Mechanisms of Free Radical Mediated Injury

脑室周围白质软化(PVL)是早产儿脑性瘫痪的主要病理基础。PVL损伤的主要细胞类型为少突胶质细胞(OL)。由于PVL的发病高峰期在髓鞘形成开始之前，PVL似乎是一种涉及髓鞘前OL(Preols)的病变，而不是成熟的髓鞘碱性蛋白表达的OLs。我们现在知道，小胶质细胞是PVL损伤的重要组成部分，诱导型一氧化氮合酶在小胶质细胞以及反应性星形胶质细胞和OL中强烈表达。本项目的假设是，过氧亚硝酸盐是一种由一氧化氮和超氧化物反应形成的剧毒活性氮物种，在PVL中发生的前OLS的死亡中起着重要作用。我们的初步结果表明， 激活的小胶质细胞对OL的作用依赖于过氧亚硝酸盐的形成。此外，我们已经开始表征过氧亚硝酸盐对细胞毒性的机制，并发现这种物质似乎激活了前OLs中的聚(ADP-核糖)聚合酶(PARP)自杀途径，这在其他类型的细胞中已经得到了很好的表征。有趣的是，我们还获得了证据表明，过氧亚硝酸盐对成熟的白斑和前白斑的毒性涉及花生四烯酸代谢的激活，尽管途径不同。这些结果表明， 至少在一些细胞中，过氧亚硝酸盐激活PARP途径的复杂性比人们所认识到的要复杂得多。本项目的具体目的是：1)研究小胶质细胞激活对前胶原细胞损伤的机制；2)研究过氧亚硝酸根对前胶原细胞损伤的途径(S)；3)研究过氧亚硝酸根在发育中脑白质缺氧/缺血损伤和炎症性损伤中的作用。这些研究将有助于阐明与PVL发病机制相关的发育白质损伤的分子机制，并为设计合理的 治疗这种疾病的方法。

Periventricular leukomalacia (PVL) is the predominant pathology underlying cerebral palsy in premature infants. The primary cell type that is injured in PVL is the oligodendrocyte (OL). Because the period of peak incidence for PVL is prior to the onset of myelination, PVL appears to be a lesion involving premyelinating OLs (preOLs), as opposed to mature, myelin basic protein expressing, OLs. We now know that microglia are an important constituent of the PVL lesion, and that inducible nitric oxide synthase is strongly expressed in microglia as well as in reactive astrocytes and OLs. The hypothesis of this project is that peroxynitrite, a highly toxic reactive nitrogen species formed by reaction of nitric oxide and superoxide, plays an important role in the death of preOLs that occurs in PVL. Our preliminary results suggest that the toxicity of activated microglia to OLs is dependent upon the formation of peroxynitrite. Moreover, we have begun to characterize the mechanisms by which peroxynitrite is toxic to cells, and have found that this substance appears to activate the poly(ADP-ribose) polymerase (PARP) suicide pathway in preOLs that has been well-characterized in other cell types. Interestingly, we have also obtained evidence that peroxynitrite toxicity to mature OLs and preOLs involves activation of arachidonic acid metabolism, although by distinct pathways. These results suggest a greater complexity to the activation of the PARP pathway by peroxynitrite, at least in some cells, than has been appreciated. The specific aims of this project are to: 1) characterize the mechanisms of injury to OLs triggered by activation of microglia; 2) characterize the pathway(s) of injury to preOLs activated by peroxynitrite; 3) test for a role for peroxynitrite in hypoxic/ischemic injury and inflammatory injury to white matter of the developing brain. These studies will help to elucidate the molecular mechanisms of injury to developing white matter pertinent to the pathogenesis of PVL, and provide a foundation for the design of rational treatments for this disorder.