Mechanistic Interplay Between Autophagy and Apoptotic Signaling in Endosulfan-Induced Dopaminergic Neurotoxicity: Relevance to the Adverse Outcome Pathway in Pesticide Neurotoxicity

Understanding role of pesticides in development of Parkinson's disease: Insights from Drosophila and rodent models

Parkinson's disease is a neurodegenerative illness linked to ageing, marked by the gradual decline of dopaminergic neurons in the midbrain. The exact aetiology of Parkinson's disease (PD) remains uncertain, with genetic predisposition and environmental variables playing significant roles in the disease's frequency. Epidemiological data indicates a possible connection between pesticide exposure and brain degeneration. Specific pesticides have been associated with important characteristics of Parkinson's disease, such as mitochondrial dysfunction, oxidative stress, and α-synuclein aggregation, which are crucial for the advancement of the disease. Recently, many animal models have been developed for Parkinson's disease study. Although these models do not perfectly replicate the disease's pathology, they provide valuable insights that improve our understanding of the condition and the limitations of current treatment methods. Drosophila, in particular, has been useful in studying Parkinson's disease induced by toxins or genetic factors. The review thoroughly analyses many animal models utilised in Parkinson's research, with an emphasis on issues including pesticides, genetic and epigenetic changes, proteasome failure, oxidative damage, α-synuclein inoculation, and mitochondrial dysfunction. The text highlights the important impact of pesticides on the onset of Parkinson's disease (PD) and stresses the need for more research on genetic and mechanistic alterations linked to the condition.

Lysosomal genes contribute to Parkinson's disease near agriculture with high intensity pesticide use

Parkinson's disease (PD), the second most common neurodegenerative disorder, develops sporadically, likely through a combination of polygenic and environmental factors. Previous studies associate pesticide exposure and genes involved in lysosomal function with PD risk. We evaluated the frequency of variants in lysosomal function genes among patients from the Parkinson's, Environment, and Genes (PEG) study with ambient pesticide exposure from agricultural sources. 757 PD patients, primarily of White European/non-Hispanic ancestry (75%), were screened for variants in 85 genes using a custom amplicon panel. Variant enrichment was calculated against the Genome Aggregation Database (gnomAD). Enriched exonic variants were prioritized by exposure to a cluster of pesticides used on cotton and severity of disease progression in a subset of 386 patients subdivided by race/ethnicity. Gene enrichment analysis identified 36 variants in 26 genes in PEG PD patients. Twelve of the identified genes (12/26, 46%) had multiple enriched variants and/or a single enriched variant present in multiple individuals, representing 61% (22/36) of the observed variation in the cohort. The majority of enriched variants (26/36, 72%) were found in genes contributing to lysosomal function, particularly autophagy, and were bioinformatically deemed functionally deleterious (31/36, 86%). We conclude that, in this study, variants in genes associated with lysosomal function, notably autophagy, were enriched in PD patients exposed to agricultural pesticides suggesting that altered lysosomal function may generate an underlying susceptibility for developing PD with pesticide exposure. Further study of gene-environment interactions targeting lysosomal function may improve understanding of PD risk in individuals exposed to pesticides.

Influence of chlorpyrifos and endosulfan and their metabolites on the virulence of Helicobacter pylori

Organochlorine (OC) and organophosphorus (OP) pesticides such as chlorpyrifos (CPF) and endosulfan (ES) have been associated with a plethora of adverse health effects. Helicobacter pylori (H. pylori) infection can lead to gastrointestinal diseases by regulating several cellular processes. Thus, the current study focuses on the effect of the co-exposure to pesticides and H. pylori on gastric epithelial cells. We have used the in-silico approach to determine the interactive potential of pesticides and their metabolites with H. pylori-associated proteins. Further, various in-vitro methods depict the potential of ES in enhancing the virulence of H. pylori. Our results showed that ES along with H. pylori affects the mitochondrial dynamics, increases the transcript expression of mitochondrial fission genes, and lowers the mitochondrial membrane potential and biomass. They also promote inflammation and lower oxidative stress as predicted by ROS levels. Furthermore, co-exposure induces the multi-nucleated cells in gastric epithelial cells. In addition, ES along with H. pylori infection follows the extrinsic pathway for apoptotic signaling. H. pylori leads to the NF-κB activation which in turn advances the β-catenin expression. The expression was further enhanced in the co-exposure condition and even more prominent in co-exposure with ES-conditioned media. Thus, our study demonstrated that pesticide and their metabolites enhance the pathogenicity of H. pylori infection.

Identification of neurotoxicology (NT)/developmental neurotoxicology (DNT) adverse outcome pathways and key event linkages with in vitro DNT screening assays

There is a need to assess compounds reliably and quickly for neurotoxicity (NT) and developmental neurotoxicity (DNT). Adverse outcome pathways (AOPs) enable the mapping of molecular events to an apical endpoint in a chemical agnostic manner and have begun to be applied in NT and DNT testing frameworks. We assessed the status of NT/DNT AOPs in the AOP-Wiki (ca. 2/1/23; https://aopwiki.org/), to characterize the state of AOP development, identify strengths and knowledge gaps, elucidate areas for improvement, and describe areas for future focus. AOPs in the Wiki database were assessed for inclusion of NT/DNT molecular events and endpoints, AOP development and endorsement, as well as the linkages of key neurodevelopmental processes with in vitro new approach methods (NAMs). This review found that 41 AOPs have been proposed detailing NT/DNT, of which eight were endorsed by working parties in OECD. Further, this review determined that learning and memory is included as an adverse outcome in eight NT/DNT AOPS, often without distinction regarding the varying forms of learning and memory, regional specification, temporal dynamics, or acquisition mechanisms involved. There is also an overlap with key events (KEs) and in vitro NAMs, which synaptogenesis appeared as a common process. Overall, progress on NT/DNT AOPs could be expanded, adding in modes of action that are missing, improvement in defining apical endpoints, as well as utilizing NAMs further to develop AOPs and identify gaps in current knowledge.

Exploring Parkinson-associated kinases for CRISPR/Cas9-based gene editing: beyond alpha-synuclein

Parkinson's disease (PD) is a debilitating neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substania nigra (SN) and is associated with progressive motor impairment. PD is classified into familial and sporadic forms. The first genetic association studies in PD reported the involvement of Synuclein alpha (SNCA) mutations in the pathobiology of familial PD. Subsequent studies suggested mutations in PTEN-induced putative kinase 1 (PINK1), PARKIN, leucine repeat kinase-2 (LRRK2), and DJ-1 causing familial PD. In addition, kinase dysregulation has been embroiled in the pathogenesis of PD. The genome-editing mechanism CRISPR (clustered regularly interspaced short palindromic repeats) has recently influenced industry and scientific discoveries and is expected to expedite neurodegenerative disease research. This review will discuss the structure, function, and history of the CRISPR/Cas9 genome editing system. Moreover, it summarizes genes-encoding kinases involved in PD pathogenesis and targeted by CRISPR/Cas9 technology, including LRRK2, PINK1, Protein kinase C-delta (PKC-γ), and adenosine monophosphate-activated protein kinase (AMPK). We provide an overview of novel kinases to be targeted by the CRISPR/Cas9 system such as G-protein coupled receptor kinases (GRKs), cyclin-G-associated kinases (GAKs), cyclin-dependent kinase 5 (CDK5), Ataxia telangiectasia mutated (ATM), c-ABL, and rearranged during transfection (RET) receptors. Additionally, we will explain the off-target effects of CRISPR/Cas9 system and how to address them. Also, we will shed light on the associated challenges and future directions that are enabling the efficient use of CRISPR/Cas9 technology in kinases research in PD. In conclusion, gene editing, in addition to gene therapy, might be a possible promising strategy for PD therapy.

Exosomes for CRISPR-Cas9 Delivery: The Cutting Edge in Genome Editing

Gene mutation correction was challenging until the discovery of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein (Cas). CRISPR is a new era for genome modification, and this technology has bypassed the limitations of previous methods such as zinc-finger nuclease and transcription activator-like effector nuclease. Currently, this method is becoming the method of choice for gene-editing purposes, especially therapeutic gene editing in diseases such as cardiovascular, neurological, renal, genetic, optical, and stem cell, as well as blood disorders and muscular degeneration. However, finding the optimum delivery system capable of carrying this large complex persists as the main challenge of this technology. Therefore, it would be ideal if the delivery vehicle could direct the introduction of editing functions to specific cells in a multicellular organism. Exosomes are membrane-bound vesicles with high biocompatibility and low immunogenicity; they offer the best and most reliable way to fill the CRISPR/Cas9 system delivery gap. This review presents the current evidence on the molecular mechanisms and challenges of CRISPR/Cas9-mediated genome modification. Also, the role of CRISPR/Cas9 in the development of treatment and diagnosis of numerous disorders, from malignancies to viral infections, has been discussed. Lastly, the focus is on new advances in exosome-delivery technologies that may play a role in CRISPR/Cas9 delivery for future clinical settings.

Realgar-Induced Neurotoxicity: Crosstalk Between the Autophagic Flux and the p62-NRF2 Feedback Loop Mediates p62 Accumulation to Promote Apoptosis

Realgar is a traditional Chinese medicine that contains arsenic. It has been reported that the abuse of medicine-containing realgar has potential central nervous system (CNS) toxicity, but the toxicity mechanism has not been elucidated. In this study, we established an in vivo realgar exposure model and selected the end product of realgar metabolism, DMA, to treat SH-SY5Y cells in vitro. Many assays, including behavioral, analytical chemistry, and molecular biology, were used to elucidate the roles of the autophagic flux and the p62-NRF2 feedback loop in realgar-induced neurotoxicity. The results showed that arsenic could accumulate in the brain, causing cognitive impairment and anxiety-like behavior. Realgar impairs the ultrastructure of neurons, promotes apoptosis, perturbs autophagic flux homeostasis, amplifies the p62-NRF2 feedback loop, and leads to p62 accumulation. Further analysis showed that realgar promotes the formation of the Beclin1-Vps34 complex by activating JNK/c-Jun to induce autophagy and recruit p62. Meanwhile, realgar inhibits the activities of CTSB and CTSD and changes the acidity of lysosomes, leading to the inhibition of p62 degradation and p62 accumulation. Moreover, the amplified p62-NRF2 feedback loop is involved in the accumulation of p62. Its accumulation promotes neuronal apoptosis by upregulating the expression levels of Bax and cleaved caspase-9, resulting in neurotoxicity. Taken together, these data suggest that realgar can perturb the crosstalk between the autophagic flux and the p62-NRF2 feedback loop to mediate p62 accumulation, promote apoptosis, and induce neurotoxicity. Realgar promotes p62 accumulation to produce neurotoxicity by perturbing the autophagic flux and p62-NRF2 feedback loop crosstalk.

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.

Putative interactions between transthyretin and endosulfan II and its relevance in breast cancer

The unregulated use of organochlorine pesticides (OCPs) has been linked to spread of breast cancer (BC), but the underlying biomolecular interactions are unknown. Using a case-control study, we compared OCP blood levels and protein signatures among BC patients. Five pesticides were found in significantly higher concentrations in breast cancer patients than in healthy controls: p',p' dichloro diphenyl trichloroethane (DDT), p'p' dichloro diphenyl dichloroethane (DDD), endosulfan II, delta-hexachlorocyclohexane (dHCH), and heptachlor epoxide A (HTEA). According to the odds ratio analysis, these OCPs, which have been banned for decades, continue to raise the risk of cancer in Indian women. Proteomic analysis of plasma from estrogen receptor-positive breast cancer patients revealed 17 dysregulated proteins, but transthyretin (TTR) was three times higher than in healthy controls, which is further validated by enzyme-linked immunosorbent assays (ELISA). Molecular docking and molecular dynamics studies revealed a competitive affinity between endosulfan II and the thyroxine-binding site of TTR, pointing towards the significance of the competition between thyroxin and endosulfan, resulting in endocrine disruption leading to breast cancer. Our study sheds light on the putative role of TTR in OCP-mediated BC, but more research is needed to decipher the underlying mechanisms that can be used to prevent the carcinogenic effects of these pesticides on women's health.

Environmental neurotoxic pesticide exposure induces gut inflammation and enteric neuronal degeneration by impairing enteric glial mitochondrial function in pesticide models of Parkinson's disease: Potential relevance to gut-brain axis inflammation in Parkinson's disease pathogenesis

Despite the growing recognition that gastrointestinal (GI) dysfunction is prevalent in Parkinson's disease (PD) and occurs as a major prodromal symptom of PD, its cellular and molecular mechanisms remain largely unknown. Among the various types of GI cells, enteric glial cells (EGCs), which resemble astrocytes in structure and function, play a critical role in the pathophysiology of many GI diseases including PD. Thus, we investigated how EGCs respond to the environmental pesticides rotenone (Rot) and tebufenpyrad (Tebu) in cell and animal models to better understand the mechanism underlying GI abnormalities. Both Rot and Tebu induce dopaminergic neuronal cell death through complex 1 inhibition of the mitochondrial respiratory chain. We report that exposing a rat enteric glial cell model (CRL-2690 cells) to these pesticides increased mitochondrial fission and reduced mitochondrial fusion by impairing MFN2 function. Furthermore, they also increased mitochondrial superoxide generation and impaired mitochondrial ATP levels and basal respiratory rate. Measurement of LC3, p62 and lysosomal assays revealed impaired autolysosomal function in ECGs during mitochondrial stress. Consistent with our recent findings that mitochondrial dysfunction augments inflammation in astrocytes and microglia, we found that neurotoxic pesticide exposure also enhanced the production of pro-inflammatory factors in EGCs in direct correlation with the loss in mitochondrial mass. Finally, we show that pesticide-induced mitochondrial defects functionally impaired smooth muscle velocity, acceleration, and total kinetic energy in a mixed primary culture of the enteric nervous system (ENS). Collectively, our studies demonstrate for the first time that exposure to environmental neurotoxic pesticides impairs mitochondrial bioenergetics and activates inflammatory pathways in EGCs, further augmenting mitochondrial dysfunction and pro-inflammatory events to induce gut dysfunction. Our findings have major implications in understanding the GI-related pathogenesis and progression of environmentally linked PD.

Comparative study of two isothiazolinone biocides, 1,2-benzisothiazolin-3-one (BIT) and 4,5-dichloro-2-n-octyl-isothiazolin-3-one (DCOIT), on barrier function and mitochondrial bioenergetics using murine brain endothelial cell line (bEND.3)

Isothiazolinone (IT) biocides are potent antibacterial substances used as preservatives and disinfectants. These biocides exert differing biocidal effects and display environmental stability based upon chemical structure. In agreement with our recent study reporting that 2-n-octyl-4-isothiazolin-3-one (OIT) induced dysfunction of the blood-brain barrier (BBB), the potential adverse health effects of two IT biocides 1,2-benzisothiazolin-3-one (BIT) and 4,5-dichloro-2-n-octyl-isothiazolin-3-one (DCOIT) were compared using brain endothelial cells (ECs) derived from murine brain endothelial cell line (bEND.3). BIT possesses an unchlorinated IT ring structure and used as a preservative in cleaning products. DCOIT contains a chlorinated IT ring structure and employed as an antifouling agent in paints. Data demonstrated that DCOIT altered cellular metabolism at a lower concentration than BIT. Both BIT and DCOIT increased reactive oxygen species (ROS) generation at the mitochondrial and cellular levels. However, the effect of DCOIT on glutathione (GSH) levels appeared to be greater than BIT. While mitochondrial membrane potential (MMP) was decreased in both BIT- and DCOIT-exposed cells, direct disturbance in mitochondrial bioenergetic flux was only observed in BIT-treated ECs. Taken together, IT biocides produced toxicity in brain EC and barrier dysfunction, but at different concentration ranges suggesting distinct differing mechanisms related to chemical structure.

Environmental neurotoxicants and inflammasome activation in Parkinson's disease - A focus on the gut-brain axis

Inflammasomes are multi-protein complexes expressed in immune cells that function as intracellular sensors of environmental, metabolic and cellular stress. Inflammasome activation in the brain, has been shown to drive neuropathology and disease progression by multiple mechanisms, making it one of the most attractive therapeutic targets for disease modification in Parkinson's Disease (PD). Extensive inflammasome activation is evident in the brains of people with PD at the sites of dopaminergic degeneration and synuclein aggregation. While substantial progress has been made on validating inflammasome activation as a therapeutic target for PD, the mechanisms by which inflammasome activation is triggered and sustained over the disease course remain poorly understood. A growing body of evidence point to environmental and occupational chemical exposures as possible triggers of inflammasome activation in PD. The involvement of the gastrointestinal system and gut microbiota in PD pathophysiology is beginning to be elucidated, especially the profound link between gut dysbiosis and immune activation. While large cohort studies confirmed specific changes in the gut microbiota in PD patients compared to age-matched healthy controls, recent research suggest that synuclein pathology could be initiated in the gastrointestinal tract. In this review, we present a summarized perspective on current understanding on inflammasome activation and the gut-brain-axis link during PD pathophysiology. We discuss multiple environmental toxicants that are implicated as the etiological agents in causing idiopathic PD and their mechanistic underpinnings during neuroinflammatory events. We additionally present future directions that needs to address the research questions related to the gut-microbiome-brain mechanisms in PD.

Gene Therapy Approach with an Emphasis on Growth Factors: Theoretical and Clinical Outcomes in Neurodegenerative Diseases

The etiology of many neurological diseases affecting the central nervous system (CNS) is unknown and still needs more effective and specific therapeutic approaches. Gene therapy has a promising future in treating neurodegenerative disorders by correcting the genetic defects or by therapeutic protein delivery and is now an attraction for neurologists to treat brain disorders, like Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, spinal muscular atrophy, spinocerebellar ataxia, epilepsy, Huntington’s disease, stroke, and spinal cord injury. Gene therapy allows the transgene induction, with a unique expression in cells’ substrate. This article mainly focuses on the delivering modes of genetic materials in the CNS, which includes viral and non-viral vectors and their application in gene therapy. Despite the many clinical trials conducted so far, data have shown disappointing outcomes. The efforts done to improve outcomes, efficacy, and safety in the identification of targets in various neurological disorders are also discussed here. Adapting gene therapy as a new therapeutic approach for treating neurological disorders seems to be promising, with early detection and delivery of therapy before the neuron is lost, helping a lot the development of new therapeutic options to translate to the clinic.

Mitochondrial dysfunction-induced H3K27 hyperacetylation perturbs enhancers in Parkinson's disease

Mitochondrial dysfunction is a major pathophysiological contributor to the progression of Parkinson’s disease (PD); however, whether it contributes to epigenetic dysregulation remains unknown. Here, we show that both chemically and genetically driven mitochondrial dysfunctions share a common mechanism of epigenetic dysregulation. Under both scenarios, lysine 27 acetylation of likely variant H3.3 (H3.3K27ac) increased in dopaminergic neuronal models of PD, thereby opening that region to active enhancer activity via H3K27ac. These vulnerable epigenomic loci represent potential transcription factor motifs for PD pathogenesis. We further confirmed that mitochondrial dysfunction induces H3K27ac in ex vivo and in vivo (MitoPark) neurodegenerative models of PD. Notably, the significantly increased H3K27ac in postmortem PD brains highlights the clinical relevance to the human PD population. Our results reveal an exciting mitochondrial dysfunction-metabolism-H3K27ac-transcriptome axis for PD pathogenesis. Collectively, the mechanistic insights link mitochondrial dysfunction to epigenetic dysregulation in dopaminergic degeneration and offer potential new epigenetic intervention strategies for PD.

Clustered regularly interspaced short palindromic repeats as an advanced treatment for Parkinson's disease

Recently, genome-editing technology like clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 has improved the translational gap in the treatments mediated through gene therapy. The advantages of the CRISPR system, such as, work in the living cells and tissues, candidate this technique for the employing in experiments and the therapy of central nervous system diseases. Parkinson's disease (PD) is a widespread, disabling, neurodegenerative disease induced by dopaminergic neuron loss and linked to progressive motor impairment. Pathophysiological basis knowledge of PD has modified the PD classification model and expresses in the sporadic and familial types. Analyses of the earliest genetic linkage have shown in PD the inclusion of synuclein alpha (SNCA) genomic duplication and SNCA mutations in the familial types of PD pathogenesis. This review analyzes the structure, development, and function in genome editing regulated through the CRISPR/Cas9. Also, it explains the genes associated with PD pathogenesis and the appropriate modifications to favor PD. This study follows the direction by understanding the PD linking analyses in which the CRISPR technique is applied. Finally, this study explains the limitations and future trends of CRISPR service in relation to the genome-editing process in PD patients' induced pluripotent stem cells.

Functionalized polyanhydride nanoparticles for improved treatment of mitochondrial dysfunction

Parkinson's disease (PD) is a devastating neurodegenerative disease affecting a large proportion of older adults. Exposure to pesticides like rotenone is a leading cause for PD. To reduce disease progression and prolong life expectancy, it is important to target disease mechanisms that contribute to dopaminergic neuronal atrophy, including mitochondrial dysfunction. Achieving targeted mitochondrial delivery is difficult for many therapeutics by themselves, necessitating higher therapeutic doses that could lead to toxicity. To minimize this adverse effect, targeted nano-carriers such as polyanhydride nanoparticles (NPs) can protect therapeutics from degradation and provide sustained release, enabling fewer administrations and lower therapeutic dose. This work expands upon the use of the polyanhydride NP platform for targeted drug delivery by functionalizing the polymer with a derivative of triphenylphosphonium called (3-carboxypropyl) triphenylphosphonium (CPTP) using a novel method that enables longer CPTP persistence on the NPs. The extent to which neurons internalized both nonfunctionalized and functionalized NPs was tested. Next, the efficacy of these nanoformulations in treating rotenone-induced mitochondrial dysfunction in the same cell line was evaluated using a novel neuroprotective drug, mito-metformin. CPTP functionalization significantly improved NP internalization by neuronal cells. This was correlated with significant protection by CPTP-functionalized, mito-metformin encapsulated NPs against rotenone-induced mitochondrial dysfunction. However, nonfunctionalized, mito-metformin encapsulated NPs and soluble mito-metformin administered at the same dose did not significantly protect cells from rotenone-induced toxicity. These results indicate that the targeted NP platform can provide enhanced dose-sparing and potentially reduce the occurrence of systemic side-effects for PD therapeutics.

Methamphetamine-induced dopaminergic neurotoxicity as a model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with a high prevalence, approximately 1 % in the elderly population. Numerous studies have demonstrated that methamphetamine (MA) intoxication caused the neurological deficits and nigrostriatal damage seen in Parkinsonian conditions, and subsequent rodent studies have found that neurotoxic binge administration of MA reproduced PD-like features, in terms of its symptomatology and pathology. Several anti-Parkinsonian medications have been shown to attenuate the motor impairments and dopaminergic damage induced by MA. In addition, it has been recognized that mitochondrial dysfunction, oxidative stress, pro-apoptosis, proteasomal/autophagic impairment, and neuroinflammation play important roles in inducing MA neurotoxicity. Importantly, MA neurotoxicity has been shown to share a common mechanism of dopaminergic toxicity with that of PD pathogenesis. This review describes the major findings on the neuropathological features and underlying neurotoxic mechanisms induced by MA and compares them with Parkinsonian pathogenesis. Taken together, it is suggested that neurotoxic binge-type administration of MA in rodents is a valid animal model for PD that may provide knowledge on the neuropathogenesis of PD.

CRISPR/Cas9 gene editing: New hope for Alzheimer's disease therapeutics

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Mutations in APP, PSEN1 and PSEN2 are known factors for AD pathobiology.

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CRISPR/Cas9 genome editing approach hold promises in AD management.

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CRISPR/Cas9 is utilized to help correct anomalous genetic functions.

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Off-target mutations may impair the functionality of edited cells.

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Non-viral vectors show better efficacy and safety than viral vectors.

Background

Alzheimer's disease (AD) is an insidious, irreversible, and progressive neurodegenerative health condition manifesting as cognitive deficits and amyloid beta (Aβ) plaques and neurofibrillary tangles. Approximately 50 million individuals are affected by AD, and the number is rapidly increasing globally. This review explores the role of CRISPR/Cas9 gene editing in the management of AD and its clinical manifestations.

Aim of Review

This review aims to provide a deep insight into the recent progress in CRISPR/Cas9-mediated genome editing and its use against neurodegenerative disorders, specifically AD. However, we have referred to its use against parkinsons’s disease (PD), Huntington’s disease (HD), and other human diseases, as is one of the most promising and emerging technologies for disease treatment.

Key Scientific Concepts of Review

The pathophysiology of AD is known to be linked with gene mutations, that is, presenilin (PSEN) and amyloid beta precursor protein (APP). However, clinical trials focused at the genetic level could not meet the desired efficiency. The CRISPR/Cas9 genome editing tool is one of the most powerful technologies for correcting inconsistent genetic signatures and now extensively used for AD management. It has significant potential for the correction of undesired gene mutations associated with AD. This technology has allowed the development of empirical AD models, therapeutic lines, and diagnostic approaches for better understanding the nervous system, from in vitro to in vivo models.

Arsenic induces autophagy-dependent apoptosis via Akt inactivation and AMPK activation signaling pathways leading to neuronal cell death

Inorganic arsenic (As³⁺), a well-known worldwide industrial and environmental pollutant, has been linked to neurodegenerative disorders (NDs). Autophagy plays an important role in controlling neuronal cell survival/death. However, limited information is available regarding the toxicological mechanism at the interplay between autophagy and As³⁺-induced neurotoxicity. The present study found that As³⁺ exposure induced a concomitant activation of apoptosis and autophagy in Neuro-2a cells, which was accompanied with the increase of phosphatidylserine exposure on outer membrane leaflets and apoptotic cell population, and the activation of caspase-3, -7, and PARP as well as the elevation of protein expressions of LC3-II, Atg-5, and Beclin-1, and the accumulation of autophagosome. Pretreatment of cells with autophagy inhibitor 3-MA, but not that of Z-VAD-FMK (a pan-caspase inhibitor), effectively prevented the As³⁺-induced autophagic and apoptotic responses, indicating that As³⁺-triggered autophagy was contributing to neuronal cell apoptosis. Furthermore, As³⁺ exposure evoked the dephosphorylation of Akt. Pretreatment with SC79, an Akt activator, could significantly attenuated As³⁺-induced Akt inactivation as well as autophagic and apoptotic events. Expectedly, inhibition of Akt signaling with LY294002 obviously enhanced As³⁺-triggered autophagy and apoptosis. Exposure to As³⁺ also dramatically increased the phosphorylation level of AMPKα. Pretreatment of AMPK inhibitor (Compound C) could markedly abrogate the As³⁺-induced phosphorylated AMPKα expression, and autophagy and apoptosis activation. Taken together, these results indicated that As³⁺ exerted its cytotoxicity in neuronal cells via the Akt inactivation/AMPK activation downstream-regulated autophagy-dependent apoptosis pathways, which ultimately lead to cell death. Our findings suggest that the regulation of Akt/AMPK signals may be a promising intervention to against As³⁺-induced neurotoxicity and NDs.

Fyn Kinase-Mediated PKCδ Y311 Phosphorylation Induces Dopaminergic Degeneration in Cell Culture and Animal Models: Implications for the Identification of a New Pharmacological Target for Parkinson's Disease

Oxidative stress, neuroinflammation and apoptosis are some of the key etiological factors responsible for dopamin(DA)ergic degeneration during Parkinson's disease (PD), yet the downstream molecular mechanisms underlying neurodegeneration are largely unknown. Recently, a genome-wide association study revealed the FYN gene to be associated with PD, suggesting that Fyn kinase could be a pharmacological target for PD. In this study, we report that Fyn-mediated PKCδ tyrosine (Y311) phosphorylation is a key event preceding its proteolytic activation in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinsonism. MPP+/MPTP induced Fyn kinase activation in N27 DAergic neuronal cells and the mouse substantia nigra. PKCδ-Y311 phosphorylation by activated Fyn initiates the apoptotic caspase-signaling cascade during DAergic degeneration. Pharmacological attenuation of Fyn activity protected DAergic neurons from MPP+-induced degeneration in primary mesencephalic neuronal cultures. We further employed Fyn wild-type and Fyn knockout (KO) mice to confirm whether Fyn is a valid pharmacological target of DAergic neurodegeneration. Primary mesencephalic neurons from Fyn KO mice were greatly protected from MPP+-induced DAergic cell death, neurite loss and DA reuptake loss. Furthermore, Fyn KO mice were significantly protected from MPTP-induced PKCδ-Y311 phosphorylation, behavioral deficits and nigral DAergic degeneration. This study thus unveils a mechanism by which Fyn regulates PKCδ's pro-apoptotic function and DAergic degeneration. Pharmacological inhibitors directed at Fyn activation could prove to be a novel therapeutic target in the delay or halting of selective DAergic degeneration during PD.

Acrylamide and its metabolite induce neurotoxicity via modulation of protein kinase C and AMP-activated protein kinase pathways

Acrylamide is known as a neurotoxicant found in commonly consumed food as well as in human body. However, the underlying mechanisms involved in neurotoxicity by acrylamide and its metabolite, glycidamide remain largely unknown. In this study, we have examined the interplay between CYP2E1, AMPK, ERK and PKC in acrylamide-induced neurotoxicity associated with autophagy in PC12 cells. Acrylamide-induced cell death was mediated by CYP2E1 expression and the activation of ERK, PKC-ɑ and PKC-δ, whereas AMPK knockdown exacerbated the acrylamide-induced neurotoxic effects. PKC-ɑ, but not PKC-δ, plays an upstream regulator of ERK and AMPK. Moreover, AMPK activation suppressed ERK, and CYP2E1 and AMPK bilaterally inhibit each other. Furthermore, acrylamide increased autophagy with impaired autophagic flux, evidenced by the increased beclin-1, LC3-II and p62 protein. Acrylamide-induced neuronal death was ameliorated by 3-methyladenine, an autophagy inhibitor, whereas neuronal death was exacerbated by chloroquine, a lysosomal inhibitor. Interestingly, PKC-δ siRNA, but not PKC-ɑ siRNA, dramatically reduced acrylamide-induced beclin-1 and LC3-II levels, whereas AMPK siRNA further increased beclin-1, LC3-II and p62 protein levels. Glycidamide, a major metabolite, mimicked acrylamide only with a higher potency. Taken together, acrylamide- and glycidamide-induced neurotoxicity may involve cytotoxic autophagy, which is mediated by interplay between PKCs and AMPK pathways.

Valeric Acid Protects Dopaminergic Neurons by Suppressing Oxidative Stress, Neuroinflammation and Modulating Autophagy Pathways

Parkinson's disease, the second common neurodegenerative disease is clinically characterized by degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) with upregulation of neuroinflammatory markers and oxidative stress. Autophagy lysosome pathway (ALP) plays a major role in degradation of damaged organelles and proteins for energy balance and intracellular homeostasis. However, dysfunction of ALP results in impairment of α-synuclein clearance which hastens dopaminergic neurons loss. In this study, we wanted to understand the neuroprotective efficacy of Val in rotenone induced PD rat model. Animals received intraperitoneal injections (2.5 mg/kg) of rotenone daily followed by Val (40 mg/kg, i.p) for four weeks. Valeric acid, a straight chain alkyl carboxylic acid found naturally in Valeriana officianilis have been used in the treatment of neurological disorders. However, their neuroprotective efficacy has not yet been studied. In our study, we found that Val prevented rotenone induced upregulation of pro-inflammatory cytokine oxidative stress, and α-synuclein expression with subsequent increase in vital antioxidant enzymes. Moreover, Val mitigated rotenone induced hyperactivation of microglia and astrocytes. These protective mechanisms prevented rotenone induced dopaminergic neuron loss in SNpc and neuronal fibers in the striatum. Additionally, Val treatment prevented rotenone blocked mTOR-mediated p70S6K pathway as well as apoptosis. Moreover, Val prevented rotenone mediated autophagic vacuole accumulation and increased lysosomal degradation. Hence, Val could be further developed as a potential therapeutic candidate for treatment of PD.

Application of microRNA profiling to understand sevoflurane-induced adverse effects on developing monkey brain

We have described that prolonged sevoflurane exposure at a clinically-relevant concentration of 2.5 % caused neuronal cell death in the developing monkey brain. Postnatal day 5 or 6 rhesus monkeys (n = 3) were exposed to 2.5 % sevoflurane for 8 h. Monkeys kept at environmental conditions in the procedure room served as controls (n = 3). Brain tissues were harvested four hours after sevoflurane exposure for histological analysis, and RNA or protein extraction. MicroRNA (miRNA) profiling on the frontal cortex of monkey brains was performed using next-generation sequencing. 417 miRNAs were identified in the frontal cortex, where most neuronal cell death was observed. 7 miRNAs were differentially expressed in frontal cortex after sevoflurane exposure. Five of these were expressed at significantly lower levels than controls and the other two miRNAs were expressed significantly higher. These differentially expressed miRNAs (DEMs) were then loaded to the Ingenuity Pathway Analysis database for pathway analysis, in which targeting information was available for 5 DEMs. The 5 DEMs target 2,919 mRNAs which are involved in pathways that contribute to various cellular functions. Of note, 78 genes that are related to axon guidance signaling were targeted, suggesting that development of the neural circuit may be affected after sevoflurane exposure. Such changes may have long-term effects on brain development and function. These findings are supplementary to our previous observations and provide more evidence for better understanding the adverse effects of sevoflurane on the developing brain after an 8 -h exposure.

CRISPR/Cas9 novel therapeutic road for the treatment of neurodegenerative diseases

CRISPR (clustered regularly interspaced short palindromic Repeats)/Cas9 is a new genetic editing technology that can be a beneficial method to advance gene therapy. CRISPR technology is a defense system of some bacteria against invading viruses. Genome editing based on the CRISPR/Cas9 system is an efficient and potential technology that can be a viable alternative to traditional methods. This system is a compound of a short guide RNAs (gRNAs) for identifying the target DNA sequence and Cas9 protein as nuclease for breaking and cutting of DNA. In this review, recent advances in the CRISPR/Cas9-mediated genome editing tools are presented as well as their use in gene therapy strategies for the treatment of neurological disorders including Parkinson's disease, Alzheimer's disease, and Huntington's disease.

Utilization of the CRISPR-Cas9 Gene Editing System to Dissect Neuroinflammatory and Neuropharmacological Mechanisms in Parkinson's Disease

Chronic and debilitating neurodegenerative diseases, such as Parkinson's disease (PD), impose an immense medical, emotional, and economic burden on patients and society. Due to a complex interaction between genetic and environmental risk factors, the etiology of PD remains elusive. However, the cumulative evidence emerging from clinical and experimental research over the last several decades has identified mitochondrial dysfunction, oxidative stress, neuroinflammation, and dysregulated protein degradation as the main drivers of PD neurodegeneration. The genome-editing system CRISPR (clustered regularly interspaced short palindromic repeats) has recently transformed the field of biotechnology and biomedical discovery and is poised to accelerate neurodegenerative disease research. It has been leveraged to generate PD animal models, such as Parkin, DJ-1, and PINK1 triple knockout miniature pigs. CRISPR has also allowed the deeper understanding of various PD gene interactions, as well as the identification of novel apoptotic pathways associated with neurodegenerative processes in PD. Furthermore, its application has been used to dissect neuroinflammatory pathways involved in PD pathogenesis, such as the PKCδ signaling pathway, as well as the roles of novel compensatory or protective pathways, such as Prokineticin-2 signaling. This review aims to highlight the historical milestones in the evolution of this technology and attempts to illustrate its transformative potential in unraveling disease mechanisms as well as in the development of innovative treatment strategies for PD. Graphical Abstract.

CRISPR System: A High-throughput Toolbox for Research and Treatment of Parkinson's Disease

In recent years, the innovation of gene-editing tools such as the CRISPR/Cas9 system improves the translational gap of treatments mediated by gene therapy. The privileges of CRISPR/Cas9 such as working in living cells and organs candidate this technology for using in research and treatment of the central nervous system (CNS) disorders. Parkinson's disease (PD) is a common, debilitating, neurodegenerative disorder which occurs due to loss of dopaminergic neurons and is associated with progressive motor dysfunction. Knowledge about the pathophysiological basis of PD has altered the classification system of PD, which manifests in familial and sporadic forms. The first genetic linkage studies in PD demonstrated the involvement of Synuclein alpha (SNCA) mutations and SNCA genomic duplications in the pathogenesis of PD familial forms. Subsequent studies have also insinuated mutations in leucine repeat kinase-2 (LRRK2), Parkin, PTEN-induced putative kinase 1 (PINK1), as well as DJ-1 causing familial forms of PD. This review will attempt to discuss the structure, function, and development in genome editing mediated by CRISP/Cas9 system. Further, it describes the genes involved in the pathogenesis of PD and the pertinent alterations to them. We will pursue this line by delineating the PD linkage studies in which CRISPR system was employed. Finally, we will discuss the pros and cons of CRISPR employment vis-à-vis the process of genome editing in PD patients' iPSCs.

Prediction Model with High-Performance Constitutive Androstane Receptor (CAR) Using DeepSnap-Deep Learning Approach from the Tox21 10K Compound Library

The constitutive androstane receptor (CAR) plays pivotal roles in drug-induced liver injury through the transcriptional regulation of drug-metabolizing enzymes and transporters. Thus, identifying regulatory factors for CAR activation is important for understanding its mechanisms. Numerous studies conducted previously on CAR activation and its toxicity focused on in vivo or in vitro analyses, which are expensive, time consuming, and require many animals. We developed a computational model that predicts agonists for the CAR using the Toxicology in the 21st Century 10k library. Additionally, we evaluate the prediction performance of novel deep learning (DL)-based quantitative structure-activity relationship analysis called the DeepSnap-DL approach, which is a procedure of generating an omnidirectional snapshot portraying three-dimensional (3D) structures of chemical compounds. The CAR prediction model, which applies a 3D structure generator tool, called CORINA-generated and -optimized chemical structures, in the DeepSnap-DL demonstrated better performance than the existing methods using molecular descriptors. These results indicate that high performance in the prediction model using the DeepSnap-DL approach may be important to prepare suitable 3D chemical structures as input data and to enable the identification of modulators of the CAR.