Role of Bone Marrow–Derived CC-Chemokine Receptor 5 in the Development of Atherosclerosis of Low-Density Lipoprotein Receptor Knockout Mice

Abstract

Objective-CC chemokine receptor CCR5 is expressed by atheroma-associated cells and could mediate leukocyte attraction into developing lesions. We examined the role of bone marrow-derived CCR5 in the development of atherosclerotic lesions after 8, 12, or 35 weeks of high-fat diet. Methods and Results-Low-density lipoprotein-receptor (LDLr)-deficient mice were lethally irradiated and transplanted with CCR5 ϩ/ϩ or CCR5 Ϫ/Ϫ bone marrow. After 8 weeks of fat diet, CCR5 deficiency in leukocytes led to 30% decrease of macrophage accumulation within the fatty streak (PϽ0.05), with no change in lesion size. After 12 weeks of fat diet, CCR5 deficiency also resulted in 30% decrease of plaque-macrophage accumulation (PϽ0.005), associated with 16% reduction in lesion size in the aortic sinus (Pϭ0.13), despite a significant increase in total cholesterol levels (Pϭ0.03). Lesions with CCR5 deficiency showed 52% reduction in matrix metalloproteinase (MMP)-9 expression (Pϭ0.02) and 2-fold increase in collagen accumulation (PϽ0.0001). These changes were associated with a significant increase of interleukin (IL)-10 mRNA expression in spleens of CCR5 Ϫ/Ϫ mice compared with CCR5 ϩ/ϩ controls. In addition, we found enhanced IL-10 production by CCR5-deficient peritoneal macrophages and decreased tumor necrosis factor (TNF)-␣ production by CCR5 Ϫ/Ϫ T cells in comparison with CCR5 ϩ/ϩ controls. CCR5 Ϫ/Ϫ and CCR5 ϩ/ϩ reconstituted animals showed no differences in plaque size or composition after 35 weeks of high-fat diet despite the persistent absence of CCR5 in plaques of mice reconstituted with CCR5 Ϫ/Ϫ bone marrow. Key Words: atherosclerosis Ⅲ chemokines Ⅲ cytokines Ⅲ inflammation A therosclerosis is a chronic inflammatory disease of the arterial wall, characterized by the accumulation of leukocytes, especially macrophages and T cells. [1][2][3][4] These cells first interact with the endothelial layer and then migrate to the subendothelial space where monocytes become lipidloaded macrophages and interact with T cells and vascular cells. These mechanisms rely on the expression of adhesion and chemotactic molecules that are produced within the vascular wall and facilitate cell migration while amplifying local immune responses. [5][6][7] The importance of chemokines in atherosclerosis was demonstrated by gene disruption experiments. As a result, various chemokines and chemokine receptors have already been reported to be expressed in atherosclerotic arteries and to play key roles in the development of atherosclerosis. 8 -14 The chemokine receptor CCR5 is expressed on cells that contribute to disease progression (macrophages, T cells, and smooth muscle cells), and has several ligands (RANTES, MIP-1␣, MIP-1␤) detected in plaques. [15][16][17][18][19] In vitro studies revealed the role of CCR5 in mediating leukocyte attraction, 20 a step critical to atherosclerosis initiation, and the ability of its ligands to induce tissue factor 17 or MMP expression, 21 which contribute to plaque complications and thrombotic processes. Moreover, genetic sc...

Ccr5 But Not Ccr1 Deficiency Reduces Development of Diet-Induced Atherosclerosis in Mice

“…18,20,22 Considering that most T helper lymphocytes present within atherosclerotic lesions are of the Th1 subpopulation and can secrete proinflammatory cytokines, 2 we hypothesized that Ccr5 deletion would reverse the proinflammatory dysbalance by shifting the content of immune and particular T cell subtypes within atherosclerotic plaques. Indeed, mice bearing the deficiency in Ccr5 displayed reduced aortic content of total T helper lymphocytes, as shown by expression of respective markers.…”

“…36 Deletion of Ccr5 reduced the secretion of proinflammatory IFN-␥ by immune cells and enhanced expression of antiinflammatory IL-10, thus counteracting the Th1/Th2 disequilibrium of atherosclerotic inflammation. Given that SMCs constitute a major source for IL-10 in the lesions, and that Ccr5 deletion in bone marrow cells had little effect on plaque area, 18 it is conceivable that Ccr5 deficiency in nonhematopoietic cells, namely in Ccr5 ϩ SMCs, 37 recruited to the lesions accounts for a main part of the antiinflammatory protection.…”

“…17 In contrast, recent data revealed that reconstitution of Ldlr Ϫ/Ϫ mice with Ccr5 Ϫ/Ϫ bone marrow improved atherosclerotic plaque quality with little effects on lesion size. 18 In the same model, deficiency in bone marrow Ccr1 did not protect but enhanced atherosclerosis progression in Ldlr Ϫ/Ϫ mice. 19 Similarly, deletion of Ccr5 but not Ccr1 led to a reduction in neointima formation after arterial wire-injury in ApoE Ϫ/Ϫ mice.…”

Monocyte subsets differentially employ CCR2, CCR5, and CX3CR1 to accumulate within atherosclerotic plaques

“…Atherosclerotic lesions are markedly diminished in apoE -/-mice that cannot express the chemokine CCL2 (1) or its receptor C-C motif chemokine receptor 2 (CCR2) (2). CCR1, CCR5, and C-X-C motif chemokine receptor 2 (CXCR2) are other chemokine receptors proposed to affect monocyte recruitment in mouse models of atherosclerosis (3)(4)(5)(6)(7). Still another chemokine receptor, CX3CR1, has been linked to atherosclerosis in both mouse models and human studies.…”

Systemic chemokine levels, coronary heart disease, and ischemic stroke events

“…34,35 It is worth noting that RANTES/CCR5 signaling and IP-10 are known promoters of T-cell recruitment and activation. 37,38 In addition, RANTES/ CCR5 restrains IL-10 production 37 while IP-10 inhibits regulatory T-cell recruitment, 38 2 pathways recently shown to play critical roles in the control of the inflammatory response to brain injury and in brain protection after an ischemic insult. 34,35 All these putative mechanisms arise from experimental models in which chemokine levels were elevated at the time or after brain injury.…”