Division of Pediatric Neurosurgery, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
Department of Radiology, Imaging Research Center, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
Fluids Barriers CNS. 2023 Jun 9;20(1):42. doi: 10.1186/s12987-023-00433-4.
Neonatal hydrocephalus is a congenital abnormality resulting in an inflammatory response and microglial cell activation both clinically and in animal models. Previously, we reported a mutation in a motile cilia gene, Ccdc39 that develops neonatal progressive hydrocephalus (prh) with inflammatory microglia. We discovered significantly increased amoeboid-shaped activated microglia in periventricular white matter edema, reduced mature homeostatic microglia in grey matter, and reduced myelination in the prh model. Recently, the role of microglia in animal models of adult brain disorders was examined using cell type-specific ablation by colony-stimulating factor-1 receptor (CSF1R) inhibitor, however, little information exists regarding the role of microglia in neonatal brain disorders such as hydrocephalus. Therefore, we aim to see if ablating pro-inflammatory microglia, and thus suppressing the inflammatory response, in a neonatal hydrocephalic mouse line could have beneficial effects.
In this study, Plexxikon 5622 (PLX5622), a CSF1R inhibitor, was subcutaneously administered to wild-type (WT) and prh mutant mice daily from postnatal day (P) 3 to P7. MRI-estimated brain volume was compared with untreated WT and prh mutants P7-9 and immunohistochemistry of the brain sections was performed at P8 and P18-21.
PLX5622 injections successfully ablated IBA1-positive microglia in both the WT and prh mutants at P8. Of the microglia that are resistant to PLX5622 treatment, there was a higher percentage of amoeboid-shaped microglia, identified by morphology with retracted processes. In PLX-treated prh mutants, there was increased ventriculomegaly and no change in the total brain volume was observed. Also, the PLX5622 treatment significantly reduced myelination in WT mice at P8, although this was recovered after full microglia repopulation by P20. Microglia repopulation in the mutants worsened hypomyelination at P20.
Microglia ablation in the neonatal hydrocephalic brain does not improve white matter edema, and actually worsens ventricular enlargement and hypomyelination, suggesting critical functions of homeostatic ramified microglia to better improve brain development with neonatal hydrocephalus. Future studies with detailed examination of microglial development and status may provide a clarification of the need for microglia in neonatal brain development.
新生儿脑积水是一种先天性异常，在临床和动物模型中都会导致炎症反应和小胶质细胞激活。此前，我们报道了一个运动纤毛基因 Ccdc39 的突变，该突变导致新生儿进行性脑积水（prh）伴有炎症性小胶质细胞。我们发现，在脑室周围白质水肿中，阿米巴样激活的小胶质细胞显著增加，灰质中成熟的稳态小胶质细胞减少，prh 模型中的髓鞘形成减少。最近，使用集落刺激因子 1 受体（CSF1R）抑制剂对成年脑疾病的动物模型中小胶质细胞的作用进行了检查，然而，关于小胶质细胞在新生儿脑疾病（如脑积水）中的作用的信息很少。因此，我们旨在观察是否可以通过消融促炎小胶质细胞（从而抑制炎症反应）来改善新生脑积水小鼠模型的状况。
在这项研究中，从出生后第 3 天到第 7 天，每天给野生型（WT）和 prh 突变小鼠皮下注射普莱克斯 5622（PLX5622），一种 CSF1R 抑制剂。在第 7-9 天，通过 MRI 估计脑容量，并对未经处理的 WT 和 prh 突变体的脑切片进行免疫组织化学分析。
PLX5622 注射可在第 8 天成功消融 WT 和 prh 突变体中的 IBA1 阳性小胶质细胞。在对 PLX5622 治疗有抗性的小胶质细胞中，有更高比例的阿米巴样小胶质细胞，通过回缩突起的形态来识别。在 PLX 处理的 prh 突变体中，脑室扩大增加，而总脑容量没有变化。此外，PLX5622 治疗在第 8 天显著降低了 WT 小鼠的髓鞘形成，但在第 20 天完全重新填充小胶质细胞后得到恢复。突变体中小胶质细胞的重新填充使第 20 天的少突胶质细胞发育不良恶化。
在新生脑积水脑内消融小胶质细胞并不能改善白质水肿，实际上还会加重脑室扩大和少突胶质细胞发育不良，这表明稳态分支小胶质细胞的关键功能对于改善新生儿脑积水的脑发育更为重要。未来的研究需要对小胶质细胞的发育和状态进行详细检查，以阐明新生儿脑发育过程中小胶质细胞的必要性。
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