Cardiac differentiation of mouse embryonic stem cells is influenced by a PPAR γ/PGC-1α-FNDC5 pathway during the stage of cardiac precursor cell formation

The Role of FNDC5/Irisin in Cardiovascular Disease

Disorders of cardiomyocyte metabolism play a crucial role in many cardiovascular diseases, such as myocardial infarction, heart failure and ischemia-reperfusion injury. In myocardial infarction, cardiomyocyte metabolism is regulated by mitochondrial changes and biogenesis, which allows energy homeostasis. There are many proteins in cells that regulate and control metabolic processes. One of them is irisin (Ir), which is released from the transmembrane protein FNDC5. Initial studies indicated that Ir is a myokine secreted mainly by skeletal muscles. Further studies showed that Ir was also present in various tissues. However, its highest levels were observed in cardiomyocytes. Ir is responsible for many processes, including the conversion of white adipose tissue (WAT) to brown adipose tissue (BAT) by increasing the expression of thermogenin (UCP1). In addition, Ir affects mitochondrial biogenesis. Therefore, the levels of FNDC5/Ir in the blood and myocardium may be important in cardiovascular disease. This review discusses the current knowledge about the role of FNDC5/Ir in cardiovascular disease.

Eight Weeks of High-Intensity Interval Static Strength Training Improves Skeletal Muscle Atrophy and Motor Function in Aged Rats via the PGC-1α/FNDC5/UCP1 Pathway

Background

Sarcopenia is a syndrome characterized by the loss of skeletal muscle mass and strength. Most studies have focused on dynamic resistance exercises for preventing muscular decline and maintaining the muscle strength of older individuals. However, this training mode is impractical for older people with osteoarthritis and a limited range of motion. The static strength training mode is more suitable for older people. Therefore, a determination of the effect and mechanism of static strength training on sarcopenia is critical.

Methods

In this study, we developed a training device designed to collect training data and evaluate the effects of static training on the upper limbs of rats. The expression of PGC-1α was locally blocked by injecting a siRNA at the midpoint of the biceps to determine whether PGC-1α signal transduction participates in the effects of high-intensity interval static training on muscle strength. Then, the rat’s motor capacity was measured after static strength training. Immunohistochemistry and Western blotting were applied to determine PGC-1α/FNDC5/UCP1 expression levels in the muscle and adipose tissue. The serum irisin level was also detected using an enzyme-linked immunosorbent assay (ELISA).

Results

Increased levels of serum irisin and local expression of FNDC5, PGC-1α, and UCP1 were observed in the biceps brachii and surrounding fatty tissue after static strength training. Static strength training showed an advantage in reducing body weight and white fat accumulation while increasing the muscle fiber volume, which resulted in a longer training time and shorter rest time.

Conclusion

Overall, these results indicated that high-intensity interval static training prevents skeletal muscle atrophy and improves the motor function of aged rats through the PGC-1α/FNDC5/UCP1 signaling pathway.

Effects of abundances of OCT-4 mRNA transcript on goat pre-implantation embryonic development

Unlike in mice, the function of pluripotent markers in early embryonic development of domestic animals remains to be elucidated and this may account for the failure to establish embryonic stem cell lines for these species. To study the functions of the OCT-4 protein which has important actions in maintenance of pluripotent and self-renewal processes during early embryonic development, there was induced reduction in relative abundance of OCT-4 mRNA transcript during goat early embryonic development by using RNA interference techniques. The injection of OCT-4 siRNA into goat IVF presumptive zygotes resulted in a decrease in the relative abundance of OCT-4 mRNA transcript; however, there was development of these embryos to the blastocyst stage at the same rate as there was in the control group. The blastocysts from the treated groups had a similar number of TE, ICM, and total cells compared to those from the control group. Although there was a greater relative abundance of NANOG, REX1, and CDX2 mRNA transcript in the embryos injected with siRNA at the 8-16 cell stage, the relative transcript abundances were similar for the control and treatment groups at the blastocyst stage. The relative abundance of SOX2 mRNA transcript was similar for the treatment and control group. It, therefore, is concluded that inhibition of abundances of OCT-4 mRNA transcript to about 20 % of that of the untreated control group did not affect blastocyst formation rate in goats. The functions of OCT-4 in maintaining ICM and TE integrity, however, remains to be assessed.

Expansion of Human Pluripotent Stem Cell-derived Early Cardiovascular Progenitor Cells by a Cocktail of Signaling Factors

Cardiovascular progenitor cells (CPCs) derived from human pluripotent stem cells (hPSCs) are proposed to be invaluable cell sources for experimental and clinical studies. This wide range of applications necessitates large-scale production of CPCs in an in vitro culture system, which enables both expansion and maintenance of these cells. In this study, we aimed to develop a defined and efficient culture medium that uses signaling factors for large-scale expansion of early CPCs, called cardiogenic mesodermal cells (CMCs), which were derived from hPSCs. Chemical screening resulted in a medium that contained a reproducible combination of three factors (A83-01, bFGF, and CHIR99021) that generated 1014 CMCs after 10 passages without the propensity for tumorigenicity. Expanded CMCs retained their gene expression pattern, chromosomal stability, and differentiation tendency through several passages and showed both the safety and possible cardio-protective potentials when transplanted into the infarcted rat myocardium. These CMCs were efficiently cryopreserved for an extended period of time. This culture medium could be used for both adherent and suspension culture conditions, for which the latter is required for large-scale CMC production. Taken together, hPSC-derived CMCs exhibited self-renewal capacity in our simple, reproducible, and defined medium. These cells might ultimately be potential, promising cell sources for cardiovascular studies.

FNDC5 alleviates oxidative stress and cardiomyocyte apoptosis in doxorubicin-induced cardiotoxicity via activating AKT

Oxidative stress and cardiomyocyte apoptosis play critical roles in doxorubicin (DOX)-induced cardiotoxicity. Previous studies indicated that fibronectin type III domain-containing 5 (FNDC5) and its cleaved form, irisin, could preserve mitochondrial function and attenuate oxidative damage as well as cell apoptosis, however, its role in DOX-induced cardiotoxicity remains unknown. Our present study aimed to investigate the role and underlying mechanism of FNDC5 on oxidative stress and cardiomyocyte apoptosis in DOX-induced cardiotoxicity. Cardiomyocyte-specific FNDC5 overexpression was achieved using an adeno-associated virus system, and then the mice were exposed to a single intraperitoneal injection of DOX (15 mg/kg) to generate DOX-induced cardiotoxicity. Herein, we found that FNDC5 expression was downregulated in DOX-treated murine hearts and cardiomyocytes. Fndc5 deficiency resulted in increased oxidative damage and apoptosis in H9C2 cells under basal conditions, imitating the phenotype of DOX-induced cardiomyopathy in vitro, conversely, FNDC5 overexpression or irisin treatment alleviated DOX-induced oxidative stress and cardiomyocyte apoptosis in vivo and in vitro. Mechanistically, we identified that FNDC5/Irisin activated AKT/mTOR signaling and decreased DOX-induced cardiomyocyte apoptosis, and moreover, we provided direct evidence that the anti-oxidant effect of FNDC5/Irisin was mediated by the AKT/GSK3β/FYN/Nrf2 axis in an mTOR-independent manner. And we also demonstrated that heat shock protein 20 was responsible for the activation of AKT caused by FNDC5/Irisin. In line with the data in acute model, we also found that FNDC5/Irisin exerted beneficial effects in chronic model of DOX-induced cardiotoxicity (5 mg/kg, i.p., once a week for three times, the total cumulative dose is 15 mg/kg) in mice. Based on these findings, we supposed that FNDC5/Irisin was a potential therapeutic agent against DOX-induced cardiotoxicity.

Effects of myostatin deficiency on PGC-1α and FNDC5 expression in three different murine muscle types

Myostatin (MSTN) is a key negative regulator of muscle growth and development. Skeletal, cardiac, and smooth muscles were isolated from MSTN knockout (MSTN-∕-) and control mice to investigate the effect of knocking out MSTN on peroxisome proliferator-activated receptor 1 coactivator (PGC-1α)-III and fibronectin domain 5 (FNDC5) expression. Various molecular biology techniques were used to analyze the changes in PGC-1α-FNDC5 in different muscle types from MSTN-∕- mice. The expression levels of PGC-1α and FNDC5 in the skeletal, cardiac, and smooth muscles of MSTN-∕- mice differed from those in the skeletal, cardiac, and smooth muscles of normal mice. This study revealed that knocking out MSTN resulted in inconsistent PGC-1α and FNDC5 expression in specific muscles. It proved for the first time that MSTN deletion attenuated the expression of PGC-1α and FNDC5 in three different murine muscle types. MSTN deletion may have additional effects on the status ofFNDC5 expression. Further research, however, is needed to confirm this conclusion.

Troglitazone activates TRPV1 and causes deacetylation of PPARγ in 3T3-L1 cells

Published research suggests that activation of transient receptor potential vanilloid subfamily 1 (TRPV1) enhances the expression and deacetylation of peroxisome proliferator-activated receptor gamma (PPARγ) to cause browning of white adipose tissue. Here, we show that TRPV1 activation by capsaicin significantly prevents high fat diet-induced obesity in mice. This is associated with an increase in the expression and deacetylation of PPARγ in the epididymal fat of these mice. Consistent with the TRPV1 activation in vivo, overexpression of TRPV1 enhanced the PPARγ and other thermogenic genes in cultured 3T3-L1 preadipocytes. To determine the interaction between TRPV1 and PPARγ signaling, we analyzed the effect of Troglitazone (Trog; a thiazolidinedione derivative and an agonist of PAARγ) treatment on cultured 3T3-L1 cells. Trog enhanced the expression of TRPV1, PPARγ and thermogenic proteins in undifferentiated 3T3-L1 cells but not in differentiated cells. Acute application of Trog stimulated a robust Ca²⁺ influx into 3T3-L1 cells and TRPV1 inhibition by capsazepine prevented this. More interestingly, Trog or capsaicin treatment caused the deacetylation of PPARγ in 3T3-L1 cells and inhibition of TRPV1 or Sirtuin 1 - prevented this. Our data suggest a novel effect of Trog to induce PPARγ deacetylation by activating TRPV1. This research has a significant implication on the role of TRPV1 and PPARγ signaling in the browning of white adipose tissue.

Fndc5 knockdown induced suppression of mitochondrial integrity and significantly decreased cardiac differentiation of mouse embryonic stem cells

Fibronectin type III domain-containing 5 protein (Fndc5) is a glycosylated protein with elevated expression in high energy demanded tissues as heart, brain, and muscle. It has been shown that upregulation of Fndc5 is regulated by peroxisome proliferator-activated receptor-γ coactivator-1 alpha (PGC-1α), which is known as a master regulator of mitochondrial function and biogenesis. Also, our group indicated that Fndc5 expression increases gradually during cardiac differentiation of mouse embryonic stem cells (mESCs). In this paper, to clarify the importance of Fndc5 in cardiac differentiation, we south to knock down Fndc5 expression by generation a stably transduced mESC line that derives the expression of a short hairpin RNA (shRNA) against Fndc5 gene following doxycycline (Dox) induction. Knock-down of Fndc5 demonstrated a considerable decrease in expression of cardiac progenitor and cardiomyocyte markers. Considering the fact that mitochondria play a crucial role in cardiac differentiation of ESCs, we investigated the role of Fndc5, as a downstream target of PGC1-α, on mitochondrial indices. Results showed that expression of nuclear encoded mitochondrial genes including PGC1-α, Atp5b, Ndufb5, and SOD2 significantly decreased. Moreover, mitochondrial membrane potential (ΔΨm) and relative ATP content of cardiomyocytes decreased markedly with relative ROS level increase. Together, our results suggest that Fndc5 attenuates process of cardiac differentiation of mESCs which is associated with modulation of mitochondrial function and gene expression.

Exercise leads to unfavourable cardiac remodelling and enhanced metabolic homeostasis in obese mice with cardiac and skeletal muscle autophagy deficiency

Autophagy is stimulated by exercise in several tissues; yet the role of skeletal and cardiac muscle-specific autophagy on the benefits of exercise training remains incompletely understood. Here, we determined the metabolic impact of exercise training in obese mice with cardiac and skeletal muscle disruption of the Autophagy related 7 gene (Atg7^h&mKO). Muscle autophagy deficiency did not affect glucose clearance and exercise capacity in lean adult mice. High-fat diet in sedentary mice led to endoplasmic reticulum stress and aberrant mitochondrial protein expression in autophagy-deficient skeletal and cardiac muscles. Endurance exercise training partially reversed these abnormalities in skeletal muscle, but aggravated those in the heart also causing cardiac fibrosis, foetal gene reprogramming, and impaired mitochondrial biogenesis. Interestingly, exercise-trained Atg7^h&mKO mice were better protected against obesity and insulin resistance with increased circulating fibroblast growth factor 21 (FGF21), elevated Fgf21 mRNA and protein solely in the heart, and upregulation of FGF21-target genes involved in thermogenesis and fatty acid oxidation in brown fat. These results indicate that autophagy is essential for the protective effects of exercise in the heart. However, the atypical remodelling elicited by exercise in the autophagy deficient cardiac muscle enhances whole-body metabolism, at least partially, via a heart-brown fat cross-talk involving FGF21.

Beiging of white adipose tissue as a therapeutic strategy for weight loss in humans

An imbalance between energy intake and expenditure leads to obesity. Adiposity associated with obesity progressively causes inflammation, type 2 diabetes, hypertension, hyperlipidemia and cardiovascular disease. Excessive dietary intake of fat results in its accumulation and storage in the white adipose tissue (WAT), whereas energy expenditure by fat utilization and oxidation predominately occurs in the brown adipose tissue (BAT). Recently, the presence of a third type of fat, referred to as beige or brite (brown in white), has been recognized in certain kinds of WAT depots. It has been suggested that WAT can undergo the process of browning in response to stimuli that induce and enhance the expression of thermogenes characteristic of those typically associated with brown fat. The resultant beige or brite cells enhance energy expenditure by reducing lipids stored within adipose tissue. This has created significant excitement towards the development of a promising strategy to induce browning/beiging in WAT to combat the growing epidemic of obesity. This review systematically describes differential locations and functions of WAT and BAT, mechanisms of beiging of WAT and a concise analysis of drug molecules and natural products that activate the browning phenomenon in vitro and in vivo. This review also discusses potential approaches for targeting WAT with compounds for site-specific beiging induction. Overall, there are numerous mechanisms that govern browning of WAT. There are a variety of newly identified targets whereby potential molecules can promote beiging of WAT and thereby combat obesity.

Systematic selection of small molecules to promote differentiation of embryonic stem cells and experimental validation for generating cardiomyocytes

Small molecules are being increasingly used for inducing the targeted differentiation of stem cells to different cell types. However, until now no systematic method for selecting suitable small molecules for this purpose has been presented. In this work, we propose an integrated and general bioinformatics- and cheminformatics-based approach for selecting small molecules which direct cellular differentiation in the desired way. The approach was successfully experimentally validated for differentiating stem cells into cardiomyocytes. All predicted compounds enhanced expression of cardiac progenitor (Gata4, Nkx2-5 and Mef2c) and mature cardiac markers (Actc1, myh6) significantly during and post-cardiac progenitor formation. The best-performing compound, Famotidine, increased the percentage of Myh6-positive cells from 33 to 56%, and enhanced the expression of Nkx2.5 and Tnnt2 cardiac progenitor and cardiac markers in protein level. The approach employed in the study is applicable to all other stem cell differentiation settings where gene expression data are available.

Impacts of Alternative Splicing Events on the Differentiation of Adipocytes

Alternative splicing was found to be a common phenomenon after the advent of whole transcriptome analyses or next generation sequencing. Over 90% of human genes were demonstrated to undergo at least one alternative splicing event. Alternative splicing is an effective mechanism to spatiotemporally expand protein diversity, which influences the cell fate and tissue development. The first focus of this review is to highlight recent studies, which demonstrated effects of alternative splicing on the differentiation of adipocytes. Moreover, use of evolving high-throughput approaches, such as transcriptome analyses (RNA sequencing), to profile adipogenic transcriptomes, is also addressed.