Aggregation of mutant cysteine string protein-α via Fe-S cluster binding is mitigated by iron chelators.

Mutations in cysteine string protein-alpha (CSP alpha) cause its aggregation and adult-onset neuronal ceroid lipofuscinosis. Abnormal binding of Fe-S clusters to CSP alpha mutants is now implicated in driving aggregation, which can be reversed in neurons by clinically approved iron chelators. Point mutations in cysteine string protein-alpha (CSP alpha) cause dominantly inherited adult-onset neuronal ceroid lipofuscinosis (ANCL), a rapidly progressing and lethal neurodegenerative disease with no treatment. ANCL mutations are proposed to trigger CSP alpha aggregation/oligomerization, but the mechanism of oligomer formation remains unclear. Here we use purified proteins, mouse primary neurons and patient-derived induced neurons to show that the normally palmitoylated cysteine string region of CSP alpha loses palmitoylation in ANCL mutants. This allows oligomerization of mutant CSP alpha via ectopic binding of iron-sulfur (Fe-S) clusters. The resulting oligomerization of mutant CSP alpha causes its mislocalization and consequent loss of its synaptic SNARE-chaperoning function. We then find that pharmacological iron chelation mitigates the oligomerization of mutant CSP alpha, accompanied by partial rescue of the downstream SNARE defects and the pathological hallmark of lipofuscin accumulation. Thus, the iron chelators deferiprone (L1) and deferoxamine (Dfx), which are already used to treat iron overload in humans, offer a new approach for treating ANCL.