Valve informed Ovine Heart <i>De Novo</i> Transcriptome Identifies an Active Valve in Model of Functional Tricuspid Regurgitation

Functional tricuspid regurgitation (FTR), the backflow from the right ventricle into the right atrium due to valvular insufficiency, is a markedly understudied and undertreated secondary disease often subsequent to left-sided heart failure. Hospitalizations and mortality are significantly correlated with FTR for patients with heart failure, yet medical management is limited and our understanding of which patients are optimal for surgical intervention is lacking. Ovine models of cardiovascular disease have generated numerous discoveries elucidating FTR pathophysiology. However, insights derived from this model system have relied upon a reference transcriptome lacking in cardiac specific transcripts, notably any of valvular origin. The objective of our study was to generate a de novo transcriptome to improve alignment for RNA sequencing studies using the ovine model. We hypothesized that a de novo transcriptome would result in better alignment and generate novel insights previously missed in ovine cardiovascular experiments. Three independent studies investigating the effects of pulmonary hypertension modeled through ovine pulmonary artery banding (PAB) were utilized to generate a de novo transcriptome. Reads from RNA sequencing of 354 samples of right ventricle, left ventricle, pulmonary artery as well as each tricuspid and mitral leaflet were assembled into a de novo ovine heart transcriptome, and isoforms that significantly differed between the various groups were identified. Alignment to the de novo transcriptome enhanced gene isoform mapping of reads by 37-45% specifically in the heart valves. Significantly different isoforms increased across all three independent experiments including an increase from 154 to 826 isoforms identified between the tricuspid and mitral valves for a single experiment. The increases in alignment allowed for more robust identification of discrepant gene ontology enrichment based on sex, such as response to hyperoxia, as well as ventricle and valve enrichments including intrinsic cardiomyopathy and Wnt signaling respectively. Understanding the pathophysiology of FTR in humans is challenging as the etiologies of the disease are often as heterogenous as the patient base we wish to study. Model systems offer a degree of control and provide numerous avenues for novel discoveries. Previous transcriptomic studies have relied upon a reference transcriptome clearly lacking in valve specific isoforms. The de novo transcriptome generated by this study not only grants the ability to better understand the transcriptomic control of FTR, but also provides a resource for future cardiovascular studies utilizing the ovine model. Differential responses to PAB based on sex identified by this study provide insight into why FTR is up to four times as prevalent in women, and identification of a robust set of isoforms differentially expressed within the tricuspid leaflets provides evidence of an active valve, remodeling in response to pulmonary hypertension and suggests an avenue for better medical management of FTR in the future. National Institution of Health 5R01HL165251-02 Corewell Health Michigan State Alliance Grant RF2021-1322 American Heart Association grant 23SCISA1144887 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.