Apoptosis of vascular smooth muscle cells induces features of plaque vulnerability in atherosclerosis

Abstract

Vascular smooth muscle cell (VSMC) apoptosis occurs in many arterial diseases, including aneurysm formation, angioplasty restenosis and atherosclerosis. Although VSMC apoptosis promotes vessel remodeling, coagulation and inflammation, its precise contribution to these diseases is unknown, given that apoptosis frequently accompanies vessel injury or alterations to flow. To study the direct consequences of VSMC apoptosis, we generated transgenic mice expressing the human diphtheria toxin receptor (hDTR, encoded by HBEGF) from a minimal Tagln (also known as SM22α) promoter. Despite apoptosis inducing loss of 50–70% of VSMCs, normal arteries showed no inflammation, reactive proliferation, thrombosis, remodeling or aneurysm formation. In contrast, VSMC apoptosis in atherosclerotic plaques of SM22α-hDTR Apoe−/− mice induced marked thinning of fibrous cap, loss of collagen and matrix, accumulation of cell debris and intense intimal inflammation. We conclude that VSMC apoptosis is 'silent' in normal arteries, which have a large capacity to withstand cell loss. In contrast, VSMC apoptosis alone is sufficient to induce features of plaque vulnerability in atherosclerosis. SM22α-hDTR Apoe−/− mice may represent an important new model to test agents proposed to stabilize atherosclerotic plaques.

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Figure 1: Administration of DT induces VSMC-specific apoptosis.
Figure 2: Death of VSMCs does not induce inflammation, proliferation or vessel remodeling or alter contractile properties.
Figure 3: VSMC apoptosis promotes features of atherosclerotic plaque vulnerability.

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Acknowledgements

This study was supported by British Heart Foundation Grants PG/02/055/13778 and RG 04/001 (to M.R.B.); PG/05/127/19872 and PS/02/001 (to A.P.D.) and the European Vascular Genomics Network of Excellence (FP6).

Author information

M.C.H.C. conducted and interpreted the majority of the experimental work and co-wrote the manuscript. N.F. performed the majority of the histological procedures. J.J.M. and A.P.D. conducted the contractile experiments and interpreted the data from them. M.G. advised on mouse pathology. T.D.L. and M.R.B. supervised and co-wrote the manuscript.

Correspondence to Martin R Bennett.

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Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

Generation and characterization of transgenic mice. (PDF 133 kb)

Supplementary Fig. 2

Genotyping of Tgln2-HBEGF and Tgln2-HBEGF Apoe−/− mice. (PDF 901 kb)

Supplementary Fig. 3

Administration of DT induces VSMC-specific apoptosis in Tgln2-HBEGF mice. (PDF 92 kb)

Supplementary Fig. 4

Administration of DT does not induce nonspecific SMC loss in SM22α-hDTR mice. (PDF 170 kb)

Supplementary Fig. 5

VSMC apoptosis does not induce lymphocyte infiltration or expression of MCP-1/JE. (PDF 149 kb)

Supplementary Fig. 6

VSMC apoptosis induces vulnerable plaques in brachiocephalic arteries. (PDF 152 kb)

Supplementary Fig. 7

VSMC apoptosis increases serum IL-6. (PDF 82 kb)

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