specifically manifesting as the increased expressions of colonic tight junction proteins (ZO-1, claudin-1, and occludin). In addition, the result showed that formononetin could reduce the NLRP3 pathway protein levels (NLRP3, ASC, IL-1β) in vivo and vitro, and MCC950, the NLRP3 specific inhibitor, could alleviate the DSS-induced mice acute colitis. Furthermore, in the foundation of administrating MCC950 to inhibit activation of NLRP3 inflammasome, we failed to observe the protective effects of formononetin on acute colitis in mice. Collectively, our study for the first time confirmed the protective effects of formononetin on DSS-induced acute colitis via inhibiting the NLRP3 inflammasome pathway activation.