Collateral artery enlargement (arteriogenesis) is a physiological process that can 'bypass'atherosclerotic supply arteries to preserve blood flow to distal tissue. Thus, pharmacological stimulation of arteriogenesis could be highly beneficial in the treatment of ischemic vascular diseases, such as coronary artery disease (CAD) and peripheral artery disease (PAD). Such treatments would be especially valuable in the setting of diabetes, which both 1) severely increases the risk of CAD and PAD and 2) inhibits native (unstimulated) arteriogenesis. Placenta growth factor (PlGF, PGF) is a VEGF-related growth factor that specifically favors the expansion of arteries via arteriogenesis. Thus, therapeutic stimulation of PlGF expression could potentially be used to enhance arteriogenesis and improve clinical outcomes in patients with CAD and PAD. However, such treatments are not currently possible, due to a lack of understanding of the basic mechanism(s) regulating PlGF expression. Our preliminary data suggests the existence of a novel mechanism regulating PlGF expression in the vascular wall. Moreover, our evidence suggests that this mechanism is dysfunctional in diabetes. Thus, dysregulation of PlGF expression may contribute to faulty arteriogenesis in diabetics. The LONG TERM GOAL of this research is to elucidate key mechanisms regulating PlGF expression under physio- and patho-physiological conditions. This project will pursue three Specific Aims.
Specific Aim 1 : Establish the basic regulatory mechanism controlling PlGF expression in the vascular wall. These studies will be performed in three complementary model systems: primary vascular smooth muscle cells (SMC) in static culture;co- cultured vascular endothelial cells (EC) and SMC which are exposed to shear stress;and isolated perfused mouse vessels.
Specific Aim 2 : Identify key steps in the basic PlGF regulatory mechanism that are altered by diabetes. These studies will confirm the physiological relevance of the mechanism(s) uncovered in Aim 1. These experiments will be conducted in mouse models of hyperglycemia (streptozotocin treatment), hyperlipidemia (high-fat diet treatment) and combined hyperglycemia/hyperlipidemia. This design will allow us 1) to determine what facet of the complex metabolic dysfunction that typically occurs in diabetes inhibits PlGF expression, and 2) to pinpoint the regulatory step at which inhibition of PlGF expression occurs.
Specific Aim 3 : Assess the ability of enhanced endogenous PlGF expression to stimulate arteriogenesis. These studies will take the results of Aim 2 to the next level by determining whether correction of the signaling defect revealed in Aim 2 can 1) reverse the inhibition of PlGF expression in diabetes, and 2) result in functional improvement as measured by capacity to undergo arteriogenesis in response to vascular occlusion. These innovative and novel studies will provide essential new information about the regulation of an important arteriogenic factor and will provide "proof of concept" for the idea that normalizing or enhancing PlGF expression can improve the arteriogenic response to vascular occlusion (due to CAD or PAD) in patients with diabetes.
PROJECT NARRATIVE Ischemic cardiovascular diseases (CVD) such as coronary artery disease are highly prevalent in diabetics and account for most of the mortality in this patient group. Stimulation of collateral artery growth (arteriogenesis) to create a physiological "bypass" is a promising treatment concept;however, greater understanding of the mechanisms controlling arteriogenesis is needed before such treatments are a reality. This research will investigate fundamental mechanisms regulating the key arteriogenic growth factor PlGF as a basis for developing new, noninvasive treatments for ischemic CVD.
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