Telocytes (TCs) are a special group of interstitial cells that have a small cell body with alternate segments such as dilations called podoms and thin segments called podomeres. Many tissues and organs in mammals contain these cells such as several structures of the heart- endocardium, myocardium, epicardium and even heart valves. There is research showing that primary cultures of heart tissues show the presence of these cells. Primary cultures also revealed that TCs connect with other cells to form a three-dimensional (3D) interstitial network. Thus, apart from connections, they can also be involved in modeling, communication and tissue homeostasis.
TCs are identified usually with transmission electron microscopy (TEM) considered as the “gold standard”. There is no immunomarker yet to target and identify TCs that requires the use of double immunolabelling. This approach can allow us to differentiate these cells from other interstitial cells. The interstitial spaces contain both fibroblasts and TCs with different functions. TCs function to form 3D networks for cell-cell communication and fibroblasts produce collagen.
As far as research is concerned, one should be able to discriminate between fibroblasts and TCs. The morphology of fibroblasts is different with shorter, thicker and fewer processes that allow one to differentiate fibroblasts and TCs. Other differences also include the difference in the microRNA profiles, genes, and proteomes. Yet, there is a possibility of getting confused between TCs and fibroblasts.
A study published by Bei and team in 2015 in PlosOne reported the primary culture of cardiac TCs and fibroblasts to differentiate these cells using staining and study immunophenotypes. The observation of morphology revealed the morphology specific to these cells. Immunofluorescence revealed that the primary culture could allow differentiation between the cells; TCs from cardiac tissues were CD34/c-kit, CD34/vimentin, and CD34/PDGFR-β positive and fibroblasts were positive for the latter two and not positive for c-kit. TCs from the liver, lung, heart valve and skeletal muscle express PDGFR-β. When compared to pericytes, TCs were found to be CD34 positive and weakly positive for α-SMA while pericytes did not express CD34. Thus, the use of CD34/c-kit, CD34/vimentin, and CD34/PDGFR-β labeling allow for differentiating TCs from fibroblasts as well as pericytes.
The primary culture also revealed that the attachment of TCs required 2–24 hours while fibroblasts attached in 2 hours. The TCs displayed the formation of long and thin telopodes with altering podoms-podomeres.
As TCs can serve as a source of cardiac mesenchymal cells, flow cytometry was performed to check for a suitable marker. TCs showed homogenous expression of CD29-a mesenchymal marker and were negative for CD45-a hematopoietic marker. This is on the lines of Bone marrow stem cells or BMSCs suggestive of the ability of these cells to give rise to MSCs that can be cultured. Thus, primary cultures allow uncovering interesting findings of lesser-known cells.
Bei Y, Zhou Q, Fu S, Lv D, Chen P, Chen Y, et al. (2015) Cardiac Telocytes and Fibroblasts in Primary Culture: Different Morphologies and Immunophenotypes. PLoS ONE 10(2): e0115991. https://doi.org/10.1371/journal.pone.0115991.