Department of Pharmacology
Richard K. Assoian, Ph.D.

Research Interests
Vascular cell biology, regulation of cell proliferation during atherosclerosis and restenosis.

Keywords
Extracellular matrix, ApoE, prostacyclin, arterial stiffening, mouse modeling, signal transduction, cell cycle control, vascular smooth muscle.

Description of Research:

Cell cycle inhibition by ApoE and prostacyclin
Vascular smooth muscle cells (VSMCs) are the major component of large vessels, and these cells are actively maintained in a quiescent state unless they undergo some type of arterial damage during cardiovascular disease. Arterial damage leads to VSMC proliferation, and this is a major factor is the development of atherosclerosis and restenosis (VSMC proliferation after vascular injury). We are interested in understanding the mechanisms that maintain VSMCs in a quiescent state and how these controls are lost during atherosclerosis and restenosis. We have shown that ApoE (a component of HDL) inhibits cell cycle progression in VSMCs in vitro and in vivo. ApoE works, at least in part, by regulating the expression of Cox-2, leading to increased production of prostacyclin (a potent VSMC anti-mitogen). In turn, prostacyclin inhibits the degradation of a particular inhibitor of the cyclin-dependent kinases, called p27kip1. We are testing the importance of the ApoE-Cox2-PGI2 pathway in vivo by monitoring atherosclerosis and restenosis in mice that are null or transgenic for ApoE, Cox2, the prostacyclin receptor, p27kip1, and Skp2 (the E3 ligase that degrades p27kip1).

Regulation of the cell cycle by arterial stiffness and matrix compliance
VSMCs remodel their extracellular matrix (ECM) during cardiovascular disease, and this is thought to regulate VSMC proliferation. We have used bioengineered matrices of varying stiffnesses to show that changes in ECM stiffness (also called its “compliance”) regulate the cell cycle in cultured primary mouse VSMCs. The compliance of freshly isolated mouse aortae and femoral arteries (measured using biophysical methods with Paul Janmey’s lab at Penn) prevent VSMC proliferation by inhibiting the mitogen-dependent induction of cyclin D1 mRNA while stiffer ECMs support VSMC proliferation by permitting cyclin D1 expression. We would now like to know if these stiffer ECMs are created as a consequence of ECM remodeling during the development of cardiovascular disease. We are also hoping to microdissect regions of vascular injury in the mouse and use transcript profiling to determine the changes in ECM components, ECM receptors, signaling pathways and cell cycle genes that are associated with arterial stiffening and VSMC proliferation at sites of cardiovascular disease in vivo. In collaboration with Ellen Puré (Wistar) we are examining the mitogenic effects of hyaluronan, a non-proteinaceous component of the ECM that we have linked to VSMC proliferation after vascular injury.

Other Studies:
Please see our research description under the Graduate Group for Cell and Molecular Biology (CAMB) for basic cell biological projects ongoing in the lab.