BACKGROUND Neuroinflammation plays an important role in ischemic brain injury and recovery, however the interplay between brain development and the neuroinflammatory response is poorly understood. We previously described age-dependent differences in the microglial response and the effect of microglial inhibition. Here we investigate whether age-dependent microglial responses may be related to pre-injury developmental differences in microglial phenotype. METHODS Measures of microglia morphology were quantified using semi-automated software analysis of immunostained sections from postnatal day 2 (P2), P9, P30 and P60 mice using IMARIS. Microglia were isolated from P2, P9, P30 and P60 mice, and expression of markers of classical and alternative microglial activation was assessed, as well as transforming growth factor beta (TGF-β) receptor, Serpine1, Mer Tyrosine Kinase (MerTK), and the suppressor of cytokine signaling (SOCS3). Hypoxia-ischemia (HI) was induced in P9 and P30 mice using unilateral carotid artery ligation and exposure to 10% oxygen for 50 min. Microglia morphology and microglial expression of genes in the TGF-β and MerTK pathways were determined in ipsilateral and contralateral hippocampus. RESULTS A progressive and significant increase in microglia branching morphology was seen in all brain regions from P2 to P30. No consistent classical or alternative activation profile was seen in isolated microglia. A clear transition to increased expression of TGF-β and its downstream effector serpine1 was seen between P9 and P30. A similar increase in expression was seen in MerTK and its downstream effector SOCS3. HI resulted in a significant decrease in branching morphology only in the P9 mice, and expression of TGF-β receptor, Serpine1, MerTK, and SOCS3 were elevated in P30 mice compared to P9 post-HI. CONCLUSION Microglia maturation is associated with changes in morphology and gene expression, and microglial responses to ischemia in the developing brain differ based on the age at which injury occurs.

中文翻译：

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在正常的大脑发育和对缺氧缺血的反应中，小胶质细胞形态和基因表达的发育差异。

背景技术神经炎症在缺血性脑损伤和恢复中起重要作用，但是人们对大脑发育和神经炎症反应之间的相互作用了解甚少。我们先前描述了小胶质细胞反应和小胶质细胞抑制作用的年龄依赖性差异。在这里我们调查年龄依赖性的小胶质细胞反应是否可能与小胶质细胞表型的损伤前发育差异有关。方法使用IMARIS，使用出生后第2天（P2），P9，P30和P60小鼠的免疫染色切片的半自动化软件分析，对小胶质细胞形态学指标进行定量。从P2，P9，P30和P60小鼠中分离出小胶质细胞，并评估了经典和替代性小胶质细胞激活标记的表达以及转化生长因子β（TGF-β）受体Serpine1，Mer酪氨酸激酶（MerTK）和细胞因子信号转导的抑制因子（SOCS3）。使用单侧颈动脉结扎并暴露于10％氧气50分钟，在P9和P30小鼠中诱发缺氧缺血（HI）。测定了同侧和对侧海马中TGF-β和MerTK途径中的小胶质细胞形态和基因的小胶质细胞表达。结果在从P2到P30的所有脑区域中，均观察到小胶质细胞分支形态的逐渐显着增加。在分离的小胶质细胞中未观察到一致的经典或替代活化特征。在P9和P30之间可以看到TGF-β及其下游效应子serpine1表达明显增加。在MerTK及其下游效应器SOCS3中发现了类似的表达增加。HI仅导致P9小鼠的分支形态显着降低，与HI后的P9相比，P30小鼠的TGF-β受体，Serpine1，MerTK和SOCS3的表达升高。结论小胶质细胞的成熟与形态和基因表达的变化有关，并且小胶质细胞对大脑缺血的反应取决于发生损伤的年龄。