Biomedical subjects

Charlotte Keller

Publications and source records attributed to Charlotte Keller.

At least 19 recordsLinked to original sources

PubMed2007

Differential regulation of IL-6 and TNF-alpha via calcineurin in human skeletal muscle cells.

Interleukin-6 increases in skeletal muscle during exercise, and evidence points to Ca2+ as an initiator of IL-6 production. However, the signalling pathway whereby this occurs is unknown. One candidate for Ca2+ -mediated IL-6 induction is calcineurin, an activator of NF-AT. Here we investigated whether skeletal myocytes produce IL-6 in a Ca2+/calcineurin-dependent manner, and whether TNF-alpha, an inducer of IL-6, is affected by these stimuli. Human skeletal muscle cell cultures were stimulated with ionomycin time-and dose-dependently to elevate intracellular Ca2+ levels, with or without addition of cyclosporin A (CSA); a calcineurin inhibitor. mRNA was extracted from myocytes and analysed for IL-6 and TNF-alpha gene expression. IL-6 mRNA increased time- and dose-dependently with ionomycin stimulation, an effect that was blunted by approximately 75% in the presence of CSA. In contrast, TNF-alpha gene expression was decreased by approximately 70% in response to ionomycin treatment, but increased in response to addition of CSA. These data demonstrate that IL-6 and TNF-alpha are regulated differentially in skeletal muscle cells in response to a Ca2+ stimulus. Blocking the calcineurin pathway resulted in inhibition of the IL-6 response to ionomycin, whereas TNF-alpha increased by addition of CSA, further indicating a differential regulation of IL-6 and TNF-alpha in human skeletal myocytes.

Calcineurin↗

PubMed2006

Visfatin mRNA expression in human subcutaneous adipose tissue is regulated by exercise.

Visfatin [pre-beta-cell colony-enhancing factor (PBEF)] is a novel adipokine that is produced by adipose tissue, skeletal muscle, and liver and has insulin-mimetic actions. Regular exercise enhances insulin sensitivity. In the present study, we therefore examined visfatin mRNA expression in abdominal subcutaneous adipose tissue and skeletal muscle biopsies obtained from healthy young men at time points 0, 3, 4.5, 6, 9, and 24 h in relation to either 3 h of ergometer cycle exercise at 60% of Vo(2 max) or rest. Adipose tissue visfatin mRNA expression increased threefold at the time points 3, 4.5, and 6 h in response to exercise (n = 8) compared with preexercise samples and compared with the resting control group (n = 7, P = 0.001). Visfatin mRNA expression in skeletal muscle was not influenced by exercise. The exercise-induced increase in adipose tissue visfatin was, however, not accompanied by elevated levels of plasma visfatin. Recombinant human IL-6 infusion to mimic the exercise-induced IL-6 response (n = 6) had no effect on visfatin mRNA expression in adipose tissue compared with the effect of placebo infusion (n = 6). The finding that exercise enhances subcutaneous adipose tissue visfatin mRNA expression suggests that visfatin has a local metabolic role in the recovery period following exercise.

Abdominal Fat↗

PubMed2006

Interleukin-6 regulation of AMP-activated protein kinase. Potential role in the systemic response to exercise and prevention of the metabolic syndrome.

Interleukin (IL)-6 is a pleiotropic hormone that has both proinflammatory and anti-inflammatory actions. AMP-activated protein kinase (AMPK) is a fuel-sensing enzyme that among its other actions responds to decreases in cellular energy state by enhancing processes that generate ATP and inhibiting others that consume ATP but are not acutely necessary for survival. IL-6 is synthesized and released from skeletal muscle in large amounts during exercise, and in rodents, the resultant increase in its concentration correlates temporally with increases in AMPK activity in multiple tissues. That IL-6 may be responsible in great measure for these increases in AMPK is suggested by the fact it increases AMPK activity both in muscle and adipose tissue in vivo and in incubated muscles and cultured adipocytes. In addition, we have found that AMPK activity is diminished in muscle and adipose tissue of 3-month-old IL-6 knockout (KO) mice at rest and that the absolute increases in AMPK activity in these tissues caused by exercise is diminished compared with control mice. Except for an impaired ability to exercise and to oxidize fatty acids, the IL-6 KO mouse appears normal at 3 months of age. On the other hand, by age 9 months, it manifests many of the abnormalities of the metabolic syndrome including obesity, dyslipidemia, and impaired glucose tolerance. This, plus the association of decreased AMPK activity with similar abnormalities in a number of other rodents, suggests that a decrease in AMPK activity may be a causal factor. Whether increases in IL-6, by virtue of their effects on AMPK, contribute to the reported ability of exercise to diminish the prevalence of type 2 diabetes, coronary heart disease, and other disorders associated with the metabolic syndrome remains to be determined.

AMP-Activated Protein Kinases↗

PubMed2005

Effect of exercise, training, and glycogen availability on IL-6 receptor expression in human skeletal muscle.

The cytokine interleukin-6 (IL-6) exerts it actions via the IL-6 receptor (IL-6R) in conjunction with the ubiquitously expressed gp130 receptor. IL-6 is tightly regulated in response to exercise, being affected by factors such as exercise intensity and duration, as well as energy availability. Although the IL-6 response to exercise has been extensively studied, little is known about the regulation of the IL-6R response. In the present study, we aimed to investigate the effect of exercise, training, and glycogen availability, factors known to affect IL-6, on the regulation of gene expression of the IL-6R in human skeletal muscle. Human subjects performed either 10 wk of training with an acute exercise bout before and after the training period, or a low-glycogen vs. normal-glycogen acute exercise trial. The IL-6R mRNA response was evaluated in both trials. In response to acute exercise, an increase in IL-6R mRNA levels was observed. Neither training nor intramuscular glycogen levels had an effect on the IL-6R mRNA response to exercise. However, after 10 wk of training, the skeletal muscle expressed a higher mRNA level of IL-6R compared with before training. The present study demonstrated that the IL-6R gene expression levels in skeletal muscle are increased in response to acute exercise, a response that is very well conserved, being affected by neither training status nor intramuscular glycogen levels, as opposed to IL-6. However, after the training period, IL-6R mRNA production was increased in skeletal muscle, suggesting a sensitization of skeletal muscle to IL-6 at rest.

Adaptation, Physiological↗

PubMed2005

Interleukin-6 receptor expression in contracting human skeletal muscle: regulating role of IL-6.

Contracting muscle fibers produce and release IL-6, and plasma levels of this cytokine are markedly elevated in response to physical exercise. We recently showed autocrine regulation of IL-6 in human skeletal muscle in vivo and hypothesized that this may involve up-regulation of the IL-6 receptor. Therefore, we investigated IL-6 receptor regulation in response to exercise and IL-6 infusion in humans. Furthermore, using IL-6-deficient mice, we investigated the role of IL-6 in the IL-6 receptor response to exercise. Human skeletal muscle biopsies were obtained in relation to: 3 h of bicycle exercise and rest (n=6+5), or recombinant human IL-6 infusion (rhIL-6) or saline infusion (n=6+6). We further obtained skeletal muscle samples from IL-6 knockout (KO) mice and wild-type C57/BL-6 mice in response to a 1-h bout of exercise. In exercising human skeletal muscle, IL-6 receptor mRNA increased sixfold with a peak at 6 h postexercise. Detection of the IL-6 receptor protein by immunohistochemistry revealed a pronounced staining following exercise that was primarily located at the cell membrane of the muscle fibers, whereas muscle gp130 expression and plasma levels of soluble IL-6 receptor were unaffected. Infusion of rhIL-6 to humans had no effect on the mRNA level of the IL-6 receptor, whereas there was an increase at the protein level. IL-6 receptor mRNA increased similarly in muscle of both IL-6 KO mice and wild-type mice in response to exercise. In conclusion, exercise increases IL-6 receptor production in human skeletal muscle. This effect is most prominent 6 h after the end of the exercise bout, suggesting a postexercise-sensitizing mechanism to IL-6 when plasma IL-6 is concomitantly low. Exercise-induced increases in IL-6 receptor mRNA most likely occurs via an IL-6 independent mechanism as shown in IL-6 KO mice and the human rhIL-6 infusion study, whereas IL-6 receptor protein levels are responsive to elevated plasma IL-6 levels.

Adult↗

PubMed2005

TNF-alpha, but not IL-6, stimulates plasminogen activator inhibitor-1 expression in human subcutaneous adipose tissue.

Plasminogen activator inhibitor-1 (PAI-1) is produced by adipose tissue, and elevated PAI-1 levels in plasma are a risk factor in the metabolic syndrome. We investigated the regulatory effects of TNF-alpha and IL-6 on PAI-1 gene induction in human adipose tissue. Twenty healthy men underwent a 3-h infusion of either recombinant human TNF-alpha (n = 8), recombinant human IL-6 (n = 6), or vehicle (n = 6). Biopsies were obtained from the subcutaneous abdominal adipose tissue at preinfusion, at 1, 2, and 3 h during the infusion, and at 2 h after the infusion. The mRNA expression of PAI-1 in the adipose tissue was measured using real-time PCR. The plasma levels of TNF-alpha and IL-6 reached 18 and 99 pg/ml, respectively, during the infusions. During the TNF-alpha infusion, adipose PAI-1 mRNA expression increased 2.5-fold at 1 h, 6-fold at 2 h, 9-fold at 3 h, and declined to 2-fold 2 h after the infusion stopped but did not change during IL-6 infusion and vehicle. These data demonstrate that TNF-alpha rather than IL-6 stimulates an increase in PAI-1 mRNA in the subcutaneous adipose tissue, suggesting that TNF-alpha may be involved in the pathogenesis of related metabolic disorders.

Adipose Tissue↗

PubMed2005

Exercise-induced metallothionein expression in human skeletal muscle fibres.

Exercise induces free oxygen radicals that cause oxidative stress, and metallothioneins (MTs) are increased in states of oxidative stress and possess anti-apoptotic effects. We therefore studied expression of the antioxidant factors metallothionein I and II (MT-I + II) in muscle biopsies obtained in response to 3 h of bicycle exercise performed by healthy men and in resting controls. Both MT-I + II proteins and MT-II mRNA expression increased significantly in both type I and II muscle fibres after exercise. Moreover, 24 h after exercise the levels of MT-II mRNA and MT-I + II proteins were still highly increased and the MT-II mRNA expression reached a 15-fold increase. As expected, immunohistochemical detection of malondialdehyde (MDA) and nitrotyrosine (NITT) showed that formation of free radicals and oxidative stress were clearly increased in exercising muscle peaking shortly after the end of exercise in both type I and II muscle fibres. This is the first report demonstrating that MT-I + II are significantly induced in human skeletal muscle fibres following exercise. As MT-I + II are antioxidant factors that protect various tissues during pathological conditions, the MT-I + II increases post exercise may represent a mechanism whereby contracting muscle fibres are protected against cellular stress and injury.

Adult↗

PubMed2005

Leptin gene expression and systemic levels in healthy men: effect of exercise, carbohydrate, interleukin-6, and epinephrine.

Leptin, an adipose tissue-derived cytokine, is correlated with adipose mass as obese persons have increased levels of leptin that decrease with weight loss. Previous studies demonstrate that high-energy-expenditure exercise decreases circulating leptin levels, whereas low-energy-expenditure exercise has no effect. We aimed to test the hypothesis that acute exercise reduced leptin mRNA levels in human adipose tissue and that this effect would be ameliorated by carbohydrate supplementation. Because exercise markedly increases circulating IL-6 and epinephrine, we investigated whether the changes in leptin seen with acute exercise could be mediated by IL-6 or epinephrine infusion. Abdominal subcutaneous adipose tissue mRNA and plasma levels of leptin were measured in healthy men in response to 3-h ergometer exercise with or without carbohydrate (CHO) ingestion (n = 8) and in response to infusion with recombinant human (rh)IL-6 (n = 11) or epinephrine (n = 8) or saline. Plasma leptin declined in response to exercise (P < 0.05) compared with rest, whereas mRNA expression in adipose tissue was unaffected. The exercise-induced decrease in plasma leptin was attenuated by CHO ingestion (P < 0.001). A 3-h epinephrine infusion decreased plasma leptin (P < 0.001) to the same level seen with 3 h of exercise, whereas leptin levels were unaffected by rhIL-6 infusion. In conclusion, both acute exercise and epinephrine infusion decreased plasma leptin to a similar extent, whereas there was no effect with rhIL-6 infusion. Acute exercise solely affected leptin plasma levels, as mRNA levels were unchanged. The exercise-induced decrease in circulating leptin was counteracted by CHO ingestion, suggesting a posttranscriptional regulatory mechanism of leptin involving substrate availability.

Adipose Tissue↗

PubMed2004

Exercise induces interleukin-8 expression in human skeletal muscle.

Skeletal muscle has been recognized as an endocrine organ, and muscle cell cultures express several cytokines with potential hormonal effects. Interleukin-8 (IL-8), a chemokine, which induces angiogenesis, is expressed in working muscles; however, the cell source of origin has not been identified. We aimed to elucidate if IL-8 protein is: (1) expressed in contracting muscle fibres and (2) whether there is a release of IL-8 from exercising muscle. Seventeen healthy male volunteers were included in two independent protocols: 3 h of ergometer bicycle exercise at 60% of VO2,max (n = 6) or rest (n = 5), and 3 h of two-legged knee-extensor exercise at 60% of maximal workload (n = 6). Repetitive muscle biopsy samples were obtained from the vastus lateralis in all experiments. A marked increase in IL-8 mRNA was found in muscle biopsy samples obtained after exercise. A marked IL-8 protein expression was demonstrated within the cytoplasm of muscle fibres in biopsy samples obtained in the recovery phase following 3 h of bicycle exercise, and the peak occurred 3-6 h postexercise. A small transient net release of IL-8 from working muscle was found at 1.5 h of knee-extensor exercise. However, the small release of IL-8 from muscle did not result in an increase in the systemic plasma concentration of IL-8, suggesting that muscle-derived IL-8 may play a local role, e.g. in angiogenesis.

Adult↗

PubMed2004

Exercise normalises overexpression of TNF-alpha in knockout mice.

TNF-alpha is linked with insulin resistance, as greater amounts of TNF are detected in muscle and adipose tissue in glycemically challenged people and TNF-alpha inhibits insulin receptor signalling. However, what modulates this overexpression of TNF-alpha is currently unknown. We examined the effect of 1 h exercise on overexpression of the TNF-alpha gene in TNF receptor 1 and 2 knockout mice. IL-6 knockout mice were included to elucidate the importance of IL-6 in regulating TNF-alpha in response to exercise. TNF-alpha gene expression was over-expressed in muscle in both TNFR knockout models. TNF-alpha overexpression returned to normal levels after exercise in the TNF-alpha receptor knockout models. In IL-6 knockout mice, a modest decrease in TNF-alpha was also observed. These data suggest that TNF-alpha-induced insulin resistance can be regulated by a single exercise bout by normalising TNF-alpha expression. This exercise effect can be mediated via IL-6, but also an IL-6 independent mechanism seems to exist.

Adipose Tissue↗

PubMed2004

AMPK activity is diminished in tissues of IL-6 knockout mice: the effect of exercise.

Following exercise, AMP-activated protein kinase (AMPK) activity is increased several fold in rat liver and adipose tissue as well as muscle; however, the mechanism by which this occurs is not known. Interleukin-6 (IL-6) is released from muscle in large amounts during and after sustained physical activity resulting in up to 100-fold increases in its plasma concentration, from 1-2 ng/ml to 50-100 ng/ml. We report here that incubation with IL-6 (30-120 ng/ml) increases the phosphorylation of AMPK (an indicator of its activation) and that of its target molecule, acetyl CoA carboxylase (ACC), in both extensor digitorum longus muscle and cultured F422a adipocytes. To assess more directly whether IL-6 regulates AMPK in vivo during exercise, measurements were carried out in skeletal muscle, liver, and adipose tissue of 3-month-old IL-6 knockout (IL-6(-/-)) and C57 black control mice. In agreement with previous studies in the rat, in control mice P-AMPK and P-ACC abundance was increased by 30-150% in the three tissues in response to exercise with the greatest increases in skeletal muscle. In contrast, in IL-6(-/-) mice, we found that the abundance of both P-AMPK and P-ACC was lower (60-90%) in muscle and adipose tissue at rest. Also the absolute increases in P-AMPK caused by exercise were diminished compared to those in control mice, although percentage increases were similar. In liver, decreases in P-AMPK and P-ACC in the IL-6(-/-) mice were more modest and the increases in their abundance caused by exercise were indistinguishable from those of control mice. The results indicate that IL-6 can activate AMPK in muscle and adipose tissue, and that this contributes to, but does not fully account for, the increase in AMPK activity in these tissues in response to exercise. They also suggest that a genetic lack of IL-6 is associated with a decrease in AMPK activity.

AMP-Activated Protein Kinases↗

PubMed2004

Epinephrine infusion increases adipose interleukin-6 gene expression and systemic levels in humans.

Exercise increases IL-6 mRNA in subcutaneous adipose tissue; however, the immediate signal for the IL-6 induction is unknown. We, therefore, explored the possible role of epinephrine in the induction of IL-6 in adipose tissue. Subcutaneous adipose tissue biopsies and blood samples were obtained from eight healthy men (mean age 27 yr, mean height 184 cm, mean weight 83 kg) in response to epinephrine infusion or in response to saline infusion. The rate of epinephrine infusion was such that circulating epinephrine concentrations mimicked that typically seen during exercise. The level of IL-6 mRNA in subcutaneous adipose tissue increased 26-fold (95% confidence interval, 9- to 166-fold) at 3 h of epinephrine infusion compared with controls (P=0.028). In addition, plasma levels of IL-6 increased in response to epinephrine infusion (P <0.001). However, epinephrine did not affect the IL-6 receptor mRNA. In conclusion, epinephrine acutely increases IL-6 mRNA levels in subcutaneous adipose tissue as well as circulating IL-6 levels in healthy men.

Adaptation, Physiological↗

PubMed2004

Metabolic and hormonal interactions between muscle and adipose tissue.

From the perspective of a muscle physiologist, adipose tissue has long been perceived predominantly as a fuel reservoir that provides muscle and other tissues with NEFA when exogenous nutrients are insufficient for their energy needs. Recently, studies have established that adipose tissue is also an endocrine organ. Among the hormones it releases are adiponectin and leptin, both of which can activate AMP-activated protein kinase and increase fatty acid oxidation in skeletal muscle and probably other tissues. Deficiencies of leptin or leptin receptor, adiponectin and IL-6 are associated with obesity, insulin resistance and a propensity to type 2 diabetes. In addition, a lack of adiponectin has been linked to atherosclerosis. Whether this pathology reflects a deficient activation of AMP-activated protein kinase in peripheral tissues remains to be determined. Finally, recent studies have suggested that skeletal muscle may also function as an endocrine organ when it releases the cytokine IL-6 into the circulation during sustained exercise. Interestingly, one of the apparent effects of IL-6 is to stimulate lipolysis, causing the release of NEFA from the adipocyte. Thus, hormonal communications exist between the adipocyte and muscle that could enable them to talk to each other. The physiological relevance of this cross talk clearly warrants further study.

Adiponectin↗

PubMed2004

IL-6 mediates hypoferremia of inflammation by inducing the synthesis of the iron regulatory hormone hepcidin.

Hypoferremia is a common response to systemic infections or generalized inflammatory disorders. In mouse models, the development of hypoferremia during inflammation requires hepcidin, an iron regulatory peptide hormone produced in the liver, but the inflammatory signals that regulate hepcidin are largely unknown. Our studies in human liver cell cultures, mice, and human volunteers indicate that IL-6 is the necessary and sufficient cytokine for the induction of hepcidin during inflammation and that the IL-6-hepcidin axis is responsible for the hypoferremia of inflammation.

Anemia↗

PubMed2004

Glucose ingestion attenuates the exercise-induced increase in circulating heat shock protein 72 and heat shock protein 60 in humans.

Heat shock protein (Hsp) 72 is a cytosolic stress protein that is highly inducible by several factors including exercise. Hsp60 is primarily mitochondrial in cellular location, plays a key role in the intracellular protein translocation and cytoprotection, is increased in skeletal muscle by exercise, and is found in the peripheral circulation of healthy humans. Glucose deprivation increases Hsp72 in cultured cells, whereas reduced glycogen availability elevates Hsp72 in contracting human skeletal muscle. To determine whether maintained blood glucose during exercise attenuates the exercise-induced increase in intramuscular and circulating Hsp72 and Hsp60, 6 males performed 120 minutes of semirecumbent cycling at approximately 65% maximal oxygen uptake on 2 occasions while ingesting either a 6.4% glucose (GLU) or sweet placebo (CON) beverage throughout exercise. Muscle biopsies, obtained before and immediately after exercise, were analyzed for Hsp72 and Hsp60 protein expression. Blood samples were simultaneously obtained from a brachial artery, a femoral vein, and the hepatic vein before and during exercise for the analysis of serum Hsp72 and Hsp60. Leg and hepatosplanchnic blood flow were measured to determine Hsp72-Hsp60 flux across these tissue beds. Neither exercise nor glucose ingestion affected the Hsp72 or Hsp60 protein expression in, or their release from, contracting skeletal muscle. Arterial serum Hsp72 increased (P < 0.05) throughout exercise in both trials but was attenuated (P < 0.05) in GLU. This may have been in part because of the increased (P < 0.05) hepatosplanchnic Hsp72 release in CON, being totally abolished (P < 0.05) in GLU. Serum Hsp60 increased (P < 0.05) after 60 minutes of exercise in CON before returning to resting levels at 120 minutes. In contrast, no exercise-induced increase in serum Hsp60 was observed in GLU. We detected neither hepatosplanchnic nor contracting limb Hsp60 release in either trial. In conclusion, maintaining glucose availability during exercise attenuates the circulating Hsp response in healthy humans.

Adult↗

PubMed2004

Does the aging skeletal muscle maintain its endocrine function?

Contracting skeletal muscles produce and release the cytokine interleukin (IL)-6 and this release is augmented by the presence of low muscle glycogen. Since muscle metabolism in elderly subjects relies on glycogen more than younger subjects, it is possible that aging is associated with an altered production of muscle-derived IL-6 during exercise. To test the relation between aging and muscle-derived IL-6, seven healthy elderly males, mean age 70+/-1 (SEM) yr and six healthy young males, mean age 26+/-2 (SEM) yr performed three hours of dynamic knee-extensor exercise at 50% of maximal work load (Wmax). IL-6 mRNA and glycogen in muscles were analysed and the IL-6 release were estimated before, during and after the exercise. Although the absolute work load in the elderly was less than half of that in the young, 41.1+/-3.1 W and 92.5+/-4.0 W, respectively, the muscle glycogen utilization after three hours of exercise did not differ between groups, 238.7+/-52.4 and 245.2+/-74.0 mmol/kg muscle in elderly and young, respectively. This could explain that the IL-6 release and the IL-6 mRNA amplification increased during exercise with no difference between groups, two-way ANOVA-P = 0.50 and 0.45, respectively. In conclusion, elderly healthy people maintain the capacity to produce and release IL-6 in response to dynamic exercise, with no difference compared to young individuals furthermore, glycogen utilization expressed in changes of glycogen related to muscle mass was equal in elderly and young subject at 50 % of Wmax.

Adult↗

PubMed2003

Interleukin-6 production by contracting human skeletal muscle: autocrine regulation by IL-6.

Interleukin-6 (IL-6) is a cytokine with immuno-regulatory functions. However, contracting skeletal muscle expresses and subsequently releases IL-6 in high amounts, and recent evidence in IL-6 deficient mice suggests a role of IL-6 in metabolism. Since IL-6 mRNA levels also increase in abdominal adipose tissue in response to exercise, we wanted to examine the possible existence of a positive feedback mechanism between muscle and adipose tissue. We obtained biopsies from human skeletal muscle and abdominal subcutaneous adipose tissue in relation to either 3h of bicycle exercise or recombinant human IL-6 infusion (rhIL-6) or saline infusion. In muscle, IL-6 mRNA increased (p<0.05) immediately after exercise, peaking at this time-point, whereas IL-6 mRNA in adipose tissue increased 1.5-h post exercise (p<0.05) displaying a different kinetic of induction. During rhIL-6 infusion, IL-6 mRNA increased 120-fold in muscle (p<0.05). In conclusion, the present study demonstrates that muscle IL-6 is regulated by an autocrine mechanism at the transcriptional level.

Adipose Tissue↗

PubMed2003

Insulin stimulates interleukin-6 and tumor necrosis factor-alpha gene expression in human subcutaneous adipose tissue.

High circulating levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) are found in patients with hyperinsulinemia. Insulin stimulates release of IL-6 from adipocyte cultures, and it stimulates IL-6 gene expression in insulin-resistant, but not control, rat skeletal muscle. In addition, TNF-alpha may be involved in the pathogenesis of insulin resistance. Therefore, we studied the effect of insulin on IL-6 and TNF-alpha gene expression in human skeletal muscle and adipose tissue. Nine healthy young volunteers participated in the study. They underwent a 6-h hyperinsulinemic euglycemic clamp at a fixed insulin infusion rate, with blood glucose clamped at fasting level. Blood samples drawn at 0, 1, 2, 3, 4, 5, and 6 h were analyzed for IL-6 and TNF-alpha. Muscle and fat biopsies, obtained at 0, 2, 4, and 6 h, were analyzed for IL-6 and TNF-alpha mRNA with real-time PCR. IL-6 mRNA increased 11-, 3-, and 5-fold at 2, 4, and 6 h, respectively, in adipose tissue (ANOVA P = 0.027), whereas there was no significant effect of insulin on skeletal muscles. Plasma IL-6 increased during insulin stimulation. TNF-alpha mRNA increased 2.4-, 1.4-, and 2.2-fold in adipose tissue (ANOVA P = 0.001) and decreased 0.74-, 0.64-, and 0.68-fold in muscle tissue (ANOVA P = 0.04). Plasma levels of TNF-alpha were constant. In conclusion, the finding that insulin stimulates IL-6 and TNF-alpha gene expression in adipose tissue only and inhibits the TNF-alpha production in skeletal muscles suggests a differential regulation of muscle- and adipose tissue-derived IL-6 and TNF-alpha.

Adipose Tissue↗