In situ analysis reveals that CFTR is expressed in only a small minority of β-cells in normal adult human pancreas

Abstract

CONTEXT: Although diabetes affects 40-50% of adults with cystic fibrosis, remarkably little is known regarding the underlying mechanisms leading to impaired pancreatic β-cell insulin secretion. Efforts towards improving the functional β-cell deficit in cystic fibrosis related diabetes (CFRD) have been hampered by an incomplete understanding of whether β-cell function is intrinsically regulated by CFTR. Definitively excluding meaningful CFTR expression in human β-cells in situ would contribute significantly to the understanding of CFRD pathogenesis. OBJECTIVE: To determine CFTR mRNA and protein expression within β-cells in situ in the unmanipulated human pancreas of donors without any known pancreatic pathology. DESIGN: In situ hybridisation for CFTR mRNA expression in parallel with insulin immunohistochemical staining; and immunofluorescence co-localisation of CFTR with insulin and the ductal marker, Keratin-7, were undertaken in pancreatic tissue blocks from 10 normal adult, non-obese deceased organ donors over a wide age range (23-71 years) with quantitative image analysis. RESULTS: CFTR mRNA was detectable in 0.45 (0.17-0.83)% (mean(range)) of insulin-positive cells. CFTR protein expression was co-localised with Keratin-7. 100% of insulin-positive cells were immunonegative for CFTR. CONCLUSIONS: For the first time, in situ CFTR mRNA expression in the unmanipulated pancreas has been shown to be present in only a very small minority (<1%) of normal adult β-cells. These data signal a need to move away from studying endocrine-intrinsic mechanisms and focus on elucidation of exocrine-endocrine interactions in human cystic fibrosis.