Paradigm shift: the primary function of the "Adiponectin Receptors" is to regulate cell membrane composition.

The ADIPOR1 and ADIPOR2 proteins (ADIPORs) are generally considered as adiponectin receptors with anti-diabetic properties. However, studies on the yeast and C. elegans homologs of the mammalian ADIPORs, and of the ADIPORs themselves in various mammalian cell models, support an updated/different view. Based on findings in these experimental models, the ADIPORs are now emerging as evolutionarily conserved regulators of membrane homeostasis that do not require adiponectin to act as membrane fluidity sensors and regulate phospholipid composition. More specifically, membrane rigidification activates ADIPOR signaling to promote fatty acid desaturation and incorporation of polyunsaturated fatty acids into membrane phospholipids until fluidity is restored. The present review summarizes the evidence supporting this new view of the ADIPORs, and briefly examines physiological consequences.

The Adiponectin Receptor Agonist AdipoRon Ameliorates Diabetic Nephropathy in a Model of Type 2 Diabetes.

Adiponectin exerts renoprotective effects against diabetic nephropathy (DN) by activating the AMP-activated protein kinase (AMPK)/peroxisome proliferative-activated receptor-α (PPARα) pathway through adiponectin receptors (AdipoRs). AdipoRon is an orally active synthetic adiponectin receptor agonist. We investigated the expression of AdipoRs and the associated intracellular pathways in 27 patients with type 2 diabetes and examined the effects of AdipoRon on DN development in male C57BLKS/J db/db mice, glomerular endothelial cells (GECs), and podocytes. The extent of glomerulosclerosis and tubulointerstitial fibrosis correlated with renal function deterioration in human kidneys. Expression of AdipoR1, AdipoR2, and Ca2+/calmodulin-dependent protein kinase kinase-ß (CaMKKß) and numbers of phosphorylated liver kinase B1 (LKB1)- and AMPK-positive cells significantly decreased in the glomeruli of early stage human DN. AdipoRon treatment restored diabetes-induced renal alterations in db/db mice. AdipoRon exerted renoprotective effects by directly activating intrarenal AdipoR1 and AdipoR2, which increased CaMKKß, phosphorylated Ser431LKB1, phosphorylated Thr172AMPK, and PPARα expression independently of the systemic effects of adiponectin. AdipoRon-induced improvement in diabetes-induced oxidative stress and inhibition of apoptosis in the kidneys ameliorated relevant intracellular pathways associated with lipid accumulation and endothelial dysfunction. In high-glucose-treated human GECs and murine podocytes, AdipoRon increased intracellular Ca2+ levels that activated a CaMKKß/phosphorylated Ser431LKB1/phosphorylated Thr172AMPK/PPARα pathway and downstream signaling, thus decreasing high-glucose-induced oxidative stress and apoptosis and improving endothelial dysfunction. AdipoRon further produced cardioprotective effects through the same pathway demonstrated in the kidney. Our results show that AdipoRon ameliorates GEC and podocyte injury by activating the intracellular Ca2+/LKB1-AMPK/PPARα pathway, suggesting its efficacy for treating type 2 diabetes-associated DN.

Expression and localization of adiponectin and its receptors in ovarian follicles during different stages of development and the modulatory effect of adiponectin on steroid production in water buffalo.

Adiponectin is an adipocyte-derived hormone regulating energy metabolism, insulin sensitivity and recently found to regulate reproduction. The current study was carried out to investigate gene and protein expression, immunolocalization of adiponectin and its receptors AdipoR1 and AdipoR2 in ovarian follicles of different developmental stages in water buffalo (Bubalus bubalis) and to investigate the effect of adiponectin on steroid production in cultured bubaline granulosa cells. qPCR, western blotting and immunohistochemistry were applied to demonstrate mRNA expression, protein expression and immunolocalization, respectively. The results indicate that adiponectin, AdipoR1 and AdipoR2 were present in granulosa cells (GC) and theca interna (TI) of ovarian follicles and the expression of adiponectin, AdipoR1, AdipoR2 in GC and AdipoR1 and AdipoR2 in TI increased with increase in follicle size (p < .05). Expression of adiponectin was high in small and medium size follicles in TI. The adiponectin and its receptors were immunolocalized in the cytoplasm of GC and TI cells. Further, in the in-vitro study, GCs were cultured and treated with recombinant adiponectin each at 0, 1 and 10 µg/ml alone or with follicle stimulating hormone (FSH) at 30 ng/ml) or Insulin-like growth factor I (IGF-I) at 10 ng/ml for 48 hr after obtaining 75%-80%s confluency. Adiponectin at 10 µg/ml increased IGF-I-induced estradiol (E2 ) and progesterone (P4 ) secretion and FSH-induced E2 secretion from GC and also increased the abundance of factors involved in E2 and P4 production (cytochrome P45019A1 [CYP19A1] and 3-beta-hydroxysteroid dehydrogenase [3ß-HSD]). In conclusion, this study provides novel evidence for the presence of adiponectin and its receptors in ovarian follicles and modulatory role of adiponectin on steroid production in buffalo.

The role of AdipoR1 and AdipoR2 in liver fibrosis.

Activation of the adiponectin (APN) signaling axis retards liver fibrosis. However, understanding of the role of AdipoR1 and AdipoR2 in mediating this response is still rudimentary. Here, we sought to elucidate the APN receptor responsible for limiting liver fibrosis by employing AdipoR1 and AdipoR2 knock-out mice in the carbon tetrachloride (CCl4) model of liver fibrosis. In addition, we knocked down receptor function in primary hepatic stellate cells (HSCs) in vitro. Following the development of fibrosis, AdipoR1 and AdipoR2 KO mice had no quantitative difference in fibrosis by Sirius red staining. However, AdipoR2 KO mice had an enhanced fibrotic signature with increased Col1-α1, TGFß-1, TIMP-1, IL-10, MMP-2 and MMP-9. Knockdown of AdipoR1 or AdipoR2 in HSCs followed by APN treatment demonstrated that AdipoR1 and AdipoR2 did not affect proliferation or TIMP-1 gene expression, while AdipoR2 modulated Col1-α1 and α-SMA gene expression, HSC migration, and AMPK activity. These finding suggest that AdipoR2 is the major APN receptor on HSCs responsible for mediating its anti-fibrotic effects.

Adiponectin regulates thermal nociception in a mouse model of neuropathic pain.

BACKGROUND: Adiponectin, a cytokine secreted by adipocytes, plays an important role in regulating glucose and lipid metabolism. However, the role of adiponectin in pain conditions is largely unknown. This study aimed to identify the role and mechanism of adiponectin in nociceptive sensitivity under physiological and pathological states utilising adiponectin knockout (KO) mice. METHODS: Wild type (WT) and adiponectin KO mice were subjected to partial sciatic nerve ligation (pSNL) or sham operation. Pain-like behavioural tests, including thermal allodynia, hyperalgesia, and mechanical allodynia, were performed before and after pSNL from Day 3-21. Dorsal root ganglions (DRGs), lumbar spinal segments at L3-5, and somatosensory cortex were collected for protein measurement via western blotting and immunofluorescence staining. RESULTS: Compared with WT mice, KO mice had significantly lower (40-50%) paw withdrawal latency to innocuous and noxious stimuli before and after pSNL. In DRG neurones from KO mice, where adiponectin receptor (AdipoR) 2 is located, phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) and heat-sensitive transient receptor potential cation channel subfamily V member 1 (TRPV1) were significantly higher (by two- to three-fold) than from WT mice. In spinal microglia and somatosensory cortical neurones, where AdipoR1 is mainly located, p-p38 MAPK and TRPV1 were also higher (by two- to three-fold) in KO compared with WT mice, and altered signalling of these molecules was exacerbated (1.2- to 1.3-fold) by pSNL. CONCLUSIONS: Our results show that adiponectin regulates thermal nociceptive sensitivity by inhibiting activation of DRG neurones, spinal microglia, and somatosensory cortical neurones in physiological and neuropathic pain states. This study has relevance for patients with adiponectin disorders, such as obesity and diabetes.

Divergent roles for adiponectin receptor 1 (AdipoR1) and AdipoR2 in mediating revascularization and metabolic dysfunction in vivo.

Adiponectin is a well described anti-inflammatory adipokine that is highly abundant in serum. Previous reports have found that adiponectin deficiency promotes cardiovascular and metabolic dysfunction in murine models, whereas its overexpression is protective. Two candidate adiponectin receptors, AdipoR1 and AdipoR2, are uncharacterized with regard to cardiovascular tissue homeostasis, and their in vivo metabolic functions remain controversial. Here we subjected AdipoR1- and AdipoR2-deficient mice to chronic hind limb ischemic surgery. Blood flow recovery in AdipoR1-deficient mice was similar to wild-type; however, revascularization in AdipoR2-deficient mice was severely attenuated. Treatment with adiponectin enhanced the recovery of wild-type mice but failed to rescue the impairment observed in AdipoR2-deficient mice. In view of this divergent receptor function in the hind limb ischemia model, AdipoR1- and AdipoR2-deficient mice were also evaluated in a model of diet-induced obesity. Strikingly, AdipoR1-deficient mice developed severe metabolic dysfunction compared with wild type, whereas AdipoR2-deficient mice were protected from diet-induced weight gain and metabolic perturbations. These data show that AdipoR2, but not AdipoR1, is functionally important in an in vivo model of ischemia-induced revascularization and that its expression is essential for the revascularization actions of adiponectin. These data also show that, in contrast to revascularization responses, AdipoR1, but not AdipoR2 deficiency, leads to diet-induced metabolic dysfunction, revealing that these receptors have highly divergent roles in vascular and metabolic homeostasis.

Myocardial mitochondrial dysfunction in mice lacking adiponectin receptor 1.

Hypoadiponectinemia is an independent predictor of cardiovascular disease, impairs mitochondrial function in skeletal muscle, and has been linked to the pathogenesis of Type 2 diabetes. In models of Type 2 diabetes, myocardial mitochondrial function is impaired, which is improved by increasing serum adiponectin levels. We aimed to define the roles of adiponectin receptor 1 (AdipoR1) and 2 (AdipoR2) in adiponectin-evoked regulation of mitochondrial function in the heart. In isolated working hearts in mice lacking AdipoR1, myocardial oxygen consumption was increased without a concomitant increase in cardiac work, resulting in reduced cardiac efficiency. Activities of mitochondrial oxidative phosphorylation (OXPHOS) complexes were reduced, accompanied by reduced OXPHOS protein levels, phosphorylation of AMP-activated protein kinase, sirtuin 1 activity, and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) signaling. Decreased ATP/O ratios suggested myocardial mitochondrial uncoupling in AdipoR1-deficient mice, which was normalized by lowering increased mitochondrial 4-hydroxynonenal levels following treatment with the mitochondria-targeted antioxidant Mn (III) tetrakis (4-benzoic acid) porphyrin. Lack of AdipoR2 did not impair mitochondrial function and coupling in the heart. Thus, lack of AdipoR1 impairs myocardial mitochondrial function and coupling, suggesting that impaired AdipoR1 signaling may contribute to mitochondrial dysfunction and mitochondrial uncoupling in Type 2 diabetic hearts.

Adiponectin regulates cutaneous wound healing by promoting keratinocyte proliferation and migration via the ERK signaling pathway.

Diabetic patients are at high risk of developing delayed cutaneous wound healing. Adiponectin plays a pivotal role in the pathogenesis of diabetes and is considered to be involved in various pathological conditions associated with diabetes; however, its role in wound repair is unknown. In this study, we elucidated the involvement of adiponectin in cutaneous wound healing in vitro and in vivo. Normal human keratinocytes expressed adiponectin receptors, and adiponectin enhanced proliferation and migration of keratinocytes in vitro. This proliferative and migratory effect of adiponectin was mediated via AdipoR1/AdipoR2 and the ERK signaling pathway. Consistent with in vitro results, wound closure was significantly delayed in adiponectin-deficient mice compared with wild-type mice, and more importantly, keratinocyte proliferation and migration during wound repair were also impaired in adiponectin-deficient mice. Furthermore, both systemic and topical administration of adiponectin ameliorated impaired wound healing in adiponectin-deficient and diabetic db/db mice, respectively. Collectively, these results indicate that adiponectin is a potent mediator in the regulation of cutaneous wound healing. We propose that upregulation of systemic and/or local adiponectin levels is a potential and very promising therapeutic approach for dealing with diabetic wounds.

Cardioprotective modulation of cardiac adiponectin and adiponectin receptors by omega-3 in the high-fat fed rats.

Obesity is an important risk factor for heart disease. This study investigated the effects of omega-3 (omega-3) on reversal of high fat (HF) diet-induced changes in the expression of the cardiac adiponectin and adiponectin receptors R1 and R2. Male rats were fed low-fat (LF; 10% energy from fat) or HF (45% energy from fat) for 16 weeks, LF-omega-3 or a HF-omega-3 (LF or HF for 16 weeks supplemented by omega-3 as 36 g/kg diet for the last 6 weeks, respectively) and a HF diet for 10 weeks to demonstrate HF effect before omega-3 administration. HF diet induced obesity, glucose intolerance, increased heart end systolic and diastolic volumes, decreased serum adiponectin, reduced expression of cardiac and adipose tissue adiponectin and adipo R1 & R2 with elevated serum tumour necrosis factor-alpha (TNF-alpha) compared to the LF diet. On the other hand, the HF-omega-3 group compared with the HF group had improved glucose tolerance (area under the glucose curve 837.14 +/- 45.7 versus 1158.5 +/- 69.8) and insulin resistance with a significant increase in serum adiponectin (4.22 +/- 0.39 versus 2.82 +/- 0.69 ng/ml) and a significant decrease in serum TNF-alpha (129.84 +/- 13.63 versus 209.8 +/- 16.42 pg/ml) and triglycerides independent of obesity. Also the data showed significant increases in the expression of cardiac and adipose tissue adiponectin and adiponectin R1 and adipose tissue adipo R2 as well as cardiac pAMP kinase with improvement in end-systolic and -diastolic volumes. These parameters were also improved compared to initial values in HF-10-week group. In conclusion, dietary omega-3 supplementation has a beneficial effect on fat-induced cardiac dysfunction and insulin resistance partly through increasing adiponectin and adiponectin receptors expression in heart and adipose tissue.

Globular adiponectin counteracts VCAM-1-mediated monocyte adhesion via AdipoR1/NF-κB/COX-2 signaling in human aortic endothelial cells.

Adiponectin (Ad) is an insulin-sensitizing adipocytokine with anti-inflammatory and vasoprotective properties. Cleavage of native full-length Ad (fAd) by elastases from activated monocytes generates globular Ad (gAd). Increased gAd levels are observed in the proximity of atherosclerotic lesions, but the physiological meaning of this proteolytic Ad fragment in the cardiovascular system is controversial. We compared molecular and biological properties of fAd and gAd in human aortic endothelial cells (HAEC). In control HAEC, both fAd and gAd acutely stimulated nitric oxide (NO) production by AMPK-dependent pathways. With respect to fAd, gAd more efficiently increased activation of NF-κB signaling pathways, resulting in cyclooxygenase-2 (COX-2) overexpression and COX-2-dependent prostacyclin 2 (PGI(2)) release. In contrast with fAd, gAd also increased p38 MAPK phosphorylation and VCAM-1 expression, ultimately enhancing adhesion of monocytes to endothelial cells. In HAEC lacking AdipoR1 (by siRNA), both activation of NF-κB as well as COX-2 overexpression by gAd were abrogated. Conversely, gAd-mediated p38MAPK activation and VCAM-1 expression were unaffected, and monocyte adhesion was greatly enhanced. In HAEC lacking COX-2 (by siRNA), reduced levels of PGI(2) further increased gAd-dependent monocyte adhesion. Our findings suggest that biological activities of fAd and gAd in endothelium do not completely overlap, with gAd possessing both AdipoR1-dependent ability to stimulate COX-2 expression and AdipoR1-independent effects related to expression of VCAM-1 and adhesion of monocytes to endothelium.

Adiponectin and adiponectin receptors in the mouse preimplantation embryo and uterus.

BACKGROUND: Adiponectin (Adipoq), a protein secreted by adipocytes in inverse proportion to the adipose mass present, modulates energy homeostasis and increases insulin sensitivity. Tissue Adipoq signaling decreases in settings of maternal diabetes, polycystic ovary syndrome (PCOS) and endometriosis, conditions which are associated with reproductive difficulty. Our objective was to define the expression and hormonal regulation of Adipoq and its receptors in the mouse preimplantation embryo and uterus. METHODS AND RESULTS: By real-time quantitative PCR, mRNA transcripts for Adipoq, AdipoR1, AdipoR2, Ppara, Ppard, FATP1 (SLC27A1) and acyl CoA oxidase (Acox1) were identified in mouse 2-cell and 8-cell embryos, while blastocyst stage embryos and trophoblast stem (TS) cells expressed mRNA for all genes except Adipoq. Protein expression of Adipoq, AdipoR1, AdipoR2, the insulin sensitive transporters GLUT8 (Slc2A8), GLUT12 (Slc2A12) and p-PRKAA1 was identified by immunofluorescence staining in all stages of preimplantation embryos including the blastocyst. In situ hybridization demonstrated the presence of Adipoq, AdipoR1 and AdipoR2 mRNA in the mouse decidual cells of the implantation site and in artificially decidualized cells, and the expression of these proteins was confirmed by western blotting. Flow cytometry confirmed cell surface expression of AdipoR1 and AdipoR2 in TS cells and decidual cells. CONCLUSIONS: These results suggest for the first time that Adipoq signaling may play an important role in preimplantation embryo development and uterine receptivity by autocrine and paracrine methods in the mouse. Implantation failures and pregnancy loss, specifically those experienced in women with maternal metabolic conditions such as diabetes, obesity and PCOS, may be the result of aberrant Adipoq and AdipoR1 and AdipoR2 expression and suboptimal decidualization in the uterus.

Mechanisms underlying the anti-proliferative actions of adiponectin in human breast cancer cells, MCF7-dependency on the cAMP/protein kinase-A pathway.

Obesity is a risk factor for breast cancer, and low blood concentrations of adiponectin are associated with high incidence and poor prognosis of breast cancer. However, the molecular mechanisms underlying such inhibitory effects of adiponectin remain to be defined. By using MCF7 cells, we investigated the mechanisms underlying the inhibitory effects of adiponectin on breast cancer cells, particularly in the context of opposing IGF-1-induced proliferation. We found that adiponectin, at 20 and 40 µg/ml, reduced MCF7 cell growth in the absence and presence of IGF-1. These inhibitory effects were primarily the result of the significant increase of cells at G(1)/G(0) phase and concomitant decrease of cells at S phase. In addition, the percentage of apoptotic cells increased more than two-fold. Within 30-min of adiponectin addition, the phosphorylation of AMPKα was sharply elevated, and the level of IGF-1-activated Akt was decreased. Prolonged exposure to adiponectin resulted in reduction of cyclin D1 and cyclin E2 expression. Adiponectin also increased intracellular levels of cAMP and the activity of protein kinase-A (PKA). The inhibitors of PKA completely abolished the adiponectin's effects on cell growth. In conclusion, our studies revealed an important cellular mechanism underlying the relationship between reduced adiponectin concentrations and breast cancer development.

Adiponectin and functional adiponectin receptor 1 are expressed by airway epithelial cells in chronic obstructive pulmonary disease.

We screened bronchoalveolar lavage (BAL) fluids from COPD-E (chronic obstructive pulmonary disease-Emphysema) and control subjects using a 120 Ab cytokine array and demonstrated that adiponectin was highly expressed in BAL in COPD-E. An adiponectin ELISA confirmed that adiponectin was highly expressed in BAL in COPD-E compared with smokers and healthy control subjects. Immunohistochemistry studies of lung sections from subjects with COPD-E demonstrated that airway epithelial cells expressed significant levels of adiponectin and adiponectin receptor (AdipoR) 1 but not AdipoR2. In vitro studies with purified populations of human lung A549 epithelial cells demonstrated that they expressed both adiponectin and AdipoR1 (but not AdipoR2) as assessed by RT-PCR, Western blot, and immunohistochemistry. Lung A549 epithelial AdipoR1were functional as incubation with adiponectin induced release of IL-8, which was inhibited by small interfering RNA to AdipoR1. Using a mouse model of COPD, tobacco smoke exposure induced both evidence of COPD as well as increased levels of adiponectin in BAL fluid and increased adiponectin expression by airway epithelial cells. As adiponectin expression in adipocytes is dependent upon NF-kappaB we determined levels of adiponectin in tobacco smoke exposed CC10-Cre(tg)/Ikkbeta(Delta/Delta) mice (deficient in the ability to activate NF-kappaB in airway epithelium). These studies demonstrated that CC10-Cre(tg)/Ikkbeta(Delta/Delta) and wild-type mice had similar levels of BAL adiponectin and airway epithelial adiponectin immunostaining. Overall, these studies demonstrate the novel observation that adiponectin and functional AdipoR1are expressed by lung epithelial cells, suggesting a potential autocrine and/or paracrine pathway for adiponectin to activate epithelial cells in COPD-E.

[Research progress in regulation of adiponectin receptors expression].

Adiponectin is an adipokine mainly secreted by adipose tissue, which exerts insulin-sensitivity, anti-inflammation, anti-atherosclerosis and cardio-protective effects. These biological effects are mediated by adiponectin receptor 1 and adiponectin receptor 2. Expression levels of adiponectin receptor affect activation of downstream signaling pathway and biological effects. Research about regulation factors of adiponectin receptor expression contributes discovering the molecular mechanism and provides new ideas for the prevention and treatment of the metabolism disorder and cardiovascular diseases.

Pectic Oligogalacturonide Facilitates the Synthesis and Activation of Adiponectin to Improve Hepatic Lipid Oxidation.

SCOPE: Adiponectin (ADPN), a kind of adipokines, plays an important role in the regulation of lipid metabolism. The objective of this study is focused on the ADPN to investigate the functional mechanisms of pectin oligosaccharide (POS) from hawthorn fruit in the improvement of hepatic fatty acid oxidation. METHOD AND RESULTS: High-fat fed mice are used in this experiment. POS is administrated with the doses of 0.25, 0.75, and 1.5 g kg-1 diet, respectively. The results demonstrate that gene and protein expressions of ADPN synthesis regulators involved in PKA/ERK/CREB and C/EBPα/PPARγ pathways are upregulated by POS administration. POS also activates the AdiopR1/AMPKα/PGC1 and AdipoR2/PPARα signaling pathways to improve the fatty acid oxidation in the liver, which is further accelerated by the enhancement of mitochondrial functions. CONCLUSION: POS can act as an ADPN activator to improve lipid metabolism, leading it to the applications of biomedical and functional foods for ameliorating chronic liver diseases resulted from a high-energy diet.

Expression and role of adiponectin receptor 1 in lipopolysaccharide-induced proliferation of cultured rat adventitial fibroblasts.

Adiponectin is an adipose-derived hormone that has anti-diabetic and anti-atherogenic effects through interaction with AdipoR1 and AdipoR2 (adiponectin receptors 1 and 2), but little is known about the expression and function of adiponectin and its receptors in adventitia and adventitial fibroblasts. In the present study, we have demonstrated that AdipoR1 is highly expressed in rat adventitia and cultured adventitial fibroblasts by quantitative real-time PCR, Western blotting and immunofluorescent staining, whereas Adipo2 is low-expressed. The expression of AdipoR1 have been observed to decrease gradually in adventitial fibroblasts in response to LPS (lipopolysaccharide) treatment. No local expression of adiponectin has been detected in adventitial tissues, indicating that serum adiponectin is the ligand for AdipoR1 in adventitial fibroblasts. In addition, treatment of recombinant adiponectin inhibited LPS-induced proliferation of adventitial fibroblasts via activation of the AMPK (adenosine monophosphate-activated protein kinase). AdipoR1 siRNA (small interfering RNA) transfection potently knocked down the receptor protein. The siRNA-AdipoR1 transfected cells and AMPK inhibitor compound C treated cells showed decreased phosphorylated level of AMPK as determined by Western blot analysis, and increased the proliferation of adventitial fibroblasts as determined by BrdU (5-bromo-29-deoxyuridine) staining. These results demonstrated that adiponectin stimulates the proliferation of adventitial fibroblasts via the AdipoR1 and AMPK signalling pathways.

PAQRs: a counteracting force to ceramides?

In recent years, sphingolipids have garnered increasing attention for their roles in modulating intracellular signaling events. Circulating factors associated with obesity promote excess accumulation of ceramide or glucosylceramide derivatives, which impair insulin action in peripheral tissues. In this issue, Villa et al. (p. 866) provide evidence that, in yeast, the progestin and adipoQ receptor superfamily of receptors mediate their effects via a novel ceramidase activity, generating sphingoid base as a second messenger.

Involvement of AdipoR receptor in adiponectin-induced motility and alpha2beta1 integrin upregulation in human chondrosarcoma cells.

Chondrosarcoma is a type of highly malignant tumor with a capacity to invade locally and cause distant metastasis. Chondrosarcoma shows a predilection for metastasis to the lungs. Adiponectin is a protein hormone secreted predominantly by differentiated adipocytes and is involved in energy homeostasis. However, the effect of adiponectin on migration activity in human chondrosarcoma cells is mostly unknown. We found that adiponectin increased the migration and expression of alpha2beta1 integrin in human chondrosarcoma cells. The protein and messenger RNA expression of adiponectin receptor (AdipoR1 and AdipoR2) in chondrosarcoma patients and chondrosarcoma cell lines were significantly higher than the normal cartilage. Moreover, primary chondrosarcoma and chondrosarcoma cell lines (SW1353 and JJ012) were more invasive than normal chondrocytes. Adiponectin-mediated migration and integrin expression was attenuated by 5'-adenosine monophosphate-activated protein kinase (AMPK) small interfering RNA and an AMPK inhibitor (Ara A and compound C). Activation of p38 and nuclear factor-kappa B (NF-kappaB) pathways after adiponectin treatment was demonstrated, and adiponectin-induced expression of integrins and migration activity was inhibited by the specific inhibitor and mutant of p38 and NF-kappaB cascades. This study showed for the first time that adiponectin mediates the migration of human chondrosarcoma cells. One mechanism underlying adiponectin-directed migration was transcriptional upregulation of alpha2beta1 integrin and activation of AdipoR receptor, AMPK, p38 and NF-kappaB pathways.

Role of adiponectin receptors, AdipoR1 and AdipoR2, in the steroidogenesis of the human granulosa tumor cell line, KGN.

BACKGROUND: Adiponectin is involved in the regulation of energy homeostasis and more recently in the reproductive functions. We have previously shown that adiponectin receptors (AdipoR1 and AdipoR2) are expressed in human granulosa cells. However, it remains to be investigated whether both AdipoR1 and AdipoR2 or only one of these receptors serve as the major receptor(s) for adiponectin in human granulosa cells. METHODS: The RNA interference (RNAi) technology was used to specifically knockdown the expression of either AdipoR1 or AdipoR2. Progesterone and estradiol levels in the conditioned media were measured by radioimmunoassay, and determination of cell proliferation by tritiated thymidine incorporation. The levels of adiponectin receptors and proteins involved in the steroidogenesis and in the signalling pathways were examined by western blot. RESULTS: We generated AdipoR1 (R1) and AdipoR2 (R2) knockdown KGN cell lines. R1 cells were apoptotic and had increased expression levels of cleaved caspase 3 and decreased levels of BAD phosphorylation and PCNA as compared with control or parental KGN cells. R2 cells had similar morphology to control or KGN cells. However, they produced less progesterone and estradiol and expressed lower levels of StAR protein in response to FSH or IGF-1 stimulation compared with control cells. Furthermore, the increase of MAPK ERK1/2 phosphorylation in response to human recombinant adiponectin and FSH was lower in R2 than control cells. CONCLUSIONS: In the human granulosa KGN cell-line, AdipoR1 seems to be involved in the cell survival whereas AdipoR2, through MAPK ERK1/2 activation, may be implicated in the regulation of steroid production.

Inhibition of new vessel growth in mouse model of laser-induced choroidal neovascularization by adiponectin peptide II.

We have investigated the effect of adiponectin (APN) peptide II on new vessel growth in mouse model of choroidal neovascularization (CNV) or wet type age-related macular degeneration (AMD). Mice were injected intraperitoneally with APN peptide II, control peptide, or PBS on day 1-7 or day 5-14. APN, AdipoR1, PCNA, and VEGF localization was investigated using confocal microscopy, immunohistochemistry, and RT-PCR. APN peptide II decreased the relative area of FITC-dextran perfused vessels by 4-fold, PCNA expression by 3-fold, and the number of PCNA stained HUVEC and MAVEC cells by 38 and 46%, respectively. We concluded that APN peptide II inhibits CNV size on days 7 and 14 by inhibiting the proliferation of endothelial cells in vivo and in vitro. APN peptide II may have therapeutic potential to inhibit CNV or wet AMD.