Effect of growth factors on DNA labeling and cytoskeletal protein expression in 17-β-estradiol and basic fibroblast growth factor pre-treated astrocyte cultures

Astrocytes react to all noxae which damage neurons. Their reactions include degeneration, hypertrophy, hyperplasia and fibre formation. Growth factors inducing proliferation and differentiation of both neurons and astrocytes in culture play a pivotal role in the dynamic flow of signaling molecules between neurons and astroglia. Estrogens as well influence astroglia and are neuroprotectants. This study has investigated the interactions between growth factors and estrogens on DNA labeling and cytoskeletal protein [glial fibrillary acidic protein (GFAP) and virnentin] expression in 22 DIV astrocyte cultures treated for 24 or 36 h under different experimental conditions. Contemporary addition of 17-beta-estradiol (E-2) with two or three growth factors for 24 h, significantly stimulated methyl-[H-3]thymidine incorporation into DNA from 22 days in vitro (DIV) astrocyte cultures. This effect reached a peak when E-2 was co-added with epidermal growth factor (EGF), basic fibroblast growth factor (bFGF) and insulin. In astrocyte cultures treated for 36 h with E-2 and EGF + insulin or bFGF + insulin added in the last 12 h, DNA labeling was remarkably increased. The parallel cyclin D I expression positively correlated with ERK2 activation. Western blot analysis for cytoskeletal proteins showed also changes of both GFAP and vimentin expression. The above data suggest the occurrence of a scheduled interaction between "competence" or "progression" growth factors and estrogens on DNA labeling and cytoskeletal protein expression during astroglial cell proliferation and differentiation in culture. A better understanding of the mechanisms of these interactions may contribute to develop strategies for controlling astroglial reaction in cerebrovascular disease including stroke and hypertensive brain damage.