Figure 4

IGF-I stimulates frataxin in astrocytes through the PI3K/Akt/mTor pathway. A, Inhibition of mRNA transcription with actinomycin D (ActD, 2 μg/ml) eliminated the stimulatory effect of IGF-I on frataxin levels. B, IGF-I significantly stimulates frataxin mRNA 6 hours after its addition to astrocyte cultures returning to basal levels at 24 hours post-addition. C, Inhibition of protein synthesis with cycloheximide (Chx, 1 μg/ml) blocked the stimulatory effects of IGF-I on Fxn levels in astrocytes. D, Inhibition of PI3 kinase with 100 μM of Ly294002 inhibited the stimulatory action of IGF-I on frataxin levels. E, Similarly, inhibition of mTor with rapamycin (100nM) also blocked the positive effect of IGF-I. F, IGF-I stimulates phosphorylation of mTOR (pmTOR). Representative blot are shown; the upper blots correspond to frataxin and the lower blots to β-actin (n=4-6, independent experiments). *p<0.05; **p<0.01, and ***p<0.001.