Lola Lyons

Date of Award

2024

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Rycyk, Athena

Second Advisor

Bohan, Amy

Area of Concentration

Biology

Abstract

Myxomatous Mitral Valve Disease (MMVD) remains to be the number one cause of Congestive Heart Failure (CHF) in dogs. Mainly characterized by mitral regurgitation in the left atrium, MMVD can lead to fatal heart failure down the line. MicroRNAs, which are small, noncoding RNAs about 21-25 nucleotides in length that regulate gene expression, can be found freely-circulating throughout the blood, extracellular fluid, intracellular fluid and interstitial fluid, or in extracellular vesicles such as exosomes. These vesicles play a role in the transportation of various molecules as well as in intercellular communication. Previous studies show microRNAs display statistically significant expression levels in dogs with MMVD compared to clinically normal dogs. This means the microRNA levels were either high or low enough in one of the dog groups to distinguish themselves as biomarkers. Since exosomes have been shown to protect the contents they are transporting, they are of special interest in microRNA studies, partially due to the potential for exosomal microRNAs to be better preserved. This project aims to first isolate exosomes from canine plasma in both normal dogs and dogs with MMVD/CHF. The isolation of exosomes will then allow for the isolation of the exosomal microRNAs in order to quantify their expression levels. Next Generation Sequencing (NGS) and subsequently Quantitative Reverse Transcription-PCR (qRT-PCR) will be performed to confirm whether or not each freely-circulating microRNA has an exosomal counterpart to obtain information on the expression levels of the two types of microRNAs. Intellectual Merit The exact cause of MMVD is still unknown, and once a dog enters heart failure, there is no way to reverse it. Currently, the only methods of diagnosis of MMVD and CHF are auscultation (listening to the heart and lungs with a stethoscope), thoracic radiography, and echocardiography. Though these methods are effective once a dog starts to show symptoms and signs of MMVD, often the disease has progressed to a point where no further actions to delay the disease are effective. Therefore, there is a need for research on a method of earlier detection of the disease that does not require using invasive measures on live dog models. Current research methods include the purposeful induction of heart failure that eventually leads to death. Detecting microRNAs expression levels in a dog with MMVD would simply require a small blood sample collection. If MMVD was caught at an early stage, well before a dog started showing clinical signs of heart failure, the disease could potentially be further delayed. This research may even lead to the development of life-saving microRNA-based therapeutic drugs to treat MMVD, using synthetic microRNA mimics and inhibitors packaged inside of exosomes, increasing or decreasing microRNA expression back to normal levels. Broader Impacts MMVD poses many challenges for not only dogs, but owners and veterinarians as well, such as the dog's quality of life, financial concerns for the owners, and the difficulty for vets to offer an accurate prognosis. However, this research offers a promising avenue not only for early disease detection and therapeutic drug development in the veterinary field, but in human medicine as well. In regard to heart disease in the broader sense, the canine heart is an ideal model for the human heart, which is a reason why live dogs have been used in the past for human medical research. This noninvasive study could alleviate ethical concerns of canine heart failure induction as well as minimize animal suffering.

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