Block of long-term potentiation by naturally secreted and synthetic amyloid beta-peptide in hippocampal slices is mediated via activation of the kinases c-Jun N-terminal kinase, cyclin-dependent kinase 5, and p38 mitogen-activated protein kinase as well as metabotropic glutamate receptor type 5

Abstract

The mechanisms of action of human synthetic and naturally secreted cell-derived amyloid beta-peptide (Abeta)(1-42) on the induction of long-term potentiation (LTP) were investigated in the medial perforant path to dentate granule cell synapses in hippocampal slices. Synthetic and cell-derived Abeta strongly inhibited high-frequency stimulation (HFS)-induced LTP at peak HFS and 1 hr after HFS. Cell-derived Abeta was much more potent than synthetic Abeta at inhibiting LTP induction, with threshold concentrations of approximately 1 and 100-200 nm, respectively. The involvement of various kinases in Abeta-mediated inhibition of LTP induction was investigated by applying Abeta in the presence of inhibitors of these kinases. The c-Jun N-terminal kinase (JNK) inhibitor JNKI prevented the block of LTP induction by both synthetic and cell-derived Abeta. The block of LTP induced by synthetic Abeta was also prevented by the JNK inhibitor anthra[1,9-cd]pyrazol-6(2H)-one, the cyclin-dependent kinase 5 (Cdk5) inhibitors butyrolactone and roscovitine, and the p38 MAP kinase (MAPK) inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-5-(4-pyridyl)-1H-imidazole but not by the p42-p44 MAP kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene. The group I-group II metabotropic glutamate receptor (mGluR) antagonist 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl)propanoic acid and the mGluR5 antagonist methyl-6-(phenylethynyl)pyridine prevented the block of LTP induction by Abeta. However, thealpha7 nicotinic ACh receptor antagonist methylcaconatine did not prevent the inhibition of LTP induction by Abeta. These studies provide evidence that the Abeta-mediated inhibition of LTP induction involves stimulation of the kinases JNK, Cdk5, and p38 MAPK after the activation of both the Abeta receptor(s) and mGluR5.

Figure 1.

Synthetic and naturally secreted cell-derived human Aβ inhibits induction but not expression of LTP. A, Control LTP induced by a single brief HFS (open circles) and LTP induction in the presence of synthetic Aβ (500 nm), applied 60 min before HFS, were significantly reduced compared with controls (filled circles). B, The lack of effect of 500 nm synthetic Aβ on baseline EPSPs. C, Control LTP induction in CHO–CM (open circles) and LTP induction in the presence of 7PA2 CM containing cell-derived Aβ (filled circles) applied 60 min before HFS were significantly reduced compared with controls. D, LTP in experiments in which synthetic Aβ was applied immediately after HFS; LTP expression was not significantly reduced compared with controls. Traces a–c illustrate EPSPs before and 20 and 60 min after HFS, respectively. In A and C, the top set of traces shows the LTP induction in controls, and the bottom set of traces shows the inhibited LTP induction.

Figure 2.

Aβ-mediated inhibition of LTP induction is prevented by JNK inhibitors. A, LTP induction in JNKI (open circles) and in 500 nm synthetic Aβ plus JNKI (filled circles) was not significantly inhibited. B, LTP induction in naturally secreted cell-derived human Aβ plus JNKI was not significantly inhibited. C, LTP induction in the JNK inhibitor SP600125 (open circles) and in synthetic Aβ plus SP600125 (filled circles) was significantly increased compared with inhibited LTP induction in Aβ. Traces a–c illustrate EPSPs before and 20 and 60 min after HFS, respectively. In A and C, the top set of traces shows the LTP induction in the kinase inhibitor alone, and the bottom set of traces shows the LTP induction in the kinase inhibitor plus Aβ.

Figure 3.

The Aβ-evoked inhibition of LTP induction is prevented by the Cdk5 inhibitors butyrolactone and roscovitine and the p38 MAP kinase inhibitor SB203580 but not the p42–p44 MAP kinase inhibitor U0126. A, LTP induction in butyrolactone (open circles) and in the presence of butyrolactone plus 500 nm synthetic Aβ (filled circles) was not significantly inhibited. B, LTP induction in roscovitine (open circles) and in the presence of roscovitine plus 500 nm synthetic Aβ (filled circles) was not significantly reduced compared with controls. C, LTP induction in SB203580 (open circles) and in 500 nm synthetic Aβ plus SB203580 (filled circles) was not significantly reduced compared with controls. D, LTP induction in U0126 (open circles) and in 500 nm synthetic Aβ plus U0126 (filled circles) was significantly reduced compared with controls. Traces a–c illustrate EPSPs before and 20 and 60 min after HFS, respectively. The top set of traces shows the LTP induction in the kinase inhibitor alone, and the bottom set of traces shows the LTP induction in the kinase inhibitor plus Aβ.

Figure 4.

Activation of mGluR5 but not the α7 nAChR is required for synthetic Aβ inhibition of LTP induction. A, LTP induction in the presence of 500 nm synthetic Aβ plus the group I–II antagonist LY341495 was not significantly reduced compared with controls. B, LTP induction in the presence of 500 nm synthetic Aβ plus the mGluR5 antagonist MPEP was not significantly reduced compared with controls. C, LTP induction in the presence of the α7 nAChR antagonist MLA and 500 nm Aβ was significantly reduced compared with controls. Traces a–c illustrate EPSPs before HFS and 20 min and 60 min after HFS, respectively.