α-Synuclein and tau concentrations in cerebrospinal fluid of patients presenting with parkinsonism: a cohort study

Cerebrospinal fluid amyloid β and tau in LRRK2 mutation carriers

OBJECTIVE

The goal of the current investigation was to examine a cohort of symptomatic and asymptomatic LRRK2 mutation carriers, in order to address whether the reported alterations in amyloid β (Aβ) and tau species in the CSF of patients with sporadic Parkinson disease (PD) are a part of PD pathogenesis, the aging process, or a comorbid disease in patients with PD, and to explore the possibility of Aβ and tau as markers of early or presymptomatic PD.

METHODS

CSF Aβ42, total tau, and phosphorylated tau were measured with Luminex assays in 26 LRRK2 mutation carriers, who were either asymptomatic (n = 18) or had a phenotype resembling sporadic PD (n = 8). All patients also underwent PET scans with 18F-6-fluoro-l-dopa (FD), 11C-(±)-α-dihydrotetrabenazine (DTBZ), and 11C-d-threo-methylphenidate (MP) to measure dopaminergic function in the striatum. The levels of CSF markers were then compared to each PET measurement.

RESULTS

Reduced CSF Aβ42 and tau levels correlated with lower striatal dopaminergic function as determined by all 3 PET tracers, with a significant association between Aβ42 and FD uptake. When cases were restricted to carriers of the G2019S mutation, the most common LRRK2 variant in our cohort, significant correlations were also observed for tau.

CONCLUSIONS

The disposition of Aβ and tau is likely important in both LRRK2-related and sporadic PD, even during early phases of the disease. A better understanding of their production, aggregation, and degradation, including changes in their CSF levels, may provide insights into the pathogenesis of PD and the potential utility of these proteins as biomarkers.

Interaction between α-synuclein and other proteins in neurodegenerative disorders

Protein aggregation is a common characteristic of many neurodegenerative disorders, and the interaction between pathological/toxic proteins to cause neurodegeneration is a hot topic of current neuroscience research. Despite clinical, genetic, and experimental differences, evidence increasingly indicates considerable overlap between synucleinopathies and tauopathies or other protein-misfolding diseases. Inclusions, characteristics of these disorders, also occurring in other neurodegenerative diseases, suggest interactions of pathological proteins engaging common downstream pathways. Novel findings that have shifted our understanding in the role of pathologic proteins in the pathogenesis of Parkinson and Alzheimer diseases have confirmed correlations/overlaps between these and other neurodegenerative disorders. The synergistic effects of α-synuclein, hyperphosphorylated tau, amyloid-β, and other pathologic proteins, and the underlying molecular pathogenic mechanisms, including induction and spread of protein aggregates, are critically reviewed, suggesting a dualism or triad of neurodegeneration in protein-misfolding disorders, although the etiology of most of these processes is still mysterious.

Role of cerebrospinal fluid and plasma biomarkers in the diagnosis of neurodegenerative disorders and mild cognitive impairment

Biomarkers are one type of laboratory testing being developed in response to the therapeutic imperative for diseases that cause cognitive impairment and dementia. The role of biomarkers is already transforming the organization and conduct of clinical trials, and if successful will likely contribute in the future to the medical management of patients with these diseases. Despite the obvious utility of practicality of blood- or urine-based biomarkers, so far results from these fluid compartments have not been reproducible. In contrast, substantial progress has been made in cerebrospinal fluid biomarkers. Here we review the stages of cerebrospinal fluid biomarker development for several common and unusual diseases that cause cognitive impairment and dementia, stressing the distinction between diagnostic and mechanistic biomarkers. Future applications will likely focus on diagnosis of latent or early-stage disease, assessment of disease progression, mechanism of injury, and response to experimental therapeutics.

Biomarkers of Parkinson's disease and Dementia with Lewy bodies

Parkinson's disease (PD) and Dementia with Lewy bodies (DLB) are progressive and disabling neurodegenerative disorders, in which signs and symptoms overlap with each other and with other neurodegenerative conditions. Currently, diagnosis, measurement of progression, and response to therapeutic intervention rely upon clinical observation. However, there remains a critical need for validated biomarkers in each of these areas. A definitive diagnostic test would improve clinical management and enrollment into clinical trials. An objective measure of progression is vitally important in identifying neuroprotective interventions. Biomarkers may also provide insight into pathogenesis, and might therefore suggest possible novel targets for therapeutic intervention. In addition, certain biomarkers might be of use in monitoring the biochemical and physiological effects of therapeutic interventions. Development of diagnostic biomarkers has focused until recently upon imaging techniques based upon measuring loss of dopamine neurons. Additionally, advances in understanding the genetic contribution to neurodegenerative disorders, in particular in PD, have identified multiple causative genes and risk factors that in some cases may help estimate PD risk. However, recent availability of increasingly sophisticated bioinformatics technology has rendered development of fluid biomarkers feasible, opening the possibility of generally accessible blood or cerebrospinal fluid (CSF) tests that could impact upon diagnosis, management, and research in PD, PDD, and DLB.

Glial dysfunction in the pathogenesis of α-synucleinopathies: emerging concepts

Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) are adult onset neurodegenerative disorders characterised by prominent intracellular α-synuclein aggregates (α-synucleinopathies). The glial contribution to neurodegeneration in α-synucleinopathies was largely underestimated until recently. However, brains of PD and DLB patients exhibit not only neuronal inclusions such as Lewy bodies or Lewy neurites but also glial α-synuclein aggregates. Accumulating experimental evidence in PD models suggests that astrogliosis and microgliosis act as important mediators of neurodegeneration playing a pivotal role in both disease initiation and progression. In MSA, oligodendrocytes are intriguingly affected by aberrant cytoplasmic accumulation of α-synuclein (glial cytoplasmic inclusions, Papp-Lantos bodies). Converging evidence from human postmortem studies and transgenic MSA models suggests that oligodendroglial dysfunction both triggers and exacerbates neuronal degeneration. This review summarises the wide range of responsibilities of astroglia, microglia and oligodendroglia in the healthy brain and the changes in glial function associated with ageing. We then provide a critical analysis of the role of glia in α-synucleinopathies including putative mechanisms promoting a chronically diseased glial microenvironment which can lead to detrimental neuronal changes, including cell loss. Finally, major therapeutic strategies targeting glial pathology in α-synucleinopathies as well as current pitfalls for disease-modification in clinical trials are discussed.

Enzyme-linked immunosorbent assays for α-synuclein with species and multimeric state specificities

Abnormal intracellular deposition of aggregated α-synuclein is the characteristic feature of a number of neurological disorders, including Parkinson's disease (PD). Although α-synuclein is typically known as a cytosolic protein, a small amount is secreted by exocytosis in both monomeric and aggregated forms. The extracellular forms of α-synuclein in human body fluids, such as cerebrospinal fluid (CSF) and blood plasma, might be a diagnostic target for PD and related diseases. Here, we characterized a new set of monoclonal antibodies against α-synuclein, and using different combinations of antibodies, we established ELISA systems to specifically detect human α-synuclein, mouse and human α-synuclein together, and multimeric forms of α-synuclein in biological samples. By employing the Tyramide signal amplification method, the sensitivity of the assay was significantly improved to detect a concentration as low as ∼12.5 pg/ml. These assays might be useful tools for quantitative analysis of α-synuclein in various forms and with high sensitivity in diverse biological samples.

Parkinson disease: PD biomarkers-use of α-synuclein reaches new levels

Biomarker development is important to the therapeutic imperative for neurodegenerative diseases, as biomarkers hold transformative promise for the design and conduct of clinical trials and, ultimately, for medical management of these diseases. Some of this promise is now being realized in Alzheimer disease, and progress in Parkinson disease is accelerating.

Biomarker-based dissection of neurodegenerative diseases

The diagnosis of neurodegenerative diseases within neurology and psychiatry are hampered by the difficulty in getting biopsies and thereby validating the diagnosis by pathological findings. Biomarkers for other types of disease have been readily adopted into the clinical practice where for instance troponins are standard tests when myocardial infarction is suspected. However, the use of biomarkers for neurodegeneration has not been fully incorporated into the clinical routine. With the development of cerebrospinal fluid (CSF) biomarkers that reflect pathological events within the central nervous system (CNS), important clinical diagnostic tools are becoming available. This review summarizes the most promising biomarker candidates that may be used to monitor different types of neurodegeneration and protein inclusions, as well as different types of metabolic changes, in living patients in relation to the clinical phenotype and disease progression over time. Our aim is to provide the reader with an updated lexicon on currently available biomarker candidates, how far they have come in development and how well they reflect pathogenic processes in different neurodegenerative diseases. Biomarkers for specific pathogenetic processes would also be valuable tools both to study disease pathogenesis directly in patients and to identify and monitor the effect of novel treatment strategies.