Hedgehog Signaling in Kidney Fibrosis: is Pericyte Survival and Proliferation regulated by Hedgehog Pathway downstream Transcription Factor Gli2?

• Applicant: Dr. Susanne Fleig
• Subject Area: Nephrology
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 226591597

Acute kidney injury is common and increasing in incidence; while it often appears to be reversible, it is associated with an increased risk of developing kidney fibrosis with progressive chronic insufficiency. A better understanding of the mechanisms of kidney damage and repair could lead to new therapeutical approaches to prevent or postpone chronic renal insufficiency. Pericytes are stromal cells that are in close contact with endothelial cells forming capillaries. These contacts are of crucial importance for vessel stability and integrity. In kidney fibrosis, loss of these cell-cell contacts leads to capillary loss. Pericytes gain a myofibroblastic phenotype via the mechanism of epithelial-mesenchymal transition and produce extracellular matrix, resulting in scar tissue and fibrosis. Hedgehog Signals are embryonic morphogens; the pathway has recently been shown to also be active in tumors of a variety of adult tissues and to be involved in regeneration processes that require activation of the resident progenitor cell pool (e.g. in skin, lung, the GI-tract and the liver). For my dissertation, I have analyzed hedgehog signaling in liver regeneration in a mouse model of non-alcoholic steatohepatitis, and found increased hedgehog activity with increased liver damage and proliferation and expansion of the progenitor cell pool in the canals of Hering. Upon activation of kidney pericytes to extracellular matrix producing myofibroblasts, hedgehog signaling becomes active; Ben Humphreys- laboratory showed hedgehog activity in fibrosis models such as the unilateral ureteral obstruction model. One of the hedgehog-transcription factors, the zink-finger protein Gli-2, seems to play a key role in this process; it is not only active within the hedgehog pathway, but can also be activated non-canonically via TGFß, EGF or FGF signaling - pathways that are important in fibrogenesis. Aim of my research project is to examine the role of Gli-2 for pericyte survival and proliferation in the kidney in vitro and in vivo. I would like to address this question during a 2-year post-doctoral fellowship at Ben Humphreys- laboratory at Harvard Medical School in Boston, MA, USA. In vitro, I plan to analyze Gli-2 in pericytes by overexpressing or inhibiting Gli-2 and measure markers of proliferation and survival. In cocultures of kidney pericytes and endothelial cells, I want to analyze the role of hedgehog in paracrine cell communication. To determine the functional role of Gli-2 in vivo, I would like to use a genetic approach using the cre/lox-technique and create mouse models with constitutional or inducible activation or inactivation of Gli-2, and induce kidney fibrosis with unilateral ureteral obstruction. The organical arsenic derivative Darinaparsin (ZIO-101) blocks hedgehog at the level of Gli-2 and is already in clinical phase-II-studies for tumor therapy; I want to examine if it is capable of diminishing fibrosis in the kidney.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Benjamin Humphreys, Ph.D.