University of Virginia Health System

Collaborating Faculty

Congenital urinary tract obstruction accounts for most cases of renal insufficiency in the infant. Using experimental animal models of unilateral ureteral obstruction (UUO), we have demonstrated that compared to the adult, the neonatal kidney is more susceptible to the injurious effects of ureteral obstruction. We are currently examining the role of growth factors and apoptosis (programmed cell death) in mediating the arrested renal growth due to ureteral obstruction. We are studying the regulation of apoptosis by the renin-angiotensin system, bcl, ceramide and oxidant injury. Our goal is to develop strategies to improve growth and development of the kidney subjected to UUO in the fetal or neonatal period.

Dr. Carey received his M.D. degree at Vanderbilt University and his residency training at the New York Hospital - Cornell Medical Center. His fellowship training was in endocrinology with Dr. Grant W. Liddle at Vanderbilt and in hypertension with Professor Sir W. Stanley Peart at the University of London (St. Mary's Hospital).

Dr. Carey is interested in the hormonal control of blood pressure, fluid and electrolyte balance and kidney function. His major research interests are in the mechanisms of paracrine hormone action within the kidney, specifically the intrarenal renin-angiotensin system and the dopaminergic system. Dr. Carey has an active program of cell biology and molecular biology with emphasis on genetic control and post transnational processing, packaging and secretion of prorennin and renin from renal juxtaglomerular cells. He is also interested in the cellular uptake and processing angiotensinogen within the kidney and the cellular formation and control of release of the angiotensin peptides. His interests in the dopaminergic system include regulation of dopamine formation and release by proximal tubular cells and the regulation of dopamine receptor function within the kidney. In addition to his cell and molecular studies, Dr. Carey has an active program of study of the role of the renal interstitium in the hormonal compartmentalization of these paracrine systems. He also has a program of clinical investigation of the renin-angiotensin and dopaminergic systems in the kidney.

Dr. Felder received his B.S. in Chemistry at William and Mary in Virginia, followed by his Ph.D. in Biochemistry at Georgetown University, in Washington, DC. He did a postdoctoral fellowship at the National Institutes of health under the direction of John Kebabian noted for his work on central dopamine receptors and second messenger systems. Dr. Felder is currently Professor of Pathology, and Director of the Medical Automation Research Center as well as Associate Director of Clinical Chemistry and Toxicology. Investigational interests include all aspects of the renal adrenergic system. Current work focuses on the renal dopaminergic system and its relationship to essential hypertension. Work is being performed on the investigation of the potential role of a receptor-coupling defect in the pathogenesis of hypertension in animal models as well as in humans. A variety of techniques are being used to investigate the relationship between the renal adrenergic system and hypertension such as molecular biology, receptor pharmacology, second messenger assays, immunohistochemistry, and in-vivo pharmacology.

The research in his laboratory focuses on the mechanisms that regulate renin gene expression and renin release in the developing kidney microvasculature. In the adult unstressed mammalian kidney, renin is synthesized and released by a small number of specialized smooth muscle cells (juxtaglomerular cells) located in the afferent arteriole at the entrance to the glomerulus. However, we have demonstrated that the vascular localization of renin synthesis, storage and release changes markedly during the process of growth and development of the kidney. Using immunocytochemical techniques, in situ hybridization histochemistry and other molecular biologic approaches, we showed that: 1) the fetal kidney expressed the renin gene, 2) expression of the renin gene is subjected to developmental changes, characterized by a decrease in a renin mRNA levels with maturation; and 3) as maturation progresses, the intrarenal distribution of renin and its encoding mRNA shift from large intrarenal arteries in the fetus to a classical, restricted juxtaglomerular site in the adult animal. This ontogenic changes in renin distribution may be of importance for the local (paracrine) regulation of perfusion pressure, glomerular growth and hemodynamics. We hypothesize that the enhanced expression of renin in early development is the result of DNA binding proteins interacting with the 5' flanking region of the renin gene. Using gel shift analysis we have identified several proteins that bind to the renin promoter. One of those proteins binds to DNA fragment that confers high luciferase expression in transient transfection assays.

A related effort in my laboratory is to characterize the cytosolic events that mediate expression of the renin gene and renin release in response to stimuli. We utilize single renal microvascular cells and the combination of two techniques: the reverse hemolytic plaque assay that allows the study of renin release by single cells, and simultaneous in situ hybridization for renin mRNA. Using these two techniques we have been able to demonstrate that neonatal renal microvascular cells have the capacity to release renin and to increase renin gene expression in response to activation of adenylate cyclase. Further studies are designed to define the regulatory proteins and DNA sequences involved in this response.

A separate effort in my laboratory involves defining the molecular and cellular mechanisms whereby the angiotensin receptor regulates nephro-vascular growth and differentiation. In this regard we have demonstrated that the angiotensin II receptor, subtype 1 (AT1), is developmentally regulated. In the newborn rat, AT1 mRNA is broadly distributed in the nephrogenic cortex, glomeruli, and intrarenal vessels.

In adult rats, however, AT1 expression is restricted to glomeruli and vessels. The high expression in the nephrogenic cortex composed of cells from different lineages, suggests a role for this receptor in renal development. In fact, blockade of the receptor with DUP753 results in abnormal nephrogenesis and vascular development. Future studies will attempt to delineate the mechanisms whereby angiotensin-receptor interactions lead to orderly (spatially and temporally) phenotypic differentiation of the kidney.

Dr. Victoria Norwood, Chief of Pediatric Nephrology, received her clinical pediatric nephrology training at Tulane University in New Orleans and her basic science research training at the University of Virginia where she joined the Division of Pediatric Nephrology in 1992. Her current research interests center on cyclooxygenases and their roles in renal function and development. Other ongoing studies include the role of angiotensin receptors in the pathogenesis of hypertension and obstructive uropathy. A variety of biochemical and molecular biologic techniques, including metanephric organ culture, cell culture, and transgenic approaches are currently being used to evaluate mechanisms of action and regulation of angiotensin receptors and cyclooxygenases in the developing kidney.

Current projects address the mechanisms mediated by vascular endothelial growth factor (VEGF) and its receptors in kidney vascularization . VEGF function is critical for vascular development. However, the molecular events that coordinate vascular development and kidney morphogenesis are unknown. VEGF is expressed in parenchymal cells contiguous to the developing kidney vasculature throughout embryonic life, postnatal development and adult life. We showed that VEGF induces vasculogenesis in metanephric organ culture and that VEGF is a chemoattractant providing direction to migrating endothelial cells during renal morphogenesis, suggesting that VEGF is important in determining the spatial organization of the renal vasculature. The mechanisms underlying the spatial organization of the vasculature during kidney development and the function of VEGF in renal epithelial cells are unknown and are the focus of our studies.

Our objective is to elucidate the mechanisms mediating directional endothelial cell migration during kidney organogenesis and vascularization. Our hypothesis is that VEGF produced by renal epithelial cells generates local concentration gradients providing a chemo-attractive cue for endothelial cell migration. We also postulate that VEGF supports the establishment and maintenance of fenestrated endothelial cell phenotype and thereby contributes to the regulation of vascular permeability. To test our hypotheses: 1) we study the mechanism of directional endothelial cell migration towards embryonic kidneys and examine the function of VEGF system in renal epithelial cells using migration assays and co-culture models. 2) We study the downstream signaling mechanisms involved in VEGF-induced directional endothelial cell migration: examine the role of integrins, FAK and MAP kinase mediated signals. 3) We will determine whether VEGF is required for the establishment and maintenance of the fenestrated phenotype of glomerular endothelial cells in vitro and study the signaling mechanisms involved. These experiments should provide fundamental information regarding VEGF-induced directional migration and advance our knowledge of the molecular mechanisms governing vascular spatial organization and renal morphogenesis. Understanding the molecular basis of guidance cues for migration should enable us to generate new strategies for prevention, diagnosis and treatment of renovascular disease and cancer.

We have ongoing collaborations with Dr. Rick. Horwitz and Pablo Visconti from the Cell Biology Department, with Dr. Thomas Parsons from the Microbiology Department and with Drs Ben Gaston, Lisa Palmer and Allen Everett from the Department of Pediatrics.

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