Author ORCID Identifier

https://orcid.org/0000-0002-1750-928X

Date of Graduation

8-2021

Document Type

Thesis (MS)

Program Affiliation

Biomedical Sciences

Degree Name

Masters of Science (MS)

Advisor/Committee Chair

Dr. Louise McCullough, MD/Ph.D.

Committee Member

Dr. Sean Marrelli, Ph.D.

Committee Member

Dr. Andrey Tsvetkov, Ph.D.

Committee Member

Dr. Venugopal Venna, Ph.D.

Committee Member

Dr. Arif Harmanci, Ph.D.

Abstract

Introduction:

It is increasingly recognized that social Isolation (SI) leads to a wide array of behavioral and cognitive deficits. Isolation and loneliness are linked to all-cause mortality, as well as mortality from stroke and other vascular diseases. In addition, isolated or lonely individuals have significantly poorer cognitive and functional outcomes following stroke and have higher rates of stroke recurrence. These detrimental effects have also been recapitulated in animal models; animals isolated prior to, or at the time of stroke, have larger infarcts than pair-housed mice. However, the mechanisms mediating the effects of social factors on stroke recovery are unknown. An emerging subtype of microglia classified as “disease- associated microglia (DAM)” has been implicated in the progression of neurological diseases such as Alzheimer’s disease (AD) and amyotrophic lateral sclerosis (ALS). MicroRNAs (miRNAs), a class of 18-25 nucleotide non-coding RNAs, have been shown to regulate the activation of microglia from a resting state to “disease-associated microglia (DAM)”. Preliminary work in the laboratory has shown post-stroke SI significantly alters miRNA profiles in the brain. Targeted miRNA-based therapies reduced pro-inflammatory cytokines and restores functional recovery in aged male mice placed in isolation immediately after stroke. Based on this preliminary data and previous reports, we hypothesize that differential expression of miRNAs may contribute to the deleterious effects of post- stroke SI through effects of accumulating presence of “disease-associated microglia”. The temporal profiles of miRNA changes were determined in mice placed in isolation three days after stroke.

Methods:

Aged (18-20 month) C57BL/6 male mice were used to examine the detrimental effects of post-stroke SI on miRNA profiles in the brain and to evaluate “disease- associated microglia (DAM)” phenotypes. Mice were randomly assigned to either continued pair housing (PH), or single housing (SI) three days after a 60-minute transient right middle cerebral artery occlusion (MCAO). At this time point (3d), the infarct is complete, and equivalent between groups, avoiding potential changes seen with differing infarct sizes. MiRNA profiling of the ipsilateral hemisphere was assessed at three time points (post-stroke SI D1, D4, and D27) using the QIAGEN NGS platform. Activation of “disease-associated microglia (DAM)” was determined by flow cytometry analysis at post-stroke SI D4.

Results:

Post-stroke SI results in a significant alteration of miRNA profiles within the brain across both acute and chronic time points. MiRNA-mRNA interactional analysis reveals miR-466i-3p, miR-10a-5p, and miR-10b-5p as pivotal nodes within the pool of miRNAs that interacted with the largest subset of miRNAs for post-stroke at SI D1, D4, and D27 respectively. Downstream pathway analysis utilizing two independent repositories showed four days of isolation results in microglial activation and 27 days of isolation leads to long-term depressive phenotypes (FDR adjusted p

Summary and Conclusions:

In summary, these results support our hypothesis that post-stroke SI results in the activation of microglia that may be regulated by particular classes of miRNAs. Studies manipulating these discovered targets are needed to determine if the detrimental effects of SI can be reversed to enhance post-stroke recovery.

Keywords

miRNAs, Ischemic Stroke, Social Isolation, Microglia

Available for download on Tuesday, August 09, 2022

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