Relationships between inflammatory and metabolic markers, exercise, and body composition in young individuals.

BACKGROUND AND AIMS: Physical exercise may help combat disease and elicits a possible "protective" anti-inflammatory effect on the body. Inflammatory cytokines, C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-α (TNFα), along with transcription factor, nuclear factor-kappa B (NFκB) in young (n=16, 21.1±2.1 years) individuals were examined in a cross-sectional descriptive study, to assess the effects of chronic stimulation on their expression and relationship with health parameters. METHODS: Fasting venous whole blood and lipid levels along with body composition measurements were obtained from young, healthy, endurance-trained NCAA Division III student-athletes and untrained individuals. Assays (ELISA) were conducted to analyze fasting plasma (CRP, IL-6, and TNFα) and isolated lymphocyte NF-κB activation (lymphocytes were isolated from whole blood samples through differential centrifugation and Ficoll-Paque). A Spearman's rank order correlation coefficient was used for associations between variables and a regression analysis was performed to determine which measurement accounted for the inflammation in this young and apparently healthy population. RESULTS: While the inflammatory markers were not associated with each other, CRP levels were associated with body composition and following regression analyses, body fat percentage (P>0.05) was a significant factor for elevated CRP. CONCLUSIONS: Chronic physical exercise eliciting lower body fat percentages in young adults may have a positive protective impact through anti-inflammatory status, minimizing disease risk in a young population. RELEVANCE FOR PATIENTS: Chronic physically active young adult patients may exhibit less inflammation and lower body fat levels which may decrease their risk for chronic disease.

The effect of a lifestyle intervention on metabolic health in young women.

With the increasing obesity rates in Western countries, an effective lifestyle intervention for fat reduction and metabolic benefits is needed. High-intensity intermittent exercise (HIIE), Mediterranean eating habits (Mediet), and fish oil (ω-3) consumption positively impact metabolic health and adiposity, although the combined effect has yet to be determined. A 12-week lifestyle intervention on adiposity, insulin resistance, and interleukin-6 (IL-6) levels of young overweight women was administered. Thirty women with a body mass index of 26.6±0.5 kg/m(2), blood pressure of 114/66±1.9/1.5 mmHg, and age of 22±0.8 years were randomly assigned to either an intervention group receiving Mediet advice, daily ω-3 supplementation, and HIIE 3 days/week for 12 weeks or a control group. The group receiving Mediet advice, daily ω-3 supplementation, and HIIE experienced a significant reduction in total body fat mass (P<0.001), abdominal adiposity (P<0.05), waist circumference (P<0.001), systolic blood pressure (P<0.05), fasting plasma insulin (P<0.05), IL-6 (P<0.001), and triglycerides (P<0.05). The greatest decreases in fasting plasma insulin (P<0.05) and IL-6 (P<0.001) occurred by week 6 of the intervention. Significant improvements in eating habits (P<0.05) and aerobic fitness (P<0.001) were also found following the intervention. A multifaceted 12-week lifestyle program comprising a Mediet, ω-3 supplementation, and HIIE induced significant improvements in fat loss, aerobic fitness, and insulin and IL-6 levels, positively influencing metabolic health.

Regional adiposity distribution and insulin resistance in young Chinese and European Australian women.

OBJECTIVE: Lower than normal leg fat mass and excessive trunk fat mass are predictive of insulin resistance (IR) in obese women of European descent. Whether this regional adiposity relationship applies to moderately overweight women of Chinese descent is undetermined. Thus, the relationship between leg and trunk fat mass and IR of young (22.3 ± 0.3 years) sedentary Australian women of either Chinese (CW; n = 22) or European (EW; n = 36) descent was examined. MATERIAL AND METHODS: Subjects underwent a maximal oxygen uptake test, blood draw, and dual energy x-ray absorptiometry to measure body composition. Fasting insulin levels and C-reactive protein (CRP) were assessed by ELISA and IR was calculated by HOMA-IR. Blood lipids and glucose were quantified by an automated enzymatic method (Cholestech LDX, USA). RESULTS: Total, arm, trunk, and leg fat was significantly greater (p < 0.05) for the EW group, whereas IR was significantly higher for CW. Fasting lipids and glucose were within normal levels for both groups, whereas CRP levels were significantly higher in EW. For EW trunk fat mass was the only variable significantly correlated with IR (r = 0.40, p < 0.05). In contrast, for CW leg fat mass was significantly correlated with IR (r = − 0.49, p < 0.05). CONCLUSIONS: Greater trunk fat mass was associated with higher IR of Australian women of European descent, whereas smaller leg fat mass was associated with higher IR of women of Chinese descent.

Phosphorylation of Irs1 at SER-522 inhibits insulin signaling.

Multisite phosphorylation of Irs1 on serine and threonine residues regulates insulin signaling that can contribute to insulin resistance. We identified by mass spectrometry the phosphorylation of Ser522 in rat Irs1 (S522(Irs1)). The functional effects of this phosphorylation site were investigated in cultured cells using a sequence-specific phosphoserine antibody. Insulin stimulated the phosphorylation of S522(Irs1) in L6 myoblasts and myotubes. S522(Irs1) phosphorylation was inhibited by wortmannin, whereas PD98059, rapamycin, or glucose-starvation had no effect. Reducing Akt expression with small interfering RNA inhibited insulin-stimulated phosphorylation of S522(Irs1), suggesting the involvement of the phosphatidylinositol 3-kinase--> Akt cascade. A S522(Irs1)-->A522(Irs1) substitution increased insulin-stimulated tyrosine phosphorylation of Irs1 and signaling, whereas a S522(Irs1)-->E522(Irs1) substitution reduced insulin-stimulated Irs1 tyrosine phosphorylation. Together, these results suggest the phosphatidylinositol 3-kinase-->Akt cascade can inhibit insulin signaling through the phosphorylation of S522(Irs1).

The reciprocal stability of FOXO1 and IRS2 creates a regulatory circuit that controls insulin signaling.

The transcription factor FoxO1 links the phosphatidylinositol 3-kinase (PI 3-kinase) --> Akt cascade to gene expression that regulates cell growth, survival, and metabolism. The receptors for insulin and IGFs factors are linked to this pathway through tyrosine phosphorylation of insulin receptor substrates-Irs1, 2, 3, and 4. However, it is unclear why Irs2 signaling predominates in certain tissues, including pancreatic beta cells, dermal fibroblasts, photoreceptors, central neurons, and metastatic mammary tumor cells. We used wild-type mouse embryo fibroblasts (MEFs)-and Irs1(-/-) or Irs2(-/-) MEFs-to establish the relation between Irs1, Irs2, and FoxO during insulin signaling. PI 3-kinase associated with Irs1 and Irs2 during insulin stimulation of wt MEFs, which strongly promoted Akt and FoxO phosphorylation, led to FoxO nuclear exclusion and degradation. However, insulin failed to activate the Akt--> FoxO cascade in Irs2(-/-) MEFs because Irs1 expression was reduced in these cells, and p110alpha-PI 3-kinase was inefficiently activated during recruitment by Irs1. By contrast, insulin stimulation of Irs1(-/-) MEFs caused FoxO degradation, not only because Irs2 expression increased but also because Irs2 efficiently activated p110alpha--> Akt cascade. Importantly, prolonged insulin stimulation restored FoxO1 expression in wild-type or Irs1(-/-) MEFs because Irs2 was degraded and Irs1 alone failed to activate sufficient p110alpha to promote the Akt--> FoxO cascade. Inhibition of Irs2 degradation with rapamycin caused persistent FoxO degradation even during prolonged insulin stimulation. The dynamic relation between Irs2 and FoxO expression, compared with the subordinate role of Irs1, can explain the dominant role of Irs2 in metabolic regulation.

Feedback inhibition of leptin receptor/Jak2 signaling via Tyr1138 of the leptin receptor and suppressor of cytokine signaling 3.

Leptin is an adipocyte-derived hormone that communicates the status of body energy stores to the brain to regulate feeding and energy balance. The inability of elevated leptin levels to adequately suppress feeding in obesity suggests attenuation of leptin action under these conditions; the activation of feedback circuits due to high leptin levels could contribute to this leptin resistance. Using cultured cells exogenously expressing the long form of the leptin receptor (LRb) or an erythropoietin receptor/LRb chimera, we show that chronic stimulation results in the attenuation of LRb signaling and the establishment of a state in which the receptor is refractory to reactivation. Mutation of LRb Tyr1138 (the site that recruits signal transducer and activator of transcription 3) alleviated this feedback inhibition, suggesting that signal transducer and activator of transcription 3 mediates the induction of a feedback inhibitor, such as suppressor of cytokine signaling 3 (SOCS3), during chronic LRb stimulation. Indeed, manipulation of the expression or activity of the LRb-binding tyrosine phosphatase, SH2-domain containing phosphatase-2, by overexpression of wild-type and dominant negative isoforms or RNA interference-mediated knockdown did not alter the attenuation of LRb signals. In contrast, SOCS3 overexpression repressed LRb signaling, whereas RNA interference-mediated knockdown of SOCS3 resulted in increased LRb signaling that was not attenuated during chronic ligand stimulation. These data suggest that Tyr1138 of LRb and SOCS3 represent major effector pathways for the feedback inhibition of LRb signaling. Furthermore, we show that mice expressing an LRb isoform mutant for Tyr1138 display increased activity of the leptin-dependent growth and immune axes, suggesting that Tyr1138-mediated feedback inhibition may regulate leptin sensitivity in vivo.

Tyrosine phosphorylation of Jak2 in the JH2 domain inhibits cytokine signaling.

Jak family tyrosine kinases mediate signaling by cytokine receptors to regulate diverse biological processes. Although Jak2 and other Jak kinase family members are phosphorylated on numerous sites during cytokine signaling, the identity and function of most of these sites remains unknown. Using tandem mass spectroscopic analysis of activated Jak2 protein from intact cells, we identified Tyr(221) and Tyr(570) as novel sites of Jak2 phosphorylation. Phosphorylation of both sites was stimulated by cytokine treatment of cultured cells, and this stimulation required Jak2 kinase activity. While we observed no gross alteration of signaling upon mutation of Tyr(221), Tyr(570) lies within the inhibitory JH2 domain of Jak2, and mutation of this site (Jak2(Y570F)) results in constitutive Jak2-dependent signaling in the absence of cytokine stimulation and enhances and prolongs Jak2 activation during cytokine stimulation. Mutation of Tyr(570) does not alter the ability of SOCS3 to bind or inhibit Jak2, however. Thus, the phosphorylation of Tyr(570) in vivo inhibits Jak2-dependent signaling independently of SOCS3-mediated inhibition. This Tyr(570)-dependent mechanism of Jak2 inhibition likely represents an important mechanism by which cytokine function is regulated.

Regulation of Jak kinases by intracellular leptin receptor sequences.

Leptin signals the status of body energy stores via the leptin receptor (LR), a member of the Type I cytokine receptor family. Type I cytokine receptors mediate intracellular signaling via the activation of associated Jak family tyrosine kinases. Although their COOH-terminal sequences vary, alternatively spliced LR isoforms (LRa-LRd) share common NH(2)-terminal sequences, including the first 29 intracellular amino acids. The so-called long form LR (LRb) activates Jak-dependent signaling and is required for the physiologic actions of leptin. In this study, we have analyzed Jak activation by intracellular LR sequences under the control of the extracellular erythropoeitin (Epo) (Epo receptor/LRb chimeras). We show that Jak2 is the requisite Jak kinase for signaling by the LRb intracellular domain and confirm the requirement for the Box 1 motif for Jak2 activation. A minimal LRb intracellular domain for Jak2 activation includes intracellular amino acids 31-48. Although the sequence requirements for intracellular amino acids 37-48 are flexible, intracellular amino acids 31-36 of LRb play a critical role in Jak2 activation and contain a loose homology motif found in other Jak2-activating cytokine receptors. The failure of short form sequences to function in Jak2 activation reflects the absence of this motif.

Activation of astrocyte intracellular signaling pathways by interleukin-1 in rat primary striatal cultures.

The striatum has been implicated as the site of action mediating neurotoxic effects of interleukin-1 (IL-1) during ischemia. However, the molecular mechanisms underlying these events have yet to be fully addressed. In the present study, primary cultures of rat striatal cells were used as a model for the study of IL-1 signaling pathways in the striatum. Immunocytochemical analyses revealed that these cultures consisted of a mixture of neurones and astrocytes and demonstrated expression of the IL-1 type I receptor (IL-1RI) on both cell types. Treatment with IL-1 (3 units/ml) for 10 min increased phosphorylation of p38 MAP kinase in striatal cells. The endogenous IL-1RI inhibitor IL-1Ra (24 ng/ml) and the p38 MAP kinase inhibitor SB203580 (10 nM) both inhibited this response. Analysis of the effects of IL-1 on nuclear translocation of the transcription factor NF-kB revealed that NF-kB became activated in a time-dependent manner. Immunocytochemistry revealed that IL-1 stimulated p38 phosphorylation and NF-kB translocation in astrocytes only. TaqMan real-time quantitative PCR analysis revealed that IL-1 stimulated gene expression of tumor necrosis factor-alpha (TNF) in striatal cultures. The p38 MAP kinase inhibitor SB203580 failed to inhibit the effects of IL-1 on NF-kB translocation or gene transcription. These studies have demonstrated significant aspects of the IL-1 signaling cascade in cultured striatum. Of particular interest is the finding that IL-1 stimulated activation of p38 MAP kinase and NF-kB in striatal astrocytes exclusively.