SNPs in FNDC5 (irisin) are associated with obesity and modulation of glucose and lipid metabolism in Saudi subjects

RS3480 Polymorphism of FNDC5/Irisin Is Associated with Type 2 Diabetes Mellitus in Maya-Mestizo Women

Objective: To investigate the possible association between rs3480 and rs16835198 of the fibronectin type III domain containing 5 (FNDC5)/Irisin and their haplotypes with the presence of type 2 diabetes mellitus (T2DM) in Maya-Mestizo women. Methods: We studied 547 postmenopausal women of Maya-Mestizo origin. The diagnosis of T2DM was based on the criteria of the American Diabetes Association. DNA was obtained from blood leukocytes. rs3480 and rs16835198 of FNDC5/Irisin were studied using real-time polymerase chain reaction allelic discrimination. Deviations from Hardy-Weinberg equilibrium and alleles differences, as well as genotype frequencies between groups, were assessed by χ2 tests. Using logistic regression analysis, the odds ratio and 95% confidence intervals were calculated to estimate the association between both polymorphisms of FNDC5/Irisin and the presence of T2DM. Pairwise linkage disequilibrium between polymorphisms was calculated by direct correlation r2, and haplotype analysis was conducted. Results: We found that the G-allele of rs3480, as well as under a dominant model, this polymorphism was significantly associated with T2DM (P = 0.028 and P = 0.003, respectively). Besides, one haplotype was associated with T2DM (P = 0.035). Conclusions: Our results suggest that the FNDC5/Irisin rs3480, and one haplotype formed by rs3480 and rs16835198 were associated with the risk of presenting T2DM in Maya-Mestizo women.

Intermittent vs. continuous swimming training on adipokines and pro-inflammatory cytokines in metabolic syndrome experimental model

OBJECTIVES

In this study, metabolic syndrome-affected rats were studied to examine how intermittent and continuous swimming training influenced adipokines and pro-inflammatory cytokines.

METHODS

Forty-eight male Wistar rats were randomized in this experimental study into four groups (n=8), including normal control (NC), metabolic syndrome (MS), continuous swimming training with metabolic syndrome (CT-MS: load 0-3% body mass, 5 d/wk, for 8 weeks), and intermittent swimming training with metabolic syndrome (IT-MS: load 5-16% body mass, 5 d/wk, for 8 weeks). The serum levels of metrnl, adipolin, irisin, leptin, TNF-α, and IL-6 were measured using the ELISA test.

RESULTS

The IT-MS and NC groups exhibited significantly lower leptin concentrations than the CT-MS group (p=0.001). The irisin, meteorin, and adipolin serum levels increased significantly in CT-MS and IT relative to the NC and CT-MS groups (p=0.001), with the changes being more pronounced in the IT group (p=0.05). TNF-α and IL-6 were inclined in the CT-MS group compared with the other three groups (p=0.001), while IL-6 was increased in the IT group (p=0.024).

CONCLUSIONS

Intermittent swimming is more effective than continuous swimming training in improving adipokines in rats with metabolic syndrome.

Association of the fibronectin type III domain-containing protein 5 rs1746661 single nucleotide polymorphism with reduced brain glucose metabolism in elderly humans

Fibronectin type III domain-containing protein 5 (FNDC5) and its derived hormone, irisin, have been associated with metabolic control in humans, with described FNDC5 single nucleotide polymorphisms being linked to obesity and metabolic syndrome. Decreased brain FNDC5/irisin has been reported in subjects with dementia due to Alzheimer's disease. Since impaired brain glucose metabolism develops in ageing and is prominent in Alzheimer's disease, here, we examined associations of a single nucleotide polymorphism in the FNDC5 gene (rs1746661) with brain glucose metabolism and amyloid-β deposition in a cohort of 240 cognitively unimpaired and 485 cognitively impaired elderly individuals from the Alzheimer's Disease Neuroimaging Initiative. In cognitively unimpaired elderly individuals harbouring the FNDC5 rs1746661(T) allele, we observed a regional reduction in low glucose metabolism in memory-linked brain regions and increased brain amyloid-β PET load. No differences in cognition or levels of cerebrospinal fluid amyloid-β42, phosphorylated tau and total tau were observed between FNDC5 rs1746661(T) allele carriers and non-carriers. Our results indicate that a genetic variant of FNDC5 is associated with low brain glucose metabolism in elderly individuals and suggest that FNDC5 may participate in the regulation of brain metabolism in brain regions vulnerable to Alzheimer's disease pathophysiology. Understanding the associations between genetic variants in metabolism-linked genes and metabolic brain signatures may contribute to elucidating genetic modulators of brain metabolism in humans.

An Association Between FNDC5, PGC-1α Genetic Variants and Obesity in Chinese Children: A Case-Control Study

BACKGROUND

Fibronectin type III domain containing protein 5 (FNDC5) gene encodes irisin that regulates adipose tissue metabolism. Peroxide-proliferator-activated receptor γ coactivator 1α (PGC-1α) is a powerful promoter of mitochondrial biosynthesis and oxidative metabolism, which plays an important role in inducing heat production and energy consumption of brown fat. PGC1-α expression stimulated an increase in expression of FNDC5.

PURPOSE

The aims of this study were to analyze the association between FNDC5, PGC-1α genetic variants and overweight or obesity in Chinese children and adolescents.

METHODS

A total of 198 children and adolescents with overweight or obesity and 198 children and adolescents with normal weight were screened according to gender and age 1:1. The healthy eating behaviors, moderate-to-vigorous physical activity time were surveyed using food frequency questionnaire and CLASS questionnaire, respectively. Genotypes of FNDC5 and PGC-1α gene were detected using SNaPshot method.

RESULTS

GT genotype of FNDC5 (rs16835198) increased the risk of overweight or obesity in boys (OR (95% CI): 1.68 (1.00, 2.93)) based on overdominant model; GG genotype of FNDC5 (rs16835198) decreased the risk of overweight or obesity in girls and boys (OR (95% CI): 0.45 (0.21,0.97), 0.45 (0.24, 0.83), respectively) based on dominant model; TT genotype of FNDC5 (rs16835198) increased the risk of overweight or obesity in girls based on recessive model (OR (95% CI): 2.46 (1.19, 5.05)), and based on the additive model (OR (95% CI): 3.82 (1.49, 9.80)). There was significant interaction between FNDC5 (rs16835198) and PGC-1α (rs3755863, rs8192678), healthy eating behaviors, moderate-to-vigorous physical activity time, interaction between PGC-1α (rs8192678) and moderate-to-vigorous physical activity time in the occurrence of overweight or obesity in Chinese children and adolescents.

CONCLUSION

FNDC5 (rs16835198) played an independent or interactive role with PGC-1α (rs3755863, rs8192678), healthy eating behaviors, moderate-to-vigorous physical activity time in the occurrence of overweight or obesity in Chinese children and adolescents.

FNDC5 Promotes Adipogenic Differentiation of Primary Preadipocytes in Mashen Pigs

Fibronectin type III domain-containing protein 5 (FNDC5) plays an important role in fat deposition, which can be cut to form Irisin to promote fat thermogenesis, resulting in a decrease in fat content. However, the mechanism of FNDC5 related to fat deposition in pigs is still unclear. In this research, we studied the expression of FNDC5 on different adiposes and its function in the adipogenic differentiation of primary preadipocytes in Mashen pigs. The expression pattern of FNDC5 was detected by qRT-PCR and Western blotting in Mashen pigs. FNDC5 overexpression and interference vectors were constructed and transfected into porcine primary preadipocytes by lentivirus. Then, the expression of key adipogenic genes was detected by qRT-PCR and the content of lipid droplets was detected by Oil Red O staining. The results showed that the expression of FNDC5 in abdominal fat was higher than that in back subcutaneous fat in Mashen pigs, whereas the expression in back subcutaneous fat of Mashen pigs was significantly higher than that of Large White pigs. In vitro, FNDC5 promoted the adipogenic differentiation of primary preadipocytes of Mashen pigs and upregulated the expression of genes related to adipogenesis, but did not activate the extracellular signal-regulated kinase (ERK) signaling pathway. This study can provide a theoretical basis for FNDC5 in adipogenic differentiation in pigs.

FNDC5/Irisin polymorphisms are associated with osteopenia in postmenopausal Mayan-Mestizo women

OBJECTIVE

This study aimed to analyze the association between rs3480 and rs16835198 of FNDC5/Irisin and their haplotypes with variations in bone mineral density (BMD) and osteopenia/osteoporosis in postmenopausal Mayan-Mestizo women.

METHODS

We studied 547 postmenopausal women of Maya-Mestizo origin. BMD was measured in the lumbar spine and total hip by dual-energy X-ray absorptiometry. DNA was obtained from blood leukocytes. rs3480 and rs16835198 of FNDC5/Irisin were studied using real-time PCR allelic discrimination. Differences between the means of BMD according to genotype were analyzed with covariance. Allele frequency differences were assessed by χ² and logistic regression was used to test for associations. Pairwise linkage disequilibrium between polymorphisms was calculated by direct correlation r², and haplotype analysis was conducted.

RESULTS

Under a recessive model, we observed a significant association of rs3480 with the presence of osteopenia at the total hip and femoral neck (p = 0.008 and p = 0.003, respectively). For rs16835198, we found an association with osteopenia at the total hip and femoral neck in a dominant model (p = 0.043 and p = 0.009, respectively).

CONCLUSIONS

We found an association of rs3480 with risk to present osteopenia at the total hip and femoral neck, while rs16835198 was associated as a protector for presence of osteopenia only at the femoral neck.

Reduced irisin levels in patients with acromegaly

Objectives

Several metabolic disturbances are seen in acromegaly however, data regarding the contribution of irisin to these disturbances is currently insufficient. In a cohort of patients with acromegaly, we measured serum irisin levels in active and controlled cases and determined independent factors that effect serum irisin including fibronectin type III domain-containing protein 5 (FNDC5) genotyping.

Methods

A cross-sectional case-control study including 46 patients with acromegaly (28 F/18 M, age: 50.3 ± 12.1 year, BMI: 30.7 ± 5.1 kg/m2) and 81 age-, gender-, body mass index- and body composition-matched healthy controls was conducted. 15 acromegalic patients (33%) had active disease. Irisin levels were measured by enzyme-linked immunosorbent assay. Three different regions (rs3480, rs1746661, and rs16835198) of FNDC5 were subjected to polymorphism analyses.

Results

Both groups were overweight and had similar body composition. Irisin levels were lower in patients with acromegaly than controls (median [IQR]: 44.8 [41.7–46.7] ng/mL vs. 51.7 [45.5–60.1] ng/mL, p≤0.001, respectively). Active and controlled patients had similar irisin levels. Irisin was not correlated with growth hormone (GH), insulin-like growth factor 1 (IGF-1), and IGF-1 index. In multiple linear regression model, somatostatin receptor ligand use (β=−20.30, 95% CI [−34]–[−6], p=0.006) was determined as the only independent factor that affect serum irisin.

Conclusions

Serum irisin levels are low in patients with acromegaly who are on somatostatin receptor ligand therapy. Single nucleotide polymorphisms (SNPs) of FNDC5 have no independent effects on circulating irisin levels under somatostatin ligand action. Endocrine muscle functions also seem to be regulated by somatostatin action, which requires further studies.

Irisin as a Novel Biomarker of Subclinical Atherosclerosis, Cardiovascular Risk and Severe Disease in Axial Spondyloarthritis

Introduction

Patients with axial spondyloarthritis (axSpA) have a high disease burden mainly due to the rheumatic disease itself, and also exhibit accelerated atherosclerosis, that leads to a higher incidence of cardiovascular (CV) disease. Accordingly, the identification of biomarkers of CV risk and inflammation in axSpA patients is clinically relevant. In this sense, given the beneficial functions exerted by the adipomyokine irisin in processes related to CV disease and inflammation, our aim was to assess, for the first time, the role of irisin as a genetic and serological biomarker of subclinical atherosclerosis, CV risk and disease severity in axSpA patients.

Methods

A large cohort of 725 Spanish patients with axSpA was included. Subclinical atherosclerosis (presence of plaques and abnormal carotid intima-media thickness values) was evaluated by carotid ultrasound. Four irisin polymorphisms (rs16835198 G/T, rs3480 A/G, rs726344 G/A, and rs1570569 G/T) were genotyped by TaqMan probes. Additionally, serum irisin levels were determined by ELISA.

Results

Low irisin levels were linked to the presence of plaques (p=0.002) and atherogenic index values ≥4 (p=0.01). Serum irisin were positively correlated with C-peptide levels (p<0.001) and negatively correlated with visual analogue scale and Bath Ankylosing Spondylitis Metrology Index (p<0.05 in all the cases). Moreover, lower irisin levels were observed in patients with sacroiliitis and in those with a negative HLA-B27 status (p<0.001 and p=0.006, respectively), as well as in those treated with non-steroidal anti-inflammatory drugs and conventional disease-modifying antirheumatic drugs (p<0.001 and p=0.002, respectively). Interestingly, the TT genotype and the T allele of rs16835198 were less frequent in axSpA patients with ASDAS >2.1 (Odds Ratio (OR): 0.48 [0.28-0.83] and OR: 0.73 [0.57-0.92], respectively, p=0.01 in both cases). Additionally, the frequency of rs1570569 T allele was higher in these patients (OR: 1.46 [1.08-1.97], p=0.01). Furthermore, the GGGT haplotype was more frequent in patients with ASDAS values >2.1 (OR: 1.73 [1.13-2.66], p=0.01).

Conclusions

Our results indicate that low serum irisin levels could be indicators of the presence of subclinical atherosclerosis, high CV risk and more severe disease in axSpA patients. In addition, irisin may also constitute a genetic biomarker of disease activity in axSpA.

LPL, FNDC5 and PPARγ gene polymorphisms related to body composition parameters and lipid metabolic profile in adolescents from Southern Italy

Background

Plasma lipid profile and anthropometric variables are known to be under strong genetic control and the identification of genetic variants associated with bioclinical parameters is of considerable public health importance. In this study, a young cohort of healthy individuals was genotyped for genes related to health and pathological conditions, to analyze the association of single nucleotide polymorphisms (SNPs) with different bioclinical parameters, adherence to the Mediterranean Diet (MD) and physical activity, studying the role of lifestyle and body composition parameters on biochemical metabolic profile.

Methods

Association analysis of single variants in the genes of lipoprotein lipase (LPL), fibronectin type III domain containing protein 5 (FNDC5), and peroxisome proliferator-activated receptor-gamma (PPARγ) and haplotype analyses were performed.

Results

Multiple (n = 14) common variants in the three genes demonstrated a significant effect on plasma lipoprotein-lipid levels and/or on biochemical parameters in our sample. Specifically, SNPs were related to lipid metabolism (rs3866471, rs4922115, rs11570892, rs248, rs316, rs1059507, rs1801282) or glycemic profile (rs3208305) or anthropometric parameters (rs3480, rs726344, rs1570569) for a total of 26 significant associations (P < 0.01 and/or P < 0.05) and two haplotypes, for the first time, were strongly associated with lipid and body composition parameters. Interestingly, we identified twenty-four new variants not previously described in the literature and a novel significant association between rs80143795 and body composition.

Conclusions

In this study we confirm the association between these SNPs on lipid metabolism and body parameters also in a young cohort, indicating the important role of these genetic factors as determinants of health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03314-w.

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

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

Associations between rs3480 and rs16835198 gene polymorphisms of FNDC5 with type 2 diabetes mellitus susceptibility: a meta-analysis

BACKGROUND

FNDC5 is a novel and important player in energy regulation related to glucose metabolism and insulin levels. Thus, it may affect the incidence of type 2 diabetes mellitus (T2DM). Nevertheless, the association between FNDC5 single nucleotide polymorphisms (SNPs) and susceptibility to T2DM remains unclear. The aim of this meta-analysis was to explore whether the SNPs, rs3480 and rs16835198, are associated with the risk of T2DM.

METHODS

Studies published before February 1^st, 2022 were screened to identify the included studies. R software was also applied for calculation of odds ratio (OR), 95% confidence interval (95% CI), heterogeneity, and sensitivity analysis.

RESULTS

Seven studies for rs3480 (involving 5475 patients with T2DM and 4855 healthy controls) and five studies for rs16835198 (involving 4217 patients with T2DM and 4019 healthy controls) were included in this meta-analysis. The results revealed a statistically significant association of rs3480 with T2DM under homozygote (GG vs AA: OR = 1.76, 95% CI = 1.31-2.37, P = 0.0002, I² = 59%) genetic model. However, there was no statistically significant correlation between rs16835198 and susceptibility to T2DM under allelic (G vs T: OR = 1.33, 95% CI = 0.94-1.89, P = 0.11, I² = 84%), heterozygote (GT vs TT: OR = 1.17, 95% CI = 0.80-1.69, P = 0.42, I² = 71%), homozygote (GG vs TT: OR = 1.35, 95% CI = 0.95-1.94, P = 0.10, I² = 62%), recessive (GG+GT vs TT: OR = 1.25, 95% CI = 0.88-1.79, P = 0.22, I² = 72%), and dominant (GG vs GT+GG: OR = 1.20, 95% CI = 0.96-1.50, P = 0.11, I² = 46%) genetic models.

CONCLUSIONS

The present meta-analysis revealed that rs3480 in FNDC5 is significantly associated with susceptibility to T2DM, while rs16835198 does not show such an association.

Dietary Intervention, When Not Associated With Exercise, Upregulates Irisin/FNDC5 While Reducing Visceral Adiposity Markers in Obese Rats

Obesity is an epidemic disease and the expansion of adipose tissue, especially visceral fat, promotes the secretion of factors that lead to comorbidities such as diabetes and cardiovascular diseases. Thus, diet and exercise have been proposed as an intervention to reverse these complications. An adipocytokine, known as irisin, mediates the beneficial effects of exercise. It has been proposed as a therapeutic potential in controlling obesity. In view of the above, this paper attempts to determine the modulation of irisin, visceral adiposity and biochemical markers in response to dietary intervention and aerobic exercise. To do this, 52 diet-induced obese male Wistar rats were divided into the following four groups: high-fat diet and exercise (HFD-Ex); HFD-Sedentary (HFD-Sed); chow-diet and exercise (CD-Exercise); and CD-Sed. The exercise-trained group performed a treadmill protocol for 60 min/day, 3 days/week for 8 weeks. Body mass (BM), body fat (BF), fat mass (FM), and fat-free mass (FFM) were analyzed. Mesenteric (MES), epididymal (EPI), and retroperitoneal (RET) adipose tissue was collected and histological analysis was performed. Biochemical irisin, triglycerides, glucose, insulin and inflammatory markers were determined and, FNDC5 protein expression was analyzed. In this study, the diet was the most important factor in reducing visceral adiposity in the short and long term. Exercise was an important factor in preserving muscle mass and reducing visceral depots after a long term. Moreover, the combination of diet and exercise can enhance these effects. Diet and exercise exclusively were the factors capable of increasing the values of irisin/FNDC5, however it did not bring cumulative effects of both interventions. Prescriptions to enhance the obesity treatments should involve reducing visceral adiposity by reducing the fat content in the diet associated with aerobic exercise.

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.

Common single nucleotide polymorphisms in the FNDC5 gene and serum irisin levels in acute myocardial infarction

OBJECTIVE

Acute myocardial infarction (AMI) is the most common type of coronary artery disease. The irisin hormone encoded by the fibronectin type III domain-containing protein-5 (FNDC5) gene is synthesized in muscle, heart, and fat tissues. The present study aims to investigate serum irisin concentrations and FNDC5 genetic variants in patients with AMI through comparison with controls.

METHODS

This study included 225 patients with AMI and 225 healthy subjects. Blood samples were obtained from patients during the first 1-24 hours after AMI. Serum irisin concentration was measured with enzyme-linked immunosorbent assay (ELISA). The variants of rs16835198, rs3480, and rs726344 in the FNDC5 gene were genotyped with real time polymerase chain reaction (RT-PCR).

RESULTS

Compared with control serum irisin concentrations were significantly lower in patients with AMI. Serum irisin concentrations of patients with AMI showed a significant and gradual decrease from 6 hours up to 24 hours (p<0.05). There were no significant differences between the patient and control groups based on genotype and allele frequencies of rs16835198, rs3480, and rs726344 in the FNDC5 gene (p>0.05). However, the frequency of the TT genotype in male patients with AMI (6.4%) was significantly lower compared with control male subjects (16.2%). In addition, the GGT haplotype was identified as the protective haplotype against the risk of AMI (p<0.001; odds ratio=0.107).

CONCLUSIONS

The findings of the study suggest that serum irisin concentration could serve as a novel biological marker for the early diagnosis of AMI.

Association of Circulating Irisin Levels with Adiposity and Glucose Metabolic Profiles in a Middle-Aged Chinese Population: A Cross-Sectional Study

OBJECTIVE

The myokine irisin has been proposed to affect obesity and metabolism disorders. However, data about the association of irisin with obesity and glucose metabolic status in humans remains controversial, and limited data are available concerning the Chinese population. This study aimed to evaluate the association between serum irisin concentrations and obesity, as well as glucose metabolic and cardiovascular factors in the middle-aged physical activity-matched Chinese Han race population.

METHODS

A total of 740 participants were included in this cross-sectional study, who were divided into a normal weight (NW) group, overweight/obese (OB) group, normal weight type 2 diabetes (DM-NW) group and overweight/obese diabetes (DM-OB) group, and physical activity was evaluated and matched for the four groups. Circulating irisin levels were analyzed and compared among the groups with different adiposity and glucose status. Linear regression analysis was performed to test the relationship between serum irisin and adiposity indices, glucose metabolic and other cardiovascular risk factors.

RESULTS

Circulating irisin levels were significantly correlated with higher levels of direct and indirect adiposity markers, including BMI, waist circumference and fat mass, and other cardiovascular risk factors, such as plasma triglyceride and low-density lipoprotein cholesterol level (p < 0.01). Diabetes patients had lower irisin levels compared to non-diabetes participants, in either normal weight and obese group, resulting in a correlation of irisin with HbA1c, HOMA-IR and HOMA-IS (p < 0.01). Linear regression analysis demonstrated that irisin serum concentrations were independently associated with sex, BMI, HbA1c, HOMA-IR and HOMA-IS (R² = 0.465).

CONCLUSION

These data indicated that circulating irisin was affected by adiposity and glucose metabolism condition in the middle-aged Chinese population. The increase of irisin under conditions of obesity may indicate its physiological function to improve glucose tolerance which is often impaired in obese subjects, but this compensatory secretion of irisin seems likely to be progressing to a secretion failure once diabetes developed.

Genetic Variants in the Activation of the Brown-Like Adipocyte Pathway and the Risk for Severe Obesity

BACKGROUND

Regular physical activity has an important role in energy expenditure and combats the development of obesity. During exercise, PPARGC1A is overexpressed, stimulating an increase of the expression of FNDC5. This protein is cleaved to release the hormone irisin, which activates a browning process in white adipose tissue through an increase in UCP1 expression. As a result, irisin leads to mitochondrial heat production and energy expenditure.

OBJECTIVES

The aim of this study was to investigate whether genetic variants in genes related to browning are associated with severe obesity and obesity-related features. This case-control study comprised 210 individuals with severe obesity (median body mass index [BMI] 45.6 [range 40.5-52.2]) and 191 normal-weight subjects (BMI 22.8 [21.1-23.9]).

METHODS

Genomic DNA was extracted from peripheral blood and the genotypes of the PPARGC1A(rs8192678, rs3736265, rs2970847, and rs3755863) and UCP1 (rs6536991 and rs12502572) genes were obtained using Taqman® assay. For the FNDC5 gene, screening of exons 3-5 as well as their intron-exon boundaries was performed using automatic sequencing.

RESULTS

Our results demonstrated that PPARGC1Ars2970847 and UCP1rs12502572 are associated with severe obesity. Furthermore, these polymorphisms influence anthropometric traits, such as BMI, body weight, and body adiposity index. Our findings also showed a dose-effect relationship between PPARGC1A rs8192678 and fasting plasma glucose. Finally, 5 rare mutations were identified in FNDC5, and 1 of these is a novel missense mutation.

CONCLUSION

This study shows that genetic variants in the activation of brown-like adipocyte pathway play an important role in the susceptibility to severe obesity.

Increased Expression of Meteorin-Like Hormone in Type 2 Diabetes and Obesity and Its Association with Irisin

Type 2 diabetes (T2D) is a growing pandemic associated with metabolic dysregulation and chronic inflammation. Meteorin-like hormone (METRNL) is an adipomyokine that is linked to T2D. Our objective was to evaluate the changes in METRNL levels in T2D and obesity and assess the association of METRNL levels with irisin. Overall, 228 Arab individuals were enrolled. Plasma levels of METRNL and irisin were assessed using immunoassay. Plasma levels of METRNL and irisin were significantly higher in T2D patients than in non-diabetic patients (p < 0.05). When the population was stratified based on obesity, METRNL and irisin levels were significantly higher in obese than in non-obese individuals (p < 0.05). We found a significant positive correlation between METRNL and irisin (r = 0.233 and p = 0.001). Additionally, METRNL and irisin showed significant correlation with various metabolic biomarkers associated with T2D and Obesity. Our data shows elevated METRNL plasma levels in individuals with T2D, further exacerbated with obesity. Additionally, a strong positive association was observed between METRNL and irisin. Further studies are necessary to examine the role of these proteins in T2D and obesity, against their ethnic background and to understand the mechanistic significance of their possible interplay.

Screening for obesity in the offspring of first-cousin consanguineous couples: A Phase-I study in Saudi Arabia

Consanguineous or cousin marriages are very common in Saudi Arabia. However, owing to limited studies and insufficient knowledge about genetic diseases/disorders, many couples are unaware of the increased health risks for their offspring. Among the inherited and complex diseases from parents’ consanguinity, obesity is common; therefore, we examined the prevalence of obesity in the offspring of first-cousin consanguineous couples in Saudi Arabia. In this questionnaire-based study, 657 individuals (mean age = 18.7 ± 10.2 years; age range = 2–65 years) who were residing in Riyadh, Saudi Arabia participated. Among them, almost 90% were native Saudis. Participants mean body mass index (BMI) was 24.5 ± 9.1 kg/m2. Sex- stratified demographic details confirmed a significant association between age and BMI (p < .001). We confirmed that adolescents and adults were more prone to develop obesity. Adults and non-Saudi participants were three times more likely to develop obesity if they had first-cousin consanguineous parents than those who did not. Of the 30% of participants who were obese, 100 will be selected for Phase II, in which we plan to perform exome sequencing.

FNDC5: A novel player in metabolism and metabolic syndrome

Half a decade ago, transmembrane protein fibronectin type III domain-containing protein 5 (FNDC5) was found to be cleaved as a novel myokine irisin, which burst into prominence for browning of white adipose tissue during exercise. However, FNDC5, the precursor of irisin, has been paid relatively little attention compared with irisin despite evidence that FNDC5 is associated with the metabolic syndrome, which accounts for one-fourth of the world's adult population and contributes to diabetes, cardiovascular disease and all-cause mortality. Besides N-terminal and C-terminal sequences, the FNDC5 protein contains an irisin domain and a short transmembrane region. FNDC5 has shown to be widely distribute in different tissues and is highly expressed in heart, brain, liver, and skeletal muscle. Clinical studies have demonstrated that FNDC5 is essential for maintaining metabolic homeostasis and dysregulation of FNDC5 will lead to systemic metabolism imbalance and the onset of metabolic disorders. Growing evidence has suggested that FNDC5 gene polymorphisms are related to health and disease in different human populations. Additionally, FNDC5 has been found relevant to the regulation of metabolism and metabolic syndrome through diverse upstream and downstream signaling pathways in experimental studies. The present review summarizes the characteristics, clinical significance, and molecular mechanisms of FNDC5 in metabolic syndrome and proposes a novel concept that FNDC5 is activated by forming a putative ligand-receptor complex. Knowledge about the role of FNDC5 may be translated into drug development and clinical applications for the treatment of metabolic disorders.

In Addition to Poor Glycemic Control, a High Level of Irisin in the Plasma Portends Early Cognitive Deficits Clinically in Chinese Patients With Type 2 Diabetes Mellitus

Background and Objectives: Irisin plays an important role in the metabolism and homeostasis of energy balance, which is involved in cognitive impairment. This study aimed to investigate the role of irisin in mild cognitive impairment (MCI) among Chinese patients with type 2 diabetes mellitus (T2DM). Methods: We recruited 133 Chinese patients with T2DM, and divided them according to the Montreal Cognitive Assessment score. Demographic data were collected and the level of irisin in the plasma was determined. In addition, the results of neuropsychological testing were examined. The concentration of irisin in the plasma was measured using an enzyme immunoassay. Results: A total of 59 patients were diagnosed with MCI and 74 patients were included as healthy-cognition controls. The level of irisin in the plasma (p = 0.043) and homeostasis model of assessment for insulin resistance (p = 0.032) in diabetic patients with MCI were higher than those observed in the healthy controls. A higher level of irisin in the plasma was associated with impaired overall cognition, specifically executive function. Linear regression analysis suggested that irisin (p = 0.017) and glycosylated hemoglobin (p = 0.036) were independent factors of diabetic MCI. Conclusions: The level of irisin in the plasma correlated with cognitive impairment in T2DM patients, particularly with executive function. These results further suggest that, in addition to poor glycemic control, a high level of irisin in the plasma portends early cognitive deficits clinically in Chinese patients with T2DM.

The Role of Irisin in Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by progressive memory dysfunction, oxidative stress, and presence of senile plaques formed by amyloid beta (Aβ) accumulation in the brain. AD is one of the most important causes of morbidity and mortality worldwide. AD has a variety of risk factors, including environmental factors, metabolic dysfunction, and genetic background. Recent research has highlighted the relationship between AD and systemic metabolic changes such as glucose and lipid imbalance and insulin resistance. Irisin, a myokine closely linked to exercise, has been associated with glucose metabolism, insulin sensitivity, and fat browning. Recent studies have suggested that irisin is involved in the process in central nervous system (CNS) such as neurogenesis and has reported the effects of irisin on AD as one of the neurodegenerative disease. Here, we review the roles of irisin with respect to AD and suggest that irisin highlight therapeutic important roles in AD. Thus, we propose that irisin could be a potential future target for ameliorating AD pathology and preventing AD onset.

Evaluation of irisin and visfatin levels in very low birth weight preterm newborns compared to full term newborns-A prospective cohort study

Premature infants represent one of the groups with increased risk for metabolic syndrome. Our study is the first one to evaluate irisin and visfatin levels, associated with the metabolic syndrome, both in blood of preterm and full-term infants, as well as in the breastmilk of their mothers. A total of 72 newborns was enrolled in the study, including 53 very low birth weight preterm infants and a control group of 19 term infants. The levels of irisin and visfatin were determined by a commercial enzyme-linked immunoabsorbent assay both in the baby serum and maternal milk twice, first during the 1^st week of life and then 4 weeks later. Preterm infants had significantly lower serum irisin levels compared to the term infants. Overall, serum irisin level during the 1^st week of life was positively correlated with several anthropometric measurements at birth, as well as during 5^th weeks of age. In contrast, serum visfatin levels during 5^th week of life were negatively correlated with z-scores of birth weight, weight and head circumference during 5^th week of age. We found a strong negative correlation between serum irisin and serum visfatin levels at both analyzed time points. The level of milk visfatin was significantly higher in the mothers of the preterm group during 5^th week of life. In conclusion, our results provide further evidence that irisin and visfatin may play physiologic roles in development of both preterm and full-term newborns during their first month after birth. Observed differences in irisin and visfatin serum and breastmilk concentrations during the earliest stages of life may contribute to development of catch up growth, but also, they might eventually lead to a higher risk for metabolic syndrome in prematurely born children in later years.

Irisin in metabolic diseases

INTRODUCTION

Irisin is a myokine/adipokine induced by the exercise in mice and humans, which is proposed to induce "browning" of white adipose tissue, its primary target, thus increasing thermogenesis and energy expenditure. Since its identification, irisin has been linked to favorable effects on metabolic diseases, including obesity, type 2 diabetes mellitus (T2DM), lipid metabolism and cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD), polycystic ovary syndrome (PCOS), and metabolic bone diseases. Generally, despite the promising profile of irisin in rodents, its effects on human are less recognized.

REVIEW

Most, but not all studies show a positive association between irisin and indices of adiposity. In T2DM, NAFLD, and CVD, most observational studies reported lower irisin levels in patients than controls. Regarding metabolic bone diseases, irisin is positively associated with bone mineral density and strength in athletes, and inversely associated with osteoporotic fractures in postmenopausal osteoporosis. In PCOS, data remain largely conflicting. Irisin does not seem to be further reduced when two metabolic diseases, e.g., T2DM and NAFLD, or obesity and NAFLD exist though more data are needed. Furthermore, it seems that diverse confounders may have affected the results of different clinical studies.

CONCLUSION

Irisin remains an appealing molecule from a pathophysiological point of view and an appealing therapeutic target for metabolic diseases, albeit much research is still needed.

A comparative study on the effects of high-fat diet and endurance training on the PGC-1α-FNDC5/irisin pathway in obese and nonobese male C57BL/6 mice

The present study was performed to clarify how a combined exercise/diet treatment could affect the expression level of the muscle fibronectin type III domain containing 5 (Fndc5) with respect to body fat mass. Male C57BL/6 mice were divided into 2 groups including low-fat (LF) and high-fat (HF) diets for 12 weeks. Then, LF fed (nonobese) and HF fed mice (obese) were divided into the following 4 groups: HF-Exercise, HF-Sedentary, LF-Exercise, and LF-Sedentary. The exercise group exercised on a motor-driven treadmill for 45 min/day, 5 days/week for 8 weeks. Mice were sacrificed 24 h after the final exercise session. Gastrocnemius muscle and the visceral adipose tissue were excised and frozen for the assessment of proliferator-activated receptor gamma coactivator 1 alpha (Pgc-1α) and Fndc5 messenger RNA (mRNA) and protein levels. Data indicated that protein level of muscle PGC-1α was decreased in HF versus LF groups and in obese versus nonobese mice. Moreover, Fndc5 mRNA levels were increased in the muscle tissue of HF versus LF groups and in obese versus nonobese mice. Also, in the gastrocnemius skeletal muscle, protein levels of FNDC5 were significantly higher in the HF fed mice, as compared with their low-fat fed counterparts, similar to what was observed for exercised versus sedentary mice. Overall, we found that the HF diet increased Fndc5 transcript levels in the skeletal muscle, but exercise had a minimal effect on the transcript level of Fndc5, whereas endurance training increased the protein content of FNDC5 in the skeletal muscle.

β-arrestin-2 is involved in irisin induced glucose metabolism in type 2 diabetes via p38 MAPK signaling

Type 2 diabetes mellitus (T2DM) is a common metabolic disease worldwide. It has been reported that irisin play regulatory role in glucose metabolism in T2DM. However, the underlying mechanism involved in that is not completely known. Herein, we determined the novel role of β-arrestin-2 in irisin-induced glucose utilization in diabetes. Effects of irisin and β-arrestin-2 on glucose utilization were investigated in a rat model of diabetes and in diabetic C2C12 cells in vitro. Results showed that irisin had positive role in glucose metabolism via regulating glucose tolerance as well as uptake in cardiac and skeletal muscle tissues, as evidenced by IPGTT, 2-deoxyglucose uptake and plasma membrane GLUT-4 assay. β-arrestin-2 also improved glucose utilization in diabetes by increasing the glucose uptake and insulin sensitivity, as shown in mice overexpressing β-arrestin-2. In diabetic C2C12 myocytes, irisin-induced GLUT4 and glucose uptake were restrained by β-arrestin-2 inhibition, but was enhanced by β-arrestin-2 overexpression. Additionally, irisin and β-arrestin-2 increased the activation of p38 MAPK in diabetic C2C12 cells, and the repression of p38 MAPK activation decreased the glucose uptake and plasma membrane GLUT-4 was enhanced by irisin and β-arrestin-2 overexpression in diabetic C2C12 cells. In conclusion, we demonstrated that β-arrestin-2 has a crucial role in irisin induced glucose metabolism in T2DM by regulating the p38 MAPK signaling. This might present a novel therapeutic target of treatment for human diabetes.