Neuronal Trafficking of Palmitoyl Protein Thioesterase Provides an Excellent Model to Study the Effects of Different Mutations Which Cause Infantile Neuronal Ceroid Lipofuscinocis

Abstract

Infantile neuronal ceroid lipofuscinosis (INCL) is a severe neurodegenerative storage disorder in children caused by mutations in the palmitoyl protein thioesterase gene (PPT1). We have investigated here four naturally occurring previously described PPT1 mutations and show that all cause severe effects on PPT1 enzyme activity in transiently transfected COS-1 cells. Two of the mutations (delPhe84 and insCys45) cause a classical INCL phenotype and two (Thr75Pro and Leu219Gln) result in a late onset disease phenotype. All these mutated PPT1 molecules have severely altered intracellular localization in transiently transfected BHK-cells, whereas in mouse primary neuron cultures different effects were observed. In neurons the delPhe84 and insCys45 mutant polypeptides were targeted to the ER. Interestingly the Thr75Pro and Leu219Gln mutations had only minor effects on the neuronal trafficking of PPT1 and the mutated polypeptides were observed in neuronal shafts and showed colocalization with the presynaptic marker SV2. Our data indicates that neuronal cells provide an excellent model to study the genotype-phenotype correlation in INCL.