Cerebrovascular disease is a major cause of dementia in elderly individuals, especially Black/African Americans. Within my dissertation, we focused on two vascular morphologies that affect small vessels: brain arteriolosclerosis (B-ASC) and multi-vascular profiles (MVPs). B-ASC is characterized by degenerative thickening of the wall of brain arterioles. The risk factors, cognitive sequelae, and co-pathologies of B-ASC are not fully understood. To address this, we used multimodal data from the National Alzheimer’s Coordinating Center, Alzheimer’s Disease Neuroimaging Initiative, and brain-banked tissue samples from the University of Kentucky Alzheimer’s Disease Center (UK-ADC) brain repository. We analyzed two age at death groups separately: < 80 years and ≥ 80 years. Hypertension was a risk factor in the < 80 years at death group. In addition, an ABCC9 gene variant (rs704180), previously associated with aging-related hippocampal sclerosis, was associated with B-ASC in the ≥ 80 years at death group. With respect to cognition as determined by test scores, severe B-ASC was associated with worse global cognition in both age groups. With brain-banked tissue samples, we described B-ASC’s relationship to hippocampal sclerosis of aging (HS-Aging), a pathology characterized by neuronal cell loss in the hippocampal region not due to Alzheimer’s disease. We also studied MVPs, which are characterized by multiple small vessel lumens within a single vascular (Virchow-Robin) space. Little information exists on the frequency, risk factors, and co-pathologies of MVPs. Therefore, we used samples and data from the UK-ADC, University of Kentucky pathology department, and University of Pittsburgh pathology department to address this information. We only found MVPs to be correlated with age. Lastly, given the high prevalence of cerebrovascular disease and dementia in Black/African Americans, we discussed the challenges and considerations for studying Blacks/African Americans in these contexts.

Cognitive decline is one of the most common symptoms from neuropathology as well as a part of natural aging. While there may be a number of factors that contribute to age-related cognitive decline, previous research has shed a light on the role of chronic hypertension. The effect of hypertension on cognitive decline through small vessel disease is referred to as Vascular Cognitive Impairment and Dementia (VCID). However, the exact molecular pathology behind VCID is not very well understood. Using a non-human primate model of hypertensive aging with the Macaca mulatta, (more commonly known as the Rhesus Macaque) this project builds on previous research implicating collagen IV as part of the cascade of molecular changes that occur in VCID. This project evaluated collagen IV thickness around blood vessels in the corpus callosum and cingulum bundle of normotensive and hypertensive monkeys. as well as determined vessel properties such as total vessel area and perimeter length to evaluate the relationship to scores from the subjects cognitive testing batteries. The results from this project will allow for an examination of the effects on hypertension on vascular properties and possible mechanisms for the development of cognitive impairments. Data collected from this research shows significant differences of collagen IV thickness in the Corpus Callosum between hypertensive and normotensive groups. Similarly, in the cingulum bundle we see that the difference between these groups in collagen IV thickness is trending towards significance. The relationship between average collagen IV densities, blood pressure at perfusion, and cognitive testing scores also showed trending relationships in both the cingulum bundle and the corpus callosum. These results demonstrate how prolonged hypertension can negatively influence cognitive abilities and implicates increases in collagen IV around small vessels in white matter as a significant factor in the molecular cascade which results in cognitive impairment.

Age-related neurologic disease is a significant and growing burden on our society. Although the largest share of research effort has typically been devoted to the common neurodegenerative illnesses (such as Alzheimer’s disease, or AD), the reality is that nearly all cases of neurodegenerative disease possess elements of mixed pathology. Vascular contributions to cognitive impairment and dementia (VCID) is a complex form of dementia, combining aspects of vascular disease and other forms of dementia, such as Alzheimer’s disease. This pathology is heterogeneous and can include cerebral amyloid angiopathy (CAA), hemorrhages, white matter infarcts, and changes to the neurovascular unit. Given the heterogeneous nature of VCID, we hypothesized that we could further elucidate mechanisms that drive dementia in VCID by examining pathology in mouse models and use this data to guide the study of human autopsy cases. Using a mouse model of VCID, we identified NHE1, a sodium hydrogen exchanger that was upregulated in these mice, as a possible candidate for a factor involved in cerebrovascular disease in humans. We saw a significant age effect of NHE1 in cases with Down syndrome (DS), leading us to further examine cerebrovascular pathology in individuals with DS. People with DS are at a high risk of developing cognitive impairment and dementia after the age of 50. In fact, virtually all adults with DS develop the neuropathology for an AD (beta-amyloid (Aß) senile plaques and tau neurofibrillary tangles) diagnosis by the age of 40 due to a triplication of chromosome 21. We found that these individuals develop CAA and microhemorrhages as a function of age, and that these rates are as severe as sporadic AD, despite an age difference of ~30 years. We also found that individuals with DS have different microglial morphologies than controls or individuals with AD. This data indicates that people with DS develop significant cerebrovascular and AD pathology, indicative of VCID. Overall, we found that mixed pathologies, specifically VCID, is an important contributor to the development of dementia and should be studied further to better understand how this pathology drives cognitive impairment. Further, it is clear that mouse models map imperfectly onto complex human diseases, and that significant work remains to be done towards achieving an adequate model of VCID.