MPTP as a mitochondrial neurotoxic model of Parkinson's disease

Inhibition of phosphodiesterase 4 by FCPR16 protects SH-SY5Y cells against MPP+-induced decline of mitochondrial membrane potential and oxidative stress

Phosphodiesterase 4 (PDE4) is a promising target for the treatment of Parkinson's disease (PD). However, the underlying mechanism has not yet been well elucidated. Additionally, most of current PDE4 inhibitors produce severe nausea and vomiting response in patients, which limit their clinical application. FCPR16 is a novel PDE4 inhibitor with little emetic potential. In the present study, the neuroprotective effect and underlying mechanism of FCPR16 against cellular apoptosis induced by 1-methyl-4-phenylpyridinium (MPP⁺) were examined in SH-SY5Y cells. FCPR16 (12.5–50 μM) dose-dependently reduced MPP⁺-induced loss of cell viability, accompanied by reductions in nuclear condensation and lactate dehydrogenase release. The level of cleaved caspase 3 and the ratio of Bax/Bcl-2 were also decreased after treatment with FCPR16 in MPP⁺-treated cells. Furthermore, FCPR16 (25 μM) significantly suppressed the accumulation of reactive oxygen species (ROS), prevented the decline of mitochondrial membrane potential (Δψm) and attenuated the expression of malonaldehyde level. Further studies disclosed that FCPR16 enhanced the levels of cAMP and the exchange protein directly activated by cAMP (Epac) in SH-SY5Y cells. Western blotting analysis revealed that FCPR16 increased the phosphorylation of cAMP response element-binding protein (CREB) and protein kinase B (Akt) down-regulated by MPP⁺ in SH-SY5Y cells. Moreover, the inhibitory effects of FCPR16 on the production of ROS and Δψm loss could be blocked by PKA inhibitor H-89 and Akt inhibitor KRX-0401. Collectively, these results suggest that FCPR16 attenuates MPP⁺-induced dopaminergic degeneration via lowering ROS and preventing the loss of Δψm in SH-SY5Y cells. Mechanistically, cAMP/PKA/CREB and Epac/Akt signaling pathways are involved in these processes. Our findings indicate that FCPR16 is a promising pre-clinical candidate for the treatment of PD and possibly other oxidative stress-related neuronal diseases.

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FCPR16 protected SH-SY5Y cells against MPP⁺-induced apoptosis.

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FCPR16 attenuated Δψm loss and ROS generation in SH-SY5Y cells treated with MPP⁺.

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FCPR16 activated cAMP/PKA/CREB and Epac/Akt signaling pathways in SH-SY5Y cells.

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Blocking cAMP/PKA/CREB or Epac/Akt pathways canceled the protective role of FCPR16.

Understanding Miro GTPases: Implications in the Treatment of Neurodegenerative Disorders

The Miro GTPases represent an unusual subgroup of the Ras superfamily and have recently emerged as important mediators of mitochondrial dynamics and for maintaining neuronal health. It is now well-established that these enzymes act as essential components of a Ca²⁺-sensitive motor complex, facilitating the transport of mitochondria along microtubules in several cell types, including dopaminergic neurons. The Miros appear to be critical for both anterograde and retrograde mitochondrial transport in axons and dendrites, both of which are considered essential for neuronal health. Furthermore, the Miros may be significantly involved in the development of several serious pathological processes, including the development of neurodegenerative and psychiatric disorders. In this review, we discuss the molecular structure and known mitochondrial functions of the Miro GTPases in humans and other organisms, in the context of neurodegenerative disease. Finally, we consider the potential human Miros hold as novel therapeutic targets for the treatment of such disease.

Defective trafficking of Kv2.1 channels in MPTP-induced nigrostriatal degeneration

Intracellular protein trafficking is tightly regulated, and improper trafficking might be the fundamental provocateur for human diseases including neurodegeneration. In neurons, protein trafficking to and from the plasma membrane affects synaptic plasticity. Voltage-gated potassium channel 2.1 (Kv2.1) is a predominant delayed rectifier potassium (K⁺ ) current, and electrical activity patterns of dopamine (DA) neurons within the substantia nigra are generated and modulated by the orchestrated function of different ion channels. The pathological hallmark of Parkinson's disease (PD) is the progressive loss of these DA neurons, resulting in the degeneration of striatal dopaminergic terminals. However, whether trafficking of Kv2.1 channels contributes to PD remains unclear. In this study, we demonstrated that MPTP/MPP⁺ increases the surface expression of the Kv2.1 channel and causes nigrostriatal degeneration by using a subchronic MPTP mouse model. The inhibition of the Kv2.1 channel by using a specific blocker, guangxitoxin-1E, protected nigrostriatal projections against MPTP/MPP⁺ insult and thus facilitated the recovery of motor coordination. These findings highlight the importance of trafficking of Kv2.1 channels in the pathogenesis of PD.

Inhibitory effects of curcumin and cyclocurcumin in 1-methyl-4-phenylpyridinium (MPP+) induced neurotoxicity in differentiated PC12 cells

Development and progression of neurodegenerative diseases like Parkinson’s disease (PD) involve multiple pathways. Thus, effective therapeutic treatments should intervene to address all these pathways simultaneously for greater success. Most of the current pharmacotherapeutic approaches just supplement striatal dopamine. Hence, natural extracts of plants with therapeutic potential have been explored. Curcuminoids belong to one such group of polyphenol which show immense therapeutic effects. Here, we have used intracellular reactive oxygen species (ROS) measurement, and two-photon fluorescence lifetime imaging microscopy (2P-FLIM) of cellular autofluorescent co-enzyme reduced nicotinamide adenine dinucleotide (NADH) to study the inhibitory effects of curcumin and cyclocurcumin in alleviating PD like neurotoxicity of 1-methyl-4-phenylpyridinium (MPP⁺) in neuronal growth factor (NGF) induced differentiated PC12 cells. Our results showed that both cyclocurcumin and curcumin reduced the level of ROS caused by MPP⁺ treatment. Moreover, a significant increase in the free, protein-bound, and average NADH fluorescence lifetimes along with a decrease in the relative contribution of free- vs. protein-bound NADH components in curcuminoids treated cells (pretreated with MPP⁺) were observed compared with those treated with MPP⁺ only. This study, which indicates that cyclocurcumin offers higher neuronal protection than curcumin, may initiate further studies of these compounds in the cure of neurodegenerative diseases.

Mitochondrial impairment and melatonin protection in parkinsonian mice do not depend of inducible or neuronal nitric oxide synthases

MPTP-mouse model constitutes a well-known model of neuroinflammation and mitochondrial failure occurring in Parkinson’s disease (PD). Although it has been extensively reported that nitric oxide (NO^●) plays a key role in the pathogenesis of PD, the relative roles of nitric oxide synthase isoforms iNOS and nNOS in the nigrostriatal pathway remains, however, unclear. Here, the participation of iNOS/nNOS isoforms in the mitochondrial dysfunction was analyzed in iNOS and nNOS deficient mice. Our results showed that MPTP increased iNOS activity in substantia nigra and striatum, whereas it sharply reduced complex I activity and mitochondrial bioenergetics in all strains. In the presence of MPTP, mice lacking iNOS showed similar restricted mitochondrial function than wild type or mice lacking nNOS. These results suggest that iNOS-dependent elevated nitric oxide, a major pathological hallmark of neuroinflammation in PD, does not contribute to mitochondrial impairment. Therefore, neuroinflammation and mitochondrial dysregulation seem to act in parallel in the MPTP model of PD. Melatonin administration, with well-reported neuroprotective properties, counteracted these effects, preventing from the drastic changes in mitochondrial oxygen consumption, increased NOS activity and prevented reduced locomotor activity induced by MPTP. The protective effects of melatonin on mitochondria are also independent of its anti-inflammatory properties, but both effects are required for an effective anti-parkinsonian activity of the indoleamine as reported in this study.

A novel iron (II) preferring dopamine agonist chelator D-607 significantly suppresses α-syn- and MPTP-induced toxicities in vivo

Here, we report the characterization of a novel hybrid D₂/D₃ agonist and iron (II) specific chelator, D-607, as a multi-target-directed ligand against Parkinson's disease (PD). In our previously published report, we showed that D-607 is a potent agonist of dopamine (DA) D₂/D₃ receptors, exhibits efficacy in a reserpinized PD animal model and preferentially chelates to iron (II). As further evidence of its potential as a neuroprotective agent in PD, the present study reveals D-607 to be protective in neuronal PC12 cells against 6-OHDA toxicity. In an in vivo Drosophila melanogaster model expressing a disease-causing variant of α-synuclein (α-Syn) protein in fly eyes, the compound was found to significantly suppress toxicity compared to controls, concomitant with reduced levels of aggregated α-Syn. Furthermore, D-607 was able to rescue DAergic neurons from MPTP toxicity in mice, a well-known PD neurotoxicity model, following both sub-chronic and chronic MPTP administration. Mechanistic studies indicated that possible protection of mitochondria, up-regulation of hypoxia-inducible factor, reduction in formation of α-Syn aggregates and antioxidant activity may underlie the observed neuroprotection effects. These observations strongly suggest that D-607 has potential as a promising multifunctional lead molecule for viable symptomatic and disease-modifying therapy for PD.

Mitochondrial DNA and primary mitochondrial dysfunction in Parkinson's disease

In 1979, it was observed that parkinsonism could be induced by a toxin inhibiting mitochondrial respiratory complex I. This initiated the long-standing hypothesis that mitochondrial dysfunction may play a key role in the pathogenesis of Parkinson's disease (PD). This hypothesis evolved, with accumulating evidence pointing to complex I dysfunction, which could be caused by environmental or genetic factors. Attention was focused on the mitochondrial DNA, considering the occurrence of mutations, polymorphic haplogroup-specific variants, and defective mitochondrial DNA maintenance with the accumulation of multiple deletions and a reduction of copy number. Genetically determined diseases of mitochondrial DNA maintenance frequently manifest with parkinsonism, but the age-related accumulation of somatic mitochondrial DNA errors also represents a major driving mechanism for PD. Recently, the discovery of the genetic cause of rare inherited forms of PD highlighted an extremely complex homeostatic control over mitochondria, involving their dynamic fission/fusion cycle, the balancing of mitobiogenesis and mitophagy, and consequently the quality control surveillance that corrects faulty mitochondrial DNA maintenance. Many genes came into play, including the PINK1/parkin axis, but also OPA1, as pieces of the same puzzle, together with mitochondrial DNA damage, complex I deficiency and increased oxidative stress. The search for answers will drive future research to reach the understanding necessary to provide therapeutic options directed not only at limiting the clinical evolution of symptoms but also finally addressing the pathogenic mechanisms of neurodegeneration in PD. © 2017 International Parkinson and Movement Disorder Society.

Analysis of Epidermal Growth Factor Receptor Related Gene Expression Changes in a Cellular and Animal Model of Parkinson's Disease

We employed transcriptome analysis of epidermal growth factor receptor related gene expression changes in cellular and animal models of Parkinson’s disease (PD). We used a well-known Parkinsonian toxin 1-methyl-4-phenylpyridine (MPP⁺) to induce neuronal apoptosis in the human neuroblastoma SH-SY5Y cell line. The MPP⁺-treatment of SH-SY5Y cells was capable of inducing neuro-apoptosis, but it remains unclear what kinds of transcriptional genes are affected by MPP⁺ toxicity. Therefore the pathways that were significantly perturbed in MPP⁺ treated human neuroblastoma SH-SY5Y cells were identified based on genome-wide gene expression data at two time points (24 and 48 h). We found that the Epidermal Growth Factor Receptor (EGFR) pathway-related genes showed significantly differential expression at all time points. The EGFR pathway has been linked to diverse cellular events such as proliferation, differentiation, and apoptosis. Further, to evaluate the functional significance of the altered EGFR related gene expression observed in MPP⁺-treated SH-SY5Y cells, the EGFR related GJB2 (Cx26) gene expression was analyzed in an MPP⁺-intoxicated animal PD model. Our findings identify that the EGFR signaling pathway and its related genes, such as Cx26, might play a significant role in dopaminergic (DAergic) neuronal cell death during the process of neuro-apoptosis and therefore can be focused on as potential targets for therapeutic intervention.

Neurological and Motor Disorders: Neuronal Store-Operated Ca2+ Signaling: An Overview and Its Function

Calcium (Ca2+) is a ubiquitous second messenger that performs significant physiological task such as neurosecretion, exocytosis, neuronal growth/differentiation, and the development and/or maintenance of neural circuits. An important regulatory aspect of neuronal Ca2+ homeostasis is store-operated Ca2+ entry (SOCE) which, in recent years, has gained much attention for influencing a variety of nerve cell responses. Essentially, activation of SOCE ensues following the activation of the plasma membrane (PM) store-operated Ca2+ channels (SOCC) triggered by the depletion of endoplasmic reticulum (ER) Ca2+ stores. In addition to the TRPC (transient receptor potential canonical) and the Orai family of ion channels, STIM (stromal interacting molecule) proteins have been baptized as key molecular regulators of SOCE. Functional significance of the TRPC channels in neurons has been elaborately studied; however, information on Orai and STIM components of SOCE, although seems imminent, is currently limited. Importantly, perturbations in SOCE have been implicated in a spectrum of neuropathological conditions. Hence, understanding the precise involvement of SOCC in neurodegeneration would presumably unveil avenues for plausible therapeutic interventions. We thus review the role of SOCE-regulated neuronal Ca2+ signaling in selecting neurodegenerative conditions.

Mice lacking Faim2 show increased cell death in the MPTP mouse model of Parkinson disease

The death receptor Fas/CD95 mediates apoptotic cell death in response to external stimuli. In neurons, Fas-induced apoptosis is prevented by Fas-apoptotic inhibitory molecule 2 (Faim2). Mice lacking Faim2 showed increased neurodegeneration in animal models of stroke and bacterial meningitis. We therefore tested the relevance of Faim2 in a classical animal model of Parkinson disease and determined the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in Faim2-deficient mice. Without MPTP treatment, there was no difference in the dopaminergic system between Faim2-deficient mice and control mice. MPTP was applied i.p. in doses of 30 mg per kg on five consecutive days. Fourteen days after the last MPTP injection, the number of dopaminergic neurons in the lateral substantia nigra, assayed by stereological counting, was reduced by 39% in control mice and 53% in Faim2-deficient mice. The density of dopaminergic fibers in the dorsal striatum was reduced by 36% in control mice and 69% in Faim2-deficient mice, in the ventral striatum 44% in control mice and 76% in Faim2-deficient mice. Fiber density recovered at 90 days after MPTP with similar density in both groups. Striatal catecholamine levels were reduced by 81-84% in both groups and recovered at 90 days. Faim2 expression was documented in mouse midbrain using quantitative reverse transcription-PCR (qRT-PCR) and found decreased after MPTP administration. Taken together, our findings demonstrate increased degeneration of dopaminergic neurons with Faim2 deficiency, indicating that Fas-induced apoptosis contributes to cell death in the MPTP mouse model. Along with the decreased expression of Faim2 after MPTP, this finding indicates that boosting Faim2 function might represent a therapeutic strategy for Parkinson disease.

Tauroursodeoxycholic Acid Protects Against Mitochondrial Dysfunction and Cell Death via Mitophagy in Human Neuroblastoma Cells

Mitochondrial dysfunction has been deeply implicated in the pathogenesis of several neurodegenerative diseases. Thus, to keep a healthy mitochondrial population, a balanced mitochondrial turnover must be achieved. Tauroursodeoxycholic acid (TUDCA) is neuroprotective in various neurodegenerative disease models; however, the mechanisms involved are still incompletely characterized. In this study, we investigated the neuroprotective role of TUDCA against mitochondrial damage triggered by the mitochondrial uncoupler carbonyl cyanide m-chlorophelyhydrazone (CCCP). Herein, we show that TUDCA significantly prevents CCCP-induced cell death, ROS generation, and mitochondrial damage. Our results indicate that the neuroprotective role of TUDCA in this cell model is mediated by parkin and depends on mitophagy. The demonstration that pharmacological up-regulation of mitophagy by TUDCA prevents neurodegeneration provides new insights for the use of TUDCA as a modulator of mitochondrial activity and turnover, with implications in neurodegenerative diseases.

Mitochondrial dysfunction in Parkinson's disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease, which is characterized by loss of dopaminergic (DA) neurons in the substantia nigra pars compacta and the formation of Lewy bodies and Lewy neurites in surviving DA neurons in most cases. Although the cause of PD is still unclear, the remarkable advances have been made in understanding the possible causative mechanisms of PD pathogenesis. Numerous studies showed that dysfunction of mitochondria may play key roles in DA neuronal loss. Both genetic and environmental factors that are associated with PD contribute to mitochondrial dysfunction and PD pathogenesis. The induction of PD by neurotoxins that inhibit mitochondrial complex I provides direct evidence linking mitochondrial dysfunction to PD. Decrease of mitochondrial complex I activity is present in PD brain and in neurotoxin- or genetic factor-induced PD cellular and animal models. Moreover, PINK1 and parkin, two autosomal recessive PD gene products, have important roles in mitophagy, a cellular process to clear damaged mitochondria. PINK1 activates parkin to ubiquitinate outer mitochondrial membrane proteins to induce a selective degradation of damaged mitochondria by autophagy. In this review, we summarize the factors associated with PD and recent advances in understanding mitochondrial dysfunction in PD.

Protection of Primary Dopaminergic Midbrain Neurons by GPR139 Agonists Supports Different Mechanisms of MPP(+) and Rotenone Toxicity

The G-protein coupled receptor 139 (GPR139) is expressed specifically in the brain in areas of relevance for motor control. GPR139 function and signal transduction pathways are elusive, and results in the literature are even contradictory. Here, we examined the potential neuroprotective effect of GPR139 agonism in primary culture models of dopaminergic (DA) neuronal degeneration. We find that in vitro GPR139 agonists protected primary mesencephalic DA neurons against 1-methyl-4-phenylpyridinium (MPP(+))-mediated degeneration. Protection was concentration-dependent and could be blocked by a GPR139 antagonist. However, the protection of DA neurons was not found against rotenone or 6-hydroxydopamine (6-OHDA) mediated degeneration. Our results support differential mechanisms of toxicity for those substances commonly used in Parkinson's disease (PD) models and potential for GPR139 agonists in neuroprotection.

Neuroprotective and anti-inflammatory effects of morin in a murine model of Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders and is characterized by loss of dopaminergic neurons in the substantia nigra (SN). Although the causes of PD are not understood, evidence suggests that oxidative stress, mitochondrial dysfunction, and inflammation are associated with its pathogenesis. Morin (3,5,7,2',4'-pentahydroxyflavone) is a flavonol found in wine and many herbs and fruits. Previous studies have suggested that morin prevents oxidative damage and inflammation and ameliorates mitochondrial dysfunction. The present study describes the neuroprotective effects of morin in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD, and we report the results of our investigation into its neuroprotective mechanism in primary neurons and astrocytes. In the mouse model, morin pretreatment ameliorated motor dysfunction, protected against dopaminergic neuronal losses in SN and striatum, and alleviated MPTP-induced astrocyte activation. In vitro studies revealed that morin protected primary cultured neurons against 1-methyl-4-phenylpyridine (MPP(+) )-mediated reactive oxygen species production and mitochondrial membrane potential (MMP) disruption. In addition, morin effectively reduced MPP(+) -induced astroglial activation and nuclear translocation of nuclear factor-κB in primary cultured astrocytes. These results indicate that morin acts via multiple neuroprotective mechanisms in our mouse model and suggest that morin be viewed as a potential treatment and preventative for PD. © 2016 Wiley Periodicals, Inc.

Mitoapocynin Treatment Protects Against Neuroinflammation and Dopaminergic Neurodegeneration in a Preclinical Animal Model of Parkinson's Disease

Mitochondrial dysfunction, oxidative stress and neuroinflammation have been implicated as key mediators contributing to the progressive degeneration of dopaminergic neurons in Parkinson's disease (PD). Currently, we lack a pharmacological agent that can intervene in all key pathological mechanisms, which would offer better neuroprotective efficacy than a compound that targets a single degenerative mechanism. Herein, we investigated whether mito-apocynin (Mito-Apo), a newly-synthesized and orally available derivative of apocynin that targets mitochondria, protects against oxidative damage, glial-mediated inflammation and nigrostriatal neurodegeneration in cellular and animal models of PD. Mito-Apo treatment in primary mesencephalic cultures significantly attenuated the 1-methyl-4-phenylpyridinium (MPP(+))-induced loss of tyrosine hydroxylase (TH)-positive neuronal cells and neurites. Mito-Apo also diminished MPP(+)-induced increases in glial cell activation and inducible nitric oxide synthase (iNOS) expression. Additionally, Mito-Apo decreased nitrotyrosine (3-NT) and 4-hydroxynonenol (4-HNE) levels in primary mesencephalic cultures. Importantly, we assessed the neuroprotective property of Mito-Apo in the MPTP mouse model of PD, wherein it restored the behavioral performance of MPTP-treated mice. Immunohistological analysis of nigral dopaminergic neurons and monoamine measurement further confirmed the neuroprotective effect of Mito-Apo against MPTP-induced nigrostriatal dopaminergic neuronal loss. Mito-Apo showed excellent brain bioavailability and also markedly attenuated MPTP-induced oxidative markers in the substantia nigra (SN). Furthermore, oral administration of Mito-Apo significantly suppressed MPTP-induced glial cell activation, upregulation of proinflammatory cytokines, iNOS and gp91phox in IBA1-positive cells of SN. Collectively, these results demonstrate that the novel mitochondria-targeted compound Mito-Apo exhibits profound neuroprotective effects in cellular and pre-clinical animal models of PD by attenuating oxidative damage and neuroinflammatory processes.

Protein kinase Cδ upregulation in microglia drives neuroinflammatory responses and dopaminergic neurodegeneration in experimental models of Parkinson's disease

Chronic microglial activation has been linked to the progressive degeneration of the nigrostriatal dopaminergic neurons evidenced in Parkinson's disease (PD) pathogenesis. The exact etiology of PD remains poorly understood. Although both oxidative stress and neuroinflammation are identified as co-contributors in PD pathogenesis, signaling mechanisms underlying neurodegenerative processes have yet to be defined. Indeed, we recently identified that protein kinase C delta (PKCδ) activation is critical for induction of dopaminergic neuronal loss in response to neurotoxic stressors. However, it remains to be defined whether PKCδ activation contributes to immune signaling events driving microglial neurotoxicity. In the present study, we systematically investigated whether PKCδ contributes to the heightened microglial activation response following exposure to major proinflammatory stressors, including α-synuclein, tumor necrosis factor α (TNFα), and lipopolysaccharide (LPS). We report that exposure to the aforementioned inflammatory stressors dramatically upregulated PKCδ with a concomitant increase in its kinase activity and nuclear translocation in both BV-2 microglial cells and primary microglia. Importantly, we also observed a marked upregulation of PKCδ in the microglia of the ventral midbrain region of PD patients when compared to age-matched controls, suggesting a role for microglial PKCδ in neurodegenerative processes. Further, shRNA-mediated knockdown and genetic ablation of PKCδ in primary microglia blunted the microglial proinflammatory response elicited by the inflammogens, including ROS generation, nitric oxide production, and proinflammatory cytokine and chemokine release. Importantly, we found that PKCδ activated NFκB, a key mediator of inflammatory signaling events, after challenge with inflammatory stressors, and that transactivation of NFκB led to translocation of the p65 subunit to the nucleus, IκBα degradation and phosphorylation of p65 at Ser536. Furthermore, both genetic ablation and siRNA-mediated knockdown of PKCδ attenuated NFκB activation, suggesting that PKCδ regulates NFκB activation subsequent to microglial exposure to inflammatory stimuli. To further investigate the pivotal role of PKCδ in microglial activation in vivo, we utilized pre-clinical models of PD. We found that PKCδ deficiency attenuated the proinflammatory response in the mouse substantia nigra, reduced locomotor deficits and recovered mice from sickness behavior in an LPS-induced neuroinflammation model of PD. Likewise, we found that PKCδ knockout mice treated with MPTP displayed a dampened microglial inflammatory response. Moreover, PKCδ knockout mice exhibited reduced susceptibility to the neurotoxin-induced dopaminergic neurodegeneration and associated motor impairments. Taken together, our studies propose a pivotal role for PKCδ in PD pathology, whereby sustained PKCδ activation drives sustained microglial inflammatory responses and concomitant dopaminergic neurotoxicity consequently leading to neurobehavioral deficits. We conclude that inhibiting PKCδ activation may represent a novel therapeutic strategy in PD treatment.

Quantification of the Metabolic State in Cell-Model of Parkinson's Disease by Fluorescence Lifetime Imaging Microscopy

Intracellular endogenous fluorescent co-enzymes, reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD), play a pivotal role in cellular metabolism; quantitative assessment of their presence in living cells can be exploited to monitor cellular energetics in Parkinson's disease (PD), a neurodegenerative disorder. Here, we applied two-photon fluorescence lifetime imaging microscopy (2P-FLIM) to noninvasively measure the fluorescence lifetime components of NADH and FAD, and their relative contributions in MPP(+) (1-methyl-4-phenylpyridinium) treated neuronal cells, derived from PC12 cells treated with nerve growth factor (NGF), to mimic PD conditions. A systematic FLIM data analysis showed a statistically significant (p < 0.001) decrease in the fluorescence lifetime of both free and protein-bound NADH, as well as free and protein-bound FAD in MPP(+) treated cells. On the relative contributions of the free and protein-bound NADH and FAD to the life time, however, both the free NADH contribution and the corresponding protein-bound FAD contribution increase significantly (p < 0.001) in MPP(+) treated cells, compared to control cells. These results, which indicate a shift in energy production in the MPP(+) treated cells from oxidative phosphorylation towards anaerobic glycolysis, can potentially be used as cellular metabolic metrics to assess the condition of PD at the cellular level.

Protective Mechanisms of Flavonoids in Parkinson's Disease

Parkinson's disease is a chronic, debilitating neurodegenerative movement disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta region in human midbrain. To date, oxidative stress is the well accepted concept in the etiology and progression of Parkinson's disease. Hence, the therapeutic agent is targeted against suppressing and alleviating the oxidative stress-induced cellular damage. Within the past decades, an explosion of research discoveries has reported on the protective mechanisms of flavonoids, which are plant-based polyphenols, in the treatment of neurodegenerative disease using both in vitro and in vivo models. In this paper, we have reviewed the literature on the neuroprotective mechanisms of flavonoids in protecting the dopaminergic neurons hence reducing the symptoms of this movement disorder. The mechanism reviewed includes effect of flavonoids in activation of endogenous antioxidant enzymes, suppressing the lipid peroxidation, inhibition of inflammatory mediators, flavonoids as a mitochondrial target therapy, and modulation of gene expression in neuronal cells.

Fyn Kinase Regulates Microglial Neuroinflammatory Responses in Cell Culture and Animal Models of Parkinson's Disease

Sustained neuroinflammation mediated by resident microglia is recognized as a key pathophysiological contributor to many neurodegenerative diseases, including Parkinson's disease (PD), but the key molecular signaling events regulating persistent microglial activation have yet to be clearly defined. In the present study, we examined the role of Fyn, a non-receptor tyrosine kinase, in microglial activation and neuroinflammatory mechanisms in cell culture and animal models of PD. The well-characterized inflammogens LPS and TNFα rapidly activated Fyn kinase in microglia. Immunocytochemical studies revealed that activated Fyn preferentially localized to the microglial plasma membrane periphery and the nucleus. Furthermore, activated Fyn phosphorylated PKCδ at tyrosine residue 311, contributing to an inflammogen-induced increase in its kinase activity. Notably, the Fyn-PKCδ signaling axis further activated the LPS- and TNFα-induced MAP kinase phosphorylation and activation of the NFκB pathway, implying that Fyn is a major upstream regulator of proinflammatory signaling. Functional studies in microglia isolated from wild-type (Fyn(+/+)) and Fyn knock-out (Fyn(-/-)) mice revealed that Fyn is required for proinflammatory responses, including cytokine release as well as iNOS activation. Interestingly, a prolonged inflammatory insult induced Fyn transcript and protein expression, indicating that Fyn is upregulated during chronic inflammatory conditions. Importantly, in vivo studies using MPTP, LPS, or 6-OHDA models revealed a greater attenuation of neuroinflammatory responses in Fyn(-/-) and PKCδ (-/-) mice compared with wild-type mice. Collectively, our data demonstrate that Fyn is a major upstream signaling mediator of microglial neuroinflammatory processes in PD.

SIGNIFICANCE STATEMENT

Parkinson's disease (PD) is a complex multifactorial disease characterized by the progressive loss of midbrain dopamine neurons. Sustained microglia-mediated neuroinflammation has been recognized as a major pathophysiological contributor to chronic degenerative processes in PD; however, the key molecular signaling mechanisms underlying microglial activation are not entirely clear. Herein, we identified a novel role for the non-receptor tyrosine kinase Fyn in regulating neuroinflammatory responses in microglia. Our data clearly suggest that the Fyn-PKCδ signaling axis acts as a major upstream signaling mediator of the sustained neuroinflammatory processes in cell culture and animal models of PD. Our finding has important clinical significance to PD because it identifies Fyn as a potential translational target for intervention of progressive neurodegenerative processes in PD.

Nuclear Translocation of Calcium/Calmodulin-dependent Protein Kinase IIδ3 Promoted by Protein Phosphatase-1 Enhances Brain-derived Neurotrophic Factor Expression in Dopaminergic Neurons

We have reported previously that dopamine D2 receptor stimulation activates calcium/calmodulin-dependent protein kinase II (CaMKII) δ3, a CaMKII nuclear isoform, increasing BDNF gene expression. However, the mechanisms underlying that activity remained unclear. Here we report that CaMKIIδ3 is dephosphorylated at Ser(332) by protein phosphatase 1 (PP1), promoting CaMKIIδ3 nuclear translocation. Neuro-2a cells transfected with CaMKIIδ3 showed cytoplasmic and nuclear staining, but the staining was predominantly nuclear when CaMKIIδ3 was coexpressed with PP1. Indeed, PP1 and CaMKIIδ3 coexpression significantly increased nuclear CaMKII activity and enhanced BDNF expression. In support of this idea, chronic administration of the dopamine D2 receptor partial agonist aripiprazole increased PP1 activity and promoted nuclear CaMKIIδ3 translocation and BDNF expression in the rat brain substantia nigra. Moreover, aripiprazole treatment enhanced neurite extension and inhibited cell death in cultured dopaminergic neurons, effects blocked by PP1γ knockdown. Taken together, nuclear translocation of CaMKIIδ3 following dephosphorylation at Ser(332) by PP1 likely accounts for BDNF expression and subsequent neurite extension and survival of dopaminergic neurons.

Targeted Overexpression of α-Synuclein by rAAV2/1 Vectors Induces Progressive Nigrostriatal Degeneration and Increases Vulnerability to MPTP in Mouse

Mutations, duplication and triplication of α-synuclein genes are linked to familial Parkinson's disease (PD), and aggregation of α-synuclein (α-syn) in Lewy bodies (LB) is involved in the pathogenesis of the disease. The targeted overexpression of α-syn in the substantia nigra (SN) mediated by viral vectors may provide a better alternative to recapitulate the neurodegenerative features of PD. Therefore, we overexpressed human wild-type α-syn using rAAV2/1 vectors in the bilateral SN of mouse and examined the effects for up to 12 weeks. Delivery of rAAV-2/1-α-syn caused significant nigrostriatal degeneration including appearance of dystrophic striatal neurites, loss of nigral dopaminergic (DA) neurons and dissolving nigral neuron bodies in a time-dependent manner. In addition, the α-syn overexpressed mice also developed significant deficits in motor function at 12 weeks when the loss of DA neurons exceeded a threshold of 50%. To investigate the sensitivity to neurotoxins in mice overexpressing α-syn, we performed an MPTP treatment with the subacute regimen 8 weeks after rAAV injection. The impact of the combined genetic and environmental insults on DA neuronal loss, striatal dopamine depletion, dopamine turnover and motor dysfunction was markedly greater than that of either alone. Moreover, we observed increased phosphorylation (S129), accumulation and nuclear distribution of α-syn after the combined insults. In summary, these results reveal that the overexpressed α-syn induces progressive nigrostriatal degeneration and increases the susceptibility of DA neurons to MPTP. Therefore, the targeted overexpression of α-syn and the combination with environmental toxins may provide valuable models for understanding PD pathogenesis and developing related therapies.

Evidence for a common biological pathway linking three Parkinson's disease-causing genes: parkin, PINK1 and DJ-1

Parkinson's disease (PD) is characterised by the loss of dopaminergic neurons in the midbrain. Autosomal recessive, early-onset cases of PD are predominantly caused by mutations in the parkin, PINK1 and DJ-1 genes. Animal and cellular models have verified a direct link between parkin and PINK1, whereby PINK1 phosphorylates and activates parkin at the outer mitochondrial membrane, resulting in removal of dysfunctional mitochondria via mitophagy. Despite the overwhelming evidence for this interaction, few studies have been able to identify a link for DJ-1 with parkin or PINK1. The aim of this review is to summarise the functions of these three proteins, and to analyse the existing evidence for direct and indirect interactions between them. DJ-1 is able to rescue the phenotype of PINK1-knockout Drosophila models, but not of parkin-knockouts, suggesting that DJ-1 may act in a parallel pathway to that of the PINK1/parkin pathway. To further elucidate a commonality between these three proteins, bioinformatics analysis established that Miro (RHOT1) interacts with parkin and PINK1, and HSPA4 interacts with all three proteins. Furthermore, 30 transcription factors were found to be common amongst all three proteins, with many of them being involved in transcriptional regulation. Interestingly, expression of these proteins and their associated transcription factors are found to be significantly down-regulated in PD patients compared to healthy controls. In summary, this review provides insight into common pathways linking three PD-causing genes and highlights some key questions, the answers to which may provide critical insight into the disease process.

Neurotoxicity of cerebro-spinal fluid from patients with Parkinson's disease on mesencephalic primary cultures as an in vitro model of dopaminergic neurons

Parkinson's disease is a degenerative disorder of the central nervous system. In spite of extensive research, neither the cause nor the mechanisms have been firmly established thus far. One assumption is that certain toxic substances may exist in the cerebro-spinal fluid (CSF) of Parkinson's disease patients. To confirm the neurotoxicity of CSF and study the potential correlation between neurotoxicity and the severity of Parkinson's disease, CSF was added to cultured cells. By observation of cell morphology, changes in the levels of lactate dehydrogenase, the ratio of tyrosine hydroxylase-positive cells, and the expression of tyrosine hydroxylase mRNA and protein, the differences between the two groups were shown. The created in vitro model of dopaminergic neurons using primary culture of mouse embryonic mesencephalic tissue is suitable for the study of neurotoxicity. The observations of the present study indicated that CSF from Parkinson's disease patients contains factors that can cause specific injury to cultured dopaminergic neurons. However, no obvious correlation was found between the neurotoxicity of CSF and the severity of Parkinson's disease.

Rotenone exerts similar stimulatory effects on H2O2 production by isolated brain mitochondria from young-adult and old rats

Chronic and systemic treatment of rodents with rotenone, a classical inhibitor of mitochondrial respiratory complex I, results in neurochemical, behavioral, and neuropathological features of Parkinson's disease. The aim of the present study was to evaluate whether brain mitochondria from old rats (24 months old) would be more susceptible to rotenone-induced inhibition of oxygen consumption and increased generation of H2O2 than mitochondria from young-adult rats (3-4 months old). Isolated brain mitochondria were incubated in the presence of different rotenone concentrations (5, 10, and 100nM), and oxygen consumption and H2O2 production were measured during respiratory states 3 (ADP-stimulated respiration) and 4 (resting respiration). Respiratory state 3 and citrate synthase activity were significantly lower in mitochondria from old rats. Mitochondria from young-adult and old rats showed similar sensitivity to rotenone-induced inhibition of oxygen consumption. Similarly, H2O2 production rates by both types of mitochondria were dose-dependently stimulated to the same extent by increasing concentrations of rotenone. We conclude that rotenone exerts similar effects on oxygen consumption and H2O2 production by isolated brain mitochondria from young-adult and old rats. Therefore, aging does not increase the mitochondrial H2O2 generation in response to complex I inhibition.

Da-bu-yin-wan and qian-zheng-san to neuroprotect the mouse model of Parkinson's disease

Da-Bu-Yin-Wan (DBYW) and Qian-Zheng-San (QZS), two classic traditional Chinese medicinal formulas, were clinically employed to treat Parkinson's disease (PD). Our previous studies demonstrated neuroprotective effects of them on mitochondrial function in PD mice induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The purpose of this research was to investigate their possible mechanisms in the light of mitochondrial ATP-sensitive potassium (mitoK_ATP) channels. The neuroprotective effect of DBYW and QZS on dopamine (DA) neurons in substantia nigra (SN) in the MPTP-induced PD mice was investigated by behavioral test (pole test) and immunohistochemistry. Adenosine triphosphate (ATP) level in the midbrain tissue was detected by firefly luciferase method. MitoK_ATP channel subunits SUR1 and Kir6.2 mRNA and protein expressions were tested by real-time PCR (RT-PCR) and Western blot. It was observed that DBYW and/or QZS served to ameliorate MPTP-induced behavioral impairment and prevent the loss of substantia nigra dopamine neurons, as well as increase ATP level in the midbrain tissue and downregulate SUR1 expression at mRNA and protein levels with no marked influence on Kir6.2. We concluded that DBYW and QZS exhibit neuroprotective effects probably through the regulation of ATP level and mitoK_ATP channel subunit expressions.

Mutual exacerbation of peroxisome proliferator-activated receptor γ coactivator 1α deregulation and α-synuclein oligomerization

OBJECTIVE

Aggregation of α-synuclein (α-syn) and α-syn cytotoxicity are hallmarks of sporadic and familial Parkinson disease (PD), with accumulating evidence that prefibrillar oligomers and protofibrils are the pathogenic species in PD and related synucleinopathies. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a key regulator of mitochondrial biogenesis and cellular energy metabolism, has recently been associated with the pathophysiology of PD. Despite extensive effort on studying the function of PGC-1α in mitochondria, no studies have addressed whether PGC-1α directly influences oligomerization of α-syn or whether α-syn oligomers impact PGC-1α expression.

MATERIALS AND METHODS

We tested whether pharmacological or genetic activation of PGC-1α or PGC-11α knockdown could modulate the oligomerization of α-syn in vitro by using an α-syn -fragment complementation assay.

RESULTS

In this study, we found that both PGC-1α reference gene (RG-PGC-1α) and the central nervous system (CNS)-specific PGC-1α (CNS-PGC-1α) are downregulated in human PD brain, in A30P α-syn transgenic animals, and in a cell culture model for α-syn oligomerization. Importantly, downregulation of both RG-PGC-1α and CNS-PGC-1α in cell culture or neurons from RG-PGC-1α-deficient mice leads to a strong induction of α-syn oligomerization and toxicity. In contrast, pharmacological activation or genetic overexpression of RG-PGC-1α reduced α-syn oligomerization and rescued α-syn-mediated toxicity.

INTERPRETATION

Based on our results, we propose that PGC-1α downregulation and α-syn oligomerization form a vicious circle, thereby influencing and/or potentiating each other. Our data indicate that restoration of PGC-1α is a promising approach for development of effective drugs for the treatment of PD and related synucleinopathies.

Cucurbitacin E has neuroprotective properties and autophagic modulating activities on dopaminergic neurons

Natural molecules are under intensive study for their potential as preventive and/or adjuvant therapies for neurodegenerative disorders such as Parkinson's disease (PD). We evaluated the neuroprotective potential of cucurbitacin E (CuE), a tetracyclic triterpenoid phytosterol extracted from the Ecballium elaterium (Cucurbitaceae), using a known cellular model of PD, NGF-differentiated PC12. In our postmitotic experimental paradigm, neuronal cells were treated with the parkinsonian toxin 1-methyl-4-phenylpyridinium (MPP⁺) to provoke significant cellular damage and apoptosis or with the potent N,N-diethyldithiocarbamate (DDC) to induce superoxide (O₂^•−) production, and CuE was administered prior to and during the neurotoxic treatment. We measured cellular death and reactive oxygen species to evaluate the antioxidant and antiapoptotic properties of CuE. In addition, we analyzed cellular macroautophagy, a bulk degradation process involving the lysosomal pathway. CuE showed neuroprotective effects on MPP⁺-induced cell death. However, CuE failed to rescue neuronal cells from oxidative stress induced by MPP⁺ or DDC. Microscopy and western blot data show an intriguing involvement of CuE in maintaining lysosomal distribution and decreasing autophagy flux. Altogether, these data indicate that CuE decreases neuronal death and autophagic flux in a postmitotic cellular model of PD.

Resveratrol attenuates oxidative stress and improves behaviour in 1 -methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) challenged mice

Background

Parkinson's disease (PD) is the most common neurodegenerative disorder, characterized by loss of dopaminergic neurons in substantia nigra and depletion of dopamine in striatum due to mitochondrial dysfunction, oxidative stress, excitotoxicity, apoptosis, inflammation and proteasome failure.

Purpose

The present study deals with the neuroprotective effect of resveratrol, a wine polyphenol (50 mg/kg body weight) against MPTP (30mg/kg body weight as i.p. administration) induced mice model of idiopathic Parkinson's disease.

Methods

A combination of behaviour tasks and biochemical parameters were tested using standard molecular tools.

Results

Pretreatment of resveratrol significantly reversed toxic effects of MPTP by increasing the levels of dopamine, its metabolites, GSH and activities of GPx and reducing levels of TBARS, catalase and SOD activities along with enhanced behavior performance.

Conclusion

The multifactorial etiology of these diseases suggests that drugs with multiple targets such as resveratrol could have therapeutic potential for these pathologies.

Mitophagy of damaged mitochondria occurs locally in distal neuronal axons and requires PINK1 and Parkin

The Parkinson’s disease–associated proteins PINK1 and Parkin mediate local mitophagy of dysfunctional mitochondria in distal neuronal axons, abrogating the need for retrograde organelle transport and ensuring rapid neuroprotection.

To minimize oxidative damage to the cell, malfunctioning mitochondria need to be removed by mitophagy. In neuronal axons, mitochondrial damage may occur in distal regions, far from the soma where most lysosomal degradation is thought to occur. In this paper, we report that PINK1 and Parkin, two Parkinson’s disease–associated proteins, mediate local mitophagy of dysfunctional mitochondria in neuronal axons. To reduce cytotoxicity and mimic physiological levels of mitochondrial damage, we selectively damaged a subset of mitochondria in hippocampal axons. Parkin was rapidly recruited to damaged mitochondria in axons followed by formation of LC3-positive autophagosomes and LAMP1-positive lysosomes. In PINK1^−/− axons, damaged mitochondria did not accumulate Parkin and failed to be engulfed in autophagosomes. Similarly, initiation of mitophagy was blocked in Parkin^−/− axons. Our findings demonstrate that the PINK1–Parkin-mediated pathway is required for local mitophagy in distal axons in response to focal damage. Local mitophagy likely provides rapid neuroprotection against oxidative stress without a requirement for retrograde transport to the soma.

Role of aldehyde dehydrogenase 2 in 1-methy-4-phenylpyridinium ion-induced aldehyde stress and cytotoxicity in PC12 cells

Aldehyde stress contributes to molecular mechanisms of cell death and the pathogenesis of Parkinson's disease (PD). The neurotoxin 1-Methy-4-Phenylpyridinium Ion (MPP(+)) is commonly used to model PD. Aldehyde dehydrogenase 2 (ALDH2) is an important enzyme detoxifying aldehydes. The aim of this study is to evaluate whether MPP(+)-induced neurotoxicity is involved in aldehyde stress by modulation of ALDH2. Our results demonstrated that treatment of PC12 cells with MPP(+) leads to aldehyde stress by increasing in loads of malondialdehyde and 4-hydroxynonenal, which indicated that MPP(+)-induced aldehyde stress contributes to its cytotoxicity in PC12 cells. We also showed that MPP(+) up-regulates the expression and activity of ALDH2 in PC12 cells and that inhibition of ALDH2 by its specific inhibitor daidzin prevents MPP(+)-induced decrease in cell viability and increases in apoptosis, oxidative stress and aldehyde stress in PC12 cells. These findings suggest that aldehyde stress contributes to MPP(+)-induced toxicity in PC12 cells by upregulation of ALDH2. This study provides a novel insight into the role of ALDH2 in the neurotoxicity of MPP(+).

The high-affinity D2/D3 agonist D512 protects PC12 cells from 6-OHDA-induced apoptotic cell death and rescues dopaminergic neurons in the MPTP mouse model of Parkinson's disease

In this study, in vitro and in vivo experiments were carried out with the high-affinity multifunctional D2/D3 agonist D-512 to explore its potential neuroprotective effects in models of Parkinson's disease and the potential mechanism(s) underlying such properties. Pre-treatment with D-512 in vitro was found to rescue rat adrenal Pheochromocytoma PC12 cells from toxicity induced by 6-hydroxydopamine administration in a dose-dependent manner. Neuroprotection was found to coincide with reductions in intracellular reactive oxygen species, lipid peroxidation, and DNA damage. In vivo, pre-treatment with 0.5 mg/kg D-512 was protective against neurodegenerative phenotypes associated with systemic administration of MPTP, including losses in striatal dopamine, reductions in numbers of DAergic neurons in the substantia nigra (SN), and locomotor dysfunction. These observations strongly suggest that the multifunctional drug D-512 may constitute a novel viable therapy for Parkinson's disease.

Upstream deregulation of calcium signaling in Parkinson's disease

Parkinson’s disease (PD) is a major health problem affecting millions of people worldwide. Recent studies provide compelling evidence that altered Ca²⁺ homeostasis may underlie disease pathomechanism and be an inherent feature of all vulnerable neurons. The downstream effects of altered Ca²⁺ handling in the distinct subcellular organelles for proper cellular function are beginning to be elucidated. Here, we summarize the evidence that vulnerable neurons may be exposed to homeostatic Ca²⁺ stress which may determine their selective vulnerability, and suggest how abnormal Ca²⁺ handling in the distinct intracellular compartments may compromise neuronal health in the context of aging, environmental, and genetic stress. Gaining a better understanding of the varied effects of Ca²⁺ dyshomeostasis may allow novel combinatorial therapeutic strategies to slow PD progression.

Animal models of neurodegenerative diseases

The prevalence of neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), increases with age, and the number of affected patients is expected to increase worldwide in the next decades. Accurately understanding the etiopathogenic mechanisms of these diseases is a crucial step for developing disease-modifying drugs able to preclude their emergence or at least slow their progression. Animal models contribute to increase the knowledge on the pathophysiology of neurodegenerative diseases. These models reproduce different aspects of a given disease, as well as the histopathological lesions and its main symptoms. The purpose of this review is to present the main animal models for AD, PD, and Huntington's disease.

Advances in non-dopaminergic treatments for Parkinson's disease

Since the 1960's treatments for Parkinson's disease (PD) have traditionally been directed to restore or replace dopamine, with L-Dopa being the gold standard. However, chronic L-Dopa use is associated with debilitating dyskinesias, limiting its effectiveness. This has resulted in extensive efforts to develop new therapies that work in ways other than restoring or replacing dopamine. Here we describe newly emerging non-dopaminergic therapeutic strategies for PD, including drugs targeting adenosine, glutamate, adrenergic, and serotonin receptors, as well as GLP-1 agonists, calcium channel blockers, iron chelators, anti-inflammatories, neurotrophic factors, and gene therapies. We provide a detailed account of their success in animal models and their translation to human clinical trials. We then consider how advances in understanding the mechanisms of PD, genetics, the possibility that PD may consist of multiple disease states, understanding of the etiology of PD in non-dopaminergic regions as well as advances in clinical trial design will be essential for ongoing advances. We conclude that despite the challenges ahead, patients have much cause for optimism that novel therapeutics that offer better disease management and/or which slow disease progression are inevitable.

Physiological Function and Characterization of TRPCs in Neurons

Ca²⁺ entry is essential for regulating vital physiological functions in all neuronal cells. Although neurons are engaged in multiple modes of Ca²⁺ entry that regulates variety of neuronal functions, we will only discuss a subset of specialized Ca²⁺-permeable non-selective Transient Receptor Potential Canonical (TRPC) channels and summarize their physiological and pathological role in these excitable cells. Depletion of endoplasmic reticulum (ER) Ca²⁺ stores, due to G-protein coupled receptor activation, has been shown to activate TRPC channels in both excitable and non-excitable cells. While all seven members of TRPC channels are predominately expressed in neuronal cells, the ion channel properties, mode of activation, and their physiological responses are quite distinct. Moreover, many of these TRPC channels have also been suggested to be associated with neuronal development, proliferation and differentiation. In addition, TRPCs also regulate neurosecretion, long-term potentiation and synaptic plasticity. Similarly, perturbations in Ca²⁺ entry via the TRPC channels have been also suggested in a spectrum of neuropathological conditions. Hence, understanding the precise involvement of TRPCs in neuronal function and in neurodegenerative conditions would presumably unveil avenues for plausible therapeutic interventions for these devastating neuronal diseases.

Progranulin gene delivery protects dopaminergic neurons in a mouse model of Parkinson's disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by tremor, rigidity and akinesia/bradykinesia resulting from the progressive loss of nigrostriatal dopaminergic neurons. To date, only symptomatic treatment is available for PD patients, with no effective means of slowing or stopping the progression of the disease. Progranulin (PGRN) is a 593 amino acid multifunction protein that is widely distributed throughout the CNS, localized primarily in neurons and microglia. PGRN has been demonstrated to be a potent regulator of neuroinflammation and also acts as an autocrine neurotrophic factor, important for long-term neuronal survival. Thus, enhancing PGRN expression may strengthen the cells resistance to disease. In the present study, we have used the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD to investigate the possible use of PGRN gene delivery as a therapy for the prevention or treatment of PD. Viral vector delivery of the PGRN gene was an effective means of elevating PGRN expression in nigrostriatal neurons. When PGRN expression was elevated in the SN_C, nigrostriatal neurons were protected from MPTP toxicity in mice, along with a preservation of striatal dopamine content and turnover. Further, protection of nigrostriatal neurons by PGRN gene therapy was accompanied by reductions in markers of MPTP-induced inflammation and apoptosis as well as a complete preservation of locomotor function. We conclude that PGRN gene therapy may have beneficial effects in the treatment of PD.

Olfaction in three genetic and two MPTP-induced Parkinson's disease mouse models

Various genetic or toxin-induced mouse models are frequently used for investigation of early PD pathology. Although olfactory impairment is known to precede motor symptoms by years, it is not known whether it is caused by impairments in the brain, the olfactory epithelium, or both. In this study, we investigated the olfactory function in three genetic Parkinson’s disease (PD) mouse models and mice treated with MPTP intraperitoneally and intranasally. To investigate olfactory function, we performed electro-olfactogram recordings (EOGs) and an olfactory behavior test (cookie-finding test). We show that neither a parkin knockout mouse strain, nor intraperitoneal MPTP treated animals display any olfactory impairment in EOG recordings and the applied behavior test. We also found no difference in the responses of the olfactory epithelium to odorants in a mouse strain over-expressing doubly mutated α-synuclein, while this mouse strain was not suitable to test olfaction in a cookie-finding test as it displays a mobility impairment. A transgenic mouse expressing mutated α-synuclein in dopaminergic neurons performed equal to control animals in the cookie-finding test. Further we show that intranasal MPTP application can cause functional damage of the olfactory epithelium.

Accumulation of mitochondrial DNA deletions within dopaminergic neurons triggers neuroprotective mechanisms

Acquired alterations in mitochondrial DNA are believed to play a pathogenic role in Parkinson's disease. In particular, accumulation of mitochondrial DNA deletions has been observed in substantia nigra pars compacta dopaminergic neurons from patients with Parkinson's disease and aged individuals. Also, mutations in mitochondrial DNA polymerase gamma result in multiple mitochondrial DNA deletions that can be associated with levodopa-responsive parkinsonism and severe substantia nigra pars compacta dopaminergic neurodegeneration. However, whether mitochondrial DNA deletions play a causative role in the demise of dopaminergic neurons remains unknown. Here we assessed the potential pathogenic effects of mitochondrial DNA deletions on the dopaminergic nigrostriatal system by using mutant mice possessing a proofreading-deficient form of mitochondrial DNA polymerase gamma (POLGD257A), which results in a time-dependent accumulation of mitochondrial DNA deletions in several tissues, including the brain. In these animals, we assessed the occurrence of mitochondrial DNA deletions within individual substantia nigra pars compacta dopaminergic neurons, by laser capture microdissection and quantitative real-time polymerase chain reaction, and determined the potential deleterious effects of such mitochondrial DNA alterations on mitochondrial function and dopaminergic neuronal integrity, by cytochrome c oxidase histochemistry and quantitative morphology. Nigral dopaminergic neurons from POLGD257A mice accumulate mitochondrial DNA deletions to a similar extent (∼40-60%) as patients with Parkinson's disease and aged individuals. Despite such high levels of mitochondrial DNA deletions, the majority of substantia nigra pars compacta dopaminergic neurons from these animals did not exhibit mitochondrial dysfunction or degeneration. Only a few individual substantia nigra pars compacta neurons appeared as cytochrome c oxidase-negative, which exhibited higher levels of mitochondrial DNA deletions than cytochrome c oxidase-positive cells (60.38±3.92% versus 45.18±2.83%). Survival of dopaminergic neurons in POLGD257A mice was associated with increased mitochondrial DNA copy number, enhanced mitochondrial cristae network, improved mitochondrial respiration, decreased exacerbation of mitochondria-derived reactive oxygen species, greater striatal dopamine levels and resistance to parkinsonian mitochondrial neurotoxins. These results indicate that primary accumulation of mitochondrial DNA deletions within substantia nigra pars compacta dopaminergic neurons, at an extent similar to that observed in patients with Parkinson's disease, do not kill dopaminergic neurons but trigger neuroprotective compensatory mechanisms at a mitochondrial level that may account for the high pathogenic threshold of mitochondrial DNA deletions in these cells.

Mitochondrial abnormality associates with type-specific neuronal loss and cell morphology changes in the pedunculopontine nucleus in Parkinson disease

Cholinergic neuronal loss in the pedunculopontine nucleus (PPN) associates with abnormal functions, including certain motor and nonmotor symptoms. This realization has led to low-frequency stimulation of the PPN for treating patients with Parkinson disease (PD) who are refractory to other treatment modalities. However, the molecular mechanisms underlying PPN neuronal loss and the therapeutic substrate for the clinical benefits following PPN stimulation remain poorly characterized, hampering progress toward designing more efficient therapies aimed at restoring the PPN's normal functions during progressive parkinsonism. Here, we investigated postmortem pathological changes in the PPN of PD cases. Our study detected a loss of neurons producing gamma-aminobutyric acid (GABA) as their output and glycinergic neurons, along with the pronounced loss of cholinergic neurons. These losses were accompanied by altered somatic cell size that affected the remaining neurons of all neuronal subtypes studied here. Because studies showed that mitochondrial dysfunction exists in sporadic PD and in PD animal models, we investigated whether altered mitochondrial composition exists in the PPN. A significant up-regulation of several mitochondrial proteins was seen in GABAergic and glycinergic neurons; however, cholinergic neurons indicated down-regulation of the same proteins. Our findings suggest an imbalance in the activity of key neuronal subgroups of the PPN in PD, potentially because of abnormal inhibitory activity and altered cholinergic outflow.

Sleep disturbances in Parkinson's disease: the contribution of dopamine in REM sleep regulation

Nearly all patients with Parkinson's disease (PD) have sleep disturbances. While it has been suggested that these disturbances involve a dopaminergic component, the specific mechanisms that contribute to this behavior are far from being fully understood. In this article, we have reviewed the current understanding of the linkage between sleep and PD, focusing on the participation of the dopaminergic system in the regulation of rapid eye movement (REM) sleep. The presence of an REM sleep behavior disorder in patients with PD might reflect the early involvement of dopaminergic neurotransmission in REM sleep-related structures. Therefore, it has been suggested that these structures are affected by an imbalance of dopamine levels. Several studies have demonstrated that neurons in the substantia nigra pars compacta (SNpc) and in the ventral tegmental area (VTA) are active during REM sleep and that sleep-related disturbances may result when these neurons are targeted by neurotoxins. We discuss current evidence suggesting the presence of a putative reciprocal connectivity between the SNpc, VTA, the pedunculopontine tegmental nucleus and reticular formation, which may exert an important influence on the REM sleep mechanism. This review provides a comprehensive overview of the literature that addresses this challenging and unrecognized component of PD.

Geraniol ameliorates the motor behavior and neurotrophic factors inadequacy in MPTP-induced mice model of Parkinson's disease

Many experiments affirm the notion that augmentation of neurotrophic factors (NTFs) activity, especially brain-derived neurotrophic factors and glial cell-derived neurotrophic factors, could prevent or halt the progress of neurodegeneration in Parkinson's disease (PD). In this study, we investigated the therapeutic accomplishment of geraniol (GE 100 mg/kg) on 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-induced mice model of PD. Current investigation proved that pretreatment with GE ameliorates the MPTP-induced alterations in behavioral, biochemical, immunohistochemical, and immunoblotting manifestations in mice. Systematically, the loss of dopaminergic neurons and reduced NTFs mRNA expressions induced by MPTP was ameliorated to a significant extent by pretreatment with GE. We found that GE confers a potent neuroprotective agent against MPTP-induced dopaminergic denervation and may become a potential therapeutic agent for PD and/or its progression.

Physiological phenotype and vulnerability in Parkinson's disease

This review will focus on the principles underlying the hypothesis that neuronal physiological phenotype-how a neuron generates and regulates action potentials-makes a significant contribution to its vulnerability in Parkinson's disease (PD) and aging. A cornerstone of this hypothesis is that the maintenance of ionic gradients underlying excitability can pose a significant energetic burden for neurons, particularly those that have sustained residence times at depolarized membrane potentials, broad action potentials, prominent Ca(2+) entry, and modest intrinsic Ca(2+) buffering capacity. This energetic burden is shouldered in neurons primarily by mitochondria, the sites of cellular respiration. Mitochondrial respiration increases the production of damaging superoxide and other reactive oxygen species (ROS) that have widely been postulated to contribute to cellular aging and PD. Many of the genetic mutations and toxins associated with PD compromise mitochondrial function, providing a mechanistic linkage between known risk factors and cellular physiology that could explain the pattern of pathology in PD. Because much of the mitochondrial burden created by this at-risk phenotype is created by Ca(2+) entry through L-type voltage-dependent channels for which there are antagonists approved for human use, a neuroprotective strategy to reduce this burden is feasible.

Mitochondrial disorders: aetiologies, models systems, and candidate therapies

It has become evident that many human disorders are characterised by mitochondrial dysfunction either at a primary level, due to mutations in genes whose encoded products are involved in oxidative phosphorylation, or at a secondary level, due to the accumulation of mitochondrial DNA (mtDNA) mutations. This has prompted keen interest in the development of cell and animal models and in exploring innovative therapeutic strategies to modulate the mitochondrial deficiencies observed in these diseases. Key advances in these areas are outlined in this review, with a focus on Leber hereditary optic neuropathy (LHON). This exciting field is set to grow exponentially and yield many candidate therapies to treat this class of disease.

Sustained resistance to acute MPTP toxicity by hypothalamic dopamine neurons following chronic neurotoxicant exposure is associated with sustained up-regulation of parkin protein

Hypothalamic tuberoinfundibular dopamine (TIDA) neurons remain unaffected in Parkinson disease (PD) while there is significant degeneration of midbrain nigrostriatal dopamine (NSDA) neurons. A similar pattern of susceptibility is observed following acute exposure to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and the resistance of TIDA neurons to MPTP is associated with increased expression of parkin and ubiquitin carboxy-terminal hydrolase L-1 (UCHL-1). In the present study, the response of TIDA and NSDA neurons to acute MPTP administration following chronic MPTP exposure was examined. Mice were treated with ten injections of either MPTP (20mg/kg; s.c.; every 3.5 days) or saline vehicle (10 ml/kg; s.c.; every 3.5 days). Following a 21 day recovery period, chronic saline- and MPTP-treated mice received an additional injection of either saline (10 ml/kg; s.c.) or MPTP (20mg/kg; s.c.) and were sacrificed 24h later. NSDA neurons displayed significant axon terminal degeneration (as reflected by decreases in DA, tyrosine hydroxylase (TH) and DA transporter concentrations in the striatum) as well as loss of TH-immunoreactive (IR) neurons in the substantia nigra (SN) following MPTP, whereas TIDA neurons revealed no overt axon terminal pathology or loss of TH-IR cell bodies. NSDA neuronal pathology was associated with transient decreases in concentrations of parkin and UCHL-1 protein in the SN, which returned to normal levels by 21 days following cessation of chronic neurotoxicant exposure. Resistance of TIDA neurons to MPTP toxicity was correlated with a transient increase in UCHL-1 and a sustained elevation in parkin in the arcuate nucleus. TIDA neurons represent a DA neuron population with a unique and inherent ability to adapt to acute and chronic toxicant administration with a sustained elevation of the neuroprotective protein parkin. The correlation between the ability to increase parkin and UCHL-1 expression and the resistance of DA neurons to neurotoxicant exposure is consistent with a functional link between these features and an underlying differential susceptibility to toxicant-associated neurodegeneration.