Interleukin-15, IL-15 Receptor-Alpha, and Obesity: Concordance of Laboratory Animal and Human Genetic Studies

Systematic Review of IL-1, IL-4, IL-6, IL-10, IL-15, and IL-18 Gene Polymorphisms and Meta-Analysis of IL-6 Variant and Its Association with Overweight and Obesity Risk in Men

Obesity is a complex health risk influenced by genetic, environmental, and lifestyle factors. This review systematically assessed the association between interleukin gene polymorphisms (rs16944, rs17561, rs1143623, rs1143633, rs1143634, rs1800587, rs2234677, and rs4848306), IL-4 (rs180275, rs1805010, IL-6 rs13306435, rs1800795, rs1800796, rs1800797, rs2228145, rs2228145, rs2229238, and rs4845623), IL-10 (rs1518110, rs1518111, rs1800871, rs1800872, rs1800896, rs1878672, rs2834167, rs3024491, rs3024496, rs3024498, and rs3024505), IL-15 (rs3136617, rs3136618, and rs2296135), and IL-18 (rs187238, rs1946518, rs2272127, rs2293225, and rs7559479) and the risk of overweight and obesity in adults, focusing on IL-6 rs1800795 through a meta-analysis. The focus on IL-6 in this review arises from its pleiotropic nature and unclear effect on obesity risk. The review included studies published from 1998 to 2023, sourced from Science Direct, EBSCOhost, Web of Science, and Google Scholar. Bias was assessed with the Cochrane Collaboration tool, and funnel plots were used for publication bias. Results were synthesized into pooled odds ratios (ORs) and confidence intervals (CIs). Thirty studies comprising approximately 29,998 participants were included. The selection criteria required that the articles include participants who were overweight or obese, and this condition needed to be linked to IL polymorphisms. In a meta-analysis, in the dominant model, the pooled OR was 1.26 (95% CI 1.08 to 1.47), indicating those with the GC/CC genotype for IL-6 rs1800795 are 1.26 times more likely to be overweight/obese than GG genotype carriers. For the recessive model, the OR was 1.25 (95% CI 1.04 to 1.51). The overdominant model showed no significant association (OR 1.08, 95% CI 0.94 to 1.25). Interleukin gene variation, particularly the IL-6 rs1800795 variant, is modestly associated with obesity risk. This suggests that other factors, such as the environment, also play a role in obesity. Thus, individuals with this particular IL-6 variant may have a slightly higher likelihood of being overweight or obese compared to those without it, but this is just one of many factors influencing obesity risk.

Skeletal muscle as a pro- and anti-inflammatory tissue: insights from children to adults and ultrasound findings

Previously regarded as a movement and posture control agent, the skeletal muscle is now recognized as an endocrine organ that may affect systemic inflammation and metabolic health. The discovery of myokines such as IL-6, released from skeletal muscle in response to physical exercise, is now one of the most recent insights. Myokines are the mediators of the balance between the pro-inflammatory and anti-inflammatory responses. This underscores the muscle function as a determinant of good health and prevention of diseases. Advances in ultrasound technology improved evaluation of muscle thickness, composition, and determining fat distribution. Combining imaging with molecular biology, researchers discovered the complicated interplay between muscle function, cytokine production and general health effects.The production of myokines with exercise showcasing the adaptability of muscles to high-stress conditions and contributing to metabolism and inflammation regulation. These findings have significant implications in order to provide improvement in metabolic and inflammatory diseases.

Interleukin 15: A new intermediary in the effects of exercise and training on skeletal muscle and bone function

Interleukin-15 (IL-15), a pro-inflammatory cytokine, is produced mainly by skeletal muscle cells, macrophages and epithelial cells. Recent research has demonstrated that IL-15 is closely related to the functions of bone and skeletal muscle in the locomotor system. There is growing evidence that exercise, an important means to regulate the immune and locomotor systems, influences IL-15 content in various tissues, thereby indirectly affecting the function of bones and muscles. Furthermore, the form, intensity, and duration of exercise determine the degree of change in IL-15 and downstream effects. This paper reviews the structure, synthesis and secretion of IL-15, the role of IL-15 in regulating the metabolism of bone tissue cells and myofibers through binding to the IL-15 receptor-α (IL-15Rα), and the response of IL-15 to different types of exercise. This review provides a reference for further analyses of the role and mechanism of action of IL-15 in the regulation of metabolism during exercise.

Cytokine and Microbiome Changes in Adolescents with Anorexia Nervosa at Admission, Discharge, and One-Year Follow-Up

Anorexia nervosa (AN) is a severe eating disorder that predominantly affects females and typically manifests during adolescence. There is increasing evidence that serum cytokine levels are altered in individuals with AN. Previous research has largely focused on adult patients, assuming a low-grade pro-inflammatory state. The serum levels of the cytokine tumour necrosis factor-alpha (TNF-α), interleukin (IL)-1β, IL-6 and IL-15, which are pro-inflammatory, were examined in 63 female adolescents with AN and 41 age-matched healthy controls (HC). We included three time points (admission, discharge, and 1-year follow-up) and investigated the clinical data to assess whether the gut microbiota was associated with cytokine alterations. Relative to the HC group, serum levels of IL-1β and IL-6 were significantly lower during the acute phase (admission) of AN. IL-1β expression was normalised to control levels after weight recovery. TNF-α levels were not significantly different between the AN and HC groups. IL-15 levels were significantly elevated in patients with AN at all time points. We found associations between cytokines and bodyweight, illness duration, depressive symptoms, and the microbiome. In contrast to most findings for adults, we observed lower levels of the pro-inflammatory cytokines IL-1β and IL-6 in adolescent patients, whereas the level of IL-15 was consistently increased. Thus, the presence of inflammatory dysregulation suggests a varied rather than uniform pro-inflammatory state.

Mapping novel QTL and fine mapping of previously identified QTL associated with glucose tolerance using the collaborative cross mice

A chronic metabolic illness, type 2 diabetes (T2D) is a polygenic and multifactorial complicated disease. With an estimated 463 million persons aged 20 to 79 having diabetes, the number is expected to rise to 700 million by 2045, creating a significant worldwide health burden. Polygenic variants of diabetes are influenced by environmental variables. T2D is regarded as a silent illness that can advance for years before being diagnosed. Finding genetic markers for T2D and metabolic syndrome in groups with similar environmental exposure is therefore essential to understanding the mechanism of such complex characteristic illnesses. So herein, we demonstrated the exclusive use of the collaborative cross (CC) mouse reference population to identify novel quantitative trait loci (QTL) and, subsequently, suggested genes associated with host glucose tolerance in response to a high-fat diet. In this study, we used 539 mice from 60 different CC lines. The diabetogenic effect in response to high-fat dietary challenge was measured by the three-hour intraperitoneal glucose tolerance test (IPGTT) test after 12 weeks of dietary challenge. Data analysis was performed using a statistical software package IBM SPSS Statistic 23. Afterward, blood glucose concentration at the specific and between different time points during the IPGTT assay and the total area under the curve (AUC0-180) of the glucose clearance was computed and utilized as a marker for the presence and severity of diabetes. The observed AUC0-180 averages for males and females were 51,267.5 and 36,537.5 mg/dL, respectively, representing a 1.4-fold difference in favor of females with lower AUC0-180 indicating adequate glucose clearance. The AUC0-180 mean differences between the sexes within each specific CC line varied widely within the CC population. A total of 46 QTL associated with the different studied phenotypes, designated as T2DSL and its number, for Type 2 Diabetes Specific Locus and its number, were identified during our study, among which 19 QTL were not previously mapped. The genomic interval of the remaining 27 QTL previously reported, were fine mapped in our study. The genomic positions of 40 of the mapped QTL overlapped (clustered) on 11 different peaks or close genomic positions, while the remaining 6 QTL were unique. Further, our study showed a complex pattern of haplotype effects of the founders, with the wild-derived strains (mainly PWK) playing a significant role in the increase of AUC values.

Arterial wall inflammation assessed by 18F-FDG-PET/CT is higher in individuals with Type 1 diabetes and associated with circulating inflammatory proteins

AIMS

The article investigates whether chronic hyperglycaemia in Type 1 diabetes (T1D) is associated with a proinflammatory immune signature and with arterial wall inflammation, driving the development of atherosclerosis.

METHODS AND RESULTS

Patients with T1D (n = 41), and healthy age-, sex-, and body mass index-matched controls (n = 20) were recruited. Arterial wall inflammation and haematopoietic activity were measured with 2'-deoxy-2'-(18F)-fluoro-D-glucose (18F-FDG) positron emission tomography/computed tomography. In addition, flow cytometry of circulating leucocytes was performed as well as targeted proteomics to measure circulating inflammatory markers. 18F-FDG uptake in the wall of the abdominal aorta, carotid arteries, and iliac arteries was higher in T1D compared with that in the healthy controls. Also, 18F-FDG uptake in the bone marrow and spleen was higher in patients with T1D. CCR2 and CD36 expressions on circulating monocytes were higher in patients with T1D, as well as several circulating inflammatory proteins. In addition, several circulating inflammatory markers (osteoprotegerin, transforming growth factor-alpha, CX3CL1, and colony-stimulating factor-1) displayed a positive correlation with FDG uptake. Within T1D, no differences were found between people with a high and low HbA1c.

CONCLUSION

These findings strengthen the concept that chronic hyperglycaemia in T1D induces inflammatory changes that fuel arterial wall inflammation leading to atherosclerosis. The degree of hyperglycaemia appears to play a minor role in driving this inflammatory response in patients with T1D.

Pharmacological and physiological roles of adipokines and myokines in metabolic-related dementia

Dementia is a detrimental neuropathologic condition with considerable physical, mental, social, and financial impact on patients and society. Patients with metabolic syndrome (MetS), a group of diseases that occur in tandem and increase the risk of neurologic diseases, have a higher risk of dementia. The ratio between muscle and adipose tissue is crucial in MetS, as these contain many hormones, including myokines and adipokines, which are involved in crosstalk and local paracrine/autocrine interactions. Evidence suggests that abnormal adipokine and myokine synthesis and release may be implicated in various MetS, such as atherosclerosis, diabetic mellitus (DM), and dyslipidemia, but their precise role is unclear. Here we review the literature on adipokine and myokine involvement in MetS-induced dementia via glucose and insulin homeostasis regulation, neuroinflammation, vascular dysfunction, emotional changes, and cognitive function.

Energy metabolism and frailty: The potential role of exercise-induced myokines - A narrative review

Frailty is a complex condition that emerges from dysregulation in multiple physiological systems. Increasing evidence suggests the potential role of age-related energy dysregulation as a key driver of frailty. Exercise is considered the most efficacious intervention to prevent and even ameliorate frailty as it up-tunes and improves the function of several related systems. However, the mechanisms and molecules responsible for these intersystem benefits are not fully understood. The skeletal muscle is considered a secretory organ with endocrine functions that can produce and secrete exercise-related molecules such as myokines. These molecules are cytokines and other peptides released by muscle fibers in response to acute and/or chronic exercise. The available evidence supports that several myokines can elicit autocrine, paracrine, or endocrine effects, partly mediating inter-organ crosstalk and also having a critical role in improving cardiovascular, metabolic, immune, and neurological health. This review describes the current evidence about the potential link between energy metabolism dysregulation and frailty and provides a theoretical framework for the potential role of myokines (via exercise) in counteracting frailty. It also summarizes the physiological role of selected myokines and their response to different acute and chronic exercise protocols in older adults.

IL-15 Participates in the Pathogenesis of Polycystic Ovary Syndrome by Affecting the Activity of Granulosa Cells

BACKGROUND

Low-grade chronic inflammation may contribute to the pathogenesis of polycystic ovary syndrome (PCOS). Interleukin-15 (IL-15) is a proinflammatory cytokine involved in the development of chronic inflammation leading to obesity-associated metabolic syndrome. However, the concentration of IL-15 in follicular fluid of patients with PCOS has yet been evaluated.

OBJECTIVES

The aim of this study is to evaluate the expression level of IL-15 in both patients with PCOS and PCOS mice model and investigate the functional effect of IL-15 on ovarian granulosa cells.

METHODS

The level of IL-15 in follicular fluid (FF) was measured using cytokine array and enzyme linked immunosorbent assay (ELISA) in two cohorts from 23 PCOS patients and 18 normo-ovulatory controls. PCOS mice model was induced by subcutaneously implanted with letrozole pellet for 21 days. The expression level of IL-15 in serum, ovarian, and subcutaneous adipose tissue in PCOS mice model was measured by ELISA, real-time polymerase chain reaction (RT-PCR), immunohistochemistry (IHC), and immunofluorescence. The effect of IL-15 on the proliferation and apoptosis of the KGN cells and mouse ovarian granulosa cells (GCs) were detected by CCK-8 assay and flow cytometry, respectively. Transcript expression of 17α-hydroxylase17,20-lyase (CYP17A1), cytochrome P450 family 19 subfamily A member 1(CYP19A1), FSH receptor (FSHR), steroidogenic acute regulatory protein (StAR), and proinflammatory cytokine were quantified using RT-PCR. The protein level and phosphorylation level of p38 MAPK and JNK are detected by Western blot. Concentration of dehydroepiandrosterone sulfate (DHEAS) and progesterone (P)were measured by ELISA.

RESULTS

IL-15 expression in follicular fluid of patients with PCOS was significantly elevated compared with the control group, and similar results were observed in the ovarian and subcutaneous adipose tissue of PCOS mice models. Furthermore, the elevated FF IL-15 levels have a positive correlation with the serum testosterone levels. FSHR co-localized with IL-15 indicating that IL-15 production originate from ovarian granulose cells. IL-15 treatment inhibited proliferation and promoted apoptosis of KGN cells and mouse GCs. Moreover, IL-15 upregulated the transcription levels of CYP17A1, IL-1b and Ifng KGN cells. Similar results were observed in mouse GCs except concentration of DHEAS was higher in IL-15 treatment. IL-15 promoted p38 MAPK and JNK phosphorylation in KGN cells, treating KGN cells with p38 MAPK inhibitor SP600125 and JNK inhibitor SB203580 could reverse the effect of IL-15 on the proliferation and function of KGN cells.

CONCLUSION

The results indicate that IL-15 is involved in the pathogenesis of PCOS potentially by affecting survival, the inflammation state and steroidogenesis of granulosa cells. The practical significance of this association between IL-15 and the pathogenesis of PCOS needs further investigation.

Innate-Immunity Genes in Obesity

The main functions of adipose tissue are thought to be storage and mobilization of the body’s energy reserves, active and passive thermoregulation, participation in the spatial organization of internal organs, protection of the body from lipotoxicity, and ectopic lipid deposition. After the discovery of adipokines, the endocrine function was added to the above list, and after the identification of crosstalk between adipocytes and immune cells, an immune function was suggested. Nonetheless, it turned out that the mechanisms underlying mutual regulatory relations of adipocytes, preadipocytes, immune cells, and their microenvironment are complex and redundant at many levels. One possible way to elucidate the picture of adipose-tissue regulation is to determine genetic variants correlating with obesity. In this review, we examine various aspects of adipose-tissue involvement in innate immune responses as well as variants of immune-response genes associated with obesity.

Sexual Dimorphism in Changes That Occur in Tissues, Organs and Plasma during the Early Stages of Obesity Development

Simple Summary

Obesity is a global health concern with numerous associated comorbidities. This study aims to provide a qualitative assessment of changes that may occur in tissues, organs, and plasma during the early stages of obesity development and how it may differ between male and female using a mouse model of diet induced obesity. Notable changes, not previously reported, were observed in the lungs, liver, kidney, spleen, and heart, which may suggest early signs of developing an obesity associated comorbidity. Leptin levels with notable sexual dimorphisms changes significantly in early obesity and was observed to also correlate with insulin levels. Interestingly, males and females showed different inflammatory cytokine profiles with females exhibiting a more anti-inflammatory cytokine profile, notably the IL-6/IL-10 axis of cytokine regulation may account for their significantly lower weight gain compared to males. Thus, this study provides valuable information which may aid in understanding the development of some obesity associated diseases at the early stages and could assist in developing effective intervention strategies in males and females.

Abstract

Despite obesity being a major health concern, information on the early clinical changes that occur in plasma and tissues during obesity development and the influence of sexual dimorphism is lacking. This study investigated changes in tissue and organ histology, macrophage infiltration, plasma hormones, lipid, and chemokine and cytokine levels in mice fed on a high fat diet for 11-weeks. An increase in adiposity, accompanied by adipocyte hypertrophy and macrophage infiltration, was observed to be significantly greater in males than females. Important changes in cell morphology and histology were noted in the lungs, liver, kidney, spleen, and heart, which may indicate early signs for developing obesity associated comorbidities. Leptin, but not adiponectin, was significantly altered during weight gain. Additionally, leptin, but not adiposity, correlated with insulin levels. Interestingly, GM-CSF, TNFα, and IL-12 (p70) were not produced in the early stages of obesity development. Meanwhile, the production of MCP-1, IP-10, RANTES, IL-10, IL-6, KC, and IL-9 were greatly influenced by sexual dimorphism. Importantly, IL-6/IL-10 axis of anti-inflammatory cytokine regulation was observed only in females and may account for their significantly lower weight gain compared to males. This study provides new knowledge on how sexual dimorphism may influence the development of obesity and associated comorbidities.

Identification of candidate biomarkers and therapeutic agents for heart failure by bioinformatics analysis

INTRODUCTION

Heart failure (HF) is a heterogeneous clinical syndrome and affects millions of people all over the world. HF occurs when the cardiac overload and injury, which is a worldwide complaint. The aim of this study was to screen and verify hub genes involved in developmental HF as well as to explore active drug molecules.

METHODS

The expression profiling by high throughput sequencing of GSE141910 dataset was downloaded from the Gene Expression Omnibus (GEO) database, which contained 366 samples, including 200 heart failure samples and 166 non heart failure samples. The raw data was integrated to find differentially expressed genes (DEGs) and were further analyzed with bioinformatics analysis. Gene ontology (GO) and REACTOME enrichment analyses were performed via ToppGene; protein-protein interaction (PPI) networks of the DEGs was constructed based on data from the HiPPIE interactome database; modules analysis was performed; target gene-miRNA regulatory network and target gene-TF regulatory network were constructed and analyzed; hub genes were validated; molecular docking studies was performed.

RESULTS

A total of 881 DEGs, including 442 up regulated genes and 439 down regulated genes were observed. Most of the DEGs were significantly enriched in biological adhesion, extracellular matrix, signaling receptor binding, secretion, intrinsic component of plasma membrane, signaling receptor activity, extracellular matrix organization and neutrophil degranulation. The top hub genes ESR1, PYHIN1, PPP2R2B, LCK, TP63, PCLAF, CFTR, TK1, ECT2 and FKBP5 were identified from the PPI network. Module analysis revealed that HF was associated with adaptive immune system and neutrophil degranulation. The target genes, miRNAs and TFs were identified from the target gene-miRNA regulatory network and target gene-TF regulatory network. Furthermore, receiver operating characteristic (ROC) curve analysis and RT-PCR analysis revealed that ESR1, PYHIN1, PPP2R2B, LCK, TP63, PCLAF, CFTR, TK1, ECT2 and FKBP5 might serve as prognostic, diagnostic biomarkers and therapeutic target for HF. The predicted targets of these active molecules were then confirmed.

CONCLUSION

The current investigation identified a series of key genes and pathways that might be involved in the progression of HF, providing a new understanding of the underlying molecular mechanisms of HF.

The Role of Exercise, Diet, and Cytokines in Preventing Obesity and Improving Adipose Tissue

The prevalence of obesity continues to rise worldwide despite evidence-based public health recommendations. The promise to adopt a healthy lifestyle is increasingly important for tackling this global epidemic. Calorie restriction or regular exercise or a combination of the two is accepted as an effective strategy in preventing or treating obesity. Furthermore, the benefits conferred by regular exercise to overcome obesity are attributed not only to reduced adiposity or reduced levels of circulating lipids but also to the proteins, peptides, enzymes, and metabolites that are released from contracting skeletal muscle or other organs. The secretion of these molecules called cytokines in response to exercise induces browning of white adipose tissue by increasing the expression of brown adipocyte-specific genes within the white adipose tissue, suggesting that exercise-induced cytokines may play a significant role in preventing obesity. In this review, we present research-based evidence supporting the effects of exercise and various diet interventions on preventing obesity and adipose tissue health. We also discuss the interplay between adipose tissue and the cytokines secreted from skeletal muscle and other organs that are known to affect adipose tissue and metabolism.

Multiple Roles in Neuroprotection for the Exercise Derived Myokine Irisin

Exercise has multiple beneficial effects on health including decreasing the risk of neurodegenerative diseases. Such effects are thought to be mediated (at least in part) by myokines, a collection of cytokines and other small proteins released from skeletal muscles. As an endocrine organ, skeletal muscle synthesizes and secretes a wide range of myokines which contribute to different functions in different organs, including the brain. One such myokine is the recently discovered protein Irisin, which is secreted into circulation from skeletal muscle during exercise from its membrane bound precursor Fibronectin type III domain-containing protein 5 (FNDC5). Irisin contributes to metabolic processes such as glucose homeostasis and browning of white adipose tissue. Irisin also crosses the blood brain barrier and initiates a neuroprotective genetic program in the hippocampus that culminates with increased expression of brain derived neurotrophic factor (BDNF). Furthermore, exercise and FNDC5/Irisin have been shown to have several neuroprotective effects against injuries in ischemia and neurodegenerative disease models, including Alzheimer's disease. In addition, Irisin has anxiolytic and antidepressant effects. In this review we present and summarize recent findings on the multiple effects of Irisin on neural function, including signaling pathways and mechanisms involved. We also discuss how exercise can positively influence brain function and mental health via the "skeletal muscle-brain axis." While there are still many unanswered questions, we put forward the idea that Irisin is a potentially essential mediator of the skeletal muscle-brain crosstalk.

Sex dimorphism in inflammatory response to obesity in childhood

BACKGROUND

Childhood overweight and obesity are a global concern, with prevalence rising dramatically over the last decades. The condition is caused by an increase in energy intake and reduction of physical activity, leading to excessive fat accumulation, followed by systemic chronic inflammation and altered function of immune cell responses. This study aimed at providing new insights regarding sex-specificity on the inflammatory response to obesity in the young patient.

DESIGN

Forty-three Brazilian obese adolescents (Female = 22 and Male=21, BMI (body mass index) Z-score average = 2.78 ± 0.51) and forty-nine eutrophic adolescents (Female = 24 and Male = 25, BMI Z-score average = -0.35 ± 0.88) were enrolled in the study. Anthropometrical analyses and blood cell counts were carried out. Using Luminex®xMAP™ technology, circulating serum cytokines, chemokines, and inflammatory biomarkers were analyzed. Two-way ANOVA test, Tukey's test, and Spearman's correlation coefficient were employed, with a significance threshold set at p < 0.05.

RESULTS

We identified increased levels of serum amyloid A (SAA), platelets, and leukocytes solely in male obese patients. We found a noteworthy sex-dependent pattern in regard to inflammatory response: obese boys showed higher TNFβ, IL15, and IL2 and lower IL10 and IL13, while obese girls showed increased TNFα, CCL3, CCL4, and IP10 content in the circulation. BMI Z-score was significantly linearly correlated with neutrophils, leukocytes, platelets, SAA, TNFα, CCL3, CCL4, IP10, and IL13 levels within the entire cohort (non-sex-dependent).

CONCLUSIONS

Our data support a complex relationship between adiposity, blood cell count, and circulating inflammatory cytokine content. High SAA levels suggest that this factor may play a critical role in local and systemic inflammation. In the eutrophic group, females presented a lower status of inflammation, as compared to males. Both obese boys and girls showed an increased inflammatory response in relation to eutrophic counterparts. Taken together, results point out to clear sex dimorphism in the inflammatory profile of obese adolescents.

Effects of short-term physical training on the interleukin-15 signalling pathway and glucose tolerance in aged rats

PURPOSE

Interleukin-15 (IL-15) is a myokine that has been proposed to modulate skeletal muscle and adipose tissue mass, as well as insulin sensitivity. However, the evidence suggesting a role for IL-15 in improving whole-body insulin sensitivity and decreasing adiposity comes mainly from studies using supraphysiological levels of this cytokine. This study examined the effect of a short-term exercise training protocol on the protein content of IL-15, it's signaling pathway, and glucose tolerance in aged rats.

METHODS

Fourteen Wistar rats were divided into Young Sedentary (Young, n = 4); Old Sedentary (Old, n = 5); Old Exercise (Old.Exe, n = 5) groups. The animals from the exercised group were submitted to a short-term physical exercise protocol for five days. At the end of physical training and after 16 h of the last exercise session, the animals were euthanized, and tissue collection was done.

RESULTS

Physical exercise decreased epididymal and mesenteric fat mass and promoted positive effects on glucose tolerance and insulin sensitivity. Muscle IL-15 protein levels were not changed following the short-term physical exercise training with no alterations in the post-exercise IL-15-JAK/STAT signaling pathway. We found a tendency to increased HIF1α and a significant increase in its regulator, PHD2, in the skeletal muscle after exercise.

CONCLUSION

The elderly rats submitted to short-term aerobic physical training did not present skeletal muscle alteration in the protein content of the IL-15 and IL-15-JAK/STAT signaling pathway. However, short-term aerobic physical training was able to modulate the expression of HIF1α and its regulator PHD2, suggesting an essential role of these proteins in improving post-exercise glucose tolerance and insulin sensitivity in elderly rats.

Exercise-Induced Myokines can Explain the Importance of Physical Activity in the Elderly: An Overview

Physical activity has been found to aid the maintenance of health in the elderly. Exercise-induced skeletal muscle contractions lead to the production and secretion of many small proteins and proteoglycan peptides called myokines. Thus, studies on myokines are necessary for ensuring the maintenance of skeletal muscle health in the elderly. This review summarizes 13 myokines regulated by physical activity that are affected by aging and aims to understand their potential roles in metabolic diseases. We categorized myokines into two groups based on regulation by aerobic and anaerobic exercise. With aging, the secretion of apelin, β-aminoisobutyric acid (BAIBA), bone morphogenetic protein 7 (BMP-7), decorin, insulin-like growth factor 1 (IGF-1), interleukin-15 (IL-15), irisin, stromal cell-derived factor 1 (SDF-1), sestrin, secreted protein acidic rich in cysteine (SPARC), and vascular endothelial growth factor A (VEGF-A) decreased, while that of IL-6 and myostatin increased. Aerobic exercise upregulates apelin, BAIBA, IL-15, IL-6, irisin, SDF-1, sestrin, SPARC, and VEGF-A expression, while anaerobic exercise upregulates BMP-7, decorin, IGF-1, IL-15, IL-6, irisin, and VEGF-A expression. Myostatin is downregulated by both aerobic and anaerobic exercise. This review provides a rationale for developing exercise programs or interventions that maintain a balance between aerobic and anaerobic exercise in the elderly.

Role of interleukin-15 in cardiovascular diseases

Interleukin (IL)‐15 is a recently identified cytokine, which belongs to the interleukin‐2(IL‐2) family, and plays an important role in innate and adaptive immunoreaction. Given the fact that the structure of IL‐15 is partially similar to IL‐2, they share some common biological effects, including immunoregulation. IL‐2 was proven to protect cardiac function in mouse myocardial infarction models. Cardiovascular diseases (CVDs) dominate the cause of mortality worldwide. Besides atherosclerosis, inflammation is also widely involved in the pathogenesis of many CVDs including hypertension, heart failure (HF) and aneurysm. IL‐15, as a pro‐inflammatory cytokine, is up‐regulated in some cardiovascular diseases, such as myocardial infarction and atherosclerosis. The current understanding of IL‐15, including its signal pathway and cellular function, was described. Furthermore, IL‐15 has a protective effect in myocardial infarction and myocarditis by decreasing cardiomyocyte death and improving heart function. The inhibited effect of IL‐15 in ductus arteriosus (DA) should be focused on. IL‐15 promoted atherogenesis. IL‐15 may be a good target in treatment of cardiovascular diabetology. Finally, future research direction of IL‐15 deserves attention. Since IL‐15 plays several roles in CVDs, understanding the role of the IL‐15/IL‐15R system may provide a scientific basis for the development of new approaches that use IL‐15 for the treatment of CVDs.

Serum interleukin 15 in anorexia nervosa: Comparison to normal weight and obese girls

Background: Interleukin 15 (IL-15) plays a key role in the muscle-fat interaction, reducing adipose tissue mass without changes in the lean body mass and reduction of food intake. Here we assess serum IL-15 levels in girls with anorexia nervosa (AN) relative to obese and normal weight female adolescents.Methods: Serum IL-15 concentrations were evaluated using a commercially available ELISA kit in 32 Polish girls with restrictive AN, 29 girls with obesity (O), and 21 healthy controls (C). Anthropometric measurements (weight, height, BMI) and laboratory assays (serum fasting glucose, insulin, HOMA-IR, total cholesterol, HDL, LDL, triglycerides, and C-reactive protein (CRP)) were performed.Results: Mean serum IL-15 in the AN group was significantly higher than in C, but lower than in O. In all examined girls, significant positive correlations between IL-15 and body weight, BMI, insulin, HOMA, LDL, triglycerides and CRP were noted. We also observed an inverse relationship between IL-15 and HDL.Conclusions: Our study demonstrated that serum IL-15 concentrations in adolescent girls with AN and obesity are significantly elevated in comparison to normal weight controls. However, the role of IL-15 in the pathogenesis of AN and obesity remains still unclear.

Skeletal muscle: A review of molecular structure and function, in health and disease

Decades of research in skeletal muscle physiology have provided multiscale insights into the structural and functional complexity of this important anatomical tissue, designed to accomplish the task of generating contraction, force and movement. Skeletal muscle can be viewed as a biomechanical device with various interacting components including the autonomic nerves for impulse transmission, vasculature for efficient oxygenation, and embedded regulatory and metabolic machinery for maintaining cellular homeostasis. The "omics" revolution has propelled a new era in muscle research, allowing us to discern minute details of molecular cross-talk required for effective coordination between the myriad interacting components for efficient muscle function. The objective of this review is to provide a systems-level, comprehensive mapping the molecular mechanisms underlying skeletal muscle structure and function, in health and disease. We begin this review with a focus on molecular mechanisms underlying muscle tissue development (myogenesis), with an emphasis on satellite cells and muscle regeneration. We next review the molecular structure and mechanisms underlying the many structural components of the muscle: neuromuscular junction, sarcomere, cytoskeleton, extracellular matrix, and vasculature surrounding muscle. We highlight aberrant molecular mechanisms and their possible clinical or pathophysiological relevance. We particularly emphasize the impact of environmental stressors (inflammation and oxidative stress) in contributing to muscle pathophysiology including atrophy, hypertrophy, and fibrosis. This article is categorized under: Physiology > Mammalian Physiology in Health and Disease Developmental Biology > Developmental Processes in Health and Disease Models of Systems Properties and Processes > Cellular Models.

Novel Associations Between Interleukin-15 Polymorphisms and Post-training Changes of Body Composition Parameters in Young Nonobese Women

Based on the important role of interleukin-15 (IL-15) in human metabolism and, in consequence, in body composition modulation, we examined whether rs1589241 and rs1057972 polymorphisms, analyzed individually or in combination, would influence the effects of a training program. Accordingly, we studied the allele and genotype distribution in a group of 163 young nonobese Caucasian women measured for selected body mass and composition, as well as biochemical parameters before and after the completion of a 12-week endurance training program. After a week-long familiarization stage, low-high impact aerobics were conducted three times a week for 60 min, at an increasing intensity from about 50 to 80% of HRmax. With reference to rs1057972 genotypes, there were two significant genotype × training interactions, in which (i) fat mass percentage (FM%) significantly decreased among the AA homozygotes (p = 0.00002) and AT heterozygotes (p = 0.00002), and (ii) fat free mass (FFM) increased only among the AT heterozygotes (p = 0.0003), whereas in the AA homozygotes there was only a borderline significance (p = 0.065). No genotype × training interactions were found for the second rs1589241 polymorphism. Moreover, the carriers of the[T;A] haplotype (when compared with reference haplotype) displayed significant decrease in FM% (p = 0.027) and increase in FFM (p = 0.014) in response to the applied training program. Our data highlight novel associations between specific IL-15 genotype and different post-training changes of FM% and FFM parameters. The results suggest that harboring the rs1057972 A allele and/or the [T;A] haplotype is favorable for achieving specific positive training-induced body composition changes.

Interleukin-15 as a myokine: mechanistic insight into its effect on skeletal muscle metabolism

Interleukin (IL)-15 is a cytokine with important immunological functions. It is highly expressed in skeletal muscle and is believed to be a myokine, a hypothesis supported by the rapid increase in circulating levels of IL-15 in response to exercise. Treatment with high doses of IL-15 results in metabolic adaptations such as improved insulin sensitivity and whole-body fatty acid oxidation and protection from high-fat-diet-induced obesity and insulin resistance. IL-15 secreted by contracting muscle may therefore act as an endocrine factor to improve adiposity and energy metabolism in different tissues. Most studies have used supraphysiological doses of IL-15 that do not represent circulating IL-15 in response to exercise. However, evidence shows that IL-15 levels are higher in muscle interstitium and that IL-15 might improve muscle glucose homeostasis and oxidative metabolism in an autocrine/paracrine manner. Nevertheless, how IL-15 signals in skeletal muscle to improve muscle energy metabolism is not understood completely, especially because the absence of the α subunit of the IL-15 receptor (IL-15Rα) results in a phenotype similar to that of overexpressing/oversecreting IL-15 in mice. In this article, we review the literature to propose a model for the regulation of IL-15 by the soluble form of IL-15Rα to explain why some findings in the literature seem, at first glance, to be contradictory.

Inflammation in human adipose tissues-Shades of gray, rather than white and brown

Chronic inflammation in adipose tissues has been associated with obesity and metabolic syndrome over the years. Various studies using animal models have contributed to our knowledge on the pro- and anti- inflammatory mediators that regulate obesity. Analyses of cytokine profiles in humans have not revealed a clear scenario. Likewise, treatments targeting inflammation to control obesity and insulin resistance has not yielded promising results. In this review we summarize the data available in human obesity and discuss the possible reasons that could explain the difficulties in treating obesity and insulin resistance by targeting pro-inflammatory cytokines.

Serum Interleukin-15 and its relationship with adiposity Indices before and after short-term endurance exercise

Objective

The myokine interleukin-15 (IL-15) is capable of modifying the metabolism of both skeletal and adipose tissue. This study compares the change in serum levels of IL-15 in obese and non-obese after a single session of submaximal exercise.

Methods

A cross-sectional study was carried out at Jinnah Medical and Dental College, Karachi, during Aug-Dec 2015, comprising of 133 medical students (aged 17-24 years). Cardiorespiratory fitness was evaluated by Queen's College Step Test. Blood was obtained both before and just after exercise and serum levels of IL-15 determined by enzyme-linked immunosorbent assay.

Results

Mean serum level of IL-15 was 3.64±1.59 pg/mL. Higher levels of IL-15 were seen in lean subjects compared to overweight/obese, both before and after three minutes of exercise (all P_trend<.001). The percent increase in IL-15 upon exercise was 12.7% higher in lean. Significant negative association was seen between interleukin-15 and adiposity, especially visceral fat (r = -.288, p=.001).

Conclusion

Interleukin-15 correlates negatively with adiposity indices, especially visceral fat. With the proven benefit of IL-15 in terms of adipose tissue stores and skeletal muscle mitochondrial biogenesis, endurance exercises, even of short duration, may possess therapeutic potential towards producing a healthier body.

Regulation of Energy Expenditure and Brown/Beige Thermogenic Activity by Interleukins: New Roles for Old Actors

Obesity rates and the burden of metabolic associated diseases are escalating worldwide Energy burning brown and inducible beige adipocytes in human adipose tissues (ATs) have attracted considerable attention due to their therapeutic potential to counteract the deleterious metabolic effects of nutritional overload and overweight. Recent research has highlighted the relevance of resident and recruited ATs immune cell populations and their signalling mediators, cytokines, as modulators of the thermogenic activity of brown and beige ATs. In this review, we first provide an overview of the developmental, cellular and functional heterogeneity of the AT organ, as well as reported molecular switches of its heat-producing machinery. We also discuss the key contribution of various interleukins signalling pathways to energy and metabolic homeostasis and their roles in the biogenesis and function of brown and beige adipocytes. Besides local actions, attention is also drawn to their influence in the central nervous system (CNS) networks governing energy expenditure.

Human Body Composition and Immunity: Visceral Adipose Tissue Produces IL-15 and Muscle Strength Inversely Correlates with NK Cell Function in Elderly Humans

Natural killer (NK) lymphocyte-mediated cytotoxicity and cytokine secretion control infections and cancers, but these crucial activities decline with age. NK cell development, homeostasis, and function require IL-15 and its chaperone, IL-15 receptor alpha (IL-15Rα). Macrophages and dendritic cells (DC) are major sources of these proteins. We had previously postulated that additional IL-15 and IL-15Rα is made by skeletal muscle and adipose tissue. These sources may be important in aging, when IL-15-producing immune cells decline. NK cells circulate through adipose tissue, where they may be exposed to local IL-15. The objectives of this work were to determine (1) if human muscle, subcutaneous adipose tissue (SAT), and visceral adipose tissue (VAT) are sources of IL-15 and IL-15 Rα, and (2) whether any of these tissues correlate with NK cell activity in elderly humans. We first investigated IL-15 and IL-15Rα RNA expression in paired muscle and SAT biopsies from healthy human subjects. Both tissues expressed these transcripts, but IL-15Rα RNA levels were higher in SAT than in skeletal muscle. We also investigated tissue obtained from surgeries and found that SAT and VAT expressed equivalent amounts of IL-15 and IL-15Rα RNA, respectively. Furthermore, stromal vascular fraction cells expressed more IL-15 RNA than did adipocytes. To test if these findings related to circulating IL-15 protein and NK cell function, we tested 50 healthy adults aged > 70 years old. Plasma IL-15 levels significantly correlated with abdominal VAT mass in the entire cohort and in non-obese subjects. However, plasma IL-15 levels did not correlate with skeletal muscle cross-sectional area and correlated inversely with muscle strength. Plasma IL-15 did correlate with NK cell cytotoxic granule exocytosis and with CCL4 (MIP-1β) production in response to NKp46-crosslinking. Additionally, NK cell responses to K562 leukemia cells correlated inversely with muscle strength. With aging, immune function declines while infections, cancers, and deaths increase. We propose that VAT-derived IL-15 and IL-15Rα is a compensatory NK cell support mechanism in elderly humans.

Interleukin-15 derived from Guanylin-GC-C-expressing macrophages inhibits fatty acid synthase in adipocytes

Recently we found that guanylin (Gn) and its receptor, guanylyl cyclase C (GC-C), are uniquely expressed in the mesenteric macrophages of some diet-resistant rats and that double-transgenic (dTg) rats overexpressing Gn and GC-C in macrophages demonstrate reduced fatty acid synthase and fat accumulation in fat tissue even when fed a high-fat diet (HFD). Lipid accumulation and fatty acid synthase mRNA levels in cocultured dTg rat adipocytes and macrophages were reduced compared with those in adipocytes cultured with WT rat macrophages. Here, we investigated whether Interleukin-15 (IL-15) derived from Gn-GC-C-expressing macrophages regulates lipid accumulation in adipocytes. IL-15 inhibited fatty acid synthase and lipid accumulation via STAT5 in cultured adipocytes. IL-15 mRNA and protein levels in the mesenteric fat of HFD-fed dTg rats were significantly higher than those of HFD-fed WT rats. Phosphorylated STAT5 levels in the mesenteric fat of HFD-fed dTg rats were increased compared with those of HFD-fed WT rats. In addition, the mRNA level of fatty acid synthase in the mesenteric fat was lower in HFD-fed dTg rats than in HFD-fed WT rats. These results support the hypothesis that IL-15 secreted from Gn-GC-C-expressing macrophages contributes to the inhibition of fatty acid synthase and lipid accumulation in adipocytes, leading to obesity resistance.

Systemic effects of a high saturated fat diet in grizzly bears (Ursus arctos horribilis)

Food sources for North America’s grizzly bear (Ursus arctos horribilis Ord, 1815) population have changed as habitats have fragmented, altering available resources and putting bears in contact with unnatural foods. Bears have evolved mechanisms to tolerate obesity, and do not develop adverse health consequences despite storing massive amounts of body fat. Captive adult grizzly bears were used to determine the effects of dietary fat on health. Group 1 was fed a diet high in polyunsaturated fatty acids (PUFA) wherein 9.5% of available calories came from saturated fatty acids (SFA). Group 2 was fed a diet wherein 28.8% of calories came from SFA. Plasma fatty acids, serum lipid profiles, insulin, inflammatory markers, systolic and diastolic blood pressure, and cardiac function parameters were measured. Serum lipids, SFA, and insulin did not differ between the two groups, although omega-3 fatty acids differed. Bears eating the SFA diet had significantly higher circulating adiponectin, interleukin-7 and interleukin-15, and tumor necrosis factor-alpha. Mild, asymptomatic systolic and diastolic dysfunctions were detected by strain echocardiography in the SFA group. The SFA diet group exhibited higher diastolic arterial pressures. Even though mild metabolic derangements were observed, grizzly bears were remarkably resistant to metabolic effects of diets high in SFA.

Interleukin-15 in obesity and metabolic dysfunction: current understanding and future perspectives

Obesity rises rapidly and is a major health concern for modern people. Importantly, it is a major risk factor in the development of numerous chronic diseases such as type 2 diabetes mellitus (T2DM). Recently, interleukin (IL)-15 has attracted considerable attention as a potential regulator for the prevention and/or treatment of obesity and T2DM. The beneficial effects include increased loss of fat mass and body weight, improved lipid and glucose metabolism, reduced white adipose tissue inflammation, enhanced mitochondrial function, alterations in the composition of muscle fibres and gut bacterial and attenuated endoplasmic reticulum stress. Although these beneficial effects are somewhat controversial, IL-15, exogenously delivered or endogenously produced, may be a promising target in the prevention and treatment of obesity and T2DM.

IL-15 Activates the Jak3/STAT3 Signaling Pathway to Mediate Glucose Uptake in Skeletal Muscle Cells

Myokines are specialized cytokines that are secreted from skeletal muscle (SKM) in response to metabolic stimuli, such as exercise. Interleukin-15 (IL-15) is a myokine with potential to reduce obesity and increase lean mass through induction of metabolic processes. It has been previously shown that IL-15 acts to increase glucose uptake in SKM cells. However, the downstream signals orchestrating the link between IL-15 signaling and glucose uptake have not been fully explored. Here we employed the mouse SKM C2C12 cell line to examine potential downstream targets of IL-15-induced alterations in glucose uptake. Following differentiation, C2C12 cells were treated overnight with 100 ng/ml of IL-15. Activation of factors associated with glucose metabolism (Akt and AMPK) and known downstream targets of IL-15 (Jak1, Jak3, STAT3, and STAT5) were assessed with IL-15 stimulation. IL-15 stimulated glucose uptake and GLUT4 translocation to the plasma membrane. IL-15 treatment had no effect on phospho-Akt, phospho-Akt substrates, phospho-AMPK, phospho-Jak1, or phospho-STAT5. However, with IL-15, phospho-Jak3 and phospho-STAT3 levels were increased along with increased interaction of Jak3 and STAT3. Additionally, IL-15 induced a translocation of phospho-STAT3 from the cytoplasm to the nucleus. We have evidence that a mediator of glucose uptake, HIF1α, expression was dependent on IL-15 induced STAT3 activation. Finally, upon inhibition of STAT3 the positive effects of IL-15 on glucose uptake and GLUT4 translocation were abolished. Taken together, we provide evidence for a novel signaling pathway for IL-15 acting through Jak3/STAT3 to regulate glucose metabolism.

IL-15 Mediates Mitochondrial Activity through a PPARδ-Dependent-PPARα-Independent Mechanism in Skeletal Muscle Cells

Molecular mediators of metabolic processes, to increase energy expenditure, have become a focus for therapies of obesity. The discovery of cytokines secreted from the skeletal muscle (SKM), termed "myokines," has garnered attention due to their positive effects on metabolic processes. Interleukin-15 (IL-15) is a myokine that has numerous positive metabolic effects and is linked to the PPAR family of mitochondrial regulators. Here, we aimed to determine the importance of PPARα and/or PPARδ as targets of IL-15 signaling. C2C12 SKM cells were differentiated for 6 days and treated every other day with IL-15 (100 ng/mL), a PPARα inhibitor (GW-6471), a PPARδ inhibitor (GSK-3787), or both IL-15 and the inhibitors. IL-15 increased mitochondrial activity and induced PPARα, PPARδ, PGC1α, PGC1β, UCP2, and Nrf1 expression. There was no effect of inhibiting PPARα, in combination with IL-15, on the aforementioned mRNA levels except for PGC1β and Nrf1. However, with PPARδ inhibition, IL-15 failed to induce the expression levels of PGC1α, PGC1β, UCP2, and Nrf1. Further, inhibition of PPARδ abolished IL-15 induced increases in citrate synthase activity, ATP production, and overall mitochondrial activity. IL-15 had no effects on mitochondrial biogenesis. Our data indicates that PPARδ activity is required for the beneficial metabolic effects of IL-15 signaling in SKM.

Exercise attenuates the major hallmarks of aging

Regular exercise has multi-system anti-aging effects. Here we summarize how exercise impacts the major hallmarks of aging. We propose that, besides searching for novel pharmaceutical targets of the aging process, more research efforts should be devoted to gaining insights into the molecular mediators of the benefits of exercise and to implement effective exercise interventions for elderly people.

IL-15/sIL-15Rα gene transfer induces weight loss and improves glucose homeostasis in obese mice

Obesity and its associated metabolic problems are a major public health issue. The objective of the current study is to investigate the therapeutic effects of interleukin 15/soluble interleukin 15 receptor-α (IL-15/sIL-15Rα) on high-fat diet-induced obesity and obesity-associated metabolic disorders. We demonstrate that the multiple hydrodynamic delivery of 2 μg IL-15/sIL-15Rα plasmid results in numerous beneficial effects, including a reduction of body weight and fat mass, an alleviation of fatty liver, an improvement in glucose homeostasis and insulin sensitivity in obese mice. These effects are accompanied by a suppressed expression of genes involved in lipid accumulation and lipogenesis, including Pparγ, Cd36, Fabp4, Mgat1, Scd-1 and Fas, and elevated mRNA levels of genes involved in adaptive thermogenesis and fatty acid β-oxidation, such as Ucp1, Ucp3, Pgc-1α, Pgc-1β, Pparα, Pparδ, Cpt1-α and Cpt1-β in obese animals. These results suggest that the overexpression of the Il-15/sIl-15Rα gene is an effective approach in treating diet-induced obesity and its associated metabolic complications.

Interleukins 6 and 15 Levels Are Higher in Subcutaneous Adipose Tissue, but Obesity Is Associated with Their Increased Content in Visceral Fat Depots

Excess adiposity is associated with chronic inflammation, which takes part in the development of obesity-related complications. The aim of this study was to establish whether subcutaneous (SAT) or visceral (VAT) adipose tissue plays a major role in synthesis of pro-inflammatory cytokines. Concentrations of interleukins (IL): 1β, 6, 8 and 15 were measured at the protein level by an ELISA-based method and on the mRNA level by real-time PCR in VAT and SAT samples obtained from 49 obese (BMI > 40 kg/m²) and 16 normal-weight (BMI 20–24.9 kg/m²) controls. IL-6 and IL-15 protein concentrations were higher in SAT than in VAT for both obese (p = 0.003 and p < 0.0001, respectively) and control individuals (p = 0.004 and p = 0.001, respectively), while for IL-1β this was observed only in obese subjects (p = 0.047). What characterized obese individuals was the higher expression of IL-6 and IL-15 at the protein level in VAT compared to normal-weight controls (p = 0.047 and p = 0.016, respectively). Additionally, obese individuals with metabolic syndrome had higher IL-1β levels in VAT than did obese individuals without this syndrome (p = 0.003). In conclusion, concentrations of some pro-inflammatory cytokines were higher in SAT than in VAT, but it was the increased pro-inflammatory activity of VAT that was associated with obesity and metabolic syndrome.

Beneficial metabolic activities of inflammatory cytokine interleukin 15 in obesity and type 2 diabetes

In obesity, chronic inflammation is believed to induce insulin resistance and impairs adipose tissue function. Although this view is supported by a large body of literature, it has been challenged by growing evidence that pro-inflammatory cytokines may favor insulin sensitivity through induction of energy expenditure. In this review article, interleukin 15 (IL-15) is used as a new example to explain the beneficial effects of the proinflammatory cytokines. IL-15 is secreted by multiple types of cells including macrophages, neutrophils and skeletal muscle cells. IL-15 expression is induced in immune cells by endotoxin and in muscle cells by physical exercise. Its transcription is induced by transcription factor NF-κB. IL-15 binds to its receptor that contains three different subunits (α, β and γ) to activate JAK/STAT, PI3K/Akt, IKK/NF-κB and JNK/AP1 pathways in cells. In the regulation of metabolism, IL-15 reduces weight gain without inhibiting food intake in rodents. IL-15 suppresses lipogenesis, stimulates brown fat function, improves insulin sensitivity through weight loss and energy expenditure. In human, circulating IL-15 is negatively associated with body weight. In the immune system, IL-15 stimulates proliferation and differentiation of T cells, NK cells, monocytes and neutrophils. In the anti-obesity effects of IL-15, T cells and NK cells are not required, but leptin receptor is required. In summary, evidence from human and rodents supports that the pro-inflammatory cytokine IL-15 may enhance energy expenditure to protect the body from obesity and type 2 diabetes. The mechanism of IL-15 action remains to be fully uncovered in the regulation of energy expenditure.

Adipocyte IL-15 regulates local and systemic NK cell development

NK cell development and homeostasis require IL-15 produced by both hematopoietic and parenchymal cells. Certain hematopoietic IL-15 sources, such as macrophages and dendritic cells, are known, whereas the source of parenchymal IL-15 remains elusive. Using two types of adipocyte-specific Il15(-/-) mice, we identified adipocytes as a parenchymal IL-15 source that supported NK cell development nonredundantly. Both adipocyte-specific Il15(-/-) mice showed reduced IL-15 production specifically in the adipose tissue but impaired NK cell development in the spleen and liver in addition to the adipose tissue. We also found that the adipose tissue harbored NK progenitors as other niches (e.g. spleen) for NK cell development, and that NK cells derived from transplanted adipose tissue populated the recipient's spleen and liver. These findings suggest that adipocyte IL-15 contributes to systemic NK cell development by supporting NK cell development in the adipose tissue, which serves as a source of NK cells for other organs.

Exercise is the real polypill

The concept of a "polypill" is receiving growing attention to prevent cardiovascular disease. Yet similar if not overall higher benefits are achievable with regular exercise, a drug-free intervention for which our genome has been haped over evolution. Compared with drugs, exercise is available at low cost and relatively free of adverse effects. We summarize epidemiological evidence on the preventive/therapeutic benefits of exercise and on the main biological mediators involved.

Association of the interleukin 15 (IL-15) gene polymorphisms with the risk of developing ulcerative colitis in Mexican individuals

Interleukin 15 (IL-15) is a Th1-related cytokine that triggers inflammatory cell recruitment with implications for pathogenesis in ulcerative colitis. The IL-15 gene is located within a 35 kb region of the q28-31 locus of chromosome 4. In the present work, the role of IL-15 gene polymorphisms as susceptibility markers for UC was evaluated. Seven polymorphisms of IL-15 (rs3806798, rs10833, rs4956403, rs2254514, rs2857261, rs10519613, and rs1057972) were genotyped by 5' exonuclease TaqMan genotyping assays in a group of 199 Mexican patients with UC and 698 Mexican Mestizo healthy unrelated individuals. UC patients and healthy controls showed similar distribution of the rs3806798, rs10833, rs4956403, rs2857261, rs10519613, and rs1057972 polymorphisms. The rs2254514 polymorphism was significantly associated with decreased risk of UC as compared to controls under both dominant and additive models (OR 0.62, Pdom = 0.014 and OR 0.65, Padd = 0.02). The rs2254514 CC genotype was associated with young age at diagnosis <40 years (P = 0.03; OR 3.67). Five polymorphisms (rs1051613, rs2254514, rs2857261, rs1057972, and rs10833) were in strong linkage disequilibrium and were included in six haplotypes: H1 (ACAAC), H2 (CCGTC), H3 (CTAAT), H4 (CCAAT), H5 (CTAAC), and H6 (CCAAC). UC patients showed an increased frequency of the H6 haplotype (P = 0.005; OR 3.2) and a decreased frequency of the H5 haplotype (P = 0.031; OR 0.40). These results suggest that the IL-15 rs2254514 polymorphism might have an important role in the development of UC in the Mexican population. We were able to distinguish one risk and one protective uncommon haplotype for the development of UC.

IL-15 is required for postexercise induction of the pro-oxidative mediators PPARδ and SIRT1 in male mice

Physical exercise induces transient upregulation of the pro-oxidative mediators peroxisome proliferator-activated receptor-δ (PPARδ), silent information regulator of transcription (sirtuin)-1 (SIRT1), PPARγ coactivator 1α (PGC-1α), and PGC-1β in skeletal muscle. To determine the role of the cytokine IL-15 in acute postexercise induction of these molecules, expression of these factors after a bout of exhaustive treadmill running was examined in the gastrocnemius muscle of untrained control and IL-15-knockout (KO) mice. Circulating IL-15 levels increased transiently in control mice after exercise. Control mice, but not IL-15-KO mice, upregulated muscle PPARδ and SIRT1 protein after exercise, accompanied by a complex pattern of mRNA expression for these factors. However, in exhaustive exercise, control mice ran significantly longer than IL-15-KO mice. Therefore, in a second experiment, mice were limited to a 20-minute run, after which a similar pattern of induction of muscle PPARδ and SIRT1 protein by control mice only was observed. In a separate experiment, IL-15-KO mice injected systemically with recombinant IL-15 upregulated muscle PPARδ and SIRT1 mRNA within 30 minutes and also exhibited increased muscle PPARδ protein levels by 3 hours. After exercise, both control and IL-15-KO mice downregulated IL-15 receptor-α (IL-15Rα) mRNA, whereas IL-15Rα-deficient mice exhibited constitutively elevated circulating IL-15 levels. These observations indicate IL-15 release after exercise is necessary for induction of PPARδ and SIRT1 at the protein level in muscle tissue and suggest that exercise releases IL-15 normally sequestered by the IL-15Rα in the resting state. These findings could be used to develop an IL-15-based strategy to induce many of the metabolic benefits of physical exercise.

Effect of treadmill exercise on interleukin-15 expression and glucose tolerance in zucker diabetic Fatty rats

BACKGROUND

Interleukin-15 (IL-15), a well-known myokine, is highly expressed in skeletal muscle and is involved in muscle-fat crosstalk. Recently, a role of skeletal muscle-derived IL-15 in the improvement of glucose homeostasis and insulin sensitivity has been proposed. However, little is known regarding the influence of endurance training on IL-15 expression in type 2 diabetic skeletal muscles. We investigated the effect of endurance exercise training on glucose tolerance and IL-15 expression in skeletal muscles using type 2 diabetic animal models.

METHODS

MALE ZUCKER DIABETIC FATTY (ZDF) AND ZDF LEAN CONTROL (ZLC) RATS WERE RANDOMLY DIVIDED INTO THREE GROUPS: sedentary ZLC, sedentary ZDF (ZDF-Con), and exercised ZDF (ZDF-Ex). The ZDF-Ex rats were forced to run a motor-driven treadmill for 60 minutes once a day 5 times per week for 12 weeks. Intraperitoneal glucose tolerance test (IPGTT) was performed after 12 weeks. Expression of IL-15 was measured using ELISA in extracted soleus (SOL) and gastrocnemius medial muscles.

RESULTS

After 12 weeks of treadmill training, reduction of body weight was observed in ZDF-Ex compared to ZDF-Con rats. Glucose tolerance using IPGTT in diabetic rats was significantly improved in ZDF-Ex rats. Furthermore, the expression of IL-15 was significantly increased (P<0.01) only in the SOL of ZDF-Ex rats compared to ZDF-Con. Additionally, IL-15 expression in SOL muscles was negatively correlated with change of body weight (R=-0.424, P=0.04).

CONCLUSION

The present study results suggest that 12 weeks of progressive endurance training significantly improved glucose tolerance with concomitant increase of IL-15 expression in SOL muscles of type 2 diabetic rats.

Treadmill exercise promotes interleukin 15 expression in skeletal muscle and interleukin 15 receptor alpha expression in adipose tissue of high-fat diet rats

Interleukin 15 (IL-15) has recently been proposed as a myokine involved in regulating lipid metabolism. We investigated the effect of exercise training on IL-15 content in skeletal muscle and expression of IL-15 receptor (IL-15R) in adipose tissue of obese rats. After 12 weeks of a high-fat diet, obese rats underwent treadmill running at 26 m/min (60 min each, 5 days/week for 8 weeks). High-fat diet induced obesity, with increased body weight, body fat, and lipid profile. The level of IL-15 immunoreactivity (IL-15-ir) in plasma and gastrocnemius muscle was lower in obese than control rats, and the mRNA level of IL-15 in gastrocnemius muscle was markedly decreased. The mRNA and protein levels of IL-15R in adipose tissue were markedly lower in obese rats. Compared with sedentary obese rats, treadmill running showed decreased body weight and elevated mRNA expression of IL-15 in muscle and elevated IL-15-ir level in plasma and muscle. The mRNA and protein level of IL-15R were increased in adipose tissue in treadmill running obese rats. Our results showed that exercise training improve obesity and reversed the downregulation of the IL-15 in muscle and IL-15R in adipose tissue induced by high-fat diet.

IL-15 overexpression promotes endurance, oxidative energy metabolism, and muscle PPARδ, SIRT1, PGC-1α, and PGC-1β expression in male mice

Endurance exercise initiates a pattern of gene expression that promotes fat oxidation, which in turn improves endurance, body composition, and insulin sensitivity. The signals from exercise that initiate these pathways have not been completely characterized. IL-15 is a cytokine that is up-regulated in skeletal muscle after exercise and correlates with leanness and insulin sensitivity. To determine whether IL-15 can induce any of the metabolic adaptations associated with exercise, substrate metabolism, endurance, and molecular expression patterns were examined in male transgenic mice with constitutively elevated muscle and circulating IL-15 levels. IL-15 transgenic mice ran twice as long as littermate control mice in a run-to-exhaustion trial and preferentially used fat for energy metabolism. Fast muscles in IL-15 transgenic mice exhibited high expression of intracellular mediators of oxidative metabolism that are induced by exercise, including sirtuin 1, peroxisome proliferator-activated receptor (PPAR)-δ, PPAR-γ coactivator-1α, and PPAR-γ coactivator-1β. Muscle tissue in IL-15 transgenic mice exhibited myosin heavy chain and troponin I mRNA isoform expression patterns indicative of a more oxidative phenotype than controls. These findings support a role for IL-15 in induction of exercise endurance, oxidative metabolism, and skeletal muscle molecular adaptations induced by physical training.

Polymorphisms of the interleukin-15 gene and their associations with fatness and muscle fiber traits in chickens

Interleukin-15 (IL-15) is a cytokine that has been proposed to modulate skeletal muscle and adipose tissue mass. In the present study, an F(2) resource population of Gushi chickens crossed with Anka broilers was used to investigate the genetic effects of the chicken IL-15 gene. Two single nucleotide polymorphisms (SNPs) (g.31224G>A and g.31266T>G) were identified in exon 5 of the IL-15 gene by means of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and DNA sequencing. Associations between the two SNPs and chicken fatness and muscle fiber traits were determined using linkage disequilibrium, haplotype construction, and association analysis. Both of the SNPs were associated with abdominal fat weight, leg muscle fiber diameter, and leg muscle fiber density (p < 0.05). Haplotypes of the two linked SNPs were associated with abdominal fat weight, fat thickness under the skin, and leg muscle fiber diameter (p < 0.05). The results suggested that the IL-15 gene might be associated with the causative mutation or the quantitative trait locus (QTL) controlling the fatness traits and muscle fiber traits in chickens.

Comparative proteomic profiling of dystroglycan-associated proteins in wild type, mdx, and Galgt2 transgenic mouse skeletal muscle

Dystroglycan is a major cell surface glycoprotein receptor for the extracellular matrix in skeletal muscle. Defects in dystroglycan glycosylation cause muscular dystrophy and alterations in dystroglycan glycosylation can impact extracellular matrix binding. Here we describe an immunoprecipitation technique that allows isolation of beta dystroglycan with members of the dystrophin-associated protein complex (DAPC) from detergent-solubilized skeletal muscle. Immunoprecipitation, coupled with shotgun proteomics, has allowed us to identify new dystroglycan-associated proteins and define changed associations that occur within the DAPC in dystrophic skeletal muscles. In addition, we describe changes that result from overexpression of Galgt2, a normally synaptic muscle glycosyltransferase that can modify alpha dystroglycan and inhibit the development of muscular dystrophy when it is overexpressed. These studies identify new dystroglycan-associated proteins that may participate in dystroglycan's roles, both positive and negative, in muscular dystrophy.