Optimizing vascular gene transfer of plasminogen activator inhibitor 1

Plasmid-mediated gene therapy for cardiovascular disease

Gene transfer within the cardiovascular system was first demonstrated in 1989 yet, despite extensive basic-science and clinical research, unequivocal benefit in the clinical setting remains to be demonstrated. Potential reasons for this include the fact that recombinant viral vectors, used in the majority of clinical studies, have inherent problems with immunogenicity that are difficult to circumvent. Attention has turned therefore to plasmid vectors, which possess many advantages over viruses in terms of safety and ease of use, and many clinical studies have now been performed using non-viral technology. This review will provide an overview of clinical trials for cardiovascular disease using plasmid vectors, recent developments in plasmid delivery and design, and potential directions for this modality of gene therapy.

Beta-adrenoceptor blockade markedly attenuates transgene expression from cytomegalovirus promoters within the cardiovascular system

OBJECTIVE

The major immediate-early cytomegalovirus enhancer/promoter (MIECMV), widely used in cardiovascular gene therapy, contains several positively regulatory cAMP response elements (CRE). Catecholamine signaling via beta-adrenoceptors might increase transgene expression from MIECMV, and if so, beta-blockers may have a detrimental effect on the efficacy of clinical cardiovascular gene therapy strategies.

METHODS AND RESULTS

Cultured smooth muscle cells were exposed to isoprenaline, atenolol, or propranolol, alone and in combination before infection with adenoviruses expressing beta-galactosidase. beta-galactosidase expression was assayed 72 hours later. Isoprenaline increased transgene expression from MIECMV up to 8-fold (P<0.001), but had no effect on a promoter containing no CRE. The effect of isoprenaline was inhibited by beta-blockade and by specific CRE-decoy oligonucleotides. Beta-blockers did not reduce transgene expression below basal levels. After adenovirus-mediated porcine intracoronary gene transfer, however, beta-blockade reduced beta-galactosidase expression by up to 250-fold compared with non-beta-blocked animals (P<0.01).

CONCLUSIONS

Enhancement of promoter activity by endogenous catecholamines is essential for high-level transgene expression from MIECMV within the vasculature. Beta-blocker-mediated suppression of transgene expression from MIECMV in vascular tissues has a significant bearing on clinical studies of cardiovascular gene transfer. This is the first described interaction to our knowledge between widely prescribed pharmaceuticals and a commonly used promoter of clinical transgene expression.

Comparison of promoter region constructs for in vivo intramuscular expression

BACKGROUND

High transgene expression is generally expected after gene transfer. However, different level, kinetics and localization of expression might be needed for relevant therapeutic applications. Former studies have compared various promoter regions driving gene expression leading to conflicting results. In the present work, two promoter families have been compared using the efficient in vivo intramuscular electrotransfer technique.

METHODS

Three promoter regions were constructed by associating the strong ubiquitous cytomegalovirus (CMV) enhancer-promoter to its homologous intron A or to a heterologous intron, or to a hybrid intron. Promoter regions derived from the muscle creatine kinase (MCK) promoter were also studied. The expression of the same transgene (SeAP or neurotrophin-3) under control of these different promoters was compared after plasmid electrotransfer in mouse tibialis-cranialis skeletal muscle.

RESULTS

Heterologous intron association to the CMV promoter did not modify gene expression kinetics nor increase gene expression level. Usefulness of intron A or hybrid intron association to the CMV promoter depended on the gene. The various MCK promoters drove efficient gene expression but lower than that obtained with the CMV promoter. Furthermore, peak value was reached earlier with MCK promoter regions (14 days).

CONCLUSION

For applications of gene transfer restricted to skeletal muscle, the MCK promoter or a MCK promoter variant would be a promising alternative to the CMV promoter. Indeed, it has been demonstrated that the use of MCK promoter limits humoral and cell-mediated immune responses. Furthermore, the MCK promoter decreases the initial expression peak that may be detrimental, drives a sustained gene expression, and improves gene transfer safety.

Identification of intracellular pathways through which TGF-beta1 upregulates PAI-1 expression in endothelial cells

Upregulation of plasminogen activator inhibitor type 1 (PAI-1) expression is a critical mechanism through which transforming growth factor-beta1 (TGF-beta1) accelerates intimal growth. The aim of this study was to identify signaling pathways through which TGF-beta1 upregulates PAI-1 expression in endothelial cells (EC) and test interventions for blocking these pathways. We transduced cultured bovine EC with an adenoviral vector containing the PAI-1 promoter fused to a beta-galactosidase reporter gene. We used these cells, along with vectors expressing potential modifiers of TGF-beta1 signaling and pharmacologic antagonists of mitogen-activated protein kinase (MAPK) pathways to identify key mediators of basal and TGF-beta1-regulated PAI-1 expression. Basal activity of the PAI-1 promoter was directly correlated with Ras activation and was blocked by a dominant negative (DN) type I TGF-beta receptor. TGF-beta1-stimulated activity of the PAI-1 promoter did not require Ras activation, and was lessened or eliminated by expression of either DN type I or type II TGF-beta receptors and by inhibition of either of two MAPKs: MEK and p38. Our results suggest unanticipated pathways of TGF-beta1 signaling in EC and point to new strategies to limit TGF-beta1-induced vascular disease.

Downregulated Expression of Plasminogen Activator Inhibitor-1 Augments Myocardial Neovascularization and Reduces Cardiomyocyte Apoptosis After Acute Myocardial Infarction

OBJECTIVES

The aim of this study was to examine whether selective plasminogen activator inhibitor type 1 (PAI-1) downregulation in the acutely ischemic heart increases the myocardial microvasculature and improves cardiomyocyte (CM) survival.

BACKGROUND

Endogenous myocardial neovascularization is an important process enabling cardiac functional recovery after acute myocardial infarction. Expression of PAI-1, a potent inhibitor of angiogenesis, is induced in ischemic heart tissue.

METHODS

A sequence-specific catalytic deoxyribonucleic acid (DNA) enzyme was used to reduce PAI-1 levels in cultured endothelial cells and in ischemic myocardium. At the time of coronary artery ligation, rats were randomized into three groups, each receiving an intramyocardial injection (IMI) of a single dose at three different sites of the peri-infarct region consisting, respectively, of DNA enzyme E2 targeting rat PAI-1 (E2), scrambled control DNA enzyme (E0), or saline. Cardiomyocyte apoptosis, capillary density, and echocardiography were studied two weeks following infarction.

RESULTS

The E2 DNA enzyme, which efficiently inhibited rat PAI-1 expression in vitro, induced prolonged suppression (>2 weeks) of PAI-1 messenger ribonucleic acid and protein in rat heart tissues after a single IMI. At two weeks, hearts from experimental rats had over five-fold greater capillary density, 70% reduction in apoptotic CMs, and four-fold greater functional recovery compared with controls.

CONCLUSIONS

These results imply a causal relationship between elevated PAI-1 levels in ischemic hearts and adverse outcomes, and they suggest that strategies to reduce cardiac PAI-1 activity may augment neovascularization and improve functional recovery.

Down-regulation of plasminogen activator inhibitor 1 expression promotes myocardial neovascularization by bone marrow progenitors

Human adult bone marrow–derived endothelial progenitors, or angioblasts, induce neovascularization of infarcted myocardium via mechanisms involving both cell surface urokinase-type plasminogen activator, and interactions between β integrins and tissue vitronectin. Because each of these processes is regulated by plasminogen activator inhibitor (PAI)-1, we selectively down-regulated PAI-1 mRNA in the adult heart to examine the effects on postinfarct neovascularization and myocardial function. Sequence-specific catalytic DNA enzymes inhibited rat PAI-1 mRNA and protein expression in peri-infarct endothelium within 48 h of administration, and maintained down-regulation for at least 2 wk. PAI-1 inhibition enhanced vitronectin-dependent transendothelial migration of human bone marrow–derived CD34⁺ cells, and resulted in a striking augmentation of angioblast-dependent neovascularization. Development of large, thin-walled vessels at the peri-infarct region was accompanied by induction of proliferation and regeneration of endogenous cardiomyocytes and functional cardiac recovery. These results identify a causal relationship between elevated PAI-1 levels and poor outcome in patients with myocardial infarction through mechanisms that directly inhibit bone marrow–dependent neovascularization. Strategies that reduce myocardial PAI-1 expression appear capable of enhancing cardiac neovascularization, regeneration, and functional recovery after ischemic insult.

Improved vascular gene transfer with a helper-dependent adenoviral vector

BACKGROUND

Adenoviral vectors are the most widely used agents for vascular gene transfer. However, the utility of adenoviral vectors for vascular gene transfer is limited by brevity of expression and by the induction of a significant host inflammatory response. Third-generation or "helper-dependent" adenoviral vectors have achieved prolonged recombinant gene expression in liver and muscle with minimal associated inflammation; however, they have never been tested for vascular gene transfer.

METHODS AND RESULTS

We constructed a helper-dependent adenoviral vector expressing rabbit urokinase plasminogen activator (HD-AduPA). HD-AduPA was compared, in a rabbit model of carotid gene transfer, with a first-generation adenovirus, also expressing rabbit uPA (FG-AduPA). uPA expression and vector DNA were measured in arteries harvested from 3 to 56 days after gene transfer. Vector-specific mRNA, vascular inflammation, and neointimal formation were assessed 14 days after gene transfer. uPA expression was lost, and vector DNA declined rapidly in arteries infused with FG-AduPA. In contrast, uPA expression and vector DNA persisted in HD-AduPA arteries for > or =56 days, with stable expression from 14 to 56 days. Increased uPA expression in HD-AduPA arteries was accompanied by high levels of vector-specific uPA mRNA. Moreover, HD-AduPA arteries had significantly less inflammation and neointimal formation than FG-AduPA arteries.

CONCLUSIONS

Helper-dependent adenoviral vectors can stably express a therapeutic gene in the vascular wall for > or =8 weeks, with minimal associated inflammation. Helper-dependent adenoviral vectors will be useful agents for vascular gene transfer and gene therapy.

A novel combination of promoter and enhancers increases transgene expression in vascular smooth muscle cells in vitro and coronary arteries in vivo after adenovirus-mediated gene transfer

Recombinant adenoviruses are employed widely for vascular gene transfer. Vascular smooth muscle cells (SMCs) are a relatively poor target for transgene expression after adenovirus-mediated gene delivery, however, even when expression is regulated by powerful, constitutive viral promoters. The major immediate-early murine cytomegalovirus enhancer/promoter (MIEmCMV) elicits substantially greater transgene expression than the human cytomegalovirus promoter (MIEhCMV) in all cell types in which they have been compared. The Woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) increases transgene expression in numerous cell lines, and fragments of the smooth muscle myosin heavy chain (SMMHC) promoter increase expression within SMC from heterologous promoters. We therefore, compared the expression of beta-galactosidase after adenovirus-mediated gene transfer of lacZ under the transcriptional regulation of a variety of combinations of the promoters and enhancers described, in vitro and in porcine coronary arteries. We demonstrate that inclusion of WPRE and a fragment of the rabbit SMMHC promoter along with MIEmCMV increases beta-galactosidase expression 90-fold in SMC in vitro and approximately 40-fold in coronary arteries, compared with vectors in which expression is regulated by MIEhCMV alone. Expression cassette modification represents a simple method of improving adenovirus-mediated vascular gene transfer efficiency and has important implications for the development of efficient cardiovascular gene therapy strategies.

Highly suppressible expression of single-chain interleukin-12 by doxycycline following adenoviral infection with a single-vector Tet-regulatory system

BACKGROUND

Adenoviral vectors have been shown to efficiently transfer DNA into a wide variety of eukaryotic cells in vitro and in vivo. However, the therapeutic benefit of this approach is limited by severe side effects as a result of uncontrolled transgene expression.

METHODS

A bi-directional promoter that controls the desired transgene as well as a tetracycline-suppressible transactivator (tTA) was cloned into the E1-region of E1-deleted recombinant adenoviral vectors. Autoregulation within this construct was obtained by tTA expression under control of the operator, to which tTA binds in the absence of tetracycline. Consequently, binding of tetracycline to tTA results in downregulation of tTA as well as the co-expressed transgene in the infected cell.

RESULTS

We were able to suppress luciferase-reporter gene expression by up to 16 000-fold in the presence of doxycycline (dox, 2 micro g/ml). Under control of this tetracycline-regulated system, single-chain interleukin-12 (scIL12) was expressed. Adenovirally mediated expression of this potentially lethal cytokine with strong activation of antitumoral immune response was downregulated by up to 6000-fold in the presence of dox. Subsequently, this downregulation also resulted in a highly significant reduction of interferon-gamma secretion by stimulated splenocytes. These mainly contribute to the toxicity of this immunotherapeutic approach.

CONCLUSIONS

With expression levels exceeding those of the cytomegalovirus (CMV) promoter in almost all cell lines tested, these new vectors will also contribute to the safety of adenoviral approaches by controlled expression without compromising on maximum expression levels.

Gene transfer of the urokinase-type plasminogen activator receptor-targeted matrix metalloproteinase inhibitor TIMP-1.ATF suppresses neointima formation more efficiently than tissue inhibitor of metalloproteinase-1

Proteases of the plasminogen activator (PA) and matrix metalloproteinase (MMP) system play an important role in smooth muscle cell (SMC) migration and neointima formation after vascular injury. Inhibition of either PAs or MMPs has previously been shown to result in decreased neointima formation in vivo. To inhibit both protease systems simultaneously, a novel hybrid protein, TIMP-1.ATF, was constructed consisting of the tissue inhibitor of metalloproteinase-1 (TIMP-1) domain, as MMP inhibitor, linked to the receptor-binding amino terminal fragment (ATF) of urokinase. By binding to the u-PA receptor this protein will not only anchor the TIMP-1 moiety directly to the cell surface, it will also prevent the local activation of plasminogen by blocking the binding of urokinase-type plasminogen activator (u-PA) to its receptor. Adenoviral expression of TIMP-1.ATF was used to inhibit SMC migration and neointima formation in human saphenous vein segments in vitro. SMC migration was inhibited by 65% in Ad.TIMP-1.ATF-infected cells. Infection with adenoviral vectors encoding the individual domains, Ad.TIMP-1 and Ad.ATF, reduced migration by 32% and 52%, respectively. Neointima formation in saphenous vein organ cultures infected with Ad.TIMP-1.ATF was inhibited by 72% compared with 42% reduction after Ad.TIMP-1 infection and 34% after Ad.ATF infection. These data show that binding of TIMP-1.ATF hybrid protein to the u-PA receptor at the cell surface strongly enhances the inhibitory effect of TIMP-1 on neointima formation in human saphenous vein cultures.

Increased expression of urokinase during atherosclerotic lesion development causes arterial constriction and lumen loss, and accelerates lesion growth

Overexpression of urokinase plasminogen activator (uPA) in endothelial cells can decrease intravascular thrombosis. However, expression of uPA is increased in atherosclerotic human arteries, which suggests that uPA might accelerate atherogenesis. To investigate whether elevated uPA expression accelerates atherogenesis, we cloned a rabbit uPA cDNA and expressed it in carotid arteries of cholesterol-fed rabbits. uPA gene transfer increased artery-wall uPA activity for at least 1 week, with a return to baseline by 2 weeks. One week after gene transfer, uPA-transduced arteries were constricted, with significantly smaller lumens and thicker walls, but no difference in intimal or medial mass. Two weeks after gene transfer, uPA- and control-transduced arteries were morphologically indistinguishable. By 4 weeks, however, uPA-transduced arteries had 70% larger intimas than control-transduced arteries (P < 0.01) and smaller lumens (P < 0.05). Intimal lesions appeared to be of similar composition in uPA- and control-transduced arteries, except that degradation of elastic laminae was evident in uPA-transduced arteries. These data suggest that elevated uPA expression in atherosclerotic arteries contributes to intimal growth and constrictive remodeling leading to lumen loss. Antagonists of uPA activity might, therefore, be useful in limiting intimal growth and preventing constrictive remodeling. Overexpression of uPA in endothelial cells to prevent intravascular thrombosis must be reconsidered, because this intervention could worsen underlying vascular disease.

Plasminogen activator inhibitor type 1 increases neointima formation in balloon-injured rat carotid arteries

BACKGROUND

Elevated plasma levels of plasminogen activator inhibitor type 1 (PAI-1) are associated with myocardial infarction, atherosclerosis, and restenosis. PAI-1 is increased in atherosclerotic arteries and failed vein grafts. No experimental data, however, support a causal relationship between elevated PAI-1 expression and vascular lesions. Paradoxically, data generated in PAI-1 knockout mice suggest that PAI-1 might decrease lesion formation after arterial injury and that PAI-1 gene transfer might prevent restenosis.

METHODS AND RESULTS

Using the rat carotid balloon injury model and a PAI-1-expressing adenoviral vector, we tested whether elevated arterial PAI-1 expression would alter neointima formation. Compared with control-transduced arteries, neointima formation in PAI-1-transduced arteries was initially retarded. By 14 days, however, the intimas of PAI-1-transduced arteries were significantly larger than intimas of control-transduced arteries (1.6+/-0.1x10(5) versus 1.2+/-0.1x10(5) micrometer(2), n=18 to 19, P<0.03). PAI-1 expression in individual arteries correlated with increased cell proliferation at 4 and 8 days after injury (R=0.6, P<0.02 and P<0.006). PAI-1 expression also correlated with fibrin(ogen) accumulation (R=0.77, P<0.001), and fibrin(ogen) accumulation correlated strongly with proliferation (R=0.86, P<0.00001).

CONCLUSIONS

Increased expression of PAI-1 in the artery wall promotes neointima growth after balloon injury. Therefore, despite encouraging data generated in other animal models, PAI-1 is not a promising agent for gene therapy to prevent restenosis. Moreover, our data associate elevated PAI-1 expression with fibrin(ogen) accumulation and increased cell proliferation. These data suggest a mechanism to explain the association between elevated PAI-1 expression and the progression of arterial disease.

Differential influence of the E4 adenoviral genes on viral and cellular promoters

BACKGROUND

Strong and stable transgene expression is fundamental to the success of recombinant adenovirus vectors in human gene therapy. However, control of transgene expression is a complex process, involving both viral and cellular factors. In this study, the influence of the E4 adenoviral region on the activity of various promoters was investigated in vitro and in vivo.

METHODS

Pairs of isogenic E1o and E1oE4o vectors were generated and compared. Levels of transgene expression were determined by Northern blot, ELISA and FACS analysis. Initiation of transcription was studied by nuclear run-on assays.

RESULTS

Similar to the viral CMV and RSV promoters, the activity of the ubiquitous cellular PGK promoter required the presence of the E4 genes in vitro and in vivo. In contrast, transgene expression from selected liver- and tumor-specific promoters did not require E4 functions.

CONCLUSION

Together with the reported low liver toxicity of E1oE4o vectors, the independence of E4 of liver-specific promoters renders such vectors interesting alternatives to the use of gutless vectors.

Splicing is required for rapid and efficient mRNA export in metazoans

Pre-mRNA splicing is among the last known nuclear events before export of mature mRNA to the cytoplasm. At present, it is not known whether splicing and mRNA export are biochemically coupled processes. In this study, we have injected pre-mRNAs containing a single intron or the same mRNAs lacking an intron (Deltai-mRNAs) into Xenopus oocyte nuclei. We find that the spliced mRNAs are exported much more rapidly and efficiently than the identical Deltai-mRNAs. Moreover, competition studies using excess Deltai-mRNA indicate that different factor(s) are involved in the inefficient export of Deltai-mRNA vs. the efficient export of spliced mRNA. Consistent with this conclusion, spliced mRNA and Deltai-mRNA, though identical in sequence, are assembled into different messenger ribonucleoprotein particles (mRNP) in vitro. Strikingly, the mRNA in the spliced mRNP, but not in the Deltai-mRNP, is exported rapidly and efficiently. We conclude that splicing generates a specific nucleoprotein complex that targets mRNA for export. Our results, revealing a link between splicing and efficient mRNA export, may explain the reports that an intron is required for efficient expression of many protein-coding genes in metazoans.