Portals for leukocyte emigration from blood vessels.
We found recently that leukocytes transmigrate across blood vessel walls at very specific sites, that we have termed “portals”. These portals are located at some, but not all, endothelial junctions, and are associated with high local surface expression of ICAM-1. This project will explore what makes these portals special, and how they are regulated.
Mechanisms of intralumenal crawling in different leukocyte sub-populations.
Recent work has shown that after blood-born monocytes and neutrophils adhere to the microvessel wall, they activate, flatten and crawl for a limited amount of time on the endothelial surface. We don’t yet know what signaling mechanisms underly this very specific amount of crawling. If they encounter a portal, they transmigrate: the majority do not, and deactivate, detach, and return to the flowing blood. We have also discovered that the primary integrins that mediate this crawling (LFA-1 and Mac-1) induce different characteristic crawling behaviors. The project will relate these differences to mechanisms of crawling and emigration in monocytes and neutrophils.
Microvascular permeability: regulation by ICAM-1.
We showed that ICAM-1 ligation activates mechanisms in endothelial cells that regulate permeability of the microvessel wall to essential molecules such as albumin. We found that regulation of permeability in non-inflamed tissues has different signaling characteristics than in inflamed tissues, despite all being dependent on ICAM-1 ligation. The project will define mechanisms for regulation of permeability by ICAM-1 under these different conditions – we are particularly interested in identifying the “switch” that shifts signaling pathways.
Endothelial calcium changes in exercise.
To model exercise we electrically induce contractions in small bundles of myocytes in muscles of anesthetized animals; responses of cells in the arteriolar wall are imaged and quantified using real time confocal intravital microscopy. In an earlier project, we made the surprising finding that endothelial calcium increases are required for this metabolically-coupled dilation. The new project will define mechanisms responsible for these calcium changes, and will explore how the resulting signals are communicated to adjacent smooth muscle cells.
A role for fibronectin in arteriolar responses (with the Hocking lab).
This project will extend earlier work in which we found that mechanical signals from the extracellular matrix protein fibronectin contribute to vascular responses in normal resting and exercising tissue (by apparently different mechanisms). We will use FN-mimetic peptides, in combination with fluorescence intravital microscopy, to probe responses in small arterioles at rest and during muscle contraction. The goal of this project is to identify the key mechanotransducing mechanisms that underly this response.