RECEPTOR INDUCTION REGULATES THE SYNERGISTIC EFFECTS OF SUBSTANCE-P WITH IL-1 AND PLATELET-DERIVED GROWTH-FACTOR ON THE PROLIFERATION OF BONE-MARROW FIBROBLASTS

The neuropeptide substance P (SP) stimulates CFU in bone marrow (BM) c ultures. Although the methylcellulose matrix used in these assays does not provide an appropriate substratum to support adherent-dependent c ells, we have observed that cultures containing optimal SP (10(-8)-10( -10) M) develop confluent areas of reticular/fibroblastoid-like cells with CFUs predominantly localized within their vicinity. Characterizat ion (cytochemical and immunofluorescence) of the reticular/fibroblasto id-like cells indicated that they were fibroblasts, the major constitu ent of the BM stroma. Hemopoietic effects by SP are mediated by the st roma that expresses SP receptors. We studied the effects of SP (10(-7) -10(-11) M) with suboptimal platelet-derived growth factor-BB (PDGF-BB ; 5 ng/ml) and IL-1 alpha (2 ng/ml), two fibrogenic cytokines, and als o hemopoietic regulators. SP by itself and in synergy with either cyto kine induced fibroblast proliferation. At optimum SP, IL-1 alpha induc ed 1.6 times the proliferation of PDGF-BB (87 +/- 7 vs 55 +/- 5; n = 1 2; p < 0.05), The effects of SP were blunted by a specific neurokinin- 1 antagonist. Scatchard analysis indicated that SP binds to BM fibrobl asts with an approximate K-d of 5 nM. SP induced steady state mRNA for IL-1 receptor IL-1R1 and PDGF-BB (PDGF-AR, PDGF-BR) receptors by 7.5- , 6.2-, and 10.5-fold, respectively. Their up-regulation may be partly responsible for the synergistic effects of SP and their ligands. Indu ction (3-fold) of neurokinin-1 mRNA by IL-1 alpha compared with no ind uction by PDGF-BB may explain the preferred synergism between SP and I L-1 alpha. This study indicates that induction of SP, IL-1 alpha, and PDGF-BB receptors is important to their synergistic effects on BM fibr oblast proliferation. These results bring new insights into stroma-med iated hemopoietic regulation.