Chaperone-mediated gene therapy with recombinant AAV-PPCA in a new mouse model of type I sialidosis

• Lysosomal sialidase NEU1 is deficient in the lysosomal storage disease sialidosis.
• NEU1 interacts with its chaperone PPCA for lysosomal localization and activation.
• Mice with type I sialidosis develop the phenotype of adult non-neuropathic patients.
• Injection of aged mutant mice with AAV-PPCA ameliorates their disease conditions.
• This in vivo gene therapy bears potential for the treatment of type I sialidosis.

The lysosomal storage disease sialidosis is caused by a primary deficiency of the sialidase N-acetyl-α-neuraminidase-1 (NEU1). Patients with type I sialidosis develop an attenuated, non-neuropathic form of the disease also named cherry red spot myoclonus syndrome, with symptoms arising during juvenile/ adult age. NEU1 requires binding to its chaperone, protective protein/cathepsin A (PPCA), for lysosomal compartmentalization, stability and catalytic activation. We have generated a new mouse model of type I sialidosis that ubiquitously expresses a NEU1 variant carrying a V54M amino acid substitution identified in an adult patient with type I sialidosis. Mutant mice developed signs of lysosomal disease after 1 year of age, predominantly in the kidney, albeit low residual NEU1 activity was detected in most organs and cell types. We demonstrate that the activity of the mutant enzyme could be effectively increased in all systemic tissues by chaperone-mediated gene therapy with a liver-tropic recombinant AAV2/8 vector expressing PPCA. This resulted in clear amelioration of the disease phenotype. These results suggest that at least some of the NEU1 mutations associated with type I sialidosis may respond to PPCA-chaperone-mediated gene therapy.