Adenoviral-mediated inhibition of Gβγ signaling limits the hyperplastic response in experimental vein grafts

Pro-resolving lipid mediators in vascular disease

Unresolved inflammation is central to the pathophysiology of commonly occurring vascular diseases such as atherosclerosis, aneurysm, and deep vein thrombosis - conditions that are responsible for considerable morbidity and mortality. Surgical or catheter-based procedures performed on affected blood vessels induce acute-on-chronic inflammatory responses. The resolution of vascular inflammation is an important driver of vessel wall remodeling and functional recovery in these clinical settings. Specialized pro-resolving lipid mediators (SPMs) derived from omega-3 polyunsaturated fatty acids orchestrate key cellular processes driving resolution and a return to homeostasis. The identification of their potent effects in classic animal models of sterile inflammation triggered interest in their vascular properties. Recent studies have demonstrated that SPMs are locally synthesized in vascular tissues, have direct effects on vascular cells and their interactions with leukocytes, and play a protective role in the injury response. Early translational work has established the potential for SPMs as vascular therapeutics, and as candidate biomarkers in vascular disease. Further investigations are needed to understand the molecular and cellular mechanisms of resolution in the vasculature, to improve tools for clinical measurement, and to better define the potential for "resolution therapeutics" in vascular patients.

A Rabbit Model for Testing Helper-Dependent Adenovirus-Mediated Gene Therapy for Vein Graft Atherosclerosis

Coronary artery bypass vein grafts are a mainstay of therapy for human atherosclerosis. Unfortunately, the long-term patency of vein grafts is limited by accelerated atherosclerosis. Gene therapy, directed at the vein graft wall, is a promising approach for preventing vein graft atherosclerosis. Because helper-dependent adenovirus (HDAd) efficiently transduces grafted veins and confers long-term transgene expression, HDAd is an excellent candidate for delivery of vein graft-targeted gene therapy. We developed a model of vein graft atherosclerosis in fat-fed rabbits and demonstrated long-term (≥20 weeks) persistence of HDAd genomes after graft transduction. This model enables quantitation of vein graft hemodynamics, wall structure, lipid accumulation, cellularity, vector persistence, and inflammatory markers on a single graft. Time-course experiments identified 12 weeks after transduction as an optimal time to measure efficacy of gene therapy on the critical variables of lipid and macrophage accumulation. We also used chow-fed rabbits to test whether HDAd infusion in vein grafts promotes intimal growth and inflammation. HDAd did not increase intimal growth, but had moderate-yet significant-pro-inflammatory effects. The vein graft atherosclerosis model will be useful for testing HDAd-mediated gene therapy; however, pro-inflammatory effects of HdAd remain a concern in developing HDAd as a therapy for vein graft disease.

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.

The expanding roles of Gβγ subunits in G protein-coupled receptor signaling and drug action

Gβγ subunits from heterotrimeric G proteins perform a vast array of functions in cells with respect to signaling, often independently as well as in concert with Gα subunits. However, the eponymous term "Gβγ" does not do justice to the fact that 5 Gβ and 12 Gγ isoforms have evolved in mammals to serve much broader roles beyond their canonical roles in cellular signaling. We explore the phylogenetic diversity of Gβγ subunits with a view toward understanding these expanded roles in different cellular organelles. We suggest that the particular content of distinct Gβγ subunits regulates cellular activity, and that the granularity of individual Gβ and Gγ action is only beginning to be understood. Given the therapeutic potential of targeting Gβγ action, this larger view serves as a prelude to more specific development of drugs aimed at individual isoforms.

Gαq G proteins modulate MMP-9 gelatinase during remodeling of the murine femoral artery

BACKGROUND

Vessels heal after injury and G protein-coupled receptors are involved in the vascular smooth muscle cell proliferation required to form intimal hyperplasia. We have previously identified the role of Gαq in vascular smooth muscle cell proliferation in vitro. This study now examines the role of Gαq in the developing intimal hyperplasia in a murine model and the impact of disruption of Gαq signaling on intimal hyperplasia development.

METHODS

We employed a murine femoral wire injury model in which a micro-wire is passed through a branch of the femoral artery and used to denude the common femoral artery. We perfusion-fixed specimens and stained sections with hematoxylin-eosin and Movat's stains such that morphometric analysis could be performed using an Image-Pro system. We also harvested additional specimens of femoral artery and snap-froze them for Western blotting or zymography, to allow for the study of G protein expression and both protease expression and activity. We used contralateral vessels as controls. We immersed additional vessels in pluronic gel containing the chemical Gαq G protein inhibitors GP-2A, siRNA to Gαq or adenovirus containing mutant inactive Gαq.

RESULTS

Gαq expression increased in a time-dependent manner after femoral artery injury. Sham-operated vessels did not produce such a response. Inhibition of Gαq reduced cell proliferation without affecting cell migration. Interruption of Gαq signaling also inhibited the development of intimal hyperplasia. Inhibition of Gαq did not alter peak urinary-type plasminogen activator activity and expression, but did increase early plasminogen activator inhibitor-1 activity and expression. Inhibition of Gαq reduced peak metalloproteinase (MMP)-9 activity at Day 3 but did not influence peak MMP-2 activity at Day 7. Protein expression for MMP-9 was also decreased, but that of MMP-2 was not affected. There were no changes in the expression or the activity of the respective inhibitors for MMP-9 and MMP-2, and tissue inhibitor of metalloproteinases-1 and -2.

CONCLUSIONS

These data demonstrate that femoral wire injury in the mouse is associated with a time-dependent increase in Gαq expression. Inhibition of Gαq alters cell proliferation and is associated with decreased MMP-9 expression and activity.

Role for Gβγ G-proteins in protease regulation during remodeling of the murine femoral artery

BACKGROUND

Intimal hyperplasia remains the principal lesion in the development of restenosis after vessel wall injury. G-protein coupled receptors are involved in smooth muscle cell proliferation but the role of Gβγ in arterial intimal hyperplasia has not been well defined. The aim of this study is to characterize the expression of Gβγ G-proteins in the developing intimal hyperplasia in a murine model and the impact of disruption of Gβγ signaling on intimal hyperplasia development.

METHODS

The murine femoral wire injury model was employed. Specimens were perfusion-fixed and sections were stained with H&E and Movat's stains such that morphometry could be performed using an Image-Pro system. Additional specimens of femoral artery were also harvested and snap frozen for Western blotting for the Gβγ expression and for Western blotting and zymography to allow for the study of gelatinase and plasminogen activator expression and activation. Contralateral vessels were used as controls. Additional vessels were immersed in pluronic gel containing an adenovirus with the Gβγ inhibitor βARK(CT).

RESULTS

The injured femoral arteries developed intimal hyperplasia, while sham vessels did not produce such a response. Cell proliferation peaked at 3-5 d and cell migration at 7 d after injury. There was a marked time-dependent increase in Gβγ over the 28 d following injury. Inhibition of Gβγ with βARK(CT) inhibited cell proliferation, cell migration and the development of intimal hyperplasia. Inhibition of Gβγ decreased peak uPA activity and expression without increasing early PAI-1 activity and expression. Inhibition of Gβγ reduced peak MMP-2 activity at d 1 but not at d 7 and also reduced peak MMP-9 activity at d 3. Protein expression for both MMP-2 and MMP-9 was also transiently decreased. There were no changes in TIMP-1 and TIMP-2 expression and activity.

CONCLUSIONS

These data demonstrate a time-dependent increase in Gβγ G-protein expression following wire injury in the mouse. Inhibition of Gβγ alters cell proliferation and migration with associated changes in MMP-2, MMP-9, and uPA expression and activity.

Gene transfer to coronary artery bypass conduits

BACKGROUND

Gene therapy is a rational approach to prevention of stenosis in saphenous vein grafts used as conduits for coronary artery bypass grafting. To explore this possibility we developed methods for adenoviral-mediated gene transfer to canine saphenous veins.

METHODS

During a single procedure, autogenous canine saphenous vein segments were transduced ex vivo and used as coronary artery bypass grafts. The proximal end of each vein was ligated, adenovirus containing the Escherichia coli beta-galactosidase gene (Ad.CMVLacZ) was delivered at titers of 2.5 x 10(9) or 5 x 10(9) plaque-forming units (pfu)/mL to the lumen through a distal heparin lock, and the segment was immersed in the viral solution for 1 hour at 37 degrees C. Control segments were exposed to diluent alone in an identical manner. Aortocoronary anastomoses were made using cardiopulmonary bypass. Transgene expression was assessed qualitatively and quantitatively after 3 days.

RESULTS

Beta-galactosidase levels showed a dose-dependent increase: 0.00 +/- 0.00 ng/mg total protein for controls; 5.60 +/- 2.27 ng/mg total protein for a viral titer of 2.5 x 10(9) pfu/mL and 11.97 +/- 6.14 ng/mg for 5 x 10(9) pfu/mL. The two dosage groups differed significantly from each other (p = 0.035) and from controls (p = 0.003). X-gal staining demonstrated mostly endothelial and scattered adventitial transgene expression.

CONCLUSIONS

Transgene expression after ex vivo gene transfer into saphenous vein grafts in a canine coronary artery bypass model indicates that this method may be useful for delivery of therapeutic genes to prevent or retard vein graft arteriosclerosis.

Overexpression of G protein-coupled receptor kinase-2 in smooth muscle cells reduces neointimal hyperplasia

The activation of vascular smooth muscle cells (SMCs) in neointimal hyperplasia involves signaling through receptor tyrosine kinases as well as G protein-coupled receptors. Overexpression of G protein-coupled receptor kinase-2 (GRK2) in SMCs can attenuate mitogenic signaling and proliferation in response to not only several G protein-coupled receptor agonists, but also platelet-derived growth factor (PDGF). To test whether overexpression of GRK2 could inhibit other SMC responses implicated in neointimal hyperplasia, we assessed SMC chemotaxis and mitogenic signaling evoked by PDGF and G(q)-coupled receptor agonists. To test the effects of GRK2 overexpression on neointimal hyperplasia in vivo, we employed a rabbit autologous vein graft model system. GRK2 overexpression reduced PDGF-promoted SMC chemotaxis by 85% (P<0.01), but had no effect on chemotaxis promoted by epidermal growth factor (EGF). Congruently, GRK2 overexpression reduced by approximately 50% (P<0.05) the [(3)H]thymidine incorporation induced by combinations of PDGF and Gq-coupled receptor agonists, but had no effect on that induced by PDGF plus EGF. PDGF-, but not EGF-promoted phosphoinositide 3-kinase activity in SMCs was also inhibited by GRK2 overexpression. In rabbit vein grafts, we achieved GRK2 overexpression in medial SMCs, reduced cell proliferation during the first week after graft implantation, and reduced steady state neointimal thickness by 29% (P<0.01), without affecting medial thickness or potentiating SMC apoptosis. Because of its ability to dampen chemotactic and mitogenic signaling through PDGF and Gq-coupled receptors, GRK2 overexpression in SMCs may be a useful therapeutic approach for neointimal hyperplasia.

Gene therapy for acute diseases

The use of gene transfer systems to study cell function makes it apparent that overexpression of a transgene can restore or improve the function of a protein and positively influence cell function in a predetermined manner for purposes of counterbalancing cellular pathophysiology. The ability of some gene transfer vehicles to produce transgene product within hours of delivery positions gene transfer as a unique pharmaceutical administration system that can quickly affect production of biologic response modifiers in a highly compartmentalized fashion. This approach can be expected to overcome many of the adverse effects and high costs of systemic delivery of recombinant pharmaceuticals. This review highlights recent advances toward development of gene therapies for acute illnesses with particular emphasis on preclinical models of disease. In this context, a growing body of data suggests that gene therapies for polygenic and non-genetic diseases such as asthma, cardiogenic and non-cardiogenic pulmonary edema, stroke, subarachnoid hemorrhage, seizures, acute myocardial infarction, endovascular thrombosis, and infections may someday be options for the treatment of patients.

G-protein expression and intimal hyperplasia after arterial injury: a role for Galpha(i) proteins

PURPOSE

Guanine nucleotide binding protein (G-protein) coupled receptors are involved in smooth muscle cell proliferation, but the role of G-proteins in arterial intimal hyperplasia has not been defined. This study examines the expression of G-proteins in the developing intimal hyperplasia after balloon injury of the rat carotid artery and specifically tests the hypothesis that the pertussis toxin sensitive G(i) G-protein subunit plays a role in the initiation of intimal hyperplasia.

METHODS

In vitro responses to serum stimulation (10% fetal bovine serum) were examined in the presence and absence of pertussis toxin (PTx). After a standard balloon injury in male Sprague-Dawley rats, the expression of G-protein subunits (alpha(o), alpha(i), alpha(q), alpha(s), and betagamma) was determined by means of Western blotting in the first 28 days. Thereafter, a second set of animals was allocated to control and PTx-treated (a Galpha(i) inhibitor; 500 ng/mL in an externally applied 30% pluronic gel) groups. Smooth muscle cell proliferation was estimated by means of thymidine analogue 5-bromo-2' deoxyuridine incorporation 2 days after injury, and vessel dimensions were determined by means of videomorphometry 14 days after injury.

RESULTS

There was inhibition of DNA synthesis and smooth muscle cell proliferation in response to serum with an IC(50) of 100 ng/mL. Three days after balloon injury, there was an increase in Galpha(i3) expression, which decreased at days 7, 14, and 28, compared with the uninjured carotid. Galpha(q) expression increased in a time-dependent manner. There was a marked time-dependent increase in Gbetagamma in the 28 days. Galpha(i2) and Galpha(s) isoforms (45 and 52 kDa) did not change significantly with time. There was no major change in Galpha(i1) and Galpha(o) in the study period. At 14 days, PTx treatment reduced intimal hyperplasia by 52% (63 +/- 4 microm vs. 30 +/- 5 microm, control vs. PTx; P <.001). Medial smooth muscle cell proliferation at day 2 was decreased in the PTx group, compared with that in the gel-coated group (15% +/- 2% and 26% +/- 3%; P = .02).

CONCLUSION

After balloon injury, there is a time-dependent increase in G-protein expression, which is subunit specific. Activation of PTx sensitive G-proteins (Galpha(i)) is involved during the initiation of intimal hyperplasia after arterial injury, and their inhibition results in a decrease in early medial cell proliferation. This acute interruption of G(i) signaling produces a long-term decrease in intimal hyperplasia.

Gene therapy for vein graft disease

Applying gene therapeutics to vein graft disease requires foundational knowledge of the underlying pathophysiology. This review details a brief description of vein graft disease, examines published and unpublished data on gene transfer to veins, and reviews the genes, which have significantly altered vascular biology.

Physiological induction of a beta-adrenergic receptor kinase inhibitor transgene preserves ss-adrenergic responsiveness in pressure-overload cardiac hypertrophy

BACKGROUND

Transgenic mice with constitutive myocardium-targeted expression of a peptide inhibitor of the ss-adrenergic receptor kinase (ssARKct) have increased in vivo cardiac function and enhanced ss-adrenergic receptor (ssAR) responsiveness.

METHODS AND RESULTS

In the present study, we created transgenic mice with myocardium-targeted ssARKct transgene expression under control of the CARP (cardiac ankyrin repeat protein) promoter, which is active during cardiac development and inactive in the normal adult mouse heart. Consistent with this, adult CARP-ssARKct transgenic mice have normal in vivo cardiac contractility and ssAR responsiveness indistinguishable from their nontransgenic littermates (NLCs). However, because CARP is in a group of fetal genes activated in the adult ventricle during hypertrophy, we subjected animals to transverse aortic constriction (TAC) to induce pressure overload. Seven days after TAC, CARP-ssARKct hearts had elevations in left ventricular mass similar to those in NLCs; however, TAC did induce demonstrable ssARKct expression in the transgenic hearts. TAC in NLC mice resulted in an upregulation of myocardial ssARK1 and a loss of ssAR-mediated inotropic reserve. Importantly, although ssARK1 was increased in the hypertrophic CARP-ssARKct mice, the in vivo loss of ssAR responsiveness was not seen after induced ssARKct expression.

CONCLUSIONS

These results demonstrate that acute ssARK1 inhibition can restore lost myocardial ssAR responsiveness and inotropic reserve in vivo. Furthermore, these mice demonstrate the novel utility of the CARP promoter as an inducible element responsive to pathophysiological conditions in the adult heart.

Overexpression of G protein-coupled receptor kinase-2 in smooth muscle cells attenuates mitogenic signaling via G protein-coupled and platelet-derived growth factor receptors

BACKGROUND

Neointimal hyperplasia involves activation of smooth muscle cells (SMCs) by several G protein-coupled receptor (GPCR) agonists, including endothelin-1, angiotensin II, thrombin, and thromboxane A(2). Signaling of many GPCRs is diminished by GPCR kinase-2 (GRK2). We therefore tested whether overexpression of GRK2 in SMCs could diminish mitogenic signaling elicited by agonists implicated in the pathogenesis of neointimal hyperplasia.

METHODS AND RESULTS

Overexpression of GRK2 was achieved in primary rabbit aortic SMCs with a recombinant adenovirus. Control SMCs were infected with an empty vector adenovirus. Inositol phosphate responses to endothelin-1, angiotensin II, thrombin agonist peptide, and platelet-derived growth factor (PDGF) were attenuated by 37% to 72% in GRK2-overexpressing cells (P<0.01), but the response to the thromboxane A(2) analogue U46619 was unaffected. GRK2 also inhibited SMC [(3)H]thymidine incorporation stimulated not only by these agonists (by 30% to 60%, P<0.01) but also by 10% FBS (by 35%, P<0. 05). However, GRK2 overexpression had no effect on epidermal growth factor-induced [(3)H]thymidine incorporation. Agonist-induced tyrosine phosphorylation of the PDGF-beta receptor, but not the epidermal growth factor receptor, was reduced in GRK2-overexpressing SMCs. GRK2 overexpression also reduced SMC proliferation in response to endothelin-1, PDGF, and 10% FBS by 62%, 51%, and 29%, respectively (P<0.01), without any effect on SMC apoptosis.

CONCLUSIONS

GRK2 overexpression diminishes SMC mitogenic signaling and proliferation stimulated by PDGF or agonists for several GPCRs. Gene transfer of GRK2 may therefore be therapeutically useful for neointimal hyperplasia.

Studying heterotrimeric G-protein-linked signal transduction using replication-deficient adenoviruses

Plasma membrane-spanning G-protein-linked receptors transduce approximately 60% of all extracellular stimuli in higher animals. Many G-protein-linked receptor pathways are yet to be elucidated, with the receptor, G-protein or effector system as yet unidentified. In addition, many fundamental issues pertaining to G-protein signalling remain unresolved, such as the factors governing the specificity of G-protein receptor coupling and the control of signal amplitude in response to G-protein activation. In order to address some of these issues, the use of replication-deficient adenoviruses as gene transfer vectors for investigations of G-protein signalling has been developed, facilitating dissection of G-protein-linked signal transduction pathways in an extensive range of cultured cells, as well as in vivo. The present review focuses on the versatility and utility of adenoviruses for the investigation of signalling by heterotrimeric G-proteins and explores some of the recent advances in adenoviral technology as they relate to the study of signal transduction.

Targets for gene therapy of vein grafts

Poor long-term patency and a lack of suitable systemic pharmacologic therapy for the prevention of vein graft failure have prompted the search for effective local gene therapy. Vein grafts are particularly well suited for gene transfer in the clinic because direct access to vein is available during surgical preparation for grafting. In this review, the available animal models are discussed and a new mouse model is highlighted. Recent advances in gene transfer technology are reviewed, including the use of adeno-associated virus and modified adenoviruses that can prolong in vivo transgene expression for months. Gene therapy is intended to reduce early thrombosis, reduce neointima formation, and prevent atherosclerosis in vein grafts. Promising antithrombotic targets include tissue plasminogen activator and thrombomodulin. Nitric oxide synthase, prostacyclin synthase, and tissue inhibitors of metalloproteinases have been used to reduce neointima formation, and vein graft atheroma remains a challenge for the future.