Effect of growth factors on nuclear and mitochondrial ADP-ribosylation processes during astroglial cell development and aging in culture

Epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), insulin-like growth factor-I (IGF-I) and insulin (INS) are powerful mitogens and may regulate gene expression in cultured astrocytes by ADP-ribosylation process. Nuclear poly-ADP ribose polymerase (PARP) and mitochondrial monoADP-ribosyltransferase (ADPRT) are the key enzymes involved in poly-ADP-ribosylation and mono ADP-ribosylation, respectively. In this investigation the effect of EGF, bFGF, IGF-I or INS on nuclear PARP and mitochondrial ADPRT activities were assessed in nuclei and mitochondria purified from developing (30 DIV) or aging (90 and 190 DIV) primary rat astrocyte cultures. A marked increase of PARP activity in bFGF or IGF-I treated astroglial cell cultures at 30 DIV was found. Nuclear PARP and mitochondrial ADPRT activities were greatly stimulated by treatment with EGF or INS alone or together in astrocyte cultures at 30 DIV. Nuclear PARP and mitochondrial ADPRT activities showed a more remarkable increase in control untreated astrocyte cultures at 190 DIV than at 90 DIV. These findings suggest that ADP-ribosylation process is involved in DNA damage and repair during cell differentiation and aging in culture. Twelve hours treatment with EGF, INS or bFGF significantly stimulated nuclear PARP and mitochondrial ADPRT activities in 190 DIV aging astrocyte cultures. The above results indicate that EGF, INS and bFGF may play a crucial role in the post-translational modification of chromosomal proteins including ADP-ribosylation process in in vitro models. This suggests that growth factors regulate genomic stability in glial cells during development and maturation, stimulating nuclear and mitochondrial ADP-ribosylation processes in developing or aging astrocyte cultures.