MPO and NO signaling in neointima formation

描述（申请人提供）：新生内膜形成是动脉粥样硬化和血管成形术后再狭窄的关键事件。虽然白细胞和新生内膜形成之间存在很强的关联，但参与这一过程的分子机制仍不清楚。髓过氧化物酶（MPO）是一种白细胞来源的血红素蛋白。在生理条件下，MPO催化过氧化氢（H2O2）和氯化物之间的反应，导致MPO衍生的氯化产物的形成。在人类动脉粥样硬化和再狭窄病变中发现高水平的MPO和MPO衍生的氯化产物，并且MPO水平升高与冠心病的存在相关。我们最近发现MPO通过直接消耗NO和通过其氯化产物抑制NO形成对一氧化氮（NO）信号传导具有强烈的负面影响。我们已经证明MPO是一种可转胞吞的蛋白质。与血管结合的MPO可以在血管壁中保留相当长的一段时间。有趣的是，血管结合的MPO不仅可以利用白细胞来源的H2O2，而且还可以利用血管非白细胞来源的H2O2来抑制NO信号传导并诱导内皮功能障碍。由于NO是已知的新生内膜形成的关键调节因子，我们假设MPO通过减少NO信号传导促进血管成形术后新生内膜形成。我们的初步数据首次显示，血管成形术后新生内膜形成时，MPO的过度表达增加，而内源性MPO的抑制减少。具体目标1的研究将进一步确定MPO在大鼠颈动脉球囊损伤后新生内膜形成中的作用。具体目标2将确定球囊损伤后MPO诱导的大鼠颈动脉新生内膜形成效应的分子机制。具体目标3将确定MPO缺陷对NO信号传导和新生内膜形成的影响，以及基因敲除小鼠中NO信号传导缺陷对血管成形术后MPO诱导的新生内膜形成的影响。目前的建议将确定一种新的介质，白细胞源性MPO，在新生内膜形成及其分子机制。阻断MPO通路可能是治疗球囊血管成形术后再狭窄的新途径。

Description (provided by applicant): Neointima formation is a key event in both atherosclerosis and restenosis after angioplasty. Although a strong association exists between leukocyte and neointima formation, the molecular mechanisms involved in this process remain unclear. Myeloperoxidase (MPO) is a leukocyte-derived heme protein. Under physiological conditions, MPO catalyzes the reaction between hydrogen peroxide (H2O2) and chloride resulting in the formation of MPO-derived chlorinating products. High levels of MPO and MPO-derived chlorinating products are found in human atherosclerotic and restenotic lesions and that elevated levels of MPO are associated with the presence of coronary heart disease. We have recently shown that MPO has a strong negative effect on nitric oxide (NO) signaling both by direct NO consumption and inhibition of NO formation via its chlorinating products. We have demonstrated that MPO is a transcytosable protein. Vessel bound MPO can remain in the vascular wall for a significant period of time. Interestingly, vessel bound MPO not only can use leukocyte-derived H2O2, but also vascular non-leukocyte-derived H2O2 to inhibit NO signaling and induce endothelial dysfunction. Since NO is a known key regulator of neointima formation, we hypothesize that MPO contributes to neointima formation after angioplasty by diminishing NO signaling. Our preliminary data have shown, for the first time, that overexpression of MPO increases, whereas inhibition of endogenous MPO decreases, neointima formation after angioplasty. Studies in specific aim 1 will further determine the role of MPO on neointima formation in rat carotid arteries after balloon injury. Specific aim 2 will identify the molecular mechanism(s) involved in the MPO-induced effect on neointima formation in rat carotid arteries after balloon injury. Specific aim 3 will determine the effect of MPO deficiency on NO signaling and neointima formation, and the effect of NO signaling deficiency on MPO-induced neointima formation after angioplasty in gene knock-out mice. The current proposal will identify a novel mediator, leukocyte-derived MPO, in neointima formation and its molecular mechanism(s). Blocking the MPO pathway might be a new therapeutic approach to restenosis after balloon angioplasty.