Physiological and pathophysiological roles of adiponectin and adiponectin receptors in the integrated regulation of metabolic and cardiovascular diseases. Int J Obes (Lond). 2008;32 Suppl 7:S13-S18. [PMID: 19136982 DOI: 10.1038/ijo.2008.233]

Impact of high-/middle-molecular-weight adiponectin on the synthesis and regulation of extracellular matrix in dermal fibroblasts

Adiponectin has been shown to play a critical role in immunity. Recently, we reported that the adiponectin levels after allogeneic stem cell transplantation were higher in recipients with chronic graft-versus-host disease (cGVHD). However, the effects of adiponectin on extracellular matrix (ECM) and regulatory factors in dermal fibroblasts remain unclear. We compared the messenger RNA (mRNA) levels of collagen type1 (COL1A), fibronectin 1 (FN1), matrix metalloproteinase (MMP)1, MMP3, tissue inhibitor of metalloproteinase (TIMP)1, TIMP3, transforming growth factor-β (TGF-β), and TGF-β receptor 2 (TGF-βR2) in human normal dermal fibroblasts cultured with and without adiponectin, and we assessed the degree of synthesis of ECMs by immunofluorescent microscopy. Furthermore, we also assessed these mRNA levels after blocking of TGF-βR2. Adiponectin induced higher mRNA levels of FN1, MMP1, MMP3, TIMP1, TIMP3, and TGF-βR2 in a dose-dependent manner, but did not significantly affect COL1A or TGF-β. In addition, adiponectin was shown to upregulate FN1, MMPs, and TIMPs after blocking of TGF-βR2. Immunofluorescent microscopy revealed that adiponectin promoted a greater synthesis of ECMs than in the control in vitro. The finding that adiponectin upregulated ECM-associated factors might mean that high levels of adiponectin could modulate dermal fibrosis was observed in recipients with cGVHD. Further basic investigation is warranted to elucidate whether the adiponectin-pathway could be a target for the treatment of sclerotic cGVHD.

Adiponectin effects on the kidney

Adiponectin is a 30-kDa polypeptide secreted primarily by adipose tissue and plays a key role in kidney disease. In obesity, reduced adiponectin levels are associated with insulin resistance, cardiovascular disease and obesity related kidney disease. The latter includes microalbuminuria, glomerulomegaly, overt proteinuria and focal segmental glomerulosclerosis. Adiponectin levels in type 2 diabetics also negatively correlate with early features of nephropathy. However, in patients with established chronic kidney disease, adiponectin levels are elevated and positively predict progression of disease. The mechanism of action of adiponectin in the kidney appears to be related to AMPK activation and NADPH oxidase. Further studies are needed to elucidate this pathway and investigate the role of potential targets of adiponectin-AMPK-Nox pathway for CKD as obesity-related CKD is increasing worldwide.

Adiponectin action in skeletal muscle

The beneficial metabolic effects of adiponectin which confer insulin-sensitizing and anti-diabetic effects are well established. Skeletal muscle is an important target tissue for adiponectin where it regulates glucose and fatty acid metabolism directly and via insulin sensitizing effects. Cell surface receptors and the intracellular signaling events via which adiponectin orchestrates metabolism are now becoming well characterized. The initially accepted dogma of adiponectin action was that the physiological effects were mediated via endocrine effects of adipose-derived adiponectin. However, in recent years it has been established that skeletal muscle can also produce and secrete adiponectin that can elicit important functional effects. There is evidence that skeletal muscle adiponectin resistance may develop in obesity and play a role in the pathogenesis of diabetes. In summary, adiponectin acting in an autocrine and endocrine manner has important metabolic and insulin sensitizing effects on skeletal muscle which contribute to the overall anti-diabetic outcome of adiponectin action.

Severely obese adolescents and adults exhibit a different association of circulating levels of adipokines and leukocyte expression of the related receptors with insulin resistance

Obese adults frequently exhibit a low-grade inflammation and insulin resistance, which have been hypothesized to be established early in childhood. Aim of this study was to evaluate the age-dependent relationships between inflammatory state and insulin resistance in obese adolescents and adults. Clinical and metabolic parameters, circulating adipokines (TNF- α , adiponectin, and leptin), ghrelin, their leukocyte receptors (TNFR1, ADIPOR2, OBRL and GHSR1a), and acute phase reactants (CRP and white blood cells) were assessed in lean and obese adolescents compared with the adult counterparts. Only obese adults had higher HOMA-IR, insulin, and triglycerides compared to the lean group. An inflammatory state was present in obese adolescents and adults, as demonstrated by the higher values of CRP and neutrophils. There were no group differences in circulating levels of TNF- α and leukocyte expression of TNFR1. Adiponectin concentrations and leukocyte expression of ADIPOR2 were higher in the lean groups than in the corresponding obese counterparts. For leptin and leukocyte expression of OBRL, the results were opposed. Circulating levels of ghrelin were higher in lean adolescents and adults than the related lean groups, while there was a higher leukocyte expression of GHSR1a in (only) lean adults than obese adults. When the analysis was performed in (lean or obese) adults, TNF- α , neutrophils, leptin, and GHSR1a were predictors of HOMA-IR. None of the considered independent variables accounted for the degree of insulin resistance in the adolescent group. In conclusion, a dissociation between the low-grade inflammation and insulin resistance is supposed to exist in the early phases of obesity.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

Comprehensive RNA-Seq expression analysis of sensory ganglia with a focus on ion channels and GPCRs in Trigeminal ganglia

The specific functions of sensory systems depend on the tissue-specific expression of genes that code for molecular sensor proteins that are necessary for stimulus detection and membrane signaling. Using the Next Generation Sequencing technique (RNA-Seq), we analyzed the complete transcriptome of the trigeminal ganglia (TG) and dorsal root ganglia (DRG) of adult mice. Focusing on genes with an expression level higher than 1 FPKM (fragments per kilobase of transcript per million mapped reads), we detected the expression of 12984 genes in the TG and 13195 in the DRG. To analyze the specific gene expression patterns of the peripheral neuronal tissues, we compared their gene expression profiles with that of the liver, brain, olfactory epithelium, and skeletal muscle. The transcriptome data of the TG and DRG were scanned for virtually all known G-protein-coupled receptors (GPCRs) as well as for ion channels. The expression profile was ranked with regard to the level and specificity for the TG. In total, we detected 106 non-olfactory GPCRs and 33 ion channels that had not been previously described as expressed in the TG. To validate the RNA-Seq data, in situ hybridization experiments were performed for several of the newly detected transcripts. To identify differences in expression profiles between the sensory ganglia, the RNA-Seq data of the TG and DRG were compared. Among the differentially expressed genes (> 1 FPKM), 65 and 117 were expressed at least 10-fold higher in the TG and DRG, respectively. Our transcriptome analysis allows a comprehensive overview of all ion channels and G protein-coupled receptors that are expressed in trigeminal ganglia and provides additional approaches for the investigation of trigeminal sensing as well as for the physiological and pathophysiological mechanisms of pain.

Adiponectin offers protection against L166P mutant DJ-1-induced neuronal cytotoxicity mediated by APPL1-dependent AMPK activation

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. L166P mutant DJ-1 has been linked with a genetic form of the disease. Preventing neurotoxicity of DJ-1 familial mutations has become a new therapeutic target for PD. Adiponectin, the most abundantly secreted adipokine, has displayed its protective roles in pathologies of various types of diseases. In this study, we investigate whether adiponectin is protective against neurotoxicity induced by familial L166P mutant DJ-1 in PD. Our results demonstrate that adiponectin treatment could attenuate increased levels of reactive oxygen species and nitric oxide induced by the DJ-1L166P mutation. In addition, adiponectin could rescue impaired mitochondrial membrane potential induced by DJ-1L166P. Importantly, we verified that both adiponectin receptors, type 1 (AdipoR1) and type 2 (AdipoR2), are expressed in human neuroblastoma M17 cells. Our results also demonstrate that the protective effects of adiponectin against DJ-1L166P-induced neuronal cytotoxicity under 1-methyl-4-phenylpyridinium ion (MPP+) treatment require binding of adiponectin to its cell surface receptors. Finally, we found that the protective effects of adiponectin against DJ-1L166P depend on AMP-activated protein kinase (AMPK) activation mediated by the endosomal adaptor protein, APPL1 (adaptor protein with phosphotyrosine binding, pleckstrin homology domains and leucine zipper motif). These data suggest that adiponectin may have potential for implementation in novel therapies against PD.

Multiple adipose depots increase cardiovascular risk via local and systemic effects

Adipose tissue modifies the development of cardiovascular disease in a complex manner: obesity is a major risk factor, especially when accompanied by a central fat distribution. For that reason the characteristics of visceral adipose tissue have attracted most of the research interest thus far, and measurement of waist circumference is now recommended for everyday clinical practice. However, the direct, causative role of visceral fat in cardiometabolic disease remains to be established. Epidemiological and clinical studies show that accumulation of fat subcutaneously, in the gluteofemoral area, is protective against cardiovascular disease, but the exact molecular mechanisms remain unclear. In the last few years, imaging has allowed the study of smaller fat depots that may interact locally with important tissues: epicardial fat with the myocardium, perivascular fat with the vessel wall and the developing atherosclerotic plaque, and renal sinus fat with the renal artery. Unraveling the heterogeneous fat distribution and metabolic phenotypes in human obesity will facilitate optimal assessment of cardiovascular risk in overweight and obese individuals.

The effects of chronic candesartan treatment on cardiac and hepatic adenosine monophosphate-activated protein kinase in rats submitted to surgical stress

INTRODUCTION

adenosine monophosphate-activated protein kinase (AMPK) plays a prominent role as a metabolic stress sensor, and it has recently been suggested that the renin-angiotensin system, in addition to its role in stress regulation, may play a significant role in regulating the AMPK system. This study aimed to evaluate the effects of candesartan, an angiotensin II receptor blocker, on cardiac and hepatic AMPK activity basally as well as after surgical stress under general anesthesia.

MATERIALS AND METHODS

Male Wistar rats were treated with 5 mg/kg/day candesartan in their drinking water for two weeks. Levels of cardiac and hepatic AMPK activity were determined, using a kinase activity assay, basally and after surgical stress under general anesthesia.

RESULTS

Chronic administration of candesartan increased hepatic AMPK activity approximately 4 times (p<0.05) while no significant change was demonstrated in cardiac AMPK. Cardiac and hepatic AMPK activities were not significantly increased by surgical stress alone performed under anesthesia. However, chronic treatment with candesartan decreased AMPK activity in both liver and heart after surgical stress under anesthesia (p<0.01 for both comparisons).

CONCLUSIONS

While chronic candesartan treatment may stimulate AMPK activity in certain organs such as the liver, when combined with surgical stress under anesthesia it inhibits pathways regulating AMPK activity.

Role of microRNA-21 in regulating 3T3-L1 adipocyte differentiation and adiponectin expression

MicroRNAs are endogenous small RNAs with a high degree of conservation, participating in a variety of vital activities. In present study, to explore the effect of microRNAs on 3T3-L1 adipocyte differentiation and adiponectin expression, the adipo-related microRNAs were screened and identified by micorRNA microarray. The highly expression plasmid of microRNA-21 with obvious expression up-regulation (miR-21) and its anti-sense (miR-21 inhibitor) were constructed and transfected into 3T3-L1 preadipocytes. The effect of miR-21 on 3T3-L1 adipocyte differentiation was observed, and the protein and mRNA expression level of adiponectin and AP-1 were analyzed. Results showed that, the expression profiles of microRNAs significantly changed during 3T3-L1 adipocyte differentiation. The expression of miR-21 was obviously up-regulated. miR-21 could significantly promote adipocyte differentiation, increase adiponectin mRNA and protein expression, while decrease AP-1 protein level. Meanwhil, miR-21 inhibitor blocked the effects of miR-21 mentioned above. The overexpression of AP-1 could absolutely reverse the stimulatory effect of miR-21 on adiponectin. miR-21 plays an important role in regulating adipocyte differentiation and adiponectin expression by inhibiting AP-1 expression.

Vanadyl acetylacetonate upregulates PPARγ and adiponectin expression in differentiated rat adipocytes

Vanadium compounds are promising agents in the therapeutic treatment of diabetes mellitus, but their mechanism of action has not been fully elucidated. The current work investigated the effects of vanadyl acetylacetonate, VO(acac)2, on peroxisome-proliferator-activated receptor γ (PPARγ) and adiponectin, which are important targets of antidiabetic drugs. The experimental results revealed that vanadyl complexes increased the expression and multimerization of adiponectin in differentiated rat adipocytes. VO(acac)2 caused activation of p38 mitogen-activated protein kinase (MAPK) and AMP-activated protein kinase (AMPK) and elevation of PPARγ levels. The specific inhibitors SB203580 (p38 MAPK inhibitor) and T0070907 (PPARγ inhibitor) decreased the expression of adiponectin; however, compound C (AMPK inhibitor) did not significantly reduce the expression of adiponectin. In addition, vanadyl complexes induced protein-protein interaction between PPARγ and a vanadium-binding chaperone, heat shock protein 60 kDa. Overall, our results suggest that vanadyl complexes may upregulate PPARγ by suppressing PPARγ degradation, and thus stimulate adiponectin expression and multimerization. The present work has provided new insights into the mechanism of the antidiabetic actions of vanadium compounds.

Adiponectin increases secretion of rat submandibular gland via adiponectin receptors-mediated AMPK signaling

Adiponectin and adiponectin receptors (AdipoR1/2) are expressed in various tissues and are involved in the regulation of multiple functions such as energy metabolism and inflammatory responses. However, the effect of adiponectin and AdipoRs in submandibular glands has not been fully evaluated. In the present study, we found that mRNA and protein of both adiponectin and AdipoR1/2 were expressed in rat submandibular glands and in the SMG-C6 cell line, as evidenced by RT-PCR and Western blot analysis. Immunofluorescence staining showed that adiponectin was diffused in the cytoplasm, while AdipoR1/2 was concentrated in the membrane of acinar cells. Saliva flow was significantly increased by full length adiponectin (fAd) or globular adiponectin (gAd) perfusion in isolated rat submandibular glands. 5-Aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR), an adenosine monophosphate activated protein kinase (AMPK) activator, also increased saliva secretion. fAd, gAd, and AICAR all increased the average width of apical tight junctions in perfused submandibular glands, and decreased transepithelial electrical resistance (TER) in SMG-C6 cells, suggesting that adiponectin promoted secretion by modulating paracellular permeability. fAd and gAd increased p-AMPK levels, while AraA, an AMPK antagonist, abolished fAd- and gAd-induced changes in secretion, tight junction ultrastructure, and TER. Moreover, both AdipoR1 and AdipoR2 were required for fAd- or gAd-induced p-AMPK and TER responses, suggesting from their inhibition following AdipoR1 or AdipoR2 knockdown, and co-knockdown of AdipoRs by RNA interference. Our results suggest that adiponectin functions as a promoter of salivary secretion in rat submandibular glands via activation of AdipoRs, AMPK, and paracellular permeability.

Association of Adiponectin Gene Polymorphism With Birth Weight in Korean Neonates

Adiponectin has been associated with insulin resistance and type 2 diabetes mellitus and possibly fetal growth. Our aim was to assess the association between the single nucleotide polymorphisms (SNPs) of the adiponectin gene (ADIPOQ) and the birth sizes. We investigated four SNPs of ADIPOQ (rs182052, rs2241766, rs1501299, and rs266729) and birth height and weight in 237 healthy full-term neonates. The neonates with the rs182052 G allele had a greater birth weight (p = .043 in the dominant model) and a higher ponderal index (p = .028 in the additive model). The rs2241766 G allele was associated with a greater birth weight (p = .016 in the recessive model). In a logistic regression analysis, the homozygotes for the rs182052 G allele and those for the rs2241766 G allele showed a significant association with a greater birth weight above 90 percentile (OR 2.75, 95% CI 1.13–6.70 and OR 5.15, 95% CI 1.66–15.99, respectively). In conclusion, we found an association between rs182052 and rs2241766 and birth weight and ponderal index among healthy neonates and suggested that adiponectin might have some roles in fetal growth.

Serum irisin levels in new-onset type 2 diabetes

AIMS

Irisin has been identified as a novel myokine that drives brown-fat-like conversion of white adipose tissue. In this cross-sectional study, we investigated whether serum irisin levels are decreased in patients with type 2 diabetes (T2D) compared with control subjects with normal glucose tolerance (NGT), and assessed the association between serum irisin levels and various metabolic parameters.

METHODS

The study population was selected from a population-based study and included 104 subjects with NGT and 104 subjects with new-onset T2D. Serum irisin and adiponectin levels and metabolic parameters were measured. Multivariate logistic regression analysis was performed to assess the association between irisin levels and newly diagnosed T2D.

RESULTS

Serum irisin levels were significantly decreased in the new-onset T2D group compared with the NGT control group (p=0.003). In a multivariable model adjusted for various metabolic parameters, increased irisin levels were associated with reduced odds (OR 0.64, 95% CI 0.47-0.88, p=0.006) of prevalent newly diagnosed T2D. Furthermore, multiple regression analysis showed that 2 h plasma glucose was an independent variable influencing serum irisin levels (p=0.004).

CONCLUSION

In the present study, we found that serum irisin levels were decreased in T2D patients and inversely associated with newly diagnosed T2D, suggesting that irisin may play a crucial role in glucose intolerance and T2D.

Extracellular conversion of adiponectin hexamers into trimers

Adiponectin is an adipocyte-secreted hormone that exists as trimers, hexamers and larger species collectively referred to as HMW (high-molecular-weight) adiponectin. Whether hexamers or HMW adiponectin serve as precursors for trimers outside the circulation is currently unknown. Here, we demonstrate that adiponectin trimers can be generated from larger oligomers secreted from primary rat adipose cells or differentiated 3T3-L1 adipocytes. Purified hexameric, but not HMW, adiponectin converted into trimers in conditioned media separated from 3T3-L1 adipocytes or, more efficiently, when enclosed in the dialysis membrane in the presence of adipocytes. Several lines of evidence indicate that the conversion is mediated by an extracellular redox system. First, N-terminal epitope-tagged hexamers converted into trimers without proteolytic removal of the tag. Secondly, appearance of trimers was associated with conversion of disulfide-bonded dimers into monomers. Thirdly, thiol-reactive agents inhibited conversion into trimers. Consistent with a redox-based mechanism, purified hexamers reductively converted into trimers in defined glutathione redox buffer with reduction potential typically found in the extracellular environment while the HMW adiponectin remained stable. In addition, conversion of hexamers into trimers was enhanced by NADPH, but not by NADP+. Collectively, these data strongly suggest the presence of an extracellular redox system capable of converting adiponectin oligomers.

Globular adiponectin enhances muscle insulin action via microvascular recruitment and increased insulin delivery

RATIONALE

Adiponectin enhances insulin action and induces nitric oxide-dependent vasodilatation. Insulin delivery to muscle microcirculation and transendothelial transport are 2 discrete steps that limit insulin's action. We have shown that expansion of muscle microvascular surface area increases muscle insulin delivery and action.

OBJECTIVE

To examine whether adiponectin modulates muscle microvascular recruitment thus insulin delivery and action in vivo.

METHODS AND RESULTS

Overnight fasted adult male rats were studied. We determined the effects of adiponectin on muscle microvascular recruitment, using contrast-enhanced ultrasound, on insulin-mediated microvascular recruitment and whole-body glucose disposal, using contrast-enhanced ultrasound and insulin clamp, and on muscle insulin clearance and uptake with (125)I-insulin. Globular adiponectin potently increased muscle microvascular blood volume without altering microvascular blood flow velocity, leading to a significantly increased microvascular blood flow. This was paralleled by a ≈30% to 40% increase in muscle insulin uptake and clearance, and ≈30% increase in insulin-stimulated whole-body glucose disposal. Inhibition of endothelial nitric oxide synthase abolished globular adiponectin-mediated muscle microvascular recruitment and insulin uptake. In cultured endothelial cells, globular adiponectin dose-dependently increased endothelial nitric oxide synthase phosphorylation but had no effect on endothelial cell internalization of insulin.

CONCLUSIONS

Globular adiponectin increases muscle insulin uptake by recruiting muscle microvasculature, which contributes to its insulin-sensitizing action.

What is the role of adiponectin in obesity related non-alcoholic fatty liver disease?

Non-alcoholic fatty liver disease (NAFLD) is recognized as the most common type of chronic liver disease in Western countries. Insulin resistance is a key factor in the pathogenesis of NAFLD, the latter being considered as the hepatic component of insulin resistance or obesity. Adiponectin is the most abundant adipose-specific adipokine. There is evidence that adiponectin decreases hepatic and systematic insulin resistance, and attenuates liver inflammation and fibrosis. Adiponectin generally predicts steatosis grade and the severity of NAFLD; however, to what extent this is a direct effect or related to the presence of more severe insulin resistance or obesity remains to be addressed. Although there is no proven pharmacotherapy for the treatment of NAFLD, recent therapeutic strategies have focused on the indirect upregulation of adiponectin through the administration of various therapeutic agents and/or lifestyle modifications. In this adiponectin-focused review, the pathogenetic role and the potential therapeutic benefits of adiponectin in NAFLD are analyzed systematically.

Delivery of adiponectin gene to skeletal muscle using ultrasound targeted microbubbles improves insulin sensitivity and whole body glucose homeostasis

Numerous studies have shown that adiponectin confers antidiabetic effects via both insulin-like and insulin-sensitizing actions. The majority of adiponectin in circulation is derived from adipocytes; however, other tissues such as skeletal muscle can produce adiponectin. This study was designed to investigate the functional significance of adiponectin produced by skeletal muscle. We encapsulated the adiponectin gene in lipid-coated microspheres filled with octafluoropropane gas that were injected into the systemic circulation and destroyed within the microvasculature of skeletal muscle using ultrasound. We first demonstrated safe and successful targeting of luciferase and green fluorescent protein reporter genes to skeletal muscle using this approach and then confirmed efficient overexpression of adiponectin mRNA and oligomeric protein forms. Glucose tolerance test indicated that overexpression of adiponectin in skeletal muscle was able to improve glucose intolerance induced by feeding mice a high-fat diet (HFD), and this correlated with improved skeletal muscle insulin signaling. We then performed hyperinsulinemic-euglycemic clamp studies and demonstrated that adiponectin overexpression attenuated the decreases in glucose infusion rate, glucose disposal, and increase in glucose appearance induced by HFD. Ultrasound-targeted microbubble destruction (UTMD) delivery of adiponectin to skeletal muscle also enhanced serum adiponectin levels and improved hepatic insulin sensitivity. In conclusion, our data show that UTMD efficiently delivers adiponectin to skeletal muscle and that this improves insulin sensitivity and glucose homeostasis.

Perivascular adipose tissue-derived adiponectin activates BK(Ca) channels to induce anticontractile responses

This study aims to identify the potential mechanisms by which perivascular adipose tissue (PVAT) reduces tone in small arteries. Small mesenteric arteries from wild-type and large-conductance Ca(2+)-activated K(+) (BKCa) channel knockout mice were mounted on a wire myograph in the presence and absence of PVAT, and contractile responses to norepinephrine were assessed. Electrophysiology studies were performed in isolated vessels to measure changes in membrane potential produced by adiponectin. Contractile responses from wild-type mouse small arteries were significantly reduced in the presence of PVAT. This was not observed in the presence of a BKCa channel inhibitor or with nitric oxide synthase (NOS) inhibition or in BKCa or adiponectin knockout mice. Solution transfer experiments demonstrated the presence of an anticontractile factor released from PVAT. Adiponectin-induced vasorelaxation and hyperpolarization in wild-type arteries were not evident in the absence of or after inhibition of BKCa channels. PVAT from BKCa or adiponectin knockout mice failed to elicit an anticontractile response in wild-type arteries. PVAT releases adiponectin, which is an anticontractile factor. Its effect on vascular tone is mediated by activation of BKCa channels on vascular smooth muscle cells and adipocytes and by endothelial mechanisms.

Maternal docosahexaenoic acid increases adiponectin and normalizes IUGR-induced changes in rat adipose deposition

Intrauterine growth restriction (IUGR) predisposes to obesity and adipose dysfunction. We previously demonstrated IUGR-induced increased visceral adipose deposition and dysregulated expression of peroxisome proliferator activated receptor- γ 2 (PPAR γ 2) in male adolescent rats, prior to the onset of obesity. In other studies, activation of PPAR γ increases subcutaneous adiponectin expression and normalizes visceral adipose deposition. We hypothesized that maternal supplementation with docosahexaenoic acid (DHA), a PPAR γ agonist, would normalize IUGR adipose deposition in association with increased PPAR γ , adiponectin, and adiponectin receptor expression in subcutaneous adipose. To test these hypotheses, we used a well-characterized model of uteroplacental-insufficiency-(UPI-) induced IUGR in the rat with maternal DHA supplementation. Our primary findings were that maternal DHA supplementation during rat pregnancy and lactation (1) normalizes IUGR-induced changes in adipose deposition and visceral PPAR γ expression in male rats and (2) increases serum adiponectin, as well as adipose expression of adiponectin and adiponectin receptors in former IUGR rats. Our novel findings suggest that maternal DHA supplementation may normalize adipose dysfunction and promote adiponectin-induced improvements in metabolic function in IUGR.

Factors related with adiponectinemia in obese and normal-weight women and with its variation in weight loss programs

OBJECTIVE

To assess different factors influencing adiponectinemia in obese and normal-weight women; to identify factors associated with the variation (Δ) in adiponectinemia in obese women following a 6-month weight loss program, according to surgical/non-surgical interventions.

METHODS

We studied 100 normal-weight women and 112 obese premenopausal women; none of them was on any medical treatment. Women were characterized for anthropometrics, daily macronutrient intake, smoking status, contraceptives use, adiponectin as well as IL-6 and TNF-α serum concentrations.

RESULTS

Adiponectinemia was lower in obese women (p < 0.001), revealing an inverse association with waist-to-hip ratio (p < 0.001; r = -0.335). Normal-weight women presented lower adiponectinemia among smokers (p = 0.041); body fat, waist-to-hip ratio, TNF-α levels, carbohydrate intake, and smoking all influence adiponectinemia (r(2) = 0.436). After weight loss interventions, a significant modification in macronutrient intake occurs followed by anthropometrics decrease (chiefly after bariatric procedures) and adiponectinemia increase (similar after surgical and non-surgical interventions). After bariatric intervention, Δ adiponectinemia was inversely correlated to Δ waist circumference and Δ carbohydrate intake (r(2) = 0.706).

CONCLUSION

Anthropometrics, diet, smoking, and TNF-α levels all influence adiponectinemia in normal-weight women, although explaining less than 50% of it. In obese women, anthropometrics modestly explain adiponectinemia. Opposite to non-surgical interventions, after bariatric surgery adiponectinemia increase is largely explained by diet composition and anthropometric changes.

Adiponectin receptors form homomers and heteromers exhibiting distinct ligand binding and intracellular signaling properties

Adiponectin binds to two widely expressed receptors (AdipoR1 and AdipoR2) that contain seven transmembrane domains but, unlike G-protein coupled receptors, present an extracellular C terminus and a cytosolic N terminus. Recently, AdipoR1 was found to associate in high order complexes. However, it is still unknown whether AdipoR2 may also form homomers or heteromers with AdipoR1 or if such interactions may be functionally relevant. Herein, we have analyzed the oligomerization pattern of AdipoRs by FRET and immunoprecipitation and evaluated both the internalization of AdipoRs in response to various adiponectin isoforms and the effect of adiponectin binding to different AdipoR combinations on AMP-activated protein kinase phosphorylation and peroxisome proliferator-activated receptor α activation. Transfection of HEK293AD cells with AdipoR1 and AdipoR2 showed that both receptors colocalize at both the plasma membrane and the endoplasmic reticulum. Co-transfection with the different AdipoR pairs yielded high FRET efficiencies in non-stimulated cells, which indicates that AdipoR1 and AdipoR2 form homo- and heteromeric complexes under resting conditions. Live FRET imaging suggested that both homo- and heteromeric AdipoR complexes dissociate in response to adiponectin, but heteromers separate faster than homomers. Finally, phosphorylation of AMP-activated protein kinase in response to adiponectin was delayed in cells wherein heteromer formation was favored. In sum, our findings indicate that AdipoR1 and AdipoR2 form homo- and heteromers that present unique interaction behaviors and signaling properties. This raises the possibility that the pleiotropic, tissue-dependent functions of adiponectin depend on the expression levels of AdipoR1 and AdipoR2 and, therefore, on the steady-state proportion of homo- and heteromeric complexes.

Exercise restores insulin, but not adiponectin, response in skeletal muscle of high-fat fed rodents

High-fat (HF) diets impair skeletal muscle response to the insulin-sensitizing adipokine adiponectin (Ad) in rodents, preceding the development of insulin resistance. Skeletal muscle insulin response in HF-fed rats can be restored with chronic exercise; whether recovery of skeletal muscle Ad response is necessary for the exercise-induced recovery of insulin-stimulated glucose transport is not known. In the current study, insulin and Ad resistance were induced in rodents with 4 wk of HF feeding (HF4; low-fat fed animals used as control). Rats were then treadmill-exercised (HF5EX1, HF6EX2) or supplemented orally with the pharmacological agent β-guadinoproprionic acid (GPA; HF5GPA1, HF6GPA2) for 1 or 2 wk with continued HF feeding. Insulin and Ad responses (glucose transport and palmitate oxidation, respectively) were assessed 48 h after the last exercise bout ex vivo in isolated solei. Insulin response was impaired following 4 wk of HF feeding and improved with 1 and 2 wk of exercise and β-GPA supplementation (HF5EX1, HF6EX2, HF5GPA1, and HF6GPA2). The recovery of insulin response generally coincided with improved Akt Thr308 phosphorylation in HF5GPA1, HF6EX2, and HF6GPA2, although not in HF5EX1. Ad-stimulated palmitate oxidation was not restored with either treatment. Total protein contents of AdipoR1, AdipoR2, APPL1, and APPL2, as well as total and phosphorylated AMPK and ACC were unaltered by diet, exercise, and β-GPA at the assessed time points. We conclude that the exercise and pharmacologically (β-GPA)-induced recovery of skeletal muscle insulin response after HF feeding is not dependent on the restoration of Ad response, as assessed ex vivo.

Not all fat is equal: differential gene expression and potential therapeutic targets in subcutaneous adipose, visceral adipose, and endometrium of obese women with and without endometrial cancer

OBJECTIVE

To identify obesity-related cancer genes in endometrial and adipose tissue depots of body mass index-matched morbidly obese women with and without endometrial cancer.

METHODS

Eight women undergoing hysterectomy (4 women with and 4 women without endometrial cancer) were matched by age (52.6 years) and body mass index (44.5 kg/m). Endometrium, visceral adipose tissue, and subcutaneous adipose tissue were collected and subjected to microarray analysis using Affymetrix Human Genome U133 Plus 2.0 Arrays. Gene set enrichment analysis used to extract biological information from the gene expression data and t test metric ranked and compared genes in the expression data set. Protein expression was measured in the endometrial samples, and serum was collected for hormone/metabolite assays.

RESULTS

No significant differences were detected in hormone/metabolite levels between groups. Gene set enrichment analysis comparisons demonstrated that endometrial, visceral adipose and subcutaneous adipose tissues displayed 40, 47, and 38 alternatively regulated gene set pathways when comparing patients with and without cancer. Nineteen gene sets were alternately regulated in both visceral and subcutaneous adipose tissues; however, eighteen of these were regulated in the opposite direction. Five pathways were significantly and alternately regulated in all 3 tissue types and included glycolysis/gluconeogenesis, ribosome, peroxisome proliferator activated receptor signaling, pathogenic Escherichia coli infection, and natural killer-mediated cytotoxicity. In the malignant endometrium, liver kinase B1 underexpression was observed in all patients with cancer. Liver kinase B1 underexpression decreased adenosine monophosphate-activated protein kinase activity toward acetyl-CoA carboxylase and implied enhanced lipid biosynthesis in obesity-induced endometrial cancer.

CONCLUSIONS

Subcutaneous and visceral adipose tissue depots have opposite patterns of gene expression in obese patients with and without endometrial cancer. The altered de novo lipogenesis and individual gene targets identified provide new potential targets for cancer treatment and prevention for at-risk obese women.

Prediagnostic circulating adipokine concentrations and risk of renal cell carcinoma in male smokers

Despite a well-established link between obesity and renal cell carcinoma (RCC), the mechanism through which obesity acts to increase cancer risk is unclear. Adiponectin, leptin and resistin are adipocyte-secreted peptide hormones that may influence RCC development through their demonstrated effects on inflammation, insulin resistance and cell growth and proliferation. We conducted a nested case-control study to evaluate whether prediagnostic serum adiponectin, leptin and resistin levels are associated with RCC risk. This case-control study (273 cases and 273 controls) was nested within the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study cohort of Finnish male smokers. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated using conditional logistic regression models, with analyte levels modeled continuously and categorically (defined using quartiles among controls). High adiponectin levels were significantly associated with reduced RCC risk (Quartile 4 versus Quartile 1: OR = 0.52, 95% CI = 0.30-0.88; P trend = 0.01). This association remained upon additional adjustment for body mass index at blood collection and exclusion of cases diagnosed within the first 2 years of follow-up. In addition, model adjustment for adiponectin resulted in a substantial attenuation of the association between BMI and RCC (OR per 5 kg/m(2) changed from 1.19 to 1.05). No clear associations with RCC were observed for leptin or resistin. Our results suggest that elevated levels of circulating adiponectin are associated with decreased subsequent risk of RCC. These findings provide the strongest evidence to date, suggesting that the association between obesity and RCC is mediated at least in part through the effects of low adiponectin.

Role of lipotoxicity in endothelial dysfunction

Vascular endothelial dysfunction is determined by both genetic and environmental factors that cause decreased bioavailability of the vasodilator nitric oxide. This is a hallmark of atherosclerosis, hypertension, and coronary heart disease, which are major complications of metabolic disorders, including diabetes and obesity. Several therapeutic interventions, including changes in lifestyle as well as pharmacologic treatments, are useful for improving endothelial dysfunction in the face of lipotoxicity. This review discusses the current understanding of molecular and physiologic mechanisms underlying lipotoxicity-mediated endothelial dysfunction as well as relevant therapeutic approaches to ameliorate dyslipidemia and consequent endothelial dysfunction that have the potential to improve cardiovascular and metabolic outcomes.

Modifications in basal and stress-induced hypothalamic AMP-activated protein kinase (AMPK) activity in rats chronically treated with an angiotensin II receptor blocker

5' adenosine monophosphate-activated protein kinase (AMPK) plays a prominent role as a metabolic stress sensor. The role of hypothalamic AMPK in response to restraint and surgical stress has not been previously investigated. It has been recently suggested that the renin-angiotensin system, in addition to its role in stress regulation, may play a significant role in regulating metabolic pathways including the regulation of the AMPK system. This study was thus aimed to evaluate the effects of candesartan, an angiotensin II AT1 receptor blocker drug, on hypothalamic AMPK activity under basal conditions and after restraint in conscious rats or after surgical stress under general anesthesia. Male Wistar rats were treated with 5 mg/kg/day candesartan in the drinking water for 2 weeks. The hypothalamic AMPK activity was determined under basal and stress conditions, using a kinase activity assay. Chronic administration of candesartan significantly increased hypothalamic AMPK activity. Hypothalamic AMPK activity was also increased by restraint stress whereas no change was observed during surgical stress under anesthesia. The high levels of hypothalamic AMPK activation observed in candesartan-treated rats were not changed by restraint stress but were reduced to control levels by anesthesia and surgery. In conclusion, chronic candesartan treatment and restraint stress in conscious rats stimulate the hypothalamic AMPK activity, whereas surgical stress under anesthesia inhibits pathways regulating the AMPK activity even in candesartan-treated rats.

The transcriptional coactivators p/CIP and SRC-1 control insulin resistance through IRS1 in obesity models

Three p160 family members, p/CIP, SRC1, and TIF2, have been identified as transcriptional coactivators for nuclear hormone receptors and other transcription factors in vitro. In a previous study, we reported initial characterization of the obesity-resistant phenotypes of p/CIP and SRC-1 double knockout (DKO) mice, which exhibit increased energy expenditure, and suggested that nuclear hormone receptor target genes were involved in these phenotypes. In this study, we demonstrate that p/CIP and SRC1 control insulin signaling in a cell-autonomous manner both in vitro and in vivo. Genetic deletion of p/CIP and SRC-1 increases glucose uptake and enhances insulin sensitivity in both regular chow- and high fat diet-fed DKO mice despite increased food intake. Interestingly, we discover that loss of p/CIP and SRC-1 results in resistance to age-related obesity and glucose intolerance. We show that expression levels of a key insulin signaling component, insulin receptor substrate 1 (IRS1), are significantly increased in two cell lines representing fat and muscle lineages with p/CIP and SRC-1 deletions and in white adipose tissue and skeletal muscle of DKO mice; this may account for increased glucose metabolism and insulin sensitivity. This is the first evidence that the p160 coactivators control insulin signaling and glucose metabolism through IRS1. Therefore, our studies indicate that p/CIP and SRC-1 are potential therapeutic targets not only for obesity but also for diabetes.

Effects of vitamin D treatment on skeletal muscle histology and ultrastructural changes in a rodent model

Vitamin D is well known for its role in maintaining calcium and phosphorus homeostasis and in promoting bone mineralization; however, more of its pleiotropic effects have been described recently. The aim of the present investigation was to study the effect of vitamin D treatment on skeletal muscles changes under different dietary conditions using an animal model. Four groups of C57BL/6J mice (n = 11 each) were maintained on either low fat diet (LFD) or high fat diet ‎‎(HFD) with and without 1α,25-dihydroxyvitamin D3 (calcitriol) for 16 weeks. Animal weigh was recorded at baseline and then regular intervals, and at the end of the study, skeletal muscle tissues were harvested for the evaluation of the histopathological and ultrastructural changes. When control C57BL/6J mice were fed high-fat diet for 12 weeks, body weight gain was significantly increased compared with mice fed a LFD. (30.2% vs. 8.4%, p < 0.01). There was a significant gradual decrease in the weight of HFD fed mice that were treated with vitamin D as compared with a steady increase in the weights of controls (6.8% vs. 28.7%, p < 0.01). While the LFD group showed some ultrastructural changes, HDF fed on mice showed great muscle structural abnormalities. The whole sarcosome along with its membrane and cristae were severely damaged with scattered myocytes in HFD group. Furthermore, the mitochondria appeared weak and were on the verge of degenerations. The bands were diminished with loss of connections among myofibrils. These changes were attenuated in the HFD group treated with vitamin D with tissues have regained their normal structural appearance. The current findings indicate an important effect of vitamin D on skeletal muscle histology under HFD conditions.

Adiponectin: anti-inflammatory and cardioprotective effects

Adipose tissue is an endocrine organ that plays an essential role in regulating several metabolic functions through the secretion of biological mediators called "adipokines". Dysregulation of adipokines plays a crucial role in obesity-related diseases. Adiponectin (APN) is the most abundant adipokine accounting for the 0.01% of total serum protein, and is involved in a wide variety of physiological processes including energy metabolism, inflammation, and vascular physiology. APN plasma levels are reduced in individuals with obesity, type 2 diabetes and coronary artery disease, all traits with low-grade chronic inflammation. It is has been suggested that the absence of APN anti-inflammatory effects may be a contributing factor to this inflammation. APN inhibits the expression of tumor necrosis factor-α-induced endothelial adhesion molecules, macrophage-to-foam cell transformation, tumor necrosis factor-α expression in macrophages and adipose tissue, and smooth muscle cell proliferation. It also has anti-apoptotic and anti-oxidant effects, which play a role in its cardioprotective action. This review will focus on APN as an anti-inflammatory, anti-atherogenic and cardioprotective plasma protein.

Functional genomic analysis of variation on beef tenderness induced by acute stress in angus cattle

Beef is one of the leading sources of protein, B vitamins, iron, and zinc in human food. Beef palatability is based on three general criteria: tenderness, juiciness, and flavor, of which tenderness is thought to be the most important factor. In this study, we found that beef tenderness, measured by the Warner-Bratzler shear force (WBSF), was dramatically increased by acute stress. Microarray analysis and qPCR identified a variety of genes that were differentially expressed. Pathway analysis showed that these genes were involved in immune response and regulation of metabolism process as activators or repressors. Further analysis identified that these changes may be related with CpG methylation of several genes. Therefore, the results from this study provide an enhanced understanding of the mechanisms that genetic and epigenetic regulations control meat quality and beef tenderness.

Chemerin and adiponectin contribute reciprocally to metabolic syndrome

Obesity and metabolic syndrome (MetS) are considered chronic inflammatory states. Chemerin, a novel adipokine, may play an important role in linking MetS and inflammation. We investigated the association of chemerin with inflammatory markers and with characteristics of MetS in apparently healthy overweight and obese adults. We studied 92 adults; 59 men and 33 women whose average body mass index (BMI) was 28.15 ± 5.08 kg/m(2). Anthropometric parameters, insulin resistance indices, lipid profiles, and inflammatory markers including high sensitivity C-reactive protein (hsCRP), pentraxin 3 (PTX3), adiponectin, and chemerin were measured. Controlling for age, gender, and BMI, serum chemerin level was positively correlated with body fat and serum triglyceride, and negatively correlated with adiponectin and high density lipoprotein cholesterol (HDL- C), and was not correlated with altered hsCRP or PTX3 levels. Among the low, moderate and high chemerin groups, high chemerin individuals are more likely to have lower HDL-C. Conversely, individuals in the low adiponectin group are more likely to have lower HDL-C and show more MetS phenotypic traits than moderate and high adiponectin subjects. To determine the relationships of chemerin and adiponectin to MetS and its components, participants were stratified into four groups based on their chemerin and adiponectin levels (high chemerin/high adiponectin, high chemerin/low adiponectin, low chemerin/high adiponectin, or low chemerin/low adiponectin). Participants who were in the high chemerin/low adiponectin group more likely to have dyslipidemia and MetS (OR: 5.79, 95% CI:1.00-33.70) compared to the other three group. Our findings suggest that chemerin and adiponectin may reciprocally participate in the development of MetS.

Long-term high-fat-diet feeding induces skeletal muscle mitochondrial biogenesis in rats in a sex-dependent and muscle-type specific manner

Background

Mitochondrial dysfunction is thought to play a crucial role in the etiology of insulin resistance, in which skeletal muscle is the main tissue contributor. Sex differences in skeletal muscle insulin and antioxidant responses to high-fat-diet (HFD) feeding have been described. The aim of this study was to elucidate whether there is a sex dimorphism in the effects of HFD feeding on skeletal muscle mitochondrial biogenesis and on the adiponectin signaling pathway, as well as the influence of the muscle type (oxidative or glycolytic).

Methods

Gastrocnemius and soleus muscles of male and female Wistar rats of 2 months of age fed with a high-fat-diet (HFD) or a low fat diet for 26 weeks were used. Mitochondrial biogenesis and oxidative damage markers, oxidative capacity and antioxidant defences were analyzed. Serum insulin sensitivity parameters and the levels of proteins involved in adiponectin signaling pathway were also determined.

Results

HFD feeding induced mitochondrial biogenesis in both sexes, but to a higher degree in male rats. Although HFD female rats showed greater antioxidant protection and maintained a better insulin sensitivity profile than their male counterparts, both sexes showed an impaired response to adiponectin, which was more evident in gastrocnemius muscle.

Conclusions

We conclude that HFD rats may induce skeletal muscle mitochondrial biogenesis as an attempt to compensate the deleterious consequences of adiponectin and insulin resistance on oxidative metabolism, and that the effects of HFD feeding are sex-dependent and muscle-type specific.

Timing of stage II lactogenesis is predicted by antenatal metabolic health in a cohort of primiparas

BACKGROUND

Time to onset of stage II lactogenesis varies widely, and delayed onset of lactogenesis (OL) is common among first-time mothers in the United States. Higher body mass index, older age, and larger infant birth weight are identified risk factors for delayed OL; all are known correlates with glucose metabolism. Our objective was to prenatally assess maternal biomarkers related to metabolic health and determine the extent to which these biomarkers predict timing of OL.

METHODS

We enrolled a population-based sample of expectant primiparas attending a single prenatal clinic. We obtained a blood sample 1-hour post-glucose load from an antenatal oral glucose challenge test and assayed for the following biomarkers: serum insulin, glucose, adiponectin, leptin, C-reactive protein, interleukin-6, resistin, and tumor necrosis factor-α. Our outcome measure was timing of OL, based on maternal report at 3-5 days postpartum. We used linear regression to model OL hour.

RESULTS

Twenty-six of 29 (90%) agreed to screening, 18 delivered at term and initiated breastfeeding, and 16 have complete data. Median (minimum-maximum) postpartum body mass index was 27.4 (21.8-34.7) kg/m(2), and median time to OL was 64 (10-121) hours. The model, OL = 232 - 34.9(ln[ratio insulin/glucose]) - 1.4(adiponectin), explained 56% of the variation in OL hour (p = 0.005) and was not weakened by potential confounders.

CONCLUSIONS

Higher serum insulin secretion relative to serum glucose after a glucose challenge and higher serum adiponectin are associated with earlier onset of OL. These findings suggest that factors associated with better glucose tolerance predict earlier OL.

A 7-d exercise program increases high-molecular weight adiponectin in obese adults

PURPOSE

High-molecular weight (HMW) adiponectin is the biologically active form of adiponectin and is related to enhanced insulin sensitivity and metabolic function. Previously, we found that 7 d of exercise improves insulin sensitivity in obese subjects; however, whether short-term exercise training affects HMW adiponectin in obese persons is unknown.

METHODS

We examined the effect of seven consecutive days of supervised vigorous exercise (60 min · d(-1), 85% HRmax) on HMW adiponectin and leptin secretion in 17 obese individuals (age = 55 ± 3 yr; body mass index = 33.7 ± 0.9 kg · m(-2)). Insulin sensitivity was calculated from an oral glucose tolerance test (ISIOGTT) using the Matsuda Index. Fasting plasma HMW adiponectin and leptin were quantified from blood samples obtained before the ISIOGTT. Glucose and insulin measures were obtained before and every 30 min during the test. Dual-energy x-ray absorptiometry was used to determine body composition, and indirect calorimetry was used to assess fat oxidation.

RESULTS

After the intervention, there was a significant increase in HMW adiponectin (3202 ± 543 vs 3878 ± 682 ng · mL(-1), P = 0.02) and a decrease in leptin (36.8 ± 5.1 vs 31.1 ± 4.2 μg · mL(-1), P = 0.03). Further, we observed an increase in ISIOGTT (1.7 ± 0.3 vs 2.1 ± 0.3, P = 0.04) and a decrease in glucose area under the curve (30,871 ± 2105 vs 28,469 ± 1657 mg · dL(-1) for 3 h, P = 0.01). The increase in HMW adiponectin was positively associated with the increase in basal fat oxidation (r = 0.57, P = 0.03), consistent with an improvement in adipose tissue metabolic function.

CONCLUSIONS

The data suggest that 7 d of exercise is sufficient not only to improve insulin sensitivity and fat oxidation but also to favorably alter adipokine secretion, independent of changes in body weight or composition.

CTRP1 protein enhances fatty acid oxidation via AMP-activated protein kinase (AMPK) activation and acetyl-CoA carboxylase (ACC) inhibition

We previously described the adipokine CTRP1, which has up-regulated expression following exposure to the anti-diabetic drug rosiglitazone and increased circulating levels in adiponectin-null mice (Wong, G. W., Krawczyk, S. A., Kitidis-Mitrokostas, C., Revett, T., Gimeno, R., and Lodish, H. F. (2008) Biochem. J. 416, 161-177). Although recombinant CTRP1 lowers blood glucose in mice, its physiological function, mechanisms of action, and roles in metabolic stress remain unknown. Here, we show that circulating levels of CTRP1 are strikingly reduced in diet-induced obese mice. Overexpressing CTRP1 in transgenic mice improved insulin sensitivity and decreased high-fat diet-induced weight gain. Reduced adiposity resulted from enhanced fatty acid oxidation and energy expenditure, effects mediated by AMP-activated protein kinase (AMPK). In skeletal muscle of transgenic mice, AMPKα and its downstream target, acetyl-CoA carboxylase (ACC), were hyperphosphorylated, indicative of AMPK activation and ACC inhibition. Inactivation of ACC promotes mitochondrial fat oxidation. Consistent with the direct effect of CTRP1 on AMPK signaling, recombinant CTRP1 administration acutely stimulated muscle AMPKα and ACC phosphorylation in vivo. In isolated soleus muscle, recombinant CTRP1 activated AMPK signaling to increase fatty acid oxidation ex vivo, an effect abrogated by an AMPK inhibitor. These results provide the first in vivo evidence that CTRP1 is a novel regulator of fatty acid metabolism.

Adiponectin action: a combination of endocrine and autocrine/paracrine effects

The widespread physiological actions of adiponectin have now been well characterized as clinical studies and works in animal models have established strong correlations between circulating adiponectin level and various disease-related outcomes. Thus, conventional thinking attributes many of adiponectin's beneficial effects to endocrine actions of adipose-derived adiponectin. However, it is now clear that several tissues can themselves produce adiponectin and there is growing evidence that locally produced adiponectin can mediate functionally important autocrine or paracrine effects. In this review article we discuss regulation of adiponectin production, its mechanism of action via receptor isoforms and signaling pathways, and its principal physiological effects (i.e., metabolic and cardiovascular). The role of endocrine actions of adiponectin and changes in local production of adiponectin or its receptors in whole body physiology is discussed.

Berberine-improved visceral white adipose tissue insulin resistance associated with altered sterol regulatory element-binding proteins, liver x receptors, and peroxisome proliferator-activated receptors transcriptional programs in diabetic hamsters

The diabetic "lipotoxicity" hypothesis presents that fat-induced visceral white adipose tissue insulin resistance plays a central role in the pathogenesis of type 2 diabetes. Berberine, a hypolipidemic agent, has been reported to have antidiabetic activities. The molecular mechanisms for this property are, however, not well clarified. Therefore in this study type 2 diabetic hamsters were induced by high-fat diet with low-dose streptozotocin. Then, we investigated the gene expression alterations and explored the molecular mechanisms underlying the therapeutic effect of berberine on fat-induced visceral white adipose tissue insulin resistance in diabetic hamsters by microarray analysis followed by real-time reverse transcription-polymerase chain reaction (RT-PCR) confirmation. Type 2 diabetic hamsters exhibited hyperglycemia and relative hyperinsulinemia, glucose intolerance, insulin resistance, intra-adipocyte lipid accumulation, significant increase in body weight and visceral white adipose tissue weight, abnormal serum adipokines levels, and deleterious dyslipidemia. Furthermore, they had increased sterol regulatory element-binding proteins (SREBPs) expression and decreased liver X receptors (LXRs) and peroxisome proliferator-activated receptors (PPARs) expression in visceral white adipose tissue. After 9-week berberine treatment, fat-induced insulin resistance and diabetic phenotype in type 2 diabetic hamsters were significantly improved. Compared with diabetic hamsters, expression of LXRs and PPARs significantly increased and SREBPs significantly decreased in visceral white adipose tissue from berberine-treated diabetic hamsters. These results suggest that altered visceral white adipose tissue LXRs, PPARs, and SREBPs transcriptional programs are involved in the therapeutic mechanisms of berberine on fat-induced visceral white adipose tissue insulin resistance in type 2 diabetic hamsters.

Genetic variants in candidate genes influencing NAFLD progression

Nonalcoholic fatty liver disease (NAFLD) is a metabolic disorder including simple steatosis and nonalcoholic steatohepatitis (NASH). Advanced stages of NASH result ultimately in fibrosis, cirrhosis, and hepatocarcinoma. A diagnosis of NASH entails an increased risk of both liver-related and cardiovascular mortality as worsening of the metabolic syndrome. Because of its escalation, many investigations have been performed to elucidate the pathophysiologic origins of the disease progression. Human epidemiologic studies describing polymorphisms in a number of genes involved in metabolic dysfunctions have contributed to clarify the causes leading to the disease evolution. In this review, we attempt to outline critically the most recently identified genetic variants in NAFLD patients to identify possible risk factors promoting the progression of the disease. The evaluation of altered genotypes together with other clinical variables may facilitate the clinical management of these patients.