RNA interference and the microRNA (miRNA) pathway can induce sequence-specific mRNA degradation and/or translational repression. The human genome encodes hundreds of miRNAs that can post-transcriptionally repress thousands of genes. Using reporter constructs, we observed that degradation of mRNAs bearing sites imperfectly complementary to the endogenous let-7 miRNA is considerably stronger in human HEK293 than HeLa cells. The degradation did not result from the Ago2-mediated endonucleolytic cleavage but it was Dicer- and Ago2-dependent. We used this feature of HEK293 to address the size of a pool of transcripts regulated by RNA silencing in a single cell type. We generated HEK293 cell lines depleted of Dicer or individual Ago proteins. The cell lines were used for microarray analyses to obtain a comprehensive picture of RNA silencing. The 3′-untranslated region sequences of a few hundred transcripts that were commonly up-regulated upon Ago2 and Dicer knock-downs showed a significant enrichment of putative miRNA-binding sites. The up-regulation upon Ago2 and Dicer knock-downs was moderate and we found no evidence, at the mRNA level, for activation of silenced genes. Taken together, our data suggest that, independent of the effect on translation, miRNAs affect levels of a few hundred mRNAs in HEK293 cells.

Aims Our aim was to identify circulating microRNAs (miRNAs) associated with acute heart failure (AHF). Methods and results Plasma miRNA profiling included 137 patients with AHF from 3 different cohorts, 20 with chronic heart failure (CHF), 8 with acute exacerbation of COPD, and 41 healthy controls. Levels of circulating miRNAs were measured using quantitative reverse transcription–polymerase chain reaction (qRT–PCR). Plasma levels of miRNAs in patients with AHF were decreased compared with CHF patients or healthy subjects, whereas no significant changes were observed between acute COPD patients and controls. Fifteen miRNAs found in the discovery phase to differ most significantly between healthy controls and patients with AHF were further investigated in an extended cohort of 100 AHF patients at admission and a separate cohort of 18 AHF patients at different time points. Out of these 15 miRNAs, 12 could be confirmed in an additional AHF validation cohort and 7 passed the Bonferroni correction threshold (miR-18a-5p, miR-26b-5p, miR-27a-3p, miR-30e-5p, miR-106a-5p, miR-199a-3p, and miR-652-3p, all P < 0.00005). A further drop in miRNA levels within 48 h after AHF admission was associated with an increased risk of 180-day mortality in a subset of the identified miRNAs. Conclusions Declining levels of circulating miRNAs were associated with increasing acuity of heart failure. Early in-hospital decreasing miRNA levels were predictive for mortality in a subset of miRNAs in patients with AHF. The discovered miRNA panel may serve as a launch-pad for molecular pathway studies to identify new pharmacological targets and miRNA-based therapies

The majority of correlations between circulating AHF-specific miRNAs were related to biomarkers predictive for a worse clinical outcome in a subgroup of worsening heart failure patients at 48hours of hospitalization. The selective findings suggest a time-dependent effect of circulating miRNAs and highlight the susceptibility to individual patient characteristics influencing potential relations between miRNAs and biomarkers.

Biomarkers play an important role in heart failure. They provide us information about the mechanisms involved in specific types of heart failure and can identify patients at higher risk. Although the majority of biomarker studies in heart failure focus on their prognostic value, the clinical applicability of prognostication in heart failure needs to be established. However, biomarkers can be used for many other purposes. For example, they can help us with the diagnosis of heart failure, and they can be used to select our therapy, leading to personalized tailored therapy. Finally, when biomarkers are causally involved in the disease process, they can even become targets for therapy. The present paper reviews the established and potential value of the novel heart failure biomarkers, mid-regional atrial natriuretic peptide, soluble ST2, growth differentiation factor 15, galectin-3, renal tubular damage markers, and microRNAs. Their potential clinical value will be discussed and compared with the reference markers, the natriuretic peptides.

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