AAV Gene Therapy Strategies for Lysosomal Storage Disorders with Central Nervous System Involvement - Gene Delivery and Therapy for Neurological Disorders - page 268

Fig. 1 Lysosomal enzymes involved in the catabolism of GM1 ganglioside to GM3
ganglioside and the lysosomal storage disorders associated with loss of each
enzyme

In this chapter, we describe the protocols used for direct
stereotaxic injection of AAV vectors into the brain of mice, cats,
sheep, and monkeys. Our experience is derived from therapeutic
studies in murine, feline, and ovine models of GM1 and GM2 gan-
gliosidoses, as well as safety/biodistribution studies in normal
juvenile cynomolgus macaques. GM1 gangliosidosis is caused by a
defi ciency in lysosomal acid

-galactosidase (EC 3.2.1.23), which
breaks down GM1 ganglioside to GM2 ganglioside and catabo-
lizes other substrates such as keratan sulfate and other galactosyl-
oligosaccharides [ 51 ]. GM2 gangliosidosis results from a defect in
ʲ

ʲ

- N -acetylhexosaminidase (Hex, EC 3.2.1.52), the next enzyme
in the stepwise degradative pathway of gangliosides that exists as
three separate isozymes defi ned by subunit composition: HexA
( ). While GM2 ganglioside is

degraded by HexA exclusively in humans, HexB participates in the
catabolic pathway in other species, especially mice [ 52 ]. Figure 1
illustrates the lysosomal enzymes involved in the catabolism of
these gangliosides in humans and the resulting disorders associated
with their defi ciencies. GM2 gangliosidoses, which encompass
Tay-Sachs disease (TSD) and Sandhoff disease (SD), are caused by
mutations in the HEXA and HEXB genes, respectively. HEXA and
HEXB encode the

ʱʲ ), HexB ( ʲʲ ), and HexS ( ʱʱ

- N -acetylhexosaminidase,
respectively [ 53 ]. Feline GM2 gangliosidosis results from a

ʱ and ʲ subunits of ʲ

sub-
unit defi ciency ( HEXB mutation), making it a model of SD while
ovine GM2 gangliosidosis ensues from

ʲ

subunit defi ciency
( HEXA mutation), providing a model of TSD.
Adeno-associated virus is a replication-defi cient parvovirus.
The single-stranded 4.7 kb DNA genome is composed of the rep
and cap genes fl anked by inverted terminal repeats (ITR). The
AAV virion is a non-enveloped 20 nm capsid composed of three
viral proteins (VP) VP1, VP2, and VP3 at a 1:1:18 ratio
(60 capsomeres total). Wild-type AAV is prevalent in humans, but

ʱ