RESUMEN

OBJECTIVE: Deletion of the lysophospholipid-sensitive receptor, G2A, in low-density lipoprotein receptor knockout (LDLR(-/-)) mice elevates plasma high-density lipoprotein (HDL) cholesterol and suppresses atherosclerosis. However, chemotactic action of G2A in monocytes/macrophages, in addition to its modulatory effect on HDL, may contribute to the proatherogenic action of G2A. METHODS AND RESULTS: We determined that deletion of G2A in LDLR(-/-) mice increases the ApoA1, ApoE, and cholesterol content of plasma HDL fractions. Hepatocytes were shown to express G2A and hepatocytes from G2A-deficient LDLR(-/-) mice secreted more ApoA1 and ApoE in HDL fractions compared to their G2A-sufficient counterparts. The atheroprotective and HDL modulatory effects of G2A deficiency were dependent on the presence of ApoE, as deletion of G2A in ApoE(-/-) and ApoE(-/-)LDLR(-/-) mice failed to raise HDL and did not suppress atherosclerosis. G2A deficiency in bone marrow-derived cells of LDLR(-/-) mice had no effect on atherosclerosis or HDL, whereas G2A deficiency in resident tissues was sufficient to raise HDL and suppress atherosclerosis. CONCLUSIONS: These data demonstrate that the chemotactic function of G2A in bone marrow-derived monocytes does not modulate atherosclerosis in LDLR(-/-) mice and suggest an ApoE-dependent function for G2A in the control of hepatic HDL metabolism that might contribute to its proatherogenic action.

Asunto(s)

Apolipoproteínas E/metabolismo , Aterosclerosis/metabolismo , Células de la Médula Ósea/metabolismo , Proteínas de Ciclo Celular/metabolismo , Hipercolesterolemia/metabolismo , Lipoproteínas HDL/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Receptores de LDL/deficiencia , Transportador 1 de Casete de Unión a ATP , Transportadoras de Casetes de Unión a ATP/metabolismo , Animales , Apolipoproteína A-I/metabolismo , Aterosclerosis/etiología , Aterosclerosis/patología , Aterosclerosis/prevención & control , Trasplante de Médula Ósea , Proteínas de Ciclo Celular/genética , Células Cultivadas , Quimiotaxis , HDL-Colesterol/metabolismo , Modelos Animales de Enfermedad , Femenino , Hepatocitos/metabolismo , Hipercolesterolemia/complicaciones , Hipercolesterolemia/patología , Lipoproteínas HDL/sangre , Macrófagos Peritoneales/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Receptores Acoplados a Proteínas G/deficiencia , Receptores Acoplados a Proteínas G/genética , Receptores de LDL/genética , Factores de Tiempo

RESUMEN

Lysophosphatidylcholine (LPC) is a chemotactic lysolipid produced during inflammation by the hydrolytic action of phospholipase A(2) enzymes. LPC stimulates chemotaxis of T cells in vitro through activation of the G protein-coupled receptor, G2A. This has led to the proposition that G2A contributes to the recruitment of T cells to sites of inflammation and thus promotes chronic inflammatory autoimmune diseases associated with the generation and subsequent tissue infiltration of auto-antigen-specific effector T cells. However, one study suggests that G2A may negatively regulate T cell proliferative responses to antigen receptor engagement and thereby attenuates autoimmunity by reducing the generation of autoreactive T cells. To address the relative contribution of these G2A-mediated effects to the pathophysiology of T cell-mediated autoimmune disease, we examined the impact of G2A inactivation on the onset and severity of murine experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). Wild type (G2A(+/+)) and G2A-deficient (G2A(-/-)) C57BL/6J mice exhibited a similar incidence and onset of disease following immunization with MOG(35-55) peptide. Disease severity was only moderately reduced in G2A(-/-) mice. Similar numbers of MOG(35-55) specific T cells were generated in secondary lymphoid organs of MOG(35-55)-immunized G2A(+/+) and G2A(-/-) mice. Comparable numbers of T cells were detected in spinal cords of G2A(+/+) and G2A(-/-) mice. We conclude that the proposed anti-proliferative and chemotactic functions of G2A are not manifested in vivo and therefore therapeutic targeting of G2A is unlikely to be beneficial in the treatment of MS.

Asunto(s)

Proteínas de Ciclo Celular/fisiología , Encefalomielitis Autoinmune Experimental/genética , Encefalomielitis Autoinmune Experimental/inmunología , Receptores Acoplados a Proteínas G/fisiología , Animales , Linfocitos T CD4-Positivos/inmunología , Linfocitos T CD8-positivos/inmunología , Proteínas de Ciclo Celular/genética , Proliferación Celular/efectos de los fármacos , Encefalomielitis Autoinmune Experimental/inducido químicamente , Citometría de Flujo/métodos , Eliminación de Gen , Glicoproteínas/efectos adversos , Interferón gamma/metabolismo , Ganglios Linfáticos/efectos de los fármacos , Ganglios Linfáticos/inmunología , Ganglios Linfáticos/patología , Activación de Linfocitos/genética , Activación de Linfocitos/inmunología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Glicoproteína Mielina-Oligodendrócito , Fragmentos de Péptidos/efectos adversos , Receptores Acoplados a Proteínas G/deficiencia , Receptores Acoplados a Proteínas G/genética , Bazo/citología , Bazo/inmunología , Bazo/patología , Linfocitos T/inmunología , Factores de Tiempo

RESUMEN

OBJECTIVE: Lysophosphatidylcholine is a major product of low-density lipoprotein (LDL) oxidation and secretory phospholipase A2-mediated lipid hydrolysis within atherosclerotic lesions. The G2A receptor mediates chemotaxis of cultured macrophages and T cells to lysophosphatidylcholine, supporting a pro-atherogenic role for this receptor in vivo. We investigated the ability of G2A to modulate atherosclerosis in mice. METHODS AND RESULTS: We measured atherosclerosis in G2A+/+ and G2A-/- LDL receptor knockout (LDLR-/-) mice. Consistent with a previous study, early lesion size at the aortic sinus was unaffected by G2A deficiency. However, G2A deficiency attenuated lesion progression at this site (42% to 44% reduction in average lesion area) and led to robust suppression of atherosclerosis throughout the aorta after short and extended periods of diet intervention (reduction in aortic lesion coverage: 62% to 73% at 9 weeks, 75% to 84% at 20 weeks). In G2A-/- LDLR-/- mice, intimal macrophage accumulation at lesion-prone sites of the aorta was significantly reduced in the absence of any detectable effect on T cell recruitment. Examination of lipoprotein profiles revealed elevated levels of circulating high-density lipoprotein (HDL) cholesterol in G2A-/- LDLR-/- mice compared with their G2A+/+ LDLR-/- counterparts after extended periods of diet intervention (54% increase in mean HDL cholesterol concentration). CONCLUSIONS: G2A provides a pro-atherogenic stimulus in vivo consistent with its chemotactic action but to which a pleiotropy of effects, including modulation of lipoprotein metabolism, may also contribute.

Asunto(s)

Aterosclerosis/metabolismo , Proteínas de Ciclo Celular/metabolismo , Lisofosfatidilcolinas/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Receptores de LDL/metabolismo , Animales , Aterosclerosis/genética , Aterosclerosis/patología , Proteínas de Ciclo Celular/genética , HDL-Colesterol/sangre , HDL-Colesterol/metabolismo , Progresión de la Enfermedad , Femenino , Regulación de la Expresión Génica/genética , Hipercolesterolemia/fisiopatología , Macrófagos/patología , Masculino , Ratones , Ratones Noqueados , Receptores Acoplados a Proteínas G/genética , Receptores de LDL/genética , Seno Aórtico/metabolismo , Seno Aórtico/patología , Túnica Íntima/patología

RESUMEN

Lysophosphatidylcholine (LPC) is considered a major proatherogenic component of oxidized low density lipoprotein based on its proinflammatory actions in vitro. LPC stimulates macrophage and T-cell chemotaxis via the G protein-coupled receptor G2A and may thus promote inflammatory cell infiltration during atherosclerotic lesion development. However, G2A also mediates proapoptotic effects of LPC and may therefore promote the death of inflammatory cells within developing lesions. To determine how these effects of LPC modify atherogenesis, we examined atherosclerotic lesion development in G2A-sufficient and G2A-deficient low density lipoprotein receptor knockout mice. Although LPC species capable of activating G2A-dependent responses were increased during lesion development, G2A-deficient mice developed lesions similar in size to those in their G2A-sufficient counterparts. Loss of G2A during atherosclerotic lesion development did not reduce macrophage and T-cell infiltration but instead resulted in increased lesional macrophage content associated with reduced numbers of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeled cells and decreased collagen deposition. These data indicate that the ability of LPC to stimulate macrophage and T-cell chemotaxis via G2A is not manifested in vivo and that G2A-mediated proapoptotic rather than chemotactic action is most penetrant during atherogenesis and may modify the stability of atherosclerotic lesions by promoting macrophage death.

Asunto(s)

Arteriosclerosis/fisiopatología , Proteínas de Ciclo Celular/fisiología , Lisofosfatidilcolinas/metabolismo , Macrófagos/fisiología , Receptores Acoplados a Proteínas G/fisiología , Receptores de LDL/deficiencia , Animales , Arteriosclerosis/patología , Femenino , Etiquetado Corte-Fin in Situ , Lípidos/sangre , Recuento de Linfocitos , Ratones , Ratones Noqueados , Receptores Acoplados a Proteínas G/biosíntesis , Linfocitos T/fisiología

RESUMEN

Despite the recognized effects of lysophosphatidylcholine upon cells of the immune system and its association with inflammatory processes, its mechanism of action has remained poorly characterized. Our recent identification of the first lysophosphatidylcholine receptor as an immunoregulatory G protein-coupled receptor named G2A whose genetic ablation results in the development of inflammatory autoimmune disease has, therefore, provided a new perspective on the role of this lysophospholipid as a modulator of immune responses. This commentary discusses the biological properties of lysophosphatidylcholine as an immunoregulatory ligand for cells of the innate and adaptive arms of the immune system. Although we focus primarily on ligand interactions with G2A, we also discuss the issue of possible functional redundancy with other receptors with recently established ligand specificities towards phosphorylcholine-containing lysolipids including lysophosphatidylcholine.

Asunto(s)

Adyuvantes Inmunológicos/farmacología , Autoinmunidad/efectos de los fármacos , Lisofosfatidilcolinas/farmacología , Receptores Acoplados a Proteínas G , Linfocitos T/efectos de los fármacos , Adyuvantes Inmunológicos/efectos adversos , Arteriosclerosis/etiología , Proteínas de Ciclo Celular/efectos de los fármacos , Proteínas de Ciclo Celular/metabolismo , Sistemas de Liberación de Medicamentos , Humanos , Inmunidad/efectos de los fármacos , Ligandos , Lisofosfatidilcolinas/efectos adversos , Linfocitos T/inmunología

RESUMEN

G2A is a lymphocyte-expressed G protein-coupled receptor whose genetic ablation results in the development of autoimmunity. Using HSV-TK reporter gene directed positron emission tomography (PET), we demonstrate that prior to any indication of the onset of illness, mice transplanted with BCR-ABL transduced G2A-deficient bone marrow harbor expanded populations of leukemic cells compared to recipients of wild-type bone marrow. The target cell type and anatomical locations of leukemia development are indistinguishable in animals transplanted with G2A+/+ or G2A-/- cells. Shorter disease latency in the G2A-deficient background is associated with an increased rate of cellular expansion. PET can be successfully applied to the temporal and spatial analysis of Bcr-Abl driven leukemic progression and should have utility for the study of other leukemias and lymphomas.

Asunto(s)

Proteínas de Ciclo Celular/metabolismo , Proteínas de Fusión bcr-abl/fisiología , Leucemia Experimental/diagnóstico por imagen , Linfoma/diagnóstico por imagen , Proteínas Oncogénicas/genética , Receptores Acoplados a Proteínas G , Animales , Médula Ósea/patología , Proteínas de Ciclo Celular/genética , Transformación Celular Neoplásica , Cartilla de ADN/química , Herpesvirus Humano 1 , Humanos , Leucemia Experimental/genética , Leucemia Experimental/metabolismo , Linfoma/metabolismo , Ratones , Ratones Endogámicos BALB C , Ratones Noqueados , ARN/metabolismo , Retroviridae/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Sensibilidad y Especificidad , Simplexvirus/enzimología , Simplexvirus/genética , Timidina Quinasa/genética , Timidina Quinasa/metabolismo , Tomografía Computarizada de Emisión