AQP4 and Huntington disease: Our coimmunostaining results with antibodies against AQP4 and collagen IV revealed reduced AQP4 immunosignals in perivascular areas (Figure 4A); the quantification of colocalized immunosignals of AQP4 and collagen IV illustrated significantly reduced AQP4 perivascular localization in human HD brains (P < 0.05, Figure 4B).