Role of LAMP-2 in Lysosome Biogenesis and Autophagy

Abstract

In LAMP-2–deficient mice autophagic vacuoles accumulate in many tissues, including liver, pancreas, muscle, and heart. Here we extend the phenotype analysis using cultured hepatocytes. In LAMP-2–deficient hepatocytes the half-life of both early and late autophagic vacuoles was prolonged as evaluated by quantitative electron microscopy. However, an endocytic tracer reached the autophagic vacuoles, indicating delivery of endo/lysosomal constituents to autophagic vacuoles. 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. The steady-state level of 300-kDa mannose 6-phosphate receptor was slightly lower in LAMP-2–deficient hepatocytes, whereas that of 46-kDa mannose 6-phosphate receptor was decreased to 30% of controls due to a shorter half-life. Less receptor was found in the Golgi region and in vesicles and tubules surrounding multivesicular 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 46-kDa mannose 6-phosphate receptors and partial mistargeting of a subset of lysosomal enzymes. Autophagic vacuoles may accumulate due to impaired capacity for lysosomal degradation

Short-chain fatty acids induced autophagy serves as an adaptive strategy for retarding mitochondria-mediated apoptotic cell death

“…*Po0.01; **Po0.001, compared with PBS control at the corresponsding time reported to be critical for the lysosomal degradation of autophagic vacuoles. 14 Propionate caused an extensive upregulation of LAMP-2 expression (Figure 1c and Supplementary Figure S2a). The upregulated LAMP-2 displayed punctate structures and colocalized with GFP-LC3 dots, indicating autolysosome formation.…”

Does Autophagy Contribute To Cell Death?

“…The loss of LAMP-2, which is required for the fusion of lysosomes with autophagosomes, leads to an accumulation of autophagic vacuoles in vivo. 98,99 Accordingly, the combined depletion of nutrients and LAMP-2 in cells in vitro leads to the acquisition of a morphology associated with type 2 cell death, which subsequently is followed by the hallmarks of apoptosis, including mitochondrial depolarization, release of cytochrome c, activation of caspase-3 and nuclear chromatin condensation. This example illustrates a shift from autophagic to apoptotic cell death morphology.…”

Early cellular changes after blockage of chaperone-mediated autophagy

“…67 In fact, amphisomes can be detected in almost all cells, but their percentage increases when autophagic clearance by lysosomes is altered. 68 To determine if such amphisomal structures contributed to the macroautophagic activity observed in the acutely LAMP-2A interfered cells, we analyzed the colocalization of LC3-positive vesicles with Texas red-conjugated transferrin, a marker for endocytic vesicles (which include early, sorting and recycling endosomes) ( Fig. 4C and D).…”