The vessel wall fibrinolytic system plays an important role in maintaining
the arterial phenotype and in regulating the arterial response to injury. P
lasminogen activator inhibitor type 1 (PAI-1) regulates tissue fibrinolysis
and is expressed in arterial tissue; however, its biological role remains
uncertain. To help elucidate the role of PAI-1 in the artery wall, and to b
egin to clarify whether manipulation of vascular PAI-1 expression might be
a target for gene therapy, we used adenoviral vectors to increase expressio
n of rat PAI-1 in rat carotid arteries. Infusion of an adenoviral vector in
which PAI-1 expression was driven by a promoter derived from the Rous sarc
oma virus (RSV) did not increase PAI-1 expression above endogenous levels.
To improve PAI-1 expression, we modified the vector by (1) truncating the 3
' untranslated region of PAI-1 to increase the mRNA half-life, (2) substitu
ting the SR alpha or the cytomegalovirus (CMV) promoter for the RSV promote
r, (3) including an intron in the expression cassette, and (4) altering the
direction of transcription of the transgene cassette. The optimal expressi
on vector, revealed by in vitro studies, contained the CMV promoter, an int
ron, and a truncated PAI-1 mRNA, This vector increased PAI-1 expression by
30-fold over control levels in vitro and by 1.6- to 2-fold over endogenous
levels in vivo, This vector will be useful for elucidating the role of PAI-
1 in arterial pathobiology, Because genes that are important in maintaining
the vascular phenotype are likely to be expressed in the vasculature, the
technical issues of how to increase in vivo expression of endogenous genes
are highly relevant to the development of genetic therapies for vascular di
sease.