Hanjoong Jo, PhD, a professor in the Wallace H. Coulter Department of Biomedical Engineering at Emory and Georgia Tech, and his colleagues used a combined engineering and molecular approach to demonstrate how changes in blood flow might contribute to the prevention or development of lipid-containing plaques that can rupture and block blood vessels, leading to heart attack and stroke. The research is published in the on-line edition of the Journal of Biological Chemistry.
The research team of biomedical engineers, cardiologists and surgeons included George P. Sorescu, Michelle Sykes, Daiana Weiss, Manu O. Platt, Aniket Saha, Jinah Hwang, Nolan Boyd, Yong C. Boo, J. David Vega and W. Robert Taylor.
Bioengineers believe that areas of the vascular system with curves, forks, and less direct flow are more likely to develop atherosclerotic plaques than are vascular areas with straight and unobstructed blood flow. Dr. Jo hypothesized that endothelial cells (the cells that line blood vessels) have a biological response to alterations in their mechanical environment. He designed a mechanical system using a test fluid to model the patterns made by blood as it flows through the body's vessels, and then exposed the fluid to mouse aortic endothelial cells. Using microarray (gene chip) technology, he screened 12,000 genes found in the endothelial cells, comparing tissue exposed to a straight and streamlined flow of blood (laminar shear) to tissue exposed to abnormal, non-linear flow patterns (oscillatory shear stress). In the cells exposed to oscillatory shear stress, he discovered a marked increase in expression of the gene that encodes the protein BMP4 (bone-morphogenetic protein-4). In the cells exposed to laminar shear, he found almost no evidence of BMP4.
To further support his results, Dr. Jo's team, in collaboration with Emory cardiologist W. Robert Taylor, MD, and Emory vascular surgeon J. David Vega, MD, screened endothelial cells from human coronary arteries of patients with atherosclerotic lesions to test for expression of BMP4. BMP4 expression was undetectable in arteries with minimal disease, but it was strongly expressed in endothelial patches found overlying an early form of atherosclerotic lesions called "foam cell lesions."
Although high blood cholesterol, high blood pressure, smoking, and a diet high in saturated fat are known to increase the likelihood of developing heart disease, the risk of physical inactivity is comparable to other factors, according to the American Heart Association. "The molecular biological response to increases or decreases in blood flow might help us explain why physical inactivity promotes disease," Dr. Jo said. "Increasing one's heart rate through vigorous exercise causes blood to flow faster through the vessels, and some exercise-related benefits may be due to endothelial expression of certain genes and proteins."
Dr. Jo hopes to use his findings about BMP4 to develop new diagnostic tests or gene-based therapies to prevent plaque formation.