Atherosclerosis, an Autoimmune Disease? What could be the culprit antigen(s)? A brief appraisal of the role

of heat shock proteins.

Mohammad Madjid, MD

Center for Vulnerable Plaque Research

University of Texas-Houston Health Science Center and

Texas Heart Institute

In1856 Virchow described atherosclerosis as “endarteritis”. A century later Russel Ross named atherosclerosis “an inflammatory disease”. Ross likened atherosclerosis to other chronic inflammatory diseases such as rheumatoid arthritis and glomerulonephritis. 1

The central role of immune system in atherosclerosis and its clinical complications is now widely accepted. Many investigators are searching to find out what antigens attract immune cells into the arterial wall and possibly later on into atherosclerotic plaques. 2,3,4

Autoantibodies against oxidized low-density lipoprotein (oxLDL), cardiolipin, beta2-glycoprotein-I and heat-shock protein 60/65 have been suggested. 2

Georg Wick, Qingbo Xu, and colleagues have hypothesized that an autoimmune reaction against heat shock protein 60s, expressed by endothelial cells in areas that are subject to increased hemodynamic stress, is the initiating event in atherogenesis. 5,6

The hypothesis indicates that because a high degree of antigenic homology exists between microbial (bacterial and parasitic) and human HSP60, the 'cost' of immunity to microbes might be the danger of cross-reactivity with human HSP60 expressed by the endothelial cells of stressed arteries subjected to classical risk factors. 7

Two major families of HSPs (60s and 70s) have been related to atherosclerosis. Unlike HSP60s, HSP70s are not reported as strong triggers of autoimmune reactions, however, Bond, Johnson and colleagues have suggested certain role for HSP70s in atherosclerosis. 8,9

Chen et al described autologous hsp60 as a danger signal to the innate immune system. 10

Xu et al. showed induction of arteriosclerosis in normocholesterolemic rabbits by immunization with heat shock protein 65. 5

George, Afek, and colleagues reported induction of arteriosclerosis in normocholesterolemic rabbits by immunization with heat shock protein 65. 11,12

A number of other experimental and observational studies have shown a significant relationship between heat shock proteins and atherosclerosis. 9,11,13,14

In humans, expression of HSP60 is correlated positively with atherosclerotic severity, with the highest levels of expression seen in the shoulder regions and around the necrotic core of atherosclerotic plaques. 15

In addition to its antigenic properties, bacterial HSP60 product may stimulate macrophages by production of cytokines such as TNF-α and also MMPs. It may as well interfere with innate immunity by binding to CD14 and activating monocytes and/or macrophages and endothelial cells. 8, 21, 22

Bocharov et al reported that HSP60 is a high-affinity high-density lipoprotein binding protein suggesting a potential mechanism to explain the known association between immunity developed against HSP60 and the development of atherosclerosis. 16

Comparing the similarities between atherosclerosis and other autoimmune disorders such as rheumatoid arthritis (as indicated by Ross in the following slide) can also give some hints about the potential role of autoimmune mechanisms in atherosclerosis and it’s complications. 1

Interestingly, recent studies have uncovered an important role for heat shock proteins in pathogenesis of rheumatoid arthritis. 17,18

Like in rheumatoid arthritis, the suggested role of HSPs in atherosclerosis may also in part explain the missing link between infectious agents and atherosclerosis where a high degree of antigenic homology between human and microbial HSPs can cause cross-reaction. 17,7

DiseaseDisease Monocytes & Monocytes & MacrophageMacrophage

LymphocyteLymphocyte GranulocyteGranulocyte Connective-Connective-Tissue CellsTissue Cells

Extracellular Extracellular MatrixMatrix

Pathogenetic MechanismsPathogenetic Mechanisms

AtherosclerosisAtherosclerosis ++ ++ -- SMCsSMCs Collagen type Collagen type I, III, IV, I, III, IV, elastin, elastin,

fibronectin, fibronectin, proteoglycanproteoglycan

Endothelial-cell injury and Endothelial-cell injury and dysfunction; fibrous cap; dysfunction; fibrous cap; new matrix formation & new matrix formation &

degeneration; necrotic core degeneration; necrotic core

CirrhosisCirrhosis ++ ++ -- FibroblastsFibroblasts Collagen type Collagen type I, IIII, III

Parenchymal cell injury, Parenchymal cell injury, new matrix and scarring new matrix and scarring

replacing necrotic replacing necrotic parenchymaparenchyma

Rheumatoid Rheumatoid arthritisarthritis ++ ++ +/-+/- Synovial Synovial

fibroblastsfibroblastsCollagen type Collagen type

I, III, I, III, fibronectin, fibronectin,

proteoglycanproteoglycan

Synovial-cell injury; erosion Synovial-cell injury; erosion of cartilage; new matrix of cartilage; new matrix

scarring (pannus)scarring (pannus)

Glomeruloscle-Glomeruloscle-rosisrosis ++ ++ -- Mesangial Mesangial

cellscellsCollagen type Collagen type

I, IV, I, IV, fibronectinfibronectin

Epithelial- and endothelial-Epithelial- and endothelial-cell injury and dysfunction; cell injury and dysfunction;

decrease in glomerular decrease in glomerular filtration; new matrix filtration; new matrix

formation; formation;

Pulmonary Pulmonary fibrosisfibrosis ++ ++ +/-+/- SMCs, SMCs,

FibroblastsFibroblastsCollagen type Collagen type

III, IV, III, IV, fibronectinfibronectin

Inflammatory exudate in Inflammatory exudate in alveoli & bronchi; organized alveoli & bronchi; organized

by extensive matrix by extensive matrix deposition and scarringdeposition and scarring

Chronic Chronic pancreatitispancreatitis ++ ++ -- FibroblastsFibroblasts Collagen, Collagen,

fibronectin, fibronectin, proteoglycanproteoglycan

Epithelial injury; periductal Epithelial injury; periductal inflammation; interstitial fat inflammation; interstitial fat

necrosis; new matrix necrosis; new matrix formationformation

Ross R. Atherosclerosis--an inflammatory disease. N Engl J Med. 1999 Jan 14;340(2):115-26

Kanwar, Krissansen, et al. found that expression of HSP60 and HSP70 was strongly upregulated very early at lesion-prone sites in the aortas of young apoE-/- knockout mice and then dramatically down-regulated in the chronic lesions of aged mice. 20

They showed that HSP60 and HSP70 were detectable in the aortas of 3-week-old apoE-/- mice and were highly expressed in the aortas of 8-week-old mice. 20

Kanwar et al. indicated that in 8-week-old apoE-/- mice, HSP60 and 70 were strongly expressed at valve commissures of the aortic sinus, extending to the free aortic wall and including expression by endothelial and intimal cells. 20

They concluded that HSP60 and HSP70 were heterogeneously expressed in lesions of 20-week-old mice. HSP60 and HSP70 were strongly expressed in advanced plaques of the abdominal aorta of 20-week-old mice, whereas medial layers lack expression. 20

In 69-week-old mice, there was complete loss of HSP60 and HSP70 in advanced complicated collagen-rich plaques of the aortic sinus. (down-regulated in aged mice) 20

As a result of this study, lesion-prone sites displayed strong endothelial HSP60 expression, whereas non–lesion-prone sites of the distal abdominal aorta lacked hsp expression. 20

Monocytes/macrophages expressing HSP70 and hsp60 (data not shown) were the most prominent cell type in lesions. 20

Summary:Summary:

1- Autoimmune reactions (cellular and humoral) against HSPs particularly HSP60s may play an important role in early stage development of atherosclerosis.

2- HSP60s and HSP70s released from necrotic cells in the core area of advanced plaques may stimulate the innate immune response to promote inflammation and attract new inflammatory cells thereby may link to complications of plaque such as rupture and or thrombosis.

3- Humoral and cellular reactions against HSP60 work in conjunction with classical proven CVD risk factors.

Debates:Debates:I. According to our current body of knowledge, the

development of atherosclerosis seems to have two major preceding components, metabolic disorder (lipid abnormality etc.) and inflammatory disorder (enhanced immune or autoimmune response). The question is which one comes first?

II. Since the complication of atherosclerosis (vulnerable plaque) is more important than it’s development (stable plaque), the question is which one of the two (1-metabolic, 2-Immune) components of atherosclerosis plays a more important role?

Debates:Debates:

III. How feasible is the idea of vaccination against HSPs or oxidized-LDL or other suggested antigens? Can we induce tolerance against HSPs without damaging the innate immune system?

IV. Which one is more feasible? Eradication of atherosclerosis by vaccination against triggers of plaque development, or, eradication of vulnerable plaque by vaccination against triggers of plaque vulnerability?

1. Ross R. Atherosclerosis--an inflammatory disease.N Engl J Med. 1999 Jan 14;340(2):115-26. Review

2. Shoenfeld Y, Sherer Y, George J, Harats D. ;Autoantibodies associated with atherosclerosis. Ann Med. 2000 Dec;32 Suppl 1:37-40. Review.

3. Hansson, G.; Immunological markers of atherosclerosis.Lancet. 1993 Jan 30;341(8840):278.

4. Witztum JL, Palinski W. ; Are immunological mechanisms relevant for the development of atherosclerosis? Clin Immunol. 1999 Feb;90(2):153-6. Review.

5. Xu Q, Dietrich H, Steiner HJ, Gown AM, Schoel B, Mikuz G, Kaufmann SH, Wick G. ; Induction of arteriosclerosis in normocholesterolemic rabbits by immunization with heat shock protein 65. Arterioscler Thromb. 1992 Jul;12(7):789-99.

6. Wick G, Schett G, Amberger A, Kleindienst R, Xu Q.; Is atherosclerosis an immunologically mediated disease?; Immunol Today. 1995 Jan;16(1):27-33. Review.

References

7. Wick G, Perschinka H, Millonig G. ; Atherosclerosis as an autoimmune disease: an update.; Trends Immunol. 2001 Dec 1;22(12):665-669.

8. Johnson AD, Berberian PA, Tytell M, Bond MG. ; Differential distribution of 70-kD heat shock protein in atherosclerosis. Its potential role in arterial SMC survival.; Arterioscler Thromb Vasc Biol. 1995 Jan;15(1):27-36.

9. Berberian PA, Myers W, Tytell M, Challa V, Bond MG.; Immunohistochemical localization of heat shock protein-70 in normal-appearing and atherosclerotic specimens of human arteries.; Am J Pathol. 1990 Jan;136(1):71-80.

10. Chen W, Syldath U, Bellmann K, Burkart V, Kolb H.; Human 60-kDa heat-shock protein: a danger signal to the innate immune system.; J Immunol. 1999 Mar 15;162(6):3212-9.

11. George J, Shoenfeld Y, Afek A, Gilburd B, Keren P, Shaish A, Kopolovic J, Wick G, Harats D.; Enhanced fatty streak formation in C57BL/6J mice by immunization with heat shock protein-65. Arterioscler Thromb Vasc Biol. 1999 Mar;19(3):505-10.

References

12. Afek A, George J, Gilburd B, Rauova L, Goldberg I, Kopolovic J, Harats D, Shoenfeld Y.; Immunization of low-density lipoprotein receptor deficient (LDL-RD) mice with heat shock protein 65 (HSP-65) promotes early atherosclerosis.; J Autoimmun. 2000 Mar;14(2):115-21.

13. Hansen PR, Chew M, Zhou J, Daugherty A, Heegaard N, Jensen P, Mouritsen S, Falk E.; Freunds adjuvant alone is antiatherogenic in apoE-deficient mice and specific immunization against TNFalpha confers no additional benefit.Atherosclerosis. 2001 Sep;158(1):87-94.

14. George J, Afek A, Gilburd B, Shoenfeld Y, Harats D.; Cellular and humoral immune responses to heat shock protein 65 are both involved in promoting fatty-streak formation in LDL-receptor deficient mice.J Am Coll Cardiol. 2001 Sep;38(3):900-5.

15. Kleindienst R, Xu Q, Willeit J, Waldenberger FR, Weimann S, Wick G.Immunology of atherosclerosis. Demonstration of heat shock protein 60 expression and T lymphocytes bearing alpha/beta or gamma/delta receptor in human atherosclerotic lesions.; Am J Pathol. 1993 Jun;142(6):1927-37.

References

16. Bocharov AV, Vishnyakova TG, Baranova IN, Remaley AT, Patterson AP, Eggerman TL.; Heat shock protein 60 is a high-affinity high-density lipoprotein binding protein.; Biochem Biophys Res Commun. 2000 Oct 14;277(1):228-35.

17. Gaston, JS.; Heat shock proteins and arthritis--new readers start here.Autoimmunity. 1997;26(1):33-42. Review.

18. Schett G, Tohidast-Akrad M, Steiner G, Smolen J.; The stressed synovium.; Arthritis Res. 2001;3(2):80-6. Review.

19. Gaston, JS. ; Heat shock proteins and arthritis--new readers start here.; Autoimmunity. 1997;26(1):33-42. Review.

20. Rupinder K. Kanwar, Jagat R. Kanwar, Dongmao Wang, Douglas J. Ormrod, and Geoffrey W. Krissansen Temporal Expression of Heat Shock Proteins 60 and 70 at Lesion-Prone Sites During Atherogenesis in ApoE-Deficient Mice

Arterioscler Thromb Vasc Biol 2001 21: 1991-1997.

References

21.21. Kol A, Sukhova GK, Lichtman AH, Libby P.Kol A, Sukhova GK, Lichtman AH, Libby P. Chlamydial heat shock protein 60 Chlamydial heat shock protein 60 localizes in human atheroma and regulates macrophage tumor necrosis factor-localizes in human atheroma and regulates macrophage tumor necrosis factor-alpha and matrix metalloproteinase expression. Circulation. 1998 Jul 28;98(4):300-alpha and matrix metalloproteinase expression. Circulation. 1998 Jul 28;98(4):300-7.7.

22.22. Kol A, Lichtman AH, Finberg RW, Libby P, Kurt-Jones EA.Kol A, Lichtman AH, Finberg RW, Libby P, Kurt-Jones EA. Cutting edge: heat Cutting edge: heat shock protein (HSP) 60 activates the innate immune response: CD14 is an shock protein (HSP) 60 activates the innate immune response: CD14 is an essential receptor for HSP60 activation of mononuclear cells. J Immunol. 2000 Jan essential receptor for HSP60 activation of mononuclear cells. J Immunol. 2000 Jan 1;164(1):13-7.1;164(1):13-7.

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