Biology Reference
In-Depth Information
Using a protocol involving sequential
in vitro
exposure to various factors,
MSCs thereby induced to express higher levels of BDNF and GDNF also
protected axotomized RGCs after transplantation into the vitreous
(
Levkovitch-Verbin et al., 2010
). However, effects of this type of cellular
graft on RGC axonal regeneration are, to our knowledge, not yet known.
10. VIRAL VECTOR DELIVERY OF NEUROTROPHIC
FACTORS
Viral vectors are modified, replication-deficient viruses in which
the viral genome is replaced by a therapeutic gene, providing an
in vivo
method for long-term, targeted supply of a trophic factor to injured neurons,
including RGCs (
Hellstr¨m&Harvey, 2011
). Initial studies used a modified
adenovirus (AdV) to deliver neurotrophic factors for protective RGC ther-
apy. AdV vectors have been trialed that encode CNTF (
van Adel, Arnold,
Phipps, Doering, & Ball, 2005; Weise et al., 2000
), BDNF (
Di Polo, Aigner,
Dunn, Bray, & Aguayo, 1998; Isenmann, Kl¨cker, Gravel, & B¨hr, 1998
), or
GDNF (
Schmeer et al., 2002; Straten et al., 2002
) under the control of the
cytomegalovirus promoter. These vectors do not appear to transduce RGCs
very efficiently, perhaps due to glial barriers, but M¨ ller glia are consistently
transduced. Transgene expression and secretion of associated proteins from
retinal cells increased RGC survival in the short-term in all cases, but an
effect on axonal regeneration into PN grafts was not seen (
Weise et al.,
2000
).RGCtransductionwithAdVcanbeachievedbyapplyingthevector
to the ON stump (
Kugler, Kl
¨
cker, Kermer, Isenmann, & B
¨
hr, 1999
).
In the past decade, numerous studies have shown that a vector based on
the adeno-associated virus serotype 2 (AAV2) is particularly effective in
transducing adult RGCs after intravitreal injection (e.g.,
Hellstr¨m et al.,
2009
). Neurotrophic factor genes that have been used with AAV vectors
include
BDNF
(
Hellstr¨m & Harvey, 2011; Leaver, Cui, Plant, et al.,
2006; Pease et al., 2009; Schuettauf et al., 2004
),
bFGF
(
Sapieha, Peltier,
Rendahl, Manning, & Di Polo, 2003; Schuettauf et al., 2004
),
GDNF
(
Wu et al., 2004
), and
CNTF
(
Leaver, Cui, Bernard & Harvey, 2006;
Leaver, Cui, et al., 2006; Pease et al., 2009
). In all cases, there was
increased RGC survival and with AAV-bFGF some limited regrowth of
RGC axons across an ON nerve crush was reported (
Sapieha et al.,
2003
). AAV-mediated transduction of TrkB also increased the survival of
injured RGCs, an effect enhanced by coadministration of rBDNF
(
Cheng, Sapieha, Kittlerova, Hauswirth, & Di Polo, 2002
). Using
