AQP4 and neuromyelitis optica: To characterize CHI3L1-mediated NF-κB pathway activation in the context of astrocyte activation initiated by AQP4-IgG — as occurs in NMO — we considered that the binding of anti-AQP4 IgG to surface AQP4 proteins on astrocytes leads to internalization and degradation of AQP4, mirroring events in NMO brains.