Possible Contribution of Altered Cholinergic Activity in the Visual Cortex in Visual Hallucinations in Parkinson's Disease.

OBJECTIVE: Up to one-third of patients with Parkinson's disease (PD) experience visual hallucinations (VHs). Lewy bodies are sparse in the visual cortices and seem unlikely to explain the hallucinations. Some neuroimaging studies have found that perfusion is reduced in the occipital lobe in individuals with VHs. Recent work has suggested that decreased cholinergic input may directly lead to the decreased perfusion. The investigators hypothesized that individuals with PD and VHs would have biochemical evidence of reduced microvascular perfusion and reduced cholinergic activity in areas of the brain that process visual images. METHODS: Tissue from Brodmann's area (BA) 18 and BA 19 was obtained from a well-characterized cohort matched for age, gender, and postmortem interval in 69 individuals (PD without VHs, N=11; PD without dementia plus VHs N=10, N=10; PD with dementia plus VHs, N=16; and control subjects, N=32). Von Willebrand factor, vascular endothelial growth factor A, and myelin-associated glycoprotein:proteolipid protein-1 (MAG:PLP1) ratio-a measure of tissue oxygenation relative to metabolic demand, acetylcholinesterase (AChE), butyrylcholinesterase (BChE), choline acetyltransferase, and α-synuclein-were quantified by enzyme-linked immunosorbent assay. The primary outcome was the MAG:PLP1 ratio. RESULTS: There was no biochemical evidence of chronic hypoperfusion in PD, although microvessel density was decreased in ventral BA 18 and BA 19. There was no between-group difference in BChE in either dorsal BA 18 or BA 19. AChE concentration was reduced in individuals with PD compared with control subjects in dorsal and ventral BA 18 and dorsal BA 19, and it was increased in ventral BA 19. These changes were most marked in the PD plus VHs group. CONCLUSIONS: These results suggest that changes in cholinergic activity rather than chronic hypoperfusion may underlie VHs in PD.

Annexin A1 restores cerebrovascular integrity concomitant with reduced amyloid-ß and tau pathology.

Alzheimer's disease, characterized by brain deposits of amyloid-ß plaques and neurofibrillary tangles, is also linked to neurovascular dysfunction and blood-brain barrier breakdown, affecting the passage of substances into and out of the brain. We hypothesized that treatment of neurovascular alterations could be beneficial in Alzheimer's disease. Annexin A1 (ANXA1) is a mediator of glucocorticoid anti-inflammatory action that can suppress microglial activation and reduce blood-brain barrier leakage. We have reported recently that treatment with recombinant human ANXA1 (hrANXA1) reduced amyloid-ß levels by increased degradation in neuroblastoma cells and phagocytosis by microglia. Here, we show the beneficial effects of hrANXA1 in vivo by restoring efficient blood-brain barrier function and decreasing amyloid-ß and tau pathology in 5xFAD mice and Tau-P301L mice. We demonstrate that young 5xFAD mice already suffer cerebrovascular damage, while acute pre-administration of hrANXA1 rescued the vascular defects. Interestingly, the ameliorated blood-brain barrier permeability in young 5xFAD mice by hrANXA1 correlated with reduced brain amyloid-ß load, due to increased clearance and degradation of amyloid-ß by insulin degrading enzyme (IDE). The systemic anti-inflammatory properties of hrANXA1 were also observed in 5xFAD mice, increasing IL-10 and reducing TNF-α expression. Additionally, the prolonged treatment with hrANXA1 reduced the memory deficits and increased synaptic density in young 5xFAD mice. Similarly, in Tau-P301L mice, acute hrANXA1 administration restored vascular architecture integrity, affecting the distribution of tight junctions, and reduced tau phosphorylation. The combined data support the hypothesis that blood-brain barrier breakdown early in Alzheimer's disease can be restored by hrANXA1 as a potential therapeutic approach.

Iron and inflammation: in vivo and post-mortem studies in Parkinson's disease.

In these present studies, in vivo and and post-mortem studies have investigated the association between iron and inflammation. Early-stage Parkinson's disease (PD) patients, of less than 5 years disease duration, showed associations of plasmatic ferritin concentrations with both proinflammatory cytokine interleukin-6 and hepcidin, a regulator of iron metabolism as well as clinical measures. In addition ratios of plasmatic ferritin and iron accumulation in deep grey matter nuclei assessed with relaxometry T2* inversely correlated with disease severity and duration of PD. On the hand, post-mortem material of the substantia nigra compacta (SNc) divided according to Braak and Braak scores, III-IV and V-VI staging, exhibited comparable microgliosis, with a variety of phenotypes present. There was an association between the intensity of microgliosis and iron accumulation as assayed by Perl's staining in the SNc sections. In conclusion, markers of inflammation and iron metabolism in both systemic and brain systems are closely linked in PD, thus offering a potential biomarker for progression of the disease.

Multiple system atrophy prions retain strain specificity after serial propagation in two different Tg(SNCA*A53T) mouse lines.

Previously, we reported that intracranial inoculation of brain homogenate from multiple system atrophy (MSA) patient samples produces neurological disease in the transgenic (Tg) mouse model TgM83+/-, which uses the prion protein promoter to express human α-synuclein harboring the A53T mutation found in familial Parkinson's disease (PD). In our studies, we inoculated MSA and control patient samples into Tg mice constructed using a P1 artificial chromosome to express wild-type (WT), A30P, and A53T human α-synuclein on a mouse α-synuclein knockout background [Tg(SNCA+/+)Nbm, Tg(SNCA*A30P+/+)Nbm, and Tg(SNCA*A53T+/+)Nbm]. In contrast to studies using TgM83+/- mice, motor deficits were not observed by 330-400 days in any of the Tg(SNCA)Nbm mice after inoculation with MSA brain homogenates. However, using a cell-based bioassay to measure α-synuclein prions, we found brain homogenates from Tg(SNCA*A53T+/+)Nbm mice inoculated with MSA patient samples contained α-synuclein prions, whereas control mice did not. Moreover, these α-synuclein aggregates retained the biological and biochemical characteristics of the α-synuclein prions in MSA patient samples. Intriguingly, Tg(SNCA*A53T+/+)Nbm mice developed α-synuclein pathology in neurons and astrocytes throughout the limbic system. This finding is in contrast to MSA-inoculated TgM83+/- mice, which develop exclusively neuronal α-synuclein aggregates in the hindbrain that cause motor deficits with advanced disease. In a crossover experiment, we inoculated TgM83+/- mice with brain homogenate from two MSA patient samples or one control sample first inoculated, or passaged, in Tg(SNCA*A53T+/+)Nbm animals. Additionally, we performed the reverse experiment by inoculating Tg(SNCA*A53T+/+)Nbm mice with brain homogenate from the same two MSA samples and one control sample first passaged in TgM83+/- animals. The TgM83+/- mice inoculated with mouse-passaged MSA developed motor dysfunction and α-synuclein prions, whereas the mouse-passaged control sample had no effect. Similarly, the mouse-passaged MSA samples induced α-synuclein prion formation in Tg(SNCA*A53T+/+)Nbm mice, but the mouse-passaged control sample did not. The confirmed transmission of α-synuclein prions to a second synucleinopathy model and the ability to propagate prions between two distinct mouse lines while retaining strain-specific properties provides compelling evidence that MSA is a prion disease.

MSA prions exhibit remarkable stability and resistance to inactivation.

In multiple system atrophy (MSA), progressive neurodegeneration results from the protein α-synuclein misfolding into a self-templating prion conformation that spreads throughout the brain. MSA prions are transmissible to transgenic (Tg) mice expressing mutated human α-synuclein (TgM83+/-), inducing neurological disease following intracranial inoculation with brain homogenate from deceased patient samples. Noting the similarities between α-synuclein prions and PrP scrapie (PrPSc) prions responsible for Creutzfeldt-Jakob disease (CJD), we investigated MSA transmission under conditions known to result in PrPSc transmission. When peripherally exposed to MSA via the peritoneal cavity, hind leg muscle, and tongue, TgM83+/- mice developed neurological signs accompanied by α-synuclein prions in the brain. Iatrogenic CJD, resulting from PrPSc prion adherence to surgical steel instruments, has been investigated by incubating steel sutures in contaminated brain homogenate before implantation into mouse brain. Mice studied using this model for MSA developed disease, whereas wire incubated in control homogenate had no effect on the animals. Notably, formalin fixation did not inactivate α-synuclein prions. Formalin-fixed MSA patient samples also transmitted disease to TgM83+/- mice, even after incubating in fixative for 244 months. Finally, at least 10% sarkosyl was found to be the concentration necessary to partially inactivate MSA prions. These results demonstrate the robustness of α-synuclein prions to denaturation. Moreover, they establish the parallel characteristics between PrPSc and α-synuclein prions, arguing that clinicians should exercise caution when working with materials that might contain α-synuclein prions to prevent disease.

Evidence for α-synuclein prions causing multiple system atrophy in humans with parkinsonism.

Prions are proteins that adopt alternative conformations that become self-propagating; the PrP(Sc) prion causes the rare human disorder Creutzfeldt-Jakob disease (CJD). We report here that multiple system atrophy (MSA) is caused by a different human prion composed of the α-synuclein protein. MSA is a slowly evolving disorder characterized by progressive loss of autonomic nervous system function and often signs of parkinsonism; the neuropathological hallmark of MSA is glial cytoplasmic inclusions consisting of filaments of α-synuclein. To determine whether human α-synuclein forms prions, we examined 14 human brain homogenates for transmission to cultured human embryonic kidney (HEK) cells expressing full-length, mutant human α-synuclein fused to yellow fluorescent protein (α-syn140*A53T-YFP) and TgM83(+/-) mice expressing α-synuclein (A53T). The TgM83(+/-) mice that were hemizygous for the mutant transgene did not develop spontaneous illness; in contrast, the TgM83(+/+) mice that were homozygous developed neurological dysfunction. Brain extracts from 14 MSA cases all transmitted neurodegeneration to TgM83(+/-) mice after incubation periods of ∼120 d, which was accompanied by deposition of α-synuclein within neuronal cell bodies and axons. All of the MSA extracts also induced aggregation of α-syn*A53T-YFP in cultured cells, whereas none of six Parkinson's disease (PD) extracts or a control sample did so. Our findings argue that MSA is caused by a unique strain of α-synuclein prions, which is different from the putative prions causing PD and from those causing spontaneous neurodegeneration in TgM83(+/+) mice. Remarkably, α-synuclein is the first new human prion to be identified, to our knowledge, since the discovery a half century ago that CJD was transmissible.

Propagation of prions causing synucleinopathies in cultured cells.

Increasingly, evidence argues that many neurodegenerative diseases, including progressive supranuclear palsy (PSP), are caused by prions, which are alternatively folded proteins undergoing self-propagation. In earlier studies, PSP prions were detected by infecting human embryonic kidney (HEK) cells expressing a tau fragment [TauRD(LM)] fused to yellow fluorescent protein (YFP). Here, we report on an improved bioassay using selective precipitation of tau prions from human PSP brain homogenates before infection of the HEK cells. Tau prions were measured by counting the number of cells with TauRD(LM)-YFP aggregates using confocal fluorescence microscopy. In parallel studies, we fused α-synuclein to YFP to bioassay α-synuclein prions in the brains of patients who died of multiple system atrophy (MSA). Previously, MSA prion detection required ∼120 d for transmission into transgenic mice, whereas our cultured cell assay needed only 4 d. Variation in MSA prion levels in four different brain regions from three patients provided evidence for three different MSA prion strains. Attempts to demonstrate α-synuclein prions in brain homogenates from Parkinson's disease patients were unsuccessful, identifying an important biological difference between the two synucleinopathies. Partial purification of tau and α-synuclein prions facilitated measuring the levels of these protein pathogens in human brains. Our studies should facilitate investigations of the pathogenesis of both tau and α-synuclein prion disorders as well as help decipher the basic biology of those prions that attack the CNS.

The anti-inflammatory Annexin A1 induces the clearance and degradation of the amyloid-ß peptide.

BACKGROUND: The toxicity of amyloid-ß (Aß) peptide present in the brain of Alzheimer's disease (AD) patients is thought to be mediated via the increased secretion of pro-inflammatory mediators, which can lead to neuronal dysfunction and cell death. In addition, we have previously shown that inflammation can affect Aß generation. More recently, we have reported that in vitro administration of the anti-inflammatory mediator Annexin A1 (ANXA1) following an inflammatory challenge suppressed microglial activation and this effect was mediated through formyl peptide receptor-like 1 (FPRL1/FPR2) signalling. The aim of this study was to determine the potential role of ANXA1 in the generation and clearance of Aß. METHODS: We first compared ANXA1 protein expression in the brains of AD patients and healthy controls as well as in the 5XFAD model of AD. To determine the role of ANXA1 in the processing of amyloid precursor protein (APP) and the degradation of Aß, N2a neuroblastoma cells were treated with human recombinant ANXA1 or transfected with ANXA1 siRNA. We also investigated the effect of ANXA1 on Aß phagocytosis and microglial activation in BV2 cells treated with synthetic Aß. RESULTS: Our data show that ANXA1 is increased in the brains of AD patients and animal models of AD at early stages. ANXA1 was able to reduce the levels of Aß by increasing its enzymatic degradation by neprilysin in N2a cells and to stimulate Aß phagocytosis by microglia. These effects were mediated through FPRL1 receptors. In addition, ANXA1 inhibited the Aß-stimulated secretion of inflammatory mediators by microglia. CONCLUSIONS: These data suggest that ANXA1 plays a pivotal role in Aß clearance and supports the use of ANXA1 as potential pharmacological tool for AD therapeutics.

Prenatal high-fat diet alters the cerebrovasculature and clearance of ß-amyloid in adult offspring.

Alzheimer's disease (AD) is characterized by the accumulation of ß-amyloid (Aß) peptides in the extracellular spaces of the brain as plaques and in the walls of blood vessels as cerebral amyloid angiopathy (CAA). Failure of perivascular drainage of Aß along cerebrovascular basement membranes contributes to the development of CAA. Mid-life hypercholesterolaemia is a risk factor for the development of AD. Maternal obesity is associated with the development of obesity, hypertension and hypercholesterolaemia in adulthood, suggesting that the risk for AD and CAA may also be influenced by the early-life environment. In the present study, we tested the hypothesis that early-life exposure to a high-fat diet results in changes to the cerebrovasculature and failure of Aß clearance from the brain. We also assessed whether vascular Aß deposition is greater in the brains of aged humans with a history of hyperlipidaemia, compared to age-matched controls with normal lipidaemia. Using a mouse model of maternal obesity, we found that exposure to a high-fat diet during gestation and lactation induced changes in multiple components of the neurovascular unit, including a down-regulation in collagen IV, fibronectin and apolipoprotein E, an up-regulation in markers of astrocytes and perivascular macrophages and altered blood vessel morphology in the brains of adult mice. Sustained high-fat diet over the entire lifespan resulted in additional decreases in levels of pericytes and impaired perivascular clearance of Aß from the brain. In humans, vascular Aß load was significantly increased in the brains of aged individuals with a history of hypercholesterolaemia. These results support a critical role for early dietary influence on the brain vasculature across the lifespan, with consequences for the development of age-related cerebrovascular and neurodegenerative diseases.

Transmission of multiple system atrophy prions to transgenic mice.

Prions are proteins that adopt alternative conformations, which become self-propagating. Increasing evidence argues that prions feature in the synucleinopathies that include Parkinson's disease, Lewy body dementia, and multiple system atrophy (MSA). Although TgM83(+/+) mice homozygous for a mutant A53T α-synuclein transgene begin developing CNS dysfunction spontaneously at ∼10 mo of age, uninoculated TgM83(+/-) mice (hemizygous for the transgene) remain healthy. To determine whether MSA brains contain α-synuclein prions, we inoculated the TgM83(+/-) mice with brain homogenates from two pathologically confirmed MSA cases. Inoculated TgM83(+/-) mice developed progressive signs of neurologic disease with an incubation period of ∼100 d, whereas the same mice inoculated with brain homogenates from spontaneously ill TgM83(+/+) mice developed neurologic dysfunction in ∼210 d. Brains of MSA-inoculated mice exhibited prominent astrocytic gliosis and microglial activation as well as widespread deposits of phosphorylated α-synuclein that were proteinase K sensitive, detergent insoluble, and formic acid extractable. Our results provide compelling evidence that α-synuclein aggregates formed in the brains of MSA patients are transmissible and, as such, are prions. The MSA prion represents a unique human pathogen that is lethal upon transmission to Tg mice and as such, is reminiscent of the prion causing kuru, which was transmitted to chimpanzees nearly 5 decades ago.

Nucleus basalis of Meynert revisited: anatomy, history and differential involvement in Alzheimer's and Parkinson's disease.

It has been well established that neuronal loss within the cholinergic nucleus basalis of Meynert (nbM) correlates with cognitive decline in dementing disorders such as Alzheimer's disease (AD). Friedrich Lewy first observed his eponymous inclusion bodies in the nbM of postmortem brain tissue from patients with Parkinson's disease (PD) and cell loss in this area can be at least as extensive as that seen in AD. There has been confusion with regard to the terminology and exact localisation of the nbM within the human basal forebrain for decades due to the diffuse and broad structure of this "nucleus". Also, while topographical projections from the nbM have been mapped out in subhuman primates, no direct clinicopathological correlations between subregional nbM and cortical pathology and specific cognitive profile decline have been performed in human tissue. Here, we review the evolution of the term nbM and the importance of standardised nbM sampling for neuropathological studies. Extensive review of the literature suggests that there is a caudorostral pattern of neuronal loss within the nbM in AD brains. However, the findings in PD are less clear due to the limited number of studies performed. Given the differing neuropsychiatric and cognitive deficits in Lewy body-associated dementias (PD dementia and dementia with Lewy bodies) as compared to AD, we hypothesise that a different pattern of neuronal loss will be found in the nbM of Lewy body disease brains. Understanding the functional significance of the subregions of the nbM could prove important in elucidating the pathogenesis of dementia in PD.

Parkinson's disease is associated with altered expression of CaV1 channels and calcium-binding proteins.

In Parkinson's disease oxidative stress and calcium-induced excitotoxicity have been considered important mechanisms leading to cell death for decades, but the factors that make some neurons vulnerable to neurodegeneration while others remain resistant are not fully understood. Studies of the disorder in animal models suggest that the voltage-gated calcium channel subtype Ca(V)1.3 has a role in making neurons susceptible to neurodegeneration and support earlier work in post-mortem human brain that suggested loss of calcium buffering capacity in neurons correlated with areas of neuronal loss in the substantia nigra of parkinsonian brain. This study examined expression of Ca(V)1 subtypes and the calcium-binding proteins calbindin, calmodulin and calreticulin in areas vulnerable and resistant to neurodegeneration in Parkinson's disease, in brain from neurologically normal individuals and patients with Parkinson's disease. In control brain the expression of a specific Ca(V)1 subtype or distribution of each calcium-binding protein did not associate with those regions prone to neurodegeneration in Parkinson's disease. Whereas, alterations in the amount of both Ca(V)1 subtypes and the calcium-binding proteins were found throughout the brain in Parkinson's disease. Some changes reflected the cell loss seen in Parkinson's disease, whereas others represented altered levels of cellular expression, which as they occurred in the absence of cell loss could not be explained as solely compensatory to the neurodegeneration. The finding of increased Ca(V)1.3 subtype expression in the cerebral cortex of early stage Parkinson's disease, before the appearance of pathological changes, supports the view that disturbed calcium homeostasis is an early feature of Parkinson's disease and not just a compensatory consequence to the neurodegenerative process. This interpretation is supported further by the finding that the ratio of Ca(V)1 subtypes differed throughout the brain in patients with Parkinson's disease compared with control subjects, in favour of an increased use of Ca(V)1.3, which would add to the metabolic burden for cells that rely on this Ca(V)1 subtype for electrical activity and could therefore render specific neuronal populations more vulnerable to neurodegeneration.

Neuropathological Assessment as an Endpoint in Clinical Trial Design.

Different neurodegenerative conditions can have complex, overlapping clinical presentations that make accurate diagnosis during life very challenging. For this reason, confirmation of the clinical diagnosis still requires postmortem verification. This is particularly relevant for clinical trials of novel therapeutics where it is important to ascertain what disease- and/or pathology-modifying effects the therapeutics have had. Furthermore, it is important to confirm that patients in the trial had the correct clinical diagnosis as this will have a major bearing on the interpretation of trial results. Here we present a simple protocol for pathological assessment of neurodegenerative changes.

Differential methylation analysis in neuropathologically confirmed dementia with Lewy bodies.

Dementia with Lewy bodies (DLB) is a common form of dementia in the elderly population. We performed genome-wide DNA methylation mapping of cerebellar tissue from pathologically confirmed DLB cases and controls to study the epigenetic profile of this understudied disease. After quality control filtering, 728,197 CpG-sites in 278 cases and 172 controls were available for the analysis. We undertook an epigenome-wide association study, which found a differential methylation signature in DLB cases. Our analysis identified seven differentially methylated probes and three regions associated with DLB. The most significant CpGs were located in ARSB (cg16086807), LINC00173 (cg18800161), and MGRN1 (cg16250093). Functional enrichment evaluations found widespread epigenetic dysregulation in genes associated with neuron-to-neuron synapse, postsynaptic specialization, postsynaptic density, and CTCF-mediated synaptic plasticity. In conclusion, our study highlights the potential importance of epigenetic alterations in the pathogenesis of DLB and provides insights into the modified genes, regions and pathways that may guide therapeutic developments.

Linking environmental risk factors with epigenetic mechanisms in Parkinson's disease.

Sporadic Parkinson's disease (PD) is a progressive neurodegenerative disease, with a complex risk structure thought to be influenced by interactions between genetic variants and environmental exposures, although the full aetiology is unknown. Environmental factors, including pesticides, have been reported to increase the risk of developing the disease. Growing evidence suggests epigenetic changes are key mechanisms by which these environmental factors act upon gene regulation, in disease-relevant cell types. We present a systematic review critically appraising and summarising the current body of evidence of the relationship between epigenetic mechanisms and environmental risk factors in PD to inform future research in this area. Epigenetic studies of relevant environmental risk factors in animal and cell models have yielded promising results, however, research in humans is just emerging. While published studies in humans are currently relatively limited, the importance of the field for the elucidation of molecular mechanisms of pathogenesis opens clear and promising avenues for the future of PD research. Carefully designed epidemiological studies carried out in PD patients hold great potential to uncover disease-relevant gene regulatory mechanisms. Therefore, to advance this burgeoning field, we recommend broadening the scope of investigations to include more environmental exposures, increasing sample sizes, focusing on disease-relevant cell types, and recruiting more diverse cohorts.

Meningeal inflammation is widespread and linked to cortical pathology in multiple sclerosis.

Meningeal inflammation in the form of ectopic lymphoid-like structures has been suggested to play a prominent role in the development of cerebral cortical grey matter pathology in multiple sclerosis. The aim of this study was to analyse the incidence and distribution of B cell follicle-like structures in an extensive collection of cases with secondary progressive multiple sclerosis with a wide age range and to determine their relationship to diffuse meningeal inflammation, white matter perivascular infiltrates and microglial activation. One hundred and twenty three cases with secondary progressive multiple sclerosis were examined for the presence of meningeal and perivascular immune cell infiltrates in tissue blocks and/or whole coronal macrosections encompassing a wide array of brain areas. Large, dense, B cell-rich lymphocytic aggregates were screened for the presence of follicular dendritic cells, proliferating B cells and plasma cells. Ectopic B cell follicle-like structures were found, with variable frequency, in 49 cases (40%) and were distributed throughout the forebrain, where they were most frequently located in the deep sulci of the temporal, cingulate, insula and frontal cortex. Subpial grey matter demyelinated lesions were located both adjacent to, and some distance from such structures. The presence of B cell follicle-like structures was associated with an accompanying quantitative increase in diffuse meningeal inflammation that correlated with the degree of microglial activation and grey matter cortical demyelination. The median age of disease onset, time to disease progression, time to wheelchair dependence and age at death all differed significantly in these cases when compared with those without B cell follicle-like structures. Our findings suggest that meningeal infiltrates may play a contributory role in the underlying subpial grey matter pathology and accelerated clinical course, which is exacerbated in a significant proportion of cases by the presence of B cell follicle-like structures.

Common signatures of differential microRNA expression in Parkinson's and Alzheimer's disease brains.

Dysregulation of microRNA gene expression has been implicated in many neurodegenerative diseases, including Parkinson's disease. However, the individual dysregulated microRNAs remain largely unknown. Previous meta-analyses have highlighted several microRNAs being differentially expressed in post-mortem Parkinson's disease and Alzheimer's disease brains versus controls, but they were based on small sample sizes. In this study, we quantified the expression of the most compelling Parkinson's and Alzheimer's disease microRNAs from these meta-analyses ('candidate miRNAs') in one of the largest Parkinson's/Alzheimer's disease case-control post-mortem brain collections available (n = 451), thereby quadruplicating previously investigated sample sizes. Parkinson's disease candidate microRNA hsa-miR-132-3p was differentially expressed in our Parkinson's (P = 4.89E-06) and Alzheimer's disease samples (P = 3.20E-24) compared with controls. Alzheimer's disease candidate microRNAs hsa-miR-132-5p (P = 4.52E-06) and hsa-miR-129-5p (P = 0.0379) were differentially expressed in our Parkinson's disease samples. Combining these novel data with previously published data substantially improved the statistical support (α = 3.85E-03) of the corresponding meta-analyses, clearly implicating these microRNAs in both Parkinson's and Alzheimer's disease. Furthermore, hsa-miR-132-3p/-5p (but not hsa-miR-129-5p) showed association with α-synuclein neuropathological Braak staging (P = 3.51E-03/P = 0.0117), suggesting that hsa-miR-132-3p/-5p play a role in α-synuclein aggregation beyond the early disease phase. Our study represents the largest independent assessment of recently highlighted candidate microRNAs in Parkinson's and Alzheimer's disease brains, to date. Our results implicate hsa-miR-132-3p/-5p and hsa-miR-129-5p to be differentially expressed in both Parkinson's and Alzheimer's disease, pinpointing shared pathogenic mechanisms across these neurodegenerative diseases. Intriguingly, based on publicly available high-throughput sequencing of RNA isolated by cross-linking immunoprecipitation data, hsa-miR-132 may interact with SNCA messenger RNA in the human brain, possibly pinpointing novel therapeutic approaches in fighting Parkinson's disease.

Mitochondrial dysfunction is a key pathological driver of early stage Parkinson's.

BACKGROUND: The molecular drivers of early sporadic Parkinson's disease (PD) remain unclear, and the presence of widespread end stage pathology in late disease masks the distinction between primary or causal disease-specific events and late secondary consequences in stressed or dying cells. However, early and mid-stage Parkinson's brains (Braak stages 3 and 4) exhibit alpha-synuclein inclusions and neuronal loss along a regional gradient of severity, from unaffected-mild-moderate-severe. Here, we exploited this spatial pathological gradient to investigate the molecular drivers of sporadic PD. METHODS: We combined high precision tissue sampling with unbiased large-scale profiling of protein expression across 9 brain regions in Braak stage 3 and 4 PD brains, and controls, and verified these results using targeted proteomic and functional analyses. RESULTS: We demonstrate that the spatio-temporal pathology gradient in early-mid PD brains is mirrored by a biochemical gradient of a changing proteome. Importantly, we identify two key events that occur early in the disease, prior to the occurrence of alpha-synuclein inclusions and neuronal loss: (i) a metabolic switch in the utilisation of energy substrates and energy production in the brain, and (ii) perturbation of the mitochondrial redox state. These changes may contribute to the regional vulnerability of developing alpha-synuclein pathology. Later in the disease, mitochondrial function is affected more severely, whilst mitochondrial metabolism, fatty acid oxidation, and mitochondrial respiration are affected across all brain regions. CONCLUSIONS: Our study provides an in-depth regional profile of the proteome at different stages of PD, and highlights that mitochondrial dysfunction is detectable prior to neuronal loss, and alpha-synuclein fibril deposition, suggesting that mitochondrial dysfunction is one of the key drivers of early disease.