Neutralization of osteopontin inhibits obesity-induced inflammation and insulin resistance

Osteocalcin, under-carboxylated osteocalcin and osteopontin are not associated with gestational diabetes mellitus but are inversely associated with leptin in non-diabetic women

OBJECTIVE

To measure serum osteocalcin (OC), under-carboxylated osteocalcin (ucOC), osteopontin (OPN), and leptin in pregnant women with gestational diabetes mellitus (GDM) and in healthy pregnant women during pregnancy and after birth and relate these markers to glucose metabolism.

METHODS

This was a prospective study including 60 women with GDM and 60 subjects with normal gestation who were evaluated at gestational week 30 and 6 weeks postpartum. Serum OC, ucOC, OPN, leptin, insulin and insulin resistance were evaluated during the study.

RESULTS

Bone biomarkers and leptin were similar between GDM and normal pregnancy. After delivery, OC, ucOC and OPN increased in both groups, while leptin decreased only in healthy controls. Bone markers did not correlate with insulin and insulin resistance in the two groups, but leptin was positively correlated with insulin and insulin resistance and negatively correlated with bone biomarkers only in healthy women. Furthermore, the women who developed diabetes postpartum had lower levels of OC than women with normal glucose tolerance.

CONCLUSION

GDM is not associated with OC, ucOC, OPN, and leptin and does not correlate with insulin resistance. At postpartum, women who develop diabetes have lower osteocalcin concentrations. Leptin correlates with insulin resistance and bone biomarkers in non-diabetic women.

Peripheral mononuclear blood cells contribute to the obesity-associated inflammatory state independently of glycemic status: involvement of the novel proinflammatory adipokines chemerin, chitinase-3-like protein 1, lipocalin-2 and osteopontin

Inflammation is a critical contributor to the pathogenesis of metabolic disorders with adipose tissue being crucial in the inflammatory response by releasing multiple adipokines with either pro- or anti-inflammatory activities with potential functions as metabolic regulators. Peripheral blood mononuclear cells (PBMC) have been proposed as representative of the inflammatory status in obesity. The aim of the present study was to evaluate the contribution of PBMC to the obesity-associated chronic inflammation analyzing the expression of novel adipokines. Samples obtained from 69 subjects were used in the study. Real-time PCR determinations were performed to quantify gene expression levels in PBMC of novel adipokines including chemerin, chitinase-3-like protein 1 (YKL-40), lipocalin-2 (LCN-2) and osteopontin (OPN), and their circulating concentrations were also determined by ELISA. We show, for the first time, that PBMC gene expression levels of chemerin (P < 0.0001), chitinase-3-like protein 1 (P = 0.010), lipocalin-2 (P < 0.0001) and osteopontin (P < 0.0001) were strongly upregulated in obesity independently of the glycemic state. Circulating concentrations of these adipokines followed the same trend being significantly higher (P < 0.05) in obese normoglycemic and type 2 diabetic patients compared to lean volunteers and also associated (P < 0.05) with their corresponding mRNA levels in PBMC. These results provide evidence that alterations in inflammation-related adipokines are manifest in PBMC, which might contribute to the low-grade chronic inflammation that characterizes obesity.

Erythropoietin and obesity-induced white adipose tissue inflammation: redefining the boundaries of the immunometabolism territory

The adipose tissue represents a critical and predominant site for the interaction between metabolic and inflammatory responses during health and disease. In the white adipose tissue microenvironment, macrophages/adipocytes cross-talk have been shown to influence the metabolic and inflammatory states of both cell types, and contribute to the development of systemic insulin resistance during obesity. Indeed, the existence of paracrine loops between mature adipocytes and macrophages, especially during obesity-induced stress, involving the release of, and response to, an array of cytokines and regulatory factors, have been extensively studied using several in vitro and in vivo model systems. Published evidence together with recent observations, brought to light the unexpected role of erythropoietin and its receptor in the regulation of white adipose tissue mass, energy homeostasis, and inflammation as demonstrated by erythropoietin effects on adipocyte development and metabolic profile, and macrophage infiltration, cytokine responses, and activation state during diet-induced obesity. In this commentary, we discuss the newly added elements and perspectives to our understanding of the erythropoietin/erythropoietin-receptor axis as a regulator of obesity-induced white adipose tissue inflammation, providing insight into its effects on cytokine responses of macrophages and adipocytes, and possible links to glucose metabolism and insulin resistance.

Osteopontin-induced brown adipogenesis from white preadipocytes through a PI3K-AKT dependent signaling

Recent studies have shown that OPN (osteopontin) plays critical roles in cell survival, differentiation, bio-mineralization, cancer and cardiovascular remodeling. However, its roles in the differentiation of brown adipocytes and the underlying mechanisms remain unclear. Therefore, the aim of this study was to investigate the roles of OPN in the brown adipogenesis and the underlying mechanisms. It was shown that the OPN successfully induced the differentiation of 3T3-L1 white preadipocytes into the PRDM16(+) (PRD1-BF1-RIZ1 homologous domain containing 16) and UCP-1(+) (uncoupling protein-1) brown adipocytes in a concentration and time-dependent manner. Also, activation of PI3K (phosphatidylinositol 3-kinase)-AKT pathway was required for the OPN-induced brown adipogenesis. The findings suggest OPN plays an important role in promoting the differentiation of the brown adipocytes and might provide a potential novel therapeutic approach for the treatment of obesity and related disorders.

Neutralization of osteopontin attenuates neutrophil migration in sepsis-induced acute lung injury

Introduction

Sepsis refers to severe systemic inflammation leading to acute lung injury (ALI) and death. Introducing novel therapies can reduce the mortality in ALI. Osteopontin (OPN), a secretory glycoprotein produced by immune reactive cells, plays a deleterious role in various inflammatory diseases. However, its role in ALI caused by sepsis remains unexplored. We hypothesize that treatment with an OPN-neutralizing antibody (anti-OPN Ab) protects mice against ALI during sepsis.

Methods

Sepsis was induced in 8-week-old male C57BL/6 mice by cecal ligation and puncture (CLP). Anti-OPN Ab or non-immunized IgG as control, at a dose of 50 μg/mouse, was intravenously injected at the time of CLP. After 20 hours, the expression of OPN and proinflammatory cytokines in tissues and plasma was examined by real-time PCR, Western blot, and ELISA. Plasma levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) and the lung myeloperoxidase (MPO) levels were determined by colorimetric assays. Lung damage and neutrophil infiltrations were determined by histological H&E and Gr-1 staining, respectively. The effect of recombinant mouse OPN (rmOPN) on human neutrophil-like cell (HL-60) migration was performed by Boyden chamber assays and the involvement of intracellular signaling molecules in HL-60 cells was revealed by Western blot.

Results

After 20 hours of sepsis, mRNA and protein levels of OPN were significantly induced in lungs, spleen, and plasma. Treatment with an anti-OPN Ab in septic mice significantly reduced the plasma levels of ALT, AST, and LDH, and the proinflammatory cytokines IL-6, IL-1β and the chemokine MIP-2, compared with the vehicle group. Similarly, the lung mRNA and protein expressions of proinflammatory cytokines and chemokine were greatly reduced in anti-OPN Ab-treated animals. The lung histological architecture, MPO and neutrophil infiltration were significantly improved in anti-OPN Ab-treated mice compared with the vehicle animals. Treatment of rmOPN in HL-60 cells significantly increased their migration, in vitro. The neutrophils treated with rmOPN remarkably increased the levels of phospho focal adhesion kinase (pFAK), phospho extracellular signal-regulated kinase (pERK) and phospho p38.

Conclusions

Our findings clearly demonstrate the beneficial outcomes of anti-OPN Ab treatment in protecting against ALI, implicating a novel therapeutic strategy in sepsis.

Vascular calcification: from pathophysiology to biomarkers

The link between vascular calcification (VC) and increased mortality is now well established. Over time, as clinical importance of this phenomenon has begun to be fully considered, scientists have highlighted more and more physiopathological mechanisms and signaling pathways that underlie VC. Several conditions such as diabetes, dyslipidemia and renal diseases are undoubtedly identified as predisposing factors. But even if the process is better understood, many questions still remain unanswered. This review briefly develops the various theories that attempt to explain mineralization genesis. Nonetheless, the main purpose of the article is to provide a profile of the various existing biomarkers of VC. Indeed, in the past years, a lot of inhibitors and promoters, which form a dense and interconnected network, were identified. Given importance to assess and control mineralization process, a focusing on accumulated knowledge of each marker seemed to be necessary. Therefore, we tried to define their respective role in the physiopathology and how they can contribute to calcification risk assessment. Among these, Klotho/fibroblast growth factor-23, fetuin-A, Matrix Gla protein, Bone morphogenetic protein-2, osteoprotegerin, osteopontin, osteonectin, osteocalcin, pyrophosphate and sclerostin are specifically discussed.

Adipocyte versus pituitary leptin in the regulation of pituitary hormones: somatotropes develop normally in the absence of circulating leptin

Leptin is a cytokine produced by white fat cells, skeletal muscle, the placenta, and the pituitary gland among other tissues. Best known for its role in regulating appetite and energy expenditure, leptin is produced largely by and in proportion to white fat cells. Leptin is also important to the maintenance and function of the GH cells of the pituitary. This was shown when the deletion of leptin receptors on somatotropes caused decreased numbers of GH cells, decreased circulating GH, and adult-onset obesity. To determine the source of leptin most vital to GH cells and other pituitary cell types, we compared two different leptin knockout models with Cre-lox technology. The global Lep-null model is like the ob/ob mouse, whereby only the entire exon 3 is deleted. The selective adipocyte-Lep-null model lacks adipocyte leptin but retains pituitary leptin, allowing us to investigate the pituitary as a potential source of circulating leptin. Male and female mice lacking adipocyte leptin (Adipocyte-lep-null) did not produce any detectable circulating leptin and were infertile, suggesting that the pituitary does not contribute to serum levels. In the presence of only pituitary leptin, however, these same mutants were able to maintain somatotrope numbers and GH mRNA levels. Serum GH trended low, but values were not significant. However, hypothalamic GHRH mRNA was significantly reduced in these animals. Other serum hormone and pituitary mRNA differences were observed, some of which varied from previous results reported in ob/ob animals. Whereas pituitary leptin is capable of maintaining somatotrope numbers and GH mRNA production, the decreased hypothalamic GHRH mRNA and low (but not significant) serum GH levels indicate an important role for adipocyte leptin in the regulation of GH secretion in the mouse. Thus, normal GH secretion may require the coordinated actions of both adipocyte and pituitary leptin.

New advances in molecular mechanisms and emerging therapeutic targets in alcoholic liver diseases

Alcoholic liver disease is a major health problem in the United States and worldwide. Chronic alcohol consumption can cause steatosis, inflammation, fibrosis, cirrhosis and even liver cancer. Significant progress has been made to understand key events and molecular players for the onset and progression of alcoholic liver disease from both experimental and clinical alcohol studies. No successful treatments are currently available for treating alcoholic liver disease; therefore, development of novel pathophysiological-targeted therapies is urgently needed. This review summarizes the recent progress on animal models used to study alcoholic liver disease and the detrimental factors that contribute to alcoholic liver disease pathogenesis including miRNAs, S-adenosylmethionine, Zinc deficiency, cytosolic lipin-1β, IRF3-mediated apoptosis, RIP3-mediated necrosis and hepcidin. In addition, we summarize emerging adaptive protective effects induced by alcohol to attenuate alcohol-induced liver pathogenesis including FoxO3, IL-22, autophagy and nuclear lipin-1α.

Osteopontin is a strong predictor of incipient diabetic nephropathy, cardiovascular disease, and all-cause mortality in patients with type 1 diabetes

OBJECTIVE

Osteopontin (OPN) is a multifunctional protein suggested to be a player in the arterial disease of patients with type 2 diabetes. However, its role for complications in patients with type 1 diabetes (T1D) is unknown. We therefore investigated the associations between OPN and diabetic vascular complications and all-cause mortality in patients with T1D.

RESEARCH DESIGN AND METHODS

Serum OPN was measured in 2,145 adults with T1D without end-stage renal disease (ESRD; dialysis or transplantation) as part of the Finnish Diabetic Nephropathy (FinnDiane) Study. Data on renal status, cardiovascular disease (CVD), and all-cause mortality during follow-up were verified from medical files, hospital discharge registries, and the Finnish National Death Registry, respectively. The median follow-up time was 10.5 (interquartile range 8.9-11.8) years.

RESULTS

Serum OPN was higher at baseline in patients who developed incident microalbuminuria (16.0 ± 0.9 vs. 14.1 ± 0.2 µg/L; P = 0.04), progressed to ESRD (28.3 ± 1.7 vs. 15.4 ± 0.2 µg/L; P < 0.001), suffered an incident CVD event (20.2 ± 1.2 vs. 15.5 ± 0.2 µg/L; P < 0.001), or died (23.3 ± 1.4 vs. 15.8 ± 0.2 µg/L; P < 0.001) during follow-up. In multivariate Cox regression analysis, OPN was independently associated with the development of incident microalbuminuria, an incident CVD event, and death, after adjustments for associated risk factors. Even after calculating reclassification indexes, OPN was predictive of CVD and all-cause mortality beyond the Framingham risk score covariates and hs-CRP.

CONCLUSIONS

Serum OPN is a strong predictor of incipient diabetic nephropathy, a first-ever CVD event, and all-cause mortality in patients with T1D. Serum OPN may be of clinical significance for the risk prediction of CVD events in patients with T1D.

Erythropoietin signaling: a novel regulator of white adipose tissue inflammation during diet-induced obesity

Obesity-induced white adipose tissue (WAT) inflammation and insulin resistance are associated with macrophage (Mф) infiltration and phenotypic shift from "anti-inflammatory" M2-like to predominantly "proinflammatory" M1-like cells. Erythropoietin (EPO), a glycoprotein hormone indispensable for erythropoiesis, has biological activities that extend to nonerythroid tissues, including antiapoptotic and anti-inflammatory effects. Using comprehensive in vivo and in vitro analyses in mice, EPO treatment inhibited WAT inflammation, normalized insulin sensitivity, and reduced glucose intolerance. We investigated EPO receptor (EPO-R) expression in WAT and characterized the role of its signaling during obesity-induced inflammation. Remarkably, and prior to any detectable changes in body weight or composition, EPO treatment reduced M1-like Mф and increased M2-like Mф in WAT, while decreasing inflammatory monocytes. These anti-inflammatory effects were found to be driven, at least in part, by direct EPO-R response in Mф via Stat3 activation, where EPO effects on M2 but not M1 Mф required interleukin-4 receptor/Stat6. Using obese ∆EpoR mice with EPO-R restricted to erythroid cells, we demonstrated an anti-inflammatory role for endogenous EPO. Collectively, our findings identify EPO-R signaling as a novel regulator of WAT inflammation, extending its nonerythroid activity to encompass effects on both Mф infiltration and subset composition in WAT.

Osteopontin deletion prevents the development of obesity and hepatic steatosis via impaired adipose tissue matrix remodeling and reduced inflammation and fibrosis in adipose tissue and liver in mice

Osteopontin (OPN) is a multifunctional extracellular matrix (ECM) protein involved in multiple physiological processes. OPN expression is dramatically increased in visceral adipose tissue in obesity and the lack of OPN protects against the development of insulin resistance and inflammation in mice. We sought to unravel the potential mechanisms involved in the beneficial effects of the absence of OPN. We analyzed the effect of the lack of OPN in the development of obesity and hepatic steatosis induced by a high-fat diet (HFD) using OPN-KO mice. OPN expression was upregulated in epididymal white adipose tissue (EWAT) and liver in wild type (WT) mice with HFD. OPN-KO mice had higher insulin sensitivity, lower body weight and fat mass with reduced adipose tissue ECM remodeling and reduced adipocyte size than WT mice under a HFD. Reduced MMP2 and MMP9 activity was involved in the decreased ECM remodeling. Crown-like structure number in EWAT as well as F4/80-positive cells and Emr1 expression in EWAT and liver increased with HFD, while OPN-deficiency blunted the increase. Moreover, our data show for the first time that OPN-KO under a HFD mice display reduced fibrosis in adipose tissue and liver, as well as reduced oxidative stress in adipose tissue. Gene expression of collagens Col1a1, Col6a1 and Col6a3 in EWAT and liver, as well as the profibrotic cytokine Tgfb1 in EWAT were increased with HFD, while OPN-deficiency prevented this increase. OPN deficiency prevented hepatic steatosis via reduction in the expression of molecules involved in the onset of fat accumulation such as Pparg, Srebf1, Fasn, Mogat1, Dgat2 and Cidec. Furthermore, OPN-KO mice exhibited higher body temperature and improved BAT function. The present data reveal novel mechanisms of OPN in the development of obesity, pointing out the inhibition of OPN as a promising target for the treatment of obesity and fatty liver.

Osteopontin: A novel regulator at the cross roads of inflammation, obesity and diabetes

Since its first description more than 20 years ago osteopontin has emerged as an active player in many physiological and pathological processes, including biomineralization, tissue remodeling and inflammation. As an extracellular matrix protein and proinflammatory cytokine osteopontin is thought to facilitate the recruitment of monocytes/macrophages and to mediate cytokine secretion in leukocytes. Modulation of immune cell response by osteopontin has been associated with various inflammatory diseases and may play a pivotal role in the development of adipose tissue inflammation and insulin resistance. Here we summarize recent findings on the role of osteopontin in metabolic disorders, particularly focusing on diabetes and obesity.

Comparative effects of gastric bypass and sleeve gastrectomy on plasma osteopontin concentrations in humans

BACKGROUND

Bariatric surgery (BS) has proven to be an effective treatment for morbid obesity. Osteopontin (OPN) is a proinflammatory cytokine involved in the development of obesity. The aim of our study was to determine the effect of weight loss following BS on circulating levels of OPN in humans.

METHODS

Body composition and circulating concentrations of OPN and markers of bone metabolism were determined in obese patients who underwent Roux-en-Y gastric bypass (RYGB; n = 40) or sleeve gastrectomy (SG; n = 11).

RESULTS

Patients who underwent RYGB or SG showed decreased body weight (P < 0.001) and body fat percentage (P < 0.001) as well as lower insulin resistance. However, plasma OPN levels were significantly increased after RYGB (P < 0.001) but remained unchanged following SG (P = 0.152). Patients who underwent RYGB also showed significantly increased C-terminal telopeptide of type-I collagen (ICTP) (P < 0.01) and osteocalcin (P < 0.001) while bone mineral density tended to decrease (P = 0.086). Moreover, OPN concentrations were positively correlated with the bone resorption marker ICTP after surgery. On the other hand, patients who underwent SG showed significantly increased ICTP levels (P < 0.05), and the change in OPN was positively correlated with the change in ICTP and negatively with the change in vitamin D after surgery (P < 0.05).

CONCLUSIONS

RYGB increased circulating OPN levels, while they remained unaltered after SG. The increase in OPN levels after RYGB could be related to the increased bone resorption in relation to its well-known effects on bone of this malabsorptive procedure in comparison to the merely restrictive SG.

Coffee intake mitigated inflammation and obesity-induced insulin resistance in skeletal muscle of high-fat diet-induced obese mice

Epidemiologic findings offer the promise that coffee or its many constituents may be useful as a dietary intervention in type 2 diabetes (T2D) prevention. We aimed to elucidate the molecular mechanisms involved in the ameliorative effects of caffeinated coffee (CC), decaffeinated coffee (DC) and unroasted caffeinated green coffee (GC) on skeletal muscle gene expression profiles and their relationships in an obesity animal model. Eight-week-old male C57BL6 mice were raised for 9 weeks ad libitum on a normal diet, a high-fat diet, or high-fat diet containing 2 % freeze-dried CC, or DC, or GC. Total RNA and protein were extracted from skeletal muscle and subjected to microarray (Mouse Genome 430 2.0, Affymetrix) and western blotting analyses, respectively. Coffee intake mitigated the insulin resistance by decreasing plasma glucose levels during an insulin tolerance test and by increasing tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), p85/IRS-1 complex and pAkt/PKB (protein kinase B). In addition, coffee intake down-regulated the anti-inflammatory genes activating transcription factor 3, FBJ osteosarcoma oncogene, heat shock protein 1A, heat shock protein 1B and synuclein, gamma and the inflammation-associated insulin signaling genes stearoyl-coenzyme A desaturase 1 and secreted phosphoprotein 1. These results provide scientific insight on the probable positive effects of coffee intake on impaired insulin signaling, inflammation and obesity, thereby providing a new perspective on the prevention of obesity and T2D.

Anti-inflammatory properties of kaempferol via its inhibition of aldosterone signaling and aldosterone-induced gene expression

Osteopontin (OPN), also called cytokine Eta-1, is a pro-inflammatory cytokine. Recent studies have shown that aldosterone increases OPN gene expression in endothelial cells. As a flavonoid compound, kaempferol has potent anti-inflammatory properties, but whether kaempferol regulates aldosterone signaling and aldosterone-induced gene expression is still unknown. Human umbilical vein endothelial cells (HUVECs) were pretreated with kaempferol (0, 1, 3, or 10 μmol/L) for 1 h prior to exposure to aldosterone (10−6 mol/L) for 24 h. Aldosterone induced generation of reactive oxygen species; OPN and cluster of differentiation 44 gene expression; phospho-p38 MAPK and NF-κB binding activity. The effect of aldosterone was abrogated by kaempferol and spironolactone (10−6 mol/L). The present results suggest that kaempferol exerts its anti-inflammatory properties via its inhibition of aldosterone signaling and aldosterone-induced gene expression in HUVECs.

An accelerated mouse model for atherosclerosis and adipose tissue inflammation

Background

Obesity and particularly the metabolic syndrome, which is often associated with obesity, combine a major risk for type 2 diabetes and cardiovascular disease. Emerging evidence indicate obesity-associated subclinical inflammation primarily originating from adipose tissue as a common cause for type 2 diabetes and cardiovascular disease. However, a suitable and well-characterized mouse model to simultaneously study obesity-associated metabolic disorders and atherosclerosis is not available yet. Here we established and characterized a murine model combining diet-induced obesity and associated adipose tissue inflammation and metabolic deteriorations as well as atherosclerosis, hence reflecting the human situation of cardio-metabolic disease.

Methods

We compared a common high-fat diet with 0.15% cholesterol (HFC), and a high-fat, high-sucrose diet with 0.15% cholesterol (HFSC) fed to LDL receptor-deficient (LDLR^-/-) mice. Insulin resistance, glucose tolerance, atherosclerotic lesion formation, hepatic lipid accumulation, and inflammatory gene expression in adipose tissue and liver were assessed.

Results

After 12–16 weeks, LDLR^-/- mice fed HFSC or HFC developed significant diet-induced obesity, adipose tissue inflammation, insulin resistance, and impaired glucose tolerance compared to lean controls. Notably, HFSC-fed mice developed significantly higher adipose tissue inflammation in parallel with significantly elevated atherosclerotic lesion area compared to those on HFC. Moreover, LDLR^-/- mice on HFSC showed increased insulin resistance and impaired glucose tolerance relative to those on HFC. After prolonged feeding (20 weeks), however, no significant differences in inflammatory and metabolic parameters as well as atherosclerotic lesion formation were detectable any more between LDLR^-/- mice fed HFSC or HFC.

Conclusion

The use of high sucrose rather than more complex carbohydrates in high-fat diets significantly accelerates development of obesity-driven metabolic complications and atherosclerotic plaque formation parallel to obesity-induced adipose tissue inflammation in LDLR^-/- mice. Hence LDLR^-/- mice fed high-fat high-sucrose cholesterol-enriched diet appear to be a suitable and time-saving animal model for cardio-metabolic disease. Moreover our results support the suggested interrelation between adipose tissue inflammation and atherosclerotic plaque formation.

Osteopontin: Versatile modulator of liver diseases

Osteopontin (OPN) is a multifunctional protein, involved in pathological conditions including inflammation, immunity, angiogenesis, fibrosis and cancer progression in various tissues. Hepatic inflammation and fibrosis induced by feeding with a diet deficient in methionine and choline (MCD diet) were markedly attenuated in OPN knockout mice when compared with wild-type mice in the model of non-alcoholic steatohepatitis (NASH). Hepatic cholangiocytes, myofibroblastic stellate cells and natural killer T cells were suggested to secret OPN in mice fed an MCD diet. Plasma and hepatic OPN levels were significantly higher in patients with NASH with advanced fibrosis than in those with early fibrosis. Hepatic OPN mRNA level was correlated with hepatic neutrophil infiltration and fibrosis in patients with alcoholic liver diseases. In those with hepatocellular carcinoma (HCC), OPN levels in plasma and HCC were prognostic factors after liver resection or transplantation. Downregulation of OPN inhibited tumor growth and lung metastasis in nude mice implanted with HCC cells. The single nucleotide polymorphism in the promoter region of the OPN gene was shown to be associated with activity of hepatitis in chronic hepatitis C patients, prognosis in patients with HCC, and growth and lung metastasis of HCC xenografts in nude mice. OPN was reported to be a downstream effecter of Hedgehog pathway, which modulates hepatic fibrosis and carcinogenesis. This review focuses on the roles of OPN in hepatic inflammation, fibrosis and cancer progression. Further elucidation of cellular interactions and molecular mechanisms associated with OPN actions may contribute to development of novel strategies for treatment of the liver diseases.

DISORDER OF INTERCELLULAR CORRELATIONS IN PATHOGENESIS OF FATTY TISSUE INFLAMMATION IN METABOLIC SYNDROME

Due to the fact that nowadays mechanisms of syntropy of pathological conditions and nosological units, united within the metabolic syndrome, remain unclear, the scientific review attempts to summarize data on the role of fatty tissue inflammation in pathogenesis of this symptom complex. The results of recent major foreign studies on evaluation of pro-inflammatory activity of adipocytes and macrophages of the fatty tissue, as well as the data on peculiarities of their interactions in abdominal obesity, which is the main component of the metabolic syndrome, were analyzed. Studing pathogenesis of fatty tissue inflammation from the perspective of evaluation of disorders in cell cooperation will allow to more deeply understand cellular and molecular mechanisms of this process as well as open new avenues for developing new pathogenetically justified approaches to metabolic syndrome treatment.

Differential responses of hepatic endoplasmic reticulum stress and inflammation in diet-induced obese rats with high-fat diet rich in lard oil or soybean oil

Scopes

To investigate the effects of high-fat diet enriched with lard oil or soybean oil on liver endoplasmic reticulum (ER) stress and inflammation markers in diet-induced obese (DIO) rats and estimate the influence of following low-fat diet feeding.

Methods and Results

Male SD rats were fed with standard low-fat diet (LF, n = 10) and two isoenergentic high-fat diets enriched with lard (HL, n = 45) or soybean oil (HS, n = 45) respectively for 10 weeks. Then DIO rats from HL and HS were fed either high-fat diet continuously (HL/HL, HS/HS) or switched to low-fat diet (HL/LF, HS/LF) for another 8 weeks. Rats in control group were maintained with low-fat diet. Body fat, serum insulin level, HOMA-IR and ectopic lipid deposition in liver were increased in HL/HL and HS/HS compared to control, but increased to a greater extent in HL/HL compared to HS/HS. Markers of ER stress including PERK and CHOP protein expression and phosphorylation of eIF2α were significantly elevated in HL/HL group while phosphorylation of IRE1α and GRP78 protein expression were suppressed in both HL/HL and HS/HS. Besides, inflammatory signals (OPN, TLR2, TLR4 and TNF-α) expressions significantly increased in HL/HL compared to others. Switching to low-fat diet reduced liver fat deposition, HOMA-IR, mRNA expression of TLR4, TNF-α, PERK in both HL/LF and HS/LF, but only decreased protein expression of OPN, PERK and CHOP in HL/LF group. In addition, HL/LF and HS/LF exhibited decreased phosphorylation of eIF2α and increased phosphorylation of IRE1α and GRP78 protein expression when compared with HL/HL and HS/HS respectively.

Conclusions

Lard oil was more deleterious in insulin resistance and hepatic steatosis via promoting ER stress and inflammation responses in DIO rats, which may be attributed to the enrichment of saturated fatty acid. Low-fat diet was confirmed to be useful in recovering from impaired insulin sensitivity and liver fat deposition in this study.

Human and experimental evidence supporting a role for osteopontin in alcoholic hepatitis

We identified, in the transcriptome analysis of patients with alcoholic hepatitis (AH), osteopontin (OPN) as one of the most up-regulated genes. Here, we used a translational approach to investigate its pathogenic role. OPN hepatic gene expression was quantified in patients with AH and other liver diseases. OPN protein expression and processing were assessed by immmunohistochemistry, western blotting and enzyme-linked immunosorbent assay. OPN gene polymorphisms were evaluated in patients with alcoholic liver disease. The role of OPN was evaluated in OPN(-/-) mice with alcohol-induced liver injury. OPN biological actions were studied in human hepatic stellate cells (HSCs) and in precision-cut liver slices. Hepatic expression and serum levels of OPN were markedly increased in AH, compared to normal livers and other types of chronic liver diseases, and correlated with short-term survival. Serum levels of OPN also correlated with hepatic expression and disease severity. OPN was mainly expressed in areas with inflammation and fibrosis. Two proteases that process OPN (thrombin and matrix metalloproteinase 7) and cleaved OPN were increased in livers with AH. Patients with AH had a tendency of a lower frequency of the CC genotype of the +1239C single-nucleotide polymorphism of the OPN gene, compared to patients with alcohol abuse without liver disease. Importantly, OPN(-/-) mice were protected against alcohol-induced liver injury and showed decreased expression of inflammatory cytokines. Finally, OPN was induced by lipopolysaccharide and stimulated inflammatory actions in HSCs.

CONCLUSION

Human and experimental data suggest a role for OPN in the pathogenesis of AH. Further studies should evaluate OPN as a potential therapeutic target.

Bone metabolism regulators and arterial stiffness in postmenopausal women

BACKGROUND

Osteoprotegerin (OPG), osteopontin (OPN) and matrix Gla protein (MGP) are markers of bone metabolism but they are also involved in vascular calcification. However, their precise role is not completely understood. Arterial stiffness is considered an independent predictor of cardiovascular events and it may be one of the causes of the increased cardiovascular risk associated with postmenopausal status. Medial and intimal calcification may increase arterial stiffness. The aim of our study was to assess the relationship of OPG, OPN and MGP with aortic pulse wave velocity (aPWV) as a marker of arterial stiffness in postmenopausal women.

MATERIALS AND METHODS

Circulating OPG, OPN and serum total MGP were measured in 144 postmenopausal women using the enzyme-linked immunosorbent assay method. Aortic PWV was determined by an oscillometric method.

RESULTS

Osteoprotegerin correlated with age (p<0.001, r=0.27), aPWV (p<0.001, r=0.32) and hypersensitive C reactive protein (hsCRP) (p<0.001, r=0.37), OPN correlated directly with hsCRP (p<0.001, r=0.39) and inversely with high density lipoprotein cholesterol (p=0.02, r=-0.02). No significant association was found between total MGP and clinical, biochemical and vascular parameters. The correlation between OPG and aPWV persisted even after the adjustment for various potential confounders (p=0.02, r=0.19). In multiple regression analysis in the whole study population the most important predictors of aPWV were OPG (β=0.230, p=0.006), hsCRP (β=0.212, p=0.01) and systolic blood pressure (β=0.163, p=0.04). After exclusion of patients treated with statins the independent predictors were hsCRP (β=0.275, p=0.005) and OPG (β=0.199, p=0.04).

CONCLUSION

Circulating OPG, but not OPN and total MGP, is associated with aPWV and may be a marker of the increased arterial stiffness and cardiovascular risk in postmenopausal women.

Interactions among bone, liver, and adipose tissue predisposing to diabesity and fatty liver

Growing epidemiological evidence connects obesity and its complications, including metabolic syndrome, diabetes, and nonalcoholic fatty liver disease (NAFLD) to reduced bone health and osteoporosis. Parallel to human studies, experimental data disclosed a complex network of interaction among adipose tissue, the liver, and the bone, which reciprocally modulate the function of each other. The main mediators of such crosstalk include hormonal/cytokine signals from the bone (osteopontin, osteocalcin, and osteoprotegerin), the liver (fetuin-A), and adipose tissue [leptin, tumor necrosis factor-α (TNF-α), and adiponectin]. Dysregulation of this network promotes the development of diabesity, NAFLD, and osteoporosis. We will review recent advances in understanding the mechanisms of bone-liver-adipose tissue interaction predisposing to obesity, diabetes, NAFLD, and osteoporosis and their potential clinical implications.

Link between GIP and osteopontin in adipose tissue and insulin resistance

Low-grade inflammation in obesity is associated with accumulation of the macrophage-derived cytokine osteopontin (OPN) in adipose tissue and induction of local as well as systemic insulin resistance. Since glucose-dependent insulinotropic polypeptide (GIP) is a strong stimulator of adipogenesis and may play a role in the development of obesity, we explored whether GIP directly would stimulate OPN expression in adipose tissue and thereby induce insulin resistance. GIP stimulated OPN protein expression in a dose-dependent fashion in rat primary adipocytes. The level of OPN mRNA was higher in adipose tissue of obese individuals (0.13 ± 0.04 vs. 0.04 ± 0.01, P < 0.05) and correlated inversely with measures of insulin sensitivity (r = -0.24, P = 0.001). A common variant of the GIP receptor (GIPR) (rs10423928) gene was associated with a lower amount of the exon 9-containing isoform required for transmembrane activity. Carriers of the A allele with a reduced receptor function showed lower adipose tissue OPN mRNA levels and better insulin sensitivity. Together, these data suggest a role for GIP not only as an incretin hormone but also as a trigger of inflammation and insulin resistance in adipose tissue. Carriers of the GIPR rs10423928 A allele showed protective properties via reduced GIP effects. Identification of this unprecedented link between GIP and OPN in adipose tissue might open new avenues for therapeutic interventions.

Impaired local production of proresolving lipid mediators in obesity and 17-HDHA as a potential treatment for obesity-associated inflammation

Obesity-induced chronic low-grade inflammation originates from adipose tissue and is crucial for obesity-driven metabolic deterioration, including insulin resistance and type 2 diabetes. Chronic inflammation may be a consequence of a failure to actively resolve inflammation and could result from a lack of local specialized proresolving lipid mediators (SPMs), such as resolvins and protectins, which derive from the n-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). We assessed obesity-induced changes of n-3-derived SPMs in adipose tissue and the effects of dietary EPA/DHA thereon. Moreover, we treated obese mice with SPM precursors and investigated the effects on inflammation and metabolic dysregulation. Obesity significantly decreased DHA-derived 17-hydroxydocosahexaenoic acid (17-HDHA, resolvin D1 precursor) and protectin D1 (PD1) levels in murine adipose tissue. Dietary EPA/DHA treatment restored endogenous biosynthesis of n-3-derived lipid mediators in obesity while attenuating adipose tissue inflammation and improving insulin sensitivity. Notably, 17-HDHA treatment reduced adipose tissue expression of inflammatory cytokines, increased adiponectin expression, and improved glucose tolerance parallel to insulin sensitivity in obese mice. These findings indicate that impaired biosynthesis of certain SPM and SPM precursors, including 17-HDHA and PD1, contributes to adipose tissue inflammation in obesity and suggest 17-HDHA as a novel treatment option for obesity-associated complications.

Interaction of osteopontin with IL-18 in obese individuals: implications for insulin resistance

Background/Objective

Osteopontin (OPN) and IL-18 are known inflammatory mediators and both participate in a wide range of biological processes linked to immunological disorders. Since an interaction between OPN and IL-18 has not been studied in obesity, we investigated whether: (i) their levels were simultaneously elevated in obese individuals; (ii) OPN was associated with IL-18 in obese individuals and (iii) their levels associated with fasting blood glucose (FBG) and BMI.

Subjects and Methods

PBMCs and plasma samples were isolated from 60 individuals including lean as well as overweight and obese individuals. Subcutaneous adipose tissue samples were obtained. OPN and IL-18 were measured by ELISA. OPN and IL-18 mRNA expression was quantified by real time quantitative RT-PCR.

Results

Obese individuals exhibited significantly increased circulating OPN levels as compared with lean individuals (obese 2865±101; lean 1681±116 pg/ml; P<0.0001). IL-18 levels were also high in obese individuals (obese 491±39, lean 301±26 pg/ml; P = 0.0009). OPN and IL-18 expression were simultaneously up-regulated (OPN: 5.4-Fold; IL-18: 8.9-Fold; P<0.05) in PBMCs from obese individuals compared to lean group. Adipose tissue from obese individuals had high expression of OPN (7.3-Fold) and IL-18 (9.6-Fold). Plasma OPN levels correlated positively with FBG levels (r = 0.32, P = 0.02). Similarly, IL-18 correlated positively with FBG levels (r = 0.406, P = 0.0042). Stepwise multiple regression analysis showed an independent association of BMI with OPN and IL-18. Interestingly, OPN levels increased progressively with an increase in IL-18 levels (r = 0.52, P = 0.0004). We also examined the regulatory role of IL-18 in OPN secretion from PBMCs. Neutralizing anti-IL-18Rα mAb reduced OPN secretion.

Conclusion

These findings represent the first observation that plasma, PBMC and adipose tissue OPN and IL-18 are simultaneously increased and correlate with each other in overweight/obese individuals which may trigger the development of obesity-associated insulin resistance. Moreover, these results provide the direct evidence that IL-18 regulates OPN production in PBMCs.

Peripheral signalling involved in energy homeostasis control

The alarming prevalence of obesity has led to a better understanding of the molecular mechanisms controlling energy homeostasis. Regulation of energy intake and expenditure is more complex than previously thought, being influenced by signals from many peripheral tissues. In this sense, a wide variety of peripheral signals derived from different organs contributes to the regulation of body weight and energy expenditure. Besides the well-known role of insulin and adipokines, such as leptin and adiponectin, in the regulation of energy homeostasis, signals from other tissues not previously thought to play a role in body weight regulation have emerged in recent years. The role of fibroblast growth factor 21 (FGF21), insulin-like growth factor 1 (IGF-I), and sex hormone-binding globulin (SHBG) produced by the liver in the regulation of body weight and insulin sensitivity has been recently described. Moreover, molecules expressed by skeletal muscle such as myostatin have also been involved in adipose tissue regulation. Better known is the involvement of ghrelin, cholecystokinin, glucagon-like peptide 1 (GLP-1) and PYY(3-36), produced by the gut, in energy homeostasis. Even the kidney, through the production of renin, appears to regulate body weight, with mice lacking this hormone exhibiting resistance to diet-induced obesity. In addition, the skeleton has recently emerged as an endocrine organ, with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The comprehension of these signals will help in a better understanding of the aetiopathology of obesity, contributing to the potential development of new therapeutic targets aimed at tackling excess body fat accumulation.

Gene silencing in adipose tissue macrophages regulates whole-body metabolism in obese mice

Adipose tissue (AT) inflammation and infiltration by macrophages is associated with insulin resistance and type 2 diabetes in obese humans, offering a potential target for therapeutics. However, whether AT macrophages (ATMs) directly contribute to systemic glucose intolerance has not been determined. The reason is the lack of methods to ablate inflammatory genes expressed in macrophages specifically localized within AT depots, leaving macrophages in other tissues unaffected. Here we report that i.p. administration of siRNA encapsulated by glucan shells in obese mice selectively silences genes in epididymal ATMs, whereas macrophages within lung, spleen, kidney, heart, skeletal muscle, subcutaneous (SubQ) adipose, and liver are not targeted. Such administration of GeRPs to silence the inflammatory cytokines TNF-α or osteopontin in epididymal ATMs of obese mice caused significant improvement in glucose tolerance. These data are consistent with the hypothesis that cytokines produced by ATMs can exacerbate whole-body glucose intolerance.

Targeted deletion of growth hormone (GH) receptor in macrophage reveals novel osteopontin-mediated effects of GH on glucose homeostasis and insulin sensitivity in diet-induced obesity

We investigated GH action on macrophage (MΦ) by creating a MΦ-specific GH receptor-null mouse model (MacGHR KO). On a normal diet (10% fat), MacGHR KO and littermate controls exhibited similar growth profiles and glucose excursions on intraperitoneal glucose (ipGTT) and insulin tolerance (ITT) tests. However, when challenged with high fat diet (HFD, 45% fat) for 18 weeks, MacGHR KO mice exhibited impaired ipGTT and ITT compared with controls. In MacGHR KO, adipose-tissue (AT) MΦ abundance was increased with skewing toward M1 polarization. Expression of pro-inflammatory cytokines (IL1β, TNF-α, IL6, and osteopontin (OPN)) were increased in MacGHR KO AT stromal vascular fraction (SVF). In MacGHR KO AT, crown-like-structures were increased with decreased insulin-dependent Akt phosphorylation. The abundance of phosphorylated NF-κB and of OPN was increased in SVF and bone-marrow-derived MΦ in MacGHR KO. GH, acting via an NF-κB site in the distal OPN promoter, inhibited the OPN promoter. Thus in diet-induced obesity (DIO), lack of GH action on the MΦ exerts an unexpected deleterious effect on glucose homeostasis by accentuating AT inflammation and NF-κB-dependent activation of OPN expression. These novel results in mice support the possibility that administration of GH could have salutary effects on DIO-associated chronic inflammation and insulin resistance in humans.

Osteopontin-dependent regulation of Th1 and Th17 cytokine responses in Trypanosoma cruzi-infected C57BL/6 mice

Osteopontin (OPN) is a multifunctional protein participating in the regulation of different Th cell lineages and critically involved in the initiation of immune responses to diverse pathogens. Our study goal was to verify whether OPN helps modulate the protective Th1 and Th17 cytokine responses in C57BL/6 mice infected with Trypanosoma cruzi, the etiological agent of Chagas disease. Parasite infection induced OPN release from murine macrophages in vitro and acute Chagas mice displayed enhanced serum levels of this cytokine at the peak of parasitemia. Upon administration of a neutralizing anti-OPN antibody, recently infected mice presented lower Th1 and Th17 responses, increased parasitemia and succumbed earlier and at higher rates to infection than non-immune IgG-receiving controls. The anti-OPN therapy also resulted in reduced circulating levels of IL-12 p70, IFN-γ, IL-17A and specific IgG(2a) antibodies. Furthermore, antibody-mediated blockade of OPN activity abrogated the ex vivo production of IL-12 p70, IFN-γ and IL-17A, while promoting IL-10 secretion, by spleen macrophages and CD4(+) T cells from T. cruzi-infected mice. Th1 and Th17 cytokine release induced by OPN preferentially involved the α(v)β(3) integrin OPN receptor, whereas concomitant down-modulation of IL-10 production would mostly depend on OPN interaction with CD44. Our findings suggest that, in resistant C57BL/6 mice, elicitation of protective Th1 and Th17 cytokine responses to T. cruzi infection is likely to be regulated by endogenous OPN.

Regulation of the pro-inflammatory cytokine osteopontin by GIP in adipocytes--a role for the transcription factor NFAT and phosphodiesterase 3B

The incretin - glucose-dependent insulinotropic polypeptide (GIP) - and the pro-inflammatory cytokine osteopontin are known to have important roles in the regulation of adipose tissue functions. In this work we show that GIP stimulates lipogenesis and osteopontin expression in primary adipocytes. The GIP-induced increase in osteopontin expression was inhibited by the NFAT (the transcription factor nuclear factor of activated T-cells) inhibitor A-285222. Also, the NFAT kinase glycogen synthase kinase (GSK) 3 was upregulated by GIP. To test whether cAMP might be involved in GIP-mediated effects on osteopontin a number of strategies were used. Thus, the β3-adrenergic receptor agonist CL316,243 stimulated osteopontin expression, an effects which was mimicked by OPC3911, a specific inhibitor of phosphodiesterase 3. Furthermore, treatment of phosphodiesterase 3B knock-out mice with CL316,243 resulted in a dramatic upregulation of osteopontin in adipose tissue which was not the case in wild-type mice. In summary, we delineate mechanisms by which GIP stimulates osteopontin in adipocytes. Given the established link between osteopontin and insulin resistance, our data suggest that GIP by stimulating osteopontin expression, also could promote insulin resistance in adipocytes.

Glucagon-like peptide-1 inhibits adipose tissue macrophage infiltration and inflammation in an obese mouse model of diabetes

AIMS/HYPOTHESIS

Obesity and insulin resistance are associated with low-grade chronic inflammation. Glucagon-like peptide-1 (GLP-1) is known to reduce insulin resistance. We investigated whether GLP-1 has anti-inflammatory effects on adipose tissue, including adipocytes and adipose tissue macrophages (ATM).

METHODS

We administered a recombinant adenovirus (rAd) producing GLP-1 (rAd-GLP-1) to an ob/ob mouse model of diabetes. We examined insulin sensitivity, body fat mass, the infiltration of ATM and metabolic profiles. We analysed the mRNA expression of inflammatory cytokines, lipogenic genes, and M1 and M2 macrophage-specific genes in adipose tissue by real-time quantitative PCR. We also examined the activation of nuclear factor κB (NF-κB), extracellular signal-regulated kinase 1/2 and Jun N-terminal kinase (JNK) in vivo and in vitro.

RESULTS

Fat mass, adipocyte size and mRNA expression of lipogenic genes were significantly reduced in adipose tissue of rAd-GLP-1-treated ob/ob mice. Macrophage populations (F4/80(+) and F4/80(+)CD11b(+)CD11c(+) cells), as well as the expression and production of IL-6, TNF-α and monocyte chemoattractant protein-1, were significantly reduced in adipose tissue of rAd-GLP-1-treated ob/ob mice. Expression of M1-specific mRNAs was significantly reduced, but that of M2-specific mRNAs was unchanged in rAd-GLP-1-treated ob/ob mice. NF-κB and JNK activation was significantly reduced in adipose tissue of rAd-GLP-1-treated ob/ob mice. Lipopolysaccharide-induced inflammation was reduced by the GLP-1 receptor agonist, exendin-4, in 3T3-L1 adipocytes and ATM.

CONCLUSIONS/INTERPRETATION

We suggest that GLP-1 reduces macrophage infiltration and directly inhibits inflammatory pathways in adipocytes and ATM, possibly contributing to the improvement of insulin sensitivity.

Differential effects of high-fat-diet rich in lard oil or soybean oil on osteopontin expression and inflammation of adipose tissue in diet-induced obese rats

PURPOSE

To examine the effect of different dietary fat types on osteopontin (OPN) expressions and inflammation of adipose tissues in diet-induced obese rats.

METHODS

Male Sprague-Dawley rats were randomly assigned to one control group fed standard diet (LF, n = 10) and two high-fat diet groups fed isoenergy diet rich in lard or soybean oil (HL or HS, n = 45 each). Diet-induced obese rats in HL and HS group were then subdivided into two groups either continuously fed high-fat diet or switched to low-fat diet for 8 more weeks. Fasting serum glucose, insulin, and OPN concentrations were assayed and QUICKI was calculated; the expression of OPN, IL-6, IL-10, TNF-α, NF-κB, and F4/80 in adipose tissue was determined.

RESULTS

Both high-fat diets lead to comparable development of obesity characterized by insulin resistance and adipose tissue inflammation. Obese rats continuously fed high-fat diet rich in lard oil exhibited the highest fasting serum insulin level and adipose tissue OPN, F4/80, TNF-α, and NF-κB expression level. In both high-fat diet groups, switching to low-fat diet resulted in less intra-abdominal fat mass, decreased expression of F4/80, TNF-α, and NF-κB, while decreased OPN expression was only observed in lard oil fed rats after switching to low-fat diet.

CONCLUSIONS

Reducing diet fat or replacing lard oil with soybean oil in high-fat diet alleviates obesity-related inflammation and insulin resistance by attenuating the upregulation of OPN and macrophage infiltration into adipose tissue induced by high-fat diet.

Distinct effects of calorie restriction on adipose tissue cytokine and angiogenesis profiles in obese and lean mice

Background

Obesity associates with low-grade inflammation and adipose tissue remodeling. Using sensitive high-throughput protein arrays we here investigated adipose tissue cytokine and angiogenesis-related protein profiles from obese and lean mice, and in particular, the influence of calorie restriction (CR).

Methods

Tissue samples from visceral fat were harvested from obese mice fed with a high-fat diet (60% of energy), lean controls receiving low-fat control diet as well as from obese and lean mice kept under CR (energy intake 70% of ad libitum intake) for 50 days. Protein profiles were analyzed using mouse cytokine and angiogenesis protein array kits.

Results

In obese and lean mice, CR was associated with 11.3% and 15.6% reductions in body weight, as well as with 4.0% and 4.6% reductions in body fat percentage, respectively. Obesity induced adipose tissue cytokine expressions, the most highly upregulated cytokines being IL-1ra, IL-2, IL-16, MCP-1, MIG, RANTES, C5a, sICAM-1 and TIMP-1. CR increased sICAM-1 and TIMP-1 expression both in obese and lean mice. Overall, CR showed distinct effects on cytokine expressions; in obese mice CR largely decreased but in lean mice increased adipose tissue cytokine expressions. Obesity was also associated with increased expressions of angiogenesis-related proteins, in particular, angiogenin, endoglin, endostatin, endothelin-1, IGFBP-3, leptin, MMP-3, PAI-1, TIMP-4, CXCL16, platelet factor 4, DPPIV and coagulation factor III. CR increased endoglin, endostatin and platelet factor 4 expressions, and decreased IGFBP-3, NOV, MMP-9, CXCL16 and osteopontin expressions both in obese and lean mice. Interestingly, in obese mice, CR decreased leptin and TIMP-4 expressions, whereas in lean mice their expressions were increased. CR decreased MMP-3 and PAI-1 only in obese mice, whereas CR decreased FGF acidic, FGF basic and coagulation factor III, and increased angiogenin and DPPIV expression only in lean mice.

Conclusions

CR exerts distinct effects on adipocyte cytokine and angiogenesis profiles in obese and lean mice. Our study also underscores the importance of angiogenesis-related proteins and cytokines in adipose tissue remodeling and development of obesity.

The osteopontin level in liver, adipose tissue and serum is correlated with fibrosis in patients with alcoholic liver disease

Background

Osteopontin (OPN) plays an important role in the progression of chronic liver diseases. We aimed to quantify the liver, adipose tissue and serum levels of OPN in heavy alcohol drinkers and to compare them with the histological severity of hepatic inflammation and fibrosis.

Methodology/Principal Findings

OPN was evaluated in the serum of a retrospective and prospective group of 109 and 95 heavy alcohol drinkers, respectively, in the liver of 34 patients from the retrospective group, and in the liver and adipose tissue from an additional group of 38 heavy alcohol drinkers. Serum levels of OPN increased slightly with hepatic inflammation and progressively with the severity of hepatic fibrosis. Hepatic OPN expression correlated with hepatic inflammation, fibrosis, TGFβ expression, neutrophils accumulation and with the serum OPN level. Interestingly, adipose tissue OPN expression also correlated with hepatic fibrosis even after 7 days of alcohol abstinence. The elevated serum OPN level was an independent risk factor in estimating significant (F≥2) fibrosis in a model combining alkaline phosphatase, albumin, hemoglobin, OPN and FibroMeter® levels. OPN had an area under the receiving operator curve that estimated significant fibrosis of 0.89 and 0.88 in the retrospective and prospective groups, respectively. OPN, Hyaluronate (AUROC: 0.88), total Cytokeratin 18 (AUROC: 0.83) and FibroMeter® (AUROC: 0.90) estimated significance to the same extent in the retrospective group. Finally, the serum OPN levels also correlated with hepatic fibrosis and estimated significant (F≥2) fibrosis in 86 patients with chronic hepatitis C, which suggested that its elevated level could be a general response to chronic liver injury.

Conclusion/Significance

OPN increased in the liver, adipose tissue and serum with liver fibrosis in alcoholic patients. Further, OPN is a new relevant biomarker for significant liver fibrosis. OPN could thus be an important actor in the pathogenesis of this chronic liver disease.

Adipose tissue gene expression analysis reveals changes in inflammatory, mitochondrial respiratory and lipid metabolic pathways in obese insulin-resistant subjects

Background

To get insight into molecular mechanisms underlying insulin resistance, we compared acute in vivo effects of insulin on adipose tissue transcriptional profiles between obese insulin-resistant and lean insulin-sensitive women.

Methods

Subcutaneous adipose tissue biopsies were obtained before and after 3 and 6 hours of intravenously maintained euglycemic hyperinsulinemia from 9 insulin-resistant and 11 insulin-sensitive females. Gene expression was measured using Affymetrix HG U133 Plus 2 microarrays and qRT-PCR. Microarray data and pathway analyses were performed with Chipster v1.4.2 and by using in-house developed nonparametric pathway analysis software.

Results

The most prominent difference in gene expression of the insulin-resistant group during hyperinsulinemia was reduced transcription of nuclear genes involved in mitochondrial respiration (mitochondrial respiratory chain, GO:0001934). Inflammatory pathways with complement components (inflammatory response, GO:0006954) and cytokines (chemotaxis, GO:0042330) were strongly up-regulated in insulin-resistant as compared to insulin-sensitive subjects both before and during hyperinsulinemia. Furthermore, differences were observed in genes contributing to fatty acid, cholesterol and triglyceride metabolism (FATP2, ELOVL6, PNPLA3, SREBF1) and in genes involved in regulating lipolysis (ANGPTL4) between the insulin-resistant and -sensitive subjects especially during hyperinsulinemia.

Conclusions

The major finding of this study was lower expression of mitochondrial respiratory pathway and defective induction of lipid metabolism pathways by insulin in insulin-resistant subjects. Moreover, the study reveals several novel genes whose aberrant regulation is associated with the obese insulin-resistant phenotype.

Role and function of macrophages in the metabolic syndrome

Macrophages are key innate immune effector cells best known for their role as professional phagocytes, which also include neutrophils and dendritic cells. Recent evidence indicates that macrophages are also key players in metabolic homoeostasis. Macrophages can be found in many tissues, where they respond to metabolic cues and produce pro- and/or anti-inflammatory mediators to modulate metabolite programmes. Certain metabolites, such as fatty acids, ceramides and cholesterol crystals, elicit inflammatory responses through pathogen-sensing signalling pathways, implicating a maladaptation of macrophages and the innate immune system to elevated metabolic stress associated with overnutrition in modern societies. The outcome of this maladaptation is a feedforward inflammatory response leading to a state of unresolved inflammation and a collection of metabolic pathologies, including insulin resistance, fatty liver, atherosclerosis and dyslipidaemia. The present review summarizes what is known about the contributions of macrophages to metabolic diseases and the signalling pathways that are involved in metabolic stress-induced macrophage activation. Understanding the role of macrophages in these processes will help us to develop therapies against detrimental effects of the metabolic syndrome.

The combined treatment of praziquantel with osteopontin immunoneutralization reduces liver damage in Schistosoma japonicum-infected mice

The aim of this study was to evaluate the therapeutic effects of osteopontin neutralization treatment on schistosome-induced liver injury in BALB/C mice. We randomly divided 100 BALB/C mice into groups A, B, C, D and group E. Mice in all groups except group A were abdominally infected with schistosomal cercariae to induce a schistosomal hepatopathological model. Mice in group C, D and group E were respectively administered with praziquantel, praziquantel plus colchicine and praziquantel plus neutralizing osteopontin antibody. We extracted mouse liver tissues at 3 and 9 weeks after the 'stool-eggs-positive' day, observed liver histopathological changes by haematoxylin-eosin and Masson trichrome staining and detected the expression of osteopontin, alpha-smooth muscle actin (α-SMA) and transforming growth factor-beta (TGF-β1) by immunohistochemistry, RT-PCR and Western blot. We found that praziquantel plus neutralizing osteopontin antibody treatment significantly decreased the granuloma dimension, the percentage of collagen and the expression of osteopontin, α-SMA and TGF-β1 compared to praziquantel plus colchicine treatment in both the acute and chronic stage of schistosomal liver damage (P<0·05). So we believe that the combined regimen of osteopontin immunoneutralization and anti-helminthic treatment can reduce the granulomatous response and liver fibrosis during the schistosomal hepatopathologic course.

Osteoprotegerin, but not osteopontin, as a potential predictor of vascular calcification in normotensive subjects

We conducted a cross-sectional observation study that included 500 asymptomatic subjects to investigate the relationship between bone metabolism and coronary artery calcification (CAC) in hypertensive conditions. Osteoprotegerin (OPG) and osteopontin (OPN) levels and their associations with hypertension were analyzed to predict CAC in 316 subjects. Multislice computed tomography was used to quantify CAC. Multivariate analysis of variance was used to test the non-interactive effects of hypertension, CAC severity and biomarker levels, and the logistic regression model was applied to predict the risk of CAC. OPG and OPN concentrations were significantly higher in the hypertensive than the normotensive subjects, at 3.0 (2.3-4.0) pmol l(-1) and 51 (21-136) ng ml(-1) vs. 2.4 (2.0-3.0) pmol l(-1) and 41 (13-63) ng ml(-1), respectively. The OPG level, but not OPN level, increased with age (r = 0.29; P = 0.0001). Zero or minimal CAC (<10 Agatston units (AU)) was observed in 63% of the subjects, mild (11-100 AU) in 17%, moderate (101-400 AU) in 12% and severe (401-1000 AU)-to-extensive (>1000 AU) in 8%. In hypertensive subjects, only glomerular filtration rate (GFR) (β = -0.67) and gender (β = 0.52) were significant predictors for CAC (R = 0.68). In normotensive patients, GFR (β = -0.81), gender (β = 0.48) and log-transformed OPG levels (β = 0.15) were significant predictors for CAC. OPG levels were associated with an increased risk of CAC in normotensive subjects only (odds ratio: 3.37; 95% confidence interval (1.63-6.57); P = 0.0002). OPG predicted a premature state of vascular calcification in asymptomatic normotensive individuals, and renal function significantly contributed to this process in both hypertensive and normotensive subjects.

Toll-like receptors 2 and 4 impair insulin-mediated brain activity by interleukin-6 and osteopontin and alter sleep architecture

Impaired insulin action in the brain represents an early step in the progression toward type 2 diabetes, and elevated levels of saturated free fatty acids are known to impair insulin action in prediabetic subjects. One potential mediator that links fatty acids to inflammation and insulin resistance is the Toll-like receptor (TLR) family. Therefore, C3H/HeJ/TLR2-KO (TLR2/4-deficient) mice were fed a high-fat diet (HFD), and insulin action in the brain as well as cortical and locomotor activity was analyzed by using telemetric implants. TLR2/4-deficient mice were protected from HFD-induced glucose intolerance and insulin resistance in the brain and displayed an improvement in cortical and locomotor activity that was not observed in C3H/HeJ mice. Sleep recordings revealed a 42% increase in rapid eye movement sleep in the deficient mice during daytime, and these mice spent 41% more time awake during the night period. Treatment of control mice with a neutralizing IL-6 antibody improved insulin action in the brain as well as cortical activity and diminished osteopontin protein to levels of the TLR2/4-deficient mice. Together, our data suggest that the lack of functional TLR2/4 protects mice from a fat-mediated impairment in insulin action, brain activity, locomotion, and sleep architecture by an IL-6/osteopontin-dependent mechanism.

Reproductive tissues maintain insulin sensitivity in diet-induced obesity

Reproductive dysfunction is associated with obesity. We previously showed that female mice with diet-induced obesity (DIO) exhibit infertility and thus serve as a model of human polycystic ovary syndrome (PCOS). We postulated that differential insulin signaling of tissues leads to reproductive dysfunction; therefore, a comparison of insulin signaling in reproductive tissues and energy storage tissues was performed. Pituitary-specific insulin receptor knockout mice were used as controls. High-fat diet-induced stress, which leads to insulin resistance, was also investigated by assaying macrophage infiltration and phosphorylated Jun NH(2)-terminal kinase (pJNK) signaling. In lean mice, reproductive tissues exhibited reduced sensitivity to insulin compared with peripheral metabolic tissues. However, in obese mice, where metabolic tissues exhibited insulin resistance, the pituitary and ovary maintained insulin sensitivity. Pituitaries responded to insulin through insulin receptor substrate (IRS)2 but not IRS1, whereas in the ovary, both IRS1 and IRS2 were activated by insulin. Macrophage infiltration and pJNK signaling were not increased in the pituitary or ovary of lean mice relative to DIO mice. The lack of inflammation and cytokine signaling in the pituitary and ovary in DIO mice compared with lean mice may be one of the reasons that these tissues remained insulin sensitive. Retained sensitivity of the pituitary and ovary to insulin may contribute to the pathophysiology of PCOS.

Osteopontin deficiency protects against obesity-induced hepatic steatosis and attenuates glucose production in mice

AIMS/HYPOTHESIS

Obesity is strongly associated with the development of non-alcoholic fatty liver disease (NAFLD). The cytokine osteopontin (OPN) was recently shown to be involved in obesity-induced adipose tissue inflammation and reduced insulin response. Accumulating evidence links OPN to the pathogenesis of NAFLD. Here we aimed to identify the role of OPN in obesity-associated hepatic steatosis and impaired hepatic glucose metabolism.

METHODS

Wild-type (WT) and Opn (also known as Spp1) knockout (Opn (-/-)) mice were fed a high-fat or low-fat diet to study OPN effects in obesity-driven hepatic alterations.

RESULTS

We show that genetic OPN deficiency protected from obesity-induced hepatic steatosis, at least in part, by downregulating hepatic triacylglycerol synthesis. Conversely, absence of OPN promoted fat storage in adipose tissue thereby preventing the obesity-induced shift to ectopic fat accumulation in the liver. Euglycaemic-hyperinsulinaemic clamp studies revealed that insulin resistance and excess hepatic glucose production in obesity were significantly attenuated in Opn (-/-) mice. OPN deficiency markedly improved hepatic insulin signalling as shown by enhanced insulin receptor substrate-2 phosphorylation and prevented upregulation of the major hepatic transcription factor Forkhead box O1 and its gluconeogenic target genes. In addition, obesity-driven hepatic inflammation and macrophage accumulation was blocked by OPN deficiency.

CONCLUSIONS/INTERPRETATION

Our data strongly emphasise OPN as mediator of obesity-associated hepatic alterations including steatosis, inflammation, insulin resistance and excess gluconeogenesis. Targeting OPN action could therefore provide a novel therapeutic strategy to prevent obesity-related complications such as NAFLD and type 2 diabetes.

Transcriptional profiling reveals a role for RORalpha in regulating gene expression in obesity-associated inflammation and hepatic steatosis

Retinoid-related orphan receptor (ROR)α4 is the major RORα isoform expressed in adipose tissues and liver. In this study we demonstrate that RORα-deficient staggerer mice (RORα(sg/sg)) fed with a high-fat diet (HFD) exhibited reduced adiposity and hepatic triglyceride levels compared with wild-type (WT) littermates and were resistant to the development of hepatic steatosis, adipose-associated inflammation, and insulin resistance. Gene expression profiling showed that many genes involved in triglyceride synthesis and storage, including Cidec, Cidea, and Mogat1, were expressed at much lower levels in liver of RORα(sg/sg) mice. In contrast, overexpression of RORα in mouse hepatoma Hepa1-6 cells significantly increased the expression of genes that were repressed in RORα(sg/sg) liver, including Sult1b1, Adfp, Cidea, and ApoA4. ChIP and promoter analysis suggested that several of these genes were regulated directly by RORα. In addition to reduced lipid accumulation, inflammation was greatly diminished in white adipose tissue (WAT) of RORα(sg/sg) mice fed with an HFD. The infiltration of macrophages and the expression of many immune response and proinflammatory genes, including those encoding various chemo/cytokines, Toll-like receptors, and TNF signaling proteins, were significantly reduced in RORα(sg/sg) WAT. Moreover, RORα(sg/sg) mice fed with an HFD were protected from the development of insulin resistance. RORα(sg/sg) mice consumed more oxygen and produced more carbon dioxide, suggesting increased energy expenditure in this genotype. Our study indicates that RORα plays a critical role in the regulation of several aspects of metabolic syndrome. Therefore, RORα may provide a novel therapeutic target in the management of obesity and associated metabolic diseases.

Osteopontin in macrophage function

The secreted phosphorylated protein osteopontin (OPN) is expressed in a variety of tissues and bodily fluids, and is associated with pathologies including tissue injury, infection, autoimmune disease and cancer. Macrophages are ubiquitous, heterogeneous cells that mediate aspects of cell and tissue damage in all these pathologies. Here, the role of OPN in macrophage function is reviewed. OPN is expressed in macrophage cells in multiple pathologies, and the regulation of its expression in these cells has been described in vitro. The protein has been implicated in multiple functions of macrophages, including cytokine expression, expression of inducible nitric oxide synthase, phagocytosis and migration. Indeed, the role of OPN in cells of the macrophage lineage might underlie its physiological role in many pathologies. However, there are numerous instances where the published literature is inconsistent, especially in terms of OPN function in vitro. Although the heterogeneity of OPN and its receptors, or of macrophages themselves, might underlie some of these inconsistencies, it is important to understand the role of OPN in macrophage biology in order to exploit its function therapeutically.

Osteopontin is required for the early onset of high fat diet-induced insulin resistance in mice

BACKGROUND

Insulin resistance is manifested in muscle, adipose tissue, and liver and is associated with adipose tissue inflammation. The cellular components and mechanisms that regulate the onset of diet-induced insulin resistance are not clearly defined.

METHODOLOGY AND PRINCIPAL FINDINGS

We initially observed osteopontin (OPN) mRNA over-expression in adipose tissue of obese, insulin resistant humans and rats which was normalized by thiazolidinedione (TZD) treatment in both species. OPN regulates inflammation and is implicated in pathogenic maladies resulting from chronic obesity. Thus, we tested the hypothesis that OPN is involved in the early development of insulin resistance using a 2-4 week high fat diet (HFD) model. OPN KO mice fed HFD for 2 weeks were completely protected from the severe skeletal muscle, liver and adipose tissue insulin resistance that developed in wild type (WT) controls, as determined by hyperinsulinemic euglycemic clamp and acute insulin-stimulation studies. Although two-week HFD did not alter body weight or plasma free fatty acids and cytokines in either strain, HFD-induced hyperleptinemia, increased adipose tissue inflammation (macrophages and cytokines), and adipocyte hypertrophy were significant in WT mice and blunted or absent in OPN KO mice. Adipose tissue OPN protein isoform expression was significantly altered in 2- and 4-week HFD-fed WT mice but total OPN protein was unchanged. OPN KO bone marrow stromal cells were more osteogenic and less adipogenic than WT cells in vitro. Interestingly, the two differentiation pathways were inversely affected by HFD in WT cells in vitro.

CONCLUSIONS

The OPN KO phenotypes we report reflect protection from insulin resistance that is associated with changes in adipocyte biology and adipose tissue inflammatory status. OPN is a key component in the development of HFD-induced insulin resistance.

Newly identified adipose tissue macrophage populations in obesity with distinct chemokine and chemokine receptor expression

OBJECTIVE

Infiltration by macrophages is a hallmark of obesity-related adipose tissue (AT) inflammation that is tightly linked to insulin resistance. Although CD11c+ AT macrophages (ATMs) have recently been shown to promote inflammation in obese mice, the knowledge on phenotype and function of different ATM populations is still very limited. This study aimed at identifying and characterizing ATM populations in obesity.

METHODS

Isolation of ATM populations defined by CD11c and mannose receptor (MR) expression and analysis of gene expression in high-fat diet-induced obese mice.

RESULTS

Obesity provoked a shift from a predominant MR+CD11c⁻ population ('MR-ATM') to two MR⁻ populations, namely MR⁻CD11c+ ('CD11c-ATM') and MR⁻CD11c⁻ (double negative, 'DN-ATM'). Although CD11c-ATMs were of a clear inflammatory M1 phenotype, DN-ATMs expressed few inflammatory mediators and highly expressed genes for alternative activation (M2) markers involved in tissue repair, such as arginase and YM1. In contrast, MR-ATMs marginally expressed M1 and M2 markers but highly expressed chemokines, including Mcp-1 (Ccl2) and Mcp-3 (Ccl7). Both CD11c-ATMs and DN-ATMs, but not MR-ATM, highly expressed a panel of chemokine receptors (namely Ccr2, Ccr5, Ccr3 and Cx3cr1), whereas the expression of Ccr7 and Ccr9 was selective for CD11c-ATMs and DN-ATMs, respectively. Notably, stressed adipocytes upregulated various chemokines capable of attracting CD11c-ATM and DN-ATM.

CONCLUSION

This study identifies a novel ATM population with a putatively beneficial role in AT inflammation. This DN-ATM population could be attracted to the obese AT by similar chemokines such as inflammatory CD11c-ATM, on which only Ccr7 is uniquely expressed.