Stetler R Anne, Cao Guodong, Gao Yanqin, Zhang Feng, Wang Suping, Weng Zhongfang, Vosler Peter, Zhang Lili, Signore Armando, Graham Steven H, Chen Jun
Department of Neurology and Center of Cerebrovascular Diseases Research, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
J Neurosci. 2008 Dec 3;28(49):13038-55. doi: 10.1523/JNEUROSCI.4407-08.2008.
Heat shock protein 27 (Hsp27), a recently discovered member of the heat shock protein family, is markedly induced in the brain after cerebral ischemia and other injury states. In non-neuronal systems, Hsp27 has potent cell death-suppressing functions. However, the mechanism of Hsp27-mediated neuroprotection has not yet been elucidated. Using transgenic and viral overexpression of Hsp27, we investigated the molecular mechanism by which Hsp27 exerts its neuroprotective effect. Overexpression of Hsp27 conferred long-lasting tissue preservation and neurobehavioral recovery, as measured by infarct volume, sensorimotor function, and cognitive tasks up to 3 weeks following focal cerebral ischemia. Examination of signaling pathways critical to neuronal death demonstrated that Hsp27 overexpression led to the suppression of the MKK4/JNK kinase cascade. While Hsp27 overexpression did not suppress activation of an upstream regulatory kinase of the MKK/JNK cascade, ASK1, Hsp27 effectively inhibited ASK1 activity via a physical association through its N-terminal domain and the kinase domain of ASK1. The N-terminal region of Hsp27 was required for neuroprotective function against in vitro ischemia. Moreover, knockdown of ASK1 or inhibition of the ASK1/MKK4 cascade effectively inhibited cell death following neuronal ischemia. This underscores the importance of this kinase cascade in the progression of ischemic neuronal death. Inhibition of PI3K had no effect on Hsp27-mediated neuroprotection, suggesting that Hsp27 does not promote cell survival via activation of PI3K/Akt. Based on these findings, we conclude that overexpression of Hsp27 confers long-lasting neuroprotection against ischemic brain injury via a previously unexplored association and inhibition of ASK1 kinase signaling.
热休克蛋白27（Hsp27）是热休克蛋白家族中最近发现的成员，在脑缺血和其他损伤状态后，其在大脑中会显著诱导表达。在非神经元系统中，Hsp27具有强大的抑制细胞死亡的功能。然而，Hsp27介导神经保护的机制尚未阐明。我们利用Hsp27的转基因和病毒过表达，研究了Hsp27发挥神经保护作用的分子机制。通过梗死体积、感觉运动功能以及局灶性脑缺血后长达3周的认知任务来衡量，Hsp27的过表达赋予了持久的组织保护和神经行为恢复。对神经元死亡至关重要的信号通路的检测表明，Hsp27的过表达导致MKK4/JNK激酶级联反应受到抑制。虽然Hsp27的过表达并未抑制MKK/JNK级联反应的上游调节激酶ASK1的激活，但Hsp27通过其N端结构域与ASK1的激酶结构域的物理结合有效地抑制了ASK1的活性。Hsp27的N端区域对于体外缺血的神经保护功能是必需的。此外，敲低ASK1或抑制ASK1/MKK4级联反应可有效抑制神经元缺血后的细胞死亡。这突出了该激酶级联反应在缺血性神经元死亡进展中的重要性。抑制PI3K对Hsp27介导的神经保护没有影响，这表明Hsp27不会通过激活PI3K/Akt来促进细胞存活。基于这些发现，我们得出结论，Hsp27的过表达通过一种先前未被探索的与ASK1激酶信号的关联和抑制作用，赋予了对缺血性脑损伤的持久神经保护。
