Dialogue Between Competence and Progression Growth Factorsand Astroglial-Conditioned Media on Nucleic Acid and Erk1/2Expression During Astroglial Cell Proliferation and Differentiationin Culture

Abstract

Growth factors are classified in competence growth factors and progessing growth factors, as reported in a papaer by Stiles and Antonisse, published on 1970.

The competence growth factors, including basic fibroblast growth factors (bFGF) and PDGF, are protein that switch from G0 phase to G1 phase of the cell cycle.

The progression growth factors, including EGF, IGF-1 and insulin are proteins that, during S phase of the cell cycle, stimulate DNA biosynthesis by activating the enzymes DNA polymerase, thymidine kinase and timidilate synthetase.

The aim of this present investigation is to study the cross-talk between exogenous growth factors and endogenous growth factors released from astroglialconditionedmedia on DNA labeling and ERK ½ expression in astrocytes in an in vitro model. To better clarify mechanism of astroglial cell proliferation /differentiation in culture, incorporation of [methyl-3H]-thymidine in astroglial cell cultures was investigated. Astrocytes cultures were pre-treated withepidermal growth factor (EGF), insulin (INS), insulin-like growth factor-I (IGF- I), and basic fibroblast growth factor (bFGF) and subsequently with astroglialconditioned media (ACM). In particular, the incorporation of [methyl-3H]-thymidine into DNA showed a significant increase in ACM from 15 days in vitro(DIV) cultures in 30 DIV astrocytes after12 h pre-treatment with growth factors. The results of enhancement in DNA labeling after pre- treatment with EGF orINS in 30 DIV astrocytes cultures and subsequent addition of ACM from 15 DIV cultures, indicate that the involvement may depend on extra cellular signalregulated kinase (ERK1) activation.

In addition, the present study seeks to elucidate the interactions between the competence growth factor bFGF and/or estrogen 17b-estradiol and the progressiongrowth factor EGF, IGF-1 and insulin on GFAP and vimentin expression in astroglial cultures under different experimental conditions. Pretreatment for 24hrwith bFGF subsequent exposure for 36hr estradiol and EGF, IGF-1 or INS was markedly increased, when the cultures where treated with two or three growthfactors. Our data demonstrate estradiol-growth factor cross-talk during astroglial cell proliferation and differentiation in culture.

In summary, the environment created by astroglial cultures can regulate their own proliferation and differentiation, through the release of soluble mediatorsfinally acting on their genomic program. This may be relevant in vivo, when scheduled events related to brain development are regulated by astrocyte-derived growth factors controlling neuronal and glial architecture from the postnatal period until the adulthood.