Increased cardiac macrophages in Sorbs2-deficient hearts: revealing a potential role for macrophage in responding to embryonic myocardial abnormalities

Macrophages are known to support cardiac development and homeostasis, contributing to tissue remodeling and repair in the adult heart. However, it remains unclear whether embryonic macrophages also respond to abnormalities in the developing heart. Previously, we reported that the structural protein Sorbs2 promotes the development of the second heart field, with its deficiency resulting in atrial septal defects (ASD). In analyzing RNA-seq data, we noted an upregulation of macrophage-related genes in Sorbs2-/- hearts. Immunostaining and lineage-tracing confirmed an increase in macrophage numbers, underscoring a macrophage response to myocardial abnormalities. Partial depletion of macrophages led to downregulation of genes involved in lipid metabolism, muscle development and organ regeneration, alongside upregulation of genes associated with DNA damage-induced senescence and cardiomyopathy. Additionally, a non-significant increase in septal defects in macrophage-depleted Sorbs2-/- hearts suggests a potential reparative function for macrophages in maintaining structural integrity. Valve formation, however, remained unaffected. Our findings suggest that embryonic macrophages might sense abnormalities in embryonic cardiomyocytes and could adaptively support cardiac structure and function development in response to myocardial abnormalities. Overall design: RNA profiling of wild-type embryonic hearts, Sorbs2 mutant hearts, and macrophage-depleted hearts at embryonic stages E12.5, E15.5, and E18.

巨噬细胞（macrophage）已知可支持心脏发育与稳态维持，并参与成体心脏的组织重塑与修复过程。然而目前尚不明确，胚胎巨噬细胞是否亦能响应发育中心脏的异常变化。此前本团队已有研究报道，结构蛋白Sorbs2可促进第二心区（second heart field）的发育，其缺失可导致心房间隔缺损（atrial septal defects, ASD）。在对RNA测序（RNA-seq）数据进行分析时，本团队观察到，Sorbs2-/-心脏中与巨噬细胞相关的基因表达显著上调。免疫染色（immunostaining）与谱系示踪（lineage-tracing）实验证实，巨噬细胞数量有所增加，进一步证实了巨噬细胞对心肌异常的响应。部分清除巨噬细胞后，参与脂质代谢、肌肉发育与器官再生的基因表达出现下调，而与DNA损伤诱导的细胞衰老及心肌病（cardiomyopathy）相关的基因则呈现上调。此外，巨噬细胞清除后的Sorbs2-/-心脏中，间隔缺损的发生率虽未出现统计学意义上的显著升高，但这一趋势提示巨噬细胞可能在维持心脏结构完整性中发挥修复功能。但心脏瓣膜的形成未受明显影响。本研究结果表明，胚胎巨噬细胞或可感知胚胎心肌细胞的异常，并能通过适应性调控，在心肌异常情况下支持心脏结构与功能的发育。实验整体设计：在胚胎发育阶段E12.5、E15.5及E18.5，分别对野生型胚胎心脏、Sorbs2突变型胚胎心脏以及巨噬细胞清除型胚胎心脏进行RNA表达谱分析。