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Updated: Apr 8, 2026
Rating L-DOPA-Induced Dyskinesias in the Unilaterally 6-OHDA-Lesioned Rat Model of Parkinson's Disease
Published on: October 4, 2021
Differential involvement of Ras-GRF1 and Ras-GRF2 in L-DOPA-induced dyskinesia
Simone Bido1, Nicola Solari2, Marzia Indrigo2
1Section of Pharmacology, Department of Medical Sciences, University of Ferrara Ferrara, Italy.
Objective:
Recent findings have shown that pharmacogenetic manipulations of the Ras-ERK pathway provide a therapeutic means to tackle l-3,4-dihydroxyphenylalanine (l-DOPA)-induced dyskinesia (LID). First, we investigated whether a prolonged l-DOPA treatment differentially affected ERK signaling in medium spiny neurons of the direct pathway (dMSNs) and in cholinergic aspiny interneurons (ChIs) and assessed the role of Ras-GRF1 in both subpopulations. Second, using viral-assisted technology, we probed Ras-GRF1 and Ras-GRF2 as potential targets in this pathway. We investigated how selective blockade of striatal Ras-GRF1 or Ras-GRF2 expression impacted on LID (induction, maintenance, and reversion) and its neurochemical correlates.
Methods:
We used both Ras-GRF1 knockout mice and lentiviral vectors (LVs) delivering short-hairpin RNA sequences (shRNAs) to obtain striatum-specific gene knockdown of Ras-GRF1 and Ras-GRF2. The consequences of these genetic manipulations were evaluated in the 6-hydroxydopamine mouse model of Parkinson's disease. Escalating doses of l-DOPA were administered and then behavioral analysis with immunohistochemical assays and in vivo microdialysis were performed.
Results:
Ras-GRF1 was found essential in controlling ERK signaling in dMSNs, but its ablation did not prevent ERK activation in ChIs. Moreover, striatal injection of LV-shRNA/Ras-GRF1 attenuated dyskinesia development and ERK-dependent signaling, whereas LV-shRNA/Ras-GRF2 was without effect, ruling out the involvement of Ras-GRF2 in LID expression. Accordingly, Ras-GRF1 but not Ras-GRF2 striatal gene-knockdown reduced l-DOPA-induced GABA and glutamate release in the substantia nigra pars reticulata, a neurochemical correlate of dyskinesia. Finally, inactivation of Ras-GRF1 provided a prolonged anti-dyskinetic effect for up to 7 weeks and significantly attenuated symptoms in animals with established LID.
Interpretation:
Our results suggest that Ras-GRF1 is a promising target for LID therapy based on Ras-ERK signaling inhibition in the striatum.
Insights
Targeting Ras-GRF1 in the striatum offers a promising therapeutic strategy for l-3,4-dihydroxyphenylalanine (LID) induced dyskinesia. Inhibiting Ras-GRF1 effectively reduces LID symptoms and associated neurochemical changes, suggesting its potential for Parkinson's disease treatment.
Area of Science:
- Neuroscience
- Pharmacology
- Molecular Biology
Background:
- l-3,4-dihydroxyphenylalanine (l-DOPA) is a primary treatment for Parkinson's disease.
- l-DOPA-induced dyskinesia (LID) is a common and debilitating side effect of long-term l-DOPA therapy.
- The Ras-ERK signaling pathway is implicated in the development of LID.
Purpose of the Study:
- To investigate the differential effects of l-DOPA on ERK signaling in striatal subpopulations.
- To assess the role of Ras-GRF1 and Ras-GRF2 in LID.
- To evaluate the therapeutic potential of targeting Ras-GRF1 or Ras-GRF2 for LID.
Main Methods:
- Utilized Ras-GRF1 knockout mice and lentiviral vectors for striatum-specific gene knockdown of Ras-GRF1 and Ras-GRF2.
- Employed the 6-hydroxydopamine mouse model of Parkinson's disease.
- Conducted behavioral analysis, immunohistochemistry, and in vivo microdialysis following l-DOPA administration.
Main Results:
- Ras-GRF1 is crucial for ERK signaling in direct pathway medium spiny neurons but not in cholinergic interneurons.
- Striatal knockdown of Ras-GRF1, but not Ras-GRF2, attenuated LID induction and maintenance.
- Ras-GRF1 inhibition reduced l-DOPA-induced neurotransmitter release and provided sustained anti-dyskinetic effects.
Conclusions:
- Ras-GRF1 plays a critical role in the development of LID.
- Targeting Ras-GRF1 in the striatum represents a viable therapeutic strategy for LID.
- Inhibition of Ras-ERK signaling via Ras-GRF1 offers a promising approach for managing l-DOPA-induced dyskinesia.
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