Endotoxin Generated Lipid Second Messengers

描述(由申请人提供)：启动和促进动脉粥样硬化形成的事件没有明确的定义，但在容易发生病变的部位，低密度脂蛋白在血管壁中的隔离是其中之一。结合的低密度脂蛋白氧化成促动脉粥样硬化的形式，与CD36等清道夫受体结合，导致不适当的细胞内脂肪堆积和泡沫细胞的形成。 动脉粥样硬化病变可以含有肺炎衣原体，这种感染构成了动脉粥样硬化的危险因素。肺炎链球菌感染巨噬细胞会导致泡沫细胞的形成，暴露在其纯化的脂多糖(LPS)中也会导致泡沫细胞的形成。脂多糖是如何诱导脂肪堆积或刺激基因转录的，目前尚不清楚。 我们发现，内毒素诱导单核细胞CD36清道夫受体基因的表达，导致表面表达增强，细胞内脂滴聚集和泡沫细胞形成。CD36由转录因子PPARGamma控制，我们发现LPS出人意料地激活了PPAR反应元件(PPRE)报告元件。事实上，内毒素通过其PPRE激活CD36启动子。PPARGamma是由脂质配体激活的；合成药物可以做到这一点，但高亲和力的生理学PPAR3配体尚不清楚。脂多糖不与PPARγ结合，因此可诱导内源性激动剂的形成。 我们发现溶血磷脂酸(LPA)是一种PPAR-γ配体和激动剂--这提供了第一个证据，表明这可能是该转录因子长期寻找的生理激动剂。LPA刺激PPRE驱动的报告分子，诱导CD36的表达，并将单核细胞分化为泡沫细胞。我们证明这种信号在几个方面独立于EDG(表面LPA受体)信号。 我们发现，脂多糖增加了细胞内的LPA水平，并且通过转基因的LPA酰基转移酶代谢这种细胞内的LPA会抑制PPAR7的激活和功能。在这里，我们建议定义内毒素诱导LPA积聚的方式，并确定LPA激活细胞内核激素受体/转录因子对泡沫细胞形成的影响。了解生理配体的身份使我们能够为合理设计的PPAR伽马抑制剂建立高通量筛选。一种不可水解性的LPA类似物阻断了PPARy的功能，并可能定义一类新的抗炎、抗血脂药物。

DESCRIPTION (provided by applicant): The events that initiate and promote atherogenesis are not well defined, but sequestration of LDL in the vascular wall at sites prone to lesion development is one. Bound LDL oxidizes to a pro-atherogenic form that is bound by scavenger receptors like CD36, leading to inappropriate intracellular lipid accumulation and foam cell formation. Atherosclerotic lesions can contain Chlamydia pneumoniae, and such infections constitute a risk factor for atherosclerosis. Macrophage infection by C. pneumoniae results in foam cell formation, as does exposure to its purified lipopolysaccharide (LPS). How LPS induces lipid accumulation or stimulates gene transcription is unknown. We find that LPS induces expression of the CD36 scavenger receptor gene in monocytes, leading to enhanced surface expression, and to intracellular lipid droplet accumulation and foam cell formation. CD36 is controlled by the transcription factor PPARgamma, and we find that LPS, unexpectedly, activates a PPAR responsive element (PPRE)-reporter. In fact, LPS activates the CD36 promoter through its PPRE. PPARgamma is activated by lipid ligands; synthetic drugs do this, but high affinity physiologic PPAR3, ligands are unknown. LPS does not bind PPARgamma, so it induced the formation of an endogenous agonist. We find that lysophosphatidic acid (LPA) is a PPARgamma ligand and agonist --providing the first evidence that this might be the long sought after physiologic agonist for this transcription factor. LPA stimulates PPRE-driven reporters, induces CD36 expression, and differentiates monocytes to foam cells. We show this signaling is independent of Edg (surface LPA receptors) signaling in several ways. We find that LPS increases cellular LPA levels, and that metabolizing this intracellular LPA by transfected LPA acyltransferase blocks PPAR7 activation and function. Here we propose to define the way in which LPS induces LPA accumulation, and determine the consequences of LPA activation of an intracellular nuclear hormone receptor/transcription factor on foam cell formation. Knowing the identity of the physiologic ligand has allowed us to establish a high throughput screen for rationally designed PPARgamma inhibitors. One non-hydrolyzable LPA analog blocks PPARy function and might define a new class of anti-infiammatory, anti-lipidic agents.