The dynamic regulation of miR-181c-5p in heart failure

Cardiac miR-181c-5p expression associates with cardiac damage and heart failure development, but the underlying molecular mechanisms are not fully understood. In this thesis we dug deeper into the dynamic role of miR-181c-5p in heart failure with diastolic dysfunction. We evaluated its cardiac endothelial localization, its in vitro and in vivo cardiac target interactions, its phenotype-and time-related expression in heart failure models, and its therapeutic potential in heart failure upon systemic inhibition. We concomitantly focused on how miR-181c-5p affects cardiac fibrosis and acts on the kidney as relevant comorbid organ in heart failure. Spatial results obtained by combined detection of miR-181c-5p with fluorescent in situ hybridization and endothelial markers with immunofluorescence demonstrated a non-ubiquitous endothelial localization of miR-181c-5p in the healthy heart with low nuclear expression. This specific spatiotemporal regulation was also detected in cardiac tissue of the failing heart, where miR-181-5p was downregulated in a cardiometabolic heart failure rat model with preserved ejection fraction (ZSF1 rats) and in a pressure overload-induced heart failure mouse model with reduced ejection fraction (TAC mice), only at later timepoints during heart failure progression. This timebound and phenotype-related expression suggests a potential function in chronic cardiac remodeling, independent of ejection fraction. Further target interaction analysis in cells and cardiac tissue using an antagomir-approach revealed three new cardiac targets (Lats1, Vegfa, Smad7) that support a role in cardiac fibrosis. However, each target interaction only occurred at specific conditions, dependent on dose and cell type, with substantial differences between in vitro and in vivo targets. Final systemic inhibition using miR-181c-5p antagomiRs for 6 weeks in a three-hit mouse model (C57/BL6 male mice with high fat diet, L-NAME, angiotensin II) mildly attenuated heart failure development by reducing Tgfbr1-mediated cardiac fibrosis. Despite these beneficial effects, inhibitor-treated heart failure mice displayed a threefold higher mortality rate that associated with a higher predisposition for renal thrombotic microangiopathy. Further histology data proved that miR-181c-5p inhibition induced severe renal damage (renal fibrosis, glomerular damage) in both healthy and heart failure mice, in part by downregulating Vegfa expression in the kidney. Summarily, this thesis sheds light on the strong dynamic mode-of-action of miR-181c-5p in the heart, and accentuates both the interesting anti-fibrotic potential of miR-181c-5p inhibition in heart failure with diastolic dysfunction, as well as its detrimental impact on renal physiology.