Pathogenesis of autophagic trypsin activation in experimental pancreatitis

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<h3>Aims</h3> Intracellular protease activation, an initiating event for pancreatitis, was suggested to begin in autophagosomes. We tested whether intracellular trypsin activation depends on auto-phagy, or autophagy on trypsin activation, in the early phase of pancreatitis. <h3>Methods</h3> We used mice expressing the fluorescent autophagy marker LC-3-GFP to prepare acini and to induce pancreatitis by supramaximal stimulation (10 nM CCK) <i>in vitro</i>. Trypsin activation was imaged by fluorescent microscopy (CBZ-Ile-Pro-Arg-AMC). <h3>Results</h3> Autophagosome formation was confirmed by the appearance of fluorescent vesicles in isolated acini of LC3-GFP-mice and a shift of LC3 to its membrane-bound LC3-II form. Significant levels were reached between 10 and 40 min following CCK stimulation. Premature trypsin activation also developed, but earlier during the first 10 min after CCK stimulation. Simultaneous fluorescent imaging of autophagosome formation (LC3-fluorescence) and trypsin activation (AMC-fluorescence) indicated that the two events arise in different compartments. Trypsin inhibition with gabexate-mesilate did not prevent autophagosome formation. <h3>Discussion</h3> While autophagy has been shown to be important in regulating the ultimate levels of intrapancreatic protease activity and pancreatitis severity, the initial activation of trypsin develops neither in autophagosomes nor does it depend on autophagy. Onset of autophagy in the pancreas, in turn, does not require trypsin activation.