Modulation of NLRP3 inflammasome through formyl peptide receptor 1 (Fpr-1) pathway as a new therapeutic target in bronchiolitis obliterans syndrome

Chronic rejection is the major leading cause of morbidity and mortality after lung transplantation. Bronchiolitis obliterans syndrome (BOS), a fibroproliferative disorder of the small airways, is the main manifestation of chronic lung allograft rejection. We investigated, using transgenic mice, the mechanisms through which the deficiency of IL-1β/IL-18, Casp-1, or Fpr-1 genes could be protective in an experimental model of BOS, induced in mice by allogeneic heterotopic tracheal transplantation. Fpr-1 KO mice showed a marked reduction in histological markers of BOS and of mast cell numbers compared to other groups. Molecular analyses indicated that the absence of the Fpr-1 gene was able to decrease NF-κB nuclear translocation and modulate NLRP3 inflammasome signaling and the mitogen-activated protein kinase (MAPK) pathway in a more significant way compared to other groups. Additionally, Fpr-1 gene deletion caused a reduction in resistance to the apoptosis, assessed by the TUNEL assay. Immunohistochemical analyses indicated changes in nitrotyrosine, PARP, VEGF, and TGF-β expression associated with the pathology, which were reduced in the absence of the Fpr1 gene more so than by the deletion of IL-1β/IL-18 and Casp-1. We underline the importance of the NLRP3 inflammasome and the pathogenic role of Fpr-1 in experimental models of BOS, which is the result of the modulation of immune cell recruitment together with the modulation of local cellular activation, suggesting this gene as a new target in the control of the pathologic features of BOS.