Valproic Acid is Neuroprotective in the Rotenone Rat Model of Parkinson’s Disease: Involvement of α-Synuclein

Valproic acid (VPA), an established antiepileptic and antimanic drug, has recently emerged as a promising neuroprotective agent. Among its many cellular targets, VPA has been recently demonstrated to be an effective inhibitor of histone deacetylases. Accordingly, we have adopted a schedule of dietary administration (2% VPA added to the chow) that results in a significant inhibition of histone deacetylase activity and in an increase of histone H3 acetylation in brain tissues of 4 weeks-treated rats. We have tested this schedule of VPA treatment in an animal model of Parkinson’s disease (PD), in which degeneration of nigro-striatal dopaminergic neurons is obtained through sub-chronic administration of the mitochondrial toxin, rotenone, via osmotic mini pumps implanted to rats. The decrease of the dopaminergic marker tyrosine hydroxylase in substantia nigra and striatum caused by 7 days toxin administration was prevented in VPA-fed rats. VPA treatment also significantly counteracted the death of nigral neurons and the 50% drop of striatal dopamine levels caused by rotenone administration. The PD-marker protein α-synuclein decreased, in its native form, in substantia nigra and striatum of rotenone-treated rats, while monoubiquitinated α-synuclein increased in the same regions. VPA treatment counteracted both these α-synuclein alterations. Furthermore, monoubiquitinated α-synuclein increased its localization in nuclei isolated from substantia nigra of rotenone-treated rats, an effect also prevented by VPA treatment. Nuclear localization of α-synuclein has been recently described in some models of PD and its neurodegenerative effect has been ascribed to histone acetylation inhibition. Thus, the ability of VPA to increase histone acetylation is a novel candidate mechanism for its neuroprotective action.     

Enhanced sensitivity of dopaminergic neurons to rotenone-induced toxicity with aging

Rotenone has been reported to induce various degrees of Parkinsonism in rats. We tested whether advancing age alters the sensitivity of dopaminergic neurons to rotenone. A low, systemic dose of rotenone had no effect on young rats, but led to a 20-30% reduction of tyrosine hydroxylase-positive neurons in the substantia nigra of older rats. The effect was specific to nigral dopaminergic neurons and may be associated with the increase of glial cell activation in older rats. These data suggest that age enhances the sensitivity of dopaminergic neurons to rotenone and should be considered when assessing models of Parkinson's disease.     

Effects of oral administration of rotenone on gastrointestinal functions in mice

Background The systemic rotenone model of Parkinson’s disease (PD) accurately replicates many aspects of the pathology of human PD, especially neurodegeneration of the substantia nigra and lesions in the enteric nervous system (ENS). Nevertheless, the precise effects of oral rotenone on the ENS have not been addressed yet. This study was therefore designed to assess the effects of a chronic oral treatment by rotenone on enteric neurochemical phenotype, gastrointestinal (GI) motility, and intestinal epithelial barrier permeability. Methods Male C57BL6N mice received once daily oral rotenone administration for 28 days. GI functions were analyzed 4 weeks after rotenone treatment. Gastrointestinal motility was assessed by measuring gastric emptying, total transit time, fecal pellet output, and bead latency. Intestinal barrier permeability was evaluated both in vivo and ex vivo. The number of enteric neurons and the enteric neurochemical phenotype were analyzed by immunohistochemistry. Tyrosine hydroxylase (TH) immunostaining of dopaminergic neurons of the substantia nigra was performed in a subset of animals. Key Results Mice treated orally with rotenone had a decrease in fecal pellet output and in jejunal alpha‐synuclein expression as compared with control animals. This was associated with a significant decrease in TH‐immunoreactive neurons in the substantia nigra. No change in gastric emptying, total transit time, intestinal epithelial barrier permeability, and enteric neurochemical phenotype was observed. Conclusions & Inferences Chronic oral treatment with rotenone only induced minor changes in the ENS and did not recapitulate the GI abnormalities seen in PD, while it replicates neurodegeneration of the substantia nigra.     

Parallel relationship between microglial activation and substantia nigra damage in a rotenone-induced Parkinson's disease rat model

BACKGROUND:Inflammatory injury induced by microglial activation plays an important role in the occurrence and development of Parkinson’s disease (PD). However, few studies have examined the relationship between microglia and substantia nigra damage or dopaminergic neuron loss in animals with rotenone-induced PD. OBJECTIVE: To explore the relationship between activated microglia and loss of the substantia nigra, and the changes in concentration and dose of rotenone in the brain of rats with rotenone-induced ...     

Biochanin A Protects Against Lipopolysaccharide-Induced Damage of Dopaminergic Neurons Both In Vivo and In Vitro via Inhibition of Microglial Activation

Neuroinflammation has been reported to be involved in the pathogenesis of Parkinson’s disease (PD). Inhibition of microglia-mediated neuroinflammation might be a potential strategy for PD treatment. Biochanin A, is an O-methylated isoflavone, classified as a kind of phytoestrogens due to its chemical structure that is similar to mammalian estrogens. It has been found to possess antifibrotic, antiapoptotic, and antioxidant effects. In the present study, we investigated the neuroprotective effects of biochanin A on lipopolysaccharide (LPS)-induced dopaminergic neurons damage both in vivo and in vitro and the related molecular mechanisms. The results showed that biochanin A treatment for 21 days significantly attenuated the behavioral dysfunction of PD rats, prevented dopaminergic neurons damage, and inhibited activation of microglia in the LPS-induced PD rats. Furthermore, biochanin A decreased the levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in the serum, and inhibited the phosphorylation of ERK, JNK, p38 in the substantia nigra of PD rats. In vitro test, biochanin A also inhibited primary microglial activation and protected dopaminergic neurons, decreased the content of nitric oxide, IL-1β, and TNF-α in supernatants, and inhibited the reactive oxygen species production. Taken together, these results suggest that biochanin A exerts protective effects on LPS-induced PD rats, and the mechanisms may be associated with the inhibition of inflammatory response and the MAPK signaling pathway.     

Neuroprotective Effect of Ghrelin in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Mouse Model of Parkinson’s Disease by Blocking Microglial Activation

Ghrelin is an endogenous ligand for growth hormone (GH) secretagogue receptor 1a (GHS-R1a) and is produced and released mainly from the stomach. It was recently demonstrated that ghrelin can function as a neuroprotective factor by inhibiting apoptotic pathways. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic neurotoxicity in rodents; previous studies suggest that activated microglia actively participate in the pathogenesis of Parkinson’s disease (PD) neurodegeneration. However, the role of microglia in the neuroprotective properties of ghrelin is still unknown. Here we show that, in the mouse MPTP PD model generated by an acute regimen of MPTP administration, systemic administration of ghrelin significantly attenuates the loss of substantia nigra pars compacta (SNpc) neurons and the striatal dopaminergic fibers through the activation of GHS-R1a. We also found that ghrelin reduced nitrotyrosine levels and improved the impairment of rota-rod performance. Ghrelin prevents MPTP-induced microglial activation in the SNpc and striatum, the expression of pro-inflammatory molecules tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β), and the activation of inducible nitric oxide synthase. The inhibitory effect of ghrelin on the activation of microglia appears to be indirect by suppressing matrix metalloproteinase-3 (MMP-3) expression in stressed dopaminergic neurons because GHS-R1a is not expressed in SNpc microglial cells. Finally, in vitro administration of ghrelin prevented 1-methyl-4-phenylpyridinium-induced dopaminergic cell loss, MMP-3 expression, microglial activation, and the subsequent release of TNF-α, IL-1β, and nitrite in mesencephalic cultures. Our data indicate that ghrelin may act as a survival factor for dopaminergic neurons by functioning as a microglia-deactivating factor and suggest that ghrelin may be a valuable therapeutic agent for neurodegenerative diseases such as PD.     

Inhibiting BDNF expression by antisense oligonucleotide infusion causes loss of nigral dopaminergic neurons

Brain derived neurotrophic factor (BDNF) expression is significantly reduced in the Parkinson's disease substantia nigra. This neurotrophin has potent affects on dopaminergic neuron survival protecting them from the neurotoxins MPTP and 6-hydroxydopamine (6-OHDA) commonly used to create animal models of Parkinson's disease and also promoting dopaminergic axonal sprouting. In this study, we demonstrate that an antisense oligonucleotide infusion (200 nM for 28 days) to prevent BDNF production in the substantia nigra of rats mimics many features of the classical animal models of Parkinson's disease. 62% of antisense treated rats rotate (P < or = 0.05) in response to dopaminergic receptor stimulation by apomorphine. 40% of substantia nigra pars compacta tyrosine hydroxylase immunoreactive neurons are lost (P < or = 0.00001) and dopamine uptake site density measured by (3)H-mazindol autoradiography is reduced by 34% (P < or = 0.005). Loss of haematoxylin and eosin stained nigral neurons is significant (P < or = 0.0001) but less extensive (34%). These observations indicate that loss of BDNF expression leads both to down regulation of the dopaminergic phenotype and to dopaminergic neuronal death. Therefore, reduced BDNF mRNA expression in Parkinson's disease substantia nigra may contribute directly to the death of nigral dopaminergic neurons and the development of Parkinson's disease.     

蛋白酶体抑制剂诱导大鼠黑质变性伴包涵体形成

目的 观察蛋白酶体抑制剂Lactacystin诱导大鼠黑质变性伴包涵体形成及运动行为学的改变,探讨蛋白酶体功能下降在帕金森病(PDl发病机制中的作用. 方法 24只SD大鼠采用随机数字表法分为kactacystin实验组和生理盐水组.每组12只,Lactacystin实验组将蛋白酶体抑制剂Lactacystin立体定向注射人大鼠左侧黑质致密部(SNc).生理盐水组注射等体积生理盐水;观察大鼠自主行为和阿朴吗啡(APO)诱导的旋转行为的改变;Nissl染色法观察SNc病理改变;免疫组化法观察SNc及纹状体酪氨酸羟化酶(TH)和SNc中α-共核蛋白的表达;透射电镜观察SNc超微结构的改变. 结果 Lactacystin实验组大鼠给药7 d后出现自发性活动减少、动作缓慢、震颤、且症状逐步加重.APO可诱导出向健侧的旋转运动;Nissl染色发现Lactacystin实验组左侧SNc神经元数量减少,尼氏体结构松散;免疫组化结果表明21 d后Lactacystin实验组左侧SNc出现变性,TH免疫阳性神经元数量减少,α-共核蛋白表达增强,纹状体内TH免疫阳性纤维数量减少;电镜观察到蛋白质聚集形成的包涵体. 结论 Lactacystin单侧SNc注射可以诱导大鼠黑质变性伴包涵体形成及大鼠行为改变.蛋白酶体功能下降可能在PD发病机制中起重要作用.     

Chronic expression of low levels of tumor necrosis factor-α in the substantia nigra elicits progressive neurodegeneration,delayed motor symptoms and microglia/macrophage activation

Inflammation, and in particular microglia activation, is regarded as a constant component of brain pathology in Parkinson's disease (PD). Microglial activation has been found in the substantia nigra (SN), one of the main brain regions affected in PD, for many years after the initiation of the disease. Although many studies point towards a deleterious role of inflammation on PD, the functional role of many of its main components has not been clarified yet. For example, tumor necrosis factor-α (TNF-α), a key pro-inflammatory cytokine, has been shown to exert toxic or no effects on the viability of dopaminergic neurons. No study has evaluated the effects of the long-lasting TNF-α expression in the SN, an experimental set-up most probably resembling the clinical situation.The aim of this study was to investigate the effects of the chronic expression of TNF-α in the adult SN at different time points. Adenoviral expression of low TNF-α levels (17–19 pg/mg) lasted for 14 days in the SN and did not induce interleukin-1β (IL-1β) expression. Long-lasting TNF-α expression caused dopaminergic cell death from day 14, increasing at 21 and 28 days compared with control animals injected with adenovectors expressing β-galactosidase. TNF-α overexpression elicited irreversible, unilateral akinesia starting at 14 days, but not earlier. These effects were accompanied by microglial activation to stage 4 and/or monocyte/macrophage recruitment from the periphery from day 7 post adenovector inoculations.Thus, we conclude that extended duration of the expression of TNF-α is necessary and sufficient for a univocal toxic effect of TNF-α on dopaminergic neurons and motor disabilities. This study provides an animal model to study early events that lead to TNF-α-mediated neuronal demise in the SN. In addition, the cellular components of the inflammation elicited by TNF-α and the lack of IL-1β expression support the growing idea of a distinct cytokine network in the brain.     

Sodium salicylate protects against rotenone‐induced Parkinsonism in rats

Complex I deficiency culminating in oxidative stress is proposed as one of the upstream mechanisms of nigral neuronal death in Parkinson's disease. We investigated whether sodium salicylate, an active metabolite of aspirin, could afford protection against rotenone‐induced oxidative stress, neuronal degeneration, and behavioral dysfunction in rats, because it has the potential to accept a molecule each of hydroxyl radical (^?OH) at the third or fifth position of its benzyl ring. Rotenone caused dose‐dependent increase in ^?OH in isolated mitochondria from the cerebral cortex and time‐ (24–48h) and dose‐dependent (0.1–100 µM) increase in the substantia nigra and the striatum, ipsilateral to the side of rotenone infusion. Administration of sodium salicylate at 12‐h intervals for 4 days showed dose‐dependent (50–100 mg/kg, i.p) reductions in the levels of ^?OH in the nigra on the fifth day. These animals showed significant attenuation in rotenone‐induced loss in striatal dopamine levels, number of nigral dopaminergic neurons, reduced and oxidized glutathione levels, and complex I activity loss, but superoxide dismutase activity was increased further. Amphetamine‐ or apomorphine‐induced ipsilateral rotations in rotenone‐treated rats were significantly reduced in rats treated with sodium salicylate. Our results indicate a direct role of ^?OH in mediating nigral neuronal death by rotenone and confirm the neuroprotective potential of salicylate in a rodent model of parkinsonism. Synapse 67:502–514, 2013. © 2013 Wiley Periodicals, Inc.     

Minocycline inhibits microglial activation and protects nigral cells after 6-hydroxydopamine injection into mouse striatum

To determine the role of immune/inflammatory factors in dopaminergic cell degeneration in parkinsonian substantia nigra, we assayed tyrosine hydroxylase (TH)-positive immunoreactive neuronal numbers with stereologic techniques and CD11b-positive immunoreactive microglial profiles following 6-hydroxydopamine (6-OHDA) injection into ipsilateral striatum of mice. We further investigated the effect of minocycline on the inhibition of microglial activation and subsequent protection of nigral cells. The relative number of microglial profiles in the substantia nigra (SN) ipsilateral to the injection increased from 31 to 32% 1-3 days after injection, and increased further to 55% by 7 days and 59% by 14 days, compared with the contralateral SN. These changes started prior to the decrease of TH immunoreactivity of 34% on day 7 and of 42% by day 14. In animals treated with minocycline, microglial activation was inhibited by 47%, and TH positive cells were protected by 21% at day 14 after 6-OHDA injection, compared with those parkinsonian animals without minocycline treatment. All these results suggest that microglial activation may be involved in the nigral cell degeneration in 6-OHDA induced parkinsonian mice.     

凝血酶诱导的小胶质细胞激活促进多巴胺能神经元变性

目的探讨凝血酶（Thrombin）诱导小胶质细胞（Micoglia）激活与黑质多巴胺能神经元变性的关系。方法采用立体定向术注射凝血酶至大鼠黑质,在不同时间点观察酪氨酸羟化酶（tyrosine hydroxylase,TH）神经元的表达及小胶质细胞的激活情况;同时检测黑质NO量及iNOS mRNA表达。结果（1）凝血酶注入大鼠黑质导致明显的黑质多巴胺能神经元变性,呈时间依赖性,TH阳性细胞数在第3d开始下降,第7d有大量的TH阳性细胞丢失,与对照侧相比下降达约53％（P〈0．01）;高倍镜下可见胞体皱缩、突起明显缩短或减少;14d时细胞数下降至21％,30d时下降至12％（P〈0．01）。（2）凝血酶注射入黑质4h后小胶质细胞开始呈现为“灌木丛样”或少量呈现“阿米巴样”：12h后小胶质细胞数目明显增加且绝大部分呈现“阿米巴样”;24h后细胞已完全激活,“阿米巴样”细胞达高峰;3d维持高峰;14d后小胶质细胞染色变淡,体积变小,“阿米巴样”细胞数目下降。（3）与对照组相比,iNOSmRNA表达明显上调及NO合成增加（P〈0．05）,并且有iNOS在小胶质细胞表达。结论凝血酶对多巴胺能神经元具有一定的损毁作用,小胶质细胞的激活先于多巴胺能神经元变性,其激活后释放的NO有可能参与多巴胺能神经元变性。     

Glutathione depletion and overproduction both initiate degeneration of nigral dopaminergic neurons

Parkinson’s disease is a neurodegenerative disorder characterized by severe motor deficits mainly due to degeneration of dopaminergic neurons in the substantia nigra. Decreased levels of the cell’s most important anti-oxidant, glutathione, have been detected in nigral neurons of Parkinson patients, but it is unknown if they are the cause or merely the consequence of the disease. To elucidate if glutathione depletion causes selective degeneration of nigral dopaminergic neurons, we down-regulated glutathione synthesis in different brain areas of adult rats by a viral vector-based RNAi approach. Decreased glutathione synthesis resulted in progressive degeneration of nigral dopaminergic neurons, while extra-nigral and striatal neurons were significantly less vulnerable. Degeneration of dopaminergic neurons was accompanied by progressive protein aggregate formation and functional motor deficits and was partially rescued by α-synuclein. That the survival of nigral dopaminergic neurons depends on the precise control of glutathione levels was further demonstrated by significant degeneration induced through moderate overproduction of glutathione. Over-expression of either of the two subunits of glutamate–cysteine ligase induced aberrant glutathiolation of cellular proteins and significant degeneration of dopaminergic neurons. Thus, while glutathione depletion was demonstrated to be a selective trigger for dopaminergic neuron degeneration, a glutathione replacement approach as a potential treatment option for Parkinson’s patients must be considered with great care. In conclusion, our data demonstrate that survival of nigral dopaminergic neurons crucially depends on a tight regulation of their glutathione levels and that the depleted glutathione content detected in the brains of Parkinson’s disease patients can be a causative insult for neuronal degeneration.     

Chronic restraint stress triggers dopaminergic and noradrenergic neurodegeneration: Possible role of chronic stress in the onset of Parkinson’s disease

Parkinson’s disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and, to a lesser extent, in the noradrenergic neurons of the locus coeruleus (LC). Most cases of PD are idiopathic and sporadic and are believed to be the result of both environmental and genetic factors. Here, to the best of our knowledge, we report the first evidence that chronic restraint stress (8 h/day, 5 days/week) substantially reduces nigral DA and LC noradrenergic neuronal cell numbers in rats. Loss of DA neurons in the SNpc was evident after 2 weeks of stress and progressed in a time-dependent manner, reaching up to 61% at 16 weeks. This reduction was accompanied by robust microglial activation and oxidative stress and was marked by nitrotyrosine in the SNpc and LC of the midbrain. These results indicate that chronic stress triggers DA and noradrenergic neurodegeneration by increasing oxidative stress, and that activated microglia in the substantia nigra and LC may play an important role in modulating the neurotoxic effects of oxidative stress. Taken together, these data suggest that exposure to chronic stress triggers DA and noradrenergic neurodegeneration, which is a cause of PD.     

黑质内注射脂多糖对不同年龄大鼠DA能神经元和小胶质细胞活性的影响

目的 探讨青年和老年大鼠黑质DA能(DA)神经元对脂多糖(LPS)所诱导的损伤作用的敏感性差异和对小胶质细胞活性的影响.方法 采用立体定向技术向大鼠单侧黑质内注入LPS建立PD大鼠模型;采用免疫组化法观察黑质酪氨酸羟化酶(TH)阳性细胞和OX6阳性小胶质细胞变化;采用Fluoro-Jade B染色法检测黑质的变性神经元.结果 黑质内注射LPS后,老年组大鼠黑质区TH阳性神经元数量较青年组明显减少(P<0.01);老年组大鼠黑质区Fluoro-Jade B阳性神经元明显多于青年组(P<0.01);青年组大鼠黑质部位的OX6阳性小胶质细胞主要是处在激活期的;而老年组大鼠黑质部位的OX6阳性小胶质细胞主要是活化期的(阿米巴样或巨噬细胞样).结论 老年大鼠的黑质DA能神经元对于LPS所诱导的损伤作用较青年大鼠更为敏感.     

利福平对鱼藤酮诱导大鼠的抗多巴胺神经元凋亡作用

目的探讨利福平抗鱼藤酮诱导帕金森病大鼠模型多巴胺神经元凋亡的作用。方法给SD大鼠背部皮下注射鱼藤酮1.5 mg/(kg.d)3周使其黑质多巴胺神经元发生凋亡,同时经灌胃给予利福平30 mg/(kg.d)干预,并通过对大鼠中脑切片进行TUNEL及Bax、Bcl-2和Caspase-3的免疫活性检测以明确利福平抗多巴胺神经元凋亡的作用。结果长期低剂量接触鱼藤酮可诱导SD大鼠中脑黑质部位出现凋亡细胞增加以及Bax、Bcl-2、Caspase-3的免疫活性的改变(P均<0.01),而应用利福平后可明显减轻这些变化(P均<0.01)。结论利福平具有抗鱼藤酮帕金森病大鼠模型的多巴胺神经元凋亡的作用,且此作用是通过上调Bcl-2和Bax的比值、抑制caspase通路而实现的。     

X-box-binding protein 1-modified neural stem cells for treatment of Parkinson’s disease

X-box-binding protein 1-transfected neural stem cells were transplanted into the right lateral ventricles of rats with rotenone-induced Parkinson’s disease. The survival capacities and differentiation rates of cells expressing the dopaminergic marker tyrosine hydroxylase were higher in X-box-binding protein 1-transfected neural stem cells compared to non-transfected cells. Moreover, dopamine and 3,4-dihydroxyphenylacetic acid levels in the substantia nigra were significantly increased, α-synuclein expression was decreased, and neurological behaviors were significantly ameliorated in rats following transplantation of X-box-binding protein 1-transfected neural stem cells. These results indicate that transplantation of X-box-binding protein 1-transfected neural stem cells can promote stem cell survival and differentiation into dopaminergic neurons, increase dopamine and 3,4-dihydroxyphenylacetic acid levels, reduce α-synuclein aggregation in the substantia nigra, and improve the symptoms of Parkinson’s disease in rats.     

c-Jun N-terminal kinase mediates lactacystin-induced dopamine neuron degeneration

Parkinson disease is characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. It has been proposed that dysfunction of the ubiquitin proteasome system plays an important role in the pathogenesis of Parkinson disease, but the mechanisms underlying ubiquitin proteasome system-related neuron degeneration are unknown. Here, we demonstrate that the proteasome inhibitor lactacystin induces phosphorylation of c-Jun N-terminal kinase (JNK) and c-Jun, the release of cytochrome c, activation of both caspase-9 and caspase-3, and sequential apoptosis of dopaminergic neurons in vitro. Most of these effects can be attenuated by the JNK inhibitor SP600125. Furthermore, infusion of lactacystin in rats in vivo also leads to phosphorylation of JNK before nigral neuron loss; chronic administration of SP600125 also blocks this loss. These results indicate that JNK is involved in proteasome inhibition-induced dopaminergic neuron degeneration through caspase-3-mediated apoptotic pathways, suggesting that this kinase may be a therapeutic target for the prevention of substantia nigra pars compacta degeneration in Parkinson disease patients.