Lysosomal responses to nutritional and contaminant stress in mussel hepatopancreatic digestive cells: a modelling study.

The lysosomal system occupies a central and crucial role in cellular food degradation (intracellular digestion), toxic responses and internal turnover (autophagy) of the hepatopancreatic digestive cell of the blue mussel Mytilus edulis. Understanding the dynamic response of this system requires factors affecting performance, conceived as a function of the throughput, degradative efficiency and lysosomal membrane stability, to be defined and quantified. A previous carbon/nitrogen flux model has been augmented by separately identifying lysosomal 'target' material (autophagocytosed or endocytosed proteins, carbohydrates and lipids) and 'internal' material (digestive enzymes and lipid membrane components). Additionally, the whole cell's energetic costs for maintaining lysosomal pH and production of these internal components have been incorporated, as has the potentially harmful effect of generation of lipofuscin on the transitory and semi-permanent lysosomal constituents. Inclusion of the three classes of nutrient organic compounds at the whole cell level allows for greater range in the simulated response, including deamination of amino acids to provide molecules as a source of energy, as well as controlling nitrogen and carbon concentrations in the cytosol. Coupled with a more functional framework of pollutant driven reactive oxygen species (ROS) production and antioxidant defence, the separate and combined effects of three stressors (nutritional quality, nutrient quantity and a polycyclic aromatic hydrocarbon [PAH-phenanthrene]) on the digestive cell are simulated and compare favourably with real data.