This application addresses broad Challenge Area (11): Regenerative Medicine, and specific Challenge Topic, 11-DK- 102: Vascular Network in engineered or regenerated tissues. Chronic kidney disease is a public health epidemic affecting millions that exacts a profound toll to health care, our communities and to individuals. Chronic kidney disease and is characterized by chronic inflammation, parenchymal cell loss and fibrosis and loss of kidney functions. Emerging evidence implicates peritubular capillary loss in mediating these processes by setting up an ischemic environment in the kidney that results in persistent inflammation. The reason why kidney injury, in contrast to other organs, specifically results in capillary loss is unclear. In recently published studies, we have described pericytes as an integral component of peritubular capillaries. Pericytes are cells of mesenchymal origin that lie adjacent to and make functional connections with endothelial cells. In the eye, pericytes are necessary for capillary stabilization and vascular integrity. Until now pericytes have been poorly described in the kidney due to lack of markers. We have developed unique tools to study pericytes in the kidney. We have definitively shown that during injury, pericytes detach from capillaries, proliferate and differentiate into scar-forming kidney fibroblasts. We now hypothesize that kidney fibrosis is a state of functional pericyte deficiency and we further hypothesize that pericyte loss explains peritubular capillary rarefaction in fibrosis. In AIM 1 we will establish the function of kidney pericytes in vivo by selectively deleting them. We will validate a novel cell-based therapy by attempting to replenish pericytes following kidney injury by adoptive transfer. We will ask whether kidney injury and fibrosis is characterized by pericyte deficiency using newly identified pericyte specific markers. We will examine whether the biologic role of pericytes is to provide pro-angiogenic signals to endothelium using an in vitro assay of pericyte function, the vascular stabilization assay, and and by selective knockdown of three candidate factors that may be integral to kidney pericyte function in this assay. In AIM 2 we will define the translational profile of pericytes in health and disease and validate candidate transcription factors that we hypothesize regulate differentiation of pericytes into myofibroblasts. Pericyte gene profiling in homeostasis and fibrotic disease will be accomplished using a novel, high throughput polysome immunoaffinity purification technique. Using a candidate gene approach we will test the potential role of three pericyte-specific transcription factors in regulation of differentiation of pericytes to myofibroblasts. We will knock-down these factors in pericytes using RNA silencing methods and test the effects of knock-down in the vascular stabilization assay. These proposals represent the first detailed study of pericyte function in the kidney and a completely novel approach to understanding vascular stabilization and regeneration in the kidney. PUBLIC HEALTH RELEVANCE: Chronic kidney disease is a public health epidemic that affects millions yet despite the regenerative capacity of the kidney, many people with chronic kidney disease suffer progressive loss of function. Emerging evidence from different disciplines indicates that loss of the small blood vessels, known as capillaries that carry oxygen and nutrients to the tubules of the kidney, may be a central problem in chronic kidney disease. We have recently discovered that kidney capillaries comprising endothelial cells are also wrapped in another type of cell called pericytes. Until now pericytes in the kidney have been poorly described and their function in the kidney has not been studied. We have developed unique tools to study pericytes in mice, and in this proposal we will investigate at a cellular and molecular level the role pericytes play in the developing vasculature, maintenance of healthy vasculature and in vascular regeneration following injury of the kidney.