Cellular Mechanisms Participating in Brain Repair of Adult Zebrafish and Mammals after Injury

Adult neurogenesis is an evolutionary conserved process occurring in all vertebrates. However, striking differences are observed between the taxa, considering the number of neurogenic niches, the neural stem cell (NSC) identity, and brain plasticity under constitutive and injury-induced conditions. Zebrafish has become a popular model for the investigation of the molecular and cellular mechanisms involved in adult neurogenesis. Compared to mammals, the adult zebrafish displays a high number of neurogenic niches distributed throughout the brain. Furthermore, it exhibits a strong regenerative capacity without scar formation or any obvious disabilities. In this review, we will first discuss the similarities and differences regarding (i) the distribution of neurogenic niches in the brain of adult zebrafish and mammals (mainly mouse) and (ii) the nature of the neural stem cells within the main telencephalic niches. In the second part, we will describe the cascade of cellular events occurring after telencephalic injury in zebrafish and mouse. Our study clearly shows that most early events happening right after the brain injury are shared between zebrafish and mouse including cell death, microglia, and oligodendrocyte recruitment, as well as injury-induced neurogenesis. In mammals, one of the consequences following an injury is the formation of a glial scar that is persistent. This is not the case in zebrafish, which may be one of the main reasons that zebrafish display a higher regenerative capacity

HDL biodistribution and brain receptors in zebrafish, using HDLs as vectors for targeting endothelial cells and neural progenitors

High density lipoproteins (HDLs) display pleiotropic functions such as anti-inflammatory, antioxidant, anti-protease, and anti-apoptotic properties. These effects are mediated by four main receptors: SCARB1 (SR-BI), ABCA1, ABCG1, and CD36. Recently, HDLs have emerged for their potential involvement in brain functions, considering their epidemiological links with cognition, depression, and brain plasticity. However, their role in the brain is not well understood. Given that the zebrafish is a well-recognized model for studying brain plasticity, metabolic disorders, and apolipoproteins, it could represent a good model for investigating the role of HDLs in brain homeostasis. By analyzing RNA sequencing data sets and performing in situ hybridization, we demonstrated the wide expression of scarb1, abca1a, abca1b, abcg1, and cd36 in the brain of adult zebrafish. Scarb1 gene expression was detected in neural stem cells (NSCs), suggesting a possible role of HDLs in NSC activity. Accordingly, intracerebroventricular injection of HDLs leads to their uptake by NSCs without modulating their proliferation. Next, we studied the biodistribution of HDLs in the zebrafish body. In homeostatic conditions, intraperitoneal injection of HDLs led to their accumulation in the liver, kidneys, and cerebral endothelial cells in zebrafish, similar to that observed in mice. After telencephalic injury, HDLs were diffused within the damaged parenchyma and were taken up by ventricular cells, including NSCs. However, they failed to modulate the recruitment of microglia cells at the injury site and the injury-induced proliferation of NSCs. In conclusion, our results clearly show a functional HDL uptake process involving several receptors that may impact brain homeostasis and suggest the use of HDLs as delivery vectors to target NSCs for drug delivery to boost their neurogenic activity

Impact du surpoids et de l'hyperglycémie sur la barrière hémato-encéphalique et la plasticité cérébrale : Effets protecteurs de P. mauritianum et d’A. borbonica, deux plantes médicinales réunionnaises

Obesity is a worldwide epidemic leading to many health concerns and is a risk factor for the development of type 2 diabetes. In Reunion Island, obesity and diabetes are widely spread among the population. Both diseases share several metabolic disorders and have been recently implicated in deteriorating brain health, contributing to cognitive impairments. The mechanisms behind the onset of altered brain homeostasis are not well understood. Besides, no therapy has yet been established to prevent brain disruptions. The aim of this thesis is to study the impact of obesity/prediabetes on brain homeostasis and cerebral plasticity, and then to alleviate these deleterious effects using medicinal plants from Reunion Island. To this end, we set up a diet-induced obesity (DIO) protocol in zebrafish (Danio rerio). Zebrafish recently emerges as a relevant model to mimic metabolic diseases (obesity and diabetes), and to investigate brain homeostasis and plasticity (i.e., blood-brain barrier (BBB) and neurogenesis). Our DIO model, established by overfeeding adult zebrafish for 4 weeks, resulted in metabolic disorders and loss of central nervous system (CNS) homeostasis. Indeed, DIO fish displayed increased body weight and body mass index (BMI), hyperglycemia, liver steatosis and disturbed redox balance. In the central nervous system, overfeeding led to BBB leakage, neuro-inflammation, cerebral oxidative stress and decreased neurogenesis. As well, a change in the locomotor behavior was observed in obese fish. In a next step, we tested the potential beneficial properties of two Reunionese plants registered in the French pharmacopeia: Antirhea borbonica (A. borbonica) and Psiloxylon mauritianum (P. mauritianum). Both plants were traditionally used for their positive effects on metabolic disruptions as “anti-diabetic” effects for A. borbonica and “anti-lipidemic” for P. mauritianum. However, the scientific data supporting these properties are lacking. First, the chemical analysis of aqueous extract of A. borbonica and P. mauritianum revealed their abundance in polyphenols, correlated to their antioxidant properties. LC-MS/MS analysis was used to determine the nature of the polyphenolic compounds in each extract. Next, we performed toxicity assays using OECD guidelines 36 (Organization for Economic Co-operation and Development) (OECD, 2013) and defined a maximum non-toxic concentration for each extract. The overnight treatment with aqueous extract of A. borbonica (0.5g/L) during the DIO protocol demonstrated its preventive properties against the deleterious effects on the CNS induced by overfeeding. Indeed, A. borbonica preserved the BBB function, prevented the increase in cerebral oxidative stress, neuro-inflammation and normalized neurogenesis. Similarly, the aqueous extract of P. mauritianum (0.25 g/L) was tested on adult DIO zebrafish and in high-fat diet (HFD) treated larvae. The treatment avoided lipid accumulation in HFD larvae. It also prevented body weight increase, BMI, hyperglycemia and liver steatosis in adult DIO zebrafish. Furthermore, brain homeostasis seems to be preserved probably through P. mauritianum anti-weight gain properties. We suggested that P. mauritianum could significantly affect lipid absorption and metabolism possibly through the modulation of gut microbiota. In conclusion, during this thesis, we have developed a simple and rapid overfeeding (DIO) model inducing peripheral and CNS disruptions similar to those encountered in mammals. For the first time, we studied the toxicity of aqueous extract of the two medicinal plants A. borbonica and P. mauritianum. We confirmed their beneficial effects on different metabolic parameters and on the brain using zebrafish model of obesity and prediabetes. Together, these data highlight the use of zebrafish to mimic metabolic diseases and to screen the beneficial properties of medicinal plants extracts.L'obésité est une épidémie mondiale entraînant de nombreux problèmes de santé et constitue un facteur de risque pour le développement du diabète de type 2. Les deux maladies partagent plusieurs troubles métaboliques et ont récemment été impliquées dans la détérioration de la santé cérébrale, contribuant aux troubles cognitifs. L'objectif de cette thèse est d'étudier l'impact de l'obésité/prédiabète sur l'homéostasie cérébrale et la plasticité cérébrale, puis d'atténuer ces effets délétères à l'aide de plantes médicinales réunionnaises. Pour cela, nous avons mis en place un protocole d'obésité induite par l'alimentation (DIO) chez le poisson zèbre (Danio rerio). Notre modèle DIO, établi en suralimentant des poissons zèbres adultes pendant 4 semaines, a entraîné des troubles métaboliques et une perte d'homéostasie du système nerveux central (SNC). Dans un second temps, nous avons testé les propriétés bénéfiques potentielles de deux plantes réunionnaises inscrites à la pharmacopée française : Antirhea borbonica (A. borbonica) et Psiloxylon mauritianum (P. mauritianum). Dans un premier temps, l'analyse chimique d'extraits aqueux d'A. borbonica et de P. mauritianum a révélé leur abondance en polyphénols, corrélée à leurs propriétés antioxydantes. Les deux plantes reflètent des effets préventifs luttant contre les effets DIO sur la périphérie et le cerveau. En conclusion, au cours de cette thèse, nous avons développé un modèle simple et rapide de suralimentation (DIO) induisant des perturbations périphériques et du SNC similaires à celles rencontrées chez les mammifères. Pour la première fois, nous avons étudié la toxicité de l'extrait aqueux des deux plantes médicinales A. borbonica et P. mauritianum. Nous avons confirmé leurs effets bénéfiques sur différents paramètres métaboliques et sur le cerveau en utilisant le modèle d'obésité et de prédiabète du poisson zèbre. Ensemble, ces données mettent en évidence l'utilisation du poisson zèbre pour imiter les maladies métaboliques et pour dépister les propriétés bénéfiques des extraits de plantes médicinales

Impact du surpoids et de l'hyperglycémie sur la barrière hémato-encéphalique et la plasticité cérébrale : Effets protecteurs de P. mauritianum et d’A. borbonica, deux plantes médicinales réunionnaises

Obesity is a worldwide epidemic leading to many health concerns and is a risk factor for the development of type 2 diabetes. In Reunion Island, obesity and diabetes are widely spread among the population. Both diseases share several metabolic disorders and have been recently implicated in deteriorating brain health, contributing to cognitive impairments. The mechanisms behind the onset of altered brain homeostasis are not well understood. Besides, no therapy has yet been established to prevent brain disruptions. The aim of this thesis is to study the impact of obesity/prediabetes on brain homeostasis and cerebral plasticity, and then to alleviate these deleterious effects using medicinal plants from Reunion Island. To this end, we set up a diet-induced obesity (DIO) protocol in zebrafish (Danio rerio). Zebrafish recently emerges as a relevant model to mimic metabolic diseases (obesity and diabetes), and to investigate brain homeostasis and plasticity (i.e., blood-brain barrier (BBB) and neurogenesis). Our DIO model, established by overfeeding adult zebrafish for 4 weeks, resulted in metabolic disorders and loss of central nervous system (CNS) homeostasis. Indeed, DIO fish displayed increased body weight and body mass index (BMI), hyperglycemia, liver steatosis and disturbed redox balance. In the central nervous system, overfeeding led to BBB leakage, neuro-inflammation, cerebral oxidative stress and decreased neurogenesis. As well, a change in the locomotor behavior was observed in obese fish. In a next step, we tested the potential beneficial properties of two Reunionese plants registered in the French pharmacopeia: Antirhea borbonica (A. borbonica) and Psiloxylon mauritianum (P. mauritianum). Both plants were traditionally used for their positive effects on metabolic disruptions as “anti-diabetic” effects for A. borbonica and “anti-lipidemic” for P. mauritianum. However, the scientific data supporting these properties are lacking. First, the chemical analysis of aqueous extract of A. borbonica and P. mauritianum revealed their abundance in polyphenols, correlated to their antioxidant properties. LC-MS/MS analysis was used to determine the nature of the polyphenolic compounds in each extract. Next, we performed toxicity assays using OECD guidelines 36 (Organization for Economic Co-operation and Development) (OECD, 2013) and defined a maximum non-toxic concentration for each extract. The overnight treatment with aqueous extract of A. borbonica (0.5g/L) during the DIO protocol demonstrated its preventive properties against the deleterious effects on the CNS induced by overfeeding. Indeed, A. borbonica preserved the BBB function, prevented the increase in cerebral oxidative stress, neuro-inflammation and normalized neurogenesis. Similarly, the aqueous extract of P. mauritianum (0.25 g/L) was tested on adult DIO zebrafish and in high-fat diet (HFD) treated larvae. The treatment avoided lipid accumulation in HFD larvae. It also prevented body weight increase, BMI, hyperglycemia and liver steatosis in adult DIO zebrafish. Furthermore, brain homeostasis seems to be preserved probably through P. mauritianum anti-weight gain properties. We suggested that P. mauritianum could significantly affect lipid absorption and metabolism possibly through the modulation of gut microbiota. In conclusion, during this thesis, we have developed a simple and rapid overfeeding (DIO) model inducing peripheral and CNS disruptions similar to those encountered in mammals. For the first time, we studied the toxicity of aqueous extract of the two medicinal plants A. borbonica and P. mauritianum. We confirmed their beneficial effects on different metabolic parameters and on the brain using zebrafish model of obesity and prediabetes. Together, these data highlight the use of zebrafish to mimic metabolic diseases and to screen the beneficial properties of medicinal plants extracts.L'obésité est une épidémie mondiale entraînant de nombreux problèmes de santé et constitue un facteur de risque pour le développement du diabète de type 2. Les deux maladies partagent plusieurs troubles métaboliques et ont récemment été impliquées dans la détérioration de la santé cérébrale, contribuant aux troubles cognitifs. L'objectif de cette thèse est d'étudier l'impact de l'obésité/prédiabète sur l'homéostasie cérébrale et la plasticité cérébrale, puis d'atténuer ces effets délétères à l'aide de plantes médicinales réunionnaises. Pour cela, nous avons mis en place un protocole d'obésité induite par l'alimentation (DIO) chez le poisson zèbre (Danio rerio). Notre modèle DIO, établi en suralimentant des poissons zèbres adultes pendant 4 semaines, a entraîné des troubles métaboliques et une perte d'homéostasie du système nerveux central (SNC). Dans un second temps, nous avons testé les propriétés bénéfiques potentielles de deux plantes réunionnaises inscrites à la pharmacopée française : Antirhea borbonica (A. borbonica) et Psiloxylon mauritianum (P. mauritianum). Dans un premier temps, l'analyse chimique d'extraits aqueux d'A. borbonica et de P. mauritianum a révélé leur abondance en polyphénols, corrélée à leurs propriétés antioxydantes. Les deux plantes reflètent des effets préventifs luttant contre les effets DIO sur la périphérie et le cerveau. En conclusion, au cours de cette thèse, nous avons développé un modèle simple et rapide de suralimentation (DIO) induisant des perturbations périphériques et du SNC similaires à celles rencontrées chez les mammifères. Pour la première fois, nous avons étudié la toxicité de l'extrait aqueux des deux plantes médicinales A. borbonica et P. mauritianum. Nous avons confirmé leurs effets bénéfiques sur différents paramètres métaboliques et sur le cerveau en utilisant le modèle d'obésité et de prédiabète du poisson zèbre. Ensemble, ces données mettent en évidence l'utilisation du poisson zèbre pour imiter les maladies métaboliques et pour dépister les propriétés bénéfiques des extraits de plantes médicinales

Impact du surpoids et de l'hyperglycémie sur la barrière hémato-encéphalique et la plasticité cérébrale : Effets protecteurs de P. mauritianum et d’A. borbonica, deux plantes médicinales réunionnaises

L'obésité est une épidémie mondiale entraînant de nombreux problèmes de santé et constitue un facteur de risque pour le développement du diabète de type 2. Les deux maladies partagent plusieurs troubles métaboliques et ont récemment été impliquées dans la détérioration de la santé cérébrale, contribuant aux troubles cognitifs. L'objectif de cette thèse est d'étudier l'impact de l'obésité/prédiabète sur l'homéostasie cérébrale et la plasticité cérébrale, puis d'atténuer ces effets délétères à l'aide de plantes médicinales réunionnaises. Pour cela, nous avons mis en place un protocole d'obésité induite par l'alimentation (DIO) chez le poisson zèbre (Danio rerio). Notre modèle DIO, établi en suralimentant des poissons zèbres adultes pendant 4 semaines, a entraîné des troubles métaboliques et une perte d'homéostasie du système nerveux central (SNC). Dans un second temps, nous avons testé les propriétés bénéfiques potentielles de deux plantes réunionnaises inscrites à la pharmacopée française : Antirhea borbonica (A. borbonica) et Psiloxylon mauritianum (P. mauritianum). Dans un premier temps, l'analyse chimique d'extraits aqueux d'A. borbonica et de P. mauritianum a révélé leur abondance en polyphénols, corrélée à leurs propriétés antioxydantes. Les deux plantes reflètent des effets préventifs luttant contre les effets DIO sur la périphérie et le cerveau. En conclusion, au cours de cette thèse, nous avons développé un modèle simple et rapide de suralimentation (DIO) induisant des perturbations périphériques et du SNC similaires à celles rencontrées chez les mammifères. Pour la première fois, nous avons étudié la toxicité de l'extrait aqueux des deux plantes médicinales A. borbonica et P. mauritianum. Nous avons confirmé leurs effets bénéfiques sur différents paramètres métaboliques et sur le cerveau en utilisant le modèle d'obésité et de prédiabète du poisson zèbre. Ensemble, ces données mettent en évidence l'utilisation du poisson zèbre pour imiter les maladies métaboliques et pour dépister les propriétés bénéfiques des extraits de plantes médicinales.Obesity is a worldwide epidemic leading to many health concerns and is a risk factor for the development of type 2 diabetes. In Reunion Island, obesity and diabetes are widely spread among the population. Both diseases share several metabolic disorders and have been recently implicated in deteriorating brain health, contributing to cognitive impairments. The mechanisms behind the onset of altered brain homeostasis are not well understood. Besides, no therapy has yet been established to prevent brain disruptions. The aim of this thesis is to study the impact of obesity/prediabetes on brain homeostasis and cerebral plasticity, and then to alleviate these deleterious effects using medicinal plants from Reunion Island. To this end, we set up a diet-induced obesity (DIO) protocol in zebrafish (Danio rerio). Zebrafish recently emerges as a relevant model to mimic metabolic diseases (obesity and diabetes), and to investigate brain homeostasis and plasticity (i.e., blood-brain barrier (BBB) and neurogenesis). Our DIO model, established by overfeeding adult zebrafish for 4 weeks, resulted in metabolic disorders and loss of central nervous system (CNS) homeostasis. Indeed, DIO fish displayed increased body weight and body mass index (BMI), hyperglycemia, liver steatosis and disturbed redox balance. In the central nervous system, overfeeding led to BBB leakage, neuro-inflammation, cerebral oxidative stress and decreased neurogenesis. As well, a change in the locomotor behavior was observed in obese fish. In a next step, we tested the potential beneficial properties of two Reunionese plants registered in the French pharmacopeia: Antirhea borbonica (A. borbonica) and Psiloxylon mauritianum (P. mauritianum). Both plants were traditionally used for their positive effects on metabolic disruptions as “anti-diabetic” effects for A. borbonica and “anti-lipidemic” for P. mauritianum. However, the scientific data supporting these properties are lacking. First, the chemical analysis of aqueous extract of A. borbonica and P. mauritianum revealed their abundance in polyphenols, correlated to their antioxidant properties. LC-MS/MS analysis was used to determine the nature of the polyphenolic compounds in each extract. Next, we performed toxicity assays using OECD guidelines 36 (Organization for Economic Co-operation and Development) (OECD, 2013) and defined a maximum non-toxic concentration for each extract. The overnight treatment with aqueous extract of A. borbonica (0.5g/L) during the DIO protocol demonstrated its preventive properties against the deleterious effects on the CNS induced by overfeeding. Indeed, A. borbonica preserved the BBB function, prevented the increase in cerebral oxidative stress, neuro-inflammation and normalized neurogenesis. Similarly, the aqueous extract of P. mauritianum (0.25 g/L) was tested on adult DIO zebrafish and in high-fat diet (HFD) treated larvae. The treatment avoided lipid accumulation in HFD larvae. It also prevented body weight increase, BMI, hyperglycemia and liver steatosis in adult DIO zebrafish. Furthermore, brain homeostasis seems to be preserved probably through P. mauritianum anti-weight gain properties. We suggested that P. mauritianum could significantly affect lipid absorption and metabolism possibly through the modulation of gut microbiota. In conclusion, during this thesis, we have developed a simple and rapid overfeeding (DIO) model inducing peripheral and CNS disruptions similar to those encountered in mammals. For the first time, we studied the toxicity of aqueous extract of the two medicinal plants A. borbonica and P. mauritianum. We confirmed their beneficial effects on different metabolic parameters and on the brain using zebrafish model of obesity and prediabetes. Together, these data highlight the use of zebrafish to mimic metabolic diseases and to screen the beneficial properties of medicinal plants extracts

Impact du surpoids et de l'hyperglycémie sur la barrière hémato-encéphalique et la plasticité cérébrale : Effets protecteurs de P. mauritianum et d’A. borbonica, deux plantes médicinales réunionnaises

Obesity is a worldwide epidemic leading to many health concerns and is a risk factor for the development of type 2 diabetes. In Reunion Island, obesity and diabetes are widely spread among the population. Both diseases share several metabolic disorders and have been recently implicated in deteriorating brain health, contributing to cognitive impairments. The mechanisms behind the onset of altered brain homeostasis are not well understood. Besides, no therapy has yet been established to prevent brain disruptions. The aim of this thesis is to study the impact of obesity/prediabetes on brain homeostasis and cerebral plasticity, and then to alleviate these deleterious effects using medicinal plants from Reunion Island. To this end, we set up a diet-induced obesity (DIO) protocol in zebrafish (Danio rerio). Zebrafish recently emerges as a relevant model to mimic metabolic diseases (obesity and diabetes), and to investigate brain homeostasis and plasticity (i.e., blood-brain barrier (BBB) and neurogenesis). Our DIO model, established by overfeeding adult zebrafish for 4 weeks, resulted in metabolic disorders and loss of central nervous system (CNS) homeostasis. Indeed, DIO fish displayed increased body weight and body mass index (BMI), hyperglycemia, liver steatosis and disturbed redox balance. In the central nervous system, overfeeding led to BBB leakage, neuro-inflammation, cerebral oxidative stress and decreased neurogenesis. As well, a change in the locomotor behavior was observed in obese fish. In a next step, we tested the potential beneficial properties of two Reunionese plants registered in the French pharmacopeia: Antirhea borbonica (A. borbonica) and Psiloxylon mauritianum (P. mauritianum). Both plants were traditionally used for their positive effects on metabolic disruptions as “anti-diabetic” effects for A. borbonica and “anti-lipidemic” for P. mauritianum. However, the scientific data supporting these properties are lacking. First, the chemical analysis of aqueous extract of A. borbonica and P. mauritianum revealed their abundance in polyphenols, correlated to their antioxidant properties. LC-MS/MS analysis was used to determine the nature of the polyphenolic compounds in each extract. Next, we performed toxicity assays using OECD guidelines 36 (Organization for Economic Co-operation and Development) (OECD, 2013) and defined a maximum non-toxic concentration for each extract. The overnight treatment with aqueous extract of A. borbonica (0.5g/L) during the DIO protocol demonstrated its preventive properties against the deleterious effects on the CNS induced by overfeeding. Indeed, A. borbonica preserved the BBB function, prevented the increase in cerebral oxidative stress, neuro-inflammation and normalized neurogenesis. Similarly, the aqueous extract of P. mauritianum (0.25 g/L) was tested on adult DIO zebrafish and in high-fat diet (HFD) treated larvae. The treatment avoided lipid accumulation in HFD larvae. It also prevented body weight increase, BMI, hyperglycemia and liver steatosis in adult DIO zebrafish. Furthermore, brain homeostasis seems to be preserved probably through P. mauritianum anti-weight gain properties. We suggested that P. mauritianum could significantly affect lipid absorption and metabolism possibly through the modulation of gut microbiota. In conclusion, during this thesis, we have developed a simple and rapid overfeeding (DIO) model inducing peripheral and CNS disruptions similar to those encountered in mammals. For the first time, we studied the toxicity of aqueous extract of the two medicinal plants A. borbonica and P. mauritianum. We confirmed their beneficial effects on different metabolic parameters and on the brain using zebrafish model of obesity and prediabetes. Together, these data highlight the use of zebrafish to mimic metabolic diseases and to screen the beneficial properties of medicinal plants extracts.L'obésité est une épidémie mondiale entraînant de nombreux problèmes de santé et constitue un facteur de risque pour le développement du diabète de type 2. Les deux maladies partagent plusieurs troubles métaboliques et ont récemment été impliquées dans la détérioration de la santé cérébrale, contribuant aux troubles cognitifs. L'objectif de cette thèse est d'étudier l'impact de l'obésité/prédiabète sur l'homéostasie cérébrale et la plasticité cérébrale, puis d'atténuer ces effets délétères à l'aide de plantes médicinales réunionnaises. Pour cela, nous avons mis en place un protocole d'obésité induite par l'alimentation (DIO) chez le poisson zèbre (Danio rerio). Notre modèle DIO, établi en suralimentant des poissons zèbres adultes pendant 4 semaines, a entraîné des troubles métaboliques et une perte d'homéostasie du système nerveux central (SNC). Dans un second temps, nous avons testé les propriétés bénéfiques potentielles de deux plantes réunionnaises inscrites à la pharmacopée française : Antirhea borbonica (A. borbonica) et Psiloxylon mauritianum (P. mauritianum). Dans un premier temps, l'analyse chimique d'extraits aqueux d'A. borbonica et de P. mauritianum a révélé leur abondance en polyphénols, corrélée à leurs propriétés antioxydantes. Les deux plantes reflètent des effets préventifs luttant contre les effets DIO sur la périphérie et le cerveau. En conclusion, au cours de cette thèse, nous avons développé un modèle simple et rapide de suralimentation (DIO) induisant des perturbations périphériques et du SNC similaires à celles rencontrées chez les mammifères. Pour la première fois, nous avons étudié la toxicité de l'extrait aqueux des deux plantes médicinales A. borbonica et P. mauritianum. Nous avons confirmé leurs effets bénéfiques sur différents paramètres métaboliques et sur le cerveau en utilisant le modèle d'obésité et de prédiabète du poisson zèbre. Ensemble, ces données mettent en évidence l'utilisation du poisson zèbre pour imiter les maladies métaboliques et pour dépister les propriétés bénéfiques des extraits de plantes médicinales

Zebrafish: A New Promise to Study the Impact of Metabolic Disorders on the Brain

Zebrafish has become a popular model to study many physiological and pathophysiological processes in humans. In recent years, it has rapidly emerged in the study of metabolic disorders, namely, obesity and diabetes, as the regulatory mechanisms and metabolic pathways of glucose and lipid homeostasis are highly conserved between fish and mammals. Zebrafish is also widely used in the field of neurosciences to study brain plasticity and regenerative mechanisms due to the high maintenance and activity of neural stem cells during adulthood. Recently, a large body of evidence has established that metabolic disorders can alter brain homeostasis, leading to neuro-inflammation and oxidative stress and causing decreased neurogenesis. To date, these pathological metabolic conditions are also risk factors for the development of cognitive dysfunctions and neurodegenerative diseases. In this review, we first aim to describe the main metabolic models established in zebrafish to demonstrate their similarities with their respective mammalian/human counterparts. Then, in the second part, we report the impact of metabolic disorders (obesity and diabetes) on brain homeostasis with a particular focus on the blood–brain barrier, neuro-inflammation, oxidative stress, cognitive functions and brain plasticity. Finally, we propose interesting signaling pathways and regulatory mechanisms to be explored in order to better understand how metabolic disorders can negatively impact neural stem cell activity

Aqueous Extract of Psiloxylon mauritianum, Rich in Gallic Acid, Prevents Obesity and Associated Deleterious Effects in Zebrafish

Obesity has reached epidemic proportions, and its prevalence tripled worldwide between 1975 and 2016, especially in Reunion Island, a French overseas region. Psiloxylon mauritianum, an endemic medicinal plant from Reunion Island registered in the French pharmacopeia, has recently gained interest in combating metabolic disorders because of its traditional lipid-lowering and “anti-diabetic” use. However, scientific data are lacking regarding its toxicity and its real benefits on metabolic diseases. In this study, we aim to determine the toxicity of an aqueous extract of P. mauritianum on zebrafish eleutheroembryos following the OECD toxicity assay (Organization for Economic Cooperation and Development, guidelines 36). After defining a non-toxic dose, we determined by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) that this extract is rich in gallic acid but contains also caffeoylquinic acid, kaempferol and quercetin, as well as their respective derivatives. We also showed that the non-toxic dose exhibits lipid-lowering effects in a high-fat-diet zebrafish larvae model. In a next step, we demonstrated its preventive effects on body weight gain, hyperglycemia and liver steatosis in a diet-induced obesity model (DIO) performed in adults. It also limited the deleterious effects of overfeeding on the central nervous system (i.e., cerebral oxidative stress, blood-brain barrier breakdown, neuro-inflammation and blunted neurogenesis). Interestingly, adult DIO fish treated with P. mauritianum display normal feeding behavior but higher feces production. This indicates that the “anti-weight-gain” effect is probably due to the action of P. mauritianum on the intestinal lipid absorption and/or on the microbiota, leading to the increase in feces production. Therefore, in our experimental conditions, the aqueous extract of P. mauritianum exhibited “anti-weight-gain” properties, which prevented the development of obesity and its deleterious effects at the peripheral and central levels. These effects should be further investigated in preclinical models of obese/diabetic mice, as well as the impact of P. mauritianum on the gut microbiota

Phenolic Profile of Herbal Infusion and Polyphenol-Rich Extract from Leaves of the Medicinal Plant Antirhea borbonica: Toxicity Assay Determination in Zebrafish Embryos and Larvae

International audienceAntirhea borbonica (A. borbonica) is an endemic plant from the Mascarene archipelago in the Indian Ocean commonly used in traditional medicine for its health benefits. This study aims (1) at exploring polyphenols profiles from two types of extracts-aqueous (herbal infusion) and acetonic (polyphenol rich) extracts from A. borbonica leaves-and (2) at evaluating their potential toxicity in vivo for the first time. We first demonstrated that, whatever type of extraction is used, both extracts displayed significant antioxidant properties and acid phenolic and flavonoid contents. By using selective liquid chromatography-tandem mass spectrometry, we performed polyphenol identification and quantification. Among the 19 identified polyphenols, we reported that the main ones were caffeic acid derivatives and quercetin-3-O-rutinoside. Then, we performed a Fish Embryo Acute Toxicity test to assess the toxicity of both extracts following the Organisation for Economic Cooperation and Development (OECD) guidelines. In both zebrafish embryos and larvae, the polyphenols-rich extract obtained by acetonic extraction followed by evaporation and resuspension in water exhibits a higher toxic effect with a median lethal concentration (LC 50 : 5.6 g/L) compared to the aqueous extract (LC 50 : 20.3 g/L). Our data also reveal that at non-lethal concentrations of 2.3 and 7.2 g/L for the polyphenol-rich extract and herbal infusion, respectively, morphological malformations such as spinal curvature, pericardial edema, and developmental delay may occur. In conclusion, our study strongly suggests that the evaluation of the toxicity of medicinal plants should be systematically carried out and considered when studying therapeutic effects on living organisms

Distribution of microglia/immune cells in the brain of adult zebrafish in homeostatic and regenerative conditions: Focus on oxidative stress during brain repair

Microglia are macrophage-like cells exerting determinant roles in neuroinflammatory and oxidative stress processes during brain regeneration. We used zebrafish as a model of brain plasticity and repair. First, by performing L-plastin (Lcp1) immunohistochemistry and using transgenic Tg(mpeg1.1:GFP) or Tg(mpeg1.1:mCherry) fish, we analyzed the distribution of microglia/immune cells in the whole brain. Specific regional differences were evidenced in terms of microglia/immune cell density and morphology (elongated, branched, highly branched, and amoeboid). Taking advantage of Tg(fli:GFP) and Tg(GFAP::GFP) enabling the detection of endothelial cells and neural stem cells (NSCs), we highlighted the association of elongated microglia/immune cells with blood vessels and rounded/amoeboid microglia with NSCs. Second, after telencephalic injury, we showed that L-plastin cells were still abundantly present at 5 days post-lesion (dpl) and were associated with regenerative neurogenesis. Finally, RNAsequencing analysis from injured telencephalon (5 dpl) confirmed the upregulation of microglia/immune cell markers and highlighted a significant increase of genes involved in oxidative stress (nox2, nrf2a, and gsr). The analysis of antioxidant activities at 5 dpl also revealed an upregulation of superoxide dismutase and persistent H2O2 generation in the injured telencephalon. Also, microglia/immune cells were shown to be a source of oxidative stress at 5 dpl. Overall, our data provide a better characterization of microglia/immune cell distribution in the healthy zebrafish brain, highlighting some evolutionarily conserved features with mammals. They also emphasize that 5 days after injury, microglia/immune cells are still activated and are associated to a persistent redox imbalance. Together, these data raise the question of the role of oxidative stress in regenerative neurogenesis in zebrafish