Is miR-21 A Therapeutic Target in Cardiovascular Disease?

microRNA-21 (miR-21) serves a multitude of functions at the molecular level through its regulation of messenger RNA. Previous research has sparked interest in the role of miR-21 as a potential therapeutic target in cardiovascular diseases. miR-21 expression contributes to the differentiation, proliferation, and maturation of many cell types, such as fibroblasts, endothelial cells, cardiomyocytes, and endothelial progenitor cells. The function of miR-21 depends upon its expression level in the specific cell types and downstream targets, which determine cell fate. Under pathological conditions, the expression level of miR-21 is altered, leading to abnormal gene regulation of downstream signaling and cardiovascular diseases such as hypertension, cardiac hypertrophy and fibrosis, atherosclerosis, and heart failure. Agomirs or antagomirs can be introduced into the respective tissue type to reverse or stop the progression of the disease. Exosomes in the extracellular vesicles, which mediate many cellular events with high biocompatibility, have a high potential of efficiently delivering miR-21 to their targeted cells. The critical role of miR-21 in cardiovascular disease (CVD) is indisputable, but there are controversial reports on the function of miR-21 in the same disease. This discrepancy sparks interest in better understanding the role of miR-21 in different tissues under different stages of various diseases and the mechanism of how miR-21 inhibitors work.

The Roles of Bone Marrow-Derived Stem Cells in Coronary Collateral Growth Induced by Repetitive Ischemia

Many clinical trials have attempted to use stem cells to treat ischemic heart diseases (IHD), but the benefits have been modest. Though coronary collaterals can be a "natural bypass" for IHD patients, the regulation of coronary collateral growth (CCG) and the role of endogenous stem cells in CCG are not fully understood. In this study, we used a bone marrow transplantation scheme to study the role of bone marrow stem cells (BMSCs) in a rat model of CCG. Transgenic GFP rats were used to trace BMSCs after transplantation; GFP bone marrow was harvested or sorted for bone marrow transplantation. After recovering from transplantation, the recipient rats underwent 10 days of repetitive ischemia (RI), with echocardiography before and after RI, to measure cardiac function and myocardial blood flow. At the end of RI, the rats were sacrificed for the collection of bone marrow for flow cytometry or heart tissue for imaging analysis. Our study shows that upon RI stimulation, BMSCs homed to the recipient rat hearts' collateral-dependent zone (CZ), proliferated, differentiated into endothelial cells, and engrafted in the vascular wall for collateral growth. These RI-induced collaterals improved coronary blood flow and cardiac function in the recipients' hearts during ischemia. Depletion of donor CD34+ BMSCs led to impaired CCG in the recipient rats, indicating that this cell population is essential to the process. Overall, these results show that BMSCs contribute to CCG and suggest that regulation of the function of BMSCs to promote CCG might be a potential therapeutic approach for IHD.

Role of endothelial CXCR4 in the development of aortic valve stenosis

Background

CXCL12/CXCR4 signaling is essential in cardiac development and repair, however, its contribution to aortic valve stenosis (AVS) remains unclear. In this study, we tested the role of endothelial CXCR4 on the development of AVS.

Materials and methods

We generated CXCR4 endothelial cell-specific knockout mice (EC CXCR4 KO) by crossing CXCR4^fl/fl mice with Tie2-Cre mice to study the role of endothelial cell CXCR4 in AVS. CXCR4^fl/fl mice were used as controls. Echocardiography was used to assess the aortic valve and cardiac function. Heart samples containing the aortic valve were stained using Alizarin Red for detection of calcification. Masson’s trichrome staining was used for the detection of fibrosis. The apex of the heart samples was stained with wheat germ agglutinin (WGA) to visualize ventricular hypertrophy.

Results

Compared with the control group, the deletion of CXCR4 in endothelial cells led to significantly increased aortic valve peak velocity and aortic valve peak pressure gradient, with decreased aortic valve area and ejection fraction. EC CXCR4 KO mice also developed cardiac hypertrophy as evidenced by increased diastolic and systolic left ventricle posterior wall thickness (LVPW), cardiac myocyte size, and heart weight (HW) to body weight (BW) ratio. Our data also confirmed increased microcalcifications, interstitial fibrosis, and thickened valvular leaflets of the EC CXCR4 KO mice.

Conclusion

The data collected throughout this study suggest the deletion of CXCR4 in endothelial cells is linked to the development of aortic valve stenosis and left ventricular hypertrophy. The statistically significant parameters measured indicate that endothelial cell CXCR4 plays an important role in aortic valve development and function. We have compiled compelling evidence that EC CXCR4 KO mice can be used as a novel model for AVS.

Abstract P1020: Differential Contribution Of Bone Marrow Cells To The Heart In Steady-state And After Repetitive Ischemia

Multiple studies have implicated the important role of migration of bone marrow (BM)-derived cells in heart after ischemia. Various BM-derived cells have been demonstrated to exert beneficial or detrimental effects in ischemia. But the response of BM to repetitive ischemia (RI) and the difference in contribution of this heterogenous population to the heart after RI remain elusive. Here, we applied an occluder on the left anterior descending coronary arteries of rats and they went under RI over a period of 10-17 days. This RI model induced coronary collateral growth and increased myocardial blood flow in the ischemic region after 10-17 days. We performed single- cell RNA sequencing and analysis of 24103 bone marrow transcriptomes isolated from the heart and bone marrow of rats in steady-state and after RI. Unsupervised clustering of cardiac neutrophils revealed 28 major clusters and 16 different cell types. Compared to steady state heart, proportion of BM derived macrophage mainly CD163 positive population was increased in the heart after RI. The proportion of BM derived natural killer cells was decreased markedly in the RI group. There was a slightly higher percentage of BM derived endothelial cells and lower smooth muscle cell and fibroblast in the RI group. While neutrophil degranulation, leukocyte activation, leukocyte migration are the major biological pathways in both groups, RI group showed activation of regeneration. We report heterogeneity of BM cells migrated to the heart during RI and redefine the BM that respond to heart ischemia and participate in induction of angiogenesis after RI.

Abstract P3023: The Regulatory Role Of Mir-21 In Heart Failure With Preserved Ejection Fraction (hfpef)

Introduction: Coronary microvascular dysfunction (CMD) is characterized by impaired endothelial-dependent vasodilation. These impairments are seen in diabetic cardiomyopathy, ischemia with no obstructive coronary artery disease, and heart failure with preserved ejection fraction (HFpEF), but detailed mechanisms have yet to be elucidated. Moreover, how microRNA (miR-21) regulates CMD in HFpEF is not entirely understood.

Methods: miR-21 knockout and wild-type (WT) mice were fed a diet high in fat and sugar (HFHS) for 6 months and blood lipid and glucose were measured. Echocardiography and treadmill exercise exertion tests were performed to assess cardiac function. Myocardial blood flow (MBF) under stress was measured by contrast echocardiography or doppler after the treatment with different dosages of norepinephrine and mean arterial blood pressure was measured simultaneously by femoral pressure catheter. Cardiac fibrosis was detected using trichrome staining and molecular pathways were elucidated via gene and protein analysis.

Results: Our preliminary data show decreased MBF during stress in WT mice fed a HFHS diet. While ejection fraction was not changed, cardiac index, stroke volume, and running distance were decreased. Furthermore, E/E’ ratio was increased in WT mice fed HFHS diet compared to the WT mice fed a chow diet, suggesting heart failure and impaired diastolic function with normal systolic function. Moreover, perivascular fibrosis was increased in the WT mice fed a HFHS diet compared to WT mice fed a chow diet. However, the ablation of miR-21 reversed all these changes in the mice fed a HFHS diet.

Conclusions: miR-21 regulates CMD and ameliorated HFpEF. Further investigation will elucidate the pathways and mechanisms converging with miR-21 to regulate HFpEF.

Abstract P3138: The Regulatory Role Of Sirtuin 6 In Coronary Microvascular Dysfunction

Introduction: Coronary microvascular dysfunction (CMD) is characterized by impaired endothelial-dependent vasodilation. These impairments are seen in diabetic cardiomyopathy, ischemia with no obstructive coronary artery disease, and heart failure with preserved ejection fraction (HFpEF), but detailed mechanisms have yet to be elucidated. Sirtuin 6 (Sirt6), an important member of the Sirtuin family, has been implicated in obesity, insulin resistance, type 2 diabetes mellitus (T2DM), and cardiovascular diseases. Sirt6 protects EC from premature senescence, oxidative stress, and atherosclerosis by sustaining high eNOS levels and preserving cell replication. Sirt6 was reported to regulate endothelial dilation in atherosclerosis in Sirt6 heterozygous mice, but how Sirt6 regulates coronary microvascular function remains to be determined.

Methods: Sirt6 knockout and wild-type (WT) mice were fed a diet high in fat and sugar (HFHS) for six months, and blood lipid and glucose were measured. Coronary arteries were isolated, and endothelial-dependent vasodilation (EDD) was assessed using myography (DMT). Echocardiography and treadmill exercise exertion tests were performed to evaluate cardiac function. Myocardial blood flow (MBF) was measured by doppler. Cardiac fibrosis was detected using trichrome staining, and molecular pathways were elucidated via gene and protein analysis.

Results: Our preliminary data show that Sirt6 was downregulated in diabetes. The EDD of coronary arterioles was impaired, and the mediator of coronary vasodilation switched from NO to H 2 O 2 in the Sirt6 knockout mice. Compared to the WT mice, myocardial blood flow is decreased, ejection fraction (EF) was not changed, the running distance was reduced, and E/E’ ratio was increased in Sirt6 knockout mice. The Sirt6 targeted proteins were identified.

Conclusions: Sirt6 regulated coronary microvascular function, and ablation of Sirt6 caused CMD and diastolic dysfunction. Further genetic profiling will elucidate the pathways and mechanisms converging with Sirt6 to regulate microvascular function.

Abstract 592: Cardioprotection During Ischemia by Induced Coronary Collateral Growth

Patients with poorly developed coronary collateral networks have a poorer prognosis after a cardiovascular event than those with well-developed collaterals. The outcome of patients with metabolic syndrome (MetS) was worse than the patient without MetS. Interestingly, coronary collateral growth is impaired in MetS. We hypothesize that coronary collaterals are critical for the cardiac protection in ischemic heart diseases (IHD) and induction of coronary collateral growth (CCG) might ameliorate the outcome of patients with MetS. We study the cardiac protection by coronary collaterals in IHD and the underlying mechanism of impaired CCG in the MetSin a mouse model of CCG. A pneumatic snare was implanted and situated around the LAD. After the mice recovery from the surgery, periodic inflation of the snare occludes the LAD; thus, producing repetitive ischemia (RI). Cardiac function was measure with echocardiography. CCG was measured by myocardial blood flow with contrast echocardiography and by collateral numbers with micro-CT or by vascular density with fluorescence scope. Our preliminary results showed that with occlusion of the LAD, there was no blood flow in the ischemic area. However, after stimulation of CCG by RI, the blood flow the ischemic area was compensated by the grown coronary collaterals and cardiac function was reserved during ischemia. Diabetic mice failed to grow coronary collaterals after RI stimulation and there was no cardiac protection from coronary collaterals during ischemia. Moreover, we studied the roles of growth differentiation factor 11 (GDF11) and miR21 in the regulation of CCG and cardiac protection in IHD. GDF11 was downregulated and miR21 was upregulated in the hearts of Zucker Obese Fatty (ZOF) rats during CCG. We used the Gdf 11 knockout mice and miR 21 knockout mice to study the underlying mechanism. GDF11 is highly expressed in myocardial blood vessels, which suggested the role of GDF11 in vascular growth. Impaired CCG of mice on high fat and high sugar was restored by miR-21 knockout. These data suggest that miR-21 is involved in the impairment of CCG in MetS.

Cardioprotection during ischemia by coronary collateral growth

Ischemic heart diseases (IHD) cause millions of deaths around the world annually. While surgical and pharmacological interventions are commonly used to treat patients with IHD, their efficacy varies from patient to patient and is limited by the severity of the disease. One promising, at least theoretically, approach for treating IHD is induction of coronary collateral growth (CCG). Coronary collaterals are arteriole-to-arteriole anastomoses that can undergo expansion and remodeling in the setting of coronary disease when the disease elicits myocardial ischemia and creates a pressure difference across the collateral vessel that creates unidirectional flow. Well-developed collaterals can restore blood flow in the ischemic area of the myocardium and protect the myocardium at risk. Moreover, such collaterals are correlated to reduced mortality and infarct size and better cardiac function during occlusion of coronary arteries. Therefore, understanding the process of CCG is highly important as a potentially viable treatment of IHD. While there are several excellent review articles on this topic, this review will provide a unified overview of the various aspects related to CCG as well as an update of the advancements in the field. We also call for more detailed studies with an interdisciplinary approach to advance our knowledge of CCG. In this review, we will describe growth of coronary collaterals, the various factors that contribute to CCG, animal models used to study CCG, and the cardioprotective effects of coronary collaterals during ischemia. We will also discuss the impairment of CCG in metabolic syndrome and the therapeutic potentials of CCG in IHD.

Kv1.3 channels facilitate the connection between metabolism and blood flow in the heart

The connection between metabolism and flow in the heart, metabolic dilation, is essential for cardiac function. We recently found redox-sensitive Kv1.5 channels play a role in coronary metabolic dilation; however, more than one ion channel likely plays a role in this process as animals null for these channels still showed limited coronary metabolic dilation. Accordingly, we examined the role of another Kv1 family channel, the energetically linked Kv1.3 channel, in coronary metabolic dilation. We measured myocardial blood flow (contrast echocardiography) during norepinephrine-induced increases in cardiac work (heart rate x mean arterial pressure) in WT, WT mice given correolide (preferential Kv1.3 antagonist), and Kv1.3-null mice (Kv1.3^-/- ). We also measured relaxation of isolated small arteries mounted in a myograph. During increased cardiac work, myocardial blood flow was attenuated in Kv1.3^-/- and in correolide-treated mice. In isolated vessels from Kv1.3^-/- mice, relaxation to H₂ O₂ was impaired (vs WT), but responses to adenosine and acetylcholine were equivalent to WT. Correolide reduced dilation to adenosine and acetylcholine in WT and Kv1.3^-/- , but had no effect on H₂ O₂ -dependent dilation in vessels from Kv1.3^-/- mice. We conclude that Kv1.3 channels participate in the connection between myocardial blood flow and cardiac metabolism.

Alignment of inducible vascular progenitor cells on a micro-bundle scaffold improves cardiac repair following myocardial infarction

Ischemic heart disease is still the leading cause of death even with the advancement of pharmaceutical therapies and surgical procedures. Early vascularization in the ischemic heart is critical for a better outcome. Although stem cell therapy has great potential for cardiovascular regeneration, the ideal cell type and delivery method of cells have not been resolved. We tested a new approach of stem cell therapy by delivery of induced vascular progenitor cells (iVPCs) grown on polymer micro-bundle scaffolds in a rat model of myocardial infarction. iVPCs partially reprogrammed from vascular endothelial cells (ECs) had potent angiogenic potential and were able to simultaneously differentiate into vascular smooth muscle cells (SMCs) and ECs in 2D culture. Under hypoxic conditions, iVPCs also secreted angiogenic cytokines such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) as measured by enzyme-linked immunosorbent assay (ELISA). A longitudinal micro-scaffold made from poly(lactic-co-glycolic acid) was sufficient for the growth and delivery of iVPCs. Co-cultured ECs and SMCs aligned well on the micro-bundle scaffold similarly as in the vessels. 3D cell/polymer micro-bundles formed by iVPCs and micro-scaffolds were transplanted into the ischemic myocardium in a rat model of myocardial infarction (MI) with ligation of the left anterior descending artery. Our in vivo data showed that iVPCs on the micro-bundle scaffold had higher survival, and better retention and engraftment in the myocardium than free iVPCs. iVPCs on the micro-bundles promoted better cardiomyocyte survival than free iVPCs. Moreover, iVPCs and iVPC/polymer micro-bundles treatment improved cardiac function (ejection fraction and fractional shortening, endocardial systolic volume) measured by echocardiography, increased vessel density, and decreased infarction size [endocardial and epicardial infarct (scar) length] better than untreated controls at 8 weeks after MI. We conclude that iVPCs grown on a polymer micro-bundle scaffold are new promising approach for cell-based therapy designed for cardiovascular regeneration in ischemic heart disease.

Centriolar SAS-7 acts upstream of SPD-2 to regulate centriole assembly and pericentriolar material formation

The centriole/basal body is a eukaryotic organelle that plays essential roles in cell division and signaling. Among five known core centriole proteins, SPD-2/Cep192 is the first recruited to the site of daughter centriole formation and regulates the centriolar localization of the other components in C. elegans and in humans. However, the molecular basis for SPD-2 centriolar localization remains unknown. Here, we describe a new centriole component, the coiled-coil protein SAS-7, as a regulator of centriole duplication, assembly and elongation. Intriguingly, our genetic data suggest that SAS-7 is required for daughter centrioles to become competent for duplication, and for mother centrioles to maintain this competence. We also show that SAS-7 binds SPD-2 and regulates SPD-2 centriolar recruitment, while SAS-7 centriolar localization is SPD-2-independent. Furthermore, pericentriolar material (PCM) formation is abnormal in sas-7 mutants, and the PCM-dependent induction of cell polarity that defines the anterior-posterior body axis frequently fails. We conclude that SAS-7 functions at the earliest step in centriole duplication yet identified and plays important roles in the orchestration of centriole and PCM assembly.

DOI:http://dx.doi.org/10.7554/eLife.20353.001

Requisite Role of Kv1.5 Channels in Coronary Metabolic Dilation

RATIONALE

In the working heart, coronary blood flow is linked to the production of metabolites, which modulate tone of smooth muscle in a redox-dependent manner. Voltage-gated potassium channels (Kv), which play a role in controlling membrane potential in vascular smooth muscle, have certain members that are redox-sensitive.

OBJECTIVE

To determine the role of redox-sensitive Kv1.5 channels in coronary metabolic flow regulation.

METHODS AND RESULTS

In mice (wild-type [WT], Kv1.5 null [Kv1.5(-/-)], and Kv1.5(-/-) and WT with inducible, smooth muscle-specific expression of Kv1.5 channels), we measured mean arterial pressure, myocardial blood flow, myocardial tissue oxygen tension, and ejection fraction before and after inducing cardiac stress with norepinephrine. Cardiac work was estimated as the product of mean arterial pressure and heart rate. Isolated arteries were studied to establish whether genetic alterations modified vascular reactivity. Despite higher levels of cardiac work in the Kv1.5(-/-) mice (versus WT mice at baseline and all doses of norepinephrine), myocardial blood flow was lower in Kv1.5(-/-) mice than in WT mice. At high levels of cardiac work, tissue oxygen tension dropped significantly along with ejection fraction. Expression of Kv1.5 channels in smooth muscle in the null background rescued this phenotype of impaired metabolic dilation. In isolated vessels from Kv1.5(-/-) mice, relaxation to H2O2 was impaired, but responses to adenosine and acetylcholine were normal compared with those from WT mice.

CONCLUSIONS

Kv1.5 channels in vascular smooth muscle play a critical role in coupling myocardial blood flow to cardiac metabolism. Absence of these channels disassociates metabolism from flow, resulting in cardiac pump dysfunction and tissue hypoxia.

Mitochondrial oxidative stress corrupts coronary collateral growth by activating adenosine monophosphate activated kinase-α signaling

OBJECTIVE

Our goal was to determine the mechanism by which mitochondrial oxidative stress impairs collateral growth in the heart.

APPROACH AND RESULTS

Rats were treated with rotenone (mitochondrial complex I inhibitor that increases reactive oxygen species production) or sham-treated with vehicle and subjected to repetitive ischemia protocol for 10 days to induce coronary collateral growth. In control rats, repetitive ischemia increased flow to the collateral-dependent zone; however, rotenone treatment prevented this increase suggesting that mitochondrial oxidative stress compromises coronary collateral growth. In addition, rotenone also attenuated mitochondrial complex I activity and led to excessive mitochondrial aggregation. To further understand the mechanistic pathway(s) involved, human coronary artery endothelial cells were treated with 50 ng/mL vascular endothelial growth factor, 1 µmol/L rotenone, and rotenone/vascular endothelial growth factor for 48 hours. Vascular endothelial growth factor induced robust tube formation; however, rotenone completely inhibited this effect (P<0.05 rotenone versus vascular endothelial growth factor treatment). Inhibition of tube formation by rotenone was also associated with significant increase in mitochondrial superoxide generation. Immunoblot analyses of human coronary artery endothelial cells with rotenone treatment showed significant activation of adenosine monophosphate activated kinase (AMPK)-α and inhibition of mammalian target of rapamycin and p70 ribosomal S6 kinase. Activation of AMPK-α suggested impairments in energy production, which was reflected by decrease in O2 consumption and bioenergetic reserve capacity of cultured cells. Knockdown of AMPK-α (siRNA) also preserved tube formation during rotenone, suggesting the negative effects were mediated by the activation of AMPK-α. Conversely, expression of a constitutively active AMPK-α blocked tube formation.

CONCLUSIONS

We conclude that activation of AMPK-α during mitochondrial oxidative stress inhibits mammalian target of rapamycin signaling, which impairs phenotypic switching necessary for the growth of blood vessels.

Induction of vascular progenitor cells from endothelial cells stimulates coronary collateral growth

RATIONALE

A well-developed coronary collateral circulation improves the morbidity and mortality of patients following an acute coronary occlusion. Although regenerative medicine has great potential in stimulating vascular growth in the heart, to date there have been mixed results, and the ideal cell type for this therapy has not been resolved.

OBJECTIVE

To generate induced vascular progenitor cells (iVPCs) from endothelial cells, which can differentiate into vascular smooth muscle cells (VSMCs) or endothelial cells (ECs), and test their capability to stimulate coronary collateral growth.

METHODS AND RESULTS

We reprogrammed rat ECs with the transcription factors Oct4, Klf4, Sox2, and c-Myc. A population of reprogrammed cells was derived that expressed pluripotent markers Oct4, SSEA-1, Rex1, and AP and hemangioblast markers CD133, Flk1, and c-kit. These cells were designated iVPCs because they remained committed to vascular lineage and could differentiate into vascular ECs and VSMCs in vitro. The iVPCs demonstrated better in vitro angiogenic potential (tube network on 2-dimensional culture, tube formation in growth factor reduced Matrigel) than native ECs. The risk of teratoma formation in iVPCs is also reduced in comparison with fully reprogrammed induced pluripotent stem cells (iPSCs). When iVPCs were implanted into myocardium, they engrafted into blood vessels and increased coronary collateral flow (microspheres) and improved cardiac function (echocardiography) better than iPSCs, mesenchymal stem cells, native ECs, and sham treatments.

CONCLUSIONS

We conclude that iVPCs, generated by partially reprogramming ECs, are an ideal cell type for cell-based therapy designed to stimulate coronary collateral growth.