Development of a polarized pancreatic ductular cell epithelium for physiological studies

Abstract

Pancreatic ductular epithelial cells comprise the majority of duct cells in pancreas, control cystic fibrosis transmembrane conductance regulator (CFTR)-dependent bicarbonate (HCO3) secretion, but are difficult to grow as a polarized monolayer. Using NIH-3T3-J2 fibroblast feeder cells and a Rho-associated kinase inhibitor, we produced well-differentiated and polarized porcine pancreatic ductular epithelial cells. Cells grown on semipermeable filters at the air-liquid interface developed typical epithelial cell morphology and stable transepithelial resistance and expressed epithelial cell markers (zona occludens-1 and -catenin), duct cell markers (SOX-9 and CFTR), but no acinar (amylase) or islet cell (chromogranin) markers. Polarized cells were studied in Ussing chambers bathed in Krebs-Ringer HCO3 solution at 37°C gassed with 5% CO2 to measure short-circuit currents (Isc). Ratiometric measurement of extracellular pH was performed with fluorescent SNARF-conjugated dextran at 5% CO2. Cells demonstrated a baseline Isc (12.2 3.2 A/cm2) that increased significantly in response to apical forskolin-IBMX (Isc: 35.4 3.8 A/cm2, P 0.001) or basolateral secretin (Isc: 31.4 2.5 A/cm2, P 0.001), both of which increase cellular levels of cAMP. Subsequent addition of apical GlyH-101, a CFTR inhibitor, decreased the current (Isc: 20.4 3.8 A/cm2, P 0.01). Extracellular pH and HCO3 concentration increased significantly after forskolin-IBMX (pH: 7.18 0.23 vs. 7.53 0.19; HCO3 concentration, 14.5 5.9 vs. 31.8 13.4 mM; P 0.05 for both). We demonstrate the development of a polarized pancreatic ductular epithelial cell epithelium with CFTR-dependent HCO3 secretion in response to secretin and cAMP. This model is highly relevant, as porcine pancreas physiology is very similar to humans and pancreatic damage in the cystic fibrosis pig model recapitulates that of humans. NEW & NOTEWORTHY Pancreas ductular epithelial cells control cystic fibrosis transmembrane conductance regulator (CFTR)-dependent bicarbonate secretion. Their function is critical because when CFTR is deficient in cystic fibrosis bicarbonate secretion is lost and the pancreas is damaged. Mechanisms that control pancreatic bicarbonate secretion are incompletely understood. We generated well-differentiated and polarized porcine pancreatic ductular epithelial cells and demonstrated feasibility of bicarbonate secretion. This novel method will advance our understanding of pancreas physiology and mechanisms of bicarbonate secretion.