Molecular Mechanisms of Retinal Damage in NMOSD via Müller Glial Cell Stimulation with Patient Sera

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune CNS disease that frequently causes severe optic neuritis, yet the molecular mechanisms driving retinal damage remain incompletely understood, especially across different NMOSD subgroups. Müller glial cells, which maintain retinal water-ion homeostasis through AQP4 and Kir4.1 channels, may represent a primary retinal target of circulating NMOSD-related autoantibodies and serum factors. We investigated how sera from AQP4-IgG+, MOG-IgG+, and double-seronegative (DSN) NMOSD patients affect the expression and localization of key Müller cell biomarkers. Human MIO-M1 Müller cells were stimulated with complement-inactivated patient or healthy control sera, and protein/mRNA levels of AQP4, Kir4.1, CRALBP, VEGF, and IL-6 were evaluated using immunofluorescence, Western blotting, and RT-qPCR. AQP4 membrane localization and internalization were assessed using WGA and EEA1 colocalization analyses. AQP4-IgG+ sera uniquely induced a marked reduction in AQP4 and Kir4.1 protein expression, together with mild AQP4 internalization and reduced membrane association. Despite protein loss, AQP4 and Kir4.1 transcripts were significantly upregulated, indicating a compensatory transcriptional response to antibody-mediated depletion. MOG-IgG + sera produced no major changes in the examined markers. In contrast, DSN sera selectively increased VEGF expression at both protein and mRNA levels, suggesting an alternative, antibody-independent mechanism of Müller cell activation. IL-6 expression showed non-significant changes across groups. These findings demonstrate subgroup-specific retinal glial responses to patient sera, with AQP4-IgG mediating early complement-independent loss of the AQP4-Kir4.1 water-ion channel complex, and DSN sera engaging distinct VEGF-related pathways. Our study establishes Müller cells as active contributors to NMOSD-associated retinal pathology and provides a foundation for exploring subgroup-tailored changes.