Of GISTs and EGISTs, ICCs and ICs

Telocytes in the interstitium of human exocrine pancreas: ultrastructural evidence

OBJECTIVES

Pancreatic interstitial cells are located among acini, ducts, nerves, and blood vessels. They are essential for pancreas development, physiology, and for oncogenic microenvironment. We identified cells with characteristic ultrastructural features of telocytes in pancreatic interstitium. Telocytes were initially described as interstitial Cajal-like cells, but it gradually became clear that they were a distinct novel cell type not directly related to canonical interstitial Cajal cells.

METHODS

Serial ultrathin sections of human pancreatic tissue were studied by transmission electron microscopy. Computer analysis software was used to obtain 2-dimensional compositions from serial micrographs and to perform morphometry.

RESULTS

Pancreatic telocytes appear as small-body cells with prolongations called telopodes. The ultrastructural features of telopodes are the following: (a) number: 1 to 3; (b) length: tens of micrometers; (c) moniliform aspect: with podoms (thicker portions) and podomers (thin segments, with a mean width of 60 nm, undetectable by light microscopy); (d) dichotomous branching forming a network; (e) establish homocellular and heterocellular junctions; (f) release of microvesicles/multivesicular bodies. Telopodes pass close to blood vessels, nerves, and pancreatic acinar cells and ducts.

CONCLUSIONS

Telocytes are present as distinct interstitial cells in the exocrine pancreatic stroma. They act as important players in intercellular signaling via stromal synapses and shed vesicle transfer.

Telocytes are the common cell of origin of both PEComas and GISTs: an evidence-supported hypothesis

We advance the hypothesis that the telocyte might be the cell of origin of both PEComas (perivascular epithelioid cell tumours) and GISTs (gastro-intestinal and extra-gastrointestinal stromal tumours). The hypothesis is supported by data from the literature reporting that both PEComas and GISTs, as well as telocytes, share the expression of several markers. These data were supplemented by original immunohistochemical tests on selected series. Specifically: (1) Melanoma markers (Melan A, MiTF) typical of PEComas are expressed by a substantial fraction of GISTs. A fraction of GISTs was also found positive for CD63, a tetraspanin protein originally described in melanomas and marking exosomes. (2) c-KIT (CD117), proper of the vast majority of GISTs, can be expressed by PEComas (as well as by telocytes). (3) Markers described in telocytes (CD34, S-100, smooth muscle actin and vascular endothelial growth factor) have been reported as positive in cases of PEComas and GISTs. Telocytes show distinctive ultrastructural features with thin, extended, telopodes and are likely involved in inter-cellular signalling via paracrine secretion as well as by shed vesicles and exosomes. These cells have been described in many locations (cavitary and non-cavitary organs) and might display potentialities of a wide spectrum of differentiation (and function). In conclusion we propose that telocytes could be the common cells of origin for both PEComas and GISTs.

Interstitial Cajal-like cells of human Fallopian tube express estrogen and progesterone receptors

Cells of the female reproductive tract are subject to hormonal control via sex steroid genomic receptors expressed at nuclear level. We previously showed that interstitial Cajal-like cells (ICLC) of human myometrium expressed estrogen and progesterone receptors (ER/PR). Our aim, based on these results, was to see if ER and/or PR could be found also in tubal ICLC. Indeed, we present here immunohistochemical evidence that ICLC of human Fallopian tube (isthmic region) have such receptors. Stromal ICLC, as well as ICLC among smooth muscle layers, were identified in tissue sections by their morphological features (e.g. several very long, moniliform, prolongations of cell body) as well as by c-kit positivity, vital staining with methylene blue or silver impregnation. Additional evidence was provided by sequential staining for c-kit and for PR on the same cell, by 'sandwich method'. In vitro, the 4th passage cell cultures from Fallopian tube muscularis exhibiting ICLC morphology showed the presence of ER-alpha and/or PR-A by immunofluorescence. In conclusion, our data suggest that ICLC could function as steroid sensors, and might be implicated in Fallopian tube motility (via gap junctions or juxta- and/or paracrine mechanisms).

Gastrointestinal stromal tumors: report of an audit and review of the literature

Gastrointestinal stromal tumors (GISTs), tumors characterized by c-KIT mutations, are the most frequent mesenchymal tumors of the digestive tract. The stomach is the most commonly involved site. Localization, size and mitotic rate are reliable predictors of survival and the two milestones of GISTs treatment are surgery and imatinib. This article is aimed to report the data of an audit, carried out on the morphological and clinical aspects of the disease and to review the present knowledge on GISTs. A total of 172 patients with GISTs (M : F=1 : 1; mean age 65 years) were recruited. The stomach was the most frequently involved site. In 50% of the cases the tumor was smaller than 5 cm, whereas major symptoms were observed in 43% of the cases. Predictors of progressive disease were present only in a small percentage of cases but the disease was in the metastatic phase in over 25% of the cases at diagnosis. Familial aggregation was rare but a consistent share of the patients (21%) had other synchronous or metachronous cancers. The most frequent mutations were in-frame deletions and point mutations of c-KIT exon 11. This report confirms in part the available data on GIST in a consecutive series of patients recruited in Italy and shows that only large collaborative multicenter studies provide data sound enough to enable making reasonable clinical and therapeutic choices, and suggests that, as a measure of secondary prevention, a diagnostic definition should be obtained in all submucosal lesions of the GI tract and that GIST patients should be screened for second tumors.

Histochemical and ultrastructural characteristics of an interstitial cell type different from ICC and resident in the muscle coat of human gut

CD117 (or c-kit) is expressed by the interstitial cells of Cajal (ICC), which are located within the gastrointestinal (GI) muscle coat and directly involved in its motility. CD34 is expressed by several cell types some of which have features and location resembling the ICC; however, a sure identification of these cells is still lacking. In order to establish whether the CD34-positive cells of the human GI tract are to be considered as ICC subpopulation or a novel independent cell type, and to hypothesize their nature and role, we verified CD34 and CD117 receptor expression under light and fluorescence microscope and performed a routine and a CD34-immuno-electron microscopy. CD34-positive cells were seen in the entire human GI tract. In the muscularis propria, shared morphologies similar to the c-kit-positive cells, in the submucosa, resembled fibroblasts. Their ultrastructure resembled that of the fibrocytes/fibroblasts and of the interstitial Cajal-like cells (ICLC). Double labelling and immunoelectro-microscopy demonstrated that they are unequivocally different to the ICC and, due to the similarities with the ICLC, we identified them as ICLC. The novelty of these results is that two types of interstitial cells are present in the GI muscle coat of humans: the ICC and the ICLC. We hypothesize a mechanical role for the septal ICLC, those at the myenteric plexus level and those bordering the muscle layers; a helping role in neurotransmission is proposed for the ICLC intercalated with the intramuscular ICC, possibly in spreading the slow waves generated by the ICC. Furthermore, the possibility that the ICLC represent the adult mesenchymal stromal cells able to guarantee the ICC renewal deserves to be considered.

Myocardial interstitial Cajal-like cells (ICLC) and their nanostructural relationships with intercalated discs: shed vesicles as intermediates

Intercalated discs (ID) are complex junctional units that connect cardiac myocytes mechanically and electrochemically. However, there is limited information concerning the cardiomyocyte interaction with interstitial non-muscle cells. Our previous studies showed that myocardial interstitial Cajal-like cells (ICLC) are located in between cardiomyocytes, blood capillaries and nerve fibres. Typically, ICLC have several very long, moniliform, cytoplasmic processes which establish closed contacts with nerve fibres, as well as each other. We report here ultrastructural evidence concerning the relationships of ICLC processes with ID. The ICLC cytoplasmic prolongations (tens micrometers length) preferentially pass by or stop nearby the ID. Transmission electron microscopy emphasized three distinct connecting features between the tips of ICLC extensions and myocytes at the ‘mouth’ of ID: free or budding shed vesicles, exocytotic multi-vesicular bodies and direct contacts. In the last case, electron-dense repetitive nanostructures (‘pillars’) (35–40 nm high and 100–150 nm wide, similar to adhesion molecules) fasten the ICLC to the myocytes. All these features suggest a juxtacrine and/or paracrine intercellular mutual modulation of ICLC and cardiomyocytes in the microenvironment of ID, possibly monitoring the cardiac functions, particularly the electrical activity.

Interstitial Cajal-like cells in human gallbladder

We describe here an interstitial Cajal-like cell type (ICLC) in human gallbladder, resembling the archetypal enteric interstitial cells of Cajal. Gallbladder ICLC were demonstrated in fresh preparations (tissue cryosections) using methylene-blue, and fixed specimens in Epon semi-thin sections stained with toluidine blue or transmission electron microscopy (TEM). The positive diagnosis of gallbladder ICLC was further verified by immunohistochemistry: CD117/c-kit, CD34, and another 16 antigens: vimentin, desmin, nestin, alpha-smooth muscle actin, NK-1, S-100, PGP-9.5, tau protein, chromogranin A, NSE, GFAP, CD1a, CD62-P, CD68, estrogen and progesterone receptors. Double immunostaining was performed for CD117, CD34 and CD117 and nestin, respectively. In fresh specimens, the spatial density of gallbladder ICLC was 100-110 cells/mm(2). ICLC mainly appeared beneath the epithelium and in muscularis (about 7%, and approximately 5%, respectively). In toto, ICLC represent in gallbladder approximately 5.5% of subepithelial cells. TEM showed that diagnostic criteria were fulfilled by ICLC. Moreover, TEM indicated that the main ultrastructural distinctive feature for ICLC, the cell processes, develop into the characteristic shape at a relatively early stage of development. It remains to be established if, in humans, ICLC are involved in gallbladder (dis)functions (e.g. pace-making, secretion (auto-, juxta- and/or paracrine), intercellular signaling, or stone formation).

Interstitial Cajal-like cells in human uterus and fallopian tube

Recently, parallels have been drawn between enteric interstitial cells of Cajal (ICC) and similar cells outside the gut-interstitial Cajal-like cells (ICLC). This article reviews our laboratory findings on ICLC in the female reproductive tract. Since the morphology and function of ICLC are still a subject of debate, our purpose was to investigate whether ICLC are present in the fallopian tube and/or uterus, and if they share ultrastructural and immunohistochemical (IHC) features and/or functional roles. We studied ICLC presence in the human fallopian tube and myometrium primarily by light microscopy, and then by transmission electron microscopy (TEM), in tissue samples and at a single cell level. Taking advantage of our ICLC studies of several organs (pancreas, mammary gland, myocardium), we assembled a set of criteria, derived from ultrastructural features of ICLC, called "platinum standard." Besides the putative pacemaker function, ICLC might have other physiological roles, depending on tissue type (e.g., intercellular signaling, immune surveillance, steroid sensors). Consequently, there is a great urge for a conceptual framework that could allow a better understanding, from a functional point of view, and more so, as the ICLC processes are the longest cellular prolongations (except neurons).

Interstitial Cajal-like cells in rat mesentery: an ultrastructural and immunohistochemical approach

Interstitial Cajal-like Cells (ICLC) were recently recognized in a plethora of non-digestive organs. Here, we describe a cell type of rat mesentery sharing ultrastructural and immunohistochemical features with ICLC. Mesenteric ICLC were demonstrated by transmission electron microscopy (TEM) and further tested by light microscope immunohistochemistry. The cell described here fulfils the TEM diagnostic criteria accepted for ICLC: location in the connective interstitium; close vicinity to nerves, capillaries and other interstitial cells; characteristic long, moniliform cell processes; specialized cell-to-cell junctions; caveolae; mitochondria at 5–10% of cytoplasmic volume; rough endoplasmic reticulum at about 1–2%; intermediate and thin filaments, microtubules; undetectable thick filaments. The processes of this mesenteric ICLC were particularly long, with a mean length of 24.91 μm (10.27–50.83 μm), and a convolution index of 2.32 (1.37–3.63) was calculated in order to measure their potential length. Mean distances versus main target cells of ICLC–nerve bundles, vessels, adipocytes and macrophages–were 110.69, 115.80, 205.07 and 34.65 nm, respectively. We also tested the expression of CD117/c-kit, CD34, vimentin, α-smooth muscle actin, nestin, NK-1, tryptase and chymase and the antigenic profile of the mesenteric ICLC was comparable if not identical with that recently observed in ICLC from other extra-digestive tissues. Due to the peculiar aspect of the mesenteric ICLC processes it can be hypothesized that these cells form a three-dimensional network within the mesentery that is at the same time resistant and deformable following stretches consequent to intestine movements, mainly avoiding blood vessels closure or controlling blood vessels rheology. It remains, however, to be established if and how such cells are connected with the archetypal enteric ICC.

Gastrointestinal stromal tumors: a contemporary review

The literature on gastrointestinal stromal tumors (GISTs) has rapidly expanded and has demonstrated how scientific advancements in diagnosis can revolutionize the understanding of disease, while paving the way for effective treatment. While KIT (CD117) immunohistochemistry has established our definition of GISTs, molecular genetics continue to refine it. Elucidation of the aberrant receptor tyrosine kinase (RTK) model of GIST pathogenesis through mutations in c-kit and platelet-derived growth factor alpha PDGFRalpha proto-oncogenes has been prerequisite to the use of imatinib mesylate (STI571, Gleevec; Novartis, Switzerland), a molecular inhibitor of several tyrosine kinases, in the treatment of GISTs. In addition to providing a means for effective treatment, clarification of the molecular pathology of GISTs may potentially offer a new classification of these tumors by correlating genotype with histological, immunohistochemical, and clinical phenotype. This article seeks to review current knowledge of GISTs, offering a practical guide to their diagnosis and describing current epidemiological, molecular biological, and therapeutic aspects.

Interstitial cells of Cajal (ICC) and gastrointestinal stromal tumor (GIST): facts, speculations, and myths

Interstitial cells of Cajal (ICC) is a peculiar cell network composed of cells having processes described by the eminent Spanish neuroanatomist of the 19th century, S. Ramon y Cajal. ICC became a fascinating subject to many investigators and it is estimated that there are over 100 publications yearly on the subject related to ICC, in the last three years. Now it is widely accepted that ICC are pace maker cells of the gut and probable progenitor cells of gastrointestinal stromal tumors (GIST). Lately, interstitial Cajal-like cells (ICLC) are being found in various organs and their physiological role is still to be defined. We have reviewed the literature trying to evaluate the validity of the current concept and found that there are a few salient points to be considered. 1) There has been some important departure in defining the identity of ICC from the original criteria of Cajal. In particular, ICC with myoid feafures in intestinal smooth muscle layers (ICC-DPM) do not seem to fit to the original description of interstitial cell network by Cajal. We have also pointed out that the current reports assigning a pace maker role to ICC vastly depend on the scientific data on "ICC with myoid features", not on "fibroblast-like ICC", which are more abundant and easier to identify. 2) There seem to be an overwhelming amount of data proving the relationship between ICC and GIST. Both are known to express c-Kit and the ultrastructural characteristics seen in GIST roughly parallel those of ICC including minimal myoid differentiation seen in the majority of GIST, supporting the current concept that GIST are ICC tumors. 3) According to the original description of Cajal, ICC was not limited to the gut, suggesting an existence of ICC in other organs. The list of organs reported to contain ICC (currently identified by immunohistochemistry and electron microscopy) is ever growing and further studies are needed to define their identity and pathophysiologic role. 4). Recent data concerning gut development suggest that both c-Kit expressing ICC (fibroblasts-like as well as muscle-like) and gut muscle cells derive from the common progenitor cells of the embryonic gut unifying the histogenetic concept of all GIST with heterogeneous cytomorphologic features. In this review we attempted to incorporate recent information on interstitial Cajal-like cells (ICLC) found in other organs to broaden our understanding of ICC in general in terms of their ultrastructure, physiology, and neoplasia.

Interstitial Cajal-like cells (ICLC) as steroid hormone sensors in human myometrium: immunocytochemical approach

Expression of estrogen (ER) and progesterone (PR) receptors was investigated in cultured human normal myometrial cells (non-pregnant uterus, fertile period). The ER and PR expression was studied by immunohistochemistry and immunofluorescence on either myocytes or interstitial Cajal-like cells (ICLC). Only those cells double immunostained for c-kit and steroid receptors were considered as ICLC. ER and/or PR immunoreactivity was localized in ICLC, primarily concentrated at the nucleus level, but it was also observed in the cell body (cytoplasm) and processes. Stronger immunopositive reaction in the ICLC nucleus for PR than for ER was noted. Under our experimental conditions, a clear positive repeatable reaction for steroid receptors could not be detected in myocytes. In conclusion, these data suggest that ICLC could be true hormonal 'sensors', possibly participating in the regulation of human myometrial contractions (via gap junctions with myocytes and/or by paracrine signaling).

Interstitial Cajal-like cells (ICLC) in atrial myocardium: ultrastructural and immunohistochemical characterization

We have previously reported (Hinescu & Popescu, 2005) the existence of interstitial Cajal-like cells (ICLC), by transmission electron microscopy, in human atrial myocardium. In the present study, ICLC were identified with non-conventional light microscopy (NCLM) on semi-thin sections stained with toluidine blue and immunohistochemistry (IHC) for CD117/c-kit, CD34, vimentin and other additional antigens for differential diagnosis. Quantitatively, on semi-thin sections, ICLC represent about 1-1.5% of the atrial myocardial volume (vs. approximately 45% working myocytes, approximately 2% endothelial cells, 3-4% for other interstitial cells, and the remaining percentage: extracellular matrix). Roughly, there is one ICLC for 8-10 working atrial myocytes in the intercellular space, beneath the epicardium, with a characteristic (pyriform, spindle or triangular) shape. These ICLC usually have 2-3 definitory processes, emerging from cell body, which usually embrace atrial myocytes (260 nm average distance plasmalemma/sarcolemma) or establish close contact with nerve fibers or capillaries (approximately 420 nm average distance to endothelial cells). Cell prolongations are characteristic: very thin (mean thickness = 0.15+/-0.1 microm), very long for a non-nervous cell (several tens of microm) and moniliform (uneven caliber). Stromal synapses between ICLC and other interstitial cells (macrophages) were found (e.g. in a multicontact type synapse, the average synaptic cleft was approximately 65 nm). Naturally, the usual cell organelles (mitochondria, smooth and rough endoplasmic reticulum, intermediate filaments) are relatively well developed. Caveolae were also visible on cell prolongations. No thick filaments were detected. IHC showed that ICLC were slightly and inconsistently positive for CD117/c-kit, variously co-expressed CD34 and EGF receptor, but appeared strongly positive for vimentin, along their prolongations. Some ICLC seemed positive for a-smooth muscle actin and tau protein, but were negative for nestin, desmin, CD13 and S-100. In conclusion, we provide further evidence of the existence of ICLC in human atrial myocardium, supporting the possible ICLC role in pacemaking, secretion (juxta- and/or paracrine), intercellular signaling (neurons and myocytes). For pathology, ICLC might as well be 'players' in arrhythmogenesis and atrial remodeling.