Deciphering human heart failure with preserved ejection fraction (HFpEF) at single cell resolution

BACKGROUND Heart failure with preserved ejection fraction (HFpEF) is a complex and growing condition, representing over half of all heart failure cases. Despite its high morbidity and mortality, its heterogeneity and limited therapeutic options pose significant challenges. Understanding the molecular mechanisms driving HFpEF is essential for the development of new therapies to improve patient outcomes. METHODS We performed single-nucleus RNA sequencing of nuclei obtained from endomyocardial biopsies of six patients with HFpEF. The obtained dataset was integrated with a dataset of 12 healthy human hearts and their transcriptomic differences were analyzed. RESULTS After quality control and integration of the datasets, nine major cardiac cell types were annotated. HFpEF cardiomyocytes were characterized by a reduction in genes associated with aerobic respiration and fatty acid metabolism and showed an upregulation of RHOA/ROCK1 signaling, which was validated using immunofluorescence staining in human HFpEF myocardial sections. Endothelial cells exhibited signs of increased apoptosis, SEMA3 signaling and signs of reduced VEGFA signaling as well as a reactivation of a fetal gene signature. In line with a prominent role of cardiac fibrosis in HFpEF, we observed increased signs of fibroblast activation and proliferation, and reduced signs of IFNɣ signaling in HFpEF which was most pronounced in activated fibroblasts. Treatment of human cardiac fibroblast with rhIFNɣ resulted in decreased collagen contents. Macrophages from HFpEF myocardium showed a pro-inflammatory transcriptomic signature and showed increased expression of MHC-II molecules. This was associated with signs of an increased IFNɣ response. CONCLUSION Our results provide insights into the transcriptional diversity of HFpEF recapitulating structural, functional, and molecular hallmarks of the disease and provide mechanistic insights which might represent therapeutic targets and biomarkers to improve outcome of patients with HFpEF. CLINICAL PERSPECTIVE What is new? We provide a single-nucleus RNA sequencing (snRNA-Seq) dataset from human HFpEF myocardium and demonstrate feasibility of snRNA-Seq from endomyocardial biopsies The snRNA-Seq data confirms signs of known molecular hallmarks of HFpEF, such as metabolic changes, inflammation and fibrosis We identify signs of regulating cellular mechanisms underlying these hallmarks, such as cytoskeleton remodeling via RhoA/ROCK1 in cardiomyocytes, and differential interferon gamma signaling in stromal and immune cells What are the clinical implications? We provide several cell type-specific cellular mechanisms which might serve as biomarkers or therapeutic targets in the treatment of HFpEF