Disease correction by combined neonatal intracranial AAV and systemic lentiviral gene therapy in Sanfilippo Syndrome type B mice

Mucopolysaccharidosis type IIIB (MPS IIIB) or Sanfilippo Syndrome type B is a lysosomal storage disease resulting from the deficiency of N-acetyl glucosaminidase (NAGLU) activity. We previously showed that intracranial adeno-associated virus (AAV) -based gene therapy results in partial improvements of several aspects of the disease. In an attempt to further correct the disease, MPS IIIB mice were treated at 2–4 days of age with intracranial AAV2/5-NAGLU (IC-AAV), intravenous lentiviral-NAGLU (IV-LENTI) or the combination of both (BOTH). The BOTH group had the most complete biochemical and histological improvements of any treatment group. Compared to untreated MPS IIIB animals, all treatments resulted in significant improvements in motor function (rotarod) and hearing (auditory-evoked brainstem response). In addition, each treatment group had a significantly increased median life span compared to the untreated group (322 days). The combination arm had the greatest increase (612 days), followed by IC-AAV (463 days) and IV-LENTI (358 days). Finally, the BOTH group had nearly normal circadian rhythm measures with improvement in time to activity onset. In summary, targeting both the systemic and central nervous system disease of MPS IIIB early in life appears to be the most efficacious approach for this inherited metabolic disorder.

Site-directed mutation of conserved cysteine residues does not inactivate the Streptococcus pyogenes hyaluronan synthase

Hyaluronan synthase (HAS), the enzyme responsible for the production of hyaluronic acid (HA), is a well-conserved membrane-bound protein in both prokaryotes and eukaryotes. This enzyme performs at least six discrete functions in producing a heterodisaccharide polymer of several million molecular weight and extruding it from the cell. Among the conserved motifs and domains within the Class I HAS family are four cysteine residues. Cysteines in many proteins are important in establishing and maintaining tertiary structure or in the coordination of catalytic functions. In the present study we utilized a combination of site-directed mutagenesis, chemical labeling, and kinetic analyses to determine the importance of specific Cys residues for catalysis and structure of the HA synthase from Streptococcus pyogenes (spHAS). The enzyme activity of spHAS was partially inhibited by cysteine-reactive chemical reagents such as N-ethylmaleimide. Quantitation of the number of Cys residues modified by these reagents, using MALDI-TOF mass spectrometry, demonstrated that there are no stable disulfide bonds in spHAS. The six Cys residues of spHAS were then mutated, individually and in various combinations, to serine or alanine. The single Cys-mutants were all kinetically similar to the wild-type enzyme in terms of their V(max) and K(m) values for HA synthesis. The Cys-null mutant, in which all Cys residues were mutated to alanine, retained approximately 66% of wild-type activity, demonstrating that despite their high degree of conservation within the HAS family, Cys residues are not absolutely necessary for HA biosynthesis by the spHAS enzyme.