Aggravated brain injury after neonatal hypoxic ischemia in microglia-depleted mice

Abstract

Abstract Background Neuroinflammation plays an important role in neonatal hypoxic-ischemic encephalopathy (HIE). Although microglia are largely responsible for injury-induced inflammatory response, they play beneficial roles in both normal and disease states. However, the effects of microglial depletion on neonatal HIE remain unclear. Methods Tamoxifen was administered to Cx3cr1 CreER/+ Rosa26 DTA/+ (microglia-depleted model) and Cx3cr1 CreER/+ Rosa26 DTA/− (control) mice at P8 and P9 to assess the effect of microglial depletion. The density of microglia was quantified using Iba-1 staining. Moreover, the proportion of resident microglia after the HI insult was analyzed using flow cytometric analysis. At P10, the HI insult was conducted using the Rice-Vannucci procedure at P10. The infarct size and apoptotic cells were analyzed at P13. Cytokine analyses were performed using quantitative polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA) at P13. Results At P10, tamoxifen administration induced > 99% microglial depletion in DTA + mice. Following HI insult, there was persisted microglial depletion over 97% at P13. Compared to male DTA − mice, male DTA + mice exhibited significantly larger infarct volumes; however, there were no significant differences among females. Moreover, compared to male DTA − mice, male DTA + mice had a significantly higher density of TUNEL + cells in the caudoputamen, cerebral cortex, and thalamus. Moreover, compared to female DTA − mice, female DTA + mice showed a significantly greater number of TUNEL + cells in the hippocampus and thalamus. Compared to DTA − mice, ELISA revealed significantly lower IL-10 and TGF-β levels in both male and female DTA + mice under both normal conditions and after HI (more pronounced). Conclusion We established a microglial depletion model that aggravated neuronal damage and apoptosis after the HI insult, which was predominantly observed in males.