Myocardial and circulating levels of microRNA-21 reflect left ventricular fibrosis in aortic stenosis patients
Introduction
Degenerative aortic stenosis (AS) has become the most frequent type of valvular disease in industrialized countries (2–7% of the population older than 65 years) and its incidence is rising in parallel to the increasing life expectancy [1]. Surgical aortic valve replacement is the only therapy with confirmed survival benefit, and at present, no medical therapy can delay the inevitability of surgery. Older age is associated with a higher frequency of comorbidity, which contributes to increased operative risk and renders decision-making for intervention more complex [2]. Under pathological pressure loading, such as AS, the left ventricle (LV) experiences a remodeling process that is characterized by the hypertrophic growth of cardiomyocytes and the increased deposition of extracellular matrix (ECM) elements [3]. The development of diffuse, reactive myocardial fibrosis is a major cause of abnormal myocardial stiffness [4] which results in systolic and/or diastolic dysfunction that is proportional to the degree of ECM deposition [5], [6], [7], [8]. The extent of myocardial fibrosis, which may not be reversible after delayed surgery, has important prognostic implications, because it is an independent predictor of perioperative mortality [9] and a key determinant of long-term functional outcome following aortic valve replacement [5], [10], [11].
MicroRNAs (miRNAs) are non-coding small RNAs that modulate the expression of target genes by repressing translation and/or inducing mRNA degradation. The aberrant expression of miRNAs is associated with multiple pathological processes, including processes that affect the cardiovascular system [12], [13], [14], [15]. To date, few studies have analyzed the differential expression profiling of miRNAs in failing human hearts of different etiologies in comparison with control patients [16], [17], [18]. The distinctive pattern of miRNA expression changes between heart diseases has led to the suggestion that miRNAs may have etiological implications and that their expression profiles could be useful as potential biomarkers for diagnosing patients and predicting the prognosis and response to therapy [19]. One particular miRNA that is consistently deregulated under various cardiovascular pathological conditions is miR-21 [20]. Through loss-of-function and gain-of-function approaches, a key regulatory role for miR-21 has been evidenced in the pathological remodeling of the myocardium induced by hemodynamic stress [21], [22], [23]. The up-regulation of miR-21 in response to cardiac injury protects fibroblasts against apoptosis, which results in LV interstitial fibrosis and hemodynamic dysfunction [22]. The relationship of miR-21 up-regulation with the remodeling of ECM has also been demonstrated in mouse models of ischemia/reperfusion and acute myocardial infarction [24], [25], [26]. miR-21 was postulated to repress the transcription of myocardial mRNA targets including sprouty homolog 1 (SPRY1) [22], phosphatase and tensin homolog (PTEN) [23] and programmed cell death 4 (PDCD4) [27], [28]. In addition, some miR-21 targets validated in extracardiac tissues [29], such as reversion-inducing-cysteine-rich protein with kazal motifs (RECK) and the tissue inhibitor of metalloproteinase 3 (TIMP3), play key roles in the control of the ECM homeostasis [30], [31] which deserve further attention in the scenario of human pressure overload.
Transforming growth factor-β1 (TGF-β1) is a crucial player in the LV remodeling response to hemodynamic stress [3] both in rodent models [32], [33] and in AS patients [5], [8], [34]. The involvement of miR-21 in the molecular mechanism underlying the effects of TGF-β1 has become a key focus of recent research. Smads, which are the canonical effectors of TGF-β signaling, regulate the transcription of primary miR-21 and its post-transcriptional processing by the DROSHA complex [35]. In TGF-β-dependent events, miR-21 is closely linked to the abnormal and excessive deposition of ECM [20], [36], and several reports determined that miR-21 acts downstream of TGF-β to modulate the genesis and progression of pathological fibrotic processes in the liver [37], kidneys [38], [39] and lungs [40]. Overall, these findings led us to hypothesize that miR-21 could be an actor in the pressure overload-induced ECM remodeling process dependent on TGF-β signaling in AS patients.
Recent reports indicate the presence of circulating miRNAs in microvesicles or protein–miRNA-complexes that can be consistently quantified in human plasma and other body fluids [41]. Several studies reported altered plasma levels of various miRNAs in cardiovascular diseases [42], including acute myocardial infarction, stable coronary artery disease, acute and chronic heart failure and myocarditis [43]. Therefore, the altered circulating levels of selected miRNAs may reflect specific cardiovascular pathologies and could be useful biomarkers for cardiovascular diseases. However, there are no data available on the possible function of circulating/extracellular miRNAs as endocrine/paracrine signaling molecules that contribute to cardiovascular disease pathogenesis.
Thus, the aim of this study was to investigate the following: (a) the role of both myocardial and plasmatic miR-21 in the maladaptive ECM remodeling induced by pressure overload in AS patients; (b) the association between validated miR-21 targets and TGF-β signaling effectors; and (c) the potential clinical value of miR-21 as a disease biomarker for pathological myocardial fibrosis progression.
Section snippets
Methods
The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology.
Results
The preoperative echocardiographic, clinical and demographic data of the patient cohorts are shown in Table 1. Patient demographic and clinical characteristics were presented as means ± standard deviation.
Discussion
Abundant evidence derived from basic research suggests a key role for several miRNAs, including miR-21, in the pathophysiology of many cardiovascular pathological processes. However, a direct assessment of their involvement in human heart diseases has rarely been addressed [19]. In the present study, which was performed in one of the largest series of intraoperative LV myocardial biopsies from AS patients, we provided evidence supporting a significant role for miR-21 in the pathological
Funding sources
This work was supported by the Instituto de Salud Carlos III [PI09/01097], Ministerio de Ciencia e Innovación (SAF2010-16894), Fundación Marqués de Valdecilla-Universidad de Cantabria [FMV-UC 09/01], and Instituto de Formación e Investigación Marqués de Valdecilla [FMV-API 10/20].
Acknowledgments
We thank Dr. Javier Llorca for statistical advice. We acknowledge the technical assistance of Amalia Cavayé, Ana Cayón, Nieves García, Elena Martín, RN, Roberto Moreta, RN and Ana Sandoval. The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology.
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- 1
The first two authors contributed equally to this work.
- 2
MAH and JFN contributed equally to the design and direction of this work and both are corresponding authors.