Molecular mechanisms of LPS preconditioning in stroke

对中风损伤的神经保护可以通过在中风前系统地给予小剂量的脂多糖(LPS)来诱导-这一过程被称为内毒素预适应或耐受。因此，对脂多糖诱导的预适应的研究为确定新的介质提供了希望，这些介质可以系统地给予给予中枢神经保护。这项应用的主要目标是研究中风患者的内毒素预适应，并确定辅助这一神经保护过程的特定分子通路。初步数据表明，内毒素预适应导致损伤的缺血脑内细胞浸润减少，并抑制细胞激活，这表明内毒素预适应改变了细胞对后续损伤刺激的反应。低剂量的内毒素治疗使巨噬细胞对随后的大剂量内毒素攻击的损害具有抵抗力，这是通过改变促炎/抗炎介质的平衡来实现的，这种平衡被称为基因组“重编程”。这项建议中的实验应检查内毒素预适应是否通过重新编程对损伤的反应而不是细胞死亡而有利于细胞存活来保护后续的缺血损伤。肿瘤坏死因子-α是脂多糖预适应中的重要介质，并可能启动卒中后的保护作用。我们在卒中后的初步数据表明，与未接受内毒素治疗的动物相比，在给予内毒素治疗之前的动物的大脑中诱导了额外的、独特的通路。在中风前接受脂多糖治疗的动物中，干扰素相关基因是上调的独特基因中的一个显性特征。我们假设，在内毒素预适应中，肿瘤坏死因子-α和I型干扰素在神经保护中发挥着重要的、非重叠的作用。我们推测，内毒素诱导的肿瘤坏死因子-α通过重新编程细胞对后续缺血的反应，从损伤和细胞死亡反应到存活反应，从而启动耐受的出现。随后，由1型干扰素调节的通路被激活，从而提供神经保护。利用体内和体外的缺血耐受模型，我们建议：1)阐明TNF-α信号在内毒素预适应后启动神经保护事件中的作用；2)确定I型IFN在内毒素预适应小鼠脑缺血损伤后建立神经保护状态中是否发挥关键作用；3)测试内毒素预适应是否导致对缺血损伤的反应的基因组重编程。这些研究应该有助于阐明脂多糖诱导的神经保护的内源性介质，并最终可能导致中风的新治疗策略。

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.