Leptin-deficient Obese Mice Research Articles

Leptin deficiency-induced obesity exacerbates ultraviolet B radiation-induced cyclooxygenase-2 expression and cell survival signals in ultraviolet B-irradiated mouse skin

Obesity has been implicated in several inflammatory diseases and in different types of cancer. Chronic inflammation induced by exposure to ultraviolet (UV) radiation has been implicated in various skin diseases, including melanoma and nonmelanoma skin cancers. As the relationship between obesity and susceptibility to UV radiation-caused inflammation is not clearly understood, we assessed the role of obesity on UVB-induced inflammation, and mediators of this inflammatory response, using the genetically obese (leptin-deficient) mouse model. Leptin-deficient obese (ob/ob) mice and wild-type counterparts (C57/BL6 mice) were exposed to UVB radiation (120 mJ/cm 2) on alternate days for 1 month. The mice were then euthanized and skin samples collected for analysis of biomarkers of inflammatory responses using immunohistochemistry, western blotting, ELISA and real-time PCR. Here, we report that the levels of inflammatory responses were higher in the UVB-exposed skin of the ob/ob obese mice than those in the UVB-exposed skin of the wild-type non-obese mice. The levels of UVB-induced cyclooxygenase-2 expression, prostaglandin-E 2 production, proinflammatory cytokines ( i.e., tumor necrosis factor-α, interleukin-1β, interleukin-6), and proliferating cell nuclear antigen and cell survival signals (phosphatidylinositol-3-kinase and p-Akt-Ser 473) were higher in the skin of the ob/ob obese mice than the those in skin of their wild-type non-obese counterparts. Compared with the wild-type non-obese mice, the leptin-deficient obese mice also exhibited greater activation of NF-κB/p65 and fewer apoptotic cells in the UVB-irradiated skin. Our study suggests for the first time that obesity in mice is associated with greater susceptibility to UVB-induced inflammatory responses and, therefore, obesity may increase susceptibility to UVB-induced inflammation-associated skin diseases, including the risk of skin cancer.

Fat and Water 1H MRI to Investigate Effects of Leptin in Obese Mice

Leptin is known to be associated with regulation of body weight and fat content. The effects of exogenous leptin on abdominal visceral (VS) and subcutaneous (SC) fat volume and hepatic fat-to-water ratio in leptin-deficient obese mice were investigated by (1)H magnetic resonance imaging (MRI). Chemical shift-selected fat and water (1)H MRI of control and leptin-treated mice were obtained 1 day before treatment and after 7 days of treatment (0.3 mg/kg/day). Hepatic fat-to-water ratio and VS fat volume decreased significantly with treatment, whereas SC fat volume did not change. Noninvasive measurement of fat and water content in different body regions using MRI should prove useful for evaluating new drugs for the treatment of obesity and other metabolic disorders.

Contribution of animal models to the understanding of the metabolic syndrome: a systematic overview

The metabolic syndrome (MetS) is one of the most important challenges to public health and biomedical research. Animal models of MetS, such as leptin-deficient obese mice, obese spontaneously hypertensive rats, JCR: LA-cp rats and the Ossabaw and Göttingen minipigs, have contributed to our understanding of the pathophysiological basis and the development of novel therapies. For a complex disease syndrome, no animal model can be expected to serve all needs of research. Although each animal model has limitations and strengths, used together in a complementary fashion, they are essential for research on the MetS and for rapid progress in understanding the aetiology and pathogenesis towards a cure. The purpose of this review is to assess how current animal models contributed to our knowledge of the human MetS, and to systematically evaluate the strengths and weaknesses of the currently available 78 animal models from 11 species.

A very low carbohydrate ketogenic diet improves glucose tolerance inob/obmice independently of weight loss

In mice of normal weight and with diet-induced obesity, a high-fat, low-carbohydrate ketogenic diet (KD) causes weight loss, reduced circulating glucose and lipids, and dramatic changes in hepatic gene expression. Many of the effects of KD are mediated by fibroblast growth factor 21 (FGF21). We tested the effects of KD feeding on ob/ob mice to determine if metabolic effects would occur in obesity secondarily to leptin deficiency. We evaluated the effect of prolonged KD feeding on weight, energy homeostasis, circulating metabolites, glucose homeostasis, and gene expression. Subsequently, we evaluated the effects of leptin and fasting on FGF21 expression in ob/ob mice. KD feeding of ob/ob mice normalized fasting glycemia and substantially reduced insulin and lipid levels in the absence of weight loss. KD feeding was associated with significant increases in lipid oxidative genes and reduced expression of lipid synthetic genes, including stearoyl-coenzyme A desaturase 1, but no change in expression of inflammatory markers. In chow-fed ob/ob mice, FGF21 mRNA was elevated 10-fold compared with wild-type animals, and no increase from this elevated baseline was seen with KD feeding. Administration of leptin to chow-fed ob/ob mice led to a 24-fold induction of FGF21. Fasting also induced hepatic FGF21 in ob/ob mice. Thus, KD feeding improved ob/ob mouse glucose homeostasis without weight loss or altered caloric intake. These data demonstrate that manipulation of dietary macronutrient composition can lead to marked improvements in metabolic profile of leptin-deficient obese mice in the absence of weight loss.

Rutecarpine ameliorates bodyweight gain through the inhibition of orexigenic neuropeptides NPY and AgRP in mice

Orexigenic neuropeptides NPY and AgRP play major roles in feeding and are closely related to obesity and diabetic metabolic syndrome. This study explored the inhibitory effect of rutecarpine on feeding and obesity in high-fat-diet-induced (C57BL/6) and leptin-deficient (ob/ob) obese mice. Both mice strains developed obesity, but the obesity was inhibited by the reduced food intake resulting from rutecarpine treatment (0.01%, p < 0.01). Blood cholesterol, non-fasting glucose, insulin, and leptin levels were reduced, compared with the control group. Rutecarpine inhibited the expression of NPY and AgRP in the arcuate nucleus (ARC) of the hypothalamus and suppressed the expression of both neuropeptides in N29-4 neuronal cells. These results indicate that rutecarpine ameliorates obesity by inhibiting food intake, which involves inhibited expression of the orexigenic neuropeptides NPY and AgRP.

Reducing glycosphingolipid content in adipose tissue of obese mice restores insulin sensitivity, adipogenesis and reduces inflammation

Adipose tissue is a critical mediator in obesity-induced insulin resistance. Previously we have demonstrated that pharmacological lowering of glycosphingolipids and subsequently GM3 by using the iminosugar AMP-DNM, strikingly improves glycemic control. Here we studied the effects of AMP-DNM on adipose tissue function and inflammation in detail to provide an explanation for the observed improved glucose homeostasis. Leptin-deficient obese (LepOb) mice were fed AMP-DNM and its effects on insulin signalling, adipogenesis and inflammation were monitored in fat tissue. We show that reduction of glycosphingolipid biosynthesis in adipose tissue of LepOb mice restores insulin signalling in isolated ex vivo insulin-stimulated adipocytes. We observed improved adipogenesis as the number of larger adipocytes was reduced and expression of genes like peroxisome proliferator-activated receptor (PPAR) γ, insulin responsive glucose transporter (GLUT)-4 and adipsin increased. In addition, we found that adiponectin gene expression and protein were increased by AMP-DNM. As a consequence of this improved function of fat tissue we observed less inflammation, which was characterized by reduced numbers of adipose tissue macrophages (crown-like structures) and reduced levels of the macrophage chemo attractants monocyte-chemoattractant protein-1 (Mcp-1/Ccl2) and osteopontin (OPN). In conclusion, pharmacological lowering of glycosphingolipids by inhibition of glucosylceramide biosynthesis improves adipocyte function and as a consequence reduces inflammation in adipose tissue of obese animals.

Ventilatory responses to chronic intracerebroventricular leptin injections in obese leptin‐deficient mice

Previous studies suggest that leptin may play an important role in the regulation of respiratory function. Obese leptin deficient mice (ob/ob) exhibit ventilatory depression when subjected to hipercarbic condition (high CO2). However, how leptin regulates pulmonary function is still unclear. We hypothesized that leptin modulates pulmonary function by acting on chemoreceptors in the brainstem. We evaluated pulmonary ventilation (VE), tidal volume (VT) and ventilatory rate (fR) of ob/ob mice under hipercarbic conditions before and after a 4‐day leptin or vehicle treatment regimen (4th ventricle injections at 10 ?g/2 ?l, n=7/group). We also determined the presence of leptin receptor protein (OB‐R) in brainstem nuclei by the imunohistochemistry. Our results demonstrate that VE (ml.kg−1.min−1) and VT (ml.kg−1) increased significantly after leptin treatment (from 3,372 ± 364 to 6,176 ± 347 and from 9.7 ± 0.9 to 16.7 ± 0.8, respectively). Leptin treatment did not alter fR. These variables were not affected by vehicle treatment. OB‐R staining was observed in various brainstem nuclei associated with the control of respiratory function, including: nucleus of the tractus solitarii, locus coeruleus, raphe nucleus and facial nucleus. These results suggest that leptin may be a powerful stimulator of the ventilatory responses by acting directly in brainstem sites responsible for the control of respiratory function.

Reducing Glycosphingolipid Content in Adipose Tissue of Obese Mice Restores Insulin Sensitivity, Adipogenesis and Reduces Inflammation

Adipose tissue is a critical mediator in obesity-induced insulin resistance. Previously we have demonstrated that pharmacological lowering of glycosphingolipids and subsequently GM3 by using the iminosugar AMP-DNM, strikingly improves glycemic control. Here we studied the effects of AMP-DNM on adipose tissue function and inflammation in detail to provide an explanation for the observed improved glucose homeostasis. Leptin-deficient obese (LepOb) mice were fed AMP-DNM and its effects on insulin signalling, adipogenesis and inflammation were monitored in fat tissue. We show that reduction of glycosphingolipid biosynthesis in adipose tissue of LepOb mice restores insulin signalling in isolated ex vivo insulin-stimulated adipocytes. We observed improved adipogenesis as the number of larger adipocytes was reduced and expression of genes like peroxisome proliferator-activated receptor (PPAR) γ, insulin responsive glucose transporter (GLUT)-4 and adipsin increased. In addition, we found that adiponectin gene expression and protein were increased by AMP-DNM. As a consequence of this improved function of fat tissue we observed less inflammation, which was characterized by reduced numbers of adipose tissue macrophages (crown-like structures) and reduced levels of the macrophage chemo attractants monocyte-chemoattractant protein-1 (Mcp-1/Ccl2) and osteopontin (OPN). In conclusion, pharmacological lowering of glycosphingolipids by inhibition of glucosylceramide biosynthesis improves adipocyte function and as a consequence reduces inflammation in adipose tissue of obese animals.

In vivo assessment of hepatic triglycerides in murine non-alcoholic fatty liver disease using magnetic resonance spectroscopy

In vivo 1H magnetic resonance spectroscopy (MRS) was used to examine the progression of fatty liver in two murine models of progressive hepatic steatosis: leptin-deficient obese ( ob/ob) mice and mice maintained on a diet deficient in methionine and choline (MCDD). Ob/ob mice displayed high levels of intracellular hepatic triglycerides as early as 9 weeks after birth, as observed with MRS and histopathology. Single voxel spectra of ob/ob liver displayed strong resonances arising from saturated (1.3 ppm) and unsaturated (2.8 and 5.3 ppm) fatty acyl chains that could be resolved in the absence of water suppression. Hepatic inflammation, induced by lipopolysaccharide administration, led to a significant increase in unsaturated and polyunsaturated fatty acyl chain resonances ( P < 0.05), indicating a change in the composition of hepatic triglycerides in lipid droplets. Mice maintained on the MCDD displayed histological evidence of hepatic steatosis as early as two weeks, progressing to macrovesicular steatohepatitis at 10 weeks. The histological changes were accompanied by significant increases in saturated and unsaturated fatty acyl chain resonances and a significant decrease in the lipid/(water + lipid) ratio ( P < 0.05). These results indicate that in vivo 1H MRS may be a suitable method to monitor the progression of steatohepatitis.

F009 Role of protein phophatases in the loss of cardioprotection against myocardial infarction by ischemic postconditioning in obese ob/ob mice

Ischemic postconditioning (IPCD) has been shown to reduce myocardial infarct size through activation of survival kinases such as Akt, ERK 1/2 as well as their common target p70S6K1, and AMPK during the early minutes of reperfusion. However, most of these results were obtained using “healthy” animals and the state of corresponding phosphatases has never been investigated in the contexte of obesity. Thus, the aims of this study were to establish whether the efficiency of IPCD is maintained in obese heart and to explore kinases but also phosphatases in this context. The effects of IPCD were investigated in 8-10 weeks old leptin-deficient obese (ob/ob) mice and C57BL/6J (WT) mice wereused as control. All animals underwent 30 min of coronary artery occlusion followed by 24 h of reperfusion associated or not with IPCD (6 cycles of 10 s occlusion/10 s reperfusion). Additional mice were sacrificed at 10 min of reperfusion for western blot analysis of P-Akt, P-ERK 1/2, P-p70S6K1, P-AMPK and the respective phosphatases PTEN, PP2C and MKP-3. In WT mice, IPCD reduced infarct size by 58 % (33±1 % vs 14±3 % for control and IPCD, respectively, p<0.05) and simultaneously increased the phosphorylated forms of Akt, ERK 1/2, p70S6K1 and AMPK but decreased cytosolic PTEN, MKP-3 and PP2C levels. In contrast, in ob/ob mice, IPCD failed to induce cardioprotection (53±4 % vs 56±5 % for infarct sizes in control and IPCD, respectively) and did not increase the phosphorylation state of all these kinases. Interestingly, the level of these coresponding phosphatases were simultaneously increased. Although IPCD reduces myocardial infarct size in healthy animals, its cardioprotective effect vanishes with obesity. The increase in PTEN, MKP-3 and PP2C levels might partly explain the lack of enhanced phosphorylation by IPCD of Akt, ERK1/2, p70S6K1 or AMPK and therefore, the loss of cardioprotection in this experimental model of obesity.

Leptin attenuates cardiac apoptosis after chronic ischaemic injury

We have previously shown that activation of leptin signalling in the heart reduces cardiac morbidity and mortality after myocardial infarction (MI). In the present study, we tested the hypothesis that leptin signalling limits cardiac apoptosis after MI through activation of signal transducer and activator of transcription (STAT)-3 responsive anti-apoptotic genes, including B-cell lymphoma (bcl)-2 and survivin, that serve to downregulate the activity of caspase-3. Hearts from C57BL/6J and three groups of leptin-deficient Ob/Ob mice (food-restricted, ad libitum, and leptin-repleted) were examined 4 weeks after permanent left coronary artery ligation or sham operation. Inflammatory and apoptotic cell number was determined in cardiac sections by immunostaining. Expression of cardiac bcl-2, survivin, and pro and active caspase-3 was determined and correlated with in vitro caspase-3 activity. In the absence of MI, both lean and obese leptin-deficient mice exhibited increased cardiac apoptosis compared with wild-type mice. After MI, the highest rates of apoptosis were seen in the infarcted tissue of lean and obese Ob/Ob mice. Further, leptin-deficient hearts, as well as hearts from wild-type mice treated with the STAT-3 inhibitor WP1066, exhibited blunted anti-apoptotic bcl-2 and survivin gene expression, and increased caspase-3 protein expression and activity. The increased caspase-3 activity and apoptosis in hearts of leptin-deficient mice after MI was significantly attenuated in Ob/Ob mice replete with leptin, reducing apoptosis to levels comparable to that observed in wild-type mice after MI. These results demonstrate that intact leptin signalling post-MI acts through STAT-3 to increase anti-apoptotic bcl-2 and survivin gene expression and reduces caspase-3 activity, consistent with a cardioprotective role of leptin in the setting of chronic ischaemic injury.

Enhanced Orexin Receptor-2 Signaling Prevents Diet-Induced Obesity and Improves Leptin Sensitivity

The hypothalamic orexin neuropeptide acutely promotes appetite, yet orexin deficiency in humans and mice is associated with obesity. Prolonged effects of increased orexin signaling upon energy homeostasis have not been fully characterized. Here, we examine the metabolic effects of orexin gain of function utilizing genetic and pharmacologic techniques in mice. Transgenic orexin overexpression confers resistance to high-fat diet-induced obesity and insulin insensitivity by promoting energy expenditure and reducing consumption. Genetic studies indicate that orexin receptor-2 (OX2R), rather than OX1R signaling, predominantly mediates this phenotype. Likewise, prolonged central administration of an OX2R-selective peptide agonist inhibits diet-induced obesity. While orexin overexpression enhances the anorectic-catabolic effects of central leptin administration, obese leptin-deficient mice are completely resistant to the metabolic effects of orexin overexpression or OX2R agonist infusion. We conclude that enhanced orexin-OX2R signaling confers resistance to diet-induced features of the metabolic syndrome through negative energy homeostasis and improved leptin sensitivity.

Sleep Modulates Hypertension in Leptin-Deficient Obese Mice

Leptin increases sympathetic activity, possibly contributing to hypertension in obese subjects. Hypertension increases cardiovascular mortality, with nighttime (sleep) blood pressure having a substantial prognostic value. We measured blood pressure in male leptin-deficient obese mice (ob/ob; n=7) and their lean wild-type littermates (+/+; n=11) during wakefulness, non-rapid-eye-movement sleep, and rapid-eye-movement sleep to investigate whether, in the absence of leptin, derangements of blood pressure are still associated with obesity and depend on the wake-sleep state. Mice were implanted with a telemetric pressure transducer and electrodes for discriminating wake-sleep states. Mean blood pressure was significantly higher in ob/ob than in +/+ mice during wakefulness (7.3+/-2.6 mm Hg) and non-rapid-eye-movement sleep (6.7+/-2.8 mm Hg) but not during rapid-eye-movement sleep (2.6+/-2.6 mm Hg). In ob/ob and +/+ mice, mean blood pressure was substantially higher during wakefulness than during non-rapid-eye-movement sleep. On passing from non-rapid-eye-movement sleep to rapid-eye-movement sleep, mean blood pressure decreased significantly in ob/ob but not in +/+ mice. The time spent during wakefulness was lower in ob/ob than in +/+ mice during the dark (active) period, whereas the opposite occurred during the light (rest) period. Consequently, mean blood pressure was significantly higher in ob/ob than in +/+ mice during the light (8.2+/-2.4 mm Hg) but not during the dark (3.0+/-2.9 mm Hg) period. These data suggest that, in the absence of leptin, obesity may entail hypertensive derangements of blood pressure, which are substantially modulated by the cardiovascular effects of the wake-sleep states.

Insulin stimulates hepatic low density lipoprotein receptor-related protein 1 (LRP1) to increase postprandial lipoprotein clearance

Background While the role of insulin in glucose uptake and its aberration in diabetes are well established, the effect of insulin on lipoprotein clearance in the postprandial phase is not yet fully understood. The dietary lipids are carried in chylomicron remnants (CR) which are taken up into the liver mainly via LDLR-related protein 1 (LRP1). In this study, the effect of insulin on LRP1-mediated hepatic CR uptake was investigated. Methods The study was based on determining the subcellular localisation of LRP1 by subcellular fractionation and immunofluorescence microscopy and correlating those findings with the hepatic uptake of fluorescently or radioactively labelled LRP1-specific ligands and CR in hepatoma cells, primary hepatocytes and mouse models. Results and conclusion In vitro and in vivo, insulin stimulated the translocation of hepatic LRP1 from intracellular vesicles to the plasma membrane, which correlates with an increased uptake of LRP1-specific ligands. In wild-type mice, a glucose-induced insulin response increased the hepatic uptake of LRP1 ligands while in leptin-deficient obese mice ( ob/ ob), which are characterised by hepatic insulin resistance, insulin-inducible LRP1 ligand uptake was abolished. Finally, upon hepatic LRP1 knockdown, insulin no longer significantly enhanced CR uptake into the liver. The insulin-induced LRP1-mediated CR uptake, as demonstrated here, suggests that impaired hepatic LRP1 translocation can contribute to the postprandial lipaemia in insulin resistance.

Myocardial ischemic postconditioning against ischemia-reperfusion is impaired in ob/ob mice

Ischemic postconditioning (IPCD) significantly reduces infarct size in healthy animals and protects the human heart. Because obesity is a major risk factor of cardiovascular diseases, the effects of IPCD were investigated in 8- to 10-wk-old leptin-deficient obese (ob/ob) mice and compared with wild-type C57BL/6J (WT) mice. All animals underwent 30 min of coronary artery occlusion followed by 24 h of reperfusion associated or not with IPCD (6 cycles of 10-s occlusion, 10-s reperfusion). Additional mice were killed at 10 min of reperfusion for Western blotting. IPCD reduced infarct size by 58% in WT mice (33+/-1% vs. 14+/-3% for control and IPCD, respectively, P<0.05) but failed to induce cardioprotection in ob/ob mice (53+/-4% vs. 56+/-5% for control and IPCD, respectively). In WT mice, IPCD significantly increased the phosphorylation of Akt (+77%), ERK1/2 (+41%), and their common target p70S6K1 (+153% at Thr389 and +57% at Thr421/Ser424). In addition, the phosphorylated AMP-activated protein kinase (AMPK)-to-total AMPK ratio was also increased by IPCD in WT mice (+64%, P<0.05). This was accompanied by decreases in phosphatase and tensin homolog deleted on chromosome 10 (PTEN), MAP kinase phosphatase (MKP)-3, and protein phosphatase (PP)2C levels. In contrast, IPCD failed to increase the phosphorylation state of all these kinases in ob/ob mice, and the level of the three phosphatases was significantly increased. Thus, although IPCD reduces myocardial infarct size in healthy animals, its cardioprotective effect vanishes with obesity. The lack of enhanced phosphorylation by IPCD of Akt, ERK1/2, p70S6K1, and AMPK might partly explain the loss of cardioprotection in this experimental model of obese mice.

Pharmacological lowering of glycosphingolipid content in adipose tissue of leptin-deficient obese mice reduces adipose tissue inflammation and improves insulin sensitivity

Pharmacological lowering of glycosphingolipid content in adipose tissue of leptin-deficient obese mice reduces adipose tissue inflammation and improves insulin sensitivity

Leptin and regulation of linear growth

Leptin, first identified as the product of the ob gene in leptin-deficient obese (ob/ob) mice, was originally described as a circulating hormone involved in feeding behavior and energy homeostasis. It was later found to be a pleiotropic hormone involved in the regulation of a variety of physiological processes. This review summarizes our recent understanding of the role of leptin as a linear growth-stimulating factor. Leptin was found to have mitogenic effects on numerous cell types in vivo and in vitro, including several cancer cells, cells of the immune system, as well as chondrocytes of the epiphyseal growth plate. Leptin stimulates linear growth by regulating the energy balance of the organism and by stimulating the production and secretion of growth hormone from the hypothalamus; at the same time, it is involved with bone remodeling and has a direct effect on the chondrocytes of the growth plate.

Leptin and Obesity Alter Expression of Myostatin and its Receptor ActRIIb in Mouse Skeletal Muscle

Myostatin is an anti-growth factor expressed in skeletal muscle that has profound effects on the mass of both tissues. PURPOSE. In the present study, we used quantitative real-time polymerase chain reaction (QRT-PCR) to determine mRNA levels for myostatin (MSTN) and its primary receptor activin RIIb (ActRIIb) in the tibialis anterior (TA) and soleus (SOL) skeletal muscles of genetically obese leptin-deficient mice, leptin-deficient mice injected with recombinant leptin for two weeks, and in dietarily obese mice. RESULTS. TA muscle mass was significantly lower in leptin-deficient ob/ob mice but SOL mass was not significantly different between ob/ob mice and wild type C57 mice. Similarly, MSTN mRNA levels were significantly increased in TA but not the SOL of ob/ob mice compared to nonobese control mice. Interestingly, leptin injection significantly decreased MSTN mRNA levels in the TA of ob/ob mice despite the fact that it had no significant affect on TA muscle mass. ActRIIb mRNA levels were unchanged by either leptin deficiency or leptin replacement in either TA or SOL. Feeding mice a high fat diet (HFD) increased body mass and fat mass at 1 week, 1 month, and 3 months compared to age-matched littermate mice fed a normal diet (ND). TA mass was significantly increased after 1 week in HFD mice compared to ND mice but was not significantly different at 1 month or 3 months on a HFD. Soleus mass was unchanged at any timepoint. Interestingly, MSTN and ActRIIb mRNA levels in the TA were unchanged at 1 week, significantly increased at 1 month, and not significantly different at 3 months in HFD mice compared to ND mice. In the soleus MSTN mRNA levels were unchanged or slightly decreased in HFD mice but ActRIIb mRNA levels were significantly increased at 1 month on a high fat diet compared to ND mice. CONCLUSIONS: In summary, both muscle mass and MSTN expression are altered by obesity, but the alterations (1) differ between genetically obese and dietarily obese mice; (2) differ between muscle types (TA vs. SOL), and (3) are not temporally associated. Thus MSTN expression appears to be regulated by increased fat/caloric intake, and may play a role in the regulation of muscle mass or metabolism during the obese state.

Effect of obesity on pulmonary inflammation induced by acute ozone exposure: role of interleukin-6

To determine the role of interleukin (IL)-6 in the increased ozone (O3)-induced inflammation and injury observed in obese vs. lean mice, lean wild-type and leptin-deficient obese (ob/ob) mice were injected with anti-IL-6 antibody (Ab) or isotype control Ab 24 h before exposure to either O3 (2 ppm for 3 h) or room air. Four or 24 h after O3 exposure, bronchoalveolar lavage (BAL) was performed, and the lungs were harvested for Western blotting. Anti-IL-6 Ab caused substantial reductions in O3-induced increases in BAL IL-6 in mice of both genotypes. Four hours following O3, ob/ob mice had increased BAL neutrophils compared with controls, and anti-IL-6-Ab virtually abolished this difference. At 24 h, O3-induced increases in BAL protein and BAL serum albumin were augmented in ob/ob vs. wild-type mice, and anti-IL-6 Ab ablated these obesity-related differences in epithelial barrier injury. O3 increased tyrosine phosphorylation of STAT-3 and STAT-1. There was no effect of obesity on STAT-3 phosphorylation, whereas obesity decreased STAT-1 expression, resulting in reduced STAT-1 phosphorylation. IL-6 neutralization did not alter STAT-3 or STAT-1 phosphorylation in ob/ob or wild-type mice. O3 increased BAL leukemia inhibitory factor (LIF) to a greater extent in obese than in lean mice, and LIF may account for effects on STAT phosphorylation. Our results suggest that IL-6 plays a complex role in pulmonary responses to O3, a role that differs between wild-type and ob/ob mice. Moreover, obesity-related differences in activation of STAT proteins may contribute to some of the differences in the response of obese vs. lean mice.

α‐ and γ‐Tocopherol protect against lipopolysaccharide (LPS) induced hepatic injury in leptin deficient obese mice

Hepatic steatosis is an obesity‐triggered fatty liver disease in which the liver becomes vulnerable to oxidative insults resulting in nonalcoholic steatohepatitis (NASH). We hypothesized that α‐ or γ‐tocopherol (α‐ or γ‐T) supplementation during hepatic steatosis would decrease the progression towards LPS‐induced NASH. Five‐wk old obese (ob/ob) and lean littermate mice were fed a control, α‐T, or γ‐T supplemented diet (1000 mg/kg) for 5 wk (18 mice/genotype/diet) and then injected with LPS prior to sacrifice at 0, 1.5 or 6 h. Obese compared to lean mice had ∼40% greater (p&lt;0.05) body weight and &gt;3‐times hepatic lipid which were unaffected by Ts or LPS. Obese compared to lean mice had greater hepatic Ts. T supplementation further increased hepatic α‐ and γ‐T by 9.7 and 10.1‐times respectively, compared to respective obese controls. LPS reduced hepatic Ts at 6 h compared to 0 and 1.5 h in obese mice. Obese mice had higher serum alanine aminotransferase (ALT) and α‐ and γ‐T supplementation in obese mice similarly reduced LPS‐induced increases in ALT at 1.5 and 6 h. α‐ and γ‐T supplementation decreased hepatic ascorbic acid (AA) in obese mice and LPS increased AA at 6 h. These data suggest that α‐ or γ‐T protected against LPS‐induced hepatic injury in obese mice likely through a common mechanism not involving AA. Additional study is underway to define the protective mechanism of T supplementation against NASH.