MiRiad Roles for MicroRNAs in Cardiac Development and Regeneration

Intracellular metabolic reprogramming mediated by micro-RNAs in differentiating and proliferating cells under non-diseased conditions

Intracellular metabolic reprogramming is a critical process the cells carry out to increase biomass, energy fulfillment and genome replication. Cells reprogram their demands from internal catabolic or anabolic activities in coordination with multiple genes and microRNAs which further control the critical processes of differentiation and proliferation. The microRNAs reprogram the metabolism involving mitochondria, the nucleus and the biochemical processes utilizing glucose, amino acids, lipids, and nucleic acids resulting in ATP production. The processes of glycolysis, tricarboxylic acid cycle, or oxidative phosphorylation are also mediated by micro-RNAs maintaining cells and organs in a non-diseased state. Several reports have shown practical applications of metabolic reprogramming for clinical utility to assess various diseases, mostly studying cancer and immune-related disorders. Cells under diseased conditions utilize glycolysis for abnormal growth or proliferation, respectively, affecting mitochondrial paucity and biogenesis. Similar metabolic processes also affect gene expressions and transcriptional regulation for carrying out biochemical reactions. Metabolic reprogramming is equally vital for regulating cell environment to maintain organs and tissues in non-diseased states. This review offers in depth insights and analysis of how miRNAs regulate metabolic reprogramming in four major types of cells undergoing differentiation and proliferation, i.e., immune cells, neuronal cells, skeletal satellite cells, and cardiomyocytes under a non-diseased state. Further, the work systematically summarizes and elaborates regulation of genetic switches by microRNAs through predominantly through cellular reprogramming and metabolic processes for the first time. The observations will lead to a better understanding of disease initiation during the differentiation and proliferation stages of cells, as well as fresh approaches to studying clinical onset of linked metabolic diseases targeting metabolic processes.

Differential expression of novel MicroRNAs from developing fetal heart of Gallus gallus domesticus implies a role in cardiac development

Heart development is a complex process regulated by multi-layered genetic as well epigenetic regulators many of which are still unknown. Besides their critical role during cardiac development, these molecular regulators emerge as key modulators of cardiovascular pathologies, where fetal cardiac genes' re-expression is witnessed. MicroRNAs have recently emerged as a crucial part of signalling cascade in both development and diseases. We aimed to identify, validate, and perform functional annotation of putative novel miRNAs using chicken as a cardiac development model system. Novel miRNAs were obtained through deep sequencing of small RNAs extracted from chicken embryonic cardiac tissue of different developmental stages. After filtering out real pre-miRNAs, their expression analysis, potential target gene's prediction and functional annotations were performed. Expression analysis revealed that miRNAs were differentially expressed during different developmental stages of chicken heart. The expression of selected putative novel miRNAs was further validated by real-time PCR. Our analysis indicated the presence of novel cardiac miRNAs that might be regulating critical cardiac development events such as cardiac cell growth, differentiation, cardiac action potential generation and signal transduction.

Possible Muscle Repair in the Human Cardiovascular System

The regenerative potential of tissues and organs could promote survival, extended lifespan and healthy life in multicellular organisms. Niches of adult stemness are widely distributed and lead to the anatomical and functional regeneration of the damaged organ. Conversely, muscular regeneration in mammals, and humans in particular, is very limited and not a single piece of muscle can fully regrow after a severe injury. Therefore, muscle repair after myocardial infarction is still a chimera. Recently, it has been recognized that epigenetics could play a role in tissue regrowth since it guarantees the maintenance of cellular identity in differentiated cells and, therefore, the stability of organs and tissues. The removal of these locks can shift a specific cell identity back to the stem-like one. Given the gradual loss of tissue renewal potential in the course of evolution, in the last few years many different attempts to retrieve such potential by means of cell therapy approaches have been performed in experimental models. Here we review pathways and mechanisms involved in the in vivo repair of cardiovascular muscle tissues in humans. Moreover, we address the ongoing research on mammalian cardiac muscle repair based on adult stem cell transplantation and pro-regenerative factor delivery. This latter issue, involving genetic manipulations of adult cells, paves the way for developing possible therapeutic strategies in the field of cardiovascular muscle repair.

Differential miRNA expression analysis during late stage terminal hindgut development in fetal rats

BACKGROUND

Terminal hindgut deformity is the leading digestive tract malformation, however, the etiology and pathogenesis remained unknown. To date, gene expression abnormalities were considered the primary cause of these diseases. miRNAs have been found to play an important role in regulating the expression of genes.

METHODS

A total of 24 pregnant rats were randomly divided into two groups. The experimental group (n=12) received 1% ethylenethiourea (125mg/kg) by gavage on gestational day 11, while the control group (n=12) received the same volume of distilled water. From each group, fetal rats were obtained by cesarean section on gestational day 16. For the extraction of total RNA, 1 cm rectum samples were obtained from four fetal rats that had similar weights. Chip hybridization was conducted after poly(A) and biotin were added to the RNA samples, and this was followed by washing, dyeing, and scanning of the chip. Differences identified in the miRNA expression profiles and the target gene analysis results were further analyzed to identify potential regulators of terminal hindgut development.

RESULTS

Compared with the control group, 111 miRNAs expressed in the terminal hindgut of the experimental group were up-regulated on gestational day 16, while 117 miRNAs were down-regulated. The ten miRNAs with the greatest differential expression profiles between the experimental and control samples were selected for target gene prediction, pathway analysis, and gene ontology analysis. A subset of these miRNAs was found to be closely related to rat fetus terminal hindgut growth and development. In addition, target gene analysis showed that miR-193 may have an important role in regulating a key gene in anorectal development, Hoxd13. This role was confirmed in a dual luciferase reporter assay when miR-193 was able to inhibit expression of a reporter gene under the control of the 3' untranslated region of the Hoxd13 gene in the human embryonic kidney cell line, 293T. Real-time PCR and Western blotting experiments further showed that the expression of Hoxd13 was significantly lower when miR-193 was highly expressed in rat intestinal epithelial cells. The differences in both sets of experiments were statistically significant compared with the negative control group (P<0.05).

CONCLUSION

These data support an important regulatory role for miRNAs in the expression of target genes during terminal hindgut development in fetal rats. In particular, miR-193-mediated inhibition of Hoxd13 was found to be significant in rat intestinal epithelial cells.

miR-21 increases c-kit+ cardiac stem cell proliferation in vitro through PTEN/PI3K/Akt signaling

The low survival rate of cardiac stem cells (CSCs) in the ischemic myocardium is one of the obstacles in ischemic cardiomyopathy cell therapy. The MicroRNA (miR)-21 and one of its target protein, the tensin homolog deleted on chromosome ten (PTEN), contributes to the proliferation of many kinds of tissues and cell types. It is reported that miR-21 promotes proliferation through PTEN/PI3K/Akt pathway, but its effects on c-kit⁺ CSC remain unclear. The authors hypothesized that miR-21 promotes the proliferation in c-kit ⁺ CSC, and evaluated the involvement of PTEN/PI3K/Akt pathway in vitro. miR-21 up-regulation with miR-21 efficiently mimics accelerated cell viability and proliferation in c-kit ⁺ CSC, which was evidenced by the CCK-8, EdU and cell cycle analyses. In addition, the over-expression of miR-21 in c-kit ⁺ CSCs notably down-regulated the protein expression of PTEN although the mRNA level of PTEN showed little change. Gain-of-function of miR-21 also increased the phosphor-Akt (p-Akt) level. Phen, the selective inhibitor of PTEN, reproduced the pro-proliferation effects of miR-21, while PI3K inhibitor, LY294002, totally attenuated the pro-survival effect of miR-21. These results indicate that miR-21 is efficient in promoting proliferation in c-kit⁺ CSCs, which is contributed by the PTEN/PI3K/Akt pathway. miR-21 holds the potential to facilitate CSC therapy in ischemic myocardium.

The crucial role and regulations of miRNAs in zebrafish development

To comprehend the events during developmental biology, fundamental knowledge about the basic machinery of regulation is a prerequisite. MicroRNA (miRNAs) act as regulators in most of the biological processes and recently, it has been concluded that miRNAs can act as modulatory factors even during developmental process from lower to higher animal. Zebrafish, because of its favorable attributes like tiny size, transparent embryo, and rapid external embryonic development, has gained a preferable status among all other available experimental animal models. Currently, zebrafish is being utilized for experimental studies related to stem cells, regenerative molecular medicine as well drug discovery. Therefore, it is important to understand precisely about the various miRNAs that controls developmental biology of this vertebrate model. In here, we have discussed about the miRNA-controlled zebrafish developmental stages with a special emphasis on different miRNA families such as miR-430, miR-200, and miR-133. Moreover, we have also reviewed the role of various miRNAs during embryonic and vascular development stages of zebrafish. In addition, efforts have been made to summarize the involvement of miRNAs in the development of different body parts such as the brain, eye, heart, muscle, and fin, etc. In each section, we have tried to fulfill the gaps of zebrafish developmental biology with the help of available knowledge of miRNA research. We hope that precise knowledge about the miRNA-regulated developmental stages of zebrafish may further help the researchers to efficiently utilize this vertebrate model for experimental purpose.

Pigmy MicroRNA: surveillance cops in Therapies kingdom

MicroRNAs (miRNAs) are well preserved in every animal. These pigmy sized non-coding RNAs (21-23 nt), scattered in genome, are responsible for micromanaging the versatile gene regulations. Involvement of miRNAs was surveillance cops in all human diseases including cardiovascular defects, tumor formation, reproductive pathways, and neurological and autoimmune disorders. The effective functional role of miRNA can be reduced by chemical entities of antisense oligonucleotides and versatile small molecules that support the views of novel therapy of different human diseases. In this study, we have updated our current understanding for designing and synthesizing miRNA-controlling therapeutic chemicals. We have also proposed various in-vivo delivery strategies and their ongoing challenges to combat the incorporation hurdles in live cells and animals. Lastly, we have demonstrated the current progress of miRNA modulation in the treatment of different human diseases that provides an alternative approach of gene therapy.

miR-21 Reduces Hydrogen Peroxide-Induced Apoptosis in c-kit+ Cardiac Stem Cells In Vitro through PTEN/PI3K/Akt Signaling

The low survival rate of cardiac stem cells (CSCs) in the infarcted myocardium hampers cell therapy for ischemic cardiomyopathy. MicroRNA-21 (miR-21) and one of its target proteins, PTEN, contribute to the survival and proliferation of many cell types, but their prosurvival effects in c-kit⁺ CSC remain unclear. Thus, we hypothesized that miR-21 reduces hydrogen peroxide- (H₂O₂-) induced apoptosis in c-kit⁺ CSC and estimated the contribution of PTEN/PI3K/Akt signaling to this oxidative circumstance. miR-21 mimics efficiently reduced H₂O₂-induced apoptosis in c-kit⁺ CSC, as evidenced by the downregulation of the proapoptosis proteins caspase-3 and Bax and upregulation of the antiapoptotic Bcl-2. In addition, the gain of function of miR-21 in c-kit⁺ CSC downregulated the protein level of PTEN although its mRNA level changed slightly; in the meantime, miR-21 overexpression also increased phospho-Akt (p-Akt). The antiapoptotic effects of miR-21 were comparable with Phen (bpV), the selective inhibitor of PTEN, while miR-21 inhibitor or PI3K's inhibitor LY294002 efficiently attenuated the antiapoptotic effect of miR-21. Taken together, these results indicate that the anti-H₂O₂-induced apoptosis effect of miR-21 in c-kit⁺ CSC is contributed by PTEN/PI3K/Akt signaling. miR-21 could be a potential molecule to facilitate the c-kit⁺ CSC therapy in ischemic myocardium.

The two faces of miR-29

Diabetes mellitus is a metabolic homeostasis disease that contributes to additional comorbidities such as cardiovascular disease (CVD) and cancer. It has a long undiagnosed latent period during which there can be irreparable damage to the pancreas and cardiovascular tissues. Recent studies have highlighted the roles of several microRNAs in CVD. Determining the microRNAs that link diabetes mellitus and CVD is an important topic to be explored. In the present review, we discuss the microRNAs that contribute to the progression of diabetes mellitus and CVD and focus on the miR-29 family microRNAs whose expression is upregulated by hyperglycemia and proinflammatory cytokines, the hallmarks of diabetes mellitus. Upregulation of miR-29 expression is a key factor in the loss of pancreatic β cells and development of the first stage of type 1 diabetes mellitus (T1DM). Additionally, miR-29-mediated suppression of myeloid cell leukemia 1 (MCL-1), an important prosurvival protein, underlies Marfan's syndrome, abdominal aortic aneurysm, and diabetes mellitus-associated cardiomyocyte disorganization. Suppression of miR-29 expression and subsequent increase in the prosurvival MCL-1, however, promotes tumor development. Therefore, miR-29 mimics that suppress MCL-1 are hailed as tumor suppressors. The critical question is whether an increase in miR-29 levels is well tolerated in conditions of comorbidities in which insulin resistance is an underlying disease. In light of increasing awareness of the interconnection of diabetes mellitus, CVD, and cancer, it is of utmost importance to understand the mechanism of action of current treatment options on all of the comorbidities and careful evaluation of cardiovascular toxicity must accompany any treatment paradigm that increases miR-29 levels.

MiR218 Modulates Wnt Signaling in Mouse Cardiac Stem Cells by Promoting Proliferation and Inhibiting Differentiation through a Positive Feedback Loop

MiRNA expression was determined in both proliferating and differentiated cardiac stem cells (CSCs) through a comprehensive miRNA microarray analysis. We selected miR218 for functional follow-up studies to examine its significance in CSCs. First, we observed that the expression of miR218 was altered in CSCs during differentiation into cardiomyocytes, and transfection of an miR218 mimic or miR218 inhibitor affected the myocardial differentiation of CSCs. Furthermore, we observed that a negative regulator of Wnt signaling, sFRP2, was a direct target of miR218, and the protein levels of sFRP2 were increased in cells transfected with the synthetic miR218 inhibitor. In contrast, transfection with the miR218 mimic decreased the expression of sFRP2 and potentiated Wnt signaling. The subsequent down-regulation of sFRP2 by shRNA potentiated Wnt signaling, contributing to a gene expression program that is important for CSC proliferation and cardiac differentiation. Specifically, canonical Wnt signaling induced miR218 transcription. Thus, miR218 and Wnt signaling were coupled through a feed-forward positive feedback loop, forming a biological regulatory circuit. Together, these results provide the first evidence that miR218 plays an important role in CSC proliferation and differentiation through the canonical Wnt signaling pathway.

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.

[Epigenetics in atherosclerosis]

The association studies based on candidate genes carried on for decades have helped in visualizing the influence of the genetic component in complex diseases such as atherosclerosis, also showing the interaction between different genes and environmental factors. Even with all the knowledge accumulated, there is still some way to go to decipher the individual predisposition to disease, and if we consider the great influence that environmental factors play in the development and progression of atherosclerosis, epigenetics is presented as a key element in trying to expand our knowledge on individual predisposition to atherosclerosis and cardiovascular disease. Epigenetics can be described as the discipline that studies the mechanisms of transcriptional regulation, independent of changes in the sequence of DNA, and mostly induced by environmental factors. This review aims to describe what epigenetics is and how epigenetic mechanisms are involved in atherosclerosis.