Perlecan mediates the antiproliferative effect of apolipoprotein E on smooth muscle cells - An underlying mechanism for the modulation of smooth muscle cell growth?

Apolipoprotein E (apoE) is known to inhibit cell proliferation; however, th e mechanism of this inhibition is not clear. We recently showed that apoE s timulates endothelial production of heparan sulfate (I-IS) enriched in hepa rin-like sequences. Because heparin and HS are potent inhibitors of smooth muscle cell (SMC) proliferation, in this study we determined apoE effects o n SMC HS production and cell growth. In confluent SMCs, apoE (10 mu g/ml) i ncreased (SO4)-S-35 incorporation into PG in media by 25-30%. The increase in the medium was exclusively due to an increase in HSPGs (2.2-fold), and a poE did not alter chondroitin and dermatan sulfate proteoglycans. In prolif erating SMCs, apoE inhibited [H-3]thymidine incorporation into DNA by 50%; however, despite decreasing cell number, apoE increased the ratio of (SO4)- S-35 to [H-3]thymidine from 2 to 3.6, suggesting increased HS per cell. Pur ified HSPGs from apoE-stimulated cells inhibited cell proliferation in the absence of apoE, ApoE did not inhibit proliferation of endothelial cells, w hich are resistant to heparin inhibition. Analysis of the conditioned mediu m from apoE stimulated cells revealed that the HSPG increase was in perleca n and that apoE also stimulated perlecan mRNA expression by >2-fold. The ab ility of apoE isoforms to inhibit cell proliferation correlated with their ability to stimulate perlecan expression. An anti-perlecan antibody complet ely abrogated the antiproliferative effect of apoE. Thus, these data show t hat perlecan is a potent inhibitor of SMC proliferation and is required to mediate the antiproliferative effect of apoE. Because other growth modulato rs also regulate perlecan expression, this may be a key pathway in the regu lation of SMC growth.