Myocardial telocytes: a specific new cellular entity

The existence of a new type of interstitial cells in the heart namely, interstitial Cajal-like cells (ICLC), has been described for the first time by Hinescu and Popescu in 2005. This study was then followed by an ascending trend of publications regarding the morphology, phenotype and distribution of myocardial ICLC in diverse species including human patients. Recently the new term ‘telocytes’ has been proposed for cells formerly known as ICLC, and the term ‘telopodes’ has been proposed for the prolongations of these cells. The identification of these cells is based on ultrastructural criteria. In addition, telocyters/telyopodes can be identified by several complementary approaches including methylene blue vital staining, silver impregnation and immunoreactivity against CD117/c-kit, vimentin, etc. This point of view presents critical data existing in literature, as well as own results, which unequivocally provide compelling evidence that telocytes are a new distinct cellular entity of myocardial interstitium. Several presumable functions of the myocardial telocytes are discussed: (i) intercellular signalling, (ii) cardiac repair/remodelling and (iii) stem cell nursing in cardiac renewal.     

Cardiac regeneration: epicardial mediated repair

The hearts of lower vertebrates such as fish and salamanders display scarless regeneration following injury, although this feature is lost in adult mammals. The remarkable capacity of the neonatal mammalian heart to regenerate suggests that the underlying machinery required for the regenerative process is evolutionarily retained. Recent studies highlight the epicardial covering of the heart as an important source of the signalling factors required for the repair process. The developing epicardium is also a major source of cardiac fibroblasts, smooth muscle, endothelial cells and stem cells. Here, we examine animal models that are capable of scarless regeneration, the role of the epicardium as a source of cells, signalling mechanisms implicated in the regenerative process and how these mechanisms influence cardiomyocyte proliferation. We also discuss recent advances in cardiac stem cell research and potential therapeutic targets arising from these studies.     

Telocytes in human skin – are they involved in skin regeneration?

Telocytes (TCs), a particular interstitial cell type, have been recently described in a wide variety of mammalian organs ( www.telocytes.com ). The TCs are identified morphologically by a small cell body and extremely long (tens to hundreds of μm), thin prolongations (less than 100 nm in diameter, below the resolving power of light microscopy) called telopodes. Here, we demonstrated with electron microscopy and immunofluorescence that TCs were present in human dermis. In particular, TCs were found in the reticular dermis, around blood vessels, in the perifollicular sheath, outside the glassy membrane and surrounding sebaceous glands, arrector pili muscles and both the secretory and excretory portions of eccrine sweat glands. Immunofluorescence screening and laser scanning confocal microscopy showed two subpopulations of dermal TCs; one expressed c‐kit/CD117 and the other was positive for CD34. Both subpopulations were also positive for vimentin. The TCs were connected to each other by homocellular junctions, and they formed an interstitial 3D network. We also found TCs adjoined to stem cells in the bulge region of hair follicles. Moreover, TCs established atypical heterocellular junctions with stem cells (clusters of undifferentiated cells). Given the frequency of allergic skin pathologies, we would like to emphasize the finding that close, planar junctions were frequently observed between TCs and mast cells. In conclusion, based on TC distribution and intercellular connections, our results suggested that TCs might be involved in skin homeostasis, skin remodelling, skin regeneration and skin repair.