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Retromer is a heteropentameric complex that plays a specialized role in endosomal protein sorting and trafficking. Here, we report a reduction in the retromer proteins—vacuolar protein sorting 35 (VPS35), VPS26A, and VPS29—in patients with amyotrophic lateral sclerosis (ALS) and in the ALS model provided by transgenic (Tg) mice expressing the mutant superoxide dismutase-1 G93A. These changes are accompanied by a reduction of levels of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit GluA1, a proxy of retromer function, in spinal cords from Tg SOD1 G93A mice. Correction of the retromer deficit by a viral vector expressing VPS35 exacerbates the paralytic phenotype in Tg SOD1 G93A mice. Conversely, lowering Vps35 levels in Tg SOD1 G93A mice ameliorates the disease phenotype. In light of these findings, we propose that mild alterations in retromer inversely modulate neurodegeneration propensity in ALS.

The blood-brain barrier (BBB) prevents most drugs from gaining access to the brain parenchyma, which is a recognized impediment to the treatment of neurodegenerative disorders like Parkinson's disease (PD). Focused ultrasound (FUS), in conjunction with systemically administered microbubbles, opens the BBB locally, reversibly and non-invasively. Herein, we show that neither FUS applied over both the striatum and the ventral midbrain, without neurotrophic factors, nor intravenous administration of neurotrophic factors (either through protein or gene delivery) without FUS, ameliorates the damage to the nigrostriatal dopaminergic pathway in the sub-acute MPTP mouse model of early-stage PD. Conversely, the combination of FUS and intravenous neurotrophic (protein or gene) delivery attenuates the damage to the nigrostriatal dopaminergic pathway, by allowing the entry of these agents into the brain parenchyma. Our findings provide evidence that the application of FUS at the early stages of PD facilitates critical neurotrophic delivery that can curb the rapid progression of neurodegeneration while improving the neuronal function, seemingly opening new therapeutic avenues for the early treatment of diseases of the central nervous system.

Focused ultrasound (FUS) in conjunction with microbubbles is a technique to achieve noninvasive, transient, and localized blood-brain barrier (BBB) opening to enhance drug delivery to the brain. Here we explored the potential of FUS-mediated delivery of anti-alpha synuclein ($\alpha$ -syn) monoclonal antibodies (mAb) for the treatment of Parkinson's disease. Transgenic A53T mice that express the human A53T $\alpha$ -syn at 6–7 months of age received 3 weekly sonications followed by one-month survival. Monoclonal anti- $-\alpha$ -syn antibodies ([MJFR1], Abcam) were mixed with in-house manufactured size-isolated microbubbles (4–5 $\mu\text{m}$ and intravenously injected before FUS sonications. Mice were sonicated using a single-element FUS transducer (center frequency 1.5 MHz) with the following acoustic parameters: peak-negative pressure 0.45 MPa, pulse length 6.7 ms, pulse repetition frequency 5 Hz, and duration of 60 $\text{s}$. Quantification using a minimum error thresholding technique demonstrated reduced $\alpha$ -syn load in mice treated with both FUS and antibody, without significant change in neuronal cell count. Reduction of a-syn aggregation was present primarily in the midbrain in both hemispheres of treated brain, but with a higher reduction in the FUS-treated hemisphere. These findings suggest that weekly treatments with FUS and anti- $-\alpha$ -syn antibodies could successfully reduce $\alpha$ -syn burden in transgenic mouse models of PD.

Focused ultrasound enhanced intranasal (IN+FUS) delivery is a unique, noninvasive approach that utilizes the olfactory pathway to administer drugs directly to the brain. Our group has shown that IN+FUS delivery of model drugs provide a more homogenous distribution of delivery when compared to IN delivery alone, and similar delivery efficiency to intravenous delivery after FUS induced BBB opening. The aim of this study was to investigate the delivery efficacy and therapeutic effects that IN+FUS administered brain-derived neurotrophic factor (BDNF) has on an early-stage Parkinsonian mouse model in order to provide an alternate and more direct administration route to the brain. Wild-type mice were given a sub-acute dose of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxin daily for 5 days, causing bilateral degeneration of the nigrostriatal dopaminergic pathway. After a stabilizing period, the mice were split into a treated group and a control group (N=7 /group). The treated group was dosed with IN+FUS of BDNF weekly for 3 weeks. Each week, 0.4 mg of BDNF was intranasally delivered followed by BBB opening in the left substantia nigra (SN) and caudate putamen (CP) using FUS and sized isolated microbubbles. The mice were then survived for 2 months to allow for any neurorestorative effects to occur. Behavioral testing through amphetamine-induced rotations was then conducted. Staining of tyrosine hydroxylase positive (TH+) neurons in the SN and terminals in the CP were used to assess the nigrostriatal dopaminergic pathway integrity. TH+ staining in the SN and CP indicated moderate neuronal survival in the ipsilateral side in treated mice while staining in untreated mice was similar bilaterally. Significant ipsilateral rotation in treated mice corroborated the immunohistochemistry findings, further validating improved ipsilateral nigrostriatal dopaminergic pathway. These findings indicate a modest neurorestorative effect of IN+FUS BDNF on MPTP mice, demonstrating the potential of an alternative and efficient drug delivery route for brain treatment with FUS. Additional immunohistochemistry assays and quantification in the SN and CP are ongoing to confirm these initial findings.

For degenerative disorders of the central nervous system, the major obstacle to therapeutic advancement has been the challenge of identifying the key molecular mechanisms underlying neuronal loss. We developed a combinatorial approach including translational profiling and brain regulatory network analysis to search for key determinants of neuronal survival or death. Following the generation of transgenic mice for cell type-specific profiling of midbrain dopaminergic neurons, we established and compared translatome libraries reflecting the molecular signature of these cells at baseline or under degenerative stress. Analysis of these libraries by interrogating a context-specific brain regulatory network led to the identification of a repertoire of intrinsic upstream regulators that drive the dopaminergic stress response. The altered activity of these regulators was not associated with changes in their expression levels. This strategy can be generalized for the elucidation of novel molecular determinants involved in the degeneration of other classes of neurons.

Accumulating evidence from genetic and biochemical studies implicates dysfunction of the autophagic-lysosomal pathway as a key feature in the pathogenesis of Parkinson's disease (PD). Most studies have focused on accumulation of neurotoxic α-synuclein secondary to defects in autophagy as the cause of neurodegeneration, but abnormalities of the autophagic-lysosomal system likely mediate toxicity through multiple mechanisms. To further explore how endolysosomal dysfunction causes PD-related neurodegeneration, we generated a murine model of Kufor–Rakeb syndrome (KRS), characterized by early-onset Parkinsonism with additional neurological features. KRS is caused by recessive loss-of-function mutations in theATP13A2gene encoding the endolysosomal ATPase ATP13A2. We show that loss of ATP13A2 causes a specific protein trafficking defect, and thatAtp13a2null mice develop age-related motor dysfunction that is preceded by neuropathological changes, including gliosis, accumulation of ubiquitinated protein aggregates, lipofuscinosis, and endolysosomal abnormalities. Contrary to predictions fromin vitrodata,in vivomouse genetic studies demonstrate that these phenotypes are α-synuclein independent. Our findings indicate that endolysosomal dysfunction and abnormalities of α-synuclein homeostasis are not synonymous, even in the context of an endolysosomal genetic defect linked to Parkinsonism, and highlight the presence of α-synuclein-independent neurotoxicity consequent to endolysosomal dysfunction.

SummaryDifferentiation of astrocytes from human stem cells has significant potential for analysis of their role in normal brain function and disease, but existing protocols generate only immature astrocytes. Using early neuralization, we generated spinal cord astrocytes from mouse or human embryonic or induced pluripotent stem cells with high efficiency. Remarkably, short exposure to fibroblast growth factor 1 (FGF1) or FGF2 was sufficient to direct these astrocytes selectively toward a mature quiescent phenotype, as judged by both marker expression and functional analysis. In contrast, tumor necrosis factor alpha and interleukin-1β, but not FGFs, induced multiple elements of a reactive inflammatory phenotype but did not affect maturation. These phenotypically defined, scalable populations of spinal cord astrocytes will be important both for studying normal astrocyte function and for modeling human pathological processes in vitro.

SummaryNon cell-autonomous processes are thought to play critical roles in the cellular maintenance of the healthy and diseased brain but mechanistic details remain unclear. We report that the interruption of a non cell-autonomous mode of sonic hedgehog (Shh) signaling originating from dopaminergic neurons causes progressive, adult-onset degeneration of dopaminergic, cholinergic, and fast spiking GABAergic neurons of the mesostriatal circuit, imbalance of cholinergic and dopaminergic neurotransmission, and motor deficits reminiscent of Parkinson’s disease. Variable Shh signaling results in graded inhibition of muscarinic autoreceptor- and glial cell line-derived neurotrophic factor (GDNF)-expression in the striatum. Reciprocally, graded signals that emanate from striatal cholinergic neurons and engage the canonical GDNF receptor Ret inhibit Shh expression in dopaminergic neurons. Thus, we discovered a mechanism for neuronal subtype specific and reciprocal communication that is essential for neurochemical and structural homeostasis in the nigrostriatal circuit. These results provide integrative insights into non cell-autonomous processes likely at play in neurodegenerative conditions such as Parkinson’s disease.

DNA damage is a proposed pathogenic factor in neurodegenerative disorders such as Parkinson disease. To probe the underpinning mechanism of such neuronal perturbation, we sought to produce an experimental model of DNA damage. We thus first assessed DNA damage by in situ nick translation and emulsion autoradiography in the mouse brain after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 4 x 20 mg/kg, ip, every 2 h), a neurotoxin known to produce a model of Parkinson disease. Here we show that DNA strand breaks occur in vivo in this mouse model of Parkinson disease with kinetics and a topography that parallel the degeneration of substantia nigra neurons, as assessed by FluoroJade labeling. Previously, nitric oxide synthase and cyclooxygenase-2 (Cox-2) were found to modulate MPTP-induced dopaminergic neuronal death. We thus assessed the contribution of these enzymes to DNA damage in mice lacking neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS), or Cox-2. We found that the lack of Cox-2 and nNOS activities but not of iNOS activity attenuated MPTP-related DNA damage. We also found that not only nuclear, but also mitochondrial, DNA is a target for the MPTP insult. These results suggest that the loss of genomic integrity can be triggered by the concerted actions of nNOS and Cox-2 and provide further support to the view that DNA damage may contribute to the neurodegenerative process in Parkinson disease.

Toxic organic cations can damage nigrostriatal dopaminergic pathways as seen in most parkinsonian syndromes and in some cases of illicit drug exposure. Here, we show that the organic cation transporter 3 (Oct3) is expressed in nondopaminergic cells adjacent to both the soma and terminals of midbrain dopaminergic neurons. We hypothesized that Oct3 contributes to the dopaminergic damage by bidirectionally regulating the local bioavailability of toxic species. Consistent with this view, Oct3 deletion and pharmacological inhibition hampers the release of the toxic organic cation 1-methyl-4-phenylpyridinium from astrocytes and protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurodegeneration in mice. Furthermore, Oct3 deletion impairs the removal of the excess extracellular dopamine induced by methamphetamine and enhances striatal dopaminergic terminal damage caused by this psychostimulant. These results may have far-reaching implications for our understanding of the mechanism of cell death in a wide range of neurodegenerative diseases and may open new avenues for neuroprotective intervention.

Over the past decade, numerous small- and large-molecule products have been developed for treatment of neurodegenerative diseases with mixed success. When administered systemically in vivo, the blood-brain barrier (BBB) inhibits their delivery to the regions affected by those diseases. A successful drug delivery system requires transient, localized, and noninvasive targeting of a specific tissue region as provided by Focused Ultrasound (FUS). Neurturin (NTN) is a neurotrophic factor that has demonstrated to have neuroprotective and regenerative effects on dopaminergic neurons in vivo using invasive drug delivery methods. Utilizing recombinant adeno-associated virus (rAAV), therapeutic genes can be delivered to the brain for long-lasting treatments. In this study, we investigate the neuroprotective and neuroregenerative effects of non-invasively delivered rAAV-GDNF vectors and NTN in a PD mouse model, respectively.

The molecules underlying neuron loss in Parkinson's disease (PD) are essentially unknown, and current therapies focus on diminishing symptoms rather than preventing neuron death. We identified RTP801 as a gene whose transcripts were highly induced in a cellular model of PD in which death of neuronal catecholaminergic PC12 cells was triggered by the PD mimetic 6-OHDA. Here, we find that RTP801 protein is also induced in this and additional cellular and animal PD models. To assess the relevance of these observations to PD, we used immunohistochemistry to compare RTP801 expression in postmortem brains from PD and control patients. For all PD brains examined, expression was highly elevated within neuromelanin-containing neurons of the substantia nigra but not in cerebellar neurons. Evaluation of the potential role of RTP801 induction in our cellular model revealed that RTP801 overexpression is sufficient to promote death but does not further elevate death caused by 6-OHDA. Furthermore, RTP801 induction is requisite for death in our cellular PD models and in 6-OHDA-treated cultured sympathetic neurons in that its knockdown by short hairpin RNAs (shRNAs) is protective. The mechanism by which 6-OHDA and RTP801 induce neuron death appears to involve repression of mammalian target of rapamycin (mTOR) kinase activity, and such death is inhibited by shRNAs targeting TSC2 (tuberous sclerosis complex), a protein with which RTP801 interacts to block mTOR activation. Our findings thus suggest that the elevation of RTP801 we detect in PD substantia nigral neurons may mediate their degeneration and death and that RTP801 and its signaling cascade may be novel potential therapeutic targets for the disease.

Impaired proteasome function is a potential mechanism for dopaminergic neuron degeneration. To model this molecular defect, we administered systemically the reversible lipophilic proteasome inhibitor, carbobenzoxy-L-isoleucyl-gamma-t-butyl-L-glutamyl-L-alanyl-L-leucinal (PSI), to rodents. In contrast to a previous report, this approach failed to cause any detectable behavioral or neuropathological abnormality in either rats or mice. Although theoretically appealing, this specific model of Parkinson's disease appears to exhibit poor reproducibility.

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Recent observations link cyclooxygenase type-2 (COX-2) to the progression of the disease. Consistent with this notion, studies with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) show that inhibition and ablation of COX-2 markedly reduce the deleterious effects of this toxin on the nigrostriatal pathway. The similarity between this experimental model and PD strongly supports the possibility that COX-2 expression is also pathogenic in PD.

Dysfunction of mitochondrial complex I is a feature of human neurodegenerative diseases such as Leber hereditary optic neuropathy and Parkinson's disease. This mitochondrial defect is associated with a recruitment of the mitochondrial-dependent apoptotic pathway in vivo . However, in isolated brain mitochondria, complex I dysfunction caused by either pharmacological or genetic means fails to directly activate this cell death pathway. Instead, deficits of complex I stimulate intramitochondrial oxidative stress, which, in turn, increase the releasable soluble pool of cytochrome c within the mitochondrial intermembrane space. Upon mitochondrial permeabilization by the cell death agonist Bax, more cytochrome c is released to the cytosol from brain mitochondria with impaired complex I activity. Given these results, we propose a model in which defects of complex I lower the threshold for activation of mitochondrial-dependent apoptosis by Bax, thereby rendering compromised neurons more prone to degenerate. This molecular scenario may have far-reaching implications for the development of effective neuroprotective therapies for these incurable illnesses.

The biochemical and cellular changes that occur following administration of 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) are remarkably similar to that seen in idiopathic Parkinson's disease (PD). In this review, we detail the molecular activities of this compound from peripheral intoxication through its various biotransformations. In addition, we detail the interplay that occurs between the different cellular compartments (neurons and glia) that eventually consort to kill substantia nigra pars compacta (SNpc) neurons.

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.

Accumulating evidence suggests that apoptotic and inflammatory factors contribute to the demise of dopaminergic neurons. In this respect, Fas, a member of the tumor necrosis factor receptor family with proapoptotic and inflammatory functions, was reported to be elevated within the striatum and substantia nigra pars compacta (SNc) of Parkinson's disease (PD) patients. Accordingly, the present investigation evaluated the function of Fas in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. Injection of MPTP increased nigral Fas expression, and mice lacking Fas displayed attenuated MPTP-induced SNc dopaminergic loss and microglial activation. In addition, Fas induction was blocked by expression of a dominant-negative c-Jun adenovirus that also protected dopamine neurons from MPTP-induced damage. Together, these data suggest the critical nature of the c-Jun-Fas signaling pathway in MPTP-induced neuronal loss. Although critical for degeneration of the soma, Fas deficiency did not significantly prevent the reduction of dopaminergic terminal fibers within the striatum or normalize the activation of striatal microglia and elevation of the postsynaptic activity marker ΔFosB induced by denervation. Interestingly, Fas-deficient mice displayed a pre-existing reduction in striatal dopamine levels and locomotor behavior when compared with wild-type mice. Despite the reduced terminals, dopamine levels were not further suppressed by MPTP treatment in mutant mice, raising the possibility of a compensatory response in basal ganglia function in Fas-deficient mice.

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) impairs mitochondrial respiration and damages dopaminergic neurons as seen in Parkinson's disease (PD). Here, we report that L-3-hydroxyacyl-CoA dehydrogenase type II/amyloid binding alcohol dehydrogenase (HADH II/ABAD), a mitochondrial oxidoreductase enzyme involved in neuronal survival, is downregulated in PD patients and in MPTP-intoxicated mice. We also show that transgenic mice with increased expression of human HADH II/ABAD are significantly more resistant to MPTP than their wild-type littermates. This effect appears to be mediated by overexpression of HADH II/ABAD mitigating MPTP-induced impairment of oxidative phosphorylation and ATP production. This study demonstrates that HADH II/ABAD modulates MPTP neurotoxicity and suggests that HADH II/ABAD mimetics may provide protective benefit in the treatment of PD.

Recent evidence indicates that cyclin-dependent kinases (CDKs, cdks) may be inappropriately activated in several neurodegenerative conditions. Here, we report that cdk5 expression and activity are elevated after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a toxin that damages the nigrostriatal dopaminergic pathway. Supporting the pathogenic significance of the cdk5 alterations are the findings that the general cdk inhibitor, flavopiridol, or expression of dominant-negative cdk5, and to a lesser extent dominant-negative cdk2, attenuates the loss of dopaminergic neurons caused by MPTP. In addition, CDK inhibition strategies attenuate MPTP-induced hypolocomotion and markers of striatal function independent of striatal dopamine. We propose that cdk5 is a key regulator in the degeneration of dopaminergic neurons in Parkinson's disease.

Parkinson disease (PD) is a neurodegenerative disorder characterized by a loss of the nigrostriatal dopaminergic neurons accompanied by a deficit in mitochondrial respiration. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that causes dopaminergic neurodegeneration and a mitochondrial deficit reminiscent of PD. Here we show that the infusion of the ketone body d-beta-hydroxybutyrate (DbetaHB) in mice confers partial protection against dopaminergic neurodegeneration and motor deficits induced by MPTP. These effects appear to be mediated by a complex II-dependent mechanism that leads to improved mitochondrial respiration and ATP production. Because of the safety record of ketone bodies in the treatment of epilepsy and their ability to penetrate the blood-brain barrier, DbetaHB may be a novel neuroprotective therapy for PD.

The molecular mechanisms mediating degeneration of midbrain dopamine neurons in Parkinson's disease (PD) are poorly understood. Here, we provide evidence to support a role for the involvement of the calcium-dependent proteases, calpains, in the loss of dopamine neurons in a mouse model of PD. We show that administration ofN-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) evokes an increase in calpain-mediated proteolysis in nigral dopamine neuronsin vivo. Inhibition of calpain proteolysis using either a calpain inhibitor (MDL-28170) or adenovirus-mediated overexpression of the endogenous calpain inhibitor protein, calpastatin, significantly attenuated MPTP-induced loss of nigral dopamine neurons. Commensurate with this neuroprotection, MPTP-induced locomotor deficits were abolished, and markers of striatal postsynaptic activity were normalized in calpain inhibitor-treated mice. However, behavioral improvements in MPTP-treated, calpain inhibited mice did not correlate with restored levels of striatal dopamine. These results suggest that protection against nigral neuron degeneration in PD may be sufficient to facilitate normalized locomotor activity without necessitating striatal reinnervation. Immunohistochemical analyses of postmortem midbrain tissues from human PD cases also displayed evidence of increased calpain-related proteolytic activity that was not evident in age-matched control subjects. Taken together, our findings provide a potentially novel correlation between calpain proteolytic activity in an MPTP model of PD and the etiology of neuronal loss in PD in humans.

Our findings in 19 new patients with cerebellar ataxia establish the existence of an ataxic syndrome due to primary CoQ10 deficiency and responsive to CoQ10 therapy. As all patients presented cerebellar ataxia and cerebellar atrophy, this suggests a selective vulnerability of the cerebellum to CoQ10 deficiency. We investigated the regional distribution of coenzyme Q10 in the brain of adult rats and in the brain of one human subject. We also evaluated the levels of coenzyme Q9 (CoQ9) and CoQ10 in different brain regions and in visceral tissues of rats before and after oral administration of CoQ10. Our results show that in rats, amongst the seven brain regions studied, cerebellum contains the lowest level of CoQ. However, the relative proportion of CoQ10 was the same (about 30% of total CoQ) in all regions studied. The level of CoQ10 is much higher in brain than in blood or visceral tissue, such as liver, heart, or kidney. Daily oral administration of CoQ10 led to substantial increases of CoQ10 concentrations only in blood and liver. Of the four regions of one human brain studied, cerebellum again had the lowest CoQ10y concentration.

Parkinson’s disease (PD) is associated with the selective death of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). While the specific cause of the neuronal loss remains elusive, the abnormal accumulation of alpha synuclein (α-syn), a major constituent of Lewy bodies, is considered to play a central role in the pathology of PD. Previous studies have shown the potential of immunotherapy with antibodies against α-syn, but such treatments remain ineffective due to the presence of the blood-brain barrier (BBB), which hinders most therapeutic agents to diffuse to the brain parenchyma. Therefore, in this study, we used focused ultrasound (FUS) in conjunction with microbubbles to transiently and noninvasively open the BBB and deliver anti-α-syn monoclonal antibodies (mAb) to the brains of transgenic PD mouse models. Preliminary histological findings demonstrate that the FUS promotes the delivery of anti-α-syn mAb to the transgenic mice overexpressing the human A53T or A30P α-synuclein. We ...

Mutations in alpha-synuclein cause a form of familial Parkinson's disease (PD), and wild-type alpha-synuclein is a major component of the intraneuronal inclusions called Lewy bodies, a pathological hallmark of PD. These observations suggest a pathogenic role for alpha-synuclein in PD. Thus far, however, little is known about the importance of alpha-synuclein in the nigral dopaminergic pathway in either normal or pathological situations. Herein, we studied this question by assessing the expression of synuclein-1, the rodent homologue of human alpha-synuclein, in both normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice. In normal mice, detectable levels of synuclein mRNA and protein were seen in all brain regions studied and especially in ventral midbrain. In the latter, there was a dense synuclein-positive nerve fiber network, which predominated over the substantia nigra, and only few scattered synuclein-positive neurons. After a regimen of MPTP that kills dopaminergic neurons by apoptosis, synuclein mRNA and protein levels were increased significantly in midbrain extracts; the time course of these changes paralleled that of MPTP-induced dopaminergic neurodegeneration. In these MPTP-injected mice, there was also a dramatic increase in the number of synuclein-immunoreactive neurons exclusively in the substantia nigra pars compacta; all synuclein-positive neurons were tyrosine hydroxylase-positive, but none coexpressed apoptotic features. These data indicate that synuclein is highly expressed in the nigrostriatal pathway of normal mice and that it is up-regulated following MPTP-induced injury. In light of the synuclein alterations, it can be suggested that, by targeting this protein, one may modulate MPTP neurotoxicity and, consequently, open new therapeutic avenues for PD.

Molecular mechanisms of apoptosis may participate in motor neuron degeneration produced by mutant copper/zinc superoxide dismutase (mSOD1), the only proven cause of amyotrophic lateral sclerosis (ALS). Consistent with this, herein we show that the spinal cord of transgenic mSOD1 mice is the site of the sequential activation of caspase-1 and caspase-3. Activated caspase-3 and its produced β-actin cleavage fragments are found in apoptotic neurons in the anterior horn of the spinal cord of affected transgenic mSOD1 mice; although such neurons are few, their scarcity should not undermine the potential importance of apoptosis in the overall mSOD1-related neurodegeneration. Overexpression of the anti-apoptotic protein Bcl-2 attenuates neurodegeneration and delays activation of the caspases and fragmentation of β-actin. These data demonstrate that caspase activation occurs in this mouse model of ALS during neurodegeneration. Our study also suggests that modulation of caspase activity may provide protective benefit in the treatment of ALS, a view that is consistent with our recent demonstration of caspase inhibition extending the survival of transgenic mSOD1 mice.

Tinuvin 123, a compound used in the manufacture of plastics, has recently been suggested to possibly cause Parkinson's disease (PD). Herein, we revisited this issue by assessing the effect of Tinuvin 123 on dopaminergic neurons of the substantia nigra following its stereotaxic injection in the rat. Twenty-one days post unilateral stereotaxic injection of Tinuvin 123, systemic injection of both apomorphine and amphetamine caused rotations toward the side of the lesion in these rats. Tinuvin 123 produced a small to moderate dose-dependent reduction in striatal levels of dopamine and metabolites on the side of the lesion. This compound also produced dramatic cell loss in the substantia nigra on the side of the lesion. However, the loss of cells lacked the phenotypic specificity for tyrosine hydroxylase (TH)-positive neurons that is expected with a dopaminergic neurotoxin. Indeed, aside from a robust glial reaction, both TH-positive and glutamic acid dehydrogenase (GAD)-positive neurons were destroyed, and near the site of the injection, there was complete tissue destruction. This study indicates that, using this mode of injection, Tinuvin 123 exerts a dramatic tissue toxicity without any evidence of specificity for dopaminergic neurons. Thus, our data argues against a role for Tinuvin 123 as an environmental toxin causing a clinical condition characterized by the selective loss of dopaminergic neurons as seen in PD.

Mutations in the copper/zinc superoxide dismutase (SOD1) gene produce an animal model of familial amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder. To test a new therapeutic strategy for ALS, we examined the effect of caspase inhibition in transgenic mice expressing mutant human SOD1 with a substitution of glycine to alanine in position 93 (mSOD1 G93A ). Intracerebroventricular administration of zVAD-fmk, a broad caspase inhibitor, delays disease onset and mortality. Moreover, zVAD-fmk inhibits caspase-1 activity as well as caspase-1 and caspase-3 mRNA up-regulation, providing evidence for a non–cell-autonomous pathway regulating caspase expression. Caspases play an instrumental role in neurodegeneration in transgenic mSOD1 G93A mice, which suggests that caspase inhibition may have a protective role in ALS.

Oxidative stress is implicated in the death of dopaminergic neurons in Parkinson's disease and in the 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP) model of Parkinson's disease. Oxidative species that might mediate this damage include hydroxyl radical, tyrosyl radical, or reactive nitrogen species such as peroxynitrite. In mice, we showed that MPTP markedly increased levels of o, o'-dityrosine and 3-nitrotyrosine in the striatum and midbrain but not in brain regions resistant to MPTP. These two stable compounds indicate that tyrosyl radical and reactive nitrogen species have attacked tyrosine residues. In contrast, MPTP failed to alter levels of ortho-tyrosine in any brain region we studied. This marker accumulates when hydroxyl radical oxidizes protein-bound phenylalanine residues. We also showed that treating whole-brain proteins with hydroxyl radical markedly increased levels of ortho-tyrosine in vitro. Under identical conditions, tyrosyl radical, produced by the heme protein myeloperoxidase, selectively increased levels of o,o'-dityrosine, whereas peroxynitrite increased levels of 3-nitrotyrosine and, to a lesser extent, of ortho-tyrosine. These in vivo and in vitro findings implicate reactive nitrogen species and tyrosyl radical in MPTP neurotoxicity but argue against a deleterious role for hydroxyl radical in this model. They also show that reactive nitrogen species and tyrosyl radical (and consequently protein oxidation) represent an early and previously unidentified biochemical event in MPTP-induced brain injury. This finding may be significant for understanding the pathogenesis of Parkinson's disease and developing neuroprotective therapies.

CCAAT/enhancer binding protein δ (C/EBPδ) is a transcriptional regulator implicated in the hepatic acute phase response and in adipogenic and myeloid cell differentiation. We found that C/EBPδ is widely expressed in the peripheral and central nervous systems, including neurons of the hippocampal formation, indicating a role in neural functions. To examine the role of C/EBPδ in vivo , we generated mice with a targeted deletion of the C/EBPδ gene. This mutation does not interfere with normal embryonic and postnatal development. Performance in a battery of behavioral tests indicates that basic neurological functions are normal. Furthermore, performance in a Morris water maze task suggests that C/EBPδ mutant mice have normal spatial learning. However, in the contextual and auditory-cue-conditioned fear task, C/EBPδ null mice displayed significantly more conditioned freezing to the test context than did wild-type controls, but equivalent conditioning to the auditory cue. These data demonstrate a selectively enhanced contextual fear response in mice carrying a targeted genomic mutation and implicate C/EBPδ in the regulation of a specific type of learning and memory.

In situ hybridization and immunohistochemistry were used to characterize the expression pattern of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors during postnatal development in the rat basal ganglia. All subunit transcripts showed some degree of developmental regulation. GluR1 and GluR2 are expressed at high levels in the neonate with reduced expression in the adult. GluR3 and GluR4 are expressed at significantly lower levels in both neonates and adults and have much more modest degrees of reduced expression in adults as compared with GluR1 and GluR2. Analysis of the flip and flop transcript isoforms indicates that GluR1 flip and flop and GluR2 flip are the predominately expressed splice variants in adults. Observed changes in the expression of the AMPA receptor transcripts indicate that there are fundamental differences in the expression of these receptor subunits in adults and neonates. This phenomenon may play a significant role in the establishment of proper synaptic circuitry within the developing basal ganglia in early postnatal life as well as contributing to differences in susceptibility to injury and disease in the aging brain.

The brain vesicular monoamine transporter (VMAT2) pumps monoamine neurotransmitters and Parkinsonism-inducing dopamine neurotoxins such as 1-methyl-4-phenyl-phenypyridinium (MPP + ) from neuronal cytoplasm into synaptic vesicles, from which amphetamines cause their release. Amphetamines and MPP + each also act at nonvesicular sites, providing current uncertainties about the contributions of vesicular actions to their in vivo effects. To assess vesicular contributions to amphetamine-induced locomotion, amphetamine-induced reward, and sequestration and resistance to dopaminergic neurotoxins, we have constructed transgenic VMAT2 knockout mice. Heterozygous VMAT2 knockouts are viable into adult life and display VMAT2 levels one-half that of wild-type values, accompanied by smaller changes in monoaminergic markers, heart rate, and blood pressure. Weight gain, fertility, habituation, passive avoidance, and locomotor activities are similar to wild-type littermates. In these heterozygotes, amphetamine produces enhanced locomotion but diminished behavioral reward, as measured by conditioned place preference. Administration of the MPP + precursor N -methyl-4-phenyl-1,2,3,6-tetrahydropyridine to heterozygotes produces more than twice the dopamine cell losses found in wild-type mice. These mice provide novel information about the contributions of synaptic vesicular actions of monoaminergic drugs and neurotoxins and suggest that intact synaptic vesicle function may contribute more to amphetamine-conditioned reward than to amphetamine-induced locomotion.

One of the hallmarks of Parkinson Disease is a deficit in Complex I of the mitochondrial complex chain in the tyrosine hydroxylase (THf)+ neurons in the substantia nigra pars compacta (SNpc) of the brain. This situation allows the dopamine neuron to be put under oxidative stress, thus leaving the DA neuron vulnerable to free radical attack. In attempts to reverse the deficit in Complex I in the cell, in earlier experiments, we used a ketone body, D-beta-hydroxybutyrate (DBHB) in the presence of MPTP to increase oxidative phosphorylation. This change in phosphorylation state afforded protection to the SNpc TH+neurons. One drawback to the use of DBHB is that it is short-acting. In our present experiment, we used a DBHB analogue, glyceryl tris(3-hydroxybutyrate, G3HB) which is the basic DBHB structure that has been altered. Compared to DBHB which increased DBHB levels in plasma by almost 100%, G3HB increased plasma DBHB levels by less than 50%, Increasing the assay sample volume increases brain tissue DBHB levels . In the in vivo studies, the combination of MPTP and G3HB seemed to cause significant mortality in the two strains of mice that we used. This high mortality rate may be strain or breeding house dependent. More studies need to be done to sort this situation out.

Parkinson Disease (PD) is the second most common neurodegenerative disease of our aged population behind Alzheimer s Disease. Epidemiological, animal and cell culture studies have shown that inflammation is a part of the PD morphological picture. It has been suggested that -synuclein (a major component of the Lewy bodies present within dopamine neurons of the PD substantia nigra {SN}) is responsible for the observed inflammatory response in the PD brain. We injected -synuclein and mutated synuclein into the substantia nigra (SN) of rats (8 ug/4ul). We also performed cell culture studies on the activation of microglia by alpha-synuclein. In our in vivo studies, we found that both alpha-synuclein and A53T mutated synuclein both caused apomorphine-induced rotations. The number of rotations were small but significant and indicates that the synucleins caused an increase in sensitivity of the dopaminergic (DA) receptors in the SN. These studies indicate that there is some interaction between DA and the synucleins. In our in vitro studies, we noted that the synucleins caused microglia to adhere to plastic surfaces. This adhesion was blocked by EDTA which indicated that the process of adhesion in this case was calcium-dependent. In our examination of cell migration using various synucleins, we found that only LTB4, a leukotriene, and CX3CL1, a chemokine, enticed microglia to migrate to naked or laminin-coated filters. While we cannot conclude from our cell culture studies that synucleins can trigger neuroinflammation, we can state that the synucleins can activate microglia and cause them to migrate.

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is the tool of choice for modeling Parkinson’s Disease (PD) in animals. Originally synthesized as a “designer drug” by drug users, MPTP, while not giving us the definitive answer as to the etiology of Parkinson’s disease, has enlightened many of us researchers about the molecules and mechanisms involved in dopamine neuron death. Herein, we provide information about some of the events that are involved here and try to make it clear just how complicated the death of the dopamine neuron in the MPTP model and possibly in PD seems to be.

Parkinson's disease (PD) is characterized mainly by a loss of nigrostriatal dopamine neurons. Thus far, the actual physiopathology of PD remains uncertain, although recent studies have found decreased activity of complex I, one of the enzymatic units of the mitochondrial respiratory chain, in various tissues of PD patients. Because most, if not all, of PD patients are treated chronically with levodopa, the precursor of dopamine, and because we have shown previously that catecholamines may alter mitochondrial respiration, we assessed the effects of chronic administration of levodopa on complex I activity in rat brain. We found that chronic administration of levodopa, at a dose used in PD patients, caused a significant reduction in complex I activity while it did not affect the activities of complex II, complex IV, and citrate synthase. Reduction in complex I activity correlated well with catecholamine innervation as the reduction was observed mainly in the striatum and substantia nigra and to a lesser extent in the frontal cortex but not in the cerebellum. Moreover, the levodopa-induced decrease of complex I activity was reversible since activities at 1, 3, and 7 days after the last injection showed a progressive return to control values. Incubation of whole brain mitochondria in vitro showed that both levodopa and dopamine inhibit complex I activity in a dose- and time- dependent manner. In contrast, other compounds such as homovanillic acid, 3,4-dihydroxyphenylacetic acid, and 3-O-methyl-dopa were minimally effective. Reduced glutathione, ascorbate, superoxide dismutase, and catalase prevented the effect of levodopa and dopamine on complex I. Various inhibitors of monoamine oxidase also prevented the effect of dopamine. In agreement with a critical role of monoamine oxidase in this effect in vitro, we observed that noncatecholamine substrates of this enzyme such as serotonin and β-phenylethylamine were potent inhibitors of complex I. However, autoxidation may also be involved in this process because the effect of levodopa, 6-hydroxydopa, and 6-hydroxydopamine on complex I activity was only partially suppressed by monoamine oxidase inhibitors. These observations demonstrate that the chronic administration of levodopa can cause alterations in mitochondrial respiratory chain activity in rats that are most likely related to an oxidative stress provoked by the increase in dopamine turnover. We suggest that this mechanism may exaggerate a mitochondrial defect already present in the brains of PD patients and thus may play a role in the progression of PD.

Parkinson's disease (PD) is the most common neurodegenerative movement disorder associated with a loss of dopaminergic neurons. The role of mitochondria in the aetiology of PD has been questioned for decades, mostly from the perspective of bioenergetic failure. For decades, a deficit in mitochondrial respiration was thought to be a key factor in PD neurodegeneration. However, excluding a few exceptions where a clinical picture of parkinsonism is associated with a mitochondrial DNA mutation, preclinical and clinical studies have failed to identify any genetic mutations in the genes encoding for the electron transport chain complexes in PD patients. More recently, it has been discovered that mutations in the genes encoding for Parkin, PINK1 (PTEN-induced putative kinase-1) and DJ-1 are associated with familial forms of PD and with mitochondrial alterations, including morphological abnormalities. These results have led many researchers to revisit the question of mitochondrial biology as a primary mechanism in PD pathogenesis, this time from an angle of perturbation in mitochondrial dynamics and not from the angle of a deficit in respiration.

Mitochondrial complex I deficits have long been associated with Parkinson disease (PD). However, it remains unknown whether such defects represent a primary event in dopaminergic neurodegeneration.Apoptosis-inducing factor (AIF) is a mitochondrial protein that, independently of its proapoptotic properties, plays an essential physiologic role in maintaining a fully functional complex I. We used AIF-deficient harlequin (Hq) mice, which exhibit structural deficits in assembled complex I, to determine whether primary complex I defects linked to AIF depletion may cause dopaminergic neurodegeneration.Despite marked reductions in mitochondrial complex I protein levels, Hq mice did not display apparent alterations in the dopaminergic nigrostriatal system. However, these animals were much more susceptible to exogenous parkinsonian complex I inhibitors, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Subtoxic doses of MPTP, unable to cause damage to wild-type animals, produced marked nigrostriatal dopaminergic degeneration in Hq mice. This effect was associated with exacerbated complex I inhibition and increased production of mitochondrial-derived reactive oxygen species (ROS) in Hq brain mitochondria. The antioxidant superoxide dismutase-mimetic compound tempol was able to reverse the increased susceptibility of Hq mice to MPTP. Supporting an instrumental role for mitochondrial-derived ROS in PD-related neurodegeneration, transgenic mice overexpressing mitochondrially targeted catalase exhibited an attenuation of MPTP-induced mitochondrial ROS and dopaminergic cell death.Structural complex I alterations linked to AIF deficiency do not cause dopaminergic neurodegeneration but increase the susceptibility of dopaminergic neurons to exogenous parkinsonian neurotoxins, reinforcing the concept that genetic and environmental factors may interact in a common molecular pathway to trigger PD.

Parkinson's disease (PD) is the most common neurodegenerative movement disorder associated with a loss of dopaminergic neurons. The role of mitochondria in the aetiology of PD has been questioned for decades, mostly from the perspective of bioenergetic failure. For decades, a deficit in mitochondrial respiration was thought to be a key factor in PD neurodegeneration. However, excluding a few exceptions where a clinical picture of parkinsonism is associated with a mitochondrial DNA mutation, preclinical and clinical studies have failed to identify any genetic mutations in the genes encoding for the electron transport chain complexes in PD patients. More recently, it has been discovered that mutations in the genes encoding for Parkin, PINK1 (PTEN-induced putative kinase-1) and DJ-1 are associated with familial forms of PD and with mitochondrial alterations, including morphological abnormalities. These results have led many researchers to revisit the question of mitochondrial biology as a primary mechanism in PD pathogenesis, this time from an angle of perturbation in mitochondrial dynamics and not from the angle of a deficit in respiration.

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson's disease. We created a LRRK2 transgenic mouse model that recapitulates cardinal features of the disease: an age-dependent and levodopa-responsive slowness of movement associated with diminished dopamine release and axonal pathology of nigrostriatal dopaminergic projection. These mice provide a valid model of Parkinson's disease and are a resource for the investigation of pathogenesis and therapeutics.

The effect of unilateral perinatal hypoxic-ischemic brain injury on striatal dopamine uptake sites and on D2 and D2 receptors was investigated in rat by using in vitro quantitative receptor binding autoradiography, 9–11 weeks after the insult. Saturation experiments revealed a significant 20% decrease in maximal binding capacity (Bmax) for [3H]spiperone-labeled D2 receptors on the side of the lesion in comparison to the non-lesioned contralateral side or to either side of control animals. There was no significant change in [3H]mazindol-labeled dopamine uptake sites or in [3H]SCH 23390-labeled D1 receptor characteristics (Bmax and Kd) on the lesioned side. We conclude that the decrease in D2 receptor binding previously observed in immature animals is persistent, whereas the decrease in D1 binding is not.

Administration of the neurotoxin 6-hydroxydopamine (6-OHDA) to rat brain causes biochemical and neuroanatomical changes to the nigrostriatal dopaminergic pathway similar to those observed in Parkinson's disease (PD). Although the cause of PD is unknown, it has been hypothesized that the neurodegenerative changes seen in PD might result from exposure to a neurotoxin. Therefore, strategies for limiting neurotoxin-induced dopaminergic damages, like those caused by 6-OHDA, may be of both clinical and basic interest. Accordingly, we tested the ability of both fetal neural (striatum) and fetal non-neural (liver) tissue implants to protect the rat striatum against the toxic effects of a subsequent intrastriatal injection of 6-OHDA. Non-grafted rats (lesion only) showed amphetamine-induced rotational behavior and a decrease in striatal [3H]mazindol-labeled dopamine uptake sites after 6-OHDA injection. In contrast, the animals grafted with striatum or liver showed no behavioral or biochemical changes. Interestingly, sham-transplanted control animals were also protected against the 6-OHDA-induced toxicity. These results suggest that the resistance of the dopaminergic system against 6-OHDA neurotoxicity observed in grafted and sham-transplanted animals is likely to be related to the surgical procedure itself. This observation points to a possible role for surgery-related events in the clinical improvement described in PD patients who underwent intracerebral transplantation.

Recent evidence has suggested a role for free radicals in tardive dyskinesia. We, therefore, investigated the effects of chronic administration of fluphenazine decanoate (FLU) and/or vitamin E (VIT E) on regional monoamine metabolism in rat brain. Chronic FLU caused significant increases in dopamine (DA) in nucleus accumbens and brainstem, significant decreases in dihydroxyphenylacetic acid (DOPAC) in frontal cortex, nucleus accumbens and hippocampus and significant decreases in homovanillic acid (HVA) in nucleus accumbens, caudate-putamen and brainstem. Coadministration of FLU and VIT E normalized HVA in caudate-putamen, nucleus accumbens and brainstem as well as DOPAC in nucleus accumbens and hippocampus. Chronic FLU caused significant increases in norepinephrine (NE) levels in all regions studied. VIT E attenuated FLU-induced increases in NE levels in nucleus accumbens and hippocampus. Significant increases in serotonin (5-HT) levels occurred in nucleus accumbens and hippocampus whereas significant decreases in 5-hydroxyindole-acetic acid (5-HIAA) occurred in all brain regions after chronic FLU. Coadministration of VIT E attenuated the changes observed in hippocampal 5-HIAA but potentiated the FLU-induced increases in 5-HT in this region. Our data suggest that VIT E can attenuate some of the FLU-induced changes in monoamine metabolism. Results are discussed in relation to possible involvement of free radicals in monoamine metabolism during chronic neuroleptic use.

Publisher Summary This chapter provides a detailed discussion on the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model of Parkinson's disease (PD). MPTP is the only known dopaminergic neurotoxin capable of causing a clinical picture in both humans and monkeys that is indistinguishable from PD. While its handling requires a series of precautions, the use of MPTP is straightforward since it does not require any particular piece of equipment such as a stereotaxic frame. Moreover, it does not require surgery on live animals as needed for 6-hydroxydopamine or rotenone. MPTP produces a reliable and reproducible lesion of the nigrostriatal dopaminergic pathway after its systemic administration, which is often not the case for other publicized poisons. While MPTP monkeys remain the gold standard for the preclinical testing of new therapies for PD, most of the studies geared toward unraveling the mechanisms underlying the demise of dopaminergic neurons have been performed primarily in mice. This chapter focuses on several questions about MPTP mouse model and shows that many of the popular objections made about this model are false. This chapter also gives an opportunity to stress some of the important limitations of this model and to discuss how these may impact the interpretations of one's data.

The power of immunohistochemical staining as a tool for the study of the neurochemical anatomy of the brain would be greatly enhanced if quantitative measures of staining were to be developed. We have here assessed the reliability and validity of two population measures of extent of fiber innervation: percent area occupied by staining, and average optical density (AOD) of staining. We have evaluated these measures for tyrosine hydroxylase-positive staining of the striatum in relation to apomorphine-induced rotational behavior in 6-hydroxydopamine lesioned rats. We have found that inter-operator reliability for the area measure is high (r = 0.98). Apomorphine-induced rotations were observed when the area measured was reduced to 2% or less of the control side, and when the density measure was reduced to 15% or less. These results are similar to those obtained previously for biochemical assay of TH activity, which showed rotations at reductions to 10% or less. We conclude that these density measures provide valid relative indices of extent of fiber innervation on the same section. The AOD measure appears to be more sensitive at lower levels of innervation.