AQP4 and leukoencephalopathy, megalencephalic: Astrocytes are functionally polarized with perisynaptic astrocyte processes enriched with the glutamate transporters EAAT1/GLAST and EAAT2/GLT-1 and the inward rectifier K+ channel 4.1 (Kir4.1)11 and with PV-AEF enriched with aquaporin 4 (AQP4), glucose transporter 1, transient receptor potential vanilloid-related channel 4 (TRPV4), Kir4.1, megalencephalic leukoencephalopathy with subcortical cysts-1 (MLC1), and GlialCAM/hepaCAM.12