Translational Renal Research brings together basic and clinical science that helps bridge laboratory discovery with the diagnosis and treatment of human kidney disease.
Diabetic Nephropathy and Stem Cell Aging
Our Goals: Identification of novel therapeutic targets in diabetic kidney disease using gene based strategies.
Diabetes is a number one diagnosis for End Stage Renal Disease. This dreaded complication accelerates the aging process in the kidney, but the cellular and molecular mechanisms that lead to the acquisition of the senescent phenotype, have not been defined. Aging tissues experience a progressive decline in homeostatic and regenerative capacities that has been linked to age related dysfunction of tissue specific stem cells. The p66 gene controls cellular responses to oxidative stress, aging and apoptosis. The primary goal of our laboratory is to understand the salutary effect of the p66 mutation is mediated by delaying activation of senescent programs that lead to irreversible cell cycle arrest, resulting in dysfunctional tissue stem cells and preventing replacement of differentiated cells lost to apoptosis and cell senescence.
Our lab demonstrated that kidneys of diabetic mice with p66 mutations express a strong protection phenotype, as judged by histology and urine albumin excretion. We are evaluating if targeted deletion of p66 confers renoprotection, at least in large part, by delaying activation of senescent programs that accelerate the aging process. We demonstrate mesenchymal stem cells (MSCs) isolated from kidneys of p66 Knock Out mouse are resistant to hyperglycemia induced apoptotic and senescent phenotypes; retaining their self-renewal and paracrine functions.
Using Microarray analysis we detected upregulation of stem cell senescence antagonizing Wnt regulatory genes in p66 deleted MSCs. Growth curves of these MSCs cultured under hyperglycemic conditions showed p66 deleted MSCs remains in the active growth phase even after day 12 when compared with control MSCs. The in vivo correlate of these observations revealed that MSCs survive long term in kidneys of p66 KO diabetic mice and show modest rates of cell turnover with barely detectable histologic markers of aging. By contrast, kidneys of diabetic mice show substantial increase in cell nuclei expressing the senescent protein p16INK4a and advanced histologic markers of aging. These findings identify p66 as an inducer of molecular and cellular events that lead to accelerated aging phenotype(s) in diabetic kidneys.
We are conducting the transplantation experiments in which p66 KO MSCs are delivered to kidneys of diabetic mice, before and after the onset of diabetes, represent a logical extension and may provide an avenue for improved outcomes in cell based therapeutics.
Ubiquitin proteasome in chronic and acute renal injury
Aim: Inhibition of ubiquitin proteasome pathway has protective effects in renal injury.
Primary glomerular disease affect both children and adults, causes 10% of end-stage renal disease, and costs 1% of Medicare dollars for renal replacement therapies. Approximately 30 to 40% of adults with membranous nephropathy (MN) progress to end-stage kidney disease and ~30% of children with minimal change disease (MCD) develop resistance to steroid therapy. Our study focuses on primary glomerular diseases MN, which is the most common primary glomerulopathy in adults, and minimal change disease (MCD), the most prevalent form of Nephrotic Syndrom in children.
The roles of oxidants and iron have been extensively demonstrated in glomerular and progressive kidney disease. The cytochrome P450 (CYP) system is crucial to the oxidant-mediated cell signaling and is present at high concentration in the endoplasmic reticulum (ER). We were the first to identify and emphasize the role of 2B1 in models of glomerular disease wherein administration of suicide CYP2B1 inhibitors and 2B1 gene silencing resulted in significant protection against proteinuria and cytotoxicity.
We demonstrate unexplored role of the ubiquitin proteasome pathway (UPS) in various models of glomerular injury. Our data indicate CYP450-2B1 as a prime target for UPS degradation. Several proteasome inhibitors that target this pathway have been developed and are currently being tried in various clinical diseases with beneficial effects. These proteasome inhibitors are a fascinating area of research and a promising field for treating progressive disease in the native kidney as well as in renal grafts.
We have identified the CYP2B6 (2B6) isozyme to human kidney podocytes. It is evident that tissue-specific expression of 2B6 may cause accumulation of active metabolites and facilitate target-organ damage. Our data indicates a significant increase in the malondialdehide (MDA) adducts in the podocytes in human MCD and MN. Our study includes the identification of Nrf2 and HRI as protective factors may pave the way toward exciting translational research and provide an avenue toward development of more effective therapies in the treatment of glomerular diseases.
We are performing animal studies to determine the role of CYP 2B1 degradation in these models of glomerular injury and the mechanism by which CYP 2B1 degradation results in glomerular injury. Our long-term goals are to utilize the data obtained in the present study for extending the concepts to other important causes of glomerular diseases such as diabetes and FSGS, the most common cause of kidney disease in the United States. Based on these concepts we plan to initiate human studies. We also plan to perform a pilot study in humans with membranous nephropathy and steroid-resistant nephrotic syndrome.