INSULIN-LIKE GROWTH-FACTORS ACT SYNERGISTICALLY WITH BASIC FIBROBLASTGROWTH-FACTOR AND NERVE GROWTH-FACTOR TO PROMOTE CHROMAFFIN CELL-PROLIFERATION

We have investigated the effects of insulin-like growth factors (IGFs) , basic fibroblast growth factor (bFGF), and nerve growth factor (NGF) on DNA synthesis in cultured chromaffin cells from fetal, neonatal, a nd adult rats by using 5-bromo-2'-deoxyuridine (BrdUrd) pulse labeling for 24 or 48 h and immunocytochemical staining of cell nuclei. After 6 days in culture in the absence of growth factors, nuclear BrdUrd inc orporation was detected in 30% of fetal chromaffin cells, 1.5% of neon atal cells, and 0.1% of adult cells. Addition of 10 nM IGF-I or IGF-II increased the fraction of BrdUrd-labeled nuclei to 50% of fetal, 20% of neonatal, and 2% of adult chromaffin cells. The ED(50) value of IGF -I- and IGF-II-stimulated BrdUrd labeling in neonatal chromaffin cells was 0.3 nM and 0.8 nM, respectively. In neonatal and adult chromaffin cells, addition of 1 nM bFGF or 2 nM NGF stimulated nuclear BrdUrd in corporation to approximately the same level as 10 nM IGF-I or IGF-II. However, the response to bFGF or NGF in combination with either IGF-I or IGF-II was more than additive, indicating that the combined effect of the IGFs and bFGF or NGF is synergistic. The degree of synergism wa s 2- to 4-fold in neonatal chromaffin cells and 10- to 20-fold in adul t chromaffin cells compared with the effect of each growth factor alon e. In contrast, the action of bFGF and NGF added together in the absen ce of IGFs was not synergistic or additive. IGF-II acted also as a sur vival factor on neonatal chromaffin cells and the cell survival was fu rther improved when bFGF or NGF was added together with IGF-II. In con clusion, we propose that IGF-I and IGF-II act in synergy with bFGF and NGF to stimulate proliferation and survival of chromaffin cells durin g neonatal growth and adult maintenance of the adrenal medulla. Our fi ndings may have implications for improving the survival of chromaffin cell implants in diseased human brain.