Stimulation of p38 MAPK by hormal preconditioning with atrial natriuretic peptide

AIM：Stress-activated signaling pathways responsible for hepatic ischemia reperfusion injury and their modulation by protective interventions are widely unknown.Preconditioning of rat livers with Atrial Natriuretic Peptide(ANP)attenuates ischemia reperfusion injury(Gerbes et al.Hepatology1998,18:1309-1317),SinANP has recently been shown to be a regulator of the p38MAPKpathway in endothelial cells(Kiemer et al.CircRes2002,90:874-881).aim of this thudy was to investigate activities of MAPK during ischemia and reperfusion and effects of ANP on MAPK.METHODS:Rat livers were perfused with KH-buffer in the presence or absence of ANP for 20min,kept in cold UWsloution for 24h,and reperfused forupto120min,Activities of p38MAPKand JNKwas determined by in vitro phosphorylation assays using MBP and c-jun as substrates.After SDS/PAGE electrophoresis,gels were quantified by phosphorimaging.RESULTS:Activity of p38MAPKin control organs decreased in the course of ischemia and reperfusion by85%,whereas ANPincreased p38 activity by up to 30-fold.JNKactivation of control livers increased in the course of ischemia and reperfusion by up to three-fold.This increase in JNK activrity was slightly elevated in ANP preconditioned organs.CONCLUSION:This work represents a systematic investigation of MAPK activation during liver ischemia and reperfusion.Employing ANP,for the first time a pharmacological approach to modulate these central signal transduction molecules is presented.

Hepatocyte cytoskeleton during ischemia and reperfusion -influence of ANP-mediated p38 MAPK activation

AIM: To determine functional consequences of this activation, whereby we focused on a potential regulation of the hepatocyte cytoskeleton during ischemia and reperfusion.METHODS: For in vivo experiments, animals received ANP (5 μg/kg) intravenously. In a different experimental setting, isolated rat livers were perfused with KH-buffer ±ANP (200 nmol/L)±SB203580 (2 μmol/L). Liverswere then kept under ischemic conditions for 24 h, and either transplanted or reperfused. Actin, Hsp27, and phosphorylated Hsp27 were determined by Western blotting, p38 MAPK activity by in vitro phosphorylation assay. F-actin distribution was determined by confocal microscopy.RESULTS: We first confirmed that ANP preconditioning leads to an activation of p38 MAPK and observedalterations of the cytoskeleton in hepatocytes of ANPpreconditioned organs. ANP induced an increase of hepatic F-actin after ischemia, which could be prevented by the p38 MAPK inhibitor SB203580 but had no effect on bile flow. After ischemia untreated livers showed a translocation of Hsp27 towards the cytoskeleton and an increase in total Hsp27, whereas ANP preconditioning prohibited translocation but caused an augmentation of Hsp27 phosphorylation. This effect is also mediated via p38 MAPK, since it was abrogated by the p38 MAPK inhibitor SB203580.CONCLUSION: This study reveals that ANP-mediated p38 MAPK activation leads to changes in hepatocyte cytoskeleton involving an elevation of phosphorylated Hsp27 and thereby for the first time shows functional consequences of ANP-induced hepatic p38 MAPK activation.