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012. PLX5622-Mediated Microglial Ablation in Ccdc39 Mouse Model of Neonatal Hydrocephalus

Authors: Farrah Nicole Brown

Introduction:
Neonatal hydrocephalus is a congenital abnormality resulting in an inflammatory response and microglial activation in patients and animal models. Recently, microglial ablation by colony stimulating factor one receptor (CSF1R) inhibitor has been tested in animal models of adult brain disorders, but little evidence exists in neonatal brain research. Previously, we reported a mutation in a motile cilia gene, Ccdc39, develops neonatal progressive hydrocephalus with inflammatory microglia. We discovered significantly increased ameboid-shaped activated microglia in periventricular white matter edema, reduced mature homeostatic microglia in grey matter, and reduced CNPase+ myelination in this model.Methods: PLX5622, a CSF1R inhibitor, was subcutaneously administered (50mg/kg) to wild types (WT) and prh mutant mice daily from postnatal day (P) 3 to 7. Immunohistochemistry of the brain sections was compared between four groups of: PLX-WT; PLX-prh; untreated-WT; and untreated-prh at P8 (n ? 5 each).
Results:
PLX5622 injections successfully ablated ? 89% of Iba1+ microglia in both the WT and prh mutants. Of the microglia which survived PLX5622 treatment, there were a higher percentage amoeboid-shaped microglia, identified by morphology with retracted processes (p=0.0224 PLX-WT and p < 0.0001 PLX-prh). PLX5622 treatment left a higher percentage of ApoE+ immature microglia (p=0.0400) in the grey matter of PLX-WT. In PLX-prh, there was no improvement in the white matter edema, and the gray matter was significantly thinner (p < 0.0001). Also, the PLX5622 treatment significantly reduced myelination in PLX-WT (p=0.0148).
Conclusion:
Incomplete microglia ablation in the neonatal brain does not improve edema or hypomyelination in hydrocephalus, suggesting critical functions of homeostatic ramified microglia in brain development. A detailed examination of neonatal brain development in microglia-ablated mice should continue to be explored through brain volume analysis with MRI, clinical outcomes through survival data, and histology with inflammatory/residential microglia markers.