August 03, 2017

Could Genomic Material Be a Biomarker for Heart Disease?

Genomic material found in extracellular vesicles could be important biomarkers for myxomatous mitral valve disease in dogs, opening the door for innovative treatment approaches for this disease.
By JoAnna Pendergrass, DVM
Exosomal microRNA (ex-miRNA) demonstrated changes in expression level with age and progression of myxomatous mitral valve disease (MMVD) in dogs, according to a study recently published in the Journal of Extracellular Vesicles.

Study results “represent a vital step forward in advancing ex-miRNAs as important biomarkers for non-ischemic heart disease,” wrote the study’s researchers.

MMVD, which primarily occurs in older small-breed dogs, is characterized by progressively-worsening heart function and often leads to congestive heart failure (CHF). It is similar to human mitral valve prolapse (MVP), which is also progressive.

Currently, MVP treatment faces challenges—limited efficacy of medical management and high mortality rates for elderly patients undergoing surgical mitral valve treatment. Using MMVD as an animal model could lead to development of novel MVP treatments, the researchers noted.

miRNAs regulate gene expression and are reportedly associated with disease. miRNA within exosomes, which are nanosized extracellular vesicles, reflect the cell of origin’s molecular activity. According to the study’s researchers, evaluating ex-miRNA in naturally occurring MMVD could provide useful insight into the relationship between miRNA and the diseased tissues from which it originates.

Study Design
Researchers enrolled 47 adult pet dogs of various breeds. Following a physical exam, echocardiography, and radiographs, dogs were divided into 3 groups: (1) healthy; (2) asymptomatic MMVD; and (3) MMVD-CHF. Total plasma miRNA and plasma ex-miRNA were isolated from whole blood samples; both isolation methods were performed to determine which miRNA was more disease relevant.

PCR was performed to identify 277 canine miRNAs. False discovery rates (FDR) were used to detect false positive miRNA expression levels between healthy and MMVD groups. In addition, heat map clustering was used to examine miRNA expression levels.

Total plasma miRNA
miRNA expression levels did not appear to cluster according to group. At an FDR of 20%, 58/277 miRNAs had significantly different expression levels between groups. However, when the FDR threshold was lowered to ≤15%, no significant differences were found.

Plasma ex-miRNA
At an FDR of 20%, only 4/277 miRNAs—miR-9, miR-181c, miR-495, and miR-599—had significantly different expression levels between groups. This proportion of false positives was significantly lower than that identified in total plasma, indicating that total plasma is inefficient at detecting disease-relevant miRNA.

To determine aging’s effect on ex-miRNA expression, researchers sub-divided the ‘healthy’ group into young (< 7 years) and old (≥ 7 years). Increased age decreased miR-9 and miR-495 expression and increased miR-599 expression.

miR-9 and miR-495 have cardioprotective effects. Expression of miR-9, which is anti-fibrotic, increased in both MMVD groups, suggesting its ability to counter the pro-fibrotic events in MMVD. Expression of miR-495, which can stimulate cardiomyocyte proliferation in advanced heart disease, markedly increased in the MMVD-CHF group.

Interestingly, expression of miR-599, which disrupts collagen production, decreased in MMVD groups. Because collagen dysregulation occurs with MMVD, researchers proposed further evaluation of miR-599’s role in MMVD progression.

Expression of miR-181c, which can lead to decreased left ventricular function, was highest in the MMVD-CHF group.

For the Future
Given the study’s results, researchers believe additional study is needed to evaluate ex-miRNA’s role in heart disease. For example, because changes in ex-miRNA expression may not be specific to CHF secondary to MMVD, future studies could include a control group of dogs with CHF due to some other form of heart disease.

Taken together, the researchers concluded that “plasma ex-miRNAs show great promise as biomarkers for MMVD disease monitoring and may also help elucidate the pathophysiology of the disease and subsequently help devise therapeutic strategies.”

Dr. JoAnna Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.

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