Atherosclerosis progression in LDL receptor-deficient and apolipoprotein E-deficient mice is independent of genetic alterations in plasminogen activator inhibitor-1

Impaired fibrinolysis has been linked to atherosclerosis in a number of experimental and clinical studies. Plasminogen activator inhibitor type 1 (PAI-1) is the primary inhibitor of plasminogen activation and has been proposed to promote atherosclerosis by facilitating fibrin deposition within developing lesions. We examined the contribution of PAI-1 to disease progression in 2 established mouse models of atherosclerosis. Mice lacking apolipoprotein E (apoE-/-) and mice lacking the low density lipoprotein receptor (LDLR-/-) were crossbred with transgenic mice overexpressing PAI-1 (resulting in PAI-1 Tg(+)/apoE-/- and PAI-1 Tg(+)/LDLR-/-, respectively) or were crossbred with mice completely deficient in PAI-1 gene expression (resulting in PAI-1-/-/apoE-/- and PAI-1-/-/LDLR-/-, respectively). All animals were placed on a western diet (21% fat and 0.15% cholesterol) at 4 weeks of age and analyzed for the extent of atherosclerosis after an additional 6, 15, or 30 weeks. Intimal and medial areas were determined by computer-assisted morphometric analysis of standardized microscopic sections from the base of the aorta. Atherosclerotic lesions were also characterized by histochemical analyses with the use of markers for smooth muscle cells, macrophages, and fibrin deposition. Typical atherosclerotic lesions were observed in all experimental animals, with greater severity at the later time points and generally more extensive lesions in apoE-/- than in comparable LDLR-/- mice. No significant differences in lesion size or histological appearance were observed among PAI-1-/-, PAI-1 Tg(+), or PAI-1 wild-type mice at any of the time points on either the apoE-/- or LDLR-/- genetic background. We conclude that genetic modification of PAI-1 expression does not significantly alter the progression of atherosclerosis in either of these well-established mouse models. These results suggest that fibrinolytic balance (as well as the potential contribution of PAI-1 to the regulation of cell migration) plays only a limited role in the pathogenesis of the simple atherosclerotic lesions observed in the mouse.     

Biglycan, a vascular proteoglycan, binds differently to HDL2 and HDL3: role of apoE

Lipoprotein retention by vascular extracellular matrix proteoglycans is important in atherogenesis. Proteoglycans bind apolipoprotein (apo)B- and apoE-containing lipoproteins. However, the colocalization of apoA-I and apoE with biglycan in atherosclerotic lesions suggests that vascular proteoglycans also may trap high density lipoproteins (HDLs). Because the major HDL subclasses may be atheroprotective to different degrees, we investigated the role of apoE in mediating HDL(2) and HDL(3) binding to the extracellular vascular proteoglycan, biglycan. ApoE-free HDL(2) and HDL(3) did not bind to purified [(35)S]SO(4)-biglycan, whereas apoE-containing HDL(2) and HDL(3) (HDL+E) did. The extent of binding correlated positively with the apoE content for both HDL(2) and HDL(3), although HDL(2)+E had a 3.5-fold higher affinity than did HDL(3)+E. ApoE on HDL(3) was cleaved into 22- and 12-kDa fragments, whereas apoE on HDL(2) remained intact. These results suggest that the cleaved apoE on HDL(3) results in diminished biglycan binding of HDL(3)+E relative to HDL(2)+E. Reducing positive charges on lysine and arginine residues on HDL+E eliminated biglycan binding, suggesting an ionic interaction. Thus, apoE is an important determinant of HDL binding to extracellular vascular proteoglycans and may play a role in HDL retention in the artery wall.     

Plasma insulin levels predict atherosclerotic lesion burden in obese hyperlipidemic mice

Despite a clear association between obesity, insulin resistance and atherosclerosis in humans, to date, no animal models have been described in which insulin resistance is associated with atherosclerotic lesion burden. Using two mouse models of obesity-induced hyperlipidemia:leptin deficient (ob/ob) mice on an apolipoprotein E deficient (apoE-/-) or low density lipoprotein receptor deficient (LDLR-/-) background, we sought to determine metabolic parameters most closely associated with atherosclerotic lesion burden. Total plasma cholesterol (TC) levels in ob/ob;apoE-/- mice and ob/ob;LDLR-/- mice were indistinguishable (682+/-48 versus 663+/-16, respectively). Analysis of lipoprotein profiles showed that cholesterol was carried primarily on VLDL in the ob/ob;apoE-/- mice and on LDL in the ob/ob;LDLR-/- mice. Plasma triglycerides (TG) were 55% lower (P<0.001), non-esterified fatty acids (NEFA) were 1.5-fold higher (P<0.01), and insulin levels were 1.7-fold higher (NS) in ob/ob;apoE-/- mice compared to ob/ob;LDLR-/- mice. Other parameters such as body weight, fat pad weight, and glucose levels were not different between the groups. Aortic sinus lesion area of ob/ob;apoE-/- mice was increased 3.2-fold above ob/ob;LDLR-/- mice (102,455+/-8565 microm2/section versus 31,750+/-4478 microm2/section, P<0.001). Lesions in ob/ob;apoE-/- mice were also more complex as evidenced by a 7.7-fold increase in collagen content (P<0.001). Atherosclerotic lesion area was positively correlated with body weight (P<0.005), NEFA (P=0.007), and insulin (P=0.002) levels in the ob/ob;LDLR-/- mice and with insulin (P=0.014) in the ob/ob;apoE-/- mice. In contrast, lesion burden was neither associated with TC and TG, nor with individual lipoprotein pools, in either animal model. These data provide a direct demonstration of the pathophysiologic relevance of hyperinsulinemia, NEFA, and increased body weight to atherosclerotic lesion formation.     

Deletion of the phosphoinositide 3-kinase p110gamma gene attenuates murine atherosclerosis

Inflammatory cell activation by chemokines requires intracellular signaling through phosphoinositide 3-kinase (PI3-kinase) and the PI3-kinase-dependent protein serine/threonine kinase Akt. Atherosclerosis is a chronic inflammatory process driven by oxidatively modified (atherogenic) lipoproteins, chemokines, and other agonists that activate PI3-kinase. Here we show that macrophage PI3-kinase/Akt is activated by oxidized low-density lipoprotein, inflammatory chemokines, and angiotensin II. This activation is markedly reduced or absent in macrophages lacking p110gamma, the catalytic subunit of class Ib PI3-kinase. We further demonstrate activation of macrophage/foam cell PI3-kinase/Akt in atherosclerotic plaques from apolipoprotein E (apoE)-null mice, which manifest an aggressive form of atherosclerosis, whereas activation of PI3-kinase/Akt was undetectable in lesions from apoE-null mice lacking p110gamma despite the presence of class Ia PI3-kinase. Moreover, plaques were significantly smaller in apoE-/-p110gamma-/- mice than in apoE-/-p110gamma+/+ or apoE-/-p110gamma+/-mice at all ages studied. In marked contrast to the embryonic lethality seen in mice lacking class Ia PI3-kinase, germ-line deletion of p110gamma results in mice that exhibit normal viability, longevity, and fertility, with relatively well tolerated defects in innate immune and inflammatory responses that may play a role in diseases such as atherosclerosis and multiple sclerosis. Our results not only shed mechanistic light on inflammatory signaling during atherogenesis, but further identify p110gamma as a possible target for pharmacological intervention in the primary and secondary prevention of human atherosclerotic cardiovascular disease.     

Molecular interactions leading to lipoprotein retention and the initiation of atherosclerosis

Atherosclerosis is distinguished by the accumulation of lipoprotein lipid within the arterial wall. An ionic interaction of positively charged regions of apolipoprotein (apo) B with matrix proteins, including proteoglycans, collagen, and fibronectin, is thought to initiate this process. Proteoglycans are complex glycoproteins containing highly negatively charged carbohydrate chains. These proteins are abundant in atherosclerosis lesions, and they associate with apoB-containing lipoproteins. Several specific regions of apoB may mediate this process. Other lipoprotein-associated proteins, including apoE and lipases, might also participate in this process. In addition, retention may occur via lipoprotein association with other matrix molecules or as a consequence of intra-arterial lipoprotein aggregation.     

Heparan sulfate in perlecan promotes mouse atherosclerosis: roles in lipid permeability, lipid retention, and smooth muscle cell proliferation

Heparan sulfate (HS) has been proposed to be antiatherogenic through inhibition of lipoprotein retention, inflammation, and smooth muscle cell proliferation. Perlecan is the predominant HS proteoglycan in the artery wall. Here, we investigated the role of perlecan HS chains using apoE null (ApoE0) mice that were cross-bred with mice expressing HS-deficient perlecan (Hspg2(Delta3/Delta3)). Morphometry of cross-sections from aortic roots and en face preparations of whole aortas revealed a significant decrease in lesion formation in ApoE0/Hspg2(Delta3/Delta3) mice at both 15 and 33 weeks. In vitro, binding of labeled mouse triglyceride-rich lipoproteins and human LDL to total extracellular matrix, as well as to purified proteoglycans, prepared from ApoE0/Hspg2(Delta3/Delta3) smooth muscle cells was reduced. In vivo, at 20 minutes influx of human (125)I-LDL or mouse triglyceride-rich lipoproteins into the aortic wall was increased in ApoE0/Hspg2(Delta3/Delta3) mice compared to ApoE0 mice. However, at 72 hours accumulation of (125)I-LDL was similar in ApoE0/Hspg2(Delta3/Delta3) and ApoE0 mice. Immunohistochemistry of lesions from ApoE0/Hspg2(Delta3/Delta3) mice showed decreased staining for apoB and increased smooth muscle alpha-actin content, whereas accumulation of CD68-positive inflammatory cells was unchanged. We conclude that the perlecan HS chains are proatherogenic in mice, possibly through increased lipoprotein retention, altered vascular permeability, or other mechanisms. The ability of HS to inhibit smooth muscle cell growth may also influence development as well as instability of lesions.     

Regression of Atherosclerosis in Apolipoprotein E-Deficient Mice is Feasible Using High-Dose Angiotensin Receptor Blocker, Candesartan

Aim: Clinical studies have suggested that renin-angiotensin inhibitors are effective for the prevention of atherosclerosis progression, but the results for the regression of established lesions are equivocal. The aim of this study was to examine the effects of different doses of the angiotensin receptor blocker (ARB) candesartan on the regression of atherosclerosis and lipid-induced nephropathy in apolipoprotein E (apoE)-deficient spontaneously hyperlipidemic (SHL) mice.Methods and Results: Male SHL were given an atherogenic diet together with salt loading to induce atherosclerosis. The mice were then treated with various doses of candesartan (0-50 mg/kg/d) for 12 weeks. Treatment with high-dose candesartan caused clear regression of atherosclerotic plaques in the aorta, which was not observed with normal-dose candesartan. Biglycan and ACAT1 expression were significantly decreased, and aortic free cholesterol: cholesterol ester ratios were increased in these mice. Treatment of cultured THP-1 macrophages in vitro with candesartan resulted in a similar decrease in ACAT1 expression. In the kidney, glomerular lipid accumulation, mesangial expansion, and albuminuria were significantly regressed after treatment with high-dose candesartan, while biglycan and ACAT1 expressions were decreased.Conclusion: These results suggest that regression of established atherosclerosis lesions in ApoE-deficient mice is feasible using high-dose candesartan, by mechanisms involving (i) a decrease in the lipid-retaining proteoglycan biglycan, and (ii) suppression of ACAT1 expression resulting in increased free cholesterol for lipid release.     

Atherosclerosis in C3H/HeJ mice reconstituted with apolipoprotein E-null bone marrow

Previous studies showed that reconstitution of atherosclerosis-susceptible C57BL/6 (B6) female mice with apolipoprotein E (apoE)-deficient (apoE(-/-)) bone marrow resulted in markedly increased atherosclerosis, despite the fact that plasma lipid levels were unchanged. To determine whether apoE(-/-) bone marrow would increase atherosclerosis in an atherosclerosis-resistant strain, female C3H/HeJ (C3H) mice were lethally irradiated and reconstituted with bone marrow from either C3H.apoE(-/-) mice or wild-type C3H mice. Four weeks after transplantation, the mice were fed an atherogenic diet for 12 weeks. We found that reconstitution of C3H mice with apoE(-/-) bone marrow resulted in a slight reduction in plasma apoE levels and a dramatic reduction in apoE and apolipoprotein B (apoB) in the aortic wall. Plasma apoB and cholesterol levels were unchanged, as were atherosclerotic lesions at the aortic root. These data indicate that reconstitution of C3H mice with apoE(-/-) bone marrow has no effect on atherosclerosis susceptibility and that apoE promotes accumulation of apoB in the vessel wall.     

Biglycan deficiency: Increased aortic aneurysm formation and lack of atheroprotection

Proteoglycans of the arterial wall play a critical role in vascular integrity and the development of atherosclerosis owing to their ability to organize extracellular matrix molecules and to bind and retain atherogenic apolipoprotein (apo)-B containing lipoproteins. Prior studies have suggested a role for biglycan in aneurysms and in atherosclerosis. Angiotensin II (angII) infusions into mice have been shown to induce abdominal aortic aneurysm development, increase vascular biglycan content, increase arterial retention of lipoproteins, and accelerate atherosclerosis. The goal of this study was to determine the role of biglycan in angII-induced vascular diseases. Biglycan-deficient or biglycan wildtype mice crossed to LDL receptor deficient (Ldlr-/-) mice (C57BL/6 background) were infused with angII (500 or 1000 ng/kg/min) or saline for 28 days while fed on normal chow, then pumps were removed, and mice were switched to an atherogenic Western diet for 6 weeks. During angII infusions, biglycan-deficient mice developed abdominal aortic aneurysms, unusual descending thoracic aneurysms, and a striking mortality caused by aortic rupture (76% for males and 48% for females at angII 1000 ng/kg/min). Histological analyses of non-aneurysmal aortic segments from biglycan-deficient mice revealed a deficiency of dense collagen fibers and the aneurysms demonstrated conspicuous elastin breaks. AngII infusion increased subsequent atherosclerotic lesion development in both biglycan-deficient and biglycan wildtype mice. However, the biglycan genotype did not affect the atherosclerotic lesion area induced by the Western diet after treatment with angII. Biglycan-deficient mice exhibited significantly increased vascular perlecan content compared to biglycan wildtype mice. Analyses of the atherosclerotic lesions demonstrated that vascular perlecan co-localized with apoB, suggesting that increased perlecan compensated for biglycan deficiency in terms of lipoprotein retention. Biglycan deficiency increases aortic aneurysm development and is not protective against the development of atherosclerosis. Biglycan deficiency leads to loosely packed aortic collagen fibers, increased susceptibility of aortic elastin fibers to angII-induced stress, and up-regulation of vascular perlecan content.     

Accelerated atherosclerosis in C57Bl/6 mice transplanted with ApoE-deficient bone marrow

Apolipoprotein E (apoE), a high affinity ligand for lipoprotein receptors, is synthesized by the liver and extrahepatic tissues, including cells of the monocyte/macrophage cell lineage. The role of monocyte/macrophage-derived apoE in atherogenesis was assessed by transplantation of apoE-deficient (apoE-/-) bone marrow into normolipidemic C57Bl/6 mice. No significant effect could be demonstrated on serum apoE levels in C57Bl/6 mice, transplanted with apoE-deficient bone marrow compared with control transplanted mice. Furthermore, no consistent effect on serum cholesteryl esters and triglyceride concentrations could be demonstrated on either a standard chow diet or a high cholesterol diet. Quantitative analysis of atherosclerosis in mice transplanted with apoE-deficient bone marrow, after two months on a high cholesterol diet, revealed a 4-fold increase in the atherosclerotic lesion area as compared to animals transplanted with apoE+/+ bone marrow. Analysis of the ability of apoE-deficient macrophages to release cholesterol after loading with acetylated LDL revealed that the release of cholesterol from apoE-deficient macrophages was impaired as compared to wild-type macrophages in the absence and the presence of specific cholesterol acceptors. In conclusion, apoE production by macrophages retards the formation of atherosclerotic plaques, possibly by mediating cholesterol efflux. We anticipate that pharmacological approaches to increase apoE synthesis and/or secretion by macrophages might be beneficial for the treatment of atherosclerosis.     

Normal production rate of apolipoprotein B in LDL receptor-deficient mice

The low density lipoprotein (LDL) receptor is well known for its role in mediating the removal of apolipoprotein B (apoB)-containing lipoproteins from plasma. Results from in vitro studies in primary mouse hepatocytes suggest that the LDL receptor may also have a role in the regulation of very low density lipoprotein (VLDL) production. We conducted in vivo experiments using LDLR-/-, LDLR+/-, and wild-type mice (LDLR indicates LDL receptor gene) in which the production rate of VLDL was measured after the injection of [35S]methionine and the lipase inhibitor Triton WR1339. Despite the fact that LDLR-/- mice had a 3.7-fold higher total cholesterol level and a 2.1-fold higher triglyceride level than those of the wild-type mice, there was no difference in the production rate of VLDL triglyceride or VLDL apoB between these groups of animals. Experiments were also conducted in apobec1-/- mice, which make only apoB-100, the form of apoB that binds to the LDL receptor. Interestingly, the apobec1-/- mice had a significantly higher production rate of apoB than did the wild-type mice. However, despite significant differences in total cholesterol and triglyceride levels, there was no difference in the production rate of total or VLDL triglyceride or VLDL apoB between LDLR-/- and LDLR+/- mice on an apobec1-/- background. These results indicate that the LDL receptor has no effect on the production rate of VLDL triglyceride or apoB in vivo in mice.     

Elastic lamina defects are an early feature of aortic lesions in the apolipoprotein E knockout mouse

The aortae from male apolipoprotein E knockout (apoE-/-) mice were examined by serial section immunohistochemistry and electron microscopy to determine the continuity of the internal elastic lamina (IEL) and its association with developing intimal lesions. While in this model, defects in the elastic laminae have previously been described beneath advanced xanthomatous lesions, this study demonstrates that disruption of the IEL may be a primary factor in the localization and pathogenesis of intimal lesions in the apoE-/- mouse. IEL defects were found beneath early lesions in animals as young as 8 weeks of age. Small defects without associated intimal alteration were also observed. The elastic tissue defects beneath early intimal lesions were usually transversely orientated with abrupt "break" edges. Regions consistent with direct enzymatic digestion of the IEL were relatively rare and only observed beneath advanced plaques, particularly in the brachiocephalic artery. The presence of IEL defects around branch sites of old C57BL/6J control mice along with their matching localization and morphology in apoE-/- appears consistent with biomechanical fatigue rather than direct enzymatic degradation. In conclusion, disruption of the IEL appears to be a prominent early, if not initial, feature of the apoE-/- model of atherosclerosis and may act as the nidus upon which intimal lesions develop.     

Leptin deficiency suppresses progression of atherosclerosis in apoE-deficient mice

Both experimental and epidemiological studies suggest that leptin is one of the molecules responsible for accelerated atherosclerosis in obese humans. To confirm the notion, we studied whether leptin accelerates atherosclerosis in apoE(-/-) mice. Leptin deficient hyperlipidemic mice (ob/ob;apoE(-/-) mice) developed significantly less atherosclerosis than apoE(-/-) mice, when fed an atherogenic diet for 16 weeks from 8 weeks of age. Histological analysis revealed that most of the atherosclerotic lesions in ob/ob;apoE(-/-) mice remained as fatty streaks, while those in apoE(-/-) mice were mainly fibrous plaques. The decrease in atherosclerosis was not due to changes in the serum levels of cholesterol, TNF-alpha, or adiponectin. Exogenous leptin significantly increased atherosclerotic areas in apoE(-/-) mice, even though it decreased food intake and body weight. Our findings support the notion that leptin accelerates atherosclerosis.     

Increased atherosclerosis in mice with increased vascular biglycan content

Objective

The response to retention hypothesis of atherogenesis proposes that atherosclerosis is initiated via the retention of atherogenic lipoproteins by vascular proteoglycans. Co-localization studies suggest that of all the vascular proteoglycans, biglycan is the one most closely co-localized with LDL. The goal of this study was to determine if over-expression of biglycan in hyperlipidemic mice would increase atherosclerosis development.

Methods

Transgenic mice were developed by expressing biglycan under control of the smooth muscle actin promoter, and were crossed to the LDL receptor deficient (C57BL/6 background) atherosclerotic mouse model. Biglycan transgenic and non-transgenic control mice were fed an atherogenic Western diet for 4–12 weeks.

Results

LDL receptor deficient mice overexpressing biglycan under control of the smooth muscle alpha actin promoter had increased atherosclerosis development that correlated with vascular biglycan content.

Conclusion

Increased vascular biglycan content predisposes to increased lipid retention and increased atherosclerosis development.     

Effect of trans-resveratrol on the thrombogenicity and atherogenicity in apolipoprotein E-deficient and low-density lipoprotein receptor-deficient mice.

Resveratrol is one of the major polyphenolics in red wine that has been shown to exert the preventive effects against cardiovascular diseases. The effect of trans-resveratrol (t-RES) administered as an ingredient of the diet on the atherothrombotic tendency was assessed in genetically hypercholesterolemic mice after laser-induced damage on endothelium. Mice lacking both apolipoprotein E and low-density lipoprotein receptor (apoE-/-/LDLR-/-) were fed with a high-fat diet with or without t-RES (9.6 and 96 mg/kg diet) for 8 weeks. The atherosclerotic tendency was morphometrically analyzed in their aortae. The thrombotic tendency was determined by inducing thrombus by the irradiation of a helium-neon laser on carotid arteries of these mice with injection of Evans blue. Atherosclerotic area and thrombus size were evaluated by image analyzing in a computer system. Even though the plasma concentrations of lipids (total cholesterol and triacylglycerol) did not change in the control and t-RES groups, a significant decrease (approximately 30%) in the formation of atheroma was observed in the aortae of the t-RES group. The size of laser-induced thrombus that mostly consisted of platelet aggregates was significantly reduced (approximately 25%) in the t-RES group compared with that in the control group. Thus, t-RES orally administrated with a high-fat diet in apoE-/-/LDLR-/- mice significantly suppressed atherosclerosis in their aortae and reduced the laser-induced thrombosis in their carotid arteries.     

Loss of SR-BI expression leads to the early onset of occlusive atherosclerotic coronary artery disease, spontaneous myocardial infarctions, severe cardiac dysfunction, and premature death in apolipoprotein E-deficient mice

Murine models of atherosclerosis, such as the apolipoprotein E (apoE) or the LDL receptor knockout mice, usually do not exhibit many of the cardinal features of human coronary heart disease (CHD), eg, spontaneous myocardial infarction, severe cardiac dysfunction, and premature death. Here we show that mice with homozygous null mutations in the genes for both the high density lipoprotein receptor SR-BI and apoE (SR-BI/apoE double knockout [dKO] mice) exhibit morphological and functional defects with similarities to those seen in human CHD. When fed a standard chow diet, these hypercholesterolemic animals developed significant atherosclerotic lesions in the aortic sinus as early as 4 to 5 weeks after birth. We now show that they also exhibited extensive lipid-rich coronary artery occlusions and spontaneously developed multiple myocardial infarctions and cardiac dysfunction (eg, enlarged hearts, reduced ejection fraction and contractility, and ECG abnormalities). Their coronary arterial lesions, which were strikingly similar to human atherosclerotic plaques, exhibited evidence of cholesterol clefts and extensive fibrin deposition, indicating hemorrhage and clotting. All of the dKO mice died by 8 weeks of age (50% mortality at 6 weeks). Thus, SR-BI/apoE dKO mice provide a new murine model for CHD and may help better define the role of lipoprotein metabolism and atherosclerosis in the pathogenesis of myocardial infarction and cardiac dysfunction. Furthermore, these animals may be useful for preclinical testing of potential genetic and/or pharmacological therapies for CHD.     

Retention of low-density lipoprotein in atherosclerotic lesions of the mouse: evidence for a role of lipoprotein lipase

Direct binding of apolipoprotein (apo)B-containing lipoproteins to proteoglycans is the initiating event in atherosclerosis, but the processes involved at later stages of development are unclear. Here, we investigated the importance of the apoB-proteoglycan interaction in the development of atherosclerosis over time and investigated the role of lipoprotein lipase (LPL) to facilitate low-density lipoprotein (LDL) retention at later stages of development. Atherosclerosis was analyzed in apoB transgenic mice expressing LDL with normal (control LDL) or reduced proteoglycan-binding (RK3359-3369SA LDL) activity after an atherogenic diet for 0 to 40 weeks. The initiation of atherosclerosis was delayed in mice expressing RK3359-3369SA LDL, but they eventually developed the same level of atherosclerosis as mice expressing control LDL. Retention studies in vivo showed that although higher levels of 131I-tyramine cellobiose-labeled control LDL (131I-TC-LDL) were retained in nonatherosclerotic aortae compared with RK3359-3369SA 131I-TC-LDL, the retention was significantly higher and there was no difference between the groups in atherosclerotic aortae. Lower levels of control 125I-TC-LDL and RK3359-3369SA 125I-TC-LDL were retained in atherosclerotic aortae from ldlr-/- mice transplanted with lpl-/- compared with lpl+/+ bone marrow. Uptake of control LDL or RK3359-3369SA LDL into macrophages with specific expression of human catalytically active or inactive LPL was increased compared with control macrophages. Furthermore, transgenic mice expressing catalytically active or inactive LPL developed the same extent of atherosclerosis. Thus, retention of LDL in the artery wall is initiated by direct LDL-proteoglycan binding but shifts to indirect binding with bridging molecules such as LPL.     

Triglyceride-rich lipoproteins from subjects with type 2 diabetes do not demonstrate increased binding to biglycan, a vascular proteoglycan.

Retention of atherogenic apolipoprotein (apo) B- and E- containing lipoproteins by their interaction with arterial wall proteoglycans is important in atherogenesis. Levels of triglyceride (TG)-rich lipoproteins, which contain both apo B and apo E, are increased in type 2 diabetes. Because increased retention of TG-rich lipoproteins in diabetes might explain, in part, the increased atherosclerosis in this disorder, TG-rich lipoproteins were isolated from fasting type 2 diabetic subjects and age-matched controls, and assessed for their ability to bind biglycan, a vascular smooth muscle cell-derived proteoglycan. The binding of TG-rich lipoproteins isolated from diabetic subjects to purified biglycan did not differ from lipoproteins isolated from control subjects. Moreover, contrary to previous reports, no difference in the apo E content of TG-rich lipoproteins was detected between the control and diabetic groups. Additionally, no difference in the binding affinity of TG-rich lipoproteins for the low-density lipoprotein receptor was observed between control and diabetic subjects. Thus, we were unable to confirm previous reports that TG-rich lipoproteins from subjects with diabetes are enriched in apo E compared with age-matched controls, consistent with the lack of difference in binding of these lipoproteins to either biglycan or the low-density lipoprotein receptor. Therefore, increased affinity of TG-rich lipoproteins for biglycan is unlikely to explain the increased atherosclerosis in type 2 diabetes.