Department of Molecular and Developmental Biology, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8575, Japan; Division of Aquaculture Biotechnology, Biotechnology Center of Ho Chi Minh City, Ho Chi Minh City, Viet Nam.
Department of Molecular and Developmental Biology, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8575, Japan.
Redox Biol. 2020 Sep;36:101667. doi: 10.1016/j.redox.2020.101667. Epub 2020 Aug 11.
The Keap1-Nrf2 pathway is an evolutionarily conserved mechanism that protects cells from oxidative stress and electrophiles. Under homeostatic conditions, Keap1 interacts with Nrf2 and leads to its rapid proteasomal degradation, but when cells are exposed to oxidative stress/electrophiles, Keap1 senses them, resulting in an improper Keap1-Nrf2 interaction and Nrf2 stabilization. Keap1 is therefore considered both an "inhibitor" of and "stress sensor" for Nrf2 activation. Interestingly, fish and amphibians have two Keap1s (Keap1a and Keap1b), while there is only one in mammals, birds and reptiles. A phylogenetic analysis suggested that mammalian Keap1 is an ortholog of fish Keap1b, not Keap1a. In this study, we investigated the differences and similarities between Keap1a and Keap1b using zebrafish genetics. We generated zebrafish knockout lines of keap1a and keap1b. Homozygous mutants of both knockout lines were viable and fertile. In both mutant larvae, the basal expression of Nrf2 target genes and antioxidant activity were up-regulated in an Nrf2-dependent manner, suggesting that both Keap1a and Keap1b can function as Nrf2 inhibitors. We also analyzed the effects of the Nrf2 activator sulforaphane in these mutants and found that keap1a-, but not keap1b-, knockout larvae responded to sulforaphane, suggesting that the stress/chemical-sensing abilities of the two Keap1s are different.
Keap1-Nrf2 通路是一种进化上保守的机制，可保护细胞免受氧化应激和亲电物的侵害。在稳态条件下，Keap1 与 Nrf2 相互作用，导致其快速被蛋白酶体降解，但当细胞暴露于氧化应激/亲电子物时，Keap1 会感知到它们，导致 Keap1-Nrf2 相互作用不当和 Nrf2 稳定。因此，Keap1 被认为既是 Nrf2 激活的“抑制剂”，也是“应激传感器”。有趣的是，鱼类和两栖类有两种 Keap1（Keap1a 和 Keap1b），而哺乳动物、鸟类和爬行动物只有一种。系统发生分析表明，哺乳动物 Keap1 是鱼类 Keap1b 的同源物，而不是 Keap1a。在这项研究中，我们使用斑马鱼遗传学研究了 Keap1a 和 Keap1b 之间的差异和相似性。我们生成了 Keap1a 和 Keap1b 的斑马鱼敲除系。这两种敲除系的纯合突变体都是有活力和可育的。在两种突变体幼虫中，Nrf2 靶基因的基础表达和抗氧化活性均以上调，呈 Nrf2 依赖性，表明 Keap1a 和 Keap1b 均可作为 Nrf2 抑制剂发挥作用。我们还分析了 Nrf2 激活剂萝卜硫素在这些突变体中的作用，发现只有 Keap1a 敲除系，而不是 Keap1b 敲除系对萝卜硫素有反应，表明这两种 Keap1 对压力/化学的感应能力不同。
