Nour K. Majbour

Levels of cerebrospinal fluid α-synuclein oligomers are increased in Parkinson’s disease with dementia and dementia with Lewy bodies compared to Alzheimer’s disease

IntroductionThe objective was to study whether α-synuclein oligomers are altered in the cerebrospinal fluid (CSF) of patients with dementia, including Parkinson disease with dementia (PDD), dementia with Lewy bodies (DLB), and Alzheimer disease (AD), compared with age-matched controls.MethodsIn total, 247 CSF samples were assessed in this study, including 71 patients with DLB, 30 patients with PDD, 48 patients with AD, and 98 healthy age-matched controls. Both total and oligomeric α-synuclein levels were evaluated by using well-established immunoassays.ResultsThe levels of α-synuclein oligomers in the CSF were increased in patients with PDD compared with the controls (P < 0.05), but not in patients with DLB compared with controls. Interestingly, the levels of α-synuclein oligomers in the CSF were also significantly higher in patients with PDD (P < 0.01) and DLB (P < 0.05) compared with patients with AD. The levels of CSF α-synuclein oligomers and the ratio of oligomeric/total-α-synuclein could distinguish DLB or PDD patients from AD patients, with areas under the curves (AUCs) of 0.64 and 0.75, respectively. In addition, total-α-synuclein alone could distinguish DLB or PDD patients from AD patients, with an AUC of 0.80.ConclusionsThe levels of α-synuclein oligomers were increased in the CSF from α-synucleinopathy patients with dementia compared with AD cases.

Differential role of CSF alpha-synuclein species, tau, and Aβ42 in Parkinson's disease

There is a great interest in developing cerebrospinal fluid (CSF) biomarkers for diagnosis and prognosis of Parkinsons disease (PD). CSF alpha synuclein (α-syn) species, namely total and oligomeric α-syn (t-α-syn and o-α-syn), have shown to be of help for PD diagnosis. Preliminary evidences show that the combination of CSF t-α-syn and classical Alzheimers disease (AD) biomarkers—β-amyloid 1–42 (Aβ42), total tau (t-tau), phosphorylated tau (p-tau)—differentiate PD patients from controls, and that reduced levels of Aβ42 represent a predictive factor for development of cognitive deterioration in PD. In this prospective study carried out in 44 PD patients and 25 neurological controls we wanted to verify whether the combination of CSF α-synuclein species—t-α-syn and o-α-syn—and classical AD biomarkers may help in differentiating PD from neurological controls, and if these biomarkers may predict cognitive decline. The median of follow-up duration was 3 years (range: 2–6 years). Mini Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) were used for monitoring cognitive changes along time, being administered once a year. Oligo/total α-syn ratio (o/t-α-syn ratio) confirmed its diagnostic value, significantly contributing to the discrimination of PD from neurological controls. A greater diagnostic accuracy was reached when combining o/t-α-syn and Aβ42/tau ratios (Sens = 0.70, Spec = 0.84, AUC = 0.82; PPV = 0.89, NPV = 0.62, LR+ = 4.40, DOR = 12.52). Low CSF Aβ42 level was associated with a higher rate of MMSE and MoCA decline, confirming its role as independent predictive factor for cognitive decline in PD. None of the other biomarkers assessed (t-tau, p-tau, t-α-syn and o-α-syn) showed to have prognostic value. We conclude that combination of CSF o/t-α-syn and Aβ42/tau ratios improve the diagnostic accuracy of PD. PD patients showing low CSF Aβ42 levels at baseline are more prone to develop cognitive decline.

Oligomeric and phosphorylated alpha-synuclein as potential CSF biomarkers for Parkinson’s disease

BackgroundDespite decades of intensive research, to date, there is no accepted diagnosis for Parkinson’s disease (PD) based on biochemical analysis of blood or CSF. However, neurodegeneration in the brains of PD patients begins several years before the manifestation of the clinical symptoms, pointing to serious flaw/limitations in this approach.ResultsTo explore the potential use of alpha-synuclein (α-syn) species as candidate biomarkers for PD, we generated specific antibodies directed against wide array of α-syn species, namely total-, oligomeric- and phosphorylated-Ser129-α-syn (t-, o- and p-S129-α-syn). Next we sought to employ our antibodies to develop highly specific ELISA assays to quantify α-syn species in biological samples. Finally we verified the usefulness of our assays in CSF samples from 46 PD patients and 48 age-matched healthy controls. We also assessed the discriminating power of combining multiple CSF α-syn species with classical Alzheimer’s disease biomarkers. The combination of CSF o-/t-α-syn, p-S129-α-syn and p-tau provided the best fitting predictive model for discriminating PD patients from controls. Moreover, CSF o-α-syn levels correlated significantly with the severity of PD motor symptoms (r = -0.37).ConclusionOur new ELISA assays can serve as research tools to address the unmet need for reliable CSF biomarkers for PD and related disorders.

Generation and characterization of novel conformation-specific monoclonal antibodies for α-synuclein pathology

α-Synuclein (α-syn), a small protein that has the intrinsic propensity to aggregate, is implicated in several neurodegenerative diseases including Parkinsons disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA), which are collectively known as synucleinopathies. Genetic, pathological, biochemical, and animal modeling studies provided compelling evidence that α-syn aggregation plays a key role in the pathogenesis of PD and related synucleinopathies. It is therefore of utmost importance to develop reliable tools that can detect the aggregated forms of α-syn. We describe here the generation and characterization of six novel conformation-specific monoclonal antibodies that recognize specifically α-syn aggregates but not the soluble, monomeric form of the protein. The antibodies described herein did not recognize monomers or fibrils generated from other amyloidogenic proteins including β-syn, γ-syn, β-amyloid, tau protein, islet amyloid polypeptide and ABri. Interestingly, the antibodies did not react to overlapping linear peptides spanning the entire sequence of α-syn, confirming further that they only detect α-syn aggregates. In immunohistochemical studies, the new conformation-specific monoclonal antibodies showed underappreciated small micro-aggregates and very thin neurites in PD and DLB cases that were not observed with generic pan antibodies that recognize linear epitope. Furthermore, employing one of our conformation-specific antibodies in a sandwich based ELISA, we observed an increase in levels of α-syn oligomers in brain lysates from DLB compared to Alzheimers disease and control samples. Therefore, the conformation-specific antibodies portrayed herein represent useful tools for research, biomarkers development, diagnosis and even immunotherapy for PD and related pathologies.

Brain propagation of transduced α-synuclein involves non-fibrillar protein species and is enhanced in α-synuclein null mice

Aggregation and neuron-to-neuron transmission are attributes of α-synuclein relevant to its pathogenetic role in human synucleinopathies such as Parkinsons disease. Intraparenchymal injections of fibrillar α-synuclein trigger widespread propagation of amyloidogenic protein species via mechanisms that require expression of endogenous α-synuclein and, possibly, its structural corruption by misfolded conformers acting as pathological seeds. Here we describe another paradigm of long-distance brain diffusion of α-synuclein that involves inter-neuronal transfer of monomeric and/or oligomeric species and is independent of recruitment of the endogenous protein. Targeted expression of human α-synuclein was induced in the mouse medulla oblongata through an injection of viral vectors into the vagus nerve. Enhanced levels of intra-neuronal α-synuclein were sufficient to initiate its caudo-rostral diffusion that likely involved at least one synaptic transfer and progressively reached specific brain regions such as the locus coeruleus, dorsal raphae and amygdala in the pons, midbrain and forebrain. Transfer of human α-synuclein was compared in two separate lines of α-synuclein-deficient mice versus their respective wild-type controls and, interestingly, lack of endogenous α-synuclein expression did not counteract diffusion but actually resulted in a more pronounced and advanced propagation of exogenous α-synuclein. Self-interaction of adjacent molecules of human α-synuclein was detected in both wild-type and mutant mice. In the former, interaction of human α-synuclein with mouse α-synuclein was also observed and might have contributed to differences in protein transmission. In wild-type and α-synuclein-deficient mice, accumulation of human α-synuclein within recipient axons in the pons, midbrain and forebrain caused morphological evidence of neuritic pathology. Tissue sections from the medulla oblongata and pons were stained with different antibodies recognizing oligomeric, fibrillar and/or total (monomeric and aggregated) α-synuclein. Following viral vector transduction, monomeric, oligomeric and fibrillar protein was detected within donor neurons in the medulla oblongata. In contrast, recipient axons in the pons were devoid of immunoreactivity for fibrillar α-synuclein, indicating that non-fibrillar forms of α-synuclein were primarily transferred from one neuron to the other, diffused within the brain and led to initial neuronal injury. This study elucidates a paradigm of α-synuclein propagation that may play a particularly important role under pathophysiological conditions associated with enhanced α-synuclein expression. Rapid long-distance diffusion and accumulation of monomeric and oligomeric α-synuclein does not necessarily involve pathological seeding but could still result in a significant neuronal burden during the pathogenesis of neurodegenerative diseases.

Elevated levels of cerebrospinal fluid α-synuclein oligomers in healthy asymptomatic LRRK2 mutation carriers

Mutations in the leucine-rich repeat kinase 2 gene are the most common cause of autosomal dominant Parkinson’s disease (PD). To assess the cerebrospinal fluid (CSF) levels of α-synuclein oligomers in symptomatic and asymptomatic leucine-rich repeat kinase 2 mutation carriers, we used enzyme-linked immunosorbent assays (ELISA) to investigate total and oligomeric forms of α-synuclein in CSF samples. The CSF samples were collected from 33 Norwegian individuals with leucine-rich repeat kinase 2 mutations: 13 patients were clinically diagnosed with PD and 20 patients were healthy, asymptomatic leucine-rich repeat kinase 2 mutation carriers. We also included 35 patients with sporadic PD (sPD) and 42 age-matched healthy controls. Levels of CSF α-synuclein oligomers were significantly elevated in healthy asymptomatic individuals carrying leucine-rich repeat kinase 2 mutations (n = 20; P < 0.0079) and in sPD group (n = 35; P < 0.003) relative to healthy controls. Increased α-synuclein oligomers in asymptomatic leucine-rich repeat kinase 2 mutation carriers showed a sensitivity of 63.0% and a specificity of 74.0%, with an area under the curve of 0.66, and a sensitivity of 65.0% and a specificity of 83.0%, with an area under the curve of 0.74 for sPD cases. An inverse correlation between CSF levels of α- synuclein oligomers and disease severity and duration was observed. Our study suggests that quantification of α-synuclein oligomers in CSF has potential value as a tool for PD diagnosis and presymptomatic screening of high-risk individuals.

Development of Nonviral Vectors Targeting the Brain as a Therapeutic Approach For Parkinson's Disease and Other Brain Disorders

Parkinsons disease (PD) is a debilitating neurodegenerative disease characterized by tremor, rigidity, bradykinesia, and postural instability, for which there is no effective treatment available till date. Here, we report the development of nonviral vectors specific for neuronal cells that can deliver short interfering RNA (siRNA) against the α-synuclein gene (SNCA), and prevent PD-like symptoms both in vitro and in vivo. These vectors not only help siRNA duplexes cross the blood-brain barrier in mice, but also stabilize these siRNAs leading to a sustainable 60-90% knockdown of α-synuclein protein. Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine rapidly develop PD-like symptoms which were significantly alleviated when SNCA was knocked down using our vectors. Together, our data not only confirm the central role of α-synuclein in the onset of PD, but also provide a proof of principle that these nonviral vectors can be used as novel tools to design effective strategies to combat central nervous system diseases.

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

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

PERFORMANCE EVALUATION OF NEW ABSORBANCE-BASED ELISAS FOR MEASURING DIFFERENT ALPHA-SYNUCLEIN (A-SYN) SPECIES IN CSF AND PLASMA

75% sensitivity and 79% specificity in accurately categorizing an older adult’s Ab+/status (positive predictive value1⁄461%, negative predictive value1⁄487%, Diagnostic Odds Ratio (DOR)1⁄411, accuracy1⁄477%; Figure 2-3). Providing context, this discrimination accuracy mirrored that observed with APOE genotype (DOR1⁄412, accuracy1⁄477%), a known Ab risk factor. Importantly, <1Hz NREM SWA accurately predicted Ab+/status even when controlling for age and gender (logistic regression; P1⁄40.012). Moreover, lower<1Hz NREM SWA increased Ab+ risk by 30%, while higher <1Hz NREM SWA reduced risk by 27%, also similar to APOE genotype. Finally,<1Hz NREM SWA not only predicted the severity of Ab burden at baseline (r1⁄4-0.69, P1⁄40.009), but also 3-5 years later (r1⁄4-0.68, P1⁄40.011), with a trend for predicting the 3-5 year change in Ab accumulation (r1⁄4-0.41, one-tailed P1⁄40.084; Figure 4). Conclusions: These data support the potential utility of <1Hz NREM SWA as a novel surrogate biomarker of Ab pathology, one that is non-invasive, safe, inexpensive, and suitable for ADrisk screening within the broader community setting, even before onset of clinical symptoms. Furthermore, this AD biomarker is predictive, heralding Ab burden years later, underscoring the benefit of greater clinician sensitivity to sleep disruption as a predisposing AD-risk factor. While clinically promising, improved precision is needed, potentially including additional sleep measures and/or other non-invasive biomarker candidates.

ALPHA-SYNUCLEIN SPECIES AS POTENTIAL CSF BIOMARKERS FOR DEMENTIA WITH LEWY BODIES

Background: The discovery of alpha-synuclein (a-syn) as a major component of Lewy bodies lead to the idea that a-syn could be a potential cerebrospinal fluid (CSF) biomarker for dementia with Lewy bodies (DLB). So far, studies measuring CSF total a-syn have yielded conflicting results. However, recent studies showed that a combination of CSF a-syn species may improve the diagnostic value of a-syn in synucleinopathies. In this study we assessed the diagnostic value of different CSF a-syn species (total-, oligomericand pS129-a-syn) for DLB. Methods:We measured the levels of CSF a-syn species in DLB (n=42), Alzheimers disease (AD) (n=39), Parkinsons disease (PD) (n=46), subjective cognitive decline (SCD) (n=31) and healthy controls (HC) (n=48) using newly developed ELISAs (Majbour et al., 2016). Linear regression analysis corrected for age and gender were performed to assess differences in a-syn levels between diagnostic groups. In addition, we used receiver operation characteristic (ROC) analysis and logistic regression analysis to determine the diagnostic accuracy between DLB and AD and between DLB and controls (SCD + HC) of (the combination of) the a-syn biomarker(s). Results: The levels of total- a-syn in CSF were decreased in DLB (1.48+/-0.08ng/ml) and PD (1.41+/-0.05ng/ml) compared to AD (2.14+/-0.14ng/ml, p