Cristina Alcacer

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease.

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinsons disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

L-DOPA activates ERK signaling and phosphorylates histone H3 in the striatonigral medium spiny neurons of hemiparkinsonian mice

In the dopamine‐depleted striatum, extracellular signal‐regulated kinase (ERK) signaling is implicated in the development of l‐DOPA‐induced dyskinesia. To gain insights on its role in this disorder, we examined the effects of l‐DOPA on the state of phosphorylation of ERK and downstream target proteins in striatopallidal and striatonigral medium spiny neurons (MSNs). For this purpose, we employed mice expressing enhanced green fluorescent protein (EGFP) under the control of the promoters for the dopamine D2 receptor (Drd2‐EGFP mice) or the dopamine D1 receptor (Drd1a‐EGFP mice), which are expressed in striatopallidal and striatonigral MSNs, respectively. In 6‐hydroxydopamine‐lesioned Drd2‐EGFP mice, l‐DOPA increased the phosphorylation of ERK, mitogen‐ and stress‐activated kinase 1 and histone H3, selectively in EGFP‐negative MSNs. Conversely, a complete co‐localization between EGFP and these phosphoproteins was observed in Drd1a‐EGFP mice. The effect of l‐DOPA was prevented by blockade of dopamine D1 receptors. The same pattern of activation of ERK signaling was observed in dyskinetic mice, after repeated administration of l‐DOPA. Our results demonstrate that in the dopamine‐depleted striatum, l‐DOPA activates ERK signaling specifically in striatonigral MSNs. This regulation may result in ERK‐dependent changes in striatal plasticity leading to dyskinesia.

Gαolf Mutation Allows Parsing the Role of cAMP-Dependent and Extracellular Signal-Regulated Kinase-Dependent Signaling in l-3,4-Dihydroxyphenylalanine-Induced Dyskinesia

Although l-3,4-dihydroxyphenylalanine (l-DOPA) remains the reference treatment of Parkinsons disease, its long-term beneficial effects are hindered by l-DOPA-induced dyskinesia (LID). In the dopamine (DA)-denervated striatum, l-DOPA activates DA D1 receptor (D1R) signaling, including cAMP-dependent protein kinase A (PKA) and extracellular signal-regulated kinase (ERK), two responses associated with LID. However, the cause of PKA and ERK activation, their respective contribution to LID, and their relationship are not known. In striatal neurons, D1R activates adenylyl-cyclase through Gαolf, a protein upregulated after lesion of DA neurons in rats and in patients. We report here that increased Gαolf levels in hemiparkinsonian mice are correlated with LID after chronic l-DOPA treatment. To determine the role of this upregulation, we performed unilateral lesion in mice lacking one allele of the Gnal gene coding for Gαolf (Gnal+/−). Despite an increase in the lesioned striatum, Gαolf levels remained below those of unlesioned wild-type mice. In Gnal+/− mice, the lesion-induced l-DOPA stimulation of cAMP/PKA-mediated phosphorylation of GluA1 Ser845 and DARPP-32 (32 kDa DA- and cAMP-regulated phosphoprotein) Thr34 was dramatically reduced, whereas ERK activation was preserved. LID occurrence was similar in Gnal+/+ and Gnal+/− mice after a 10-d l-DOPA (20 mg/kg) treatment. Thus, in lesioned animals, Gαolf upregulation is critical for the activation by l-DOPA of D1R-stimulated cAMP/PKA but not ERK signaling. Although the cAMP/PKA pathway appears to be required for LID development, our results indicate that its activation is unlikely to be the main source of LID. In contrast, the persistence of l-DOPA-induced ERK activation in Gnal+/− mice supports its causal role in LID development.

Mechanisms of Dopamine D1 Receptor-Mediated ERK1/2 Activation in the Parkinsonian Striatum and Their Modulation by Metabotropic Glutamate Receptor Type 5

In animal models of Parkinson′s disease, striatal overactivation of ERK1/2 via dopamine (DA) D1 receptors is the hallmark of a supersensitive molecular response associated with dyskinetic behaviors. Here we investigate the pathways involved in D1 receptor-dependent ERK1/2 activation using acute striatal slices from rodents with unilateral 6-hydroxydopamine (6-OHDA) lesions. Application of the dopamine D1-like receptor agonist SKF38393 induced ERK1/2 phosphorylation and downstream signaling in the DA-denervated but not the intact striatum. This response was mediated through a canonical D1R/PKA/MEK1/2 pathway and independent of ionotropic glutamate receptors but blocked by antagonists of L-type calcium channels. Coapplication of an antagonist of metabotropic glutamate receptor type 5 (mGluR5) or its downstream signaling molecules (PLC, PKC, IP3 receptors) markedly attenuated SKF38393-induced ERK1/2 activation. The role of striatal mGluR5 in D1-dependent ERK1/2 activation was confirmed in vivo in 6-OHDA-lesioned animals treated systemically with SKF38393. In one experiment, local infusion of the mGluR5 antagonist MTEP in the DA-denervated rat striatum attenuated the activation of ERK1/2 signaling by SKF38393. In another experiment, 6-OHDA lesions were applied to transgenic mice with a cell-specific knockdown of mGluR5 in D1 receptor-expressing neurons. These mice showed a blunted striatal ERK1/2 activation in response to SFK38393 treatment. Our results reveal that D1-dependent ERK1/2 activation in the DA-denervated striatum depends on a complex interaction between PKA- and Ca2+-dependent signaling pathways that is critically modulated by striatal mGluR5.

Convulsant Doses of a Dopamine D1 Receptor Agonist Result in Erk-Dependent Increases in Zif268 and Arc/Arg3.1 Expression in Mouse Dentate Gyrus

Activation of dopamine D1 receptors (D1Rs) has been shown to induce epileptiform activity. We studied the molecular changes occurring in the hippocampus in response to the administration of the D1-type receptor agonist, SKF 81297. SKF 81297 at 2.5 and 5.0 mg/kg induced behavioural seizures. Electrophysiological recordings in the dentate gyrus revealed the presence of epileptiform discharges peaking at 30–45 min post-injection and declining by 60 min. Seizures were prevented by the D1-type receptor antagonist, SCH 23390, or the cannabinoid CB1 receptor agonist, CP 55,940. The effect of SKF 81297 was accompanied by increased phosphorylation of the extracellular signal-regulated protein kinases 1 and 2 (ERK), in the granule cells of the dentate gyrus. This effect was also observed in response to administration of other D1-type receptor agonists, such as SKF83822 and SKF83959. In addition, SKF 81297 increased the phosphorylation of the ribosomal protein S6 and histone H3, two downstream targets of ERK. These effects were prevented by genetic inactivation of D1Rs, or by pharmacological inhibition of ERK. SKF 81297 was also able to enhance the levels of Zif268 and Arc/Arg3.1, two immediate early genes involved in transcriptional regulation and synaptic plasticity. These changes may be involved in forms of activity-dependent plasticity linked to the manifestation of seizures and to the ability of dopamine to affect learning and memory.

Chemogenetic stimulation of striatal projection neurons modulates responses to Parkinson’s disease therapy

Parkinson’s disease (PD) patients experience loss of normal motor function (hypokinesia), but can develop uncontrollable movements known as dyskinesia upon treatment with L-DOPA. Poverty or excess of movement in PD has been attributed to overactivity of striatal projection neurons forming either the indirect (iSPNs) or the direct (dSPNs) pathway, respectively. Here, we investigated the two pathways’ contribution to different motor features using SPN type–specific chemogenetic stimulation in rodent models of PD (PD mice) and L-DOPA–induced dyskinesia (LID mice). Using the activatory Gq-coupled human M3 muscarinic receptor (hM3Dq), we found that chemogenetic stimulation of dSPNs mimicked, while stimulation of iSPNs abolished the therapeutic action of L-DOPA in PD mice. In LID mice, hM3Dq stimulation of dSPNs exacerbated dyskinetic responses to L-DOPA, while stimulation of iSPNs inhibited these responses. In the absence of L-DOPA, only chemogenetic stimulation of dSPNs mediated through the Gs-coupled modified rat muscarinic M3 receptor (rM3Ds) induced appreciable dyskinesia in PD mice. Combining D2 receptor agonist treatment with rM3Ds-dSPN stimulation reproduced all symptoms of LID. These results demonstrate that dSPNs and iSPNs oppositely modulate both therapeutic and dyskinetic responses to dopamine replacement therapy in PD. We also show that chemogenetic stimulation of different signaling pathways in dSPNs leads to markedly different motor outcomes. Our findings have important implications for the design of effective antiparkinsonian and antidyskinetic drug therapies.

Mitogen- and stress-activated protein kinase 1 is required for specific signaling responses in dopamine-denervated mouse striatum, but is not necessary for l-DOPA-induced dyskinesia

In advanced Parkinsons disease, l-DOPA treatment causes the appearance of abnormal involuntary movements or l-DOPA-induced dyskinesia (LID). LID results in part from l-DOPA-induced activation of extracellular signal-regulated kinase (ERK) in the dopamine-denervated striatum. Activated ERK triggers nuclear responses, including phosphorylation of mitogen- and stress-activated protein kinase 1 (MSK1) and histone H3, and transcription of genes such as FosB. To determine the role of MSK1, wild type and MSK1 knockout mice with unilateral 6-hydroxydopamine lesion in the dorsolateral striatum were chronically treated with l-DOPA. The absence of MSK1 had no effect on the lesion or l-DOPA-induced ERK activation, but reduced l-DOPA-induced phosphorylation of histone H3 and FosB accumulation in the dopamine-denervated striatum. MSK1 deficiency also prevented the increase in Gαolf, the stimulatory α subunit of G protein coupling striatal dopamine D1 receptor to adenylyl cyclase. However, the intensity of LID was similar in MSK1-deficient and wild type mice. In conclusion, l-DOPA-induced activation of MSK1 contributes to histone H3 phosphorylation, induction of FosB, and Gαolf up-regulation but appears not to be necessary for the development of LID.

Signaling Mechanisms in l-DOPA-Induced Dyskinesia

l-DOPA-induced dyskinesia is a major complication of dopamine replacement therapy in Parkinson’s disease. Clinical and experimental studies indicate that this complication develops because of a substantial loss of dopaminergic afferents to the motor part of the striatum, causing both pre- and postsynaptic changes in the nigrostriatal system. Moreover, a number of non-dopaminergic neurotransmitters modulate both the risk and the severity of this motor complication of treatment. This chapter reviews molecular changes occurring in the dopamine-denervated striatum in animal models of l-DOPA-induced dyskinesia, which have been partly verified by human studies. We will review a wide scope of alterations ranging from the phenomenon of dopamine D1 receptor supersensitivity (which is key to abnormal signaling responses in striatal neurons) to the role played by glutamate receptors and the altered regulation of gene and protein expression. We will finally review the evidence for a gliovascular contribution to the pathogenesis of l-DOPA-induced dyskinesia. It is our hope that the pathophysiological insights derived from animal models of l-DOPA-induced dyskinesia will soon lead to new therapeutics for the suppression or prevention of this debilitating condition.