Activation of the Immunoregulatory Cation Channel TMEM176B by a Nitroalkene Derivative of Salicylate Prolongs Graft Survival

Background. Targeting emerging immunoregulatory molecules may open new therapeutic perspectives to control alloresponses and alleviate the burden of immunosuppressors. Transmembrane protein 176B (TMEM176B) is an intracellular cation channel highly expressed by myeloid cells. We have shown that TMEM176B is associated with allograft tolerance. Moreover, it controls the tolerogenic function of dendritic cells and inhibits NOD-, LRR-, and pyrin domain-containing protein 3 inflammasome. Here, we speculated that pharmacological activation of TMEM176B by the nitroalkene derivative of 5-(2-nitroethenyl) salicylic acid (SANA) may prolong allograft survival through active immunoregulatory mechanisms. Methods. SANA impact on TMEM176B activity was studied in vitro and in vivo. We assessed the potential efficacy of SANA treatment in prolonging graft survival in 2 allograft models: a mouse skin model with minor mismatches and a rat heart model with fully mismatches. Wild type and Tmem176b −/− recipient mice were used. Graft survival and innate and adaptive immune response were analyzed at the skin graft and draining lymph nodes through flow cytometry studies. Results. SANA was identified as an activator of TMEM176B-dependent ion transport. SANA prolongs allograft survival in a Tmem176b -dependent manner. SANA triggered the expression of the immunoregulatory enzyme heme oxygenase-1 in wild type but not in Tmem176b −/− MHCII + CD11c high CD11b + conventional dendritic cells within the graft. SANA therapy was associated with increased CD4 + Forkhead box P3 + regulatory T (Treg) in the graft. The heme oxygenase-1 inhibitor tin protoporphyrin IX completely blocked the effect of SANA on graft survival and Treg in vivo. Furthermore, Treg modulation by anti-CD3 antibodies improves the graft-protecting effect of SANA. Conclusions. SANA-mediated activation of TMEM176B triggers an immunoregulatory pathway that prolongs skin and heart graft survival.