Cortical alpha-synuclein load is associated with amyloid-beta plaque burden in a subset of Parkinson's disease patients

Clinical and diagnostic implications of Alzheimer's disease copathology in Lewy body disease

Concomitant Alzheimer's disease (AD) pathology is a frequent event in the context of Lewy body disease (LBD), occurring in approximately half of all cases. Evidence shows that LBD patients with AD copathology show an accelerated disease course, a greater risk of cognitive decline and an overall poorer prognosis. However, LBD-AD cases may show heterogeneous motor and non-motor phenotypes with a higher risk of dementia and, consequently, be not rarely misdiagnosed. In this review, we summarize the current understanding of LBD-AD by discussing the synergistic effects of AD neuropathological changes and Lewy pathology and their clinical relevance. Furthermore, we provide an extensive overview of neuroimaging and fluid biomarkers under assessment for use in LBD-AD and their possible diagnostic and prognostic values. AD pathology can be predicted in vivo by means of CSF, MRI and PET markers, whereas the most promising technique to date for identifying Lewy pathology in different biological tissues is the α-synuclein seed amplification assay. Pathological imaging and CSF AD biomarkers are associated with a higher likelihood of cognitive decline in LBD but do not always mirror the neuropathological severity as in pure AD. Implementing the use of blood-based AD biomarkers might allow faster screening of LBD patients for AD copathology, thus improving the overall diagnostic sensitivity for LBD-AD. Finally, we discuss the literature on novel candidate biomarkers being exploited in LBD-AD to investigate other aspects of neurodegeneration, such as neuroaxonal injury, glial activation and synaptic dysfunction. The thorough characterization of AD copathology in LBD should be taken into account when considering differential diagnoses of dementia syndromes, to allow prognostic evaluation on an individual level, and to guide symptomatic and disease-modifying therapies.

Interplay between the glymphatic system and neurotoxic proteins in Parkinson's disease and related disorders: current knowledge and future directions

Parkinson's disease is a common neurodegenerative disorder that is associated with abnormal aggregation and accumulation of neurotoxic proteins, including α-synuclein, amyloid-β, and tau, in addition to the impaired elimination of these neurotoxic protein. Atypical parkinsonism, which has the same clinical presentation and neuropathology as Parkinson's disease, expands the disease landscape within the continuum of Parkinson's disease and related disorders. The glymphatic system is a waste clearance system in the brain, which is responsible for eliminating the neurotoxic proteins from the interstitial fluid. Impairment of the glymphatic system has been proposed as a significant contributor to the development and progression of neurodegenerative disease, as it exacerbates the aggregation of neurotoxic proteins and deteriorates neuronal damage. Therefore, impairment of the glymphatic system could be considered as the final common pathway to neurodegeneration. Previous evidence has provided initial insights into the potential effect of the impaired glymphatic system on Parkinson's disease and related disorders; however, many unanswered questions remain. This review aims to provide a comprehensive summary of the growing literature on the glymphatic system in Parkinson's disease and related disorders. The focus of this review is on identifying the manifestations and mechanisms of interplay between the glymphatic system and neurotoxic proteins, including loss of polarization of aquaporin-4 in astrocytic endfeet, sleep and circadian rhythms, neuroinflammation, astrogliosis, and gliosis. This review further delves into the underlying pathophysiology of the glymphatic system in Parkinson's disease and related disorders, and the potential implications of targeting the glymphatic system as a novel and promising therapeutic strategy.

Risk factors for cognitive decline in non-demented elders with amyloid-beta positivity

BACKGROUND

As a currently incurable but preventable disease, the prevention and early diagnosis of Alzheimer's disease (AD) has long been a research hotspot. Amyloid deposition has been shown to be a major pathological feature of AD. Notably, not all the people with amyloid-beta (Aβ) pathology will have significant cognitive declines and eventually develop AD. Therefore, the aim of this study was to explore the risk factors for cognitive decline in Aβ-positive participants.

METHODS

We included 650 non-demented participants who were Aβ-positive at baseline from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Mixed effects and COX regression models were applied to assess 37 potential risk factors. Mixed effects models were employed to assess the temporal associations between potential risk factors and four cognitive assessment scales. COX regression models were used to assess the impact of potential risk factors on cognitive diagnosis conversion. Univariate and multivariate analyses were applied to the above models. Additionally, we used the Cochran-Armitage trend test to examine whether the incidence of cognitive decline increased with the number concurrent of risk factors.

RESULTS

Six factors (low diastolic pressure, low body mass index, retired status, a history of drug abuse, Parkinsonism, and depression) were the identified risk factors and four factors (a history of urinary disease, musculoskeletal diseases, no major surgical history, and no prior dermatologic-connective tissue diseases) were found to be suggestive risk factors. The incidence of cognitive decline in the Aβ-positive participants gradually increased as the number of concurrent risk factors increased (p for trend = 0.0005).

CONCLUSIONS

Our study may facilitate the understanding of the potential pathological processes in AD and provide novel targets for the prevention of cognitive decline among participants with Aβ positivity.

Amyloid-beta and tau protein beyond Alzheimer's disease

ABSTRACT

The aggregation of amyloid-beta peptide and tau protein dysregulation are implicated to play key roles in Alzheimer's disease pathogenesis and are considered the main pathological hallmarks of this devastating disease. Physiologically, these two proteins are produced and expressed within the normal human body. However, under pathological conditions, abnormal expression, post-translational modifications, conformational changes, and truncation can make these proteins prone to aggregation, triggering specific disease-related cascades. Recent studies have indicated associations between aberrant behavior of amyloid-beta and tau proteins and various neurological diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as retinal neurodegenerative diseases like Glaucoma and age-related macular degeneration. Additionally, these proteins have been linked to cardiovascular disease, cancer, traumatic brain injury, and diabetes, which are all leading causes of morbidity and mortality. In this comprehensive review, we provide an overview of the connections between amyloid-beta and tau proteins and a spectrum of disorders.

Tau maturation in the clinicopathological spectrum of Lewy body and Alzheimer's disease

OBJECTIVE

Alzheimer's disease neuropathologic change and alpha-synucleinopathy commonly co-exist and contribute to the clinical heterogeneity of dementia. Here, we examined tau epitopes marking various stages of tangle maturation to test the hypotheses that tau maturation is more strongly associated with beta-amyloid compared to alpha-synuclein, and within the context of mixed pathology, mature tau is linked to Alzheimer's disease clinical phenotype and negatively associated with Lewy body dementia.

METHODS

We used digital histology to measure percent area-occupied by pathology in cortical regions among individuals with pure Alzheimer's disease neuropathologic change, pure alpha-synucleinopathy, and a co-pathology group with both Alzheimer's and alpha-synuclein pathologic diagnoses. Multiple tau monoclonal antibodies were used to detect early (AT8, MC1) and mature (TauC3) epitopes of tangle progression. We used linear/logistic regression to compare groups and test the association between pathologies and clinical features.

RESULTS

There were lower levels of tau pathology (β = 1.86-2.96, p < 0.001) across all tau antibodies in the co-pathology group compared to the pure Alzheimer's pathology group. Among individuals with alpha-synucleinopathy, higher alpha-synuclein was associated with greater early tau (AT8 β = 1.37, p < 0.001; MC1 β = 1.2, p < 0.001) but not mature tau (TauC3 p = 0.18), whereas mature tau was associated with beta-amyloid (β = 0.21, p = 0.01). Finally, lower tau, particularly TauC3 pathology, was associated with lower frequency of both core clinical features and categorical clinical diagnosis of dementia with Lewy bodies.

INTERPRETATION

Mature tau may be more closely related to beta-amyloidosis than alpha-synucleinopathy, and pathophysiological processes of tangle maturation may influence the clinical features of dementia in mixed Lewy-Alzheimer's pathology.

Lysosomal Polygenic Burden Drives Cognitive Decline in Parkinson's Disease with Low Alzheimer Risk

BACKGROUND

Genetics influence cognitive progression in Parkinson's disease, possibly through mechanisms related to Lewy and Alzheimer's disease pathology. Lysosomal polygenic burden has recently been linked to more severe Lewy pathology post mortem.

OBJECTIVES

To assess the influence of lysosomal polygenic burden on cognitive progression in Parkinson's disease patients with low Alzheimer's disease risk.

METHODS

Using Cox regression we assessed association between lysosomal polygenic scores and time to Montreal Cognitive Assessment score ≤ 21 in the Parkinson's Progression Markers Initiative cohort (n = 374), with replication in data from the Parkinson's Disease Biomarker Program (n = 777). Patients were stratified by Alzheimer's disease polygenic risk.

RESULTS

The lysosomal polygenic score was associated with faster progression of cognitive decline in patients with low Alzheimer's disease risk in both datasets (P = 0.0032 and P = 0.0054, respectively).

CONCLUSION

Our study supports complex interplay between genetics and neuropathology in Parkinson's disease-related cognitive impairment, emphasizing the role of lysosomal polygenic burden. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Prevalence of Concomitant Pathologies in Parkinson's Disease: Implications for Prognosis, Diagnosis, and Insights into Common Pathogenic Mechanisms

Pathologies characteristic of Alzheimer's disease (i.e., hyperphosphorylated tau and amyloid-β (Aβ) plaques), cardiovascular disease, and limbic predominant TDP-43 encephalopathy (LATE) often co-exist in patients with Parkinson's disease (PD), in addition to Lewy body pathology (α-synuclein). Numerous studies point to a putative synergistic relationship between hyperphosphorylation tau, Aβ, cardiovascular lesions, and TDP-43 with α-synuclein, which may alter the stereotypical pattern of pathological progression and accelerate cognitive decline. Here we discuss the prevalence and relationships between common concomitant pathologies observed in PD. In addition, we highlight shared genetic risk factors and developing biomarkers that may provide better diagnostic accuracy for patients with PD that have co-existing pathologies. The tremendous heterogeneity observed across the PD spectrum is most likely caused by the complex interplay between pathogenic, genetic, and environmental factors, and increasing our understanding of how these relate to idiopathic PD will drive research into finding accurate diagnostic tools and disease modifying therapies.

Evaluation of N- and O-Linked Indole Triazines for a Dual Effect on α-Synuclein and Tau Aggregation

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder underlying dementia in the geriatric population. AD manifests by two pathological hallmarks: extracellular amyloid-β (Aβ) peptide-containing senile plaques and intraneuronal neurofibrillary tangles comprised of aggregated hyperphosphorylated tau protein (p-tau). However, more than half of AD cases also display the presence of aggregated α-synuclein (α-syn)-containing Lewy bodies. Conversely, Lewy bodies disorders have been reported to have concomitant Aβ plaques and neurofibrillary tangles. Our drug discovery program focuses on the synthesis of multitarget-directed ligands to abrogate aberrant α-syn, tau (2N4R), and p-tau (1N4R) aggregation and to slow the progression of AD and related dementias. To this end, we synthesized 11 compounds with a triazine-linker and evaluated their effectiveness in reducing α-syn, tau isoform 2N4R, and p-tau isoform 1N4R aggregation. We utilized biophysical methods such as thioflavin T (ThT) fluorescence assays, transmission electron microscopy (TEM), photoinduced cross-linking of unmodified proteins (PICUP), and M17D intracellular inclusion cell-based assays to evaluate the antiaggregation properties and cellular protection of our best compounds. We also performed disaggregation assays with isolated Aβ-plaques from human AD brains. Our results demonstrated that compound 10 was effective in reducing both oligomerization and fibril formation of α-syn and tau isoform 2N4R in a dose-dependent manner via ThT and PICUP assays. Compound 10 was also effective at reducing the formation of recombinant α-syn, tau 2N4R, and p-tau 1N4R fibrils by TEM. Compound 10 reduced the development of α-syn inclusions in M17D neuroblastoma cells and stopped the seeding of tau P301S using biosensor cells. Disaggregation experiments showed smaller Aβ-plaques and less paired helical filaments with compound 10. Compound 10 may provide molecular scaffolds for further optimization and preclinical studies for neurodegenerative proteinopathies.

Lysosomal polygenic risk is associated with the severity of neuropathology in Lewy body disease

Intraneuronal accumulation of misfolded α-synuclein is the pathological hallmark of Parkinson's disease and dementia with Lewy bodies, often co-occurring with variable degrees of Alzheimer's disease related neuropathology. Genetic association studies have successfully identified common variants associated with disease risk and phenotypic traits in Lewy body disease, yet little is known about the genetic contribution to neuropathological heterogeneity. Using summary statistics from Parkinson's disease and Alzheimer's disease genome-wide association studies, we calculated polygenic risk scores and investigated the relationship with Lewy, amyloid-β and tau pathology. Associations were nominated in neuropathologically defined samples with Lewy body disease from the Netherlands Brain Bank (n = 217) and followed up in an independent sample series from the Mayo Clinic Brain Bank (n = 394). We also generated stratified polygenic risk scores based on single-nucleotide polymorphisms annotated to eight functional pathways or cell types previously implicated in Parkinson's disease and assessed for association with Lewy pathology in subgroups with and without significant Alzheimer's disease co-pathology. In an ordinal logistic regression model, the Alzheimer's disease polygenic risk score was associated with concomitant amyloid-β and tau pathology in both cohorts. Moreover, both cohorts showed a significant association between lysosomal pathway polygenic risk and Lewy pathology, which was more consistent than the association with a general Parkinson's disease risk score and specific to the subset of samples without significant concomitant Alzheimer's disease related neuropathology. Our findings provide proof of principle that the specific risk alleles a patient carries for Parkinson's and Alzheimer's disease also influence key aspects of the underlying neuropathology in Lewy body disease. The interrelations between genetic architecture and neuropathology are complex, as our results implicate lysosomal risk loci specifically in the subset of samples without Alzheimer's disease co-pathology. Our findings hold promise that genetic profiling may help predict the vulnerability to specific neuropathologies in Lewy body disease, with potential relevance for the further development of precision medicine in these disorders.

Novel systemic delivery of a peptide-conjugated antisense oligonucleotide to reduce α-synuclein in a mouse model of Alzheimer's disease

Neurodegenerative disorders of aging are characterized by the progressive accumulation of proteins such as α-synuclein (α-syn) and amyloid beta (Aβ). Misfolded and aggregated α-syn has been implicated in neurological disorders such as Parkinson's disease, and Dementia with Lewy Bodies, but less so in Alzheimer's Disease (AD), despite the fact that accumulation of α-syn has been confirmed in over 50% of postmortem brains neuropathologically diagnosed with AD. To date, no therapeutic strategy has effectively or consistently downregulated α-syn in AD. Here we tested the hypothesis that by using a systemically-delivered peptide (ApoB11) bound to a modified antisense oligonucleotide against α-syn (ASO-α-syn), we can downregulate α-syn expression in an AD mouse model and improve behavioral and neuropathologic phenotypes. Our results demonstrate that monthly systemic treatment with of ApoB11:ASO α-syn beginning at 6 months of age reduces expression of α-synuclein in the brains of 9-month-old AD mice. Downregulation of α-syn led to reduction in Aβ plaque burden, prevented neuronal loss and astrogliosis. Furthermore, we found that AD mice treated with ApoB11:ASO α-syn had greatly improved hippocampal and spatial memory function in comparison to their control counterparts. Collectively, our data supports the reduction of α-syn through use of systemically-delivered ApoB11:ASO α-syn as a promising future disease-modifying therapeutic for AD.

Morphological characteristics differentiate dementia with Lewy bodies from Parkinson disease with and without dementia

Dementia with Lewy bodies (DLB) and Parkinson disease (PD) with and without dementia are entities of a spectrum of Lewy body diseases. About 26.3% of all PD patients develop dementia increasing up to 83%. Parkinson disease-dementia (PDD) and DLB share many clinical and morphological features that separate them from non-demented PD (PDND). Clinically distinguished by the temporal sequence of motor and cognitive symptoms, the pathology of PDD and DLB includes variable combinations of Lewy body (LB) and Alzheimer (AD) lesions, both being more severe in DLB, but much less frequent and less severe in PDND. The objective of this study was to investigate the morphological differences between these three groups. 290 patients with pathologically confirmed PD were reviewed. 190 of them had clinical dementia; 110 met the neuropathological criteria of PDD and 80 of DLB. The major demographic and clinical data were obtained from medical records. Neuropathology included semiquantitative assessment of LB and AD pathologies including cerebral amyloid angiopathy (CAA). PDD patients were significantly older than PDND and DLB ones (83.9 vs 77.9 years, p < 0.05); the age of DLB patients was between them (80.0 years), while the disease duration was shortest in DLB. Brain weight was lowest in DLB, which showed higher Braak LB scores (mean 5.2 vs 4.2) and highest Braak tau stages (mean 5.2 vs 4.4 and 2.3, respectively). Thal Aβ phases were also highest in DLB (mean 4.1 vs 3.0 and 1.8, respectively). Major findings were frequency and degree of CAA, being highest in DLB (95% vs 50% and 24%, with scores 2.9 vs 0.7 and 0.3, respectively), whereas other small vessel lesions showed no significant differences. Striatal Aβ deposits also differentiated DLB from the other groups. This and other studies of larger cohorts of PD patients indicate that the association of CAA and cortical tau-but less-LB pathologies are associated with more severe cognitive decline and worse prognosis that distinguish DLB from PDD and PDND. The particular impact of both CAA and tau pathology supports the concept of a pathogenic continuum ranging from PDND to DLB + AD within the spectrum of age-related synucleinopathies.

Plasma GFAP associates with secondary Alzheimer's pathology in Lewy body disease

OBJECTIVE

Within Lewy body spectrum disorders (LBSD) with α-synuclein pathology (αSyn), concomitant Alzheimer's disease (AD) pathology is common and is predictive of clinical outcomes, including cognitive impairment and decline. Plasma phosphorylated tau 181 (p-tau₁₈₁ ) is sensitive to AD neuropathologic change (ADNC) in clinical AD, and plasma glial fibrillary acidic protein (GFAP) is associated with the presence of β-amyloid plaques. While these plasma biomarkers are well tested in clinical and pathological AD, their diagnostic and prognostic performance for concomitant AD in LBSD is unknown.

METHODS

In autopsy-confirmed αSyn-positive LBSD, we tested how plasma p-tau₁₈₁ and GFAP differed across αSyn with concomitant ADNC (αSyn+AD; n = 19) and αSyn without AD (αSyn; n = 30). Severity of burden was scored on a semiquantitative scale for several pathologies (e.g., β-amyloid and tau), and scores were averaged across sampled brainstem, limbic, and neocortical regions.

RESULTS

Linear models showed that plasma GFAP was significantly higher in αSyn+AD compared to αSyn (β = 0.31, 95% CI = 0.065-0.56, and P = 0.015), after covarying for age at plasma, plasma-to-death interval, and sex; plasma p-tau₁₈₁ was not (P = 0.37). Next, linear models tested associations of AD pathological features with both plasma analytes, covarying for plasma-to-death, age at plasma, and sex. GFAP was significantly associated with brain β-amyloid (β = 15, 95% CI = 6.1-25, and P = 0.0018) and tau burden (β = 12, 95% CI = 2.5-22, and P = 0.015); plasma p-tau₁₈₁ was not associated with either (both P > 0.34).

INTERPRETATION

Findings indicate that plasma GFAP may be sensitive to concomitant AD pathology in LBSD, especially accumulation of β-amyloid plaques.

Hippocampal Reduction of α-Synuclein via RNA Interference Improves Neuropathology in Alzheimer's Disease Mice

BACKGROUND

Alzheimer's disease (AD) cases are often characterized by the pathological accumulation of α-synuclein (α-syn) in addition to amyloid-β (Aβ) and tau hallmarks. The role of α-syn has been extensively studied in synucleinopathy disorders, but less so in AD. Recent studies have shown that α-syn may also play a role in AD and its downregulation may be protective against the toxic effects of Aβ accumulation.

OBJECTIVE

We hypothesized that selectively knocking down α-syn via RNA interference improves the neuropathological and biochemical findings in AD mice.

METHODS

Here we used amyloid precursor protein transgenic (APP-Tg) mice to model AD and explore pathologic and behavioral phenotypes with knockdown of α-syn using RNA interference. We selectively reduced α-syn levels by stereotaxic bilateral injection of either LV-shRNA α-syn or LV-shRNA-luc (control) into the hippocampus of AD mice.

RESULTS

We found that downregulation of α-syn results in significant reduction in the number of Aβ plaques. In addition, mice treated with LV-shRNA α-syn had amelioration of abnormal microglial activation (Iba1) and astrocytosis (GFAP) phenotypes in AD mice.

CONCLUSION

Our data suggests a novel link between Aβ and α-syn pathology as well as a new therapeutic angle for targeting AD.

Association between the LRP1B and APOE loci in the development of Parkinson's disease dementia

Parkinson's disease is one of the most common age-related neurodegenerative disorders. Although predominantly a motor disorder, cognitive impairment and dementia are important features of Parkinson's disease, particularly in the later stages of the disease. However, the rate of cognitive decline varies among Parkinson's disease patients, and the genetic basis for this heterogeneity is incompletely understood. To explore the genetic factors associated with rate of progression to Parkinson's disease dementia, we performed a genome-wide survival meta-analysis of 3,923 clinically diagnosed Parkinson's disease cases of European ancestry from four longitudinal cohorts. In total, 6.7% of individuals with Parkinson's disease developed dementia during study follow-up, on average 4.4 ± 2.4 years from disease diagnosis. We have identified the APOE ε4 allele as a major risk factor for the conversion to Parkinson's disease dementia [hazards ratio = 2.41 (1.94-3.00), P = 2.32 × 10-15], as well as a new locus within the ApoE and APP receptor LRP1B gene [hazards ratio = 3.23 (2.17-4.81), P = 7.07 × 10-09]. In a candidate gene analysis, GBA variants were also identified to be associated with higher risk of progression to dementia [hazards ratio = 2.02 (1.21-3.32), P = 0.007]. CSF biomarker analysis also implicated the amyloid pathway in Parkinson's disease dementia, with significantly reduced levels of amyloid β42 (P = 0.0012) in Parkinson's disease dementia compared to Parkinson's disease without dementia. These results identify a new candidate gene associated with faster conversion to dementia in Parkinson's disease and suggest that amyloid-targeting therapy may have a role in preventing Parkinson's disease dementia.

Optic radiation atrophy in Lewy body disease with visual hallucination on phase difference enhanced magnetic resonance images

Visual hallucinations (VH) occur commonly in Lewy body disease (LBD), including Parkinson's disease (PD), PD with dementia, and dementia with Lewy bodies. We aimed to use phase difference enhanced imaging (PADRE) to assess structural abnormalities of optic radiation (OR) in patients with Lewy body disease (LBD) concomitant with VH. Firstly, two radiologists reviewed the OR appearances in healthy subjects (HS) on PADRE. Next, based on the OR abnormalities, two reviewers assessed the PADRE images from 18 HS and 38 and 110 patients with LBD, with and without VH, respectively, in a blinded manner. Finally, all patients with LBD without VH were eventually followed up for at least 5 years after magnetic resonance imaging to determine the appearance of VH. The radiologists identified three layers, namely external sagittal stratum, internal sagittal stratum, and tapetum, in OR on the PADRE in HS. Moreover, they were able to consensually define the OR as abnormal when the layers were obscured and the disappearance of the cranial side. The sensitivity/specificity of abnormal OR for each case was 68%/81% (LBD with VH vs. LBD without VH). Furthermore, VH appeared in 12 of the 21 (57%) patients with LBD and abnormal OR during the follow-up period. However, no patients without abnormal OR reported VH. Patients with LBD and VH demonstrated the abnormal OR. This, in turn, might be a useful marker to distinguish the patients with VH from those without VH and HS. Moreover, abnormal OR on PADRE may precede the appearance of VH in LBD.

Immunohistochemical Demonstration of the pGlu79 α-Synuclein Fragment in Alzheimer’s Disease and Its Tg2576 Mouse Model

The deposition of β-amyloid peptides and of α-synuclein proteins is a neuropathological hallmark in the brains of Alzheimer’s disease (AD) and Parkinson’s disease (PD) subjects, respectively. However, there is accumulative evidence that both proteins are not exclusive for their clinical entity but instead co-exist and interact with each other. Here, we investigated the presence of a newly identified, pyroglutamate79-modified α-synuclein variant (pGlu79-aSyn)—along with the enzyme matrix metalloproteinase-3 (MMP-3) and glutaminyl cyclase (QC) implicated in its formation—in AD and in the transgenic Tg2576 AD mouse model. In the human brain, pGlu79-aSyn was detected in cortical pyramidal neurons, with more distinct labeling in AD compared to control brain tissue. Using immunohistochemical double and triple labelings and confocal laser scanning microscopy, we demonstrate an association of pGlu79-aSyn, MMP-3 and QC with β-amyloid plaques. In addition, pGlu79-aSyn and QC were present in amyloid plaque-associated reactive astrocytes that were also immunoreactive for the chaperone heat shock protein 27 (HSP27). Our data are consistent for the transgenic mouse model and the human clinical condition. We conclude that pGlu79-aSyn can be generated extracellularly or within reactive astrocytes, accumulates in proximity to β-amyloid plaques and induces an astrocytic protein unfolding mechanism involving HSP27.

Are there morphological differences between Parkinson's disease-dementia and dementia with Lewy bodies?

Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB) are two major neurocognitive disorders in the spectrum of Lewy body diseases that overlap in many clinical and neuropathological features, although they show several differences. Clinically distinguished mainly based on the duration of parkinsonism prior to development of dementia, their morphology is characterized by a variable combination of Lewy body (LB) and Alzheimer's disease (AD) pathologies, the latter usually being more frequent and severe in DLB.

OBJECTIVE

The aims of the study were to investigate essential neuropathological differences between PDD and DLB in a larger cohort of autopsy cases.

METHODS

110 PDD autopsy cases were compared with 78 DLB cases. The major demographic, clinical (duration of illness, final MMSE) and neuropathological data were assessed retrospectively. Neuropathological studies used standardized methods and immunohistochemistry for phospho-tau, β-amyloid (Aß) and α-synuclein, with semiquantitative assessment of the major histological lesions.

RESULTS

PDD patients were significantly older at death than DLB ones (mean 83.9 vs. 79.8 years), with a significantly longer disease duration (mean 9.2 vs. 6.7 years). Braak LB scores and particularly neuritic Braak stages were significantly higher in the DLB group (mean 5.1and 5.1 vs. 4.2 and 4.4, respectively), as were Thal Aβ phases (mean 4.1 vs. 3.0). Diffuse striatal Aβ plaques were considerable in 55% and moderate in 45% of DLB cases, but were extremely rare in PDD. The most significant differences concerned the frequency and degree of cerebral amyloid angiopathy (CAA), being significantly higher in DLB (98.7 vs. 50%, and mean degree of 2.9 vs. 0.72, respectively). Worse prognosis in DLB than in PDD was linked to both increased Braak neuritic stages and more severe CAA.

INTERPRETATION

These and other recent studies imply the association of CAA, more severe concomitant AD pathology, and striatal Aβ load with cognitive decline and more rapid disease process that distinguishes DLB from PDD, while the influence of other cerebrovascular diseases or co-pathologies in both disorders was not specifically examined. The importance of both CAA and tau pathology in DLB and much less in PDD supports the concept of a pathogenetic continuum from Parkinson's disease (PD) - > PDD - > DLB - > DLB + AD and subtypes of AD with LB pathology within the spectrum of age-related proteinopathies.

Morphological basis of Parkinson disease-associated cognitive impairment: an update

Cognitive impairment is one of the most salient non-motor symptoms of Parkinson disease (PD) that poses a significant burden on the patients and carers as well as being a risk factor for early mortality. People with PD show a wide spectrum of cognitive dysfunctions ranging from subjective cognitive decline and mild cognitive impairment (MCI) to frank dementia. The mean frequency of PD with MCI (PD-MCI) is 25.8% and the pooled dementia frequency is 26.3% increasing up to 83% 20 years after diagnosis. A better understanding of the underlying pathological processes will aid in directing disease-specific treatment. Modern neuroimaging studies revealed considerable changes in gray and white matter in PD patients with cognitive impairment, cortical atrophy, hypometabolism, dopamine/cholinergic or other neurotransmitter dysfunction and increased amyloid burden, but multiple mechanism are likely involved. Combined analysis of imaging and fluid markers is the most promising method for identifying PD-MCI and Parkinson disease dementia (PDD). Morphological substrates are a combination of Lewy- and Alzheimer-associated and other concomitant pathologies with aggregation of α-synuclein, amyloid, tau and other pathological proteins in cortical and subcortical regions causing destruction of essential neuronal networks. Significant pathological heterogeneity within PD-MCI reflects deficits in various cognitive domains. This review highlights the essential neuroimaging data and neuropathological changes in PD with cognitive impairment, the amount and topographical distribution of pathological protein aggregates and their pathophysiological relevance. Large-scale clinicopathological correlative studies are warranted to further elucidate the exact neuropathological correlates of cognitive impairment in PD and related synucleinopathies as a basis for early diagnosis and future disease-modifying therapies.

Evaluation of common and rare variants of Alzheimer's disease-causal genes in Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) and Alzheimer's disease (AD) are the most common neurodegenerative diseases in the elderly. Recently, some variants of AD-causal genes (APP, PSEN1, PSEN2) have been reported in PD. In this study, we investigated the association between coding variants of AD-causal genes and PD in a large Chinese population cohort.

METHODS

We performed whole-exome sequencing (WES) on 1,917 patients with early-onset or familial PD and 1,652 controls, and whole-genome sequencing (WGS) on 1,962 sporadic late-onset PD and 1,279 controls. Genetic and phenotypic data were analyzed with regression analyses and the optimized sequence kernel association test. Further validation study was performed by Fisher's exact test.

RESULTS

We found that rs75733498 in the PSEN2 gene was significantly associated with early-onset or familial PD; however, no significant relationship was discovered between rs75733498 and sporadic late-onset PD. The result of the validation study still revealed a significant association between rs75733498 and PD. We observed a suggestive association with APP gene in early-onset or familial PD when considering damaging missense variants alone (p = 0.018) or combined with loss-of-function variants (p = 0.029). Further phenotypic analysis did not demonstrate any significant associations.

CONCLUSION

Our results support a possible genetic contribution of AD-causal genes to PD. These findings warrant further genetic and functional confirmation, and more powerful association studies will better decipher the mechanisms of PD.

Quantifying regional α -synuclein, amyloid β, and tau accumulation in lewy body dementia

OBJECTIVE

Parkinson disease (PD) is defined by the accumulation of misfolded α-synuclein (α-syn) in Lewy bodies and Lewy neurites. It affects multiple cortical and subcortical neuronal populations. The majority of people with PD develop dementia, which is associated with Lewy bodies in neocortex and referred to as Lewy body dementia (LBD). Other neuropathologic changes, including amyloid β (Aβ) and tau accumulation, occur in some LBD cases. We sought to quantify α-syn, Aβ, and tau accumulation in neocortical, limbic, and basal ganglia regions.

METHODS

We isolated insoluble protein from fresh frozen postmortem brain tissue samples for eight brains regions from 15 LBD, seven Alzheimer disease (AD), and six control cases. We measured insoluble α-syn, Aβ, and tau with recently developed sandwich ELISAs.

RESULTS

We detected a wide range of insoluble α-syn accumulation in LBD cases. The majority had substantial α-syn accumulation in most regions, and dementia severity correlated with neocortical α-syn. However, three cases had low neocortical levels that were indistinguishable from controls. Eight LBD cases had substantial Aβ accumulation, although the mean Aβ level in LBD was lower than in AD. The presence of Aβ was associated with greater α-syn accumulation. Tau accumulation accompanied Aβ in only one LBD case.

INTERPRETATION

LBD is associated with insoluble α-syn accumulation in neocortical regions, but the relatively low neocortical levels in some cases suggest that other changes contribute to impaired function, such as loss of neocortical innervation from subcortical regions. The correlation between Aβ and α-syn accumulation suggests a pathophysiologic relationship between these two processes.

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.

Novel Tracers and Radionuclides in PET Imaging

The use of PET imaging agents in oncology, cardiovascular disease, and neurodegenerative disease shows the power of this technique in evaluating the molecular and biological characteristics of numerous diseases. These agents provide crucial information for designing therapeutic strategies for individual patients. Novel PET tracers are in continual development and many have potential use in clinical and research settings. This article discusses the potential applications of tracers in diagnostics, the biological characteristics of diseases, the ability to provide prognostic indicators, and using this information to guide treatment strategies including monitoring treatment efficacy in real time to improve outcomes and survival.

Variability in the type and layer distribution of cortical Aβ pathology in familial Alzheimer's disease

Familial Alzheimer's disease (FAD) is caused by autosomal dominant mutations in the PSEN1, PSEN2 or APP genes, giving rise to considerable clinical and pathological heterogeneity in FAD. Here we investigate variability in clinical data and the type and distribution of Aβ pathologies throughout the cortical layers of different FAD mutation cases. Brain tissue from 20 FAD cases [PSEN1 pre-codon 200 (n = 10), PSEN1 post-codon 200 (n = 6), APP (n = 4)] were investigated. Frontal cortex sections were stained immunohistochemically for Aβ, and Nissl to define the cortical layers. The frequency of different amyloid-beta plaque types was graded for each cortical layer and the severity of cerebral amyloid angiopathy (CAA) was determined in cortical and leptomeningeal blood vessels. Comparisons were made between FAD mutations and APOE4 status, with associations between pathology, clinical and genetic data investigated. In this cohort, possession of an APOE4 allele was associated with increased disease duration but not with age at onset, after adjusting for mutation sub-group and sex. We found Aβ pathology to be heterogeneous between cases although Aβ load was highest in cortical layer 3 for all mutation groups and a higher Aβ load was associated with APOE4. The PSEN1 post-codon 200 group had a higher Aβ load in lower cortical layers, with a small number of this group having increased cotton wool plaque pathology in lower layers. Cotton wool plaque frequency was positively associated with the severity of CAA in the whole cohort and in the PSEN1 post-codon 200 group. Carriers of the same PSEN1 mutation can have differing patterns of Aβ deposition, potentially because of differences in risk factors. Our results highlight possible influences of APOE4 genotype, and PSEN1 mutation type on Aβ deposition, which may have effects on the clinical heterogeneity of FAD.

Temporal trajectory of biofluid markers in Parkinson's disease

Full dynamics of biofluid biomarkers have been unknown in patients with Parkinson’s disease (PD). Using data from 396 PD patients and 182 controls in the Parkinson's Progression Markers Initiative (PPMI) database, we estimated long-term temporal trajectories of CSF α-synuclein (α-syn), amyloid-β (Aβ), total tau (t-tau), phosphorylated tau (p-tau) and serum neurofilament light chain (NfL) by integrating function between the baseline levels and annual changes. At baseline, PD patients showed lower CSF α-syn, Aβ, t-tau and p-tau levels than those of the controls. In all PD patients, CSF α-syn and Aβ decreased in a negative exponential pattern before the onset of motor symptoms, whereas CSF t-tau and p-tau, and serum NfL increased. Patients with cognitive impairment exhibited faster decline of Aβ and α-syn and faster rise of t-tau, p-tau and NfL, when compared to those without. Similarly, low Aβ group showed earlier decline of α-syn, faster rise of t-tau, p-tau and NfL, and faster decline of cognitive performances, when compared to high Aβ group. Our results suggest that longitudinal changes in biomarkers can be influenced by cognitive impairment and Aβ burden at baseline. PD patients with Aβ pathology may be associated with early appearance of α-synuclein pathology, rapid progression of axonal degeneration and neurodegeneration, and consequently greater cognitive decline.

Lewy Body Dementias: A Coin with Two Sides?

Lewy body dementias (LBDs) consist of dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD), which are clinically similar syndromes that share neuropathological findings with widespread cortical Lewy body deposition, often with a variable degree of concomitant Alzheimer pathology. The objective of this article is to provide an overview of the neuropathological and clinical features, current diagnostic criteria, biomarkers, and management of LBD. Literature research was performed using the PubMed database, and the most pertinent articles were read and are discussed in this paper. The diagnostic criteria for DLB have recently been updated, with the addition of indicative and supportive biomarker information. The time interval of dementia onset relative to parkinsonism remains the major distinction between DLB and PDD, underpinning controversy about whether they are the same illness in a different spectrum of the disease or two separate neurodegenerative disorders. The treatment for LBD is only symptomatic, but the expected progression and prognosis differ between the two entities. Diagnosis in prodromal stages should be of the utmost importance, because implementing early treatment might change the course of the illness if disease-modifying therapies are developed in the future. Thus, the identification of novel biomarkers constitutes an area of active research, with a special focus on α-synuclein markers.

Interaction of CSF α-synuclein and amyloid beta in cognition and cortical atrophy

INTRODUCTION

Lewy body-related pathology is commonly observed at autopsy in individuals with dementia, but in vivo biomarkers for α-synucleinopathy are lacking.

METHODS

Baseline cerebrospinal fluid (CSF) biomarkers, polygenic risk score (PRS) for Parkinson's disease (PRS-PD) and Alzheimer's disease (PRS-AD), longitudinal cognitive scores, and magnetic resonance imaging were measured in 217 participants from the Alzheimer's Disease Neuroimaging Initiative. Linear mixed models were used to find the relationship of CSF biomarkers and the PRS with cognition and cortical atrophy.

RESULTS

Higher PRS-PD and PRS-AD were associated with lower CSF α-synuclein and amyloid beta (Aβ), respectively. Lower CSF α-synuclein and the interaction of CSF α-synuclein and Aβ were associated with lower cognitive scores and global cortical atrophy most prominently in the occipital cortex.

DISCUSSION

Lower CSF α-synuclein could be a biomarker for α-synucleinopathy, and the simultaneous evaluation of CSF biomarkers for AD and CSF α-synuclein could reveal the independent and interactive effects on cognition and cortical atrophy.

Neuropathological and Biomarker Findings in Parkinson's Disease and Alzheimer's Disease: From Protein Aggregates to Synaptic Dysfunction

There is mounting evidence that Parkinson’s disease (PD) and Alzheimer’s disease (AD) share neuropathological hallmarks, while similar types of biomarkers are being applied to both. In this review we aimed to explore similarities and differences between PD and AD at both the neuropathology and the biomarker levels, specifically focusing on protein aggregates and synapse dysfunction. Thus, amyloid-β peptide (Aβ) and tau lesions of the Alzheimer-type are common in PD and α-synuclein Lewy-type aggregates are frequent findings in AD. Modern neuropathological techniques adding to routine immunohistochemistry might take further our knowledge of these diseases beyond protein aggregates and down to their presynaptic and postsynaptic terminals, with potential mechanistic and even future therapeutic implications. Translation of neuropathological discoveries to the clinic remains challenging. Cerebrospinal fluid (CSF) and positron emission tomography (PET) markers of Aβ and tau have been shown to be reliable for AD diagnosis. Conversely, CSF markers of α-synuclein have not been that consistent. In terms of PET markers, there is no PET probe available for α-synuclein yet, while the AD PET markers range from consistent evidence of their specificity (amyloid imaging) to greater uncertainty of their reliability due to off-target binding (tau imaging). CSF synaptic markers are attractive, still needing more evidence, which currently suggests those might be non-specific markers of disease progression. It can be summarized that there is neuropathological evidence that protein aggregates of AD and PD are present both at the soma and the synapse. Thus, a number of CSF and PET biomarkers beyond α-synuclein, tau and Aβ might capture these different faces of protein-related neurodegeneration. It remains to be seen what the longitudinal outcomes and the potential value as surrogate markers of these biomarkers are.

The Impact of Amyloid-Beta Positivity with 18F-Florbetaben PET on Neuropsychological Aspects in Parkinson's Disease Dementia

The neuropathology of Parkinson’s disease dementia (PDD) is heterogenous, and the impacts of each pathophysiology and their synergistic effects are not fully understood. The aim of this study was to evaluate the frequency and impacts of co-existence with Alzheimer’s disease in patients with PDD by using 18F-florbetaben PET imaging. A total of 23 patients with PDD participated in the study. All participants underwent 18F-florbetaben PET and completed a standardized neuropsychological battery and assessment of motor symptoms. The results of cognitive tests, neuropsychiatric symptoms, and motor symptoms were analyzed between the positive and negative 18F-florbetaben PET groups. Four patients (17.4%) showed significant amyloid burden. Patients with amyloid-beta showed poorer performance in executive function and more severe neuropsychiatric symptoms than those without amyloid-beta. Motor symptoms assessed by UPDRS part III and the modified H&Y Scale were not different between the two groups. The amyloid PET scan of a patient with PDD can effectively reflect a co-existing Alzheimer’s disease pathology. Amyloid PET scans might be able to help physicians of PDD patients showing rapid progression or severe cognitive/behavioral features.

Differential protein expression in diverse brain areas of Parkinson's and Alzheimer's disease patients

Many hypotheses have been postulated to define the etiology of sporadic Parkinson's and Alzheimer's disorders (PD and AD) but there is no consensus on what causes these devastating age-related diseases. Braak staging of both pathologies helped researchers to better understand the progression and to identify their prodromal and symptomatic phases. Indeed, it is well accepted that Lewy body pathology and neurofibrillary tangles appearance correlates with disease progression and severity of symptoms in PD and AD, respectively. Additionally, several studies in PD and AD models try to disclose which cellular mechanisms are defaulted and trigger the neurodegenerative process that culminates with neuronal death causing PD and AD classical symptomatology. Herein, we determined expression levels of proteins involved in microtubule assembly, autophagic-lysosomal pathway and unfolded protein response in the cortex, hippocampus and SNpc of PD and AD patients, vascular dementia patients and aged-match controls. The differential expression allowed us to determine which pathways are determinant to synaptic dysfunction and to establish a time line for disease progression. Our results allow us to challenge the hypothesis that both PD and AD pathologies are caused by α-synuclein or Aβ pathology propagation throughout the brain in a prion-like manner.

Urate and Homocysteine: Predicting Motor and Cognitive Changes in Newly Diagnosed Parkinson's Disease

BACKGROUND

Urate and homocysteine are potential biomarkers for disease progression in Parkinson's disease (PD). Baseline serum urate concentration has been shown to predict motor but not cognitive decline. The relationship between serum homocysteine concentration and cognitive and motor impairment is unknown.

OBJECTIVES

The aim of this study was to examine the association between baseline serum urate and homocysteine, and prospective measures of disease progression and cognition over 54 months in early PD.

METHODS

154 newly diagnosed PD participants and 99 age-matched controls completed a schedule of assessments at baseline, 18, 36 and 54 months. The Movement Disorders Society Unified Parkinson's Disease Scale Part III (MDS-UPDRS III) was used to assess motor severity. The Montreal Cognitive Assessment (MoCA) was used to assess global cognition. Serum samples drawn at baseline were analysed for urate, homocysteine, red cell folate and vitamin B12 concentrations.

RESULTS

Baseline urate was 331.4±83.8 and 302.7±78.0μmol/L for control and PD participants, respectively (p = 0.015). Baseline homocysteine was 9.6±3.3 and 11.1±3.8μmol/L for controls and PD participants, respectively (p < 0.01). Linear mixed effects modelling showed that lower baseline urate (β= 0.02, p < 0.001) and higher homocysteine (β= 0.29, p < 0.05) predicted decline in motor function. Only higher homocysteine concentrations at baseline, however, predicted declining MoCA scores over 54 months (β= 0.11, p < 0.01).

CONCLUSIONS

Lower serum urate concentration is associated with worsening motor function; while higher homocysteine concentration is associated with change in motor function and cognitive decline. Therefore, urate and homocysteine may be suitable biomarkers for predicting motor and cognitive decline in early PD.

Biological links between traumatic brain injury and Parkinson's disease

Parkinson's Disease (PD) is a progressive neurodegenerative disorder with no cure. Clinical presentation is characterized by postural instability, resting tremors, and gait problems that result from progressive loss of A9 dopaminergic neurons in the substantia nigra pars compacta. Traumatic brain injury (TBI) has been implicated as a risk factor for several neurodegenerative diseases, but the strongest evidence is linked to development of PD. Mild TBI (mTBI), is the most common and is defined by minimal, if any, loss of consciousness and the absence of significant observable damage to the brain tissue. mTBI is responsible for a 56% higher risk of developing PD in U.S. Veterans and the risk increases with severity of injury. While the mounting evidence from human studies suggests a link between TBI and PD, fundamental questions as to whether TBI nucleates PD pathology or accelerates PD pathology in vulnerable populations remains unanswered. Several promising lines of research point to inflammation, metabolic dysregulation, and protein accumulation as potential mechanisms through which TBI can initiate or accelerate PD. Amyloid precursor protein (APP), alpha synuclein (α-syn), hyper-phosphorylated Tau, and TAR DNA-binding protein 43 (TDP-43), are some of the most frequently reported proteins upregulated following a TBI and are also closely linked to PD. Recently, upregulation of Leucine Rich Repeat Kinase 2 (LRRK2), has been found in the brain of mice following a TBI. Subset of Rab proteins were identified as biological substrates of LRRK2, a protein also extensively linked to late onset PD. Inhibition of LRRK2 was found to be neuroprotective in PD and TBI models. The goal of this review is to survey current literature concerning the mechanistic overlap between TBI and PD with a particular focus on inflammation, metabolic dysregulation, and aforementioned proteins. This review will also cover the application of rodent TBI models to further our understanding of the relationship between TBI and PD.

Cognitive training interventions for dementia and mild cognitive impairment in Parkinson's disease

BACKGROUND

Approximately 60% to 80% of people with Parkinson's disease (PD) experience cognitive impairment that impacts on their quality of life. Cognitive decline is a core feature of the disease and can often present before the onset of motor symptoms. Cognitive training may be a useful non-pharmacological intervention that could help to maintain or improve cognition and quality of life for people with PD dementia (PDD) or PD-related mild cognitive impairment (PD-MCI).

OBJECTIVES

To determine whether cognitive training (targeting single or multiple domains) improves cognition in people with PDD and PD-MCI or other clearly defined forms of cognitive impairment in people with PD.

SEARCH METHODS

We searched the Cochrane Dementia and Cognitive Improvement Group Trials Register (8 August 2019), the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, CINAHL, and PsycINFO. We searched reference lists and trial registers, searched relevant reviews in the area and conference proceedings. We also contacted experts for clarifications on data and ongoing trials.

SELECTION CRITERIA

We included randomised controlled trials where the participants had PDD or PD-MCI, and where the intervention was intended to train general or specific areas of cognitive function, targeting either a single domain or multiple domains of cognition, and was compared to a control condition. Multicomponent interventions that also included motor or other elements were considered eligible.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened titles, abstracts, and full-text articles for inclusion in the review. Two review authors also independently undertook extraction of data and assessment of methodological quality. We used GRADE methods to assess the overall quality of the evidence.

MAIN RESULTS

Seven studies with a total of 225 participants met the inclusion criteria for this review. All seven studies compared the effects of a cognitive training intervention to a control intervention at the end of treatment periods lasting four to eight weeks. Six studies included people with PD living in the community. These six studies recruited people with single-domain (executive) or multiple-domain mild cognitive impairment in PD. Four of these studies identified participants with MCI using established diagnostic criteria, and two included both people with PD-MCI and people with PD who were not cognitively impaired. One study recruited people with a diagnosis of PD dementia who were living in long-term care settings. The cognitive training intervention in three studies targeted a single cognitive domain, whilst in four studies multiple domains of cognitive function were targeted. The comparison groups either received no intervention or took part in recreational activities (sports, music, arts), speech or language exercises, computerised motor therapy, or motor rehabilitation combined with recreational activity. We found no clear evidence that cognitive training improved global cognition. Although cognitive training was associated with higher scores on global cognition at the end of treatment, the result was imprecise and not statistically significant (6 trials, 178 participants, standardised mean difference (SMD) 0.28, 95% confidence interval (CI) -0.03 to 0.59; low-certainty evidence). There was no evidence of a difference at the end of treatment between cognitive training and control interventions on executive function (5 trials, 112 participants; SMD 0.10, 95% CI -0.28 to 0.48; low-certainty evidence) or visual processing (3 trials, 64 participants; SMD 0.30, 95% CI -0.21 to 0.81; low-certainty evidence). The evidence favoured the cognitive training group on attention (5 trials, 160 participants; SMD 0.36, 95% CI 0.03 to 0.68; low-certainty evidence) and verbal memory (5 trials, 160 participants; SMD 0.37, 95% CI 0.04 to 0.69; low-certainty evidence), but these effects were less certain in sensitivity analyses that excluded a study in which only a minority of the sample were cognitively impaired. There was no evidence of differences between treatment and control groups in activities of daily living (3 trials, 67 participants; SMD 0.03, 95% CI -0.47 to 0.53; low-certainty evidence) or quality of life (5 trials, 147 participants; SMD -0.01, 95% CI -0.35 to 0.33; low-certainty evidence). There was very little information on adverse events. We considered the certainty of the evidence for all outcomes to be low due to risk of bias in the included studies and imprecision of the results. We identified six ongoing trials recruiting participants with PD-MCI, but no ongoing trials of cognitive training for people with PDD.

AUTHORS' CONCLUSIONS

This review found no evidence that people with PD-MCI or PDD who receive cognitive training for four to eight weeks experience any important cognitive improvements at the end of training. However, this conclusion was based on a small number of studies with few participants, limitations of study design and execution, and imprecise results. There is a need for more robust, adequately powered studies of cognitive training before conclusions can be drawn about the effectiveness of cognitive training for people with PDD and PD-MCI. Studies should use formal criteria to diagnose cognitive impairments, and there is a particular need for more studies testing the efficacy of cognitive training in people with PDD.

Diabetes as a risk factor for Alzheimer's disease in the Middle East and its shared pathological mediators

The incidence of Alzheimer's disease (AD) has risen exponentially worldwide over the past decade. A growing body of research indicates that AD is linked to diabetes mellitus (DM) and suggests that impaired insulin signaling acts as a crucial risk factor in determining the progression of this devastating disease. Many studies suggest people with diabetes, especially type 2 diabetes, are at higher risk of eventually developing Alzheimer's dementia or other dementias. Despite nationwide efforts to increase awareness, the prevalence of Diabetes Mellitus (DM) has risen significantly in the Middle East and North African (MENA) region which might be due to rapid urbanization, lifestyle changes, lack of physical activity and rise in obesity. Growing body of evidence indicates that DM and AD are linked because both conditions involve impaired glucose homeostasis and altered brain function. Current theories and hypothesis clearly implicate that defective insulin signaling in the brain contributes to synaptic dysfunction and cognitive deficits in AD. In the periphery, low-grade chronic inflammation leads to insulin resistance followed by tissue deterioration. Thus insulin resistance acts as a bridge between DM and AD. There is pressing need to understand on how DM increases the risk of AD as well as the underlying mechanisms, due to the projected increase in age related disorders. Here we aim to review the incidence of AD and DM in the Middle East and the possible link between insulin signaling and ApoE carrier status on Aβ aggregation, tau hyperphosphorylation, inflammation, oxidative stress and mitochondrial dysfunction in AD. We also critically reviewed mutation studies in Arab population which might influence DM induced AD. In addition, recent clinical trials and animal studies conducted to evaluate the efficiency of anti-diabetic drugs have been reviewed.

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

Studies have shown an overlap of Aβ 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 Aβ plaques, we injected α-syn preformed fibrils (α-syn mpffs) into mice with abundant Aβ plaques. Aβ 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 Aβ plaques enhance endogenous α-syn seeding and spreading over time post-injection with mpffs.

White matter DNA methylation profiling reveals deregulation of HIP1, LMAN2, MOBP, and other loci in multiple system atrophy

Multiple system atrophy (MSA) is a fatal late-onset neurodegenerative disease. Although presenting with distinct pathological hallmarks, which in MSA consist of glial cytoplasmic inclusions (GCIs) containing fibrillar α-synuclein in oligodendrocytes, both MSA and Parkinson’s disease are α-synucleinopathies. Pathologically, MSA can be categorized into striatonigral degeneration (SND), olivopontocerebellar atrophy (OPCA) or mixed subtypes. Despite extensive research, the regional vulnerability of the brain to MSA pathology remains poorly understood. Genetic, epigenetic and environmental factors have been proposed to explain which brain regions are affected by MSA, and to what extent. Here, we explored for the first time epigenetic changes in post-mortem brain tissue from MSA cases. We conducted a case–control study, and profiled DNA methylation in white mater from three brain regions characterized by severe-to-mild GCIs burden in the MSA mixed subtype (cerebellum, frontal lobe and occipital lobe). Our genome-wide approach using Illumina MethylationEPIC arrays and a powerful cross-region analysis identified 157 CpG sites and 79 genomic regions where DNA methylation was significantly altered in the MSA mixed-subtype cases. HIP1, LMAN2 and MOBP were amongst the most differentially methylated loci. We replicated these findings in an independent cohort and further demonstrated that DNA methylation profiles were perturbed in MSA mixed subtype, and also to variable degrees in the other pathological subtypes (OPCA and SND). Finally, our co-methylation network analysis revealed several molecular signatures (modules) significantly associated with MSA (disease status and pathological subtypes), and with neurodegeneration in the cerebellum. Importantly, the co-methylation module having the strongest association with MSA included a CpG in SNCA, the gene encoding α-synuclein. Altogether, our results provide the first evidence for DNA methylation changes contributing to the molecular processes altered in MSA, some of which are shared with other neurodegenerative diseases, and highlight potential novel routes for diagnosis and therapeutic interventions.

Interactions between Soluble Species of β-Amyloid and α-Synuclein Promote Oligomerization while Inhibiting Fibrillization

Aggregations of β-amyloid (Aβ) and α-synuclein (αS) into oligomeric and fibrillar assemblies are the pathological hallmarks of Alzheimer's and Parkinson's diseases, respectively. Although Aβ and αS affect different regions of the brain and are separated at the cellular level, there is evidence of their eventual interaction in the pathology of both disorders. Characterization of interactions of Aβ and αS at various stages of their aggregation pathways could reveal mechanisms and therapeutic targets for the prevention and cure of these neurodegenerative diseases. In this study, we comprehensively examined the interactions and their molecular manifestations using an array of characterization tools. We show for the first time that αS monomers and oligomers, but not αS fibrils, inhibit Aβ fibrillization while promoting oligomerization of Aβ monomers and stabilizing preformed Aβ oligomers via coassembly, as judged by Thioflavin T fluorescence, transmission electron microscopy, and SDS- and native-PAGE with fluorescently labeled peptides/proteins. In contrast, soluble Aβ species, such as monomers and oligomers, aggregate into fibrils, when incubated alone under the otherwise same condition. Our study provides evidence that the interactions with αS soluble species, responsible for the effects, are mediated primarily by the C-terminus of Aβ, when judged by competitive immunoassays using antibodies recognizing various fragments of Aβ. We also show that the C-terminus of Aβ is a primary site for its interaction with αS fibrils. Collectively, these data demonstrate aggregation state-specific interactions between αS and Aβ and offer insight into a molecular basis of synergistic biological effects between the two polypeptides.

Upcoming diagnostic biomarkers with promising prospects in neurological disorders

An exponential increase in the prevalence of neurological disorders requires substantial steps to be taken for their prevention and treatment. Neurodiagnostic biomarkers are gaining momentum presently in order to enhance the diagnostic accuracy of neurodegenerative disorders, to precisely assess their advancement and to monitor the efficiency of therapeutic interventions. Therefore, the primary focus of the present review is the recent development in this field of neurodiagnostic biomarkers, and the current state of biomarker exploration in the context of various neurodegenerative diseases. This review encompasses an updated and detailed account of specific (β-Amyloid, Tau and Phospho-tau 181, Tar-DNA binding protein-43, Progranulin, a-synuclein, Clusterin, etc) and non-specific (genetic, synaptic, inflammatory and coagulation) neurodiagnostic biomarkers and the recent advances in this growing field. This comprehensive review also suggests the utilization of neurodiagnostic markers in network approaches and personalized medication that will eventually improvise the existing diagnostic and therapeutic complexities of neurodiagnostic biomarkers.

Endogenous mouse huntingtin is highly abundant in cranial nerve nuclei, co-aggregates to Abeta plaques and is induced in reactive astrocytes in a transgenic mouse model of Alzheimer's disease

Pathogenic variants of the huntingtin (HTT) protein and their aggregation have been investigated in great detail in brains of Huntington's disease patients and HTT-transgenic animals. However, little is known about the physiological brain region- and cell type-specific HTT expression pattern in wild type mice and a potential recruitment of endogenous HTT to other pathogenic protein aggregates such as amyloid plaques in cross seeding events. Employing a monoclonal anti-HTT antibody directed against the HTT mid-region and using brain tissue of three different mouse strains, we detected prominent immunoreactivity in a number of brain areas, particularly in cholinergic cranial nerve nuclei, while ubiquitous neuronal staining appeared faint. The region-specific distribution of endogenous HTT was found to be comparable in wild type rat and hamster brain. In human amyloid precursor protein transgenic Tg2576 mice with amyloid plaque pathology, similar neuronal HTT expression patterns and a distinct association of HTT with Abeta plaques were revealed by immunohistochemical double labelling. Additionally, the localization of HTT in reactive astrocytes was demonstrated for the first time in a transgenic Alzheimer's disease animal model. Both, plaque association of HTT and occurrence in astrocytes appeared to be age-dependent. Astrocytic HTT gene and protein expression was confirmed in primary cultures by RT-qPCR and by immunocytochemistry. We provide the first detailed analysis of physiological HTT expression in rodent brain and, under pathological conditions, demonstrate HTT aggregation in proximity to Abeta plaques and Abeta-induced astrocytic expression of endogenous HTT in Tg2576 mice.

Review: Clinical, neuropathological and genetic features of Lewy body dementias

Lewy body dementias are the second most common neurodegenerative dementias after Alzheimer's disease and include dementia with Lewy bodies and Parkinson's disease dementia. They share similar clinical and neuropathological features but differ in the time of dementia and parkinsonism onset. Although Lewy bodies are their main pathological hallmark, several studies have shown the emerging importance of Alzheimer's disease pathology. Clinical amyloid-β imaging using Pittsburgh Compound B (PiB) supports neuropathological studies which found that amyloid-β pathology is more common in dementia with Lewy bodies than in Parkinson's disease dementia. Nevertheless, other co-occurring pathologies, such as cerebral amyloid angiopathy, TDP-43 pathology and synaptic pathology may also influence the development of neurodegeneration and dementia. Recent genetic studies demonstrated an important role of APOE genotype and other genes such as GBA and SNCA which seem to be involved in the pathophysiology of Lewy body dementias. The aim of this article is to review the main clinical, neuropathological and genetic aspects of dementia with Lewy bodies and Parkinson's disease dementia. This is particularly relevant as future management for these two conditions may differ.

Beta Amyloid Deposition Is Not Associated With Cognitive Impairment in Parkinson's Disease

The extent to which Alzheimer neuropathology, particularly the accumulation of misfolded beta-amyloid, contributes to cognitive decline and dementia in Parkinson's disease (PD) is unresolved. Here, we used Florbetaben PET imaging to test for any association between cerebral amyloid deposition and cognitive impairment in PD, in a sample enriched for cases with mild cognitive impairment. This cross-sectional study used Movement Disorders Society level II criteria to classify 115 participants with PD as having normal cognition (PDN, n = 23), mild cognitive impairment (PD-MCI, n = 76), or dementia (PDD, n = 16). We acquired 18F-Florbetaben (FBB) amyloid PET and structural MRI. Amyloid deposition was assessed between the three cognitive groups, and also across the whole sample using continuous measures of both global cognitive status and average performance in memory domain tests. Outcomes were cortical FBB uptake, expressed in centiloids and as standardized uptake value ratios (SUVR) using the Centiloid Project whole cerebellum region as a reference, and regional SUVR measurements. FBB binding was higher in PDD, but this difference did not survive adjustment for the older age of the PDD group. We established a suitable centiloid cut-off for amyloid positivity in Parkinson's disease (31.3), but there was no association of FBB binding with global cognitive or memory scores. The failure to find an association between PET amyloid deposition and cognitive impairment in a moderately large sample, particularly given that it was enriched with PD-MCI patients at risk of dementia, suggests that amyloid pathology is not the primary driver of cognitive impairment and dementia in most patients with PD.

Predicting cognitive decline with non-clinical markers in Parkinson's disease (PRECODE-2)

OBJECTIVES

To investigate whether baseline [¹²³I]FP-CIT SPECT and CSF markers can predict cognitive impairment (CI) in PD patients, and provide a profile of those most at risk.

METHODS

262 de novo PD patients from the Parkinson's Progression Markers Initiative database were stratified into two CI groups at the 36-month follow-up: MoCA-defined diagnosis: PD patients who had a MoCA score < 26; neuropsychological test-defined diagnosis: PD patients with MoCA-defined diagnosis and at least two test scores (of six; irrespective of test domain) greater than 1.5 standard deviation below the mean score in healthy controls. Predictive variables of CI were divided into deciles, providing us with ideal cutoff values for each variable.

RESULTS

At the 36-month follow-up, 108/262 (41.2%) PD patients had CI as defined by the MoCA, of which 40/108 (37.0%) had neuropsychological test-defined CI. Baseline CSF Aβ42 (hazard ratio [HR]: 0.996, confidence interval [CI]: 0.992-0.999, p = 0.025), CSF total tau ([HR]: 1.023, [CI]: 1.002-1.044, p = 0.031) and caudate [¹²³I]FP-CIT SPECT uptake ([HR]: 0.332, [CI]: 0.115-0.960, p = 0.042) were predictors of CI. Patients with reduced CSF Aβ42 (< 384.6 pg/mL), increased CSF total tau (> 45.0 pg/mL) and reduced caudate [¹²³I]FP-CIT SPECT uptake (< 1.82) had a 65% risk of developing CI at 36-month follow-up.

CONCLUSION

We report a characteristic profile (reduced CSF Aβ42, increased CSF total tau and reduced caudate [¹²³I]FP-CIT SPECT uptake) that enables identification of early PD patients at risk of developing CI. These findings confirm previous reports of low CSF Aβ42, elevated CSF total tau and reduced dopaminergic integrity being associated with cognitive decline in PD.

Relationship Between Tau, β Amyloid and α-Synuclein Pathologies

It is becoming increasing clear that multiple pathological lesions co-exist in the brains of the demented and non-demented elderly, and with putative interactions revealed at the molecular level in addition to the cumulative effects on brain damage, mounting evidence suggests manifestation of multiple protein aggregates will have implications for the clinical course of many neurodegenerative diseases associated with dementia. In this section we will discuss how the presence of multiple pathological lesions can affect the pathological and clinical phenotype of neurodegenerative disorders.

The Influence of Body Mass Index at Diagnosis on Cognitive Decline in Parkinson's Disease

BACKGROUND AND PURPOSE

Associations between alterations in body mass index (BMI) and cognitive function have been reported in Parkinson's disease (PD). We investigated whether the BMI at a PD diagnosis is associated with cognitive decline and the future development of dementia.

METHODS

We recruited 70 patients with de novo PD who underwent neuropsychological testing every 3 years and were followed up for more than 6 years. We classified patients into the following three groups based on their BMI at the diagnosis: under-/normal weight (n=21), overweight (n=22), and obese (n=27). We evaluated differences in the rate of cognitive decline over time among the groups using linear mixed models and the conversion rate to dementia using survival analysis.

RESULTS

The obese patients with PD showed a slower deterioration of global cognitive function as well as language and memory functions than did the under-/normal-weight group during the 6-year follow-up. The three BMI groups showed different rates of conversion to dementia (log-rank test: p=0.026). The combined overweight and obese group showed a lower risk of developing dementia compared with the under-/normal-weight group (hazard ratio= 0.36, 95% CI=0.12-0.82, p=0.046).

CONCLUSIONS

We have demonstrated that a higher-than-normal BMI at the time of a PD diagnosis has a protective effect against the deterioration of cognitive function and the conversion to dementia.

Hiding in plain sight: a brain lesion in a patient with a history of colon and breast cancer

We present a case of a 76-year-old woman who was admitted to our hospital with a low Glasgow Coma Scale score. She had a medical history of breast and colon cancer. The CT scan showed possible diagnosis of brain metastasis. However, the MRI scan showed this to be a completely different diagnosis.

Fluid-based proteomics targeted on pathophysiological processes and pathologies in neurodegenerative diseases

Neurodegenerative dementias constitute a broad group of diseases in which abnormally folded proteins accumulate in specific brain regions and result in tissue reactions that eventually cause neuronal dysfunction and degeneration. Depending on where in the brain this happens, symptoms appear which may be used to classify the disorders on clinical grounds. However, brain changes in neurodegenerative dementias start to accumulate many years prior to symptom onset and there is a poor correlation between the clinical picture and what pathology that is the most likely to cause it. Thus, novel drug candidates having disease-modifying effects that is targeting the underlying pathology and changes the course of the disease needs to be defined using objective biomarker-based measures since the clinical symptoms are often non-specific and overlap between different disorders. Furthermore, the treatment should ideally be initiated as soon as symptoms are evident or when biomarkers confirm an underlying pathology (pre-clinical phase of the disease) to reduce irreversible damage to, for example, neurons, synapses and axons. Clinical trials in the pre-clinical phase bring a greater importance to biomarkers since by definition the clinical effects are difficult or slow to discern in a population that is not yet clinically affected. Here, we discuss neuropathological changes that may underlie neurodegenerative dementias, including how they can be detected and quantified using currently available biofluid-based biomarkers and how more of them could be identified using targeted proteomics approaches. This article is part of the special issue "Proteomics".