SDF-1alpha/CXCR4 axis is instrumental in neointimal hyperplasia and recruitment of smooth muscle progenitor cells

Recent evidence infers a contribution of smooth muscle cell (SMC) progenitors and stromal cell-derived factor (SDF)-1alpha to neointima formation after arterial injury. Inhibition of plaque area and SMC content in apolipoprotein E-deficient mice repopulated with LacZ+ or CXCR4-/- BM or lentiviral transfer of an antagonist reveals a crucial involvement of local SDF-1alpha and its receptor CXCR4 in neointimal hyperplasia via recruitment of BM-derived SMC progenitors. After arterial injury, SDF-1alpha expression in medial SMCs is preceded by apoptosis and inhibited by blocking caspase-dependent apoptosis. SDF-1alpha binds to platelets at the site of injury, triggers CXCR4- and P-selectin-dependent arrest of progenitor cells on injured arteries or matrix-adherent platelets, preferentially mobilizes and recruits c-kit-/platelet-derived growth factor receptor (PDGFR)-beta+/lineage-/sca-1+ progenitors for neointimal SMCs without being required for their differentiation. Hence, the SDF-1alpha/CXCR4 axis is pivotal for vascular remodeling by recruiting a subset of SMC progenitors in response to apoptosis and in concert with platelets, epitomizing its importance for tissue repair and identifying a prime target to limit lesion development.     

Perlecan-induced suppression of smooth muscle cell proliferation is mediated through increased activity of the tumor suppressor PTEN

We were interested in the elucidation of the interaction between the heparan sulfate proteoglycan, perlecan, and PTEN in the regulation of vascular smooth muscle cell (SMC) growth. We verified serum-stimulated DNA synthesis, and Akt and FAK phosphorylation were significantly reduced in SMCs overexpressing wild-type PTEN. Our previous studies showed perlecan is a potent inhibitor of serum-stimulated SMC growth. We report in the present study, compared with SMCs plated on fibronectin, serum-stimulated SMCs plated on perlecan exhibited increased PTEN activity, decreased FAK and Akt activities, and high levels of p27, consistent with SMC growth arrest. Adenoviral-mediated overexpression of constitutively active Akt reversed perlecan-induced SMC growth arrest while morpholino antisense-mediated loss of endogenous PTEN resulted in increased growth and phosphorylation of FAK and Akt of SMCs on perlecan. Immunohistochemical and Western analyses of balloon-injured rat carotid artery tissues showed a transient increase in phosphoPTEN (inactive) after injury, correlating to high rates of neointimal cell replication; phosphoPTEN was largely limited to actively replicating SMCs. Similarly, in the developing rat aorta, we found increased PTEN activity associated with increased perlecan deposition and decreased SMC replication rates. However, significantly decreased PTEN activity was detected in aortas of perlecan-deficient mouse embryos, consistent with SMC hyperplasia observed in these animals, compared with E17.5 heterozygous controls that produce abundant amounts of perlecan at this developmental time point. Our data show PTEN is a potent endogenously produced inhibitor of SMC growth and increased PTEN activity mediates perlecan-induced suppression of SMC proliferation.     

Chemokines in vascular dysfunction and remodeling

Vascular remodeling stands for structural changes of the vessel wall in response to various noxious stimuli, which results in reorganization of the vessel wall architecture. Luminal narrowing because of neointima formation and constrictive remodeling leading to hypoperfusion is the most relevant clinical effect. Smooth muscle cell (SMC) accumulation, inflammatory cell recruitment, and endothelial regeneration are the critical parts in obstructive vascular remodeling. Chemokines and chemokine receptors have a great impact on initiating and progressing neointimal formation by controlling each step of the remodeling process. SDF-1alpha regulates vascular repair by CXCR4-dependent smooth muscle progenitor cell recruitment, which contributes to the maladaptive response to injury. The three distinct chemokine-chemokine receptor pairs MCP-1/CCR2, RANTES/CCR5, and Fractalkine/CX(3)CR1 direct lesional leukocyte infiltration. In addition MCP-1/CCR2 and Fractalkine/CX(3)CR1 increase neointimal SMC expansion. In contrast, KC/Gro-alpha supports endothelial recovery through CXCR2, which attenuates neointima formation. These findings highlight the importance to characterize specific functions of the chemokine network to enable therapeutic intervention.     

Cyclic strain stimulates L-proline transport in vascular smooth muscle cells

BACKGROUND: The increase in vessel wall strain in hypertension contributes to arterial remodeling by stimulating vascular smooth muscle cell (SMC) proliferation and collagen synthesis. Because L-proline is essential for the synthesis of collagen and cell growth, we examined whether cyclic strain regulates the transcellular transport of L-proline by vascular SMC. METHODS: Cultured rat aortic SMCs were subjected to mechanical strain using the Flexercell 3000 Strain Unit. RESULTS: Cyclic strain increased L-proline transport in a time- and strain-degree-dependent manner that was inhibited by cycloheximide or actinomycin D. Kinetic studies indicated that cyclic strain-induced L-proline uptake was mediated by an increase in transport capacity independent of any change in the affinity for L-proline. Cyclic strain stimulated the expression of system A amino acid transporter 2 mRNA in a time-dependent fashion that paralleled the increase in L-proline transport. Cyclic strain also induced the release of transforming growth factor-beta1 in a time- and strain-dependent manner. Moreover, conditioned media from SMCs exposed to cyclic strain stimulated the transport of L-proline in control, static SMCs and this was significantly attenuated by a transforming growth factor-beta1 neutralizing antibody. CONCLUSIONS: These results demonstrate that cyclic strain stimulates L-proline transport by inducing system A amino acid transporter 2 gene expression through the autocrine release of transforming growth factor-beta1. The ability of cyclic strain to induce system A amino acid transporter 2 expression may promote arterial remodeling in hypertension by providing vascular SMCs with the necessary intracellular levels of L-proline required for collagen synthesis and cell growth.     

SDF-1alpha/CXCR4 decreases endothelial progenitor cells apoptosis under serum deprivation by PI3K/Akt/eNOS pathway

Recent studies have demonstrated that stromal cell-derived factor-1alpha (SDF-1alpha)/CXCR4 interaction regulates multiple cell signal pathways and a variety of cellular functions such as cell migration, proliferation, survival and angiogenesis. In present study, we aimed to determine the effect of SDF-1alpha on endothelial progenitor cells (EPCs) apoptosis induced by serum deprivation and the implication of phosphoinositide 3-kinase (PI3K)/Akt and mitogen-activated protein kinases (MAPKs) signaling in this effect. EPCs were isolated and characterized. SDF-1alpha decreased EPCs apoptosis induced by serum deprivation in a dose-dependent manner and the inhibitory effect was CXCR4 dependent as confirmed by the total abolishment by AMD3100, a CXCR4-specific peptide antagonist. SDF-1alpha treatment also significant decreased caspase-3 expression and activity. The inhibitory effect of SDF-1alpha on EPCs apoptosis was nearly completely abolished by PI3K inhibitors (either Wortmannin or LY294002) and partially abolished by NOS inhibitor, N(G)-nitro-arginine methyl ester, whereas inhibitors of MAPKs had no significant effect on this inhibitory effect. The treatment of EPCs with SDF-1alpha resulted in time-dependent Akt, eNOS, extracellular-regulated kinase (ERK1/2), p38 MAPK and c-Jun N-terminal kinase (JNK) phosphorylations. These findings suggest that PI3K/Akt/eNOS activation, but not MAPKs activation, is required for the inhibitory effect of SDF-1alpha on EPCs apoptosis.     

Chemokines induce matrix metalloproteinase-2 through activation of epidermal growth factor receptor in arterial smooth muscle cells

OBJECTIVE: Matrix metalloproteinases (MMP) are critical to smooth muscle cell (SMC) migration in vivo. MMP-2 dysregulation has been implicated in the pathogenesis of abnormal arterial remodeling, aneurysm formation, and atherosclerotic plaque structure and stability. The chemokine receptors CCR3 and CXCR4 are present and functional on SMC and are up-regulated in vascular diseases such as atherosclerosis. We sought to determine a potential mechanism for chemokine receptor-mediated effects on the vasculature by asking whether the chemokines eotaxin (CCL11), the ligand for CCR3, and stromal cell-derived cell factor (SDF-1, CXCL12), the ligand for CXCR4, induce MMP-2 in SMC. Studies were then performed to define the signaling pathways involved. METHODS AND RESULTS: As determined by RT-PCR, Western blotting and zymography, SDF-1 and eotaxin induce MMP-2 mRNA, protein, and activity in SMC. An anti-CCR3 antibody and a CXCR4 antagonist blocked proMMP-2 induction by SDF-1 and eotaxin, the respective ligands for the chemokine receptors CXCR4 and CCR3, suggesting that the inductions by these chemokines are receptor-mediated. Receptor cross-talk between G-protein-coupled receptors (GPCR) and the epidermal growth factor receptor (EGFR) is a method of expanding the GPCRs' signaling repertoire. We demonstrate, for the first time to our knowledge, that in SMC, chemokine induction of proMMP-2 is dependent on activation of the EGFR. Interestingly, by blocking the ligand binding domain of EGFR, we demonstrate that activation of EGFR by SDF-1 and eotaxin occurs through different cellular pathways. CONCLUSION: The pro-inflammatory chemokines eotaxin and SDF induce proMMP-2 activation of EGFR through two different pathways. SDF and eotaxin, as regulators of proMMP-2 expression and by engaging in receptor cross-talk, may play critical roles in atherosclerosis, restenosis, and plaque rupture. These ligands and their respective receptors, CXCR4 and CCR3, therefore may serve as future potential therapeutic targets.     

Proteomic and metabolomic analysis of smooth muscle cells derived from the arterial media and adventitial progenitors of apolipoprotein E-deficient mice

We have recently demonstrated that stem cell antigen 1-positive (Sca-1(+)) progenitors exist in the vascular adventitia of apolipoprotein E-deficient (apoE(-/-)) mice and contribute to smooth muscle cell (SMC) accumulation in vein graft atherosclerosis. Using a combined proteomic and metabolomic approach, we now characterize these local progenitors, which participate in the formation of native atherosclerotic lesions in chow-fed apoE(-/-) mice. Unlike Sca-1(+) progenitors from embryonic stem cells, the resident Sca-1(+) stem cell population from the vasculature acquired a mature aortic SMC phenotype after platelet-derived growth factor-BB stimulation. It shared proteomic and metabolomic characteristics of apoE(-/-) SMCs, which were clearly distinct from wild-type SMCs under normoxic and hypoxic conditions. Among the differentially expressed proteins were key enzymes in glucose metabolism, resulting in faster glucose consumption and a compensatory reduction in baseline interleukin-6 secretion. The latter was associated with a marked upregulation of insulin-like growth factor binding proteins (IGFBPs) 3 and 6. Notably, reconstitution of interleukin-6 to levels measured in the conditioned medium of wild-type SMCs attenuated the elevated IGFBP expression in apoE(-/-) SMCs and their vascular progenitors. This coregulation of apoE, interleukin-6, and IGFBPs was replicated in wild-type SMCs from hypercholesterolemic mice and confirmed by silencing apoE expression in SMCs from normocholesterolemic mice. In summary, we provide evidence that Sca-1(+) progenitors contribute to native atherosclerosis in apoE(-/-) mice, that apoE deficiency and hypercholesterolemia alter progenitor cell behavior, and that inflammatory cytokines such as interleukin-6 act as metabolic regulators in SMCs of hyperlipidemic mice.     

Galectin 1 modulates attachment, spreading and migration of cultured vascular smooth muscle cells via interactions with cellular receptors and components of extracellular matrix

Galectin 1 (Gal-1), a lactose-binding lectin, is a component of vascular extracellular matrix and secreted by human vascular smooth muscle cells (SMCs). The purpose of this study was to investigate a possible role of Gal-1 in controlling adhesion and migration of cultured human vascular SMCs. Gal-1 co-localised with laminin and cellular fibronectin in extracellular matrix (ECM) secreted by cultured human vascular SMCs. Recombinant glutathione S-transferase (GST)-Gal-1 fusion protein bound to laminin and cellular fibronectin in ELISA. GST-Gal-1 inhibited SMC attachment to laminin via interactions with both SMCs and laminin. GST-Gal-1 inhibited SMC spreading on plastic or on laminin, but not on cellular fibronectin. GST-Gal-1 modulated SMC migration on laminin and inhibited migration on cellular fibronectin. GST-Gal-1 bound to several 35S-labelled proteins in SMC extracts including laminin and alpha1beta1 integrin, identified by depletion of SMC protein extracts with respective antibodies. We conclude that Gal-1 is able to modulate SMC attachment, spreading and migration via interactions with ECM proteins and alpha1beta1 integrin.     

Regulation of endothelial cell branching morphogenesis by endogenous chemokine stromal-derived factor-1

The chemokine stromal-derived factor-1 (SDF-1) and its unique receptor, CXCR4, are required for normal cardiovascular development, but a critical role for SDF-1 in postnatal vascular remodeling and the mechanisms underlying SDF-1/CXCR-4 vasculogenesis are unclear. Here we show that SDF-1 is expressed by the vascular endothelium from selected healthy and tumor tissues. In vitro, primary endothelial cells constitutively express SDF-1 that is detected in the cytoplasm, on the cell surface, and in the culture supernatant. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) increase SDF-1 expression in endothelial cells. In functional studies, pertussis toxin and antibodies to SDF-1 or CXCR-4 disrupt extracellular matrix-dependent endothelial cell tube formation in vitro. This morphogenic process is associated with time-dependent modulation of surface CXCR-4 expression that changes from being diffuse to being polarized and subsequently lost. In vivo, pertussis toxin and neutralizing antibodies directed at SDF-1 inhibit growth factor-dependent neovascularization. These results indicate that SDF-1/CXCR-4 identifies VEGF- and bFGF-regulated autocrine signaling systems that are essential regulators of endothelial cell morphogenesis and angiogenesis.     

Enhancement of intracellular signaling associated with hematopoietic progenitor cell survival in response to SDF-1/CXCL12 in synergy with other cytokines

Stromal cell-derived factor 1 (SDF-1/CXCL12) is a multifunctional cytokine. We previously reported that myelopoiesis was enhanced in SDF-1 alpha transgenic mice, probably due in part to SDF-1 alpha enhancement of myeloid progenitor cell (MPC) survival. To understand signaling pathways involved in this activity, we studied the effects on factor-dependent cell line MO7e cells incubated with SDF-1 alpha alone or in combination with other cytokines. SDF-1 alpha induced transient activation of extracellular stress-regulated kinase (ERK1/2), ribosomal S6 kinase (p90RSK) and Akt, molecules implicated in cell survival. Moreover, ERK1/2, p90RSK, and Akt were synergistically activated by SDF-1 alpha in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF), Steel factor (SLF), or thrombopoietin (TPO). Similar effects were seen after pretreatment of MO7e cells with SDF-1 alpha followed by stimulation with the other cytokines, suggesting a priming effect of SDF-1 alpha. Nuclear factor-kappa B (NF-kappa B) did not appear to be involved in SDF-1 alpha actions, alone or in combination with other cytokines. These intracellular effects were consistent with enhanced myeloid progenitor cell survival by SDF-1 alpha after delayed addition of growth factors. SDF-1 alpha alone supported survival of highly purified human cord blood CD34(+++) cells, less purified human cord blood, and MO7e cells; this effect was synergistically enhanced when SDF-1 alpha was combined with low amounts of other survival-promoting cytokines (GM-CSF, SLF, TPO, and FL). SDF-1 may contribute to maintenance of MPCs in bone marrow by enhancing cell survival alone and in combination with other cytokines.     

Altered SDF-1/CXCR4 axis in patients with primary myelofibrosis and in the Gata1 low mouse model of the disease

OBJECTIVE: To assess whether alterations in the stromal cell-derived factor-1 (SDF-1)/CXCR4 occur in patients with primary myelofibrosis (PMF) and in Gata1 low mice, an animal model for myelofibrosis, and whether these abnormalities might account for increased stem/progenitor cell trafficking. MATERIALS AND METHODS: In the mouse, SDF-1 mRNA levels were assayed in liver, spleen, and marrow. SDF-1 protein levels were quantified in plasma and marrow and CXCR4 mRNA and protein levels were evaluated on stem/progenitor cells and megakaryocytes purified from the marrow. SDF-1 protein levels were also evaluated in plasma and in marrow biopsy specimens obtained from normal donors and PMF patients. RESULTS: In Gata1 low mice, the plasma SDF-1 protein was five times higher than normal in younger animals. Furthermore, SDF-1 immunostaining of marrow sections progressively increased with age. Similar abnormalities were observed in PMF patients. In fact, plasma SDF-1 levels in PMF patients were significantly higher (by twofold) than normal (p < 0.01) and SDF-1 immunostaining of marrow biopsy specimens demonstrated increased SDF-1 deposition in specific areas. In two of the patients, SDF-1 deposition was normalized by curative therapy with allogenic stem cell transplantation. Similar to what already has been reported for PMF patients, the marrow from Gata1 low mice contained fewer CXCR4 pos CD117 pos cells and these cells expressed low levels of CXCR4 mRNA and protein. CONCLUSION: Similar abnormalities in the SDF-1/CXCR4 axis are observed in PMF patients and in the Gata1 low mice model of myelofibrosis. We suggest that these abnormalities contribute to the increased stem/progenitor cell trafficking observed in this mouse model as well as patients with PMF.     

Regional differences in integrin expression: role of alpha(5)beta(1) in regulating smooth muscle cell functions

There is increasing evidence to suggest that coronary smooth muscle cells (SMCs) differ from noncoronary SMCs. As integrin adhesion molecules regulate many SMC functions, we hypothesized that differences in integrin expression on coronary and noncoronary SMCs may account for cellular differences. Analysis of integrin expression on freshly isolated porcine coronary and noncoronary SMCs revealed that coronary SMCs express significantly less alpha(5)beta(1) than noncoronary SMCs, whereas the expression of total beta(1) and that of alpha(v)beta(3) are similar. Consistent with these findings, coronary SMCs demonstrated significantly less adhesion to fibronectin, compared with carotid artery SMCs. As alpha(5)beta(1)-mediated signaling has been associated with cellular proliferation, the effects of differential alpha(5)beta(1) expression on cell proliferation were examined by comparing primary coronary and carotid artery SMC proliferation. Coronary SMC growth was significantly lower than that of carotid artery SMCs when plated on fibronectin or type I collagen. Blocking alpha(5)beta(1) function on carotid artery SMCs produced a significant decrease in cellular proliferation, resulting in growth similar to that of coronary SMCs. Furthermore, blocking alpha(5)beta(1), but not alpha(v)beta(3), inhibited loss of alpha-smooth muscle actin in proliferating SMCs. Proliferating coronary SMCs were found to upregulate alpha(5)beta(1) expression, further indicating a role for alpha(5)beta(1) in SMC growth. These results suggest that dissimilar alpha(5)beta(1) integrin expression may mediate regional differences in phenotype of vascular SMCs.     

Treatment of circulating CD34(+) cells with SDF-1alpha or anti-CXCR4 antibody enhances migration and NOD/SCID repopulating potential

OBJECTIVE: Stromal cell-derived factor-1alpha (SDF-1alpha) has been implicated in homing and engraftment of primitive hematopoietic progenitor cells (HPC) in studies demonstrating reduced NOD/SCID repopulating potential of HPC exposed to supra-physiologic concentrations of SDF-1alpha or anti-CXCR4. Outcome of CXCR4 signaling in some cells has been shown to be dependent on the concentration of SDF-1alpha. We aimed to determine whether similar concentration-dependent responses to CXCR4 signaling are present in CD34(+)cells. MATERIALS AND METHODS: Human peripheral blood (PB), mobilized PB (MPB), or bone marrow (BM) CD34(+) cells were incubated for 30 minutes with different concentrations of SDF-1alpha or anti-CXCR4, washed, then assessed for in vitro hematopoietic potential, migration, and NOD/SCID repopulating potential. RESULTS: Exposure of MPB or PB CD34(+) cells to 100 ng/mL SDF-1alpha increased tyrosine phosphorylation without subsequent proliferation or apoptosis. Spontaneous and SDF-1alpha-directed migration also increased in pretreated cells, despite previous exposure to SDF-1alpha. Cells exposed to 1 microg anti-CXCR4/10(6) cells displayed similar increases in activation and migration as cells exposed to SDF-1alpha, demonstrating the ability of anti-CXCR4 to activate the CXCR4 receptor. Interestingly, chimerism in NOD/SCID mice transplanted with MPB CD34(+) cells pretreated with SDF-1alpha or anti-CXCR4 was increased, while exposure of these cells to 10- to 100-fold higher concentrations of these proteins inhibited in vitro migration and NOD/SCID repopulating potential. Migration and NOD/SCID repopulating potential of BM CD34(+) cells remained unchanged after treatment with either protein. CONCLUSIONS: These results illustrate the ability of SDF-1alpha and anti-CXCR4 to augment repopulating potential of CD34(+) cells, and suggest that HPC function can be favorably modulated through specific CXCR4 signaling.     

Stromal cell-derived factor-1alpha stimulates tyrosine phosphorylation of multiple focal adhesion proteins and induces migration of hematopoietic progenitor cells: roles of phosphoinositide-3 kinase and protein kinase C

The stromal cell-derived factor-1 (SDF-1) is an alpha chemokine that binds to the CXCR4 receptor. Knock-out studies in mice demonstrate that this ligand-receptor pair is essential in hematopoiesis. One function of SDF-1 appears to be the regulation of migration of hematopoietic progenitor cells. We previously characterized signal transduction pathways induced by SDF-1alpha in human hematopoietic progenitors and found tyrosine phosphorylation of focal adhesion components, including the related adhesion focal tyrosine kinase (RAFTK), the adaptor molecule p130 Cas, and the cytoskeletal protein paxillin. To better understand the functional role of signaling molecules connecting the CXCR4 receptor to the process of hematopoietic migration, we studied SDF-1alpha-mediated pathways in a model hematopoietic progenitor cell line (CTS), as well as in primary human bone marrow CD34(+) cells. We observed that several other focal adhesion components, including focal adhesion kinase (FAK) and the adaptor molecules Crk and Crk-L, are phosphorylated on SDF-1alpha stimulation. Using a series of specific small molecule inhibitors, both protein kinase C (PKC) and phosphoinositide-3 kinase (PI-3K) appeared to be required for SDF-1alpha-mediated phosphorylation of focal adhesion proteins and the migration of both CTS and primary marrow CD34(+) cells, whereas the mitogen-activated protein kinases ERK-1 and -2 were not. These studies further delineate the molecular pathways mediating hematopoietic progenitor migration and response to an essential chemokine, SDF-1alpha. (Blood. 2000;95:2505-2513)     

The human hematopoietic stem cell compartment is heterogeneous for CXCR4 expression

The chemokine stromal derived factor-1alpha (SDF-1alpha) has been implicated recently in the chemotaxis of primitive human hematopoietic cells, suggesting that pluripotent human stem cells express the SDF-1alpha receptor, CXCR4. By using flow cytometry and confocal microscopy, we have identified and isolated primitive subsets of human CXCR4(+) and CXCR4(-) cells. Distinctions in the progenitor content and response to SDF-1alpha in vitro indicate that CXCR4(+) and CXCR4(-) cells represent discrete populations of primitive blood cells. The i.v. transplantation of these subfractions into immune-deficient mice established that both possess comparable engraftment capacity in vivo. Human myeloid, lymphoid, and primitive CD34(+) CXCR4(+) cells were present in chimeric animals transplanted with either subset, indicating that CXCR4(+) and CXCR4(-) stem cells have equivalent proliferative and differentiative abilities. Our study indicates that the human stem cell compartment is heterogeneous for CXCR4 expression, suggesting that the relationship between CXCR4 expression and stem cell repopulating function is not obligatory.     

Short-term inhibition of DPP-4 enhances endothelial regeneration after acute arterial injury via enhanced recruitment of circulating progenitor cells

Background

Endothelial injuries regularly occur in atherosclerosis and during interventional therapies of the arterial occlusive disease. Disturbances in the endothelial integrity can lead to insufficient blood supply and bear the risk of thrombus formation and acute vascular occlusion. At present, effective therapeutics to restore endothelial integrity are barely available.We analyzed the effect of pharmacological DPP-4-inhibition by Sitagliptin on endogenous progenitor cell-based endothelial regeneration via the SDF-1α/CXCR4-axis after acute endothelial damage in a mouse model of carotid injury.

Methods and Results

Induction of a defined endothelial injury was performed in the carotid artery of C57Bl/6 mice which led to a local upregulation of SDF-1α expression. Animals were treated with placebo, Sitagliptin or Sitagliptin + AMD3100. Using mass spectrometry we could prove that Sitagliptin prevented cleavage of the chemokine SDF-1α. Accordingly, increased SDF-1α concentrations enhanced recruitment of systemically applied and endogenous circulating CXCR4 + progenitor cells to the site of vascular injury followed by a significantly accelerated reendothelialization as compared to placebo-treated animals. Improved endothelial recovery, as well as recruitment of circulating CXCR4 + progenitor cells (CD133 +, Flk1 +), was reversed by CXCR4-antagonization through AMD3100. In addition, short-term Sitagliptin treatment did not significantly promote neointimal or medial hyperplasia.

Conclusion

Sitagliptin can accelerate endothelial regeneration after acute endothelial injury. DPP-4 inhibitors prevent degradation of the chemokine SDF-1α and thus improve the recruitment of regenerative circulating CXCR4 + progenitor cells which mediate local endothelial cell proliferation without adversely affecting vessel wall architecture.     

Wilms' tumor 1-associating protein regulates the proliferation of vascular smooth muscle cells

Smooth muscle cells (SMCs) are called on to proliferate during vascular restructuring but must return to a nonproliferative state if remodeling is to appropriately terminate. To identify mediators of the reacquisition of replicative quiescence, we undertook gene expression screening in a uniquely plastic human SMC line. As proliferating SMCs shifted to a contractile and nonproliferative state, expression of TIMP-3, Axl, and KIAA0098 decreased whereas expression of complement C1s, cathepsin B, cellular repressor of E1A-activated genes increased. Wilms' tumor 1-associating protein (WTAP), a nuclear constituent of unknown function, was also upregulated as SMCs became nonproliferative. Furthermore, WTAP in the intima of injured arteries was substantially upregulated in the late stages of repair. Introduction of WTAP complementary DNA into human SMCs inhibited their proliferation, with a corresponding decrease in DNA synthesis and an increase in apoptosis. Knocking down endogenous WTAP increased SMC proliferation, because of increased DNA synthesis and G(1)/S phase transition, together with reduced apoptosis. WTAP was found to associate with the Wilms' tumor-1 protein in human SMCs and WTAP overexpression inhibited the binding of WT1 to an oligonucleotide containing a consensus WT1 binding site, whereas WTAP knockdown accentuated this interaction. Expression of the WT1 target genes, amphiregulin and Bcl-2, was suppressed in WTAP-overexpressing SMCs and increased in WTAP-deficient SMCs. Moreover, exogenous amphiregulin rescued the antiproliferative effect of WTAP. These findings identify WTAP as a novel regulator of the cell cycle and cell survival and implicate a WTAP-WT1 axis as a novel pathway for controlling vascular SMC phenotype.     

Platelets and stromal cell-derived factor-1 in progenitor cell recruitment

Stromal cell-derived factor-1 (SDF-1) is a CXC chemokine that binds to its sole counterreceptor, CXCR4. It is well reported that the SDF-1/CXCR4 signaling pathway is of vital importance to human development and to various pathophysiological phenomena, including hematopoiesis, angiogenesis, atherosclerosis, cancer growth, metastasis, and human immunodeficiency virus infection. SDF-1 promotes mobilization of bone marrow-derived endothelial progenitor cells (EPCs) to the circulation in response to vascular injury. Recently, we found that platelets express and release SDF-1 into the microcirculation upon activation and we observed that platelet-derived SDF-1 is functionally involved in recruitment of EPCs to arterial thrombi in vivo. This review discusses the unique functions of this chemokine and the newly discovered impact of platelet-derived SDF-1 into the recruitment of progenitor cells to vascular injury areas, and its subsequent effects in atherosclerosis, vascular repair, and angiogenesis.