Maysam Takapoo

Nox1 transactivation of epidermal growth factor receptor promotes N-cadherin shedding and smooth muscle cell migration.

AIMS In atherosclerosis and restenosis, vascular smooth muscle cells (SMCs) migrate into the subendothelial space and proliferate, contributing to neointimal formation. The goal of this study was to define the signalling pathway by which Nox1 NAPDH oxidase mediates SMC migration. METHODS AND RESULTS SMCs were cultured from thoracic aorta from Nox1(-/y) (Nox1 knockout, KO) and wild-type (WT) mice. In response to thrombin, WT but not Nox1 KO SMCs generated increased levels of reactive oxygen species (ROS). Deficiency of Nox1 prevented thrombin-induced phosphorylation of Src and the subsequent transactivation of the epidermal growth factor receptor (EGFR) at multiple tyrosine residues. Next, activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and matrix metalloproteinase-9 (MMP-9) by thrombin was inhibited by the EGFR inhibitor AG1478 and in Nox1 KO SMCs. Thrombin-induced shedding of N-cadherin from the plasma membrane was dependent on the presence of Nox1 and was blocked by AG1478 and an inhibitor of metalloproteinases. Migration of SMCs to thrombin was impaired in the Nox1 KO SMCs and was restored by expression of Nox1. Finally, treatment of WT SMCs with AG1478 abrogated Nox1-dependent SMC migration. CONCLUSIONS The Nox1 NADPH oxidase signals through EGFR to activate MMP-9 and promote the shedding of N-cadherin, thereby contributing to SMC migration.

A critical role for chloride channel-3 (CIC-3) in smooth muscle cell activation and neointima formation.

Objective—We have shown that the chloride-proton antiporter chloride channel-3 (ClC-3) is required for endosome-dependent signaling by the Nox1 NADPH oxidase in SMCs. In this study, we tested the hypothesis that ClC-3 is necessary for proliferation of smooth muscle cells (SMCs) and contributes to neointimal hyperplasia following vascular injury. Methods and Results—Studies were performed in SMCs isolated from the aorta of ClC-3-null and littermate control (wild-type [WT]) mice. Thrombin and tumor necrosis factor-&agr; (TNF-&agr;) each caused activation of both mitogen activated protein kinase extracellular signal-regulated kinases 1 and 2 and the matrix-degrading enzyme matrix metalloproteinase-9 and cell proliferation of WT SMCs. Whereas responses to thrombin were preserved in ClC-3-null SMCs, the responses to TNF-&agr; were markedly impaired. These defects normalized following gene transfer of ClC-3. Carotid injury increased vascular ClC-3 expression, and compared with WT mice, ClC-3-null mice exhibited a reduction in neointimal area of the carotid artery 28 days after injury. Conclusion—ClC-3 is necessary for the activation of SMCs by TNF-&agr; but not thrombin. Deficiency of ClC-3 markedly reduces neointimal hyperplasia following vascular injury. In view of our previous findings, this observation is consistent with a role for ClC-3 in endosomal Nox1-dependent signaling. These findings identify ClC-3 as a novel target for the prevention of inflammatory and proliferative vascular diseases.

Activation of NADPH Oxidase 1 Increases Intracellular Calcium and Migration of Smooth Muscle Cells

Redox-dependent migration and proliferation of vascular smooth muscle cells (SMCs) are central events in the development of vascular proliferative diseases; however, the underlying intracellular signaling mechanisms are not fully understood. We tested the hypothesis that activation of Nox1 NADPH oxidase modulates intracellular calcium ([Ca2+]i) levels. Using cultured SMCs from wild-type and Nox1 null mice, we confirmed that thrombin-dependent generation of reactive oxygen species requires Nox1. Thrombin rapidly increased [Ca2+]i, as measured by fura-2 fluorescence ratio imaging, in wild-type but not Nox1 null SMCs. The increase in [Ca2+]i in wild-type SMCs was inhibited by antisense to Nox1 and restored by expression of Nox1 in Nox1 null SMCs. Investigation into potential mechanisms by which Nox1 modulates [Ca2+]i showed that thrombin-induced inositol triphosphate generation and thapsigargin-induced intracellular calcium mobilization were similar in wild-type and Nox1 null SMCs. To examine the effects of Nox1 on Ca2+ entry, cells were either bathed in Ca2+-free medium or exposed to dihydropyridines to block L-type Ca2+ channel activity. Treatment with nifedipine or removal of extracellular Ca2+ reduced the thrombin-mediated increase of [Ca2+]i in wild-type SMCs, whereas the response in Nox1 null SMCs was unchanged. Sodium vanadate, an inhibitor of protein tyrosine phosphatases, restored the thrombin-induced increase of [Ca2+]i in Nox1 null SMCs. Migration of SMCs was impaired with deficiency of Nox1 and restored with expression of Nox1 or the addition of sodium vanadate. In summary, we conclude that Nox1 NADPH oxidase modulates Ca2+ mobilization in SMCs, in part through regulation of Ca2+ influx, to thereby promote cell migration.

Glutathione peroxidase-deficient smooth muscle cells cause paracrine activation of normal smooth muscle cells via cyclophilin A

BACKGROUND/AIMS Reduced activity of the antioxidant glutathione peroxidase-1 (GPx1) correlates with increased risk of cardiovascular events in patients with coronary artery disease. However, it remains unclear whether this imbalance in antioxidant capacity directly contributes to activation of vascular cells. In response to oxidative stress, smooth muscle cells (SMCs) secrete the pro-inflammatory immunomodulator cyclophilin A (CyPA). We hypothesized that reduction in vascular cell GPx1 activity causes secretion of CyPA and paracrine-mediated activation of NF-κB and proliferation of SMCs. METHODS/RESULTS Using a murine model of GPx1 deficiency (GPx1(+/-)), we found elevated levels of hydrogen peroxide levels and increased secretion of CyPA in both arterial segments and cultured SMCs as compared to wild type (WT). Conditioned media from GPx1(+/-) SMCs caused increased NF-κB activation of quiescent WT SMCs, and this was inhibited by the antioxidant N-acetyl-l-cysteine or by cyclosporine A (CsA). In co-culture experiments, SMCs derived from GPx1(+/-) aorta caused increased proliferation of WT SMCs, which was also inhibited by CsA. CONCLUSIONS Reduction in vascular cell GPx1 activity and the associated increase in oxidative stress cause CyPA-mediated paracrine activation of SMCs. These findings identify a novel mechanism by which an imbalance in antioxidant capacity may contribute to vascular disease.

Smooth Muscle Cell–targeted RNA Aptamer Inhibits Neointimal Formation

Inhibition of vascular smooth muscle cell (VSMC) proliferation by drug eluting stents has markedly reduced intimal hyperplasia and subsequent in-stent restenosis. However, the effects of antiproliferative drugs on endothelial cells (EC) contribute to delayed re-endothelialization and late stent thrombosis. Cell-targeted therapies to inhibit VSMC remodeling while maintaining EC health are necessary to allow vascular healing while preventing restenosis. We describe an RNA aptamer (Apt 14) that functions as a smart drug by preferentially targeting VSMCs as compared to ECs and other myocytes. Furthermore, Apt 14 inhibits phosphatidylinositol 3-kinase/protein kinase-B (PI3K/Akt) and VSMC migration in response to multiple agonists by a mechanism that involves inhibition of platelet-derived growth factor receptor (PDGFR)-β phosphorylation. In a murine model of carotid injury, treatment of vessels with Apt 14 reduces neointimal formation to levels similar to those observed with paclitaxel. Importantly, we confirm that Apt 14 cross-reacts with rodent and human VSMCs, exhibits a half-life of ~300 hours in human serum, and does not elicit immune activation of human peripheral blood mononuclear cells. We describe a VSMC-targeted RNA aptamer that blocks cell migration and inhibits intimal formation. These findings provide the foundation for the translation of cell-targeted RNA therapeutics to vascular disease.Inhibition of vascular smooth muscle cell (VSMC) proliferation by drug eluting stents has markedly reduced intimal hyperplasia and subsequent in-stent restenosis. However, the effects of antiproliferative drugs on endothelial cells (EC) contribute to delayed re-endothelialization and late stent thrombosis. Cell-targeted therapies to inhibit VSMC remodeling while maintaining EC health are necessary to allow vascular healing while preventing restenosis. We describe an RNA aptamer (Apt 14) that functions as a smart drug by preferentially targeting VSMCs as compared to ECs and other myocytes. Furthermore, Apt 14 inhibits phosphatidylinositol 3-kinase/protein kinase-B (PI3K/Akt) and VSMC migration in response to multiple agonists by a mechanism that involves inhibition of platelet-derived growth factor receptor (PDGFR)-β phosphorylation. In a murine model of carotid injury, treatment of vessels with Apt 14 reduces neointimal formation to levels similar to those observed with paclitaxel. Importantly, we confirm that Apt 14 cross-reacts with rodent and human VSMCs, exhibits a half-life of ~300 hours in human serum, and does not elicit immune activation of human peripheral blood mononuclear cells. We describe a VSMC-targeted RNA aptamer that blocks cell migration and inhibits intimal formation. These findings provide the foundation for the translation of cell-targeted RNA therapeutics to vascular disease.

61. Vascular Smooth Muscle Cell RNA Aptamers for the Treatment of Cardiovascular Disease

Cardiovascular disease (CVD) is the leading cause of mortality in many countries. Many vascular disorders, including in-stent restenosis, arteriosclerosis, vein graft disease, and cardiac allograft arteriopathy are caused by pathological vascular smooth muscle cell (VSMC) remodeling following injury. An ideal therapeutic intervention would target the VSMCs without impairing the injured vessel re-endothelialization. However, current therapies do not selectively prevent pathological VSMC remodeling leading to impaired re-endothelization, late stent thrombosis and death. Thus, there is a clear need for cell-targeted treatment and prevention options of pathological VSMC remodeling.Our group has described the development of VSMC-specific, aptamers for (1) modulating signaling pathways associated with pathological VSMC remodeling and (2) delivering therapeutic molecules to these cells in vivo. Here we demonstrate that one of these aptamers, Vapt14, inhibits protein kinase B (PKB)/Akt activation and VSMC migration in response to multiple agonists by a mechanism that involves inhibition of platelet-derived growth factor receptor (PDGFR)-beta phosphorylation. In a murine model of carotid injury, treatment of vessels with Vapt14 reduces intimal:medial thickness to levels comparable to that of paclitaxel. Importantly, we confirm that Vapt14 cross-reacts with rodent and human VSMCs, exhibits a half-life of ~300 hours in human serum, and does not elicit immune activation of human peripheral blood mononuclear cells (PBMCs) in vitro. In addition, we confirm delivery of Vapt14 to VSMC in vitro and in vivo with fluorescence microscopy. Studies are being expanded to evaluate aptamer-mediated delivery of therapeutic biomolecules (e.g. small molecules, RNAi modulators) to areas of vascular injury. In summary this work provides an essential foundation for the translation of cell-targeted RNA therapeutics to multiple hyperplastic vascular diseases.