It is shown that early complement associated pruning of inhibitory synapses precedes overt α-synuclein aggregation and neuronal loss in prodromal synucleinopathy, indicating disease-context dependent relationships between αSyn pathology and neurodegeneration.
Abstract
Parkinson’s disease (PD) is characterized by degeneration of dopaminergic neurons in the substantia nigra pars compacta, but the molecular events preceding neuronal loss remain unclear. Here, we combine spatial transcriptomics, spatial proteomics, and α-synuclein (αSyn) seed amplification assays to profile post-mortem midbrain tissue from controls, incidental Lewy body disease (iLBD), PD, Alzheimer’s disease (AD), and AD with Lewy body pathology (AD + LBP). We find that αSyn seeding activity correlates with dopaminergic neuron loss in PD-spectrum cases but not in AD-associated LBP, indicating disease-context dependent relationships between αSyn pathology and neurodegeneration. In iLBD, before overt substantia nigra Lewy pathology or detectable αSyn aggregation, we detect increased expression of the complement component C1QC together with loss of inhibitory synaptic markers. These findings support early complement-associated remodeling of inhibitory synapses as a potential pathogenic event preceding overt αSyn aggregation and neuronal degeneration in PD. Parkinson’s disease is associated with dopaminergic neuron loss, but the molecular events preceding degeneration remain unclear. Here, the authors show that early complement associated pruning of inhibitory synapses precedes overt α-synuclein aggregation and neuronal loss in prodromal synucleinopathy.
The biomarker and therapeutic potential of STX1A remains preliminary because diagnostic performance, disease specificity, longitudinal stability, and causal relevance have not been adequately validated and future studies using cell-type-specific STX1A manipulation, rescue experiments, electrophysiology, and multicenter longitudinal cohorts are required to define the biological and clinical significance of STX1A in PD.
Rui Xu, Rui Li, Hongmei Li et al.· Frontiers in Aging Neuroscie...· 0 citations
Histopathologic staging models of neuronal α-synuclein pathology (n-asyn) in Lewy body disease (LBD) seldom evaluate brain regions with direct synaptic connectivity to model the role of microglial processes. We address this gap by testing the hypothesis that, within the well-defined synaptic connectivity of the intrahippocampal circuit, n-asyn is associated with activated microglial phenotypes. We selected a cohort of autopsy-confirmed LBD patients and minimal age-related copathologies (n = 62) and a control cohort of cognitively healthy patients with isolated hippocampal tau accumulation (i.e., primary age-related tauopathy, PART; n = 12), to control for neurodegenerative pathology without amyloid plaques. We immunostained consecutive hippocampal sections for n-asyn and established markers of activated microglial phenotypes, Iba1, HLA-DR, and CD68. With validated digital histology methods, we measured percent area occupied (%AO) of each marker in 6 hippocampal subfields to compare and correlate microglial morphologic and proteomic activation phenotypes between cohorts and used linear mixed effects models to compare the %AO between subfields while covariying for demographics. We also constructed groups of n-asyn restricted to the cornu ammonis (CA) 2–3 subfields (Focal Subtype) or widespread n-asyn within additional subfields (Widespread Subtype) to model hypothesized n-asyn spread within the intrahippocampal circuit. LBD patients exhibited increased HLA-DR and CD68%AO in most hippocampal subfields compared with PART. In LBD patients, all microglial markers were the highest in the CA2. CA2 n-asyn correlated with HLA-DR and CD68 but not Iba1%AO. Patients classified as Widespread Subtype had worse cognitive impairment and increased CA2 HLA-DR and CD68%AO. CA2 HLA-DR and CD68%AO correlated with distal n-asyn in retrograde, but not anterograde connected subfields. Our data show that activated microglial phenotypes in the CA2 of LBD patients are associated with worse clinical outcomes and retrograde n-asyn transmission. These data suggest that measures of microglial states can refine LBD histopathological progression models.
Esteban Luna, K. Cousins, Sheina Emrani et al.· Acta Neuropathologica· 0 citations
Dementia with Lewy bodies (DLB) is increasingly conceptualised not merely as a disorder of neuronal death but as a primary synaptopathy in which the functional collapse of synaptic transmission and plasticity precedes, and predicts, neurodegeneration and clinical decline. Two genetic determinants dominate the heritable risk architecture of DLB: the α-synuclein gene SNCA, in which both copy-number variation and missense mutations exert dose- and conformation-dependent effects, and GBA1, encoding the lysosomal hydrolase glucocerebrosidase (GCase), the single most influential genetic risk factor for the disease. Here we synthesise evidence that these loci converge on a shared pathogenic endpoint—the impairment of activity-dependent synaptic plasticity. We argue that GBA1 loss-of-function and the resulting accumulation of glucosylceramide stabilise specific neurotoxic α-synuclein proteoforms, including soluble oligomers and self-templating conformational strains bearing defined post-translational modifications. These proteoforms are trafficked to, and enriched within, presynaptic terminals, where they disrupt SNARE-complex assembly and synaptic-vesicle dynamics, while postsynaptically they perturb NMDA and AMPA receptor trafficking, dysregulate dendritic calcium, and compromise synaptic mitochondrial bioenergetics. The net consequence is a metaplastic shift away from long-term potentiation (LTP) and toward aberrant long-term depression (LTD), a signature of synaptic failure detectable before frank pathology. We map these molecular events onto disease-relevant circuits—particularly the cholinergic basal forebrain and hippocampal–cortical and thalamocortical networks—and relate them to the defining neuropsychiatric features of DLB, including cognitive fluctuations and recurrent visual hallucinations. Finally, we evaluate emerging therapeutic strategies that target the GBA1–α-synuclein axis and that aim to restore synaptic plasticity directly. Positioning DLB within the framework of genetically determined plasticity deficits clarifies its kinship with other neuropsychiatric disorders and identifies the synapse as the most tractable node for early, disease-modifying intervention. We further examine how GBA1 allele severity and zygosity grade the phenotype, which genetic and environmental factors modify penetrance in carriers, and what distinguishes this synaptopathy from those driven by PSEN1/PSEN2, MAPT, or HTT, and we summarise the therapeutic pipeline—including enzyme augmentation and adeno-associated viral GBA1 gene therapy—that targets it.
Substantia nigra pars compacta dopamine neuron loss and Lewy pathology, aggregates of α-synuclein, characterize Parkinson’s disease and Dementia with Lewy Bodies. Lewy pathology localizes to cortical neurons, and is found as Lewy neurites in the striatum, but its effects on excitatory synaptic function are just beginning to be understood. Corticostriatal projections regulate motor and cognitive behaviors impaired in these disorders. Here, α-synuclein aggregation was induced in mouse M2 cortex, a vulnerable region in human disease. Early after initiation, aggregates localized to corticostriatal vesicular glutamate transporter 1 (vGLUT1)-positive terminals, with sparing of spiny projection neuron (SPN) soma, and dopamine terminals and neurons. Corticostriatal presynaptic aggregates significantly impaired glutamatergic transmission, without overt cortical neuron loss, and were associated with decreased synaptic density and volume. Thus, formation of presynaptic α-synuclein aggregates impairs corticostriatal function without degeneration of cortical neurons or striatal dopamine terminals, suggesting pathologic α-synuclein is sufficient for synaptic loss. Our findings also point to early synaptic dysfunction as a therapeutic target in Lewy body diseases.
Charlotte F. Brzozowski, Zoe Fokakis, Marissa A. Menard et al.· bioRxiv· 0 citations
A “cellular state–pathological network–therapeutic window” framework is proposed and the roles of microglia in amyloid-β plaque seeding and compaction, NLRP3 inflammasome activation, mitochondrial DNA–cGAS–STING signaling, complement-mediated synaptic engulfment, and bidirectional microglia–tau feedback are systematically discussed.
Lian-Jing Xu, Ying Zhang, Li Jiang et al.· Frontiers in Cellular Neuros...· 0 citations
Background: Parkinson’s disease (PD) exhibits remarkable clinical heterogeneity, with substantial variability in motor progression, cognitive decline, and the development of non-motor manifestations. Although the propagation of pathological alpha-synuclein is considered a central mechanism of PD pathogenesis, it does not fully explain why specific neuronal populations demonstrate differential susceptibility to degeneration. Emerging evidence suggests that selective neuronal vulnerability is determined by the interaction of multiple biological domains, including calcium homeostasis, mitochondrial bioenergetic capacity, lysosomal function, axonal architecture, synaptic resilience, and neuroinflammatory responses. Methods: A structured critical narrative review was performed using PubMed/MEDLINE, Scopus, and Web of Science databases from inception to March 2025. Only full-text articles published in English and peer-reviewed journals were included. Evidence from human post-mortem studies, genetic analyses, biomarker investigations, experimental models, induced pluripotent stem cell studies, and longitudinal clinical cohorts were systematically synthesised to identify the principal mechanisms underlying selective neuronal vulnerability and their potential translational application. To capture evidence published after this electronic cut-off, a supplementary manual review of reference lists of key systematic reviews and landmark publications was conducted up to the date of manuscript submission; references with 2025 or 2026 publication dates entered through this supplementary process. The supplementary manual review was conducted as a targeted scan of reference lists of key systematic reviews and high-impact publications identified during the primary search and did not constitute an independent updated systematic search. Results: Five interconnected biological domains emerged as key determinants of neuronal susceptibility in PD: calcium-mediated metabolic stress associated with autonomous pacemaker activity, mitochondrial dysfunction and energetic failure, impaired lysosomal degradation and proteostasis (particularly involving the GBA1–glucocerebrosidase pathway), vulnerability related to extensive axonal and synaptic architecture, and neuroinflammatory mechanisms involving microglial and astrocytic activation. Among these domains, the lysosomal pathway currently provides the strongest translational link between molecular mechanisms and measurable clinical outcomes. Based on this integrated framework, we propose the Parkinson’s Vulnerability Index (PVI), a hypothesis-generating multidimensional model combining genetic, enzymatic, alpha-synuclein seeding, cognitive, olfactory, and neuroimaging biomarkers to facilitate biological stratification and improve the design of mechanism-targeted clinical trials. Conclusions: Selective neuronal vulnerability provides a complementary framework to alpha-synuclein propagation models for understanding the heterogeneity of PD. The proposed PVI is not intended as a diagnostic or prognostic clinical instrument but as a research tool requiring prospective validation. Future precision medicine approaches in PD may benefit from integrating vulnerability-related biomarkers with existing biological staging systems to identify patients most likely to benefit from targeted disease-modifying therapies.
Livia Livinț-Popa, Andreea Nicolaie, A. Maștaleru et al.· Medical Science· 0 citations