Researchers in the Shohet Laboratory are engaged in exploring the response of the stressed heart in mouse models.
1. Hypoxia Inducible Factor-1
A better understanding of angiogenesis, the induction of new blood vessel growth, has the potential to improve treatment of many diseases. We are especially interested in myocardial ischemia. Hypoxia inducible factor-1 (HIF-1) is a transcription factor that directs the genomic response to hypoxia. This protein is rapidly degraded under normal levels of oxygen. When oxygen levels decrease, the protein accumulates and directs a cascade of gene regulation that determines the response to hypoxia. In our studies we use a modified HIF-1alpha cDNA in which the degradation mechanisms no longer operate, resulting in constitutive activation of the protein. We have inserted this mutated form into a tet-regulated transgenic line and are thus able to express active HIF-1 in a normoxic environment in the hearts of adult mice. This is an advance over transgenic models that modify activity during development. We are evaluating the phenotype of HIF-1 expression with transcriptional, histological and physiological determinations. Using this model we have identified a novel inhibitor of HIF, a microRNA important in excitation-contraction coupling, and HIF-dependent RNA splicing events.
2. Ultrasound Targeted Microbubble Destruction (UTMD)
Though protein and gene therapy strategies are promising, there has yet to be developed a highly efficient, reliable method for local in vivo delivery. We have helped to develop a technique, termed ultrasound targeted microbubble destruction (UTMD), that directs local delivery of expression constructs to specific regions in a minimally invasive manner. Microbubbles, which are composed of a perfluorocarbon gas encapsulated in a polymer, protein, or lipid shell, are frequently, and safely, used as contrast agents for ultrasonic imaging of the cardiovascular system. An ultrasonic signal of the appropriate frequency can disrupt the bubbles. We have attached both plasmids and proteins to microbubbles, injected them into animals, and obtained efficient delivery to target organs by destroying the microbubbles with a properly guided ultrasonic signal. This is a platform technology with broad applicability. Presently we are using it to investigate delivery of gene therapy vectors to the liver, brain, and heart.
Here, a microbubble is destroyed by ultrasound, thus releasing the plasmid vector in the shell into the surrounding tissue (Physics Today, December 2005).
3. Human Genetics
Phenotypic differences between different human populations are often explained by genetic variation. We expect that the understanding of genetic variation in various populations will contribute to the mechanistic understanding of how cardiovascular disease develops, and why it affects different ethnic groups in distinct ways. We have recently established a clinical recruitment effort for the GenTAC study, which is a national consortium that studies aortic dilation and dissection. If you or your family has early onset aortic disease and would like to participate in an effort to understand the illness please contact Dr. Shohet. We are also interested in any families that have a high frequency of cardiovascular illness or even more than a single case of unusual cardiac disease.
Dr. Ralph V. Shohet
Professor of Medicine