Abstract
The brain is partitioned from the periphery by the blood brain barrier (BBB). The BBB is maintained by cell types that regulate the micro-environment within the brain. During neurological diseases such as Alzheimer’s disease (AD) and Huntington’s disease (HD) the BBB becomes dysfunctional, and is associated with inflammation, including the recruitment of neutrophils that promote oxidative stress. During neuroinflammation, neutrophils are recruited to the brain vasculature, where the enzyme myeloperoxidase (MPO) can produce oxidants such as hypochlorous acid (HOCl) and hypothiocyanous acid (HOSCN). Cells regulating the BBB contain cytoskeletal and junctional proteins that are important structures in maintaining BBB function, but are sensitive to oxidation. The better studied neutrophil oxidants hydrogen peroxide (H2O2) and HOCl have been shown to disrupt BBB function, but the impact of HOSCN has not been explored.
In this thesis, I found increased neutrophil numbers in the vasculature of brain samples from patients diagnosed with AD and HD. In both AD and HD, MPO was mostly confined to neutrophils at the vasculature. However, in AD, a small amount of non-vascular MPO was present, and this was associated with the AD hallmarks tangles and amyloid plaques. Secondly, with the use of primary mouse brain endothelial cell (BEC) cultures, I found that HOSCN lowered trans-endothelial electrical resistance and increased the permeability of the BEC monolayer. This coincided with altered claudin-5 localization, loss of VE-cadherin and less dynamic microtubules. Thirdly, cultured primary mouse brain pericytes exposed to HOSCN showed lower microtubule counts and increased oxidation and phosphorylation of microtubule stabilizing protein collapsin response mediator protein 2 (CRMP2). Oxidation of CRMP2 coincided with shrinking and reduced migration of cells.
Understanding the effects of HOSCN on BBB function is useful for understanding how inflammation can disrupt the brain vasculature during neuroinflammation. Determination of the molecular mechanisms by which MPO-derived oxidants impact cells of the BBB could lead to the development of new strategies for slowing disease progression of neurological disease.