Decline in transcriptional activity of Nrf2 causes age-related loss of glutathione synthesis, which is reversible with lipoic acid
Decline in transcriptional activity of Nrf2 causes age-related loss of glutathione synthesis, which is reversible with lipoic acid
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DOI：
10.1073/pnas.0400282101
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发表时间：
2004-03-09
影响因子：
11.1
通讯作者：
Hagen, TM
中科院分区：
文献类型：
--
作者：
Suh, JH;Shenvi, SV;Hagen, TM
衰老大鼠肝脏中谷胱甘肽（GSH）含量显著下降。由于GSH水平部分反映了其合成能力，我们测量了GSH合成中的速率控制酶γ-谷氨酰半胱氨酸连接酶（GCL）的水平和活性。GCL的催化亚基（GCLC）和调节亚基（GCLM）随年龄增长分别下降47%和52%（P < 0.005）。随着亚基水平的降低，GCL活性也下降了53%（P < 0.05）。由于核因子红细胞2相关因子2（Nrf 2）通过抗氧化反应元件（ARE）控制基础和诱导型GCLC和GCLM表达，我们假设衰老导致Nrf 2介导的GCL表达失调。我们观察到大约50%的总（P < 0.001）和核（P < 0.0001）Nrf 2水平的年龄相关损失，这表明Nrf 2依赖的基因转录减弱。通过使用凝胶位移和超位移测定，注意到老年大鼠与年轻大鼠相比Nrf 2/ARE结合显著降低。为了确定Nrf 2转录活性的组成性丧失是否也影响Nrf 2核转位的诱导性质，用（R）-α-硫辛酸（LA; 40 mg/kg i. p.长达48 h）处理老年大鼠，这是一种显示出在体外诱导Nrf 2活化并在体内提高GSH水平的二硫化合物。LA给药12 h后增加老年大鼠核Nrf 2水平。LA也诱导Nrf 2结合的ARE，因此，更高的GCLC水平和GCL活性，观察LA注射后24小时。因此，年龄相关的GSH合成损失可能是由ARE介导的基因表达失调引起的，但化学保护剂，如LA，可以减轻这种损失。
Glutathione (GSH) significantly declines in the aging rat liver. Because GSH levels are partly a reflection of its synthetic capacity, we measured the levels and activity of gamma-glutamylcysteine ligase (GCL), the rate-controlling enzyme in GSH synthesis. With age, both the catalytic (GCLC) and modulatory (GCLM) subunits of GCL decreased by 47% and 52%, respectively (P < 0.005). Concomitant with lower subunit levels, GCL activity also declined by 53% (P < 0.05). Because nuclear factor erythroid2-related factor 2 (Nrf2) governs basal and inducible GCLC and GCLM expression by means of the antioxidant response element (ARE), we hypothesized that aging results in dysregulation of Nrf2-mediated GCL expression. We observed an approximate to50% age-related loss in total (P < 0.001) and nuclear (P < 0.0001) Nrf2 levels, which suggests attenuation in Nrf2-dependent gene transcription. By using gel-shift and supershift assays, a marked reduction in Nrf2/ARE binding in old vs. young rats was noted. To determine whether the constitutive loss of Nrf2 transcriptional activity also affects the inducible nature of Nrf2 nuclear translocation, old rats were treated with (R)-alpha-lipoic acid (LA; 40 mg/kg i.p. up to 48 h), a disulficle compound shown to induce Nrf2 activation in vitro and improve GSH levels in vivo. LA administration increased nuclear Nrf2 levels in old rats after 12 h. LA also induced Nrf2 binding to the ARE, and, consequently, higher GCLC levels and GCL activity were observed 24 h after LA injection. Thus, the age-related loss in GSH synthesis may be caused by dysregulation of ARE-mediated gene expression, but chemoprotective agents, like LA, can attenuate this loss.