IGFBP-3, hypoxia and TNF-alpha inhibit adiponectin transcription

Obesity contributes to hepatocellular carcinoma development via immunosuppressive microenvironment remodeling

It is generally recognized that the initiation of obesity-related hepatocellular carcinoma (HCC) is closely associated with hepatic inflammation. However, the paradoxical role of inflammation in the initiation and progression of HCC is highlighted by the fact that the inflammatory HCC is accompanied by significant immune effector cells infiltration compared to non-inflammatory HCC and HCC with enhanced immune response exhibits better survival. Importantly, the cancer progression has been primarily attributed to the immunosuppression, which can also be induced by obesity. Furthermore, the increased risk of viral infection and thus viral-HCC in obese individuals supports the view that obesity contributes to HCC via immunosuppression. Here, we have reviewed the various mechanisms responsible for obesity-induced tumor immune microenvironment and immunosuppression in obesity-related HCC. We highlight that the obesity-induced immunosuppression originates from lipid disorder as well as metabolic reprogramming and propose potential therapeutic strategy for HCC based on the current success of immunotherapy.

Translational control of murine adiponectin expression by an upstream open reading frame element

Adiponectin, an adipocyte-specific secretory protein encoded by the ADIPOQ gene has a causal role in insulin resistance. Anti-diabetic drugs increase plasma adiponectin by a poorly understood, post-transcriptional mechanism enhancing insulin sensitivity. Deletion analysis of a reporter bearing the mouse Adipoq mRNA 5'-leader identified an inhibitory cis-regulatory sequence. The 5'-leader harbours two potential upstream open reading frames (uORFs) overlapping the principal downstream ORF. Mutation of the uORF ATGs increased reporter translation ~3-fold, indicative of a functional uORF. uORFs are common in mammalian mRNAs; however, only a select group resist translational repression by the integrated stress response (ISR). Thapsigargin (TG), which induces endoplasmic reticulum (ER) stress and the ISR, enhanced expression of a reporter bearing the Adipoq 5'-leader; polysome profiling verified translation-stimulation. TG-stimulated translation was absent in cells defective in Ser51 phosphorylation of eukaryotic initiation factor 2α (eIF2α), required for the ISR. To determine its role in expression and function of endogenous adiponectin, the upstream uORF was disrupted by CRISPR-Cas9-mediated mutagenesis of differentiated mouse 3T3-L1 adipocytes. uORF disruption in adipocytes increased adiponectin expression, triacylglycerol accumulation, and glucose uptake, and inhibited paracrine muscle and liver cell expression of gluconeogenic enzymes, establishing an important role of the uORF in adiponectin-mediated responses to stress.

Extrahepatic factors in hepatic immune regulation

The liver is a site of complex immune activity. The hepatic immune system tolerates harmless immunogenic loads in homeostasis status, shelters liver function, while maintaining vigilance against possible infectious agents or tissue damage and providing immune surveillance at the same time. Activation of the hepatic immunity is initiated by a diverse repertoire of hepatic resident immune cells as well as non-hematopoietic cells, which can sense “danger signals” and trigger robust immune response. Factors that mediate the regulation of hepatic immunity are elicited not only in liver, but also in other organs, given the dual blood supply of the liver via both portal vein blood and arterial blood. Emerging evidence indicates that inter-organ crosstalk between the liver and other organs such as spleen, gut, lung, adipose tissue, and brain is involved in the pathogenesis of liver diseases. In this review, we present the features of hepatic immune regulation, with particular attention to the correlation with factors from extrahepatic organ. We describe the mechanisms by which other organs establish an immune association with the liver and then modulate the hepatic immune response. We discuss their roles and distinct mechanisms in liver homeostasis and pathological conditions from the cellular and molecular perspective, highlighting their potential for liver disease intervention. Moreover, we review the available animal models and methods for revealing the regulatory mechanisms of these extrahepatic factors. With the increasing understanding of the mechanisms by which extrahepatic factors regulate liver immunity, we believe that this will provide promising targets for liver disease therapy.

Adiponectin and Asthma: Knowns, Unknowns and Controversies

Adiponectin is an adipokine associated with the healthy obese phenotype. Adiponectin increases insulin sensitivity and has cardio and vascular protection actions. Studies related to adiponectin, a modulator of the innate and acquired immunity response, have suggested a role of this molecule in asthma. Studies based on various asthma animal models and on the key cells involved in the allergic response have provided important insights about this relation. Some of them indicated protection and others reversed the balance towards negative effects. Many of them described the cellular pathways activated by adiponectin, which are potentially beneficial for asthma prevention or for reduction in the risk of exacerbations. However, conclusive proofs about their efficiency still need to be provided. In this article, we will, briefly, present the general actions of adiponectin and the epidemiological studies supporting the relation with asthma. The main focus of the current review is on the mechanisms of adiponectin and the impact on the pathobiology of asthma. From this perspective, we will provide arguments for and against the positive influence of this molecule in asthma, also indicating the controversies and sketching out the potential directions of research to complete the picture.

Sex differences in the link between blood cobalt concentrations and insulin resistance in adults without diabetes

Background

Little is known about the effects of environmental cobalt exposure on insulin resistance (IR) in the general adult population. We investigated the association between cobalt concentration and IR.

Methods

A total of 1281 subjects aged more than 20 years with complete blood cobalt data were identified from the National Health and Nutrition Examination Survey (NHANES) 2015–2016 cycle. Blood cobalt levels were analyzed for their association with IR among all populations and subgroups by sex. Regression coefficients and 95% confidence intervals (CIs) of blood cobalt concentrations in association with fasting glucose, insulin and homeostatic model assessment of insulin resistance (HOMA-IR) were estimated using multivariate linear regression after adjusting for age, sex, ethnicity, alcohol consumption, body mass index, education level, and household income. A multivariate generalized linear regression analysis was further carried out to explore the association between cobalt exposure and IR.

Results

A negative association between blood cobalt concentration (coefficient = − 0.125, 95% CI − 0.234, − 0.015; P = 0.026) and HOMA-IR in female adults in the age- and sex-adjusted model was observed. However, no associations with HOMA-IR, fasting glucose, or insulin were found in the overall population. In the generalized linear models, participants with the lowest cobalt levels had a 2.74% (95% CI 0.04%, 5.50%) increase in HOMA-IR (P for trend = 0.031) compared with subjects with the highest cobalt levels. Restricted cubic spline regression suggested that a non-linear relationship may exist between blood cobalt and HOMA-IR.

Conclusions

These results provide epidemiological evidence that low levels of blood cobalt are negatively associated with HOMA-IR in female adults.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12199-021-00966-w.

The Adiponectin Paradox in the Elderly: Associations With Body Composition, Physical Functioning, and Mortality

Background

To determine if adiponectin levels are associated with weight loss, low muscle mass, and physical functioning among the elderly and to determine independent associations with incident disability and death.

Methods

Included were 3,044 participants from the Health, Aging and Body Composition Study, who had whole-body dual energy absorptiometry performed to evaluate appendicular lean mass index (ALMI, kg/m2) and fat mass index (FMI, kg/m2), computed tomography measures of thigh muscle density, weight histories, estimates of physical functioning, and adiponectin levels at enrollment. Associations between adiponectin levels and body composition, weight loss, and physical functioning were assessed in multivariable linear regression models. Associations between adiponectin and incident disability and mortality were assessed in mediation analyses, adjusting for other factors.

Results

Greater adiponectin at baseline was independently associated with low FMI Z-score, lower waist circumference, low ALMI Z-score, low muscle density, a history of weight loss, and poor physical functioning (all p < .05). Greater adiponectin levels (per SD) were associated with incident disability [HR: 1.14 (1.08, 1.20), p < .001] and greater mortality [HR: 1.17 (1.10, 1.25), p < .001] in models adjusting for demographic factors, adiposity, and comorbid conditions. The association was completely attenuated and no longer significant (all p > 0.05) when adjusting for body composition, muscle density, weight loss, and physical functioning at baseline.

Conclusions

Greater serum adiponectin levels are associated with historical weight loss, low skeletal muscle mass, low muscle density, and poor physical functioning. High adiponectin is associated with a greater risk of incident disability and death, but not independently of these factors.

Adiponectin, Obesity, and Cancer: Clash of the Bigwigs in Health and Disease

Adiponectin is one of the most important adipocytokines secreted by adipocytes and is called a “guardian angel adipocytokine” owing to its unique biological functions. Adiponectin inversely correlates with body fat mass and visceral adiposity. Identified independently by four different research groups, adiponectin has multiple names; Acrp30, apM1, GBP28, and AdipoQ. Adiponectin mediates its biological functions via three known receptors, AdipoR1, AdipoR2, and T-cadherin, which are distributed throughout the body. Biological functions of adiponectin are multifold ranging from anti-diabetic, anti-atherogenic, anti-inflammatory to anti-cancer. Lower adiponectin levels have been associated with metabolic syndrome, type 2 diabetes, insulin resistance, cardiovascular diseases, and hypertension. A plethora of experimental evidence supports the role of obesity and increased adiposity in multiple cancers including breast, liver, pancreatic, prostrate, ovarian, and colorectal cancers. Obesity mediates its effect on cancer progression via dysregulation of adipocytokines including increased production of oncogenic adipokine leptin along with decreased production of adiponectin. Multiple studies have shown the protective role of adiponectin in obesity-associated diseases and cancer. Adiponectin modulates multiple signaling pathways to exert its physiological and protective functions. Many studies over the years have shown the beneficial effect of adiponectin in cancer regression and put forth various innovative ways to increase adiponectin levels.

Knockdown of a disintegrin A metalloprotease 12 (ADAM12) during adipogenesis reduces cell numbers, delays differentiation, and increases lipid accumulation in 3T3-L1 cells

Mouse models have shown that a disintegrin A metalloprotease 12 (ADAM12) is implicated during adipogenesis; the molecular pathways are not well understood. Stealth RNA interference was used to knock down ADAM12 in 3T3-L1 cells. Using gene profiling and metabolic enzymatic markers, we have identified signaling pathways ADAM12 impacts upon during proliferation, differentiation, and maturation of adipocytes. ADAM12 reduced cell numbers in proliferating preadipocytes, delayed differentiation of preadipocytes to adipocytes, and increased lipid accumulation in mature adipocytes. The pathway most affected by ADAM12 knockdown was regulation of insulin-like growth factor (IGF) activity by insulin-like growth factor binding proteins (IGFBPs); ADAM12 is known to cleave IGFBP3 and IGFBP5. The IGF/mTOR signaling pathway was down-regulated, supporting a role for ADAM12 in the IGFBP/IGF/mTOR-growth pathway. PPARγ signaling was also down-regulated by ADAM12 knockdown. Gene ontology (GO) analysis revealed that the extracellular matrix was the cellular compartment most impacted. Filtering for matrisome genes, connective tissue growth factor (Ctgf) was up-regulated. CTGF and IGBP3 can interact with PPARγ to hinder its regulation. Increased expression of these molecules could have influenced PPARγ signaling reducing differentiation and an imbalance of lipids. We believe ADAM12 regulates cell proliferation of preadipocytes through IGFBP/IGF/mTOR signaling and delays differentiation through altered PPAR signaling to cause an imbalance of lipids within mature adipocytes.

Organ-Organ Crosstalk and Alcoholic Liver Disease

Alcohol consumption is a common custom worldwide, and the toxic effects of alcohol on several target organs are well-understood. Given the poor prognosis of treating clinically-relevant alcoholic liver disease (ALD) (i.e., alcoholic hepatitis (AH) and cirrhosis), additional research is required to develop more effective therapies. While the stages of ALD have been well-characterized, targeted therapies to prevent or reverse this process in humans are still needed. Better understanding of risk factors and mechanisms underlying disease progression can lead to the development of rational therapies to prevent or reverse ALD in the clinic. A potential area of targeted therapy for ALD may be organ–organ communication in the early stages of the disease. In contrast to AH and end-stage liver diseases, the involvement of multiple organs in the development of ALD is less understood. The impact of these changes on pathology to the liver and other organs may not only influence disease progression during the development of the disease, but also outcomes of end stages diseases. The purpose of this review is to summarize the established and proposed communication between the liver and other organ systems that may contribute to the development and progression of liver disease, as well as to other organs. Potential mechanisms of this organ–organ communication are also discussed.

Role of Mitochondria-Associated Endoplasmic Reticulum Membrane in Inflammation-Mediated Metabolic Diseases

Inflammation is considered to be one of the most critical factors involved in the development of complex metabolic diseases such as type 2 diabetes, cancer, and cardiovascular disease. A few decades ago, the discovery of mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) was followed by the identification of its roles in regulating cellular homeostatic processes, ranging from cellular bioenergetics to apoptosis. MAM provides an excellent platform for numerous signaling pathways; among them, inflammatory signaling pathways associated with MAM play a critical role in cellular defense during pathogenic infections and metabolic disorders. However, induction of MAM causes deleterious effects by amplifying mitochondrial reactive oxygen species generation through increased calcium transfer from the ER to mitochondria, thereby causing mitochondrial damage and release of mitochondrial components into the cytosol as damage-associated molecular patterns (DAMPs). These mitochondrial DAMPs rapidly activate MAM-resident inflammasome components and other inflammatory factors, which promote inflammasome complex formation and release of proinflammatory cytokines in pathological conditions. Long-term stimulation of the inflammasome instigates chronic inflammation, leading to the pathogenesis of metabolic diseases. In this review, we summarize the current understanding of MAM and its association with inflammation-mediated metabolic diseases.

Peripheral blood leptin and resistin levels as clinical activity biomarkers in Mexican Rheumatoid Arthritis patients

OBJECTIVE

To evaluate the association between the clinical activity of RA patients and serum adipocytokines (Leptin, Adiponectin and Resistin) and inflammatory cytokines.

METHODS

All RA patients fulfilled ACR 1987 criteria and were treated with DMARDs. Adipocytokine and inflammatory cytokine levels were evaluated using ELISA.

RESULTS

121 patients were included in the study. Stratifying according to DAS28 (low, moderate and high activity), there were significant differences for Leptin, Resistin, IL-6 and IL-17, however, no differences were seen for Adiponectin, TNFα or IL-1β. Clinical activity positively correlated with Leptin, Resistin, IL-17 and IL-6 levels, but not with Adiponectin, TNFα or IL-1β. Adiponectin levels negatively correlated with TNFα and positively correlated with IL-1β. IL-1β positively correlated with IL-6 and negatively correlated with TNFα and IL-17.

CONCLUSION

Circulating Leptin, Resistin, IL-6 and IL-17 levels positively correlate with RA clinical activity in a manner independent of the subject's BMI. Complex relationships between inflammatory cytokines were observed in RA patients suggesting that other metabolic or inflammatory factors could be involved.

Molecular cloning, expression profiles and promoter analysis of insulin-like growth factor binding protein-4 (IGFBP-4) in Japanese flounder (Paralichthys olivaceus)

We cloned and characterized cDNA sequence of insulin-like growth factor binding protein-4 (IGFBP-4) from Japanese flounder (Paralichthys olivaceus). The 1493 bp full-length cDNA sequence contained an open reading frame (ORF) of 780 bp, which encoded a protein of 259 amino acids. The deduced amino acid sequences included a putative signal peptide of 28 amino acid residues resulting in a mature protein of 231 amino acids. Twenty cysteine residues and two conserved IGFBPs motif (GCGCCXXC and CWCV) were found in the N- and C-terminal domain. In the over 13 kbp genomic sequence, four exons, three introns, and 5'-/3'-flanking sequences were identified. Sequence alignment and phylogenetic analysis showed that Japanese flounder IGFBP-4 was indeed the ortholog of the human IGFBP-4 gene and shared high identities with other teleost IGFBP-4 genes. The promoter region was also analyzed and several potential transcription factor (TF) binding sites were determined which may modulate the IGFBP-4 expression. Quantitative real-time PCR analysis revealed that IGFBP-4 mRNA was observed in various tissues, with intestine showing the highest expression. The maternal transcripts of IGFBP-4 gene existed in the early embryonic stages and then increased in the following stages until hatching, suggesting that IGFBP-4 may be involved in the fish early development. The expression level of IGFBP-4 mRNA was relatively higher at 3 days post hatching (dph) and 15 dph, and gradually decreased during the metamorphosis period. All these results indicated that IGFBP-4 plays a significant role in IGF regulating vertebrate growth and development.

Linking pre-diabetes with benign prostate hyperplasia. IGFBP-3: a conductor of benign prostate hyperplasia development orchestra?

Benign prostatic hyperplasia (BPH) represents a pattern of non-malignant growth of prostatic fibromuscular stroma. Metabolic disturbances such us pre-diabetes and metabolic syndrome may have a role in BPH pathophysiology. A potential explanation for the above relationship involves the insulin-like growth factor (IGF) axis as well as IGF binding proteins, (IGFBPs) of which the most abundant form is IGFBP-3. Therefore, the aim of the present study was to investigate the association between intra-prostatic levels of IGF-1, IGF-2 as well as to evaluate the role of locally expressed IGFBP-3 in BPH development in pre-diabetes. A total of 49 patients admitted to the Urology department of a tertiary urban Greek hospital, for transurethral prostate resection, or prostatectomy and with pre-diabetes [impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) or both] were finally included. The majority of the sample consisted of subjects with IGT (51.0%), followed by IFG and IGT (32.7%) and isolated IFG (16.3%). For all participants a clinical examination was performed and blood samples were collected. In addition, total prostate (TP) volume or transitional zone (TZ) volume were estimated by transrectal ultrasonography. The results of the multivariate analysis regarding TP volume showed that higher PSA (p<0.001), larger waist circumference (p=0.007) and higher IGFBP-3 expression levels (p<0.001) independently predicted higher TP volume. The results regarding the volume of the TZ showed that higher PSA (p<0.001), larger waist circumference (p<0.001) and higher IGFBP-3 expression levels (p=0.024) were independently associated with higher TZ volume. Our findings show that intra-prostatic levels of IGFBP-3, PSA and waist circumference, but not overall obesity, are positively associated with prostate volume. IGFBP-3 seems to be a multifunctional protein, which can potentiate or inhibit IGF activity.

Enzamin ameliorates adipose tissue inflammation with impaired adipocytokine expression and insulin resistance in db/db mice

The effects of Enzamin on obesity-related metabolic disorders in obese db/db mice were examined to explore a novel agent for the prevention of insulin resistance. Db/db mice were treated with water containing Enzamin (0·1 and 1·0 %) for 8 weeks from 6 weeks of age. Enzamin treatment at 1·0 %, but not at 0·1 %, significantly decreased the fasting plasma glucose, serum total cholesterol and TAG levels in db/db mice, without affecting body weight gain and body fat composition. Furthermore, insulin sensitivity and glucose tolerance were improved by the treatment of db/db mice with 1·0 % Enzamin. Immunohistochemical studies and gene expression analysis showed that 1·0 % Enzamin treatment suppressed macrophage accumulation and inflammation in the adipose tissue. In addition, 1·0 % Enzamin treatment increased serum adiponectin in db/db mice. Treatment with 1·0 % Enzamin also significantly suppressed the expression of NADPH oxidase subunits, suggesting an antioxidative effect for Enzamin in the adipose tissue. Furthermore, in vitro experiments demonstrated that the lipopolysaccharide-induced inflammatory reaction was significantly suppressed by Enzamin treatment in macrophages. Enzamin treatment increased the expression of GLUT4 mRNA in muscle, but not GLUT2 mRNA in the liver of db/db mice. Enzamin also increased the mRNA expression of carnitine palmitoyltransferase 1a (CPT1a, muscle isoform) in db/db mice, whereas Enzamin treatment did not affect the mRNA expression of CPT1b (liver isoform) in db/db mice. In conclusion, our data indicate that Enzamin can improve insulin resistance by ameliorating impaired adipocytokine expression, presumably through its anti-inflammatory action, and that Enzamin possesses a potential for preventing the metabolic syndrome.

Interplay of pro- and anti-inflammatory cytokines to determine lipid accretion in adipocytes

OBJECTIVE

Obesity is associated with an increase in various pro-inflammatory and anti-inflammatory cytokines, but the interplay of these cytokines is incompletely understood. We conducted experiments to test a broader hypothesis that a dynamic interplay of pro-inflammatory and anti-inflammatory cytokines controls lipid storage in adipocytes.

DESIGN

Three experiments were designed to test the overall hypothesis that proinflammatory cytokine (for example, tumor necrosis factor-α (TNF-α) inhibits anti-inflammatory cytokine (for example, adiponectin) activity in an attempt to limit excess lipid accumulation in adipocytes.

RESULTS

Experiment one showed that in pro-inflammatory animal models (ap2-P65, ob/ob and high-fat diet-induced obese mice), the increase in TNF-α expression was associated with a decrease in adiponectin expression. Experiment two showed that in 3T3-L1 adipocytes, TNF-α significantly reduced lipid accumulation and glucose uptake induced by adiponectin, and increased lipolysis. Experiment three showed that in 3T3-L1 adipocytes, TNF-α reduced mRNA and protein expression of adiponectin. Adiponectin gene transcription and mRNA stability were both reduced by TNF-α. The expression of peroxisome proliferator-activated receptor gamma, an activator of adiponectin gene promoter, was reduced by TNF-α. The inhibitory activity of TNF-α was blocked by the chemical inhibitors of NF-κB and super suppressor IκBα.

CONCLUSIONS

TNF-α opposes the action of adiponectin in the regulation of lipid metabolism, and inhibits adiponectin expression at transcriptional and post-transcriptional levels. The results suggest that pro-inflammatory cytokine inhibit anti-inflammatory cytokine in adipocytes to reduce lipid storage. This suggests a potential role of anti-inflammatory cytokines in the control of adipose tissue expansion.

Role of adipokines and cytokines in obesity-associated breast cancer: therapeutic targets

Obesity is the cause of a large proportion of breast cancer incidences and mortality in post-menopausal women. In obese people, elevated levels of various growth factors such as insulin and insulin-like growth factors (IGFs) are found. Elevated insulin level leads to increased secretion of estrogen by binding to the circulating sex hormone binding globulin (SHBG). The increased estrogen-mediated downstream signaling favors breast carcinogenesis. Obesity leads to altered expression profiles of various adipokines and cytokines including leptin, adiponectin, IL-6, TNF-α and IL-1β. The increased levels of leptin and decreased adiponectin secretion are directly associated with breast cancer development. Increased levels of pro-inflammatory cytokines within the tumor microenvironment promote tumor development. Efficacy of available breast cancer drugs against obesity-associated breast cancer is yet to be confirmed. In this review, we will discuss different adipokine- and cytokine-mediated molecular signaling pathways involved in obesity-associated breast cancer, available therapeutic strategies and potential therapeutic targets for obesity-associated breast cancer.

IGFBP-3 and TNF-α regulate retinal endothelial cell apoptosis

PURPOSE

We hypothesized that loss of insulin-like growth factor binding protein 3 (IGFBP-3) signaling would produce neuronal changes in the retina similar to early diabetes.

METHODS

To understand better the role of IGFBP-3 in the retina, IGFBP-3 knockout (KO) mice were evaluated for neuronal, vascular, and functional changes compared to wild-type littermates. We also cultured retinal endothelial cells (REC) in normoglycemia or hyperglycemia to determine the interaction between IGFBP-3 and TNF-α, as data indicate that both proteins are regulated by β-adrenergic receptors and respond antagonistically. We also treated some cells with Compound 49b, a novel β-adrenergic receptor agonist we have reported previously to regulate IGFBP-3 and TNF-α.

RESULTS

Electroretinogram analyses showed decreased B-wave and oscillatory potential amplitudes in the IGFBP-3 KO mice, corresponding to increased apoptosis. Retinal thickness and cell numbers in the ganglion cell layer were reduced in the IGFBP-3 KO mice. As expected, loss of IGFBP-3 was associated with increased TNF-α levels. When TNF-α and IGFBP-3 were applied to REC, they worked antagonistically, with IGFBP-3 inhibiting apoptosis and TNF-α promoting apoptosis. Due to their antagonistic nature, results suggest that apoptosis of REC may depend upon which protein (IGFBP-3 versus TNF-α) is active.

CONCLUSIONS

Taken together, loss of IGFBP-3 signaling results in a phenotype similar to neuronal changes observed in diabetic retinopathy in the early phases, including increased TNF-α levels.

Mechanisms of chronic state of inflammation as mediators that link obese adipose tissue and metabolic syndrome

The metabolic syndrome is a cluster of cardiometabolic alterations that include the presence of arterial hypertension, insulin resistance, dyslipidemia, and abdominal obesity. Obesity is associated with a chronic inflammatory response, characterized by abnormal adipokine production, and the activation of proinflammatory signalling pathways resulting in the induction of several biological markers of inflammation. Macrophage and lymphocyte infiltration in adipose tissue may contribute to the pathogenesis of obesity-mediated metabolic disorders. Adiponectin can either act directly on macrophages to shift polarization and/or prime human monocytes into alternative M2-macrophages with anti-inflammatory properties. Meanwhile, the chronic inflammation in adipose tissue is regulated by a series of transcription factors, mainly PPARs and C/EBPs, that in conjunction regulate the expression of hundreds of proteins that participate in the metabolism and storage of lipids and, as such, the secretion by adipocytes. Therefore, the management of the metabolic syndrome requires the development of new therapeutic strategies aimed to alter the main genetic pathways involved in the regulation of adipose tissue metabolism.

Mechanisms of chronic state of inflammation as mediators that link obese adipose tissue and metabolic syndrome

The metabolic syndrome is a cluster of cardiometabolic alterations that include the presence of arterial hypertension, insulin resistance, dyslipidemia, and abdominal obesity. Obesity is associated with a chronic inflammatory response, characterized by abnormal adipokine production, and the activation of proinflammatory signalling pathways resulting in the induction of several biological markers of inflammation. Macrophage and lymphocyte infiltration in adipose tissue may contribute to the pathogenesis of obesity-mediated metabolic disorders. Adiponectin can either act directly on macrophages to shift polarization and/or prime human monocytes into alternative M2-macrophages with anti-inflammatory properties. Meanwhile, the chronic inflammation in adipose tissue is regulated by a series of transcription factors, mainly PPARs and C/EBPs, that in conjunction regulate the expression of hundreds of proteins that participate in the metabolism and storage of lipids and, as such, the secretion by adipocytes. Therefore, the management of the metabolic syndrome requires the development of new therapeutic strategies aimed to alter the main genetic pathways involved in the regulation of adipose tissue metabolism.

Lymphotoxin-α is a novel adiponectin expression suppressor following myocardial ischemia/reperfusion

Recent clinical observations demonstrate adiponectin (APN), an adipocytokine with potent cardioprotective actions, is significantly reduced following myocardial ischemia/reperfusion (MI/R). However, mechanisms responsible for MI/R-induced hypoadiponectinemia remain incompletely understood. Adult male mice were subjected to 30-min MI followed by varying reperfusion periods. Adipocyte APN mRNA and protein expression and plasma APN and TNFα concentrations were determined. APN expression/production began to decline 3 h after reperfusion (reaching nadir 12 h after reperfusion), returning to control levels 7 days after reperfusion. Plasma TNFα levels began to increase 1 h after reperfusion, peaking at 3 h and returning to control levels 24 h after reperfusion. TNFα knockout significantly increased plasma APN levels 12 h after reperfusion but failed to improve APN expression/production 72 h after reperfusion. In contrast, TNF receptor-1 (TNFR1) knockout significantly restored APN expression 12 and 72 h after reperfusion, suggesting that other TNFR1 binding cytokines contribute to MI/R-induced APN suppression. Among many cytokines increased after MI/R, lymphotoxin-α (LTα) was the only cytokine remaining elevated 24-72 h after reperfusion. LTα knockout did not augment APN levels 12 h post-reperfusion, but did so by 72 h. Finally, in vitro treatment of adipocytes with TNFα and LTα at concentrations seen in MI/R plasma additively inhibited APN expression/production in TNFR1-dependent fashion. Our study demonstrates for the first time that LTα is a novel suppressor of APN expression and contributes to the sustained hypoadiponectinemia following MI/R. Combining anti-TNFα with anti-LTα strategies may achieve the best effects restoring APN in MI/R patients.

Signal Transduction Pathways Mediated by Secreted and Non-secreted Forms of intact Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) and its 1-97 N-terminal Fragment in PC-3 Human Prostate Cancer Cells

Our previous results indicated that both the secreted and the intracellular form of full length and 1-97 N-terminal fragment of IGFBP-3 induces apoptosis in PC-3 human prostate cancer cells in an IGF-dependent and independent manner. This study was undertaken to delineate possible down-stream signaling pathways that are involved in this process. Intact IGFBP-3 and its N-terminal 1-97 fragments with or without a signal pro-peptide was fused to YFP and expressed in PC-3 human prostate cancer cells. In some cases, the putative IGF-binding site present in full length IGFBP-3 and its N-terminal fragment was also mutated. Extent of apoptosis was quantified using FACS. Up-regulation of total Stat-1 and activation of phospho-Stat-1 was shown by western blot. TGF-β signal was measured by luciferase reporter assay. Results from inhibitor studies indicated that both the Caspase 8 and caspase 9 pathways are involved in IGFBP-3 (non-secreted form) induced apoptosis in PC-3 cells. Exogenous addition of IGFBP-3 to PC-3 cells increased Stat-1 protein expression/tyrosine phosphorylation. Interestingly, results also showed that knockdown of Stat-1 by siRNA potentiated the IGFBP-3 induced apoptosis in PC-3 cells. In addition, both full-length IGFBP-3 and its 1-97 N-terminal fragments inhibited TGFβ signaling in these cells. This is the first report that compares the signal transduction pathways involved in apoptotic pathways mediated by IGFBP-3 in PC-3 human prostate cancer cells. Non-secreted form of full length IGFBP-3 and its N-terminal fragments induced apoptosis in PC-3 cells via activation of caspase 8 and caspase 9. We noted that both secreted and non-secreted forms of IGFBP-3 are involved in modulating Stat-1 and TGF-β pathways to induce apoptotic actions in PC-3 cells. Surprisingly, only non-secreted form of IGFBP-3 and its N-terminal fragments are involved in the induction of apoptosis in PC-3 cells via caspase 8 and caspase 9 activation. These studies clearly demonstrate that secreted and non-secreted FL and its 1-97 N-terminal fragments induce apoptosis in PC-3 cells by regulating different mechanistic pathways.

Differentially expressed genes in adipocytokine signaling pathway of adipose tissue in pregnancy

Objective

To profile the differential gene expression of the KEGG Adipocytokine Signaling pathway in omental compared to subcutaneous tissue in normal pregnancy.

Study Design

Subjects included 14 nonobese, normal glucose tolerant, healthy pregnant women. Matched omental and subcutaneous tissue were obtained at elective cesarean delivery. Gene expression was evaluated using microarray and validated by RT-PCR. Differential gene expression was defined as ≥1.5 fold increase at p < 0.05.

Results

Six genes were significantly downregulated with two upregulated genes in omental tissue. Downregulation of Adiponectin and Insulin Receptor substrate, key genes mediating insulin sensitivity, were observed with borderline upregulation of GLUT-1. There were downregulations of CD36 and acyl-CoA Synthetase Long-chain Family Member 1which are genes involved in fatty acid uptake and activation. There was a novel expression of Carnitine palmitoyltransferase 1C.

Conclusion

Differential gene expression of Adipocytokine Signaling Pathway in omental relative to subcutaneous adipose tissue in normal pregnancy suggests a pattern of insulin resistance, hyperlipidemia, and inflammation.

Functional relationship between high mobility group A1 (HMGA1) protein and insulin-like growth factor-binding protein 3 (IGFBP-3) in human chondrocytes

Introduction

Insulin-like growth factor I (IGF-I) regulates articular cartilage homeostasis. During osteoarthritis (OA), the anabolic responses of chondrocytes to IGF-I are likely to be prevented by the enhanced production of IGF-binding proteins (IGFBPs), especially IGFBP-3. The aim of this study is to evaluate whether the architectural transcription factor high mobility group A1 (HMGA1) influences IGFBP-3 overexpression in vitro, in cultured chondrocytic cell lines, and ex vivo, in human osteoarthritic cartilage compared to healthy human cartilage controls.

Methods

Quantitative real-time reverse transcription-PCR (qRT-PCR) was performed to assess the relative transcript levels of HMGA1 and IGFBP-3 in vitro, in the human chondrocytic cell lines T/C-28a4 and C-28/I2. An electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation (ChIP) and transient transfection assays were performed to investigate the HMGA1-IGFBP-3 gene interaction. Samples of articular cartilage were harvested from osteoarthritic patients and controls and analyzed by qRT-PCR for HMGA1 and IGFBP-3 mRNA levels.

Results

A parallelism between HMGA1 protein levels and IGFBP-3 gene expression has been observed in T/C-28a4 and C-28/I2 cells. The interaction of HMGA1 with the IGFBP-3 gene promoter has been demonstrated by EMSA and ChIP. In transient transfections, IGFBP-3 promoter activity increased in cells overexpressing HMGA1 and decreased in cells pretreated with siRNA detected against HMGA1. IGFBP-3 mRNA expression was higher in cartilage from patients with OA, where the increased expression of IGFBP-3 closely paralleled the increased expression of HMGA1 mRNA.

Conclusions

Our observations indicate that increased HMGA1 expression in human chondrocytes is associated with increased expression of IGFBP-3. It is tempting to speculate that, through the regulation of IGFBP3 expression, HMGA1 may act as a pathogenetic factor for OA.

Hypoadiponectinaemia in diabetes mellitus type 2: molecular mechanisms and clinical significance

1. This review focuses on the regulatory mechanisms of adiponectin (APN) gene expression during physiologic conditions and both the clinical significance and underlying molecular mechanisms of hypoadiponectinaemia during pathologic conditions. 2. Adiponectin is a versatile cardiovascular protective factor. It plays an important role in regulating insulin sensitivity and energy homeostasis, with anti-inflammatory and anti-atherosclerotic properties. 3. Adiponectin gene expression is downregulated in both obesity and diabetes mellitus type 2. Hypoadiponectinaemia is an independent risk factor for coronary artery disease in type 2 diabetic patients. 4. Exogenous supplementation of recombinant APN attenuates insulin resistance, improving metabolic disorders. Therefore, APN-targeted pharmaceutical strategies increasing circulating APN levels may be therapeutic against type 2 diabetes. 5. There is great value in elucidating the regulatory mechanisms of APN gene expression during physiologic and pathologic conditions. APN biosynthesis regulation includes transcriptional expression and post-translational modification, oligomerization, and secretion. Under pathological conditions, including obesity and diabetes mellitus type 2, hypoxia, oxidative stress, and inflammation suppress APN mRNA levels and its secretion.

Adiponectin: regulation of its production and its role in human diseases

Adiponectin is a white and brown adipose tissue hormone, also known as gelatin-binding protein-28 (GBP28), AdipoQ, adipocyte complement-related protein (ACRP30), or apM1. Adiponectin circulates in the bloodstream in trimeric, hexameric, and high-molecular-mass species, while different forms of adiponectin have been found to play distinct roles in the balance of energy homoeostasis. Adiponectin is an insulin sensitizing hormone that exerts its action through its receptors AdipoR1, AdipoR2, and T-cadherin. AdipoR1 is expressed abundantly in muscle, whereas AdipoR2 is predominantly expressed in the liver. Adiponectin is inversely proportional to obesity, diabetes, and other insulin-resistant states. In this review we present the current findings regarding the regulation of its production and several new findings pertaining to its biological effects. Adiponectin enhances AMPK and the PPARα pathway in the liver and skeletal muscle. Adiponectin increases fatty acids oxidation, which lowers circulating free fatty acids and prevents insulin resistance. Adiponectin has been reported to exert an antiatherosclerotic effect. It inhibits macrophage activation and foam cell accumulation, while it also augments endothelial nitrous oxide production and protects the vasculature by reducing platelet aggregation and vasodilation. Apart from causing metabolic dysfunction, adiponectin deficiency may also contribute to coronary heart disease, steatohepatitis, insulin resistance, nonalcoholic fatty liver disease, and a wide array of cancers. In this study, we present ample evidence that adiponectin mediates multiple molecular pathways. We therefore support the concept that it shows distinct potential for being of therapeutic value in the treatment of obesity related diseases, ranging from metabolic syndrome to malignancies.

Screening for adiponectin secretion regulators

Adiponectin is an adipokine secreted from adipocytes and plays important roles in the suppression of metabolic syndromes that can result in type 2 diabetes, obesity, and atherosclerosis. Adiponectin is a promising drug target because a number of studies have shown that upregulation of adiponectin has a number of therapeutic benefits. Extensive efforts have revealed various adiponectin regulators, such as cytokines, transcription factors, and drugs. Cytokines, such as tumor necrosis factor α, IL-6, and IL-18, downregulate adiponectin production. On the other hand, transcription factors such as peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT-enhancer-binding protein α, and forkhead box O1 (FoxO1) upregulate adiponectin expression, although the activating transcription factor 3 and cAMP response element-binding protein downregulate it. Although a number of therapeutic drugs have been reported as adiponectin secretion regulators, most of them act through PPARγ-dependent mechanisms, leaving PPARγ-derived side effects as a concern. Using high-throughput screening, we have identified PPARγ-independent adiponectin secretion regulators as potential drug candidates with a novel mechanism of action.

Lifestyle factors increasing adiponectin synthesis and secretion

Adiponectin is an anti-inflammatory adipokine released from adipose tissue that is known to exert insulin-sensitizing effects in skeletal muscle and liver. Given that the secretion of adiponectin is impaired in obesity and related pathologies, strategies to enhance its synthesis and secretion are of interest. There is evidence that several lifestyle factors, including consumption of dietary long-chain n-3 PUFA, TZD administration, and weight loss can increase adiponectin synthesis and secretion. The effect of chronic exercise, independent of weight loss, is variable and less convincing. Potential mechanisms by which such lifestyle factors exert their favorable effects on adiponectin include activation of PPARγ and AMPK, regulation of posttranslational modifications, and changes in adipose tissue morphology and macrophage infiltration. As a clear role for adiponectin in mitigating obesity-related impairments in lipid metabolism and insulin sensitivity is evident, further research investigating factors that enhance adiponectin synthesis and secretion is distinctly warranted.

Adiponectin and PPARγ: cooperative and interdependent actions of two key regulators of metabolism

The recent advances in the understanding of adiponectin and other adipokines have highlighted the role of adipose tissue as an active endocrine organ. One of the central regulators of adipocyte biology is peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor that induces the adipogenic gene expression program during development, promotes adipose remodeling, and regulates the functions of adipocytes in lipid storage, adipokine secretion, and energy homeostasis. Activation of PPARγ results in increased insulin sensitivity in skeletal muscle and liver and improves the secretory profile of adipose tissue, favoring release of insulin-sensitizing adipokines, such as adiponectin, and reducing inflammatory cytokines. Increased adiponectin production is likely a significant mediator of the systemic effects of PPARγ activation. This chapter will review the interplay between PPARγ and adiponectin in regulating metabolism, presenting evidence that PPARγ regulates adiponectin gene expression, processing, and secretion and that the two proteins have overlapping effects on downstream metabolic pathways.

Adiponectin promotes syncytialisation of BeWo cell line and primary trophoblast cells

BACKGROUND

In human pregnancy, a correct placentation depends on trophoblast proliferation, differentiation, migration and invasion. These processes are highly regulated by placental hormones, growth factors and cytokines. Recently, we have shown that adiponectin, an adipokine, has anti-proliferative effects on trophoblastic cells. Here, we complete this study by demonstrating that adiponectin modulates BeWo and human villous cytotrophoblast cell differentiation.

RESULTS

We showed that hCG secretion was up-regulated by adiponectin treatment in both BeWo cells and human cytotrophoblasts from very early placentas (5-6 weeks). The expression of two trophoblast differentiation markers, leptin and syncytin 2, was also up-regulated by adiponectin in BeWo cells. Moreover, adiponectin treatment induced a loss of E-cadherin staining in these cells. In parallel, we demonstrated that AdipoR1 and AdipoR2 are up-regulated during forskolin induced BeWo cell differentiation, reinforcing the role of adiponectin in trophoblast syncytialization. SiRNA mediated down-regulation of AdipoR1 and AdipoR2 was used to demonstrate that adiponectin effects on differentiation were essentially mediated by these receptors. Finally, using a specific inhibitor, we demonstrated that the PKA signalling pathway could be one pathway involved in adiponectin effects on trophoblast differentiation.

CONCLUSION

Adiponectin enhances the differentiation process of trophoblast cells and could thus be involved in functional syncytiotrophoblast formation.

Adiponectin and breast cancer

Adiponectin, an adipose tissue-derived hormone, has been studied intensively for the past decade because of its anti-inflammatory, anti-atherogenic, and anti-diabetic properties. Recent advances suggest that adiponectin also plays an important role in the development and progression of various cancers, especially obesity-related cancers. In this review, the authors focus on the potential role of adiponectin in breast cancer, an obesity- and endocrine-associated tumor. Epidemiological studies have shown that plasma adiponectin level is a risk factor for breast cancer in post-menopausal women. Adiponectin and its receptors are expressed on both breast cancer line cells and tumor tissues. Furthermore, exogenous adiponectin has exhibited therapeutic potential in animal models. Underlying mechanisms include the inhibition of cell proliferation and promotion of apoptosis, the regulation of tumorigenic-related factors, and the suppression of angiogenesis. The signaling pathways linking adiponectin with tumorigenesis might provide potential drug targets for the future. However, more convincing evidence is needed to fully elucidate the exact role of adiponectin in breast cancer, since both its beneficial effects and possible mechanisms remain controversial.

Adiponectin and breast cancer

Adiponectin, an adipose tissue-derived hormone, has been studied intensively for the past decade because of its anti-inflammatory, anti-atherogenic, and anti-diabetic properties. Recent advances suggest that adiponectin also plays an important role in the development and progression of various cancers, especially obesity-related cancers. In this review, the authors focus on the potential role of adiponectin in breast cancer, an obesity- and endocrine-associated tumor. Epidemiological studies have shown that plasma adiponectin level is a risk factor for breast cancer in post-menopausal women. Adiponectin and its receptors are expressed on both breast cancer line cells and tumor tissues. Furthermore, exogenous adiponectin has exhibited therapeutic potential in animal models. Underlying mechanisms include the inhibition of cell proliferation and promotion of apoptosis, the regulation of tumorigenic-related factors, and the suppression of angiogenesis. The signaling pathways linking adiponectin with tumorigenesis might provide potential drug targets for the future. However, more convincing evidence is needed to fully elucidate the exact role of adiponectin in breast cancer, since both its beneficial effects and possible mechanisms remain controversial.

Inflammatory mediators and insulin resistance in obesity: role of nuclear receptor signaling in macrophages

Visceral obesity is coupled to a general low-grade chronic inflammatory state characterized by macrophage activation and inflammatory cytokine production, leading to insulin resistance (IR). The balance between proinflammatory M1 and antiinflammatory M2 macrophage phenotypes within visceral adipose tissue appears to be crucially involved in the development of obesity-associated IR and consequent metabolic abnormalities. The ligand-dependent transcription factors peroxisome proliferator activated receptors (PPARs) have recently been implicated in the determination of the M1/M2 phenotype. Liver X receptors (LXRs), which form another subgroup of the nuclear receptor superfamily, are also important regulators of proinflammatory cytokine production in macrophages. Disregulation of macrophage-mediated inflammation by PPARs and LXRs therefore underlies the development of IR. This review summarizes the role of PPAR and LXR signaling in macrophages and current knowledge about the impact of these actions in the manifestation of IR and obesity comorbidities such as liver steatosis and diabetic osteopenia.

Transcriptional and post-translational regulation of adiponectin

Adiponectin is an adipose-tissue-derived hormone with anti-diabetic, anti-atherogenic and anti-inflammatory functions. Adiponectin circulates in the bloodstream in trimeric, hexameric and high-molecular-mass species, and different forms of adiponectin have been found to play distinct roles in the regulation of energy homoeostasis. The serum levels of adiponectin are negatively correlated with obesity and insulin resistance, yet the underlying mechanisms remain elusive. In the present review, we summarize recent progress made on the mechanisms regulating adiponectin gene transcription, multimerization and secretion. We also discuss the potential relevance of these studies to the development of new clinical therapy for insulin resistance, Type 2 diabetes and other obesity-related metabolic disorders.

TNF-alpha, a potent lipid metabolism regulator

As a multifunctional cytokine, tumor necrosis factor alpha (TNF-alpha) exerts a series of biological actions in different cells, tissues, organs, and species and has been demonstrated to regulate and interfere with energy metabolism, especially lipid homeostasis. A large body of researches suggested that the effects of TNF-alpha on lipid metabolism mainly include five aspects: (1) suppresses free fatty acid (FFA) uptake and promotes lipogenesis; (2) induces lipolysis; (3) inhibits lipid-metabolism-related enzymes activity; (4) regulates cholesterol metabolism; (5) regulates other adipocyte-derived adipokines. The molecular mechanisms underlying these actions are complex and several signal transduction pathways might be involved. Regulation of metabolism-related gene expression at transcriptional and protein levels and impact on enzymes activity might be of importance. Identification and verification of these pathways might provide novel potential strategies and drug targets for dyslipidemia therapy. However, the inconsistent and even conflict conclusions on lipid profile drawn from human subjects after infliximab therapy poses the possibility that the effect of TNF-alpha on lipid metabolism might be more complicated than it appeared to be.

Actions of IGF binding proteins and related proteins in adipose tissue

The insulin-like growth factors (IGFs), their binding proteins (IGFBPs) and structurally related proteins have been identified in adipose tissue but their roles in adipose tissue are poorly understood. IGF-I and IGFBP-3 expression increase during human preadipocyte differentiation. However, whereas IGF-I stimulates this process, IGFBP-3 is inhibitory both to preadipocyte differentiation and to differentiated adipocyte function. The direct interaction of IGFBP-3 with peroxisome proliferator-activated receptor-gamma is believed to contribute to its inhibitory effect on differentiation. Connective tissue growth factor (CTGF/CCN2) shares weak structural homology and functional similarities with IGFBP-3, including inhibition of preadipocyte differentiation. This review examines the current knowledge of IGFBP regulation and actions in adipocytes and proposes a common regulatory pathway involving IGFBP-3 and CTGF/CCN2.

Hyperglycemia in critical illness: a review

Hyperglycemia is commonplace in the critically ill patient and is associated with worse outcomes. It occurs after severe stress (e.g., infection or injury) and results from a combination of increased secretion of catabolic hormones, increased hepatic gluconeogenesis, and resistance to the peripheral and hepatic actions of insulin. The use of carbohydrate-based feeds, glucose containing solutions, and drugs such as epinephrine may exacerbate the hyperglycemia. Mechanisms by which hyperglycemia cause harm are uncertain. Deranged osmolality and blood flow, intracellular acidosis, and enhanced superoxide production have all been implicated. The net result is derangement of endothelial, immune and coagulation function and an association with neuropathy and myopathy. These changes can be prevented, at least in part, by the use of insulin to maintain normoglycemia.