Genetic inactivation of mitochondria-targeted redox enzyme p66ShcA preserves neuronal viability and mitochondrial integrity in response to oxidative challenges

Kimmy Su,Dennis Bourdette,Michael Forte

doi:10.3389/fphys.2012.00285

Kimmy Su, Dennis Bourdette + Show 1 more

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https://doi.org/10.3389/fphys.2012.00285

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Abstract

Mitochondria are essential to neuronal viability and function due to their roles in ATP production, intracellular calcium regulation, and activation of apoptotic pathways. Accordingly, mitochondrial dysfunction has been indicated in a wide variety of neurodegenerative diseases, including Alzheimer's disease (AD), Huntington's disease, amyotrophic lateral sclerosis, stroke, and multiple sclerosis (MS). Recent evidence points to the permeability transition pore (PTP) as a key player in mitochondrial dysfunction in these diseases, in which pathologic opening leads to mitochondrial swelling, rupture, release of cytochrome c, and neuronal death. Reactive oxygen species (ROS), which are inducers of PTP opening, have been prominently implicated in the progression of many of these neurodegenerative diseases. In this context, inactivation of a mitochondria-targeted redox enzyme p66ShcA (p66) has been recently shown to prevent the neuronal cell death leading to axonal severing in the murine model of MS, experimental autoimmune encephalomyelitis (EAE). To further characterize the response of neurons lacking p66, we assessed their reaction to treatment with stressors implicated in neurodegenerative pathways. Specifically, p66-knockout (p66-KO) and wild-type (WT) neurons were treated with hydrogen peroxide (H2O2) and nitric oxide (NO), and assessed for cell viability and changes in mitochondrial properties, including morphology and ROS production. The results showed that p66-KO neurons had greater survival following treatment with each stressor and generated less ROS when compared to WT neurons. Correspondingly, mitochondria in p66-KO neurons showed diminished morphological changes in response to these challenges. Overall, these findings highlight the importance of developing mitochondria-targeted therapeutics for neurodegenerative disorders, and emphasize p66, mitochondrial ROS, and the PTP as key targets for maintaining mitochondrial and neuronal integrity.

Highlights

The importance of mitochondrial function in the integrity and stability of neurons and neuronal networks is well established (Hajnóczky and Hoek, 2007; Rizzuto et al, 2008; Szabadkai and Duchen, 2008; Duchen and Szabadkai, 2010)
In addition to assessing viability, we have examined the morphology of mitochondria in response to these stresses, as previous studies have shown that morphology changes correlate with eventual neuronal damage under various noxious conditions associated with neurodegenerative diseases (Solenski et al, 2002; Nikic et al, 2011)
Greater cell viability was demonstrated in p66-KO cultures compared to WT cultures at various treatment concentrations of H2O2 and DETA-nitric oxide (NO), each of which p66ShcA-KO neurons are resistant to oxidative challenges has been demonstrated to drive related apoptotic processes in neurons (e.g., Tamatani et al, 1998; Mailly et al, 1999; Brune, 2005)

Summary

INTRODUCTION

The importance of mitochondrial function in the integrity and stability of neurons and neuronal networks is well established (Hajnóczky and Hoek, 2007; Rizzuto et al, 2008; Szabadkai and Duchen, 2008; Duchen and Szabadkai, 2010). Under conditions of increased cellular stress, p66 has been proposed to function in a positive feed-forward loop, whereby ROS stresses lead to increased levels of p66-generated ROS, which induce cell death through persistent PTP opening In such a model, the PTP has been proposed to constitute the immediate downstream target of mitochondrial p66 action in the activation of cell death pathways, a hypothesis that is in keeping with the recent demonstration that O−2 sparks may be one of the key triggers for PTP opening in situ (Wang et al, 2008). We demonstrate that neurons lacking p66 exhibit protection in response to oxidative challenges as well as preservation of mitochondrial morphology and reduction of mitochondrial ROS production These results strengthen the theory that mitochondria-targeted redox enzyme p66 functions as a direct upstream activator of PTP-mediated neuronal death in neurodegenerative diseases

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