Introduction Heart failure with preserved ejection fraction (HEpEF) carries significantly high morbidity and mortality. HFpEF is associated with preserved contractile function and can present with diastolic dysfunction, cardiac fibrosis and hypothyroidism (low levels of thyroid hormones, THs). We previously demonstrated safe, cardioprotective effects with treatment of active form of THs in multiple rodent models of cardiovascular disorders. Long‐noncoding ribonucleic acids (lncRNAs; >200 nucleotides long) account for large majority of the genome with significant transcriptional potential. However, their role in HFpEF associated with TH dysfunction is unclear. We hypothesized that lncRNAs act as mediators in development of hypothyroid HFpEF. Methods Hearts were isolated from obese ZSF1 rats that presented with HFpEF phenotype. Wild type and ZSF1 lean rats served as controls. Cardiac ultrasound and morphometric analyses were performed. RNA was isolated from left ventricular (LV) tissues and studied using Agilent LncRNA Microarray platform and analyzed using Feature Extraction and GeneSpring. Fibroblasts were isolated from wild type adult rat hearts and treated with TH receptor inhibitor. Real‐time quantitative polymerase chain reaction was used to study lncRNA expression. Results Studies revealed that total thyroxine TH levels significantly decreased in five‐six‐month old (early; p<0.05) ZSF1 obese rats compared to ZSF1 lean controls (45% decrease) and wild type controls (42% decrease), and this remained low at 13 months (late; p<0.05). Total tri‐iodothyronine TH levels also followed similar pattern in the early time‐point (37%‐42% decrease). ZSF1 obese rats showed increased normalized heart weight, LV weight and liver weight indicating cardiac hypertrophy and development of HF. In early obese rats, echocardiography showed preserved LV EF and significantly elevated E/E’ indicating diastolic dysfunction (p<0.05). LncRNA Microarray analysis including unsupervised hierarchical clustering showed that several unique lncRNAs were significantly altered (p<0.05; >2‐fold change) in obese LVs compared to the lean or wild type control counterparts and select lncRNA expression was validated with qPCR. Furthermore, isolated wild type adult rat cardiac fibroblasts subjected to TH receptor inhibition (mimicking hypothyroidism) in vitro showed significant increase in lncRNA expression that was also increased in obese ZSF1 hearts presenting with hypothyroidism (p<0.05). Conclusions These results indicate that lncRNAs may play important roles in in HFpEF pathogenesis associated with hypothyroidism. These studies will serve as significant step in identification of key lncRNAs in cardiac‐thyroid axis offering potentially valuable translational opportunities.

Noncoding RNAs are emerging as vital players in cardiovascular diseases. Thyroid hormones (THs) are crucial for cardiovascular survival; however, correction of systemic hypothyroidism (low serum THs) may not improve cardiac tissue-level hypothyroidism or cardiac function. Mechanistically, the understanding of noncoding transcriptomic interactions influencing TH-mediated cardiac effects is unclear. Adult C57BL/6J mixed-sex mice were randomized into Control, Hypothyroid (HypoTH), Hyperthyroid (HyperTH), and HypoTH-Triiodothyronine restoration groups. Physiological, morphological, biochemical, molecular, and whole transcriptomic studies and appropriate statistical analyses were performed. HypoTH showed significant atrophy, depressed cardiac function, and decreased serum THs versus controls, and Triiodothyronine supplementation restored them. HyperTH significantly increased serum THs with hypertrophy. Real-time PCR showed significantly altered inflammatory and immune lncRNAs. The transcriptomic sequencing revealed significant differential expressions of lncRNAs, miRNAs, and mRNAs. Eleven novel circRNAs significantly decreased with increased THs. Multiple pathways were GO-/KEGG-enriched, including cardiac, thyroid, cancer, mitochondrial, inflammatory, adrenergic, metabolic, immune-mediated, vesicular, etc. We also uncovered significant novel co-expression and interactions of lncRNA-miRNA, lncRNA-miRNA-mRNA, lncRNA-mRNA, circRNA-miRNA, and miRNA-mRNA, and splicing events. This includes a novel pathway by which the predominant cardiac TH receptor alpha may interact with specific lncRNAs and miRNAs. This is the first study reporting a comprehensive transcriptome-wide interactome in the cardiac–thyroid axis.

Background: Noncoding RNAs are emerging as key players in cardiovascular diseases. Both Hypothyroidism (HypoTH; low thyroid hormones [THs]) and hyperthyroidism (HyperTH; high THs) can be deleterious to the heart. We recently showed the involvement of long noncoding RNAs (lncRNAs) in HypoTH under caloric restriction. However, a comprehensive view of the cardiac transcriptome and its interactions under altered TH states is lacking. We hypothesized that cardiac noncoding interaction networks are significantly altered in the cardiac-TH regulatory axis. Methods: In this randomized, blinded study (2.5 mon), adult C57 mixed-sex mice (n=8-10/group; 5 females, 3-5 males) were divided into Control, HypoTH (low iodine diet with oral methimazole), HyperTH (1 microgram [ug]/gram Thyroxine, T4; intraperitoneal) and HypoTH+T3 (similar to HypoTH with oral 12 ug/kilogram/day Triiodothyronine, T3). Morphometrics, ultrasound, immunosorbent assay, Quantitative real-time PCR (qPCR) and whole transcriptome sequencing were performed. Statistical analyses were done by Tukey’s analysis of variance (with post hoc), Benjamini & Hochberg and others using Prism, R, etc. RNA quality was validated by Nanodrop, gel electrophoresis and Bioanalyzer. Results: In mixed-sex mice, HypoTH showed significant cardiac atrophy (whole heart, LV and right ventricle), low serum total T3 and T4 levels (p<0.001), low heart rate, (p<0.01) diminished systolic LV posterior (p<0.05) and septal wall thicknesses (p<0.01) and fractional shortening (-34%; p<0.01) compared to controls. T3 therapy showed feedback inhibition of T4 (p<0.001) and restored all other parameters including LV systolic diameter (p<0.05). Among others, HyperTH had cardiac hypertrophy and increased T3 and T4 (p<0.05) compared to controls (p<0.001). Similar significant results were obtained in males and females. qPCR of shorter-term treatment showed significantly altered lncRNAs in inflammatory and immune pathways. Whole transcriptome sequencing showed numerous differentially expressed, significantly altered and enriched ( GO and KEGG) targets across the groups among all RNA species studied (p-adjusted; padj<0.05). These include novel and known lncRNAs, microRNAs (miRNAs) and messenger (m) RNAs that change in opposite directions in low vs high TH groups. These also include 11 novel circular RNAs (circRNAs; CIRI2) decreased with HyperTH (padj<0.05). We also uncovered novel co-expression and interactions of miRNA-mRNA, miRNA-lncRNA, mRNA-lncRNA, circRNA-miRNA and miRNA-lncRNA-mRNA (including TH receptor alpha; miRanda, Cytoscape) and also splicing and base editing events (padj<0.05). Conclusions: This is the first cross-disciplinary study reporting a comprehensive cardiac transcriptome-wide interactome network of circRNA, lncRNA, miRNA and mRNA in a TH-responsive manner. This offers significant translational potential to develop diadiagnostic and therapeutic targets for cardiac-endocrine co-morbid conditions. NYITCOM at A-State, ABI This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.