6-Hydroxydopamine induces mitochondrial ERK activation

Abstract

Reactive oxygen species (ROS) are implicated in 6-hydroxydopamine (6-OHDA) injury to catecholaminergic neurons; however, the mechanism(s) are unclear. In addition to ROS generated during autoxidation, 6-OHDA may initiate secondary cellular sources of ROS that contribute to toxicity. Using a neuronal cell line, we found that catalytic metalloporphyrin antioxidants conferred protection if added 1 hour after exposure to 6-OHDA, whereas the hydrogen peroxide scavenger catalase failed to protect if added more than 15 min after 6-OHDA. There was a temporal correspondence between loss of protection and loss of the ability of the antioxidant to inhibit 6-OHDA-induced ERK phosphorylation. Time course studies of aconitase inactivation, as an indicator of intracellular superoxide, and MitoSOX red, a mitochondria targeted ROS indicator, demonstrate early intracellular ROS followed by a delayed phase of mitochondrial ROS production, associated with phosphorylation of a mitochondrial pool of ERK. Furthermore, upon initiation of mitochondrial ROS and ERK activation, 6-OHDA-injured cells became refractory to rescue by metalloporphyrin antioxidants. Together with previous studies showing that inhibition of the ERK pathway confers protection from 6-OHDA toxicity, and that phosphorylated ERK accumulates in mitochondria of degenerating human Parkinson's disease neurons, these studies implicate mitochondrial ERK activation in Parkinsonian oxidative neuronal injury.

Mitochondrially localized ERK2 regulates mitophagy and autophagic cell stress

“…24 Early transient ERK1/2 activation accompanied by nuclear translocation is associated with enhanced neuronal survival, 21,22,54,55 while cytoplasmic ERK1/2 without evidence of nuclear localization is typical of degenerating neurons of Alzheimer's disease, 50 and in PD and related models. 25,35 While it is not possible to tell from human autopsy studies whether ERK1/2 regulates mitochondrial turnover or is passively localized to mitochondria and AVs, the current study indicates that activity level-dependent localization of ERK2 to mitochondria is sufficient to induce mitophagy. Moreover, dominant interfering ERK2-KD expression and the MEK inhibitor U0126 prevented both generation and colocalization of ERK2 granules with mitochondria, suppressing 6-OHDA induced mitophagy ( Fig.…”

“…The mechanism by which activated ERK2 is enriched in mitochondria is still unknown. While the involvement of mitochondrial reactive oxygen species in redox activation of ERK1/2 suggests a role for in situ phosphorylation, 35,56 the GFP-ERK2 data supports a mechanism involving mitochondrial translocation. Given that phospho-activated ERK represents only a few percent of total cellular ERK, 57 trafficking of this component to a subset of mitochondria may not be detected by standard biochemical fractionation methods.…”

“…32,33 Treatment of dopaminergic cells with 6-OHDA elicits robust activation of ERK1/2, and pharmacological inhibition of ERK activation enhances neuronal survival. 34,35 Interestingly, 6-OHDA elicits a delayed phase of mitochondrial ROS production 35 that is associated with increased mitochondrial ERK activation. 26,35 The potential function(s) of mitochondrially localized ERK activation during neuronal injury are still undefined.…”

Cytochrome c-mediated oxidation of hydroethidine and mito-hydroethidine in mitochondria: Identification of homo- and heterodimers

“…Moreover, recent research suggests that mitochondrial cytochromes could also oxidize HE to a dimeric product [8]. The probe (MitoSOX ™ Red) is being used in the detection and quantitation of mitochondria-generated superoxide [9][10][11]. As mitochondria are enriched with cyt c 3+ (0.1 to 5 mM) [12,13] within the intermembrane compartment, we decided to investigate this reaction in detail.…”

Neuroprotective Effects of Carpinus tschonoskii MAX on 6-Hydroxydopamine-Induced Death of PC12 Cells

“…We also found that 6-OHDA increased the phosphorylation of MAP kinases such as ERK1/2 ( Fig. 6; Kulich et al, 2007), whereas the phosphoylation of Akt was decreased in a dose-dependent manner compared to the control ( Fig. 7; Jiang and Yu, 2005).…”