Wenxuan Zhang

IL-17A Is Proatherogenic in High-Fat Diet-Induced and Chlamydia pneumoniae Infection-Accelerated Atherosclerosis in Mice

The role of IL-17 in atherogenesis remains controversial. We previously reported that the TLR/MyD88 signaling pathway plays an important role in high-fat diet as well as Chlamydophila pneumoniae infection-mediated acceleration of atherosclerosis in apolipoprotein E-deficient mice. In this study, we investigated the role of the IL-17A in high-fat diet (HFD)- and C. pneumoniae-induced acceleration of atherosclerosis. The aortic sinus plaque and aortic lesion size and lipid composition as well as macrophage accumulation in the lesions were significantly diminished in IL-17A−/− mice fed an HFD compared with wild-type (WT) C57BL/6 control mice. As expected, C. pneumoniae infection led to a significant increase in size and lipid content of the atherosclerotic lesions in WT mice. However, IL-17A−/− mice developed significantly less acceleration of lesion size following C. pneumoniae infection compared with WT control despite similar levels of blood cholesterol levels. Furthermore, C. pneumoniae infection in WT but not in IL-17A−/− mice was associated with significant increases in serum concentrations of IL-12p40, CCL2, IFN-γ, and numbers of macrophages in their plaques. Additionally, in vitro studies suggest that IL-17A activates vascular endothelial cells, which secrete cytokines that in turn enhance foam cell formation in macrophages. Taken together, our data suggest that IL-17A is proatherogenic and that it plays an important role in both diet-induced atherosclerotic lesion development, and C. pneumoniae infection-mediated acceleration of atherosclerotic lesions in the presence of HFD.

Thymic CD8 + T Cell Production Strongly Influences Tumor Antigen Recognition and Age-Dependent Glioma Mortality

For unknown reasons, advanced age remains a dominant predictor of poor clinical outcome for nearly all cancers. A decrease in the production of T cells by the thymus accompanies normal aging and parallels the age-dependent increase in cancer progression, but the specific impact of immunity on tumor progression in general is unknown. Glioblastoma multiforme (GBM), the most common primary brain neoplasm, is characterized by rapid age-dependent rates of progression and death. In this study, we show levels of CD8+ recent thymic emigrants (RTEs) accounted for the prognostic power of age on clinical outcome in GBM patients. CD8+ RTEs, typically a tiny proportion of CD8+ T cells, remarkably accounted for the majority of tumor Ag-binding small precursor cells in PBMC from these patients and from healthy individuals. Large blasting tumor Ag-binding cells comprised of CD8+ RTEs and phenotypically related cells were predominantly expanded following experimental vaccination of GBM patients. Quantification of CD8+ RTE expansion in vivo correlated strongly with vaccine-elicited cytokine responses, and estimated numbers of expanding CD8+ RTEs were consistent predictors of clinical outcome in vaccinated GBM patients. Targeted mutant (CD8β−/−) mice specifically deficient in thymic CD8+ T cell production uniquely displayed an age-specific decrease in glioma host survival as well as a strong correlation between host survival and thymus cellular production. These findings suggest that levels and function of newly produced CD8+ T cells critically influence age-dependent cancer mortality and exert one of the strongest known influences on GBM outcome by predominantly mediating clinically beneficial antitumor immune responses.

TLR2 and MyD88 Contribute to Lactobacillus casei Extract–Induced Focal Coronary Arteritis in a Mouse Model of Kawasaki Disease

Background— Kawasaki disease is the most common cause of acquired cardiac disease and acute vasculitis in children, targets the coronary arteries, and can occasionally be fatal. The pathogenesis and the molecular mechanisms remain unknown. After injection of Lactobacillus casei cell-wall extract (LCCWE), mice develop a focal coronary arteritis that histopathologically resembles Kawasaki disease, but the mechanism remains unclear. Here, we tested the hypothesis that signaling by Toll-like receptors (TLRs) through their key downstream adaptor molecule myeloid differentiation factor 88 (MyD88) is required for the cellular activation and coronary arteritis produced by LCCWE. Methods and Results— Bone marrow–derived macrophages from TLR2- or MyD88-deficient mice were unresponsive to LCCWE-induced stimulation. In contrast, macrophages obtained from TLR4-deficient mice produced the same amount of interleukin-6 as macrophages from wild-type mice after stimulation with LCCWE. Intraperitoneal injection of LCCWE produced severe focal coronary arteritis in TLR4−/− and C57BL/6 control mice but not in TLR2−/− or MyD88−/− mice. Collectively, these results indicate that LCCWE is a potent inducer of nuclear factor-&kgr;B via TLR2 but not TLR4 and that this activation proceeds via the MyD88-dependent signaling pathway. In vivo studies suggest that TLR2−/− mice are protected from LCCWE-induced coronary arteritis and that this protection is mediated through the adaptor molecule MyD88. Conclusions— Our results provide important insights into the molecular signaling in this mouse model of coronary arteritis. We show here that LCCWE-induced coronary arteritis is dependent on intact TLR2 and MyD88 signaling.

Mastoparan, a G protein agonist peptide, differentially modulates TLR4- and TLR2-mediated signaling in human endothelial cells and murine macrophages.

Previous studies have implicated a role for heterotrimeric G protein-coupled signaling in B cells, monocytes, and macrophages stimulated with LPS and have shown that G proteins coimmunoprecipitate with membrane-bound CD14. In this study, we have extended these observations in human dermal microvessel endothelial cells (HMEC) that lack membrane-bound CD14 and in murine macrophages to define further the role of heterotrimeric G proteins in TLR signaling. Using the wasp venom-derived peptide, mastoparan, to disrupt G protein-coupled signaling, we identified a G protein-dependent signaling pathway in HMEC stimulated with TLR4 agonists that is necessary for the activation of p38 phosphorylation and kinase activity, NF-κB and IL-6 transactivation, and IL-6 secretion. In contrast, HMEC activation by TLR2 agonists, TNF-α, or IL-1β was insensitive to mastoparan. In the murine macrophage cell line, RAW 264.7, and in primary murine macrophages, G protein dysregulation by mastoparan resulted in significant inhibition of LPS-induced signaling leading to both MyD88-dependent and MyD88-independent gene expression, while TLR2-mediated gene expression was not significantly inhibited. In addition to inhibition of TLR4-mediated MAPK phosphorylation in macrophages, mastoparan blunted IL-1R-associated kinase-1 kinase activity induced by LPS, but not by TLR2 agonists, yet failed to affect phosphorylation of Akt by phosphoinositol-3-kinase induced by either TLR2- or TLR4-mediated signaling. These data confirm the importance of heterotrimeric G proteins in TLR4-mediated responses in cells that use either soluble or membrane-associated CD14 and reveal a level of TLR and signaling pathway specificity not previously appreciated.

DNA repair gene O6-methylguanine-DNA methyltransferase: Promoter hypermethylation associated with decreased expression and G:C to A:T mutations of p53 in brain tumors

The DNA repair enzyme O6‐methylguanine‐DNA methyltransferase (MGMT) removes alkylating adducts from the O6 position of guanine and protects cells from cytotoxic and mutagenic effects. Expression of MGMT is decreased in some cancers, which may be the result of methylation of CpG islands of both the promoter and coding regions of the gene. We studied the methylation status of the MGMT promoter in a very large collection of brain tumors (85) using methylation‐specific polymerase chain reaction (PCR). Aberrant methylation occurred in 48% of 85 human brain tumor samples. Quantitative real‐time PCR showed that expression of MGMT mRNA levels was significantly decreased (P < 0.001) in those brain tumors that had methylation of the promoter region of their MGMT gene. MGMT can prevent G to A mutations by removing alkyl groups from the O6 position of guanine. We found a significantly increased frequency of G:C to A:T mutations of the p53 gene in brain tumors having a methylated MGMT promoter compared with those having an unmethylated MGMT promoter (P < 0.05), and all the non–CpG dinucleotide G:C to A:T mutations of p53 were in samples with a methylated MGMT promoter.

Characterization of Defective CD4−CD8− T Cells in Murine Tumors Generated Independent of Antigen Specificity

Immune-based therapy confers limited benefits to hosts bearing late-stage tumors. Mounting evidence points to local suppression of T cell function as the most substantial barrier to effective antitumor immunity in hosts with large tumor burdens. Despite this, events responsible for locally defective T cells and immune suppression in tumors remain unclear. We describe in this study a predominant T cell population localized within two murine tumors that is characterized by expression of apoptotic markers and TCRαβ/CD3, but not CD4, CD8, or NK-associated markers. These defective cells resembled double negative (DN) T cells in lpr mice, harbored defects in the expression of T cell signaling molecules, and produced the anti-inflammatory cytokine, IL-10. Conditions known to increase or decrease the accumulation of lpr DN T cells had corresponding effects on local DN tumor infiltrating lymphocyte (TIL) levels and inversely impacted host survival. Adoptive transfer into s.c. tumors demonstrated that naive CD8+ T cells were highly susceptible to becoming DN TIL, and local supplementation of tumors with nontumor Ag-bearing MHC class I-expressing fibroblasts decreased both this susceptibility and endogenous DN TIL levels. These findings identify a major defective T cell population with suppressive potential within tumors. The data also suggest that local T cell defectiveness is controlled by the tumor environment independent of cognate Ag specificity per se. Decreasing defective DN TIL levels by increasing noncognate peptide MHC class I availability, or modulating TCR or cytokine signaling may facilitate host survival by bolstering endogenous immunity to late-stage tumors, and may help improve therapeutic tumor vaccines.

Marked Acceleration of Atherosclerosis After Lactobacillus casei–Induced Coronary Arteritis in a Mouse Model of Kawasaki Disease

Objective—The purpose of this study was to investigate whether Lactobacillus casei cell wall extract–induced Kawasaki disease (KD) accelerates atherosclerosis in hypercholesterolemic mice. Method and Results—Apolipoprotein E knockout or low-density lipoprotein receptor knockout mice were injected with Lactobacillus casei cell wall extract (KD mice) or PBS, fed high-fat diet for 8 weeks, and atherosclerotic lesions in aortic sinuses, arch (AC), and whole aorta were assessed. KD mice had larger, more complex aortic lesions with abundant collagen, and both extracellular and intracellular lipid and foam cells, compared with lesions in control mice despite similar cholesterol levels. Both apolipoprotein E knockout KD and low-density lipoprotein receptor knockout KD mice showed dramatic acceleration in atherosclerosis versus controls, with increases in en face aortic atherosclerosis and plaque size in both the aortic sinuses and AC plaques. Accelerated atherosclerosis was associated with increased circulating interleukin-12p40, interferon-&ggr;, tumor necrosis factor-&agr;, and increased macrophage, dendritic cell, and T-cell recruitment in lesions. Furthermore, daily injections of the interleukin-1Ra, which inhibits Lactobacillus casei cell wall extract–induced KD vasculitis, prevented the acceleration of atherosclerosis. Conclusion—Our results suggest an important pathophysiologic link between coronary arteritis/vasculitis in the KD mouse model and subsequent atherosclerotic acceleration, supporting the concept that a similar relation may also be present in KD patients. These results also suggest that KD in childhood may predispose to accelerated and early atherosclerosis as adults.