Keywords

Introduction

Cardiovascular disease is the leading cause of morbidity and mortality in developed countries. Cardiovascular remodeling is thought to be an important aspect of disease progression in heart failure (HF), regardless of cause. It is manifested clinically by changes in cardiac size, shape, and function in response to aging, cardiac injury, or increased load. The importance of remodeling as a pathogenic mechanism is not completely understood because the factors leading to remodeling have not been fully investigated. Generally, pathological processes of the heart are associated with an altered expression profile of genes that are important for cardiac function (Fig. 10.1) [1].

Fig. 10.1
figure 1

Pathological processes of the heart under stress

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The regulation of cardiac gene expression is complex, with individual genes controlled by multiple transcription factors associated with their regulatory enhancer/promoter sequences to activate gene expression [2]. Moreover, epigenetic regulation of gene expression and alternative splicing mechanisms also further complicate the patterns of gene expression. microRNAs (miRNAs; miRs) have reshaped our view of how gene expression is regulated by adding another layer of regulation at the posttranscriptional level. Cardiovascular remodeling encompassed many pathologies including cardiac hypertrophy, myocardial ischemia/myocardial infarction (MI), cardiac fibrosis, arrhythmia, and vascular diseases that will be discussed in more detail in the following sections (Fig. 10.2).

Fig. 10.2
figure 2

Dysregulated microRNAs in cardiovascular disease

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The implications of miRNA-derived regulation in cardiovascular pathology have only been recognized very recently, and research on miRNAs in relation to such diseases has now become a rapidly evolving field. In this chapter, we will summarize the current understanding of miRNA function in the pathogenesis of cardiovascular remodeling.

Cardiac Hypertrophy

Left ventricular hypertrophy is a common finding in patients with hypertension and it can be diagnosed either using an electrocardiogram or by echocardiography. Because cardiac hypertrophy, an increase in heart size, is associated with nearly all forms of HF, it is of great clinical importance that we understand the mechanisms responsible for cardiac hypertrophy. Therefore, the regulation of hypertrophy-associated genes has attracted great interest from many researchers.

Pathological hypertrophy is mainly caused by hypertension, loss of myocytes following ischemic damage, and genetic alterations that cause cardiomyopathy. Moreover, metabolic abnormality or neurohormonal activation can also lead to hypertrophy [3]. Pathological hypertrophy is the phenotypic endpoint that has been most studied in relation to miRNAs in the heart to date.

Clinical studies in human hearts have indicated that the fetal gene expression program is reactivated in pathologic hypertrophy and failing hearts, which results in a switching of structural proteins from adult to fetal isoforms [4]. It is well known that there is a decrease in the fast-shortening-velocity isoform (α-myosin heavy chain) coupled with an increase in the slow-shortening-velocity isoform (β-myosin heavy chain [β-MHC]) during the transition from cardiac hypertrophy to HF [5]. This contributes to the decrease in contractile function in failing human hearts. Interestingly, transcriptome analysis of failing and fetal hearts revealed a similar pattern of miRNA expression. More than 80 % of the deregulated miRNAs in failing hearts displayed a similar expression pattern as in fetal hearts, suggesting that reactivation of a fetal miRNA program may contribute to the gene expression pattern of failing hearts [6]. The most consistent changes were upregulation of miR-21, miR-29b, miR-129, miR-210, miR-211, miR-212, and miR-423, with downregulation of miR-30, miR-182, and miR-526. Interestingly, gene expression analysis revealed that most of the upregulated genes were characterized by the presence of a significant number of the predicted binding sites for downregulated miRNAs and vice versa.

In animal models of cardiac hypertrophy, whole arrays of miRNAs have indicated that separate miRNAs are upregulated, downregulated, or remain unchanged with respect to their levels in a normal heart [6–12]. In these studies, some miRNAs have been more frequently reported than others, indicating the possibility that these miRNAs might have common roles in hypertrophy pathogenesis.

Tissue-specific expression of miRNAs was first reported in 2002 [13]. It is known that there is a family of so-called myomiRs that are encoded within the introns of the separate myosin heavy chain genes. miR-208a, miR-208b, and miR-499 are located within the Myh6, Myh7, and Myh7b genes, respectively. It was reported that miR-208−/− mice show reduced cardiac hypertrophy in response to pressure overload [14]. Targets of miR-208a include thyroid hormone receptor-associated protein 1 [14, 15], suggesting that miR-208a initiates cardiomyocyte hypertrophy by regulating triiodothyronine-dependent repression of β-MHC expression. miR-27a also regulates β-MHC gene expression by targeting TRβ1 in cardiomyocytes [16]. Overexpression of miR-208a was sufficient to upregulate Myh7 and to elicit cardiac hypertrophy, resulting in systolic dysfunction [15]. Although miR-208a is required for cardiac hypertrophy, the role of miR-208b in these pathologic conditions remains to be elucidated. miR-499 is encoded in an intron of the myh7 gene and is considered likely to play a role in myosin gene regulation [17, 18].

miR-1 is also a cardiac and skeletal muscle-specific miRNA, and it is probably one of the most abundant miRNAs in the heart. It was reported to target a cytoskeletal regulatory protein, twinfilin 1 (Twf1) , which binds to actin monomers and prevents their assembly into filaments [19]. Downregulation of miR-1 induced by hypertrophic stimuli, such as transverse aortic constriction or α-adrenergic stimulation with phenylephrine, results in increased Twf1 expression, and overexpression of Twf1 is sufficient to induce cardiac hypertrophy. Another target of miR-1 is insulin-like growth factor (IGF-1), IGF-1 receptor [20], calmodulin 1 and 2, Mef2a [21], and sodium calcium exchanger [22]. Repression of miR-1 and upregulation of IGF-1 was also demonstrated in models of cardiac hypertrophy [20]. miR-1 is downregulated in patients with aortic stenosis [11] and acromegaly associated cardiac hypertrophy [20].

miR-1 is encoded by two bicistronic clusters—miR-133a-1/miR-1-2 and miR-133a-2/miR-1-1. As well as miR-1, miR-133 also has the potential to attenuate agonist-induced hypertrophy [23, 24], whereas repression of miR-133 sensitized the myocardium to excessive cardiac growth. Therefore, these clusters generate antagonizing effects on the stimulation of cardiac hypertrophy.

In contrast, miR-195 was sufficient to drive pathologic cardiac growth when overexpressed in neonatal cardiac myocytes and in transgenic mice [7]. These results suggested that miR-195 is a pro-hypertrophic factor that actively participates in the hypertrophic process; however, no direct targets of miR-195 have been reported in the context of cardiac hypertrophy.

Myocardial Ischemia and Cell Death

A rapidly increasing number of studies have shown that cardiac and circulating miRNAs are markedly altered in myocardial ischemia or MI. These novel findings shed new light on the mechanisms that lead to MI complications, post-MI ventricular remodeling, and cardiac repair. Furthermore, recent studies showed that circulating miRNAs may represent novel and sensitive biomarkers of MI and, possibly, also function as an intercellular signaling mechanism (see Chap. 7 of the volume “microRNA: Basic Science” for a detailed discussion of miRNA and cardiac regeneration).

Cardiomyocyte death/apoptosis is a key cellular event in ischemic hearts. There are miRNAs that have been shown to exert proapoptotic effects by targeting key cardioprotective proteins. It was found that miR-320 expression was consistently dysregulated in ischemic hearts [25]. Ren et al. identified heat-shock protein 20 (HSP20), a known cardioprotective protein, as a target of miR-320. Knockdown of endogenous miR-320 provided protection against cardiomyocyte apoptosis through the upregulation of HSP20. miR-34 family members promote growth arrest and apoptosis [26]. Therapeutic inhibition of miR-34 attenuated ischemia-induced remodeling and improved cardiac recovery [27]. One of the targets of miR-34 was shown to be a protein phosphatase 1 nuclear targeting subunit (Pnuts) [28].

On the other hand, there are a number of miRNAs that exert an antiapoptotic function by targeting important proapoptotic proteins. The miRNA expression signature in rat hearts at 6 h after MI revealed that miR-21 expression was significantly downregulated in infracted areas but was upregulated in border areas [29]. Adenoviral transfer of miR-21 in vivo decreased cell apoptosis in the border and infracted areas through its target gene, programmed cell death 4 (PDCD4), and the activator protein 1 (AP1) pathway. miR-24 also inhibited cardiomyocyte apoptosis via repression of the proapoptotic protein Bim [30]. Ex vivo miR-24 enrichment, together with miR-21 and miR-221, improved the therapeutic potential of cardiac progenitor cells upon transplantation in ischemic rodents [31]. Similarly, miR-499 and miR-30 family members diminished apoptosis in injured hearts by attenuating activation of dynamin-related protein-1 and thus inhibiting mitochondrial fission [32, 33].

Early reperfusion of the ischemic heart remains the most effective intervention for improving clinical outcomes after a MI. However, abnormal increases in intracellular Ca2+ during myocardial reperfusion can cause cardiomyocyte death, known as ischemia-reperfusion (I/R) injury. Cardiac I/R injury is also accompanied by dynamic changes in the expression of miRNAs; for example, miR-214 is upregulated during ischemic injury. Genetic deletion of miR-214 in mice caused a loss of cardiac contractility, increased apoptosis, and excessive fibrosis in response to I/R injury [34]. The cardioprotective roles of miR-214 during I/R injury were attributed to repression of the mRNA encoding sodium/calcium exchanger 1, a key regulator of Ca2+ influx; and to repression of several downstream effectors of Ca2+ signaling that mediate cell death. These results suggested a pivotal role for miR-214 as a regulator of cardiomyocyte Ca2+ homeostasis and survival during cardiac injury. Moreover, CaMKIIδ is a shared target of both miR-214 and miR-145 [35]. miR-145 concomitantly protects cardiomyocytes from reactive oxygen species by targeting Bnip3 [36]. Boosting miR-214 and miR-145 levels to attenuate Ca2+ overload and cardiac cell death may provide a valuable therapeutic benefit for the treatment or prevention of heart failure after I/R injury.

Recent studies have shown that some miRNAs are present in circulating blood and that they are included in exosomes and microparticles [37, 38]. Recently, results obtained in studies of cancer suggest that the profiles of blood circulating miRNAs might reflect the changes observed in cancerous tissue [39]. This concept has also proved valid in cardiovascular disease [40], and circulating specific miRNAs have been reported in patients with MI [41, 42]. Moreover, plasma levels of endothelial cell-enriched miRNAs, such as miR-126, miR-17, and miR-92a, inflammation-associated miR-155, and smooth muscle-enriched miR-145 were reported to be significantly reduced in coronary artery disease (CAD) patients compared with healthy controls. These results also indicated that they can be used as biomarker candidates for CAD [43]. Therefore, the source and the mechanism of the change determined the set of miRNAs that can be used for myocardial ischemia/MI.

Cardiac Fibrosis

Cardiac fibrosis is a major aspect of myocardial remodeling and an important contributor to the development of cardiac dysfunction in diverse pathologic conditions, such as MI, in ischemic, dilated, and hypertrophic cardiomyopathies, and HF [44–49]. The extracellular deposition of collagen by fibroblasts contributes to this adverse remodeling. Cardiac fibrosis leads to an increased mechanical stiffness, initially causing diastolic dysfunction, and eventually resulting in systolic dysfunction and overt HF. In addition, fibrosis can also disturb the electrical continuity between cardiomyocytes, leading to conduction slowing and hence an increase in the chance of arrhythmias. It is also possible that the enhanced diffusion distance for cardiac substrates and oxygen to cardiac myocytes, caused by fibrosis, negatively influences the myocardial balance between energy demand and supply [46, 47].

miR-21 is expressed in all cell types of the cardiovascular system, most prominently in cardiac fibroblasts but rather weakly in cardiomyocytes. Furthermore, miR-21 is among the most strongly upregulated miRNAs in response to a variety of forms of cardiac stress [7, 50, 51]. Thum et al. showed that miR-21 is upregulated in cardiac fibroblasts in the failing heart, where it represses the expression of Sprouty homolog 1 (SPRY1) , a negative regulator of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK-MAPK) signaling pathway [52]. Upregulation of miR-21 in response to cardiac injury was shown to enhance ERK-MAPK signaling, leading to fibroblast proliferation and fibrosis. Moreover, miR-21-dependent targeting of SPRY1 and PDCD4 was shown to promote the fibroblastoid phenotype in epicardial-to-mesenchymal transition [53]. Phosphatase and tensin homologue (PTEN) has also been demonstrated to be a direct target of miR-21 in cardiac fibroblasts [54]. Previous reports characterized PTEN as a suppressor of matrix metalloprotease-2 (MMP-2) expression [55, 56]. I/R injury in the heart induced miR-21 in cardiac fibroblasts in the infracted region. Thus, I/R injury-induced miR-21-limited PTEN function and caused activation of the Akt pathway and increased MMP-2 expression in cardiac fibroblasts.

On the other hand, miR-29 family members, miR-133, and miR-30 directly downregulated key profibrotic proteins. The miR-29 family is composed of three members, miR-29a, b, and c. It was shown that the miR-29 family, which is highly expressed in fibroblasts, targets mRNAs encoding a multitude of extracellular matrix (ECM)-related proteins involved in fibrosis, including col1a1, col3a1, elastin, and fibrillin [50]. miR-29 was dramatically repressed in the border zone flanking the infracted area in a mouse model of MI. Downregulation of miR-29 would be predicted to counter the repression of these mRNAs and enhance fibrotic responses. Therefore, it is tempting to speculate that upregulation of miR-29 may be a therapeutic option for MI.

Connective tissue growth factor (CTGF) , a key molecule involved in fibrosis, was shown to be regulated by miR-133 and miR-30, which are both consistently downregulated in several models of pathologic hypertrophy and HF [57]. The authors indicated that miR-133 and miR-30 are downregulated during cardiac disease, which inversely correlated with the upregulation of CTGF. In vitro experiments designed to overexpress or inhibit these miRNAs can effectively repress CTGF expression by interacting directly with the 3′-untranslated region (UTR) region of the CTGF mRNA.

Together, these data indicate that miRNAs are important regulators of cardiac fibrosis and are involved in structural heart disease.

Arrhythmias

One of the earliest reports of involvement of miRNA regulation of cardiac repolarization came from Zhou et al. in 2007 with the targeted deletion of miR-1-2 in mice. Surface electrocardiography in mutant mice demonstrated reduced average heart rate, accelerated atrioventricular conduction, and slowed ventricular conduction [58]. They found Irx5 as a target for miR-1-2, which belongs to the Iroquois family of homeodomain-containing transcription factors that regulate cardiac repolarization by repressing transcription of KCND2. KCND2 encodes a K+ channel subunit (Kv4.2) responsible for the transient outward K+ current (Ito) that is the major determinant of the transmural repolarization gradient in the ventricular wall. The increase in Irx5 protein levels in miR-1-2 mutants corresponded with a decrease in KCND2 expression.

Additional evidence supporting a role for miR-1 in cardiac repolarization and arrhythmogenesis came from a rat model of MI induced by occlusion of the coronary artery. It was established that gap junction protein a1 (GJA1; encoding connexin43 [Cx43]) and potassium inwardly rectifying channel, subfamily J, member 2 (KCNJ2; encoding the K+ channel subunit Kir2.1) are target genes for miR-1 [59]. Cx43 is critical for inter-cell conductance of excitation [60–62], and Kir2.1 governs cardiac membrane potential [63, 64], both of which are important determinants for cardiac excitability.

To date, the cardiac ion channel genes that have been confirmed experimentally to be targets of miR-1 or miR-133 include GJA1/Cx43/IJ [59], KCNJ2/Kir2.1/IK1 [59], potassium voltage-gated channel, subfamily H (eag-related) member 2 (KCNH2)/human ether-à-go-go-related gene (HERG)/IKr [65], potassium voltage-gated channel, KQT-like subfamily, member 1 (KCNQ1)/KvLQT1/IKs [66], and potassium voltage-gated channel, Isk-related family, member 1 (KCNE1)/mink/IKs [66]. The fact that altered expression of miRNAs can deregulate expression of cardiac ion channels provided novel insight into the molecular understanding of cardiac excitability.

miR-212 has been found to be upregulated in both animal models and human HF [6]. KCNJ2/Kir2.1 3′-UTR contains potential miR-212 binding sites and transfection of HeLa cells with miR-212 reduced inward rectifier K+ current density, as demonstrated by whole-cell patch-clamp recordings [67].

It was also reported that miR-328 is upregulated in the atria of dogs with induced atrial fibrillation (AF) and targets the L-type calcium channel [68]. Strikingly, inhibition of miR-328 levels with an antagomir reversed the conditions. The fact that genetic knockdown of endogenous miR-328 reduced AF vulnerability also suggests the potential of miR-328 as a target for AF treatment.

Circulating miRNAs, which can be potential biomarkers for AF, were also sought. Plasma miR-150 levels from AF patients were substantially lower than that from healthy people in a cohort of 105 participants [69]. miRNAs may serve as molecular diagnostic markers for AF in the future.

Angiogenesis and Vascular Disease

miRNAs are also important in vascular development, physiology, and disease. Initial evidence for the functional roles of miRNAs in vascular development was provided by the observation that mice carrying a Dicer hypomorphic allele died prenatally with severely disrupted blood vessel formation [70].

Profiling of endothelially expressed miRNAs has been performed using human umbilical vein endothelial cells. These results revealed high expression levels of miR-221/222, miR-21, let-7 family, miR-17-92 cluster, miR-23-24 cluster, and miR-126 in vascular endothelial cells. Among them, miR-126 is the only miRNA considered to be expressed specifically in endothelial cells [71].

Studies focusing on individual miRNAs or miRNA clusters suggested the importance of miRNAs in endothelial cell function and angiogenesis. The miR-17-92 cluster is one of the most important miRNAs for the regulation of angiogenesis. It encodes six miRNAs (miR-17, miR-18a, miR-19a, miR-20a, miR-19b-1, and miR-92-1), which are tightly grouped within an 800 base-pair region, and it is transcriptionally regulated by c-Myc [72]. In particular, miR-18 preferentially suppressed CTGF, whereas miR-19 targeted the potent angiogenesis-inhibitor thrombospondin-1 to promote tumor angiogenesis [73]. On the other hand, miR-92a controlled the growth of new blood vessels (angiogenesis) [74]. Forced overexpression of miR-92a in endothelial cells blocked angiogenesis, and systemic administration of an antagomir to inhibit miR-92a led to enhanced blood vessel growth and functional recovery of damaged tissue in mouse models of limb ischemia and MI. Therefore, miR-92a may serve as a valuable therapeutic target in the setting of ischemic disease.

miR-126 is an abundant, endothelial cell-enriched miRNA that is encoded in the second intron of an endothelial cell-specific gene, Egfl7, and mechano-sensitive zinc finger transcription factor Klf2a was shown to induce miR-126 expression to activate vascular endothelial growth factor signaling [75]. This work described a novel genetic mechanism in which a miRNA facilitated integration of a physiological stimulus with growth factor signaling in endothelial cells to guide angiogenesis. On the other hand, transfection of endothelial cells with an oligonucleotide that decreased miR-126 permitted an increase in tumor necrosis factor-α stimulated vascular adhesion molecule 1 expression and increased leukocyte adherence to endothelial cells [76]. The apparent role of miR-126 in angiogenesis has led to increasing interest in miR-126 overexpression as a therapeutic approach. It has been reported that systemic delivery of miR-126 by miRNA-loaded bubble liposomes improved blood flow and may be useful for the treatment of hind-limb ischemia [77].

There is increasing evidence that specific miRNAs are involved in angiogenesis. So far, pro-angiogenic miRNAs include let7f and miR-27b [78], miR-17-92 cluster [73], miR-126 [79, 80], miR-130a [81], miR-210, and miR-378 [82, 83]. miRNAs that exert anti-angiogenic effects include miR-15/16 [84, 85], miR-20a/b [84], miR-92a [74], and miR-221/222 [86, 87].

In the context of vascular remodeling, Ji et al. identified miRNAs that are aberrantly expressed in the vascular walls after balloon injury [88]. Modulating an aberrantly overexpressed miR-21 via antisense-mediated depletion had a significant negative effect on neointimal lesion formation. They also demonstrated that Pten and Bcl2 were involved in miR-21-mediated cellular effects. The same group also revealed that miR-221 and miR-222 expression levels were elevated in rat carotid arteries after angioplasty [89]. Moreover, they found that p27 (Kip1) and p57 (Kip2) were target genes involved in miR-221- and miR-222-mediated effects on vascular smooth muscle cell (VSMC) growth. Knockdown of miR-221 and miR-222 resulted in decreased VSMC proliferation both in vitro and in vivo.

miR-145 is selectively expressed in VSMCs of the vascular wall, and its expression was significantly downregulated in vascular walls with neointimal lesion formation. The target of miR-145 is KLF5 and its downstream signaling molecule, myocardin. Restoration of miR-145 in balloon-injured arteries via Ad-miR-145 inhibited neointimal growth and might be used for treatment of a variety of proliferative vascular disorders.

Aortic aneurysms are a common clinical condition that can cause death due to aortic dissection or rupture. The association between aortic aneurysm pathogenesis and altered TGF-β signaling, inflammation and apoptosis has been the subject of numerous investigations. Recently, a TGF-β-responsive miR-29 [90, 91] and miR-21 [92] whose targets include Pten, Spry1, Pdcd4, and Bcl2 have been identified to play roles in cellular phenotypic modulation during aortic development. It was demonstrated that decreasing the levels of miR-29b or increasing the levels of miR-21 in the aortic wall could attenuate aortic aneurysm progression in a porcine pancreatic elastase infusion and angiotensin II infusion model of abdominal aortic aneurysms in mice [90, 92].

Heart Failure

Because all of the previously described pathologies, i.e. cardiac hypertrophy, fibrosis, arrhythmia, and CAD can cause HF, all of the miRNAs discussed so far are also relevant to this disease entity.

Many profiling studies have been conducted and revealed a large number of miRNAs that are differentially expressed in HF, pointing to a new mode of regulation of cardiovascular diseases [9, 11, 12, 21, 57, 93].

A diverse range of circulating miRNAs have been studied for the detection of HF. Tijsen et al. tried to determine whether miRNAs make it possible to distinguish clinical HF not only from healthy controls but also from non-HF forms of dyspnea [40]. They revealed that miR423-5p was most strongly related to the clinical diagnosis of HF and receiver-operator-characteristics curve analysis showed miR423-5p to be a diagnostic predictor of HF, with an area under the curve of 0.91 (p < 0.001).

From a diagnostic perspective, Goren et al. tried to evaluate a multimarker approach to HF diagnosis [94]. They measured the levels of 186 miRNAs in the sera of 30 stable chronic systolic HF patients and 30 controls. The differences in miRNA levels between the two groups were characterized, and a score, based on the levels of four specific miRNAs with the most significant increase in the HF group (miR-423-5p, miR-320a, miR-22, and miR-92b) was defined. Interestingly, the score was utilized to discriminate HF patients from controls with a sensitivity and specificity of 90 %. Moreover, in the HF group, there was a significant association between the score and important clinical parameters such as elevated serum natriuretic peptide levels, a wide QRS, and dilatation of the left ventricle and left atrium. These results suggested that a multimarker approach is useful for the detection of not only HF but also left ventricular structure and function.

miRNAs are also related to a more specific cause of HF, such as chemotherapy-induced HF or obesity-related HF. It has been proposed that miRNAs can exert their roles in response to treatment with chemotherapeutic agents. For example, it was suggested that upregulation of miR-146a after doxorubicin (Dox) treatment is involved in acute Dox-induced cardiotoxicity by targeting ErbB4 [95]. Inhibition of both ErbB2 and ErbB4 signaling may be one of the reasons why those patients who receive concurrent therapy with Dox and trastuzumab suffer from HF.

miRNA microarray analyses and real-time polymerase chain reaction have revealed that miR-451 levels were significantly increased in type 2 diabetes mellitus mouse hearts [96]. Calcium-binding protein 39 (Cab39) is a scaffold protein of liver kinase B1 (LKB1), an upstream kinase of AMP-activated protein kinase (AMPK). Cab39 is a direct target of miR-451 in neonatal rat cardiac myocytes, and Cab39 overexpression rescued lipotoxicity. Protein levels of Cab39 and phosphorylated AMPK were increased and phosphorylated mammalian target of rapamycin was reduced in cardiomyocyte-specific miR-451 knockout mouse hearts compared with control mouse hearts. Thus, these results demonstrated that miR-451 is involved in diabetic cardiomyopathy through suppression of the LKB1/AMPK pathway.

Conclusion

miRNAs have emerged as powerful and dynamic modifiers of cardiovascular diseases. The miRNA species discussed above are able to directly regulate the expression of transcription factors, signaling molecules, contractile proteins, and play critical roles in cardiovascular remodeling. Work from several investigators have demonstrated the ability of exogenously administered miRNA inhibitors or miRNA mimics to modulate these pathological processes, thereby ameliorating cardiovascular diseases, which is promising and potentially opens the door for novel therapeutic approaches in the future. The potential of circulating miRNAs as biomarkers for cardiovascular diseases is also in its early stages. Their roles as prognostic biomarkers have yet to be elucidated, and larger studies with longer follow-up periods will be needed.