Abstract Body: Background: Vascular cognitive impairment (VCI) is the second most frequent subtype of dementia following Alzheimer's disease. However, the underlying mechanism has not been fully understood and there is no effective treatment for VCI. MicroRNAs (miRNAs) play critical roles in the pathologies of cerebral ischemia and dementia. This study aims to identify key miRNAs that may mediate cognitive outcomes using multiple microinfarction (MMI), a VCI model.

Methods: MMI was induced by the administration of cholesterol crystals (70-100µm) into the internal carotid artery. Male Wistar rats (10-12 month) subjected to MMI or sham operation were euthanized 28 days after MMI (n=8/group). Total RNAs were isolated from the striatal tissues and miRNA-sequencing was performed. AAV-PHP.Eb carrying miR-145-5p sponge was delivered by the Intracerebroventricular injection at 2 days prior to MMI to knockdown miR-145-5p. The mNSS (modified Neurological Severity Score) and cognition tests were examined at 2 weeks after MMI.

Results: MiRNA-sequencing analysis showed that compared to sham rats, MMI significantly up- and down-regulated 4 and 9 miRNAs respectively. Bioinformatics analysis revealed that these miRNAs were highly associated with the oligodendrocytes/myelination (miR-210 and miR-125), BBB (miR-665 and miR-29), and inflammation (miR-322), etc. Amongst them, miR-145 was the top upregulated miRNA in the striatum after MMI. In situ hybridization demonstrated that miR-145 expression was highly upregulated in the smooth muscle cells, which was negatively correlated with the decrease of contraction marker of smooth muscle cells (SMCs). Treatment of MMI rats with AAV-miR-145 sponge significantly reduced sensorimotor deficits assayed by lower mNSS score. Furthermore, MMI rats administered AAV-miR-145 spent less time on the closed arm in the EPM (AAV-miR-145 VS control AAV: 182±28 VS 263±9 (s), P=0.01) and showed less freezing time in the OFT (AAV-miR-145 VS control AAV: 205±9 VS 246±11 (s), P=0.015), compared with those treated with control AAV. These data indicate that inhibition of miR-145 reduces depression-like behavior and cognitive deficit induced by MMI.

Conclusion: Our results uncovered the deregulated miRNAs associated with myelination, white matter and vascular damage after MMI. Also, our data suggest that miR-145 could be a potential therapeutic target by the regulation of SMCs against VCI. Thus, our data provides new insights into the molecular mechanisms underlying VCI.