Yan Hong, Harding John J, Xing Kuiyi, Lou Marjorie F
Department of Ophthalmology, Tangdu Hospital, Fourth Military Medical University, Xi'an 710038, China.
Curr Eye Res. 2007 May;32(5):455-63. doi: 10.1080/02713680701257837.
Glutathione reductase (GR) plays a key role in maintaining thiol groups in the lens, and its activity decreases with aging and cataract formation. Mammalian thioredoxin (Trx) and thioredoxin reductase (TrxR), or the Trx/TrxR system, participates in the repair of oxidatively damaged lens proteins and enzymes. Alpha-crystallin, a molecular chaperone, prevents the aggregation of partially denatured proteins under various stress conditions. Thioltransferase (TTase, or glutaredoxin) can maintain the homeostasis of lens protein thiols thus protecting against oxidative stress. We investigated whether the Trx/TrxR system can revive GR activity in both the cortex and nucleus of human cataract and clear aged lenses and whether alpha-crystallin and TTase can help this effect. The GR activity in the cortex and nucleus of the cataractous lenses was significantly lower than that of the aged clear lenses. The highest activity in the cortex was observed in the clear aged lenses. The combination of Trx and TrxR revived the activity of GR from both the cortex and nucleus of aged clear lenses. However, in cataract lenses (grade II and grade IV), there was a statistically significant recovery of GR activity in the cortex, but not in the nucleus. No recovery was observed when Trx or TrxR were used separately. Alpha-crystallin successfully revived GR activity in the cortex of cataract grade II lenses, but not in the nucleus. The combination of alpha-crystallin and Trx/TrxR gave a further increase of activity. TTase alone revived some of the GR activity but together with the Trx/TrxR system gave no statistically significant enhancement of GR activity. These results indicate that both disulfide bond formation and protein unfolding are responsible for GR inactivation.
谷胱甘肽还原酶（GR）在维持晶状体中的巯基方面起着关键作用，其活性会随着衰老和白内障形成而降低。哺乳动物硫氧还蛋白（Trx）和硫氧还蛋白还原酶（TrxR），即Trx/TrxR系统，参与氧化损伤的晶状体蛋白质和酶的修复。α-晶状体蛋白作为一种分子伴侣，可防止部分变性蛋白质在各种应激条件下聚集。巯基转移酶（TTase，即谷氧还蛋白）可维持晶状体蛋白质巯基的稳态，从而抵御氧化应激。我们研究了Trx/TrxR系统是否能恢复人白内障皮质和核中的GR活性并清除老化晶状体，以及α-晶状体蛋白和TTase是否能辅助这一作用。白内障晶状体皮质和核中的GR活性显著低于老化透明晶状体。在老化透明晶状体的皮质中观察到最高活性。Trx和TrxR的组合可恢复老化透明晶状体皮质和核中GR的活性。然而，在白内障晶状体（II级和IV级）中，皮质中GR活性有统计学意义的恢复，但核中没有。单独使用Trx或TrxR时未观察到恢复。α-晶状体蛋白成功恢复了II级白内障晶状体皮质中的GR活性，但核中没有。α-晶状体蛋白与Trx/TrxR的组合使活性进一步增加。单独的TTase恢复了部分GR活性，但与Trx/TrxR系统一起并未使GR活性有统计学意义的增强。这些结果表明二硫键形成和蛋白质解折叠均导致GR失活。
