Cardiovascular diseases exert a massive burden on human health, and our long term objective is to attenuate the excessive accumulation of vascular smooth muscle cells (VSMCs) that is central to many of these diseases. The tunica media of the normal artery is composed of alternating circumferential layers of VSMCs and elastic lamellae. Diverse arterial disorders, including atherosclerosis, restenosis, pulmonary hypertension and supravalvular aortic stenosis (SVAS) are plagued by defective elastic lamellae as well as hypermuscularization. SVAS, a devastating human disease characterized by an increased VSMC burden that occludes large arteries, is caused by heterozygous null mutations in the elastin gene ELN. Similarly, elastin mutant mice develop hypermuscularization and stenosis of large arteries, such as the aorta. Major vascular surgery is the only current treatment for SVAS as no effective pharmacological options are available. A major obstacle to developing effective therapies for vascular disorders is the poor understanding of the cellular source(s) of excess VSMCs; indeed no prior studies have traced the lineage of any cell populations in elastin mutants. In addition, the molecular and cellular mechanisms underlying aortic hypermuscularization in elastin mutants are not well defined. Our initial studies indicate that integrin 3 expression and integrin signaling is robustly upregulated in the elastin mutant aorta and that reduction of 3 levels or activity attenuates the excessive muscularization. Furthermore, reduction of the dosage of the gene encoding 3, Itgb3, extends the viability of Eln(-/-) pups which is unprecedented for any genetic or pharmacological intervention. A potentially attractive strategy for reducing arterial hypermuscularization in SVAS is attenuating the increased 3 expression. Although little is known regarding regulation of 3 expression, the growth arrest-specific homeobox (Gax) transcription factor is expressed in VSMCs and Gax overexpression reduces 3 levels, proliferation and migration. We hypothesize that in elastin mutants, Gax downregulation induces integrin 3 expression in pre-existing aortic smooth muscle resulting in aberrant VSMC orientation, proliferation and migration and thus aortic stenosis. This proposal utilizes studies of transgenic mutant mice, VSMCs isolated from the murine aorta and human SVAS aortic tissue and cells to test this hypothesis in three specific aims: 1) in the elastin mutant aorta, identify the cellular source(s) of excessive VSMCs; 2) in elastin deficient mice, murine VSMCs and human SVAS-derived smooth muscle cells, elucidate the molecular and cellular mechanisms underlying integrin 3-induced excess aortic muscularization; and 3) elucidate the role of Gax in mediating enhanced integrin 3 expression and hypermuscularization in elastin mutants. Taken together, our proposed studies will delineate mechanisms underlying the identified link between elastin deficiency, integrin 3 and aortic hypermuscularization and thereby provide concrete steps towards developing novel therapeutic strategies for SVAS and other vasculoproliferative diseases.
Many devastating human diseases of the arteries are characterized by excessive smooth muscle which effectively decreases the artery diameter, thereby resulting in inadequate blood flow beyond the narrowing. Herein, we use a genetic mouse model of one such human disease (i.e., supravalvular aortic stenosis) to identify the cellular origins of the excess smooth muscle cells and novel mechanisms underlying their accumulation. These studies promise to identify novel therapeutic strategies to combat human arterial disease.
