Isogenic human iPSC Parkinson's model shows nitrosative stress-induced dysfunction in MEF2-PGC1α transcription

Experimental models of Parkinson's disease: Challenges and Opportunities

Parkinson's disease (PD) is a widespread neurodegenerative disorder occurs due to the degradation of dopaminergic neurons present in the substantia nigra pars compacta (SNpc). Millions of people are affected by this devastating disorder globally, and the frequency of the condition increases with the increase in the elderly population. A significant amount of progress has been made in acquiring more knowledge about the etiology and the pathogenesis of PD over the past decades. Animal models have been regarded to be a vital tool for the exploration of complex molecular mechanisms involved in PD. Various animals used as models for disease monitoring include vertebrates (zebrafish, rats, mice, guinea pigs, rabbits and monkeys) and invertebrate models (Drosophila, Caenorhabditis elegans). The animal models most relevant for study of PD are neurotoxin induction-based models (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 6-Hydroxydopamine (6-OHDA) and agricultural pesticides (rotenone, paraquat), pharmacological models (reserpine or haloperidol treated rats), genetic models (α-synuclein, Leucine-rich repeat kinase 2 (LRRK2), DJ-1, PINK-1 and Parkin). Several non-mammalian genetic models such as zebrafish, Drosophila and Caenorhabditis elegance have also gained popularity in recent years due to easy genetic manipulation, presence of genes homologous to human PD, and rapid screening of novel therapeutic molecules. In addition, in vitro models (SH-SY5Y, PC12, Lund human mesencephalic (LUHMES) cells, Human induced pluripotent stem cell (iPSC), Neural organoids, organ-on-chip) are also currently in trend providing edge in investigating molecular mechanisms involved in PD as they are derived from PD patients. In this review, we explain the current situation and merits and demerits of the various animal models.

Tetramethylpyrazine nitrone exerts neuroprotection via activation of PGC-1α/Nrf2 pathway in Parkinson's disease models

INTRODUCTION

Parkinson's disease (PD) is common neurodegenerative disease where oxidative stress and mitochondrial dysfunction play important roles in its progression. Tetramethylpyrazine nitrone (TBN), a potent free radical scavenger, has shown protective effects in various neurological conditions. However, the neuroprotective mechanisms of TBN in PD models remain unclear.

OBJECTIVES

We aimed to investigate TBN's neuroprotective effects and mechanisms in PD models.

METHODS

TBN's neuroprotection was initially measured in MPP+/MPTP-induced PD models. Subsequently, a luciferase reporter assay was used to detect peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α) promoter activity. Effects of TBN on antioxidant damage and the PGC-1α/Nuclear factor erythroid-2-related factor 2 (Nrf2) pathway were thoroughly investigated.

RESULTS

In MPP+-induced cell model, TBN (30-300 μM) increased cell survival by 9.95 % (P < 0.05), 16.63 % (P < 0.001), and 24.09 % (P < 0.001), respectively. TBN enhanced oxidative phosphorylation (P < 0.05) and restored PGC-1α transcriptional activity suppressed by MPP+ (84.30 % vs 59.03 %, P < 0.01). In MPTP-treated mice, TBN (30 mg/kg) ameliorated motor impairment, increased striatal dopamine levels (16.75 %, P < 0.001), dopaminergic neurons survival (27.12 %, P < 0.001), and tyrosine hydroxylase expression (28.07 %, P < 0.01). Selegiline, a positive control, increased dopamine levels (15.35 %, P < 0.001) and dopaminergic neurons survival (25.34 %, P < 0.001). Additionally, TBN reduced oxidative products and activated the PGC-1α/Nrf2 pathway. PGC-1α knockdown diminished TBN's neuroprotective effects, decreasing cell viability from 73.65 % to 56.87 % (P < 0.001).

CONCLUSION

TBN has demonstrated consistent effectiveness in MPP+-induced midbrain neurons and MPTP-induced mice. Notably, the therapeutic effect of TBN in mitigating motor deficits and neurodegeneration is superior to selegiline. The neuroprotective mechanisms of TBN are associated with activation of the PGC-1α/Nrf2 pathway, thereby reducing oxidative stress and maintaining mitochondrial function. These findings suggest that TBN may be a promising therapeutic candidate for PD, warranting further development and investigation.

Induction of Pluripotent Stem Cells from Muscle Cells of Large Yellow Croaker (Larimichthys Crocea) Via Electrotransfection

Induced pluripotent stem cells (iPSCs) are a new type of pluripotent cells reprogrammed from somatic cells back into an embryonic-like pluripotent state of stem cells to study development, disease and potential gene therapies. The induction and regulation mechanisms of iPSCs in fish are still unclear. By using the transfection technique, we investigated the crucial function of the OSKMNL factor co-expression for somatic reprogramming in the muscle cell line of large yellow croaker (Larimichthys crocea) (LYCMs) and successfully established a stable iPSCs line (Lc-OSNL-iPSCs). Stable culturing of iPSCs with high alkaline phosphatase activity and a stable karyotype was achieved. The qRT-PCR and immunofluorescence labeling results revealed that Lc-OSNL-iPSCs displayed a high expression level of pluripotent marker genes such as Nanog, Oct4, and Sox2. There were significant differences between Lc-OSNL-iPSCs, Lc-OSKMNL-iPSCs, and LYCMs, and the expression of several genes in maintaining cell pluripotency was up-regulated when the pluripotency signal pathway of stem cells was activated. The technical system for inducing iPSCs of Larimichthys crocea was constructed in this study. This system can serve as a basic model to understand germ cell differentiation mechanism, gender control, genetics, and breeding of large yellow croaker and a platform for studying iPSCs in fish. Interestingly, the acquired iPSCs serves as a useful material for the directional induction of muscle stem cells, thereby establishing the groundwork for obtaining "artificial fish" in the future.

The impact of nimodipine combined with Ginkgo biloba extract on cognitive function and ADL scores in patients with Parkinson's disease: A retrospective study

This study aims to explore the value of nimodipine combined with Ginkgo biloba extract in improving cognitive function and daily living abilities in patients with Parkinson's disease. Clinical data from 551 patients with Parkinson's disease admitted to the Neurology Department of the Affiliated Hospital of Beihua University from January 2022 to December 2022 were retrospectively collected. Cognitive function and daily living abilities were assessed in patients before treatment, and a reevaluation was conducted after 12 weeks of medication. Patients treated solely with nimodipine were categorized into the monotherapy group, while patients treated with nimodipine combined with Ginkgo biloba extract were included in the combination group. After 1:1 propensity score matching, a total of 83 pairs of patients were matched, and differences in relevant indicators between the 2 groups were compared. The total effective rate of treatment in the combination group was 90.36%, which was higher than the control group at 72.29% (P < .05). However, after treatment, the observation group showed higher Mini-Mental State Examination and activities of daily living scores compared to the control group (P < .05). The combined treatment of nimodipine and Ginkgo biloba extract in patients with Parkinson's disease has a significant effect and can effectively improve cognitive function and enhance daily living abilities.

Analysis of LRRN3, MEF2C, SLC22A, and P2RY12 Gene Expression in the Peripheral Blood of Patients in the Early Stages of Parkinson's Disease

Parkinson's disease (PD) is one of the most common human neurodegenerative diseases. Belated diagnoses of PD and late treatment are caused by its elongated prodromal phase. Thus, searching for new candidate genes participating in the development of the pathological process in the early stages of the disease in patients who have not yet received therapy is relevant. Changes in mRNA and protein levels have been described both in the peripheral blood and in the brain of patients with PD. Thus, analysis of changes in the mRNA expression in peripheral blood is of great importance in studying the early stages of PD. This work aimed to analyze the changes in MEF2C, SLC22A4, P2RY12, and LRRN3 gene expression in the peripheral blood of patients in the early stages of PD. We found a statistically relevant and PD-specific change in the expression of the LRRN3 gene, indicating a disruption in the processes of neuronal regeneration and the functioning of synapses. The data obtained during the study indicate that this gene can be considered a potential biomarker of the early stages of PD.

In and out: Benchmarking in vitro, in vivo, ex vivo, and xenografting approaches for an integrative brain disease modeling pipeline

Human cellular models and their neuronal derivatives have afforded unprecedented advances in elucidating pathogenic mechanisms of neuropsychiatric diseases. Notwithstanding their indispensable contribution, animal models remain the benchmark in neurobiological research. In an attempt to harness the best of both worlds, researchers have increasingly relied on human/animal chimeras by xenografting human cells into the animal brain. Despite the unparalleled potential of xenografting approaches in the study of the human brain, literature resources that systematically examine their significance and advantages are surprisingly lacking. We fill this gap by providing a comprehensive account of brain diseases that were thus far subjected to all three modeling approaches (transgenic rodents, in vitro human lineages, human-animal xenografting) and provide a critical appraisal of the impact of xenografting approaches for advancing our understanding of those diseases and brain development. Next, we give our perspective on integrating xenografting modeling pipeline with recent cutting-edge technological advancements.

Toxic interactions between dopamine, α-synuclein, monoamine oxidase, and genes in mitochondria of Parkinson's disease

Parkinson's disease is characterized by its distinct pathological features; loss of dopamine neurons in the substantia nigra pars compacta and accumulation of Lewy bodies and Lewy neurites containing modified α-synuclein. Beneficial effects of L-DOPA and dopamine replacement therapy indicate dopamine deficit as one of the main pathogenic factors. Dopamine and its oxidation products are proposed to induce selective vulnerability in dopamine neurons. However, Parkinson's disease is now considered as a generalized disease with dysfunction of several neurotransmitter systems caused by multiple genetic and environmental factors. The pathogenic factors include oxidative stress, mitochondrial dysfunction, α-synuclein accumulation, programmed cell death, impaired proteolytic systems, neuroinflammation, and decline of neurotrophic factors. This paper presents interactions among dopamine, α-synuclein, monoamine oxidase, its inhibitors, and related genes in mitochondria. α-Synuclein inhibits dopamine synthesis and function. Vice versa, dopamine oxidation by monoamine oxidase produces toxic aldehydes, reactive oxygen species, and quinones, which modify α-synuclein, and promote its fibril production and accumulation in mitochondria. Excessive dopamine in experimental models modifies proteins in the mitochondrial electron transport chain and inhibits the function. α-Synuclein and familiar Parkinson's disease-related gene products modify the expression and activity of monoamine oxidase. Type A monoamine oxidase is associated with neuroprotection by an unspecific dose of inhibitors of type B monoamine oxidase, rasagiline and selegiline. Rasagiline and selegiline prevent α-synuclein fibrillization, modulate this toxic collaboration, and exert neuroprotection in experimental studies. Complex interactions between these pathogenic factors play a decisive role in neurodegeneration in PD and should be further defined to develop new therapies for Parkinson's disease.

Network analysis of S-nitrosylated synaptic proteins demonstrates unique roles in health and disease

Nitric oxide can covalently modify cysteine thiols on target proteins to alter that protein's function in a process called S-nitrosylation (SNO). S-nitrosylation of synaptic proteins plays an integral part in neurotransmission. Here we review the function of the SNO-proteome at the synapse and whether clusters of SNO-modification may predict synaptic dysfunction associated with disease. We used a systematic search strategy to concatenate SNO-proteomic datasets from normal human or murine brain samples. Identified SNO-modified proteins were then filtered against proteins reported in the Synaptome Database, which provides a detailed and experimentally verified annotation of all known synaptic proteins. Subsequently, we performed an unbiased network analysis of all known SNO-synaptic proteins to identify clusters of SNO proteins commonly involved in biological processes or with known disease associations. The resulting SNO networks were significantly enriched in biological processes related to metabolism, whereas significant gene-disease associations were related to Schizophrenia, Alzheimer's, Parkinson's and Huntington's disease. Guided by an unbiased network analysis, the current review presents a thorough discussion of how clustered changes to the SNO-proteome influence health and disease.

Midbrain organoids for Parkinson's disease (PD) - A powerful tool to understand the disease pathogenesis

Brain Organiods (BOs) are a promising technique for researching disease progression in the human brain. These organoids, which are produced from human induced pluripotent stem cells (HiPSCs), can construct themselves into structured frameworks. In the context of Parkinson's disease (PD), recent advancements have been made in the development of Midbrain organoids (MBOs) models that consider key pathophysiological mechanisms such as alpha-synuclein (α-Syn), Lewy bodies, dopamine loss, and microglia activation. However, there are limitations to the current use of BOs in disease modelling and drug discovery, such as the lack of vascularization, long-term differentiation, and absence of glial cells. To address these limitations, researchers have proposed the use of spinning bioreactors to improve oxygen and nutrient perfusion. Modelling PD utilising modern experimental in vitro models is a valuable tool for studying disease mechanisms and elucidating previously unknown features of PD. In this paper, we exclusively review the unique methods available for cultivating MBOs using a pumping system that mimics the circulatory system. This mechanism may aid in delivering the required amount of oxygen and nutrients to all areas of the organoids, preventing cell death, and allowing for long-term culture and using co-culturing techniques for developing glial cell in BOs. Furthermore, we emphasise some of the significant discoveries about the BOs and the potential challenges of using BOs will be discussed.

Development of Midbrain Dopaminergic Neurons and the Advantage of Using hiPSCs as a Model System to Study Parkinson's Disease

Midbrain dopaminergic (mDA) neurons are significantly impaired in patients inflicted with Parkinson's disease (PD), subsequently affecting a variety of motor functions. There are four pathways through which dopamine elicits its function, namely, nigrostriatal, mesolimbic, mesocortical and tuberoinfundibular dopamine pathways. SHH and Wnt signalling pathways in association with favourable expression of a variety of genes, promotes the development and differentiation of mDA neurons in the brain. However, there is a knowledge gap regarding the complex signalling pathways involved in development of mDA neurons. hiPSC models have been acclaimed to be effective in generating complex disease phenotypes. These models mimic the microenvironment found in vivo thus ensuring maximum reliability. Further, a variety of therapeutic compounds can be screened using hiPSCs since they can be used to generate neurons that could carry an array of mutations associated with both familial and sporadic PD. Thus, culturing hiPSCs to study gene expression and dysregulation of cellular processes associated with PD can be useful in developing targeted therapies that will be a step towards halting disease progression.

Promising use of metformin in treating neurological disorders: biomarker-guided therapies

Neurological disorders are a diverse group of conditions that affect the nervous system and include neurodegenerative diseases (Alzheimer's disease, multiple sclerosis, Parkinson's disease, Huntington's disease), cerebrovascular conditions (stroke), and neurodevelopmental disorders (autism spectrum disorder). Although they affect millions of individuals around the world, only a limited number of effective treatment options are available today. Since most neurological disorders express mitochondria-related metabolic perturbations, metformin, a biguanide type II antidiabetic drug, has attracted a lot of attention to be repurposed to treat neurological disorders by correcting their perturbed energy metabolism. However, controversial research emerges regarding the beneficial/detrimental effects of metformin on these neurological disorders. Given that most neurological disorders have complex etiology in their pathophysiology and are influenced by various risk factors such as aging, lifestyle, genetics, and environment, it is important to identify perturbed molecular functions that can be targeted by metformin in these neurological disorders. These molecules can then be used as biomarkers to stratify subpopulations of patients who show distinct molecular/pathological properties and can respond to metformin treatment, ultimately developing targeted therapy. In this review, we will discuss mitochondria-related metabolic perturbations and impaired molecular pathways in these neurological disorders and how these can be used as biomarkers to guide metformin-responsive treatment for the targeted therapy to treat neurological disorders.

Induced pluripotent stem cells (iPSCs): molecular mechanisms of induction and applications

The induced pluripotent stem cell (iPSC) technology has transformed in vitro research and holds great promise to advance regenerative medicine. iPSCs have the capacity for an almost unlimited expansion, are amenable to genetic engineering, and can be differentiated into most somatic cell types. iPSCs have been widely applied to model human development and diseases, perform drug screening, and develop cell therapies. In this review, we outline key developments in the iPSC field and highlight the immense versatility of the iPSC technology for in vitro modeling and therapeutic applications. We begin by discussing the pivotal discoveries that revealed the potential of a somatic cell nucleus for reprogramming and led to successful generation of iPSCs. We consider the molecular mechanisms and dynamics of somatic cell reprogramming as well as the numerous methods available to induce pluripotency. Subsequently, we discuss various iPSC-based cellular models, from mono-cultures of a single cell type to complex three-dimensional organoids, and how these models can be applied to elucidate the mechanisms of human development and diseases. We use examples of neurological disorders, coronavirus disease 2019 (COVID-19), and cancer to highlight the diversity of disease-specific phenotypes that can be modeled using iPSC-derived cells. We also consider how iPSC-derived cellular models can be used in high-throughput drug screening and drug toxicity studies. Finally, we discuss the process of developing autologous and allogeneic iPSC-based cell therapies and their potential to alleviate human diseases.

The Role of Protein S-Nitrosylation in Mitochondrial Quality Control in Central Nervous System Diseases

S-Nitrosylation is a reversible covalent post-translational modification. Under physiological conditions, S-nitrosylation plays a dynamic role in a wide range of biological processes by regulating the function of substrate proteins. Like other post-translational modifications, S-nitrosylation can affect protein conformation, activity, localization, aggregation, and protein interactions. Aberrant S-nitrosylation can lead to protein misfolding, mitochondrial fragmentation, synaptic damage, and autophagy. Mitochondria are essential organelles in energy production, metabolite biosynthesis, cell death, and immune responses, among other processes. Mitochondrial dysfunction can result in cell death and has been implicated in the development of many human diseases. Recent evidence suggests that S-nitrosylation and mitochondrial dysfunction are important modulators of the progression of several diseases. In this review, we highlight recent findings regarding the aberrant S- nitrosylation of mitochondrial proteins that regulate mitochondrial biosynthesis, fission and fusion, and autophagy. Specifically, we discuss the mechanisms by which S-nitrosylated mitochondrial proteins exercise mitochondrial quality control under pathological conditions, thereby influencing disease. A better understanding of these pathological events may provide novel therapeutic targets to mitigate the development of neurological diseases.

Genetic and pharmacological reduction of CDK14 mitigates synucleinopathy

Parkinson's disease (PD) is a debilitating neurodegenerative disease characterized by the loss of midbrain dopaminergic neurons (DaNs) and the abnormal accumulation of α-Synuclein (α-Syn) protein. Currently, no treatment can slow nor halt the progression of PD. Multiplications and mutations of the α-Syn gene (SNCA) cause PD-associated syndromes and animal models that overexpress α-Syn replicate several features of PD. Decreasing total α-Syn levels, therefore, is an attractive approach to slow down neurodegeneration in patients with synucleinopathy. We previously performed a genetic screen for modifiers of α-Syn levels and identified CDK14, a kinase of largely unknown function as a regulator of α-Syn. To test the potential therapeutic effects of CDK14 reduction in PD, we ablated Cdk14 in the α-Syn preformed fibrils (PFF)-induced PD mouse model. We found that loss of Cdk14 mitigates the grip strength deficit of PFF-treated mice and ameliorates PFF-induced cortical α-Syn pathology, indicated by reduced numbers of pS129 α-Syn-containing cells. In primary neurons, we found that Cdk14 depletion protects against the propagation of toxic α-Syn species. We further validated these findings on pS129 α-Syn levels in PD patient neurons. Finally, we leveraged the recent discovery of a covalent inhibitor of CDK14 to determine whether this target is pharmacologically tractable in vitro and in vivo. We found that CDK14 inhibition decreases total and pathologically aggregated α-Syn in human neurons, in PFF-challenged rat neurons and in the brains of α-Syn-humanized mice. In summary, we suggest that CDK14 represents a novel therapeutic target for PD-associated synucleinopathy.

Optogenetic and chemogenetic approaches for modeling neurological disorders in vivo

Animal models of human neurological disorders provide valuable experimental tools which enable us to study various aspects of disorder pathogeneses, ranging from structural abnormalities and disrupted metabolism and signaling to motor and mental deficits, and allow us to test novel therapies in preclinical studies. To be valid, these animal models should recapitulate complex pathological features at the molecular, cellular, tissue, and behavioral levels as closely as possible to those observed in human subjects. Pathological states resembling known human neurological disorders can be induced in animal species by toxins, genetic factors, lesioning, or exposure to extreme conditions. In recent years, novel animal models recapitulating neuropathologies in humans have been introduced. These animal models are based on synthetic biology approaches: opto- and chemogenetics. In this paper, we review recent opto- and chemogenetics-based animal models of human neurological disorders. These models allow for the creation of pathological states by disrupting specific processes at the cellular level. The artificial pathological states mimic a range of human neurological disorders, such as aging-related dementia, Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, epilepsy, and ataxias. Opto- and chemogenetics provide new opportunities unavailable with other animal models of human neurological disorders. These techniques enable researchers to induce neuropathological states varying in severity and ranging from acute to chronic. We also discuss future directions for the development and application of synthetic biology approaches for modeling neurological disorders.

Mutant α-synuclein causes death of human cortical neurons via ERK1/2 and JNK activation

Synucleinopathies refer to a group of disorders characterized by SNCA/α-synuclein (α-Syn)-containing cytoplasmic inclusions and neuronal cell loss in the nervous system including the cortex, a common feature being cognitive impairment. Still, the molecular pathogenesis of cognitive decline remains poorly understood, hampering the development of effective treatments. Here, we generated induced pluripotent stem cells (iPSCs) derived from familial Parkinson's disease (PD) patients carrying SNCA A53T mutation, differentiating them into cortical neurons by a direct conversion method. Patient iPSCs-derived cortical neurons harboring mutant α-Syn exhibited increased α-Syn-positive aggregates, shorter neurites, and time-dependent vulnerability. Furthermore, RNA-sequencing analysis, followed by biochemical validation, identified the activation of the ERK1/2 and JNK cascades in cortical neurons with SNCA A53T mutation. This result was consistent with a reverted phenotype of neuronal death in cortical neurons when treated with ERK1/2 and JNK inhibitors, respectively. Our findings emphasize the role of ERK1/2 and JNK cascades in the vulnerability of cortical neurons in synucleinopathies, and they could pave the way toward therapeutic advancements for synucleinopathies.

CRISPR/Cas9 system and its applications in nervous system diseases

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system is an acquired immune system of many bacteria and archaea, comprising CRISPR loci, Cas genes, and its associated proteins. This system can recognize exogenous DNA and utilize the Cas9 protein's nuclease activity to break DNA double-strand and to achieve base insertion or deletion by subsequent DNA repair. In recent years, multiple laboratory and clinical studies have revealed the therapeutic role of the CRISPR/Cas9 system in neurological diseases. This article reviews the CRISPR/Cas9-mediated gene editing technology and its potential for clinical application against neurological diseases.

Metabolic Bypass Rescues Aberrant S-nitrosylation-Induced TCA Cycle Inhibition and Synapse Loss in Alzheimer's Disease Human Neurons

In Alzheimer's disease (AD), dysfunctional mitochondrial metabolism is associated with synaptic loss, the major pathological correlate of cognitive decline. Mechanistic insight for this relationship, however, is still lacking. Here, comparing isogenic wild-type and AD mutant human induced pluripotent stem cell (hiPSC)-derived cerebrocortical neurons (hiN), evidence is found for compromised mitochondrial energy in AD using the Seahorse platform to analyze glycolysis and oxidative phosphorylation (OXPHOS). Isotope-labeled metabolic flux experiments revealed a major block in activity in the tricarboxylic acid (TCA) cycle at the α-ketoglutarate dehydrogenase (αKGDH)/succinyl coenzyme-A synthetase step, metabolizing α-ketoglutarate to succinate. Associated with this block, aberrant protein S-nitrosylation of αKGDH subunits inhibited their enzyme function. This aberrant S-nitrosylation is documented not only in AD-hiN but also in postmortem human AD brains versus controls, as assessed by two separate unbiased mass spectrometry platforms using both SNOTRAP identification of S-nitrosothiols and chemoselective-enrichment of S-nitrosoproteins. Treatment with dimethyl succinate, a cell-permeable derivative of a TCA substrate downstream to the block, resulted in partial rescue of mitochondrial bioenergetic function as well as reversal of synapse loss in AD-hiN. These findings have therapeutic implications that rescue of mitochondrial energy metabolism can ameliorate synaptic loss in hiPSC-based models of AD.

Dopaminergic neuronal death via necroptosis in Parkinson's disease: A review of the literature

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive dysfunction and loss of dopaminergic neurons of the substantia nigra pars compacta (SNc). Several pathways of programmed cell death are likely to play a role in dopaminergic neuron death, such as apoptosis, necrosis, pyroptosis and ferroptosis, as well as cell death associated with proteasomal and mitochondrial dysfunction. A better understanding of the molecular mechanisms underlying dopaminergic neuron death could inform the design of drugs that promote neuron survival. Necroptosis is a recently characterized regulated cell death mechanism that exhibits morphological features common to both apoptosis and necrosis. It requires activation of an intracellular pathway involving receptor-interacting protein 1 kinase (RIP1 kinase, RIPK1), receptor-interacting protein 3 kinase (RIP3 kinase, RIPK3) and mixed lineage kinase domain-like pseudokinase (MLKL). The potential involvement of this programmed cell death pathway in the pathogenesis of PD has been studied by analysing biomarkers for necroptosis, such as the levels and oligomerization of phosphorylated RIPK3 (pRIPK3) and phosphorylated MLKL (pMLKL), in several PD preclinical models and in PD human tissue. Although there is evidence that other types of cell death also have a role in DA neuron death, most studies support the hypothesis that this cell death mechanism is activated in PD tissues. Drugs that prevent or reduce necroptosis may provide neuroprotection for PD. In this review, we summarize the findings from these studies. We also discuss how manipulating necroptosis might open a novel therapeutic approach to reduce neuronal degeneration in PD.

DeePhys: A machine learning-assisted platform for electrophysiological phenotyping of human neuronal networks

Reproducible functional assays to study in vitro neuronal networks represent an important cornerstone in the quest to develop physiologically relevant cellular models of human diseases. Here, we introduce DeePhys, a MATLAB-based analysis tool for data-driven functional phenotyping of in vitro neuronal cultures recorded by high-density microelectrode arrays. DeePhys is a modular workflow that offers a range of techniques to extract features from spike-sorted data, allowing for the examination of functional phenotypes both at the individual cell and network levels, as well as across development. In addition, DeePhys incorporates the capability to integrate novel features and to use machine-learning-assisted approaches, which facilitates a comprehensive evaluation of pharmacological interventions. To illustrate its practical application, we apply DeePhys to human induced pluripotent stem cell-derived dopaminergic neurons obtained from both patients and healthy individuals and showcase how DeePhys enables phenotypic screenings.

iSCORE-PD: an isogenic stem cell collection to research Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder caused by complex genetic and environmental factors. Genome-edited human pluripotent stem cells (hPSCs) offer the uniique potential to advance our understanding of PD etiology by providing disease-relevant cell-types carrying patient mutations along with isogenic control cells. To facilitate this experimental approach, we generated a collection of 55 cell lines genetically engineered to harbor mutations in genes associated with monogenic PD (SNCA A53T, SNCA A30P, PRKN Ex3del, PINK1 Q129X, DJ1/PARK7 Ex1-5del, LRRK2 G2019S, ATP13A2 FS, FBXO7 R498X/FS, DNAJC6 c.801 A>G+FS, SYNJ1 R258Q/FS, VPS13C A444P, VPS13C W395C, GBA1 IVS2+1). All mutations were generated in a fully characterized and sequenced female human embryonic stem cell (hESC) line (WIBR3; NIH approval number NIHhESC-10-0079) using CRISPR/Cas9 or prime editing-based approaches. We implemented rigorous quality controls, including high density genotyping to detect structural variants and confirm the genomic integrity of each cell line. This systematic approach ensures the high quality of our stem cell collection, highlights differences between conventional CRISPR/Cas9 and prime editing and provides a roadmap for how to generate gene-edited hPSCs collections at scale in an academic setting. We expect that our isogenic stem cell collection will become an accessible platform for the study of PD, which can be used by investigators to understand the molecular pathophysiology of PD in a human cellular setting.

Recalibrating the Why and Whom of Animal Models in Parkinson Disease: A Clinician's Perspective

Animal models have been used to gain pathophysiologic insights into Parkinson's disease (PD) and aid in the translational efforts of interventions with therapeutic potential in human clinical trials. However, no disease-modifying therapy for PD has successfully emerged from model predictions. These translational disappointments warrant a reappraisal of the types of preclinical questions asked of animal models. Besides the limitations of experimental designs, the one-size convergence and oversimplification yielded by a model cannot recapitulate the molecular diversity within and between PD patients. Here, we compare the strengths and pitfalls of different models, review the discrepancies between animal and human data on similar pathologic and molecular mechanisms, assess the potential of organoids as novel modeling tools, and evaluate the types of questions for which models can guide and misguide. We propose that animal models may be of greatest utility in the evaluation of molecular mechanisms, neural pathways, drug toxicity, and safety but can be unreliable or misleading when used to generate pathophysiologic hypotheses or predict therapeutic efficacy for compounds with potential neuroprotective effects in humans. To enhance the translational disease-modification potential, the modeling must reflect the biology not of a diseased population but of subtypes of diseased humans to distinguish What data are relevant and to Whom.

Potential benefits of medium chain fatty acids in aging and neurodegenerative disease

Neurodegenerative diseases are a large class of neurological disorders characterized by progressive dysfunction and death of neurones. Examples include Alzheimer's disease, Parkinson's disease, frontotemporal dementia, and amyotrophic lateral sclerosis. Aging is the primary risk factor for neurodegeneration; individuals over 65 are more likely to suffer from a neurodegenerative disease, with prevalence increasing with age. As the population ages, the social and economic burden caused by these diseases will increase. Therefore, new therapies that address both aging and neurodegeneration are imperative. Ketogenic diets (KDs) are low carbohydrate, high-fat diets developed initially as an alternative treatment for epilepsy. The classic ketogenic diet provides energy via long-chain fatty acids (LCFAs); naturally occurring medium chain fatty acids (MCFAs), on the other hand, are the main components of the medium-chain triglyceride (MCT) ketogenic diet. MCT-based diets are more efficient at generating the ketone bodies that are used as a secondary energy source for neurones and astrocytes. However, ketone levels alone do not closely correlate with improved clinical symptoms. Recent findings suggest an alternative mode of action for the MCFAs, e.g., via improving mitochondrial biogenesis and glutamate receptor inhibition. MCFAs have been linked to the treatment of both aging and neurodegenerative disease via their effects on metabolism. Through action on multiple disease-related pathways, MCFAs are emerging as compounds with notable potential to promote healthy aging and ameliorate neurodegeneration. MCFAs have been shown to stimulate autophagy and restore mitochondrial function, which are found to be disrupted in aging and neurodegeneration. This review aims to provide insight into the metabolic benefits of MCFAs in neurodegenerative disease and healthy aging. We will discuss the use of MCFAs to combat dysregulation of autophagy and mitochondrial function in the context of "normal" aging, Parkinson's disease, amyotrophic lateral sclerosis and Alzheimer's disease.

S-Nitrosylation-mediated dysfunction of TCA cycle enzymes in synucleinopathy studied in postmortem human brains and hiPSC-derived neurons

A causal relationship between mitochondrial metabolic dysfunction and neurodegeneration has been implicated in synucleinopathies, including Parkinson disease (PD) and Lewy body dementia (LBD), but underlying mechanisms are not fully understood. Here, using human induced pluripotent stem cell (hiPSC)-derived neurons with mutation in the gene encoding α-synuclein (αSyn), we report the presence of aberrantly S-nitrosylated proteins, including tricarboxylic acid (TCA) cycle enzymes, resulting in activity inhibition assessed by carbon-labeled metabolic flux experiments. This inhibition principally affects α-ketoglutarate dehydrogenase/succinyl coenzyme-A synthetase, metabolizing α-ketoglutarate to succinate. Notably, human LBD brain manifests a similar pattern of aberrantly S-nitrosylated TCA enzymes, indicating the pathophysiological relevance of these results. Inhibition of mitochondrial energy metabolism in neurons is known to compromise dendritic length and synaptic integrity, eventually leading to neuronal cell death. Our evidence indicates that aberrant S-nitrosylation of TCA cycle enzymes contributes to this bioenergetic failure.

A pesticide and iPSC dopaminergic neuron screen identifies and classifies Parkinson-relevant pesticides

Parkinson's disease (PD) is a complex neurodegenerative disease with etiology rooted in genetic vulnerability and environmental factors. Here we combine quantitative epidemiologic study of pesticide exposures and PD with toxicity screening in dopaminergic neurons derived from PD patient induced pluripotent stem cells (iPSCs) to identify Parkinson's-relevant pesticides. Agricultural records enable investigation of 288 specific pesticides and PD risk in a comprehensive, pesticide-wide association study. We associate long-term exposure to 53 pesticides with PD and identify co-exposure profiles. We then employ a live-cell imaging screening paradigm exposing dopaminergic neurons to 39 PD-associated pesticides. We find that 10 pesticides are directly toxic to these neurons. Further, we analyze pesticides typically used in combinations in cotton farming, demonstrating that co-exposures result in greater toxicity than any single pesticide. We find trifluralin is a driver of toxicity to dopaminergic neurons and leads to mitochondrial dysfunction. Our paradigm may prove useful to mechanistically dissect pesticide exposures implicated in PD risk and guide agricultural policy.

CRISPR/Cas9 assisted stem cell therapy in Parkinson's disease

Since its discovery in 2012, CRISPR Cas9 has been tried as a direct treatment approach to correct the causative gene mutation and establish animal models in neurodegenerative disorders. Since no strategy developed until now could completely cure Parkinson's disease (PD), neuroscientists aspire to use gene editing technology, especially CRISPR/Cas9, to induce a permanent correction in genetic PD patients expressing mutated genes. Over the years, our understanding of stem cell biology has improved. Scientists have developed personalized cell therapy using CRISPR/Cas9 to edit embryonic and patient-derived stem cells ex-vivo. This review details the importance of CRISPR/Cas9-based stem cell therapy in Parkinson's disease in developing PD disease models and developing therapeutic strategies after elucidating the possible pathophysiological mechanisms.

The small GTPase Rit2 modulates LRRK2 kinase activity, is required for lysosomal function and protects against alpha-synuclein neuropathology

In Parkinson's disease (PD) misfolded alpha-synuclein (aSyn) accumulates in the substantia nigra, where dopaminergic neurons are progressively lost. The mechanisms underlying aSyn pathology are still unclear, but they are hypothesized to involve the autophagy-lysosome pathway (ALP). LRRK2 mutations are a major cause of familial and sporadic PD, and LRRK2 kinase activity has been shown to be involved in pS129-aSyn inclusion modulation. We observed selective downregulation of the novel PD risk factor RIT2 in vitro and in vivo. Rit2 overexpression in G2019S-LRRK2 cells rescued ALP abnormalities and diminished aSyn inclusions. In vivo, viral mediated overexpression of Rit2 operated neuroprotection against AAV-A53T-aSyn. Furthermore, Rit2 overexpression prevented the A53T-aSyn-dependent increase of LRRK2 kinase activity in vivo. On the other hand, reduction of Rit2 levels leads to defects in the ALP, similar to those induced by the G2019S-LRRK2 mutation. Our data indicate that Rit2 is required for correct lysosome function, inhibits overactive LRRK2 to ameliorate ALP impairment, and counteracts aSyn aggregation and related deficits. Targeting Rit2 could represent an effective strategy to combat neuropathology in familial and idiopathic PD.

The Role of MEF2 Transcription Factor Family in Neuronal Survival and Degeneration

The family of myocyte enhancer factor 2 (MEF2) transcription factors comprises four highly conserved members that play an important role in the nervous system. They appear in precisely defined time frames in the developing brain to turn on and turn off genes affecting growth, pruning and survival of neurons. MEF2s are known to dictate neuronal development, synaptic plasticity and restrict the number of synapses in the hippocampus, thus affecting learning and memory formation. In primary neurons, negative regulation of MEF2 activity by external stimuli or stress conditions is known to induce apoptosis, albeit the pro or antiapoptotic action of MEF2 depends on the neuronal maturation stage. By contrast, enhancement of MEF2 transcriptional activity protects neurons from apoptotic death both in vitro and in preclinical models of neurodegenerative diseases. A growing body of evidence places this transcription factor in the center of many neuropathologies associated with age-dependent neuronal dysfunctions or gradual but irreversible neuron loss. In this work, we discuss how the altered function of MEF2s during development and in adulthood affecting neuronal survival may be linked to neuropsychiatric disorders.

Aberrant protein S-nitrosylation contributes to hyperexcitability-induced synaptic damage in Alzheimer's disease: Mechanistic insights and potential therapies

Alzheimer's disease (AD) is arguably the most common cause of dementia in the elderly and is marked by progressive synaptic degeneration, which in turn leads to cognitive decline. Studies in patients and in various AD models have shown that one of the early signatures of AD is neuronal hyperactivity. This excessive electrical activity contributes to dysregulated neural network function and synaptic damage. Mechanistically, evidence suggests that hyperexcitability accelerates production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that contribute to neural network impairment and synapse loss. This review focuses on the pathways and molecular changes that cause hyperexcitability and how RNS-dependent posttranslational modifications, represented predominantly by protein S-nitrosylation, mediate, at least in part, the deleterious effects of hyperexcitability on single neurons and the neural network, resulting in synaptic loss in AD.

iPSCs-Derived Neurons and Brain Organoids from Patients

Induced pluripotent stem cells (iPSCs) can be differentiated into specific neurons and brain organoids by adding induction factors and small molecules in vitro, which carry human genetic information and recapitulate the development process of human brain as well as physiological, pathological, and pharmacological characteristics. Hence, iPSC-derived neurons and organoids hold great promise for studying human brain development and related nervous system diseases in vitro, and provide a platform for drug screening. In this chapter, we summarize the development of the differentiation techniques for neurons and brain organoids from iPSCs, and their applications in studying brain disease, drug screening, and transplantation.

Identifying NFKB1, STAT3, and CDKN1A as Baicalein's Potential Hub Targets in Parkinson's Disease-related α-synuclein-mediated Pathways by Integrated Bioinformatics Strategies

BACKGROUND

The overexpression, accumulation, and cell-to-cell transmission of α-synuclein leads to the deterioration of Parkinson's disease (PD). Previous studies suggest that Baicalein (BAI) can bind to α-synuclein and inhibit α-synuclein aggregation and secretion. However, it is still unclear whether BAI can intervene with the pathogenic molecules in α-synuclein-mediated PD pathways beyond directly targeting α-synuclein per se.

METHODS

This study aimed to systematically investigate BAI's potential targets in PD-related A53T mutant α-synuclein-mediated pathways by integrating data mining, network pharmacological analysis, and molecular docking simulation techniques.

RESULTS

The results suggest that BAI may target genes that are dysregulated in synaptic transmission, vesicle trafficking, gene transcription, protein binding, extracellular matrix formation, and kinase activity in α-synucleinmediated pathways. NFKB1, STAT3, and CDKN1A are BAI's potential hub targets in these pathways.

CONCLUSION

Our findings highlight BAI's potentiality to modulate α-synuclein-mediated pathways beyond directly targeting α-synuclein per se.

Exercise and mitochondrial remodeling to prevent age-related neurodegeneration

Healthy brain activity requires precise ion and energy management creating a strong reliance on mitochondrial function. Age-related neurodegeneration leads to a decline in mitochondrial function and increased oxidative stress, with associated declines in mitochondrial mass, respiration capacity, and respiration efficiency. The interdependent processes of mitochondrial protein turnover and mitochondrial dynamics, known together as mitochondrial remodeling, play essential roles in mitochondrial health and therefore brain function. This mini-review describes the role of mitochondria in neurodegeneration and brain health, current practices for assessing both aspects of mitochondrial remodeling, and how exercise mitigates the adverse effects of aging in the brain. Exercise training elicits functional adaptations to improve brain health, and current literature strongly suggests that mitochondrial remodeling plays a vital role in these positive adaptations. Despite substantial implications that the two aspects of mitochondrial remodeling are interdependent, very few investigations have simultaneously measured mitochondrial dynamics and protein synthesis. An improved understanding of the partnership between mitochondrial protein turnover and mitochondrial dynamics will provide a better understanding of their role in both brain health and disease, as well as how they induce protection following exercise.

The contribution of an imbalanced redox signalling to neurological and neurodegenerative conditions

Nitric oxide and other redox active molecules such as oxygen free radicals provide essential signalling in diverse neuronal functions, but their excess production and insufficient scavenging induces cytotoxic redox stress which is associated with numerous neurodegenerative and neurological conditions. A further component of redox signalling is mediated by a homeostatic regulation of divalent metal ions, the imbalance of which contributes to neuronal dysfunction. Additional antioxidant molecules such as glutathione and enzymes such as super oxide dismutase are involved in maintaining a physiological redox status within neurons. When cellular processes are perturbed and generation of free radicals overwhelms the antioxidants capacity of the neurons, a resulting redox damage leads to neuronal dysfunction and cell death. Cellular sources for production of redox-active molecules may include NADPH oxidases, mitochondria, cytochrome P450 and nitric oxide (NO)-generating enzymes, such as endothelial, neuronal and inducible NO synthases. Several neurodegenerative and developmental neurological conditions are associated with an imbalanced redox state as a result of neuroinflammatory processes leading to nitrosative and oxidative stress. Ongoing research aims at understanding the causes and consequences of such imbalanced redox homeostasis and its role in neuronal dysfunction.

Intracellular Accumulation of α-Synuclein Aggregates Promotes S-Nitrosylation of MAP1A Leading to Decreased NMDAR-Evoked Calcium Influx and Loss of Mature Synaptic Spines

Cortical synucleinopathies, including dementia with Lewy bodies and Parkinson's disease dementia, collectively known as Lewy body dementia, are characterized by the aberrant aggregation of misfolded α-synuclein (α-syn) protein into large inclusions in cortical tissue, leading to impairments in proteostasis and synaptic connectivity and eventually resulting in neurodegeneration. Here, we show that male and female rat cortical neurons exposed to exogenous α-syn preformed fibrils accumulate large, detergent-insoluble, PS129-labeled deposits at synaptic terminals. Live-cell imaging of calcium dynamics coupled with assessment of network activity reveals that aberrant intracellular accumulation of α-syn inhibits synaptic response to glutamate through NMDARs, although deficits manifest slowly over a 7 d period. Impairments in NMDAR activity temporally correlated with increased nitric oxide synthesis and S-nitrosylation of the dendritic scaffold protein, microtubule-associated protein 1A. Inhibition of nitric oxide synthesis via the nitric oxide synthase inhibitor l-NG-nitroarginine methyl ester blocked microtubule-associated protein 1A S-nitrosylation and normalized NMDAR-dependent inward calcium transients and overall network activity. Collectively, these data suggest that loss of synaptic function in Lewy body dementia may result from synucleinopathy-evoked nitrosative stress and subsequent NMDAR dysfunction.SIGNIFICANCE STATEMENT This work shows the importance of the redox state of microtubule-associated protein 1A in the maintenance of synaptic function through regulation of NMDAR. We show that α-syn preformed fibrils promote nitric oxide synthesis, which triggers S-nitrosylation of microtubule-associated protein 1A, leading to impairment of NMDAR-dependent glutamate responses. This offers insight into the mechanism of synaptic dysfunction in Lewy body dementia.

S-Glutathionylation and S-Nitrosylation in Mitochondria: Focus on Homeostasis and Neurodegenerative Diseases

Redox post-translational modifications are derived from fluctuations in the redox potential and modulate protein function, localization, activity and structure. Amongst the oxidative reversible modifications, the S-glutathionylation of proteins was the first to be characterized as a post-translational modification, which primarily protects proteins from irreversible oxidation. However, a growing body of evidence suggests that S-glutathionylation plays a key role in core cell processes, particularly in mitochondria, which are the main source of reactive oxygen species. S-nitrosylation, another post-translational modification, was identified >150 years ago, but it was re-introduced as a prototype cell-signaling mechanism only recently, one that tightly regulates core processes within the cell’s sub-compartments, especially in mitochondria. S-glutathionylation and S-nitrosylation are modulated by fluctuations in reactive oxygen and nitrogen species and, in turn, orchestrate mitochondrial bioenergetics machinery, morphology, nutrients metabolism and apoptosis. In many neurodegenerative disorders, mitochondria dysfunction and oxidative/nitrosative stresses trigger or exacerbate their pathologies. Despite the substantial amount of research for most of these disorders, there are no successful treatments, while antioxidant supplementation failed in the majority of clinical trials. Herein, we discuss how S-glutathionylation and S-nitrosylation interfere in mitochondrial homeostasis and how the deregulation of these modifications is associated with Alzheimer’s, Parkinson’s, amyotrophic lateral sclerosis and Friedreich’s ataxia.

Patient-derived three-dimensional cortical neurospheres to model Parkinson's disease

There are currently no preventive or disease-modifying therapies for Parkinson's Disease (PD). Failures in clinical trials necessitate a re-evaluation of existing pre-clinical models in order to adopt systems that better recapitulate underlying disease mechanisms and better predict clinical outcomes. In recent years, models utilizing patient-derived induced pluripotent stem cells (iPSC) have emerged as attractive models to recapitulate disease-relevant neuropathology in vitro without exogenous overexpression of disease-related pathologic proteins. Here, we utilized iPSC derived from patients with early-onset PD and dementia phenotypes that harbored either a point mutation (A53T) or multiplication at the α-synuclein/SNCA gene locus. We generated a three-dimensional (3D) cortical neurosphere culture model to better mimic the tissue microenvironment of the brain. We extensively characterized the differentiation process using quantitative PCR, Western immunoblotting and immunofluorescence staining. Differentiated and aged neurospheres revealed alterations in fatty acid profiles and elevated total and pathogenic phospho-α-synuclein levels in both A53T and the triplication lines compared to their isogenic control lines. Furthermore, treatment of the neurospheres with a small molecule inhibitor of stearoyl CoA desaturase (SCD) attenuated the protein accumulation and aberrant fatty acid profile phenotypes. Our findings suggest that the 3D cortical neurosphere model is a useful tool to interrogate targets for PD and amenable to test small molecule therapeutics.

Protein aggregation and calcium dysregulation are hallmarks of familial Parkinson's disease in midbrain dopaminergic neurons

Mutations in the SNCA gene cause autosomal dominant Parkinson's disease (PD), with loss of dopaminergic neurons in the substantia nigra, and aggregation of α-synuclein. The sequence of molecular events that proceed from an SNCA mutation during development, to end-stage pathology is unknown. Utilising human-induced pluripotent stem cells (hiPSCs), we resolved the temporal sequence of SNCA-induced pathophysiological events in order to discover early, and likely causative, events. Our small molecule-based protocol generates highly enriched midbrain dopaminergic (mDA) neurons: molecular identity was confirmed using single-cell RNA sequencing and proteomics, and functional identity was established through dopamine synthesis, and measures of electrophysiological activity. At the earliest stage of differentiation, prior to maturation to mDA neurons, we demonstrate the formation of small β-sheet-rich oligomeric aggregates, in SNCA-mutant cultures. Aggregation persists and progresses, ultimately resulting in the accumulation of phosphorylated α-synuclein aggregates. Impaired intracellular calcium signalling, increased basal calcium, and impairments in mitochondrial calcium handling occurred early at day 34-41 post differentiation. Once midbrain identity fully developed, at day 48-62 post differentiation, SNCA-mutant neurons exhibited mitochondrial dysfunction, oxidative stress, lysosomal swelling and increased autophagy. Ultimately these multiple cellular stresses lead to abnormal excitability, altered neuronal activity, and cell death. Our differentiation paradigm generates an efficient model for studying disease mechanisms in PD and highlights that protein misfolding to generate intraneuronal oligomers is one of the earliest critical events driving disease in human neurons, rather than a late-stage hallmark of the disease.

S-nitrosylated PARIS Leads to the Sequestration of PGC-1α into Insoluble Deposits in Parkinson's Disease Model

Neuronal accumulation of parkin-interacting substrate (PARIS), a transcriptional repressor of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), has been observed in Parkinson's disease (PD). Herein, we showed that PARIS can be S-nitrosylated at cysteine 265 (C265), and S-nitrosylated PARIS (SNO-PARIS) translocates to the insoluble fraction, leading to the sequestration of PGC-1α into insoluble deposits. The mislocalization of PGC-1α in the insoluble fraction was observed in S-nitrosocysteine-treated PARIS knockout (KO) cells overexpressing PARIS WT but not S-nitrosylation deficient C265S mutant, indicating that insolubility of PGC-1α is SNO-PARIS-dependent. In the sporadic PD model, α-synuclein preformed fibrils (α-syn PFFs)-injected mice, we found an increase in PARIS, SNO-PARIS, and insoluble sequestration of PGC-1α in substantia nigra (SN), resulting in the reduction of mitochondrial DNA copy number and ATP concentration that were restored by N(ω)-nitro-L-arginine methyl ester, a nitric oxide synthase (NOS) inhibitor. To assess the dopaminergic (DA) neuronal toxicity by SNO-PARIS, lentiviral PARIS WT, C265S, and S-nitrosylation mimic C265W was injected into the SN of either PBS- or α-syn PFFs-injected mice. PARIS WT and C265S caused DA neuronal death to a comparable extent, whereas C265W caused more severe DA neuronal loss in PBS-injected mice. Interestingly, there was synergistic DA loss in both lenti-PARIS WT and α-syn PFFs-injected mice, indicating that SNO-PARIS by α-syn PFFs contributes to the DA toxicity in vivo. Moreover, α-syn PFFs-mediated increment of PARIS, SNO-PARIS, DA toxicity, and behavioral deficits were completely nullified in neuronal NOS KO mice, suggesting that modulation of NO can be a therapeutic for α-syn PFFs-mediated neurodegeneration.

Rare and undiagnosed diseases: From disease-causing gene identification to mechanism elucidation

Rare and undiagnosed diseases substantially decrease patient quality of life and have increasingly become a heavy burden on healthcare systems. Because of the challenges in disease-causing gene identification and mechanism elucidation, patients are often confronted with difficulty obtaining a precise diagnosis and treatment. Due to advances in sequencing and multiomics analysis approaches combined with patient-derived iPSC models and gene-editing platforms, substantial progress has been made in the diagnosis and treatment of rare and undiagnosed diseases. The aforementioned techniques also provide an operational basis for future precision medicine studies. In this review, we summarize recent progress in identifying disease-causing genes based on GWAS/WES/WGS-guided multiomics analysis approaches. In addition, we discuss recent advances in the elucidation of pathogenic mechanisms and treatment of diseases with state-of-the-art iPSC and organoid models, which are improved by cell maturation level and gene editing technology. The comprehensive strategies described above will generate a new paradigm of disease classification that will significantly promote the precision and efficiency of diagnosis and treatment for rare and undiagnosed diseases.

Human Induced Pluripotent Stem Cell Phenotyping and Preclinical Modeling of Familial Parkinson's Disease

Parkinson's disease (PD) is primarily idiopathic and a highly heterogenous neurodegenerative disease with patients experiencing a wide array of motor and non-motor symptoms. A major challenge for understanding susceptibility to PD is to determine the genetic and environmental factors that influence the mechanisms underlying the variations in disease-associated traits. The pathological hallmark of PD is the degeneration of dopaminergic neurons in the substantia nigra pars compacta region of the brain and post-mortem Lewy pathology, which leads to the loss of projecting axons innervating the striatum and to impaired motor and cognitive functions. While the cause of PD is still largely unknown, genome-wide association studies provide evidence that numerous polymorphic variants in various genes contribute to sporadic PD, and 10 to 15% of all cases are linked to some form of hereditary mutations, either autosomal dominant or recessive. Among the most common mutations observed in PD patients are in the genes LRRK2, SNCA, GBA1, PINK1, PRKN, and PARK7/DJ-1. In this review, we cover these PD-related mutations, the use of induced pluripotent stem cells as a disease in a dish model, and genetic animal models to better understand the diversity in the pathogenesis and long-term outcomes seen in PD patients.

Mitophagy and reactive oxygen species interplay in Parkinson's disease

Mitophagy impairment and oxidative stress are cardinal pathological hallmarks in Parkinson's disease (PD), a common age-related neurodegenerative condition. The specific interactions between mitophagy and reactive oxygen species (ROS) have attracted considerable attention even though their exact interplay in PD has not been fully elucidated. We highlight the interactions between ROS and mitophagy, with a focus on the signalling pathways downstream to ROS that triggers mitophagy and draw attention to potential therapeutic compounds that target these pathways in both experimental and clinical models. Identifying a combination of ROS inhibitors and mitophagy activators to provide a physiologic balance in this complex signalling pathways may lead to a more optimal outcome. Deciphering the exact temporal relationship between mitophagy and oxidative stress and their triggers early in the course of neurodegeneration can unravel mechanistic clues that potentially lead to the development of compounds for clinical drug trials focusing on prodromic PD or at-risk individuals.

Unraveling pathological mechanisms in neurological disorders: the impact of cell-based and organoid models

Cell-based models are a promising tool in deciphering the molecular mechanisms underlying the pathogenesis of neurological disorders as well as aiding in the discovery and development of future drug therapies. The greatest challenge is creating cell-based models that encapsulate the vast phenotypic presentations as well as the underlying genotypic etiology of these conditions. In this article, we discuss the recent advancements in cell-based models for understanding the pathophysiology of neurological disorders. We reviewed studies discussing the progression of cell-based models to the advancement of three-dimensional models and organoids that provide a more accurate model of the pathophysiology of neurological disorders in vivo. The better we understand how to create more precise models of the neurological system, the sooner we will be able to create patient-specific models and large libraries of these neurological disorders. While three-dimensional models can be used to discover the linking factors to connect the varying phenotypes, such models will also help to understand the early pathophysiology of these neurological disorders and how they are affected by their environment. The three-dimensional cell models will allow us to create more specific treatments and uncover potentially preventative measures in neurological disorders such as autism spectrum disorder, Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis.

High-content phenotyping of Parkinson's disease patient stem cell-derived midbrain dopaminergic neurons using machine learning classification

Combining multiple Parkinson's disease (PD) relevant cellular phenotypes might increase the accuracy of midbrain dopaminergic neuron (mDAN) in vitro models. We differentiated patient-derived induced pluripotent stem cells (iPSCs) with a LRRK2 G2019S mutation, isogenic control, and genetically unrelated iPSCs into mDANs. Using automated fluorescence microscopy in 384-well-plate format, we identified elevated levels of α-synuclein (αSyn) and serine 129 phosphorylation, reduced dendritic complexity, and mitochondrial dysfunction. Next, we measured additional image-based phenotypes and used machine learning (ML) to accurately classify mDANs according to their genotype. Additionally, we show that chemical compound treatments, targeting LRRK2 kinase activity or αSyn levels, are detectable when using ML classification based on multiple image-based phenotypes. We validated our approach using a second isogenic patient-derived SNCA gene triplication mDAN model which overexpresses αSyn. This phenotyping and classification strategy improves the practical exploitability of mDANs for disease modeling and the identification of novel LRRK2-associated drug targets.

Pathological structural conversion of α-synuclein at the mitochondria induces neuronal toxicity

Aggregation of alpha-synuclein (α-Syn) drives Parkinson's disease (PD), although the initial stages of self-assembly and structural conversion have not been directly observed inside neurons. In this study, we tracked the intracellular conformational states of α-Syn using a single-molecule Förster resonance energy transfer (smFRET) biosensor, and we show here that α-Syn converts from a monomeric state into two distinct oligomeric states in neurons in a concentration-dependent and sequence-specific manner. Three-dimensional FRET-correlative light and electron microscopy (FRET-CLEM) revealed that intracellular seeding events occur preferentially on membrane surfaces, especially at mitochondrial membranes. The mitochondrial lipid cardiolipin triggers rapid oligomerization of A53T α-Syn, and cardiolipin is sequestered within aggregating lipid-protein complexes. Mitochondrial aggregates impair complex I activity and increase mitochondrial reactive oxygen species (ROS) generation, which accelerates the oligomerization of A53T α-Syn and causes permeabilization of mitochondrial membranes and cell death. These processes were also observed in induced pluripotent stem cell (iPSC)-derived neurons harboring A53T mutations from patients with PD. Our study highlights a mechanism of de novo α-Syn oligomerization at mitochondrial membranes and subsequent neuronal toxicity.

CRISPR and iPSCs: Recent Developments and Future Perspectives in Neurodegenerative Disease Modelling, Research, and Therapeutics

Neurodegenerative diseases are prominent causes of pain, suffering, and death worldwide. Traditional approaches modelling neurodegenerative diseases are deficient, and therefore, improved strategies that effectively recapitulate the pathophysiological conditions of neurodegenerative diseases are the need of the hour. The generation of human-induced pluripotent stem cells (iPSCs) has transformed our ability to model neurodegenerative diseases in vitro and provide an unlimited source of cells (including desired neuronal cell types) for cell replacement therapy. Recently, CRISPR/Cas9-based genome editing has also been gaining popularity because of the flexibility they provide to generate and ablate disease phenotypes. In addition, the recent advancements in CRISPR/Cas9 technology enables researchers to seamlessly target and introduce precise modifications in the genomic DNA of different human cell lines, including iPSCs. CRISPR-iPSC-based disease modelling, therefore, allows scientists to recapitulate the pathological aspects of most neurodegenerative processes and investigate the role of pathological gene variants in healthy non-patient cell lines. This review outlines how iPSCs, CRISPR/Cas9, and CRISPR-iPSC-based approaches accelerate research on neurodegenerative diseases and take us closer to a cure for neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, Amyotrophic Lateral Sclerosis, and so forth.

Nitrosative stress in Parkinson's disease

Parkinson’s Disease (PD) is a neurodegenerative disorder characterized, in part, by the loss of dopaminergic neurons within the nigral-striatal pathway. Multiple lines of evidence support a role for reactive nitrogen species (RNS) in degeneration of this pathway, specifically nitric oxide (NO). This review will focus on how RNS leads to loss of dopaminergic neurons in PD and whether RNS accumulation represents a central signal in the degenerative cascade. Herein, we provide an overview of how RNS accumulates in PD by considering the various cellular sources of RNS including nNOS, iNOS, nitrate, and nitrite reduction and describe evidence that these sources are upregulating RNS in PD. We document that over 1/3 of the proteins that deposit in Lewy Bodies, are post-translationally modified (S-nitrosylated) by RNS and provide a broad description of how this elicits deleterious effects in neurons. In doing so, we identify specific proteins that are modified by RNS in neurons which are implicated in PD pathogenesis, with an emphasis on exacerbation of synucleinopathy. How nitration of alpha-synuclein (aSyn) leads to aSyn misfolding and toxicity in PD models is outlined. Furthermore, we delineate how RNS modulates known PD-related phenotypes including axo-dendritic-, mitochondrial-, and dopamine-dysfunctions. Finally, we discuss successful outcomes of therapeutics that target S-nitrosylation of proteins in Parkinson’s Disease related clinical trials. In conclusion, we argue that targeting RNS may be of therapeutic benefit for people in early clinical stages of PD.

Early Signs of Molecular Defects in iPSC-Derived Neural Stems Cells from Patients with Familial Parkinson’s Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, classically associated with extensive loss of dopaminergic neurons of the substantia nigra pars compacta. The hallmark of the disease is the accumulation of pathogenic conformations of the presynaptic protein, α-synuclein (αSyn), and the formation of intraneuronal protein aggregate inclusions. Neurodegeneration of dopamine neurons leads to a prominent dopaminergic deficiency in the basal ganglia, responsible for motor disturbances. However, it is now recognized that the disease involves more widespread neuronal dysfunction, leading to early and late non-motor symptoms. The development of in vitro systems based on the differentiation of human-induced pluripotent stem cells provides us the unique opportunity to monitor alterations at the cellular and molecular level throughout the differentiation procedure and identify perturbations that occur early, even at the neuronal precursor stage. Here we aim to identify whether p.A53T-αSyn induced disturbances at the molecular level are already present in neural precursors. Towards this, we present data from transcriptomics analysis of control and p.A53T-αSyn NPCs showing altered expression in transcripts involved in axon guidance, adhesion, synaptogenesis, ion transport, and metabolism. The comparative analysis with the transcriptomics profile of p.A53T-αSyn neurons shows both distinct and overlapping pathways leading to neurodegeneration while meta-analysis with transcriptomics data from both neurodegenerative and neurodevelopmental disorders reveals that p.A53T-pathology has a significant overlap with the latter category. This is the first study showing that molecular dysregulation initiates early at the p.A53T-αSyn NPC level, suggesting that synucleinopathies may have a neurodevelopmental component.

The Parkinson's disease protein alpha-synuclein is a modulator of processing bodies and mRNA stability

Alpha-synuclein (αS) is a conformationally plastic protein that reversibly binds to cellular membranes. It aggregates and is genetically linked to Parkinson's disease (PD). Here, we show that αS directly modulates processing bodies (P-bodies), membraneless organelles that function in mRNA turnover and storage. The N terminus of αS, but not other synucleins, dictates mutually exclusive binding either to cellular membranes or to P-bodies in the cytosol. αS associates with multiple decapping proteins in close proximity on the Edc4 scaffold. As αS pathologically accumulates, aberrant interaction with Edc4 occurs at the expense of physiologic decapping-module interactions. mRNA decay kinetics within PD-relevant pathways are correspondingly disrupted in PD patient neurons and brain. Genetic modulation of P-body components alters αS toxicity, and human genetic analysis lends support to the disease-relevance of these interactions. Beyond revealing an unexpected aspect of αS function and pathology, our data highlight the versatility of conformationally plastic proteins with high intrinsic disorder.

Induced pluripotent stem cells: a tool for modeling Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder. Among its pathologies, progressive loss of dopaminergic (DA) neurons in the substantia nigra is characteristic and contributes to many of the most severe symptoms of PD. Recent advances in induced pluripotent stem cell (iPSC) technology have made it possible to generate patient-derived DA neuronal cell culture and organoid models of PD. These models have contributed to understanding disease mechanisms and the identification of novel targets and therapeutic candidates. Still needed are better ways to model the age-related aspects of PD, as well as a deeper understanding of the interactions among disease-modifying genes and between genetic and environmental contributions to the etiology and progression of PD.