Noncoding RNAs (long noncoding RNAs and small RNAs) are emerging as critical modulators of phenotypic changes associated with physiological and pathological contexts in a variety of cardiovascular diseases (CVDs). Although it has been well established that hereditable genetic alterations and exposure to risk factors are crucial in the development of CVDs, other critical regulators of cell function impact on disease processes. Here we discuss noncoding RNAs have only recently been identified as key players involved in the progression of disease. In particular, we discuss micro RNA (miR)-143/145 since they represent one of the most characterised microRNA clusters regulating smooth muscle cell (SMC) differentiation and phenotypic switch in response to vascular injury and remodelling. MiR143HG is a well conserved long noncoding RNA (lncRNA), which is the host gene for miR-143/145 and recently implicated in cardiac specification during heart development. Although the lncRNA-miRNA interactions have not been completely characterised, their crosstalk is now beginning to emerge and likely requires further research focus. In this review we give an overview of the biology of the genomic axis that is miR-143/145 and MiR143HG, focusing on their important functional role(s) in the cardiovascular system.

Rationale: In the microenvironment of atherosclerotic lesions, vascular smooth muscle cells (vSMCs) switch to a dedifferentiated state but the underlying molecular mechanisms driving this switch are not fully understood. Long noncoding RNAs (lncRNAs) are dysregulated during vascular pathology, but relatively little is known about their involvement in controlling vSMCs function. CARMN is a lncRNA located immediately upstream of the microRNAs (miRNAs) miR-143 and miR-145, both involved in vSMCs function. Objective: We investigated the role of the lncRNA CARMN, independent from miR-143 and miR-145, as potential a regulator of vSMC phenotypes in vitro and the consequences of its loss during the development of atherosclerosis in vivo. We hypothesized that loss of CARMN is a primary event controlling the functional switch towards pro-atherogenic vSMC phenotype and accelerates the development of the plaques in vivo. Methods and Results: Expression of CARMN lncRNA was silenced using GapmeRs in human coronary arterial smooth muscle cells (hCASMCs), revealing that GapmeR-mediated loss of CARMN negatively affects miR-143 and miR-145 miRNA expression. RNA sequencing of CARMN-depleted hCASMCs revealed large transcriptomic changes, associated with vSMC proliferation, migration, inflammation, lipid metabolism and dedifferentiation. The use of miR-143 and miR-145 mimics revealed that CARMN regulates hCASMC proliferation in a miRNA-independent manner. In human and mouse, CARMN and associated miRNAs were downregulated in advanced versus early atherosclerotic lesions. Using a CRISPR-Cas9 knock-out approach, we explored the implications of CARMN depletion during atherosclerosis in vivo. Consistent with in vitro results, the knock-out of CARMN impaired the expression of miR-143 and miR-145 under homeostatic conditions. Importantly, when atherosclerosis was induced in these mice, CARMN knock-out increased the volume, size, pro-inflammatory LGALS3-expressing cells content and altered plaque composition, yielding an advanced phenotype. Conclusions: We identified the early loss of CARMN lncRNA as critical event which primes vSMCs towards a pro-atherogenic phenotype in vitro and accelerates the development of atherosclerosis in vivo.