**1.2 Specific roles of the telocyte network: hollow organs**

A common role proposed for the 3-D TCs scaffold in the hollow organs is to follow organ distension and relaxation avoiding anomalous deformation and controlling blood vessels closure or rheology. However, because of the anatomical complexity of such districts and the great variety of cell populations herein interacting with the TCs, many other roles are conceivable, suggesting that these cells, as connecting devices in the stromal space, might take center stage in the integration of all the information coming from the vascular, nervous, and immune systems, as well as from tissue-resident stem cells.

The present overview of the literature focused on the spatial organization, morphological, and histochemical peculiarities of the TCs, according to their location in different organs. This may help to point out the presumptive roles of the homo- and hetero-cellular TCs networks. With this aim, the TCs networks located in some representative hollow organs that have been more intensively studied, such as the

**73**

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

of the correct and coordinated behavior of the apparatus.

**2.1 Gastrointestinal telocyte network in healthy condition**

In the human and mouse gastrointestinal tract, the TCs form widespread networks in the mucosa, submucosa, muscle layers, at the myenteric plexus level, at the submucosal border of the muscular mucosae, in the circular muscle layer, and around nerve strands, blood vessels, funds of gastric glands, and intestinal crypts [32, 39]. Immunohistochemically, all the TCs residing in the different layers of the gastrointestinal tract wall can be identified as CD34+/PDGFRα+ interstitial cells [32]. In the lamina propria and submucosa, the 3D homo-cellular TCs network has a structural role, forming the scaffolding that can direct the collagen fibers/bundles and define the spaces where the several elements of the connective tissue accommodate. Although it cannot be excluded that these TCs could eventually be recruited for the ECM synthesis, the abovementioned structural function is likely to be the main one. However, the role attributed to the TCs lining the basal-lateral surface of the glandular crypts [32, 39], where epithelial stem cells are located is particularly intriguing, since these TCs have been proposed to influence the proliferation and differentiation of stem cells due to their ability to produce and secrete a variety of molecules [40], the close relationships they recurrently establish with the "stem cell niches" [34, 40], and the expression on their surface of the functional receptor PDGFRα whose activation is critical in mammalian organogenesis [39]. In this context, it is worth mentioning that a very recent study demonstrated that the subepithelial plexus formed by PDGFRα+ TCs acts as a crucial source of Wnt proteins, which are essential to support intestinal crypt stem cell proliferation and epithelial renewal [23]. In the muscle coat, by both immunohistochemistry (PDGFRα and CD34 immunolabeling) and electron microscopy, the TCs processes were observed to constitute 3D networks intermingling with those of the ICCs and to establish cell-to-cell contacts with them [32, 34]. Interestingly, within the gut muscle layers the TCs and ICCs networks can be clearly distinguished based on their different immunophenotypes, as the TCs are CD34+/PDGFRα+ and negative for c-kit, and vice versa, the ICC are c-kit+ and negative for either CD34 or PDGFRα [32]

gastrointestinal and reproductive tracts, the urinary bladder, and in the cardiac parenchyma, in both healthy and disease conditions, have been taken into consideration.

The gastrointestinal tract consists of different hollow organs which have some similar and some different shapes and functions. Every organ modifies its lumen caliber and thickness several times throughout the day, following food transit. Food intake might happen several times per day, with different types and quantities, and the food transit varies according to the different regions, from the stomach to the colon. The cells of the lining epithelium do not change their shape, while microvilli height importantly changes. Under the mucosa, made by the epithelium, the lamina propria, and the muscular mucosae, there is the submucosa that has different morphological organization and function. Finally, the muscle coat is responsible for gastrointestinal contractility. Two motile activities, coordinated by the enteric nervous system and the ICCs, are present: peristalsis, a constant ab-oral movement that does not importantly modify the lumen caliber, and the relaxation/contraction related to food arrival/mixing for digestion and absorption/transit which promotes sustained lumen caliber changes. Region-specific mechanical and functional interrelationships between all the components of this complex apparatus are at the basis

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

**2. Gastrointestinal tract**

gastrointestinal and reproductive tracts, the urinary bladder, and in the cardiac parenchyma, in both healthy and disease conditions, have been taken into consideration.
