Interstitial Cells in the Musculature of the Gastrointestinal Tract: Cajal and Beyond

Insights on Platelet-Derived Growth Factor Receptor α-Positive Interstitial Cells in the Male Reproductive Tract

Male infertility is a significant factor in approximately half of all infertility cases and is marked by a decreased sperm count and motility. A decreased sperm count is caused by not only a decreased production of sperm but also decreased numbers successfully passing through the male reproductive tract. Smooth muscle movement may play an important role in sperm transport in the male reproductive tract; thus, understanding the mechanism of this movement is necessary to elucidate the cause of sperm transport disorder. Recent studies have highlighted the presence of platelet-derived growth factor receptor α (PDGFRα)-positive interstitial cells (PICs) in various smooth muscle organs. Although research is ongoing, PICs in the male reproductive tract may be involved in the regulation of smooth muscle movement, as they are in other smooth muscle organs. This review summarizes the findings to date on PICs in male reproductive organs. Further exploration of the structural, functional, and molecular characteristics of PICs could provide valuable insights into the pathogenesis of male infertility and potentially lead to new therapeutic approaches.

Regulation of PDGFRα+ cells and ICC in progesterone-mediated slow colon transit in pregnant mice

Background

Progesterone can inhibit intestinal smooth muscle contraction; however, the specific mechanism remains unclear. Besides smooth muscle cells, smooth muscle has two important mesenchymal cells, namely interstitial cells of Cajal (ICC) and PDGFRα+ cells, which induce the contraction and relaxation of smooth muscles. We aimed to explore the regulation of PDGFRα+ cells and ICC in progesterone-mediated colon slow transit in pregnant mice.

Methods

Colon transit experiments were performed in vivo and in vitro to observe slow colon transit. The expression of PDGFRα and c-KIT was detected by Western blot, RT-PCR, and immunofluorescence. An isometric tension experiment was performed to investigate smooth muscle contractions.

Results

The colon transit time in pregnant mice was longer than that in non-pregnant mice. Progesterone significantly blocks colonic smooth muscle contractions. However, when the relaxation and contraction of PDGFRα+ cells and ICC are blocked, progesterone cannot inhibit smooth muscle contraction. When the function of only PDGFRα+ cells are blocked, progesterone has a more obvious inhibitory effect on smooth muscle in the non-pregnant group than that in the pregnant group. However, when ICC alone was blocked, progesterone inhibited smooth muscle contractions more clearly in pregnant mice. The protein and mRNA expression of PDGFRα was higher and c-KIT was lower in pregnant mice. PDGFRα+ cells and ICC from smooth muscle all co-localize progesterone receptors.

Conclusions

Under the regulation of progesterone, the relaxation function of PDGFRα+ cells is enhanced and the contraction function of ICC is weakened, leading to the slow colon transit of pregnant mice.

New insights into intestinal macrophages in necrotizing enterocolitis: the multi-functional role and promising therapeutic application

Necrotizing enterocolitis (NEC) is an inflammatory intestinal disease that profoundly affects preterm infants. Currently, the pathogenesis of NEC remains controversial, resulting in limited treatment strategies. The preterm infants are thought to be susceptible to gut inflammatory disorders because of their immature immune system. In early life, intestinal macrophages (IMφs), crucial components of innate immunity, demonstrate functional plasticity and diversity in intestinal development, resistance to pathogens, maintenance of the intestinal barrier, and regulation of gut microbiota. When the stimulations of environmental, dietary, and bacterial factors interrupt the homeostatic processes of IMφs, they will lead to intestinal disease, such as NEC. This review focuses on the IMφs related pathogenesis in NEC, discusses the multi-functional roles and relevant molecular mechanisms of IMφs in preterm infants, and explores promising therapeutic application for NEC.

Ferroptosis Induction and YAP Inhibition as New Therapeutic Targets in Gastrointestinal Stromal Tumors (GISTs)

GISTs are sarcomas of the gastrointestinal tract often associated with gain-of-function mutations in KIT or PDGFRA receptor genes. While most GISTs initially respond to tyrosine kinase inhibitors, relapses due to acquired resistance frequently occur. The induction of ferroptosis, an iron-dependent form of non-apoptotic cell death, emerged as a novel therapeutic approach in cancers and remains poorly characterized in GISTs. We studied hallmarks of ferroptosis, i.e., lipid peroxidation, iron and glutathione content, and GPX4 protein expression in imatinib-sensitive (GIST882) and -resistant (GIST48) GIST cell lines. GIST cells were highly sensitive to the induction of ferroptosis by RSL3, which was reversed by liproxstatin and deferoxamine. Lipid peroxidation and ferroptosis were mediated by VP and CA3 in GIST cells through a significant decrease in antioxidant defenses. Moreover, VP, but surprisingly not CA3, inhibited a series of target genes downstream of YAP in GIST cells. The ferroptosis marker TFRC was also investigated by immunohistochemistry in GIST tissue arrays. TFRC expression was observed in all samples. High TFRC expression was positively correlated with high-risk GISTs, elevated mitotic count, and YAP nuclear localization, reflecting YAP activation. This study highlights ferroptosis as a novel cell death mechanism in GISTs, and a potential therapeutic target to overcome resistance to tyrosine kinase inhibitors.

Studies of ultrastructure, gene expression, and marker analysis reveal that mouse bladder PDGFRA+ interstitial cells are fibroblasts

Fibroblasts are crucial to normal and abnormal organ and tissue biology, yet we lack basic insights into the fibroblasts that populate the bladder wall. Candidates may include bladder interstitial cells (also referred to as myofibroblasts, telocytes, and interstitial cells of Cajal-like cells), which express the fibroblast-associated marker PDGFRA along with VIM and CD34 but whose form and function remain enigmatic. By applying the latest insights in fibroblast transcriptomics, coupled with studies of gene expression, ultrastructure, and marker analysis, we observe the following: 1) that mouse bladder PDGFRA+ cells exhibit all of the ultrastructural hallmarks of fibroblasts including spindle shape, lack of basement membrane, abundant endoplasmic reticulum and Golgi, and formation of homotypic cell-cell contacts (but not heterotypic ones); 2) that they express multiple canonical fibroblast markers (including Col1a2, CD34, LY6A, and PDGFRA) along with the universal fibroblast genes Col15a1 and Pi16 but they do not express Kit; and 3) that PDGFRA+ fibroblasts include suburothelial ones (which express ACTA2, CAR3, LY6A, MYH10, TNC, VIM, Col1a2, and Col15a1), outer lamina propria ones (which express CD34, LY6A, PI16, VIM, Col1a2, Col15a1, and Pi16), intermuscular ones (which express CD34, VIM, Col1a2, Col15a1, and Pi16), and serosal ones (which express CD34, PI16, VIM, Col1a2, Col15a1, and Pi16). Collectively, our study revealed that the ultrastructure of PDFRA+ interstitial cells combined with their expression of multiple canonical and universal fibroblast-associated gene products indicates that they are fibroblasts. We further propose that there are four regionally distinct populations of fibroblasts in the bladder wall, which likely contribute to bladder function and dysfunction.NEW & NOTEWORTHY We currently lack basic insights into the fibroblasts that populate the bladder wall. By exploring the ultrastructure of mouse bladder connective tissue cells, combined with analyses of their gene and protein expression, our study revealed that PDGRA+ interstitial cells (also referred to as myofibroblasts, telocytes, and interstitial cells of Cajal-like cells) are fibroblasts and that the bladder wall contains multiple, regionally distinct populations of these cells.

Interstitial cells of Cajal in Wsh/Wsh c-kit mutant mice

The c-Kit receptor tyrosine kinase regulates the development and differentiation of several progenitor cells. In the gastrointestinal (GI) tract, the c-Kit regulates the development of the interstitial cells of Cajal (ICC) that are responsible for motility regulation of the GI musculature. W-sash (W^sh) is an inversion mutation upstream of the c-kit promoter region that affects a key regulatory element, resulting in cell-type-specific altered gene expression, leading to a decrease in the number of mast cells, melanocytes, and ICC. We extensively examined the GI tract of W^sh/W^sh mice using immunohistochemistry and electron microscopy. Although the musculature of the W^sh/W^sh mice did not show any c-Kit immunoreactivity, we detected intensive immunoreactivity for transmembrane member 16A (TMEM16A, anoctamin-1), another ICC marker. TMEM16A immunopositive cells were observed as ICC-MY in the gastric corpus-antrum and the large intestine, ICC-DMP in the small intestine, and ICC-SM in the colon. Electron microscopic analysis revealed these cells as ICC from their ultrastructural features, such as numerous mitochondria and caveolae, and their close contact with nerve terminals. In the developmental period, we examined 14.5 and 18.5 day embryos but did not observe c-Kit immunoreactivity in the W^sh/W^sh small intestine. From this study, ICC subtypes developed and maturated structurally without c-Kit expression. W^sh/W^sh mice are a new model to investigate the effects of c-Kit and unknown signaling on ICC development and function.

Investigation of Novel c-Kit-expressing Smooth Muscle Cells in Murine Cecum

In the gastrointestinal tract musculatures, c-Kit receptor tyrosine kinase is specifically expressed in interstitial cells of Cajal (ICC). ICC are distributed among the smooth muscle cells and are either bipolar or multipolar in shape. Our previous and current study shows that c-Kit-immunopositive smooth muscle cells are present in the murine cecum. Here, we found that c-Kit-expressing smooth muscle cells (named Kit-SM cells) are situated at the submucosal surface of the circular muscle layer. These cells showed smooth muscle actin and myosin immunoreactivities and ultrastructural features such as thick and thin filaments and caveolae. Kit-SM cells also expressed TMEM16A and LRIG1, which are known to be expressed in ICC. Although the functional significance of Kit-SM cells has yet to be revealed, these cells can be considered to have proliferation or differentiation potential in the cecal musculature.

c-Kit-stem cell factor signal-independent development of interstitial cells of Cajal in murine small intestine

c-Kit receptor tyrosine kinase and its ligand stem cell factor (SCF) play critical roles in regulating the development and proliferation of various cells, including the interstitial cells of Cajal (ICC) in the gastrointestinal tract. Many subtypes of ICC are known to be lacking in c-Kit-SCF-insufficient mice, such as W/W^v and Sl/Sl^d, whereas ICC-deep muscular plexus (DMP) in small intestine are not lacking. In this study, we examine ICC-DMP development in normal and c-Kit-SCF signal-insufficient mice. In normal mice, numerous ICC-DMP labeled with c-Kit and neurokinin 1 receptor (NK1R) antibodies were observed only in the duodenum on the day of birth, in the duodenum and the jejunum on postnatal day 4 and throughout the small intestine after postnatal day 6. In W mutant mice (W/W^v, W^v/W^v, W/W), ICC-DMP investigated using c-Kit and NK1R immunoreactivities were similar to that in normal mice. c-Kit ligand SCF-deficient mice (Sl/Sl) also showed almost identical ICC-DMP development and proliferation as normal mice. These results show that the development and proliferation of ICC-DMP occur in the postnatal period independent of c-Kit-SCF signaling.

Potentiation of imatinib by cilostazol in sensitive and resistant gastrointestinal stromal tumor cell lines involves YAP inhibition

Despite the introduction of tyrosine kinase inhibitors, gastrointestinal stromal tumors (GIST) resistance remains a major clinical challenge. We previously identified phosphodiesterase 3A (PDE3A) as a potential therapeutic target expressed in most GIST. The PDE3 inhibitor cilostazol reduced cell viability and synergized with the tyrosine kinase inhibitor imatinib (Gleevec™) in the imatinib-sensitive GIST882 cell line. Here, we found that cilostazol potentiated imatinib also in the imatinib-resistant GIST48 cell line. Cilostazol induced nuclear exclusion, hence inactivation, of the transcriptional co-activator YAP, in a cAMP-independent manner. Verteporfin, a YAP/TEAD interaction inhibitor, reduced by 90% the viability of both GIST882 and GIST48 cells. Our results highlight the potential use of compounds targeting PDE3A or YAP in combined multitherapy to tackle GIST resistance.

Phosphodiesterase 3A: a new player in development of interstitial cells of Cajal and a prospective target in gastrointestinal stromal tumors (GIST)

We previously identified phosphodiesterase 3A (PDE3A) as a marker for interstitial cells of Cajal (ICC) in adult mouse gut. However, PDE3A expression and function during gut development and in ICC-derived gastrointestinal stromal tumors (GIST) remained unknown. Here we found that PDE3A was expressed throughout ICC development and that ICC density was halved in PDE3A-deficient mice. In the human imatinib-sensitive GIST882 cell line, the PDE3 inhibitor cilostazol halved cell viability (IC₅₀ 0.35 μM) and this effect synergized with imatinib (Chou-Talalay's CI₅₀ 0.15). Recently the compound 6-(4-(diethylamino)-3-nitrophenyl)-5-methyl-4,5-dihydropyridazin-3(2H)-one, or DNMDP was found to be cytotoxic selectively for cells expressing both PDE3A and Schlafen12 (SLFN12) (de Waal L et al. Nat Chem Bio 2016), identifying a new, non-catalytic, role for PDE3A. 108 out of 117 (92%) of our human GIST samples displayed both PDE3A and SLFN12 immunoreactivity. GIST882 cells express both PDE3A and SLFN12 and DNMDP decreased their viability by 90%. Our results suggest a role for PDE3A during ICC development and open novel perspectives for PDE3A in targeted GIST therapy, on one hand by the synergism between imatinib and cilostazol, a PDE3 inhibitor already in clinical use for other indications, and, on the other hand, by the neomorphic, druggable, PDE3A-SLFN12 cytotoxic interplay.

Persistent distention of colon damages interstitial cells of Cajal through Ca2+ -ERK-AP-1-miR-34c-SCF deregulation

Gastrointestinal motility disorders (GMDs) are attributed to loss of interstitial cells of Cajal (ICC), whose survival and function are deeply dependent on the activation of KIT/SCF signalling. Based on the facts that gastrointestinal distention is common in GMD patients and SCF produced by smooth muscle cells (SMCs) is usually decreased before ICC loss, we considered a possible contribution of persistent gastrointestinal distention/stretch to SCF deficiency. In this study, chronic colonic distention mouse model, diabetic gastrointestinal paresis mouse model, cultured mouse colonic SMCs and colon specimens from Hirschsprung's disease patients were used. The results showed that SCF was clearly decreased in distent colon of mice and patients, and microRNA array and real-time PCR indicated a concomitant increase of miR-34c in distent colon. A negative regulation of miR-34c on SCF expression was confirmed by luciferase reporter assays together with knock-down and overexpression of miR-34c in cultured colonic SMCs. Using EMSA and ChIP assays, we further consolidated that in response to persistent stretch, the transcription factor AP-1/c-Jun was highly activated in colonic SMCs and significantly promoted miR-34c transcription by binding to miR-34c promoter. Knock-down or overexpression of AP-1/c-Jun in cultured colonic SMCs leads to down- or up-regulation of miR-34c, respectively. In addition, the activation of AP-1/c-Jun was through ERK1/2 signalling provoked by Ca²⁺ overload in colonic SMCs that were subject to persistent stretch. In conclusion, our data demonstrated that persistent distention/stretch on colonic SMCs could suppress SCF production probably through Ca²⁺ -ERK-AP-1-miR-34c deregulation, resulting in ICC loss or impairment and GMD progress.

Hyperplasia of interstitial cells of cajal in sprouty homolog 4 deficient mice

Gastrointestinal stromal tumors, which are thought to derive from interstitial cells of Cajal or their precursors, often harbor an oncogenic mutation of the KIT receptor tyrosine kinase. Sprouty homolog 4, a known negative regulator of ERK pathway, has been identified in the interstitial cells of Cajal in the Kit^K641E murine model of gastrointestinal stromal tumors. Sprouty homolog 4 was upregulated both at the mRNA and protein level in these cells, suggesting that Sprouty homolog 4 is downstream of oncogenic KIT activation and potentially engaged in the negative feedback loop of ERK activation in this model. Here, we used Kit^K641E heterozygous and Sprouty homolog 4 knock out animals to quantify interstitial cells of Cajal in situ, using quantitative immunofluorescence for the receptor tyrosine kinase Kit and for phosphodiesterase 3a (PDE3A). In the antrum of Sprouty homolog 4 knock out mice, hyperplasia of interstitial cells of Cajal was reminiscent of the Kit^K641E heterozygous mice antrum. Additionally, the density of interstitial cells of Cajal was higher in the colon of adult Sprouty homolog 4 knock out mice than in WT littermates, although hyperplasia seemed more severe in Kit^K641E heterozygous mice. Functional transit studies also show similarities between Sprouty homolog 4 knock out and Kit^K641E heterozygous mice, as the total transit time in 9 month old animals was significantly increased in both genotypes compared to WT littermates. We concluded that the lack of Sprouty homolog 4 expression leads to hyperplasia of the interstitial cells of Cajal and is functionally associated with a delayed transit time.

Crosstalk between muscularis macrophages and enteric neurons regulates gastrointestinal motility

Intestinal peristalsis is a dynamic physiologic process influenced by dietary and microbial changes. It is tightly regulated by complex cellular interactions; however, our understanding of these controls is incomplete. A distinct population of macrophages is distributed in the intestinal muscularis externa. We demonstrate that, in the steady state, muscularis macrophages regulate peristaltic activity of the colon. They change the pattern of smooth muscle contractions by secreting bone morphogenetic protein 2 (BMP2), which activates BMP receptor (BMPR) expressed by enteric neurons. Enteric neurons, in turn, secrete colony stimulatory factor 1 (CSF1), a growth factor required for macrophage development. Finally, stimuli from microbial commensals regulate BMP2 expression by macrophages and CSF1 expression by enteric neurons. Our findings identify a plastic, microbiota-driven crosstalk between muscularis macrophages and enteric neurons that controls gastrointestinal motility. PAPERFLICK:

Interstitial cells: regulators of smooth muscle function

Smooth muscles are complex tissues containing a variety of cells in addition to muscle cells. Interstitial cells of mesenchymal origin interact with and form electrical connectivity with smooth muscle cells in many organs, and these cells provide important regulatory functions. For example, in the gastrointestinal tract, interstitial cells of Cajal (ICC) and PDGFRα(+) cells have been described, in detail, and represent distinct classes of cells with unique ultrastructure, molecular phenotypes, and functions. Smooth muscle cells are electrically coupled to ICC and PDGFRα(+) cells, forming an integrated unit called the SIP syncytium. SIP cells express a variety of receptors and ion channels, and conductance changes in any type of SIP cell affect the excitability and responses of the syncytium. SIP cells are known to provide pacemaker activity, propagation pathways for slow waves, transduction of inputs from motor neurons, and mechanosensitivity. Loss of interstitial cells has been associated with motor disorders of the gut. Interstitial cells are also found in a variety of other smooth muscles; however, in most cases, the physiological and pathophysiological roles for these cells have not been clearly defined. This review describes structural, functional, and molecular features of interstitial cells and discusses their contributions in determining the behaviors of smooth muscle tissues.

Mitochondrial calcium handling within the interstitial cells of Cajal

The interstitial cells of Cajal (ICC) drive rhythmic pacemaking contractions in the gastrointestinal system. The ICC generate pacemaking signals by membrane depolarizations associated with the release of intracellular calcium (Ca(2+)) in the endoplasmic reticulum (ER) through inositol-trisphosphate (IP3) receptors (IP3R) and uptake by mitochondria (MT). This Ca(2+) dynamic is hypothesized to generate pacemaking signals by calibrating ER Ca(2+) store depletions and membrane depolarization with ER store-operated Ca(2+) entry mechanisms. Using a biophysically based spatio-temporal model of integrated Ca(2+) transport in the ICC, we determined the feasibility of ER depletion timescale correspondence with experimentally observed pacemaking frequencies while considering the impact of IP3R Ca(2+) release and MT uptake on bulk cytosolic Ca(2+) levels because persistent elevations of free intracellular Ca(2+) are toxic to the cell. MT densities and distributions are varied in the model geometry to observe MT influence on free cytosolic Ca(2+) and the resulting frequencies of ER Ca(2+) store depletions, as well as the sarco-endoplasmic reticulum Ca(2+) ATP-ase (SERCA) and IP3 agonist concentrations. Our simulations show that high MT densities observed in the ICC are more relevant to ER establishing Ca(2+) depletion frequencies than protection of the cytosol from elevated free Ca(2+), whereas the SERCA pump is more relevant to containing cytosolic Ca(2+) elevations. Our results further suggest that the level of IP3 agonist stimulating ER Ca(2+) release, subsequent MT uptake, and eventual activation of ER store-operated Ca(2+) entry may determine frequencies of rhythmic pacemaking exhibited by the ICC across species and tissue types.

Interstitial cells of Cajal integrate excitatory and inhibitory neurotransmission with intestinal slow-wave activity

The enteric nervous system contains excitatory and inhibitory neurons, which control contraction and relaxation of smooth muscle cells as well as gastrointestinal motor activity. Little is known about the exact cellular mechanisms of neuronal signal transduction to smooth muscle cells in the gut. Here we generate a c-Kit(CreERT2) knock-in allele to target a distinct population of pacemaker cells called interstitial cells of Cajal. By genetic loss-of-function studies, we show that interstitial cells of Cajal, which generate spontaneous electrical slow waves and thus rhythmic contractions of the smooth musculature, are essential for transmission of signals from enteric neurons to gastrointestinal smooth muscle cells. Interstitial cells of Cajal, therefore, integrate excitatory and inhibitory neurotransmission with slow-wave activity to orchestrate peristaltic motor activity of the gut. Impairment of the function of interstitial cells of Cajal causes severe gastrointestinal motor disorders. The results of our study show at the genetic level that these disorders are not only due to loss of slow-wave activity but also due to disturbed neurotransmission.

Spatial analysis of slowly oscillating electric activity in the gut of mice using low impedance arrayed microelectrodes

Smooth and elaborate gut motility is based on cellular cooperation, including smooth muscle, enteric neurons and special interstitial cells acting as pacemaker cells. Therefore, spatial characterization of electric activity in tissues containing these electric excitable cells is required for a precise understanding of gut motility. Furthermore, tools to evaluate spatial electric activity in a small area would be useful for the investigation of model animals. We thus employed a microelectrode array (MEA) system to simultaneously measure a set of 8×8 field potentials in a square area of ∼1 mm². The size of each recording electrode was 50×50 µm², however the surface area was increased by fixing platinum black particles. The impedance of microelectrode was sufficiently low to apply a high-pass filter of 0.1 Hz. Mapping of spectral power, and auto-correlation and cross-correlation parameters characterized the spatial properties of spontaneous electric activity in the ileum of wild-type (WT) and W/W^v mice, the latter serving as a model of impaired network of pacemaking interstitial cells. Namely, electric activities measured varied in both size and cooperativity in W/W^v mice, despite the small area. In the ileum of WT mice, procedures suppressing the excitability of smooth muscle and neurons altered the propagation of spontaneous electric activity, but had little change in the period of oscillations. In conclusion, MEA with low impedance electrodes enables to measure slowly oscillating electric activity, and is useful to evaluate both histological and functional changes in the spatio-temporal property of gut electric activity.

Expression and significance of neuroligins in myenteric cells of Cajal in Hirschsprung's disease

PURPOSE

The aim of this study was to investigate the expression and significance of neuroligins in myenteric cells of Cajal (ICC-MY) in Hirschsprung's disease (HSCR).

METHODS

Longitudinal muscle with adherent myenteric plexus (LMMP) from surgical excision waste colon of HSCR children were prepared by peeling off the mucous layer, sub-mucosal layer and circular muscle. Neuroligins, c-Kit (c-Kit-immunoreactivity representing ICC) and their relationship were assessed by double labeling immunofluorescence staining. ICC-MY were dissociated and cultured from LMMP by enzymolysis method, and were purified and analyzed using a combination of magnetic-activated cell sorting (MACS) and flow cytometry (FCM). Western-blot analysis was applied to compare and evaluate the expression levels of neuroligins in ICC-MY which were dissociated from different segments of HSCR (ganglionic colonic segment, transitional colonic segment and aganglionic colonic segment).

RESULTS

Neuroligins and c-Kit were expressed on the same cells (ICC-MY); ICC-MY were dissociated, cultured and purified. For HSCR, neuroligins were expressed significantly in ICC-MY from ganglionic colonic segments, moderately in those from transitional colonic segments and down-regulated significantly in those from aganglionic colonic segments.

CONCLUSIONS

Neuroligins were expressed in ICC-MY of human beings, and the expression varies from different segments of HSCR. This abnormal expression might play an important role in the pathogenesis of this disease through affecting the synaptic function of ICC-MY.

Esophageal telocytes and hybrid morphologies

TCs (telocytes) are actually defined as stromal cells with specific long and thin prolongations, called Tp (telopodes). They have been positively identified in various tissues and we now report their presence in the esophagus. These cells were identified by TEM (transmission electron microscopy) in esophageal samples of Wistar rats (n = 5) occurring beneath the basal epithelial layer, in submucosa, closely related to smooth and striated muscular fibres, as also in the adventitia. They are closely related to mast cells, macrophages and microvessels. Hybrid morphologies of stromal cells processes were found: cytoplasmic processes continued distally in a telopodial fashion. Telopodes alone may not be sufficient, however, for a safe diagnosis of TCs in TEM. A larger set of specific standards (such as the telopodial emergence, and the size of the cell body and telopodes) should be considered to differentiate TCs from various species of fibroblasts. The morphological and ultrastructural features should distinguish between TCs and interstitial cells of Cajal in the digestive tract.

Identification of interstitial Cajal-like cells in the human thoracic duct

Interstitial Cajal-like cells (ICLCs) are speculated to be pacemakers in smooth muscle tissues. While the human thoracic duct (TD) is spontaneously active, the origin of this activity is unknown. We hypothesized that ICLCs could be present in the TD and using histological techniques, immunohistochemistry and immunofluorescence we have investigated the presence of ICLCs, protein markers for ICLCs and the cellular morphology of the human TD. Transmission electron microscopy was employed to investigate ultrastructure. Methylene blue staining, calcium-dependent fluorophores and confocal microscopy were used to identify ICLCs in live tissue. Methylene blue stained cells with morphology suggestive of ICLCs in the TD. Immunoreactivity localized the ICLC protein markers c-kit, CD34 and vimentin to many cells and processes associated with smooth muscle cells (SMCs): coexpression of c-kit with vimentin or CD34 was observed in some cells. Electron microscopy analysis confirmed ICLCs as a major cell type of the human TD. Lymphatic ICLCs possess caveolae, dense bands, a patchy basal lamina, intermediate filaments and specific junctions to SMCs. ICLCs were ultrastructurally differentiable from other interstitial cells observed: fibroblasts, mast cells, macrophages and pericytes. Lymphatic ICLCs were localized to the subendothelial region of the wall as well as in intimate association with smooth muscle bundles throughout the media. ICLCs were morphologically distinct with multiple processes and also spindle shapes. Confocal imaging with calcium-dependent fluorophores corroborated cell morphology and localization observed in fixed tissues. Lymphatic ICLCs thus constitute a significant cell type of the human TD and physically interact with lymphatic SMCs.

Ultra-structural identification of interstitial cells of Cajal in the zebrafish Danio rerio

The interstitial cells of Cajal (ICCs) are important mediators of gastrointestinal (GI) motility because of their role as pacemakers in the GI tract. In addition to their function, ICCs are also structurally distinct cells most easily identified by their ultra-structural features and expression of the tyrosine kinase receptor c-KIT. ICCs have been described in mammals, rodents, birds, reptiles, and amphibians, but there are no reports at the ultra-structural level of ICCs within the GI tract of an organism from the teleost lineage. We describe the presence of cells in the muscularis of the zebrafish intestine; these cells have similar features to ICCs in other vertebrates. The ICC-like cells are associated with the muscularis, are more electron-dense than surrounding smooth muscle cells, possess long cytoplasmic processes and mitochondria, and are situated opposing enteric nervous structures. In addition, immunofluorescent and immunoelectron-microscopic studies with antibodies targeting the zebrafish ortholog of a putative ICC marker, c-KIT (kita), showed c-kit immunoreactivity in zebrafish ICCs. Taken together, these data represent the first ultra-structural characterization of cells in the muscularis of the zebrafish Danio rerio and suggest that ICC differentiation in vertebrate evolution dates back to the teleost lineage.

Ultrastructural identification of interstitial cells of Cajal in hen oviduct

The interstitial cells of Cajal (ICC) are widely believed to be neuroeffector cells of smooth muscle activity in all tubular organs, including the oviduct. The avian oviduct involves the secretion, sheathing, and transportation of a large-sized egg, but there is no information available on ICC in this special organ. We have demonstrated the presence of ICC in different segments throughout the oviduct in the laying hen and provided details on their ultrastructure by transmission electron microscopy technique, for the first time. The observed ICC appeared bipolar and multipolar cells of different shapes, with varying nuclear morphologies, a thin rim of electron-dense cytoplasm, and an infrequent basal lamina. They showed moniliform primary processes with one or 2 secondary or terminal processes. We found ICC near smooth muscle cells, nerve fibers, and the epithelia, where they make specialized contacts in the form of close membrane associations or gap-like junctions and peg-and-socket-like junctions. Intricate labyrinthine-type networking contacts were also present in ICC processes. Moreover, we report for the first time, that ICC in avian oviduct make interdigitating contacts with the epithelium. Cytoplasmic organelles identified in ICC include numerous well-developed mitochondria, abundant rough endoplasmic reticulum, and dispersed intermediate filaments. Many caveolae and vesicles were also present. Golgi bodies and centrioles were rare. Fibroblasts, on the other hand, were distinct cells with larger cytoplasmic area, more rough endoplasmic reticulum, and less mitochondrial content. No basal lamina, intermediate filaments, or caveolae were present in fibroblasts. Their processes were shorter and showed no contacts with smooth muscle cells or nerves. We conclude that these ICC might also have a key role in the regulatory mechanisms of motility and transportation in the hen oviduct, as already proved in mammalian oviduct. Such role of ICC might also be responsible for the function of the muscular infundibulum, where the fertilization takes place, and that moves to surround the released ovum, failure of which results in the internal laying.

Differentiation of interstitial cells of Cajal in the human distal colon

At the end of the embryonic period of human development, interstitial cells of Cajal (ICC) are present in the esophagus, stomach, and proximal duodenum, around the inception of the myenteric plexus (MP) ganglia. In the small and large bowel, ICC appear later. The object of the present study was to determine the timing of appearance and pattern of distribution of ICC in the human embryonic and fetal distal colon. Human distal colon specimens were obtained from 8 embryos and 14 fetuses without gastrointestinal disorders. The specimens were 7-16 weeks of gestational age. The specimens were exposed to anti-c-kit antibodies to investigate ICC differentiation. Enteric plexuses were immunohistochemically examined using anti-neuron-specific enolase, and the differentiation of smooth muscle cells was studied with anti-desmin antibodies. In the distal colon, ICC emerged at weeks 10-11 of the fetal period in the form of two parallel belts of densely packed cells extending at the submucous plexus (SMP) and the MP level. These cells correspond to ICC of the SMP (ICC-SMP) and ICC of the MP (ICC-MP). The simultaneous appearance of ICC at the SMP and MP level in the distal colon can be explained by the fact that there are differences in the migration of neural crest cells in particular portions of the digestive tube. In conclusion, in humans, there was a difference in the patterns of development of ICC in the distal colon compared to the rest of the gut.

Interstitial cells of Cajal in the gastrointestinal musculature of W(jic) c-kit mutant mice

Interstitial cells of Cajal (ICC) generate electrical rhythmicity and transduce neural signals in the gastrointestinal musculature. ICC express the proto-oncogene c-kit, a receptor tyrosine kinase, and are identified morphologically by c-Kit immunoreactivity. The c-kit gene is allelic with the murine white-spotting locus W, and mutations of c-kit are known as W mutations. W mutations affect various developmental aspects of hematopoietic cells, germ cells, melanocytes, mast cells and ICC. We examined W(jic)/W(jic) mutant mice that have a mutation in the tyrosine kinase domain resulting in severe loss of protein function. W(jic)/W(jic) homozygotes exhibited white coats and black eyes. The gross morphology of the gastrointestinal tract showed no abnormality in mutant mice other than a forestomach papilloma. In the stomach, intramuscular ICC (ICC-IM) were missing, and myenteric ICC (ICC-MY) were reduced in number. In the small intestine, the number of ICC-MY was severely reduced; however there was a normal distribution of deep muscular plexus ICC (ICC-DMP). In the cecum, the numbers of ICC-IM and ICC-MY were severely depleted. ICC-IM were almost entirely absent in the colon, whereas ICC-MY loss was restricted to the distal colon. Patterns of ICC deficiency were generally similar between W(jic)/W(jic) mice and W/W(v) mutants, which lack a specific type of ICC. The enteric nervous system of the mutant mice appeared normal. From these findings, we conclude that W(jic)/W(jic) mice represent a distinct, novel genotype resulting in a lack of a specific type of ICC in the gastrointestinal musculature.

Slow wave propagation and plasticity of interstitial cells of Cajal in the small intestine of diabetic rats

The number of myenteric interstitial cells of Cajal (ICC-MY), responsible for the generation and propagation of the slow wave in the small intestine, has been shown to decrease in diabetes, suggesting impairment of slow-wave (SW) propagation and related motility. To date, however, this expected decrease in SW propagation has neither been recorded nor analysed. Eleven rats were treated with streptozotocin and housed in pairs with 11 age-matched control animals. After 3 or 7 months, segments of duodenum, jejunum and ileum were isolated and divided into two parts. One part was processed for immediate freezing, cryosectioning and immunoprobing using anti-c-Kit antibody to quantify ICC-MY. The second part was superfused in a tissue bath, and SW propagation was recorded with 121 extracellular electrodes. In addition, a cellular automaton was developed to study the effects of increasing the number of inactive cells on overall propagation. The number of ICC-MY was significantly reduced after 3 months of diabetes, but rebounded to control levels after 7 months of diabetes. Slow-wave frequencies, velocities and extracellular amplitudes were unchanged at any stage of diabetes. The cellular automaton showed that SW velocity was not linearly related to the number of inactive cells. The depletion of ICC-MY is not as severe as is often assumed and in fact may rebound after some time. In addition, at least in the streptozotocin model, the initial reduction in ICC-MY is not enough to affect SW propagation. Diabetic intestinal dysfunction may therefore be more affected by impairments of other systems, such as the enteric system or the muscle cells.

Extrahepatic and intrahepatic human portal interstitial Cajal cells

Portal interstitial cells of Cajal (PICCs), acting as vascular pacemakers, were previously only identified in nonhumans. Moreover, there is no evidence available about the presence of such cells within the liver. The objective of the study is to evaluate whether or not PICCs are identifiable in humans and, if they are, whether or not they are following the scaffold of portal vein (PV) branches within the liver. We obtained extrahepatic PVs and liver samples from six adult human cadavers, negative for liver disease, in accordance with ethical rules. They were stained with hematoxylin-eosin (HE) and Giemsa, and then we performed immunohistochemistry on formalin-fixed paraffin-embedded specimens for CD117/c-kit, a marker of the Cajal's cells. Immune labeling was also performed for S-100 protein, desmin, glial fibrillary acidic protein (GFAP), neurofilaments, α-smooth muscle actin (α-SMA), and CD34. c-kit-Positive PICCs were identified within the extrahepatic PV, in portal spaces, and septa. On adjacent sections, these PICCs were negative for all the other antibodies used. In conclusion, our study confirms the presence of extrahepatic PICCs on humans, which may act as a possible intrinsic pacemaker in the human PV. However, the intrahepatic PICCs, which were evidenced here for the first time, are in need for further experimental studies to evaluate their functional role. A promising further direction of the study is the PICCs role in the idiopathic portal hypertension.

Crohn's disease: ultrastructure of interstitial cells in colonic myenteric plexus

The role of the interstitial cells of Cajal (ICC) in chronic inflammatory bowel disease, i.e., ulcerative colitis (UC) and Crohn's disease (CD), remains unclear. Ultrastructural alterations in ICC in the colonic myenteric plexus (ICC-MP) have been reported previously in UC, but descriptions of ICC-MP and other interstitial cells in the myenteric region of the colon are lacking for CD. In the present study, we characterized the ultrastructure of interstitial cells, nerves, and glial cells in the myenteric region in Crohn's colitis (CC). In comparison with controls, varicosities of the myenteric bundles were dilated and appeared to be empty. Lipid droplets and lipofuscin-bodies were prominent in glial cells and neurons. ICC-MP were scanty but, as in controls, had caveolae, prominent intermediate filaments, cytoplasmic dense bodies, and membrane-associated dense bands with a patchy basal lamina. ICC-MP were similar in the various colonic regions. ICC-MP in CC showed no signs of degeneration or cytological changes. As in controls, fibroblast-like cells had abundant coated vesicles but lacked prominent intermediate filaments and caveolae. Macrophages also appeared as in controls. In comparison with ICC-MP in UC, the cytology of ICC-MP in CC were thus undisturbed. The ultrastructural differences between UC and CC might reflect pathophysiological differences of importance for understanding pathogenetic differences between CD and UC.

Ulcerative colitis: ultrastructure of interstitial cells in myenteric plexus

Interstitial cells of Cajal (ICC) are key regulatory cells in the gut. In the colon of patients with severe ulcerative colitis (UC), myenteric ICC had myoid ultrastructural features and were in close contact with nerve terminals. In all patients as opposed to controls, some ICC profiles showed degenerative changes, such as lipid droplets and irregular vacuoles. Nerve terminals often appeared swollen and empty. Glial cells, muscle cells, and fibroblast-like cells (FLC) showed no alterations. FLC enclosed macrophages (MLC), which were in close contact with naked axon terminals. The organization and cytological changes may be of pathophysiological significance in patients with UC.

Is gastrointestinal dysfunction induced by gastric cancer peritoneal metastasis relevant to impairment of interstitial cells of Cajal?

Although impaired gastrointestinal motility from gastric cancer peritoneal metastasis (GCPM) causes extraordinary pain, its cause is unclear. Interstitial cells of Cajal (ICC) are apparently pacemaker cells, and their loss could cause motor dysfunction. In this study, we developed a mouse model for GCPM, and investigated electrophysiological changes in the small intestine and attendant changes in ICC. We found decreased ICC and disrupted electrical rhythm in the model. Pathologic ICC changes were well described. Cancer peritoneal metastasis may impair intestinal myoelectrical activity by damaging ICC and ICC networks. Interstitial cells of Cajal will be a target of palliative treatment and merit further study.

Interstitial cells of Cajal: pacemaker cells of the pancreatic duct?

OBJECTIVES

Ramon y Cajal discovered interstitial cells in the pancreas associated with intrinsic nerves. It was our aim to provide evidence for or against the hypothesis that the pancreatic duct harbors interstitial cells of Cajal (ICCs) that may function as pacemakers for duct motility.

METHODS

We used immunohistochemistry using c-Kit as the ICC marker and protein gene product 9.5 for nerves. Electron microscopy further characterized the cells and their interrelationships.

RESULTS

c-Kit-positive cells were associated with smooth muscle cells and nerve fibers of the duct wall and were rich in mitochondria, rough endoplasmic reticulum, and intermediate filaments; they possessed occasional caveolae and had a discontinuous basal lamina. They were connected by small gap junctions to each other and to smooth muscle cells. c-Kit-positive cells around large blood vessels were similar. c-Kit-positive cells within acini were similar in structure but were not associated with smooth muscle cells.

CONCLUSIONS

The c-Kit-positive cells around the main duct were identified as ICCs and have the morphological criteria to likely function as pacemaker cells for the previously observed spontaneous rhythmic pancreatic duct contractions. Interstitial cells of Cajal around the large blood vessels likely affect vessel wall rhythmicity.

Crohn's disease of the colon: ultrastructural changes in submuscular interstitial cells of Cajal

Interstitial cells of Cajal (ICC) at the submuscular border of the human colon (ICC-SMP) are the proposed pacemaker cells of the musculature. In patients with Crohn's disease (CD) of the colon, ICC-SMP showed characteristic cytological changes from controls. The changes comprised secondary lysosomes in connection with lipid droplets and cytoplasmic vacuoles or multiple empty, confluent and often outbulging vacuoles merging with cisterns of granular endoplasmic reticulum and clusters of glycogen granules. These changes were most pronounced in patients with macroscopical mucosal inflammation but were also demonstrable in uninvolved colonic segments. Relationships of ICC to other cells were undisturbed. The changes were selective to ICC-SMP, as glial cells, muscle cells and fibroblast-like cells at the submuscular border showed no cytological alterations compared with controls. Varicosities of the submuscular plexus were often empty and dilated. Fibroblast-like cells selectively encased macrophages and mast cells. The cytological changes in ICC-SMP in CD are thus similar to changes seen in ulcerative colitis and may be of pathophysiological significance with regard to the motility and sensory disturbances seen in patients with CD.

Localization of NK1 receptors and roles of substance-P in subepithelial fibroblasts of rat intestinal villi

Subepithelial fibroblasts of the intestinal villi, which form a contractile cellular network beneath the epithelium, are in close contact with epithelial cells, nerve varicosities, capillaries, smooth muscles and immune cells, and secrete extracellular matrix molecules, growth factors and cytokines, etc. Cultured subepithelial fibroblasts of the rat duodenal villi display various receptors such as endothelins, ATP, substance-P and bradykinin, and release ATP in response to mechanical stimulation. In this study, the presence of functional NK1 receptors (NK1R) was pharmacologically confirmed in primary culture by Ca(2+) measurement, and the effects of substance-P were measured in an acute preparation of epithelium-free duodenal villi from 2- to 3-week-old rats using a two-photon laser microscope. Substance-P elicited an increase in the intracellular Ca(2+) concentration and contraction of the subepithelial fibroblasts in culture and the isolated villi. The localization of NK1R and substance-P in the villi was examined by light and electron microscopic immunohistochemistry. NK1R-like immunoreactivity was intensely localized on the plasma membrane of villous subepithelial fibroblasts in 10-day- to 4-week-old rats and mice and was decreased or absent in adulthood. The pericryptal fibroblasts of the small and large intestine were NK1R immuno-negative. These villous subepithelial fibroblasts form synapse-like structures with both substance-P-immunopositive and -immunonegative nerve varicosities. Here, we propose that the mutual interaction between villous subepithelial fibroblasts and afferent neurons via substance-P and ATP plays important roles in the maturation of the structure and function of the small intestine.

Distribution and possible role of PDGF-AA and PDGFR-alpha in the gastrointestinal tract of adult guinea pigs

It was reported that a signaling pathway of platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) played a critical role in the developing gut of mice. Overexpression of the PDGFR-alpha gene in gastrointestinal stromal tumors (GISTs) indicated that parts of tumor cells originated from PDGFR-alpha-positive cells, but a more detailed distribution of PDGFR-alpha and possible role in the adult mammalian gut are still unclear. In the present study, we examined the expression of both PDGF-AA and its receptor PDGFR-alpha in the gastrointestinal (GI) tract of adult guinea pigs using western blotting and immunohistochemistry. PDGF-AA-immunoreactive cells were mainly distributed in the mucosal epithelium of the stomach, small intestine, and large intestine. Only a few PDGF-AA-positive cells were seen in the longitudinal muscle layer of the large intestine. In contrast, PDGFR-alpha-positive cells were widely distributed throughout the GI tract, including the lamina propria, muscular layer, and subserosa. Double staining showed that the distribution of the PDGFR-alpha-positive cells in the muscular layer were similar to those of the interstitial cells of Cajal (ICCs), and they were associated with ICCs and enteric nerves, but no double-labeled cells were observed by anti-PDGFR or Kit antibody. It was noted that PDGFR-alpha-positive cells were also stained with a vimentin monoclonal antibody. Based on the double staining and morphological features, we consider the PDGFR-alpha-positive cells belong to a subtype of fibroblast. Our results not only provide a roadmap for understanding the function of the PDGF/PDGFR signaling pathway in both normal adult mammals and during gut injury and repair but also might help in understanding the growth and development of GISTs in the clinic.

Immunohistochemical demonstration of c-Kit-negative fibroblast-like cells in murine gastrointestinal musculature

In the gastrointestinal musculature, interstitial cells of Cajal (ICC) distribute and regulate the gastrointestinal motility. Another type of mesenchymal cell, known as the fibroblast-like cell (FLC), has also been reported to be juxtaposed to the ICC. In this study, we examined the immunohistochemical properties of FLC in the murine gastrointestinal musculature using antibodies to small conductance Ca(2+)-activated K(+) channel 3 (SK3), platelet-derived growth factor receptor alpha (PDGFRalpha), and CD34. SK3-immunopositive (SK3-ip) cells were observed in the musculature throughout the gastrointestinal tract. These SK3-ip cells were distinct from the ICC that were identified by c-Kit immunoreactivity. In the muscular layers, SK3-ip cells were bipolar in shape and were associated with the intramuscular ICC and nerve fiber bundles. In the myenteric layer multipolar-shaped SK3-ip cells encompassed the myenteric ganglia. SK3-ip cells in the subserosal plane formed a cellular network with their ramified processes. The distribution pattern of the SK3-ip cells in the ICC-deficient W(v)/W(v) mutant mice was similar to that in normal mice. We also demonstrated that SK3-ip cells showed the intense PDGFRalpha immunoreactivity that was previously examined in FLC. However, CD34 immunoreactivity, one of the markers of human FLC, was not observed in SK3-ip cells with the exception of subserosal FLC. Thus, our observations indicate that SK3- and PDGFRalpha-double immunopositive cells are FLC in the murine gastrointestinal musculature and behave as a basic cellular element throughout the gastrointestinal musculature.

Interstitial cells of Cajal, macrophages and mast cells in the gut musculature: morphology, distribution, spatial and possible functional interactions

Interstitial cells of Cajal (ICC) are recognized as pacemaker cells for gastrointestinal movement and are suggested to be mediators of neuromuscular transmission. Intestinal motility disturbances are often associated with a reduced number of ICC and/or ultrastructural damage, sometimes associated with immune cells. Macrophages and mast cells in the intestinal muscularis externa of rodents can be found in close spatial contact with ICC. Macrophages are a constant and regularly distributed cell population in the serosa and at the level of Auerbach's plexus (AP). In human colon, ICC are in close contact with macrophages at the level of AP, suggesting functional interaction. It has therefore been proposed that ICC and macrophages interact. Macrophages and mast cells are considered to play important roles in the innate immune defence by producing pro-inflammatory mediators during classical activation, which may in itself result in damage to the tissue. They also take part in alternative activation which is associated with anti-inflammatory mediators, tissue remodelling and homeostasis, cancer, helminth infections and immunophenotype switch. ICC become damaged under various circumstances - surgical resection, possibly post-operative ileus in rodents - where innate activation takes place, and in helminth infections - where alternative activation takes place. During alternative activation the muscularis macrophage can switch phenotype resulting in up-regulation of F4/80 and the mannose receptor. In more chronic conditions such as Crohn's disease and achalasia, ICC and mast cells develop close spatial contacts and piecemeal degranulation is possibly triggered.

Unique contractile and structural protein expression in dog ileal inner circular smooth muscle

This study was designed to test the hypothesis that there is heterogeneous expression of contractile and structural proteins between the smooth muscle cells (SMCs) in the inner and outer circular muscle (ICM and OCM) layers of the ileum. Immunohistochemical staining and quantitation of fresh frozen sections of the dog ileum was performed using protein specific antibodies. Smooth muscle (SM) SMA myosin heavy chain (MHC), alpha- and gamma-SM actin, and vinculin all show greater expression in the ICM relative to the OCM. SMB MHC and fibronectin show the opposite pattern, with greater expression in the OCM relative to the ICM. Differences in expression of these proteins are consistent with proposed differences in function of these muscle layers. Hypotheses regarding muscle tone and the coordination and regulation of peristalsis via these different muscle layers based on this data can now be made and tested.

Igf1r+/CD34+ immature ICC are putative adult progenitor cells, identified ultrastructurally as fibroblast-like ICC in Ws/Ws rat colon

The colon of Ws/Ws mutant rats shows impairment of pacemaker activity and altered inhibitory neurotransmission. The present study set out to find structural correlates to these findings to resolve mechanisms. In the colon of Ws/Ws rats, interstitial cells of Cajal associated with Auerbach's plexus (ICC-AP) were significantly decreased and ICC located at the submuscular plexus and intramuscular ICC were rarely observed based on immunohistochemistry and electron microscopy. Ultrastructural investigations revealed that there was no overall loss of all types of interstitial cells combined. Where loss of ICC was observed, a marked increase in fibroblast-like ICC (FL-ICC) was found at the level of AP. Immunoelectron microscopy proved FL-ICC to be c-Kit(-) but gap junction coupled to each other and to c-Kit(+) ICC; they were associated with enteric nerves and occupied space normally occupied by ICC in the wild-type rat colon, suggesting them to be immature ICC. In addition, a marked increase in immunoreactivity for insulin-like growth factor 1 receptor (Igf1r) occurred, co-localized with CD34 but not with c-Kit. A significantly higher number of Igf1r(+)/CD34(+) cells were found in Ws/Ws compared to wild-type rat colons. These CD34(+)/Igf1r(+) cells in the Ws/Ws colon occupied the same space as FL-ICC. Hence we propose that a subset of immature ICC (FL-ICC) consists of adult progenitor cells. Immunohistochemistry revealed a reduction of neurons positive for neuronal nitric oxide synthase. The functional capabilities of the immature ICC and the regenerative capabilities of the adult progenitor cells need further study. The morphological features described here show that the loss of pacemaker activity is not associated with failure to develop a network of interstitial cells around AP but a failure to develop this network into fully functional pacemaker cells. The reduction in nitrergic innervation associated with the Ws mutation may be the result of a reduction in nitrergic neurons.

Microelectrode array evaluation of gut pacemaker activity in wild-type and W/W(v) mice

Interstitial cells of Cajal in the myenteric plexus region (ICC-MyP) form a network and generate basal pacemaking electrical activity. This morphological feature leads us to believe that these cells may be essential for the coordinating actions of gastrointestinal (GI) motility. We aim to propose a new method for functional assessment of ICC electrical activity and its network. Field potentials in a approximately 1 mm(2) region were simultaneously measured using an 8x8 microelectrode array (MEA) with a polar distance of 150 microm. The extracellular solution contained nifedipine and tetrodotoxin (TTX) to suppress activities of smooth muscle cells and neurons, respectively. We compared spatial electrical activities between ileal muscle preparations from wild-type (WT) and W/W(v) mice. In spatio-temporal analyses, basal electrical activities were well synchronized with a propagation delay in WT, while those in W/W(v) were small in amplitude and irregular in occurrence. The power spectrum in WT had a prominent peak corresponding to the frequency of ICC-MyP pacemaker activity, while that of W/W(v) lacked it. Consequently, the ratio of the spectral power in 9.4-27.0 cpm was significantly larger in WT than in W/W(v). In conclusion, MEA measurements demonstrated that the network-forming ICC-MyP not only generates but also coordinates basal electrical activities. Disorders of GI motility based on morphological and functional impairments of ICC network with the range of several hundreds of micrometers, could be uncovered in future extensive studies.

Ultrastructure of interstitial cells of Cajal in myenteric plexus of human colon

The role of the interstitial cells of Cajal (ICC) associated with the myenteric plexus (ICC-MP) as regulators of the motility of the colonic external muscle remains unclear. Ultrastructural studies of myenteric interstitial cells are lacking in human colon. We therefore characterized the distinctive ultrastructure of these cells in the myenteric region of the colon by transmission electron microscopy of the region between the main muscle layers in all parts of the colon in unaffected areas of resected specimens from nine adult human patients. ICC-MP were similar in various colonic regions and had myoid features such as scattered caveolae, prominent intermediate filaments, and cytoplasmic dense bodies. We found characteristic dense membrane-associated bands with a patchy basal lamina, invaginating cellular protrusions (peg and socket junctions) between ICC and between ICC and muscle cells, and close contacts (<100 nm) between ICC and nerves. No gap junctions were observed. Fibroblast-like cells (FLC) were abundant showing well-developed secretory organelles, including coated vesicles, but lacked prominent intermediate filaments and caveolae. FLC had a patchy basal lamina, and peg and socket junctions were observed between them. Macrophage-like cells frequently occurred in close apposition with FLC and, more seldomly, with ICC-MP. The ultrastructure of ICC and FLC in the myenteric region of the human colon thus differs characteristically, but significant overlaps in the ultrastructure between ICC and FLC might complicate any interpretation in pathological ultrastructural studies of the human colonic muscle layer.

Updating old ideas and recent advances regarding the Interstitial Cells of Cajal

Since their discovery by Cajal in 1889, the Interstitial Cells of Cajal (ICC) have generated much controversy in the scientific community. Indeed, the nervous, muscle or fibroblastic nature of the ICC has remained under debate for more than a century, as has their possible physiological function. Cajal and his colleagues considered them to be neurons, while contemporary histologists like Kölliker and Dogiel categorized these cells as fibroblasts. More recently, the role of ICC in the origin of slow-wave peristaltism has been elucidated, and several studies have shown that they participate in neurotransmission (intercalation theory). The fact that ICC assemble in the circular muscular layer and that they originate from cells which emerge from the ventral neural tube (VENT cells), a source of neurons, glia and ICC precursors other than the neural crest, suggests a neural origin for this particular subset of ICC. The discovery that ICC express the Kit protein, a type III tyrosine kinase receptor encoded by the proto-oncogene c-kit, has helped better understand their physiological role and implication in pathological conditions. Gleevec, a novel molecule designed to inhibit the mutant activated version of c-Kit receptors, is the drug of choice to treat the so-called gastrointestinal stromal tumours (GIST), the most common non-epithelial neoplasm of the gastrointestinal tract. Here we review Cajal's original contributions with the aid of unique images taken from Cajal's histological slides (preserved at the Cajal Museum, Cajal Institute, CSIC). In addition, we present a historical review of the concepts associated with this particular cell type, emphasizing current data that has advanced our understanding of the role these intriguing cells fulfil.

Kit K641E oncogene up-regulates Sprouty homolog 4 and trophoblast glycoprotein in interstitial cells of Cajal in a murine model of gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GIST) are thought to derive from the interstitial cells of Cajal (ICC) or an ICC precursor. Oncogenic mutations of the receptor tyrosine kinase KIT are present in most GIST. KIT K642E was originally identified in sporadic GIST and later found in the germ line of a familial GIST cohort. A mouse model harbouring a germline Kit K641E mutant was created to model familial GIST. The expression profile was investigated in the gastric antrum of the Kit(K641E) murine GIST model by microarray, quantitative PCR and immunofluorescence. Gja1/Cx43, Gpc6, Gpr133, Pacrg, Pde3a, Prkar2b, Prkcq/Pkce, Rasd2, Spry4 and Tpbg/5T4 were found to be up-regulated. The proteins encoded by Gja1/Cx43, Pde3a, Prkcq/Pkce were localized in Kit-ir ICC in wild-type and Kit(K641E) animals while Spry4 and Tpbg/5T4 were detected in Kit-ir cells only in Kit(K641E), but not in Kit(WT/WT) animals. Most up-regulated genes in this mouse model belong to the gene expression profile of human GIST but also to the profile of normal Kit(+) ICC in the mouse small intestine. Spry4 and Tpbg/5T4 may represent candidates for targeted therapeutic approaches in GIST with oncogenic KIT mutations.

W(sh)/W(sh) c-Kit mutant mice possess interstitial cells of Cajal in the deep muscular plexus layer of the small intestine

The c-Kit receptor tyrosine kinase regulates the development and differentiation of various progenitor cells. W mutant mice with spontaneous mutations in the c-kit gene show various phenotypes such as anemia, infertility, loss of coat color and mast cells. c-Kit also regulates the development of the interstitial cells of Cajal (ICC) that are responsible for the motility regulation of the gastrointestinal musculature. W(sh)/W(sh) mice possess an inversion mutation upstream of the c-kit promoter region; this mutation is responsible for reducing c-Kit activity, leading to a decrease in the number of mast cells, melanocytes, and ICC. We extensively examined the small intestine of W(sh)/W(sh) mice by using immunohistochemistry and electron microscopy. Although the musculature of the W(sh)/W(sh) mice did not show any c-Kit immunoreactivity, there were neurokinin 1 receptor (NK1R)-immunopositive cells that were associated with the nerve fibers in the deep muscular plexus (DMP) region. These NK1R-immunopositive cells showed a bipolar shape with long processes and were identified as ICC in the DMP layer (ICC-DMP). Electron microscopic analysis revealed that ICC-DMP had numerous mitochondria, caveolae, and gap junctions and were closely associated with nerve terminals. In contrast, ICC were not observed at the myenteric layer. In the small intestine of the W(sh)/W(sh) mice, we detected ICC-DMP that showed NK1R immunoreactivity and ultrastructural characters. This type of ICC may develop and maturate structurally without c-Kit expression and regulate gastrointestinal motility.

Interstitial cells of Cajal contain signalling molecules for transduction of nitrergic stimulation in guinea pig caecum

Nitric oxide (NO) is an inhibitory signalling molecule in the gastrointestinal (GI) tract that is released from neurons and from leucocytes during inflammation. NO stimulates soluble guanylate cyclase (sGC), elevates cyclic guanosine 3',5'-monophospate (cGMP), and subsequently activates cGMP-dependent protein kinase (PKG). Targets for NO in the guinea pig caecum were investigated by characterizing the cellular distribution of sGC, cGMP and PKG. Immunoreactivity for both isoforms of sGC, sGCalpha1 and sGCbeta1, was observed in the interstitial cells of Cajal (ICC) and enteric neurons in the tunica muscularis. Double labelling with anti-Kit and anti-sGC antibodies showed sGCalpha1 and sGCbeta1-like immunoreactivity (LI) in almost all intramuscular (IM) and myenteric ICC. Neuronal processes with neuronal NO synthase were closely apposed to ICC expressing sGC-LI. Cells with sGC-LI possessed ultrastructural features of ICC-IM: caveolae, close association with nerve bundles and contacts with smooth muscle cells (SMC). Sodium nitroprusside, added with the phosphodiesterase inhibitors (3-isobutyl-1-methylxanthine and zaprinast), enhanced cGMP-LI in almost all ICC and in some enteric neurons. Nerve stimulation also increased cGMP-LI in ICC and enteric neurons. In contrast, no resolvable increase in cGMP-LI was observed in any cells when the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one was present. ICC and SMC also expressed PKG type I-LI. These data show that ICC express the downstream signalling molecules necessary to transduce nitrergic signals and activate inhibitory pathways and thus are primary targets for NO released from neurons and other cells in the GI tract.

Cardiac renewing: interstitial Cajal-like cells nurse cardiomyocyte progenitors in epicardial stem cell niches

Recent studies suggested that various cell lineages exist within the subepicardium and we supposed that this area could host cardiac stem cell niches (CSCNs). Using transmission electron microscopy, we have found at least 10 types of cells coexisting in the subepicardium of normal adult mice: adipocytes, fibroblasts, Schwann cells and nerve fibres, isolated smooth muscle cells, mast cells, macrophages, lymphocytes, interstitial Cajal-like cells (ICLCs) and cardiomyocytes progenitors (CMPs). The latter cells, sited in the area of origin of coronary arteries and aorta, showed typical features of either very immature or developing cardiomyocytes. Some of these cells were connected to each other to form columns surrounded by a basal lamina and embedded in a cellular network made by ICLCs. Complex intercellular communication occurs between the ICLCs and CMPs through electron-dense nanostructures or through shed vesicles. We provide here for the first time the ultrastructural description of CSCN in the adult mice myocardium, mainly containing ICLCs and CMPs. The existence of resident CMPs in different developmental stages proves that cardiac renewing is a continuous process. We suggest that ICLCs might act as supporting nurse cells of the cardiac niches and may be responsible for activation, commitment and migration of the stem cells out of the niches. Briefly, not only resident cardiac stem cells but also ICLCs regulate myocyte turnover and contribute to both cardiac cellular homeostasis and endogenous repair/remodelling after injuries.

c-Kit-negative fibroblast-like cells express platelet-derived growth factor receptor alpha in the murine gastrointestinal musculature

Platelet-derived growth factor receptors (PDGFRs) belong to the same kinase group as c-Kit receptor tyrosine kinase that is specifically expressed in the interstitial cells of Cajal (ICC) in the gastrointestinal tract. In this study, we examined PDGFRalpha immunoreactivity in the murine gastrointestinal tract. PDGFRalpha-immunopositive (PDGFRalpha-ip) cells were observed in the musculature in all parts of the gastrointestinal tract. Although PDGFRalpha-ip cells were distinct from ICC and neurons, these cells were closely associated with intramuscular ICC and enteric nerve fibers. In the myenteric layer, PDGFRalpha-ip cells formed a cellular network with their ramified processes and encompassed myenteric ganglia. Numerous PDGFRalpha-ip cells were observed in the subserosal plane and showed a multipolar shape. The distribution pattern of the PDGFRalpha-ip cells in the ICC-deficient W(v)/W(v) mutant mice was the same as that in normal mice. PDGFRalpha-ip cells that showed intense immunoreactivity of SK3 potassium channel were considered to correspond to fibroblast-like cells or non-Cajal interstitial cells. Our observations suggest that PDGFRalpha-ip cells are basic cellular elements throughout the gastrointestinal musculature and are involved in the gastrointestinal functions.

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.

Ultrastructure of Cajal-like interstitial cells in the human detrusor

The aim of this ultrastructural study was to examine the human detrusor for interstitial cells of Cajal (ICC)-like cells (ICC-L) by conventional transmission electron microscopy (TEM) and immuno-transmission electron microscopy (I-TEM) with antibodies directed towards CD117 and CD34. Two main types of interstitial cells were identified by TEM: ICC-L and fibroblast-like cells (FLC). ICC-L were bipolar with slender (0.04 microm) flattened dendritic-like processes, frequently forming a branching labyrinth network. Caveolae and short membrane-associated dense bands were present. Mitochondria, rough endoplasmic reticulum and Golgi apparatus were observed in the cell somata and cytoplasmic processes. Intermediate filaments were abundant but no thick filaments were found. ICC-L were interconnected by close appositions, gap junctions and peg-and-socket junctions (PSJ) but no specialised contacts to smooth muscle or nerves were apparent. FLC were characterised by abundant rough endoplasmic reticulum but no caveolae or membrane-associated dense bands were observed; gap junctions and PSJ were absent and intermediate filaments were rare. By I-TEM, CD34 gold immunolabelling was present in long cytoplasmic processes corresponding to ICC-L between muscle fascicles but CD117 gold immunolabelling was negative. Thus, ICC-like cells are present in the human detrusor. They are CD34-immunoreactive and have a myoid ultrastructure clearly distinguishable from fibroblast-like cells. ICC-L may be analogous to interstitial cells of Cajal in the gut.