AdipoR1 mRNA Research Articles

Cloning, expression and chromosome localization of porcine adiponectin and adiponectin receptors genes

Adiponectin is a cytokine secreted specifically by adipocytes that has been proposed to enhance insulin sensitivity and prevent atherosclerosis. Adiponectin receptors (adipoR1 and adipoR2) are recently found in mice which act as receptors for globular and full-length adiponectin to mediate the fatty-acid oxidation and glucose uptake in muscle and liver. The primary goal of this study was to examine chromosome localization of porcine adiponectin and adiponectin receptors and the gene expression pattern in various tissues of pigs of the three genes. Radiation hybrid mapping demonstrated that porcine adiponectin, adipoR1 and adipoR2 were located to chromosome13q36–41, 10p11 and 5q25, in the regions that were syntenic to the homologs of human genes, respectively. Semi-quantitative RT-PCR showed that porcine adiponectin mRNA was specifically expressed in adipose tissue and porcine adipoR1 and adipoR2 mRNA were ubiquitously expressed in many tissues except brain. Comparison to adipoR2 mRNA which was highly expressed in liver, heart, kidney, adipose tissues and lung, adipoR1 mRNA was expressed at relatively high levels in porcine muscle, leukocytes and epididymis. Our data provide basic molecular information useful for the further investigation on the function of the three genes.

Expression and Regulation of Adiponectin and Receptor in Human and Rat Placenta

Adiponectin is an adipocyte hormone involved in glucose and lipid metabolism. Recently, two receptors of this protein, called adiponectin receptor 1 (Adipo-R1) and Adipo-R2, have been cloned. The aim of this study was to examine whether adiponectin and its receptors are expressed in human and rat placentas and to evaluate the regulation of these factors by gestational age and nutritional status. Our results demonstrate that adiponectin and Adipo-R2 are localized in both human and rat placentas. Human adiponectin and Adipo-R2 are presented in cytotrophoblast and syncytiotrophoblast cells. However, rat adiponectin and Adipo-R2 change their specific cell type immunostaining during gestation. Furthermore, placental adiponectin mRNA expression is increased during pregnancy in the rat, whereas Adipo-R2 has the contrary pattern. We also assessed the effect of food restriction (30%) during gestation, and we observed that adiponectin mRNA levels decrease after 16 d of undernutrition. In contrast, placental Adipo-R2 mRNA is unchanged by undernutrition. Finally, treatment with adiponectin during gestation decreases Adipo-R2, glucose transporter 3, lipoprotein lipase, and TGF-beta mRNA expression. Taken together, our results suggest that, at least in rodents, adiponectin may be involved in the regulation of several placental functions.

Prolactin and growth hormone regulate adiponectin secretion and receptor expression in adipose tissue

Adiponectin is a hormone secreted from adipose tissue, and serum levels are decreased with obesity and insulin resistance. Because prolactin (PRL) and growth hormone (GH) can affect insulin sensitivity, we investigated the effects of these hormones on the regulation of adiponectin in human adipose tissue in vitro and in rodents in vivo. Adiponectin secretion was significantly suppressed by PRL and GH in in vitro cultured human adipose tissue. Furthermore, PRL increased adiponectin receptor 1 (AdipoR1) mRNA expression and GH decreased AdipoR2 expression in the cultured human adipose tissue. In transgenic mice expressing GH, and female mice expressing PRL, serum levels of adiponectin were decreased. In contrast, GH receptor deficient mice had elevated adiponectin levels, while PRL receptor deficient mice were unaffected. In conclusion, we demonstrate gene expression of AdipoR1 and AdipoR2 in human adipose tissue for the first time, and show that these are differentially regulated by PRL and GH. Both PRL and GH reduced adiponectin secretion in human adipose tissue in vitro and in mice in vivo. Decreased serum adiponectin levels have been associated with insulin resistance, and our data in human tissue and in transgenic mice suggest a role for adiponectin in PRL and GH induced insulin resistance.

Adiponectin receptor gene expression in human skeletal muscle cells is not regulated by fibrates and thiazolidinediones

Thiazolidinediones as PPARgamma agonists and fibrates as PPARalpha agonists improve insulin sensitivity in insulin-responsive tissues. Recent data show an induction of adiponectin receptor 2 (AdipoR2) by PPARalpha and PPARgamma agonists in human macrophages. In this study, we examined the effects of thiazolidinediones and fibrates on the expression of adiponectin receptors in human skeletal muscle cells, an important cell type in the context of insulin resistance. In vitro differentiated human myotubes treated with troglitazone or rosiglitazone (20 h) showed no significant changes in AdipoR1 and AdipoR2 mRNA expression. PPARgamma activation was controlled by determination of PPARgamma mRNA induction. Likewise, differentiated myotubes treated with Wy-14,643 or fenofibrate (20 h) revealed no significant regulation of AdipoR1 and AdipoR2 mRNA. PPARalpha activation was assessed by measuring PDHK4 mRNA expression. Induction of AdipoR gene expression in human skeletal muscle cells is not involved in the insulin-sensitizing effects of thiazolidinediones or fibrates.

Impaired Activation of AMP-Kinase and Fatty Acid Oxidation by Globular Adiponectin in Cultured Human Skeletal Muscle of Obese Type 2 Diabetics

Adiponectin is an adipocyte-derived hormone associated with antidiabetic actions. In rodent skeletal muscle, globular adiponectin (gAD) activates AMP-kinase (AMPK) and stimulates fatty acid oxidation effects mediated through the adiponectin receptors, AdipoR1 and AdipoR2. In the present study, we examined the mRNA expression of adiponectin receptors and the effects of gAD on AMPK activity and fatty acid oxidation in skeletal muscle myotubes from lean, obese, and obese type 2 diabetic subjects. Myotubes from all groups expressed approximately 4.5-fold more AdipoR1 mRNA than AdipoR2, and obese subjects tended to have higher AdipoR1 expression (P = 0.052). In lean myotubes, gAD activates AMPKalpha1 and -alpha2 by increasing Thr172 phosphorylation, an effect associated with increased acetyl-coenzyme A carboxylase (ACCbeta) Ser221 phosphorylation and enhanced rates of fatty acid oxidation, effects similar to those observed after pharmacological AMPK activation by 5-aminoimidazole-4-carboxamide riboside. In obese myotubes, the activation of AMPK signaling by gAD at low concentrations (0.1 mug/ml) was blunted, but higher concentrations (0.5 mug/ml) stimulated AMPKalpha1 and -alpha2 activities, AMPK and ACCbeta phosphorylation, and fatty acid oxidation. In obese type 2 diabetic myotubes, high concentrations of gAD stimulated AMPKalpha1 activity and AMPK phosphorylation; however, ACCbeta phosphorylation and fatty acid oxidation were unaffected. Reduced activation of AMPK signaling and fatty acid oxidation in obese and obese diabetic myotubes was not associated with reduced protein expression of AMPKalpha and ACCbeta or the expression and activity of the upstream AMPK kinase, LKB1. These data suggest that reduced activation of AMPK by gAD in obese and obese type 2 diabetic subjects is not caused by reduced adiponectin receptor expression but that aspects downstream of the receptor may inhibit AMPK signaling.

Expression of adiponectin and its receptors in swine1,2

Adiponectin is an adipocyte-derived hormone that plays an important role in lipid metabolism and glucose homeostasis. Objectives of this study were 1) to determine the presence and distribution of adiponectin and its receptors 1 and 2 (adipoR1 and adipoR2) in porcine tissues; 2) to characterize pig adiponectin, adipoR1, and adipoR2 mRNA levels in various fat depots from three different breeds of pigs; and 3) to study, in stromal-vascular cell culture, the effects of leptin and tumor necrosis factor-alpha (TNFalpha) on pig adiponectin, adipoR1, and adipoR2 gene expression. To this end, fat Chinese Upton Meishan (UM, n = 10), lean Ham Line (HL, n = 10), and Large White (LW, n = 10) gilts were used. We report the isolation of partial cDNA sequences of pig adipoR1 and adipoR2. Porcine-deduced AA sequences share 97 to 100% homology with human and murine sequences. Pig adipoR1 mRNA is abundant in skeletal muscle, visceral fat, and s.c. fat tissues, whereas adipoR2 mRNA is predominantly expressed in liver, heart, skeletal muscle, and visceral and s.c. fat tissues. Pig adiponectin mRNA levels in s.c. and visceral fat tissues were not associated with plasma insulin and glucose in fasting animals. Subcutaneous (r = -0.44, P < 0.05), visceral (r = -0.43, P < 0.05), and total body fat (r = -0.42, P < 0.05) weights were negatively correlated with adiponectin mRNA levels measured in visceral, but not s.c., fat. Pig adipoR1 and adipoR2 mRNA levels, in visceral fat, were less expressed in fat UM gilts than in the lean HL gilts (P < 0.05). Inverse associations were found between s.c. (r = -0.57, P < 0.01), visceral (r = -0.46, P < 0.05), and total body fat (r = -0.56, P < 0.01) weights and adipoR2 mRNA levels in visceral fat only. We were unable to find such associations for adipoR1 mRNA levels in the overall gilt population. The current study demonstrated that TNFalpha downregulates adiponectin and adipoR2, but not adi-poR1, mRNA levels in stromal-vascular cell culture. Moreover, leptin significantly decreased adiponectin mRNA levels, whereas there was no effect on adiponectin receptors. We conclude that adiponectin and adi-poR2 mRNA levels, but not adipoR1, are modulated in pig visceral fat tissues. Furthermore, our results indicate that TNFalpha interferes with adiponectin function by downregulation of adipoR2 but not of adipoR1 mRNA levels in pigs.

Is Adiponectin Involved in the Pathogenesis of Nonalcoholic Steatohepatitis?

Animal studies have suggested that adiponectin may play a role in the pathogenesis of alcoholic and nonalcoholic fatty liver disease. Studies are limited that evaluated the role of adiponectin in the pathogenesis of nonalcoholic steatohepatitis (NASH). To further our understanding of the role of adiponectin in the pathogenesis of NASH, the following studies were conducted. Serum adiponectin was measured and correlated with anthropometric and nutritional variables in 21 patients with biopsy-proven NASH and 19 age-, gender-, body mass index-, and body fat-matched controls. The effect of a mixed meal on serum adiponectin levels in a subgroup of patients (n = 24) with NASH and controls was assessed. In a separate cohort, liver samples belonging to healthy (n = 11), steatotic (n = 12), and NASH (n = 12) patients were used to further explore the role of adiponectin by measuring the expression of adiponectin and adiponectin receptor (AdipoR2) mRNA. Patients with NASH had significantly lower levels of serum adiponectin than controls (4.9 +/- 2.7 vs. 7.3 +/- 3.5 microg/mL, P = 0.02). While no significant correlation existed between serum adiponectin and anthropometric or nutritional variables, it was independently associated with age, high density lipoprotein, and triglycerides. Mixed meal had no effect on serum adiponectin either in patients with NASH or in controls. There was no expression of adiponectin mRNA in any of liver samples studied. However, AdipoR2 mRNA expression was higher in NASH than in steatotic and normal liver tissue. These data show that adiponectin may have a role in the pathogenesis of human NASH and should be investigated further.

Regulation of adiponectin receptor R1 and R2 gene expression in adipocytes of C57BL/6 mice

Adiponectin has gained significant attention as a mediator of insulin sensitivity. Recently, two receptors of this adipocyte-secreted hormone, adiponectin receptor 1 (AdipoR1) and 2 (AdipoR2), have been cloned. To improve our understanding of the regulation of these receptors in adipocytes, AdipoR1 and AdipoR2 mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction in brown adipocytes and adipocytes from epigonadal and subcutaneous adipose tissue of C57BL/6 mice as a function of feeding and circadian clocks. AdipoR1 gene expression was higher in brown adipose tissue and epigonadal adipose tissue, but lower in subcutaneous fat in fasted as compared to random-fed mice. In parallel, AdipoR2 mRNA levels were also higher in epigonadal adipose tissue of fasted as compared to fed mice, however, there was no regulation of AdipoR2 mRNA in brown and subcutaneous fat depending on the feeding state. Furthermore, AdipoR2 gene expression was significantly higher in epigonadal as compared to subcutaneous fat. Interestingly, a parallel circadian gene expression pattern for both AdipoR1 and AdipoR2 with lower expression between 20:00 and 06:00 h in brown, epigonadal, and subcutaneous adipose tissue was also found. In conclusion, our results suggest a fat depot specific regulation of AdipoR1 and AdipoR2 gene expression in brown and white fat by fasting. In addition, we have identified a coordinated circadian pattern of AdipoR1 and AdipoR2 gene expression in these tissues.

Regulation of adiponectin receptor gene expression in diabetic mice

Adiponectin is an adipocyte-derived factor that plays pivotal roles in lipid and glucose metabolism in muscle and liver. The following two adiponectin receptor types were recently identified: AdipoR1 is abundantly expressed in muscle, whereas AdipoR2 is predominantly expressed in the liver. To clarify the regulation of adiponectin receptor gene expression in diabetic states, we examined mRNA levels of AdipoR1 in the muscles of diabetic animals by Northern blotting. The level of AdipoR1 mRNA was increased approximately 2.5-fold in muscle of streptozotocin (STZ) diabetic mice, but the normal level was restored by insulin administration, indicating that insulin has an inhibitory effect on AdipoR1 expression. To confirm this inhibitory effect of insulin, we performed in vitro experiments using C2C12 skeletal muscle cells. Insulin treatment for 24 h decreased AdipoR1 expression by approximately 60% in C2C12 cells. In addition, this effect was mediated by the phosphatidylinositol 3-kinase-dependent pathway rather than the mitogen-activated protein kinase pathway. AdipoR1 expression in insulin-resistant diabetic mice was also investigated. AdipoR1 expression was decreased by 36% in type 2 diabetic obese db/db mice compared with lean mice. In contrast, hepatic AdipoR2 expression was not significantly changed in either STZ mice or genetically obese mice. Our results indicate that regulation of AdipoR1, but not that of AdipoR2, may be involved in glucose and lipid metabolism in diabetic states.

Cloning and expression of porcine adiponectin and adiponectin receptor 1 and 2 genes in pigs1

In mice, adiponectin receptors (AdipoR) have been found to mediate the effect of adiponectin in muscle and liver in regulation of glucose and fatty acid metabolism. The purposes of this study were to clone these receptors from pig tissues by reverse transcription PCR using mRNA from skeletal muscle and adipose tissue and to investigate the expression of these genes in various pig tissues. Sequences of adiponectin, AdipoR1, and AdipoR2 were determined and found to be highly homologous to those of the human and mouse. The AA sequences predicted for the full-length cDNA of porcine adiponectin, AdipoR1, and AdipoR2 were similar to those of the human and mouse, ranging from 81 to 97% homology, suggesting similar functions of these genes in pigs as in other species. Transcripts for adiponectin were abundant in s.c. adipose tissue in Lee-Sung pigs and in crossbred pigs. Transcripts for AdipoR1 were abundant in heart and skeletal muscle and also detected to a lesser extent (P < 0.05) in adipose tissue, liver, and spleen of the Lee-Sung pigs. Transcripts for AdipoR2 were abundant in s.c. adipose tissue and present to a lesser extent (P < 0.05) in the liver, heart, skeletal muscle, and spleen. These results indicate that the effect of adiponectin may be mediated through these receptors in various porcine tissues. Fasting for 8 h did not have a significant effect on the expression of adiponectin and AdipoR1 mRNA, but it increased (P < 0.05) the AdipoR2 mRNA in the s.c. adipose tissue of crossbred pigs. These results indicate that the AdipoR2-mediated fatty acid oxidation may be responsible at least in part for the fasted state fatty acid oxidation in porcine adipose tissues. The successful cloning of pig adiponectin and adiponectin receptors will enhance the understanding of the involvement of these genes in regulating energy metabolism in pigs.

Expression of adiponectin receptor mRNA in human skeletal muscle cells is related to in vivo parameters of glucose and lipid metabolism.

The adiponectin receptors, AdipoR1 and AdipoR2, are thought to transmit the insulin-sensitizing, anti-inflammatory, and atheroprotective effects of adiponectin. In this study, we examined whether AdipoR mRNA expression in human myotubes correlates with in vivo measures of insulin sensitivity. Myotubes from 40 metabolically characterized donors expressed 1.8-fold more AdipoR1 than AdipoR2 mRNA (588 +/- 35 vs. 321 +/- 39 fg/microg total RNA). Moreover, the expression levels of both receptors correlated with each other (r = 0.45, P < 0.01). AdipoR1 mRNA expression was positively correlated with in vivo insulin and C-peptide concentrations, first-phase insulin secretion, and plasma triglyceride and cholesterol concentrations before and after adjustment for sex, age, waist-to-hip ratio, and body fat. Expression of AdipoR2 mRNA clearly associated only with plasma triglyceride concentrations. In multivariate linear regression models, mRNA expression of AdipoR1, but not AdipoR2, was a determinant of first-phase insulin secretion independent of insulin sensitivity and body fat. Finally, insulin did not directly modify myotube AdipoR1 mRNA expression in vitro. In conclusion, we provide evidence that myotube mRNA levels of both receptors are associated with distinct metabolic functions but not with insulin sensitivity. AdipoR1, but not AdipoR2, expression correlated with insulin secretion. The molecular nature of this link between muscle and beta-cells needs to be further clarified.

Dual action of adiponectin on insulin secretion in insulin-resistant mice

Adiponectin is secreted by adipocytes and has been implicated as a mediator of insulin sensitivity. In this study, the acute effects of adiponectin on islets isolated from normal or diet-induced insulin resistant mice were examined. In normal islets, adiponectin (5 μg/ml) had no significant effect on insulin secretion. In contrast, in islets from mice rendered insulin resistant by high-fat feeding, adiponectin inhibited insulin secretion at 2.8 mM ( P < 0.01) but augmented insulin secretion at 16.7 mM glucose ( P < 0.05). The augmentation of glucose-stimulated insulin secretion by adiponectin was accompanied by increased glucose oxidation ( P < 0.005), but without any significant effect on palmitate oxidation or the islet ATP/ADP ratio. Furthermore, RT-PCR revealed the expression of the adiponectin receptor AdipoR1 mRNA in mouse islets, however, with no difference in the degree of expression level between the two feeding groups. The results thus uncover a potential dual role for adiponectin to modify insulin secretion in insulin resistance.

Growth hormone is a positive regulator of adiponectin receptor 2 in 3T3-L1 adipocytes

The fat-derived protein adiponectin is an important insulin-sensitizing adipocytokine which is downregulated in insulin resistance and obesity. Recently, two receptors of this adipose-expressed protein called adiponectin receptor 1 (AdipoR1) and 2 (AdipoR2) have been cloned. To clarify expression and regulation of these receptors in fat cells, AdipoR1 and AdipoR2 mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction during differentiation of 3T3-L1 adipocytes and after treatment with various hormones known to induce insulin resistance. Interestingly, AdipoR2 synthesis was significantly increased up to 4.8-fold during differentiation of 3T3-L1 preadipocytes, whereas AdipoR1 expression was only augmented up to 1.4-fold. Furthermore, growth hormone (GH) induced AdipoR2, but not AdipoR1 mRNA by up to 2.4-fold in a dose- and time-dependent fashion with significant stimulation detectable at concentrations as low as 5 ng/ml GH and as early as 2 h after effector addition. The positive effect of GH on AdipoR2 expression could be reversed by withdrawal of the hormone for 24 h. In contrast, other key hormones involved in the regulation of insulin resistance and energy metabolism such as insulin, isoproterenol, dexamethasone, triiodothyronine, angiotensin 2, tumor necrosis factor α, and interleukin-6 did not influence AdipoR1 and AdipoR2 synthesis in vitro. Taken together, our results suggest that AdipoR2 expression is differentiation-dependent and selectively regulated by GH implying a potential role of this hormone in adiponectin-associated alterations of insulin sensitivity and energy homeostasis.

Adiponectin mediates an antiproliferative response in human MDA-MB 231 breast cancer cells

Numerous epidemiological studies have documented that obesity is a risk factor for breast cancer especially in post-menopausal women. However, the molecular basis of this association is not well known. In contrast to leptin, plasma levels of adiponectin, another major adipokine, are decreased in obese subjects. Therefore, we and others hypothesized that adiponectin may be a paracrine factor negatively controlling mammary tumor development. We recently demonstrated growth inhibition of the estrogen-sensitive breast cancer MCF-7 cell line by adiponectin. The purpose of the present study was to determine whether this anti-proliferative effect of adiponectin also applies to the MDA-MB 231 estrogen-insensitive breast epithelial cancer cell line. Our results demonstrate that i) the adiponectin-specific receptors AdipoR1 and R2 are expressed in these cells, and ii) the subphysiological concentrations of recombinant adiponectin inhibit MDA-MB 231 cell growth and concomitantly enhance the expression of Bax and p53, two pro-apoptotic genes. Moreover, the invalidation of AdipoR1 and R2 mRNA experiments demonstrated that the anti-proliferative and pro-apoptotic effects of adiponectin were partially mediated via AdipoR1 and R2. We describe, for the first time, that AdipoR mRNA expression was down-regulated by adiponectin and leptin in MDA-MB 231 cells. Taken altogether, these results strongly suggest that the two adipokines should be considered as i) additional factors of breast cancer risk, and ii) may therefore be potential targets in breast cancer therapy.