ABSTRACT
Leukocytosis is associated with increased cardiovascular disease risk in humans and develops in hypercholesterolemic atherosclerotic animal models. Leukocytosis is associated with the proliferation of hematopoietic stem and multipotential progenitor cells (HSPCs) in mice with deficiencies of the cholesterol efflux-promoting ABC transporters ABCA1 and ABCG1 in BM cells. Here, we have determined the role of endogenous apolipoprotein-mediated cholesterol efflux pathways in these processes. In Apoeâ»/â» mice fed a chow or Western- type diet, monocytosis and neutrophilia developed in association with the proliferation and expansion of HSPCs in the BM. In contrast, Apoa1â»/â» mice showed no monocytosis compared with controls. ApoE was found on the surface of HSPCs, in a proteoglycan-bound pool, where it acted in an ABCA1- and ABCG1-dependent fashion to decrease cell proliferation. Accordingly, competitive BM transplantation experiments showed that ApoE acted cell autonomously to control HSPC proliferation, monocytosis, neutrophilia, and monocyte accumulation in atherosclerotic lesions. Infusion of reconstituted HDL and LXR activator treatment each reduced HSPC proliferation and monocytosis in Apoeâ»/â» mice. These studies suggest a specific role for proteoglycanbound ApoE at the surface of HSPCs to promote cholesterol efflux via ABCA1/ABCG1 and decrease cell proliferation, monocytosis, and atherosclerosis. Although endogenous apoA-I was ineffective, pharmacologic approaches to increasing cholesterol efflux suppressed stem cell proliferative responses.
Subject(s)
Apolipoproteins E/physiology , Atherosclerosis/pathology , Atherosclerosis/physiopathology , Hematopoietic Stem Cells/pathology , Hematopoietic Stem Cells/physiology , Monocytes/pathology , ATP Binding Cassette Transporter 1 , ATP Binding Cassette Transporter, Subfamily G, Member 1 , ATP-Binding Cassette Transporters/metabolism , Animals , Apolipoprotein A-I/deficiency , Apolipoprotein A-I/genetics , Apolipoprotein A-I/physiology , Apolipoproteins E/deficiency , Apolipoproteins E/genetics , Cell Proliferation , Cholesterol/metabolism , Disease Models, Animal , Humans , Leukocytosis/pathology , Leukocytosis/physiopathology , Lipoproteins/metabolism , Mice , Mice, Inbred C57BL , Mice, Knockout , Models, Cardiovascular , Proteoglycans/metabolism , Receptors, LDL/deficiency , Receptors, LDL/genetics , Receptors, LDL/physiologyABSTRACT
OBJECTIVE: Common genetic variants in a 58-kb region of chromosome 9p21, near the CDKN2A/CDKN2B tumor suppressor locus, are strongly associated with coronary artery disease. However, the underlying mechanism of action remains unknown. METHODS AND RESULTS: We previously reported a congenic mouse model harboring an atherosclerosis susceptibility locus and the region of homology with the human 9p21 locus. Microarray and transcript-specific expression analyses showed markedly decreased Cdkn2a expression, including both p16(INK4a) and p19(ARF), but not Cdkn2b (p15(INK4b)), in macrophages derived from congenic mice compared with controls. Atherosclerosis studies in subcongenic strains revealed genetic complexity and narrowed 1 locus to a small interval including Cdkn2a/b. Bone marrow (BM) transplantation studies implicated myeloid lineage cells as the culprit cell type, rather than resident vascular cells. To directly test the role of BM-derived Cdkn2a transcripts in atherogenesis and inflammatory cell proliferation, we performed a transplantation study using Cdkn2a(-/-) cells in the Ldlr(-/-) mouse model. Cdkn2a-deficient BM recipients exhibited accelerated atherosclerosis, increased Ly6C proinflammatory monocytes, and increased monocyte/macrophage proliferation compared with controls. CONCLUSION: These data provide a plausible mechanism for accelerated atherogenesis in susceptible congenic mice, involving decreased expression of Cdkn2a and increased proliferation of monocyte/macrophages, with possible relevance to the 9p21 human locus.
Subject(s)
Atherosclerosis/metabolism , Atherosclerosis/pathology , Cell Proliferation , Cyclin-Dependent Kinase Inhibitor p16/metabolism , Macrophages/pathology , Monocytes/pathology , Animals , Atherosclerosis/genetics , Bone Marrow Transplantation , Cyclin-Dependent Kinase Inhibitor p16/genetics , Disease Models, Animal , Genes, p16 , Genetic Predisposition to Disease/genetics , Macrophages/metabolism , Mice , Mice, Congenic , Mice, Knockout , Monocytes/metabolism , Receptors, LDL/deficiency , Receptors, LDL/geneticsABSTRACT
OBJECTIVE: Susceptibility to atherosclerosis is genetically complex, and modifier genes that do not operate via traditional risk factors are largely unknown. A mouse genetics approach can simplify the genetic analysis and provide tools for mechanistic studies. METHODS AND RESULTS: We previously identified atherosclerosis susceptibility QTL (Athsq1) on chromosome 4 acting independently of systemic risk factors. We now report confirmation of this locus in congenic strains carrying the MOLF-derived susceptibility allele in the C57BL/6J-Ldlr(-/-) genetic background. Homozygous congenic mice exhibited up to 4.5-fold greater lesion area compared to noncongenic littermates (P<0.0001). Analysis of extracellular matrix composition revealed prominent accumulation of versican, a presumed proatherogenic matrix component abundant in human lesions but almost absent in the widely-used C57BL/6 murine atherosclerosis model. The results of a bone marrow transplantation experiment suggested that both accelerated lesion development and versican accumulation are mediated, at least in part, by macrophages. Interestingly, comparative mapping revealed that the Athsq1 congenic interval contains the mouse region homologous to a widely-replicated CHD locus on human chromosome 9p21. CONCLUSIONS: These studies confirm the proatherogenic activity of a novel gene(s) in the MOLF-derived Athsq1 locus and provide in vivo evidence for a causative role of versican in lesion development.
