Cellular Dysfunctions in Juvenile Neuronal Ceroid Lipofuscinosis

• Applicant: Privatdozent Dr. Guido Hermey
• Subject Area: Cell Biology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 425373668

Juvenile Neuronal Ceroid Lipofuscinosis (JNCL) is the most common neurodegenerative disease affecting children. The pathological hallmark is intracellular accumulation of lysosomal autofluorescent storage material. JNCL is caused by mutations in the gene CLN3. Therefore, investigating CLN3, a transmembrane protein of unknown function, is a prerequisite to understand the molecular and cellular mechanisms underlying JNCL. In agreement with other studies, we demonstrated a predominant late endosomal/lysosomal localization of overexpressed CLN3. To test the hypothesis that ablation of CLN3 causes autophagic-lysosomal dysfunction, we already generated CLN3 deficient cells. In addition, we identified Pen2, a subunit of the γ-secretase, as CLN3 interacting protein. We observed that both proteins co-immunoprecipitate, co-localize and are co-transported in late endosomes and lysosomes. We produced isogenic Pen2 knockout cells to investigate, if both proteins share functions in the autophagic-lysosomal system and if CLN3 modulates γ-secretase activity. Our preliminary work demonstrates that ablation of CLN3 does not alter γ-secretase processing of overexpressed substrates and that in agreement with studies by others Pen2 is indispensable for the proteolytic function of γ-secretase. Additional experiments are required to address processing of endogenous γ-secretase substrates. In addition, our current results demonstrate that ablation of CLN3 or Pen2 reduce the activity of at least one lysosomal enzyme and cause in both knockout cell lines to a similar degree increased autophagosome formation. Here, we propose experiments to characterize the generated knockout cell lines in more detail. In additional rescue experiments, we will analyze disease-associated mutations to relate our findings to disease pathology. The proposed project will bring together studies on cellular dysfunction of CLN3, which mutations underlie the childhood neurodegenerative disease JNCL, and Pen2, a subunit of the γ-secretase, which malfunction has been related to the adult onset neurodegenerative disease, Alzheimer’s disease. Thus, this project will advance knowledge on cellular dysfunctions underlying neurodegenerative diseases.

• DFG Programme: Research Grants