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.
Parkinson's disease is the second most common neurodegenerative disease and its pathogenesis is closely associated with oxidative stress. Deposition of aggregated α‐synuclein (α‐Syn) occurs in familial and sporadic forms of Parkinson's disease. Here, we studied the effect of oligomeric α‐Syn on one of the major markers of oxidative stress, lipid peroxidation, in primary co‐cultures of neurons and astrocytes. We found that oligomeric but not monomeric α‐Syn significantly increases the rate of production of reactive oxygen species, subsequently inducing lipid peroxidation in both neurons and astrocytes. Pre‐incubation of cells with isotope‐reinforced polyunsaturated fatty acids (D‐PUFAs) completely prevented the effect of oligomeric α‐Syn on lipid peroxidation. Inhibition of lipid peroxidation with D‐PUFAs further protected cells from cell death induced by oligomeric α‐Syn. Thus, lipid peroxidation induced by misfolding of α‐Syn may play an important role in the cellular mechanism of neuronal cell loss in Parkinson's disease.
The gene encoding leucine‐rich repeat kinase 2 (LRRK2) comprises a major risk factor for Parkinson's disease. Recently, it has emerged that LRRK2 plays important roles in the immune system. LRRK2 is induced by interferon‐γ (IFN‐γ) in monocytes, but the signaling pathway is not known. Here, we show that IFN‐γ‐mediated induction of LRRK2 was suppressed by pharmacological inhibition and RNA interference of the extracellular signal‐regulated kinase 5 (ERK5). This was confirmed by LRRK2 immunostaining, which also revealed that the morphological responses to IFN‐γ were suppressed by ERK5 inhibitor treatment. Both human acute monocytic leukemia THP‐1 cells and human peripheral blood monocytes stimulated the ERK5‐LRRK2 pathway after differentiation into macrophages. Thus, LRRK2 is induced via a novel, ERK5‐dependent IFN‐γ signal transduction pathway, pointing to new functions of ERK5 and LRRK2 in human macrophages.
Dopamine replacement therapy in Parkinson's disease is associated with several unwanted effects, of which dyskinesia is the most disabling. The development of new therapeutic interventions to reduce the impact of dyskinesia in Parkinson's disease is therefore a priority need. This review summarizes the key molecular mechanisms that underlie dyskinesia. The role of dopamine receptors and their associated signaling mechanisms including dopamine‐cAMP‐regulated neuronal phosphoprotein, extracellular signal‐regulated kinase, mammalian target of rapamycin, mitogen and stress‐activated kinase‐1 and Histone H3 are summarized, along with an evaluation of the role of cannabinoid and nicotinic acetylcholine receptors. The role of synaptic plasticity and animal behavioral results on dyskinesia are also evaluated. The most recent therapeutic advances to treat Parkinson's disease are discussed, with emphasis on the possibilities and limitations of non‐pharmacological interventions such as physical activity, deep brain stimulation, transcranial magnetic field stimulation and cell replacement therapy. The review suggests new prospects for the management of Parkinson's disease‐associated motor symptoms, especially the development of dyskinesia.
Reduced expression of a ~150 kDa protein was unexpectedly observed while investigating Norrin protein in a transgenic murine model in which Müller cells can be selectively and inducibly disrupted. Isolation of this unknown protein via ion exchange and hydrophobic interaction chromatography followed by Tandem mass spectrometry identified it as Inter‐photoreceptor retinoid‐binding protein (IRBP). Significantly reduced IRBP mRNA expression was observed at the early and late stages after Müller cell disruption. IRBP protein expression was also consistently reduced to 5.7% of the control level as early as 1 week after Müller cell disruption. This down‐regulation of IRBP was accompanied by focal hyperfluorescent dots and cytotoxic N‐retinylidene‐N‐retinylethanolamine (A2E) accumulation. In vitro treatment of cone photoreceptor cell lines with conditioned medium collected from stressed Müller cells suggested that Müller cells regulated photoreceptors expression of IRBP via secreted factor(s). In vivo studies suggested that one of these secreted factors was tumour necrosis factor alpha (TNFα). These findings suggest that dysregulation of IRBP expression caused by Müller cell dysfunction may be an important early event in photoreceptor degeneration in some retinal diseases.
Lewy bodies, mainly composed of α‐synuclein (αS), are pathological hallmarks of Parkinson's disease and dementia with Lewy bodies. Epidemiological studies showed that green tea consumption or habitual intake of phenolic compounds reduced Parkinson's disease risk. We previously reported that phenolic compounds inhibited αS fibrillation and destabilized preformed αS fibrils. Cumulative evidence suggests that low‐order αS oligomers are neurotoxic and critical species in the pathogenesis of α‐synucleinopathies. To develop disease modifying therapies for α‐synucleinopathies, we examined effects of phenolic compounds (myricetin (Myr), curcumin, rosmarinic acid (RA), nordihydroguaiaretic acid, and ferulic acid) on αS oligomerization. Using methods such as photo‐induced cross‐linking of unmodified proteins, circular dichroism spectroscopy, the electron microscope, and the atomic force microscope, we showed that Myr and RA inhibited αS oligomerization and secondary structure conversion. The nuclear magnetic resonance analysis revealed that Myr directly bound to the N‐terminal region of αS, whereas direct binding of RA to monomeric αS was not detected. Electrophysiological assays for long‐term potentiation in mouse hippocampal slices revealed that Myr and RA ameliorated αS synaptic toxicity by inhibition of αS oligomerization. These results suggest that Myr and RA prevent the αS aggregation process, reducing the neurotoxicity of αS oligomers.
Olfactory sensory neurons (OSNs) are the initial site for olfactory signal transduction. Therefore, their survival is essential to olfactory function. In the current study, we demonstrated that while odorant stimulation promoted rodent OSN survival, it induced generation of reactive oxygen species in a dose‐ and time‐dependent manner as well as loss of membrane potential and fragmentation of mitochondria. The MEK‐Erk pathway played a critical role in mediating these events, as its inhibition decreased odorant stimulation‐dependent OSN survival and exacerbated intracellular stress measured by reactive oxygen species generation and heat‐shock protein 70 expression. The phosphoinositide pathway, rather than the cyclic AMP pathway, mediated the odorant‐induced activation of the MEK‐Erk pathway. These findings provide important insights into the mechanisms of activity‐driven OSN survival, the role of the phosphoinositide pathway in odorant signaling, and demonstrate that odorant detection and odorant stimulation‐mediated survival proceed via independent signaling pathways. This mechanism, which permits independent regulation of odorant detection from survival signaling, may be advantageous if not diminished by repeated or prolonged odor exposure.
Epidemiological studies have indicated an inverse association between high uricemia and incidence of Parkinson's disease (PD). To investigate the link between endogenous urate and neurotoxic changes involving the dopaminergic nigrostriatal system, this study evaluated the modifications in the striatal urate levels in two models of PD. To this end, a partial dopaminergic degeneration was induced by 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) in mice, while a severe dopaminergic degeneration was elicited by unilateral medial forebrain bundle infusion of 6‐hydroxydopamine (6‐OHDA) in rats. Urate levels were measured by in vivo microdialysis at 7 or 14 days from toxin exposure. The results obtained demonstrated higher urate levels in the dopamine‐denervated striatum of 6‐OHDA‐lesioned rats compared with the intact striatum. Moreover, an inverse correlation between urate and dopamine levels was observed in the same area. In contrast, only a trend to significant increase in striatal urate was observed in MPTP‐treated mice. These results demonstrate that a damage to the dopaminergic nigrostriatal system elevates the striatal levels of urate, and suggest that this could be an endogenous compensatory mechanism to attenuate dopaminergic neurodegeneration. This finding may be important in light of the epidemiological and preclinical evidences that indicate a link between urate and development of PD.
In Parkinson's disease (PD), profound putamen dopamine (DA) depletion reflects denervation and a shift from vesicular sequestration to oxidative deamination of cytoplasmic DA in residual terminals. PD also involves cardiac sympathetic denervation. Whether PD entails myocardial norepinephrine (NE) depletion and a sequestration–deamination shift have been unknown. We measured apical myocardial tissue concentrations of NE, DA, and their neuronal metabolites 3,4‐dihydroxyphenylglycol (DHPG), and 3,4‐dihydroxyphenylacetic acid (DOPAC) from 23 PD patients and 23 controls and ascertained the extent of myocardial NE depletion in PD. We devised, validated in VMAT2‐Lo mice, and applied 5 neurochemical indices of the sequestration–deamination shift—concentration ratios of DOPAC:DA, DA:NE, DHPG:NE, DOPAC:NE, and DHPG:DOPAC—and used a kinetic model to estimate the extent of the vesicular storage defect. The PD group had decreased myocardial NE content (p < 0.0001). The majority of patients (70%) had severe NE depletion (mean 2% of control), and in this subgroup all five indices of a sequestration–deamination shift were increased compared to controls (p < 0.001 for each). Vesicular storage in residual nerves was estimated to be decreased by 84–91% in this subgroup. We conclude that most PD patients have severe myocardial NE depletion, because of both sympathetic denervation and decreased vesicular storage in residual nerves.
The cytochrome P450 2D (CYP2D) mediates synthesis of serotonin from 5‐methoxytryptamine (5‐MT), shown in vitro for cDNA‐expressed CYP2D‐isoforms and liver and brain microsomes. We aimed to demonstrate this synthesis in the brain in vivo. We measured serotonin tissue content in brain regions after 5‐MT injection into the raphe nuclei (Model‐A), and its extracellular concentration in rat frontal cortex and striatum using an in vivo microdialysis (Model‐B) in male Wistar rats. Naïve rats served as control animals. 5‐MT injection into the raphe nuclei of PCPA‐(tryptophan hydroxylase inhibitor)‐pretreated rats increased the tissue concentration of serotonin (from 40 to 90% of the control value, respectively, in the striatum), while the CYP2D inhibitor quinine diminished serotonin level in some brain structures of those animals (Model‐A). 5‐MT given locally through a microdialysis probe markedly increased extracellular serotonin concentration in the frontal cortex and striatum (to 800 and 1000% of the basal level, respectively) and changed dopamine concentration (Model‐B). Quinine alone had no effect on serotonin concentration; however, given jointly with 5‐MT, it prevented the 5‐MT‐induced increase in cortical serotonin in naïve rats and in striatal serotonin in PCPA‐treated animals. These results indicate that the CYP2D‐catalyzed alternative pathway of serotonin synthesis from 5‐MT is relevant in the brain in vivo, and set a new target for the action of psychotropics.
Japanese encephalitis virus (JEV), a single‐stranded RNA (ssRNA) virus, is the leading cause of encephalitis in Asia. Microglial activation is one of the key events in JEV‐induced neuroinflammation. Although the various microRNAs (miRNAs) has been shown to regulate microglia activation during pathological conditions including neuroviral infections, till date, the involvement of miRNAs in JEV infection has not been evaluated. Hence, we sought to evaluate the possible role of miRNAs in mediating JEV‐induced microglia activation. Initial screening revealed significant up‐regulation of miR‐29b in JEV‐infected mouse microglial cell line (BV‐2) and primary microglial cells. Furthermore, using bioinformatics tools, we identified tumor necrosis factor alpha‐induced protein 3, a negative regulator of nuclear factor‐kappa B signaling as a potential target of miR‐29b. Interestingly, in vitro knockdown of miR‐29b resulted in significant over‐expression of tumor necrosis factor alpha‐induced protein 3, and subsequent decrease in nuclear translocation of pNF‐κB. JEV infection in BV‐2 cell line elevated inducible nitric oxide synthase, cyclooxygenase‐2, and pro‐inflammatory cytokine expression levels, which diminished after miR‐29b knockdown. Collectively, our study demonstrates involvement of miR‐29b in regulating JEV‐ induced microglial activation.
X‐linked Adrenoleukodystrophy (X‐ALD), an inherited peroxisomal metabolic neurodegenerative disorder, is caused by mutations/deletions in the ATP‐binding cassette transporter (ABCD1) gene encoding peroxisomal ABC transporter adrenoleukodystrophy protein (ALDP). Metabolic dysfunction in X‐ALD is characterized by the accumulation of very long chain fatty acids ≥ C22:0) in the tissues and plasma of patients. Here, we investigated the mitochondrial status following deletion of ABCD1 in B12 oligodendrocytes and U87 astrocytes. This study provides evidence that silencing of peroxisomal protein ABCD1 produces structural and functional perturbations in mitochondria. Activities of electron transport chain‐related enzymes and of citric acid cycle (TCA cycle) were reduced; mitochondrial redox status was dysregulated and the mitochondrial membrane potential was disrupted following ABCD1 silencing. A greater reduction in ATP levels and citrate synthase activities was observed in oligodendrocytes as compared to astrocytes. Furthermore, most of the mitochondrial perturbations induced by ABCD1 silencing were corrected by treating cells with suberoylanilide hydroxamic acid, an Histone deacetylase inhibitor. These observations indicate a novel relationship between peroxisomes and mitochondria in cellular homeostasis and the importance of intact peroxisomes in relation to mitochondrial integrity and function in the cell types that participate in the pathobiology of X‐ALD. These observations suggest suberoylanilide hydroxamic acid as a potential therapy for X‐ALD.
We explored the interplay between the intracellular energy sensor AMP‐activated protein kinase (AMPK), extracellular signal‐regulated kinase (ERK), and autophagy in phorbol myristate acetate (PMA)‐induced neuronal differentiation of SH‐SY5Y human neuroblastoma cells. PMA‐triggered expression of neuronal markers (dopamine transporter, microtubule‐associated protein 2, β‐tubulin) was associated with an autophagic response, measured by the conversion of microtubule‐associated protein light chain 3 (LC3)‐I to autophagosome‐bound LC3‐II, increase in autophagic flux, and expression of autophagy‐related (Atg) proteins Atg7 and beclin‐1. This coincided with the transient activation of AMPK and sustained activation of ERK. Pharmacological inhibition or RNA interference‐mediated silencing of AMPK suppressed PMA‐induced expression of neuronal markers, as well as ERK activation and autophagy. A selective pharmacological blockade of ERK prevented PMA‐induced neuronal differentiation and autophagy induction without affecting AMPK phosphorylation. Conversely, the inhibition of autophagy downstream of AMPK/ERK, either by pharmacological agents or LC3 knockdown, promoted the expression of neuronal markers, thus indicating a role of autophagy in the suppression of PMA‐induced differentiation of SH‐SY5Y cells. Therefore, PMA‐induced neuronal differentiation of SH‐SY5Y cells depends on a complex interplay between AMPK, ERK, and autophagy, in which the stimulatory effects of AMPK/ERK signaling are counteracted by the coinciding autophagic response.
Vitamin C is an essential factor for neuronal function and survival, existing in two redox states, ascorbic acid (AA), and its oxidized form, dehydroascorbic acid (DHA). Here, we show uptake of both AA and DHA by primary cultures of rat brain cortical neurons. Moreover, we show that most intracellular AA was rapidly oxidized to DHA. Intracellular DHA induced a rapid and dramatic decrease in reduced glutathione that was immediately followed by a spontaneous recovery. This transient decrease in glutathione oxidation was preceded by an increase in the rate of glucose oxidation through the pentose phosphate pathway (PPP), and a concomitant decrease in glucose oxidation through glycolysis. DHA stimulated the activity of glucose‐6‐phosphate dehydrogenase, the rate‐limiting enzyme of the PPP. Furthermore, we found that DHA stimulated the rate of lactate uptake by neurons in a time‐ and dose‐dependent manner. Thus, DHA is a novel modulator of neuronal energy metabolism by facilitating the utilization of glucose through the PPP for antioxidant purposes.
Localized translation of axonal mRNAs contributes to developmental and regenerative axon growth. Although untranslated regions (UTRs) of many different axonal mRNAs appear to drive their localization, there has been no consensus RNA structure responsible for this localization. We recently showed that limited expression of ZBP1 protein restricts axonal localization of both β‐actin and GAP‐43 mRNAs. β‐actin 3′UTR has a defined element for interaction with ZBP1, but GAP‐43 mRNA shows no homology to this RNA sequence. Here, we show that an AU‐rich regulatory element (ARE) in GAP‐43′s 3′UTR is necessary and sufficient for its axonal localization. Axonal GAP‐43 mRNA levels increase after in vivo injury, and GAP‐43 mRNA shows an increased half‐life in regenerating axons. GAP‐43 mRNA interacts with both HuD and ZBP1, and HuD and ZBP1 co‐immunoprecipitate in an RNA‐dependent fashion. Reporter mRNA with the GAP‐43 ARE competes with endogenous β‐actin mRNA for axonal localization and decreases axon length and branching similar to the β‐actin 3′UTR competing with endogenous GAP‐43 mRNA. Conversely, over‐expressing GAP‐43 coding sequence with its 3′UTR ARE increases axonal elongation and this effect is lost when just the ARE is deleted from GAP‐43′s 3′UTR.
Phenylketonuria (PKU), if not detected and treated in newborns, causes severe neurological dysfunction and cognitive and behavioral deficiencies. Despite the biochemical characterization of PKU, the molecular mechanisms underlying PKU‐associated brain dysfunction remain poorly understood. The aim of this study was to gain insights into the pathogenesis of this neurological damage by analyzing protein expression profiles in brain tissue of Black and Tan BRachyury‐PahEnu2 mice (a mouse model of PKU). We compared the cerebral protein expression of homozygous PKU mice with that of their heterozygous counterparts using two‐dimensional difference gel electrophoresis analysis, and identified 21 differentially expressed proteins, four of which were over‐expressed and 17 under‐expressed. An in silico bioinformatic approach indicated that protein under‐expression was related to neuronal differentiation and dendritic growth, and to such neurological disorders as progressive motor neuropathy and movement disorders. Moreover, functional annotation analyses showed that some identified proteins were involved in oxidative metabolism. To further investigate the proteins involved in the neurological damage, we validated two of the proteins that were most strikingly under‐expressed, namely, Syn2 and Dpysl2, which are involved in synaptic function and neurotransmission. We found that Glu2/3 and NR1 receptor subunits were over‐expressed in PKU mouse brain. Our results indicate that differential expression of these proteins may be associated with the processes underlying PKU brain dysfunction, namely, decreased synaptic plasticity and impaired neurotransmission.
Aging, the main risk factor for Parkinson's disease (PD), is associated with increased α–synuclein levels in substantia nigra pars compacta (SNc). Excess α‐synuclein spurs Lewy‐like pathology and dysregulates the activity of protein phosphatase 2A (PP2A). PP2A dephosphorylates many neuroproteins, including the catecholamine rate‐limiting enzyme, tyrosine hydroxylase (TH). A loss of nigral dopaminergic neurons induces PD movement problems, but before those abnormalities occur, behaviors such as olfactory loss, anxiety, and constipation often manifest. Identifying mouse models with early PD behavioral changes could provide a model in which to test emerging therapeutic compounds. To this end, we evaluated mice expressing A53T mutant human (A53T) α–synuclein for behavior and α–synuclein pathology in olfactory bulb, adrenal gland, and gut. Aging A53T mice exhibited olfactory loss and anxiety that paralleled olfactory and adrenal α‐synuclein aggregation. PP2A activity was also diminished in olfactory and adrenal tissues harboring insoluble α‐synuclein. Low adrenal PP2A activity co‐occurred with TH hyperactivity, making this the first study to link adrenal synucleinopathy to anxiety and catecholamine dysregulation. Aggregated A53T α–synuclein recombinant protein also had impaired stimulatory effects on soluble recombinant PP2A. Collectively, the data identify an excellent model in which to screen compounds for their ability to block the spread of α‐synuclein pathology associated with pre‐motor stages of PD.
Long‐term nicotine exposure induces alterations in dopamine transmission in nucleus accumbens that sustain the reinforcing effects of smoking. One approach to understand the adaptive changes that arise involves measurement of endogenous dopamine release using voltammetry. We therefore treated rats for 2–3 months with nicotine and examined alterations in nAChR subtype expression and electrically evoked dopamine release in rat nucleus accumbens shell, a region key in addiction. Long‐term nicotine treatment selectively decreased stimulated α6β2* nAChR‐mediated dopamine release compared with vehicle‐treated rats. It also reduced α6β2* nAChRs, suggesting the receptor decline may contribute to the functional loss. This decreased response in release after chronic nicotine treatment was still partially sensitive to the agonist nicotine. Studies with an acetylcholinesterase inhibitor demonstrated that the response was also sensitive to increased endogenous acetylcholine. However, unlike the agonists, nAChR antagonists decreased dopamine release only in vehicle‐ but not nicotine‐treated rats. As antagonists function by blocking the action of acetylcholine, their ineffectiveness suggests that reduced acetylcholine levels partly underlie the dampened α6β2* nAChR‐mediated function in nicotine‐treated rats. As long‐term nicotine modifies dopamine release by decreasing α6β2* nAChRs and their function, these data suggest that interventions that target this subtype may be useful for treating nicotine dependence.
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