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Telocytes (TCs) are a controversial cell type characterized by the presence of a particular kind of prolongations, known as telopodes, which are long, thin, and moniliform. A number of attempts has been made to establish the molecular phenotype of cardiac TCs (i.e., expression of c-kit, CD34, vimentin, PDGRFα, PDGRFβ, etc.). We designed an immunohistochemical study involving cardiac tissue samples obtained from 10 cadavers with the aim of determining whether there are TC-like interstitial cells that populate the interstitial space other than the mural microvascular cells. We applied the markers for CD31, CD34, PDGRFα, CD117/c-kit, and α-smooth muscle actin (α-SMA). We found that, in relation to two-dimensional cuts, the endothelial tubes could be misidentified as TC-like cells, the difference being the positive identification of endothelial lumina. Moreover, we found that cardiac pericytes express PDGRFα, CD117/c-kit, and α-SMA, and that they could also be misidentified as TCs when using light microscopy. We reviewed the respective values of the previously identified markers for achieving a clear-cut identification of cardiac TCs, highlighting the critical lack of specificity.

Introduction Atrial fibrillation (AF) is nowadays considered to be one of the most important causes of heart failure, stroke, cognitive decline, vascular dementia, sudden death and overall cardiovascular morbidity. Recently were published a few articles suggesting a possible involvement of telocytes in the development of atrial fibrillation. The purpose of this article is to analyze the results obtained in the field systematically, and to see if there is enough data to support a possible involvement of telocytes in arrhythmogenesis. Materials and methods To this end, we performed a systematic review of the relevant scientific literature, indexed in PubMed, Web of Science, and Scopus. Results and discussions Our systematic review of the published data identified five articles containing original data, based on which the association between telocytes and atrial fibrillation was inferred in later studies. We analyzed the usefulness of the information contained in the original articles to support this association, showing a lack of definite proofs correlating telocytes with atrial fibrillation. Conclusions Even if a few articles implied a potential association between AF and telocytes, the current data is not enough to support it. Moreover, even an association between the morphology, characteristics, or density of the telocytes in the atrium/pulmonary veins and AF is potentially speculative, and more studies should be performed before implying it with a reasonable degree of certainty.

The discovery of cardiac stem cells (CSCs) able to renew the pool of cardiomyocyte raised the question of how these cells can be recognized and directed towards cardiac reconstruction after severe ischemic injury. The functional studies demonstrated that the differentiation of adult cardiac stem cells reproduce the stages observed in the embryonic development. Each stage is characterized by a complex molecular signature, which can be used for identification and molecular targeting. Three major markers have been used to isolate CSCs: c-kit, Sca-1, and Isl1 and different progenitor populations have been described: side-population (SP), cardiosphere-derived, epicardial-derived. Combinations between the main three markers and other transcription factors, cell surface proteins and regulatory RNAs may delimit even further the cardiac precursors. Accumulation of data leads to the idea that a single, yet unidentified unique cardiac stem cell is at the origin of those observed variants. In this review, we intended to summarize the actual knowledge about the main molecular markers of cardiac stem cells.