Striatal overexpression of DeltaFosB reproduces chronic levodopa-induced involuntary movements

The Role of ΔFosB in the Pathogenesis of Levodopa-Induced Dyskinesia: Mechanisms and Therapeutic Strategies

Levodopa-induced dyskinesia (LID) represents a significant complication associated with the long-term administration of levodopa (L-DOPA) for the treatment of Parkinson's disease (PD). This review examines the critical role of ΔFosB, a transcription factor, in the pathogenesis of LID and explores potential therapeutic interventions. ΔFosB accumulates within the striatum in response to chronic dopaminergic stimulation, thereby driving maladaptive changes that culminate in dyskinesia. Its persistent expression modifies gene transcription, influencing neuronal plasticity and contributing to the sustained presence of dyskinetic movements. This study explains how ΔFosB functions at the molecular level, focusing on its connections with dopamine D1 receptors, the cAMP/PKA signaling pathway, and its regulatory effects on downstream targets such as DARPP-32 and GluA1 AMPA receptor subunits. Additionally, it examines how neuronal nitric oxide synthase (nNOS) affects ΔFosB levels and the development of LID. This review also considers the interactions between ΔFosB and other signaling pathways, such as ERK and mTOR, in the context of LID and striatal plasticity. Emerging therapeutic strategies targeting ΔFosB and its associated pathways include pharmacological interventions like ranitidine, 5-hydroxytryptophan, and carnosic acid. Furthermore, this study addresses the role of JunD, another component of the AP-1 transcription factor complex, in the pathogenesis of LID. Understanding the molecular mechanisms by which ΔFosB contributes to LID offers promising avenues for developing novel treatments that could mitigate dyskinesia and improve the quality of life for PD patients undergoing long-term L-DOPA therapy.

Sitagliptin attenuates L-dopa-induced dyskinesia by regulating mitochondrial proteins and neuronal activity in a 6-OHDA-induced mouse model of Parkinson's disease

L-dopa-induced dyskinesia (LID) is an incapacitating complication of long-term administration of L-dopa therapy that commonly affects patients with Parkinson's disease (PD) due to the widespread use of the causative drug. Herein, we investigated the therapeutic potential of sitagliptin, a drug used to treat type 2 diabetes mellitus, to treat LID. 6-hydroxydopamine (6-OHDA) was unilaterally injected into the left side of the substantia nigra pas compacta to induce a mouse model of PD. After four weeks of 6-OHDA induction, L-dopa was administered with or without sitagliptin for 11 consecutive days. LID was monitored using abnormal involuntary movement (AIM) scoring, conducted on days 5 and 10 of L-dopa treatment. Comparative proteomic analysis was performed on the 6-OHDA-lesioned striatum by comparing groups treated with vehicle + L-dopa and sitagliptin + L-dopa. Sitagliptin combined with L-dopa significantly attenuated AIM scores in 6-OHDA-lesioned mice. Proteomic analysis following sitagliptin treatment showed an increase in proteins involved in mitochondrial function regulation and a decrease in proteins associated with cytoskeleton function regulation. Changes in the expression of Ndufb2, a subunit of NADH: ubiquinone oxidoreductase (complex I), and Arc, an immediate early gene (IEG), which showed the most significant increase and decrease, respectively, were validated using western blotting and RT-PCR analysis. These findings suggest that sitagliptin may have therapeutic potential by enhancing mitochondrial functions and suppressing neuronal activity in the striatum, thereby mitigating the incapacitating complications associated with long-term L-dopa use in patients with PD.

Long-lasting expression of FosB/ΔFosB immunoreactivity following acute stress in the paraventricular and supraoptic nuclei of the rat hypothalamus

We examined expression profiles of FosB/∆FosB immunoreactivity and fosB gene transcripts in the paraventricular nucleus of the hypothalamus (PVH) and the supraoptic nucleus (SON) of rats following acute surgical stress (SS) and restraint stress (RS) and compared them with those of c-Fos immunoreactivity and c-fos mRNA. Following SS, the number of FosB/ΔFosB-ir cells markedly increased, the time course of which was slow-onset and long-lasting, in contrast with rapid-onset and short-lived c-Fos expression. Characteristically long-lasting FosB/ΔFosB expression was also observed following RS. On the other hand, fosB mRNA was short-lived, and its time course not much different from that of c-fos mRNA; thus, the long-lasting expression of FosB/∆FosB immunoreactivity may be attributed to the longer half-life of FosB proteins, and not to the persistent expression of fosB gene transcripts. Following SS, FosB/ΔFosB immunoreactivity was present mainly in PVH corticotropin-releasing factor (CRF) neurons and SON vasopressin (AVP) neurons, while c-Fos immunoreactivity in either PVH CRF neurons, or AVP and oxytocin neurons in PVH and SON. Following RS, FosB/ΔfosB- and c-Fos expression was almost restricted to PVH CRF neurons. The present study raises the possibility that FosB proteins in discrete populations of hypothalamic neuroendocrine neurons may play roles in forming adaptability to and/or resilience against stress, which takes longer than the acute phase response.

Targeting serum response factor (SRF) deactivates ΔFosB and mitigates Levodopa-induced dyskinesia in a mouse model of Parkinson's disease

L-3,4-dihydroxyphenylalanine (L-DOPA) is currently the preferred treatment for Parkinson's Disease (PD) and is considered the gold standard. However, prolonged use of L-DOPA in patients can result in involuntary movements known as Levodopa-induced dyskinesia (LID), which includes uncontrollable dystonia affecting the trunk, limbs, and face. The role of ΔFosB protein, a truncated splice variant of the FosB gene, in LID has been acknowledged, but its underlying mechanism has remained elusive. Here, using a mouse model of Parkinson's disease treated with chronic levodopa we demonstrate that serum response factor (SRF) binds to the FosB promoter, thereby activating FosB expression and levodopa induced-dyskinetic movements. Western blot analysis demonstrates a significant increase in SRF expression in the dyskinetic group compared to the control group. Knocking down SRF significantly reduced abnormal involuntary movements (AIMS) and ΔFosB expression compared to the control. Conversely, overexpression of SRF led to an increase in ΔFosB expression and worsened levodopa-induced dyskinesia. To shed light on the regulatory role of the Akt signaling pathway in this phenomenon, we administered the Akt agonist SC79 to PD mouse models via intraperitoneal injection, followed by L-DOPA administration. The expression of SRF, ΔFosB, and phosphorylated Akt (p-Akt) significantly increased in this group compared to the group receiving normal saline to signify that these happen through Akt signaling pathway. Collectively, our findings identify a promising therapeutic target for addressing levodopa-induced dyskinesia.

AMPK-mediated autophagy pathway activation promotes ΔFosB degradation to improve levodopa-induced dyskinesia

BACKGROUND

Parkinson's disease patients on chronic levodopa often suffer from motor complications, which tend to reduce their quality of life. Levodopa-induced dyskinesia (LID) is one of the most prevalent motor complications, often characterized by abnormal involuntary movements, and the pathogenesis of LID is still unclear but recent studies have suggested the involvement of autophagy.

METHODS

The onset of LID was mimicked by chronic levodopa treatment in a unilateral 6-hydroxydopamine (6-OHDA) -lesion rat model. Overexpression of ΔFosB in HEK293 cells to mimic the state of ΔFosB accumulation. The modulation of the AMP-activated protein kinase (AMPK)-mediated autophagy pathway using by metformin, AICAR (an AMPK activator), Compound C (an AMPK inhibitor) and chloroquine (an autophagy pathway inhibitor). The severity of LID was assessed by axial, limb, and orofacial (ALO) abnormal involuntary movements (AIMs) score and in vivo electrophysiology. The activity of AMPK pathway as well as autophagy markers and FosB-ΔFosB levels were detected by western blotting. RT-qPCR was performed to detect the transcription level of FosB-ΔFosB. The mechanism of autophagy dysfunction was further explored by immunofluorescence and transmission electron microscopy.

RESULTS

In vivo experiments demonstrated that chronic levodopa treatment reduced AMPK phosphorylation, impaired autophagosome-lysosomal fusion and caused FosB-ΔFosB accumulation in the striatum of PD rats. Long-term metformin intervention improved ALO AIMs scores as well as reduced the mean power of high gamma (hγ) oscillations and the proportion of striatal projection neurons unstable in response to dopamine for LID rats. Moreover, the intervention of metformin promoted AMPK phosphorylation, ameliorated the impairment of autophagosome-lysosomal fusion, thus, promoting FosB-ΔFosB degradation to attenuate its accumulation in the striatum of LID rats. However, the aforementioned roles of metformin were reversed by Compound C and chloroquine. The results of in vitro studies demonstrated the ability of metformin and AICAR to attenuate ΔFosB levels by promoting its degradation, while Compound C and chloroquine could block this effect.

CONCLUSIONS

In conclusion, our results suggest that long-term metformin treatment could promote ΔFosB degradation and thus attenuate the development of LID through activating the AMPK-mediated autophagy pathway. Overall, our results support the AMPK-mediated autophagy pathway as a novel therapeutic target for LID and also indicate that metformin is a promising therapeutic candidate for LID.

Activation of mGlu2/3 receptors in the striatum alleviates L-DOPA-induced dyskinesia and inhibits abnormal postsynaptic molecular expression

Group II metabotropic glutamate receptors (mGlu2/3 receptors) have been regarded as promising candidates for the treatment of L-DOPA-induced dyskinesia (LID); however, confirmation is still lacking. As the hub of the basal ganglia circuit, the striatum plays a critical role in action control. Supersensitive responsiveness of glutamatergic corticostriatal input may be the key mechanism for the development of LID. In this study, we first examined the potency of LY354740 (12 mg/kg, i.p.) in modulating glutamate and dopamine release in lesioned striatum of stable LID rats. Then, we injected LY354740 (20nmoL or 40nmoL in 4 μL of sterile 0.9 % saline) directly into the lesioned striatum to verify its ability to reduce or attenuate L-DOPA-induced abnormal involuntary movements. In experiment conducted in established LID rats, after continuous injection for 4 days, we found that LY354740 significantly reduced the expression of dyskinesia. In another experiment conducted in parkinsonism rat models, we found that LY354740 attenuated the development of LID with an inverted-U dose-response curve. The role of LY354740 in modulating striatal expressions of LID-related molecular changes was also assessed after these behavioral experiments. We found that LY354740 significantly inhibited abnormal expressions of p-Fyn/p-NMDA/p-ERK1/2/p-HistoneH3/ΔFosB, which is in line with its ability to alleviate abnormal involuntary movements in both LID expression and induction phase. Our study indicates that activation of striatal mGlu2/3 receptors can attenuate the development of dyskinesia in parkinsonism rats and provide some functional improvements in LID rats by inhibiting LID-related molecular changes.

Cerebellar stimulation prevents Levodopa-induced dyskinesia in mice and normalizes activity in a motor network

Chronic Levodopa therapy, the gold-standard treatment for Parkinson's Disease (PD), leads to the emergence of involuntary movements, called levodopa-induced dyskinesia (LID). Cerebellar stimulation has been shown to decrease LID severity in PD patients. Here, in order to determine how cerebellar stimulation induces LID alleviation, we performed daily short trains of optogenetic stimulations of Purkinje cells (PC) in freely moving LID mice. We demonstrated that these stimulations are sufficient to suppress LID or even prevent their development. This symptomatic relief is accompanied by the normalization of aberrant neuronal discharge in the cerebellar nuclei, the motor cortex and the parafascicular thalamus. Inhibition of the cerebello-parafascicular pathway counteracted the beneficial effects of cerebellar stimulation. Moreover, cerebellar stimulation reversed plasticity in D1 striatal neurons and normalized the overexpression of FosB, a transcription factor causally linked to LID. These findings demonstrate LID alleviation and prevention by daily PC stimulations, which restore the function of a wide motor network, and may be valuable for LID treatment.

Carnosic Acid Alleviates Levodopa-Induced Dyskinesia and Cell Death in 6-Hydroxydopamine-lesioned Rats and in SH-SY5Y Cells

The present study investigated the impact of carnosic acid (CA) from rosemary on the levodopa (_L-dopa)-induced dyskinesia (LID) in rats treated with 6-hydroxydopamine (6-OHDA). To establish the model of LID, 6-OHDA-lesioned rats were injected intraperitoneally with 30 mg/kg _L-dopa once a day for 36 days. Rats were daily administrated with 3 or 15 mg/kg CA by oral intubation prior to _L-dopa injection for 4 days. Rats pretreated with CA had reduced _L-dopa-induced abnormal involuntary movements (AIMs) and ALO scores (a sum of axial, limb, and orofacial scores). Moreover, the increases of dopamine D1-receptor, p-DARPP-32, ΔFosB, p-ERK1/2, and p-c-Jun ser63, along with the decrease in p-c-Jun ser73, induced by _L-dopa in 6-OHDA-treated rats were significantly reversed by pretreatment with CA. In addition, we used the model of SH-SY5Y cells to further examine the neuroprotective mechanisms of CA on _L-dopa-induced cytotoxicity. SH-SY5Y cells were treated with CA for 18 h, and then co-treated with 400 μM _L-dopa for the indicated time points. The results showed that pretreatment of CA attenuated the cell death and nuclear condensation induced by _L-dopa. By the immunoblots, the reduction of Bcl-2, p-c-Jun ser73, and parkin and the induction of cleaved caspase 3, cleaved Poly (ADP-ribose) polymerase, p-ERK1/2, p-c-Jun ser63, and ubiquitinated protein by _L-dopa were improved in cells pretreated with CA. In conclusion, CA ameliorates the development of LID via regulating the D1R signaling and prevents _L-dopa-induced apoptotic cell death through modulating the ERK1/2-c-Jun and inducing the parkin. This study suggested that CA can be used to alleviate the adverse effects of LID for PD patients.

Striatal Control of Movement: A Role for New Neuronal (Sub-) Populations?

The striatum is a very heterogenous brain area, composed of different domains and compartments, albeit lacking visible anatomical demarcations. Two populations of striatal spiny projection neurons (SPNs) build the so-called direct and indirect pathway of the basal ganglia, whose coordinated activity is essential to control locomotion. Dysfunction of striatal SPNs is part of many movement disorders, such as Parkinson’s disease (PD) and L-DOPA-induced dyskinesia. In this mini review article, I will highlight recent studies utilizing single-cell RNA sequencing to investigate the transcriptional profiles of striatal neurons. These studies discover that SPNs carry a transcriptional signature, indicating both their anatomical location and compartmental identity. Furthermore, the transcriptional profiles reveal the existence of additional distinct neuronal populations and previously unknown SPN sub-populations. In a parallel development, studies in rodent models of PD and L-DOPA-induced dyskinesia (LID) report that direct pathway SPNs do not react uniformly to L-DOPA therapy, and that only a subset of these neurons is underlying the development of abnormal movements. Together, these studies demonstrate a new level of cellular complexity for striatal (dys-) function and locomotor control.

Initiation of L-DOPA Treatment After Detection of Diabetes-Induced Retinal Dysfunction Reverses Retinopathy and Provides Neuroprotection in Rats

Purpose

L-DOPA treatment initiated at the start of hyperglycemia preserves retinal and visual function in diabetic rats. Here, we investigated a more clinically relevant treatment strategy in which retinal and visual dysfunction designated the beginning of the therapeutic window for L-DOPA treatment.

Methods

Spatial frequency thresholds using optomotor response and oscillatory potential (OP) delays using electroretinograms were compared at baseline, 3, 6, and 10 weeks after streptozotocin (STZ) between diabetic and control rats. L-DOPA/carbidopa treatment (DOPA) or vehicle was delivered orally 5 days per week beginning at 3 weeks after STZ, when significant retinal and visual deficits were measured. At 10 weeks after STZ, retinas were collected to measure L-DOPA, dopamine, and 3,4-dihydroxyphenylacetic acid (DOPAC) levels using high-performance liquid chromatography.

Results

Spatial frequency thresholds decreased at 6 weeks in diabetic vehicle rats (28%), whereas diabetic DOPA rats had stable thresholds (<1%) that maintained to 10 weeks, creating significantly higher thresholds compared with diabetic vehicle rats (P < 0.0001). OP2 implicit times in response to dim, rod-driven stimuli were decreased in diabetic compared with control rats (3 weeks, P < 0.0001; 10 weeks, P < 0.01). With L-DOPA treatment, OP2 implicit times recovered in diabetic rats to be indistinguishable from control rats by 10 weeks after STZ. Rats treated with L-DOPA showed significantly increased retinal L-DOPA (P < 0.001) and dopamine levels (P < 0.05).

Conclusions

L-DOPA treatment started after the detection of retinal and visual dysfunction showed protective effects in diabetic rats.

Translational Relevance

Early retinal functional deficits induced by diabetes can be used to identify an earlier therapeutic window for L-DOPA treatment which protects from further vision loss and restores retinal function.

Striatal ΔFosB gene suppression inhibits the development of abnormal involuntary movements induced by L-Dopa in rats

L-Dopa-induced dyskinesia (LID) is associated with upregulation of striatal ΔFosB in animal models and patients with Parkinson’s disease (PD). A mechanistic role of ΔFosB is suspected because its transgenic overexpression leads to early appearance of LID in rodents and primates. The present study in rodents is aimed at exploring the therapeutic potential of striatal ΔFosB gene suppression to control LID in patients with PD. To determine the effect of reducing striatal ΔFosB expression, we used RNAi gene knockdown in a rat model of PD and assessed abnormal involuntary movements (AIMs) in response to L-Dopa. Rats with dopamine depletion received striatal injections of rAAV-ΔFosB shRNA or a control virus before exposure to chronic L-Dopa treatment. Development of AIMs during the entire L-Dopa treatment period was markedly inhibited by ΔFosB gene knockdown and its associated molecular changes. The antiparkinsonian action of L-Dopa was unchanged by ΔFosB gene knockdown. These results suggest a major role for ΔFosB in the development of LID, and support exploring strategies to reduce striatal ΔFosB levels in patients with PD.

Transcriptomic approach predicts a major role for transforming growth factor beta type 1 pathway in L-Dopa-induced dyskinesia in parkinsonian rats

Dyskinesia induced by long-term L-Dopa (LID) therapy in Parkinson disease is associated with altered striatal function whose molecular bases remain unclear. Here, a transcriptomic approach was applied for comprehensive analysis of distinctively regulated genes in striatal tissue, their specific pathways, and functional- and disease-associated networks in a rodent model of LID. This approach has identified transforming growth factor beta type 1 (TGFβ1) as a highly upregulated gene in dyskinetic animals. TGFβ1 pathway is a top aberrantly regulated pathway in the striatum following LID development based on differentially expressed genes (> 1.5 fold change and P < 0.05). The induction of TGFβ1 pathway specific genes, TGFβ1, INHBA, AMHR2 and PMEPA1 was also associated with regulation of NPTX2, PDP1, SCG2, SYNPR, TAC1, TH, TNNT1 genes. Transcriptional network and upstream regulator analyses have identified AKT-centered functional and ERK-centered disease networks revealing the association of TGFβ1, IL-1β and TNFα with LID development. Therefore, results support that TGFβ1 pathway is a major contributor to the pathogenic mechanisms of LID.

Dopamine D1 receptor signalling in dyskinetic Parkinsonian rats revealed by fiber photometry using FRET-based biosensors

As with many G protein-coupled receptors (GPCRs), the signalling pathways regulated by the dopamine D1 receptor (D1R) are dynamic, cell type-specific, and can change in the face of disease or drug exposures. In striatal neurons, the D1R activates cAMP/protein kinase A (PKA) signalling. However, in Parkinson's disease (PD), alterations in this pathway lead to functional upregulation of extracellular regulated kinases 1/2 (ERK1/2), contributing to L-DOPA-induced dyskinesia (LID). In order to detect D1R activation in vivo and to study the progressive dysregulation of D1R signalling in PD and LID, we developed ratiometric fiber-photometry with Förster resonance energy transfer (FRET) biosensors and optically detected PKA and ERK1/2 signalling in freely moving rats. We show that in Parkinsonian animals, D1R signalling through PKA and ERK1/2 is sensitized, but that following chronic treatment with L-DOPA, these pathways become partially desensitized while concurrently D1R activation leads to greater induction of dyskinesia.

Discovery of phenanthridine analogues as novel chemical probes disrupting the binding of DNA to ΔFosB homodimers and ΔFosB/JunD heterodimers

The transcription factor ΔFosB accumulates in response to chronic insults such as drugs of abuse, L-3,4-dihydroxyphenylalanine (l-DOPA) or stress in specific regions of the brain, triggering long lasting neural and behavioral changes that underlie aspects of drug addiction, dyskinesia, and depression. Thus, small molecule chemical probes are urgently needed to investigate biological functions of ΔFosB. Herein we describe the identification of a novel phenanthridine analogue ZL0220 (27) as an active and promising ΔFosB chemical probe with micromolar inhibitory activities against ΔFosB homodimers and ΔFosB/JunD heterodimers.

Striatal Nurr1, but not FosB expression links a levodopa-induced dyskinesia phenotype to genotype in Fisher 344 vs. Lewis hemiparkinsonian rats

Numerous genes, and alterations in their expression, have been identified as risk factors for developing levodopa-induced dyskinesia (LID). However, our understanding of the complexities of molecular changes remains insufficient for development of clinical treatment. In the current study we used gene array, in situ hybridization, immunohistochemistry, and microdialysis to provide a unique compare and contrast assessment of the relationship of four candidate genes to LID, employing three genetically distinct rat strains (Sprague-Dawley (SD), Fischer-344 (F344) and Lewis-RT.1) showing differences in dyskinesia susceptibility and 'first-ever LID' versus 'chronic LID' expression in subjects displaying equal dyskinesia severity. In these studies, rat strains were easily distinguishable for their LID propensity with: 1) a majority of SD rats expressing LID (LID+) and a subset being resistant (LID-); 2) all F344 rats readily developing (LID+); and 3) all Lewis rats being LID-resistant (LID-). Following chronic levodopa, LID+ SD rats showed significant increases in candidate gene expression: Nr4a2/(Nurr1) > > Trh > Inhba = Fosb. However, SD rats with long-standing striatal dopamine (DA) depletion treated with first-ever versus chronic high-dose levodopa revealed that despite identical levels of LID severity: 1) Fosb and Nurr1 transcripts but not protein were elevated with acute LID expression; 2) FOSB/ΔFOSB and NURR1 proteins were elevated only with chronic LID; and 3) Trh transcript and protein were elevated only with chronic LID. Strikingly, despite similar levodopa-induced striatal DA release in both LID-expressing F344 and LID-resistant Lewis rats, Fosb, Trh, Inhba transcripts were significantly elevated in both strains; however, Nurr1 mRNA was significantly increased only in LID+ F344 rats. These findings suggest a need to reevaluate currently accepted genotype-to-phenotype relationships in the expression of LID, specifically that of Fosb, a transcription factor generally assumed to play a causal role, and Nurr1, a transcription factor that has received significant attention in PD research linked to its critical role in the survival and function of midbrain DA neurons but who's striatal expression, generally below levels of detection, has remained largely unexplored as a regulator of LID. Finally these studies introduce a novel 'model' (inbred F344 vs inbred Lewis) that may provide a powerful tool for investigating the role for 'dyskinesia-resistance' genes downstream of 'dyskinesia-susceptibility' genes in modulating LID expression, a concept that has received considerably less attention and offers a new ways of thinking about antidyskinetic therapies.

mGluR5 Allosteric Modulation Promotes Neurorecovery in a 6-OHDA-Toxicant Model of Parkinson's Disease

Parkinson's disease is a neurodegenerative disease characterized by a loss of dopaminergic substantia nigra neurons and depletion of dopamine. To date, current therapeutic approaches focus on managing motor symptoms and trying to slow neurodegeneration, with minimal capacity to promote neurorecovery. mGluR5 plays a key role in neuroplasticity, and altered mGluR5 signaling contributes to synucleinopathy and dyskinesia in patients with Parkinson's disease. Here, we tested whether the mGluR5-negative allosteric modulator, (2-chloro-4-[2[2,5-dimethyl-1-[4-(trifluoromethoxy) phenyl] imidazol-4-yl] ethynyl] pyridine (CTEP), would be effective in improving motor deficits and promoting neural recovery in a 6-hydroxydopamine (6-OHDA) mouse model. Lesions were induced by 6-ODHA striatal infusion, and 30 days later treatment with CTEP (2 mg/kg) or vehicle commenced for either 1 or 12 weeks. Animals were subjected to behavioral, pathological, and molecular analyses. We also assessed how long the effects of CTEP persisted, and finally, using rapamycin, determined the role of the mTOR pathway. CTEP treatment induced a duration-dependent improvement in apomorphine-induced rotation and performance on rotarod in lesioned mice. Moreover, CTEP promoted a recovery of striatal tyrosine hydroxylase-positive fibers and normalized FosB levels in lesioned mice. The beneficial effects of CTEP were paralleled by an activation of mammalian target of rapamycin (mTOR) pathway and elevated brain-derived neurotrophic factor levels in the striatum of lesioned mice. The mTOR inhibitor, rapamycin (sirolimus), abolished CTEP-induced neurorecovery and rescue of motor deficits. Our findings indicate that mTOR pathway is a useful target to promote recovery and that mGluR5 allosteric regulators may potentially be repurposed to selectively target this pathway to enhance neuroplasticity in patients with Parkinson's disease.

Knock-Down of GPR88 in the Dorsal Striatum Alters the Response of Medium Spiny Neurons to the Loss of Dopamine Input and L-3-4-Dyhydroxyphenylalanine

The effects of L-3-4-dyhydroxyphenylalanine (L-DOPA) treatment for replacing the dopamine (DA) loss in Parkinson’s disease (PD) progressively wear off and are hindered by the development of dyskinesia, prompting the search for new treatments. The orphan G protein-coupled receptor 88 (Gpr88) represents a potential new target, as it is highly and almost exclusively expressed in the projecting gamma-Aminobutyric Acid-ergic (GABAergic) medium spiny neurons of the striatum, is implicated in motor activity, and is downregulated by 6-hydroxydopamine (6-OHDA) lesions, an effect that is reversed by L-DOPA. Thus, to evaluate Gpr88 as a potential target for the management of PD and L-DOPA–induced dyskinesia (LID), we inactivated Gpr88 by lentiviral-mediated knock-down with a specifically designed microRNA (miR) (KD-Gpr88) in a 6-OHDA rat model of hemiparkinsonism. Then, we investigated the effects of the KD-Gpr88 in the DA-deprived dorsal striatum on circling behavior and LID as well as on specific markers of striatal neuron activity. The KD-Gpr88 reduced the acute amphetamine-induced and increased L-DOPA–induced turning behavior. Moreover, it normalized the upregulated expression of striatal Gad67 and proenkephalin provoked by the 6-OHDA lesion. Finally, despite promoting ΔFosB accumulation, the KD-Gpr88 was associated neither with the upregulation of prodynorphin, which is causally linked to the severity of LID, nor with the aggravation of LID following chronic L-DOPA treatment in 6-OHDA–lesioned rats. These results thus justify further evaluation of Gpr88 as a potentially novel target for the management of PD as an alternative to L-DOPA therapy.

The Rodent Models of Dyskinesia and Their Behavioral Assessment

Dyskinesia, a major motor complication resulting from dopamine replacement treatment, manifests as involuntary hyperkinetic or dystonic movements. This condition poses a challenge to the treatment of Parkinson's disease. So far, several behavioral models based on rodent with dyskinesia have been established. These models have provided an important platform for evaluating the curative effect of drugs at the preclinical research level over the past two decades. However, there are differences in the modeling and behavioral testing procedures among various laboratories that adversely affect the rat and mouse models as credible experimental tools in this field. This article systematically reviews the history, the pros and cons, and the controversies surrounding rodent models of dyskinesia as well as their behavioral assessment protocols. A summary of factors that influence the behavioral assessment in the rodent dyskinesia models is also presented, including the degree of dopamine denervation, stereotaxic lesion sites, drug regimen, monitoring styles, priming effect, and individual and strain differences. Besides, recent breakthroughs like the genetic mouse models and the bilateral intoxication models for dyskinesia are also discussed.

Role of striatal ΔFosB in l-Dopa-induced dyskinesias of parkinsonian nonhuman primates

Long-term dopamine (DA) replacement therapy in Parkinson's disease (PD) leads to the development of abnormal involuntary movements known as l-Dopa-induced dyskinesia (LID). The transcription factor ΔFosB that is highly up-regulated in the striatum following chronic l-Dopa exposure may participate in the mechanisms of altered neuronal responses to DA generating LID. To identify intrinsic effects of elevated ΔFosB on l-Dopa responses, we induced transgenic ΔFosB overexpression in the striatum of parkinsonian nonhuman primates kept naïve of l-Dopa treatment. Elevated ΔFosB levels led to consistent appearance of LID since the initial acute l-Dopa tests. In line with this motor response, striatal projection neurons (SPNs) responded to DA with changes in firing frequency that reversed at the peak of the motor response, and these unstable SPN activity changes in response to DA are typically associated with the emergence of LID. Transgenic ΔFosB overexpression also induced up-regulation of other molecular markers of LID. These results support an autonomous role of striatal ΔFosB in the adaptive mechanisms altering motor responses to chronic DA replacement in PD.

VGLUT3 gates psychomotor effects induced by amphetamine

Several subtypes of modulatory neurons co-express vesicular glutamate transporters (VGLUTs) in addition to their cognate vesicular transporters. These neurons are believed to establish new forms of neuronal communication. The atypical VGLUT3 is of particular interest since in the striatum this subtype is found in tonically active cholinergic interneurons (TANs) and in a subset of 5-HT fibers. The striatum plays a major role in psychomotor effects induced by amphetamine. Whether and how VGLUT3-operated glutamate/ACh or glutamate/5HT co-transmissions modulates psychostimulants-induced maladaptive behaviors is still unknown. Here, we investigate the involvement of VGLUT3 and glutamate co-transmission in amphetamine-induced psychomotor effects and stereotypies. Taking advantage of constitutive and cell-type specific VGLUT3-deficient mouse lines, we tackled the hypothesis that VGLUT3 could gate psychomotor effects (locomotor activity and stereotypies) induced by acute or chronic administration of amphetamine. Interestingly, VGLUT3-null mice demonstrated blunted amphetamine-induced stereotypies as well as reduced striatal ∆FosB expression. VGLUT3-positive varicosities within the striatum arise in part from 5HT neurons. We tested the involvement of VGLUT3 deletion in serotoninergic neurons in amphetamine-induced stereotypies. Mice lacking VGLUT3 specifically in 5HT fibers showed no alteration to amphetamine sensitivity. In contrast, specific deletion of VGLUT3 in cholinergic neurons partially phenocopied the effects observed in the constitutive knock-out mice. Our results show that constitutive deletion of VGLUT3 modulates acute and chronic locomotor effects induced by amphetamine. They point to the fact that the expression of VGLUT3 in multiple brain areas is pivotal in gating amphetamine-induced psychomotor adaptations. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Differential Expression of Striatal ΔFosB mRNA and FosB mRNA After Different Levodopa Treatment Regimens in a Rat Model of Parkinson's Disease

Levodopa-induced dyskinesia (LID) is the main side effect associated with levodopa treatment and represents the biggest challenge for Parkinson's disease therapy. While the overexpression of ΔFosB transcription factor is related to the development of LID, few studies have been undertaken on fosB gene transcriptional regulation induced by levodopa in vivo. The aim of this study is to evaluate the expression of ΔFosB mRNA and FosB mRNA in the striatum after acute, chronic, and subchronic levodopa treatment in rats with unilateral 6-OHDA-lesion in the medial forebrain bundle. qRT-PCR was used to compare the levels of ΔFosB and FosB mRNA expression in the dopamine-denervated striatum following levodopa treatment. While the results obtained after a single levodopa dose indicate a significant increase of ∆FosB mRNA expression in the striatum 1 h post-injection, the levels returned to baseline values after 24 h. After subchronic levodopa treatment, the levels of ∆FosB and FosB mRNA expression were lower 1 h post-administration of levodopa in comparison with acute effect. However, after chronic levodopa treatment, ∆FosB mRNA expression in the striatum persisted in dyskinetic rats only, and positive correlation was found between the levels of ∆FosB mRNA expression 1 h after levodopa administration and the level of dyskinetic severity. In summary, acute levodopa treatment led to highly increased levels of ∆FosB mRNA expression in the striatum. While repeated administration induced a partial desensitization of the fosB gene in the striatum, it did not suppress its activity completely, which could explain why dyskinesia appears after chronic levodopa treatment.

TRH Analog, Taltirelin Improves Motor Function of Hemi-PD Rats Without Inducing Dyskinesia via Sustained Dopamine Stimulating Effect

Thyrotropin-releasing hormone (TRH) and its analogs are able to stimulate the release of the endogenic dopamine (DA) in the central nervous system. However, this effect has not been tested in the Parkinson’s disease (PD), which is characterized by the DA deficiency due to the dopaminergic neurons loss in the substantia nigra. Here, we investigated the therapeutic effect of Taltirelin, a long-acting TRH analog on 6-hydroxydopamine-lesioned hemi-Parkinsonian rat model. 1–10 mg/kg Taltirelin i.p. administration significantly improved the locomotor function and halted the electrophysiological abnormities of PD animals without inducing dyskinesia even with high-dose for 7 days treatment. Microdialysis showed that Taltirelin gently and persistently promoted DA release in the cortex and striatum, while L-DOPA induced a sharp rise of DA especially in the cortex. The DA-releasing effect of Taltirelin was alleviated by reserpine, vanoxerine (GBR12909) or AMPT, indicating a mechanism involving vesicular monoamine transporter-2 (VMAT-2), dopamine transporter (DAT) and tyrosine hydroxylase (TH). The in vivo and in vitro experiments further supported that Taltirelin affected the regulation of TH expression in striatal neurons, which was mediated by p-ERK1/2. Together, this study demonstrated that Taltirelin improved motor function of hemi-PD rats without inducing dyskinesia, thus supporting a further exploration of Taltirelin for PD treatment.

A MAPK/c-Jun-mediated switch regulates the initial adaptive and cell death responses to mitochondrial damage in a neuronal cell model

Parkinson's disease (PD) is defined by the progressive loss of dopaminergic neurons. Mitochondrial dysfunction and oxidative stress are associated with PD although it is not fully understood how neurons respond to these stresses. How adaptive and apoptotic neuronal stress response pathways are regulated and the thresholds at which they are activated remains ambiguous. Utilising SH-SY5Y neuroblastoma cells, we show that MAPK/AP-1 pathways are critical in regulating the response to mitochondrial uncoupling. Here we found the AP-1 transcription factor c-Jun can act in either a pro- or anti-apoptotic manner, depending on the level of stress. JNK-mediated cell death in differentiated cells only occurred once a threshold of stress was surpassed. We also identified a novel feedback loop between Parkin activity and the c-Jun response, suggesting defective mitophagy may initiate MAPK/c-Jun-mediated neuronal loss observed in PD. Our data supports the hypothesis that blocking cell death pathways upstream of c-Jun as a therapeutic target in PD may not be appropriate due to crossover of the pro- and anti-apoptotic responses. Boosting adaptive responses or targeting specific aspects of the neuronal death response may therefore represent more viable therapeutic strategies.

Striatonigral neurons divide into two distinct morphological-physiological phenotypes after chronic L-DOPA treatment in parkinsonian rats

Dendritic regression of striatal spiny projection neurons (SPNs) is a pathological hallmark of Parkinson's disease (PD). Here we investigate how chronic dopamine denervation and dopamine replacement with L-DOPA affect the morphology and physiology of direct pathway SPNs (dSPNS) in the rat striatum. We used a lentiviral vector optimized for retrograde labeling (FuG-B-GFP) to identify dSPNs in rats with 6-hydroxydopamine (6-OHDA) lesions. Changes in morphology and physiology of dSPNs were assessed through a combination of patch-clamp recordings and two photon microscopy. The 6-OHDA lesion caused a significant reduction in dSPN dendritic complexity. Following chronic L-DOPA treatment, dSPNs segregated into two equal-sized clusters. One group (here called "cluster-1"), showed sustained dendritic atrophy and a partially normalized electrophysiological phenotype. The other one ("cluster-2") exhibited dendritic regrowth and a strong reduction of intrinsic excitability. Interestingly, FosB/∆FosB induction by L-DOPA treatment occurred preferentially in cluster-2 dSPNs. Our study demonstrates the feasibility of retrograde FuG-B-GFP labeling to study dSPNs in the rat and reveals, for the first time, that a subgroup of dSPNs shows dendritic sprouting in response to chronic L-DOPA treatment. Investigating the mechanisms and significance of this response will greatly improve our understanding of the adaptations induced by dopamine replacement therapy in PD.

CaMKII inhibition ameliorated levodopa-induced dyskinesia by downregulating tyrosine hydroxylase activity in an experimental model of Parkinson's disease

Levodopa (L-dopa) remains the best treatment for Parkinson's disease (PD). However, long-term L-dopa treatment induces dyskinesia. The mechanism of L-dopa-induced dyskinesia (LID) is not fully understood. Enhanced activity of protein kinase A (PKA) and pulsatile dopamine (DA) stimulation plays an important role in LID. Tyrosine hydroxylase (TH) is the rate-limiting enzyme for DA synthesis. Decreased TH activity causes reduced pulsatile DA stimulation, which in turn reduces LID. Moreover, TH is a substrate of CaMKII. However, it is unknown whether inhibition of CaMKII reduces LID by downregulating the activity of TH. In this study, we found that CaMKII antagonist KN-93 reduced DA released in PC12 cells; in the meantime, KN-93 reduced phosphorylated levels of CaMKIIα and TH at Ser 40. Intrastriatal administration of KN-93 reduced LID without affecting the antiparkinsonian effect of L-dopa in PD mice. Mechanistically, KN-93 treatmentreduced phosphorylated CaMKIIα levels and subsequently downregulated phosphorylated TH at Ser 40 expression. Consequently, extracellular DA efflux was reduced andthe activation threshold of the PKA pathway was lowered. Moreover, KN-93 treatment reduced the expression of Arc and Penk, two immediate early genes, induced by chronic L-dopa. These data indicate that inhibition of CaMKIIα decreases LID at least partially by suppressing TH activity and subsequently reducing extracellular DA efflux and the activity of the PKA pathway, suggesting that CaMKIIα may be an alternative target for the treatment of LID.

Signal transduction in L-DOPA-induced dyskinesia: from receptor sensitization to abnormal gene expression

A large number of signaling abnormalities have been implicated in the emergence and expression of l-DOPA-induced dyskinesia (LID). The primary cause for many of these changes is the development of sensitization at dopamine receptors located on striatal projection neurons (SPN). This initial priming, which is particularly evident at the level of dopamine D1 receptors (D1R), can be viewed as a homeostatic response to dopamine depletion and is further exacerbated by chronic administration of l-DOPA, through a variety of mechanisms affecting various components of the G-protein-coupled receptor machinery. Sensitization of dopamine receptors in combination with pulsatile administration of l-DOPA leads to intermittent and coordinated hyperactivation of signal transduction cascades, ultimately resulting in long-term modifications of gene expression and protein synthesis. A detailed mapping of these pathological changes and of their involvement in LID has been produced during the last decade. According to this emerging picture, activation of sensitized D1R results in the stimulation of cAMP-dependent protein kinase and of the dopamine- and cAMP-regulated phosphoprotein of 32 kDa. This, in turn, activates the extracellular signal-regulated kinases 1 and 2 (ERK), leading to chromatin remodeling and aberrant gene transcription. Dysregulated ERK results also in the stimulation of the mammalian target of rapamycin complex 1, which promotes protein synthesis. Enhanced levels of multiple effector targets, including several transcription factors have been implicated in LID and associated changes in synaptic plasticity and morphology. This article provides an overview of the intracellular modifications occurring in SPN and associated with LID.

A Subpopulation of Striatal Neurons Mediates Levodopa-Induced Dyskinesia

Parkinson's disease is characterized by the progressive loss of midbrain dopamine neurons. Dopamine replacement therapy with levodopa alleviates parkinsonian motor symptoms but is complicated by the development of involuntary movements, termed levodopa-induced dyskinesia (LID). Aberrant activity in the striatum has been hypothesized to cause LID. Here, to establish a direct link between striatal activity and dyskinesia, we combine optogenetics and a method to manipulate dyskinesia-associated neurons, targeted recombination in active populations (TRAP). We find that TRAPed cells are a stable subset of sensorimotor striatal neurons, predominantly from the direct pathway, and that reactivation of TRAPed striatal neurons causes dyskinesia in the absence of levodopa. Inhibition of TRAPed cells, but not a nonspecific subset of direct pathway neurons, ameliorates LID. These results establish that a distinct subset of striatal neurons is causally involved in LID and indicate that successful therapeutic strategies for treating LID may require targeting functionally selective neuronal subtypes.

Reprogramming neurodegeneration in the big data era

Recent genome-wide association studies (GWAS) have identified numerous genetic risk variants for late-onset Alzheimer's disease (AD) and Parkinson's disease (PD). However, deciphering the functional consequences of GWAS data is challenging due to a lack of reliable model systems to study the genetic variants that are often of low penetrance and non-coding identities. Pluripotent stem cell (PSC) technologies offer unprecedented opportunities for molecular phenotyping of GWAS variants in human neurons and microglia. Moreover, rapid technological advances in whole-genome RNA-sequencing and epigenome mapping fuel comprehensive and unbiased investigations of molecular alterations in PSC-derived disease models. Here, we review and discuss how integrated studies that utilize PSC technologies and genome-wide approaches may bring new mechanistic insight into the pathogenesis of AD and PD.

Animal models of L-DOPA-induced dyskinesia: the 6-OHDA-lesioned rat and mouse

Appearance of L-DOPA-induced dyskinesia (LID) represents a major limitation in the pharmacological therapy with the dopamine precursor L-DOPA. Indeed, the vast majority of parkinsonian patients develop dyskinesia within 9-10 years of L-DOPA oral administration. This makes the discovery of new therapeutic strategies an important need. In the last decades, several animal models of Parkinson's disease (PD) have been developed, to both study mechanisms underlying PD pathology and treatment-induced side effects (i.e., LID) and to screen for new potential anti-parkinsonian and anti-dyskinetic treatments. Among all the models developed, the 6-OHDA-lesioned rodents represent the models of choice to mimic PD motor symptoms and LID, thanks to their reproducibility and translational value. Under L-DOPA treatment, rodents sustaining 6-OHDA lesions develop abnormal involuntary movements with dystonic and hyperkinetic features, resembling what seen in dyskinetic PD patients. These models have been extensively validated by the evidence that dyskinetic behaviors are alleviated by compounds reducing dyskinesia in patients and non-human primate models of PD. This article will focus on the translational value of the 6-OHDA rodent models of LID, highlighting their main features, advantages and disadvantages in preclinical research.

Antidyskinetic Effects of MEK Inhibitor Are Associated with Multiple Neurochemical Alterations in the Striatum of Hemiparkinsonian Rats

L-DOPA-induced dyskinesia (LID) represents one of the major problems of the long-term therapy of patients with Parkinson's disease (PD). Although, the pathophysiologic mechanisms underlying LID are not completely understood, activation of the extracellular signal regulated kinase (ERK) is recognized to play a key role. ERK is phosphorylated by mitogen-activated protein kinase kinase (MEK), and thus MEK inhibitor can prevent ERK activation. Here the effect of the MEK inhibitor PD98059 on LID and the associated molecular changes were examined. Rats with unilateral 6-OHDA lesions of the nigrostriatal pathway received daily L-DOPA treatment for 3 weeks, and abnormal involuntary movements (AIMs) were assessed every other day. PD98059 was injected in the lateral ventricle daily for 12 days starting from day 10 of L-DOPA treatment. Striatal molecular markers of LID were analyzed together with gene regulation using microarray. The administration of PD98059 significantly reduced AIMs. In addition, ERK activation and other associated molecular changes including ΔFosB were reversed in rats treated with the MEK inhibitor. PD98059 induced significant up-regulation of 418 transcripts and down-regulation of 378 transcripts in the striatum. Tyrosine hydroxylase (Th) and aryl hydrocarbon receptor nuclear translocator (Arnt) genes were down-regulated in lesioned animals and up-regulated in L-DOPA-treated animals. Analysis of protein levels showed that PD98059 reduced the striatal TH. These results support the association of p-ERK1/2, ΔFosB, p-H3 to the regulation of TH and ARNT in the mechanisms of LID, and pinpoint other gene regulatory changes, thus providing clues for identifying new targets for LID therapy.

Intrastriatal injection of ionomycin profoundly changes motor response to l-DOPA and its underlying molecular mechanisms

Long-term l-DOPA treatment of Parkinson's disease is accompanied with fluctuations of motor responses and l-DOPA-induced dyskinesia (LID). Phosphorylation of the dopamine and c-AMP regulated phosphoprotein of 32kDa (DARPP-32) plays a role in the pathogenesis of LID, and thus dephosphorylation of this protein by activated calcineurin may help reduce LID. One important activator of calcineurin is the Ca²⁺ ionophore ionomycin. Here, we investigated whether intrastriatal injection of ionomycin to hemiparkinsonian rats produced changes in l-DOPA responses including LID. We also analyzed the effects of ionomycin on key molecular mediators of LID. Results confirmed our hypothesis that ionomycin could downregulate the phosphorylation of DARPP32 at Thr-34 and reduce LID. Besides, ionomycin decreased two established molecular markers of LID, FosB/ΔFosB and phosphorylated ERK1/2. Ionomycin also decreased the phosphorylation of three main subunits of the NMDA receptor, NR1 phosphorylated at ser896, NR2A phosphorylated at Tyr-1325, and NR2B phosphorylated at Tyr-1472. Furthermore, the anti-LID effect of striatally injected ionomycin was not accompanied by reduction of the antiparkinsonian action of l-DOPA. These data indicate that ionomycin largely interacts with striatal mechanisms that are critical to the l-DOPA motor response highlighting the role of protein dephosphorylation by calcineurin.

G protein-coupled receptor kinases as regulators of dopamine receptor functions

Actions of the neurotransmitter dopamine in the brain are mediated by dopamine receptors that belong to the superfamily of G protein-coupled receptors (GPCRs). Mammals have five dopamine receptor subtypes, D1 through D5. D1 and D5 couple to Gs/olf and activate adenylyl cyclase, whereas D2, D3, and D4 couple to Gi/o and inhibit it. Most GPCRs upon activation by an agonist are phosphorylated by GPCR kinases (GRKs). The GRK phosphorylation makes receptors high-affinity binding partners for arrestin proteins. Arrestin binding to active phosphorylated receptors stops further G protein activation and promotes receptor internalization, recycling or degradation, thereby regulating their signaling and trafficking. Four non- visual GRKs are expressed in striatal neurons. Here we describe known effects of individual GRKs on dopamine receptors in cell culture and in the two in vivo models of dopamine-mediated signaling: behavioral response to psychostimulants and L-DOPA- induced dyskinesia. Dyskinesia, associated with dopamine super-sensitivity of striatal neurons, is a debilitating side effect of L-DOPA therapy in Parkinson's disease. In vivo, GRK subtypes show greater receptor specificity than in vitro or in cultured cells. Overexpression, knockdown, and knockout of individual GRKs, particularly GRK2 and GRK6, have differential effects on signaling of dopamine receptor subtypes in the brain. Furthermore, deletion of GRK isoforms in select striatal neuronal types differentially affects psychostimulant-induced behaviors. In addition, anti-dyskinetic effect of GRK3 does not require its kinase activity: it is mediated by the binding of its RGS-like domain to Gαq/11, which suppresses Gq/11 signaling. The data demonstrate that the dopamine signaling in defined neuronal types in vivo is regulated by specific and finely orchestrated actions of GRK isoforms.

Palmitoyl Serotonin Inhibits L-dopa-induced Abnormal Involuntary Movements in the Mouse Parkinson Model

L-3,4-dihydroxyphenylalanine (L-DOPA) is the most common treatment for patients with Parkinson's disease (PD). However, long term use of L-DOPA for PD therapy lead to abnormal involuntary movements (AIMs) known as dyskinesia. Fatty acid amide hydrolase (FAAH) is enriched protein in basal ganglia, and inhibition of the protein reduces dyskinetic behavior of mice. Palmitoyl serotonin (PA-5HT) is a hybrid molecule patterned after arachidonoyl serotonin, antagonist of FAAH. However, the effect of PA-5HT on L-DOPA-induced dyskinesia (LID) in PD have not yet been elucidated. To investigate whether PA-5HT relieve LID in PD and decrease hyperactivation of dopamine D1 receptors, we used the 6-hydroxydopomine (6-OHDA)-lesioned mouse model of PD and treated the L-DOPA (20 mg/kg) for 10 days with PA-5HT (0.3 mg/kg/day). The number of wall contacts with the forelimb in the cylinder test was significantly decreased by 6-OHDA lesion in mice and the pharmacotherapeutic effect of L-DOPA was also revealed in PA-5HT-treated mice. Moreover, in AIMs test, PA-5HT-treated mice showed significant reduction of locomotive, axial, limb, and orofacial AIMs score compared to the vehicle-treated mice. LID-induced hyper-phosphorylation of ERK1/2 and overexpression of FosB/ΔFosB was markedly decreased in 6-OHDA-lesioned striatum of PA-5HT-treated mice, indicating that PA-5HT decreased the dopamine D1 receptor-hyperactivation induced by chronic treatment of L-DOPA in dopamine-denervated striatum. These results suggest that PA-5HT effectively attenuates the development of LID and enhance of ERK1/2 phosphorylation and FosB/ΔFosB expression in the hemi-parkinsonian mouse model. PA-5HT may have beneficial effect on the LID in PD.

Inhibition of Glycogen Synthase Kinase-3β (GSK-3β) as potent therapeutic strategy to ameliorates L-dopa-induced dyskinesia in 6-OHDA parkinsonian rats

Levodopa (L-dopa) is the dominating therapy drug for exogenous dopaminergic substitution and can alleviate most of the manifestations of Parkinson's disease (PD), but long-term therapy is associated with the emergence of L-dopa-induced dyskinesia (LID). Evidence points towards an involvement of Glycogen Synthase Kinase-3β (GSK-3β) in development of LID. In the present study, we found that animals rendered dyskinetic by L-dopa treatment, administration of TDZD8 (2mg/kg) obviously prevented the severity of AIM score, as well as improvement in motor function (P < 0.05). Moreover, the TDZD8-induced reduction in dyskinetic behavior correlated with a reduction in molecular correlates of LID. TDZD8 reduced the phosphorylation levels of tau, DARPP32, ERK and PKA protein, which represent molecular markers of LID, as well as reduced L-dopa-induced FosB mRNA and PPEB mRNA levels in the lesioned striatum. In addition, we found that TDZD8 antidyskinetic properties were overcome by D1 receptor, as pretreatment with SKF38393 (5 mg/kg, 10 mg/kg, respectively), a D1 receptor agonist, blocked TDZD8 antidyskinetic actions. This study supported the hypothesis that GSK-3β played an important role in the development and expression of LID. Inhibition of GSK-3β with TDZD8 reduced the development of ALO AIM score and associated molecular changes in 6-OHDA-lesioned rats.

A Pharmacogenetic Discovery: Cystamine Protects Against Haloperidol-Induced Toxicity and Ischemic Brain Injury

Haloperidol is an effective antipsychotic agent, but it causes Parkinsonian-like extrapyramidal symptoms in the majority of treated subjects. To address this treatment-limiting toxicity, we analyzed a murine genetic model of haloperidol-induced toxicity (HIT). Analysis of a panel of consomic strains indicated that a genetic factor on chromosome 10 had a significant effect on susceptibility to HIT. We analyzed a whole-genome SNP database to identify allelic variants that were uniquely present on chromosome 10 in the strain that was previously shown to exhibit the highest level of susceptibility to HIT. This analysis implicated allelic variation within pantetheinase genes (Vnn1 and Vnn3), which we propose impaired the biosynthesis of cysteamine, could affect susceptibility to HIT. We demonstrate that administration of cystamine, which is rapidly metabolized to cysteamine, could completely prevent HIT in the murine model. Many of the haloperidol-induced gene expression changes in the striatum of the susceptible strain were reversed by cystamine coadministration. Since cystamine administration has previously been shown to have other neuroprotective actions, we investigated whether cystamine administration could have a broader neuroprotective effect. Cystamine administration caused a 23% reduction in infarct volume after experimentally induced cerebral ischemia. Characterization of this novel pharmacogenetic factor for HIT has identified a new approach for preventing the treatment-limiting toxicity of an antipsychotic agent, which could also be used to reduce the extent of brain damage after stroke.

A Role for Mitogen- and Stress-Activated Kinase 1 in L-DOPA-Induced Dyskinesia and ∆FosB Expression

BACKGROUND

Abnormal regulation of extracellular signal-regulated kinases 1 and 2 has been implicated in 3,4-dihydroxy-l-phenylalanine (L-DOPA)-induced dyskinesia (LID), a motor complication affecting Parkinson's disease patients subjected to standard pharmacotherapy. We examined the involvement of mitogen- and stress-activated kinase 1 (MSK1), a downstream target of extracellular signal-regulated kinases 1 and 2, and an important regulator of transcription in LID.

METHODS

6-Hydroxydopamine was used to produce a model of Parkinson's disease in MSK1 knockout mice and in ∆FosB- or ∆cJun-overexpressing transgenic mice, which were assessed for LID following long-term L-DOPA administration. Biochemical processes were evaluated by Western blotting or immunofluorescence. Histone H3 phosphorylation was analyzed by chromatin immunoprecipitation followed by promotor-specific quantitative polymerase chain reaction.

RESULTS

Genetic inactivation of MSK1 attenuated LID and reduced the phosphorylation of histone H3 at Ser10 in the striatum. Chromatin immunoprecipitation analysis showed that this reduction occurred at the level of the fosB gene promoter. In line with this observation, the accumulation of ∆FosB produced by chronic L-DOPA was reduced in MSK1 knockout. Moreover, inducible overexpression of ∆FosB in striatonigral medium spiny neurons exacerbated dyskinetic behavior, whereas overexpression of ∆cJun, which reduces ∆FosB-dependent transcriptional activation, counteracted LID.

CONCLUSIONS

Results indicate that abnormal regulation of MSK1 contributes to the development of LID and to the concomitant increase in striatal ∆FosB, which may occur via increased histone H3 phosphorylation at the fosB promoter. Results also show that accumulation of ∆FosB in striatonigral neurons is causally related to the development of dyskinesia.

Are cyclooxygenase-2 and nitric oxide involved in the dyskinesia of Parkinson's disease induced by L-DOPA?

Inflammatory mechanisms are proposed to play a role in L-DOPA-induced dyskinesia. Cyclooxygenase-2 (COX2) contributes to inflammation pathways in the periphery and is constitutively expressed in the central nervous system. Considering that inhibition of nitric oxide (NO) formation attenuates L-DOPA-induced dyskinesia, this study aimed at investigating if a NO synthase (NOS) inhibitor would change COX2 brain expression in animals with L-DOPA-induced dyskinesia. To this aim, male Wistar rats received unilateral 6-hydroxydopamine microinjection into the medial forebrain bundle were treated daily with L-DOPA (21 days) combined with 7-nitroindazole or vehicle. All hemi-Parkinsonian rats receiving l-DOPA showed dyskinesia. They also presented increased neuronal COX2 immunoreactivity in the dopamine-depleted dorsal striatum that was directly correlated with dyskinesia severity. Striatal COX2 co-localized with choline-acetyltransferase, calbindin and DARPP-32 (dopamine-cAMP-regulated phosphoprotein-32), neuronal markers of GABAergic neurons. NOS inhibition prevented L-DOPA-induced dyskinesia and COX2 increased expression in the dorsal striatum. These results suggest that increased COX2 expression after L-DOPA long-term treatment in Parkinsonian-like rats could contribute to the development of dyskinesia.

Gadd45β ameliorates L-DOPA-induced dyskinesia in a Parkinson's disease mouse model

The dopamine precursor 3,4-dihydroxyphenyl-l-alanine (L-DOPA) is currently the most efficacious pharmacotherapy for Parkinson's disease (PD). However, long-term L-DOPA treatment leads to the development of abnormal involuntary movements (AIMs) in patients and animal models of PD. Recently, involvement of growth arrest and DNA damage-inducible 45β (Gadd45β) was reported in neurological and neurobehavioral dysfunctions. However, little is known about the role of Gadd45β in the dopaminergic nigrostriatal pathway or L-DOPA-induced dyskinesia (LID). To address this issue, we prepared an animal model of PD using unilateral 6-hydroxydopamine (6-OHDA) lesions in the substantia nigra of Gadd45β(+/+) and Gadd45β(-/-) mice. Dyskinetic symptoms were triggered by repetitive administration of L-DOPA in these 6-OHDA-lesioned mice. Whereas dopamine denervation in the dorsal striatum decreased Gadd45β mRNA, chronic L-DOPA treatment significantly increased Gadd45β mRNA expression in the 6-OHDA-lesioned striatum of wild-type mice. Using unilaterally 6-OHDA-lesioned Gadd45β(+/+) and Gadd45β(-/-) mice, we found that mice lacking Gadd45β exhibited long-lasting increases in AIMs following repeated administration of L-DOPA. By contrast, adeno-associated virus-mediated expression of Gadd45β in the striatum reduced AIMs in Gadd45β knockout mice. The deficiency of Gadd45β in LID increased expression of ΔFosB and c-Fos in the lesioned striatum 90 min after the last administration of L-DOPA following 11days of daily L-DOPA treatments. These data suggest that the increased expression of Gadd45β induced by repeated administration of L-DOPA may be beneficial in patients with PD.

Aberrant epigenome in iPSC-derived dopaminergic neurons from Parkinson's disease patients

The epigenomic landscape of Parkinson's disease (PD) remains unknown. We performed a genomewide DNA methylation and a transcriptome studies in induced pluripotent stem cell (iPSC)-derived dopaminergic neurons (DAn) generated by cell reprogramming of somatic skin cells from patients with monogenic LRRK2-associated PD (L2PD) or sporadic PD (sPD), and healthy subjects. We observed extensive DNA methylation changes in PD DAn, and of RNA expression, which were common in L2PD and sPD. No significant methylation differences were present in parental skin cells, undifferentiated iPSCs nor iPSC-derived neural cultures not-enriched-in-DAn. These findings suggest the presence of molecular defects in PD somatic cells which manifest only upon differentiation into the DAn cells targeted in PD. The methylation profile from PD DAn, but not from controls, resembled that of neural cultures not-enriched-in-DAn indicating a failure to fully acquire the epigenetic identity own to healthy DAn in PD. The PD-associated hypermethylation was prominent in gene regulatory regions such as enhancers and was related to the RNA and/or protein downregulation of a network of transcription factors relevant to PD (FOXA1, NR3C1, HNF4A, and FOSL2). Using a patient-specific iPSC-based DAn model, our study provides the first evidence that epigenetic deregulation is associated with monogenic and sporadic PD.

Adolescent exposure to cocaine increases anxiety-like behavior and induces morphologic and neurochemical changes in the hippocampus of adult rats

Repeated exposure to cocaine during adolescence may affect both physical and psychological conditions in the brain, and increase the risk of psychiatric disorders and addiction behaviors in adulthood. Adolescence represents a critical development period for the hippocampus. Moreover, different regions of the hippocampus are involved in different functions. Dorsal hippocampus (dHP) has been implicated in learning and memory, whereas ventral hippocampus (vHP) plays an important role in emotional processing. In this study, the rats that were exposed to cocaine during adolescence (postnatal days, P28-P42) showed higher anxiety-like behavior in the elevated plus maze test in adulthood (P80), but displayed normal spatial learning and memory in the Morris water maze test. Furthermore, repeated exposure to cocaine during adolescence lead to alterations in morphology of pyramidal neurons, activities of astrocytes, and levels of proteins that involved in synaptic transmission, apoptosis, inflammation and addiction in both dHP and vHP of adult rats. These findings suggest that repeated exposure to cocaine during adolescence in rats may elicit morphologic and neurochemical changes in the hippocampus when the animals reach adulthood. These changes may contribute to the increased susceptibility for psychiatric disorders and addiction seen in adults.

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 Parkinson's 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.

GRK3 suppresses L-DOPA-induced dyskinesia in the rat model of Parkinson's disease via its RGS homology domain

Degeneration of dopaminergic neurons causes Parkinson's disease. Dopamine replacement therapy with L-DOPA is the best available treatment. However, patients develop L-DOPA-induced dyskinesia (LID). In the hemiparkinsonian rat, chronic L-DOPA increases rotations and abnormal involuntary movements modeling LID, via supersensitive dopamine receptors. Dopamine receptors are controlled by G protein-coupled receptor kinases (GRKs). Here we demonstrate that LID is attenuated by overexpression of GRK3 in the striatum, whereas knockdown of GRK3 by microRNA exacerbated it. Kinase-dead GRK3 and its separated RGS homology domain (RH) suppressed sensitization to L-DOPA, whereas GRK3 with disabled RH did not. RH alleviated LID without compromising anti-akinetic effect of L-DOPA. RH binds striatal Gq. GRK3, kinase-dead GRK3, and RH inhibited accumulation of ∆FosB, a marker of LID. RH-dead mutant was ineffective, whereas GRK3 knockdown exacerbated ∆FosB accumulation. Our findings reveal a novel mechanism of GRK3 control of the dopamine receptor signaling and the role of Gq in LID.

Intranigral administration of substance P receptor antagonist attenuated levodopa-induced dyskinesia in a rat model of Parkinson's disease

Levodopa (L-dopa) remains the most effective drug in the treatment of Parkinson's disease (PD). However, L-dopa-induced dyskinesia (LID) has hindered its use for PD patients. The mechanisms of LID are not fully understood. Substance P (SP) receptor antagonist has been shown to reduce parkinsonism in animal models of PD, and ameliorate LID in PD rats. But the concrete mechanism is not fully understood. To address this issue, we produced a rat model of PD using 6-hydroxydompamine (6-OHDA) injections, and valid PD rats were intranigrally administrated with different doses of SP receptor antagonist LY303870 (5 nmol/day, 10 nmol/day and 20 nmol/day) following L-dopa (6 mg/kg/day, i.p.) plus benserazide (12 mg/kg/day, i.p.) for 23 days. We found that nigral SP levels were increased on days 3, 7 and 14 and decreased on day 21 after 6-hydroxydompamine lesions. But nigral SP levels kept increasing after repeated L-dopa administration in PD rats. Intranigral administration of low and moderate LY303870 reduced abnormal involuntary movements (AIMs) while improving motor deficits in PD rats treated with L-dopa plus benserazide. Microdialysis revealed that LY303870 (10 nmol/day) treatment attenuated the increase of striatal dopamine and the reduction of γ-aminobutyric acid in ventromedial thalamus of PD rats primed with L-dopa. Additionally, LY303870 (10 nmol/day) treatment prior to L-dopa administration reduced the phosphorylated levels of dopamine- and cyclic adenosine monophosphate-regulated phosphoprotein of 32 kDa at Thr 34 and extracellular signal-regulated kinases 1/2 as well as the levels of activity-regulated cytoskeleton-associated protein and Penk in L-dopa-primed PD rats. Taken together, these data showed that low and moderate SP receptor antagonists LY303870 could ameliorate LID via neurokinin 1 receptor without affecting therapeutic effect of L-dopa.

Striatal tyrosine hydroxylase-positive neurons are associated with L-DOPA-induced dyskinesia in hemiparkinsonian mice

L-3,4-Dihydroxyphenylalanine (L-DOPA) is the therapeutic gold standard in Parkinson's disease. However, long-term treatment is complicated by the induction of debilitating abnormal involuntary movements termed L-DOPA-induced dyskinesias (LIDs). Until today the underlying mechanisms of LID pathogenesis are not fully understood. The aim of this study was to reveal new factors, which may be involved in the induction of LID. We have focused on the expression of striatal tyrosine hydroxylase-positive (TH+) neurons, which are capable of producing either L-DOPA or dopamine (DA) in target areas of ventral midbrain DAergic neurons. To address this issue, a daily L-DOPA dose was administered over the course of 15 days to mice with unilateral 6-hydroxydopamine-induced lesions of the medial forebrain bundle and LIDs were evaluated. Remarkably, the number of striatal TH+ neurons strongly correlated with both induction and severity of LID as well as ΔFosB expression as an established molecular marker for LID. Furthermore, dyskinetic mice showed a marked augmentation of serotonergic fiber innervation in the striatum, enabling the decarboxylation of L-DOPA to DA. Axial, limb and orolingual dyskinesias were predominantly associated with TH+ neurons in the lateral striatum, whereas medially located TH+ neurons triggered locomotive rotations. In contrast, identified accumbal and cortical TH+ cells did not contribute to the generation of LID. Thus, striatal TH+ cells and serotonergic terminals may cooperatively synthesize DA and subsequently contribute to supraphysiological synaptic DA concentrations, an accepted cause in LID pathogenesis.

Dual κ-agonist/μ-antagonist opioid receptor modulation reduces levodopa-induced dyskinesia and corrects dysregulated striatal changes in the nonhuman primate model of Parkinson disease

OBJECTIVE

Effective medical management of levodopa-induced dyskinesia (LID) remains an unmet need for patients with Parkinson disease (PD). Changes in opioid transmission in the basal ganglia associated with LID suggest a therapeutic opportunity. Here we determined the impact of modulating both mu and kappa opioid receptor signaling using the mixed agonist/antagonist analgesic nalbuphine in reducing LID and its molecular markers in the nonhuman primate model.

METHODS

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated macaques with advanced parkinsonism and reproducible LID received a range of nalbuphine doses or saline subcutaneously as: (1) monotherapy, (2) acute coadministration with levodopa, and (3) chronic coadministration for 1 month. Animals were assessed by blinded examiners for motor disability and LID severity using standardized rating scales. Plasma levodopa levels were determined with and without nalbuphine, and postmortem brain samples were subjected to Western blot analyses.

RESULTS

Nalbuphine reduced LID in a dose-dependent manner by 48% (p < 0.001) without compromising the anti-PD effect of levodopa or changing plasma levodopa levels. There was no tolerance to the anti-LID effect of nalbuphine given chronically. Nalbuphine coadministered with levodopa was well tolerated and did not cause sedation. Nalbuphine monotherapy had no effect on motor disability. Striatal tissue analyses showed that nalbuphine cotherapy blocks several molecular correlates of LID, including overexpression of ΔFosB, prodynorphin, dynorphin A, cyclin-dependent kinase 5, and increased phosphorylation of DARPP-32 at threonine-34.

INTERPRETATION

Nalbuphine reverses the molecular milieu in the striatum associated with LID and is a safe and effective anti-LID agent in the primate model of PD. These findings support repurposing this analgesic for the treatment of LID.

Gene expression analyses identify Narp contribution in the development of L-DOPA-induced dyskinesia

In Parkinson's disease, long-term dopamine replacement therapy is complicated by the appearance of L-DOPA-induced dyskinesia (LID). One major hypothesis is that LID results from an aberrant transcriptional program in striatal neurons induced by L-DOPA and triggered by the activation of ERK. To identify these genes, we performed transcriptome analyses in the striatum in 6-hydroxydopamine-lesioned mice. A time course analysis (0-6 h after treatment with L-DOPA) identified an acute signature of 709 genes, among which genes involved in protein phosphatase activity were overrepresented, suggesting a negative feedback on ERK activation by l-DOPA. l-DOPA-dependent deregulation of 28 genes was blocked by pretreatment with SL327, an inhibitor of ERK activation, and 26 genes were found differentially expressed between highly and weakly dyskinetic animals after treatment with L-DOPA. The intersection list identified five genes: FosB, Th, Nptx2, Nedd4l, and Ccrn4l. Nptx2 encodes neuronal pentraxin II (or neuronal activity-regulated pentraxin, Narp), which is involved in the clustering of glutamate receptors. We confirmed increased Nptx2 expression after L-DOPA and its blockade by SL327 using quantitative RT-PCR in independent experiments. Using an escalating L-DOPA dose protocol, LID severity was decreased in Narp knock-out mice compared with their wild-type littermates or after overexpression of a dominant-negative form of Narp in the striatum. In conclusion, we have identified a molecular signature induced by L-DOPA in the dopamine-denervated striatum that is dependent on ERK and associated with LID. Here, we demonstrate the implication of one of these genes, Nptx2, in the development of LID.