Differences In Atherosclerosis Susceptibility Research Articles

Vascular smooth muscle cell gene regulation

Vascular smooth muscle cell (VSMC) remodeling is a hallmark of vascular diseases such as atherosclerosis, which underlie heart attack and stroke. Regional differences in atherosclerosis susceptibility in the vasculature correlate with the embryonic origin of SMC, suggesting that developmental history is disease-relevant. For example, neuroectoderm-derived cells colonise the atherogeneic aortic arch whereas VSMC in the generally disease-free descending aorta is of paraxial mesoderm origin. Embryonic origin-specific molecular and functional differences have been observed in VSMCs in vitro and in vivo, and transplantation studies demonstrated that developmental history of VSMC progenitors affect the phenotype of mature cells. Here we investigate the mechanisms underlying this developmental memory. We have established stem cell differentiation models to generate SMC of different embryonic lineages from mouse pluripotent cells. Using this model we demonstrate that upregulation of VSMC genes in response to TGFbeta/PDGF treatment depends on the developmental state of the cells. Epigenetic analysis revealed a lineage-specific correlation with chromatin reconfiguration at SMC genes and subsequent analysis of ex vivo VSMC has identified candidate chromatin modifiers that may be responsible for these changes. By increasing our understanding of how developmental history affects VSMCs this work will help elucidate the mechanisms underlying vascular disease risk.

Abstract 142: Transcriptome-wide Expression Quantitative Trait Loci Mapping for Atherosclerosis Susceptibility Reveals Surf4 as Novel Candidate Gene

Previous work in an F2 intercross between atherosclerosis-susceptible C57BL/6 and atherosclerosis-resistant BALB/cByJ (BALB) mice on the LDL-receptor deficient background revealed a quantitative trait locus (QTL) for atherosclerotic lesion size at rs33142586 on chromosome (Chr) 2 in female mice (n=183) (Burkhardt et al., Arterioscler Thromb Vasc Biol; 31:775-84, 2011). The aim of the present study was to identify genetic variants responsible for differences in atherosclerosis-susceptibility between the two strains. We hypothesized that the causal genes could be identified by transcriptome-wide expression analyses followed by functional validation. 25,697 transcripts were analyzed in aortas (n=165) and livers (n=176) of F2 mice using Illumina Ref8 expression arrays. Expression levels were correlated with single nucleotide polymorphism (n=31) on Chr2 by expression QTL (eQTL) mapping. Genes co-segregating with the atherosclerosis QTL were identified as potential candidate genes. Results were validated by quantitative real-time PCR (qRT-PCR) in livers (n=176) and bone marrow-derived macrophages (BMDM, n=184) of F2 mice. Expression patterns of candidate genes were examined in different tissues of F0 mice, followed by functional studies. eQTL mapping identified Surf4 as the only cis -regulated gene co-segregating with the Chr2 QTL in aortas (LOD array =17.6), livers (LOD array =11.5, LOD qRT-PCR =23.2) and BMDM (LOD qRT-PCR =15.7). Surf4 mRNA was significantly increased in F2 mice carrying the BALB allele at rs33142586 and BALB F0 mice. Increased Surf4 expression was associated with reduced atherosclerosis lesion size in F2 mice. Immunohistochemical staining revealed expression of Surf4 in vascular endothelial cells of the aorta. RNAi of Surf4 lead to increased staurosporine- and cycloheximide-induced apoptosis and decreased proliferation compared to control siRNA in RAW 264.7 cells, which are two key mechanisms of atherosclerosis. In conclusion, we identified Surf4 as a novel candidate gene of atherosclerosis susceptibility co-segregating a QTL for atherosclerosis on mouse Chr2. In current work, its functional role in atherogenesis is being further investigated in in-vitro experiments.

Differences in Health Status Affect Susceptibility and Mapping of Genetic Loci for Atherosclerosis (Fatty Streak) in Inbred Mice

We observed differences in atherosclerosis susceptibility in mouse inbred strains over the years as the health status of our animal rooms increased. Therefore, we investigated the effect of animal room health status on atherosclerosis susceptibility in different strains. As these data can also be used for genome-wide association mapping, we performed a mapping study and compared our results with previously found quantitative trait loci for atherosclerosis in mouse and humans. Males and females from 48 inbred strains were housed in 2 animal rooms with different health status and given an atherogenic diet. We compared atherosclerosis susceptibility between animal rooms and between sexes and found that susceptibility is dependent on both health status and sex. Subsequently, the data were used for associations with loci on the mouse genome using 63 222 single nucleotide polymorphism. Three loci in males and 4 loci in females were identified using the data from the low-health status room. No significant associations were identified using the data from the high-health status room. Health status influences susceptibility to atherosclerosis and suggests that microbiological pressure plays an important role in the development of atherosclerosis in many strains. As we were only able to map susceptibility loci using the data from the lower health status room, we argue that susceptibility under these conditions is determined by a few key loci, whereas in the higher health status room different mechanisms might play a role in the differences in atherosclerosis susceptibility between strains and we did not have enough power to map the loci that are involved.

Genetic Susceptibility of the Arterial Wall Is an Important Determinant of Atherosclerosis in C57BL/6 and FVB/N Mouse Strains

How genetic variations among inbred mouse strains translate into differences in atherosclerosis susceptibility is of significant interest for the development of new therapeutic strategies. The objective of the present study was to examine whether genetically controlled arterial wall properties influence atherosclerosis susceptibility in FVB/N (FVB) and C57BL/6 (B6) apolipoprotein E knockout (apoE(-/-)) mouse strains. Common carotid artery segments from B6 apoE(-/-), F1 apoE(-/-), and FVB apoE(-/-) mice were transplanted to hybrid F1 apoE(-/-) mice, which can accept grafts from both parental strains without adaptive immune responses. The mice were fed a high-fat diet, and atherosclerosis was induced in the transplanted artery segments by placement of a perivascular constrictive collar. Artery segments from B6 apoE(-/-) mice developed much larger atherosclerotic lesions than artery segments from FVB or F1 apoE(-/-) mice. No differences in aortic arch atherosclerosis of the recipient mice were observed between groups. Genetically controlled factors acting at the level of the arterial wall are important determinants of atherosclerosis susceptibility in FVB apoE(-/-) and B6 apoE(-/-) mice.

Cosegregation of Aortic Root Atherosclerosis and Intermediate Lipid Phenotypes on Chromosomes 2 and 8 in an Intercross of C57BL/6 and BALBc/ByJ Low-Density Lipoprotein Receptor −/− Mice

We sought to identify novel atherosclerosis-modifying loci and their potential functional links in a genome-wide approach using cosegregation analysis of atherosclerosis and related intermediate phenotypes in mice. We carried out an F2 intercross between atherosclerosis-susceptible C57BL/6 mice and atherosclerosis-resistant BALB/cByJ mice on the low-density lipoprotein receptor(-/-) background to examine the genetic basis for their differences in atherosclerosis susceptibility. Atherosclerotic lesion size and a comprehensive panel of 61 atherosclerosis-related phenotypes, including plasma levels of lipids, cytokines, and chemokines were measured in 376 F2 mice. Quantitative trait locus mapping revealed a novel significant locus (logarithm of odds, 6.18) for atherosclerosis on proximal mouse chromosome (Chr) 2 (Ath39), which was associated with major variations in lesion size (14%). Plasma very-low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, lanosterol, and phytosterol levels cosegregated with atherosclerosis at this locus. Moreover, these lipid traits showed significant correlations with lesion size, suggesting that they share the same underlying genetic factor. We also describe a second male-specific locus on Chr 8 (Ath40) where atherosclerosis and lipids cosegregated. Our study revealed new loci for atherosclerosis susceptibility on mouse Chr 2 and 8, which might exert their effects on lesion size via plasma lipid levels.

Microarray analysis of gene expression in mouse aorta reveals role of the calcium signaling pathway in control of atherosclerosis susceptibility

Inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) exhibit a marked difference in atherosclerotic lesion formation when deficient in apolipoprotein E (apoE(-/-)), and the arterial wall has been identified as a source of the difference in atherosclerosis susceptibility. In the present study, differences in gene expression in aortic walls of the two strains were analyzed by microarrays. Total RNA was extracted from the aorta of 6-wk-old female B6 and C3H apoE(-/-) mice fed a chow or Western diet. There were 1,514 genes in chow fed mice and 590 genes in Western fed mice that were found to be differentially expressed between the two strains. Pathway analysis of differentially expressed genes suggested a role for the calcium signaling pathway in regulating atherosclerosis susceptibility. Oxidized LDL (oxLDL) induced a dose-dependent rise in cytosolic calcium levels in B6 endothelial cells. oxLDL-induced monocyte chemoattractant protein-1 production was inhibited by pretreatment with calcium chelator EGTA or intracellular calcium trapping compound BAPTA, indicating that calcium ions mediate the effect of oxLDL on monocyte chemoattractant protein-1 induction. The present findings demonstrate involvement of the calcium signaling pathway in the inflammatory process of atherogenesis.

Direct Evidence for a Crucial Role of the Arterial Wall in Control of Atherosclerosis Susceptibility

Inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) exhibit marked differences in atherosclerosis susceptibility. We sought to determine whether the difference in atherosclerosis susceptibility resides at the level of arterial walls. Thoracic aortic segments from 8-week-old female B6 and C3H apolipoprotein E-deficient mice were transplanted into the infrarenal aorta of 10-week-old female F1 mice. After transplantation, recipients were maintained on a chow diet for 16 weeks. The donor aortic segments of B6 mice developed significantly larger atherosclerotic lesions than those of C3H (44,983+/-11,702 versus 5600+/-4885 microm2 per section; P=0.011). Expression of vascular cell adhesion molecule (VCAM)-1 by endothelial cells was examined both in vitro and in vivo. B6 mice expressed significantly more VCAM-1 than their C3H counterparts. Sequence analysis of VCAM-1 cDNA revealed a nucleotide difference in the coding region that resulted in substitution of an amino acid in the protein product. These data provide direct proof that factors operating in the vessel wall, particularly endothelial cells, can serve as atherosclerosis modifiers and suggest a possibility for the contribution of VCAM-1 to atherosclerosis susceptibility.

Arginine/Arginase NO NO NO

Arginine is a semi-essential amino acid that plays a critical role in several metabolic pathways. The best known of these is as the immediate precursor of urea in the liver and to a lesser extent in the intestine.1 The enzyme responsible for the cleavage of arginine to produce urea is arginase, which is the only enzyme in the urea cycle that comes in two forms, arginase I, a cytosolic enzyme, and arginase II, a mitochondrial enzyme. These enzymes exist not only in the liver and intestine where urea is generated but are also widely distributed in the body. Ornithine, the other product of the cleavage of arginine by arginase, is a precursor of proline and polyamines such as spermine, spermidine, and putrescine. Arginine is also the precursor of nitric oxide (NO). See page 365 In an important article authored by Teupser and colleagues,2 arginase in macrophages has been identified as a candidate gene influencing atheroresponsiveness. They created and studied two strains of rabbits with genetically determined high (HAR) and low (LAR) atherosclerosis susceptibility. Subtractive suppression hybridization was used to screen for genes that were more highly expressed in macrophages from LAR rabbits. Among the 42 clones identified were four differentially expressed genes with potential relevance to atherogenesis. These were OC2 protein, fibronectin, ferritin H-chain, and arginase I. Despite their identification in the screen, the first three genes were not differentially expressed in macrophages between HAR and LAR animals when checked by quantitative RT-PCR. In contrast, arginase I was more highly expressed in LAR than HAR macrophages, and its expression level was correlated with higher arginase enzymatic activity. They further identified a length polymorphism of the mRNA for arginase I that was attributable to the presence (long variant) or absence (short variant) of a 413-bp C repeat in the …

Analysis of Intimal Proteoglycans in Atherosclerosis-prone and Atherosclerosis-resistant Human Arteries by Mass Spectrometry

The propensity to develop atherosclerosis varies markedly among different sites in the human vasculature. To determine a possible cause for such differences in atherosclerosis susceptibility, a proteomics-based approach was used to assess the extracellular proteoglycan core protein composition of intimal hyperplasia from both the atherosclerosis-prone internal carotid artery and the atherosclerosis-resistant internal thoracic artery. The intimal proteoglycan composition in these preatherosclerotic lesions was found to be more complex than previously appreciated with up to eight distinct core proteins present, including the large extracellular proteoglycans versican and aggrecan, the basement membrane proteoglycan perlecan, the class I small leucine-rich proteoglycans biglycan and decorin, and the class II small leucine-rich proteoglycans lumican, fibromodulin, and prolargin/PRELP (proline arginine-rich end leucine-rich repeat protein). Although most of these proteoglycans seem to be present in similar amounts at the two locations, there was a selective enhanced deposition of lumican in the intima of the atherosclerosis-prone internal carotid artery compared with the intima of the atherosclerosis-resistant internal thoracic artery. The enhanced deposition of lumican in the intima of an atherosclerosis prone artery has important implications for the pathogenesis of atherosclerosis.

Lipid retention in the arterial wall of two mouse strains with different atherosclerosis susceptibility

LDL deposition in the subendothelium of arterial walls is the initial event in the development of atherosclerosis. The deposited LDL undergoes oxidative modification by arterial wall cells to become oxidized LDL and consequently contributes to atherosclerotic formation. Using mouse strains C57BL/6J (B6) and C3H/HeJ (C3H), which differ markedly in susceptibility to atherosclerosis, we determined whether variation in subendothelial retention of apolipoprotein B (apoB)-containing lipoproteins constitutes a genetic component in atherosclerosis. Lipoprotein retention was quantitated by Western blot analysis to detect the presence of apoB in aortic walls before foam cells developed. In both dietary and apoE-deficient models, B6 mice exhibited up to a 2-fold increase of apoB in the aortic wall compared with C3H mice. This increase could not be attributed to differences in plasma lipid levels of the two strains. In vitro, endothelial cells from C3H mice took up more acetylated and oxidized LDL but not native LDL and converted more native LDL to oxidized LDL than did endothelial cells from B6 mice. C3H mice expressed more scavenger receptor A in their aortic wall than B6 mice. Thus, variation in the subendothelial retention of apoB-containing lipoproteins cannot explain the dramatic difference in atherosclerosis susceptibility between B6 and C3H mice, and endothelial cells may play a role in alleviating lipid accumulation in arterial walls.

Effects of oxidant-induced injury on heme oxygenase and glutathione in cultured aortic endothelial cells from atherosclerosis-susceptible and -resistant Japanese quail.

Recent studies on cultured aortic endothelial cells (AECs) from atherosclerosis-susceptible (SUS) and -resistant (RES) strains of Japanese quail suggest that differences in atherosclerosis susceptibility between RES and SUS may be due to differences in endothelial heme oxygenase (HO) and antioxidant components. We have now investigated the effects of oxidant-induced injury on HO and glutathione (GSH) in AECs from SUS and RES quail. We report that cultured AECs from SUS and RES birds differ in their response to oxidative stress. AECs from the SUS strain cells are more susceptible than those from the RES strain to oxidative stress induced by tert-butylhydroperoxide, as judged by lower HO activity, HO-1 expression, ferritin and GSH levels. Aortic endothelial cells from SUS birds also showed higher levels of catalytic iron, TBARS production and LDH release compared with RES cells, indicating that SUS AECs are more susceptible to oxidative stress than cells from the resistant strain. Furthermore, independently of genetic status, AECs from old birds have higher TBARS and lower levels of HSP70 induction than AECs from younger birds, suggesting that aging is associated with a decreased ability of AECs to respond to oxidative stress, and this may be relevant to the permissive effect of aging on the process of atherogenesis. Our results indicate that genetic factors and endogenous antioxidant systems in the blood vessel wall may be important in determining the susceptibility of vascular cells to oxidative stress and atherosclerotic plaque formation.

Heme oxygenase and antioxidant status in cultured aortic endothelial cells isolated from atherosclerosis-susceptible and -resistant Japanese quail.

We have investigated heme oxygenase (HO) and antioxidant status in the novel isolation and characterization of aortic endothelial cells (AECs) from a random bred wild-type strain (WILD) and selectively bred atherosclerosis-susceptible (SUS) and -resistant (RES) strains of Japanese quail. Cultured AECs expressed acetylated LDL, and were probed with endothelial and smooth muscle cell specific antibodies to confirm purity of culture. Subconfluent monolayers of RES AECs had higher HO activity than SUS AECs. At confluence, HO activity levels were similar among strains. However, RES AECs had higher HO-1 protein than WILD and SUS cells. Although ferritin protein levels were similar among the three strains, catalytic iron was higher in SUS AECs than WILD and RES cells. Glutathione levels were highest in SUS cells, intermediate in WILD, and lowest in RES, while glutathione reductase was higher in WILD and RES AECs than SUS AECs. We suggest that differences in atherosclerosis susceptibility between RES and SUS may be due, at least in part, to differences in endothelial HO and antioxidant components.

Chlamydia pneumoniae does not increase atherosclerosis in the aortic root of apolipoprotein E-deficient mice.

In epidemiological studies, an association between cardiovascular disease and Chlamydia pneumoniae (C pneumoniae) infection has been observed. Although C pneumoniae has been shown to be present in atherosclerotic lesions, a causal relationship between C pneumoniae infection and atherosclerosis has not been demonstrated. To study this question, we used 2 strains of apolipoprotein (apo) E-deficient mice. Eight-week-old mice on an FVB background that were maintained on either a low- or a high-fat diet were infected 3 times at 1-week intervals with C pneumoniae, and atherosclerotic lesions were measured in the aortic root at 10 weeks after the primary infection. In each of the diet groups, no difference in the extent of atherosclerosis could be observed between the C pneumoniae-infected and control animals. In further studies, 2 strains of apoE-deficient mice (FVB or C57BL/6J background) were infected 4 times at 3- to 4-week intervals, and the extent of atherosclerosis was analyzed 18 weeks later. The mice were kept on either a low- or a high-fat diet. The high-fat diet increased atherosclerosis, and a difference in atherosclerosis susceptibility between the mouse strains was observed. However, C pneumoniae infection did not influence lesion size in either mouse strain. On the other hand, C pneumoniae could not be demonstrated by polymerase chain reaction in any of the atherosclerotic lesions of the infected animals studied. A small decrease in serum cholesterol and triglyceride levels 3 days after the primary infection occurred, but after that no differences in serum lipid levels compared with those in noninfected animals were evident. In the myocardium of C pneumoniae-infected mice, no inflammatory signs could be observed. We conclude that under the experimental conditions used, C pneumoniae infection does not accelerate atherogenic changes in the aortic root of apoE-deficient mice.

Cholesterol efflux is defective in macrophages from atherosclerosis-susceptible White Carneau pigeons relative to resistant show racer pigeons.

White Carneau (WC) pigeons are susceptible to the development of aortic atherosclerosis, whereas Show Racer (SR) pigeons are resistant, even though there are no differences in the known risk factors, including plasma cholesterol levels, lipoproteins, blood pressure, etc. Although this suggests that the difference in atherosclerosis susceptibility between WC and SR pigeons may be mediated at the level of the arterial wall, we have yet to identify a mechanism that can account for this difference. In pigeons as in other species (including humans), macrophages play a major role in the pathogenesis of atherosclerosis. Pigeon macrophages have multiple mechanisms for the uptake of lipoproteins and the accumulation of cholesteryl esters. To date, however, no differences in lipoprotein uptake between macrophages of WC and SR pigeons have been identified that could explain the difference in atherosclerosis susceptibility. In the present study we explored the alternative hypothesis that there are differences in the rate of cholesteryl ester clearance from peritoneal macrophages isolated from the two breeds of pigeons. Cholesterol efflux studies were conducted with elicited pigeon peritoneal macrophages that were loaded with cholesteryl ester either in vitro by incubation with rabbit beta-very low density lipoprotein or in vivo by isolation of macrophages from birds fed a cholesterol-containing diet. Using these techniques we were able to load WC and SR macrophages consistently with cholesteryl esters to levels typical of arterial foam cells (150-1,150 micrograms/mg cell protein). Under these cholesterol loading conditions there was no net efflux of cholesterol from either WC or SR macrophages when incubated for up to 24 hours in the presence of pigeon or human high density lipoprotein (HDL), fetal bovine serum, or lipoprotein-deficient serum. Under the same conditions, efflux of cholesterol from mouse peritoneal macrophages was stimulated by human and pigeon HDL. Despite the inability of HDL, lipoprotein-deficient serum, or fetal bovine serum to promote net cholesterol efflux, apoprotein (apo) HDL/phosphatidylcholine (PC) vesicles stimulated cholesteryl ester clearance from both WC and SR pigeon macrophages but at a significantly slower rate from WC pigeon macrophages. When incubated in the presence of excess apoHDL/PC (400 micrograms/ml), the rate of depletion of cellular cholesteryl esters was log-linear for at least 48 hours. WC macrophages cleared an average of only 9% of their cholesteryl esters in 24 hours when incubated with excess apoHDL/PC, whereas SR macrophages reduced their cholesteryl ester content by an average of 42%.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipoprotein metabolism by macrophages from atherosclerosis-susceptible White Carneau and resistant Show Racer pigeons.

The presence of specific receptors for the metabolism of acetylated low density lipoprotein (AcLDL) and beta-migrating very low density lipoprotein (beta-VLDL) was demonstrated in thioglycolate-elicited peritoneal macrophages from both atherosclerosis-susceptible White Carneau (WC) and resistant Show Racer (SR) pigeons. Macrophages from both breeds metabolized AcLDL through a single class of receptors that were similar, but not identical, to the scavenger receptors described in mammalian macrophages. Both pigeon and mammalian AcLDL bound to this receptor. At 37 degrees C, AcLDL was internalized and degraded in the lysosomes, and cholesterol esterification and cholesteryl ester accumulation were stimulated. As in mammalian macrophages, AcLDL receptor activity was not down-regulated by cholesterol loading. In contrast, AcLDL binding was poorly competed for by fucoidin or polyinosinic acid, and the magnitude of cholesteryl ester accumulation was only about one-half of that seen with mouse peritoneal macrophages. Pigeon beta-VLDL bound to both a high and a low affinity site on pigeon macrophages. Binding to the high affinity site was calcium-dependent, pronase-sensitive, and down-regulated by cholesterol loading. Cholesterol esterification and cholesteryl ester accumulation with beta-VLDL were stimulated to an equal or greater extent than with AcLDL. Unlike mammalian macrophages, the pigeon beta-VLDL receptor did not require apolipoprotein E, as evidenced by the lack of apoE in pigeon lipoproteins and by the failure of rabbit beta-VLDL, containing apoE, to compete for binding. Pigeon LDL, but not mammalian LDL, was recognized by the pigeon beta-VLDL receptor, suggesting that like the mammalian beta-VLDL receptor, the pigeon beta-VLDL receptor may be a form of an LDL receptor. This was an unexpected finding since pigeon fibroblasts and smooth muscle cells in culture do not express LDL receptors. Thus, pigeon macrophages have receptors for the uptake of abnormal lipoproteins that could play a role in the development of macrophage-derived foam cells that are prevalent in the early stages of atherosclerosis in this species. No quantitative or qualitative differences in these receptors, however, were identified that could account for the differences in atherosclerosis susceptibility between the WC and SR breeds.

Characterization of a genetic difference in the platelet aggregation response of two inbred mouse strains, C57BL/6 and C3H/He

An in vitro platelet aggregation assay has been used to characterize the platelet response of two inbred mouse strains, C57BL/6J and C3H/J. Arachidonic acid, ADP, ristocetin, and collagen, but not epinephrine, were effective inducers of platelet aggregation in C57BL/6 mice. In C3H mice, however, platelets responded differently to some, but not all, inducers of platelet aggregation. The difference between the two strains was particularly striking for arachidonic acid; at 0.375 μM arachidonic acid, platelets from C57BL/6 mice aggregated well, but platelets from C3H mice failed to aggregate. The two strains also differed in serotonin release from platelets. When the pool of platelet serotonin was labeled by incubating platelets with [ 14C]serotonin, the amount of label subsequently released from platelets in response to 0.375 μM arachidonic acid was 20.5% ± 2.5 SE for C57BL/6 mice and 1.5% ± 1.5 SE for C3H mice. The platelets from F 1 progeny of a cross between C57BL/6 and C3H mice were indistinguishable in aggregation response from the C57BL/6 parent. The defect in aggregation response found in C3H mice appears to reside in the platelets rather than in the plasma. Experiments which involved adding the plasma of one strain to the washed platelets of the other strain indicated that C57BL/6 platelets aggregated well whether they were resuspended in plasma from C57BL/6 or C3H mice, while C3H platelets failed to aggregate regardless of the origin of the plasma. Strain C57BL/6 is susceptible to diet-induced formation of atherosclerotic lesions, but strain C3H is resistant to lesion formation. This genetic difference in atherosclerosis susceptibility is not related to the genetic difference in platelet aggregation since a recombinant inbred strain, BXH-9, is susceptible to atherosclerosis like the C57BL/6 parent but has the reduced platelet aggregation response of the C3H parent.

Regional aortic differences in atherosclerosis susceptibility. Relationship to lipid concentration and prostaglandin biosynthesis.

In spontaneously atherosclerosis-susceptible White Carneau pigeons intimal cushions are noted consistently at the coeliac branch of aorta at birth. While these cushions do not progress into atherosclerotic lesions, the area across from the cushion (so called "lesion area") develop a classic atherosclerotic plaque by three years of age. In order to explain this regional aortic susceptibility to atherosclerosis, cholesterol and cholesteryl ester concentrations and prostaglandin biosynthesis in the two aortic regions were examined. It was found that the concentration of free and esterified cholesterol was higher in the intimal cushion area. Examination of the formation of various prostaglandins from C14-arachidonic acid indicates a striking increase in PGE2 synthesis in the lesion area with no difference in the formation of 6-keto PGF1 alpha (stable product of PGI2). These studies suggest that one of the earliest changes noted in the "lesion area" that differs from the intimal cushion is the enhanced formation of PGE2.

Regional aortic differences in atherosclerosis-susceptibility: changes in prostaglandin biosynthesis and cholesterol accumulation in response to desoxycorticosterone (DOCA)-salt induced hypertension.

In spontaneously atherosclerosis-susceptible White Carneau pigeons, intimal cushions that appear at birth near the coeliac branch of aorta do not progress into atherosclerotic lesions. However, the area across from the intimal cushion (so called 'lesion area') a) accumulates cholesteryl esters b) synthesizes more PGE2 and c) eventually develops into complicated atherosclerotic plaques. When DOCA-salt hypertension is induced in the pigeons, the 'initimal cushion' area displays a) accumulation of increasing amounts of cholesteryl esters and b) increase in the synthesis of all prostaglandins (particularly PGE2) from C14-arachidonic acid and c) approaches similarity to the 'lesion area' in the magnitude of these changes. These results suggest that under the influence of a risk factor, the 'intimal cushion' can acquire biochemical properties of the atherogenic areas of the aorta.