Publications

BACKGROUND: Diffusible Aβ oligomers (oAβ) confer cytotoxicity in Alzheimer's disease. The dynamic complexity of this hydrophobic analyte means few immunoassays exist to quantify oAβ in CSF and plasma.

METHODS: We characterized antibody 71A1 to a cyclized dimer of Aβ9-18 for oAβ preference over monomers by surface plasmon resonance. We improved an earlier bead-based immunoassay by using 71A1 streptavidin plates for capture and N-terminal antibody 3D6 for detection. Numerous controls systematically validated accuracy.

RESULTS: 71A1 showed highly selective binding kinetics to Aβ oligomers over monomers. It enriched bioactive oligomers from AD brain that altered neuronal excitatory currents and calcium transients. 71A1/3D6 immunoassay exhibited specificity and reproducibility in human biofluids. CSF oAβ levels correlated positively with CSF tau and phosphorylated-tau-181. APP and PS1 FAD mutations increased oAβ levels in human neuronal media.

CONCLUSIONS: CSF oAβ levels rise in concert with rising tau levels. A new plate-based ELISA offers improved consistency, less sample volume, and lower cost, thus better suited to quantify this challenging analyte.

BACKGROUND: Parkinson's disease (PD) is a complex multifactorial disorder with a genetic component in about 15% of cases. Multiplications and point mutations in SNCA gene, encoding α-synuclein (aSyn), are linked to rare familial forms of PD.

OBJECTIVE: Our goal was to assess the clinical presentation and the biological effects of a novel K58N aSyn mutation identified in a patient with PD.

METHODS: We describe the clinical presentation associated with the novel mutation, together with genetic testing through whole exome sequencing (WES). Furthermore, we conducted extensive biophysical and cellular assays to assess the functional consequences of this novel variant.

RESULTS: The patient exhibited typical features of sporadic PD with early onset and a benign disease course. WES showed a novel heterozygous missense variant in SNCA (NM_000345.4, c.174G>C; p.K58N). A positive family history of PD was evident, because both a parent and a grandparent had been diagnosed with PD but were deceased. The patient underwent deep brain stimulation surgery 13 years postdiagnosis, showing stable, long-term improvements in motor symptoms. Biophysical studies demonstrated K58N substitution causes local structural effects, disrupts membrane binding, and enhances aSyn in vitro aggregation. In cellular systems, K58N aSyn produces fewer inclusions per cell and does not form condensates. The variant increases aSyn cytoplasmic distribution and displays aberrant activity-dependent dynamic serine-129 phosphorylation.

CONCLUSIONS: The clinical presentation associated with the novel K58N aSyn mutation suggests a relatively benign PD course consistent with the phenotypic spectrum of idiopathic PD. Overall, our molecular studies provide novel insight into the biology and pathobiology of aSyn. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Alpha-synuclein (αSyn) inclusions, termed Lewy bodies, are the characteristic neuropathological feature of Parkinson's disease. Growing evidence points towards a role of aberrant liquid-liquid phase separation in the dysregulation of αSyn and sequence of events that lead to the formation of Lewy bodies. However, the triggers leading to aberrant phase separation are unknown, as is the relevance of this phenomenon to the neurodegeneration process. In this study, we showed that αSyn spontaneously phase separates into condensates in the presence of lipid droplets. These lipid droplet-rich condensates represent a toxic species of αSyn that prevents the turnover of the entrapped lipid droplets; they are also toxic to neighbouring mitochondria which are depolarized and undergo increased mitophagy. These findings underscore the increasing importance of lipid droplets in the pathogenesis of neurodegenerative diseases, and Parkinson's disease in particular. The lipid droplets are significantly enriched within the neuromelanin in midbrain dopaminergic neurons in the substantia nigra and could therefore uniquely facilitate the early αSyn-associated neurodegeneration of this region in PD. Our findings reveal a novel pathway implicated in the dysregulation of αSyn that connects aberrant liquid-liquid phase separation, lipid droplets and mitochondrial toxicity.

BACKGROUND: Parkinson's disease (PD) affects millions of people worldwide, but only 5-10% of patients suffer from a monogenic forms of the disease with Mendelian inheritance. SNCA, the gene encoding for the protein alpha-synuclein (aSyn), was the first to be associated with familial forms of PD and, since then, several missense variants and multiplications of the gene have been established as rare causes of autosomal dominant forms of PD. In this study, we report the identification of a novel SNCA mutation in a patient that presented with a complex neurogenerative disorder, and unconventional neuropathological findings. We also performed in depth molecular studies of the effects of the novel aSyn mutation.

METHODS: A patient carrying the novel aSyn missense mutation and the family members were studied. We present the clinical features, genetic testing-whole exome sequencing (WES), and neuropathological findings. The functional consequences of this aSyn variant were extensively investigated using biochemical, biophysical, and cellular assays.

RESULTS: The patient exhibited a complex neurodegenerative disease that included generalized myocloni, bradykinesia, dystonia of the left arm and apraxia. WES identified a novel heterozygous SNCA variant (cDNA 40G > A; protein G14R). Neuropathological examination showed extensive atypical aSyn pathology with frontotemporal lobar degeneration (FTLD)-type distribution and nigral degeneration pattern with abundant ring-like neuronal inclusions, and few oligodendroglial inclusions. Sanger sequencing confirmed the SNCA variant in one healthy, 86-year-old parent of the patient suggesting incomplete penetrance. NMR studies suggest that the G14R mutation induces a local structural alteration in aSyn, and lower thioflavin T binding in in vitro fibrillization assays. Interestingly, the G14R aSyn fibers display different fibrillar morphologies than Lewy bodies as revealed by cryo-electron microscopy. Cellular studies of the G14R variant revealed increased inclusion formation, enhanced membrane association, and impaired dynamic reversibility of serine-129 phosphorylation.

CONCLUSIONS: The atypical neuropathological features observed, which are reminiscent of those observed for the G51D aSyn variant, suggest a causal role of the SNCA variant with a distinct clinical and pathological phenotype, which is further supported by the properties of the mutant aSyn.

α-Synuclein (αS) is an abundant presynaptic protein that regulates neurotransmission. It is also a key protein implicated in a broad class of neurodegenerative disorders termed synucleinopathies, including Parkinson's disease (PD) and Lewy body dementia (LBD). Pathological αS deposits in these diseases, Lewy bodies (LBs)/neurites (LNs), contain about 90% of αS in its phospho-serine129 (pS129) form. Therefore, pS129 is widely used as a surrogate marker of pathology. However, recent findings demonstrate that pS129 is also physiologically triggered by neuronal activity to positively regulate synaptic transmission. In this opinion article, we contrast the literature on pathological and physiological pS129, with a special focus on the latter. We emphasize that pS129 is ambiguous and knowledge about the context is necessary to correctly interpret changes in pS129.

The neuronal protein α-synuclein is centrally involved in the neurodegeneration occurring in Parkinson's disease and related synucleinopathies. α-Synuclein's membrane-induced 3-11 helix conformation has a hydrophobic membrane-embedded half and a hydrophilic cytosolic half. Here, we studied the significance of (a) the surprising hydrophobicity of amino-acids at cytosol-exposed helix position 8; (b) the absence of positively charged lysine/arginine from all cytosol-exposed positions (1-5-8-9). We found that (a) further increasing hydrophobicity or adding lysine, but not glutamate, at position 8 augments both membrane interaction and S129 phosphorylation; (b) adding lysines at cytosol-exposed positions 1, 5, 8, or 9 has similar effects. Variants abundantly present in membranes by biochemical fractionation markedly colocalized with transferrin-receptor (an endosomal marker) in immunofluorescence-microscopy, indicating accumulation at vesicle membranes. Thus, we observed a striking correlation between membrane attraction and S129 phosphorylation, relevant for understanding α-synuclein biology in health and disease.

Alpha-synuclein (αS)-rich Lewy bodies and neurites in the cerebral cortex correlate with the presence of dementia in Parkinson disease (PD) and Dementia with Lewy bodies (DLB), but whether αS influences synaptic vesicle dynamics in human cortical neurons is unknown. Using a new iPSC-based assay platform for measuring synaptic vesicle cycling, we found that in human cortical glutamatergic neurons, increased αS from either transgenic expression or triplication of the endogenous locus in patient-derived neurons reduced synaptic vesicle cycling under both stimulated and spontaneous conditions. Thus, using a robust, easily adopted assay platform, we show for the first time αS-induced synaptic dysfunction in human cortical neurons, a key cellular substrate for PD dementia and DLB.

The heterogeneity of protein-rich inclusions and its significance in neurodegeneration is poorly understood. Standard patient-derived iPSC models develop inclusions neither reproducibly nor in a reasonable time frame. Here, we developed screenable iPSC "inclusionopathy" models utilizing piggyBac or targeted transgenes to rapidly induce CNS cells that express aggregation-prone proteins at brain-like levels. Inclusions and their effects on cell survival were trackable at single-inclusion resolution. Exemplar cortical neuron α-synuclein inclusionopathy models were engineered through transgenic expression of α-synuclein mutant forms or exogenous seeding with fibrils. We identified multiple inclusion classes, including neuroprotective p62-positive inclusions versus dynamic and neurotoxic lipid-rich inclusions, both identified in patient brains. Fusion events between these inclusion subtypes altered neuronal survival. Proteome-scale α-synuclein genetic- and physical-interaction screens pinpointed candidate RNA-processing and actin-cytoskeleton-modulator proteins like RhoA whose sequestration into inclusions could enhance toxicity. These tractable CNS models should prove useful in functional genomic analysis and drug development for proteinopathies.

In Parkinson's disease and other synucleinopathies, the elevation of α-synuclein phosphorylated at Serine129 (pS129) is a widely cited marker of pathology. However, the physiological role for pS129 has remained undefined. Here we use multiple approaches to show for the first time that pS129 functions as a physiological regulator of neuronal activity. Neuronal activity triggers a sustained increase of pS129 in cultured neurons (200% within 4 h). In accord, brain pS129 is elevated in environmentally enriched mice exhibiting enhanced long-term potentiation. Activity-dependent α-synuclein phosphorylation is S129-specific, reversible, confers no cytotoxicity, and accumulates at synapsin-containing presynaptic boutons. Mechanistically, our findings are consistent with a model in which neuronal stimulation enhances Plk2 kinase activity via a calcium/calcineurin pathway to counteract PP2A phosphatase activity for efficient phosphorylation of membrane-bound α-synuclein. Patch clamping of rat SNCA-/- neurons expressing exogenous wild-type or phospho-incompetent (S129A) α-synuclein suggests that pS129 fine-tunes the balance between excitatory and inhibitory neuronal currents. Consistently, our novel S129A knock-in (S129AKI) mice exhibit impaired hippocampal plasticity. The discovery of a key physiological function for pS129 has implications for understanding the role of α-synuclein in neurotransmission and adds nuance to the interpretation of pS129 as a synucleinopathy biomarker.

α-Synuclein phosphorylation at serine-129 (pS129) is a widely used surrogate marker of pathology in Parkinson's disease and other synucleinopathies. However, we recently demonstrated that phosphorylation of S129 is also a physiological activator of synaptic transmission. In a feed-forward fashion, neuronal activity triggers reversible pS129. Here, we show that Parkinson's disease-linked missense mutations in SNCA impact activity-dependent pS129. Under basal conditions, cytosol-enriched A30P, H50Q, and G51D mutant forms of α-synuclein exhibit reduced pS129 levels in rat primary cortical neurons. A53T pS129 levels are similar to wild-type, and E46K pS129 levels are higher. A30P and E46K mutants show impaired reversibility of pS129 after stimulation. For the engineered profoundly membrane-associated α-synuclein mutant "3K" (E35K + E46K + E61K), de-phosphorylation was virtually absent after blocking stimulation, implying that reversible pS129 is severely compromised. Importantly, pS129 excess resulting from proteasome inhibition is also associated with reduced reversibility by neuronal inhibition, kinase inhibition, or phosphatase activation. Our findings suggest that perturbed pS129 dynamics are probably a shared characteristic of pathology-associated α-synuclein, with possible implications for synucleinopathy treatment and diagnosis.