, a Novel Gene Preferentially Expressed in Aortic Smooth Muscle Cells, Is Down-regulated by Vascular Injury

Abstract

Despite the importance of phenotypic alterations in arterial smooth muscle cells (ASMC) during the pathogenesis of arteriosclerosis, little is known about genes that define differentiated ASMC. Using differential mRNA display, we isolated a novel gene preferentially expressed in the rat aorta and termed this gene APEG-1. The cDNA of rat APEG-1 contained an open reading frame encoding 113 amino acids, which would predict a basic protein of 12.7 kDa. The amino acid sequence of rat APEG-1 was highly conserved among human and mouse homologues (97 and 98%, respectively). Using an APEG-1 fusion protein containing an N-terminal c-Myc tag, we identified APEG-1 as a nuclear protein. By in situ hybridization, APEG-1 mRNA was expressed in rat ASMC. Although APEG-1 was expressed highly in differentiated ASMC in vivo, its expression was quickly down-regulated and disappeared in dedifferentiated ASMC in culture. In vivo, APEG-1 mRNA levels decreased by more than 80% in response to vascular injury as ASMC changed from a quiescent to a proliferative phenotype. Taken together, these data indicate that APEG-1 is a novel marker for differentiated ASMC and may have a role in regulating growth and differentiation of this cell type. Arterial smooth muscle cells (ASMC)1 constitute the major portion of the blood vessel wall, and their main function is to regulate vascular tone. By controlling vascular tone, ASMC have an important role in regulating blood pressure. Fully differentiated ASMC in normal vessel walls proliferate at an extremely low rate and express unique contractile proteins, ion channels, and signaling molecules required for their contractile function (1). In contrast to skeletal and cardiac muscle cells (2, 3), ASMC are not terminally differentiated in adult animals. In response to vascular injuries caused by smoking, hypercholesterolemia, hyperhomocystenemia, hypertension, or trauma (such as balloon angioplasty), ASMC dedifferentiate and change from a quiescent and contractile phenotype to a proliferative and synthetic phenotype (1, 4 -9). This proliferation of vascular smooth muscle cells is one of the most prominent features of arteriosclerosis, the leading cause of death in developed countries (4). Similar alterations in ASMC phenotypes occur during angiogenesis in solid tumors and may have an important role in determining the growth rate of these tumors (10 -12). Despite the importance of alteration of ASMC phenotypes in vascular diseases, little is known about molecular mechanisms regulating differentiation of this cell type (1). This is due, at least in part, to a lack of differentiation markers of ASMC.Several genes encoding proteins specific to smooth muscle cells, including smooth muscle ␣-actin, calponin, SM-22, and caldesmon, have been used as markers for differentiated smooth muscle cells (13-18). However, their expression is not limited to vascular smooth muscle cells. Recently, a homeobox gene gax has been shown to be highly expressed in vascular smooth muscle cells and may regulate their proliferation (19...

A Comparison of Aorta and Vena Cava Medial Message Expression by cDNA Array Analysis Identifies a Set of 68 Consistently Differentially Expressed Genes, All in Aortic Media

“…APEG-1 has been shown in rats to be differentially expressed between aorta and vena cava and downregulated after carotid balloon injury. 16 NMMHC-B, also called SMemb, has been previously reported to be differentially expressed in vivo in vascular smooth muscle, in human normal intima and intima of coronary arteries after angioplasty, 17 and in 2 rabbit models of intima formation. 18 Vimentin has been shown to be expressed in balloon-injured rat carotid neointima, whereas another intermediate filament, desmin, disappears 19 and is expressed in "synthetic" smooth muscle cells in culture.…”

“…previously identified with the aorta, aortic preferentially expressed gene 1 (APEG-1) 10 and elastin. 11,12 It is important to stress that we have examined 5 individual animals to produce this data set, eliminating false-positive results due to animal variation in elevations of gene expression or random measurement error.…”

Impaired Abdominal Wall Development and Deficient Wound Healing in Mice Lacking Aortic Carboxypeptidase-Like Protein

“…Immunofluorescence staining of MASMC was performed with cells grown on glass coverslips as described previously (8). MASMC were also stained by an immunocytochemical technique with a biotinylated secondary antibody and a peroxidase 3Ј, 3-diaminobenzidine (DAB) kit (Vector Laboratories, Burlingame, Calif.).…”

Upstream Stimulatory Factors (USF-1/USF-2) Regulate Human cGMP-dependent Protein Kinase I Gene Expression in Vascular Smooth Muscle Cells

“…In contrast, the APEG-1 promoter was reported to be differentially regulated by USF-1 and USF-2 proteins acting as activators and suppressors, respectively (34). One similarity between the human PKG-I and the SMC-specific genes described here lies in the fact that vascular injury induces a decrease in both PKG-I expression and the expression of these SMC-specific gene products (39,40). Whether USF proteins are involved in PKG-I down-regulation in vascular injury is not known.…”