Cerulein hyperstimulation decreases AMP-activated protein kinase levels at the site of maximal zymogen activation

Abstract

Shugrue CA, Alexandre M, Diaz de Villalvilla A, Kolodecik TR, Young LH, Gorelick FS, Thrower EC. Cerulein hyperstimulation decreases AMP-activated protein kinase levels at the site of maximal zymogen activation. Am J Physiol Gastrointest Liver Physiol 303: G723-G732, 2012. First published July 26, 2012; doi:10.1152/ajpgi.00082.2012.-The premature activation of digestive enzyme zymogens in the pancreatic acinar cell is an important initiating event in acute pancreatitis. We have previously demonstrated that vacuolar ATPase (vATPase) activity is required for zymogen activation. Adenosine monophosphate-activated protein kinase (AMPK) regulates vATPase function in kidney and epididymal clear cells. To determine whether AMPK could affect pancreatitis responses, its effects were first examined in a cellular model of pancreatitis, cerulein-hyperstimulated (100 nM) pancreatic acini. This treatment caused a prominent increase in trypsin and chymotrypsin activities. Pretreatment with AICAR or metformin (AMPK activators) or compound C (an AMPK inhibitor) reduced or increased cerulein-induced zymogen activation, respectively. The association of the vATPase E subunit with membranes, a marker of its activation, tended to be inversely related to AMPK activity (assessed by AICAR and compound C treatments). Cerulein treatment did not change AMPK (␣ and ␤) levels but did lead to an increase in its activation (phosphorylation of Thr172) and induced the time-dependent translocation of the enzyme to a Triton-insoluble compartment. Basal in vivo studies showed that AMPK was widely distributed between membrane and soluble fractions generated by differential centrifugation. After cerulein hyperstimulation, AMPK levels selectively decreased in fractions containing the highest levels of active zymogens. These studies suggest that AMPK activity has a protective role in the pancreatic acinar cell that inhibits zymogen activation in the basal state, and this AMPK effect is reduced during pancreatitis. Therapies that prevent the selective reduction of AMPK in compartments that support zymogen activation could reduce injury during pancreatitis. pancreatic acini; vacuolar ATPase THE PANCREATIC ACINAR CELL comprises over 90% of the exocrine pancreas and synthesizes and secretes the enzymes needed to digest nutrients. Many of the digestive enzymes are stored in the acinar cells as inactive zymogens that become activated only after reaching the small intestine. Premature activation of these zymogens within acinar cells appears to have a critical role in initiating acute pancreatitis (17). Experimental models of acute pancreatitis have been developed in which isolated acinar cells or whole animals are treated with supraphysiological concentrations of cerulein (an orthologue of the hormone cholecystokinin) to induce the early stages of the disease.AMP-activated kinase (AMPK) is a heterotrimeric serine/ threonine kinase, composed of ␣-, ␤-, and ␥-subunits, with the ␣-subunit possessing the catalytic kinase domain. Phosphorylation of the Thr172 resid...

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