Adding a "Notch" to Cardiovascular Disease Therapeutics: A MicroRNA-Based Approach

Abstract

Dysregulation of the Notch pathway is implicated in the pathophysiology of cardiovascular diseases (CVDs), but, as of today, therapies based on the re-establishing the physiological levels of Notch in the heart and vessels are not available. A possible reason is the context-dependent role of Notch in the cardiovascular system, which would require a finely tuned, cell-specific approach. MicroRNAs (miRNAs) are short functional endogenous, non-coding RNA sequences able to regulate gene expression at post-transcriptional levels influencing most, if not all, biological processes. Dysregulation of miRNAs expression is implicated in the molecular mechanisms underlying many CVDs. Notch is regulated and regulates a large number of miRNAs expressed in the cardiovascular system and, thus, targeting these miRNAs could represent an avenue to be explored to target Notch for CVDs. In this Review, we provide an overview of both established and potential, based on evidence in other pathologies, crosstalks between miRNAs and Notch in cellular processes underlying atherosclerosis, myocardial ischemia, heart failure, calcification of aortic valve, and arrhythmias. We also discuss the potential advantages, as well as the challenges, of using miRNAs for a Notch-based approach for the diagnosis and treatment of the most common CVDs.

Keywords: Notch; arrhytmia; atherosclerosis; calcific aortic valve disease; heart failure; ischemia-reperfusion injury; miRNA; myocardial ischemia.

FIGURE 1

Schematic representation of the Notch pathway and miRNA biogenesis. (A) The Notch precursor is cleaved by a furin-like protease in the Golgi apparatus and then transported to the plasma membrane. Notch receptor on the membrane is activated by the binding with ligands present on adjacent cells, which induces a second proteolytic cut mediated by A Disintegrin And Metalloprotease (ADAM) 10 or 17, followed by a third cleavage by the γ-secretase complex that releases the Notch intracellular domain (NICD). In the “canonical” Notch signaling, NICD translocates into the nucleus and, through the interaction with the transcription factor CBF1/Suppressor of Hairless/LAG1 (CSL) and the Mastermind-like (MAML) adaptor proteins, modulates the transcription of several target genes. In the “non-canonical” signaling, Notch modulates Wnt/β-catenin, mammalian target of the rapamycin 2 complex (mTORC2)/Akt, Nuclear Factor kappa B (NF-κB), IkB kinase (IKK)-α/β and phosphatase and tensin homolog (PTEN)-induced kinase (PINK1) on mitochondria, independently from CSL. NECD: Notch extracellular domain. (B) In the nucleus, genes coding for miRNAs are transcribed by RNA polymerase II or III into primary miRNAs (pri-miRNAs), which are processed by the complex consisting of RNA-binding protein DGCR8 and type III RNase Drosha, into a stem-loop structure called precursor miRNAs (pre-miRNAs). Afterward, pre-miRNA is transported into the cytoplasm by Exportin-5 complex (Exportin -5^_ Ran-GTP), where pre-miRNA is processed by another type III RNase enzyme Dicer to form the mature miRNA duplex. The two strands of the duplex are loaded into Argonaute (Ago) protein to form the RNA-induced silencing complex (RISC); one strand (also called guide strand) is selected to form the functional RISC complex, the other strand (passenger strand) is released from Ago and degraded (Medley et al., 2021). For most miRNAs, one strand is preferentially loaded into Ago, forming the functional RISC, while the other is released and degraded. However, for some miRNAs, both strands give rise to functional miRNAs that are loaded into the RISC. Functional miRNAs regulate gene expression at post-transcriptional level mainly by binding their seed region (nucleotides 2–8) to the 3′-untranslated region (UTR) of their target mRNAs. The interaction miRNA/mRNA modulates gene expression by inhibiting translation or inducing degradation of a specific mRNA depending on the complementarity of the sequence.

FIGURE 2

Overview of miRNAs that regulate the Notch pathway in cardiovascular diseases (CVDs). Possible strategies to modulate Notch with miRNAs in CVDs: atherosclerosis (A), calcification of aortic valve (B), myocardial ischemia/reperfusion (C), heart failure (D), and arrhythmia (E). For each pathology, the microRNAs that could be overexpressed (through the use of AgomiR) or downregulated (through the use of AntagomiR) to interfere with disease progression are indicated. The asterisk indicates that the role of miRNAs in specific CVD is still poorly investigated. ECs, endothelial cells; VSMCs, vascular smooth muscle cells; VICs, valve interstitial cells; CAVD, calcific aortic valve disease.