Introduction:
Myxomatous mitral valve disease (MMVD) is a degenerative condition characterized by tissue fibrosis and matrix remodeling which ultimately progresses to leaflet prolapse. While recent work has shown that transforming growth factor beta (TGF-β) signaling contributes to the pathogenesis of MMVD, upstream regulators of this and other pathways remain poorly understood.
Hypothesis:
We sought to use high-throughput RNA sequencing coupled with microRNA (miRNA) sequencing to identify novel molecular targets as well as upstream regulators contributing to MMVD.
Methods:
We conducted mRNA and miRNA sequencing on normal (n = 10) and myxomatous human mitral valve samples (n = 10). Differential expression was identified using linear modeling and parallel random forest analyses. Canonical pathways were identified by Ingenuity Pathway Analyses (IPA). Predicted miRNA targets were identified using TargetScanHuman 6.2.
Results:
We found 2784 mRNAs that were differentially expressed between normal and myxomatous mitral valves, which IPA largely categorized in to pro-fibrotic, matrix remodeling and cellular proliferation signaling. In miRNA sequenced from the same samples, 67 miRNAs were differentially-expressed between normal and myxomatous mitral valves. Increased expression of TGF-β ligands, collagen isoforms, and matrix metalloproteinases were associated with reductions in miRNAs predicted to target them. Conversely, mRNA levels of the “protective” genes TGFβ-induced factor homeobox 1, salt-inducible kinase 1, TIMP metallopeptidase inhibitor 4, and cyclin-dependent kinase inhibitor 1C mRNA levels were decreased in myxomatous tissue, and miRNAs predicted to target these genes (e.g., miR-656, miR-379-3p, miR-664a-3p, and miR-34c-5p) were significantly increased.
Conclusions:
Collectively, these data not only identify novel genes that are differentially regulated in MMVD, but also suggest miRNAs may play an active role in suppressing key protective molecules in MMVD. Thus, anti-mIRs therapy may be a viable therapeutic target to restore anti-fibrotic and anti-proliferative molecules in the valve and slow progression of MMVD. Future mechanistic studies will lay a critical foundation for translational work in these areas.
Novel Mechanisms Contributing to Fibrosis and Matrix Remodeling in Myxomatous Mitral Valve Disease
