MMP9 and aortic valve stenosis: In all groups, the massive downregulation of the MMP9 gene and the upregulation of the TIMP gene probably reflected the activation of a negative retro control mechanism linked to fibrosis deposition and matrix turnover, as activation of MMPs and inhibition of TIMPs have been identified as promoters of fibrosis and mineralization in AS (Shen et al., 2017).