AQP4 and brain ischemia: Notably, in the brains of rats with Parkinson’s disease and cerebral ischemia, MMP-9 not only co-localizes with AQP4 but also an increase in MMP-9 expression results in altered AQP4 polarity, (i.e., “depolarization”), MMP-9 disturbs aquaporin-4 polarization by cleaving β-dystroglycan (Si et al., 2024; Yan et al., 2016).