Insulin-like growth factors act synergistically with basic fibroblast growth 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, and 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 incorporation was detected in 30% of fetal chromaffin cells, 1.5% of neonatal 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 ED50 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 incorporation 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 was 2- to 4-fold in neonatal chromaffin cells and 10- to 20-fold in adult chromaffin cells compared with the effect of each growth factor alone. In contrast, the action of bFGF and NGF added together in the absence of IGFs was not synergistic or additive. IGF-II acted also as a survival factor on neonatal chromaffin cells and the cell survival was further improved when bFGF or NGF was added together with IGF-II. In conclusion, we propose that IGF-I and IGF-II act in synergy with bFGF and NGF to stimulate proliferation and survival of chromaffin cells during neonatal growth and adult maintenance of the adrenal medulla. Our findings may have implications for improving the survival of chromaffin cell implants in diseased human brain.