Lim Julie C, Perwick Rebecca D, Li Bo, Donaldson Paul J
Department of Physiology, School of Medical Sciences, New Zealand National Eye Centre, University of Auckland, New Zealand.
Department of Physiology, School of Medical Sciences, New Zealand National Eye Centre, University of Auckland, New Zealand.
Exp Eye Res. 2017 Aug;161:193-204. doi: 10.1016/j.exer.2017.06.012. Epub 2017 Jun 15.
The energy required to drive lens transparency is derived from the metabolism of glucose. In the lens, the uptake of glucose is likely to involve either facilitative glucose uptake mediated by members of the GLUT family or Na dependent glucose uptake via members of the SGLT family, or both. While GLUT1 and GLUT3 have previously been identified in the rat lens, the expression of SGLTs is unknown. Since antibodies directed against the N and C-terminal epitopes of the GLUT and SGLT family are now commercially available, the purpose of this study is to extend our screening of glucose transporters in the rat lens to include the SGLTs and compare the expression profiles of GLUTs and SGLTs in the different regions of the rat, bovine and human lens. Using a combination of reverse transcriptase PCR, western blotting and immunohistochemistry, we have shown that GLUT1 appears to be the predominant glucose transporter in the rat lens since it was expressed in all regions of the lens. In contrast GLUT3, SGLT1 and SGLT2 had more restricted expression patterns and were only found localised to the inner cortex and core regions of the rat lens. GLUT1 was the only transporter found in the epithelium and appears to exist as a full length form in this region, while in differentiating fiber cells; GLUT1 appears to undergo a modification to its N-terminus. Translating our work to bovine and human lenses revealed that GLUT1 is the only glucose transporter expressed in bovine and human lenses. While GLUT1 in the bovine lens appears to be unmodified throughout the entire lens, GLUT1 in human lenses appears to be N-terminally modified in all regions, including the epithelium. Finally, it appears that GLUT1 expression is maintained in all regions of the human lens with increasing age indicating that there is no further regional or age-dependent processing of GLUT1 in the human lens. Taken together, these studies have identified GLUT1 to be the primary transporter that mediates glucose uptake in the rat, bovine and human lens.
维持晶状体透明性所需的能量来自葡萄糖代谢。在晶状体中，葡萄糖的摄取可能涉及由GLUT家族成员介导的易化性葡萄糖摄取，或通过SGLT家族成员进行的钠依赖性葡萄糖摄取，或两者兼有。虽然此前已在大鼠晶状体中鉴定出GLUT1和GLUT3，但SGLT的表达情况尚不清楚。由于目前市面上可买到针对GLUT和SGLT家族N端和C端表位的抗体，本研究的目的是将我们对大鼠晶状体中葡萄糖转运体的筛选扩展至包括SGLT，并比较GLUT和SGLT在大鼠、牛和人晶状体不同区域的表达谱。通过逆转录酶PCR、蛋白质印迹和免疫组织化学相结合的方法，我们发现GLUT1似乎是大鼠晶状体中主要的葡萄糖转运体，因为它在晶状体的所有区域均有表达。相比之下，GLUT3、SGLT1和SGLT2的表达模式更为局限，仅在大鼠晶状体的内皮质和核心区域有表达。GLUT1是上皮细胞中唯一发现的转运体，且在该区域似乎以全长形式存在，而在分化的纤维细胞中，GLUT1的N端似乎会发生修饰。将我们的研究成果应用于牛和人晶状体后发现，GLUT1是牛和人晶状体中唯一表达的葡萄糖转运体。虽然牛晶状体中的GLUT1在整个晶状体中似乎未发生修饰，但人晶状体中的GLUT1在包括上皮细胞在内的所有区域似乎都有N端修饰。最后，随着年龄增长，人晶状体所有区域的GLUT1表达似乎都得以维持，这表明人晶状体中GLUT1不存在进一步的区域或年龄依赖性加工。综上所述，这些研究已确定GLUT1是介导大鼠、牛和人晶状体中葡萄糖摄取的主要转运体。
