Expanding insights on the involvement of endoplasmic reticulum stress in Parkinson’s disease

Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Antioxidants and Redox Signaling (Impact Factor: 7.67). 06/2007; 9(5):553-61. DOI: 10.1089/ars.2006.1524
Source: PubMed

ABSTRACT Parkinson's disease (PD) is the second most common neurodegenerative disease characterized by selective loss of dopaminergic neurons and the presence of Lewy bodies. The pathogenesis of PD remains incompletely understood. Environmental factors, oxidative damage, misfolded protein aggregates, ubiquitin-proteasome system impairment, and mitochondrial dysfunction might all be involved. Recent studies point to activation of endoplasmic reticulum (ER) stress-mediated cell death linked to PD. Accumulation of unfolded and/or misfolded proteins in the ER lumen induces ER stress. To withstand such potentially lethal conditions, intracellular signaling pathways collectively termed the unfolded protein responses (UPR) are activated. The UPR include translational attenuation, induction of ER resident chaperones, and degradation of misfolded proteins through the ER-associated degradation. In case of severe and/or prolonged ER stress, cellular signals leading to cell death are activated. Accumulating evidence suggests that ER stress induced by aberrant protein degradation is implicated in PD. Here the authors review the emerging role of ER stress in PD and related disorders, and highlight current knowledge in this field that may reveal novel insight into disease mechanisms and help to provide novel avenues to potential therapies.

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    ABSTRACT: Parkinson's disease (PD) is the second most common neurodegenerative disease in developed countries. The core motor symptoms are attributable to the degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc). Why these neurons succumb in PD is not clear. One potential clue has come from the observation that the engagement of L-type Ca²⁺ channels during autonomous pacemaking elevates the sensitivity of SNc DA neurons to mitochondrial toxins used to create animal models of PD, suggesting that Ca²⁺ entry is a factor in their selective vulnerability. Recent work has shown that this Ca²⁺ entry also elevates mitochondrial oxidant stress and that this stress is exacerbated by deletion of DJ-1, a gene associated with an early onset, recessive form of PD. Epidemiological data also support a linkage between L-type Ca²⁺ channels and the risk of developing PD. This review examines the hypothesis that the primary factor driving neurodegenerative changes in PD is the metabolic stress created by Ca²⁺ entry, particularly in the face of genetic or environmental factors that compromise oxidative defenses or proteostatic competence.
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    ABSTRACT: The assembling of distinct signaling protein complexes at the endoplasmic reticulum (ER) membrane controls several stress responses related to calcium homeostasis, autophagy, ER morphogenesis and protein folding. Diverse pathological conditions interfere with the function of the ER altering protein folding, a condition known as "ER stress". Adaptation to ER stress depends on the activation of the unfolded protein response (UPR) and protein degradation pathways such as autophagy. Under chronic or irreversible ER stress, cells undergo apoptosis, where the BCL-2 protein family plays a crucial role at the mitochondria to trigger cytochrome c release and apoptosome assembly. Several BCL2 family members also regulate physiological processes at the ER through dynamic interactomes. Here we provide a comprehensive view of the roles of the BCL-2 family of proteins in mediating the molecular crosstalk between the ER and mitochondria to initiate apoptosis, in addition to their emerging functions in adaptation to stress, including autophagy, UPR, calcium homeostasis and organelle morphogenesis. We envision a model where BCL-2-containing complexes may operate as stress rheostats that, beyond their known apoptosis functions at the mitochondria, determine the amplitude and kinetics of adaptive responses against ER-related injuries. This article is part of a Special Issue entitled Mitochondria: the deadly organelle.
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    ABSTRACT: Key Research Accomplishments: -the discovery that calcium entry through L-type channels during normal pacemaking elevates the sensitivity of SNc dopaminergic neurons to toxins; -the discovery that L-type calcium channels participate in but are not necessary for pacemaking; -the discovery that serum concentration of the dihydropyridine isradipine required to achieve protection of SNc dopaminergic neurons against toxins in animal models is similar to that achieved in humans by FDA approved doses; -the discovery that calcium entry through L-type channels during pacemaking elevates mitochondrial oxidant stress and leads to the engagement of a DJ-1-dependent oxidant defense system involving uncoupling proteins.