Supplementary Material for: Formyl peptide receptor type 2 (FPR2) deficiency in myeloid cells amplifies sepsis-induced cardiac dysfunction

Using a global formyl-peptide receptor (Fpr)2 knockout mouse colony, we have reported the modulatory properties of this pro-resolving receptor in polymicrobial sepsis. Herein, we have used a humanized FPR2 (hFPR2) mouse colony bearing an intact or a selective receptor deficiency in myeloid cells to dwell on the cellular mechanisms. hFPR2 mice and myeloid cell-specific hFPR2 KO (abbreviated to KO) mice were subjected to cecal ligation and puncture (CLP)-induced polymicrobial sepsis. Compared with hFPR2 mice, CLP caused exacerbated cardiac dysfunction (assessed by echocardiography), worsened clinical outcome and impaired bacteria clearance in KO mice. This pathological scenario was paralleled by increased recruitment of pro-inflammatory monocytes and reduced M2-like macrophages within the KO hearts. In peritoneal exudates of KO mice, we quantified increased neutrophil and MHC II+ macrophage numbers, but decreased monocyte/macrophage and MHC II- macrophage recruitment. hFPR2 up-regulation was absent in myeloid cells and local production of lipoxin A4 was reduced in septic KO mice. Administration of the FPR2 agonist Annexin A1 (AnxA1) improved cardiac function in hFPR2 septic mice, but had limited beneficial effects in KO mice, in which the FPR2 ligand failed to polarize macrophages towards an MHC II- phenotype. In conclusion, FPR2 deficiency in myeloid cells exacerbates cardiac dysfunction and worsens clinical outcome in polymicrobial sepsis. The improvement of cardiac function and the host immune response by AnxA1 is more effective in hFPR2 competent septic mice.

本研究团队曾利用全局甲酰肽受体2（formyl-peptide receptor 2, Fpr2）敲除小鼠群，报道了该促分解受体在多微生物脓毒症中的调控特性。本研究采用携带完整髓系细胞FPR2或髓系细胞选择性受体缺陷的人源化FPR2（humanized FPR2, hFPR2）小鼠群，深入探究其细胞层面的作用机制。我们对hFPR2小鼠及髓系细胞特异性hFPR2敲除（下文简称KO）小鼠实施盲肠结扎穿刺（cecal ligation and puncture, CLP）以构建多微生物脓毒症模型。与hFPR2小鼠相比，KO小鼠经CLP造模后心功能不全程度加重（经超声心动图评估）、临床结局更差且细菌清除能力受损。该病理状态伴随KO小鼠心脏内促炎性单核细胞招募增多、M2样巨噬细胞浸润减少。在KO小鼠的腹腔渗出液中，我们检测到中性粒细胞及MHC II阳性巨噬细胞数量增加，但单核细胞/巨噬细胞及MHC II阴性巨噬细胞的招募量降低。脓毒症KO小鼠的髓系细胞中未出现hFPR2的上调表达，且局部脂氧素A4的生成量减少。给予FPR2激动剂膜联蛋白A1（Annexin A1, AnxA1）可改善hFPR2脓毒症小鼠的心功能，但对KO小鼠的获益效果有限——该模型中FPR2配体无法将巨噬细胞极化为MHC II阴性表型。综上，髓系细胞的FPR2缺陷会加重多微生物脓毒症小鼠的心功能损伤并恶化其临床结局。AnxA1对心功能及宿主免疫应答的改善作用，在具备功能性hFPR2的脓毒症小鼠中效果更为显著。