CD28 deletion improves obesity-induced liver steatosis but increases adiposity in mice.

BACKGROUND/OBJECTIVES: Lymphocytes have a critical role in visceral adipose tissue (AT) inflammation. The CD28 costimulatory molecule is required for lymphocyte activation and for the development of a functional regulatory T cells (Tregs) compartment; however, its role during obesity is unknown. METHODS: During diet-induced obesity, we investigated the effects of selective interference with CD28 signaling using knockout mice (Cd28KO) and a CTLA4-Ig fusion protein inhibiting CD28-B7 interactions. RESULTS: Cd28 deficiency decreased pathogenic T cells and Treg content within AT without changing the macrophages number. Cd28KO epididymal but not subcutaneous fat was characterized by enlarged adipocytes, reduced levels of inflammatory cytokines and increased Glut4, adiponectin and lipogenic enzyme mRNA levels. This was associated with reduced inflammation, fat accumulation and enhanced glucose metabolism in liver. Weight gain and fasting glucose tolerance were not affected. CTLA4-Ig injections reduced the number of T cells in epididymal AT (epiAT) but not the inflammatory cytokines levels and failed to improve liver fat accumulation. CONCLUSIONS: Deletion of CD28 creates a new pro/anti-inflammatory balance in epiAT and liver and exerts a protective effect against hepatic steatosis.

Systemic inhibition and liver-specific over-expression of PAI-1 failed to improve survival in all-inclusive populations or homogenous cohorts of CLP mice.

BACKGROUND: The role of plasminogen activator inhibitor type-1 (PAI-1) in abdominal sepsis remains elusive. OBJECTIVES: To study the influence of inhibition and over-expression of PAI-1 upon survival in cecal ligation and puncture (CLP) sepsis. METHODS: (i) Mice underwent moderate CLP and received 10 mg kg(-1) of either monoclonal anti-PAI-1 (MA-MP6H6) or control (MA-Control) antibody intravenously at 0, 18 or 30 h post-CLP. The 30-h treatment group was additionally stratified into mice predicted to survive (P-SUR) or die (P-DIE) based on IL 6 measured at 24 h post-CLP. (ii) PAI-1 expression was induced with pLIVE.PAI-1 plasmid administered 72 h pre-CLP. Blood was sampled for 5 days and survival was monitored for 28 days. RESULTS: MA-MP6H6 effectively neutralized active PAI-1 and fully restored fibrinolysis while PAI-1 over-expression was liver-specific and correlated with PAI-1 increase in the blood. Without stratification, MA-MP6H6 co-/post-treatment conferred no survival benefit. Prospective stratification (IL-6 cut-off: 14 ng mL(-1) ) suggested increased mortality by MA-MP6H6 treatment in P-SUR that reached 30% difference (vs. MA-Control; P < 0.05) after a retrospective cut-off readjustment to 3.3 ng mL(-1) for better P-SUR homogeneity. Subsequent prospective anti-PAI-1 treatment in P-SUR mice with 3.3 ng mL(-1) cut-off demonstrated a negative but statistically insignificant effect: mortality was higher by 17% after MA-MP6H6 vs. MA-Control. Over-expression of PAI 1 did not alter post-CLP survival. Neither PAI-1 inhibition nor over-expression meaningfully modified inflammatory response and/or organ function. CONCLUSIONS: Restoration of fibrinolysis in early abdominal sepsis was not beneficial and it may prove detrimental in subjects with the lowest risk of death, while preemptive PAI-1 up-regulation at the current magnitude was not protective.

Progression of atherosclerosis in ApoE-deficient mice that express distinct molecular forms of TNF-alpha.

TNFalpha (TNF) critically regulates inflammation-driven atherosclerosis. Because the transmembrane (tmTNF) and soluble (sTNF) forms of TNF possess distinct immuno-modulatory properties, we hypothesized that they might differentially regulate atherosclerosis progression. Three groups of male ApoE(-/-) mice were studied: one expressing wild-type TNF (WT-TNF); one expressing exclusively a mutated non-cleavable form of TNF (KI-TNF); and one deficient in TNF (KO-TNF). Mice aged 5 weeks were fed the high-fat diet for 5 (T5) and 15 weeks (T15) or a standard chow diet for 15 weeks. At T5, in mice fed the high-fat diet, no significant differences in lesion area were observed among the three groups, either in valves or in aortas. At T15, lesion areas in valves were significantly lower in KO-TNF mice compared with those in WT-TNF mice, whereas in KI-TNF mice, they were intermediate between KO- and WT-TNF mice but not significantly different from these two groups. In aortas, lesions in KI-TNF were comparable to those of KO-TNF, both being significantly lower than those in WT-TNF. Theses differences were not linked to circulating lipids, or to macrophage, actin, and collagen contents of lesions. At T15, in mice fed the chow diet, lesion areas in valves and the aortic arch were not significantly different between the three groups. Levels of IL-6, IFNgamma, IL-10, and Foxp3 mRNAs in spleens and production of IL-6, IL-10, MCP-1, RANTES, and TNFR-2 by peritoneal macrophages at T15 of the high-fat diet showed a decrease in pro-inflammatory status, more marked in KO-TNF than in KI-TNF mice. Apoptosis was reduced only in KO-TNF mice. In conclusion, these data show that TNF effects on atherosclerosis development are detectable at stages succeeding fatty streaks and that wild-type TNF is superior to tmTNF alone in promoting atherosclerosis. TNF-dependent progression of atherosclerosis is probably linked to the differential production of pro-inflammatory mediators whether tmTNF is preponderant or essentially cleaved.

Chronic plasminogen activator inhibitor-1 (PAI-1) overexpression dampens CD25+ lymphocyte recruitment after lipopolysaccharide endotoxemia in mouse lung.

BACKGROUND: Plasma plasminogen activator inhibitor-1 (PAI-1) level rises during sepsis and confers a worse prognosis. PAI-1 participation to sepsis has been poorly documented and was mainly associated with fibrin deposits. Beside fibrin deposits, increased tissue PAI-1 expression may contribute to the poor outcome of endotoxemia through other mechanisms. OBJECTIVE AND METHODS: During lipopolysaccharide (LPS) challenge, the role of PAI-1 in the early phase of inflammation was examined in the lungs of transgenic mice that either overexpress or lack the PAI-1 gene (PAI-1Tg or PAI-1(-/-)). RESULTS: Analysis of leukocytes revealed that neutrophil and macrophage infiltrations did not differ for PAI-1Tg and wild-type (WT) mice. Remarkably, CD25+ lymphocyte infiltration was totally blunted in PAI-1Tg lungs and inversely correlated with fibrin depositions. In parallel, mRNA levels of the regulatory T cell (Treg) markers FoxP3, CTLA-4, and GITR were significantly lower in PAI-1Tg than in WT lungs after LPS challenge. These data are supported by opposite results in PAI-1(-/-) lungs. The systemic compartments (spleen and peripheral blood) showed no decrease in CD25+, CD4+ CD25+ lymphocytes, and Treg markers in PAI-1Tg mice after LPS injection compared with WT mice. In addition, plasma and lung concentrations of interleukin-6 (IL-6) and macrophage inflammatory protein-1alpha (MIP-1alpha) were significantly higher in PAI-1Tg mice than WT mice. CONCLUSION: Our results suggest that chronic tissue PAI-1 overexpression influences the early phase of the inflammatory response during endotoxemia through the control of T lymphocyte traffic.

C3H/HeJ mice carrying a toll-like receptor 4 mutation are protected against the development of insulin resistance in white adipose tissue in response to a high-fat diet.

AIMS/HYPOTHESIS: Inflammation is associated with obesity and has been implicated in the development of diabetes and atherosclerosis. During gram-negative bacterial infection, lipopolysaccharide causes an inflammatory reaction via toll-like receptor 4 (TLR4), which has an essential function in the induction of innate and adaptative immunity. Our aim was to determine what role TLR4 plays in the development of metabolic phenotypes during high-fat feeding. MATERIALS AND METHODS: We evaluated metabolic consequences of a high-fat diet in TLR4 mutant mice (C3H/HeJ) and their respective controls. RESULTS: TLR4 inactivation reduced food intake without significant modification of body weight, but with higher epididymal adipose tissue mass and adipocyte hypertrophy. It also attenuated the inflammatory response and increased glucose transport and the expression levels of adiponectin and lipogenic markers in white adipose tissue. In addition, TLR4 inactivation blunted insulin resistance induced by lipopolysaccharide in differentiated adipocytes. Increased feeding efficiency in TLR4 mutant mice was associated with lower mass and lower expression of uncoupling protein 1 gene in brown adipose tissue. Finally, TLR4 inactivation slowed the development of hepatic steatosis, reducing the liver triacylglycerol content and also expression levels of lipogenic and fibrosis markers. CONCLUSIONS/INTERPRETATION: TLR4 influences white adipose tissue inflammation and insulin sensitivity, as well as liver fat storage, and is important in the regulation of metabolic phenotype during a fat-enriched diet.

Influence of t-pA and u-PA on adipose tissue development in a murine model of diet-induced obesity.

To investigate the potential role of tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA) in development of adipose tissue, we have used a nutritionally induced obesity model in t-PA (t-PA-/-) and u-PA (u-PA-/-) deficient mice. Five week old male wild-type (WT), t-PA-/- or u-PA-/- mice (n = 9 to 16) were fed a high fat diet (HFD, 42% fat). After 16 weeks of HFD, the body weight of t-PA-/- mice was significantly higher than that of WT mice (48 +/- 1.1 g vs. 39 +/- 2.2 g, p = 0.004). The total weight of the isolated subcutaneous (sc) fat deposit was higher in t-PA-/- than in WT mice (2.4 +/- 0.22 g vs. 1.2 +/- 0.29 g, p = 0.002). accompanied with higher adipocyte diameters (80 +/- 1.7 microm vs. 61 +/- 4.7 microm, p < 0.01). These differences were not observed in the intra-abdominal fat deposit. The number of stroma cells in both adipose tissue territories was increased in t-PA-/- as compared to WT mice (2.0 +/- 0.13 vs. 1.5 +/- 0.10, p = 0.2 and 3.0 +/- 0.17 vs 1.6 +/- 0.17, p = 0.0001, stroma cells/adipocytes in sc and intra-abdominal tissue, respectively), partly as a result of an increased number of endothelial cells (192 +/- 9 vs. 154 +/-18, p = 0.06 and 108 +/- 13 vs. 69 +/- 8, p = 0.04 CD31 stained/adipocyte area). In contrast the weight gain and adipose tissue development in u-PA-/- mice was not different from that in WT mice. These data suggest that t-PA but not u-PA plays a role in adipose tissue development.

Subcutaneous abdominal, but not femoral fat expression of plasminogen activator inhibitor-1 (PAI-1) is related to plasma PAI-1 levels and insulin resistance and decreases after weight loss.

AIMS/HYPOTHESIS: Abdominal fat produces plasminogen activator inhibitor-1 (PAI-1) and could contribute to increased plasma PAI-1 values in human obesity associated with insulin resistance. Femoral fat, which is not associated with insulin resistance, is thought to be metabolically different from the abdominal fat. This study aimed to assess PAI-1 expression in these two fat territories in obese and lean subjects and to determine if concomitant changes of plasma and adipose tissue PAI-1 values occur after weight reduction. METHODS: In 24 obese and 16 lean subjects, PAI-1 expression in abdominal and femoral subcutaneous fat, plasma PAI-1, insulin, triglyceride concentrations and insulin resistance were determined at the start of the study and in obese subjects after a 3-month weight reduction programme as well. RESULTS: PAI-1 mRNA content in the abdominal subcutaneous fat was higher in obese than in lean subjects and positively correlated with plasma PAI-1 values (p < 0.01) and markers of insulin resistance (p < 0.05). In 18 obese subjects, re-examined after successful dieting, PAI-1 mRNA content decreased in the abdominal subcutaneous fat along with plasma PAI-1. However, the absolute changes of these two variables were not associated. In contrast, PAI-1 mRNA content in the femoral subcutaneous fat did not differ between lean and obese subjects, was not associated with plasma PAI-1 values or with markers of insulin resistance, and did not change after weight loss. CONCLUSION/INTERPRETATION: Only the abdominal, but not the femoral subcutaneous fat PAI-1 expression is a potential contributor to increases in plasma PAI-1 in obesity. Both plasma and abdominal subcutaneous fat PAI-1 values decreased significantly after weight reduction, although their absolute changes were not associated.

Plasminogen activator inhibitor 1, transforming growth factor-beta1, and BMI are closely associated in human adipose tissue during morbid obesity.

In adipose tissue from both obese mice and humans, plasminogen activator inhibitor 1 (PAI-1) expression has been reported to be upregulated to levels of increased plasma PAI-1. This elevated expression has been shown to be partly controlled by tumor necrosis factor (TNF)-alpha in mice. In humans, increased PAI-1 expression is associated with insulin resistance characterized by visceral fat accumulation. Therefore, the aim of this study was to investigate the expression pattern of PAI-1 and TNF-alpha (antigen and mRNA) in visceral human adipose fat in comparison with subcutaneous (SC) fat. Because transforming growth factor (TGF)-beta1 is a potent inducer of PAI-1 synthesis and has been shown to influence adipocyte metabolism, this work was extended to TGF-beta1 quantification. A total of 32 obese individuals (BMI 42 +/- 6.8 kg/m2) were investigated. Freshly collected visceral adipose tissue did not exhibit a higher content of PAI-1 or TGF-beta1 than did SC tissue. Although most of the TNF-alpha values were at the detection limit of the methods, TNF-alpha antigen was 3-fold higher and TNF-alpha mRNA was 1.2-fold higher in visceral fat. The levels of tissue TGF-beta1 antigen correlated well with those of PAI-1 antigen, regardless of the fat depot studied (SC tissue: n = 21, r = 0.72, P = 0.0006; visceral tissue: n = 20, r = 0.49, P < 0.03), and they were both significantly associated with BMI. Conversely, no relationship was observed between the levels of TNF-alpha and PAI-1 or TNF-alpha and BMI. Tissue PAI-1 levels were also significantly correlated with those of circulating PAI-1. These results describe, in severe obesity, a proportional increase in tissue PAI-1 and TGF-beta1 in visceral and SC tissues. This increased PAI-1 expression could be the result of tissue cytokine disturbances, such as elevated TGF-beta1 expression.