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Jennifer L. Bromberg-White, Elissa Boguslawski, Nicholas S. Duesbery; The Importance Of MAPK Signaling In The Development Of Retinal Neovascularization. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4862.
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We have previously shown that MAPK signaling plays a key role in retinal angiogenesis, and that inhibition of the MAPK pathways by anthrax lethal toxin (LeTx) can profoundly alter vascular morphogenesis (Bromberg-White et. al.  PLoS One, e6956). Furthermore, we have shown that MAPK signaling inhibition results in a persistent lack of development and progression of oxygen-induced retinopathy. The goal of this study is to determine the mechanism of MAPK signaling in the development and progression of retinal neovascularization.
Using a model of oxygen-induced retinopathy, LeTx, was injected intravitreally during hypoxia, and subsequent effects on vitreal cytokine expression, and macrophage recruitment and infiltration were analyzed. In addition, to better understand the resulting persistent inhibition of neovascularization by LeTx, the effect of MAPK pathway inactivation on retinal vasculature during early development was determined.
LeTx administration had no effect on macrophage recruitment signals from the hypoxic retina following oxygen-induced retinopathy. Moreover, the recruitment and presence of macrophages within the hypoxic retina were unchanged following LeTx treatment. MAPK pathway inhibition did not result in the alteration of the environment within the hypoxic retina from a pro-angiogenic to an anti-angiogenic one, and VEGF levels remained at an elevated level even with the persistent lack of neovascular growth and continued hypoxic environment. Additionally, immature retinal vasculature during normal development was persistently destroyed following MAPK inhibition, while mature vessels from adult animals were unaffected.
These results indicate that the persistent inhibition of neovascularization by LeTx is not due to a loss in macrophage recruitment, nor due to the development of an anti-angiogenic environment within the hypoxic retina. The maintained levels of VEGF without the concomitant induction of neovascular growth or revascularization of the vaso-obliterated zone suggests either an inability of vessels present to respond to the pro-angiogenic stimuli, or the blockage of cells required for the process (such as endothelial progenitor cells) to be recruited to the hypoxic retina. The persistent destruction of immature vessels during normal vascular development in the retina suggests an extreme sensitivity of immature vessels to MAPK signaling inhibition, implying a critical role of these pathways for angiogenic growth during normal development and oxygen-induced retinopathy.
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