Uncovering the role of connexins and Yap in blood brain barrier hyperpermeability and microvascular injury in cerebral amyloid angiopathy
Authors: Muyu Situ 1 and Anuska V. Andjelkovic 2
Affiliations: 1 Neuroscience Graduate Program, University of Michigan, Ann Arbor, MI
2 Department of Pathology and Neurosurgery, University of Michigan, Ann Arbor, MI
Cerebral Amyloid Angiopathy (CAA) is a cerebral small vessels disease characterized by accumulation of amyloid-β (Aβ) around the small caliber vessels (arterioles and capillaries). Structural alterations and loss of integrity in the neurovascular unit/blood-brain barrier (NVU/BBB) in CAA results in “leakier” microvessels, microhemorrhage, increased stroke risk, and cognitive impairment. Although a significant body of evidence has pinpointed several potential mechanisms (i.e., neuroinflammation and oxidative metabolism) to drive BBB injury in CAA, molecular mechanisms remain to be fully elucidated. To determine the profile of microvascular injury in CAA murine model (Tg-SwDI mice), we performed RNA sequencing analysis on the isolated brain microvessels. Transcriptome profiling revealed alteration in genes like gap junction proteins, connexin 43 (Cx43) and Cx45, and Yap1 (Yes-associated protein), a component of the Hippo signaling pathway involved in remodeling of actin cytoskeleton, extracellular matrix, and regulation of inflammation. Our present study aims to understand how changes and interactions between Cx43/Cx45, and Yap modifies barrier integrity and promotes cerebrovascular injury in the CAA condition.
Using in vitro (Aβ 1-40 and Aβ 1-42 exposure) and in vivo models (Tg-SwDI mice), we performed assessment of cell structural changes (immunocytochemistry, confocal microscopy), functional (optical tweezers method), FRAP assay, in vitro permeability assay) and signaling events (western blotting and proximity ligation assay) associated with alteration of brain endothelial cells (BECs) mechanics and barrier permeability in CAA settings.
Consequences of Aβ-afflicted brain microvessels and Aβ exposure in BECs promotes an overall increased protein expression and a redistribution of Yap expression from the cytoplasm to the nucleus, contributing to structural changes, such cellular stiffening and cell permeability. Similarly, Aβ promotes upregulation of Cx43 and Cx45 (i.e., GJs and HCs formation and activity) as well as loss of tight junction integrity resulting in a hyperpermeable barrier. Inhibition (via selective inhibitors) and/or modifications of each component expression (via siRNA transfection) or whole Yap/Cx43/Cx45 axis alters the cell mechanics and consequently barrier permeability. Conclusion (36) Collectively, our data suggest that vascular Aβ deposition in CAA pathology promotes injury and junctional alterations through a Cx43/Cx45/Yap axis in the brain endothelium contributing to development of CAA associated pathology (i.e., BBB hyperpermeability, and microbleeds).