Neuroinflammatory processes in Parkinson's disease

Neuroinflammation in Alzheimer's disease and Parkinson's disease: are microglia pathogenic in either disorder?

Microglial activation similar to that which occurs in peripheral macrophages during inflammatory attack was first demonstrated in the Alzheimer's disease (AD) brain two decades ago. Localization to pathologically vulnerable regions of AD cortex, localization to sites of specific AD pathology such as amyloid-beta peptide (Abeta) deposits, and the ability of activated microglia to release toxic inflammatory factors suggested that the activation of microglia in AD might play a pathogenic role. However, proving this hypothesis in a disease in which so many profound pathologies occur (e.g., Abeta deposition, neurofibrillary tangle formation, inflammation, neuronal loss, neuritic loss, synaptic loss, neuronal dysfunction, vascular alterations) has proven difficult. Although investigations of microglia in Parkinson's disease (PD) are more recent and therefore less extensive, demonstration of a pathogenic role for microglial activation may actually be much simpler in PD than AD because the root pathological event in PD, loss of dopamine (DA)-secreting substantia nigra neurons, is already well established. Indeed, indirect but converging evidence of a pathogenic role for activated microglia in PD has already begun to emerge. The nigra reportedly has the highest density of microglia in brain, and, in PD, nigral microglia are not only highly activated but also highly clustered around dystrophic DA neurons. 6-OHDA and MPTP models of PD in rodents induce substantia nigra microglial activation. More cogent, injections of the classic microglial/macrophage activator lipopolysaccharide into or near the rodent nigra cause a specific loss of DA neurons there. Culture models with human microglia and human cellular targets replicate this phenomenon. Notably, nearly all the proposed etiologies of PD, including brain bacterial and viral exposure, pesticides, drug contaminants, and repeated head trauma, are known to cause brain inflammation. A mechanism by which activated microglia might specifically target DA neurons remains a critical missing link in the proof of a pathogenic role for activated microglia in PD. If such a link could be established, however, clinical intervention trials with agents that dampen microglial activation might be warranted in PD.

Analysis of potential transcriptomic biomarkers for Huntington's disease in peripheral blood

Highly quantitative biomarkers of neurodegenerative disease remain an important need in the urgent quest for disease-modifying therapies. For Huntington's disease (HD), a genetic test is available (trait marker), but necessary state markers are still in development. In this report, we describe a large battery of transcriptomic tests explored as state biomarker candidates. In an attempt to exploit the known neuroinflammatory and transcriptional perturbations of disease, we measured relevant mRNAs in peripheral blood cells. The performance of these potential markers was weak overall, with only one mRNA, immediate early response 3 (IER3), showing a modest but significant increase of 32% in HD samples compared with controls. No statistically significant differences were found for any other mRNAs tested, including a panel of 12 RNA biomarkers identified in a previous report [Borovecki F, Lovrecic L, Zhou J, Jeong H, Then F, Rosas HD, Hersch SM, Hogarth P, Bouzou B, Jensen RV, et al. (2005) Proc Natl Acad Sci USA 102:11023-11028]. The present results may nonetheless inform the future design and testing of HD biomarker strategies.

Tripchlorolide protects against MPTP-induced neurotoxicity in C57BL/6 mice

Many current studies of Parkinson's disease (PD) suggest that inflammation is involved in the neurodegenerative process. Tripchlorolide (TW397), a traditional Chinese herbal compound with anti-inflammatory and immunosuppressive properties, has been shown to protect dopaminergic neurons against, and restore their function after, the neurotoxicity induced by 1-methyl-4-phenylpyridinium ions in vitro. This study was designed to investigate the effect of TW397 in vivo in the PD model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned C57BL/6 mice. In the animals that received vehicle-only (i.e., no TW397) treatment with MPTP i.p. injection, the survival ratios of tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the substantia nigra pars compacta and TH-IR fibres in the striatum were only 59 and 13%, respectively, compared with the normal controls. Intriguingly, in conjunction with MPTP, treatment with TW397, 1 microg/kg for 16 days, once per day, dramatically improved the survival rate of the TH-IR neurons and TH-IR fibres to 80 and 43% of the control. The treatment with TW397 also significantly improved the level of dopamine in the substantia nigra and striatum to 157 and 191%, respectively, of the MPTP- plus vehicle-treated group. In addition, in MPTP-treated animals the rota-rod performances of those treated with 0.5 or 1 microg/kg TW397 were significantly improved, by approximately 2- and 3-fold, respectively, relative to vehicle-treated animals. The neuroprotective effect of TW397 was coincident with an attenuated astroglial response within the striatum. These data demonstrate a neuroprotective action of TW397 in vivo against MPTP toxicity, with important implications for the treatment of PD.

Pathogenesis of Parkinson's disease: oxidative stress, environmental impact factors and inflammatory processes

Current hypothesis of neuronal degeneration in Parkinson's disease (PD) have been proposed, including formation of free radicals and oxidative stress, mitochondrial dysfunction, excitotoxicity, trophic factor deficiency, inflammatory processes, genetic factors, environmental impact factors, toxic action of nitric oxide, apoptosis, and so on. This review mainly discussed oxidative stress, environmental impact factors, and inflammatory processes in PD.

Response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) differs in mouse strains and reveals a divergence in JNK signaling and COX-2 induction prior to loss of neurons in the substantia nigra pars compacta

Parkinson's disease (PD) is a neurodegenerative disease whose hallmark pathological features include a selective loss of dopaminergic neurons in the midbrain. Recent studies have described the activation of a stress-induced signal cascade, c-Jun N-terminal kinase (JNK)-mediated activation of c-Jun, and an increase in the expression of a downstream effector, cyclooxygenase 2 (COX-2), in postmortem PD brains. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces selective neuronal loss in the midbrain similar to that seen in PD, also induces JNK-mediated activation of c-Jun and generates a COX-2 response in C57BL/6J mice. However, mice exhibit a strain-dependent susceptibility to MPTP. Identifying the point(s) of molecular divergence in the MPTP-induced response may provide insight into the cause of PD or a means to identify susceptibility to PD in humans. Here we examined JNK signaling and COX-2 induction in two strains of mice, the MPTP-sensitive C57BL/6J and the MPTP-resistant Swiss Webster (SW). We show that C57BL/6J and SW strains differ in JNK and c-Jun activation in response to MPTP. In addition, the MPTP-induced COX-2 response occurs exclusively in C57BL/6J mice. Furthermore, strain-specific responses to MPTP are not due to differences in MPP(+) levels and are not secondary to cell death. These results provide evidence toward a mechanism of strain-dependent sensitivity to MPTP.

Higher frequency of regulatory T cells in the elderly and increased suppressive activity in neurodegeneration

The involvement of regulatory T cells (Treg) in autoimmune-disease development has been demonstrated. However, their alteration during ageing and age-related diseases has not been thoroughly investigated yet. Alzheimer (AD) and Parkinson disease (PD), are related to protein-misfolding and are accompanied by neuroinflammation. Since, it has been hypothesized that the neuroinflammation attempts to prevent disease development, we speculated that changes in Treg might affect any relevant immune mechanism. The analysis of Treg from AD and PD patients as well as non-affected individuals, revealed that the frequency of Treg (CD4(+)Foxp3(+)) increases with age and is accompanied by intensified suppressive activity for Treg in patients.

Apoptotic neuronal death in Parkinson's disease: Involvement of nitric oxide

Apoptosis of nigral dopaminergic neurons by various mechanisms is an emerging phenomenon involved in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Both extrinsic and intrinsic pathways seems to be involved in death of nigral neurons, intrinsic pathway however, seems to be more important due to the energy crisis. Apoptosis by intrinsic pathway is executed by several initiators and effector caspases, which have been found activated in PD patients, experimental models as well as in neuronal cultures. Nitric oxide (NO) seems to be a central molecule due to its ability to modulate both pro and antiapoptotic phenomenon. The review focuses on the diverse extrinsic and intrinsic factors, signaling pathways and their modulation by NO leading to the death of dopaminergic neurons.

Correlation between levels of pigment epithelium-derived factor and vascular endothelial growth factor in the striatum of patients with Parkinson's disease

Parkinson's disease (PD) is caused by progressive degeneration of nigrostriatal dopaminergic neurons and can potentially be treated by intrastriatal delivery of neurotrophic factors. Pigment epithelium-derived factor (PEDF), which exhibits protective effects on various neuronal populations, is up-/down-regulated in the cerebrospinal fluid in some neurodegenerative conditions. Here we investigated the level of PEDF protein in the striatum and immunoreactivity for PEDF in the substantia nigra (SN) of patients with PD to assess its role in the pathophysiology of PD. We also studied changes in PEDF expression in the striatum of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We found a transient and rapid up-regulation of PEDF transcripts and a marked increase in immunoreactivity for PEDF protein in response to MPTP administration in mice. However, there were no significant changes in striatal levels of PEDF and immunoreactivity for PEDF in the SN of PD patients compared with age-matched non-PD patients. Intriguingly, the striatal levels of PEDF and vascular endothelial growth factor (VEGF), which has opposite functions to PEDF in terms of angiogenesis and vascular permeability, correlated positively in PD patients. Our results suggest up-regulation of PEDF in response to acute insult to the dopaminergic pathway, but such response might be disturbed in patients with advanced PD. The correlation between PEDF and VEGF striatal levels in PD patients suggests that concerted neurotrophic functions of these factors or structural changes in blood vessel walls play an important role in the pathophysiology of PD.

Autoantibodies to alpha-synuclein in inherited Parkinson's disease

Neurodegeneration in Parkinson's disease (PD) is accompanied by a local immune reaction in the affected brain regions. It is well established that alpha-synuclein is directly implicated in the pathogenesis of PD. Development of the disease is often associated with changes of expression and cellular compartmentalisation of this protein; moreover, its oligomers or protofibrils are often released to the CSF and plasma of patients. Aggregated alpha-synuclein can trigger the activation of microglia; however, its capacity to induce production of specific autoantibodies (AAb) has not been assessed. In this study, we examined the presence of AAb against synuclein family members in the peripheral blood serum of PD patients and control individuals. Presence of AAb against beta-synuclein or gamma-synuclein showed no association with PD. Multi-epitopic AAb against alpha-synuclein were detected in 65% of all patients tested and their presence strongly correlated with an inherited mode of the disease but not with other disease-related factors. The frequency of the presence of AAb in the studied group of patients with sporadic form of PD was not significantly different from the frequency in the control group but very high proportion (90%) of patients with familial form of the disease were positive for AAb against alpha-synuclein. We hypothesise that these AAb could be involved in pathogenesis of the inherited form of PD.

Tumor necrosis factor-alpha promoter polymorphism is associated with the risk of Parkinson's disease

Inflammatory events may contribute to the pathogenesis of Parkinson's disease (PD). We conducted a case-control study in a cohort of 369 PD cases and another cohort of 326 ethnically matched controls to investigate the association of tumor necrosis factor-alpha (TNF-alpha) promoter single nucleotide polymorphisms (SNPs) with the risk of PD. The overall genotype distribution at T-1031C and C-857T sites showed significant difference between PD cases and controls (P = 0.0062 and 0.0035, respectively). However, only the more frequent -1031 CC genotype was evidently associated with PD (P = 0.0085, odds ratio: 2.96; 95% CI: 1.38-7.09). Pairwise SNP linkage disequilibrium showed -1031 and -863 sites are in strong linkage disequilibrium (D' = 0.93, Delta(2) = 0.80). Pairwise haplotype analysis among the four sites showed that -1031C-863A may act as a risk haplotype among PD cases (P = 0.0028, odds ratio: 2.18; 95% CI: 1.33-3.69).

Chronic lithium administration attenuates up-regulated brain arachidonic acid metabolism in a rat model of neuroinflammation

Neuroinflammation, caused by a 6-day intracerebroventricular infusion of lipopolysaccharide (LPS) in rats, is associated with the up-regulation of brain arachidonic acid (AA) metabolism markers. Because chronic LiCl down-regulates markers of brain AA metabolism, we hypothesized that it would attenuate increments of these markers in LPS-infused rats. Incorporation coefficients k* of AA from plasma into brain, and other brain AA metabolic markers, were measured in rats that had been fed a LiCl or control diet for 6 weeks, and subjected in the last 6 days on the diet to intracerebroventricular infusion of artificial CSF or of LPS. In rats on the control diet, LPS compared with CSF infusion increased k* significantly in 28 regions, whereas the LiCl diet prevented k* increments in 18 of these regions. LiCl in CSF infused rats increased k* in 14 regions, largely belonging to auditory and visual systems. Brain cytoplasmic phospholipase A(2) activity, and prostaglandin E(2) and thromboxane B(2) concentrations, were increased significantly by LPS infusion in rats fed the control but not the LiCl diet. Chronic LiCl administration attenuates LPS-induced up-regulation of a number of brain AA metabolism markers. To the extent that this up-regulation has neuropathological consequences, lithium might be considered for treating human brain diseases accompanied by neuroinflammation.

Role of neuronal nitric oxide in the dopamine deficit of HPRT-deficient mice

Lesch-Nyhan disease is a debilitating disorder caused by a lack of purine salvage activity. Basal ganglia dopamine deficits manifest in both patients and hypoxanthine phosphoribosyltransferase (HPRT) mutant mice. We previously reported decreased activity in an oxidant sensitive enzyme in the brain of HPRT-deficient mice. In the present study, we have investigated whether one source of free radicals, neuronal nitric oxide synthase (NOS1), contributes to the dopamine deficit associated with HPRT deficiency. HPRT knockout and wild-type mice were bred, either to lack, or to have the full complement of NOS1 alleles. Double mutant mice had striatal dopamine and dopamine metabolite levels indistinguishable from the HPRT single mutant counterparts. These results indicate that NOS1 produced nitric oxide does not contribute to the dopamine deficit seen in HPRT deficiency.

Autotransplantation of bone marrow-derived stem cells as a therapy for neurodegenerative diseases

Neurodegenerative diseases are characterized by a progressive degeneration of selective neural populations. This selective hallmark pathology and the lack of effective treatment modalities make these diseases appropriate candidates for cell therapy. Bone marrow-derived mesenchymal stem cells (MSCs) are self-renewing precursors that reside in the bone marrow and may further be exploited for autologous transplantation. Autologous transplantation of MSCs entirely circumvents the problem of immune rejection, does not cause the formation of teratomas, and raises very few ethical or political concerns. More than a few studies showed that transplantation of MSCs resulted in clinical improvement. However, the exact mechanisms responsible for the beneficial outcome have yet to be defined. Possible rationalizations include cell replacement, trophic factors delivery, and immunomodulation. Cell replacement theory is based on the idea that replacement of degenerated neural cells with alternative functioning cells induces long-lasting clinical improvement. It is reasoned that the transplanted cells survive, integrate into the endogenous neural network, and lead to functional improvement. Trophic factor delivery presents a more practical short-term approach. According to this approach, MSC effectiveness may be credited to the production of neurotrophic factors that support neuronal cell survival, induce endogenous cell proliferation, and promote nerve fiber regeneration at sites of injury. The third potential mechanism of action is supported by the recent reports claiming that neuroinflammatory mechanisms play an important role in the pathogenesis of neurodegenerative disorders. Thus, inhibiting chronic inflammatory stress might explain the beneficial effects induced by MSC transplantation. Here, we assemble evidence that supports each theory and review the latest studies that have placed MSC transplantation into the spotlight of biomedical research.

Paeoniflorin attenuates neuroinflammation and dopaminergic neurodegeneration in the MPTP model of Parkinson's disease by activation of adenosine A1 receptor

1. This study examined whether Paeoniflorin (PF), the major active components of Chinese herb Paeoniae alba Radix, has neuroprotective effect in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD). 2. Subcutaneous administration of PF (2.5 and 5 mg kg(-1)) for 11 days could protect tyrosine hydroxylase (TH)-positive substantia nigra neurons and striatal nerve fibers from death and bradykinesia induced by four-dose injection of MPTP (20 mg kg(-1)) on day 8. 3. When given at 1 h after the last dose of MPTP, and then administered once a day for the following 3 days, PF (2.5 and 5 mg kg(-1)) also significantly attenuated the dopaminergic neurodegeneration in a dose-dependent manner. Post-treatment with PF (5 mg kg(-1)) significantly attenuated MPTP-induced proinflammatory gene upregulation and microglial and astrocytic activation. 4. Pretreatment with 0.3 mg kg(-1) 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A1 receptor (A1AR) antagonist, 15 min before each dose of PF, reversed the neuroprotective and antineuroinflammatory effects of PF. 5. In conclusion, this study demonstrated that PF could reduce the MPTP-induced toxicity by inhibition of neuroinflammation by activation of the A1AR, and suggested that PF might be a valuable neuroprotective agent for the treatment of PD.

Neuroinflammation, Oxidative Stress and the Pathogenesis of Parkinson's Disease

Neuroinflammatory processes play a significant role in the pathogenesis of Parkinson's disease (PD). Epidemiologic, animal, human, and therapeutic studies all support the presence of an neuroinflammatory cascade in disease. This is highlighted by the neurotoxic potential of microglia . In steady state, microglia serve to protect the nervous system by acting as debris scavengers, killers of microbial pathogens, and regulators of innate and adaptive immune responses. In neurodegenerative diseases, activated microglia affect neuronal injury and death through production of glutamate, pro-inflammatory factors, reactive oxygen species, quinolinic acid amongst others and by mobilization of adaptive immune responses and cell chemotaxis leading to transendothelial migration of immunocytes across the blood-brain barrier and perpetuation of neural damage. As disease progresses, inflammatory secretions engage neighboring glial cells, including astrocytes and endothelial cells, resulting in a vicious cycle of autocrine and paracrine amplification of inflammation perpetuating tissue injury. Such pathogenic processes contribute to neurodegeneration in PD. Research from others and our own laboratories seek to harness such inflammatory processes with the singular goal of developing therapeutic interventions that positively affect the tempo and progression of human disease.

Nigrostriatal dopaminergic neurodegeneration in the weaver mouse is mediated via neuroinflammation and alleviated by minocycline administration

The murine mutant weaver (gene symbol, wv) mouse, which carries a mutation in the gene encoding the G-protein inwardly rectifying potassium channel Girk2, exhibits a diverse range of defects as a result of postnatal cell death in several different brain neuron subtypes. Loss of dopaminergic nigrostriatal neurons in the weaver, unlike cerebellar granule neuronal loss, is via a noncaspase-mediated mechanism. Here, we present data demonstrating that degeneration of midbrain dopaminergic neurons in weaver is mediated via neuroinflammation. Furthermore, in vivo administration of the anti-inflammatory agent minocycline attenuates nigrostriatal dopaminergic neurodegeneration. This has novel implications for the use of the weaver mouse as a model for Parkinson's disease, which has been associated with increased neuroinflammation.

Neuroprotective therapy in Parkinson disease

During the past decade, there has been a remarkable progress in our understanding of the biology of Parkinson disease (PD), which has been translated into searching for novel therapy for PD. Much focus is shifted from the development of drugs that only relieve PD symptoms to new generation of remedies that can potentially protect dopaminergic neurons and modify the disease course. Several novel therapeutic approaches have been tested in preclinical experiments and in clinical trials, including molecules targeting on genes involved in the pathogenesis of the disease, neurotrophic factors critical for dopaminergic neuron survival and function, new generation of dopamine receptor agonists that may possess neuroprotective effects, and agents of antioxidation, antiinflammation, and antiapoptosis. The results of these studies will shed new light to our hope that PD can be cured in the future.

NO-cGMP signaling and regenerative medicine involving stem cells

Nitric oxide (NO) is a short lived diatomic free radical species synthesized by nitric oxide synthases (NOS). The physiological roles of NO depend on its local concentrations as well as availability and the nature of downstream target molecules. At low nanomolar concentrations, activation of soluble guanylyl cyclase (sGC) is the major event initiated by NO. The resulting elevation in the intracellular cyclic GMP (cGMP) levels serves as signals for regulating diverse cellular and physiological processes. The participation of NO and cGMP in diverse physiological processes is made possible through cell type specific spatio-temporal regulation of NO and cGMP synthesis and signal diversity downstream of cGMP achieved through specific target selection. Thus cyclic GMP directly regulates the activities of its downstream effectors such as Protein Kinase G (PKG), Cyclic Nucleotide Gated channels (CNG) and Cyclic nucleotide phosphodiesterases, which in turn regulate the activities of a number of proteins that are involved in regulating diverse cellular and physiological processes. Localization and activity of the NO-cGMP signaling pathway components are regulated by G-protein coupled receptors, receptor and non receptor tyrosine kinases, phosphatases and other signaling molecules. NO also serves as a powerful paracrine factor. At micromolar concentrations, NO reacts with superoxide anion to form reactive peroxinitrite, thereby leading to the oxidation of important cellular proteins. Extensive research efforts over the past two decades have shown that NO is an important modulator of axon outgrowth and guidance, synaptic plasticity, neural precursor proliferation as well as neuronal survival. Excessive NO production as that evoked by inflammatory signals has been identified as one of the major causative reasons for the pathogenesis of a number of neurodegenerative diseases such as ALS, Alzheimers and Parkinson diseases. Regenerative therapies involving transplantation of embryonic stem cells (ES cells) and ES cell derived lineage committed neural precursor cells have recently shown promising results in animal models of Parkinson disease (PD). Recent studies from our laboratory have shown that a functional NO-cGMP signaling system is operative early during the differentiation of embryonic stem cells. The cell type specific, spatio-temporally regulated NO-cGMP signaling pathways are well suited for inductive signals to use them for important cell fate decision making and lineage commitment processes. We believe that manipulating the NO-cGMP signaling system will be an important tool for large scale generation of lineage committed precursor cells to be used for regenerative therapies.

PEP-1-SOD fusion protein efficiently protects against paraquat-induced dopaminergic neuron damage in a Parkinson disease mouse model

Parkinson disease (PD) is a common neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra (SN). However, the mechanism of the pathology of PD still remains poorly understood. Because the administration of the herbicide paraquat triggers selective dopaminergic neuronal cell death, exposure of mice to this herbicide is one valuable model for studying the pathological aspects of PD. In this study, we investigated the protective effects of PEP-1-SOD in vitro and in vivo under exposure to the herbicide paraquat. The viability of neuronal cells treated with paraquat was markedly increased by transduced PEP-1-SOD. When the PEP-1-SOD fusion protein was injected intraperitoneally into mice, a completely protective effect against dopaminergic neuronal cell death in the SN was observed. This protective effect was synergistically increased when the PEP-1-SOD was cotransduced with Tat-alpha-synuclein. These results suggest that PEP-1-SOD provides a strategy for therapeutic delivery in various human diseases related to reactive oxygen species, including PD.

Activation of non-neuronal cells within the prenatal developing brain of sheep with neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs, Batten disease) are fatal inherited lysosomal storage diseases of children characterized by increasing blindness, seizures and profound neurodegeneration but the mechanisms leading to these pathological changes remain unclear. Sheep with a CLN6 form that have a human-like brain and disease progression are invaluable for studying pathogenesis. A study of preclinical pathology in these sheep revealed localized glial activation at only 12 days of age, particularly in cortical regions that subsequently degenerate. This has been extended by examining fetal tissue from 60 days of gestation onwards. A striking feature was the presence of reactive astrocytes and the hypertrophy and proliferation of perivascular cells noted within the developing white matter of the cerebral cortex 40 days before birth. Astrocytic activation was evident within the cortical gray matter 20 days before birth, and was confined to the superficial laminae 12 days after birth. Clusters of activated microglia were detected in upper neocortical gray matter laminae shortly after birth. Neuronal development in affected sheep was undisturbed at these early ages. This prenatal activation of non-neuronal cells within the affected brain indicates the onset of pathogenesis during brain development and that an ordered sequence of glial activation precedes neurodegeneration.

Temporal effects of paraquat/maneb on microglial activation and dopamine neuronal loss in older rats

We investigated the effects of combined systemic exposure to the herbicide paraquat (PQ) and the fungicide maneb (MB) in 6-month-old rats, an animal model of Parkinson's disease resulting from environmental toxin exposure. Following two doses of PQ (10 mg/kg) and MB (30 mg/kg), 52% of animals developed fatal lung injury. Examination of the remaining animals showed degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta 6 weeks, but not 4 weeks, following PQ/MB. In contrast, microglial activation was observed at 4 weeks, but had abated by 6 weeks. Compared with our previous findings in younger rats, these results suggest increased susceptibility of older animals to lung and brain toxicity from PQ/MB exposure. Microglial activation preceded, and therefore likely contributed to, DA neurodegeneration. Further, electron microscopy revealed an abnormal appearance of the Golgi apparatus at 4 weeks that was confirmed using double immunostaining for tyrosine hydroxylase and Golgi. This suggests that PQ/MB causes protein processing dysfunction in nigral DA neurons that may be either a direct effect of PQ/MB or the result of microglial activation.

Interaction of alpha-synuclein and dopamine metabolites in the pathogenesis of Parkinson's disease: a case for the selective vulnerability of the substantia nigra

Parkinson's disease (PD) is the most common movement disorder. Major disease symptoms are due to the loss of dopaminergic (DA) neurons in substantia nigra (SN). The pathologic hallmark of PD is Lewy bodies (LBs) in the SN and the major protein in LBs is alpha-synuclein (AS). A plethora of evidence points towards the culpability of AS in the pathogenesis of PD including: (1) linkage of AS mutations to familial forms of PD, (2) triplication of the AS locus causing PD, and (3) overexpression of AS in transgenic mice and Drosophila leads to PD-like phenotypes. Studies of purified AS have revealed its ability to interact with diverse molecules including monoamines. Monoamine metabolism is associated with oxidative stress conditions that may contribute to DA-AS interactions promoting aggregation and neuronal damage. However, in order to explain the selective vulnerability of DA neurons there needs to be a link between DA metabolism and AS aggregation. Since only the DA neurons contain significant amounts of DA, this has been hypothesized to account for the selective vulnerability of SN neurons. However, DA itself may not be toxic at physiologic relevant doses, so it is probable that other DA metabolites may play a major role in AS aggregation. In this review, we discuss the role of the DA metabolite 3,4-dihydroxyphenylacetaldehyde to provide a plausible link between DA production and metabolism, AS aggregation and the pathogenesis of PD.

Oxidation and cytotoxicity of 6-OHDA are mediated by reactive intermediates of COX-2 overexpressed in PC12 cells

Parkinson's disease is characterized by a progressive loss of dopaminergic neurons, likely associated with dysregulation of oxidation of catechols, such as dopamine (DA) and 6-hydroxydopamine (6-OHDA), and resulting in oxidative stress. The involvement of cyclooxygenase-2 (COX-2) in pathogenesis of Parkinson's disease has been suggested. However, specific COX-2 triggered mechanisms participating in catalysis of DA oxidation and enhanced catechol-induced cytotoxicity remain poorly characterized. Here, we demonstrate that in a model biochemical system, recombinant heme-reconstituted COX-2 induced oxidation of 6-OHDA in the course of its peroxidase (H(2)O(2)-dependent) and cyclooxygenase (arachidonic acid (AA)-dependent) catalytic half-cycles. Similarly, COX-2 was able to stimulate 6-OHDA oxidation during its peroxidase- and cyclooxygenase half-cycles and caused oxidative stress in homogenates of PC12 cells stably overexpressing the enzyme (but not in mock-transfected cells). In addition, the increased levels of COX-2 were associated with enhanced cytotoxicity of 6-OHDA in stably transfected PC12 cells. Finally, co-oxidation of 6-OHDA by COX-2 triggered production of superoxide radicals critical for both propagation of 6-OHDA oxidation and induction of oxidative stress in COX-2 overexpressing cells. Thus, we conclude that both peroxidase and cyclooxygenase half-cycles of COX-2-catalyzed reactions are essential for COX-2-dependent activation of 6-OHDA oxidation, oxygen radical production, oxidative stress, and cytotoxicity.

Behavioral and morphological effects of minocycline in the 6-hydroxydopamine rat model of Parkinson's disease

The neuropathology in many neurodegenerative diseases is mediated by inflammatory cascades that influence neuronal dysfunction and death. Minocycline reduces the neurodegeneration observed in various models of Parkinson's. We exploited the unilateral 6-hydroxydopamine (6-OHDA) lesion model to assess the effect of minocycline on related neurodegeneration. Thirty Fisher 344 rats were divided into three daily treatment groups: (1) after: 45 mg/kg of minocycline beginning 24 h after lesioning; (2) before: 45 mg/kg of minocycline beginning 3 days before 6-OHDA lesioning; (3) control: corresponding saline-treated controls. Animals were assessed for apomorphine-induced rotations for 4 weeks. A longitudinal model for repeated measures showed that both after and before groups had significantly lower rotations than controls (P < 0.001 for both comparisons). Pair-wise group comparisons showed that the before animals rotated less compared to controls (mean rotations: 164 +/- 38 versus 386 +/- 49, respectively, P = 0.001). After animals also rotated significantly less then controls (mean rotations: 125 +/- 41 versus 386 +/- 49, respectively, P < 0.001). Animals receiving minocycline displayed reduced tyrosine hydroxylase-positive cell loss in the lesioned nigra versus contralateral nonlesioned nigra, compared to controls (mean differences: 5065 for after, 3550 for before, and 6483 for controls; P = 0.158 for after versus controls, P = 0.019 for before versus controls). The remaining lesioned nigral cells of both minocycline-treated groups were larger than controls, with the most robust cell size and fiber density observed in the after group. These data suggest that the therapeutic potential of minocycline may depend on the time of drug administration relative to neuropathogenic event.

Transduced Tat-α-Synuclein Protects against Oxidative Stress In vitro and In vivo

Parkinson's disease (PD) is a common neurodegenerative disorder and is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. Although many studies showed that the aggregation of alpha-synuclein might be involved in the pathogenesis of PD, its protective properties against oxidative stress remain to be elucidated. In this study, human wild type and mutant alpha-synuclein genes were fused with a gene fragment encoding the nine amino acid transactivator of transcription (Tat) protein transduction domain of HIV-1 in a bacterial expression vector to produce a genetic in-frame WT Tat-alpha-synuclein (wild type) and mutant Tat-alpha-synucleins (mutants; A30P and A53T), respectively, and we investigated the protective effects of wild type and mutant Tat-alpha-synucleins in vitro and in vivo. WT Tat-alpha-synuclein rapidly transduced into an astrocyte cells and protected the cells against paraquat induced cell death. However, mutant Tat-alpha-synucleins did not protect at all. In the mice models exposed to the herbicide paraquat, the WT Tat-alpha-synuclein completely protected against dopaminergic neuronal cell death, whereas mutants failed in protecting against oxidative stress. We found that these protective effects were characterized by increasing the expression level of heat shock protein 70 (HSP70) in the neuronal cells and this expression level was dependent on the concentration of transduced WT Tat-alpha-synuclein. These results suggest that transduced Tat-alpha-synuclein might protect cell death from oxidative stress by increasing the expression level of HSP70 in vitro and in vivo and this may be of potential therapeutic benefit in the pathogenesis of PD.

Protective role of heat shock and heat shock protein 70 in lactacystin-induced cell death both in the rat substantia nigra and PC12 cells

Proteasomal dysfunction plays an important role in the pathogenesis of Parkinson disease (PD). Although clinical and experimental evidence continues to accumulate indicating heat shock protein 70 (HSP70) is significant in the pathogenesis of PD, few studies have been made to investigate the role of HSP70 under the condition of proteasome dysfunction. In in vivo study, we infused lactacystin into the unilateral substantia nigra (SN) of Sprague-Dawley rats with or without preceding whole body hyperthermia (WBH). Immunohistochemical studies showed the death of dopaminergic neurons and activated microglia in the SN. Lactacystin with prior WBH increased the expression of HSP70 more than did lactacystin alone and decreased lactacystin-induced dopaminergic neuronal death in the SN. In PC12 cells, heat shock pretreatment decreased lactacystin-induced cell death. Although additional treatment of nocodazole, ammonium chloride, and 3-methyladenine augmented cell death by lactacystin, heat shock pretreated to these drugs offsets their additional toxicity. These results indicate that heat shock proteins, especially HSP70, could play an important role under the condition of proteasome dysfunction in part by fostering aggresome formation and lysosome-mediated autophagy.

CREB and NF-kappaB transcription factors regulate sensitivity to excitotoxic and oxidative stress induced neuronal cell death

1. Glutamate-NMDA receptor excitotoxicity and oxidative stress are two common mechanisms associated with most neurodegenerative diseases. We hypothesize that the vital state of neurons is regulated in part by two key transcription factors, CREB and NF-kappaB. To test this hypothesis we used hippocampal-entorhinal cortex slice cultures. 2. Glutamate neurotoxicity and oxidative stress neurotoxicity, using hydrogen peroxide (H(2)O(2)) are both associated with a decrease in CREB DNA binding and an increase in NF-kappaB DNA binding. 3. Agents that modulate CREB and NF-kappaB DNA-binding activity alter neurotoxicity. Rolipram, a phosphodiesterase IV inhibitor, increased CREB DNA binding activity and decreased toxicity, whereas TNFalpha, increased NF-kappaB DNA-binding activity and increased neurotoxicity to both glutamate and H(2)O(2). Ethanol decreased CREB and increased NF-kappaB DNA-binding activity and increased neurotoxicity to both glutamate and H(2)O(2). 4. Brain-derived neurotrophic factor (BDNF) is a transcriptionally regulated trophic factor whose expression follows sensitivity to toxicity suggesting it is one of the transcriptionally regulated factors that contributes to neuronal vitality secondary to the balance of CREB-NF-kappaB-activated transcription. Together these studies suggest that neurotoxicity through glutamate-NMDA receptors or oxidative stress is dependent upon CREB and NF-kappaB DNA transcription that regulates vitality of neurons.

DNA microarray analysis of striatal gene expression in symptomatic transgenic Huntington's mice (R6/2) reveals neuroinflammation and insulin associations

Huntington's disease (HD) is an inherited, progressive neurodegenerative disorder caused by CAG repeat expansion in the gene that codes for the protein huntingtin. The underlying neuropathological events leading to the selectivity of striatal neuronal loss are unknown. However, the huntingtin mutation interferes at several levels of normal cell function. The complexity of this disease makes microarray analysis an appealing technique to begin the identification of common pathways that may contribute to the pathology. In this study, striatal tissue was extracted for gene expression profiling from wild-type and symptomatic transgenic Huntington mice (R6/2) expressing part of the human Huntington's disease gene. We interrogated a 15 K high-density mouse EST array not previously used for HD and identified 170 significantly differentially expressed ESTs in symptomatic R6/2 mice. Of the 80 genes with known function, 9 genes had previously been identified as altered in HD. 71 known genes were associated with HD for the first time. The data obtained from this study confirm and extend previous observations using DNA microarray techniques on genetic models for HD, revealing novel changes in expression in a number of genes not previously associated with HD. Further bioinformatic analysis, using software to construct biological association maps, focused attention on proteins such as insulin and TH1-mediated cytokines, suggesting that they may be important regulators of affected genes. These results may provide insight into the regulation and interaction of genes that contribute to adaptive and pathological processes involved in HD.

Protein aggregation in the pathogenesis of familial and sporadic Parkinson's disease

Parkinson's disease (PD) is a slowly progressive, age-related, neurodegenerative disorder. The cause and mechanism of neuronal death have been elusive. However, recent genetic, postmortem and experimental evidence show that protein accumulation and aggregation are prominent occurrences in both sporadic and familial PD. The relevance of these events to other cellular and biochemical changes, and to the neurodegenerative process, is being unraveled. It is increasingly evident that one or a combination of defects, including mutations, oxidative stress, mitochondrial impairment and dysfunction of the ubiquitin-proteasome system, lead to an excess production and aggregation of abnormal proteins in PD. In this respect, altered protein handling appears to be a central factor in the pathogenic process occurring in the various hereditary and sporadic forms of PD. This suggests that manipulation of proteolytic systems is a rational approach in the development of neuroprotective therapies that could modify the pathological course of PD.

Postmortem brain fatty acid profile of levodopa-treated Parkinson disease patients and parkinsonian monkeys

Fatty acids play a critical role in brain function but their specific role in the pathophysiology of Parkinson disease (PD) and levodopa-induced motor complications is still unknown. From a therapeutic standpoint, it is important to determine the relation between brain fatty acids and PD because the brain fatty acid content depends on nutritional intake, a readily manipulable environmental factor. Here, we report a postmortem analysis of fatty acid profile by gas chromatography in the brain cortex of human patients (12 PD patients and nine Controls) as well as in the brain cortex of monkeys (four controls, five drug-naive MPTP monkeys and seven levodopa-treated MPTP monkeys). Brain fatty acid profile of cerebral cortex tissue was similar between PD patients and Controls and was not correlated with age of death, delay to autopsy or brain pH. Levodopa administration in MPTP monkeys increased arachidonic acid content (+7%; P < 0 .05) but decreased docosahexaenoic acid concentration (-15%; P < 0.05) and total n-3:n-6 polyunsaturated fatty acids ratio (-27%; P < 0.01) compared to drug-naive MPTP animals. Interestingly, PD patients who experienced motor complications to levodopa had higher arachidonic acid concentrations in the cortex compared to Controls (+13.6%; P < 0.05) and to levodopa-treated PD patients devoid of motor complications (+14.4%; P < 0.05). Furthermore, PD patients who took an above-median cumulative dose of levodopa had a higher relative amount of saturated fatty acids but lower monounsaturated fatty acids in their brain cortex (P < 0.01). These results suggest that changes in brain fatty acid relative concentrations are associated with levodopa treatment in PD patients and in a non-human primate model of parkinsonism.

Progressive dopamine neuron loss following supra-nigral lipopolysaccharide (LPS) infusion into rats exposed to LPS prenatally

Toxin-induced animal models of Parkinson's disease (PD) exhibit many of the same neuroinflammatory changes seen in patients suggesting a role for inflammation in DA neuron loss. Yet, despite this inflammation, the progressive loss of DA neurons that characterizes PD is rarely seen in animals. We infused lipopolysaccharide (LPS) or saline into 7-month-old rats that had been exposed to LPS or saline prenatally and assessed them for DA neuron loss and inflammatory measures (interleukin 1 beta, tumor necrosis factor-alpha, glutathione, and activated microglia) over a period of 84 days to examine the role of pre-existing inflammation in progressive DA neuron loss. LPS infusion into both prenatal treatment groups produced neuroinflammation during the 14 days of LPS infusion that subsequently reverted toward normal over the next 70 days. In animals with pre-existing inflammation (i.e., prenatal LPS), however, the acute changes seen were attenuated, but took much longer to return to normal suggesting a prolonged inflammatory response. These inflammatory changes were consistent with the greater acute DA neuron loss seen in the prenatal saline controls and the progressive DA neuron loss seen only in the animals exposed to LPS prenatally. Interestingly, both prenatal treatment groups exhibited increases in microglia over the entire 84-day course of the study. These data suggest that pre-existing neuroinflammation prolongs the inflammatory response that occurs with a second toxic exposure, which may be responsible for progressive DA neuron loss. This provides further support for the "multiple hit" hypothesis of PD.

L-DOPA treatment from the viewpoint of neuroprotection. Possible mechanism of specific and progressive dopaminergic neuronal death in Parkinson's disease

With regard to the mechanism of selective dopaminergic neuronal death, experimental results of studies on the neurotoxicity of MPTP and rotenone indicate that degeneration of dopamine neurons is closely related to mitochondrial dysfunction, inflammatory process and oxidative stress, particularly with regard to the generation of quinones as dopamine neuron-specific oxidative stress. Thus, it is now clear that the presence of high levels of discompartmentalized free dopamine in dopaminergic neurons may explain the specific vulnerability of dopaminergic neurons through the generation of highly toxic quinones.

Estrogen, neuroinflammation and neuroprotection in Parkinson's disease: glia dictates resistance versus vulnerability to neurodegeneration

Post-menopausal estrogen deficiency is recognized to play a pivotal role in the pathogenesis of a number of age-related diseases in women, such as osteoporosis, coronary heart disease and Alzheimer's disease. There are also sexual differences in the progression of diseases associated with the nigrostriatal dopaminergic system, such as Parkinson's disease, a chronic progressive degenerative disorder characterized by the selective degeneration of mesencephalic dopaminergic neurons in the substancia nigra pars compacta. The mechanism(s) responsible for dopaminergic neuron degeneration in Parkinson's disease are still unknown, but oxidative stress and neuroinflammation are believed to play a key role in nigrostriatal dopaminergic neuron demise. Estrogen neuroprotective effects have been widely reported in a number of neuronal cell systems including the nigrostriatal dopaminergic neurons, via both genomic and non-genomic effects, however, little is known on estrogen modulation of astrocyte and microglia function in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease. We here highlight estrogen modulation of glial neuroinflammatory reaction in the protection of mesencephalic dopaminergic neurons and emphasize the cardinal role of glia-neuron crosstalk in directing neuroprotection vs neurodegeneration. In particular, the specific role of astroglia and its pro-/anti-inflammatory mechanisms in estrogen neuroprotection are presented. This study shows that astrocyte and microglia response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine injury vary according to the estrogenic status with direct consequences for dopaminergic neuron survival, recovery and repair. These findings provide a new insight into the protective action of estrogen that may possibly contribute to the development of novel therapeutic treatment strategies for Parkinson's disease.

A possible role for humoral immunity in the pathogenesis of Parkinson's disease

The pathogenesis of idiopathic Parkinson's disease is unknown, but nigral degeneration and depigmentation are associated with microglial inflammation and anti-inflammatory medications appear to protect against the disease. The possibility that humoral immunity may play a role in initiating or regulating the inflammation has been suggested by experimental studies triggering dopamine cell death using a variety of transfer strategies and the observation of CD8+ T lymphocytes and complement in the nigra in Parkinson's disease. We analysed the association between degeneration and humoral immune markers in brain tissue of patients with idiopathic (n = 13) or genetic (n = 2 with alpha-synuclein and n = 1 with parkin mutations) Parkinson's disease and controls without neurological disease (n = 12) to determine the humoral immune involvement in Parkinson's disease. Formalin-fixed tissue samples from the substantia nigra and primary visual cortex for comparison were stained for alpha-synuclein, major histocompatibility complex II (HLA), immunoglobulin M (IgM), immunoglobulin G (IgG), IgG subclasses 1-4 and IgG receptors FcgammaR I-III. Antigen retrieval and both single immunoperoxidase and double immunofluorescence procedures were employed to determine the cell types involved and their pattern and semiquantitative densities. Significant dopamine neuron loss occurred in all patients with Parkinson's disease, negatively correlating with disease duration (r = -0.76, P = 0.002). Although all patients had increased inflammatory HLA immunopositive microglia, the degree of inflammation was similar throughout the disease (r = 0.08, P = 0.82). All patients with Parkinson's disease had IgG binding on dopamine neurons but not IgM binding. Lewy bodies were strongly immunolabelled with IgG. A mean 30 +/- 12% of dopamine nigral neurons were immunoreactive for IgG in Parkinson's disease with the proportion of IgG immunopositive neurons negatively correlating with the degree of cell loss in the substantia nigra (r = -0.67, P < 0.0001) and positively correlating with the number of HLA immunopositive microglia (r = 0.51, P = 0.01). Most neuronal IgG was the IgG1 subclass with some IgG3 and less IgG2 also found in the damaged substantia nigra. The high affinity activating IgG receptor, FcgammaRI, was expressed on nearby activated microglia. The low affinity activating IgG receptor, FcgammaRIII was expressed on cells morphologically resembling lymphocytes, whereas immunoreactivity for the inhibitory IgG receptor FcgammaRII was absent in all cases. This pattern of humoral immune reactivity is consistent with an immune activation of microglia leading to the targeting of dopamine nigral neurons for destruction in both idiopathic and genetic cases of Parkinson's disease.

Alterations of T-lymphocyte populations in Parkinson disease

Immune reaction-related inflammation may be important in the pathogenesis of Parkinson disease (PD). To elucidate peripheral immunologic alterations in PD, we characterized extended peripheral T-lymphocyte populations in 33 patients with PD and 34 normal subjects. Patients with PD had significantly decreased CD4+:CD8(+)T-cell ratios (P<0.001), fewer CD4(+)CD25(+)T cells (P<0.01), and significantly increased ratios of IFN-gamma-producing to IL-4-producing T cells (P<0.001). The characteristics of predominant expression of CD8(+)T cells, depletion of CD4(+)CD25(high) cells, and a shift to a T(H)1-type immune response in the peripheral immune system in PD patients may reflect an immune reaction-associated inflammatory process in the brain.

Norharman-induced motoric impairment in mice: neurodegeneration and glial activation in substantia nigra

The beta-carboline norharman is present in cooked food and tobacco smoke and show structural resemblance to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. C57BL/6 mice were injected subcutaneously with norharman (3 and 10 mg/kg) twice per day for five consecutive days. Eighteen hours after the last dose an increased expression of glial fibrillary acidic protein and fluoro-jade staining were demonstrated whereas the number of tyrosine hydroxylase positive cells were unchanged in the substantia nigra. Two weeks after the last treatment a decreased motor activity was observed whereas cognitive functions remained intact. In cultured PC12 cells norharman treatment induced mitochondrial dysfunction and increased the number of caspase-3 and TUNEL-positive cells. The results demonstrate that norharman induced apoptosis in cultured cells as well as early neurodegeneration, glial activation and sustained motor deficits in mice and suggest that exposure to norharman may contribute to idiopathic Parkinson's disease.

Role of chronic infection and inflammation in the gastrointestinal tract in the etiology and pathogenesis of idiopathic parkinsonism. Part 2: response of facets of clinical idiopathic parkinsonism to Helicobacter pylori eradication. A randomized, double-blind, placebo-controlled efficacy study

BACKGROUND

Links between etiology/pathogenesis of neuropsychiatric disease and infection are increasingly recognized.

AIM

Proof-of-principle that infection contributes to idiopathic parkinsonism.

METHODS

Randomized, double-blind, placebo-controlled efficacy study of proven Helicobacter pylori eradication on the time course of facets of parkinsonism. Intervention was 1 week's triple eradication therapy/placebos. Routine deblinding at 1 year (those still infected received open-active), with follow-up to 5 years post-eradication. Primary outcome was mean stride length at free-walking speed, sample size 56 for a difference, active vs. placebo, of 3/4 (between-subject standard deviation). Recruitment of subjects with idiopathic parkinsonism and H. pylori infection was stopped at 31, because of marked deterioration with eradication failure. Interim analysis was made in the 20 who had reached deblinding, seven of whom were receiving antiparkinsonian medication (long-t(1/2), evenly spaced) which remained unchanged.

RESULTS

Improvement in stride-length, on active (n = 9) vs. placebo (11), exceeded size of effect on which the sample size was calculated when analyzed on intention-to-treat basis (p = .02), and on protocol analysis of six weekly assessments, including (p = .02) and excluding (p = .05) those on antiparkinsonian medication. Active eradication (blind or open) failed in 4/20, in whom B-lymphocyte count was lower. Their mean time course was: for stride-length, -243 (95% CI -427, -60) vs. 45 (-10, 100) mm/year in the remainder (p = .001); for the ratio, torque to extend to flex relaxed arm, 349 (146, 718) vs. 58 (27, 96)%/ year (p < .001); and for independently rated, visual-analog scale of stance-walk videos (worst-best per individual identical with 0-100 mm), -64 vs. -3 mm from anterior and -50 vs. 11 lateral (p = .004 and .02).

CONCLUSIONS

Interim analysis points to a direct or surrogate (not necessarily unique) role of a particular infection in the pathogenesis of parkinsonism. With eradication failure, bolus release of antigen from killed bacteria could aggravate an effect of ongoing infection.

Tissue transglutaminase during mouse central nervous system development: lack of alternative RNA processing and implications for its role(s) in murine models of neurotrauma and neurodegeneration

Tissue transglutaminase (tTG) is a member of a multigene family principally involved in catalyzing the formation of protein cross-links. Unlike other members of the transglutaminase family, tTG is multifunctional since it also serves as a guanosine triphosphate (GTP) binding protein (Galpha(h)) and participates in cell adhesion. Different isoforms of tTG can be produced by proteolysis or alternative splicing. We find that tTG mRNA is expressed at low levels in the mouse CNS relative to other tissues, and at lower levels in the CNS of mouse in comparison to that of human or rat. tTG mRNA levels are higher in the heart compared to the CNS, for example, and much higher in the liver. Within the CNS, tTG message is lowest in the adult cerebellum and thalamus and highest in the frontal cortex and striatum. In the hippocampus, tTG expression is highest during embryonic development and falls off dramatically after 1 week of life. We did not find alternative splicing of the mouse tTG. At the protein level, the predominant isoform is approximately 62 kDa. In summary, tTG, an important factor in neuronal survival, is expressed at low levels in the mouse CNS and, unlike rat and human tTG, does not appear to be regulated by alternative splicing. These findings have implications for analyses of rodent tTG expression in human neurodegenerative and neurotrauma models where alternative processing may be an attractive pathogenetic mechanism. They further impact on drug discovery paradigms, where modulation of activity may have therapeutic value.

The acute and the long-term effects of nigral lipopolysaccharide administration on dopaminergic dysfunction and glial cell activation

Sustained reactive microgliosis may contribute to the progressive degeneration of nigral dopaminergic neurons in Parkinson's disease (PD), in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exposed human and in non-human primates. However, the temporal relationship between glial cell activation and nigral cell death is relatively unexplored. Consequently, the effects of acute (24 h) and chronic (30 days) glial cell activation induced by unilateral supranigral lipopolysaccharide (LPS) administration were studied in rats. At 24 h, LPS administration caused a marked reduction in the number of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the substantia nigra (SN) but striatal TH-ir was unaffected. By 30 days, the loss of TH-positive neurons in the LPS-treated nigra was no greater than at 24 h although a heterogeneous loss of striatal TH-ir was present. The loss of nigrostriatal neurons was of functional significance, as at 30 days, LPS-treated rats exhibited ipsiversive circling in response to (+)-amphetamine administration. At 24 h, there was a moderate increase in glial fibrillary acidic protein (GFAP)-ir astrocytes in the SN but a marked elevation of p47phox positive OX-42-ir microglia, and intense inducible nitric oxide synthase (iNOS)-ir and 3-nitrotyrosine (3-NT)-ir was present. However, by 30 days the morphology of OX-42-ir microglia returned to a resting state, the numbers were greatly reduced and no 3-NT-ir was present. At 30 days, GFAP-ir astrocytes were markedly increased in number and iNOS-ir was present in fibrillar astrocyte-like cells. This study shows that acute glial activation leading to dopaminergic neuron degeneration is an acute short-lasting response that does not itself perpetuate cell death or lead to prolonged microglial activation.

MPTP and SNpc DA neuronal vulnerability: role of dopamine, superoxide and nitric oxide in neurotoxicity. Minireview

Parkinson disease (PD) is a common neurodegenerative disease of unknown origin that is characterized, mainly, by a significant reduction in the number of dopamine neurons in the substantia nigra pars compacta (SNpc) of the brain and a dramatic reduction in dopamine levels in the corpus striatum. For reasons that we do not know, the dopamine neuron seems to be more vulnerable to damage than any other neuron in the brain. Although hypotheses of damage to the dopamine neuron include oxidative stress, growth factor decline, excitotoxicity, inflammation in the SNpc and protein aggregation, oxidative stress in the nigrostriatal dopaminergic system garners a significant amount of attention. In the oxidative stress hypothesis of PD, superoxide, nitric oxide and dopamine all conspire to create an environment that can be detrimental to the dopamine neuron. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), the tool of choice for investigations into the mechanisms involved in the death of dopamine neurons in PD, has been used extensively in attempts to sort out what happens in and around the dopamine neuron. Herein, we review the roles of dopamine, superoxide and nitric oxide in the demise of the dopamine neuron in the MPTP model of PD as it relates to the death of the dopamine neuron noted in PD.

Oxidative stress and inflammation in Parkinson's disease: is there a causal link?

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a dramatic loss of dopaminergic neurons in the substantia nigra (SN). Among the many pathogenic mechanisms thought to contribute to the demise of these cells, dopamine-dependent oxidative stress has classically taken center stage due to extensive experimental evidence showing that dopamine-derived reactive oxygen species and oxidized dopamine metabolites are toxic to nigral neurons. In recent years, however, the involvement of neuro-inflammatory processes in nigral degeneration has gained increasing attention. Not only have activated microglia and increased levels of inflammatory mediators been detected in the striatum of deceased PD patients, but a large body of animal studies points to a contributory role of inflammation in dopaminergic cell loss. Recently, postmortem examination of human subjects exposed to the parkinsonism-inducing toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), revealed the presence of activated microglia decades after drug exposure, suggesting that even a brief pathogenic insult can induce an ongoing inflammatory response. Perhaps not surprisingly, non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to reduce the risk of developing PD. In the past few years, various pathways have come to light that could link dopamine-dependent oxidative stress and microglial activation, finally ascribing a pathogenic trigger to the chronic inflammatory response characteristic of PD.

Granulocyte colony-stimulating factor is not protective against selective dopaminergic cell death in vitro

In the present study, we evaluated the potential neuroprotective effect of granulocyte colony-stimulating factor (G-CSF), a hematopoietic growth factor in two different culture models in which dopaminergic (DA) neurons die selectively: first, in a culture model in which death of DA neurons occurs spontaneously and second, in a toxin-based paradigm, the in vitro 1-methyl-4-phenylpyridinium model of PD. In neither of the two models, a treatment with G-CSF, could prevent or halt the progressive neurodegeneration. However, we cannot rule out that G-CSF might exert neuroprotective or even deleterious effects in in vivo models of PD, based on the significant increase in the number of microglial cells observed after G-CSF treatment.

Parkin gene therapy for alpha-synucleinopathy: a rat model of Parkinson's disease

Parkin is known to mitigate alpha-synuclein-induced neuronal cell death in vitro, which suggests that the parkin gene therapy is a candidate for therapeutic strategies for Parkinson's disease (PD). In the present study, the parkin gene therapy was investigated for its ameliorative effects on alpha-synucleinopathy in substantia nigra (SN) of rats. A recombinant adeno-associated viral (rAAV) vector system has frequently been used for the gene transfer to rat SN, and we have previously demonstrated that this technique induced the alpha-synucleinopathy, which closely resembles pathogenetic changes in PD. Therefore, in the present study, the effect of parkin was examined by co-infection of rAAV-parkin with rAAV-alpha-synuclein into dopaminergic neurons in SN. At 13 weeks post-rAAV infection, alpha-synuclein overexpression induced dopaminergic neuron loss, while co-expression of parkin mitigated the alpha-synuclein toxicity. Moreover, alpha-synuclein-induced dopaminergic neuron loss consequently resulted in motor dysfunction, which was also mitigated by parkin. Taken together, our results indicate that the parkin gene therapy is effective against alpha-synucleinopathy, suggesting its potential suitability for patients with PD.

Cyclopentenone eicosanoids as mediators of neurodegeneration: a pathogenic mechanism of oxidative stress-mediated and cyclooxygenase-mediated neurotoxicity

The activation of cyclooxygenase enzymes in the brain has been implicated in the pathogenesis of numerous neurodegenerative conditions. Similarly, oxidative stress is believed to be a major contributor to many forms of neurodegeneration. These 2 distinct processes are united by a common characteristic: the generation of electrophilic cyclopentenone eicosanoids. These cyclopentenone compounds are defined structurally by the presence of an unsaturated carbonyl moiety in their prostane ring, and readily form Michael adducts with cellular thiols, including those found in glutathione and proteins. The cyclopentenone prostaglandins (PGs) PGA2, PGJ2, and 15-deoxy-delta(12,14) PGJ2, enzymatic products of cyclooxygenase-mediated arachidonic acid metabolism, exert a complex array of potent neurodegenerative, neuroprotective, and anti-inflammatory effects. Cyclopentenone isoprostanes (A2/J2-IsoPs), products of non-enzymatic, free radical-mediated arachidonate oxidation, are also highly bioactive, and can exert direct neurodegenerative effects. In addition, cyclopentenone products of docosahexaenoic acid oxidation (cyclopentenone neuroprostanes) are also formed abundantly in the brain. For the first time, the formation and biological actions of these various classes of reactive cyclopentenone eicosanoids are reviewed, with emphasis on their potential roles in neurodegeneration. The accumulating evidence suggests that the formation of cyclopentenone eicosanoids in the brain may represent a novel pathogenic mechanism, which contributes to many neurodegenerative conditions.

In mice, production of plasma IL-1 and IL-6 in response to MPTP is related to behavioral lateralization

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces dopaminergic neuron death in substantia nigra and dopamine loss in striatum, similar to those observed in Parkinson disease. Given MPTP can also induce alterations in brain cytokines and in peripheral immune parameters, we hypothesize that MPTP can induce an elevation of plasma cytokines. We have previously shown that cytokine production depends on behavioral lateralization in certain conditions. Therefore, we further postulate that the MPTP-induced plasma cytokines are related to behavioral lateralization. To answer these questions, C57BL/6J male mice, selected for paw preference, were injected with 25 mg/kg MPTP ip for five consecutive days and were decapitated at day 1, day 3, or day 14 after the last injection. Striatal DA and DOPAC concentration were measured by HPLC and plasma levels of IL-1beta and IL-6 were quantified by ELISA. The results showed that after MPTP treatment, striatal DA content was dramatically decreased, IL-1beta levels increased on day 3, while IL-6 levels increased on day 14. Interestingly, behavioral lateralization influenced DA/DOPAC ratio as well as plasma IL-1beta and IL-6 levels. In left-pawed mice, MPTP induced a higher decrease of DA/DOPAC ratio than in right-pawed mice. The increase of IL-1beta was observed in left-pawed but not in right-pawed mice. The elevation of IL-6 was higher in right-pawed mice than in left-pawed mice. These results have clearly demonstrated our hypotheses, that MPTP can induce increase of plasma IL-1beta and IL-6 levels in mice, and this effect is shaped by behavioral lateralization.

Triptolide protects dopaminergic neurons from inflammation-mediated damage induced by lipopolysaccharide intranigral injection

Converging lines of evidence suggest that neuroinflammatory processes may account for the progressive death of dopaminergic neurons in Parkinson's disease (PD). Therefore, anti-inflammatory strategies have attracted much interest for their potential to prevent further deterioration of PD. Our previous study showed that triptolide, a traditional Chinese herbal compound with anti-inflammatory and immunosuppressive properties, protected dopaminergic neurons from lipopolysaccharide (LPS)-induced damage in primary embryonic midbrain cell cultures. To examine further if triptolide can protect dopaminergic neurons from inflammation-mediated damage in vivo, microglial activation and injury of dopaminergic neurons were induced by LPS intranigral injection, and the effects of triptolide treatment on microglial activation and survival ratio and function of dopaminergic neurons were investigated. Our results demonstrated that microglial activation induced by a single intranigral dose of 10 mug of LPS reduced the survival ratio of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the substantia nigra pars compacta (SNpc) to 29% and the content of dopamine (DA) in striatum to 37% of the non-injected side. Intriguingly, treatment with triptolide of 5 mug/kg for 24 days once per day dramatically improved the survival rate of TH-ir neurons in the SNpc to 79% of the non-injected side. Meanwhile, treatment with triptolide of 1 or 5 mug/kg for 24 days once per day significantly improved DA level in striatum to 70% and 68% of the non-injected side, respectively. Complement receptor 3 (CR3) immunohistochemical staining revealed that triptolide treatment potently inhibited LPS-elicited deleterious activation of microglia in SNpc. The excessive production of cytokines, such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta, was significantly abolished by triptolide administration. These results, together with our previous data in vitro, highly suggest the effectiveness of triptolide in protecting dopaminergic neurons against inflammatory challenge.

Association between the neuron-specific RNA-binding protein ELAVL4 and Parkinson disease

Inflammatory processes have been implicated in the cascade of events that lead to nerve cell death. In the nervous system, a number of genes involved in inflammation pathways are regulated post-transcriptionally via the interaction of their mRNAs with specific RNA-binding Hu proteins, the vertebrate homologues of the Drosophila ELAV (for embryonic lethal abnormal vision). The gene encoding ELAVL4, a member of the Hu family of proteins, is located 2 Mb from the chromosome 1p linkage region peak for age-at-onset (AAO) of Parkinson disease (PD) (LOD = 3.41). Nine single-nucleotide polymorphisms (SNPs) in ELAVL4 were genotyped for 266 multiplex families (1,223 samples). Additional genotyping in 377 singleton families was performed for a subset of five SNPs (SNPs 1-5) that were not in linkage disequilibrium. SNP 2 (located in the first intron of ELAVL4) showed a strong significant association with AAO of PD (P = 0.006), and SNP 5 (a coding SNP in ELAVL4) showed a moderately significant association (P = 0.035). Haplotype analysis revealed that the A-C haplotype at SNPs 2 and 3 has the strongest significant association with AAO (P = 0.0001) among all combinations of two or three loci. The A-C haplotype remained significant for AAO after the inclusion of the C allele at SNP 5 to this haplotype (A-C-C haplotype, P = 0.00018). Although SNP 5 was found to associate with PD risk in the early-onset subset of PD families (at least one affected with AAO <40 years, 60 families), we believe that it is a by-product of its association with AAO. Taken together, these results suggest a potential role for ELAVL4 as a modifier gene for AAO of PD.

Glucocorticoid receptor–nitric oxide crosstalk and vulnerability to experimental parkinsonism: pivotal role for glia–neuron interactions

Inflammation and oxidative stress have been closely associated with the pathogenesis of neurodegenerative disorders, including Parkinson's disease (PD). The expression of inducible nitric oxide synthase (iNOS) in astrocytes and microglia and the production of large amounts of nitric oxide (NO) are thought to contribute to dopaminergic neuron demise. Increasing evidence, however, indicates that activated astroglial cells play key roles in neuroprotection and can promote recovery of CNS functions. Endogenous glucocorticoids (GCs) via glucocorticoid receptors (GRs) exert potent anti-inflammatory and immunosuppressive effects and are key players in protecting the brain against stimulation of innate immunity. Here we review our work showing that exposure to a dysfunctional GR from early embryonic life in transgenic (Tg) mice expressing GR antisense RNA represents a key vulnerability factor in the response of nigrostriatal dopaminergic neurons to the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and further report that exacerbation of dopaminergic neurotoxicity with no recovery is determined by failure of astroglia to exert neuroprotective effects. Aberrant iNOS gene expression and increased glia vulnerability to cell death characterized the response of GR-deficient mice to stimulation of innate immunity. More importantly, GR-deficient glial cells failed to protect fetal dopaminergic neurons against oxidative stress-induces cell death, whereas wild-type glia afforded neuroprotection. Thus, lack of iNOS/NO regulation by GCs can program an aberrant GR-NO crosstalk in turn responsible for loss of astroglia neuroprotective function in response to stimulation of innate immunity, pointing to glia and efficient GR-NO dialogue as pivotal factors orchestrating neuroprotection in experimental parkinsonism.