High expression of antioxidant proteins in dendritic cells: possible implications in atherosclerosis

Dendritic cells (DCs) display the unique ability to activate naive T cells and to initiate primary T cell responses revealed in DC-T cell alloreactions. DCs frequently operate under stress conditions. Oxidative stress enhances the production of inflammatory cytokines by DCs. We performed a proteomic analysis to see which major changes occur, at the protein expression level, during DC differentiation and maturation. Comparative two-dimensional gel analysis of the monocyte, immature DC, and mature DC stages was performed. Manganese superoxide dismutase (Mn-SOD) reached 0.7% of the gel-displayed proteins at the mature DC stage. This important amount of Mn-SOD is a primary antioxidant defense system against superoxide radicals, but its product, H(2)O(2), is also deleterious for cells. Peroxiredoxin (Prx) enzymes play an important role in eliminating such peroxide. Prx1 expression level continuously increased during DC differentiation and maturation, whereas Prx6 continuously decreased, and Prx2 peaked at the immature DC stage. As a consequence, DCs were more resistant than monocytes to apoptosis induced by high amounts of oxidized low density lipoproteins containing toxic organic peroxides and hydrogen peroxide. Furthermore DC-stimulated T cells produced high levels of receptor activator of nuclear factor kappaB ligand, a chemotactic and survival factor for monocytes and DCs. This study provides insights into the original ability of DCs to express very high levels of antioxidant enzymes such as Mn-SOD and Prx1, to detoxify oxidized low density lipoproteins, and to induce high levels of receptor activator of nuclear factor kappaB ligand by the T cells they activate and further emphasizes the role that DCs might play in atherosclerosis, a pathology recognized as a chronic inflammatory disorder.Comment: cpyright: American Society of Biochemistry and Molecular Biolog

Th1 Disabled Function in Response to TLR4 Stimulation of Monocyte-Derived DC from Patients Chronically-Infected by Hepatitis C Virus

Background: Lack of protective antibodies and inefficient cytotoxic responses are characteristics of chronic hepatitis C infection. A defect in dendritic cell (DC) function has thus been suspected, but this remains a controversial issue. Methods and Findings: Here we show that monocyte-derived DC (MoDC) from chronically-infected patients can mature in response to TLR1/2, TLR2/6 or TLR3 ligands. In contrast, when stimulated with the TLR4 ligand LPS, MoDC from patients show a profound defect in inducing IFNc secretion by allogeneic T cells. This defect is not due to defective phenotypic maturation or to the presence of HCV-RNA in DC or monocytes but is correlated to reduced IL-12 secretion by DC. Restoration of DC ability to stimulate IFNc secretion can be obtained by blocking MEK activation in DC, indicating that MEK/ ERK pathway is involved in the Th1 defect of MoDC. Monocytes from HCV patients present increased spontaneous secretion of cytokines and chemokines, especially MIP-1b. Addition of MIP-1b on healthy monocytes during differentiation results in DC that have Th1 defect characteristic of MoDC from HCV patients, suggesting that MIP-1b secretion by HCV monocytes participates in the Th1 defect of DC. Conclusions: Our data indicate that monocytes from HCV patients are activated in vivo. This interferes with their differentiation into DC, leading to deficient TLR4 signaling in these cells that are enable to induce a Th1 response. Thi

Secretion of Hepatitis C Virus Envelope Glycoproteins Depends on Assembly of Apolipoprotein B Positive Lipoproteins

The density of circulating hepatitis C virus (HCV) particles in the blood of chronically infected patients is very heterogeneous. The very low density of some particles has been attributed to an association of the virus with apolipoprotein B (apoB) positive and triglyceride rich lipoproteins (TRL) likely resulting in hybrid lipoproteins known as lipo-viro-particles (LVP) containing the viral envelope glycoproteins E1 and E2, capsid and viral RNA. The specific infectivity of these particles has been shown to be higher than the infectivity of particles of higher density. The nature of the association of HCV particles with lipoproteins remains elusive and the role of apolipoproteins in the synthesis and assembly of the viral particles is unknown. The human intestinal Caco-2 cell line differentiates in vitro into polarized and apoB secreting cells during asymmetric culture on porous filters. By using this cell culture system, cells stably expressing E1 and E2 secreted the glycoproteins into the basal culture medium after one week of differentiation concomitantly with TRL secretion. Secreted glycoproteins were only detected in apoB containing density fractions. The E1–E2 and apoB containing particles were unique complexes bearing the envelope glycoproteins at their surface since apoB could be co-immunoprecipitated with E2-specific antibodies. Envelope protein secretion was reduced by inhibiting the lipidation of apoB with an inhibitor of the microsomal triglyceride transfer protein. HCV glycoproteins were similarly secreted in association with TRL from the human liver cell line HepG2 but not by Huh-7 and Huh-7.5 hepatoma cells that proved deficient for lipoprotein assembly. These data indicate that HCV envelope glycoproteins have the intrinsic capacity to utilize apoB synthesis and lipoprotein assembly machinery even in the absence of the other HCV proteins. A model for LVP assembly is proposed

Reprogramming of Central Carbon Metabolism in Myeloid Cells upon Innate Immune Receptor Stimulation

Immunometabolism is a relatively new field of research that aims at understanding interconnections between the immune system and cellular metabolism. This is now well-documented for innate immune cells of the myeloid lineage such as macrophages and myeloid dendritic cells (DCs) when they engage their differentiation or activation programs. Several studies have shown that stimulation of DCs or macrophages by the binding of pathogen-associated molecular patterns (PAMPs) to pattern recognition receptors (PRRs) leads to increased glycolytic activity and rewiring of central carbon metabolism. These metabolic modulations are essential to support and settle immunological functions by providing energy and immunoregulatory metabolites. As the understanding of molecular mechanisms progressed, significant differences between cell types and species have also been discovered. Pathways leading to the regulation of central carbon metabolism in macrophages and DCs by PRR signaling and consequences on cellular functions are reviewed here

How do viruses interfere with Toll-like receptor 4?

International audienc

Modified lipoproteins provide lipids that modulate dendritic cell immune function

International audienceBoth physiological and pathological situations can result in biochemical changes of low-density lipoproteins (LDL). Because they can deliver signals to dendritic cells (DC), these modified lipoproteins now appear as regulators of the immune response. Among these modified lipoproteins, oxidized LDL (oxLDL) that accumulate during inflammatory conditions have been extensively studied. Numerous studies have shown that oxLDL induce the maturation of DC, enhancing their ability to activate IFNγ secretion by T cells. LDL treated by secreted phospholipase A(2) also promote DC maturation. Among the bioactive lipids generated by oxidation or phospholipase treatment of LDL, lysophosphatidylcholine (LPC) and some saturated fatty acids induce DC maturation whereas some unsaturated fatty acids or oxidized derivatives have opposite effects. Among other factors, the nuclear receptor peroxisome-proliferator activated receptor γ (PPARγ) plays a crucial role in this regulation. Non-modified lipoproteins also contribute to the regulation of DC function, suggesting that the balance between native and modified lipoproteins, as well as the biochemical nature of the LDL modifications, can regulate the activation threshold of DC. Here we discuss two pathological situations in which the impact of LDL modifications on inflammation and immunity could play an important role. During atherosclerosis, modified LDL accumulating in the arterial intima may interfere with DC maturation and function, promoting a Th1 immune response and a local inflammation favoring the development of the pathology. In patients chronically infected, the hepatitis C virus (HCV) interferes with lipoprotein metabolism resulting in the production of infectious modified lipoproteins. These lipo-viral-particles (LVP) are modified low-density lipoproteins containing viral material that can alter DC maturation and affect specific toll-like receptor signaling. In conclusion, lipoprotein modifications play an important role in the regulation of immunity by delivering signals of danger to DC and modulating their function

Sensing environmental lipids by dendritic cell modulates its function.

International audienceBecause of its oxidative modification during the acute-phase response to an aggression, low density lipoprotein (LDL) can be regarded as a source of lipid mediators that can act both to promote and inhibit inflammation. This can be exemplified by the production of anti-inflammatory oxidized fatty acids and proinflammatory lysophosphatidylcholine (LPC) during LDL oxidation. We have shown previously that oxidized LDL (oxLDL) plays an active role at the interface between innate and adaptive immunity by delivering instructive molecules such as LPC, which promotes mature dendritic cell (DC) generation from differentiating monocytes. It is shown in this study that LPC affects the signaling pathway of peroxisome proliferator-activated receptors (PPARs). LPC-induced DC maturation is associated with complete inhibition of PPARgamma activity and up-regulation of the activity of an uncharacterized nuclear receptor that bind peroxisome proliferator response element. Oxidized fatty acids generated during LDL oxidation are natural ligands for PPARgamma and inhibit oxLDL- and LPC-induced maturation. Inhibition experiments with synthetic PPARgamma ligands suggested a PPARgamma-dependent and independent effect of LPC on DC maturation. Therefore, the relative amount of oxidized fatty acids and LPC influences the immunological functions of oxLDL on DC, in part by regulating the PPAR pathway. By sensing the biochemical composition of lipoprotein particles, the innate immune system may thus identify various endogenous signals that influence the immune response during the acute-phase reaction. The therapeutic emulsion intralipid also blocks LPC action on PPAR activity and DC maturation. Intralipid may thus be an alternative therapeutic strategy for some chronic inflammatory diseases

1-Methyl-tryptophan can interfere with TLR signaling in dendritic cells independently of IDO activity.

International audienceThe compound 1-methyl-tryptophan (1-MT) is a competitive inhibitor of IDO that can break tolerance and induce fetus, graft, and tumor rejection. Because of its broad effect on immune-related mechanisms, the direct action of 1-MT on human monocyte-derived dendritic cells (DC) was analyzed. It is shown here that the effect of 1-MT on DC is dependent on the maturation pathway. Although 1-MT had no effect on DC stimulated by the TLR3 ligand poly(I:C), it strongly enhanced the Th1 profile of DC stimulated with TLR2/1 or TLR2/6 ligands. Drastic changes in the function of DC stimulated by the TLR4 ligand LPS were induced by 1-MT. These cells could still activate allogeneic and syngeneic T cells but stimulation yielded T cells secreting IL-5 and IL-13 rather than IFN-gamma. This action of 1-MT correlated with an increased phosphorylation of p38 and ERK MAPKs and sustained activation of the transcription factor c-Fos. Inhibiting p38 and ERK phosphorylation with synthetic inhibitors blocked the effect of 1-MT on LPS-stimulated DC. Thus, 1-MT can modulate DC function depending on the maturation signal and independently of its action on IDO. This is consistent with previous observations and will help further understanding the mechanisms of DC polarization