Transforming growth factor-β1 promotes fibrosis but attenuates calcification of valvular tissue applied as three-dimensional calcific aortic valve disease model.

Calcific aortic valve disease (CAVD) is characterized by valvular fibrosis and calcification and driven by differentiating valvular interstitial cells (VICs). Expression data from patient biopsies suggest that TGF-β1 is implicated in CAVD pathogenesis. However, CAVD models using isolated VICs failed to deliver clear evidence on the role of TGF-β1. Thus, employing cultures of aortic valve leaflets we investigated effects of TGF-β1 in a tissue-based three-dimensional (3-D) CAVD model. We found that TGF-β1 induced phosphorylation of SMAD3 and expression of SMAD7 indicating effective downstream signal transduction in valvular tissue. Thus, TGF-β1 increased VIC contents of rough ER, Golgi and secretory vesicles as well as tissue levels of RNA and protein. In addition, TGF-β1 raised expression of proliferation marker cyclin D1, attenuated VIC apoptosis and upregulated VIC density. Moreover, TGF-β1 intensified myofibroblastic VIC differentiation as evidenced by increased α-SMA and collagen type I along with diminished vimentin expression. In contrast, TGF-β1 attenuated phosphorylation of SMAD1/5/8 and upregulation of β-catenin while inhibiting osteoblastic VIC differentiation as revealed by downregulation of osteocalcin expression, ALP activity and ECM incorporation of hydroxyapatite. Collectively, these effects resulted in blocking of valvular tissue calcification and associated disintegration of collagen fibers. Instead, TGF-β1 induced development of fibrosis. Overall, in a tissue-based 3-D CAVD model TGF-β1 intensifies expressional and proliferative activation along with myofibroblastic differentiation of VICs thus triggering dominant fibrosis. Simultaneously, by inhibiting SMAD1/5/8 activation and canonical Wnt/β-catenin signaling TGF-β1 attenuates osteoblastic VIC differentiation thus blocking valvular tissue calcification. These findings question a general phase-independent CAVD-promoting role of TGF-β1.