Glucocorticoid Receptors (GR) in Mitochondria: The Role in Chronic Stress

已有研究表明，慢性应激在临床上与患者抑郁的形成有关，荷尔蒙被认为与某些情绪障碍的临床表现有关。慢性束缚应激诱导啮齿动物大脑某些区域神经元的形态重组，这种影响也伴随着行为变化。尽管这些效应的确切机制尚不清楚，但越来越多的数据表明，糖皮质激素受体的神经保护和线粒体功能的改变可能在调节各种形式的突触和神经元可塑性方面发挥重要作用；我们试图研究在慢性应激过程中类固醇激素对线粒体功能的调节。 糖皮质激素在调节突触和神经事件中起着重要的双向作用，低剂量增强突触和神经元的可塑性，而长期和高剂量则产生抑制作用。我们进行了一系列实验，以阐明这些双相效应背后的机制。我们发现：1)糖皮质激素受体(GRs)在皮质酮处理后与抗细胞凋亡蛋白Bcl2形成复合体；2)皮质酮急性处理后，GRs与Bcl2一起移位到线粒体中。然而，在三天的治疗后，高剂量而不是低剂量的皮质酮导致线粒体中GR和Bcl2水平的下降。此外，长期皮质酮处理也以倒U形的方式调节线粒体功能的三个独立指标，即线粒体的钙保持能力、线粒体氧化和膜电位。皮质酮对线粒体功能的这种调节与神经保护相关：即，低剂量皮质酮治疗显示出神经保护作用，而高剂量治疗则增强了海人酸(一种神经毒素)诱导的皮质神经元毒性。与体外研究一样，大剂量皮质酮长期治疗后，前额叶皮质线粒体中Bcl2水平显著降低，GR水平也显著降低。这些发现有可能有助于更全面地了解糖皮质激素和慢性应激调节细胞可塑性和弹性的机制，并为未来改进治疗方法的发展提供信息。 最近的研究主要集中在GR/Bcl2转运的分子机制上。BAG-1是锂和丙戊酸的下游靶标，与创伤后应激障碍和抑郁症相关基因FKBP51、糖皮质激素受体(GRs)、Bcl2、热休克蛋白70相互作用，并抑制皮质酮(Cort)反应中GR受体的核转位。我们研究了皮质醇治疗后线粒体中BAG-1和FKBP51的水平。我们发现BAG1和FKBP51在培养的皮质神经元线粒体中的分布在皮质醇处理后显著增加；有趣的是，皮质醇治疗后GR和Bcl2线粒体水平也有类似的影响。此外，FKBP51与BAG-1形成复合体，经皮质酮处理后FKBP51与BAG-1复合体的形成增加。然而，BAG-1在神经元匀浆中的总蛋白表达减少，表明CORT对其进行了复杂的调控。值得注意的是，在BAG-1转基因小鼠中过表达BAG-1不仅阻止了线粒体中GR/Bcl-2的减少，而且还阻止了皮质醇治疗后无快乐样行为的形成。野生型FVB小鼠在皮质醇治疗后糖精消耗减少；然而，BAG-1转基因小鼠没有，这表明对高剂量皮质醇具有弹性。这些数据表明，在慢性应激和糖皮质激素调节细胞的可塑性和恢复力，最终对应激性精神障碍的敏感性/恢复力的发展的机制中，关键可塑性分子向线粒体的运输可能发挥重要作用。

Chronic stress has been shown to be associated clinically with formation of depression in patients and hormones are known to mediate certain clinical manifestations of mood disorders. Chronic restraint stress induces a morphological reorganization of neurons in certain areas of rodent brain, effects that are also accompanied by behavioral changes. Although the precise mechanisms underlying these effects remain to be elucidated, a growing body of data suggests that alterations in neuroprotection and mitochondrial functions of glucocorticoid receptors may play an important role in regulating various forms of synaptic and neuronal plasticity; we have sought to investigate the mitochondrial functions regulated by steroid hormones during chronic stress. Glucocorticoids play an important biphasic role in modulating synaptic and neural events, with low doses enhancing synaptic and neuronal plasticity and chronic, higher doses producing inhibition. We undertook a series of experiments to elucidate the mechanisms underlying these biphasic effects. We found that 1) glucocorticoid receptors (GRs) formed a complex with the anti-apoptotic protein Bcl-2 in response to corticosterone treatment, and 2) translocated with Bcl-2 into mitochondria after acute treatment with low or high doses of corticosterone in primary cortical neurons. However, after three days of treatment, high but not low doses of corticosterone resulted in a decrease in GR and Bcl-2 levels in mitochondria. In addition, three independent measures of mitochondrial function, mitochondrial calcium holding capacity, mitochondrial oxidation, and membrane potential were also regulated by long-term corticosterone treatment in an inverted U-shape. This regulation of mitochondrial function by corticosterone correlated with neuroprotection: that is, treatment with low doses of corticosterone demonstrated a neuroprotective effect, whereas treatment with high doses enhanced kainic acid (KA, a neural toxin)-induced toxicity of cortical neurons. As with the in vitro studies, Bcl-2 levels in the mitochondria of the prefrontal cortex were significantly decreased, along with GR levels, after long-term treatment with high-dose corticosterone. These findings have the potential to contribute to a more complete understanding of the mechanisms by which glucocorticoids and chronic stress regulate cellular plasticity and resilience, and to inform the future development of improved therapeutic treatments. Recent studies focused on the molecular mechanism of the GR/Bcl-2 trafficking. BAG-1, a downstream target of lithium and valproate, interacts with PTSD- and depression-associated gene FKBP51, glucocorticoid receptors (GRs), Bcl-2, heat shock protein 70, and inhibits GR receptor nuclear translocation in response to corticosterone (CORT). We studied BAG-1 and FKBP51 levels in the mitochondria after CORT treatment. We found that BAG1 and FKBP51 distribution in the mitochondria was significantly increased in response to CORT treatment in cultured cortical neurons; interestingly, similar effects were seen with GR and Bcl-2 mitochondrial levels after CORT. Furthermore, FKBP51 formed a complex with BAG-1, and the formation of FKBP51 and BAG-1complex increased after CORT treatment. However, total BAG-1 protein expression was decreased in neuronal homogenates, suggesting a complex regulation by CORT. Notably, BAG-1 overexpression in BAG-1 transgenic mice not only blocked the reduction of GR/Bcl-2 in the mitochondria, but also the formation of anhedonic-like behavior after CORT treatment. Wild type FVB mice showed a reduction in saccharine consumption after CORT treatment; however, BAG-1 transgenic mice did not, suggesting a resilience to high dose CORT. These data suggest that the regulation of the trafficking of key plasticity molecules to the mitochondria may play an important role in the mechanisms by which chronic stress and glucocorticoids regulate cellular plasticity and resilience, and ultimately sensitivity/resilience to the development of stress-induced psychiatric disorders.