Year: 2007
Type: article
Abstract: Oxidative stress induced by glutathione depletion in the mouse HT22 neuronal cell line and embryonic rat immature cortical neurons causes a delayed, sustained activation of extracellular signal-regulated kinases-1/2 (ERK1/2), which results in cell death. Previous studies from our lab have shown that this sustained activation of ERK1/2 is mediated primarily by a selective, reversible inhibition of ERK1/2-directed phosphatases. However, the mechanisms underlying the inhibition remain unclear.Results from this thesis demonstrate that the inhibition of ERK1/2 phosphatases in HT22 cells and immature neurons is a consequence of oxidative stress induced by glutathione depletion as phosphatase activity is restored in cells treated with the antioxidant BHA. This agent leads to reduced ERK1/2 activation and neuroprotection. However, we also show that an increase in free intracellular Zn2+ that accompanies glutathione depletion-induced oxidative stress in HT22 cells and immature neurons contributes to selective inhibition of ERK1/2 phosphatase activity and consequently ERK1/2 activation and cell death. ERK1/2 also functions to maintain elevated levels of Zn2+. Thus the elevation of intracellular Zn2+ within neurons subjected to oxidative stress can trigger a robust positive feedback loop operating through activated ERK1/2 that rapidly sets into motion a Zn2+ -dependent pathway of cell death. Previous data from our lab have suggested that PP2A, a Serine/Threonine protein phosphatase, is the predominant ERK1/2 phosphatase in primary neurons. I have confirmed this result by using specific peptide inhibitor of PP2A. Furthermore, I have revealed for the first time the reversible cysteine oxidation in the catalytic subunit of PP2A, suggesting that PP2A may be the phosphatase that is susceptible to oxidation and inactivation following glutamate treatment in HT22 cells and primary neurons.ERK1/2 activation contributes to neuronal death following focal ischemia/reperfusion. In the third part of my thesis, I investigated the mechanisms responsible for ERK1/2 activation following ischemia/reperfusion. I have demonstrated that the selective inhibition of ERK1/2 phosphatases contributes to ERK1/2 activation following ischemia/reperfusion in both focal and global ischemia models. Altogether, these results implicate the inhibition of ERK1/2 phosphatases as an important mechanism for ERK1/2 activation in oxidatively stressed neurons.
Author: Yeung Ho
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W58084357