Simulated microgravity increases CD226+ Lin- CD117- Sca1+ mesenchymal stem cells in mice

Microgravity is one of the most common causes counting for the bone loss. Mesenchymal stem cells (MSCs) contribute greatly to the differentiation and function of bone related cells. The development of novel MSCs biomarkers is critical for implementing effective therapies for microgravity induced bone loss. We aimed to find the new molecules involved in the differentiation and function of MSCs in mouse simulated microgravity model. We found CD226 was preferentially expressed on a subset of MSCs. Simulation of microgravity treatment significantly increased the proportion of CD226+ Lin- CD117- Sca1+ MSCs. The CD226+ MSCs produced higher IL-6, M-CSF, RANKL and lower CD200 expression, and promoted osteoclast differentiation. This study provides pivotal information to understand the role of CD226 in MSCs, and inspires new ideas for prevention of bone loss related diseases.

Costimulatory Molecule CD226 Regulates Atopic Dermatitis in a Mouse Model

This study investigated the role of CD226 in a 2,4-dinitrochlorobenzene (DNCB)-induced mouse model of atopic dermatitis. The results showed that the lack of CD226 (global and CD4+ T-cell specific) significantly increased ear thickness, reddening, swelling, and scaling of the skin as well as inflammatory cell and mast cell infiltration. RT-qPCR results demonstrated that the mRNA expressions of atopic dermatitis-related inflammatory cytokines and chemokines were markedly increased in the draining lymph nodes and lesioned ear skin tissues of global and CD4+ T-cell-specific CD226-deficient mice compared with that in control mice. In vitro assessment revealed that CD226 directly modulates TGFβ-mediated regulatory T (Treg) cell differentiation and proliferation. Notably, Treg cell-specific deletion of CD226 (Cd226fl/flFoxp3cre mice) resulted in more severe dermatitis and epidermal thickening than those observed in littermate mice upon DNCB treatment. Subsequent analysis showed that the infiltration of Treg cells in ear lesions and the number of Tregs in the spleen were significantly reduced in Cd226fl/flFoxp3cre mice after DNCB treatment. In addition, the lack of CD226 induced apoptosis of Treg cells through the activation of caspase 3. Therefore, these results suggest that CD226 has potential efficacy in atopic dermatitis, correlating with Treg cell inhibition.

The Effect of CD226 on the Balance between Inflammatory Monocytes and Small Peritoneal Macrophages in Mouse Ulcerative Colitis

Ulcerative colitis (UC) is a refractory and recurring inflammatory bowel disease (IBD). Monocytes and macrophages are major components of the mononuclear phagocyte system (MPS), and the balance between inflammatory monocytes and small peritoneal macrophages plays important roles in UC. However, the mechanisms governing the balance between inflammatory monocytes and small peritoneal macrophages in UC need to be clarified further. Here, we found that the expression levels of CD226 on different subsets of monocytes/macrophages are varied in UC mice. The expression levels of CD226 on patrolling monocytes (pMos) and small peritoneal macrophages (SPMs) were markedly increased, while the expression levels of CD226 on inflammatory monocytes (iMos) were decreased in UC mice. Significantly, the percentage of iMos was enhanced while the percentage of SPMs were decreased in CD226 knockout UC mice compared with that in wildtype UC mice. Moreover, CD226 deficiency suppressed the migration capacity of macrophages. Therefore, our data suggest that CD226 plays critical roles in regulating the function and balance of monocytes/macrophages in mouse UC and targeting CD226 in MPS may be developed as a potent therapy for UC.

CD226 deficiency attenuates the homeostasis and suppressive capacity of Tr1 cells

T regulatory type 1 (Tr1) cells act as a key regulator in maintaining peripheral immune tolerance. Several costimulatory molecules for T cells have been identified in Tr1 cells, but their intrinsic functions are still unclear. Here we showed CD226 was highly expressed in Tr1 cells. CD226-deficient Tr1 cells were defective in proliferation and sensitive to apoptosis. In addition, CD226-deficient Tr1 cells showed lower inhibitory capacity of T cell proliferation and reduced IL-10 production. CD226 deficiency also inhibited Tr1 cell differentiation in vitro. When stimulated with IL-2, CD226-deficient Tr1 cells showed impaired STAT5 signaling. Therefore, our data suggest CD226 might play an important role in Tr1 cell homeostasis, function and differentiation. This study facilitates further biological characterization of this regulatory T cell subset.

CD226 Deletion Reduces Type 1 Diabetes in the NOD Mouse by Impairing Thymocyte Development and Peripheral T Cell Activation

The costimulatory molecule CD226 is highly expressed on effector/memory T cells and natural killer cells. Costimulatory signals received by T cells can impact both central and peripheral tolerance mechanisms. Genetic polymorphisms in CD226 have been associated with susceptibility to type 1 diabetes and other autoimmune diseases. We hypothesized that genetic deletion of Cd226 in the non-obese diabetic (NOD) mouse would impact type 1 diabetes incidence by altering T cell activation. CD226 knockout (KO) NOD mice displayed decreased disease incidence and insulitis in comparison to wild-type (WT) controls. Although female CD226 KO mice had similar levels of sialoadenitis as WT controls, male CD226 KO mice showed protection from dacryoadenitis. Moreover, CD226 KO T cells were less capable of adoptively transferring disease compared to WT NOD T cells. Of note, CD226 KO mice demonstrated increased CD8⁺ single positive (SP) thymocytes, leading to increased numbers of CD8⁺ T cells in the spleen. Decreased percentages of memory CD8⁺CD44⁺CD62L^- T cells were observed in the pancreatic lymph nodes of CD226 KO mice. Intriguingly, CD8⁺ T cells in CD226 KO mice showed decreased islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-tetramer and CD5 staining, suggesting reduced T cell receptor affinity for this immunodominant antigen. These data support an important role for CD226 in type 1 diabetes development by modulating thymic T cell selection as well as impacting peripheral memory/effector CD8⁺ T cell activation and function.

Role of Co-stimulatory Molecules in T Helper Cell Differentiation

CD4⁺ T cells play a central role in orchestrating the immune response to a variety of pathogens but also regulate autoimmune responses, asthma, allergic responses, as well as tumor immunity. To cover this broad spectrum of responses, naïve CD4⁺ T cells differentiate into one of several lineages of T helper cells, including Th1, Th2, Th17, and T_FH, as defined by their cytokine pattern and function. The fate decision of T helper cell differentiation integrates signals delivered through the T cell receptor, cytokine receptors, and the pattern of co-stimulatory signals received. In this review, we summarize the contribution of co-stimulatory and co-inhibitory receptors to the differentiation and maintenance of T helper cell responses.

Differences in B7 and CD28 family gene expression in the peripheral blood between newly diagnosed young-onset and adult-onset type 1 diabetes patients

Type-1 diabetes (T1D) is a heterogeneous autoimmune disease, and there are pathogenetic differences between young- and adult-onset T1D patients. We hypothesized that the expressions of genes involved in costimulatory immune system pathways in peripheral blood are differently regulated in young- and adult-onset T1D. Study group I consisted of 80 children, adolescents, and young adults (age range 1.4-21.4 y; 31 controls and 49 T1D patients). Study group II consisted of 48 adults (age range 22.0-78.4 y; 30 controls and 18 T1D patients). The mRNA expression levels of CD86, CD28, CD25, CD226, CD40, BTLA, GITR, PDCD1, FoxP3, TGF-β, ICOS, sCTLA4, flCTLA4, and CD80 were measured in peripheral blood. Genetic polymorphisms (HLA haplotypes; rs231806, rs231775, and rs3087243 in CTLA4; rs763361 in CD226; and rs706778 in CD25) and T1D-associated autoantibodies were analyzed. In group I, there was significantly lower expression of CD226 in T1D patients than in the controls. In group II, there were significantly higher expression levels of CD86 and TGF-β in T1D patients than in the controls. In the T1D patients in group I, the upregulated CD80 expression correlated with the expression of both CTLA4 splice variants (sCTLA4 and flCTLA4). In contrast, in group II, upregulated CD86 correlated with TGF-β and CD25. In group I, the inhibitory CD80-CTLA4 pathway was activated, whereas, in group II, the activation CD86-CD28 pathway and TGF-β production were activated. These results emphasize the differences between young-onset and adult-onset T1D in the regulation of costimulatory pathways. These differences should be considered when developing novel treatments for T1D.

CD226 interaction with CD155 impacts on retention and negative selection of CD8 positive thymocytes as well as T cell differentiation to follicular helper cells in Peyer's Patches

The immunoglobulin-like glycoprotein CD226 represents a receptor activating cytotoxic T and NK cells taking part in tumour surveillance. In addition, CD226 is involved in the differentiation of naïve CD4(+) T cells into effector cells. CD155 that is widely over-expressed on tumour cells, was identified as a counter-receptor of CD226 rendering many cancer cells sensitive to NK driven elimination. However, CD155 was also assigned a role in the establishment of follicular helper T cells in the small intestine and the final maturation of CD8 positive thymocytes. Here we show that mice lacking CD226 are distinguished by virtually identical phenotypes as already reported for CD155 deficient mice: a paucity of follicular helper T cells in Peyer's Patches and of terminally matured CD8 T cells in thymus. Moreover, like CD155, CD226 is involved in negative selection of CD8 thymocytes. These observations establish a firm link between the functions of CD155 and CD226 in several T cell differentiation steps.

Differential genomic targeting of the transcription factor TAL1 in alternate haematopoietic lineages

Expression of the basic helix-loop-helix transcription factor TAL1/SCL is required for erythrocyte differentiation; aberrant expression in lymphoid cells leads to oncogenic transformation. Here, global analysis of TAL1 binding in erythroid and malignant T cells identifies cell type specific functional interaction with the transcription factors RUNX and ETS1.

TAL1/SCL is a master regulator of haematopoiesis whose expression promotes opposite outcomes depending on the cell type: differentiation in the erythroid lineage or oncogenesis in the T-cell lineage. Here, we used a combination of ChIP sequencing and gene expression profiling to compare the function of TAL1 in normal erythroid and leukaemic T cells. Analysis of the genome-wide binding properties of TAL1 in these two haematopoietic lineages revealed new insight into the mechanism by which transcription factors select their binding sites in alternate lineages. Our study shows limited overlap in the TAL1-binding profile between the two cell types with an unexpected preference for ETS and RUNX motifs adjacent to E-boxes in the T-cell lineage. Furthermore, we show that TAL1 interacts with RUNX1 and ETS1, and that these transcription factors are critically required for TAL1 binding to genes that modulate T-cell differentiation. Thus, our findings highlight a critical role of the cellular environment in modulating transcription factor binding, and provide insight into the mechanism by which TAL1 inhibits differentiation leading to oncogenesis in the T-cell lineage.