Aortic Valve Interstitial Cell Activation Does Not Occur at Low Tissue Stiffness During Embryogenesis

An estimated 2.5 percent of the American population has heart valve (HV) disease and more than 100,000 US patients require a prosthetic valve replacement each year [1]. However, prosthetic valves can cause accelerated calcification leading to recurrence of HV disease in patients [2]. Thus, the development of a suitable tissue-engineered heart valve (TEHV) would greatly benefit patients with HV disease. Aortic valve interstitial cells (AVICs) play a crucial role in the progression of aortic valve disease as well as the maintenance of normal valve. Therefore, in order to design a suitable TEHV, these specialized cells need to be better understood. AVICs are known to synthesize ECM and express matrix degrading enzymes and their inhibitors that mediate and regulate remodeling of ECM components [3]. Interestingly, it was recently established that AVICs sense the stiffness of their surrounding ECM in vivo and are phenotypically responsive to mechanical cues with AVICs differentiating into myofibroblasts or osteoblasts, which are pathologic markers. Specifically, soft collagen gels (∼34kPa) caused less differentiation of AVICs than stiffer collagen gel (∼100kPa) [4]. However, for these experiments the AVICs were cultured on tissue culture polystyrene (TCPS) for at least one passage, and it is likely that AVICs cultured on TCPS might retain modified characteristics of AVICs in tissue prior to seed them on soft gels because of the memory to rigid substrate stiffness. Therefore, in this study, we examined the phenotype and function of AVICs on substrates that mimic ECM stiffness of adult leaflet as well as of developing embryo. In addition, we examine the effects of transforming growth factor-β1 (TGF-β1) which has been the most extensively studied cytokine initiator of fibrotic response of AVICs.