Deficiency of the lysosomal protein CLN5 alters lysosomal function and movement

Batten disease is a devastating childhood rare neurodegenerative disease characterized by rapid deterioration of cognition and movement, leading to death within ten to thirty years of age. One of the thirteen Batten disease forms, CLN5 Batten disease, is caused by mutations in the CLN5 gene leading to motor deficits, mental deterioration, cognitive impairment, visual impairment, and epileptic seizures in children. A characteristic pathology in CLN5 Batten disease is the defects in lysosomes, leading to neuronal dysfunction. In this study, we aimed to investigate the lysosomal changes in CLN5-deficient human neurons. We used an induced pluripotent stem cell system, which generates pure human cortical-like glutamatergic neurons. Using CRISPRi, we inhibited the expression of CLN5 in human neurons. The CLN5-deficient human neurons showed neutralised lysosomal acidity and reduced lysosomal enzyme activity measured by microscopy and flow cytometry. Furthermore, the CLN5-deficient human neurons also showed impaired lysosomal movement - a phenotype that has never been reported in CLN5 Batten disease. Lysosomal trafficking is key to maintain local degradation of cellular wastes, especially in long neuronal projections and our results from the human neuronal model present a key finding to understand the underlying lysosomal pathology in neurodegenerative diseases.