Patricia A. Detmers

Toll Receptors: a Central Element in Innate Immune Responses

Innate immunity is an evolutionarily ancient system that provides multicellular organisms with immediately available defense mechanisms against a wide variety of pathogens without requiring prior exposure. Hallmarks of innate immune responses include the ability to (i) recognize structures that are

Deficiency in Inducible Nitric Oxide Synthase Results in Reduced Atherosclerosis in Apolipoprotein E-Deficient Mice

Inducible NO synthase (iNOS) present in human atherosclerotic plaques could contribute to the inflammatory process of plaque development. The role of iNOS in atherosclerosis was tested directly by evaluating the development of lesions in atherosclerosis-susceptible apolipoprotein E (apoE)−/− mice that were also deficient in iNOS. ApoE−/− and iNOS−/− mice were cross-bred to produce apoE−/−/iNOS−/− mice and apoE−/−/iNOS+/+ controls. Males and females were placed on a high fat diet at the time of weaning, and atherosclerosis was evaluated at two time points by different methods. The deficiency in iNOS had no effect on plasma cholesterol, triglyceride, or nitrate levels. Morphometric measurement of lesion area in the aortic root at 16 wk showed a 30–50% reduction in apoE−/−/iNOS−/− mice compared with apoE−/−/iNOS+/+ mice. Although the size of the lesions in apoE−/−/iNOS−/− mice was reduced, the lesions maintained a ratio of fibrotic:foam cell-rich:necrotic areas that was similar to controls. Biochemical measurements of aortic cholesterol in additional groups of mice at 22 wk revealed significant 45–70% reductions in both male and female apoE−/−/iNOS−/− mice compared with control mice. The results indicate that iNOS contributes to the size of atherosclerotic lesions in apoE-deficient mice, perhaps through a direct effect at the site of the lesion.

Activation of Peroxisome Proliferator-Activated Receptor γ Does Not Inhibit IL-6 or TNF-α Responses of Macrophages to Lipopolysaccharide In Vitro or In Vivo

We have investigated the potential use of peroxisome proliferator-activated receptor γ (PPARγ) agonists as anti-inflammatory agents in cell-based assays and in a mouse model of endotoxemia. Human peripheral blood monocytes were treated with LPS or PMA and a variety of PPARγ agonists. Although 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) at micromolar concentrations significantly inhibited the production of TNF-α and IL-6, four other high affinity PPARγ ligands failed to affect cytokine production. Similar results were obtained when the monocytes were allowed to differentiate in culture into macrophages that expressed significantly higher levels of PPARγ or when the murine macrophage cell line RAW 264.7 was used. Furthermore, saturating concentrations of a potent PPARγ ligand not only failed to block cytokine production, but also were unable to block the inhibitory activity of 15d-PGJ2. Thus, activation of PPARγ does not appear to inhibit the production of cytokines by either monocytes or macrophages, and the inhibitory effect observed with 15d-PGJ2 is most likely mediated by a PPARγ-independent mechanism. To examine the anti-inflammatory activity of PPARγ agonists in vivo, db/db mice were treated with a potent thiazolidinedione that lowered their elevated blood glucose and triglyceride levels as expected. When thiazolidinedione-treated mice were challenged with LPS, they displayed no suppression of cytokine production. Rather, their blood levels of TNF-α and IL-6 were elevated beyond the levels observed in control db/db mice challenged with LPS. Comparable results were obtained with the corresponding lean mice. Our data suggest that compounds capable of activating PPARγ in leukocytes will not be useful for the treatment of acute inflammation.

TLR2 Recognizes a Bacterial Lipopeptide through Direct Binding

The TLRs play an important role in the initiation of cellular innate immune responses to a wide range of bacterial products, including LPS and lipoproteins. Although rapid progress has been made on signaling functions of activated TLRs, the molecular mechanisms that lead to TLR activation are still poorly understood. We report in this study that the extracellular domain of TLR2 interacts directly with synthetic bacterial lipopeptide (sBLP), a potent analog of bacterial lipoproteins. Using fluorescently labeled sBLP complexed to soluble recombinant CD14 (rsCD14), we observed specific binding of sBLP to the surface of cells expressing TLR2 transgenes and to a recombinant soluble form of the TLR2 ectodomain. TLR2-mediated binding of sBLP at the cell surface did not require prior induction of intracellular signals. In addition, using a chimeric TLR2/TLR4 construct, we showed that the leucine-rich region of TLR2 carries the specificity for binding of the agonist and for initiating signaling. Specific binding of fluorescent sBLP to purified sTLR2 required sCD14. However, sCD14 was not part of the complex formed by soluble TLR2 and sBLP. Together, these data provide evidence that TLR2 recognizes sBLP through direct binding.

A target for cholesterol absorption inhibitors in the enterocyte brush border membrane.

Uptake of cholesterol by the intestinal absorptive epithelium can be selectively blocked by specific small molecules, like the sterol glycoside, L-166,143. Furthermore, (3)H-labeled L-166,143 administered orally to hamsters binds specifically to the intestinal mucosa, suggesting the existence of a cholesterol transporter. Using autoradiography, the binding site of (3)H-L-166,143 in the hamster small intestine was localized to the very apical aspect of the absorptive epithelial cells. Label was competed by non-radioactive L-166,143 and two structurally distinct cholesterol absorption inhibitors, suggesting a common site of action for these compounds. L-166,143 blocked uptake of (3)H-cholesterol into enterocytes in vivo, as demonstrated by autoradiography, suggesting that it inhibits a very early step of cholesterol absorption, incorporation into the brush border membrane. This conclusion was confirmed by studies in which intestinal brush borders were isolated from hamsters dosed with (3)H-cholesterol in the presence or absence of L-166,143. Uptake of (3)H-cholesterol into the membranes was substantially inhibited by the compound. In contrast, an inhibitor of acyl CoA:cholesterol acyltransferase, did not affect uptake of (3)H-cholesterol into the brush border membranes. These results strongly support the existence of a specific transporter that facilitates the movement of cholesterol from bile acid micelles into the brush border membranes of enterocytes.

Toll-like receptor 2 (TLR2) mediates activation of stress-activated MAP kinase p38

Early events in the response of cells to lipopolysaccharide (LPS) include activation of NF‐κB and stress‐activated MAP kinase p38. Recent studies have shown that the human Toll‐like receptor 2 (TLR2) mediates activation of NF‐κB in response to commercial preparations of LPS (comLPS), membrane lipoproteins, and Gram‐positive bacterial products. Here, we show that expression of TLR2 in human embryonic kidney 293 cells enabled p38 phosphorylation in response to comLPS, a synthetic bacterial lipoprotein, and B. subtilis. Activation of p38 was confirmed by an in vitro kinase assay using ATF2 as substrate and by an assay measuring activation of the downstream effector of p38, MAP kinase‐activated protein kinase in cells. Thus, TLR2 initiated the signaling pathway for p38 in response to bacterial products.

Simvastatin has anti-inflammatory and anti-atherosclerotic activities independent of plasma cholesterol-lowering

Abstract—Inhibitors of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase, such as simvastatin, lower circulating cholesterol levels and prevent myocardial infarction. Several studies have shown an unexpected effect of HMG-CoA reductase inhibitors on inflammation. Here, we confirm that simvastatin is anti-inflammatory by using a classic model of inflammation: carrageenan-induced foot pad edema. Simvastatin administered orally to mice 1 hour before carrageenan injection significantly reduced the extent of edema. Simvastatin was comparable to indomethacin in this model. To determine whether the anti-inflammatory activity of simvastatin might affect atherogenesis, simvastatin was tested in mice deficient in apoE. Mice were dosed daily for 6 weeks with simvastatin (100 mg/kg body wt). Simvastatin did not alter plasma lipids. Atherosclerosis was quantified through the measurement of aortic cholesterol content. Aortas from control mice (n=20) contained 56±4 nmol total cholesterol/mg wet wt tissue, 38±2 nmol free cholesterol/mg, and 17±2 nmol cholesteryl ester/mg. Simvastatin (n=22) significantly (P <0.02) decreased these 3 parameters by 23%, 19%, and 34%, respectively. Histology of the atherosclerotic lesions showed that simvastatin did not dramatically alter lesion morphology. These data support the hypothesis that simvastatin has antiatherosclerotic activity beyond its plasma cholesterol–lowering activity.

Specificity and Regulation of CD18-Dependent Adhesions

The ability of polymorphonuclear leukocytes (PMN) to adhere to other cells and substrates is under strict physiological regulation. This is best illustrated by considering PMN circulating within the vasculature. These cells show negligible affinity for the endothelial cells (EC) which surround them. When PMN encounter chemotactic factors this situation is rapidly altered, and the adhesion of PMN to EC is dramatically enhanced. In normal circumstances, stimulated PMN soon break their adhesion to EC and either return to the circulation or leave the vasculature by diapedesis. Thus, PMN possess the means of transiently making then breaking adhesion to EC and other substrates in response to specific stimuli.

Deficiency in sPLA2 does not affect HDL levels or atherosclerosis in mice

Secretory non-pancreatic phospholipase A(2) (sPLA(2)) has been implicated in inflammation and has been found in human atherosclerotic lesions. To test the effect of sPLA(2) deficiency on atherosclerosis, C57BL/Ks mice (apoE(+/+) and PLA(2)(++) were bred with C57BL/6 apoE knockout mice which are sPLA(2)(--) due to a spontaneous mutation. Sibling pairs of mice (apoE(--)/sPLA(2)(++) and apoE(--)/sPLA(2)(--)) on high fat Western diets were dissected at 22 weeks. In vitro enzyme assays confirmed higher serum sPLA(2) activity in the sPLA(2)(++) compared to sPLA(2)(--) for both sexes, while sPLA(2)(--) males had slightly higher serum cholesterol and phospholipids. Analysis of lipoprotein profiles by FPLC showed no effect of sPLA(2) genotype on any measured parameters. Atherosclerosis was quantitated by assaying cholesterol in aortic extracts. Male sPLA(2) trended slightly higher than sPLA(2)(++) with no statistical significance. Female sPLA(2)(++) and sPLA(2)(--) mice showed no significant differences in any of the measured parameters. These results suggest that the endogenous mouse sPLA(2) gene does not significantly affect HDL or atherosclerosis in mice.