Published online before print May 17, 2007, doi: 10.1161/CIRCRESAHA.106.146183
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© 2007 American Heart Association, Inc.
Molecular Medicine |
Genetic Deletion of Pregnancy-Associated Plasma Protein-A Is Associated With Resistance to Atherosclerotic Lesion Development in Apolipoprotein E–Deficient Mice Challenged With a High-Fat Diet
From the Division of Division of Endocrinology, Metabolism, and Nutrition (A.C.H., C.A.C.) and the Division of Cardiovascular Diseases (R.D.S.), Mayo Clinic College of Medicine, Rochester, Minn.
Correspondence to Cheryl A. Conover, PhD, Mayo Clinic, 200 First Street SW, 5-194 Joseph, Rochester, MN 55905. E-mail Conover.Cheryl{at}Mayo.edu
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Abstract |
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Pregnancy-associated plasma protein–A (PAPP-A), a metalloproteinase in the insulin-like growth factor (IGF) system, is markedly upregulated in human atherosclerotic plaque. To determine whether PAPP-A plays an active role in the development of atherosclerosis, we crossed mice lacking apolipoprotein E (ApoE) with PAPP-A–deficient mice, generating ApoE knock-out (KO), PAPP-A KO, wild-type (WT/WT), and ApoE/PAPP-A double KO (KO/KO) mice. These mice were fed a high-fat diet starting at 7 weeks of age. Total serum cholesterol levels were elevated similarly in the ApoE KO and KO/KO mice and were 10-fold higher than in the WT/WT and PAPP-A KO mice. WT/WT and PAPP-A KO mice showed little or no lesion development even after 20 weeks of diet. ApoE KO mice had a progressive increase in aortic lesion area over 20 weeks of diet. In comparison, lesion area was reduced 60% to 80% in KO/KO mice. Lesions of ApoE KO aortas had 8- to 20-fold increases in PAPP-A, IGFBP-4, and IGF-I mRNA levels compared with nonlesional areas, whereas IGF-I receptor levels were equivalent—conditions for enhanced lesional IGF activity. Consistent with this, an in vivo marker of IGF-I receptor-mediated action was increased 10-fold in lesions from ApoE KO compared with KO/KO aortas. These data indicate that PAPP-A plays a critical role in lesion development in a mouse model of atherosclerosis, at least in part, through amplification of local IGF-I bioavailability.
Key Words: pregnancy-associated plasma protein-A • apolipoprotein E-deficient mice • atherosclerosis • insulin-like growth factor-I
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Introduction |
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Atherosclerosis, one of the major diseases of the Western world, is a complex inflammatory response to chronic injury that involves several cell types and associated cytokines, growth factors, and enzyme systems.1,2 The regulation of atherosclerotic lesion initiation and progression is unclear. Recently, pregnancy-associated plasma protein–A (PAPP-A), a newly recognized metalloproteinase in the insulin-like growth factor (IGF) system,3,4 has been implicated in the vascular repair process and as a marker of acute coronary syndromes.5–9 In vitro, PAPP-A has been shown to cleave inhibitory IGF binding protein-4 (IGFBP-4) thereby increasing local IGF bioavailability and receptor activation.10–12 It has been proposed that PAPP-A serves a similar function in the injury-repair response in vivo. PAPP-A expression was markedly upregulated in coronary artery lesions after vascular injury induced by balloon angioplasty in pigs.5 Furthermore, immunospecific PAPP-A was demonstrated in ruptured and eroded plaques from human arterial specimens, with the most intense staining associated with activated macrophages and smooth muscle cells.6,7 Thus, PAPP-A clearly is associated with vascular lesions, but does PAPP-A play an active role in the development of atherosclerosis and/or lesion progression or is it simply a marker of the injury response?
To address this question, we generated mice with targeted deletion of the PAPP-A gene13 and crossed them with apolipoprotein (ApoE)-deficient mice. The atherosclerotic lesions in these ApoE knock-out mice have been well characterized and resemble human lesions in their sites of predilection and progression from fatty streaks of lipid-laden macrophages to the fibroproliferative stage.14–17 These lesions principally occur at the aortic root, lesser curvature of the arch, and at principal branch points of the aorta. At an advanced stage, the lesions containing macrophages and smooth muscle cells have thick fibrous caps and necrotic lipid cores. These lesions are exacerbated when the mice are fed a high-fat Western-style diet.14–16 Thus, ApoE knock-out mice cross-bred with PAPP-A knock-out mice allow in vivo testing of the hypothesis that PAPP-A is directly involved in the development of atherosclerosis.
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Materials and Methods |
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Mice
Mice that carry a targeted mutation in the PAPP-A gene on a mixed C57Bl6/129 background have been characterized previously.13 ApoE knock-out (KO) mice on a C57Bl6 background were purchased from The Jackson Laboratory (Bar Harbor, Me). These studies were approved by Mayo’s Institutional Animal Care and Use Committee.
PAPP-A KO mice, both male and female, are 60% to 70% the size of wild-type and heterozygous littermates.13,18 Therefore, in initial crosses, ApoE KO females (normal size) were crossed with PAPP-A KO males (small size) to facilitate pup-bearing for the female. Offspring heterozygous for both genes (normal size) were then crossed to produce double homozygous wild-type (WT/WT), double homozygous KO (KO/KO), and single KO (PAPP-A KO, ApoE KO) mice. Western-style diet (21% by weight [42% of calories] fat and 0.15% by weight cholesterol [Harlan Tekland]) was started at 7 weeks of age.
Genotyping
PAPP-A mutations were detected by PCR using a common forward primer, 5'-taagcaggggtgggtcctt-3', and PAPP-A (5'-cactcctcagctctggctttca-3') and Neo (5'-tcgccttctatcgccttcttg-3') reverse primers. The ApoE genotype was determined by PCR screening using The Jackson Laboratory protocol (http://jaxmice.jax.org).
Lesion Analysis
Mice were anesthetized and blood was collected from the retro-orbital plexus for measurement of total serum cholesterol. The heart and aorta were perfused with 20 mL phosphate buffered saline containing 20 mmol/L BHT and 2 mmol/L EDTA at the rate of 1 mL per minute. After perfusion, the aorta was dissected to the iliac bifurcation, fat and connective tissue were removed, and the heart and aortic arch were separated from the aorta. The remaining aorta was opened longitudinally and pinned in place on black wax for en face lesion analysis. Lipid rich lesions were stained with Sudan IV, as described.19 Images were captured using a Nikon SMZ80 dissecting scope, a Nikon DMX200F Camera, and Nikon Act-1 software v2.62 (Nikon USA, Melville, NY). Image analysis was performed using Adobe Photoshop software v6.0.1 (Adobe Systems Incorporated). Lesion area was calculated for each animal as a percent of total aortic area, and lesion number was expressed in terms of plaques per 50 mm2 of aortic area.
Histology and Immunohistochemistry
Serial 5-µm sections were cut distally from the aortic root. After staining in hematoxylin for 5 minutes, sections were washed in tap water and destained in 1% acid ethanol. After washing with tap water, sections were stained with eosin for 5 minutes, rinsed in tap water, dehydrated in 100% ethanol, cleared, and mounted. Necrotic core regions were defined as acellular areas of lesions lacking nuclei and cytoplasm.20 Cholesterol clefts are needle-like spaces caused by the dissolving out of cholesterol crystals.
Polarization microscopy was used to detect interstitial collagen. Collagen types I and III are identified by birefringence under polarized light illumination.21 Sections were rinsed with distilled water and incubated with 0.1% Sirius red in saturated picric acid for 60 minutes. Sections were rinsed 2 times with 0.01N HCl and then immersed in distilled water. Sections were dehydrated in 2 changes of 100% ethanol, cleared, and mounted. Sections were photographed under polarized light using identical exposure settings for all sections. Birefringence was measured for each lesion and reported as a percent of total lesion area.
A minimum of 4 5-µm sections were stained for macrophages (Mac-3 or Rat IgG1 isotype control, BD Pharmingen, San Diego, Calif) and smooth muscle actin (SMA [Spring Bioscience, Fremont, Calif] or normal rabbit serum [Jackson ImmunoResearch Labs, West Grove, Pa].) Sections were rehydrated, and 10 mmol/L sodium citrate with 0.05% Tween 20 pH 6.0 was used for heat-induced epitope retrieval. Sections were washed with phosphate buffered saline (PBS), and endogenous peroxidase was blocked with 3% H2O2 in PBS before the addition of serum-free protein block (Dako Cytomation). Primary and control antibodies were diluted to 50 µg/mL for Mac-3 and 10 µg/mL for SMA in antibody diluent (Dako Cytomation), added to the sections, and incubated overnight at 4°C. Sections were then incubated with either a 1:200 dilution of polyclonal biotinylated anti-rat for Mac-3 staining (Dako Cytomation) or a 1:100 peroxidase goat anti-rabbit for SMA (Jackson ImmunoResearch Labs). ExtraAvidin-peroxidase (Sigma) was diluted 1:50 and added to Mac-3 stained sections. Staining was visualized by the addition of liquid DAB+ substrate (Dako Cytomation) for 10 minutes. Images were captured with a Microphot-FXA microscope, DXM1200F digital camera, and Act-1 software v2.62. Images were analyzed using Photoshop software v 6.0.1 (Adobe Systems Inc.).
RNA Isolation and Quantitative PCR
Aortas were removed and immediately placed in RNAlater (Ambion). After 24 hours at 4°C each artery was cleaned of fat and the medial-intimal layers separated from the adventitia. Lesions were excised from the medial-intimal layer of each artery. Lesion and nonlesion RNA were isolated in parallel using the RNase mini kit (Qiagen) following the isolation protocol for heart, muscle, and skin tissue. For comparing ApoEKO and KO/KO, RNA from the aortic arch was isolated similarly. One µg of RNA from each sample was reverse-transcribed with Taqman reverse-transcription reagents, random hexamers, and Multiscribe reverse transcriptase (Applied Biosystems). Quantitative PCR reactions were conducted using the primer sequences (see supplemental Table I, available online at http://circres.ahajournals.org) and the iCycler iQ Detection System. Amplification plots were analyzed with iCycler iQ Detection System analysis software v3.0.6070 (Bio-Rad). Gene expression was normalized to ribosomal protein L19 as an internal control.
Statistical Analyses
ANOVA and post hoc t tests were used for comparison of multiple groups. Results are presented as mean±SEM. Data that were not normally distributed (necrotic core and cholesterol cleft area) were analyzed with the Mann–Whitney test, and median and range values are presented. Significance was set at P<0.05.
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Diet
All 4 genotypes of mice generated from heterozygous matings (designated WT/WT, ApoE KO, PAPP-A KO, KO/KO) gained weight on the high-fat diet, although the small size consequence of the PAPP-A gene knockout was maintained on the ApoE-null background (Table 1). Furthermore, total serum cholesterol levels (n=7 to 12 per group) were elevated similarly in the ApoE KO and KO/KO mice on the high fat diet (1312±93 mg/dL and 1403±176 mg/dL) and were 10 times higher than cholesterol levels in WT/WT and PAPP-A KO mice (146±9 mg/dL and 146±13 mg/dL). Triglyceride levels were also elevated in ApoE KO and KO/KO mice (288±38 mg/dL and 261±18 mg/dL) compared with WT/WT and PAPP-A KO mice (80±3 mg/dL and 85±6 mg/dL). Thus, there was no evidence of differential food consumption among the four groups.
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Lesion Analysis
Lesions in the descending aorta to the iliac bifurcation were stained with Sudan IV and evaluated for lesion area and number in the 4 mouse genotypes after 5, 10, and 20 weeks on the high fat diet. WT/WT and PAPP-A KO mice showed little or no lesion development even after 20 weeks of a high fat diet (data not shown). An example of the en face staining of ApoE KO and KO/KO aortas is shown in Figure 1. As summarized in Figure 2A, both male and female ApoE KO mice had a progressive increase in lesion area with weeks on diet, resulting in massive fatty lesions especially around branch points of vessels. Lesion area was markedly reduced in the KO/KO mice (Figures 1 and 2
A). In female KO/KO mice, there was a 72% reduction in lesion area at 10 weeks (P=0.0001) and at 20 weeks (P=0.011). Although there was a 52% reduction at 5 weeks, this difference was not statistically significant. In males, there was a 42% reduction in lesion area at 5 weeks (P=0.25), an 80% reduction at 10 weeks (P=0.009), and a 58% reduction at 20 weeks (P=0.039). There was no significant difference in lesion number between ApoE KO and KO/KO mice, except in the female mice at 10 weeks of diet (Figure 2B).
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Lesion Histology
Sections of the ascending aorta from ApoE KO and KO/KO mice were examined histologically for general structure and collagen content and immunochemically for macrophage and smooth muscle actin staining. Representative images are presented in Figures 3 and 4, and quantitative results summarized in Table 2. Macrophage staining as a percent of plaque area was significantly greater (1.8-fold) in KO/KO compared with ApoE KO aortas, although the absolute amount of macrophage staining in the lesions did not differ. In addition, there were no significant differences in expression of macrophage-derived proinflammatory cytokines, interleukin-1ß (IL-1ß) and tumor necrosis factor-
(TNF-). Ratios of mRNA expression in KO/KO:ApoE KO were 1.02 for TNF- and 1.54 for IL-1ß. The percentages of smooth muscle actin–staining cells and collagen content among plaques were not significantly different between the 2 groups. Large lipid areas were more apparent in the ApoE KO compared with KO/KO lesions. Many KO/KO lesions appeared to be essentially fatty streaks containing lipid-laden foam cells (Figure 3) rather than the more complex lesions of ApoE KO mice (Figure 4), which showed deep medial involvement and significantly greater necrotic cores area. Cholesterol cleft area also appeared to be greater in lesions of ApoE KO mice, but there was considerable variability and differences were not statistically significant (Table 2, supplemental Figure I).
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Expression of PAPP-A and IGF System Components
PAPP-A increases the IGF available to interact with receptor in vitro through its ability to proteolyze inhibitory IGFBP-4.3,10–12 In this study, we analyzed levels of PAPP-A, IGF-I, IGFBP-4, and IGF-I receptor mRNA in aortic tissue of ApoE KO mice, separating lesion and nonlesional areas. The results are presented in Figure 5. PAPP-A mRNA was expressed at 20-fold higher levels in lesional areas compared with nonlesional areas of ApoE KO aorta. Interesting, IGF-I and IGFBP-4 mRNA levels were also elevated (20- and 8-fold, respectively) in lesional compared with nonlesional areas, whereas IGF-I receptor mRNA levels were similar in the 2 groups. Thus, it appears that PAPP-A, IGF-I, and IGFBP-4 are coordinately upregulated in atherosclerotic lesions, which in the proposed model would promote IGF-I bioavailability in these focal areas. One approach to assess bioactivity of IGF in vivo is to assay for expression of IGF-I-responsive genes. IGF-I has been shown to increase IGFBP-5 expression in vitro and in vivo.24–27 Thus, increased IGFBP-5 mRNA abundance has been used to indicate increased IGF-I signaling through the IGF-I receptor. IGFBP-5 mRNA was 10-fold elevated in aortas of ApoE KO mice compared with KO/KO mice (Figure 6).
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Discussion |
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This study (1) establishes an active role for PAPP-A in the development of atherosclerosis, (2) presents in vivo evidence that PAPP-A functions through regulation of local IGF-I bioavailability, and (3) provides rationale for exploring novel strategies aimed at PAPP-A, a relatively accessible extracellular enzyme, to control atherosclerosis.
PAPP-A is highly expressed in atherosclerotic plaque and is a proposed new marker of acute coronary syndromes.6–9 However, there remained the question of whether lesional PAPP-A was a potential therapeutic target, ie, was increased PAPP-A part of a compensatory mechanism attempting to limit lesion development or was it fundamentally proatherogenic? The results of this study are unequivocal in that loss of PAPP-A resulted in a favorable outcome in an animal model of atherosclerosis. Thus, in the absence of PAPP-A, mice on the ApoE-null background had a 70% to 80% reduction in lesion area after 10 weeks on a high fat diet compared with ApoE KO mice with wild-type PAPP-A gene expression. This is in spite of similarly elevated cholesterol and triglyceride levels in the 2 groups of mice. There was some lesion development between 10 and 20 weeks of high fat diet in the KO/KO mice, but lesional area was still significantly reduced by 60% to 70% in the aortas of these mice compared with ApoE KO mice. Major differences in lesion number between ApoE KO and KO/KO mice were not apparent. We can conclude from these results that loss of PAPP-A has a predominant effect on lesion progression rather than lesion initiation, and that the effects of PAPP-A are moderating rather than absolute. The latter fits with the emerging notion of PAPP-A as a modulator of IGF action (discussed below) rather than as an essential growth factor itself.
The histopathology of lesions in sections of the ascending aorta, qualitatively similar in ApoE KO and KO/KO mice, was also consistent with the notion that PAPP-A is involved in lesion progression. ApoE KO lesions exhibited features of advanced fibroproliferative plaques with medial extensions and large lipid pools, including necrotic cores. On the other hand, many of the lesions in KO/KO aorta, even after 20 weeks on a high fast diet, resembled early stage fatty lesions predominantly composed of lipid-enriched macrophages.
Macrophages have been demonstrated to be important in lesion development in large part through secretion of proinflammatory proatherogenic cytokines such as TNF- and IL-1ß. Thus, ApoE KO mice also deficient in TNF- show a 50% decrease in lesion size by 10 weeks on a high fat diet.28 TNF- and IL-1ß are potent stimulators of PAPP-A gene expression in coronary artery smooth muscle cells.29 Thus, we speculate that upregulation of PAPP-A in vascular cells by macrophage-derived cytokines is an important component of lesion development, and, in the absence of this target gene, lesion development is blunted in spite of the continued presence of macrophages and similar levels of TNF- and IL-1ß expression in aortas from KO/KO and ApoE KO mice. Indeed, the percentage of lesion staining for macrophages was higher in KO/KO compared with ApoE KO mice, whereas the absolute area of macrophage staining was approximately the same in the 2 groups. Thus, there appears to be no effect of PAPP-A on macrophage recruitment and the early phase of lesion development. Importantly, PAPP-A is not expressed by macrophages, but PAPP-A surface-associates with macrophages and retains proteolytic activity.30
The exact means by which PAPP-A promotes and, therefore loss of PAPP-A limits, atherogenesis is unclear. However, our findings support PAPP-A regulation of local IGF bioactivity through IGFBP-4 proteolysis as a major mechanism. IGF-I, IGFBP-4, and PAPP-A are significantly upregulated in lesional areas compared with nonlesional areas of ApoE KO aortas, whereas there is no difference in IGF-I receptor expression in the 2 areas. A plausible model for these findings is that increases in both IGF-I and IGFBP-4 create a pericellular reservoir of bound and thus "unavailable" IGF-I that is released for receptor activation on PAPP-A–induced cleavage of IGFBP-4. It has been difficult to assess bioavailability of IGF in vivo, and confirmation of IGF-I receptor activation, such as phosphorylation status, is not feasible in these in vivo studies in mice because of the amount of tissue that would be needed. However, recent studies using expression of the IGF-I–responsive gene, IGFBP-5, as an in vivo marker of IGF-I receptor–mediated activity have been informative.22–27 We found that IGFBP-5 mRNA abundance was 10-fold elevated in lesions from ApoE KO mice compared with KO/KO mice, consistent with increased IGF-I bioavailability as has been demonstrated in cell culture studies.31 It is of note that IGFBP-5 has been reported to be a substrate for PAPP-A in vitro.32 However, possible significance of IGFBP-5 proteolysis in vivo is currently unknown, and there are several IGFBP-5 proteases besides PAPP-A. PAPP-A appears to be the only physiological IGFBP-4 protease.11,13
Local regulation of IGF-I bioavailability is important because IGF-I can stimulate several of the processes leading to lesion progression including vascular smooth muscle cell proliferation, migration, and collagen production, and macrophage chemotaxis, phagocytosis of lipoprotein, and release of inflammatory cytokines (reviewed in 33,34). Zaina et al35 showed that ApoE KO mice developed significantly smaller lesions when IGF-II was also deleted. Direct evidence for a role of paracrine expression of IGF in smooth muscle cell growth was shown in transgenic mice selectively overexpressing IGF-I in smooth muscle by means of a mouse smooth muscle-actin promoter.36 Overexpression of the IGF-I transgene was associated with smooth muscle cell hyperplasia in these mice. Thus, reduction of local IGF bioavailability through loss of PAPP-A–induced IGFBP proteolysis could serve to block the ability of smooth muscle cells to proliferate and synthesize collagen in response to IGF-I. This would be consistent with previous findings that the targeted deletion of the PAPP-A gene reduced neointimal lesion formation after carotid ligation, mainly because of the attenuation of smooth muscle cell migration and proliferation through decreases in local IGF bioavailability.27 However, we did not see reduction in smooth muscle actin staining or collagen content in KO/KO lesions in this study. This could be because of the stage of the lesions in the two groups of mice and deserves further study. Effects of reduction of IGF-I signaling through inhibition of PAPP-A on activated macrophages remains to be determined, but a blunting of IGF-I–stimulated lipoprotein uptake37 would be consistent with the observed phenotype of the KO/KO lesions.
In conclusion, these findings implicate PAPP-A in promoting lesion progression through regulation of local IGF action, and suggest PAPP-A as a potential therapeutic target for atherosclerosis.
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Acknowledgments |
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Sources of Funding
This work was supported by NIH Grant HL74871.
Disclosures
None.
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Footnotes |
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Original received December 7, 2006; revision received April 30, 2007; accepted May 3, 2007.
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References |
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1. Ross R. Atherosclerosis: an inflammatory disease. N Engl J Med. 1999; 340: 115–126.
2. Glass CK, Witztum JL. Atherosclerosis: the road ahead. Cell. 2001; 104: 503–516.[CrossRef][Medline] [Order article via Infotrieve]
3. Lawrence JB, Oxvig C, Overgaard MT, Sottrup-Jensen L, Gleich GJ, Hays LG, Yates JR III, Conover CA. The insulin-like growth factor (IGF)-dependent IGF binding protein-4 protease secreted by human fibroblasts is pregnancy-associated plasma protein-A. Proc Natl Acad Sci U S A. 1999; 96: 3149–3153.
4. Boldt HB, Overgaard MT, Laursen LS, Weyer K, Sottrup-Jensen L, Oxvig C. Mutational analysis of the proteolytic domain of pregnancy-associated plasma protein-A (PAPP-A): classification as a metzincin. Biochem J. 2001; 358: 359–367.[CrossRef][Medline] [Order article via Infotrieve]
5. Bayes-Genis A, Schwartz RS, Lewis DA, Overgaard MT, Christiansen M, Oxvig C, Ashai K, Holmes DR Jr., Conover CA. Insulin-like growth factor binding protein-4 protease produced by smooth muscle cells increases in the coronary artery after angioplasty. Arterioscler Thromb Vasc Biol. 2001; 21: 335–341.
6. Bayes-Genis A, Conover CA, Overgaard MT, Bailey KR, Christiansen M, Holmes DR Jr., Virmani R, Oxvig C, Schwartz RS. Pregnancy-associated plasma protein A as a marker of acute coronary syndromes. N Engl J Med. 2001; 345: 1022–1029.
7. Sangiorgi G, Mauriello A, Bonanno E, Oxvig C, Conover CA, Christiansen M, Trimarchi S, Rampoldi V, Holmes DR Jr, Schwartz RS, Spagnoli LG. Pregnancy-associated plasma protein-A is markedly expressed by monocyte-macrophage cells in vulnerable and ruptured carotid atherosclerotic plaques: A link between inflammation and cerebrovascular events. J Am Coll Cardiol. 2006; 47: 2201–2211.
8. Lund J, Qin Q-P, Ilva T, Pettersson K, Voipio-Pulkki L-M, Porela P, Pulkki K. Circulating pregnancy-associated plasma protein A predicts outcome in patients with acute coronary syndrome but no troponin I elevation. Circulation. 2003; 108: 1924–1926.
9. Heeschen C, Dimmeler S, Hamm CW, Fichtlscherer S, Simoons ML, Zeiher AM, CAPTIRE Study Investigators. Pregnancy-associated plasma protein-A levels in patients with acute coronary syndromes: comparison with markers of systemic inflammation, platelet activation, and myocardial necrosis. J Am Coll Cardiol. 2005; 45: 229–237.
10. Ortiz CO, Chen B-K, Bale LK, Overgaard MT, Oxvig C, Conover CA. Transforming growth factor-ß regulation of the insulin-like growth factor binding protein-4 protease system in cultured human osteoblasts. J Bone Miner Res. 2003; 18: 1066–1072.[CrossRef][Medline] [Order article via Infotrieve]
11. Byun D, Mohan S, Yoo M, Sexton C, Baylink DJ, Qin X. Pregnancy-associated plasma protein-A accounts for the insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) proteolytic activity in human pregnancy serum and enhances the mitogenic activity of IGF by degrading IGFBP-4 in vitro. J Clin Endocrinol Metab. 2001; 86: 847–854.
12. Jia D, Heersche JNM. Pregnancy-associated plasma protein-A proteolytic activity in rat vertebral cell cultures: stimulation by dexamethasone: a potential mechanism for glucocorticoid regulation of osteoprogenitor proliferation and differentiation. J Cell Physiol. 2003; 204: 848–858.
13. Conover CA, Bale LK, Overgaard MT, Johnstone EW, Laursen UH, Fuchtbauer E-M, Oxvig C, van Deursen J. Metalloproteinase pregnancy-associated plasma protein A is a critical growth regulatory factor during fetal development. Development. 2003; 131: 1187–1194.[CrossRef]
14. Smith JD, Breslow JL. The emergence of mouse models of atherosclerosis and their relevance to clinical research. J Intern Med. 1997; 242: 99–109.[CrossRef][Medline] [Order article via Infotrieve]
15. Nakashima Y, Plump AS, Raines EW, Breslow JL, Ross R. ApoE-deficient mice develop lesions of all phases of atherosclerosis throughout the arterial tree. Arterioscler Thromb. 1994; 14: 133–140.
16. Plump AS, Smith JD, Hayek T, Aalto-Setala K, Walsh A, Verstuyft JG, Rubin EM, Breslow JL. Severe hypercholesterolemia and atherosclerosis in apolipoprotein E-deficient mice created by homologous recombination in ES cells. Cell. 1992; 71: 343–353.[CrossRef][Medline] [Order article via Infotrieve]
17. Reddick RL, Zhang SH, Maeda N. Atherosclerosis in mice lacking Apo E: evaluation of lesional development and progression. Atheroscler Thromb. 1994; 14: 141–147.
18. Bale LK, Conover CA. Disruption of insulin-like growth factor-II imprinting during embryonic development rescues the dwarf phenotype of mice null for pregnancy-associated plasma protein-A. J Endocrinol. 2005; 186: 325–331.
19. Tangirala RK, Rubin EM, Palinski W. Quantitation of atherosclerosis in murine models: correlation between lesions in the aortic origin and in the entire aorta, and differences in the extent of lesions between sexes in LDL receptor-deficient and apolipoprotein E-deficient mice. J Lipid Res. 1995; 36: 2320–2328.[Abstract]
20. Han S, Liang CP, DeVries-Seimon T, Ranallatta M, Welch CL, Collins-Fletcher K, Accili D, Tabas I, Tall AR. Cell Metab. 2006; 3: 257–266.[CrossRef][Medline] [Order article via Infotrieve]
21. Whittaker P, Kloner RA, Boughner DR, Pickering JG. Quantitative assessment of myocardial collagen with picrosirus red staining and circularly polarized light. Basic Res Cardiol. 1994; 89: 397–410.[CrossRef][Medline] [Order article via Infotrieve]
22. Conover CA, Clarkson JT, Bale LK. Effect of glucocorticoid on insulin-like growth factor (IGF) regulation of IGF-binding protein expression in fibroblasts. Endocrinology. 1995; 136: 1403–1410.[Abstract]
23. Duan C, Hawes SB, Prevette T, Clemmons DR. Insulin-like growth factor-I (IGF-I) regulates IGF-binding protein-5 synthesis through transcriptional activation of the gene in aortic smooth muscle cells. J Biol Chem. 1996; 271: 4280–4288.
24. Nichols TC, du Laney T, Zheng B, Bellinger DA, Nickols GA, Engleman W, Clemmons DR. Reduction in atherosclerotic lesion size in pigs by Vß3 inhibitors is associated with inhibition of insulin-like growth factor-I-mediated signaling. Circ Res. 1999; 85: 1040–1045.
25. Adamo ML, Ma X, Ackert-Bicknell CL, Donahue LR, Beamer WG, Rosen CJ. Genetic increase in serum insulin-like growth factor-I (IGF-I) in C3H/HeJ compared with C57BL/6J mice is associated with increased transcription from the IGF-I exon 2 promoter. Endocrinology. 2006; 147: 2944–2955.
26. Ye P, D’Ercole J. Insulin-like growth factor I (IGF-I) regulates IGF binding protein-5 gene expression in the brain. Endocrinology. 1998; 139: 65–71.
27. Resch ZT, Simari RD, Conover CA. Targeted disruption of the PAPP-A gene is associated with diminished smooth muscle cell response to insulin-like growth factor-I and resistance to neointimal hyperplasia following vascular injury. Endocrinology. 2006; 147: 5634–5640.
28. Branen L, Hovgaard L, Nitulescu M, Bengtsson E, Nilsson J, Jovinge S. Inhibition of tumor necrosis factor- reduces atherosclerosis in apolipoprotein E knockout mice. Arterioscler Thromb Vasc Biol. 2004; 24: 2137–2142.
29. Conover CA, Bale LK, Harrington SC, Resch ZT, Overgaard MT, Oxvig C. Cytokine stimulation of pregnancy associated plasma protein-A expression in human coronary artery smooth muscle cells: inhibition by resveratrol. Am J Physiol. 2006; 290: C183–C188.
30. Conover CA, Harrington SC, Bale LK, Oxvig C. Surface association of pregnancy associated plasma protein-A accounts for its co-localization with activated macrophages. Am J Physiol (Heart Circ Physiol). 2007; 292: H994–H1000,2007.
31. Duan C, Liimatta MB, Bottum OL. Insulin-like growth factor (IGF)-I regulates IGF-binding protein-5 gene expression through the phosphatidylinositol 3-kinase, protein kinase B/Akt, and p70 S6 kinase signaling pathway. J Biol Chem. 1999; 274: 37147–37153.
32. Laursen LS, Overgaard MT, Soe R, Boldt HB, Sottrup-Jensen L, Giudice LC, Conover CA, Oxvig C. Pregnancy-associated plasma protein-A (PAPP-A) cleaves insulin-like growth factor binding protein (IGFBP)-5 independent of IGF: implications for the mechanism of IGFBP-4 proteolysis by PAPP-A. FEBS Lett. 2001; 504: 36–40.[CrossRef][Medline] [Order article via Infotrieve]
33. Bayes-Genis A, Conover CA, Schwartz RS. The insulin-like growth factor axis: a review of atherosclerosis and restenosis. Circ Res. 2000; 86: 125–130.
34. Delafontaine P, Song YH, Li Y. Expression, regulation, and function of IGF-1, IGF-1R, and IGF-1 binding proteins in blood vessels. Arterioscler Thromb Vasc Biol. 2004; 24: 435–444.
35. Zaina S, Pettersson L, Ahren B, Branen L, Hasan AB, Lindholm M, Mattsson R, Thyberg J, Nilsson J. Insulin-like growth factor II plays a central role in atherosclerosis in a mouse model. J Biol Chem. 2002; 277: 4505–4511.
36. Wang J, Niu W, Nikiforov Y, Naito S, Chernausek S, Witte D, LeRoith D, Stauch A, Fagin JA. Targeted overexpression of IGF-I evokes distinct patterns of organ remodeling in smooth muscle cell tissue beds of transgenic mice. J Clin Invest. 1997; 100: 1425–1439.[Medline] [Order article via Infotrieve]
37. Hochberg Z, Hertz P, Maor G, Oiknine J, Aviram M. Growth hormone and insulin-like growth factor-I increase macrophage uptake and degradation of low density lipoprotein. Endocrinology. 1992; 131: 430–435.
38. Moreno PR, Lodder RA, Purushothaman KR, Charash WE, O’Connor WN, Muller JE. Detection of lipid pool, thin fibrous cap, and inflammatory cells in human aortic atherosclerotic plaques by near-infrared spectroscopy. Circulation. 2002; 105: 923–927.
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