Cardiac fibrosis represents a significant health burden, with endothelial dysfunction and damaged perivascular microenvironment increasingly recognized as key contributors to fibrotic remodeling. The urokinase plasminogen activator receptor (uPAR), a critical component of the urokinase system, plays a pivotal role in vascular remodeling and fibrosis. While prior evidence indicates that uPAR deficiency leads to microvascular dysfunction and perivascular fibrosis, the underlying mechanisms remain poorly defined. This study investigates how uPAR deficiency contributes to fibrotic remodeling of the cardiac perivascular-like microenvironment. Single-cell RNA sequencing data analysis and immunofluorescence staining on mouse heart cryosections were performed to characterize uPAR expression within the cardiac perivascular microenvironment. To model this microenvironment in vitro, cardiospheres (CSs) were generated from non-myocyte cardiac cells of wild-type and uPAR-knockout mice. CRISPR/Cas9-generated Plaur knockout (KO) 3T3 fibroblasts (FBs) were employed as model stromal cells. Pro-fibrotic activation of FBs was induced by TGFβ1 treatment. Comparative analyses of extracellular matrix (ECM) deposition, fibrotic cell transformation, and comprehensive secretome profiling was conducted using western blotting. Our findings demonstrated that uPAR was expressed by endothelial cells (ECs) and FBs within the cardiac perivascular microenvironment. uPAR deficiency exacerbated profibrotic stimuli in CSs, including elevated active TGFβ1, impaired integrin functions, and altered cell secretome. These alterations collectively disrupt critical cell-cell and cell-matrix interactions, leading to increased ECM deposition, EC loss and decreased cell viability. Using Plaur KO FBs, we demonstrated that uPAR deficiency amplified TGFβ1-mediated Akt signaling pathway and ECM deposition. Our study reveals that uPAR loss drives fibrotic remodeling of the cardiac perivascular-like microenvironment and exacerbates TGFβ1-mediated effects, highlighting its potential as a therapeutic target for cardiac fibrosis.

Mesothelial cells line serosal cavities and internal organs, playing a vital role in maintaining serosal integrity and homeostasis. Their remarkable plasticity and ability to undergo mesothelial-to-mesenchymal transition (MMT) position them as key regulators of tissue repair. However, when normal repair processes fail, mesothelial cells can acquire a profibrotic phenotype. They actively contribute to all stages of fibrosis development, including inflammation, fibrin accumulation, myofibroblast differentiation, and extracellular matrix (ECM) remodeling. Fibrotic progression involves multiple cell types, and communication among them is essential for its perpetuation. Mesothelial cells are implicated in bidirectional crosstalk with fibroblasts, macrophages, lymphocytes, and endothelial cells of the serosal microenvironment through direct contact, paracrine signaling, and extracellular vesicle exchange. These interactions regulate immune cell recruitment, cytokine balance, endothelial permeability, and ECM deposition, while, in turn, immune and endothelial cells modulate mesothelial activation, proliferation, and transition. Understanding this complex network of intercellular communication provides new insights into fibrosis pathogenesis and reveals promising targets for antifibrotic therapies.

Background/Objectives: Acomys cahirinus exhibits more favorable cardiac remodeling after ischemic injury than Mus musculus, yet the molecular organization of the intact myocardium remains poorly characterized. This study aimed to identify baseline interspecies differences in the adult left ventricle, with particular emphasis on ventricular cardiomyocyte transcriptional states. Methods: Intact left ventricles from adult male A. cahirinus and M. musculus were analyzed by single-nucleus RNA sequencing using three biological samples per species. Cross-species integration was followed by cell type annotation, pseudobulk differential expression analysis, Augur-based assessment of interspecies separability, coexpression module analysis, and focused reintegration analysis of ventricular cardiomyocytes. Cardiomyocyte profiles were further compared with published embryonic and early postnatal M. musculus heart datasets. Results: Both species contained comparable major myocardial cell populations, whereas marked interspecies transcriptional differences persisted within individual cell types. Ventricular cardiomyocytes exhibited the largest number of differentially expressed genes and were classified into three transcriptional states: contractile, matrix-associated, and alternative. Adult A. cahirinus cardiomyocytes retained a mature cardiomyocyte phenotype but showed greater enrichment of developmental, morphogenetic, and Hippo-associated gene programs than adult M. musculus cardiomyocytes. Their transcriptional profile did not correspond to embryonic or early postnatal mouse states. The integrated atlas further identified interspecies differences in fibroblast-associated and extracellular matrix-related programs. Conclusions: The intact myocardium of A. cahirinus exhibits cell type-specific transcriptional differences relative to M. musculus. Ventricular cardiomyocytes display a distinct mature transcriptional configuration rather than a direct immature state, which may contribute to the favorable response of A. cahirinus to myocardial injury.

Epicardial mesothelium plays a pivotal role in postinfarction cardiac repair by generating fibroblasts, producing extracellular matrix, and releasing paracrine mechanisms. However, interspecies differences have not been sufficiently studied, particularly in in vivo models of scar-free healing such as the African spiny mouse (Acomys cahirinus). This study aimed to compare the profibrotic response of epicardial mesothelial cells (MCs) from Acomys and C57BL/6 mice to hypoxic stress, a key factor in postinfarction recovery. We isolated epicardial MCs from the African spiny mouse (Acomys cahirinus), a species with documented cardiac regenerative capabilities, and from C57BL/6 laboratory mice. Using a CoCl2-induced hypoxia model in vitro, we assessed cell viability, morphological changes, and expression of epithelial and fibroblast markers. In vivo, following experimental myocardial infarction (MI), we evaluated tissue hypoxia (pimonidazole adducts), epicardial activation (layer thickness, Wt1+ and TBX18+ progenitor cells), and collagen accumulation. The study was conducted using real-time PCR, Western blotting, immunohistochemical analysis and microscopic examination. In vitro, MCs from both species exhibited an epithelial-like phenotype under normoxic conditions, expressing E-cadherin and cytokeratin 18. Hypoxia (200 µM CoCl2) induced a comparable response in both Acomys and C57BL/6 cells, characterized by a shift to a spindle-shaped, fibroblast-like morphology, decreased E-cadherin expression, and increased pro-collagen 1 and α-SMA expression. Following MI, both species exhibited similarly extensive hypoxic areas affecting the epicardial zone. Epicardial activation dynamics were comparable: from day 3 post-MI, epicardial thickness increased significantly, and Wt1+ and TBX18+ progenitor cells accumulated, peaking during the first week. Collagen accumulation in the epicardial region was similar between species, although the number of Wt1+ cells was higher in C57BL/6 on day 7. Despite the well-known superior regenerative capacity of spiny mice, epicardial MCs from Acomys and C57BL/6 demonstrated similar signs of profibrotic responses to hypoxic stimulation both in vitro and following MI. These findings suggest that species-specific regenerative outcomes may not be attributable to differential acute epicardial sensitivity to hypoxia, but rather to downstream mechanisms or additional factors influencing the cardiac repair process. This study provides the first characterization of Acomys epicardial MCs and establishes a foundation for further investigation of evolutionarily conserved and species-specific mechanisms of cardiac regeneration.

Mesothelial cells (MCs) are highly relevant for studying the pathogenesis of serosal diseases, fibrosis, inflammation, and tumor progression. However, the isolation and maintenance of an epithelial-like phenotype of MCs in vitro remain methodologically challenging due to their tendency to undergo mesothelial-to-mesenchymal transition (MMT). In this work, we propose a combined protocol utilizing collagen IV coating, conditioned medium, and short-term ROCK inhibitor treatment, which improves cell survival. This approach enables the establishment of primary human cultures suitable for investigating mesothelial cell functional activity and for assessing the efficacy of potential therapeutic strategies.

Cardiospheres (CSs) are widely used to boost the pro-reparative potential of adult cardiac cells, mediated through their unique secretome profile. The original CS generation method relies on self-assembly of cardiac explant-derived cells (EDCs) on poly-D-lysine (PDL)-coated plates, but yields inconsistently sized spheroids, restricting broader applications. To address this, we employed ultra-low attachment (ULA) U-well plates to promote uniform spheroid assembly. We systematically compared CSs generated from mouse EDCs using the standard method, based on PDL-coated plates, and the alternative approach, based on ULA U-well plates. Both methods produced viable CSs mimicking the cardiac microenvironment, including mesenchymal cells/fibroblasts, smooth muscle, endothelial, and progenitor cells. PDL-formed CSs were characterized by size heterogeneity, increased stiffness, and reduced endothelial cell content. Despite that, they demonstrated elevated secretion of angiogenesis-related factors and robust proangiogenic potential in vivo. In contrast, generation of mCSs on ULA U-well plates resulted in the formation of soft spheroids with uniform size, enhanced vascularization (CD31+ cells), and increased MCP-1 secretion. In summary, the alternative U-well-based approach enables the generation of uniform spheroids with high spontaneous vascularization, while traditionally formed CSs using PDL-coated plates maintain their superior proangiogenic potential.

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.

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 MatrigelTM. 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.

The cardiac perivascular niche is a cellular microenvironment of a blood vessel. The principles of niche regulation are still poorly understood. We studied the effect of TGFβ1 on cells forming the cardiac perivascular niche using 3D cell culture (cardiospheres). Cardiospheres contained progenitor (c-Kit), endothelial (CD31), and mural (αSMA) cells, basement membrane proteins (laminin) and extracellular matrix proteins (collagen I, fibronectin). TGFβ1 treatment decreased the length of CD31+ microvasculature, VE cadherin protein level, and proportion of NG2+ cells, and increased proportion of αSMA+ cells and transgelin/SM22α protein level. We supposed that this effect is related to the stabilizing function of TGFβ1 on vascular cells: decreased endothelial cell proliferation, as shown for HUVEC, and activation of mural cell differentiation.

Fibrinolytics delivered into the general circulation lack selectivity for nascent thrombi, reducing efficacy and increasing the risk of bleeding. Urokinase-type plasminogen activator (uPA) transgenically expressed within murine platelets provided targeted thromboprophylaxis without causing bleeding but is not clinically feasible. Recent advances in generating megakaryocytes prompted us to develop a potentially clinically relevant means to produce "antithrombotic" platelets from CD34+ hematopoietic stem cell-derived in vitro-grown megakaryocytes. CD34+ megakaryocytes internalize and store in alpha granules (alpha-granules) single-chain uPA (scuPA) and a plasmin-resistant thrombinactivatable variant (uPAT). Both uPAs colocalized with internalized factor V (FV), fibrinogen and plasminogen, low-density lipoprotein receptor-related protein 1 (LRP1), and interferoninduced transmembrane protein 3, but not with endogenous von Willebrand factor (VWF). Endocytosis of uPA by CD34+ megakaryocytes was mediated, in part, via LRP1 and alpha IIb beta 3. scuPA-containing megakaryocytes degraded endocytosed intragranular FV but not endogenous VWF in the presence of internalized plasminogen, whereas uPATmegakaryocytes did not significantly degrade either protein. We used a carotid artery injury model in nonobese diabetic-severe combined immunodeficiency IL2r gamma null (NSG) mice homozygous for VWFR1326H(a mutation switching binding VWF specificity from mouse to human glycoprotein Ib alpha) to test whether platelets derived from scuPA- or uPATmegakaryocytes would prevent thrombus formation. NSG/VWFR1326H mice exhibited a lower thrombotic burden after carotid artery injury compared with NSG mice unless infused with human platelets or megakaryocytes, whereas intravenous injection of uPAmegakaryocytes generated sufficient uPA-containing human platelets to lyse nascent thrombi. These studies describe the use of in vitro-generated megakaryocytes as a potential platform for delivering uPA or other ectopic proteins within platelet alpha-granules to sites of vascular injury.

The increasing burden of vascular dysfunction on healthcare systems worldwide results in higher morbidity and mortality rates across pathologies, including cardiovascular diseases. Vasculopathy is suggested to be caused by the dysregulation of vascular niches, a microenvironment of vascular structures comprising anatomical structures, extracellular matrix components, and various cell populations. These elements work together to ensure accurate control of the vascular network. In recent years, autophagy has been recognized as a crucial regulator of the vascular microenvironment responsible for maintaining basic cell functions such as proliferation, differentiation, replicative senescence, and apoptosis. Experimental studies indicate that autophagy activation can be enhanced or inhibited in various pathologies associated with vascular dysfunction, suggesting that autophagy plays both beneficial and detrimental roles. Here, we review and assess the principles of autophagy organization and regulation in non-tumor vascular niches. Our analysis focuses on significant figures in the vascular microenvironment, highlighting the role of autophagy and summarizing evidence that supports the systemic or multiorgan nature of the autophagy effects. Finally, we discuss the critical organizational and functional aspects of the vasculogenic niche, specifically in relation to autophagy. The resulting dysregulation of the vascular microenvironment contributes to the development of vascular dysfunction.

Epicardium, the outer epithelial layer of the heart forming from extracardiac primordium, plays a fundamental role in myocardial embryogenesis by generating epicardial-derived cells (cardiac fibroblasts, mesenchymal cells, vascular smooth muscle cells). In the adult heart, epicardium occurs as a mesothelial layer, which, in injured heart, recalls its “embryonic program” and transforms into mesenchymal cells contributing, by such a way, to myocardial reparation. This process is facilitated by hypoxic conditions arising during injury. In general, regulation of this process may be a potential methodology for treatment of cardiovascular diseases.

One of the largest challenges to the implementation of cardiac cell therapy is identifying selective reparative targets to enhance stem/progenitor cell therapeutic efficacy. In this work, we hypothesized that such a target could be an urokinase-type plasminogen activator receptor (uPAR)-a glycosyl-phosphatidyl-inositol-anchored membrane protein, interacting with urokinase. uPAR is able to form complexes with various transmembrane proteins such as integrins, activating intracellular signaling pathway and thus regulating multiple cell functions. We focused on studying the CD117+ population of cardiac mesenchymal progenitor cells (MPCs), expressing uPAR on their surface. It was found that the number of CD117+ MPCs in the heart of the uPAR-/- mice is lower, as well as their ability to proliferate in vitro compared with cells from wild-type animals. Knockdown of uPAR in CD117+ MPCs of wild-type animals was accompanied by a decrease in survival rate and Akt signaling pathway activity and by an increase in the level of caspase activity in these cells. That suggests the role of uPAR in supporting cell survival. After intramyocardial transplantation of uPAR(-) MPCs, reduced cell retention and angiogenesis stimulation were observed in mice with myocardial infarction model compared to uPAR(+) cells transplantation. Taken together, the present results appear to prove a novel mechanism of uPAR action in maintaining the survival and angiogenic properties of CD117+ MPCs. These results emphasize the importance of the uPAR as a potential pharmacological target for the regulation of reparative properties of myocardial mesenchymal progenitor cells.

Pericarditis is a group of polyetiological diseases often associated with emergence of life–threatening conditions. Poor knowledge of underlying cellular mechanisms and lack of relevant approaches to investigation of pericarditis result in major challenges in diagnosis and treatment.The aim of this work was to identify changes in the activity of autophagy in epicardial cells in acute pericarditis.Materials and methods. Acute pericarditis in mice was induced by intrapericardial injection of Freund's adjuvant in the study group (n=15). The control group included animals receiving either intrapericardial injection of phosphate-buffered saline (PBS) (n=15), or sham surgery without injections (n=7). On Days 3 or 5 after surgery the animals were euthanized under isoflurane anesthesia. Immunofluorescence staining of cardiac tissue cryo-sections and immunoblotting were used to assess the intensity of inflammation and autophagy in the epicardium.Results. Inflammation and other signs of acute pericarditis resulting in thickening of some epicardial areas were found: 68+9% in the control (after PBS injection) and 124+22% after Freund's adjuvant injection (p=0.009); other signs included cellular infiltration of epicardium and multiple adhesions. The epicardial layer exhibited signs of mesothelial cells reorganization with 11-fold increase of autophagy markers LC3 II/LC3 I ratio: 0.07+0.02 in the control group (after PBS injection) and 0.84+0.07 - in acute pericarditis (p=0.04), and accumulation of collagen fibers.Conclusion. Development of acute pericarditis is accompanied by activation of epicardial mesothelial cells, intensified autophagy and development of fibrous changes in epicacardial/ subepicardial areas.

Ischemic heart disease and its complications, such as myocardial infarction and heart failure, are the leading causes of death in modern society. The adult heart innately lacks the capacity to regenerate the damaged myocardium after ischemic injury. Multiple lines of evidence indicated that stem-cell-based transplantation is one of the most promising treatments for damaged myocardial tissue. Different kinds of stem cells have their advantages for treating ischemic heart disease. One facet of their mechanism is the paracrine effect of the transplanted cells. Particularly promising are stem cells derived from cardiac tissue per se, referred to as cardiosphere-derived cells (CDCs), whose therapeutic effect is mediated by the paracrine mechanism through secretion of multiple bioactive molecules providing immunomodulatory, angiogenic, anti-fibrotic, and anti-inflammatory effects. Although secretome-based therapies are increasingly being used to treat various cardiac pathologies, many obstacles remain because of population heterogeneity, insufficient understanding of potential modulating compounds, and the principles of secretome regulation, which greatly limit the feasibility of this technology. In addition, components of the inflammatory microenvironment in ischemic myocardium may influence the secretome content of transplanted CDCs, thus altering the efficacy of cell therapy. In this work, we studied how Tumor necrosis factor alpha (TNFa), as a key component of the pro-inflammatory microenvironment in damaged myocardium from ischemic injury and heart failure, may affect the secretome content of CDCs and their angiogenic properties. We have shown for the first time that TNFa may act as a promising compound modulating the CDC secretome, which induces its profiling to enhance proangiogenic effects on endothelial cells. These results allow us to elucidate the underlying mechanisms of the impact of the inflammatory microenvironment on transplanted CDCs and may contribute to the optimization of CDC efficiency and the development of the technology for producing the CDC secretome with enhanced proangiogenic properties for cell-free therapy.

Fundamental research in recent years has allowed us to reassess the molecular and cellular mechanisms of cardiac ontogenesis and its repair after damage. The epicardium, the outer, tightly adjoining layer of the cardiac wall formed by epicardial mesothelial cells, collagen and elastic fibers, has gained special relevance as an important participant of reparative processes. Better insight into poorly understood epicardial function is challenged due to anatomical issues and lack of relevant cellular models. The aim of this study was to develop a spheroid 3D model of the epicardial microenvironment and determine responses of spheroids to hypoxia. Materials and methods. Spheroids were harvested in V-shaped culture dishes with a low adhesion coating. Immunofluorescent staining of cryosections, histological methods and real-time PCR were used for characterization of cultured spheroids. Results. We demonstrated that cultivation of cells under low adhesion conditions in V-shaped culture dishes resulted in the formation of spheroids with an average size of 136+21 µm and cell viability rates of over 98%. The cells in the spheroids cultured under normoxic conditions formed tight junctions and were characterized by a low level of proliferation and the ability to synthesize extracellular matrix proteins. Under hypoxia cells in the spheroids showed partial loss of intercellular contacts, acquired a spindle shape, started to express HIF1a, SNAIL, COL1Al and accumulate collagen. All these features demonstrated the activation of mesothelial(endothelial)-mesenchymal transition strongly resembling epicardial cellular responses to ischemia in vivo. Conclusion. An epicardial spheroid cell culture model suitable for study cellular responses to hypoxic environment was developed. This model can be used to clarify mechanisms regulating epicardial microenvironment and test new targeted candidate drugs.