Interleukin-38 and Insulin Resistance.

Insulin resistance, i.e., decreased biological response to insulin, is a risk factor for many diseases, such as obesity, type 2 diabetes (T2DM), cardiovascular disease, polycystic ovary syndrome, some forms of cancer and neurodegenerative diseases. One of its main causes is chronic low-grade inflammation, mediated by the proinflammatory pathways, such as the c-Jun N-terminal kinase (JNK) pathway and the nuclear factor kappa B (NFκB) pathway. Interleukin (IL)-38 (IL-38) is a newly discovered cytokine that belongs to the IL-1 family. There are three hypothetical pathways through which IL-38 may bind to the specific receptors and inhibit their proinflammatory activity. Those pathways are associated with IL-36 receptor (IL-36R), IL-1 receptor accessory protein-like 1 (IL1RAPL1) and IL-1 receptor 1 (IL1R1). There are studies linking IL-38 to improve insulin sensitivity through the difference in serum IL-38 in patients with insulin resistance or the correlation of IL-38 concentrations with insulin resistance indexes. However, many questions still remain regarding the biological activity of IL-38 itself and its role in the pathogenesis of insulin resistance. The goal of this study is to showcase IL-38, its biological activity, hypothesized signaling pathways, connection with insulin resistance and future perspectives of research on IL-38. We present that IL-38 associated signaling can be a potential target for the treatment of insulin resistance and associated diseases.

Weight-Reducing Dietary Intervention Increases the Ability of Hyperinsulinemia to Suppress Serum Ghrelin Concentration in Individuals with Obesity.

BACKGROUND: Ghrelin is an orexigenic peptide secreted mainly by the stomach. Serum ghrelin concentrations are suppressed after a meal, probably due to insulin release. Individuals with obesity are characterized by a lower fasting serum ghrelin and a lower ghrelin decrease after a meal. The effect of weight loss on the ability of insulin to suppress serum ghrelin concentration remains unknown. OBJECTIVE: The aim of the present study was to analyze the effect of weight-reducing dietary intervention on the ability of hyperinsulinemia to suppress serum ghrelin concentration in young individuals with uncomplicated obesity. METHODS: We examined 38 individuals with marked overweight or obesity, who underwent a 12-wk dietary intervention program. Serum ghrelin concentration was measured before and after a 2-h hyperinsulinemic-euglycemic clamp, both pre- and post-intervention. Twenty normal-weight individuals served as a control group and were examined at baseline only. RESULTS: Individuals with overweight/obesity were characterized by a lower fasting serum ghrelin concentration than normal-weight individuals (P = 0.006). Insulin decreased serum ghrelin concentration in both groups (P < 0.001); however, this decrease was markedly lower in individuals with overweight/obesity than in normal-weight individuals (99.70 ± 136.37 vs. 215.45 ± 250.28 pg/mL; P = 0.026). Fasting serum ghrelin concentration increased after the intervention. After weight-reducing dietary intervention, the decrease in serum ghrelin concentration after the clamp was significantly greater than the pre-intervention value (99.70 ± 136.37 vs. 221.82 ± 228.75 pg/mL; P = 0.002). CONCLUSIONS: Weight-reducing dietary intervention restores the ability of hyperinsulinemia to suppress serum ghrelin concentration. It may suggest an enhanced feeling of satiety after moderate weight loss in individuals with overweight/obesity.

The Ca2+/Calmodulin-dependent Calcineurin/NFAT Signaling Pathway in the Pathogenesis of Insulin Resistance in Skeletal Muscle.

Skeletal muscle is the tissue directly involved in insulin-stimulated glucose uptake. Glucose is the primary energy substrate for contracting muscles, and proper metabolism of glucose is essential for health. Contractile activity and the associated Ca2+signaling regulate functional capacity and muscle mass. A high concentration of Ca2+and the presence of calmodulin (CaM) leads to the activation of calcineurin (CaN), a protein with serine-threonine phosphatase activity. The signaling pathway linked with CaN and transcription factors like the nuclear factor of activated T cells (NFAT) is essential for skeletal muscle development and reprogramming of fast-twitch to slow-twitch fibers. CaN activation may promote metabolic adaptations in muscle cells, resulting in better insulin-stimulated glucose transport. The molecular mechanisms underlying the altered insulin response remain unclear. The role of the CaN/NFAT pathway in regulating skeletal muscle hypertrophy is better described than its involvement in the pathogenesis of insulin resistance. Thus, there are opportunities for future research in that field. This review presents the role of CaN/NFAT signaling and suggests the relationship with insulin-resistant muscles.

Subcutaneous adipose tissue circadian gene expression: Relationship with insulin sensitivity, obesity, and the effect of weight-reducing dietary intervention.

OBJECTIVE: The circadian rhythms are controlled by the central clock in the hypothalamic suprachiasmatic nuclei and by the peripheral clocks in tissues, including adipose tissue. The adipose tissue circadian clock may be associated with the regulation of insulin action; however, human data are limited. The aim of this study was to analyze the expression of subcutaneous adipose tissue circadian genes as they relate to obesity and insulin sensitivity before and after diet-induced weight loss. METHODS: The study group comprised 38 individuals who were overweight or obese. The individuals completed a 12-wk dietary intervention program. Hyperinsulinemic-euglycemic clamp and subcutaneous adipose tissue biopsy were performed before and after the program. Sixteen normal weight individuals were examined at baseline and served as a control group. RESULTS: At baseline, individuals who were overweight/obese had lower adipose tissue expression of NR1D1, NR1D2, DBP, PER1, and PER2 than normal weight individuals. The expression of ARNTL, CLOCK, and CRY did not differ between the groups. A weight-reducing dietary intervention resulted in an increase in the expression of adipose tissue NR1D2 and DBP, which was positively related to insulin sensitivity both before (in the entire study group and in the subgroup of overweight/obese individuals) and after the dietary intervention. CONCLUSIONS: Adipose tissue circadian gene expression is decreased in obesity and this decrease may be partially reversed by dietary intervention. Among circadian genes, NR1D2 and DBP seem to be specifically associated with insulin action.

Skeletal muscle integrin expression in non-obese men with varying degrees of insulin sensitivity.

The remodeling of skeletal muscle extracellular matrix (ECM) components is related to the degree of insulin resistance (IR). Membrane receptors such as integrins provide two-way signaling ("inside-out" and "outside-in" signaling) between ECM components of skeletal muscle (e.g., collagen, laminin, fibronectin) and intracellular signaling pathways. The aim of the study was to analyze the relationship between the expression of integrins in skeletal muscle and insulin sensitivity (IS) in young, healthy, non-obese volunteers. We studied 36 healthy non-obese male participants. Subjects were divided into three subgroups on the basis of the hyperinsulinemic-euglycemic clamp: upper IS tertile, medium IS tertile, and lower IS tertile. Vastus lateralis muscle biopsies were performed before each clamp. Next, analysis of integrin mRNA expression was performed. Waist circumference, percent body fat, fasting serum insulin, total cholesterol, triglycerides and LDL-cholesterol were higher in the lower IS tertile subgroup compared to the other two subgroups (p < 0.05). The lower IS tertile showed increased expression of ITGA5, ITGA6, ITGA7, SPARC (p < 0.05) in comparison with the upper IS tertile and ITGA6 (p < 0.05) compared to the medium IS tertile. ITGA2, ITGA3, ITGA5, ITGA6, ITGA7, SPARC correlated inversely with IS (p < 0.05). Skeletal muscle integrin are associated with low IS in healthy nonobese men. Our data suggest that factors associated with ECM in muscle may be involved in modulation of insulin action even at the early stages of the development of IR.

Link between insulin resistance and skeletal muscle extracellular matrix remodeling.

Skeletal muscle is the main metabolic tissue responsible for glucose homeostasis in the body. It is surrounded by the extracellular matrix (ECM) consisting of three layers: epimysium, perimysium, and endomysium. ECM plays an important role in the muscle, as it provides integrity and scaffolding cells. The observed disturbances in this structure are related to the abnormal remodeling of the ECM (through an increase in the concentration of its components). ECM rearrangement may impair insulin action by increasing the physical barrier to insulin transport and reducing insulin transport into muscle cells as well as by directly inhibiting insulin action through integrin signaling. Thus, improper ECM remodeling may contribute to the development of insulin resistance (IR) and related comorbidities. In turn, IR-associated conditions may further aggravate disturbances of ECM in skeletal muscle. This review describes the major components of the ECM that are necessary for its proper function. Particular attention was also paid to receptors (integrins) involved in the signaling of metabolic pathways. Finally, changes in ECM components in the context of clinical and animal studies are discussed. This article will help the reader to systematize knowledge related to the ECM and to better understand the relationship between ECM remodeling and IR, and its role in the pathogenesis of T2DM. The information in this article presents the concept of the role of ECM and its remodeling in the pathogenesis of IR, which may contribute to developing new therapeutic solutions.

Changes in Adipose Tissue Gene Expression of the Core Components of the Hippo Signaling Pathway in Young Adults with Uncomplicated Overweight or Obesity Following Weight Loss.

BACKGROUND: Appropriate adipogenesis leads to the "healthy" expansion of adipose tissue and is a crucial component in maintaining metabolic homeostasis. The Hippo signaling network may balance adipocyte proliferation/differentiation regulating adipogenic footpath. OBJECTIVES: Our study aimed to assess subcutaneous adipose tissue (SAT) expression of genes involved in Hippo signaling network in subjects with marked overweight or obesity after dietary intervention (DI) in relation to obesity and insulin sensitivity. METHODS: Forty overweight or obese subjects (O/O) [mean ± SD age 33 ± 7 y, 45% men, BMI (in kg/m2) 32.9 ± 3.1] completed DI [low-calorie diet (20 kcal/kg of proper body weight) for 12 wks]. The control group comprising 20 normal-weight subjects (mean ± SD age: 24 ± 2 y, 40% men, BMI: 22.4 ± 2.3 ) was examined at baseline only. Hyperinsulinemic-euglycemic clamp and SAT biopsy with gene expression analysis were performed. Student's t-test for unpaired and paired samples and Pearson correlation analysis were applied. This is an exploratory analysis of the DI program. RESULTS: SAT mRNA expression of mammalian sterile 20-like kinase 2 (MST2) encoded by serine/threonine kinase 3 gene (STK3)-->, large tumor suppressor kinase 2 (LATS2), and salvador family WW domain containing protein 1 (SAV1), the upstream members of the Hippo pathway, were decreased (21%, 40%, and 36%, respectively) in O/O in comparison with weight subjects individuals before DI (all P < 0.05). At baseline, positive correlations between SAT SAV1, LATS2 expression and adiponectin (ADIPOQ) (r = 0.50, P < 0.001; r = 0.53, P = 0.004, respectively) and solute carrier family 2 member 4 (SLC2A4) (r = 0.35, P = 0.007; r = 0.28, P = 0.03, respectively) expression were observed in the entire study group. Body weight of the O/O group decreased during DI (11.2 ± 3.8 kg, P < 0.001), and there was an increase in insulin sensitivity (by 27%) and SAT expression of STK3, LATS2 (both by 19%), and SAV1 (by 26%) (all P < 0.05). After DI, SAT SLC2A4 expression was correlated with STK3 (r = 0.47, P = 0.003), LATS2 (r = 0.56, P < 0.001), and yes-associated protein (r = 0.50, P = 0.001) expression. CONCLUSIONS: Obesity is associated with altered mRNA expression of upstream effectors of the Hippo pathway in SAT in young adults. DI may improve adipogenic capacity. J Nutr 20XX;xx:xx-xx.

Skeletal muscle RUNX1 is related to insulin sensitivity through its effect on myogenic potential.

Objective: Skeletal muscle is the major site of insulin action. There are limited data on the relationship between insulin action and skeletal muscle myogenic/regenerative potential. RUNX1 is a transcription factor which plays a role in muscle development and regeneration. The aim of our study was to assess the role of skeletal muscle myogenic/regenerative potential in the development of insulin resistance through the studies on RUNX1 transcription factor. Design: This study is a cross-sectional study. Experimental part with myoblast cell line culture. Methods: We examined 41 young healthy volunteers, 21 normal weight and 20 with overweight or obesity. Hyperinsulinemic-euglycemic clamp and vastus lateralis muscle biopsy were performed. In L6 myoblast and human skeletal muscle myoblasts (hSkMM) cell cultures, RUNX1 was silenced at two stages of development. Cell growth, the expression of markers of myogenesis, nuclei fusion index, Akt phosphorylation and glucose uptake were measured. Results: Skeletal muscle RUNX1 expression was decreased in overweight/obese individuals in comparison with normal-weight individuals and was positively related to insulin sensitivity, independently of BMI. Runx1 loss-of-function at the stage of myoblast inhibited myoblast proliferation and differentiation and reduced insulin-stimulated Akt phosphorylation and insulin-stimulated glucose uptake. In contrast, Runx1 knockdown in myotubes did not affect Akt phosphorylation, glucose uptake and other parameters studied. Conclusions: Myogenic/regenerative potential of adult skeletal muscle may be an important determinant of insulin action. Our data suggest that muscle RUNX1 may play a role in the modulation of insulin action through its effect on myogenesis.

The relationships between FLAIS, a novel insulin sensitivity index, and cardiovascular risk factors in a population-based study.

BACKGROUND: Insulin resistance is a risk factor for cardiovascular disease. Recently, we have developed a novel index, FLAIS (Fasting Laboratory Assessment of Insulin Sensitivity), which accurately reflects insulin sensitivity, measured with hyperinsulinemic-euglycemic clamp, in different groups of subjects. The aim of the present study was to assess the relationship of FLAIS with cardiovascular risk factors in a population-based study. METHODS: The study group comprised 339 individuals from the ongoing Bialystok Plus study, without previously known diabetes. Clinical examination, oral glucose tolerance test and the measurement of blood laboratory parameters were performed. RESULTS: Prediabetes (impaired fasting glucose and/or impaired glucose tolerance) was diagnosed in 165 individuals whereas type 2 diabetes was diagnosed in 19 subjects. FLAIS was lower in individuals with prediabetes and diabetes in comparison with individuals with normal glucose tolerance. FLAIS was significantly related to waist circumference, systolic and diastolic blood pressure, triglycerides, HDL-cholesterol and LDL-cholesterol in the entire study group and in the subgroups with normal glucose tolerance and with prediabetes/diabetes. HOMA-IR, QUICKI and Matsuda index were not related to blood pressure and LDL-cholesterol in individuals with normal glucose tolerance. Majority of the adjusted models with FLAIS were characterized by better fit with the data in comparison with other indices for all cardiovascular risk factors except waist circumference. CONCLUSIONS: FLAIS represents useful index to assess the cluster of insulin resistance-associated cardiovascular risk factors in general population.

Relation of adipose tissue and skeletal muscle FKBP5 expression with insulin sensitivity and the regulation of FKBP5 by insulin and free fatty acids.

PURPOSE: Recent studies suggest that FK506 binding protein 51 (FKBP51), a negative regulator of glucocorticoid response, encoded by FKBP5, may influence insulin action. The aim of the present study was to assess the relationship between subcutaneous adipose tissue (AT) and skeletal muscle FKBP5 expression in relation to insulin sensitivity in healthy individuals and to study its regulation by insulin and circulating free fatty acid (FFA) elevation. METHODS: The study group comprised 96 male subjects, 49 normal-weight and 47 overweight/obese. Hyperinsulinemic clamp, subcutaneous AT and skeletal muscle biopsies were performed. In a subgroup of 20 subjects, two 6 h clamps were performed, with and without Intralipid/heparin infusion, and tissue biopsies were obtained before and after each clamp. RESULTS: AT FKBP5 expression was lower in overweight/obese individuals in comparison with normal-weight individuals (p = 0.004). Muscle FKBP5 expression did not differ between the groups, however, it was inversely related to insulin sensitivity (r = -0.32, p = 0.002). FKBP5 expression decreased in AT (p = 0.003) and increased in muscle (p < 0.0001) after insulin infusion. Intralipid/heparin diminished insulin-induced increase in muscle FKBP5. CONCLUSION: Our data show that lower AT FKBP5 expression is related to obesity, whereas muscle FKBP5 expression is associated with insulin resistance. AT and muscle FKBP5 expression is differentially regulated by insulin.

Adipose Tissue and Skeletal Muscle Expression of Genes Associated with Thyroid Hormone Action in Obesity and Insulin Resistance.

Background: Thyroid hormone (TH) regulates metabolic pathways which may interfere with insulin action. There is limited knowledge on adipose tissue (AT) and skeletal muscle (SM) expression of genes associated with TH action in relation to insulin sensitivity. The aim of this study was to analyze AT and SM expression of the genes associated with TH action in subjects with different degree of insulin sensitivity and the regulation of these genes by insulin and free fatty acids (FFA). Methods: The study group comprised 72 euthyroid male subjects: 36 normal weight subjects and 36 overweight/obese subjects. Two-hour hyperinsulinemic-euglycemic clamp and tissue biopsies were performed. In the subgroup of 20 subjects, 9 normal weight subjects and 11 overweight/obese subjects, clamp was prolonged to 6 hours and another clamp with Intralipid/heparin infusion was performed after 1 week. Tissue biopsies were performed before and after each clamp. Results: Overweight/obese subjects had higher AT DIO2, DIO3, and NCOR1, lower AT THRA and PPARGC1A, higher SM NCOR1, and lower SM DIO2, DIO3, PPARGC1A, and ATP2A2 expression. In AT, DIO2 and PPARGC1A increased, whereas NCOR1 and FOXO1 decreased after the clamp only in normal weight individuals. DIO3 decreased in both groups. In SM, NCOR1 decreased, whereas PPARGC1A and ATP2A2 increased after the clamp only in normal weight individuals. Tissue THRA and THRB decreased in both groups. Intralipid/heparin abolished these effects. Conclusions: Alterations in AT and SM expression of TH-related gene indicate a decreased tissue TH action in obesity. Inability to increase TH-related gene expression in obesity and during FFA oversupply may contribute to the aggravation of lipotoxicity.

Novel Laboratory Index, Based on Fasting Blood Parameters, Accurately Reflects Insulin Sensitivity.

CONTEXT: Simple and reliable measurement of insulin sensitivity may be important for the prevention of insulin-resistance-related diseases. Surrogate indices of insulin sensitivity are of limited utility in population without signs of metabolic syndrome. OBJECTIVE: The aim of our study was to provide simple and accurate index of insulin sensitivity. DESIGN: The study group comprised 150 young healthy participants. Hyperinsulinemic-euglycemic clamp was performed. Regression models with different laboratory parameters were constructed. Validation cohort 1 comprised independent group of 110 subjects, including individuals with prediabetes and newly diagnosed type 2 diabetes. Validation cohort 2 comprised 38 obese subjects before and after diet-induced weight loss. Validation cohort 3 comprised 60 nondiabetic subjects from an independent center. RESULTS: The supervised principal component model established optimal set of variables correlated with insulin sensitivity. This model (Fasting Laboratory Assessment of Insulin Sensitivity [FLAIS]) used red blood cell count, alanine aminotransferase activity, serum C-peptide, SHBG, IGF-binding protein 1, and adiponectin concentrations. FLAIS exhibited strong correlation with clamp-derived insulin sensitivity. The sensitivity of the model was 90% and the specificity was 68%. In validation cohort 1, differences in FLAIS among the groups paralleled those observed with the clamp, with the lowest values in prediabetes and diabetes. In validation cohort 2, FLAIS reflected the change in insulin sensitivity after weight loss. The main findings were confirmed in validation cohort 3. CONCLUSION: We provide simple and accurate method of assessing insulin sensitivity, which allows to identify insulin resistance even in the population without overt metabolic disturbances.

Serum and adipose tissue chemerin is differentially related to insulin sensitivity.

OBJECTIVE: The aim of the study was to assess serum chemerin concentration and s.c. adipose tissue (SAT) chemerin expression in relation to insulin sensitivity and obesity in young healthy subjects. DESIGN: We performed a cross-sectional study including 128 subjects, 44 with normal weight, 44 with overweight and 40 with obesity. METHODS: Hyperinsulinemic-euglycemic clamp and SAT biopsy were performed. Next, 30 subjects with obesity underwent 12-week weight-reducing dietary intervention. RESULTS: Serum chemerin was higher and SAT chemerin expression was lower in subjects with obesity in comparison with other groups. The relationship of serum chemerin with SAT expression and insulin sensitivity were positive in normal weight and overweight individuals, and negative in individuals with obesity. In the entire study population, serum chemerin was also positively related to hsCRP, serum fetuin A and alanine aminotransferase. SAT chemerin was positively related to insulin sensitivity, SAT insulin signaling and adipogenic genes. Weight loss decreased serum chemerin, whereas SAT chemerin increased in subjects with the highest increase in insulin sensitivity. CONCLUSIONS: Serum and SAT chemerin is differentially associated with insulin sensitivity and the relationship between serum chemerin and insulin sensitivity depends on adiposity. SAT chemerin is positively associated with insulin sensitivity across a wide range of BMIs and may be proposed as a biomarker of metabolically healthy SAT. Our results suggest that SAT is not the main source of serum chemerin in obesity.

Changes in adipose tissue lipolysis gene expression and insulin sensitivity after weight loss.

OBJECTIVE: Insulin resistance is a major pathophysiological link between obesity and its metabolic complications. Weight loss (WL) is an effective tool to prevent obesity-related diseases; however, the mechanisms of an improvement in insulin sensitivity (IS) after weight-reducing interventions are not completely understood. The aim of the present study was to analyze the relationships between IS and adipose tissue (AT) expression of the genes involved in the regulation of lipolysis in obese subjects after WL. METHODS: Fifty-two obese subjects underwent weight-reducing dietary intervention program. The control group comprised 20 normal-weight subjects, examined at baseline only. Hyperinsulinemic-euglycemic clamp and s.c. AT biopsy with subsequent gene expression analysis were performed before and after the program. RESULTS: AT expression of genes encoding lipases (PNPLA2, LIPE and MGLL) and lipid-droplet proteins enhancing (ABHD5) and inhibiting lipolysis (PLIN1 and CIDEA) were decreased in obese individuals in comparison with normal-weight individuals. The group of 38 obese participants completed dietary intervention program and clamp studies, which resulted in a significant WL and an improvement in mean IS. However, in nine subjects from this group IS did not improve in response to WL. AT expression of PNPLA2, LIPE and PLIN1 increased only in the group without IS improvement. CONCLUSIONS: Excessive lipolysis may prevent an improvement in IS during WL. The change in AT PNPLA2 and LIPE expression was a negative predictor of the change in IS after WL.

The effect of moderate weight loss, with or without (1, 3)(1, 6)-ß-glucan addition, on subcutaneous adipose tissue inflammatory gene expression in young subjects with uncomplicated obesity.

PURPOSE: Obesity is characterized by insulin resistance and low-grade systemic and adipose tissue (AT) inflammation. It remains unclear whether beneficial effects of weight loss are related to AT inflammation. We aimed to assess the effect of weight loss during low-calorie diet on insulin sensitivity, AT expression of genes associated with inflammation in young subjects with obesity. Furthermore, we estimated the effects of immunomodulatory (1, 3)(1, 6)-ß-glucan (BG) on the above parameters. METHODS: The study group comprised 52 subjects with obesity. Twelve-week dietary intervention was applied, with randomization to receive or not 500 mg BG daily. Euglycemic hyperinsulinemic clamp, subcutaneous AT biopsy were performed before and after the program. Twenty normal-weight subjects, examined at baseline, served as a control group. RESULTS: At baseline, obese subjects had lower insulin sensitivity, lower AT ADIPOQ, JAK1, and JAK2 expression and higher AT expression of LEP, IL6ST, STAT3, MIF, CCL2, MMP9, and IL18. Forty obese subjects completed dietary intervention program, which resulted in 11.3% weight loss and 27% increase in insulin sensitivity (both p < 0.0001). AT IL6R, IL6ST, JAK1, and JAK2 expression increased, whereas MIF, CCL2, MMP9, and IL18 gene expression did not change in response to weight loss. BG addition had no effect on any of the parameters studied. CONCLUSIONS: Our data indicate that reduction in AT inflammation is not required for an improvement in insulin action during weight loss in subjects with uncomplicated obesity. BG does not have effects during dietary intervention.

Wnt Signaling Genes in Adipose Tissue and Skeletal Muscle of Humans With Different Degrees of Insulin Sensitivity.

CONTEXT: The ß-catenin-dependent Wnt signaling plays a role in adipogenesis, myogenesis, and glucose homeostasis. OBJECTIVE: The aim of this study was to assess adipose tissue and skeletal muscle expression of Wnt/ß-catenin signaling genes in a young healthy population according to insulin sensitivity and its regulation by hyperinsulinemia and free fatty acids. DESIGN: We examined 117 male volunteers. The participants were divided into subgroups of high-insulin sensitivity (IS) and low-IS on the basis of a 2-hour euglycemic clamp. In 20 subjects, the clamp was prolonged to 6 hours. After 1 week, another 6-hour clamp, with Intralipid/heparin infusion, was performed. Tissue biopsies were performed before each clamp and after 6-hour clamps. Additionally, we collected muscle biopsies from another group of 16 male subjects for cell cultures. Myotubes were treated with insulin separately and in combination with palmitate. RESULTS: We found decreased adipose tissue WNT10B, FZD1/8, LRP5, DVL2, CTNN1B, TCF7L2, and AXIN2 and increased muscle WNT10B, FZD1/8, LRP6, DVL1, GSK3B, CTNNB1, TCF7L2, AXIN2, MYC, and CCND1 expression in the low-IS group. Hyperinsulinemia resulted in a decrease in adipose tissue FZD4, LRP5/6, TCF7L2, and AXIN2 and an increase in muscle FZD1/8, DVL1/2/3, TCF7L2, AXIN2, and MYC expression. These changes disappeared after free fatty acid elevation. In myotubes, insulin increased the expression of FZD1, DVL2, CTNNB1, and TCF7L2, whereas palmitate abolished these effects. CONCLUSIONS: The association of ß-catenin-dependent Wnt signaling with insulin resistance is tissue specific. Observed changes might reflect a compensatory mechanism to increase muscle glucose uptake and to generate new fat cells in insulin-resistant conditions.

Obesity Is Associated With Gene Expression and Imaging Markers of Iron Accumulation in Skeletal Muscle.

CONTEXT: Different genetic and imaging iron markers are known to be increased in the liver, adipose tissue, and brain of obese subjects. OBJECTIVE: We aimed to investigate these markers in human skeletal muscle. DESIGN, SETTING, PATIENTS, AND OUTCOME MEASURES: Markers of iron accumulation were measured in three different territories: Iron gene markers (TFRC1, TF, SLC11A2, FTL, FTH1, and SLC40A1) were studied in abdominal rectus abdominis (Cohort 1, n = 26) and quadriceps (Cohort 2, n = 13) muscle using real-time PCR, whereas paravertebral muscle R2* signal (as surrogate of iron content) (Cohort 3, n = 43) was evaluated by means of magnetic resonance imaging. INTERVENTION: In a subgroup of 14 obese participants from Cohort 3, a diet-induced weight loss was performed. RESULTS: Rectus abdominis muscle age-adjusted gene expression of SLC40A1 (ferroportin) (r = 0.47; P = .04), SLC11A2 (r = 0.50; P = .03) and CYBA (r = 0.62; P = .006) increased with body fatness. In obese participants from Cohort 1, muscle CYBA gene expression was positively correlated with serum ferritin. This association was replicated in quadriceps from obese participants (Cohort 2). Paravertebral muscle R2* was positively associated with body mass index, waist circumference, and fat mass (measured by dual-energy x-ray absorptiometry) in parallel with hepatic iron content, serum ferritin, and hepcidin. In multivariate regression analyses, obesity parameters (P < .0001) and hsCRP concentration (P < .05) contributed independently to the variance of sex-, serum hepcidin- and age-adjusted muscle R2*. Of note, weight loss intervention resulted in decreased muscle R2* (P = .02) in correlation with the change of serum ferritin (r = 0.69; P = .01). CONCLUSIONS: These findings emphasize a significant iron accumulation in human skeletal muscle in association with obesity. The mechanisms implicated in these observations should be studied further.

Relationship Between Serum IL-12 and p40 Subunit Concentrations and Lipid Parameters in Overweight and Obese Women.

BACKGROUND: Obesity is a chronic low-grade inflammatory state associated with the development of insulin resistance, type 2 diabetes mellitus, and atherosclerosis. Interleukin-12 (IL-12) is a proinflammatory cytokine composed of a 40-kD (p40) subunit and a 35-kD (p35) subunit. p40 might have an independent role in initiating the immune response. Recent findings indicate that IL-12 could be involved in the development of obesity-associated co-morbidities, especially atherosclerosis. It is unclear if there are alternations in circulating concentrations of total IL-12 and its subunit p40 in young subjects with increased adiposity without overt metabolic disturbances. The aim of the present study was to estimate serum total IL-12 together with its p40 subunit in young overweight and obese women and to investigate the associations of these parameters with insulin sensitivity and serum lipids. METHODS: We studied 77 healthy women (37 lean and 40 obese or overweight). Anthropometric measurements, blood biochemical analyses, determination of serum IL-12, IL-12p40 concentrations, and euglycemic-hyperinsulinemic clamp were performed. RESULTS: We demonstrated an increase in serum p40 in obese subjects (P=0.029). We found positive correlations between p40 and fat mass (r=0.24, P=0.04) and significant negative associations with high-density lipoprotein cholesterol (HDL-C) (r=-0.27, P=0.002). Detectable concentrations of serum IL-12 were observed in 55% of subjects. Individuals with detectable serum concentrations of IL-12 had significantly higher levels of serum triglycerides (P=0.049). A significant association between IL-12 and serum total cholesterol (r=0.32, P=0.042) was observed in this subgroup. No association between p40 or IL-12 and insulin sensitivity was found. CONCLUSIONS: Our data indicate that the IL-12/IL-12p40 system may be associated with lipid abnormalities in obese subjects.