Irisin a Novel Metabolic Biomarker: Present Knowledge and Future Directions

Irisin: muscle's novel player in endoplasmic reticulum stress and disease

Irisin, an exercise-induced myokine, exhibits elevated levels during physical activity, yet its role in modulating the unfolded protein response (UPR) remains poorly understood. This comprehensive review pioneers an in-depth examination of irisin-mediated endoplasmic reticulum (ER) stress mitigation across various diseases. We provide a nuanced characterization of irisin's molecular profile, biological activity, and significance as a skeletal muscle-derived cytokine analogue. Our discussion elucidates the complex interplay between exercise, irisin signalling, and metabolic outcomes, highlighting key molecular interactions driving salutary effects. Moreover, we delineate the UPR's role as a critical ER stress countermeasure and underscore irisin's pivotal function in alleviating this stress, revealing potential therapeutic avenues for disease management. Exercise-induced release of irisin ameliorates ER stress through AMPK phosphorylation during various diseases (Icon image source: www.flaticon.com ).

Evaluation of adipokines, oxidative stress, and inflammatory markers in gout patients

Objectives

This study aims to investigate the role of adipokines, oxidative stress, and inflammatory markers in the pathogenesis of gout.

Patients and methods

Between September 2021 and December 2022, a total of 88 volunteers including 44 patients (37 males, 7 females; mean age: 56.5±11.6 years; range, 30 to 77 years) with gout disease and 44 age- and sex-matched healthy controls (37 males, 7 females; mean age: 54.3±12.1 years; range, 30 to 78 years) were retrospectively analyzed. Serum interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-α), irisin, resistin, total oxidant status (TOS), and total antioxidant status (TAS) levels were analyzed.

Results

The mean serum irisin levels were significantly higher in patients with gout than in the healthy controls (405.6±97.3 and 316.0±80.8 pg/mL, respectively). The mean IL-10 levels were significantly lower in patients with gout than in healthy controls (90.8±71.9 and 172.7±128.6 pg/mL, respectively). There was no statistically significant difference in the serum resistin, TNF-α, TOS, or TAS levels between the groups (p>0.05).

Conclusion

Our study results show that serum irisin and IL-10 seem to be candidate biomarkers of diagnosis of gout.

Irisin: A Multifaceted Hormone Bridging Exercise and Disease Pathophysiology

The fibronectin domain-containing protein 5 (FNDC5), or irisin, is an adipo-myokine hormone produced during exercise, which shows therapeutic potential for conditions like metabolic disorders, osteoporosis, sarcopenia, obesity, type 2 diabetes, and neurodegenerative diseases, including Alzheimer's disease (AD). This review explores its potential across various pathophysiological processes that are often considered independent. Elevated in healthy states but reduced in diseases, irisin improves muscle-adipose communication, insulin sensitivity, and metabolic balance by enhancing mitochondrial function and reducing oxidative stress. It promotes osteogenesis and mitigates bone loss in osteoporosis and sarcopenia. Irisin exhibits anti-inflammatory effects by inhibiting NF-κB signaling and countering insulin resistance. In the brain, it reduces amyloid-β toxicity, inflammation, and oxidative stress, enhancing brain-derived neurotrophic factor (BDNF) signaling, which improves cognition and synaptic health in AD models. It also regulates dopamine pathways, potentially alleviating neuropsychiatric symptoms like depression and apathy. By linking physical activity to systemic health, irisin emphasizes its role in the muscle-bone-brain axis. Its multifaceted benefits highlight its potential as a therapeutic target for AD and related disorders, with applications in prevention, in treatment, and as a complement to exercise strategies.

Comparative Effects of Basil Seed Consumption and Endurance Exercise on Irisin, Interleukin 6 (IL-6), Tumor Necrosis Factor-Alpha (TNF-α), and Leptin Levels: A Prospective Observational Study

Background and objective There is growing concern regarding metabolic and inflammatory disorders globally, underscoring the need for effective nonpharmacological interventions. Irisin, interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), and leptin are biomarkers of metabolic and inflammatory health. In this study, we aimed to investigate the comparative effects of basil seed supplementation or endurance exercise on biomarkers of chronic oxidative stress. Methods This prospective observational study enrolled 60 participants who were randomly divided into two groups: Group A (basil seeds, n=30) and Group B (endurance exercise, n=30). Participants in Group A consumed 10 grams of soaked basil seeds daily for eight weeks, while those in Group B underwent a supervised endurance exercise regimen (45 minutes/day, five days/week). Biomarkers, including irisin, IL-6, TNF-α, and leptin, were quantified using enzyme-linked immunosorbent assay (ELISA) both at baseline and post-intervention. Within-group and between-group differences were analyzed using paired and independent t-tests, with a significance threshold of p<0.05. Results Overall, the baseline characteristics in Group A (age: 35.4 ± 5.0 years; BMI: 24.5 ± 2.3 kg/m²) and B (age: 34.9 ± 4.8 years; BMI: 24.9 ± 2.4 kg/m²) were comparable (p>0.05). Significant changes were observed in both groups post-intervention. Irisin levels increased moderately in group A (47.23 ± 4.8 µg/mL to 50.79 ± 5.13 µg/mL, p<0.01), and IL-6, TNF-α, and leptin decreased (IL-6: 28.2 ± 2.13 pg/mL to 18.1 ± 2.01 pg/mL, p<0.01; TNF-α: 34.5 ± 2.72 pg/mL to 23.6 ± 2.64 pg/mL, p<0.01; and leptin: 8.4 ± 1.96 ng/mL to 3.9 ± 0.83 ng/mL, p<0.01). Group B showed a significant increase in irisin (44.04 ± 3.58 µg/mL to 150.1 ± 9.32 µg/mL, p<0.001) and a non-significant rise in IL-6 (31.65 ± 2.4 pg/mL to 35.64 ± 3.17 pg/mL, p>0.05). TNF-α levels increased in Group B (31.65 ± 3.27 pg/mL vs. 61.66 ± 3.85 pg/mL, p<0.001) and decreased in Group A, while leptin levels slightly decreased in Group B (7.94 ± 1.27 ng/mL vs. 4.19 ± 0.64 ng/mL, p>0.05). Conclusions Supplementation with basil seed and exercise training with endurance exercise had distinct effects on biomarkers of metabolism and inflammation. Irisin levels were significantly improved by endurance exercise, while basil seeds were most effective in reducing IL-6, TNF-α, and leptin. The findings suggest that basil seeds and exercise provide synergistic effects against metabolic and inflammatory diseases.

Assessment of brain-derived neurotrophic factor and irisin concentration in children with chronic kidney disease: a pilot study

Patients suffering from chronic kidney disease (CKD) are particularly placed at risk of multiorgan complications. One of them is malnutrition, which adds up to a higher mortality factor among them. This study was designed to determine the usefulness of brain-derived neurotrophic factor (BDNF) and irisin assays in the assessment of CKD development. The study group included 28 children with CKD at stages 2-5 treated conservatively. The outcome of our study revealed decreased serum BDNF and irisin levels in CKD patients, whereas urine concentrations were increased for BDNF and decreased for irisin, comparing to healthy controls. There was a positive correlation between anthropometric measures and urine BDNF concentration, as well as anthropometric measures and both serum and urine irisin levels in the study group, however no dependence of the tested markers on the stage of CKD was observed. In recent years, a role of myokines was described as vital for maintaining metabolic homeostasis therefore we suspect a potential role of these multifaceted markers in detecting malnutrition in CKD children.

Mechanism and physical activities in bone-skeletal muscle crosstalk

Bone and skeletal muscle work in coordination to maintain the function of the musculoskeletal system, in which skeletal muscle contraction drives the movement of the bone lever system while bone provides insert sites for skeletal muscle through the bone-muscle junction. Existing evidence suggests that factors secreted by skeletal muscle and bone mediate the interaction between the two tissues. Herein, we focused on the relationship between skeletal muscle and bone and the underlying mechanism of the interaction. Exercise can promote bone strength and secrete osteocalcin and insulin-like growth factor I into the blood, thus improving muscle quality. In addition, exercise can also promote myostatin, interleukin-6, Irisin, and apelin in muscles to enter the blood so that they can act on bones to maintain the balance between bone absorption and bone formation. There is a special regulatory axis interleukin-6/osteocalcin between myokines and osteokines, which is mainly influenced by exercise. Therefore, we pay attention to the important factors in the bone-muscle intersection that are affected by exercise, which were found or their functions were expanded, which strengthened the connection between organs of the whole body, highlighting the importance of exercise and contributing to the diagnosis, prevention, and treatment of osteoporosis and sarcopenia in the clinic.

Irisin and Triglyceride Glucose Index as Markers of Dyslipidemia in Young Adults

Irisin, is a new myokine, considered a favorable metabolic factor and inversely associated with non-communicable diseases. The biological activities of irisin are currently unknown; however, they include browning white adipose tissue, insulin sensitivity, and anti-inflammatory and antioxidant effects. Triglyceride glucose index is a notable insulin resistance marker that predicts the risk of metabolic dyslipidemia and cardiovascular risk. The study aimed to evaluate the relation of irisin and Triglyceride glucose index (TyG) in young adults to assess the cardiovascular risk. This observational cross-sectional study included 80 participants aged 18 to 35 years (male and females) with cut-off TyG > 4.5 as the prime criteria. With consent, anthropometric measurements were documented. Fasting lipid profile parameters were analyzed, and atherogenic lipid ratios and TyG index were calculated. Serum irisin was analyzed in Bio-Rad ELISA using a standardized Abbkine kit. Decreased irisin levels (0.32 ± 0.04ng/ml) and increased TyG index (4.95 ± 0.012) were observed in the participants with elevated triglyceride levels. The lipid profile parameters and atherogenic lipid ratios were observed to be elevated in males as compared to females. Correlation of irisin with lipid parameters revealed statistically significant positive correlation with HDLc (r = + 0.305) and negative correlation with non-HDLc (r = - 0.393), TC/HDLc (r = -0.508), LDLc/HDLc (r= -0.475) and TyG (r = -0.28). The study concludes that decreased irisin and increased TyG index in young adults reflect the state of metabolic dyslipidemia which enables the identification of individuals with metabolic and atherogenic risk.

Adipo-myokine Irisin, a Promising Antioxidant against Nicotine Induced Oxidative Stress in BALB/c mice

Objectives

To determine the role of r-irisin in attenuating nicotine-induced oxidative stress by estimating serum oxidative stress markers and antioxidant enzymes in BALB/c mice.

Method

This 18 month experimental study was carried out at Foundation University Islamabad and National Institute of Health starting in 2020. Thirty healthy BALB/c mice were divided into three groups. Group-I (control group) received normal saline 1ml/kg body weight intra-peritoneally daily for 28 days. Experimental group, Group-II received nicotine 2mg/kg body weight intra-peritoneally, for 28 days to induce oxidative stress. Experimental Group-III was given r-irisin 0.5 μg/g body weight/day via tail vein injection, for the last 14 days in addition to intraperitoneal nicotine for 28 days. On 29th day, intra-cardiac blood samples were taken for estimation of serum antioxidant enzymes [Superoxide dismutase (SOD), Reduced Glutathione (GSH) and Catalases (CAT)], and Thiobarbituric Acid-Reactive Substances (TBARS) levels as lipid peroxidation marker using ELISA. SPSS version 24 was used for statistical analysis. Significant difference in parameters across groups was calculated using one way ANOVA. P-value of < 0.05 was considered significant.

Results

Group-II showed statistically significant increase in serum lipid peroxidation marker (TBARS) levels (p<0.001) and reduction in serum anti-oxidative enzymes (SOD, CAT, GSH) levels (p< 0.001) as compared to Group-I. In Group-III, with co administration of r-irisin, significant improvement in antioxidant enzymes levels and reduction in TBARS levels was observed (p< 0.001) as compared to Group-II.

Conclusion

Irisin ameliorates nicotine induced oxidative stress by improving serum anti-oxidant enzyme levels and reducing serum lipid peroxidation marker.

Role of irisin in bone diseases

Bone diseases are common among middle-aged and elderly people, and harm to activities of daily living (ADL) and quality of life (QOL) for patients. It is crucial to search for key regulatory factors associated with the development of bone diseases and explore potential therapeutic targets for bone diseases. Irisin is a novel myokine that has been discovered in recent years. Accumulating evidence indicates that irisin has beneficial effects in the treatment of various diseases such as metabolic, cardiovascular and neurological disorders, especially bone-related diseases. Recent studies had shown that irisin plays the role in various bone diseases such as osteoarthritis, osteoporosis and other bone diseases, suggesting that irisin may be a potential molecule for the prevention and treatment of bone diseases. Therefore, in this review, by consulting the related domestic and international literature of irisin and bone diseases, we summarized the specific regulatory mechanisms of irisin in various bone diseases, and provided a systematic theoretical basis for its application in the diagnosis and treatment of the bone diseases.

Irisin: An anti-inflammatory exerkine in aging and redox-mediated comorbidities

Human beings lead largely sedentary lives. From an evolutionary perspective, such lifestyle is not beneficial to health. Exercise can promote many enabling pathways, particularly through circulating exerkines, to optimize individual health and quality of life. Such benefits might explain the protective effects of exercise against aging and noncommunicable diseases. Nevertheless, the miRNA-mediated molecular mechanisms and exerkine interorgan crosstalk that underlie the beneficial effects of exercise remain poorly understood. In this mini review, we focused on the exerkine, irisin, mainly produced by muscle contraction during adaptation to exercise and its beneficial effects on body homeostasis. Herein, the complex role of irisin in metabolism and inflammation is described, including its subsequent effects on thermogenesis through browning to control obesity and improve glycemic regulation for diabetes mellitus control, its potential to improve cognitive function (via brain derived neurotrophic factor), and its pathways of action and role in aging.

Exercise-induced modulation of myokine irisin in bone and cartilage tissue—Positive effects on osteoarthritis: A narrative review

Osteoarthritis is a chronic degenerative musculoskeletal disease characterized by pathological changes in joint structures along with the incidence of which increases with age. Exercise is recommended for all clinical treatment guidelines of osteoarthritis, but the exact molecular mechanisms are still unknown. Irisin is a newly discovered myokine released mainly by skeletal muscle in recent years—a biologically active protein capable of being released into the bloodstream as an endocrine factor, the synthesis and secretion of which is specifically induced by exercise-induced muscle contraction. Although the discovery of irisin is relatively recent, its role in affecting bone density and cartilage homeostasis has been reported. Here, we review the production and structural characteristics of irisin and discuss the effects of the different types of exercise involved in the current study on irisin and the role of irisin in anti-aging. In addition, the role of irisin in the regulation of bone mineral density, bone metabolism, and its role in chondrocyte homeostasis and metabolism is reviewed. A series of studies on irisin have provided new insights into the mechanisms of exercise training in improving bone density, resisting cartilage degeneration, and maintaining the overall environmental homeostasis of the joint. These studies further contribute to the understanding of the role of exercise in the fight against osteoarthritis and will provide an important reference and aid in the development of the field of osteoarthritis prevention and treatment.

Circulating Irisin Levels in Patients with Chronic Plaque Psoriasis

Irisin is an adipo-myokine, mainly synthetized in skeletal muscles and adipose tissues, that is involved in multiple processes. Only a few studies have evaluated serum irisin in psoriatic patients. This study aims to analyze serum irisin levels in patients with chronic plaque psoriasis, to compare them with values in controls, and to assess whether concentration of circulating irisin correlates with the severity of psoriasis, calculated by means of Psoriasis Area and Severity Index (PASI). We enrolled 46 patients with chronic plaque psoriasis; the control group included 46 sex- and age-matched subjects without any skin or systemic diseases. Serum irisin levels were measured by competitive enzyme linked immunosorbent assay. Our results showed a non-significant increase in serum irisin concentration in psoriatic patients compared to controls. A negative non-linear correlation between PASI and irisin levels was detected in psoriatic patients. Indeed, dividing patients according to psoriasis severity, the negative association between irisin and PASI was stronger in patients with mild psoriasis than in patients with higher PASI scores. Several control variables we tested showed no significant impact on serum irisin. However, erythrocyte sedimentation rate in the normal range was associated with significantly higher irisin levels in psoriatic patients. In conclusion, although irisin levels were not significantly different between controls and psoriatic patients, irisin was found to be negatively associated with psoriasis severity, especially in subjects with low PASI scores; however, further studies are needed to clarify the role of irisin in subjects with psoriasis.

Relationships between Body Weight Status and Serum Levels of Adipokine, Myokine and Bone Metabolism Parameters in Healthy Normal Weight and Thin Children

Optimal body weight and body composition for age are relevant to child development and healthy life. Changes in lean mass and fat mass as well as its distribution are associated with alterations in the secretion of myokines and adipokines by muscle and adipose tissues. These factors are very important for bone health. The aim of the study was to assess serum leptin, adiponectin, resistin, visfatin and omentin as adipokines and myostatin and irisin as myokines with regard to their associations with bone parameters in healthy normal weight and thin children. We studied 81 healthy prepubertal children (aged 5 to 9 years) divided into three groups: group A—35 children with a BMI z-score between +1 and −1 SD; group B—36 children with a BMI z-score between −1 and −2 SD; and group C—10 thin children with a BMI z-score of <−2 SD. We observed significantly (p < 0.001) lower fat mass, fat/lean mass ratio and bone mineral density (BMD) across weight status with the lowest values in the group of thin children. We noticed significantly (p < 0.05) lower concentrations of 25-hydroxyvitamin D, resistin and high-molecular-weight (HMW) adiponectin but higher levels of myostatin as the BMI z-score deceased. We found that BMI and leptin levels were directly correlated with fat mass, lean mass, bone mineral content (BMC) and BMD. Resistin levels were negatively associated with lean mass, while visfatin concentrations were positively related to total BMD. In healthy prepubertal children there were differences in body composition and in bone mineral density across decreasing BMI status. We suggest that changes in serum myostatin and 25-hydroxyvitamin D levels may play a role in bone status of thin children. Moreover, significant relations between adipokines and bone parameters may confirm crosstalk between fat tissue and bone in these children.

Molecular Basis of Irisin Regulating the Effects of Exercise on Insulin Resistance

Insulin resistance is recognized as one major feature of metabolic syndrome, and frequently emerges as a difficult problem encountered during long-term pharmacological treatment of diabetes. Insulin resistance often causes organs or tissues, such as skeletal muscle, adipose, and liver, to become less responsive or resistant to insulin. Exercise can promote the physiological function of those organs and tissues and benefits insulin action via increasing insulin receptor sensitivity, glucose uptake, and mitochondrial function. This is done by decreasing adipose tissue deposition, inflammatory cytokines, and oxidative stress. However, understanding the mechanism that regulates the interaction between exercise and insulin function becomes a challenging task. As a novel myokine, irisin is activated by exercise, released from the muscle, and affects multi-organ functions. Recent evidence indicates that it can promote glucose uptake, improve mitochondrial function, alleviate obesity, and decrease inflammation, as a result leading to the improvement of insulin action. We here will review the current evidence concerning the signaling pathways by which irisin regulates the effect of exercise on the up-regulation of insulin action in humans and animals.

The Changes of Irisin and Inflammatory Cytokines in the Age-Related Macular Degeneration and Retinal Vein Occlusion

Purpose

Age-related macular degeneration (AMD) and retinal vein occlusion (RVO) are irreversible chorioretinal diseases, which might induce severe damage in visual function. The metabolic factor and inflammatory factors might play important roles in the pathogenesis of AMD and RVO. The levels of irisin and 14 cytokines were analyzed in aqueous humor of AMD and RVO eyes to evaluate the roles of irisin and inflammatory factors.

Methods

We collected aqueous humor samples from patients with AMD (n = 27), RVO (n = 30), and cataract (as control, n = 23) eyes. Samples were assayed using ELISA kit for irisin and a multiplex immunoassay kit for 14 cytokines. The macular thickness (MT) was measured with OCT in all included eyes.

Results

MT in the RVO group is significantly higher than that in the AMD or control group. Irisin levels in the aqueous samples of AMD and RVO eyes were both significantly lower than that in the control. Furthermore, a positive correlation was found between irisin and MT in the RVO. Compared with the controls, AMD eyes had significantly higher levels of BDNF, VEGF-A, VEGF-R1, VEGF-R2, IL-10, TNF-α, VCAM-1, IP-10, and MCP-1. Similarly, RVO eyes had significantly higher levels of BDNF, VEGF-A, VEGF-R1, VEGF-R2, IL-6, IL-8, IL-10, TNF-α, ICAM-1, VCAM-1, IP-10, and MCP-1. However, there was no significant difference between the levels of PDGF-BB or TNF-β in these three groups. A negative correlation was found between VEGF-A and MT in AMD, as well as in control. Furthermore, a positive correlation was found between IL-6 and MT in the 80 included eyes, as well as in RVO. A positive correlation was found between ICAM-1 and MT in the 80 included eyes, as well as in RVO.

Conclusions

The metabolic factor, irisin levels in the aqueous humor are decreased in AMD and RVO eyes and show a positive correlation between irisin and MT in RVO eyes, prompting researchers to explore the relationship between irisin and macular edema. We also identified the higher expression of vascular growth factors (VEGF-A, VEGF-R1, and PDGF-BB), inflammatory cytokines (IL-6, IL-8, IL-10, and TNF-α), and chemokines (ICAM-1, VCAM-1, IP-10, and MCP-1) in AMD and RVO eyes.

Irisin Activates M1 Macrophage and Suppresses Th2-Type Immune Response in Rats with Pelvic Inflammatory Disease

Objective

To investigate the mechanism of irisin to treat rats with acute pelvic inflammatory disease (APID).

Methods

Female rats were established as APID. Firstly, the content of IL-6, IL-8, TNF-α, and NF-kB was tested in rats' serum by enzyme linked immunosorbent assay (ELISA). Interferon-γ (IFN-γ) and IL-4 in the supernatant of pelvic homogenates were also detected. The mRNA expression of the inducible nitric oxide synthase (iNOS), TNF-α, chemokine ligand 1 (CXCL1), arginase-1(Arg1), and chitinase-3-like-3 (Chi313) genes in the pelvic cavity was detected by quantitative reverse transcription polymerase chain reaction (RT-qPCR). IFN-γ and IL-4 secreted by spleen CD4⁺T cells and CD8⁺T cells were counted by flow cytometry, and the ratio of IFN-γ/IL-4 in CD4⁺T cells and CD8⁺T cells in the spleen was also detected by flow cytometry.

Results

Irisin reduced the levels of IL-6, IL-8, TNF-α, and NF-kB in serum. Compared with the APID group, the expression level of IL-4 in the APID + Irisin group was reduced in the homogenate. At the same time, Irisin promotes the activation of M1 macrophages in the uterus, ovaries, and uterine tubes of rats with APID. Irisin also inhibited Th2-type immune response.

Conclusions

Irisin activates M1 macrophage and suppresses Th2-type immune response in APID rats.

Renal failure suppresses muscle irisin expression, and irisin blunts cortical bone loss in mice

BACKGROUND

Chronic renal failure induces bone mineral disorders and sarcopenia. Skeletal muscle affects other tissues, including bone, by releasing myokines. However, the effects of chronic renal failure on the interactions between muscle and bone remain unclear.

METHODS

We investigated the effects of renal failure on bone, muscle, and myokines linking muscle to bone using a mouse 5/6 nephrectomy (Nx) model. Muscle mass and bone mineral density (BMD) were analysed by quantitative computed tomography 8 weeks after Nx.

RESULTS

Nephrectomy significantly reduced muscle mass in the whole body (12.1% reduction, P < 0.05), grip strength (10.1% reduction, P < 0.05), and cortical BMD at the femurs of mice (9.5% reduction, P < 0.01) 8 weeks after surgery, but did not affect trabecular BMD at the femurs. Among the myokines linking muscle to bone, Nx reduced the expression of irisin, a proteolytic product of fibronectin type III domain-containing 5 (Fndc5), in the gastrocnemius muscles of mice (38% reduction, P < 0.01). Nx increased myostatin mRNA levels in the gastrocnemius muscles of mice (54% increase, P < 0.01). In simple regression analyses, cortical BMD, but not trabecular BMD, at the femurs was positively related to Fndc5 mRNA levels in the gastrocnemius muscles of mice (r = 0.651, P < 0.05). The weekly administration of recombinant irisin to mice ameliorated the decrease in cortical BMD, but not muscle mass or grip strength, induced by Nx (6.2% reduction in mice with Nx vs. 3.3% reduction in mice with Nx and irisin treatment, P < 0.05).

CONCLUSIONS

The present results demonstrated that renal failure decreases the expression of irisin in the gastrocnemius muscles of mice. Irisin may contribute to cortical bone loss induced by renal failure in mice as a myokine linking muscle to bone.

FNDC5/irisin facilitates muscle−adipose−bone connectivity through ubiquitination-dependent activation of runt-related transcriptional factors RUNX1/2

In the past decade, the cleavage protein irisin derived from fibronectin type III domain–containing protein 5 (FNDC5) in exercise-stimulated skeletal muscle has increasingly become a biomarker associated with metabolic syndrome and osteoporosis in humans. However, it is unclear how this protein facilitates muscle−adipose−bone connectivity in metabolic and skeletal homeostasis. In this study, we unexpectedly observed that the FNDC5 gene can be markedly activated during the differentiation of brown adipocytes but not white adipocytes, and that FNDC5 is specifically expressed in mouse brown adipose tissues (BATs). But unlike it in the skeletal muscles, the expression of FNDC5/irisin in BAT is promoted by cold exposure rather than exercise in mice. Analysis of promoter activity and chromatin immunoprecipitation further showed that peroxisome proliferator–activated receptor γ coactivator-1α and thyroid hormone receptors cooperate on the FNDC5 gene promoter to induce its transcription. We found that FNDC5/irisin stimulates the runt-related transcriptional factors RUNX1/2 via a focal adhesion kinase–dependent pathway in both bone and subcutaneous white adipose tissues. Mechanistically, focal adhesion kinase is stimulated by FNDC5/irisin and then facilitates E3 ubiquitin–protein ligase WW domain–containing protein 2 to ubiquitinate and subsequently activate RUNX1/2, culminating in the activation of osteoblast-related or thermogenesis-related genes. Interestingly, the PR domain containing protein 16 that is crucial for subcutaneous white adipose “browning” and skeletal development was found to form a complex with RUNX1/2 in a WW domain–containing protein 2-dependent manner. These findings elucidate a signaling mechanism by which FNDC5/irisin supports the muscle−adipose−bone connectivity, especially BAT−bone connectivity.

Beneficial effects of MgSO4 on TFAM, UPC3 and FNDC5 mRNA expressions in skeletal muscle of type 2 diabetic rats: a possible mechanism to improve insulin resistance

BACKGROUND

Hypomagnesemia has been associated with development of type 2 diabetes mellitus (T2DM) and its complications. Irisin has beneficial effects on glucose uptake and improves hepatic glucose and lipid metabolism. In this study, we aimed to evaluate the effects of long-term treatment of MgSO₄ and insulin on insulin resistance, dyslipidemia, serum and hepatic irisin levels, skeletal muscle gene expression of fibronectin type III domain-containing protein 5 (FNDC5), mitochondrial transcription factor A (TFAM) and mitochondrial uncoupling protein 3 (UCP3) in T2DM rats.

METHODS AND RESULTS

Twenty-four rats were divided into four groups: Control group, diabetic control (DC) using a high-fat diet + streptozotocin, insulin-treated diabetic group (DC + Ins), MgSO₄-treated diabetic group (DC + Mg). At the end of therapies, serum concentrations of FBG, TG, insulin, Ox-LDL, along with serum and hepatic irisin levels were measured. FNDC5, TFAM, and UCP3 mRNA expressions were measured in the skeletal muscle by Real-time PCR. In comparison with DC group, MgSO₄ therapy resulted in decreased FBG, TG, Ox-LDL, improved serum insulin and irisin levels, and increased mRNA expressions of FNDC5, UCP3 and TFAM. Insulin therapy significantly decreased FBG, Ox-LDL, FNDC5 and serum irisin levels compared with the control group. While, insulin therapy markedly increased TFAM and UCP3 compared with the DC group.

CONCLUSIONS

In conclusion, MgSO₄ can improve insulin resistance and hyperlipidemia partly through decreasing Ox-LDL, increasing serum irisin levels as well as increasing FNDC5, TFAM, and UCP3 mRNA expressions in T2DM rats. These findings can be considered in the management of diabetes treatment.

Do skeletal muscle composition and gene expression as well as acute exercise-induced serum adaptations in older adults depend on fitness status?

Background

Inactive physical behavior among the elderly is one risk factor for cardiovascular disease, immobility and increased all-cause mortality. We aimed to answer the question whether or not circulating and skeletal muscle biomarkers are differentially expressed depending on fitness status in a group of elderly individuals.

Methods

Twenty-eight elderly individuals (73.36 ± 5.46 years) participated in this exploratory study after participating as part of the multinational SITLESS-clinical trial (implementation of self-management and exercise programs over 16 weeks). A cardiopulmonary exercise test (CPX) and resting skeletal muscle biopsy were performed to determine individual physiological performance capacity. Participants were categorized into a high physical fitness group (HPF) and a low physical fitness group (LPF) depending on peak oxygen uptake (VO₂peak). Serum blood samples were taken before (pre) and after (post) CPX and were examined regarding serum BDNF, HSP70, Kynurenine, Irisin and Il-6 concentrations. Skeletal muscle tissue was analyzed by silver staining to determine the myosin heavy chain (MyHC) composition and selected genes by qRT-PCR.

Results

HPF showed lower body weight and body fat, while skeletal muscle mass and oxygen uptake at the first ventilatory threshold (VO₂T1) did not differ between groups. There were positive associations between VO₂peak and VO₂VT1 in HPF and LPF. MyHC isoform quantification revealed no differences between groups. qRT-PCR showed higher expression of BDNF and BRCA1 in LPF skeletal muscle while there were no differences in other examined genes regarding energy metabolism. Basal serum concentrations of Irisin were higher in HPF compared to LPF with a trend towards higher values in BDNF and HSP70 in HPF. Increases in Il-6 in both groups were observed post.

Conclusions

Although no association between muscle composition/VO₂peak with fitness status in older people was detected, higher basal Irisin serum levels in HPF revealed slightly beneficial molecular serum and muscle adaptations.

Trial registration

ClinicalTrials.gov, NCT02629666. Registered 19 November 2015.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-021-02666-0.

Muscle-brain communication in pain: The key role of myokines

Pain is the most common reason for a physician visit, which accounts for a considerable proportion of the global burden of disease and greatly affects patients' quality of life. Therefore, there is an urgent need to identify new therapeutic targets involved in pain. Exercise-induced hypoalgesia (EIH) is a well known phenomenon observed worldwide. However, the available evidence demonstrates that the mechanisms of EIH remain unclear. One of the most accepted hypotheses has been the activation of several endogenous systems in the brain. Recently, the concept that the muscle acts as a secretory organ has attracted increasing attention. Proteins secreted by the muscle are called myokines, playing a critical role in communicating with other organs, such as the brain. This review will focus on several myokines and discuss their roles in EIH.

Inverse correlation between serum irisin and cardiovascular risk factors among Chinese overweight/obese population

BACKGROUND

Irisin is a novel myokine associated with obesity, which is a traditional cardiovascular risk factor (CVRF). The present study aimed to investigate the association between serum irisin and a single CVRF as well as the clustering of CVRFs among Chinese overweight/obese population.

METHODS

A total of 98 overweight and 93 obese subjects without clinical treatments were enrolled in this study. Subjects were then divided into two groups, based on the serum irisin level: a low irisin group (1.10-13.44 ng/ml) and a high irisin group (13.49-29.9 ng/ml). The clustering of CVRFs, smoking, diabetes mellitus, dyslipidemia and hypertension, was classified as 0, 1, 2 and ≥ 3 CVRFs. The demographic and baseline clinical characteristics of all participants were collected and serum irisin was measured.

RESULTS

The high serum irisin group had significantly higher high-density lipoprotein cholesterol but lower fasting plasma glucose than the low serum irisin group. Additionally, the high serum irisin group had a significantly lower prevalence of smoking, diabetes mellitus and dyslipidemia than the low serum irisin group. Increased serum irisin was significantly associated with a reduced risk of smoking and dyslipidemia in both the unadjusted and adjusted models. Furthermore, high serum irisin significantly reduced the risk of the prevalence of 1, 2 and ≥ 3 CVRFs.

CONCLUSIONS

among the Chinese overweight/obese populations, high serum irisin is negatively associated with smoking, dyslipidemia and the clustering of CVRFs. Thus, high serum irisin is potentially associated with a low risk of cardiovascular diseases in the Chinese overweight/obese population.

Adropin and Irisin Deficiencies Are Associated With Presence of Diagonal Earlobe Crease in CAD Patients

Background and Aims: Diagonal earlobe crease (ELC) has been considered a potential cutaneous marker of atherosclerosis. However, the potential mechanism by which ELC and atherosclerosis are linked has not been adequately defined. Roles of adropin and irisin, novel biomarkers of endothelial function, in ELC have not been well-studied. This study aimed to test whether individuals with ELC are deficient in adropin and irisin, a characteristic that would likely promote endothelial dysfunction and provide a plausible common pathological basis for atherosclerosis and ELC.

Methods: Patients diagnosed with coronary artery disease (CAD) with (n = 45) and without (n = 45) ELC were consecutively enrolled in the study. The ages of the patients enrolled ranged from 40–70 years. Other patients (n = 45) without ELC or CAD were recruited as the control group. All patients underwent coronary angiography. Serum adropin and irisin concentrations were assessed via enzyme-linked immunosorbent assay.

Results: Circulating levels of irisin in the ELC group were significantly lower than those in the non-ELC group, and were highest in the control group. Serum adropin levels of the ELC group were significantly lower than those of the non-ELC group (P < 0.001). Interestingly, although the serum adropin level of the control group was greater than that of the non-ELC group, the difference failed to achieve statistical significance. In subgroup analysis of CAD and ELC, both serum adropin and irisin levels of the CAD and ELC groups were lower than those of the control group (P < 0.001). Receiver-operating characteristic curve analysis revealed that adropin and irisin have similar prognostic power for CAD and ELC.

Conclusions: Low adropin and irisin were significantly associated with CAD and ELC. The deficiencies in adropin and irisin may be a common cause of both atherosclerosis and ELC, which explains why patients with ELC are prone to CAD.

Long-Term Effect of Exercise on Irisin Blood Levels-Systematic Review and Meta-Analysis

Physical exercise may activate a number of important biochemical processes in the human body. The aim of this systematic review and meta-analysis was to identify the long-term effect of physical activity on irisin blood levels. We searched PubMed, Scopus, and Web of Science for articles addressing the long-term effect of physical exercise on irisin blood levels. Fifty-nine articles were included in the final qualitative and quantitative syntheses. A statistically significant within-group effect of exercise on irisin blood levels was in 33 studies; out of them, the irisin level increased 23× and decreased 10×. The significant positive between-groups effect was found 11×. Furthermore, the meta-analysis indicated that physical exercise had a significant positive effect on irisin blood levels (SMD = 0.39 (95% CI 0.27–0.52)). Nevertheless, considerably high heterogeneity was found in all the analyses. This systematic review and meta-analysis indicate that physical exercise might increase irisin blood levels; however, the results of individual studies were considerably inconsistent, which questions the methodological detection of irisin by ELISA kits.

The Associations Between Serum Concentrations of Irisin and Glucose-dependent Insulinotropic Polypeptide with Body Mass Index Among Women with and Without Polycystic Ovary Syndrome

BACKGROUND

The actions of adipocytokines may be a connective factor between obesity and polycystic ovary syndrome (PCOS). It is suggested that irisin, as recently described cytokine secreted by skeletal muscles and glucose-dependent insulinotropic polypeptide (GIP) as an incretin hormone that induces cytokine expression, may play key roles in favoring obesity in these women.

OBJECTIVES

We aimed to evaluate the association between body mass index (BMI) and serum concentrations of irisin/GIP in women with and without PCOS in the linear and non-linear models.

METHODS

This cross-sectional study was conducted among 159 PCOS and 82 healthy eumenorrheic non-hirsute women aged 20 - 50 years. The fractional-polynomial model was used to develop a model of continuous risk factors, which evaluates non-linear associations between irisin/GIP and BMI among women with and without PCOS.

RESULTS

Women with PCOS were significantly younger (28.2 ± 5.8 vs. 33.0 ± 7.8 years, P < 0.001) and had a greater BMI (26.6 ± 5.2 vs. 25.2 ± 4.8 kg/m², P = 0.04) than the healthy counterparts. There were no significant linear and non-linear associations between serum concentration of irisin/GIP and BMI in both groups. The analysis of pair-wise age and BMI matching of women with PCOS and controls confirmed these findings.

CONCLUSIONS

This study showed that irisin and GIP have no association with BMI in women with or without PCOS. This finding could help to better understand the underlying pathophysiological status of PCOS, insulin resistance, and obesity-related disorders. Further large cohort studies are needed to confirm these findings.

Does a Vegetarian Diet Affect the Levels of Myokine and Adipokine in Prepubertal Children?

Myokines are cytokines secreted by muscle and exert autocrine, paracrine, or endocrine effects. Myokines mediate communication between muscle and other organs, including adipose tissue. The aim of the study was to assess serum myokines and their relationships with adipokines and anthropometric and nutritional parameters in children following vegetarian and omnivorous diets. One hundred and five prepubertal children were examined. Among them there were 55 children on a vegetarian diet and 50 children on an omnivorous diet. Concentrations of myokines (myostatin, irisin) and adipokines (leptin, adiponectin, omentin, visfatin) in serum were determined by enzyme-linked immunosorbent assay (ELISA). We observed comparable median values of serum myokines and adipokines (except of leptin concentration) in both of the studied groups of children. We also found several correlations between myokine and adipokine levels and certain nutritional parameters. Serum myostatin was positively correlated with omentin levels in vegetarians and omnivores (p = 0.002). Serum irisin was positively associated with omentin (p = 0.045) levels in omnivores and inversely with visfatin concentration (p = 0.037) in vegetarians. Myostatin concentration was negatively correlated with the percentage of energy from protein (p = 0.014), calcium (p = 0.046), and vitamin A (p = 0.028) intakes in vegetarians and with dietary vitamin C (p = 0.041) and vitamin E (p = 0.021) intakes in omnivores. In multivariate regression analyses, positive correlations of serum myostatin with omentin levels were revealed in both study groups (β = 0.437, p < 0.001 for vegetarians; and β = 0.359, p = 0.001 for omnivores). Consuming a lacto-ovo-vegetarian diet did not influence serum levels of myokines (myostatin, irisin) and adipokines such as adiponectin, visfatin, and omentin in prepubertal children. However, leptin levels were significantly lower in vegetarians compared with omnivores. The observed significant positive correlations between myostatin and omentin concentrations might suggest tissue cross-talk between skeletal muscle and fat tissue. Further studies, carried out in a larger group of children following different dietary patterns, could be important to fully understand the relations between muscle, adipose tissues, and nutrition.

Role of the Myokine Irisin on Bone Homeostasis: Review of the Current Evidence

Bone is a highly dynamic tissue that is constantly adapting to micro-changes to facilitate movement. When the balance between bone building and resorption shifts more towards bone resorption, the result is reduced bone density and mineralization, as seen in osteoporosis or osteopenia. Current treatment strategies aimed to improve bone homeostasis and turnover are lacking in efficacy, resulting in the search for new preventative and nutraceutical treatment options. The myokine irisin, since its discovery in 2012, has been shown to play an important role in many tissues including muscle, adipose, and bone. Evidence indicate that irisin is associated with increased bone formation and decreased bone resorption, leading to reduced risk of osteoporosis in post-menopausal women. In addition, low serum irisin levels have been found in individuals with osteoporosis and osteopenia. Irisin targets key signaling proteins, promoting osteoblastogenesis and reducing osteoclastogenesis. The present review summarizes the existing evidence regarding the effects of irisin on bone homeostasis.

Aerobic exercise modulates noncoding RNA network upstream of FNDC5 in the Gastrocnemius muscle of high-fat-diet-induced obese mice

The purpose of the study was to determine the influence of aerobic exercise with a fat-rich diet on ncRNAs expression associated with FNDC5 in the Gastrocnemius muscle of the obese mice. Twenty-five male mice were grouped into two categories of normal diet (ND) and high-fat diet (HF) treatments for three months. For the subsequent treatment, HF-fed animals (obese) were proceeded in four groups: HF-Trained (n = 5), HF-Untrained (n = 5), ND-Trained (n = 5), and ND-Untrained (n = 5). Simultaneously, ND fed mice (n = 5) continued receiving normal diet and being untrained. In the training group, exercise was applied using a treadmill for 2 months. The Gastrocnemius muscle was excised for the assessment of FNDC5 mRNA, protein levels, and ncRNAs. Using bioinformatics tools, two potential miRNAs, miR-129-5p and miR-140-5p, and four lncRNAs constructing a network with FNDC5 were identified. Significant decrease was observed in both miR-129-5p and miR-140-5p in the HF-fed mice vs. ND-fed mice (p < 0.01). Significant increase of lncRNAs Meg3, Malat1, Neat1, and Kcnq1ot1 correlating in the network was also detected (p < 0.001 for all lncRNAs) in HF-fed mice and trained mice (p < 0.001 for Neat1, Meg3, and Kcnq1ot1). The present study suggests that an increase in the muscle FNDC5 of the high-fat diet mice is governed by an expression regulation of suggested ncRNAs, which were revealed by bioinformatics study to be involved in the insulin resistance and glucose homeostasis pathways.

Bone-to-Brain: A Round Trip in the Adaptation to Mechanical Stimuli

Besides the classical ones (support/protection, hematopoiesis, storage for calcium, and phosphate) multiple roles emerged for bone tissue, definitively making it an organ. Particularly, the endocrine function, and in more general terms, the capability to sense and integrate different stimuli and to send signals to other tissues, has highlighted the importance of bone in homeostasis. Bone is highly innervated and hosts all nervous system branches; bone cells are sensitive to most of neurotransmitters, neuropeptides, and neurohormones that directly affect their metabolic activity and sensitivity to mechanical stimuli. Indeed, bone is the principal mechanosensitive organ. Thanks to the mechanosensing resident cells, and particularly osteocytes, mechanical stimulation induces metabolic responses in bone forming (osteoblasts) and bone resorbing (osteoclasts) cells that allow the adaptation of the affected bony segment to the changing environment. Once stimulated, bone cells express and secrete, or liberate from the entrapping matrix, several mediators (osteokines) that induce responses on distant targets. Brain is a target of some of these mediator [e.g., osteocalcin, lipocalin2, sclerostin, Dickkopf-related protein 1 (Dkk1), and fibroblast growth factor 23], as most of them can cross the blood-brain barrier. For others, a role in brain has been hypothesized, but not yet demonstrated. As exercise effectively modifies the release and the circulating levels of these osteokines, it has been hypothesized that some of the beneficial effects of exercise on brain functions may be associated to such a bone-to-brain communication. This hypothesis hides an interesting clinical clue: may well-addressed physical activities support the treatment of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases?

Irisin Has a Protective Role against Osteoporosis in Ovariectomized Rats

The reduction in estrogen levels results in a decrease in bone density at menopause. Irisin is a myokine that modulates the benefits of exercise, which may include bone health. This study was planned to examine irisin's impact in preventing osteoporosis after ovariectomy. 4 groups of female albino rats (10 rats/group): control, sham-operated, ovariectomized (OVX-control), and OVX-irisin-treated. Serum levels of bone markers [osteocalcin (OC), bone alkaline phosphatase (BALP), tartrate-resistant acid phosphatase (TRAP), calcium (Ca⁺⁺), phosphorus (P)], glucose, and insulin were being measured. Body mass index, Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), dry and ash femur weight, and bone contents of Ca⁺⁺ and P were investigated. The femur was examined histopathologically. The OVX-control group showed an increase in serum levels of OC, BALP, TRAP, calcium, phosphorus, BMI, glucose, insulin, and HOMA-IR (P < 0.05) and a reduction in dry and ash weight of the femur, the concentration of calcium and phosphorus content in bone ash (P < 0.05). The OVX-irisin-treated group exhibited a decrease in serum levels of OC, BALP and TRAP, calcium, phosphorus, BMI, glucose, insulin, HOMA-IR (P < 0.05), and a rise in dry and ash weight of the femur, the concentration of calcium and phosphorus in bone ash (P < 0.05). Histological examination of the distal femur diaphysis of the OVX-irisin-treated group exhibited proper bone architecture and density compared with that of the OVX-control group. It is concluded that irisin treatment in the OVX rats safeguarded the regular bone architecture and normal levels of serum bone biomarkers. Irisin may be a possible novel target in the prohibition of postmenopausal osteoporosis.

Effect of four different forms of high intensity training on BDNF response to Wingate and Graded Exercise Test

This study examined the effects of a nine-week intervention of four different high-intensity training modalities [high-intensity functional training (HIFT), high-intensity interval training (HIIT), high-intensity power training (HIPT), and high-intensity endurance training (HIET)] on the resting concentration of brain-derived neurotropic factor (BDNF). In addition, we evaluated the BDNF responses to Graded Exercise Test (GXT) and Wingate Anaerobic Test (WAnT) in men. Thirty-five healthy individuals with body mass index 25.55 ± 2.35 kg/m2 voluntarily participated in this study and were randomly assigned into four training groups. During nine-weeks they completed three exercise sessions per week for one-hour. BDNF was analyzed before and after a GXT and WAnT in two stages: (stage 0-before training and stage 9-after nine weeks of training). At stage 0, an increase in BDNF concentration was observed in HIFT (33%; p < 0.05), HIPT (36%; p < 0.05) and HIIT (38%; p < 0.05) after GXT. Even though HIET showed an increase in BDNF (10%) this was not statistically significant (p > 0.05). At stage 9, higher BDNF levels after GXT were seen only for the HIFT (30%; p < 0.05) and HIIT (18%; p < 0.05) groups. Reduction in BDNF levels were noted after the WAnT in stage 0 for HIFT (- 47%; p < 0.01), HIPT (- 49%; p < 0.001), HIET (- 18%; p < 0.05)], with no changes in the HIIT group (- 2%). At stage 9, BDNF was also reduced after WAnT, although these changes were lower compared to stage 0. The reduced level of BDNF was noted in the HIFT (- 28%; p < 0.05), and HIPT (- 19%;p < 0.05) groups. Additionally, all groups saw an improvement in VO2max (8%; p < 0.001), while BDNF was also correlated with lactate and minute ventilation and selected WAnT parameters. Our research has shown that resting values of BDNF after nine weeks of different forms of high-intensity training (HIT) have not changed or were reduced. Resting BDNF measured at 3th (before GXT at stage 9) and 6th day after long lasting HITs (before WAnT at stage 9) did not differed (before GXT), but in comparison to the resting value before WAnT at the baseline state, was lower in three groups. It appears that BDNF levels after one bout of exercise is depended on duration time, intensity and type of test/exercise.

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.

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.

Concentrations of Circulating Irisin and Myostatin in Race and Endurace Purebred Arabian Horses-Preliminary Study

Simple Summary

Irisin and myostatin are regulatory proteins produced by muscle cells. The aim of the study was to evaluate the effect of exercise on plasma irisin and myostatin concentrations in horses in different types of training (speed versus endurance). To find out, we tested 20 Arabian horses, submitted to the two different equestrian disciplines, and consequently different training regimes. The first group of horses realized a short-term, high-speed bout of exercise whereas the second group of horses were submitted to long-lasting, endurance effort. The obtained results showed that the single bout of exercise induced an increase in plasma myostatin concentration. Plasma irisin level decreased during the race season in racehorses. This means that irisin and myostatin may play a regulatory role in the maintenance of the energy balance processes.

Abstract

Skeletal muscle is considered to be the largest endocrine organ determining the maintenance of energy homeostasis. Adaptive changes in skeletal muscles in response to physical exercise influence the production as well as secretion of myokines, which are bioactive factors that play a crucial role in energy expenditure processes. The aim of the study was to investigate the impact of two different types of exercise on the circulating level of two of these, myostatin and irisin, in trained horses. Twenty purebred Arabian horses were involved in the study: 10 three-year-old horses trained on the racetrack and 10 endurance horses aged 7.4 ± 1.9 years. The horses from both groups were regularly trained throughout the entire season, during which they also participated in Polish National competitions. To assess the influence of the training sessions on plasma myostatin and irisin concentrations, blood samples taken at rest and 30 min after the end of exercise were analyzed. In the studied horses, the single bout of exercise did not influence plasma irisin but induced an increase in plasma myostatin concentration. In racehorses, plasma irisin concentration decreased with the length of the training season. Plasma myostatin was higher in endurance horses than in three-year-old racehorses. Lack of exercise-induced fluctuation in circulating irisin in studied horses suggests that myostatin released in response to exercise provides a negative feedback signal to irisin release.

Integrin-Ligand Interactions in Inflammation, Cancer, and Metabolic Disease: Insights Into the Multifaceted Roles of an Emerging Ligand Irisin

Integrins are transmembrane proteins that mediate cellular adhesion and migration to neighboring cells or the extracellular matrix, which is essential for cells to undertake diverse physiological and pathological pathways. For integrin activation and ligand binding, bidirectional signaling across the cell membrane is needed. Integrins aberrantly activated under pathologic conditions facilitate cellular infiltration into tissues, thereby causing inflammatory or tumorigenic progressions. Thus, integrins have emerged to the forefront as promising targets for developing therapeutics to treat autoimmune and cancer diseases. In contrast, it remains a fact that integrin-ligand interactions are beneficial for improving the health status of different tissues. Among these ligands, irisin, a myokine produced mainly by skeletal muscles in an exercise-dependent manner, has been shown to bind to integrin αVβ5, alleviating symptoms under unfavorable conditions. These findings may provide insights into some of the underlying mechanisms by which exercise improves quality of life. This review will discuss the current understanding of integrin-ligand interactions in both health and disease. Likewise, we not only explain how diverse ligands play different roles in mediating cellular functions under both conditions via their interactions with integrins, but also specifically highlight the potential roles of the emerging ligand irisin in inflammation, cancer, and metabolic disease.

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.

Irisin and Autophagy: First Update

Aging and sedentary life style are considered independent risk factors for many disorders. Under these conditions, accumulation of dysfunctional and damaged cellular proteins and organelles occurs, resulting in a cellular degeneration and cell death. Autophagy is a conserved recycling pathway responsible for the degradation, then turnover of cellular proteins and organelles. This process is a part of the molecular underpinnings by which exercise promotes healthy aging and mitigate age-related pathologies. Irisin is a myokine released during physical activity and acts as a link between muscles and other tissues and organs. Its main beneficial function is the change of subcutaneous and visceral adipose tissue into brown adipose tissue, with a consequential increase in thermogenesis. Irisin modulates metabolic processes, acting on glucose homeostasis, reduces systemic inflammation, maintains the balance between resorption and bone formation, and regulates the functioning of the nervous system. Recently, some of its pleiotropic and favorable properties have been attributed to autophagy induction, posing irisin as an important regulator of autophagy by exercise. This review article proposes to bring together for the first time the "state of the art" knowledge regarding the effects of irisin and autophagy. Furthermore, treatments on relation between exercise/myokines and autophagy have been also achieved.

Irisin in Liver Cirrhosis

BACKGROUND

Sarcopenia is a prevalent muscle abnormality characterized by progressive and generalized loss of skeletal muscle mass and strength, common among patients with decompensated advanced chronic liver disease (dACLD). Irisin is a recently identified myokine, which is mainly expressed and secreted by skeletal muscle. Pointing to the essential role of irisin in metabolic regulation and energy expenditure we hypothesize that it plays an important role in cirrhosis development and progression.

AIM

To assess irisin serum levels in patients with dACLD, with different cirrhosis stage and etiology. To analyze relationship between sarcopenia and irisin serum levels.

METHODS

Serum irisin concentrations were measured with commercially available ELISA kits in 88 cirrhotic patients. Recorded parameters of muscle mass were hand-grip strength (HGS), mid-arm muscle circumference (MAC), and transversal psoas muscle index (TPMI).

RESULTS

There was no difference in serum irisin levels between cirrhotic patients with different Child-Pugh (CTP) and model of end-stage liver disease (MELD) score, and those with and without ascites. The Liver Frailty Index (LFI) was significantly higher in patients with more advanced liver disease according to CTP and MELD. There was no association between serum irisin level with MAC (r = 0.04, p = 0.74) nor with TPMI (r = 0.20, p = 0.06). We observed significant negative correlation between serum irisin level and age (r = -0.35, p < 0.001).

CONCLUSIONS

Serum irisin levels did not correlate with sarcopenia. There was no difference in serum irisin levels between cirrhotic patients with and without diabetes. There was no difference in serum irisin levels among patients with more severe dACLD, although we observed significant LFI increase among patients with more advanced liver disease.

Serum Irisin Levels and Clinical Implication in Elderly Patients With Type 2 Diabetes Mellitus

Background

The aim of this study is to evaluate the level and role of serum irisin in elderly patients with type 2 diabetes mellitus (T2DM) using case-control study.

Methods

A total of 71 patients with T2DM were selected as the case group according to the inclusion criteria and exclusion criteria; and the ratio of 1:1 was calculated according to the inclusion rate of the residents. The cohort established in Guankou Town, Jimei District, Xiamen City, Fujian Province, China and the residents of this cohort were selected at the age of 60 and above. A total of 71 healthy subjects were included as the control group with the same gender and the age with a difference of ± 5 years old. The clinical data of the subjects were collected to determine their previous history, blood pressure, body mass index (BMI), hemoglobin (HB), liver function test, renal function test, fasting blood glucose and serum lipid. The irisin level in serum was measured by enzyme-linked immunosorbent assay (ELISA). The data were analyzed by using SPSS17.0 software. Single factor analysis using Chi-square test or t-test was performed to compare the differences between T2DM patients with the control group of the general data, clinical indicators and irisin level in serum. Logistic regression was used to analyze the protective factors and risk factors of diabetes mellitus.

Results

The results of single factor analysis showed that the level of irisin in T2DM group was significantly lower than that in the control group (703.37 ± 241.51 ng/mL and 800.22 ± 275.59 ng/mL, respectively). The levels of BMI, systolic blood pressure (SBP), diastolic blood pressure (DBP), triglyceride (TG) and fasting plasma glucose (FPG) in T2DM group were higher than those in control group, and differences were statistically significant. Logistic regression analysis indicated that irisin may be a protective factor for type 2 diabetes (odds ratio (OR) = 0.997, 95% confidence interval (CI): 0.994 - 0.999).

Conclusions

The serum irisin level in T2DM group was significantly lower than that in control group, suggesting that irisin may be a protective factor for type 2 diabetes.

Crosstalk of Brain and Bone-Clinical Observations and Their Molecular Bases

As brain and bone disorders represent major health issues worldwide, substantial clinical investigations demonstrated a bidirectional crosstalk on several levels, mechanistically linking both apparently unrelated organs. While multiple stress, mood and neurodegenerative brain disorders are associated with osteoporosis, rare genetic skeletal diseases display impaired brain development and function. Along with brain and bone pathologies, particularly trauma events highlight the strong interaction of both organs. This review summarizes clinical and experimental observations reported for the crosstalk of brain and bone, followed by a detailed overview of their molecular bases. While brain-derived molecules affecting bone include central regulators, transmitters of the sympathetic, parasympathetic and sensory nervous system, bone-derived mediators altering brain function are released from bone cells and the bone marrow. Although the main pathways of the brain-bone crosstalk remain ‘efferent’, signaling from brain to bone, this review emphasizes the emergence of bone as a crucial ‘afferent’ regulator of cerebral development, function and pathophysiology. Therefore, unraveling the physiological and pathological bases of brain-bone interactions revealed promising pharmacologic targets and novel treatment strategies promoting concurrent brain and bone recovery.

Endosomal-lysosomal dysfunction in metabolic diseases and Alzheimer's disease

The endosomal-lysosomal pathways and related autophagic processes are responsible for proteostasis, involving complexes between lysosomes and autophagosomes. Lysosomes are a key component of homeostasis, involved in cell signaling, metabolism, and quality control, and they experience functional compromise in metabolic diseases, aging, and neurodegenerative diseases. Many genetic mutations and risk factor genes associated with proteinopathies, as well as with metabolic diseases like diabetes, negatively influence endocytic trafficking and autophagic clearance. In contrast, health-improving exercise induces autophagy-lysosomal degradation, perhaps promoting efficient digestion of injured organelles so that undamaged organelles ensure cellular healthiness. Reductions in lysosomal hydrolases are implicated in Alzheimer's, Parkinson's, and lysosomal storage diseases, as well as obesity-related pathology, and members of the cathepsin enzyme family are involved in clearing both Aβ42 and α-synuclein. Upregulation of cathepsin hydrolases improves synaptic and memory functions in models of dementia and in exercising humans, thus identifying lysosomal-related systems as vital for healthy cognitive aging.

Irisin prevents dexamethasone-induced atrophy in C2C12 myotubes

Irisin is a myokine secreted mainly from skeletal muscle that is known for having beneficial metabolic effects via enhancement of energy expenditure and insulin sensitivity. Studies show that irisin also acts as an autocrine/paracrine to promote myogenesis and muscle growth. However, the protective role of irisin against muscular wasting remains unclear. We confirmed that irisin secretion was upregulated by electrical pulse stimulation an in vitro exercise mimetic model. Next, we tested if irisin exerted an anti-atrophic effect on cultured C2C12 myotubes treated with dexamethasone (DEX), a representative inducer of muscular atrophy. Treatment of cultured myotubes with DEX reduced myotube size and increased proteasome activity, which were attenuated by irisin. Also, irisin effectively prevented dephosphorylation of forkhead box O (FoxO) 3α and upregulation of muscle-specific ubiquitin ligases in DEX-treated myotubes. The protective effect of irisin on DEX-mediated myotube atrophy was partially regulated by insulin-like growth factor-1-dependent signaling. These results suggested that irisin may prevent glucocorticoid-induced muscle atrophy by inhibiting FoxO-mediated ubiquitin-proteasome overactivity.

Association of polymorphisms of preptin, irisin and adropin genes with susceptibility to coronary artery disease and hypertension

OBJECTIVES

Preptin, irisin and adropin are 3 new players in energy regulation that are related body mass index, lipids, glucose and insulin levels which may affect incidence of cardiovascular diseases. The aim of the present study was to evaluate eight single nucleotide polymorphisms (SNPs) of preptin genes (rs1003483, rs1004446, rs2239681, rs680, and rs3741204), irisin (rs16835198 and rs3480) and adropin (rs2281997) gene in patients with coronary artery disease (CAD) and hypertension.

METHODS

This case-control study was carried out on 372 volunteers, which were divided into 3 subgroups including: CAD patients with hypertension (CAD+H+), CAD patients with no hypertension (CAD+H-), and non-hypertensive non-CAD subjects as control group (CAD-H-) as health control. Genomic DNA from whole blood was extracted and eight SNPs were assessed using polymerase chain reaction- ligase detection reaction method.

RESULTS

A significant difference was found in the genotype and allele frequency of preptin rs1003483 gene in CAD+H+ compared to CAD+H- groups (P = .019 and P = .018, respectively). Allele frequency of rs1003483 was significantly different between CAD+H- groups and healthy control groups (P = .043). There also existed a significant difference the genotype frequency of rs1004446 gene in CAD+H+ compared to CAD+H- groups (P = .027).

CONCLUSIONS

The findings of present study revealed that the preptin rs1003483 and rs1004446 gene polymorphism might serve as predisposing factor in CAD and hypertension.

Role of irisin in androgen-deficient muscle wasting and osteopenia in mice

Androgen deficiency plays a crucial role in the pathogenesis of male osteoporosis and sarcopenia. Myokines have recently been identified as humoral factors that are involved in the interactions between muscle and bone; however, the influence of androgen deficiency on these interactions remains unclear. Therefore, we herein investigated the roles of humoral factors linking muscle to bone using orchidectomized mice with sarcopenia and osteopenia. Orchidectomy (ORX) significantly reduced muscle mass, grip strength, and trabecular bone mineral density (BMD) in mice. Among the myokines examined, ORX only significantly reduced fibronectin type III domain-containing 5 (Fndc5) mRNA levels in both the soleus and gastrocnemius muscles of mice. In simple regression analyses, Fndc5 mRNA levels in the soleus muscle positively correlated with trabecular BMD, but not cortical BMD. The administration of irisin, a product of Fndc5, significantly protected against the decrease induced in trabecular BMD, but not muscle mass, by androgen deficiency in mice. In conclusion, the present results demonstrated that androgen deficiency decreases the expression of irisin in the skeletal muscle of mice. Irisin may be involved in muscle/bone relationships negatively affected by androgen deficiency.

Hepatic FNDC5 is a potential local protective factor against Non-Alcoholic Fatty Liver

The proteolytic cleavage of Fibronectin type III domain-containing 5 (FNDC5) generates soluble irisin. Initially described as being mainly produced in muscle during physical exercise, irisin mediates adipose tissue thermogenesis and also regulates carbohydrate and lipid metabolism. The aim of this study was to evaluate the hepatic expression of FNDC5 and its role in hepatocytes in Non-Alcoholic Fatty Liver (NAFL). Here we report that hepatic expression of FNDC5 increased with hepatic steatosis and liver injury without impacting the systemic level of irisin in mouse models of NAFLD (HFD and MCDD) and in obese patients. The increased Fndc5 expression in fatty liver resulted from its upregulation in hepatocytes and non-parenchymal cells in mice. The local production of Fndc5 in hepatocytes was influenced by genotoxic stress and p53-dependent pathways. The down-regulation of FNDC5 in human HepG2 cells and in primary mouse hepatocytes increased the expression of PEPCK, a key enzyme involved in gluconeogenesis associated with a decrease in the expression of master genes involved in the VLDL synthesis (CIDEB and APOB). These alterations in FNDC5-silenced cells resulted to increased steatosis and insulin resistance in response to oleic acid and N-acetyl glucosamine, respectively. The downregulation of Fndc5 also sensitized primary hepatocytes to apoptosis in response to TNFα, which has been associated with decreased hepatoprotective autophagic flux. In conclusion, our human and experimental data strongly suggest that the hepatic expression of FNDC5 increased with hepatic steatosis and its upregulation in hepatocytes could dampen the development of NAFLD by negatively regulating steatogenesis and hepatocyte death.

Moderate intensity exercise in hypoxia increases IGF-1 bioavailability and serum irisin in individuals with type 1 diabetes

AIM

This study aimed to determine the effect of moderate intensity continuous exercise (Ex) and hypoxia (Hyp) on serum brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1) and its binding protein-3 (IGFBP-3), irisin and cytokines levels in patients with type 1 diabetes (T1D).

METHODS

A total of 14 individuals with T1D (age: 28.7 ± 7.3 years) and 14 healthy adults (age: 27.1 ± 3.9 years) performed 40-min continuous Ex at moderate intensity (50% lactate threshold) on a cycle ergometer in normoxia (Nor) and Hyp (FiO₂ = 15.1%) Biochemical factors, glucose concentrations and physiological variables were measured at rest, immediately and up to 24 h after both Ex protocols.

RESULTS

Patients with T1D had significantly lower pre-Ex serum concentrations of BDNF (p < 0.05, p < 0.01), and total IGF-1 (p < 0.001, p < 0.05) and significantly higher irisin levels (p < 0.05, p < 0.01) in Nor and Hyp, compared with healthy subjects. Ex significantly increased in T1D group serum BDNF (in Nor only p < 0.05) and total IGF-1 levels in Nor and Hyp (p < 0.001 and p < 0.01, respectively). Immediately after Ex in Hyp, freeIGF-1 (p < 0.05) and irisin levels (p < 0.001) were significantly higher compared with the levels induced by Ex alone. Free IGF-1 and irisin serum levels remained elevated in 24 h post-Ex in Hyp. In T1D, significant blood glucose (BG) decrease was observed immediately after Ex in Hyp (p < 0.001) and in 24 h recovery (p < 0.001) compared with pre-Ex level.

CONCLUSION

The study results suggest that moderate intensity continuous Ex has beneficial effect on BDNF and IGF-1 levels. Ex in hypoxic conditions may be more effective in increasing availability of IGF-1. The alterations in the post-Ex irisin levels and IGF-1 system may be contributing to more effective glycaemia control in patients with T1D.