The Influence of Matrix Bound Nanovesicles on Inflammation-Driven Prosthetic Heart Valve Failure

Bioprosthetic tissue valves consisting of glutaraldehyde-fixed bovine pericardium (gluBP) are the standard of care for aortic valve replacement. However, failure of bioprosthetic tissue valves typically occurs after 10-15 years due to structural valve degeneration (SVD), a gradual process of stenosis or regurgitation resulting from calcification, fibrotic tissue deposition, or cusp tearing. The mechanisms are not fully understood, but macrophage-driven inflammation is thought to contribute to the pathologic remodeling of SVD. Extracellular matrix (ECM) bioscaffolds promote an anti-inflammatory macrophage phenotype and facilitate a constructive remodeling outcome in multiple clinical applications. Extracellular vesicles embedded within the ECM, termed matrix bound nanovesicles (MBV), and their associated lipid, miRNA and protein cargo have recently been shown to recapitulate anti-inflammatory effects in macrophages. Alteration of the MBV intraluminal cargo can have dramatic implications on their bioactivity. More specifically, elimination of the cytokine interleukin-33 (IL-33) within MBV negates their anti-inflammatory effects. The present dissertation first expands our current understanding of MBV and then evaluates the therapeutic potential of MBV in altering cellular processes associated with SVD of bioprosthetic valves, including macrophage activation, fibrosis, and calcification, both in vitro and in vivo. The contribution of IL-33 cargo to MBV-mediated effects are also examined. Results show that MBV are a distinct subpopulation of extracellular vesicle with lipid, protein, and miRNA composition that changes with cell source and disease progression. The anti-inflammatory effects induced by MBV in macrophages is dependent on the repertoire of genes regulated by IL-33 cargo independently of its canonical receptor. MBV direct phenotypical changes in fibroblast activation and mineralization primarily through indirect, macrophage-mediated effects. In a rodent subcutaneous implant model, systemic administration of MBV containing IL-33 cargo shifted the host inflammatory response to a gluBP implant toward an anti-inflammatory phenotype but did not significantly impact the calcification response. These results signify the importance of the MBV cargo protein IL-33 in eliciting an anti-inflammatory phenotype in macrophages and provides guidance for the designing of next generation biomaterials and tissue engineering strategies