Introduction: The prevalence of dementia worldwide is projected to double by the year 2030 and triple by 2050. Vascular cognitive impairment and dementia (VCID) encompasses diseases that lead to cognitive decline and dementia due to cerebrovascular disease. VCID is the second most common form of dementia after Alzheimer’s disease, accounting for approximately 15-40% of all dementia cases.  Reductions in cerebral blood flow from intracranial and extracranial atherosclerosis increase VCID risk, even in the absence of overt clinical or imaging evidence of stroke/embolization.  The pathology seen in patients with chronic cerebral hypoperfusion, such as inflammation, neuronal loss, white matter abnormalities, and blood-brain barrier disruption, has been successfully modeled in mice using bilateral common carotid artery stenosis (BCAS).  Most BCAS studies have used young male mice, overlooking potential age and sex differences in the response to cerebral hypoperfusion. In this study, we induced BCAS in aged male and female mice to examine sex differences in white matter damage, neuroinflammation, and cognitive decline.

Methods: Aging 16-18-month old male and female C57BL/6 mice were randomly assigned into experimental groups and subjected to BCAS or sham surgery. Cognitive function was assessed with behavioral testing at baseline and every 30 days post-surgery (PSD) until the endpoint at 90 PSD to identify cognitive differences in CCH. Magnetic Resonance Imaging (MRI) was performed at 45 and 90 PSD to assess differences in ventricle volume and corpus callosum thickness. At 90 days, brain tissue was collected and processed to investigate the impact of CCH on cellular and molecular levels using histological myelin staining (Kluver-Barrera) and immunohistochemistry (Iba1 and MBP). Flow cytometry was also performed to evaluate neuroinflammation and oxidative stress.

Results: BCAS in aged mice induced structural brain alterations consistent with CCH and sex-specific differences were observed. MRI revealed significant ventricular enlargement in BCAS females compared to both sham females and BCAS males by 45 days post-surgery (PSD), and this finding was sustained through endpoint at 90 PSD. Thinning of the corpus callosum was also observed in BCAS females by 90 PSD, indicating progressive white matter degeneration. No deficits in gross locomotor activity were seen in open field testing (OFT) as result of BCAS-induced CCH. Additionally, no significant differences were found between groups in the time spent moving or the time spent in the center zone during OFT. No significant differences were observed in spatial working memory (Y-Maze), activities of daily living (nesting), or long-term memory retention (fear conditioning). However, significant differences were found in histological and molecular analyses. Kluver-Barrera (KB) staining revealed hippocampal and cortical myelin loss in BCAS females compared to shams. Immunohistochemistry (IHC) staining with Iba1 found increased microglial activation in the fimbria of the hippocampus and internal capsule in BCAS females. Flow cytometry demonstrated significantly elevated oxidative stress in brain endothelial cells and bone marrow-derived macrophages in BCAS females.

Conclusions: The BCAS model is a well-established mouse model for investigating VCID through its induction of chronic cerebral hypoperfusion. We examined aged male and female mice using the BCAS model to explore the effects of chronic CCH on cerebrovascular integrity and cognitive function. In this study, we demonstrated that BCAS-induced CCH leads to sustained structural changes to the brain; however, we found minimal changes in cognition. Studies further exploring the cognitive impact of BCAS are needed to further determine sex-specific differences in VCID and enhance our understanding of the disease.

Advisory Committee:

• Louise McCullough, MD, PhD, Chair
• Devin McBride, PhD
• Sean Marrelli, PhD
• Antonio Teixeira, MD, PhD
• Venugopal Venna, PhD