Abstract
BackgroundChronic cerebral hypoperfusion (CCH) causes white matter damage and cognitive impairment, in which astrogliosis is the major pathology. However, underlying cellular mechanisms are not well defined. Activation of Na+/H+ exchanger-1 (NHE1) in reactive astrocytes causes astrocytic hypertrophy and swelling. In this study, we examined the role of NHE1 protein in astrogliosis, white matter demyelination, and cognitive function in a murine CCH model with bilateral carotid artery stenosis (BCAS).MethodsSham, BCAS, or BCAS mice receiving vehicle or a selective NHE1 inhibitor HOE642 were monitored for changes of the regional cerebral blood flow and behavioral performance for 28 days. Ex vivo MRI-DTI was subsequently conducted to detect brain injury and demyelination. Astrogliosis and demyelination were further examined by immunofluorescence staining. Astrocytic transcriptional profiles were analyzed with bulk RNA-sequencing and RT-qPCR.ResultsChronic cerebral blood flow reduction and spatial working memory deficits were detected in the BCAS mice, along with significantly reduced mean fractional anisotropy (FA) values in the corpus callosum, external capsule, and hippocampus in MRI DTI analysis. Compared with the sham control mice, the BCAS mice displayed demyelination and axonal damage and increased GFAP+ astrocytes and Iba1+ microglia. Pharmacological inhibition of NHE1 protein with its inhibitor HOE642 prevented the BCAS-induced gliosis, damage of white matter tracts and hippocampus, and significantly improved cognitive performance. Transcriptome and immunostaining analysis further revealed that NHE1 inhibition specifically attenuated pro-inflammatory pathways and NADPH oxidase activation.ConclusionOur study demonstrates that NHE1 protein is involved in astrogliosis with pro-inflammatory transformation induced by CCH, and its blockade has potentials for reducing astrogliosis, demyelination, and cognitive impairment.
Highlights
Chronic cerebral hypoperfusion (CCH) causes white matter damage and cognitive impairment, in which astrogliosis is the major pathology
Effects of Na+/H+ exchanger-1 (NHE1) blockade on the bilateral carotid artery stenosis (BCAS)-induced microstructural changes of hippocampus As the Y maze spontaneous alternation rate indicates for spatial working memory, which requires hippocampal integrity [33], we examined whether HOE642 treatment affected BCAS-induced damage in the hippocampus
To further investigate that blockade of NHE1 protein reduced the Reactive oxygen species (ROS) production and pro-inflammation resulting from attenuating NOX2 activity in white matter reactive astrocytes, we examined changes of expression of phosphorylated cytosolic subunit p47 (p-p47 phox) of NOX2 in astrocytes in corpus callosum (CC) and external capsule (EC) white matter tracts, since phosphorylation of cytosolic subunits p40, p47, and p67 is required for NOX2 activation [39]
Summary
Chronic cerebral hypoperfusion (CCH) causes white matter damage and cognitive impairment, in which astrogliosis is the major pathology. In a mouse neonatal hypoxia–ischemia brain injury model, pharmacological inhibition of NHE1 by its potent inhibitor HOE642 reduced corpus callosum white matter damage and improved cognitive function [23] These studies demonstrated that activation of glial NHE1 protein is involved in gliosis and neuroinflammation after acute ischemic or hypoxia neonatal brain injury. Post-BCAS administration of the selective NHE1 inhibitor HOE642 significantly decreased astrogliosis, preserved white matter and hippocampus integrity, and improved cognitive function by preventing astrocytic ROS production and inflammatory transcriptomes. These findings revealed the potential of pharmacological blockade of NHE1 protein in reducing cerebral hypoperfusion-induced chronic brain injury and cognitive impairment
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