Glial Interactions in Premyelinating Oligodendrocyte Destruction

描述(申请人提供)：人类脑室周围白质软化症(PVL)是脑性瘫痪下脑白质损伤的主要形式，也是早产幸存者慢性神经功能障碍的主要原因。随着新生儿重症监护的进展，弥漫性白质损伤已成为PVL的主要形式，其特征是小胶质细胞和星形胶质细胞显著激活，髓鞘前少突胶质细胞选择性丢失，髓鞘形成障碍。未成熟大脑的炎症与缺氧/缺血和母婴感染有关。然而，它促进Preol销毁的机制仍然不确定。我们先前证明，激活的小胶质细胞通过产生过氧亚硝酸盐直接杀死PreOL，星形胶质细胞将这种Preol死亡机制“切换”到依赖肿瘤坏死因子(TNF)的机制。我们随后发现，人PVL中反应性星形胶质细胞积聚了大量神经酰胺，神经酰胺是一种在细胞死亡和炎症中起关键作用的信号鞘糖脂，神经酰胺与肿瘤坏死因子通过星形胶质细胞依赖机制协同作用，导致前OL的凋亡死亡。此外，星形胶质细胞通过激活小胶质细胞显著促进肿瘤坏死因子的产生。由于肿瘤坏死因子是在PVL中产生的，我们的结果提示星形胶质细胞在放大细胞因子对前OLS的毒性方面发挥了重要作用，从而增加了弥漫性白质损伤。因此，在之前的赠款周期中，我们确定了一个新的致病过程，在这个过程中，激活的星形胶质细胞和小胶质细胞共同作用于调节Preol死亡。在更新中，我们假设星形胶质细胞通过诱导Galectin-9放大小胶质细胞的促炎反应，并且星形胶质细胞神经酰胺代谢的中断容易导致前驱OL的炎性破坏。我们的具体目标是(1)确定Galectin-9在调节小胶质细胞免疫反应中的功能；(2)确定星形胶质细胞神经酰胺代谢改变增强Preol损伤的机制；(3)研究调节鞘氨醇-1-磷酸信号通路是否对PVL大鼠模型具有保护作用。我们将利用Galectin-9缺陷小鼠来确定Galectin-9在调节中枢神经系统炎症反应中的作用。我们还将使用液相色谱-串联质谱仪监测不同实验范式下生物活性鞘脂的变化，并确定参与Preol损伤和保护的特定鞘脂途径。这个项目可能会对Preol破坏的机制产生新的见解，并将 为白质损伤的治疗干预提供靶向特定鞘脂信号通路的框架。

DESCRIPTION (provided by applicant): Human periventricular leukomalacia (PVL) is the major form of cerebral white matter injury underlying cerebral palsy and a leading cause of chronic neurological deficits in survivors of premature birth. With advances in neonatal intensive care, diffuse white matter injury has emerged as the principle form of PVL, characterized by prominent activation of microglia and astrocytes, selective loss of premyelinating oligodendrocytes (preOLs) and disturbances in myelination. Inflammation in the immature brain is associated with hypoxia/ischemia and maternal/fetal infection. However, the mechanism by which it contributes to preOL destruction remains uncertain. We demonstrated previously that activated microglia directly kill preOLs through production of peroxynitrite and that astrocytes "switch" this preOL death mechanism to one dependent upon tumor necrosis factor (TNF). We subsequently found that reactive astrocytes in human PVL accumulate significant amounts of ceramide, a signaling sphingolipid with critical roles in cell death and inflammation, and that ceramide acts synergistically with TNF causing apoptotic death of preOLs through an astrocyte dependent mechanism. Moreover, astrocytes markedly promote TNF production by activated microglia. As TNF is generated in PVL, our results suggest that astrocytes play an important role in amplifying cytokine toxicity to preOLs, thereby augmenting diffuse white matter damage. Thus, in the previous grant cycle, we identified a novel, pathogenic process in which activated astrocytes and microglia act co-operatively in regulating preOL demise. In the renewal, we hypothesize that astrocytes amplify microglial proinflammatory responses through induction of galectin-9 and that disruption of ceramide metabolism in astrocytes predisposes preOLs to inflammatory destruction. Our specific aims are (1) to determine the function of galectin-9 in regulating microglia immune responses; (2) to determine the mechanism by which altered ceramide metabolism in astrocytes potentiates preOL injury; and (3) to investigate whether modulating sphingosine-1-phosphate signaling pathway confers protection in a rat model of PVL. We will use galectin-9 deficient mice to establish the function of galectin-9 in regulating CNS inflammatory responses. We will also employ liquid chromatography tandem mass spectrometry to monitor changes of bioactive sphingolipids under various experimental paradigms and identify specific sphingolipid pathways involved in preOL injury and protection. This project is likely to generate novel insights into the mechanism of preOL destruction, and will provide the framework for targeting specific sphingolipid signaling pathways for therapeutic interventions of white matter injury.