Huaizhu Wu

T-Cell Accumulation and Regulated on Activation, Normal T Cell Expressed and Secreted Upregulation in Adipose Tissue in Obesity

Background— Obesity is associated with chronic inflammation, which includes increased macrophage accumulation in adipose tissue (AT) and upregulation of chemokines and cytokines. T cells also play important roles in chronic inflammatory diseases such as atherosclerosis but have not been well studied in obesity. Methods and Results— Flow cytometric analysis showed higher numbers of T cells and macrophages in AT of diet-induced obese insulin-resistant male mice than in lean mice and obese females (P<0.05). RNase protection assay, ELISA, and flow cytometry indicated gender-dependent upregulation of mRNA and protein levels of regulated on activation, normal T cell expressed and secreted (RANTES) and its receptor CCR5 in AT of obese mice. Adipocytes, stromal/vascular cells from mouse AT, and human and murine adipocytes expressed RANTES. RANTES mRNA levels were negatively correlated with adiponectin in mouse AT. Adiponectin-deficient mice fed high-fat diet showed higher RANTES mRNA levels in AT than wild-type mice. Activated T cells coincubated with preadipocytes in vitro significantly suppressed preadipocyte-to-adipocyte differentiation. Obese humans with metabolic syndrome had higher mRNA levels of RANTES and CCR5 in subcutaneous AT than lean humans. RANTES and CCR5 mRNA levels were significantly higher in visceral than subcutaneous AT of morbidly obese humans. RANTES mRNA levels were positively correlated with CD3 and CD11b in human visceral AT. Conclusions— Obesity is associated with increased accumulation of T cells and macrophages in AT, which may play important roles in obesity-related disease by influencing preadipocyte/adipocyte functions. RANTES is an adipokine that is upregulated in AT by obesity in both mice and humans.

Functional role of CD11c+ monocytes in atherogenesis associated with hypercholesterolemia

Background— Monocyte activation and migration into the arterial wall are key events in atherogenesis associated with hypercholesterolemia. CD11c/CD18, a &bgr;2 integrin expressed on human monocytes and a subset of mouse monocytes, has been shown to play a distinct role in human monocyte adhesion on endothelial cells, but the regulation of CD11c in hypercholesterolemia and its role in atherogenesis are unknown. Methods and Results— Mice genetically deficient in CD11c were generated and crossbred with apolipoprotein E (apoE)−/− mice to generate CD11c−/−/apoE−/− mice. Using flow cytometry, we examined CD11c on blood leukocytes in apoE−/− hypercholesterolemic mice and found that compared with wild-type and apoE−/− mice on a normal diet, apoE−/− mice on a Western high-fat diet had increased CD11c+ monocytes. Circulating CD11c+ monocytes from apoE−/− mice fed a high-fat diet exhibited cytoplasmic lipid vacuoles and expressed higher levels of CD11b and CD29. Deficiency of CD11c decreased firm arrest of mouse monocytes on vascular cell adhesion molecule-1 and E-selectin in a shear flow assay, reduced monocyte/macrophage accumulation in atherosclerotic lesions, and decreased atherosclerosis development in apoE−/− mice on a high-fat diet. Conclusions— CD11c, which increases on blood monocytes during hypercholesterolemia, plays an important role in monocyte recruitment and atherosclerosis development in an apoE−/− mouse model of hypercholesterolemia.

CD11c/CD18 Expression Is Upregulated on Blood Monocytes During Hypertriglyceridemia and Enhances Adhesion to Vascular Cell Adhesion Molecule-1

Objective—Atherosclerosis is associated with monocyte adhesion to the arterial wall that involves integrin activation and emigration across inflamed endothelium. Involvement of &bgr;2-integrin CD11c/CD18 in atherogenesis was recently shown in dyslipidemic mice, which motivates our study of its inflammatory function during hypertriglyceridemia in humans. Methods and Results—Flow cytometry of blood from healthy subjects fed a standardized high-fat meal revealed that at 3.5 hours postprandial, monocyte CD11c surface expression was elevated, and the extent of upregulation correlated with blood triglycerides. Monocytes from postprandial blood exhibited an increased light scatter profile, which correlated with elevated CD11c expression and uptake of lipid particles. Purified monocytes internalized triglyceride-rich lipoproteins isolated from postprandial blood through low-density lipoprotein–receptor–related protein-1, and this also elicited CD11c upregulation. Laboratory-on-a-chip analysis of whole blood showed that monocyte arrest on a vascular cell adhesion molecule-1 (VCAM-1) substrate under shear flow was elevated at 3.5 hours and correlated with blood triglyceride and CD11c expression. At 7 hours postprandial, blood triglycerides decreased and monocyte CD11c expression and arrest on VCAM-1 returned to fasting levels. Conclusion—During hypertriglyceridemia, monocytes internalize lipids, upregulate CD11c, and increase adhesion to VCAM-1. These data suggest that analysis of monocyte inflammation may provide an additional framework for evaluating individual susceptibility to cardiovascular disease.

CD11c Expression in Adipose Tissue and Blood and Its Role in Diet-Induced Obesity

Objective—To examine CD11c, a &bgr;2-integrin, on adipose tissue (AT) leukocytes and blood monocytes and its role in diet-induced obesity. Methods and Results—High-fat diet–induced obese C57BL/6 mice, CD11c-deficient mice, and obese humans were studied. CD11c, leukocytes, and chemokines/cytokines were examined in AT and/or blood by flow cytometry, RNase protection assay, quantitative polymerase chain reaction, or enzyme-linked immunosorbent assay. Obese C57BL/6 mice had increased CD11c in AT and blood compared with lean controls. CD11c messenger RNA positively correlated with monocyte chemoattractant protein 1 in human visceral AT. Obese humans with metabolic syndrome had a higher CD11c level on blood monocytes compared with lean humans. Low-fat diet–induced weight loss reduced blood monocyte CD11c in obese mice and humans. Mouse and human monocyte CD11c levels and mouse AT CD11c messenger RNA correlated with insulin resistance. CD11c deficiency in mice did not alter weight gain but decreased inflammation, evidenced by a lower T-cell number and reduced levels of major histocompatibility complex class II, C-C chemokine ligand 2 (CCL5), CCL4, and interferon &ggr; in AT, and ameliorated insulin resistance and glucose intolerance associated with diet-induced obesity. Conclusions—Diet-induced obesity increased CD11c in both AT and blood in mice and humans. CD11c plays an important role in T-cell accumulation and activation in AT, and contributes to insulin resistance associated with obesity.

Proatherogenic conditions promote autoimmune T helper 17 cell responses in vivo

Patients with systemic autoimmune diseases show increased incidence of atherosclerosis. However, the contribution of proatherogenic factors to autoimmunity remains unclear. We found that atherogenic mice (herein referred to as LDb mice) exhibited increased serum interleukin-17, which was associated with increased numbers of T helper 17 (Th17) cells in secondary lymphoid organs. The environment within LDb mice was substantially favorable for Th17 cell polarization of autoreactive T cells during homeostatic proliferation, which was considerably inhibited by antibodies directed against oxidized low-density lipoprotein (oxLDL). Moreover, the uptake of oxLDL induced dendritic-cell-mediated Th17 cell polarization by triggering IL-6 production in a process dependent on TLR4, CD36, and MyD88. Furthermore, self-reactive CD4(+) T cells that expanded in the presence of oxLDL induced more profound experimental autoimmune encephalomyelitis. These findings demonstrate that proatherogenic factors promote the polarization and inflammatory function of autoimmune Th17 cells, which could be critical for the pathogenesis of atherosclerosis and other related autoimmune diseases.

Deficiency of CD11b or CD11d Results in Reduced Staphylococcal Enterotoxin-Induced T Cell Response and T Cell Phenotypic Changes

The β2 integrin CD11a is involved in T cell-APC interactions, but the roles of CD11b, CD11c, and CD11d in such interactions have not been examined. To evaluate the roles of each CD11/CD18 integrin in T cell-APC interactions, we tested the ability of splenocytes of CD11-knockout (KO) mice to respond to staphylococcal enterotoxins (SEs), a commonly used superantigen. The defect in T cell proliferation with SEA was more severe in splenocytes from mice deficient in CD18, CD11b, or CD11d than in CD11a-deficient splenocytes, with a normal response in CD11c-deficient splenocytes. Mixing experiments showed that the defect of both CD11b-KO and CD11d-KO splenocytes was, unexpectedly, in T cells rather than in APC. Cytometric analysis failed to detect CD11b or CD11d on resting or activated T cells or on thymocytes of wild-type adult mice, nor did Abs directed to these integrins block responses in culture, suggesting that T cells educated in CD11b-KO or CD11d-KO mice were phenotypically altered. Consistent with this hypothesis, T cells from CD11b-KO and CD11d-KO splenocytes exhibited reduced intensity of CD3 and CD28 expression and decreased ratios of CD4/CD8 cells, and CD4+ T cells were reduced among CD11b-KO and CD11d-KO thymocytes. CD11b and CD11d were coexpressed on a subset of early wild-type fetal thymocytes. We postulate that transient thymocyte expression of both CD11b and CD11d is nonredundantly required for normal thymocyte and T cell development, leading to phenotypic changes in T cells that result in the reduced response to SE stimulation.

Foamy Monocytes Form Early and Contribute to Nascent Atherosclerosis in Mice With Hypercholesterolemia

Objective—To examine infiltration of blood foamy monocytes, containing intracellular lipid droplets, into early atherosclerotic lesions and its contribution to development of nascent atherosclerosis. Approach and Results—In apoE–/– mice fed Western high-fat diet (WD), >10% of circulating monocytes became foamy monocytes at 3 days on WD and >20% of monocytes at 1 week. Foamy monocytes also formed early in blood of Ldlr–/–Apobec1–/– (LDb) mice on WD. Based on CD11c and CD36, mouse monocytes were categorized as CD11c–CD36–, CD11c–CD36+, and CD11c+CD36+. The majority of foamy monocytes were CD11c+CD36+, whereas most nonfoamy monocytes were CD11c–CD36– or CD11c–CD36+ in apoE–/– mice on WD. In wild-type mice, CD11c+CD36+ and CD11c–CD36+, but few CD11c–CD36–, monocytes took up cholesteryl ester–rich very low-density lipoproteins (CE-VLDLs) isolated from apoE–/– mice on WD, and CE-VLDL uptake accelerated CD11c–CD36+ to CD11c+CD36+ monocyte differentiation. Ablation of CD36 decreased monocyte uptake of CE-VLDLs. Intravenous injection of DiI-CE-VLDLs in apoE–/– mice on WD specifically labeled CD11c+CD36+ foamy monocytes, which infiltrated into nascent atherosclerotic lesions and became CD11c+ cells that were selectively localized in atherosclerotic lesions. CD11c deficiency reduced foamy monocyte infiltration into atherosclerotic lesions. Specific and consistent depletion of foamy monocytes (for 3 weeks) by daily intravenous injections of low-dose clodrosome reduced development of nascent atherosclerosis. Conclusions—Foamy monocytes, which form early in blood of mice with hypercholesterolemia, infiltrate into early atherosclerotic lesions in a CD11c-dependent manner and play crucial roles in nascent atherosclerosis development.

Attenuated adipose tissue and skeletal muscle inflammation in obese mice with combined CD4+ and CD8+ T cell deficiency

OBJECTIVES High-fat diet (HFD) feeding in mice is characterized by accumulation of αβ T cells in adipose tissue. However, the contribution of αβ T cells to obesity-induced inflammation of skeletal muscle, a major organ of glucose uptake, is unknown. This study was undertaken to evaluate the effect of αβ T cells on insulin sensitivity and inflammatory state of skeletal muscle and adipose tissue in obesity. Furthermore, we investigated whether CD4+IFNγ+ (TH1) cells are involved in skeletal muscle and adipose tissue metabolic dysfunction that accompanies obesity. METHODS Mice lacking αβ T cells (T cell receptor beta chain-deficient [TCRb-/-] mice) were fed HFD for 12 weeks. Obesity-induced skeletal muscle and adipose tissue inflammation was assessed by flow cytometry and quantitative RT-PCR. To investigate the effect of TH1 cells on skeletal muscle and adipose tissue inflammation and metabolic functions, we injected 5×10(5) TH1 cells or PBS weekly over 12 weeks into HFD-fed TCRb-/- mice. We also cultured C2C12 myofibers and 3T3-L1 adipocytes with TH1-conditioned medium. RESULTS We showed that similar to adipose tissue, skeletal muscle of obese mice have higher αβ T cell content, including TH1 cells. TCRb-/- mice were protected against obesity-induced hyperglycemia and insulin resistance. We also demonstrated suppressed macrophage infiltration and reduced inflammatory cytokine expression in skeletal muscle and adipose tissue of TCRb-/- mice on HFD compared to wild-type obese controls. Adoptive transfer of TH1 cells into HFD-fed TCRb-/- mice resulted in increased skeletal muscle and adipose tissue inflammation and impaired glucose metabolism. TH1 cells directly impaired functions of C2C12 myotubes and 3T3-L1 adipocytes in vitro. CONCLUSIONS We conclude that reduced adipose tissue and skeletal muscle inflammation in obese TCRb-/- mice is partially attributable to the absence of TH1 cells. Our results suggest an important role of TH1 cells in regulating inflammation and insulin resistance in obesity.

Essential role of CD11a in CD8 + T-cell accumulation and activation in adipose tissue

Objective— T cells, particularly CD8+ T cells, are major participants in obesity-linked adipose tissue (AT) inflammation. We examined the mechanisms of CD8+ T-cell accumulation and activation in AT and the role of CD11a, a &bgr;2 integrin. Approach and Results— CD8+ T cells in AT of obese mice showed activated phenotypes with increased proliferation and interferon-&ggr; expression. In vitro, CD8+ T cells from mouse AT displayed increased interferon-&ggr; expression and proliferation to stimulation with interleukin-12 and interleukin-18, which were increased in obese AT. CD11a was upregulated in CD8+ T cells in obese mice. Ablation of CD11a in obese mice dramatically reduced T-cell accumulation, activation, and proliferation in AT. Adoptive transfer showed that CD8+ T cells from wild-type mice, but not from CD11a-deficient mice, infiltrated into AT of recipient obese wild-type mice. CD11a deficiency also reduced tumor necrosis factor-&agr;–producing and interleukin-12–producing macrophages in AT and improved insulin resistance. Conclusions— Combined action of cytokines in obese AT induces proliferative response of CD8+ T cells locally, which, along with increased infiltration, contributes to CD8+ T-cell accumulation and activation in AT. CD11a plays a crucial role in AT inflammation by participating in T-cell infiltration and activation.

Skeletal muscle inflammation and insulin resistance in obesity

Obesity is associated with chronic inflammation, which contributes to insulin resistance and type 2 diabetes mellitus. Under normal conditions, skeletal muscle is responsible for the majority of insulin-stimulated whole-body glucose disposal; thus, dysregulation of skeletal muscle metabolism can strongly influence whole-body glucose homeostasis and insulin sensitivity. Increasing evidence suggests that inflammation occurs in skeletal muscle in obesity and is mainly manifested by increased immune cell infiltration and proinflammatory activation in intermyocellular and perimuscular adipose tissue. By secreting proinflammatory molecules, immune cells may induce myocyte inflammation, adversely regulate myocyte metabolism, and contribute to insulin resistance via paracrine effects. Increased influx of fatty acids and inflammatory molecules from other tissues, particularly visceral adipose tissue, can also induce muscle inflammation and negatively regulate myocyte metabolism, leading to insulin resistance.