The role of CD36 in ischemic inflammation and injury

描述(申请人提供)：中风引起的脑损伤主要是从神经中心的角度来看的，主要关注原发损伤部位及其半影区。然而，从最近的研究中得出的一个重要概念，包括我们自己的观点，支持这样一种观点，即外周炎症状态影响原发损伤的结果。本研究的目的是探讨脑缺血对外周免疫功能的调节机制(S)及其在卒中后中枢神经系统损伤中的作用。具体地说，我们认为脾单核细胞通过一种新的CD36机制在卒中介导的损伤中发挥关键作用。卒中可导致外周血单核细胞渗入原发损伤部位。单核细胞转运是一个严格控制的事件，涉及表达或不表达促炎趋化因子受体CCR2的单核细胞亚群的顺序招募。高脂血症扩大了脾中CCR2+单核细胞亚群，加速了心脑血管疾病的进展。我们最近做了一项令人兴奋的观察，将脾与中风的病理联系起来；与高脂血症相关的损伤越大，脾重量减轻越大，脑缺血后CCR2的表达越高。这导致我们假设，在高脂血症条件下，脾CCR2+单核细胞参与了中风引起的脑损伤。此外，我们发现CD36是一种炎症介质，参与了卒中所致的脑损伤。缺乏CD36的小鼠逆转了与高脂血症相关的表型，并导致脑内CCR2表达减少和较小的梗塞。这些观察结果导致了随后的假设，即CD36调节了脾CCR2+单核细胞对脑梗塞的动员。因此，靶向CD36具有神经保护作用。目的1确定脾CCR2+单核细胞在卒中后损伤中的作用。我们将建立卒中后脑和脾中CCR2+单核细胞亚群的时间变化。脾单核细胞的必要性和充分性将在接受脾切除的小鼠和通过过继转移接受外源脾单核细胞的脾切除小鼠中进行研究。目的2将确定CD36是否调节CCR2单核细胞转运到脑梗塞。我们将评估卒中后CD36表达和缺陷小鼠脾和脑中CCR2+单核细胞的变化。体内单核细胞转运将通过过继转移的GFP+单核细胞进行评估。进一步的体外研究将确定CD36缺乏对CCR2+单核细胞亚群的影响，以及它们在循环中获得CCR2+表型的能力。AIM 3将利用几种方法来抑制CD36。为了选择性地抑制单核细胞CD36，将使用CD36缺陷的单核细胞。使用CD36抑制剂进行急性缺血后治疗和慢性预防性治疗的其他药理学方法将补充基于遗传细胞的方法。了解外周血单核细胞对原发损伤的影响可能会为神经免疫调节在中风和一系列炎症性疾病中的治疗应用打开大门。 公共卫生相关性：高血脂水平与外周炎症有关，并加速心脑血管疾病的进展。目前的提案研究了在高脂血症的情况下，脾如何能够改善中风引起的脑损伤的结果，而脾曾经被认为是免疫系统的一个“可有可无”的外周器官。了解潜在的事件将产生新的治疗策略来阻止或减缓炎症性疾病的进展。

DESCRIPTION (provided by applicant): Stroke-induced brain injury has been viewed mainly from a neurocentric perspective, with much attention given to the primary injury site and its penumbra. However, an important notion derived from recent studies, including our own, favor a view that the peripheral inflammatory state influences the outcome of primary injury. The goal of this proposal is to investigate the mechanism(s) by which peripheral immunity may be regulated by cerebral ischemia and how this contributes to CNS damage in stroke. Specifically, we propose that spleen monocytes play a critical role in stroke-mediated injury through a novel CD36 mechanism. Stroke induces infiltration of peripheral monocytes into primary injury sites. The monocyte trafficking is a tightly controlled event that involves sequential recruitment of monocyte subsets that either express or do not express the pro-inflammatory chemokine receptor CCR2. Hyperlipidemia expands the CCR2+ monocyte subset in the spleen and accelerates the progression of cardio- and cerebrovascular diseases. We recently made an exciting observation that links the spleen to stroke pathology; the larger the injury associated with hyperlipidemia, the greater the reduction in spleen weight, and the higher the expression of CCR2 in the post- ischemic brain. This led us to hypothesize that the spleen CCR2+ monocytes contribute to stroke-induced brain injury in hyperlipidemic conditions. Furthermore, we identified CD36 as an inflammatory mediator that contributes to stroke induced brain injury. CD36 deficiency in mice reversed the hyperlipidemia-associated phenotype and resulted in reduced CCR2 expression in the brain and a smaller infarct. These observations led to the subsequent hypotheses that CD36 regulates the mobilization of spleen CCR2+ monocytes to the infarct. Therefore, targeting CD36 is neuroprotective. Aim 1 will determine the role of spleen CCR2+ monocytes in injury following stroke. We will establish temporal changes of CCR2+ monocyte subsets in the brain and spleen following stroke. The necessity and sufficiency of spleen monocytes will be investigated in mice that have undergone a splenectomy and in splenectomized mice that have received exogenous spleen monocytes via adoptive transfer. Aim 2 will determine if CD36 regulates CCR2 monocyte trafficking to infarct. We will assess CCR2+ monocytes in the spleen and brain of CD36-expressing and -deficient mice after stroke. Monocyte trafficking will be evaluated in vivo by adoptively transferred GFP+ monocytes. Additional in vitro study will determine the effect of CD36 deficiency on CCR2+ monocyte subsets and their ability to acquire the CCR2+ phenotype in circulation. Aim 3 will utilize several approaches to inhibit CD36. To selectively inhibit monocyte CD36, CD36-deficient monocytes will used. Additional pharmacological approaches using a CD36 inhibitor for acute post-ischemic treatment and chronic preventive treatment will complement the genetic cell- based approach. Understanding of peripheral monocyte influence on the primary injury may open the door to the therapeutic application of neuro-immune modulation for stroke and a host of inflammatory diseases. PUBLIC HEALTH RELEVANCE: Elevated plasma lipid levels are associated with peripheral inflammation and accelerate the progression of cardio- and cerebrovascular diseases. The current proposal investigates how the spleen, once thought to be a "dispensable" peripheral organ of the immune system, can amend the outcome of stroke-induced brain injury in the hyperlipidemic condition. Understanding the underlying events will give rise to novel therapeutic strategies to block or slow down the inflammatory disease progression.