Epicardium: interstitial Cajal-like cells (ICLC) highlighted by immunofluorescence

During the last few years, there is an increasing interest in the role of the epicardium in cardiac development, myocardial remodelling or repair and regeneration. Several types of cells were described in the subepicardial loose connective tissue, beneath the epicardial mesothe-lium. We showed previously (repeatedly) the existence of interstitial Cajal-like cells (ICLCs) in human and mammalian myocardium, either in atria or in ventricles. Here, we describe ICLCs in adult mice epicardium and primary culture as well as in situ using frozen sections. The identification of ICLCs was based on phase contrast microscopy and immunophenotyping. We found cells with characteristic morphologic aspects: spindle-shaped, triangular or polygonal cell body and typical very long (tens to hundreds micrometres) and very thin cyto-plasmic processes, with a distinctive ‘beads-on-a-string’ appearance. The dilations contain mitochondria, as demonstrated by MitoTracker Green FM labelling of living cells. Epicardial ICLCs were found positive for c-kit/CD117 and/or CD34. However, we also observed ICLCs positive for c-kit and vimentin. In conclusion, ICLCs represent a distinct cell type in the subendocardium, presumably comprising at least two subpopulations: (i) c-kit/CD34-positive and (ii) only c-kit-positive. ICLCs might be essential as progenitor (or promoter) cells for developing cardiomyocyte lineages in normal and/or injured heart.

A distinct type of cell in myocardium: interstitial Cajal-like cells (ICLCs)

The existence of a novel type of interstitial cells in the heart, interstitial Cajal-like cells (ICLCs), had been described for the first time in 2005. Their identification was mainly based on ultrastructural criteria: very long (tens up to hundreds of micrometres) and moniliform prolongations, which are extremely thin (less than 0.2 μm), below the resolving power of light microscopy. Myocardial ICLCs were also identified by methylene-blue vital staining, silver impregnation, and immunoreactivity for CD 34, vimentin, CD117/c-kit, etc. Although a series of studies provided evidence for the existence of ICLCs in human atria and rat ventricles, further investigations in other laboratories, using additional techniques, are required to substantiate the consistency of these findings. Here we provide further evidence for the existence of ICLCs in human and mammalian hearts (by transmission and scanning electron microscopy, as well as confocal laser scanning microscopy). Noteworthy, we confirm that ICLCs communicate with neighbouring cells via shedding (micro)vesicles. Although these so-called ICLCs represent a distinct type of cells, different from classical interstitial cells of Cajal, or fibroblasts, their role(s) in myocardium remain(s) to be established. Several hypotheses are proposed: (i) adult stromal (mesenchymal) stem cells, which might participate in cardiac repair/remodelling; (ii) intercellular signalling (e.g. via shedding microvesicles); (iii) chemo-mechanical transducers and (iv) players in pacemaking and/or arrhytmogenesis, and so on.

Myocardial interstitial Cajal-like cells (ICLC) in caveolin-1 KO mice

Abstract We compared, by transmission electron microscopy (TEM), the ultrastructure of interstitial Cajal-like cells (ICLC) in normal mammalian myocardium versus caveolin-1 null mice. TEM showed that myocardial ICLCs of caveolin-1-deficient mice retain their main ultrastructural characteristics, for example, location among cardiomyocytes, close vicinity to nerves and/or blood capillaries, specialized cell-to-cell junctions, presence of 2-3 typical processes, which are very long (several tens of micrometres), but are very thin (0.1-0.2 microm) and moniliform. However, the most striking modification of myocardial ICLC in caveolin-1 KO mice was the absence of caveolae. Beyond this main observation, three other findings could be reported: (1) the absence of caveolae in capillary endothelium, (2) persistence of (some) caveolae at the level of cardiomyocte sarcolemma or vascular smooth muscle cell sarcolemma and (3) (un)expected ultrastructural modifications such as increased thickness of capillary basement membrane and increased autophagy of several cardiomyocytes.

Interstitial Cajal-like cells (ICLC) in myocardial sleeves of human pulmonary veins

We present here evidence for the existence of a new type of interstitial cell in human myocardial sleeves of pulmonary veins: interstitial Cajal-like cell (ICLC). This cell fulfils the criteria for positive diagnosis of ICLC, including CD 117/c-kit positivity. Transmission electron microscopy revealed typical ICLC with 2 or 3 very long processes (several tens of mm) suddenly emerging from the cellular body. Also, these processes appear moniliform but extremely thin (0.1–0.4 mm) under the resolving power of the usual microscopy. Cell processes establish close spatial relationships between each other, as well as with capillaries and nerve endings. ICLC appear located among the myocardial cells and particularly at the border between the myocardial sleeve and pulmonary vein wall.

Electron microscope tomography: further demonstration of nanocontacts between caveolae and smooth muscle sarcoplasmic reticulum

A spatial relationship between caveolae and sarcoplasmic reticulum (SR) in smooth muscle cells (SMC) was previously reported in computer-assisted three-dimensional reconstruction from transmission electron microscope serial sections. The knowledge of the three-dimensional organization of the cortical space of SMC is essential to understand caveolae function at the cellular level. Cellular tomography using transmission electron microscopy tomography (EMT) is the only available technology to reliably chart the inside of a cell and is therefore an essential technology in the study of organellar nanospatial relationships. Using EMT we further demonstrate here that caveolae and peripheral SR in visceral SMC build constantly spatial units, presumably responsible for a vectorial control of free Ca2+ cytoplasmic concentrations in definite nanospaces.

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.

Human placenta: de visu demonstration of interstitial Cajal-like cells

Traditional interstitial cells of Cajal (ICC) are present in the digestive tube and are supposed to act as pacemakers and neuromodulators. However, interstitial Cajal-like cells (ICLCs) were found outside the gastrointestinal tract, in various organs (e.g. ureter, bladder, fallopian tube, uterus, pancreas, mammary gland, myocardium etc.) and looking for such ICLC is a priority in our laboratories. We report here unequivocal visual evidence that ICLCs are present in the mesenchymal tissue of the villi from human term placenta. The following methods were used: a. vital staining with methylene blue (cryosections); b. silver impregnation (paraffin sections); c. Epon-embedded sections (approximately 1 microm) of glutaraldehyde/osmium fixed tissue, stained with toluidine blue; d. primary cell cultures (or second-passage cells) to reveal the characteristic, very long, moniliform cell processes and mitochondrial localization at dilations (molecular fluorescence probe: Mito Tracker Green); e. immunofluorescence for c-kit/CD117 marker or other characteristic proteins; f. transmission electron microscopy to establish the identity of ICLC.

Caveolae in smooth muscles: nanocontacts

Smooth muscle cell (SMC) caveolae have been investigated by quantitative and qualitative analysis of transmission electron microscopy (TEM) images of rat stomach, bladder and myometrium, guinea pig taenia coli, human ileum, and rat aortic SMCs. Ultrathin (below 30 nm) serial sections were used for examination of caveolar morphology and their connections with SMC organelles. Average caveolar diameter was smaller in vascular SMCs (70 nm, n=50) than in visceral SMCs (77 nm, n=100), but with the same morphology. Most of the caveolae, featured as flask-shaped plasma membrane (PM) invaginations, opened to the extracellular space through a 20 nm stoma (21, 3nm) having a 7 nm thick diaphragm. A small percentage of caveolae (3%), gathered as grape-like clusters, did not open directly to the extracellular space, but to irregular PM pockets having a 20-30 nm opening to the extracellular space. In visceral SMCs, caveolae were disposed in 4 - 6 rows, parallel to myofilaments, whilst aortic SMCs caveolae were arranged as clusters. This caveolar organization in rows or clusters minimizes the occupied volume, providing more space for the contractile machinery. The morphometric analysis of relative volumes (% of cell volume) showed that caveolae were more conspicuous in visceral than in vascular SMCs (myometrium - 2.40%; bladder - 3.66%, stomach - 2.61%, aorta - 1.43%). We also observed a higher number of caveolae per length unit of cell membrane in most visceral SMCs compared to vascular SMCs (myometrium - 1.06/μm, bladder - 0.74/μm, aorta - 0.57/μm, stomach - 0.48/μm). Caveolae increase the cellular perimeter up to 15% and enlarge the surface area of the plasma membrane about 80% in SMCs. Three-dimensional reconstructions (15μ³) showed that most caveolae, in both visceral and vascular SMCs, have nanocontacts with SR (87%), or with mitochondria (10%), and only 3%, apparently, have no contact with these organelles. Usually, 15 nm wide junctional spaces exist between caveolae and SR, some of them with nanostructural links between each other or with mitochondria: direct contacts (space < 2 nm or none) and molecular links, so called ‘feet’ (about 12 nm electron dense structures between organellar membranes). Direct contacts possibly allow molecular translocation between the two membranes. Electron-dense ‘feet’-like structures suggest a molecular link between these organelles responsible for intracellular Ca²⁺ homeostasis (excitation-contraction coupling or pharmaco-mechan-ical coupling). Close appositions (∼15 nm) have also been observed between caveolae and perinuclear SR cisterna, suggesting that caveolae might be directly implicated in excitation-transcription coupling.

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.

Caveolar nanospaces in smooth muscle cells

Caveolae, specialized membrane nanodomains, have a key role in signaling processes, including calcium handling in smooth muscle cells (SMC). We explored the three-dimensional (3D) architecture of peripheral cytoplasmic space at the nanoscale level and the close spatial relationships between caveolae, sarcoplasmic reticulum (SR), and mitochondria, as ultrastructural basis for an excitation-contraction coupling system and, eventually, for excitation - transcription coupling. About 150 electron micrographs of SMC showed that superficial SR and peripheral mitochondria are rigorously located along the caveolar domains of plasma membrane, alternating with plasmalemmal dense plaques. Electron micrographs made on serial ultrathin sections were digitized, then computer-assisted organellar profiles were traced on images, and automatic 3D reconstruction was obtained using the ‘Reconstruct’ software. The reconstruction was made for 1 μm³ in rat stomach (muscularis mucosae) and 10 μm³ in rat urinary bladder (detrusor smooth muscle). The close appositions (about 15 nm distance) of caveolae, peripheral SR, and mitochondria create coherent cytoplasmic nanoscale subdomains. Apparently, 80% of caveolae establish close contacts with SR and about 10% establish close contacts with mitochondria in both types of SMC. Thus, our results show that caveolae and peripheral SR build Ca²⁺release units in which mitochondria often could play a part. The caveolae-SR couplings occupy 4.19% of the cellular volume in stomach and 3.10% in rat urinary bladder, while caveolae-mitochondria couplings occupy 3.66% and 3.17%, respectively. We conclude that there are strategic caveolae-SR or caveolae-mitochondria contacts at the nanoscale level in the cortical cytoplasm of SMC, presumably responsible for a vectorial control of free Ca²⁺ cytoplasmic concentrations in definite nanospaces. This may account for slective activation of specific Ca²⁺ signaling pathways.

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).

Insights into the interstitium of ventricular myocardium: interstitial Cajal-like cells (ICLC)

We have previously described interstitial Cajal-like cells (ICLC) in human atrial myocardium. Several complementary approaches were used to verify the existence of ICLC in the interstitium of rat or human ventricular myocardium: primary cell cultures, vital stainings (e.g.: methylene blue), traditional stainings (including silver impregnation), phase contrast and non-conventional light microscopy (Epon-embedded semithin sections), transmission electron microscopy (TEM) (serial ultrathin sections), stereology, immunohistochemistry (IHC) and immunofluorescence (IF) with molecular probes. Cardiomyocytes occupy about 75% of rat ventricular myocardium volume. ICLC represent approximately 32% of the number of interstitial cells and the ratio cardiomyocytes/ICLC is about 70/1. In the interstitium, ICLC establish close contacts with nerve fibers, myocytes, blood capillaries and with immunoreactive cells (stromal synapses). ICLC show characteristic cytoplasmic processes, frequently two or three, which are very long (tens up to hundreds of microm), very thin (0.1-0.5 microm thick), with uneven caliber, having dilations, resulting in a moniliform aspect. Gap junctions between such processes can be found. Usually, the dilations are occupied by mitochondria (as revealed by Janus green B and MitoTracker Green FM) and elements of endoplasmic reticulum. Characteristically, some prolongations are flat, with a veil-like appearance, forming a labyrinthic system. ICLC display caveolae (about 1 caveola/ 1 microm cell membrane length, or 2-4% of the relative cytoplasmic volume). Mitochondria and endoplasmic reticulum (rough and smooth) occupy 5-10% and 1-2% of cytoplasmic volume, respectively. IHC revealed positive staining for CD34, EGFR and vimentin and, only in a few cases for CD117. IHC was negative for: desmin, CD57, tau, chymase, tryptase and CD13. IF showed that ventricular ICLC expressed connexin 43. We may speculate that possible ICLC roles might be: intercellular signaling (neurons, myocytes, capillaries etc.) and/or chemomechanical sensors. For pathology, it seems attractive to think that ICLC might participate in the process of cardiac repair/remodeling, arrhythmogenesis and, eventually, sudden death.

Interstitial Cajal-like cells (ICLC) in human resting mammary gland stroma. Transmission electron microscope (TEM) identification

We have previously shown the existence of ICLC in human resting mammary gland stroma by means of methylene blue (vital) staining and c-kit immunopositivity (immunofluorescence and immunohistochemistry). In addition, we reported the phenotype characteristics of these ICLC in vitro (primary cell cultures). Since the identification of ICLC outside the gut requires, at this moment, the obligatory use of TEM, we used this technique and provide unequivocal evidence for the presence of ICLC in the intralobular stroma of human resting mammary gland. According to the 'platinum standard' (10 TEM criteria for the certitude diagnosis of ICLC), we found interstitial cells with the following characteristics: 1. location: among the tubulo-alveolar structures, in the non-epithelial space; 2. caveolae: approximately 2.5% of cell volume; 3. mitochondria: approximately 10% of cell volume; 4. endoplasmic reticulum: either smooth or rough, approximately 2-3% of cell volume; 5. cytoskeleton: intermediate and thin filaments, as well as microtubules are present; 6. myosin thick filaments: undetectable; 7. basal lamina: occasionally found; 8. gap junctions: occasionally found; 9. close contacts with targets: nerve fibers, capillaries, immunoreactive cells by 'stromal synapses'; 10. characteristic cytoplasmic processes: i) number: frequently 2-3; ii) length: several tens of mum; iii) thickness: uneven caliber, 0.1-0.5 microm, with dilations, but very thin from the emerging point; iv) aspect: moniliform, usually with mitochondria located in dilations; v) branching: dichotomous pattern; vi) Ca(2+) release units: are present; vii) network labyrinthic system: overlapping cytoplasmic processes. It remains to be established which of the possible roles that we previously suggested for ICLC (e.g. juxta- and/or paracrine secretion, uncommited progenitor cells, immunological surveillance, intercellular signaling, etc.) are essential for the epithelium/stroma equilibrium in the mammary gland under normal or pathological conditions.

Interstitial Cajal-like cells (ICLC) in human atrial myocardium

We present here visual evidence for the existence of a new type of interstitial cells in human atrial myocardium: interstitial Cajal-like cells (ICLC). These cells fulfil the so-called 'platinum standard' (a set of 10 ultrastructural criteria for the positive diagnosis of ICLC). Conventional transmission electron microscopy (TEM), followed by reconstructions from serial photomicrographs, revealed typical ICLC with 2 or 3 long, moniliform processes (several tens of micrometers long and 0.1-0.5 microm thick), emerging from the (small) cell body. Cell processes dichotomously branch and have mitochondria (at the level of dilations), caveolae and Ca(2+) release units. Cell prolongations establish close spatial relationships between each other, as well as with capillaries, myocardial cells, and other connective tissue cells. Our preliminary data suggest that ICLC exist in rat ventricular myocardium, too.

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.

Cajal-type cells from human mammary gland stroma: phenotype characteristics in cell culture

We report here the in vitro isolation of Cajal-like interstitial cells from human inactive mammary-gland stroma. Primary cell cultures examined in phase-contrast microscopy or after vital methylene-blue staining revealed a cell population with characteristic morphological phenotype: fusiform, triangular or polygonal cell body and the corresponding (very) long, slender, moniliform cytoplasmic processes. Giemsa staining pointed out the typical knobbed aspect of cell prolongations. Immunofluorescence (IF) showed, like in situ immunohistochemistry, that Cajal-type cells in vitro (primary cultures), expressed c-kit/CD117 and vimentin. In conclusion, the images presented here reinforce our previous hypothesis that human mammary glands have a distinct population of Cajal-like cells in non-epithelial tissue compartments.

The connective connection: interstitial cells of Cajal (ICC) and ICC-like cells establish synapses with immunoreactive cells. Electron microscope study in situ

We present transmission electron microscope (TEM) evidence that ICC and ICC-like cells frequently establish close contacts (synapses) with several types of immunoreactive cells (IRC): lymphocytes, plasma cells, eosinophils, basophils, macrophages and mast cells. Such synapses were found in various organs: human mammary gland and myometrium, as well as rat stomach, gut, bladder and uterus. Specimens were observed by conventional TEM on ultrathin sections. Based on morphometric analyses and computer-aided 3-D reconstructions from serial sections, we propose an operational definition of ICC-IRC synapses: cell-to-cell close contacts where the two cells are separated by only approximately 15 nm, equivalent to twice the plasmalemmal thickness. Two types of such synapses were found: (i) uniform ('plain') synapses (PS). close contact extending for >200 nm, and (ii) multi-contact ('kiss and run') synapses (MS)--with multiple, focal, close-contact points alternating with regions of wider intermembrane distance. For instance, a typical PS between a rat bladder ICC-like cell and an eosinophil was 2.48 microm long and 11+/-4 nm wide. By contrast, a MS synapse in rat myometrium (between an ICC-like cell and an eosinophil) was 8.64 microm long and had 13 contact points. The synaptic cleft measured 15+/-8 nm at contact points and approximately 100 nm or more in wider areas. These synapses are different from gap junctions usually seen between ICC and between ICC and smooth muscle cells. We previously proposed that ICC-like cells might represent stromal progenitor cells, participate in juxtacrine/paracrine signaling and play a role in immune surveillance. The nanoscopic distances between the two contiguous membranes suggest a juxtacrine cell-to-cell signaling (chemical synapse), via juxtacrinins, a specific case of phenomenins. However, the (micro)vesicles found in the synaptic cleft may correspond to an exosome-based mechanism.

C-kit immunopositive interstitial cells (Cajal-type) in human myometrium

Previous reports describing Cajal-like interstitial cells in human uterus are contradictory in terms of c-kit immunoreactivity: either negative (but vimentin-positive) in pregnant myometrium, or positive, presumably in the endometrium. The aim of this study was to verify the existence of human myometrial Cajal-like interstitial cells (m-CLIC). Six different, complementary approaches were used: 1) methylene-blue supravital staining of tissue samples (cryosections), 2) methylene blue and Janus green B vital staining (m-CLIC and mitochondrial markers, respectively), and 3) extracellular single-unit electrophysiological recordings in cell cultures, 4) non-conventional light microscopy on glutaraldehyde/osmium fixed, Epon-embedded semi-thin sections (less than 1 microm) stained with toluidine blue (TSM), 5) transmission electron microscopy (TEM), and 6) immunofluorescence (IF). We found m-CLIC in myometrial cryosections and in cell cultures. In vitro, m-CLIC represented approximately 7% of the total cell number. m-CLIC had 2-3 characteristic processes which were very long (approximately 60 microm), very thin (< or =0.5 microm) and moniliform. The dilated portions of processes usually accommodated mitochondria. In vitro, m-CLIC exhibited spontaneous electrical activity (62.4+/-7.22 mV membrane potentials, short duration: 1.197+/-0.04 ms). Moreover, m-CLIC fulfilled the usual TEM criteria, the so-called 'gold' or 'platinum' standards (e.g. the presence of discontinuous basal lamina, caveolae, endoplasmic reticulum, and close contacts between each other, with myocytes, nerve fibers and/or capillaries etc.). IF showed that m-CLIC express CD117/c-kit, sometimes associated with CD34, with vimentin along their processes. In conclusion, we describe myometrial Cajal-like interstitial cells that have affinity for methylene blue and Janus green B vital dyes, fulfill (all) TEM criteria, express CD117/c-kit and have spontaneous electric activity.

Snapshots of mammary gland interstitial cells: methylene-blue vital staining and c-kit immunopositivity

We show here that methylene-blue supravital staining of specimens from normal human mammary gland reveals (selectively) interstitial (stromal) cells, with 2-3 long (20-80 microm), thin, moniliform processes. Such cells appear c-kit/CD117 positive, either by immunohistochemistry (IHC) or immunofluorescence (IF). Since these features (affinity for methylene blue, c-kit positivity, and characteristic processes) define archetypal interstitial cells of Cajal (ICC) in light microscopy, our results suggest the existence of Cajal-like cells in the interstitium of human normal mammary gland.

Novel type of interstitial cell (Cajal-like) in human fallopian tube

We describe here--presumably for the first time--a Cajal-like type of tubal interstitial cells (t-ICC), resembling the archetypal enteric ICC. t-ICC were demonstrated in situ and in vitro on fresh preparations (tissue cryosections and primary cell cultures) using methylene-blue, crystal-violet, Janus-Green B or MitoTracker-Green FM Probe vital stainings. Also, t-ICC were identified in fixed specimens by light microscopy (methylene-blue, Giemsa, trichrome stainings, Gomori silver-impregnation) or transmission electron microscopy (TEM). The positive diagnosis of t-ICC was strengthened by immunohistochemistry (IHC; CD117/c-kit+ and other 14 antigens) and immunofluorescence (IF; CD117/c-kit+ and other 7 antigens). The spatial density of t-ICC (ampullar-segment cryosections) was 100-150 cells/mm2. Non-conventional light microscopy (NCLM) of Epon semithin-sections revealed a network-like distribution of t-ICC in lamina propria and smooth muscle meshwork. t-ICC appeared located beneath of epithelium, in a 10-15 microm thick 'belt', where 18+/-2% of cells were t-ICC. In the whole lamina propria, t-ICC were about 9%, and in muscularis approximately 7%. In toto, t-ICC represent ~8% of subepithelial cells, as counted by NCLM. In vitro, t-ICC were 9.9+/-0.9% of total cell population. TEM showed that the diagnostic 'gold standard' (Huizinga et al., 1997) is fulfilled by 'our' t-ICC. However, we suggest a 'platinum standard', adding a new defining criterion- characteristic cytoplasmic processes (number: 1-5; length: tens of microm; thickness: < or =0.5 microm; aspect: moniliform; branching: dichotomous; organization: network, labyrinthic-system). Quantitatively, the ultrastructural architecture of t-ICC is: nucleus, 23.6+/-3.2% of cell volume, with heterochromatin 49.1+/-3.8%; mitochondria, 4.8+/-1.7%; rough and smooth endoplasmic-reticulum (1.1+/-0.6%, 1.0+/-0.2%, respectively); caveolae, 3.4+/-0.5%. We found more caveolae on the surface of cell processes versus cell body, as confirmed by IF for caveolins. Occasionally, the so-called 'Ca2+-release units' (subplasmalemmal close associations of caveolae+endoplasmic reticulum+mitochondria) were detected in the dilations of cell processes. Electrophysiological single unit recordings of t-ICC in primary cultures indicated sustained spontaneous electrical activity (amplitude of membrane potentials: 57.26+/-6.56 mV). Besides the CD117/c-kit marker, t-ICC expressed variously CD34, caveolins 1&2, alpha-SMA, S-100, vimentin, nestin, desmin, NK-1. t-ICC were negative for: CD68, CD1a, CD62P, NSE, GFAP, chromogranin-A, PGP9.5, but IHC showed the possible existence of (neuro)endocrine cells in tubal interstitium. We call them 'JF cells'. In conclusion, the identification of t-ICC might open the door for understanding some tubal functions, e.g. pace-making/peristaltism, secretion (auto-, juxta- and/or paracrine), regulation of neurotransmission (nitrergic/purinergic) and intercellular signaling, via the very long processes. Furthermore, t-ICC might even be uncommitted bipotential progenitor cells.

Interstitial cells of Cajal in pancreas

We show here (presumably for the first time) a special type of cell in the human and rat exocrine pancreas. These cells have phenotypic characteristics of the enteric interstitial cells of Cajal (ICC). To identify pancreatic interstitial cells of Cajal (pICC) we used routine light microscopy, non-conventional light microscopy (less than 1 mum semi-thin sections of Epon-embedded specimens cut by ultramicrotomy and stained with Toluidine blue), transmission electron microscopy (TEM), and immunocytochemistry. The results showed that pICC can be recognized easily by light microscopy, particularly on semi-thin sections, as well as by TEM. Two-dimensional reconstructions from serial photos suggest a network-like spatial distribution of pICC. pICC represent 3.3+/-0.5% of all pancreatic cells, and seem to establish close spatial relationships with: capillaries (43%), acini (40%), stellate cells (14%), nerve fibres (3%). Most of pICC (88%) have 2 or 3 long processes (tens of mum) emerging from the cell body. TEM data show that pICC meet the criteria for positive diagnosis as ICC (e.g. numerous mitochondria, 8.7+/-0.8% of cytoplasm). Immunocytochemistry revealed that pICC are CD117/c-kit and CD34 positive. We found pICC positive (40-50%) for smooth muscle alpha-actin or S-100, and, occasionally, for CD68, NK1 neurokinin receptor and vimentin. The reactions for desmin and chromogranin A were negative in pICC. At present, only hypotheses and speculations can be formulated on the possible role of the pICC (e.g., juxtacrine and/or paracrine roles). In conclusion, the quite-established dogma: "ICC only in cavitary organs" is overpassed.

[Expression of stem cell markers on fetal and tumoral human liver cells in primary culture]

Hepatic stem cells can be identified by the expression of putative markers such as CD117 (c-kit), CD90 (Thy-1), CD34, and HLA-DR. We have identified populations expressing these markers in both fetal and tumoral human liver by flow cytometry, using monoclonal antibodies against CD90, CD117, CD34, and HLA-DR. In tumoral liver CD117+/CD90+ cells were found in decreasing number from the neoplastic (2.48 +/- 0.67) and peritumoral region (0.88 +/- 0.12) to the area of para-tumoral (normal) parenchyma (0.13 +/- 0.04). The CD117+/CD34+ cells showed the following distribution: 0.35 +/- 0.05% in the tumoral region, 1.01 +/- 0.23% in the peritumoral region and 0.35 +/- 0.01 in the para-tumoral region. Using the same markers on fetal liver cells we have also identified small populations of CD117+/CD90+ cells (0.28 +/- 0.07%) and CD117+/CD34+ cells (1.13 +/- 0.24%), presumably resident stem cells or hematopoietic stem cells. Immunomagnetic negative separation was then performed on fetal liver cells using monoclonal antibodies against specific markers of hematopoietic lineages such as CD3, 14, 16, 19, 22, and CD56 to eliminate this population. The remaining cells were then incubated with fluorescently labeled monoclonal antibodies against CD90 and CD117 and analyzed using fluorescence microscopy. As expected these markers were expressed on the majority of the selected cells (89.28 +/- 9.56%). Isolation using appropriate markers and initiation of primary cultures is a first step to the therapeutic use of fetal stem cells and for the study of adult liver stem cells involvement in carcinogenesis.

The antiphospholipid antibodies

Antiphospholipid antibodies (APLAs) are a group of autoantibodies directed against certain phospholipids, or their protein cofactors. Assay of APLAs is important because their interaction with anionic phospholipid-protein cofactors can generate a syndrome of hypercoagulability associated with a wide variety of thromboembolic events. This article presents the characteristics of some APLAs [anticardiolipin antibodies (aCLAs), lupus anticoagulant (LA) and anti-beta2-glycoprotein I antibodies (anti-beta2-GPIAs)], their action, and their interaction with blood and endothelial cells. The presence of APLAs has been reported in many diseases (autoimmune diseases, atherosclerosis, infections, malignancies), being related to pathogenic mechanisms and/or to a more severe evolution of the disease.

Dantrolene protects neurons against kainic acid induced apoptosis in vitro and in vivo

Apoptotic cell death induced by kainic acid (KA) in cultures of rat cerebellar granule cells (CGC) and in different brain regions of Wistar rat pups on postnatal day 21 (P21) was studied. In vitro, KA (100-500 microM) induced a concentration-dependent loss of cell viability in MTT assay and cell death had apoptotic morphology as studied by chromatin staining with propidium iodide (PI). In vivo, twenty-four hours after induction of status epilepticus (SE) by an intraperitoneal KA injection (5 mg/kg) we quantified apoptotic cells in hippocampus (CA1 and CA3), parietal cortex and cerebellum using PI staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) technique. We report that dantrolene, a specific ryanodine receptor antagonist, was able to significantly reduce the apoptotic cell death in CGC cultures and in hyppocampal CA1 and parietal cortex regions. Our finding can be valuable for neuroprotective therapy strategies in patients with repeated generalized seizures or status epilepticus.

Stem cells (p63(+)) in keratinocyte cultures from human adult skin

Epidermal stem cells (ESC) are responsible for maintaining skin cellular homeostasis, as they give rise to fast-dividing transit amplifying cells committed to terminal differentiation, while retaining their self-renewal capacity. However, no pure ESC cultures are available and no highly specific cytochemical marker was identified. We report here the experimental conditions allowing the selective enrichment in ESC, using cultured adult human keratinocytes. The main step was the selection of cells able to rapidly adhere to human collagen type IV in vitro. Thus, an increased proportion of putative ESC of about 65% was obtained, as demonstrated by p63 expression.