Biology Reference
In-Depth Information
connected to central targets, these numbers remain remarkably similar
15 months after surgery (
Hellstr¨m & Harvey, 2011
). In contrast, a single
ocular injection of AAV2-BDNF (4
m
l; 1
10
12
gc/ml) in adult rats also
increased the viability of axotomized RGCs (on average, about 16,400
RGCs, 4 weeks postinjury), but the proportion of these surviving RGCs that
regenerated an axon into a PNgraft was only about 8% (
Hellstr¨m&Harvey,
2011
). Note here that after injection of either the CNTF or the BDNFAAV2
vector, there was an increase not only in GFP-labeled RGC numbers but
also in total viable RGCs, consistent with the proposal that virally
transduced cells release trophic factors that can provide paracrine support
for neighboring nonmodified cells. This is an issue that will be revisited later
when discussing the effects of neurotrophins onRGC dendritic architecture.
11. COMBINED GENE THERAPY AND
PHARMACOTHERAPY
Previous studies using rCNTF showed that coinjection with the cyclic
AMP analogue CPT-cAMP significantly increased the proportion of surviv-
ing RGCs capable of regenerating an axon into an autologous PN graft (
Cui
et al., 2003
). This enhancement is mediated by a number of kinase systems
including PKA, PI3K/AKT, and MAPK/ERK (
Park et al., 2004
), and
also by moderation of a CNTF-induced increase in SOCS3 expression
(
Park et al., 2009
). Interestingly, CPT-cAMP does not augment RGC
regenerative responses in PN-grafted eyes injected with AAV2-CNTF,
in part perhaps due to the observation that upregulation of SOCS genes
is much less after CNTF gene therapy compared to bolus recombinant
cytokine injections (
Hellstr
¨
m, Muhling, et al., 2011
). Surprisingly, in eyes
injected with rCNTF, CPT-cAMP and AAV2-BDNF, while there was an
increase in RGC survival (on average, about 28,000 RGCs), this combina-
torial treatment had no effect on axonal regeneration, with only 7% of this
increased RGC population regenerating an axon into a PN graft (
Hellstr¨m
& Harvey, 2011
). Clearly, signaling systems activated by sustained, vector-
mediated BDNF expression dominated RGC responses, overriding the
normally effective stimulus to axonal elongation provided by intravitreal
injections of rCNTF and CPT-cAMP. BDNF is known to be an arboriza-
tion factor for RGCs and can affect synaptic input and dendritic growth
(
Cohen-Cory & Lom, 2004; Du & Poo, 2004; Rodger, Drummond,
Hellstrom, Robertson, & Harvey, 2012
). Apparent BDNF interference in
long-distance RGC axon growth has been reported by others using
