The Role of TGF-alpha in the Pathogenesis of ARPKD

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DESCRIPTION (adapted from the application) Autosomal recessive polycystic kidney disease (ARPKD) is an inherited kidney disorder characterized by massive kidney enlargement and hepatic fibrosis. Progression to end-stage renal disease is usually inevitable, often in the first years of life. A growing body of literature has established a key role for the epidermal growth factor receptor (EGFR) in the pathogenesis of abnormal cell proliferation and cyst expansion. In contrast, the expression, regulation, and function of the EGFR ligands have not been studied systematically in these diseases. Published data demonstrate that the EGFR ligand, transforming growth factor-alpha (TGF-alpha), is overexpressed in cystic tissues and cells and transgenic mice that overexpress TGF-alpha develop renal cysts. Using TGF-alpha as a paradigm, the proposed research will examine the physiologic effects of ligand upregulation and identify factors that contribute to EGFR ligand overexpression in ARPKD. The central hypothesis is that aberrant EGFR ligand expression is a common feature modulating the cellular pathophysiology of PKD. The specific aims of the project are: 1. To examine the physiologic effects of TGF-alpha upregulation in cyst formation and enlargement and to identify specific factors mediating TGF-alpha upregulation. Specific hypothesis to be tested include: a) TGF-alpha upregulation results in increased production of itself (auto-induction) and other EGFR ligands (cross-induction); b) secreted, not membrane-bound TGF-alpha, is the more important biologically-active moiety in ARPKD; c) TGF-alpha regulates EGFR expression by direct effects on EGFR mRNA transcription and stability; and d) abnormal expression of AP-2 and VHL, factors known to regulate TGF-alpha expression, mediate increased TGF-alpha expression in ARPKD. Primary and immortalized collecting tubule (CT) cell lines derived from cystic bpk mice (a murine model of ARPKD) and noncystic littermates will be used to assess the in vitro effects of exogenous TGF-alpha administration, TGF-alpha overexpression, and TGF-alpha/EGFR interactions. AP-2 and VHL protein and mRNA expression in cystic and control tissues and cells will be determined, and the role of each protein in TGF-alpha regulation assessed. 2. To determine the in vivo effects of blocking TGF-alpha production on disease progression in ARPKD. The hypothesis to be tested is that TGF-alpha has a key role in the pathogenesis of ARPKD. This will be tested by breeding the bpk mouse with a TGF-alpha knockout mouse and assessing the impact on disease progression and expression of EGFR and other EGFR ligands. These studies will provide new insights into the biology of EGFR ligands in ARPKD. Although the proposed research focuses on ARPKD, insights provided by these studies may contribute to a broader understanding of autosomal dominant polycystic kidney disease (ADPKD) as well.