[show abstract][hide abstract] ABSTRACT: Although human atherosclerosis is associated with aging, direct evidence of cellular senescence and the mechanism of senescence in vascular smooth muscle cells (VSMCs) in atherosclerotic plaques is lacking. We examined normal vessels and plaques by histochemistry, Southern blotting, and fluorescence in situ hybridization for telomere signals. VSMCs in fibrous caps expressed markers of senescence (senescence-associated beta-galactosidase [SAbetaG] and the cyclin-dependent kinase inhibitors [cdkis] p16 and p21) not seen in normal vessels. In matched samples from the same individual, plaques demonstrated markedly shorter telomeres than normal vessels. Fibrous cap VSMCs exhibited markedly shorter telomeres compared with normal medial VSMCs. Telomere shortening was closely associated with increasing severity of atherosclerosis. In vitro, plaque VSMCs demonstrated morphological features of senescence, increased SAbetaG expression, reduced proliferation, and premature senescence. VSMC senescence was mediated by changes in cyclins D/E, p16, p21, and pRB, and plaque VSMCs could reenter the cell cycle by hyperphosphorylating pRB. Both plaque and normal VSMCs expressed low levels of telomerase. However, telomerase expression alone rescued plaque VSMC senescence despite short telomeres, normalizing the cdki/pRB changes. In vivo, plaque VSMCs exhibited oxidative DNA damage, suggesting that telomere damage may be induced by oxidant stress. Furthermore, oxidants induced premature senescence in vitro, with accelerated telomere shortening and reduced telomerase activity. We conclude that human atherosclerosis is characterized by senescence of VSMCs, accelerated by oxidative stress-induced DNA damage, inhibition of telomerase and marked telomere shortening. Prevention of cellular senescence may be a novel therapeutic target in atherosclerosis.
Circulation Research 08/2006; 99(2):156-64. · 11.86 Impact Factor
[show abstract][hide abstract] ABSTRACT: Cell cycle inhibitors are promising agents to prevent or treat human coronary in-stent stenosis (ISS). However, their lack of specificity for ISS vascular smooth muscle cells (VSMCs) may inhibit medial VSMC proliferation and suppress vessel healing.
To identify inhibitor targets that differentially regulate proliferation of ISS vs. medial VSMCs, we examined cell cycle regulation in human VSMCs derived from (A) normal media, (B) ISS sites and (C) primary atherosclerotic plaques (P-VSMCs) using time-lapse videomicroscopy, flow cytometry, immunoblotting and immunohistochemistry.
ISS-VSMC proliferation was intermediate between P-VSMCs and medial VSMCs. Compared with medial cells, P-VSMCs expressed increased p16 and p21, reduced p27, reduced cyclins D(1) and E, and reduced pRb phosphorylation. In contrast, ISS-VSMCs expressed high levels of cyclins E and A with pRb hyperphosphorylation, both in vitro and in vivo, associated with increased and chronic cell proliferation in vivo. Roscovitine, a selective CDK2 inhibitor, inhibited VSMC proliferation by both pRb-dependent and independent pathways and more potently in ISS-VSMCs than medial VSMCs.
Human ISS-VSMCs have marked differences in the stable expression of multiple cell cycle regulators, suggesting that ISS-VSMCs derive from P-VSMCs driven to proliferate through cyclin E overexpression. The critical role for cyclin E-CDK2 enables the identification of the first agent that selectively inhibits ISS-VSMC proliferation.
Cardiovascular Research 01/2004; 60(3):673-83. · 5.94 Impact Factor