A systematic analysis of 40 random genes in cultured vascular smooth muscle subtypes reveals a heterogeneity of gene expression and identifies the tight junction gene zonula occludens 2 as a marker of epithelioid "pup" smooth muscle cells and a participant in carotid neointimal formation
Ld. Adams et al., A systematic analysis of 40 random genes in cultured vascular smooth muscle subtypes reveals a heterogeneity of gene expression and identifies the tight junction gene zonula occludens 2 as a marker of epithelioid "pup" smooth muscle cells and a participant in carotid neointimal formation, ART THROM V, 19(11), 1999, pp. 2600-2608
An accumulation of evidence suggests that vascular smooth muscle is compose
d of cell subpopulations with distinct patterns of gene expression. Much of
this evidence has come from serendipitous discoveries of genes marking phe
notypically distinct aortic cultures derived from 12-day-old and 3-month-ol
d rats. To identify more systematic differences, we isolated 40 genes at ra
ndom from libraries of these 2 cultures and examined message expression pat
terns. To determine consistency of differential expression, we measured mRN
A levels in 4 sets of cultures in 6 phenotypically distinct aortic cell. cl
ones and in balloon injured rat carotid arteries to determine the relevance
of these differences in vitro to in vivo biology. The following 5 consiste
ntly differentially expressed genes were identified in vitro: zonula occlud
ens 2 (ZO-2); peroxisome proliferator-activated receptor delta (PPAR delta)
; secreted protein, acidic and rich in cysteine (SPARC); alpha 1(I)collagen
; and A2, an uncharacterized gene. We examined these 5 clones during caroti
d artery injury and an inconsistently differentially expressed clone Krox-2
4 because, as an early response transcription factor, it could be involved
in the injury response. PPAR delta, A2, and Krox-24 mRNAs were upregulated
during the day after injury. ZO-2 and alpha 1(I)collagen messages were modu
lated for up to a month, whereas SPARC message showed no consistent change.
An analysis of ZO-2 and other tight junction genes indicates that tight ju
nctions may play a role in smooth muscle biology. These data suggest that a
systematic analysis of these libraries is likely to identify a very large
number of differentially expressed genes. ZO-2 is particularly intriguing b
oth because of this tight junction gene's pattern of prolonged over-express
ion after injury and because of its potential role in determining the disti
nctive epithelioid phenotype of smooth muscle cells identified in rat and o
ther species.