BDNF rs10501087, rs1491850 and rs11030094 polymorphisms associated with delayed progression in early-stage Parkinson's disease.

Parkinson's disease (PD) is heterogenous in its presentation, progression and response to therapies. Genetic polymorphisms may account for some of this variability. Several single nucleotide polymorphisms (SNPs) in the brain-derived neurotrophic factor gene BDNF have been associated with differing clinical outcomes from different dopaminergic replacement strategies, and one of these, the rs6265 SNP, has been associated with a milder clinical phenotype in the unmedicated, early-stage of PD. We examined if other BDNF SNPs with potential pharmacogenetic effects also are associated with different rates of disease progression. The Deprenyl And Tocopherol Antioxidative Therapy Of Parkinsonism (DATATOP) study was analyzed retrospectively. DNA samples (n = 217) were genotyped for the BDNF rs908867, rs11030094, rs10501087, rs1157659, and rs1491850 SNPs, and the primary endpoint was time to initiate symptomatic pharmacotherapy. Genotypes were compared using the Cox proportional hazard ratio (HR) with baseline age, sex, site, time since PD diagnosis and rs6265 genotype as covariates. The primary endpoint was associated with a delay with three SNPs: rs10501087 [HR (95% Confidence Interval) = 28.3 (3.6-223.1, p = 0.002) and 7.6 (1.9-29.8, p = 0.004) for T/T and T/C subjects, respectively, vs. C/C subjects], rs1491850 [HR = 3.3 (1.3-8.4, p = 0.04) and 2.8 (1.3-6.4, p = 0.03) for T/T and T/C subjects, respectively, vs. C/C subjects] and rs11030094 [HR = 2.5 (1.1-5.6, p = 0.03) and 2.0 (1.3-6.4, p = 0.03) for A/A and A/G subjects, respectively, vs. G/G subjects]. From the primary endpoint, specific rs10501087, rs1491850, and rs11030094 SNP genotypes are associated with a slower rate of PD progression in the unmedicated state. A prospective clinical trial examining many BDNF SNPs is warranted.

Large-Scale SARS-CoV-2 Testing Utilizing Saliva and Transposition Sample Pooling.

Identification and isolation of contagious individuals along with quarantine of close contacts, is critical for slowing the spread of COVID-19. Large-scale testing in a surveillance or screening capacity for asymptomatic carriers of COVID-19 provides both data on viral spread and the follow-up ability to rapidly test individuals during suspected outbreaks. The COVID-19 early detection program at Michigan State University has been utilizing large-scale testing in a surveillance or screening capacity since fall of 2020. The methods adapted here take advantage of the reliability, large sample volume, and self-collection benefits of saliva, paired with a cost-effective, reagent conserving two-dimensional pooling scheme. The process was designed to be adaptable to supply shortages, with many components of the kits and the assay easily substituted. The processes outlined for collecting and processing SARS-CoV-2 samples can be adapted to test for future viral pathogens reliably expressed in saliva. By providing this blueprint for universities or other organizations, preparedness plans for future viral outbreaks can be developed.

BDNF rs6265 Genotype Influences Outcomes of Pharmacotherapy and Subthalamic Nucleus Deep Brain Stimulation in Early-Stage Parkinson's Disease.

INTRODUCTION: The efficacy of pharmacotherapy and deep brain stimulation of the subthalamic nucleus in treating Parkinson's disease motor symptoms is highly variable and may be influenced by patient genotype. The relatively common (prevalence about one in three) and protein-altering rs6265 single nucleotide polymorphism (C > T) in the gene BDNF has been associated with different clinical outcomes with levodopa. OBJECTIVE: We sought to replicate this reported association in early-stage Parkinson's disease subjects and to examine whether a difference in clinical outcomes was present with subthalamic nucleus deep brain stimulation. MATERIALS AND METHODS: Fifteen deep brain stimulation and 13 medical therapy subjects were followed for 24 months as part of the Vanderbilt DBS in Early Stage PD clinical trial (NCT00282152, FDA IDE #G050016). Primary outcome measures were the Unified Parkinson's Disease Rating Scale (UPDRS) and Parkinson's Disease Questionnaire-39. RESULTS: Outcomes with drug therapy in subjects carrying the rs6265 T allele were significantly worse following 12 months of treatment compared to C/C subjects (UPDRS: +20 points, p = 0.019; PDQ-39: +16 points, p = 0.018). In contrast, rs6265 genotype had no effect on overall motor response to subthalamic nucleus deep brain stimulation at any time point; further, rs6265 C/C subjects treated with stimulation were associated with worse UPDRS part II scores at 24 months compared to medical therapy. CONCLUSIONS: Genotyping for the rs6265 polymorphism may be useful for predicting long-term response to drug therapy and counseling Parkinson's disease patients regarding whether to consider earlier subthalamic nucleus deep brain stimulation. Validation in a larger cohort of early-stage Parkinson's disease subjects is warranted.

α-Synuclein antisense oligonucleotides as a disease-modifying therapy for Parkinson's disease.

Parkinson's disease (PD) is a prevalent neurodegenerative disease with no approved disease-modifying therapies. Multiplications, mutations, and single nucleotide polymorphisms in the SNCA gene, encoding α-synuclein (aSyn) protein, either cause or increase risk for PD. Intracellular accumulations of aSyn are pathological hallmarks of PD. Taken together, reduction of aSyn production may provide a disease-modifying therapy for PD. We show that antisense oligonucleotides (ASOs) reduce production of aSyn in rodent preformed fibril (PFF) models of PD. Reduced aSyn production leads to prevention and removal of established aSyn pathology and prevents dopaminergic cell dysfunction. In addition, we address the translational potential of the approach through characterization of human SNCA-targeting ASOs that efficiently suppress the human SNCA transcript in vivo. We demonstrate broad activity and distribution of the human SNCA ASOs throughout the nonhuman primate brain and a corresponding decrease in aSyn cerebral spinal fluid (CSF) levels. Taken together, these data suggest that, by inhibiting production of aSyn, it may be possible to reverse established pathology; thus, these data support the development of SNCA ASOs as a potential disease-modifying therapy for PD and related synucleinopathies.

BDNF rs6265 Variant Alters Outcomes with Levodopa in Early-Stage Parkinson's Disease.

Disease outcomes are heterogeneous in Parkinson's disease and may be predicted by gene variants. This study investigated if the BDNF rs6265 single nucleotide polymorphism (SNP) is associated with differential outcomes with specific pharmacotherapy treatment strategies in the "NIH Exploratory Trials in PD Long-term Study 1" (NET-PD LS-1, n = 540). DNA samples were genotyped for the rs6265 SNP and others (rs11030094, rs10501087, rs1491850, rs908867, and rs1157659). The primary measures were the Unified Parkinson's Disease Rating Scale (UPDRS) and its motor component (UPDRS-III). Groups were divided by genotype and treatment regimen (levodopa monotherapy vs levodopa with other medications vs no levodopa). T allele carriers were associated with worse UPDRS outcomes compared to C/C subjects when treated with levodopa monotherapy (+ 6 points, p = 0.02) and to T allele carriers treated with no levodopa treatment strategies (UPDRS: + 8 points, p = 0.01; UPDRS-III: + 6 points, p = 0.01). Similar effects of worse outcomes associated with levodopa monotherapy were observed in the BDNF rs11030094, rs10501087, and rs1491850 SNPs. This study suggests the levodopa monotherapy strategy is associated with worse disease outcomes in BDNF rs6265 T carriers. Pending prospective validation, BDNF variants may be precision medicine factors to consider for symptomatic treatment decisions for early-stage PD patients.

Striatal Nurr1, but not FosB expression links a levodopa-induced dyskinesia phenotype to genotype in Fisher 344 vs. Lewis hemiparkinsonian rats.

Numerous genes, and alterations in their expression, have been identified as risk factors for developing levodopa-induced dyskinesia (LID). However, our understanding of the complexities of molecular changes remains insufficient for development of clinical treatment. In the current study we used gene array, in situ hybridization, immunohistochemistry, and microdialysis to provide a unique compare and contrast assessment of the relationship of four candidate genes to LID, employing three genetically distinct rat strains (Sprague-Dawley (SD), Fischer-344 (F344) and Lewis-RT.1) showing differences in dyskinesia susceptibility and 'first-ever LID' versus 'chronic LID' expression in subjects displaying equal dyskinesia severity. In these studies, rat strains were easily distinguishable for their LID propensity with: 1) a majority of SD rats expressing LID (LID+) and a subset being resistant (LID-); 2) all F344 rats readily developing (LID+); and 3) all Lewis rats being LID-resistant (LID-). Following chronic levodopa, LID+ SD rats showed significant increases in candidate gene expression: Nr4a2/(Nurr1) > > Trh > Inhba = Fosb. However, SD rats with long-standing striatal dopamine (DA) depletion treated with first-ever versus chronic high-dose levodopa revealed that despite identical levels of LID severity: 1) Fosb and Nurr1 transcripts but not protein were elevated with acute LID expression; 2) FOSB/ΔFOSB and NURR1 proteins were elevated only with chronic LID; and 3) Trh transcript and protein were elevated only with chronic LID. Strikingly, despite similar levodopa-induced striatal DA release in both LID-expressing F344 and LID-resistant Lewis rats, Fosb, Trh, Inhba transcripts were significantly elevated in both strains; however, Nurr1 mRNA was significantly increased only in LID+ F344 rats. These findings suggest a need to reevaluate currently accepted genotype-to-phenotype relationships in the expression of LID, specifically that of Fosb, a transcription factor generally assumed to play a causal role, and Nurr1, a transcription factor that has received significant attention in PD research linked to its critical role in the survival and function of midbrain DA neurons but who's striatal expression, generally below levels of detection, has remained largely unexplored as a regulator of LID. Finally these studies introduce a novel 'model' (inbred F344 vs inbred Lewis) that may provide a powerful tool for investigating the role for 'dyskinesia-resistance' genes downstream of 'dyskinesia-susceptibility' genes in modulating LID expression, a concept that has received considerably less attention and offers a new ways of thinking about antidyskinetic therapies.

Developmental exposure to the organochlorine pesticide dieldrin causes male-specific exacerbation of α-synuclein-preformed fibril-induced toxicity and motor deficits.

Human and animal studies have shown that exposure to the organochlorine pesticide dieldrin is associated with increased risk of Parkinson's disease (PD). Previous work showed that developmental dieldrin exposure increased neuronal susceptibility to MPTP toxicity in male C57BL/6 mice, possibly via changes in dopamine (DA) packaging and turnover. However, the relevance of the MPTP model to PD pathophysiology has been questioned. We therefore studied dieldrin-induced neurotoxicity in the α-synuclein (α-syn)-preformed fibril (PFF) model, which better reflects the α-syn pathology and toxicity observed in PD pathogenesis. Specifically, we used a "two-hit" model to determine whether developmental dieldrin exposure increases susceptibility to α-syn PFF-induced synucleinopathy. Dams were fed either dieldrin (0.3 mg/kg, every 3-4 days) or vehicle corn oil starting 1 month prior to breeding and continuing through weaning of pups at postnatal day 22. At 12 weeks of age, male and female offspring received intrastriatal α-syn PFF or control saline injections. Consistent with the male-specific increased susceptibility to MPTP, our results demonstrate that developmental dieldrin exposure exacerbates PFF-induced toxicity in male mice only. Specifically, in male offspring, dieldrin exacerbated PFF-induced motor deficits on the challenging beam and increased DA turnover in the striatum 6 months after PFF injection. However, male offspring showed neither exacerbation of phosphorylated α-syn aggregation (pSyn) in the substantia nigra (SN) at 1 or 2 months post-PFF injection, nor exacerbation of PFF-induced TH and NeuN loss in the SN 6 months post-PFF injection. Collectively, these data indicate that developmental dieldrin exposure produces a male-specific exacerbation of synucleinopathy-induced behavioral and biochemical deficits. This sex-specific result is consistent with both previous work in the MPTP model, our previously reported sex-specific effects of this exposure paradigm on the male and female epigenome, and the higher prevalence and more severe course of PD in males. The novel two-hit environmental toxicant/PFF exposure paradigm established in this project can be used to explore the mechanisms by which other PD-related exposures alter neuronal vulnerability to synucleinopathy in sporadic PD.

Orexinergic modulation of serotonin neurons in the dorsal raphe of a diurnal rodent, Arvicanthis niloticus.

The hypothalamic neuropeptide, orexin (or hypocretin), is implicated in numerous physiology and behavioral functions, including affective states such as depression and anxiety. The underlying mechanisms and neural circuits through which orexin modulates affective responses remain unclear. The objective of the present study was to test the hypothesis that the serotonin (5-HT) system of the dorsal raphe nucleus (DRN) is a downstream target through which orexin potentially manifests its role in affective states. Using a diurnal rodent, the Nile grass rat (Arvicanthis niloticus), we first characterized the expression of the orexin receptors OX1R and OX2R in the DRN using in situ hybridization. The results revealed distinct distributions of OX1R and OX2R mRNAs, with OX1R predominantly expressed in the dorsal and lateral wings of the DRN that are involved in affective processes, while OX2R was mostly found in the ventral DRN that is more involved in sensory-motor function. We next examined how the orexin-OX1R pathway regulates 5-HT in the DRN and some of its projection sites using a selective OX1R antagonist SB-334867 (10 mg/kg, i.p.). A single injection of SB-334867 decreased 5-HT-ir fibers within the anterior cingulate cortex (aCgC); five once-daily administrations of SB-334867 decreased 5-HT-ir not only in the aCgC but also in the DRN, oval bed nucleus of the stria terminalis (ovBNST), nucleus accumbens shell (NAcSh), and periaqueductal gray (PAG). HPLC analysis revealed that five once-daily administrations of SB-334867 did not affect 5-HT turnover to any of the five sites, although it increased the levels of both 5-HT and 5-HIAA in the NAcSh. These results together suggest that orexinergic modulation of DRN 5-HT neurons via OX1Rs may be one pathway through which orexin regulates mood and anxiety, as well as perhaps other neurobiological processes.

Parkinson's disease-linked D620N VPS35 knockin mice manifest tau neuropathology and dopaminergic neurodegeneration.

Mutations in the vacuolar protein sorting 35 ortholog (VPS35) gene represent a cause of late-onset, autosomal dominant familial Parkinson's disease (PD). A single missense mutation, D620N, is considered pathogenic based upon its segregation with disease in multiple families with PD. At present, the mechanism(s) by which familial VPS35 mutations precipitate neurodegeneration in PD are poorly understood. Here, we employ a germline D620N VPS35 knockin (KI) mouse model of PD to formally establish the age-related pathogenic effects of the D620N mutation at physiological expression levels. Our data demonstrate that a heterozygous or homozygous D620N mutation is sufficient to reproduce key neuropathological hallmarks of PD as indicated by the progressive degeneration of nigrostriatal pathway dopaminergic neurons and widespread axonal pathology. Unexpectedly, endogenous D620N VPS35 expression induces robust tau-positive somatodendritic pathology throughout the brain as indicated by abnormal hyperphosphorylated and conformation-specific tau, which may represent an important and early feature of mutant VPS35-induced neurodegeneration in PD. In contrast, we find no evidence for α-synuclein-positive neuropathology in aged VPS35 KI mice, a hallmark of Lewy body pathology in PD. D620N VPS35 expression also fails to modify the lethal neurodegenerative phenotype of human A53T-α-synuclein transgenic mice. Finally, by crossing VPS35 KI and null mice, our data demonstrate that a single D620N VPS35 allele is sufficient for survival and early maintenance of dopaminergic neurons, indicating that the D620N VPS35 protein is fully functional. Our data raise the tantalizing possibility of a pathogenic interplay between mutant VPS35 and tau for inducing neurodegeneration in PD.

Bdnf variant is associated with milder motor symptom severity in early-stage Parkinson's disease.

INTRODUCTION: Parkinson's disease (PD) progression is heterogeneous. Variants in PD-related genes may alter disease progression or severity. We examined if the single nucleotide variant rs6265 in the gene Bdnf alters clinical phenotype in early-stage, unmedicated PD. METHODS: A retrospective analysis was conducted using data collected in the Deprenyl And Tocopherol Antioxidative Therapy Of Parkinsonism (DATATOP) study. DNA samples (n = 217) were genotyped for the Bdnf rs6265 variant, and the primary endpoint was time to initiate levodopa. The Parkinson's Progression Markers Initiative (PPMI) was used for validation (n = 383). RESULTS: The primary endpoint of time to initiate levodopa was associated with a delay in subjects with two copies of the rs6265 minor (Met66) allele (HR: 4.9; 95% CI: 1.3-18.8). Secondary endpoints were not different among genotypes. PPMI subjects with two Met66 alleles demonstrated significantly lower total and part III Movement Disorder Society - United Parkinson's Disease Rating Scale (MDS-UPDRS) scores at baseline, as well as more tremor-related symptoms, but not a delay in initiation of maintenance pharmacotherapy. CONCLUSIONS: Data from two distinct, unmedicated, early-stage PD cohorts suggest that carrying two copies of the rs6265 Met66 allele (∼4% of the population) is associated with less severity in motor symptoms and potentially a slower rate of progression.

Silencing Alpha Synuclein in Mature Nigral Neurons Results in Rapid Neuroinflammation and Subsequent Toxicity.

Human studies and preclinical models of Parkinson's disease implicate the involvement of both the innate and adaptive immune systems in disease progression. Further, pro-inflammatory markers are highly enriched near neurons containing pathological forms of alpha synuclein (α-syn), and α-syn overexpression recapitulates neuroinflammatory changes in models of Parkinson's disease. These data suggest that α-syn may initiate a pathological inflammatory response, however the mechanism by which α-syn initiates neuroinflammation is poorly understood. Silencing endogenous α-syn results in a similar pattern of nigral degeneration observed following α-syn overexpression. Here we aimed to test the hypothesis that loss of α-syn function within nigrostriatal neurons results in neuronal dysfunction, which subsequently stimulates neuroinflammation. Adeno-associated virus (AAV) expressing an short hairpin RNA (shRNA) targeting endogenous α-syn was unilaterally injected into the substantia nigra pars compacta (SNc) of adult rats, after which nigrostriatal pathology and indices of neuroinflammation were examined at 7, 10, 14 and 21 days post-surgery. Removing endogenous α-syn from nigrostriatal neurons resulted in a rapid up-regulation of the major histocompatibility complex class 1 (MHC-1) within transduced nigral neurons. Nigral MHC-1 expression occurred prior to any overt cell death and coincided with the recruitment of reactive microglia and T-cells to affected neurons. Following the induction of neuroinflammation, α-syn knockdown resulted in a 50% loss of nigrostriatal neurons in the SNc and a corresponding loss of nigrostriatal terminals and dopamine (DA) concentrations within the striatum. Expression of a control shRNA did not elicit any pathological changes. Silencing α-syn within glutamatergic neurons of the cerebellum did not elicit inflammation or cell death, suggesting that toxicity initiated by α-syn silencing is specific to DA neurons. These data provide evidence that loss of α-syn function within nigrostriatal neurons initiates a neuronal-mediated neuroinflammatory cascade, involving both the innate and adaptive immune systems, which ultimately results in the death of affected neurons.

Subthalamic Nucleus Deep Brain Stimulation Does Not Modify the Functional Deficits or Axonopathy Induced by Nigrostriatal α-Synuclein Overexpression.

Subthalamic nucleus deep brain stimulation (STN DBS) protects dopaminergic neurons of the substantia nigra pars compacta (SNpc) against 6-OHDA and MPTP. We evaluated STN DBS in a parkinsonian model that displays α-synuclein pathology using unilateral, intranigral injections of recombinant adeno-associated virus pseudotype 2/5 to overexpress wildtype human α-synuclein (rAAV2/5 α-syn). A low titer of rAAV2/5 α-syn results in progressive forelimb asymmetry, loss of striatal dopaminergic terminal density and modest loss of SNpc dopamine neurons after eight weeks, corresponding to robust human-Snca expression and no effect on rat-Snca, Th, Bdnf or Trk2. α-syn overexpression increased phosphorylation of ribosomal protein S6 (p-rpS6) in SNpc neurons, a readout of trkB activation. Rats received intranigral injections of rAAV2/5 α-syn and three weeks later received four weeks of STN DBS or electrode implantation that remained inactive. STN DBS did not protect against α-syn-mediated deficits in forelimb akinesia, striatal denervation or loss of SNpc neuron, nor did STN DBS elevate p-rpS6 levels further. ON stimulation, forelimb asymmetry was exacerbated, indicating α-syn overexpression-mediated neurotransmission deficits. These results demonstrate that STN DBS does not protect the nigrostriatal system against α-syn overexpression-mediated toxicity. Whether STN DBS can be protective in other models of synucleinopathy is unknown.

Subthalamic Nucleus Deep Brain Stimulation Employs trkB Signaling for Neuroprotection and Functional Restoration.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is the most common neurosurgical treatment for Parkinson's disease motor symptoms. In preclinical models, STN DBS provides neuroprotection for substantia nigra (SN) dopamine neurons and increases BDNF in the nigrostriatal system and primary motor cortex. However, whether BDNF signaling in the SN participates in the neuroprotective effects of DBS remains unknown. We demonstrate that STN DBS in male rats activates signaling downstream of tropomyosin receptor kinase type B (trkB), namely, phosphorylation of Akt and ribosomal protein S6, in SN neurons. Long-term trkB blockade abolished STN DBS-mediated neuroprotection of SN neurons following progressive 6-hydroxydopamine lesion and was associated with decreased phosphorylated ribosomal protein S6 immunoreactivity. Acute trkB blockade in rats with stable nigrostriatal denervation attenuated the forelimb akinesia improvement normally induced by STN DBS. These results suggest that STN DBS increases BDNF-trkB signaling to contribute to the neuroprotective and symptomatic efficacy of STN DBS.SIGNIFICANCE STATEMENT Subthalamic nucleus deep brain stimulation (STN DBS) is increasingly used in mid- to late-stage Parkinson's disease (PD) but with an incomplete knowledge of its molecular mechanisms. STN DBS is neuroprotective against neurotoxicants in animal models and increases BDNF. This study is the first to show that BDNF signaling through the cognate tropomyosin receptor kinase type B (trkB) receptor occurs in substantia nigra pars compacta neurons and is required for neuroprotection. In addition, blockade of trkB unexpectedly reduced the functional benefit of STN DBS on a short timescale that is inconsistent with canonical trkB signaling pathways, suggesting a noncanonical role for trkB in STN DBS-mediated behavioral effects. Together, these data implicate trkB signaling in the symptomatic efficacy and disease-modifying potential of STN DBS.

Exendin-4 Treatment Improves LPS-Induced Depressive-Like Behavior Without Affecting Pro-Inflammatory Cytokines.

BACKGROUND: Exendin-4 is a peptide agonist of the glucagon-like peptide-1 (GLP-1) receptor, currently in clinical trials as a potential disease-modifying therapy for Parkinson's disease. In light of this, it is important to understand potential modes of action of exendin-4 in the brain. Exendin-4 is neuroprotective and has been proposed to be directly anti-inflammatory, and that this is one way it reduces neurodegeneration. However, prior studies have focused on animal models involving both neurodegeneration and inflammation, therefore, it is also possible that the observed decreased inflammation is secondary to reduced neurodegeneration. OBJECTIVE: To investigate whether exendin-4 directly reduces inflammation in the brain following an insult that involves neuroinflammation but not neurodegeneration, namely systemic administration of lipopolysaccharide (LPS). METHODS: Rats were administered LPS systemically and were treated with either 0.5 µg/kg exendin-4 or saline vehicle injections over 5 days. Behavior was evaluated with forced swim test. We assayed TNF-α and IL-1ß levels in cerebrospinal fluid and cytokine mRNA expression in striatal, hippocampal and cortical tissues using qPCR. We determined brain monoamines using high-performance liquid chromatography. Finally, we isolated primary brain microglia from rats and measured cytokine production after exendin-4 treatment and LPS stimulation. RESULTS: Exendin-4 treatment did not affect cytokine mRNA expression in brain, cytokine levels in cerebrospinal fluid or cytokine production from cultured microglia, although there was a trend towards increased striatal dopamine. Importantly, exendin-4 significantly prevented depressive-like behavior at 24 hours after LPS injection, indicating that the drug engaged a target in the brain. Depressive-like behavior was associated with altered dopamine turnover in the striatum. CONCLUSION: We did not detect any anti-inflammatory effects of exendin-4. In previous studies exploring the effects of exendin-4 on brain insults involving neurodegeneration, observations of reduced inflammation might have been secondary to mitigation of neuronal death. Our results indicate that the effects of exendin-4 on behavior may be due to effects on dopamine synthesis or metabolism.

Is Alpha-Synuclein Loss-of-Function a Contributor to Parkinsonian Pathology? Evidence from Non-human Primates.

Accumulation of alpha-synuclein (α-syn) in Lewy bodies and neurites of midbrain dopamine neurons is diagnostic for Parkinson's disease (PD), leading to the proposal that PD is a toxic gain-of-function synucleinopathy. Here we discuss the alternative viewpoint that α-syn displacement from synapses by misfolding and aggregation results in a toxic loss-of-function. In support of this hypothesis we provide evidence from our pilot study demonstrating that knockdown of endogenous α-syn in dopamine neurons of non-human primates reproduces the pattern of nigrostriatal degeneration characteristic of PD.

Sonic Hedgehog Controls the Phenotypic Fate and Therapeutic Efficacy of Grafted Neural Precursor Cells in a Model of Nigrostriatal Neurodegeneration.

The expression of soluble growth and survival promoting factors by neural precursor cells (NPCs) is suggested to be a prominent mechanism underlying the protective and regenerative effects of these cells after transplantation. Nevertheless, how and to what extent specific NPC-expressed factors contribute to therapeutic effects is not well understood. Using RNA silencing, the current study investigated the roles of two donor NPC molecules, namely glial cell-line derived neurotrophic factor (GDNF) and sonic hedgehog (SHH), in the protection of substantia nigra dopamine neurons in rats treated with 6-hydroxydopamine (6-OHDA). Analyses indicate that as opposed to the knock-down of GDNF, SHH inhibition caused a profound decline in nigrostriatal neuroprotection. Further, SHH silencing also curbed endogenous neurogenesis and the migration of host brdU+/dcx+ neural precursors into the striatum, which was present in the animals receiving control or GDNF silenced NPCs. A change in graft phenotype, mainly reflected by a reduced proportion of undifferentiated nestin+ cells, as well as a significantly greater host microglial activity, suggested an important role for these processes in the attenuation of neuroprotection and neurogenesis upon SHH silencing. Overall these studies reveal core mechanisms fundamental to grafted NPC-based therapeutic effects, and delineate the particular contributions of two graft-expressed molecules, SHH and GDNF, in mediating midbrain dopamine neuron protection, and host plasticity after NPC transplantation.

Behavioural and neurobiological consequences of macrophage migration inhibitory factor gene deletion in mice.

BACKGROUND: Evidence from clinical studies and animal models show that inflammation can lead to the development of depression. Macrophage migration inhibitory factor (MIF) is an important multifunctional cytokine that is synthesized by several cell types in the brain. MIF can increase production of other cytokines, activates cyclooxygenase (COX)-2 and can counter-regulate anti-inflammatory effects of glucocorticoids. Increased plasma levels of MIF are associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation and depressive symptoms in patients. In contrast, MIF knockout (KO) mice have been found to exhibit increased depressive-like behaviour. The exact role for MIF in depression is therefore still controversial. To further understand the role of MIF in depression, we studied depressive-like behaviour in congenic male and female MIF KO mice and wild-type (WT) littermates and the associated neurobiological mechanisms underlying the behavioural outcome. METHODS: MIF KO and WT mice were tested for spontaneous locomotor activity in the open-field test, anhedonia-like behaviour in the sucrose preference test (SPT), as well as behavioural despair in the forced swim test (FST) and tail suspension test (TST). Brain and serum levels of cytokines, the enzymes COX-2 and indoleamine-2,3-dioxygenase (IDO) and the glucocorticoid hormone corticosterone were measured by RT-qPCR and/or high-sensitivity electrochemiluminescence-based multiplex immunoassays. Monoamines and metabolites were examined using HPLC. RESULTS: We found that MIF KO mice of both sexes displayed decreased depressive-like behaviour as measured in the FST. In the TST, a similar, but non-significant, trend was also found. IFN-γ levels were decreased, and dopamine metabolism increased in MIF KO mice. Decreased brain IFN-γ levels predicted higher striatal dopamine levels, and high dopamine levels in turn were associated with reduced depressive-like behaviour. In the SPT, there was a sex-specific discrepancy, where male MIF KO mice showed reduced anhedonia-like behaviour whereas female KO mice displayed increased anhedonia-like behaviour. Our results suggest that this relates to the increased corticosterone levels detected in female, but not male, MIF KO mice. CONCLUSIONS: Our findings support that MIF is involved in the generation of depressive-like symptoms, potentially by the effects of IFN-γ on dopamine metabolism. Our data further suggests a sex-specific regulation of the involved mechanisms.

High-Frequency Stimulation of the Rat Entopeduncular Nucleus Does Not Provide Functional or Morphological Neuroprotection from 6-Hydroxydopamine.

Deep brain stimulation (DBS) is the most common neurosurgical treatment for Parkinson's disease (PD). Whereas the globus pallidus interna (GPi) has been less commonly targeted than the subthalamic nucleus (STN), a recent clinical trial suggests that GPi DBS may provide better outcomes for patients with psychiatric comorbidities. Several laboratories have demonstrated that DBS of the STN provides neuroprotection of substantia nigra pars compacta (SNpc) dopamine neurons in preclinical neurotoxin models of PD and increases brain-derived neurotrophic factor (BDNF). However, whether DBS of the entopeduncular nucleus (EP), the homologous structure to the GPi in the rat, has similar neuroprotective potential in preclinical models has not been investigated. We investigated the impact of EP DBS on forelimb use asymmetry and SNpc degeneration induced by 6-hydroxydopamine (6-OHDA) and on BDNF levels. EP DBS in male rats received unilateral, intrastriatal 6-OHDA and ACTIVE or INACTIVE stimulation continuously for two weeks. Outcome measures included quantification of contralateral forelimb use, stereological assessment of SNpc neurons and BDNF levels. EP DBS 1) did not ameliorate forelimb impairments induced by 6-OHDA, 2) did not provide neuroprotection for SNpc neurons and 3) did not significantly increase BDNF levels in any of the structures examined. These results are in sharp contrast to the functional improvement, neuroprotection and BDNF-enhancing effects of STN DBS under identical experimental parameters in the rat. The lack of functional response to EP DBS suggests that stimulation of the rat EP may not represent an accurate model of clinical GPi stimulation.

Intrastriatal injection of pre-formed mouse α-synuclein fibrils into rats triggers α-synuclein pathology and bilateral nigrostriatal degeneration.

Previous studies demonstrate that intrastriatal injections of fibrillar alpha-synuclein (α-syn) into mice induce Parkinson's disease (PD)-like Lewy body (LB) pathology formed by aggregated α-syn in anatomically interconnected regions and significant nigrostriatal degeneration. The aim of the current study was to evaluate whether exogenous mouse α-syn pre-formed fibrils (PFF) injected into the striatum of rats would result in accumulation of LB-like intracellular inclusions and nigrostriatal degeneration. Sprague-Dawley rats received unilateral intrastriatal injections of either non-fibrillized recombinant α-syn or PFF mouse α-syn in 1- or 2- sites and were euthanized at 30, 60 or 180 days post-injection (pi). Both non-fibrillized recombinant α-syn and PFF α-syn injections resulted in phosphorylated α-syn intraneuronal accumulations (i.e., diffuse Lewy neurite (LN)- and LB-like inclusions) with significantly greater accumulations following PFF injection. LB-like inclusions were observed in several areas that innervate the striatum, most prominently the frontal and insular cortices, the amygdala, and the substantia nigra pars compacta (SNpc). α-Syn accumulations co-localized with ubiquitin, p62, and were thioflavin-S-positive and proteinase-k resistant, suggesting that PFF-induced pathology exhibits properties similar to human LBs. Although α-syn inclusions within the SNpc remained ipsilateral to striatal injection, we observed bilateral reductions in nigral dopamine neurons at the 180-day time-point in both the 1- and 2-site PFF injection paradigms. PFF injected rats exhibited bilateral reductions in striatal dopaminergic innervation at 60 and 180 days and bilateral decreases in homovanillic acid; however, dopamine reduction was observed only in the striatum ipsilateral to PFF injection. Although the level of dopamine asymmetry in PFF injected rats at 180 days was insufficient to elicit motor deficits in amphetamine-induced rotations or forelimb use in the cylinder task, significant disruption of ultrasonic vocalizations was observed. Taken together, our findings demonstrate that α-syn PFF are sufficient to seed the pathological conversion and propagation of endogenous α-syn to induce a progressive, neurodegenerative model of α-synucleinopathy in rats.

The longitudinal transcriptomic response of the substantia nigra to intrastriatal 6-hydroxydopamine reveals significant upregulation of regeneration-associated genes.

We hypothesized that the study of gene expression at 1, 2, 4, 6 and 16 weeks in the substantia nigra (SN) after intrastriatal 6-OHDA in the Sprague-Dawley rat (rattus norvegicus) would identify cellular responses during the degenerative process that could be axoprotective. Specifically, we hypothesized that genes expressed within the SN that followed a profile of being highly upregulated early after the lesion (during active axonal degeneration) and then progressively declined to baseline over 16 weeks as DA neurons died are indicative of potential protective responses to the striatal 6-OHDA insult. Utilizing a κ-means cluster analysis strategy, we demonstrated that one such cluster followed this hypothesized expression pattern over time, and that this cluster contained several interrelated transcripts that are classified as regeneration-associated genes (RAGs) including Atf3, Sprr1a, Ecel1, Gadd45a, Gpnmb, Sox11, Mmp19, Srgap1, Rab15,Lifr, Trib3, Tgfb1, and Sema3c. All exemplar transcripts tested from this cluster (Sprr1a, Ecel1, Gadd45a, Atf3 and Sox11) were validated by qPCR and a smaller subset (Sprr1a, Gadd45a and Sox11) were shown to be exclusively localized to SN DA neurons using a dual label approach with RNAScope in situ hybridization and immunohistochemistry. Upregulation of RAGs is typically associated with the response to axonal injury in the peripheral nerves and was not previously reported as part of the axodegenerative process for DA neurons of the SN. Interestingly, as part of this cluster, other transcripts were identified based on their expression pattern but without a RAG provenance in the literature. These "RAG-like" transcripts need further characterization to determine if they possess similar functions to or interact with known RAG transcripts. Ultimately, it is hoped that some of the newly identified axodegeneration-reactive transcripts could be exploited as axoprotective therapies in PD and other neurodegenerative diseases.