Growth promoting effects of IGF-I on fetal hypothalamic cell lines under serum-free culture conditions

Recent evidence indicates that the insulin-like family of peptides may act as endogenous trophic factors in the central nervous system. To further examine this possibility we have investigated the effects of three insulin-like peptides on the in vitro growth of fetal hypothalamic cell lines. Two virally transformed rat hypothalamic cell lines which have been developed in our laboratory (A-6 and F-12) were used. Cells were plated at varying densities and cultured in the presence or absence of either insulin-like growth factor I (IGF-I), insulin, or multiplication stimulating activity (MSA or IGF-II), in serum-free medium for 1 wk. Cell growth was assessed by counting or by measuring cellular incorporation of ³H-thymidine. Of the three peptides tested IGF-I was the most potent in eliciting cell growth. Insulin also stimulated growth of both cell lines, but was 100 times less potent for A-6 cells while it was equipotent with IGF-I in F-12 cells. MSA had no effect on either cell line. Both IGF-I and insulin showed dose-response effects in increasing cell growth. We also found that the two cell lines had the greatest response to IGF-I at low cell densities. Finally, time-course experiments suggested that a continued presence of the peptide is essential for the growth-promoting effects. We conclude that IGF-I is a potent growth factor for virally transformed cell lines derived from the rat fetal hypothalamus. Since both IGF-I immunoreactivity and IGF-I receptors have been located in this diencephalic area these results suggest that IGF-I may constitute a mitogenic signal for hypothalamic cells during neurogenesis.