The role of aquaporin 4 in apoptosis after intracerebral hemorrhage

BACKGROUND: We previously reported that aquaporin-4 deletion (AQP4(−/−)) in mice increased edema and altered blood-brain barrier integrity following intracerebral hemorrhage (ICH). To date, little is known about the role of AQP4 in apoptosis after ICH. The purpose of this study was to examine the role of AQP4 in apoptosis and its mechanisms after ICH using AQP4(−/−) mice. METHODS: We compared the survival rate and neurological deficits in wild-type (AQP4(+/+)) mice with those in AQP4(−/−) mice following ICH. Histological changes were detected with terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining and Hoechst staining. The cell types involved were determined by immunocytochemical studies. We also measured activated caspase-3, caspase-9, caspase-8, Bax, and Bcl-2 with Western blotting at 1, 3, and 7 days after ICH. A cytokine protein assay was used to detect cytokines in AQP4(+/+) and AQP4(−/−) mice following ICH, and the results were verified by ELISA. RESULTS: We found more apoptotic cells in AQP4(−/−) mice following ICH; the cell types involved were predominantly neurons and astrocytes. Western blotting showed that the expression of activated caspase-3 and caspase-8 was significantly increased (P <0.05). Moreover, we demonstrated a greater enhancement in the release of TNF-α and IL-1β, as well as their receptors, in AQP4(−/−) mice following ICH than in AQP4(+/+) mice by cytokine protein assay and Western blotting (P <0.05). The inhibitors of TNF-α and IL-1β reduced apoptotic cells after ICH in AQP4(−/−) mice compared with wild-type mice (P <0.05). CONCLUSIONS: AQP4 deletion increases apoptosis following ICH, and the underlying mechanism may be through cytokines, especially TNF-α and IL-1β, initiating the apoptotic cascade, as well as activation of caspase-3 and caspase-8.