Reduced expression of peroxisome-proliferator activated receptor gamma coactivator-1α enhances α-synuclein oligomerization and down regulates AKT/GSK3β signaling pathway in human neuronal cells that inducibly express α-synuclein

doi:10.1016/j.neulet.2010.02.034

Neuroscience Letters

Volume 473, Issue 2, 5 April 2010, Pages 120-125

https://doi.org/10.1016/j.neulet.2010.02.034 Get rights and content

Abstract

Intracellular accumulation of filamentous α-synuclein (α-Syn) aggregates to form Lewy bodies is a pathologic hallmark of Parkinson's disease. To determine whether mitochondrial impairment plays a role in the accumulation of α-Syn oligomer, we used 3D5 cell culture model of human neuronal type whereby conditional overexpression of wild-type α-Syn via the tetracycline-off (TetOff) induction mechanism results in formation of inclusions that exhibit many characteristics of Lewy bodies. In the present study, we compromised mitochondrial function in 3D5 cells by using shRNA to knockdown peroxisome-proliferator activated receptor gamma coactivator-1α (PGC-1α), a key regulator of mitochondrial biogenesis and cellular energy metabolism and found that PGC-1α suppression at both protein and mRNA levels results in α-Syn accumulation (i.e. monomeric and oligomeric species in the TetOff-induced cells and monomeric only in the non-induced). These changes were accompanied with reduced mitochondrial potential as well as decreased levels of AKT, GSK3β (total and Ser⁹-phosphorylated) and p53 that are important for cell survival. The extent to which these proteins decreased following PGC-1α knockdown, in contrast to what was demonstrable with the viability assay, is greater in the induced than the non-induced. Together these findings indicate that such knockdown increases the propensity to accumulate α-Syn oligomers, but the accumulation appears to have very little toxic impact to the neuronal cells.

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Acknowledgments

We thank Ms. Katrina Willams and Dr. Brian M. Necela at Mayo Clinic for their assistance in Quantitative Real time PCR analysis, Dr. Daniel P. Kelly at Washington University for providing PGC-1α antibody. This study was funded by Grant No. P50NS40256 from the National Institute of Health and by the Mayo Foundation (S.H. Yen).

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The cytoprotective of CA is related to the enhancement of mitochondrial biogenesis by inhibiting PARIS and inducing PGC-1α by parkin. The activation of PGC-1α-mediated mitochondrial biogenesis by CA prevents the degeneration of dopaminergic neurons, CA may have therapeutic application in PD.
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The transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) is a critical regulator of genes involved in neuronal metabolism, neurotransmission, and morphology. Reduced PGC-1α expression has been implicated in several neurological and psychiatric disorders. An understanding of PGC-1α’s roles in different cell types will help determine the functional consequences of PGC-1α dysfunction and/or deficiency in disease. Reports from our laboratory and others suggest a critical role for PGC-1α in inhibitory neurons with high metabolic demand such as fast-spiking interneurons. Here, we document a previously unrecognized role for PGC-1α in maintenance of gene expression programs for synchronous neurotransmitter release, structure, and metabolism in neocortical and hippocampal excitatory neurons. Deletion of PGC-1α from these neurons caused ambulatory hyperactivity in response to a novel environment and enhanced glutamatergic transmission in neocortex and hippocampus, along with reductions in mRNA levels from several PGC-1α neuron-specific target genes. Given the potential role for a reduction in PGC-1α expression or activity in Huntington Disease (HD), we compared reductions in transcripts found in the neocortex and hippocampus of these mice to that of an HD knock-in model; few of these transcripts were reduced in this HD model. These data provide novel insight into the function of PGC-1α in glutamatergic neurons and suggest that it is required for the regulation of structural, neurosecretory, and metabolic genes in both glutamatergic neuron and fast-spiking interneuron populations in a region-specific manner. These findings should be considered when inferring the functional relevance of changes in PGC-1α gene expression in the context of disease.
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Moreover, progressive Parkinsonism was observed in mice with conditional disruption of the PGC-1α target gene TFAM (Ekstrand et al., 2007). In 3D5 cells conditionally overexpressing α-synuclein, knockdown of PGC-1α increased α-synuclein oligomers/aggregates and decreased levels of AKT, GSK3β and p53 (Ebrahim et al., 2010) and α-synuclein toxicity can be reduced by pharmacological activation or overexpression of PGC-1α (Eschbach et al., 2015). In addition, α-synuclein was shown to bind to the PGC-1α promoter in brain tissue and reduced promoter activity of PGC-1α and its target gene expression in vitro (Siddiqui et al., 2012).
Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide. PGC-1α, encoded by PPARGC1A, is a transcriptional co-activator that has been implicated in the pathogenesis of neurodegenerative disorders. We recently discovered multiple new PPARGC1A transcripts that initiate from a novel promoter located far upstream of the reference gene promoter, are CNS-specific and are more abundant than reference gene transcripts in whole brain. These CNS-specific transcripts encode two main full-length and several truncated isoforms via alternative splicing. Truncated CNS-isoforms include 17 kDa proteins that lack the second LXXLL motif serving as an interaction site for several nuclear receptors. We now determined expression levels of CNS- and reference gene transcripts in 5 brain regions of 21, 8, and 13 deceased subjects with idiopathic PD, Lewy body dementia and controls without neurodegenerative disorders, respectively. We observed reductions of CNS-specific transcripts (encoding full-length isoforms) only in the substantia nigra pars compacta of PD and Lewy body dementia. However, in the substantia nigra and globus pallidus of PD cases we found an up-regulation of transcripts encoding the 17 kDa proteins that inhibited the co-activation of several transcription factors by full-length PGC-1α proteins in transfection assays. In two established animal models of PD, the PPARGC1A expression profiles differed from the profile in human PD in that the levels of CNS- and reference gene transcripts were decreased in several brain regions. Furthermore, we identified haplotypes in the CNS-specific region of PPARGC1A that appeared protective for PD in a clinical cohort and a post-mortem sample (P = .0002). Thus, functional and genetic studies support a role of the CNS-specific PPARGC1A locus in PD.
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In addition to enhancing gene transcription via activated AMPK, PGC-1α and NRF-1 & −2 in old rats, LA can reduce alpha-syn accumulation in substantia nigra to protect against dopamine cell loss and improve motor function (Li et al., 2015). This property may result from the induction of PGC-1α, since PGC-1α suppression results in alpha-syn accumulation and oligomerisation (Ebrahim et al., 2010), while overexpression of PGC-1α reduces alpha-syn oligomers and toxicity (Eschbach et al., 2015; Wareski et al., 2009; Zheng et al., 2010). Furthermore, nigral neurons are more likely to degenerate in the presence of accumulated alpha-syn in PGC-1α null conditions (Ciron et al., 2015).
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Reduced expression of peroxisome-proliferator activated receptor gamma coactivator-1α enhances α-synuclein oligomerization and down regulates AKT/GSK3β signaling pathway in human neuronal cells that inducibly express α-synuclein

Abstract

Section snippets

Acknowledgments

J. Biol. Chem.

Neurobiol. Dis.

Biochim. Biophys. Acta

Cell

Neurobiol. Dis.

Am. J. Pathol.

Cell

J. Biol. Chem.

Cell

Cell

Exp. Neurol.

Dynamic regulation of PGC-1alpha localization and turnover implicates mitochondrial adaptation in calorie restriction and the stress response

Aging Cell.