The Deficiency Of B Lymphocyte ABC-transporter A1 Effects On Atherosclerosis

Atherosclerosis,a process of progressive vascular thickening and hardening,is a chronic inflammatory disease caused by lipid accumulation in the large and medium sized arteries.The lesions contain lipids and lots of leukocytes（i.e.macrophages and lymphocytes）and vascular cells（i.e.smooth muscle cells）.ATP binding cassette transporter A1（ABCA1）is a membrance-associated protein that mediates the reverse cholesterol transport to prevent the formation of foam cells and modulate inflammation,thereby protects against atherosclerosis.Bone marrow transplant experiments were used to prove that bone marrow-derived ABCA1 is atheroprotective.As the main cells in atherosclerotic lesions,macrophages are believed to be the effector cells of bone marrow-derived ABCA1 for long time.However,macrophage-specific ABCA1deficiency did not affect the development of atherosclerosis.Recent studies found that B lymphocytes play an important role in atherosclerosis.Thus,we speculate that B lymphocyte ABCA1 may be atheroprotective..Aims:To determine the effects of B lymphocyte ABCA1 deficiency on atherosclerosis and find out the underlying mechanisms.Methods:The Cre/Loxp systerm was used to generate B lymphocyte–specific ABCA1 knockout（KO）mice(ABCA1^CD19-/CD19-).The deficiency of ABCA1 in B lymhocytes was validated by PCR,Q-PCR,and the cholesterol efflux experiments.ABCA1^CD19-/CD19-mice were backcrossed to LDLr KO background(ABCA1^CD19-/CD19-LDLr^-/-mice).High cholesterol/high fat Western-type diet（WTD）was used to induce the formation of atherosclerotic lesions.Histological and immunohistochemistry stainings were performed to detect the lesion size and components.Flow cytometry was employed to determine the proliferation,differentiation,and apoptosis of B lymphocytes.Enzyme-linked immunosorbent assay（ELISA）was used to determine the antibody production of B lymphocytes and the levels of anti-ox-LDL antibodies in WTD-fed mice.Results:The expression of ABCA1 in B lymphocytes of ABCA1^CD19-/CD19-mice is only 3.6%（p<0.001）of control B lymphocytes.The deficiency of ABCA1 almost completely block the cholesterol efflux from B lymphocytes to apoAI（90%,p<0.001）.Also the cholesterol efflux to HDL was inhibited 30%（p<0.01）.Compared with the control mice,ABCA1^CD19-/CD19-mice had similar levels of ABCA1 expression in non-B splenocytes.The cholesterol efflux capacity of peritoneal macrophages from both ABCA1^flox/flox and ABCA1^CD19-/CD19-mice was comparable.These data indicate that the deficiency of ABCA1 is indeed only induced in B lymphocytes.WTD were given to both ABCA1^CD19-/CD19-LDLr^-/-and ABCA1^flox/flox LDLr^-/-mice for 9 weeks to induce the formation of atherosclerotic lesions.Despite no effects on plasma total cholesterol levels,the B lymphocyte-specific ABCA1 deficiency stimulates the enlargement of spleen（1.2-fold,p<0.05）and atherosclerotic plaques（353.3±26.69 vs 286.6±14.34,p<0.05）.The relative percent of B lymphocytes and their subclasses in the circulation,peritoneal cavity,and spleen are similar bwteen ABCA1^flox/flox LDLr^-/-and ABCA1^CD19-/CD19-LDLr^-/-mice.Interestingly,the deficiency of ABCA1 promotes the proliferation（1.17-fold,p<0.05）and the IgG production（²-fold,p<0.05）of splenic B lymphocytes.In addition,the plasma levels of anti-ox-LDL IgG（2.01-fold,p<0.05）but not IgM were increased in ABCA1^CD19-/CD19-LDLr^-/-mice compared to ABCA1^flox/flox LDLr^-/-mice.Conclusion:B lymphocyte ABCA1 could prevent the development of atherosclerosis by suppressing the proliferation and antibody production of B lymphocytes.B lymphocyte ABCA1 may thus become a potential therapeutic target for cardiovascular diseases.