Insulin/Foxo1 pathway regulates expression levels of adiponectin receptors and adiponectin sensitivity

Molecular characterization of an adiponectin receptor homolog in the white leg shrimp, Litopenaeus vannamei

Adiponectin (AdipoQ) and its receptors (AdipoRs) are strongly related to growth and development of skeletal muscle, as well as glucose and lipid metabolism in vertebrates. Herein we report the identification of the first full-length cDNA encoding an AdipoR homolog (Liv-AdipoR) from the decapod crustacean Litopenaeus vannamei using a combination of next generation sequencing (NGS) technology and bioinformatics analysis. The full-length Liv-AdipoR (1,245 bp) encoded a protein that exhibited the canonical seven transmembrane domains (7TMs) and the inversed topology that characterize members of the progestin and adipoQ receptor (PAQR) family. Based on the obtained sequence information, only a single orthologous AdipoR gene appears to exist in arthropods, whereas two paralogs, AdipoR1 and AdipoR2, have evolved in vertebrates. Transcriptional analysis suggested that the single Liv-AdipoR gene appears to serve the functions of two mammalian AdipoRs. At 72 h after injection of 50 pmol Liv-AdipoR dsRNA (340 bp) into L. vannamei thoracic muscle and deep abdominal muscle, transcription levels of Liv-AdipoR decreased by 93% and 97%, respectively. This confirmed optimal conditions for RNAi of Liv-AdipoR. Knockdown of Liv-AdipoR resulted in significant changes in the plasma levels of ammonia, 3-methylhistine, and ornithine, but not plasma glucose, suggesting that that Liv-AdipoR is important for maintaining muscle fibers. The chronic effect of Liv-AdipoR dsRNA injection was increased mortality. Transcriptomic analysis showed that 804 contigs were upregulated and 212 contigs were downregulated by the knockdown of Liv-AdipoR in deep abdominal muscle. The significantly upregulated genes were categorized as four main functional groups: RNA-editing and transcriptional regulators, molecular chaperones, metabolic regulators, and channel proteins.

CHIP(-/-)-Mouse Liver: Adiponectin-AMPK-FOXO-Activation Overrides CYP2E1-Elicited JNK1-Activation, Delaying Onset of NASH: Therapeutic Implications

Genetic ablation of C-terminus of Hsc70-interacting protein (CHIP) E3 ubiquitin-ligase impairs hepatic cytochrome P450 CYP2E1 degradation. Consequent CYP2E1 gain of function accelerates reactive O2 species (ROS) production, triggering oxidative/proteotoxic stress associated with sustained activation of c-Jun NH2-terminal kinase (JNK)-signaling cascades, pro-inflammatory effectors/cytokines, insulin resistance, progressive hepatocellular ballooning and microvesicular steatosis. Despite this, little evidence of nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) was found in CHIP(-/-)-mice over the first 8-9-months of life. We herein document that this lack of tissue injury is largely due to the concurrent up-regulation and/or activation of the adiponectin-5'-AMP-activated protein kinase (AMPK)-forkhead box O (FOXO)-signaling axis stemming from at the least three synergistic features: Up-regulated expression of adipose tissue adiponectin and its hepatic adipoR1/adipoR2 receptors, stabilization of hepatic AMPKα1-isoform, identified herein for the first time as a CHIP-ubiquitination substrate (unlike its AMPKα2-isoform), as well as nuclear stabilization of FOXOs, well-known CHIP-ubiquitination targets. Such beneficial predominance of the adiponectin-AMPK-FOXO-signaling axis over the sustained JNK-elevation and injurious insulin resistance in CHIP(-/-)-livers apparently counteracts/delays rapid progression of the hepatic microvesicular steatosis to the characteristic macrovesicular steatosis observed in clinical NASH and/or rodent NASH-models.

Resveratrol increases AdipoR1 and AdipoR2 expression in type 2 diabetic nephropathy

BACKGROUND

Adiponectin has multiple functions including insulin sensitization, anti-inflammation and antiatherogenesis in various organs. Adiponectin activates 5'-adenosine monophosphate-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor (PPAR)α via the adiponectin receptor (AdipoR) 1 and 2, which are critical for regulating lipids and glucose homeostasis and for controlling oxidative stress. We investigated whether resveratrol can inhibit renal damage in type 2 diabetic db/db mice and the underlying mechanisms of its effects.

METHODS

Four groups of male C57 BLKS/J db/m and db/db mice and human glomerular endothelial cells (HGECs) were used. Resveratrol was administered to diabetic and nondiabetic mice by oral gavage for 12 weeks starting at 8 weeks of age.

RESULTS

In db/db mice, resveratrol increased serum adiponectin levels and decreased albuminuria, glomerular matrix expansion, inflammation and apoptosis in the glomerulus. Resveratrol increased the phosphorylation of AMPK and silent information regulator T1 (SIRT1), and decreased phosphorylation of downstream effectors class O forkhead box (FoxO)1 and FoxO3a via increasing AdipoR1 and AdipoR2 in the renal cortex. Furthermore, resveratrol increased expression of PPARγ coactivator (PGC)-1α, estrogen-related receptor-1α, and phosphorylated acetyl-CoA carboxylase and decreased sterol regulatory element-binding protein 1. This effect lowered the content of nonesterified fatty acid and triacylglycerol in the kidneys, decreasing apoptosis, oxidative stress and activating endothelial nitric oxide synthase. Resveratrol prevented cultured HGECs from undergoing high-glucose-induced oxidative stress and apoptosis by activating the AMPK-SIRT1-PGC-1α axis and PPARα through increases in AdipoR1 and AdipoR2 expression.

CONCLUSIONS

These results suggest that resveratrol prevents diabetic nephropathy by ameliorating lipotoxicity, oxidative stress, apoptosis and endothelial dysfunction via increasing AdipoR1 and AdipoR2 expression.

High protein/fish oil diet prevents hepatic steatosis in NONcNZO10 mice; association with diet/genetics-regulated micro-RNAs

OBJECTIVE

NONcNZO10 (NZ10) mice are predisposed to obesity and develop type 2 diabetes (T2D) and hepatic steatosis even when maintained on a control diet (CD) of 6% fat. Studies were designed to determine whether this extreme susceptibility phenotype could be alleviated by diet and if so the molecular targets of diet.

METHODS

NZ10 and SWR/J (SWR) control mice were fed a CD or a test diet of high protein and fish oil (HPO) for 19 weeks and then analyzed for steatosis, blood chemistry, hepatic gene and micro-RNA expression.

RESULTS

HPO diet prevented steatosis, significantly increased serum adiponectin and reduced serum cholesterol and triglycerides only in NZ10 mice. The HPO diet repressed hepatic expression of fatty acid metabolic regulators including PPAR-γ, sterol regulatory element-binding protein-c1, peroxisome proliferator-activated receptor gamma co-activator-1, fatty acid synthase, fatty acid binding protein-4, and apolipoprotein A4 genes only in NZ10 mice. Also repressed by a HPO diet were adiponectinR2 receptor, leptin-R, PPAR-α, pyruvate dehydrogenase kinase isoforms 2 and 4, AKT2 and GSK3β. Micro-RNA (miR) arrays identified miRs that were diet and/or genetics regulated. QRTPCR confirmed increased expression of miR-205 and suppression of a series of miRs including miRs-411, 155, 335 and 21 in the NZ10-HPO group, each of which are implicated in the progression of diabetes and/or steatosis. Evidence is presented that miR-205 co-regulates with PPARγ and may regulate fibrosis and EMT during the progression of steatosis in the livers of NZ10-CD mice. The dietary responses of miR-205 are tissue-specific with opposite effects in adipose and liver.

CONCLUSION

The results confirm that a HPO diet overrides the genetic susceptibility of NZ10 mice and this correlates with the suppression of key genes and perhaps micro-RNAs involved in hyperglycemia, dyslipidemia and inflammation including master PPAR regulators, adiponectin and leptin receptors.

Adiponectin resistance in skeletal muscle: pathophysiological implications in chronic heart failure

Skeletal muscle wasting is a common complication of chronic heart failure (CHF) and linked to poor patient prognosis. In recent years, adiponectin was postulated to be centrally involved in CHF-associated metabolic failure and muscle wasting. This review discusses current knowledge on the role of adiponectin in CHF. Particular emphasis will be given to the complex interaction mechanisms and the intracellular pathways underlying adiponectin resistance in skeletal muscle of CHF patients. In this review, we propose that the resistance process is multifactorial, integrating abnormalities emanating from insulin signalling, mitochondrial biogenesis, and ceramide metabolism.

Long-term oral administration of osteocalcin induces insulin resistance in male mice fed a high-fat, high-sucrose diet

Uncarboxylated osteocalcin (GluOC), a bone-derived hormone, regulates energy metabolism by stimulating insulin secretion, pancreatic β-cell proliferation, and adiponectin expression in adipocytes. Previously, we showed that long-term intermittent or daily oral administration of GluOC reduced the fasting blood glucose level, improved glucose tolerance, and increased the fasting serum insulin concentration as well as pancreatic β-cell area in female mice fed a normal or high-fat, high-sucrose diet. We have now performed similar experiments with male mice and found that such GluOC administration induced glucose intolerance, insulin resistance, and adipocyte hypertrophy in those fed a high-fat, high-sucrose diet. In addition, GluOC increased the circulating concentration of testosterone and reduced that of adiponectin in such mice. These phenotypes were not observed in male mice fed a high-fat, high-sucrose diet after orchidectomy, but they were apparent in orchidectomized male mice or intact female mice that were fed such a diet and subjected to continuous testosterone supplementation. Our results thus reveal a sex difference in the effects of GluOC on glucose homeostasis. Given that oral administration of GluOC has been considered a potentially safe and convenient option for the treatment or prevention of metabolic disorders, this sex difference will need to be taken into account in further investigations.

Pancreatic regulation of glucose homeostasis

In order to ensure normal body function, the human body is dependent on a tight control of its blood glucose levels. This is accomplished by a highly sophisticated network of various hormones and neuropeptides released mainly from the brain, pancreas, liver, intestine as well as adipose and muscle tissue. Within this network, the pancreas represents a key player by secreting the blood sugar-lowering hormone insulin and its opponent glucagon. However, disturbances in the interplay of the hormones and peptides involved may lead to metabolic disorders such as type 2 diabetes mellitus (T2DM) whose prevalence, comorbidities and medical costs take on a dramatic scale. Therefore, it is of utmost importance to uncover and understand the mechanisms underlying the various interactions to improve existing anti-diabetic therapies and drugs on the one hand and to develop new therapeutic approaches on the other. This review summarizes the interplay of the pancreas with various other organs and tissues that maintain glucose homeostasis. Furthermore, anti-diabetic drugs and their impact on signaling pathways underlying the network will be discussed.

Tumor necrosis factor-α impairs adiponectin signalling, mitochondrial biogenesis, and myogenesis in primary human myotubes cultures

Skeletal muscle metabolic changes are common in patients with chronic heart failure (HF). Previously, we demonstrated a functional skeletal muscle adiponectin resistance in HF patients with reduced left ventricular ejection fraction (HFrEF). We aimed to examine the impact of adiponectin receptor 1 (AdipoR1) deficiency and TNF-α treatment on adiponectin signaling, proliferative capacity, myogenic differentiation, and mitochondrial biogenesis in primary human skeletal muscle cells. Primary cultures of myoblasts and myotubes were initiated from the musculus vastus lateralis of 10 HFrEF patients (left ventricular ejection fraction; 31.30 ± 2.89%) and 10 age- and gender-matched healthy controls. Healthy control cultures were transfected with siAdipoR1 and/or exposed to TNF-α (10 ng/ml; 72 h). Primary cultures from HFrEF patients preserved the features of adiponectin resistance in vivo. AdipoR1 mRNA was negatively correlated with time to reach maximal cell index (r = -0.7319, P = 0.003). SiRNA-mediated AdipoR1 silencing reduced pAMPK (P < 0.01), AMPK activation (P = 0.046), and myoblast proliferation rate (xCELLigence Real-Time Cellular Analysis; P < 0.0001). Moreover, TNF-α decreased the mRNA expression of genes involved in glucose (APPL1, P = 0.0002; AMPK, P = 0.021), lipid (PPARα, P = 0.025; ACADM, P = 0.003), and mitochondrial (FOXO3, P = 0.018) metabolism, impaired myogenesis (MyoD1, P = 0.053; myogenin, P = 0.048) and polarized cytokine secretion toward a growth-promoting phenotype (IL-10, IL-1β, IFN-γ, P < 0.05 for all; Meso Scale Discovery Technology). Major features of adiponectin resistance are retained in primary cultures from the skeletal muscle of HFrEF patients. In addition, our results suggest that an increased inflammatory constitution contributes to adiponectin resistance and confers alterations in skeletal muscle differentiation, growth, and function.

Adiponectin downregulation is associated with volume overload-induced myocyte dysfunction in rats

AIM

Adiponectin has been reported to exert protective effects during pathological ventricular remodeling, but the role of adiponectin in volume overload-induced heart failure remains unclear. In this study we investigated the effect of adiponectin on cardiac myocyte contractile dysfunction following volume overload in rats.

METHODS

Volume overload was surgically induced in rats by infrarenal aorta-vena cava fistula. The rats were intravenously administered adenoviral adiponectin at 2-, 6- and 9-weeks following fistula. The protein expression of adiponectin, adiponectin receptors (AdipoR1/R2 and T-cadherin) and AMPK activity were measured using Western blot analyses. Isolated ventricular myocytes were prepared at 12 weeks post-fistula to examine the contractile performance of myocytes and intracellular Ca(2+) transient.

RESULTS

A-V fistula resulted in significant reductions in serum and myocardial adiponectin levels, myocardial adiponectin receptor (AdipoR1/R2 and T-cadherin) levels, as well as myocardial AMPK activity. Consistent with these changes, the isolated myocytes exhibited significant depression in cell shortening and intracellular Ca(2+) transient. Administration of adenoviral adiponectin significantly increased serum adiponectin levels and prevented myocyte contractile dysfunction in fistula rats. Furthermore, pretreatment of isolated myocytes with recombinant adiponectin (2.5 μg/mL) significantly improved their contractile performance in fistula rats, but had no effects in control or adenoviral adiponectin-administered rats.

CONCLUSION

These results demonstrate a positive correlation between adiponectin downregulation and volume overload-induced ventricular remodeling. Adiponectin plays a protective role in volume overload-induced heart failure.

Adiponectin/adiponectin receptor in disease and aging

Adipocytes are not merely organs for energy conservation but endocrine organs secreting a wide array of physiologically active substances, i.e., adipokines. Of these adipokines, adiponectin is known to exert anti-diabetic and anti-atherosclerotic effects via adiponectin receptors (AdipoR)s, AdipoR1 and AdipoR2. Adiponectin has also recently been shown to regulate longevity signaling thus prolonging lifespan. Therefore, the strategy for activating adiponectin/AdipoR signaling pathways are expected to provide a solid basis for the prevention and treatment of obesity-related diseases such as the metabolic syndrome, type 2 diabetes and cardiovascular disease, as well as for ensuring healthy longevity in humans.

Lipopolysaccharide induces a downregulation of adiponectin receptors in-vitro and in-vivo

Background. Adipose tissue contributes to the inflammatory response through production of cytokines, recruitment of macrophages and modulation of the adiponectin system. Previous studies have identified a down-regulation of adiponectin in pathologies characterised by acute (sepsis and endotoxaemia) and chronic inflammation (obesity and type-II diabetes mellitus). In this study, we investigated the hypothesis that LPS would reduce adiponectin receptor expression in a murine model of endotoxaemia and in adipoocyte and myocyte cell cultures.

Methods. 25 mg/kg LPS was injected intra-peritoneally into C57BL/6J mice, equivalent volumes of normal saline were used in control animals. Mice were killed at 4 or 24 h post injection and tissues harvested. Murine adipocytes (3T3-L1) and myocytes (C2C12) were grown in standard culture, treated with LPS (0.1 µg/ml–10 µg/ml) and harvested at 4 and 24 h. RNA was extracted and qPCR was conducted according to standard protocols and relative expression was calculated.

Results. After LPS treatment there was a significant reduction after 4 h in gene expression of adipo R1 in muscle and peri-renal fat and of adipo R2 in liver, peri-renal fat and abdominal wall subcutaneous fat. After 24 h, significant reductions were limited to muscle. Cell culture extracts showed varied changes with reduction in adiponectin and adipo R2 gene expression only in adipocytes.

Conclusions. LPS reduced adiponectin receptor gene expression in several tissues including adipocytes. This reflects a down-regulation of this anti-inflammatory and insulin-sensitising pathway in response to LPS. The trend towards base line after 24 h in tissue depots may reflect counter-regulatory mechanisms. Adiponectin receptor regulation differs in the tissues investigated.

Inhibition of adipogenic differentiation of human SGBS preadipocytes by androgen-regulated microRNA miR-375

Late-onset hypogonadism (LOH), defined as a combination of low serum testosterone (T) levels in combination with clinical signs and symptoms of androgen deficiency in ageing men, is nowadays a well-characterized disease. Testosterone therapy in males affected by hypogonadism leads to a significant decrease of fat mass. In humans, the exact molecular mechanism of T effects on inhibition of adipogenesis is still unknown. We hypothesized that specific microRNAs could be regulated by androgens which might cause an inhibition of adipogenic differentiation. To confirm this hypothesis, human mesenchymal stem cells and a preadipocyte cell line were differentiated into mature adipocytes and in parallel treated with testosterone and dihydrotestosterone. The expression level of miR-375 was upregulated during adipogenic differentiation and downregulated after androgen treatment. Furthermore, we could show that after androgen treatment the decreased expression of miR-375 led to increased expression levels of adiponectin receptor 2 (ADIPOR2) compared to untreated adipocytes. Moreover, inhibition of miR-375 also mediated a decreased adipogenic differentiation and increased ADIPOR2 expression levels. In summary, we identified miR-375 as an androgen regulated microRNA, which could play an important role for understanding the mechanism of the increase in visceral fat mass and the associated insulin resistance caused by testosterone deficiency.

Imidazoline-like drugs improve insulin sensitivity through peripheral stimulation of adiponectin and AMPK pathways in a rat model of glucose intolerance

Altered adiponectin signaling and chronic sympathetic hyperactivity have both been proposed as key factors in the pathogenesis of metabolic syndrome. We recently reported that activation of I1 imidazoline receptors (I1R) improves several symptoms of the metabolic syndrome through sympathoinhibition and increases adiponectin plasma levels in a rat model of metabolic syndrome (Fellmann L, Regnault V, Greney H, et al. J Pharmacol Exp Ther 346: 370-380, 2013). The present study was designed to explore the peripheral component of the beneficial actions of I1R ligands (i.e., sympathoinhibitory independent effects). Aged rats displaying insulin resistance and glucose intolerance were treated with LNP509, a peripherally acting I1R agonist. Glucose tolerance, insulin sensitivity, and adiponectin signaling were assessed at the end of the treatment. Direct actions of the ligand on hepatocyte and adipocyte signaling were also studied. LNP509 reduced the area under the curve of the intravenous glucose tolerance test and enhanced insulin hypoglycemic action and intracellular signaling (Akt phosphorylation), indicating improved glucose tolerance and insulin sensitivity. LNP509 stimulated adiponectin secretion acting at I1R on adipocytes, resulting in increased plasma levels of adiponectin; it also enhanced AMPK phosphorylation in hepatic tissues. Additionally, I1R activation on hepatocytes directly enhanced AMPK phosphorylation. To conclude, I1R ligands can improve insulin sensitivity acting peripherally, independently of sympathoinhibition; stimulation of adiponectin and AMPK pathways at insulin target tissues may account for this effect. This may open a promising new way for the treatment of the metabolic syndrome.

Adiponectin receptor 1 (ADIPOR1) rs1342387 polymorphism and risk of cancer: a meta-analysis

Many studies have indicated possible associations between a polymorphism of adiponectin receptor 1 (ADIPOR1) rs1342387 and risk of cancer, but contradictory results have been reported. The main aim of this study was to draw a reliable conclusion about the relationship between the rs1342387 polymorphism and cancer incidence, by conducting a literature search of Pubmed, Embase, Wanfang and Cochrane libraries. Eleven studies including 3, 738 cases and 4, 748 controls were identified in this meta-analysis. The ADIPOR1 rs1342387 polymorphism was associated with risk of colorectal cancer for all genetic comparison models (GG vs AA, OR: 1.44, 95%CI: 1.21 -1.70; G carriers vs A carriers, OR: 1.23, 95%CI: 1.11 -1.36; dominant model, OR: 1.28, 95%CI: 1.10 -1.49 and recessive model, OR: 1.31, 95%CI: 1.12 -1.55). Stratified by ethnicity, the rs1342387 polymorphism was significantly associated with risk of colorectal cancer in Asian ancestry for all genetic comparison models (GG vs AA, OR: 1.56, 95%CI: 1.26-1.92; G carriers vs. A carriers OR: 1.30, 95%CI: 1.18 -1.43; dominant model OR: 1.31, 95%CI: 1.08 -1.60 and recessive model OR: 1.44, 95%CI: 1.26 -1.64), but not in Caucasian or mixed (Caucasian mainly) groups. In summary, the ADIPOR1 rs1342387 polymorphism is significantly associated with risk of colorectal cancer among individuals of Asian ancestry.

High fat diet induced changes in gastric vagal afferent response to adiponectin

Food intake is regulated by vagal afferent signals from the stomach. Adiponectin, secreted primarily from adipocytes, also has a role in regulating food intake. However, the involvement of vagal afferents in this effect remains to be established. We aimed to determine if adiponectin can modulate gastric vagal afferent (GVA) satiety signals and further whether this is altered in high fat diet (HFD)-induced obesity. Female C57BL/6J mice were fed either a standard laboratory diet (SLD) or a HFD for 12weeks. Plasma adiponectin levels were assayed, and the expression of adiponectin in the gastric mucosa was assessed using real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The location of adiponectin protein within the gastric mucosa was determined by immunohistochemistry. To evaluate the direct effect of adiponectin on vagal afferent endings we determined adiponectin receptor expression in whole nodose ganglia (NDG) and also specifically in GVA neurons using retrograde tracing and qRT-PCR. An in vitro preparation was used to determine the effect of adiponectin on GVA response to mechanical stimulation. HFD mice exhibited an increased body weight and adiposity and showed delayed gastric emptying relative to SLD mice. Plasma adiponectin levels were not significantly different in HFD compared to SLD mice. Adiponectin mRNA was detected in the gastric mucosa of both SLD and HFD mice and presence of protein was confirmed immunohistochemically by the detection of adiponectin immunoreactive cells in the mucosal layer of the stomach. Adiponectin receptor 1 (ADIPOR1) and 2 (ADIPOR2) mRNA was present in both the SLD and HFD whole NDG and also specifically traced gastric mucosal and muscular neurons. There was a reduction in ADIPOR1 mRNA in the mucosal afferents of the HFD mice relative to the SLD mice. In HFD mice adiponectin potentiated gastric mucosal afferent responses to mucosal stroking, an effect not observed in SLD mice. Adiponectin reduced the responses of tension receptors to circular stretch to a similar extent in both SLD and HFD mice. In conclusion, adiponectin modulates GVA satiety signals. This modulatory effect is altered in HFD-induced obesity. It remains to be conclusively determined whether this modulation is involved in the regulation of food intake and what the whole animal phenotypic consequence is.

Expression of Adiponectin Receptors on Peripheral Blood Leukocytes of Hypertensive Children Is Associated with the Severity of Hypertension

The aim of the study was to find out whether peripheral blood leukocyte adiponectin receptors 1 and 2 (AdipoR1, AdipoR2) protein expression patterns (flow cytometry) differ between the primary hypertension children (n = 57) and healthy controls (n = 19) and if their expression levels are related to selected clinical parameters. The group of 26 patients [AdipoR(-)] showed lower and the group of 31 patients [AdipoR(+)] showed higher AdipoRs protein expression than the control and each other (P < 0.01 for neutrophils, P < 0.05 for monocytes). The AdipoR(+) leukocytes expressed higher AdipoR1 mRNA levels (RT-PCR) than AdipoR(-) ones and controls (P = 0.022 and P = 0.007, resp.). Despite greater BMI, the AdipoR(-) patients had unchanged serum adiponectin levels. In contrast, AdipoR(+) patients had lower serum adiponectin concentrations than the AdipoR(-) ones and controls (P < 0.001). The AdipoR(+) patients had higher blood pressure (P = 0.042) and greater carotid intima-media thickness (P = 0.017) than the AdipoR(-) ones. The stage of hypertension was associated with increased neutrophil but not monocyte AdipoR1 density (AdipoR1 MFI) (P < 0.05). Severe ambulatory hypertension was presented more often in AdipoR(+) patients than in AdipoR(-) ones (51.6% versus 26.9%, resp.; P < 0.01). In conclusion, neutrophil AdipoRs upregulation was associated with early stages of vascular injury, hypertension severity, and low serum levels of adiponectin.

Combined Adiponectin Deficiency and Resistance in Obese Patients: Can It Solve Part of the Puzzle in Nonalcoholic Steatohepatitis

BACKGROUND:

Nonalcoholic fatty liver disease (NAFLD) has become the most prevalent cause of liver disease, nonalcoholic steatohepatitis (NASH) and fibrosis in obese patients identifies the risk group with increased incidence of liver-related deaths.

AIM:

To clarify the role of serum adiponectin and its receptor liver gene expression in the progression of liver damage in NAFLD.

METHODS:

Fifty four (54) obese patients with NAFLD preliminary diagnosed by liver ultra-sound were recruited. Full medical history, anthropometric measurement, biochemical studies, serum adiponectin level, liver biopsy for histological examination and NAS score to identify NASH patients, and assessment of adiponectin receptor gene expression by RT-PCR, were conducted for each patients. Fifteen ages matched average weight healthy adult had been chosen as a control for serum adiponectin level.

RESULTS:

According to NAS score, patients were divided into non- NASH (8 patients), and NASH (46 patients). Serum adiponectin level was significantly lower in NAFLD patients compared to normal participants (p < 0.004). Serum adiponectin level was lower in NASH patients (4.437 ± 2.569 ng/dl in NASH vs. 5.138 ± 2.841 ng/dl in non-NASH). Adiponectin receptor liver gene expression was lower in NASH patients (0.8459 ± 0.4671 vs. 1.0688 ± 0.3965 in non-NASH).

CONCLUSION:

Both adiponectin deficiency and resistance had a role in progression of simple liver steatosis to severe injury in obese patients.

Relationships among Body Condition, Insulin Resistance and Subcutaneous Adipose Tissue Gene Expression during the Grazing Season in Mares

Obesity and insulin resistance have been shown to be risk factors for laminitis in horses. The objective of the study was to determine the effect of changes in body condition during the grazing season on insulin resistance and the expression of genes associated with obesity and insulin resistance in subcutaneous adipose tissue (SAT). Sixteen Finnhorse mares were grazing either on cultivated high-yielding pasture (CG) or semi-natural grassland (NG) from the end of May to the beginning of September. Body measurements, intravenous glucose tolerance test (IVGTT), and neck and tailhead SAT gene expressions were measured in May and September. At the end of grazing, CG had higher median body condition score (7 vs. 5.4, interquartile range 0.25 vs. 0.43; P=0.05) and body weight (618 kg vs. 572 kg ± 10.21 (mean ± SEM); P=0.02), and larger waist circumference (P=0.03) than NG. Neck fat thickness was not different between treatments. However, tailhead fat thickness was smaller in CG compared to NG in May (P=0.04), but this difference disappeared in September. Greater basal and peak insulin concentrations, and faster glucose clearance rate (P=0.03) during IVGTT were observed in CG compared to NG in September. A greater decrease in plasma non-esterified fatty acids during IVGTT (P<0.05) was noticed in CG compared to NG after grazing. There was down-regulation of insulin receptor, retinol binding protein 4, leptin, and monocyte chemoattractant protein-1, and up-regulation of adiponectin (ADIPOQ), adiponectin receptor 1 and stearoyl-CoA desaturase (SCD) gene expressions in SAT of both groups during the grazing season (P<0.05). Positive correlations were observed between ADIPOQ and its receptors and between SCD and ADIPOQ in SAT (P<0.01). In conclusion, grazing on CG had a moderate effect on responses during IVGTT, but did not trigger insulin resistance. Significant temporal differences in gene expression profiles were observed during the grazing season.

Effect of Extended-Release Niacin/Laropiprant Combination on Plasma Adiponectin and Insulin Resistance in Chinese Patients with Dyslipidaemia

Objectives. This study examined whether the increase of adiponectin associated with extended-release (ER) niacin/laropiprant combination attenuates the adverse effect of niacin on glucose and insulin resistance in Hong Kong Chinese patients with dyslipidaemia. Methods. Patients (N = 121) were treated with ER niacin/laropiprant 1 g/20 mg for 4 weeks and then the dose was doubled for an additional 8 weeks. Measurements of fasting lipids, glucose, insulin, and adiponectin were performed at baseline and during the study. Results. There were significant (P < 0.001) increases in glucose (9.4 ± 13.1%), insulin (70.2 ± 91.0%), HOMA-IR (87.8 ± 103.9%), and adiponectin (169.3 ± 111.6%). The increase in adiponectin was significantly associated with increase in glucose (r = 0.221, P < 0.05), insulin (r = 0.184, P < 0.05), and HOMA-IR (r = 0.237, P < 0.01) and the association remained significant after adjustment for changes in body weight or body fat mass. Conclusion. Treatment with ER niacin/laropiprant led to a significant increase in adiponectin levels but worsening of glucose levels and insulin resistance, and the increase in adiponectin and insulin resistance were correlated suggesting the increase in adiponectin did not ameliorate the deterioration in insulin resistance. Clinical trial is registered with number on WHO-ICTRP: ChiCTR-ONC-10001038.

Aerobic training increases the expression of adiponectin receptor genes in the peripheral blood mononuclear cells of young men

Little is known about the effect of exercise training on the expression of adiponectin receptor genes in peripheral blood mononuclear cells (PBMCs). In this study, we investigated the effects of aerobic training on the expression of AdipoR1 and AidpoR2 mRNAs in PBMCs, whole body insulin sensitivity, and circulating adiponectins in men. Thirty young men were randomly assigned to either a control (n=15) or an exercise (n=15) group. Subjects assigned to the exercise group underwent a 12-week jogging and/or running programme on a motor-driven treadmill at an intensity of 60%-75% of the age-based maximum heart rate with duration of 40 minutes per session and a frequency of 5 days per week. Two-way mixed ANOVA with repeated measures was used to test any significant time-by-group interaction effects for the measured variables at p=0.05. We found significant time-by-group interaction effects for waist circumference (p=0.001), VO2max (p<0.001), fasting insulin (p=0.016), homeostasis model assessment for insulin resistance (HOMA-IR) (p=0.010), area under the curve (AUC) for insulin response during the 75-g oral glucose tolerance test (p=0.002), high-molecular weight (HMW) adiponectin (p=0.016), and the PBMC mRNA levels of AdipoR1 (p<0.001) and AdipoR2 (p=0.001). The exercise group had significantly increased mRNA levels of AdipoR1 and AdipoR2 in PBMCs, along with increased whole body insulin sensitivity and HMW adiponectin, decreased waist circumference, and increased VO2max compared with the control group. In summary, the current findings suggest that exercise training modulates the expression of AdipoR1 and AdipoR2 mRNAs in PBMCs, implying that manipulation of the expression of these genes could be a potential surrogate for lifestyle intervention-mediated improvements of whole body insulin sensitivity and glucose homeostasis.

Adiponectin resistance and proinflammatory changes in the visceral adipose tissue induced by fructose consumption via ketohexokinase-dependent pathway

An epidemic of obesity and type 2 diabetes is linked with the increase in consumption of fructose-containing sugars, such as sucrose and high-fructose corn syrup. In mammalian cells, fructose is metabolized predominantly via phosphorylation to fructose-1 phosphate by ketohexokinase (KHK) or by alternative pathways. Here we demonstrate that a KHK-dependent pathway mediates insulin resistance and inflammatory changes in the visceral fat in response to high fructose. We used mice (males, C57BL/6 background) including littermate wild-type control and mice lacking both isoforms of KHK (KHK-null). Fructose diet induced metabolic syndrome, including visceral obesity, insulin resistance, proinflammatory changes in the visceral fat (production of proinflammatory adipokines and macrophage infiltration), the endoplasmic reticulum stress signaling, and decrease of the high-molecular weight adiponectin followed by decrease in the downstream signaling. KHK-KO mice consuming the same high-fructose diet remained lean, with normal insulin sensitivity and healthy visceral adipose tissue with normal adiponectin function not distinguishable from the control by any of the tested parameters. This study demonstrates that blocking KHK and redirecting fructose metabolism to alternative pathways is an effective way to prevent visceral obesity and insulin resistance induced by high fructose, a widespread component of Western diets.

MicroRNA-218 targets adiponectin receptor 2 to regulate adiponectin signaling

Adiponectin exerts an antidiabetic function through the adiponectin receptors 1 and 2 (AdipoR1 and AdipoR2). The mechanism regulating the expression of adiponectin receptors remains to be elucidated. Bioinformatics analysis demonstrated that microRNA (miR)‑218 targets the 3' untranslated region (3'UTR) of the AdipoR2 mRNA. The present study aimed to investigate whether miR-218 regulated the expression of AdipoR2 using immunoblotting, reverse transcription quantitative polymerase chain reaction and luciferase assays. The protein level and the mRNA level of AdipoR2 were reduced when miR‑218 was expressed in HepG2 cells. Additionally, overexpression of miR‑218 repressed the activity of a luciferase reporter containing the 3'UTR of AdipoR2. Furthermore, the present study aimed to determine whether miR-218 regulated glucose metabolism through detecting signaling pathways and glucose uptake. The phosphorylation of AMP‑activated protein kinase and p38 mitogen‑activated protein kinase was reduced in miR‑218‑expressing cells. In addition, miR‑218 inhibited adiponectin‑induced glucose uptake. The present results suggested that miR‑218 targets AdipoR2 to inhibit adiponectin signaling.

Signaling pathway for adiponectin expression in adipocytes by osteocalcin

In addition to providing skeletal support, the bone is an endocrine organ that produces osteocalcin, whose uncarboxylated form (GluOC) increases insulin secretion either directly or indirectly by promoting incretin secretion. We have now investigated the signaling pathway by which GluOC increases expression of adiponectin in adipocytes. Activation of its putative receptor GPRC6A by GluOC induced the intracellular accumulation of cAMP and consequent activation of protein kinase A (PKA) in differentiated 3T3-L1 adipocytes. It also induced phosphorylation of CREB (cAMP response element binding protein), but this effect appeared to be mediated indirectly by extracellular signal-regulated kinase (ERK) rather than directly by PKA, given that it was attenuated by the ERK signaling inhibitor U0126. Activated PKA also induced activation of the tyrosine kinase Src, the small GTPase Rap1, an upstream of ERK and CREB phosphorylation. Activated CREB up-regulated the expression of peroxisome proliferator-activated receptor γ (PPARγ), which in turn led to induction of adiponectin expression. Finally, intermittent oral administration of GluOC in mice reduced the size of gonadal white adipocytes as well as increased the expression of PPARγ and adiponectin in these cells. Our results have thus revealed the signaling pathway by which GluOC induces adiponectin expression in adipocytes.

Skeletal muscle glucose metabolism and inflammation in the development of the metabolic syndrome

Insulin resistance and metabolic dysfunction in skeletal muscle play a major role in the development of the metabolic syndrome and type 2 diabetes. Numerous mechanisms have been proposed to explain the pathophysiology of obesity-linked metabolic dysfunction and this review will focus on the contributing role of adiponectin and inflammation. The beneficial effects of adiponectin on both insulin action and inflammation are now well documented and will be reviewed. More recent work provided new insights into adiponectin signaling mechanisms. The development of strategies to mimic adiponectin action holds promise that adiponectin-based compounds may translate into effective therapeutic applications. We will also discussed the novel role of long chain ω-3 PUFA-derived resolution mediators, which in addition to resolving inflammation, can also exert glucoregulatory effects in models of obesity and insulin resistance. We will focus on one resolution mediator, protectin DX (PDX), which was recently shown to act as a muscle interleukin-6 secretagogue. PDX and its isomer PD1 also enhance adiponectin expression and action. Ultimately, it is via a better understanding the molecular mechanisms of action via which inflammation, insulin resistance and metabolic dysfunction occur in skeletal muscle, and also how they crosstalk with each other, that we can generate new and improved therapies for obesity-linked metabolic complications.

Serum adiponectin is associated with worsened overall survival in a prospective cohort of hepatocellular carcinoma patients

BACKGROUND

Hepatocellular carcinoma (HCC) is the third leading cause of cancer deaths worldwide. The rise in metabolic syndrome has contributed to this trend. Adipokines, such as adiponectin, are associated with prognosis in several cancers, but have not been well studied in HCC.

METHODS

We prospectively enrolled 140 patients with newly diagnosed or recurrent HCC with Child-Pugh (CP) class A or B cirrhosis. We examined associations between serum adipokines, clinicopathological features of HCC, and time to death. We also examined a subset of tumors with available pathology for tissue adiponectin receptor (AR) expression by immunohistochemistry.

RESULTS

The median age of subjects was 62 years; 79% were men, 59% had underlying hepatitis C, and 36% were diabetic. Adiponectin remained a significant predictor of time to death (hazard ratio 1.90; 95% confidence interval 1.05-3.45; p = 0.03) in a multivariable adjusted model that included age, alcohol history, CP class, stage, and serum α-fetoprotein level. Cytoplasmic AR expression (AR1 and AR2) in tumors trended higher in those with higher serum adiponectin levels and in those with diabetes mellitus, but the association was not statistically significant.

CONCLUSIONS

In this hypothesis-generating study, we found the serum adiponectin level to be an independent predictor of overall survival in a diverse cohort of HCC patients.

IMPACT

Understanding how adipokines affect the HCC outcome may help develop novel treatment and prevention strategies.

Orally active osteoanabolic agent GTDF binds to adiponectin receptors, with a preference for AdipoR1, induces adiponectin-associated signaling, and improves metabolic health in a rodent model of diabetes

Adiponectin is an adipocytokine that signals through plasma membrane-bound adiponectin receptors 1 and 2 (AdipoR1 and -2). Plasma adiponectin depletion is associated with type 2 diabetes, obesity, and cardiovascular diseases. Adiponectin therapy, however, is yet unavailable owing to its large size, complex multimerization, and functional differences of the multimers. We report discovery and characterization of 6-C-β-D-glucopyranosyl-(2S,3S)-(+)-5,7,3',4'-tetrahydroxydihydroflavonol (GTDF) as an orally active adiponectin mimetic. GTDF interacted with both AdipoRs, with a preference for AdipoR1. It induced adiponectin-associated signaling and enhanced glucose uptake and fatty acid oxidation in vitro, which were augmented or abolished by AdipoR1 overexpression or silencing, respectively. GTDF improved metabolic health, characterized by elevated glucose clearance, β-cell survival, reduced steatohepatitis, browning of white adipose tissue, and improved lipid profile in an AdipoR1-expressing but not an AdipoR1-depleted strain of diabetic mice. The discovery of GTDF as an adiponectin mimetic provides a promising therapeutic tool for the treatment of metabolic diseases.

Phloretin promotes adipocyte differentiation in vitro and improves glucose homeostasis in vivo

Adipocyte dysfunction is associated with many metabolic diseases such as obesity, insulin resistance and diabetes. Previous studies found that phloretin promotes 3T3-L1 cells differentiation, but the underlying mechanisms for phloretin's effects on adipogenesis remain unclear. In this study, we demonstrated that phloretin enhanced the lipid accumulation in porcine primary adipocytes in a time-dependent manner. Furthermore, phloretin increased the utilization of glucose and nonesterified fatty acid, while it decreased the lactate output. Microarray analysis revealed that genes associated with peroxisome proliferator-activated receptor-γ (PPARγ), mitogen-activated protein kinase and insulin signaling pathways were altered in response to phloretin. We further confirmed that phloretin enhanced expression of PPARγ, CAAT enhancer binding protein-α (C/EBPα) and adipose-related genes, such as fatty acids translocase and fatty acid synthase. In addition, phloretin activated the Akt (Thr308) and extracellular signal-regulated kinase, and therefore, inactivated Akt targets protein. Wortmannin effectively blocked the effect of phloretin on Akt activity and the protein levels of PPARγ, C/EBPα and fatty acid binding protein-4 (FABP4/aP2). Oral administration of 5 or 10 mg/kg phloretin to C57BL BKS-DB mice significantly decreased the serum glucose level and improved glucose tolerance. In conclusion, phloretin promotes the adipogenesis of porcine primary preadipocytes through Akt-associated signaling pathway. These findings suggested that phloretin might be able to increase insulin sensitivity and alleviate the metabolic diseases.

Inherent insulin sensitivity is a major determinant of multimeric adiponectin responsiveness to short-term weight loss in extreme obesity

High molecular weight (HMW-A) adiponectin levels mirror alterations in glucose homeostasis better than medium (MMW-A) and low molecular weight (LMW-A) components. In 25 patients with wide-range extreme obesity (BMI 40-77 kg/m(2)), we aimed to explore if improvements of multimeric adiponectin following 4-wk weight loss reflect baseline OGTT-derived insulin sensitivity (ISIOGTT) and disposition index (DIOGTT). Compared to 40 lean controls, adiponectin oligomers were lower in extreme obesity (p < 0.001) and, within this group, HMW-A levels were higher in insulin-sensitive (p < 0.05) than -resistant patients. In obese patients, short-term weight loss did not change total adiponectin levels and insulin resistance, while the distribution pattern of adiponectin oligomers changed due to significant increment of HMW-A (p < 0.01) and reduction of MMW-A (p < 0.05). By multivariate analysis, final HMW-A levels were significantly related to baseline ISIOGTT and final body weight (adjusted R(2) = 0.41). Our data suggest that HMW adiponectin may reflect baseline insulin sensitivity appropriately in the context of extreme obesity. Especially, we documented that HMW-A is promptly responsive to short-term weight loss prior to changes in insulin resistance, by a magnitude that is proportioned to whole body insulin sensitivity. This may suggest an insulin sensitivity-dependent control operated by HMW-A on metabolic dynamics of patients with extreme obesity.

The role of adiponectin signaling in metabolic syndrome and cancer

The increased prevalence of obesity has mandated extensive research focused on mechanisms responsible for associated clinical complications. Emerging from the focus on adipose tissue biology as a vitally important adipokine is adiponectin which is now believed to mediate anti-diabetic, anti-atherosclerotic, anti-inflammatory, cardioprotective and cancer modifying actions. Adiponectin mediates these primarily beneficial effects via direct signaling effects and via enhancing insulin sensitivity via crosstalk with insulin signaling pathways. Reduced adiponectin action is detrimental and occurs in obesity via decreased circulating levels of adiponectin action or development of adiponectin resistance. This review will focus on cellular mechanisms of adiponectin action, their crosstalk with insulin signaling and the resultant role of adiponectin in cardiovascular disease, diabetes and cancer and reviews data from in vitro cell based studies through animal models to clinical observations.

A high-fat maternal diet decreases adiponectin receptor-1 expression in offspring

In early life, over-nutrition may increase the risk of insulin resistance in the adult stage. Adiponectin and its receptor may play a key role in this process. This study aimed to identify the effect of a high-fat (HF) maternal diet on metabolic parameters and muscle adiponectin signaling in young adult offspring. We found that offspring born to dams fed HF chow (HF; 31% of calories from fat) had elevated body and adipose tissue weight and higher serum glucose levels after glucose challenge at three weeks (W3) and eight weeks (W8) of age. Offspring exposed to a HF diet also had higher serum adiponectin levels at W3 compared to controls. However, adiponectin levels were significantly decreased compared to controls by W8. Adiponectin receptor 1 mRNA expression in skeletal muscle was decreased in the HF group at W3 and W8, and there was no difference between the two groups in adiponectin receptor 2 expression. Furthermore, glucose transporter 4 mRNA and protein expression was decreased in the skeletal muscle of the HF group at W3 and W8. Our results suggest that a HF maternal diet decreases adiponectin receptor 1 expression in the offspring, which could contribute to reduced sensitivity to adiponectin and to adverse nutritional programing outcomes.

FoxO transcription factors: their roles in the maintenance of skeletal muscle homeostasis

Forkhead box class O family member proteins (FoxOs) are highly conserved transcription factors with important roles in cellular homeostasis. The four FoxO members in humans, FoxO1, FoxO3, FoxO4, and FoxO6, are all expressed in skeletal muscle, but the first three members are the most studied in muscle. In this review, we detail the multiple modes of FoxO regulation and discuss the central role of these proteins in the control of skeletal muscle plasticity. FoxO1 and FoxO3 are key factors of muscle energy homeostasis through the control of glycolytic and lipolytic flux, and mitochondrial metabolism. They are also key regulators of protein breakdown, as they modulate the activity of several actors in the ubiquitin–proteasome and autophagy–lysosomal proteolytic pathways, including mitochondrial autophagy, also called mitophagy. FoxO proteins have also been implicated in the regulation of the cell cycle, apoptosis, and muscle regeneration. Depending of their activation level, FoxO proteins can exhibit ambivalent functions. For example, a basal level of FoxO factors is necessary for cellular homeostasis and these proteins are required for adaptation to exercise. However, exacerbated activation may occur in the course of several diseases, resulting in metabolic disorders and atrophy. A better understanding of the precise functions of these transcriptions factors should thus lead to the development of new therapeutic approaches to prevent or limit the muscle wasting that prevails in numerous pathological states, such as immobilization, denervated conditions, neuromuscular disease, aging, AIDS, cancer, and diabetes.

Central adiponectin acutely improves glucose tolerance in male mice

Adiponectin, an adipocyte-derived hormone, regulates glucose and lipid metabolism. It is also antiinflammatory. During obesity, adiponectin levels and sensitivity are reduced. Whereas the action of adiponectin in the periphery is well established the neuroendocrine role of adiponectin is largely unknown. To address this we analyzed the expression of adiponectin and the 2 adiponectin receptors (AdipoR1 and AdipoR2) in response to fasting and to diet-induced and genetic obesity. We also investigated the acute impact of adiponectin on central regulation of glucose homeostasis. Adiponectin (1 μg) was injected intracerebroventricularly (ICV), and glucose tolerance tests were performed in dietary and genetic obese mice. Finally, the influence of ICV adiponectin administration on central signaling cascades regulating glucose homeostasis and on markers of hypothalamic inflammation was assessed. Gene expression of adiponectin was down-regulated whereas AdipoR1 was up-regulated in the arcuate nucleus of fasted mice. High-fat (HF) feeding increased AdipoR1 and AdipoR2 gene expression in this region. In mice on a HF diet and in leptin-deficient mice acute ICV adiponectin improved glucose tolerance 60 minutes after injection, whereas normoglycemia in control mice was unaffected. ICV adiponectin increased pAKT, decreased phospho-AMP-activated protein kinase, and did not change phospho-signal transducer and activator of transcription 3 immunoreactivity. In HF-fed mice, ICV adiponectin reversed parameters of hypothalamic inflammation and insulin resistance as determined by the number of phospho-glycogen synthase kinase 3 β(Ser9) and phospho-c-Jun N-terminal kinase (Thr183/Tyr185) immunoreactive cells in the arcuate nucleus and ventromedial hypothalamus. This study demonstrates that the insulin-sensitizing properties of adiponectin are at least partially based on a neuroendocrine mechanism that involves centrally synthesized adiponectin.

A novel ADIPOQ mutation (p.M40K) impairs assembly of high-molecular-weight adiponectin and is associated with early-onset obesity and metabolic syndrome

CONTEXT

The phenotypic effects of ADIPOQ mutations early in life, prior to type 2 diabetes onset, have not been studied.

AIM

The objective of the study was to characterize the impact of a novel ADIPOQ mutation in vitro and in vivo.

DESIGN

The design of the study was ADIPOQ screening, adiponectin oligomerization, and cardiometabolic phenotype assessment.

SUBJECTS

Fourteen hypoadiponectinemic (<3 μg/mL) and 686 normoadiponectinemic young adults (23-25 y) were prospectively followed up since birth.

MAIN OUTCOME MEASURES

Human and recombinant murine mutant adiponectin oligomerization, the proband's ADIPOQ and ADIPOR1/R2 adipose tissue (AT) expression, and cardiometabolic profile were measured.

RESULTS

The heterozygous ADIPOQ p.M40K mutation was identified in one hypoadiponectinemic male (2.4 μg/mL) and three other family members. Carriers presented a marked reduction of serum high-molecular weight to total adiponectin ratio when compared with controls (9.4% ± 1% vs 56.6% ± 13%; P < .05) and family noncarriers (9.4% ± 1% vs 42% ± 0.5%; P = .05). Both mRNA and protein levels of adiponectin were increased in the AT of the proband (2.3- and 1.6-fold, respectively). However, the high-molecular weight to total adiponectin ratio of adiponectin was decreased (3.3-fold). Moreover, the expressions of ADIPOR1 and ADIPOR2 were significantly down-regulated in the AT of the proband (6- and 1.2-fold, respectively). The results were confirmed by in vitro studies on the recombinant murine homologous mutation (p.M43K). The proband's cardiometabolic phenotype progression was further characterized: born small for gestational age and adolescence-onset obesity; insulin resistance (homeostasis assessment model of insulin resistance of 4.7), and dyslipidemia at 25 years; decreased high-molecular weight adiponectin (0.24 μg/mL = 10%), hypertension (180/120 mm Hg), steatosis (fat liver = 40% ± 6%), increased carotid intima-media thickness at 31 years, and type 2 diabetes (glycosylated hemoglobin = 6.6%) at 34 years of age. Of note, all of the affected family members presented features of metabolic syndrome.

CONCLUSION

The newly identified ADIPOQ p.M40K mutation associates with severe cardiometabolic dysfunction due to the impairment of high-molecular weight adiponectin complex formation.

Orange-spotted grouper (Epinephelus coioides) adiponectin receptors: molecular characterization, mRNA expression, and subcellular location

Adiponectin is an abundantly secreted adipokine from adipose tissue in mammals, which plays important roles in the regulation of glucose and lipid metabolism. The biological function of adiponectin is mediated by at least two receptors (AdipoR1 and AdipoR2). Although both of them were identified in mammals, there are few researches about adiponectin and its receptors in teleosts. In this study, two types of adiponectin receptors have been isolated and characterized in the orange-spotted grouper (Epinephelus coioides). The cDNAs of grouper AdipoR1 and AdipoR2 are 1444 and 2034 bp in length, encoding proteins of 376 amino acids and 375 amino acids, respectively. Multiple alignment results showed that there was a variable region at the N-terminal of AdipoR1/R2, which has never been reported. Both AdipoR1 and AdipoR2 were found to be widely expressed in various tissues of grouper. Compared to AdipoR2, AdipoR1 expressed at higher levels in the nervous system and pituitary gland, but at lower levels in some peripheral tissues, including heart, liver, adipose tissue, stomach, intestine and especially gonad. Fasting and refeeding experiments showed that the mRNA expressions of AdipoR1/R2 were up-regulated by fasting in the muscle and adipose tissue of grouper, and restored rapidly to normal levels after refeeding. However, the mRNA expressions of AdipoR1/R2 in the hypothalamus and liver of grouper were insensitive to fasting. By indirect immunofluorescence, we demonstrated that grouper AdipoR1/R2 were integral membrane proteins; the C-terminals were extracellular, while the N-terminals were intracellular.

Roles of adiponectin and oxidative stress in obesity-associated metabolic and cardiovascular diseases

The recent increase in populations with obesity is a worldwide social problem, and the enhanced susceptibility of obese people to metabolic and cardiovascular diseases has become a growing health threat. An understanding of the molecular basis for obesity-associated disease development is required to prevent these diseases. Many studies have revealed that the mechanism involves various bioactive molecules that are released from adipose tissues and designated as adipocytokines/adipokines. Adiponectin is an adipocytokine that exerts insulin-sensitizing effects in the liver and skeletal muscle via adenosine monophosphate-activated protein kinase and proliferator-activated receptor α activation. Additionally, adiponectin can suppress atherosclerosis development in vascular walls via various anti-inflammatory effects. In contrast, oxidative stress is a harmful factor that systemically increases during obesity and promotes the development of diabetes, atherosclerosis, and various other diseases. In obese mice, oxidative stress is enhanced in adipose tissue before diabetes development, but not in the liver, skeletal muscle, and aorta, suggesting that in obesity, adipose tissue may be a major source of reactive oxygen species (ROS). ROS suppress adiponectin production in adipocytes. Treatment of obese mice with anti-oxidative agents improves insulin resistance and restores adiponectin production. Recent studies have demonstrated that adiponectin protects against oxidative stress-induced damage in the vascular endothelium and myocardium. Thus, decreased circulating adiponectin levels and increased oxidative stress, which are closely linked to each other, should be deeply involved in obesity-associated metabolic and cardiovascular disease pathogenesis.

Autonomic nerves and perivascular fat: interactive mechanisms

The evidence describing the autonomic innervation of body fat is reviewed with a particular focus on the role of the sympathetic neurotransmitters. In compiling the evidence, a strong case emerges for the interaction between autonomic nerves and perivascular adipose tissue (PVAT). Adipocytes have been shown to express receptors for neurotransmitters released from nearby sympathetic varicosities such as adrenoceptors (ARs), purinoceptors and receptors for neuropeptide Y (NPY). Noradrenaline can modulate both lipolysis (via α2- and β3-ARs) and lipogenesis (via α1- and β3-ARs). ATP can inhibit lipolysis (via P1 purinoceptors) or stimulate lipolysis (via P2y purinoceptors). NPY, which can be produced by adipocytes and sympathetic nerves, inhibits lipolysis. Thus the sympathetic triad of transmitters can influence adipocyte free fatty acid (FFA) content. Substance P (SP) released from sensory nerves has also been shown to promote lipolysis. Therefore, we propose a mechanism whereby sympathetic neurotransmission can simultaneously activate smooth muscle cells in the tunica media to cause vasoconstriction and alter FFA content and release from adjacent adipocytes in PVAT. The released FFA can influence endothelial function. Adipocytes also release a range of vasoactive substances, both relaxing and contractile factors, including adiponectin and reactive oxygen species. The action of adipokines (such as adiponectin) and reactive oxygen species (ROS) on cells of the vascular adventitia and nerves has yet to be fully elucidated. We hypothesise a strong link between PVAT and autonomic fibres and suggest that this poorly understood relationship is extremely important for normal vascular function and warrants a detailed study.

A novel role of globular adiponectin in treatment with HFD/STZ induced T2DM combined with NAFLD rats

Aims. To evaluate the effects of globular adiponectin (gAd) on treatment of type 2 diabetic rats combined with NAFLD. Materials and Methods. Twenty-one male wistar rats were fed with normal diet (7 rats) or high fat diet (HFD) (14 rats) for 4 weeks, and then HFD-fed rats were injected with streptozotocin (STZ) to induce type 2 diabetes mellitus (T2DM). Half of T2DM rats were randomly injected with gAd intraperitoneally for 7 days. The expressions of adiponectin receptors (adipoR1/R2) in liver and skeletal muscle tissues were detected through western blotting or RT-qPCR, respectively. Results. Globular adiponectin alleviated the hepatic steatosis and increased insulin secretion. In liver, both the protein and mRNA expressions of adipoR2 in T2DM group decreased (P < 0.05, resp.) in contrast to NC group and increased (P < 0.05 and P < 0.001, resp.) after gAd treatment. But the protein and mRNA expressions of adipoR1 increased (P < 0.05, resp.) in T2DM group and no change was found in the gAd-treated group. In skeletal muscle, the protein and mRNA expressions of adipoR1 and adipoR2 were upregulated in T2DM group and were downregulated after gAd treatment. Conclusions. Globular adiponectin could ameliorate the hepatic steatosis and vary the expressions of adiponectin receptors in liver and skeletal muscle by stimulating insulin secretion.

RNA-binding protein PTB and microRNA-221 coregulate AdipoR1 translation and adiponectin signaling

Adiponectin receptor 1 (AdipoR1) mediates adiponectin's pleiotropic effects in muscle and liver and plays an important role in the regulation of insulin resistance and diabetes. Here, we demonstrate a pivotal role for microRNA-221 (miR-221) and the RNA-binding protein polypyrimidine tract-binding protein (PTB) in posttranscriptional regulation of AdipoR1 during muscle differentiation and in obesity. RNA-immunoprecipitation and luciferase reporter assays illustrated that both PTB and miR-221 bind AdipoR1-3'UTR and cooperatively inhibit AdipoR1 translation. Depletion of PTB or miR-221 increased, while overexpression of these factors decreased, AdipoR1 protein synthesis in both muscle and liver cells. During myogenesis, downregulation of PTB and miR-221 robustly induced AdipoR1 translation, providing a mechanism for enhanced AdipoR1 protein expression and activation in differentiated muscle cells. In addition, since both PTB and miR-221 are upregulated in liver and muscle of genetic and dietary mouse models of obesity, this novel translational mechanism may be at least partly responsible for the reduction in AdipoR1 protein levels in obesity. These findings highlight the importance of translational control in regulating AdipoR1 protein expression and adiponectin signaling. Given that adiponectin is reduced in obesity, induction of AdipoR1 could potentially enhance adiponectin beneficial effects and ameliorate insulin resistance and diabetes.

Targeting tissue-specific metabolic signaling pathways in aging: the promise and limitations

It has been well established that most of the age-related diseases such as insulin resistance, type 2 diabetes, hypertension, cardiovascular disease, osteoporosis, and atherosclerosis are all closely related to metabolic dysfunction. On the other hand, interventions on metabolism such as calorie restriction or genetic manipulations of key metabolic signaling pathways such as the insulin and mTOR signaling pathways slow down the aging process and improve healthy aging. These findings raise an important question as to whether improving energy homeostasis by targeting certain metabolic signaling pathways in specific tissues could be an effective anti-aging strategy. With a more comprehensive understanding of the tissue-specific roles of distinct metabolic signaling pathways controlling energy homeostasis and the cross-talks between these pathways during aging may lead to the development of more effective therapeutic interventions not only for metabolic dysfunction but also for aging.