Irisin Increased the Number and Improved the Function of Endothelial Progenitor Cells in Diabetes Mellitus Mice

New insights into the roles of Irisin in diabetic cardiomyopathy and vascular diseases

Diabetes mellitus (DM) is a prevalent chronic disease in the 21st century due to increased lifespan and unhealthy lifestyle choices. Extensive research indicates that exercise can play a significant role in regulating systemic metabolism by improving energy metabolism and mitigating various metabolic disorders, including DM. Irisin, a well-known exerkine, was initially reported to enhance energy expenditure by indicating the browning of white adipose tissue (WAT) through peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) signaling. In this review, we summarize the potential mechanisms underlying the beneficial effects of Irisin on glucose dysmetabolism, including reducing gluconeogenesis, enhancing insulin energy expenditure, and promoting glycogenesis. Additionally, we highlight Irisin's potential to improve diabetic vascular diseases by stimulating nitric oxide (NO) production, reducing oxidative and nitrosative stress, curbing inflammation, and attenuating endothelial cell aging. Furthermore, we discuss the potential of Irisin to improve diabetic cardiomyopathy by preventing cardiomyocyte loss and reducing myocardial hypertrophy and fibrosis. Given Irisin's promising functions in managing diabetic cardiomyopathy and vascular diseases, targeting Irisin for therapeutic purposes could be a fruitful avenue for future research and clinical interventions.

Hydrogen Sulfide and Irisin, Potential Allies in Ensuring Cardiovascular Health

Irisin is a myokine secreted under the influence of physical activity and exposure to low temperatures and through different exogenous stimuli by the cleavage of its precursor, fibronectin type III domain-containing protein 5 (FNDC5). It is mainly known for maintaining of metabolic homeostasis, promoting the browning of white adipose tissue, the thermogenesis process, and glucose homeostasis. Growing experimental evidence suggests the possible central role of irisin in the regulation of cardiometabolic pathophysiological processes. On the other side, hydrogen sulfide (H2S) is well recognized as a pleiotropic gasotransmitter that regulates several homeostatic balances and physiological functions and takes part in the pathogenesis of cardiometabolic diseases. Through the S-persulfidation of cysteine protein residues, H2S is capable of interacting with crucial signaling pathways, exerting beneficial effects in regulating glucose and lipid homeostasis as well. H2S and irisin seem to be intertwined; indeed, recently, H2S was found to regulate irisin secretion by activating the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)/FNDC5/irisin signaling pathway, and they share several mechanisms of action. Their involvement in metabolic diseases is confirmed by the detection of their lower circulating levels in obese and diabetic subjects. Along with the importance of metabolic disorders, these modulators exert favorable effects against cardiovascular diseases, preventing incidents of hypertension, atherosclerosis, heart failure, myocardial infarction, and ischemia-reperfusion injury. This review, for the first time, aims to explore the role of H2S and irisin and their possible crosstalk in cardiovascular diseases, pointing out the main effects exerted through the common molecular pathways involved.

The emerging roles of irisin in vascular calcification

Vascular calcification is a common accompanying pathological change in many chronic diseases, which is caused by calcium deposition in the blood vessel wall and leads to abnormal blood vessel function. With the progress of medical technology, the diagnosis rate of vascular calcification has explosively increased. However, due to its mechanism's complexity, no effective drug can relieve or even reverse vascular calcification. Irisin is a myogenic cytokine regulating adipose tissue browning, energy metabolism, glucose metabolism, and other physiological processes. Previous studies have shown that irisin could serve as a predictor for vascular calcification, and protect against hypertension, diabetes, chronic kidney disease, and other risk factors for vascular calcification. In terms of mechanism, it improves vascular endothelial dysfunction and phenotypic transformation of vascular smooth muscle cells. All the above evidence suggests that irisin plays a predictive and protective role in vascular calcification. In this review, we summarize the association of irisin to the related risk factors for vascular calcification and mainly explore the role of irisin in vascular calcification.

Effects of recreational SCUBA diving practiced once a week on neurohormonal response and myokines-mediated communication between muscles and the brain

Objective

During physical activity, activation of muscular, endocrine, and nervous systems, results in intensive crosstalk between muscles and other organs, which enables response to physiological stress. In SCUBA diving, extreme environmental conditions represent an additional challenge for homeostasis maintenance, but underlying mechanisms are largely unknown. We aimed to contribute to the understanding of neurohormonal response and muscle-brain crosstalk by measuring the concentrations of the selected hormones secreted by the pituitary-target organ axis and myokines involved in the muscle-brain endocrine loop in recreational SCUBA (rSCUBA) divers.

Methods

Fourteen male divers performed five open-water recreational dives (one per week, depth of 20–30 m, lasting 30 min, between 9 and 10 am), after a winter non-diving period of 5 months. Blood samples were collected immediately before and after the first, third, and fifth dives. Adrenocorticotropic hormone (ACTH), cortisol, thyroid-stimulating hormone (TSH), free thyroxine (fT4), prolactin, total testosterone, growth hormone (GH), insulin-like growth factor-1 (IGF-1), irisin, brain-derived neurotrophic factor (BDNF), S100B, glial fibrillary acidic protein (GFAP), and neuron-specific enolase (NSE) were measured using commercially available immunoassays.

Results

Cortisol and ACTH levels decreased after every dive, while total testosterone decreased only after the first dive. No significant changes in post-dive values, as well as the cumulative effect on any other measured hormone, were observed. Although irisin and BDNF levels decreased after the first and third dives, the fifth dive caused a significant increase in both myokines. Changes in IGF-1 levels were not observed. All three dives caused a significant increase in S100B levels. A statistically significant decrease in GFAP concentration was observed after every dive, while NSE pre-dive concentration declined over the studied period. The cumulative effect on myokine levels was reflected in a continuous decline in irisin and BDNF pre-dive levels throughout the studied period, but an increasing trend after the fifth dive was observed.

Conclusions

Observed changes in myokines and hormone levels point to a specific response to rSCUBA practiced once a week, most likely due to extreme environmental conditions. Further studies on communication between muscles and other organ systems, particularly on the muscle-brain endocrine loop, are required for a deeper understanding of the adaptation mechanisms to this kind of physiological stress.

Association of Plasma Irisin Levels with Circulating Endothelial Microparticles (EMPs) and Endothelial Progenitor Cells (EPCs) in Children Born Prematurely

Prematurity has been linked with endothelial dysfunction in later life. The purpose of this study was to evaluate the association between plasma irisin, an adipomyokine reported to protect the functional integrity of vascular endothelium, and circulating endothelial microparticles (EMPs) and endothelial progenitor cells (EPCs), consisting early biomarkers of endothelial dysfunction, in preterm-born children. We studied 131 prepubertal children; 61 preterm and 70 born at term (controls). Plasma irisin was determined by ELISA. Circulating CD62E(+), CD144(+) and CD31(+)/CD42b(-) EMPs, and CD34(+)/VEGFR-2(+)/CD45(-) and CD34(+)/VEGFR-2(+)/CD45dim EPCs, were determined by flow cytometry. Body mass index, waist-to-hip ratio, neck circumference, systolic and diastolic blood pressure, and biochemical parameters (glucose, lipids, insulin, HOMA-IR) were also evaluated. Plasma irisin was significantly lower (p = 0.001), whereas circulating EMPs and EPCs were higher, in children born prematurely compared to controls. Irisin was recognized as independent predictor for CD144(+) and CD31(+)/CD42b(-) EMPs, CD34(+)/VEGFR-2(+)/CD45(-) and CD34(+)/VEGFR-2(+)/CD45dim EPCs in the total study population, and for CD31(+)/CD42b(-) EMPs in the preterm group. In conclusion, plasma irisin correlates independently with circulating EMP and EPC subpopulations in prepubertal children and in preterm-born ones. Further studies in children will potentially elucidate the link between irisin and the primary stages of prematurity-related endothelial dysfunction.

Irisin, an Effective Treatment for Cardiovascular Diseases?

Irisin, as one of the myokines induced by exercise, has attracted much attention due to its important physiological functions such as white fat browning, the improvement in metabolism, and the alleviation of inflammation. Despite the positive role that irisin has been proven to play in the prevention and treatment of cardiovascular diseases, whether it can become a biomarker and potential target for predicting and treating cardiovascular diseases remains controversial, given the unreliability of its detection methods, the uncertainty of its receptors, and the species differences between animals and humans. This paper was intended to review the role of irisin in the diagnosis and treatment of cardiovascular diseases, the potential molecular mechanism, and the urgent problems to be solved in hopes of advancing our understanding of irisin as well as providing data for the development of new and promising intervention strategies by discussing the causes of contradictory results.

The Effect of Irisin on Proliferation, Apoptosis, and Expression of Metastasis Markers in Prostate Cancer Cell Lines

INTRODUCTION

Irisin is a newly discovered myokine released from skeletal muscle during exercise. The matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that play a key role in the metastatic process via degrading extracellular matrix. The aim of this study was to investigate the effect of irisin on expression of metastatic markers MMP2 and MMP9 and induced apoptosis in human prostate cancer cells.

METHODS

In this study, we examined the effect of different concentrations of irisin on induced apoptosis and cell viability of two cell lines, LNCaP and DU-145, by using flow cytometry and MTT assay, respectively. The expression of MMP2 and MMP9 genes was also analyzed by real-time PCR after irisin treatment. Data were analyzed using the comparative cycle threshold 2^-∆∆Ct method.

RESULTS

Cell viability was reduced in both LNCaP and DU-145 cell lines at different concentrations of irisin. However, this decreased cell viability was strongly significant (p < 0.05) only at 5 and 10 nM concentrations of irisin in the LNCaP cell line. Furthermore, irisin could induce apoptosis in both cell lines at a concentration of 10 nM compared to 5 nM. Real-time PCR results also demonstrated a decreased expression in MMP2 and MMP9 genes in a concentration-dependent manner in both cell lines.

CONCLUSION

These results showed the anticancer effects of irisin on cell viability of both LNCaP and DU-145 cell lines and also on the expression of MMP2 and MMP9 genes occurred in a dose- and time-dependent manner.

The Emerging Role of Irisin in Cardiovascular Diseases

Irisin, a novel hormone like polypeptide, is cleaved and secreted by an unknown protease from a membrane‐spanning protein, FNDC5 (fibronectin type III domain‐containing protein 5). The current knowledge on the biological functions of irisin includes browning white adipose tissue, regulating insulin use, and anti‐inflammatory and antioxidative properties. Dysfunction of irisin has shown to be involved in cardiovascular diseases such as hypertension, coronary artery disease, myocardial infarction, and myocardial ischemia–reperfusion injury. Moreover, irisin gene variants are also associated with cardiovascular diseases. In this review, we discuss the current knowledge on irisin‐mediated regulatory mechanisms and their roles in the pathogenesis of cardiovascular diseases.

Fibronectin type III domain-containing 5 in cardiovascular and metabolic diseases: a promising biomarker and therapeutic target

Cardiovascular and metabolic diseases are the leading causes of death and disability worldwide and impose a tremendous socioeconomic burden on individuals as well as the healthcare system. Fibronectin type III domain-containing 5 (FNDC5) is a widely distributed transmembrane glycoprotein that can be proteolytically cleaved and secreted as irisin to regulate glycolipid metabolism and cardiovascular homeostasis. In this review, we present the current knowledge on the predictive and therapeutic role of FNDC5 in a variety of cardiovascular and metabolic diseases, such as hypertension, atherosclerosis, ischemic heart disease, arrhythmia, metabolic cardiomyopathy, cardiac remodeling, heart failure, diabetes mellitus, and obesity.

Irisin in atherosclerosis

Irisin, a novel exercise-induced myokine, has been shown to play important roles in increasing white adipose tissue browning, regulating energy metabolism and improving insulin resistance. Growing evidence suggests a direct role for irisin in preventing atherosclerosis (AS) by inhibiting oxidative stress, improving dyslipidemia, facilitating anti-inflammation, reducing cellular damage and recovering endothelial function. In addition, some studies have noted that serum irisin levels play an essential role in cardiovascular diseases (CVDs) risk prediction, highlighting that irisin has the potential to be a useful predictive marker and therapeutic target of AS, especially in monitoring therapeutic efficacy. This review summarizes the understanding of irisin-mediated regulation in essential biological pathways and functions in atherosclerosis and prompts further exploitation of the biological properties of irisin in the pathogenesis of atherosclerosis.

Role of Irisin in Myocardial Infarction, Heart Failure, and Cardiac Hypertrophy

Irisin is a myokine derived from the cleavage of fibronectin type III domain-containing 5. Irisin regulates mitochondrial energy, glucose metabolism, fatty acid oxidation, and fat browning. Skeletal muscle and cardiomyocytes produce irisin and affect various cardiovascular functions. In the early phase of acute myocardial infarction, an increasing irisin level can reduce endothelial damage by inhibiting inflammation and oxidative stress. By contrast, higher levels of irisin in the later phase of myocardial infarction are associated with more cardiovascular events. During different stages of heart failure, irisin has various influences on mitochondrial dysfunction, oxidative stress, metabolic imbalance, energy expenditure, and heart failure prognosis. Irisin affects blood pressure and controls hypertension through modulating vasodilatation. Moreover, irisin can enhance vasoconstriction via the hypothalamus. Because of these dual effects of irisin on cardiovascular physiology, irisin can be a critical therapeutic target in cardiovascular diseases. This review focuses on the complex functions of irisin in myocardial ischemia, heart failure, and cardiac hypertrophy.

Cardiometabolic Effects of Irisin in Patients with End-Stage Renal Disease on Regular Hemo- or Peritoneal Dialysis

INTRODUCTION

Data on the role of irisin in vascular calcification in patients with end-stage renal diseases on regular dialysis are inconsistent, and the underlying mechanisms are not clearly defined. The present study was designed to explore the association of serum irisin with vascular stiffness and with the impact of well-established risk factors.

METHODS

The clinical study enrolled 52 hemodialysis (HD) and 15 continuous ambulatory peritoneal dialysis (PD) patients with an age of >18 years receiving dialysis therapy for >3 months. Patients who had major pathologies affecting carbohydrate, lipid, and bone metabolism and those who had acute cardiovascular events were excluded. Thirty-seven healthy subjects matched for age and sex served as controls. Routine biochemical parameters were measured in fasting serum samples by standard methods. Serum irisin was determined using the commercial ELISA kit (BioVendor Laboratory Medicine Inc., Brno, Czech Republic). Arterial stiffness parameters - carotid-femoral pulse wave velocity (cf PWV) and augmentation index (Aix) - were measured using applanation tonometry (SphygmoCor System; AtCor Medical, Sydney, Australia). Body composition was assessed by segmental bioelectric impedance (InBody 2.0; Biospace Co. Ltd., Seoul, Korea).

RESULTS

It was demonstrated that serum irisin levels were markedly depressed (p < 0.05), while the cf PWV significantly increased (p < 0.05) in HD/PD patients as compared to controls. Serum irisin proved to be independent of serum insulin, glucose, and HOMA-IR. However, it was inversely related to HbA1c (β = -0.544, p = 0.035), iPTH (β = -0.260, p = 0.035), and alkaline phosphatase (r = -0.325, p = 0.007). Furthermore, significant negative relationships were found of irisin to serum triglyceride and indices of body fat mass. Retrospective analysis at a follow-up period of 40 months revealed a direct relationship of irisin to all-cause mortality (p = 0.039).

CONCLUSIONS

Our study demonstrated that serum irisin levels are reduced in uremic patients on regular HD/PD but failed to establish significant associations of irisin deficiency with vascular stiffness. However, the significant negative relationship of irisin to HbA1c, iPTH, and alkaline phosphatase suggests that it improves insulin sensitivity, inhibits bone resorption, mitigates bone-vascular interaction, and protects vascular function.

Progress and Challenges in the Biology of FNDC5 and Irisin

In 2002, a transmembrane protein-now known as FNDC5-was discovered and shown to be expressed in skeletal muscle, heart, and brain. It was virtually ignored for 10 years, until a study in 2012 proposed that, in response to exercise, the ectodomain of skeletal muscle FNDC5 was cleaved, traveled to white adipose tissue, and induced browning. The wasted energy of this browning raised the possibility that this myokine, named irisin, might mediate some beneficial effects of exercise. Since then, more than 1000 papers have been published exploring the roles of irisin. A major interest has been on adipose tissue and metabolism, following up the major proposal from 2012. Many studies correlating plasma irisin levels with physiological conditions have been questioned for using flawed assays for irisin concentration. However, experiments altering irisin levels by injecting recombinant irisin or by gene knockout are more promising. Recent discoveries have suggested potential roles of irisin in bone remodeling and in the brain, with effects potentially related to Alzheimer's disease. We discuss some discrepancies between research groups and the mechanisms that are yet to be determined. Some important questions raised in the initial discovery of irisin, such as the role of the mutant start codon of human FNDC5 and the mechanism of ectodomain cleavage, remain to be answered. Apart from these specific questions, a promising new tool has been developed-mice with a global or tissue-specific knockout of FNDC5. In this review, we critically examine the current knowledge and delineate potential solutions to resolve existing ambiguities.

Irisin: A New Code Uncover the Relationship of Skeletal Muscle and Cardiovascular Health During Exercise

Exercise not only produces beneficial effects on muscle itself via various molecular pathways, but also mediates the interaction between muscles and other organs in an autocrine/paracrine manner through myokines, which plays a positive role in maintaining overall health. Irisin, an exercise-derived myokine, has been found involved in the regulation of some cardiovascular diseases. However, the relationship between irisin and cardiovascular health is not fully elucidated and there are some divergences on the regulation of irisin by exercise. In this review, we present the current knowledge on the origin and physiology of irisin, describe the regulation of irisin by acute and chronic exercises, and discuss the divergences of the related research results. Importantly, we discuss the role of irisin as a biomarker in the diagnosis of cardiovascular diseases and describe its treatment and molecular mechanism in some cardiovascular diseases. It is expected that irisin will be used as a therapeutic agent to combat cardiovascular diseases or other disorders caused by inactivity in the near future.

Irisin and Incretin Hormones: Similarities, Differences, and Implications in Type 2 Diabetes and Obesity

Incretins are gut hormones that potentiate glucose-stimulated insulin secretion (GSIS) after meals. Glucagon-like peptide-1 (GLP-1) is the most investigated incretin hormone, synthesized mainly by L cells in the lower gut tract. GLP-1 promotes β-cell function and survival and exerts beneficial effects in different organs and tissues. Irisin, a myokine released in response to a high-fat diet and exercise, enhances GSIS. Similar to GLP-1, irisin augments insulin biosynthesis and promotes accrual of β-cell functional mass. In addition, irisin and GLP-1 share comparable pleiotropic effects and activate similar intracellular pathways. The insulinotropic and extra-pancreatic effects of GLP-1 are reduced in type 2 diabetes (T2D) patients but preserved at pharmacological doses. GLP-1 receptor agonists (GLP-1RAs) are therefore among the most widely used antidiabetes drugs, also considered for their cardiovascular benefits and ability to promote weight loss. Irisin levels are lower in T2D patients, and in diabetic and/or obese animal models irisin administration improves glycemic control and promotes weight loss. Interestingly, recent evidence suggests that both GLP-1 and irisin are also synthesized within the pancreatic islets, in α- and β-cells, respectively. This review aims to describe the similarities between GLP-1 and irisin and to propose a new potential axis-involving the gut, muscle, and endocrine pancreas that controls energy homeostasis.

Incidence of stroke and its association with glycemic control and lifestyle in Japanese patients with type 2 diabetes mellitus: The Fukuoka diabetes registry

AIMS

We prospectively investigated the incidence of stroke and its subtypes, risk factors and prognosis in Japanese patients with type 2 diabetes.

METHODS

A total of 4,875 participants with type 2 diabetes (mean age 65.4 years, male 57%, previous stroke 10%) were investigated for the development of stroke for 5 years. Risk factors were evaluated using multivariable adjusted Cox proportional models.

RESULTS

The incidence rates per 1,000 person-years were 6.7 for new-onset stroke (ischemic 5.5, hemorrhagic 1.2) and 22.7 for recurrent stroke (ischemic 18.8, hemorrhagic 3.8), respectively. Ischemic stroke was significantly associated with age, male, reduced regular physical activity, HbA_1c, diabetic kidney disease and previous stroke. Lacunar infarction was significantly associated with obesity, reduced regular physical activity, HbA_1c and diabetic kidney disease, whereas atherothrombotic stroke was significantly associated with age, reduced intake of dietary fiber, reduced regular physical activity, HbA_1c and previous stroke. Recurrent stroke was significantly associated with depressive symptom. Thirty-day and one-year survival was 76% and 64% for hemorrhagic stroke, and 96% and 91% for ischemic stroke, respectively.

CONCLUSIONS

The current study reemphasized the importance of glycemic control and lifestyle modification such as regular physical exercise for stroke prevention in patients with type 2 diabetes.

The optimal therapeutic irisin dose intervention in animal model: A systematic review

Background and Aim:

Irisin, a novel myocyte-secreted hormone, was proposed to mediate some of the beneficial effects of exercise such as browning of adipocytes, thermogenesis, and metabolic homeostasis. Recently, several animals’ models’ studies have been performed to investigate the therapeutic impact of irisin in several disorders. Several interventional trials used different doses. However, optimum dose was not determined. This systematic review aims to identify the optimal dose of interventional irisin in mice and rat animal models.

Materials and Methods:

Online databases PubMed, Google Scholar, and Springer were systematically searched from 2012 to 2019. The words searched were irisin, irisin and animal model, physical activity, and irisin and irisin dosage. Non-irisin doses, in vitro studies, and factors influencing irisin levels were excluded.

Results:

Eleven of the total 391 qualifying studies were included. A daily injection of 500 μg/kg irisin may be the optimum dose of effect in mice and rats.

Conclusion:

More studies are required to determine the optimum dose of irisin to be used as a therapeutic intervention based on animal model.

The Potential Role of Irisin in Vascular Function and Atherosclerosis: A Review

Exercise is an effective intervention for both the prevention and the treatment of obesity and insulin resistance because skeletal muscle secretes many bioactive proteins that contribute to the beneficial effect of exercise. It has been revealed that irisin plays an important role in metabolic homeostasis and both acute and chronic exercises increase circulating irisin in experimental animal models and in humans. Although previous studies have reported that the irisin-related signaling mechanism may play a beneficial role in the treatment of metabolic diseases including obesity, metabolic syndrome, insulin resistance, and diabetes mellitus, studies on whether irisin plays a key role in vascular function and vascular complications are still insufficient. Therefore, the current review aims to summarize the accumulating evidence showing the potential role of irisin, especially in vascular reactivity and vascular abnormalities such as atherosclerosis.

Serum Irisin Levels, Endothelial Dysfunction, and Inflammation in Pediatric Patients with Type 2 Diabetes Mellitus and Metabolic Syndrome

The prevalence of type 2 diabetes mellitus (T2DM) and metabolic syndrome (MetS) has increased in the pediatric population. Irisin, an adipomyokine, is involved in white adipose tissue browning, energy expenditure, insulin sensitivity, and anti-inflammatory pathways. Data on the associations among circulating irisin levels, soluble cell adhesion molecules (sCAMs), and inflammatory cytokines is scarce in children and adolescents with MetS and T2DM. Subjects aged 6-16 years were grouped into T2DM, MetS, and healthy controls. Serum irisin levels were significantly lower in the MetS (6.6 [2.8-18.0] ng/mL) and T2DM (6.8 [2.2-23.2] ng/mL) groups compared with controls (30.3 [24.6-57.1] ng/mL). Negative correlations between irisin and the BMI percentile (R = -0.358), WC percentile (R = -0.308), and triglycerides (R = -0.284) were identified, while positive associations with TC (R = 0.287), HDL-c (R = 0.488), and LDL-c (R = 0.414) were observed. Significant negative correlations were found between irisin and sNCAM (R = -0.382), sICAM-2 (R = -0.300), sVCAM-1 (R = -0.292), MCP-1 (R = -0.308), and IFN-α2 (R = -0.406). Of note, lower concentrations of most sCAMs (sICAM-1, sPSGL-1, sP-selectin, sEpCAM, sICAM-2, sALCAM, sPECAM-1, sCD44, sVCAM-1, sICAM-3, sL-selectin, and sNCAM) were shown in T2DM subjects compared with MetS patients. Lower irisin levels induce a lack of inhibition of oxidative stress and inflammation. In T2DM, higher ROS, AGEs, glucotoxicity, and inflammation trigger endothelial cell apoptosis, which downregulates the sCAM expression as a compensatory mechanism to prevent further vascular damage. In opposition, in subjects with MetS that have not yet developed T2DM and its accompanying stressors, the upregulation of the sCAM expression is ensued.

MiR-137 Restricts the Viability and Migration of HTR-8/SVneo Cells by Downregulating FNDC5 in Gestational Diabetes Mellitus

BACKGROUND

An increasing number of studies have described the pathological changes of placenta tissues in gestational diabetes mellitus (GDM), although the underlying mechanisms involved in this process remain uncertain. The aim of the present study was to verify the possible role of microRNA-137 (miR)-137 and FNDC5 in regulating the biological function of trophoblasts in high glucose (HG) conditions during the GDM period.

METHODS

Expression levels of miR-137 and FNDC5 were measured in placenta specimens, the HG-treated trophoblast cell line HTR-8/SVneo and miR-137- overexpressing HTR-8/SVneo cells using reverse transcription quantitative-PCR or western blotting. The viability of HTR-8/SVneo cells was tested using a Cell Counting kit- 8 (CCK8) assay, with cell migration assessed using scratch and transwell assays.

RESULTS

It was observed that the expression levels of miR-137 were increased and the expression levels of FNDC5 were decreased in the placenta tissues of women with severe GDM and in HG-exposed HTR-8/SVneo cells. In addition, upregulating miR-137 in HTR-8/SVneo cells downregulated the expression levels of FNDC5. The viability and migration of HTR-8/SVneo cells were suppressed by increased miR-137 expression levels, and upregulating FNDC5 in miR-137-overexpressing HTR-8/SVneo cells resulted in the reversal of all these effects.

CONCLUSIONS

The data from the present study suggest that miR-137 suppresses the viability and migration of trophoblasts via downregulating FNDC5 in GDM, which may contribute to the pathology of placenta tissues and occurrence of adverse pregnancy outcomes.

Irisin increases the expression of anorexigenic and neurotrophic genes in mouse brain

BACKGROUND

Irisin, a newly discovered muscle-derived hormone, acts in different organs and tissues, improving energy homeostasis. In this study, we assessed, for the first time, the effects of intraperitoneal irisin injections on circulating levels of leptin and ghrelin, mRNA expression of the major hypothalamic appetite regulators and brain neurotrophic factors, as well as feeding behaviour in healthy mice.

METHODS

Twelve male 6-week-old C57BL/6 mice were randomized into two groups and intraperitoneally injected daily with irisin (0.5 μg/g body weight) or vehicle (phosphate-buffered saline [PBS]) for 14 days. On the last day of observation, leptin and ghrelin levels were measured with an enzyme-linked immunosorbent assay (ELISA). mRNA levels of genes of interest were analysed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) in brain extracts.

RESULTS

Irisin administration did not change leptin or ghrelin serum concentrations. However, irisin injection increased CART, POMC, NPY, and BDNF mRNA levels, without affecting the mRNA expression of AgRP, orexin, PMCH, and UCP2. Finally, over the time frame of irisin treatment, body weight and feeding behaviour were unaltered.

CONCLUSIONS

These results suggest that intraperitoneal injection of irisin, although without effects on feeding behaviour and body weight, can increase the expression of anorexigenic and neurotrophic genes in mouse brain.

Irisin functions to inhibit malignant growth of human pancreatic cancer cells via downregulation of the PI3K/AKT signaling pathway

Introduction

Irisin is a newly identified cytokine that has gained increasing attention because of its potential therapeutic applications in metabolic diseases and human cancers. Recently, accumulating evidence indicates that irisin plays an important role in the development and metastasis of various tumors. The aim of this study was to evaluate the effects and underlying mechanisms of irisin on malignant growth of pancreatic cancer cells.

Materials and methods

The anti-proliferative effect of irisin was examined using the CCK-8 assay. Irisin-induced apoptosis was determined by the annexin V-FITC/PI staining assay. The effects of irisin on cell migration and invasion were assessed using the scratch-induced wound healing assay and transwell invasion assay, respectively. The expression and phosphorylation of signaling proteins were detected by Western blot analysis.

Results

Our results showed that irisin inhibited cell proliferation and induced apoptosis of pancreatic cancer cells in a dose-dependent manner. In addition, irisin decreased the migration and invasion of pancreatic cancer cells. Finally, Western blot analysis revealed that irisin downregulated the PI3K/AKT signaling pathway.

Conclusion

Our findings suggest that irisin is a novel therapeutic agent for pancreatic cancer.

Correlation between the blood level of irisin and the severity of acute myocardial infarction in exercise-trained rats

Background Acute myocardial infarction is a major cause of death all over the world. Irisin is a novel myokine released after exercise. This work aimed to study the correlation between the serum irisin level and the severity of the acute myocardial infarction in the exercise-trained rats. Methods Forty-eight male rats were classified into four groups (12 for each): group I, control sedentary (C); group II, exercise-trained (EX) (swimming for 8 weeks); group III, isoprenaline-induced infarct (MI); and group IV, exercise-trained infarct (EX-MI) (swimming for 8 weeks followed by isoprenaline-induced infarction). ECG was recorded at start and end of the study, before and after induction of infarction. The serum level of irisin, lipid peroxidation [malondialdehyde (MDA)], total antioxidant status (TAS), creatine phosphokinase-MB (CK-MB), and troponin I was determined. The hearts were excised for histopathology and immunohistochemistry for caspase-3. Results The infarct rats showed significant prolongation in QTc interval and elevation in the ST segment as well as significant elevation of serum CK-MB, troponin I, and MDA, whereas TAS and serum irisin level were significantly decreased. With exercise, we observed a high positive correlation between the serum irisin and QRS duration (+0.643), amplitude (+0.860), and TAS (+0.887). In addition, there was a high negative correlation between the serum irisin and ST elevation (-0.865), QTc (-0.886), CK-MB (-0.891), troponin (-0.882), and MDA (-0.868). This was confirmed by the negative correlation between serum irisin and both collagen deposition and caspase-3 expression (-0.823 and -0.822, respectively). Conclusions We recommend regular exercise or taking recombinant irisin as a supplement to protect at-risk individuals against acute myocardial infarction.

Common Injuries and Repair Mechanisms in the Endothelial Lining

Objective:

Endothelial cells (ECs) are important metabolic and endocrinal organs which play a significant role in regulating vascular function. Vascular ECs, located between the blood and vascular tissues, can not only complete the metabolism of blood and interstitial fluid but also synthesize and secrete a variety of biologically active substances to maintain vascular tension and keep a normal flow of blood and long-term patency. Therefore, this article presents a systematic review of common injuries and healing mechanisms for the vascular endothelium.

Data Sources:

An extensive search in the PubMed database was undertaken, focusing on research published after 2003 with keywords including endothelium, vascular, wounds and injuries, and wound healing.

Study Selection:

Several types of articles, including original studies and literature reviews, were identified and reviewed to summarize common injury and repair processes of the endothelial lining.

Results:

Endothelial injury is closely related to the development of multiple cardiovascular and cerebrovascular diseases. However, the mechanism of vascular endothelial injury is not fully understood. Numerous studies have shown that the mechanisms of EC injury mainly involve inflammatory reactions, physical stimulation, chemical poisons, concurrency of related diseases, and molecular changes. Endothelial progenitor cells play an important role during the process of endothelial repair after such injuries. What's more, a variety of restorative cells, changes in cytokines and molecules, chemical drugs, certain RNAs, regulation of blood pressure, and physical fitness training protect the endothelial lining by reducing the inducing factors, inhibiting inflammation and oxidative stress reactions, and delaying endothelial caducity.

Conclusions:

ECs are always in the process of being damaged. Several therapeutic targets and drugs were seeked to protect the endothelium and promote repair.

The protective effect of Irisin against ischemia-reperfusion injury after perforator flap grafting in rats

BACKGROUND

Ischemia-reperfusion injury is one of the reasons for failure of flap grafting. In the present study, we investigated the protective effect of irisin on the survival of perforator flaps in rats.

METHODS

A total of 48 adult Sprague-Dawley rats were divided into 2 groups and subjected to vascular clipping of perforator flap. Rats in the experimental group (n = 24) received daily tail intravenous injection of irisin (2 ng/g) for 3 days, while the rest rats in the control group (n = 24) received injection of saline solution of the same dose. On the 7th post-operative day, the surviving area of the flaps were recorded as the percentage of the total flap area. Histology study with haematoxylin and eosin staining were performed in all flaps. Flaps were also evaluated with lead oxide-gelatine-enhanced flap angiography. Immunohistochemical study was performed to evaluate the expression of ErG, a marker of vascular endothelial cells. The tissue of "choke vessels" was excised for quantification of p-Akt/Akt by western blot assay on the 7th post-operative day.

RESULTS

On the 7th post-operative day, the percentage of surviving flap area was significantly larger in the rats with irisin administration (experimental group), compared with the control group (P = 0.011). The density of microvessels was significantly higher in the experimental group (P = 0.03) in the histological study and angiography, with a higher expression level of ErG in the immunochemical study (P = 0.01). The p-Akt/Akt was also higher in the experimental group in Western blotting analysis (P < 0.001).

CONCLUSION

Irisin has a beneficial effect on protecting perforator flaps from ischemic-reperfusion injury following the flap grafting surgery. It was potentially achieved by promoting proliferation of vascular endothelial cells after flap revascularization. Upregulation of the PI3K/Akt signaling pathway was potentially related with this process.

Association of Irisin Circulating Level with Diabetic Retinopathy: A Case-Control Study

Obesity and obesity induced type 2 diabetes development and progression have been associated with sedentary lifestyle. Irisin, a newly discovered myokine, has been demonstrated at lower levels in obese and type 2 diabetes patients compared to controls. The main aim of this study is to explore association of Irisin with diabetic retinopathy (DR). A total of 233 healthy and adults participated in this study. Participants were divided into four categories: a healthy control group and an age-match subset of patients with type 2 diabetes; a positive control group of patients with type 2 diabetes not affected by DR (No DR); and patients with type 2 diabetes affected by DR (non-proliferative DR (NPDR) and proliferative DR (PDR)). Plasma samples were quantified for Irisin measurement, lipid profile and HbA1c. Comparison of the age-matched groups of healthy controls and patients with type 2 diabetes revealed lower Irisin plasma level in type 2 diabetes group. Analyses revealed negative correlations of Irisin to HbA1c and LDL levels and positive correlation to HDL level. Comparing Irisin level in No DR and DR groups revealed a higher level in No DR group and analysis per DR classification indicated higher Irisin level in NPDR group. Our results demonstrate not only correlation of plasma Irisin level with DR stages, but also significantly different Irisin level among them. This is promising in terms of researching Irisin as a potential associating marker for type 2 diabetes and DR development and progression.

The association between irisin levels, element distribution and oxidative stress markers in adolescent swimmers

The objective of this investigation was to compare irisin concentration and its relation with oxidative stress markers, antioxidant enzymes and element levels in both male adolescent swimmers and sedentary controls. Twelve male swimmers aged between 11 and 18 years, who performed regular swimming training for at least 2 years and 12 age- and gender-matched sedentary controls participated in this study. After anthropometric measurements were performed, fasting venous blood samples were taken at rest. Irisin, malondialdehyde (MDA) as a marker of oxidative stress, superoxide dismutase (SOD) as a marker of antioxidant enzyme and elements (Zn, Cu, Se, Cr, Ni, Al, Fe) were analyzed in these samples. MDA levels were lower but Zn levels and Zn/Cu ratio were higher in the swimmers than in sedentary controls (p < 0.05). There was no statistically significant difference in the irisin levels and SOD activities between the groups (p > 0.05). The results of the current study suggested that exercise training has antioxidant effects and may reduce oxidative damage. Exercise training has also limited effects on irisin levels in the adolescents.

Is irisin the new player in exercise-induced adaptations or not? A 2017 update

Irisin is produced by a proteolytic cleavage of fibronectin type III domain-containing protein 5 (FNDC5) and has emerged as a potential mediator of exercise-induced energy metabolism. The purpose of this study was to review the results of studies that investigated irisin responses to acute and chronic exercise and provide an update. A comprehensive search in the databases of MEDLINE was performed (74 exercise studies). The focus of the analysis was on data concerning FNDC5 mRNA expression in skeletal muscle and circulating irisin concentration relatively to exercise mode, intensity, frequency and duration and the characteristics of the sample used. Circulating irisin levels may either not relate to FNDC5 transcription or expression of the later precedes irisin rise in the blood. Acute speed/strength and endurance exercise protocols represent potent stimuli for irisin release if they are characterized by adequate intensity and/or duration. There are no reports regarding irisin responses to field sport activities. Although animal studies suggest that irisin may also respond to systematic exercise training, the majority of human studies has produced contradictory results. Certain methodological issues need to be considered here such as the analytical assays used to measure irisin concentration in the circulation. Results may also be affected by subjects’ age, conditioning status and exercise intensity. The role of irisin as a moderator of energy metabolism during exercise remains to be seen.

Danshensu accelerates angiogenesis after myocardial infarction in rats and promotes the functions of endothelial progenitor cells through SDF-1α/CXCR4 axis

The present study was performed to investigate the potential role of Danshensu in therapeutic angiogenesis in ischemic myocardium and endothelial progenitor cells (EPCs) function. The rat model of myocardial infarction (MI) injury was induced by left anterior descending coronary artery ligation for 14 days. Danshensu significantly alleviated myocardial ischemia injury by ameliorating left ventricular function and reducing infarct size. Furthermore, Danshensu potentiated post-ischemia neovascularization as evidenced by increased microvessel density in infarction boundary zone, as well as the expression of marker proteins vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF). Moreover, Danshensu notably promoted stromal cell-derived factor-1α (SDF-1α) level in plasma and C-X-C chemokine receptor type 4 (CXCR4) expression in peri-infarction myocardium, and AMD3100 (CXCR4 antagonist) could reverse the angiogenic and cardioprotective effects of Danshensu. For in vitro study, EPCs were isolated from bone marrow of rats. On the one hand, Danshensu provided significant cytoprotection against hypoxia insult by boosting EPCs viability and inhibiting apoptosis, and upregulated Akt phosphorylation. On the other hand, Danshensu enhanced proangiogenic functions of EPCs on cell migration and tube formation, and increased SDF-1α and CXCR4 expression. Likewise, the cytoprotection and proangiogenic functions of Danshensu on EPCs were partly negated by LY294002 (PI3K antagonist) and CXCR4 siRNA, respectively. Taken together, our results suggested that the cardioprotection of Danshensu in MI rats may be related to promoting myocardial neovascularization. The possible mechanisms may involve improving EPCs survival in hypoxia condition through Akt phosphorylation, and accelerating EPCs proangiogenic functions through SDF-1α/CXCR4 axis.

Irisin protects macrophages from oxidized low density lipoprotein-induced apoptosis by inhibiting the endoplasmic reticulum stress pathway

Irisin is a newly discovered myokine which can relieve metabolic disorders and resist atherosclerosis. The effects of irisin on ox-LDL-induced macrophage apoptosis and endoplasmic reticulum stress-related pathways were observed in vitro. RAW264.7 macrophages were cultured in vitro and pretreated with irisin at 20, 40 and 80 ng/ml for 30 min, followed by culture with 100 mg/L ox-LDL and 5 mg/L tunicamycin (TM) for 12 h. The cell viability and apoptosis were detected by MTT assay and annexin V-FITC double staining. The nuclear translocation of activating transcription factor 6 (ATF6) was detected by immunofluorescence assay. Western blot was used to detect the expressions of p-PERK, p-eIF2α, C/EBP homologous protein (CHOP) and Bcl-2. Irisin reduced lipid accumulation in macrophages in a concentration-dependent pattern and significantly inhibited apoptosis induced by ox-LDL and TM. Compared with ox-LDL and TM groups, the expressions of CHOP, p-PERK and p-eIF2α in the irisin group significantly decreased, the translocation of ATF6 from cytoplasm to nucleus was significantly weakened, and Bcl-2 expression significantly increased. Irisin can alleviate the apoptosis of macrophages induced by ox-LDL, which may be achieved by inhibiting the PERK/eIF2α/CHOP and ATF6/CHOP endoplasmic reticulum stress signaling pathways.

Exercise training with dietary restriction enhances circulating irisin level associated with increasing endothelial progenitor cell number in obese adults: an intervention study

Objective

Circulating endothelial progenitor cells (EPCs) correlate negatively with obesity. Previous studies have shown that exercise significantly restores circulating EPC levels in obese people; however, the underlying mechanisms have not been elucidated. Recently, irisin has been reported to have a critical role in the regulation of EPCs. This exercise-induced myokine has been demonstrated to play a therapeutic role in obesity. In this study, we hypothesized that the increase in circulating irisin may form a link with increasing EPC levels in obese people after exercise.

Methods

Seventeen obese adults completed an 8-week program of combined exercise and dietary intervention. Clinical characteristics, blood biochemistry, and circulating irisin levels of subjects were measured before and after eight weeks of training. EPC levels were evaluated via flow cytometry, and EPC migratory and adhesive functions were also determined.

Results

Circulating irisin levels significantly increased following the 8-week training program (P < 0.05). We furthermore observed an improvement in EPC numbers (P < 0.05), and EPC migratory and adhesive functions (P < 0.001 and P < 0.05, respectively) after the intervention. Additionally, we detected a positive correlation between changes in irisin and changes in EPC number (r = 0.52, P < 0.05).

Discussion

For the first time, a positive correlation between increasing irisin levels and increasing EPC levels has been reported after an 8-week program, consisting of exercise and dietary intervention. This result suggests a novel effect of irisin on the regulation of EPC mobilization, which might contribute to improvement of endothelial function in obese people.

Physiology and role of irisin in glucose homeostasis

Irisin is a myokine that leads to increased energy expenditure by stimulating the 'browning' of white adipose tissue. In the first description of this hormone, increased levels of circulating irisin, which is cleaved from its precursor fibronectin type III domain-containing protein 5, were associated with improved glucose homeostasis by reducing insulin resistance. Consequently, several studies attempted to characterize the role of irisin in glucose regulation, but contradictory results have been reported, and even the existence of this hormone has been questioned. In this Review, we present the current knowledge on the physiology of irisin and its role in glucose homeostasis. We describe the mechanisms involved in the synthesis, secretion, circulation and regulation of irisin, and the controversies regarding the measurement of irisin. We also discuss the direct effects of irisin on glucose regulatory mechanisms in different organs, the indirect effects and interactions with other hormones, and the important open questions with regard to irisin in those organs. Finally, we present the results from animal interventional studies and from human clinical studies investigating the association of irisin with obesity, insulin resistance, type 2 diabetes mellitus and the metabolic syndrome.

Macro- and microvascular endothelial dysfunction in diabetes

Endothelial cells, as well as their major products nitric oxide (NO) and prostacyclin, play a key role in the regulation of vascular homeostasis. Diabetes mellitus is an important risk factor for cardiovascular disease. Diabetes-induced endothelial dysfunction is a critical and initiating factor in the genesis of diabetic vascular complications. The present review focuses on both large blood vessels and the microvasculature. The endothelial dysfunction in diabetic macrovascular complications is characterized by reduced NO bioavailability, poorly compensated for by increased production of prostacyclin and/or endothelium-dependent hyperpolarizations, and increased production or action of endothelium-derived vasoconstrictors. The endothelial dysfunction of microvascular complications is primarily characterized by decreased release of NO, enhanced oxidative stress, increased production of inflammatory factors, abnormal angiogenesis, and impaired endothelial repair. In addition, non-coding RNAs (microRNAs) have emerged as participating in numerous cellular processes. Thus, this reviews pays special attention to microRNAs and their modulatory role in diabetes-induced vascular dysfunction. Some therapeutic strategies for preventing and restoring diabetic endothelial dysfunction are also highlighted.

Irisin suppresses the migration, proliferation, and invasion of lung cancer cells via inhibition of epithelial-to-mesenchymal transition

Irisin is involved in promoting metabolism, immune regulation, and affects chronic inflammation in many systemic diseases, including gastric cancer. However, the role of irisin in lung cancer is not well characterized. To determine whether irisin has a protective effect against lung cancer, we cultured A549 and NCI-H446 lung cancer cells and treated them with irisin. We detected the proliferation by MTT assay, and assessed the migration and invasion of the cells by scratch wound healing assay and Tran-swell assay. The expression levels of epithelial-to-mesenchymal transition (EMT) markers and the related signaling pathways were detected by western blot analysis. Meanwhile, an inhibitor of PI3K was used to investigate the effect of irsin. Finally, the expression of Snail was detected. We demonstrated that irisin inhibits the proliferation, migration, and invasion of lung cancer cells, and has a novel role in mediating the PI3K/AKT pathway in the cells. Irisin can reverse the activity of EMT and inhibit the expression of Snail via mediating the PI3K/AKT pathway, which is a key regulator of Snail. These results revealed that irisin inhibited EMT and reduced the invasion of lung cancer cells via the PI3K/AKT/Snail pathway.