Research reportEffect of MPTP on mRNA expression of PGC-1α in mouse brain
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.
References (40)
- et al.
ALS-causing mutations differentially affect PGC-1alpha expression and function in the brain vs. peripheral tissues
Neurobiol. Dis.
(2017) - et al.
Effect of acute exposure to 3-nitropropionic acid on activities of endogenous antioxidants in the rat brain
Neurosci. Lett.
(1998) - et al.
NT-PGC-1alpha protein is sufficient to link beta3-adrenergic receptor activation to transcriptional and physiological components of adaptive thermogenesis
J. Biol. Chem.
(2012) - et al.
A novel PGC-1alpha isoform in brain localizes to mitochondria and associates with PINK1 and VDAC
Biochem. Biophys. Res. Commun.
(2013) - et al.
Association of PGC-1alpha polymorphisms with age of onset and risk of Parkinson's disease
BMC Med. Genet.
(2011) - et al.
Reduced expression of peroxisome-proliferator activated receptor gamma coactivator-1alpha enhances alpha-synuclein oligomerization and down regulates AKT/GSK3beta signaling pathway in human neuronal cells that inducibly express alpha-synuclein
Neurosci. Lett.
(2010) - et al.
PGC-1, a versatile coactivator
Trends Endocrinol. Metab.
(2001) - et al.
Biochemical, behavioral and immunohistochemical alterations in MPTP-treated mouse model of Parkinson's disease
Pharmacol. Biochem. Behav.
(2004) - et al.
Analysis of relative gene expression data using real-time quantitative PCR and the 2(-Delta Delta C(T)) Method
Methods
(2001) - et al.
A PGC-1alpha isoform induced by resistance training regulates skeletal muscle hypertrophy
Cell
(2012)