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M. Sapieha, I. DeGongre, W.W. Hauswirth, A. Di Polo; Extracellular Signal–Regulated Kinases 1/2 Mediate Retinal Ganglion Cell Axon Regeneration Induced by Fibroblast–Growth Factor–2 . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1286.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We previously demonstrated that gene transfer of Fibroblast Growth Factor–2 (FGF–2) to adult retinal ganglion cells (RGCs) stimulated axonal regeneration following acute optic nerve injury. Here we elucidated the molecular signaling pathways that regulate FGF–2–induced RGC axon growth in vivo. Methods: Recombinant adeno–associated virus (AAV) serotype 2 containing a FGF–2 transgene (AAV.FGF–2) was injected into the vitreous chamber of adult rats. Following FGF–2 gene transfer, the activation of candidate intracellular signaling cascades, including Erk1/2, Akt kinase, and phospholipase Cγ (PLCγ), were analyzed by western blot analysis using phospho–specific antibodies. To investigate nerve regeneration, RGC axons were labeled with the anterograde tracer cholera–toxin ß–subunit (CTß) and growing axons were quantified in optic nerve sections at two weeks after micro–crush lesion. The role of Erk1/2 on axon regeneration was investigated by injection of PD98059, a selective pharmacological inhibitor of Erk1/2 activation, at the time of optic nerve injury. Results: AAV.FGF–2 mediated strong and sustained upregulation of FGF–2 in adult RGCs that resulted in robust axonal regeneration following optic nerve injury. FGF–2 gene transfer induced a marked increase in phosphorylated, active Erk1/2. In contrast, the basal levels of phosphorylated Akt or PLCγ remained unchanged after AAV.FGF–2 treatment. Intraocular injection of the Erk1/2 inhibitor PD98059 at the time of optic nerve injury resulted in a striking reduction in RGC axon regeneration promoted by AAV.FGF–2. For example, quantitative analysis demonstrated a 78% decrease in the number of axons extending at 500 µm and 1000 µm from the site of lesion following combined treatment with AAV.FGF–2 and PD98059 compared to control eyes. Conclusions: This study identifies the Erk1/2 pathway as a key signaling component in the regulation of RGC axon regeneration mediated by FGF–2.
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