The first session, “Proteomics: Basic Principles and Clinical Applications” was chaired by Alan S. L. Yu, M.D. (Nephrology Division, USC) and Alicia McDonough, Ph.D. (Director, Systems Biology and Disease Program, and Department of Physiology and Biophysics, USC).
Proteomics is the study of the entire complement of proteins expressed in a cell, tissue, or body fluid. Jon Klein, M.D., Ph.D. (University of Louisville, Kentucky) gave a succinct introduction to this complex field. As an example of biomarker discovery, he described a study in patients with type I diabetes mellitus and microalbuminuria using 2-dimensional polyacrylamide difference gel electrophoresis (2D-DIGE) and mass spectrometry to identify urinary peptides differentially expressed in patients with rapid declines in glomerular filtration rate (GFR) as compared to non-decliners. Julian Whitelegge, Ph.D. (Pasarow Mass Spectrometry Laboratory, UCLA) described new techniques to measure the mass of intact proteins, as opposed to the usual method of digesting them into peptide fragments, and discussed their advantage in defining the native covalent state of a protein. He also discussed ways that his group has addressed the difficult problem of performing mass spectrometry on integral membrane proteins.
Mark Knepper, M.D., Ph.D. (Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung and Blood Institute) described the isolation of a novel source of proteins, exosomes, which are small vesicles originating from the multivesicular bodies and shed by virtually every renal epithelial cell type into the urine. Because exosomes account for only 3% of total protein in normal human urine, their isolation can result in a great enrichment for epithelial proteins and may be the best source of biomarkers for renal tubulopathies. Kevin Lemley, M.D., Ph.D. (Division of Nephrology, Children’s Hospital Los Angeles) reviewed the potential clinical utility of counting urinary podocytes. Podocytes are glomerular epithelial cells. In normal individuals, he showed that apoptotic podocytes are shed into the urine, presumably as a normal consequence of senescence, while in active glomerular diseases, viable podocytes somehow detach from the glomeruli and can be isolated in large numbers from the urine.
The second session, “Exploring New Technology in Evaluating Kidney Function and Disease” was chaired by Donald J. Marsh, M.D. (Department of Bioengineering, USC), and Laurence H. Kedes, M.D. (Director, Institute of Genetic Medicine, USC). Christopher Wilcox, M.D., Ph.D. (Division of Nephrology and Hypertension, Georgetown University Medical Center) reviewed the technique of RNA interference, which is a new and effective way to knock down expression of almost any gene and has potentially broad investigative and therapeutic applicability. He demonstrated how RNA interference constructs can be efficiently introduced into the rat kidney and used to dissect out the role of oxidative stress responsive genes in the pathogenesis of angiotensin fl-dependent hypertension. Alicia McDonough, Ph.D. reviewed studies from her group that have elucidated the mechanism of regulation of proximal tubule sodium transporters by trafficking along the villus axis in response to hypertension and angiotensin II. A membrane fractionation and mass spectrometry approach was used to identify several proteins important in membrane trafficking that appear to track with the Na-H exchanger in response to angiotensin 11 inhibition, thus illustrating the power of proteomics. Janos Peti-Peterdi, M.D., Ph.D. (Department of Physiology and Biophysics, USC) introduced in vivo imaging of the kidney, which has the ability to measure function of the live kidney in real time. His group has used these techniques to show that diabetic rats develop angiotensin II dependent hypertension and that this can be accounted for in part by the acute and chronic effects of hyperglycemia to stimulate renin release.
The final session of the day, “Stem Cell Research in Kidney Disease”, was chaired by Martin Pera, Ph.D. (former Director, Institute for Stem Cell and Regenerative Medicine, USC) and Laurie DeLeve, M.D., Ph.D., (Division of Gastrointestinal and Liver Disease, USC). Stem cells are cells that can divide indefinitely and have the potential to differentiate into any specialized cell type. They are generally divided into embryonic stem cells, and adult or somatic stem cells. Joseph Bonventre, M.D., Ph.D. (Renal Division, Brigham and Women’s Hospital and Harvard Medical School) reviewed the evidence for the involvement of adult stem cells in repair of renal tubules after ischemic acute renal failure. He showed that bone marrow-derived stem cells do migrate to the kidney in response to injury and are beneficial in the repair process but, surprisingly, demonstrated that they are not the major source of mesenchymal cells for regeneration of the tubule epithelium. Seung Kim, M.D., Ph.D. (Department of Developmental Biology, Stanford University School of Medicine) reviewed the empirical approach that his group has taken, using the pancreas as a model tissue, to identify progenitor cells that can be used to regenerate insulin-producing cells in vitro. This approach is based on flow cytometry to fractionate cell lineages, using cell-surface proteins known to be differentiation-dependent as candidate markers, followed by specialized cell culture methods to induce differentiation. Roger De Filippo, M.D. (Division of Urology, Children’s Hospital Los Angeles and Saban Research Institute) reviewed the use of amniotic fluid stem cells as a non-destructive source of fetal stem cells and showed data demonstrating their potential in bioengineering new tissues. He also showed that these cells can regenerate renal tubule epithelial cells in vitro, and if injected intravenously can migrate to the kidney, thus representing a potential cell therapy for kidney injury. David Humes, M.D. (Department of Medicine, University of Michigan Medical School) reviewed the concepts of renal bio-replacement and gave an update on his renal tubule assist device (RAD), which is a hollow fiber hemofiltration cartridge lined with live human proximal tubule epithelial cells. He reported the preliminary results of a recently completed Phase II randomized, controlled clinical trial of 58 patients with acute renal and multi-organ failure which showed promising results: RAID therapy reduced 28-day mortality by 28% compared to conventional hemofiltration and the trend in improved survival was sustained through 90 and 180 days.