MicroRNAs in Cancer and Cardiovascular Disease

Although cardiac tumor formation is rare, accumulating evidence suggests that the two leading causes of deaths, cancers, and cardiovascular diseases are similar in terms of pathogenesis, including angiogenesis, immune responses, and fibrosis. These similarities have led to the creation of new exciting field of study called cardio-oncology. Here, we review the similarities between cancer and cardiovascular disease from the perspective of microRNAs (miRNAs). As miRNAs are well-known regulators of translation by binding to the 3′-untranslated regions (UTRs) of messenger RNAs (mRNAs), we carefully dissect how a specific set of miRNAs are both oncomiRs (miRNAs in cancer) and myomiRs (muscle-related miRNAs). Furthermore, from the standpoint of similar pathogenesis, miRNAs categories related to the similar pathogenesis are discussed; namely, angiomiRs, Immune-miRs, and fibromiRs.


Introduction
Cancer and cardiovascular disease are the leading causes of death across the globe accounting for one in six deaths [1] and 32% of all deaths worldwide [2], respectively, according to World Health Organization (WHO). Both cancer and cardiovascular disease are the umbrella terms commonly used to describe several disease etiologies. Each etiology of cancer and cardiovascular disease (e.g., lung cancer and ischemic heart disease, respectively) has its own distinct cause and progression pattern. However, recent research suggests that many aspects of cancer and cardiovascular disease are similar in terms of pathogenesis [3][4][5], leading to the development of specific field of study called cardio-oncology [6,7]. For example, both diseases involve dysregulated functionalities in vasculature, where abnormal vasculature (called, tumor vasculature [8]) occurs in cancer, while coronary artery disease is a type of cardiovascular disease caused by the narrowing or blockage of coronary arteries [9]. Another example is the involvement of immune responses, where prolonged or chronic inflammation is a hallmark of cancer [10][11][12] as well as cardiovascular disease [13][14][15]. The activation of immune responses often leads to the deposition of excessive extracellular matrices [16,17], which are another hallmark of cancer [17] and cardiac fibrosis as the end-stage of heart failure [18].
The miR-17~92 cluster was first reported in tumorigenesis [65] and is one of well-studied miRNA clusters [66,67]. By crossing miR-17~92 floxed mice with an i vascular endothelial cell specific Cre driver (Cdh5-cre/ERT2), Chamorro-Jorgan demonstrated that retinal angiogenesis was reduced during the development mice [68]. Furthermore, the vascular endothelial growth factor (VEGF)-induced tumor angiogenesis were reduced, suggesting that VEGF regulates miR-17~9 expression leading to the regulation of angiogenesis. The involvement of the m cluster is well documented in various diseases, including cardiovascular disease miR-133 regulates the cardiac hypertrophy and improves the myocardial function after infarction, while it is associated with multiple tumors. miR-133 targets 3 -UTR of CDC42 and regulates PAKs, thus preventing the growth and metastasis of gastric cancer. Similarly, miR-133 prevents the proliferation, migration, and invasion of lung cancer by targeting MMP14 and PKM2. Furthermore, miR-133 is involved also in the pathogenesis of glioblastoma and oral and prostate cancer.
The miR-17~92 cluster was first reported in tumorigenesis [65] and is one of the most well-studied miRNA clusters [66,67]. By crossing miR-17~92 floxed mice with an inducible vascular endothelial cell specific Cre driver (Cdh5-cre/ERT2), Chamorro-Jorganes et al. demonstrated that retinal angiogenesis was reduced during the development of these mice [68]. Furthermore, the vascular endothelial growth factor (VEGF)-induced ear and tumor angiogenesis were reduced, suggesting that VEGF regulates miR-17~92 cluster expression leading to the regulation of angiogenesis. The involvement of the miR-17~92 cluster is well documented in various diseases, including cardiovascular disease [69,70]. Since the miR-17~92 cluster consists of miR-17, miR-18a, miR-19a, miR-20a, miR-19b-1, and miR-92a-1, each miRNA in this cluster is also shown to be important for angiogenesis, including tumorigenesis and cardiovascular disease. For example, miR-92a is dysregulated in many forms of cancer, suggesting it is a potential diagnostic biomarker as well as a therapeutic target [71]. In the cardiovascular system, Bonauer et al. demonstrated that overexpression of miR-92a in endothelial cells inhibited angiogenesis in murine models of limb ischemia and myocardial infarction, while the silencing of miR-92a via antagomiR resulted in enhanced angiogensis and the functional recovery of the damaged tissues in murine disease models, suggesting miR-92a as a potential therapeutic target for ischemia diseases [72].
The miR-200 family is another well studied miRNA family that includes miR-141, miR-200a, miR-200b, miR-200c, and miR-429 [73]. In cancer, the miR-200 family is shown to play functional roles in cell malignant transformation and preventing tumor initiation [74]. By profiling epicardial adipose tissue from coronary artery disease (CAD) patients and non-CAD atherosclerotic patients, Zhang et al. demonstrated that the expressions of miR-141-3p, miR-200b, miR-200c-3p, and miR-429 are up-regulated in CAD patients compared to non-CAD patients [75]. By performing a series of experiments in vitro, the authors demonstrated that the overexpression of miR-200b-3p in human umbilical vein endothelial cells (HUVECs) resulted in increased apoptosis under oxidative stress. Mechanistically, miR-300b-3p targets histone deacetylase 4 (HDAC4) as the overexpression of HDAC4 reduced the increased apoptosis induced by inhibiting miR-200b-3p, suggesting that miR-200b-3p is a potential therapeutic target for atherosclerosis. models of limb ischemia and myocardial infarction, while the silencing of miR-92a via antagomiR resulted in enhanced angiogensis and the functional recovery of the damaged tissues in murine disease models, suggesting miR-92a as a potential therapeutic target for ischemia diseases [72].
The miR-200 family is another well studied miRNA family that includes miR- 141, miR-200a, miR-200b, miR-200c, and miR-429 [73]. In cancer, the miR-200 family is shown to play functional roles in cell malignant transformation and preventing tumor initiation [74]. By profiling epicardial adipose tissue from coronary artery disease (CAD) patients and non-CAD atherosclerotic patients, Zhang et al. demonstrated that the expressions of miR- 141-3p, miR-200b, miR-200c-3p, and miR-429 are up-regulated in CAD patients compared to non-CAD patients [75]. By performing a series of experiments in vitro, the authors demonstrated that the overexpression of miR-200b-3p in human umbilical vein endothelial cells (HUVECs) resulted in increased apoptosis under oxidative stress. Mechanistically, miR-300b-3p targets histone deacetylase 4 (HDAC4) as the overexpression of HDAC4 reduced the increased apoptosis induced by inhibiting miR-200b-3p, suggesting that miR-200b-3p is a potential therapeutic target for atherosclerosis.
MiR-34a is a tumor suppressor and considered as a diagnostic and prognostic biomarker as well as a therapeutic target in various cancers, including head and neck squamous cell carcinoma, thyroid cancer, and cancer stem cells [76,77]. Interestingly, the expression of miR-34a is increased in senescent HUVECs and in the heart and spleen of older mice [78]. When overexpressed, miR-34a suppressed cell cycle and proliferation by inhibiting sirtuin 1 (SIRT1). Because ageing is a hot topic to be investigated, subsequent research shows the functional importance of miR-34a in cell types other than endothelial cells in the heart, including in cardiomyocytes [79,80], fibroblasts [81], and smooth muscle cells [82,83]. This is not an isolated case as many other angiomiRs (and other miRNAs) are expressed rather ubiquitously, suggesting that examining miRNAs as a common mechanism of action for cardio-oncology is not a big surprise.  MiR-34a is a tumor suppressor and considered as a diagnostic and prognostic biomarker as well as a therapeutic target in various cancers, including head and neck squamous cell carcinoma, thyroid cancer, and cancer stem cells [76,77]. Interestingly, the expression of miR-34a is increased in senescent HUVECs and in the heart and spleen of older mice [78]. When overexpressed, miR-34a suppressed cell cycle and proliferation by inhibiting sirtuin 1 (SIRT1). Because ageing is a hot topic to be investigated, subsequent research shows the functional importance of miR-34a in cell types other than endothelial cells in the heart, including in cardiomyocytes [79,80], fibroblasts [81], and smooth muscle cells [82,83]. This is not an isolated case as many other angiomiRs (and other miRNAs) are expressed rather ubiquitously, suggesting that examining miRNAs as a common mechanism of action for cardio-oncology is not a big surprise.

Immune Responses: Immuno-miRs
Prolonged inflammation is a hallmark of cancer [10] that immune systems can have both positive and negative effects on regarding the development of tumors and prognostics of cancer patients [84]. Indeed, immunotherapy is a type of treatment using one's own immune system to fight cancer, but the success rates of immunotherapy drugs vary between 15-30% in most tumor types, while 50-80% in melanoma [85]. As the immune system is a complex system involving many different cell types (e.g., basophils, eosinophils, lymphocytes, macrophages, monocytes, and neutrophils) to fight against infection [86,87], understanding the immune system is also important in cardiovascular disease [88][89][90]. For example, myocardial infarction leads to the loss of cardiomyocytes, which are replaced by non-contracting scar tissue [91,92]. The immune system is a double-edged sword in the remodeling process of the infarcted heart as macrophages are necessary for repair in the acute phase as their systemic depletion results in impaired scar formation and the rupture of the left ventricle of the heart. However, the accumulation of macrophages in non-infarcted regions of the left ventricle leads to progressive myocyte attrition, collagen deposition, and loss of the pump function of the heart in a chronic phase of remodeling of the infarcted heart. As miRNAs are expressed in many immune cells and finetune the important signaling pathways, the list of immuno-miRs is growing rapidly [93,94]. As such, specialized databases for immune-miRs are available, including IRNdb [95], RNA2Immune [96], and RNAimmuno [97]. In the following, examples of immune-miRs are explained in cancer and cardiovascular disease.
Monocytes are a type of white blood cells (leukocytes) that can differentiate into macrophages and dendritic cells [98]. Furthermore, monocyte-derived macrophages can be polarized into inflammatory subtype, M1, and anti-inflammatory subtype, M2 [99]. The cascade of differentiation and polarizations are controlled by the coordinate actions of cytokines, which can be regulated at the transcriptional and post-transcriptional levels, where miRNAs can regulate the translation of transcription factors responsible for cytokine gene expressions. These microRNAs include miR-125a-3p and miR-26a-2 in M1 macrophages, while miR-27a, miR-29b-1, miR-132, miR-193b, and miR-222 constitute the M2 macrophages [100] (Figure 3A). For example, miR-222 targets ADAM metallopeptidase domain 17 (ADAM17) to modulate multidrug resistance in colorectal carcinoma [101] ( Figure 3B). In breast cancer, the overexpression of miR-222 inhibits the chemotaxis of tumorassociated macrophages by targeting C-X-C motif chemokine ligand 12 (CXCL12) [102]. In the serum, the level of miR-222 is independently associated with atrial fibrillation (irregular heart rhythm) in patients with degenerative valvular heart disease [103]. In addition, the level of miR-222 is elevated in acute viral myocarditis caused by Coxsackievirus B3 [104]. Although the functions of miR-222 are mainly reported in cardiomyocytes [104][105][106] and cardiac fibroblasts [107,108], it is clear that immune-miRs in monocytes and macrophages are important regulators of immune responses in cancer and cardiovascular disease. receptor associated factor 6 (TRAF6) [121]. This is just of many miRNAs contained in exosomes.
The studying of immunology has intensified in recent years due to the rise of coronavirus disease 2019 (COVID-19) [122][123][124][125]. As there is a substantial risk of heart problems associated with COVID-19 and mRNA vaccines [126][127][128][129], it is likely that more and more miRNAs will be identified in the heart, which may have been studied in cancer previously to expand the list of immune-miRs in the cardio-oncology field.  Enriched in immune cells, miR-155 is a master regulator of immune responses [109] ( Figure 3C). In breast cancer, the increased expression of miR-155 is associated with high tumor grade, advanced stage, and lymph node metastasis [110]. Similarly, miR-155 is overexpressed in other forms of cancer, including esophageal cancer [111], liver cancer [112], and lung cancer [113], which calls for miR-155 as a diagnostic and prognostic cancer biomarker [114] as well as therapeutic target [115]. As shown in the previous section, miR-155 is an angiomiR so its function is well known in the endothelial cells and atherosclerosis [116,117]. Besides endothelial cells, miR-155 is highly expressed in monocytes and macrophages, which Pankratz et al. used in knockout mice to elegantly demonstrate that miR-155 regulates angiogenesis and arteriogenesis by controlling their target genes, angiotensin II receptor type 1 (AGTR1) and suppressor of cytokine signaling 1 (SOCS1) in endothelial and monocyte/macrophages, respectively [118].
Extracellular RNAs (exRNAs) are a type of cell-cell communication that are produced by a donor cell and are released into the extracellular environment (e.g., body fluid, circulation) [119]. They are contained in the lipid particles, such as extracellular vehicles (EVs), including exosomes. ExRNAs include proteins and RNAs, including miRNAs. For example, miR-146a-5p is enriched in the hepatocellular carcinoma-derived exosomes [120] Cells 2022, 11, 3551 7 of 14 ( Figure 3D). The transcription factor, spalt like transcription factor 4 (SALL4), binds to the promoter of miR-146a-5p to directly control its expression in exosomes, thereby regulates the polarization of macrophages into M2 tumor-associated macrophages. In contrast, cardiomyocyte-derived exosomal miR-146a-5p promotes M1 macrophage polarization while inhibiting M2 macrophage polarization by targeting TNF receptor associated factor 6 (TRAF6) [121]. This is just of many miRNAs contained in exosomes.
The studying of immunology has intensified in recent years due to the rise of coronavirus disease 2019 (COVID-19) [122][123][124][125]. As there is a substantial risk of heart problems associated with COVID-19 and mRNA vaccines [126][127][128][129], it is likely that more and more miRNAs will be identified in the heart, which may have been studied in cancer previously to expand the list of immune-miRs in the cardio-oncology field.

Fibrosis: fibromiRs
Fibrosis is a process in which fibroblasts and other mesenchymal cells are activated to become myofibroblasts to secrete an excess number of extracellular matrices (ECM; e.g., collagens, glycosaminoglycans, and glycoproteins) [130] ( Figure 4A). It is the end stage of many diseases, including cardiovascular disease [18]. In cancer, cancer-associated fibroblasts (CAFs) promote tumorigenic features, including ECM deposition, epithelialto-mesenchymal transition (EMT), and metastasis [131]. To understand fibrosis, many screening studies have been performed to identify differentially expressed genes and miRNAs, which are collectively called fibromiRs [132][133][134][135]. For example, miR-21 is the most studied fibromiR [136][137][138][139] (Figure 4B). Not only is it highly expressed in many forms of cancer and suggested as potential diagnostic biomarkers of cancer types (breast, pancreatic, colorectal, and prostate cancer) [140], miR-21 stimulates MAP kinase signaling in cardiac fibroblasts, thereby contributing to myocardial disease [141]. Furthermore, miR-21 targets matrix metallopeptidase 2 (Mmp2) in cardiac fibroblasts of the infarcted heart via phosphatase and the tensin homolog (PTEN) pathway [142], suggesting the important signaling roles of miR-21 in both cancer and cardiovascular disease.
Multiple reports show that another oncomiR, miR-22, is highly involved in tumor progression in multiple tumors, including breast cancer [143], acute myeloid leukemia (AML) [144], and hepatocellular carcinoma (HCC) [145,146]. The effect of miR-22 on HCC seems to be related to the early effect of miR-22 on liver fibrosis through its regulation of bone morphogenic protein 7 (BMP7) [147] (Figure 4C), which starts from a degenerative process and ultimately leads to HCC developing. Interestingly, miR-22 is reported to have the same effect on cardiac fibrosis [148] via the regulation of Sirt1 and HDAC4. As the role of miR-22 in fibrosis is conserved in multiple diseases and tissues, this miRNA could serve as a potential therapeutic target in liver [149] and cardiac fibrosis [150].
Although fibroblasts can be found throughout the human body, they are heterogeneous populations of cells without any single cell surface marker that is specific for fibroblasts as many markers are expressed in other cell types, including epithelial and immune cells [151,152]. In this regard, microRNAs are involved in activating fibroblasts, which contribute to the heterogeneity of fibroblasts [153]. For example, the members of the miR-200 family, miR-141 and miR-200a, target C-X-C motif chemokine ligand 12 (CXCL12; also known as CXCL12β) to regulate the immunosuppressive activity of a subtype of carcinoma-associated fibroblasts in ovarian cancer [154]. Besides the miR-200 family being angiomiRs as written in above subsection, miR-200b is negatively regulated by the epigenetic factor, DNA methyltransferase 3 alpha (Dnmt3a), to control autophagy in rat cardiac fibroblasts [155]. In addition, small RNA-seq experiment using rat cardiac fibroblasts induced with transforming growth factor-β1 (TGF-β1) showed 3 up-(miR-325-3p, miR-325-5p, and miR-210-5p) and 21 down-regulated miRNAs (e.g., miR-19a-3p, miR-19b-3p, miR-144-3p, and miR-200b-3p), potentially targeting genes involved in calcium and glutamatergic synapse signaling pathways [156]. Taken together, there are many shared fibromiRs between CAFs and cardiac fibroblasts.

Conclusions
To maintain the homeostasis of the tissues and remodeling of the tissues upon damages, angiogenesis, immune responses, and fibrosis are interconnected. As such, miRNAs are identified to be involved in each cellular activity as angiomiRs, immuno-miRs, and fibromiRs, respectively. Not surprisingly, some miRNAs (e.g., miR-17~92 cluster, miR-34a, and miR-200 family) are involved in all three cellular activities, which some overlapping miRNAs are responsible for such cellular activities and responses. This is particularly interesting as cancer is considered as a complex adaptive ecosystem [157], in which cancer cells and the stromal cells transform, cooperate, and even co-evolve with each other over time and space [158]. Thus, it will be interesting to further investigate miRNAs from the perspective of the ecosystem in cancer and possibly in cardiovascular disease.
As cancer and cardiovascular disease are two of the leading causes of death worldwide, it will be exciting to find a common disease mechanism. As reviewed above, miRNAs are shared between these life-threatening diseases. Given that miRNAs are investigated as potential therapeutic targets, increased communication between researchers working with cancer and cardiovascular disease is necessary to find a potential cure for these diseases. To this end, the rise of the cardio-oncology field should

Conclusions
To maintain the homeostasis of the tissues and remodeling of the tissues upon damages, angiogenesis, immune responses, and fibrosis are interconnected. As such, miRNAs are identified to be involved in each cellular activity as angiomiRs, immuno-miRs, and fibromiRs, respectively. Not surprisingly, some miRNAs (e.g., miR-17~92 cluster, miR-34a, and miR-200 family) are involved in all three cellular activities, which some overlapping miRNAs are responsible for such cellular activities and responses. This is particularly interesting as cancer is considered as a complex adaptive ecosystem [157], in which cancer cells and the stromal cells transform, cooperate, and even co-evolve with each other over time and space [158]. Thus, it will be interesting to further investigate miRNAs from the perspective of the ecosystem in cancer and possibly in cardiovascular disease.
As cancer and cardiovascular disease are two of the leading causes of death worldwide, it will be exciting to find a common disease mechanism. As reviewed above, miRNAs are shared between these life-threatening diseases. Given that miRNAs are investigated as potential therapeutic targets, increased communication between researchers working with cancer and cardiovascular disease is necessary to find a potential cure for these diseases. To this end, the rise of the cardio-oncology field should facilitate a further understanding of the pathogeneses of these two diseases, possibly through miRNAs.