Aim To study the effect of hypoxia on the activity of epithelial-mesenchymal transition (EMT) in epicardial cells, which provides formation of a specialized microenvironment.Material and methods This study used a model of experimental myocardial infarction created by ligation of the anterior descendent coronary artery. The activity of epicardial cells after a hypoxic exposure was studied with the hypoxia marker, pimonidazole, bromodeoxyuridine, immunofluorescent staining of heart cryosections, and in vitro mesothelial cell culture.Results The undamaged heart maintained the quiescent condition of mesothelial cells and low levels of their proliferation, extracellular matrix protein production, and of the EMT activity. Acute ischemic injury induced moderate hypoxia in the epicardial/subepicardial region. This caused a global rearrangement of this region due to the initiation of EMT in cells, changes in the cell composition, and accumulation of extracellular matrix proteins. We found that the initiation of EMT in mesothelial cells may result in the formation of smooth muscle cell precursors, fibroblasts, and a population of Sca-1+ cardiac progenitor cells, which may both participate in construction of new blood vessels and serve as a mesenchymal link for the paracrine support of microenvironmental cells. In in vitro experiments, we showed that 72‑h hypoxia facilitated activation of EMT regulatory genes, induced dissembling of intercellular contacts, cell uncoupling, and increased cell plasticity.Conclusion The epicardium of an adult heart serves as a “reparative reserve” that can be reactivated by a hypoxic exposure. This creates a basis for an approach to influence the epicardium to modulate its activity for regulating reparative processes.
Neoangiogenesis is the key process determining myocardial regeneration after infarction. The urokinase-type plasminogen activator receptor (uPAR) is known to play an important role in the regulation of endothelial cell function and postnatal angiogenesis. However, uPAR its involvement in the regulation of the properties of vascular progenitor cells remains poorly studied. Aim: to evaluate uPAR expression on the surface of resident cardiac vascular progenitor cells (rcVPCs) and its impact on angiogenic cell properties in vitro as well as postinfarction cardiac vascularization. Materials and Methods. We used immunofluorescent analysis of cryosections of a murine myocardial infarction model to characterize vessels and rcVPCs, and evaluatedв the angiogenic properties potential of vasculogenic progenitor cells using the «tube assay» and induction ofinducing differentiation in a specialized medium. Results. We have found that the majority of Sca-1+ rcVPCs express the urokinase receptor and endothelial cell markers on their surface and are capable of proliferation and integration into the newly formed vessels in the injured area, indicating their possible involvement in thecontribution to vascularization process after infarction. After acute ischemic injury, the accumulation of vasculogenic progenitor cells (8+2 and 27+7 cells per visual field, respectively; P = 0.032) and vascularization processes (85+11 and 166+25 capillaries per visual field, respectively; P = 0.033) were observed in myocardium of uPAR-/- animals, compared with wild-type animals. Our studies demonstrated that Sca-1+ rcVCPs derived from uPAR-/- murine hearts demonstrated a reduced ability to form capillary-like structures and endothelial differentiation compared with Sca-1+ rcVCPs from hearts of wild-type mice. Conclusion. Thus, uPAR deficiency may lead to impaired vasculogenic properties of Sca-1+ rcVCPs, which is likely due to the loss of regulatory influence of specific ligands and the ability to interact with signaling mediators such as integrins. From the viewpoint of regenerative medicine, the modulation of uPAR activity can be considered as a potential targetpromising approach for targeted regulation of vasculogenic progenitor cells properties and postnatal angiogenesis.Highlight The urokinase-type plasminogen activator receptor is involved in the regulation of the angiogenic properties of Sca1+ vasculogenic progenitor cells.
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