NCOR1 orchestrates macrophage inflammation in heart failure with preserved ejection fraction: a translational study

Abstract Background/Introduction Inflammatory response is a key player in heart failure with preserved ejection fraction (HFpEF) but the underlying mechanisms are poorly understood. Recent studies have shown a critical involvement of cardiac macrophage activation in myocardial remodeling thus contributing to HFpEF. Purpose To investigate the role of cardiac macrophage inflammation in experimental and human HFpEF. Methods We employed a translational approach combining human and murine LV myocardial tissue, FACS analysis of cardiac immune cells, in vitro experiments in RAW 264.7 cells exposed to metabolic stress by palmitic acid (PA), bone marrow-derived macrophages from healthy and HFpEF mice, cardiomyocytes (H9c2), endothelial cells (HAECs) as well as ex vivo functional analyses in LV tissues. Human LV myocardial samples were used to evaluate the pro-inflammatory activity of macrophages in the HFpEF myocardium. Induction of HFpEF in mice was done through a validated mouse model combining metabolic (high-fat diet) and hemodynamic stress (L-NAME). Cardiac function was investigated by high resolution ultrasound imaging (Vevo3100) and the LV myocardial samples were used to study the macrophage polarization and their inflammatory activity. Based on interrogation of available RNA-seq datasets – showing the transcriptional repressor NCOR1 as a relevant signature in macrophages during cardiac inflammation, we generated myeloid cell-specific NCOR1 knockout (Ncor1-KO) transgenic mice to investigate the in vivo effects of NCOR1 deletion on the HFpEF phenotype. Results The expression of macrophage markers in human LV specimens showed an increase in pro-inflammatory macrophages (M1) and a decrease in regulatory macrophages (M2) as compared to age-matched control mice. HFpEF mice showed increased expression of vascular adhesion molecules (ICAM1, ICAM2, E-selectin) and a significant recruitment of M1 macrophages as proved by qPCR, WB, and flow cytometry analysis. Of interest, diastolic dysfunction - assessed by E/A ratio and isovolumic relaxation time (IVRT) – and lung congestion were significantly reduced in mice with macrophage NCOR1 deletion as compared to WT littermates, while exercise tolerance was significantly improved. These findings were associated with a reduction of myocardial inflammation (TNF-a, IL6, IL-1b) in Ncor1-KO mice. In vitro assays showed that stimulation of macrophages with PA induced M1 type switch and increased NCOR1, TNF-a, IL-6, and IL-1b levels, whereas NCOR1 depletion prevented detrimental changes of macrophage secretome (Fig.2). Conclusion NCOR1 is a crucial regulator of immune response and macrophage inflammation in the heart. Our findings highlight its potential as a target for therapies aimed at preventing myocardial damage in HFpEF.