CREB-mediated IL-6 expression is required for 15(S)-hydroxyeicosatetraenoic acid-induced vascular smooth muscle cell migration

Arachidonic acid promotes skin wound healing through induction of human MSC migration by MT3-MMP-mediated fibronectin degradation

Arachidonic acid (AA) is largely released during injury, but it has not been fully studied yet how AA modulates wound repair with stem cells. Therefore, we investigated skin wound-healing effect of AA-stimulated human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) in vivo and its molecular mechanism in vitro. We found that transplantation of hUCB-MSCs pre-treated with AA enhanced wound filling, re-epithelization, and angiogenesis in a mouse skin excisional wound model. AA significantly promoted hUCB-MSCs migration after a 24 h incubation, which was inhibited by the knockdown of G-protein-coupled receptor 40 (GPR40). AA activated mammalian target of rapamycin complex 2 (mTORC2) and Akt^ser473 through the GPR40/phosphoinositide 3-kinase (PI3K) signaling, which was responsible for the stimulation of an atypical protein kinase C (PKC) isoform, PKCζ. Subsequently, AA stimulated phosphorylation of p38 MAPK and transcription factor Sp1, and induced membrane type 3-matrix metalloproteinase (MT3-MMP)-dependent fibronectin degradation in promoting hUCB-MSCs motility. Finally, the silencing of MT3-MMP in AA-stimulated hUCB-MSCs failed to promote the repair of skin wounds owing to impaired cell motility. In conclusion, AA enhances skin wound healing through induction of hUCB-MSCs motility by MT3-MMP-mediated fibronectin degradation, which relies on GPR40-dependent mTORC2 signaling pathways.

STAT3-mediated MMP-2 expression is required for 15-HETE-induced vascular adventitial fibroblast migration

OBJECTIVE

Vascular adventitial fibroblasts (VAFs) migration was involved in neointima formation, and increased 15-HETE levels contributed to vascular remodeling. However, how 15-HETE-induced VAF migration was not clear.

METHODS AND RESULTS

15-HETE-stimulated VAF phenotypic changes and migration as measured by the wound healing assay required STAT3 phosphorylation. JNK1 and CREB inhibition blocked 15-HETE-induced STAT3 activation and VAF changes. 15-HETE-induced MMP-2 expression and secretion were analyzed by Western blot and ELISA, respectively. MMP-2 knockdown blocked VAF migration and phenotypic alterations. JNK1, STAT3 and CREB blockade suppressed 15-HETE-induced MMP-2 expression in VAFs. MMP-2 promoter activity was assessed by chromatin immunoprecipitation using anti-STAT3 antibodies, which demonstrated that STAT3 was essential for 15-HETE-induced MMP-2 expression. Rats that suffered from hypoxia injury with or without treatment were examined. Pulmonary artery remodeling was obviously observed, and even the media was broken. MMP-2-positive staining was observed in the adventitia and intima. MMP-2 Serum secretion was enhanced as detected by ELISA, and MMP-2 and α-SMA protein expressions were increased after inducing hypoxia in the rats, which was restored in rats that had been administrated with NDGA.

CONCLUSION

These results reveal that STAT3-mediated MMP-2 expression is required for 15-HETE induced-VAF migration.

ROS-dependent Syk and Pyk2-mediated STAT1 activation is required for 15(S)-hydroxyeicosatetraenoic acid-induced CD36 expression and foam cell formation

15(S)-Hydroxyeicosatetraenoic acid (15(S)-HETE), the major 15-lipoxygenase 1/2 (15-LO1/2) metabolite of arachidonic acid (AA), induces CD36 expression through xanthine oxidase and NADPH oxidase-dependent ROS production and Syk and Pyk2-dependent STAT1 activation. In line with these observations, 15(S)-HETE also induced foam cell formation involving ROS, Syk, Pyk2, and STAT1-mediated CD36 expression. In addition, peritoneal macrophages from Western diet-fed ApoE(-/-) mice exhibited elevated levels of xanthine oxidase and NADPH oxidase activities, ROS production, Syk, Pyk2, and STAT1 phosphorylation, and CD36 expression compared to those from ApoE(-/-):12/15-LO(-/-) mice and these events correlated with increased lipid deposits, macrophage content, and lesion progression in the aortic roots. Human atherosclerotic arteries also showed increased 15-LO1 expression, STAT1 phosphorylation, and CD36 levels as compared to normal arteries. Together, these findings suggest that 12/15-LO metabolites of AA, particularly 12/15(S)-HETE, might play a crucial role in atherogenesis by enhancing foam cell formation.

Vascular endothelial tight junctions and barrier function are disrupted by 15(S)-hydroxyeicosatetraenoic acid partly via protein kinase C ε-mediated zona occludens-1 phosphorylation at threonine 770/772

Disruption of tight junctions (TJs) perturbs endothelial barrier function and promotes inflammation. Previously, we have shown that 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), the major 15-lipoxygenase 1 (15-LO1) metabolite of arachidonic acid, by stimulating zona occludens (ZO)-2 tyrosine phosphorylation and its dissociation from claudins 1/5, induces endothelial TJ disruption and its barrier dysfunction. Here, we have studied the role of serine/threonine phosphorylation of TJ proteins in 15(S)-HETE-induced endothelial TJ disruption and its barrier dysfunction. We found that 15(S)-HETE enhances ZO-1 phosphorylation at Thr-770/772 residues via PKCε-mediated MEK1-ERK1/2 activation, causing ZO-1 dissociation from occludin, disrupting endothelial TJs and its barrier function, and promoting monocyte transmigration; these effects were reversed by T770A/T772A mutations. In the arteries of WT mice ex vivo, 15(S)-HETE also induced ZO-1 phosphorylation and endothelial TJ disruption in a PKCε and MEK1-ERK1/2-dependent manner. In line with these observations, in WT mice high fat diet feeding induced 12/15-lipoxygenase (12/15-LO) expression in the endothelium and caused disruption of its TJs and barrier function. However, in 12/15-LO(-/-) mice, high fat diet feeding did not cause disruption of endothelial TJs and barrier function. These observations suggest that the 12/15-LO-12/15(S)-HETE axis, in addition to tyrosine phosphorylation of ZO-2, also stimulates threonine phosphorylation of ZO-1 in the mediation of endothelial TJ disruption and its barrier dysfunction.

The transcription factor CREB enhances interleukin-17A production and inflammation in a mouse model of atherosclerosis

The enzyme 15-lipoxygenase (15-LO) plays a role in atherogenesis (also known as atherosclerosis), but the underlying mechanisms are unclear. We found that 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], the major 15-LO-dependent metabolite of arachidonic acid, stimulated the production of reactive oxygen species (ROS) by monocytes through the xanthine oxidase-mediated activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. ROS production led to the Syk-, Pyk2-, and mitogen-activated protein kinase (MAPK)-dependent production of the proinflammatory cytokine interleukin-17A (IL-17A) in a manner that required the transcription factor CREB (cyclic adenosine monophosphate response element-binding protein). In addition, this pathway was required for the 15(S)-HETE-dependent migration and adhesion of monocytes to endothelial cells. Consistent with these observations, we found that peritoneal macrophages from apolipoprotein E-deficient (ApoE-/-) mice fed a high-fat diet (a mouse model of atherosclerosis) exhibited increased xanthine oxidase and NADPH oxidase activities; ROS production; phosphorylation of Syk, Pyk2, MAPK, and CREB; and IL-17A production compared to those from similarly fed ApoE-/-:12/15-LO-/- mice. These events correlated with increased lipid deposits and numbers of monocytes and macrophages in the aortic arches of ApoE-/- mice, which resulted in atherosclerotic plaque formation. Together, these observations suggest that 15(S)-HETE exacerbates atherogenesis by enhancing CREB-dependent IL-17A production and inflammation.

Platelet factor 4 mediates vascular smooth muscle cell injury responses

Activated platelets release many inflammatory molecules with important roles in accelerating vascular inflammation. Much is known about platelet and platelet-derived mediator interactions with endothelial cells and leukocytes, but few studies have examined the effects of platelets on components of the vascular wall. Vascular smooth muscle cells (VSMCs) undergo phenotypic changes in response to injury including the production of inflammatory molecules, cell proliferation, cell migration, and a decline in the expression of differentiation markers. In this study, we demonstrate that the platelet-derived chemokine platelet factor 4 (PF4/CXCL4) stimulates VSMC injury responses both in vitro and in vivo in a mouse carotid ligation model. PF4 drives a VSMC inflammatory phenotype including a decline in differentiation markers, increased cytokine production, and cell proliferation. We also demonstrate that PF4 effects are mediated, in part, through increased expression of the transcription factor Krüppel-like factor 4. Our data indicate an important mechanistic role for platelets and PF4 in VSMC injury responses both in vitro and in vivo.

Role of 15-hydroxyeicosatetraenoic acid in hemozoin-induced lysozyme release from human adherent monocytes

Natural hemozoin (nHZ), a lipid-bound ferriprotoporphyrin IX crystal produced by Plasmodium parasites after hemoglobin catabolism, seriously compromises the functions of human monocytes, and 15-hydroxyeicosatetraenoic acid (15-HETE) and 4-hydroxynonenal (4-HNE), two nHZ lipoperoxidation products, have been related to such a functional impairment. nHZ was recently shown to promote inflammation-mediated lysozyme release from human monocytes through p38 mitogen-activated protein kinase- (MAPK)- and nuclear factor (NF)-κB-dependent mechanisms. This study aimed at identifying the molecule of nHZ lipid moiety that was responsible for these effects. Results showed that 15-HETE mimicked nHZ effects on lysozyme release, whereas 4-HNE did not. 15-HETE-enhanced lysozyme release was abrogated by anti-TNF-α and anti-IL-1β-blocking antibodies and mimicked by recombinant cytokines; on the contrary, MIP-1α/CCL3 was not involved as a soluble mediator of 15-HETE effects. Moreover, 15-HETE early activated p38 MAPK and NF-κB pathways by inducing p38 MAPK phosphorylation; cytosolic I-κBα phosphorylation and degradation; NF-κB nuclear translocation and DNA-binding. Inhibition of both routes through chemical inhibitors (SB203580, quercetin, artemisinin, and parthenolide) prevented 15-HETE-dependent lysozyme release. Collectively, these data suggest that 15-HETE plays a major role in nHZ-enhanced monocyte degranulation.

Role of epigenetic mechanisms in the vascular complications of diabetes

Diabetes and metabolic disorders are leading causes of micro- and macrovascular complications. Furthermore, efforts to treat these complications are hampered by metabolic memory, a phenomenon in which prior exposure to hyperglycemia predisposes diabetic patients to the continued development of vascular diseases despite subsequent glycemic control. Persistently increased levels of oxidant stress and inflammatory genes are key features of these pathologies. Biochemical and molecular studies showed that hyperglycemia induced activation of NF-κB, signaling and actions of advanced glycation end products and other inflammatory mediators play key roles in the expression of pathological genes. In addition, epigenetic mechanisms such as posttranslational modification of histones and DNA methylation also play central roles in gene regulation by affecting chromatin structure and function. Recent studies have suggested that dysregulation of such epigenetic mechanisms may be involved in metabolic memory leading to persistent changes in the expression of genes associated with diabetic vascular complications. Further exploration of these mechanisms by also taking advantages of recent advances in high throughput epigenomics technologies will greatly increase our understanding of epigenetic variations in diabetes and its complications. This in turn can lead to the development of novel new therapies.

Cyclic adenosine monophosphate response-element binding protein activation by mitogen-activated protein kinase-activated protein kinase 3 and four-and-a-half LIM domains 5 plays a key role for vein graft intimal hyperplasia

OBJECTIVE

Intimal hyperplasia (IH) is the main cause of vein graft stenosis or failure after bypass surgery. Basic investigations are proceeding in an animal model of mechanically desquamated arteries, and numerous molecules for potential IH treatments have been identified; however, neither insights into the mechanism of IH nor substantially effective treatments for its suppression have been developed. The goals of the present study are to use human vein graft samples to identify therapeutic target genes that control IH and to investigate the therapeutic efficacy of these candidate molecules in animal models.

METHODS

Using microarray analysis of human vein graft samples, we identified two previously unrecognized IH-related genes, mitogen-activated protein kinase-activated protein kinase 3 (MAPKAPK3) and four-and-a-half LIM domains 5 (FHL5).

RESULTS

Transfer of either candidate gene resulted in significantly elevated vascular smooth muscle cell (VSMC) proliferation and migration. Interestingly, cotransfection of both genes increased VSMC proliferation in an additive manner. These genes activated cyclic adenosine monophosphate response-element (CRE) binding protein (CREB), but their mechanisms of activation were different. MAPKAPK3 phosphorylated CREB, but FHL5 bound directly to CREB. A CREB dominant-negative protein, KCREB, which blocks its ability to bind CRE, repressed VSMC proliferation and migration. In a wire-injury mouse model, gene transfer of KCREB plasmid significantly repressed IH. In this vessel tissue, CRE-activated gene expression was repressed. Furthermore, we confirmed the changes in MAPKAPK3 and FHL5 expression using vein graft samples from eight patients.

CONCLUSIONS

We successively identified two previously unrecognized IH activators, MAPKAPK3 and FHL5, using human vein graft samples. Gene transfer of KCREB repressed IH in an animal model. Inhibition of CREB function is a promising gene therapy strategy for IH.

TLR 2 induces vascular smooth muscle cell migration through cAMP response element-binding protein-mediated interleukin-6 production

OBJECTIVE

Migration of vascular smooth muscle cells (VSMCs) from the media into intima contributes to the development of atherosclerosis. Gene deletion experiments implicate a role for toll-like receptor 2 (TLR2) in atherogenesis. However, the underlying mechanisms remain unclear. We postulate that TLR2 promotes VSMC migration by enhancing interleukin (IL)-6 production.

METHODS AND RESULTS

Migration assays revealed that TLR2 agonists promoted VSMC migration but not cell proliferation or viability. TLR2 deficiency or inhibition of TLR2 signaling with anti-TLR2 antibody suppressed TLR2 agonist-induced VSMC migration and IL-6 production, which was mediated via p38 mitogen-associated protein kinase and extracellular signal-regulated kinase 1/2 signaling pathways. Neutralizing anti-IL-6 antibodies impaired TLR2-mediated VSMC migration and formation of filamentous actin fiber and lamellipodia. Blockade of p38 mitogen-associated protein kinase or extracellular signal-regulated kinase 1/2 activation inhibited TLR2 agonist pam3CSK4-induced phosphorylation of cAMP response element-binding protein, which regulates IL-6 promoter activity through the cAMP response element site. Moreover, cAMP response element-binding protein small interfering RNA inhibited pam3CSK4-induced IL-6 production and VSMC migration. Additionally, Rac1 small interfering RNA inhibited pam3CSK4-induced VSMC migration but not IL-6 production.

CONCLUSIONS

Our results suggest that on ligand binding, TLR2 activates p38 mitogen-associated protein kinase and extracellular signal-regulated kinase 1/2 signaling in VSMCs. These signaling pathways act in concert to activate cAMP response element-binding protein and subsequent IL-6 production, which in turn promotes VSMC migration via Rac1-mediated actin cytoskeletal reorganization.

Smooth muscle-specific expression of calcium-independent phospholipase A2β (iPLA2β) participates in the initiation and early progression of vascular inflammation and neointima formation

Whether group VIA phospholipase A(2) (iPLA(2)β) is involved in vascular inflammation and neointima formation is largely unknown. Here, we report that iPLA(2)β expression increases in the vascular tunica media upon carotid artery ligation and that neointima formation is suppressed by genetic deletion of iPLA(2)β or by inhibiting its activity or expression via perivascular delivery of bromoenol lactone or of antisense oligonucleotides, respectively. To investigate whether smooth muscle-specific iPLA(2)β is involved in neointima formation, we generated transgenic mice in which iPLA(2)β is expressed specifically in smooth muscle cells and demonstrate that smooth muscle-specific expression of iPLA(2)β exacerbates ligation-induced neointima formation and enhanced both production of proinflammatory cytokines and vascular infiltration by macrophages. With cultured vascular smooth muscle cell, angiotensin II, arachidonic acid, and TNF-α markedly induce increased expression of IL-6 and TNF-α mRNAs, all of which were suppressed by inhibiting iPLA(2)β activity or expression with bromoenol lactone, antisense oligonucleotides, and genetic deletion, respectively. Similar suppression also results from genetic deletion of 12/15-lipoxygenase or inhibiting its activity with nordihydroguaiaretic acid or luteolin. Expression of iPLA(2)β protein in cultured vascular smooth muscle cells was found to depend on the phenotypic state and to rise upon incubation with TNF-α. Our studies thus illustrate that smooth muscle cell-specific iPLA(2)β participates in the initiation and early progression of vascular inflammation and neointima formation and suggest that iPLA(2)β may represent a novel therapeutic target for preventing cardiovascular diseases.

Calcium signaling in vascular smooth muscle cells: from physiology to pathology

Cyclic variations in calcium (Ca(2+)) concentrations, through a process called excitation-contraction coupling, allow regulation of vascular smooth muscle cells contractility and thus modulation of vascular tone and blood pressure. As a second messenger, Ca(2+) also activates signaling cascades leading to transcription factors activation in a process called excitation-transcription coupling. Furthermore, recent evidences indicate an interaction between post-transcriptional regulation by microRNAs (miRNAs) and Ca(2+) signaling. All these actors, which are frequently altered in vascular diseases, will be reviewed here.

Inflammation-related gene expression by lipid oxidation-derived products in the progression of atherosclerosis

Vascular areas of atherosclerotic development persist in a state of inflammation, and any further inflammatory stimulus in the subintimal area elicits a proatherogenic response; this alters the behavior of the artery wall cells and recruits further inflammatory cells. In association with the inflammatory response, oxidative events are also involved in the development of atherosclerotic plaques. It is now unanimously recognized that lipid oxidation-derived products are key players in the initiation and progression of atherosclerotic lesions. Oxidized lipids, derived from oxidatively modified low-density lipoproteins (LDLs), which accumulate in the intima, strongly modulate inflammation-related gene expression, through involvement of various signaling pathways. In addition, considerable evidence supports a proatherogenic role of a large group of potent bioactive lipids called eicosanoids, which derive from oxidation of arachidonic acid, a component of membrane phospholipids. Of note, LDL lipid oxidation products might regulate eicosanoid production, modulating the enzymatic degradation of arachidonic acid by cyclooxygenases and lipoxygenases; these enzymes might also directly contribute to LDL oxidation. This review provides a comprehensive overview of current knowledge on signal transduction pathways and inflammatory gene expression, modulated by lipid oxidation-derived products, in the progression of atherosclerosis.

Vascular effects of glycoprotein130 ligands--part I: pathophysiological role

The vessel wall is no longer considered as only an anatomical barrier for blood cells but is recognized as an active endocrine organ. Dysfunction of the vessel wall occurs in various disease processes including atherosclerosis, hypertension, peripheral artery disease, aneurysms, and transplant and diabetic vasculopathies. Different cytokines were shown to modulate the behavior of the cells, which constitute the vessel wall such as immune cells, endothelial cells and smooth muscle cells. Glycoprotein 130 (gp130) is a common cytokine receptor that controls the activity of a group of cytokines, namely, interleukin (IL)-6, oncostatin M (OSM), IL-11, ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), cardiotrophin-like cytokine (CLC), IL-27, and neuropoietin (NP). Gp130 and associated cytokines have abundantly diverse functions. Part I of this review focuses on the pathophysiological functions of gp130 ligands. We specifically describe vascular effects of these molecules and discuss the respective underlying molecular and cellular mechanisms.

Identification of a cAMP-response element in the regulator of G-protein signaling-2 (RGS2) promoter as a key cis-regulatory element for RGS2 transcriptional regulation by angiotensin II in cultured vascular smooth muscles

Mice deficient in regulator of G-protein signaling-2 (RGS2) have severe hypertension, and RGS2 genetic variations occur in hypertensive humans. A potentially important negative feedback loop in blood pressure homeostasis is that angiotensin II (Ang II) increases vascular smooth muscle cell (VSMC) RGS2 expression. We reported that Group VIA phospholipase A(2) (iPLA(2)β) is required for this response (Xie, Z., Gong, M. C., Su, W., Turk, J., and Guo, Z. (2007) J. Biol. Chem. 282, 25278-25289), but the specific molecular causes and consequences of iPLA(2)β activation are not known. Here we demonstrate that both protein kinases C (PKC) and A (PKA) participate in Ang II-induced VSMC RGS2 mRNA up-regulation, and that actions of PKC and PKA precede and follow iPLA(2)β activation, respectively. Moreover, we identified a conserved cAMP-response element (CRE) in the murine RGS2 promoter that is critical for cAMP-response element-binding protein (CREB) binding and RGS2 promoter activation. Forskolin-stimulated RGS2 mRNA up-regulation is inhibited by CREB sequestration or specific disruption of the CREB-RGS2 promoter interaction, and Ang II-induced CREB phosphorylation and nuclear localization are blocked by iPLA(2)β pharmacologic inhibition or genetic ablation. Ang II-induced intracellular cyclic AMP accumulation precedes CREB phosphorylation and is diminished by inhibiting iPLA(2), cyclooxygenase, or lipoxygenase. Moreover, three single nucleotide polymorphisms identified in hypertensive patients are located in the human RGS2 promoter CREB binding site. Point mutations corresponding to these single nucleotide polymorphisms interfere with stimulation of human RGS2 promoter activity by forskolin. Our studies thus delineate a negative feedback loop to attenuate Ang II signaling in VSMC with potential importance in blood pressure homeostasis and the pathogenesis of human essential hypertension.

Cyclic AMP response element-binding protein prevents endothelial permeability increase through transcriptional controlling p190RhoGAP expression

Increased endothelial permeability contributes to the morbidity and mortality associated with chronic inflammatory diseases, including acute lung injury. Cyclic AMP response element-binding protein (CREB) transcriptional factor induces genes that regulate inflammation and vascular remodeling. However, the role of CREB in regulating endothelial barrier function is unknown. Here, we demonstrate that CREB maintains basal endothelial barrier function and suppresses endothelial permeability increase by diverse agonists such as thrombin, lipopolysaccharide, histamine, and VEGF. We show that CREB transcriptionally controls the expression of p190RhoGAP-A, a GTPase-activating protein that inhibits small GTPase RhoA. Impairing CREB function using small interfering RNA or dominant-negative (dn)-CREB mutant (dn-CREB) markedly suppressed p190RhoGAP-A expression, increased RhoA activity, induced actin stress fiber formation, and produced an amplified and protracted increase in endothelial permeability in response to thrombin. Rescuing p190RhoGAP-A expression restored the permeability defect in dn-CREB-transducing endothelial cells. These findings were recapitulated in vivo because dn-CREB expression in mice vasculature increased basal lung microvessel permeability and exaggerated permeability increase induced by thrombin and lipopolysaccharide. Inhibiting RhoA signaling restored endothelial barrier dysfunction in the dn-CREB-expressing lung microvasculature. These results uncover a pivotal role of CREB in regulating endothelial barrier function by restricting RhoA signaling through controlling p190RhoGAP-A expression.

Key Role of 15-Lipoxygenase/15-Hydroxyeicosatetraenoic Acid in Pulmonary Vascular Remodeling and Vascular Angiogenesis Associated With Hypoxic Pulmonary Hypertension

We have found that 15-hydroxyeicosatetraenoic acid (15-HETE) induced by hypoxia was an important mediator in the regulation of hypoxic pulmonary hypertension, including the pulmonary vasoconstriction and remodeling. However, the underlying mechanisms of the remodeling induced by 15-HETE are poorly understood. In this study, we performed immunohistochemistry, pulmonary artery endothelial cells migration and tube formation, pulmonary artery smooth muscle cells bromodeoxyuridine incorporation, and cell cycle analysis to determine the role of 15-HETE in hypoxia-induced pulmonary vascular remodeling. We found that hypoxia induced pulmonary vascular medial hypertrophy and intimal endothelial cells migration and angiogenesis, which were mediated by 15-HETE. Moreover, 15-HETE regulated the cell cycle progression and made more smooth muscle cells from the G 0 /G 1 phase to the G 2 /M+S phase and enhanced the microtubule formation in cell nucleus. In addition, we found that the Rho-kinase pathway was involved in 15-HETE–induced endothelial cells tube formation and migration and smooth muscle cell proliferation. Together, these results show that 15-HETE mediates hypoxia-induced pulmonary vascular remodeling and stimulates angiogenesis via the Rho-kinase pathway.

Cilostazol promotes vascular smooth muscles cell differentiation through the cAMP response element-binding protein-dependent pathway

OBJECTIVE

Cilostazol, a potent type 3 phosphodiesterase inhibitor, has recently been found to reduce neointimal formation by inhibiting vascular smooth muscle cell (VSMC) proliferation. The aim of this study is to investigate whether cilostazol exerts an action on phenotypic modulation of VSMCs, another important process in the pathogenesis of neointimal formation.

METHODS AND RESULTS

Cilostazol may convert VSMCs from a serum-induced dedifferentiation state to a differentiated state, as indicated by a spindle-shaped morphology and an increase in the expression of smooth muscle cell differentiation marker contractile proteins. The upregulation of contractile proteins by cilostazol involves the cAMP/protein kinase A (PKA) signaling pathway, because the cAMP analog mimicked and specific cAMP/PKA inhibitors opposed the effect of cilostazol. Furthermore, cilostazol-activated cAMP response element (CRE)-binding protein (CREB), including phosphorylation at Ser133 and its nuclear translocation. Deletion and mutational analysis of the contractile protein promoters along with chromatin immunoprecipitation using anti-CREB antibody showed that CRE is essential for cilostazol-induced contractile protein expression. Transfection of dominant-negative CREB (mutated Ser133) plasmid in VSMCs blocked cilostazol-stimulated contractile protein expression. In vivo, cilostazol upregulated contractile proteins and induced the activation of CREB in the neointima of balloon-injured arteries.

CONCLUSIONS

Cilostazol promotes VSMC differentiation through the cAMP/PKA/CREB signaling cascade.

15-Lipoxygenase-1-enhanced Src-Janus kinase 2-signal transducer and activator of transcription 3 stimulation and monocyte chemoattractant protein-1 expression require redox-sensitive activation of epidermal growth factor receptor in vascular wall remodeling

To understand the mechanisms by which 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE) activates signal transducer and activator of transcription 3 (STAT3), we studied the role of epidermal growth factor receptor (EGFR). 15(S)-HETE stimulated tyrosine phosphorylation of EGFR in a time-dependent manner in vascular smooth muscle cells (VSMCs). Interference with EGFR activation blocked 15(S)-HETE-induced Src and STAT3 tyrosine phosphorylation, monocyte chemoattractant protein-1 (MCP-1) expression and VSMC migration. 15(S)-HETE also induced tyrosine phosphorylation of Janus kinase 2 (Jak2) in VSMCs, and its inhibition substantially reduced STAT3 phosphorylation, MCP-1 expression, and VSMC migration. In addition, Src formed a complex with EGFR and Jak2, and its inhibition completely blocked Jak2 and STAT3 phosphorylation, MCP-1 expression, and VSMC migration. 15(S)-HETE induced the production of H(2)O(2) via an NADPH oxidase-dependent manner and its scavengers, N-acetyl cysteine (NAC) and catalase suppressed 15(S)-HETE-stimulated EGFR, Src, Jak2, and STAT3 phosphorylation and MCP-1 expression. Balloon injury (BI) induced EGFR, Src, Jak2, and STAT3 phosphorylation, and inhibition of these signaling molecules attenuated BI-induced MCP-1 expression and smooth muscle cell migration from the medial to the luminal surface resulting in reduced neointima formation. In addition, inhibition of EGFR blocked BI-induced Src, Jak2, and STAT3 phosphorylation. Similarly, interference with Src activation suppressed BI-induced Jak2 and STAT3 phosphorylation. Furthermore, adenovirus-mediated expression of dnJak2 also blocked BI-induced STAT3 phosphorylation. Consistent with the effects of 15(S)-HETE on the activation of EGFR-Src-Jak2-STAT3 signaling in VSMCs in vitro, adenovirus-mediated expression of 15-lipoxygenase 1 (15-Lox1) enhanced BI-induced EGFR, Src, Jak2, and STAT3 phosphorylation leading to enhanced MCP-1 expression in vivo. Blockade of Src or Jak2 suppressed BI-induced 15-Lox1-enhanced STAT3 phosphorylation, MCP-1 expression, and neointima formation. In addition, whereas dominant negative Src blocked BI-induced 15-Lox1-enhanced Jak2 phosphorylation, dnJak2 had no effect on Src phosphorylation. Together, these observations demonstrate for the first time that the 15-Lox1-15(S)-HETE axis activates EGFR via redox-sensitive manner, which in turn mediates Src-Jak2-STAT3-dependent MCP-1 expression leading to vascular wall remodeling.

Activation of cytosolic phospholipase A2 downstream of the Src-phospholipase D1 (PLD1)-protein kinase C γ (PKCγ) signaling axis is required for hypoxia-induced pathological retinal angiogenesis

In view of understanding the mechanisms of retinal neovascularization, we had reported previously that vascular endothelial growth factor (VEGF)-induced pathological retinal angiogenesis requires the activation of Src-PLD1-PKCγ signaling. In the present work, we have identified cytosolic phospholipase A(2) (cPLA(2)) as an effector molecule of Src-PLD1-PKCγ signaling in the mediation of VEGF-induced pathological retinal angiogenesis based on the following observations. VEGF induced cPLA(2) phosphorylation in a time-dependent manner in human retinal microvascular endothelial cells (HRMVECs). VEGF also induced arachidonic acid (AA) release in a dose-, time-, and cPLA(2)-dependent manner. Depletion of cPLA(2) levels inhibited VEGF-induced HRMVEC DNA synthesis, migration, and tube formation. In addition, the exogenous addition of AA rescued VEGF-induced HRMVEC DNA synthesis, migration, and tube formation from inhibition by down-regulation of cPLA(2). Inhibition of Src, PLD1, or PKCγ attenuated VEGF-induced cPLA(2) phosphorylation and AA release. Consistent with these findings, hypoxia induced cPLA(2) phosphorylation and activity in VEGF-Src-PLD1-PKCγ-dependent manner in a mouse model of oxygen-induced retinopathy. In addition, siRNA-mediated down-regulation of cPLA(2) levels in the retina abrogated hypoxia-induced retinal endothelial cell proliferation and neovascularization. These observations suggest that cPLA(2)-dependent AA release is required for VEGF-induced Src-PLD1-PKCγ-mediated pathological retinal angiogenesis.

Functional and pathological roles of the 12- and 15-lipoxygenases

The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer's disease and Parkinson's disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases.

Angiotensin II-induced vascular smooth muscle cell migration and growth are mediated by cytochrome P450 1B1-dependent superoxide generation

Cytochrome P450 1B1, expressed in vascular smooth muscle cells, can metabolize arachidonic acid in vitro into several products including 12- and 20-hydroxyeicosatetraenoic acids that stimulate vascular smooth muscle cell growth. This study was conducted to determine whether cytochrome P450 1B1 contributes to angiotensin II-induced rat aortic smooth muscle cell migration, proliferation, and protein synthesis. Angiotensin II stimulated migration of these cells, measured by the wound healing approach, by 1.78-fold; and DNA synthesis, measured by [(3)H]thymidine incorporation, by 1.44-fold after 24 hours; and protein synthesis, measured by [(3)H]leucine incorporation, by 1.40-fold after 48 hours. Treatment of vascular smooth muscle cells with the cytochrome P450 1B1 inhibitor 2,4,3',5'-tetramethoxystilbene or transduction of these cells with adenovirus cytochrome P450 1B1 small hairpin RNA but not its scrambled control reduced the activity of this enzyme and abolished angiotensin II- and arachidonic acid-induced cell migration, as well as [(3)H]thymidine and [(3)H]leucine incorporation. Metabolism of arachidonic acid to 5-, 12-, 15-, and 20-hydoxyeicosatetraenoic acids in these cells was not altered, but angiotensin II- and arachidonic acid-induced reactive oxygen species production and extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase activity were inhibited by 2,4,3',5'-tetramethoxystilbene and cytochrome P450 1B1 small hairpin RNA (shRNA) and by Tempol, which inactivates reactive oxygen species. Tempol did not alter cytochrome P450 1B1 activity. These data suggest that angiotensin II-induced vascular smooth muscle cell migration and growth are mediated by reactive oxygen species generated from arachidonic acid by cytochrome P450 1B1 and activation of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase.

AP-1 (Fra-1/c-Jun)-mediated induction of expression of matrix metalloproteinase-2 is required for 15S-hydroxyeicosatetraenoic acid-induced angiogenesis

To understand the involvement of matrix metalloproteinases (MMPs) in 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE)-induced angiogenesis, we have studied the role of MMP-2. 15(S)-HETE induced MMP-2 expression and activity in a time-dependent manner in human dermal microvascular endothelial cells (HDMVECs). Inhibition of MMP-2 activity or depletion of its levels attenuated 15(S)-HETE-induced HDMVEC migration, tube formation, and Matrigel plug angiogenesis. 15(S)-HETE also induced Fra-1 and c-Jun expression in a Rac1-MEK1-JNK1-dependent manner. In addition, 15(S)-HETE-induced MMP-2 expression and activity were mediated by Rac1-MEK1-JNK1-dependent activation of AP-1 (Fra-1/c-Jun). Cloning and site-directed mutagenesis of MMP-2 promoter revealed that AP-1 site proximal to the transcriptional start site is required for 15(S)-HETE-induced MMP-2 expression, and Fra-1 and c-Jun are the essential components of AP-1 that bind to MMP-2 promoter in response to 15(S)-HETE. Hind limb ischemia led to an increase in MEK1 and JNK1 activation and Fra-1, c-Jun, and MMP-2 expression resulting in enhanced neovascularization and recovery of blood perfusion in wild-type mice as compared with 12/15-Lox(-/-) mice. Together, these results provide the first direct evidence for a role of 12/15-Lox-12/15(S)-HETE axis in the regulation of ischemia-induced angiogenesis.

15(S)-hydroxyeicosatetraenoic acid-induced angiogenesis requires Src-mediated Egr-1-dependent rapid induction of FGF-2 expression

To understand the mechanisms underlying 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE]-induced angiogenesis, we studied the role of Egr-1. 15(S)-HETE induced Egr-1 expression in a time-dependent manner in human dermal microvascular endothelial cells (HDMVECs). Blockade of Egr-1 via forced expression of its dominant-negative mutant attenuated 15(S)-HETE-induced HDMVEC migration and tube formation as well as Matrigel plug angiogenesis. 15(S)-HETE-induced Egr-1 expression requires Src activation. In addition, adenovirus-mediated expression of dominant-negative mutant of Src blocked 15(S)-HETE's effects on migration and tube formation of HDMVECs and Matrigel plug angiogenesis. 15(S)-HETE induced fibroblast growth factor-2 (FGF-2) expression rapidly via Src-mediated production of Egr-1. Cloning and mutational analysis of FGF-2 promoter revealed that Egr-1 binding site proximal to transcription start site is required for 15(S)-HETE-induced FGF-2 expression. Neutralizing antibody-mediated suppression of FGF-2 function also attenuated the effects of 15(S)-HETE on HDMVEC migration and tube formation as well as Matrigel plug angiogenesis. Furthermore, in contrast to wild-type mice, 12/15-LOX(-/-) mice exhibited decreased Matrigel plug angiogenesis in response to AA, which was rescued by 15(S)-HETE. On the basis of these observations, we conclude that 15(S)-HETE-induced angiogenesis requires Src-mediated Egr-1-dependent rapid induction of FGF-2. These findings may suggest that 15(S)-HETE could be a potential endogenous regulator of pathologic angiogenesis associated with atherosclerosis and restenosis.

Src-dependent STAT-3-mediated expression of monocyte chemoattractant protein-1 is required for 15(S)-hydroxyeicosatetraenoic acid-induced vascular smooth muscle cell migration

To understand the role of human 15-lipoxygenase 1 (15-LOX1) in vascular wall remodeling, we have studied the effect of the major 15-LOX1 metabolite of arachidonic acid, 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), on vascular smooth muscle cell (VSMC) migration both in vitro and in vivo. Among 5(S)-HETE, 12(S)-HETE, and 15(S)-HETE, 15(S)-HETE potentially stimulated more vascular smooth muscle cell (VSMC) migration. In addition, 15(S)-HETE-induced VSMC migration was dependent on Src-mediated activation of signal transducer and activator of transcription-3 (STAT-3). 15(S)-HETE also induced monocyte chemoattractant protein-1 (MCP-1) expression via Src-STAT-3 signaling, and neutralizing anti-MCP-1 antibodies completely negated 15(S)-HETE-induced VSMC migration. Cloning and characterization of a 2.6-kb MCP-1 promoter revealed the presence of four putative STAT-binding sites, and the site that is proximal to the transcription start site was found to be essential for 15(S)-HETE-induced Src-STAT-3-mediated MCP-1 expression. Rat carotid arteries that were subjected to balloon injury and transduced with Ad-15-LOX1 upon exposure to [(3)H]arachidonic acid ex vivo produced 15-HETE as a major eicosanoid and enhanced balloon injury-induced expression of MCP-1 in smooth muscle cells in Src and STAT-3-dependent manner in vivo. Adenovirus-mediated delivery of 15-LOX1 into rat carotid artery also led to recruitment and homing of macrophages to medial region in response to injury. In addition, transduction of Ad-15-LOX1 into arteries enhanced balloon injury-induced smooth muscle cell migration from media to intima and neointima formation. These results show for the first time that 15-LOX1-15(S)-HETE axis plays a major role in vascular wall remodeling after balloon angioplasty.