Molecular mechanisms of LPS preconditioning in stroke

脑卒中前全身给予小剂量脂多糖（LPS）可诱导脑卒中损伤的神经保护作用，这一过程称为LPS预处理或耐受。因此，LPS诱导的预处理的研究提供了希望，在确定新的介质，可以全身给药，赋予中枢神经保护。本申请的主要目的是研究中风中的LPS预处理，并确定辅助这种神经保护过程的特定分子通路。初步数据表明，LPS预处理导致减少细胞浸润到损伤的缺血性脑和抑制细胞活化，这表明LPS预处理改变细胞对随后的伤害性刺激的反应性。巨噬细胞的低剂量LPS处理通过促炎/抗炎介质平衡的转变（称为基因组"重编程"）使它们对随后的高剂量LPS攻击的损伤具有抗性。本提案中的实验将检查LPS预处理是否通过重编程对损伤的反应而远离细胞死亡并有利于细胞存活来对随后的缺血性损伤提供保护。TNF-α是LPS预处理中的重要介质，并可能引发导致卒中后保护的事件。我们中风后的初步数据表明，与未接受LPS治疗的动物相比，在给予LPS治疗的动物的脑中诱导了额外的独特途径。干扰素相关基因是中风前给予LPS治疗的动物中上调的独特基因中的主导特征。我们假设TNF-α和I型IFN在LPS预处理中发挥重要的非重叠作用，导致神经保护作用。我们推测，LPS诱导的TNF-α通过将对随后缺血的细胞反应从损伤和细胞死亡之一重新编程为存活来引发耐受性的出现。随后，由1型IFN调节的途径被激活，从而赋予神经保护作用。使用缺血耐受的体内和体外模型，我们建议：1）阐明TNF-α信号传导在LPS预处理后引发神经保护事件中的作用; 2）确定I型IFN在LPS预处理小鼠缺血损伤后建立神经保护状态中是否起关键作用;和3）测试LPS预处理是否导致对缺血损伤的反应的基因组重编程。这些研究有助于阐明LPS诱导的神经保护的内源性介质，并可能最终导致新的治疗策略。

Neuroprotection against stroke injury can be induced by a small dose of lipopolysaccharide (LPS) given systemically prior to a stroke-a process known as LPS preconditioning or tolerance. As such, the study of LPS-induced preconditioning offers promise in identifying new mediators that can be administered systemically to confer neuroprotection centrally. The primary goal of this application is to investigate LPS preconditioning in stroke and define the specific molecular pathways that sub serve this neuroprotective process. Preliminary data suggest that LPS preconditioning leads to decreased cellular infiltration into the injured ischemic brain and suppressed cellular activation, which suggests that LPS preconditioning alters cellular responsiveness to subsequent injurious stimuli. Low dose LPS treatment of macrophages renders them resistant to the damage of subsequent high dose LPS challenge via a shift in the balance of proinflammatory/anti-inflammatory mediators referred to as genomic 'reprogramming'. Experiments in this proposal shall examine whether LPS preconditioning confers protection to subsequent ischemic injury by reprogramming the response to injury away from cell death and in favor of cell survival. TNF-alpha is an essential mediator in LPS preconditioning and may prime the events that lead to protection following stroke. Our preliminary data following stroke indicate that additional, unique pathways are induced in the brains of animals given prior LPS treatment compared to those not so treated. Interferon-associated genes are a dominant feature among the unique genes upregulated in animals given LPS treatment prior to a stroke. We hypothesize that TNF-alpha and Type I IFNs play essential, non-overlapping roles that lead to neuroprotection in LPS preconditioning. We postulate that LPS-induced TNF-alpha primes the emergence of tolerance by reprogramming the cellular response to subsequent ischemia from one of injury and cell death to that of survival. Subsequently, pathways regulated by Type 1 IFNs are activated which confer neuroprotection. Using in vivo and in vitro models of ischemic tolerance we propose to: 1) Elucidate the role of TNF-alpha signaling in priming the neuroprotective events following LPS preconditioning; 2) Determine whether Type I IFNs play a critical role in establishing a neuroprotective state following ischemic injury in LPS preconditioned mice; and 3) Test whether LPS preconditioning leads to genomic reprogramming of the response to ischemic injury. These studies should help clarify the endogenous mediators of neuroprotection induced by LPS and may ultimately lead to new therapeutic strategies for stroke.