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A. R. Harvey, M. Hellstrom; Impact of rAAV2 Mediated Expression of CNTF or Suppressor of Cytokine Signaling 3 (SOCS3) on Adult Retinal Ganglion Cell Regeneration. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5190.
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© ARVO (1962-2015); The Authors (2016-present)
Intravitreal injections of ciliary neurotrophic factor (CNTF) promote the regrowth of adult axotomized rat retinal ganglion cell (RGC) axons. Here we use recombinant (r) adeno-associated virus 2 (AAV2) vectors to further analyse the cellular mechanisms that regulate this cytokine induced regenerative response.
Bicistronic rAAV2 vectors encoding green fluorescent protein (GFP) and either a modified, secretable form of CNTF or suppressor of cytokine signaling 3 (SOCS3) were injected into the left vitreal chamber of adult rats 14 days prior to left optic nerve (ON) cut. A peripheral nerve (PN) segment was then autografted onto the ON. Some rats also received additional injections of rCNTF or the cyclic AMP analogue CPT-cAMP. Fluorogold was injected into PN grafts after 4 weeks and the number of viable and regenerating RGCs was determined. Quantitative PCR of retinal tissues was also carried out.
AAV2-CNTF-GFP increased RGC survival and axon regeneration, but co-administration of CPT-cAMP did not further enhance regrowth. Unlike rCNTF injections (Park, MCN 2009, 41:313), vector-mediated delivery of CNTF did not result in sustained up-regulation of SOCS mRNAs. AAV2 mediated over-expression of SOCS3 decreased RGC axon regrowth into PN grafts by 65-70%, even in the presence of injected rCNTF. Reduced RGC survival was also seen in the latter condition.
CPT-cAMP enhances the regenerative effects of rCNTF (Cui, MCN 2003, 22:49), in part by reducing retinal SOCS up-regulation (Park, MCN 2009, 41:313). Lack of such upregulation after CNTF gene therapy may partly explain the lack of a clear additive effect of CPT-cAMP on AAV-CNTF induced RGC regrowth. The importance of SOCS3 in regulating cytokine-induced effects is confirmed by our observation that SOCS3 over expression significantly inhibited regeneration of axotomized RGCs. These data reveal differences in the effects of growth factors that are dependent on the mode of delivery, and suggest novel ways to maximize growth support to compromised RGCs.
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