Atherosclerosis: cell biology and lipoproteins.
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Arteriosclerosis↗
Biomedical subjects
Alan Daugherty
Publications and source records attributed to Alan Daugherty.
Dietary fat interacts with PCBs to induce changes in lipid metabolism in mice deficient in low-density lipoprotein receptor.
There is evidence that dietary fat can modify the cytotoxicity of polychlorinated biphenyls (PCBs) and that coplanar PCBs can induce inflammatory processes critical in the pathology of vascular diseases. To test the hypothesis that the interaction of PCBs with dietary fat is dependent on the type of fat, low-density lipoprotein receptor-deficient (LDL-R(-/-)) mice were fed diets enriched with either olive oil or corn oil for 4 weeks. Half of the animals from each group were injected with PCB-77. Vascular cell adhesion molecule-1 (VCAM-1) expression in aortic arches was nondetectable in the olive-oil-fed mice but was highly expressed in the presence of PCB-77. PCB treatment increased liver neutral lipids and decreased serum fatty acid levels only in mice fed the corn-oil-enriched diet. PCB treatment increased mRNA expression of genes involved in inflammation, apoptosis, and oxidative stress in all mice. Upon PCB treatment, mice in both olive- and corn-oil-diet groups showed induction of genes involved in fatty acid degradation but with up-regulation of different key enzymes. Genes involved in fatty acid synthesis were reduced only upon PCB treatment in corn-oil-fed mice, whereas lipid transport/export genes were altered in olive-oil-fed mice. These data suggest that dietary fat can modify changes in lipid metabolism induced by PCBs in serum and tissues. These findings have implications for understanding the interactions of nutrients with environmental contaminants on the pathology of inflammatory diseases such as atherosclerosis.
Animals↗
Hypercholesterolemia stimulates angiotensin peptide synthesis and contributes to atherosclerosis through the AT1A receptor.
BACKGROUND: Hypercholesterolemia-induced atherosclerosis is attenuated by either pharmacological antagonism of AT1 receptors or AT1A receptor deficiency. However, the mechanism underlying the pronounced responses to angiotensin II (Ang II) antagonism has not been determined. We hypothesized that hypercholesterolemia stimulates the production of angiotensin peptides to provide a rationale for the profound effect of AT1A receptor deficiency on atherogenesis. METHODS AND RESULTS: Atherosclerotic lesions were analyzed in LDL receptor-deficient mice. Immunocytochemical analysis demonstrated that atherosclerotic lesions contained all the components of the conventional pathway for Ang II synthesis. AT1A receptor deficiency caused a marked decrease in atherosclerotic lesion size in both the aortic root and arch of male and female mice, without a discernible effect on composition. AT1A receptor deficiency-induced reductions in atherosclerosis were independent of systolic blood pressure and measurements of oxidation and chemoattractants. Aortic AT2 receptor mRNA expression was not altered in AT1A receptor-deficient mice, and AT2 receptor deficiency had no effect on lesion area or cellular composition. Hypercholesterolemia greatly augmented the systemic renin-angiotensin system, as demonstrated by large increases in plasma concentrations of angiotensinogen and angiotensin peptides (Ang II, III, IV, and 4-8). These increases were ablated in hypercholesterolemic AT1A receptor-deficient mice. CONCLUSIONS: AT1A receptor deficiency had a striking effect in reducing hypercholesterolemia-induced atherosclerosis in LDL receptor-negative mice. Hypercholesterolemia was associated with increased systemic angiotensinogen and angiotensin peptides, which were reduced in AT1A receptor-deficient mice. These results demonstrate that hypercholesterolemia-induced stimulation of angiotensin peptide production provides a basis for the marked effect of AT1A receptor deficiency in reducing atherosclerosis.
Amino Acid Sequence↗
Alpha(1,3)fucosyltransferases FucT-IV and FucT-VII control susceptibility to atherosclerosis in apolipoprotein E-/- mice.
OBJECTIVE: These studies examine the contributions of alpha(1,3)fucosyltransferases (FucT) IV and VII to the generation of selectin counter-receptors necessary for selectin-dependent atherogenesis. They also determine the functional contribution of FucT-IV and FucT-VII to shear-dependent tethering of monocytes to P-selectin, a process believed to be required for atherogenesis. METHODS AND RESULTS: Atherosclerotic lesion size and histology were determined in apolipoprotein E-/- mice sufficient or deficient in FucT-IV or FucT-VII. Lesion size was subtly reduced in FucT-IV-deficient mice and significantly reduced in FucT-VII-deficient mice. FucT deficiency did not alter lesion histology, plasma total cholesterol, or the lipoprotein distribution profile. Atheroprotection in FucT-IV or FucT-VII deficiency aligned with subtle and profound reductions, respectively, of P-selectin counter-receptor activity on peripheral blood monocytes as determined by tethering to P-selectin-IgG in vitro under shear flow. CONCLUSIONS: FucT-VII-mediated alpha(1,3)fucosylation of selectin ligands is a necessary concomitant to atherogenesis in apoE-/- mice and is required for P-selectin-dependent peripheral blood monocyte adhesion under shear stress. FucT-IV deficiency yields subtle deficits in monocyte P-selectin counter-receptor activity and is associated with a subtle decrement in atherosclerosis. These studies identify an important role for FucT-VII in atherogenesis, and a subsidiary role for FucT-IV, and implicate leukocyte selectin counter-receptors in the pathogenesis of atherosclerosis.
Animals↗
Activation of the systemic and adipose renin-angiotensin system in rats with diet-induced obesity and hypertension.
In obesity-related hypertension, activation of the renin-angiotensin system (RAS) has been reported despite marked fluid volume expansion. Adipose tissue expresses components of the RAS and is markedly expanded in obesity. This study evaluated changes in components of the adipose and systemic RAS in diet-induced obese hypertensive rats. RAS was quantified in adipose tissue and compared with primary sources for the circulating RAS. Male Sprague-Dawley rats were fed either a low-fat (LF; 11% kcal as fat) or moderately high-fat (32% kcal as fat) diet for 11 wk. After 8 wk, rats fed the moderately high-fat diet segregated into obesity-prone (OP) and obesity-resistant (OR) groups based on their body weight gain (body weight: OR, 566 +/- 10; OP, 702 +/- 20 g; P < 0.05). Mean arterial blood pressure was increased in OP rats (LF: 97 +/- 2; OR: 97 +/- 2; OP: 105 +/- 1 mmHg; P < 0.05). Quantification of mRNA expression by real-time PCR demonstrated a selective increase (2-fold) in angiotensinogen gene expression in retroperitoneal adipose tissue from OP vs. OR and LF rats. Similarly, plasma angiotensinogen concentration was increased in OP rats (LF: 390 +/- 48; OR: 355 +/- 24; OP: 530 +/- 22 ng/ml; P < 0.05). In contrast, other components of the RAS were not altered in OP rats. Marked increases in the plasma concentrations of angiotensin peptides were observed in OP rats (angiotensin II: LF: 95 +/- 31; OR: 59 +/- 20; OP: 295 +/- 118 pg/ml; P < 0.05). These results demonstrate increased activity of the adipose and systemic RAS in obesity-related hypertension.
Adipose Tissue↗
Orchidectomy, but not ovariectomy, regulates angiotensin II-induced vascular diseases in apolipoprotein E-deficient mice.
In humans, the incidence and severity of abdominal aortic aneurysms (AAA) are greater in males than in females. Chronic infusion of angiotensin II (AngII) into apolipoprotein E-deficient (apoE(-/-)) mice promotes atherosclerosis and causes the formation of AAAs. Just as human males are more susceptible to developing AAAs, male mice are more susceptible to AngII-induced AAAs. We hypothesized that sex steroid hormones mediate gender differences in AngII-induced AAA through regulation of the renin-angiotensin system. To define the role of ovarian hormones, female apoE(-/-) mice were subjected to ovariectomy or sham operation and infused with AngII (1000 ng/kg x min) for 28 d. Ovariectomy had no effect on AngII-induced atherosclerosis, nor did it influence the incidence or severity of AAA. To define the role of testicular hormones, male apoE(-/-) mice were subjected to orchidectomy (orx) or sham operation and infused with AngII (1000 ng/kg x min) for 28 d. Orx resulted in a profound reduction in AAA incidence (85% vs. 18%, sham vs. orx; P = 0.003) to the level observed in females (25%). However, orx had no effect on AngII-induced reductions in plasma renin concentration or spleen AngII receptor density. In contrast, orx resulted in an increase in atherosclerosis (0.46 +/- 0.07 vs. 1.20 +/- 0.21 mm(2), sham vs. orx; P = 0.002). These results suggest that estrogen does not mediate gender differences in AngII-induced AAA. In contrast, androgens mediate a higher incidence of AngII- induced AAA, through mechanisms that do not appear to involve circulating renin or angiotensin receptor density.
Angiotensin II↗
Depletion of natural killer cell function decreases atherosclerosis in low-density lipoprotein receptor null mice.
OBJECTIVE: Natural killer (NK) cells are a key component of innate immunity. Despite being identified in human and mouse atherosclerotic lesions, the role of NK cells in the disease process in unknown. To determine this role, we created chimeric atherosclerosis-susceptible low-density lipoprotein (LDL) receptor null (ldl-r-/-) mice that were deficient in functional NK cells through expression of a transgene encoding for Ly49A. METHODS AND RESULTS: Bone marrow cells from Ly49A transgenic and nontransgenic littermates were used to repopulate the hematopoietic system of lethally-irradiated female ldl-r-/- mice. After a recovery period to permit sufficient engraftment, mice were placed on a diet enriched in saturated fat and cholesterol. After 8 weeks, there was no difference in either serum total cholesterol concentrations or lipoprotein cholesterol distribution in mice repopulated with nontransgenic versus Ly49A transgenic marrow cells. Using immunohistochemistry, we detected NK cells in atherosclerotic lesions of both groups of mice. However, deficiency of functional NK cells significantly reduced the size of atherosclerosis by 70% (P=0.0002) in cross-sectional analysis of the aortic root and by 38% (P=0.004) in en face analysis of the intimal surface of the aortic arch. CONCLUSIONS: These studies demonstrate that NK cells infiltrate the vessel wall and promote atherosclerotic lesion development.
Animals↗
Role of metabolism and receptor responsiveness in the attenuated responses to Angiotensin II in mice compared to rats.
Chronic infusion of Angiotensin II (AngII) to rats is a well-characterized model for determining AngII physiology. Genetic manipulations have strengthened knowledge of AngII; however, they do not permit an increase in AngII to be initiated at a selected age, duration and dose. Therefore, exogenous AngII administration remains an important technique to define its biological effect. We previously noted that infusion of AngII to mice had minimal effects compared to the same dose given to rats. In this study, we compared the effects of chronic infusion of the same dose of AngII to C57BL/6 mice and Sprague-Dawley rats, two commonly used rodent models. Rats administered AngII exhibited reductions (by 22%) in body weight, which were not evident in mice. AngII increased blood pressure by 54 mm Hg in rats, but had no effect in mice. Vascular histology demonstrated that AngII caused medial hypertrophy in rats, with adventitial expansion in mice. Plasma concentrations of AngII and its catabolic fragments were elevated (twofold) in mice compared to rats. Angiotensin receptor affinity, density and distribution were similar in rats and mice. Infusion of AngII decreased AngII receptor density in the kidney (by 78%) and spleen (by 29%) of mice, but had no effect in rats. AngII produced a sustained contractile response in rat aortic strips, but minimal responses in mouse aorta. These results demonstrate that differences in circulating angiotensin peptides, AngII receptor regulation, and vascular reactivity contribute to diminished responses to AngII infusion in mice compared to rats. Results from this study suggest that considerably higher doses of AngII may be required to elicit physiologic effects of AngII in mice.
Angiotensin II↗
Mouse models of abdominal aortic aneurysms.
Many mouse models of abdominal aortic aneurysms have been developed that use a diverse array of methods for producing the disease, including genetic manipulation and chemical induction. These models could provide insight into potential mechanisms in the development of this disease. Although experimental studies on abdominal aortic aneurysms (AAAs) have used a variety of mammalian and avian approaches, there is an increasing reliance on the use of mice. The models recapitulate some facets of the human disease including medial degeneration, inflammation, thrombus formation, and rupture. Most of the mouse models of AAA are evoked either by genetically defined approaches or by chemical means. The genetic approaches are spontaneous and engineered mutations. These include defects in extracellular matrix maturation, increased degradation of elastin and collagen, aberrant cholesterol homeostasis, and enhanced production of angiotensin peptides. The chemical approaches include the intraluminal infusion of elastase, periaortic incubations of calcium chloride, and subcutaneous infusion of AngII. A common feature of these models is the reduction of AAA incidence and severity by the prophylactic administration of matrix metalloproteinase (MMP) inhibitors or genetically engineered deficiencies of specific members of this proteolytic protein family. The validation of mouse models of AAAs will provide insight into the mechanisms of progression of the human disease.
Angiotensin II↗
Angiotensin II and abdominal aortic aneurysms.
Abdominal aortic aneurysms (AAAs) have devastating effects on the morbidity and mortality of a large portion of the elderly population. Current therapeutic options for AAAs are limited to surgical approaches, because there are no proven pharmacologic treatments. Recently, there is evolving evidence that angiotensin II (Ang II) participates in the initiation and propagation of AAAs. Animal studies have consistently demonstrated the ability of Ang II to promote the formation of AAAs, although the mechanisms of this effect have not been defined. Further definition of the role of the renin-angiotensin system in AAA formation and progression will identify potential therapeutic strategies for treatment of this disease.
Angiotensin II↗
Angiotensin II-mediated development of vascular diseases.
Angiotensin II (AngII) has well-characterized effects on blood pressure and fluid balance that adversely affect atherosclerotic cardiovascular disease. More recently, there is a realization that AngII exerts direct effects on arterial wall cells to influence atherosclerotic lesion formation. Several groups have shown that infusion of AngII into hyperlipidemic mice rapidly and profoundly augments lesion formation. The increase in lesions from AngII was not attributable to elevated blood pressure. The lesions formed from AngII infusion are overtly similar to those formed during hypercholesterolemia, with infiltration of macrophages and T lymphocytes. Unexpectedly, AngII infusion into these mice also led to the development of abdominal aortic aneurysms. These aneurysms exhibit many aspects of the human disease including medial degeneration, inflammation, thrombus, and rupture. The definition of the cellular mechanisms by which Ang II promotes these vascular pathologies may provide new therapeutic strategies.
Angiotensin II↗
Atherosclerosis: cell biology and lipoproteins.
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Arteriosclerosis↗
IL-5 links adaptive and natural immunity in reducing atherosclerotic disease.
Oxidized LDL induces changes in several facets of the immune system, although the relationships between these facets and their contributions to atherogenesis have yet to be fully elucidated. A report in this issue of the JCI provides a novel demonstration of the adaptive immune system influencing the production of natural antibodies. The results demonstrate that injection of malondialdehyde-modified LDL promotes a Th2 response that in turn increases the titers of the natural antibody T15/EO6, which recognizes the oxidized phospholipid POVPC. Atherosclerotic lesion size in LDL receptor-deficient mice is reduced as a consequence of the increase in natural antibody titers, and IL-5 is identified as the link between the adaptive and natural immune systems.
Animals↗
Near-infrared spectrometry of abdominal aortic aneurysm in the ApoE-/- mouse.
Abdominal aortic aneurysms (AAAs) occur in 5-7% of people over age 60 in the United States. Early intervention in the disease process could have a significant impact on the incidence of complications and on patient survival, but identifying incipient aneurysms can be difficult. ApoE knockout mice develop AAAs following infusion of angiotensin II (AngII) by osmotic minipump into the subcutaneous space of mice at doses ranging from 500 to 1000 ng kg(-1) min(-1) for 7-28 days. These mice are used as models of AAA development. This study tested the hypothesis that near-IR spectrometry and PCR can determine AngII dose (SEE = 26 ng kg(-1) min(-1), SEP = 37 ng kg(-1) min(-1), r2 = 0.99) and collagen/elastin (C/E) ratio (SEE = 0.38, SEP = 0.39, r2 = 0.85) in mouse aortas.
Angiotensin II↗
Aortic dissection precedes formation of aneurysms and atherosclerosis in angiotensin II-infused, apolipoprotein E-deficient mice.
OBJECTIVE: We sought to define the temporal characteristics of angiotensin II (AngII)-induced abdominal aortic aneurysms (AAAs) and to provide mechanistic insight into the development of this vascular pathology in apolipoprotein E-deficient (apoE-/-) mice. METHODS AND RESULTS: Male apoE-/- mice were infused with AngII for 1 to 56 days. Suprarenal arteries were sequentially sectioned, and cellular features were defined by histologic and immunocytochemical techniques. The initial identified event was medial accumulation of macrophages in regions of elastin degradation. Subsequent medial dissection was associated with luminal dilation and thrombus formation. Thrombi were usually constrained by adventitial tissue, although approximately 10% of mice died due to rupture. Thrombi led to profound inflammation that was characterized by infiltration of macrophages and T and B lymphocytes. Remodeling of the tissues was associated with regeneration of elastin fibers and reendothelialization of the dilated luminal surface. Aneurysmal tissue underwent profound neovascularization. Atherosclerotic lesions were only detected after development of the aneurysms. CONCLUSIONS: The initial event in AngII-induced AAA is a focal dissection in the suprarenal region. The progression of AAA precedes the development of overt atherosclerotic lesions.
Aneurysm↗
Class A scavenger receptor-mediated adhesion and internalization require distinct cytoplasmic domains.
Class A scavenger receptors (SR-A) are transmembrane glycoproteins that mediate both ligand internalization and cell adhesion. Previous studies have identified specific amino acids in the cytoplasmic tail of SR-A that regulate receptor internalization; however, the role of cytoplasmic domains in regulating cell adhesion has not been addressed. To investigate the role of cytoplasmic domains in SR-A-mediated adhesion and to address whether SR-A-mediated adhesion and internalization require distinct cytoplasmic domains, different SR-A constructs were stably expressed in human embryonic kidney (HEK 293) cells. Deleting the entire cytoplasmic tail (SR-A Delta 1-55) greatly reduced receptor protein abundance. Retaining the six amino acids proximal to the membrane (SR-A Delta 1-49) restored receptor protein abundance. Although SR-A Delta 1-49 localized to the cell surface, cells expressing this receptor failed to internalize the ligand acetylated low density lipoprotein. Replacing the cytoplasmic tail of SR-A with that of the transferrin receptor (TfR/SR-A) resulted in retention of the chimeric receptor in the endoplasmic reticulum suggesting a specific role for the membrane-proximal amino acids in trafficking SR-A from the endoplasmic reticulum to the Golgi. Like SR-A expressing cells, cells expressing SR-A Delta 1-49 displayed increased spreading and adhesion, demonstrating that the membrane-proximal amino acids were sufficient for SR-A-mediated cell adhesion. Together, our results indicate a critical role for the membrane-proximal amino acids in SR-A trafficking and demonstrate that SR-A-mediated adhesion and internalization require distinct cytoplasmic domains.
Amidohydrolases↗
AGI-1067: a multifunctional phenolic antioxidant, lipid modulator, anti-inflammatory and antiatherosclerotic agent.
To explore the therapeutic efficacy and potential mechanisms of action of a new class of antiatherosclerotic drugs, AGI-1067 [mono[4-[[1-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]thio]-1-methylethyl]thio]-2,6-bis(1,1-dimethylethyl)phenyl] ester] (butanedioc acid) was tested in several animal models of atherosclerosis. AGI-1067, a novel phenolic antioxidant, was well tolerated in a 1-year study in hypercholesterolemic cynomolgus monkeys. It lowered low-density lipoprotein cholesterol (LDLc) by 41 and 90% at oral doses of 50 and 150 mg/kg, respectively and increased high-density lipoprotein cholesterol (HDLc) by 107% at the higher dose. In contrast, another phenolic antioxidant, probucol, had a modest LDLc-lowering effect (15% at 250 mg/kg) while decreasing HDLc (37% at 150 mg/kg). Histopathology of the aortas and coronary arteries revealed no atherosclerosis in the AGI-1067 (150 mg/kg) group and minimal-to-moderate atherosclerosis in the vehicle and probucol (150 mg/kg) groups. AGI-1067 also inhibited atherosclerosis in LDL receptor-deficient (LDLr -/-) mice and apolipoprotein E-deficient (ApoE -/-) mice even in the absence of a lipid-lowering effect. In LDLr -/- mice, AGI-1067 reduced aortic atherosclerosis by 49%. In ApoE -/- mice, AGI-1067 reduced atherosclerosis by 25, 41, and 49% in the arch, thoracic, and abdominal regions of the aorta. AGI-1067 also reduced vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1) mRNA levels in lungs of lipopolysaccharide-stimulated mice. At the cellular level, AGI-1067 inhibited tumor necrosis factor-alpha-inducible expression of VCAM-1, MCP-1, and E-selectin in human aortic endothelial cells (IC50 values = 6, 10, and 25 microM, respectively). These data show that AGI-1067 can inhibit atherosclerosis not only via its lipid-lowering effects but also by having direct anti-inflammatory effects on the vessel wall and suggest that it may be a novel therapeutic agent for coronary artery disease.
Animals↗
Macrophage-expressed group IIA secretory phospholipase A2 increases atherosclerotic lesion formation in LDL receptor-deficient mice.
OBJECTIVE: Transgenic mice expressing human group IIA secretory phospholipase A(2) (group IIA sPLA(2)) spontaneously develop atherosclerotic lesions. The mechanism for this proatherogenic effect is likely multifactorial, because HDL-cholesterol is significantly lower and LDL/VLDL cholesterol is slightly higher in transgenic mice compared with nontransgenic littermates. In the present study, we show for the first time that elicited peritoneal macrophages from transgenic mice express human group IIA sPLA(2). This study tested whether macrophage-expressed sPLA(2) contributes to atherogenesis. METHODS AND RESULTS: Bone marrow cells from either sPLA(2) transgenic mice or control C57BL/6 mice were transplanted into LDL receptor-deficient mice. After hematopoietic engraftment, animals were fed a diet enriched with saturated fat and cholesterol for 12 weeks. Despite a lack of effect on serum lipoprotein concentrations, the presence of bone marrow-derived cells expressing human group IIA sPLA(2) resulted in a significant increase in the extent of atherosclerosis in the aortic arch (12.8+/-1.4% versus 7.4+/-0.9%; P<0.005) and aortic sinus (0.3+/-0.03 mm(2) versus 0.2+/-0.04 mm(2); P<0.05). CONCLUSIONS: Group IIA sPLA(2) can contribute to atherosclerotic lesion development through a mechanism that is independent of systemic lipoprotein metabolism.
Animals↗