Impaired brain insulin signalling in Parkinson's disease.

AIMS: Brain insulin resistance (i.e., decreased insulin/insulin-like growth factor-1 [IGF-1] signalling) may play a role in the pathophysiology of Parkinson's disease (PD), and several anti-diabetic drugs have entred clinical development to evaluate their potential disease-modifying properties in PD. A measure of insulin resistance is the amount of the downstream messenger insulin receptor substrate-1 that is phosphorylated at serine residues 312 (IRS-1pS312) or 616 (IRS-1pS616). We assessed IRS-1pS312 and IRS-1pS616 expression in post-mortem brain tissue of PD patients and a preclinical rat model based on viral-mediated expression of A53T mutated human α-synuclein (AAV2/9-h-α-synA53T). METHODS: IRS-1pS312 and IRS-1pS616 staining intensity were determined by immunofluorescence in both neurons and glial cells in the substantia nigra pars compacta (SNc) and putamen of PD patients and controls without known brain disease. We further explored a possible relation between α-synuclein aggregates and brain insulin resistance in PD patients. Both insulin resistance markers were also measured in the SNc and striatum of AAV2/9-h-α-synA53T rats. RESULTS: We found higher IRS-1pS312 staining intensity in nigral dopaminergic neurons and a trend for higher IRS-1pS312 staining intensity in putaminal neurons of PD patients. We observed no differences for IRS-1pS616 staining intensity in neurons or IRS-1pS312 staining intensity in glial cells. IRS-1pS312 showed high co-localisation within the core of nigral Lewy bodies. Like PD patients, AAV2/9-h-α-synA53T rats showed higher IRS-1pS312 staining intensity in the SNc and striatum than controls, whereas IRS-1pS616 was not different between groups. CONCLUSIONS: Our results provide evidence for brain insulin resistance in PD and support the rationale for repurposing anti-diabetic drugs for PD treatment.

α-Synuclein modulates tau spreading in mouse brains.

α-Synuclein (α-syn) and tau aggregates are the neuropathological hallmarks of Parkinson's disease (PD) and Alzheimer's disease (AD), respectively, although both pathologies co-occur in patients with these diseases, suggesting possible crosstalk between them. To elucidate the interactions of pathological α-syn and tau, we sought to model these interactions. We show that increased accumulation of tau aggregates occur following simultaneous introduction of α-syn mousepreformed fibrils (mpffs) and AD lysate-derived tau seeds (AD-tau) both in vitro and in vivo. Interestingly, the absence of endogenous mouse α-syn in mice reduces the accumulation and spreading of tau, while the absence of tau did not affect the seeding or spreading capacity of α-syn. These in vivo results are consistent with our in vitro data wherein the presence of tau has no synergistic effects on α-syn. Our results point to the important role of α-syn as a modulator of tau pathology burden and spreading in the brains of AD, PDD, and DLB patients.

Amyloid-Beta (Aß) Plaques Promote Seeding and Spreading of Alpha-Synuclein and Tau in a Mouse Model of Lewy Body Disorders with Aß Pathology.

Studies have shown an overlap of Aß plaques, tau tangles, and α-synuclein (α-syn) pathologies in the brains of Alzheimer's disease (AD) and Parkinson's disease (PD) with dementia (PDD) patients, with increased pathological burden correlating with severity of cognitive and motor symptoms. Despite the observed co-pathology and concomitance of motor and cognitive phenotypes, the consequences of the primary amyloidogenic protein on the secondary pathologies remain poorly understood. To better define the relationship between α-syn and Aß plaques, we injected α-syn preformed fibrils (α-syn mpffs) into mice with abundant Aß plaques. Aß deposits dramatically accelerated α-syn pathogenesis and spread throughout the brain. Remarkably, hyperphosphorylated tau (p-tau) was induced in α-syn mpff-injected 5xFAD mice. Finally, α-syn mpff-injected 5xFAD mice showed neuron loss that correlated with the progressive decline of cognitive and motor performance. Our findings suggest a "feed-forward" mechanism whereby Aß plaques enhance endogenous α-syn seeding and spreading over time post-injection with mpffs.

Slow Progressive Accumulation of Oligodendroglial Alpha-Synuclein (α-Syn) Pathology in Synthetic α-Syn Fibril-Induced Mouse Models of Synucleinopathy.

Synucleinopathies are composed of Parkinson disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). Alpha-synuclein (α-Syn) forms aggregates mainly in neurons in PD and DLB, while oligodendroglial α-Syn aggregates are characteristic of MSA. Recent studies have demonstrated that injections of synthetic α-Syn preformed fibrils (PFFs) into the brains of wild-type (WT) animals induce intraneuronal α-Syn aggregates and the subsequent interneuronal transmission of α-Syn aggregates. However, injections of α-Syn PFFs or even brain lysates of patients with MSA have not been reported to induce oligodendroglial α-Syn aggregates, raising questions about the pathogenesis of oligodendroglial α-Syn aggregates in MSA. Here, we report that WT mice injected with mouse α-Syn (m-α-Syn) PFFs develop neuronal α-Syn pathology after short postinjection (PI) intervals on the scale of weeks, while oligodendroglial α-Syn pathology emerges after longer PI intervals of several months. Abundant oligodendroglial α-Syn pathology in white matter at later time points is reminiscent of MSA. Furthermore, comparison between young and aged mice injected with m-α-Syn PFFs revealed that PI intervals rather than aging correlate with oligodendroglial α-Syn aggregation. These results provide novel insights into the pathological mechanisms of oligodendroglial α-Syn aggregation in MSA.

Changes in striatal activity and functional connectivity in a mouse model of Huntington's disease.

Hereditary Huntington's disease (HD) is associated with progressive motor, cognitive and psychiatric symptoms. A primary consequence of the HD mutation is the preferential loss of medium spiny projection cells with relative sparing of local interneurons in the striatum. In addition, among GABAergic striatal projection cells, indirect pathway cells expressing D2 dopamine receptors are lost earlier than direct pathway cells expressing D1 receptors. To test in vivo the functional integrity of direct and indirect pathways as well as interneurons in the striatum of male R6/1 transgenic mice, we assessed their c-Fos expression levels induced by a striatal-dependent cognitive task and compared them with age-matched wild-type littermates. We found a significant increase of c-Fos+ nuclei in the dorsomedial striatum, and this only at 2 months, when our HD mouse model is still pre-motor symptomatic, the increase disappearing with symptom manifestation. Contrary to our expectation, the indirect pathway projection neurons did not undergo any severer changes of c-Fos expression regardless of age in R6/1 mice. We also found a decreased activation of interneurons that express parvalbumin in the dorsomedial striatum at both presymptomatic and symptomatic ages. Finally, analysis of c-Fos expression in extended brain regions involved in the cognitive learning used in our study, demonstrates, throughout ages studied, changes in the functional connectivity between regions in the transgenic mice. Further analysis of the cellular and molecular changes underlying the transient striatal hyperactivity in the HD mice may help to understand the mechanisms involved in the disease onset.

Viral-mediated oligodendroglial alpha-synuclein expression models multiple system atrophy.

BACKGROUND: MSA is a fatal neurodegenerative disorder characterized by a combination of autonomic dysfunction, cerebellar ataxia, and l-dopa unresponsive parkinsonism. The hallmark of MSA is the accumulation of α-synuclein, forming cytoplasmic inclusions in oligodendrocytes. Adeno-associated viruses allow efficient targeting of disease-associated genes in selected cellular ensembles and have proven efficient for the neuronal overexpression of α-synuclein in the substantia nigra in the context of PD. OBJECTIVES: We aimed to develop viral-based models of MSA. METHODS: Chimeric viral vectors expressing either human wild-type α-synuclein or green fluorescent protein under the control of mouse myelin basic protein were injected in the striatum of rats and monkeys. Rats underwent a longitudinal motor assessment before histopathological analysis at 3 and 6 months. RESULTS: Injection of vectors expressing α-synuclein in the striatum resulted in >80% oligodendroglial selectivity in rats and >60% in monkeys. Rats developed progressive motor deficits that were l-dopa unresponsive when assessed at 6 months. Significant loss of dopaminergic neurons occurred at 3 months, further progressing at 6 months, together with a loss of striatal neurons. Prominent α-synuclein accumulation, including phosphorylated and proteinase-K-resistant α-synuclein, was detected in the striatum and substantia nigra. CONCLUSIONS: Viral-mediated oligodendroglial expression of α-synuclein allows replicating some of the key features of MSA. This flexible strategy can be used to investigate, in several species, how α-synuclein accumulation in selected oligodendroglial populations contributes to the pathophysiology of MSA and offers a new framework for preclinical validation of therapeutic strategies. © 2017 International Parkinson and Movement Disorder Society.

Insulin resistance and exendin-4 treatment for multiple system atrophy.

See Stayte and Vissel (doi:10.1093/awx064) for a scientific commentary on this article. Multiple system atrophy is a fatal sporadic adult-onset neurodegenerative disorder with no symptomatic or disease-modifying treatment available. The cytopathological hallmark of multiple system atrophy is the accumulation of α-synuclein aggregates in oligodendrocytes, forming glial cytoplasmic inclusions. Impaired insulin/insulin-like growth factor-1 signalling (IGF-1) and insulin resistance (i.e. decreased insulin/IGF-1) have been reported in other neurodegenerative disorders such as Alzheimer's disease. Increasing evidence also suggests impaired insulin/IGF-1 signalling in multiple system atrophy, as corroborated by increased insulin and IGF-1 plasma concentrations in multiple system atrophy patients and reduced IGF-1 brain levels in a transgenic mouse model of multiple system atrophy. We here tested the hypothesis that multiple system atrophy is associated with brain insulin resistance and showed increased expression of the key downstream messenger insulin receptor substrate-1 phosphorylated at serine residue 312 in neurons and oligodendrocytes in the putamen of patients with multiple system atrophy. Furthermore, the expression of insulin receptor substrate 1 (IRS-1) phosphorylated at serine residue 312 was more apparent in inclusion bearing oligodendrocytes in the putamen. By contrast, it was not different between both groups in the temporal cortex, a less vulnerable structure compared to the putamen. These findings suggest that insulin resistance may occur in multiple system atrophy in regions where the neurodegenerative process is most severe and point to a possible relation between α-synuclein aggregates and insulin resistance. We also observed insulin resistance in the striatum of transgenic multiple system atrophy mice and further demonstrate that the glucagon-like peptide-1 analogue exendin-4, a well-tolerated and Federal Drug Agency-approved antidiabetic drug, has positive effects on insulin resistance and monomeric α-synuclein load in the striatum, as well as survival of nigral dopamine neurons. Additionally, plasma levels of exosomal neural-derived IRS-1 phosphorylated at serine residue 307 (corresponding to serine residue 312 in humans) negatively correlated with survival of nigral dopamine neurons in multiple system atrophy mice treated with exendin-4. This finding suggests the potential for developing this peripheral biomarker candidate as an objective outcome measure of target engagement for clinical trials with glucagon-like peptide-1 analogues in multiple system atrophy. In conclusion, our observation of brain insulin resistance in multiple system atrophy patients and transgenic mice together with the beneficial effects of the glucagon-like peptide-1 agonist exendin-4 in transgenic mice paves the way for translating this innovative treatment into a clinical trial.

Reducing C-terminal truncation mitigates synucleinopathy and neurodegeneration in a transgenic model of multiple system atrophy.

Multiple system atrophy (MSA) is a sporadic orphan neurodegenerative disorder. No treatment is currently available to slow down the aggressive neurodegenerative process, and patients die within a few years after disease onset. The cytopathological hallmark of MSA is the accumulation of alpha-synuclein (α-syn) aggregates in affected oligodendrocytes. Several studies point to α-syn oligomerization and aggregation as a mediator of neurotoxicity in synucleinopathies including MSA. C-terminal truncation by the inflammatory protease caspase-1 has recently been implicated in the mechanisms that promote aggregation of α-syn in vitro and in neuronal cell models of α-syn toxicity. We present here an in vivo proof of concept of the ability of the caspase-1 inhibitor prodrug VX-765 to mitigate α-syn pathology and to mediate neuroprotection in proteolipid protein α-syn (PLP-SYN) mice, a transgenic mouse model of MSA. PLP-SYN and age-matched wild-type mice were treated for a period of 11 wk with VX-765 or placebo. VX-765 prevented motor deficits in PLP-SYN mice compared with placebo controls. More importantly, VX-765 was able to limit the progressive toxicity of α-syn aggregation by reducing its load in the striatum of PLP-SYN mice. Not only did VX-765 reduce truncated α-syn, but it also decreased its monomeric and oligomeric forms. Finally, VX-765 showed neuroprotective effects by preserving tyrosine hydroxylase-positive neurons in the substantia nigra of PLP-SYN mice. In conclusion, our results suggest that VX-765, a drug that was well tolerated in a 6 wk-long phase II trial in patients with epilepsy, is a promising candidate to achieve disease modification in synucleinopathies by limiting α-syn accumulation.

Targeting α-synuclein: Therapeutic options.

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

Region-Specific Alterations of Matrix Metalloproteinase Activity in Multiple System Atrophy.

BACKGROUND: MSA is a sporadic progressive neurodegenerative disorder characterized by a variable combination of parkinsonism, cerebellar ataxia, and autonomic dysfunction. The pathological hallmark of MSA is the accumulation of alpha-synuclein aggregates in the cytoplasm of oligodendrocytes along with neuronal loss and neuroinflammation, as well as blood-brain barrier dysfunction and myelin deterioration. Matrix metalloproteinases are zinc-dependent endopeptidases involved in the remodeling of the extracellular matrix, demyelination, and blood-brain barrier permeability. Several lines of evidence indicate a role for these enzymes in various pathological processes, including stroke, multiple sclerosis, Parkinson's, and Alzheimer's disease. METHODS: This study aimed to assess potential alterations of matrix metalloproteinase-1, -2, -3, and -9 expression or activity in MSA postmortem brain tissue. RESULTS: Gelatin zymography revealed increased matrix metalloproteinase-2 activity in the putamen, but not in the frontal cortex, of MSA patients relative to controls. Immunohistochemistry revealed increased number of glial cells positive for matrix metalloproteinase-1, -2, and -3 in the putamen and frontal cortex of MSA patients. Double immunofluorescence revealed that matrix metalloproteinase-2 and -3 were expressed in astrocytes and microglia. Only matrix metalloproteinase-2 colocalized with alpha-synuclein in oligodendroglial cytoplasmic inclusions. CONCLUSION: These results demonstrate widespread alterations of matrix metalloproteinase expression in MSA and a pattern of increased matrix metalloproteinase-2 expression and activity affecting preferentially a brain region severely affected (putamen) over a relatively spared region (frontal cortex). Elevated matrix metalloproteinase expression may thus contribute to the disease process in MSA by promoting blood-brain barrier dysfunction and/or myelin degradation.

Insulin, IGF-1 and GLP-1 signaling in neurodegenerative disorders: targets for disease modification?

Insulin and Insulin Growth Factor-1 (IGF-1) play a major role in body homeostasis and glucose regulation. They also have paracrine/autocrine functions in the brain. The Insulin/IGF-1 signaling pathway contributes to the control of neuronal excitability, nerve cell metabolism and cell survival. Glucagon like peptide-1 (GLP-1), known as an insulinotropic hormone has similar functions and growth like properties as insulin/IGF-1. Growing evidence suggests that dysfunction of these pathways contribute to the progressive loss of neurons in Alzheimer's disease (AD) and Parkinson's disease (PD), the two most frequent neurodegenerative disorders. These findings have led to numerous studies in preclinical models of neurodegenerative disorders targeting insulin/IGF-1 and GLP-1 signaling with currently available anti-diabetics. These studies have shown that administration of insulin, IGF-1 and GLP-1 agonists reverses signaling abnormalities and has positive effects on surrogate markers of neurodegeneration and behavioral outcomes. Several proof-of-concept studies are underway that attempt to translate the encouraging preclinical results to patients suffering from AD and PD. In the first part of this review, we discuss physiological functions of insulin/IGF-1 and GLP-1 signaling pathways including downstream targets and receptors distribution within the brain. In the second part, we undertake a comprehensive overview of preclinical studies targeting insulin/IGF-1 or GLP-1 signaling for treating AD and PD. We then detail the design of clinical trials that have used anti-diabetics for treating AD and PD patients. We close with future considerations that treat relevant issues for successful translation of these encouraging preclinical results into treatments for patients with AD and PD.