Phospholipase D is a target for inhibition of astroglial proliferation by ethanol

The proliferation of astrocytes during early brain development is driven by growth factors and is accompanied by the activation of phospholipase D (PLD). Ethanol disrupts PLD signaling in astrocytes, a process which may contribute to delayed brain growth of fetuses exposed to alcohol during pregnancy. We here report that insulin-like growth factor 1 (IGF-1) is a strong mitogen for rat astrocytes (EC50 0.2 μg/ml) and a strong stimulator of astroglial PLD activity; both effects are inhibited by ethanol and 1-butanol, but not t-butanol, suggesting participation of PLD. Downregulation of PLD1 and exposure to the PLD1 inhibitor VU0359595 attenuated PLD activity and strongly reduced the mitogenic activity of serum and IGF-1. The PLD2 inhibitor VU0285655-1 also reduced PLD activity but had lesser effects on IGF-1-driven proliferation. PLD2 down-regulation affected serum - but not IGF-1-induced proliferation. In separate experiments, alcohol treatment of murine astrocytes taken from PLD-deficient animals revealed an insensitivity of PLD1(-/-) cells to 1-butanol whereas PLD2(-/-) cells were not affected. We conclude that astroglial proliferation induced by IGF-1 is critically dependent on the PLD signaling pathway, with a stronger contribution from PLD1 than PLD2. The teratogenic effects of ethanol may be explained, at least in part, by disruption of the IGF1-PLD signaling pathway.