A <i>Drosophila</i> model of mucopolysaccharidosis IIIB

Mucopolysaccharidosis type IIIB is a rare lysosomal storage disorder caused by defects in alpha-N-acetylglucosaminidase (NAGLU) and characterized by severe effects in the central nervous system. Mutations in NAGLU cause accumulation of partially degraded heparan sulfate in lysosomes. The consequences of these mutations on whole-genome gene expression and their causal relationships to neural degeneration remain unknown. Here, we used the functional Drosophila melanogaster ortholog of NAGLU, Naglu, to develop a fly model for MPS IIIB induced by gene deletion (NagluKO), missense (NagluY160C), and nonsense (NagluW422X) mutations. We used the Drosophila activity monitoring system to analyze activity and sleep and found sex- and age-dependent hyperactivity and sleep defects in mutant flies. Fluorescence microscopy on mutant fly brains using Lysotracker dye revealed a significant increase in acidic compartments. Differentially expressed genes determined from RNA sequencing of fly brains are involved in biological processes that affect nervous system development. A genetic interaction network constructed using known interacting partners of these genes consists of 2 major subnetworks, one of which is enriched in genes associated with synaptic function and the other with neurodevelopmental processes. Our data indicate that lysosomal dysfunction arising from disruption of heparan sulfate breakdown has widespread effects on the steady state of intracellular vesicle transport, including vesicles associated with synaptic transmission. Evolutionary conservation of fundamental biological processes predicts that the Drosophila model of mucopolysaccharidosis type IIIB can serve as an in vivo system for the future development of therapies for mucopolysaccharidosis type IIIB and related disorders.