Differential cyclin E expression in human in-stent stenosis smooth muscle cells identifies targets for selective anti-restenosis therapy

Epigenetic dysregulation in cardiovascular aging and disease

Cardiovascular disease (CVD) is the leading cause of mortality and morbidity for all sexes, racial and ethnic groups. Age, and its associated physiological and pathological consequences, exacerbate CVD incidence and progression, while modulation of biological age with interventions track with cardiovascular health. Despite the strong link between aging and CVD, surprisingly few studies have directly investigated heart failure and vascular dysfunction in aged models and subjects. Nevertheless, strong correlations have been found between heart disease, atherosclerosis, hypertension, fibrosis, and regeneration efficiency with senescent cell burden and its proinflammatory sequelae. In agreement, senotherapeutics have had success in reducing the detrimental effects in experimental models of cardiovascular aging and disease. Aside from senotherapeutics, cellular reprogramming strategies targeting epigenetic enzymes remain an unexplored yet viable option for reversing or delaying CVD. Epigenetic alterations comprising local and global changes in DNA and histone modifications, transcription factor binding, disorganization of the nuclear lamina, and misfolding of the genome are hallmarks of aging. Limited studies in the aging cardiovascular system of murine models or human patient samples have identified strong correlations between the epigenome, age, and senescence. Here, we compile the findings in published studies linking epigenetic changes to CVD and identify clear themes of epigenetic deregulation during aging. Pending direct investigation of these general mechanisms in aged tissues, this review predicts that future work will establish epigenetic rejuvenation as a potent method to delay CVD.

The Role of Vascular Aging in Atherosclerotic Plaque Development and Vulnerability

BACKGROUND

The ongoing demographical shift is leading to an unprecedented aging of the population. As a consequence, the prevalence of age-related diseases, such as atherosclerosis and its thrombotic complications is set to increase in the near future. Endothelial dysfunction and vascular stiffening characterize arterial aging and set the stage for the development of cardiovascular diseases. Atherosclerotic plaques evolve over time, the extent to which these changes might affect their stability and predispose to sudden complications remains to be determined. Recent advances in imaging technology will allow for longitudinal prospective studies following the progression of plaque burden aimed at better characterizing changes over time associated with plaque stability or rupture. Oxidative stress and inflammation, firmly established driving forces of age-related CV dysfunction, also play an important role in atherosclerotic plaque destabilization and rupture. Several genes involved in lifespan determination are known regulator of redox cellular balance and pre-clinical evidence underlines their pathophysiological roles in age-related cardiovascular dysfunction and atherosclerosis.

OBJECTIVE

The aim of this narrative review is to examine the impact of aging on arterial function and atherosclerotic plaque development. Furthermore, we report how molecular mechanisms of vascular aging might regulate age-related plaque modifications and how this may help to identify novel therapeutic targets to attenuate the increased risk of CV disease in elderly people.

Myocardin-Dependent Kv1.5 Channel Expression Prevents Phenotypic Modulation of Human Vessels in Organ Culture

Objective:

We have previously described that changes in the expression of Kv channels associate to phenotypic modulation (PM), so that Kv1.3/Kv1.5 ratio is a landmark of vascular smooth muscle cells phenotype. Moreover, we demonstrated that the Kv1.3 functional expression is relevant for PM in several types of vascular lesions. Here, we explore the efficacy of Kv1.3 inhibition for the prevention of remodeling in human vessels, and the mechanisms linking the switch in Kv1.3 /Kv1.5 ratio to PM.

Approach and Results:

Vascular remodeling was explored using organ culture and primary cultures of vascular smooth muscle cells obtained from human vessels. We studied the effects of Kv1.3 inhibition on serum-induced remodeling, as well as the impact of viral vector-mediated overexpression of Kv channels or myocardin knock-down. Kv1.3 blockade prevented remodeling by inhibiting proliferation, migration, and extracellular matrix secretion. PM activated Kv1.3 via downregulation of Kv1.5. Hence, both Kv1.3 blockers and Kv1.5 overexpression inhibited remodeling in a nonadditive fashion. Finally, myocardin knock-down induced vessel remodeling and Kv1.5 downregulation and myocardin overexpression increased Kv1.5, while Kv1.5 overexpression inhibited PM without changing myocardin expression.

Conclusions:

We demonstrate that Kv1.5 channel gene is a myocardin-regulated, vascular smooth muscle cells contractile marker. Kv1.5 downregulation upon PM leaves Kv1.3 as the dominant Kv1 channel expressed in dedifferentiated cells. We demonstrated that the inhibition of Kv1.3 channel function with selective blockers or by preventing Kv1.5 downregulation can represent an effective, novel strategy for the prevention of intimal hyperplasia and restenosis of the human vessels used for coronary angioplasty procedures.

Modified CDKN2B (p15) and CDKN2A (p16) DNA methylation profiles in urban pesticide applicators

Gene-specific changes in DNA methylation by pesticides in occupationally exposed populations have not been studied extensively. Of particular concern are changes in the methylation profile of tumor-suppressor, such as CDKN2B and CDKN2A, genes involved in oncogenesis. The aim of this study was to evaluate the methylation profiles of CDKN2B and CDKN2A genes in urban pesticide applicators and their relationship with occupational exposure to pesticides. A cross-sectional study was conducted in 186 urban pesticide applicators (categorized as high or moderate exposures) and 102 participants without documented occupational exposures to pesticides. Acute and chronic pesticide exposures were evaluated by direct measurement of urinary dialkylphosphates, organophosphate metabolites, and a structured questionnaire, respectively. Anthropometric characteristics, diet, clinical histories, and other variables were estimated through a validated self-reported survey. DNA methylation was determined by pyrosequencing of bisulfite-treated DNA. Decreased DNA methylation of the CDKN2B gene was observed in pesticide-exposed groups compared to the non-exposed group. In addition, increased methylation of the CDKN2A promoter was observed in the moderate-exposure group compared to the non-exposed group. Bivariate analysis showed an association between CDKN2B methylation and pesticide exposure, general characteristics, smoking status, and micronutrients, while changes in CDKN2A methylation were associated with pesticide exposure, sex, educational level, body mass index, smoking status, supplement intake, clinical parameters, and caffeine consumption. These data suggest that pesticide exposure modifies the methylation pattern of CDKN2B and CDKN2A genes and raise important questions about the role that these changes may play in the regulation of cell cycle activities, senescence, and aging.

Vascular aging: Molecular mechanisms and potential treatments for vascular rejuvenation

Aging is the main risk factor contributing to vascular dysfunction and the progression of vascular diseases. In this review, we discuss the causes and mechanisms of vascular aging at the tissue and cellular level. We focus on Endothelial Cell (EC) and Smooth Muscle Cell (SMC) aging due to their critical role in mediating the defective vascular phenotype. We elaborate on two categories that contribute to cellular dysfunction: cell extrinsic and intrinsic factors. Extrinsic factors reflect systemic or environmental changes which alter EC and SMC homeostasis compromising vascular function. Intrinsic factors induce EC and SMC transformation resulting in cellular senescence. Replenishing or rejuvenating the aged/dysfunctional vascular cells is critical to the effective repair of the vasculature. As such, this review also elaborates on recent findings which indicate that stem cell and gene therapies may restore the impaired vascular cell function, reverse vascular aging, and prolong lifespan.

Vascular Smooth Muscle Cells in Atherosclerosis

The historical view of vascular smooth muscle cells (VSMCs) in atherosclerosis is that aberrant proliferation of VSMCs promotes plaque formation, but that VSMCs in advanced plaques are entirely beneficial, for example preventing rupture of the fibrous cap. However, this view has been based on ideas that there is a homogenous population of VSMCs within the plaque, that can be identified separate from other plaque cells (particularly macrophages) using standard VSMC and macrophage immunohistochemical markers. More recent genetic lineage tracing studies have shown that VSMC phenotypic switching results in less-differentiated forms that lack VSMC markers including macrophage-like cells, and this switching directly promotes atherosclerosis. In addition, VSMC proliferation may be beneficial throughout atherogenesis, and not just in advanced lesions, whereas VSMC apoptosis, cell senescence, and VSMC-derived macrophage-like cells may promote inflammation. We review the effect of embryological origin on VSMC behavior in atherosclerosis, the role, regulation and consequences of phenotypic switching, the evidence for different origins of VSMCs, and the role of individual processes that VSMCs undergo in atherosclerosis in regard to plaque formation and the structure of advanced lesions. We think there is now compelling evidence that a full understanding of VSMC behavior in atherosclerosis is critical to identify therapeutic targets to both prevent and treat atherosclerosis.

Ageing induced vascular smooth muscle cell senescence in atherosclerosis

Atherosclerosis is a disease of ageing in that its incidence and prevalence increase with age. However, atherosclerosis is also associated with biological ageing, manifest by a number of typical hallmarks of ageing in the atherosclerotic plaque. Thus, accelerated biological ageing may be superimposed on the effects of chronological ageing in atherosclerosis. Tissue ageing is seen in all cells that comprise the plaque, but particularly in vascular smooth muscle cells (VSMCs). Hallmarks of ageing include evidence of cell senescence, DNA damage (including telomere attrition), mitochondrial dysfunction, a pro-inflammatory secretory phenotype, defects in proteostasis, epigenetic changes, deregulated nutrient sensing, and exhaustion of progenitor cells. In this model, initial damage to DNA (genomic, telomeric, mitochondrial and epigenetic changes) results in a number of cellular responses (cellular senescence, deregulated nutrient sensing and defects in proteostasis). Ultimately, ongoing damage and attempts at repair by continued proliferation overwhelm reparative capacity, causing loss of specialised cell functions, cell death and inflammation. This review summarises the evidence for accelerated biological ageing in atherosclerosis, the functional consequences of cell ageing on cells comprising the plaque, and the causal role that VSMC senescence plays in atherogenesis.

Inhibitory effects of roscovitine on proliferation and migration of vascular smooth muscle cells in vitro

Abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) are the major cause of in-stent restenosis (ISR). Intervention proliferation and migration of VSMCs is an important strategy for antirestenotic therapy. Roscovitine, a second-generation cyclin-dependent kinase inhibitor, can inhibit cell cycle of multiple cell types. We studied the effects of roscovitine on cell cycle distribution, proliferation and migration of VSMCs in vitro by flow cytometry, BrdU incorporation and wound healing assay, respectively. Our results showed that roscovitine increased the proportion of G0/G1 phase cells after 12 h (69.57±3.65 vs. 92.50±1.68, P=0.000), 24 h (80.87±2.24 vs. 90.25±0.79, P=0.000) and 48 h (88.08±3.86 vs. 88.87±2.43, P=0.427) as compared with control group. Roscovitine inhibited proliferation and migration of VSMCs in a concentration-dependent way. With the increase of concentration, roscovitine showed increased capacity for growth and migration inhibition. Roscovitine (30 μmol/L) led to an almost complete VSMCs growth and migration arrest. Combined with its low toxicity and selective inhibition to ISR-VSMCs, roscovitine may be a potential drug in the treatment of vascular stenosis diseases and particularly useful in the prevention and treatment of ISR.

Aging and atherosclerosis: mechanisms, functional consequences, and potential therapeutics for cellular senescence

Atherosclerosis is classed as a disease of aging, such that increasing age is an independent risk factor for the development of atherosclerosis. Atherosclerosis is also associated with premature biological aging, as atherosclerotic plaques show evidence of cellular senescence characterized by reduced cell proliferation, irreversible growth arrest and apoptosis, elevated DNA damage, epigenetic modifications, and telomere shortening and dysfunction. Not only is cellular senescence associated with atherosclerosis, there is growing evidence that cellular senescence promotes atherosclerosis. This review examines the pathology of normal vascular aging, the evidence for cellular senescence in atherosclerosis, the mechanisms underlying cellular senescence including reactive oxygen species, replication exhaustion and DNA damage, the functional consequences of vascular cell senescence, and the possibility that preventing accelerated cellular senescence is a therapeutic target in atherosclerosis.

A novel roscovitine derivative potently induces G1-phase arrest in platelet-derived growth factor-BB-activated vascular smooth muscle cells

Abnormal vascular smooth muscle cell (VSMC) proliferation contributes to the pathogenesis of restenosis. Thus, drugs interfering with cell cycle progression in VSMC are promising candidates for an antirestenotic therapy. In this study, we pharmacologically characterize N-5-(2-aminocyclohexyl)-N-7-benzyl-3-isopropyl-1(2)H-pyrazolo[4,3-d]pyrimidine-5,7-di-amine (LGR1406), a novel derivative of the cyclin-dependent kinase (CDK) inhibitor roscovitine (ROSC), in PDGF-BB-activated VSMC. Cell proliferation was quantified measuring DNA synthesis via 5-bromo-2'-deoxyuridine incorporation. Analysis of cell cycle distribution was done by flow cytometry using propidium iodide-stained nuclei. Key regulators of the cell cycle and relevant signaling pathways were dissected by Western blot analyses. In addition, in vitro kinase assays and in silico studies regarding the pharmacokinetic profile of both compounds were performed. LGR1406 shows a stronger (IC(50) = 3.0 muM) antiproliferative activity than ROSC (IC(50) = 16.9 muM), halting VSMCs in G(0)/G(1) phase of the cell cycle, whereas ROSC does not arrest but rather delays cell cycle progression. Neither of the compounds interferes with early PDGF-BB-induced signaling pathways (p38, extracellular signal-regulated kinase 1/2, c-Jun NH(2)-terminal kinase, Akt, signal transducer and activator of transcription 3), and both inhibit CDKs, with LGR1406 exerting a slightly higher potency against CDK1/2 and 4 than ROSC. Expression of cyclins A and E as well as hyperphosphorylation of the pocket proteins retinoblastoma protein and p107 are negatively affected by both compounds, although to a different extent. In silico calculations predicted a much higher metabolic stability for LGR1406 compared with ROSC. Altogether, ROSC derivatives, such as LGR1406 seem to be promising compounds for further development in antirestenotic therapy.

Role of E2F1-cyclin E1-cyclin E2 circuit in human coronary smooth muscle cell proliferation and therapeutic potential of its downregulation by siRNAs

Aberrant coronary vascular smooth muscle cell (CSMC) proliferation is a pivotal event underlying intimal hyperplasia, a phenomenon impairing the long-term efficacy of bypass surgery and angioplasty procedures. Consequently research has become focused on efforts to identify molecules that are able to control CSMC proliferation. We investigated downregulation of CSMC growth by small interfering RNAs (siRNAs) targeted against E2F1, cyclin E1, and cyclin E2 genes, whose contribution to CSMC proliferation is only now being recognized. Chemically synthesized siRNAs were delivered by two different transfection reagents to asynchronous and synchronous growing human CSMCs cultivated either in normo- or hyperglycemic conditions. The depletion of each of the three target genes affected the expression of the other two genes, demonstrating a close regulatory control. The clearest effects associated with the inhibition of the E2F1-cyclin E1/E2 circuit were the reduction in the phosphorylation levels of the retinoblastoma protein pRB and a decrease in the amount of cyclin A2. At the phenotypic level the downmodulation of CSMC proliferation resulted in a decrease of S phase matched by an increase of G1-G0 phase cell amounts. The antiproliferative effect was cell-donor and transfectant independent, reversible, and effective in asynchronous and synchronous growing CSMCs. Importantly, it was also evident in hyperglycemia, a condition that underlies diabetes. No significant aspecific cytotoxicity was observed. Our data demonstrate the interrelation among E2F1-cyclin E1-cyclin E2 and the pivotal role this circuit exerts in CSMC proliferation. Additionally, our work validates the concept of utilizing anti-E2F1-cyclin E1-cyclin E2 siRNAs to develop a potential novel therapy to control intimal hyperplasia.

Roscovitine inhibits ERK1/2 activation induced by angiotensin II in vascular smooth muscle cells

Roscovitine is a potent CDK inhibitor often used as a biological tool in cell-cycle studies, but its working mechanism and real targets in vascular smooth muscle cells (VSMCs) remain unclear. In this study, we observed that ERK1/2 phosphorylation induced by Ang II was abrogated by pretreating VSMCs with roscovitine for 15h. Pretreating VSMCs with roscovitine also inhibited Ang II-induced c-Jun expression and phosphorylation. We further demonstrated that roscovitine could suppress the DNA binding activity of c-Jun and activation of angiotensinogen promoter by Ang II. These results suggest that roscovitine represses Ang II-induced angiotensinogen expression by inhibiting activation of ERK1/2 and c-Jun.

Ageing and atherosclerosis: Mechanisms and therapeutic options

Atherosclerosis is the cause of most heart attacks and strokes, and is par excellence, a disease of ageing. Whilst disease prevalence and incidence increases with increasing decade of life, there is also evidence of accelerated cellular ageing in atherosclerosis. Such evidence includes impaired cell proliferation, early culture senescence and cell cycle markers of senescence in vitro and in vivo. Cell senescence is also characterised by loss of telomeres from the ends of chromosomes. Cellular ageing increases with disease severity, acting as a marker for disease, but also directly promotes atherosclerosis. Cellular ageing appears to be due to both abnormal proliferation of cells in an attempt to repair vessel damage, and a response to the damage itself. This review summarises the evidence of vascular cell senescence in atherosclerosis, the causes and consequences of accelerated cellular ageing in atherosclerosis, and identifies potential therapeutic options for both prevention and treatment.

Differential effects of insulin-like growth factor-1 and atheroma-associated cytokines on cell proliferation and apoptosis in plaque smooth muscle cells of symptomatic and asymptomatic patients with carotid stenosis

Morbidity and mortality from atherosclerosis are associated with complicated atherosclerotic lesions due to plaque rupture, which is regulated by a balance between proliferation and apoptosis of vascular smooth muscle cells (VSMC). We examined insulin-like growth factor-1 (IGF-1)-induced survival of plaque VSMC from carotid endarterectomy specimens and investigated the underlying cellular mechanisms in the presence and absence of IL-12 and IFN-gamma. Both IL-12 and IFN-gamma were strongly expressed in symptomatic atherosclerotic plaques as compared with asymptomatic plaques. In asymptomatic plaque VSMC, IGF-1 induced the survival and proliferation of VSMC and accelerated VSMC into S-phase. IL-12 or IFN-gamma inhibited proliferation and VSMC were arrested in the G0-G1 phase. IGF-1 markedly inhibited the expression of p27(kip) and p21(cip) and significantly induced cyclin E and cyclin D. Both cytokines by themselves increased the expression of p27(kip) and p21(cip) and inhibited cyclin E and cyclin D. On the contrary, in symptomatic VSMC there was already increased apoptosis of VSMC and there was no significant effect of IGF-1 or inflammatory cytokines on proliferation, apoptosis or the expression of p27(kip) and p21(cip) and cyclin D and E. These data suggest that IGF-1 is more potent in inducing the survival of VSMC from the endarterectomy specimens of asymptomatic patients as compared to that of symptomatic subjects and cytokines associated with atheroma lesions decrease the activity of IGF-1-induced survival in the VSMC of asymptomatic plaques. The different expression and activity of cell cycle regulatory proteins could be responsible for apoptosis of VSMC and destabilization of atherosclerotic plaques.

Vascular Smooth Muscle Cells Undergo Telomere-Based Senescence in Human Atherosclerosis

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 β-galactosidase [SAβG] 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 SAβG 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.

Vessel wall apoptosis and atherosclerotic plaque instability

Atherosclerotic cardiovascular disease remains the leading cause of death in the industrialized world. Most cardiovascular deaths result from acute coronary syndromes, including unstable angina pectoris and acute myocardial infarction. Coronary syndromes often arise from acute coronary thrombosis, itself commonly a result of disruption or rupture of the fibrous cap of a lipid-laden atherosclerotic plaque. Despite this huge clinical burden of atherosclerotic plaque instability, our understanding of the molecular mechanisms mediating atherosclerotic plaque disruption and rupture, at a cellular level, remains limited. Placed in a clinical context, this review discusses our current understanding of the molecular basis for atherosclerotic plaque instability, with particular emphasis on the process of apoptosis-or programmed cell death-seen increasingly as playing a key role in a number of cell types within the vessel wall.

Hammerhead ribozymes targeted against cyclin E and E2F1 cooperate to down-regulate coronary smooth muscle cell proliferation

BACKGROUND

Anti-proliferative drugs released from endo-vascular stents have substantially contributed to reduce in-stent restenosis rates in coronary arteries bearing single primary lesions by down-regulating coronary smooth muscle cell (CSMC) growth. However, the considerably lower drug efficacy shown in treatment of more complex coronary lesions suggests that alternative anti-proliferative approaches can be beneficial. Thus, we explored the use of hammerhead ribozymes as tools to knock down cyclin E and E2F1, two potent activators of cell proliferation which cooperate to promote the G1 to S phase transition.

METHODS

Two ribozymes, one directed against cyclin E and the other against E2F1 mRNAs, were delivered by liposomes to cultured human CSMCs. The influences on cell proliferation were measured evaluating BrdU incorporation into newly synthesised DNA. The effects on cell cycle phase distribution were determined by BrdU and 7-aminoactinomycin D incorporation into DNA.

RESULTS

Both ribozymes exhibited a sequence-specific and dose-dependent reduction in BrdU incorporation, which, at a concentration of 280 nM, persisted up to 4 days after transfection of CSMCs. A combined administration of the two ribozymes (210+210 nM) resulted in a more pronounced decrease in BrdU incorporation compared to the administration of an equimolar amount (420 nM) of each of them. Finally, both ribozymes induced a significant (P<0.05) reduction in S phase cells with a concomitant increase of G1/G0 and G2-M phase cells, compared to controls.

CONCLUSIONS

The ribozymes selected represent potent tools to prevent CSMC proliferation, especially when administered together, and thus are ideal candidates for in vivo application.