Role of nuclear factor of activated T cell (NFAT) transcription factors in skin and vascularized cardiac allograft rejection

The Transcription Factor NFATc1 Supports the Rejection of Heterotopic Heart Allografts

The immune suppressants cyclosporin A (CsA) and tacrolimus (FK506) are used worldwide in transplantation medicine to suppress graft rejection. Both CsA and FK506 inhibit the phosphatase calcineurin (CN) whose activity controls the immune receptor-mediated activation of lymphocytes. Downstream targets of CN in lymphocytes are the nuclear factors of activated T cells (NFATs). We show here that the activity of NFATc1, the most prominent NFAT factor in activated lymphocytes supports the acute rejection of heterotopic heart allografts. While ablation of NFATc1 in T cells prevented graft rejection, ectopic expression of inducible NFATc1/αA isoform led to rejection of heart allografts in recipient mice. Acceptance of transplanted hearts in mice bearing NFATc1-deficient T cells was accompanied by a reduction in number and cytotoxicity of graft infiltrating cells. In CD8⁺ T cells, NFATc1 controls numerous intracellular signaling pathways that lead to the metabolic switch to aerobic glycolysis and the expression of numerous lymphokines, chemokines, and their receptors, including Cxcr3 that supports the rejection of allogeneic heart transplants. These findings favors NFATc1 as a molecular target for the development of new strategies to control the cytotoxicity of T cells upon organ transplantation.

Chelerythrine ameliorates acute cardiac allograft rejection in mice

The improvement in graft survival over the past decade has been mainly due to calcineurin inhibitors, which interfere with the calcium-mediated pathway. Recently, other pathways such as those mediated by protein kinase C (PKC) are coming into view. The purpose of this study was to assess the immunosuppressive properties of chelerythrine, a specific PKC inhibitor, in preventing acute rejection in murine heterotopic heart transplantation. Mice were randomly divided into control and chelerythrine treated group. The control group received PBS while the chelerythrine treated group was given intraperitoneal injection doses (1, 5, 10mg/kg) of chelerythrine from day 0 to day 14 after heart transplantation. Six days after transplantation, cardiac allografts were harvested for further tests. The mean survival time (MST) of the cardiac allograft in untreated animals was 8days while graft MSTs observed in chelerythrine treated group was 13 and 23days at 5 and 10mg/kg treatment doses, respectively (P<0.05). Histologic assessment of the allograft in chelerythrine group showed a significant decline in histologic rejection score, as well as CD4+ and CD8+ T cell infiltration and ICAM-1+ endothelial cell activation. Down-regulation of Th1/Th2 cytokine expression was observed in chelerythrine treatment group. Meanwhile, chelerythrine was also found to inhibit the dephosphorylation of phosphorylated nuclear factor of activated T cells (NFAT) protein 1 and 4.

NFAT inhibitor tributylhexadecylphosphoniumbromide, ameliorates high fructose induced insulin resistance and nephropathy

High fructose diet (HFrD)-induced insulin resistance (IR) has been reported to be associated with an increase in albuminuria, glomerular hypertrophy and inflammation in kidney. However, the molecular mechanisms associated with high fructose-induced IR and renal dysfunction are still unclear. In the present study, we have investigated the role of nuclear factor of activated T-cell (NFAT) and its inhibitor, Tributylhexadecylphosphoniumbromide (THPB) in high fructose-induced IR and renal injury. NFAT inhibition by THPB treatment significantly improved HFrD-induced insulin resistance. Treatment with THPB markedly reduced high fructose diet-induced protein expression of NFATc4, PTEN and also alleviated expression of inflammatory markers in kidneys of HFrD rats. Further, THPB treatment not only improved acute ANG II responses but also repressed the processes of renal fibrosis, ECM accumulation, foot process effacement and renal apoptosis in HFrD rats. Taken together, we for the first time provide evidence that HFrD -induced insulin resistance and renal injury is associated with dysregulated NFATc4/PTEN signalling and THPB prevents this dysregulation through inhibition of NFATc4. Thus, targeting NFATc4 can be a novel therapeutic approach for preventing HFrD induced- IR and renal injury.

A CB2-Selective Cannabinoid Suppresses T-Cell Activities and Increases Tregs and IL-10

We have previously shown that agonists selective for the cannabinoid receptor 2 (CB2), including O-1966, inhibit the Mixed Lymphocyte Reaction (MLR), an in vitro correlate of organ graft rejection, predominantly through effects on T-cells. Current studies explored the mechanism of this immunosuppression by O-1966 using mouse spleen cells. Treatment with O-1966 dose-relatedly decreased levels of the active nuclear forms of the transcription factors NF-κB and NFAT in wild-type T-cells, but not T-cells from CB2 knockout (CB2R k/o) mice. Additionally, a gene expression profile of purified T-cells from MLR cultures generated using a PCR T-cell activation array showed that O-1966 decreased mRNA expression of CD40 ligand and CyclinD3, and increased mRNA expression of Src-like-adaptor 2 (SLA2), Suppressor of Cytokine Signaling 5 (SOCS5), and IL-10. The increase in IL-10 was confirmed by measuring IL-10 protein levels in MLR culture supernatants. Further, an increase in the percentage of regulatory T-cells (Tregs) was observed in MLR cultures. Pretreatment with anti-IL-10 resulted in a partial reversal of the inhibition of proliferation and blocked the increase of Tregs. Additionally, O-1966 treatment caused a dose-related decrease in the expression of CD4 in MLR cultures from wild-type, but not CB2R k/o, mice. These data support the potential of CB2-selective agonists as useful therapeutic agents to prolong graft survival in transplant patients, and strengthens their potential as a new class of immunosuppressive agents with broader applicability.

Inflammatory signalling associated with brain dead organ donation: from brain injury to brain stem death and posttransplant ischaemia reperfusion injury

Brain death is associated with dramatic and serious pathophysiologic changes that adversely affect both the quantity and quality of organs available for transplant. To fully optimise the donor pool necessitates a more complete understanding of the underlying pathophysiology of organ dysfunction associated with transplantation. These injurious processes are initially triggered by catastrophic brain injury and are further enhanced during both brain death and graft transplantation. The activated inflammatory systems then contribute to graft dysfunction in the recipient. Inflammatory mediators drive this process in concert with the innate and adaptive immune systems. Activation of deleterious immunological pathways in organ grafts occurs, priming them for further inflammation after engraftment. Finally, posttransplantation ischaemia reperfusion injury leads to further generation of inflammatory mediators and consequent activation of the recipient's immune system. Ongoing research has identified key mediators that contribute to the inflammatory milieu inherent in brain dead organ donation. This has seen the development of novel therapies that directly target the inflammatory cascade.

MicroRNA-155 regulates T cell proliferation through targeting GSK3β in cardiac allograft rejection in a murine transplantation model

Here we investigated the activity and regulation of miR-155 during cardiac allograft rejection (AR), and to examine the feasibility of using miR-155 as a biomarker of graft status. Expression of miR-155 in graft-infiltrating lymphocytes (GIL), T cells isolated from spleen (TFS), and lymphocytes separated from blood (LFB) was significantly increased during cardiac AR while GSK3β was downregulated in GIL and TFS. Inhibition of miR-155 impaired lymphocyte proliferation and enhanced the expression of GSK3β. Moreover, pharmacological inactivation of GSK3β resulted in rescue of the proliferative capability of T cells pretreated with a miR-155 inhibitor. Luciferase reporter assay confirmed that miR-155 interacted with the 3'-untranslated region (UTR) of GSK3β directly. In particular, the miR-155 in LFB can distinguish recipients with AR from syngeneic controls from POD 3 and later. The present study provides a better understanding of the pathophysiological process underlying cardiac AR progression.