Immune and stromal remodeling underlies radiation-induced heart injury: insights from single-cell transcriptomics

Radiation-induced heart injury (RIHI) is a major late toxicity of thoracic radiotherapy, yet the cellular and molecular mechanisms driving its progression remain poorly defined.

Single-cell RNA sequencing (scRNA-seq) was performed on rat hearts and matched peripheral blood mononuclear cells (PBMCs) 12 weeks after whole-heart irradiation (20 Gy) or sham control, profiling 38,941 cardiac cells across 15 types and 41,097 PBMCs across 9 types. Differential expression, pathway enrichment, pseudotime, and ligand-receptor interaction analyses were conducted. Key findings in endothelial cells and fibroblasts were validated by Western blotting and flow cytometry.

Major cardiac populations, including cardiomyocytes, endothelial cells (ECs), fibroblasts, neutrophils, macrophages, T cells, NK cells, and B cells, were defined in control and RIHI hearts. Following irradiation, ECs showed distinct subtype shifts with marked MHC-II upregulation, while fibroblasts exhibited iron accumulation, pro-inflammatory activation, and antigen-presenting properties. These stromal alterations coincided with myeloid activation (macrophage and IL-1β⁺ neutrophil programs) and T/NK cell polarization toward cytotoxic yet partially exhausted states, together with enhanced B-cell antigen presentation. Collectively, these findings delineate a stromal-immune cascade linking radiation injury to chronic cardiac inflammation.

RIHI progresses through a stromal-immune cascade where EC and fibroblast immunogenic reprogramming initiates sustained myeloid and lymphoid activation, creating a pro-inflammatory cardiac microenvironment. These findings highlight non-hematopoietic antigen presentation as a therapeutic target in thoracic radiotherapy, particularly when combined with immune checkpoint inhibitors.