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

Neuroprotective effects of punicalagin and/or micronized zeolite clinoptilolite on manganese-induced Parkinson's disease in a rat model: Involvement of multiple pathways

BACKGROUND

Manganism, a central nervous system dysfunction correlated with neurological deficits such as Parkinsonism, is caused by the substantial collection of manganese chloride (MnCl2) in the brain.

OBJECTIVES

To explore the neuroprotective effects of natural compounds, namely, micronized zeolite clinoptilolite (ZC) and punicalagin (PUN), either individually or in combination, against MnCl2-induced Parkinson's disease (PD).

METHODS

Fifty male albino rats were divided into 5 groups (Gps). Gp I was used as the control group, and the remaining animals received MnCl2 (Gp II-Gp V). Rats in Gps III and IV were treated with ZC and PUN, respectively. Gp V received both ZC and PUN as previously reported for the solo-treated plants.

RESULTS

ZC and/or PUN reversed the depletion of monoamines in the brain and decreased acetyl choline esterase activity, which primarily adjusted the animals' behavior and motor coordination. ZC and PUN restored the balance between glutamate/γ-amino butyric acid content and markedly improved the brain levels of brain-derived neurotrophic factor and nuclear factor erythroid 2-related factor 2/heme oxygenase-1 and decreased glycogen synthase kinase-3 beta activity. ZC and PUN also inhibited inflammatory and oxidative markers, including nuclear factor kappa-light-chain-enhancer of activated B cells, Toll-like receptor 4, nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 and caspase-1. Bcl-2-associated X-protein and B-cell leukemia/lymphoma 2 protein (Bcl-2) can significantly modify caspase-3 expression. ZC and/or PUN ameliorated PD in rats by decreasing the levels of endoplasmic reticulum (ER) stress markers (p-protein kinase-like ER kinase (PERK), glucose-regulated protein 78, and C/EBP homologous protein (CHOP)) and enhancing the levels of an autophagy marker (Beclin-1).

DISCUSSION AND CONCLUSION

ZC and/or PUN mitigated the progression of PD through their potential neurotrophic, neurogenic, anti-inflammatory, antioxidant, and anti-apoptotic activities and by controlling ER stress through modulation of the PERK/CHOP/Bcl-2 pathway.

Astrocyte-neuron communication through the complement C3-C3aR pathway in Parkinson's disease

Neuroinflammation and autoimmunity are pivotal in the pathogenesis of neurodegenerative diseases. Complement activation and involvement of astrocyte-neuron C3/C3aR pathway have been observed, yet the mechanisms influencing α-synuclein (α-syn) pathology and neurodegeneration remain unclear. In this study, elevated levels of complement C3 were detected in the plasma of α-syn PFF-induced mice and the substantia nigra of A53T transgenic mice. Colocalization of complement C3 with astrocytes was also observed. Overexpression of complement C3 exacerbated motor dysfunction, dopaminergic neuron loss, and phosphorylated α-syn expression in mice injected with α-syn preformed fibrils (α-syn PFFs). Conversely, downregulation of complement C3 protected α-syn PFF-induced mice. Molecular investigations revealed that inhibition of Toll-like receptor 2 (TLR2) or NF-κB reduced complement C3 expression in primary astrocytes following α-syn PFF treatment. Astrocyte-neuron communication via the C3/C3aR pathway influenced α-syn PFF-induced neuronal apoptosis and α-syn pathology, potentially through modulation of GSK3β. These findings underscore the critical role of astrocyte-neuron communication via the C3/C3aR pathway in PD pathogenesis, highlighting its potential as a therapeutic target.

GSK-3β Allosteric Inhibition: A Dead End or a New Pharmacological Frontier?

Most kinase inhibitors are designed to bind to highly homologous ATP-binding sites, which leads to promiscuity and possible off-target effects. Allostery is an alternative approach to pursuing selectivity. However, allostery is difficult to exploit due to the wide variety of underlying mechanisms and the potential involvement of long-range conformational effects that are difficult to pinpoint. GSK-3β is involved in several pathologies. This critical target has an ATP-binding site that is highly homologous with the orthosteric sites of other kinases. Unsurprisingly, there is also great similarity between the ATP-binding sites of GSK-3β and its isomer, which is not redundant and thus would benefit from selective inhibition. Allostery would also allow for a moderate and tunable inhibition, which is ideal for GSK-3β, because this target is involved in multiple pathways, some of which must be preserved. However, despite considerable research efforts, only one allosteric GSK-3β inhibitor has reached the clinic. Moreover, unlike other kinases, there are no X-ray structures of GSK-3β in complex with allosteric inhibitors in the PDB data bank. This review aims to summarize the state of the art in allosteric GSK-3β inhibitor investigations, highlighting the aspects that make this target challenging for an allosteric approach.

GSK3β inhibitor TDZD8 ameliorates brain damage through both ROS scavenging and inhibition of apoptosis in hyperglycaemic subarachnoid haemorrhage rats

Hyperglycaemia is known to be associated with unfavourable outcomes in subarachnoid haemorrhage (SAH), but the pathogenic mechanism is unclear, and there is also a lack of effective therapeutic drugs in clinical practice. Phosphorylation of GSK3β at serine 9 can inhibit its activity to further worsen SAH. The aim of the present study was to evaluate the protective effect and the potential mechanism of the GSK3β inhibitor TDZD8 on brain injury in a hyperglycaemic SAH rat model. Hyperglycaemia was induced by intraperitoneal injection of streptozocin for 3 days. The SAH model was established by injecting fresh autologous femoral artery blood into the prechiasmatic cistern. p-GSK3β (Ser9) expression was induced by intraperitoneal injection of TDZD8 (30 min post-SAH). The expression levels of GSK3β, p-GSK3β, SOD1/2, caspase 3, Bax and Bcl-2 were detected by western blot analysis. Terminal deoxynucleotidyl transferase dUTP nick end-labelling (TUNEL) staining was used to detect neuronal apoptosis of basal temporal lobe. Neurological scores were calculated to determine behavioural recovery. Neuronal survival was detected by Nissl staining. Hyperglycaemia significantly decreased p-GSK3β expression, further exacerbated neurobehavioural deficits and increased oxidative stress and neuronal apoptosis in the brain after SAH compared to normal glycaemic SAH rats and hyperglycaemic rats. In addition, hyperglycaemic SAH rats had obvious oxidative stress and apoptosis. However, TDZD8 effectively decreased cleaved caspase 3 expression and TUNEL-positive cells and increased the Bcl2/Bax ratio, expression of SOD1/2 and activity of superoxide dismutase (SOD) enzyme compared with hyperglycaemic SAH rats. The GSK3β inhibitor TDZD8 has therapeutic potential for hyperglycaemic SAH. The neuroprotective effect of TDZD8 appears to be mediated through its antioxidative and antiapoptotic activity.

Agathobaculum butyriciproducens Shows Neuroprotective Effects in a 6-OHDA-Induced Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is the second-most prevalent neurodegenerative disease and is characterized by dopaminergic neuronal death in the midbrain. Recently, the association between alterations in PD pathology and the gut microbiota has been explored. Microbiota-targeted interventions have been suggested as a novel therapeutic approach for PD. Agathobaculum butyriciproducens SR79^T (SR79) is an anaerobic bacterium. Previously, we showed that SR79 treatment induced cognitive improvement and reduced Alzheimer's disease pathologies in a mouse model. In this study, we hypothesized that SR79 treatment may have beneficial effects on PD pathology. To investigate the therapeutic effects of SR79 on PD, 6-hydroxydopamine (6-OHDA)-induced mouse models were used. D-Amphetamine sulfate (d-AMPH)-induced behavioral rotations and dopaminergic cell death were analyzed in unilateral 6-OHDA-lesioned mice. Treatment with SR79 significantly decreased ipsilateral rotations induced by d-AMPH. Moreover, SR79 treatment markedly activated the AKT/GSK3β signaling pathway in the striatum. In addition, SR79 treatment affected the Nrf2/ARE signaling pathway and its downstream target genes in the striatum of 6-OHDA-lesioned mice. Our findings suggest a protective role of SR79 in 6-OHDA-induced toxicity by regulating the AKT/Nrf2/ARE signaling pathway and astrocyte activation. Thus, SR79 may be a potential microbe-based intervention and therapeutic strategy for PD.

Recent Advances in Dopamine D3 Receptor Heterodimers: Focus on Dopamine D3 and D1 Receptor-Receptor Interaction and Striatal Function

G protein-coupled receptors (GPCR) heterodimers represent new entities with unique pharmacological, signalling, and trafficking properties, with specific distribution restricted to those cells where the two interacting receptors are co-expressed. Like other GPCR, dopamine D3 receptors (D3R) directly interact with various receptors to form heterodimers: data showing the D3R physical interaction with both GPCR and non-GPCR receptors have been provided including D3R interaction with other dopamine receptors. The aim of this chapter is to summarize current knowledge of the distinct roles of heterodimers involving D3R, focusing on the D3R interaction with the dopamine D1 receptor (D1R): the D1R-D3R heteromer, in fact, has been postulated in both ventral and motor striatum. Interestingly, since both D1R and D3R have been implicated in several pathological conditions, including schizophrenia, motor dysfunctions, and substance use disorders, the D1R-D3R heteromer may represent a potential drug target for the treatment of these diseases.

α-Synuclein Induces the GSK-3-Mediated Phosphorylation and Degradation of NURR1 and Loss of Dopaminergic Hallmarks

In Parkinson’s disease, the dysfunction of the dopaminergic nigrostriatal tract involves the loss of function of dopaminergic neurons of the substantia nigra pars compacta followed by death of these neurons. The functional recovery of these neurons requires a deep knowledge of the molecules that maintain the dopaminergic phenotype during adulthood and the mechanisms that subvert their activity. Previous studies have shown that transcription factor NURR1, involved in differentiation and maintenance of the dopaminergic phenotype, is downregulated by α-synuclein (α-SYN). In this study, we provide a mechanistic explanation to this finding by connecting α-SYN-induced activation of glycogen synthase kinase-3 (GSK-3) with NURR1 phosphorylation followed by proteasomal degradation. The use of sequential deletion mutants and single point mutants of NURR1 allowed the identification of a domain comprising amino acids 123-PSSPPTPSTPS-134 that is targeted by GSK-3 and leads to subsequent ubiquitination and proteasome degradation. This study provides a detailed analysis of the regulation of NURR1 stability by phosphorylation in synucleinopathies such as Parkinson’s disease.

Administration of quercetin improves mitochondria quality control and protects the neurons in 6-OHDA-lesioned Parkinson's disease models

Mounting evidence suggests that mitochondrial dysfunction and impaired mitophagy lead to Parkinson’s disease (PD). Quercetin, one of the most abundant polyphenolic flavonoids, displays many health-promoting biological effects in many diseases. We explored the neuroprotective effect of quercetin in vivo in the 6-hydroxydopamine (6-OHDA)-lesioned rat model of PD and in vitro in 6-OHDA-treated PC12 cells. In vitro, we found that quercetin (20 μM) treatment improved mitochondrial quality control, reduced oxidative stress, increased the levels of the mitophagy markers PINK1 and Parkin and decreased α-synuclein protein expression in 6-OHDA-treated PC12 cells. Moreover, our in vivo findings demonstrated that administration of quercetin also relieved 6-OHDA-induced progressive PD-like motor behaviors, mitigated neuronal death and reduced mitochondrial damage and α-synuclein accumulation in PD rats. Furthermore, the neuroprotective effect of quercetin was suppressed by knockdown of either Pink1 or Parkin.

Targeting ROS-Dependent AKT/GSK-3β/NF-κB and DJ-1/Nrf2 Pathways by Dapagliflozin Attenuates Neuronal Injury and Motor Dysfunction in Rotenone-Induced Parkinson's Disease Rat Model

Dapagliflozin, a selective sodium-glucose co-transporter 2 (SGLT2) inhibitor, has emerged as a promising neuroprotective agent in murine models of epilepsy and obesity-induced cognitive impairment through its marked antioxidant/antiapoptotic features. However, the impact of dapagliflozin on the pathogenesis of Parkinson's disease (PD) is lacking. Hence, the present study aimed at exploring the potential neuroprotective effects of dapagliflozin against PD-associated neurodegenerative aberrations/motor dysfunction in rotenone-induced PD rat model. Rotenone (1.5 mg/kg) was subcutaneously administered every other day for 3 weeks. The expression of target signals was investigated using qPCR, Western blotting, ELISA, and immunohistochemistry. Dapagliflozin (1 (mg/kg)/day, by gavage for 3 weeks) attenuated PD motor dysfunction and improved motor coordination in the open-field and rotarod tests without triggering hypoglycemia. It also diminished the histopathologic alterations and α-synuclein expression and augmented tyrosine hydroxylase and dopamine levels. Dapagliflozin markedly alleviated neuronal oxidative stress via lowering lipid peroxides with consequent restoration of the disturbed DJ-1/Nrf2 pathway. Moreover, dapagliflozin counteracted ROS-dependent neuronal apoptosis and upregulated GDNF and its downstream PI3K/AKT/GSK-3β (Ser9) pathway. Meanwhile, it suppressed neuroinflammation via curbing the activation of NF-κB pathway and TNF-α levels. Together, these pleiotropic neuroprotective effects highlight the promising role of dapagliflozin in the management of PD.

β‑Lapachone ameliorates L‑DOPA‑induced dyskinesia in a 6‑OHDA‑induced mouse model of Parkinson's disease

The dopamine precursor 3,4-dihydroxyphenyl- l-alanine (L-DOPA) is the most widely used symptomatic treatment for Parkinson's disease (PD); however, its prolonged use is associated with L-DOPA-induced dyskinesia in more than half of patients after 10 years of treatment. The present study investigated whether co-treatment with β-Lapachone, a natural compound, and L-DOPA has protective effects in a 6-hydroxydopamine (6-OHDA)-induced mouse model of PD. Unilateral 6-OHDA-lesioned mice were treated with vehicle or β-Lapachone (10 mg/kg/day) and L-DOPA for 11 days. Abnormal involuntary movements (AIMs) were scored on days 5 and 10. β-Lapachone (10 mg/kg) co-treatment with L-DOPA decreased the AIMs score on both days 5 and 10. β-Lapachone was demonstrated to have a beneficial effect on the axial and limb AIMs scores on day 10. There was no significant suppression in dopamine D1 receptor-related and ERK1/2 signaling in the DA-denervated striatum by β-Lapachone-cotreatment with L-DOPA. Notably, β-Lapachone-cotreatment with L-DOPA increased phosphorylation at the Ser9 site of glycogen synthase kinase 3β (GSK-3β), indicating suppression of GSK-3β activity in both the unlesioned and 6-OHDA-lesioned striata. In addition, astrocyte activation was markedly suppressed by β-Lapachone-cotreatment with L-DOPA in the striatum and substantia nigra of the unilateral 6-OHDA model. These findings suggest that β-Lapachone cotreatment with L-DOPA therapy may have therapeutic potential for the suppression or management of the development of L-DOPA-induced dyskinesia in patients with PD.

A Focused Update on Tardive Dyskinesia

Tardive dyskinesia (TD) is a delayed and potentially irreversible motor complication following chronic exposure to centrally acting dopamine receptor antagonists, mainly of the class of antipsychotics drugs. New generations of antipsychotic drugs reduced its mean prevalence to 20%, but it continues to mar the drug experience and social integration in a significant fraction of patients. The underlying molecular cascade remains elusive, explaining in part why TD management is so often difficult. Protocol variations between experimental laboratories and inter-species differences in the biological response to antipsychotic drugs have added layers of complexity. The traditional dopamine D2 receptor supersensitivity hypothesis was revisited in an experimental nonhuman primate model. Findings in the striatum revealed a strong upregulation of D3, not D2, receptors specific to dyskinetic animals, and indirect evidence suggestive of a link between overactivation of glycogen synthase kinase-3β signaling and TD. New effective vesicular monoamine transporter type 2 inhibitors alleviating TD have been approved in the USA. They were integrated to an emerging stepwise treatment algorithm for troublesome TD, which also includes consideration for changes in the current antipsychotic drug regimen and recognition of potentially aggravating factors such as anticholinergic co-medications. These advances may benefit TD.

Structural modeling of GSK3β implicates the inactive (DFG-out) conformation as the target bound by TDZD analogs

Glycogen synthase kinase-3β (GSK3β) controls many physiological pathways, and is implicated in many diseases including Alzheimer’s and several cancers. GSK3β-mediated phosphorylation of target residues in microtubule-associated protein tau (MAPTAU) contributes to MAPTAU hyperphosphorylation and subsequent formation of neurofibrillary tangles. Inhibitors of GSK3β protect against Alzheimer’s disease and are therapeutic for several cancers. A thiadiazolidinone drug, TDZD-8, is a non-ATP-competitive inhibitor targeting GSK3β with demonstrated efficacy against multiple diseases. However, no experimental data or models define the binding mode of TDZD-8 with GSK3β, which chiefly reflects our lack of an established inactive conformation for this protein. Here, we used metadynamic simulation to predict the three-dimensional structure of the inactive conformation of GSK3β. Our model predicts that phosphorylation of GSK3β Serine9 would hasten the DFG-flip to an inactive state. Molecular docking and simulation predict the TDZD-8 binding conformation of GSK3β to be inactive, and are consistent with biochemical evidence for the TDZD-8–interacting residues of GSK3β. We also identified the pharmacophore and assessed binding efficacy of second-generation TDZD analogs (TDZD-10 and Tideglusib) that bind GSK3β as non-ATP-competitive inhibitors. Based on these results, the predicted inactive conformation of GSK3β can facilitate the identification of novel GSK3β inhibitors of high potency and specificity.

Glycogen synthase kinase-3 inhibition rescues sex-dependent contextual fear memory deficit in human immunodeficiency virus-1 transgenic mice

BACKGROUND AND PURPOSE

A significant number of HIV-1 patients on antiretroviral therapy develop HIV-associated neurocognitive disorders (HAND). Evidence indicate that biological sex may regulate HAND pathogenesis, but the mechanisms remain unknown. We investigated synaptic mechanisms associated with sex differences in HAND, using the HIV-1-transgenic 26 (Tg26) mouse model.

EXPERIMENTAL APPROACH

Contextual- and cue-dependent memories of male and female Tg26 mice and littermate wild type mice were assessed in a fear conditioning paradigm. Hippocampal electrophysiology, immunohistochemistry, western blot, qRT-PCR and ELISA techniques were used to investigate cellular, synaptic and molecular impairments.

KEY RESULTS

Cue-dependent memory was unaltered in male and female Tg26 mice, when compared to wild type mice. Male, but not female, Tg26 mice showed deficits in contextual fear memory. Consistently, only male Tg26 mice showed depressed hippocampal basal synaptic transmission and impaired LTP induction in area CA1. These deficits in male Tg26 mice were independent of hippocampal neuronal loss and microglial activation but were associated with increased HIV-1 long terminal repeat mRNA expression, reduced hippocampal synapsin-1 protein, reduced BDNF mRNA and protein, reduced AMPA glutamate receptor (GluA1) phosphorylation levels and increased glycogen synthase kinase 3 (GSK3) activity. Importantly, selective GSK3 inhibition using 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione increased levels of synapsin-1, BDNF and phosphorylated-GluA1 proteins, restored hippocampal basal synaptic transmission and LTP, and improved contextual fear memory in male Tg26 mice.

CONCLUSION AND IMPLICATIONS

Sex-dependent impairments in contextual fear memory and synaptic plasticity in Tg26 mice are associated with increased GSK3 activity. This implicates GSK3 inhibition as a potential therapeutic strategy to improve cognition in HIV-1 patients.

BDNF as a Promising Therapeutic Agent in Parkinson's Disease

Brain-derived neurotrophic factor (BDNF) promotes neuroprotection and neuroregeneration. In animal models of Parkinson’s disease (PD), BDNF enhances the survival of dopaminergic neurons, improves dopaminergic neurotransmission and motor performance. Pharmacological therapies of PD are symptom-targeting, and their effectiveness decreases with the progression of the disease; therefore, new therapeutical approaches are needed. Since, in both PD patients and animal PD models, decreased level of BDNF was found in the nigrostriatal pathway, it has been hypothesized that BDNF may serve as a therapeutic agent. Direct delivery of exogenous BDNF into the patient’s brain did not relieve the symptoms of disease, nor did attempts to enhance BDNF expression with gene therapy. Physical training was neuroprotective in animal models of PD. This effect is mediated, at least partly, by BDNF. Animal studies revealed that physical activity increases BDNF and tropomyosin receptor kinase B (TrkB) expression, leading to inhibition of neurodegeneration through induction of transcription factors and expression of genes related to neuronal proliferation, survival, and inflammatory response. This review focuses on the evidence that increasing BDNF level due to gene modulation or physical exercise has a neuroprotective effect and could be considered as adjunctive therapy in PD.

β-arrestin2 alleviates L-dopa-induced dyskinesia via lower D1R activity in Parkinson's rats

The cause of the L-dopa–induced dyskinesia (LID) has been ascribed to G-protein coupled receptor (GPCR) supersensitivity and uncontrolled downstream signaling. It is now supposed that β-arrestin2 affects GPCR signaling through its ability to scaffold various intracellular molecules. We used the rAAV (recombinant adeno-associated virus) vectors to overexpress and ablation of β-arrestin2. L-dopa-induced changes in expression of signaling molecules and other proteins in the striatum were examined by western blot and immunohistochemically. Our data demonstrated that via AAV-mediated overexpression of β-arrestin2 attenuated LID performance in 6-OHDA-lesioned rodent models. β-arrestin2 suppressed LID behavior without compromising the antiparkinsonian effects of L-dopa. Moreover, we also found that the anti-dyskinetic effect of β-arrestin2 was reversed by SKF38393, a D1R agonist. On the contrary, the rat knockdown study demonstrated that reduced availability of β-arrestin2 deteriorated LID performance, which was counteracted by SCH23390, a D1R antagonist. These data not only demonstrate a central role for β-arrestin2/GPCR signaling in LID, but also show the D1R signal pathway changes occurring in response to dopaminergic denervation and pulsatile administration of L-dopa.

7,8,4'-Trihydroxyisoflavone, a Metabolized Product of Daidzein, Attenuates 6-Hydroxydopamine-Induced Neurotoxicity in SH-SY5Y Cells

Daidzein isolated from soybean (Glycine max) has been widely studied for its antioxidant and anti-inflammatory activities. However, the protective effects of 7,8,4'-trihydroxyisoflavone (THIF), a major metabolite of daidzein, on 6-hydroxydopamine (OHDA)-induced neurotoxicity are not well understood. In the current study, 7,8,4'-THIF significantly inhibited neuronal cell death and lactate dehydrogenase (LDH) release induced by 6-OHDA in SH-SY5Y cells, which were used as an in vitro model of Parkinson' disease (PD). Moreover, pretreatment with 7,8,4'-THIF significantly increased the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) and decreased malondialdehyde (MDA) activity in 6-OHDA-induced SH-SY5Y cells. In addition, 7,8,4'-THIF significantly recovered 6-OHDA-induced cleaved caspase-3, cleaved caspase-9, cleaved poly-ADP-ribose polymerase (PARP), increased Bax, and decreased Bcl-2 levels. Additionally, 7,8,4'-THIF significantly restored the expression levels of phosphorylated c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase 1/2 (ERK 1/2), phosphatidylinositol 3-kinases (PI3K)/Akt, and glycogen synthase kinase-3 beta (GSK-3β) in 6-OHDA-induced SH-SY5Y cells. Further, 7,8,4'-THIF significantly increased the reduced tyrosine hydroxylase (TH) level induced by 6-OHDA in SH-SY5Y cells. Collectively, these results suggest that 7,8,4'-THIF protects against 6-OHDA-induced neuronal cell death in cellular PD models. Also, these effects are mediated partly by inhibiting activation of the MAPK and PI3K/Akt/GSK-3β pathways.

Levodopa/Benserazide PLGA Microsphere Prevents L-Dopa-Induced Dyskinesia via Lower β-Arrestin2 in 6-Hydroxydopamine Parkinson's Rats

Prolonged pulsatile administration of Levodopa (L-dopa) can generate L-dopa–induced dyskinesia (LID). Numerous research has reported that continuous dopamine delivery (CDD) was useful in reducing the severity of LID. 6-OHDA lesioned rats were divided into two groups to receive intermittent L-dopa stimulation (L-dopa/benserazide) or Levodopa/benserazide PLGA microsphere (LBPM) for 3 weeks. rAAV (recombinant adeno-associated virus) vector was used to overexpress and ablation of β-arrestin2. We found that LBPM developed less AIM severity compared with standard L-dopa administration, whereas selective deletion of β-arrestin2 in striatum neurons dramatically enhanced the severity of dyskinesia by LBPM. On the contrary, the effects of LBPM in terms of ALO AIM were further relieved by β-arrestin2 overexpression. Furthermore, no significant change in motor behavior was seen either in inhibition or overexpression of β-arrestin2. In short, our experiments provided evidence that LBPM’s prevention of LID behavior was likely due to β-arrestin2, suggesting that a therapy modulating β-arrestin2 may offer a more efficient anti-dyskinetic method with a low risk of untoward effects.

Parkinson's Disease is Associated with Dysregulations of a Dopamine-Modulated Gene Network Relevant to Sleep and Affective Neurobehaviors in the Striatum

In addition to the characteristic motor symptoms, Parkinson’s disease (PD) often involves a constellation of sleep and mood symptoms. However, the mechanisms underlying these comorbidities are largely unknown. We have previously reconstructed gene networks in the striatum of a population of (C57BL/6J x A/J) F2 mice and associated the networks to sleep and affective phenotypes, providing a resource for integrated analyses to investigate perturbed sleep and affective functions at the gene network level. Combining this resource with PD-relevant transcriptomic datasets from humans and mice, we identified four networks that showed elevated gene expression in PD patients, including a circadian clock and mitotic network that was altered similarly in mouse models of PD. We then utilized multiple types of omics data from public databases and linked this gene network to postsynaptic dopamine signaling in the striatum, CDK1-modulated transcriptional regulation, and the genetic susceptibility of PD. These findings suggest that dopamine deficiency, a key aspect of PD pathology, perturbs a circadian/mitotic gene network in striatal neurons. Since the normal functions of this network were relevant to sleep and affective behaviors, these findings implicate that dysregulation of functional gene networks may be involved in the emergence of non-motor symptoms in PD. Our analyses present a framework for integrating multi-omics data from diverse sources in mice and humans to reveal insights into comorbid symptoms of complex diseases.

Dopamine D1 receptor activation improves adult hippocampal neurogenesis and exerts anxiolytic and antidepressant-like effect via activation of Wnt/β-catenin pathways in rat model of Parkinson's disease

Parkinson's disease (PD) is primarily characterized by midbrain dopamine depletion. Dopamine acts through dopamine receptors (D1 to D5) to regulate locomotion, motivation, pleasure, attention, cognitive functions and formation of newborn neurons, all of which are likely to be impaired in PD. Reduced hippocampal neurogenesis associated with dopamine depletion has been demonstrated in patients with PD. However, the precise mechanism to regulate multiple steps of adult hippocampal neurogenesis by dopamine receptor(s) is still unknown. In this study, we tested whether pharmacological agonism and antagonism of dopamine D1 and D2 receptor regulate nonmotor symptoms, neural stem cell (NSC) proliferation and fate specification and explored the cellular mechanism(s) underlying dopamine receptor (D1 and D2) mediated adult hippocampal neurogenesis in rat model of PD-like phenotypes. We found that single unilateral intra-medial forebrain bundle administration of 6-hydroxydopamine (6-OHDA) reduced D1 receptor level in the hippocampus. Pharmacological agonism of D1 receptor exerts anxiolytic and antidepressant-like effects as well as enhanced NSC proliferation, long-term survival and neuronal differentiation by positively regulating Wnt/β-catenin signaling pathway in hippocampus in PD rats. shRNA lentivirus mediated knockdown of Axin-2, a negative regulator of Wnt/β-catenin signaling potentially attenuated D1 receptor antagonist induced anxiety and depression-like phenotypes and impairment in adult hippocampal neurogenesis in PD rats. Our results suggest that improved nonmotor symptoms and hippocampal neurogenesis in PD rats controlled by D1-like receptors that involve the activation of Wnt/β-catenin signaling.

The GSK3β inhibitor, TDZD-8, rescues cognition in a zebrafish model of okadaic acid-induced Alzheimer's disease

Currently, no treatments exist that are able to directly treat against Alzheimer's disease (AD), and we are facing an inevitable increase in the near future of the amount of patients who will suffer from AD. Most animal models of AD are limited by not being able to recapitulate the entire pathology of AD. Recently an AD model in zebrafish was established by using the protein phosphatase 2A inhibitor, okadaic acid (OKA). Administering OKA to zebrafish was able to recapitulate most of the neuropathology associated with AD. Therefore, providing a drug discovery model for AD that is also time and cost efficient. This study was designed to investigate the effects of GSK3β inhibition by 4-benzyl-2-methyl-1, 2, 4-thiadiazolidine-3, 5-dione (TDZD-8) on this newly developed AD model. Fish were divided into 4 groups and each group received a different treatment. The fish were divided into a control group, a group treated with 1 μM TDZD-8 only, a group treated with 1 μM TDZD-8 + 100 nM OKA, and a group treated with 100 nM OKA only. Administering the GSK3β inhibitor to zebrafish concomitantly with OKA proved to be protective. TDZD-8 treatment reduced the mortality rate, the ratio of active: inactive GSK3β, pTau (Ser199), and restored PP2A activity. This further corroborates the use of GSKβ inhibitors in the treatment against AD and bolsters the use of the OKA-induced AD-like zebrafish model for drug discovery.

Modulation of CaMKIIa-GluN2B interaction in levodopa-induced dyskinesia in 6-OHDA-lesioned Parkinson's rats

Long-term treatment with L-dopa leads to involuntary aimless movements called L-dopa-induced dyskinesia (LID) has hindered its use in Parkinson's disease (PD) patients. Emerging evidence suggests a possible role of CaMKIIa and its interacting partners in the development of LID. In this study, we found that CaMKIIa was found to form complexes with GluN2B after chronic administration of L-dopa in adult rat striatal neurons. Intrastriatal injection of KN-93 significantly reduced the level of GluN2B in CaMKIIa precipitates with a dose dependent response, as well as reduced the Global ALO AIM score without ablation of the therapeutic response to L-dopa. In parallel, intrastriatal injection of MK-801 significantly alleviated the level of CaMKIIa in GluN2B precipitates compared to LID group (p < 0.01), and this is accompanied by realizing improvement of the Global ALO AIM score also without affect the efficacy of L-dopa. In summary, the present study indicated that CaMKIIa-GluN2B interaction had an important role in the development of LID. Disrupt of this link by intrastriatal infusion of KN-93 or MK-801 ameliorated dyskinesia in 6-OHDA-lesioned PD rats.

Validation of a New Scoring Scale for Behavioral Assessment of L-Dopa-Induced Dyskinesia in the Rat: A New Tool for Early Decision-Making in Drug Development

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated nonhuman primate (NHP) has been described as the most translatable model for experimental reproduction of L-dopa-induced dyskinesia (LID). However, from a drug discovery perspective, the risk associated with investment in this type of model is high due to the time and cost. The 6-hydroxydopamine (6-OHDA) rat dyskinesia model is recommended for testing compounds but relies on onerous, and nonstandard behavioral rating scales. We sought to develop a simplified and sensitive method aiming at assessing LID in the rat. The purpose was to validate a reliable tool providing earlier insight into the antidyskinetic potential of compounds in a time/cost-effective manner before further investigation in NHP models. Unilaterally 6-OHDA-lesioned rats were administered L-dopa (20 mg/kg) and benserazide (5 mg/kg) daily for 3 weeks starting 4 weeks postlesion, then coadministered with amantadine (20-30-40 mg/kg). An adapted rating scale was used to score LID frequency and a severity coefficient was applied depending on the features of the observed behavior. A gradual increase (about 3-fold) in LID score was observed over the 3 weeks of L-dopa treatment. The rating scale was sensitive enough to highlight a dose-dependent amantadine-mediated decrease (about 2.2-fold) in LID score. We validated a simplified method, able to reflect different levels of severity in the assessment of LID and, thus, provide a reliable tool for drug discovery.

Selegiline increases on time without exacerbation of dyskinesia in 6-hydroxydopamine-lesioned rats displaying l-Dopa-induced wearing-off and abnormal involuntary movements

3,4-Dihydroxy-l-phenylalanine (l-Dopa) remains the most effective drug for treating the motor symptoms of Parkinson's disease (PD). However, its long-term use is limited due to motor complications such as wearing-off and dyskinesia. A clinical study in PD patients with motor complications has demonstrated that selegiline, a monoamine oxidase type B inhibitor, is effective in reducing off time without worsening dyskinesia, although another study has shown worsening dyskinesia. Here, using unilateral 6-hydroxydopamine-lesioned rats showing degeneration of nigrostriatal dopaminergic neurons and l-Dopa-induced motor complications, we determined the efficacy of selegiline in controlling l-Dopa-induced motor fluctuations and exacerbated dyskinesia. Repeated administration of l-Dopa/benserazide (25/6.25 mg/kg, intraperitoneally, twice daily for 22 days) progressively shortened rotational response duration (on time) and augmented peak rotation in lesioned rats. Single subcutaneous injection of selegiline (10 mg/kg) extended l-Dopa-induced shortened on time without augmenting peak rotation. Furthermore, l-Dopa/benserazide (25/6.25 mg/kg, intraperitoneally, once daily for 7 days) progressively increased abnormal involuntary movements (l-Dopa-induced dyskinesia, LID) and peak rotation. Single subcutaneous injection of selegiline (10 mg/kg) did not exacerbate LID or alter mRNA expression of prodynorphin (PDy) and activity-regulated cytoskeleton-associated protein (Arc), both mRNAs associated with LID in the lesioned striatum. Despite undetectable plasma concentrations of selegiline and its metabolites at 24 h post-administration, these on time and LID effects did not decrease, suggesting involvement of irreversible mechanisms. Altogether, these results indicate that selegiline is effective in increasing on time without worsening dyskinesia.

Antidyskinetic Treatment with MTEP Affects Multiple Molecular Pathways in the Parkinsonian Striatum

Parkinson's disease is characterized by dopaminergic neuron loss and dopamine (DA) depletion in the striatum. Standard treatment is still focused on the restoration of dopamine with exogenous L-Dopa, which however causes L-Dopa-induced dyskinesia (LID). Several studies have shown that antagonism of the metabotropic glutamate receptor 5 alleviates LID, but the underlying mechanisms have remained unclear. We set out to determine where this alleviation may depend on restoring the equilibrium between the two main striatofugal pathways. For this purpose, we examined molecular markers of direct and indirect pathway involvement (prodynorphin and proenkephalin, resp.) in a rat model of LID treated with the mGluR5 antagonist MTEP. Our results show that MTEP cotreatment significantly attenuates the upregulation of prodynorphin mRNA induced by L-Dopa while also decreasing the expression levels of proenkephalin mRNA. We also examined markers of the mGluR5-related PKC/MEK/ERK1/2 signaling pathway, finding that both the expression of PKC epsilon and the phosphorylation of MEK and ERK1/2 had decreased significantly in the MTEP-treated group. Taken together, our results show that pharmacological antagonism of mGluR5 normalizes several abnormal molecular responses in the striatum in this experimental model of LID.

Chronic over-nutrition and dysregulation of GSK3 in diseases

Loss of cellular response to hormonal regulation in maintaining metabolic homeostasis is common in the process of aging. Chronic over-nutrition may render cells insensitive to such a hormonal regulation owing to overstimulation of certain signaling pathways, thus accelerating aging and causing diseases. The glycogen synthase kinase 3 (GSK3) plays a pivotal role in relaying various extracellular and intracellular regulatory signals critical to cell growth, survival, regeneration, or death. The main signaling pathway regulating GSK3 activity through serine-phosphorylation is the phosphoinositide 3-kinase (PI3K)/phosphoinositide-dependent kinase-1 (PDK1)/Akt relay that catalyzes serine-phosphorylation and thus inactivation of GSK3. In addition, perilipin 2 (PLIN2) has recently been shown to regulate GSK3 activation through direct association with GSK3. This review summarizes current understanding on environmental and nutritional factors contributing to GSK3 regulation (or dysregulation) through the PI3K/PDK1/Akt/GSK3 axis, and highlights the newly discovered role that PLIN2 plays in regulating GSK3 activity and GSK3 downstream pathways.