University of Vermont

College of Medicine

Freeman Laboratory - Department of Surgery

tbi_blood_vessels.html

Effects of traumatic brain injury on endothelial Ca2+ signals and vasodilatory function

 

The goal of this project is to elucidate the mechanistic basis and functional consequence of changes in vascular physiology that occur following acute brain injury.

Acute brain injury casuses systemic effects including hypertension through sustained activation of the sympathetic nervous system (SNS). Vasoconstriction is normally opposed by endothelial cell (EC) vasodilatory pathways, with endothelial dysfunction being a hallmark of vascular disease. There is a fundamental knowledge gap in our understanding of the long-term impact of acute brain injury on systemic endothelial function, which is of profound importance given the contribution of cardiovascular effects of TBI to morbidity and mortality.

We hypothesize that TBI increases ROS in endothelial cells, altering EC Ca2+ signals and uncoupling both NO and EDHF vasodilatory pathways. We will focus on the underlying cellular mechanisms involved in endothelial responses that may be differentially affected by TBI in mesenteric arteries, including endothelial ion channel activity and VSM membrane potential. Our expected results will challenge the prevailing clinical paradigm, reframing our understanding of acute brain injury to include not only neurological and cerebrovascular effects, but also interactions between ROS and ion channels of the systemic vascular endothelium. This revised view may also lead to novel therapeutic targets to improve patient outcomes.

Aim #1. To elucidate the molecular basis of increased EC Ca2+ signals in mesenteric arteries following TBI. We hypothesize that increased EC Ca2+ signals after TBI reflect transient receptor potential (TRP)-mediated Ca2+ influx and/or IP3-mediated Ca2+ release. High-speed confocal Ca2+ imaging of intact endothelium in the presence of specific Ca2+ channel blockers will reveal whether oscillatory signals are due to IP3-triggered intracellular Ca2+ release or entry of extracellular Ca2+ via TRP channels.

Aim #2. To characterize the functional consequences of increased EC Ca2+ signals on arterial function following TBI. We hypothesize that endothelial dilatory influences are impaired following TBI due to differential alteration of NO- and EDHF-mediated vasodilatory pathways. We will confirm that impaired ACh-mediated vasodilation is due to impaired endothelial function by measuring vasodilations and VSM membrane potentials in arteries that have been denuded of endothelium, or in the presence of NO donors that act independently of the endothelium. We will use specific agents to block dilatory pathways (NOS or SK/IK channels) to determine the relative contribution of each pathway to vasodilation and membrane hyperpolarization after TBI.

Aim #3. To determine the effects of ROS on EC Ca2+ signals, arterial function, and hypertension following TBI. We hypothesize that in vitro treatment of isolated arteries with tempol, to decrease ROS,28 or with tetrahydrabiopterin (BH4), to support eNOS activity,29 will restore EC-mediated vasodilatory pathways in mesenteric arteries. Furthermore, in vivo treatment of animals with tempol or BH4will attenuate systemic blood pressure elevation after TBI. We will also measure ROS in arteries using fluorescent indicators in isolated arteries. In conjunction with the results expected from Aims 1 and 2, this will provide a therapeutic target to improve endothelial vasodilatory capacity following acute brain injury.

Last modified January 04 2012 02:12 PM