Myocardial Telocyte-Like Cells: A Review Including New Evidence

Abstract

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.

The Telocytes in the Subepicardial Niche

“…Both appear as large and degranulating cells. All these observations support recent and consistent evidence for TCs' failure to be categorized as a distinctive cell type [11,24,26].…”

“…The immunophenotype of TCs 'is similar to that of interstitial, endothelial, smooth muscle, mast and haematopoietic stem cells and neurons' [18]. Increasing evidence strongly suggests that, rather than being a distinctive cell type, TCs are just a cell morphology [11] of other TC-like cell types (fibroblasts, immune cells, endothelial cells, stem cells, etc.) [19][20][21], or a morphology resulted if thin, flat, pancake-like cells are cut and documented on two-dimensional slices [22].…”

“…They were previously considered interstitial Cajal-like cells (ICLCs) [2][3][4][5][6][7][8][9][10]. Telocytes are small-sized cells residing in stem niches; they project long, slender, and moniliform prolongations, which are known as telopodes [11][12][13][14]. In recent years, TCs have been noted in almost all organs and tissues in the human body [15,16].…”

Extracorporeal Shock Waves Increase Markers of Cellular Proliferation in Bronchial Epithelium and in Primary Bronchial Fibroblasts of COPD Patients

“…Markers of cell proliferation include CD117 (c-Kit or SCFR), a receptor tyrosine kinase protein that binds to stem cell factor (SCF), expressed on hematopoietic stem cells. It can also be expressed by mast cells, melanocytes in the skin, interstitial cells of Cajal in the digestive and urogenital tract [24], cardiac pericytes [25], amniotic fluid stem cells [26], stem/progenitor cells in conducting airway epithelium of porcine lung [27], and dendritic cells in the lung [28]. Another marker of cell proliferation is proliferating cell nuclear antigen (PCNA).…”

An Immunohistochemical Study of Gastric Mucosa and Critical Review Indicate That the Subepithelial Telocytes Are Prelymphatic Endothelial Cells

“…The TCs identification by immunohistochemistry is still uncertain. Additionally, TCs do not appear in the accepted Terminologia Histologica, and considerable artifactual results that have been used to support TCs as a novel cell type, are extensively documented [4,5,6,7]. Moreover, recent reviews suggest that TCs have not been adequately distinguished from lymphatic endothelial cells (LECs) in previous studies [5], which makes their morphological identification as well as their repeatedly claimed CD34+ immunophenotype [8,9,10,11,12] insufficient for a firm assessment.…”