Characterization of mouse GBP28 and its induction by exposure to cold

Molecular Mechanisms of Lipid-Based Metabolic Adaptation Strategies in Response to Cold

Temperature changes and periods of detrimental cold occur frequently for many organisms in their natural habitats. Homeothermic animals have evolved metabolic adaptation strategies to increase mitochondrial-based energy expenditure and heat production, largely relying on fat as a fuel source. Alternatively, certain species are able to repress their metabolism during cold periods and enter a state of decreased physiological activity known as torpor. By contrast, poikilotherms, which are unable to maintain their internal temperature, predominantly increase membrane fluidity to diminish cold-related damage from low-temperature stress. However, alterations of molecular pathways and the regulation of lipid-metabolic reprogramming during cold exposure are poorly understood. Here, we review organismal responses that adjust fat metabolism during detrimental cold stress. Cold-related changes in membranes are detected by membrane-bound sensors, which signal to downstream transcriptional effectors, including nuclear hormone receptors of the PPAR (peroxisome proliferator-activated receptor) subfamily. PPARs control lipid metabolic processes, such as fatty acid desaturation, lipid catabolism and mitochondrial-based thermogenesis. Elucidating the underlying molecular mechanisms of cold adaptation may improve beneficial therapeutic cold treatments and could have important implications for medical applications of hypothermia in humans. This includes treatment strategies for hemorrhagic shock, stroke, obesity and cancer.

The impact of fasting on adipose tissue metabolism

Fasting and starvation were common occurrences during human evolution and accordingly have been an important environmental factor shaping human energy metabolism. Humans can tolerate fasting reasonably well through adaptative and well-orchestrated time-dependent changes in energy metabolism. Key features of the adaptive response to fasting are the breakdown of liver glycogen and muscle protein to produce glucose for the brain, as well as the gradual depletion of the fat stores, resulting in the release of glycerol and fatty acids into the bloodstream and the production of ketone bodies in the liver. In this paper, an overview is presented of our current understanding of the effects of fasting on adipose tissue metabolism. Fasting leads to reduced uptake of circulating triacylglycerols by adipocytes through inhibition of the activity of the rate-limiting enzyme lipoprotein lipase. In addition, fasting stimulates the degradation of stored triacylglycerols by activating the key enzyme adipose triglyceride lipase. The mechanisms underlying these events are discussed, with a special interest in insights gained from studies on humans. Furthermore, an overview is presented of the effects of fasting on other metabolic pathways in the adipose tissue, including fatty acid synthesis, glucose uptake, glyceroneogenesis, autophagy, and the endocrine function of adipose tissue.

Adiponectin receptor PAQR-2 signaling senses low temperature to promote C. elegans longevity by regulating autophagy

Temperature is a key factor for determining the lifespan of both poikilotherms and homeotherms. It is believed that animals live longer at lower body temperatures. However, the precise mechanism remains largely unknown. Here, we report that autophagy serves as a boost mechanism for longevity at low temperature in the nematode Caenorhabditis elegans. The adiponectin receptor AdipoR2 homolog PAQR-2 signaling detects temperature drop and augments the biosynthesis of two ω-6 polyunsaturated fatty acids, γ-linolenic acid and arachidonic acid. These two polyunsaturated fatty acids in turn initiate autophagy in the epidermis, delaying an age-dependent decline in collagen contents, and extending the lifespan. Our findings reveal that the adiponectin receptor PAQR-2 signaling acts as a regulator linking low temperature with autophagy to extend lifespan, and suggest that such a mechanism may be evolutionally conserved among diverse organisms.

Vagal hyperactivity due to ventromedial hypothalamic lesions increases adiponectin production and release

In obese humans and animals, adiponectin production and release in adipose tissue are downregulated by feedback inhibition, resulting in decreased serum adiponectin. We investigated adiponectin production and release in ventromedial hypothalamic (VMH)-lesioned animals. VMH-lesioned mice showed significant increases in food intake and body weight gain, with hyperinsulinemia and hyperleptinemia at 1 and 4 weeks after VMH-lesioning. Serum adiponectin was elevated in VMH-lesioned mice at 1 and 4 weeks, despite adipocyte hypertrophy in subcutaneous and visceral adipose tissues and increased body fat. Adiponectin production and mRNA were also increased in both adipose tissues in VMH-lesioned mice at 1 week. These results were replicated in VMH-lesioned rats at 1 week. Daily atropine administration for 5 days or subdiaphragmatic vagotomy completely reversed the body weight gain and eliminated the increased adiponectin production and release in these rats, with reversal to a normal serum adiponectin level. Parasympathetic nerve activation by carbachol infusion for 5 days in rats increased serum adiponectin, with increased adiponectin production in visceral and subcutaneous adipose tissues without changes of body weight. These results demonstrate that activation of the parasympathetic nerve by VMH lesions stimulates production of adiponectin in visceral and subcutaneous adipose tissues and adiponectin release, resulting in elevated serum adiponectin.

PAQR-2 may be a regulator of membrane fluidity during cold adaptation

PAQR-2 is a C. elegans homolog of the mammalian adiponectin receptors. We have recently shown that PAQR-2 is essential for the ability of C. elegans to grow at its lower temperature range, i.e., 15 °C, and that the likely role of PAQR-2 during cold adaptation is to regulate membrane fluidity by promoting fatty acid desaturation. Here we present a summary of this work, with an emphasis on placing our C. elegans findings in the context of mammalian biology.

PAQR-2 regulates fatty acid desaturation during cold adaptation in C. elegans

C. elegans PAQR-2 is homologous to the insulin-sensitizing adiponectin receptors in mammals, and essential for adaptation to growth at 15°C, a low but usually acceptable temperature for this organism. By screening for novel paqr-2 suppressors, we identified mutations in genes involved in phosphatidylcholine synthesis (cept-1, pcyt-1 and sams-1) and fatty acid metabolism (ech-7, hacd-1, mdt-15, nhr-49 and sbp-1). We then show genetic evidence that paqr-2, phosphatidylcholines, sbp-1 and Δ9-desaturases form a cold adaptation pathway that regulates the increase in unsaturated fatty acids necessary to retain membrane fluidity at low temperatures. This model is supported by the observations that the paqr-2 suppressors normalize the levels of saturated fatty acids, and that low concentrations of detergents that increase membrane fluidity can rescue the paqr-2 mutant.

Cold-blooded organisms such as insects, fish or worms must make physiological adjustments when the temperature in their environment decreases. One essential adaptive measure is to increase the fluidity of the cellular membranes that are made of fatty molecules and would tend to harden at low temperatures, just as butter would. In our study we identify genes that are regulated by PAQR-2, a membrane protein that we show to be essential for adjusting the membrane fluidity during cold adaptation in the nematode C. elegans. Interestingly, the genes influenced by PAQR-2 are all involved in fatty acid metabolism. We speculate that the human homologs of PAQR-2, which are receptors for the hormone adiponectin, may have similar functions.

Nutritional and hormonal modulation of adiponectin and its receptors adipoR1 and adipoR2

Adiponectin is the most abundant plasma protein synthesized mostly by adipose tissue and is an insulin-sensitive hormone, playing a central role in glucose and lipid metabolism. Adiponectin effects are mediated via two receptors, adipoR1 and adipoR2. Several hormones and diet components that are involved in insulin resistance may impair insulin sensitivity at least in part by decreasing adiponectin and adiponectin receptors. Adiponectin expression and serum levels are associated with the amount and type of fatty acids and carbohydrate consumed. Other food items, such as vitamins, alcohol, sodium, green tea, and coffee, have been reported to modify adiponectin levels. Several hormones, including testosterone, estrogen, prolactin, glucocorticoids, catecholamines, and growth hormone, have been shown to inhibit adiponectin production, but the studies are still controversial. Even so, adiponectin is a potential therapeutic target in the treatment of diabetes mellitus and other diseases associated with hypoadiponectinemia.

Cold exposure increases adiponectin levels in men

Sympathetic nerve activation is recognized at the adipose tissue level during cold exposure. Adiponectin is a key protein produced by adipose tissue, but its acute modulation remains unknown in humans exposed to cold. The aim of this study were (1) to examine the acute effects of cold exposure on circulating adiponectin and (2) to determine whether the changes are modulated by (a) an acute glucose ingestion as well as (b) a short-term modulation in carbohydrate (CHO) availability. Using a random crossover design, 6 healthy men were exposed to cold for 120 minutes with ingestion of beverages containing low (Control, 0.04 g/min) or high (High, 0.8 g/min) amounts of glucose during the course of the experiment (study 1). In study 2, 6 healthy men were exposed twice to cold for 120 minutes after equicaloric low-CHO diet and exercise and high-CHO diet without exercise. Plasma adiponectin concentrations were quantified before and during cold exposure. In study 1, adiponectin levels did not change during High, whereas a 20% rise was observed during Control (condition x time interaction, P = .06). In study 2, adiponectin levels increased by approximately 70% during cold exposure after both low- and high-CHO diets (effect of time, P < .05). A 120-minute period of cold exposure is accompanied by a significant increase in adiponectin levels in young healthy men. The rise in adiponectin levels observed during shivering is inhibited with glucose ingestion but not after diets varying in CHO content.

Short-term beta-adrenergic regulation of leptin, adiponectin and interleukin-6 secretion in vivo in lean and obese subjects

AIM

Adipose tissue and skeletal muscle are endocrine organs, secreting substances that have been implicated in obesity-related disorders. This study examined short-term beta-adrenergic regulation of circulating leptin, adiponectin and interleukin-6 (IL-6) concentrations and secretion from abdominal subcutaneous adipose tissue and muscle (IL-6) in vivo in lean and obese subjects.

METHODS

Systemic concentrations and net fluxes of leptin, adiponectin and IL-6 across abdominal subcutaneous adipose tissue and forearm skeletal muscle (IL-6) were assessed before and during beta-adrenergic stimulation (intravenous isoprenaline infusion) in 13 lean and 10 obese men.

RESULTS

Basal circulating leptin concentrations were higher in the obese (p < 0.001), while circulating adiponectin (p = 0.45) and IL-6 concentrations (p = 0.41) were not different between groups. beta-Adrenergic stimulation decreased leptin concentrations in both groups (p < 0.01), but did not reduce net abdominal subcutaneous adipose tissue leptin release. Increased leptin clearance and/or decreased leptin secretion from other fat depots may explain the reduction in leptin concentrations. Adiponectin concentrations remained unchanged during beta-adrenergic stimulation in both groups. beta-Adrenergic stimulation increased IL-6 concentration, which was more pronounced in the obese (p = 0.01 vs. lean). This cannot be explained by increased IL-6 release per unit abdominal subcutaneous adipose tissue and muscle but might be because of the increased fat mass and fat-free mass at whole-body level.

CONCLUSIONS

Short-term beta-adrenergic stimulation decreases leptin concentrations, which cannot be explained by reduced net leptin release from abdominal subcutaneous adipose tissue, while it elevates IL-6 concentration partly by increased release from this fat depot and muscle. Finally, beta-adrenergic stimulation has no short-term regulatory role in adiponectin secretion.

Diazoxide enhances basal metabolic rate and fat oxidation in obese Zucker rats

Persistent suppression of hyperinsulinemia in genetically obese (fa/fa) Zucker rats by diazoxide (DZ) reduces food intake and weight gain; improves insulin sensitivity, glycemic control, and lipid profile; and enhances beta(3)-adrenergic function and lipolysis in adipose tissue. The aim of this study was to elucidate the effects of DZ on basal metabolic rate (BMR), fat oxidation, and adrenergic function of lean and obese Zucker rats. Diazoxide (150 mg/kg/d) or vehicle (control) was administered for 4 weeks in 7-week-old obese and lean Zucker rats (n = 8-9 per subgroup). Animals underwent indirect calorimetry, body composition analysis, and determination of uncoupling proteins (UCPs) messenger RNA (mRNA) in brown and white adipose tissues (BAT and WAT) and skeletal muscle (SM), beta(3)-adrenergic receptor (AR) mRNA in BAT and WAT, beta(2)-AR in SM as well as WAT, and SM adenylate cyclase (AC) activity at the completion of study. Diazoxide treatment decreased food intake, weight gain, and body fat in obese rats (P < .01). Although DZ treatment lowered fasting plasma glucose, insulin, leptin, adiponectin, and lipids in obese rats (P < .01), it increased adiponectin-leptin ratio (P < .01). Plasma adiponectin-leptin ratio was inversely correlated with fat mass in obese and lean rats (r = -0.86, P < .0001). Diazoxide treatment resulted in higher BMR and fat oxidation rate in obese compared with control animals (P < .01), without any effect in lean animals. Furthermore, plasma adiponectin was inversely correlated with BMR (-0.56, P < .001) and lipid oxidation rate (-0.61, P < .0005) and was positively correlated with nonprotein respiratory quotient (r = 0.41, P < .01) in obese and lean rats. This was associated with increased beta(3)-AR mRNA expression in BAT and WAT (P < .01), UCP-1 and UCP-3 in BAT and AC activity in WAT (P < .02), and AC activity in SM of DZ obese rats compared with controls (P < .01), without significant change in SM beta(2)-AR mRNA expressions. Diazoxide attenuation of hyperinsulinemia decreased the rate of weight gain but enhanced insulin sensitivity, BMR, and fat oxidation in obese rats. This was associated with increased receptor- and non-receptor-mediated adrenergic function in adipose and muscle tissues in obese rats, respectively. These metabolic changes in obese Zucker rats suggest that antiobesity effects of DZ appear to be not only through its anorectic effect, modification of disturbed insulin metabolism, and inhibition of lipogenesis, but also due to augmentation of adrenergic function, energy expenditure, and fat utilization.

Physiological, pharmacological, and nutritional regulation of circulating adiponectin concentrations in humans

Adiponectin is an adipocyte hormone that links visceral adiposity with insulin resistance and atherosclerosis. It is unique among adipocyte-derived hormones in that its circulating concentrations are inversely proportional to adiposity, and low adiponectin concentrations predict the development of type 2 diabetes and cardiovascular disease. Consequently, in the decade since its discovery, adiponectin has generated immense interest as a potential therapeutic target for the metabolic syndrome and diabetes. This review summarizes current research regarding the regulation of circulating adiponectin concentrations by physiological, pharmacological, and nutritional factors, with an emphasis on human studies. In humans, plasma adiponectin concentrations are influenced by age and gender, and are inversely proportional to visceral adiposity. In vitro studies suggest that adiponectin production may be determined primarily by adipocyte size and insulin sensitivity, with larger, insulin-resistant adipocytes producing less adiponectin. While adiponectin concentrations are unchanged after meal ingestion, they are increased by significant weight loss, such as after bariatric surgery. In addition, adiponectin production is inhibited by a number of hormones, including testosterone, prolactin, glucocorticoids and growth hormone, and by inflammation and oxidative stress in adipose tissue. Smoking decreases, while moderate alcohol consumption increases, circulating adiponectin concentrations. Dietary fatty acid composition in rodents influences adiponectin production via ligand-activated nuclear receptors (PPARs); however, current evidence in humans is equivocal. In addition to PPAR agonists (such as thiazolidinediones and fibrates), a number of pharmacological agents (angiotensin receptor type 1 blockers, ACE inhibitors, and cannabinoid receptor antagonists) used in treatment of the metabolic syndrome also increase adiponectin concentrations in humans.

Relationship between blood adipocytokines and resting energy expenditure in young and elderly women

It has been demonstrated in a previous study that resting energy expenditure (REE) is associated with adiponectin levels in the blood. However, body composition was not taken into consideration in that study. The purpose of the present study was to again investigate the relationship between blood adipocytokines and REE, adjusted by body composition, in both young and elderly women. REE and blood adipocytokines were measured in 115 young (age: 22.3+/-2.1 y, BMI: 21.3+/-1.9 kg/m(2)) and 71 elderly (63.4+/-6.5 y, 22.9+/- 2.3 kg/m(2)) women. Dual energy X-ray absorptiometry was used to measure percent body fat. Fat mass and fat free mass (FFM) were calculated. REE (kcal/d and kcal/kg BW/d) was lower in elderly women than in young women, but no significant difference was observed in REE, expressed as kcal/kg FFM/d, between the two groups. Although elderly women had a higher percent body fat and higher serum leptin concentrations than young women, plasma adiponectin concentrations did not differ between young and elderly women. In elderly women, REE (kcal/d) was significantly and inversely correlated with plasma adiponectin concentration (r=-0.386, p<0.001), but REE expressed per kilogram of BW or FFM was not significantly correlated. Furthermore, no significant correlation was observed between REE (kcal/d) and concentrations of plasma adiponectin or serum leptin, after adjusting for potential confounders such as body composition and hormones, in either age group. These results suggest that adipocytokines do not influence REE in adult women.

Serum concentrations of adiponectin in patients with hyperthyroidism before and after control of thyroid function

OBJECTIVE

Thyroid hormone affects adipocyte function, which in turn influences lipid and carbohydrate metabolism. Adiponectin is one of the adipocytokines that regulates lipid and carbohydrate metabolism. The aim of our study was to evaluate circulating levels of adiponectin in patients with thyroid dysfunction before and after normalization of thyroid function with appropriate medication.

DESIGN & METHODS

One hundred and twenty patients with hyperthyroidism were recruited at the time of diagnosis. Measurements of free T4 (FT4), thyroid-stimulating hormone (TSH), thyrotropin binding inhibitor immunoglobulin (TBII), adiponectin, fasting blood glucose, fasting serum insulin, lipid profile, and body mass index (BMI) were taken before and after 6 months of medical treatment, at which point all patients were in a euthyroid state.

RESULTS

Any change in BMI was strongly correlated with changes in serum-adiponectin levels (r = -0.789, p<0.001). Any change in serum FT4 was also correlated with changes in BMI and serum adiponectin levels (r = -0.254, p = 0.05 and r = 0.501, p = 0.029 respectively). After controlling for BMI changes, we found correlation also between serum FT4 and adiponectin (r = 0.29, p = 0.005). Multivariate-regression analysis still revealed BMI to be a statistically strong predictor for serum-adiponectin level (p<0.001). However, that analysis also revealed thyroid function level as another predictor (p = 0.029).

CONCLUSIONS

Although BMI is the best predictor of adiponectin, that thyroid hormone might influence circulating levels of adiponectin.

Adipocytes, myofibers, and cytokine biology: new horizons in the regulation of growth and body composition

Muscle growth in meat animals is a complex process governed by integrated signals emanating from multiple endocrine and immune cells. A generalized phenomenon among meat animal industries is that animals commonly fail to meet their genetic potential for growth in commercial production settings. Therefore, understanding the impact of stress and disease on muscle growth is essential to improving production efficiency. The adipocyte in particular seems to be well positioned as an interface between energy status and immune function, and may thus influence nutrient partitioning and growth through a combination of signals that influence fat metabolism, glucose uptake, and insulin sensitivity. Adipocytes and myofibers are active participants in the innate immune response, and as such, produce a number of metabolic regulators, including leptin, adiponectin, and proinflammatory cytokines. Specifically, adipocytes and muscle cells respond directly to bacterial lipopolysaccharide (LPS) by producing interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNFalpha). However, adipocytes are also the predominant source of the antiinflammatory hormone adiponectin, which regulates the nuclear factor kappa-B transcription factor. The ability to recognize antigens and produce regulatory molecules strategically positions adipocytes and myofibers to regulate growth locally, and to reciprocally regulate metabolism peripherally.

Basic endocrine products of adipose tissue in states of thyroid dysfunction

Over the past decade it has been established that adipose tissue is capable of secreting a variety of hormones, cytokines, growth factors, and other peptides that are capable of changing adipocyte biology as well as different organ systems, like the central nervous system, liver, pancreas, and skeletal muscles. Also, it is well known that changes of thyroid function are associated with marked changes in both body weight and energy expenditure. In recent years an extensive research is under way to explore the mutual roles of different adipokines and thyroid hormones. The aim of this review is to summarize our current knowledge on the role of basic peptides of adipose tissue, such as adiponectin, interleukin-6, tumor necrosis factor-alpha, and resistin, in states of altered thyroid function.

Environmental influences on adiponectin levels in humans

In addition to its classic role in the storage and release of nonesterified fatty acids, the adipocyte is now recognized as a critical source of many endocrine signals. Of these signals, adiponectin has been found to promote lipid oxidation and glucose uptake in skeletal muscles and to reduce glucose output in the liver. Because of the effects of adiponectin on these organs, the search for factors or conditions that could positively influence the synthesis of this adipocyte-derived protein has drawn a great deal of interest. This brief review explores the effects of environmental influences such as weight loss, acute food intake, exercise, and cold exposure on circulating adiponectin levels in humans.

A high-fat diet has a tissue-specific effect on adiponectin and related enzyme expression

OBJECTIVE

This study was designed to test whether adiponectin plays a role in diet-induced obesity and insulin resistance and acts as a mediator to induce or inhibit specific metabolic pathways involved in lipid metabolism

RESEARCH METHODS AND PROCEDURES

Forty C57BL/6J male mice were fed either a high-fat (HF) or control diet for 4 months, and adiponectin, its receptors, and enzyme expression in liver and muscle tissue were measured.

RESULTS

Mice fed the HF diet exhibited significantly greater weight gain, abnormal oral glucose tolerance test curves, and elevated homeostasis model assessment of insulin resistance (5.3 +/- 0.89 vs. 2.8 +/- 0.39). A significant reduction of adiponectin RNA expression (51%) and protein levels (15%) was observed in the adipose tissue of HF animals; however, serum adiponectin levels did not differ between groups (7.12 +/- 0.34 mug/mL vs. 6.44 +/- 0.38 microg/mL). Expression of hepatic mRNA of AdipoR1 and AdipoR2 was reduced by 15% and 25%, respectively, in animals fed the HF diet. In contrast, receptor mRNA expression of AdipoR1 and AdipoR2 increased by 25% and 30%, respectively, in muscle tissue. No effect was found on hepatic adenosine monophosphate-activated protein kinase expression; however, a significant reduction of phosphoadenosine monophosphate kinase levels in muscles was observed. Hepatic acetyl-coenzyme A carboxylase was similar between groups, but in muscles, the inactive form phosphoacetyl-coenzyme A carboxylase was significantly reduced (p < 0.05).

DISCUSSION

The HF diet led to decreased insulin sensitivity accompanied by impaired activity of adiponectin-related enzymes in skeletal muscles but not in the liver. These results suggest that the HF diet has a tissue-specific effect on adiponectin and associated enzyme expression.

Adiponectin levels and cardiovascular risk factors in hypothyroidism and hyperthyroidism

OBJECTIVE

Adiponectin, an adipose tissue-derived hormone, has been reported to have anti-inflammatory and anti-atherogenic effects. The physiological effect of adiponectin on the metabolic changes and its relation with cardiovascular risk factors in thyroid dysfunction states is still not clear. The aim of the study was to evaluate plasma adiponectin level and its relation to cardiovascular risk factors in patients with thyroid dysfunction.

PATIENTS AND MEASUREMENTS

Sixty-seven patients with hypothyroidism, 56 patients with hyperthyroidism and 52 age- and sex-matched euthyroid subjects were enrolled in the study. Adiponectin, C-reactive protein (CRP), homocysteine (Hcy), lipid parameters, Lipoprotein(a) [Lp (a)], Apolipoprotein (Apo) A, Apo B and fibrinogen levels were measured in all subjects. Insulin sensitivity was determined using the Homeostasis Model Assessment (HOMA-IR).

RESULTS

Circulating adiponectin levels were not different between the groups (16.2 +/- 5.0, 15.1 +/- 3.7, 15.9 +/- 4.8 ng/ml; hypothyroid, hyperthyroid, euthyroid group, respectively). Plasma adiponectin levels correlated negatively with body mass index (BMI) and HOMA-IR index and positively with high-density lipoprotein cholesterol (HDL-C) in all groups. There was a significant correlation between adiponectin and CRP levels in both hypothyroid and hyperthyroid groups. In all groups, adiponectin levels did not correlate with age, systolic blood pressure, diastolic blood pressure and thyroid hormones. Multiple regression analysis revealed BMI and HDL-C levels to be the most important predictors of circulating adiponectin levels.

CONCLUSIONS

Plasma adiponectin levels are associated with BMI and HDL-C levels in patients with hypothyroidism and hyperthyroidism. But there is not a direct relation of adiponectin with thyroid hormones in these patients.

Cold exposure suppresses serum adiponectin levels through sympathetic nerve activation in mice

OBJECTIVE

Several lines of evidence suggest important roles for adiponectin in glucose and lipid metabolism and atherosclerosis. However, the mechanisms regulating serum adiponectin levels and adiponectin production are still not completely understood. Our aim was to determine whether adiponectin synthesis is physiologically regulated by the sympathetic nervous system (SNS).

RESEARCH METHODS AND PROCEDURES

Mice were exposed to cold (4 degrees C) for 12 hours and for 24 hours with or without inhibition of noradrenaline synthesis or pan-beta adrenergic function, followed by measurement of serum adiponectin concentrations and levels of adiponectin and uncoupling protein (UCP) 1 expressions in various white adipose tissues (WATs).

RESULTS

Cold exposure significantly reduced serum adiponectin concentrations without changing body weights or WAT sizes in either subcutaneous or intra-abdominal fat tissues. The serum adiponectin reduction was associated with a decrease in adiponectin mRNA expression in subcutaneous, epididymal, and mesenteric fat tissues. In these adipose tissues, UCP1 expression was markedly enhanced, suggesting SNS activation in these tissues. Administration of alpha-methyl-p-tyrosine or a combination of SR59230A and propranolol reversed the cold-exposure-induced decreases in serum adiponectin concentrations and adiponectin mRNA expression in these tissues. In contrast, in retroperitoneal fat, the effects of cold exposure on adiponectin and UCP1 expressions were strikingly weak but were not reversed by SNS inhibitors.

DISCUSSION

SNS physiologically regulates serum adiponectin levels and adiponectin synthesis in WATs in vivo, although responsiveness to SNS stimulation differs markedly among WATs. Sympathetic activation might be involved in development of the metabolic syndrome by modulation of serum adiponectin concentrations.

A novel enzyme-linked immunosorbent assay specific for high-molecular-weight adiponectin

Human plasma contains at least three forms of adiponectin: a trimer, a hexamer, and a high-molecular-weight (HMW) multimer. We purified HMW adiponectin from human plasma using its affinity to gelatin and obtained monoclonal antibodies against it. On Western blot analysis, the reactivity of these monoclonal antibodies was shown to be restricted to a non-heat-denatured form of adiponectin molecules. On heating, the collagen-like domain of adiponectin molecules became denatured, and thus the trimer form could not be maintained. From these, monoclonal antibodies against HMW adiponectin were suggested to react with the intact trimer of adiponectin. With these monoclonal antibodies, we developed a sandwich ELISA system for quantifying adiponectin in human serum. Its specificity was verified by analysis of serum fractions separated by gel-filtration chromatography, and our ELISA system was found to be HMW adiponectin-specific. With this novel ELISA, the HMW adiponectin concentrations were 8.4 +/- 5.5 microg/ml (mean +/- SD) in healthy women and 6.2 +/- 3.6 microg/ml in healthy men. Also, serum with a lower HMW adiponectin concentration was shown to have a lower HMW ratio (i.e., HMW adiponectin/total adiponectin).

Thyroid status influence on adiponectin, acylation stimulating protein (ASP) and complement C3 in hyperthyroid and hypothyroid subjects

BACKGROUND

Thyroid abnormalities (hyperthyroid and hypothyroid) are accompanied by changes in intermediary metabolism including alterations in body weight, insulin resistance and lipid profile. The aims of this study were to examine plasma ASP, its precursor C3 and adiponectin in hyperthyroid and hypothyroid subjects as compared to controls.

METHODS

A total of 99 subjects were recruited from endocrinology/out-patient clinics: 46 hyperthyroid subjects, 23 hypothyroid subjects and 30 control subjects. Subjects were evaluated for FT4, FT3, TSH, glucose, insulin, complete lipid profile and the adipokines: adiponectin, acylation stimulating protein (ASP) and complement C3.

RESULTS

Hyperthyroidism was associated with a 95% increase in adiponectin (p = 0.0002), a 47% decrease in C3 (p < 0.0001), no change in ASP and increased ASP/C3 ratio (p = 0.0012). Hypothyroidism was associated with a 31% increase in ASP (p = 0.008). Adiponectin and C3 correlated with FT3 (r = 0.383, p = 0.004 and r = -0.277, p = 0.007, respectively) and FT4 (r = 0.464, p = 0.003 and r = -0.225, p = 0.03, respectively). ASP correlated with TSH (r = 0.202, p = 0.04). Adiponectin did not correlate with either ASP or C3, only ASP and C3 correlated (r = -0.197, p = 0.05). Adiponectin was negatively correlated with BMI, total cholesterol and plasma triglyceride, while C3 was positively correlated with BMI and total cholesterol. Surprisingly, adiponectin was positively correlated with insulin (r = 0.293, p = 0.02) and HOMA-IR (r = 0.373, p = 0.003) while C3 was negatively correlated with glucose (r = -0.242, p = 0.022, insulin (r = -0.184, p = 0.05) and HOMA-IR.

CONCLUSION

These changes suggest that thyroid disease may be accompanied by changes in adipokines, which may contribute to the phenotype expressed.

Adiponectin, leptin and thyroid hormones in patients with chronic renal failure and on renal replacement therapy: are they related?

BACKGROUND

Renal function affects thyroid function and adipocytokines in many ways. We aimed to assess the adipocytokines adiponectin and leptin in relation to thyroid function in patients with chronic renal failure treated conservatively, in haemodialysed patients and in kidney allograft recipients.

METHODS

The study was performed on 33 patients with chronic renal failure, 64 haemodialysed patients, 54 kidney allograft recipients and 38 healthy volunteers. Thyroid volume was estimated sonographically, thyroid hormones were determined by Micropartide Enzyme Immunoassay (MEIA), and serum adiponectin and leptin were assessed by radioimmunoassay.

RESULTS

Serum thyroid-stimulating hormone (TSH), free T4 and free T3 were within the normal range. Adiponectin correlated significantly with free T3, haematocrit, haemoglobin, platelet count, body mass index (BMI) and urea in kidney allograft recipients. In haemodialysed patients, adiponectin correlated with free T4 and TSH, whereas leptin correlated with free T3. Multiple regression analysis showed that adiponectin was independently related only to the serum concentration of free T3 and urea in kidney transplant recipients and to free T4 and adequacy of dialysis in haemodialysed patients. In univariate analysis in patients with chronic renal failure, adiponectin correlated with free T3 and platelet count, and in healthy volunteers adiponectin correlated only with free T3 and triglycerides, and leptin correlated with BMI.

CONCLUSIONS

We described novel relationships between adiponectin and thyroid hormones in patients with kidney diseases. However, possible pre-existing thyroid dysfunction prior to transplantation (during dialysis therapy) and immunosuppression after transplantation make all these findings relatively complex. Therefore, the relationships between adiponectin and the thyroid axis in patients with chronic renal failure, in haemodialysed subjects or in kidney transplant recipients merit additional studies.

Adiponectin values are unchanged during pregnancy in rats

Adiponectin is believed to be a key factor in determining insulin sensitivity. In turn, insulin sensitivity is known to change from an enhanced state in early pregnancy to a reduced one in late pregnancy. A role for adiponectin in these changes has been proposed for mice but questioned for humans. We addressed this issue in rats by measuring adiponectin expression in both visceral and subcutaneous white adipose tissue, together with tissue content and release of the hormone in non-pregnant and in pregnant rats by days 8, 15 and 19 of pregnancy. Plasma concentration was also determined. No differences were found in any of the parameters measured between non-pregnant and pregnant rats at any time of pregnancy despite changes in white adipose tissue mass and insulin sensitivity. Adiponectin was also detected in cerebrospinal fluid at a concentration 1,000 times lower than in plasma, but again no differences were found between non-pregnant and pregnant animals. It is concluded that adiponectin does not play any role in regulating changes in insulin sensitivity during pregnancy in rats.

Reduced adipose tissue mass and hypoleptinemia in iNOS deficient mice: effect of LPS on plasma leptin and adiponectin concentrations

The aim of this study was to evaluate the impact of the lack of inducible NO synthase (iNOS) on body weight and adipose tissue mass as well as on plasma leptin and adiponectin in basal conditions and 6 h after lipopolysaccharide (LPS) administration in mice. Body weight was not different among male, six-week-old wild-type (WT) and iNOS-/- animals. However, the amount of epididymal white adipose tissue (EWAT) in iNOS-/- mice was significantly reduced (P<0.05). Circulating leptin and leptin mRNA in EWAT were decreased in iNOS-/- mice (P<0.05 and P<0.01, respectively). Plasma adiponectin and adiponectin mRNA were unchanged. LPS administration increased plasma leptin in both genotypes (P<0.05). Neither genotype nor treatment changed plasma adiponectin. In summary, iNOS-/- mice exhibited normal body weight but reduced adipose mass accompanied by hypoleptinemia. Leptin responsiveness to LPS in iNOS-/- mutants is preserved, showing that the LPS-induced rise in leptin is independent of the presence of functional iNOS. In addition, iNOS deficiency or LPS does not influence expression and circulating levels of adiponectin.

Role of disulfide bonds in Acrp30/adiponectin structure and signaling specificity. Different oligomers activate different signal transduction pathways

Acrp30/adiponectin is an adipocyte-derived serum protein with important roles in regulation of lipid and glucose metabolism, but which of its isoforms are biologically active remains controversial. We addressed this issue by first characterizing the structure of each individual Acrp30 oligomer and the determinants responsible for multimer formation. Freeze etch electron microscopy showed the trimer to exhibit a ball-and- stick-like structure containing a large globular sphere, an extended collagen stalk, and a smaller sphere on the opposite end of the stalk. The hexamer consists of two adjacent trimeric globular domains and a single stalk composed of collagen domains from two trimers. Although not necessary for trimer formation or stability, two of the three monomers in an Acrp30 trimer are covalently linked by a disulfide bond between cysteine residues at position 22. In contrast, assembly of hexameric and higher molecular weight (HMW) forms of Acrp30 depends upon formation of Cys22-mediated disulfide bonds because their reduction with dithiothreitol or substitution of Cys22 with alanine led exclusively to trimers. HMW and hexamer isoforms of Acrp30 activated NF-kappaB in C2C12 cells, but trimers, either natural, formed by reduction of Acrp30 hexamer, or formed by the C22A mutant, did not. In contrast, incubation of isolated rat extensor digitorum longus with naturally formed Acrp30 trimers or trimeric C22A Acrp30 led to increased phosphorylation of AMP-activated protein kinase-alpha at Thr172 and its activation. Hexameric and HMW Acrp30 could not activate AMP-activated protein kinase. Thus, trimeric and HMW/hexameric Acrp30 activate different signal transduction pathways, and Acrp30 represents a novel example of the control of ligand signaling via changes in its oligomerization state.

Novel interactions of adiponectin with the endocrine system and inflammatory parameters

Several markers of chronic immune activation have been found in association with obesity and insulin resistance. We aimed to study the interaction of adiponectin with chronic inflammation and known components of the insulin resistance syndrome. Insulin sensitivity (minimal model analysis) and plasma soluble fractions of TNF-alpha receptor 1 (sTNFR1) and 2 (sTNFR2), adrenal and thyroid function, and adiponectin were evaluated in 68 apparently healthy subjects. An additional group of type 2 diabetic patients (n = 19) similarly studied, except for insulin sensitivity, were also included in the analysis. As reported by others, serum adiponectin concentrations were higher in women than in men (13.55 +/- 9.79 vs. 8.64 +/- 7.83 mg/liter; P = 0.018). They were also higher in healthy subjects compared with diabetic patients (10.35 +/- 8.48 vs. 7.41 +/- 8.31 mg/liter; P = 0.021). As expected also, circulating adiponectin was significantly associated with waist to hip ratio (r = -0.28; P = 0.013), diastolic blood pressure (r = -0.25; P = 0.027), fasting plasma high-density lipoprotein cholesterol (r = 0.35; P = 0.001), triglycerides (r = -0.37; P = 0.001), and insulin sensitivity (r = 0.30; P = 0.011). Additionally, subjects in the higher quartile of circulating adiponectin had lower sTNFR2 concentrations (3.05 vs. 4.37 microg/liter; P = 0.012), a trend to lower sTNFR1 concentrations (1.76 vs. 2.20 microg/liter; P = 0.055), higher concentration of serum morning cortisol (16.86 vs. 13.52 microg/dl; P = 0.027), and higher serum free T(4) levels (1.31 vs. 1.20 ng/dl; P = 0.038). Multiple regression analysis models were constructed to predict adiponectin concentrations. Predictive variables in these models included insulin sensitivity, waist to hip ratio and free T(4), contributing to 17%, 10%, and 8% of adiponectin variance, respectively, These findings suggest that circulating adiponectin differentially modulates insulin action and that thyroid-axis, inflammatory cytokines, and the adrenal cortex might intervene in this modulation.

Changes in the distribution pattern of gelatin-binding protein of 28 kDa (adiponectin) in myocardial remodelling after ischaemic injury

AIMS

Gelatin-binding protein of 28 kDa (GBP28) is a collagen-like plasma protein having a binding capacity with collagens. We investigated GBP28 role on myocardial remodelling as well as the diagnostic significance of GBP28 immunostaining in myocardial infarction.

METHODS AND RESULTS

Myocardial tissues obtained from 47 autopsied hearts with infarction were immunostained with antibodies against GBP28, fibronectin, type III and IV collagens, and prolyl 4-hydroxylase. GBP28 was distributed in interstitium of infarcted lesions at an early stage. GBP28 was linearly found both along the border with vital myocardium and at the periphery of surviving cardiomyocyte around the lesion at granulative stage. However, it was not observed in the scar. GBP28 distribution patterns were similar to those of fibronectin in infarcted lesions and those of type IV collagen at the periphery of cardiomyocyte. Type III collagen was not recognized in the early-stage lesion but increased along with scar maturation. Prolyl 4-hydroxylase was found in surviving cardiomyocytes around the lesion during all stages and in interstitial cells appeared in granulation tissue.

CONCLUSION

GBP28 plays a role as a scaffold of newly formed collagen in myocardial remodelling after ischaemic injury, and GBP28 immunostaining may assist in a diagnosis of healing stage.

Oligomerization state-dependent activation of NF-kappa B signaling pathway by adipocyte complement-related protein of 30 kDa (Acrp30)

Adipocyte complement-related protein of 30 kDa (Acrp30)/adiponectin is an adipocyte-derived hormone that affects lipid and glucose metabolism in muscle and liver, but its physical and biochemical properties are poorly characterized. Here we have used several approaches to show that Acrp30 expressed in and purified from Escherichia coli and human embryonic kidney 293T cells forms trimers and hexamers; 293T cells also produce a higher molecular weight species. Similar Acrp30 oligomers were found in mouse serum as well as in 3T3-L1 adipocyte-conditioned medium, although in different proportions. In parallel, we assessed whether Acrp30 is a signaling molecule by searching for promoter or enhancer elements that respond to Acrp30 or its isolated trimeric globular C-terminal domain, gAcrp30. Acrp30 addition to C2C12 myocytes or myotubes led to activation of NF-kappa B transcription factor in a manner dependent upon phosphorylation and degradation of I kappa B-alpha. Importantly, only hexameric and larger isoforms of Acrp30 activated NF-kappa B; trimeric Acrp30 or gAcrp30 could not activate NF-kappa B. Our data indicate that oligomerization of Acrp30 is important for at least some of its biological activities, and changes in the relative abundance of each oligomeric isoform in plasma may regulate Acrp30 activity.

ACRP30, a new hormone controlling fat and glucose metabolism

Adipocyte complement-related protein of 30 kDa (ACRP30) is a secreted serum protein expressed exclusively in differentiated adipocytes. Recent studies have indicated that its expression and serum levels are reduced in humans and animals with obesity and insulin resistance. Metabolic studies have demonstrated a role for ACRP30 in the regulation of glucose and lipid homeostasis. This review will describe the current literature on the biochemistry of ACRP30 and its physiological functions. We will also discuss issues that are relevant to the directions of future research.

Change in expression of GBP28/adiponectin in carbon tetrachloride-administrated mouse liver

GBP28 (gelatin-binding protein of 28 kDa)/adiponectin is an adipocyte-producing plasma protein proposed to interact with the extracellular matrix. To examine the production of GBP28 in non-adipose tissues, we herein analyzed its expression and localization in mouse livers before and after CCl(4) treatment. In immunohistochemical analyses, the boundary of hepatocytes provided positive signals for GBP28 after 3-6 h and their cytoplasm was intensely stained after 18 h of CCl(4) treatment. Quantitative RT-PCR and in situ hybridization revealed that GBP28 mRNA expression was markedly elevated in CCl(4)-treated mouse livers. These results suggest that the circulating GBP28 binds the extracellular matrices of hepatocytes during the initial stage of CCl(4)-induced hepatic injury and the damaged hepatocytes themselves started to produce GBP28 thereafter. The induced expression of GBP28 was also observed in human hepatoma HepG2 cells after treatment with IL-6. Thus, GBP28 is also produced by the liver, where it undergoes tissue damage-induced transcriptional regulation.