DEVELOPMENTAL REGULATION OF PERLECAN GENE-EXPRESSION IN AORTIC SMOOTH-MUSCLE CELLS

Heparan sulfate proteoglycans (HSPGs) are believed to act as potent en dogenous regulators of vascular smooth muscle cell (SMC) replication, migration, gene expression and differentiation. Here we describe the p attern of expression of perlecan, the predominant basement membrane HS PG, during aortic development in the rat. Expression of perlecan mRNA and protein in the aortic SMC was first significantly observed at day e19 (day 19 of embryonic development), a time which marks a dramatic s witch in SMC replication rate and growth phenotype. Expression of perl ecan message and protein was high throughout fetal and early neonatal life, and it remained readily detectable in the adult aorta. Using a d ouble-labeling technique (in situ hybridization for perlecan message c oupled with bromodeoxyuridine immunohistochemistry), we determined the relationship between DNA. synthesis and perlecan mRNA expression in i ndividual SMC at days e17-e21; we found that perlecan gene expression was largely limited to non-replicating cells. Consistent with the in v ivo data, perlecan mRNA was undetectable in cultured e17 SMC by Northe rn or RT-PCR analysis, while in cultured adult SMC, perlecan mRNA was significantly higher in non-replicating (serum-starved) cultures compa red to replicating cultures. Treatment of growth-arrested adult SMC cu ltures with heparin caused a further accumulation in perlecan mRNA lev els. The data suggest that the expression of perlecan by vascular SMC is regulated by apparent developmental age as well as by cellular grow th state. The developmentally times expression of perlecan in the aort ic wall may contribute to the establishment and/or maintenance of vasc ular SMC differentiation and quiescence.