Resolving the intertwining of inflammation and fibrosis in human heart failure at single-cell level

Inflammation and fibrosis are intertwined mechanisms fundamentally involved in heart failure. Detailed deciphering gene expression perturbations and cell–cell interactions of leukocytes and non-myocytes is required to understand cell-type-specific pathology in the failing human myocardium. To this end, we performed single-cell RNA sequencing and single T cell receptor sequencing of 200,615 cells in both human dilated cardiomyopathy (DCM) and ischemic cardiomyopathy (ICM) hearts. We sampled both lesion and mild-lesion tissues from each heart to sequentially capture cellular and molecular alterations to different extents of cardiac fibrosis. By which, left (lesion) and right ventricle (mild-lesion) for DCM hearts were harvest while infarcted (lesion) and non-infarcted area (mild-lesion) were dissected from ICM hearts. A novel transcription factor AEBP1 was identified as a crucial cardiac fibrosis regulator in ACTA2⁺ myofibroblasts. Within fibrotic myocardium, an infiltration of a considerable number of leukocytes was witnessed, especially cytotoxic and exhausted CD8⁺ T cells and pro-inflammatory CD4⁺ T cells. Furthermore, a subset of tissue-resident macrophage, CXCL8^hiCCR2⁺HLA-DR^hi macrophage was particularly identified in severely fibrotic area, which interacted with activated endothelial cell via DARC, that potentially facilitate leukocyte recruitment and infiltration in human heart failure.