Postmortem studies in Parkinson's disease

Neuroprotective role of Carvacrol via Nrf2/HO-1/NLRP3 axis in Rotenone-induced PD mice model

Parkinson's disease (PD) is a multifactorial neurodegenerative disorder whose cause is unclear. Neuroinflammation is recognized as one of the major pathogenic mechanisms involved in the development and progression of PD. NLRP3 inflammasome is the most widely studied inflammatory mediator in various diseases including PD. Several phytoconstituents have shown neuroprotective role in PD. Carvacrol is a phenolic monoterpene commonly found in the essential oils derived from plants belonging to Lamiaceae family. It is well known for its anti-inflammatory and antioxidant properties and has been widely explored in several diseases. In this study, we explored the role of Carvacrol in suppressing neuroinflammation by regulating NLRP3 inflammasome through Nrf2/HO-1 axis and subsequently, inflammatory cytokines like IL-1β, IL-18 in Rotenone induced PD mice model. Three doses (25 mg/kg, 50 mg/kg, 100 mg/kg p.o.) of Carvacrol were administered to, respectively, three groups (LD, MD, HD), one hour after administration of Rotenone (1.5 mg/kg, i.p.), every day, for 21 days. Treatment with Carvacrol ameliorated the motor impairment caused by Rotenone. It alleviated neurotoxicity and reduced inflammatory cytokines. Further, Carvacrol also alleviated oxidative stress and increased antioxidant enzymes. From these results, we show that Carvacrol exerts neuroprotective effects in PD via anti-inflammatory and antioxidant mechanisms and could be a potential therapeutic option in PD.

Acupuncture influences multiple diseases by regulating gut microbiota

Acupuncture, an important green and side effect-free therapy in traditional Chinese medicine, is widely use both domestically and internationally. Acupuncture can interact with the gut microbiota and influence various diseases, including metabolic diseases, gastrointestinal diseases, mental disorders, nervous system diseases, and other diseases. This review presents a thorough analysis of these interactions and their impacts and examines the alterations in the gut microbiota and the potential clinical outcomes following acupuncture intervention to establish a basis for the future utilization of acupuncture in clinical treatments.

Metformin improves cognitive dysfunction through SIRT1/NLRP3 pathway-mediated neuroinflammation in db/db mice

Diabetes mellitus (DM), an important public health problem, aggravates the global economic burden. Diabetic encephalopathy (DE) is a serious complication of DM in the central nervous system. Metformin has been proven to improve DE. However, the mechanism is still unclear. In this study, the db/db mice, a common model used for DE, were employed to explore and study the neuroprotective effect of metformin and related mechanisms. Behavioral tests indicated that metformin (100 or 200 mg/kg/day) could significantly improve the learning and memory abilities of db/db mice. The outcomes from the oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) demonstrate that metformin effectively modulates glucose and insulin signaling pathways in db/db mice. The results of body weight and blood lipid panel (total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol) show that metformin promotes the level of lipid metabolism in db/db mice. Furthermore, data from oxidative stress assays, which measured levels of malondialdehyde, superoxide dismutase, catalase, and glutathione peroxidase, suggest that metformin suppresses oxidative stress-induced brain damage in db/db mice. In addition, western blot, Nissl staining, and immunofluorescence results showed that metformin increased the expressions of nerve growth factor and postsynaptic density 95 and repaired neuronal structural damage. For the mechanism study, metformin activated SIRT1 and inhibited the expression of NLRP3 inflammasome (NLRP3, ASC, caspase-1, IL-1β, and IL-18) and inflammatory cytokines (TNFα and IL-6). In conclusion, metformin could ameliorate cognitive dysfunction through the SIRT1/NLRP3 pathway, which might be a promising mechanism for DE treatment.

Genetically Encoded and Modular SubCellular Organelle Probes (GEM-SCOPe) reveal lysosomal and mitochondrial dysfunction driven by PRKN knockout

Cellular processes including lysosomal and mitochondrial dysfunction are implicated in the development of many diseases. Quantitative visualization of mitochondria and lysosoesl is crucial to understand how these organelles are dysregulated during disease. To address a gap in live-imaging tools, we developed GEM-SCOPe (Genetically Encoded and Modular SubCellular Organelle Probes), a modular toolbox of fluorescent markers designed to inform on localization, distribution, turnover, and oxidative stress of specific organelles. We expressed GEM-SCOPe in differentiated astrocytes and neurons from a human pluripotent stem cell PRKN-knockout model of Parkinson's disease and identified disease-associated changes in proliferation, lysosomal distribution, mitochondrial transport and turnover, and reactive oxygen species. We demonstrate GEM-SCOPe is a powerful panel that provide critical insight into the subcellular mechanisms underlying Parkinson's disease in human cells. GEM-SCOPe can be expanded upon and applied to a diversity of cellular models to glean an understanding of the mechanisms that promote disease onset and progression.

Aging accelerates locomotor decline in PINK1 knockout rats in association with decreased nigral, but not striatal, dopamine and tyrosine hydroxylase expression

Parkinson's disease (PD) rodent models provide insight into the relationship between nigrostriatal dopamine (DA) signaling and locomotor function. Although toxin-based rat models produce frank nigrostriatal neuron loss and eventual motor decline characteristic of PD, the rapid nature of neuronal loss may not adequately translate premotor traits, such as cognitive decline. Unfortunately, rodent genetic PD models, like the Pink1 knockout (KO) rat, often fail to replicate the differential severity of striatal DA and tyrosine hydroxylase (TH) loss, and a bradykinetic phenotype, reminiscent of human PD. To elucidate this inconsistency, we evaluated aging as a progression factor in the timing of motor and non-motor cognitive impairments. Male PINK1 KO and age-matched wild type (WT) rats were evaluated in a longitudinal study from 3 to 16 months old in one cohort, and in a cross-sectional study of young adult (6-7 months) and aged (18-19 months) in another cohort. Young adult PINK1 KO rats exhibited hyperkinetic behavior associated with elevated DA and TH in the substantia nigra (SN), which decreased therein, but not striatum, in the aged KO rats. Additionally, norepinephrine levels decreased in aged KO rats in the prefrontal cortex (PFC), paired with a higher DA levels in young and aged KO. Although a younger age of onset characterizes familial forms of PD, our results underscore the critical need to consider age-related factors. Moreover, the results indicate that compensatory mechanisms may exist to preserve locomotor function, evidenced by increased DA in the SN early in the lifespan, in response to deficient PINK1 function, which declines with aging and the onset of motor decline.

Silencing Parkinson's risk allele Rit2 sex-specifically compromises motor function and dopamine neuron viability

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and arises from dopamine (DA) neuron death selectively in the substantia nigra pars compacta (SNc). Rit2 is a reported PD risk allele, and recent single cell transcriptomic studies identified a major RIT2 cluster in PD DA neurons, potentially linking Rit2 expression loss to a PD patient cohort. However, it is still unknown whether Rit2 loss itself impacts DA neuron function and/or viability. Here we report that conditional Rit2 silencing in mouse DA neurons drove motor dysfunction that occurred earlier in males than females and was rescued at early stages by either inhibiting the DA transporter (DAT) or with L-DOPA treatment. Motor dysfunction was accompanied by decreased DA release, striatal DA content, phenotypic DAergic markers, DA neurons, and DAergic terminals, with increased pSer129-alpha synuclein and pSer935-LRRK2 expression. These results provide clear evidence that Rit2 loss is causal for SNc cell death and motor dysfunction, and reveal key sex-specific differences in the response to Rit2 loss.

Aging hastens locomotor decline in PINK1 knockout rats in association with decreased nigral, but not striatal, dopamine and tyrosine hydroxylase expression

Parkinson's disease (PD) rodent models provide insight into the relationship between nigrostriatal dopamine (DA) signaling and locomotor function. Although toxin-based rat models produce frank nigrostriatal neuron loss and eventual motor decline characteristic of PD, the rapid nature of neuronal loss may not adequately translate premotor traits, such as cognitive decline. Unfortunately, rodent genetic PD models, like the Pink1 knockout (KO) rat, often fail to replicate the differential severity of striatal DA and tyrosine hydroxylase (TH) loss, and a bradykinetic phenotype, reminiscent of human PD. To elucidate this inconsistency, we evaluated aging as a progression factor in the timing of motor and non-motor cognitive impairments. Male PINK1 KO and age-matched wild type (WT) rats were evaluated in a longitudinal study from 3 to 16 months old in one cohort, and in a cross-sectional study of young adult (6-7 months) and aged (18-19 months) in another cohort. Young adult PINK1 KO rats exhibited hyperkinetic behavior associated with elevated DA and TH in the substantia nigra (SN), which decreased therein, but not striatum, in the aged KO rats. Additionally, norepinephrine levels decreased in aged KO rats in the prefrontal cortex (PFC), paired with a higher DA content in young and aged KO. Although a younger age of onset characterizes familial forms of PD, our results underscore the critical need to consider age-related factors. Moreover, the results indicate that compensatory mechanisms may exist to preserve locomotor function, evidenced by increased DA in the SN early in the lifespan, in response to deficient PINK1 function, which declines with aging and the onset of motor impairment.

Unravelling the Parkinson's puzzle, from medications and surgery to stem cells and genes: a comprehensive review of current and future management strategies

Parkinson's disease (PD) is a neurodegenerative disorder, prevalent in the elderly population. Neuropathological hallmarks of PD include loss of dopaminergic cells in the nigro-striatal pathway and deposition of alpha-synuclein protein in the neurons and synaptic terminals, which lead to a complex presentation of motor and non-motor symptoms. This review focuses on various aspects of PD, from clinical diagnosis to currently accepted treatment options, such as pharmacological management through dopamine replacement and surgical techniques such as deep brain stimulation (DBS). The review discusses in detail the potential of emerging stem cell-based therapies and gene therapies to be adopted as a cure, in contrast to the present symptomatic treatment in PD. The potential sources of stem cells for autologous and allogeneic stem cell therapy have been discussed, along with the progress evaluation of pre-clinical and clinical trials. Even though recent techniques hold great potential to improve the lives of PD patients, we present the importance of addressing the safety, efficacy, ethical, cost, and regulatory concerns before scaling them to clinical use.

CRISPR/sgRNA-directed synergistic activation mediator (SAM) as a therapeutic tool for Parkinson´s disease

Parkinson`s disease (PD) is the second most prevalent neurodegenerative disease, and different gene therapy strategies have been used as experimental treatments. As a proof-of-concept for the treatment of PD, we used SAM, a CRISPR gene activation system, to activate the endogenous tyrosine hydroxylase gene (th) of astrocytes to produce dopamine (DA) in the striatum of 6-OHDA-lesioned rats. Potential sgRNAs within the rat th promoter region were tested, and the expression of the Th protein was determined in the C6 glial cell line. Employing pseudo-lentivirus, the SAM complex and the selected sgRNA were transferred into cultures of rat astrocytes, and gene expression and Th protein synthesis were ascertained; furthermore, DA release into the culture medium was determined by HPLC. The DA-producing astrocytes were implanted into the striatum of 6-OHDA hemiparkinsonian rats. We observed motor behavior improvement in the lesioned rats that received DA-astrocytes compared to lesioned rats receiving astrocytes that did not produce DA. Our data indicate that the SAM-induced expression of the astrocyte´s endogenous th gene can generate DA-producing astrocytes that effectively reduce the motor asymmetry induced by the lesion.

Rit2 silencing in dopamine neurons drives a Parkinsonian phenotype

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and arises from dopamine (DA) neuron death selectively in the substantia nigra pars compacta (SNc). Rit2 is a reported PD risk allele, and recent single cell transcriptomic studies identified a major RIT2 cluster in PD DA neurons, potentially linking Rit2 expression loss to a PD patient cohort. However, it is still unknown whether Rit2 loss itself is causative for PD or PD-like symptoms. Here we report that conditional Rit2 silencing in mouse DA neurons drove motor dysfunction that occurred earlier in males than females and was rescued at early stages by either inhibiting the DA transporter (DAT) or with L-DOPA treatment. Motor dysfunction was accompanied by decreased DA release, striatal DA content, phenotypic DAergic markers, DA neurons, and DAergic terminals, with increased pSer129-alpha synuclein and pSer935-LRRK2 expression. These results provide the first evidence that Rit2 loss is causal for SNc cell death and a PD-like phenotype, and reveal key sex-specific differences in the response to Rit2 loss.

Advanced human iPSC-based preclinical model for Parkinson's disease with optogenetic alpha-synuclein aggregation

Human induced pluripotent stem cells (hiPSCs) offer advantages for disease modeling and drug discovery. However, recreating innate cellular pathologies, particularly in late-onset neurodegenerative diseases with accumulated protein aggregates including Parkinson's disease (PD), has been challenging. To overcome this barrier, we developed an optogenetics-assisted α-synuclein (α-syn) aggregation induction system (OASIS) that rapidly induces α-syn aggregates and toxicity in PD hiPSC-midbrain dopaminergic neurons and midbrain organoids. Our OASIS-based primary compound screening with SH-SY5Y cells identified 5 candidates that were secondarily validated with OASIS PD hiPSC-midbrain dopaminergic neurons and midbrain organoids, leading us to finally select BAG956. Furthermore, BAG956 significantly reverses characteristic PD phenotypes in α-syn preformed fibril models in vitro and in vivo by promoting autophagic clearance of pathological α-syn aggregates. Following the FDA Modernization Act 2.0's emphasis on alternative non-animal testing methods, our OASIS can serve as an animal-free preclinical test model (newly termed "nonclinical test") for the synucleinopathy drug development.

A structural magnetic resonance imaging review of clinical motor outcomes from deep brain stimulation in movement disorders

Patients with movement disorders treated by deep brain stimulation do not always achieve successful therapeutic alleviation of motor symptoms, even in cases where surgery is without complications. Magnetic resonance imaging (MRI) offers methods to investigate structural brain-related factors that may be predictive of clinical motor outcomes. This review aimed to identify features which have been associated with variability in clinical post-operative motor outcomes in patients with Parkinson's disease, dystonia, and essential tremor from structural MRI modalities. We performed a literature search for articles published between 1 January 2000 and 1 April 2022 and identified 5197 articles. Following screening through our inclusion criteria, we identified 60 total studies (39 = Parkinson's disease, 11 = dystonia syndromes and 10 = essential tremor). The review captured a range of structural MRI methods and analysis techniques used to identify factors related to clinical post-operative motor outcomes from deep brain stimulation. Morphometric markers, including volume and cortical thickness were commonly identified in studies focused on patients with Parkinson's disease and dystonia syndromes. Reduced metrics in basal ganglia, sensorimotor and frontal regions showed frequent associations with reduced motor outcomes. Increased structural connectivity to subcortical nuclei, sensorimotor and frontal regions was also associated with greater motor outcomes. In patients with tremor, increased structural connectivity to the cerebellum and cortical motor regions showed high prevalence across studies for greater clinical motor outcomes. In addition, we highlight conceptual issues for studies assessing clinical response with structural MRI and discuss future approaches towards optimizing individualized therapeutic benefits. Although quantitative MRI markers are in their infancy for clinical purposes in movement disorder treatments, structural features obtained from MRI offer the powerful potential to identify candidates who are more likely to benefit from deep brain stimulation and provide insight into the complexity of disorder pathophysiology.

Effects of Flavonoids on Cancer, Cardiovascular and Neurodegenerative Diseases: Role of NF-κB Signaling Pathway

Flavonoids are polyphenolic phytochemical compounds found in many plants, fruits, vegetables, and leaves. They have a multitude of medicinal applications due to their anti-inflammatory, antioxidative, antiviral, and anticarcinogenic properties. Furthermore, they also have neuroprotective and cardioprotective effects. Their biological properties depend on the chemical structure of flavonoids, their mechanism of action, and their bioavailability. The beneficial effects of flavonoids have been proven for a variety of diseases. In the last few years, it is demonstrated that the effects of flavonoids are mediated by inhibiting the NF-κB (Nuclear Factor-κB) pathway. In this review, we have summarized the effects of some flavonoids on the most common diseases, such as cancer, cardiovascular, and human neurodegenerative diseases. Here, we collected all recent studies describing the protective and prevention role of flavonoids derived from plants by specifically focusing their action on the NF-κB signaling pathway.

Emerging roles of GPR109A in regulation of neuroinflammation in neurological diseases and pain

Neuroinflammation plays a critical role in the pathological process of multiple neurological disorders and pathological pain conditions. GPR109A, a Gi protein-coupled receptor, has emerged as an important therapeutic target for controlling inflammation in various tissues and organs. In this review, we summarized current data about the role of GPR109A in neuroinflammation. Specifically, we focused on the pharmacological features of GPR109A and signaling pathways used by GPR109A to ameliorate neuroinflammation and symptoms in Alzheimer's disease, Parkinson's disease, multiple sclerosis, stroke, and pathological pain conditions.

Fountain of youth—Targeting autophagy in aging

As our society ages inexorably, geroscience and research focusing on healthy aging is becoming increasingly urgent. Macroautophagy (referred to as autophagy), a highly conserved process of cellular clearance and rejuvenation has attracted much attention due to its universal role in organismal life and death. Growing evidence points to autophagy process as being one of the key players in the determination of lifespan and health. Autophagy inducing interventions show significant improvement in organismal lifespan demonstrated in several experimental models. In line with this, preclinical models of age-related neurodegenerative diseases demonstrate pathology modulating effect of autophagy induction, implicating its potential to treat such disorders. In humans this specific process seems to be more complex. Recent clinical trials of drugs targeting autophagy point out some beneficial effects for clinical use, although with limited effectiveness, while others fail to show any significant improvement. We propose that using more human-relevant preclinical models for testing drug efficacy would significantly improve clinical trial outcomes. Lastly, the review discusses the available cellular reprogramming techniques used to model neuronal autophagy and neurodegeneration while exploring the existing evidence of autophagy’s role in aging and pathogenesis in human-derived in vitro models such as embryonic stem cells (ESCs), induced pluripotent stem cell derived neurons (iPSC-neurons) or induced neurons (iNs).

Endonuclease VIII-like 1 deficiency potentiates nigrostriatal dopaminergic neuron degeneration in a male mouse model of Parkinson's disease

Parkinson's disease (PD) is a common movement disorder caused by a characteristic loss of dopaminergic neurons in the substantia nigra and degeneration of dopamine terminals in the dorsal striatum. Previous studies have suggested that oxidative stress-induced DNA damage may be involved in PD pathogenesis, as steady-state levels of several types of oxidized nucleobases were shown to be elevated in PD brain tissues. These DNA lesions are normally removed from the genome by base excision repair, which is initiated by DNA glycosylase enzymes such as endonuclease VIII-like 1 (Neil1). In this study, we show that Neil1 plays an important role in limiting oxidative stress-induced degeneration of dopaminergic neurons. In particular, Neil1-deficient male mice exhibited enhanced sensitivity to nigrostriatal degeneration after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, and Neil1-deficient animals had higher levels of γH2AX-marked DNA damage than wild-type (WT) controls, regardless of treatment status. Moreover, MPTP-treated Neil1^-/- male mice had slightly elevated expression of genes related to the nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent antioxidant pathway. Treatment with the Nrf2 activator, monomethyl fumarate, reduced PD-like behaviors and pathology in Neil1^-/- male mice, suggesting that Neil1 is an important defense molecule in an oxidative cellular environment. Taken together, these results suggest that Neil1 DNA glycosylase may play an important role in limiting oxidative stress-mediated PD pathogenesis.

Unscrambling the Role of Redox-Active Biometals in Dopaminergic Neuronal Death and Promising Metal Chelation-Based Therapy for Parkinson's Disease

Biometals are all metal ions that are essential for all living organisms. About 40% of all enzymes with known structures require biometals to function correctly. The main target of damage by biometals is the central nervous system (CNS). Biometal dysregulation (metal deficiency or overload) is related to pathological processes. Chronic occupational and environmental exposure to biometals, including iron and copper, is related to an increased risk of developing Parkinson's disease (PD). Indeed, biometals have been shown to induce a dopaminergic neuronal loss in the substantia nigra. Although the etiology of PD is still unknown, oxidative stress dysregulation, mitochondrial dysfunction, and inhibition of both the ubiquitin-proteasome system (UPS) and autophagy are related to dopaminergic neuronal death. Herein, we addressed the involvement of redox-active biometals, iron, and copper, as oxidative stress and neuronal death inducers, as well as the current metal chelation-based therapy in PD.

DNA Methylation Signature of Aging: Potential Impact on the Pathogenesis of Parkinson's Disease

Regulation of gene expression by epigenetic modifications means lasting and heritable changes in the function of genes without alterations in the DNA sequence. Of all epigenetic mechanisms identified thus far, DNA methylation has been of particular interest in both aging and age-related disease research over the last decade given the consistency of site-specific DNA methylation changes during aging that can predict future health and lifespan. An increasing line of evidence has implied the dynamic nature of DNA (de)methylation events that occur throughout the lifespan has a role in the pathophysiology of aging and age-associated neurodegenerative conditions, including Parkinson's disease (PD). In this regard, PD methylome shows, to some extent, similar genome-wide changes observed in the methylome of healthy individuals of matching age. In this review, we start by providing a brief overview of studies outlining global patterns of DNA methylation, then its mechanisms and regulation, within the context of aging and PD. Considering diverging lines of evidence from different experimental and animal models of neurodegeneration and how they combine to shape our current understanding of tissue-specific changes in DNA methylome in health and disease, we report a high-level comparison of the genomic methylation landscapes of brain, with an emphasis on dopaminergic neurons in PD and in natural aging. We believe this will be particularly useful for systematically dissecting overlapping genome-wide alterations in DNA methylation during PD and healthy aging, and for improving our knowledge of PD-specific changes in methylation patterns independent of aging process.

Advances in NURR1-Regulated Neuroinflammation Associated with Parkinson's Disease

Neuroinflammation plays a crucial role in the progression of neurodegenerative disorders, particularly Parkinson's disease (PD). Glial cell activation and subsequent adaptive immune involvement are neuroinflammatory features in familial and idiopathic PD, resulting in the death of dopaminergic neuron cells. An oxidative stress response, inflammatory mediator production, and immune cell recruitment and activation are all hallmarks of this activation, leading to chronic neuroinflammation and progressive neurodegeneration. Several studies in PD patients' cerebrospinal fluid and peripheral blood revealed alterations in inflammatory markers and immune cell populations that may lead to or exacerbate neuroinflammation and perpetuate the neurodegenerative process. Most of the genes causing PD are also expressed in astrocytes and microglia, converting their neuroprotective role into a pathogenic one and contributing to disease onset and progression. Nuclear receptor-related transcription factor 1 (NURR1) regulates gene expression linked to dopaminergic neuron genesis and functional maintenance. In addition to playing a key role in developing and maintaining neurotransmitter phenotypes in dopaminergic neurons, NURR1 agonists have been shown to reverse behavioral and histological abnormalities in animal PD models. NURR1 protects dopaminergic neurons from inflammation-induced degeneration, specifically attenuating neuronal death by suppressing the expression of inflammatory genes in microglia and astrocytes. This narrative review highlights the inflammatory changes in PD and the advances in NURR1-regulated neuroinflammation associated with PD. Further, we present new evidence that targeting this inflammation with a variety of potential NURR1 target therapy medications can effectively slow the progression of chronic neuroinflammation-induced PD.

Circulating (Poly)phenol Metabolites: Neuroprotection in a 3D Cell Model of Parkinson's Disease

SCOPE

Diets rich in (poly)phenols have been associated with positive effects on neurodegenerative disorders, such as Parkinson's disease (PD). Several low-molecular weight (poly)phenol metabolites (LMWPM) are found in the plasma after consumption of (poly)phenol-rich food. It is expected that LMWPM, upon reaching the brain, may have beneficial effects against both oxidative stress and neuroinflammation, and possibly attenuate cell death mechanisms relate to the loss of dopaminergic neurons in PD.

METHODS AND RESULTS

This study investigates the neuroprotective potential of two blood-brain barrier permeant LMWPM, catechol-O-sulfate (cat-sulf), and pyrogallol-O-sulfate (pyr-sulf), in a human 3D cell model of PD. Neurospheroids were generated from LUHMES neuronal precursor cells and challenged by 1-methyl-4-phenylpyridinium (MPP⁺ ) to induce neuronal stress. LMWPM pretreatments were differently neuroprotective towards MPP⁺ insult, presenting distinct effects on the neuronal transcriptome. Particularly, cat-sulf pretreatment appeared to boost counter-regulatory defense mechanisms (preconditioning). When MPP⁺ is applied, both LMWPM positively modulated glutathione metabolism and heat-shock response, as also favorably shifting the balance of pro/anti-apoptotic proteins.

CONCLUSIONS

Our findings point to the potential of LMWPM to trigger molecular mechanisms that help dopaminergic neurons to cope with a subsequent toxic insult. They are promising molecules to be further explored in the context of preventing and attenuating parkinsonian neurodegeneration.

Apigenin Attenuates Functional and Structural Alterations via Targeting NF-kB/Nrf2 Signaling Pathway in LPS-Induced Parkinsonism in Experimental Rats : Apigenin Attenuates LPS-Induced Parkinsonism in Experimental Rats

Parkinson's disease (PD) is a progressive hypokinetic movement disorder caused by selective degeneration of dopaminergic neurons in striatum and dopamine deficiency in a region of the midbrain. LPS is an endotoxin, used as animal model to induce microglial activation, neuroinflammation, oxidative stress, and neurotransmitter alteration with PD-like symptoms. Therefore, to prevent neuroinflammation and neurotransmitter changes and to restore normal brain physiology, we tried apigenin (AGN) alone and in combination with piperine (bioenhancer), in LPS experimental model of rats. In this study, rats were treated with single unilateral intranigral injection of LPS at a dose of 5 μg/5 μl on day 0. The oral administration of AGN (25 and 50 mg/kg; p.o.) alone, AGN (25 mg/kg; p.o.) in combination with piperine (2.5 mg/kg; p.o.), and bromocriptine (10mg/kg; p.o.) started from day 7th once in a day. Intranigral injection of LPS significantly altered body weight and behavioral parameters assessed on weekly basis. Furthermore, the biochemical and neuroinflammatory analysis confirmed (on day 22nd) increased level of nitrite, MDA, SOD, TNF-α, IL-1β, IL-6, and caspase-1, and decreased level of CAT, GSH, and complex-I. Furthermore, altered level of neurotransmitters (DA, GABA, and glutamate) and cellular changes were observed from histopathological and immunohistochemistry (NF-kB and Nrf-2) analysis. Treatment with AGN (25 and 50 mg/kg; p.o.) alone and AGN (25 mg/kg; p.o.) in combination with piperine (2.5 mg/kg; p.o.) significantly attenuated the alteration in body weight, motor impairments, oxidative stress, neuroinflammation, and neurotransmitters in rat brain. The neuroprotective effect of AGN against LPS-induced cell death is attributed by modulating NF-kB and Nrf2 signaling pathway in the striatum.

Human Brain-Based Models Provide a Powerful Tool for the Advancement of Parkinson’s Disease Research and Therapeutic Development

Parkinson’s disease (PD) is the second most common neurodegenerative disease and affects approximately 2–3% of the population over the age of 65. PD is characterised by the loss of dopaminergic neurons from the substantia nigra, leading to debilitating motor symptoms including bradykinesia, tremor, rigidity, and postural instability. PD also results in a host of non-motor symptoms such as cognitive decline, sleep disturbances and depression. Although existing therapies can successfully manage some motor symptoms for several years, there is still no means to halt progression of this severely debilitating disorder. Animal models used to replicate aspects of PD have contributed greatly to our current understanding but do not fully replicate pathological mechanisms as they occur in patients. Because of this, there is now great interest in the use of human brain-based models to help further our understanding of disease processes. Human brain-based models include those derived from embryonic stem cells, patient-derived induced neurons, induced pluripotent stem cells and brain organoids, as well as post-mortem tissue. These models facilitate in vitro analysis of disease mechanisms and it is hoped they will help bridge the existing gap between bench and bedside. This review will discuss the various human brain-based models utilised in PD research today and highlight some of the key breakthroughs they have facilitated. Furthermore, the potential caveats associated with the use of human brain-based models will be detailed.

Methylated Cytochrome P450 and the Solute Carrier Family of Genes Correlate With Perturbations in Bile Acid Metabolism in Parkinson’s Disease

Parkinson’s disease (PD) is second most prevalent neurodegenerative disorder following Alzheimer’s disease. Parkinson’s disease is hypothesized to be caused by a multifaceted interplay between genetic and environmental factors. Herein, and for the first time, we describe the integration of metabolomics and epigenetics (genome-wide DNA methylation; epimetabolomics) to profile the frontal lobe from people who died from PD and compared them with age-, and sex-matched controls. We identified 48 metabolites to be at significantly different concentrations (FDR q < 0.05), 4,313 differentially methylated sites [5’-C-phosphate-G-3’ (CpGs)] (FDR q < 0.05) and increased DNA methylation age in the primary motor cortex of people who died from PD. We identified Primary bile acid biosynthesis as the major biochemical pathway to be perturbed in the frontal lobe of PD sufferers, and the metabolite taurine (p-value = 5.91E-06) as being positively correlated with CpG cg14286187 (SLC25A27; CYP39A1) (FDR q = 0.002), highlighting previously unreported biochemical changes associated with PD pathogenesis. In this novel multi-omics study, we identify regulatory mechanisms which we believe warrant future translational investigation and central biomarkers of PD which require further validation in more accessible biomatrices.

Midbrain organoids mimic early embryonic neurodevelopment and recapitulate LRRK2-p.Gly2019Ser-associated gene expression

Human brain organoid models that recapitulate the physiology and complexity of the human brain have a great potential for in vitro disease modeling, in particular for neurodegenerative diseases, such as Parkinson disease. In the present study, we compare single-cell RNA-sequencing data of human midbrain organoids to the developing human embryonic midbrain. We demonstrate that the in vitro model is comparable to its in vivo equivalents in terms of developmental path and cellular composition. Moreover, we investigate the potential of midbrain organoids for modeling early developmental changes in Parkinson disease. Therefore, we compare the single-cell RNA-sequencing data of healthy-individual-derived midbrain organoids to their isogenic LRRK2-p.Gly2019Ser-mutant counterparts. We show that the LRRK2 p.Gly2019Ser variant alters neurodevelopment, resulting in an untimely and incomplete differentiation with reduced cellular variability. Finally, we present four candidate genes, APP, DNAJC6, GATA3, and PTN, that might contribute to the LRRK2-p.Gly2019Ser-associated transcriptome changes that occur during early neurodevelopment.

DA-9805 protects dopaminergic neurons from endoplasmic reticulum stress and inflammation

Parkinson's disease (PD) is a multifactorial neurodegenerative disease with damages to mitochondria and endoplasmic reticulum (ER), followed by neuroinflammation. We previously reported that a triple herbal extract DA-9805 in experimental PD toxin-models had neuroprotective effects by alleviating mitochondrial damage and oxidative stress. In the present study, we investigated whether DA-9805 could suppress ER stress and neuroinflammation in vitro and/or in vivo. Pre-treatment with DA-9805 (1 μg/ml) attenuated upregulation of glucose-regulated protein 78 (GRP78), C/EBP homologous protein (CHOP) and cleaved caspase-3 in SH-SY5Y neuroblastoma cells treated with thapsigargin (1 µg/ml) or tunicamycin (2 µg/ml). In addition, DA-9805 prevented the production of IL-1β, IL-6, TNF-α and nitric oxide through inhibition of NF-κB activation in BV2 microglial cells stimulated with lipopolysaccharides (LPS). Intraperitoneal injection of LPS (10 mg/kg) into mice can induce acute neuroinflammation and dopaminergic neuronal cell death. Oral administration of DA-9805 (10 or 30 mg/kg/day for 3 days before LPS injection) prevented loss of dopaminergic neurons and activation of microglia and astrocytes in the substantia nigra in LPS-injected mouse models. Taken together, these results indicate that DA-9805 can effectively prevent ER stress and neuroinflammation, suggesting that DA-9805 is a multitargeting and disease-modifying therapeutic candidate for PD.

Dynamics of Choline-Containing Phospholipids in Traumatic Brain Injury and Associated Comorbidities

The incidences of traumatic brain injuries (TBIs) are increasing globally because of expanding population and increased dependencies on motorized vehicles and machines. This has resulted in increased socio-economic burden on the healthcare system, as TBIs are often associated with mental and physical morbidities with lifelong dependencies, and have severely limited therapeutic options. There is an emerging need to identify the molecular mechanisms orchestrating these injuries to life-long neurodegenerative disease and a therapeutic strategy to counter them. This review highlights the dynamics and role of choline-containing phospholipids during TBIs and how they can be used to evaluate the severity of injuries and later targeted to mitigate neuro-degradation, based on clinical and preclinical studies. Choline-based phospholipids are involved in maintaining the structural integrity of the neuronal/glial cell membranes and are simultaneously the essential component of various biochemical pathways, such as cholinergic neuronal transmission in the brain. Choline or its metabolite levels increase during acute and chronic phases of TBI because of excitotoxicity, ischemia and oxidative stress; this can serve as useful biomarker to predict the severity and prognosis of TBIs. Moreover, the effect of choline-replenishing agents as a post-TBI management strategy has been reviewed in clinical and preclinical studies. Overall, this review determines the theranostic potential of choline phospholipids and provides new insights in the management of TBI.

Oxidative Stress and Neurodegeneration: Interconnected Processes in PolyQ Diseases

Neurodegenerative polyglutamine (polyQ) disorders are caused by trinucleotide repeat expansions within the coding region of disease-causing genes. PolyQ-expanded proteins undergo conformational changes leading to the formation of protein inclusions which are associated with selective neuronal degeneration. Several lines of evidence indicate that these mutant proteins are associated with oxidative stress, proteasome impairment and microglia activation. These events may correlate with the induction of inflammation in the nervous system and disease progression. Here, we review the effect of polyQ-induced oxidative stress in cellular and animal models of polyQ diseases. Furthermore, we discuss the interplay between oxidative stress, neurodegeneration and neuroinflammation using as an example the well-known neuroinflammatory disease, Multiple Sclerosis. Finally, we review some of the pharmaceutical interventions which may delay the onset and progression of polyQ disorders by targeting disease-associated mechanisms.

Alpha-Synuclein as a Biomarker of Parkinson's Disease: Good, but Not Good Enough

Parkinson's disease (PD) is the second most common neurodegenerative disorder of the elderly, presenting primarily with symptoms of motor impairment. The disease is diagnosed most commonly by clinical examination with a great degree of accuracy in specialized centers. However, in some cases, non-classical presentations occur when it may be difficult to distinguish the disease from other types of degenerative or non-degenerative movement disorders with overlapping symptoms. The diagnostic difficulty may also arise in patients at the early stage of PD. Thus, a biomarker could help clinicians circumvent such problems and help them monitor the improvement in disease pathology during anti-parkinsonian drug trials. This review first provides a brief overview of PD, emphasizing, in the process, the important role of α-synuclein in the pathogenesis of the disease. Various attempts made by the researchers to develop imaging, genetic, and various biochemical biomarkers for PD are then briefly reviewed to point out the absence of a definitive biomarker for this disorder. In view of the overwhelming importance of α-synuclein in the pathogenesis, a detailed analysis is then made of various studies to establish the biomarker potential of this protein in PD; these studies measured total α-synuclein, oligomeric, and post-translationally modified forms of α-synuclein in cerebrospinal fluid, blood (plasma, serum, erythrocytes, and circulating neuron-specific extracellular vesicles) and saliva in combination with certain other proteins. Multiple studies also examined the accumulation of α-synuclein in various forms in PD in the neural elements in the gut, submandibular glands, skin, and the retina. The measurements of the levels of certain forms of α-synuclein in some of these body fluids or their components or peripheral tissues hold a significant promise in establishing α-synuclein as a definitive biomarker for PD. However, many methodological issues related to detection and quantification of α-synuclein have to be resolved, and larger cross-sectional and follow-up studies with controls and patients of PD, parkinsonian disorders, and non-parkinsonian movement disorders are to be undertaken.

Emerging targets for the diagnosis of Parkinson's disease: examination of systemic biomarkers

Parkinson's disease (PD) is a highly prevalent and irreversible neurodegenerative disorder that is typically diagnosed in an advanced stage. Currently, there are no approved biomarkers that reliably identify PD patients before they have undergone extensive neuronal damage, eliminating the opportunity for future disease-modifying therapies to intervene in disease progression. This unmet need for diagnostic and therapeutic biomarkers has fueled PD research for decades, but these efforts have not yet yielded actionable results. Recently, studies exploring mechanisms underlying PD progression have offered insights into multisystemic contributions to pathology, challenging the classic perspective of PD as a disease isolated to the brain. This shift in understanding has opened the door to potential new biomarkers from multiple sites in the body. This review focuses on emerging candidates for PD biomarkers in the context of current diagnostic approaches and multiple organ systems that contribute to disease.

Vesicular glutamate transporter modulates sex differences in dopamine neuron vulnerability to age-related neurodegeneration

Age is the greatest risk factor for Parkinson's disease (PD) which causes progressive loss of dopamine (DA) neurons, with males at greater risk than females. Intriguingly, some DA neurons are more resilient to degeneration than others. Increasing evidence suggests that vesicular glutamate transporter (VGLUT) expression in DA neurons plays a role in this selective vulnerability. We investigated the role of DA neuron VGLUT in sex- and age-related differences in DA neuron vulnerability using the genetically tractable Drosophila model. We found sex differences in age-related DA neurodegeneration and its associated locomotor behavior, where males exhibit significantly greater decreases in both DA neuron number and locomotion during aging compared with females. We discovered that dynamic changes in DA neuron VGLUT expression mediate these age- and sex-related differences, as a potential compensatory mechanism for diminished DA neurotransmission during aging. Importantly, female Drosophila possess higher levels of VGLUT expression in DA neurons compared with males, and this finding is conserved across flies, rodents, and humans. Moreover, we showed that diminishing VGLUT expression in DA neurons eliminates females' greater resilience to DA neuron loss across aging. This offers a new mechanism for sex differences in selective DA neuron vulnerability to age-related DA neurodegeneration. Finally, in mice, we showed that the ability of DA neurons to achieve optimal control over VGLUT expression is essential for DA neuron survival. These findings lay the groundwork for the manipulation of DA neuron VGLUT expression as a novel therapeutic strategy to boost DA neuron resilience to age- and PD-related neurodegeneration.

Towards physiologically relevant human pluripotent stem cell (hPSC) models of Parkinson's disease

The derivation of human embryonic stem cells followed by the discovery of induced pluripotent stem cells and leaps in genome editing approaches have continuously fueled enthusiasm for the development of new models of neurodegenerative diseases such as Parkinson's disease (PD). PD is characterized by the relative selective loss of dopaminergic neurons (DNs) in specific areas of substantia nigra pars compacta (SNpc). While degeneration in late stages can be widespread, there is stereotypic early degeneration of these uniquely vulnerable neurons. Various causes of selective vulnerability have been investigated but much remains unclear. Most studies have sought to identify cell autonomous properties of the most vulnerable neurons. However, recent findings from genetic studies and model systems have added to our understanding of non-cell autonomous contributions including regional-specific neuro-immune interactions with astrocytes, resident or damage-activated microglia, neuro-glia cell metabolic interactions, involvement of endothelial cells, and damage to the vascular system. All of these contribute to specific vulnerability and, along with aging and environmental factors, might be integrated in a complex stressor-threshold model of neurodegeneration. In this forward-looking review, we synthesize recent advances in the field of PD modeling using human pluripotent stem cells, with an emphasis on organoid and complex co-culture models of the nigrostriatal niche, with emerging CRISPR applications to edit or perturb expression of causal PD genes and associated risk factors, such as GBA, to understand the impact of these genes on relevant phenotypes.

Dexmedetomidine protects against degeneration of dopaminergic neurons and improves motor activity in Parkinson's disease mice model

Parkinson’s disease (PD) is the result of dopaminergic (DA) neuronal death in the substantianigra pars compacta (SNc). Current treatments for PD such as L-dopa are limited in effectiveness and fail to address the cause. Targeted anti-inflammatory therapies, particularly directed at nuclear factor kappa B (NF‐κB) activity in alleviating degeneration of DA-neurons is of evolving interest. In the present study, we hypothesised that dexmedetomidine (DEX), an alpha-2 receptor adrenergic agonist, suppress the inflammatory responses associated with PD and restores dopaminergic levels by alleviating substantia nigral degeneration. Male mice (C57Bl/10, 8–11 months old and of 34–40 g of weight) were divided into: the control, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and MPTP + dexmedetomidine (MPTP + DEX) (n = 26 each group). Dex restored dopamine levels in SNpc of MPTP-induced PD mice model. Results of immunohisto staining revealed that Dex treatment post-MPTP induction restored TH-positive cells, with only 12.37% increase (^##p < 0.01 vs MPTP) on the third day and a steep 55% increase (^###p < 0.001 vs MPTP) following the seventh day of Dex treatment. Moreover, the expressions of proinflammatory markers regulated by NF-κB were diminished in Dex + MPTP group. In addition, cylinder test revealed that Dex treatment improved asymmetric limb usage pattern in MPTP induced mice over the course of 7 days. Hence, in this study, we provided insight on the effect of Dex in the inhibition of NF-κB1 regulated proinflammatory mediators to improve dopamine levels and reduce SNpc dopaminergic neuronal degeneration.

Potential of Antibiotics for the Treatment and Management of Parkinson Disease: An Overview

Evidences have emerged over the last 2 decades to ascertain the proof of concepts viz. mitochondrial dysfunction, inflammation-derived oxidative damage and cytokine-induced toxicity that play a significant role in Parkinson's disease (PD). The available pharmacotherapies for PD are mainly symptomatic and typically indications of L-DOPA to restrain dopamine deficiency and their consequences. In the 21st century, the role of the antibiotics has emerged at the forefront of medicine in health and human illness. There are several experimental and pre-clinical evidences that supported the potential use of antibiotic as neuroprotective agent. The astonishing effects of antibiotics and their neuroprotective properties against neurodegeneration and neuro-inflammation would be phenomenal for the development of effective therapy against PD. Antibiotics are also testified as useful not only to prevent the formation of alpha-synuclein but also act on mitochondrial dysfunction and neuro-inflammation. Thus, the possible therapy with antibiotics in PD would impact both the pathways leading to neuronal cell death in substantia nigra and pars compacta in midbrain. Moreover, the antibiotic based pharmacotherapy will open a scientific research passageway to add more to the evidence based and rational use of antibiotics for the treatment and management of PD and other neurodegenerative disorders.

Energy, Entropy and Quantum Tunneling of Protons and Electrons in Brain Mitochondria: Relation to Mitochondrial Impairment in Aging-Related Human Brain Diseases and Therapeutic Measures

Adult human brains consume a disproportionate amount of energy substrates (2-3% of body weight; 20-25% of total glucose and oxygen). Adenosine triphosphate (ATP) is a universal energy currency in brains and is produced by oxidative phosphorylation (OXPHOS) using ATP synthase, a nano-rotor powered by the proton gradient generated from proton-coupled electron transfer (PCET) in the multi-complex electron transport chain (ETC). ETC catalysis rates are reduced in brains from humans with neurodegenerative diseases (NDDs). Declines of ETC function in NDDs may result from combinations of nitrative stress (NS)-oxidative stress (OS) damage; mitochondrial and/or nuclear genomic mutations of ETC/OXPHOS genes; epigenetic modifications of ETC/OXPHOS genes; or defects in importation or assembly of ETC/OXPHOS proteins or complexes, respectively; or alterations in mitochondrial dynamics (fusion, fission, mitophagy). Substantial free energy is gained by direct O2-mediated oxidation of NADH. Traditional ETC mechanisms require separation between O2 and electrons flowing from NADH/FADH2 through the ETC. Quantum tunneling of electrons and much larger protons may facilitate this separation. Neuronal death may be viewed as a local increase in entropy requiring constant energy input to avoid. The ATP requirement of the brain may partially be used for avoidance of local entropy increase. Mitochondrial therapeutics seeks to correct deficiencies in ETC and OXPHOS.

A New Synuclein-Transgenic Mouse Model for Early Parkinson's Reveals Molecular Features of Preclinical Disease

Understanding Parkinson's disease (PD), in particular in its earliest phases, is important for diagnosis and treatment. However, human brain samples are collected post-mortem, reflecting mainly end-stage disease. Because brain samples of mouse models can be collected at any stage of the disease process, they are useful in investigating PD progression. Here, we compare ventral midbrain transcriptomics profiles from α-synuclein transgenic mice with a progressive, early PD-like striatal neurodegeneration across different ages using pathway, gene set, and network analysis methods. Our study uncovers statistically significant altered genes across ages and between genotypes with known, suspected, or unknown function in PD pathogenesis and key pathways associated with disease progression. Among those are genotype-dependent alterations associated with synaptic plasticity and neurotransmission, as well as mitochondria-related genes and dysregulation of lipid metabolism. Age-dependent changes were among others observed in neuronal and synaptic activity, calcium homeostasis, and membrane receptor signaling pathways, many of which linked to G-protein coupled receptors. Most importantly, most changes occurred before neurodegeneration was detected in this model, which points to a sequence of gene expression events that may be relevant for disease initiation and progression. It is tempting to speculate that molecular changes similar to those changes observed in our model happen in midbrain dopaminergic neurons before they start to degenerate. In other words, we believe we have uncovered molecular changes that accompany the progression from preclinical to early PD.

Regulation of AKT/AMPK signaling, autophagy and mitigation of apoptosis in Rutin-pretreated SH-SY5Y cells exposed to MPP. Metab Brain Dis 2021;36:315-326. [PMID: 33146846 DOI: 10.1007/s11011-020-00641-z]

Accumulating evidence suggest that apoptosis, autophagy and dysregulation of signaling pathways are common mechanisms involved in Parkinson's disease (PD) pathogenesis, and thus development of therapeutic agents targeting these mechanisms may be useful for the treatment of this disease. Although rutin (a bioflavonoid) is reported to have pharmacological benefits such as antioxidant, anti-inflammatory and antitumor activities, there are very few reports on the activity of this compound in 1-methyl-4-phenylpyridinium (MPP⁺)-induced PD models. Accordingly, we investigated the effects of rutin on apoptosis, autophagy and cell signaling markers (AKT/AMPK) in SH-SY5Y cells exposed to MPP⁺. Results show reduced changes in nuclear morphology and mitigation of caspase 3/7 and 9 activities in rutin pre-treated cells exposed to MPP⁺. Likewise, rutin regulated cell signaling pathways (AKT/AMPK) and significantly decreased protein expression levels of cleaved PARP, cytochrome c, LC3-II and p62. Also, rutin significantly increased protein expression levels of full-length caspase 3 in SH-SY5Y cells treated with MPP⁺. Transmission electron microscope (TEM) images demonstrated a reduction in autophagosomes in rutin-pretreated SH-SY5Y cells exposed to MPP⁺. These results provide experimental support for rutin's neuroprotective activity against MPP⁺-induced toxicity in SH-SY5Y cells, which is as a promising therapeutic agent for clinical trials in humans.

Mitophagy impairment in neurodegenerative diseases: Pathogenesis and therapeutic interventions

Neurons are specialized cells, requiring a lot of energy for its proper functioning. Mitochondria are the key cellular organelles and produce most of the energy in the form of ATP, required for all the crucial functions of neurons. Hence, the regulation of mitochondrial biogenesis and quality control is important for maintaining neuronal health. As a part of mitochondrial quality control, the aged and damaged mitochondria are removed through a selective mode of autophagy called mitophagy. However, in different pathological conditions, this process is impaired in neuronal cells and lead to a variety of neurodegenerative disease (NDD). Various studies indicate that specific protein aggregates, the characteristics of different NDDs, affect this process of mitophagy, adding to the severity and progression of diseases. Though, the detailed process of this association is yet to be explored. In light of the significant role of impaired mitophagy in NDDs, further studies have also investigated a large number of therapeutic strategies to target mitophagy in these diseases. Our current review summarizes the abnormalities in different mitophagy pathways and their association with different NDDs. We have also elaborated upon various novel therapeutic strategies and their limitations to enhance mitophagy in NDDs that may help in the management of symptoms and increasing the life expectancy of NDD patients. Thus, our study provides an overview of mitophagy in NDDs and emphasizes the need to elucidate the mechanism of impaired mitophagy prevalent across different NDDs in future research. This will help designing better treatment options with high efficacy and specificity.

Arbutin effectively ameliorates the symptoms of Parkinson's disease: the role of adenosine receptors and cyclic adenosine monophosphate

An antagonistic communication exists between adenosinergic and dopaminergic signaling in the basal ganglia, which suggests that the suppression of adenosine A_2A receptors-cyclic adenosine monophosphate pathway may be able to restore the disrupted dopamine transmission that results in motor symptoms in Parkinson’s disease (PD). Arbutin is a natural glycoside that possesses antioxidant, anti-inflammatory, and neuroprotective properties. The purpose of this study was to investigate whether arbutin could ameliorate the symptoms of PD and to examine the underlying mechanism. In this study, Swiss albino mouse models of PD were established by the intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine for 4 successive days, with the concurrent intraperitoneal administration of arbutin (50 and 100 mg/kg) for 7 days. The results showed that arbutin significantly reduced lipid peroxidation, total nitrite levels, and inflammation in the substantia nigra and striatum of PD mouse models. In addition, arbutin decreased the activity of endogenous antioxidants, reduced the levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and γ-aminobutyric acid, and minimized neurodegeneration in the striatum. Arbutin also reduced the abnormal performance of PD mouse models in the open field test, bar test, pole test, and rotarod test. The therapeutic efficacy of arbutin was similar to that of madopar. The intraperitoneal injection of the A_2AR agonist CGS21680 (0.5 mg/kg) attenuated the therapeutic effects of arbutin, whereas the intraperitoneal injection of forskolin (3 mg/kg) enhanced arbutin-mediated improvements. These findings suggest that arbutin can improve the performance of PD mouse models by inhibiting the function of the A_2AR and enhancing the effects of cyclic adenosine monophosphate. This study was approved by the Institutional Animal Ethics Committee (1616/PO/Re/S/12/CPCSEA) on November 17, 2019 (approval No. IAEC/2019/010).

L-DOPA regulates α-synuclein accumulation in experimental parkinsonism

AIMS

Widespread accumulation of misfolded α-synuclein aggregates is a key feature of Parkinson's disease (PD). Although the pattern and extent of α-synuclein accumulation through PD brains is known, the impact of chronic dopamine-replacement therapy (the gold-standard pharmacological treatment of PD) on the fate of α-synuclein is still unknown. Here, we investigated the distribution and accumulation of α-synuclein in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) non-human primate model of PD and determined the effect of chronic L-DOPA treatment on MPTP-induced α-synuclein pathology.

METHODS

We measured the density of α-synuclein and tau immuno-positive neurons in the substantia nigra, putamen, hippocampal CA1 region, temporal cortex and dentate nucleus of control, MPTP and MPTP+L-DOPA-treated monkeys. Moreover, we also extracted and quantified Triton-X (TX) soluble and insoluble α-synuclein in putamen and hippocampus samples from a separate cohort of control, MPTP and MPTP+L-DOPA-treated monkeys.

RESULTS

MPTP-induced α-synuclein accumulation in NHP model of PD was not limited to the substantia nigra but also occurred in the putamen, hippocampal CA1 region and temporal cortex. Tau was increased only in the temporal cortex. Moreover, increased intraneuronal TX insoluble α-synuclein was truncated, but not in the structural form of Lewy bodies. The MPTP-induced increase in α-synuclein levels was abolished in animals having received L-DOPA in all the brain regions, except in the substantia nigra.

CONCLUSIONS

Dopamine replacement therapy can dramatically ameliorate α-synuclein pathology in the MPTP NHP model of PD. Therefore, patient's dopaminergic medication should be systematically considered when assessing α-synuclein as a biomarker for diagnosis, monitoring disease progression and response to disease-modifying treatments.

Acupuncture inhibits neuroinflammation and gut microbial dysbiosis in a mouse model of Parkinson's disease

Growing evidences show that gut microbiota is associated with the pathogenesis of Parkinson's disease (PD) and the gut-brain axis can be promising target for the development of the therapeutic strategies for PD. Acupuncture has been used to improve brain functions and inflammation in neurological disorders such as PD, and to recover the gastrointestinal dysfunctions in various gastrointestinal disorders. Thus, we investigated whether acupuncture could improve Parkinsonism and gut microbial dysbiosis induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. First, we observed that acupuncture treatment at acupoints GB34 and ST36 could improve motor functions and comorbid anxiety in PD mice. Next, we found that acupuncture increased the levels of dopaminergic fibers and neurons in the striatum and the substantia nigra, respectively. Acupuncture also restored the overexpression of microglia and astrocyte as well as conversion of Bax and Bcl-2 expression in both the striatum and the substantia nigra, indicating that inflammatory responses and apoptosis were blocked by acupuncture. Additionally, via 16S rRNA sequence analysis, we observed that the relative abundance of 18 genera were changed in acupuncture-treated mice compared to the PD mice. Of them, Butyricimonas, Holdemania, Frisingicoccus, Gracilibacter, Phocea, and Aestuariispira showed significant correlations with anxiety as well as motor functions. Furthermore, the predicted functional analyses showed that acupuncture restored the physiology functions such as glutathione metabolism, methane metabolism, and PD pathway. In conclusion, we suggest that the effects of acupuncture on the enhanced motor function and the protection of the dopaminergic neurons may be associated with the regulation of the gut microbial dysbiosis and thus the inhibition of the neuroinflammation in the PD mice.

Is the Immunological Response a Bottleneck for Cell Therapy in Neurodegenerative Diseases?

Neurodegenerative disorders such as Parkinson's (PD) and Huntington's disease (HD) are characterized by a selective detrimental impact on neurons in a specific brain area. Currently, these diseases have no cures, although some promising trials of therapies that may be able to slow the loss of brain cells are underway. Cell therapy is distinguished by its potential to replace cells to compensate for those lost to the degenerative process and has shown a great potential to replace degenerated neurons in animal models and in clinical trials in PD and HD patients. Fetal-derived neural progenitor cells, embryonic stem cells or induced pluripotent stem cells are the main cell sources that have been tested in cell therapy approaches. Furthermore, new strategies are emerging, such as the use of adult stem cells, encapsulated cell lines releasing trophic factors or cell-free products, containing an enriched secretome, which have shown beneficial preclinical outcomes. One of the major challenges for these potential new treatments is to overcome the host immune response to the transplanted cells. Immune rejection can cause significant alterations in transplanted and endogenous tissue and requires immunosuppressive drugs that may produce adverse effects. T-, B-lymphocytes and microglia have been recognized as the main effectors in striatal graft rejection. This review aims to summarize the preclinical and clinical studies of cell therapies in PD and HD. In addition, the precautions and strategies to ensure the highest quality of cell grafts, the lowest risk during transplantation and the reduction of a possible immune rejection will be outlined. Altogether, the wide-ranging possibilities of advanced therapy medicinal products (ATMPs) could make therapeutic treatment of these incurable diseases possible in the near future.

Genetic predispositions of Parkinson's disease revealed in patient-derived brain cells

Parkinson's disease (PD) is the second most prevalent neurological disorder and has been the focus of intense investigations to understand its etiology and progression, but it still lacks a cure. Modeling diseases of the central nervous system in vitro with human induced pluripotent stem cells (hiPSC) is still in its infancy but has the potential to expedite the discovery and validation of new treatments. Here, we discuss the interplay between genetic predispositions and midbrain neuronal impairments in people living with PD. We first summarize the prevalence of causal Parkinson's genes and risk factors reported in 74 epidemiological and genomic studies. We then present a meta-analysis of 385 hiPSC-derived neuronal lines from 67 recent independent original research articles, which point towards specific impairments in neurons from Parkinson's patients, within the context of genetic predispositions. Despite the heterogeneous nature of the disease, current iPSC models reveal converging molecular pathways underlying neurodegeneration in a range of familial and sporadic forms of Parkinson's disease. Altogether, consolidating our understanding of robust cellular phenotypes across genetic cohorts of Parkinson's patients may guide future personalized drug screens in preclinical research.

Downregulation of eEF1A/EFT3-4 Enhances Dopaminergic Neurodegeneration After 6-OHDA Exposure in C. elegans Model

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by the aggregation of α-synuclein protein and selective death of dopaminergic (DA) neurons in the substantia nigra of the midbrain. Although the molecular pathogenesis of PD is not completely understood, a recent study has reported that eukaryotic translation elongation factor 1 alpha (eEF1A) declined in the PD-affected brain. Therefore, the roles of eEF1A1 and eEF1A2 in the prevention of DA neuronal cell death in PD are aimed to be investigated. Herein, by using Caenorhabditis elegans as a PD model, we investigated the role of eft-3/eft-4, the worm homolog of eEF1A1/eEF1A2, on 6-hydroxydopamine (6-OHDA)-induced DA neuron degeneration. Our results demonstrated that the expressions of eft-3 and eft-4 were decreased in the 6-OHDA-induced worms. RNA interference (RNAi) of eft-3 and eft-4 resulted in dramatic exacerbation of DA neurodegeneration induced by 6-OHDA, as well as aggravated the food-sensing behavior, ethanol avoidance, and decreased lifespan when compared with only 6-OHDA-induced worms. Moreover, downregulation of eft-3/4 in 6-OHDA-induced worms suppressed the expression of the anti-apoptotic genes, including PI3K/age-1, PDK-1/pdk-1, mTOR/let-363, and AKT-1,2/akt-1,2, promoting the expression of apoptotic genes such as BH3/egl-1 and Caspase-9/ced-3. Collectively, these findings indicate that eEF1A plays an important role in the 6-OHDA-induced neurodegeneration through the phosphatidylinositol 3-kinase (PI3K)/serine/threonine protein kinase (Akt)/mammalian target of rapamycin (mTOR) pathway and that eEF1A isoforms may be a novel and effective pro-survival factor in protective DA neurons against toxin-induced neuronal death.

Advancement in the modelling and therapeutics of Parkinson's disease

Since the discovery of L-dopa in the middle of the 20th century (1960s), there is not any neuroprotective therapy available although significant development has been made in the treatment of symptomatic Parkinson's disease (PD). Neurological disorders like PD can be modelled in animals so as to recapitulates most of the symptoms seen in PD patients. In aging population, PD is the second most common neurodegenerative disease after Alzheimer's disease, even though significant outcomes have been achieved in PD research yet it still is a mystery to solve the treatments for PD. In the last two decades, PD models have provided enhanced precision into the understanding of the process of PD disease, its etiology, pathology, and molecular mechanisms behind it. Furthermore, at the same time as cellular models have helped to recognize specific events, animal models, both toxic and genetic, have replicated almost all of the hallmarks of PD and are very helpful for testing and finding new strategies for neuroprotection. Recently, in both classical and newer models, major advances have been done in the modelling of supplementary PD features have come into the light. In this review, we have try to provide an updated summary of the characteristics of these models related to in vitro and in vivo models, animal models for PD, stem cell model for PD, newer 3D model as well as the strengths and limitations of these most popular PD models.

Parkinson's Disease-Associated Changes in the Expression of Neurotrophic Factors and their Receptors upon Neuronal Differentiation of Human Induced Pluripotent Stem Cells

Parkinson's disease (PD) is a neurodegenerative pathology resulting from the degeneration of dopaminergic (DA) neurons in the substantia nigra (SN). Neurotrophic factors (NTFs) and their receptors are key regulators of the survival, differentiation, and development of neurons. However, the role of these factors in the pathogenesis of PD is still unclear. Here, we analyzed the expression of NTFs and their receptors in human induced pluripotent stem cells (iPSCs) derived from the fibroblasts of patients with PD and healthy donors (HDs). Four PD-derived iPSC lines with different mutations and three cell lines from HDs at different stages of neuronal differentiation were used for RT-qPCR analysis and ELISA. We found that the mRNA levels of most analyzed genes were altered in PD-derived cells compared with those in HD-derived cells at all stages. Importantly, irrespective of PD-associated mutations, the mRNA levels of the BDNF and GDNF genes were mostly increased or unchanged in predominantly DA terminally differentiated neurons (TDNs) compared with those in HD-derived cells. Strikingly, in contrast to BDNF and GDNF mRNA levels, BDNF and GDNF protein levels were lower in almost all PD-derived TDNs than in HD-derived cells, thus indicating the dysregulation of NTF expression at the post-transcriptional level. We suggest that this dysregulation is one of the important signs of PD development.

Dopamine D1 receptor agonism induces dynamin related protein-1 inhibition to improve mitochondrial biogenesis and dopaminergic neurogenesis in rat model of Parkinson's disease

Dopamine (DA) neurotransmitter act on dopamine receptors (D1-D5) to regulate motor functions, reward, addiction and cognitive behavior. The depletion of DA in midbrain due to degeneration of nigral dopaminergic (DAergic) neurons leads to Parkinson's disease (PD). DA agonist and levodopa (L-DOPA) are the only therapies used for symptomatic relief in PD. However, the role of DA receptors in PD pathogenesis and how they are associated with mitochondrial functions and DAergic neurogenesis is still not known. Here, we investigated the mechanistic aspect of DA D1 receptor mediated control of DAergic neurogenesis, motor behavior and mitochondrial functions in rat PD model. The pharmacological activation of D1 receptors markedly improved motor deficits, mitochondrial biogenesis, ATP levels, mitochondrial membrane potential and defended nigral DAergic neurons against 6-hydroxydopamine (6-OHDA) induced neurotoxicity in adult rats. However, the D1 agonist mediated effects were abolished following D1 receptor antagonist treatment in 6-OHDA lesioned rats. Interestingly, pharmacological inhibition of dynamin related protein-1 (Drp-1) by Mdivi-1 in D1 antagonist treated PD rats, significantly restored behavioral deficits, mitochondrial functions, mitochondrial biogenesis and increased the number of newborn DAergic neurons in substantia nigra pars compacta (SNpc). Drp-1 inhibition mediated neuroprotective effects in PD rats were associated with increased level of protein kinase-B/Akt and extracellular-signal-regulated kinase (ERK). Taken together, our data suggests that dopamine D1 receptor mediated reduction in mitochondrial fission and enhanced DAergic neurogenesis may involve Drp-1 inhibition which led to improved behavioral recovery in PD rats.

Gami-Chunggan Formula Prevents Motor Dysfunction in MPTP/p-Induced and A53T α-Synuclein Overexpressed Parkinson's Disease Mouse Model Though DJ-1 and BDNF Expression

The Gami–Chunggan formula (GCF) is a modification of the Chunggan (CG) decoction, which has been used to treat movement disorders such as Parkinson’s disease (PD) in Traditional East Asian Medicine. To evaluate the neuroprotective effects of GCF in chronic PD animal models, we used either a 5-week treatment of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine with probenecid (MPTP/p) or the α-synuclein A53T overexpressed PD mouse model. C57BL/6 mice were treated with MPTP, in combination with probenecid, for 5 weeks. GCF was administered simultaneously with MPTP injection for 38 days. The A53T α-synuclein overexpressed mice were also fed with GCF for 60 days. Using behavioral readouts and western blot analyses, it was observed that GCF prevents motor dysfunction in the MPTP/p-induced and A53T α-synuclein overexpressed mice. Moreover, GCF inhibited the reduction of dopaminergic neurons in the substantia nigra (SN) and fibers in the striatum (ST) against MPTP/p challenge. The expression of DJ-1 was increased but that of α-synuclein was decreased in the SN of PD-like brains by GCF administration. In vitro experiments also showed that GCF inhibited 6-OHDA-induced neurotoxicity in SH-SY5Y neuroblastoma cell lines and that it did so to a greater degree than CG. Furthermore, GCF induced BDNF expression through phosphorylation of Akt, ERK, CREB, and AMPK in the SN of PD-like brains. Therefore, use of the herbal medicine GCF offers a potential remedy for neurodegenerative disorders, including Parkinson’s disease.