Development Characteristics Of Interstitial Cells Of Cajal In The Gastrointestinal Tracts Of Postnatal Mammals

Interstitial cells of Cajal(ICCs) are a special kind of interstitial cells that distribute throughout the gastrointestinal tract and form a cellular network. They play a very important role in the regulation of gastrointestinal(GI) motility by generating and propagating spontaneous electric slow-wave activity and mediating excitatory and inhibitory neurotransmission. ICCs can also mediate responses to stretch and serve as mechanosensors. Recent clinical studies have indicated that some GI motility disorders of neonates and young children such as infantile hypertrophic pyloric stenosis(IHPS), neonatal pseudo-obstruction, Hirschsprung's disease(HD) and temporary post-operational entero-paralysis are associated with ICCs. Although the etiologies of these diseases have not been elucidated, they are all characterized by a reduction of ICCs numbers and impairment of the cellular network, indicating that the delaying or disorder of ICCs development may lead to the GI motility dysfunction of neonates. Information on the development of ICCs may help us to understand the etiology and pathophysiology of disorders characterized by a deficiency of ICCs, and provides us with new insight into the treatment of relevant disease.Previous studies have shown that the number of ICCs increased with the gestational age and formed a cellular network similar to that of adult before birth. Traditionally ICCs were thought to own the ability to proliferate only in fetus and early period after birth. There is, however, relatively little published research on postnatal development and proliferation of ICCs.ICCs start to express the gene product of c-kit proto-oncogene, typeâ…¢receptor tyrosine kinase(Kit) from the embryonic period and expression persists throughout life. This receptor not only can be a specific marker of ICCs, but also is essential for the development, proliferation, differentiation, survival and functional maintenance of ICCs. In conditions involving GI motility disorders, the expression of Kit is, however, greatly down-regulated or even entirely lost, which makes it almost impossible to label these ICCs using an anti-Kit antibody. An alternative marker of ICCs, which allows better monitoring of the fate of ICCs in conditions involving the reduced Kit expression, is, therefore, needed.The primary objective of this study is to investigate the development pattern of ICCs after birth and the potential role of CD44 as an identifying mark for ICCs by using morphology techniques such as BrdU incorporation and immunofluorescentce staining.The results show that:1. The length, diameter and surface area of intestine kept on increasing and reached the level of adult animal at the age of P32. At P0, ICCs in bowel wall mostly gathered around myenteric nerve plexus and arranged into a loose network connected to each other via 2-3 short and slim processes. With the age increase, the branches of ICCs got thicker and longer and the number of IC-MY also increased. At P32, the total cell number of ICCs increased more than 15-fold and formed a complete and compact network similar to those of adult.2. BrdU injection study results show that about 28% of Kit labeled ICCs are BrdU positive at P2, and the percentage increased to 65% at P32 indicating that the proliferation is a major method for ICCs to expand their volumes. It has been found that the proliferation of ICCs is age-dependent and can persist from neonatal to almost adult life. The study results also indicate that some Kit+/BrdU+/CD44+/CD34+/IGF-IR+ cells could be the precursor of ICCs and these cells could proliferate and further differentiate into mature ICCs.3. With the help of Kit/CD44/vimentin (another marker of ICCs) triple immunofluorescence staining, the study results show that: the CD44 expressed in those of Kit+ and vimentin+ ICCs in the GI tract of adult guinea pigs and mice; in the muscle layers of the digestive tract wall, only ICCs were immuno-positive for CD44 and there was no other major cells label for this protein; there existed a very small group of Kit-/CD44+ cells in the GI tract, which may be the progenitors of ICCs. These CD44+ cells truly corresponded to the ICCs in the GI tract, and could be utilized as a special marker in the GI tract.