Elsevier

Brain Research

Volume 1660, 1 April 2017, Pages 20-26
Brain Research

Research report
Effect of MPTP on mRNA expression of PGC-1α in mouse brain

https://doi.org/10.1016/j.brainres.2017.01.032Get rights and content

Highlights

  • Expression of PGC-1α transcripts was assessed following different MPTP treatments.

  • PGC-1α expression was significantly elevated ninety minutes after acute MPTP treatment.

  • This elevation did not persist 7 days following the last MPTP injection.

  • Chronic low-dose of MPTP as preconditioning induced no changes in PGC-1α levels.

  • MPTP may induce a short-term compensatory mechanism via the PGC-1α system.

Abstract

The peroxisome proliferator-activated receptor-γ (PPARγ) coactivator 1α (PGC-1α) is a key regulator of mitochondrial biogenesis, respiration and adaptive thermogenesis. Besides the full-length protein (FL-PGC-1α), several other functionally active PGC-1α isoforms were identified as a result of alternative splicing (e.g., N-truncated PGC-1α; NT-PGC-1α) or alternative promoter usage (e.g., central nervous system-specific PGC-1α isoforms; CNS-PGC-1α). Achieving neuroprotection via CNS-targeted pharmacological stimulation is limited due to poor penetration of the blood brain barrier (BBB) by the proposed pharmaceutical agents, so preconditioning emerged as another option. The current study aimed to examine of how the expression levels of FL-, NT-, CNS- and reference PGC-1α isoforms change in different brain regions following various 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment regimens, including chronic low-dose treatment for preconditioning. Ninety minutes following the acute treatment regimen, the expression levels of FL-, NT- and CNS-PGC-1α isoforms increased significantly in the striatum, cortex and cerebellum. However, this elevation diminished 7 days following the last MPTP injection in the acute treatment regimen. The chronic low-dose administration of MPTP, which did not cause significant toxic effects in light of the relatively unaltered dopamine levels, did not result in any significant change of PGC-1α expression. The elevation of PGC-1α levels following acute treatment may demonstrate a short-term compensatory mechanism against mitochondrial damage induced by the complex I inhibitor MPTP. However, drug-induced preconditioning by chronic low-dose MPTP seems not to induce protective responses via the PGC-1α system.

Introduction

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons, and the presence of Lewy bodies in the substantia nigra (SN) pars compacta (Forno, 1996). Although the precise pathomechanism of PD is not fully understood, several molecular mechanisms of neuronal death were described in the pathogenesis, including mitochondrial dysfunction, energy deficit and oxidative stress (Bose and Beal, 2016). It is postulated that life-long cumulative low-dose exposure to mitochondrial toxins may contribute to the pathogenesis of certain neurodegenerative disorders (Harris and Blain, 2004). The delineation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced Parkinsonian symptoms yielded one of the first pieces of evidence that mitochondrial dysfunction is involved in PD pathogenesis (Forno et al., 1993). Accordingly, systemic MPTP administration has been widely used to study disease mechanisms in various in vivo animal studies (Javitch et al., 1985).

Besides environmental factors, several causative or susceptibility genes have been identified in PD, many of them having direct implications in mitochondrial dysfunction (Kalinderi et al., 2016). Peroxisome proliferator-activated receptor-gamma (PPARγ) coactivator-1 alpha (PGC-1α) is one of them, which may play a role in PD pathogenesis. PGC-1α is a multifunctional transcriptional coactivator of nuclear respiratory factors 1 and 2 (NRF-1, -2), estrogen-related receptors (ERRs) and PPARs amongst others, and hereby regulates mitochondrial function and biogenesis (Knutti and Kralli, 2001).

Analysis of human brain samples indicated that PD is associated with the increased methylation of PGC-1α promoter and the reduced expression of PGC-1α itself (Su et al., 2015) and its downstream-regulated genes in the SN of PD patients (Zheng et al., 2010). Furthermore, possible associations of PGC-1α polymorphisms with PD risk, age of onset and longevity were described as well (Clark et al., 2011). Reduced expression of PGC-1α leads to enhanced α-synuclein oligomerization, too (Ebrahim et al., 2010), and accordingly, overexpression of PGC-1α produced neuroprotection against α-synuclein- and rotenone-induced neurotoxicity (Zheng et al., 2010).

Several PGC-1α isoforms were identified as a result of alternative splicing and alternative promoter usage (Martinez-Redondo et al., 2015). The proximal promoter of PGC-1α has been reported as an important key regulator in several neurodegenerative diseases, including PD (Su et al., 2015). With regard to alternative splicing, besides the full-length protein (FL-PGC-1α), the N-truncated PGC-1α (NT-PGC-1α) isoform was discovered, which is a shorter, but active isoform of PGC-1α (Zhang et al., 2009). Recent studies identified further different tissue-specific isoforms of PGC-1α, including central nervous system-specific isoforms (CNS-PGC-1α (Ruas et al., 2012, Soyal et al., 2012)). The novel CNS-specific isoforms originated from a new promoter located 587 kb upstream of exon 2 (Choi et al., 2013, Soyal et al., 2012). A recent study demonstrated that both PGC-1α reference gene and CNS-PGC-1α are downregulated in human PD brain and in experimental models with α-synuclein oligomerization, and that the pharmacological activation or genetic overexpression of PGC-1α reference gene reduced α-synuclein oligomerization and toxicity (Eschbach et al., 2015). In contrast, the loss of PGC-1α enhances the vulnerability of SN pars compacta dopaminergic neurons to α-synuclein toxicity (Ciron et al., 2015). These data suggest that PGC-1α downregulation and α-synuclein oligomerization form a vicious circle (Eschbach et al., 2015). Similarly to PD, certain mutations in amyotrophic lateral sclerosis inhibit the expression of CNS-specific isoforms, indicating this as a common finding in neurodegeneration (Bayer et al., 2017).

St-Pierre et al. described that PGC-1α-deficient mice are more sensitive to MPTP toxicity compared to the controls (St-Pierre et al., 2006). Interestingly, the sub-chronic administration of MPTP to mice resulted in the significant elevation of PGC-1α expression in the striatum after 24 h that was normalized following 72 h (Swanson et al., 2013). This may represent an adaptive mechanism to neurotoxicity. Accordingly, the protective effect of PGC-1α was demonstrated previously as well; pioglitazone- and resveratrol-induced activation of PGC-1α was protective against MPTP toxicity (Breidert et al., 2002, Dehmer et al., 2004). However, there is a seeming controversy with regard to the effect of genetically-induced overexpression of PGC-1α on MPTP neurotoxicity. On the one hand, the transgenic overexpression of PGC-1α was proven to be protective against MPTP (Mudo et al., 2012), on the other hand, the adenovirus vector-mediated overexpression of PGC-1α resulted in dopamine depletion in the SN (Ciron et al., 2012) and consequently enhanced susceptibility to MPTP (Clark et al., 2012). Clarification of this issue needs further studies.

Evidence suggests a beneficial role of PGC-1α stimulation in neurodegenerative disorders. However, CNS-targeted pharmacological stimulation is limited due to the poor penetration of the blood brain barrier (BBB) by the above-mentioned compounds, so preconditioning emerged as another option to achieve neuroprotection. It was previously demonstrated that the acute administration of the selective complex II inhibitor 3-nitropropionic acid (3-NP) increased the expression of both FL- and NT-PGC-1α isoforms in the striatum of C57Bl/6 mice (Torok et al., 2015). As the available data are limited with regard to the alteration of tissue-specific PGC-1α expression in the brain following MPTP administration, this study aimed to examine the expression levels of several PGC-1α isoforms in different brain regions following various MPTP treatment regimens. The hypothesis that low doses of MPTP may produce compensatory, protective alterations in the PGC-1α system was tested as well.

Section snippets

Gene expression analysis

Ninety minutes following the last MPTP injection of the acute treatment of MPTP, the FL-PGC-1α and NT-PGC-1α expression significantly increased in the striatum (FL-PGC-1α: ctrl: 0.97 (0.92–1.04), MPTP: 1.47 (1.21–1.83), p = 0.0048; NT-PGC-1α: ctrl: 0.44 (0.40–0.49), MPTP: 0.70 (0.56–0.78), p = 0.019), cortex (FL-PGC-1α: ctrl: 0.96 (0.91–1.06), MPTP: 1.23 (1.15–1.43), p = 0.009; NT-PGC-1α: ctrl: 0.46 (0.43–0.48), MPTP: 0.69 (0.59–0.71), p = 0.0012) and cerebellum (FL-PGC-1α: ctrl: 1.50 (1.27–1.90),

Discussion

PGC-1α is essential in normal mitochondrial function and its deficiency may contribute to neurodegeneration, while its stimulation was demonstrated to be neuroprotective in certain models (Breidert et al., 2002, Dehmer et al., 2004, Eschbach et al., 2015, Mudo et al., 2012). Accordingly, the pharmacological induction of PGC-1α expression may be considered as a neuroprotective approach, but currently this possibility seems to be limited in light of the reduced BBB penetration of the potential

Animals

12-Week-old C57Bl/6J male mice were used in this study. The animal strain was originally obtained from Jackson Labs (Jackson Laboratories, Bar Harbor, ME, USA).

The animals were housed in cages and maintained under standard laboratory conditions with 12–12 h light–dark cycle and free access to food and water. The experiments were carried out in accordance with the European Communities Council Directive (86/609/EEC) and were approved by the local animal care committee.

Treatment and sample handling

MPTP was dissolved in

Funding sources

The study was supported by the Hungarian Brain Research Program – Grant No. KTIA_13_NAP-A-II/18 and MTA-SZTE Neuroscience Research Group. Denes Zadori was supported by the Janos Bolyai Research Scholarship of the Hungarian Academy of Sciences.

Conflict of interest

The authors declare there is no conflict of interest.

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