Modern therapies aimed at stimulating heart vascularization are critical for regenerating damaged heart tissue and treating ischemic heart disease. Approaches based on developmental biology concepts, particularly those involving the use of cells to coordinate vascular network formation, are of great interest. In this context, epicardial mesothelial cells (MCs) have emerged as a key regulator of blood and lymphatic vessel development during cardiogenesis. However, therapeutic targeting of MCs remains challenging because of anatomical constraints and the difficulties related to isolation of viable cell cultures for research. In this study, we demonstrate for the first time that the pericardial fluid contains cell layers, being an easily accessible source of cardiac MCs. These cells exhibit a characteristic epithelial-like morphology and robust in vitro proliferation, and an ability to undergo epicardial-to-mesenchymal transition in response to TGFβ1. They secrete a broad range of proangiogenic and proinflammatory factors and exert a potent effect on endothelial cells, stimulating proangiogenic behavior and promoting vascular structure formation on Matrigel^TM. Treating MCs with TGF-β1 enhances the secretion of VEGF, G-CSF, GM-CSF and MCP-3, thereby boosting their proangiogenic properties. Therefore, pericardial fluid is an easily accessible source of MCs for studying their regulatory mechanisms, for being applied in tissue engineering, and for developing approaches to improve heart vascularization.

Epicardial mesothelial cells (EMCs), which form the epicardium, play a crucial role in cardiac homeostasis and repair. Upon damage, EMCs reactivate embryonic development programs, contributing to wound healing, progenitor cell amplification, and regulation of lymphangiogenesis, angiogenesis, and fibrosis. However, the mechanisms governing EMC activation and subsequent regulation remain poorly understood. We hypothesized that hepatocyte growth factor (HGF), a pleiotropic regulator of various cellular functions, could modulate EMC activity. To verify this hypothesis, we developed HGF-overexpressing mesenchymal stromal cell sheets (HGF-MSC CSs) and evaluated their effects on EMCs in vitro and in vivo. This study has revealed, for the first time, that EMCs express the c-Met (HGF receptor) on their surface and that both recombinant HGF and HGF-MSC CSs secretome cause c-Met phosphorylation, triggering downstream intracellular signaling. Our findings demonstrate that the HGF-MSC CSs secretome promotes cell survival under hypoxic conditions by modulating the level of autophagy. At the same time, HGF-MSC CSs stimulate EMC proliferation, promoting their amplification in the damage zone. These data demonstrate that HGF-MSC CSs can be considered a promising regulator of epicardial cell activity involved in heart repair after ischemic damage.

Despite advancements in investigation of cardiac fibrosis mechanisms, molecular and cellular regulation of this process remains insufficiently explored. In this context, examination of novel targets capable of regulating the state of cardiac fibroblasts and their profibrotic properties becomes a pivotal area of research. These processes include autophagy as an evolutionary conservative mechanism contributing to maintenance of cellular homeostasis through utilization of macromolecules and organelles via lysosomal degradation pathway. The objective was to investigate autophagy in cardiac fibroblasts at the early stages of cardiac dysfunction caused by pressure overload. Experimental studies showed that modelling of transverse aortic constriction promotes pressure overload with cardiomyocyte hypertrophy, perivascular fibrosis and interstitial accumulation of collagen. These morphological changes were accompanied by reduced autophagy activity in cardiac tissue. A detailed bioinformatic analysis of transcriptome of single cells revealed that modelling of cardiac dysfunction was not accompanied by changes in expression of genes associated with autophagy in total pool of cardiac fibroblasts and its subpopulations. Thus, fibroblasts demonstrated differences in specialized response to pressure overload of the heart compared to total myocardial cell pool. No change in expression of genes associated with autophagy is probably in favor of suppression of adaptation of cardiac tissue to new conditions of functioning. Autophagy as a diagnostic marker of cardiac fibrosis progression requires confirmation and additional studies.