A Review of the Dual Role of MicroRNA-21 in Cardiovascular Diseases: Risk Factor or a Potential Therapeutic Target

: Cardiovascular diseases [CVD] are the number one reason for morbidity and mortality in the modern world, and their incidence is increasing at an incredible pace. Increasing evidence has shown the significant functions of microRNAs in the cardiovascular system and has highlighted their potential application as a new era of diagnostic and therapeutic targets for CVD that can improve the prognosis and life expectancy of patients. Among more than 2,000 microRNAs, microRNA-21 [miR-21] is highly expressed in human hearts and has earned the interest of researchers as a potential biomarker in a wide range of common heart conditions. Here, we summarized recent research progress regarding the significant role of miR-21 in CVD, focusing on cardiotoxicity, heart arrhythmias, cardiomyopathies, and hypertension. Several signaling pathways [TGF-β1/Smad2 signaling, FGFR1/FGF21/PPARγ, NF-κB/miR-21/SMAD7, miR-21/SPRY1/ERK/mTOR …] and molecular targets [BTG2, PDCD4, PTEN, STAT3…] were reported to be controlled, at least partially, by miR-21 and are linked to CVD pathogenesis. Most investigations highlighted miR-21 cardioprotective functions in heart injury, while some other studies showed that this miR is elevated in the serum/tissue of patients, promoting fibrosis and cardiac dysfunction. This dual role can be explained by the fact that miR-21 has multiple regulatory functions depending on the microenvironment, downstream signaling, and target genes, which indicates that cell-type-specific investigations should receive more attention. With further investigations, miR-21 can be considered a novel tailored therapy with favorable outcomes.