Role of smooth muscle cells in the initiation and early progression of atherosclerosis

Endogenous testosterone attenuates neointima formation after moderate coronary balloon injury in male swine

AIMS

Previous studies from our laboratory have demonstrated that testosterone increases coronary smooth muscle protein kinase C delta (PKC delta) both in vivo and in vitro and inhibits coronary smooth muscle proliferation by inducing G(0)/G(1) cell cycle arrest in a PKC delta-dependent manner. The purpose of the present study was to determine whether endogenous testosterone limits coronary neointima (NI) formation in a porcine model of post-angioplasty restenosis.

METHODS AND RESULTS

Sexually mature, male Yucatan miniature swine were either left intact (IM), castrated (CM), or castrated with testosterone replacement (CMT; Androgel, 10 mg/day). Angioplasty was performed in both the left anterior descending and left circumflex coronary arteries with balloon catheter overinflation to induce either moderate (1.25-1.3 x diameter; 3 x 30 s) or severe (1.4x diameter; 3 x 30 s) injury, and animals were allowed to recover for either 10 or 28 days. Injured coronary sections were dissected, fixed, stained (Verheoff-Van Gieson, Ki67, PKC delta, p27), and analysed. Vessels without internal elastic laminal rupture were excluded. Following moderate injury, intimal area, intima-to-media ratio (I/M), and I/M normalized to rupture index (RI) were increased in CM compared with IM and CMT. RI, medial area, and intimal/medial thickness (IMT) were not different between groups. NI formation was inversely related to serum testosterone concentration. Conversely, following severe injury, there were no significant differences between the groups. Testosterone inhibited proliferation and stimulated PKC delta and p27(kip1) expression during NI formation (10 days post-injury).

CONCLUSION

These findings demonstrate that endogenous testosterone limits coronary NI formation in male swine and provides support for a protective role for testosterone in coronary vasculoproliferative diseases, such as restenosis and atherosclerosis.

Impaired vascular function in small resistance arteries of LOX-1 overexpressing mice on high-fat diet

AIMS

LOX-1 is a major vascular receptor for oxidized low-density lipoprotein (oxLDL). In this study, we analysed the impact of LOX-1 overexpression and high dietary fat intake on vascular function in small resistance arteries.

METHODS AND RESULTS

Relaxation of mesenteric arteries was measured using a wire myograph. Compared with the control group, mice overexpressing LOX-1 on a high-fat diet (FD) had preserved vascular smooth muscle relaxation, but impaired endothelium-dependent relaxation via NO. Vascular NO availability was decreased by exaggerated formation of reactive oxygen species and decreased endothelial NO synthase expression. Endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation via cytochrome P450 metabolites was increased in LOX-1 + FD animals, but did not completely compensate for the loss of NO. Currents of calcium-activated potassium channels with large conductance (BKCa channels) were measured by the voltage-clamp method. The BKCa current amplitudes were not altered in endothelial cells, but highly increased in vascular smooth muscle cells from resistance arteries of LOX-1-overexpressing mice on FD. BK(Ca) currents were activated by low-dose H2O2 and cytochrome P450 metabolites 11,12-EET and 14,15-EET as EDHF in control mice.

CONCLUSION

LOX-1 overexpression and FD caused functional changes in endothelial and vascular smooth muscle cells of small resistance arteries.

Coronary spasm preferentially occurs at branch points: an angiographic comparison with atherosclerotic plaque

BACKGROUND

Coronary spasm plays an important role in the pathogenesis of ischemic heart disease. However, similarities and differences between coronary spasm and atherosclerosis are not known. We examined the angiographic characteristics of coronary spasm in comparison with those of atherosclerosis.

METHODS AND RESULTS

Thirty-two left anterior descending arteries, 11 left circumflex arteries, and 23 right coronary arteries with spasm and atherosclerotic plaque were analyzed for the localization of spasm in comparison with that of plaque in 47 patients (38 men and 9 women, mean age 66.8+/-10.3 yrs). Spasm predominantly occurred at the branch point as compared with plaque in each of the 3 arteries (76.7% versus 23.3%, P<0.0001; 72.7% versus 9.1%, P<0.039; and 60.0% versus 10.0%, P=0.002, in the left anterior descending, left circumflex, and right coronary arteries, respectively). Spasm involved the proximal segment less frequently as compared with plaque in each of the 3 arteries (56.7% versus 93.3%, P<0.0001; 18.2% versus 81.8%, P=0.016; and 15.0% versus 75.0%, P<0.0001 in the left anterior descending, left circumflex, and right coronary arteries, respectively). Most spasms occurred at the nonplaque site in each of the 3 arteries (73.3%, P=0.018; 100%, P<0.0001; and 75.0%, P=0.041 in the left anterior descending, left circumflex, and right coronary arteries, respectively).

CONCLUSIONS

Coronary spasm preferentially occurred at branch points and nonplaque sites, whereas the atherosclerotic lesion was predominantly localized at the nonbranch points of the curved proximal segments. Coronary spasm may thus be a manifestation of a distinct type of arteriosclerosis different from the lipid-laden coronary atherosclerosis.

Human IL-8 regulates smooth muscle cell VCAM-1 expression in response to endothelial cells exposed to atheroprone flow

OBJECTIVE

Interleukin-8 (IL-8) is a soluble human-specific chemokine implicated in the development of the chronic inflammatory disease atherosclerosis. Recently, we showed that atheroprone hemodynamics induced IL-8 secretion from endothelial cells (ECs) concurrent with increased EC/smooth muscle cell (SMC) VCAM-1 expression in a human hemodynamic coculture model. Despite an IL-8 association with inflammation, we show here that blocking IL-8 activity during atheroprone flow resulted in increased levels of EC/SMC VCAM-1 expression. We tested the hypothesis that IL-8 limits SMC VCAM-1 expression in response to inflammatory stimuli, either atheroprone flow or cytokine interleukin-1beta (IL-1beta) addition.

METHODS AND RESULTS

Atheroprone flow increased monocyte adhesion in both EC/SMCs, concurrent with the induction of VCAM-1 protein. VCAM-1 antisera attenuated this response. IL-1beta upregulated VCAM-1 in SMCs by 3-fold, a response inhibited by the addition of IL-8 at 24 hours. Neither IL-1beta nor IL-8 induced proliferation or migration. Neutralization of the IL-8 receptor, CXCR2, further induced VCAM-1 in the presence of IL-1beta, and phospho-p38 was required for NF-kappaB activation and VCAM-1 expression. Additionally, IL-8 reduced p38 activation and NF-kappaB activity induced by IL-1beta alone.

CONCLUSIONS

Together, these findings provide evidence for a novel role whereby IL-8 limits the inflammatory response in ECs/SMCs via VCAM-1 modulation.

Molecular mechanisms of collagen isotype-specific modulation of smooth muscle cell phenotype

OBJECTIVE

Smooth muscle cell (SMC) phenotypic modulation, an important component of atherosclerosis progression, is critically regulated by the matrix, with normal components of the healthy SMC matrix limiting modulation and atherosclerosis-associated transitional matrix proteins promoting phenotypic modulation. We sought to determine how collagen IV (which comprises the healthy artery wall) and monomeric collagen I (which comprises atherosclerotic lesions) differentially affect SMC phenotype.

METHODS AND RESULTS

Plating SMCs on collagen IV resulted in elevated expression of SMC contractility proteins compared to collagen I. Concurrent with enhanced contractile gene expression, collagen IV stimulates binding of SRF to CArG boxes in the promoters of smooth muscle actin and smooth muscle myosin heavy chain. Coll IV also stimulated the expression of myocardin, a critical SRF coactivator required to drive expression of SMC specific genes. In contrast to collagen IV, collagen I stimulated enhanced expression of the inflammatory protein vascular cell adhesion molecule (VCAM)-1. NF-kappaB and NFAT-binding sites in the VCAM-1 promoter are critical for collagen I-mediated expression of VCAM-1 promoter activity. However, only inhibitors of NFAT, not NF-kappaB, were able to reduce collagen I-associated VCAM expression, and collagen I but not collagen IV stimulated NFAT transcriptional activity.

CONCLUSIONS

These results show for the first time that collagen IV and collagen I differentially affect smooth muscle phenotypic modulation through multiple pathways.

A necessary role of miR-221 and miR-222 in vascular smooth muscle cell proliferation and neointimal hyperplasia

MicroRNAs (miRNAs) comprise a novel class of endogenous, small, noncoding RNAs that negatively regulate gene expression. Functionally, an individual miRNA is as important as a transcription factor because it is able to regulate the expression of its multiple target genes. Recently, miR-221 and miR-222 have been found to play a critical role in cancer cell proliferation. However, their roles in vascular smooth muscle cell (VSMC) biology are currently unknown. In the present study, the time course changes and cellular distribution of miR-221 and miR-222 expression were identified in rat carotid arteries after angioplasty, in which their expression was upregulated and localized in VSMCs in the injured vascular walls. In cultured VSMCs, miR-221 and miR-222 expression was increased by growth stimulators. Knockdown of miR-221 and miR-222 resulted in decreased VSMC proliferation in vitro. Using both gain-of-function and loss-of-function approaches, we found that p27(Kip1) and p57(Kip2) were 2 target genes that were involved in miR-221- and miR-222-mediated effect on VSMC growth. Finally, knockdown of miR-221 and miR-222 in rat carotid arteries suppressed VSMC proliferation in vivo and neointimal lesion formation after angioplasty. The results indicate that miR-221 and miR-222 are novel regulators for VSMC proliferation and neointimal hyperplasia. These findings may also represent promising therapeutic targets in proliferative vascular diseases.

Proinflammatory phenotype of perivascular adipocytes: influence of high-fat feeding

Adipose tissue depots originate from distinct precursor cells, are functionally diverse, and modulate disease processes in a depot-specific manner. However, the functional properties of perivascular adipocytes, and their influence on disease of the blood vessel wall, remain to be determined. We show that human coronary perivascular adipocytes exhibit a reduced state of adipocytic differentiation as compared with adipocytes derived from subcutaneous and visceral (perirenal) adipose depots. Secretion of antiinflammatory adiponectin is markedly reduced, whereas that of proinflammatory cytokines interleukin-6, interleukin-8, and monocyte chemoattractant protein-1, is markedly increased in perivascular adipocytes. These depot-specific differences in adipocyte function are demonstrable in both freshly isolated adipose tissues and in vitro-differentiated adipocytes. Murine aortic arch perivascular adipose tissues likewise express lower levels of adipocyte-associated genes as compared with subcutaneous and visceral adipose tissues. Moreover, 2 weeks of high-fat feeding caused further reductions in adipocyte-associated gene expression, while upregulating proinflammatory gene expression, in perivascular adipose tissues. These changes were observed in the absence of macrophage recruitment to the perivascular adipose depot. We conclude that perivascular adipocytes exhibit reduced differentiation and a heightened proinflammatory state, properties that are intrinsic to the adipocytes residing in this depot. Dysfunction of perivascular adipose tissue induced by fat feeding suggests that this unique adipose depot is capable of linking metabolic signals to inflammation in the blood vessel wall.

Role of Src tyrosine kinase in the atherogenic effects of the 12/15-lipoxygenase pathway in vascular smooth muscle cells

OBJECTIVE

The 12/15-Lipoxygenase (12/15-LO) and its metabolite 12(S)-Hydroxyeicosatetraenoic acid [12(S)-HETE] mediate proatherogenic responses in vascular smooth muscle cells (VSMCs). We examined the role of the nonreceptor tyrosine kinase Src in the signaling and epigenetic chromatin mechanisms involved in these processes.

METHODS AND RESULTS

Rat VSMCs (RVSMCs) were stimulated with 12(S)-HETE (0.1 micromol/L) in the presence or absence of the Src inhibitor PP2 (10 micromol/L). Src activation and downstream signaling events including inflammatory gene expression and chromatin histone H3-Lys-9/14 acetylation were examined by immunoblotting, RT-PCR, and chromatin immunoprecipitation assays, respectively. 12(S)-HETE significantly activated Src, focal adhesion kinase, Akt, p38MAPK, and CREB. Expression of monocyte chemoattractant protein-1 and interleukin-6 genes and histone H3-Lys-9/14 acetylation on their promoters were also increased by 12(S)-HETE. PP2 inhibited these responses as well as 12(S)-HETE-induced VSMC migration. Furthermore, dominant negative mutants of Src, CREB, and a histone acetyltransferase p300 significantly blocked 12(S)-HETE-induced inflammatory gene expression. In addition, growth factor induced Src signaling and downstream events including H3-Lys-9/14 acetylation and migration were significantly attenuated in VSMCs derived from 12/15-LO(-/-) mice relative to WT.

CONCLUSIONS

Src kinase signaling plays a central role in the proatherogenic responses mediated by 12/15-LO and its oxidized lipid metabolite 12(S)-HETE in VSMCs.

Inflammation at the molecular interface of atherogenesis: an anthropological journey

Despite the multifactorial nature of atherosclerosis, substantial evidence has established inflammation as an often surreptitious, yet critical and unifying driving force which promotes disease progression. To this end, research has defined molecular networks initiated by cytokines, growth factors and other pro-inflammatory molecules which promote hallmarks of atherosclerosis such as endothelial dysfunction, macrophage infiltration, LDL oxidation, cell proliferation and thrombosis. Although commonly associated with risk factors such as dyslipidemia, diabetes and hypertension, the global etiology of atherosclerosis may be alternatively attributed to underlying anthropological pressures. The agricultural, industrial and technological revolutions produced alterations in dietary, social and economic factors which have collectively exaggerated the exposure of the human genome to environmental stimuli. Furthermore, advances in sanitation, nutrition, and medicine have increased the lifespan of humans, effectively prolonging blood vessel exposure to these factors. As a result, the vasculature has become conditioned to respond to injury with what is arguably an overzealous immunological response; thus setting the stage for the prevalence of cardiovascular disease, including atherosclerotic plaque development in Western populations. Evidence suggests that each of these alterations can be linked to specific mediators in the inflammatory process. Integration of these factors with an inflammation-based hypothesis of atherosclerosis has yet to be extrapolated to observations in the realms of basic and clinical sciences and is the focus of this review.

Role of hydrogen sulfide in the development of atherosclerotic lesions in apolipoprotein E knockout mice

OBJECTIVE

We explored the effect of hydrogen sulfide (H(2)S) on atherosclerotic progression, particularly on intracellular adhesion molecule-1 (ICAM-1) in apolipoprotein-E knockout (apoE(-/-)) mice and human umbilical vein endothelial cells (HUVECs).

METHODS AND RESULTS

ApoE(-/-) mice were treated with sodium hydrosulfide (NaHS) or DL-propargylglycine (PPG); HUVECs were pretreated with NaHS. Compared with control mice, apoE(-/-) mice showed decreased plasma H(2)S level and aortic H(2)S production but increased plasma ICAM-1 and aortic ICAM-1 protein and mRNA. Compared with apoE(-/-) mice, apoE(-/-)+NaHS mice showed increased plasma H(2)S level, but decreased size of atherosclerotic plaque and plasma and aortic ICAM-1 levels, whereas apoE(-/-)+PPG mice showed decreased plasma H(2)S level but enlarged plaque size and increased plasma and aortic ICAM-1 levels. NaHS suppressed ICAM-1 expression in tumor necrosis factor (TNF)-alpha-treated HUVECs. NaHS inhibited IkappaB degradation and NF-kappaB nuclear translocation in HUVECs treated with TNF-alpha.

CONCLUSIONS

The vascular CSE/H(2)S pathway was disturbed in apoE(-/-) mice. H(2)S exerted an antiatherogenic effect and inhibited ICAM-1 expression in apoE(-/-) mice. H(2)S inhibited ICAM-1 expression in TNF-alpha-induced HUVECs via the NF-kappaB pathway.

Tannin extracted from Sumac inhibits vascular smooth muscle cell migration

BACKGROUND

Vascular smooth muscle cell (VSMC) migration is integral in the pathogenesis of atherosclerosis. Sumac (Rhus coriaria) berries are believed to have atheroprotective effects. Therefore, Sumac, which is a rich source of tannin antioxidants, was tested for its capacity to inhibit VSMC migratory activity.

MATERIALS & METHODS

Tannin was extracted and purified from ground Sumac. Cultured rat carotid VSMCs were treated with different concentrations of tannin. After 10 days of tannin treatment, VSMC migratory activity in response to platelet-derived growth factor-BB was measured by transmembrane migration assay. An equal number of VSMCs was loaded on top of the inserts and at the bottom of the wells. After fixation and staining, cells migrating through the inserts and cells seeded at the bottom of the wells were counted.

RESULTS

A significant reduction (62%) of VSMC migration was evident in tannin-treated cells. To rule out any possible toxicity and cell death, cells at the bottom of the wells were also counted. No difference between the tannin-treated group and the controls was observed in the number of cells seeded at the bottom of the wells.

CONCLUSION

Our data suggest that tannin extracted from Sumac possesses potent antimigratory activity. Sumac may have potential for the prevention or treatment of atherosclerosis and its clinical manifestations. Further experiments, especially in vivo, are required to examine the atheroprotective effect of Sumac.

CD40-CD40 ligand interactions in oxidative stress, inflammation and vascular disease

CD40 ligand (CD40L) and its receptor CD40 participate in numerous inflammatory pathways that contribute to multiple pathophysiological processes. A role for CD40-CD40L interactions has been identified in atherosclerosis, and such interactions are known to destabilize atherosclerotic plaques by inducing the expression of cytokines, chemokines, growth factors, matrix metalloproteinases and pro-coagulant factors. The CD40-CD40L interaction has also been implicated in immune system disorders. Recent studies have suggested that CD40-CD40L interactions regulate oxidative stress and affect various signaling pathways in both the immunological and cardiovascular systems. Here, we discuss the emerging role of CD40-CD40L-mediated processes in oxidative stress, inflammatory pathways and vascular diseases. Understanding the roles and regulation of CD40-CD40L-mediated oxidative signaling in immune and non-immune cells could facilitate the development of therapeutics targeting diverse inflammatory diseases.

Role of the histone H3 lysine 4 methyltransferase, SET7/9, in the regulation of NF-kappaB-dependent inflammatory genes. Relevance to diabetes and inflammation

Nuclear factor kappa-B (NF-kappaB)-regulated inflammatory genes, such as TNF-alpha (tumor necrosis factor-alpha), play key roles in the pathogenesis of inflammatory diseases, including diabetes and the metabolic syndrome. However, the nuclear chromatin mechanisms are unclear. We report here that the chromatin histone H3-lysine 4 methyltransferase, SET7/9, is a novel coactivator of NF-kappaB. Gene silencing of SET7/9 with small interfering RNAs in monocytes significantly inhibited TNF-alpha-induced inflammatory genes and histone H3-lysine 4 methylation on these promoters, as well as monocyte adhesion to endothelial or smooth muscle cells. Chromatin immunoprecipitation revealed that SET7/9 small interfering RNA could reduce TNF-alpha-induced recruitment of NF-kappaB p65 to inflammatory gene promoters. Inflammatory gene induction by ligands of the receptor for advanced glycation end products was also attenuated in SET7/9 knockdown monocytes. In addition, we also observed increased inflammatory gene expression and SET7/9 recruitment in macrophages from diabetic mice. Microarray profiling revealed that, in TNF-alpha-stimulated monocytes, the induction of 25% NF-kappaB downstream genes, including the histone H3-lysine 27 demethylase JMJD3, was attenuated by SET7/9 depletion. These results demonstrate a novel role for SET7/9 in inflammation and diabetes.