In this proposal, we hypothesize that tubular epithelial hypoxia plays a key role in the development of renal fibrosis and is a major contributor to the progression of chronic renal disease, ultimately leading to the complete destruction of functional renal tissue. A key mediator of cellular adaptation to hypoxia is Hypoxia-lnducible-Factor-1 (HIF-1), a ubiquitously expressed basic-helix-loop-helix transcription factor, mostly known for its regulation of genes involved in vascular remodeling, erythropoiesis, and enhanced glucose metabolism. Here we propose that HIF-1 promotes renal fibrosis by altering the expression of genes and the biological behavior of renal epithelial cells towards a myofibroblast phenotype, as a result of changes within the microvasculature and hemodynamics of the kidney that lead to localized hypoxia during chronic renal injury. Furthermore, increased HIF-1 biological activity has been reported in response to numerous non-hypoxic stimuli including nitric oxide, tumor necrosis factor alpha, and angiotensin II, all of which have significant roles in the pathogenesis of chronic renal diseases. In order to examine the role of hypoxic signaling in the pathogenesis of renal fibrosis, we have chosen 2 major experimental approaches that are based on conditional knock-out and hypoxia-response-element reporter mice, and on the use of primary and immortalized wild type, and HIF-1 deficient renal epithelial cells. The proposed studies will include: a) an animal model of renal fibrosis which makes use of conditional HIF-1a knock-out mice, b) cell culture based experiments examining epithelial to mesenchymal transition (EMT) as well as cell motility assays; and c) gene expression and gene regulation studies. With this pilot project we propose to a) define the role of HIF-1 in an animal model of tubulointerstitial fibrosis, b) to explore HIF-1's role in the hypoxic induction of EMT and its effects on cell motility and c) to explore whether or not HIF-1 can act synergistically with TGF-B1, a key mediator of EMT and ECM production. Overall, this pilot project aims at establishing a research program which investigates the effects of hypoxia (HIF-dependent and HIF-independent mechanisms) on epithelial signaling networks critical for the development of tubulointerstitial fibrosis and the progression of chronic renal disease. Knowledge generated from such work will ultimately add to our understanding of how critical profibrotic transcriptional circuits interact with each other and how changes in the cellular microenvironment modulate these networks under specific disease conditions. Data generated from this grant would be used to guide a grant proposal for 5-year NIH funding. ? ? ?
| Higgins, Debra F; Kimura, Kuniko; Bernhardt, Wanja M et al. (2007) Hypoxia promotes fibrogenesis in vivo via HIF-1 stimulation of epithelial-to-mesenchymal transition. J Clin Invest 117:3810-20 |
