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Richard H. Foxton, Arthur Finkelstein, David T. Shima, Yin-Shan Ng; Direct VEGF-A Mediated Neuroprotection: Mechanistic Studies in RGCs. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5438.
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VEGF-A plays a significant role in CNS neuron development, migration and neuroprotection. We previously determined a neuroprotective role for VEGF-A in the rodent retina, and found VEGFR2 was primarily involved in the response. Using retinal ganglion cell (RGC) cultures we sought to determine if VEGF-A is directly protective, and elucidate the receptors and downstream signalling pathways involved.
Primary RGCs from P1-2 rats were pre-treated with VEGFR1, 2 and neuropilin-1 agonists. 24 hours later H2O2 and staurosporine were added to induce death. Calcein staining quantified viable cells remaining in culture, whilst TUNEL verified whether death was apoptotic. We used caspase and PI3K inhibitors to investigate downstream signalling pathways mediating cell death and VEGF-A protection. Expression of VEGF receptors was explored using immunocytochemistry and real-time PCR.
PCR and immunocytochemistry staining indicated the presence of VEGFR2, which was approximately 17-fold higher than VEGFR1 in RGCs. Both VEGF164, 120 and VEGF-E protected RGCs from H2O2 and staurosporine-induced death, increasing the number of live cells up to 90% following H2O2, and offering full protection vs. staurosporine. In contrast, PlGF-1 and PlGF-2 did not protect cells, suggesting VEGF-A neuroprotection was mediated via VEGFR2, and did not require neuropilin-1 binding. TUNEL staining revealed cell death was apoptotic, and was reduced upon VEGF120 pre-treatment. Pan-caspase inhibitors also protected RGCs, illustrating that apoptosis was partially caspase-dependent. PI3K inhibitors LY292004 and wortmannin dose-dependently abolished VEGF120 protection following H2O2 and staurosporine, indicating protection was mediated via PI3K signalling.
These data illustrate that VEGF-A is directly protective to RGCs, via a VEGFR2 mechanism. Protection is against apoptotic, caspase-dependent death, via PI3K signalling pathways. These findings emphasize that further studies are needed to determine if neurons will be adversely affected following long-term treatment of ocular neovascular disease with VEGF-A antagonists.
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