Cathepsin B inhibition blocks amyloidogenesis in the mouse models of neurological lysosomal diseases MPS IIIC and sialidosis.

Neuronal accumulation of amyloid aggregates is a hallmark of brain pathology in neurological lysosomal storage diseases (LSDs), including mucopolysaccharidoses (MPS); however, the molecular mechanism underlying this pathology has not been understood. We demonstrate that elevated lysosomal cathepsin B (CTSB) levels and CTSB leakage to the cytoplasm triggers amyloidogenesis in two neurological LSDs. CTSB levels were elevated 3- to 5-fold in the cortices of mouse models of MPS IIIC (Hgsnat-Geo and Hgsnat (P304L) ) and sialidosis (Neu1 (ΔEx3) ), as well as in cortical samples of MPS I, IIIA, IIIC, and IIID patients. CTSB was found in the cytoplasm of pyramidal layer IV-V cortical neurons containing thioflavin-S(+), β-amyloid(+) aggregates consistent with a pro-senile phenotype. In contrast, CTSB-deficient MPS IIIC (Hgsnat (P304L) /Ctsb (-/-) ) mice as well as Hgsnat (P304L) and Neu1 (ΔEx3) mice chronically treated with irreversible brain-penetrable CTSB inhibitor E64 showed a drastic reduction in neuronal thioflavin-S(+)/APP(+) deposits. Neurons of Hgsnat (P304L) /Ctsb (-/-) mice and E64-treated Hgsnat (P304L) mice also showed reduced levels of P62(+), LC3(+) puncta, G(M2) ganglioside, and misfolded subunit C of mitochondrial ATP synthase, consistent with restored autophagy. E64 treatment also rescued hyperactivity and reduced anxiety in Hgsnat (P304L) mice, implying that CTSB may become a novel pharmacological target for MPS III and similar LSDs.