Toll-like receptor 4 deficiency decreases atherosclerosis but does not protect against inflammation in obese low-density lipoprotein receptor-deficient mice.

OBJECTIVE: Obesity is associated with insulin resistance, chronic low-grade inflammation, and atherosclerosis. Toll-like receptor 4 (TLR4) participates in the cross talk between inflammation and insulin resistance, being activated by both lipopolysaccharide and saturated fatty acids. The present study was undertaken to determine whether TLR4 deficiency has a protective role in inflammation, insulin resistance, and atherosclerosis induced by a diabetogenic diet. METHODS AND RESULTS: TLR4 and low-density lipoprotein (LDL) receptor double knockout mice and LDL receptor-deficient mice were fed either a normal chow or a diabetogenic diet for 24 weeks. TLR4 and LDL receptor double knockout mice fed a diabetogenic diet showed improved plasma cholesterol and triglyceride levels but developed obesity, hyperinsulinemia, and glucose intolerance equivalent to obese LDL receptor-deficient mice. Adipocyte hypertrophy, macrophage accumulation, and local inflammation were not attenuated in intraabdominal adipose tissue in TLR4 and LDL receptor double knockout mice. However, TLR4 deficiency led to markedly decreased atherosclerosis in obese TLR4 and LDL receptor double knockout mice. Compensatory upregulation of TLR2 expression was observed both in obese TLR4-deficient mice and in palmitate-treated TLR4-silenced 3T3-L1 adipocytes. CONCLUSIONS: TLR4 deficiency decreases atherosclerosis without affecting obesity-induced inflammation and insulin resistance in LDL receptor-deficient mice. Alternative pathways may be responsible for adipose tissue macrophage infiltration and insulin resistance that occurs in obesity.

Reduced vascular nitric oxide-cGMP signaling contributes to adipose tissue inflammation during high-fat feeding.

OBJECTIVE: Obesity is characterized by chronic inflammation of adipose tissue, which contributes to insulin resistance and diabetes. Although nitric oxide (NO) signaling has antiinflammatory effects in the vasculature, whether reduced NO contributes to adipose tissue inflammation is unknown. We sought to determine whether (1) obesity induced by high-fat (HF) diet reduces endothelial nitric oxide signaling in adipose tissue, (2) reduced endothelial nitric oxide synthase (eNOS) signaling is sufficient to induce adipose tissue inflammation independent of diet, and (3) increased cGMP signaling can block adipose tissue inflammation induced by HF feeding. METHODS AND RESULTS: Relative to mice fed a low-fat diet, an HF diet markedly reduced phospho-eNOS and phospho-vasodilator-stimulated phosphoprotein (phospho-VASP), markers of vascular NO signaling. Expression of proinflammatory cytokines was increased in adipose tissue of eNOS-/- mice. Conversely, enhancement of signaling downstream of NO by phosphodiesterase-5 inhibition using sildenafil attenuated HF-induced proinflammatory cytokine expression and the recruitment of macrophages into adipose tissue. Finally, we implicate a role for VASP, a downstream mediator of NO-cGMP signaling in mediating eNOS-induced antiinflammatory effects because VASP-/- mice recapitulated the proinflammatory phenotype displayed by eNOS-/- mice. CONCLUSIONS: These results imply a physiological role for endothelial NO to limit obesity-associated inflammation in adipose tissue and hence identify the NO-cGMP-VASP pathway as a potential therapeutic target in the treatment of diabetes.

Antioxidants inhibit the ability of lysophosphatidylcholine to regulate proteoglycan synthesis.

OBJECTIVE: We previously have shown that lysophosphatidylcholine (lysoPC) regulates proteoglycan synthesis by vascular smooth muscle cells (SMCs). Given the accumulating evidence for reactive oxygen species (ROS) as mediators of a variety of effects of lysoPC, the present study evaluates the potential role of ROS as intermediate molecules in the regulation of proteoglycan synthesis by lysoPC. METHODS AND RESULTS: LysoPC (10 micromol/L) was found to stimulate rapid and sustained generation of ROS by SMC, as indicated using a fluorescent probe for measuring intracellular oxidants and fluorescence-activated cell sorting. This was not associated with cytotoxicity, as evaluated by fluorescence microscopy using MitoTracker Red or propidium iodide, cell number, cell protein, or lactate dehydrogenase release. Pretreatment with catalase or superoxide dismutase, specific scavengers of hydrogen peroxide and superoxide, respectively, blocked the ability of lysoPC to stimulate both accumulation of ROS and proteoglycan synthesis. Most importantly, these enzymatic antioxidants prevented lysoPC from stimulating the synthesis of proteoglycans with enhanced lipoprotein-binding properties, as quantified by a gel shift binding assay. CONCLUSIONS: These findings strongly suggest that ROS are key mediators in the ability of lysoPC to regulate proteoglycan synthesis and that these effects can be inhibited by antioxidants.