Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediated gene delivery

A major role for VCAM-1, but not ICAM-1, in early atherosclerosis

VCAM-1 and ICAM-1 are endothelial adhesion molecules of the Ig gene superfamily that may participate in atherogenesis by promoting monocyte accumulation in the arterial intima. Both are expressed in regions predisposed to atherosclerosis and at the periphery of established lesions, while ICAM-1 is also expressed more broadly. To evaluate functions of VCAM-1 in chronic disease, we disrupted its fourth Ig domain, producing the murine Vcam1(D4D) allele. VCAM-1(D4D) mRNA and protein were reduced to 2-8% of wild-type allele (Vcam1(+)) levels but were sufficient to partially rescue the lethal phenotype of VCAM-1-null embryos. After crossing into the LDL receptor-null background, Vcam1(+/+) and Vcam1(D4D/D4D) paired littermates were generated from heterozygous intercrosses and fed a cholesterol-enriched diet for 8 weeks. The area of early atherosclerotic lesions in the aorta, quantified by en face oil red O staining, was reduced significantly in Vcam1(D4D/D4D) mice, although cholesterol levels, lipoprotein profiles, and numbers of circulating leukocytes were comparable to wild-type. In contrast, deficiency of ICAM-1 either alone or in combination with VCAM-1 deficiency did not alter nascent lesion formation. Therefore, although expression of both VCAM-1 and ICAM-1 is upregulated in atherosclerotic lesions, our data indicate that VCAM-1 plays a dominant role in the initiation of atherosclerosis.

Cholesterol signaling at the endoplasmic reticulum occurs in npc1(-/-) but not in npc1(-/-), LDLR(-/-) mice

It remains controversial whether deficiency of the Niemann-Pick C1 (npc1) protein results in altered cholesterol signaling at the endoplasmic reticulum (ER). In this report, we have measured the processed, nuclear form of sterol regulatory element binding protein (SREBP)-1 in livers of npc1 wild-type, heterozygous, and homozygous deficient mice, alone, and in combination with deficiencies of the low density lipoprotein receptor (LDLR) or the multiple drug resistant (mdr)1a, P-glycoprotein. Cleavage of SREBPs to activated forms normally occurs when the ER is deficient in cholesterol. A large decrease in processed SREBP-1 was evident in fasted npc1(-/-) mice and npc1(-/-), mdr1a(-/-) mice, with no decrease evident in npc1(-/-), LDLR(-/-) mice. These results suggest that the increase in cellular cholesterol which occurs in npc1(-/-) and in npc1(-/-), mdr1a(-/-) mice includes the sites responsible for cholesterol signaling, while the similar increase in cholesterol found in npc1(-/-), LDLR(-/-) mice does not.

Roles of acyl-coenzyme A:cholesterol acyltransferase-1 and -2

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme that produces cholesteryl esters in various tissues. In mammals, two ACAT genes (ACAT1 and ACAT2) have been identified. Together, these two enzymes are involved in storing cholesteryl esters as lipid droplets, in macrophage foam-cell formation, in absorbing dietary cholesterol, and in supplying cholesteryl esters as part of the core lipid for lipoprotein synthesis and assembly. The key difference in tissue distribution of ACAT1 and ACAT2 between humans, mice and monkeys is that, in adult human liver (including hepatocytes and bile duct cells), the major enzyme is ACAT1, rather than ACAT2. There is compelling evidence implicating a role for ACAT1 in macrophage foam-cell formation, and for ACAT2 in intestinal cholesterol absorption. However, further studies at the biochemical and cell biological levels are needed in order to clarify the functional roles of ACAT1 and ACAT2 in the VLDL or chylomicron synthesis/assembly process.

Growth hormone reduces plasma cholesterol in LDL receptor-deficient mice

Growth hormone (GH) has pleiotropic effects on cholesterol and lipoprotein metabolism. Pituitary GH is important for the normal regulation of hepatic LDL receptors (LDLR), for the enzymatic activity of bile acid regulatory cholesterol 7alpha-hydroxylase (C7alphaOH), and for the maintenance of resistance to dietary cholesterol. The present study aimed to determine whether GH has beneficial effects on plasma lipids and hepatic cholesterol metabolism in mice devoid of LDLR. Compared with wild-type controls, LDLR-deficient mice had approximately 250% elevated plasma total cholesterol and approximately 50% increased hepatic cholesterol levels; hepatic HMG CoA reductase activity was reduced by 70%, whereas C7alphaOH activity was increased by 40%. In LDLR mice, GH infusion reduced plasma cholesterol and triglycerides up to 40%, whereas HMG CoA reductase and C7alphaOH activities were stimulated by approximately 50% and 110% respectively. GH also stimulated HMG CoA reductase and C7alphaOH activities in control mice, whereas hepatic LDLR and plasma lipoproteins were unchanged. The effects of cholestyramine and atorvastatin on C7alphaOH in LDLR-deficient mice were potentiated by GH, and this was associated with a further reduction in plasma cholesterol. GH treatment reduces plasma cholesterol and triglycerides and stimulates C7alphaOH activity in mice devoid of LDLR, particularly in combination with resin or statin treatment. The potential of GH therapy in patients with homozygous familial hypercholesterolemia should be evaluated.

Clinical significance of preheparin serum lipoprotein lipase mass in coronary vasospasm

The present study investigated the clinical significance of preheparin serum lipoprotein lipase (LPL) mass in coronary vasospasm by examining its relationship with the acetylcholine-induced coronary artery response in patients without angiographically demonstrable atherosclerotic coronary artery disease (CAD). The subjects were 39 men who had suspected CAD and who underwent coronary angiography. Coronary vasospasm was defined as a marked luminal narrowing or total occlusion provoked by the intracoronary administration of acetylcholine. Preheparin LPL mass was lower (p<0.05) in 25 subjects in whom vasospasm was induced by the acetylcholine provocation test than in the 14 subjects with a negative response. As regards preheparin LPL mass, the subjects with multiple vessel spasm had significantly low concentrations (p<0.05) compared with single vessel spasm, although serum lipid levels were not significantly different. Multiple regression analysis revealed only preheparin LPL mass had a significant absolute t-value (2.016) among the coronary risk factors. Low preheparin LPL mass is interpreted as reflecting an impaired acetylcholine-induced coronary relaxation in coronary vasospasm and preheparin LPL mass may be useful as a marker of early stage coronary atherosclerosis that is not detectable by angiography.

A novel cellular phenotype for familial hypercholesterolemia due to a defect in polarized targeting of LDL receptor

Basolateral targeting of membrane proteins in polarized epithelial cells typically requires cytoplasmic domain sorting signals. In the familial hypercholesterolemia (FH)-Turku LDL receptor allele, a mutation of glycine 823 residue affects the signal required for basolateral targeting in MDCK cells. We show that the mutant receptor is mistargeted to the apical surface in both MDCK and hepatic epithelial cells, resulting in reduced endocytosis of LDL from the basolateral/sinusoidal surface. Consequently, virally encoded mutant receptor fails to mediate cholesterol clearance in LDL receptor-deficient mice, suggesting that a defect in polarized LDL receptor expression in hepatocytes underlies the hypercholesterolemia in patients harboring this allele. This evidence directly links the pathogenesis of a human disease to defects in basolateral targeting signals, providing a genetic confirmation of these signals in maintaining epithelial cell polarity.

Analysis of glomerulosclerosis and atherosclerosis in lecithin cholesterol acyltransferase-deficient mice

To evaluate the biochemical and molecular mechanisms leading to glomerulosclerosis and the variable development of atherosclerosis in patients with familial lecithin cholesterol acyl transferase (LCAT) deficiency, we generated LCAT knockout (KO) mice and cross-bred them with apolipoprotein (apo) E KO, low density lipoprotein receptor (LDLr) KO, and cholesteryl ester transfer protein transgenic mice. LCAT-KO mice had normochromic normocytic anemia with increased reticulocyte and target cell counts as well as decreased red blood cell osmotic fragility. A subset of LCAT-KO mice accumulated lipoprotein X and developed proteinuria and glomerulosclerosis characterized by mesangial cell proliferation, sclerosis, lipid accumulation, and deposition of electron dense material throughout the glomeruli. LCAT deficiency reduced the plasma high density lipoprotein (HDL) cholesterol (-70 to -94%) and non-HDL cholesterol (-48 to -85%) levels in control, apoE-KO, LDLr-KO, and cholesteryl ester transfer protein-Tg mice. Transcriptome and Western blot analysis demonstrated up-regulation of hepatic LDLr and apoE expression in LCAT-KO mice. Despite decreased HDL, aortic atherosclerosis was significantly reduced (-35% to -99%) in all mouse models with LCAT deficiency. Our studies indicate (i) that the plasma levels of apoB containing lipoproteins rather than HDL may determine the atherogenic risk of patients with hypoalphalipoproteinemia due to LCAT deficiency and (ii) a potential etiological role for lipoproteins X in the development of glomerulosclerosis in LCAT deficiency. The availability of LCAT-KO mice characterized by lipid, hematologic, and renal abnormalities similar to familial LCAT deficiency patients will permit future evaluation of LCAT gene transfer as a possible treatment for glomerulosclerosis in LCAT-deficient states.

Heme oxygenase-1 inhibits atherosclerotic lesion formation in ldl-receptor knockout mice

Heme oxygenase-1 (HO-1) is induced by a variety of conditions associated with oxidative stress. We demonstrated that mildly oxidized LDL markedly induces HO-1 in human aortic endothelial and smooth muscle cell cocultures and that its induction results in the attenuation of monocyte chemotaxis resulting from treatment with mildly oxidized LDL in vitro. To elucidate the role of HO-1 in the development of atherosclerotic lesions in vivo, we modulated HO-1 expression in LDL-receptor knockout mice fed high-fat diets. During 6-week high-fat diet trials, intraperitoneal injections of hemin (H group) or hemin and desferrioxamine (HD group) to induce HO-1, Sn-protoporphyrin IX to inhibit HO-1 (Sn group), and saline as control (C group) were performed. Both the H and HD groups showed significantly less mean atherosclerotic lesions in the proximal aorta compared with the C group, whereas the Sn group showed larger lesion compared with the C group. Modulation of HO expression and HO activities were confirmed by Northern blot analysis and HO activity assay. Immunohistochemical studies revealed significant HO-1 expression in atherosclerotic lesions, where oxidized phospholipids also localized. Major cell types expressing HO-1 were macrophages and foam cells in the lesions. HO modulations affected plasma lipid hydroperoxide (LPO) levels and nitrite/nitrate levels. These results suggest that HO-1, induced under hyperlipidemia, functioned as an intrinsic protective factor against atherosclerotic lesion formation, possibly by inhibiting lipid peroxidation and influencing the nitric oxide pathway.

Long-term stable correction of low-density lipoprotein receptor-deficient mice with a helper-dependent adenoviral vector expressing the very low-density lipoprotein receptor

BACKGROUND

Familial hypercholesterolemia (FH) that results from LDL receptor (LDLR) deficiency affects approximately 1 in 500 persons in the heterozygous state and approximately 1 in 1 million persons in the homozygous state. We tested a novel gene therapy strategy for the treatment of FH in a mouse model.

METHODS AND RESULTS

We delivered the VLDL receptor (VLDLR) to the liver of LDLR-deficient mice and compared the effect of a helper-dependent adenoviral vector with all viral coding sequences deleted (HD-Ad-mVLDLR) with a first-generation vector (FG-Ad-mVLDLR), an HD-Ad (HD-Ad-0) that contained no expression cassette, and dialysis buffer (DB). A single intravenous injection of HD-Ad-mVLDLR led to a lowering of plasma cholesterol that lasted >/=6 months. Acute liver toxicity (as measured with liver enzyme elevation) occurred after FG-Ad-mVLDLR but not after HD-Ad-mVLDLR, HD-Ad-0, or DB treatment. At 6 months, VLDLR was detected in the liver with Western blotting and with immunofluorescence staining only in HD-Ad-mVLDLR-treated mice. Aortic atherosclerosis was almost completely prevented in these animals.

CONCLUSIONS

HD-Ad-mediated intravenous delivery of VLDLR to hepatocytes is well tolerated. It produces long-term lowering of plasma cholesterol and prevents atherosclerosis development in LDLR-deficient mice. These data provide support for the feasibility and safety of this approach for therapy of human subjects.

Hypercholesterolemia exacerbates virus-induced immunopathologic liver disease via suppression of antiviral cytotoxic T cell responses

The immune system has to be optimally balanced to be highly effective against infections with cytopathic microbial pathogens and must guarantee efficient destruction of cells infected with noncytopathic agents while leaving the integrity of noninfected cells largely unaltered. We describe here the effects of genetically induced hypercholesterolemia on cellular immunity in apolipoprotein E (ApoE(-/-)) and low density lipoprotein receptor-deficient (LDLR(-/-)) mice during infection with the hepatotropic lymphocytic choriomeningitis virus WE strain. In both ApoE(-/-) and LDLR(-/-) mice hypercholesterolemia aggravated virus-induced immunopathologic liver disease. ApoE(-/-) mice exhibited a higher susceptibility to virus-induced immunopathology than LDLR(-/-) mice and usually succumbed to immunopathologic disease when infected with high doses of virus. Initial virus spread was not influenced by the hypercholesterolemia, whereas clearance of the virus from spleen and nonlymphoid organs, including liver, was delayed. Activation of antiviral CTL, measured by ex vivo cytotoxicity and IFN-gamma production, and recruitment of specific CTL into blood and liver were impaired in hypercholesterolemic mice, indicating that hypercholesterolemia had a significant suppressive effect on cellular immunity. Taken together, these data provide evidence that hypercholesterolemia suppresses antiviral immune responses, thereby changing the host-virus balance, and can increase susceptibility to acute or chronic and potentially lethal virus-induced immunopathologic disease. These findings impinge on our understanding of hypercholesterolemia as a disease parameter and may explain aspects of the frequent association of persistent pathogens with hypercholesterolemia-induced diseases, such as atherosclerosis.

7-Ketocholesterol delivered to mice in chylomicron remnant-like particles is rapidly metabolised, excreted and does not accumulate in aorta

Cholesterol oxidation products (oxysterols) have been implicated in atherogenesis due to their presence in atherosclerotic tissue and their potent effects in vitro. One of the major oxysterols currently of interest is 7-ketocholesterol (7K) and it has been suggested that the diet is an important source of this oxysterol. This investigation tested the hypothesis that 7K, delivered in a physiologically relevant vehicle, chylomicron remnant-like emulsion (CMR), would be metabolised and excreted by mice in a similar manner and to a similar extent as previously observed in rats when delivered in a chemically modified lipoprotein, acetylated low-density lipoprotein (acLDL). Indeed, the metabolism of 14C-7K delivered in CMR mirrored that of acLDL and was much more rapid than (3)H-cholesterol delivered simultaneously. The 7K-derived (14)C was cleared from the liver, appeared in the intestine and was excreted in the faeces. A substantial proportion of the 7K-derived (14)C in the intestine and faeces was aqueous-soluble, indicating metabolism to polar products, presumably bile acids. Moreover, while cholesterol-derived (3)H increased in the aorta, (14)C appeared transiently and there was no observable accumulation within 24 h. The data confirm our previous findings of rapid hepatic metabolism of 7K when delivered in acLDL and demonstrate that 7K delivered in a vehicle of dietary significance is similarly metabolised and excreted. Indeed, the data encourage further investigation into the contribution that dietary oxysterols may or may not make to atherogenesis.

Sequencing of the coding exons of the LRP1 and LDLR genes on individual DNA samples reveals novel mutations in both genes

Five coding polymorphisms in de LRP1 gene, i.e. A217V, A775P, D2080N, D2632E and G4379S were discovered by sequencing its 89 exons in three test-groups of 22 healthy individuals, 29 Alzheimer patients and 18 individuals with different clinical and molecularly uncharacterized lipid metabolism problems. No genetic defect was evident in the LRP1 gene of any of the Alzheimer's disease (AD) patients, further excluding LRP1 as a major genetic problem in AD. Lipoprotein receptor related protein (LRP) A217V (exon 6) was clearly present in all groups as a polymorphism, while D2632E was observed only once in a healthy volunteer. On the other hand, LRP1 alleles A775P, D2080N, and G4379 were encountered only in patients with FH or with undefined problems of lipid metabolism. This finding forced one to also analyze the LDL receptor (LDLR) gene, for which a method was devised to sequence the entire region comprising LDLR exons 2-18. The resulting sequence contig of 33567 nucleotides yielded finally an exact physical map that corrects published and listed LDLR gene maps in many positions. In addition, next to known mutations in LDLR that cause FH, four novel LDLR defects were defined, i.e. del e7-10, exon 9 mutation N407T, a 20 bp insertion in exon 4, and a double mutation C292W/K290R in exon 6. No evidence for pathology connected to the LRP1 'mutations' was obtained by subsequent screening for the five LRP1 variants in larger groups of 110 FH patients and 118 patients with molecularly undefined, clinical problems of cholesterol and/or lipid metabolism. In three individuals with a mutant LDLR gene a variant LRP1 allele was also present, but without direct, obvious clinical compound effects, indicating that the variant LRP1 alleles must, for the present, be considered polymorphisms.

Doubling expression of the low density lipoprotein receptor by truncation of the 3'-untranslated region sequence ameliorates type iii hyperlipoproteinemia in mice expressing the human apoe2 isoform

The primary receptor mediating clearance of apolipoprotein (apo)E- and apoB100-containing lipoproteins from the circulation is the low density lipoprotein (LDL) receptor. Reduced expression of the LDLR is believed to be a precipitating factor in the pathogenesis of type III hyperlipoproteinemia (HLP) in some humans homozygous for the apoE2 allele (APOE*2). To test the effect of genetic changes in LDL receptor expression on the pathogenesis of type III HLP, we have generated a variant allele at the endogenous mouse Ldlr locus that expresses the human LDL receptor transcript. Transcription of the human LDLR minigene is regulated by the endogenous mouse promoter sequence, but a truncation of 3'-untranslated region results in increased mRNA stability. Consequently, in liver of heterozygotes, steady state levels of mouse and human LDLR transcripts are 50 and 180% the levels of total transcript in wild type mice, respectively. Overall, the 2.3-fold normal level of LDLR message in heterozygotes completely ameliorates type III HLP caused by the homozygosity for the human APOE*2 allele, normalizing their plasma lipoprotein profile. We conclude that a modest increase in expression of the LDLR through message stabilization is sufficient to prevent precipitation of type III HLP in mice.

Acute exposure to a high cholesterol diet attenuates myocardial ischemia-reperfusion injury in cholesteryl ester transfer protein mice

BACKGROUND

Previous experiments have demonstrated that acute exposure to a high-cholesterol diet (HCD) increases the severity of myocardial infarction in animals. Recent results suggest that the process is modulated by multiple genes and their interactions with circulating cholesterol.

DESIGN

In the present study cholesteryl-ester-transfer-protein (CETP) transgenic mice were generated and fed a normal rodent-chow diet, HCD for 1 week, or a HCD for 6 weeks in order to define the role of CETP in myocardial infarction after acute exposure to a HCD.

METHODS

Cholesterol levels in mice of all groups were measured. Separate groups of mice were exposed to 30 min of in-vivo occlusion of coronary artery and 2 h of reperfusion. We assessed the sizes of the ischemic zone and infarct using Evans blue and 2,3,5-triphenyltetrazolium chloride.

RESULTS

The extent of infarction (percentage infarct/area at risk) was significantly less (P < 0.05) after 1 week of a HCD (18.7 +/- 7.0%) than those for the normal diet group (51.4 +/- 5.5%) and the group fed a HCD for 6 weeks (44.4 +/- 5.2%). Additionally, there was significantly less infiltration of neutrophils into the ischemic-reperfused mouse hearts for mice fed a HCD for 1 week. Levels of reduced and oxidized glutathione in the hearts of CETP mice were measured for separate groups of animals. The reduced:oxidized-glutathione ratio was significantly (P < 0.01) lower for mice fed a HCD for 1 week (1.5 +/- 0.1) than it was for mice fed a normal diet (3.6 +/- 0.3) and a HCD for 6 weeks (3.3 +/- 0.2).

CONCLUSIONS

These data suggest that activity of CETP in hypercholesterolemic mice has an acute effect on size of infarct after 1 week of a HCD. This suggests that CETP induces tolerance of ischemia in the mice fed a HCD via mild oxidative stress.

Increased atherosclerosis in LDL receptor-null mice lacking ACAT1 in macrophages

During atherogenesis, circulating macrophages migrate into the subendothelial space, internalize cholesterol-rich lipoproteins, and become foam cells by progressively accumulating cholesterol esters. The inhibition of macrophage acyl coenzyme A:cholesterol acyltransferase (ACAT), which catalyzes the formation of cholesterol esters, has been proposed as a strategy to reduce foam cell formation and to treat atherosclerosis. We show here, however, that hypercholesterolemic LDL receptor-deficient (LDLR(-/-)) mice reconstituted with ACAT1-deficient macrophages unexpectedly develop larger atherosclerotic lesions than control LDLR(-/-) mice. The ACAT1-deficient lesions have reduced macrophage immunostaining and more free cholesterol than control lesions. Our findings suggest that selective inhibition of ACAT1 in lesion macrophages in the setting of hyperlipidemia can lead to the accumulation of free cholesterol in the artery wall, and that this promotes, rather than inhibits, lesion development.

The LDL receptor is the major pathway for beta-VLDL uptake by mouse peritoneal macrophages

In order to determine the contribution of the low density lipoprotein receptor (LDL-R) to the removal of apoB-containing native lipoproteins by macrophages, we compared the uptake of beta-VLDL in peritoneal macrophages (MPM) from wild type mice and mice lacking the LDL-R. The d<1.006 g/ml lipoproteins obtained from apoE deficient mice fed a high fat diet were poorly degraded by macrophages and caused only a slight formation of CE in macrophages from both types of mice. On the other hand, d<1.006 g/ml lipoproteins obtained from LDL-R deficient mice fed a high fat diet, beta-VLDL with apoE, were avidly taken up by and markedly stimulated CE formation in wild type macrophages, but not in macrophages lacking the LDL-R. The degradation of 125I-labeled-apoE-containing beta-VLDL by wild type MPM was poorly inhibited by unlabeled human LDL, and beta-VLDL without apoE had no effects. In conclusion, we propose that the in vitro uptake of native apoE-enriched lipoproteins by murine macrophages is primarily mediated by the LDL receptor and not by other apoE-recognizing receptor systems such as: the LDL receptor related protein, the VLDL receptor or the triglyceride-rich lipoprotein receptor.

Remodeling of the vessel wall after copper-induced injury is highly attenuated in mice with a total deficiency of plasminogen activator inhibitor-1

Clinical studies have indicated that high plasma levels of fibrinogen, or decreased fibrinolytic potential, are conducive to an increased risk of cardiovascular disease. Other investigations have shown that insoluble fibrin promotes atherosclerotic lesion formation by affecting smooth muscle cell proliferation, collagen deposition, and cholesterol accumulation. To directly assess the physiological impact of an imbalanced fibrinolytic system on both early and late stages of this disease, mice deficient for plasminogen activator inhibitor-1 (PAI-1(-/-)) were used in a model of vascular injury/repair, and the resulting phenotype compared to that of wild-type (WT) mice. A copper-induced arterial injury was found to generate a lesion with characteristics similar to many of the clinical features of atherosclerosis. Fibrin deposition in the injured arterial wall at early (7 days) and late (21 days) times after copper cuff placement was prevalent in WT mice, but was greatly diminished in PAI-1(-/-) mice. A multilayered neointima with enhanced collagen deposition was evident at day 21 in WT mice. In contrast, only diffuse fibrin was identified in the adventitial compartments of arteries from PAI-1(-/-) mice, with no evidence of a neointima. Neovascularization was observed in the adventitia and was more extensive in WT arteries, relative to PAI-1(-/-) arteries. Additionally, enhanced PAI-1 expression and fat deposition were seen only in the arterial walls of WT mice. The results of this study emphasize the involvement of the fibrinolytic system in vascular repair processes after injury and indicate that alterations in the fibrinolytic balance in the vessel wall have a profound effect on the development and progression of vascular lesion formation.

Reduction of atherosclerosis despite hypercholesterolemia in lyn-deficient mice fed a high-fat diet

Oxidation and other modifications of serum low-density lipoprotein (LDL) are associated with the development of atherosclerosis, and a scavenger receptor and CD40 signalling are also known to play important roles in the process. We previously showed that the Src family protein-tyrosine kinase Lyn is physically and/or functionally associated with macrophage type-I and type-II class-A scavenger receptors (MSR-A) and CD40. In this study, we addressed whether Lyn is involved in the build-up of serum lipid levels and in atherosclerotic changes. When fed a normal diet, lyn-deficient mice had serum lipid levels that were no different from those of wild-type mice. By contrast, lyn-deficient mice fed a high-fat diet showed serum lipid levels that were much higher than those seen in wild-type mice. Curiously, however, the lyn-deficient mice fed either diet showed no increase in incidence of atherosclerotic lesions compared with wild-type mice. This may be partly explained by our data showing suppression of proliferation of peritoneal macrophages in response to oxidized LDL in the absence of Lyn, and failure of stimulation of the CD40 pathway in lyn-deficient macrophages to induce expression of monocytic chemoattractant protein-1 (MCP-1), which is related to atherosclerosis. These results suggest that Lyn plays an important role in the metabolism of serum lipids and in the development of atherosclerotic lesions on high-fat diets.

Essential role for the (hepatic) LDL receptor in macrophage apolipoprotein E-induced reduction in serum cholesterol levels and atherosclerosis

Apolipoprotein E (apoE) is a high affinity ligand for several receptor systems in the liver, including the low-density lipoprotein (LDL) receptor, and non-LDL receptor sites, like the LDL receptor-related protein (LRP), the putative remnant receptor and/or proteoglycans. Although the liver is the major source of apoE synthesis, apoE is also produced by a wide variety of other cell types, including macrophages. In the present study, the role of the LDL receptor in the removal of lipoprotein remnants, enriched with macrophage-derived apoE from the circulation, was determined using the technique of bone marrow transplantation (BMT). Reconstitution of macrophage apoE production in apoE-deficient mice resulted in a serum apoE concentration of only 2% of the concentration in wild-type C57Bl/6 mice. This low level of apoE nevertheless reduced VLDL and LDL cholesterol 12-fold (P<0.001) and fourfold (P<0.001), respectively, thereby reducing serum cholesterol levels and the susceptibility to atherosclerosis. In contrast, reconstitution of macrophage apoE synthesis in mice lacking both apoE and the LDL receptor induced only a twofold (P<0.001) reduction in VLDL cholesterol and had no significant effect on atherosclerotic lesion development, although serum apoE levels were 93% of the concentration in normal C57Bl/6 mice. In conclusion, a functional (hepatic) LDL receptor is essential for the efficient removal of macrophage apoE-enriched lipoprotein remnants from the circulation and thus for normalization of serum cholesterol levels and protection against atherosclerotic lesion development in apoE-deficient mice.

Defining the atherogenicity of large and small lipoproteins containing apolipoprotein B100

Apo-E-deficient apo-B100-only mice (APOE:(-/-)APOB:(100/100)) and LDL receptor-deficient apo-B100-only mice (LDLR:(-/-)APOB:(100/100)) have similar total plasma cholesterol levels, but nearly all of the plasma cholesterol in the former animals is packaged in VLDL particles, whereas, in the latter, plasma cholesterol is found in smaller LDL particles. We compared the apo-B100-containing lipoprotein populations in these mice to determine their relation to susceptibility to atherosclerosis. The median size of the apo-B100-containing lipoprotein particles in APOE:(-/-)APOB:(100/100) plasma was 53.4 nm versus only 22.1 nm in LDLR:(-/-)APOB:(100/100) plasma. The plasma levels of apo-B100 were three- to fourfold higher in LDLR:(-/-)APOB:(100/100) mice than in APOE:(-/-)APOB:(100/100) mice. After 40 weeks on a chow diet, the LDLR:(-/-)APOB:(100/100) mice had more extensive atherosclerotic lesions than APOE:(-/-)APOB:(100/100) mice. The aortic DNA synthesis rate and the aortic free and esterified cholesterol contents were also higher in the LDLR:(-/-)APOB:(100/100) mice. These findings challenge the notion that all non-HDL lipoproteins are equally atherogenic and suggest that at a given cholesterol level, large numbers of small apo-B100-containing lipoproteins are more atherogenic than lower numbers of large apo-B100-containing lipoproteins.

Preheparin serum lipoprotein lipase mass is negatively related to coronary atherosclerosis

In preheparin serum, there exists lipoprotein lipase (LPL) mass with little activity. The clinical significance of this preheparin serum LPL mass (preheparin LPL mass) is unclear. We studied the levels of preheparin LPL mass in patients with coronary atherosclerosis, comparing the results with those in healthy men. We also evaluated the correlation between preheparin LPL mass and the severity of coronary atherosclerosis by comparing with other risk factors such as age, smoking, family history, hypertension, hyperuricemia, diabetes mellitus, total cholesterol, triglyceride, high density lipoprotein-cholesterol and body mass index. The subjects, 70 men presenting with symptoms of coronary artery disease, underwent coronary angiographic examination. Significant narrowness was defined as > or = 75%. Control group comprised 77 men who had annual health checks and showed no abnormal findings. Preheparin LPL mass in the stenosis group was lower than normal coronary group and also than the control group. Multivariate analysis showed that preheparin LPL mass had the highest t-value (-2.53) for the number of lesions among the risk factors listed above. These results suggest that low preheparin LPL mass may be deeply involved in the progression of coronary atherosclerosis.

ICAM-1 deficiency reduces atherosclerotic lesions in double-knockout mice (ApoE(-/-)/ICAM-1(-/-)) fed a fat or a chow diet

Intercellular adhesion molecule (ICAM)-1, a major adhesion molecule, plays a critical role in the homing of leukocytes to sites of atherosclerotic lesions. However, very little is known on the role of ICAM-1 in initiating and perpetuating vascular lesions in ApoE(-/-) mice fed a chow or a fat diet. This study has investigated the mean aortic lesions in mice (C57BL6 background) with a single-knockout (ApoE(-/-)) or double-knockout (DKO; ApoE(-/-), ICAM-1(-/-)) fed a chow or a fat diet over a period of 3, 6, 15, and 20 weeks. A 3-fold reduction in lesion size was observed at all time points in DKO mice fed a chow diet. However, in DKO mice fed a fat diet, a marked reduction in the aortic lesion was observed at 3 and 15 weeks, which did not reach a significant level at 6 and 20 weeks. This study shows in essence that DKO mice are protected from developing significant lesions for up to 6 weeks when fed a chow diet and from 3 to 6 weeks when fed a fat diet. After 6 weeks, the lesion size of the DKO mice follows that of the single-knockout mice when fed a chow diet and gets to the same level in mice fed a fat diet. Plasma cholesterol levels were not altered as a result of ICAM-1 deficiency. These studies show that ICAM-1 is implicated in the formation and progression of atherosclerotic lesions.

Cholesterol is sequestered in the brains of mice with Niemann-Pick type C disease but turnover is increased

In Niemann-Pick Type C (NPC) disease, the concentration of cholesterol increases with age in every tissue except the brain. This study investigates whether accumulation of cholesterol might also occur within the cells of the central nervous system (CNS), but be obscured by the simultaneous loss of sterol from myelin as neurodegeneration proceeds. At birth, when there is little myelin in the CNS, the concentration of cholesterol is significantly elevated in every region of the brain in the homozygous NPC mouse. At 7 wk of age, myelination is nearly complete. In the NPC mouse, however, there is striking neurodegeneration and a reduction in both myelin protein and myelin cholesterol. Furthermore, net loss of cholesterol from the CNS is much higher in the NPC mouse than in the control animal (2.23 versus 1.37 mg/day per kg) so that the concentration of sterol in most regions of the brain is reduced. This neurodegeneration and loss of myelin cholesterol is not prevented by deletion of either the low-density lipoprotein receptor or apolipoprotein E in the NPC animal. Thus, the cholesterol sequestration seen in every organ in NPC disease also occurs in cells of the CNS and may be etiologically related to the neurodegeneration.

Hepatic microvascular responses to ischemia-reperfusion in low-density lipoprotein receptor knockout mice

The overall objective of this study was to determine whether genetically induced hypercholesterolemia alters the inflammatory and microvascular responses of mouse liver to ischemia-reperfusion (I/R). The accumulation of rhodamine 6G-labeled leukocytes and the number of nonperfused sinusoids (NPS) were monitored (by intravital microscopy) in the liver of wild-type (WT) and low-density lipoprotein receptor-deficient (LDLr(-/-)) mice for 1 h after a 30-min period of normothermic ischemia. Plasma alanine transaminase (ALT) levels were used to monitor hepatocellular injury. Microvascular leukostasis as well as increases in NPS and plasma ALT were observed at 60 min after hepatic I/R in both WT and in LDLr(-/-) mice; however, these responses were greatly exaggerated in LDLr(-/-) mice. Pretreatment of LDLr(-/-) mice with gadolinium chloride, which reduces Kupffer cell function, attenuated the hepatic leukostasis, NPS, and hepatocellular injury elicited by I/R. Similar protection against I/R was observed in LDLr(-/-) mice pretreated with antibodies directed against tumor necrosis factor-alpha, intercellular adhesion molecule-1 (ICAM-1), or P-selectin. These findings indicate that chronic hypercholesterolemia predisposes the hepatic microvasculature to the deleterious effects of I/R. Kupffer cell activation and the leukocyte adhesion receptors ICAM-1 and P-selectin appear to contribute to the exaggerated inflammatory responses observed in the postischemic liver of LDLr(-/-) mice.

RNA editing: cytidine to uridine conversion in apolipoprotein B mRNA

RNA editing is a post-transcriptional process that changes the informational capacity within the RNA. These processes include alterations made by nucleotide deletion, insertion and base conversion. A to I and C to U conversion occurs in mammals and these editing events are catalysed by RNA binding deaminases. C to U editing of apoB mRNA was the first mammalian editing event to be identified. The minimal protein complex necessary for apoB mRNA editing has been determined and consists of APOBEC-1 and ACF. Overexpression of APOBEC-1 in transgenic animals caused liver dysplasia and APOBEC-1 has been identified in neurofibromatosis type 1 tumours, suggesting that RNA editing may be another mechanism for tumourigenesis. Several APOBEC-1-like proteins have been identified, including a family of APOBEC-1-related proteins with unknown function on chromosome 22. This review summarises the different types of RNA editing and discusses the current status of C to U apoB mRNA editing. This knowledge is very important in understanding the structure and function of these related proteins and their role in biology.

Genetic modifiers of atherosclerosis in mice

Atherosclerosis is a complex, multifactorial disease with both genetic and environmental determinants. Experimental investigation of the effects of these determinants on the development and progression of atherosclerosis has been greatly facilitated by the use of targeted mouse models of the disease, particularly those resulting from the absence of functional genes for apolipoprotein E or the low density lipoprotein receptor (LDLR). This review focuses on the influence on atherosclerosis of combining apoE or LDLR deficiencies with factors affecting atherogenesis, including (1) inflammatory processes, (2) glucose metabolism, (3) blood pressure, and (4) coagulation and fibrinolysis. We also discuss the general problem of using the mouse to test the effects on atherogenesis of human polymorphic variations and future ways of enhancing the usefulness of these mouse models.

Adoptive transfer of beta(2)-glycoprotein I-reactive lymphocytes enhances early atherosclerosis in LDL receptor-deficient mice

BACKGROUND

It has been proposed that autoimmune factors can influence the progression of atherosclerosis. We have previously shown that immunization of LDL receptor-deficient (LDL-RD mice) with beta(2)-glycoprotein I (beta2GPI; a principal target of "autoimmune" antiphospholipid antibodies) enhances early atherosclerosis. In the present study, we tested the hypothesis that adoptive transfer of beta2GPI-reactive T cells can accelerate fatty streak formation in LDL-RD mice.

METHODS AND RESULTS

LDL-RD mice were immunized with human beta2GPI. An additional group of mice were immunized with beta2GPI and boosted with the same antigen 3 weeks later. Control mice with immunized with human serum albumin. Lymphocytes obtained from the draining lymph node cells or from splenocytes of beta2GPI- or human serum albumin-immunized mice were stimulated in vitro with beta2GPI or with the mitogen concavalin A, respectively. The cultured lymphocytes were transferred intraperitoneally to syngenic LDL-RD mice, and the mice were fed a high-fat "Western" diet for 5 weeks until death. Mice injected with lymphocytes from draining lymph nodes or spleens of beta2GPI-immunized animals displayed larger fatty streaks than those induced by control treated animals. T-cell-depleted splenocytes from beta2GPI were unable to promote lesion formation in the mice.

CONCLUSIONS

The present study provides the first direct evidence for a role of antigen (beta2GPI)-reactive T cells in the promotion of fatty streaks in mice.

Apolipoprotein E receptors: linking brain development and Alzheimer's disease

Alzheimer's disease is a debilitating neurodegenerative disorder that afflicts an increasing part of our ageing population. An isoform of apolipoprotein E, a protein that mediates the transport of lipids and cholesterol in the circulatory system, predisposes carriers of this allele to the common late-onset form of the disease. How this protein is related to a neurodegenerative disorder is an enigma. Mounting evidence indicates that apolipoprotein E receptors, which are abundantly expressed in most neurons in the central nervous system, also fulfill critical functions during brain development and may profoundly influence the pathogenesis of Alzheimer's disease.

Assessment of efficiency and safety of adenovirus mediated gene transfer into normal and damaged murine livers

BACKGROUND

When recombinant adenoviruses are infused directly into the circulation, transgene expression is almost completely restricted to the liver.

AIMS

Efficiency and safety of adenovirus mediated gene transfer into damaged livers were examined in mice with liver cirrhosis or fulminant hepatitis.

METHODS

Liver cirrhosis and fulminant hepatitis were induced by intraperitoneal administration of thioacetamide and D-galactosamine followed by lipopolysaccharide, respectively. Mice were infused with adenoviruses carrying the Escherichia coli beta-galactosidase gene, lacZ gene, into the tail vein. Transduction efficiency of the lacZ gene was estimated histochemically by X-gal staining and quantitatively using a chemiluminescent assay. Activation of adenovirus specific T cells and development of neutralising antibodies against adenovirus were also examined.

RESULTS

Histochemical evaluation revealed that approximately 40%, 80%, and 40% of cells in normal, cirrhotic, and fulminant hepatitis livers, respectively, were stained blue using X-gal staining. Quantitative analyses revealed that levels of lacZ expression in cirrhotic livers were approximately 2.5-fold and sixfold greater than those in normal and fulminant hepatitis livers, respectively. Although transgene expression in fulminant hepatitis livers was significantly lower than that in normal livers, marked levels of transgene expression were achieved even in fulminant hepatitis livers. Significant adverse effects of adenoviruses were not observed in damaged livers. There were no significant differences in cellular or humoral immune responses to adenoviruses among animals with normal, cirrhotic, and fulminant hepatitis livers.

CONCLUSIONS

Our results suggest that gene therapy with adenoviruses may be used efficiently and safely, even in patients with severe liver disease.

In vivo adenovirus-mediated suicide gene therapy of orthotopic bladder cancer

These studies were undertaken to determine the feasibility, safety, and efficacy of suicide gene therapy using adenoviral-mediated herpes simplex virus thymidine kinase (ADV/RSV-tk) and the prodrug ganciclovir (GCV) in an orthotopic murine bladder cancer model. We utilized a replication-defective adenoviral construct containing the beta-galactosidase gene as a control and the herpes simplex virus thymidine kinase gene as the therapeutic vector under the transcription control of the Rous sarcoma virus long terminal repeat promoter. Intravesically created, orthotopic bladder tumors were established in syngeneic C3H/He female mice. India ink injection and beta-galactosidase studies were performed to determine if transurethral administration, direct tumor injection, or the combination was the most efficient route of virus administration. Optimal dosing of ADV/RSV-tk was determined by direct tumor injection with increasing viral doses and treatment with GCV. Treatment efficacy, long-term survival, and toxicity were determined in separate but similar controlled experiments. Growth curve studies demonstrated reliable tumor formation by 14 days. Direct transvesical tumor injection resulted in the best distribution and intratumor gene expression as measured by X-gal staining. Dose-ranging experiments demonstrated an optimal viral dose of 5 x 10(8) plaque-forming units and a greater than twofold reduction in tumor growth for the animals treated with ADV/RSV-tk compared to controls. Efficacy studies demonstrated a greater than threefold reduction in tumor growth. No clinical or gross pathologic toxicity was detected. Long-term survival results suggested a survival benefit for the treatment animals compared to controls. We conclude that ADV/RSV-tk in combination with GCV provides effective therapy for orthotopic murine bladder cancer by significantly inhibiting tumor growth with limited toxicity to the host. These data provide further support for testing this suicide gene therapy strategy in human Phase I trials.

Prolonged correction of hyperlipidemia in mice with familial hypercholesterolemia using an adeno-associated viral vector expressing very-low-density lipoprotein receptor

Adeno-associated viral vectors were used to deliver the gene for very-low-density lipoprotein (VLDL) receptor (VLDLR) to liver of a murine model of familial hypercholesterolemia (FH). Infusion of adeno-associated virus-VLDLR into the portal circulation of FH mice resulted in a 40% reduction in serum cholesterol and triglyceride that was stable for the duration of the study (30 weeks). Fractionation of serum lipids revealed a reduction of both VLDL and low-density lipoprotein. Expression of transgene-derived VLDLR was confirmed in livers of recipient animals by Western blot analysis and immunohistochemistry; vector DNA was present at 1 copy/cell. Vector-treated animals had significantly less lipid accumulation in liver and reduced atherosclerosis in the aorta.

Overexpression of 15-lipoxygenase in vascular endothelium accelerates early atherosclerosis in LDL receptor-deficient mice

To study the possible role of the human lipid-oxidizing enzyme 15-lipoxygenase (15-LO) in atherosclerosis, we overexpressed it specifically in the vascular wall of C57B6/SJL mice by using the murine preproendothelin-1 promoter. The mice overexpressing 15-LO were crossbred with low density lipoprotein (LDL) receptor-deficient mice to investigate atherogenesis. High levels of 15-LO were expressed in the atherosclerotic lesion in the double-transgenic mice as assessed by immunohistochemistry. The double-transgenic, 15-LO-overexpressing, LDL receptor-deficient mice (LDLR-/-/15LO) developed significantly larger atherosclerotic lesions at the aortic sinus compared with lesions in the LDL receptor-deficient (LDLR-/-) mice after 3 and 6 weeks (107,000 versus 28,000 microm(2) [P:<0.001] and 121,000 versus 87,000 microm(2) [P:<0.05], respectively) of an atherogenic diet. LDL from the LDLR-/-/15LO mice was more susceptible to oxidation than was the LDL from the control LDLR-/- mice, as shown by a shorter lag period for copper-induced conjugated diene formation. On the other hand, no differences were found in the levels of serum anti-oxidized LDL antibodies between the study groups. There were also no differences with respect to the density of macrophages and T lymphocytes infiltrating the lesions in both experimental groups. Taken together, these results support the hypothesis that 15-LO overexpression in the vessel wall is associated with enhanced atherogenesis.

Macrophage lipoprotein lipase promotes foam cell formation and atherosclerosis in low density lipoprotein receptor-deficient mice

The role of macrophage lipoprotein lipase (LPL) expression in atherosclerotic lesion formation was examined in low density lipoprotein receptor (LDLR(-/-)) mice using dietary conditions designed to induce either fatty streak lesions or complex atherosclerotic lesions. First, LDLR(-/-) mice chimeric for macrophage LPL expression were created by transplantation of lethally irradiated female LDLR(-/-) mice with LPL(-/-) (n = 12) or LPL(+/+) (n = 14) fetal liver cells as a source of hematopoietic cells. To induce fatty streak lesions, these mice were fed a Western diet for 8 weeks, resulting in severe hypercholesterolemia. There were no differences in plasma post-heparin LPL activity, serum lipid levels, or lipoprotein distribution between these two groups. The mean lesion area in the proximal aorta in LPL(-/-) --> LDLR(-/-) mice was significantly reduced by 33% compared with LPL(+/+) --> LDLR(-/-) mice, and a similar reduction (38%) in lesion area was found by en face analysis of the aortae. To induce complex atherosclerotic lesions, female LDLR(-/-) mice were lethally irradiated, transplanted with LPL(-/-) (n = 14), LPL(+/-) (n = 13), or LPL(+/+) (n = 14) fetal liver cells, and fed the Western diet for 19 weeks. Serum cholesterol and triglyceride levels did not differ between the three groups. After 19 weeks of diet, the lesions in the proximal aorta were complex with relatively few macrophages expressing LPL protein and mRNA in LPL(+/+) --> LDLR(-/-) mice. Analysis of cross-sections of the proximal aorta demonstrated no differences in the extent of lesion area between the groups, whereas en face analysis of the aortae revealed a dose-dependent effect of macrophage LPL on mean aortic lesion area in LPL(-/-) --> LDLR(-/-), LPL(-/+) --> LDLR(-/-), and LPL(+/+) --> LDLR(-/-) mice (1.8 +/- 0. 2%, 3.5 +/- 0.5% and 5.9 +/- 0.8%, respectively). Taken together, these data indicate that macrophage LPL expression in the artery wall promotes atherogenesis during foam cell lesion formation, but this impact may be limited to macrophage-rich lesions.

Low density lipoprotein receptor of macrophages facilitates atherosclerotic lesion formation in C57Bl/6 mice

Macrophage-derived foam cells play an important role in the initiation and progression of atherosclerosis. To examine the role of the macrophage low density lipoprotein receptor (LDLr) in atherosclerotic lesion formation, bone marrow from LDLr knockout [LDLr(-/-)] mice was transplanted into irradiated wild-type C57Bl/6 [LDLr(+/+)] mice. After 3 months on an atherogenic diet, C57Bl/6 mice, reconstituted with LDLr(-/-) bone marrow, showed a mean lesion area of 34.7 x 10(3)+/-22.4 x 10(3) microm(2) compared with 100. 8 x 10(3)+/-33.0 x 10(3) microm(2) (P<0.001) in control C57Bl/6 mice that were transplanted with LDLr(+/+) bone marrow. There were no significant differences in total serum cholesterol, triglyceride levels, and lipoprotein profiles between the 2 groups. Histochemical analysis of macrophage LDLr expression in the atherosclerotic lesions indicated that C57Bl/6 mice, reconstituted with LDLr(+/+) bone marrow, showed extensive staining of the foam cells in the atherosclerotic lesions, whereas mice reconstituted with LDLr(-/-) bone marrow showed only a few LDLr-positive foam cells. In vitro, peritoneal macrophages isolated from wild-type C57Bl/6 mice were, respectively, 4.7- and 10.7-fold more effective in cell association and degradation of atherogenic (125)I-beta-very low density lipoprotein than were LDLr(-/-) peritoneal macrophages, establishing that the LDLr on macrophages is important for the interaction of macrophages with beta-very low density lipoprotein. It is concluded that the LDLr on macrophages can facilitate the development of atherosclerosis, possibly by mediating the uptake of atherogenic lipoproteins.

Autoimmunity in atherosclerosis: lessons from experimental models

The modern view of atherosclerosis is of a chronic inflammatory disorder. In accord with this paradigm, the process of uninhibited influx of fat to the vessel wall results from an 'adequate' response to various forms of injury (i.e. turbulence, infections, modified lipoproteins). This idea has been further extended by several groups, to assume that the atherosclerotic lesion can be the target of an autoimmune mediated attack. According to this hypothesis, the site of initiation of the plaque should bear/express the target autoantigen, whereas concomitantly a respective immune response is generated in the periphery. The examples illuminating this notion are beta2GPI as a target autoantigen, HSP60/65 an oxidized-LDL. Herein we present evidence to support the involvement of autoimmune mechanisms in atherogenesis based on the experience from experimental models and human studies.

Charting the fate of the "good cholesterol": identification and characterization of the high-density lipoprotein receptor SR-BI

Risk for cardiovascular disease due to atherosclerosis increases with increasing concentrations of low-density lipoprotein (LDL) cholesterol and is inversely proportional to the levels of high-density lipoprotein (HDL) cholesterol. The receptor-mediated control of plasma LDL levels has been well understood for over two decades and has been a focus for the pharmacologic treatment of hypercholesterolemia. In contrast, the first identification and characterization of a receptor that mediates cellular metabolism of HDL was only recently reported. This receptor, called scavenger receptor class B type I (SR-BI), is a fatty acylated glycoprotein that can cluster in caveolae-like domains on the surfaces of cultured cells. SR-BI mediates selective lipid uptake from HDL to cells. The mechanism of selective lipid uptake is fundamentally different from that of classic receptor-mediated endocytic uptake via coated pits and vesicles (e.g. the LDL receptor pathway) in that it involves efficient receptor-mediated transfer of the lipids, but not the outer shell proteins, from HDL to cells. In mice, SR-BI plays a key role in determining the levels of plasma HDL cholesterol and in mediating the regulated, selective delivery of HDL-cholesterol to steroidogenic tissues and the liver. Significant alterations in SR-BI expression can result in cardiovascular and reproductive disorders. SR-BI may play a similar role in humans; thus, modulation of its activity may provide the basis of future approaches to the treatment and prevention of atherosclerotic disease.

Absence of ACAT-1 attenuates atherosclerosis but causes dry eye and cutaneous xanthomatosis in mice with congenital hyperlipidemia

Acyl-CoA:cholesterol acyltransferase (ACAT) catalyzes esterification of cellular cholesterol. To investigate the role of ACAT-1 in atherosclerosis, we have generated ACAT-1 null (ACAT-1-/-) mice. ACAT activities were present in the liver and intestine but were completely absent in adrenal, testes, ovaries, and peritoneal macrophages in our ACAT-1-/- mice. The ACAT-1-/- mice had decreased openings of the eyes because of atrophy of the meibomian glands, a modified form of sebaceous glands normally expressing high ACAT activities. This phenotype is similar to dry eye syndrome in humans. To determine the role of ACAT-1 in atherogenesis, we crossed the ACAT-1-/- mice with mice lacking apolipoprotein (apo) E or the low density lipoprotein receptor (LDLR), hyperlipidemic models susceptible to atherosclerosis. High fat feeding resulted in extensive cutaneous xanthomatosis with loss of hair in both ACAT-1-/-:apo E-/- and ACAT-1-/-:LDLR-/- mice. Free cholesterol content was significantly increased in their skin. Aortic fatty streak lesion size as well as cholesteryl ester content were moderately reduced in both double mutant mice compared with their respective controls. These results indicate that the local inhibition of ACAT activity in tissue macrophages is protective against cholesteryl ester accumulation but causes cutaneous xanthomatosis in mice that lack apo E or LDLR.