The effect of mechanical stimuli on the mitral valve interstitial cell : implications for heart valve disease and surgical repair
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In the diseases of the mitral valve (MV), such as mitral regurgitation (MR) and degenerative myxomatous MV disease (MMVD), several pathological factors have been shown to affect tissue structure and composition that ultimately lead to valve failure. Current clinical treatments for both functional and degenerative MR include repair by ring annuloplasty (AP). Though beneficial in the short-term, AP has been shown to be less promising long term with repair failure as high as 60%. Mechanical stress is a strong etiological factor: alterations in mechanical loading caused by surgical repair lead to stress-induced changes in mitral valve interstitial cell (MVIC) function that affect both tissue structure and composition, ultimately leading to repair failure. A common thread needed to address these issues is the link between tissue-level stresses and cellular homeostatic responses. MVIC deformation is a major driver for cellular mechanoregulation. As such, a quantitative understanding of MVIC responses to mechanical stimulation in vivo is necessary. We thus hypothesize that abnormal mechanical stimuli lead to non-physiological MVIC deformations that result in phenotypic activation and altered biosynthetic activity. Exploiting this knowledge can lead to improved surgical repair techniques for both functional and degenerative MR. We address our hypothesis in four parts. First, we evaluate the remodeling of the MV anterior leaflet after ischemic MR using an in vivo ovine model, laying out an essential prerequisite for the rest of the dissertation. Second, we characterize the three-dimensional microenvironment of the MVIC under physiological loading, allowing us to develop more structurally accurate computational models that incorporate the heterogeneities of the cellular microenvironment. Third, we use an integrated experimental-computational approach to elucidate the link between MVIC deformation and biosynthetic response in an intact tissue system under simplified deformations. And finally, we design and develop a more physiologically-relevant bioreactor and use it investigate the response of MVICs to a range of simulated physiological and non-physiological loading conditions. Our integrated approaches allowed us to identify MVIC deformation as a key player in leaflet tissue homeostatic regulation and use it as a metric that makes the critical link between in vitro responses to equivalent in vivo behavior.