Microparticles as Messengers of Communication Between Blood and Vascular Cells

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DESCRIPTION (provided by applicant): This RC1 grant application is responsive to Challenge Area "04-Clinical Research" and specifically to the NHLBI Challenge Topic 04-HL-103: "Assess the role of leukocyte interaction with platelets, erythrocytes, and endothelium in the pathogenesis of heart, lung, and blood diseases." A significant knowledge gap is how the platelet communicates with other blood and vascular cells. Knowledge of this process could lead to improved disease management and biomarker development. The small anucleate platelet plays a seminal role not only in hemostasis, but also in diabetes and cardiovascular disease which affect millions of Americans. Further interest in the platelet is fueled by the fact that millions of units of platelets are transfused each year, sometimes with deleterious consequences. Platelets are now also recognized as key inducers of inflammation. Our laboratory discovered that platelets abundantly express the transcription factor peroxisome proliferator activated receptor-gamma (PPAR?) and that PPAR? ligands dampen platelet activation. Ligand activated PPAR? is a previously unrecognized target that attenuates unwanted platelet activation in patients with type 2 diabetes or cardiovascular disease. PPAR? is viewed as an anti-inflammatory transcription factor, which also functions via non-nuclear mechanisms. Our team recently discovered that PPAR? is released from platelets in microparticles (MPs). MPs are submicron membrane vesicles that contain bioactive proteins and mediators. PPAR? containing MPs are taken up by and dampen macrophage function. We also discovered that type-2 diabetics produce MPs that have abnormally low levels of PPAR? and are likely to stimulate inflammation rather than inhibit it. We propose the overall challenge and hypothesis that PPAR? in MPs influences other cells by a transcellular mechanism. To complete this challenge in 2 years we assembled an outstanding multidisciplinary team to complete 2 aims. Aim 1: Investigate platelet MPs containing PPAR? and determine their ability to influence key white blood cell and vascular cell functions. Purified platelets from normal and type-2 diabetics will be used to generate MPs in vitro under controlled conditions. We will study their ability to be taken up and influence blood monocytes/macrophages and blood vessel endothelial cells. Thus, we will identify a new form of cell-cell communication. Genetic systems and a preclinical mouse model will be used to study the role of PPAR?-containing platelet MPs in health and disease. Aim 2: Discovery and characterization of MPs containing PPAR? in the blood of normal humans and those with type-2 diabetes. We will determine the cellular sources in blood of PPAR? containing MPs. While some MPs will be of platelet origin (Aim 1), others could come from white blood cells or vascular endothelial cells. The patterns of MPs and cell of origin could be used as a biomarker of disease and response to therapy. This new information could be used to develop an "artificial MP" to deliver PPAR? to cells of choice leading to a new therapeutic paradigm in diabetes and cardiovascular disease. Type-2 diabetes and its consequences, particularly cardiovascular disease, affect millions of Americans. This project will study how small blood cells called platelets, which prevent bleeding, communicate with other blood and vascular cells in healthy and type-2 diabetic individuals. Platelets, when stimulated, release small parts of themselves that contain instructions that other cells take up and which then change their behavior. Understanding this new way of cell to cell communication will lead to new methods and biomarkers to detect disease and to new ways of delivering therapy to reduce the consequences of diabetes and other diseases. PUBLIC HEALTH RELEVANCE: Type-2 diabetes and its consequences, particularly cardiovascular disease, affect millions of Americans. This project will study how small blood cells called platelets, which prevent bleeding, communicate with other blood and vascular cells in healthy and type-2 diabetic individuals. Platelets, when stimulated, release small parts of themselves that contain instructions that other cells take up and which then change their behavior. Understanding this new way of cell to cell communication will lead to new methods and biomarkers to detect disease and to new ways of delivering therapy to reduce the consequences of diabetes and other diseases.