The role of lysosomes and subcellular distribution of lysosomal enzymes in early acute pancreatitis

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Acute pancreatitis is characterized by a premature and intracellular activation of digestive proteases (zymogens). Trypsinogen is activated by the lysosomal protease cathepsin B (CTSB), given that both enzymes are in close proximity. It is hypothesized that colocalization is mediated by fusion of lysosomes and secretory vesicles, enabling intracellular activation of trypsinogen.Our previous work has shown that other cathepsins, namely CTSD and CTSC, are also involved in acute pancreatitis. We could further demonstrate that cathepsins interact with each other. In preliminary studies we could show that a selective permeabilization of lysosomes in acinar cells leads to a reduction of intracellular CTSB activity, but not of trypsinogen activation.The aim of this project is to determine whether premature protease activation at the onset of pancreatitis involves lysosomes as organelles, missorting of lysosomal enzymes into the secretory compartment, or the fusion of lysosomes with secretory vesicles. Therefore effects of lysosomal permeabilization on acute pancreatitis will be examined by ex vivo and in vivo experiments. In addition, the subcellular distribution of cathepsins and severity of acute pancreatitis will be investigated in mice with knockout for CLN8, which is responsible for intracellular transport of lysosomal enzymes. Third, the interaction of lysosomes with subcellular compartments including secretory vesicles will be investigated in a mouse model with a conditional pancreas-specific knockout for Rab7, a GTPase, being involved in fusion of lysosomes with other organelles.