Expression Pattern of Lysosomal Protective Protein/Cathepsin A: Implications for the analysis of hnman galactosialidosis

The lysosome represents a well characterized, membrane-contained intracellular digestive system. Iu this important organelle a battery of lysosomal hydro lases and accessory proteins work in concert on the step-wise conversion of macromolecular substrates into small biological building blocks, which are either reutHized by the cell 01' discarded. A failure of any of these enzymes to properly exert their hydrolytic activity results in the progressive accumulation of partially degraded· metabolltes that are retained ('stored') in the lysosome. The genetic disorders caused by a malfunction of the lysosomal system are collectively known as lysosomal storage disorders, aud are normally associated with a single enzyme deficiency. One known exception is the disease galactosialldosis which is due to partial or complete loss of activity of two glycosidases, acid p-D-galactosidase and N-acetyl-a-neuraminidase, because of a primary defect in the carboxypeptidase protective protein/cathepsin A (PPCA). The latter enzyme associates with both glycosidases soon after syntbesis, and is essential for their proper intracellular routing, lysosomal stability and activity. Aside from the protective function, PPCA has cathepsin Aldeamidase activity on a selected number ofneuropeptides. The aim of the experimental work presented in tbis thesis was to gain insigbts into the transcription regulation of the PPCA gene and the expression of PPCA mRNA and protein In mouse tissues. These studies have coutributed to the understanding of the phenotypic abnormalities in the murine model of galactosialldosis, which reflected to a large extent the distribution pattern of the protein in normal tissues. Given the fact that the observed pathology in galactosialldosis is iu part caused by tbe secondary neuraminidase deficiency, the isolation and characterization of the murine neuraminidase was instrumental to better understand in whicb way tbe two enzymes depend on each otber and cooperate ill vivo.