Developmental regulation of perlecan gene expression in aortic smooth muscle cells

Heparan sulfate proteoglycans (HSPGs) are believed to act as potent endogenous regulators of vascular smooth muscle cell (SMC) replication, migration, gene expression and differentiation. Here we describe the pattern of expression of perlecan, the predominant basement membrane HSPG, 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 switch in SMC replication rate and growth phenotype. Expression of perlecan message and protein was high throughout fetal and early neonatal life, and it remained readily detectable in the adult aorta. Using a double-labeling technique (in situ hybridization for perlecan message coupled with bromodeoxyuridine immunohistochemistry), we determined the relationship between DNA synthesis and perlecan mRNA expression in individual SMC at days e17-e21; we found that perlecan gene expression was largely limited to non-replicating cells. Consistent with the in vivo data, perlecan mRNA was undetectable in cultured e17 SMC by Northern or RT-PCR analysis, while in cultured adult SMC, perlecan mRNA was significantly higher in non-replicating (serum-starved) cultures compared to replicating cultures. Treatment of growth-arrested adult SMC cultures with heparin caused a further accumulation in perlecan mRNA levels. The data suggest that the expression of perlecan by vascular SMC is regulated by apparent developmental age as well as by cellular growth state. The developmentally times expression of perlecan in the aortic wall may contribute to the establishment and/or maintenance of vascular SMC differentiation and quiescence.