Approaches to enhance expression after adenovirus-mediated gene transfer to the carotid artery

Abstract

The goal of this study was to enhance transgene expression after adenoviral-mediated gene transfer to the carotid artery. We used an adenoviral vector with a transgene that expresses β-galactosidase, driven by the human cytomegalovirus (CMV) promoter/enhancer. The CMV promoter drives constitutive expression, and response elements within the enhancer allow inducible expression through binding of active transcription factors, such as cAMP response element binding protein (CREB) and nuclear factor kappa B (NFκB). Rings of rabbit carotid artery were incubated ex vivo with a replication-deficient adenovirus that expresses β-galactosidase (AdCMV-βgal). Virus was removed from the medium, and forskolin or phorbol-12-myristate-13-acetate (PMA), which can induce activation of CREB or NFκB, respectively, were added to the medium. Pyrrolidine dithiocarbamate (PDTC) was used to inhibit activation of NFκB. Following incubation for 24 hours, β-galactosidase activity was assessed by chemiluminescent reporter assay. Forskolin and PMA enhanced transgene expression in the carotid artery. Activity increased from 56 ± 13 mU/mg protein (mean ± SE) in rings of carotid treated with virus alone (109 pfu) to 159 ± 23 mU/mg protein (P < 0.05) in rings treated with forskolin, and to 189 ± 40 mU/mg protein (P < 0.05) in rings treated with PMA. Phorbol didecanoate, an inactive phorbol, did not affect expression of β-galactosidase. After pre-incubation with PDTC prior to PMA, expression of β-galactosidase was less than in rings incubated with PMA alone (29 ± 11, P < 0.05). Histochemical staining of carotid artery for β-galactosidase demonstrated enhanced endothelial expression following administration of PMA. These findings suggest that expression after gene transfer to the carotid artery using an adenoviral vector with the CMV promoter/enhancer may be enhanced by PMA and forskolin, perhaps by activation of transcription factors.