University of Virginia Health System

Email Address: bei6n@virginia.edu

Signaling Microdomains

Throughout the microvasculature, the endothelial cells (EC) and the smooth muscle cells (SMC) make cellular contact within a highly restricted space that normally separates the two cell types, creating myoendothelial junctions (MEJs). There is abundant evidence suggesting the MEJ is critical for vascular function in such diverse processes as: regulation of vessel tone and blood flow, blood pressure, SMC proliferation, vascular development, normal and pathological angiogenesis and vascular wound healing. However, the small size of the MEJ and its inaccessibility have made investigation of its functions difficult and limited in scope. Our lab has a keen interest in this unique structure, and is attempting to dissect its function in the microvasculature. We are tackling the MEJ problem by integrating novel cell and molecular biology with classical microvascular physiology techniques.

Our research has demonstrated that the Ca²⁺ signaling between EC and SMC via the MEJ is more highly organized than commonly recognized. We have determined that heterocellular calcium coupling between the two cell types appears to be polarized, i.e., heterocellular signaling from EC to SMC is wholly dependent on the rise in EC [Ca²⁺]_i whereas signaling from SMC to EC has both a Ca²⁺ and an IP₃ component.

How does this polarization occur? We have found a pool of releasable Ca²⁺ in the endoplasmic reticulum which extends down to the MEJ both in vivo and in vitro and recent unpublished data has demonstrated that inositol 1,4,5 trisphosphate receptors (IP₃-R) are present on the EC side of the MEJ but not on the SMC side; an observation found in vivo and in vitro. Ongoing work on ryanodine receptor isoforms has demonstrated a similar polarity. Thus, the MEJ appears to be a highly structured organization of signaling complexes. This idea is perfectly consistent with the commonly observed assembly of signaling centers. We are working to determine how this signaling microdomain functions to control EC and SMC integration.

Oxidized Phospholipids

Our lab is also interested in the role that connexins play in atherosclerosis. There is now abundant evidence that connexin protein expression is progressively and differentially altered in EC and SMC as the atherosclerotic plaque develops, but the physiological mechanisms, or the reason why this occurs, is unclear.

To this end, we are utilizing pro-atherosclerotic oxidized phospholipids as a model to study pathological (i.e., atherosclerotic) intercellular communication in the larger arteries (e.g., carotids, aorta). Using the oxidized phospholipids, we have found in vivo and vitro changes in connexin expression which correlated with changes in connexin expression observed in atherosclerotic lesions. We are expanding this work to examine two main lipid components of the oxidized phospholipids, one of the lipid which induces changes in PKA and another which induces Ca²⁺ transients and PKC elevations. How these lipids effect connexin phosphorylation and function differentially in EC and SMC is currently being pursued.