Atherosclerosis and Lipoproteins |
From the Wistar Institute and The Ludwig Institute for Cancer Research, Philadelphia, Pa; and the Department of Medicine and the Graduate Group in Immunology, University of Pennsylvania School of Medicine, Philadelphia.
Correspondence to Ellen Puré, PhD, The Wistar Institute, 3601 Spruce St, Philadelphia, PA 19104. E-mail pure{at}wistar.org
| Abstract |
|---|
|
|
|---|
Methods and Results We demonstrate that CD44 is upregulated and functionally activated in aortic arch in the atherogenic environment of apoE/ mice relative to wild-type (C57BL/6) controls. Moreover, CD44 activation even in apoE/ mice is selective to lesion-prone regions because neither the thoracic aorta from apoE/ mice nor the aortic arch of C57BL/6 mice exhibited upregulation of CD44 compared with thoracic aorta of CD57BL/6 mice. Consistent with these observations, gene expression profiling using cDNA microarrays and quantitative polymerase chain reaction revealed that
155 of 19 200 genes analyzed were differentially regulated in the aortic arch, but not in the thoracic aorta, in apoE/ CD44/ mice compared with apoE/ CD44+/+ mice. However, these genes were not regulated by CD44 in the context of a C57BL/6 background, illustrating the selective impact of CD44 on gene expression in a proatherogenic environment. The patterns of differential gene expression implicate CD44 in focal adhesion formation, extracellular matrix deposition, and angiogenesis, processes critical to atherosclerosis.
Conclusions CD44 is an early mediator of atherogenesis by virtue of its ability to regulate vascular gene expression in response to a proatherogenic environment.
We demonstrate that CD44 is selectively upregulated and functionally activated in lesion-prone aortic arch of apoE/ mice before lesion development. Furthermore, gene expression profiling revealed a selective impact of CD44 on vascular gene expression in response to a proatherogenic environment illustrating that CD44 is an early mediator of atherogenesis.
Key Words: CD44 apoE gene expression vascular hyaluronan atherosclerosis
| Introduction |
|---|
|
|
|---|
CD44 is a widely expressed cellular adhesion molecule that serves as a principal receptor for extracellular matrix (ECM) components such as hyaluronan (HA), which accumulates in atherosclerotic lesions.4,5 CD44 was demonstrated to play a role in cellular growth, activation, and migration, mediates signal transduction, and regulates gene expression.6 CD44 promotes adhesion of leukocytes to ECs,7,8 induces the release of inflammatory mediators from macrophages, and regulates the proliferation and migration of VSMCs.9,10
We demonstrated that CD44-deficient apolipoprotein E (apoE)null mice developed markedly reduced atherosclerosis compared with CD44 wild-type apoE-null littermates.11 Data presented in that study, together with previous reports, indicated that CD44 promotes atherosclerosis by mediating inflammatory cell recruitment and the activation of leukocytes and VSMCs.8,12
To identify vascular genes regulated by CD44 that may predispose the vessel wall to development of atherosclerosis, we compared the global gene expression profile between CD44 wild-type and CD44-null apoE-deficient (apoE/) mice before the development of lesion in regions of aorta that are susceptible to the development of atherosclerosis to varying degrees (arch >abdominal >thoracic). We identified genes that were selectively regulated by CD44 in aortic arch but not in thoracic aorta of apoE/ mice. Genes identified by this global approach indicated that CD44 may promote atherogenesis by regulating focal adhesion formation, ECM deposition, and angiogenesis. In contrast, the majority of these genes were not regulated by CD44 in the aortic arch of C57BL/6 mice. We conclude that CD44 contributes to atherogenesis in part by modulating vascular gene expression in response to a proatherogenic environment.
| Materials and Methods |
|---|
|
|
|---|
| Results |
|---|
|
|
|---|
2-fold when compared with the aortic arch from C57BL/6 mice and compared with thoracic and abdominal aorta from apoE/ and C57BL/6 mice, which were comparable to each other (Figure 1A). These results were confirmed by immunoblotting with KM81 antibody, which recognizes all isoforms of CD44. Furthermore, immunoblotting indicated that the
85-kDa standard form of CD44 is the predominant isoform of CD44 expressed in all regions of aorta from apoE/ and C57BL/6 mice at this age (Figure 1B, top).
|
To determine whether the receptor was functionally activated, CD44 from aortic tissue was analyzed using a functional HA binding assay as described.15 HA binding to a single
85-kDa species that comigrated with the standard form of CD44 was markedly upregulated in CD44 immune complexes isolated from aortic arch of apoE/ mice compared with aortic arch of C57BL/6 and thoracic and abdominal aorta from apoE/ and C57BL/6 mice (Figure 1B, bottom). HA binding was shown to be specific to CD44 by inhibition of binding in the presence of a blocking antibody (KM81) against the HA binding site of the receptor (data not shown). The extent of the increase in HA binding,
6-fold (Figure 1C), cannot be explained simply by the increase in expression of CD44 (
2-fold), indicating that CD44 was functionally activated.
CD44-Dependent Regulation of Vascular Gene Expression in ApoE/ Mice
To investigate the mechanisms by which vascular CD44 impacts atherogenesis, we compared the gene expression profiles in aortic arch and thoracic aorta isolated from CD44-null and CD44-wild type apoE/ mice. To focus on the role of vascular CD44 in the absence of potentially confounding contributions from infiltrating inflammatory cells, gene expression analysis was performed on RNA isolated from aortic tissue of 10-week-old mice before lesion formation. The lack of lesion was confirmed by en face analysis of aorta from age- and sex-matched apoE/ mice (data not shown).
Furthermore, we did not detect expression of RNA of hematopoietic lineage-specific markers in the aortic tissues used in the microarray analysis nor by qPCR for CD68 as a marker for macrophages or CD3 for T cells. On the other hand, qPCR analysis of VSMC- and EC-specific genes,
-smooth muscle cell actin, and CD31 (platelet endothelial cell adhesion molecule [PECAM]-1), respectively, indicated that the expression analysis reflected EC and VSMC transcripts (supplemental Figure I, available online at http://atvb.ahajournals.org). Thus, it can be concluded that the differential gene expression we describe largely reflects CD44-dependent regulation in vascular cells such as VSMCs or ECs.
In view of the gender bias in atherosclerosis, the data from male and female mice were analyzed separately. However, we focused our analysis on genes that were differentially regulated by CD44 in a gender-independent fashion. Based on these criteria, 207 genes were identified by microarray analysis as regulated by CD44 in aortic arch of apoE/ CD44/ mice relative to apoE/ CD44+/+ mice (supplemental Table I) including ECM proteins, adhesion receptors, intracellular signaling molecules, and transcription factors.
qPCR Validation of Differentially Expressed Genes
qPCR was performed for a randomly selected subset of the genes identified in the microarray analysis as differentially regulated in the aortic arch of apoE/ CD44/ mice compared with apoE/ CD44+/+ mice. Of a total of 65 genes analyzed by qPCR, 49 genes was confirmed (Table). This represents a validation rate of 75% of the genes tested. Based on this validation rate, without taking into account genes not represented on our arrays or the potential for false negatives in the array analysis, we predict that
155 genes are regulated by CD44 in the aortic arch of apoE/ mice independent of gender. Interestingly, another HA receptor, HA-mediated motility receptor, which was not in the gene list of the array, also was upregulated in aortic arch of apoE/ CD44/ mice as validated by qPCR (Table), indicating a compensatory role of HA-mediated motility receptor for CD44-deficiency.
|
We also performed gene ontology analysis using IPA tool. Six networks and 9 functions were identified that are associated with the differentially expressed genes and that are also associated with processes involve in atherosclerosis, including cellular assembly and organization, cell-cell interaction and signaling, and cellular movement. The details of the analysis results were shown in online supplements.
Protein Level Validation of Differentially Expressed Genes
Of the differentially expressed genes validated by qPCR, several were also analyzed at the protein level by immunoblotting (Figure 2A and 2B) and immunohistochemistry (Figure 2C). Differential protein expression was observed for the majority of cases tested, including Hsp90, Actb, and Zyxin, for example. We were particularly interested in the impact of CD44 on the expression of the antiangiogenic factor endostatin because its precursor protein, collagen XVIII, was one of the genes most affected at the RNA level and was implicated recently in atherogenesis.16,17 We found that endostatin was indeed elevated in aortic arch of apoE/ CD44/ mice compared with apoE/ CD44+/+ mice.
|
Immunohistochemistry showed comparably high levels of Actb in ECs, whereas VSMCs in the tunica media had enriched levels of Actb in apoE/ CD44/ mice. Hsp90 and Zyxin appeared to be upregulated in the aortic arch of apoE/ CD44/ mice in ECs and VSMCs. We also noted a marked increase in the intensity of nuclear staining of Zyxin and Hsp90 in the aortae of apoE/ CD44/ mice, suggesting that CD44 may regulate their subcellular localization and thereby their functions.
CD44-Dependent Regulation of Vascular Gene Expression Is Associated With the Focal Susceptibility of ApoE/ Mice to Develop Atherosclerosis
As described above, vascular CD44 is functionally activated in a proatherogenic environment. An important question is whether the CD44-dependent regulation of vascular gene expression we observed in the aortic arch of apoE/ mice is constitutive or induced by a proatherogenic environment. It was also critical to define whether CD44-mediated gene regulation is selective to vascular regions susceptible to the development of lesions.
To address the first of these issues, we performed qPCR analysis for a subset of the genes in a nonatherogenic environment by comparing vascular gene expression in CD44-deficient and CD44 wild-type C57BL/6 mice. Of 16 genes tested (from the set of 49 genes validated by qPCR in the context of an apoE-null background), we found that the majority were not differentially expressed in the aortic arch of CD44-deficient mice compared with wild-type C57BL/6 mice (Figure 3A). Together with the data in Figure 1, these results indicate that the differential gene expression in aortic arch between apoE/ CD44/ mice and apoE/ CD44+/+ mice reflects a role of CD44 in the response to early proatherogenic processes in apoE/ mice, such as hypercholesterolemia or early inflammatory signals.
|
To determine whether regulation of gene expression by CD44 in apoE/ mice is selective to regions susceptible to atherosclerotic lesion formation, we compared gene expression in thoracic aorta between age- and sex-matched apoE/ CD44/ mice and apoE/ CD44+/+ mice. Of the 207 differentially expressed genes regulated by CD44 in aortic arch, only 7 of these genes were also differentially expressed in the thoracic aorta of apoE/ CD44/ compared with apoE/ CD44+/+ mice (Figure 3B; supplemental Table I). These results indicate that CD44-dependent effects on vascular gene expression in apoE/ mice are largely selective to atherosclerosis-prone regions of the aorta, providing additional support for the notion that CD44-dependent regulation of gene expression is induced in response to local proatherogenic signals.
| Discussion |
|---|
|
|
|---|
The apoE/ mouse model shares many early events associated with atherogenesis in man, including hypercholesterolemia, lipoprotein accumulation, localization to regions of disturbed blood flow,18 and inflammation.19,20 Our results indicate that the expression and function of CD44 and CD44-dependent regulation of vascular gene expression is invoked by one or more of these proatherogenic stimuli. However, comparable levels of total plasma cholesterol between apoE/ CD44/ and apoE/ CD44+/+ mice exclude hypercholesterolemia as a direct cause sufficient to induce the differential gene regulation observed (data not shown). That the CD44-dependent effects on vascular gene expression are largely selective to atherosclerosis-prone regions in apoE/ but not C57BL/6 mice, further supports our conclusion that CD44 regulates vascular gene expression in response to a local proatherogenic environment. This is in keeping with our previous observations that CD44 plays important roles that are evident in disease states rather than under normal homeostatic conditions.11
The finding that CD44 is an early regulator of atherosclerotic disease begs the question as to what causes its upregulation in prelesion vasculature. The focal regulation of CD44 we observed suggests that mechanosignal transduction attributable to decreased shear stress at sites of disturbed flow may induce and activate CD44 on vascular cells, which is consistent with a recent report that CD44 is upregulated in vascular wall in response to hypercholesterolemia21 and disturbed flow.2 Furthermore, genes regulated by mechanosignal transduction independent of CD44 may regulate CD44 expression and activity in atherosclerosis-prone areas before lesion formation. Regardless of the mechanism by which CD44 is regulated, our study indicates that the accumulation of HA22 and the upregulation of vascular CD44 promote atherogenesis by regulating vascular gene expression.
Interestingly, in most pathways, whereas the majority of the genes were negatively regulated by CD44, several genes were positively regulated in each connectivity; despite this finding, the net effect of CD44 regulation on signaling and vascular cell functions in each pathway is not necessarily negated. The pathway analysis indicates that CD44 is primarily involved in 3 critical pathological processes in the vessel wall: focal adhesion formation, deposition of ECM, and angiogenesis, all of which have been implicated in atherosclerosis.
Focal adhesion plaques are structures that form at the ends of actin fibers and serve as sites for force transmission, thereby playing a role in the initiation and progression of atherosclerosis in response to disturbed blood flow.23 A role for CD44 in focal adhesion is consistent with indirect evidence of cross-talk between CD44 and integrins. The gene expression profiling indicates that CD44 may regulate the assembly of adhesion complexes by regulating the expression of focal adhesion molecules such as zyxin, ß-actin, syndecan 4, Thy1, and integrins.
The ECM participates in several key atherogenic events, such as cell migration and proliferation, lipoprotein retention, and thrombosis, as well as plaque stabilization.24,25 CD44 is critical to the formation of HA-rich pericellular matrix and turnover, thus influencing the adhesion and migration of cells.26 However, we did not detect a significant difference in HA content in the vessel wall between apoE/ CD44/ and apoE/ CD44+/+ mice (data not shown). This may be attributable to the upregulation of hyaluronidase Mgea5 or a possible compensatory effect of upregulation of another HA receptor, HA-mediated motility receptor, in apoE/ CD44/ mice that can compensate for the loss of CD44 in HA turnover.27 The CD44-dependent differential expression of ECM components, such as ECM1, Col18
1, Ltbp, and Npnt, may also change the nature of the interactions with their receptors, thereby indirectly regulating related signaling pathways.
Increased neovascularization is also a feature of atherosclerosis.28 Several antiangiogenic and proangiogenic effects of CD44 have been described in the context of tumors.29 However, the role of CD44 in angiogenesis in atherosclerosis has not been investigated. We found several genes involved in angiogenesis are regulated by CD44, including Col18
1, ECM1, Itgb5, Hsp90, Sdc4, Thy1, and Wnt2. Some of these have reported proangiogenic roles such as Thy1, whereas others, such as endostatin, have antiangiogenic roles. Endostatin, the C-terminal fragment of col18
1, is a potent antiangiogenic peptide reported to reduce intimal neovascularization and plaque growth in apoE/ mice16 and enhance lipoprotein retention in subendothelial matrix.17 Therefore, additional studies to determine the role of CD44 in angiogenesis in atherosclerosis will be of interest.
We used global analysis of gene expression in the aortae of apoE/ mice to determine the functional significance of the early activation of CD44 in atherosclerosis-prone environment. These experiments led to our discovery of CD44-dependent regulation of multiple genes in various pathways that may play a critical role in the response to a local proatherogenic environment. The role of the CD44-regulated genes identified in this study in vascular function will be investigated using genetic approaches that target specific components of these genes. Alternatively, these genes can be targeted in vitro and in vivo using a pharmacological approach to determine their roles in vascular cell function. In addition, development of a conditional CD44 knockout mouse will help define the role of CD44 expressed in specific vascular cell types.
In summary, the putative links we established herein provide new insights into the potential mechanisms by which CD44 regulates atherogenesis and underscore its distinct roles in the homeostatic versus the inflammatory state. These data provide a framework for developing novel targets for the treatment of atherosclerotic disease.
| Acknowledgments |
|---|
This study was supported by public health service grants from the National Health Institute (HL65507, HL70121, HL62250, and PO1-HL-06225006) and a grant from the Pennsylvania Department of Health.
Disclosures
None.
| Footnotes |
|---|
| References |
|---|
|
|
|---|
2. Passerini AG, Polacek DC, Shi C, Francesco NM, Manduchi E, Grant GR, Pritchard WF, Powell S, Chang GY, Stoeckert CJ Jr, Davies PF. Coexisting proinflammatory and antioxidative endothelial transcription profiles in a disturbed flow region of the adult porcine aorta. Proc Natl Acad Sci U S A. 2004; 101: 24822487.
3. Dong ZM, Wagner DD. Leukocyte-endothelium adhesion molecules in atherosclerosis. J Lab Clin Med. 1998; 132: 369375.[CrossRef][Medline] [Order article via Infotrieve]
4. Riessen R, Wight TN, Pastore C, Henley C, Isner JM. Distribution of hyaluronan during extracellular matrix remodeling in human restenotic arteries and balloon-injured rat carotid arteries. Circulation. 1996; 93: 11411147.
5. Matsui Y, Rittling SR, Okamoto H, Inobe M, Jia N, Shimizu T, Akino M, Sugawara T, Morimoto J, Kimura C, Kon S, Denhardt D, Kitabatake A, Uede T. Osteopontin deficiency attenuates atherosclerosis in female apolipoprotein E-deficient mice. Arterioscler Thromb Vasc Biol. 2003; 23: 10291034.
6. Ponta H, Sherman L, Herrlich PA. CD44: from adhesion molecules to signaling regulators. Nat RevMol Cell Biol. 2003; 4: 3345.
7. DeGrendele HC, Estess P, Picker LJ, Siegelman MH. CD44 and its ligand hyaluronate mediate rolling under physiologic flow: a novel lymphocyte-endothelial cell primary adhesion pathway. J Exp Med. 1996; 183: 11191130.
8. Khan AI, Kerfoot SM, Heit B, Liu L, Andonegui G, Ruffell B, Johnson P, Kubes P. Role of CD44 and hyaluronan in neutrophil recruitment. J Immunol. 2004; 173: 75947601.
9. Hodge-Dufour J, Noble PW, Horton MR, Bao C, Wysoka M, Burdick MD, Strieter RM, Trinchieri G, Puré E. Induction of IL-12 and chemokines by hyaluronan requires adhesion-dependent priming of resident but not elicited macrophages. J Immunol. 1997; 159: 24922500.
10. McKee CM, Penno MB, Cowman M, Bao C, Noble PW. Hyaluronan (HA) fragments induce chemokine gene expression in alveolar macrophages. The role of HA size and CD44. J Clin Invest. 1996; 98: 24032413.[Medline] [Order article via Infotrieve]
11. Cuff CA, Kothapalli D, Azonobi I, Chun S, Zhang Y, Belkin R, Yeh C, Secreto A, Assoian RK, Rader DJ, Puré E. The adhesion receptor CD44 promotes atherosclerosis by mediating inflammatory cell recruitment and vascular cell activation. J Clin Invest. 2001; 108: 10311040.[CrossRef][Medline] [Order article via Infotrieve]
12. Nandi A, Estess P, Siegelman MH. Hyaluronan anchoring and regulation on the surface of vascular endothelial cells is mediated through the functionally active form of CD44. J Biol Chem. 2000; 275: 1493914948.
13. Brown KL, Maiti A, Johnson P. Role of sulfation in CD44-mediated hyaluronan binding induced by inflammatory mediators in human CD14(+) peripheral blood monocytes. J Immunol. 2001; 167: 53675374.
14. Levesque MC, Haynes BF. Activated T lymphocytes regulate hyaluronan binding to monocyte CD44 via production of IL-2 and IFN-
. J Immunol. 2001; 166: 188196.
15. Cichy J, Bals R, Potempa J, Mani A, Puré E. Proteinase-mediated release of epithelial cell-associated CD44. Extracellular CD44 complexes with components of cellular matrices. J Biol Chem. 2002; 277: 4444044447.
16. Moulton KS, Olsen BR, Sonn S, Fukai N, Zurakowski D, Zeng X. Loss of collagen XVIII enhances neovascularization and vascular permeability in atherosclerosis. Circulation. 2004; 110: 13301336.
17. Zeng X, Chen J, Miller YI, Javaherian K, Moulton KS. Endostatin binds biglycan and LDL and interferes with LDL retention to the subendothelial matrix during atherosclerosis. J Lipid Res. 2005; 46: 18491859.
18. Greenow K, Pearce NJ, Ramji DP. The key role of apolipoprotein E in atherosclerosis. J Mol Med. 2005; 83: 329342.[CrossRef][Medline] [Order article via Infotrieve]
19. Ali K, Middleton M, Pure E, Rader DJ. Apolipoprotein E suppresses the type I inflammatory response in vivo. Circ Res. 2005; 97: 16.
20. Grainger DJ, Reckless J, and McKilligin E. Apolipoprotein E modulates clearance of apoptotic bodies in vitro and in vivo, resulting in a systemic proinflammatory state in apolipoprotein E-deficient mice. J Immunol. 2004; 173: 63666375.
21. Dattilo JB, Dattilo MP, Yager DR, and Makhoul RG. Hypercholesterolemia alters the gene expression of novel components of the extracellular matrix in experimental vein grafts. Ann Vasc Surg. 1998; 12: 168173.[CrossRef][Medline] [Order article via Infotrieve]
22. Li M, Rosenfeld L, Vilar RE, Cowman MK. Degradation of hyaluronan by peroxynitrite. Arch Biochem Biophys. 1997; 341: 245250.[CrossRef][Medline] [Order article via Infotrieve]
23. Shyy JY, Chien S. Role of integrins in endothelial mechanosensing of shear stress. Circ Res. 2002; 91: 769775.
24. Coats WD Jr, Faxon DP. The role of the extracellular matrix in arterial remodelling. Semin Interv Cardiol. 1997; 2: 167176.[Medline] [Order article via Infotrieve]
25. Heeneman S, Cleutjens JP, Faber BC, Creemers EE, van Suylen RJ, Lutgens E, Cleutjens KB, Daemen MJ. The dynamic extracellular matrix: intervention strategies during heart failure and atherosclerosis. J Pathol. 2003; 200: 516525.[CrossRef][Medline] [Order article via Infotrieve]
26. Knudson CB. Hyaluronan receptor-directed assembly of chondrocyte pericellular matrix. J Cell Biol. 1993; 120: 825834.
27. Nedvetzki S, Gonen E, Assayag N, Reich R, Williams RO, Thurmond RL, Huang JF, Neudecker BA, Wang FS, Turley EA, Naor D. RHAMM, a receptor for hyaluronan-mediated motility, compensates for CD44 in inflamed CD44-knockout mice: a different interpretation of redundancy. Proc Natl Acad Sci U S A. 2004; 101: 1808118086.
28. Winter PM, Morawski AM, Caruthers SD, Fuhrhop RW, Zhang H, Williams TA, Allen JS, Lacy EK, Robertson JD, Lanza GM, Wickline SA. Molecular imaging of angiogenesis in early-stage atherosclerosis with alpha(v) beta3-integrin-targeted nanoparticles. Circulation. 2003; 108: 22702274.
29. Pall T, Gad A, Kasak L, Drews M, Stromblad S, Kogerman P. Recombinant CD44-HABD is a novel and potent direct angiogenesis inhibitor enforcing endothelial cell-specific growth inhibition independently of hyaluronic acid binding. Oncogene. 2004; 23: 78747881.[CrossRef][Medline] [Order article via Infotrieve]
This article has been cited by other articles:
![]() |
B. J. Bennett, S. S. Wang, X. Wang, X. Wu, and A. J. Lusis Genetic Regulation of Atherosclerotic Plaque Size and Morphology in the Innominate Artery of Hyperlipidemic Mice Arterioscler Thromb Vasc Biol, March 1, 2009; 29(3): 348 - 355. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. Verschuren, J. de Vries-van der Weij, S. Zadelaar, R. Kleemann, and T. Kooistra LXR agonist suppresses atherosclerotic lesion growth and promotes lesion regression in apoE*3Leiden mice: time course and mechanisms J. Lipid Res., February 1, 2009; 50(2): 301 - 311. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. Zhao, E. Lee, A. M. Zukas, M. K. Middleton, M. Kinder, P. S. Acharya, J. A. Hall, D. J. Rader, and E. Pure CD44 Expressed on Both Bone Marrow-Derived and Non-Bone Marrow-Derived Cells Promotes Atherogenesis in ApoE-Deficient Mice Arterioscler Thromb Vasc Biol, July 1, 2008; 28(7): 1283 - 1289. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
ATVB Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 2007 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |