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.

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 β2 integrin.

APPROACH AND RESULTS

CD8(+) T cells in AT of obese mice showed activated phenotypes with increased proliferation and interferon-γ expression. In vitro, CD8(+) T cells from mouse AT displayed increased interferon-γ 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-α-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.

ApoE and the role of very low density lipoproteins in adipose tissue inflammation

OBJECTIVE

To identify the role of triglyceride-rich lipoproteins (TGRLs) and apoE, a major apolipoprotein in TGRLs, in adipose tissue inflammation with high-fat diet (HFD)-induced obesity.

METHODS

Male apoE(-/-) and C57BL/6J wild-type (WT) mice fed HFD for 12 weeks were assessed for metabolic and inflammatory parameters. ApoE(-/-) and WT mice were orally gavaged with [(3)H]palmitic acid to examine the role of apoE in fat delivery to adipose tissue. VLDL from obese apoE(-/-) mice were intravenously injected into lean WT or apoE(-/-) mice to test potential contribution of TGRLs-derived fat delivery to inflammation in adipose tissue and the role of apoE.

RESULTS

ApoE(-/-) mice gained less body weight, and had less fat mass and lower triglyceride levels in skeletal muscle than WT. ApoE(-/-) mice on HFD had better insulin sensitivity than WT even when comparing body weight-matched mice. Compared to WT mice, apoE(-/-) mice on HFD had lower levels of inflammatory cytokines/chemokines and CD11c in adipose tissue, and lower levels of inflammatory markers in skeletal muscle. At 6 h after oral gavage with [(3)H]palmitic acid, incorporation of [(3)H]palmitic acid into adipose tissue and skeletal muscle was lower in apoE(-/-) mice. After repeated daily injection for 3 days, VLDL from obese apoE(-/-) mice induced inflammation in adipose tissue of recipient WT but not apoE(-/-) mice.

CONCLUSION

In HFD-induced obesity, apoE plays an important role in inflammation in adipose tissue and skeletal muscle, likely by mediating TGRL-derived fat delivery to these tissues.

Abstract 138: Deficiency of CD11a Reduces CD8+ T-Cell Activation and Proliferation in Adipose Tissue of Obese Mice

T cells, particularly CD8 + T cells, are major participants in obesity-linked adipose tissue (AT) inflammation. CD11a, a β 2 -integrin, is crucial for T cell adhesion and interactions with antigen-presenting cells. It has been shown that stimulation of CD11a lowered the threshold of T cell activation, yet the role of CD11a in T cell activation in AT remains unknown. We used CD11a -/- mice to test the hypothesis that CD11a deficiency reduces CD8 + T cell activation in AT. Mice fed high-fat diet for 3 months were used as an obesity model, with mice on normal diet as lean controls. CD8 + T cells and related cytokines were examined in AT by flow cytometry or quantitative RT-PCR. Compared to lean wild-type (WT) mice, obese WT mice had increased numbers of activated CD8 + T cells, with higher proportions of CD11a high CD8 + memory T cells, CD44 + CD62L - effector memory CD8 + T cells and CD44 + CD69 + effector CD8 + T cells; and increased mRNA levels of granzyme B and IFN-γ in AT. Compared to obese WT, obese CD11a -/- mice had lower proportions of CD44 + CD62L - effector memory CD8 + T cells and CD44 + CD69 + effector CD8 + T cells, and decreased mRNA levels of granzyme B and IFN-γ (P<0.01), implying decreased activation of CD8 + T cells. IL-2, IL-12 and IL-18 levels were increased in AT of obese WT compared to that of leans, and were lower in AT of obese CD11a -/- mice than that of obese WT. In vitro treatment with IL-2, IL-12 and IL-18 induced proliferation and expression of IFN-γ and CD69 in CD8 + cells isolated from AT of WT mice. Compared to those from WT mice, CD8 + T cells from AT of CD11a -/- mice showed decreased response to cytokine stimulation with fewer cells expressing IFN-γ (7.0±1.1% in CD11a -/- vs. 11.3±1.1% in WT, n=3-5/group, P<0.05). In addition, using Edu labeling techniques, we studied proliferation of CD8 + T cells in AT in vivo. At 3 hours after intraperitoneal injection of Edu, no Edu + T cells appeared in blood but we found CD8 + /Edu + T cells in AT of WT mice, indicating CD8 + T cells proliferated in AT. Compared to obese WT mice, obese CD11a -/- mice had decreased proportion of proliferating CD8 + T cells in AT (1.3±0.4% in CD11a -/- vs. 2.4±0.1% in WT, n=3/group, P<0.01). In conclusion, we demonstrated that CD11a played a crucial role in CD8 + T cell activation and proliferation in AT associated with obesity.

Effect of the cannabinoid receptor-1 antagonist rimonabant on inflammation in mice with diet-induced obesity

We studied whether cannabinoid receptor (CB1) blockade with rimonabant has an anti-inflammatory effect in obese mice, and whether this effect depends on weight loss and/or diet consumption. High-fat diet (HFD)-induced obese mice were treated orally with rimonabant (HFD-R) or vehicle (HFD-V) for 4 weeks. Paired-feeding was conducted in two additional groups of obese mice to achieve either the same body weight (HFD-BW) or the same HFD intake (HFD DI) as HFD-R. All these groups of mice were maintained on HFD throughout, with mice on normal diet (ND) throughout as lean controls. Rimonabant treatment of obese mice induced marked diet-intake reduction and weight loss during the first week, which was followed by maintenance of low body weight but not diet-intake reduction. Lower HFD intake was required to reach the same degree of weight loss in HFD-BW. HFD-DI had similar weight loss initially, but then started to gain weight, reaching a higher body weight than HFD-R. Despite the same degree of weight loss, HFD-R had less fat mass and lower adipogenic gene expression than HFD-BW. Compared to HFD-V or HFD-DI, HFD-R had reduced inflammation in adipose tissue (AT) and/or liver indicated primarily by lower monocyte chemoattractant protein-1 (MCP-1) levels. However, MCP-1 levels were not significantly different between HFD-R and HFD-BW. In vitro incubation of rimonabant with AT explants did not change MCP-1 levels. Thus, rimonabant induced weight loss in obese mice by diet-intake-dependent and -independent fashions. Rimonabant decreased inflammation in obese mice, possibly through a primary effect on weight reduction.

CD11c expression in adipose tissue and blood and its role in diet-induced obesity

OBJECTIVE

To examine CD11c, a beta(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 gamma 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.

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.

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

The beta(2) 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.

Ligand-dependent regulation of vascular endothelial growth factor and erythropoietin expression by a plasmid-based autoinducible GeneSwitch system

We investigated the ability of an improved mifepristone-dependent GeneSwitch system to regulate the expression of genes for two therapeutic proteins: vascular endothelial growth factor (VEGF) and erythropoietin. The GeneSwitch system consisted of two plasmids, one encoding the chimeric GeneSwitch protein, the other an inducible transgene. When the constitutive CMV promoter of the GeneSwitch plasmid was replaced by an autoinducible promoter consisting of four copies of GAL4 DNA binding sites linked to a minimal thymidine kinase promoter, the tightness of transgene regulation was improved by an order of magnitude. Quantitative RT-PCR analysis of GeneSwitch mRNA confirmed that the autoinducible promoter was responsive to mifepristone. We demonstrated the ability of the improved GeneSwitch system to regulate the expression of VEGF or erythropoietin in a biologically relevant manner after delivery of plasmids to the hind-limb muscle of adult mice. This ability of the autoinducible GeneSwitch system to regulate the expression of therapeutic proteins in mice indicates its potential for use in human gene therapy applications.

Relative contribution of LFA-1 and Mac-1 to neutrophil adhesion and migration

To differentiate the unique and overlapping functions of LFA-1 and Mac-1, LFA-1-deficient mice were developed by targeted homologous recombination in embryonic stem cells, and neutrophil function was compared in vitro and in vivo with Mac-1-deficient, CD18-deficient, and wild-type mice. LFA-1-deficient mice exhibit leukocytosis but do not develop spontaneous infections, in contrast to CD18-deficient mice. After zymosan-activated serum stimulation, LFA-1-deficient neutrophils demonstrated activation, evidenced by up-regulation of surface Mac-1, but did not show increased adhesion to purified ICAM-1 or endothelial cells, similar to CD18-deficient neutrophils. Adhesion of Mac-1-deficient neutrophils significantly increased with stimulation, although adhesion was lower than for wild-type neutrophils. Evaluation of the strength of adhesion through LFA-1, Mac-1, and CD18 indicated a marked reduction in firm attachment, with increasing shear stress in LFA-1-deficient neutrophils, similar to CD18-deficient neutrophils, and only a modest reduction in Mac-1-deficient neutrophils. Leukocyte influx in a subcutaneous air pouch in response to TNF-alpha was reduced by 67% and 59% in LFA-1- and CD18-deficient mice but increased by 198% in Mac-1-deficient mice. Genetic deficiencies demonstrate that both LFA-1 and Mac-1 contribute to adhesion of neutrophils to endothelial cells and ICAM-1, but adhesion through LFA-1 overshadows the contribution from Mac-1. Neutrophil extravasation in response to TNF-alpha in LFA-1-deficient mice dramatically decreased, whereas neutrophil extravasation in Mac-1-deficient mice markedly increased.

Relative Contribution of LFA-1 and Mac-1 to Neutrophil Adhesion and Migration

To differentiate the unique and overlapping functions of LFA-1 and Mac-1, LFA-1-deficient mice were developed by targeted homologous recombination in embryonic stem cells, and neutrophil function was compared in vitro and in vivo with Mac-1-deficient, CD18-deficient, and wild-type mice. LFA-1-deficient mice exhibit leukocytosis but do not develop spontaneous infections, in contrast to CD18-deficient mice. After zymosan-activated serum stimulation, LFA-1-deficient neutrophils demonstrated activation, evidenced by up-regulation of surface Mac-1, but did not show increased adhesion to purified ICAM-1 or endothelial cells, similar to CD18-deficient neutrophils. Adhesion of Mac-1-deficient neutrophils significantly increased with stimulation, although adhesion was lower than for wild-type neutrophils. Evaluation of the strength of adhesion through LFA-1, Mac-1, and CD18 indicated a marked reduction in firm attachment, with increasing shear stress in LFA-1-deficient neutrophils, similar to CD18-deficient neutrophils, and only a modest reduction in Mac-1-deficient neutrophils. Leukocyte influx in a subcutaneous air pouch in response to TNF-α was reduced by 67% and 59% in LFA-1- and CD18-deficient mice but increased by 198% in Mac-1-deficient mice. Genetic deficiencies demonstrate that both LFA-1 and Mac-1 contribute to adhesion of neutrophils to endothelial cells and ICAM-1, but adhesion through LFA-1 overshadows the contribution from Mac-1. Neutrophil extravasation in response to TNF-α in LFA-1-deficient mice dramatically decreased, whereas neutrophil extravasation in Mac-1-deficient mice markedly increased.

Stem cell factor induction is associated with mast cell accumulation after canine myocardial ischemia and reperfusion

BACKGROUND

Myocardial infarction is associated with an intense inflammatory reaction leading to healing and scar formation. Because mast cells are a significant source of fibrogenic factors, we investigated mast cell accumulation and regulation of stem cell factor (SCF), a potent growth and tactic factor for mast cells, in the healing myocardium.

METHODS AND RESULTS

Using a canine model of myocardial ischemia and reperfusion, we demonstrated a striking increase of mast cell numbers during the healing phase of a myocardial infarction. Mast cell numbers started increasing after 72 hours of reperfusion, showing maximum accumulation in areas of collagen deposition (12.0+/-2.6-fold increase; P<0.01) and proliferating cell nuclear antigen (PCNA) expression. The majority of proliferating cells were identified as alpha-smooth muscle actin-positive myofibroblasts or factor VIII-positive endothelial cells. Mast cells did not appear to proliferate. Using a nuclease protection assay, we demonstrated induction of SCF mRNA within 72 hours of reperfusion. Immunohistochemical studies demonstrated that a subset of macrophages was the source of SCF immunoreactivity in the infarcted myocardium. SCF protein was not found in endothelial cells and myofibroblasts. Intravascular tryptase-positive, FITC-avidin-positive, CD11b-negative mast cell precursors were noted in the area of healing and in the cardiac lymph after 48 to 72 hours of reperfusion.

CONCLUSIONS

Mast cells increase in number in areas of collagen deposition and PCNA expression after myocardial ischemia. The data provide evidence of mast cell precursor infiltration into the areas of cellular injury. SCF is induced in a subset of macrophages infiltrating the healing myocardium. We suggest an important role for SCF in promoting chemotaxis and growth of mast cell precursors in the healing heart.

Molecular evidence for induction of intracellular adhesion molecule-1 in the viable border zone associated with ischemia-reperfusion injury of the dog heart

BACKGROUND

Acute inflammation may play a role in injury during reperfusion following myocardial ischemia. Studies in vitro suggest that intracellular adhesion molecule-1 (ICAM-1) mediates neutrophil adherence to cardiac myocytes and neutrophil-mediated injury. We have shown cytokine activity in postischemic cardiac lymph sufficient to maximally express ICAM-1 on myocytes and that ICAM-1 mRNA is found in the previously ischemic myocardium early in reperfusion.

METHODS AND RESULTS

In the present study, we used in situ hybridization techniques to detect ICAM-1 mRNA and examine the cells of origin, relation to cell injury, and relation to inflammatory infiltration after 1 hour of ischemia and varying times of reperfusion. By 1 hour of reperfusion, ICAM-1 mRNA was detected in much of the ischemic myocardium, except in areas of contraction band necrosis. At 2 and 3 hours, a clear demarcation of necrotic areas surrounding ischemic areas of viable myocardium with ICAM-1 mRNA staining was present, and ICAM-1 mRNA staining increased with time. Nonischemic areas had no visible ICAM-1 mRNA staining in the first 3 hours. By 24 hours of reperfusion, ICAM-1 mRNA was present in both control and ischemic segments (excluding the necrotic areas) compatible with a generalized circulation of cytokines persistent at 24 hours. In the absence of reperfusion, ICAM-1 mRNA staining was not seen in the first 3 hours and was markedly reduced at 24 hours. The interface of viable and necrotic cells also contained the most extensive inflammatory infiltration.

CONCLUSIONS

Evidence is presented that induction of ICAM-1 mRNA has highly specific localization to ischemic but viable myocardium. Induction of ICAM-1 mRNA transcription in early reperfusion may render the viable "border zone" susceptible to neutrophil-induced injury.