Palmitoyl protein thioesterase 1 (PPT1) deficiency causes endocytic defects connected to abnormal saposin processing.
Infantile neuronal ceroid lipofuscinosis (INCL) is a severe neurodegenerative disorder of the childhood caused by mutations in the gene encoding palmitoyl protein thioesterase 1 (PPT1). PPT1 localizes to late endosomes/lysosomes of non-neuronal cells and in neurons also to presynaptic areas. PPT1-deficiency causes massive death of cortical neurons and most tissues show an accumulation of saposins A and D. We have here studied endocytic pathways, saposin localization and processing in PPT1-deficient fibroblasts to elucidate the cellular defects resulting in accumulation of specific saposins. We show that PPT1-deficiency causes a defect in fluid-phase and receptor-mediated endocytosis, whereas marker uptake and recycling endocytosis remain intact. Furthermore, we show that saposins A and D are more abundant and relocalized in PPT-deficient fibroblasts and mouse primary neurons. Metabolic labeling and immunoprecipitation analyses revealed hypersecretion and abnormal processing of prosaposin, implying that the accumulation of saposins may result from endocytic defects. We show for the first time a connection between saposin storage and a defect in the endocytic pathway of INCL cells. These data provide new insights into the metabolism of PPT1-deficient cells and offer a basis for further studies on cellular processes causing neuronal death in INCL and other neurodegenerative diseases.
National Public Health Institute, Department of Molecular Medicine, Biomedicum Helsinki, P.O. Box 104, 00251 Helsinki, Finland.
Laura
L
Ahtiainen
Kaisu
K
Luiro
Maria
M
Kauppi
Jaana
J
Tyynelä
Outi
O
Kopra
Anu
A
Jalanko
D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D003911:Dextrans / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D007223:Infant; D008077:Lipoproteins, LDL / Q000378:metabolism; D018942:Macrolides / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009472:Neuronal Ceroid-Lipofuscinoses / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D012503:Saponins / Q000378:metabolism*; D049231:Saposins / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000378:metabolism; D013869:Thiolester Hydrolases / Q000172:deficiency* / Q000235:genetics; D014168:Transferrin / Q000378:metabolism
D003911:Dextrans; D008077:Lipoproteins, LDL; D018942:Macrolides; D012503:Saponins; D049231:Saposins; D014168:Transferrin; C039217:fluorescein isothiocyanate bovine serum albumin; C015219:fluorescein isothiocyanate dextran; C110714:holotransferrin; D012710:Serum Albumin, Bovine; C025946:3-methyladenine; C040929:bafilomycin A1; D013869:Thiolester Hydrolases; C095299:palmitoyl-protein thioesterase; D016650:Fluorescein-5-isothiocyanate; D000225:Adenine