| Research Abstract |
We have generated mice deficient for lysosome-associated membrane protein-2 (LAMP-2) to investigate the physiological role of this protein. LAMP-2 deficiency leads to premature postnatal death of about. half of all LAMP-2 deficient mice. In several LAMP-2-deficient tissues, including muscle, heart, pancreas, and liver, an accumulation of autophagic vacuoles was observed. We also observed a reduced contractile function of the heart muscle. In this study, we extend the phenotype analysis using cultured hepatocytes. Enzyme activity measurements showed that the trafficking of some lysosomal enzymes to lysosomes was impaired. Immunoprecipitation of metabolically labeled cathepsin D indicated reduced intracellular retention and processing in the knockout cells. Interestingly, the steady-state level of 46-kDa mannose 6-phosphate receptor (MPR46) was decreased to 30% of controls due to a shorter half-life. Less receptor was found in the Golgi and in endosomes, suggesting impaired recycling from endosomes to the Golgi. More receptor was found in autophagic vacuoles, which may explain its shorter half-life. Our data indicate that in hepatocytes LAMP-2 deficiency either directly or indirectly leads to impaired recycling of MPR46 and partial mistargeting of a subset of lysosomal enzymes. Autophagic vacuoles may accumulale due to impaired capacity for lysosomal degradation.
|
