Transcriptional regulation of macrophage inflammation in the 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 (1). Recent studies have shown a critical involvement of cardiac macrophage recruitment and activation in myocardial remodelling (2,3). Purpose here we sought to determine the role of 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 primary macrophages and cardiac cells 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. In vitro experiments included RAW 264.7 cells polarization through a metabolic stress model via palmitic acid (PA) and the assessment of macrophage phenotype switching in the presence or the absence of NCOR1. To study the crosstalk of macrophages with the surrounding cardiac cells, cardiomyocytes (H9c2) and endothelial cells (HAECS) were exposed to conditioned media from cultured RAW. Afterwards, cellular function and the pro-inflammatory cytokine levels were investigated. 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 to the myocardium. Of interest, cardiac function and myocardial inflammation (TNF-a, IL6, IL-1b) were significantly reduced 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 co-regulator of immune response and macrophage inflammation in the heart. Our findings pave the way for mechanism-based therapies to prevent HFpEF development.