Aging reshapes cardiac extravascular leukocyte transcription through bidirectional remodeling during LPS-induced endotoxemia

Sepsis disproportionately affects older adults and is frequently complicated by cardiac dysfunction. However, how aging alters the transcriptional responses of cardiac extravascular immune cells during systemic inflammation remains poorly understood. Here, we investigated aging-dependent transcriptional remodeling of cardiac immune cells using an LPS-induced endotoxemia model in young and aged C57BL/6 mice. Mice received intraperitoneal LPS (5 mg/kg body weight) or vehicle, and cardiac extravascular leukocytes were isolated from ex vivo retrogradely perfused hearts 24 h later for single-cell RNA sequencing. Aging was associated with bidirectional transcriptional remodeling, characterized by both up- and downregulation of gene programs, particularly in cardiac macrophages, monocyte-like macrophages, T cells, and B cells following LPS challenge. A shared feature across these four cell populations was reduced representation of mitochondrial-associated transcriptional programs, indicating aging-dependent remodeling of mitochondrial biology across cardiac myeloid and lymphoid lineages during systemic inflammation. In parallel, cell type-specific transcriptional remodeling revealed distinct functional-associated responses. Macrophages and monocyte-like macrophages exhibited increased tissue-remodeling and repair-associated transcriptional programs. Both T and B cells showed reduced metabolic programs but increased actin cytoskeleton organization. T cells additionally exhibited reduced cytotoxicity-associated and enhanced Th17-associated transcriptional programs, whereas B cells showed reduced antigen-processing and presentation programs. Cell-cell communication analysis suggested aging-associated differences in immune cell interactions following LPS challenge and potential features of cardiac inflammaging at baseline. Together, these findings demonstrate that aging bidirectionally reshapes the cardiac immune response to systemic inflammation, characterized by shared remodeling of mitochondrial-associated programs and cell type-specific changes in inflammatory, metabolic, cytoskeletal, and effector-associated programs. These aging-dependent transcriptional changes occurred in the context of the greater severity of illness observed in aged mice following LPS-induced endotoxemia.