Macrophages directly contribute collagen to scar formation during zebrafish heart regeneration and mouse heart repair

Canonical roles for macrophages in mediating the fibrotic response after a heart attack (myocardial infarction) include turnover of the extracellular matrix and activation of cardiac fibroblasts to initiate collagen deposition. Here we reveal through studying the functional kinetics of fibrosis during zebrafish heart regeneration and mouse heart repair that macrophages can directly contribute collagen to the forming scar. Unbiased transcriptomics revealed an up-regulation of collagen isoforms in both zebrafish and mouse macrophages following injury. Adoptive transfer of macrophages from collagen-tagged transgenic zebrafish and splenic monocyte-derived macrophages from adult mouse GFPtpz-collagen donors, enhanced scar formation and induced fibrosis, respectively, via cell autonomous production of collagen. In zebrafish, macrophage-specific targeting of collagen 4a binding protein and cognate collagen 4a1 followed by transfer led to significantly reduced scarring in cryo-injured hosts. These findings contrast with the current model of scarring whereby collagen deposition is exclusively attributed to myofibroblasts, and implicate macrophages as direct contributors to fibrosis during heart repair. Whole nuclear transcriptome profiling of macrohages in response to 2 types of heart injury (ventricular resection and cryo-injury) at 3 different stages of regenerative process in the zebrafish heart.

巨噬细胞(macrophage)在介导心脏病发作（心肌梗死，myocardial infarction）后的纤维化反应中，其经典功能包括细胞外基质(extracellular matrix)重塑，以及激活心脏成纤维细胞(fibroblasts)以启动胶原沉积(collagen deposition)。本研究通过解析斑马鱼(zebrafish)心脏再生与小鼠(mouse)心脏修复过程中纤维化的功能动力学特征，揭示巨噬细胞可直接为新生瘢痕组织提供胶原。无偏倚转录组学(transcriptomics)分析显示，损伤刺激后，斑马鱼与小鼠巨噬细胞内的胶原亚型(collagen isoforms)表达均显著上调。本研究分别采用胶原标记的转基因斑马鱼巨噬细胞，以及成年小鼠GFPtpz-胶原(GFPtpz-collagen)供体的脾脏单核细胞源性巨噬细胞(splenic monocyte-derived macrophages)开展过继转移(adoptive transfer)实验，结果证实二者可分别通过细胞自主性(cell autonomous)胶原合成，促进瘢痕形成与纤维化进程。在斑马鱼模型中，靶向巨噬细胞的胶原4a结合蛋白(collagen 4a binding protein)及其同源胶原4a1(collagen 4a1)并进行细胞转移后，可显著降低冷冻损伤(cryo-injury)宿主的瘢痕形成程度。上述研究结果与当前认为胶原沉积仅由肌成纤维细胞(myofibroblasts)介导的瘢痕形成经典模型相悖，并证实巨噬细胞是心脏修复过程中纤维化的直接贡献者。本数据集涵盖斑马鱼心脏再生过程中三个不同阶段，响应心室切除(ventricular resection)与冷冻损伤两种心脏损伤的巨噬细胞全核转录组(whole nuclear transcriptome)分析数据。