Exacerbation of Hepatic Damage in Endothelial Aquaporin 1 Transgenic Mice after Experimental Heatstroke.

Abstract Background: Heatstroke is a life-threatening disease that causes body fluid loss and electrolyte abnormalities due to exposure to high ambient temperature (AT) and relative humidity (RH). Recently, global warming has increased the number of heatstroke patients worldwide. Aquaporin 1 (AQP1) is a water-selective protein that plays an important role in water homeostasis. However, the role of AQP1 in heatstroke has not been elucidated yet. Therefore, in this study, we examined the role of endothelial AQP1 using Tie2-Cre/LNL-AQP1 double transgenic (dTG) mice with an upregulation of aqp1 on endothelial cells. Methods: Tie2-Cre/LNL-AQP1 dTG mice were generated by breeding CAG-LNL(STOP)-AQP1 Tg and Tie2-Cre Tg mice. The transgenes were evaluated in the brain because brain vessels do not express aqp1. For production of experimental heatstroke, the mice were kept in a heatstroke chamber that was pre-heated at 41 °C AT and >99% RH for 1 h, and the blood, brain, kidney, and liver were collected 24 h later. Blood samples were analyzed for biochemical parameters such as electrolytes and tissue damage markers, and the organs were examined via morphological and immunohistological (3-nitrotyrosine (3-NT), AQP1, and Iba-1) staining. Results: Although no difference was observed in aqp1 expression in the whole brain, aqp1 was detected only in Tie2-Cre/LNL-AQP1 dTG mice after capillary deprivation. Moreover, AQP1 immunostaining also revealed immunoreaction in blood vessels. After heat exposure, electrolyte abnormalities were observed in both the wild and Tie2-Cre/LNL-AQP1 dTG mice compared to non-heat stroke wild mice. Hepatic damage markers, aspartate aminotransferase and alanine aminotransferase, were increased, and serum lactate dehydrogenase levels were significantly higher in Tie2-Cre/LNL-AQP1 dTG mice than in wild mice. Hematoxylin-eosin staining and 3-NT immunoreactivity in the liver also supported hepatic damage. Moreover, the number of hepatic vasculature adherent Iba-1 positive cells was significantly higher in Tie2-Cre/LNL-AQP1 dTG mice than in wild mice. Conclusions: In the present study, for the first time, we suggested that endothelial AQP1 contributes to hepatic damage after heatstroke.