Glial Interactions in Premyelinating Oligodendrocyte Destruction

描述（由申请人提供）：人脑室周围白质软化症（PVL）是脑瘫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的显著激活，髓鞘前少突胶质细胞（preOLs）的选择性丧失和髓鞘形成的紊乱。未成熟大脑的炎症与缺氧/缺血和母体/胎儿感染有关。然而，其促进预ol破坏的机制仍不确定。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，而星形胶质细胞将这种preOL死亡机制“切换”为依赖肿瘤坏死因子（TNF）的死亡机制。我们随后发现，人类PVL中的反应性星形胶质细胞积累了大量的神经酰胺，神经酰胺是一种信号传导鞘脂，在细胞死亡和炎症中起关键作用，并且神经酰胺通过星形胶质细胞依赖机制与TNF协同作用，导致preol的凋亡死亡。此外，星形胶质细胞通过激活的小胶质细胞显著促进TNF的产生。由于TNF在PVL中产生，我们的研究结果表明星形胶质细胞在放大细胞因子对preol的毒性中起重要作用，从而增加弥漫性白质损伤。因此，在之前的资助周期中，我们发现了一种新的致病过程，激活的星形胶质细胞和小胶质细胞在调节ol前死亡中协同作用。在更新中，我们假设星形胶质细胞通过诱导半乳糖凝集素-9放大小胶质细胞的促炎反应，而星形胶质细胞中神经酰胺代谢的破坏使前驱胶质细胞易受炎症破坏。我们的具体目标是：(1)确定半乳糖凝集素-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ol前损伤的机制；(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。我们将使用半乳糖凝集素-9缺陷小鼠来建立半乳糖凝集素-9在调节中枢神经系统炎症反应中的功能。我们还将采用液相色谱串联质谱法监测各种实验范式下生物活性鞘脂的变化，并确定鞘脂参与预ol损伤和保护的特定途径。这个项目可能会对预ol的破坏机制产生新的见解，并且会

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.