Neutralization of osteopontin inhibits obesity-induced inflammation and insulin resistance

Extracellular Matrix Remodeling of Adipose Tissue in Obesity and Metabolic Diseases

The extracellular matrix (ECM) is a network of different proteins and proteoglycans that controls differentiation, migration, repair, survival, and development, and it seems that its remodeling is required for healthy adipose tissue expansion. Obesity drives an excessive lipid accumulation in adipocytes, which provokes immune cells infiltration, fibrosis (an excess of deposition of ECM components such as collagens, elastin, and fibronectin) and inflammation, considered a consequence of local hypoxia, and ultimately insulin resistance. To understand the mechanism of this process is a challenge to treat the metabolic diseases. This review is focused at identifying the putative role of ECM in adipose tissue, describing its structure and components, its main tissue receptors, and how it is affected in obesity, and subsequently the importance of an appropriate ECM remodeling in adipose tissue expansion to prevent metabolic diseases.

Increased plasma osteopontin levels are associated with nonalcoholic fatty liver disease in patients with type 2 diabetes mellitus

Nonalcoholic fatty liver disease (NAFLD) commonly occurs in patients with type 2 diabetes mellitus (T2DM). Osteopontin (OPN) is a multifunctional protein with pleiotropic physiological functions. This study aimed to investigate the interrelation between circulating OPN and NAFLD in T2DM patients. Overall, 249 subjects were classified into 4 groups: 53 patients with NAFLD and T2DM; 57 with newly diagnosed T2DM; 59 with NAFLD; and 80 healthy age- and sex-matched controls. Serum OPN was measured by ELISA. The OPN distribution in the pooled data was divided into quartiles; significant trends across increasing quartiles were estimated by the Cochran-Armitage trend test. Compared with the controls, circulating OPN concentrations were significantly elevated in NAFLD patients and T2DM patients with or without NAFLD. Serum OPN levels were higher in the overweight/obese group than that in the lean group. Circulating OPN levels were positively correlated with CRP, age, BMI, SBP, DBP, HbA1c, UA, TGs, WBCs, neutrophils, FBG, and HOMA-IR and negatively correlated with ADP, albumin and HDL. Age, albumin, HbA1c, HDL and hsCRP were independently related to circulating OPN. The relative risks for NAFLD, T2DM and T2DM with NAFLD increased significantly along with increasing OPN quartiles based on the Cochran-Armitage trend test. OPN is an optimal predictor in the diagnosis of T2DM with NAFLD and T2DM and may contribute to the aggravation of the metabolic state.

Transcriptome profiling of brain myeloid cells revealed activation of Itgal, Trem1, and Spp1 in western diet-induced obesity

Background

Environmental factors are critical in the development of age-related cognitive decline and dementia. A western diet (WD) can cause nutrient deficiency and inflammation that could impact cognition directly. It is increasingly recognized that innate immune responses by brain myeloid cells, such as resident microglia, and infiltrating peripheral monocytes/macrophages may represent an essential link between a WD, cognitive decline, and dementia. Our previous data demonstrated that chronic consumption of a WD induced inflammation through brain myeloid cells in aging mice and a mouse model of Alzheimer’s disease (AD). However, the subtypes of myeloid cells that contribute to the WD-induced inflammation remain unclear.

Methods

C57BL/6J (B6), myeloid cell reporter mice (B6.Ccr2^RFP/+Cx3cr1^GFP/+), and Ccr2-deficient mice (B6.Ccr2^RFP/RFP) were fed a WD or a control chow diet (CD) from 2 to 6 or 12 months of age. CD11b+CD45^lo and CD11b+CD45^hi cells from WD- and CD-fed B6 or Ccr2-deficient mice were characterized using flow cytometry, RNA-sequencing, and immunofluorescence.

Results

Ccr2::RFP expressing myeloid cells were significantly increased in brains of WD- compared to CD-fed mice, but were not elevated in Ccr2-deficient WD-fed mice. The percent of CD11b+CD45^hi cells was significantly increased in WD- compared to CD-fed mice. Comparison of RNA-sequencing data with immune cell data in ImmGen supports that CD11b+CD45^hi cells from WD-fed mice are enriched for peripheral monocytes and neutrophils. Ingenuity pathway analysis predicted these cells elicit proinflammatory responses that may be damaging to the brain. Using stringent criteria for gene expression levels between CD11b+CD45^hi and CD11b+CD45^lo cells, we identified approximately 70 genes that we predict are uniquely expressed in infiltrating cells, including Itgal, Trem1, and Spp1 (osteopontin, OPN). Finally, we show a significantly greater number of OPN+IBA1– cells in WD- compared to CD-fed mice that we propose are activated neutrophils based on ImmGen data. OPN+IBA1– cells are not significantly increased in Ccr2-deficient WD-fed mice.

Conclusions

These data further support the model that peripheral myeloid cells enter the brain in response to diet-induced obesity. Elucidating their contribution to age-related cognitive decline and age-related neurodegenerative diseases should offer new avenues for therapeutic intervention in Alzheimer’s disease and related dementias, where diet/obesity are major risk factors.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1527-z) contains supplementary material, which is available to authorized users.

Impact of Lipotoxicity on Tissue "Cross Talk" and Metabolic Regulation

Obesity-associated comorbidities include non-alcoholic fatty liver disease, Type 2 diabetes, and cardiovascular disease. These diseases are associated with accumulation of lipids in non-adipose tissues, which can impact many intracellular cellular signaling pathways and functions that have been broadly defined as "lipotoxic." This review moves beyond understanding intracellular lipotoxic outcomes and outlines the consequences of lipotoxicity on protein secretion and inter-tissue "cross talk," and the impact this exerts on systemic metabolism.

Antibody-mediated targeting of cleavage-specific OPN-T cell interactions

T cells are crucial players in obesity-mediated adipose tissue inflammation. We hypothesized that osteopontin (OPN), an inflammatory protein with enhanced activity when proteolytically cleaved, affects the number of viable T cells in adipose tissue and assessed inhibition of the interaction between T cells and thrombin and matrix metalloproteinases-cleaved OPN using antibodies and postimmune sera. Gene expression of T cell markers in adipose tissue from wild-type (wt) and Spp1-/- (OPN deficient) mice was analyzed after 16 weeks of high fat diet (HFD) or low fat diet (LFD) feeding. CD3, CD8 and OPN gene expression in omental adipose tissue from individuals with obesity was measured. OPN-T cell interactions were assessed with a fluorescence-based adhesion assay and blocked with antibodies targeting OPN. Comparison of T cell gene expression in adipose tissue from wt and Spp1-/- mice showed that OPN affected the number of T cells while in humans, levels of OPN correlated with T cell markers in omental adipose tissue. The interaction between T cells and cleaved OPN was blocked by postimmune sera following OPN peptide vaccinations and with monoclonal antibodies. In conclusion, levels of OPN affected the number of T cells in obesity and antibodies against cleaved OPN antagonize OPN-T cell interactions.

Cytokines and Abnormal Glucose and Lipid Metabolism

Clear evidence indicates that cytokines, for instance, adipokines, hepatokines, inflammatory cytokines, myokines, and osteokines, contribute substantially to the development of abnormal glucose and lipid metabolism. Some cytokines play a positive role in metabolism action, while others have a negative metabolic role linking to the induction of metabolic dysfunction. The mechanisms involved are not fully understood, but are associated with lipid accumulation in organs and tissues, especially in the adipose and liver tissue, changes in energy metabolism, and inflammatory signals derived from various cell types, including immune cells. In this review, we describe the roles of certain cytokines in the regulation of metabolism and inter-organ signaling in regard to the pathophysiological aspects. Given the disease-related changes in circulating levels of relevant cytokines, these factors may serve as biomarkers for the early detection of metabolic disorders. Moreover, based on preclinical studies, certain cytokines that can induce improvements in glucose and lipid metabolism and immune response may emerge as novel targets of broader and more efficacious treatments and prevention of metabolic disease.

Comparative Secretome Analyses of Primary Murine White and Brown Adipocytes Reveal Novel Adipokines

The adipose organ, including white and brown adipose tissues, is an important player in systemic energy homeostasis, storing excess energy in form of lipids while releasing energy upon various energy demands. Recent studies have demonstrated that white and brown adipocytes also function as endocrine cells and regulate systemic metabolism by secreting factors that act locally and systemically. However, a comparative proteomic analysis of secreted factors from white and brown adipocytes and their responsiveness to adrenergic stimulation has not been reported yet. Therefore, we studied and compared the secretome of white and brown adipocytes, with and without norepinephrine (NE) stimulation. Our results reveal that carbohydrate-metabolism-regulating proteins are preferably secreted from white adipocytes, while brown adipocytes predominantly secrete a large variety of proteins. Upon NE stimulation, an increased secretion of known adipokines is favored by white adipocytes while brown adipocytes secreted higher amounts of novel adipokines. Furthermore, the secretory response between NE-stimulated and basal state was multifaceted addressing lipid and glucose metabolism, adipogenesis, and antioxidative reactions. Intriguingly, NE stimulation drastically changed the secretome in brown adipocytes. In conclusion, our study provides a comprehensive catalogue of novel adipokine candidates secreted from white and brown adipocytes with many of them responsive to NE. Given the beneficial effects of brown adipose tissue activation on its endocrine function and systemic metabolism, this study provides an archive of novel batokine candidates and biomarkers for activated brown adipose tissue.

Fra-2 Expression in Osteoblasts Regulates Systemic Inflammation and Lung Injury through Osteopontin

Inflammatory responses require mobilization of innate immune cells from the bone marrow. The functionality of this process depends on the state of the bone marrow microenvironment. We therefore hypothesized that molecular changes in osteoblasts, which are essential stromal cells of the bone marrow microenvironment, influence the inflammatory response. Here, we show that osteoblast-specific expression of the AP-1 transcription factor Fra-2 (Fra-2^Ob-tet) induced a systemic inflammatory state with infiltration of neutrophils and proinflammatory macrophages into the spleen and liver as well as increased levels of proinflammatory cytokines, such as interleukin-1β (IL-1β), IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF). By in vivo inhibition of osteopontin (OPN) in Fra-2^Ob-tet mice, we demonstrated that this process was dependent on OPN expression, which mediates alterations of the bone marrow niche. OPN expression was transcriptionally enhanced by Fra-2 and stimulated mesenchymal stem cell (MSC) expansion. Furthermore, in a murine lung injury model, Fra-2^Ob-tet mice showed increased inflammatory responses and more severe disease features via an enhanced and sustained inflammatory response to lipopolysaccharide (LPS). Our findings demonstrate for the first time that molecular changes in osteoblasts influence the susceptibility to inflammation by altering evasion of innate immune cells from the bone marrow space.

Serum levels of osteopontin predict diabetes remission after bariatric surgery

AIM

Bariatric surgery has been shown to effectively improve glycaemic control in morbidly obese subjects. However, the molecular bases of this association are still elusive and may act independently of weight loss. Here, our retrospective study has investigated the inflammatory molecule osteopontin (OPN) as a potential predictor of type 2 diabetes mellitus (T2DM) remission.

METHODS

Baseline serum levels of OPN were analyzed in 41 T2DM patients who underwent bariatric surgery. Anthropometric measures and biochemical variables, including insulin sensitivity indices (HOMA2), were assessed at baseline and at 1 and 3 years after surgery.

RESULTS

At baseline, patients who experienced T2DM remission had increased waist circumference, body weight and BMI, and higher serum OPN, compared with non-remitters. Patients with and without T2DM remission improved their lipid and glucose profiles, although insulin resistance indices were only improved in the T2DM remission group. In the overall cohort of both T2DM remission and non-remission patients, baseline circulating levels of OPN significantly correlated with reductions of body weight and BMI over time, and insulin sensitivity improved as well. However, only the HOMA2-%S remained independently associated with serum OPN on multivariate linear regression analysis (B: 0.227, 95% CI: 0.067-0.387, β = 0.831; P = 0.010). Baseline values of OPN predicted 3-year T2DM remission independently of body weight loss, lower BMI and duration of diabetes (OR: 1.046, 95% CI: 1.004-1.090; P = 0.033).

CONCLUSION

Although larger studies are still needed to confirm our preliminary results, pre-operative OPN serum levels might be useful for predicting 3-year T2DM remission independently of weight loss in patients undergoing bariatric surgery.

The multiple functions and mechanisms of osteopontin

Osteopontin (OPN) is a highly phosphorylated glycophosphoprotein having acidic characteristics and rich in aspartic acid. OPN, a multifunctional protein, has important functions on cardiovascular diseases, cancer, diabetes and kidney stone diseases and in the process of inflammation, biomineralization, cell viability and wound healing. Osteopontin acts on organisms by playing a key role in secretion levels of interleukin-10 (IL-10), interleukin-12 (IL-12), interleukin-3 (IL-3), interferon-γ (IFN-γ), integrin αvB3, nuclear factor kappa B (NF-kB), macrophage and T cells, regulating the osteoclast function and affecting CD44 receptors. The aim of the present review is to address majority of different functions of OPN protein which are known, suspected or suggested through the data obtained about this protein yet.

The Stomach as an Endocrine Organ: Expression of Key Modulatory Genes and Their Contribution to Obesity and Non-alcoholic Fatty Liver Disease (NAFLD)

PURPOSE OF REVIEW

Obesity is currently seen in epidemic proportions globally and is one of the largest contributors to the development of NAFLD. The spectrum of NAFLD, particularly the progressive forms of NASH, is likely to become the leading cause of liver disease in the next decade.

RECENT FINDINGS

Soluble molecules, encoded by the stomach tissue, have been shown to have pleiotropic effects in both central and peripheral systems involved in energy homeostasis and obesity regulation. As such, the stomach is one of the important players in the complex, multi-system deregulation leading to obesity and NAFLD. The understanding of the stomach tissue as an active endocrine organ that contributes to the signaling milieu leading to the development of obesity and NAFLD is crucial.

Identification of novel diagnostic biomarkers for deep venous thrombosis

The combination of a negative D-dimer and a Wells score can rule out, but not confirm, a diagnosis of deep venous thrombosis (DVT). We aimed to identify new diagnostic biomarkers for DVT and to investigate their relationship with hypercoagulability markers [D-dimer and activated protein C-protein C inhibitor (APC-PCI) complex]. We screened 92 cardiovascular-specific proteins in plasma samples from 45 confirmed DVT patients and 45 age- and sex-matched non-DVT patients selected from a prospective multicentre diagnostic management study (SCORE) by Proseek Multiplex CVDIII^96×96 . Plasma levels of 30 proteins were significantly different between DVT and non-DVT patients. After Bonferroni correction, plasma levels of seven proteins: P-selectin, transferrin receptor protein 1, von Willebrand factor, tissue factor pathway inhibitor, osteopontin (OPN), bleomycin hydrolase and ST2 protein remained significantly different. The area under curve (AUC) for these proteins ranged from 0·70 to 0·84. Furthermore, all seven identified proteins were significantly associated with markers of hypercoagulability. A combination of OPN and APC-PCI had the best ability to discriminate DVT from non-DVT patients (AUC = 0·94; sensitivity = 89% and specificity = s84%). In conclusion, we identified multiple proteins associated with markers of hypercoagulability and with a potential to become novel diagnostic biomarkers for DVT.

Circulating osteopontin and its association with liver fat content in non-obese women with polycystic ovary syndrome: a case control study

BACKGROUND

Osteopontin (OPN) plays an important role in inflammatory processes and insulin resistance. Polycystic ovary syndrome (PCOS) is a reproductive metabolic disease associated with insulin resistance and metabolic abnormalities, including high levels of liver fat content (LFC). The objective of this study was to explore whether circulating OPN independently contributes to elevated LFC in non-obese PCOS patients.

METHODS

This study included 61 non-obese PCOS patients and 56 age-matched healthy women from Shanghai, China. After an overnight fast, all participants underwent anthropometric measurements, oral glucose tolerance tests, lipid profile and sex hormone measurements. Quantitative measurement of LFC by ultrasonography was performed. OPN concentrations were measured using ELISA. An independent samples t-test and the Mann-Whitney U test were performed to compare variables between the two groups; one-way ANOVA and Kruskal-Wallis test were performed to compare four subgroups of patients. Correlations were determined by Spearman's correlation tests. Stepwise multiple linear regression analyses were performed to assess for independent contributors. A receiver operating characteristic curve with the maximum Youden index was calculated for the optimal cut-off value.

RESULTS

In non-obese PCOS women, circulating OPN levels were increased in the subgroups with a higher body mass index (BMI) and free androgen index (FAI), and the LFC levels were increased in the elevated OPN subgroups. Moreover, increased OPN was associated with increased FAI and LFC in PCOS women, and the association between OPN and LFC was independent of triglyceride, HOMA-IR and FAI after adjusting for PCOS status in all participants. OPN combined with FAI and hsCRP may better predict NAFLD than WHR in this study cohort. However, there was no significant difference in circulating OPN levels between non-obese PCOS and normal control women.

CONCLUSIONS

Increased OPN levels may be related to FAI and elevated LFC in non-obese women with PCOS.

Methylglyoxal-bis-guanylhydrazone inhibits osteopontin expression and differentiation in cultured human monocytes

Monocyte activation and polarization play essential roles in many chronic inflammatory diseases. An imbalance of M1 and M2 macrophage activation (pro-inflammatory and alternatively activated, respectively) is believed to be a key aspect in the etiology of these diseases, thus a therapeutic approach that regulates macrophage activation could be of broad clinical relevance. Methylglyoxal-bis-guanylhydrazone (MGBG), a regulator of polyamine metabolism, has recently been shown to be concentrated in monocytes and macrophages, and interfere with HIV integration into the DNA of these cells in vitro. RNA expression analysis of monocytes from HIV+ and control donors with or without MGBG treatment revealed the only gene to be consistently down regulated by MGBG to be osteopontin (OPN). The elevated expression of this pro-inflammatory cytokine and monocyte chemoattractant is associated with various chronic inflammatory diseases. We demonstrate that MGBG is a potent inhibitor of secreted OPN (sOPN) in cultured monocytes with 50% inhibition achieved at 0.1 μM of the drug. Furthermore, inhibition of OPN RNA transcription in monocyte cultures occurs at similar concentrations of the drug. During differentiation of monocytes into macrophages in vitro, monocytes express cell surface CD16 and the cells undergo limited DNA synthesis as measured by uptake of BrdU. MGBG inhibited both activities at similar doses to those regulating OPN expression. In addition, monocyte treatment with MGBG inhibited differentiation into both M1 and M2 classes of macrophages at non-toxic doses. The inhibition of differentiation and anti-OPN effects of MGBG were specific for monocytes in that differentiated macrophages were nearly resistant to MGBG activities. Thus MGBG may have potential therapeutic utility in reducing or normalizing OPN levels and regulating monocyte activation in diseases that involve chronic inflammation.

Osteopontin-deficient progenitor cells display enhanced differentiation to adipocytes

OBJECTIVE

Osteopontin (OPN, Spp1) is a protein upregulated in white adipose tissue (WAT) of obese subjects. Deletion of OPN protects mice from high-fat diet-induced WAT inflammation and insulin resistance. However, the alterations mediated by loss of OPN in WAT before the obesogenic challenge have not yet been investigated. Therefore, we hypothesised that the lack of OPN might enhance the pro-adipogenic micro environment before obesity driven inflammation.

METHODS

OPN deficiency was tested in visceral (V) and subcutaneous (SC) WAT from WT and Spp1^-/- female mice. Gene expression for hypoxia, inflammation and adipogenesis was checked in WT vs. Spp1^-/- mice (n=15). Adipocytes progenitor cells (APC) were isolated by fluorescence cell sorting and role of OPN deficiency in adipogenesis was investigated by cell images and RT-PCR.

RESULTS

We show that Spp1^-/- maintained normal body and fat-pad weights, although hypoxia and inflammation markers were significantly reduced. In contrast, expression of genes involved in adipogenesis was increased in WAT from Spp1^-/- mice. Strikingly, APC from Spp1^-/- were diminished but differentiated more efficiently to adipocytes than those from control mice.

CONCLUSIONS

APC from SC-WAT of lean OPN-deficient mice display an enhanced capacity for differentiating to adipocytes. These alterations may explain the healthy expansion of WAT in the OPN-deficient model which is associated with reduced inflammation and insulin resistance.

Targeted Microbiome Intervention by Microencapsulated Delayed-Release Niacin Beneficially Affects Insulin Sensitivity in Humans

OBJECTIVE

Gut microbiota represent a potential novel target for future prediabetes and type 2 diabetes therapies. In that respect, niacin has been shown to beneficially affect the host-microbiome interaction in rodent models.

RESEARCH DESIGN AND METHODS

We characterized more than 500 human subjects with different metabolic phenotypes regarding their niacin (nicotinic acid [NA] and nicotinamide [NAM]) status and their gut microbiome. In addition, NA and NAM delayed-release microcapsules were engineered and examined in vitro and in vivo in two human intervention studies (bioavailability study and proof-of-concept/safety study).

RESULTS

We found a reduced α-diversity and Bacteroidetes abundance in the microbiome of obese human subjects associated with a low dietary niacin intake. We therefore developed delayed-release microcapsules targeting the ileocolonic region to deliver increasing amounts of NA and NAM to the microbiome while preventing systemic resorption to avoid negative side effects (e.g., facial flushing). In vitro studies on these delayed-release microcapsules revealed stable conditions at pH 1.4, 4.5, and 6.8, followed by release of the compounds at pH 7.4, simulating the ileocolonic region. In humans in vivo, gut-targeted delayed-release NA but not NAM produced a significant increase in the abundance of Bacteroidetes. In the absence of systemic side effects, these favorable microbiome changes induced by microencapsulated delayed-release NA were associated with an improvement of biomarkers for systemic insulin sensitivity and metabolic inflammation.

CONCLUSION

Targeted microbiome intervention by delayed-release NA might represent a future therapeutic option for prediabetes and type 2 diabetes.

Association of plasma osteopontin with diabetic retinopathy in Asians with type 2 diabetes

Purpose

Osteopontin (OPN) is a proinflammatory cytokine with diverse functions. Increased levels of OPN in vitreous fluid have been reported in patients with diabetic retinopathy (DR); however, studies on circulating OPN levels in DR are limited. We aim to examine the association of plasma OPN levels with the presence and severity of DR in a multiethnic cohort with type 2 diabetes mellitus (type 2 diabetes) in Singapore.

Methods

Plasma levels of OPN were measured using enzyme-linked immunosorbent assay. Digital color fundus photographs were assessed for DR. DR severity was categorized into non-proliferative DR (NPDR) and proliferative DR (PDR). Gradable fundus photographs and OPN measurements for 443 patients were used for analysis. A logistic regression model was used to evaluate the association of OPN with DR.

Results

DR was diagnosed in 174 (39.3%) patients, including 132 (75.9%) with NPDR and 42 (24.1%) with PDR. The median of OPN was higher in the patients with DR (64.7 [49.7-89.5] ng/ml) than in the patients without DR (51.7 [38.9-66.9] ng/ml; p<0.001). After adjustment for clinical and biochemical factors, a 1-unit increase in nature logarithm (ln)-transformed OPN was associated with the presence of DR (2.770 [1.599-3.800], p<0.001). The area under the curve (AUC) increased statistically significantly after the addition of OPN (0.805[0.763-0.846] versus 0.825 [0.785-0.865], p=0.011). In the severity analyses, the median of OPN was statistically significantly higher in the patients with PDR (76.8 [55.0-103.6] ng/ml) than in the patients with NPDR (61.7 [47.7-87.3] ng/ml; p=0.017). After adjustment, the 1-unit increase in lnOPN remained associated with NPDR (2.673 [1.519-4.704], p=0.001) and PDR (3.389 [1.254-9.226], p=0.017), respectively (p-trend=0.001).

Conclusions

Plasma OPN levels were associated with the presence and severity of DR in patients with type 2 diabetes, suggesting OPN may be useful as a potential biomarker for DR.

Effects of short-term dry immersion on bone remodeling markers, insulin and adipokines

Background

Dry immersion (DI), a ground-based model of microgravity previously used in Russia, has been recently implemented in France. The aim of this study was to analyze early events in a short-term DI model in which all conditions are met to investigate who is first challenged from osteo- or adipo-kines and to what extent they are associated to insulin-regulating hormones.

Methods

Twelve healthy men were submitted to a 3-day DI. Fasting blood was collected during pre-immersion phase for the determination of the baseline data collection (BDC), daily during DI (DI_24h, DI_48H and DI_72h), then after recovery (R_+3h and R_+24h). Markers of bone turnover, phosphocalcic metabolism, adipokines and associated factors were measured.

Results

Bone resorption as assessed by tartrate-resistant acid phosphatase isoform 5b and N-terminal crosslinked telopeptide of type I collagen levels increased as early as DI_24h. At the same time, total procollagen type I N- and C-terminal propeptides and osteoprotegerin, representing bone formation markers, decreased. Total osteocalcin [OC] was unaffected, but its undercarboxylated form [Glu-OC] increased from DI_24h to R_+3h. The early and progressive increase in bone alkaline phosphatase activities suggested an increased mineralization. Dickkopf-1 and sclerostin, as negative regulators of the Wnt-β catenin pathway, were unaltered. No change was observed either in phosphocalcic homeostasis (calcium and phosphate serum levels, 25-hydroxyvitamin D, fibroblast growth factor 23 [FGF23]) or in inflammatory response. Adiponectemia was unchanged, whereas circulating leptin concentrations increased. Neutrophil gelatinase-associated lipocalin [lipocalin-2], a potential regulator of bone homeostasis, was found elevated by 16% at R_+3h compared to DI_24h. The secretory form of nicotinamide phosphoribosyl-transferase [visfatin] concentrations almost doubled after one day of DI and remained elevated. Serum insulin-like growth factor 1 levels progressively increased. Fasting insulin concentrations increased during the entire DI, whereas fasting glucose levels tended to be higher only at DI_24h and then returned to BDC values. Changes in bone resorption parameters negatively correlated with changes in bone formation parameters. Percent changes of ultra-sensitive C-reactive protein positively correlated with changes in osteopontin, lipocalin-2 and fasting glucose. Furthermore, a positive correlation was found between changes in FGF23 and Glu-OC, the two main osteoblast-/osteocyte-derived hormones.

Conclusion

Our results demonstrated that DI induced an unbalanced remodeling activity and the onset of insulin resistance. This metabolic adaptation was concomitant with higher levels of Glu-OC. This finding confirms the role of bone as an endocrine organ in humans. Furthermore, visfatin for which a great responsiveness was observed could represent an early and sensitive marker of unloading in humans.

Osteopontin regulates the cross-talk between phosphatidylcholine and cholesterol metabolism in mouse liver

Osteopontin (OPN) is involved in different liver pathologies in which metabolic dysregulation is a hallmark. Here, we investigated whether OPN could alter liver, and more specifically hepatocyte, lipid metabolism and the mechanism involved. In mice, lack of OPN enhanced cholesterol 7α-hydroxylase (CYP7A1) levels and promoted loss of phosphatidylcholine (PC) content in liver; in vivo treatment with recombinant (r)OPN caused opposite effects. rOPN directly decreased CYP7A1 levels through activation of focal adhesion kinase-AKT signaling in hepatocytes. PC content was also decreased in OPN-deficient (OPN-KO) hepatocytes in which de novo FA and PC synthesis was lower, whereas cholesterol (CHOL) synthesis was higher, than in WT hepatocytes. In vivo inhibition of cholesterogenesis normalized liver PC content in OPN-KO mice, demonstrating that OPN regulates the cross-talk between liver CHOL and PC metabolism. Matched liver and serum samples showed a positive correlation between serum OPN levels and liver PC and CHOL concentration in nonobese patients with nonalcoholic fatty liver. In conclusion, OPN regulates CYP7A1 levels and the metabolic fate of liver acetyl-CoA as a result of CHOL and PC metabolism interplay. The results suggest that CYP7A1 is a main axis and that serum OPN could disrupt liver PC and CHOL metabolism, contributing to nonalcoholic fatty liver disease progression in nonobese patients.

Urinary Osteopontin Predicts Incident Chronic Kidney Disease, while Plasma Osteopontin Predicts Cardiovascular Death in Elderly Men

BACKGROUND AND OBJECTIVES

The matricellular protein osteopontin is involved in the pathogenesis of both kidney and cardiovascular disease. However, whether circulating and urinary osteopontin levels are associated with the risk of these diseases is less studied.

DESIGN SETTING PARTICIPANTS AND MEASUREMENTS

A community-based cohort of elderly men (Uppsala Longitudinal Study of Adult Men [ULSAM]; n = 741; mean age: 77 years) was used to study the associations between plasma and urinary osteopontin, incident chronic kidney disease, and the risk of cardiovascular death during a median of 8 years of follow-up.

RESULTS

There was no significant cross-sectional correlation between plasma and urinary osteopontin (Spearman ρ = 0.07, p = 0.13). Higher urinary osteopontin, but not plasma osteopontin, was associated with incident chronic kidney disease in multivariable models adjusted for age, cardiovascular risk factors, baseline glomerular filtration rate, urinary albumin/creatinine ratio, and the inflammatory markers interleukin 6 and high-sensitivity C-reactive protein (odds ratio for 1 standard deviation [SD] of urinary osteopontin, 1.42, 95% CI 1.00-2.02, p = 0.048). Conversely, plasma osteopontin, but not urinary osteopontin, was independently associated with cardiovascular death (multivariable hazard ratio per SD increase, 1.35, 95% CI 1.14-1.58, p < 0.001, and 1.00, 95% CI 0.79-1.26, p = 0.99, respectively). The addition of plasma osteopontin to a model with established cardiovascular risk factors significantly increased the C-statistics for the prediction of cardiovascular death (p < 0.002).

CONCLUSIONS

Higher urinary osteopontin specifically predicts incident chronic kidney disease, while plasma osteopontin specifically predicts cardiovascular death. Our data put forward osteopontin as an important factor in the detrimental interplay between the kidney and the cardiovascular system. The clinical implications, and why plasma and urinary osteopontin mirror different pathologies, remain to be established.

Osteopontin Deficiency Suppresses Intestinal Tumor Development in Apc-Deficient Min Mice

Osteopontin (OPN) is a secreted phosphoglycoprotein, and is a transcriptional target of aberrant Wnt signaling. OPN is upregulated in human colon cancers, and is suggested to enhance cancer progression. In this study, the effect of deficiency of OPN on intestinal tumor development in Apc-deficient Min mice was investigated. At 16 weeks of age, the number of small intestinal polyps in Min/OPN(+/−) and Min/OPN(−/−) mice was lower than that of Min/OPN(+/+) mice. Colorectal tumor incidences and multiplicities in Min/OPN(+/−) and Min/OPN(−/−) mice were significantly lower than those in Min/OPN(+/+) mice, being 48% and 0.6 ± 0.8, 50% and 0.8 ± 0.9 vs. 80% and 1.6 ± 1.7, respectively. OPN expression in colorectal tumors was strongly upregulated in Min/OPN(+/+) compared to adjacent non-tumor parts, but was decreased in Min/OPN(+/−) and not detected in Min/OPN(−/−). Targets of OPN, matrix metalloproteinases (MMPs)-3, -9, and -13 were lowered by OPN deficiency. Macrophage marker F4/80 in colorectal tumors was also lowered by OPN deficiency. MMP-9 expression was observed in tumor cells and tumor-infiltrating neutrophils. These results indicate that induction of OPN by aberrant Wnt signaling could enhance colorectal tumor development in part by upregulation of MMP-3, -9, and -13 and infiltration of macrophage and neutrophils. Suppression of OPN expression could contribute to tumor prevention, but complete deficiency of OPN may cause some adverse effects.

Sarcopenic obesity or obese sarcopenia: A cross talk between age-associated adipose tissue and skeletal muscle inflammation as a main mechanism of the pathogenesis

Sarcopenia, an age-associated decline in skeletal muscle mass coupled with functional deterioration, may be exacerbated by obesity leading to higher disability, frailty, morbidity and mortality rates. In the combination of sarcopenia and obesity, the state called sarcopenic obesity (SOB), some key age- and obesity-mediated factors and pathways may aggravate sarcopenia. This review will analyze the mechanisms underlying the pathogenesis of SOB. In obese adipose tissue (AT), adipocytes undergo hypertrophy, hyperplasia and activation resulted in accumulation of pro-inflammatory macrophages and other immune cells as well as dysregulated production of various adipokines that together with senescent cells and the immune cell-released cytokines and chemokines create a local pro-inflammatory status. In addition, obese AT is characterized by excessive production and disturbed capacity to store lipids, which accumulate ectopically in skeletal muscle. These intramuscular lipids and their derivatives induce mitochondrial dysfunction characterized by impaired β-oxidation capacity and increased reactive oxygen species formation providing lipotoxic environment and insulin resistance as well as enhanced secretion of some pro-inflammatory myokines capable of inducing muscle dysfunction by auto/paracrine manner. In turn, by endocrine manner, these myokines may exacerbate AT inflammation and also support chronic low grade systemic inflammation (inflammaging), overall establishing a detrimental vicious circle maintaining AT and skeletal muscle inflammation, thus triggering and supporting SOB development. Under these circumstances, we believe that AT inflammation dominates over skeletal muscle inflammation. Thus, in essence, it redirects the vector of processes from "sarcopenia→obesity" to "obesity→sarcopenia". We therefore propose that this condition be defined as "obese sarcopenia", to reflect the direction of the pathological pathway.

Osteopontin: its potential role in cancer of children and young adults

Objective: Osteopontin (OPN) is aglyco-phosphoprotein, involved in tissue remodeling, inflammation and boneresorption. In various adult neoplasms OPN was shown to correlate with cancer progression, invasiveness and metastasis. Aim: to define the role of OPN in malignancies of children and young adults. Material and methods: a structured PubMed and Google Scholar literature analysis based on reports published in English between I'1995 and XII'2015. Results: 14 studies (four on hematological malignancies, four on bone tumors, three on CNS tumors, two on dendritic proliferative diseases and one on renal tumors) were identified. Higher levels of serum and cerebro-spinal fluid OPN protein, and high expressions of OPN mRNA and SPP1 gene were present in more aggressive and advanced childhood malignancies. In children with acute lymphoblastic leukemia with CNS involvement and with atypical teratoid/rhabdoid tumor (AT/RT) and medulloblastoma, the serum and CSF OPN levels reflected tumor bulk and response to therapy, while in children with AT/RT and multisystem Langerhans cell histiocytosis with high-risk organs involvement, high OPN serum levels correlated with poorer survival. To the contrary, in osteosarcoma, high OPN mRNA and SPP1 gene expressions correlated with better survival and good response to chemotherapy. Conclusions: The literature review suggests that OPN may play important roles in the development and progression of selected cancers of children and young adults, including acute lymphoblastic leukemia, malignant gliomas, AT/RT and Langerhans cell histiocytosis. However, limited number of published studies prevents from definite concluding on the clinical utility of OPN as a marker of diagnosis, prognosis and treatment monitoring in these pediatric cancers. Further studies performed in more numerous groups of patients with particular types of cancers of children and young adults are warranted.

Osteopontin Affects Insulin Vesicle Localization and Ca2+ Homeostasis in Pancreatic Beta Cells from Female Mice

Type 2 diabetic patients suffer from insulin resistance and reduced insulin secretion. Osteopontin (OPN), a versatile protein expressed in several tissues throughout the body including the islets of Langerhans, has previously been implicated in the development of insulin resistance. Here we have investigated the role of OPN in insulin secretion using an OPN knock out mouse model (OPN^-/-). Ultra-structural analyzes of islets from OPN^-/- and WT mice indicated weaker cell-cell connections between the islet cells in the OPN^-/- mouse compared to WT. Analysis of the insulin granule distribution in the beta cells showed that although OPN^-/- and WT beta cells have the same number of insulin granules OPN^-/- beta cells have significantly fewer docked granules. Both OPN^-/- and WT islets displayed synchronized Ca²⁺ oscillations indicative of an intact beta cell communication. OPN^-/- islets displayed higher intracellular Ca²⁺ concentrations when stimulated with 16.7 mM glucose than WT islets and the initial dip upon elevated glucose concentrations (which is associated with Ca²⁺ uptake into ER) was significantly lower in these islets. Glucose-induced insulin secretion was similar in OPN^-/- and WT islets. Likewise, non-fasted blood glucose levels were the same in both groups. In summary, deletion of OPN results in several minor beta-cell defects that can be compensated for in a healthy system.

Osteopontin: Relation between Adipose Tissue and Bone Homeostasis

Osteopontin (OPN) is a multifunctional protein mainly associated with bone metabolism and remodeling. Besides its physiological functions, OPN is implicated in the pathogenesis of a variety of disease states, such as obesity and osteoporosis. Importantly, during the last decades obesity and osteoporosis have become among the main threats to health worldwide. Because OPN is a protein principally expressed in cells with multifaceted effects on bone morphogenesis and remodeling and because it seems to be one of the most overexpressed genes in the adipose tissue of the obese contributing to osteoporosis, this mini review will highlight recent insights about relation between adipose tissue and bone homeostasis.

Peptide-based vaccination against OPN integrin binding sites does not improve cardio-metabolic disease in mice

Obesity causes insulin resistance via a chronic low-grade inflammation. This inflammation is characterized by elevated pro-inflammatory markers and macrophage accumulation in the adipose tissue (AT). AT inflammation is a key factor causing insulin resistance and thus type 2 diabetes, both linked to atherosclerotic cardiovascular disease. Osteopontin (OPN), a well-known inflammatory cytokine, is involved in obesity-linked complications including AT inflammation, insulin resistance, atherosclerosis and CVD. During inflammation, OPN is proteolytically cleaved by matrix metalloproteinases or thrombin leading to increased OPN activity. Therefore, OPN provides a new interesting target for immunological prevention and treatment of obesity-associated diseases. The aim of our study was to evaluate peptide-based vaccines against integrin binding sites of OPN and to examine whether these active immunotherapies are functional in reducing metabolic tissue inflammation, insulin resistance, and atherosclerosis in a cardio-metabolic (Ldlr^-/- mice) and a diet-induced obesity model (WT mice). However, atherosclerosis, insulin resistance and AT inflammation were not diminished after treatment with OPN-derived peptides in murine models. Lack of efficacy was based on a failure to induce antibodies capable to bind epitopes in the context of functional OPN protein. In conclusion, our data point to unexpected challenges in the immunotherapeutic targeting of adhesive motives, such as RGD containing sequences, on endogenous proteins.

Significant obesity-associated gene expression changes occur in the stomach but not intestines in obese mice

The gastrointestinal (GI) tract can have significant impact on the regulation of the whole‐body metabolism and may contribute to the development of obesity and diabetes. To systemically elucidate the role of the GI tract in obesity, we performed a transcriptomic analysis in different parts of the GI tract of two obese mouse models: ob/ob and high‐fat diet (HFD) fed mice. Compared to their lean controls, significant changes in the gene expression were observed in both obese mouse groups in the stomach (ob/ob: 959; HFD: 542). In addition, these changes were quantitatively much higher than in the intestine. Despite the difference in genetic background, the two mouse models shared 296 similar gene expression changes in the stomach. Among those genes, some had known associations to obesity, diabetes, and insulin resistance. In addition, the gene expression profiles strongly suggested an increased gastric acid secretion in both obese mouse models, probably through an activation of the gastrin pathway. In conclusion, our data reveal a previously unknown dominant connection between the stomach and obesity in murine models extensively used in research.

Osteopontin is a key player for local adipose tissue macrophage proliferation in obesity

Objective

Recent findings point towards an important role of local macrophage proliferation also in obesity-induced adipose tissue inflammation that underlies insulin resistance and type 2 diabetes. Osteopontin (OPN) is an inflammatory cytokine highly upregulated in adipose tissue (AT) of obese and has repeatedly been shown to be functionally involved in adipose-tissue inflammation and metabolic sequelae. In the present work, we aimed at unveiling both the role of OPN in human monocyte and macrophage proliferation as well as the impact of OPN deficiency on local macrophage proliferation in a mouse model for diet-induced obesity.

Methods

The impact of recombinant OPN on viability, apoptosis, and proliferation was analyzed in human peripheral blood monocytes and derived macrophages. Wild type (WT) and OPN knockout mice (SPP1KO) were compared with respect to in vivo adipose tissue macrophage and in vitro bone marrow-derived macrophage (BMDM) proliferation.

Results

OPN not only enhanced survival and decreased apoptosis of human monocytes but also induced proliferation similar to macrophage colony stimulating factor (M-CSF). Even in fully differentiated monocyte-derived macrophages, OPN induced a proliferative response. Moreover, proliferation of adipose tissue macrophages in obese mice was detectable in WT but virtually absent in SPP1KO. In BMDM, OPN also induced proliferation while OPN as well as M-CSF-induced proliferation was similar in WT and SPP1KO.

Conclusions

These data confirm that monocytes and macrophages not only are responsive to OPN and migrate to sites of inflammation but also they survive and proliferate more in the presence of OPN, a mechanism also strongly confirmed in vivo. Therefore, secreted OPN appears to be an essential player in AT inflammation, not only by driving monocyte chemotaxis and macrophage differentiation but also by facilitating local proliferation of macrophages.

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Osteopontin enhances survival and decreases apoptosis of human monocytes.

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Osteopontin induces proliferation of differentiated macrophages.

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Osteopontin facilitates local adipose tissue macrophage proliferation in obesity.

Role of Osteopontin in Liver Diseases

Osteopontin (OPN), a multifunctional protein, is involved in numerous pathological conditions including inflammation, immunity, angiogenesis, fibrogenesis and carcinogenesis in various tissues. Extensive studies have elucidated the critical role of OPN in cell signaling such as regulation of cell proliferation, migration, inflammation, fibrosis and tumor progression. In the liver, OPN interacts with integrins, CD44, vimentin and MyD88 signaling, thereby induces infiltration, migration, invasion and metastasis of cells. OPN is highlighted as a chemoattractant for macrophages and neutrophils during injury in inflammatory liver diseases. OPN activates hepatic stellate cells (HSCs) to exert an enhancer in fibrogenesis. The role of OPN in hepatocellular carcinoma (HCC) has also generated significant interests, especially with regards to its role as a diagnostic and prognostic factor. Interestingly, OPN acts an opposing role in liver repair under different pathological conditions. This review summarizes the current understanding of OPN in liver diseases. Further understanding of the pathophysiological role of OPN in cellular interactions and molecular mechanisms associated with hepatic inflammation, fibrosis and cancer may contribute to the development of novel strategies for clinical diagnosis, monitoring and therapy of liver diseases.

Age-associated vascular inflammation promotes monocytosis during atherogenesis

Aging leads to a proinflammatory state within the vasculature without disease, yet whether this inflammatory state occurs during atherogenesis remains unclear. Here, we examined how aging impacts atherosclerosis using Ldlr(-/-) mice, an established murine model of atherosclerosis. We found that aged atherosclerotic Ldlr(-/-) mice exhibited enhanced atherogenesis within the aorta. Aging also led to increased LDL levels, elevated blood pressure on a low-fat diet, and insulin resistance after a high-fat diet (HFD). On a HFD, aging increased a monocytosis in the peripheral blood and enhanced macrophage accumulation within the aorta. When we conducted bone marrow transplant experiments, we found that stromal factors contributed to age-enhanced atherosclerosis. To delineate these stromal factors, we determined that the vasculature exhibited an age-enhanced inflammatory response consisting of elevated production of CCL-2, osteopontin, and IL-6 during atherogenesis. In addition, in vitro cultures showed that aging enhanced the production of osteopontin by vascular smooth muscle cells. Functionally, aged atherosclerotic aortas displayed higher monocyte chemotaxis than young aortas. Hence, our study has revealed that aging induces metabolic dysfunction and enhances vascular inflammation to promote a peripheral monocytosis and macrophage accumulation within the atherosclerotic aorta.

Osteopontin affects macrophage polarization promoting endocytic but not inflammatory properties

OBJECTIVE

Macrophages are the main drivers of obesity-induced adipose tissue (AT) inflammation that causes insulin resistance. Macrophages polarize toward different inflammatory (M1) or protective (M2) phenotypes. Osteopontin (OPN) is an inflammatory cytokine highly expressed in AT in obesity and known to be involved in chronic inflammatory processes. It was hypothesized that OPN polarizes macrophages into a proinflammatory phenotype.

METHODS

AT macrophages (ATMs) of OPN-deficient (Spp1(-/-) ) and wild-type C57BL/6 (WT) mice with obesity and bone marrow-derived macrophages (BMDMs) of Spp1(-/-) and WT mice as well as human monocyte-derived macrophages (MDMs) polarized in the presence of OPN were investigated.

RESULTS

While ATM infiltration was lower in Spp1(-/-) upon high-fat diet, Spp1(-/-) ATMs expressed more M1 and less M2 markers but less tumor necrosis factor-α compared with WT. There was no effect of OPN deficiency on BMDM polarization. In human MDMs, the presence of OPN during polarization ambiguously altered M1/M2-related marker expression and diminished LPS-induced inflammatory cytokine production. Strikingly, phagocytic activity was elevated by the presence of OPN during polarization in both human MDMs and murine BMDMs.

CONCLUSIONS

In contradiction to our hypothesis, data indicated that OPN does not induce inflammatory macrophages but was a signal to induce phagocytosis, which may be required due to increased adipocyte death in obesity.

Identification of matrix metalloproteinase-12 as a candidate molecule for prevention and treatment of cardiometabolic disease

Obesity is strongly associated with metabolic syndrome, a combination of risk factors that predispose to the development of the cardiometabolic diseases: atherosclerotic cardiovascular disease and type 2 diabetes mellitus. Prevention of metabolic syndrome requires novel interventions to address this health challenge. The objective of this study was the identification of candidate molecules for the prevention and treatment of insulin resistance and atherosclerosis, conditions that underlie type 2 diabetes mellitus and cardiovascular disease, respectively. We used an unbiased bioinformatics approach to identify molecules that are upregulated in both conditions by combining murine and human data from a microarray experiment and meta-analyses. We obtained a pool of eight genes that were upregulated in all the databases analysed. This included well known and novel molecules involved in the pathophysiology of type 2 diabetes mellitus and cardiovascular disease. Notably, matrix metalloproteinase 12 (MMP12) was highly ranked in all analyses and was therefore chosen for further investigation. Analyses of visceral and subcutaneous white adipose tissue from obese compared to lean mice and humans convincingly confirmed the up-regulation of MMP12 in obesity at mRNA, protein and activity levels. In conclusion, using this unbiased approach an interesting pool of candidate molecules was identified, all of which have potential as targets in the treatment and prevention of cardiometabolic diseases.

Adipose extracellular matrix remodelling in obesity and insulin resistance

The extracellular matrix (ECM) of adipose tissues undergoes constant remodelling to allow adipocytes and their precursor cells to change cell shape and function in adaptation to nutritional cues. Abnormal accumulation of ECM components and their modifiers in adipose tissues has been recently demonstrated to cause obesity-associated insulin resistance, a hallmark of type 2 diabetes. Integrins and other ECM receptors (e.g. CD44) that are expressed in adipose tissues have been shown to regulate insulin sensitivity. It is well understood that a hypoxic response is observed in adipose tissue expansion during obesity progression and that hypoxic response accelerates fibrosis and inflammation in white adipose tissues. The expansion of adipose tissues should require angiogenesis; however, the excess deposition of ECM limits the angiogenic response of white adipose tissues in obesity. While recent studies have focused on the metabolic consequences and the mechanisms of adipose tissue expansion and remodelling, little attention has been paid to the role played by the interaction between peri-adipocyte ECM and their cognate cell surface receptors. This review will address what is currently known about the roles played by adipose ECM, their modifiers, and ECM receptors in obesity and insulin resistance. Understanding how excess ECM deposition in the adipose tissue deteriorates insulin sensitivity would provide us hints to develop a new therapeutic strategy for the treatment of insulin resistance and type 2 diabetes.

Peptide- and Amine-Modified Glucan Particles for the Delivery of Therapeutic siRNA

Translation of siRNA technology into the clinic is limited by the need for improved delivery systems that target specific cell types. Macrophages are particularly attractive targets for RNAi therapy because they promote pathogenic inflammatory responses in a number of important human diseases. We previously demonstrated that a multicomponent formulation of β-1,3-d-glucan-encapsulated siRNA particles (GeRPs) can specifically and potently silence genes in mouse macrophages. A major advance would be to simplify the GeRP system by reducing the number of delivery components, thus enabling more facile manufacturing and future commercialization. Here we report the synthesis and evaluation of a simplified glucan-based particle (GP) capable of delivering siRNA in vivo to selectively silence macrophage genes. Covalent attachment of small-molecule amines and short peptides containing weak bases to GPs facilitated electrostatic interaction of the particles with siRNA and aided in the endosomal release of siRNA by the proton-sponge effect. Modified GPs were nontoxic and were efficiently internalized by macrophages in vitro. When injected intraperitoneally (i.p.), several of the new peptide-modified GPs were found to efficiently deliver siRNA to peritoneal macrophages in lean, healthy mice. In an animal model of obesity-induced inflammation, i.p. administration of one of the peptide-modified GPs (GP-EP14) bound to siRNA selectively reduced the expression of target inflammatory cytokines in the visceral adipose tissue macrophages. Decreasing adipose tissue inflammation resulted in an improvement of glucose metabolism in these metabolically challenged animals. Thus, modified GPs represent a promising new simplified system for the efficient delivery of therapeutic siRNAs specifically to phagocytic cells in vivo for modulation of inflammation responses.

Inhibition of Cellular Adhesion by Immunological Targeting of Osteopontin Neoepitopes Generated through Matrix Metalloproteinase and Thrombin Cleavage

Osteopontin (OPN), a secreted protein involved in inflammatory processes and cancer, induces cell adhesion, migration, and activation of inflammatory pathways in various cell types. Cells bind OPN via integrins at a canonical RGD region in the full length form as well as to a contiguous cryptic site that some have shown is unmasked upon thrombin or matrix metalloproteinase cleavage. Thus, the adhesive capacity of osteopontin is enhanced by proteolytic cleavage that may occur in inflammatory conditions such as obesity, atherosclerosis, rheumatoid arthritis, tumor growth and metastasis. Our aim was to inhibit cellular adhesion to recombinant truncated proteins that correspond to the N-terminal cleavage products of thrombin- or matrix metalloproteinase-cleaved OPN in vitro. We specifically targeted the cryptic integrin binding site with monoclonal antibodies and antisera induced by peptide immunization of mice. HEK 293 cells adhered markedly stronger to truncated OPN proteins than to full length OPN. Without affecting cell binding to the full length form, the raised monoclonal antibodies specifically impeded cellular adhesion to the OPN fragments. Moreover, we show that the peptides used for immunization were able to induce antisera, which impeded adhesion either to all OPN forms, including the full-length form, or selectively to the corresponding truncated recombinant proteins. In conclusion, we developed immunological tools to selectively target functional properties of protease-cleaved OPN forms, which could find applications in treatment and prevention of various inflammatory diseases and cancers.

Isotretinoin increased carotid intima-media thickness in acne patients

BACKGROUND

Isotretinoin (Iso) in acne treatment may cause dyslipidemia and increase in liver enzymes. Moreover, its effect on lipid and glucose metabolism may induce atherosclerotic complications. The aim of this study was to evaluate carotid intima-media thickness (CIMT), osteopontin (OPN), lipid, high sensitive C-reaktive protein (hs-CRP) levels, and insulin resistance (HOMA-IR) in acne patients before and after Iso treatment.

MATERIALS

Twenty-one acne patients were treated with Iso (0.5-0.8 mg/kg) for four months. Blood tests for lipid profile, fasting glucose, liver enzymes, OPN, HOMA-IR, hs-CRP and CIMT measurements were performed before and after Iso treatment. Serum levels of OPN and, hs-CRP were measured by ELISA and particle-enhanced turbidimetric immunoassay respectively.

RESULTS

Iso treatment significantly increased lipid levels, CIMT (0.60-0.74 mm; p ˂0.001); whereas it non-significantly increased HOMA-IR (0.91-1.87; p =0.70), OPN (4.32-5.44 ng/ml; p =0.27), and hs-CRP (0.08-0.09 mg/dl; p =0.88) levels. There was no correlation between OPN and CIMT (p =0.77).

CONCLUSION

Isotretinoin treatment for four months significantly increased CIMT in acne patients. Hippokratia 2016, 20(1): 14-18.

Osteopontin is a proximal effector of leptin-mediated non-alcoholic steatohepatitis (NASH) fibrosis

INTRODUCTION

Liver fibrosis develops when hepatic stellate cells (HSC) are activated into collagen-producing myofibroblasts. In non-alcoholic steatohepatitis (NASH), the adipokine leptin is upregulated, and promotes liver fibrosis by directly activating HSC via the hedgehog pathway. We reported that hedgehog-regulated osteopontin (OPN) plays a key role in promoting liver fibrosis. Herein, we evaluated if OPN mediates leptin-profibrogenic effects in NASH.

METHODS

Leptin-deficient (ob/ob) and wild-type (WT) mice were fed control or methionine-choline deficient (MCD) diet. Liver tissues were assessed by Sirius-red, OPN and αSMA IHC, and qRT-PCR for fibrogenic genes. In vitro, HSC with stable OPN (or control) knockdown were treated with recombinant (r)leptin and OPN-neutralizing or sham-aptamers. HSC response to OPN loss was assessed by wound healing assay. OPN-aptamers were also added to precision-cut liver slices (PCLS), and administered to MCD-fed WT (leptin-intact) mice to determine if OPN neutralization abrogated fibrogenesis.

RESULTS

MCD-fed WT mice developed NASH-fibrosis, upregulated OPN, and accumulated αSMA+ cells. Conversely, MCD-fed ob/ob mice developed less fibrosis and accumulated fewer αSMA+ and OPN+ cells. In vitro, leptin-treated HSC upregulated OPN, αSMA, collagen 1α1 and TGFβ mRNA by nearly 3-fold, but this effect was blunted by OPN loss. Inhibition of PI3K and transduction of dominant negative-Akt abrogated leptin-mediated OPN induction, while constitutive active-Akt upregulated OPN. Finally, OPN neutralization reduced leptin-mediated fibrogenesis in both PCLS and MCD-fed mice.

CONCLUSION

OPN overexpression in NASH enhances leptin-mediated fibrogenesis via PI3K/Akt. OPN neutralization significantly reduces NASH fibrosis, reinforcing the potential utility of targeting OPN in the treatment of patients with advanced NASH.

Wogonin suppresses osteopontin expression in adipocytes by activating PPARα

AIM

Wogonin (5,7-dihydroxy-8-methoxyflavone), a major bioactive compound of the flavonoid family, is commonly extracted from the traditional Chinese medicine Scutellaria baicalensis and possesses antioxidant and anti-inflammatory activities and is assumed to have anti-diabetes function. Indeed, a current study has shown that it can possibly treat metabolic disorders such as those found in db/db mice. However, the underlying molecular mechanism remains largely unclear. The aim of this study was to investigate the impact of wogonin on osteopontin (OPN) expression in adipose tissue from type 1 diabetic mice and in 3T3-L1 adipocytes.

METHODS

Type 1 diabetes was induced by streptozotocin (STZ) injection. 3T3-L1 preadipocytes were converted to 3T3-L1 adipocytes through treatment with insulin, dexamethasone, and 3-isobutyl-1-methylxanthine (IBMX). Western blot analysis and RT-PCR were performed to detect protein expression and mRNA levels, respectively.

RESULTS

Wogonin treatment suppressed the increase in serum OPN levels and reduced OPN expression in adipose tissue from STZ-induced type 1 diabetic mice. Administration of wogonin enhanced PPARα expression and activity. Silencing of PPARα diminished the inhibitory effects of wogonin on OPN expression in 3T3-L1 adipocytes. Furthermore, the levels of c-Fos and phosphorylated c-Jun were reduced in wogonin-treated adipose tissue and 3T3-L1 adipocytes. In addition, wogonin treatment dramatically mitigated p38 MAPK phosphorylation. Pharmacological inhibition of p38 MAPK by its specific inhibitor SB203580 increased PPARα activity and decreased OPN expression.

CONCLUSION

Our results suggest that wogonin downregulated OPN expression in adipocytes through the inhibition of p38 MAPK and the sequential activation of the PPARα pathway. Given the adverse effects of high OPN levels on metabolism, our results provide evidence for the potential administration of wogonin as a treatment for diabetes.

Osteopontin neutralisation abrogates the liver progenitor cell response and fibrogenesis in mice

BACKGROUND

Chronic liver injury triggers a progenitor cell repair response, and liver fibrosis occurs when repair becomes deregulated. Previously, we reported that reactivation of the hedgehog pathway promotes fibrogenic liver repair. Osteopontin (OPN) is a hedgehog-target, and a cytokine that is highly upregulated in fibrotic tissues, and regulates stem-cell fate. Thus, we hypothesised that OPN may modulate liver progenitor cell response, and thereby, modulate fibrotic outcomes. We further evaluated the impact of OPN-neutralisation on murine liver fibrosis.

METHODS

Liver progenitors (603B and bipotential mouse oval liver) were treated with OPN-neutralising aptamers in the presence or absence of transforming growth factor (TGF)-β, to determine if (and how) OPN modulates liver progenitor function. Effects of OPN-neutralisation (using OPN-aptamers or OPN-neutralising antibodies) on liver progenitor cell response and fibrogenesis were assessed in three models of liver fibrosis (carbon tetrachloride, methionine-choline deficient diet, 3,5,-diethoxycarbonyl-1,4-dihydrocollidine diet) by quantitative real time (qRT) PCR, Sirius-Red staining, hydroxyproline assay, and semiquantitative double-immunohistochemistry. Finally, OPN expression and liver progenitor response were corroborated in liver tissues obtained from patients with chronic liver disease.

RESULTS

OPN is overexpressed by liver progenitors in humans and mice. In cultured progenitors, OPN enhances viability and wound healing by modulating TGF-β signalling. In vivo, OPN-neutralisation attenuates the liver progenitor cell response, reverses epithelial-mesenchymal-transition in Sox9+ cells, and abrogates liver fibrogenesis.

CONCLUSIONS

OPN upregulation during liver injury is a conserved repair response, and influences liver progenitor cell function. OPN-neutralisation abrogates the liver progenitor cell response and fibrogenesis in mouse models of liver fibrosis.

The receptor CD44 is associated with systemic insulin resistance and proinflammatory macrophages in human adipose tissue

AIMS/HYPOTHESIS

Proinflammatory immune cell infiltration in human adipose tissue is associated with the development of insulin resistance. We previously identified, via a gene expression-based genome-wide association study, the cell-surface immune cell receptor CD44 as a functionally important gene associated with type 2 diabetes. We then showed that, compared with controls, Cd44 knockout mice were protected from insulin resistance and adipose tissue inflammation during diet-induced obesity. We thus sought to test whether CD44 is associated with adipose tissue inflammation and insulin resistance in humans.

METHODS

Participants included 58 healthy, overweight/moderately obese white adults who met predetermined criteria for insulin resistance or insulin sensitivity based on the modified insulin-suppression test. Serum was collected from 43 participants to measure circulating concentrations of CD44. Subcutaneous adipose tissue was obtained from 17 participants to compare CD44, its ligand osteopontin (OPN, also known as SPP1) and pro-inflammatory gene expression. CD44 expression on adipose tissue macrophage (ATM) surfaces was determined by flow cytometry.

RESULTS

Serum CD44 concentrations were significantly increased in insulin-resistant (IR) participants. CD44 gene expression in subcutaneous adipose tissue was threefold higher in the IR subgroup. The expression of OPN, CD68 and IL6 was also significantly elevated in IR individuals. CD44 gene expression correlated significantly with CD68 and IL6 expression. CD44 density on ATMs was associated with proinflammatory M1 polarisation.

CONCLUSIONS/INTERPRETATION

CD44 and OPN in human adipose tissue are associated with localised inflammation and systemic insulin resistance. This receptor-ligand pair is worthy of further research as a potentially modifiable contributor to human insulin resistance and type 2 diabetes.