Differential gene expression in functional classes of interstitial cells of Cajal in murine small intestine

Targeting Disease Persistence in Gastrointestinal Stromal Tumors

SummaryGastrointestinal stromal tumors (GISTs) represent 20%-40% of human sarcomas. Although approximately half of GISTs are cured by surgery, prognosis of advanced disease used to be poor due to the high resistance of these tumors to conventional chemo- and radiotherapy. The introduction of molecularly targeted therapy (e.g., with imatinib mesylate) following the discovery of the role of oncogenic mutations in the receptor tyrosine kinases KIT and platelet-derived growth factor α (PDGFRA) significantly increased patient survival. However, GIST cells persist in 95%-97% of imatinib-treated patients who eventually progress and die of the disease because of the emergence of clones with drug-resistant mutations. Because these secondary mutations are highly heterogeneous, even second- and third-line drugs that are effective against certain genotypes have only moderately increased progression-free survival. Consequently, alternative strategies such as targeting molecular mechanisms underlying disease persistence should be considered. We reviewed recently discovered cell-autonomous and microenvironmental mechanisms that could promote the survival of GIST cells in the presence of tyrosine kinase inhibitor therapy. We particularly focused on the potential role of adult precursors for interstitial cells of Cajal (ICCs), the normal counterpart of GISTs. ICC precursors share phenotypic characteristics with cells that emerge in a subset of patients treated with imatinib and in young patients with GIST characterized by loss of succinate dehydrogenase complex proteins and lack of KIT or PDGFRA mutations. Eradication of residual GIST cells and cure of GIST will likely require individualized combinations of several approaches tailored to tumor genotype and phenotype.

SIGNIFICANCE

Gastrointestinal stromal tumors (GISTs) are one of the most common connective tissue cancers. Most GISTs that cannot be cured by surgery respond to molecularly targeted therapy (e.g., with imatinib); however, tumor cells persist in almost all patients and eventually acquire drug-resistant mutations. Several mechanisms contribute to the survival of GIST cells in the presence of imatinib, including the activation of "escape" mechanisms and the selection of stem-like cells that are not dependent on the expression of the drug targets for survival. Eradication of residual GIST cells and cure of GIST will likely require individualized combinations of several approaches tailored to the genetic makeup and other characteristics of the tumors.

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.

Modeling of stochastic behavior of pacemaker potential in interstitial cells of Cajal

It is widely accepted that interstitial cells of Cajal (ICCs) generate pacemaker potentials to propagate slow waves along the whole gastrointestinal tract. Previously, we constructed a biophysically based model of ICCs in mouse small intestine to explain the pacemaker mechanism. Our previous model, however, could not explain non-uniformity of pacemaker potentials and random occurrence of unitary potentials, thus we updated our model. The inositol 1,4,5-trisphosphate (IP3)-mediated Ca(2+) mobilization is a key event to drive the cycle of pacemaker activity and was updated to reproduce its stochastic behavior. The stochasticity was embodied by simulating random opening and closing of individual IP3-mediated Ca(2+) channel. The updated model reproduces the stochastic features of pacemaker potentials in ICCs. Reproduced pacemaker potentials are not uniform in duration and interval. The resting and peak potentials are -75.5 ± 1.1 mV and -0.8 ± 0.5 mV, respectively (n = 55). Frequency of pacemaker potential is 14.3 ± 0.4 min(-1) (n = 10). Width at half-maximal amplitude of pacemaker potential is 902 ± 6 ms (n = 55). There are random events of unitary potential-like depolarization. Finally, we compared our updated model with a recently published model to speculate which ion channel is the best candidate to drive pacemaker depolarization. In conclusion, our updated mathematical model could now reproduce stochastic features of pacemaker activity in ICCs.

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.

The significance of interstitial cells in neurogastroenterology

Smooth muscle layers of the gastrointestinal tract consist of a heterogeneous population of cells that include enteric neurons, several classes of interstitial cells of mesenchymal origin, a variety of immune cells and smooth muscle cells (SMCs). Over the last number of years the complexity of the interactions between these cell types has begun to emerge. For example, interstitial cells, consisting of both interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor alpha-positive (PDGFRα(+)) cells generate pacemaker activity throughout the gastrointestinal (GI) tract and also transduce enteric motor nerve signals and mechanosensitivity to adjacent SMCs. ICC and PDGFRα(+) cells are electrically coupled to SMCs possibly via gap junctions forming a multicellular functional syncytium termed the SIP syncytium. Cells that make up the SIP syncytium are highly specialized containing unique receptors, ion channels and intracellular signaling pathways that regulate the excitability of GI muscles. The unique role of these cells in coordinating GI motility is evident by the altered motility patterns in animal models where interstitial cell networks are disrupted. Although considerable advances have been made in recent years on our understanding of the roles of these cells within the SIP syncytium, the full physiological functions of these cells and the consequences of their disruption in GI muscles have not been clearly defined. This review gives a synopsis of the history of interstitial cell discovery and highlights recent advances in structural, molecular expression and functional roles of these cells in the GI tract.

The significance of interstitial cells in neurogastroenterology

Smooth muscle layers of the gastrointestinal tract consist of a heterogeneous population of cells that include enteric neurons, several classes of interstitial cells of mesenchymal origin, a variety of immune cells and smooth muscle cells (SMCs). Over the last number of years the complexity of the interactions between these cell types has begun to emerge. For example, interstitial cells, consisting of both interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor alpha-positive (PDGFRα(+)) cells generate pacemaker activity throughout the gastrointestinal (GI) tract and also transduce enteric motor nerve signals and mechanosensitivity to adjacent SMCs. ICC and PDGFRα(+) cells are electrically coupled to SMCs possibly via gap junctions forming a multicellular functional syncytium termed the SIP syncytium. Cells that make up the SIP syncytium are highly specialized containing unique receptors, ion channels and intracellular signaling pathways that regulate the excitability of GI muscles. The unique role of these cells in coordinating GI motility is evident by the altered motility patterns in animal models where interstitial cell networks are disrupted. Although considerable advances have been made in recent years on our understanding of the roles of these cells within the SIP syncytium, the full physiological functions of these cells and the consequences of their disruption in GI muscles have not been clearly defined. This review gives a synopsis of the history of interstitial cell discovery and highlights recent advances in structural, molecular expression and functional roles of these cells in the GI tract.

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.

Functional role of the Ca²⁺-activated Cl⁻ channel DOG1/TMEM16A in gastrointestinal stromal tumor cells

DOG1, a Ca(2+)-activated Cl(-) channel (CaCC), was identified in 2004 to be robustly expressed in gastrointestinal stromal tumors (GIST). It was rapidly included as a tumor marker in routine diagnostics, but the functional role remained unknown. CaCCs are important regulators of normal physiological functions, but also implicated in tumorigenesis, cancer progression, metastasis, cell migration, apoptosis, proliferation and viability in several malignancies. We therefore investigated whether DOG1 plays a role in the three latter in GIST by utilizing in vitro cell model systems. Confocal microscopy identified different subcellular localizations of DOG1 in imatinib-sensitive and imatinib-resistant cells. Electrophysiological studies confirmed that DOG1-specific pharmacological agents possess potent activating and inhibiting properties. Proliferation assays showed small effects up to 72 h, and flow cytometric analysis of adherent cells with 7-AAD/Annexin V detected no pharmacological effects on viable GIST cells. However, inhibition of DOG1 conveyed pro-apoptotic effects among early apoptotic imatinib-resistant cells. In conclusion, DOG1 generates Cl(-) currents in GIST that can be regulated pharmacologically, with small effects on cell viability and proliferation in vitro. Inhibition of DOG1 might act pro-apoptotic on some early apoptotic GIST cell populations. Further studies are warranted to fully illuminate the function of DOG1 and its potential as therapeutic target.

Computational modeling of anoctamin 1 calcium-activated chloride channels as pacemaker channels in interstitial cells of Cajal

Interstitial cells of Cajal (ICC) act as pacemaker cells in the gastrointestinal tract by generating electrical slow waves to regulate rhythmic smooth muscle contractions. Intrinsic Ca(2+) oscillations in ICC appear to produce the slow waves by activating pacemaker currents, currently thought to be carried by the Ca(2+)-activated Cl(-) channel anoctamin 1 (Ano1). In this article we present a novel model of small intestinal ICC pacemaker activity that incorporates store-operated Ca(2+) entry and a new model of Ano1 current. A series of simulations were carried out with the ICC model to investigate current controversies about the reversal potential of the Ano1 Cl(-) current in ICC and to predict the characteristics of the other ion channels that are necessary to generate slow waves. The model results show that Ano1 is a plausible pacemaker channel when coupled to a store-operated Ca(2+) channel but suggest that small cyclical depolarizations may still occur in ICC in Ano1 knockout mice. The results predict that voltage-dependent Ca(2+) current is likely to be negligible during the slow wave plateau phase. The model shows that the Cl(-) equilibrium potential is an important modulator of slow wave morphology, highlighting the need for a better understanding of Cl(-) dynamics in ICC.

Structure and function of TMEM16 proteins (anoctamins)

TMEM16 proteins, also known as anoctamins, are involved in a variety of functions that include ion transport, phospholipid scrambling, and regulation of other membrane proteins. The first two members of the family, TMEM16A (anoctamin-1, ANO1) and TMEM16B (anoctamin-2, ANO2), function as Ca2+-activated Cl- channels (CaCCs), a type of ion channel that plays important functions such as transepithelial ion transport, smooth muscle contraction, olfaction, phototransduction, nociception, and control of neuronal excitability. Genetic ablation of TMEM16A in mice causes impairment of epithelial Cl- secretion, tracheal abnormalities, and block of gastrointestinal peristalsis. TMEM16A is directly regulated by cytosolic Ca2+ as well as indirectly by its interaction with calmodulin. Other members of the anoctamin family, such as TMEM16C, TMEM16D, TMEM16F, TMEM16G, and TMEM16J, may work as phospholipid scramblases and/or ion channels. In particular, TMEM16F (ANO6) is a major contributor to the process of phosphatidylserine translocation from the inner to the outer leaflet of the plasma membrane. Intriguingly, TMEM16F is also associated with the appearance of anion/cation channels activated by very high Ca2+ concentrations. Furthermore, a TMEM16 protein expressed in Aspergillus fumigatus displays both ion channel and lipid scramblase activity. This finding suggests that dual function is an ancestral characteristic of TMEM16 proteins and that some members, such as TMEM16A and TMEM16B, have evolved to a pure channel function. Mutations in anoctamin genes (ANO3, ANO5, ANO6, and ANO10) cause various genetic diseases. These diseases suggest the involvement of anoctamins in a variety of cell functions whose link with ion transport and/or lipid scrambling needs to be clarified.

Cholinergic signalling-regulated KV7.5 currents are expressed in colonic ICC-IM but not ICC-MP

Interstitial cells of Cajal (ICC) and the enteric nervous system orchestrate the various rhythmic motor patterns of the colon. Excitation of ICC may evoke stimulus-dependent pacemaker activity and will therefore have a profound effect on colonic motility. The objective of the present study was to evaluate the potential role of K(+) channels in the regulation of ICC excitability. We employed the cell-attached patch clamp technique to assess single channel activity from mouse colon ICC, immunohistochemistry to determine ICC K(+) channel expression and single cell RT-PCR to identify K(+) channel RNA. Single channel activity revealed voltage-sensitive K(+) channels, which were blocked by the KV7 blocker XE991 (n = 8), which also evoked inward maxi channel activity. Muscarinic acetylcholine receptor stimulation with carbachol inhibited K(+) channel activity (n = 8). The single channel conductance was 3.4 ± 0.1 pS (n = 8), but with high extracellular K(+), it was 18.1 ± 0.6 pS (n = 22). Single cell RT-PCR revealed Ano1-positive ICC that were positive for KV7.5. Double immunohistochemical staining of colons for c-Kit and KV7.5 in situ revealed that intramuscular ICC (ICC-IM), but not ICC associated with the myenteric plexus (ICC-MP), were positive for KV7.5. It also revealed dense cholinergic innervation of ICC-IM. ICC-IM and ICC-MP networks were found to be connected. We propose that the pacemaker network in the colon consists of both ICC-MP and ICC-IM and that one way of exciting this network is via cholinergic KV7.5 channel inhibition in ICC-IM.

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.

DOG1 regulates growth and IGFBP5 in gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GIST) are characterized by activating mutations of KIT or platelet-derived growth factor receptor α(PDGFRA), which can be therapeutically targeted by tyrosine kinase inhibitors (TKI) such as imatinib. Despite long-lasting responses, most patients eventually progress after TKI therapy. The calcium-dependent chloride channel DOG1 (ANO1/TMEM16A), which is strongly and specifically expressed in GIST, is used as a diagnostic marker to differentiate GIST from other sarcomas. Here, we report that loss of DOG1 expression occurs together with loss of KIT expression in a subset of GIST resistant to KIT inhibitors, and we illustrate the functional role of DOG1 in tumor growth, KIT expression, and imatinib response. Although DOG1 is a crucial regulator of chloride balance in GIST cells, we found that RNAi-mediated silencing or pharmacologic inhibition of DOG1 did not alter cell growth or KIT signaling in vitro. In contrast, DOG1 silencing delayed the growth of GIST xenografts in vivo. Expression profiling of explanted tumors after DOG1 blockade revealed a strong upregulation in the expression of insulin-like growth factor-binding protein 5 (IGFBP5), a potent antiangiogenic factor implicated in tumor suppression. Similar results were obtained after selection of imatinib-resistant DOG1- and KIT-negative cells derived from parental DOG1 and KIT-positive GIST cells, where a 5,000-fold increase in IGFBP5 mRNA transcripts were documented. In summary, our findings establish the oncogenic activity of DOG1 in GIST involving modulation of IGF/IGF receptor signaling in the tumor microenvironment through the antiangiogenic factor IGFBP5.

Expression of transient receptor potential channels and cholinergic muscarinic acetylcholine receptors in human gastrointestinal stromal tumors

AIM: To investigate the expression of transient receptor potential channels (TRPCs) and cholinergic muscarinic acetylcholine receptors (CHRMs) in human gastrointestinal stromal tumors (GISTs).

METHODS: Immunohistochemical method was used to detect the expression of TRPC and CHRM in GISTs.

RESULTS: GISTs expressed TRPC1, TRPC3, CHRM2 and CHRM3, and the positive rate was 57.5%, 47.5%, 22.5% and 55.0%, respectively. The expression levels of TRPC and CHRM decreased as the malignant potential grade of biological behaviors GISTs increased.

CONCLUSION: Our finding that GISTs express TRPC1, TRPC3, CHRM2 and CHRM3 provides new evidence for the origination of GIST from interstitial cells of Cajal.

Distribution of TMEM100 in the mouse and human gastrointestinal tract--a novel marker of enteric nerves

Identification of markers of enteric neurons has contributed substantially to our understanding of the development, normal physiology, and pathology of the gut. Previously identified markers of the enteric nervous system can be used to label all or most neuronal structures or for examining individual cells by labeling just the nucleus or cell body. Most of these markers are excellent but have some limitations. Transmembrane protein 100 (TMEM100) is a gene at locus 17q32 encoding a 134-amino acid protein with two hypothetical transmembrane domains. TMEM100 expression has not been reported in adult mammalian tissues but does appear in the ventral neural tube of embryonic mice and plays a role in signaling pathways associated with development of the enteric nervous system. We showed that TMEM100 messenger RNA is expressed in the gastrointestinal tract and demonstrated that TMEM100 is a membrane-associated protein. Furthermore TMEM100 immunoreactivity was restricted to enteric neurons and vascular tissue in the muscularis propria of all regions of the mouse and human gastrointestinal tract. TMEM100 immunoreactivity colocalized with labeling for the pan-neuronal marker protein gene product 9.5 (PGP9.5) but not with the glial marker S100ß or Kit, a marker of interstitial cells of Cajal. The signaling molecule, bone morphogenetic protein (BMP) 4, was also expressed in enteric neurons of the human colon and co-localized with TMEM100. TMEM100 is also expressed in neuronal cell bodies and fibers in the mouse brain and dorsal root ganglia. We conclude that TMEM100 is a novel, membrane-associated marker for enteric nerves and is as effective as PGP9.5 for identifying neuronal structures in the gastrointestinal tract. The expression of TMEM100 in the enteric nervous system may reflect a role in the development and differentiation of cells through a transforming growth factor β, BMP or related signaling pathway.

Interstitial cells in the primate gastrointestinal tract

Kit immunohistochemistry and confocal reconstructions have provided detailed 3-dimensional images of ICC networks throughout the gastrointestinal (GI) tract. Morphological criteria have been used to establish that different classes of ICC exist within the GI tract and physiological studies have shown that these classes have distinct physiological roles in GI motility. Structural studies have focused predominately on rodent models and less information is available on whether similar classes of ICC exist within the GI tracts of humans or non-human primates. Using Kit immunohistochemistry and confocal imaging, we examined the 3-dimensional structure of ICC throughout the GI tract of cynomolgus monkeys. Whole or flat mounts and cryostat sections were used to examine ICC networks in the lower esophageal sphincter (LES), stomach, small intestine and colon. Anti-histamine antibodies were used to distinguish ICC from mast cells in the lamina propria. Kit labeling identified complex networks of ICC populations throughout the non-human primate GI tract that have structural characteristics similar to that described for ICC populations in rodent models. ICC-MY formed anastomosing networks in the myenteric plexus region. ICC-IM were interposed between smooth muscle cells in the stomach and colon and were concentrated within the deep muscular plexus (ICC-DMP) of the intestine. ICC-SEP were found in septal regions of the antrum that separated circular muscle bundles. Spindle-shaped histamine(+) mast cells were found in the lamina propria throughout the GI tract. Since similar sub-populations of ICC exist within the GI tract of primates and rodents and the use of rodents to study the functional roles of different classes of ICC is warranted.

Ionic conductances regulating the excitability of colonic smooth muscles

The tunica muscularis of the gastrointestinal (GI) tract contains two layers of smooth muscle cells (SMC) oriented perpendicular to each other. SMC express a variety of voltage-dependent and voltage-independent ionic conductance(s) that develop membrane potential and control excitability. Resting membrane potentials (RMP) vary through the GI tract but generally are within the range of -80 to -40 mV. RMP sets the 'gain' of smooth muscle and regulates openings of voltage-dependent Ca(2+) channels. A variety of K(+) channels contribute to setting RMP of SMC. In most regions, RMP is considerably less negative than the K(+) equilibrium potential, due to a finely tuned balance between background K(+) channels and non-selective cation channels (NSCC). Variations in expression patterns and openings of K(+) channels and NSCC account for differences of the RMP in different regions of the GI tract. Smooth muscle excitability is also regulated by interstitial cells (interstitial cells of Cajal (ICC) and PDGFRα(+) cells) that express additional conductances and are electrically coupled to SMC. Thus, 'myogenic' activity results from the integrated behavior of the SMC/ICC/PDGFRα(+) cell (SIP) syncytium. Inputs from excitatory and inhibitory motor neurons are required to produce the complex motor patterns of the gut. Motor neurons innervate three cell types in the SIP, and receptors, second messenger pathways, and ion channels in these cells mediate postjunctional responses. Studies of isolated SIP cells have begun to unravel the mechanisms responsible for neural responses. This review discusses ion channels that set and regulate RMP of SIP cells and how neurotransmitters regulate membrane potential.

ENDOGLIN/CD105 is expressed in KIT positive cells in the gut and in gastrointestinal stromal tumours

ENDOGLIN/CD105 (ENG) is a transmembrane glycoprotein and an auxiliary unit of the transforming growth factor-β (TGF-β); receptor, expressed predominantly in vascular endothelium. Noteworthy, Eng mRNA expression has been reported also in Kit⁺ interstitial cells of Cajal (ICC) in the mouse intestine. Gastrointestinal stromal tumours (GIST) are thought to derive from ICC. Here we have investigated Eng expression in the Kit^K641E mouse GIST model, in human GIST and in the Ba/F3 cell model. In wild type (WT) mouse antrum, Eng immunoreactivity (-ir) was detected in CD34⁺/CD31⁺ endothelium and in Kit⁺ ICC. In Kit^K641E mice, hyperplasia of Kit⁺ cells made Eng-ir even more evident. Quantitative PCR confirmed the increased expression of Eng transcript in Kit^K641E mice. On human GIST TMA, 26/49 cases stained positive for ENG. Strong ENG staining was associated with malignant and high-risk tumours. ENG negative cases were predominantly of the epithelioid type or harboured PDGFRA mutation. In vitro, Eng mRNA was up-regulated in Ba/F3 cell lines stably expressing various oncogenic Kit mutations (K641E, del559, del814). This effect appeared to be independent of Kit activation, as neither the stimulation of WT Kit by its ligand SCF, nor the inhibition of Kit autophosphorylation by imatinib mesylate in oncogenic mutants, altered Eng expression. Elevated Eng expression in Kit oncogenic mutants appeared rather to be indirectly mediated by DNA hypomethylation, because treatment with the demethylating agent 5-Aza/dC increased Eng mRNA expression in Kit^WT cells. ENG expression in ICC and in GIST deserves further consideration as ENG is emerging as a potential target for cancer therapy.

Cloning and functional analysis of FLJ20420: a novel transcription factor for the BAG-1 promoter

BAG-1 is an anti-apoptotic protein that interacts with a variety of cellular molecules to inhibit apoptosis. The mechanisms by which BAG-1 interacts with other proteins to inhibit apoptosis have been extensively explored. However, it is currently unknown how BAG-1 expression is regulated at the molecular level, especially in cancer cells. Here we reported to clone a novel down-regulated BAG-1 expression gene named FLJ20420 using hBAG-1 promoter as a probe to screen Human Hela 5′ cDNA library by Southernwestern blot. The FLJ20420 gene encodes a ∼26-kDa protein that is localized in both the cytoplasm and nucleus. We proved that FLJ20420 protein can specially bind hBAG-1 promoter region by EMSA in vivo and ChIP assay in vivo. Northern blot analysis revealed a low level of FLJ20420 transcriptional expression in normal human tissues (i.e., brain, placenta, lung, liver, kidney, pancreas and cervix), except for heart and skeletal muscles, which showed higher levels. Furthermore, enhanced FLJ20420 expression was observed in tumor cell lines (i.e., MDA468, BT-20, MCF-7, C33A, HeLa and Caski). Knockdown of endogenous FLJ20420 expression significantly increased BAG-1 expression in A549 and L9981 cells, and also significantly enhanced their sensitivity to cisplatin-induced apoptosis. A microarray assay of the FLJ20420 siRNA –transfectants showed altered expression of 505 known genes, including 272 upregulated and 233 downregulated genes. Finally, our gene array studies in lung cancer tissue samples revealed a significant increase in FLJ20420 expression in primary lung cancer relative to the paired normal lung tissue controls (p = 0.0006). The increased expression of FLJ20420 corresponded to a significant decrease in BAG-1 protein expression in the primary lung cancers, relative to the paired normal lung tissue controls (p = 0.0001). Taken together, our experiments suggest that FLJ20420 functions as a down-regulator of BAG-1 expression. Its abnormal expression may be involved in the oncogenesis of human malignancies such as lung cancer.

Differential expression of neural markers in KIT and PDGFRA wild-type gastrointestinal stromal tumours

AIMS

To compare the genomic signatures of wild-type (WT) and mutated GISTs and the murine interstitial cells of Cajal (ICCs) to find markers of cell differentiation and other functions that may identify cells that give rise to WT tumours.

METHODS AND RESULTS

We analysed the gene expression profiles of a total of 30 tumour samples (four WT GISTs and 26 mutated GISTs), selected the genes most differentially expressed (P < 0.001:448 probe sets) and validated these results by quantitative polymerase chain reaction (PCR) and immunohistochemistry. In addition, we conducted a meta-analysis merging data from human GISTs with a genomic data set from murine ICCs. The gene expression profiles of WT and mutated GISTs differed profoundly, especially in the expression of those genes restricted primarily to neural tissues. We found that mature ICCs are more similar to mutated GISTs than WT GISTs.

CONCLUSIONS

WT GISTs have different genomic profiles from both mutated GISTs and murine mature ICCs. Considering that IGF1R expression is common to both WT GISTs and putative precursor ICCs, this study suggests that WT GISTs may derive either from ICCs at a different step of differentiation or from a different cell of origin.

Targeting ion channels for the treatment of gastrointestinal motility disorders

Gastrointestinal (GI) functional and motility disorders are highly prevalent and responsible for long-term morbidity and sometimes mortality in the affected patients. It is estimated that one in three persons has a GI functional or motility disorder. However, diagnosis and treatment of these widespread conditions remains challenging. This partly stems from the multisystem pathophysiology, including processing abnormalities in the central and peripheral (enteric) nervous systems and motor dysfunction in the GI wall. Interstitial cells of Cajal (ICCs) are central to the generation and propagation of the cyclical electrical activity and smooth muscle cells (SMCs) are responsible for electromechanical coupling. In these and other excitable cells voltage-sensitive ion channels (VSICs) are the main molecular units that generate and regulate electrical activity. Thus, VSICs are potential targets for intervention in GI motility disorders. Research in this area has flourished with advances in the experimental methods in molecular and structural biology and electrophysiology. However, our understanding of the molecular mechanisms responsible for the complex and variable electrical behavior of ICCs and SMCs remains incomplete. In this review, we focus on the slow waves and action potentials in ICCs and SMCs. We describe the constituent VSICs, which include voltage-gated sodium (Na(V)), calcium (Ca(V)), potassium (K(V), K(Ca)), chloride (Cl(-)) and nonselective ion channels (transient receptor potentials [TRPs]). VSICs have significant structural homology and common functional mechanisms. We outline the approaches and limitations and provide examples of targeting VSICs at the pores, voltage sensors and alternatively spliced sites. Rational drug design can come from an integrated view of the structure and mechanisms of gating and activation by voltage or mechanical stress.

CD133 and CD44 are universally overexpressed in GIST and do not represent cancer stem cell markers

Although imatinib mesylate has been a major breakthrough in the treatment of advanced gastrointestinal stromal tumors (GIST), complete responses are rare and most patients eventually develop resistance to the drug. Thus, the possibility of an imatinib-insensitive cell subpopulation within GIST tumors, harboring stem cell characteristics, may be responsible for the clinical failures. However, the existence of a cancer stem cell component in GIST has not been yet established. This study was aimed to determine whether expression of commonly used stem cell markers in other malignancies, that is, CD133 and CD44, might identify cells with characteristics of cancer stem/progenitor cells in human GIST. CD133 and CD44 expression in GIST explants was analyzed by flow cytometry, immunofluorescence, and gene expression. Their transcription levels were correlated with clinical and molecular factors in a large, well-annotated cohort of GIST patients. FACS sorted GIST cells based on CD133 and CD44 expression were isolated and used to assess phenotypic characteristics, ability to maintain their surface expression, sensitivity to imatinib, and expression signature. The enrichment in CD133/CD44 cells in the side population (SP) assay was also investigated. CD133 expression was consistently found in GIST. CD133(-) cells formed more colonies, were more invasive in a matrigel assay, and showed enrichment in the SP cells, compared to CD133(+) cells. CD133 expression was also detected in the two imatinib-sensitive GIST cell lines, while was absent in the imatinib-resistant lines. Our results show that CD133 and CD44 are universally expressed in GIST, and may represent a lineage rather than a cancer stem cell marker.

On the origin of rhythmic calcium transients in the ICC-MP of the mouse small intestine

Interstitial cells of Cajal associated with the myenteric plexus (ICC-MP) are pacemaker cells of the small intestine, producing the characteristic omnipresent electrical slow waves, which orchestrate peristaltic motor activity and are associated with rhythmic intracellular calcium oscillations. Our objective was to elucidate the origins of the calcium transients. We hypothesized that calcium oscillations in the ICC-MP are primarily regulated by the sarcoplasmic reticulum (SR) calcium release system. With the use of calcium imaging, study of the effect of T-type calcium channel blocker mibefradil revealed that T-type channels did not play a major role in generating the calcium transients. 2-Aminoethoxydiphenyl borate, an inositol 1,4,5 trisphosphate receptor (IP(3)R) inhibitor, and U73122, a phospholipase C inhibitor, both drastically decreased the frequency of calcium oscillations, suggesting a major role of IP(3) and IP(3)-induced calcium release from the SR. Immunohistochemistry proved the expression of IP(3)R type I (IP(3)R-I), but not type II (IP(3)R-II) and type III (IP(3)R-III) in ICC-MP, indicating the involvement of the IP(3)R-I subtype in calcium release from the SR. Cyclopiazonic acid, a SR/endoplasmic reticulum calcium ATPase pump inhibitor, strongly reduced or abolished calcium oscillations. The Na-Ca exchanger (NCX) in reverse mode is likely involved in refilling the SR because the NCX inhibitor KB-R7943 markedly reduced the frequency of calcium oscillations. Immunohistochemistry revealed 100% colocalization of NCX and c-Kit in ICC-MP. Testing a mitochondrial NCX inhibitor, we were unable to show an essential role for mitochondria in regulating calcium oscillations in the ICC-MP. In summary, ongoing IP(3) synthesis and IP(3)-induced calcium release from the SR, via the IP(3)R-I, are the major drivers of the calcium transients associated with ICC pacemaker activity. This suggests that a biochemical clock intrinsic to ICC determines the pacemaker frequency, which is likely directly linked to kinetics of the IP(3)-activated SR calcium channel and IP(3) metabolism.

Anoctamins and gastrointestinal smooth muscle excitability

Interstitial cells of Cajal (ICC) generate electrical pacemaker activity in gastrointestinal smooth muscles. We investigated whether Tmem16a, which encodes anoctamin 1 (ANO1), a Ca(2+)-activated Cl(-) channel, might be involved in pacemaker activity in ICC. The Tmem16a transcripts and ANO1 were expressed robustly in GI muscles, specifically in ICC in murine, non-human primate (Macaca fascicularis) and human GI tracts. Splice variants of Tmem16a, as well as other paralogues of the Tmem16 family, were expressed in gastrointestinal muscles. Calcium-activated Cl(-) channel blocking drugs, niflumic acid and DIDS blocked slow waves in intact muscles of mouse, primate and human small intestine and stomach. Slow waves failed to develop in Tmem16a knock-out mice (Tmem16a(tm1Bdh/tm1Bdh)). The pacemaker mechanism was investigated in isolated ICC from transgenic mice with constitutive expression of copepod super green fluorescent protein (copGFP). Depolarization of ICC activated inward currents due to a Cl(-)-selective conductance. Removal of extracellular Ca(2+), replacement of Ca(2+) with Ba(2+), or extracellular Ni(2+) (30 μM) blocked the inward current. Single Ca(2+)-activated Cl(-) channels with a unitary conductance of 7.8 pS were resolved in excised patches from ICC. The inward current was blocked in a concentration-dependent manner by niflumic acid (IC(50) = 4.8 μM). The role of ANO1 in cholinergic responses in ICC was also investigated. Carbachol activated Ca(2+)-activated Cl(-) currents in ICC, and responses to cholinergic nerve stimulation were blocked by niflumic acid in intact muscles. Anoctamin 1 is a prominent conductance in ICC, and these channels appear to be involved in pacemaker activity and in responses to enteric excitatory neurotransmitters.

Biophysically based modeling of the interstitial cells of cajal: current status and future perspectives

Gastrointestinal motility research is progressing rapidly, leading to significant advances in the last 15 years in understanding the cellular mechanisms underlying motility, following the discovery of the central role played by the interstitial cells of Cajal (ICC). As experimental knowledge of ICC physiology has expanded, biophysically based modeling has become a valuable tool for integrating experimental data, for testing hypotheses on ICC pacemaker mechanisms, and for applications in in silico studies including in multiscale models. This review is focused on the cellular electrophysiology of ICC. Recent evidence from both experimental and modeling domains have called aspects of the existing pacemaker theories into question. Therefore, current experimental knowledge of ICC pacemaker mechanisms is examined in depth, and current theories of ICC pacemaking are evaluated and further developed. Existing biophysically based ICC models and their physiological foundations are then critiqued in light of the recent advances in experimental knowledge, and opportunities to improve these models are identified. The review concludes by examining several potential clinical applications of biophysically based ICC modeling from the subcellular through to the organ level, including ion channelopathies and ICC network degradation.

Generalized neuromuscular hypoplasia, reduced smooth muscle myosin and altered gut motility in the klotho model of premature aging

BACKGROUND

  Gastrointestinal symptoms, particularly constipation, increase with aging, but their underlying mechanisms are poorly understood due to lack of experimental models. Previously we established the progeric klotho mouse as a model of aging-associated anorexia and gastric dysmotility. We also detected reduced fecal output in these animals; therefore, the aim of this study was to investigate in vivo function and cellular make-up of the small intestinal and colonic neuromuscular apparatus.

METHODS

Klotho expression was studied by RT-PCR and immunohistochemistry. Motility was assessed by dye transit and bead expulsion. Smooth muscle and neuron-specific gene expression was studied by Western immunoblotting. Interstitial cells of Cajal (ICC) and precursors were analyzed by flow cytometry, confocal microscopy, and three-dimensional reconstruction. HuC/D(+) myenteric neurons were enumerated by fluorescent microscopy.

KEY RESULTS

Klotho protein was detected in neurons, smooth muscle cells, and some ICC classes. Small intestinal transit was slower but whole-gut transit of klotho mice was accelerated due to faster colonic transit and shorter intestinal lengths, apparent only after weaning. Fecal water content remained normal despite reduced output. Smooth muscle myosin expression was reduced. ICC, ICC precursors, as well as nitrergic and cholinergic neurons maintained their normal proportions in the shorter intestines.

CONCLUSIONS & INFERENCES

Progeric klotho mice express less contractile proteins and develop generalized intestinal neuromuscular hypoplasia mainly arising from stunted postweaning growth. As reduced fecal output in these mice occurs in the presence of accelerated colonic and whole-gut transit, it likely reflects reduced food intake rather than intestinal dysmotility.

Neurotensin receptor 1 is expressed in gastrointestinal stromal tumors but not in interstitial cells of Cajal

Gastrointestinal stromal tumors (GIST) are thought to derive from the interstitial cells of Cajal (ICC) or an ICC precursor. Oncogenic mutations of the KIT or PDGFRA receptor tyrosine kinases are present in the majority of GIST, leading to ligand-independent activation of the intracellular signal transduction pathways. We previously investigated the gene expression profile in the murine Kit^K641E GIST model and identified Ntsr1 mRNA, encoding the Neurotensin receptor 1, amongst the upregulated genes. Here we characterized Ntsr1 mRNA and protein expression in the murine Kit^K641E GIST model and in tissue microarrays of human GIST. Ntsr1 mRNA upregulation in Kit^K641E animals was confirmed by quantitative PCR. Ntsr1 immunoreactivity was not detected in the Kit positive ICC of WT mice, but was present in the Kit positive hyperplasia of Kit^K641E mice. In the normal human gut, NTSR1 immunoreactivity was detected in myenteric neurons but not in KIT positive ICC. Two independent tissue microarrays, including a total of 97 GIST, revealed NTSR1 immunoreactivity in all specimens, including the KIT negative GIST with PDGFRA mutation. NTSR1 immunoreactivity exhibited nuclear, cytoplasmic or mixed patterns, which might relate to variable levels of NTSR1 activation. As studies using radio-labeled NTSR1 ligand analogues for whole body tumor imaging and for targeted therapeutic interventions have already been reported, this study opens new perspectives for similar approaches in GIST.

Acupuncture improves the repair and regeneration of interstitial cells of Cajal in rats after enteroenterostomy

AIM: To explore the mechanism by which acupuncture promotes intestinal motility.

METHODS: Thirty Sprague-Dawley rats were randomly divided into blank group, model group (receiving colocolic anastomosis) and acupuncture group. The acupuncture group underwent acupuncture at Zusanli, Sanyinjiao and Taichong daily for three continuous days. After acupuncture treatment, defecation was observed and intestinal propulsive rate was measured. Tissue samples of the colon which was 2 cm below the caecum were taken to observe the ultrastructure of interstitial cells of Cajal (ICC) and the Ache-ICC-SMC network.

RESULTS: In the acupuncture group, the time to first postoperative passage of feces was shortened and intestinal propulsive rate was improved compared with the model group [(2.00 ± 0.47) d vs (2.50 ± 0.53) d, (66.30 ± 4.21)% vs (46.33 ± 5.56)% , both P < 0.05]. Compared with the blank group, the damage of ICC ultrastructure in the model group was more significant while that in the acupuncture group was milder. In the model group, the ENS-ICC-SMC structure was disorganized, and the number of ICC and their fluorescence intensity were greatly decreased compared with the blank group [(18.67 ± 6.11) vs(32.33 ± 5.51), (35.00 ± 9.54) vs (58.67 ± 10.21), both P < 0.05]. In contrast, in the acupuncture group, the damage of the network structure was milder, and the number of ICC and their fluorescence intensity were increased compared with the model group [(30.33 ± 3.21) vs (18.67 ± 6.11), (56.67 ± 9.45) vs (35.00 ± 9.54), both P < 0.05]. Similar results were also obtained for the number of VAChT-positive nerve fibres [(18.67 ± 3.79) vs (20.67 ± 3.21), (20.33 ± 5.13) vs (34.67 ± 6.81), (23.00 ± 4.58) vs (18.67 ± 3.79), (36.00 ± 8.19) vs (20.33 ± 5.13), all P < 0.05].

CONCLUSION: Acupuncture can improve intestinal motility in rats after abdominal operation perhaps by improving the repair and regeneration of ICC.

ETV1 is a lineage survival factor that cooperates with KIT in gastrointestinal stromal tumours

Gastrointestinal stromal tumour (GIST) is the most common human sarcoma and is primarily defined by activating mutations in the KIT or PDGFRA receptor tyrosine kinases1,2. KIT is highly expressed in interstitial cells of Cajal (ICCs)—the presumed cell of origin for GIST—as well as in hematopoietic stem cells, melanocytes, mast cells and germ cells2,3. Yet, families harbouring germline activating KIT mutations and mice with knock-in Kit mutations almost exclusively develop ICC hyperplasia and GIST4–7, suggesting that the cellular context is important for KIT to mediated oncogenesis. Here we show that the ETS family member ETV1 is highly expressed in the subtypes of ICCs sensitive to oncogenic KIT mediated transformation8, and is required for their development. In addition, ETV1 is universally highly expressed in GISTs and is required for growth of imatinib-sensitive and resistant GIST cell lines. Transcriptome profiling and global analyses of ETV1-binding sites suggest that ETV1 is a master regulator of an ICC-GIST-specific transcription network mainly through enhancer binding. The ETV1 transcriptional program is further regulated by activated KIT, which prolongs ETV1 protein stability and cooperates with ETV1 to promote tumourigenesis. We propose that GIST arises from ICCs with high levels of endogenous ETV1 expression that, when coupled with an activating KIT mutation, drives an oncogenic ETS transcription program. This differs from other ETS-dependent tumours such as prostate cancer, melanoma, and Ewing sarcoma where genomic translocation or amplification drives aberrant ETS expression9–11 and represents a novel mechanism of oncogenic transcription factor activation.

Loss of Kitlow progenitors, reduced stem cell factor and high oxidative stress underlie gastric dysfunction in progeric mice

Gastrointestinal functions decline with ageing leading to impaired quality of life, and increased morbidity and mortality. Neurodegeneration is believed to underlie ageing-associated dysmotilities but the mechanisms have not been fully elucidated. We used progeric mice deficient in the anti-ageing peptide Klotho to investigate the contribution of key cell types of the gastric musculature to ageing-associated changes in stomach function and the underlying mechanisms. Klotho expression, enteric neurons, interstitial cells of Cajal (ICC), smooth muscle cells and electrical activity were assessed by immunofluorescence, confocal microscopy, 3-dimensional reconstruction, flow cytometry, quantitative RT-PCR, Western immunoblotting and intracellular recordings. Gastric emptying of solids was analysed by the [13C]octanoic acid breath test. Circulating and tissue trophic factors were measured by enzyme immunoassays and quantitative RT-PCR. The role of oxidative stress was investigated in organotypic cultures. Klotho expression was detected in gastric glands, myenteric neurons and smooth muscle cells. Progeric Klotho-deficient mice had profound loss of ICC and ICC stem cells without a significant decrease in neuron counts, expression of neuronal nitric oxide synthase or smooth muscle myosin. Slow wave amplitude and nitrergic inhibitory junction potentials were reduced while solid emptying was unchanged. Klotho-deficient mice were marantic and had low insulin, insulin-like growth factor-I and membrane-bound stem cell factor. Klotho deficiency accentuated oxidative stress and ICC loss. We conclude that Klotho-deficient, progeric mice display a gastric phenotype resembling human ageing and involving profound ICC loss. Klotho protects ICC by preserving their precursors, limiting oxidative stress, and maintaining nutritional status and normal levels of trophic factors important for ICC differentiation.

Zmynd15 encodes a histone deacetylase-dependent transcriptional repressor essential for spermiogenesis and male fertility

Spermatogenesis is a complex process through which male germ line stem cells undergo a multi-step differentiation program and sequentially become spermatogonia, spermatocytes, spermatids, and eventually spermatozoa. In this process, transcription factors act as switches that precisely regulate the expression of genes that in turn control the developmental program of male germ cells. Transcription factors identified to be essential for normal haploid gene expression all display transcription-activating effects and thus serve as the "on" switch for haploid gene expression. Here, we report that ZMYND15 acts as a histone deacetylase-dependent transcriptional repressor and controls normal temporal expression of haploid cell genes during spermiogenesis. Inactivation of Zmynd15 results in early activation of transcription of numerous important haploid genes including Prm1, Tnp1, Spem1, and Catpser3; depletion of late spermatids; and male infertility. ZMYND15 represents the first transcriptional repressor identified to be essential for sperm production and male fertility.

Interstitial cells of Cajal and gastrointestinal inflammation and immunity

Interstitial cells of Cajal (ICC) in gastrointestinal tract are closely linked to gastrointestinal inflammation and dysmotility from various causes. During gastrointestinal inflammation, ICC show varying degrees of changes in their structure, number and functions. In addition, the immune mechanisms involved in the pathogenesis of gastrointestinal inflammation have also attracted wide attention. In this article, we will review the changes in ICC in gastrointestinal inflammation and immunity.

Physiology, injury, and recovery of interstitial cells of Cajal: basic and clinical science

In the last 15 years, our understanding of the cellular basis of gastrointestinal function has been altered irreversibly by the discovery that normal gastrointestinal motility requires interstitial cells of Cajal (ICC). Research in this relatively short time period has modified our original concept that the core unit that controls motility is made up of nerves and smooth muscle, to one that now includes ICC. This concept has now expanded to beyond the gastrointestinal tract, suggesting that it may be a fundamental property of the regulation of smooth muscle function that requires rhythmic contraction. ICC are distributed throughout the gastrointestinal tract, have important functions in the control of gastrointestinal motility and are often abnormal in diseased states. Recently, significant steps forward have been made in our understanding of the physiology of ICC as well as mechanisms of injury and recovery. These advances will be the focus of this review.

A Ca(2+)-activated Cl(-) conductance in interstitial cells of Cajal linked to slow wave currents and pacemaker activity

Interstitial cells of Cajal (ICC) are unique cells that generate electrical pacemaker activity in gastrointestinal (GI) muscles. Many previous studies have attempted to characterize the conductances responsible for pacemaker current and slow waves in the GI tract, but the precise mechanism of electrical rhythmicity is still debated. We used a new transgenic mouse with a bright green fluorescent protein (copGFP) constitutively expressed in ICC to facilitate study of these cells in mixed cell dispersions. We found that ICC express a specialized 'slow wave' current. Reversal of tail current analysis showed this current was due to a Cl(-) selective conductance. ICC express ANO1, a Ca(2+)-activated Cl(-) channel. Slow wave currents are not voltage dependent, but a secondary voltage-dependent process underlies activation of these currents. Removal of extracellular Ca(2+), replacement of Ca(2+) with Ba(2+), or extracellular Ni(2+) (30 microm) blocked the slow wave current. Single Ca(2+)-activated Cl() channels with a unitary conductance of 7.8 pS were resolved in excised patches of ICC. These are similar in conductance to ANO1 channels (8 pS) expressed in HEK293 cells. Slow wave current was blocked in a concentration-dependent manner by niflumic acid (IC(50) = 4.8 microm). Slow wave currents are associated with transient depolarizations of ICC in current clamp, and these events were blocked by niflumic acid. These findings demonstrate a role for a Ca(2+)-activated Cl(-) conductance in slow wave current in ICC and are consistent with the idea that ANO1 participates in pacemaker activity.

A Ca(2+)-activated Cl(-) conductance in interstitial cells of Cajal linked to slow wave currents and pacemaker activity

Interstitial cells of Cajal (ICC) are unique cells that generate electrical pacemaker activity in gastrointestinal (GI) muscles. Many previous studies have attempted to characterize the conductances responsible for pacemaker current and slow waves in the GI tract, but the precise mechanism of electrical rhythmicity is still debated. We used a new transgenic mouse with a bright green fluorescent protein (copGFP) constitutively expressed in ICC to facilitate study of these cells in mixed cell dispersions. We found that ICC express a specialized 'slow wave' current. Reversal of tail current analysis showed this current was due to a Cl(-) selective conductance. ICC express ANO1, a Ca(2+)-activated Cl(-) channel. Slow wave currents are not voltage dependent, but a secondary voltage-dependent process underlies activation of these currents. Removal of extracellular Ca(2+), replacement of Ca(2+) with Ba(2+), or extracellular Ni(2+) (30 microm) blocked the slow wave current. Single Ca(2+)-activated Cl() channels with a unitary conductance of 7.8 pS were resolved in excised patches of ICC. These are similar in conductance to ANO1 channels (8 pS) expressed in HEK293 cells. Slow wave current was blocked in a concentration-dependent manner by niflumic acid (IC(50) = 4.8 microm). Slow wave currents are associated with transient depolarizations of ICC in current clamp, and these events were blocked by niflumic acid. These findings demonstrate a role for a Ca(2+)-activated Cl(-) conductance in slow wave current in ICC and are consistent with the idea that ANO1 participates in pacemaker activity.

Expression of anoctamin 1/TMEM16A by interstitial cells of Cajal is fundamental for slow wave activity in gastrointestinal muscles

Interstitial cells of Cajal (ICC) generate pacemaker activity (slow waves) in gastrointestinal (GI) smooth muscles, but the mechanism(s) of pacemaker activity are controversial. Several conductances, such as Ca(2+)-activated Cl() channels (CaCC) and non-selective cation channels (NSCC) have been suggested to be involved in slow wave depolarization. We investigated the expression and function of a new class of CaCC, anoctamin 1 (ANO1), encoded by Tmem16a, which was discovered to be highly expressed in ICC in a microarray screen. GI muscles express splice variants of the Tmem16a transcript in addition to other paralogues of the Tmem16a family. ANO1 protein is expressed abundantly and specifically in ICC in all regions of the murine, non-human primate (Macaca fascicularis) and human GI tracts. CaCC blocking drugs, niflumic acid and 4,4-diisothiocyano-2,2-stillbene-disulfonic acid (DIDS) reduced the frequency and blocked slow waves in murine, primate, human small intestine and stomach in a concentration-dependent manner. Unitary potentials, small stochastic membrane depolarizations thought to underlie slow waves, were insensitive to CaCC blockers. Slow waves failed to develop by birth in mice homozygous for a null allele of Tmem16a (Tmem16a(tm1Bdh)(/tm1Bdh)) and did not develop subsequent to birth in organ culture, as in wildtype and heterozygous muscles. Loss of function of ANO1 did not inhibit the development of ICC networks that appeared structurally normal as indicated by Kit antibodies. These data demonstrate the fundamental role of ANO1 in the generation of slow waves in GI ICC.

Immunohistochemical study of CD44 immunopositive cells in the muscular layers of the gastrointestinal tract in adult guinea pigs and mice

This study investigates whether CD44 immunopositive cells truly correspond to the interstitial cells of Cajal (ICCs) in the muscular layers of the gastrointestinal tract in guinea pigs and Balb/c mice using immunohistochemistry with antibodies directed against CD44, Kit, vimentin and neurofilament 200 (NF200). All the sub-groups of ICCs were immunopositive for the anti-Kit antibody in the muscular layers of stomach, small intestine and colon in both cross sections and whole-mount preparations. Kit/CD44/vimentin triple immunolabeling showed that all the ICCs in different segments and muscular layers of the digestive tract were CD44, Kit and vimentin immunopositive. Kit/CD44/NF200 triple immunolabeling revealed that neither enteric nerves nor other major cells were CD44 immunopositive in the muscular layers, apart from the ICCs. CD44 and Kit were co-localized in the same group of cells, apart from a very small number (0.6%) of CD44 immunopositive cells that were not Kit immunopositive. Our results indicate that these CD44 immunopositive cells truly correspond to ICCs, thus immunolocalisation of CD44 can be used as a special marker, in addition to Kit, to identify ICCs in the digestive tract in adult guinea pigs and mice.

Molecular and functional characterization of Kv7 K+ channel in murine gastrointestinal smooth muscles

Members of the K(v)7 voltage-gated K(+) channel family are important determinants of cardiac and neuronal membrane excitability. Recently, we and others have shown that K(v)7 channels are also crucial regulators of smooth muscle activity. The aim of the present study was to assess the K(v)7 expression in different parts of the murine gastrointestinal (GI) tract and to assess their functional roles by use of pharmacological agents. Of KCNQ/K(v)7 members, both KCNQ4/K(v)7.4 and KCNQ5/K(v)7.5 genes and proteins were the most abundantly expressed K(v)7 channels in smooth muscles throughout the GI tract. Immunohistochemical staining also revealed that K(v)7.4 and K(v)7.5 but not K(v)7.1 were expressed in the circular muscle layer of the colon. In segments of distal colon circular muscle exhibiting spontaneous phasic contractions, the nonselective K(v)7 blockers XE991 and linopirdine increased the integral of tension. Increases in the integral of tension were also observed under conditions of neuronal blockade. Similar effects, although less marked, were observed in the proximal colon. As expected, the K(v)7.1-selective blocker chromanol 293B had no effect in either type of segment. These data show that K(v)7.x especially K(v)7.4 and K(v)7.5 are expressed in different regions of the murine gastrointestinal tract and blockers of K(v)7 channels augment inherent contractile activity. Drugs that selectively block K(v)7.4/7.5 might be promising therapeutics for the treatment of motility disorders such as constipation associated with irritable bowel syndrome.

Ano1 is a selective marker of interstitial cells of Cajal in the human and mouse gastrointestinal tract

Populations of interstitial cells of Cajal (ICC) are altered in several gastrointestinal neuromuscular disorders. ICC are identified typically by ultrastructure and expression of Kit (CD117), a protein that is also expressed on mast cells. No other molecular marker currently exists to independently identify ICC. The expression of ANO1 (DOG1, TMEM16A), a Ca(2+)-activated Cl(-) channel, in gastrointestinal stromal tumors suggests it may be useful as an ICC marker. The aims of this study were therefore to determine the distribution of Ano1 immunoreactivity compared with Kit and to establish whether Ano1 is a reliable marker for human and mouse ICC. Expression of Ano1 in human and mouse stomach, small intestine, and colon was investigated by immunofluorescence labeling using antibodies to Ano1 alone and in combination with antibodies to Kit. Colocalization of immunoreactivity was demonstrated by epifluorescence and confocal microscopy. In the muscularis propria, Ano1 immunoreactivity was restricted to cells with the morphology and distribution of ICC. All Ano1-positive cells in the muscularis propria were also Kit positive. Kit-expressing mast cells were not Ano1 positive. Some non-ICC in the mucosa and submucosa of human tissues were Ano1 positive but Kit negative. A few (3.2%) Ano1-positive cells in the human gastric muscularis propria were labeled weakly for Kit. Ano1 labels all classes of ICC and represents a highly specific marker for studying the distribution of ICC in mouse and human tissues with an advantage over Kit since it does not label mast cells.

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.

Ether-a-go-go-related gene 3 is the main candidate for the E-4031-sensitive potassium current in the pacemaker interstitial cells of Cajal

The interstitial cells of Cajal (ICC), as pacemaker cells of the gut, contribute to rhythmic peristalsis and muscle excitability through initiation of slow-wave activity, which subsequently actively propagates into the musculature. An E-4031-sensitive K(+) current makes a critical contribution to membrane potential in ICC. This study provides novel features of this current in ICC in physiological solutions and seeks to identify the channel isoform. In situ hybridization and Kit immunohistochemistry were combined to assess ether-a-go-go-related gene (ERG) mRNA expression in ICC in mouse jejunum, while the translated message was assessed by immunofluorescence colocalization of ERG and Kit proteins. E-4031-sensitive currents in cultured ICC were studied by the whole cell patch-clamp method, with physiological K(+) concentration in the bath and the pipette. In situ hybridization combined with Kit immunohistochemistry detected m-erg1 and m-erg3, but not m-erg2, mRNA in ICC. ERG3 protein was colocalized with Kit-immunoreactive ICC in jejunum sections, but ERG1 protein was visualized only in the smooth muscle cells. At physiological K(+) concentration, the E-4031-sensitive outward current in ICC was different from its counterpart in cardiac and gut smooth muscle cells. In particular, inactivation upon depolarization and recovery from inactivation by hyperpolarization were modest in ICC. In summary, the E-4031-sensitive currents influence the kinetics of the pacemaker activity in ICC and contribute to maintenance of the resting membrane potential in smooth muscle cells, which together constitute a marked effect on tissue excitability. Whereas this current is mediated by ERG1 in smooth muscle, it is primarily mediated by ERG3 in ICC.

Modulation of murine gastric antrum smooth muscle STOC activity and excitability by phospholamban

We investigated intracellular Ca(2+) waves, spontaneous transient outward currents (STOCs), and membrane potentials of gastric antrum smooth muscle cells from wild-type and phospholamban-knockout mice. The NO donor sodium nitroprusside (SNP) increased intracellular Ca(2+) wave activity in wild-type antrum smooth muscle cells, but had no effect on the constitutively elevated intracellular Ca(2+) wave activity of phospholamban-knockout cells. STOC activity was also constitutively elevated in phospholamban-knockout antrum smooth muscle cells relative to wild-type cells. SNP or 8-bromo-cGMP increased the STOC activity of wild-type antrum smooth muscle cells, but had no effect on STOC activity of phospholamban-knockout cells. Iberiotoxin, but not apamin, inhibited STOC activity in wild-type and phospholamban-knockout antrum smooth muscle cells. In the presence of SNP, STOC activity in wild-type and phospholamban-knockout antrum smooth muscle cells was inhibited by ryanodine, but not 2-APB. The cGMP-dependent protein kinase inhibitor KT5823 reversed the increase in STOC activity evoked by SNP in wild-type antrum smooth muscle cells, but had no effect on STOC activity in phospholamban-knockout cells. The resting membrane potential of phospholamban-knockout antrum smooth muscle cells was hyperpolarized by approximately -6 mV compared to wild-type cells. SNP hyperpolarized the resting membrane potential of wild-type antrum smooth muscle cells to a greater extent than phospholamban-knockout antrum smooth muscles. Despite the hyperpolarized membrane potential, slow wave activity was significantly increased in phospholamban-knockout antrum smooth muscles compared to wild-type smooth muscles. These results suggest that phospholamban is an important component of the mechanisms regulating the electrical properties of gastric antrum smooth muscles.

Interstitial cells of Cajal in health and disease

The gastrointestinal tract serves the physiological function of digesting and absorbing nutrients from food and physically mixing and propelling these contents in an oral to anal direction. These functions require the coordinated interaction of several cell types, including enteric nerves, immune cells and smooth muscle. Interstitial cells of Cajal (ICC) are now recognized as another cell type that are required for the normal functioning of the gastrointestinal tract. Abnormalities in ICC numbers and networks are associated with several gastrointestinal motility disorders. This review will describe what is known about the function and role of ICC both in health and in a variety of motility disorders with a focus on unresolved issues pertaining to their role in the control of gastrointestinal motility.

The LIM and SH3 domain protein family: structural proteins or signal transducers or both?

LIM and SH3 Protein 1 (LASP-1) was initially identified from a cDNA library of metastatic axillary lymph nodes (MLN) more than a decade ago. It was found to be overexpressed in human breast and ovarian cancer and became the first member of a newly defined LIM-protein subfamily of the nebulin group characterized by the combined presence of LIM and SH3 domains. LASP2, a novel LASP1-related gene was first identified and characterized in silico. Subsequently it proved to be a splice variant of the Nebulin gene and therefore was also termed LIM/nebulette. LASP-1 and -2 are highly conserved in their LIM, nebulin-like and SH3 domains but differ significantly at their linker regions. Both proteins are ubiquitously expressed and involved in cytoskeletal architecture, especially in the organization of focal adhesions. Here we present the first systematic review to summarize all relevant data concerning their domain organization, expression profiles, regulating factors and function. We compile evidence that both, LASP-1 and LASP-2, are important during early embryo- and fetogenesis and are highly expressed in the central nervous system of the adult. However, only LASP-1 seems to participate significantly in neuronal differentiation and plays an important functional role in migration and proliferation of certain cancer cells while the role of LASP-2 is more structural. The increased expression of LASP-1 in breast tumours correlates with high rates of nodal-metastasis and refers to a possible relevance as a prognostic marker.

Progenitors of interstitial cells of cajal in the postnatal murine stomach

BACKGROUND & AIMS

Maintaining the integrity of networks of interstitial cells of Cajal (ICC) is essential to preserve orderly contractile activity and neuroregulation in the gastrointestinal tract and to restore these functions after tissue damage or surgeries. Maintenance of ICC requires insulin-dependent or insulin-like growth factor I (IGF-I)-dependent production of membrane-bound stem cell factor (SCF) and may involve regeneration from local progenitors. Our goal was to identify ICC precursors in postnatal murine gastric muscles.

METHODS

We used flow cytometry and immunohistochemistry to examine freshly dissected and cultured muscles for cells expressing CD34, an adhesion molecule expressed by stromal tumors; CD44, which occurs on mesenchymal stem cells; and receptors for SCF (Kit), insulin (Insr), and IGF-I (Igf1r). Slow waves were studied by intracellular recording.

RESULTS

In gastric muscles, we identified rare, Kit(low)CD44(+)CD34(+)Insr(+)Igf1r(+) cells resembling common embryonic precursors of ICC and smooth muscle. These putative progenitors were absent from organotypic cultures lacking mature ICC (Kit(+)CD44(+)CD34(-)Insr(-)Igf1r(-)) due to prolonged insulin/IGF-I deprivation but were rescued by IGF-I that also prevented ICC loss. Soluble SCF failed to prevent the loss of mature ICC but dramatically expanded the putative progenitors, which supported robust slow wave activity despite retaining an immature, Kit(+)CD44(+)CD34(+)Insr(+)Igf1r(+) phenotype. Differentiation of these cells into mature, network-forming ICC required IGF-I. Conversely, restoration of ICC networks by IGF-I after prolonged insulin and IGF-I deprivation required the survival of the presumed progenitors.

CONCLUSIONS

Kit(low)CD44(+)CD34(+)Insr(+)Igf1r(+) cells may be local progenitors for gastric ICC and stromal tumors. Loss of these cells may contribute to gastrointestinal dysmotilities.

Interstitial cells of Cajal in diabetic gastroenteropathy

Gastroenteropathy causes considerable morbidity in patients with diabetes mellitus and represents a major healthcare burden. Current treatments are largely symptomatic and frequently ineffective. Development of new therapeutic options is hampered by poor understanding of the underlying pathomechanisms. Experimental studies and sparse human data indicate that diabetic gastroenteropathy is multifactorial and involves not only parasympathetic and sympathetic autonomic nerves, but also enteric neurons, smooth muscle cells and interstitial cells of Cajal (ICC). ICC are mesenchymal cells that occur throughout the muscular coat of the gastrointestinal tract and provide functions critical for normal gastrointestinal motility including generation and propagation of electrical slow waves and mediation of bidirectional communication between the autonomic nervous system and smooth muscle cells. Through these functions, and in concert with other cell types of the gastrointestinal muscles, ICC support basic gastrointestinal functions such as digestion, absorption and waste removal. Loss or dysfunction of ICC in various dysmotilities and their animal models has been shown to lead to gastric dysrhythmias, gastroparesis, slow intestinal transit, impaired neuroeffector mechanisms and altered visceral afferent signalling that are considered hallmarks of diabetic gastroenteropathy. These findings and an increasing body of evidence indicating disruptions of ICC networks in diabetes suggest that the loss of ICC in this disorder is probably of functional significance and could even be a major pathogenetic factor. Future research should focus on the identification of the molecular and cellular mechanisms underlying ICC loss in diabetes and the translation of the experimental findings into treatments.