Fetal alcohol syndrome is a neurological and developmental disorder caused by exposure of developing brain to ethanol. Administration of osmotin to rat pups reduced ethanol-induced apoptosis in cortical and hippocampal neurons. Osmotin, a plant protein, mitigated the ethanol-induced increases in cytochrome c, cleaved caspase-3, and PARP-1. Osmotin and ethanol reduced ethanol neurotoxicity both in vivo and in vitro by reducing the protein levels of cleaved caspase-3, intracellular [Ca2+]cyt, and mitochondrial transmembrane potential collapse, and also upregulated antiapoptotic Bcl-2 protein. Osmotin is a homolog of adiponectin, and it controls energy metabolism via phosphorylation. Adiponectin can protect hippocampal neurons against ethanol-induced apoptosis. Abrogation of signaling via receptors AdipoR1 or AdipoR2, by transfection with siRNAs, reduced the ability of osmotin and adiponectin to protect neurons against ethanol-induced neurodegeneration. Metformin, an activator of AMPK (adenosine monophosphate-activated protein kinase), increased whereas Compound C, an inhibitor of AMPK pathway, reduced the ability of osmotin and adiponectin to protect against ethanol-induced apoptosis. Osmotin exerted its neuroprotection via Bcl-2 family proteins and activation of AMPK signaling pathway. Modulation of AMPK pathways by osmotin, adiponectin, and metformin hold promise as a preventive therapy for fetal alcohol syndrome.
osmotin; adiponectin; ethanol; neuroprotection; FAS
Adiponectin is an adipocyte-secreted adipokine with pleiotropic actions. Clinical evidence has shown that serum adiponectin levels are increased and that adiponectin can protect pancreatic beta cells against apoptosis, which suggests that adiponectin may play an anti-apoptotic role in pancreatic cancer (PC). Here, we investigated the effects of adiponectin on PC development and elucidated the underlying molecular mechanisms. Adiponectin deficiency markedly attenuated pancreatic tumorigenesis in vivo. We found that adiponectin significantly inhibited the apoptosis of both human and mouse pancreatic cancer cells via adipoR1, but not adipoR2. Furthermore, adiponectin can increase AMP-activated protein kinase (AMPK) phosphorylation and NAD-dependent deacetylase sirtuin-1 (Sirt1) of PC cells. Knockdown of AMPK or Sirt1 can increase the apoptosis in PC cells. AMPK up-regulated Sirt1, and Sirt1 can inversely phosphorylate AMPK. Further studies have shown that Sirt1 can deacetylate peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α), which can increase the expression levels of mitochondrial genes. Thus, adiponectin exerts potent anti-apoptotic effects on PC cells via the activation of AMPK/Sirt1/PGC1α signaling. Finally, adiponectin can elevate β-catenin levels. Taken together, these novel findings reveal an unconventional role of adiponectin in promoting pancreatic cancers, and suggest that the effects of adiponectin on tumorigenesis are highly tissue-dependent.
Adiponectin; AMPK; Sirt1; PGC1α; Apoptosis; Pancreatic cancer
Adiponectin and adiponectin receptors (AdipoR1/2) are expressed in various tissues and are involved in the regulation of multiple functions such as energy metabolism and inflammatory responses. However, the effect of adiponectin and AdipoRs in submandibular glands has not been fully evaluated. In the present study, we found that mRNA and protein of both adiponectin and AdipoR1/2 were expressed in rat submandibular glands and in the SMG-C6 cell line, as evidenced by RT-PCR and Western blot analysis. Immunofluorescence staining showed that adiponectin was diffused in the cytoplasm, while AdipoR1/2 was concentrated in the membrane of acinar cells. Saliva flow was significantly increased by full length adiponectin (fAd) or globular adiponectin (gAd) perfusion in isolated rat submandibular glands. 5-Aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR), an adenosine monophosphate activated protein kinase (AMPK) activator, also increased saliva secretion. fAd, gAd, and AICAR all increased the average width of apical tight junctions in perfused submandibular glands, and decreased transepithelial electrical resistance (TER) in SMG-C6 cells, suggesting that adiponectin promoted secretion by modulating paracellular permeability. fAd and gAd increased p-AMPK levels, while AraA, an AMPK antagonist, abolished fAd- and gAd-induced changes in secretion, tight junction ultrastructure, and TER. Moreover, both AdipoR1 and AdipoR2 were required for fAd- or gAd-induced p-AMPK and TER responses, suggesting from their inhibition following AdipoR1 or AdipoR2 knockdown, and co-knockdown of AdipoRs by RNA interference. Our results suggest that adiponectin functions as a promoter of salivary secretion in rat submandibular glands via activation of AdipoRs, AMPK, and paracellular permeability.
Adiponectin is a hormone produced in and released from adipose cells, which has been shown to have anti-diabetic and anti-inflammatory actions in peripheral cells. Two cell surface adiponectin receptors (ADRs) mediate the majority of the known biological actions of adiponectin. Thus far, ADR expression in the brain has been demonstrated in the arcuate and the paraventricular nucleus of hypothalamus, where its activation affects food intake. Recent findings suggest that levels of circulating adiponectin increase after an ischemic stroke, but the role of adiponectin receptor activation in stroke pathogenesis and its functional outcome is unclear.
Ischemic stroke was induced in C57BL/6 mice by middle cerebral artery occlusion (MCAO) for 1 h, followed by reperfusion. Primary cortical neuronal cultures were established from individual embryonic neocortex. For glucose deprivation (GD), cultured neurons were incubated in glucose-free Locke's medium for 6, 12 or 24 h. For combined oxygen and glucose deprivation (OGD), neurons were incubated in glucose-free Locke's medium in an oxygen-free chamber with 95% N2/5% CO2 atmosphere for either 3, 6, 9, 12 or 24 h. Primary neurons and brain tissues were analysed for Adiponectin and ADRs using reverse transcriptase polymerase chain reaction (RT-PCR), immunoblot and immunochemistry methods.
Cortical neurons express ADR1 and ADR2, and that the levels of ADR1 are increased in neurons in response to in vitro or in vivo ischemic conditions. Neurons treated with either globular or trimeric adiponectin exhibited increased vulnerability to oxygen and glucose deprivation which was associated with increased activation of a pro-apoptotic signaling cascade involving p38 mitogen-activated protein kinase (p38MAPK) and AMP-activated protein kinase (AMPK).
This study reveals a novel pathogenic role for adiponectin and adiponectin receptor activation in ischemic stroke. We show that cortical neurons express ADRs and reveal a pro-apoptotic role for ADR1 activation in neurons, which may render them vulnerable to ischemic death.
Cardiomyocyte apoptosis is an important remodeling event contributing to heart failure and adiponectin may mediate cardioprotective effects at least in part via attenuating apoptosis. Here we used hypoxia-reoxygenation (H/R) induced apoptosis in H9c2 cells to examine the effect of adiponectin and cellular mechanisms of action. We first used TUNEL labeling in combination with laser scanning cytometry to demonstrate that adiponectin prevented H/R-induced DNA fragmentation. The anti-apoptotic effect of adiponectin was also verified via attenuation of H/R-induced phosphatidylserine exposure using annexin V binding. H/R-induced apoptosis via the mitochondrial-mediated intrinsic pathway of apoptosis as assessed by cytochrome c release into cytosol and caspase-3 activation, both of which were attenuated by adiponectin. Mechanistically, we demonstrated that adiponectin enhanced anti-oxidative potential in these cells which led to attenuation of the increase in intracellular reactive oxygen species (ROS) caused by H/R. To further address the mechanism of adiponctins anti-apoptotic effects we used siRNA to efficiently knockdown adiponectin receptor (AdipoR1) expression and found that this attenuated the protective effects of adiponectin on ROS production and caspase 3 activity. Knockdown of APPL1, an important intracellular binding partner for AdipoR, also significantly reduced the ability of adiponectin to prevent H/R-induced ROS generation and caspase 3 activity. In summary, H/R-induced ROS generation and activation of the intrinsic apoptotic pathway was prevented by adiponectin via AdipoR1/APPL1 signaling and increased anti-oxidant potential.
Although well-established, the underlying mechanisms involved in obesity-related plasma adiponectin decline remain elusive. Oxidative stress is associated with obesity and insulin resistance and considered to contribute to the progression toward obesity-related metabolic disorders. In this study, we investigated the effects of 4-hydroxynonenal (4-HNE), the most abundant lipid peroxidation end product, on adiponectin production and its potential implication in obesity-related adiponectin decrease. Long-term high-fat diet feeding led to obesity in mouse, accompanied by decreased plasma adiponectin and increased adipose tissue 4-HNE content. Exposure of adipocytes to exogenous 4-HNE resulted in decreased adiponectin secretion in a dose-dependent manner, which was consistent with significantly decreased intracellular adiponectin protein abundance. In contrast, adiponectin gene expression was significantly elevated by 4-HNE treatment, which was concomitant with increased peroxisome proliferator-activated receptor gamma (PPAR-γ) gene expression and transactivity. The effect was abolished by T0070907, a PPAR-γ antagonist, suggesting that PPAR-γ activation plays a critical role in this process. To gain insight into mechanisms involved in adiponectin protein decrease, we examined the effects of 4-HNE on adiponectin protein degradation. Cycloheximide (CHX)-chase assay revealed that 4-HNE exposure accelerated adiponectin protein degradation, which was prevented by MG132, a potent proteasome inhibitor. Immunoprecipitation assay showed that 4-HNE exposure increased ubiquitinated adiponectin protein levels. These data altogether indicated that 4-HNE enhanced adiponectin protein degradation via ubiquitin–proteasome system. Finally, we demonstrated that supplementation of HF diet with betaine, an antioxidant and methyl donor, alleviated high-fat-induced adipose tissue 4-HNE increase and attenuated plasma adiponectin decline. Taken together, our findings suggest that the lipid peroxidation product 4-HNE can differentially regulates adiponectin gene expression and protein abundance and may play a mechanistic role in obesity-related plasma adiponectin decline.
Oxidative stress; 4-HNE; Adiponectin; PPAR-γ; Proteasome; Betaine
Beta-amyloid (Aβ ) neurotoxicity is important in Alzheimer’s disease (AD) pathogenesis. Aβ neurotoxicity causes oxidative stress, inflammation and mitochondrial damage resulting in neuronal degeneration and death. Oxidative stress, inflammation and mitochondrial failure are also pathophysiological mechanisms of type 2 diabetes (T2DM) which is characterized by insulin resistance. Interestingly, T2DM increases risk to develop AD which is associated with reduced neuronal insulin sensitivity (central insulin resistance). We studied the potential protective effect of adiponectin (an adipokine with insulin-sensitizing, anti-inflammatory and anti-oxidant properties) against Aβ neurotoxicity in human neuroblastoma cells (SH-SY5Y) transfected with the Swedish amyloid precursor protein (Sw-APP) mutant, which overproduced Aβ with abnormal intracellular Aβ accumulation. Cytotoxicity was measured by assay for lactate dehydrogenase (LDH) released upon cell death and lysis. Our results revealed that Sw-APP transfected SH-SY5Y cells expressed both adiponectin receptor 1 and 2, and had increased AMP-activated protein kinase (AMPK) activation and enhanced nuclear factor-kappa B (NF-κB) activation compared to control empty-vector transfected SH-SY5Y cells. Importantly, adiponectin at physiological concentration of 10 µg/ml protected Sw-APP transfected SH-SY5Y cells against cytotoxicity under oxidative stress induced by hydrogen peroxide. This neuroprotective action of adiponectin against Aβ neurotoxicity-induced cytotoxicity under oxidative stress involved 1) AMPK activation mediated via the endosomal adaptor protein APPL1 (adaptor protein with phosphotyrosine binding, pleckstrin homology domains and leucine zipper motif) and possibly 2) suppression of NF-κB activation. This raises the possibility of novel therapies for AD such as adiponectin receptor agonists.
Background & Aims
Epidemiological studies have shown that obesity is a risk factor for hepatocellular carcinoma (HCC). Lower adiponectin levels are associated with poor prognosis in obese HCC patients hence it is plausible that adiponectin acts as a negative regulator of HCC. Here, we investigated the effects of adiponectin on HCC development and elucidated the underlying molecular mechanisms.
We utilized various in vitro assays using Huh7 and HepG2 HCC cells to examine the signal transduction pathways involved in protective function of adiponectin in HCC. These studies were followed by in vivo approaches using HCC xenografts and tumor analysis. Results from in vitro and in vivo findings were corroborated using human HCC tissue micro-array (TMA) and analysis of clinicopathological characteristics.
Adiponectin treatment resulted in increased apoptosis of HCC cells via activation of caspase-3. Adiponectin increased phosphorylation of c-Jun-N-terminal kinase (JNK) and inhibition of JNK-phosphorylation inhibited adiponectin-induced apoptosis and caspase-3 activation. Adiponectin increased phosphorylation of AMP-activated protein kinase (AMPK) and tumor suppressor TSC2 and inhibited mammalian target of rapamycin (mTOR) phosphorylation. Inhibition of AMPK phosphorylation not only inhibited adiponectin-induced JNK phosphorylation but also effectively blocked biological effects of adiponectin. In vivo study showed that adiponectin treatment substantially reduced liver tumorigenesis in nude mice. Importantly, analysis of adiponectin expression levels in TMA of human HCC patients revealed an inverse correlation of adiponectin expression with tumor size.
These novel findings show protective role of adiponectin in liver tumorigenesis and could help explain poor prognosis of obese HCC patients who typically have low adiponectin levels.
Hepatocellular carcinoma; Adiponectin; TSC2; mTOR
Diabetes increases the morbidity/mortality of ischemic heart disease, but the underlying mechanisms are incompletely understood. Deficiency of both AMP-activated protein kinase (AMPK) and adiponectin occurs in diabetes, but whether AMPK is cardioprotective or a central mediator of adiponectin cardioprotection in vivo remains unknown.
Methods and Results
Male adult mice with cardiomyocyte-specific overexpression of a mutant AMPKα2 subunit (AMPK-DN) or wild-type (WT) littermates were subjected to in vivo myocardial ischemia/reperfusion (MI/R) and treated with vehicle or adiponectin. In comparison to WT, AMPK-DN mice subjected to MI/R endured greater cardiac injury (larger infarct size, more apoptosis, and poorer cardiac function) likely as a result of increased oxidative stress in these animals. Treatment of AMPK-DN mice with adiponectin failed to phosphorylate cardiac acetyl-CoA carboxylase as it did in WT mouse heart. However, a significant portion of the cardioprotection of adiponectin against MI/R injury was retained in AMPK-DN mice. Furthermore, treatment of AMPK-DN mice with adiponectin reduced MI/R-induced cardiac oxidative and nitrative stress to the same degree as that seen in WT mice. Finally, treating AMPK-DN cardiomyocytes with adiponectin reduced simulated MI/R-induced oxidative/nitrative stress and decreased cell death (P<0.01).
Collectively, our results demonstrated that AMPK deficiency significantly increases MI/R injury in vivo but has minimal effect on the antioxidative/antinitrative protection of adiponectin.
adipocytokine; apoptosis; diabetes mellitus; myocardial infarction; signal transduction
The adipocyte-derived secretory factor adiponectin promotes insulin sensitivity,
decreases inflammation and promotes cell survival. To date, no unifying mechanism explains how
adiponectin can exert such a variety of beneficial systemic effects. Here, we show that
adiponectin potently stimulates a ceramidase activity associated with its two receptors,
adipoR1 and adipoR2, and enhances ceramide catabolism and formation of its anti-apoptotic
metabolite – sphingosine-1-phosphate (S1P), independently of AMPK. Using models of
inducible apoptosis in pancreatic β-cells and cardiomyocytes, we show that transgenic
overproduction of adiponectin decreases caspase-8 mediated death, while genetic adiponectin
ablation enhances apoptosis in vivo through a sphingolipid-mediated pathway.
Ceramidase activity is impaired in cells lacking both adiponectin receptor isoforms, leading to
elevated ceramide levels and enhanced susceptibility to palmitate-induced cell death. Combined,
our observations suggest a novel unifying mechanism of action for the beneficial systemic
effects exerted by adiponectin, with sphingolipid metabolism as its core upstream
Neutrophils are abundant, short-lived leukocytes that play a key role in the immune defense against microbial infections. These cells die by apoptosis following activation and uptake of microbes and will also enter apoptosis spontaneously at the end of their lifespan if they do not encounter a pathogen. Adiponectin exerts anti-inflammatory effects on neutrophil antimicrobial functions, but whether this abundant adipokine influences neutrophil apoptosis is unknown. Here we report that adiponectin in the physiological range (1–10 μg/ml) reduced apoptosis in resting neutrophils, decreasing caspase-3 cleavage and maintaining Mcl-1 expression by stabilizing this anti-apoptotic protein. We show that adiponectin induced phosphorylation of AMP-activated kinase (AMPK), protein kinase B (PKB), extracellular signal-regulated kinase (ERK 1/2) and p38 mitogen activated protein kinase (MAPK). Pharmacological inhibition of AMPK, PKB and ERK 1/2 ablated the pro-survival effects of adiponectin and treatment of neutrophils with an AMPK specific activator (AICAR) and AMPK inhibitor (compound C) respectively decreased and increased apoptosis. Finally, activation of AMPK by AICAR or adiponectin also decreased ceramide accumulation in the neutrophil cell membrane, a process involved in the early stages of spontaneous apoptosis, giving another possible mechanism downstream of AMPK activation for the inhibition of neutrophil apoptosis.
Adiponectin; Neutrophils; Apoptosis; Mcl-1; AMPK
Adiponectin plays a protective role in the development of obesity-linked disorders. We demonstrated that adiponectin exerts beneficial actions on acute ischemic injury in mice hearts. However, the effects of adiponectin treatment in large animals and its feasibility in clinical practice have not been investigated. This study investigated the effects of intracoronary administration of adiponectin on myocardial ischemia-reperfusion (I/R) injury in pigs.
Methods and Results
The left anterior descending coronary artery was occluded in pigs for 45 minutes and then reperfused for 24 hours. Recombinant adiponectin protein was given as a bolus intracoronary injection during ischemia. Cardiac functional parameters were measured by a manometer-tipped catheter. Apoptosis was evaluated by terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling staining. Tumor necrosis factor-α and interleukin-10 transcripts were analyzed by real-time polymerase chain reaction. Serum levels of derivatives of reactive oxygen metabolites and biological antioxidant potential were measured. Adiponectin protein was determined by immunohistochemical and Western blot analyses. Intracoronary administration of adiponectin protein led to a reduction in myocardial infarct size and improvement of left ventricular function in pigs after I/R. Injected adiponectin protein accumulated in the I/R-injured heart. Adiponectin treatment resulted in decreased tumor necrosis factor-α and increased interleukin-10 mRNA levels in the myocardium after I/R. Adiponectin-treated pigs had reduced apoptotic activity in the I/R-injured heart and showed increased biological antioxidant potential levels and decreased derivatives of reactive oxygen metabolite levels in the blood stream after I/R.
These data suggest that adiponectin protects against I/R injury in a preclinical pig model through its ability to suppress inflammation, apoptosis, and oxidative stress. Administration of intracoronary adiponectin could be a useful adjunctive therapy for acute myocardial infarction.
adiponectin; myocardial infarction; reperfusion
Adiponectin is an adipocyte-derived cytokine that has attracted much attention because of its insulin-sensitizing effects in liver and skeletal muscle. Two adiponectin receptors, AdipoR1 and AdipoR2, have been cloned, but relatively little is known about their intracellular signaling mechanisms. We found that full-length adiponectin rapidly and robustly activates the ERK1/2 mitogen-activated protein kinase pathway in primary vascular smooth muscle, vascular endothelial cells, and hepatocytes. In a HEK293 cell model, we found that downregulating AdipoR1 and AdipoR2 simultaneously, but not individually, by RNA interference attenuated adiponectin-induced ERK1/2 activation, suggesting that either receptor was sufficient to mediate the response. Downregulation of T-cadherin, another adiponectin binding protein, enhanced the response. Downregulation of APPL1, an adapter protein and putative mediator of AdipoR1/R2 signaling, impaired adiponectin-stimulated ERK1/2 activation. Inhibiting PKA modestly attenutated ERK1/2 activation, while inhibition of Src family tyrosine kinases with PP2 abolished the response. The small GTPase inhibitor Clostridium difficile toxin B also produced complete inhibition. Adiponectin caused rapid, PP2-sensitive activation of Ras, but not the cAMP-regulated small GTPase, Rap1, suggesting that Src-dependent Ras activation is the dominant mechanism of adiponectin-stimulated ERK1/2 activation. To test whether Ras-ERK1/2 signaling by adiponectin was physiologically-relevant, we determined the effects of overexpressing AdipoR1, adiponectin, or both, on the rate of HEK293 cell growth. Overexpression of adiponectin alone, but not AdipoR1 alone, supported growth under serum-free conditions, while simultaneous expression of both led to further enhancement. Additional results suggest that adiponectin can exert proliferative effects by activating Ras signaling pathways.
Adiponectin; Mitogen-Activated Protein Kinase; Mitogenesis; Ras; Tyrosine Kinase
Adiponectin, a fat tissue-derived adipokine, exhibits beneficial effects against insulin resistance, cardiovascular disease, inflammatory conditions, and cancer. Circulating adiponectin levels are decreased in obese individuals, and this feature correlates with increased risk of developing several metabolic, immunological and neoplastic diseases. Thus, pharmacological replacement of adiponectin might prove clinically beneficial, especially for the obese patient population. At present, adiponectin-based therapeutics are not available, partly due to yet unclear structure/function relationships of the cytokine and difficulties in converting the full size adiponectin protein into a viable drug.
We aimed to generate adiponectin-based short peptide that can mimic adiponectin action and be suitable for preclinical and clinical development as a cancer therapeutic. Using a panel of 66 overlapping 10 amino acid-long peptides covering the entire adiponectin globular domain (residues 105-254), we identified the 149-166 region as the adiponectin active site. Three-dimensional modeling of the active site and functional screening of additional 330 peptide analogs covering this region resulted in the development of a lead peptidomimetic, ADP 355 (H-DAsn-Ile-Pro-Nva-Leu-Tyr-DSer-Phe-Ala-DSer-NH2). In several adiponectin receptor-positive cancer cell lines, ADP 355 restricted proliferation in a dose-dependent manner at 100 nM-10 μM concentrations (exceeding the effects of 50 ng/mL globular adiponectin). Furthermore, ADP 355 modulated several key signaling pathways (AMPK, Akt, STAT3, ERK1/2) in an adiponectin-like manner. siRNA knockdown experiments suggested that ADP 355 effects can be transmitted through both adiponectin receptors, with a greater contribution of AdipoR1. In vivo, intraperitoneal administration of 1 mg/kg/day ADP 355 for 28 days suppressed the growth of orthotopic human breast cancer xenografts by ~31%. The peptide displayed excellent stability (at least 30 min) in mouse blood or serum and did not induce gross toxic effects at 5-50 mg/kg bolus doses in normal CBA/J mice.
ADP 355 is a first-in-class adiponectin receptor agonist. Its biological activity, superior stability in biological fluids as well as acceptable toxicity profile indicate that the peptidomimetic represents a true lead compound for pharmaceutical development to replace low adiponectin levels in cancer and other malignancies.
The glutamate-induced excitotoxicity pathway has been reported in several neurodegenerative diseases. Molecules that inhibit the release of glutamate or cause the overactivation of glutamate receptors can minimize neuronal cell death in these diseases. Osmotin, a homolog of mammalian adiponectin, is a plant protein from Nicotiana tabacum that was examined for the first time in the present study to determine its protective effects against glutamate-induced synaptic dysfunction and neurodegeneration in the rat brain at postnatal day 7. The results indicated that glutamate treatment induced excitotoxicity by overactivating glutamate receptors, causing synaptic dysfunction and neuronal apoptosis after 4 h in the cortex and hippocampus of the postnatal brain. In contrast, post-treatment with osmotin significantly reversed glutamate receptor activation, synaptic deficit and neuronal apoptosis by stimulating the JNK/PI3K/Akt intracellular signaling pathway. Moreover, osmotin treatment abrogated glutamate-induced DNA damage and apoptotic cell death and restored the localization and distribution of p53, p-Akt and caspase-3 in the hippocampus of the postnatal brain. Finally, osmotin inhibited glutamate-induced PI3K-dependent ROS production in vitro and reversed the cell viability decrease, cytotoxicity and caspase-3/7 activation induced by glutamate. Taken together, these results suggest that osmotin might be a novel neuroprotective agent in excitotoxic diseases.
glutamate; excitotoxicity; adiponectin; osmotin; neurodegeneration
Adiponectin, an abundant adipose tissue-derived protein, exerts protective effect against cardiovascular disease. Adiponectin receptors (AdipoR1 and AdipoR2) mediate the beneficial effects of adiponectin on the cardiovascular system. However, the alteration of AdipoRs in cardiac remodeling is not fully elucidated. Here, we investigated the effect of angiotensin II (AngII) on cardiac AdipoRs expression and explored the possible molecular mechanism. AngII infusion into rats induced cardiac hypertrophy, reduced AdipoR1 but not AdipoR2 expression, and attenuated the phosphorylations of adenosine monophosphate-activated protein kinase and acetyl coenzyme A carboxylase, and those effects were all reversed by losartan, an AngII type 1 (AT1) receptor blocker. AngII reduced expression of AdipoR1 mRNA and protein in cultured neonatal rat cardiomyocytes, which was abolished by losartan, but not by PD123319, an AT2 receptor antagonist. The antioxidants including reactive oxygen species (ROS) scavenger NAC, NADPH oxidase inhibitor apocynin, Nox2 inhibitor peptide gp91 ds-tat, and mitochondrial electron transport chain complex I inhibitor rotenone attenuated AngII-induced production of ROS and phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. AngII-reduced AdipoR1 expression was reversed by pretreatment with NAC, apocynin, gp91 ds-tat, rotenone, and an ERK1/2 inhibitor PD98059. Chromatin immunoprecipitation assay demonstrated that AngII provoked the recruitment of c-Myc onto the promoter region of AdipoR1, which was attenuated by PD98059. Moreover, AngII-induced DNA binding activity of c-Myc was inhibited by losartan, NAC, apocynin, gp91 ds-tat, rotenone, and PD98059. c-Myc small interfering RNA abolished the inhibitory effect of AngII on AdipoR1 expression. Our results suggest that AngII inhibits cardiac AdipoR1 expression in vivo and in vitro and AT1 receptor/ROS/ERK1/2/c-Myc pathway is required for the downregulation of AdipoR1 induced by AngII.
Contribution of individual adiponectin isoforms to lipolysis regulation remains unknown. We investigated the impact of full-length, trimeric and globular adiponectin isoforms on spontaneous lipolysis in subcutaneous abdominal (SCAAT) and visceral adipose tissues (VAT) of obese and non-obese subjects. Furthermore, we explored the role of AMPK (5'-AMP-activated protein kinase) in adiponectin-dependent lipolysis regulation and expression of adiponectin receptors type 1 and 2 (AdipoR1 and AdipoR2) in SCAAT and VAT. Primary adipocytes isolated from SCAAT and VAT of obese and non-obese women were incubated with 20 µg/ml of: A) full-length adiponectin (physiological mixture of all adiponectin isoforms), B) trimeric adiponectin isoform or C) globular adiponectin isoform. Glycerol released into media was used as a marker of lipolysis. While full-length adiponectin inhibited lipolysis by 22% in non-obese SCAAT, globular isoform inhibited lipolysis by 27% in obese SCAAT. No effect of either isoform was detected in non-obese VAT, however trimeric isoform inhibited lipolysis by 21% in obese VAT (all p<0.05). Trimeric isoform induced Thr172 p-AMPK in differentiated preadipocytes from a non-obese donor, while globular isoform induced Ser79 p-ACC by 32% (p<0.05) and Ser565 p-HSL by 52% (p = 0.08) in differentiated preadipocytes from an obese donor. AdipoR2 expression was 17% and 37% higher than AdipoR1 in SCAAT of obese and non-obese groups and by 23% higher in VAT of obese subjects (all p<0.05). In conclusion, the anti-lipolytic effect of adiponectin isoforms is modified with obesity: while full-length adiponectin exerts anti-lipolytic action in non-obese SCAAT, globular and trimeric isoforms show anti-lipolytic activity in obese SCAAT and VAT, respectively.
Adiponectin is a protein hormone secreted predominantly by differentiated adipocytes and is involved in energy homeostasis. Adiponectin expression is significantly high in the synovial fluid of patients with osteoarthritis (OA). Intercellular adhesion molecule-1 (ICAM-1) is an important adhesion molecule that mediates monocyte adhesion and infiltration during OA pathogenesis. Adiponectin-induced expression of ICAM-1 in human OA synovial fibroblasts (OASFs) was examined by using qPCR, flow cytometry and western blotting. The intracellular signaling pathways were investigated by pretreated with inhibitors or transfection with siRNA. The monocyte THP-1 cell line was used for an adhesion assay with OASFs. Stimulation of OASFs with adiponectin induced ICAM-1 expression. Pretreatment with AMP-activated protein kinase (AMPK) inhibitors (AraA and compound C) or transfection with siRNA against AMPKα1 and two AMPK upstream activator- liver kinase B1 (LKB1) and calmodulin-dependent protein kinase II (CaMKII) diminished the adiponectin-induced ICAM-1 expression. Stimulation of OASFs with adiponectin increased phosphorylation of LKB1, CaMKII, AMPK, and c-Jun, resulting in c-Jun binding to AP-1 element of ICAM-1 promoter. In addition, adiponectin-induced activation of the LKB1/CaMKII, AMPK, and AP-1 pathway increased the adhesion of monocytes to the OASF monolayer. Our results suggest that adiponectin increases ICAM-1 expression in human OASFs via the LKB1/CaMKII, AMPK, c-Jun, and AP-1 signaling pathway. Adiponectin-induced ICAM-1 expression promoted the adhesion of monocytes to human OASFs. These findings may provide a better understanding of the pathogenesis of OA and can utilize this knowledge to design a new therapeutic strategy.
The molecular effects of obesity are mediated by alterations in the levels of adipocytokines. High leptin level associated with obese state is a major cause of breast cancer progression and metastasis, whereas adiponectin is considered a “guardian angel adipocytokine” for its protective role against various obesity-related pathogenesis including breast cancer. In the present study, investigating the role of adiponectin as a potential inhibitor of leptin, we show that adiponectin treatment inhibits leptin-induced clonogenicity and anchorage-independent growth. Leptin-stimulated migration and invasion of breast cancer cells is also effectively inhibited by adiponectin. Analyses of the underlying molecular mechanisms reveal that adiponectin suppresses activation of two canonical signaling molecules of leptin signaling axis: extracellular signal-regulated kinase (ERK) and Akt. Pretreatment of breast cancer cells with adiponectin protects against leptin-induced activation of ERK and Akt. Adiponectin increases expression and activity of the physiological inhibitor of leptin signaling, protein tyrosine phosphatase 1B (PTP1B), which is found to be integral to leptin-antagonist function of adiponectin. Inhibition of PTP1B blocks adiponectin-mediated inhibition of leptin-induced breast cancer growth. Our in vivo studies show that adenovirus-mediated adiponectin treatment substantially reduces leptin-induced mammary tumorigenesis in nude mice. Exploring therapeutic strategies, we demonstrate that treatment of breast cancer cells with rosiglitazone results in increased adiponectin expression and inhibition of migration and invasion. Rosiglitazone treatment also inhibits leptin-induced growth of breast cancer cells. Taken together, these data show that adiponectin treatment can inhibit the oncogenic actions of leptin through blocking its downstream signaling molecules and raising adiponectin levels could be a rational therapeutic strategy for breast carcinoma in obese patients with high leptin levels.
Adiponectin is the most abundant peptide secreted by adipocytes, being a key component in the interrelationship between adiposity, insulin resistance and inflammation. Central obesity accompanied by insulin resistance is a key factor in the development of metabolic syndrome (MS) and future macrovascular complications. Moreover, the remarkable correlation between coronary artery disease (CAD) and alterations in glucose metabolism has raised the likelihood that atherosclerosis and type 2 diabetes mellitus (T2DM) may share a common biological background. We summarize here the current knowledge about the influence of adiponectin on insulin sensitivity and endothelial function, discussing its forthcoming prospects and potential role as a therapeutic target for MS, T2DM, and cardiovascular disease. Adiponectin is present in the circulation as a dimer, trimer or protein complex of high molecular weight hexamers, >400 kDa. AdipoR1 and AdipoR2 are its major receptors in vivo mediating the metabolic actions. Adiponectin stimulates phosphorylation and AMP (adenosin mono phosphate) kinase activation, exerting direct effects on vascular endothelium, diminishing the inflammatory response to mechanical injury and enhancing endothelium protection in cases of apolipoprotein E deficiency. Hypoadiponectinemia is consistently associated with obesity, MS, atherosclerosis, CAD, T2DM. Lifestyle correction helps to favorably modify plasma adiponectin levels. Low adiponectinemia in obese patients is raised via continued weight loss programs in both diabetic and nondiabetic individuals and is also accompanied by reductions in pro-inflammatory factors. Diet modifications, like intake of fish, omega-3 supplementation, adherence to a Mediterranean dietary pattern and coffee consumption also increase adiponectin levels. Antidiabetic and cardiovascular pharmacological agents, like glitazones, glimepiride, angiotensin converting enzyme inhibitors and angiotensin receptor blockers are also able to improve adiponectin concentration. Fibric acid derivatives, like bezafibrate and fenofibrate, have been reported to enhance adiponectin levels as well. T-cadherin, a membrane-associated adiponectin-binding protein lacking intracellular domain seems to be a main mediator of the antiatherogenic adiponectin actions. The finding of novel pharmacologic agents proficient to improve adiponectin plasma levels should be target of exhaustive research. Interesting future approaches could be the development of adiponectin-targeted drugs chemically designed to induce the activaton of its receptors and/or postreceptor signaling pathways, or the development of specific adiponectin agonists.
Adipokines; Adiponectin; Atherosclerosis; Coronary artery disease; Diabetes mellitus; Metabolic syndrome; Obesity; T-cadherin
Liver X receptors (LXRs) have been recognized as a promising therapeutic target for atherosclerosis; however, their role in insulin sensitivity is controversial. Adiponectin plays a unique role in maintaining insulin sensitivity. Currently, no systematic experiments elucidating the role of LXR activation in insulin function based on adiponectin signaling have been reported. Here, we investigated the role of LXR activation in insulin resistance based on adiponectin signaling, and possible mechanisms. C57BL/6 mice maintained on a regular chow received the LXR agonist, T0901317 (30 mg/kg.d) for 3 weeks by intraperitoneal injection, and differentiated 3T3-L1 adipocytes were treated with T0901317 or GW3965. T0901317 treatment induced significant insulin resistance in C57BL/6 mice. It decreased adiponectin gene transcription in epididymal fat, as well as serum adiponectin levels. Activity of AMPK, a key mediator of adiponectin signaling, was also decreased, resulting in decreased Glut-4 membrane translocation in epididymal fat. In contrast, adiponectin activity was not changed in the liver of T0901317 treated mice. In vitro, both T0901317 and GW3965 decreased adiponectin expression in adipocytes in a dose-dependent manner, an effect which was diminished by LXRα silencing. ChIP-qPCR studies demonstrated that T0901317 decreased the binding of PPARγ to the PPAR-responsive element (PPRE) of the adiponectin promoter in a dose-dependent manner. Furthermore, T0901317 exerted an antagonistic effect on the expression of adiponectin in adipocytes co-treated with 3 µM Pioglitazone. In luciferase reporter gene assays, T0901317 dose-dependently inhibited PPRE-Luc activity in HEK293 cells co-transfected with LXRα and PPARγ. These results suggest that LXR activation induces insulin resistance with decreased adiponectin signaling in epididymal fat, probably due to negative regulation of PPARγ signaling. These findings indicate that the potential of LXR activation as a therapeutic target for atherosclerosis may be limited by the possibility of exacerbating insulin resistance-related disease.
Obesity is linked with an increased risk of lymphedema, which is a serious clinical problem. Adiponectin is a circulating adipokine that is down‐regulated in obese states. We investigated the effects of adiponectin on lymphatic vessel formation in a model of lymphedema and dissected its mechanisms.
Methods and Results
A mouse model of lymphedema was created via ablation of tail surface lymphatic network. Adiponectin‐knockout mice showed the greater diameter of the injured tail compared with wild‐type mice, which was associated with lower numbers of lymphatic endothelial cells (LECs). Systemic delivery of adiponectin reduced the thickness of the injured tail and enhanced LEC formation in wild‐type and adiponectin‐knockout mice. Adiponectin administration also improved the edema of injured tails in obese KKAy mice. Treatment with adiponectin protein stimulated the differentiation of human LECs into tubelike structures and increased LEC viability. Adiponectin treatment promoted the phosphorylation of AMP‐activated protein kinase (AMPK), Akt, and endothelial nitric oxide synthase n LECs. Blockade of AMPK or Akt activity abolished adiponectin‐stimulated increase in LEC differentiation and viability and endothelial nitric oxide synthase phosphorylation. Inhibition of AMPK activation also suppressed adiponectin‐induced Akt phosphorylation in LECs. In contrast, inactivation of Akt signaling had no effects on adiponectin‐mediated AMPK phosphorylation in LECs. Furthermore, adiponectin administration did not affect the thickening of the damaged tail in endothelial nitric oxide synthase–knockout mice.
Adiponectin can promote lymphatic vessel formation via activation of AMPK/Akt/endothelial nitric oxide synthase signaling within LECs, thereby leading to amelioration of lymphedema.
adiponectin; Akt; AMPK; eNOS; lymphangiogenesis
Adiponectin and intracellular 5′adenosine monophosphate-activated protein kinase (AMPK) are important modulators of glucose and fat metabolism. Cinnamon exerts beneficial effects by improving insulin sensitivity and blood lipids, e.g., through increasing adiponectin concentrations and AMPK activation. The underlying mechanism is unknown. The Gi/Go-protein-coupled receptor (GPR) 109A stimulates adiponectin secretion after binding its ligand niacin. Trans-cinnamic acid (tCA), a compound of cinnamon is another ligand. We hypothesize whether AMPK activation and adiponectin secretion by tCA is transmitted by GPR signaling. Differentiated 3T3-L1 cells were incubated with pertussis toxin (PTX), an inhibitor of Gi/Go-protein-coupling, and treated with different tCA concentrations. Treatment with tCA increased adiponectin and the pAMPK/AMPK ratio (p ≤ 0.001). PTX incubation abolished the increased pAMPK/AMPK ratio and adiponectin secretion. The latter remained increased compared to controls (p ≤ 0.002). tCA treatment stimulated adiponectin secretion and AMPK activation; the inhibitory effect of PTX suggests GPR is involved in tCA stimulated signaling.
trans-cinnamic acid; Adiponectin; 5′adenosine monophosphate-activated protein kinase; G-protein-coupled receptor 109A
Although increasing evidence indicates that an adipokine adiponectin exerts protective actions on heart, its effects on coronary angiogenesis following pressure overload have not been examined previously. Because disruption of angiogenesis during heart growth leads to contractile dysfunction and heart failure, we hypothesized that adiponectin modulates cardiac remodeling in response to pressure overload through its ability to regulate adaptive angiogenesis.
Methods and Results
Adiponectin-knockout (APN-KO) and wild-type (WT) mice were subjected to pressure overload caused by transverse aortic constriction (TAC). APN-KO mice exhibited greater cardiac hypertrophy, pulmonary congestion, left ventricular (LV) interstitial fibrosis and LV systolic dysfunction after TAC surgery compared with WT mice. APN-KO mice also displayed reduced capillary density in the myocardium after TAC, which was accompanied by a significant decrease in expression of vascular endothelial growth factor (VEGF) and phosphorylation of AMP-activated protein kinase (AMPK). Inhibition of AMPK in WT mice resulted in aggravated LV systolic function, attenuated myocardial capillary density and decreased VEGF expression in response to TAC. The adverse effects of AMPK inhibition on cardiac function and angiogenic response following TAC were diminished in APN-KO mice relative to WT mice. Moreover, adenovirus-mediated VEGF delivery reversed the TAC-induced deficiencies in cardiac microvessel formation and ventricular function observed in the APN-KO mice. In cultured cardiac myocytes, adiponectin treatment stimulated VEGF production, which was inhibited by inactivation of AMPK signaling pathway.
Adiponectin deficiency can accelerate the transition from cardiac hypertrophy to heart failure during pressure overload through disruption of AMPK-dependent angiogenic regulatory axis.
adiponectin; AMPK; cardiac angiogenesis; pressure overload; heart failure
Chronic ethanol feeding decreases expression of adiponectin by adipocytes and circulating adiponectin. Adiponectin treatment during chronic ethanol feeding prevents liver injury in mice. Chronic ethanol feeding also increases oxidative and endoplasmic reticulum (ER) stress in adipose tissue. Here we tested the hypothesis that supplemental taurine, an amino acid that functions as a chemical chaperone/osmolyte and enhances cellular anti-oxidant activity, would prevent ethanol-induced decreases in adiponectin expression and attenuate liver injury. Serum adiponectin concentrations decreased as early as 4–7 days after feeding rats a 36% ethanol diet. This rapid decrease was associated with increased oxidative, but not ER, stress in subcutaneous adipose tissue. Taurine prevented ethanol-induced oxidative stress and increased inflammatory cytokine expression in adipose tissue. Ethanol feeding also rapidly decreased expression of transcription factors regulating adiponectin expression (C/EBPα, PPARγ and PPARα) in subcutaneous adipose tissue. Taurine prevented the ethanol-induced decrease in C/EBPα and PPARα normalizing adiponectin mRNA and serum adiponectin concentrations. In the liver, taurine prevented ethanol-induced oxidative stress and attenuated TNF-α expression and steatosis, at least in part, by increasing expression of genes involved in fatty acid oxidation.
In subcutaneous adipose tissue, taurine decreased ethanol-induced oxidative stress and cytokine expression, as well as normalized expression of adiponectin mRNA. Taurine prevented ethanol-induced decreases in serum adiponectin; normalized adiponectin was associated with a reduction in hepatic oxidative stress, TNF-α expression and steatosis. Taken together, these data demonstrate that taurine has important protective effects against ethanol-induced tissue injury in both adipose and liver.
Adiponectin; Ethanol feeding; Taurine