The role of genetic modifiers, inflammation and CFTR in the pathogenesis of Cystic fibrosis related diabetes

Cystic fibrosis related diabetes (CFRD) generally reflects insufficient and/or delayed production of insulin, developing slowly over years to decades. Multiple mechanisms have been implicated in the pathogenesis of CFRD. CFTR function itself is a strong determinant of CFRD risk. Variants in CFTR that result in residual CFTR function and exocrine pancreatic sufficiency reduce the risk of CFRD by ten to twenty fold. Two groups of hypotheses have been proposed for the mechanism of CFTR impairing insulin secretion in CFRD: (1) β-cell dysfunction results from β cell intrinsic CFTR-dependent mechanisms of insulin secretion. (2) β-cell dysfunction results from factors outside the β cell. Genome-wide association studies have identified multiple susceptibility genes for type 2 diabetes, including TCF7L2, CDKN2A/B, CDKAL1, and IGF2BP2, as containing genetic modifiers of CFRD. These findings support the presence of intrinsic β cell defects playing a role in CFRD pathogenesis. Oxidative stress and inflammation are β cell-extrinsic mechanisms involved with CFRD. CFTR mutations render β cells more susceptible to oxidative stress and also leads to defects in α-cell function, resulting in reduced suppression of glucagon secretion. Furthermore, CFRD is characterized by β cell loss secondary to intra-islet inflammation. Recent studies have demonstrated the presence of multiple inflammatory mediators within the human CF islet. This review presents a concise overview of the current understanding of genetic modifiers of CFRD, oxidative stress, islet inflammation, and the controversies about the role of CFTR in the islet.