RESUMEN
In order to explore the feasibility of inducing the human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) to differentiate into insulin-secreting cells with biological products alone, hUC-MSCs were separated and purified from the whole umbilical cord by the sequent digestion of collagenase II and trypsin followed by two-step centrifugation. hUC-MSCs were induced with IMDM culture medium containing epidermal growth factor (EGF), basic fibroblast growth factor (bFGF) and Ginkgo biloba extract (GBE). Before and after the induction, the morphological changes were observed under inverse microscope; the islet-related genes were detected by RT-PCR; islet-like clusters (ILCs) were identified by dithizone (DTZ) staining; PDX-1 and immunoreactive insulin (IRI) were examined by immunofluorescence method; the quantity and quality of IRI secretion were assayed by chemiluminescence immunoassay and Western blot respectively. The results showed that the purified hUC-MSCs presented long spindle-like shape and parallel or spiral arrangement which are typical morphological features of MSCs. After the induction, hUC-MSCs changed gradually into round or oval shape and gathered together to form ILCs; there were more than one hundred clusters on the growth surface of a flask of T25; ILCs were stained into positive mauve by DTZ and positive for PDX-1 and IRI; Western blot displayed that most of the IRI was proinsulin (PI). Therefore, hUC-MSCs can rapidly differentiate into insulin-secreting cells under the sole induction of EGF, bFGF, GBE and IMDM, but ILCs are not mature enough to produce sufficient true insulin.