Stimulation of proliferation and maturation of rat astroblasts in serum-free culture by an astroglial growth factor.

Astroblasts from brain hemispheres of newborn rats were cultivated for 5 days in a complete medium containing 10% fetal calf serum. Cultures were then grown in basal medium in absence of serum. In these conditions, after 15 days only a few cells remained. When the basal culture medium was supplemented with insulin and transferrin (IT medium) the number of the remaining cells was twice higher. However, it was still lower than that found in the 5-day cultures before serum was removed. Thus the IT medium does not allow a good survival of the cells. Addition to the medium of an astroglial growth factor (AGF) from bovine brain soluble extract led to a tenfold increase of the cell number compared to cultures maintained in the basal medium alone. Effects of the factor on cell survival and on proliferation were examined independently. It was found that the factor did not greatly increase the survival of the cells but that it stimulated the proliferation. Addition of the growth factor to the IT medium elicited an increase of the level of S-100 protein and of the activity of glutamine synthetase, two proteins which are specific to astroglial cells in the central nervous system. These results indicate that the astroglial brain factor allows growth and maturation of the rat astroblasts maintained in serum-free medium.