The growth suppressor p27(Kip1) protects against diet-induced atherosclerosis

Comparative Proteome Analysis of Epicardial and Subcutaneous Adipose Tissues from Patients with or without Coronary Artery Disease

BACKGROUND AND AIMS

Owing to its unique anatomical structure and metabolism, epicardial adipose tissue (EAT) has attracted amount of attention in coronary artery disease (CAD) research. Here, we analyzed differences in proteome composition in epicardial (EAT) and subcutaneous adipose tissues (SAT) from patients with or without CAD.

METHODS

EAT and SAT samples were collected from 6 CAD patients and 6 non-CAD patients. Isobaric Tagging for Relative and Absolute Quantitation (iTRAQ) analysis combined with liquid chromatography tandem-mass spectrometry (LC-MS/MS) was performed to identify the differentially expressed proteins.

RESULTS

In total, 2348 proteins expressed in EAT and 2347 proteins expressed in SAT were separately identified. 385 differentially expressed proteins were found in EAT and 210 proteins were found in SAT in CAD patients compared to non-CAD patients. Many proteins differentially expressed in EAT of CAD patients were involved in biological functions associated with CAD development such as cell-to-cell signaling and interaction, inflammatory response, and lipid metabolism. Differential expressions of proteins (MMP9, S100A9, and clusterin) in EAT or SAT were involved in several signaling pathways such as mitochondrial dysfunction, acute phase inflammation, and LXR/RXR activation, which was confirmed by western blotting, and similar results were obtained.

CONCLUSIONS

The largest profiles of differentially expressed proteins in EAT and SAT between CAD patients and non-CAD patients were identified. The significant signal pathways, mitochondrial dysfunction, and LXR/RXR activation, which differential proteins were involved in, were firstly found to play roles in EAT of CAD patients, and clusterin was firstly found to be upregulated in EAT of CAD patients.

miR-146a deficiency in hematopoietic cells is not involved in the development of atherosclerosis

Background

Atherosclerosis involves activation of the IRAK1/TRAF6/NF-κB inflammatory cascade, which is negatively regulated by miR146a. Previous studies showed that the TT genotype of rs2431697, located near the miR-146a gene, drives lower miR-146a transcription and predicts adverse cardiovascular events in anticoagulated atrial fibrillation patients. Moreover, systemic miR-146a administration protects mice from atherosclerosis. Here we evaluated the ability of miR-146a expression in the hematopoietic component to regulate atherosclerosis in low-density lipoprotein receptor-null mice (Ldlr^-/-).

Methods and results

Lethally-irradiated Ldlr^-/- mice transplanted with bone marrow from wild-type or miR-146a-null mice were fed an atherogenic diet for 8 and 20 weeks. Irak1, Traf6 and MIR146A expression were quantified in thoracic aorta by qRT-PCR and Western blot. Aortic plaque size and composition were characterized by Oil-Red staining and immunohistochemistry and leukocyte recruitment by intravital microscopy. Blood cell counts were similar in fat-fed Ldlr^-/-mice with or without hematopoietic miR-146a expression. However, plasma cholesterol decreased in fat-fed Ldlr^-/-mice transplanted with bone marrow deficient for miR-146a. Finally, aortic atherosclerosis burden and recruitment of leukocytes into the vessel wall were undistinguishable between the two groups, despite higher levels of Irak1 and Traf6 mRNA and protein in the aorta of fat-fed mice lacking hematopoietic miR-146a expression.

Conclusions

miR-146a deficiency exclusively in hematopoietic cells modulates cholesterol levels in plasma and the expression of its targets in the artery wall of fat-fed Ldlr^-/- mice, but does not accelerate atherosclerosis. Atheroprotection upon systemic miR-146a administration may therefore be caused by specific effects on vascular cells.

Senescent cells: a therapeutic target for cardiovascular disease

Cellular senescence, a major tumor-suppressive cell fate, has emerged from humble beginnings as an in vitro phenomenon into recognition as a fundamental mechanism of aging. In the process, senescent cells have attracted attention as a therapeutic target for age-related diseases, including cardiovascular disease (CVD), the leading cause of morbidity and mortality in the elderly. Given the aging global population and the inadequacy of current medical management, attenuating the health care burden of CVD would be transformative to clinical practice. Here, we review the evidence that cellular senescence drives CVD in a bimodal fashion by both priming the aged cardiovascular system for disease and driving established disease forward. Hence, the growing field of senotherapy (neutralizing senescent cells for therapeutic benefit) is poised to contribute to both prevention and treatment of CVD.

MicroRNA-296: a promising target in the pathogenesis of atherosclerosis?

Atherosclerosis has been recognized as an inflammatory disease involving the vascular wall. MicroRNAs are a group of small noncoding RNAs to regulate gene expression at the transcriptional level through mRNA degradation or translation repression. Recent studies suggest that miR-296 may play crucial roles in the regulation of angiogenesis, inflammatory response, cholesterol metabolism, hypertension, cellular proliferation and apoptosis. In this review, we primarily discussed the molecular targets of miR-296 involved in the development of atherosclerosis, which may provide a basis for future investigation and a better understanding of the biological functions of miR-296 in atherosclerosis.

Defective p27 phosphorylation at serine 10 affects vascular reactivity and increases abdominal aortic aneurysm development via Cox-2 activation

Phosphorylation at serine 10 (S10) is the major posttranslational modification of the tumor suppressor p27, and is reduced in both human and mouse atherosclerosis. Moreover, a lack of p27-phospho-S10 in apolipoprotein E-null mice (apoE-/-) leads to increased high-fat diet-induced atherosclerosis associated with endothelial dysfunction and augmented leukocyte recruitment. In this study, we analyzed whether p27-phospho-S10 modulates additional endothelial functions and associated pathologies. Defective p27-phospho-S10 increases COX-2 activity in mouse aortic endothelial cells without affecting other key regulators of vascular reactivity, reduces endothelium-dependent dilation, and increases arterial contractility. Lack of p27-phospho-S10 also elevates aortic COX-2 expression and thromboxane A₂ production, increases aortic lumen diameter, and aggravates angiotensin II-induced abdominal aortic aneurysm development in apoE-/- mice. All these abnormal responses linked to defective p27-phospho-S10 are blunted by pharmacological inhibition of COX-2. These results demonstrate that defective p27-phospho-S10 modifies endothelial behavior and promotes aneurysm formation via COX-2 activation.

Senescent cells: an emerging target for diseases of ageing

Chronological age represents the single greatest risk factor for human disease. One plausible explanation for this correlation is that mechanisms that drive ageing might also promote age-related diseases. Cellular senescence, which is a permanent state of cell cycle arrest induced by cellular stress, has recently emerged as a fundamental ageing mechanism that also contributes to diseases of late life, including cancer, atherosclerosis and osteoarthritis. Therapeutic strategies that safely interfere with the detrimental effects of cellular senescence, such as the selective elimination of senescent cells (SNCs) or the disruption of the SNC secretome, are gaining significant attention, with several programmes now nearing human clinical studies.

Herbal composition of Cinnamomum cassia, Pinus densiflora, Curcuma longa and Glycyrrhiza glabra prevents atherosclerosis by upregulating p27 (Kip1) expression

Background

Kiom-18 is a novel composition of Cinnamomum cassia, Pinus densiflora, Curcuma longa and Glycyrrhiza glabra. Curcuma longa and Glycyrrhiza glabra, which are traditional medicines in Asia, have been reported to demonstrate preventive effects against atherosclerosis; however, they have not yet been developed into functional atherosclerosis treatments. We therefore studied the anti-atherosclerotic effects and possible molecular mechanisms of Kiom-18 using vascular smooth muscle cells (VSMCs).

Methods

To assess the anti-proliferative effect of Kiom-18 in vitro, we performed thymidine incorporation, cell cycle progression, immunoblotting and immunofluorescence assays in VSMCs stimulated by platelet derived-growth factor (PDGF)-BB. In addition, we used LDLr knockout mice to identify the effects of Kiom-18 as a preliminary result in an atherosclerosis animal model.

Results

Kiom-18 inhibited platelet-derived growth factor (PDGF)-BB-stimulated-VSMC proliferation and DNA synthesis. Additionally, Kiom-18 arrested the cell cycle transition of G₀/G₁ stimulated by PDGF-BB and its cell cycle-related proteins. Correspondingly, the level of p27^kip1 expression was upregulated in the presence of the Kiom-18 extract. Moreover, in an atherosclerosis animal model of LDLr knockout mice, Kiom-18 extract showed a preventive effect for the formation of atherosclerotic plaque and suppressed body weight, fat weight, food treatment efficiency, neutrophil count, and triglyceride level.

Conclusions

These results indicate that Kiom-18 exerts anti-atherosclerotic effects by inhibiting VSMC proliferation via G₀/G₁ arrest, which upregulates p27^Kip1 expression.

Human miR-221/222 in Physiological and Atherosclerotic Vascular Remodeling

A cluster of miR-221/222 is a key player in vascular biology through exhibiting its effects on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). These miRNAs contribute to vascular remodeling, an adaptive process involving phenotypic and behavioral changes in vascular cells in response to vascular injury. In proliferative vascular diseases such as atherosclerosis, pathological vascular remodeling plays a prominent role. The miR-221/222 cluster controls development and differentiation of ECs but inhibits their proangiogenic activation, proliferation, and migration. miR-221/222 are primarily implicated in maintaining endothelial integrity and supporting quiescent EC phenotype. Vascular expression of miR-221/222 is upregulated in initial atherogenic stages causing inhibition of angiogenic recruitment of ECs and increasing endothelial dysfunction and EC apoptosis. In contrast, these miRNAs stimulate VSMCs and switching from the VSMC "contractile" phenotype to the "synthetic" phenotype associated with induction of proliferation and motility. In atherosclerotic vessels, miR-221/222 drive neointima formation. Both miRNAs contribute to atherogenic calcification of VSMCs. In advanced plaques, chronic inflammation downregulates miR-221/222 expression in ECs that in turn could activate intralesion neoangiogenesis. In addition, both miRNAs could contribute to cardiovascular pathology through their effects on fat and glucose metabolism in nonvascular tissues such as adipose tissue, liver, and skeletal muscles.

The emerging role of senescent cells in tissue homeostasis and pathophysiology

Cellular senescence is a state of permanent growth arrest and is thought to play a pivotal role in tumor suppression. Cellular senescence may play an important role in tumor suppression, wound healing, and protection against tissue fibrosis in physiological conditions in vivo. However, accumulating evidence that senescent cells may have harmful effects in vivo and may contribute to tissue remodeling, organismal aging, and many age-related diseases also exists. Cellular senescence can be induced by various intrinsic and extrinsic factors. Both p53/p21 and p16/RB pathways are important for irreversible growth arrest in senescent cells. Senescent cells secret numerous biologically active factors. This specific secretion phenotype by senescent cells may largely contribute to physiological and pathological consequences in organisms. Here I review the molecular basis of cell cycle arrest and the specific secretion phenotype in cellular senescence. I also summarize the current knowledge of the role of cellular senescence in vivo in physiological and pathological settings.

Functional genomics of the CDKN2A/B locus in cardiovascular and metabolic disease: what have we learned from GWASs?

Genome-wide association studies (GWASs) provide an unprecedented opportunity to examine, on a large scale, the association of common genetic variants with complex diseases like type 2 diabetes (T2D) and cardiovascular disease (CVD), thus allowing the identification of new potential disease loci. Using this approach, numerous studies have associated SNPs on chromosome 9p21.3 situated near the cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B) locus with the risk for coronary artery disease (CAD) and T2D. However, identifying the function of the nearby gene products (CDKN2A/B and ANRIL) in the pathophysiology of these conditions requires functional genomic studies. We review the current knowledge, from studies using human and mouse models, describing the function of CDKN2A/B gene products, which may mechanistically link the 9p21.3 risk locus with CVD and diabetes.

Quantification of Cellular Proliferation in Mouse Atherosclerotic Lesions

Excessive cell proliferation within atherosclerotic plaques plays an important role in the progression of atherosclerosis. Macrophage proliferation in particular has become a major focus of attention in the cardiovascular field because it appears to mediate most of macrophage expansion in mouse atherosclerotic arteries. Therefore, quantification of cell proliferation is an essential part of the characterization of atherosclerotic plaques in experimental studies. This chapter describes two variants of a simple immunostaining protocol that allow for the quantification of cellular proliferation in mouse atherosclerotic lesions based on the detection of the proliferation-associated antigen Ki-67.

Cellular senescence: from physiology to pathology

Recent discoveries are redefining our view of cellular senescence as a trigger of tissue remodelling that acts during normal embryonic development and upon tissue damage. To achieve this, senescent cells arrest their own proliferation, recruit phagocytic immune cells and promote tissue renewal. This sequence of events - senescence, followed by clearance and then regeneration - may not be efficiently completed in aged tissues or in pathological contexts, thereby resulting in the accumulation of senescent cells. Increasing evidence indicates that both pro-senescent therapies and antisenescent therapies can be beneficial. In cancer and during active tissue repair, pro-senescent therapies contribute to minimize the damage by limiting proliferation and fibrosis, respectively. Conversely, antisenescent therapies may help to eliminate accumulated senescent cells and to recover tissue function.

p27 kip1 haplo-insufficiency improves cardiac function in early-stages of myocardial infarction by protecting myocardium and increasing angiogenesis by promoting IKK activation

p27^kip1 (p27) is widely known as a potent cell cycle inhibitor in several organs, especially in the heart. However, its role has not been fully defined during the early phase of myocardial infarction (MI). In this study, we investigated the relationships between p27, vascular endothelial growth factor/hepatocyte growth factor (VEGF/HGF) and NF-κB in post-MI cardiac function repair both in vivo and in the hypoxia/ischemia-induced rat myocardiocyte model. In vivo, haplo-insufficiency of p27 improved cardiac function, diminished the infarct zone, protected myocardiocytes and increased angiogenesis by enhancing the production of VEGF/HGF. In vitro, the presence of conditioned medium from hypoxia/ischemia-induced p27 knockdown myocardiocytes reduced the injury caused by hypoxia/ischemia in myocardiocytes, and this effect was reversed by VEGF/HGF neutralizing antibodies, consistent with the cardioprotection being due to VEGF/HGF secretion. We also observed that p27 bound to IKK and that p27 haplo-insufficiency promoted IKK/p65 activation both in vivo and in vitro, thereby inducing the NF-κB downstream regulator, VEGF/HGF. Furthermore, IKKi and IKK inhibitor negated the effect of VEGF/HGF. Therefore, we conclude that p27 haplo-insufficiency protects against heart injury by VEGF/HGF mediated cardioprotection and increased angiogenesis through promoting IKK activation.

A form of the metabolic syndrome associated with mutations in DYRK1B

BACKGROUND

Genetic analysis has been successful in identifying causative mutations for individual cardiovascular risk factors. Success has been more limited in mapping susceptibility genes for clusters of cardiovascular risk traits, such as those in the metabolic syndrome.

METHODS

We identified three large families with coinheritance of early-onset coronary artery disease, central obesity, hypertension, and diabetes. We used linkage analysis and whole-exome sequencing to identify the disease-causing gene.

RESULTS

A founder mutation was identified in DYRK1B, substituting cysteine for arginine at position 102 in the highly conserved kinase-like domain. The mutation precisely cosegregated with the clinical syndrome in all the affected family members and was absent in unaffected family members and unrelated controls. Functional characterization of the disease gene revealed that nonmutant protein encoded by DYRK1B inhibits the SHH (sonic hedgehog) and Wnt signaling pathways and consequently enhances adipogenesis. Furthermore, DYRK1B promoted the expression of the key gluconeogenic enzyme glucose-6-phosphatase. The R102C allele showed gain-of-function activities by potentiating these effects. A second mutation, substituting proline for histidine 90, was found to cosegregate with a similar clinical syndrome in an ethnically distinct family.

CONCLUSIONS

These findings indicate a role for DYRK1B in adipogenesis and glucose homeostasis and associate its altered function with an inherited form of the metabolic syndrome. (Funded by the National Institutes of Health.).

Age-dependent defective TGF-beta1 signaling in patients undergoing coronary artery bypass grafting

Background

Transforming growth factor beta (TGF-β1) is a pleiotropic cytokine, which is deregulated in atherosclerosis; however the role of age in this process is unknown. We aimed to assess whether TGF-β1 signaling is affected by age.

Methods

Vascular smooth muscle cells (VSMC) were obtained from patients undergoing abdominal surgery. Levels of TGF-β1 were measured by ELISA in sera from 169 patients undergoing coronary artery bypass grafting (CABG). The p27 expression was determined by Western blot from internal mammary arteries (IMA) obtained from CABG patients (n = 13). In VSMC from these patients undergoing abdominal surgery, secretion of TGF-β1 was determined by ELISA of cell-conditioned media.

Results

In VSMC from aged patients we observed a lower TGF-β1 secretion, measured as TGF-β1 concentration in cell conditioned medium (p < 0.001). This effect was correlated to an age-dependent decrease of p27 expression in IMA from aged CABG patients. In a similar manner, there was an age-dependent decrease of serum TGF-β1 levels in CABG patients (p = 0.0195).

Conclusions

VSMC from aged patients showed a higher degree of cellular senescence and it was associated to a lower TGF-β1 secretion and signaling.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Fortilin reduces apoptosis in macrophages and promotes atherosclerosis

Atherosclerosis, a deadly disease insufficiently addressed by cholesterol-lowering drugs, needs new therapeutic strategies. Fortilin, a 172-amino acid multifunctional polypeptide, binds p53 and blocks its transcriptional activation of Bax, thereby exerting potent antiapoptotic activity. Although fortilin-overexpressing mice reportedly exhibit hypertension and accelerated atherosclerosis, it remains unknown if fortilin, not hypertension, facilitates atherosclerosis. Our objective was to test the hypothesis that fortilin in and of itself facilitates atherosclerosis by protecting macrophages against apoptosis. We generated fortilin-deficient (fortilin(+/-)) mice and wild-type counterparts (fortilin(+/+)) on a LDL receptor (Ldlr)(-/-) apolipoprotein B mRNA editing enzyme, catalytic polypeptide 1 (Apobec1)(-/-) hypercholesterolemic genetic background, incubated them for 10 mo on a normal chow diet, and assessed the degree and extent of atherosclerosis. Despite similar blood pressure and lipid profiles, fortilin(+/-) mice exhibited significantly less atherosclerosis in their aortae than their fortilin(+/+) littermate controls. Quantitative immunostaining and flow cytometry analyses showed that the atherosclerotic lesions of fortilin(+/-) mice contained fewer macrophages than those of fortilin(+/+) mice. In addition, there were more apoptotic cells in the intima of fortilin(+/-) mice than in the intima of fortilin(+/+) mice. Furthermore, peritoneal macrophages from fortilin(+/-) mice expressed more Bax and underwent increased apoptosis, both at the baseline level and in response to oxidized LDL. Finally, hypercholesterolemic sera from Ldlr(-/-)Apobec1(-/-) mice induced fortilin in peritoneal macrophages more robustly than sera from control mice. In conclusion, fortilin, induced in the proatherosclerotic microenvironment in macrophages, protects macrophages against Bax-induced apoptosis, allows them to propagate, and accelerates atherosclerosis. Anti-fortilin therapy thus may represent a promising next generation antiatherosclerotic therapeutic strategy.

Elevation of miR-221 and -222 in the internal mammary arteries of diabetic subjects and normalization with metformin

Diabetes is a major risk factor for cardiovascular disease and is associated with increased intimal thickening and accelerated vascular smooth muscle cell (VSMC) proliferation. We measured the expression of two microRNAs that promote intimal thickening, miR-221/222, and mRNA encoding a downstream target, p27(Kip1), in internal mammary artery (IMA) segments collected from 37 subjects undergoing coronary artery bypass grafting. The segments were stratified into three groups: non-diabetic subjects (ND), diabetic subjects not on metformin (DMMet-), and diabetic subjects on metformin (DMMet+). The DMMet- group exhibited a significant increase in miR-221/222 and decrease in p27(Kip1) mRNA compared to both the ND and DMMet+ groups. miR-221/222 levels inversely correlated with metformin dose. VSMCs isolated from the IMAs of the DMMet- group proliferate at a faster rate than those of the ND and DMMet+ groups. Further studies into the importance of miR-221/222 in the increased intimal thickening observed in diabetic subjects is warranted.

Dysregulation of the Mammalian Target of Rapamycin and p27Kip1 Promotes Intimal Hyperplasia in Diabetes Mellitus

The proliferation and migration of vascular smooth muscle cells (VSMCs) in the intima of an artery, known as intimal hyperplasia, is an important component of cardiovascular diseases. This is seen most clearly in the case of in-stent restenosis, where drug eluting stents are used to deliver agents that prevent VSMC proliferation and migration. One class of agents that are highly effective in the prevention of in-stent restenosis is the mammalian Target of Rapamycin (mTOR) inhibitors. Inhibition of mTOR blocks protein synthesis, cell cycle progression, and cell migration. Key to the effects on cell cycle progression and cell migration is the inhibition of mTOR-mediated degradation of p27Kip1 protein. p27Kip1 is a cyclin dependent kinase inhibitor that is elevated in quiescent VSMCs and inhibits the G1 to S phase transition and cell migration. Under normal conditions, vascular injury promotes degradation of p27Kip1 protein in an mTOR dependent manner. Recent reports from our lab suggest that in the presence of diabetes mellitus, elevation of extracellular signal response kinase activity may promote decreased p27Kip1 mRNA and produce a relative resistance to mTOR inhibition. Here we review these findings and their relevance to designing treatments for cardiovascular disease in the presence of diabetes mellitus.

STAT1 requirement for PKR-induced cell cycle arrest in vascular smooth muscle cells in response to heparin

Interferons (IFNs) are a family of cytokines that exhibit antiviral, antiproliferative, and immunomodulatory properties. PKR (protein kinase, RNA activated) is of central importance in mediating the antiproliferative actions of IFNs. Our research has established that PKR inhibits vascular smooth muscle cell (VSMC) proliferation by regulating G1 to S transition. Many cardiovascular diseases result from complications of atherosclerosis, a chronic and progressive inflammatory condition often characterized by excessive proliferation of VSMC. Thus, an effective method for inhibiting VSMC proliferation is likely to arrest atherosclerosis and restenosis at early stages. Our research establishes that PKR activation in VSMC leads to a G1 arrest brought about by an inhibition of cyclin-dependent kinase 2 (Cdk2) activity by p27(kip1). In quiescent VSMC, p27(kip1) levels are high and when stimulated by serum/growth factors, p27(kip1) levels drop by destabilization of the protein. Under conditions that lead to activation of PKR, there is a marked inhibition of p27(kip1) down-regulation due to increased stability of p27(kip1) protein. In order to understand the mechanism of heparin-induced stabilization of p27(kip1) in VSMC, we examined the involvement of the Signal Transducer and Activator of Transcription-1 (STAT1), which is an important player in mediating antiproliferative effects of IFNs. Our results demonstrate that PKR overexpression in VSMC leads to an increase in p27(kip1) protein levels and this increase requires the catalytic activity of PKR. PKR activation induced by antiproliferative agent heparin leads to phosphorylation of STAT1 on serine 727, which is essential for the cell cycle block. STAT1 null VSMCs are largely defective in heparin-induced cell cycle arrest and in PKR null cells the STAT1 phosphorylation in response to heparin was absent. These results establish that heparin causes STAT1 phosphorylation on serine 727 via activation of PKR and that this event is required for the G1 arrest in VSMC.

miR-221/222 compensates for Skp2-mediated p27 degradation and is a primary target of cell cycle regulation by prostacyclin and cAMP

p27(kip1) (p27) is a cdk-inhibitory protein with an important role in the proliferation of many cell types. SCF(Skp2) is the best studied regulator of p27 levels, but Skp2-mediated p27 degradation is not essential in vivo or in vitro. The molecular pathway that compensates for loss of Skp2-mediated p27 degradation has remained elusive. Here, we combine vascular injury in the mouse with genome-wide profiling to search for regulators of p27 during cell cycling in vivo. This approach, confirmed by RT-qPCR and mechanistic analysis in primary cells, identified miR-221/222 as a compensatory regulator of p27. The expression of miR221/222 is sensitive to proteasome inhibition with MG132 suggesting a link between p27 regulation by miRs and the proteasome. We then examined the roles of miR-221/222 and Skp2 in cell cycle inhibition by prostacyclin (PGI(2)), a potent cell cycle inhibitor acting through p27. PGI(2) inhibited both Skp2 and miR221/222 expression, but epistasis, ectopic expression, and time course experiments showed that miR-221/222, rather than Skp2, was the primary target of PGI(2). PGI(2) activates Gs to increase cAMP, and increasing intracellular cAMP phenocopies the effect of PGI(2) on p27, miR-221/222, and mitogenesis. We conclude that miR-221/222 compensates for loss of Skp2-mediated p27 degradation during cell cycling, contributes to proteasome-dependent G1 phase regulation of p27, and accounts for the anti-mitogenic effect of cAMP during growth inhibition.

Apolipoprotein E-mediated cell cycle arrest linked to p27 and the Cox2-dependent repression of miR221/222

OBJECTIVE

In addition to its effects on cholesterol levels, apoE3 has lipid-independent effects that contribute to cardiovascular protection; one of these effects is the ability to inhibit cell cycling in VSMCs. The goal of this study was to identify and characterize cell cycle-regulatory mechanisms responsible for the anti-mitogenic effect of apoE.

METHODS AND RESULTS

Primary VSMCs were stimulated with serum in the absence or presence of apoE3. apoE3 upregulated expression of the cdk inhibitor, p27(kip1), in primary VSMCs, and this effect required Cox2 and activation of PGI(2)-IP signaling. The microRNA family, miR221/222 has recently been identified as a post-translational regulator of p27, and apoE3 inhibited miR221/222 expression in a Cox2- and PGI(2)/IP-dependent manner. Moreover, reconstituted miR222 expression was sufficient to override the effects of apoE on p27 expression and S phase entry. The ability to repress expression of miR221/222 is shared by apoE3-containing HDL but is absent from apoA-1, LDL and apoE-depleted HDL. All three apoE isoforms regulate miR221/222, and the effect is independent of the C-terminal lipid-binding domain. miR221/222 levels are increased in the aortae of apoE3-null mice and reduced when apoE3 expression is reconstituted by adeno-associated virus infection. Thus, regulation of miR221/222 by apoE3 occurs in vivo as well as in vitro.

CONCLUSIONS

ApoE inhibits VSMC proliferation by regulating p27 through miR221/222. Control of cell cycle-regulatory microRNAs adds a new dimension to the spectrum of cardiovascular protective effects afforded by apoE and apoE-HDL.

Macrophage proliferation and apoptosis in atherosclerosis

PURPOSE OF REVIEW

Atherosclerosis is driven by cardiovascular risk factors that cause the recruitment of circulating immune cells beneath the vascular endothelium. Infiltrated monocytes differentiate into different macrophage subtypes with protective or pathogenic activities in vascular lesions. We discuss current knowledge about the molecular mechanisms that regulate lesional macrophage proliferation and apoptosis, two processes that occur during atherosclerosis development and regulate the number and function of macrophages within the atherosclerotic plaque.

RECENT FINDINGS

Lesional macrophages in early phases of atherosclerosis limit disease progression by phagocytizing modified lipoproteins, cellular debris and dead cells that accumulate in the plaque. However, macrophages in advanced lesions contribute to a maladaptive, nonresolving inflammatory response that can lead to life-threatening acute thrombotic diseases (myocardial infarction or stroke). Macrophage-specific manipulation of genes involved in cell proliferation and apoptosis modulates lesional macrophage accumulation and atherosclerosis burden in mouse models, and studies are beginning to elucidate the underlying mechanisms.

SUMMARY

Despite recent advances in our understanding of macrophage proliferation and apoptosis in atherosclerotic plaques, it remains unclear whether manipulating these processes will be beneficial or harmful. Advances in these areas may translate into more efficient therapies for the prevention and treatment of atherothrombosis.

Effect of 9p21.3 coronary artery disease locus neighboring genes on atherosclerosis in mice

BACKGROUND

The human 9p21.3 chromosome locus has been shown to be an independent risk factor for atherosclerosis in multiple large-scale genome-wide association studies, but the underlying mechanism remains unknown. We set out to investigate the potential role of the 9p21.3 locus neighboring genes, including Mtap, the 2 isoforms of Cdkn2a, p16Ink4a and p19Arf, and Cdkn2b, in atherosclerosis using knockout mice models.

METHODS AND RESULTS

Gene-targeted mice for neighboring genes, including Mtap, Cdkn2a, p19Arf, and Cdkn2b, were each bred to mice carrying the human APO*E3 Leiden transgene that sensitizes the mice for atherosclerotic lesions through elevated plasma cholesterol. We found that the mice heterozygous for Mtap developed larger lesions compared with wild-type mice (49623±21650 versus 18899±9604 μm(2) per section [mean±SD]; P=0.01), with morphology similar to that of wild-type mice. The Mtap heterozygous mice demonstrated changes in metabolic and methylation profiles and CD4(+) cell counts. The Cdkn2a knockout mice had smaller lesions compared with wild-type and heterozygous mice, and there were no significant differences in lesion size in p19Arf and Cdkn2b mutants compared with wild type. We observed extensive, tissue-specific compensatory regulation of the Cdkn2a and Cdkn2b genes among the various knockout mice, making the effects on atherosclerosis difficult to interpret.

CONCLUSIONS

Mtap plays a protective role against atherosclerosis, whereas Cdkn2a appears to be modestly proatherogenic. However, no relation was found between the 9p21 genotype and the transcription of 9p21 neighboring genes in primary human aortic vascular cells in vitro. There is extensive compensatory regulation in the highly conserved 9p21 orthologous region in mice.

Comparison of ROCK and EGFR activation pathways in the progression of glomerular injuries in AngII-infused rats

AIM

The roles of rho-kinase (ROCK) and epidermal growth factor receptor (EGFR) were studied using an angiotensin II (AngII)-dependent hypertension rat model.

METHOD

Male Wistar rats were infused with AngII at a rate of 400 ng/kg body weight (BW)/min for 14 days. Effects of ROCK inhibitor, fasudil (20 mg/kg BW), and EGFR inhibitor, gefitinib (3 mg/kg BW), were studied.

RESULTS

AngII infusion increased blood pressure (BP; 220 ± 19 mmHg) as well as the number of proliferating cells in glomeruli judged by Ki67 and proliferating cell nuclear antigen immunostaining and urinary protein excretion (118 ± 19 mg/day). AngII also decreased p27 expression and increased cyclin D1 expression in glomeruli, as well as induced dissociation of the nephrin- and podocin-immunostaining patterns in podocytes. Treatment with fasudil or gefitinib completely inhibited glomerular cell proliferation without changing the BP. Although the decreased p27 expression was reversed by both treatments, cyclin D1 induction was abolished only by gefitinib. Fasudil significantly reduced proteinuria (57.2 ± 17.5 mg/day), but not gefitinib (133.3 ± 30.9 mg/day). The dissociation of podocin and nephrin was ameliorated by fasudil, but not by gefitinib.

CONCLUSION

ROCK and EGFR have distinct roles in proteinuria and glomerular cell proliferation in this model.

Increased gene dosage of the Ink4/Arf locus does not attenuate atherosclerosis development in hypercholesterolaemic mice

RATIONALE

Human genome-wide association studies have identified genetic variants in the chromosome 9p21 region that confer increased risk of coronary artery disease and other age-related diseases. These variants are located in a block of high linkage disequilibrium with the neighboring Ink4/Arf tumor-suppressor locus (also named CDKN2A/CDKN2B). Since previous studies suggest an atheroprotective role of the Ink4/Arf locus, here we assessed whether gain-of-function of the encoded genes can be exploited therapeutically to reduce atherosclerosis.

METHODS

Generation and characterization of apolipoprotein E-null mice carrying an additional transgenic copy of the entire Ink4/Arf locus (apoE-/-Super-Ink4/Arf) that reproduces the normal expression and regulation of the endogenous locus.

RESULTS

Although liver and aorta of apoE-/-Super-Ink4/Arf mice only showed a trend towards increased Ink4/Arf transcript levels compared to apoE-/- controls, cultured macrophages with increased Ink4/Arf gene dosage exhibited augmented apoptosis induced by irradiation with ultraviolet light, indicating that low level of transgene overexpression can lead to augmented Ink4/Arf function. However, increased Ink4/Arf gene dosage did not affect atherosclerosis development in different vascular regions of both male and female apoE-/- mice fed either normal or high-fat diet. Increased gene dosage of Ink4/Arf similarly had no effect on atheroma cell composition or collagen content, an index of plaque stability.

CONCLUSION

In contrast with previous studies demonstrating cancer resistance in Super-Ink4/Arf mice carrying an additional transgenic copy of the entire Ink4/Arf locus, our results cast doubt on the potential of Ink4/Arf activation as a strategy for the treatment of atherosclerotic disease.

Deficient p27 Phosphorylation at Serine 10 Increases Macrophage Foam Cell Formation and Aggravates Atherosclerosis Through a Proliferation-Independent Mechanism

Objective—

Genetic ablation of the growth suppressor p27 Kip1 (p27) in the mouse aggravates atherosclerosis coinciding with enhanced arterial cell proliferation. However, it is unknown whether molecular mechanisms that limit p27's protective function contribute to atherosclerosis development and whether p27 exerts proliferation-independent activities in the arterial wall. This study aims to provide insight into both questions by investigating the role in atherosclerosis of p27 phosphorylation at serine 10 (p27-phospho-Ser10), a major posttranslational modification of this protein.

Methods and Results—

Immunoblotting studies revealed a marked reduction in p27-phospho-Ser10 in atherosclerotic arteries from apolipoprotein E–null mice, and expression of the nonphosphorylatable mutant p27Ser10Ala, either global or restricted to bone marrow, accelerated atherosclerosis. p27Ser10Ala expression did not affect cell proliferation in early and advanced atheroma but activated RhoA/Rho-associated coiled-coil containing protein kinase (ROCK) signaling and promoted macrophage foam cell formation in a ROCK-dependent manner. Supporting the clinical relevance of these findings, human atherosclerotic coronary arteries exhibited a prominent reduction in p27-phospho-Ser10 and increased ezrin/radixin/moesin protein phosphorylation, a marker of RhoA/ROCK activation.

Conclusion—

Scarce phosphorylation of p27 at Ser10 is a hallmark of human and mouse atherosclerosis and promotes disease progression in mice. This proatherogenic effect is mediated by a proliferation-independent mechanism that involves augmented foam cell formation owing to increased RhoA/ROCK activity. These findings unveil a new atheroprotective action of p27 and identify p27-phospho-Ser10 as an attractive target for the treatment of atherosclerosis.

Minocycline reduces plaque size in diet induced atherosclerosis via p27(Kip1)

OBJECTIVE

Minocycline, a tetracycline derivate, mediates vasculoprotective effects independent of its antimicrobial properties. Thus, minocycline protects against diabetic nephropathy and reduces neointima formation following vascular injury through inhibition of apoptosis or migration, respectively. Whether minocycline has an effect on primary atherogenesis remains unknown.

METHODS

Using morphological and immunohistochemical analyses we determined de novo atherogenesis in ApoE-/- mice receiving a high fat diet (HFD) with or without minocycline treatment. The effect of minocycline on proliferation, expression of p27(Kip1) or PARP-1 (Poly [ADP-ribose] polymerase 1), or on PAR (poly ADP-ribosylation) modification in vascular smooth muscle cells (VSMC) was analyzed in ex vivo and in vitro (primary human and mouse VSMC).

RESULTS AND CONCLUSION

Minocycline reduced plaque size and stenosis in ApoE-/- HFD mice. This was associated with a lower number and less proliferation of VSMC, reduced PAR (poly ADP-ribosylation) modification and increased p27(Kip1) expression within the plaques. In agreement with the ex vivo data minocycline reduced proliferation, PARP-1 expression, PAR modification while inducing p27 expression in human and mouse VSMC in vitro. These effects were observed at a low minocycline concentration (10 μM), which had no effect on VSMC migration or apoptosis. Minocycline inhibited PARP-1 and induced p27(Kip1) expression in VSMC as efficiently as the specific PARP-1 inhibitor PJ 34. Knock down of p27(Kip1) abolished the antiproliferative effect of minocycline. These data establish a novel antiatherosclerotic mechanism of minocycline during de novo atherogenesis, which depends on p27(Kip1) mediated inhibition of VSMC proliferation.

The physiological significance of p27(KIP1) expression in detrusor function

PURPOSE

Bladder outlet obstruction results in smooth muscle cell hyperplasia, decreased bladder wall compliance, and lower and upper urinary tract pathology. The cyclin-dependent kinase inhibitor p27(KIP1) regulates bladder smooth muscle cell proliferation in response to bladder outlet obstruction but little is known about its physiological role in the bladder. We investigated the role of p27(KIP1) in the structure and function of the detrusor layer of the bladder wall.

MATERIALS AND METHODS

We used immunoblotting and reverse transcriptase-polymerase chain reaction to examine cell cycle regulation in response to increased mechanical tension in an in vitro model of tension induced smooth muscle cell proliferation and an in vivo model of bladder outlet obstruction. We compared unobstructed bladders of p27(+/+) and p27(-/-) mice (Jackson Laboratory, Bar Harbor, Maine) structurally by histological staining and functionally by in vivo cystometric measurements of bladder capacity, detrusor compliance and detrusor leak point pressure.

RESULTS

Increased tension decreased p27(KIP1) at the protein level in human bladder smooth muscle cells and in intact murine bladder smooth muscle. p27(-/-) mice had bladder smooth muscle cell hyperplasia even in the absence of bladder outlet obstruction. While p27 loss had little effect on detrusor leak point pressure, p27(-/-) mice had significantly decreased bladder capacity and detrusor compliance.

CONCLUSIONS

To our knowledge we provide the first report of the in vivo significance of p27(KIP1) in the regulation of detrusor function using a cystometric approach. We identified a role for p27(KIP1) in protecting against dysregulated smooth muscle cell proliferation, bladder capacity and detrusor compliance under normotensive conditions.

Deficiency of cyclin-dependent kinase inhibitors p21Cip1 and p27Kip1 accelerates atherogenesis in apolipoprotein E-deficient mice

Cyclin-dependent kinase inhibitors, p21(Cip1) and p27(Kip1), are upregulated during vascular cell proliferation and negatively regulate growth of vascular cells. We hypothesized that absence of either p21(Cip1) or p27(Kip1) in apolipoprotein E (apoE)-deficiency may increase atherosclerotic plaque formation. Compared to apoE(-/-) aortae, both apoE(-/-)/p21(-/-) and apoE(-/-)/p27(-/-) aortae exhibited significantly more atherosclerotic plaque following a high-cholesterol regimen. This increase was particularly observed in the abdominal aortic regions. Deficiency of p27(Kip1) accelerated plaque formation significantly more than p21(-/-) in apoE(-/-) mice. This increased plaque formation was in parallel with increased intima/media area ratios. Deficiency of p21(Cip1) and p27(Kip1) accelerates atherogenesis in apoE(-/-) mice. These findings have significant implications for our understanding of the molecular basis of atherosclerosis associated with excessive proliferation of vascular cells.

p19(ARF) deficiency reduces macrophage and vascular smooth muscle cell apoptosis and aggravates atherosclerosis

OBJECTIVES

The goal of this study was to investigate the role in atherosclerosis of the tumor suppressor protein ARF (human p14(ARF), mouse p19(ARF)) encoded by the CDKN2A gene.

BACKGROUND

Atherosclerosis is characterized by excessive proliferation and apoptosis, 2 cellular processes regulated by CDKN2A. Although recent genome-wide association studies have linked atherosclerotic diseases to a genomic region in human chromosome 9p21 near the CDKN2A locus, the mechanisms underlying this gene-disease association remain undefined, and no causal link has been established between CDKN2A and atherosclerosis.

METHODS

Atherosclerosis-prone apolipoprotein E (apoE)-null and doubly deficient apoE-p19(ARF) mice were fed an atherogenic diet and sacrificed to quantify atherosclerosis burden in whole-mounted aortas and in aortic cross-sections. Proliferation and apoptosis were investigated in atherosclerotic lesions and in primary cultures of macrophages and vascular smooth muscle cells obtained from both groups of mice.

RESULTS

Genetic disruption of p19(ARF) in apoE-null mice augments aortic atherosclerosis without affecting body weight, plasma lipoproteins, or plaque's proliferative activity. Notably, p19(ARF) deficiency significantly attenuates apoptosis both in atherosclerotic lesions and in cultured macrophages and vascular smooth muscle cells, 2 major cellular constituents of atheromatous plaques.

CONCLUSIONS

Our findings establish a direct link between p19(ARF), plaque apoptosis, and atherosclerosis, and suggest that human genetic variants associated to diminished CDKN2A expression may accelerate atherosclerosis by limiting plaque apoptosis.

Tumor suppressor p27(Kip1) undergoes endolysosomal degradation through its interaction with sorting nexin 6

A large body of evidence supports the hypothesis that proteasomal degradation of the growth suppressor p27(Kip1) (p27) facilitates mammalian cell cycle progression. However, very few studies have addressed the possibility of proteasome-independent mechanisms of p27 proteolysis. Here we provide evidence for a novel pathway of p27 degradation via the lysosome that is mediated by its interaction with the endosomal protein sorting nexin 6 (SNX6), a member of the sorting nexin family of vesicular trafficking regulators. p27 and SNX6 interact in vitro and in vivo in mammalian cells, partially colocalize in endosomes, and are present in purified endosomal fractions. Gain- and loss-of-function studies revealed that SNX6 induces endosomal accumulation of p27. Moreover, p27 is detected in lysosomes and inhibition of lysosome-dependent proteolysis impairs serum-mediated down-regulation of p27 in a SNX6-dependent manner. To validate the localization of p27 in these organelles, we analyzed several cell lines using two different anti-p27 antibodies, several organelle-specific markers [e.g., early endosome antigen 1, lysosomal-associated membrane protein (LAMP) 1, LAMP2, and LysoTracker], and overexpression of fluorescent p27 and SNX6. Remarkably, silencing of SNX6 attenuates p27 down-regulation in the G(1) phase of the mitotic cell cycle and delays cell cycle progression. We therefore conclude that, in addition to the proteasome-dependent pathway, SNX6-mediated endolysosomal degradation of p27 also contributes to cell cycle progression in mammalian cells.

Targeted deletion of the 9p21 non-coding coronary artery disease risk interval in mice

Sequence polymorphisms in a 58-kilobase (kb) interval on chromosome 9p21 confer a markedly increased risk of coronary artery disease (CAD), the leading cause of death worldwide. The variants have a substantial effect on the epidemiology of CAD and other life-threatening vascular conditions because nearly one-quarter of Caucasians are homozygous for risk alleles. However, the risk interval is devoid of protein-coding genes and the mechanism linking the region to CAD risk has remained enigmatic. Here we show that deletion of the orthologous 70-kb non-coding interval on mouse chromosome 4 affects cardiac expression of neighbouring genes, as well as proliferation properties of vascular cells. Chr4(Delta70kb/Delta70kb) mice are viable, but show increased mortality both during development and as adults. Cardiac expression of two genes near the non-coding interval, Cdkn2a and Cdkn2b, is severely reduced in chr4(Delta70kb/Delta70kb) mice, indicating that distant-acting gene regulatory functions are located in the non-coding CAD risk interval. Allele-specific expression of Cdkn2b transcripts in heterozygous mice showed that the deletion affects expression through a cis-acting mechanism. Primary cultures of chr4(Delta70kb/Delta70kb) aortic smooth muscle cells exhibited excessive proliferation and diminished senescence, a cellular phenotype consistent with accelerated CAD pathogenesis. Taken together, our results provide direct evidence that the CAD risk interval has a pivotal role in regulation of cardiac Cdkn2a/b expression, and suggest that this region affects CAD progression by altering the dynamics of vascular cell proliferation.

Control of cell proliferation in atherosclerosis: insights from animal models and human studies

Excessive hyperplastic cell growth within occlusive vascular lesions has been recognized as a key component of the inflammatory response associated with atherosclerosis, restenosis post-angioplasty, and graft atherosclerosis after coronary artery bypass. Understanding the molecular mechanisms that regulate arterial cell proliferation is therefore essential for the development of new tools for the treatment of these diseases. Mammalian cell proliferation is controlled by a large number of proteins that modulate the mitotic cell cycle, including cyclin-dependent kinases, cyclins, and tumour suppressors. The purpose of this review is to summarize current knowledge about the role of these cell cycle regulators in the development of native and graft atherosclerosis that has arisen from animal studies, histological examination of specimens from human patients, and genetic studies.

p27kip1-838C>A single nucleotide polymorphism is associated with restenosis risk after coronary stenting and modulates p27kip1 promoter activity

BACKGROUND

The cyclin-dependent kinase inhibitor p27(kip1) is a key regulator of smooth muscle cell and leukocyte proliferation in vascular disease, including in-stent restenosis. We therefore hypothesized that common genetic variations or single nucleotide polymorphisms in p27(kip1) may serve as a useful tool in risk stratification for in-stent restenosis.

METHODS AND RESULTS

Three single nucleotide polymorphisms concerning the p27(kip1) gene (-838C>A, rs36228499; -79C>T, rs34330; +326G>T, rs2066827) were determined in a cohort of 715 patients undergoing coronary angioplasty and stent placement. We discovered that the p27(kip1)-838C>A single nucleotide polymorphism is associated with clinical in-stent restenosis; the -838AA genotype decreases the risk of target vessel revascularization (hazard ratio, 0.28; 95% confidence interval, 0.10 to 0.77). This finding was replicated in another cohort study of 2309 patients (hazard ratio, 0.61; 95% confidence interval, 0.40 to 0.93). No association was detected between this end point and the p27(kip1)-79C>T and +326G>T single nucleotide polymorphisms. We subsequently studied the functional importance of the -838C>A single nucleotide polymorphism and detected a 20-fold increased basal p27(kip1) transcriptional activity of the -838A allele containing promoter.

CONCLUSIONS

Patients with the p27(kip1)-838AA genotype have a decreased risk of in-stent restenosis corresponding with enhanced promoter activity of the -838A allele of this cell-cycle inhibitor, which may explain decreased smooth muscle cell proliferation.

Atherosclerosis development in apolipoprotein E-null mice deficient for CD69

AIMS

Atherosclerosis is a chronic inflammatory disease regulated by immune mechanisms. CD69 is a cell surface receptor rapidly induced after leukocyte activation at sites of chronic inflammation. Genetic disruption of CD69 in the mouse aggravates collagen-induced arthritis (CIA), and partial depletion of CD69-expressing cells with anti-CD69 monoclonal antibody (mAb) prevents CIA development in wild-type mice, suggesting that this receptor negatively modulates immune and inflammatory responses. It has been recently reported that CD69 is upregulated in a large subset of T cells in atherosclerosis-prone apolipoprotein E-null mice (apoE(-/-)). In this study, we investigated whether altering CD69 function affects atherosclerosis development.

METHODS AND RESULTS

We studied native and diet-induced atherosclerosis in apoE(-/-) and doubly deficient apoE(-/-)CD69(-/-) mice and performed expression studies in tissues and primary cells derived from these animals. Plasma cholesterol level was unaffected by CD69 genetic inactivation. Although this genetic manipulation led to an elevated production of interferon gamma and interleukin 10 by activated T cells, apoE(-/-) and apoE(-/-)CD69(-/-) mice fed control and high-fat diet exhibited atheromas of similar size and composition when analysed at different stages of the disease. Likewise, anti-CD69 mAb treatment had no effect on plasma cholesterol and atherosclerosis burden in fat-fed apoE(-/-) mice.

CONCLUSION

In contrast to previous studies highlighting the protective function of CD69 against CIA, an autoimmune inflammatory disease, our results rule out a significant role for CD69 against atherosclerosis in apoE(-/-) mice, an experimental disease model featuring a local inflammatory response triggered and sustained by alterations in lipid homeostasis.

Regulatory role of vitamins E and C on extracellular matrix components of the vascular system

The protective effect of vitamins E (alpha-tocopherol) and C (L-ascorbic acid) in the prevention of cardiovascular disease (CVD) has been shown in a number of situations but a secure correlation is not universally accepted. Under certain conditions, both, L-ascorbic acid and alpha-tocopherol can exhibit antioxidant properties and thus may reduce the formation of oxidized small molecules, proteins and lipids, which are a possible cause of cellular de-regulation. However, non-antioxidant effects have also been suggested to play a role in the prevention of atherosclerosis. Vitamin E and C can modulate signal transduction and gene expression and thus affect many cellular reactions such as the proliferation of smooth muscle cells, the expression of cell adhesion and extracellular matrix molecules, the production of O(2)(-) by NADPH-oxidase, the aggregation of platelets and the inflammatory response. Vitamins E and C may modulate the extracellular matrix environment by affecting VSMC differentiation and the expression of connective tissue proteins involved in vascular remodeling as well as the maintenance of vascular wall integrity. This review summarizes individually the molecular activities of vitamins E and C on the cells within the connective tissue of the vasculature, which are centrally involved in the maintenance of an intact vascular wall as well as in the repair of atherosclerotic lesions during disease development.

Expression of Cell-Cycle-Regulating Genes in the Development of Atherosclerosis in Japanese Quail (Coturnix japonica)

The levels of mRNA expression in regulatory genes that are involved in the pathological changes of aortic atherosclerotic and fibroblastic intimal thickening was investigated in Japanese quail. The quail were divided into a control diet group and an atherogenic diet group. The quail were euthanized at 2, 4, 8, and 12 wk after consuming either a control diet or an atherogenic diet. Thereafter, both histological and immunohistochemical studies and mRNA expression analysis of the cell-cycle-regulating genes in aortic atherosclerotic lesions were performed on selected ascending aortas and their large branches. In the atherogenic diet group, aortic lipid-containing intimal and atheromatous lesions were seen mainly at 8 and 12 wk, respectively. Semiquantitative reverse-transcription PCR was used to analyze the alterations of mRNA expression on the development of atherosclerotic lesions. Messenger RNA expression of the c-fos and c-src genes showed peak levels at 8 wk in the atherogenic diet group. However, no significant alteration of c-jun mRNA expression was noted during the entire experimental period. According to the progression of aortic atherosclerotic lesions, c-myc mRNA expression in the atherogenic diet group increased chronologically, and the highest level was observed at 12 wk. Alterations in mRNA expression of proliferating cell nuclear antigen and the p27 gene were similar to that of c-myc. The levels of c-myc, proliferating cell nuclear antigen, and p27 mRNA expression was significantly correlated with the degree of aortic atherosclerotic lesion development at 12 wk in our experiment.

Beneficial effect of atorvastatin on left ventricular remodeling in spontaneously hypertensive rats

This study was designed to investigate whether atorvastatin has a beneficial effect on left ventricular (LV) remodeling in spontaneously hypertensive rats (SHR), and then explore the underlying mechanisms involved. 12 SHRs were randomized to receive either distilled water (SHR group, n = 6) or atorvastatin (ATV group, n = 6) for 10 weeks. Age-matched Wistar-Kyoto rats (WKY) gavaged by distilled water were used as normal controls (WKY group, n = 6). By using these rats, we observed the effects of atorvastatin on LV hypertrophy and fibrosis, and investigated atorvastatin-induced cell apoptosis and p27 protein expression. In addition, the serum lipid concentration and blood pressure level were also measured in this study. 10 weeks later, a significant decrease in the cardiosomatic ratio, LV weight to body weight ratio and cardiomyocyte transverse diameter, as well as myocardial hydroxyproline and collagen content was observed in the atorvastatin-treated SHR. In addition, atorvastatin increased the positive rate of cell apoptosis and p27 protein expression. A decreased serum lipid concentration and a reduced systolic blood pressure level were also found in the atorvastatin-treated SHR. These findings demonstrated a beneficial effect of atorvastatin on adverse LV remodeling in SHR, and the induction of cell apoptosis and upregulation of p27 protein may serve as the underlying mechanisms of this action.

Atheroma development in apolipoprotein E-null mice is not regulated by phosphorylation of p27(Kip1) on threonine 187

Excessive cellular proliferation is thought to contribute to neointimal lesion development during atherosclerosis and restenosis after angioplasty. Inhibition of cyclin-dependent kinase (CDK) activity by p27 inhibits mammalian cell growth. Mounting evidence indicates that p27 negatively regulates neointimal thickening in animal models of restenosis and atherosclerosis, and its expression in human neointimal lesions is consistent with such a protective role. Cell cycle progression is facilitated by cyclinE/CDK2-dependent phosphorylation of p27 on threonine 187 (T187) during late G1. The purpose of this study was to assess whether this phosphorylation event plays a role during atherosclerosis. To this end, we generated apolipoprotein E-null mice with both p27 alleles replaced by a mutated form non-phosphorylatable at T187 (apoE-/-p27T187A mice) and investigated the kinetics of atheroma development in these animals compared to apoE-/- controls with an intact p27 gene. Fat feeding resulted in comparable level of hypercholesterolemia in both groups of mice. Surprisingly, aortic p27 expression was not increased in fat-fed apoE-/-p27T187A mice compared with apoE-/- controls. Moreover, atheroma size, lesion cellularity, proliferation, and apoptotic rates were undistinguishable in both groups of fat-fed mice. Thus, in contrast to previous studies that highlight the importance of p27 phosphorylation at T187 on the control of p27 expression and function in different tissues and pathophysiological scenarios, our findings demonstrate that this phosphorylation event is not implicated in the control of aortic p27 expression and atheroma progression in hypercholesterolemic mice.

p21Cip1 is required for the development of monocytes and their response to serum transfer-induced arthritis

One of the central functions of cyclin-dependent kinase inhibitors, such as p21, p27, or p16, is to prevent entry into the cell cycle. However, the question remains as to whether they have other functions in the cell. We previously demonstrated that overexpression of p21 in fibroblasts isolated from patients with rheumatoid arthritis decreases the production of pro-inflammatory molecules. Overexpression of p21 has been also shown to reduce the development of experimental arthritis in mice and rats. To explore the role of endogenous p21 in the development of arthritis, we induced arthritis in p21(-/-) mice using the K/BxN serum transfer model of arthritis. Mice deficient in p21 were more resistant to serum transfer-induced arthritis (K/BxN) than wild-type (wt) control mice. Fewer macrophages were detected in p21(-/-) as compared to wt joints following transfer of K/BxN serum. Chemotaxis assays of bone marrow-derived macrophages from p21(-/-) and wt mice revealed no difference in migration. However, there was a substantial decrease in inflammatory monocytes circulating in peripheral blood and in monocyte precursors in bone marrow of p21(-/-) mice as compared to wt mice. Adoptive transfer of wt bone marrow-derived macrophages into p21(-/-) mice restored the sensitivity to serum transfer-induced arthritis. These data suggest a novel role for p21 in regulating the development and/or differentiation of monocytic populations that are crucial for the induction of inflammatory arthritis.

Macrophage retinoblastoma deficiency leads to enhanced atherosclerosis development in ApoE-deficient mice

The cellular composition of an atherosclerotic lesion is determined by cell infiltration, proliferation, and apoptosis. The tumor suppressor gene retinoblastoma (Rb) has been shown to regulate both cell proliferation and cell death in many cell types. To study the role of macrophage Rb in the development of atherosclerosis, we used apoE-deficient mice with a macrophage-restricted deletion of Rb (Rb(del) mice) and control littermates (Rb(fl) mice). After 12 wk feeding a cholesterol-rich diet, the Rb(del) mice showed a 51% increase in atherosclerotic lesion area with a 39% increase in the relative number of advanced lesions. Atherosclerotic lesions showed a 13% decrease in relative macrophage area and a 46% increase in relative smooth muscle cell area, reflecting the more advanced state of the lesions. The increase in atherosclerosis was independent of in vitro macrophage modified lipoprotein uptake or cytokine production. Whereas macrophage-restricted Rb deletion did not affect lesional macrophage apoptosis, a clear 2.6-fold increase in lesional macrophage proliferation was observed. These studies demonstrate that macrophage Rb is a suppressing factor in the progression of atherosclerosis by reducing macrophage proliferation.

Cyclin-Dependent Kinase Inhibitor p27 Kip1 , But Not p21 WAF1/Cip1 , Is Required for Inhibition of Hypoxia-Induced Pulmonary Hypertension and Remodeling by Heparin in Mice

Heparin has growth inhibitory effects on pulmonary artery smooth muscle cell (PASMC) in vitro and in vivo. However, the mechanism has not been fully defined. In this study, we investigated the role of cyclin-dependent kinase inhibitors, p21(WAF1/cip1) (p21) and p27Kip1 (p27), in the inhibitory effect of heparin on PASMC proliferation in vitro and on hypoxia-induced pulmonary hypertension in vivo using p21 and p27-null mice. In vitro, loss of the p27 gene negated the inhibitory effect of heparin on PASMC proliferation, but p21 was not critical for this inhibition. In vivo, heparin significantly inhibited the development of hypoxia-induced pulmonary hypertension and remodeling, as evidenced by decreased right ventricular systolic pressure, ratio of right ventricular weight to left ventricle plus septum weight, and percent wall thickness of pulmonary artery, in p21(+/+), p21(-/-), p27(+/+), and p27(+/-), but not in p27(-/-) mice. We also observed that hypoxia decreased p27 expression significantly in mouse lung, which was restored by heparin. Heparin inhibited Ki67 proliferative index in terminal bronchial vessel walls in p27(+/+) and p27(+/-), but not in p27(-/-) mice exposed to hypoxia. Therefore, we conclude that the cyclin-dependent kinase inhibitor p27, but not p21, is required for the inhibition of hypoxic pulmonary vascular remodeling by heparin.