Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794-8661, United States.
Biochem Biophys Res Commun. 2013 Nov 15;441(2):333-8. doi: 10.1016/j.bbrc.2013.10.058. Epub 2013 Oct 19.
The scope of this investigation was to understand the role of aquaporin 5 (AQP5) for maintaining lens transparency and homeostasis. Studies were conducted using lenses of wild-type (WT) and AQP5 knockout (AQP5-KO) mice. Immunofluorescent staining verified AQP5 expression in WT lens sections and lack of expression in the knockout. In vivo and ex vivo, AQP5-KO lenses resembled WT lenses in morphology and transparency. Therefore, we subjected the lenses ex vivo under normal (5.6mM glucose) and hyperglycemic (55.6mM glucose) conditions to test for cataract formation. Twenty-four hours after incubation in hyperglycemic culture medium, AQP5-KO lenses showed mild opacification which was accelerated several fold at 48 h; in contrast, WT lenses remained clear even after 48 h of hyperglycemic treatment. AQP5-KO lenses displayed osmotic swelling due to increase in water content. Cellular contents began to leak into the culture medium after 48 h. We reason that water influx through glucose transporters and glucose cotransporters into the cells could mainly be responsible for creating hyperglycemic osmotic swelling; absence of AQP5 in fiber cells appears to cause lack of required water efflux, challenging cell volume regulation and adding to osmotic swelling. This study reveals that AQP5 could play a critical role in lens microcirculation for maintaining transparency and homeostasis, especially by providing protection under stressful conditions. To the best of our knowledge, this is the first report providing evidence that AQP5 facilitates maintenance of lens transparency and homeostasis by regulating osmotic swelling caused by glucose transporters and cotransporters under hyperglycemic stressful conditions.
本研究旨在探讨水通道蛋白 5（AQP5）在维持晶状体透明性和内环境稳定中的作用。该研究使用野生型（WT）和 AQP5 敲除（AQP5-KO）小鼠的晶状体进行。免疫荧光染色证实了 WT 晶状体切片中 AQP5 的表达，而在敲除晶状体中则缺乏表达。在体内和体外，AQP5-KO 晶状体在形态和透明性上与 WT 晶状体相似。因此，我们将体外培养的晶状体置于正常（5.6mM 葡萄糖）和高渗（55.6mM 葡萄糖）条件下，以测试白内障的形成。在高渗培养物中孵育 24 小时后，AQP5-KO 晶状体出现轻度混浊，48 小时后混浊加速数倍；相比之下，WT 晶状体即使在高渗处理 48 小时后仍保持透明。AQP5-KO 晶状体由于含水量增加而出现渗透肿胀。细胞内容物在孵育 48 小时后开始漏入培养基中。我们推测，通过葡萄糖转运体和协同转运体进入细胞的水流入可能是造成高渗肿胀的主要原因；纤维细胞中 AQP5 的缺失似乎导致所需的水流出减少，这对细胞体积调节构成挑战，并增加了渗透肿胀。本研究揭示了 AQP5 在维持晶状体透明性和内环境稳定方面的关键作用，特别是在应激条件下提供保护作用。据我们所知，这是首个报道提供证据表明，AQP5 通过调节高渗应激条件下葡萄糖转运体和协同转运体引起的渗透肿胀，来维持晶状体的透明性和内环境稳定。
