PRODUCTION OF ACTIVIN-A AND FOLLISTATIN IN CULTURED RAT VASCULAR SMOOTH-MUSCLE CELLS

Activin A, a member of the transforming growth factor beta supergene f amily, modulates DNA synthesis in cultured rat vascular smooth muscle cells (VSMC) (Kopma et al. (1993) Exp. Cell. Res. 206, 152-156). In th e present study, we studied the production of activin A and follistati n in VSMC. When VSMCs cultured in a 24-well plate were cultured with 1 0% fetal calf serum (FCS) for 24 h, 0.94 +/- 0.20 pmol/well (mean +/- SE, n = 6) of bioactive activin was released into the culture media. R everse-transcription polymerase chain-reaction revealed the expression of mRNA for the beta(A) subunit of inhibin but not for either the bet a(B) or alpha subunit. Bioactivity of activin was increased in quiesce nt cells treated with FCS or platelet-derived growth factor (PDGF) but not with angiotensin II (Ang II) or insulin-like growth factor-I (IGF -I). Ang II or IGF-I did not stimulate DNA synthesis by itself but, wh en these two agents were combined, they increased nuclear labeling by 16.4% and release of bioactive activin by 170% of basal. The dose-resp onse relationship and time course study indicated that PDGF-mediated r elease of activin correlated with initiation of DNA synthesis. Steady state expression of mRNA for the beta(A) subunit was markedly elevated 12 h after the addition of PDGF and was reduced thereafter. To assess the significance of autocrine activin, the effect of PDGF was determi ned in the presence and absence of excess of exogenous follistatin. Th e PDGF-mediated DNA synthesis was enhanced by the addition of excess f ollistatin. In addition to the production of activin, PDGF also enhanc ed release of follistatin from VSMC. These results indicate that VSMC synthesize and release both activin and follistatin and that the activ in-follistatin system may modulate DNA synthesis in VSMC.