Animal models of neurodegenerative diseases

Neurostimulation devices to treat Alzheimer's disease

The use of neurostimulation devices for the treatment of Alzheimer's disease (AD) is a growing field. In this review, we examine the mechanism of action and therapeutic indications of these neurostimulation devices in the AD process. Rapid advancements in neurostimulation technologies are providing non-pharmacological relief to patients affected by AD pathology. Neurostimulation therapies include electrical stimulation that targets the circuitry-level connection in important brain areas such as the hippocampus to induce therapeutic neuromodulation of dysfunctional neural circuitry and electromagnetic field (EMF) stimulation that targets anti-amyloid molecular pathways to promote the degradation of beta-amyloid (Aβ). These devices target specific or diffuse cortical and subcortical brain areas to modulate neuronal activity at the electrophysiological or molecular pathway level, providing therapeutic effects for AD. This review attempts to determine the most effective and safe neurostimulation device for AD and provides an overview of potential and current clinical indications. Several EMF devices have shown a beneficial or harmful effect in cell cultures and animal models but not in AD human studies. These contradictory results may be related to the stimulation parameters of these devices, such as frequency, penetration depth, power deposition measured by specific absorption rate, time of exposure, type of cell, and tissue dielectric properties. Based on this, determining the optimal stimulation parameters for EMF devices in AD and understanding their mechanism of action is essential to promote their clinical application, our review suggests that repeated EMF stimulation (REMFS) is the most appropriate device for human AD treatments. Before its clinical application, it is necessary to consider the complicated and interconnected genetic and epigenetic effects of REMFS-biological system interaction. This will move forward the urgently needed therapy of EMF in human AD.

Comparison of Malondialdehyde, Acetylcholinesterase, and Apoptosis-Related Markers in the Cortex and Hippocampus of Cognitively Dysfunctional Mice Induced by Scopolamine

Objectives: Until now, many researchers have conducted evaluations on hippocampi for analyses of cognitive dysfunction models using scopolamine. However, depending on the purposes of these analyses, there are differences in the experimental results for the hippocampi and cortexes. Therefore, this study intends to compare various analyses of cognitive dysfunction after scopolamine administration with each other in hippocampi and cortexes. Methods: Scopolamine was administered at three dosages in mice: 0.5, 1, and 3 mg/kg. And this study evaluates the differences in cognitive function and the expression of malondialdehyde (MDA), acetylcholinesterase (AChE), and brain-derived neurotrophic factor (BDNF) in mice's hippocampi and cortexes based on scopolamine dosages. Results: The Morris water maze test was conducted between 1 and 3 h after scopolamine injection to assess its duration. A significant decrease in behavioral ability was evaluated at 1 h, and we observed a similar recovery to the normal group at 3 h. And the Morris water maze escape latency showed differences depending on scopolamine concentration. While the escape waiting time in the control group and scop 0.5 administration group remained similar to that seen before administration, the administration of scop 1 and 3 increased it. In the experimental group administered scop 1 and 3, cerebral MDA levels in the cerebral cortex significantly increased. In the hippocampus, the MDA level in the scopolamine-administered groups slightly increased compared to the cortex. A Western blotting assay shows that Bax and Bcl-xl showed a tendency to increase or decrease depending on the concentration, but BDNF increased in scop 0.5, and scop 1 and 3 did not show a significant decrease compared to the control at the cerebral cortex. In the hippocampus, BDNF showed a concentration-dependent decrease in expression. Conclusions: This study's findings indicate that chemical analyses for MDA and AChE can be performed in the cerebral cortex, while the hippocampus is better suited for protein analysis of apoptosis and BDNF.

Brazilian kefir fraction mitigates the Alzheimer-like phenotype in Drosophila melanogaster with β-amyloid overexpression model

Alzheimer's disease (AD) is a progressive neurodegenerative condition and the primary form of dementia among elderly people. The amyloidogenic hypothesis is the main theory that explains this phenomenon and describes the extracellular accumulation of amyloid beta (Aβ) peptides. Model organisms such as Drosophila melanogaster have been utilized to improve the understanding of this disease and its treatment. This study evaluated the effects of peptide and metabolic fractions of Brazilian kefir on a strain of D. melanogaster that expresses human Aβ peptide 1-42 in the eye. The parameters assessed included ommatidial organization, vacuole area, retinal thickness, and Aβ peptide quantification. The present study revealed that the fractions, particularly the peptidic fraction, significantly reduced the vacuole area and increased the retina thickness in treated flies, indicating an improvement in neurodegeneration phenotype. The peptidic fraction was also found to alter Aβ aggregation dynamics, inhibiting Aβ fibril formation, as revealed by dynamic light scattering. This study demonstrated that kefir fractions, particularly the peptidic fraction < 10 kDa, have the potential to regulate Aβ aggregation and alleviate neurodegeneration in a Drosophila melanogaster AD-like model. These findings suggest that kefir fractions could be viable for the bioprospection of novel drug prototypes for AD treatment, providing valuable insights into strategies targeting Aβ aggregation and neurodegeneration in AD.

Effects of housing density on anxiety-like behavior of zebrafish in the plus maze with ramp

Population density in experimental animals is a crucial factor in maintaining the wellbeing of the organisms. Inadequate housing conditions can compromise the validity and reliability of research results, making comparisons between studies difficult. In sociable species such as zebrafish (Danio rerio), which are housed in groups, overcrowding or undercrowding represents a variable that needs to be considered. In this study, we evaluated the effects of housing at different densities for different exposure times on the anxiety response measured in the Plus Maze with Ramp test in zebrafish. The subjects (144) were divided into three large groups according to the housing time (1, 7, and 30 days). Each group was divided into six subgroups based on the density of the fish (0.25, 0.5, 1, 2, 4, 6 fish/liter, n = 8) and housed in a 4-liter aquarium. After the housing conditions, each animal was tested individually in the PMR. Time and housing density altered the exploratory behavior of zebrafish. Increased housing time reduced the time spent in the ramp arms, with groups kept for 30 days spending less time in this compartment. Density increased the time spent in the flat arms in groups with 2 and 6 fish/liter and, conversely, reduced the exploration of the ramp arms. Isolation, on the other hand, increased the exploration of the ramp arms, indicating an anxiolytic effect. In this study, we demonstrate that housing conditions can act as low-intensity chronic stressors that alter anxiety-like behavior in zebrafish when tested in the PMR protocol.

Targeting inflammasome complexes as a novel therapeutic strategy for mood disorders

INTRODUCTION

Inflammasome complexes, especially NLRP3, have gained great attention as a potential therapeutic target in mood disorders. NLRP3 triggers a caspase 1-dependent release of the inflammatory cytokines IL-1β and IL-18, and seems to interact with purinergic and kynurenine pathways, all of which are implicated in mood disorders development and progression.

AREAS COVERED

Emerging evidence supports NLRP3 inflammasome as a promising pharmacological target for mood disorders. We discussed the available evidence from animal models and human studies and provided a reflection on drawbacks and perspectives for this novel target.

EXPERT OPINION

Several studies have supported the involvement of NLRP3 inflammasome in MDD. However, most of the evidence comes from animal models. The role of NLRP3 inflammasome in BD as well as its anti-manic properties is not very clear and requires further exploration. There is evidence of anti-manic effects of P2×R7 antagonists associated with reduction in the brain levels of IL-1β and TNF-α in a murine model of mania. The involvement of other NLRP3 inflammasome expressing cells besides microglia, like astrocytes, and of other inflammasome complexes in mood disorders also deserves further investigation. Preclinical and clinical characterization of NLRP3 and other inflammasomes in mood disorders is needed before considering translational approaches, including clinical trials.

Mammalian Models in Alzheimer's Research: An Update

A form of dementia distinct from healthy cognitive aging, Alzheimer's disease (AD) is a complex multi-stage disease that currently afflicts over 50 million people worldwide. Unfortunately, previous therapeutic strategies developed from murine models emulating different aspects of AD pathogenesis were limited. Consequently, researchers are now developing models that express several aspects of pathogenesis that better reflect the clinical situation in humans. As such, this review seeks to provide insight regarding current applications of mammalian models in AD research by addressing recent developments and characterizations of prominent transgenic models and their contributions to pathogenesis as well as discuss the advantages, limitations, and application of emerging models that better capture genetic heterogeneity and mixed pathologies observed in the clinical situation.

Inflammation-Mediated Responses in the Development of Neurodegenerative Diseases

Since its first description over a century ago, neurodegenerative diseases (NDDs) have impaired the lives of millions of people worldwide. As one of the major threats to human health, NDDs are characterized by progressive loss of neuronal structure and function, leading to the impaired function of the CNS. While the precise mechanisms underlying the emergence of NDDs remains elusive, association of neuroinflammation with the emergence of NDDs has been suggested. The immune system is tightly controlled to maintain homeostatic milieu and failure in doing so has been shown catastrophic. Here, we review current concepts on the cellular and molecular drivers responsible in the induction of neuroinflammation and how such event further promotes neuronal damage leading to neurodegeneration. Experimental data generated from cell culture and animal studies, gross and molecular pathologies of human CNS samples, and genome-wide association study are discussed to provide deeper insights into the mechanistic details of neuroinflammation and its roles in the emergence of NDDs.

Caenorhabditis elegans as a model system to evaluate neuroprotective potential of nano formulations

The impact of neurodegenerative illnesses on society is significant, but the mechanisms leading to neuronal malfunction and death in these conditions remain largely unknown despite identifying essential disease genes. To pinpoint the mechanisms behind the pathophysiology of neurodegenerative diseases, several researchers have turned to nematode C. elegans instead of using mammals. Since C. elegans is transparent, free-living, and amenable to culture, it has several benefits. As a result, all the neurons in C. elegans can be easily identified, and their connections are understood. Human proteins linked to Neurodegeneration can be made to express in them. It is also possible to analyze how C. elegans orthologs of the genes responsible for human neurodegenerative diseases function. In this article, we focused at some of the most important C. elegans neurodegeneration models that accurately represent many elements of human neurodegenerative illness. It has been observed that studies using the adaptable C. elegans have helped us in better understanding of human diseases. These studies have used it to replicate several aspects of human neurodegeneration. A nanotech approach involves engineering materials or equipments interacting with biological systems at the molecular level to trigger physiological responses by increasing stimulation, responding, and interacting with target sites while minimizing side effects, thus revolutionizing the treatment and diagnosis of neurodegenerative diseases. Nanotechnologies are being used to treat neurological disorders and deliver nanoscale drugs. This review explores the current and future uses of these nanotechnologies as innovative therapeutic modalities in treatment of neurodegenerative diseases using C elegans as an experimental model.

Inflammasome activation and assembly in Huntington's disease

Huntington's disease (HD) is a rare neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. Inflammasomes are multiprotein complexes capable of sensing pathogen-associated and damage-associated molecular patterns, triggering innate immune pathways. Activation of inflammasomes results in a pro-inflammatory cascade involving, among other molecules, caspases and interleukins. NLRP3 (nucleotide-binding domain, leucine-rich-repeat containing family, pyrin domain-containing 3) is the most studied inflammasome complex, and its activation results in caspase-1 mediated cleavage of the pro-interleukins IL-1β and IL-18 into their mature forms, also inducing a gasdermin D mediated form of pro-inflammatory cell death, i.e. pyroptosis. Accumulating evidence has implicated NLRP3 inflammasome complex in neurodegenerative diseases. The evidence in HD is still scant and mostly derived from pre-clinical studies. This review aims to present the available evidence on NLRP3 inflammasome activation in HD and to discuss whether targeting this innate immune system complex might be a promising therapeutic strategy to alleviate its symptoms.

iPSCs in Neurodegenerative Disorders: A Unique Platform for Clinical Research and Personalized Medicine

In the past, several animal disease models were developed to study the molecular mechanism of neurological diseases and discover new therapies, but the lack of equivalent animal models has minimized the success rate. A number of critical issues remain unresolved, such as high costs for developing animal models, ethical issues, and lack of resemblance with human disease. Due to poor initial screening and assessment of the molecules, more than 90% of drugs fail during the final step of the human clinical trial. To overcome these limitations, a new approach has been developed based on induced pluripotent stem cells (iPSCs). The discovery of iPSCs has provided a new roadmap for clinical translation research and regeneration therapy. In this article, we discuss the potential role of patient-derived iPSCs in neurological diseases and their contribution to scientific and clinical research for developing disease models and for developing a roadmap for future medicine. The contribution of humaniPSCs in the most common neurodegenerative diseases (e.g., Parkinson’s disease and Alzheimer’s disease, diabetic neuropathy, stroke, and spinal cord injury) were examined and ranked as per their published literature on PUBMED. We have observed that Parkinson’s disease scored highest, followed by Alzheimer’s disease. Furthermore, we also explored recent advancements in the field of personalized medicine, such as the patient-on-a-chip concept, where iPSCs can be grown on 3D matrices inside microfluidic devices to create an in vitro disease model for personalized medicine.

Dysregulated Brain Protein Phosphorylation Linked to Increased Human Tau Expression in the hTau Transgenic Mouse Model

Altered protein phosphorylation is a major pathologic modification in tauopathies and Alzheimer's disease (AD) linked to abnormal tau fibrillar deposits in neurofibrillary tangles (NFTs) and pre-tangles and β-amyloid deposits in AD. hTau transgenic mice, which express 3R and less 4R human tau with no mutations in a murine knock-out background, show increased tau deposition in neurons but not NFTs and pre-tangles at the age of nine months. Label-free (phospho)proteomics and SWATH-MS identified 2065 proteins in hTau and wild-type (WT) mice. Only six proteins showed increased levels in hTau; no proteins were down-regulated. Increased tau phosphorylation in hTau was detected at Ser199, Ser202, Ser214, Ser396, Ser400, Thr403, Ser404, Ser413, Ser416, Ser422, Ser491, and Ser494, in addition to Thr181, Thr231, Ser396/Ser404, but not at Ser202/Thr205. In addition, 4578 phosphopeptides (corresponding to 1622 phosphoproteins) were identified in hTau and WT mice; 64 proteins were differentially phosphorylated in hTau. Sixty proteins were grouped into components of membranes, membrane signaling, synapses, vesicles, cytoskeleton, DNA/RNA/protein metabolism, ubiquitin/proteasome system, cholesterol and lipid metabolism, and cell signaling. These results showed that over-expression of human tau without pre-tangle and NFT formation preferentially triggers an imbalance in the phosphorylation profile of specific proteins involved in the cytoskeletal-membrane-signaling axis.

Antimicrobial and antioxidant activity of Panax ginseng and Hedysarum neglectum root crop extracts

In order to ensure the timely and uninterrupted supply of medicinal plant raw materials, the methods of cultivation of plant cell cultures, namely, the production of plant root cultures, are relevant. In this paper, the geroprotective potential of Hedysarum neglectum Ledeb and Panax ginseng C. A. Mey root cultures is studied. They were cultured under in vitro conditions by transforming the rhizome (H. neglectum) and seed seedlings (P. ginseng) with Agrobacterium rhizogenes 15834 Swiss. To identify the geroprotective potential, the antimicrobial disc-diffusion method and the antioxidant activity were analyzed by titration of KMnO4 extracts of plant root cultures. The qualitative and quantitative composition was analyzed using high-performance liquid chromatography, thin-layer chromatography, and gas chromatography with mass spectrometry. In the course of the work, the presence of antimicrobial and antioxidant activity of plant root culture extracts was established. Biologically active substances contained in extracts of Hedysarum neglectum Ledeb root crops and Panax ginseng C. A. Mey are characterized by geroprotective potential, so they can act as a source of natural antioxidants in the functional nutrition of the geroprotective orientation.

Equine pituitary pars intermedia dysfunction: a spontaneous model of synucleinopathy

Equine pituitary pars intermedia dysfunction (PPID) is a common endocrine disease of aged horses that shows a similar pathophysiology as Parkinson’s Disease (PD) with increased levels of α-synuclein (α-syn). While α-syn is thought to play a pathogenic role in horses with PPID, it is unclear if α-syn is also misfolded in the pars intermedia and could similarly promote self-aggregation and propagation. Consequently, α-syn was isolated from the pars intermedia from groups of healthy young and aged horses, and aged PPID-afflicted horses. Seeding experiments confirmed the prion-like properties of α-syn isolated from PPID-afflicted horses. Next, detection of α-syn fibrils in pars intermedia via transmission electron microscopy (TEM) was exclusive to PPID-afflicted horses. A bank of fragment peptides was designed to further characterize equine α-syn misfolding. Region 62–87 of equine and human α-syn peptides was found to be most prone to aggregation according to Tango bioinformatic program and kinetics of aggregation via a thioflavin T fluorescence assay. In both species, fragment peptide 62–87 is capable of generating mature fibrils as demonstrated by TEM. The combined animal, bioinformatic, and biophysical studies provide evidence that equine α-syn is misfolded in PPID horses.

Human pluripotent stem cell-derived brain organoids as in vitro models for studying neural disorders and cancer

The sheer complexities of brain and resource limitation of human brain tissue greatly hamper our understanding of the brain disorders and cancers. Recently developed three-dimensional (3D) brain organoids (BOs) are self-organized and spontaneously differentiated from human pluripotent stem cells (hPSCs) in vitro, which exhibit similar features with cell type diversity, structural organization, and functional connectivity as the developing human brain. Based on these characteristics, hPSC-derived BOs (hPDBOs) provide new opportunities to recapitulate the complicated processes during brain development, neurodegenerative disorders, and brain cancers in vitro. In this review, we will provide an overview of existing BO models and summarize the applications of this technology in modeling the neural disorders and cancers. Furthermore, we will discuss the challenges associated with their use as in vitro models for disease modeling and the potential future direction.

A New Approach to Model Sporadic Alzheimer's Disease by Intracerebroventricular Streptozotocin Injection in APP/PS1 Mice

Alzheimer's disease (AD) is the most common cause of dementia among elderly people. Majority of AD cases are sporadic (SAD) with unknown cause. Transgenic animal models closely reflect the familial (genetic) aspect of the disease but not the sporadic type. However, most new drug candidates which are tested positive in transgenic animal models failed in clinical studies so far. Herein, we aim to develop an AD animal model that combines most of the neuropathological features seen in sporadic AD in humans with amyloid plaques observed in transgenic mice. Four-month-old wild-type and APP/PS1 AD mice were given a single intracerebroventricular (ICV) injection of 3 mg/kg streptozotocin (STZ), a diabetogenic agent. Three weeks later, their cognitive behavior was assessed, and their brain tissues were collected for biochemical and histological analysis. STZ produced cognitive deficits in both non-transgenic mice and AD mice. Biochemical analysis showed a severe decline in synaptic proteins, increase in tau phosphorylation, oxidative stress, disturbed brain insulin signaling with extensive neuroinflammation, and cell death. Significant increase was also observed in the level of the soluble beta amyloid precursor protein (APP) fragments and robust accumulation of amyloid plaques in AD mice compared to the control. These results suggest that STZ ICV treatment causes disturbance in multiple metabolic and cell signaling pathways in the brain that facilitated amyloid plaque accumulation and tau phosphorylation. Therefore, this animal model can be used to evaluate new AD therapeutic agents for clinical translation.

Inflammation in Huntington's disease: A few new twists on an old tale

Huntington's disease (HD) is a neurodegenerative disease characterized by prominent loss of neurons in the striatum and cortex. Traditionally research in HD has focused on brain changes as they cause progressive motor dysfunction, cognitive decline and psychiatric disorders. The discovery that huntingtin protein (HTT) and its mutated form (mHTT) are expressed not only in the brain but also in different organs and tissues paved the way for the hypothesis that HD might affect regions beyond the central nervous system (CNS). Besides pathological deposition of mHTT, other mechanisms, including inflammation, seem to underlie HD pathogenesis and progression. Altered inflammation can be evidenced even before the onset of classical symptoms of HD. Herein, we will discuss current pre-clinical and clinical evidence on immune/inflammatory changes in peripheral organs during HD development and progression. The understanding of the impact of inflammation on peripheral organs may open new venues for the development of novel therapeutic targets in HD.

Multiscale brain research on a microfluidic chip

One major challenge in current brain research is generating an integrative understanding of the brain's functions and disorders from its multiscale neuronal architectures and connectivity. Thus, innovative neurotechnology tools are urgently required for deciphering the multiscale functional and structural organizations of the brain at hierarchical scales from the molecular to the organismal level by multiple brain research initiatives launched by the European Union, United States, Australia, Canada, China, Korea, and Japan. To meet this demand, microfluidic chips (μFCs) have rapidly evolved as a trans-scale neurotechnological toolset to enable multiscale studies of the brain due to their unique advantages in flexible microstructure design, multifunctional integration, accurate microenvironment control, and capacity for automatic sample processing. Here, we review the recent progress in applying innovative μFC-based neuro-technologies to promote multiscale brain research and uniquely focus on representative applications of μFCs to address challenges in brain research at each hierarchical level. We discuss the current trend of combinational applications of μFCs with other neuro- and biotechnologies, including optogenetics, brain organoids, and 3D bioprinting, for better multiscale brain research. In addition, we offer our insights into the existing outstanding questions at each hierarchical level of brain research that could potentially be addressed by advancing microfluidic techniques. This review will serve as a timely guide for bioengineers and neuroscientists to develop and apply μFC-based neuro-technologies for promoting basic and translational brain research.

Neuroinflammation: An overview of neurodegenerative and metabolic diseases and of biotechnological studies

Neuroinflammation is an important factor contributing to cognitive impairment and neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), ischemic injury, and multiple sclerosis (MS). These diseases are characterized by inexorable progressive injury of neuron cells, and loss of motor or cognitive functions. Microglia, which are the resident macrophages in the brain, play an important role in both physiological and pathological conditions. In this review, we provide an updated discussion on the role of ROS and metabolic disease in the pathological mechanisms of activation of the microglial cells and release of cytotoxins, leading to the neurodegenerative process. In addition, we also discuss in vivo models, such as zebrafish and Caenorhabditis elegans, and provide new insights into therapeutics bioinspired by neuropeptides from venomous animals, supporting high throughput drug screening in the near future, searching for a complementary approach to elucidating crucial mechanisms associated with neurodegenerative disorders.

Effects of Sub-Chronic MPTP Exposure on Behavioral and Cognitive Performance and the Microbiome of Wild-Type and mGlu8 Knockout Female and Male Mice

Motor dysfunction is a hallmark of Parkinson's disease (PD); however, non-motor symptoms such as gastrointestinal dysfunction often arise prior to motor symptoms. Alterations in the gut microbiome have been proposed as the earliest event in PD pathogenesis. PD symptoms often demonstrate sex differences. Glutamatergic neurotransmission has long been linked to PD pathology. Metabotropic glutamate receptors (mGlu), a family of G protein-coupled receptors, are divided into three groups, with group III mGlu receptors mainly localized presynaptically where they can inhibit glutamate release in the CNS as well as in the gut. Additionally, the gut microbiome can communicate with the CNS via the gut-brain axis. Here, we assessed whether deficiency of metabotropic glutamate receptor 8 (mGlu8), group III mGlu, modulates the effects of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), on behavioral and cognitive performance in female and male mice. We studied whether these effects are associated with changes in striatal tyrosine hydroxylase (TH) levels and the gut microbiome. Two-week sub-chronic MPTP increased activity of female and male wild-type (WT) and mGlu8 knockout (KO) mice in the open field. MPTP also showed genotype- and sex-dependent effects. MPTP increased the time WT, but not KO, females and males spent exploring objects. In WT mice, MPTP improved sensorimotor function in males but impaired it in females. Further, MPTP impaired cued fear memory in WT, but not KO, male mice. MPTP reduced striatal TH levels in WT and KO mice but these effects were only pronounced in males. MPTP treatment and genotype affected the diversity of the gut microbiome. In addition, there were significant associations between microbiome α-diversity and sensorimotor performance, as well as microbiome composition and fear learning. These results indicate that specific taxa may directly affect motor and fear learning or that the same physiological effects that enhance both forms of learning also alter diversity of the gut microbiome. MPTP's effect on motor and cognitive performance may then be, at least in part, be mediated by the gut microbiome. These data also support mGlu8 as a novel therapeutic target for PD and highlight the importance of including both sexes in preclinical studies.

CRISPR/Cas9 Technology as an Emerging Tool for Targeting Amyotrophic Lateral Sclerosis (ALS)

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 nuclease (Cas9) is a genome editing tool that has recently caught enormous attention due to its novelty, feasibility, and affordability. This system naturally functions as a defense mechanism in bacteria and has been repurposed as an RNA-guided DNA editing tool. Unlike zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), CRISPR/Cas9 takes advantage of an RNA-guided DNA endonuclease enzyme, Cas9, which is able to generate double-strand breaks (DSBs) at specific genomic locations. It triggers cellular endogenous DNA repair pathways, contributing to the generation of desired modifications in the genome. The ability of the system to precisely disrupt DNA sequences has opened up new avenues in our understanding of amyotrophic lateral sclerosis (ALS) pathogenesis and the development of new therapeutic approaches. In this review, we discuss the current knowledge of the principles and limitations of the CRISPR/Cas9 system, as well as strategies to improve these limitations. Furthermore, we summarize novel approaches of engaging the CRISPR/Cas9 system in establishing an adequate model of neurodegenerative disease and in the treatment of SOD1-linked forms of ALS. We also highlight possible applications of this system in the therapy of ALS, both the inherited type as well as ALS of sporadic origin.

Depression in Parkinson's Disease: The Contribution from Animal Studies

Besides being better known for causing motor impairments, Parkinson's disease (PD) can also cause many nonmotor symptoms, like depression and anxiety, which can cause significant loss of life quality and may not respond to regular drugs treatment. In this review, we discuss the depression in PD, based on data from studies in humans and rodents. Depression frequency seems higher in PD patients than in general population, despite high variation in data due to diagnosis disparities. Development of depression in PD seems more likely to be caused by the nigrostriatal pathway degeneration than as a consequence of the awareness of disease prognostic, and it seems to be related to dopaminergic, noradrenergic, and serotoninergic synapses deficits. The dopaminergic role could be more significant, since it can modulate the release of the others, and its depletion is progressive, due to the degenerative feature of PD. Highly regarded in major depression, serotonin can be depleted in rats after nigrostriatal damage, but data from human patients are more conflicting. Animal studies can help in understanding the neurobiological mechanisms of depression in PD and the pursuit for more effective drugs for its treatment, but they lack the complexity of the disease progression, especially the nondopaminergic degeneration.

Comparative Studies on Behavioral, Cognitive and Biomolecular Profiling of ICR, C57BL/6 and Its Sub-Strains Suitable for Scopolamine-Induced Amnesic Models

Cognitive impairment and behavioral disparities are the distinctive baseline features to investigate in most animal models of neurodegenerative disease. However, neuronal complications are multifactorial and demand a suitable animal model to investigate their underlying basal mechanisms. By contrast, the numerous existing neurodegenerative studies have utilized various animal strains, leading to factual disparity. Choosing an optimal mouse strain for preliminary assessment of neuronal complications is therefore imperative. In this study, we systematically compared the behavioral, cognitive, cholinergic, and inflammatory impairments of outbred ICR and inbred C57BL/6 mice strains subject to scopolamine-induced amnesia. We then extended this study to the sub-strains C57BL/6N and C57BL/6J, where in addition to the above-mentioned parameters, their endogenous antioxidant levels and cAMP response-element binding protein (CREB)/brain-derived neurotrophic factor (BDNF) protein expression were also evaluated. Compared with the ICR strain, the scopolamine-inflicted C57BL/6 strains exhibited a substantial reduction of spontaneous alternation and an approximately two-fold increase in inflammatory protein expression, compared to the control group. Among the sub-strains, scopolamine-treated C57BL/6N strains exhibited declined step-through latency, elevated acetylcholinesterase (AChE) activity and inflammatory protein expression, associated with reduced endogenous antioxidant levels and p-CREB/BDNF expression, compared to the control and tacrine-treated groups. This indicates that the C57BL/6N strains exhibit significantly enhanced scopolamine-induced neuronal impairment compared to the other evaluated strains.

Comparative transcriptomics in human and mouse

Cross-species comparisons of genomes, transcriptomes and gene regulation are now feasible at unprecedented resolution and throughput, enabling the comparison of human and mouse biology at the molecular level. Insights have been gained into the degree of conservation between human and mouse at the level of not only gene expression but also epigenetics and inter-individual variation. However, a number of limitations exist, including incomplete transcriptome characterization and difficulties in identifying orthologous phenotypes and cell types, which are beginning to be addressed by emerging technologies. Ultimately, these comparisons will help to identify the conditions under which the mouse is a suitable model of human physiology and disease, and optimize the use of animal models.

Behavioral Phenotyping and Pathological Indicators of Parkinson's Disease in C. elegans Models

Parkinson's disease (PD) is a neurodegenerative disorder with symptoms that progressively worsen with age. Pathologically, PD is characterized by the aggregation of α-synuclein in cells of the substantia nigra in the brain and loss of dopaminergic neurons. This pathology is associated with impaired movement and reduced cognitive function. The etiology of PD can be attributed to a combination of environmental and genetic factors. A popular animal model, the nematode roundworm Caenorhabditis elegans, has been frequently used to study the role of genetic and environmental factors in the molecular pathology and behavioral phenotypes associated with PD. The current review summarizes cellular markers and behavioral phenotypes in transgenic and toxin-induced PD models of C. elegans.

Regulation of motor proteins, axonal transport deficits and adult-onset neurodegenerative diseases

Neurons affected in a wide variety of unrelated adult-onset neurodegenerative diseases (AONDs) typically exhibit a "dying back" pattern of degeneration, which is characterized by early deficits in synaptic function and neuritic pathology long before neuronal cell death. Consistent with this observation, multiple unrelated AONDs including Alzheimer's disease, Parkinson's disease, Huntington's disease, and several motor neuron diseases feature early alterations in kinase-based signaling pathways associated with deficits in axonal transport (AT), a complex cellular process involving multiple intracellular trafficking events powered by microtubule-based motor proteins. These pathogenic events have important therapeutic implications, suggesting that a focus on preservation of neuronal connections may be more effective to treat AONDs than addressing neuronal cell death. While the molecular mechanisms underlying AT abnormalities in AONDs are still being analyzed, evidence has accumulated linking those to a well-established pathological hallmark of multiple AONDs: altered patterns of neuronal protein phosphorylation. Here, we present a short overview on the biochemical heterogeneity of major motor proteins for AT, their regulation by protein kinases, and evidence revealing cell type-specific AT specializations. When considered together, these findings may help explain how independent pathogenic pathways can affect AT differentially in the context of each AOND.

Bamboo leaf extract improves spatial learning ability in a rat model with senile dementia

Senile dementia (SD) is a syndrome characterized by progressive neurological deterioration. Treatment for the disease is still under investigation. Bamboo leaf extract (B-extract) has been known for its biological efficacy in anti-oxidant and anti-cancer activities. However, study on B-extract for its protection against dementia is very limited. The effect of B-extract on a rat model with SD was examined. B-extract improved spatial learning ability of the dementia rats. The hippocampus of dementia model rats showed reduced levels of acetylcholine (ACh), epinephrine (E), norepinephrine (NE), and dopamine (DA), and increased activities of acetylcholine esterase (AChE) and monoamine oxidase (MAO). Treatment with B-extract 20 mg/(kg·d) for 7 weeks significantly inhibited the enzyme activity compared with untreated dementia rats, and raised the levels of ACh, E, and DA in the hippocampus. In addition, treatment with B-extract elevated the level of γ-aminobutyric acid (GABA), but reduced the level of glutamate (Glu) in the brain. These data suggest that B-extract might be a potential drug in treating impairment of spatial memory in dementia rats by regulating the central neurotransmitter function.

UPS Activation in the Battle Against Aging and Aggregation-Related Diseases: An Extended Review

Aging is a biological process accompanied by gradual increase of damage in all cellular macromolecules, i.e., nucleic acids, lipids, and proteins. When the proteostasis network (chaperones and proteolytic systems) cannot reverse the damage load due to its excess as compared to cellular repair/regeneration capacity, failure of homeostasis is established. This failure is a major hallmark of aging and/or aggregation-related diseases. Dysfunction of the major cellular proteolytic machineries, namely the proteasome and the lysosome, has been reported during the progression of aging and aggregation-prone diseases. Therefore, activation of these pathways is considered as a possible preventive or therapeutic approach against the progression of these processes. This chapter focuses on UPS activation studies in cellular and organismal models and the effects of such activation on aging, longevity and disease prevention or reversal.

CRISPR/Cas9: a powerful genetic engineering tool for establishing large animal models of neurodegenerative diseases

Animal models are extremely valuable to help us understand the pathogenesis of neurodegenerative disorders and to find treatments for them. Since large animals are more like humans than rodents, they make good models to identify the important pathological events that may be seen in humans but not in small animals; large animals are also very important for validating effective treatments or confirming therapeutic targets. Due to the lack of embryonic stem cell lines from large animals, it has been difficult to use traditional gene targeting technology to establish large animal models of neurodegenerative diseases. Recently, CRISPR/Cas9 was used successfully to genetically modify genomes in various species. Here we discuss the use of CRISPR/Cas9 technology to establish large animal models that can more faithfully mimic human neurodegenerative diseases.

Insights into Neuroinflammation in Parkinson's Disease: From Biomarkers to Anti-Inflammatory Based Therapies

Parkinson's disease (PD) is the second most common neurodegenerative disorder worldwide, being characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Among several putative factors that may contribute to PD pathogenesis, inflammatory mechanisms may play a pivotal role. The involvement of microglial activation as well as of brain and peripheral immune mediators in PD pathophysiology has been reported by clinical and experimental studies. These inflammatory biomarkers evaluated by imaging techniques and/or by biological sample analysis have become valuable tools for PD diagnosis and prognosis. Regardless of the significant increase in the number of people suffering from PD, there are still no established disease-modifying or neuroprotective therapies for it. There is growing evidence of protective effect of anti-inflammatory drugs on PD development. Herein, we reviewed the current literature regarding the central nervous system and peripheral immune biomarkers in PD and advances in diagnostic and prognostic tools as well as the neuroprotective effects of anti-inflammatory therapies.

Compensatory mechanisms in genetic models of neurodegeneration: are the mice better than humans?

Neurodegenerative diseases are one of the main causes of mental and physical disabilities. Neurodegeneration has been estimated to begin many years before the first clinical symptoms manifest, and even a prompt diagnosis at this stage provides very little advantage for a more effective treatment as the currently available pharmacotherapies are based on disease symptomatology. The etiology of the majority of neurodegenerative diseases remains unknown, and even for those diseases caused by identified genetic mutations, the direct pathways from gene alteration to final cell death have not yet been fully elucidated. Advancements in genetic engineering have provided many transgenic mice that are used as an alternative to pharmacological models of neurodegenerative diseases. Surprisingly, even the models reiterating the same causative mutations do not fully recapitulate the inevitable neuronal loss, and some fail to even show phenotypic alterations, which suggests the possible existence of compensatory mechanisms. A better evaluation of these mechanisms may not only help us to explain why neurodegenerative diseases are mostly late-onset disorders in humans but may also provide new markers and targets for novel strategies designed to extend neuronal function and survival. The aim of this mini-review is to draw attention to this under-explored field in which investigations may reasonably contribute to unveiling hidden reserves in the organism.

The mGluR5 positive allosteric modulator, CDPPB, ameliorates pathology and phenotypic signs of a mouse model of Huntington's disease

Huntington's disease (HD) is an autosomal-dominant neurodegenerative disorder caused by a polyglutamine expansion in the amino-terminal region of the huntingtin protein (htt), leading to motor dysfunction, cognitive decline, psychiatric alterations, and death. The metabotropic glutamate receptor 5 (mGluR5) has been implicated in HD and we have recently demonstrated that mGluR5 positive allosteric modulators (PAMs) are neuroprotective in vitro. In the present study we demonstrate that the mGluR5 PAM, CDPPB, is a potent neuroprotective drug, in vitro and in vivo, capable of delaying HD-related symptoms. The HD mouse model, BACHD, exhibits many HD features, including neuronal cell loss, htt aggregates, motor incoordination and memory impairment. However, chronic treatment of BACHD mice with CDPPB 1.5 mg/kg s.c. for 18 weeks increased the activation of cell signaling pathways important for neuronal survival, including increased AKT and ERK1/2 phosphorylation and augmented the BDNF mRNA expression. CDPPB chronic treatment was also able to prevent the neuronal cell loss that takes place in the striatum of BACHD mice and decrease htt aggregate formation. Moreover, CDPPB chronic treatment was efficient to partially ameliorate motor incoordination and to rescue the memory deficit exhibited by BACHD mice. Importantly, no toxic effects or stereotypical behavior were observed upon CDPPB chronic treatment. Thus, CDPPB is a potential drug to treat HD, preventing neuronal cell loss and htt aggregate formation and delaying HD symptoms.

Protein phosphorylation in neurodegeneration: friend or foe?

Protein misfolding and aggregation is a common hallmark in neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and fronto-temporal dementia (FTD). In these disorders, the misfolding and aggregation of specific proteins occurs alongside neuronal degeneration in somewhat specific brain areas, depending on the disorder and the stage of the disease. However, we still do not fully understand the mechanisms governing protein aggregation, and whether this constitutes a protective or detrimental process. In PD, alpha-synuclein (aSyn) forms protein aggregates, known as Lewy bodies, and is phosphorylated at serine 129. Other residues have also been shown to be phosphorylated, but the significance of phosphorylation in the biology and pathophysiology of the protein is still controversial. In AD and in FTD, hyperphosphorylation of tau protein causes its misfolding and aggregation. Again, our understanding of the precise consequences of tau phosphorylation in the biology and pathophysiology of the protein is still limited. Through the use of a variety of model organisms and technical approaches, we are now gaining stronger insight into the effects of phosphorylation in the behavior of these proteins. In this review, we cover recent findings in the field and discuss how targeting phosphorylation events might be used for therapeutic intervention in these devastating diseases of the nervous system.