Abstract 1765: Immunosuppressive Potential of Ibp - A Novel Inhibitor of the Calcineurin/NF-AT Cascade

Abstract

Background: The calcineurin (Cn)/NF-AT signaling cascade plays a crucial role during T-cell activation and development of myocardial hypertrophy. We previously demonstrated that, in addition to NF-AT, Cn is translocated to the nucleus. We also developed a synthetic peptide (IBP) which inhibited the nuclear import of Cn without affecting calcineurin phosphatase activity. The antihypertrophic effect of IBP on the rat myocardium was shown in vivo and in vitro . Here we extended our studies on a potential use of IBP in the prevention of transplant rejection. Methods and results: Coimmunoprecipitation experiments revealed that the synthetic IBP peptide, which is identical to the nuclear localization sequence of calcineurin, disrupts importin/calcineurin interaction. We further demonstrated that inhibition of the importin/calcineurin interaction by the small competitive peptide (IBP) is sufficient to inactivate the calcineurin/NF-AT signaling cascade. Inhibitory effects of IBP on T-cell activation were analyzed by [H 3 ]-thymidine incorporation (7135 ± 2503 vs. 2957 ± 1161 [%]) in activated T-cells in vitro (dentritic cells were used as antigen stimulation). To verify immunosuppressive effect of IBP in vitro , heterotopic heart transplantations were performed on rats. Following transplantation rats were treated with IBP (i.p. 130mg/kg/d) or peanut oil as control (i.p. 1 ml peanut oil/d) for 14 days. Time until transplant rejection was significantly prolonged in IBP treated animals compared to control group (15.2 ± 1.5 day vs. 4 ± 2.8 day; n = 8; p < 0.05). Immunohistochemical studies from transplanted hearts demonstrated that the synthetic calcineurin inhibitory peptide IBP prevented calcineurin nuclear translocation in infiltrating T cells in the donor hearts. Conclusions: The synthetic inhibitory peptide IBP disrupts the calcineurin/NF-AT cascade by inhibition of Cn nuclear import. This suppresses T-cell activation in vitro and in vivo, thereby revealing a potential use of IBP as novel agent to protect donor organs from rejection.