Genetic enhancement of Ras-ERK pathway does not aggravate L-DOPA-induced dyskinesia in mice but prevents the decrease induced by lovastatin

Irene Ruiz-Dediego,María I Loza,Stefania Fasano,José-Rubén Garcia-Montes,José Brea,Rosario Moratalla,Riccardo Brambilla,Oscar Solís

doi:10.1038/s41598-018-33713-3

Abstract

Increasing evidence supports a close relationship between Ras-ERK1/2 activation in the striatum and L-DOPA-induced dyskinesia (LID). ERK1/2 activation by L-DOPA takes place through the crosstalk between D1R/AC/PKA/DARPP-32 pathway and NMDA/Ras pathway. Compelling genetic and pharmacological evidence indicates that Ras-ERK1/2 inhibition prevents LID onset and may even revert already established dyskinetic symptoms. However, it is currently unclear whether exacerbation of Ras-ERK1/2 activity in the striatum may further aggravate dyskinesia in experimental animal models. Here we took advantage of two genetic models in which Ras-ERK1/2 signaling is hyperactivated, the Nf1+/− mice, in which the Ras inhibitor neurofibromin is reduced, and the Ras-GRF1 overexpressing (Ras-GRF1 OE) transgenic mice in which a specific neuronal activator of Ras is enhanced. Nf1+/− and Ras-GRF1 OE mice were unilaterally lesioned with 6-OHDA and treated with an escalating L-DOPA dosing regimen. In addition, a subset of Nf1+/− hemi-parkinsonian animals was also co-treated with the Ras inhibitor lovastatin. Our results revealed that Nf1+/− and Ras-GRF1 OE mice displayed similar dyskinetic symptoms to their wild-type counterparts. This observation was confirmed by the lack of differences between mutant and wild-type mice in striatal molecular changes associated to LID (i.e., FosB, and pERK1/2 expression). Interestingly, attenuation of Ras activity with lovastatin does not weaken dyskinetic symptoms in Nf1+/− mice. Altogether, these data suggest that ERK1/2-signaling activation in dyskinetic animals is maximal and does not require further genetic enhancement in the upstream Ras pathway. However, our data also demonstrate that such a genetic enhancement may reduce the efficacy of anti-dyskinetic drugs like lovastatin.

Highlights

Extensive work indicates that extracellular signal-regulated kinase 1/2 (ERK1/2) activation in the striatum plays a critical role in the emergence of LID1–12
The major finding of this study is that the onset and expression of L-DOPA-induced dyskinesia (LID) in neurofibromatosis type 1 (Nf1)+/− and in Ras-GRF1 OE mice are indistinguishable from WT
Since previous works indicate that there is a correlation between Ras-ERK1/2 activity levels and intensity of dyskinetic symptoms[1,2,6,8,39], we expected that Nf1+/− and Ras-GRF1 OE mice would exhibit more dyskinesia than WT animals

Summary

Introduction

Extensive work indicates that extracellular signal-regulated kinase 1/2 (ERK1/2) activation in the striatum plays a critical role in the emergence of LID1–12. This activation takes place by two interplaying cascades: the D1R/cAMP/PKA/DARPP-32 pathway and the NMDA/Ras pathway. In addition to D1R-pathway, the ERK1/2 cascade can be activated by the NMDA receptor via Ras[21,22] In this pathway, lovastatin, a drug widely used to treat hyperlipidemia and able to reduce Ras activity by inhibiting its isoprenylation, significantly attenuates the phosphorylation of ERK1/2 and the development of LID23,24. We investigated the role of ERK1/2 over-activation in LID with two different approaches: a “direct” approach using Ras-GRF1 overexpressing (Ras-GRF1 OE) transgenic mice, and an “indirect” intervention, favoring the maintenance of Ras in its active form by decreasing the neurofibromin levels using Nf1+/− transgenic animals

Methods

Results

Conclusion