Identification of CD44 as a Cell-Surface Marker for Kit Negative Interstitial Cells of Cajal in Adult Mouse Colon.

Loss of Kit protein expression is proven to influence the plasticity of interstitial cells of Cajal (ICCs) and may contribute to gastrointestinal (GI) dysfunctions. The role and fate of Kit negative ICCs are unclear, and cell-specific markers for the Kit ICCs are unknown. In this study, we treated adult mice with imatinib (a Kit signaling blocker) for 8 or 16 days and investigated whether CD44 is a specific marker for the Kit negative ICCs in the adult mouse colon. We aimed at examining the protein and mRNA level of CD44 and Kit by using Western blot and real-time RT-PCR, respectively. Our results indicated that Kit expression was downregulated for both protein and mRNA levels after imatinib treatment for 8 or 16 days as compared to the vehicle-treated mice. Interestingly, CD44 expression remained unchanged throughout the treatment. Immunostaining on whole-mount preparations for Kit and CD44 showed that CD44 was exclusively co-localized with Kit in the ICCs of the vehicle-treated mouse colon. After imatinib treatment, a number of CD44+/Kit- cells with elaborated processes were observed with an evident decrease of Kit+ cell number within the muscular layers (ICC-IM) and around the myenteric nerve plexus (ICC-MY) as compared to vehicle-treated mice. After discontinuing imatinib for 16 days, Kit+ ICC-MY and ICC-IM were completely co-localized with normalization of CD44 and Kit+ cell numbers. Overall, our results identify CD44 as a cell-specific surface marker for Kit-ICCs and may be useful to understand the role and fate of Kit- ICCs in GI disorders.