Adeno-associated virus mediated gene therapy in a murine model of Morquio syndrome type A

Morquio A disease (MPS IVA) is an autosomal recessive disorder caused by the deficiency of N-acetyl-galactosamine-6-sulfate sulfatase (GALNS), leading to accumulation of keratan-sulfate and chondroitin-6-sulfate mainly in bone and cornea. As a first step towards the development of a gene therapy for MPS IVA, we used adenoassociated virus derived-vectors for the evaluation of two variables: (a) the effect of the promoter region on GALNS expression, and (b) the effect of the co-expression with the Sulfatase Modifying Factor 1 (SUMF1) gene on the enzyme activity. The results showed that in HEK293 cells the eukaryotic promoters human alpha-antitrypsine (AAT) and human elongation factor 1-alpha (EF1) allowed similar GALNS activity levels than those in cells transfected with a vector containing the cytomegalovirus (CMV) promoter. GALNS activity in the lysated from cells cotransfected with SUMF1 was increased up to fourfold and allowed the enzyme activity detection in the culture media. In-vivo the enzyme activity in plasma and tissues from MPS IVA adult mice infused with AAT-GALNS was around 40% of wild-type levels after 12 weeks post-infusion. These GALNS levels were increased around twofold in animals coinfused with GALNS and SUMF1. GALNS activity in bone from animals infused with AAT-GALNS was not observed while coinfusion with the SUMF1 vector allowed a significant increment in the enzyme activity. No difference in urine GAG levels was observed between MPS IVA untreated, MPS treated and wild-type animals, showing the need to use a different biomarker or quantification method. In summary these results are the first evidence of the enzymatic correction in a murine model of MPS IVA by gene therapy and show the advantage of the co-expression with SUMF1 in order to obtain therapeutic levels of enzyme activity.