Effect of obesity and exercise on the expression of the novel myokines, Myonectin and Fibronectin type III domain containing 5

Combined serum CTRP7 and CTRP15 levels as a novel biomarker for insulin resistance and type 2 diabetes mellitus

Aims

This study aimed to examine the alterations in the serum CTRP7 and CTRP15 concentrations in patients newly diagnosed with type 2 diabetes mellitus (T2DM) and to assess the diagnostic potential of the log10 (CTRP7+CTRP15) for insulin resistance (IR) and T2DM.

Methods

Serum CTRP7, CTRP15, and adiponectin levels were measured using an enzyme-linked immunosorbent assay (ELISA). Bioinformatics analysis was conducted to investigate CTRP7 and CTRP15-related genes and metabolic signaling pathways.

Results

Log10 (CTRP7+CTRP15) levels were notably elevated in the impaired glucose tolerance (IGT) and T2DM cohorts compared with those in the normal control (NGT) cohort. Log10(CTRP7+CTRP15) exhibited positive correlations with HOMA-IR, area under the glucose curve (AUCg), HbA1c%, triglyceride (TG), visceral adiposity index (VAI), body mass index (BMI), and free fatty acid (FFA), levels but negative correlations with adiponectin. Multivariate stepwise regression analysis revealed that HOMA-IR, BMI, HbA1c and FFA levels were independent factors affecting the log10 (CTRP7+CTRP15). Logistic regression analysis revealed that log10 (CTRP7+CTRP15) was independently associated with T2DM and significantly associated with increased risk. Receiver operating characteristic (ROC) curve analysis indicated that the predictive value of log10 (CTRP7+CTRP15) for T2DM and IR was superior to that of CTRP7 or CTRP15 alone. Intervention studies demonstrated that insulin, FFAs and acute exercise contribute to the elevation of serum CTRP7 levels, while hyperglycemia inhibited CTRP7 secretion. Short-term changes in blood glucose, insulin, FFA and acute exercise had minimal effects on serum CTRP15 levels. Bioinformatics analysis revealed that CTRP7 and CTRP15 interact with multiple metabolism-related genes and are enriched in glucose and lipid metabolism-related pathways.

Conclusion

Log10 (CTRP7+CTRP15) may serve as a valuable diagnostic marker for the management of metabolic-related diseases, particularly T2DM and IR.

Effects of an energy drink on myonectin in the liver, kidney and skeletal muscle of exercised rats

Myonectin is a hormone that is produced mainly by skeletal muscle. We investigated the effects of exercise and energy drink (ED) administration on myonectin expression in skeletal muscle, liver and kidney tissue in rats; myonectin is produced by all three tissues. We used 28 male albino rats in four groups: untreated control (C), exercise (E), energy drink (ED) and exercise + energy drink (E + ED). The E and E + ED groups were exercised using a treadmill for 4 weeks. We also administered 3.5 ml/kg/day ED during week 1, 7 ml/kg/day during week 2 and 10 ml/kg/day during weeks 3 and 4 in the E and E + ED groups. We used ELISA to measure the levels of myonectin in skeletal muscle, liver and kidney tissues. We used immunohistochemical staining to investigate the localization and intensity of myonectin in these tissues. The amount of myonectin in skeletal muscle tissue was increased significantly in all experimental groups compared to group C. The amount of myonectin in the ED group was significantly greater than group E. No significant difference was observed in liver tissue; however, the amount of myonectin in the liver of group C was the greatest among all groups. The amount of myonectin in kidney tissue exhibited no significant difference among groups. Consumption of ED during exercise increased the amount of myonectin in kidney and skeletal muscle tissues and decreased it in liver tissue. We suggest that consumption of ED might adapt metabolism to incresed exercise by controling synthesis of myonectin in liver, kidney and skeletal muscle.

Effects of myonectin on porcine intramuscular adipocyte differentiation and exogenous free fatty acid utilization

As an important factor secreted by skeletal muscle, myonectin can regulate lipid metabolism and energy metabolism, but its role in the utilization of peripheral free fatty acids (FFAs) by porcine intramuscular fat cells remains to be further investigated. In this study, porcine intramuscular adipocytes were treated with recombinant myonectin and palmitic acid (PA), either alone or in combination, and then were examined for their uptake of exogenous FFAs, intracellular lipid synthesis and catabolism, and mitochondrial oxidation of fatty acids. The results showed that myonectin decreased the area of lipid droplets in intramuscular adipocytes (p < 0.05) and significantly increased (p < 0.05) the expression levels of hormone-sensitive lipase (HSL) and lipoprotein lipase (LPL). Moreover, myonectin can up-regulate the expression of p38 mitogen-activated protein kinase (p38 MAPK). Myonectin significantly promoted the uptake of peripheral FFAs (p < 0.01), improved (p < 0.05) the expression of fatty transport protein 1 (FATP1) and fatty acid binding protein 4 (FABP4) in intramuscular adipocytes. Myonectin also significantly increased (p < 0.05) the expression levels of fatty acid oxidation markers: transcription factor (TFAM), uncoupling protein-2 (UCP2) and oxidative respiratory chain marker protein complex I (NADH-CoQ) in mitochondria of intramuscular adipocytes. In summary, myonectin promoted the absorption, transport, and oxidative metabolism of exogenous FFAs in mitochondria, thereby inhibiting lipid deposition in porcine intramuscular adipocytes.

Lack of association between serum myonectin levels and sarcopenia in older Asian adults

Myonectin is a muscle-secreted factor that helps maintain homeostasis in the body by regulating several functions, including lipid metabolism. Previous studies suggested that myonectin may play a role in muscle health in an autocrine manner, but its impact on human skeletal muscle is still unclear. We aimed to investigate the relationship of serum myonectin levels with sarcopenia and related muscle parameters. We conducted a cross-sectional study of 142 older adults whose muscle mass, grip strength, gait speed, chair stands, and short physical performance battery (SPPB) were evaluated in the geriatric clinic of a tertiary medical center. Sarcopenia was defined based on Asian-specific cutoff values, and circulating myonectin levels were measured using an enzyme immunoassay. Before and after adjusting for age, sex, and body mass index, the serum myonectin level was not significantly different when the patients were stratified by status of sarcopenia, muscle mass, muscle strength, and physical performance. Furthermore, whether given as a continuous variable or divided into quartile groups, the serum myonectin level had no association with the skeletal muscle mass, grip strength, gait speed, chair stand test, or SPPB score. Our findings did not confirm the potential role of myonectin in muscle metabolism observed in experimental research. Thus, serum myonectin levels cannot predict the risk of sarcopenia in older Asian adults.

The Role of Crosstalk between Adipose Cells and Myocytes in the Pathogenesis of Sarcopenic Obesity in the Elderly

As a result of aging, body composition changes, with a decline in muscle mass and an increase in adipose tissue (AT), which reallocates from subcutaneous to visceral depots and stores ectopically in the liver, heart and muscles. Furthermore, with aging, muscle and AT, both of which have recognized endocrine activity, become dysfunctional and contribute, in the case of positive energy balance, to the development of sarcopenic obesity (SO). SO is defined as the co-existence of excess adiposity and low muscle mass and function, and its prevalence increases with age. SO is strongly associated with greater morbidity and mortality. The pathogenesis of SO is complex and multifactorial. This review focuses mainly on the role of crosstalk between age-related dysfunctional adipose and muscle cells as one of the mechanisms leading to SO. A better understanding of this mechanisms may be useful for development of prevention strategies and treatments aimed at reducing the occurrence of SO.

Insight into the role of myokines and myogenic regulatory factors under hypobaric hypoxia induced skeletal muscle loss

Aim: The present study aimed to analyze the role of myokines and the regeneration capacity of skeletal muscle during chronic hypobaric hypoxia (HH).Method: Male SD rats were exposed to HH for 1d, 3d, and 7d.Results: Exposure to HH enhanced the levels of decorin, irisin, IL-6 and IL-15 till 3 days of hypoxia and on 7 day of exposure, no significant changes were observed in relation to control. A significant upregulation in myostatin, AMPK, SMAD3, SMAD4, FOXO-1, MURF-1 expression was observed with prolonged HH exposure as compared to normoxic control. Further, myogenesis-related markers, PAX-7, Cyclin D1, and MYOG were downregulated during chronic HH exposure in comparison to control. Energy metabolism regulators such as SIRT1, PGC-1α, and GLUT-4, were also increased on 1d HH exposure that showed a declining trend on chronic HH exposure.Conclusion: These results indicated the impairment in the levels of myokines and myogenesis during prolonged hypoxia. Chronic HH exposure enhanced the levels of myostatin and reduced the regeneration or repair capacity of the skeletal muscles. Myokine levels could be a predictive biomarker for evaluating skeletal muscle performance and loss at high altitudes.

Plasma Complement C1q/tumor necrosis factor-related protein 15 concentration is associated with polycystic ovary syndrome

Polycystic ovarian syndrome (PCOS) is a common poignant endocrine disorder affecting women, posing a close association with metabolic syndrome and obesity. Existing literature characterizes PCOS with deranged levels of several adipokines and myokines. CTRP15 is a paralogue of adiponectin, mainly expressed by skeletal muscles, and plays a key role in insulin, glucose, and lipid metabolism. In the current study, we aim to determine the circulating levels of CTRP15 and evaluate its association with cardiometabolic and inflammatory parameters in PCOS women. This case-control study included 120 PCOS patients (60 Recurrent pregnancy loss (RPL) and 60 infertile (inf) PCOS) and 60 healthy non-PCOS controls. Serum levels of hs-CRP were measured by commercial kits, while serum levels of adiponectin and CTRP15 were determined using the ELISA technique. Serum levels of CTRP15 were significantly elevated in PCOS-RPL and PCOS-inf subgroups when compared to controls (94.80 ± 27.08 and 87.77 ± 25.48 vs. 54.78 ± 15.45, both P < 0.001). Moreover, serum adiponectin was considerably lower in the PCOS group and subgroups (P < 0.001), while serum hs-CRP, fasting insulin, HOMA-IR, and free testosterone were significantly higher when compared to the non-PCOS group (P < 0.05). Furthermore, CTRP15 closely associated with FSH, HOMA-IR, hs-CRP, and BMI. These results highlight a possible involvement of CTRP15 in the pathogenesis of PCOS. The elevated levels of CTRP15 might be a compensatory mechanism for the metabolic dysregulations (excess adiposity, insulin resistance, metaflammation) associated with the syndrome. Nevertheless, future studies are necessary to unravel the underlying mechanism.

Multifactorial Mechanism of Sarcopenia and Sarcopenic Obesity. Role of Physical Exercise, Microbiota and Myokines

Obesity and ageing place a tremendous strain on the global healthcare system. Age-related sarcopenia is characterized by decreased muscular strength, decreased muscle quantity, quality, and decreased functional performance. Sarcopenic obesity (SO) is a condition that combines sarcopenia and obesity and has a substantial influence on the older adults’ health. Because of the complicated pathophysiology, there are disagreements and challenges in identifying and diagnosing SO. Recently, it has become clear that dysbiosis may play a role in the onset and progression of sarcopenia and SO. Skeletal muscle secretes myokines during contraction, which play an important role in controlling muscle growth, function, and metabolic balance. Myokine dysfunction can cause and aggravate obesity, sarcopenia, and SO. The only ways to prevent and slow the progression of sarcopenia, particularly sarcopenic obesity, are physical activity and correct nutritional support. While exercise cannot completely prevent sarcopenia and age-related loss in muscular function, it can certainly delay development and slow down the rate of sarcopenia. The purpose of this review was to discuss potential pathways to muscle deterioration in obese individuals. We also want to present the current understanding of the role of various factors, including microbiota and myokines, in the process of sarcopenia and SO.

Increased serum myonectin and irisin levels with myonectin and FNDC5 expressions in polycystic ovary syndrome: a case control study

The aim of this study is to assess the FNDC5 and myonectin expressions and serum levels of myonectin and irisin in women with PCOS. 90 participants were included in this case-control study. 45 of these participants were with PCOS, and 45 of them were healthy volunteers matched for age and body mass index (BMI). Serum irisin and myonectin levels were measured with commercially available enzyme-linked immune sorbent assay (ELISA) kits. Expression of the myonectin and FNDC5 genes were determined by RT-PCR analysis. It was found out that FSI, HOMA-IR, LH, LH/FSH, TT, serum irisin and serum myonectin levels, myonectin mRNA expression, and FNDC5 mRNA expression were higher in the PCOS group, whereas HDL-C level was lower in the PCOS group (p < .05). When the groups were compared, it was detected that IR and HA were significantly higher in the PCOS group (p < .05). Serum irisin and myonectin levels, and myonectin and FNDC5 mRNA expressions were increased in women with PCOS. These molecules can be target molecules in PCOS pathophysiology and treatment.IMPACT STATEMENTWhat is already known on this subject? Although the aetiology of PCOS is not fully understood, it is thought that insulin resistance may play a critical role. In recent studies, the relationship of cytokines secreted from skeletal muscle with insulin resistance has been shown. The effects of irisin and myonectin, which are members of the myokine family, on lipid and glucose metabolism are known.What do the results of this study add? Although there are many studies in the literature regarding serum irisin levels in women with PCOS, their results are confusing. There is a study in the literature investigating the relationship between myonectin and PCOS. In our study, we evaluated myonectin and FNDC mRNA expressions in addition to serum irisin and myonectin levels. As a result, we found that markers and their mRNA expressions were lower in patients with PCOS compared to controls.What are the implications of these findings for clinical practice and/or further research? We think that the results of our study will shed light on future studies. Due to their effects on adipose tissue, these markers may play a role in the aetiology of long-term complications of PCOS. Moreover, they can become pharmacological targets in preventing these complications.

Cell Types Used for Cultured Meat Production and the Importance of Myokines

The world’s population continues to increase, meaning we require more consistent protein supply to meet demand. Despite the availability of plant-based protein alternatives, animal meat remains a popular, high-quality protein source. Research studies have focused on cultured meat (meat grown in vitro) as a safe and more efficient alternative to traditional meat. Cultured meat is produced by in vitro myogenesis, which involves the processing of muscle satellite and mature muscle cells. Meat culture efficiency is largely determined by the culture conditions, such as the cell type and cell culture medium used and the biomolecular composition. Protein production can be enhanced by providing the optimum biochemical and physical conditions for skeletal muscle cell growth, while myoblasts play important roles in skeletal muscle formation and growth. This review describes the cell types used to produce cultured meat and the biological effects of various myokines and cytokines, such as interleukin-6, leukemia inhibitory factor, interleukin-4, interleukin-15, and interleukin-1β, on skeletal muscle and myogenesis and their potential roles in cultured meat production.

Irisin serum increasing pattern is higher at moderate-intensity continuous exercise than at moderate-intensity interval exercise in obese females

Lifestyle, unhealthy eating patterns, and low physical activity become trigger factors of obesity. Therefore, lifestyle modification with an exercise-based nonpharmacological approach is one of the strategies for combat obesity. This study aims to analyse the response of moderate-intensity interval and continuous exercise to irisin level increasing pattern on the obese female. A total of 21 obese females were enrolled in this study and given moderate-intensity interval exercise (MIIE) and moderate-intensity continuous exercise (MICE). ELISA was used to quantify the serum level of irisin in all samples. Statistical analysis was performed using one way-ANOVA and Tukey’s honestly significant difference (HSD) post hoc test. Mean irisin levels of pre-exercise at control (CON), MIIE, and MICE were 3.26±1.28l, 3.44±0.56 and 3.89±1.08 ng/ml, respectively (P=0.519). The mean irisin level of 10 min post-exercise was 2.99±0.86 ng/ml at CON, 4.82±1.01 ng/ml at MIIE, and 5.99±1.27 ng/ml at MICE (P=0.000). The mean irisin levels of 6 h post-exercise were 3.04±0.60, 4.56±0.87, and 5.73±1.02 ng/ml at CON, MIIE, and MICE, respectively (P=0.000). The mean irisin level of 24 h post-exercise was 3.04±0.91 ng/ml at CON, 4.64±0.69 ng/ml at MIIE, and 5.69±1.53 ng/ml at MICE (P=0.002). We conclude that the post-exercise serum irisin level increased in both MICE and MIIE subjects, and the post-exercise serum irisin level maintained higher in the MICE than in the MIIE in the obese female subjects.

Irisin protects female mice with LPS-induced endometritis through the AMPK/NF-κB pathway

OBJECTIVES

This research was designed to determine the role of irisin in lipopolysaccharide (LPS)-induced endometritis in female mice.

MATERIALS AND METHODS

Animals were randomly assigned into sham, sham + irisin, LPS, LPS + irisin (0.1, 1, 10 μg/kg), and LPS + irisin + compound C groups. Histological features and expression of AMPK, NF-κB, inflammatory mediators, and oxidative stress markers were compared among different groups.

RESULTS

The results showed that LPS resulted in obvious uterus damage, meanwhile, the inflammatory mediators (COX-2, iNOS, IL-1β, IL-6, and TNF-α), as well as NF-κB in the uterine tissue, were significantly increased and the level of adenosine monophosphate-activated protein kinase (AMPK) was reduced. Nevertheless, pretreatment with irisin reversed the phenomena caused by LPS. Interestingly, compound C (AMPK inhibitor) abolished irisin's effects on the uterus, which suggested that irisin's beneficial function was achieved through regulating the AMPK-NF-κB pathway. Moreover, LPS-induced alterations of oxidative factors (MnSOD, GSH, and MDA) were reversed significantly by pretreatment with irisin. This data indicated irisin's beneficial function was also related to antioxidation besides anti-inflammation.

CONCLUSION

Our study implies that irisin is a potential therapeutic agent for endometritis.

The Effect of Irisin as a Metabolic Regulator and Its Therapeutic Potential for Obesity

Obesity is a worldwide health problem due to the imbalance of energy intake and energy expenditure. Irisin, a newly identified exercise-responsive myokine, which is produced by the proteolytic cleavage of fibronectin type III domain-containing protein 5 (FNDC5), has emerged as a promising therapeutic strategy to combat obesity and obesity-related complications. Various studies in mice have shown that irisin could respond to systematic exercise training and promote white-to-brown fat transdifferentiation, but the role and function of irisin in humans are controversial. In this review, we systematically introduced and analyzed the factors that may contribute to these inconsistent results. Furthermore, we also described the potential anti-inflammatory properties of irisin under a variety of inflammatory conditions. Finally, the review discussed the existing unresolved issues and controversies about irisin, including the transcription of the irisin precursor FNDC5 gene in humans, the cleavage site of the yet unknown proteolytic enzyme that cleaves irisin from FNDC5, and the reliability of irisin levels measured with available detection methods.

Erythroferrone structure, function, and physiology: Iron homeostasis and beyond

Erythroferrone (ERFE) is the main erythroid regulator of hepcidin, the homeostatic hormone controlling plasma iron levels and total body iron. When the release of erythropoietin from the kidney stimulates the production of new red blood cells, it also increases the synthesis of ERFE in bone marrow erythroblasts. Increased ERFE then suppresses hepcidin synthesis, thereby mobilizing cellular iron stores for use in heme and hemoglobin synthesis. Recent mechanistic studies have shown that ERFE suppresses hepcidin transcription by inhibiting bone morphogenetic protein signaling in hepatocytes. In ineffective erythropoiesis, pathological overproduction of ERFE by an expanded population of erythroblasts suppresses hepcidin and causes iron overload, even in non-transfused patients. ERFE may be a useful biomarker of ineffective erythropoiesis and an attractive target for treating its systemic effects.

A comparison of CrossFit and concurrent training on myonectin, insulin resistance and physical performance in healthy young women

OBJECTIVE

To compare the effect of CrossFit and concurrent aerobic + resistance training (CT) on circulating myonectin levels, insulin resistance index, and physical performance in young women.

MATERIALS AND METHODS

Thirty healthy women were randomly assigned to CrossFit (n = 16) and CT (n = 14) groups, exercising three sessions per week for eight weeks. Serum myonectin levels, insulin resistance index, body composition, and performance variables were evaluated before and after the intervention period.

RESULTS

Neither the CrossFit nor the CT group improved in myonectin levels and insulin resistance index. While, fat percentage, muscle mass, upper-limb strength, VO_2max, HR at rest, lower body mean power output, and upper body peak power output improved more after CrossFit than the CT.

CONCLUSION

It seems that CrossFit exercises by targeting multiple fitness components in one exercise session may allow participants to perform more activity in less time.

Irisin Protects Against Motor Dysfunction of Rats with Spinal Cord Injury via Adenosine 5'-Monophosphate (AMP)-Activated Protein Kinase-Nuclear Factor Kappa-B Pathway

The aim of the present research was to investigate the effects of irisin, a skeletal muscle-derived myokine, on spinal cord injury (SCI) in rats and explore the possible mechanisms. SCI model was constructed in male SD rats. The effects of irisin on SCI rats were assessed via behavior tests including Basso, Beattie, and Bresnahan (BBB) scoring method and inclined plane test, followed by histomorphology tests including HE staining, Nissl staining, and transmission electron microscope examination. Biochemical analyses including PCR, Western blots and ELISA were employed to further evaluate the changes at molecular level of SCI rats. In addition, lipopolysaccharide (LPS)-induced cell damage model was established in PC12 cells to verify the mechanism of irisin's effect on nerve cells in vitro. Results showed that the BBB score and the angle of incline significantly decreased after SCI surgery, however, chronic irisin treatment improved SCI-induced motor dysfunction. HE and Nissl staining assays showed that SCI surgery induced histological injury of spinal cord, which could be reversed by irisin treatment. Morphological abnormality of nerve cells caused by SCI also could be alleviated by irisin. Further biochemical analyses showed that irisin inhibited SCI-induced overexpression of Interleukin-1β (IL-1β), Interleukin- 6 (IL-6), tumor necrosis factor alpha (TNF-α), inducible nitricoxidesynthase (iNOS) and Cyclooxygenase-2 (COX-2)], as well as nuclear factor kappa-B (NF-κB)p65 in rats, and the positive function of irisin could be reversed by Compound C treatment. In our in vitro study, LPS-induced declines of cell viability and neurite length of PC12 cell were inhibited by irisin treatment, and irisin inhibited LPS-induced overexpression of NF-κBp65, IL-1β, IL-6, TNF-α, iNOS and COX-2. These changes could be reversed by activated protein kinase (AMPK) siRNA pre-treatment. Taken together, irisin could protect the rats from SCI, and its protection is associated with the regulation of adenosine 5'-monophosphate-activated protein kinase (AMPK)- NF-κB signaling pathway.

Impact of diets rich in olive oil, palm oil or lard on myokine expression in rats

It has recently emerged that myokines may be an important skeletal muscle adaptive response to obesogenic diets in sedentary subjects (who do not exercise). This study aimed to assess the influence of various high fat (HF) diets rich in either crude palm oil (cPO), refined palm oil (rPO), olive oil (OO) or lard on the modulation of myokine gene expression in the gastrocnemius. Five groups of 8 rats were each fed HF or control diet for 12 weeks. Systemic parameters concerning glucose, insulin, inflammation, cholesterol, triglycerides (TG) and transaminases were assessed by routine methods or ELISA. Akt and ACC phosphorylation were analyzed by WB in the soleus. Mitochondrial density, inflammation, and the gene expression of 17 myokines and the apelin receptor (Apj) were assessed by qPCR in the gastrocnemius. We found that HF diet-fed rats were insulin resistant and Akt phosphorylation decreased in the soleus muscle, but without any change in Glut4 gene expression. Systemic (IL-6) and muscle inflammation (NFκB and IκB) were not affected by the HF diets as well as TBARS, and ASAT level was enhanced with OO diet. Soleus pACC phosphorylation and gastrocnemius mitochondrial density were not significantly altered. The gene expression of some myokines was respectively increased (myostatin and Il-15) and decreased (Fndc5 and apelin) with the HF diets, whatever the type of fat used. The gene expression of two myokines with anti-inflammatory properties, Il-10 and myonectin, was dependent on the type of fat used and was most increased respectively with cPO or both rPO and OO diets. In conclusion, high-fat diets can differentially modulate the expression of some myokines, either in a dependent manner or independently of their composition.

Quantitative assessment of TLR4 gene polymorphisms and T2DM risk: A meta-analysis

BACKGROUND

Numerous studies have evaluated the association between TLR4 gene polymorphisms and T2DM risk. However, the findings were inconsistent and controversial.

METHODS

In order to drive a more precise estimation, we carried out a meta-analysis based on 41 studies involving 23,250 cases and 24,760 controls. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the strength of association.

RESULTS

Our meta-analysis provides evidence that rs4986790 polymorphism was associated with an increased risk of T2DM in Asian (AG vs. AA, OR = 1.23, 95% CI = 1.01-1.50, p = 0.042; G vs. A, OR = 1.21, 95% CI = 1.01-1.44, p = 0.041). Rs4986791 polymorphism was related to an increased risk of T2DM both in Asian (AG vs. AA, OR = 1.76, 95% CI = 1.11-2.80, p = 0.017; G vs. A, OR = 1.63, 95% CI = 1.04-2.55, p = 0.034) and Caucasian (GG vs. AA, OR = 2.42, 95% CI = 1.23-4.75, p = 0.010). Rs11536889 polymorphism may have a protective effect on T2DM in Chinese populations (CC vs. GG, OR = 0.62, 95% CI = 0.40-0.96, p = 0.031; GC vs. GG, OR = 0.77, 95% CI = 0.61-0.98, p = 0.034; CC vs. GC/GG, OR = 0.81, 95% CI = 0.69-0.96, p = 0.013; C vs. G, OR = 0.76, 95% CI = 0.59-0.97, p = 0.027), whereas rs1927911 may have no impact.

CONCLUSIONS

These findings supported that rs4986790, rs4986791, and rs11536889 may contribute to the risk of T2DM.

Serum myonectin is increased after laparoscopic sleeve gastrectomy

Objective

Myonectin, a newly discovered myokine, enhances fatty acid uptake in cultured adipocytes and hepatocytes and suppresses circulating levels of free fatty acids in mice. Recent studies showed that serum myonectin concentration is negatively correlated with obesity. This study was undertaken to evaluate the change of serum myonectin in obese patients after laparoscopic sleeve gastrectomy.

Methods

This study was performed in a population of 42 obese and 58 control subjects from April of 2018 to December of 2019. All obese subjects underwent laparoscopic sleeve gastrectomy. Anthropometric measurements, lipid profiles, HbA1c and serum myonectin were assessed at baseline and six months after laparoscopic sleeve gastrectomy.

Results

Serum myonectin concentrations were significantly lower in the obese patients than in the controls. Serum myonectin concentrations were increased at six months after laparoscopic sleeve gastrectomy. Simple linear regression analysis indicated that serum myonectin was negatively correlated with weight, waist circumference, hip circumference, body mass index, fasting plasma glucose, homeostasis model assessment of insulin resistance and HbA1c. Only body mass index was still inversely correlated with serum myonectin after multiple linear regression analysis.

Conclusion

Serum myonectin is correlated with obesity and increased after laparoscopic sleeve gastrectomy.

Myonectin inhibits the differentiation of osteoblasts and osteoclasts in mouse cells

Myonectin is a myokine, which is involved in the pathophysiology of diabetes and obesity, and various myokines are involved in the interactions between skeletal muscle and bone. However, roles of myonectin in bone have still remained unknown. We therefore examined the effects of myonectin on mouse osteoblast and osteoclast differentiation in vitro. Myonectin significantly suppressed the mRNA levels of osteogenic genes and alkaline phosphatase (ALP) activity in mouse osteoblasts. As for osteoclasts, myonectin significantly suppressed osteoclast formation as well as the mRNA levels of osteoclast-related genes enhanced by receptor activator nuclear factor κB ligand (RANKL) from mouse monocytic RAW264.7 cells. Moreover, myonectin significantly suppressed osteoclast formation from mouse bone marrow cells in the presence of macrophage-colony stimulating factor and RANKL. On the other hand, myonectin significantly suppressed RANKL-induced oxygen consumption rate and peroxisome proliferator-activated receptor γ coactivator-1β mRNA levels in RAW264.7 cells, although myonectin did not affect these mitochondrial biogenesis parameters in mouse osteoblasts. In conclusion, the present study demonstrated that myonectin suppresses the differentiation and ALP activity in mouse osteoblasts. Moreover, myonectin suppressed osteoclast differentiation from mouse bone marrow and RAW264.7 cells partly through an inhibition of mitochondrial biogenesis.

Myokines in skeletal muscle physiology and metabolism: Recent advances and future perspectives

Myokines are molecules produced and secreted by skeletal muscle to act in an auto-, para- and endocrine manner to alter physiological function of target tissues. The growing number of effects of myokines on metabolism of distant tissues provides a compelling case for crosstalk between skeletal muscle and other tissues and organs to regulate metabolic homoeostasis. In this review, we summarize and discuss the current knowledge regarding the impact on metabolism of several canonical and recently identified myokines. We focus specifically on myostatin, β-aminoisobutyric acid, interleukin-15, meteorin-like and myonectin, and discuss how these myokines are induced and regulated as well as their overall function. We also review how these myokines may serve as potential prognostic biomarkers that reflect whole-body metabolism and how they may be attractive therapeutic targets for treating muscle and metabolic diseases.

TLR4 Polymorphisms (896A>G and 1196C>T) Affect the Predisposition to Diabetic Nephropathy in Type 2 Diabetes Mellitus

PURPOSE

Type 2 diabetes mellitus (T2DM) is a disease with a steadily increasing incidence throughout the world. Some molecules regulating the innate immune responses such as toll-like receptor 4 (TLR4) have shown to be involved in late diabetic complications. This study aimed to investigate the association of TLR4 gene polymorphisms with clinicopathological aspects of T2DM in the Iranian population.

PATIENTS AND METHODS

Two TLR4 896A>G and 1196C>T polymorphisms were assessed in 100 T2DM patients and 100 healthy controls using sequence-specific primers PCR. Demographic, anthropometric, and biochemical parameters were obtained from the participants.

RESULTS

After logistic regression, in 1196C>T, a significant association was shown between diabetic nephropathy (DN) and CT genotype (P= 0.04, OR= 4.35, CI= (1.04-18.1)). TG level has increased significantly in both T2DM and control subjects with CT genotype (P= 0.027, OR= 1.005, 95% CI= (1.001-1.01)). For 896A>G variant, a significant association was also detected between AG genotype and increased oral glucose tolerance test (OGTT) level (P= 0.048, OR= 1.003, 95% CI= (1.00-1.005)).

CONCLUSION

Although minor alleles of 1196C>T and 896A>G variants have not directly been associated with type 2 diabetes, by involving in the dysregulation of serum TG and blood sugar levels, they might increase the risk of DN.

Circulating Serum Myonectin Levels in Obesity and Type 2 Diabetes Mellitus

OBJECTIVE

Myonectin is one of the myokines and has gained interest as a potential new strategy to combat obesity and its associated disorders, such as type 2 diabetes mellitus (T2DM).The objective of this study was to investigate circulating serum myonectin levels in nondiabetes and T2DM and elucidate possible relationships between serum myonectin levels and metabolic parameters in patients with T2DM.

DESIGN

A total of 362 Chinese patients with T2DM and 100 age- and sex-matched healthy controls were recruited in this study. Clinical characteristics, blood biochemistry, and circulating myonectin levels were measured by enzyme-linked immunosorbent assay.

RESULTS

Circulating myonectin levels were significantly decreased in T2DM compared with controls. Obese nondiabetic controls had significantly lower serum myonectin levels compared with lean nondiabetic controls. In diabetic patients, serum myonectin concentrations were significantly negatively correlated with body mass index (BMI), total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), C-reactive protein (CRP), hemoglobin A1c (HbA1c), fasting insulin (Fins), the homeostatic model assessment of insulin resistance (HOMA-IR), visceral fat area, and subcutaneous fat area. After adjusting for covariates, multivariate stepwise regression analysis demonstrated that BMI, LDL-C, TG, HOMA-IR, and visceral fat were the main independent predictors of low serum myonectin concentrations.

CONCLUSIONS

Circulating myonectin levels were decreased in T2DM patients and in obese subjects. Moreover, serum myonectin levels were correlated with metabolic markers of T2DM. These data suggest that myonectin may be a useful marker in predicting the development of obesity and T2DM.

Effects of Aerobic Exercises on Serum Levels of Myonectin and Insulin Resistance in Obese and Overweight Women

Background and Aim: Obesity is associated with cardiovascular diseases, metabolic syndrome, and diabetes and insulin resistance. Myonectin is a myokine mostly secreted from skeletal muscles and inversely associated with obesity. The aim of the present study was to evaluate the effects of 8 weeks of aerobic exercises on serum levels of myonectin and insulin resistance in obese and overweight women.

Materials and Methods: Eighty obese women were assigned to exercise (34) and control groups (46). The exercise program comprised three weekly 45-minute sessions of aerobic exercise training for 8 weeks that included running with 50–70% of maximum heart rate (first 2 weeks – 50%; second week – 60%; third week – 65%; and the last 2 weeks by 70% of maximum heart rate). Twenty-four hours before and after the training session, fasting myonectin serum levels were measured. ANCOVA was used to assess differences between the groups.

Results: Serum levels of myonectin in the experimental group increased significantly (P=0.000); however, insulin resistance significantly decreased in the experimental group (P=0.000).

Conclusion: Therefore, considering the role of myonectin in increasing fatty acid uptake, exercise training can play an essential role in decreasing obesity-related diseases and metabolic syndrome; this effect is partly related to the roles of myonectin. Therefore, the use of this type of exercise is recommended to reduce the risk of diseases associated with obesity and metabolic syndrome.

Role of Myokines in Regulating Skeletal Muscle Mass and Function

Loss of skeletal muscle mass and strength has recently become a hot research topic with the extension of life span and an increasingly sedentary lifestyle in modern society. Maintenance of skeletal muscle mass is considered an essential determinant of muscle strength and function. Myokines are cytokines synthesized and released by myocytes during muscular contractions. They are implicated in autocrine regulation of metabolism in the muscle as well as in the paracrine/endocrine regulation of other tissues and organs including adipose tissue, the liver, and the brain through their receptors. Till date, secretome analysis of human myocyte culture medium has revealed over 600 myokines. In this review article, we summarize our current knowledge of major identified and characterized myokines focusing on their biological activity and function, particularly in muscle mass and function.

Circulating C1q/TNF-related protein isoform 15 is a marker for the presence of metabolic syndrome

BACKGROUND

C1q/TNF-related protein isoform 15 (CTRP15) has been reported to be related to glucose and lipid metabolism, but the results are inconsistent. Metabolic syndrome (MetS) is a cluster of metabolic disorders. The aim of this study is to determine circulating CTRP15 levels in individuals with MetS and investigate the association among circulating CTRP15 and markers for MetS as well as insulin resistance.

METHODS

A total of 341 individuals were recruited for this cross-sectional study. These subjects were screened for MetS. Serum CTRP15 concentrations were measured by ELISA.

RESULTS

Serum CTRP15 levels were significantly higher in MetS individuals relative to those of the healthy individuals. Circulating CTRP15 correlated positively with WHR, BMI, SBP, FAT %, 2 h-BG, FIns, 2 h-Ins, TG, FFA, HbA1c, HOMA-IR, and AUC_glucose , while negatively with HDL-C and ISI. Multiple linear regression showed that HOMA-IR and HDL-C are independently related factors influencing serum CTRP15 concentrations. In addition, binary logistic regression analysis showed that serum CTRP15 concentrations were significantly related to MetS. When the mean concentrations of circulating CTRP15 in MetS subjects were stratified by the number of components of the MetS, circulating CTRP15 was found to increase progressively with increasing number of the MetS components. Finally, ROC curve analysis showed that the best cutoff values for circulating CTRP15 to predict MetS and insulin resistance were 63.6 and 64.0 μg/L.

CONCLUSIONS

Serum CTRP15 concentrations were associated with the key components of MetS and insulin resistance.

Physical Exercise-Induced Myokines and Muscle-Adipose Tissue Crosstalk: A Review of Current Knowledge and the Implications for Health and Metabolic Diseases

Physical exercise has beneficial effects on metabolic diseases, and a combined therapeutic regimen of regular exercise and pharmaceutical treatment is often recommended for their clinical management. However, the mechanisms by which exercise produces these beneficial effects are not fully understood. Myokines, a group of skeletal muscle (SkM) derived peptides may play an important part in this process. Myokines are produced, expressed and released by muscle fibers under contraction and exert both local and pleiotropic effects. Myokines such as IL-6, IL-10, and IL-1ra released during physical exercise mediate its health benefits. Just as exercise seems to promote the myokine response, physical inactivity seems to impair it, and could be a mechanism to explain the association between sedentary behavior and many chronic diseases. Myokines help configure the immune-metabolic factor interface and the health promoting effects of physical exercise through the release of humoral factors capable of interacting with other tissues, mainly adipose tissue (AT). AT itself secretes proinflammatory cytokines (adipokines) as a result of physical inactivity and it is well recognized that AT inflammation can lead to the development of metabolic diseases, such as type 2 diabetes mellitus (T2DM) and atherosclerosis. On the other hand, the browning phenotype of AT has been suggested to be one of the mechanisms through which physical exercise improves body composition in overweight/obese individuals. Although, many cytokines are involved in the crosstalk between SkM and AT, in respect of these effects, it is IL-6, IL-15, irisin, and myostatin which seem to have the decisive role in this “conversation” between AT and SkM. This review article proposes to bring together the latest “state of the art” knowledge regarding Myokines and muscle-adipose tissue crosstalk. Furthermore, it is intended to particularly focus on the immune-metabolic changes from AT directly mediated by myokines.

FNDC5 expression in Purkinje neurons of adult male rats with acute spinal cord injury following treatment with methylprednisolone

Spinal cord injury (SCI) is a serious and complex medical condition that can happen to anyone. At present, therapy mainly focuses on rehabilitation and pharmacological treatment, such as methylprednisolone (MP). Supra-spinal changes in certain structures, such as the cerebellum, that receive many afferents from the spinal cord might be one reason for unsuccessful therapeutic outcomes. Recently, the expression of FNDC5 was reported in cerebellar Purkinje cells as a possible neuroprotective agent. In the present study, we considered the expression of FNDC5 in Purkinje cells following SCI with and without MP administration in adult rats with SCI. Thirty-five adult male rats were used in this study. The animals were randomly allocated into five groups, including SCI, spinal cord injury with methylprednisolone treatment (SCI + MP), operation sham, control, and operation sham with MP. Induction of SCI was achieved by using special clips to compress the spinal cord at a determined level. After a certain interval time, the animals underwent study for FNDC5 expression, apoptosis by using immunohistochemistry, Western blotting, and TUNEL and Nissl staining. Our results showed a significant decrease in the number of Purkinje cells following SCI. Therapy with MP inhibits apoptosis in irFNDC5 Purkinje cells and restores them. Expression of FNDC5 significantly increased in SCI and decreased following MP therapy. We also showed other cerebellar cells with FNDC5 immunoreactivity in the two other cerebellar layers that were firstly reported. Since irisin is known as a plasma product of FNDC5, we think it might be a plasma marker following therapeutic efforts for SCI; however, it needs further research. In addition, it is possible that changes in FNDC5 expression in Purkinje cells might be related to neurogenesis in the cerebellum with unknown mechanisms.

An update on the role of irisin in the regulation of endocrine and metabolic functions

Irisin is a novel myokine and adipokine that has gained much attention recently due to its mechanisms of action. Irisin is secreted following proteolytic cleavage of its precursor fibronectin type III domain containing 5 (FNDC5). Following its release, irisin exerts its major action by increasing the expression of mitochondrial uncoupling protein 1 (UCP 1), which facilitates the conversion of white adipose tissue (WAT) into beige adipose tissue. Irisin is distributed in various body tissues and several actions have been attributed to its presence in those tissues. It has been suggested that it plays a role in metabolic diseases, ageing, inflammation and neurogenesis. However, the circulating levels of irisin are modulated by several factors such as diet, obesity, exercise, pharmacological agents and different pathological conditions. In this review, we have discussed the mechanisms by which irisin influences the functions of different body systems and how external factors in turn affect the circulating level of irisin. In conclusion, modification of circulating irisin level may help in the management of a variety of endocrine and metabolic disorders.

Myonectin Predicts the Development of Type 2 Diabetes

CONTEXT

Myonectin has been identified as a myokine, expressed predominantly in skeletal muscle. However, its clinical implications are largely unknown.

OBJECTIVE

The aim of this study is to investigate the relationship between myonectin (C1q tumor necrosis factor-α-related protein isoform 15) and type 2 diabetes mellitus (T2DM) in cross-sectional and interventional studies.

DESIGN

In a separate study, oral glucose tolerance tests, a 45-minute bout of exercise, lipid infusions, and euglycemic-hyperinsulinemic clamps (EHCs) were performed to investigate the association of myonectin with homeostasis model assessment of insulin resistance (HOMA-IR) and T2DM. Circulating myonectin was measured by enzyme-linked immunosorbent assay.

PATIENTS

One hundred four newly diagnosed T2DM (nT2DM), 109 impaired glucose tolerance (IGT), and 128 healthy individuals were recruited for this study.

RESULTS

nT2DM and IGT subjects had higher circulating myonectin concentrations than normal subjects (82.3 ± 47.6 and 68.9 ± 46.6 vs. 45.2 ± 23.5 µg/L, P < 0.05 or P < 0.01). It was also found that in nT2DM individuals, circulating myonectin was higher than in IGT subjects. Plasma myonectin correlated positively with waist/hip ratio, percentage of body fat, triglyceride, fasting blood glucose, 2-hour blood glucose after glucose overload, fasting insulin, hemoglobin A1c, and HOMA-IR and negatively with the insulin sensitivity index in all of the study population. Multivariate logistic regression analysis revealed that circulating myonectin levels were significantly correlated with IGT and T2DM. A 45-minute bout of exercise did not change circulating myonectin levels in healthy, young individuals. Circulating myonectin levels were not significantly altered in response to an oral glucose challenge or EHC. In addition, acute elevated free fatty acid levels induced by lipid infusion had no effects on circulating myonectin.

CONCLUSIONS

These data suggest that myonectin may be a useful marker in predicting the development of prediabetes and diabetes.

Myokines related to leukocyte recruitment are down-regulated in osteosarcoma

Myokines are cytokines that are secreted by muscle cells during exercises, muscle development and pathology. Studies have shown that expression of some individual myokines was altered in tumors. However, comprehensive analyses of myokines' expression in osteosarcoma (OS), the most common malignant tumor in musculoskeletal system, have not been performed. In this study, we analyzed the expression of 35 myokines in osteosarcoma, peritumoral skeletal muscle, and cancellous bone by qRT-PCR. Heatmap analysis based on the expression pattern of these myokines revealed that OS is more likely derived from cancellous bone than peritumoral skeletal muscle. Thus, we compared the expression of myokines between OS and cancellous bone to reveal a potential role of myokines in OS development. Our results showed that expression of 19 myokines in OS was significantly lower than that in cancellous bone. KEGG signaling pathway analysis showed that these 19 myokines are involved in several important signaling pathways, one of which was associated with leukocyte recruitment in TNF-α signaling. We verified that expression of these leukocyte recruitment-related myokines were down-regulated in OS cell line MNNG compared to those in human BMSC. Downregulation of the myokines related to leukocyte recruitment suggests that escaping from host immune system may help the occurrence of osteosarcoma.

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.

Irisin and Fibronectin Type III Domain-Containing 5 Responses to Exercise in Different Environmental Conditions

Fibronectin type III domain-containing 5 (FNDC5) is a skeletal muscle membrane-bound precursor to the myokine irisin. Irisin is involved in stimulating adipose tissue to become more metabolically active in order to produce heat. The purpose of this study was to determine the effects of exercise in a hot (33 °C), cold (7 °C), and room temperature (RT, 20 °C) environment on the skeletal muscle gene expression of FNDC5 and the plasma concentrations of irisin. Twelve recreationally trained males completed three separate, 1 h cycling bouts at 60% of W_max in a hot, cold, and RT environment followed by three hours of recovery at room temperature. Blood samples were taken from the antecubital vein and muscle biopsies were taken from the vastus lateralis pre-, post-, and 3 h post-exercise. Plasma concentrations of irisin did not change from pre- (9.23 ± 2.68 pg·mL^-1) to post-exercise (9.6 ± 0.2 pg·mL^-1, p = 0.068), but did decrease from post-exercise to 3 h post-exercise (8.9 ± 0.5 pg·mL^-1, p = 0.047) regardless of temperature. However, when plasma volume shifts were considered, no differences were found in irisin (p = 0.086). There were no significant differences between trials for irisin plasma concentrations (p > 0.05). No significant differences in FNDC5 were observed between the hot, cold, or RT or pre-, post-, or 3 h post-exercise time points (p > 0.05). These data indicate that the temperature in which exercise takes place does not influence FNDC5 transcription or circulating irisin in a human model.

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.

Adaptation of iron requirement to hypoxic conditions at high altitude

Adequate acclimatization time to enable adjustment to hypoxic conditions is one of the most important aspects for mountaineers ascending to high altitude. Accordingly, most reviews emphasize mechanisms that cope with reduced oxygen supply. However, during sojourns to high altitude adjustment to elevated iron demand is equally critical. Thus in this review we focus on the interaction between oxygen and iron homeostasis. We review the role of iron 1) in the oxygen sensing process and erythropoietin (Epo) synthesis, 2) in gene expression control mediated by the hypoxia-inducible factor-2 (HIF-2), and 3) as an oxygen carrier in hemoglobin, myoglobin, and cytochromes. The blood hormone Epo that is abundantly expressed by the kidney under hypoxic conditions stimulates erythropoiesis in the bone marrow, a process requiring high iron levels. To ensure that sufficient iron is provided, Epo-controlled erythroferrone that is expressed in erythroid precursor cells acts in the liver to reduce expression of the iron hormone hepcidin. Consequently, suppression of hepcidin allows for elevated iron release from storage organs and enhanced absorption of dietary iron by enterocytes. As recently observed in sojourners at high altitude, however, iron uptake may be hampered by reduced appetite and gastrointestinal bleeding. Reduced iron availability, as observed in a hypoxic mountaineer, enhances hypoxia-induced pulmonary hypertension and may contribute to other hypoxia-related diseases. Overall, adequate systemic iron availability is an important prerequisite to adjust to high-altitude hypoxia and may have additional implications for disease-related hypoxic conditions.

Irisin and Myonectin Regulation in the Insulin Resistant Muscle: Implications to Adipose Tissue: Muscle Crosstalk

Myokines are peptides produced and secreted by the skeletal muscle, with autocrine, paracrine, and endocrine actions. Many of them are overexpressed during physical exercise and appear to contribute to the benefits of exercise to metabolic homeostasis. Irisin, resulting from the cleavage of the membrane protein FNDC5, was shown to induce adipocyte browning, with increased lipid oxidation and thermogenesis. Myonectin was only recently discovered and initial studies revealed a role in fatty acid uptake and oxidation in adipose tissue and liver. However, the mechanisms of their regulation by exercise are not entirely established. Impaired secretion and action of myokines, such as irisin and myonectin, may have a role in the establishment of insulin resistance. On the other hand, several studies have shown that insulin resistance in the skeletal muscle may change myokines expression and secretion. This may have consequences on lipid and glucose metabolism in adipose tissue and lead to a vicious cycle between impaired myokines production and insulin resistance. This review summarizes the current knowledge about the influence of skeletal muscle insulin resistance on the secretion of irisin and myonectin, as well as its impact on adipose tissue metabolism.