Blockade of kit signaling induces transdifferentiation of interstitial cells of cajal to a smooth muscle phenotype.

BACKGROUND & AIMS: Interstitial cells of Cajal (ICC) serve as pacemaker cells and mediators of neurotransmission from the enteric nervous system to gastrointestinal muscles. ICC develop from mesenchymal cells that express c-Kit, and signaling via Kit receptors is necessary for normal development of ICC. We studied the fate of functionally developed ICC after blockade of Kit receptors to determine whether ICC undergo cell death or whether the phenotype of the cells is modified. The fate of undeveloped ICC was also investigated. METHODS: Neutralizing, anti-Kit monoclonal antibody (ACK2) was administered to mice for 8 days after birth. ICC in the small intestine were examined by immunohistochemistry and electron microscopy. Occurrence of apoptosis was also assayed. RESULTS: When Kit receptors were blocked, ICC nearly disappeared from the small intestine. Apoptosis was not detected in regions where ICC are normally distributed. Remaining Kit-immunopositive cells in the pacemaker region of the small intestine developed ultrastructural features similar to smooth muscle cells, including prominent filament bundles and expression of the muscle-specific intermediate filament protein, desmin, and smooth muscle myosin. ICC of the deep muscular plexus normally develop after birth in the mouse. Precursors of these cells remained in an undifferentiated state when Kit was blocked. CONCLUSIONS: These data, along with previous studies showing that ICC in the pacemaker region of the small intestine and longitudinal muscle cells develop from the same Kit-immunopositive precursor cells, suggest inherent plasticity between the ICC and smooth muscle cells that is regulated by Kit-dependent cell signaling.     

Interstitial cells of Cajal mediate inhibitory neurotransmission in the stomach.

The structural relationships between interstitial cells of Cajal (ICC), varicose nerve fibers, and smooth muscle cells in the gastrointestinal tract have led to the suggestion that ICC may be involved in or mediate enteric neurotransmission. We characterized the distribution of ICC in the murine stomach and found two distinct classes on the basis of morphology and immunoreactivity to antibodies against c-Kit receptors. ICC with multiple processes formed a network in the myenteric plexus region from corpus to pylorus. Spindle-shaped ICC were found within the circular and longitudinal muscle layers (IC-IM) throughout the stomach. The density of these cells was greatest in the proximal stomach. IC-IM ran along nerve fibers and were closely associated with nerve terminals and adjacent smooth muscle cells. IC-IM failed to develop in mice with mutations in c-kit. Therefore, we used W/W(V) mutants to test whether IC-IM mediate neural inputs in muscles of the gastric fundus. The distribution of inhibitory nerves in the stomachs of c-kit mutants was normal, but NO-dependent inhibitory neuro-regulation was greatly reduced. Smooth muscle tissues of W/W(V) mutants relaxed in response to exogenous sodium nitroprusside, but the membrane potential effects of sodium nitroprusside were attenuated. These data suggest that IC-IM play a critical serial role in NO-dependent neurotransmission: the cellular mechanism(s) responsible for transducing NO into electrical responses may be expressed in IC-IM. Loss of these cells causes loss of electrical responsiveness and greatly reduces responses to nitrergic nerve stimulation.     

Stem Cell Factor/Kit Signal Insufficiency Contributes to Hypoxia-Induced Intestinal Motility Dysfunctions in Neonatal Mice

Background

Gastrointestinal (GI) motility disorders represent a group of problems that more constantly encountered in preterm infants. However, whether hypoxia exposure contributes to the GI dysfunctions is still unclear.

Methods

Newborn mice were exposed to hypoxia (10%) from P1 to P7. Intestinal motilities were examined by a strain gauge transducer. The proliferation of ICCs was detected by using immunostaining for BrdU, Ki67, Kit, Ano1, and insulin-like growth factor 1 receptor (IGF-1R+). Smooth muscle cells and enteric neurons were revealed by immunostaining for α-SMA and NF200, respectively. Apoptosis was assessed by TUNEL assay. Kit signal pathway was examined by western blot and qPCR.

Results

Intestinal motilities were found weakened significantly in the hypoxic small intestines as compared to controls on P8. Kit+ or Ano1+ interstitial cells of Cajal (ICCs) were found obviously decreased in the myenteric ICCs (ICC-MY) of neonatal mice after exposed to hypoxia. A large number of ICC progenitors (IGF-1R+) were found highly mitotic (BrdU+ Ki67+) to populate ICC during early postnatal development in the normoxic mice. We found the ICC proliferation was significantly inhibited upon hypoxia exposure, without increasing apoptosis (TUNEL+). We next identified that Kit phosphorylation was inhibited 3 days after hypoxia exposure. The inhibition of Kit signaling was largely due to decreased the expression of the ligand of Kit receptor, stem cell factor (SCF), in the intestinal walls. Exposure to imatinib, a Kit receptor inhibitor, for 3 days from P4 phenocopied the effect of hypoxia on the neonatal pups that resulted in inhibited intestinal motilities and decreased Kit+ ICC numbers.

Conclusion

All together, our findings indicate the SCF/Kit signaling insufficiency may contribute to the underdevelopment of ICCs and intestinal motility dysfunction upon hypoxia exposure. The decease in ICC density is likely due to the cell cycle arrest of ICC progenitor cells.

     

胰岛素样生长因子-1对糖尿病大鼠结肠平滑肌细胞表达干细胞因子的影响

背景：糖尿病胃肠动力障碍与Cajal间质细胞（ICC）数量和超微结构异常有关。前期实验发现胰岛素样生长因子-1（IGF-1）可诱导正常大鼠胃肠平滑肌细胞（SMC）表达干细胞因子（SCF）,从而有利于ICC的生存。目的：探讨IGF-1对糖尿病大鼠结肠SMC表达SCF的影响及其信号转导通路。方法：以链脲霉素建立糖尿病大鼠模型。分离、培养正常和糖尿病大鼠结肠SMC,设不同浓度（0、50、100、150μg/L）、不同时间（0、8、16、24、48h）IGF-1十预组和MEK抑制剂PD98059＋IGF-1、P13K抑制剂LY294002＋IGF-1干预组．以RT—PCR和蛋白质印迹法检测SMC中的SCF表达。结果：糖尿病大鼠结肠SMC的生长速度较正常大鼠减慢。无血清培养条件下．正常和糖尿病结肠SMC中SCFmRNA和蛋白表达较低,IGF-1可诱导SCF表达增加,最大有效浓度为100μg／L,诱导高峰时间正常对照组为16h,糖尿病组为24h。经PD98059预处理的SMC,IGF-1诱导的SCF表达部分受抑．IN294002预处理对IGF-1的作用无明显影响。结论：0～100μg／L IGF-1在24h内能以剂量和时间依赖性方式诱导糖尿病大鼠结肠SMC表达SCF．但效应弱于其对正常大鼠结肠SMC的作用,该作用的发挥可能部分依赖于ERKMAPK信号通路。     

The Importance of Interstitial Cells of Cajal in the Gastrointestinal Tract

Gastrointestinal (GI) motility function and its regulation is a complex process involving collaboration and communication of multiple cell types such as enteric neurons, interstitial cells of Cajal (ICC), and smooth muscle cells. Recent advances in GI research made a better understanding of ICC function and their role in the GI tract, and studies based on different types of techniques have shown that ICC, as an integral part of the GI neuromuscular apparatus, transduce inputs from enteric motor neurons, generate intrinsic electrical rhythmicity in phasic smooth muscles, and have a mechanical sensation ability. Absence or improper function of these cells has been linked to some GI tract disorders. This paper provides a general overview of ICC; their discovery, subtypes, function, locations in the GI tract, and some disorders associated with their loss or disease, and highlights some controversial issues with regard to the importance of ICC in the GI tract.     

Neuropathy in the brain-in-the-gut

* The enteric nervous system has sensory neurons, interneurons and motor neurons and functions as a brain-in-the-gut. * Smooth muscles of the digestive tract are autogenic in the absence of neural control. * Enteric inhibitory motor neurons control excitability of the autogenic musculature. * The neuropathic form of chronic intestinal pseudo-obstruction is a form of disinhibitory motor disease linked with neuropathic degeneration in the enteric nervous system. * Patients with inflammatory degenerative neuropathy may progress from irritable bowel syndrome (IBS)-like symptoms to chronic pseudo-obstruction. * Detection of anti-enteric neuronal antibodies may be a useful diagnostic test for early stages of inflammatory degenerative neuropathy in patients with symptoms of a functional gastrointestinal disorder. Awareness is increasing that autoimmune attack targeted to neuronal elements of the enteric nervous system may underlie irritable bowel-like symptoms that progress to chronic pseudo-obstruction. The inflammatory neuropathy disrupts the integrative functions of the brain-in-the-gut, including reduction in the population of inhibitory motor neurons to the musculature. Extreme loss of inhibitory motor neurons is manifest as disinhibitory motor disease characterized by achalasia in smooth muscle sphincters and hyperactive, disorganized contractile behaviour of intestinal circular muscle which results in pseudo-obstruction. Detection of anti-enteric neuronal antibodies in the serum of patients with early symptoms of a functional gastrointestinal motility disorder may prove to be a useful diagnostic test for inflammatory enteric neuropathy.     

Cajal间质细胞与糖尿病胃轻瘫的关系

Cajal间质细胞（ICC）是胃肠道中与肠神经细胞和平滑肌密切相关的间质细胞,网络状分布于整个胃肠组织,对胃肠慢波的产生及胃肠动力的维持起关键作用。研究表明,糖尿病胃轻瘫（DGP）患者及其动物模型均存在ICC数目明显减少、结构破坏、且与神经末梢及平滑肌之间的连接减少。因此,ICC的异常可能是DGP的重要原因之一。本文就ICC与DGP的研究现状进行探讨。     

Electrical activity of the intestine of mice with hereditary megacolon and absence of enteric ganglion cells

Mice with a recessive gene which reduces the number of ganglion cells of the large intestine and produces megacolon similar to Hirschsprung's disease were studied. Electrical activity of the small bowel consisted of electrical slow waves and action potentials and showed no difference between the mice with megacolon and their normal siblings. Electrical slow waves and action potentials occurred in the large intestine of both normal and abnormal mice. The principal difference between normal mice and their abnormal siblings was increased incidence of discharge of action potentials associated with uncoordinated phasic contractions superimposed upon tonic contracture of the circular muscle layer of the distal aganglionic segment in the abnormal mouse. The distended colon of the abnormal mouse and the entire length of the normal bowel showed bursts of action potentials which accompanied peristaltic waves of circular muscle contraction. During propulsive motility in the rectum, activation of the circular muscle was preceded by coordinated contraction of the longitudinal muscle only in the normal bowel. Symptoms of megacolon can be accounted for by the absence of spontaneously active inhibitory neurons from the enteric plexuses of the distal segment of the large bowel.     

Interstitial cells of Cajal are present in human extrahepatic bile ducts

Background and Aims: Interstitial cells of Cajal (ICC) are distributed with smooth muscle throughout the gastrointestinal tract and are involved in regulating motility. ICC were recently discovered in the wall of the human gallbladder. This study sought to determine whether ICC are present in human bile ducts. Methods: Biliary tract samples were obtained from several sources: surgical specimens (n = 16, 11 women, mean age 61 years); archival post‐mortem specimen (n = 1, 86 years, man); and cadavers (n = 2, 68 and 80 years, men). Paraffin‐embedded sections (3 µm) from the gallbladder (fundus, body and neck) and both extrahepatic and intrahepatic bile ducts were investigated. A double immunofluorescence protocol using polyclonal and monoclonal c‐kit antibodies and mast cell tryptase was used to distinguish c‐kit‐positive cells with typical ICC morphology from c‐kit‐positive mast cells. Small bowel samples were used as positive controls. ICC in the gallbladder were confirmed by ultrastructural study. Results: c‐kit‐positive cells with characteristic ICC morphology were identified in the subepithelial and muscular layers of the gallbladder and extrahepatic bile ducts. They were most prominent within the muscle layer of the extrahepatic bile ducts where they were organized into loosely arranged laminae running parallel to circular smooth muscle fibers. ICC were not found in intrahepatic bile ducts. Conclusion: This study demonstrates for the first time that ICC are present in human extrahepatic bile ducts where they are more densely aggregated than in the gallbladder. This cellular network is likely to be involved in biliary tract motility and its related disorders.     

Characteristics of cholinergic neuroeffector transmission of ganglionic and aganglionic colon in Hirschsprung's disease.

Differences in the release and content of acetylcholine and the alpha 2 adrenoceptor mediated interaction between noradrenergic and cholinergic neurons were investigated by neurochemical and pharmacological methods in aganglionic and ganglionic segments of isolated human colon taken from children suffering from Hirschsprung's disease. Both at rest and during transmural stimulation the release of acetylcholine was significantly higher in the spastic (aganglionic) segment than in the proximal dilated bowel. Significant differences were found in the tissue concentration of acetylcholine between ganglionic and aganglionic specimens. The pattern of response to transmural stimulation was also different in the spastic and dilated bowel. Transmural stimulation induced relaxation and contraction in ganglionic specimens but only contractions in aganglionic specimens. The sensitivity of the smooth muscle in the aganglionic portion to exogenous acetylcholine and to field stimulation was found to be higher than in the ganglionic portion. While noradrenaline added to the organ bath reduced the stimulation-evoked release of acetylcholine from spastic segments, via an alpha 2 adrenoceptor mediated process, yohimbine did not enhance the release. It is suggested that in Hirschsprung's disease the increased acetylcholine release, the enhanced sensitivity of smooth muscle cells to acetylcholine, and the lack of alpha 2 adrenoceptor mediated noradrenergic modulation of acetylcholine release from cholinergic interneurons might be responsible for the spasm of aganglionic segments.     

干细胞因子对糖尿病结肠Cajal间质细胞的影响

目的 探讨糖尿病(DM)小鼠干细胞因子(SCF)对结肠Cajal间质细胞(ICC)异常的影响.方法 40只雄性C57/BL6小鼠分为正常对照组,DM组、正常+抗-SCF组、DM+SCF组,每组10只.DM成模后6周处死小鼠,以流式细胞仪、透射电镜、Western印迹法观察近端结肠组织中ICC的变化,以Western印迹、酶联免疫吸附实验(ELISA)检测结肠组织和血清中SCF的表达情况.结果 DM小鼠血清和近端结肠组织中SCF均明显降低,伴有结肠中ICC数量减少、超微结构显著破坏;正常+抗-SCF组,血清和近端结肠组织中SCF均明显降低,并伴有结肠中ICC数量减少、超微结构显著破坏(类似DM组);DM+SCF干预后,血清和近端结肠组织中SCF水平增高,ICC的数量以及超微结构病变得到显著改善.结论 DM小鼠血清和近端结肠组织中SCF水平的下降,可能是DM结肠中ICC数量减少和超微结构破坏的原因;外源性SCF能改善DM相关的胃肠道ICC病变.     

Homing of the bone marrow-derived interstitial cells of Cajal is decreased in diabetic mouse intestine

Background: Interstitial cells of Cajal (ICCs), which express c‐Kit receptor tyrosine kinase (KIT), play an important role in gastrointestinal motility. Loss of ICCs likely contributes to diabetic gastrointestinal motility disorder, however, the mechanism of attrition remains unknown. Here, we test the hypothesis that the bone marrow‐derived progenitors are an important source of intestinal ICCs and that decreased homing of these progenitors in diabetes contributes to ICC diminution. Methods: Wild type mice were X‐ray irradiated, transplanted with bone marrow (BMT) from green fluorescence protein (GFP)‐transgenic (TG)‐mice and subsequently made diabetic by streptozotocin (STZ) injection. Intestinal homing of GFP‐positive bone marrow‐derived cells was examined 2 or 5 months after STZ treatment. Results: In the BMT‐mice, we found many GFP‐positive bone marrow‐derived cells (BMDCs) in most parts of the intestinal area, the number of BMDCs was significantly decreased in diabetic mice compared with nondiabetic controls. As a representative area, we further examined the myenteric plexus of the proximal small intestine, and found that the cell numbers of ICCs marked by c‐Kit‐positive immunoreactivity were decreased by more than 40% in diabetic versus nondiabetic mice. Furthermore, numbers of c‐Kit+/GFP+ and c‐Kit+/GFP‐ cells were similar in nondiabetic mice, and decreased by 45.8% and 42.0%, respectively, in diabetic mice. Conclusion: These results suggest that the decreased homing from the bone marrow is a major cause of ICC loss in the intestine in diabetes mellitus.     

Idiopathic constipation is not associated with increased NCAM expression on intestinal muscle

Our previous study of neural cell adhesion molecule (NCAM) in childhood Hirschsprung's disease demonstrated increased expression on intestinal muscle, especially muscularis mucosae, in aganglionic bowel. The present study was undertaken to test whether this increased NCAM expression is a feature of congenital aganglionosis rather than being a nonspecific feature of constipation. We studied specimens from six patients (20–60 years old; five women and one man) operated on for idiopathic long-standing constipation, using immunocytochemistry for NCAM and protein gene product 9.5 (PGP 9.5). Results showed that in adult constipated bowel the pattern of NCAM expression is similar to that seen in controls. There was no expression of NCAM on muscle in any of the specimens studied. Thus, it seems likely that increased NCAM expression in gastrointestinal smooth muscle in congenital aganglionosis is a result of the abnormal innervation rather than any symptomatic or clinical feature.     

Plasticity of electrical pacemaking by interstitial cells of Cajal and gastric dysrhythmias in W/W mutant mice

BACKGROUND & AIMS: Interstitial cells of Cajal (ICC) generate and propagate slow waves in the stomach. Gastric peristalsis depends on a proximal-to-distal gradient in slow wave frequency. We tested whether the gastric frequency gradient was an intrinsic property of ICC and whether dysrhythmias result from disruptions of ICC networks. METHODS: We studied wild-type (WT) and W/W(V) mice, which have only myenteric (pacemaker) ICC in the stomach. ICC distributions were analyzed by Kit immunofluorescence. Pacemaking in tissues was studied by intracellular electrophysiologic recording and in cultured ICC by monitoring mitochondrial [Ca(2+)] oscillations with rhod-2 fluorescence or membrane potential with DiBAC(4)(3) fluorescence. RESULTS: Slow wave frequencies were constant throughout WT gastric muscle sheets containing corpus and antrum. Separating the antrum from the corpus caused a significant drop in antral slow wave frequency. ICC from WT antrums also displayed significantly slower pacemaker frequencies than corpus ICC, but the corpus pacemaker frequency dominated in cocultures of corpus and antrum ICC. Myenteric ICC networks were reduced in W/W(V) mice, particularly in the corpus. In W/W(V) mice, separating the antrum from the corpus failed to reduce antral slow wave frequency. Antral pacemaker frequency in ICC from W/W(V) stomachs was the same as in corpus ICC. CONCLUSIONS: The proximal-to-distal slow wave frequency gradient and entrainment of distal electrical activity by proximal pacemakers are fundamental properties of gastric ICC. Chronic depletion of ICC networks disrupts the proximal-to-distal frequency gradient, and emergence of ectopic pacemakers in the antrum may be caused by "reprogramming" of the ICC pacemaker apparatus.     

Neuronal nitric oxide in the gut

Motility of the gastrointestinal tract is directly controlled by enteric inhibitory and excitatory motor neurons that innervate the layers of smooth muscle. Inhibitory motor neurons mediate receptive and accommodative relaxations and control the opening of sphincters, thus playing an important role in normal gut motility. Recent studies have demonstrated that nitric oxide (NO) is an important neurotransmitter released by inhibitory motor neurons in animal and human gut. Antagonists of nitric oxide synthase (NOS), the synthetic enzyme for NO, reduce the effectiveness of transmission from inhibitory motor neurons. Exogenous NO mimics inhibitory nerve activation, and a variety of compounds that affect the availability of endogenously produced NO modulate relaxations of gastrointestinal smooth muscle. It is clear, however, that NO is unlikely to be the only transmitter released by enteric inhibitory motor neurons: several other substances such as vasoactive intestinal polypeptide (VIP), or related peptides, and adenosine triphosphate (ATP) are also likely to contribute to nerve-mediated inhibition. The identification of NO as a major inhibitory neurotransmitter to gastrointestinal smooth muscle fills an important gap in our understanding of the physiological control of motility and opens up a wide range of new experimental possibilities. It may eventually lead to the development of new drugs for motility disorders. It should be noted, however, that NO is important in the brain, in cardiovascular control, in blood cell function and in many other organ systems, suggesting that it may be difficult to achieve specific pharmacological intervention targeted on inhibitory neurotransmission in the gut, without undesirable side effects.     

Megacolon in adulthood after surgical treatment of Hirschsprung＇s disease in early childhood

Hirschsprung's disease(HD) is a disorder associated with congenital malformation of the enteric nervous system with segmental aganglionosis. Prevailing therapy includes a resection of the affected part of the bowel. However, patients often do not obtain complete functional improvement after surgical treatment. We present the case of a 25-year-old woman who had surgical treatment of HD in early childhood. After that procedure she had clinical features of constipation for years in the end, passing of stool once a week, requiring laxatives and enemas. We diagnosed an incomplete resection of the aganglionic bowel via rectal biopsy and resected the remaining aganglionic segment. Two months after surgery the patient's bowel function improved to a frequency of 1-4 stools per day. We conclude that regular follow-up is required to identify HD patients with persistent alterations of bowel function after surgery. In patients presenting with constipation, recognition of a remaining aganglionic segment or other alterations of the enteric nervous system should be aimed at in an early stage.     

Isolation and cultivation of neuronal precursor cells from the developing human enteric nervous system as a tool for cell therapy in dysganglionosis

Background The human enteric nervous system (ENS) descends from migrating neural crest cells (NCC) and is structured into different plexuses embedded in the gastrointestinal tract wall. The development of this entity strongly depends on the supply of an appropriate support with trophic factors during organogenesis. The lack of important factors, such as glial cell line-derived neurotrophic factor, leads to severe disturbances in the ENS and, thus, to motility disorders in children. The isolation of neuronal precursor cells as well as their transplantation after expansion in vitro is therefore a hopeful new approach concerning all forms of dysganglionosis in children.Methods We therefore established a way to isolate and expand precursor cells from the developing and postnatal human ENS. Bowel samples were obtained from human fetuses and children (from the 9th week of gestation to 5 years postnatal). Myenteric plexus was isolated by enzymatical digestion and cultivated until spheroid aggregates, the so-called neurospheres, developed. These neurospheres could be differentiated and also be transplanted after dissociation into aganglionic bowel in vitro.Results Enteric neurospheres could be grown from different gestational ages, including postmortem material. Undifferentiated proliferating precursor cells were kept in culture for up to 72 days and could be differentiated in neurons and glial cells in vitro.Conclusion The first results using isolated enteric neurospheres in aganglionic bowel are quite promising and are a basis to develop an appropriate cell therapy for all kinds of dysganglionosis, especially for cases where a surgical approach is not sufficient or not even possible.