Alzheimers Disease Project: Neuroimmune responses and therapeutics of alpha-synucleinopathies of the aging population

National Institute On Aging

Investigators

Linked publications, trials & patents

Abstract

To harness the immune system to better understand the mechanisms of neurodegeneration and to develop therapies for synucleinopathies affecting the aging population—such as DLB, PD, AD, and ADRD—we propose three Aims. Aim 1 investigates the role of innate immune responses and combinatorial immunotherapy targeting LRRK2, Toll-like receptors (TLRs), p38, NFAT, and protein aggregates (e.g., α-syn, Aβ, Tau) in PD/DLB. Aim 2 assesses downstream pro-inflammatory signaling pathways, including MAPK-p38, NFAT, and NF-κB. Aim 3 evaluates the role of aging in T cell–mediated adaptive immune responses in PD/DLB pathogenesis and the development of immunotherapies for synucleinopathies. During this period, we published seven manuscripts, primarily focusing on understanding PD/DLB pathogenesis and developing novel pharmacological and immunotherapeutic strategies. Progress for Aim 1 In previous studies, we identified several immune receptors mediating neuroinflammation in synucleinopathies, including TLR2. We also determined which species of α-syn bind to TLR2 to trigger inflammatory responses. α-Syn is believed to exist in a spectrum of aggregate forms, including oligomeric and fibrillar species. Recent findings show that aggregates from synucleinopathy patients exhibit heterogeneous structural phenotypes and localization patterns, potentially reflecting the clinical and pathological variability of these diseases. We therefore investigated the pathogenic interactions between TLR2 and distinct α-syn polymorphs. Induced pluripotent stem cell (iPSC)-derived microglia were treated with structurally distinct α-syn species: monomers, preformed fibrils (PFF), sonicated PFF (sPFF), matured fibrils (Fib), kinetically stable oligomers (KSO), dopamine-stabilized oligomers (DO), and epigallocatechin gallate (EGCG)-stabilized oligomers (EO). Using multi-omics analysis, we characterized the microglial responses to each α-syn polymorph and compared the activated intracellular signaling cascades. TLR1–9 live-cell reporter assays revealed that KSO and sPFF have agonist activity for TLR2 and TLR4, respectively (Chang et al., Exp Mol Med, 2025, in press). We also assessed the neurotoxicity of α-syn polymorphs in differentiated neuronal cultures. While most polymorphs showed neurotoxic effects at studied concentrations, DO induced greater toxicity at lower doses compared to others. Moreover, α-syn polymorphs commonly induced apoptotic neuronal death via autophagic impairment (Chang et al., Exp Neurobiol, 2025). These results highlight that microglia and neurons display differential sensitivity to α-syn species—an important consideration for biomarker development and therapeutic targeting. In a collaboration with Dr. Lee's lab at Chung-Ang University in Korea, we suggested Quinic acid as a potential modulator for neuroinflammation in neurodegeneration (Park et al., Biomol Therapy 2024). Progress for Aim 2 Previously, we demonstrated that once extracellular α-syn binds to TLR2 (Kim et al., Science Transl Med, 2020), LRRK2promotes neuroinflammation by selectively phosphorylating and inducing nuclear translocation of the immune transcription factor NFATc2. To evaluate the therapeutic potential of targeting TLR2 and NFATc2, we used a functional inhibitory antibody against TLR2 and a cell-permeable LRRK2 kinase inhibitor in a synucleinopathy mouse model. Treatments reduced neurotoxic inflammation and neuropathology compared to controls. This project is ongoing, with continued data analysis. In collaboration with Dr. Sumbria's lab at Chapman University, we targeted TNF, a major pro-inflammatory cytokine by delivering engineered anti-TNF agents in a synucleinopathy model. Results showed reduced α-syn pathology, neuroinflammation, and neurodegeneration, and are currently under analysis. We also accelerated pathology by injecting PFFs into synucleinopathy models, with ongoing analysis of outcomes. Collaborating with the Gerez lab in Germany, we investigated α-syn propagation using a novel reporter system. A secreted, aggregation-prone form of α-syn was expressed in wild-type mice via a hybrid promoter and AAV9 delivery. This model recapitulated key PD/DLB features, including substantia nigra synucleinopathy, neuronal loss, neuroinflammation, and motor deficits (Gerez et al., NPJ Parkinson’s Disease, 2024). Progress for Aim 3 Recent studies suggest that microglial activation is associated with CNS infiltration of peripheral lymphocytes, such as natural killer T (NKT) cells, exacerbating disease pathology (Earls & Lee, Exp Mol Med, 2020; Holbrook et al., J Neuroinflammation, 2023). To modulate the interaction between resident CNS immune cells and infiltrating lymphocytes, we collaborated with Dr. Rissman’s lab at USC. We delivered anti-CD1d antibodies into synucleinopathy mice to inhibit CD1d, which presents lipid antigens to NKT cells. Peripheral T cell profiling revealed no significant change in T cell populations, but anti-CD1d treatment reduced glial activation and glial–NKT interactions. Neurotoxic cytokine levels were also reduced. Notably, α-syn pathology and dopaminergic neuronal damage were ameliorated (Iba et al., J Neuroinflammation, 2024). Additionally, we depleted microglia in aged synucleinopathy mice using the CSF1R inhibitor PLX3397. Microglial depletion alleviated neuronal and synaptic degeneration and partially improved motor deficits. These findings underscore microglia’s critical role in synucleinopathy pathogenesis and support microglial modulation as a viable therapeutic approach (Kim et al., Brain, Behavior, and Immunity, 2025). Furthermore, Afify et al. proposed that CD1d inhibition may have therapeutic relevance for AD and ADRD patients (Afify et al., Front Neurosci, 2024). Other related studies included mapping p-α-synuclein distribution in control and PD brains using PLA (Arlinghaus et al., J Parkinson’s Dis, 2023) and spatial transcriptomics in both mouse models and human DLB brains (Horan-Portelance et al., bioRxiv, 2024). We also collaborated with Drs. Traynor and Scholz at LNG to study the genetic architecture of FTD, DLB, and MSA, contributing neuropathological expertise, animal models, and human tissue samples (Chia et al., Neuron, 2024).