Pilot 3: Biochemical Mechanisms Mediating Impaired Insulin Secretion in Mouse Models of Cystic Fibrosis

P.I.: Ian Sweet, PhD
Research Associate Professor
Metabolism, Endocrinology and Nutrition
Director, Islet Core, UW DERC
Affiliate Investigator, Benaroya Research Institute

Cystic fibrosis (CF) is a congenital disease arising from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) and affects about 30,000 people nationwide. Mutations of the CFTR gene affect functioning of the chloride ion channels in epithelial cell membranes, leading to the many symptoms of CF. As CF patients age, there is an increased incidence of diabetes mellitus, occurring in almost half the patients with the disease. This form of diabetes has features of both type 1 and type 2 diabetes and is called Cystic Fibrosis Related Diabetes (CFRD). The most conceptually attractive factor responsible for the increased incidence of diabetes is diminished insulin secretion due to impaired beta cell function. We have obtained preliminary data showing that insulin secretion is significantly decreased in islets from CFTR knockout mice. Based on these data, we hypothesize that the loss of CFTR function is related to a loss in cAMP-stimulated insulin secretion. The PI of this application has been Director of the Islet Cell Functional Analysis Core, part of an NIDDK-funded Diabetes Research Center, for the last 10 years, and has established and validated a wide array of assays specifically to characterize biochemical mechanisms regulating islet secretory function involving metabolic, electrogenic and signaling factors. We propose to use these assays, as well as assays available through the Inflammation Core of the CF Research and Translation Center, to characterize and study the properties of islets from mouse models of CF that indicate the role of CFTR mutations in CFRD. To accomplish this, we will carry out 2 specific aims, one that will focus on in vitro experiments designed to determine the intracellular mechanisms mediating the impaired secretory function due to the CFTR mutation. The second aim will focus on in vivo conditions where it will be determined whether conditions resulting from the development of CF (as simulated by infecting mice with Pseudomonas aeruginosa) further decrease secretory function. The results of these studies will provide data that has both fundamental and clinical implications and will support a future R01 application to be submitted by the PI.