# Rapamycin preserves cardiac function in autoimmune myocarditis by reprogramming Cxcl9+ macrophages via the mTORC1–C/EBPβ–OSM axis

## TL;DR

Rapamycin helps protect heart function in autoimmune myocarditis by changing harmful macrophages through a specific molecular pathway.

## Contribution

The study identifies a novel mechanism by which rapamycin reprograms Cxcl9+ macrophages via the mTORC1–C/EBPβ–OSM axis in autoimmune myocarditis.

## Key findings

- Rapamycin preserved cardiac function and reduced inflammation and fibrosis in autoimmune myocarditis mice.
- Rapamycin reprogrammed Cxcl9+ macrophages by inhibiting mTOR signaling and suppressing inflammatory pathways.
- Blocking OSM in vivo also reduced myocardial inflammation and preserved heart function.

## Abstract

Myocarditis is an inflammatory disease of the myocardium that can progress to chronic inflammatory cardiomyopathy and heart failure. Aberrant activation and metabolic reprogramming of macrophages drive myocardial inflammation and injury, yet effective targeted therapies remain limited.

Experimental autoimmune myocarditis (EAM) was induced in BALB/c mice by α-myosin heavy chain immunization. Rapamycin was administered during the inflammatory phase. Cardiac function and injury were evaluated by echocardiography, Millar catheterization, histology, qPCR, and ELISA. Single-cell RNA sequencing (scRNA-seq) of cardiac CD45+ cells, coupled with pseudotime trajectory, SCENIC regulon, and NicheNet analyses, was performed to delineate macrophage heterogeneity, lineage dynamics, and macrophage–cardiomyocyte communication. Functional validation included Seahorse metabolic assays and Cebpb-overexpressing bone marrow–derived macrophage (BMDM)–cardiomyocyte co-culture experiments, along with in vivo OSM-neutralizing antibody (OSM-nAb) intervention.

Rapamycin preserved cardiac function and alleviated myocardial inflammation and fibrosis in EAM mice, accompanied by reduced cytokine release and cardiac injury markers. scRNA-seq revealed that rapamycin reprogrammed cardiac monocyte–macrophages by inhibiting mTOR signaling, restoring mitochondrial metabolism, and suppressing inflammatory, glycolytic, and senescence pathways. It specifically targeted pathogenic Cxcl9+ macrophages by disrupting the mTORC1–C/EBPβ axis and limiting their differentiation from Plac8+ monocytes. Rapamycin further protected cardiomyocytes by blocking C/EBPβ-dependent OSM-mediated macrophage–cardiomyocyte crosstalk. Therapeutic OSM neutralization in vivo similarly mitigated myocardial inflammation and fibrosis while preserving ventricular contractility.

Rapamycin preserves cardiac function in autoimmune myocarditis by reprogramming Cxcl9+ macrophages via the mTORC1–C/EBPβ–OSM axis. Targeting OSM provides mechanistic validation and highlights a translational therapeutic strategy for myocarditis and chronic inflammatory cardiomyopathy.

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