Abstract
The neuronal ceroid lipofuscinoses comprise a group of neurodegenerative disorders with similar clinical manifestations whose precise mechanisms of disease are presently unknown. We created multiple cell lines each with different levels of reduction of expression of the gene coding for the type 2 variant of the disease, Tripeptidyl peptidase (Tpp1), in the cellular slime mould Dictyostelium discoideum. Knocking down Tpp1 in Dictyostelium resulted in the accumulation of autofluorescent material, a characteristic trait of Batten disease. Phenotypic characterisation of the mutants revealed phenotypic deficiencies in growth and development, whilst endocytic uptake of nutrients was enhanced. Furthermore, the severity of the phenotypes correlated with the expression levels of Tpp1. We propose that the phenotypic defects are due to altered Target of Rapamycin (TOR) signalling. We show that treatment of wild type Dictyostelium cells with rapamycin (a specific TOR complex inhibitor) or antisense inhibition of expression of Rheb (Ras homologue enriched in the brain) (an upstream TOR complex activator) phenocopied the Tpp1 mutants. We also show that overexpression of Rheb rescued the defects caused by antisense inhibition of Tpp1. These results suggest that the TOR signalling pathway is responsible for the cytopathological outcomes in the Dictyostelium Tpp1 model of Batten disease.
Highlights
The neuronal ceroid lipofuscinoses (NCLs), known as Batten disease, are a group of progressive neurodegenerative disorders typically appearing in childhood
These results suggest that the Target of Rapamycin (TOR) signalling pathway is responsible for the cytopathological outcomes in the Dictyostelium Tpp1 model of Batten disease
Least squares method to an exponential equation and in (C) to a linear equation. These results suggest a role for TOR signalling in the Dictyostelium Tpp1 antisense
Summary
The neuronal ceroid lipofuscinoses (NCLs), known as Batten disease, are a group of progressive neurodegenerative disorders typically appearing in childhood. Tpp1F mutants do not contain any N-glycosylation sites, in contrast to Tpp1A and mammalian CLN2, and do not display any obvious defects in growth and development [18]. To further investigate the role of Tpp we have created Dictyostelium mutant strains which have reduced expression of Tpp1A through antisense inhibition. CLN2 homologue identified at the time, and as this protein displays protein sequence and protein structure conservation to mammalian CLN2, is N-glycosylated, displays Tpp activity and a previously constructed null mutant displays developmental defects similar to other lysosomal mutants. This implicates the TOR signalling pathway as a possible mechanism for the downstream cytopathological effects of Tpp loss
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