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. 2010 Nov 17;30(46):15616–15627. doi: 10.1523/JNEUROSCI.3888-10.2010

Figure 3.

Figure 3.

Inhibition of ERK1/2, but not mTOR, corrects excessive protein synthesis in the Fmr1 KO. A, Schematic illustrates experimental timeline: WT and Fmr1 KO hippocampal slices are recovered, incubated with 25 μm ActD ± inhibitor for 30 min, then protein synthesis measured ± inhibitor for 30 min. B, Protein synthesis and ERK1/2 activation were measured in slices incubated ± 5 μm U0126. Exposure to 5 μm U0126 significantly reduces protein synthesis in Fmr1 KO (t test, *p < 0.006), but not WT (t test p = 0.15) slices (n = 9). This concentration of U0126 significantly reduced ERK1/2 activation in both WT (t test, *p < 0.01) and Fmr1 KO (t test, *p < 0.005) slices (n = 4). C, Protein synthesis and p70S6K activation were measured in slices incubated ± 20 nm rapamycin. Exposure to 20 nm rapamycin does not correct protein synthesis in the Fmr1 KO (WT control vs KO control, t test, *p < 0.03; WT rapamycin vs KO rapamycin, t test, *p < 0.02; n = 13). This dose of rapamycin robustly reduces p70S6K activation in both WT (t test, *p < 0.02) and Fmr1 KO (t test, *p < 0.002) slices (n = 7). Quantified changes are shown in representative immunoblots. N represents number of animals per group, where 1–2 slices were analyzed per animal. Error bars represent SEM. D, Our results suggest the illustrated model of the relationship between mGluR5-mediated ERK1/2 activation and synaptic protein synthesis in WT and Fmr1 KO. In the Fmr1 KO, the loss of FMRP renders the activation of protein synthesis the more sensitive to basal levels of mGluR5-ERK1/2 activity. Inhibition of basal mGluR5-ERK1/2 with MPEP or U0126 leads to a significant decrease in Fmr1 KO, but not WT protein synthesis due to this hypersensitivity. Conversely, DHPG does not elevate the level of protein synthesis in the Fmr1 KO because mGluR5-ERK1/2-mediated protein synthesis is already saturated.