Dopamine and Methamphetamine Differentially Affect Electron Transport Chain Complexes and Parkin in Rat Striatum: New Insight into Methamphetamine Neurotoxicity

Methamphetamine (METH) is a highly abused psychostimulant that is neurotoxic to dopaminergic (DAergic) nerve terminals in the striatum and increases the risk of developing Parkinson's disease (PD). In vivo, METH-mediated DA release, followed by DA-mediated oxidative stress and mitochondrial dysfunction in pre- and postsynaptic neurons, mediates METH neurotoxicity. METH-triggered oxidative stress damages parkin, a neuroprotective protein involved in PD etiology via its involvement in the maintenance of mitochondria. It is not known whether METH itself contributes to mitochondrial dysfunction and whether parkin regulates complex I, an enzymatic complex downregulated in PD. To determine this, we separately assessed the effects of METH or DA alone on electron transport chain (ETC) complexes and the protein parkin in isolated striatal mitochondria. We show that METH decreases the levels of selected complex I, II, and III subunits (NDUFS3, SDHA, and UQCRC2, respectively), whereas DA decreases the levels only of the NDUFS3 subunit in our preparations. We also show that the selected subunits are not decreased in synaptosomal mitochondria under similar experimental conditions. Finally, we found that parkin overexpression does not influence the levels of the NDUFS3 subunit in rat striatum. The presented results indicate that METH itself is a factor promoting dysfunction of striatal mitochondria; therefore, it is a potential drug target against METH neurotoxicity. The observed decreases in ETC complex subunits suggest that DA and METH decrease activities of the ETC complexes via oxidative damage to their subunits and that synaptosomal mitochondria may be somewhat "resistant" to DA- and METH-induced disruption in mitochondrial ETC complexes than perikaryal mitochondria. The results also suggest that parkin does not regulate NDUFS3 turnover in rat striatum.

DJ-1 as a neuroprotective protein in models of Parkinson's disease

Katarzyna Piorkowska-Stanco

Parkinson's disease (PD) is a common progressive neurodegenerative disorder characterized clinically by the combination of motor symptoms like bradykinesia, tremor, rigidity and postural instability. The pathology of PD is related to the degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNpc) leading to the deficiency of dopamine in the striatal projection areas of these neurons. The pathogenesis of PD is not fully elucidated yet, however there is strong evidence that protein aggregation, mitochondrial dysfunction and oxidative stress play a primary role in the etiology of the disease. Most of PD cases are sporadic, however, several genes have been characterized to cause familial forms of the disease. Among them, mutations in DJ-1 were identified in families with autosomal-recessive early-onset PD and account for 2% of inherited PD cases. The DJ-1 protein was identified as an important player in cellular defense against oxidative stress as it possibly acts as an oxidative stress-induced chaperone and inhibits the formation of inclusions of α-synuclein, another protein related to PD. Alpha-synuclein mutations cause an autosomal dominant form of the disease. Moreover, this protein is a main component of Lewy Bodies, a pathological hallmark of PD. The goal of the experiments during my thesis was to investigate the potential protective effect of DJ-1 in toxin-based [6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)] as well as genetic models of PD in vivo. Towards this goal, the DJ-1 protein was over-expressed in rodent SNpc through the injections of recombinant adeno-associated viral vector (rAAV). In the first study, the DJ-1 over-expression led to significant protection of dopaminergic cells and spontaneous motor behavior in 6-OHDA-lesioned animals. However, this effect of DJ-1 was not confirmed when DJ-1 was over-expressed in the brains of mice lesioned with MPTP. In the third part of the study, the nigral over-expression of mutated a-synuclein (A30P mutation found in familial PD cases) was chosen as the genetic model of PD, already developed in our lab. Interestingly, significant preservation of spontaneous behavior was obtained when a-synuclein (A30P) was co-injected with DJ-1. However, this was accompanied by a modest protection of dopaminergic cells, suggesting the implication of other, subtle mechanisms regulating DJ-1-related basal ganglia output. Although the DJ-1 protection of dopaminergic cells was not always achieved, the effect of DJ-1 on the spontaneous behavior implies the interesting capacity of this protein. Our results suggest that DJ-1 is one of key factors playing role in maintenance of dopaminergic function. For a possible clinical application, DJ-1 may have to be linked with another neuroprotecting factor to assure a stronger protection effect.

EPFL2007

PGC-1 alpha activity in nigral dopamine neurons determines vulnerability to alpha-synuclein

Wojciech Janusz Bobela, Graham Knott, Bernard Schneider, Lu Zheng

Introduction: Mitochondrial dysfunction and oxidative stress are critical factors in the pathogenesis of age-dependent neurodegenerative diseases. PGC-1 alpha, a master regulator of mitochondrial biogenesis and cellular antioxidant defense, has emerged as a possible therapeutic target for Parkinson's disease, with important roles in the function and survival of dopaminergic neurons in the substantia nigra. The objective of this study is to determine if the loss of PGC-1 alpha activity contributes to alpha-synuclein-induced degeneration. Results: We explore the vulnerability of PGC-1 alpha null mice to the accumulation of human alpha-synuclein in nigral neurons, and assess the neuroprotective effect of AAV-mediated PGC-1 alpha expression in this experimental model. Using neuronal cultures derived from these mice, mitochondrial respiration and production of reactive oxygen species are assessed in conditions of human alpha-synuclein overexpression. We find ultrastructural evidence for abnormal mitochondria and fragmented endoplasmic reticulum in the nigral dopaminergic neurons of PGC-1 alpha null mice. Furthermore, PGC-1 alpha null nigral neurons are more prone to degenerate following overexpression of human alpha-synuclein, an effect more apparent in male mice. PGC-1 alpha overexpression restores mitochondrial morphology, oxidative stress detoxification and basal respiration, which is consistent with the observed neuroprotection against alpha-synuclein toxicity in male PGC-1 alpha null mice. Conclusions: Altogether, our results highlight an important role for PGC-1 alpha in controlling the mitochondrial function of nigral neurons accumulating alpha-synuclein, which may be critical for gender-dependent vulnerability to Parkinson's disease.

Biomed Central Ltd2015

The effect of the functional interaction between PGC-1α and Parkin on mitochondrial quality control in Parkinson's disease

Lu Zheng

Although several genetic factors have been directly associated to Parkinsonâs disease (PD), no single pathway has emerged to explain the etiology of this neurodegenerative disease. To further understand the cause of Parkinsonâs disease (PD), it is therefore important to deter-mine if and which functional interactions exist between gene products linked to this complex brain disorder. Mutations in the gene encoding the E3 ubiquitin ligase Parkin are associated to autosomal recessive PD with early onset. Although the Parkin protein carries out various critical func-tions in the cell, its role in mitochondria quality control, by inducing the autophagic degrada-tion of damaged mitochondria, has attracted a lot of attention. Furthermore, Parkin has been found to control the transcription of PGC-1Î±, a master regulator of mitochondrial biogenesis. Based on the important role that mitochondria are considered to play in PD, and the evi-dence for the coordinated expression of Parkin and PGC-1Î±, we sought to explore in neurons how these two factors functionally interact to regulate mitochondria turnover and quality control. In cortical neuronal cultures, we found that Parkin and PGC-1Î± have synergistic effects on mitochondrial biogenesis, and that the co-expression of these two factors leads to a dramatic increase in the number of mitochondria per cell. We further explored the effects of these fac-tors on the mitochondrial function. Parkin was shown to enhance the maximal respiration rate of neurons exposed to a mitochondrial uncoupling agent only in the presence of PGC-1Î±. Consistent with this effect, the co-expression of Parkin and PGC-1Î± leads to rapid recovery of the mitochondrial membrane potential following mitochondrial uncoupling. Next, we explored the molecular changes, which may underlie the cooperation between Par-kin and PGC-1Î±. The expression of Tfam, an important mitochondrial transcription factor, was found to be controlled synergistically by these two factors. Furthermore, PGC-1Î± en-hances the turnover of Mfn2, a key ubiquitylation target of Parkin. This result suggests that part of the functional interaction between PGC-1Î± and Parkin may be mediated via the co-regulation of Mfn2, a critical factor in mitochondrial physiology which controls the dynamics of mitochondria as well as their association with the endoplasmic reticulum (ER). In the rat substantia nigra, Parkin activity has significant protective effects on the survival and function of nigral dopaminergic neurons in which the chronic expression of PGC-1Î± is in-duced. Ultrastructural analysis shows that the conjunction of these two factors controls the density of mitochondria and their interaction with the ER. In PGC-1Î±-expressing dopamin-ergic neurons, the co-expression of mutated variants of Parkin associated with familial PD leads to accelerated degeneration. Overall, this study shows that Parkin, in conjunction with the transcription co-regulator PGC-1Î±, may play an important role in modulating the biogenesis of mitochondria as well as the quality control of this organelle. In nigral dopaminergic neurons which may critically depend on the mitochondria for their function and survival, the functional interaction be-tween these two factors should be further explored in the context of PD.