**1. Introduction: the telocytes**

Discovered 13 years ago, telocytes (TCs) still represent a subject of debate regarding their role. TCs were first described in 2005, in the interstitial space surrounding exocrine acini in the pancreas, and considered as cells closely resembling the interstitial cells of Cajal (ICCs) by Romanian scientists from Carol Davila University of Medicine and Pharmacy in Bucharest, Romania, which entitled their first publication *Interstitial Cells of Cajal in Pancreas* [1]. Subsequent publications of this team described these cells under the name of interstitial Cajal-like cells and characterized them with the aid of electron microscopy and immunoctyo(histo) chemistry [2–6]. In 2010, professor Popescu, the Bucharest team leader, along with professor Faussone-Pellegrini, who is considered to be the international leading expert in ICCs (the gut pacemaker cells), have agreed that TCs and ICCs can be regarded as completely different cell populations based on the ultrastructural peculiarities, and went on to give them the name of "telocytes" [7]. In the following years, TCs have been described in numerous organs, and appear to be omnipresent in stromal space of humans and laboratory mammals where they form networks [8–10] by making contacts with each other (homo-cellular contacts). This is possible due to their unique and exceptionally long (several tens to hundreds of μm) cell prolongations called telopodes [7]. As professor Popescu liked to say "the shortest possible definition for telocytes is cells with telopodes" [11]. Telopodes are characterized by a succession of thin, filamentous regions (podomers) and dilated areas (podoms) with bead-like appearance [12]. TCs were revealed to have a third dimension that was only recently observed by FIB-SEM tomography, telopodes being represented by a veil- or ribbon-like extensions that compartmentalize the interstitial space [13]. Apart from the ability to form networks, TCs also can provide local communication with different cells and also to deliver extracellular vesicles to establish distant communication [14–18]. A detailed representation of the TCs contacts is illustrated in **Figure 1**.

To find out the function(s) of these cells, many methods of investigation have been employed, ranging from classical microscopy—optical and electronic—to advanced genomics and proteomics techniques. Thus, differentiation of TCs from mesenchymal stem cell adipocytes, fibroblasts, and endothelial cells was achieved [19–22].

The discovery and description of TCs have given rise to many controversies. From the publication of the first article to the present, the interest generated by TCs can be traced in the graph summarizing the number of articles published annually in PubMed (**Figure 2**). Though not yet described in speciality treatises as a distinct cellular type, this prospect does not seem to be far, the evidence being the increase in the number of articles published in the most prestigious journals such as Nature [23–25]. The discussion of these controversies is dealt with in detail by two recent reviews, in which there are enough arguments for and against the existence of TCs as a new cell type [26, 27]. We believe that in the shortest time new biomarkers will

## **Figure 1.**

*Artistic representation of a 3D view of the contacts of a telocyte. TCs are regarded as interconnection devices due to their homo- and hetero-cellular junctions, as well as to their proximity to structures like blood vessels, nerve fibers, and muscle fibers. Image courtesy of Iurie Roatesi. Reproduced with permission from Ref. [75].*

**71**

**Figure 3.**

**Figure 2.**

*Telocytes: New Connecting Devices in the Stromal Space of Organs*

be found to prove the existence of this particular type of cell, and here is just one

*Trends of publications searched in PubMed with "Telocytes" as a key word between 2010 and 2019.*

Our attention in this chapter is focused on synthesizing the available information relating to the main categories of interest that emerge from the chart shown in **Figure 3**, namely gastrointestinal tract, urinary bladder, reproductive tract, and heart.

The ability of these cells to form 3-D stromal networks can be considered a discriminant element for their recognition under the light microscope [8],

step to the description of their possible functions.

*Histogram of publications on telocytes categorized by categories of interest.*

**1.1 The telocyte network**

*DOI: http://dx.doi.org/10.5772/intechopen.89383*

### **Figure 2.**

*Innovations in Cell Research and Therapy*

contacts is illustrated in **Figure 1**.

[19–22].

professor Faussone-Pellegrini, who is considered to be the international leading expert in ICCs (the gut pacemaker cells), have agreed that TCs and ICCs can be regarded as completely different cell populations based on the ultrastructural peculiarities, and went on to give them the name of "telocytes" [7]. In the following years, TCs have been described in numerous organs, and appear to be omnipresent in stromal space of humans and laboratory mammals where they form networks [8–10] by making contacts with each other (homo-cellular contacts). This is possible due to their unique and exceptionally long (several tens to hundreds of μm) cell prolongations called telopodes [7]. As professor Popescu liked to say "the shortest possible definition for telocytes is cells with telopodes" [11]. Telopodes are characterized by a succession of thin, filamentous regions (podomers) and dilated areas (podoms) with bead-like appearance [12]. TCs were revealed to have a third dimension that was only recently observed by FIB-SEM tomography, telopodes being represented by a veil- or ribbon-like extensions that compartmentalize the interstitial space [13]. Apart from the ability to form networks, TCs also can provide local communication with different cells and also to deliver extracellular vesicles to establish distant communication [14–18]. A detailed representation of the TCs

To find out the function(s) of these cells, many methods of investigation have been employed, ranging from classical microscopy—optical and electronic—to advanced genomics and proteomics techniques. Thus, differentiation of TCs from mesenchymal stem cell adipocytes, fibroblasts, and endothelial cells was achieved

The discovery and description of TCs have given rise to many controversies. From the publication of the first article to the present, the interest generated by TCs can be traced in the graph summarizing the number of articles published annually in PubMed (**Figure 2**). Though not yet described in speciality treatises as a distinct cellular type, this prospect does not seem to be far, the evidence being the increase in the number of articles published in the most prestigious journals such as Nature [23–25]. The discussion of these controversies is dealt with in detail by two recent reviews, in which there are enough arguments for and against the existence of TCs as a new cell type [26, 27]. We believe that in the shortest time new biomarkers will

*Artistic representation of a 3D view of the contacts of a telocyte. TCs are regarded as interconnection devices due to their homo- and hetero-cellular junctions, as well as to their proximity to structures like blood vessels, nerve fibers, and muscle fibers. Image courtesy of Iurie Roatesi. Reproduced with permission from Ref. [75].*

**70**

**Figure 1.**

*Trends of publications searched in PubMed with "Telocytes" as a key word between 2010 and 2019.*

**Figure 3.** *Histogram of publications on telocytes categorized by categories of interest.*

be found to prove the existence of this particular type of cell, and here is just one step to the description of their possible functions.

Our attention in this chapter is focused on synthesizing the available information relating to the main categories of interest that emerge from the chart shown in **Figure 3**, namely gastrointestinal tract, urinary bladder, reproductive tract, and heart.
