Lysosomal dysfunction disrupts presynaptic maintenance and restoration of presynaptic function prevents neurodegeneration in lysosomal storage diseases

Abstract

Lysosomal storage disorders ( LSD s) are inherited diseases characterized by lysosomal dysfunction and often showing a neurodegenerative course. There is no cure to treat the central nervous system in LSD s. Moreover, the mechanisms driving neuronal degeneration in these pathological conditions remain largely unknown. By studying mouse models of LSD s, we found that neurodegeneration develops progressively with profound alterations in presynaptic structure and function. In these models, impaired lysosomal activity causes massive perikaryal accumulation of insoluble α‐synuclein and increased proteasomal degradation of cysteine string protein α ( CSP α). As a result, the availability of both α‐synuclein and CSP α at nerve terminals strongly decreases, thus inhibiting soluble NSF attachment receptor ( SNARE ) complex assembly and synaptic vesicle recycling. Aberrant presynaptic SNARE phenotype is recapitulated in mice with genetic ablation of one allele of both CSP α and α‐synuclein. The overexpression of CSP α in the brain of a mouse model of mucopolysaccharidosis type IIIA , a severe form of LSD , efficiently re‐established SNARE complex assembly, thereby ameliorating presynaptic function, attenuating neurodegenerative signs, and prolonging survival. Our data show that neurodegenerative processes associated with lysosomal dysfunction may be presynaptically initiated by a concomitant reduction in α‐synuclein and CSP α levels at nerve terminals. They also demonstrate that neurodegeneration in LSD s can be slowed down by re‐establishing presynaptic functions, thus identifying synapse maintenance as a novel potentially druggable target for brain treatment in LSD s. image Neurodegeneration associated with lysosomal dysfunction in lysosomal storage disorders ( LSD s) may be linked to impaired presynaptic maintenance initiated by a reduction in α‐synuclein and CSP α levels at nerve terminals. α‐Synuclein and cysteine string protein (CSP)α are two key chaperones, which ensure efficient SNARE complex formation and synaptic vesicle recycling by maintaining physiological SNARE levels at nerve terminals. Lysosomal dysfunction causes both the accumulation of undegraded α‐synuclein in insoluble aggregates perikarya and the enhanced proteasomal degradation of CSPα. The unbalanced proteostasis results in the simultaneous depletion of α‐synuclein and CSPα at nerve terminals. This in turn caused a reduction in presynaptic SNARE levels, thus leading to synaptic dysfunction. Viral‐mediated CSPα overexpression in a mouse model of mucopolysaccharidosis type IIIA mice (a severe neurodegenerative LSD) exerted a protective action against neurodegeneration by re‐establishing efficient SNARE complex formation and improving presynaptic function.