OBJECTIVEFurther studies have been conducted to evaluate the roles of Ngn3 in adult islet maintenance and renewal.

METHODSIslets were isolated from 6 - 8 week old male C57BL/6 mice. After common bile duct cannulation, the pancreas was resected and digested in collagenase V (2.5 mg/ml). Islets were then handpicked and 10 - 12 islets were plated in 60 mm culture dish and cultivated with RPMI-1640, which contained 12.5 mmol/L HEPES, 5.2 mmol/L glucose and 2% fetal bovine serum (FBS). Islet cells were analyzed by immunocytochemistry methods for A6, insulin, glucagon, nestin, Ngn3 and 5-bromo-2'-deoxy-uridine (BrdU).

RESULTSThe results of these studies indicated that less than 15 percent of proliferated islet cells were Ngn3 expressing cells, in which about one third of the Ngn3 positive cells co-expressed A6. The existence of Ngn3 in cultured islet cells is consistent with the results from other's findings both in embryogenesis and adult islet studies. A significant finding of our study is that the existence of A6 and Ngn3 co-expressing cells in the cultured islet. A6 is a marker for identifying bile duct epithelial cell oriented hepatic progenitor cells. Islet-derived A6 cells are possibly born in the adult pancreatic duct and migrate into islets. A6 cells co-express Ngn3 when these cells commit to endocrine lineage within the islets. More interestingly, islet-derived A6 positive cells have the potential to transdifferentiate into hepatic cells.

CONCLUSIONThe presence of Ngn3(+) and A6(+) cells in the cultured islets suggests that the four established islet cell types arise from a common endocrine lineage residing within the adult islets. A6 and Ngn3 are useful markers for understanding intra-islet adult stem cell lineages in our future studies. This approach may allow for significant advances in understanding the IPC proliferation and differentiation, and open the possibility of using intra-islet adult stem cells for diabetes treatment.