Dysregulation of valvular interstitial cell let-7c, miR-17, miR-20a, and miR-30d in naturally occurring canine myxomatous mitral valve disease.

Canine myxomatous mitral valve disease (MMVD) resembles the early stages of myxomatous pathology seen in human non-syndromic mitral valve prolapse, a common valvular heart disease in the adult human population. Canine MMVD is seen in older subjects, suggesting age-related epigenetic dysregulation leading to derangements in valvular cell populations and matrix synthesis or degradation. We hypothesized that valvular interstitial cells (VICs) undergo disease-relevant changes in miRNA expression. In primary VIC lines from diseased and control valves, miRNA expression was profiled using RT-qPCR and next generation sequencing. VICs from diseased valves showed phenotypic changes consistent with myofibroblastic differentiation (vimentinlow+, α-SMAhigh+), increases in senescence markers (p21, SA-ß-gαl), and decreased cell viability and proliferation potential. RT-qPCR and miRNA sequencing analyses both showed significant (p<0.05) downregulation of let-7c, miR-17, miR-20a, and miR-30d in VICs from diseased valves compared to controls. Decreased let-7c, miR-17, and miR-20a may contribute to myofibroblastic differentiation in addition to cell senescence, and decreased miR-30d may disinhibit cell apoptosis. These data support the hypothesis that epigenetic dysregulation plays an important role in age-related canine MMVD.

Circulating exosome microRNA associated with heart failure secondary to myxomatous mitral valve disease in a naturally occurring canine model.

Myxomatous mitral valve disease (MMVD) is functionally and histologically identical to mitral valve prolapse (MVP) in humans. Currently, there are no medical treatments that can delay the progression of this valvular disease or associated cardiac remodelling. Therefore, there is a need to understand the molecular pathology associated with MMVD and MVP better, and thus identify potential therapeutic targets. Circulating exosomes contain small RNA, including miRNA, which reflect cell physiology and pathology. This study explored the association between circulating exosomal miRNA (ex-miRNA) content and MMVD, heart failure due to MMVD (MMVD-CHF) and ageing, which is strongly associated with MMVD. Ex-miRNA was isolated from old normal/healthy dogs (n = 6), young normal dogs (n = 7), dogs with MMVD (n = 7) and dogs with MMVD-CHF (n = 7). Separately, total plasma miRNA was isolated from normal dogs (n = 8), dogs with MMVD (n = 8) and dogs with MMVD-CHF (n = 11). Using reverse transcription quantitative polymerase chain reaction, exosomal miR-181c (p = 0.003) and miR-495 (p = 0.0001) significantly increased in dogs with MMVD-CHF compared to the other three groups. Exosomal miR-9 (p = 0.002) increased in dogs with MMVD and MMVD-CHF compared to age-matched (old) normal dogs. Exosomal miR-599 (p = 0.002) decreased in dogs with MMVD compared to old normal dogs. In total plasma, 58 miRNA were deemed significantly different (p < 0.04) between normal dogs, dogs with MMVD and dogs with MMVD-CHF. However, in contrast to ex-miRNA, none of the miRNA in total plasma remained statistically significant if the false discovery rate was <15%. Changes in ex-miRNA are observed in dogs as they age (miR-9, miR-495 and miR-599), develop MMVD (miR-9 and miR-599) and progress from MMVD to CHF (miR-181c and miR-495). Ex-miRNA expression-level changes appear to be more specific to disease states than total plasma miRNA. RESPONSIBLE EDITOR Elena Aikawa, Harvard Medical School, USA.