T he metabolic syndrome comprises a cluster of risk factors, including obesity, insulin resistance, hepatic steatosis, and dyslipidemia. It is associated with a variety of cardiovascular diseases such as atherosclerosis, myocardial infarction, and stroke.1 Chronic, low-grade inflammation in key metabolic organs such as the liver and visceral adipose tissue (VAT) Background-Costimulatory cascades such as the CD40L-CD40 dyad enhance immune cell activation and inflammation during atherosclerosis. Here, we tested the hypothesis that CD40 directly modulates traits of the metabolic syndrome in diet-induced obesity in mice. Methods and Results-To induce the metabolic syndrome, wild-type or CD40 −/− mice consumed a high-fat diet for 20 weeks. Unexpectedly, CD40−/− mice exhibited increased weight gain, impaired insulin secretion, augmented accumulation of inflammatory cells in adipose tissue, and enhanced proinflammatory gene expression. This proinflammatory and adverse metabolic phenotype could be transplanted into wild-type mice by reconstitution with CD40-deficient lymphocytes, indicating a major role for CD40 in T or B cells in this context. Conversely, therapeutic activation of CD40 signaling by the stimulating antibody FGK45 abolished further weight gain during the study, lowered glucose levels, improved insulin sensitivity, and suppressed adipose tissue inflammation. Mechanistically, CD40 activation decreased the expression of proinflammatory cytokines in T cells but not in B cells or macrophages. Finally, repopulation of lymphocyte-free Rag1 −/− mice with CD40 −/− T cells provoked dysmetabolism and inflammation, corroborating a protective role of CD40 on T cells in the metabolic syndrome. Finally, levels of soluble CD40 showed a positive association with obesity in humans, suggesting clinical relevance of our findings. Conclusions-We present the surprising finding that CD40 deficiency on T cells aggravates whereas activation of CD40 signaling improves adipose tissue inflammation and its metabolic complications. Therefore, positive modulation of the CD40 pathway might describe a novel therapeutic concept against cardiometabolic disease. T-regulatory (T reg ) cells, CD8 + T cells, and related chemokines and cytokines such as RANTES (regulated on activation normal T cell expressed and secreted) and interferon-γ (IFNγ) colocalize within the inflammatory cell compartment in adipose tissue. 7 In lean adipose tissue, the vast majority of T lymphocytes share features of anti-inflammatory, interleukin (IL)-13-, IL-4-, and IL-10-secreting Th2 or T reg cells. 8In obesity, proinflammatory Th1 cells expressing IFNγ overwhelm Th2 cells.9 Th1 cells, in turn, activate proinflammatory cytokine-secreting macrophages and promote their conversion from M2-like, IL-10-secreting, alternatively activated macrophages to classically activated, M1-like macrophages. 10,11Despite description of the kinetics of cellular infiltration and the associated cytokine/chemokine profiles during the development of obesity, the underlying cause modu...

BackgroundAdipose tissue inflammation fuels the metabolic syndrome. We recently reported that CD40L – an established marker and mediator of cardiovascular disease – induces inflammatory cytokine production in adipose cells in vitro. Here, we tested the hypothesis that CD40L deficiency modulates adipose tissue inflammation in vivo.Methodology/Principal FindingsWT or CD40L−/− mice consumed a high fat diet (HFD) for 20 weeks. Inflammatory cell recruitment was impaired in mice lacking CD40L as shown by a decrease of adipose tissue macrophages, B-cells, and an increase in protective T-regulatory cells. Mechanistically, CD40L-deficient mice expressed significantly lower levels of the pro-inflammatory chemokine MCP-1 both, locally in adipose tissue and systemically in plasma. Moreover, levels of pro-inflammatory IgG-antibodies against oxidized lipids were reduced in CD40L−/− mice. Also, circulating low-density lipoproteins and insulin levels were lower in CD40L−/− mice. However, CD40L−/− mice consuming HFD were not protected from the onset of diet-induced obesity (DIO), insulin resistance, and hepatic steatosis, suggesting that CD40L selectively limits the inflammatory features of diet-induced obesity rather than its metabolic phenotype. Interestingly, CD40L−/− mice consuming a low fat diet (LFD) showed both, a favorable inflammatory and metabolic phenotype characterized by diminished weight gain, improved insulin tolerance, and attenuated plasma adipokine levels.ConclusionWe present the novel finding that CD40L deficiency limits adipose tissue inflammation in vivo. These findings identify CD40L as a potential mediator at the interface of cardiovascular and metabolic disease.

The co-stimulatory immune molecule CD40L figures prominently in a variety of inflammatory conditions including arterial disease. Recently, we made the surprising finding that CD40L mediates atherogenesis independently of its classic receptor CD40 via a novel interaction with the leukocyte integrin Mac-1. Here, we hypothesised that selective blockade of the CD40L-Mac-1 interaction may also retard restenosis. We induced neointima formation in C57/BL6 mice by ligation of the left carotid artery. Mice were randomised to daily intraperitoneal injections of either cM7, a small peptide selectively inhibiting the CD40L-Mac-1 interaction, scM7, a scrambled control peptide, or saline for 28 days. Interestingly, cM7-treated mice developed neointima of similar size compared with mice receiving the control peptide or saline as assessed by computer-assisted analysis of histological cross sections. These data demonstrate that the CD40L-Mac-1 interaction is not required for the development of restenosis. In contrast, CD40-deficient mice subjected to carotid ligation in parallel, developed significantly reduced neointimal lesions compared with respective wild-type controls (2872 ± 843 µm² vs 35469 ± 11870 µm²). Flow cytometry in CD40-deficient mice revealed reduced formation of platelet-granulocyte and platelet-inflammatory monocyte- aggregates. In vitro, supernatants of CD40-deficient platelet-leukocyte aggregates attenuated proliferation and increased apoptosis of smooth muscle cells. Unlike in the setting of atherosclerosis, CD40L mediates neointima formation via its classic receptor CD40 rather than via its recently described novel interaction with Mac-1. Therefore, selective targeting of CD40L-Mac-1 binding does not appear to be a favorable strategy to fight restenosis.

Tumor necrosis factor (TNF) receptor-associated factors (TRAFs) are cytoplasmic adaptor proteins of the TNF/interleukin (IL)-1/Toll-like receptor superfamily. Ligands of this family such as TNFα, CD40L, and IL-1β promote chronic inflammatory processes such as atherosclerosis and restenosis, the latter being a common adverse reaction after vascular interventions. We previously reported overexpression of TRAF5 in murine and human atheromata and TRAF5-dependent proinflammatory functions in vitro. However, the role of TRAF5 in restenosis remains unsettled. To evaluate whether TRAF5 affects neointima formation, TRAF5^–/–LDLR^–/– and TRAF5^+/+LDLR^–/– mice consuming a high cholesterol diet (HCD) received wire-induced injury of the carotid artery. After 28 days, TRAF5-deficient mice showed a 45% decrease in neointimal area formation compared with TRAF5-compentent mice. Furthermore, neointimal vascular smooth muscle cells (vSMC) and macrophages decreased whereas collagen increased in TRAF5-deficient mice. Mechanistically, the latter expressed lower transcript levels of the matrix metalloproteinases 2 and 9, both instrumental in extracellular matrix degradation and vSMC mobilization. Additionally, TRAF5-specific siRNA interference rendered murine vSMC less proliferative upon CD40L stimulation. In accordance with these findings, fewer vSMC isolated from TRAF5-deficient aortas were in a proliferative state as assessed by Ki67 and cyclin B1 expression. In conclusion, TRAF5 deficiency mitigates neointima formation in mice, likely through a TRAF5-dependent decrease in vSMC proliferation.

Background: Adipose tissue inflammation fuels the metabolic syndrome. We recently reported that CD40L -an established marker and mediator of cardiovascular disease -induces inflammatory cytokine production in adipose cells in vitro. Here, we tested the hypothesis that CD40L deficiency modulates adipose tissue inflammation in vivo.Methodology/Principal Findings: WT or CD40L 2/2 mice consumed a high fat diet (HFD) for 20 weeks. Inflammatory cell recruitment was impaired in mice lacking CD40L as shown by a decrease of adipose tissue macrophages, B-cells, and an increase in protective T-regulatory cells. Mechanistically, CD40L-deficient mice expressed significantly lower levels of the pro-inflammatory chemokine MCP-1 both, locally in adipose tissue and systemically in plasma. Moreover, levels of proinflammatory IgG-antibodies against oxidized lipids were reduced in CD40L 2/2 mice. Also, circulating low-density lipoproteins and insulin levels were lower in CD40L 2/2 mice. However, CD40L 2/2 mice consuming HFD were not protected from the onset of diet-induced obesity (DIO), insulin resistance, and hepatic steatosis, suggesting that CD40L selectively limits the inflammatory features of diet-induced obesity rather than its metabolic phenotype. Interestingly, CD40L 2/2 mice consuming a low fat diet (LFD) showed both, a favorable inflammatory and metabolic phenotype characterized by diminished weight gain, improved insulin tolerance, and attenuated plasma adipokine levels. Conclusion:We present the novel finding that CD40L deficiency limits adipose tissue inflammation in vivo. These findings identify CD40L as a potential mediator at the interface of cardiovascular and metabolic disease.