Medaka fish Parkinson's disease model

A review on neurodegeneration in the fast-ageing killifish, the first animal model to study the natural occurrence of neuronal cell loss

Thanks to medical and technological improvements, our world population has become ever-greying. In consequence, the incidence and prevalence of age-related central nervous system neuropathies, such as Alzheimer's (AD) and Parkinson's disease (PD), are increasing tremendously. Despite many research efforts, the precise aetiology of these age-related neurodegenerative disorders remains elusive, highlighting the urgent need for more effective treatments. Current preclinical research mainly uses animal models that do not fully recapitulate the complex cellular context in which these diseases occur, thereby lacking good construct validity. Indeed, most investigations are performed using relatively young animals, thereby ignoring the ageing environment in which neurodegenerative diseases manifest. This points out a major hiatus in current research: a vertebrate model organism that combines the complex disease context (onset, spreading and further manifestation into functional impairment) with an ageing environment. In recent years, the African turquoise killifish has emerged as a promising novel animal model to study age-related neurodegenerative disorders that combines these essential features. In this review, we bundle all reported findings up till now and provide a detailed overview of the neurodegenerative events within the central nervous system of this teleost fish, with a focus on PD.

Fish Behavior as a Neural Proxy to Reveal Physiological States

Behaviors are the integrative outcomes of the nervous system, which senses and responds to the internal physiological status and external stimuli. Teleosts are aquatic organisms which are more easily affected by the surrounding environment compared to terrestrial animals. To date, behavioral tests have been widely used to assess potential environmental risks using fish as model animals. In this review, we summarized recent studies regarding the effects of internal and external stimuli on fish behaviors. We concluded that behaviors reflect environmental and physiological changes, which have possible implications for environmental and physiological assessments.

Zebrafish and Medaka: Important Animal Models for Human Neurodegenerative Diseases

Animal models of human neurodegenerative disease have been investigated for several decades. In recent years, zebrafish (Danio rerio) and medaka (Oryzias latipes) have become popular in pathogenic and therapeutic studies about human neurodegenerative diseases due to their small size, the optical clarity of embryos, their fast development, and their suitability to large-scale therapeutic screening. Following the emergence of a new generation of molecular biological technologies such as reverse and forward genetics, morpholino, transgenesis, and gene knockout, many human neurodegenerative disease models, such as Parkinson's, Huntington's, and Alzheimer's, were constructed in zebrafish and medaka. These studies proved that zebrafish and medaka genes are functionally conserved in relation to their human homologues, so they exhibit similar neurodegenerative phenotypes to human beings. Therefore, fish are a suitable model for the investigation of pathologic mechanisms of neurodegenerative diseases and for the large-scale screening of drugs for potential therapy. In this review, we summarize the studies in modelling human neurodegenerative diseases in zebrafish and medaka in recent years.

Modeling Parkinson's Disease: Not Only Rodents?

Parkinson’s disease (PD) is a common chronic progressive multifactorial neurodegenerative disease. In most cases, PD develops as a sporadic idiopathic disease. However, in 10%–15% of all patients, Mendelian inheritance of the disease is observed in an autosomal dominant or autosomal recessive manner. To date, mutations in seven genes have been convincingly confirmed as causative in typical familial forms of PD, i.e., SNCA, LRRK2, VPS35, PRKN, PINK1, GBA, and DJ-1. Family and genome-wide association studies have also identified a number of candidate disease genes and a common genetic variability at 90 loci has been linked to risk for PD. The analysis of the biological function of both proven and candidate genes made it possible to conclude that mitochondrial dysfunction, lysosomal dysfunction, impaired exosomal transport, and immunological processes can play important roles in the development of the pathological process of PD. The mechanisms of initiation of the pathological process and its earliest stages remain unclear. The study of the early stages of the disease (before the first motor symptoms appear) is extremely complicated by the long preclinical period. In addition, at present, the possibility of performing complex biochemical and molecular biological studies familial forms of PD is limited. However, in this case, the analysis of the state of the central nervous system can only be assessed by indirect signs, such as the level of metabolites in the cerebrospinal fluid, peripheral blood, and other biological fluids. One of the potential solutions to this problem is the analysis of disease models, in which it is possible to conduct a detailed in-depth study of all aspects of the pathological process, starting from its earliest stages. Many modeling options are available currently. An analysis of studies published in the 2000s suggests that toxic models in rodents are used in the vast majority of cases. However, interesting and important data for understanding the pathogenesis of PD can be obtained from other in vivo models. Within the framework of this review, we will consider various models of PD that were created using various living organisms, from unicellular yeast (Saccharomyces cerevisiae) and invertebrate (Nematode and Drosophila) forms to various mammalian species.

Automated Operant Conditioning Devices for Fish. Do They Work?

Simple Summary

Automated training devices are commonly used for investigating learning, memory, and other cognitive functions in warm-blood vertebrates, whereas manual training procedures are the standard in fish and other lower vertebrates, thus limiting comparison among species. Here, we directly compared the two different approaches to training in guppies (Poecilia reticulata) by administering numerical discrimination tasks of increasing difficulty. The automated device group showed a much lower performance compared to the traditionally-trained group. We modified some features of the automated device in order to improve its efficiency. Increasing the decision time or inter-trial interval was ineffective, while reducing the cognitive load and allowing subjects to reside in the test tank improved numerical performance. Yet, in no case did subjects match the performance of traditionally-trained subjects, suggesting that small teleosts may be limited in their capacity to cope with operant conditioning devices.

Abstract

The growing use of teleosts in comparative cognition and in neurobiological research has prompted many researchers to develop automated conditioning devices for fish. These techniques can make research less expensive and fully comparable with research on warm-blooded species, in which automated devices have been used for more than a century. Tested with a recently developed automated device, guppies (Poecilia reticulata) easily performed 80 reinforced trials per session, exceeding 80% accuracy in color or shape discrimination tasks after only 3–4 training session, though they exhibit unexpectedly poor performance in numerical discrimination tasks. As several pieces of evidence indicate, guppies possess excellent numerical abilities. In the first part of this study, we benchmarked the automated training device with a standard manual training procedure by administering the same set of tasks, which consisted of numerical discriminations of increasing difficulty. All manually-trained guppies quickly learned the easiest discriminations and a substantial percentage learned the more difficult ones, such as 4 vs. 5 items. No fish trained with the automated conditioning device reached the learning criterion for even the easiest discriminations. In the second part of the study, we introduced a series of modifications to the conditioning chamber and to the procedure in an attempt to improve its efficiency. Increasing the decision time, inter-trial interval, or visibility of the stimuli did not produce an appreciable improvement. Reducing the cognitive load of the task by training subjects first to use the device with shape and color discriminations, significantly improved their numerical performance. Allowing the subjects to reside in the test chamber, which likely reduced the amount of attentional resources subtracted to task execution, also led to an improvement, although in no case did subjects match the performance of fish trained with the standard procedure. Our results highlight limitations in the capacity of small laboratory teleosts to cope with operant conditioning automation that was not observed in laboratory mammals and birds and that currently prevent an easy and straightforward comparison with other vertebrates.

Degeneration of dopaminergic neurons and impaired intracellular trafficking in Atp13a2 deficient zebrafish

ATP13A2 is the autosomal recessive causative gene for juvenile-onset Parkinson’s disease (PARK9, Parkinson’s disease 9), also known as Kufor-Rakeb syndrome. The disease is characterized by levodopa-responsive Parkinsonism, supranuclear gaze palsy, spasticity, and dementia. Previously, we have reported that Atp13a2 deficient medaka fish showed dopaminergic neurodegeneration and lysosomal dysfunction, indicating that lysosome-autophagy impairment might be one of the key pathogeneses of Parkinson’s disease. Here, we established Atp13a2 deficient zebrafish using CRISPR/Cas9 gene editing. We found that the number of TH + neurons in the posterior tuberculum and the locus coeruleus significantly reduced (dopaminergic neurons, 64 % at 4 months and 37 % at 12 months, p < 0.001 and p < 0.05, respectively; norepinephrine neurons, 52 % at 4 months and 40 % at 12 months, p < 0.001 and p < 0.05, respectively) in Atp13a2 deficient zebrafish, proving the degeneration of dopaminergic neurons. In addition, we found the reduction (60 %, p < 0.05) of cathepsin D protein expression in Atp13a2 deficient zebrafish using immunoblot. Transmission electron microscopy analysis using middle diencephalon samples from Atp13a2 deficient zebrafish showed lysosome-like bodies with vesicle accumulation and fingerprint-like structures, suggesting lysosomal dysfunction. Furthermore, a significant reduction (p < 0.001) in protein expression annotated with vesicle fusion with Golgi apparatus in Atp13a2 deficient zebrafish by liquid-chromatography tandem mass spectrometry suggested intracellular trafficking impairment. Therefore, we concluded that Atp13a2 deficient zebrafish exhibited degeneration of dopaminergic neurons, lysosomal dysfunction and the possibility of intracellular trafficking impairment, which would be the key pathogenic mechanism underlying Parkinson’s disease.

Age- and α-Synuclein-Dependent Degeneration of Dopamine and Noradrenaline Neurons in the Annual Killifish Nothobranchius furzeri

Parkinson's disease (PD) is a neurodegenerative disease characterized by α-synuclein-positive inclusion bodies and loss of neurons, including dopaminergic neurons. Difficulty in replicating PD phenotypes using animal models partly limits the understanding of PD and the therapy required. Although PD is strongly associated with aging, most experimental animals may not exhibit age-related symptoms. Herein, we demonstrate that Nothobranchius furzeri, a rapidly aging teleost with a short life span, exhibits age-dependent degeneration of dopaminergic and noradrenergic neurons and progression of α-synuclein pathologies. These pathological phenotypes are similar to those observed in human patients with PD. Amelioration of the cell loss by genetic depletion of α-synuclein suggests that α-synuclein is not a bystander but a causative protein of neurodegeneration. N. furzeri can reveal mechanisms underlying PD, especially of the idiopathic form that affects a majority of patients with PD, including α-synuclein-dependent neurodegeneration, age-dependent phenotypes, and progression of α-synuclein pathology.

The transcriptional response of skin to fluorescent light exposure in viviparous (Xiphophorus) and oviparous (Danio, Oryzias) fishes

Differences in light sources are common in animal facilities and potentially can impact experimental results. Here, the potential impact of lighting differences on skin transcriptomes has been tested in three aquatic animal models commonly utilized in biomedical research, (Xiphophorus maculatus (platyfish), Oryzias latipes (medaka) and Danio rerio (zebrafish). Analysis of replicate comparative RNA-Seq data showed the transcriptional response to commonly utilized 4100K or "cool white" fluorescent light (FL) is much greater in platyfish and medaka than in zebrafish. FL induces genes associated with inflammatory and immune responses in both medaka and zebrafish; however, the platyfish exhibit suppression of genes involved with immune/inflammation, as well as genes associated with cell cycle progression. Furthermore, comparative analyses of gene expression data from platyfish UVB exposures, with medaka and zebrafish after exposure to 4100K FL, show comparable effects on the same stress pathways. We suggest the response to light is conserved, but that long-term adaptation to species specific environmental niches has resulted in a shifting of the wavelengths required to incite similar "genetic" responses in skin. We forward the hypothesis that the "genetic perception" of light may have evolved differently than ocular perception and suggest that light type (i.e., wavelengths emitted) is an important parameter to consider in experimental design.

Parkinson's Disease Model

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide. It is known that there are many factors, either genetic or environmental factors, involved in PD, but the mechanism of PD is still not fully understood. Several animal models have been established to study the mechanisms of PD. Among these models, Drosophila melanogaster has been utilized as a valuable model to get insight into important features of PD. Drosophila melanogaster possesses a well-developed dopaminergic (DA) neuron system which is known to play an important role in PD pathogenesis. The well understanding of DA neurons from early larval through adult stage makes Drosophila as a powerful model for investigating the progressive neurodegeneration in PD. Besides, the short life cycle of Drosophila melanogaster serves an advantage in studying epidemiological features of PD. Most of PD symptoms can be mimicked in Drosophila model such as progressive impairment in locomotion, DA neuron degeneration, and some other non-motor symptoms. The Drosophila models of PD, therefore, show a great potential in application for PD genetic and drug screening.

The Proteasome Inhibition Model of Parkinson's Disease

The pathological hallmarks of Parkinson's disease are the progressive loss of nigral dopaminergic neurons and the formation of intracellular inclusion bodies, termed Lewy bodies, in surviving neurons. Accumulation of proteins in large insoluble cytoplasmic aggregates has been proposed to result, partly, from a failure in the function of intracellular protein degradation pathways. Evidence in support for such a hypothesis emerged in the beginning of the years 2000 with studies demonstrating structural and functional deficits in the ubiquitin-proteasome pathway in post-mortem nigral tissue of patients with Parkinson's disease. These fundamental findings have inspired the development of a new generation of animal models based on the use of proteasome inhibitors to disturb protein homeostasis and trigger nigral dopaminergic neurodegeneration. In this review, we provide an updated overview of the current approaches in employing proteasome inhibitors to model Parkinson's disease, with particular emphasis on rodent studies. In addition, the mechanisms underlying proteasome inhibition-induced cell death and the validity criteria (construct, face and predictive validity) of the model will be critically discussed. Due to its distinct, but highly relevant mechanism of inducing neuronal death, the proteasome inhibition model represents a useful addition to the repertoire of toxin-based models of Parkinson's disease that might provide novel clues to unravel the complex pathogenesis of this disorder.

An optimized method for counting dopaminergic neurons in zebrafish

In recent years, considerable effort has been devoted to the development of a fish model for Parkinson’s disease (PD) to examine the pathological mechanisms of neurodegeneration. To effectively evaluate PD pathology, the ability to accurately and reliably count dopaminergic neurons is important. However, there is currently no such standardized method. Due to the relatively small number of dopaminergic neurons in fish, stereological estimation would not be suitable. In addition, serial sectioning requires proficiency to not lose any sections, and it permits double counting due to the large size of some of the dopaminergic neurons. In this study, we report an optimized protocol for staining dopaminergic neurons in zebrafish and provide a reliable counting method. Finally, using our optimized protocol, we confirmed that administration of 6-hydroxydopamine (a neurotoxin) or the deletion of the PINK1 gene (one of the causative genes of familiar PD) in zebrafish caused significant reduction in the number of dopaminergic and noradrenergic neurons. In summary, this method will serve as an important tool for the appropriate evaluation and establishment of fish PD models.

Lesions of the dorsal striatum impair orienting behaviour of salamanders without affecting visual processing in the tectum

In amphibians, visual information in the midbrain tectum is relayed via the thalamus to telencephalic centres. Lesions of the dorsal thalamus of the salamander Plethodon shermani result in impairment of orienting behaviour and in modulation of spike pattern of tectal neurons. These effects may be induced by an interruption of a tectum-thalamus-telencephalon-tectum feedback loop enabling spatial attention and selection of visual objects. The striatum is a potential candidate for involvement in this pathway; accordingly, we investigated the effects of lesioning the dorsal striatum. Compared to controls and sham lesioned salamanders, striatum-lesioned animals exhibited a significantly lower number of orienting responses toward one of two competing prey stimuli. Orienting towards stimuli was impaired, while the spike pattern of tectal cells was unaffected, because both in controls and striatum-lesioned salamanders the spike number significantly decreased at presentation of one prey stimulus inside the excitatory receptive field and another one in the surround compared to that at single presentation inside the excitatory receptive field. We conclude that the dorsal striatum contributes to orienting behaviour, but not to an inhibitory feedback signal onto tectal neurons. The brain area engaged in the feedback loop during visual object discrimination and selection has yet to be identified. Information processing in the amphibian striatum includes multisensory integration; the striatum generates behavioural patterns that influence (pre)motor processing in the brainstem. This situation resembles the situation found in rats, in which the dorsolateral striatum is involved in stimulus-response learning regardless of the sensory modality, as well as in habit formation.