Aleria Dolgodvorova

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.

Myocardial edema is a common symptom of pathological processes in the heart, causing aggravation of cardiovascular diseases and leading to irreversible myocardial remodeling. Patient-based studies show that myocardial edema is associated with arrhythmias. Currently, there are no studies that have examined how edema may influence changes in calcium dynamics in the functional syncytium. We performed optical mapping of calcium dynamics on a monolayer of neonatal rat cardiomyocytes with Fluo-4. The osmolality of the solutions was adjusted using the NaCl content. The initial Tyrode solution contained 140 mM NaCl (1T) and the hypoosmotic solutions contained 105 (0.75T) and 70 mM NaCl (0.5T). This study demonstrated a sharp decrease in the calcium wave propagation speed with a decrease in the solution osmolality. The successive decrease in osmolality also showed a transition from a normal wavefront to spiral wave and multiple wavelets of excitation with wave break. Our study demonstrated that, in a cellular model, hypoosmolality and, as a consequence, myocardial edema, could potentially lead to fatal ventricular arrhythmias, which to our knowledge has not been studied before. At 0.75T spiral waves appeared, whereas multiple wavelets of excitation occurred in 0.5T, which had not been recorded previously in a two-dimensional monolayer under conditions of cell edema without changes in the pacing protocol.