Combining CRISPR-Cas9 and brain imaging to study the link from genes to molecules to networks.

Receptors, transporters, and ion channels are important targets for therapy development in neurological diseases, but their mechanistic role in pathogenesis is often poorly understood. Gene editing and in vivo imaging approaches will help to identify the molecular and functional role of these targets and the consequence of their regional dysfunction on the whole-brain level. We combine CRISPR-Cas9 gene editing with in vivo positron emission tomography (PET) and functional MRI (fMRI) to investigate the direct link between genes, molecules, and the brain connectome. The extensive knowledge of the Slc18a2 gene encoding the vesicular monoamine transporter (VMAT2), involved in the storage and release of dopamine, makes it an excellent target for studying the gene network relationships while structurally preserving neuronal integrity and function. We edited the Slc18a2 in the substantia nigra pars compacta of adult rats and used in vivo molecular imaging besides behavioral, histological, and biochemical assessments to characterize the CRISPR-Cas9-mediated VMAT2 knockdown. Simultaneous PET/fMRI was performed to investigate molecular and functional brain alterations. We found that stage-specific adaptations of brain functional connectivity follow the selective impairment of presynaptic dopamine storage and release. Our study reveals that recruiting different brain networks is an early response to the dopaminergic dysfunction preceding neuronal cell loss. Our combinatorial approach is a tool to investigate the impact of specific genes on brain molecular and functional dynamics, which will help to develop tailored therapies for normalizing brain function.

Effects of mutant huntingtin in oxytocin neurons on non-motor features of Huntington's disease.

BACKGROUND: Early non-motor features including anxiety, depression and altered social cognition are present in Huntington's disease (HD). The underlying neurobiological mechanisms are not known. Oxytocin (OXT) is involved in the regulation of emotion, social cognition and metabolism, and our previous work showed that the OXT system is affected early in HD. The aim of the study was to investigate the potential causal relationship between the selective expression of mutant huntingtin (mHTT) in OXT neurons and the development of non-motor features and neuropathology. METHODS: To express mHTT only in OXT neurons, we used a novel flex-switch adeno-associated viral vector design to selectively express either mHTT or wild-type HTT in the paraventricular nucleus of the hypothalamus using OXT-Cre-recombinase mice. We also performed a mirror experiment to selectively delete mHTT in OXT neurons using the BACHD mouse model. Mice underwent a battery of behavioural tests to assess psychiatric and social behaviours 3 months post-injection or at 2 months of age, respectively. Post-mortem analyses were performed to assess the effects on the OXT system. RESULTS: Our results show that selective expression of mHTT in OXT neurons was associated with the formation of mHTT inclusions and a 26% reduction of OXT-immunopositive neurons as well as increased anxiety-like behaviours compared with uninjected mice. However, selective deletion of mHTT from OXT neurons alone was not sufficient to alter the metabolic and psychiatric phenotype of the BACHD mice at this early time point. CONCLUSIONS: Our results indicate that mHTT expression can exert cell-autonomous toxic effects on OXT neurons without affecting the non-motor phenotype at early time points in mice.

DNAJB6 suppresses alpha-synuclein induced pathology in an animal model of Parkinson's disease.

BACKGROUND: α-synuclein (α-syn) aggregation can lead to degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) as invariably observed in patients with Parkinson's Disease (PD). The co-chaperone DNAJB6 has previously been found to be expressed at higher levels in PD patients than in control subjects and was also found in Lewy bodies. Our previous experiments showed that knock out of DNAJB6 induced α-syn aggregation in cellular level. However, effects of overexpression of DNAJB6 against α-syn aggregation remains to be investigated. METHODS: We used a α-syn CFP/YFP HEK293 FRET cell line to investigate the effects of overexpression of DNAJB6 in cellular level. α-syn aggregation was induced by transfection α-syn preformed fibrils (PPF), then was measured FRET analysis. We proceeded to investigate if DNAJB6b can impair α-syn aggregation and toxicity in an animal model and used adeno associated vira (AAV6) designed to overexpress of human wt α-syn, GFP-DNAJB6 or GFP in rats. These vectors were injected into the SNpc of the rats, unilaterally. Rats injected with vira to express α-syn along with GFP in the SNpc where compared to rats expressing α-syn and GFP-DNAJB6. We evaluated motor functions, dopaminergic cell death, and axonal degeneration in striatum. RESULTS: We show that DNAJB6 prevent α-syn aggregation induced by α-syn PFF's, in a cell culture model. In addition, we observed α-syn overexpression caused dopaminergic cell death and that this was strongly reduced by co-expression of DNAJB6b. The lesion caused by α-syn overexpression resulted in behavior deficits, which increased over time as seen in stepping test, which was rescued by co-expression of DNAJB6b. CONCLUSION: We here demonstrate for the first time that DNAJB6 is a strong suppressor of α-syn aggregation in cells and in animals and that this results in a suppression of dopaminergic cell death and PD related motor deficits in an animal model of PD.

Viral-based rodent and nonhuman primate models of multiple system atrophy: Fidelity to the human disease.

Multiple system atrophy (MSA) is a rare and extremely debilitating progressive neurodegenerative disease characterized by variable combinations of parkinsonism, cerebellar ataxia, dysautonomia, and pyramidal dysfunction. MSA is a unique synucleinopathy, in which alpha synuclein-rich aggregates are present in the cytoplasm of oligodendroglia. The precise origin of the alpha synuclein (aSyn) found in the glial cytoplasmic inclusions (GCIs) as well the mechanisms of neurodegeneration in MSA remain unclear. Despite this fact, cell and animal models of MSA rely on oligodendroglial overexpression of aSyn. In the present study, we utilized a novel oligotrophic AAV, Olig001, to overexpress aSyn specifically in striatal oligodendrocytes of rats and nonhuman primates in an effort to further characterize our novel viral vector-mediated MSA animal models. Using two cohorts of animals with 10-fold differences in Olig001 vector titers, we show a dose-dependent formation of MSA-like pathology in rats. High titer of Olig001-aSyn in these animals were required to produce the formation of pS129+ and proteinase K resistant aSyn-rich GCIs, demyelination, and neurodegeneration. Using this knowledge, we injected high titer Olig001 in the putamen of cynomolgus macaques. After six months, histological analysis showed that oligodendroglial overexpression of aSyn resulted in the formation of hallmark GCIs throughout the putamen, demyelination, a 44% reduction of striatal neurons and a 12% loss of nigral neurons. Furthermore, a robust inflammatory response similar to MSA was produced in Olig001-aSyn NHPs, including microglial activation, astrogliosis, and a robust infiltration of T cells into the CNS. Taken together, oligodendroglial-specific viral vector-mediated overexpression of aSyn in rats and nonhuman primates faithfully reproduces many of the pathological disease hallmarks found in MSA. Future studies utilizing these large animal models of MSA would prove extremely valuable as a pre-clinical platform to test novel therapeutics that are so desperately needed for MSA.

Effects of mutant huntingtin inactivation on Huntington disease-related behaviours in the BACHD mouse model.

AIMS: Huntington disease (HD) is a fatal neurodegenerative disorder with no disease-modifying treatments approved so far. Ongoing clinical trials are attempting to reduce huntingtin (HTT) expression in the central nervous system (CNS) using different strategies. Yet, the distribution and timing of HTT-lowering therapies required for a beneficial clinical effect is less clear. Here, we investigated whether HD-related behaviours could be prevented by inactivating mutant HTT at different disease stages and to varying degrees in an experimental model. METHODS: We generated mutant BACHD mice with either a widespread or circuit-specific inactivation of mutant HTT by using Cre recombinase (Cre) under the nestin promoter or the adenosine A2A receptor promoter respectively. We also simulated a clinical gene therapy scenario with allele-specific HTT targeting by injections of recombinant adeno-associated viral (rAAV) vectors expressing Cre into the striatum of adult BACHD mice. All mice were assessed using behavioural tests to investigate motor, metabolic and psychiatric outcome measures at 4-6 months of age. RESULTS: While motor deficits, body weight changes, anxiety and depressive-like behaviours are present in BACHD mice, early widespread CNS inactivation during development significantly improves rotarod performance, body weight changes and depressive-like behaviour. However, conditional circuit-wide mutant HTT deletion from the indirect striatal pathway during development and focal striatal-specific deletion in adulthood failed to rescue any of the HD-related behaviours. CONCLUSIONS: Our results indicate that widespread targeting and the timing of interventions aimed at reducing mutant HTT are important factors to consider when developing disease-modifying therapies for HD.

Comparison of Locus Coeruleus Pathology with Nigral and Forebrain Pathology in Parkinson's Disease.

BACKGROUND: Pathology in the noradrenergic A6 locus coeruleus has not been compared with more rostral dopaminergic A9 substantia nigra and A10 ventral tegmental area, and cholinergic Ch4 basal nucleus and Ch1/2 septal regions in the same cases of Parkinson's disease (PD). OBJECTIVE: To determine whether there is a gradient of caudal to rostral cell loss in PD. METHODS: Postmortem brains were collected from longitudinally followed donors with PD (n = 14) and aged-matched healthy donors (n = 13), six with restricted brainstem Lewy pathology (RLP), fixed in formalin and serial tissue slabs processed for cell and pathological quantitation. Noradrenergic A6 neurons were assessed and compared with previously published midbrain and basal forebrain data. From these data, regression estimates of pathological onset and progression were determined. RESULTS: Restricted Lewy pathology (RLP) cases had high pathological variability but no significant reduction in neurons. Pathology containing A6 neuron loss started at PD diagnosis and progressed faster (2.4% p.a) than the loss of dopaminergic A9 neurons (2% loss p.a.). Cases with dementia had significantly more pathology in noradrenergic and cholinergic neurons, had greater noradrenergic A6 neuron loss (29% more, progressing at 3.2% p.a.), and a selective loss of lateral A10 nonmelanized dopamine-producing neurons (starting a decade following diagnosis). CONCLUSIONS: These findings show that in the same Parkinson's disease cases cell loss in these neurotransmitter systems does not follow a strict caudal to rostral trajectory and suggests symptom onset may relate to substantial pathology in the noradrenergic A6 locus coeruleus neurons in people with reduced dopamine-producing A9 substantia nigra neurons. © 2021 International Parkinson and Movement Disorder Society.

How is alpha-synuclein cleared from the cell?

The levels and conformers of alpha-synuclein are critical in the pathogenesis of Parkinson's Disease and related synucleinopathies. Homeostatic mechanisms in protein degradation and secretion have been identified as regulators of alpha-synuclein at different stages of its intracellular trafficking and transcellular propagation. Here we review pathways involved in the removal of various forms of alpha-synuclein from both the intracellular and extracellular environment. Proteasomes and lysosomes are likely to play complementary roles in the removal of intracellular alpha-synuclein species, in a manner that depends on alpha-synuclein post-translational modifications. Extracellular alpha-synuclein is cleared by extracellular proteolytic enzymes, or taken up by neighboring cells, especially microglia and astrocytes, and degraded within lysosomes. Exosomes, on the other hand, represent a vehicle for egress of excess burden of the intracellular protein, potentially contributing to the transfer of alpha-synuclein between cells. Dysfunction in any one of these clearance mechanisms, or a combination thereof, may be involved in the initiation or progression of Parkinson's disease, whereas targeting these pathways may offer an opportunity for therapeutic intervention. This article is part of the Special Issue "Synuclein".

In vivo quantification of glial activation in minipigs overexpressing human α-synuclein.

Parkinson's disease is characterized by a progressive loss of substantia nigra (SN) dopaminergic neurons and the formation of Lewy bodies containing accumulated alpha-synuclein (α-syn). The pathology of Parkinson's disease is associated with neuroinflammatory microglial activation, which may contribute to the ongoing neurodegeneration. This study investigates the in vivo microglial and dopaminergic response to overexpression of α-syn. We used positron emission tomography (PET) and the 18 kDa translocator protein radioligand, [11 C](R)PK11195, to image brain microglial activation and (+)-α-[11 C]dihydrotetrabenazine ([11 C]DTBZ), to measure vesicular monoamine transporter 2 (VMAT2) availability in Göttingen minipigs following injection with recombinant adeno-associated virus (rAAV) vectors expressing either mutant A53T α-syn or green fluorescent protein (GFP) into the SN (4 rAAV-α-syn, 4 rAAV-GFP, 5 non-injected control minipigs). We performed motor symptom assessment and immunohistochemical examination of tyrosine hydroxylase (TH) and transgene expression. Expression of GFP and α-syn was observed at the SN injection site and in the striatum. We observed no motor symptoms or changes in striatal [11 C]DTBZ binding potential in vivo or striatal or SN TH staining in vitro between the groups. The mean [11 C](R)PK11195 total volume of distribution was significantly higher in the basal ganglia and cortical areas of the α-syn group than the control animals. We conclude that mutant α-syn expression in the SN resulted in microglial activation in multiple sub- and cortical regions, while it did not affect TH stains or VMAT2 availability. Our data suggest that microglial activation constitutes an early response to accumulation of α-syn in the absence of dopamine neuron degeneration.

Gene therapy for Parkinson's disease: Disease modification by GDNF family of ligands.

Gene transfer is a promising drug delivery method of advanced therapeutic entities for Parkinson's disease. One advantage over conventional therapies, such as peripheral delivery of the dopamine pre-cursor l-DOPA, is site-specific expression of proteins with regenerative, disease-modifying and potentially neuroprotective capacity. Several clinical trials have been performed to test the capacity of glial-cell line derived neurotrophic factor and neurturin to rescue degenerating dopaminergic neurons in the substantia nigra and their axon terminals in the striatum by delivery of these neurotrophic factors either as purified protein or by means of viral vector mediated gene delivery to the brain. Although gene therapy approaches tested so far have been shown to be safe, none met their primary endpoints in phase II clinical trials designed and powered to test the efficacy of the intervention. Within the scope of this review we aim to describe the state-of-the-art in the field, how different technical parameters were translated from pre-clinical studies in non-human primates to clinical trials, and what these trials taught us regarding important factors that may pave the way to the success of gene therapy for the treatment of Parkinson's disease.

Toxic effects of human and rodent variants of alpha-synuclein in vivo.

In Parkinson's disease, abnormal alpha-synuclein (asyn) accumulation leads to the formation of soluble oligomeric species thought to be toxic to cells as well as intraneuronal inclusions. To date, the precise mechanisms leading to aggregation of asyn in the brain is not well-understood. Previous studies in yeast, drosophila, and transgenic mice suggested that a non-A beta component depleted version of human asyn [h-asyn(D70-83)] or human beta-synuclein (h-bsyn), naturally lacking this centrally located hydrophobic region, are less prone to form aggregates in vitro and are expected to be less toxic compared to h-asyn in vivo, although not all experimental studies unequivocally support the latter view. To address this outstanding issue, we directly compared the neurotoxicity of human asyn against that of h-asyn(D70-83), h-bsyn as well as rat asyn using an adeno-associated viral vector to express these proteins in a dose-response study where the vector load was varied over two orders of magnitude. By quantifying the neurodegeneration of rat substantia nigra dopamine neurons here we show that h-asyn, h-bsyn, and h-asyn(D70-83) display comparable neurotoxicity across the vector doses tested. On the other hand, rat asyn and GFP control vectors displayed a different profile, where no detectable neurodegeneration was seen except at the highest vector titer. Thus, the two main conclusions of our study are that (i) deletion of the central hydrophobic region in h-asyn is not sufficient to alter its neurotoxic properties and (ii) expression of the widely used GFP control protein can cause measurable neurodegeneration at high titers.

How can rAAV-α-synuclein and the fibril α-synuclein models advance our understanding of Parkinson's disease?

Animal models of Parkinson's disease (PD) are important for understanding the mechanisms of the disease and can contribute to developing and validating novel therapeutics. Ideally, these models should replicate the cardinal features of PD, such as progressive neurodegeneration of catecholaminergic neurons and motor defects. Many current PD models emphasize pathological forms of α-synuclein, based on findings that autosomal dominant mutations in α-synuclein and duplications/triplications of the SNCA gene cause PD. In addition, Lewy bodies and Lewy neurites, primarily composed of α-synuclein, represent the predominant pathological characteristics of PD. These inclusions have defined features, such as insolubility in non-ionic detergent, hyperphosphorylation, proteinase K sensitivity, a filamentous appearance by electron microscopy, and ß-sheet structure. Furthermore, it has become clear that Lewy bodies and Lewy neurites are found throughout the peripheral and central nervous system, and could account not only for motor symptoms, but also for non-motor symptoms of the disease. The goal of this review is to describe two new α-synuclein-based models: the recombinant adeno-associated viral vector-α-synuclein model and the α-synuclein fibril model. An advantage of both models is that they do not require extensive crossbreeding of rodents transgenic for α-synuclein with other rodents transgenic for genes of interest to study the impact of such genes on PD-related pathology and phenotypes. In addition, abnormal α-synuclein can be expressed in brain regions relevant for disease. Here, we discuss the features of each model, how each model has contributed thus far to our understanding of PD, and the advantages and potential caveats of each model. This review describes two α-synuclein-based rodent models of Parkinson's disease: the rAAV-α-synuclein model and the α-synuclein fibril model. The key features of these models are described, and the extent to which they recapitulate features of PD, such as α-synuclein inclusion formation, loss of dopaminergic synapses in the striatum, motor defects, inflammation, and dopamine neuron death. This article is part of a special issue on Parkinson disease.

Assessment of brain metabolite correlates of adeno-associated virus-mediated over-expression of human alpha-synuclein in cortical neurons by in vivo (1) H-MR spectroscopy at 9.4 T.

In this study, we used proton-localized spectroscopy ((1) H-MRS) for the acquisition of the neurochemical profile longitudinally in a novel rat model of human wild-type alpha-synuclein (α-syn) over-expression. Our goal was to find out if the increased α-syn load in this model could be linked to changes in metabolites in the frontal cortex. Animals injected with AAV vectors encoding for human α-syn formed the experimental group, whereas green fluorescent protein expressing animals were used as the vector-treated control group and a third group of uninjected animals were used as naïve controls. Data were acquired at 2, 4, and 8 month time points. Nineteen metabolites were quantified in the MR spectra using LCModel software. On the basis of 92 spectra, we evaluated any potential gender effect and found that lactate (Lac) levels were lower in males compared to females, while the opposite was observed for ascorbate (Asc). Next, we assessed the effect of age and found increased levels of GABA, Tau, and GPC+PCho. Finally, we analyzed the effect of treatment and found that Lac levels (p = 0.005) were specifically lower in the α-syn group compared to the green fluorescent protein and control groups. In addition, Asc levels (p = 0.05) were increased in the vector-injected groups, whereas glucose levels remained unchanged. This study indicates that the metabolic switch between glucose-lactate could be detectable in vivo and might be modulated by Asc. No concomitant changes were found in markers of neuronal integrity (e.g., N-acetylaspartate) consistent with the fact that α-syn over-expression in cortical neurons did not result in neurodegeneration in this model. We acquired the neurochemical profile longitudinally in a rat model of human wild-type alpha-synuclein (α-syn) over-expression in cortical neurons. We found that Lactate levels were reduced in the α-syn group compared to the control groups and Ascorbate levels were increased in the vector-injected groups. No changes were found in markers of neuronal integrity consistent with the fact that α-syn over-expression did not result in frank neurodegeneration.

Controlled Striatal DOPA Production From a Gene Delivery System in a Rodent Model of Parkinson's Disease.

Conventional symptomatic treatment for Parkinson's disease (PD) with long-term L-3,4-dihydroxyphenylalanine (DOPA) is complicated with development of drug-induced side effects. In vivo viral vector-mediated gene expression encoding tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GCH1) provides a drug delivery strategy of DOPA with distinct advantages over pharmacotherapy. Since the brain alterations made with current gene transfer techniques are irreversible, the therapeutic approaches taken to the clinic should preferably be controllable to match the needs of each individual during the course of their disease. We used a recently described tunable gene expression system based on the use of destabilized dihydrofolate reductase (DD) and generated a N-terminally coupled GCH1 enzyme (DD-GCH1) while the TH enzyme was constitutively expressed, packaged in adeno-associated viral (AAV) vectors. Expression of DD-GCH1 was regulated by the activating ligand trimethoprim (TMP) that crosses the blood-brain barrier. We show that the resulting intervention provides a TMP-dose-dependent regulation of DOPA synthesis that is closely linked to the magnitude of functional effects. Our data constitutes the first proof of principle for controlled reconstitution of dopamine capacity in the brain and suggests that such next-generation gene therapy strategies are now mature for preclinical development toward use in patients with PD.

Global optogenetic activation of inhibitory interneurons during epileptiform activity.

Optogenetic techniques provide powerful tools for bidirectional control of neuronal activity and investigating alterations occurring in excitability disorders, such as epilepsy. In particular, the possibility to specifically activate by light-determined interneuron populations expressing channelrhodopsin-2 provides an unprecedented opportunity of exploring their contribution to physiological and pathological network activity. There are several subclasses of interneurons in cortical areas with different functional connectivity to the principal neurons (e.g., targeting their perisomatic or dendritic compartments). Therefore, one could optogenetically activate specific or a mixed population of interneurons and dissect their selective or concerted inhibitory action on principal cells. We chose to explore a conceptually novel strategy involving simultaneous activation of mixed populations of interneurons by optogenetics and study their impact on ongoing epileptiform activity in mouse acute hippocampal slices. Here we demonstrate that such approach results in a brief initial action potential discharge in CA3 pyramidal neurons, followed by prolonged suppression of ongoing epileptiform activity during light exposure. Such sequence of events was caused by massive light-induced release of GABA from ChR2-expressing interneurons. The inhibition of epileptiform activity was less pronounced if only parvalbumin- or somatostatin-expressing interneurons were activated by light. Our data suggest that global optogenetic activation of mixed interneuron populations is a more effective approach for development of novel therapeutic strategies for epilepsy, but the initial action potential generation in principal neurons needs to be taken in consideration.

Ser129 phosphorylation of endogenous α-synuclein induced by overexpression of polo-like kinases 2 and 3 in nigral dopamine neurons is not detrimental to their survival and function.

Phosphorylation of the α-synuclein (α-syn) protein at Ser129 [P(S129)-α-syn] was found to be the most abundant form in intracellular inclusions in brains from Parkinson's disease (PD) patients. This finding suggests that P(S129)-α-syn plays a central role in the pathogenesis of PD. However, it is at present unclear whether P(S129)-α-syn is pathogenic driving the neurodegenerative process. Rodent studies using neither the phosphomimics of human α-syn nor co-expression of human wild-type α-syn and kinases phosphorylating α-syn at Ser129 gave consistent results. One major concern in interpreting these findings is that human α-syn was expressed above physiological levels inducing neurodegeneration in rat nigral neurons. In order to exclude this confounding factor, we took a different approach and increased the phosphorylation level of endogenous α-syn. For this purpose, we took advantage of recombinant adeno-associated viral (rAAV) vectors to deliver polo-like kinase (PLK) 2 or PLK3 in the substantia nigra and investigated whether increased levels of P(S129)-α-syn compromised the function and survival of nigral dopaminergic neurons. Interestingly, we observed that hyperphosphorylated α-syn did not induce nigral dopaminergic cell death, as assessed at 1 and 4months. Furthermore, histological analysis did not show any accumulation of α-syn protein or formation of inclusions. Using in vivo microdialysis, we found that the only measurable functional alteration was the depolarisation-induced release of dopamine, while the in vivo synthesis rate of DOPA and dopamine baseline release remained unaltered. Taken together, our results suggest that phosphorylation of α-syn at Ser129 does not confer a toxic gain of function per se.

Hypothalamic expression of mutant huntingtin contributes to the development of depressive-like behavior in the BAC transgenic mouse model of Huntington's disease.

Psychiatric symptoms such as depression and anxiety are important clinical features of Huntington's disease (HD). However, the underlying neurobiological substrate for the psychiatric features is not fully understood. In order to explore the biological origin of depression and anxiety in HD, we used a mouse model that expresses the human full-length mutant huntingtin, the BACHD mouse. We found that the BACHD mice displayed depressive- and anxiety-like features as early as at 2 months of age as assessed using the Porsolt forced swim test (FST), the sucrose preference test and the elevated plus maze (EPM). BACHD mice subjected to chronic treatment with the anti-depressant sertraline were not different to vehicle-treated BACHD mice in the FST and EPM. The behavioral manifestations occurred in the absence of reduced hippocampal cell proliferation/neurogenesis or upregulation of the hypothalamic-pituitary-adrenal axis. However, alterations in anxiety- and depression-regulating genes were present in the hypothalamus of BACHD mice including reduced mRNA expression of neuropeptide Y, tachykinin receptor 3 and vesicular monoamine transporter type 2 as well as increased expression of cocaine and amphetamine regulated transcript. Interestingly, the orexin neuronal population in the hypothalamus was increased and showed cellular atrophy in old BACHD mice. Furthermore, inactivation of mutant huntingtin in a subset of the hypothalamic neurons prevented the development of the depressive features. Taken together, our data demonstrate that the BACHD mouse recapitulates clinical HD with early psychiatric aspects and point to the role of hypothalamic dysfunction in the development of depression and anxiety in the disease.

Overexpression of α-synuclein in oligodendrocytes does not increase susceptibility to focal striatal excitotoxicity.

BACKGROUND: Multiple system atrophy (MSA) is a fatal adult-onset neurodegenerative disease characterized by α-synuclein (α-syn) positive oligodendroglial cytoplasmic inclusions. The latter are associated with a neuronal multisystem neurodegeneration targeting central autonomic, olivopontocerebellar and striatonigral pathways, however the underlying mechanisms of neuronal cell death are poorly understood. Previous experiments have shown that oligodendroglial α-syn pathology increases the susceptibility to mitochondrial stress and proteasomal dysfunction leading to enhanced MSA-like neurodegeneration. Here we analyzed whether oligodendroglial α-syn overexpression in a transgenic mouse model of MSA synergistically interacts with focal neuronal excitotoxic damage generated by a striatal injection of quinolinic acid (QA) to affect the degree of striatal neuronal loss. RESULTS: QA injury led to comparable striatal neuronal loss and optical density of astro- and microgliosis in the striatum of transgenic and control mice. Respectively, no differences were identified in drug-induced rotation behavior or open field behavior between the groups. CONCLUSIONS: The failure of oligodendroglial α-syn pathology to exacerbate striatal neuronal loss resulting from QA excitotoxicity contrasts with enhanced striatal neurodegeneration due to oxidative or proteolytic stress, suggesting that enhanced vulnerability to excitotoxicity does not occur in oligodendroglial α-synucleinopathy like MSA.

Hippocampal Lewy pathology and cholinergic dysfunction are associated with dementia in Parkinson's disease.

The neuropathological substrate of dementia in patients with Parkinson's disease is still under debate, particularly in patients with insufficient alternate neuropathology for other degenerative dementias. In patients with pure Lewy body Parkinson's disease, previous post-mortem studies have shown that dopaminergic and cholinergic regulatory projection systems degenerate, but the exact pathways that may explain the development of dementia in patients with Parkinson's disease remain unclear. Studies in rodents suggest that both the mesocorticolimbic dopaminergic and septohippocampal cholinergic pathways may functionally interact to regulate certain aspects of cognition, however, whether such an interaction occurs in humans is still poorly understood. In this study, we performed stereological analyses of the A9 and A10 dopaminergic neurons and Ch1, Ch2 and Ch4 cholinergic neurons located in the basal forebrain, along with an assessment of α-synuclein pathology in these regions and in the hippocampus of six demented and five non-demented patients with Parkinson's disease and five age-matched control individuals with no signs of neurological disease. Moreover, we measured choline acetyltransferase activity in the hippocampus and frontal cortex of eight demented and eight non-demented patients with Parkinson's disease, as well as in the same areas of eight age-matched controls. All patients with Parkinson's disease exhibited a similar 80-85% loss of pigmented A9 dopaminergic neurons, whereas patients with Parkinson's disease dementia presented an additional loss in the lateral part of A10 dopaminergic neurons as well as Ch4 nucleus basalis neurons. In contrast, medial A10 dopaminergic neurons and Ch1 and Ch2 cholinergic septal neurons were largely spared. Despite variable Ch4 cell loss, cortical but not hippocampal cholinergic activity was consistently reduced in all patients with Parkinson's disease, suggesting significant dysfunction in cortical cholinergic pathways before frank neuronal degeneration. Patients with Parkinson's disease dementia were differentiated by a significant reduction in hippocampal cholinergic activity, by a significant loss of non-pigmented lateral A10 dopaminergic neurons and Ch4 cholinergic neurons (30 and 55% cell loss, respectively, compared with neuronal preservation in control subjects), and by an increase in the severity of α-synuclein pathology in the basal forebrain and hippocampus. Overall, these results point to increasing α-synuclein deposition and hippocampal dysfunction in a setting of more widespread degeneration of cortical dopaminergic and cholinergic pathways as contributing to the dementia occurring in patients with pure Parkinson's disease. Furthermore, our findings support the concept that α-synuclein deposition is associated with significant neuronal dysfunction in the absence of frank neuronal loss in Parkinson's disease.

Optogenetic inhibition of chemically induced hypersynchronized bursting in mice.

Synchronized activity is common during various physiological operations but can culminate in seizures and consequently in epilepsy in pathological hyperexcitable conditions in the brain. Many types of seizures are not possible to control and impose significant disability for patients with epilepsy. Such intractable epilepsy cases are often associated with degeneration of inhibitory interneurons in the cortical areas resulting in impaired inhibitory drive onto the principal neurons. Recently emerging optogenetic technique has been proposed as an alternative approach to control such seizures but whether it may be effective in situations where inhibitory processes in the brain are compromised has not been addressed. Here we used pharmacological and optogenetic techniques to block inhibitory neurotransmission and induce epileptiform activity in vitro and in vivo. We demonstrate that NpHR-based optogenetic hyperpolarization and thereby inactivation of a principal neuronal population in the hippocampus is effectively attenuating seizure activity caused by disconnected network inhibition both in vitro and in vivo. Our data suggest that epileptiform activity in the hippocampus caused by impaired inhibition may be controlled by optogenetic silencing of principal neurons and potentially can be developed as an alternative treatment for epilepsy.

α-Synuclein expression and Nrf2 deficiency cooperate to aggravate protein aggregation, neuronal death and inflammation in early-stage Parkinson's disease.

Although α-synuclein (α-SYN) aggregation is a hallmark of sporadic and familial Parkinson's disease (PD), it is not known how it contributes to early events of PD pathogenesis such as oxidative and inflammatory stress. Here, we addressed this question in a new animal model based on stereotaxic delivery of an adeno-associated viral vector (rAAV) for expression of human α-SYN in the ventral midbrain of mice lacking the transcription factor Nrf2 (Nrf2(-/-)). Two months after surgery, Nrf2(-/-) mice exhibited exacerbated degeneration of nigral dopaminergic neurons and increased dystrophic dendrites, reminiscent of Lewy neurites, which correlated with impaired proteasome gene expression and activity. Dopaminergic neuron loss was associated with an increase in neuroinflammation and gliosis that were intensified in Nrf2(-/-) mice. In response to exogenously added α-SYN, Nrf2(-/-) microglia failed to activate the expression of two anti-inflammatory genes, heme oxygenase-1 (HO-1) and nicotinamide adenine dinucleotide phosphate quinone oxidorreductase-1 (NQO1). This impaired Nrf2 response correlated with a shift in the microglial activation profile, towards increased production of proinflammatory markers, IL-6, IL-1ß and iNOS and reduced phagocytic capacity of fluorescent beads, and lower messenger RNA levels for TAM receptors Axl and Mer. Postmortem brain tissue samples from patients in early- to middle-stage progression of PD showed increased HO-1 expression in astrocytes and microglia, suggesting an attempt of the diseased brain to compensate these hallmarks of PD through activation of the Nrf2 pathway. This study demonstrates that α-SYN and Nrf2 deficiency cooperate on protein aggregation, neuroinflammation and neuronal death and provides a bifactorial animal model to study early-stage PD.