The role of stromal and immune cells in atrial disease [II]

In atrial fibrillation, disturbed electrical conduction disrupts the coordinated contraction of the heart's antechambers, increasing the risk of stroke and heart failure. The rising prevalence of this disease approaches 9% in patients >65 years. Studying freshly isolated human atrial tissue and a new mouse model, we here decipher how immune and stromal cells contribute to the structural tissue remodeling that underlies atrial fibrillation. Single-cell transcriptomes from control and diseased human atria documented macrophage doubling at the expense of endothelial and mural cells. An inflammatory monocyte and a pro-fibrotic SPP1+ macrophage cluster expanded in patients with atrial fibrillation. To experimentally perturb pathways observed in patients, we matched their risk factors Hypertension, Obesity and Mitral valvE Regurgitation (HOMER) in mice. Atrial single-cell transcriptomes obtained in HOMER mice, which developed enlarged, fibrillation-prone atria, recapitulated human cell composition and transcriptome variations. Recruitment drove the expansion of atrial macrophages; accordingly, inhibition of monocyte migration reduced arrhythmia in Ccr2-/- HOMER mice. Deleting Spp1 established macrophage-derived osteopontin as a pleiotropic signal that promotes atrial fibrillation through pro-fibrotic, inflammatory crosstalk with an arsenal of local immune and stromal cells. Taken together, we identify SPP1+ macrophages as targets for immunomodulatory therapy in atrial fibrillation. Overall design: Single-cell mRNA sequencing was used to investigate the transcriptomic differences between non-cardiomyocytes FACS-purified from left atrial tissues collected from 2 C57BL/6 bone marrow transplanted (BMT) and 2 Spp1-/- BMT mice exposed to Hypertension, Obesity and Mitral valvE Regurgitation (HOMER).

心房颤动（atrial fibrillation）发作时，紊乱的电传导会破坏心脏心房的协同收缩功能，提升脑卒中（stroke）与心力衰竭（heart failure）的发病风险。该疾病的患病率逐年攀升，在65岁以上人群中已接近9%。
本研究借助新鲜分离的人类心房组织与新型小鼠模型，解析免疫细胞与基质细胞如何参与心房颤动背后的组织结构重塑过程。
对对照组与患病组人类心房开展的单细胞转录组（single-cell transcriptomes）分析显示，巨噬细胞（macrophage）数量翻倍，以内皮细胞（endothelial cells）与壁细胞（mural cells）的减少为代价。心房颤动患者体内，炎性单核细胞与促纤维化SPP1+巨噬细胞亚群发生扩增。
为在实验层面干预患者体内观察到的信号通路，我们在小鼠中复刻了其三大核心风险因素：高血压（Hypertension）、肥胖（Obesity）与二尖瓣反流（Mitral valvE Regurgitation，简称HOMER）。对成功构建该造模模型、出现心房扩大且易诱发颤动的HOMER小鼠开展心房单细胞转录组分析，其细胞组成与转录组变化均可复现人类患者的特征。
单核细胞的招募驱动了心房巨噬细胞的扩增；相应地，抑制单核细胞迁移可减轻Ccr2基因敲除（Ccr2-/-）的HOMER小鼠的心律失常症状。
敲除Spp1基因证实，巨噬细胞来源的骨桥蛋白（osteopontin）是一种多效性信号分子，可通过与多种局部免疫及基质细胞发生促纤维化、促炎性串扰，进而促进心房颤动的发生发展。
综上，本研究认定SPP1+巨噬细胞可作为心房颤动免疫调节治疗的潜在靶点。
整体实验设计：本研究采用单细胞mRNA测序技术，对暴露于高血压、肥胖与二尖瓣反流（HOMER）造模条件的2只C57BL/6骨髓移植（BMT）小鼠及2只Spp1基因敲除骨髓移植（Spp1-/- BMT）小鼠的左心房组织中，经荧光激活细胞分选（FACS）纯化的非心肌细胞的转录组差异进行分析。