GSK3b mediates convergence of protection signaling to limit mitochondrial damage

环境压力集中在线粒体上，可以触发或抑制细胞死亡。可兴奋的有丝分裂后细胞（如心脏中的心肌细胞和脑中的神经元）响应于亚致死性有害应激而参与提供保护以免受随后的损伤的机制。这些保护机制涉及内源性信号传导的激活，这可以赋予对氧化剂和与缺氧/复氧相关的其他应激的显着抵抗力（即，在心脏病发作或中风期间），这促进了细胞存活能力的增强。然而，上游信号传导机制仍然是一个活跃的辩论领域，并且末端效应器仍然没有解决。 我们发现，长时间缺氧后的复氧降低了活性氧（ROS-）阈值的线粒体通透性转换（mPTP）在心肌细胞中，细胞存活率是急剧负相关的去极化线粒体的分数。我们证明了各种各样的心脏/神经保护剂通过不同的上游机制发挥作用，通过限制mPTP诱导来促进细胞存活。我们发现，保护可以以2种依赖于和不依赖于调节线粒体肿胀的一般方式触发，其通过抑制GSK-3b对末端效应物（渗透性转换孔复合物）的作用而会聚，从而防止mPTP。表现出记忆的细胞保护（即，预处理（"预处理"）是由触发的线粒体肿胀（由于通过流入和/或滞留增强的K+积累）引起的，引起增强的底物氧化和ROS产生，导致PKC的氧化还原活化，其反过来抑制GSK-3b（通过ser-9的磷酸化）。例如，二氮嗪激活的线粒体ATP依赖性K+通道（mitoKATP，我们已经鉴定并正在鉴定）和Ca2+激活的K+通道都可以作为线粒体K+内流机制（可以介导线粒体调节性肿胀依赖性保护等）。δ-阿片肽DADLE和NHE抑制剂HOE 642（cariporide）和HOE 694各自产生独立于mitoKATP的线粒体调节性肿胀依赖性保护。或者，受体酪氨酸激酶或某些G-蛋白偶联受体活化通过抑制GSK-3b，经由PKB/Akt和mTOR/p70s6k、PKC或PKA途径，增强细胞保护（没有线粒体肿胀或持久记忆）。后一类的例子包括胰岛素（通过Akt和mTOR/p70s6k）和直接GSK-3抑制剂Li+。 我们发现，GSK-3b的siRNA敲低，而不是GSK-3a，诱导保护状态，并且表达GSK-3b的心脏限制性、组成性活性、不可复制形式（GSK-3b S9A）的转基因小鼠对有效诱导WT小鼠保护状态的整个上游信号电池具有抗性。 我们得出结论，GSK-3b（特别是其失活）是一个主要的，所需的整合点的上游信号作用于一个负责心脏保护的末端效应（线粒体通透性转换孔）。 当细胞保护信号通路被激活时，我们发现Bcl-2家族成员将GSK-3b的信号传递到孔处或孔附近的靶标上。 因此，通过抑制GSK-3b（通过Bcl-2蛋白中继）对末端效应物（渗透性转换孔复合物）的这些信号传导途径的会聚以限制mPTP诱导的作用是心肌细胞保护的一般机制。 我们建议，临床治疗策略，旨在抑制主开关激酶，GSK-3b，以保护渗透性转换孔复合物从mPTP诱导，将有效地减少心肌梗死的大小在心脏病发作或中风发作，防止心肌细胞和神经元的死亡（分别）。 正在研究与年龄相关的缺血预适应能力丧失的潜在信号缺陷，这可能导致与健康老龄化相关的可测试的临床治疗。

Environmental stresses converge on the mitochondria that can trigger or inhibit cell death. Excitable, post-mitotic cells (such as cardiac myocytes in heart, and neurons in brain), in response to sub-lethal noxious stress engage mechanisms affording protection from subsequent insults. These protection mechanisms involve activation of endogenous signaling which can confer significant resistance to oxidant and other stresses associated with hypoxia/reoxygenation (i.e., during a heart attack or stroke), which promotes the enhanced capacity for cell survival. However, the upstream signaling mechanisms have remained an area of active debate, and the end effector(s) have remained unsolved. We show that reoxygenation after prolonged hypoxia reduces the reactive oxygen species- (ROS-) threshold for the mitochondrial permeability transition (mPTP) in cardiac myocytes, and that cell survival is steeply negatively correlated with the fraction of depolarized mitochondria. We demonstrate that a wide variety of cardio/neuroprotective agents acting via distinct upstream mechanisms all promote cell survival by limiting mPTP induction. We found that protection can be triggered in 2 general ways dependent and independent of regulatory mitochondrial swelling which converge via inhibition of GSK-3b on the end effector, the permeability transition pore complex, preventing the mPTP. Cell protection exhibiting a memory (i.e., "preconditioning") results from triggered mitochondrial swelling (due to enhanced K+ accumulation via influx and/or retention) causing enhanced substrate oxidation and ROS production, leading to redox activation of PKC which in turn inhibits GSK-3b (via phosphorylation of ser-9). Both the diazoxide-activated mitochondrial ATP dependent K+ channel (mitoKATP, which we have identified and are now chararcterizing), and the Ca2+-activated K+ channel, for example, can serve as mitochondrial K+ influx mechanisms (that can mediate mitochondrial regulatory swelling-dependent protection, etc). The delta-opioid peptide, DADLE, and the NHE-inhibitors, HOE 642 (cariporide) and HOE 694, each produce mitochondrial regulatory swelling-dependent protection independently of the mitoKATP. Alternatively, receptor tyrosine kinase or certain G-protein coupled receptor activation elicits cell protection (without mitochondrial swelling or durable memory) by inhibiting GSK-3b, via either PKB/Akt and mTOR/p70s6k, PKC, or PKA pathways. Examples of this latter class include insulin (via Akt and mTOR/p70s6k) and the direct GSK-3 inhibitor, Li+. We found that siRNA knock-down of GSK-3b, but not GSK-3a, induced the protection state, and that transgenic mice expressing a cardiac-restricted, constitutively active, non-inhibitable form of GSK-3b (GSK-3b S9A) were resistant to a whole battery of upstream signals that were effective to induce the protected state in WT mice. We concluded that GSK-3b (and specifically its inactivation) is a major, required integration point for a multitude of upstream signals acting on an end-effector responsible for cardioprotection (the mitochondrial permeability transition pore). When cell protection signaling pathways are activated, we found that the Bcl-2 family members relay the signal from GSK-3b onto a target at or in close proximity to the pore. Thus, the effect of the convergence of these signaling pathways via inhibition of GSK-3b, relayed through Bcl-2 proteins, on the end effector, the permeability transition pore complex, to limit mPTP induction, is the general mechanism of cardiomyocyte protection. We propose that clinical treatment strategies designed to inhibit the master switch kinase, GSK-3b, to protect the permeability transition pore complex from mPTP induction, would be effective to reduce the size of infarction during episodes of heart attack or stroke by preventing the death of cardiac myocytes and neurons (respectively). Signaling defects underlying the age-assocciated loss of the capacity for ischemic preconditioning are being examined which could lead to testable clinical therapies relevant to the preservation of healthy aging.