13 Role of local progenitors in the sustenance of networks of interstitial cells of Cajal (ICC) in the murine stomach

Abstract

Depletion of ICC networks and consequent changes in electrical slow wave activity and neuromuscular neurotransmission play important roles in diabetic and idiopathic gastroparesis. We have shown that reduced insulin/IGF‐I signaling and consequent decrease in stem cell factor (SCF) production underlie the ICC depletion of diabetic gastroparesis. It is, however, unclear whether the ICC loss is caused primarily by the accelerated attrition of mature cells or their impaired regeneration. In this study we identified local ICC progenitors and studied their role in the sustenance of gastric ICC networks. We investigated the expression of CD34, a putative marker for ICC precursors, and receptors for SCF (Kit), insulin, and IGF‐I in murine gastric muscles by flow cytometry and immunohistochemistry. In freshly dissected tissues, CD34 was not detected in KitBright ICC but a small population of KitLow cells expressed high levels of CD34. These cells were oval‐shaped, had no processes, and occurred in small clusters on the serosal and submucosal surfaces of the gastric musculature and in the myenteric region. Unlike mature ICC, they expressed insulin and IGF‐I receptors. KitLowCD34+ cells were undetectable and Kit+ ICC were profoundly reduced in gastric muscles cultured in the absence of growth factors for up to 85 days. Soluble SCF added to the culture media for 32–85 days rescued KitLowCD34+ cells and caused their growth into densely packed clusters in the myenteric region or thick chords containing bipolar cells within the muscle layers. These cells had elevated Kit and reduced CD34 expression. Cultures treated in a similar manner with IGF‐I to stimulate both soluble and membrane‐bound SCF were dominated by normal, Kit+CD34– ICC networks. IGF‐I treatments were only effective when initiated within the first 2–4 weeks of culturing, although mature, Kit+ ICC were able to survive longer. In adult H‐2Kb‐tsA58 mice harbouring the temperature‐sensitive large tumour antigen encoded by a mutant strain of simian virus 40, stimulating cell proliferation by culturing at 33°C prevented the decline of gastric ICC even in the absence of exogenous growth factors. We conclude that maintenance of gastric ICC probably involves their regeneration from rare KitLowCD34+ precursors that depend on a nearly uninterrupted supply of insulin or IGF‐I. While the development of these cells into ICC can be initiated with soluble SCF, their expansion and conversion into mature, CD34– ICC also requires membrane‐bound SCF. Supported by NIH Grants DK58185 and RR16464.