Telocytes role during the postnatal development of the Mongolian gerbil jejunum

Abstract

Telocytes are recently categorised CD34-positive interstitial cells that comprise the cells which were previously called interstitial Cajal-like cells (ICLCs). These were detected in the stroma of various organs such as the prostate, lungs, mammary glands, liver, gallbladder, and jejunum, among others. Several functions have been proposed for telocytes, such as a supportive role in smooth muscle contraction and immune function in adult organs, and tissue organisation and paracrine signalling during development, as well as others. In the jejunum, little is known about the function of telocytes in the adult organ, or is there any information about when these cells develop or if they could have an auxiliary role in the development of the jejunum. The present study employed histological, immunohistochemical and immunofluorescence techniques on histological sections of the jejunum of Mongolian gerbil pups on two different days of postnatal development of the jejunum, covering the maturation period of the organ. By immunolabelling for CD34, it was observed that telocytes are already present in the jejunum during the first week of postnatal life and exist in close association with the developing muscularis mucosae, which are therefore TGFβ1-positive. The telocytes are still present at the end of the first month of life, and a portion of them present co-localisation with c-Kit. Fibroblast-like cells, which are exclusively c-Kit-positive, are also observed, which may indicate the presence of interstitial Cajal cells (ICCs). Finally, it can be hypothesised that a portion of the telocytes may give rise to ICCs, which are c-Kit-positive but CD34 negative.

Introduction

Telocytes are newly described cells that are located in the interstices of various organs. These include cells which were previously called interstitial Cajal-like cells (ICLCs) that have been described in several organs (Popescu and Faussone-Pellegrini, 2010), whereas the interstitial cells of Cajal (ICCs) are exclusive to the gastrointestinal tract and were discovered by Ramón y Cajal (1911), so were assumed to be interstitial neurons. Later, it was found that ICCs originate from the mesoderm and a pacemaker role in smooth muscle contraction in the intestine was proposed for them (Thuneberg, 1982). ICCs have c-Kit as the main marker (Komuro and Zhou 1996; Pasternak et al., 2016; Aleksandrovych et al. 2017), which is a receptor that binds to stem cell factor (SCF) and induces calcium mobilization through a kinase of the src family and phosphoinositide 3-kinase (PI3K) (Liang et al., 2013). This receptor would be central to the pacemaker function exerted by the ICCs (Drumm et al. 2014). Telocytes have CD34 as the main marker and a portion of them are also c-kit-positive (Cretoiu et al. 2012); before the establishment of the term telocytes, CD34-positive ICLCs that did not show c-Kit labelling were detected in the intestine (Iino and Nojyo 2009). These cells correspond to that which was later conceptualised as intestinal telocytes (Cretoiu et al. 2012).

Telocytes are morphologically distinct from fibroblasts, with long cytoplasmic projections called telopodes, which in turn have a monoliform aspect, with alternation between dilated regions, podoms (which carry mitochondria, endoplasmic reticulum and cavelola) and fibrillar-like regions called podomers (Popescu and Faussone-Pellegrini, 2010). There is evidence that telocytes differ from fibroblasts in terms of the proteome, morphology and gene expression (Kang et al. 2015; Xiao and Bei, 2016; Zhang et al., 2006) and from ICCs, which have a pyramidal cell body and shorter cytoplasmic projections (Popescu and Faussone-Pellegrini, 2010). Telocytes have characteristics of progenitor cells, as proposed for a wide subset of CD34-positive cells (Sidney et al., 2014); it was hypothesised that these cells could give rise to fibroblasts and myofibroblasts, playing an active role in tissue repair in the skin (Díaz-Flores et al. 2016), as well as to cardiomyocytes (Bei et al. 2015) or even ICCs (Sanches et al., 2017a, Sanches et al., 2017b). In addition, telocytes undergo the intense synthesis of paracrine factors in their vesicles, which would also indicate possible roles in stromal development, as well as the expression of proteins associated with homeostasis and stromal repair (Zheng et al., 2014).

Such cells were described in the liver (Xiao et al., 2013), gallbladder (Pasternak et al. 2012, 2013a-b; Matyja et al. 2013), lungs (Zheng et al., 2012) skin (Ceafalan et al. In the panties (Nicolescu and Popescu, 2012), mammary glands (Mou et al., 2013), parotid glands (Nicolescu et al., 2011), kidneys (Qi et al., 2012), uterus (Creţoiu et al. 2012), prostate (Corradi et al. 2013), duodenum (Carmona et al. 2011) and jejunum (Cretoiu et al. 2012). In the jejunum, a role in intercellular signalling has been hypothesised, such as a role in the control of local organ homeostasis in the duodenum; however, the function of these cells in the intestine is still elusive, and there is no information about the presence of these cells throughout intestinal development. The development of the jejunum of rats is a complex process, which begins in the foetal life. At birth, the jejunum, like the rest of the intestine, is not yet fully mature. From birth to weaning, the rat intestine continues to develop, with an increase in proliferative activity, in villi width and in immunological activity (Cummins et al. 1988; Montgomery et al., 1999, Sureda et al., 2017). The complete network of cell interactions and molecular pathways related to the jejunum development has not been completely elucidated; thus, the presence of telocytes during intestinal development could indicate a greater complexity to this process. Telocytes were also assumed to play a role in the development of the myocardium (Faussone-Pellegrini and Bani, 2010; Bani, 2016) and the prostate (Sanches et al., 2016), especially in terms of tissue organisation and smooth muscle development.

The Mongolian gerbil is a rodent species that is easy to handle in the laboratory, making it promising for experimental manipulation (Kuehn and Zucker, 1968; Norris and Adams, 1972; Spitzer and Semple, 1995). Several experiments ranging from studies on the nervous system, diabetes, and cancer to reproductive biology investigations were performed with gerbils, due to the previously mentioned factors, their hormonal peculiarities and their high susceptibility to epilepsy and tumorigenesis (Loskota et al., 1974; Spitzer and Semple, 1995; Santos and Taboga, 2006, Taboga, Vilamaior and Góes, 2009, Salyards et al., 2013, Sanches et al., 2017b, Li et al. 2016). The gerbil has a gestation period of about 25 days, which is longer than that of mice, which lasts for about 19 days (Sugimura et al., 1986), and that of rats, which lasts for approximately 21 days (Hayashi et al. 1991). Thus, the Mongolian gerbil tends to show a more pronounced postnatal development (Sanches et al., 2014). The weaning period also occurs later, at the end of the first postnatal month (Norris and Adams, 1972), while in the rat, it occurs at the end of the third week (Cummins et al. 1988); therefore, the gerbil becomes useful for studies of the development of the intestine, considering that part of the intestinal development occurs during the postnatal period until the onset of weaning (Sureda et al., 2017). The current study aims to evaluate the presence of telocytes in two distinct periods of the postnatal development of the jejunum in the Mongolian gerbil, as well as to investigate a possible implication of these cells in it.