Normal Lysosomal Morphology and Function in LAMP-1-deficient Mice

Lysosomal membranes contain two highly glycosylated proteins, designated LAMP-1 and LAMP-2, as major components. LAMP-1 and LAMP-2 are structurally related. To investigate the physiological role of LAMP-1, we have generated mice deficient for this protein. LAMP-1-deficient mice are viable and fertile. In LAMP-1-deficient brain, a mild regional astrogliosis and altered immunoreactivity against cathepsin-D was observed. Histological and ultrastructural analyses of all other tissues did not reveal abnormalities. Lysosomal properties, such as enzyme activities, lysosomal pH, osmotic stability, density, shape, and subcellular distribution were not changed in comparison with controls. Western blot analyses of LAMP-1-deficient and heterozygote tissues revealed an up-regulation of the LAMP-2 protein pointing to a compensatory effect of LAMP-2 in response to the LAMP-1 deficiency. The increase of LAMP-2 was neither correlated with an increase in the level of lamp-2 mRNAs nor with increased half-life time of LAMP-2. This findings suggest a translational regulation of LAMP-2 expression.