Mineralocorticoid receptor promotes cardiac macrophage inflammaging

Inflammaging, a pro-inflammatory status that characterizes aging and primarily involving macrophages, is a master driver of age-related diseases. Mineralocorticoid receptor (MR) activation in macrophages critically regulates inflammatory and fibrotic processes. However, macrophage-specific mechanisms and the role of the macrophage MR for the regulation of inflammation and fibrotic remodeling in the aging heart have not yet been elucidated. Transcriptome profiling of cardiac macrophages from male/female young (4 months-old), middle (12 months-old) and old (18 and 24 months-old) mice revealed that myeloid cell-restricted MR deficiency prevents macrophage differentiation toward a pro-inflammatory phenotype. Pathway enrichment analysis showed that several biological processes related to inflammation and cell metabolism were modulated by the MR in aged macrophages. Further, transcriptome analysis of aged cardiac fibroblasts revealed that macrophage MR deficiency reduced the activation of pathways related to inflammation and upregulation of ZBTB16, a transcription factor involved in fibrosis. Phenotypic characterization of macrophages showed a progressive replacement of the TIMD4⁺MHC-II^neg/low macrophage population by TIMD4⁺MHC-II^int/high and TIMD4^-MHC-II^int/high macrophages in the aging heart. By integrating cell sorting and transwell experiments with TIMD4⁺/TIMD4^-macrophages and fibroblasts from old MR^flox/MR^LysMCre hearts, we showed that the inflammatory crosstalk between TIMD4^- macrophages and fibroblasts may imply the macrophage MR and the release of mitochondrial superoxide anions. Macrophage MR deficiency reduced the expansion of the TIMD4^- macrophage population and the emergence of fibrotic niches in the aging heart, thereby protecting against cardiac inflammation, fibrosis, and dysfunction. This study highlights the MR as an important mediator of cardiac macrophage inflammaging and age-related fibrotic remodeling.