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Articles by J. L Witztum
Total Records ( 3 ) for J. L Witztum
  J Sun , K Hartvigsen , M. Y Chou , Y Zhang , G. K Sukhova , J Zhang , M Lopez Ilasaca , C. J Diehl , N Yakov , D Harats , J George , J. L Witztum , P Libby , H Ploegh and G. P. Shi
 

Background— Adaptive immunity and innate immunity play important roles in atherogenesis. Invariant chain (CD74) mediates antigen-presenting cell antigen presentation and T-cell activation. This study tested the hypothesis that CD74-deficient mice have reduced numbers of active T cells and resist atherogenesis.

Methods and Results— In low-density lipoprotein receptor–deficient (Ldlr–/–) mice, CD74 deficiency (Ldlr–/–Cd74–/–) significantly reduced atherosclerosis and CD25+-activated T cells in the atheromata. Although Ldlr–/–Cd74–/– mice had decreased levels of plasma immunoglobulin (Ig) G1, IgG2b, and IgG2c against malondialdehyde-modified LDL (MDA-LDL), presumably as a result of impaired antigen-presenting cell function, Ldlr–/–Cd74–/– mice showed higher levels of anti–MDA-LDL IgM and IgG3. After immunization with MDA-LDL, Ldlr–/–Cd74–/– mice had lower levels of all anti–MDA-LDL Ig isotypes compared with Ldlr–/– mice. As anticipated, only Ldlr–/– splenocytes responded to in vitro stimulation with MDA-LDL, producing Th1/Th2 cytokines. Heat shock protein-65 immunization enhanced atherogenesis in Ldlr–/– mice, but Ldlr–/– Cd74–/– mice remained protected. Compared with Ldlr–/– mice, Ldlr–/–Cd74–/– mice had higher anti–MDA-LDL autoantibody titers, fewer lesion CD25+-activated T cells, impaired release of Th1/Th2 cytokines from antigen-presenting cells after heat shock protein-65 stimulation, and reduced levels of all plasma anti–heat shock protein-65 Ig isotypes. Cytofluorimetry of splenocytes and peritoneal cavity cells of MDA-LDL– or heat shock protein-65–immunized mice showed increased percentages of autoantibody-producing marginal zone B and B-1 cells in Ldlr–/–Cd74–/– mice compared with Ldlr–/– mice.

Conclusions— Invariant chain deficiency in Ldlr–/– mice reduced atherosclerosis. This finding was associated with an impaired adaptive immune response to disease-specific antigens. Concomitantly, an unexpected increase in the number of innate-like peripheral B-1 cell populations occurred, resulting in increased IgM/IgG3 titers to the oxidation-specific epitopes.

  S. H Choi , R Harkewicz , J. H Lee , A Boullier , F Almazan , A. C Li , J. L Witztum , Y. S Bae and Y. I. Miller
 

Toll-like receptor (TLR)4 recognizes microbial pathogens, such as lipopolysaccharide, and mediates lipopolysaccharide-induced proinflammatory cytokine secretion, as well as microbial uptake by macrophages. In addition to exogenous pathogens, TLR4 recognizes modified self, such as minimally oxidized low-density lipoprotein (mmLDL). Here we report that mmLDL and its active components, cholesteryl ester hydroperoxides, induce TLR4-dependent fluid phase uptake typical of macropinocytosis. We show that mmLDL induced recruitment of spleen tyrosine kinase (Syk) to a TLR4 signaling complex, TLR4 phosphorylation, activation of a Vav1-Ras-Raf-MEK-ERK1/2 signaling cascade, phosphorylation of paxillin, and activation of Rac, Cdc42, and Rho. These mmLDL-induced and TLR4- and Syk-dependent signaling events and cytoskeletal rearrangements lead to enhanced uptake of small molecules, dextran, and, most importantly, both native and oxidized LDL, resulting in intracellular lipid accumulation. An intravenous injection of fluorescently labeled mmLDL in wild-type mice resulted in its rapid accumulation in circulating monocytes, which was significantly attenuated in TLR4-deficient mice. These data describe a novel mechanism leading to enhanced lipoprotein uptake in macrophages that would contribute to foam cell formation and atherosclerosis. These data also suggest that cholesteryl ester hydroperoxides are an endogenous ligand for TLR4. Because TLR4 is highly expressed on the surface of circulating monocytes in patients with chronic inflammatory conditions, and cholesteryl ester hydroperoxides are present in plasma, lipid uptake by monocytes in circulation may contribute to the pathological roles of monocytes in chronic inflammatory diseases.

  P Wiesner , S. H Choi , F Almazan , C Benner , W Huang , C. J Diehl , A Gonen , S Butler , J. L Witztum , C. K Glass and Y. I. Miller
 

Rationale: Oxidized low-density lipoprotein (LDL) is an important determinant of inflammation in atherosclerotic lesions. It has also been documented that certain chronic infectious diseases, such as periodontitis and chlamydial infection, exacerbate clinical manifestations of atherosclerosis. In addition, low-level but persistent metabolic endotoxemia is often found in diabetic and obese subjects and is induced in mice fed a high-fat diet.

Objective: In this study, we examined cooperative macrophage activation by low levels of bacterial lipopolysaccharide (LPS) and by minimally oxidized LDL (mmLDL), as a model for subclinical endotoxemia-complicated atherosclerosis.

Methods and Results: We found that both in vitro and in vivo, mmLDL and LPS (Kdo2-LipidA) cooperatively activated macrophages to express proinflammatory cytokines Cxcl2 (MIP-2), Ccl3 (MIP-1), and Ccl4 (MIP-1β). Importantly, the mmLDL and LPS cooperative effects were evident at a threshold LPS concentration (1 ng/mL) at which LPS alone induced only a limited macrophage response. Analyzing microarray data with a de novo motif discovery algorithm, we found that genes transcribed by promoters containing an activator protein (AP)-1 binding site were significantly upregulated by costimulation with mmLDL and LPS. In a nuclear factor–DNA binding assay, the cooperative effect of mmLDL and LPS costimulation on c-Jun and c-Fos DNA binding, but not on p65 or p50, was dependent on mmLDL-induced activation of extracellular signal-regulated kinase (ERK) 1/2. In addition, mmLDL induced c-Jun N-terminal kinase (JNK)-dependent derepression of AP-1 by removing nuclear receptor corepressor (NCoR) from the chemokine promoters.

Conclusions: The cooperative engagement of AP-1 and nuclear factor (NF)-B by mmLDL and LPS may constitute a mechanism of increased transcription of inflammatory cytokines within atherosclerotic lesions.

 
 
 
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