Stress-inducible phosphoprotein 1 (HOP/STI1/STIP1) regulates the accumulation and toxicity of α-synuclein in vivo

The predominantly pre-synaptic intrinsically disordered protein α-synuclein is prone to misfolding and aggregation in synucleinopathies, such as Parkinson’s disease (PD) and Dementia with Lewy bodies (DLB). Molecular chaperones play important roles in protein misfolding diseases and members of the chaperone machinery are often deposited in Lewy bodies. Here, we show that the Hsp90 co-chaperone STI1 co-immunoprecipitated α-synuclein, and co-deposited with Hsp90 and Hsp70 in insoluble protein fractions in two mouse models of α-synuclein misfolding. STI1 and Hsp90 also co-localized extensively with filamentous S129 phosphorylated α-synuclein in ubiquitin-positive inclusions. In PD human brains, STI1 transcripts were increased, and in neurologically healthy brains, STI1 and α-synuclein transcripts correlated. Nuclear Magnetic Resonance (NMR) analyses revealed direct interaction of α-synuclein with STI1 and indicated that the STI1 TPR2A, but not TPR1 or TPR2B domains, interacted with the C-terminal domain of α-synuclein. In vitro, the STI1 TPR2A domain facilitated S129 phosphorylation by Polo-like kinase 3. Moreover, mice over-expressing STI1 and Hsp90ß presented elevated α-synuclein S129 phosphorylation accompanied by inclusions when injected with α-synuclein pre-formed fibrils. In contrast, reduced STI1 function decreased protein inclusion formation, S129 α-synuclein phosphorylation, while mitigating motor and cognitive deficits as well as mesoscopic brain atrophy in α-synuclein-over-expressing mice. Our findings reveal a vicious cycle in which STI1 facilitates the generation and accumulation of toxic α-synuclein conformers, while α-synuclein-induced proteostatic stress increased insoluble STI1 and Hsp90

EFFECTS OF CHRONIC EXPOSURE TO SELENIUM ON SOCIAL BEHAVIOUR AND SOCIAL LEARNING IN ZEBRAFISH (Danio rerio)

Elevated levels of contaminants from human activities have become a major threat to animals, particularly within aquatic ecosystems. Selenium (Se) is a naturally occurring element with a narrow range of safe intake. Excessive selenium has toxicological effects, while too little causes nutritional deficits. The adverse neurobehavioural effects of Se have been investigated in both humans and fishes, but little is known about its effects on social behaviour and social learning or serotonin signalling in the brain. Considerable evidence shows that excessive exposure to Se causes toxic bioaccumulation in female fish, with Se transferring to the developing embryos leading to a diverse range of adverse health in offspring. Therefore, in this thesis, I investigated dietary exposure and transgenerational effects of chronic exposure to Se on different aspects of social behaviour including antipredator response, group preference, and social learning in zebrafish (Danio rerio), with a particular focus on alterations in the serotonergic pathway. In the first experiment of chapter one, I documented that exposure of adult zebrafish to the highest concentration (31.5 µg Se/g dry weight) of dietary selenomethionine (Se-Met), caused elevated levels of baseline fear behaviour, with fish swimming lower in the water column and in tighter shoals compared to fish in the other treatments. With this high level of baseline stress, these fish did not significantly intensify antipredator (fear) behaviours in response to exposure to chemical alarm cues. In group preference tests, when individual fish were given an opportunity to shoal with groups of different sizes, fish exposed to the highest Se-Met concentration spent significantly less time in groups. In the social learning test, I found that zebrafish exposed to the highest concentration of Se-Met (34.1 µg Se/g dry weight) displayed significantly lower escape responses compared to fish in control and lower exposure groups (3.6 and 12.8 µg Se/g dry weight). These impaired behaviours were associated with higher oxidative stress and dysregulation in mRNA expression of 5-HT receptors (htr1aa, htr1b, htr1d, htr2aa, htr2b, and htrcl1), 5-HT synthesis (tph2), its reuptake (slc6a4a) as well as monoamine oxidase (mao), an important enzyme in the degradation of 5-HT. In my final experiment, female zebrafish were treated with different concentrations of Se-Met and bred with untreated male zebrafish to produce the F1-generation required to investigate the transgenerational effects of dietary Se on social behaviour and social learning in zebrafish. Offspring were raised to adulthood (6-month-old) without Se exposure. Then, in a series of behavioural tests, I found offspring that were maternally exposed to high levels of Se showed behavioural signs of stress (although no physical impairment), had weaker group preferences, and also demonstrated impaired social learning. These neurobehavioural deficits appear to be linked to perturbations in the serotonergic system in the brain, as maternal exposure to high Se concentrations led to dysregulation of this neurotransmitter (e.g., altered transcription of 5-HT receptors). Overall, my study highlights that Se contamination impairs multiple social behaviours and social learning, and it has important trans-generational consequences even in the absence of direct Se exposure

Proximate causes and ultimate effects of common antidepressants, fluoxetine and venlafaxine, on fish behavior

Salahinejad A, Attaran A, Meuthen D, Chivers DP, Niyogi S. Proximate causes and ultimate effects of common antidepressants, fluoxetine and venlafaxine, on fish behavior. Science of the total environment. 2021;807(Pt 2): 150846.Antidepressant (AD) drugs are widely prescribed for the treatment of psychiatric disorders, including depression and anxiety disorders. The continuous use of ADs causes significant quantities of these bioactive chemicals to enter the aquatic ecosystems mainly through wastewater effluent discharge. This may result in many aquatic organisms being inadvertently affected by these drugs. Fluoxetine (FLX) and venlafaxine (VEN) are currently among the most widely detected ADs in aquatic systems. A growing body of experimental evidence demonstrates that FLX and VEN have a substantial capacity to induce neurotoxicity and cause behavioral dysfunctions in a wide range of teleost species. At the same time, these studies often report seemingly contradictory results that are confounding in nature. Hence, we clearly require comprehensive reviews that attempt to find overarching patterns and establish possible causes for these variable results. This review aims to explore the current state of knowledge regarding the neurobehavioral effects of FLX and VEN on fishes. This study also discusses the potential mechanistic linkage between the neurotoxicity of ADs and behavioral dysfunction and identifies key knowledge gaps and areas for future research. Copyright © 2021 Elsevier B.V. All rights reserved

Effects of common antiepileptic drugs on teleost fishes

Salahinejad A, Meuthen D, Attaran A, Chivers DP, Ferrari MCO. Effects of common antiepileptic drugs on teleost fishes. Science of The Total Environment. 2023;866: 161324.Antiepileptic drugs (AEDs) are globally prescribed to treat epilepsy and many other psychiatric disorders in humans. Their high consumption, low metabolic rate in the human body and low efficiency of wastewater treatment plants (WWTPs) in eliminating these chemicals results in the frequent occurrence of these pharmaceutical drugs in aquatic systems. Therefore, aquatic organisms, including ecologically and economically important teleost fishes, may be inadvertently exposed to these chemicals. Due to their physiological similarity with humans, fishes may be particularly vulnerable to AEDs. Almost all AED drugs are detectable in natural aquatic ecosystems, but diazepam (DZP) and carbamazepine (CBZ) are among the most widely detected AEDs to date. Recent studies suggest that these drugs have a substantial capacity to induce neurotoxicity and behavioral abnormality in fishes. Here we review the current state of knowledge regarding the potential mode of action of DZP and CBZ as well as that of some other AEDs on teleosts and put observable behavioral effects into a mechanistic context. We find that following their intended mode of action in humans, AEDs also disrupt the GABAergic, glutamatergic and serotonergic systems as well as parasympathetic neurotransmitters in fishes. Moreover, AEDs have non-specific modes of action in teleosts ranging from estrogenic activity to oxidative stress. These physiological changes are often accompanied by dose-dependent disruptions of anxiety, locomotor activity, social behaviors, food uptake, and learning and memory, but DZP and CBZ consistently induced anxiolytic effects. Thereby, AED exposure severely compromises individual fitness across teleost fish species, which may lead to population and ecosystem impairment. We also showcase promising avenues for future research by highlighting where we lack data when it comes to effects of certain AEDs, AED concentrations and behavioral endpoints

Chronic exposure to bisphenol S induces oxidative stress, abnormal anxiety, and fear responses in adult zebrafish (Danio rerio)

Salahinejad A, Attaran A, Naderi M, Meuthen D, Niyogi S, Chivers DP. Chronic exposure to bisphenol S induces oxidative stress, abnormal anxiety, and fear responses in adult zebrafish (Danio rerio). The Science of the total environment. 2020;750: 141633.Bisphenol S (BPS) is increasingly used in a wide range of industrial and consumer products, resulting in its ubiquitous distribution across the environment, including aquatic ecosystems. Although it is commonly known as a weak/moderate estrogenic compound, there has been a growing acknowledgment of the potential of BPS to cause toxicity by inducing oxidative stress. Oxidative stress is a major participant in the development of anxiety-like behaviors in humans and animals. Therefore, the present study was designed to examine the impact of BPS on anxiety-like behavior and fear responses in adult zebrafish and also to elucidate the possible linkage between the BPS neurotoxicity and oxidative status of the brain. To this end, adult male and female zebrafish were exposed to 0 (control), 1, 10, and 30mug/L of BPS and 1mug/L of 17-beta-estradiol (E2) for 75days. Following exposure, changes in anxiety and fear-related responses were evaluated by applying a novel tank test and by exposing focal fish to chemical alarm cues. Additionally, we evaluated the expression of multiple antioxidant genes in the zebrafish brain. Our results indicate that BPS, irrespective of exposure concentration, and E2 significantly decreased bottom-dwelling behavior and the latency to enter the upper water column. Furthermore, exposure to the highest concentration of BPS and E2 induced a significant decrease in fear-related responses. The impaired anxiety and reduced fear-related responses were associated with a down-regulation in the transcription of genes involved in enzymatic antioxidant defense. Taken together, our results suggest that chronic exposure to BPS impairs anxiety and fear responses in adult zebrafish, possibly by inducing oxidative stress in the brain. Copyright © 2020 Elsevier B.V. All rights reserved

Maternal exposure to bisphenol S induces neuropeptide signaling dysfunction and oxidative stress in the brain, and abnormal social behaviors in zebrafish (Danio rerio) offspring

Salahinejad A, Attaran A, Meuthen D, Rachamalla M, Chivers DP, Niyogi S. Maternal exposure to bisphenol S induces neuropeptide signaling dysfunction and oxidative stress in the brain, and abnormal social behaviors in zebrafish (Danio rerio) offspring. Science of The Total Environment. 2022;830: 154794

Maternal exposure to bisphenol S reduces anxiety and impairs collective antipredator behavior of male zebrafish (Danio rerio) offspring through dysregulation of their serotonergic system

Salahinejad A, Meuthen D, Attaran A, Niyogi S, Chivers DP, Ferrari MCO. Maternal exposure to bisphenol S reduces anxiety and impairs collective antipredator behavior of male zebrafish (Danio rerio) offspring through dysregulation of their serotonergic system. Aquatic Toxicology. 2023;267: 106800.Bisphenol S (BPS) is a common endocrine-disrupting chemical globally used in several consumer and industrial products. Although previous studies suggested that BPS induces multiple effects in exposed organisms, very little is known about its intergenerational effect on offspring behavior and/or the potential underlying mechanisms. To this end, adult female zebrafish Danio rerio were exposed to BPS (0, 10, 30g/L) and 1g/L of 17-beta-estradiol (E2) as a positive control for 60 days. Afterwards, female fish were bred with untreated males, and their offspring were raised to 6 months old in control water. Maternal exposure to BPS decreased male offspring anxiety and antipredator behaviors while boldness remained unaffected. Specifically, maternal exposure to 10 and 30g/L BPS and 1g/L E2 were found to impact male offspring anxiety levels as they decreased the total time that individuals spent in the dark zone in the light/dark box test and increased the total track length in the center of the open field test. In addition, maternal exposure to all concentrations of BPS and E2 disrupted antipredator responses of male offspring by decreasing shoal cohesion in the presence of chemical alarm cues derived from conspecifics, which communicated high risk. To elucidate the possible molecular mechanism underlying these neuro-behavioral effects of BPS, we assessed the serotonergic system via changes in mRNA expression of serotonin receptors, including the 5-HT1A, 5-HT1B, and 5-HT1D subtypes, the serotonin transporter and monoamine oxidase (MAO). The impaired anxiety and antipredator responses were associated with reduced levels of 5-HT1A subtype and MAO mRNA expression within the brain of adult male offspring. Collectively, the results of this study demonstrate that maternal exposure to environmental concentrations of BPS can interfere with the serotonergic signaling pathway in the developing brain, subsequently leading to the onset of a suite of behavioral deficits in adult offspring. Copyright © 2023 Elsevier B.V. All rights reserved

Effects of chronic exposure to bisphenol-S on social behaviors in adult zebrafish: Disruption of the neuropeptide signaling pathways in the brain

Salahinejad A, Naderi M, Attaran A, Meuthen D, Niyogi S, Chivers DP. Effects of chronic exposure to bisphenol-S on social behaviors in adult zebrafish: Disruption of the neuropeptide signaling pathways in the brain. Environmental Pollution. 2020;262: 113992