RESUMO
Macrophage internalization of modified lipoproteins is thought to play a critical role in the initiation of atherogenesis. Two scavenger receptors, scavenger receptor A (SR-A) and CD36, have been centrally implicated in this lipid uptake process. Previous studies showed that these receptors mediated the majority of cholesterol ester accumulation in macrophages exposed to oxidized LDL and that mice with deletions of either receptor exhibited marked reductions in atherosclerosis. This work has contributed to an atherosclerosis paradigm: scavenger receptor-mediated oxidized lipoprotein uptake is required for foam cell formation and atherogenesis. In this study, Apoe-/- mice lacking SR-A or CD36, backcrossed into the C57BL/6 strain for 7 generations, were fed an atherogenic diet for 8 weeks. Hyperlipidemic Cd36-/-Apoe-/- and Msr1-/-Apoe-/- mice showed significant reductions in peritoneal macrophage lipid accumulation in vivo; however, in contrast with previous reports, this was associated with increased aortic sinus lesion areas. Characterization of aortic sinus lesions by electron microscopy and immunohistochemistry showed abundant macrophage foam cells, indicating that lipid uptake by intimal macrophages occurs in the absence of CD36 or SR-A. These data show that alternative lipid uptake mechanisms may contribute to macrophage cholesterol ester accumulation in vivo and suggest that the roles of SR-A and CD36 as proatherosclerotic mediators of modified LDL uptake in vivo need to be reassessed.
Assuntos
Arteriosclerose/metabolismo , Antígenos CD36/metabolismo , Ésteres do Colesterol/metabolismo , Hiperlipidemias/metabolismo , Lipoproteínas LDL/metabolismo , Receptores Imunológicos/metabolismo , Animais , Apolipoproteínas E/genética , Apolipoproteínas E/metabolismo , Arteriosclerose/genética , Arteriosclerose/patologia , Antígenos CD36/genética , Dieta Aterogênica , Células Espumosas/metabolismo , Células Espumosas/patologia , Hiperlipidemias/genética , Hiperlipidemias/patologia , Macrófagos Peritoneais/metabolismo , Macrófagos Peritoneais/patologia , Camundongos , Camundongos Knockout , Receptores Imunológicos/genética , Receptores Depuradores , Receptores Depuradores Classe A , Seio Aórtico/metabolismo , Seio Aórtico/patologiaRESUMO
BACKGROUND: Studies to define the overall contribution of lymphocytes to lesion formation in atherosclerosis-susceptible mice have demonstrated relatively subtle effects; the use of lymphocyte-deficient mice, however, compromises both the effector and regulatory arms of the immune system. Here, we tested the hypothesis that deletion of CXCL10 (IP-10), a chemokine specific for effector T cells that has been localized within atherosclerotic lesions, would significantly inhibit atherogenesis. METHODS AND RESULTS: Compound deficient Apoe(-/-)/Cxcl10(-/-) mice fed a Western-style diet for either 6 or 12 weeks demonstrated significant reductions in atherogenesis as compared with Apoe(-/-) controls, as assessed by both aortic en face and cross-sectional analyses. Immunohistochemical studies revealed a decrease in the accumulation of CD4+ T cells, whereas quantitative polymerase chain reaction analysis of lesion-rich aortic arches demonstrated a marked reduction in mRNA for CXCR3, the CXCL10 chemokine receptor. Although overall T-cell accumulation was diminished significantly, we found evidence to suggest that regulatory T-cell (Treg) numbers and activity were enhanced, as assessed by increased message for the Treg-specific marker Foxp3, as well as increases in immunostaining for the Treg-associated cytokines interleukin-10 and transforming growth factor-beta1. We also documented naturally occurring Treg cells in human atherosclerotic lesions. CONCLUSIONS: We provide novel evidence for a functional role for the effector T-cell chemoattractant CXCL10 in atherosclerotic lesion formation by modulating the local balance of the effector and regulatory arms of the immune system.
Assuntos
Aterosclerose/fisiopatologia , Quimiocinas CXC/fisiologia , Doença da Artéria Coronariana/patologia , Doença da Artéria Coronariana/fisiopatologia , Linfócitos T/fisiologia , Animais , Aorta/patologia , Apolipoproteínas E/análise , Apolipoproteínas E/deficiência , Apolipoproteínas E/fisiologia , Aterosclerose/patologia , Contagem de Linfócito CD4 , Linfócitos T CD4-Positivos/química , Linfócitos T CD4-Positivos/fisiologia , Quimiocina CXCL10 , Quimiocinas CXC/análise , Quimiocinas CXC/deficiência , Quimiocinas CXC/genética , Doença da Artéria Coronariana/etiologia , Vasos Coronários/patologia , Citometria de Fluxo , Fatores de Transcrição Forkhead/análise , Fatores de Transcrição Forkhead/genética , Fatores de Transcrição Forkhead/fisiologia , Imuno-Histoquímica , Interleucina-10/análise , Interleucina-10/genética , Interleucina-10/fisiologia , Camundongos , Camundongos Mutantes , Reação em Cadeia da Polimerase , RNA Mensageiro/análise , RNA Mensageiro/genética , Receptores CXCR3 , Receptores de Quimiocinas/análise , Receptores de Quimiocinas/genética , Receptores de Quimiocinas/fisiologia , Transdução de Sinais/fisiologia , Linfócitos T/química , Fator de Crescimento Transformador beta/análise , Fator de Crescimento Transformador beta/genética , Fator de Crescimento Transformador beta/fisiologia , Fator de Crescimento Transformador beta1RESUMO
BACKGROUND: It is known that 5-lipoxygenase and its product, leukotriene B4 (LTB4), are highly expressed in several human pathologies, including atherosclerotic plaque. LTB(4) signals primarily through its high-affinity G protein-coupled receptor BLT1, which is expressed on specific leukocyte subsets. BLT1 receptor expression and function on other atheroma-associated cell types is unknown. METHODS AND RESULTS: To directly assess the role of the LTB4-BLT1 pathway in atherogenesis, we bred BLT1(-/-) mice into the atherosclerosis-susceptible apoE(-/-) strain. Compound-deficient apoE(-/-)/Blt1(-/-) mice fed a Western-type diet had a marked reduction in plaque formation compared with apoE(-/-) controls. Immunohistochemical analysis of atherosclerotic lesions in compound-deficient mice revealed a striking decrease in smooth muscle cells (SMCs) and significant decreases in macrophages and T cells. We report here novel evidence of the expression and function of BLT1 on vascular SMCs. LTB4 triggered SMC chemotaxis, which was pertussis toxin sensitive in Blt1(+/+) SMCs and absent in Blt1(-/-) cells, suggesting that BLT1 was the dominant receptor mediating effector functions through a G protein-coupled signaling pathway. Furthermore, BLT1 colocalized with SMCs in human atherosclerotic lesions. CONCLUSIONS: These new findings extend the role of inducible BLT1 to nonleukocyte populations and suggest an important target for intervention to modulate the response to vascular injury.
Assuntos
Aterosclerose/prevenção & controle , Leucotrieno B4/farmacologia , Músculo Liso Vascular/citologia , Miócitos de Músculo Liso/citologia , Receptores do Leucotrieno B4/fisiologia , Receptores Purinérgicos P2/fisiologia , Animais , Apolipoproteínas E/fisiologia , Aterosclerose/etiologia , Movimento Celular , Imuno-Histoquímica , Camundongos , Camundongos Endogâmicos C57BL , Receptores CCR2 , Receptores de Quimiocinas/fisiologia , Receptores do Leucotrieno B4/deficiência , Receptores Purinérgicos P2/deficiência , Transdução de SinaisRESUMO
Mutations in the A class of ATP-binding cassette transporters (ABCA) are causally implicated in three human diseases: Tangier disease (ABCA1), Stargadt's macular degeneration (ABCA4), and neonatal respiratory failure (ABCA3). Both ABCA1 and ABCA4 have been shown to transport lipids across cellular membranes, and ABCA3 may play a similar role in transporting pulmonary surfactant. Although the functions of the other 10 ABCA class transporters identified in the human genome remain obscure, ABCA7-transfected cells have been shown to efflux lipids in response to stimulation by apolipoprotein A-I. In an effort to elucidate the physiologic role of ABCA7, we generated mice lacking this transporter (Abca7-/- mice). Homozygous null mice were produced from intercrosses of heterozygous null mice at the expected Mendelian frequency and developed normally without any obvious phenotypic abnormalities. Cholesterol and phospholipid efflux stimulated by apolipoprotein A-I from macrophages isolated from wild type and Abca7-/- mice did not differ, suggesting that these activities may not be central to the physiological role of the transporter in vivo. Abca7-/- females, but not males, had significantly less visceral fat and lower total serum and high density lipoprotein cholesterol levels than wild type, gender-matched littermates. ABCA7 expression was detected in hippocampal and cortical neurons by in situ hybridization and in brain and white adipose tissue by Western blotting. Induction of adipocyte differentiation from 3T3 fibroblasts in culture led to a marked increase in ABCA7 expression. These studies suggest that ABCA7 plays a novel role in lipid and fat metabolism that Abca7-/- mice can be used to elucidate.