Lentiviral Vectors in Huntington’s Disease Research and Therapy - Viral Vector Approaches in Neurobiology and Brain Diseases - page 186

Viral RNA genome

LTR Promoter Transgene WPRE LTR

Lipid
membrane

VSV-G

Capsid p24

Specific promoter

Protease

LTR Specific promoter Transgene WPRE LTR

Matrix

Integrase

Reverse
transcriptase

LTR Promoter Transgene WPRE miRT LTR

Fig. 1 Schematic representation of a lentiviral vector and strategies for modifying tropism. In most cases, LVs
are pseudotyped with a VSV-G envelope, which confers a neuronal tropism. The viral particle contains the
enzymes essential for replication and a copy of the single-strand RNA genome. Three strategies have been
proposed for modifying the tropism of LVs: changing the envelope glycoprotein, using a tissue-specifi c pro-
moter, or adding an miRNA-target sequence to restrict transgene expression. LTR: Long-terminal repeat

Various strategies have been developed for modifying the neuronal
tropism of LVs and investigating the role of other cell populations
in HD. They make use of the various steps in the process of viral
gene delivery (1) to modify the envelopes for pseudotyping, (2) to
introduce tissue-specifi c promoters, and (3) to integrate miRNA
targeting sequences blocking transgene expression into cells
expressing the corresponding sequence (Fig. 1 ).

1.3 Altering the
Tropism of Lentiviral
Vectors

LVs overexpressing or silencing specifi c genes have been exten-
sively used for functional studies in the CNS. In the context of
HD, gene transfer with lentiviral vectors has been successfully used
(1) to develop relevant models of HD by producing mutant Htt,
(2) to investigate the molecular mechanisms underlying neuronal
death, and (3) to administer candidate treatments to the CNS.

1.4 Lentiviral
Vectors as a Tool
for Studying
Neurodegenerative
Diseases

Since 1993 and the cloning of the Htt gene, numerous in vitro and
in vivo genetic models have been produced and these models have
greatly contributed to the unraveling of pathogenic pathways in
HD. As a complementary approach, viral vectors have been used to
model CNS neurodegeneration through the overproduction of
disease-causing proteins. This original way of creating genotypic
models in animals overcomes some of the limitations of studies in
transgenic animals, including the mild neuropathology observed.
A growing number of publications have demonstrated the potential
value of this versatile, highly fl exible experimental paradigm [ 18 ].
The fi rst-generation model of HD was based on VSV-G-
pseudotyped LVs. de Almeida and coworkers developed a rat
model based on the production of a short mutant Htt fragment in

1.4.1 Lentiviral Vectors
for Modeling HD