Manipulating the matrix to improve arteriovenous fistula patency

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Project Summary A cornerstone of several common therapies for human diseases is the use of a vein as a conduit to increase blood flow such as the arteriovenous fistula (AVF), the preferred access for hemodialysis. However, the poor maturation and patency of AVF, especially in women and requiring additional re-do procedures and surgery, reflects our imperfect understanding of the biology of venous remodeling that leads to successful venous adaptation to the arterial environment. This knowledge gap creates an unmet need for novel approaches to enhance venous remodeling and thereby to increase successful clinical use of venous conduits. Successful venous remodeling requires deposition of extracellular matrix (ECM), enabling mechanical strength to resist hemodialysis procedures that puncture the AVF wall with large bore needles 3 times a week. Transforming growth factor (TGF)-β1 regulates numerous cellular functions, including ECM deposition and remodeling. We present exciting new data that: 1) our innovative mouse model of AVF faithfully recapitulates human AVF maturation including an ~1/3 failure rate; 2) female mice with AVF have diminished magnitudes of shear stress compared to male mice; 3) we can manipulate TGF-β1 function in vivo and TGF-β1 is required for successful early AVF remodeling; 4) in failed mouse AVF there is increased ECM, late TGF-β1 expression and smad2/tak1 phosphorylation; 5) there is increased smad2/tak1 phosphorylation in human AVF surgically removed for failure; 6) we developed an innovative nanoparticle tool to manipulate TGF-β1 signaling in vivo. Our data suggest that surgical creation of a fistula stimulates early TGF-β1 activation via smad2/3 and/or tak1 phosphorylation that is critical for successful early venous adaptation and AVF maturation. We hypothesize that exuberant late TGF-β1 activity results in excessive ECM deposition and neointimal hyperplasia causing AVF failure. Reducing late TGF-β1 activity should reduce ECM deposition and neointimal hyperplasia, thereby improving AVF patency. We will use our innovative in vivo model, as well as a novel bioreactor and molecular tools, to test our hypothesis with the following specific aims: Aim I: Determine whether there are sex differences in TGF-β signaling in vitro and AVF remodeling in vivo. Aim II: Determine optimal delivery to reduce late TGF-β1 signaling thereby enhancing venous adaptation and improving AVF patency. Aim III: Determine whether smad2 or tak1 function is a mechanism of TGFβ1-mediated AVF remodeling. This work will have lasting impact by establishing whether excessive TGF-β activity leads to AVF failure, and whether reducing late TGF-β activity is a valuable strategy for clinical translation to enhance AVF patency. We will also determine whether the reduced AVF maturation in women is due to insufficient venous remodeling or increased neointimal hyperplasia. We use an innovative strategy and novel tools to manipulate TGF-β signaling to alter vessel wall composition and strength and thereby improve AVF patency.