1Universitätsklinikum Frankfurt Med. Klinik III - Kardiologie, Angiologie Frankfurt am Main, Deutschland; 2Universitätsklinikum Frankfurt Zentrum für Molekulare Medizin, Institut für Kardiovaskuläre Regeneration Frankfurt am Main, Deutschland; 3Goethe Universität Frankfurt am Main Institute of Cardiovascular Regeneration and Department of Cardiology Frankfurt am Main, Deutschland; 4Goethe Universität Frankfurt am Main Zentrum für Molekulare Medizin, Institut für Kardiovaskuläre Regeneration Frankfurt am Main, Deutschland
Aims: Heart failure with preserved ejection fraction (HFpEF) is characterized by diastolic dysfunction and cardiac hypertrophy. Leukocytes are an integral part of the healthy myocardium, which may have protective functions but also contribute to cardiac pathologies. This study aims to unravel phenotypic and genetic changes in cardiac immune cells during heart failure with preserved ejection fraction.
Methods and results: We implemented a model of nitrosative stress, in which mice were treated with a combination of high-fat diet with the administration Nω-nitro-L-arginine methyl ester (L-NAME) for 11 weeks. Mice were analyzed with echocardiography and histology to verify the presence of HFpEF features. Inflammatory changes were assessed with flow cytometry and histology. Single-cell RNA sequencing was performed on sorted cardiac leukocytes in mice with HFpEF. The myocardium in HFpEF is characterised by changes in leukocyte composition and the emergence of Trem2-expressing macrophages, which might mediate both tissue inflammation and the adaptive response to cardiac injury. Specifically, the fractalkine receptor CX3CR1 was upregulated in Trem2-expressing macrophages. Therefore, we tested the effect of the CX3CR1 inhibitor AZD8797 in HFpEF development. Here, we observed echocardiographic improvements (E/E’ ratio and left atrial size) and reduced cardiac fibrosis using histology. Flow cytometric analysis showed reduced macrophage infiltration in AZD8797-treated hearts. To further gain mechanistic insights, we used iPSC-derived self-assembling cardiac organoids, which also contain macrophages. HFpEF was induced in these cardiac organoids using an analogous regimen as in the HFpEF mouse model with a high-fat (200µM Palmitate) and L-NAME (2.1 mM)-supplemented medium. AZD8797 treatment of HFpEF organoids significantly reduced markers of cardiac hypertrophy (ANP, BNP) and inflammation (Il1b, Il6).
Conclusion: CX3CR1 is expressed in a subset of TREM2 expressing macrophages, which substantially expand in a mouse model of HFpEF. CX3CR1 inhibition results in an improvement of cardiac function in mice with HFpEF. Mechanistically, CX3CR1 inhibition reduced cardiac macrophage recruitment and fibrosis in vivo. Using an HFpEF organoid model, CX3CR1 inhibition curbed cardiac hypertrophy and inflammation in vitro.
Further analysis of the effects instigated by TREM2 expressing macrophages is required, especially as anti-TREM2 therapies are tested in oncology trials and Alzheimers disease.