Plasma α‐synuclein in patients with Parkinson's disease with and without treatment

Alpha‐synuclein (α‐syn) is an intracellular protein with a high tendency to aggregation. It is the major component of Lewy bodies and may play a key role in the pathogenesis of Parkinson's disease (PD). α‐Syn is also released by neurons and can be detected in biological fluids, such as plasma. The purpose of this study was to determine whether plasma α‐syn concentrations are elevated in newly diagnosed PD patients before treatment (nontreated PD group, ntPD; n = 53) and to compare them with concentrations in PD patients with at least 1 year of specific treatment (tPD; n = 42) and in healthy controls (n = 60). Plasma α‐syn concentrations in the ntPD and tPD groups were similar and significantly higher than in healthy controls. In conclusion, α‐syn was elevated early in the development of PD and specific PD treatment did not change plasma α‐syn levels. © 2010 Movement Disorder Society     

Microglial TNF‐α mediates enhancement of dopaminergic degeneration by brain angiotensin

In vitro and in vivo models of Parkinson's disease were used to investigate whether TNF‐α plays a major role in the enhancement of the microglial response and dopaminergic degeneration induced by brain angiotensin hyperactivity. Treatment of primary mesencephalic cultures with low doses of the neurotoxin MPP⁺ induced a significant loss of dopaminergic neurons, which was enhanced by cotreatment with angiotensin II and inhibited by TNF‐α inhibitors. Treatment of primary cultures with angiotensin induced a marked increase in levels of TNF‐α, which was inhibited by treatment with angiotensin type‐1‐receptor antagonists, NADPH‐oxidase inhibitors and NFK‐β inhibitors. However, TNF‐α levels were not significantly affected by treatment with angiotensin in the absence of microglia. The microglial origin of the angiotensin‐induced increase in TNF‐α levels was confirmed using dopaminergic (MES 23.5) and microglial (N9) cell lines. Inhibition of the microglial Rho‐kinase activity also blocked the AII‐induced increase in TNF‐α levels. Treatment of the dopaminergic cell line with TNF‐α revealed that NFK‐β activation mediates the deleterious effect of microglial TNF‐α on dopaminergic neurons. Treatment of mice with MPTP also induced significant increases in striatal and nigral TNF‐α levels, which were inhibited by angiotensin type‐1‐receptor antagonists or NFK‐β inhibitors. The present results show that microglial TNF‐α plays a major role in angiotensin‐induced dopaminergic cell death and that the microglial release of TNF‐α is mediated by activation of angiotensin type‐1 receptors, NADPH‐oxidase, Rho‐kinase and NFK‐β. GLIA 2014;62:145–157     

Exercise modifies α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor expression in striatopallidal neurons in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned mouse

The α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic‐acid‐type glutamate receptor (AMPAR) plays a critical role in modulating experience‐dependent neuroplasticity, and alterations in AMPAR expression may underlie synaptic dysfunction and disease pathophysiology. Using the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) mouse model of dopamine (DA) depletion, our previous work showed exercise increases total GluA2 subunit expression and the contribution of GluA2‐containing channels in MPTP mice. The purpose of this study was to determine whether exercise‐dependent changes in AMPAR expression after MPTP are specific to the striatopallidal (D₂R) or striatonigral (D₁R) medium spiny neuron (MSN) striatal projection pathways. Drd₂‐eGFP‐BAC transgenic mice were used to delineate differences in AMPAR expression between striatal D₂R‐MSNs and D₁R‐MSNs. Striatal AMPAR expression was assessed by immunohistochemical (IHC) staining, Western immunoblotting (WB) of preparations enriched for postsynaptic density (PSD), and alterations in the current–voltage relationship of MSNs. We found DA depletion results in the emergence of GluA2‐lacking AMPARs selectively in striatopallidal D₂R‐MSNs and that exercise reverses this effect in MPTP mice. Exercise‐induced changes in AMPAR channels observed after DA depletion were associated with alterations in GluA1 and GluA2 subunit expression in postsynaptic protein, D₂R‐MSN cell surface expression, and restoration of corticostriatal plasticity. Mechanisms regulating experience‐dependent changes in AMPAR expression may provide innovative therapeutic targets to increase the efficacy of treatments for basal ganglia disorders, including Parkinson's disease. © 2013 Wiley Periodicals, Inc.     

Baicalein attenuates astroglial activation in the 1‐methyl‐4‐phenyl‐1,2,3,4‐tetrahydropyridine‐induced Parkinson's disease model by downregulating the activations of nuclear factor‐κB,ERK, and JNK

In Parkinson's disease (PD), neuroinflammation plays a critical role in the neurodegenerative process. Furthermore, activated microglia and astrocytes, responsible for activated immune response in the central nervous system, are found in regions associated with dopaminergic neuronal death. The flavonoid baicalein is known to have antibacterial, antiviral, and antiinflammatory activities. In the present study, the neuroprotective effects of baicalein were examined in a murine 1‐methyl‐4‐phenyl‐1,2,3,4‐tetrahydropyridine (MPTP) model of PD. Low doses of baicalein improved motor ability and prevented dopaminergic neuron loss caused by MPTP. In addition, microglial and astrocyte activations were reduced in PD mice pretreated with baicalein. Further study of primary astrocytes revealed that baicalein suppressed the 1‐methyl‐4‐phenylpyridine‐induced nuclear translocation of nuclear factor‐κB and reduced the activations of JNK and ERK, suggesting that the neuroprotective effects of baicalein in our PD model were due to attenuated astrocyte activation. The findings of this study indicate that baicalein could be useful for the treatment of PD and other neuroinflammation‐related neurodegenerative diseases. © 2013 Wiley Periodicals, Inc.     

Simvastatin prevents neuroinflammation by inhibiting N‐methyl‐D‐aspartic acid receptor 1 in 6‐hydroxydopamine‐treated PC12 cells

This study investigates the impact of simvastatin on neuroinflammation in experimental parkinsonian cell models. 6‐Hydroxydopamine (6‐OHDA)‐treated pheochromocytoma‐12 (PC12) cells were used to investigate the neuroprotective nature of simvastatin. After incubation with 6‐OHDA, simvastatin, and/or N‐methyl‐D‐aspartic acid receptor 1 (NMDAR1) siRNA for 24 hr, test kits were used to detect the levels of lactate dehydrogenase (LDH) and glutamate released from PC12 cells exposed to different culture media. The mRNA levels of tumor necrosis factor (TNF)‐α, interleukin (IL)?1β, and IL‐6 were determined by RT‐PCR, and the protein levels were analyzed by Western blot. NMDAR1 were also determined by RT‐PCR and the protein levels were analyzed by Western blot. LDH and glutamate levels in 6‐OHDA‐incubated PC12 cells increased compared with those in the controls, and incubation with simvastatin inhibited this elevation. Silencing of NMDAR1 with siRNA inhibited the expression of LDH and glutamate to a degree similar to simvastatin. The expression levels of NMDAR1, TNF‐α, IL‐1β, and IL‐6 were significantly upregulated after treatment with 6‐OHDA. The 6‐OHDA‐stimulated mRNA and protein levels of the proinflammatory cytokines NMDAR1, TNF‐α, IL‐1β, and IL‐6 were reduced by simvastatin. Silencing of NMDAR1 with siRNA decreased the NMDAR1, TNF‐α, IL‐1β, and IL‐6 mRNA and protein expression levels in 6‐OHDA‐stimulated PC12 cells. Simvastatin could also inhibit the expression of NMDAR1 and cytokines to a degree similar to silencing of NMDAR1 with siRNA. Our results suggest that NMDAR1 modulation could explain the anti‐inflammatory mechanisms of simvastatin in experimental parkinsonian cell models. © 2014 Wiley Periodicals, Inc.     

α‐Synuclein abnormalities in mouse models of peroxisome biogenesis disorders

α‐Synuclein (αS) is a presynaptic protein implicated in Parkinson's disease (PD). Growing evidence implicates mitochondrial dysfunction, oxidative stress, and αS–lipid interactions in the gradual accumulation of αS in pathogenic forms and its deposition in Lewy bodies, the pathological hallmark of PD and related synucleinopathies. The peroxisomal biogenesis disorders (PBD), with Zellweger syndrome serving as the prototype of this group, are characterized by malformed and functionally impaired peroxisomes. Here we utilized the PBD mouse models Pex2–/–, Pex5–/–, and Pex13–/– to study the potential effects of peroxisomal dysfunction on αS‐related pathogenesis. We found increased αS oligomerization and phosphorylation and its increased deposition in cytoplasmic inclusions in these PBD mouse models. Furthermore, we show that αS abnormalities correlate with the altered lipid metabolism and, specifically, with accumulation of long chain, n‐6 polyunsaturated fatty acids that occurs in the PBD models. © 2009 Wiley‐Liss, Inc.     

Sensitive and specific detection of α‐synuclein in human plasma

α‐Synuclein (αsyn) mutations, overexpression, misfolding, and aggregation are associated with Parkinson's disease. This protein has been intensively studied in neuronal systems. However, αsyn is also present in extracellular fluids, such as cerebrospinal fluid and blood plasma. Recent studies have attempted to quantify its levels and compare these in various extracellular fluids of control and Parkinson's disease subjects. Data from these studies have been difficult to interpret, suggesting that more sensitive, standardized, and well‐characterized assays of larger cohorts are required. Here, we describe the development of a new ELISA specifically for quantifying αsyn in human plasma. An initial assay, using a commercial anti‐αsyn monoclonal antibody (211; Santa Cruz Biotechnology, Santa Cruz, CA) and based on a published protocol, was adapted for use in human plasma. In addition, we have developed a novel αsyn‐specific antibody for the assay that has very high sensitivity and signal:noise characteristics. Assays with either antibody showed high specificity for αsyn, and detected it in a variety of sample types, including plasma. These assays can now be employed on large cohorts of patients and control subjects to determine whether plasma levels are altered in disease. Although measuring extracellular αsyn levels may prove to be a useful biomarker of Parkinson's disease, it should also be a powerful tool for basic research aimed at understanding the normal and pathological physiology of αsyn secretion. © 2010 Wiley‐Liss, Inc.     

Inhibition of dopamine and choline acetyltransferase concentrations in rat CNS neurons by rat α1- and α2-macroglobulins

Previous studies have implicated human alpha-2-macroglobulin (α₂M) as a potential regulator of neuronal development and function. Rat alpha-1-macroglobulin (α₁M) and acute-phase alpha-2-macroglobulin (α₂M) are murine homologues of human α₂M. In this report, we tested the effect of intracranially infused serotonin-activated rat α₁M (5HT-α₁M) on the concentration of dopamine (DA) in the corpus striatum in vivo and the effect of 5HT-activated rat α₁M and α₂M on the choline acetyltransferase (ChAT) activity upon embryonic basal forebrain neurons in culture. The results show that direct infusion of 0.65 nmole rat 5HT-α₁M into the adult rat corpus striatum produced a consistent attenuation upon striatal DA concentrations. This decrease was particularly prominent at 5–7 days post-infusion. In addition, rat 5HT-α₁M and rat 5HT-α₂M, like human 5HT-α₂M, all significantly inhibited ChAT activity of embryonic rat cerebral cortex neurons. Although normal human α₂M and rat α₂M were either marginally or insignificantly inhibitory in this preparation, normal rat α₁M dose-dependently inhibited ChAT activity. These results demonstrate that monoamine-activated α-macroglobulins from rat depress dopaminergic and cholinergic neurotransmitter systems in the CNS, and this suggests a potential regulatory role of these alpha-macroglobulins in neurotransmitter metabolism. J. Neurosci. Res. 51:541–550, 1998. © 1998 Wiley-Liss, Inc.     

Targeting α‐synuclein: Therapeutic options

The discovery of the central role of α‐synuclein (αSyn) in the pathogenesis of Parkinson's disease (PD) has powered, in the last decade, the emergence of novel relevant models of this condition based on viral vector‐mediated expression of the disease‐causing protein or inoculation of toxic species of αSyn. Although the development of these powerful tools and models has provided considerable insights into the mechanisms underlying neurodegeneration in PD, it has also been translated into the expansion of the landscape of preclinical therapeutic strategies. Much attention is now brought to the proteotoxic mechanisms induced by αSyn and how to block them using strategies inspired by intrinsic cellular pathways such as the enhancement of cellular clearance by the lysosomal‐autophagic system, through proteasome‐mediated degradation or through immunization. The important effort undertaken by several laboratories and consortia to tackle these issues and identify novel targets warrants great promise for the discovery not only of neuroprotective approaches but also of restorative strategies for PD and other synucleinopathies. In this viewpoint, we summarize the latest advances in this new area of PD research and will discuss promising approaches and ongoing challenges. © 2016 International Parkinson and Movement Disorder Society     

Higher nigrostriatal dopamine neuron loss in early than late onset Parkinson's disease?—A [99mTc]‐TRODAT‐1 SPECT study

Early-onset Parkinson's disease (EOPD) is distinct from the classic late-onset PD (LOPD) because of its slower disease progression. The aim of this study was to compare dopamine neuronal loss in EOPD with that of LOPD with the same disease duration, through dopamine transporter (DAT) estimation. Fourteen patients, seven EOPD (<50 years) and seven LOPD, matched for disease duration were scanned with [(99m)Tc]-TRODAT-1-SPECT (INER-Taiwan), and were assessed with standard PD scales. EOPD patients had 34% lower striatal DAT binding potential (BP) compared with that of LOPD patients (BP = 0.29 +/- 0.12, BP = 0.44 +/- 0.12, P < 0.02) with similar PD severity. These results suggest that EOPD patients have greater dopamine density loss than LOPD patients without motor-symptom worsening.     

Neuropathologic analysis of Lewy‐related α‐synucleinopathy in olfactory mucosa

We analyzed the incidence and extent of Lewy‐related α‐synucleinopathy (LBAS) in the olfactory mucosa, as well as the central and peripheral nervous systems of consecutive autopsy cases from a general geriatric hospital. The brain and olfactory mucosa were immunohistochemically examined using antibodies raised against phosphorylated α‐synuclein. Thirty‐nine out of 105 patients (37.1%) showed LBAS in the central or peripheral nervous systems. Seven patients presented LBAS (Lewy neurites) in the olfactory lamina propria mucosa. One out of the seven cases also showed a Lewy neurite in a bundle of axons in the cribriform plate, but α‐synuclein deposits were not detected in the olfactory receptor neurons. In particular, high incidence of α‐synuclein immunopositive LBAS in the olfactory mucosa was present in the individuals with clinically as well as neuropathologically confirmed Parkinson's disease and dementia with Lewy bodies (6/8 cases, 75%). However, this pathologic alteration was rare in the cases with incidental or subclinical Lewy body diseases (LBD) (one out of 31 cases, 3.2%). In the olfactory bulb, the LBAS was usually present in the glomeruli and granular cells of most symptomatic and asymptomatic cases with LBD. Our studies further confirmed importance of the olfactory entry zone in propagation of LBAS in the human aging nervous system.