Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA.
Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA; SUNY Eye Institute, New York, NY, USA.
Biochem Biophys Res Commun. 2014 Oct 3;452(4):986-91. doi: 10.1016/j.bbrc.2014.09.032. Epub 2014 Sep 16.
Aquaporin 0 (AQP0) is a transmembrane channel that constitutes ∼45% of the total membrane protein of the fiber cells in mammalian lens. It is critical for lens transparency and homeostasis as mutations and knockout cause autosomal dominant lens cataract. AQP0 functions as a water channel and as a cell-to-cell adhesion (CTCA) molecule in the lens. Our recent in vitro studies showed that the CTCA function of AQP0 could be crucial to establish lens refractive index gradient (RING). However, there is a lack of in vivo data to corroborate the role of AQP0 as a fiber CTCA molecule which is critical for creating lens RING. The present investigation is undertaken to gather in vivo evidence for the involvement of AQP0 in developing lens RING. Lenses of wild type (WT) mouse, AQP0 knockout (heterozygous, AQP0(+/-)) and AQP0 knockout lens transgenically expressing AQP1 (heterozygous AQP0(+/)(-)/AQP1(+/)(-)) mouse models were used for the study. Data on AQP0 protein profile of intact and N- and/or C-terminal cleaved AQP0 in the lens by MALDI-TOF mass spectrometry and SDS-PAGE revealed that outer cortex fiber cells have only intact AQP0 of ∼28kDa, inner cortical and outer nuclear fiber cells have both intact and cleaved forms, and inner nuclear fiber cells have only cleaved forms (∼26-24kDa). Knocking out of 50% of AQP0 protein caused light scattering, spherical aberration (SA) and cataract. Restoring the lost fiber cell membrane water permeability (Pf) by transgene AQP1 did not reinstate complete lens transparency and the mouse lenses showed light scattering and SA. Transmission and scanning electron micrographs of lenses of both mouse models showed increased extracellular space between fiber cells. Water content determination study showed increase in water in the lenses of these mouse models. In summary, lens transparency, CTCA and compact packing of fiber cells were affected due to the loss of 50% AQP0 leading to larger extracellular space, more water content and SA, possibly due to alteration in RING. To our knowledge, this is the first report identifying the role of AQP0 in RING development to ward off lens SA during focusing.
水通道蛋白 0（AQP0）是一种跨膜通道，构成哺乳动物晶状体纤维细胞总膜蛋白的 ∼45%。它对于晶状体的透明度和动态平衡至关重要，因为突变和敲除会导致常染色体显性晶状体白内障。AQP0 作为水通道和晶状体中的细胞间黏附（CTCA）分子发挥作用。我们最近的体外研究表明，AQP0 的 CTCA 功能对于建立晶状体折射率梯度（RING）可能至关重要。然而，目前缺乏体内数据来证实 AQP0 作为纤维 CTCA 分子的作用，该分子对于创建晶状体 RING 至关重要。本研究旨在为 AQP0 参与晶状体 RING 发育提供体内证据。本研究使用了野生型（WT）小鼠、AQP0 敲除（杂合子，AQP0(+/-)）和 AQP0 敲除晶状体转基因表达 AQP1（杂合子 AQP0(+/)(-)/AQP1(+/)(-））小鼠模型的晶状体。MALDI-TOF 质谱和 SDS-PAGE 对完整和 N-和/或 C-末端切割的 AQP0 的晶状体中 AQP0 蛋白图谱的数据显示，外皮层纤维细胞仅具有约 28kDa 的完整 AQP0，内皮层和外核纤维细胞既有完整形式也有切割形式，而内核纤维细胞仅具有切割形式（∼26-24kDa）。敲除 50%的 AQP0 蛋白会导致光散射、球差（SA）和白内障。通过转基因 AQP1 恢复丢失的纤维细胞膜水通透性（Pf）并不能使晶状体完全透明，并且这些小鼠的晶状体表现出光散射和 SA。两种小鼠模型的晶状体的透射和扫描电子显微镜照片显示纤维细胞之间的细胞外空间增加。水含量测定研究表明，这些小鼠模型的晶状体中的水分增加。总之，由于失去 50%的 AQP0 导致细胞外空间更大、含水量更高和 SA，晶状体的透明度、CTCA 和纤维细胞的紧密排列受到影响，这可能是由于 RING 的改变所致。据我们所知，这是首次报道确定 AQP0 在 RING 发育中的作用，以在聚焦过程中防止晶状体 SA。
