Plasma free fatty acids are potent adipogenic factors for epicardial progenitor cells in the atria

Background The epicardial adipose tissue (EAT) is an important risk factor of atrial fibrillation notably in patients with metabolic diseases such as obesity. Adipocytes that compose the EAT derive from epicardial progenitor cells (EPDCs) resident in the epicardial layer that are normally quiescent. However, little is known about factors and mechanisms that cause the reactivation of EPDC and their differentiation into adipocytes. Hypothesis. long chain fatty acids (FA) present in serum of dysmetabolic patients can induce the adipogenic differentiation of EPDCs. Methods/Results EPDC were harvested from rat atria one week after an acute heart failure complicating a surgical myocardial infarction, an experimental condition known to reactivate the atrial epicardium. Then, cells were cultured in presence of a high concentration of two FA, oleate and palmitate (Ole-Pal). At day 7 of culture in presence of Ole-Pal, while only around 30% of bulk EPDCs acquired an adipocyte phenotype, 100% of the subset of EPDCs expressing the preadipocyte marker Pref1 showed an adipocyte phenotype with notably lipid droplet positive staining (n=6). Preff-1 is a transmembrane protein that can be cleaved by a protease TACE. At day 3 of culture of EPDCs-Pref1+ with FA, the soluble part of Pref-1 was detected (ELISA assay) in the supernatant whereas no more membrane Pref-1 staining of EPDCs-Pref1+ was observed and indicating protein cleavage. Furthermore, the inhibition of the cleavage of Pref1 by TIMP3, a biological inhibitor of TACE, maintained Pref-1s at the plasma membrane while EPDCs continued to proliferate (Ki67 labelling, n=3) and did not differentiate into adipocyte. Furthermore, expression of Dlk1 the gene encoding Pref1 was decreased at day 3 of culture while adipogenic genes, Pparγ and Perilipin, were increased (n=6). In situ both immunolabeling and single cells-RNA sequencing analysis indicated a transient expression of Dlk1/Pref-1 cells during early atrial remodeling in rat. Conclusion. Long chain FA induces the adipogenic differentiation of a subpopulation of EPDC expressing the pre adipogenic gene Dlk1/Pref-1. DLK1/Pref1 maintains preadipocyte progenitor cells in a proliferative state as in other cell types. We identified an early mechanism regulating EAT accumulation in the atria.