Macrophage p53 controls macrophage death in atherosclerotic lesions of apolipoprotein E deficient mice.

The cellular composition of atherosclerotic lesions is determined by many factors including cell infiltration, proliferation and cell death. Tumor suppressor gene p53 has been shown to regulate both cell proliferation and cell death in many cell types. In the present study, we investigated the role of macrophage p53 in the pathogenesis of early and advanced atherosclerosis. Using the Cre-loxP system we found that absence of macrophage p53 (p53(del)) strongly reduces apoptosis of macrophages both in early and advanced atherosclerotic lesions (-59% and -37%, respectively). Consequently, in advanced atherosclerosis, reduced apoptosis upon absence of macrophage p53, coincided with increased acellular necrotic core formation (+96%), increased macrophage content (+24%), and reduced cholesterol cleft accumulation (-41%). Proliferation was not affected by the absence of macrophage p53 in both early and advanced atherosclerosis. However, these significant changes in lesional cell death did not affect total lesion area in both early and advanced atherosclerosis, neither in the aortic root nor in the aortic arch and thoracic aorta in ApoE-deficient mice. Our data demonstrate that macrophage p53 is an important regulator of macrophage apoptosis, thereby preventing necrotic death of lesional macrophages. The regulation of this cell death balance directly affects lesion composition.

Dual PPARalpha/gamma agonist tesaglitazar reduces atherosclerosis in insulin-resistant and hypercholesterolemic ApoE*3Leiden mice.

OBJECTIVE: We investigated whether the dual PPARalpha/gamma agonist tesaglitazar has anti-atherogenic effects in ApoE*3Leiden mice with reduced insulin sensitivity. METHODS AND RESULTS: ApoE*3Leiden transgenic mice were fed a high-fat (HF) insulin-resistance-inducing diet. One group received a high-cholesterol (HC) supplement (1% wt/wt; HC group). A second group received the same HC supplement along with tesaglitazar (T) 0.5 micromol/kg diet (T group). A third (control) group received a low-cholesterol (LC) supplement (0.1% wt/wt; LC group). Tesaglitazar decreased plasma cholesterol by 20% compared with the HC group; cholesterol levels were similar in the T and LC groups. Compared with the HC group, tesaglitazar caused a 92% reduction in atherosclerosis, whereas a 56% reduction was seen in the cholesterol-matched LC group. Furthermore, tesaglitazar treatment significantly reduced lesion number beyond that expected from cholesterol lowering and induced a shift to less severe lesions. Concomitantly, tesaglitazar reduced macrophage-rich and collagen areas. In addition, tesaglitazar reduced inflammatory markers, including plasma SAA levels, the number of adhering monocytes, and nuclear factor kappaB-activity in the vessel wall. CONCLUSIONS: Tesaglitazar has anti-atherosclerotic effects in the mouse model that go beyond plasma cholesterol lowering, possibly caused by a combination of altered lipoprotein profiles and anti-inflammatory vascular effects.

Macrophage retinoblastoma deficiency leads to enhanced atherosclerosis development in ApoE-deficient mice.

The cellular composition of an atherosclerotic lesion is determined by cell infiltration, proliferation, and apoptosis. The tumor suppressor gene retinoblastoma (Rb) has been shown to regulate both cell proliferation and cell death in many cell types. To study the role of macrophage Rb in the development of atherosclerosis, we used apoE-deficient mice with a macrophage-restricted deletion of Rb (Rb(del) mice) and control littermates (Rb(fl) mice). After 12 wk feeding a cholesterol-rich diet, the Rb(del) mice showed a 51% increase in atherosclerotic lesion area with a 39% increase in the relative number of advanced lesions. Atherosclerotic lesions showed a 13% decrease in relative macrophage area and a 46% increase in relative smooth muscle cell area, reflecting the more advanced state of the lesions. The increase in atherosclerosis was independent of in vitro macrophage modified lipoprotein uptake or cytokine production. Whereas macrophage-restricted Rb deletion did not affect lesional macrophage apoptosis, a clear 2.6-fold increase in lesional macrophage proliferation was observed. These studies demonstrate that macrophage Rb is a suppressing factor in the progression of atherosclerosis by reducing macrophage proliferation.

Increased vulnerability of pre-existing atherosclerosis in ApoE-deficient mice following adenovirus-mediated Fas ligand gene transfer.

OBJECTIVE: The death receptor Fas and Fas ligand (FasL) are present in human advanced atherosclerotic plaques. The activation of the Fas/FasL pathway of apoptosis has been implicated in plaque vulnerability. In the present study, we investigated whether overexpression of FasL in pre-existing atherosclerotic lesions can induce lesion remodelling and rupture-related events. METHODS AND RESULTS: Carotid atherogenesis was initiated in apolipoprotein E-deficient mice by placement of a perivascular silastic collar. The resulting plaques were incubated transluminally with recombinant adenovirus carrying FasL (Ad-FasL, lateral) or control beta-galactosidase (Ad-LacZ, contralateral). Transfection was restricted to the smooth muscle cell-rich cap of the plaque, and FasL expression led to a three-fold increase in apoptosis in the cap one day after gene transfer. Three days after gene transfer, FasL expression led to a 38% reduction in the number of cap cells. Two weeks after Ad-FasL transfer, non-thrombotic rupture, intra-plaque haemorrhage, buried caps and iron deposits were observed in 6 out of 17 Ad-FasL-treated carotid arteries versus 0 out of 17 controls (P=0.009), indicative of enhanced plaque vulnerability. CONCLUSIONS: These data demonstrate that advanced murine plaques are sensitive to Fas/FasL-induced apoptosis, which may indicate that stimulation of this pathway could result in plaque remodelling towards a more vulnerable phenotype.

Tumor necrosis factor-alpha promotes atherosclerotic lesion progression in APOE*3-Leiden transgenic mice.

OBJECTIVE: Tumor necrosis factor-alpha (TNFalpha) is a pleiotropic cytokine exerting both inflammatory and cell death modulatory activity, and is thought to play a role in the pathogenesis of atherosclerosis. Studies in mice indicated that TNFalpha affects atherosclerosis minimally or not under conditions that allow fatty streak formation. Here, we examined the possible role of TNFalpha in advanced and complex atherosclerotic lesions. METHODS AND RESULTS: To induce atherosclerosis, TNFalpha-deficient (Tnf-/-) APOE*3-Leiden and control APOE*3-Leiden only mice were fed a cholesterol-rich diet. Comparable levels of plasma cholesterol and triglycerides and the systemic inflammatory parameters, serum amyloid A and soluble intercellular adhesion molecule-1 were found in APOE*3-LeidenTnf-/- and control mice. Although absence of TNFalpha did not affect the quantitative area of atherosclerosis, APOE*3-LeidenTnf-/- mice had a higher relative number of early lesions (46.1% vs. 21.4%) and a lower relative number of advanced lesions (53.9% vs. 78.6%, P=0.04). In addition, the advanced lesions in APOE*3-LeidenTnf-/- mice showed less necrosis (9.9+/-12.1% vs. 23.4+/-19.3% of total lesion area, P=0.04) and an increase in apoptosis (1.5+/-1.5% vs. 0.4+/-0.6% of total nuclei, P=0.03). CONCLUSIONS: Our data indicate that TNFalpha stimulates the formation of lesions towards an advanced phenotype, with more lesion necrosis and a lower incidence of apoptosis.