Glial fibrillary acidic protein and vimentin expression is regulated by glucocorticoids and neurotrophic factors in primary rat astroglial cultures.

The neurotrophic factors epidermal growth factor (EGF), basic fibroblast growth factor, (bFGF), insulin-like growth factor I (IGF-I) and insulin (INS) regulate neural and astroglial cell functions. Glucocorticoids may influence the metabolism of astroglial compartment and are key hormones in neurodegenerative events. This study was designed to assess the interactions between growth factors and dexamethasone (DEX) on cytoskeletal proteins (GFAP and vimentin) expression in 25 days in vitro (DIV) astrocyte cultures. An increase in GFAP and vimentin expression was observed after 12 h pretreatment with bFGF and subsequent treatment for 60 h with DEX. GFAP immunoreactivity was decreased after 24 h progression growth factors (EGF, IGF-I and INS) addition, when compared to control 36 h DEX and bFGF-pretreated cultures for the last 12 h. Vimentin immunoreactivity was decreased after 12 h bFGF pretreatment and subsequent 60 h DEX addition in astrocyte cultures compared to 12 h bFGF-pretreated ones. Pretreatment for 36 h with DEX plus bFGF in the last 12 h and subsequent treatment for 24 h with DMEM (Dulbecco's modified Eagle medium; DMEM) + BSA (bovine serum albumine) (harvesting), or with progression growth factors (EGF, IGF-I or INS) alone or two of them together, stimulated GFAP expression, compared to untreated controls. Immunochemical analysis of the mitogen-activated protein kinase ERK2 suggests an involvement of this enzyme in the control of GFAP expression. The above findings support the view of an interactive and complex dialogue between growth factors and glucocorticoids during astroglial cell proliferation and maturation in culture. This may have implications in therapeutic approach of neurologic disorders associated with astrogliosis, including cerebrovascular disease.