Objective: To investigate the crosstalk between D1 receptor (D1R) and the signaling of Fyn protein kinase in a mice model of levodopa (L-DOPA) induced dyskinesias (LID).

Background: In order to control the development of LID in PD therapy it is necessary to deeply understand the multiple cellular and molecular changes that take place in the striatum. Plenty of evidence have linked the upregulation of D1R signaling and LID expression. We have previously explored the pathway Pleiotrophin/RPTPζ/b/Fyn, which is altered as a consequence of dopaminergic cell loss and L-DOPA treatment. RPTPζ/b interacts with PSD95 at the postsynaptic density complex and regulates Fyn, a key molecule involved in synaptic plasticity and cytoskeleton stability. We have already demonstrated a significant increase in the amount of phosphorylated Fyn protein in the striatum of dyskinetic animals.

Methods: We reproduced the model of LID both in Fyn knock-out (KO) and wild type (WT) mice. Dopaminergic fibers were damaged with unilateral injection of 6-OHDA and mice were treated with daily doses of L-DOPA for 2 weeks (6-OHDA+L-DOPA). Additional experimental groups were used as control for surgery (sham+vehicle), treatment (sham+L-DOPA) and lesion (6-OHDA+vehicle). We performed behavioral tests to determine abnormal involuntary movements (AIMs). Dopaminergic denervation was confirmed by immunodetection of TH in the SNpc. Molecular markers of LID, TH and other proteins were determined by Western blot.

Results: As previously reported, Fyn-KO mice displayed lower levels of AIMs than WT littermates. Here we compared the amount and/or state of phosphorylation of several proteins related with D1R and the Fyn cascade, such as Fyn, Tau, FosB/ΔFosB, ERK and p70S6K, both in WT and Fyn-KO mice striata. We have reproduced previously reported changes in the regulation of several LID markers on WT mice while the regulation of some of these proteins in Fyn-KO mice was significantly altered.

Conclusions: The lower level of LIDs in Fyn-KO mice appears to be associated to a downregulation of the transcription factor ΔFosB. Other candidate molecules are under further analysis to unravel the mechanism by which Fyn participates in the development of dyskinesias.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/dissecting-the-molecular-mechanisms-of-fyn-mediated-levodopa-induced-dyskinesias/