Reciprocal regulation of tissue-type and urokinase-type plasminogen activators in the differentiation of murine preadipocyte line 3T3-L1 and the hormonal regulation of fibrinolytic factors in the mature adipocytes

Cinnamon extract improves abnormalities in glucose tolerance by decreasing Acyl-CoA synthetase long-chain family 1 expression in adipocytes

We previously demonstrated that cinnamon extract (CE) alleviates streptozotocin-induced type 1 diabetes in rats. The present study aimed to elucidate the detailed molecular target of cinnamon in cultured adipocytes and epididymal adipose tissue of type 2 diabetes model mice. Two-dimensional gel electrophoresis was employed to determine the molecular target of cinnamon in adipocytes. The function of Acyl-CoA synthetase long-chain family-1 (ACSL1), a molecular target of cinnamon that was identified in this study, was further investigated in 3T3-L1 adipocytes using specific inhibitors. Type 2 diabetes model mice (KK-Ay/TaJcl) were used to investigate the effect of CE on glucose tolerance, ACSL1 expression, and related signal molecules in vivo. CE decreased ACSL1 mRNA and protein expression in 3T3-L1 adipocytes but increased glucose uptake and AMPK signaling activation; moreover, a similar effect was observed with an ACSL1 inhibitor. CE improved glucose tolerance and downregulated ACSL1 in mice adipose tissue in vivo. ACSL1 was demonstrated as a molecular target of CE in type 2 diabetes both in a cell culture system and diabetic mouse model.

Halophila beccarii extract ameliorate glucose uptake in 3T3-L1 adipocyte cells and improves glucose homeostasis in streptozotocin-induced diabetic rats

The regulation of carbohydrate metabolizing enzymes is an effective way of reducing blood glucose levels and improving glycogen synthesis during the management of type 2 diabetes. The present investigation was conducted to explain the detailed mechanism with which a Seagrass, Halophila beccarii extract (HBE) enhances the glucose uptake in the 3T3-L1 adipocyte cell culture system in invitro. HBE stimulates the glucose uptake by the translocation of glucose transporter 4 (GLUT4) on to plasma cell membrane through induction of insulin receptor substrate 1 (IRS-1)/protein kinase B (Akt) signaling pathways. To assess the effect of HBE on T2DM, we used invivo experimental diabetes rat models induced with streptozotocin (STZ) to perform oral GTT and ITT. Furthermore, we assessed the enzymatic profile of Glycolysis, Pentose phosphate pathway, and gluconeogenesis from liver tissue homogenate. After long-term exposure with HBE, our results confirmed, that HBE improves the glucose uptake in 3T3-L1 cell lines by up-regulation of glucose transporter type 4 (GLUT4) through uptake of glucose by the adipocytes. The resulting data indicated that HBE had a great potentiality in preventing diabetes and maintaining glucose homeostasis through improving glucose uptake. The present data also showed that HBE with its insulin mimetic activity activates glycogen synthesis and enhances glucose utilization by regulating the carbohydrate metabolic enzymes. The similarity between HBE and insulin indicates that the HBE follows the mechanisms same as the insulin signaling pathway to show the antidiabetic activity.

EID1 suppresses lipid accumulation by inhibiting the expression of GPDH in 3T3-L1 preadipocytes

The imbalance between food intake and energy expenditure causes high accumulation of triglycerides in adipocytes. Obesity is related with the increased lipid accumulation in white adipose tissue, which is a major risk factor for the development of metabolic disorders, such as type 2 diabetes and cardiovascular disease. This study highlights the role of E1A-like inhibitor of differentiation 1 (EID1) in the modulation of adipogenesis through the downregulation of glycerol-3-phosphate dehydrogenase (GPDH), which is a key enzyme in the synthesis of triglycerides and is considered to be a marker of adipogenesis. By analyzing DNA microarray data, we found that when EID1 is overexpressed in preadipocytes (3T3-L1 cells) during adipocyte differentiation, EID1 inhibits lipid accumulation through the downregulation of GPDH. In contrast, EID1 is not involved in the regulation of intracellular glucose via the translocation of glucose transporter. A confocal image analysis showed that EID1 is located in the nucleus of preadipocytes in the form of speckles, which could be involved as a regulator of the transcriptional process. We further confirmed that EID1 is able to bind to the promoter sequence of GPDH in the nucleus. These findings provide a molecular explanation for the inhibitory effect of EID1 on lipid accumulation in adipocytes.

Role of plasminogen activator inhibitor-1 in glucocorticoid-induced diabetes and osteopenia in mice

Long-term use of glucocorticoids (GCs) causes numerous adverse effects, including glucose/lipid abnormalities, osteoporosis, and muscle wasting. The pathogenic mechanism, however, is not completely understood. In this study, we used plasminogen activator inhibitor-1 (PAI-1)-deficient mice to explore the role of PAI-1 in GC-induced glucose/lipid abnormalities, osteoporosis, and muscle wasting. Corticosterone markedly increased the levels of circulating PAI-1 and the PAI-1 mRNA level in the white adipose tissue of wild-type mice. PAI-1 deficiency significantly reduced insulin resistance and glucose intolerance but not hyperlipidemia induced by GC. An in vitro experiment revealed that active PAI-1 treatment inhibits insulin-induced phosphorylation of Akt and glucose uptake in HepG2 hepatocytes. However, this was not observed in 3T3-L1 adipocytes and C2C12 myotubes, indicating that PAI-1 suppressed insulin signaling in hepatocytes. PAI-1 deficiency attenuated the GC-induced bone loss presumably via inhibition of apoptosis of osteoblasts. Moreover, the PAI-1 deficiency also protected from GC-induced muscle loss. In conclusion, the current study indicated that PAI-1 is involved in GC-induced glucose metabolism abnormality, osteopenia, and muscle wasting in mice. PAI-1 may be a novel therapeutic target to mitigate the adverse effects of GC.

Cinnamon extract enhances glucose uptake in 3T3-L1 adipocytes and C2C12 myocytes by inducing LKB1-AMP-activated protein kinase signaling

We previously demonstrated that cinnamon extract (CE) ameliorates type 1 diabetes induced by streptozotocin in rats through the up-regulation of glucose transporter 4 (GLUT4) translocation in both muscle and adipose tissues. This present study was aimed at clarifying the detailed mechanism(s) with which CE increases the glucose uptake in vivo and in cell culture systems using 3T3-L1 adipocytes and C2C12 myotubes in vitro. Specific inhibitors of key enzymes in insulin signaling and AMP-activated protein kinase (AMPK) signaling pathways, as well as small interference RNA, were used to examine the role of these kinases in the CE-induced glucose uptake. The results showed that CE stimulated the phosphorylation of AMPK and acetyl-CoA carboxylase. An AMPK inhibitor and LKB1 siRNA blocked the CE-induced glucose uptake. We also found for the first time that insulin suppressed AMPK activation in the adipocyte. To investigate the effect of CE on type 2 diabetes in vivo, we further performed oral glucose tolerance tests and insulin tolerance tests in type 2 diabetes model rats administered with CE. The CE improved glucose tolerance in oral glucose tolerance tests, but not insulin sensitivity in insulin tolerance test. In summary, these results indicate that CE ameliorates type 2 diabetes by inducing GLUT4 translocation via the AMPK signaling pathway. We also found insulin antagonistically regulates the activation of AMPK.

Connective tissue growth factor/CCN-2 is upregulated in epididymal and subcutaneous fat depots in a dietary-induced obesity model

Connective tissue growth factor (CTGF), also known as CCN-2, is a cysteine-rich secreted protein that is involved in a range of biological processes, including regulation of cell growth and differentiation. Our previous in vitro studies have shown that CCN-2 inhibits adipocyte differentiation, although whether CCN-2 is regulated in vivo in adipogenesis is undetermined and was investigated in this study. C57BL/6 male mice were fed either standard laboratory chow (ND) or a diet high in fat (HFD; 45% fat) for 15 or 24 wk. HFD animals that gained >5 g in weight (termed HFD-fat) were insulin resistant and were compared with HFD-fed animals, which failed to gain weight (termed HFD-lean). HFD-fat mice had significantly increased CCN-2 mRNA levels in both the subcutaneous and epididymal fat pads, whereas CCN-2 mRNA was not induced in the epididymal site in HFD-lean mice. Also in HFD-fed animals, epididymal CCN-2 mRNA correlated positively with key genes involved in adipocyte differentiation, adiponectin and PPARγ (P < 0.001 and P < 0.002, respectively). Additionally, epididymal CCN-2 mRNA correlated positively with two markers of tissue turnover, PAI-1 in HFD-fat mice only and TIMP-1, but only in the HFD-lean mice. Collectively, these findings suggest that CCN-2 plays a role in adipocyte differentiation in vivo and thus in the pathogenesis of obesity linked with insulin resistance.

Elastase and tryptase govern TNFα-mediated production of active chemerin by adipocytes

Chemerin is a leukocyte chemoattractant and adipokine with important immune and metabolic roles. Chemerin, secreted in an inactive form prochemerin, undergoes C-terminal proteolytic cleavage to generate active chemerin, a ligand for the chemokine-like receptor-1 (CMKLR1). We previously identified that adipocytes secrete and activate chemerin. Following treatment with the obesity-associated inflammatory mediator TNFα, unknown adipocyte mechanisms are altered resulting in an increased ratio of active to total chemerin production. Based on these findings we hypothesized adipocytes produce proteases capable of modifying chemerin and its ability to activate CMKRL1. 3T3-L1 adipocytes expressed mRNA of immunocyte and fibrinolytic proteases known to activate chemerin in vitro. Following treatment with a general protease inhibitor cocktail (PIC), the TNFα-stimulated increase in apparent active chemerin concentration in adipocyte media was amplified 10-fold, as measured by CMKLR1 activation. When the components of the PIC were investigated individually, aprotinin, a serine protease inhibitor, blocked 90% of the TNFα-associated increase in active chemerin. The serine proteases, elastase and tryptase were elevated in adipocyte media following treatment with TNFα and their targeted neutralization recapitulated the aprotinin-mediated effects. In contrast, bestatin, an aminopeptidase inhibitor, further elevated the TNFα-associated increase in active chemerin. Our results support that adipocytes regulate chemerin by serine protease-mediated activation pathways and aminopeptidase deactivation pathways. Following TNFα treatment, increased elastase and tryptase modify the balance between activation and deactivation, elevating active chemerin concentration in adipocyte media and subsequent CMKLR1 activation.

Effect of dibutyryl cyclic adenosine monophosphate on the gene expression of plasminogen activator inhibitor-1 and tissue factor in adipocytes

INTRODUCTION

Hypertrophic adipocytes in obese states express the elevated levels of plasminogen activator inhibitor-1 (PAI-1) and tissue factor (TF). An increase in the intracellular concentration of cyclic adenosine monophosphate (cAMP) promotes triglyceride hydrolysis and may improve dysregulation of adipocyte metabolism. Here, we investigate the effect of dibutyryl-cAMP (a phosphodiesterase-resistant analog of cAMP) on the gene expression of PAI-1 and TF in adipocytes.

MATERIALS AND METHODS

Differentiated 3T3-L1 adipocytes were treated with dibutyryl-cAMP and agents that would be expected to elevate intracellular cAMP, including cilostazol (a phosphodiesterase inhibitor with anti-platelet and vasodilatory properties), isoproterenol (a beta adrenergic agonist) and forskolin (an adenylyl cyclase activator). The levels of PAI-1 and TF mRNAs were measured using real-time quantitative reverse transcription-PCR.

RESULTS AND CONCLUSIONS

The treatment of adipocytes with dibutyryl-cAMP resulted in the inhibition of both lipid accumulation and TF gene expression. However, PAI-1 gene expression was slightly but significantly increased by dibutyryl-cAMP. On the other hand, cilostazol inhibited the expression of PAI-1 without affecting lipid accumulation. When the adipocytes were treated with cilostazol in combination with isoproterenol or forskolin, the inhibitory effect of cilostazol on PAI-1 gene expression was counteracted, thus suggesting that inhibition by cilostazol may not be the result of intracellular cAMP accumulation by phosphodiesterase inhibition. These results suggest the implication of cAMP in regulation of the gene expression of TF and PAI-1 in adipocytes. Our findings will serve as a useful basis for further research in therapy for obesity-associated thrombosis.

CCAAT/enhancer binding protein alpha, beta and delta gene variants: associations with obesity related phenotypes in the Leeds Family Study

OBJECTIVE

To identify novel polymorphisms in the genes encoding the transcription factors CCAAT/enhancer binding protein alpha, beta and delta ( CEBPA, CEBPB, CEBPD) and investigate associations between polymorphisms and obesity-related phenotypes.

METHODS

Denaturing high-performance liquid chromatography (HPLC) was used to screen for novel gene variants and polymorphisms were genotyped in stored DNA from participants of the Leeds Family Study (537 subjects from 89 families). Genotype and haplotype analyses were carried out in STATA and PBAT, respectively.

RESULTS

Twenty-five polymorphisms were identified; 11 in CEBPA, 12 in CEBPB and 2 in CEBPD. Several allelic variants were associated at a nominal 5% level with waist-to-hip ratio (-919G>A in CEBPA, -412G>T and 646C>T in CEBPB), leptin (1558G>A in CEBPA, -1051A>G and 1383T>- in CEBPB) and adiponectin (1382G>T and 1903G>T in CEBPB). Effects of CEBPA and CEBPB allelic variants were independent, but variants within each gene were in linkage disequilibrium. Several associations were observed between other obesity-related traits and allelic variants in CEBPA and CEBPB, but not CEBPD.

CONCLUSION

These findings suggest that common allelic variants in CEBPA and CEBPB could influence abdominal obesity and related metabolic abnormalities associated with type 2 diabetes and cardiovascular disease in healthy White Northern European families, although results require independent confirmation.

Transition of pathophysiological significance of plasminogen activator inhibitor-From a chief player in antiinflammation, antifibrinolysis to that in the development of insulin resistance

In the early phase of research, plasminogen activator inhibitor (PAI) was regarded as a negative regulator of fibrinolytic system, but the later study clarified that the changes in PAI level is closely related to risk factors of various pathologic processes of the lifestyle-related diseases. It is accepted that PAI-1 is a risk factor of the cardiovascular event in lifestyle-related diseases by recent researches analyzing the detailed function of PAI-1. In this review paper, we described the transition of pathophysiological significance of PAI based on many research papers especially from ours, which clarified the mechanism on protein expression of PAI, especially PAI-1.

Connective tissue growth factor inhibits adipocyte differentiation

Adipocyte differentiation is a key process implicated in the pathogenesis of obesity and insulin resistance. Its regulation is triggered by a cascade of transcription factors, including the CCAAT/enhancer binding proteins (C/EBPs) and peroxisome proliferator-activated receptor-gamma (PPARgamma). Growth factors such as transforming growth factor-beta1 (TGF-beta1) are known to inhibit adipocyte differentiation in vitro, via the C/EBP pathway, and in vivo, but whether a downstream mediator of TGF-beta1, connective tissue growth factor (CTGF), also known as CCN2, has a similar role is unknown. Mouse 3T3-L1 cells were differentiated into adipocytes by using standard methods, and effects and regulation of CTGF were studied. Intervention with recombinant human CTGF during differing stages of differentiation caused an inhibition in the development of the adipocyte phenotype, according to the gene expression of the differentiation markers adiponectin and PPARgamma, as well as suppression of lipid accumulation and expression of the lipogenic enzyme glycerol-3-phosphate dehydrogenase. Whereas CTGF gene expression promptly fell by 90% as 3T3-L1 preadipocytes differentiated into mature adipocytes, CTGF mRNA expression was induced by added TGF-beta1. CTGF applied to cells early in the course of differentiation inhibited total cell protein levels and nuclear localization of the beta-isoform of C/EBP (C/EBP-beta) and, subsequently, total cell C/EBP-alpha levels. CTGF also inhibited the adipocyte differentiation program in primary cultures of mouse preadipocytes. Expression of CTGF mRNA was twofold higher in the central fat depots of mice compared with subcutaneous fat, suggesting a potential role for CTGF in vivo. In summary, these data show that CTGF inhibits the adipocyte differentiation program.

Hydrogenated fat diet intake during pregnancy and lactation modifies the PAI-1 gene expression in white adipose tissue of offspring in adult life

We examine whether feeding pregnant and lactating rats hydrogenated fats rich in trans fatty acids modifies the plasma lipid profiles and the expression of adipokines involved with insulin resistance and cardiovascular disease in their 90-day-old offspring. Pregnant and lactating Wistar rats were fed with either a control diet (C group) or one enriched with hydrogenated vegetable fat (T group). Upon weaning, the male pups were sorted into four groups: CC, mothers were receiving C and pups were kept on C; CT, mothers were receiving C and pups were fed with T; TT, mothers were receiving T and pups were kept on T; TC, mothers were receiving T and pups were fed with C. Pups' food intake and body weight were quantified weekly and the pups were killed at day 90 of life by decapitation. Blood and carcass as well as retroperitoneal, epididymal, and subcutaneous white adipose tissues were collected. Food intake and body weight were lower in TC and TT, and metabolic efficiency was reduced in TT. Offspring of TT and TC rats had increased white adipose tissue PAI-1 gene expression. Insulin receptor was higher in TT than other groups. Ingestion of hydrogenated vegetable fat by the mother during gestation and lactation could promote deleterious consequences, even after the withdrawal of the causal factor.

PPARdelta enhances keratinocyte proliferation in psoriasis and induces heparin-binding EGF-like growth factor

Psoriasis is a common skin disease involving keratinocyte proliferation and altered differentiation, as well as T-cell activation. Here, we show that altered gene transcription in psoriatic skin lesions is highly reproducible between independent data sets. Analysis of gene expression confirmed dysregulation in all expected functional categories, such as IFN signaling and keratinocyte differentiation, and allowed molecular fingerprinting of a previously characterized dendritic cell subset associated with psoriasis tumor necrosis factor alpha (TNF-alpha)- and inducible nitric oxide synthase (iNOS)-producing CD11b(INT) DC (Tip-DC). Unexpectedly, a large group of dysregulated transcripts was related to fatty acid signaling and adipocyte differentiation, exhibiting a pattern consistent with the activation of peroxisome proliferator-activated receptor delta (PPARdelta). PPARdelta itself was strongly induced in psoriasis in vivo. In primary keratinocytes, PPARdelta was induced by the transcription factor activator protein 1, in particular by junB, but not by canonical WNT signaling, in contrast to its regulation in colon carcinoma cells. Activation of PPARdelta enhanced proliferation of keratinocytes, while this was inhibited by knockdown of PPARdelta. Finally, heparin-binding EGF-like growth factor (HB-EGF), known to induce epidermal hyperplasia and itself overexpressed in psoriasis, was identified as a direct target gene of PPARdelta. The present data suggest that activation of PPARdelta is a major event in psoriasis, contributing to the hyperproliferative phenotype by induction of HB-EGF.

Glucagon as a determinant of fibrinolytic activity in men with different stages of glucose tolerance: impact of glucagon on fibrinolysis

Glucagon plays an important role in postprandial hyperglycemia in type 2 diabetes (T2DM), and coexists with insulin resistance and impaired fibrinolysis. We analyzed the response of plasminogen activator inhibitor-1 (PAI-1) to a lipid-glucose-protein test and the relationship between glucagon and PAI-1, tissue plasminogen activator (t-PA) and PAI-1/t-PA in 26 men with normal glucose tolerance (NGT), nine with impaired glucose tolerance (IGT) and 12 with T2DM. Fasting and postprandial PAI-1 were higher in T2DM versus NGT (P < 0.05). In univariate analysis in NGT, fasting and area under the curve (AUC) PAI-1 showed a strong relationship with fasting (P = 0.003, P = 0.006) and postprandial (P = 0.041, P = 0.045) glucagon, t-PA with fasting glucagon (P = 0.014), and PAI-1/t-PA with fasting (P = 0.047) and AUC glucagon (P = 0.017). In IGT fasting, AUC PAI-1 and PAI-1/t-PA were associated with AUC glucagon (P = 0.035, P = 0.032, P = 0.023). In NGT with the fasting metabolic parameters and insulin resistance as independent variables, fasting glucagon remained an independent covariate for PAI-1 and PAI-1/t-PA. In another model, postprandial glucagon was independently associated with PAI-1/t-PA in NGT (P < 0.05). Besides the already established determinants, we found an independent association between glucagon and fibrinolysis in NGT. Further studies are needed to identify the link between glucagon, insulin resistance and hemostasis.

Regulation of PAI-1 gene expression during adipogenesis

Obesity is characterized by elevated levels of circulating plasminogen activator inhibitor-1 (PAI-1), which contribute towards the development of secondary disorders such as type 2 diabetes mellitus and cardiovascular complications. This increase in plasma PAI-1 levels is attributed to an increase in PAI-1 derived from adipose tissue. This study shows that adipose tissue evolved into a major PAI-1 producing organ by gaining capacity during adipocyte differentiation to respond to inducers of PAI-1 transcription. This is mediated by a decrease in E2F1 protein levels, an increase in pRB levels and a decrease in pRB phosphorylation, all leading to a decrease in levels of free E2F, a known transcriptional repressor of PAI-1. Depletion of E2F1-3 was sufficient for inducers such as insulin to potently induce PAI-1 gene expression in pre-adipocytes. Conversely, forced release of pRB-bound endogenous E2F using cell-penetrating peptides can suppress PAI-1 gene expression in adipocytes. This study describes the novel paradigm of cellular differentiation-associated increase in PAI-1 gene expression which is mediated by a decrease in repressor activity, and describes a way of desensitising terminally differentiated cells to PAI-1 inducing agents by restoring endogenous repressor activity.

Plasminogen activator inhibitor-1 expression and secretion are stimulated by growth hormone and interleukin-6 in 3T3-L1 adipocytes

Various adipocytokines have been described which influence insulin sensitivity and vascular function profoundly and might, therefore, potentially link obesity, insulin resistance, and atherosclerosis. Among those, plasminogen activator inhibitor (PAI)-1 is an adipose-secreted factor upregulated in obesity and insulin resistance that inhibits fibrinolysis. Furthermore, recent studies in knockout mice suggest that PAI-1 directly impairs insulin sensitivity. In the current study, the impact of growth hormone (GH) and interleukin (IL)-6 on PAI-1 mRNA synthesis and secretion was determined in 3T3-L1 adipocytes. Interestingly, 500 ng/ml GH and 30 ng/ml IL-6 increased PAI-1 secretion five-fold and 3.6-fold, respectively. Furthermore, GH and IL-6 induced PAI-1 mRNA by up to 7.3-fold, and 3.6-fold, respectively, in a time-dependent fashion with significant stimulation seen at concentrations as low as 5 ng/ml GH and 10 ng/ml IL-6. Other insulin resistance-inducing hormones which stimulated PAI-1 synthesis included insulin, TNFalpha, and dexamethasone. Studies using pharmacological inhibitors suggested that basal and GH-induced PAI-1 synthesis were at least in part mediated by p44/42 mitogen-activated protein kinase but not janus kinase 2 and phosphatidylinositol 3-kinase. Taken together, our results show a differential regulation of PAI-1 mRNA by insulin resistance-inducing hormones including GH and IL-6.

Plasminogen activator inhibitor-1 modulates adipocyte differentiation

Increased plasminogen activator inhibitor-1 (PAI-1) is linked to obesity and insulin resistance. However, the functional role of PAI-1 in adipocytes is unknown. This study was designed to investigate effects and underlying mechanisms of PAI-1 on glucose uptake in adipocytes and on adipocyte differentiation. Using primary cultured adipocytes from PAI-1(+/+) and PAI-1(-/-) mice, we found that PAI-1 deficiency promoted adipocyte differentiation, enhanced basal and insulin-stimulated glucose uptake, and protected against tumor necrosis factor-alpha-induced adipocyte dedifferentiation and insulin resistance. These beneficial effects were associated with upregulated glucose transporter 4 at basal and insulin-stimulated states and upregulated peroxisome proliferator-activated receptor-gamma (PPARgamma) and adiponectin along with downregulated resistin mRNA in differentiated PAI-1(-/-) vs. PAI-1(+/+) adipocytes. Similarly, inhibition of PAI-1 with a neutralizing anti-PAI-1 antibody in differentiated 3T3-L1 adipocytes further promoted adipocyte differentiation and glucose uptake, which was associated with increased expression of transcription factors PPARgamma, CCAAT enhancer-binding protein-alpha (C/EBPalpha), and the adipocyte-selective fatty acid-binding protein aP2, thus mimicking the phenotype in PAI-1(-/-) primary adipocytes. Conversely, overexpression of PAI-1 by adenovirus-mediated gene transfer in 3T3-L1 adipocytes inhibited differentiation and reduced PPARgamma, C/EBPalpha, and aP2 expression. This was also associated with a decrease in urokinase-type plasminogen activator mRNA expression, decreased plasmin activity, and increased collagen I mRNA expression. Collectively, these results indicate that absence or inhibition of PAI-1 in adipocytes protects against insulin resistance by promoting glucose uptake and adipocyte differentiation via increased PPARgamma expression. We postulate that these PAI-1 effects on adipocytes may, at least in part, be mediated via modulation of plasmin activity and extracellular matrix components.

Modulation of PAI-1 and proMMP-9 syntheses by soluble TNFalpha and its receptors during differentiation of the human monocytic HL-60 cell line

During phorbol ester-induced differentiation of HL-60 monocytic cells, tumor necrosis factoralpha (TNFalpha) synthesis and secretion are increased, which contributes to the autocrine regulation of TNFalpha-responsive genes. We investigated how, during phorbol ester-induced differentiation of HL-60 cells, the secreted TNFalpha modulated plasminogen activator inhibitor type I (PAI-1) and gelatinase B (MMP-9) syntheses, two proteins involved in pericellular proteolysis. The differentiation-induced release of TNFalpha, was abolished by the hydroxamate-based matrix metalloproteinase (MMP) inhibitor, RU36156. RU36156 or a neutralizing anti-TNFalpha significantly down-regulated PAI-1 synthesis exclusively during the early phases of differentiation (from promyelocyte to monocytic-like cells), which underlined the activating role of autocrine TNFalpha during this time range. As cells progressed to monocyte/macrophage phenotype, they still released TNFalpha, but RU36156 or anti-TNFalpha no longer had an effect on PAI-1 synthesis. This lack of effect was not due to a default of TNFalpha signaling since PAI-1 synthesis was still stimulated in response to exogenous TNFalpha. TNFalpha receptor RI was also actively released and was shown to reduce TNFalpha activity which may account for the inability of soluble TNFalpha to up-regulate PAI-1 synthesis. In later mature stage, cells became susceptible to exogenous TNFalpha-induced apoptosis and rapidly lost their ability to respond to TNFalpha. The MMP-9 synthesis followed similar regulation as PAI-1. Isolated human blood monocytes-derived macrophages behave like HL-60-derived macrophages. In conclusion, these results show that during leukocyte differentiation, time windows exist during which the autocrine TNFalpha is active and then down-regulated by RI, which may temper a continuous up-regulation of the synthesis of proteins involved in pericellular proteolysis.

Coagulation and fibrinolysis abnormalities in obesity

Abnormalities in coagulation and haemostasis represent a well-known link between obesity and thrombosis (both arterial and venous). Several studies have shown that obese patients have higher plasma concentrations of all pro-thrombotic factors (fibrinogen, vonWillebrand factor (vWF), and factor VII), as compared to non-obese controls, with a positive association with central fat. Similarly, plasma concentrations of plasminogen activator inhibitor-1 (PAI-1) have been shown to be higher in obese patients as compared to non-obese controls and to be directly correlated with visceral fat. Furthermore, obesity is characterized by higher plasma concentrations of anti-thrombotic factors, such as tissue-type plasminogen activator (t-PA) and protein C, as compared to non-obese controls, the increase in these factors being likely to represent a protective response partly counteracting the increase in pro-thrombotic factors. The issue of whether adipose tissue contributes directly to plasma PAI-1, its products stimulating other cells to produce PAI-1, or whether it primarily contributes indirectly has not yet been resolved. It has been proposed that the secretion of interleukin-6 (IL-6) by adipose tissue, combined with the actions of adipose tissue-expressed TNF-alpha in obesity, could underlie the association of insulin resistance with endothelial dysfunction, coagulopathy, and coronary heart disease. The role of leptin in impairing haemostasis and promoting thrombosis has been recently reported. Finally, some hormonal abnormalities (androgen, F, catecholamines) associated with the accumulation of body fat may contribute to the impairment of coagulative pathway in obesity. As to intervention strategies, dietary (i.e., low-fat high-fiber diet) and lifestyle (i.e., physical activity) measures have been demonstrated to be effective in improving the obesity-associated pro-thrombotic risk profile.