Abstract WP323: Late-Stage Degeneration Due to Middle-Cerebral Artery Occlusion Observed in White Matter Tracts and Specific Forebrain Regions in Middle-Aged Female Rats is Attenuated by mir20a-3p Treatment: A Magnetic Resonance-Diffusion Tensor Imaging and Conventional Morphometry Study

Abstract

Introduction: Our earlier studies show that the small non-coding RNA, mir20a-3p, is neuroprotective after stroke, and reduces sensory-motor impairments in the acute phase and cognitive decline in the long-term in female rats. Cognitive decline due to vascular diseases, such as stroke, is associated with volume loss in the cortex, the limbic structures and white matter tracts. In this study, we examined the volume of forebrain white matter tracts, cortical and limbic structures in animals with characterized cognitive impairment due to stroke, and the efficacy of microRNA treatment. Methodology: Middle-aged females were subjected to ischemic stroke using endothelin 1, injected adjacent to the left middle cerebral artery (MCA). Mir-20a-3p mimic (n=10) or scrambled oligo (n=8) was administered i.v. 4h, 24h and 70d post stroke. Animals were assessed periodically for cognitive performance up to 100d after stroke using both the cued fear conditioning test and the novel object recognition test (NORT). After perfusion fixation, T2 and diffusion tensor imaging (DTI) magnetic resonance imaging of the brain was performed. Thereafter, brains were processed for Weil myelin staining, followed by quantification of the corpus callosum and internal capsule. Results: Stroke resulted in impairment in both the cued fear conditioning test and the NORT, which was attenuated by mir-20a-3p treatment. Compared to sham (no-stroke) animals, volumetric analysis of DTI scans showed a significant reduction in the volume of substantia nigra (p<0.02) and the entorhinal cortex (P=0.0402) in stroke +scrambled group, but not in Stroke+ Mir20 treated group. White matter tracts showed a significant reduction in the corpus callosum and internal capsule volume in the ischemic hemisphere as compared to non-ischemic hemisphere in MCAo animals treated with the scrambled oligo. In contrast, sham and MCAo+Mir-20a-3p animals displayed no hemispheric differences in volume in either tract. Conclusion: Cognitive changes measured with remote fear memory retrieval and NORT were associated with volume reductions in the substantia nigra, the entorhinal cortex, and the major forebrain white matter tracts due to stroke. These stroke-induced deficits were attenuated in Mir-20-3p treated animals.