The Telocytes: Ten Years after Their Introduction in the Scientific Literature. An Update on Their Morphology, Distribution, and Potential Roles in the Gut

Abstract

Ten years ago, the term ‘telocyte’ was introduced in the scientific literature to describe a ‘new’ cell type described in the connective tissue of several organs by Popescu and Faussone-Pellegrini (2010). Since then, 368 papers containing the term ‘telocyte’ have been published, 261 of them in the last five years. These numbers underscore the growing interest in this cell type in the scientific community and the general acceptance of the name telocyte to indicate this interstitial cell. Most of these studies, while confirming the importance of transmission electron microscopy to identify the telocytes with certainty, highlight the variability of their immune phenotypes. This variability was interpreted as due to (i) the ability of the telocytes to adapt to the different sites in which they reside; (ii) the distinct functions they are likely to perform; and (iii) the existence of telocyte subtypes. In the present paper, an overview of the last 10 years of literature on telocytes located in the gut will be attempted, confining the revision to the morphological findings. A distinct chapter will be dedicated to the recently hypothesized role of the telocytes the intestinal mucosa. Through this review, it will be shown that telocytes, despite their variability, are a unique interstitial cell.

The 3D Pattern of the Rainbow Trout (Oncorhynchus mykiss) Enterocytes and Intestinal Stem Cells

“…These were identified as telocytes, and the ablation of these peculiar cells caused a perturbation of the gene expression pattern of enterocytes, suggesting that their function is to ensure the maintenance of an efficient epithelium at the villus tip [40]. Telocytes have been identified as a subepithelial source of proliferative signals to the stem/progenitor cell compartment of the intestinal stem-cell niche in both mouse [41,42] and human [43,44]. Therefore, it is reasonable to assume that a similar function may also be played by these cells in RT.…”

Telocyte and Cajal cell distribution in renal pelvis, ureteropelvic junction (UPJ), and proximal ureter in normal upper urinary tract and UPJ obstruction: reappraisal of the aetiology of UPJ obstruction

“…Interstitial cells of Cajal were demonstrated by transmission electron microscopy (TEM) studies. They are distinct from smooth muscle cells, fibroblasts, and monocytes, the surface membrane has abundant invaginations and prominent endoplasmic reticulum, they are characterized by being uninucleate with thin cytoplasm and numerous mitochondria [4,5,7,8,19,11,20]. Low density or altered function of Cajal cells were attributes to the etiology of UPJ obstruction [3,4,7,15,21].…”

“…The nucleus contains condensed heterochromatin; the surrounding cytoplasm is scarce and encompasses few organelles [2,10,17,19]. Ultrastructural features characterizing and differentiating telocytes and Cajal cells were described in detail by Vannuchi et al [17,18,19]. Telocytes were attributed to the etiology of UPJ obstruction [21].…”

A Two-Step Immunomagnetic Microbead-Based Method for the Isolation of Human Primary Skin Telocytes/CD34+ Stromal Cells

“…In fact, the majority of studies that have so far investigated TCs in physiologic and pathologic tissues are mainly descriptive and focused on the ultrastructural, morphologic, and immunophenotypic characterization of these cells within their resident tissues, leaving much of their proposed functions still a matter of debate [ 22 , 29 , 55 , 56 ]. In this regard, the ability of TCs to form complex interstitial networks and communicate with neighboring cells by establishing multiple intercellular contacts or releasing extracellular vesicles containing bioactive molecules, together with the evidence that such TC networks are severely impaired in a variety of pathologies, led to proposing that these cells may exert a wide spectrum of functions important for the maintenance of tissue homeostasis [ 2 , 4 , 5 , 10 , 28 , 29 , 57 , 58 ]. For instance, owing to their strategic position in relation to tissue-resident stem cell niches in various organs and satellite cells in the skeletal muscle, it has been postulated that TCs may play a pivotal role in stem cell survival, proliferation, differentiation, maturation, and guidance, eventually stimulating tissue regenerative processes [ 5 , 19 , 52 , 59 , 60 , 61 , 62 ].…”

“…Ultrastructural alterations and loss of TCs have also been reported during fibrotic tissue remodeling, which led to attributing them a possible role in the regulation of neighboring fibroblast functionality [ 28 , 34 , 37 , 38 ]. In addition, TCs seem to possess electrophysiologic properties, as reported in myometrium, myocardium, and the enteric neuromuscular compartment, where they have been proposed to contribute to the spreading of the slow waves generated by the pacemaker interstitial cells of Cajal [ 2 , 5 , 26 , 44 , 58 , 67 , 68 ]. In light of the above, it is clear that the possibility to use purified and in vitro expanded TCs in coculture with other cell populations, including stem cells, ECs, immune cells, and fibroblasts, may represent an extremely useful tool to definitively unravel the effective functional roles and implications of these stromal cells in different pathologic conditions.…”