Introduction: Vascular cognitive impairment (VCI) refers to cognitive decline attributed to vascular risk factors. Vascular dysfunction produces cerebral hypoperfusion and the brain uses the hypoxia inducible factor (HIF) pathway to compensate and restore oxygen availability. White matter is vulnerable to hypoxia, and an emerging area of interest aims to understand whether epigenetic processes contribute to this. A handful of reports showed that manipulating small, non-coding microRNAs (miRNAs) may provide new therapeutic strategies in animal models of VCI. The aim of this study was to use a hypothesis free approach to profile miRNA changes in the white matter of a mouse model.

Methods: Twenty male C57BL6 mice were randomised to undergo bilateral carotid artery stenosis (BCAS) or sham surgery. This involved wrapping microcoils with 180 or 500µm diameters, respectively, around both carotid arteries. Subsequently, RNA was harvested from the white matter, hippocampus, and cortex at either 7 or 30d post-surgery and electrophysiology was performed on the optic nerves. RNA was sequenced and bioinformatics analysis was performed (Genewiz, UK). A false discovery rate of <0.05 was applied to the bioinformatics analysis to confirm differentially expressed miRNAs (DEMs). Electrophysiology data, compound action potentials (CAPs) are presented as mean ± standard error and unpaired t-tests or mixed two-way repeated measures ANOVAs were used. 

Results: At 7 and 30d post surgery, all the sham optic nerves consistently displayed a third peak in the recorded CAP, but most of the BCAS nerves did not. There was also differential expression of several miRNAs following BCAS in the hippocampus and white matter at both timepoints. The greatest number of DEMs (76) were observed in the hippocampus, and 45 survived multiple comparisons. There were 10 and 29 DEMs in the white matter at 7 and 30d, respectively, and mmu-let-7K, miR-30d-5p, and mmu8-miR-362-5p all survived multiple comparisons. Pathway analysis suggests the genes regulated by these DEMs are associated with cell signalling and axon guidance. 

Conclusions: The variability in the optic nerve function after BCAS suggests that hypoperfusion may impact white matter most via disruption to the smallest diameters axons. Our data driven approach identified several miRNAs that are differentially regulated in the white matter following hypoxia. While further investigation is required to characterise the roles of these miRNAs, these results suggest epigenetic processes are involved, and we hope this could eventually lead to new therapeutic targets in the future.