Bone Marrow Plasminogen Activator Inhibitor-1 Influences the Development of Obesity

Classical and nonclassical effects of angiotensin-converting enzyme: How increased ACE enhances myeloid immune function

As part of the classical renin-angiotensin system, the peptidase angiotensin-converting enzyme (ACE) makes angiotensin II which has myriad effects on systemic cardiovascular function, inflammation, and cellular proliferation. Less well known is that macrophages and neutrophils make ACE in response to immune activation which has marked effects on myeloid cell function independent of angiotensin II. Here, we discuss both classical (angiotensin) and nonclassical functions of ACE and highlight mice called ACE 10/10 in which genetic manipulation increases ACE expression by macrophages and makes these mice much more resistant to models of tumors, infection, atherosclerosis, and Alzheimer's disease. In another model called NeuACE mice, neutrophils make increased ACE and these mice are much more resistant to infection. In contrast, ACE inhibitors reduce neutrophil killing of bacteria in mice and humans. Increased expression of ACE induces a marked increase in macrophage oxidative metabolism, particularly mitochondrial oxidation of lipids, secondary to increased peroxisome proliferator-activated receptor α expression, and results in increased myeloid cell ATP. ACE present in sperm has a similar metabolic effect, and the lack of ACE activity in these cells reduces both sperm motility and fertilization capacity. These nonclassical effects of ACE are not due to the actions of angiotensin II but to an unknown molecule, probably a peptide, that triggers a profound change in myeloid cell metabolism and function. Purifying and characterizing this peptide could offer a new treatment for several diseases and prove potentially lucrative.

Benefits of Tranexamic Acid in Total Knee Arthroplasty: A Classification and Regression Tree Analysis in Function of Instrumentation, BMI, and Gender

Tranexamic acid (TXA) is an antifibrinolytic drug that reduces blood loss in patients that undergo Total knee arthroplasty (TKA). Few studies compare its effect on conventional instrumentation (CI) versus patient-specific instrumentation (PSI). The main objective of this study was to understand analytically how TXA usage in both instrumentations influenced blood loss in TKA differently and see if the differences seen could be explained by the patient's body mass index (BMI) and gender. This nonrandomized retrospective study sample consisted of 688 TKA procedures performed on patients who had symptomatic arthrosis resistant to conservative treatment. Descriptive analysis was used to evaluate blood loss using hemoglobin (Hb) mean values and mean variation (%). The Classification and Regression Tree (CRT) method was applied to understand how the independent variables affected the dependent variable. Comparing patients submitted to the same instrumentation, where some received TXA and others did not, patients that received TXA had lower blood loss. Comparing patients who underwent TKA with different instrumentations and without the use of TXA, it was found that patients who underwent TKA with PSI had lower blood loss than those who underwent TKA with CI. However, when these same instruments were compared again, but associated with the use of TXA, the opposite was true with patients undergoing TKA with PSI showing greater blood loss than patients undergoing TKA with CI. TXA usage in TKA is significantly beneficial in minimizing blood loss and regardless of instrumentation. When using TXA, the lowest blood loss was obtained in patients with higher BMI and submitted to TKA with CI. This is most likely explained by the synergistic antifibrotic effect of TXA with adipokines, such as plasminogen activator inhibitor-1 (PAI-1), found in the femoral bone marrow which is perforated using CI. If, however, TXA wasn't used, the lowest blood loss was obtained in patients submitted to TKA with PSI.

Fat-1 Transgenic Mice With Augmented n3-Polyunsaturated Fatty Acids Are Protected From Liver Injury Caused by Acute-On-Chronic Ethanol Administration

Alcohol-associated liver disease (ALD) is the leading cause of liver disease worldwide, and alcohol-associated hepatitis (AH), a severe form of ALD, is a major contributor to the mortality and morbidity due to ALD. Many factors modulate susceptibility to ALD development and progression, including nutritional factors such as dietary fatty acids. Recent work from our group and others showed that modulation of dietary or endogenous levels of n6-and n3-polyunsaturated fatty acids (PUFAs) can exacerbate or attenuate experimental ALD, respectively. In the current study, we interrogated the effects of endogenous n3-PUFA enrichment in a mouse model which recapitulates features of early human AH using transgenic fat-1 mice which endogenously convert n6-PUFAs to n3-PUFAs. Male wild type (WT) and fat-1 littermates were provided an ethanol (EtOH, 5% v/v)-containing liquid diet for 10 days, then administered a binge of EtOH (5 g/kg) by oral gavage on the 11^th day, 9 h prior to sacrifice. In WT mice, EtOH treatment resulted in liver injury as determined by significantly elevated plasma ALT levels, whereas in fat-1 mice, EtOH caused no increase in this biomarker. Compared to their pair-fed controls, a significant EtOH-mediated increase in liver neutrophil infiltration was observed also in WT, but not fat-1 mice. The hepatic expression of several cytokines and chemokines, including Pai-1, was significantly lower in fat-1 vs WT EtOH-challenged mice. Cultured bone marrow-derived macrophages isolated from fat-1 mice expressed less Pai-1 and Cxcl2 (a canonical neutrophil chemoattractant) mRNA compared to WT when stimulated with lipopolysaccharide. Further, we observed decreased pro-inflammatory M1 liver tissue-resident macrophages (Kupffer cells, KCs), as well as increased liver T regulatory cells in fat-1 vs WT EtOH-fed mice. Taken together, our data demonstrated protective effects of endogenous n3-PUFA enrichment on liver injury caused by an acute-on-chronic EtOH exposure, a paradigm which recapitulates human AH, suggesting that n3-PUFAs may be a viable nutritional adjuvant therapy for this disease.

PAI-1 Exacerbates White Adipose Tissue Dysfunction and Metabolic Dysregulation in High Fat Diet-Induced Obesity

Background: Plasminogen activator inhibitor (PAI)-1 levels and activity are known to increase during metabolic syndrome and obesity. In addition, previous studies have implicated PAI-1 in adipose tissue (AT) expansion while also contributing to insulin resistance. As inflammation is also known to occur in AT during obesity, we hypothesized that in a high-fat diet (HFD)-induced obese mouse model PAI-1 contributes to macrophage-mediated inflammation and metabolic dysfunction.

Methods: Four- to five-weeks-old male C57B6/6J mice were fed a HFD (45%) for 14 weeks, while age-matched control mice were fed a standard laboratory chow diet (10% fat). Additional studies were performed in PAI-1 knockout mice and wild type mice treated with an inhibitor (PAI-039) of PAI-1. Macrophage polarization were measured by real time PCR.

Results: HFD mice showed increased expression of PAI-1 in visceral white AT (WAT) that also displayed increased macrophage numbers. PAI-1 deficient mice exhibited increased numbers of anti-inflammatory macrophages in WAT and were resistant to HFD-induced obesity. Similarly, pharmacological inhibition of PAI-1 using PAI-039 significantly decreased macrophage infiltration in WAT and improved metabolic status in HFD-induced wild-type mice. Importantly, the numbers of M1 macrophages appeared to be increased by the HFD and decreased by either genetic PAI-1 depletion or PAI-039 treatment.

Conclusions: Collectively, our findings provide support for PAI-1 contributing to the development of inflammation in adipose tissue and explain the mechanism of inflammation modulated by PAI-1 in the disordered metabolism in HFD-induced obesity.

Thrombin promotes diet-induced obesity through fibrin-driven inflammation

Obesity promotes a chronic inflammatory and hypercoagulable state that drives cardiovascular disease, type 2 diabetes, fatty liver disease, and several cancers. Elevated thrombin activity underlies obesity-linked thromboembolic events, but the mechanistic links between the thrombin/fibrin(ogen) axis and obesity-associated pathologies are incompletely understood. In this work, immunohistochemical studies identified extravascular fibrin deposits within white adipose tissue and liver as distinct features of mice fed a high-fat diet (HFD) as well as obese patients. Fibγ390-396A mice carrying a mutant form of fibrinogen incapable of binding leukocyte αMβ2-integrin were protected from HFD-induced weight gain and elevated adiposity. Fibγ390-396A mice had markedly diminished systemic, adipose, and hepatic inflammation with reduced macrophage counts within white adipose tissue, as well as near-complete protection from development of fatty liver disease and glucose dysmetabolism. Homozygous thrombomodulin-mutant ThbdPro mice, which have elevated thrombin procoagulant function, gained more weight and developed exacerbated fatty liver disease when fed a HFD compared with WT mice. In contrast, treatment with dabigatran, a direct thrombin inhibitor, limited HFD-induced obesity development and suppressed progression of sequelae in mice with established obesity. Collectively, these data provide proof of concept that targeting thrombin or fibrin(ogen) may limit pathologies in obese patients.

Plasminogen activator inhibitor links obesity and thrombotic cerebrovascular diseases: The roles of PAI-1 and obesity on stroke

One of the global socioeconomic phenomena occurred during the last decades is the increased prevalence of obesity, with direct consequence on the risk of developing thrombotic disorders. As the physiological inhibitor of tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA), plasminogen activator inhibitor-1 (PAI-1) is well known for its role in fibrinolysis. More and more evidences have shown that PAI-1 involves in physiopathologic mechanisms of many diseases and metabolic disorder. Increased serum level of PAI-1 has been observed in obesity and it also contributes to the development of adipose tissue and then has effects on obesity. Meantime, obesity affects also the PAI-1 levels. These evidences indicate the complicated interaction between PAI-1 and obesity. Many clinic studies have confirmed that obesity relates to the stroke outcome although there are many contradictory results. Simultaneously, correlation is found between plasma PAI-1 and thrombotic cerebrovascular diseases. This article reviews contemporary knowledge regarding the complex interplay of obesity, PAI-1 and stroke.

Novel Role of Endogenous Catalase in Macrophage Polarization in Adipose Tissue

Macrophages are important components of adipose tissue inflammation, which results in metabolic diseases such as insulin resistance. Notably, obesity induces a proinflammatory phenotypic switch in adipose tissue macrophages, and oxidative stress facilitates this switch. Thus, we examined the role of endogenous catalase, a key regulator of oxidative stress, in the activity of adipose tissue macrophages in obese mice. Catalase knockout (CKO) exacerbated insulin resistance, amplified oxidative stress, and accelerated macrophage infiltration into epididymal white adipose tissue in mice on normal or high-fat diet. Interestingly, catalase deficiency also enhanced classical macrophage activation (M1) and inflammation but suppressed alternative activation (M2) regardless of diet. Similarly, pharmacological inhibition of catalase activity using 3-aminotriazole induced the same phenotypic switch and inflammatory response in RAW264.7 macrophages. Finally, the same phenotypic switch and inflammatory responses were observed in primary bone marrow-derived macrophages from CKO mice. Taken together, the data indicate that endogenous catalase regulates the polarization of adipose tissue macrophages and thereby inhibits inflammation and insulin resistance.

Effect of photoperiod on the feline adipose transcriptome as assessed by RNA sequencing

Background

Photoperiod is known to cause physiological changes in seasonal mammals, including changes in body weight, physical activity, reproductive status, and adipose tissue gene expression in several species. The objective of this study was to determine the effects of day length on the adipose transcriptome of cats as assessed by RNA sequencing. Ten healthy adult neutered male domestic shorthair cats were used in a randomized crossover design study. During two 12-wk periods, cats were exposed to either short days (8 hr light:16 hr dark) or long days (16 hr light:8 hr dark). Cats were fed a commercial diet to maintain baseline body weight to avoid weight-related bias. Subcutaneous adipose biopsies were collected at wk 12 of each period for RNA isolation and sequencing.

Results

A total of 578 million sequences (28.9 million/sample) were generated by Illumina sequencing. A total of 170 mRNA transcripts were differentially expressed between short day- and long day-housed cats. 89 annotated transcripts were up-regulated by short days, while 24 annotated transcripts were down-regulated by short days. Another 57 un-annotated transcripts were also different between groups. Adipose tissue of short day-housed cats had greater expression of genes involved with cell growth and differentiation (e.g., myostatin; frizzled-related protein), cell development and structure (e.g., cytokeratins), and protein processing and ubiquitination (e.g., kelch-like proteins). In contrast, short day-housed cats had decreased expression of genes involved with immune function (e.g., plasminogen activator inhibitor 1; chemokine (C-C motif) ligand 2; C-C motif chemokine 5; T-cell activators), and altered expression of genes associated with carbohydrate and lipid metabolism.

Conclusions

Collectively, these gene expression changes suggest that short day housing may promote adipogenesis, minimize inflammation and oxidative stress, and alter nutrient metabolism in feline adipose tissue, even when fed to maintain body weight. Although this study has highlighted molecular mechanisms contributing to the seasonal metabolic changes observed in cats, future research that specifically targets and studies these biological pathways, and the physiological outcomes that are affected by them, is justified.

Ubiquitin-specific protease 2-69 in macrophages potentially modulates metainflammation

Macrophages play a critical role in chronic inflammation and metabolic diseases. We identified a longer splice variant of ubiquitin specific protease (USP) 2-69 as a novel molecule that modulates pathways implicated in metabolic disorders. Expression levels of aP2/FABP4 and PAI-1/SERPINE1 genes were increased by 4- and 1.8-fold, respectively, after short hairpin RNA-mediated knockdown (KD) of the USP2 gene, and such expression was alleviated by overexpression of USP2-69 in human myeloid cell lines. Supernatants derived from USP2-KD cells induced IL6 (∼6-fold) and SAA3 (∼15-fold) in 3T3-L1 adipocytes to suggest the anti-inflammatory properties of USP2. In addition, we observed a 30% decrease in the number of macrophages in mesenteric adipose tissue derived from USP2-69 transgenic mice fed a high-fat diet for 14 wk compared with that in their C57BL/6 littermates (P<0.01), which was consistent with a ∼40% decrease in transcription of aP2 and PAI-1. The aP2 locus exhibited elevated chromatin accessibility (>2.1-fold), methylation of histone H3 lysine 4 (>4.5-fold), and acetylation of histone H4 (>2.5-fold) in USP2-KD cells. Transfection of isopeptidase-mutated USP2-69 did not alter chromatin conformation on the aP2 locus in USP2-KD cells. Our results suggest that USP2-69 suppresses meta-inflammatory molecules involved in the development of type-2 diabetes.

Urokinase plasminogen activator induces pro-fibrotic/m2 phenotype in murine cardiac macrophages

Objective

Inflammation and fibrosis are intertwined in multiple disease processes. We have previously found that over-expression of urokinase plasminogen activator in macrophages induces spontaneous macrophage accumulation and fibrosis specific to the heart in mice. Understanding the relationship between inflammation and fibrosis in the heart is critical to developing therapies for diverse myocardial diseases. Therefore, we sought to determine if uPA induces changes in macrophage function that promote cardiac collagen accumulation.

Methods and Results

We analyzed the effect of the uPA transgene on expression of pro-inflammatory (M1) and pro-fibrotic (M2) genes and proteins in hearts and isolated macrophages of uPA overexpressing mice. We found that although there was elevation of the pro-inflammatory cytokine IL-6 in hearts of transgenic mice, IL-6 is not a major effector of uPA induced cardiac fibrosis. However, uPA expressing bone marrow-derived macrophages are polarized to express M2 genes in response to IL-4 stimulation, and these M2 genes are upregulated in uPA expressing macrophages following migration to the heart. In addition, while uPA expressing macrophages express a transcriptional profile that is seen in tumor–associated macrophages, these macrophages promote collagen expression in cardiac but not embryonic fibroblasts.

Conclusions

Urokinase plasminogen activator induces an M2/profibrotic phenotype in macrophages that is fully expressed after migration of macrophages into the heart. Understanding the mechanisms by which uPA modulates macrophage function may reveal insights into diverse pathologic processes.

Gastric expression of plasminogen activator inhibitor (PAI)-1 is associated with hyperphagia and obesity in mice

The adipokine plasminogen activator inhibitor (PAI)-1 is increased in plasma of obese individuals and exhibits increased expression in the stomachs of individuals infected with Helicobacter. To investigate the relevance of gastric PAI-1, we used 1.1 kb of the H(+)/K(+)β subunit promoter to overexpress PAI-1 specifically in mouse gastric parietal cells (PAI-1-H/Kβ mice). We studied the physiological, biochemical, and behavioral characteristics of these and mice null for PAI-1 or a putative receptor, urokinase plasminogen activator receptor (uPAR). PAI-1-H/Kβ mice had increased plasma concentrations of PAI-1 and increased body mass, adiposity, and hyperphagia compared with wild-type mice. In the latter, food intake was inhibited by cholecystokinin (CCK)8s, but PAI-1-H/Kβ mice were insensitive to the satiating effects of CCK8s. PAI-1-H/Kβ mice also had significantly reduced expression of c-fos in the nucleus tractus solitarius in response to CCK8s and refeeding compared with wild-type mice. Exogenous PAI-1 reversed the effects of CCK8s on food intake and c-fos levels in the nucleus tractus solitarius of wild-type mice, but not uPAR-null mice. Infection of C57BL/6 mice with Helicobacter felis increased gastric abundance of PAI-1 and reduced the satiating effects of CCK8s, whereas the response to CCK8s was maintained in infected PAI-1-null mice. In cultured vagal afferent neurons, PAI-1 inhibited stimulation of neuropeptide Y type 2 receptor (Y2R) expression by CCK8s. Thus, gastric expression of PAI-1 is associated with hyperphagia, moderate obesity, and resistance to the satiating effects of CCK indicating a new role in suppressing signals from the upper gut that inhibit food intake.

Fatty acid-induced production of plasminogen activator inhibitor-1 by adipose macrophages is greater in middle-aged versus younger adult participants

BACKGROUND

Human aging is associated with heightened risk of diabetes and cardiovascular disease. Increased fat mass may contribute to age-related diseases by harboring inflammatory macrophages that produce metabolically important proteins such as plasminogen activator inhibitor-1 (PAI-1). Elevated PAI-1 concentrations have been implicated in the pathogenesis of such aging-related conditions as insulin resistance, obesity, and atherosclerosis. We have previously reported that increased plasma free fatty acid (FFA) concentrations augment both circulating PAI-1 concentrations and PAI-1 production by adipose tissue macrophages (ATMs).

METHODS

Because increasing age is associated with increased infiltration and reactivity of adipose macrophages, we performed euglycemic-hyperinsulinemic clamp studies and adipose tissue biopsies with and without elevated FFA concentrations in 31 nondiabetic participants stratified by age, to determine whether middle-aged individuals manifest heightened insulin resistance and PAI-1 production by ATMs in response to elevated nutrient signals relative to their young adult peers.

RESULTS

We observed that elevating FFA concentrations under euglycemic-hyperinsulinemic clamp conditions induced the same degree of insulin resistance in both middle-aged and younger body mass index-matched adults, whereas systemic PAI-1 concentrations were significantly increased in the middle-aged group. Likewise, elevated FFA and insulin concentrations induced larger increases in PAI-1 gene expression in the whole fat and ATMs of middle-aged compared with younger adult participants.

CONCLUSIONS

These studies reveal a heightened adipose inflammatory response to increased FFA and insulin availability in middle-aged individuals relative to younger adults, suggesting that increased susceptibility to the effects of fatty acid excess may contribute to the pathogenesis of age-related diseases.

Deficiency of ACE2 in Bone-Marrow-Derived Cells Increases Expression of TNF-α in Adipose Stromal Cells and Augments Glucose Intolerance in Obese C57BL/6 Mice

Deficiency of ACE2 in macrophages has been suggested to promote the development of an inflammatory M1 macrophage phenotype. We evaluated effects of ACE2 deficiency in bone-marrow-derived stem cells on adipose inflammation and glucose tolerance in C57BL/6 mice fed a high fat (HF) diet. ACE2 activity was increased in the stromal vascular fraction (SVF) isolated from visceral, but not subcutaneous adipose tissue of HF-fed mice. Deficiency of ACE2 in bone marrow cells significantly increased mRNA abundance of F4/80 and TNF-α in the SVF isolated from visceral adipose tissue of HF-fed chimeric mice, supporting increased presence of inflammatory macrophages in adipose tissue. Moreover, deficiency of ACE2 in bone marrow cells modestly augmented glucose intolerance in HF-fed chimeric mice and increased blood levels of glycosylated hemoglobin. In summary, ACE2 deficiency in bone marrow cells promotes inflammation in adipose tissue and augments obesity-induced glucose intolerance.

Dietary strawberry powder reduces blood glucose concentrations in obese and lean C57BL/6 mice, and selectively lowers plasma C-reactive protein in lean mice

The purpose of the present study was to test the anti-inflammatory and blood glucose (BG)-regulating capacity of strawberries in a mouse model of diet-induced obesity. A total of thirty-six male C57BL/6J mice were randomly divided into four groups (nine mice per group). Mice were fed a low-fat diet (LF, 13 % fat), the LF supplemented with 2·6 % freeze-dried strawberry powder (LFSB), a high-fat diet (HF, 44 % fat) or the HF supplemented with 2·6 % strawberry powder (HFSB). Blood samples were collected to measure BG, inflammation and systemic markers for endocrine function of pancreas and adipose tissue. Splenocytes were harvested at the end of the study and activated with either anti-cluster of differentiation (CD) 3/anti-CD28 antibodies or lipopolysaccharide to test immune responsiveness. The HF increased non-fasted BG, insulin, soluble intracellular adhesion molecule-1, E-selectin, leptin, resistin and plasminogen activator protein-1 (P < 0·05). High dietary fat decreased IL-4 production from activated splenocytes (P < 0·05). BG concentrations were lower in the mice supplemented with SB (10·64 mmol/l) compared to the non-supplemented mice (11·37 mmol/l; P = 0·0022). BG values were approximately 6·5 % lower in the supplemented mice. Additionally, SB lowered plasma C-reactive protein in the LFSB group compared to the other three groups (P < 0·05). The dietary intake of SB approximated one human serving of strawberries. These results, although modest, support a promising role for dietary strawberries in reducing the risks associated with obesity and diabetes, and regulating the levels of inflammatory markers in non-obese individuals.

Particulate matter-induced lung inflammation increases systemic levels of PAI-1 and activates coagulation through distinct mechanisms

Background

Exposure of human populations to ambient particulate matter (PM) air pollution significantly contributes to the mortality attributable to ischemic cardiovascular events. We reported that mice treated with intratracheally instilled PM develop a prothrombotic state that requires the release of IL-6 by alveolar macrophages. We sought to determine whether exposure of mice to PM increases the levels of PAI-1, a major regulator of thrombolysis, via a similar or distinct mechanism.

Methods and Principal Findings

Adult, male C57BL/6 and IL-6 knock out (IL-6^−/−) mice were exposed to either concentrated ambient PM less than 2.5 µm (CAPs) or filtered air 8 hours daily for 3 days or were exposed to either urban particulate matter or PBS via intratracheal instillation and examined 24 hours later. Exposure to CAPs or urban PM resulted in the IL-6 dependent activation of coagulation in the lung and systemically. PAI-1 mRNA and protein levels were higher in the lung and adipose tissue of mice treated with CAPs or PM compared with filtered air or PBS controls. The increase in PAI-1 was similar in wild-type and IL-6^−/− mice but was absent in mice treated with etanercept, a TNF-α inhibitor. Treatment with etanercept did not prevent the PM-induced tendency toward thrombus formation.

Conclusions

Mice exposed to inhaled PM exhibited a TNF-α-dependent increase in PAI-1 and an IL-6-dependent activation of coagulation. These results suggest that multiple mechanisms link PM-induced lung inflammation with the development of a prothrombotic state.

Oxidized LDL and lysophosphatidylcholine stimulate plasminogen activator inhibitor-1 expression through reactive oxygen species generation and ERK1/2 activation in 3T3-L1 adipocytes

Plasminogen activator inhibitor-1 (PAI-1) is secreted from adipose tissue and is considered to be a risk factor for both atherosclerosis and insulin resistance. Here we report for the first time that PAI-1 expression is enhanced by oxidized low-density lipoprotein (OxLDL) and its lipid component lysophosphatidylcholine (LPC) in mouse 3T3-L1 adipocytes. In fully differentiated 3T3-L1 cells, OxLDL treatment increased the mRNA expression and protein secretion of PAI-1 in a dose- and time-dependent manner, whereas native LDL had no effect. The addition of an anti-CD36 antibody suppressed OxLDL-stimulated PAI-1 expression by 50%, suggesting that adipose-derived CD36 contributes to roughly half of the PAI-1 expression stimulated by OxLDL. In addition, pharmacological experiments showed that the OxLDL-stimulated enhancement in PAI-1 expression was mediated through the generation of reactive oxygen species (ROS) and phosphorylation of extracellular signal-regulated kinase 1/2. Furthermore, LPC, a major lipid component of OxLDL, was responsible for the enhanced expression of PAI-1 as phospholipase A(2)-treated acetyl LDL, which generates LPC, strongly stimulated PAI-1 expression, whereas acetyl LDL itself had no such activity. These data demonstrate that the uptake of OxLDL and, in particular, its lipid component LPC into adipocytes triggers aberrant ROS-mediated PAI-1 expression, which may be involved in the pathogenesis of metabolic syndrome.

Plasminogen activator inhibitor type-1 is an independent marker of metabolic disorders in young adults born small for gestational age

BACKGROUND

Metabolic syndrome (MS) has been associated with being born small for gestational age (SGA). In epidemiological studies plasminogen activator inhibitor type-1 (PAI-1) levels have been associated with MS. Few studies have examined this association in subjects born SGA.

PATIENTS AND METHODS

Five hundred and fifty-seven SGA adults (birth weight < 10th percentile) were compared with 671 subjects with a birth weight between the 25th and 75th percentiles (control group). MS was defined using the World Health Organization (WHO) definition. Active PAI-1 was measured on citrated plasma with bio-immunoassay.

RESULTS

MS was more prevalent in the SGA group (8.7%) than in the control group (5.5%; P = 0.03). In both groups, PAI-1 concentrations were significantly correlated with waist circumference, plasma triglycerides, homeostatic model assessment-insulin resistance (HOMA-IR) and associated with male sex and MS. PAI-1 concentrations were significantly increased in the SGA group (12.2 ± 21.2 vs. 10.0 ± 13.5 IU mL⁻¹, P = 0.03) and this remained after adjustment of metabolic variables (P = 0.009). PAI-1 concentrations above 4.9 IU mL⁻¹ (= median of PAI-1 concentration in the control group) were present in 94% of the subjects with MS. Moreover, the adjusted odds ratio (OR) for having elevated PAI-1 was 1.48 (1.08; 1.95) in the SGA group in comparison with the control group (P = 0.005).

CONCLUSIONS

 PAI-1 plasma concentrations were significantly increased in SGA subjects independently of MS. These data suggest that elevation of PAI-1 concentrations might be an indication of an abnormal secretion at the level of the adipose tissue, endothelial cells or liver and implicated in metabolic disorders reported in SGA subjects.

Review: Therapeutic potential of plasminogen activator inhibitor-1 inhibitors

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of fibrinolysis and regulates cell migration and fibrosis. Preclinical studies using genetically altered mice and biological or small molecule inhibitors have elucidated a role for PAI-1 in the pathogenesis of thrombosis, vascular remodeling, renal injury, and initiation of diabetes. Inhibition of PAI-1 is a potential therapeutic strategy in these diseases.

Characterization of a novel class of polyphenolic inhibitors of plasminogen activator inhibitor-1

Plasminogen activator inhibitor type 1, (PAI-1) the primary inhibitor of the tissue-type (tPA) and urokinase-type (uPA) plasminogen activators, has been implicated in a wide range of pathological processes, making it an attractive target for pharmacologic inhibition. Currently available small-molecule inhibitors of PAI-1 bind with relatively low affinity and do not inactivate PAI-1 in the presence of its cofactor, vitronectin. To search for novel PAI-1 inhibitors with improved potencies and new mechanisms of action, we screened a library selected to provide a range of biological activities and structural diversity. Five potential PAI-1 inhibitors were identified, and all were polyphenolic compounds including two related, naturally occurring plant polyphenols that were structurally similar to compounds previously shown to provide cardiovascular benefit in vivo. Unique second generation compounds were synthesized and characterized, and several showed IC(50) values for PAI-1 between 10 and 200 nm. This represents an enhanced potency of 10-1000-fold over previously reported PAI-1 inactivators. Inhibition of PAI-1 by these compounds was reversible, and their primary mechanism of action was to block the initial association of PAI-1 with a protease. Consistent with this mechanism and in contrast to previously described PAI-1 inactivators, these compounds inactivate PAI-1 in the presence of vitronectin. Two of the compounds showed efficacy in ex vivo plasma and one blocked PAI-1 activity in vivo in mice. These data describe a novel family of high affinity PAI-1-inactivating compounds with improved characteristics and in vivo efficacy, and suggest that the known cardiovascular benefits of dietary polyphenols may derive in part from their inactivation of PAI-1.

Getting the message across: mechanisms of physiological cross talk by adipose tissue

Obesity is associated with resistance of skeletal muscle to insulin-mediated glucose uptake, as well as resistance of different organs and tissues to other metabolic and vascular actions of insulin. In addition, the body is exquisitely sensitive to nutrient imbalance, with energy excess or a high-fat diet rapidly increasing insulin resistance, even before noticeable changes occur in fat mass. There is a growing acceptance of the fact that, as well as acting as a storage site for surplus energy, adipose tissue is an important source of signals relevant to, inter alia, energy homeostasis, fertility, and bone turnover. It has also been widely recognized that obesity is a state of low-grade inflammation, with adipose tissue generating substantial quantities of proinflammatory molecules. At a cellular level, the understanding of the signaling pathways responsible for such alterations has been intensively investigated. What is less clear, however, is how alterations of physiology, and of signaling, within one cell or one tissue are communicated to other parts of the body. The concepts of cell signals being disseminated systemically through a circulating "endocrine" signal have been complemented by the view that local signaling may similarly occur through autocrine or paracrine mechanisms. Yet, while much elegant work has focused on the alterations in signaling that are found in obesity or energy excess, there has been less attention paid to ways in which such signals may propagate to remote organs. This review of the integrative physiology of obesity critically appraises the data and outlines a series of hypotheses as to how interorgan cross talk takes place. The hypotheses presented include the "fatty acid hypothesis,", the "portal hypothesis,", the "endocrine hypothesis,", the "inflammatory hypothesis,", the "overflow hypothesis,", a novel "vasocrine hypothesis," and a "neural hypothesis," and the strengths and weaknesses of each hypothesis are discussed.

Macrophage content in subcutaneous adipose tissue: associations with adiposity, age, inflammatory markers, and whole-body insulin action in healthy Pima Indians

OBJECTIVE

In severely obese individuals and patients with diabetes, accumulation and activation of macrophages in adipose tissue has been implicated in the development of obesity-associated complications, including insulin resistance. We sought to determine whether in a healthy population, adiposity, sex, age, or insulin action is associated with adipose tissue macrophage content (ATMc) and/or markers of macrophage activation.

RESEARCH DESIGN AND METHODS

Subcutaneous ATMc from young adult Pima Indians with a wide range of adiposity (13-46% body fat, by whole-body dual-energy X-ray absorptiometry) and insulin action (glucose disposal rate 1.6-9 mg/kg estimated metabolic body size/min, by glucose clamp) were measured. We also measured expression in adipose tissue of factors implicated in macrophage recruitment and activation to determine any association with ATMc and insulin action.

RESULTS

ATMc, as assessed by immunohistochemistry (Mphi) and by macrophage-specific gene expression (CD68, CD11b, and CSF1R), were correlated with percent body fat, age, and female sex. Gene expression of CD68, CD11b, and CSF1R but not Mphi was correlated negatively with glucose disposal rate but not after adjustment for percent body fat, age, and sex. However, adipose tissue expression of plasminogen activator inhibitor type-1 (PAI-1) and CD11 antigen-like family member C (CD11c), markers produced by macrophages, were negatively correlated with adjusted glucose disposal rate (r = -0.28, P = 0.05 and r = -0.31, P = 0.03).

CONCLUSIONS

ATMc is correlated with age and adiposity but not with insulin action independent of adiposity in healthy human subjects. However, PAI-1 and CD11c expression are independent predictors of insulin action, indicating a possible role for adipose tissue macrophage activation.

Inflamed adipose tissue, insulin resistance and vascular injury

Type 2 diabetes is the most common metabolic disorder today and has reached epidemic proportions in many countries. Insulin resistance and inflammation play a central role in the pathogenesis of type 2 diabetes and are present long before the onset of the disease. During this time, many of the complications associated with type 2 diabetes are initiated. Of major concern is the two- to fourfold increase in cardiovascular morbidity and mortality in this group compared to a nondiabetic population. Obesity, characterized by enlarged fat cells, and insulin resistance are, like type 2 diabetes, associated with impaired adipogenesis and a low-grade chronic inflammation that to a large extent emanates from the adipose tissue. Both these processes contribute to unfavourable alterations of the circulating levels of several bioactive molecules (adipokines) that are secreted from the adipose tissue, many of which have documented inhibitory effects on insulin sensitivity in the liver and peripheral tissues and, in addition, have negative effects on the cardiovascular system.Here we review current knowledge of the adipose tissue as an endocrine organ, the local and systemic effects of a chronic state of low-grade inflammation residing in the adipose tissue, and, in particular, the effects of inflammation and circulating adipokines on the vascular wall.

Characterization of human mesenchymal stem cell secretome at early steps of adipocyte and osteoblast differentiation

Background

It is well established that adipose tissue plays a key role in energy storage and release but is also a secretory organ and a source of stem cells. Among different lineages, stem cells are able to differentiate into adipocytes and osteoblasts. As secreted proteins could regulate the balance between both lineages, we aimed at characterizing the secretome of human multipotent adipose-derived stem cell (hMADS) at an early step of commitment to adipocytes and osteoblasts.

Results

A proteomic approach, using mono-dimensional electrophoresis and tandem mass spectrometry, allowed us to identify a total of 73 proteins at day 0 and day 3 of adipocyte and osteoblast differentiation. Analysis of identified proteins showed that 52 % corresponded to classical secreted proteins characterized by a signal peptide, that 37 % previously described in the extracellular compartment were devoid of signal peptide and that 11 % neither exhibited a signal peptide nor had been previously described extracellularly. These proteins were classified into 8 clusters according to their function. Quantitative analysis has been performed for 8 candidates: PAI-1, PEDF, BIGH3, PTX3, SPARC, ENO1, GRP78 and MMP2. Among them, PAI-1 was detected at day 0 and day 3 of osteoblast differentiation but never in adipocyte secretome. Furthermore we showed that PAI-1 mRNA was down-regulated in the bone of ovariectomized mice.

Conclusion

Given its regulation during the early events of hMADS cell differentiation and its status in ovariectomized mice, PAI-1 could play a role in the adipocyte/osteoblast balance and thus in bone diseases such as osteoporosis.

Adipokines: linking obesity and cardiovascular disease

Obesity is fast becoming one of the most important contributors to cardiovascular disease. Adipose tissue is gaining recognition as a key endocrine organ that secretes a growing number of adipokines, linking adiposity with inflammation, endothelial dysfunction and the initiation of atherosclerosis. In particular, accumulation of visceral adipose tissue is implicated in the development of cardiovascular disease as it is associated with increased macrophage infiltration and oversecretion of proinflammatory and prothrombotic factors, such as TNF-α, IL-6, plasminogen activator inhibitor-1, leptin, resistin and angiotensinogen, and reduced secretion of the antiatherogenic factor adiponectin. As adipokines represent a key molecular link between obesity and the atherogenic state, research directed at understanding the physiology and biochemistry of these factors should open the door for discovery of novel therapeutics.

Links Between Adipose Tissue and Thrombosis in the Mouse

Obesity has become a global epidemic and carries a considerable negative impact in regard to quality of life and life expectancy. A primary problem is that obese individuals are at increased risk of suffering from cardiovascular disease complications such as myocardial infarction and stroke. Because fat accumulation is a consistent aspect of obesity, mechanisms that may link adipose tissue to cardiovascular disease complications should be considered. Proteins expressed from adipose tissue, known as adipokines, are hypothesized to have important effects on the progression and incidence of cardiovascular disease complications. This review examines the evidence that adipokines play a direct role in vascular thrombosis, an important event in cardiovascular disease complications.

Deficiency of plasminogen activator inhibitor-2 impairs nutritionally induced murine adipose tissue development

BACKGROUND

A functional role for several components of the fibrinolytic (plasminogen/plasmin) system in development of adipose tissue has been demonstrated. No information is available, however, on a potential role of plasminogen activator inhibitor-2 (PAI-2) in obesity.

METHODS

In vitro, 3T3-F442A murine pre-adipocytes were differentiated into mature adipocytes. In vivo, 5-week-old male PAI-2-deficient (PAI-2(-/-)) mice and wild-type (WT) controls of the same genetic background (C57Bl/6) were kept on a high fat diet (HFD, caloric value of 20.1 kJ g(-1)) for 15 weeks.

RESULTS

Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed expression of PAI-2 mRNA during in vitro differentiation of pre-adipocytes and in vivo in s.c. and gonadal (GON) adipose tissues of WT mice, where it was localized both in the stromal/vascular cell fraction and in adipocytes. During HFD feeding, food intake and body weight gain were comparable for WT and PAI-2(-/-) mice. Subcutaneous plus GON fat mass was, however, significantly lower in PAI-2(-/-) mice (3.15 +/- 0.21 vs. 3.91 +/- 0.18 g; P < 0.05). Immunohistochemical analysis of adipose tissues revealed significant adipocyte hypotrophy in s.c. fat of PAI-2(-/-) mice (about 25% reduction in size; P < 0.01). Blood vessel density, normalized to adipocyte number, was comparable in s.c. fat, but was lower (P < 0.05) in GON fat of PAI-2(-/-) mice. Adipose tissue-associated fibrinolytic activity was not affected by PAI-2 deficiency.

CONCLUSION

PAI-2 promotes adipose tissue development in mice via a mechanism independent of its antifibrinolytic effect.

Nitric oxide dysregulates adipocytokine expression in 3T3-L1 adipocytes

Obesity is associated with infiltration of macrophages into adipose tissue, and macrophages are an important source of nitric oxide (NO). Dysregulated production of fat-derived secretory factor, adipocytokine, leads to obesity-linked metabolic disorders. However, it has not been fully determined whether NO might have direct effects on adipocytokine expressions. Here, we show that NO donor treatment downregulated gene expression and secretion of adiponectin, and upregulated mRNA levels of PAI-1 and IL-6. NO donor reduced promoter activity of adiponectin through PPARgamma responsive element. Moreover, NO donor activated JNK and NF-kappaB pathways, and inhibitors of these pathways rescued NO-mediated upregulation of PAI-1 and IL-6. Analysis of adipose tissue of high-fat-fed obese mice showed upregulation of PAI-1 and IL-6 expression, increased synthesis of NO, and downregulation of adiponectin. Our results suggest that increased NO synthesis might be partly responsible for dysregulation of adipocytokines in adipose tissue.

Macrophage TNF-alpha contributes to insulin resistance and hepatic steatosis in diet-induced obesity

Obesity is commonly associated with development of insulin resistance and systemic evidence of inflammation. Macrophages contribute to inflammatory amplification in obesity and may contribute directly to insulin resistance and the development of nonalcoholic fatty liver disease through the production of inflammatory cytokines, including tumor necrosis factor (TNF)-alpha. To test this hypothesis, we transplanted male wild-type (WT) and TNF-alpha deficient (KO) mice with either TNF-alpha-sufficient (TNF-alpha(+/+)) or TNF-alpha-deficient (TNF-alpha(-/-)) bone marrow. After consuming a high-fat diet for 26 wk, metabolic and morphometric characteristics of the animals were analyzed. While there were no differences in terms of relative weight gain, body composition analysis yielded a lower relative adipose and higher relative lean mass in mice lacking TNF-alpha, which was partially explained by reduced epididymal fat pad and liver weight. TNF-alpha(-/-) -->KO mice exhibited enhanced insulin sensitivity compared with that observed in TNF-alpha(+/+)-->KO mice; remarkably, no protection against insulin resistance was provided by transplanting TNF-alpha(-/-) bone marrow in WT mice compared with TNF-alpha(+/+)-->WT. The preserved insulin sensitivity seen in TNF-alpha(-/-)-->KO mice provided protection against the development of hepatic steatosis. Taken together, these data indicate that macrophage-derived TNF-alpha contributes to the pattern and extent of fat accumulation and insulin resistance in diet-induced obesity; however, this contribution is negligible in the presence of host-derived TNF-alpha.

Plasminogen activator inhibitor-1, adipose tissue and insulin resistance

PURPOSE OF REVIEW

Plasminogen activator inhibitor (PAI)-1 is a physiological inhibitor of plasminogen activators (urokinase and tissue types) and vitronectin. It is synthesized by adipose tissue, and its levels in plasma are increased in obesity and reduced with weight loss. Circulating PAI-1 level predicts development of type 2 diabetes, suggesting that it may be causally related to development of obesity. A role for PAI-1 in development of obesity has only partially been established, however. This review summarizes current knowledge, gives context to developments thus far and discusses controversies.

RECENT FINDINGS

In addition to its role in atherothrombosis, PAI-1 might be involved in adipose tissue development. PAI-1 is produced by ectopic fat depots under the influence of inducers. Among the most recently described inducers are inflammation, oxidative stress and circadian clock protein. PAI-1 may play several roles in contributing to obesity: through indirect effects on insulin signalling, by influencing adipocyte differentiation and by regulating recruitment of inflammatory cells within adipose tissue.

SUMMARY

These recent findings emphasize the involvement of PAI-1 in controlling the biology of adipose tissue; PAI-1 is an attractive new therapeutic target to retard the metabolic complications that accompany obesity.