FNDC5/Irisin inhibits pathological cardiac hypertrophy

Therapeutic potential of exercise-hormone irisin in Alzheimer's disease

Irisin is a myokine that is generated by cleavage of the membrane protein fibronectin type III domain-containing protein 5 (FNDC5) in response to physical exercise. Studies reveal that irisin/FNDC5 has neuroprotective functions against Alzheimer's disease, the most common form of dementia in the elderly, by improving cognitive function and reducing amyloid-β and tau pathologies as well as neuroinflammation in cell culture or animal models of Alzheimer's disease. Although current and ongoing studies on irisin/FNDC5 show promising results, further mechanistic studies are required to clarify its potential as a meaningful therapeutic target for alleviating Alzheimer's disease. We recently found that irisin treatment reduces amyloid-β pathology by increasing the activity/levels of amyloid-β-degrading enzyme neprilysin secreted from astrocytes. Herein, we present an overview of irisin/FNDC5's protective roles and mechanisms against Alzheimer's disease.

The cerebroprotection and prospects of FNDC5/irisin in stroke

Stroke, the leading cause of disability and cognitive impairment, is also the second leading cause of death worldwide. The drugs with multi-targeted brain cytoprotective effects are increasingly being advocated for the treatment of stroke. Irisin, a newly discovered myokine produced by cleavage of fibronectin type III domain 5, has been shown to regulate glucose metabolism, mitochondrial energy, and fat browning. A large amount of evidence indicated that irisin could exert anti-inflammatory, anti-apoptotic, and antioxidant properties in a variety of diseases such as myocardial infarction, inflammatory bowel disease, lung injury, and kidney or liver disease. Studies have found that irisin is widely distributed in multiple brain regions and also plays an important regulatory role in the central nervous system. The most common cause of a stroke is a sudden blockage of an artery (ischemic stroke), and in some circumstances, a blood vessel rupture can also result in a stroke (hemorrhagic stroke). After a stroke, complicated pathophysiological processes lead to serious brain injury and neurological dysfunction. According to recent investigations, irisin may protect elements of the neurovascular unit by acting on multiple pathological processes in stroke. This review aims to outline the currently recognized effects of irisin on stroke and propose possible directions for future research.

Irisin as an agent for protecting against osteoporosis: A review of the current mechanisms and pathways

BACKGROUND

Osteoporosis is recognized as a skeletal disorder characterized by diminished bone tissue quality and density. Regular physical exercise is widely acknowledged to preserve and enhance bone health, but the detailed molecular mechanisms involved remain unclear. Irisin, a factor derived from muscle during exercise, influences bone and muscle. Since its discovery in 2012, irisin has been found to promote bone growth and reduce bone resorption, establishing a tangible link between muscle exertion and bone health. Consequently, the mechanism by which irisin prevents osteoporosis have attracted significant scientific interest.

AIM OF THE REVIEW

This study aims to elucidate the multifaceted relationship between exercise, irisin, and bone health. Focusing on irisin, a muscle-derived factor released during exercise, we seek to understand its role in promoting bone growth and inhibiting resorption. Through a review of current research article on irisin in osteoporosis, Our review provides a deep dive into existing research on influence of irisin in osteoporosis, exploring its interaction with pivotal signaling pathways and its impact on various cell death mechanisms and inflammation. We aim to uncover the molecular underpinnings of how irisin, secreted during exercise, can serve as a therapeutic strategy for osteoporosis.

KEY SCIENTIFIC CONCEPTS OF THE REVIEW

Irisin, secreted during exercise, plays a vital role in bridging muscle function to bone health. It not only promotes bone growth but also inhibits bone resorption. Specifically, Irisin fosters osteoblast proliferation, differentiation, and mineralization predominantly through the ERK, p38, and AMPK signaling pathways. Concurrently, it regulates osteoclast differentiation and maturation via the JNK, Wnt/β-catenin and RANKL/RANK/OPG signaling pathways. This review further delves into the profound significance of irisin in osteoporosis and its involvement in diverse cellular death mechanisms, including apoptosis, autophagy, ferroptosis, and pyroptosis.

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

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

Can irisin be developed as the molecular evolutionary clock based on the origin and functions?

Irisin, a myokine identified in 2012, has garnered research interest for its capacity to induce browning of adipocytes and improve metabolic parameters. As such, the potential therapeutic applications of this exercise-induced peptide continue to be explored. Though present across diverse animal species, sequence analysis has revealed subtle variation in the irisin protein. In this review, we consider the effects of irisin on disease states in light of its molecular evolution. We summarize current evidence for irisin's influence on pathologies and discuss how sequence changes may inform development of irisin-based therapies. Furthermore, we propose that the phylogenetic variations in irisin could potentially be leveraged as a molecular clock to elucidate evolutionary relationships.

Exercise derived myokine irisin as mediator of cardiorespiratory, metabolic and thermal adjustments during central and peripheral chemoreflex activation

Exercise elicits physiological adaptations, including hyperpnea. However, the mechanisms underlying exercise-induced hyperpnea remain unresolved. Skeletal muscle acts as a secretory organ, releasing irisin (IR) during exercise. Irisin can cross the blood-brain barrier, influencing muscle and tissue metabolism, as well as signaling in the central nervous system (CNS). We evaluated the effect of intracerebroventricular or intraperitoneal injection of IR in adult male rats on the cardiorespiratory and metabolic function during sleep-wake cycle under room air, hypercapnia and hypoxia. Central IR injection caused an inhibition on ventilation (VE) during wakefulness under normoxia, while peripheral IR reduced VE during sleep. Additionally, central IR exacerbates hypercapnic hyperventilation by increasing VE and reducing oxygen consumption. As to cardiovascular regulation, central IR caused an increase in heart rate (HR) across all conditions, while no change was observed following peripheral administration. Finally, central IR attenuated the hypoxia-induced regulated hypothermia and increase sleep episodes, while peripheral IR augmented CO2-induced hypothermia, during wakefulness. Overall, our results suggest that IR act mostly on CNS exerting an inhibitory effect on breathing under resting conditions, while stimulating the hypercapnic ventilatory response and increasing HR. Therefore, IR seems not to be responsible for the exercise-induced hyperpnea, but contributes to the increase in HR.

Maternal prednisone exposure during pregnancy elevates susceptibility to osteoporosis in female offspring: The role of mitophagy/FNDC5 alteration in skeletal muscle

Maternal exposure to glucocorticoids has been associated with adverse outcomes in offspring. However, the consequences and mechanisms of gestational exposure to prednisone on susceptibility to osteoporosis in the offspring remain unclear. Here, we found that gestational prednisone exposure enhanced susceptibility to osteoporosis in adult mouse offspring. In a further exploration of myogenic mechanisms, results showed that gestational prednisone exposure down-regulated FNDC5/irisin protein expression and activation of OPTN-dependent mitophagy in skeletal muscle of adult offspring. Additional experiments elucidated that activated mitophagy significantly inhibited the expression of FNDC5/irisin in skeletal muscle cells. Likewise, we observed delayed fetal bone development, downregulated FNDC5/irisin expression, and activated mitophagy in fetal skeletal muscle upon gestational prednisone exposure. In addition, an elevated total m6A level was observed in fetal skeletal muscle after gestational prednisone exposure. Finally, gestational supplementation with S-adenosylhomocysteine (SAH), an inhibitor of m6A activity, attenuated mitophagy and restored FNDC5/irisin expression in fetal skeletal muscle, which in turn reversed fetal bone development. Overall, these data indicate that gestational prednisone exposure increases m6A modification, activates mitophagy, and decreases FNDC5/irisin expression in skeletal muscle, thus elevating osteoporosis susceptibility in adult offspring. Our results provide a new perspective on the earlier prevention and treatment of fetal-derived osteoporosis.

Hydrogen Sulfide and Irisin, Potential Allies in Ensuring Cardiovascular Health

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

The mechanisms of exercise improving cardiovascular function by stimulating Piezo1 and TRP ion channels: a systemic review

Mechanosensitive ion channels are widely distributed in the heart, lung, bladder and other tissues, and plays an important role in exercise-induced cardiovascular function promotion. By reviewing the PubMed databases, the results were summarized using the terms "Exercise/Sport", "Piezo1", "Transient receptor potential (TRP)" and "Cardiovascular" as the keywords, 124-related papers screened were sorted and reviewed. The results showed that: (1) Piezo1 and TRP channels play an important role in regulating blood pressure and the development of cardiovascular diseases such as atherosclerosis, myocardial infarction, and cardiac fibrosis; (2) Exercise promotes cardiac health, inhibits the development of pathological heart to heart failure, regulating the changes in the characterization of Piezo1 and TRP channels; (3) Piezo1 activates downstream signaling pathways with very broad pathways, such as AKT/eNOS, NF-κB, p38MAPK and HIPPO-YAP signaling pathways. Piezo1 and Irisin regulate nuclear localization of YAP and are hypothesized to act synergistically to regulate tissue mechanical properties of the cardiovascular system and (4) The cardioprotective effects of exercise through the TRP family are mostly accomplished through Ca2+ and involve many signaling pathways. TRP channels exert their important cardioprotective effects by reducing the TRPC3-Nox2 complex and mediating Irisin-induced Ca2+ influx through TRPV4. It is proposed that exercise stimulates the mechanosensitive cation channel Piezo1 and TRP channels, which exerts cardioprotective effects. The activation of Piezo1 and TRP channels and their downstream targets to exert cardioprotective function by exercise may provide a theoretical basis for the prevention of cardiovascular diseases and the rehabilitation of clinical patients.

Exploration of the Potential Biomarker FNDC5 for Discriminating Heart Failure in Patients with Coronary Atherosclerosis

Coronary atherosclerosis leading to ischemic artery disease is one of the etiological factors to develop heart failure (HF). This study aimed to investigate potential biomarkers for discriminating HF in atherosclerotic patients. This study included 40 consecutive atherosclerotic patients who underwent angiography. Concentrations of B-type natriuretic peptide (BNP), fibronectin type III domain containing 5 (FNDC5), and Phosphodiesterase 9A (PDE9A) were measured in 20 atherosclerotic patients with HF symptoms/signs and 20 without HF symptoms/signs. Circulating BNP levels were elevated, while FNDC5 levels were reduced in atherosclerotic patients with HF symptoms/signs compared to those without HF symptoms/signs. Pearson correlation analysis showed a significant correlation between FNDC5 and BNP. Receiver Operating Characteristics analysis indicated that both FNDC5 and BNP were able to discriminate HF in atherosclerotic patients. Our findings suggest that FNDC5, along with BNP, has independent value as a biomarker for discriminating HF in patients with coronary atherosclerosis.

The Role of FNDC5/Irisin in Cardiovascular Disease

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

The role of irisin in kidney diseases

Irisin is a hormone that is produced mainly by skeletal muscles in response to exercise. It has been found to have a close correlation with obesity and diabetes mellitus for its energy expenditure and metabolic properties. Recent research has revealed that irisin also possesses anti-inflammatory, anti-oxidative and anti-apoptotic properties, which make it associated with major chronic diseases, such as chronic kidney disease (CKD), liver diseases, osteoporosis, atherosclerosis and Alzheimer s disease. The identification of irisin has not only opened up new possibilities for monitoring metabolic and non-metabolic diseases but also presents a promising therapeutic target due to its multiple biological functions. Studies have shown that circulating irisin levels are lower in CKD patients than in non-CKD patients and decrease with increasing CKD stage. Furthermore, irisin also plays a role in many CKD-related complications like protein energy wasting (PEW), cardiovascular disease (CVD) and chronic kidney disease-mineral and bone disorder (CKD-MBD). In this review, we present the current knowledge on the role of irisin in kidney diseases and their complications.

Irisin improves diabetic cardiomyopathy-induced cardiac remodeling by regulating GSDMD-mediated pyroptosis through MITOL/STING signaling

Diabetic cardiomyopathy (DCM) is a common complication of diabetes mellitus (DM). However, the mechanisms underlying DCM-induced cardiac injury remain unclear. Recently, the role of cyclic GMP-AMP synthase/stimulator of interferon gene (cGAS/STING) signaling and pyroptosis in DCM has been investigated. Based on our previous results, this study was designed to examine the impact of irisin, mitochondrial ubiquitin ligase (MITOL/MARCH5), and cGAS/STING signaling in DCM-induced cardiac dysfunction and the effect of gasdermin D (GSDMD)-dependent pyroptosis. High-fat diet-induced mice and H9c2 cells were used for cardiac geometry and function or pyroptosis-related biomarker assessment at the end of the experiments. Here, we show that DCM impairs cardiac function by increasing cardiac fibrosis and GSDMD-dependent pyroptosis, including the activation of MITOL and cGAS/STING signaling. Our results confirmed that the protective role of irisin and MITOL was partially offset by the activation of cGAS/STING signaling. We also demonstrated that GSDMD-dependent pyroptosis plays a pivotal role in the pathological process of DCM pathogenesis. Our results indicate that irisin treatment protects against DCM injury, mitochondrial homeostasis, and pyroptosis through MITOL upregulation.

Impact of Exercise Intensity on Cerebral BDNF Levels: Role of FNDC5/Irisin

The positive effects of physical exercise (EX) are well known to be mediated by cerebral BDNF (brain-derived neurotrophic factor), a neurotrophin involved in learning and memory, the expression of which could be induced by circulating irisin, a peptide derived from Fibronectin type III domain-containing protein 5 (FNDC5) produced by skeletal muscle contraction. While the influence of EX modalities on cerebral BDNF expression was characterized, their effect on muscle FNDC5/Irisin expression and circulating irisin levels remains to be explored. The present study involved Wistar rats divided into four experimental groups: sedentary (SED), low- (40% of maximal aerobic speed, MAS), intermediate- (50% of MAS) and high- (70% of MAS) intensities of treadmill EX (30 min/day, 7 days). Soleus (SOL) versus gastrocnemius (GAS) FNDC5 and hippocampal BDNF expressions were evaluated by Western blotting. Additionally, muscular FNDC5/Irisin localization and serum/hippocampal irisin levels were studied by immunofluorescence and ELISA, respectively. Our findings revealed that (1) serum irisin and hippocampal BDNF levels vary with EX intensity, showing a threshold intensity at 50% of MAS; (2) hippocampal BDNF levels positively correlate with serum irisin but not with hippocampal FNDC5/Irisin; and (3) GAS, in response to EX intensity, overexpresses FNDC5/Irisin in type II muscle fibers. Altogether, peripheral FNDC5/Irisin levels likely explain EX-dependent hippocampal BDNF expression.

Exercise-induced modulation of myokine irisin on muscle-bone unit in the rat model of post-traumatic osteoarthritis

BACKGROUND AND AIM

Post-traumatic osteoarthritis (PTOA) is a subtype of osteoarthritis (OA). Exercise may produce and release the myokine irisin through muscle fiber contraction. However, the effect of exercise-promoted irisin production on the internal interactions of the muscle-bone unit in PTOA studies remains unclear.

METHODS

Eighteen 8-week-old Sprague-Dawley (SD) rats were randomly divided into three groups: Sham/sedentary (Sham/Sed), PTOA/sedentary (PTOA/Sed), and PTOA/treadmill-walking (PTOA/TW). The PTOA model was established by transection of anterior cruciate ligament (ACLT) and destabilization of medial meniscus (DMM). After 4 weeks of modeling, the PTOA/TW group underwent treadmill exercise (15 m/min, 30 min/d, 5 d/ week, 8 weeks), and the other two groups were free to move in the cage. Evaluation and correlation analysis of muscle, cartilage, subchondral bone and serological indexes were performed after euthanasia.

RESULTS

Eight weeks of treadmill exercise effectively alleviated the trauma-induced OA phenotype, thereby maintaining cartilage and subchondral bone integrity in PTOA, and reducing quadriceps atrophy and myofibril degradation. Exercise reversed the down-regulated expression of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) and fibronectin type III structural domain protein 5 (FNDC5) in muscle tissue of PTOA rats, and increased the blood irisin level, and the irisin level was positively correlated with the expression of PGC-1α and FNDC5. In addition, correlation analysis showed that irisin metabolism level was strongly negatively correlated with Osteoarthritis Research Society International (OARSI) and subchondral bone loss, indicating that irisin may be involved in cartilage biology and PTOA-related changes in cartilage and subchondral bone. Moreover, the metabolic level of irisin was strongly negatively correlated with muscle fiber cross-sectional area (CSA), Atrogin-1 and muscle ring-finger protein-1(MuRF-1) expression, suggesting that irisin may alleviate muscle atrophy through autocrine action.

CONCLUSION

Treadmill exercise can alleviate the atrophy and degeneration of muscle fibers in PTOA rats, reduce the degradation of muscle fibrin, promote the expression of serum irisin, and alleviate the degeneration of articular cartilage and subchondral bone loss in PTOA rats. These results indicate that treadmill exercise can affect the process of PTOA by promoting the expression of myokine irisin in rat muscle-bone unit.

Potential role of irisin in lung diseases and advances in research

Irisin, a myokine, is secreted by the movement of skeletal muscles. It plays an important role in metabolic homeostasis, insulin resistance, anti-inflammation, oxidative stress, and bone metabolism. Several studies have reported that irisin-related signaling pathways play a critical role in the treatment of various diseases, including obesity, cardiovascular disease, diabetes, and neurodegenerative disorders. Recently, the potential role of irisin in lung diseases, including chronic obstructive pulmonary disease, acute lung injury, lung cancer, and their associated complications, has received increasing attention. This article aims to explore the role of irisin in lung diseases, primarily focusing on the underlying molecular mechanisms, which may serve as a marker for the diagnosis as well as a potential target for the treatment of lung diseases, thus providing new strategies for their treatment.

Study on the correlation between lifestyle and negative conversion time in patients diagnosed with coronavirus disease (COVID-19): a retrospective cohort study

BACKGROUND

As of early December 2022, China eased the coronavirus disease (COVID-19) restriction, affecting over 80% of the country's population and posing a severe threat to public health. Previous studies mostly focused factors on the severity/mortality rate of hospitalized COVID-19 patients, but limited studies explored factors associated with virus-negative conversion, particularly lifestyles. Therefore, the aim of our study was to analyze the correlation between lifestyle factors and the negative conversion time in COVID-19 patients.

METHODS

We recruited individuals aged 18 years or older who had a clear time record for both the diagnosis and negative conversion of COVID-19 and completed the electronic questionnaire with no missing data. Dietary data collected from the questionnaire was analyzed using exploratory factor analysis to establish dietary patterns. Age segmentation was performed using restricted cubic spline (RCS) plots. The association between lifestyle factors and the time to negative conversion in different age groups, was assessed using Kaplan-Meier plots and Cox regression analysis.

RESULT

Out of 514 participants, all achieved viral negative conversion within a median time of 11 days. Based on nutrient intake, we identified four dietary patterns. The relationship between age and negative conversion rate, as depicted by RCS plots, exhibited an inverted "U" shape. We categorized age into three segments: <35 years, 35-45 years, and ≥ 45 years. For individuals under 35, our study indicated that a higher protein intake was linked to a faster recovery among COVID-19 patients, while medical staff or those receiving prescription treatments exhibited a slower recovery rate (P < 0.05). The 35 ~ 45 age group showed that adequate sleep and physical exercise were associated with a shorter time to negative conversion, whereas southern regions and a higher intake of carbohydrates were related with a longer conversion time (P < 0.05). Among individuals aged ≥ 45 years, the negative conversion time was primarily associated with physical exercise and being a medical staff member(P < 0.05).

CONCLUSION

Our research suggests that adequate sleep, physical exercise and a higher protein intake can help alleviate COVID-19 symptoms, while a higher level of carbohydrates intake may hinder recovery from COVID-19.

Batokine in Central Nervous System Diseases

Brown adipose tissue (BAT) is a special type of fat tissue in mammals and is also a key endocrine organ in the human body. Batokine, the endocrine effector of BAT, plays a neuroprotective role and improves the prognosis by exerting anti-apoptotic and anti-inflammatory effects, as well as by improving vascular endothelial function and other mechanisms in nerve injury diseases. The present article briefly reviewed several types of batokines related to central nervous system (CNS) diseases. Following this, the potential therapeutic value and future research direction of batokines for CNS diseases were chiefly discussed from the aspects of protective mechanism and signaling pathway.

The Role of Adipokines and Myokines in the Pathogenesis of Different Obesity Phenotypes-New Perspectives

Obesity is a characteristic disease of the twenty-first century that is affecting an increasing percentage of society. Obesity expresses itself in different phenotypes: normal-weight obesity (NWO), metabolically obese normal-weight (MONW), metabolically healthy obesity (MHO), and metabolically unhealthy obesity (MUO). A range of pathophysiological mechanisms underlie the occurrence of obesity, including inflammation, oxidative stress, adipokine secretion, and other processes related to the pathophysiology of adipose tissue (AT). Body mass index (BMI) is the key indicator in the diagnosis of obesity; however, in the case of the NWO and MONW phenotypes, the metabolic disturbances are present despite BMI being within the normal range. On the other hand, MHO subjects with elevated BMI values do not present metabolic abnormalities. The MUO phenotype involves both a high BMI value and an abnormal metabolic profile. In this regard, attention has been focused on the variety of molecules produced by AT and their role in the development of obesity. Nesfatin-1, neuregulin 4, myonectin, irisin, and brain-derived neurotrophic factor (BDNF) all seem to have protective effects against obesity. The primary mechanism underlying the action of nesfatin-1 involves an increase in insulin sensitivity and reduced food intake. Neuregulin 4 sup-presses lipogenesis, decreases lipid accumulation, and reduces chronic low-grade inflammation. Myonectin lowers the amount of fatty acids in the bloodstream by increasing their absorption in the liver and AT. Irisin stimulates the browning of white adipose tissue (WAT) and consequently in-creases energy expenditure, additionally regulating glucose metabolism. Another molecule, BDNF, has anorexigenic effects. Decorin protects against the development of hyperglycemia, but may also contribute to proinflammatory processes. Similar effects are shown in the case of visfatin and chemerin, which may predispose to obesity. Visfatin increases adipogenesis, causes cholesterol accumulation in macrophages, and contributes to the development of glucose intolerance. Chemerin induces angiogenesis, which promotes the expansion of AT. This review aims to discuss the role of adipokines and myokines in the pathogenesis of the different obesity phenotypes.

Irisin deficiency exacerbates diet-induced insulin resistance and cardiac dysfunction in type II diabetes in mice

Irisin is involved in the regulation of a variety of physiological conditions, metabolism, and survival. We and others have demonstrated that irisin contributes critically to modulation of insulin resistance and the improvement of cardiac function. However, whether the deletion of irisin will regulate cardiac function and insulin sensitivity in type II diabetes remains unclear. We utilized the CRISPR/Cas-9 genome-editing system to delete irisin globally in mice and high-fat diet (HFD)-induced type II diabetes model. We found that irisin deficiency did not result in developmental abnormality during the adult stage, which illustrates normal cardiac function and insulin sensitivity assessed by glucose tolerance test in the absence of stress. The ultrastructural analysis of the transmission electronic microscope (TEM) indicated that deletion of irisin did not change the morphology of mitochondria in myocardium. Gene expression profiling showed that several key signaling pathways related to integrin signaling, extracellular matrix, and insulin-like growth factors signaling were coordinately downregulated by deletion of irisin. However, when mice were fed a high-fat diet and chow food for 16 wk, ablation of irisin in mice exposed to HFD resulted in much more severe insulin resistance, metabolic derangements, profound cardiac dysfunction, and hypertrophic response and remodeling as compared with wild-type control mice. Taken together, our results indicate that the loss of irisin exacerbates insulin resistance, metabolic disorders, and cardiac dysfunction in response to HFD and promotes myocardial remodeling and hypertrophic response. This evidence reveals the molecular evidence and the critical role of irisin in modulating insulin resistance and cardiac function in type II diabetes.NEW & NOTEWORTHY By utilizing the CRISPR/Cas-9 genome-editing system and high-fat diet (HFD)-induced type II diabetes model, our results provide direct evidence showing that the loss of irisin exacerbates cardiac dysfunction and insulin resistance while promoting myocardial remodeling and a hypertrophic response in HFD-induced diabetes. This study provides new insight into understanding the molecular evidence and the critical role of irisin in modulating insulin resistance and cardiac function in type II diabetes.

Pediatric Type 1 Diabetes: Mechanisms and Impact of Technologies on Comorbidities and Life Expectancy

Type 1 diabetes (T1D) is one of the most common chronic diseases in childhood, with a progressively increasing incidence. T1D management requires lifelong insulin treatment and ongoing health care support. The main goal of treatment is to maintain blood glucose levels as close to the physiological range as possible, particularly to avoid blood glucose fluctuations, which have been linked to morbidity and mortality in patients with T1D. Indeed, the guidelines of the International Society for Pediatric and Adolescent Diabetes (ISPAD) recommend a glycated hemoglobin (HbA1c) level < 53 mmol/mol (<7.0%) for young people with T1D to avoid comorbidities. Moreover, diabetic disease strongly influences the quality of life of young patients who must undergo continuous monitoring of glycemic values and the administration of subcutaneous insulin. In recent decades, the development of automated insulin delivery (AID) systems improved the metabolic control and the quality of life of T1D patients. Continuous subcutaneous insulin infusion (CSII) combined with continuous glucose monitoring (CGM) devices connected to smartphones represent a good therapeutic option, especially in young children. In this literature review, we revised the mechanisms of the currently available technologies for T1D in pediatric age and explored their effect on short- and long-term diabetes-related comorbidities, quality of life, and life expectation.

Elevated Expression of ADAM10 in Skeletal Muscle of Patients with Idiopathic Inflammatory Myopathies Could Be Responsible for FNDC5/Irisin Unbalance

Dermatomyositis (DM) and immune-mediated necrotizing myopathy (IMNM) are two rare diseases belonging to the group of idiopathic inflammatory myopathies (IIM). Muscle involvement in DM is characterized by perifascicular atrophy and poor myofiber necrosis, while IMNM is characterized by myofiber necrosis with scarce inflammatory infiltrates. Muscle biopsies and laboratory tests are helpful in diagnosis, but currently, few biomarkers of disease activity and progression are available. In this context, we conducted a cohort study of forty-one DM and IMNM patients, aged 40-70 years. In comparison with control subjects, in the muscle biopsies of these patients, there was a lower expression of FNDC5, the precursor of irisin, a myokine playing a key role in musculoskeletal metabolism. Expectedly, the muscle cross-sectional areas of these patients were reduced, while, surprisingly, serum irisin levels were higher than in CTRL, as were mRNA levels of ADAM10, a metalloproteinase recently shown to be the cleavage agent for FNDC5. We hypothesize that elevated expression of ADAM10 in the skeletal muscle of DM and IMNM patients might be responsible for the discrepancy between irisin levels and FNDC5 expression. Future studies will be needed to understand the mechanisms underlying exacerbated FNDC5 cleavage and muscle irisin resistance in these inflammatory myopathies.

Neuroplasticity to autophagy cross-talk in a therapeutic effect of physical exercises and irisin in ADHD

Adaptive neuroplasticity is a pivotal mechanism for healthy brain development and maintenance, as well as its restoration in disease- and age-associated decline. Management of mental disorders such as attention deficit hyperactivity disorder (ADHD) needs interventions stimulating adaptive neuroplasticity, beyond conventional psychopharmacological treatments. Physical exercises are proposed for the management of ADHD, and also depression and aging because of evoked brain neuroplasticity. Recent progress in understanding the mechanisms of muscle-brain cross-talk pinpoints the role of the myokine irisin in the mediation of pro-cognitive and antidepressant activity of physical exercises. In this review, we discuss how irisin, which is released in the periphery as well as derived from brain cells, may interact with the mechanisms of cellular autophagy to provide protein recycling and regulation of brain-derived neurotrophic factor (BDNF) signaling via glia-mediated control of BDNF maturation, and, therefore, support neuroplasticity. We propose that the neuroplasticity associated with physical exercises is mediated in part by irisin-triggered autophagy. Since the recent findings give objectives to consider autophagy-stimulating intervention as a prerequisite for successful therapy of psychiatric disorders, irisin appears as a prototypic molecule that can activate autophagy with therapeutic goals.

Effect of Exercise Interventions on Irisin and Interleukin-6 Concentrations and Indicators of Carbohydrate Metabolism in Males with Metabolic Syndrome

Irisin (IR) is a biomarker that is associated with metabolic syndrome (MetS). However, the available evidence on the association of IR, physical activity, and MetS status are contradictory. Therefore, the present study aimed to investigate the effect of exercise intervention on IR and interleukin-6 (IL-6) levels and indicators of carbohydrate metabolism in males with MetS. The study included 62 males with MetS (age 36.6 ± 6.9 years, BMI 33.6 ± 4.4 kg/m²) randomly assigned to: examined group 1 (EG1, n = 21) with aerobic exercise intervention, examined group 2 (EG2, n = 21) with combined aerobic and resistance exercise intervention, both for 12 weeks, and the control group (CG, n = 20) without intervention. Anthropometric measurements, body composition (body fat [BF], fat free mass [FFM]) as well as a biochemical blood analysis (irisin [IR], interleukin-6 [IL-6], insulin [INS] and glucose [GL]) were performed at baseline, 6 and 12 weeks of intervention, and 4 weeks after ending the intervention (follow-up). Intergroup and intragroup comparisons were performed. In EG1, an increase in IR level was observed as well as decreases in IL-6, BF, and GL levels in relation to the initial measurement. In EG2, decreases in IL-6, BF, and INS levels were observed as well as an increase in FFM level. In CG, no changes were found. Aerobic-resistance exercise led to a greater reduction in the concentrations of IL-6 and INS and more favorable changes in body composition (BF and FFM) than the use of aerobic training alone in males with MetS.

Predictive value of serum irisin for chronic heart failure in patients with type 2 diabetes mellitus

We hypothesize that serum irisin can have additional discriminative potency for heart failure (HF) in individuals with type 2 diabetes mellitus (T2DM). The study group comprised 226 consecutive T2DM patients (153 patients with any HF phenotypes and 30 patients without HF) aged 41 to 65 years. The plasma levels N-terminal brain natriuretic pro-peptide (NT-proBNP) and irisin were detected by ELISA at the baseline of the study. We found that the most appropriate cut-off value of irisin (HF versus non-HF) were 10.4 ng/mL (area under curve [AUC] = 0.96, sensitivity = 81.0%, specificity = 88.0%; P = 0.0001). Cutoff point of NT-proBNP that distinguished patients with HF and without it was 750 pmol/L (AUC = 0.78; sensitivity = 72.7%, specificity 76.5%, p = 0.0001). Using multivariate comparative analysis we established that concentrations of irisin < 10.4 ng/mL (odds ration [OR] = 1.30; P = 0.001) and NT-proBNP > 750 pmol/mL (OR = 1.17; P = 0.042), left atrial volume index (LAVI) > 34 mL/m² (OR = 1.06; P = 0.042) independently predicted HF. Irisin being added to NT-proBNP improved predictive modality for HF, whereas combination of NT-proBNP and LAVI > 34 mL/m² did not. In conclusion, we established that irisin had independent predicted potency for HF in patients with established T2DM.

Irisin protects against obesity-related chronic kidney disease by regulating perirenal adipose tissue function in obese mice

Background

Compared with typical visceral fat deposits in obesity and metabolic syndrome, perirenal adipose tissue (PRAT) dysfunction is more closely linked to obesity-related chronic kidney disease (OB-CKD). The myokine irisin reportedly promotes positive outcomes in metabolic disease. This study investigated whether irisin could reduce urinary albumin excretion and demonstrate renoprotective effects through the regulation of PRAT function in obese mice.

Methods

C57BL/6 J mice received a high-fat diet (HFD) with or without concurrent administration of irisin. Glucose tolerance, plasma levels of free fatty acids, and urinary albumin excretion were assessed, along with renal morphology. The vascular endothelial growth factor and nitric oxide in glomeruli were also analyzed, in addition to PRAT function-associated proteins.

Results

Irisin administration significantly reduced the final body weight, fat mass, and free fatty acids, without reducing PRAT mass, in HFD mice. Furthermore, irisin decreased urinary albumin excretion and attenuated both renal fibrosis and lipid accumulation. Irisin administration led to increases in PRAT function-associated proteins, including sirtuin1, uncoupling protein-1, and heme-oxygenase-1. Ex vivo treatment of PRAT and glomeruli with irisin also restored PRAT function. Finally, irisin treatment restored the vascular endothelial growth factor–nitric oxide axis.

Conclusions

Irisin attenuated metabolic disorders and protected against OB-CKD by normalizing the PRAT–kidney axis. These results suggest that agents targeting PRAT activation might be useful for treatment of OB-CKD.

Circulating Irisin Level as a Biomarker for Pure Aortic Stenosis and Aortic Valve Calcification

Irisin, a myokine mainly secreted by skeletal and cardiac muscles, is actively involved in cardiovascular diseases. However, whether irisin is associated with aortic stenosis remains unknown. Two hundred ninety-three severe AS patients who underwent transcatheter aortic valve implantation were enrolled and followed-up for 35 months on average. Enzyme-linked immunosorbent assay (ELISA) was applied to measure circulating irisin levels. Patients were divided into two groups based on the median plasma irisin level. We found that high plasma irisin levels were independently associated with pure aortic stenosis (PAS) after adjusting for age, body mass index, history of peripheral vascular disease, and creatinine (OR = 3.015, 95% CI 1.775-5.119, P < 0.001). ROC curve analysis showed a significant predictive value of irisin for PAS (AUC = 0.647, 95% CI 0.583-0.711, P < 0.001). The severity of aortic valve calcification was negatively associated with plasma irisin levels (P < 0.05). In conclusion, irisin is an independent predictor for PAS and is negatively associated with the severity of aortic valve calcification.

Irisin, an Effective Treatment for Cardiovascular Diseases?

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

Discriminative Value of Serum Irisin in Prediction of Heart Failure with Different Phenotypes among Patients with Type 2 Diabetes Mellitus

Recent studies have shown that circulating levels of irisin are prognostic factors in heart failure (HF), but no data are available on the predictive role of irisin in patients with type 2 diabetes mellitus (T2DM) and different phenotypes of HF. The aim of the study was to investigate whether serum levels of irisin predict HF in T2DM patients. We prospectively included 183 participants with T2DM aged 41 to 62 years (30 non-HF patients and 153 HF patients) and 25 healthy volunteers in the study and evaluated clinical data, hemodynamics and biomarkers (N-terminal pro-brain natriuretic peptide (NT-proBNP) and irisin). Serum levels of irisin < 8.30 ng/mL were found to be a better indicator of HF with reduced ejection fraction (HFrEF) than irisin ≥ 8.30 ng/mL, but the predictive cut-off point for NT-proBNP remained the same as for HF with mildly reduced ejection fraction (HFmrEF). Serum levels of irisin < 10.4 ng/mL significantly improved the predictive ability of NT-proBNP for HF with preserved ejection fraction (HFpEF). In conclusion, we found that decreased serum levels of irisin significantly predicted HFpEF, rather than HFmrEF and HFrEF, in T2DM patients. This finding may open a new approach to HF risk stratification in T2DM patients.

Irisin, a fascinating field in our times

Irisin is a muscle-secreted hormone that is generated by cleavage of membrane protein FNDC-5 (fibronectin type III domain-containing protein 5). Irisin is considered to be a mediator of exercise-induced metabolic improvements, such as browning of white adipose tissue, and is known to alleviate several chronic non-metabolic diseases. Thus, irisin may be an ideal therapeutic target for metabolic and non-metabolic diseases. However, several controversies regarding irisin have hindered its clinical translation. We review the generation, regulation (especially in exercise), and metabolic as well as therapeutic effects of irisin on metabolic and non-metabolic diseases. Furthermore, we discuss controversies regarding irisin and highlight potential future research directions.

The emerging neuroprotective roles of exerkines in Alzheimer’s disease

Despite the extensive knowledge of the beneficial effects of physical exercise, a sedentary lifestyle is still a predominant harm in our society. Sedentarism is one of the major modifiable risk factors for metabolic diseases such as diabetes mellitus, obesity and neurological disorders, including Alzheimer’s disease (AD)–characterized by synaptic failure, amyloid protein deposition and memory loss. Physical exercise promotes neuroprotective effects through molecules released in circulation and mediates the physiological crosstalk between the periphery and the brain. This literature review summarizes the current understanding of the roles of exerkines, molecules released during physical exercise, as systemic and central factors that mediate the beneficial effects of physical exercise on cognition. We highlight the neuroprotective role of irisin—a myokine released from the proteolytic cleavage of fibronectin type III domain-containing protein 5 (FNDC5) transmembrane protein. Lastly, we review evidence pointing to physical exercise as a potential preventative and interventional strategy against cognitive decline in AD.

Irisin Regulates Cardiac Responses to Exercise in Health and Diseases: a Narrative Review

Exercise has been recognized as an important non-pharmacological approach for the prevention, treatment, and rehabilitation of cardiovascular diseases, but the mechanisms of exercise in promoting cardiovascular health remain unclear. Exercise generates cardiac benefits via stimulating muscle to secret hundreds of myokines that directly enter circulation and target heart tissue. Therefore, inter-organ communication between skeletal muscle and heart may be one important regulating pattern, and such communication can occur through secretion of molecules, frequently known as myokines. Irisin, a newly identified myokine, is cleaved from fibronectin type III domain-containing protein 5 (FNDC5) and secreted by the stimulation of exercise. Recently, accumulating evidence focusing on the interaction between irisin and cardiac function has been reported. This review highlights the molecular signaling by which irisin regulates the benefits of exercise on cardiac function both in physiological and pathological process, and discusses the clinical potential of irisin in treating heart diseases. Exercise generates various cardiovascular benefits through stimulating skeletal muscle to secrete irisin. The exercise "hormone" irisin, both produced by exercise or recombinant form, exerts therapeutic effects in a group of cardiovascular disorders including heart failure, myocardial infarction, atherosclerosis and hypertension. However, the molecular mechanisms involved remain ambiguous.This review highlights the most up-to-date findings to bridge the gap between exercise, irisin and cardiovascular diseases, and discusses the potential clinical prospect of irisin.

Irisin: A promising treatment for neurodegenerative diseases

The beneficial effects of exercise on human brain function have been demonstrated in previous studies. Myokines secreted by muscle have attracted increasing attention because of their bridging role between exercise and brain health. Regulated by PPARγ coactivator 1α, fibronectin type III domain-containing protein 5 releases irisin after proteolytic cleavage. Irisin, a type of myokine, is secreted during exercise, which induces white adipose tissue browning and relates to energy metabolism. Recently, irisin has been shown to exert a protective effect on the central nervous system. Irisin secretion triggers an increase in brain-derived neurotrophic factor levels in the hippocampus, contributing to the amelioration of cognition impairments. Irisin also plays an important role in the survival, differentiation, growth, and development of neurons. This review summarizes the role of irisin in neurodegenerative diseases and other neurological disorders. As a novel positive mediator of exercise in the brain, irisin may effectively prevent or decelerate the progress of neurodegenerative diseases in models and also improve cognitive functions. We place emphasis herein on the potential of irisin for prevention rather than treatment in neurodegenerative diseases. In ischemic diseases, irisin can alleviate the pathophysiological processes associated with stroke. Meanwhile, irisin has anxiolytic and antidepressant effects. The potential therapeutic effects of irisin in epilepsy and pain have been initially revealed. Due to the pleiotropic and beneficial properties of irisin, the possibility of irisin treating other neurological diseases could be gradually explored in the future.

Mechanism of CNS regulation by irisin, a multifunctional protein

Exercise not only builds up our body but also improves cognitive function. Skeletal muscle secretes myokine during exercise as a large reservoir of signaling molecules, which can be considered as a medium between exercise and brain health. Irisin is a circulating myokine derived from the Fibronectin type III domain-containing protein 5 (FNDC5). Irisin regulates energy metabolism because it can stimulate the "Browning" of white adipose tissue. It has been reported that irisin can cross the blood-brain barrier and increase the expression of a brain-derived neurotrophic factor (BDNF) in the hippocampus, which improves learning and memory. In addition, the neuroprotective effect of irisin has been verified in various disease models. Therefore, this review summarizes how irisin plays a neuroprotective role, including its signal pathway and mechanism. In addition, we will briefly discuss the therapeutic potential of irisin for neurological diseases.

Association of irisin levels with cardiac magnetic resonance, inflammatory, and biochemical parameters in patients with chronic heart failure versus controls

BACKGROUND AND AIMS

Chronic heart failure (CHF) represents a significant cause of morbidity and mortality globally. Metabolic maladaptation has proven to be critical in the progression of this condition. Preclinical studies have shown that irisin, an adipomyokine involved in metabolic regulations, can induce positive cardioprotective effects by improving cardiac remodeling, cardiomyocyte viability, calcium delivery, and reducing inflammatory mediators. However, data on clinical studies identifying the associations between irisin levels and functional imaging parameters are scarce in CHF patients. The objective of this study was to determine the association of irisin levels with cardiac imaging measurements through cardiac magnetic resonance, inflammatory markers, and biochemical parameters in patients with CHF compared with control subjects.

METHODS AND RESULTS

Thirty-two subjects diagnosed with CHF and thirty-two healthy controls were evaluated in a cross-sectional study. Serum irisin levels were significantly lower in patients with CHF than in controls. This is the first study to report a significant positive correlation between irisin levels and cardiac magnetic resonance parameters such as left ventricular ejection fraction, fraction shortening, and global radial strain. A negative correlation was demonstrated between irisin levels and brain natriuretic peptide, insulin levels, and Homeostatic model assessment for insulin resistance index. We did not observe significant correlations between irisin levels and inflammatory cytokines.

CONCLUSIONS

Given the importance of fraction shortening and global radial strain as accurate markers of ventricular wall motion, these results support the hypothesis that irisin may play an essential role in maintaining an adequate myocardial wall architecture, deformation, and thickness.

Irisin is an Effector Molecule in Exercise Rehabilitation Following Myocardial Infarction (Review)

Background: Regular exercise is an effective non-pharmacological therapy for treatment and prevention of cardiovascular disease (CVD). The therapeutic benefits of exercise are mediated partly through improved vascular and increase in metabolic health. Release of exercise-responsive myokines, including irisin, is associated with beneficial effects of exercise in CVD patients.

Observations: The present review provides an overview of the role of exercise in cardiac rehabilitation of patients with myocardial infarction (MI). Further, the role of irisin as a motion-responsive molecule in improving vascular and metabolic health is explored. Possible mechanism of cardioprotective effect of irisin-mediated exercise on myocardial infarction are also summarized in this review.

Conclusion and significance of the review: Irisin is associated with reduced inflammation, antioxidant properties, and anti-apoptotic effect, implying that it is a potential key mediator of the beneficial effects of exercise on vascular and metabolic health. The findings show that irisin is a promising therapeutic target for treatment of patients with cardiovascular disease, particularly post-MI. Further research should be conducted to elucidate the potential mechanisms of cardioprotective effects of irisin and explored whether irisin induced by exercise exerts rehabilitation effects post-MI.

Irisin reduces the abnormal reproductive and metabolic phenotypes of PCOS by regulating the activity of brown adipose tissue in mice

Polycystic ovary syndrome (PCOS) is a common endocrine and metabolic disease in women, with clinical manifestations of anovulation and hyperandrogenaemia. The treatment of PCOS mainly focuses on improving clinical symptoms, such as insulin sensitivity or menstrual disorder, through drug treatment. However, due to the pathogenesis diversity of PCOS, there is still a lack of effective treatment in clinics. Metabolic disorder is the key factor in the occurrence of PCOS. Brown adipose tissue (BAT) is a special adipose tissue in the human body that can participate in metabolic balance by improving heat production. BAT has been demonstrated to be an important substance involved in the metabolic disorder of PCOS. Although increasing evidence indicates that BAT transplantation can improve the symptoms of PCOS, it is difficult to achieve BAT transplantation at present due to technical limitations. Stimulation of BAT activation by exogenous substances may be an effective alternative therapy for PCOS. In this study, we investigated the effects of Irisin on dehydroepiandrosterone (DHEA)-induced PCOS in mice and evaluated the effect of Irisin on serum hormone levels and changes in body temperature, body weight and ovarian morphology. In our study, we found that Irisin can enhance the thermogenesis and insulin sensitivity of PCOS mice by activating the function of BAT. In addition, Irisin treatment can correct the menstrual cycle of PCOS mice, improve the serum steroid hormone disorder status, and reduce the formation of ovarian cystic follicles. In conclusion, our results showed that Irisin treatment significantly improved the metabolic disorder of PCOS and may provide a new and alternative therapy for the treatment of this pathology.

Preventive Effect of Ellagic Acid on Cardiac Dysfunction in Diabetic Mice through Regulating DNA Hydroxymethylation

Ellagic acid (EA) improves mitochondrial dysfunction and protects diabetic hearts. The mitochondrial tricarboxylic acid (TCA) cycle regulates DNA 5-hydroxymethylcytosine (5hmC) levels by affecting activity of 10-11 translocation enzymes (TETs). Therefore, we hypothesized that EA prevents diabetic cardiac dysfunction by modulating DNA 5hmC levels. C57BL/6J mice were fed a high-fat diet to induce diabetes and treated with EA (100 mg kg^-1 day^-1) for 8 weeks. Serum concentrations of glucose, insulin, and triglyceride and aspartate transaminase and creatine kinase activities were significantly lower in the EA group than the diabetes mellitus (DM) group. DNA 5hmC levels of mice hearts were significantly higher in the EA group than the DM group. The protein levels of TET, complexes I/III/V were significantly higher in the EA group than the DM group. The results shows that EA has a preventive effect on diabetic cardiac dysfunction, which may be achieved by upregulating TET activity through improving the TCA cycle, to reshape DNA 5hmC levels of mice hearts.

FNDC5/irisin reduces ferroptosis and improves mitochondrial dysfunction in hypoxic cardiomyocytes by Nrf2/HO-1 Axis

Myocardial infarction is characterized by cardiomyocyte death and mitochondrial dysfunction induced by ischemia. Ferroptosis, a novel form of cell death, has been found to play critical roles under ischemic conditions. Recently, several studies have shown that fibronectin type III domain-containing 5 (FNDC5) and its cleaved form, irisin, protect the heart against injury. However, its protective effect on ferroptosis and mitochondrial impairments is still unclear. Thus, our aim was to investigate the role of irisin in ferroptosis and mitochondrial dysfunction in cardiomyocytes under hypoxic conditions. Cardiomyocytes were treated with FNDC5 overexpression and/or irisin under normoxic and hypoxic conditions. Cell viability was assessed by CCK-8 assay. Reactive oxygen species production was evaluated by dihydroethidium staining. In addition, the intracellular ferrous iron level (Fe²⁺ ) and the relative concentration of MDA and ATP content were determined using an iron assay kit, lipid peroxidation assay kit and ATP bioluminescent assay kit. The SOD level in cells was measured using an ELISA kit. Furthermore, an immunoblotting assay was used to determine ferroptosis-related mitochondrial proteins. Hypoxia promoted cell death, increased ferroptosis and caused mitochondrial dysfunction in cardiomyocytes. Interestingly, FNDC5 overexpression and/or irisin administration elevated cell viability, decreased ferroptosis and reversed mitochondrial impairments induced by hypoxia. Mechanistically, FNDC5/irisin reduced ferroptosis and reversed mitochondrial impairments by Nrf2/HO-1 axis in hypoxic cardiomyocytes. Thus, we have demonstrated that FNDC5/irisin plays a protective role in ferroptosis and mitochondrial dysfunction in hypoxia-induced cardiomyocyte. This article is protected by copyright. All rights reserved.

HIF-1α Negatively Regulates Irisin Expression Which Involves in Muscle Atrophy Induced by Hypoxia

Exposure to high altitude environment leads to skeletal muscle atrophy. As a hormone secreted by skeletal muscles after exercise, irisin contributes to promoting muscle regeneration and ameliorating skeletal muscle atrophy, but its role in hypoxia-induced skeletal muscle atrophy is still unclear. Our results showed that 4 w of hypoxia exposure significantly reduced body weight and gastrocnemius muscle mass of mice, as well as grip strength and the duration time of treadmill exercise. Hypoxic treatment increased HIF-1α expression and decreased both the circulation level of irisin and its precursor protein FNDC5 expression in skeletal muscle. In in vitro, CoCl₂-induced chemical hypoxia and 1% O₂ ambient hypoxia both reduced FNDC5, along with the increase in HIF-1α. Moreover, the decline in the area and diameter of myotubes caused by hypoxia were rescued by inhibiting HIF-1α via YC-1. Collectively, our research indicated that FNDC5/irisin was negatively regulated by HIF-1α and could participate in the regulation of muscle atrophy caused by hypoxia.

Irisin at the crossroads of inter-organ communications: Challenge and implications

The physiological functions of organs are intercommunicated occurring through secreted molecules. That exercise can improve the physiological function of organs or tissues is believed by secreting myokines from muscle to target remote organs. However, the underlying mechanism how exercise regulates the inter-organ communications remains incompletely understood yet. A recently identified myokine-irisin, primarily found in muscle and adipose and subsequently extending to bone, heart, liver and brain, provides a new molecular evidence for the inter-organ communications. It is secreted under the regulation of exercise and mediates the intercommunications between exercise and organs. To best our understanding of the regulatory mechanism, this review discusses the recent evidence involving the potential molecular pathways of the inter-organ communications, and the interactions between signalings and irisin in regulating the impact of exercise on organ functions are also discussed.

Irisin, Exercise, and COVID-19

Muscle and adipose tissue produce irisin during exercise. Irisin is thermogenic adipomyokine, improves glucose and lipid metabolism, and ameliorates the effects of obesity-driven inflammation, metabolic syndrome, and diabetes. In addition, exercise-induced irisin activates anti-inflammatory pathways and may play an essential role in improving the outcomes of inflammatory conditions, such as coronavirus disease (COVID-19). COVID-19 infection can activate different intracellular receptors and modulate various pathways during the course of the disease. The cytokine release storm (CRS) produced is significant because it promotes the context for systemic inflammation, which increases the risk of mortality in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV2). In addition, viral infection and the resulting organ damage may stimulate the mitogen-activated protein kinase(MAPK) and toll-like receptor 4 (TLR4)/toll interleukin receptor (TIR)-domain-containing adaptor (MyD88) pathways while negatively modulating the AMP-activated protein kinase (AMPK) pathway, leading to increased inflammatory cytokine production. Exercise-induced irisin may counteract this inflammatory modulation by decreasing cytokine production. Consequently, increased irisin levels, as found in healthy patients, may favor a better prognosis in patients with SARS-CoV2. This review aims to explore the molecular mechanisms underlying the anti-inflammatory properties of irisin in mitigating CRS and preventing severe outcomes due to infection with SARS-CoV2.

Role of irisin in physiology and pathology

Irisin, out-membrane part of fibronectin type III domain-containing 5 protein (FNDC5), was activated by Peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α) during physical exercise in skeletal muscle tissues. Most studies have reported that the concentration of irisin is highly associated with health status. For instance, the level of irisin is significantly lower in patients with obesity, osteoporosis/fractures, muscle atrophy, Alzheimer's disease, and cardiovascular diseases (CVDs) but higher in patients with cancer. Irisin can bind to its receptor integrin αV/β5 to induce browning of white fat, maintain glucose stability, keep bone homeostasis, and alleviate cardiac injury. However, it is unclear whether it works by directly binding to its receptors to regulate muscle regeneration, promote neurogenesis, keep liver glucose homeostasis, and inhibit cancer development. Supplementation of recombinant irisin or exercise-activated irisin might be a successful strategy to fight obesity, osteoporosis, muscle atrophy, liver injury, and CVDs in one go. Here, we summarize the publications of FNDC5/irisin from PubMed/Medline, Scopus, and Web of Science until March 2022, and we review the role of FNDC5/irisin in physiology and pathology.

Circ_nuclear factor I X (circNfix) attenuates pressure overload-induced cardiac hypertrophy via regulating miR-145-5p/ATF3 axis

Cardiac hypertrophy can cause heart failure. However, the mechanisms underlying the progression of cardiac hypertrophy remain unclear. Emerging evidence suggests that circular RNAs (circRNAs) play a critical role in cardiac hypertrophy. However, the association between circ_nuclear factor I X (circNfix) and cardiac hypertrophy remain largely unknown. Therefore, the aim of the present study was to explore the role of circNfix in cardiac hypertrophy. In order to detect the function of circNfix in cardiac hypertrophy, cardiomyocytes were stimulated with angiotensin II (Ang II) to mimic the pathogenesis of the disease. In addition, pressure overload-induced cardiac hypertrophy in a mouse model was established using transverse aortic constriction (TAC) surgery. The mechanism via which circNfix regulated cardiac hypertrophy was investigated using RNA pull-down and luciferase reporter assays, and fluorescence in situ hybridization (FISH). circNfix was downregulated in Ang II-treated cardiomyocytes. Similarly, circNfix expression was markedly downregulated in mice following TAC surgery. In addition, circNfix overexpression significantly prevented the progression of cardiac hypertrophy in TAC-treated mice. Luciferase activity and RNA pull-down assays indicated that circNfix could indirectly target activating transcription factor 3 (ATF3) by binding with microRNA (miR)-145-5p in cardiomyocytes. miR-145-5p overexpression or ATF3 knockdown could reverse the effects of circNfix in Ang II-treated mouse cardiomyocytes. circNfix attenuated pressure overload-induced cardiac hypertrophy by regulating the miR-145-5p/ATF3 axis. Therefore, circNfix may serve as a molecular target for cardiac hypertrophy treatment.

Exercise Ameliorates Diabetic Kidney Disease in Type 2 Diabetic Fatty Rats

Lifestyle improvement, including through exercise, has been recognized as an important mode of therapy for the suppression of diabetic kidney disease (DKD). However, the detailed molecular mechanisms by which exercise exerts beneficial effects in the suppression of DKD have not yet been fully elucidated. In this study, we investigate the effects of treadmill exercise training (TET) for 8 weeks (13 m/min, 30 min/day, 5 days/week) on kidney injuries of type 2 diabetic male rats with obesity (Wistar fatty (fa/fa) rats: WFRs) at 36 weeks of age. TET significantly suppressed the levels of albuminuria and urinary liver-type fatty-acid-binding protein (L-FABP), tubulointerstitial fibrosis, inflammation, and oxidative stress in the kidneys of WFRs. In addition, TET mitigated excessive apoptosis and restored autophagy in the renal cortex, as well as suppressed the development of morphological abnormalities in the mitochondria of proximal tubular cells, which were also accompanied by the restoration of AMP-activated kinase (AMPK) activity and suppression of the mechanistic target of rapamycin complex 1 (mTORC1). In conclusion, TET ameliorates diabetes-induced kidney injury in type 2 diabetic fatty rats.

Irisin Stimulates the Release of CXCL1 From Differentiating Human Subcutaneous and Deep-Neck Derived Adipocytes via Upregulation of NFκB Pathway

Thermogenic brown and beige adipocytes might open up new strategies in combating obesity. Recent studies in rodents and humans have indicated that these adipocytes release cytokines, termed "batokines". Irisin was discovered as a polypeptide regulator of beige adipocytes released by myocytes, primarily during exercise. We performed global RNA sequencing on adipocytes derived from human subcutaneous and deep-neck precursors, which were differentiated in the presence or absence of irisin. Irisin did not exert an effect on the expression of characteristic thermogenic genes, while upregulated genes belonging to various cytokine signaling pathways. Out of the several upregulated cytokines, CXCL1, the highest upregulated, was released throughout the entire differentiation period, and predominantly by differentiated adipocytes. Deep-neck area tissue biopsies also showed a significant release of CXCL1 during 24 h irisin treatment. Gene expression data indicated upregulation of the NFκB pathway upon irisin treatment, which was validated by an increase of p50 and decrease of IκBα protein level, respectively. Continuous blocking of the NFκB pathway, using a cell permeable inhibitor of NFκB nuclear translocation, significantly reduced CXCL1 release. The released CXCL1 exerted a positive effect on the adhesion of endothelial cells. Together, our findings demonstrate that irisin stimulates the release of a novel adipokine, CXCL1, via upregulation of NFκB pathway in neck area derived adipocytes, which might play an important role in improving tissue vascularization.

The Emerging Role of Irisin in Cardiovascular Diseases

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

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

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