Role of inflammation and macrophages in the formation of the atrial cardiomyopathy associated with obesity
Authors: Nadine N S , Mezdaout N M , Trenquier E T , Mougenot N M , Chabbat Courrede C C C , Lanthiez F L , Gautier E L G , Boissonnas A B , Ponnaiah M P , Chaffin M C , Simonson B S , Ellinor P E , Lebreton G L B , Hatem S H 
Published: October 2024

Abstract

Introduction
The atrial fibrillation (AF), the most frequent cardiac arrhythmia in clinical practice is often associated with an atrial cardiomyopathy (ACM) which is favoured by several clinical conditions including metabolic diseases such as obesity. Recently, the epicardial adipose tissue (EAT) has emerged as an important component of ACM notably in the context of metabolic diseases. Epicardial progenitor cells (EPC) are the main source of EAT. The replacement of EAT by fibrosis is arrhythmogenic and involved inflammation but not yet characterized. The hypothesis tested here is that macrophages are central players for both the recruitment of EPC and replacement of EAT by fibrosis.

Purpose-Aims
First to characterize subpopulation of macrophages involves in the progression of ACM. Second, to study how the inflammatory environment regulates EPC differentiation.

Method
A spatial gene expression was used to analyze human samples (n=4) (Agreement, CODECOH, Declaration or authorization of activities involving the preservation and preparation of human body parts for scientific purposes DC-2020-4183). A well-characterized mouse model of atrial cardiomyopathy associated with obesity induced by high fat diet (HFD) was used to characterize macrophages associated with progression of ACM by using immunolabeling together with single nuclei RNA sequencing approaches. ACM was characterized by using echocardiography and atrial burst pacing to evaluate determine AF vulnerability. Transgenic RGB-MAC mice with macrophages tagged with McApple-Csf1R and ECGFP-CX3CR1 or with a knock-out for CCR2 were used to follow infiltration of myeloid cells in the atrial at the different stages of the ACM. Bi-photon microscopy was used to visualize cell subpopulations in the distinct area of the atrial wall. In some experiments EPC and macrophages were cocultured with transwell.

Results
Macrophages were detected in subepicardium of human atrial samples in area of fibro-fatty infiltrates. After 2 months of HFD, monocytes were infiltrated atria and macrophages were overexpressed in atria from 1 to 4 months of HFD. Using Bi-photon microscopy it was possible to visualise resident ECGFP-CX3CR1+ macrophages at the contact of EAT whereas McApple-Csfr1r+ macrophages were at the junction with fibrosis (figure 1). Preliminary data generated by single nuclei RNA sequencing showed clusters of different subpopulations of macrophages at different time point of the ACM (figure 2). We will present results on the effects of suppression of the CCR2 subpopulation of macrophages on characteristics of the ACM.

Conclusion
Distinct populations of macrophages i.e resident and monocyte-derived macrophages, participate to the distinct stages of the ACM caused by obesity in mice.Myeloid cells infiltration in epicardiumCCR2+cells infiltration in EAT-fibrosis