2,032 research outputs found

    Ancestral Dvelopmental Exposure to Methylmercury Induces Transgenerational Inheritance of Visual and Neurobehavioral Deficits

    Get PDF
    Methylmercury (MeHg) is an environmental neurotoxicant of global concern. It is considered one of the top ten chemicals of public health concern by the World Health Organization. Prenatal exposure to MeHg has been associated with altered neurodevelopment, neurobehavioral and neurocognitive functions. The effects of low dose MeHg exposure are more subtle and can range from impaired motor function to sensory defects. Using quantitative neurobehavioral assays and zebrafish as a model organism, our laboratory has demonstrated that developmental MeHg exposure causes neurological dysfunction in adult zebrafish. Recently, a wide range of environmental insults (e.g., pesticides, fungicides, plasticizers and endocrine disruptors) has been shown to induce disease phenotypes in individuals whose great grandparents were exposed to the toxicant. This phenomenon is known as transgenerational inheritance. To date, studies have shown that in transgenerational inheritance of diseases due to developmental exposure, heritable changes occurred in the epigenome not the genome and were transmitted to subsequent generations without further exposure. Based on this evidence, we hypothesized that ancestral developmental exposure to MeHg induces transgenerational neurobehavioral deficits in F3 generation zebrafish. The F1-generation zebrafish embryos (less than 4 hour post fertilization) were exposed to either 0, 0.001, 0.003, 0.01, 0.03 or 0.1 µM MeHg for 24 hrs. These concentrations of MeHg are sublethal and environmentally relevant. Quantitative neurobehavioral assays for visual startle response and locomotor activity were used to assess MeHg-induced neurotoxicity in F3 generation. Our study demonstrated that developmental exposure to MeHg induces transgenerational visual deficits and locomotor dysfunctions in zebrafish. Altered retinal electrophysiology was also observed in the transgenerational population with visual deficits. To identify the genes and pathways involved with the phenotypes observed in the transgenerational population, we analyzed the whole transcriptome of the brain and retina of the transgenerational lineage animals, using RNAseq. Tissue specific altered gene expression was observed in both brain and retina. This is the first evidence of a transgenerational transcriptome induced by ancestral developmental exposure to MeHg. Gene set enrichment analysis revealed the correlation between dysregulated functional pathways and the observed phenotypic variation, including vision, phototransduction, motor activity, and retinal electrophysiology. Our studies also identify that the mode of germline transmission varies between the transgenerational phenotypes. This research has identified new mechanisms associated with MeHg-induced phenotypes which may have significant impacts on public health, in terms of developing biomarkers to identify susceptible populations and developing preventative measures. The long term effects of MeHg observed in this study could be used to improve the awareness of reproductive age group women to monitor the type of fish that they consume. Since we observed the neurobehavioral deficits in a fish species, our findings have ecological impacts including the feeding behavior of fish, survival and reproduction. The findings made in this thesis also set the stage for future research into the identification of new transgenerational phenotypes associated with ancestral developmental exposure to MeHg

    New Neurons for the Inner Ear: Neurogenesis in the Zebrafish Statoacoustic Ganglion during Growth, Homeostasis and Regeneration

    Get PDF
    The vertebrate inner ear is a remarkable sensory organ, harboring two different senses: the auditory system, responsible for hearing, and the vestibular system, responsible for balance. Even though the anatomical structure of the vertebrate inner ear is very complex, only three different cell types are mainly involved on a cellular level in the perception of sound as well as balance and movement: sensory hair cells that are surrounded by supporting cells receive the stimulus and transfer it via sensory neurons to the brain. Worldwide, millions of people suffer from sensorineural hearing loss, caused by the loss of sensory hair cells and/or their innervating neurons within the inner ear. In mammals, including humans, both cell types are only produced during fetal stages making loss of these cells and the resulting consequences irreversible. In contrast, it is known that zebrafish produce sensory hair cells throughout life and additionally possess the remarkable capacity to regenerate them upon lesion. However, it is unknown whether new sensory neurons are also formed throughout life in the zebrafish statoacoustic ganglion (SAG), which transduces signals from the inner ear to the brain. Moreover, it is unknown whether sensory neurons are replaced upon loss. Hence, the first aim of this study was to investigate whether new sensory neurons are produced beyond larval stages. To this end, analysis of different transgenic lines combined with immunohistochemistry against known markers for neuronal stem and progenitor cells, neurons, glia and myelinating cells as well as markers for proliferation were used to identify distinct cell populations and anatomical landmarks in the juvenile and adult SAG. In the juvenile SAG, a pool of highly proliferating Neurod/Nestin-positive neuronal progenitors produces large amounts of new sensory neurons. In contrast, at adult stages this neurogenic niche transitions to a quiescent state, in which Neurod/Nestin-positive neuronal progenitor cells are no longer proliferating and the neurogenesis rate is very low. Moreover, BrdU pulse chase experiments revealed the existence of a proliferative but otherwise marker-negative cell population that replenishes the Neurod/Nestinpositive progenitor pool throughout life, indicating a neural stem cell-like cell population upstream of the neuronal progenitor cell pool. Additionally, expression of glia markers and a switch in the myelination pattern was found to mark the peripheral and central nervous system transitional zone (PCTZ) as a prominent landmark of the SAG. To further study the nature of the proliferating but otherwise unknown stem cell-like cell population replenishing the Neurod/Nestin-positive neuronal progenitor pool, the transcriptome of proliferating cells and their progeny of the juvenile and adult SAG was analyzed via single cell RNA-sequencing using the Smart-Seq2 technology. Therefore, a pipeline including preparation of the SAG as well as cell dissociation followed by fluorescence-activated cell sorting was established to obtain single cells from the SAG. The fluorescent reporters Tg(pcna:GFP) and Tg(nestin:mCherry-CreERT2) were used to label proliferating cells (GFP-only positive), proliferating progenitors (GFP/mCherry-double positive as well as nonproliferating progenitor cells (mCherry-positive). Additionally, based on the perdurance of the fluorophores in the progeny of the cells expressing the reporter constructs, this sorting strategy also enables to sort the progeny of proliferating cells differentiating into neuronal progenitor cells (GFP/mCherry-double positive but not expressing pcna) to trace back the putative stem cell-like cell population replenishing the Neurod/Nestin-positive progenitor population. Similar, the sorting strategy also included newborn neurons as the progeny of neuronal progenitors (mCherry-positive but not expressing nestin). In the transcriptome data obtained from the juvenile SAG, the majority of the analyzed cells could be assigned to the neuronal lineage, reflecting the neuronal differentiation trajectory from neuronal progenitor cells transitioning to newborn neurons and even further differentiating into mature neurons. Additionally, two different putative neuronal stem cell-like cell clusters were identified which are currently under validation. In contrast, in the adult transcriptome data the majority of cells were identified as cells from the sensory lineage, including cells expressing markers specific for hair cells and the sensory epithelium. Only a minority of cells came from the neuronal lineage, with the group of newborn and differentiating neurons clustering together in one cluster. Very few cells were identified as neuronal progenitor cells and did not cluster together, whereas both putative stem cell-like cell populations could be identified as distinct cluster. However, validation of the putative stem cell population remains subject to further studies. The second aim of this thesis was to investigate the regenerative capacity of the adult SAG and to study whether the neurogenic progenitor cell niche can be reactivated and to give rise to new sensory neurons upon damage. Therefore, a lesion paradigm using unilateral injections into the otic capsule was established. Upon lesion, mature SAG neurons undergo apoptosis and a massive infiltration with immune cells was found. Importantly, the Neurod-positive progenitor cells reentered the cell cycle displaying a peak in proliferation at 8 days post lesion before they returned to homeostatic levels at 57 days post lesion. In parallel to reactive proliferation, an increase in neurogenesis from the Neurod-positive progenitor pool was observed. Reactive neurogenesis started at around 4 days post lesion, peaked at 8 days post lesion decreased again to low homeostatic levels at 57 days post lesion. The administration of the thymidine analog BrdU to label proliferating cells and their progeny revealed the generation of new sensory neurons from proliferating neuronal progenitor cells within 19 days post lesion. Interestingly, reactive proliferation as well as an increased neurogenesis rate were also detected in the unlesioned SAG, revealing a systemic effect of the unilateral lesions. Taken together, this study is the first to show that neurogenesis in the zebrafish SAG persists way beyond larval stages. New neurons descend from a population of Neurod/Nestin-positive neuronal progenitor cells that is highly proliferative during juvenile stages but turn quiescent at adulthood. Nevertheless, this neuronal progenitor cell pool is replenished throughout life by a currently unknown neuronal stem cell-like cell population. Additional this study reveals the regenerative capacity of the adult SAG: upon lesion Neurod/Nestin-positive progenitor cells are reactivated to re-enter the cell cycle, proliferate and give rise to new neurons leading to an increased neurogenesis rate to replace lost mature neurons. Studying the underlying genes and pathways in zebrafish compared to mammalian species will hopefully provide valuable insights that will help developing cures for auditory and vestibular neuropathies in the future

    Zebrafish as a Model for Developmental Neurotoxicity Assessment: The Application of the Zebrafish in Defining the Effects of Arsenic, Methylmercury, or Lead on Early Neurodevelopment

    Get PDF
    Developmental exposure to neurotoxic chemicals presents significant health concerns because of the vulnerability of the developing central nervous system (CNS) and the immature brain barrier. To date, a short list of chemicals including some metals have been identified as known developmental neurotoxicants; however, there are still numerous chemicals that remain to be evaluated for their potential developmental neurotoxicity (DNT). To facilitate evaluation of chemicals for DNT, the zebrafish vertebrate model system has emerged as a promising tool. The zebrafish possesses a number of strengths as a test species in DNT studies including an abundance of embryos developing ex utero presenting ease in chemical dosing and microscopic assessment at all early developmental stages. Additionally, rapid neurodevelopment via conserved molecular pathways supports the likelihood of recapitulating neurotoxic effects observed in other vertebrates. In this review, we describe the biological relevance of zebrafish as a complementary model for assessment of DNT. We then focus on a metalloid and two metals that are known developmental neurotoxicants (arsenic, methylmercury, and lead). We summarize studies in humans and traditional vertebrate models and then detail studies defining the toxicity of these substances using the zebrafish to support application of this model system in DNT studies

    Systems Biology-Based Analysis Indicates Global Transcriptional Impairment in Lead-Treated Human Neural Progenitor Cells

    Get PDF
    Lead poisoning effects are wide and include nervous system impairment, peculiarly during development, leading to neural damage. Lead interaction with calcium and zinc-containing metalloproteins broadly affects cellular metabolism since these proteins are related to intracellular ion balance, activation of signaling transduction cascades, and gene expression regulation. In spite of lead being recognized as a neurotoxin, there are gaps in knowledge about the global effect of lead in modulating the transcription of entire cellular systems in neural cells. In order to investigate the effects of lead poisoning in a systemic perspective, we applied the transcriptogram methodology in an RNA-seq dataset of human embryonic-derived neural progenitor cells (ES-NP cells) treated with 30 µM lead acetate for 26 days. We observed early downregulation of several cellular systems involved with cell differentiation, such as cytoskeleton organization, RNA, and protein biosynthesis. The downregulated cellular systems presented big and tightly connected networks. For long treatment times (12 to 26 days), it was possible to observe a massive impairment in cell transcription profile. Taking the enriched terms together, we observed interference in all layers of gene expression regulation, from chromatin remodeling to vesicle transport. Considering that ES-NP cells are progenitor cells that can originate other neural cell types, our results suggest that lead-induced gene expression disturbance might impair cells’ ability to differentiate, therefore influencing ES-NP cells’ fate

    Autologous Peripheral Nerve Grafts to the Brain for the Treatment of Parkinson\u27s Disease

    Get PDF
    Parkinson’s disease (PD) is a disorder of the nervous system that causes problems with movement (motor symptoms) as well as other problems such as mood disorders, cognitive changes, sleep disorders, constipation, pain, and other non-motor symptoms. The severity of PD symptoms worsens over time as the disease progresses, and while there are treatments for the motor and some non-motor symptoms there is no known cure for PD. Thus there is a high demand for therapies to slow the progressive neurodegeneration observed in PD. Two clinical trials at the University of Kentucky College of Medicine (NCT02369003, NCT01833364) are currently underway that aim to develop a disease-modifying therapy that slows the progression of PD. These clinical trials are evaluating the safety and feasibility of an autologous peripheral nerve graft to the substantia nigra in combination with Deep Brain Stimulation (DBS) for the treatment of PD. By grafting peripheral nerve tissue to the Substantia Nigra, the researchers aim to introduce peripheral nerve tissue, which is capable of functional regeneration after injury, to the degenerating Substantia Nigra of patients with PD. The central hypothesis of these clinical trials is that the grafted tissue will slow degeneration of the target brain region through neural repair actions of Schwann cells as well as other pro-regenerative features of the peripheral nerve tissue. This dissertation details analysis of the peripheral nerve tissue used in the above clinical trials with respect to tissue composition and gene expression, both of injury-naive human peripheral nerve as well as the post-conditioning injury nerve tissue used in the grafting procedure. RNA-seq analysis of sural nerve tissue pre and post-conditioning show significant changes in gene expression corresponding with transdifferentiation of Schwann cells from a myelinating to a repair phenotype, release of growth factors, activation of macrophages and other immune cells, and an increase in anti-apoptotic and neuroprotective gene transcripts. These results reveal in vivo gene expression changes involved in the human peripheral nerve injury repair process, which has relevance beyond this clinical trial to the fields of Schwann cell biology and peripheral nerve repair. To assess the neurobiology of the graft post-implantation we developed an animal model of the grafting procedure, termed Neuro-Avatars, which feature human graft tissue implanted into athymic nude rats. Survival and infiltration of human graft cells into the host brain were shown using immunohistochemistry of Human Nuclear Antigen. Surgical methods and outcomes from the ongoing development of this animal model are reported. To connect the results of these laboratory studies to the clinical trial we compared the severity of motor symptoms before surgery to one year post-surgery in patients who received the analyzed graft tissue. Motor symptom severity was assessed using the Unified Parkinson’s Disease Rating Scale Part III. Finally, the implications and future directions of this research is discussed. In summary, this dissertation advances the translational science cycle by using clinical trial findings and samples to answer basic science questions that will in turn guide future clinical trial design

    Loss of slc39a14 causes simultaneous manganese hypersensitivity and deficiency in zebrafish

    Get PDF
    Manganese neurotoxicity is a hallmark of Hypermanganesemia with Dystonia 2, an inherited manganese transporter defect caused by mutations in SLC39A14. To identify novel potential targets of manganese neurotoxicity we performed transcriptome analysis of slc39a14-/- mutant zebrafish unexposed and exposed to MnCl2. Differentially expressed genes mapped to the central nervous system and eye, and pathway analysis suggested that calcium dyshomeostasis and activation of the unfolded protein response are key features of manganese neurotoxicity. Consistent with this interpretation, MnCl2 exposure led to decreased whole animal calcium levels, locomotor defects and changes in neuronal activity within the telencephalon and optic tectum. In accordance with reduced tectal activity, slc39a14-/- zebrafish showed changes in visual phototransduction gene expression, absence of visual background adaptation and a diminished optokinetic reflex. Finally, numerous differentially expressed genes in mutant larvae normalised upon MnCl2 treatment indicating that, in addition to neurotoxicity, manganese deficiency is present either subcellularly or in specific cells or tissues. Overall, we assembled a comprehensive set of genes that mediate manganese-systemic responses and found a highly correlated and modulated network associated with calcium dyshomeostasis and cellular stress

    Bioactive Molecules from Indian Medicinal Plants as Possible Candidates for the Management of Neurodegenerative Disorders

    Get PDF
    The present review gives an account of various bioactive molecules obtained from Indian medicinal plants for neurological degenerative disorders. Emphasis is laid on their correlation with the plants used in traditional system of medicine in India. The methodology involved in present review was enlisting of medicinal plants used for neurodegenerative disorders followed by their chemistry. A correlation with the chemical constituents and their recent findings has been done. Many medicinal plants such as Aloe vera and Bacopa monnieri have documented correlations and also need to be explored more. Molecules like garcinol (34), which was originally an anticancer compound, have good correlation as neuroprotective agent. Likewise many plants that have not been explored but are used in traditional system of medicine have also been listed. Jaggery and honey, which are used in traditional formulations in large quantity, also have natural products that are used as neuroprotective agents. In conclusion, a lot more study is required to correlate the medicinal plants and herbal formulations to have much more natural products for neurodegenerative disorders

    Neuroinflammatory targets and treatments for epilepsy validated in experimental models

    Get PDF
    A large body of evidence that has accumulated over the past decade strongly supports the role of inflammation in the pathophysiology of human epilepsy. Specific inflammatory molecules and pathways have been identified that influence various pathologic outcomes in different experimental models of epilepsy. Most importantly, the same inflammatory pathways have also been found in surgically resected brain tissue from patients with treatment-resistant epilepsy. New antiseizure therapies may be derived from these novel potential targets. An essential and crucial question is whether targeting these molecules and pathways may result in anti-ictogenesis, antiepileptogenesis, and/or disease-modification effects. Therefore, preclinical testing in models mimicking relevant aspects of epileptogenesis is needed to guide integrated experimental and clinical trial designs. We discuss the most recent preclinical proof-of-concept studies validating a number of therapeutic approaches against inflammatory mechanisms in animal models that could represent novel avenues for drug development in epilepsy. Finally, we suggest future directions to accelerate preclinical to clinical translation of these recent discoveries

    RNA-Seq Reveals Acute Manganese Exposure Increases Endoplasmic Reticulum Related and Lipocalin mRNAs in Caenorhabditis elegans

    Get PDF
    Manganese (Mn) is an essential nutrient; nonetheless, excessive amounts can accumulate in brain tissues causing manganism, a severe neurological condition. Previous studies have suggested oxidative stress, mitochondria dysfunction, and impaired metabolism pathways as routes for Mn toxicity. Here, we used the nematode Caenorhabditis elegans to analyze gene expression changes after acute Mn exposure using RNA-Seq. L1 stage animals were exposed to 50 mM MnCl2 for 30 min and analyzed at L4. We identified 746 up- and 1828 downregulated genes (FDR corrected p < 0.05; two-fold change) that included endoplasmic reticulum related abu and fkb family genes, as well as six of seven lipocalin-related (lpr) family members. These were also verified by qRT-PCR. RNA interference of lpr-5 showed a dramatic increase in whole body vulnerability to Mn exposure. Our studies demonstrate that Mn exposure alters gene transcriptional levels in different cell stress pathways that may ultimately contribute to its toxic effects
    • …
    corecore