RESUMO
OBJECTIVE: To generate Abcg1(-/-) Apoe(-/-) mice to understand the mechanism and cell types involved in changes in atherosclerosis after loss of ABCG1. METHODS AND RESULTS: ABCG1 is highly expressed in macrophages and endothelial cells, 2 cell types that play important roles in the development of atherosclerosis. Abcg1(-/-) Apoe(-/-) and Apoe(-/-) mice and recipient Apoe(-/-) mice that had undergone transplantation with bone marrow from Apoe(-/-) or Abcg1(-/-) Apoe(-/-) mice were fed a Western diet for 12 or 16 weeks before quantification of atherosclerotic lesions. These studies demonstrated that loss of ABCG1 from all tissues, or from only hematopoietic cells, was associated with significantly smaller lesions that contained increased numbers of TUNEL- and cleaved caspase 3-positive apoptotic Abcg1(-/-) macrophages. We also identified specific oxysterols that accumulate in the brains and macrophages of the Abcg1(-/-) Apoe(-/-) mice. These oxysterols promoted apoptosis and altered the expression of proapoptotic genes when added to macrophages in vitro. CONCLUSIONS: Loss of ABCG1 from all tissues or from only hematopoietic cells results in smaller atherosclerotic lesions populated with increased apoptotic macrophages, by processes independent of ApoE. Specific oxysterols identified in tissues of Abcg1(-/-) Apoe(-/-) mice may be critical because they induce macrophage apoptosis and the expression of proapoptotic genes.
Assuntos
Apolipoproteínas E/deficiência , Apoptose , Aterosclerose/prevenção & controle , Colesterol/metabolismo , Lipoproteínas/deficiência , Macrófagos/metabolismo , Membro 1 da Subfamília G de Transportadores de Cassetes de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/genética , Animais , Apolipoproteínas E/genética , Apoptose/genética , Aterosclerose/genética , Aterosclerose/metabolismo , Aterosclerose/patologia , Proteína Agonista de Morte Celular de Domínio Interatuante com BH3/genética , Transplante de Medula Óssea , Encéfalo/metabolismo , Encéfalo/patologia , Caspase 3/metabolismo , Células Cultivadas , Modelos Animais de Doenças , Genótipo , Marcação In Situ das Extremidades Cortadas , Lipoproteínas/genética , Lipoproteínas LDL/metabolismo , Macrófagos/patologia , Camundongos , Camundongos Knockout , Oxirredução , Fenótipo , Proteínas Proto-Oncogênicas c-bcl-2/genética , RNA Mensageiro/metabolismo , Fatores de TempoRESUMO
ABCG1 and ABCG4 are highly homologous members of the ATP binding cassette (ABC) transporter family that regulate cellular cholesterol homeostasis. In adult mice, ABCG1 is known to be expressed in numerous cell types and tissues, whereas ABCG4 expression is limited to the central nervous system (CNS). Here, we show significant differences in expression of these two transporters during development. Examination of beta-galactosidase-stained tissue sections from Abcg1(-/-)LacZ and Abcg4(-/-)LacZ knockin mice shows that ABCG4 is highly but transiently expressed both in hematopoietic cells and in enterocytes during development. In contrast, ABCG1 is expressed in macrophages and in endothelial cells of both embryonic and adult liver. We also show that ABCG1 and ABCG4 are both expressed as early as E12.5 in the embryonic eye and developing CNS. Loss of both ABCG1 and ABCG4 results in accumulation in the retina and/or brain of oxysterols, in altered expression of liver X receptor and sterol-regulatory element binding protein-2 target genes, and in a stress response gene. Finally, behavioral tests show that Abcg4(-/-) mice have a general deficit in associative fear memory. Together, these data indicate that loss of ABCG1 and/or ABCG4 from the CNS results in changes in metabolic pathways and in behavior.
Assuntos
Transportadores de Cassetes de Ligação de ATP/biossíntese , Envelhecimento/metabolismo , Sistema Nervoso Central/metabolismo , Embrião de Mamíferos/metabolismo , Lipoproteínas/biossíntese , Retina/metabolismo , Subfamília G de Transportadores de Cassetes de Ligação de ATP , Membro 1 da Subfamília G de Transportadores de Cassetes de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/genética , Envelhecimento/genética , Animais , Comportamento Animal , Encéfalo/embriologia , Encéfalo/metabolismo , Sistema Nervoso Central/citologia , Sistema Nervoso Central/embriologia , Condicionamento Clássico , Medo , Regulação da Expressão Gênica no Desenvolvimento , Lipoproteínas/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Microscopia Eletrônica de Transmissão , Retina/embriologia , Retina/ultraestrutura , beta-Galactosidase/genéticaRESUMO
Every cell is separated from its external environment by a lipid membrane. Survival depends on the regulated and selective transport of nutrients, waste products and regulatory molecules across these membranes, a process that is often mediated by integral membrane proteins. The largest and most diverse of these membrane transport systems is the ATP binding cassette (ABC) family of membrane transport proteins. The ABC family is a large evolutionary conserved family of transmembrane proteins (>250 members) present in all phyla, from bacteria to Homo sapiens, which require energy in the form of ATP hydrolysis to transport substrates against concentration gradients. In prokaryotes the majority of ABC transporters are involved in the transport of nutrients and other macromolecules into the cell. In eukaryotes, with the exception of the cystic fibrosis transmembrane conductance regulator (CFTR/ABCC7), ABC transporters mobilize substrates from the cytoplasm out of the cell or into specific intracellular organelles. This review focuses on the members of the ABCG subfamily of transporters, which are conserved through evolution in multiple taxa. As discussed below, these proteins participate in multiple cellular homeostatic processes, and functional mutations in some of them have clinical relevance in humans.