Differential expression of aquaporin-4 isoforms localizes with neuromyelitis optica disease activity

Neuromyelitis optica (NMO) is a devastating neuroinflammatory disorder that specifically targets the spinal cord and optic nerves. Aquaporin-4 (AQP4) is the target of the NMO-IgG biomarker. AQP4 is expressed as two isoforms: M1 and M23, which have different functions in the central nervous system (CNS). We characterized the expression pattern of these AQP4 isoform mRNAs in humans and found a pattern of AQP4 expression that correlates with NMO disease localization. The ratio of M1:M23 mRNA is highest in the optic nerve and spinal cord, followed by brainstem, then the cerebral and cerebellar cortices.