Deep Hypothermic Low Flow Induced Cerebral Neuroinflammation And White Matter Injury

Objective Risk of postnatal brain injury is dramatically increased during cardiac surgery,where antenatal and preoperative factors governing aberrant brain maturation are combined with long periods of deep hypothermic low cerebral blood flow(DHLF)cardiopulmonary bypass(CPB).Our understanding of underlying cellular and molecular mechanisms related to DHLF induced cerebral hypoxia-ischemia injuries remains limited.Here this pilot study aims to evaluate the pathological responses of neural cells to long-term DHLF,utilizing a focal cerebral ischemia reperfusion mouse model.Methods C57BL/6J mice were subjected to bilateral common carotid artery occlusion,and sham operation used as controls.Biochemical and immuno-histological experiments were conducted to analyze the cellular states of neuron,astroglia,oligodendroglia,and microglia after 2.5h DHLF followed by reperfusion at 0h,24h and 2weeks,respectively.Results We found that microglia exhibited immediate reaction with a ramified phenotype presented by Ionized calcium-binding adapter molecule1(Iba1)staining,whereas other neural cells showed no morphological and quantitative alteration after 2.5h DHLF with no reperfusion.Interestingly,2.5h DHLF followed by 24h reperfusion elicited the neuronal perikaryon distribution of NeuN(Neuronal Nuclei),compared to its diffused localization in the neuronal nuclei in the brain of sham operation group.Furthermore,we also detected the Nlrp3-IL1β inflammsome pathway activation in several brain regions at 24 h after DHLF.Additionally,immunohistological analysis showed Iba1+and Glial fibrillary acidic protein(GFAP)+cells were dramatically increased in the brain,and the upregulated Ibal and GFAP protein levels were also confirmed by western blot at the time point of 24 h after DHLF.To examine the effects of DHLF on postnatal myelination,MRI and EM was undertaken to examine the control and DHLF-brain after 2weeks.We found that the volume of corpus callosum was significantly decreased,and the percent of myelinated axons in the corpus callosum was also reduced.Immunofluorescence and western blots against myelin proteins Mbp and Plp confirmed the deficient myelination,which is attributable to the reduced oligodendrogenesis indicated by the decreased oligodendroglial marker Olig2+cells in the DHLF brain.The downregulation of Akt kinase activity may be implicated in the disruption of developmental myelination induced by the long-term DHLF,just as Akt1 knockout brain also exhibits the defective myelination in the cerebral cortex.Conclusion Taken together,these findings demonstrate that microglia immediately and morphologically reacted to the long-term DHLF,and subsequent reperfusion invokes neuronal pathology,and neuroinflammation characterized by enhanced astrocytosis,microglial activation and the NOD-like receptors(Nlrp3)-IL1 βinflammsome activation;the downregulation of Akt kinase activity is implicated in the defective myelination in the DHLF brain.