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Original articles

Disorders of Interstitial Cells of Cajal

Burns, Alan J

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Journal of Pediatric Gastroenterology and Nutrition: December 2007 - Volume 45 - Issue - p S103-S106
doi: 10.1097/MPG.0b013e31812e65e0
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Abstract

MORPHOLOGY AND LOCATIONS OF ICC WITHIN THE GI TRACT

In the later part of the 19th century, a network of small anastomosing cells located within the gut muscle layers was described by the Spanish neuroanatomist Ramon Santiago y Cajal, who was awarded the Nobel Prize in 1906. These cells, which appeared to be situated between the nerve endings and smooth muscle, would later become known as interstitial cells of Cajal (ICCs). Until recent times, the major difficulty in studying ICCs was the lack of specific histological stains or immunohistochemical markers that would enable ICCs to be distinguished from the enteric neurons and smooth-muscle cells that comprise the neuromuscular apparatus within the gastrointestinal (GI) tract. Consequently, for many years ICCs were mostly identified by their ultrastructural characteristics (the gold standard), or by certain histochemical stains, such as vital methylene blue, each of which have their drawbacks in terms of the painstaking nature of the analysis or lack of cell specificity, respectively. Because of these deficiencies, until the early 1990s there was considerable controversy as to the identity of different classes of ICC, their roles within the gut, their interactions with other cell types, and their embryologic origin and development. However, a breakthrough in ICC analysis came with the finding that the protooncogene c-kit, which encodes a receptor tyrosine kinase (1), the ligand for which is stem cell factor (2), is expressed by ICCs and that anti-Kit antibody specifically labels these cells (3–5). Subsequently, using anti-Kit antibody, ICCs have been shown, in humans and laboratory animals, to have a range of different morphologies in different regions of the gut (6,7). For example, long, thin, spindle-shaped ICCs are distributed within the plane of the muscularis (ICC-IM), whilst highly branching, network-forming ICCs are closely associated with the myenteric plexus (ICC-MY) of the enteric nervous system. The distribution of morphologically different classes of ICC within various layers of the GI musculature (8) strongly suggested that different ICCs may perform distinct physiological roles in the gut.

PHYSIOLOGICAL ROLES OF ICC

Because Cajal and subsequent researchers observed ICCs in close association with enteric neurons and smooth muscle, it was logical to predict that ICCs could play a role in controlling gut motility (9,10). An important breakthrough in demonstrating such a physiological role was achieved by blocking the development of ICC networks using either injection of anti-Kit antibody into newborn mice, or genetically using W mutant mice that have loss-of-function mutations in c-kit. In such experiments, animals developed that lacked ICC-MY within the small intestine and also lacked intestinal pacemaker activity (3–5,11). These results demonstrated that ICCs are necessary for pacing electrical slow-wave activity and contractions within GI muscles. Similar results, showing loss of ICCs and loss of regular intestinal activity, were obtained in steel mutant mice (12), which lack the stem-cell factor ligand for the Kit receptor.

In W mutant mice, which lack ICC-MY in the pacemaking region of the small intestine, intramuscular ICCs also are deficient. Because ICC-IM are normally closely apposed to varicose nerve terminals and electrically coupled via gap junctions to neighbouring smooth-muscle cells (13), a role for ICCs in the mediation of neurotransmission seemed likely, as originally proposed by Cajal. This theory was confirmed by analysing stomach tissues from W mutant mice, which are deficient in ICC-IM but have normal patterns of enteric nerve fibres and smooth-muscle cells. Experiments clearly demonstrated a lack of nitric oxide–mediated neuroregulation of smooth muscle, because the muscle relaxed in the presence of an exogenous NO donor, but the membrane potential effects were greatly attenuated (13). These and more recent findings (14) confirm that ICC-IM play a fundamental role in the reception and transduction of both inhibitory and excitatory enteric motor neurotransmission (15).

ICC IN HUMAN GI MOTILITY DISORDERS

The findings outlined above, obtained from laboratory animals, highlight the key roles played by ICCs in the regulation of GI motility, and suggest that alterations in ICC networks in humans also could have an impact on gut motility and/or GI diseases. Indeed, loss of ICCs or disruption of ICC networks has been reported in a wide range of GI diseases, including achalasia, chronic intestinal pseudoobstruction, Hirschsprung disease, inflammatory bowel diseases, slow transit constipation, and others (6,16) (Table 1).

TABLE 1
TABLE 1:
GI pathologies and corresponding status of interstitial cells of Cajal (ICC) as identified by Kit-labelling, ICC number, ultrastructure, or a combination of these criteria

A number of important factors should be kept in mind when studying ICCs in disease states. For example, ICCs are derived from mesenchymal cells that express c-kit(17,18), and as outlined above antibodies against the extracellular domain of the Kit receptor have been used extensively to immunolabel and identify ICCs in different species, including humans. However, in disease states, a lack of kit-labelling may either indicate an actual loss of ICCs from the gut tissues or only a loss of kit-positivity from ICCs which remain in situ. In the latter case, transmission electron microscopy may be necessary to reveal ICCs based on well-defined ultrastructural criteria. However, there is little such information regarding normal ICCs in disease states, and if ICC features change under pathophysiological conditions, then it may be difficult to recognise cells as ICCs. Indeed, experimental findings support the idea that ICCs can change phenotype under certain conditions. For example, in studies in which Kit receptors were blocked during development, ICCs almost entirely disappeared from the small intestine. However, this loss of ICCs was not accounted for using assays for cell death, and closer examination revealed that remaining ICCs developed ultrastructural features similar to smooth-muscle cells (19). These findings point to an inherent plasticity between ICCs and smooth-muscle cells that is regulated by Kit signalling (19,20). ICCs have been shown not only to be capable of transdifferentiation (19) but also to have some capacity for regeneration. In experiments in which the mouse intestine was exposed to a chemical insult that induced loss of the myenteric plexus and the closely associated ICC-MY, a few weeks later, cells with ICC-like features began to reappear (21). These data, reporting on transdifferentiation and regeneration of ICCs, highlight the difficulty in distinguishing what is cause and what is consequence in the relationship between ICCs and the generation of certain gut motility disorders. Are defects in ICC networks the cause of motility disorders, or are disrupted ICC networks a consequence of gut dysfunction?

A good example of the conflicting evidence obtained regarding potential loss/reduction of ICCs and gut motility is the congenital gut defect Hirschsprung disease (HSCR), which presents as absence of enteric ganglia in the distal hindgut and associated obstructed gut, resulting in severe constipation (22). Some studies of HSCR tissues have reported a reduction in the cellular density of ICCs or “disrupted” ICC networks within the aganglionic segment (23,24), whereas others have observed normal ICC networks in the aganglionic bowel (25,26). One may argue that in the aganglionic segment of HSCR gut, which by definition is devoid of enteric neurons, ICC networks would not develop normally because these cells normally occur in close association with neurons or nerve fibres of the enteric nervous system. Animal models of gut aganglionosis have been used to further investigate this problem. In chick or mouse gut, deprived of neural crest cells that are the precursors of enteric neurons, ICC have been found to develop normally in the absence of neurons (17,18). Similarly, ls/ls−/− and Gdnf−/− mutant mice, which are deficient in enteric neurons in varying lengths of the gut, appear to have similar distributions of ICCs and normal slow waves (27), although in ls/ls−/− mice there appear to be different electrical activity and neural responses (28). Overall, these data from animal models provide strong evidence that ICCs can develop normally in the absence of enteric neurons. Translating these findings back to HSCR in humans is still problematic for the reasons outlined above, but they would imply that any deficiency in ICCs in HSCR gut would not likely be due to a loss of enteric neurons.

SUMMARY AND FUTURE DIRECTIONS

In the last 10 to 15 years, great progress has been made in our understanding of the morphology and physiological roles of ICCs, the small network-forming cells distributed throughout the smooth-muscle wall of the gastrointestinal tract. These advances have been made primarily because of the discovery that ICCs express c-kit, the protooncogene that encodes the receptor tyrosine kinase, Kit. Activation of Kit signalling is required for ICC development, and antibody against Kit can be used as a simple, efficient means of specifically labelling ICCs. Developmental biologists have determined that ICCs are mesenchyme-derived cells, belonging to the family of smooth-muscle cells. Morphological studies have identified different phenotypic classes of ICCs, which have different regulatory roles within the gut. ICCs associated with the myenteric plexus act as pacemaker cells within the phasic regions of the GI tract, whilst intramuscular ICCs act as mediators of neural inputs from the enteric nervous system.

Future work will likely be geared toward achieving a better understanding of the interrelationship between ICCs and the generation of human gut motility disorders. This will necessitate a range of investigations using morphological and physiological studies, using perhaps alternative markers to Kit; a better understanding of the genetics and/or cell biology of ICCs; further studies on animal models of GI disease states; and more detailed immunohistochemical investigations on tissues from patients with GI pathologies. With the advances such investigations should bring, it may be possible to restore functional populations of ICCs in patients experiencing loss of these highly specialised cells identified by Cajal >100 years ago.

REFERENCES

1. Chabot B, Stephenson DA, Chapman VM, et al. The proto-oncogene c-kit encoding a transmembrane tyrosine kinase receptor maps to the mouse W locus. Nature 1988; 335:88–89.
2. Zsebo KM, Williams DA, Geissler EN, et al. Stem cell factor is encoded at the Sl locus of the mouse and is the ligand for the c-kit tyrosine kinase receptor. Cell 1990; 63:213–224.
3. Ward SM, Burns AJ, Torihashi S, et al. Mutation of the proto-oncogene c-kit blocks development of interstitial cells and electrical rhythmicity in murine intestine. J Physiol 1994; 480:91–97.
4. Torihashi S, Ward SM, Nishikawa S, et al. C-kit-dependent development of interstitial cells and electrical activity in the murine gastrointestinal tract. Cell Tissue Res 1995; 280:97–111.
5. Huizinga JD, Thuneberg L, Kluppel M, et al. W/kit gene required for interstitial cells of Cajal and for intestinal pacemaker activity. Nature 1995; 373:347–349.
6. Vanderwinden JM, Rumessen JJ. Interstitial cells of Cajal in human gut and gastrointestinal disease. Microsc Res Tech 1999; 47:344–360.
7. Rumessen JJ, Vanderwinden JM. Interstitial cells in the musculature of the gastrointestinal tract: Cajal and beyond. Int Rev Cytol 2003; 229:115–208.
8. Burns AJ, Herbert TM, Ward SM, et al. Interstitial cells of Cajal in the guinea-pig gastrointestinal tract as revealed by c-kit immunohistochemistry. Cell Tissue Res 1997; 290:11–20.
9. Thuneberg L. Interstitial cells of Cajal: intestinal pacemaker cells? Adv Anat Embryol Cell Biol 1982; 71:1–130.
10. Faussone-Pellegrini MS. Interstitial cells of Cajal: once negligible players, now blazing protagonists. Ital J Anat Embryol 2005; 110:11–31.
11. Maeda H, Yamagata A, Nishikawa S, et al. Requirement of c-kit for development of intestinal pacemaker system. Development 1992; 116:369–375.
12. Ward SM, Burns AJ, Torihashi S, et al. Impaired development of interstitial cells and intestinal electrical rhythmicity in steel mutants. Am J Physiol 1995; 269(6 Pt 1):C1577–C1585.
13. Burns AJ, Lomax AE, Torihashi S, et al. Interstitial cells of Cajal mediate inhibitory neurotransmission in the stomach. Proc Natl Acad Sci USA 1996; 93:12008–12013.
14. Ward SM, McLaren GJ, Sanders KM. Interstitial cells of Cajal in the deep muscular plexus mediate enteric motor neurotransmission in the mouse small intestine. J Physiol 2006; 573(Pt 1):147–159.
15. Ward SM, Sanders KM, Hirst GD. Role of interstitial cells of Cajal in neural control of gastrointestinal smooth muscles. Neurogastroenterol Motil 2004; 16(Suppl 1):112–117.
16. Sanders KM, Ordog T, Ward SM. Physiology and pathophysiology of the interstitial cells of Cajal: from bench to bedside. IV. Genetic and animal models of GI motility disorders caused by loss of interstitial cells of Cajal. Am J Physiol Gastrointest Liver Physiol 2002; 282:G747–G756.
17. Lecoin L, Gabella G, Le Douarin N. Origin of the c-kit-positive interstitial cells in the avian bowel. Development 1996; 122:725–733.
18. Young HM, Ciampoli D, Southwell BR, et al. Origin of interstitial cells of Cajal in the mouse intestine. Dev Biol 1996; 180:97–107.
19. Torihashi S, Nishi K, Tokutomi Y, et al. Blockade of kit signaling induces transdifferentiation of interstitial cells of Cajal to a smooth muscle phenotype. Gastroenterology 1999; 117:140–148.
20. Sanders KM, Ordog T, Koh SD, et al. Development and plasticity of interstitial cells of Cajal. Neurogastroenterol Motil 1999; 11:311–338.
21. Faussone-Pellegrini MS, Vannucchi MG, Ledder O, et al. Plasticity of interstitial cells of Cajal: a study of mouse colon. Cell Tissue Res 2006; 325:211–217.
22. Young HM, Newgreen D, Burns AJ. The development of the enteric nervous system in relation to Hirschsprung's disease. In: Ferretti P, Copp A, Tickle C, et al., editors. Embryos, Genes, and Birth Defects. Chichester, UK: John Wiley & Sons; 2006. pp. 263–300.
23. Yamataka A, Kato Y, Tibboel D, et al. A lack of intestinal pacemaker (c-kit) in aganglionic bowel of patients with Hirschsprung's disease. J Pediatr Surg 1995; 30:441–444.
24. Vanderwinden JM, Rumessen JJ, Liu H, et al. Interstitial cells of Cajal in human colon and in Hirschsprung's disease. Gastroenterology 1996; 111:901–910.
25. Horisawa M, Watanabe Y, Torihashi S. Distribution of c-kit immunopositive cells in normal human colon and in Hirschsprung's disease. J Pediatr Surg 1998; 33:1209–1214.
26. Newman CJ, Laurini RN, Lesbros Y, et al. Interstitial cells of Cajal are normally distributed in both ganglionated and aganglionic bowel in Hirschsprung's disease. Pediatr Surg Int 2003; 19:662–668.
27. Ward SM, Ordog T, Bayguinov JR, et al. Development of interstitial cells of Cajal and pacemaking in mice lacking enteric nerves. Gastroenterology 1999; 117:584–594.
28. Ward SM, Gershon MD, Keef K, et al. Interstitial cells of Cajal and electrical activity in ganglionic and aganglionic colons of mice. Am J Physiol Gastrointest Liver Physiol 2002; 283:G445–G456.
Keywords:

Gastrointestinal motility; Interstitial cells of Cajal; Kit; Motility disorders

© 2007 Lippincott Williams & Wilkins, Inc.