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Induction of Paralysis and Visual System Injury in Mice by T Cells Specific for Neuromyelitis Optica Autoantigen Aquaporin-4
Published on: August 21, 2017
AQP4-IgG-Induced Astrocyte-Derived Small Extracellular Vesicles Carrying Mitochondrial DNA Regulate the
Juan Zhou1,2, Haipeng Li2, Ying Wen2
1Department of Neurology, The First Affiliated Hospital of Jinan University, 613 West Huangpu Ave, Guangzhou, 510632, China.
Abstract:
Neuromyelitis optica spectrum disorder (NMOSD) is a rare but serious inflammatory demyelinating disease. A key characteristic of NMOSD is the presence of a pathogenic autoantibody in serum called aquaporin-4 immunoglobulin G (AQP4-IgG). This study investigates the mechanism of astrocyte-derived small extracellular vesicles (EVs) carrying mitochondrial DNA (mtDNA) to promote AQP4-IgG-induced microglial activation in neuromyelitis optica (NMO) via the toll-like receptor 9 (TLR9)/myeloid differentiation primary response 88 (MyD88)/nuclear factor-kappa B (NF-κB) pathway. Serum IgG was isolated from NMOSD patients (AQP4-IgG) and healthy controls (Con-IgG). Astrocytes were treated with AQP4-IgG or Con-IgG. EVs were isolated via ultracentrifugation, characterized, and examined for internalization. Microglia were exposed to EVs, and mtDNA levels were assessed. An NMO mouse model was established, with neurological damage, mouse behaviors, tissue damage, and microglial characterization evaluated using modified neurological severity score, open-field test, rotarod test, luxol fast blue staining, and flow cytometry. Inflammatory cytokines, TLR9, MyD88, p65, IκBα, p-p65, and p-IκBα in BV2 cells and spinal cord tissues were analyzed via ELISA, RT-qPCR, and western blot. AQP4-IgG-induced astrocyte-derived EVs increased Iba1-high-expressing and CD86/tumor necrosis factor-α-high-expressing cells, reduced CD206/transforming growth factor-β-high-expressing cells, and boosted inflammatory responses. AQP4-IgG-induced EVs carried mtDNA to activate microglia via the TLR9/MyD88/NF-κB pathway. TLR9/MyD88/NF-κB pathway inhibition reversed AQP4-IgG-induced EVs' promotion on microglial activation. In vivo, AQP4-IgG-induced EVs-mtDNA exacerbated microglial activation and NMO through the TLR9/MyD88/NF-κB pathway. AQP4-IgG-induced EVs carried mtDNA to upregulate TLR9, further activating the MyD88/NF-κB pathway, thereby promoting microglial activation and transition toward pro-inflammatory gene-high-expressing cells to drive NMO progression.
Insights
Neuromyelitis optica spectrum disorder (NMOSD) involves astrocyte-derived extracellular vesicles (EVs) carrying mitochondrial DNA (mtDNA) that activate microglia, driving disease progression via the TLR9/MyD88/NF-κB pathway. Inhibiting this pathway reverses microglial activation, offering a potential therapeutic target for NMOSD.
Area of Science:
- Neuroimmunology
- Cellular and Molecular Neuroscience
- Demyelinating Diseases Research
Background:
- Neuromyelitis optica spectrum disorder (NMOSD) is a severe autoimmune disease targeting the central nervous system.
- Aquaporin-4 immunoglobulin G (AQP4-IgG) autoantibodies are key biomarkers and drivers of NMOSD pathogenesis.
- Microglial activation plays a critical role in NMOSD-associated inflammation and tissue damage.
Purpose of the Study:
- To investigate the role of astrocyte-derived extracellular vesicles (EVs) carrying mitochondrial DNA (mtDNA) in AQP4-IgG-induced microglial activation.
- To elucidate the specific signaling pathway involved, focusing on toll-like receptor 9 (TLR9)/myeloid differentiation primary response 88 (MyD88)/nuclear factor-kappa B (NF-κB).
- To evaluate the therapeutic potential of targeting this pathway in an NMOSD model.
Main Methods:
- Isolation and characterization of EVs from astrocytes treated with AQP4-IgG or control IgG.
- Assessment of mtDNA content within EVs and microglial activation markers (e.g., Iba1, CD86, CD206).
- Establishment and evaluation of an NMOSD mouse model, including behavioral tests and molecular analysis of inflammatory pathways (TLR9, MyD88, NF-κB).
Main Results:
- AQP4-IgG-induced EVs carrying mtDNA significantly promoted microglial activation and pro-inflammatory responses.
- The TLR9/MyD88/NF-κB pathway was identified as the key mediator of EV-induced microglial activation.
- Inhibition of the TLR9/MyD88/NF-κB pathway attenuated microglial activation and ameliorated neurological damage in vivo.
Conclusions:
- Astrocyte-derived EVs carrying mtDNA are crucial mediators of AQP4-IgG-induced microglial activation in NMOSD.
- The TLR9/MyD88/NF-κB pathway is a central mechanism driving NMOSD pathogenesis.
- Targeting the EV-mtDNA-TLR9 axis represents a promising therapeutic strategy for NMOSD.
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