Calcific aortic valve disease (CAVD), the most common cause of aortic stenosis, affects ~2% of the general US population and given their age, a higher fraction of veterans. In the absence of effective medical therapies, CAVD treatment is limited to surgical or percutaneous valve replacement. Efforts aimed at developing an effective medical therapy for CAVD have failed in part due to knowledge gaps, lack of representative animal models, and lack of tools to assess valvular biology in vivo. The overarching goals of this project are to develop and validate a novel molecular imaging approach and leverage it as a component of multimodality molecular and structural imaging to identify and evaluate novel therapeutic agents for CAVD. The hallmarks of CAVD include valvular interstitial cell osteoblastic differentiation, extracellular matrix remodeling, and leaflet calcification. Molecular imaging tracers, including those recently developed by our group that target matrix metalloproteinase (MMP)-12, can potentially detect and track these biological processes in vivo. Gene expression profiling has singled out MMP-12 as the most highly upregulated gene in human CAVD and our preliminary data suggest that MMP-12 deletion may ameliorate aortic valve remodeling. This in conjunction with other lines of evidence suggest that MMP-12 may serve as a therapeutic target to prevent progression of CAVD. The novel observations that calcified nodules can regress in vitro and this regression can be modulated by pharmacologic interventions, suggest that valvular interstitial cells may acquire an osteolytic phenotype. Taking advantage of this phenomenon, we have established an in vitro screening platform to select agents that promote reversal of valvular interstitial cell calcification. Here, we seek to evaluate MMP-12 as a diagnostic and therapeutic target in CAVD, and identify novel agents that reverse aortic valve calcification. Using a combination of genetically modified mice, including a novel murine model of CAVD that phenocopies human disease, and novel MMP-12-targeted tracers and inhibitors, we will validate MMP-12 imaging for tracking valvular biology in vivo; and through serial high-resolution multimodality molecular and structural imaging in vivo followed by tissue analysis in vitro, we will evaluate the effect of MMP-12 inhibition on CAVD progression, and in the case of agents identified through screening, their effect on regression of aortic valve calcification. Combined, these studies will identify novel therapeutics with a direct path to clinical translation, while advancing our knowledge on CAVD pathobiology. This may ultimately transform the management of patients with aortic stenosis.