Mechanisms underlying the adverse impact of mitochondrial dysfunction and its prevention on the ubiquitin/proteasome pathway: Relevance to Parkinson disease
Item
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Title
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Mechanisms underlying the adverse impact of mitochondrial dysfunction and its prevention on the ubiquitin/proteasome pathway: Relevance to Parkinson disease
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Identifier
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d_2009_2013:6e4f86742cf3:11948
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identifier
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12618
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Creator
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Wang, Hu,
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Contributor
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Maria Figueiredo Pereira
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Date
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2013
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Language
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English
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Publisher
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City University of New York.
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Subject
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Molecular biology | Neurosciences | Mitochondria | Parkin | Parkinson Disease | Ubiquitin/Proteasome pathway
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Abstract
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Neuroinflammation has long been accepted as a probable factor in Parkinson disease(PD). Besides neuroinflammation, mitochondrial impairment and ubiquitin/proteasome pathway (UPP) dysfunction have also been recognized as important contributors to the pathogenesis of PD.;Parkin, which plays a central role in the link between mitochondria and the UPP, is mutated in both familial and sporadic forms of PD. The function of Parkin was first described as an E3 ubiquitin ligase that delivers its substrates to the proteasome to be degraded. However, recent findings discovered another important role for Parkin, which is its involvement in mitochondrial quality control and mitochondrial dynamics.;Since neuroinflammation, mitochondrial impairment, UPP dysfunction and Parkin are all involved in PD pathogenesis, it is of great interest and importance to investigate the interaction among these pathogenic elements. Therefore, the MAJOR AIMS of these studies were to: (1) Investigate whether Parkin is affected by neuroinflammation, mitochondrial and UPP dysfunction, and assess approaches to protect from these insults. (2) Determine the mechanisms by which mitochondrial impairment disturbs the UPP.;Rat E18 midbrain and cerebral cortical neuronal cultures were used to carry-out our specific aims.;We used a pharmacological approach to mimic neuroinflammation, as well as mitochondrial and proteasomal dysfunction. The neuronal cultures were treated with: (1) Prostaglandin J2 (PGJ2), an endogenous product of inflammation, which inhibits mitochondrial complex I and impairs proteasomal function. (2) Mitochondrial toxins that target the electron transport chain (ETC): a) Oligomycin, which inhibits ATP synthase (complex V); b) Antimycin, which inhibits complex III; c) Rotenone, which inhibits complex I; (3) Epoxomicin, a specific and irreversible proteasomal inhibitor.;The results from the first aim reveal that: (1) Upon mitochondrial dysfunction a new form of Parkin (newParkin) is detected that is generated by calpain cleavage of full length Parkin. To our knowledge, we are the first to report this new form of Parkin. (2) NewParkin generated upon mitochondrial impairment translocates to mitochondria, and dissociates from the 26S proteasome. (3) Phosphorylation attenuates Parkin cleavage induced by mitochondrial impairment. (4) The endogenous product of inflammation PGJ2 and the proteasomal inhibitor epoxomicin, also lead to Parkin cleavage but under these conditions, cleavage is mediated by caspase and not calpain activation. (5) Increasing intracellular cAMP with the lipophilic peptide PACAP27 mitigates some of the adverse effects of the product of inflammation PGJ2, including caspase activation, caspase-mediated cleavage of Parkin, and loss of neuronal viability. (6) Partially replenishing intracellular ATP with the nearly planar creatine analog cyclocreatine, diminishes Parkin cleavage triggered by mitochondrial impairment.;The results from the second aim reveal that: (1) Mitochondrial toxins which deplete intracellular ATP levels, lead to the downregulation of protein ubiquitination, by adversely affecting the first step of the ubiquitination cascade, i.e. E1-mediated ubiquitin activation, which is ATP-dependent. (2) Mitochondrial toxins downregulate 26S proteasome assembly via selective processing of the Rpn 10 subunit of the 26S proteasome by calpain cleavage. To our knowledge, we are the first to identify this unique calpain substrate. (3) The 26S proteasome deficit induced by the mitochondrial toxins is accompanied by a rise in 20S proteasome levels. (4) These events were induced by acute (16h) and long term (up to seven days) mitochondrial impairment.;In summary, our results addressed the complex relationship among neuroinflammation, mitochondrial impairment, proteasomal dysfunction and Parkin, all of which are relevant to Parkinson Disease (PD). We identified the PARKIN-mitochondria-UPP link as highly vulnerable to stress conditions, revealing a relevant mechanistic pathway to exploit for protecting against the progressive nature of PD. We identified two pharmacological approaches to diminish the adverse effects of an impaired PARKIN-mitochondria-UPP link, by increasing intracellular cAMP as well as ATP levels with PACAP27 and cyclocreatine, respectively. Our findings provide a new basis for the development of novel and more effective therapeutic strategies that prevent/stop neurodegeneration in PD.
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Type
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dissertation
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Source
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2009_2013.csv
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degree
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Ph.D.
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Program
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Biology
