Exercise-induced Myokine Research Articles

Circulating Irisin is Increased in Type 2 Diabetes Mellitus and Correlates with Fasting Glucose Levels

Abstract Background/aims Irisin is a hormone expressed in muscle, which is an exercise-induced myokine triggering browning of white adipose tissue and increases metabolic genes expression. Methods We investigated the irisin levels in 39 type 2 diabetes mellitus patients (T2D) compared to 39 control individuals. Results Irisin plasma levels were higher in T2D patients when compared with the control group ( p p p =0.011, respectively). Obese T2D individuals showed higher irisin levels when compared with non-obese control ( p =0.003), but no difference was observed when compared with obese controls ( p >0.05). A positive correlation was observed between irisin and fasting glucose levels in the T2D group ( r =0.341, p =0.033). No difference regarding irisin levels was found when T2D individuals who practice physical activity and sedentary individuals were compared ( p =0.632). Conclusion This result indicates that T2D is associated with an irisin release in order to compensate the insulin resistance observed in the skeletal muscle on diabetes, and that the poor glycaemic control contributes for enhancement of this state.

High Serum Irisin Level as an Independent Predictor of Diabetes Mellitus

Irisin, a novel exercise-induced myokine, has been suggested to regulate energy homeostasis and insulin sensitivity. However, it remains unclear whether circulating irisin plays a role in the development of DM in human. We investigated the possible association between circulating irisin levels and incident DM in a 2.6-year longitudinal study of a population-based cohort comprised of rural Korean subjects.We conducted a longitudinal study within the Korean Genome and Epidemiology Study on Atherosclerosis Risk of Rural Areas in the Korean General Population (KoGES-ARIRANG) study from November 2005 to January 2008. Cases (n=85) were patients with incident DM during the follow-up period and controls (n = 85) were matched to incident DM cases based on sex and age at baseline. The relative risk of serum irisin/adiponectin level for incident DM was analyzed using conditional logistic regression analysis.Baseline irisin_ENREF_1 levels were significantly higher in subjects who developed DM than in subjects who did not. The serum irisin level was positively associated with glycated hemoglobin (HbA1c) and postprandial glucose. Irisin was negatively associated with adiponectin (R = –0.189, P = 0.014). After adjustment for potential confounders, including body mass index, the odds ratios [95% confidence intervals] for incident DM increased in a graded manner as the serum irisin level increased (Quartile 1 vs Quartile 2 vs Quartile 3 vs Quartile 4 = 1 vs 0.80 [0.28–2.35] vs 3.33 [1.11–10.00] vs 4.10 [1.35–12.44], respectively), whereas the odds ratios for incident DM decreased in a graded manner as the serum adiponectin level increased.High serum irisin was independently associated with the development of DM, indicating that irisin may be a useful predictor of DM in Korean adults.

Irisin promotes osteoblast proliferation and differentiation via activating the MAP kinase signaling pathways.

Physical exercise is able to improve skeletal health. However, the mechanisms are poorly known. Irisin, a novel exercise-induced myokine, secreted by skeletal muscle in response to exercise, have been shown to mediate beneficial effects of exercise in many disorders. In the current study, we demonstrated that irisin promotes osteoblast proliferation, and increases the expression of osteoblastic transcription regulators, such as Runt-related transcription factor-2, osterix/sp7; and osteoblast differentiation markers, including alkaline phosphatase, collagen type 1 alpha-1, osteocalcin, and osteopontin in vitro. Irisin also increase ALP activity and calcium deposition in cultured osteoblast. These osteogenic effects were mediated by activating the p38 mitogen-activated protein kinase (p-p38 MAPK) and extracellular signal-regulated kinase (ERK). Inhibition of p38 MAPK by SB023580 or pERK by U0126 abolished the proliferation and up-regulatory effects of irisin on Runx2 expression and ALP activity. Together our observation suggest that irisin directly targets osteoblast, promoting osteoblast proliferation and differentiation via activating P38/ERK MAP kinase signaling cascades in vitro. Whether irisin can be utilized as the therapeutic agents for osteopenia and osteoporosis is worth to be further pursued.

Role of endogenous irisin, a novel myokine, in cognitive functions and insulin sensitivity in exercised diabetic rats

Background Irisin, an exercise-induced myokine, has broad implications for metabolism and energy homeostasis. The aim of this work was to investigate the irisin expression and its receptor and the signaling pathway in relation to cognitive functions to allow for a better understanding of its role in an exercised diabetic model. Materials and methods A total of 40 adult male albino rats were divided equally into four groups. The first group included control rats (the control group). The remaining animals were used to establish a type 2 diabetic model and were further divided into the following: the diabetic sedentary group; the chronic exercised diabetic group; and the acute exercised diabetic group. At the end of the study period, the behavioral assessment was carried out for all groups in a T-maze. After scarification, gastrocnemius muscles, whole brains, and abdominal adipose tissues were excised for the measurement of gene expression of muscle irisin, brain irisin receptors, brain-derived neurotrophic factor (BDNF), brain MAPK and adipose tissue uncoupling protein 1 (UCP1), and MAPK. In addition, insulin sensitivity indices and serum lipid profile were measured for the studied groups. Results Muscle irisin expression was significantly elevated in chronic and acute exercised diabetic rats (P Conclusion Our results suggest that raised muscle irisin levels for both types of exercise are involved in the improvement of cognitive functions and insulin sensitivity in diabetic rats. However, further studies should clarify its precise role in relation to fat browning.

Irisin Controls Growth, Intracellular Ca2+ Signals, and Mitochondrial Thermogenesis in Cardiomyoblasts.

Exercise offers short-term and long-term health benefits, including an increased metabolic rate and energy expenditure in myocardium. The newly-discovered exercise-induced myokine, irisin, stimulates conversion of white into brown adipocytes as well as increased mitochondrial biogenesis and energy expenditure. Remarkably, irisin is highly expressed in myocardium, but its physiological effects in the heart are unknown. The objective of this work is to investigate irisin’s potential multifaceted effects on cardiomyoblasts and myocardium. For this purpose, H9C2 cells were treated with recombinant irisin produced in yeast cells (r-irisin) and in HEK293 cells (hr-irisin) for examining its effects on cell proliferation by MTT [3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay and on gene transcription profiles by qRT-PCR. R-irisin and hr-irisin both inhibited cell proliferation and activated genes related to cardiomyocyte metabolic function and differentiation, including myocardin, follistatin, smooth muscle actin, and nuclear respiratory factor-1. Signal transduction pathways affected by r-irisin in H9C2 cells and C57BL/6 mice were examined by detecting phosphorylation of PI3K-AKT, p38, ERK or STAT3. We also measured intracellular Ca2+ signaling and mitochondrial thermogenesis and energy expenditure in r-irisin-treated H9C2 cells. The results showed that r-irisin, in a certain concentration rage, could activate PI3K-AKT and intracellular Ca2+ signaling and increase cellular oxygen consumption in H9C2 cells. Our study also suggests the existence of irisin-specific receptor on the membrane of H9C2 cells. In conclusion, irisin in a certain concentration rage increased myocardial cell metabolism, inhibited cell proliferation and promoted cell differentiation. These effects might be mediated through PI3K-AKT and Ca2+ signaling, which are known to activate expression of exercise-related genes such as follistatin and myocardin. This work supports the value of exercise, which promotes irisin release.

Dihydromyricetin stimulates irisin secretion partially via the PGC-1α pathway

Irisin, derived from FNDC5, is an exercise-induced myokine that can stimulate the ‘browning’ of white adipose tissue, which is regulated by peroxisome proliferator-activated receptor γ coactivator 1 α (PGC-1α). Dihydromyricetin (DHM), a natural flavonoid, exerts its activities through PGC-1α activation. Here, we explored whether DHM could mimic the effects of exercise on irisin secretion. DHM administration increased circulating irisin in rats and humans. Notably, the serum irisin level had a greater correlation to the level of circulating DHM than to the amount of exercise. DHM treatment upregulated PGC-1α and FNDC5 expression, enhanced energy metabolism, as evidenced by NMR-based metabonomics analysis, and partially abolished the suppressive effects of Pgc-1α siRNA on FNDC5 expression. These results suggest that DHM can stimulate irisin secretion partially via the PGC-1α pathway. As a potent exercise mimetic, DHM is expected to benefit patients suffering from metabolic diseases, especially those who cannot undergo rigorous exercise.

Circulating irisin levels are positively associated with metabolic risk factors in sedentary subjects.

IntroductionA physically active life-style plays an independent role in the protection against type 2 diabetes and cardiovascular diseases. Irisin, a novel exercise-induced myokine, activates thermogenesis in rodents through increasing beige fat cells abundance within white fat. We aimed to investigate circulating irisin levels in association with the degree of physical activity and various metabolic parameters in humans.MethodsCirculating irisin levels (ELISA) and metabolic parameters were analyzed in 428 subjects (195 men/233 women). Participants were classified according to their self-reported physical activity and to their area of residence.ResultsCirculating irisin levels were higher in active than in sedentary subjects (p= 0.006). Rural inhabitants showed higher circulating irisin levels than urban subjects (p < 0.0001). The increase in irisin levels related to an active lifestyle was only observed in rural citizens (p = 0.014). Among sedentary participants, irisin levels were positively associated with metabolic risk factors (BMI, fasting insulin, HOMA and fasting triglycerides). The area of residence (β= - 0.592, p= < 0.0001) contributed independently to circulating irisin levels variance after controlling for age, gender, BMI, HOMAIR, triglycerides and physical activity.ConclusionsIn sedentary participants, circulating irisin levels were positively associated with parameters related to an increased cardiometabolic risk. The present study confirmed that an active lifestyle increases circulating irisin levels, but only among subjects living in a rural environment. Area of residence might be a determinant of irisin levels.

Irisin in response to exercise in humans with and without metabolic syndrome.

Irisin is a recently identified exercise-induced myokine. However, the circulating levels of irisin in response to different types of exercise in subjects with metabolic syndrome are unknown. This study aimed to study the levels of irisin in healthy males and subjects with metabolic syndrome at baseline and in response to exercise. Each individual completed high-intensity interval exercise (HIIE), continuous moderate-intensity exercise (CME), and resistance exercise (RE) sessions in a random, crossover design. Percentage change in circulating irisin levels was examined. Two different irisin assays were used to compare the results of the RE study. Circulating irisin increased immediately after HIIE, CME, and RE and declined 1 hour later. The increase was greater in response to resistance compared with either high-intensity intermittent exercise or CME. Change in irisin in response to exercise did not differ between individuals with and without metabolic syndrome. Exercise is able to increase circulating irisin levels in individuals with the metabolic syndrome as well as healthy individuals. Whether this increase may contribute to the beneficial effects of exercise on patients with the metabolic syndrome remains to be studied further.

OP2-4 - The effect of Irisin on antioxidant system in liver

Nonalcoholic fatty liver disease (NAFLD) is a global health problem and lead to subacute liver failure, cirrhosis and/or hepatocellular carcinoma. An increased generation of reactive oxygen species (ROS) and antioxidant depletion is found in the liver of obese patients with NAFLD. Irisin is a recently identified exercise-induced myokine. It increases total energy consumption, reduces body weight, and insulin resistance. It was shown that irisin levels were significantly lower in patients with NAFLD.The aim of the present study was to investigate the effect of irisin on prooxidant-antioxidant balance in liver.In the first phase; AML12 liver cells were divided into 4 groups: control, hydrogen peroxide (H2O2)-treated, 10nM irisin-treated and 50nM irisin-treated groups. ROS accumulation in these groups was analyzed by FACS. In the second phase; to see if there is any protective role of irisin on ROS production in the liver, AML12 liver cells were divided into 4 groups: control, H2O2 -treated, H2O2+10nM irisin-treated and H2O2+50nM-irisin treated groups. After measuring ROS accumulation again in these groups, the levels of enzymes related with prooxidant-antioxidant balance via oxidative stress in liver were measured by western blotting.In H2O2 treatment groups, ROS production was increased in AML12 liver cells, on the other hand in irisin treatment groups ROS production was slightly changed. Irisin might be a potential target for metabolic diseases like NAFLD.

Irisin stimulates muscle growth-related genes and regulates adipocyte differentiation and metabolism in humans

Irisin is a recently identified exercise-induced myokine suggested to induce browning of white adipocytes. Deficiency of myostatin, and thus stimulation of muscle growth, has also been reported to induce irisin and its precursor FNDC5 expression in muscle and drive the browning of white adipocytes in mice, implying that irisin may be related to muscle growth in addition to its beneficial effects in adipocytes. In humans, the effect of irisin in muscle hypertrophy as well as adipocyte metabolism has not been fully investigated. Primary cultured human myocytes/adipocytes and 3T3-L1 cells were used to examine irisin-regulated gene/protein expression. Lipid accumulation, ATP content, glycolysis, lipolysis and metabolite profile were measured in control and irisin-treated (10 and 50 nM) adipocytes. In human myocytes, FNDC5 mRNA and irisin secretion were increased during myogenic differentiation, along with PGC1α and myogenin expression. Irisin treatment significantly increased insulin-like growth factor 1 and decreased myostatin gene expression through ERK pathway. PGC1α4, a newly discovered PGC1α isoform specifically related to muscle hypertrophy, was also upregulated. In human adipocytes, irisin induced uncoupling protein 1 and consequently increased adipocyte energy expenditure, expression of metabolic enzymes and metabolite intermediates, resulting in inhibition of lipid accumulation. Irisin and FNDC5 treatment also reduced preadipocyte differentiation, suggesting an additional mechanism in suppressing fat mass. These results suggest that irisin/FNDC5 has a pleiotropic role in muscle and improvement of adipocyte metabolism in humans.

Irisin and FGF21 Are Cold-Induced Endocrine Activators of Brown Fat Function in Humans

Rediscovery of cold-activated brown adipose tissue (BAT) in humans has boosted research interest in identifying BAT activators for metabolic benefits. Of particular interest are cytokines capable of fat browning. Irisin, derived from FNDC5, is an exercise-induced myokine that drives brown-fat-like thermogenesis in murine white fat. Here we explored whether cold exposure is an afferent signal for irisin secretion in humans and compared it with FGF21, abrown adipokine in rodents. Cold exposure increased circulating irisin and FGF21. We found an induction of irisin secretion proportional to shivering intensity, in magnitude similar to exercise-stimulated secretion. FNDC5 and/or FGF21 treatment upregulated human adipocyte brown fat gene/protein expression and thermogenesis in a depot-specific manner. These results suggest exercise-induced irisin secretion could have evolved from shivering-related muscle contraction, serving to augment brown fat thermogenesis in concert with FGF21. Irisin-mediated muscle-adipose crosstalk may represent a thermogenic, cold-activated endocrine axis that is exploitable in obesity therapeutics development.

Abstract 5400: Exercise activates AMP-activated protein kinase in breast cancer cells.

Abstract Objective: Cancer cells are characterized by a changed cellular metabolism, favoring glycolysis. AMPK, a serine/threonine kinase regulates cellular metabolism, and induces fatty acid oxidation and has in regard to this, been shown to suppress tumor cell growth. During physical activity, which is associated with a reduced cancer risk, working muscles secrete myokines, known to activate AMPK. This could indicate a connection between AMPK activity, myokine release from the working muscle, and an anti-cancer response. We hypothesize that exercise-induced myokine secretion causes an anti-cancer response via AMPK activation. Methods: Exercise-induced AMPK activation was studied in two models, 1) A cell study using the two breast cancer cell lines, MDA-MB-231 and MCF-7, incubated with exercise-conditioned serum, representing a myokine pool. Serum was collected from 9 females during a 2 hours cycling bout, and during a subsequent 3 hours rest. Following incubation, cell viability and AMPK phosphorylation was determined in the cells. 2) An In Vivo model, where the two cell lines were injected into nude mice. When the tumors reached 6 mm in diameter, the mice were subjected to 1 hour forced swimming bout, after which the tumors were dissected and analyzed for pAMPK content. Results: 1) Cell study: Two hours of cycling induced a 6-fold increase in serum IL-6, as expected. Incubating cancer cells with this post-exercise serum resulted in a significant reduction in the viability of MCF-7 cells, while no effect on the viability of MDA-MB-231 cells were observed. Preliminary data show increased AMPK phosphorylation in both MDA-MB-231 and MCF-7 cells after incubation with 5% exercise-conditioned serum. 2) In vivo study: 1 hour of swimming resulted in significantly increased AMPK phosphorylation in the MCF-7 tumors. Conclusion: Our preliminary data indicate that exercise-induced factors can cause decreased viability and increased AMPK activity in MCF-7 cells, while MDA-MB-231 cells need further investigation. Acknowledgement: The Centre of Inflammation and Metabolism (CIM) is supported by a grant from the Danish National research Foundation (#02-512-55). This study was further supported by the Danish Medical Research Council and the Lundbeck Foundation. Citation Format: Grith W. Højfeldt, Christine Dethlefsen, Bente K. Pedersen, Pernille Hojman. Exercise activates AMP-activated protein kinase in breast cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5400. doi:10.1158/1538-7445.AM2013-5400

Rev-erbβ Regulates the Expression of Genes Involved in Lipid Absorption in Skeletal Muscle Cells: EVIDENCE FOR CROSS-TALK BETWEEN ORPHAN NUCLEAR RECEPTORS AND MYOKINES

Rev-erbbeta is an orphan nuclear receptor that selectively blocks trans-activation mediated by the retinoic acid-related orphan receptor-alpha (RORalpha). RORalpha has been implicated in the regulation of high density lipoprotein cholesterol, lipid homeostasis, and inflammation. Reverbbeta and RORalpha are expressed in similar tissues, including skeletal muscle; however, the pathophysiological function of Rev-erbbeta has remained obscure. We hypothesize from the similar expression patterns, target genes, and overlapping cognate sequences of these nuclear receptors that Rev-erbbeta regulates lipid metabolism in skeletal muscle. This lean tissue accounts for >30% of total body weight and 50% of energy expenditure. Moreover, this metabolically demanding tissue is a primary site of glucose disposal, fatty acid oxidation, and cholesterol efflux. Consequently, muscle has a significant role in insulin sensitivity, obesity, and the blood-lipid profile. We utilize ectopic expression in skeletal muscle cells to understand the regulatory role of Rev-erbbeta in this major mass peripheral tissue. Exogenous expression of a dominant negative version of mouse Rev-erbbeta decreases the expression of many genes involved in fatty acid/lipid absorption (including Cd36, and Fabp-3 and -4). Interestingly, we observed a robust induction (>15-fold) in mRNA expression of interleukin-6, an "exercise-induced myokine" that regulates energy expenditure and inflammation. Furthermore, we observed the dramatic repression (>20-fold) of myostatin mRNA, another myokine that is a negative regulator of muscle hypertrophy and hyperplasia that impacts on body fat accumulation. This study implicates Rev-erbbeta in the control of lipid and energy homoeostasis in skeletal muscle. In conclusion, we speculate that selective modulators of Rev-erbbeta may have therapeutic utility in the treatment of dyslipidemia and regulation of muscle growth.