The roles of Na+/H+ exchanger regulatory factor 1 and aquaporin-1 in the pathomechanism of experimental acute pancreatitis

Introduction: Pancreatic ductal epithelial cells (PDEC) secrete an alkaline HCO_3^- rich isotonic fluid. The secretion of HCO_3^- across the apical membrane of PDEC is mediated by cystic fibrosis transmembrane conductance regulator Cl- channel (CFTR) and solute carrier family 26 (SLC26) anion exchangers. Na+/H+ exchanger regulatory factor isoform 1 (NHERF 1) is a cytosolic adaptor protein, which binds CFTR on the apical membrane of epithelial cells. Aquaporins (AQPs) facilitate the transepithelial water flow involved in epithelial fluid secretion in numerous tissues. Acute pancreatitis (AP) is a serious disorder in which specific treatment is still not possible. Accumulating evidence indicate that decreased pancreatic ductal fluid secretion plays an essential role in AP. The role of NHERF-1 in the pancreas has not yet been investigated despite the fact that CFTR, a key regulator of epithelial function, is controlled by this scaffolding protein Also the functions of AQPs in the pancreas are less characterized. Our aim was to characterize the function of NHERF-1 and AQP1 in AP. Methods: We used 12 16 week old WT, NHERF 1 knock-out (KO) and AQP1 KO male mice. In the AP groups, mice were injected 7 or 10 times hourly, intraperitoneally (i.p.) with 50 µg/kg cerulein. In another AP model, 4 % Na taurocholate was administered i.d. via the punctured duodenum. Control animals were injected i.p. or i.d. with PS instead of cerulein or Na taurocholate (n=6-8). Animals were sacrificed at 12 hours in case of the cerulein model or 24 hours in the Na taurocholate experiment. Laboratory [serum amylase or, pancreatic myeloperoxidase (MPO) activity, pancreatic IL 1β concentrations] and histological parameters (pancreatic necrosis, edema, inflammatory cell infiltration) were measured to evaluate disease severity. Expression of HSP 72, IκB α, and IκB β contents were determined by Western blot analysis. Our results showed that the induction of AP was successful in both models and also in both strains. The injection of mice with cerulein or Na taurocholate increased the measured laboratory and histological parameters vs. the control groups. The measured laboratory (serum amylase, HSP72) and histological parameters (necrosis, apoptosis) were significantly elevated in AP mice injected with cerulein vs. control mice. In accord with the measured pancreatic MPO , trypsinogen activity, IκB α, IκB β, or pancreatic IL 1β concentrations were not significantly altered in the NHERF 1 KO group vs. the WT AP groups. In case of the Na taurocholate-induced AP, pancreatic necrosis, hemorrhage and MPO activity were significantly increased in the NHERF 1 KO group vs. the WT AP group. However, the pancreatic edema, leukocyte infiltration, IL 1β concentrations and serum amylase activity were significantly elevated in the WT or NHERF 1 KO AP vs. respective control groups but not in the NHERF 1 KO vs WT AP groups. The pancreatic leukocyte infiltration, edema, necrosis or serum amylase activity were significantly increased in cerulein-treated vs. control groups. In accord with the histological results, only necrosis and serum amylase activity were increased significantly in the AQP1 KO vs. WT AP groups. In conclusion, after complete evaluation of the data, we can say that the AP in both NHERF 1 or AQP1 KO groups were more severe. These results may be due the reduced HCO_3^- and fluid secretion.