Sialylated form of the neural cell adhesion molecule (NCAM) - A new tool for the identification and sorting of beta-cell subpopulations with different functional activity

To clarify the relationship between variations in beta -cell mass and pancr eatic function, we investigated the possibility to analyze, quantify, and s ort beta -cell subpopulations with different functional maturity. To this a im, we tested the reliability of the sialylated form of neural cell adhesio n molecule (NCAM) (PSA-NCAM) as a marker of beta -cell functional activity. Islet cells isolated from adult rats were analyzed for their PSA-NCAM abun dance using an anti-PSA-NCAM antibody. We found that PSA-NCAM is expressed only in beta -cells. The PSA-NCAM labeling was also studied with a fluoresc ence-activated cell sorter. We showed that the beta -cell population is het erogeneous for PSA-NCAM labeling. To directly determine the relationship be tween PSA-NCAM labeling and beta -cell activity, in vitro insulin secretion studies were performed on sorted beta -cell subpopulations using a perifus ion technique. Two beta -cell subpopulations were analyzed: one that was hi ghly labeled for PSA-NCAM and another that was poorly labeled. Insulin secr etion from high PSA-NCAM-labeled beta -cells was significantly higher than that in low PSA-NCAM-labeled beta -cells. This differential expression in t he beta -cell population was well correlated with differences in glucose re sponsiveness. PSA-NCAM seems thus suitable for use as a tool to identify be ta -cell subpopulations according to their glucose responsiveness.