Growth restriction and exendin 4 promote endocrine expression in cultured islet cells derived from patients with persistent hyperinsulinemic hypoglycemia of infancy (PHHI)
Islets derived from patients with persistent hyperinsulinemic hypoglycemia of infancy, PHHI, show a significant capacity to proliferate in vitro without the addition of growth factors. However, as with other differentiated cells, PHHI-derived islet cells show a loss of differentiated function with repeated subculture. Here, we have investigated methods of extending the differentiated function of PHHI-derived endocrine cells following in vitro expansion. The experiments were carried out on 13 primary pancreatic cell cultures from patients with PHHI, the majority of which (n = 11) were glucose unresponsive--a distinctive feature of PHHI disease. After a 20-day period of cell expansion in 10% FCS, cells were switched to media containing varying concentrations of FCS with or without exendin 4 and endocrine function was measured using ELISA and RT-PCR for insulin and PDX-1. Switching the expanded cultures to low serum was shown to slow cell division while maintaining the residual differentiated endocrine characteristics of all the cultures tested. Exendin 4 was shown to further enhance the improved insulin secretion shown by low serum cultures, although in glucose nonresponsive cells, this was at the expense of insulin stores. However, we did observe that exendin 4 could upregulate insulin secretion, insulin storage, and PDX-1 expression in glucose responsive PHHI cultures.