Macro advances in microRNAs and myocardial regeneration

Development of a potency assay for CD34+ cell-based therapy

We have previously shown that intracardiac delivery of autologous CD34+ cells after acute myocardial infarction (AMI) is safe and leads to long term improvement. We are now conducting a multicenter, randomized, controlled Phase I/IIb study in post-AMI to investigate the safety and efficacy of intramyocardial injection of expanded autologous CD34+ cells (ProtheraCytes) (NCT02669810). Here, we conducted a series of in vitro studies characterizing the growth factor secretion, exosome secretion, gene expression, cell surface markers, differentiation potential, and angiogenic potential of ProtheraCytes clinical batches to develop a potency assay. We show that ProtheraCytes secrete vascular endothelial growth factor (VEGF) and its concentration is significantly correlated with the number of CD34+ cells obtained after expansion. ProtheraCytes also secrete exosomes containing proangiogenic miRNAs (126, 130a, 378, 26a), antiapoptotic miRNAs (21 and 146a), antifibrotic miRNAs (133a, 24, 29b, 132), and miRNAs promoting myocardial regeneration (199a and 590). We also show that ProtheraCytes have in vitro angiogenic activity, express surface markers of endothelial progenitor cells, and can differentiate in vitro into endothelial cells. After the in vitro characterization of multiple ProtheraCytes clinical batches, we established that measuring the concentration of VEGF provided the most practical, reliable, and consistent potency assay.

Cardiac miR-19a/19b was induced and hijacked by CVB3 to facilitate virus replication via targeting viral genomic RdRp-encoding region

Coxsackievirus B3 (CVB3) is one of the major pathogens of viral myocarditis, lacking specific anti-virus therapeutic options. Increasing evidence has shown an important involvement of the miR-17-92 cluster both in virus infection and cardiovascular development and diseases, while its role in CVB3-induced viral myocarditis remains unclear. In this study, we found that miR-19a and miR-19b were significantly up-regulated in heart tissues of CVB3-infected mice and exerted a significant facilitatory impact on CVB3 biosynthesis and replication, with a more pronounced effect observed in miR-19b, by targeting the encoding region of viral RNA-dependent RNA polymerase 3D (RdRp, 3Dpol) to increase viral genomic RNA stability. The virus-promoting effects were nullified by the synonymous mutations in the viral 3Dpol-encoding region, which corresponded to the seed sequence shared by miR-19a and miR-19b. In parallel, treatment with miR-19b antagomir not only resulted in a noteworthy suppression of CVB3 replication and infection in infected cells, but also demonstrated a significant reduction in the cardiac viral load of CVB3-infected mice, resulting in a considerable alleviation of myocarditis. Collectively, our study showed that CVB3-induced cardiac miR-19a/19b contributed to viral myocarditis via facilitating virus biosynthesis and replication, and targeting miR-19a/19b might represent a novel therapeutic target for CVB3-induced viral myocarditis.

Targeting cardiomyocyte proliferation as a key approach of promoting heart repair after injury

Cardiovascular diseases such as myocardial infarction (MI) is a major contributor to human mortality and morbidity. The mammalian adult heart almost loses its plasticity to appreciably regenerate new cardiomyocytes after injuries, such as MI and heart failure. The neonatal heart exhibits robust proliferative capacity when exposed to varying forms of myocardial damage. The ability of the neonatal heart to repair the injury and prevent pathological left ventricular remodeling leads to preserved or improved cardiac function. Therefore, promoting cardiomyocyte proliferation after injuries to reinitiate the process of cardiomyocyte regeneration, and suppress heart failure and other serious cardiovascular problems have become the primary goal of many researchers. Here, we review recent studies in this field and summarize the factors that act upon the proliferation of cardiomyocytes and cardiac repair after injury and discuss the new possibilities for potential clinical treatment strategies for cardiovascular diseases.

Exercise-Induced Adult Cardiomyocyte Proliferation in Mammals

Loss of cardiomyocytes is a vital manifestation and predisposing factor of many cardiovascular diseases and will eventually lead to heart failure (HF). On the other hand, adult mammalian cardiomyocytes have a very limited regenerative capacity and cannot achieve self-repair of the myocardium after injury. Therefore, it is necessary to promote regeneration and repair of the myocardium through effective intervention means. Exercise plays an important role in the prevention and rehabilitation of cardiovascular diseases. Exercise can improve ischemia-reperfusion injury, reduce the size of the infarcted area, and improve the quality of life of patients. In addition, exercise has also been shown to be able to elevate the proliferative potential of adult cardiomyocytes and promote myocardial regeneration. Studies have shown that newly formed cardiomyocytes in adult mammalian hearts are mainly derived from pre-existing cardiomyocytes. By regulating various cytokines, transcription factors, and microRNAs (miRNAs), exercise can promote the dedifferentiation and proliferation of pre-existing cardiomyocytes to form new cardiomyocytes. Therefore, this paper focuses on the recent research progress of exercise-induced adult cardiomyocyte proliferation and explores its potential molecular mechanism.

Adjuvant breast cancer treatments cardiotoxicity and modern methods of detection and prevention of cardiac complications

The most common cancer diagnosis in female population is breast cancer, which affects every year about 2.0 million women worldwide. In recent years, significant progress has been made in oncological therapy, in systemic treatment, and in radiotherapy of breast cancer. Unfortunately, the improvement in the effectiveness of oncological treatment and prolonging patients' life span is associated with more frequent occurrence of organ complications, which are side effects of this treatment. Current recommendations suggest a periodic monitoring of the cardiovascular system in course of oncological treatment. The monitoring includes the assessment of occurrence of risk factors for cardiovascular diseases in combination with the evaluation of the left ventricular systolic function using echocardiography and electrocardiography as well as with the analysis of the concentration of cardiac biomarkers. The aim of this review was critical assessment of the breast cancer therapy cardiotoxicity and the analysis of methods its detections. The new cardio-specific biomarkers in serum, the development of modern imaging techniques (Global Longitudinal Strain and Three-Dimensional Left Ventricular Ejection Fraction) and genotyping, and especially their combined use, may become a useful tool for identifying patients at risk of developing cardiotoxicity, who require further cardiovascular monitoring or cardioprotective therapy.

Integrated regulatory network based on lncRNA-miRNA-mRNA-TF reveals key genes and sub-networks associated with dilated cardiomyopathy

Dilated Cardiomyopathy (DCM) is a multifactorial condition often leading to heart failure in many clinical cases. Due to the high number of DCMincidence reported as familial, a gene level network based study was conducted utilizing high throughput next generation sequencing data. We exploited the exome and transcriptome sequencing data in NCBI-SRA database to construct a high confidence scale-free regulatory network consisting of lncRNA, miRNA, mRNA and Transcription Factors (TFs). Analysis of RNA-Seq data revealed 477 differentially expressed coding transcripts and 77 lncRNAs. 268 miRNAs regulated either lncRNAs or mRNAs. Out of the 477 coding transcripts that are deregulated, 82 were TFs. We identified three major hub nodeslncRNA (XIST), miRNA (hsa-miR-195-5p) and mRNA (NOVA1) from the network. We also found putative disease associations of DCM with diabetes and DCM with hypoventillation syndrome. Five highly connected modules were also identified from the network. The hubs showed significant connectivity with the modules.Through this study we were able to gain insights into the underlying lncRNA-miRNA-mRNA-TF network. From a high throughput dataset we have isolated a handful of probable targets that may be utilized for studying the mechanisms of DCM development and progression to heart failure.

Identification of Novel miRNAs Involved in Cardiac Repair Following Infarction in Fetal and Adolescent Sheep Hearts

Aims

Animal models have been used to show that there are critical molecular mechanisms that can be activated to induce myocardial repair at specific times in development. For example, specific miRNAs are critical for regulating the response to myocardial infarction (MI) and improving the response to injury. Manipulating these miRNAs in small animal models provides beneficial effects post-MI; however it is not known if these miRNAs are regulated similarly in large mammals. Studying a large animal where the timing of heart development in relation to birth is similar to humans may provide insights to better understand the capacity to repair a developing mammalian heart and its application to the adult heart.

Methods

We used a sheep model of MI that included permanent ligation of the left anterior descending (LAD) coronary artery. Surgery was performed on fetuses (at 105 days gestation when all cardiomyocytes are mononucleated and proliferative) and adolescent sheep (at 6 months of age when all cardiomyocytes contribute to heart growth by hypertrophy). A microarray was utilized to determine the expression of known miRNAs within the damaged and undamaged tissue regions in fetal and adolescent hearts after MI.

Results

73 miRNAs were up-regulated and 58 miRNAs were down-regulated significantly within the fetal infarct compared to remote cardiac samples. From adolescent hearts 69 non-redundant miRNAs were up-regulated and 63 miRNAs were down-regulated significantly in the infarct area compared to remote samples. Opposite differential expression profiles of 10 miRNAs within tissue regions (Infarct area, Border zone and Remote area of the left ventricle) occurred between the fetuses and adolescent sheep. These included miR-558 and miR-1538, which when suppressed using LNA anti-miRNAs in cell culture, increased cardiomyoblast proliferation.

Conclusion

There were significant differences in miRNA responses in fetal and adolescent sheep hearts following a MI, suggesting that the modulation of novel miRNA expression may have therapeutic potential, by promoting proliferation or repair in a damaged heart.

The Hippo pathway in the heart: pivotal roles in development, disease, and regeneration

The Hippo-YAP (Yes-associated protein) pathway is an evolutionarily and functionally conserved regulator of organ size and growth with crucial roles in cell proliferation, apoptosis, and differentiation. This pathway has great potential for therapeutic manipulation in different disease states and to promote organ regeneration. In this Review, we summarize findings from the past decade revealing the function and regulation of the Hippo-YAP pathway in cardiac development, growth, homeostasis, disease, and regeneration. In particular, we highlight the roles of the Hippo-YAP pathway in endogenous heart muscle renewal, including the pivotal role of the Hippo-YAP pathway in regulating cardiomyocyte proliferation and differentiation, stress response, and mechanical signalling. The human heart lacks the capacity to self-repair; therefore, the loss of cardiomyocytes after injury such as myocardial infarction can result in heart failure and death. Despite substantial advances in the treatment of heart failure, an enormous unmet clinical need exists for alternative treatment options. Targeting the Hippo-YAP pathway has tremendous potential for developing therapeutic strategies for cardiac repair and regeneration for currently intractable cardiovascular diseases such as heart failure. The lessons learned from cardiac repair and regeneration studies will also bring new insights into the regeneration of other tissues with limited regenerative capacity.

Stimulating Cardiogenesis as a Treatment for Heart Failure

After myocardial injury, cardiomyocyte loss cannot be corrected by using currently available clinical treatments. In recent years, considerable effort has been made to develop cell-based cardiac repair therapies aimed at correcting for this loss. An exciting crop of recent studies reveals that inducing endogenous repair and proliferation of cardiomyocytes may be a viable option for regenerating injured myocardium. Here, we review current heart failure treatments, the state of cardiomyocyte renewal in mammals, and the molecular signals that stimulate cardiomyocyte proliferation. These signals include growth factors, intrinsic signaling pathways, microRNAs, and cell cycle regulators. Animal model cardiac regeneration studies reveal that modulation of exogenous and cell-intrinsic signaling pathways can induce reentry of adult cardiomyocytes into the cell cycle. Using direct myocardial injection, epicardial patch delivery, or systemic administration of growth molecules, these studies show that inducing endogenous cardiomyocytes to self-renew is an exciting and promising therapeutic strategy to treat cardiac injury in humans.

YAP Partially Reprograms Chromatin Accessibility to Directly Induce Adult Cardiogenesis In Vivo

Specialized adult somatic cells, such as cardiomyocytes (CMs), are highly differentiated with poor renewal capacity, an integral reason underlying organ failure in disease and aging. Among the least renewable cells in the human body, CMs renew approximately 1% annually. Consistent with poor CM turnover, heart failure is the leading cause of death. Here, we show that an active version of the Hippo pathway effector YAP, termed YAP5SA, partially reprograms adult mouse CMs to a more fetal and proliferative state. One week after induction, 19% of CMs that enter S-phase do so twice, CM number increases by 40%, and YAP5SA lineage CMs couple to pre-existing CMs. Genomic studies showed that YAP5SA increases chromatin accessibility and expression of fetal genes, partially reprogramming long-lived somatic cells in vivo to a primitive, fetal-like, and proliferative state.

The role of miRNA regulation in fetal cardiomyocytes, cardiac maturation and the risk of heart disease in adults

Myocardial infarction is a primary contributor towards the global burden of cardiovascular disease. Rather than repairing the existing damage of myocardial infarction, current treatments only address the symptoms of the disease and reducing the risk of a secondary infarction. Cardiac regenerative capacity is dependent on cardiomyocyte proliferation, which concludes soon after birth in humans and precocial species such as sheep. Human fetal cardiac tissue has some ability to repair following tissue damage, whereas a fully matured human heart has minimal capacity for cellular regeneration. This is in contrast to neonatal mice and adult zebrafish hearts, which retain the ability to undergo cardiomyocyte proliferation and can regenerate cardiac tissue after birth. In mice and zebrafish models, microRNAs (miRNAs) have been implicated in the regulation of genes involved in cardiac cell cycle progression and regeneration. However, the significance of miRNA regulation in cardiomyocyte proliferation for humans and other large mammals, where the timing of heart development in relation to birth is similar, remains unclear. miRNAs may be valuable targets for therapies that promote cardiac repair after injury. Therefore, elucidating the role of specific miRNAs in large animals, where heart development closely resembles that of humans, remains vitally important for identifying therapeutic targets that may be translated into clinical practice focused on tissue repair.

MicroRNA-199a acts as a potential suppressor of cardiomyocyte autophagy through targeting Hspa5

Autophagy is an adaptive response to cardiomyocytes survival under stress conditions. MicroRNAs (miRNAs, miR) have been described to act as potent modulators of autophagy. To investigate whether and how miR-199a modulated autophagy in vitro, primary cardiomyocytes were treated under starvation to induce autophagy. Results showed that down-regulation of miR-199a was sufficient to activate cardiomyocytes autophagy. MiR-199a suppressed cardiomyocytes autophagy through direct inhibiting heat shock protein family A member 5 (Hspa5). Forced overexpression of Hspa5 recovered the inhibitory effect of miR-199a in autophagy activation. Our results suggested miR-199a as an effective suppressor of starvation-induced cardiomyocytes autophagy and that Hspa5 was a direct target during this process. These results extend the understanding of the role and pathway of miR-199a in cardiomyocytes autophagy, and may introduce a potential therapeutic strategy for the protection of cardiomyocytes in myocardial infarction or ischemic heart disease.

The MicroRNA-199a/214 Cluster Targets E-Cadherin and Claudin-2 and Promotes High Glucose-Induced Peritoneal Fibrosis

Serum response factor (SRF) was found to be involved in the phenotypic transition and fibrosis of the peritoneal membrane during treatment with peritoneal dialysis (PD), but the exact mechanism remains unclear. SRF regulates microRNAs (miRNAs) that contain the SRF-binding consensus (CArG) element in the promoter region. Therefore, we investigated whether the miR-199a/214 gene cluster, which contains a CArG element in its promoter, is directly regulated by SRF. High-glucose (HG) treatment significantly unregulated the expression of the miR-199a-5p/214-3p gene cluster in human peritoneal mesothelial cells (HPMCs). By chromatin immunoprecipitation and reporter assays, we found that SRF binds to the miR-199a-5p/214-3p gene cluster promoter after HG stimulation. In vitro, in HPMCs, silencing of miR-199a-5p or miR-214-3p inhibited the HG-induced phenotypic transition and cell migration but enhanced cell adhesion, whereas ectopic expression of mimic oligonucleotides had the opposite effects. Both miR-199a-5p and miR-214-3p targeted claudin-2 and E-cadherin mRNAs. In a PD rat model, treatment with an SRF inhibitor silenced miR-199a-5p and miR-214-3p and alleviated HG-PD fluid-induced damage and fibrosis. Overall, this study reveals a novel SRF-miR-199a/miR-214-E-cadherin/claudin-2 axis that mediates damage and fibrosis in PD.

Cardiomyocyte proliferation in zebrafish and mammals: lessons for human disease

Cardiomyocytes proliferate profusely during early development and for a brief period after birth in mammals. Within a month after birth, this proliferative capability is dramatically reduced in mammals unlike lower vertebrates where it persists into adult life. The zebrafish, for example, retains the ability to regenerate the apex of the heart following resection by a mechanism predominantly driven by cardiomyocyte proliferation. Differences in proliferative capacity of cardiomyocytes in adulthood between mammals and lower vertebrates are closely liked to ontogenetic or phylogenetic factors. Elucidation of these factors has the potential to provide enormous benefits if they lead to the development of therapeutic strategies that facilitate cardiomyocyte proliferation. In this review, we highlight the differences between Mammalian and Zebrafish cardiomyocytes, which could explain at least in part the different proliferative capacities in these two species. We discuss the advantages of the zebrafish as a model of cardiomyocyte proliferation, particularly at the embryonic stage. We also identify a number of key molecular pathways with potential to reveal key steps in switching cardiomyocytes from a quiescent to a proliferative phenotype.

Diverse impact of xeno-free conditions on biological and regenerative properties of hUC-MSCs and their extracellular vesicles

Growing evidence indicates that intracellular signaling mediated by extracellular vesicles (EVs) released by stem cells plays a considerable role in triggering the regenerative program upon transplantation. EVs from umbilical cord mesenchymal stem cells (UC-MSC-EVs) have been shown to enhance tissue repair in animal models. However, translating such results into clinical practice requires optimized EV collection procedures devoid of animal-originating agents. Thus, in this study, we analyzed the influence of xeno-free expansion media on biological properties of UC-MSCs and UC-MSC-EVs for future applications in cardiac repair in humans. Our results show that proliferation, differentiation, phenotype stability, and cytokine secretion by UC-MSCs vary depending on the type of xeno-free media. Importantly, we found distinct molecular and functional properties of xeno-free UC-MSC-EVs including enhanced cardiomyogenic and angiogenic potential impacting on target cells, which may be explained by elevated concentration of several pro-cardiogenic and pro-angiogenic microRNA (miRNAs) present in the EVs. Our data also suggest predominantly low immunogenic capacity of certain xeno-free UC-MSC-EVs reflected by their inhibitory effect on proliferation of immune cells in vitro. Summarizing, conscious selection of cell culture conditions is required to harvest UC-MSC-EVs with the optimal desired properties including enhanced cardiac and angiogenic capacity, suitable for tissue regeneration.

KEY MESSAGE

Type of xeno-free media influences biological properties of UC-MSCs in vitro. Certain xeno-free media promote proliferation and differentiation ability of UC-MSCs. EVs collected from xeno-free cultures of UC-MSCs are biologically active. Xeno-free UC-MSC-EVs enhance cardiac and angiogenic potential of target cells. Type of xeno-free media determines immunomodulatory effects mediated by UC-MSC-EVs.

The Role of microRNAs in Animal Cell Reprogramming

Our concept of cell reprogramming and cell plasticity has evolved since John Gurdon transferred the nucleus of a completely differentiated cell into an enucleated Xenopus laevis egg, thereby generating embryos that developed into tadpoles. More recently, induced expression of transcription factors, oct4, sox2, klf4, and c-myc has evidenced the plasticity of the genome to change the expression program and cell phenotype by driving differentiated cells to the pluripotent state. Beyond these milestone achievements, research in artificial cell reprogramming has been focused on other molecules that are different than transcription factors. Among the candidate molecules, microRNAs (miRNAs) stand out due to their potential to control the levels of proteins that are involved in cellular processes such as self-renewal, proliferation, and differentiation. Here, we review the role of miRNAs in the maintenance and differentiation of mesenchymal stem cells, epimorphic regeneration, and somatic cell reprogramming to induced pluripotent stem cells.

miR-153 regulates apoptosis and autophagy of cardiomyocytes by targeting Mcl-1

MicroRNAs (miRs) are a class of important regulators, which are involved in the regulation of apoptosis. Oxidative stress‑induced apoptosis is the predominant factor accounting for cardiac ischemia‑reperfusion injury. miR‑153 has been previously shown to have an antitumor effect in cancer. However, whether miR‑153 is involved in oxidative stress‑induced apoptosis in the heart remains to be elucidated. To this end, the present study used reverse transcription‑quantitative polymerase chain reaction to detect miR-153 levels upon oxidative stress, and evaluated apoptosis, autophagy and expression of critical genes by western blotting. A luciferase assay was also used to confirm the potential target gene. In the present study, it was found that the expression of miR‑153 was significantly increased upon H2O2 stimulation, and the inhibition of endogenous miR‑153 decreased apoptosis. To further identify the mechanism underlying the pro‑apoptotic effect of miR‑153, the present study analyzed the 3'untranslated region of myeloid cell leukemia‑1 (Mcl‑1), and found that Mcl‑1 was potentially targeted by miR‑153. The forced expression of miR‑153 inhibited the expression of Mcl‑1 and luciferase activity, which was reversed by its antisense inhibitor. Furthermore, it was shown that the inhibition of miR‑153 induced autophagy during oxidative stress, and that its effects of autophagy induction and apoptosis inhibition were efficiently abrogated by Mcl‑1 small interfering RNA. In conclusion, the results of the present study elucidated a novel mechanism by which miR‑153 regulates the survival of cardimyocytes during oxidative stress through the modulation of apoptosis and autophagy. These effects may be mediated directly by targeting Mcl‑1. These finding revealed the potential clinical value of miR‑153 in the treatment of cardiovascular disease.

Inhibition of miR-15a Promotes BDNF Expression and Rescues Dendritic Maturation Deficits in MeCP2-Deficient Neurons

In both the embryonic and adult brain, a critical step in neurogenesis is neuronal maturation. Deficiency of MeCP2 leads to Rett syndrome, a severe neurodevelopmental disorder. We have previously shown that MeCP2 plays critical roles in the maturation step of new neurons during neurogenesis. MeCP2 is known to regulate the expression of brain-derived neurotrophic factor (BDNF), a potent neurotrophic factor for neuronal maturation. Nevertheless, how MeCP2 regulates BDNF expression and how MeCP2 deficiency leads to reduced BDNF expression remain unclear. Here, we show that MeCP2 regulates the expression of a microRNA, miR-15a. We find that miR-15a plays a significant role in the regulation of neuronal maturation. Overexpression of miR-15a inhibits dendritic morphogenesis in immature neurons. Conversely, a reduction in miR-15a has the opposite effect. We further show that miR-15a regulates expression levels of BDNF, and exogenous BDNF could partially rescue the neuronal maturation deficits resulting from miR-15a overexpression. Finally, inhibition of miR-15a could rescue neuronal maturation deficits in MeCP2-deficient adult-born new neurons. These results demonstrate a novel role for miR-15a in neuronal development and provide a missing link in the regulation of BDNF by MeCP2.

The role of microRNAs in cardiac development and regenerative capacity

The mammalian heart has long been considered to be a postmitotic organ. It was thought that, in the postnatal period, the heart underwent a transition from hyperplasic growth (more cells) to hypertrophic growth (larger cells) due to the conversion of cardiomyocytes from a proliferative state to one of terminal differentiation. This hypothesis was gradually disproven, as data were published showing that the myocardium is a more dynamic tissue in which cardiomyocyte karyokinesis and cytokinesis produce new cells, leading to the hyperplasic regeneration of some of the muscle mass lost in various pathological processes. microRNAs have been shown to be critical regulators of cardiomyocyte differentiation and proliferation and may offer the novel opportunity of regenerative hyperplasic therapy. Here we summarize the relevant processes and recent progress regarding the functions of specific microRNAs in cardiac development and regeneration.

MicroRNA-590 Inhibits Lipoprotein Lipase Expression and Prevents Atherosclerosis in apoE Knockout Mice

Recent studies have suggested that miR-590 may play critical roles in cardiovascular disease. This study was designed to determine the effects of miR-590 on lipoprotein lipase (LPL) expression and development of atherosclerosis in apolipoprotein E knockout (apoE^−/−) mice and explore the potential mechanisms. En face analysis of the whole aorta revealed that miR-590 significantly decreased aortic atherosclerotic plaque size and lipid content in apoE^−/− mice. Double immunofluorescence staining in cross-sections of the proximal aorta showed that miR-590 agomir reduced CD68 and LPL expression in macrophages in atherosclerotic lesions. MiR-590 agomir down-regulated LPL mRNA and protein expression as analyzed by RT-qPCR and western blotting analyses, respectively. Consistently, miR-590 decreased the expression of CD36 and scavenger receptor A1 (SRA1) mRNA and protein. High-performance liquid chromatography (HPLC)analysis confirmed that treatment with miR-590 agomir reduced lipid levels either in plasma orinabdominal cavity macrophages of apoE^−/− mice. ELISA analysis showed that miR-590 agomir decreased plasma levels of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), monocyte chemotactic protein-1 (MCP-1), interleukin-1β (IL-1β)and interleukin-6 (IL-6). In contrast, treatment with miR-590 antagomir prevented or reversed these effects. Taken together, these results reveal a novel mechanism of miR-590 effects, and may provide new insights into the development of strategies for attenuating lipid accumulation and pro-inflammatory cytokine secretion.

MicroRNA Clusters in the Adult Mouse Heart: Age-Associated Changes

The microRNAs and microRNA clusters have been implicated in normal cardiac development and also disease, including cardiac hypertrophy, cardiomyopathy, heart failure, and arrhythmias. Since a microRNA cluster has from two to dozens of microRNAs, the expression of a microRNA cluster could have a substantial impact on its target genes. In the present study, the configuration and distribution of microRNA clusters in the mouse genome were examined at various inter-microRNA distances. Three important microRNA clusters that are significantly impacted during adult cardiac aging, the miR-17-92, miR-106a-363, and miR-106b-25, were also examined in terms of their genomic location, RNA transcript character, sequence homology, and their relationship with the corresponding microRNA families. Multiple microRNAs derived from the three clusters potentially target various protein components of the cdc42-SRF signaling pathway, which regulates cytoskeleton dynamics associated with cardiac structure and function. The data indicate that aging impacted the expression of both guide and passenger strands of the microRNA clusters; nutrient stress also affected the expression of the three microRNA clusters. The miR-17-92, miR-106a-363, and miR-106b-25 clusters are likely to impact the Cdc42-SRF signaling pathway and thereby affect cardiac morphology and function during pathological conditions and the aging process.

Small RNA: from development to regeneration

A microRNA cluster that targets the Hippo pathway can reintroduce terminally differentiated cardiomyocytes into the cell cycle, promoting heart regeneration (Tian et al., this issue).

In vivo modulation and quantification of microRNAs during axolotl tail regeneration

The ability to regenerate diseased, injured, or missing complex tissue is widespread throughout lower vertebrates and invertebrates; however, our knowledge of the molecular mechanisms that regulate this amazing ability is still in its infancy. Many recent papers have shown important roles for microRNAs in regulating regeneration in a number of species. The ability to detect and quantify miRNA expression fluctuations at a single cell level in vivo in different cell types during processes like regeneration is very informative. In this chapter, we describe how to use a dual-fluorescent green fluorescent protein (GFP)-reporter/monomeric red fluorescent protein (mRFP)-sensor (DFRS) plasmid to quantitate the dynamics of specific miRNAs over time following miRNA mimic injection as well as during regeneration. In this bicistronic vector, the mRFP allows for verification of miRNA expression, while the GFP functions as an internal control to normalize miRNA expression and thus obtain quantitative results. In addition, we demonstrate how this technique revealed dynamic miR-23a expression and function during tail regeneration.