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Philippe M D'Onofrio, Brian Choi, Paulo D Koeberle; The Mechanisms of ERK1/2 Involvement in Neuron Death after Ischemic Injury and Axotomy. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2507.
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ERK1/2 is an intracellular messenger that is involved in cell proliferation, growth, and survival. However, it has also been implicated in mechanisms of regulated necrosis following injury from ischemia or traumatic damage. Previous work conducted in our lab found that the function of ERK1/2 (pro-survival or pro-death) varies with time after injury, and in this work we continue to elucidate the mechanisms that it affects at varying times after injury, as well as their impact on neuron death. This work is important becuase it contributes to revealing the dynamic changes of cell death mechanisms and their regulation.
Experiments were conducted both in vitro, in HEK 293 cells, and in vivo, in adult Sprague-Dawley rats. Ischemic damage was done in vitro via oxygen-glucose deprivation (OGD), and in vivo via opthalmic artery ligation. Optic nerve transection was also used to induce neuron-specific damage in the retina. Results were quantified via cell-density assay in vitro and via immunohistochemistry with RBPMS antibody in vivo. Intraocular injections of Adeno-associated virus or peptides were used to target treatments to RGCs. Elements of intracellular mechanisms were assayed via western blot and PCR.
Inhibition of ERK1/2 in the first days immediately following injury improved cell survival, an effect which was lost at later times. Inhibition of ERK1/2 reduced the activation of RIP1, RIP3, and MLKL, all of which are involved in the mechanisms of necroptosis. As well, sequestration of ERK1/2 to the cytoplasm, as opposed to allowing it to migrate into the nucleus, reduced the re-entry of injured neurons into cell cycle, and improved neuron survival. Inhibition of ERK1/2 also reduced the expression of MMP-2 and MMP-9 in the extracellular environment, thereby preserving extracellular matrix integrity and cellular contact, maintaining pro-survival signaling through focal adhesion kinasee.
ERK1/2 is involved in 3 mechanisms within neurons: necroptosis activation via RIP1, RIP3, and MLKL; re-initiation of cell-cycle; expression of MMPs. Inhibition of ERK1/2 at times immediately following injury were most effective at preventing RGC death. These results demonstrate there is a critical window immediately following neuron injury, which ends prior to the initiation of apoptosis, in which many mechanisms can be targeted and effectively blocked to improve neuron survival.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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