Primary fibroblasts from CSPα mutation carriers recapitulate hallmarks of the adult onset neuronal ceroid lipofuscinosis

Mutations in the co-chaperone protein, CSP alpha, cause an autosomal dominant, adult-neuronal ceroid lipofuscinosis (AD-ANCL). The current understanding of CSPa function exclusively at the synapse fails to explain the autophagy-lysosome pathway (ALP) dysfunction in cells from AD-ANCL patients. Here, we demonstrate unexpectedly that primary dermal fibroblasts from pre-symptomatic mutation carriers recapitulate in vitro features found in the brains of AD-ANCL patients including auto-fluorescent storage material (AFSM) accumulation, CSP alpha aggregates, increased levels of lysosomal proteins and lysosome enzyme activities. AFSM accumulation correlates with CSP alpha aggregation and both are susceptible to pharmacological modulation of ALP function. In addition, we demonstrate that endogenous CSP alpha is present in the lysosome-enriched fractions and co-localizes with lysosome markers in soma, neurites and synaptic boutons. Overexpression of CSP alpha wild-type (WT) decreases lysotracker signal, secreted lysosomal enzymes and SNAP23-mediated lysosome exocytosis. CSP alpha WT, mutant and aggregated CSP alpha are degraded mainly by the ALP but this disease-causing mutation exhibits a faster rate of degradation. Co-expression of both WT and mutant CSP alpha cause a block in the fusion of autophagosomes/lysosomes. Our data suggest that aggregation-dependent perturbation of ALP function is a relevant pathogenic mechanism for AD-ANCL and supports the use of AFSM or CSP alpha aggregation as biomarkers for drug screening purposes