The Dct−/− Mouse Model to Unravel Retinogenesis Misregulation in Patients with Albinism

We have recently identified encoding dopachrome tautomerase (DCT) as the eighth gene for oculocutaneous albinism (OCA). Patients with loss of function of suffer from eye hypopigmentation and retinal dystrophy. Here we investigate the eye phenotype in mice. We show that their retinal pigmented epithelium (RPE) is severely hypopigmented from early stages, contrasting with the darker melanocytic tissues. Multimodal imaging reveals specific RPE cellular defects. Melanosomes are fewer with correct subcellular localization but disrupted melanization. RPE cell size is globally increased and heterogeneous. P-cadherin labeling of newborn RPE reveals a defect in adherens junctions similar to what has been described in tyrosinase-deficient embryos. The first intermediate of melanin biosynthesis, dihydroxyphenylalanine (L-Dopa), which is thought to control retinogenesis, is detected in substantial yet significantly reduced amounts in postnatal mouse eyecups. L-Dopa synthesis in the RPE alone remains to be evaluated during the critical period of retinogenesis. The mouse should prove useful in understanding the molecular regulation of retinal development and aging of the hypopigmented eye. This may guide therapeutic strategies to prevent vision deficits in patients with albinism.Approches de génétique moléculaire et fonctionnelle pour déchiffrer les mécanismes physiopathologiques de l'albinisme oculocutané

Microglia modulates hippocampal synaptic transmission and sleep duration along the light/dark cycle

Microglia, the brain's resident macrophages, actively contributes to the homeostasis of cerebral parenchyma by sensing neuronal activity and supporting synaptic remodeling and plasticity. While several studies demonstrated different roles for astrocytes in sleep, the contribution of microglia in the regulation of sleep/wake cycle and in the modulation of synaptic activity in the different day phases has not been deeply investigated. Using light as a zeitgeber cue, we studied the effects of microglial depletion with the colony stimulating factor-1 receptor antagonist PLX5622 on the sleep/wake cycle and on hippocampal synaptic transmission in male mice. Our data demonstrate that almost complete microglial depletion increases the duration of NREM sleep and reduces the hippocampal excitatory neurotransmission. The fractalkine receptor CX3CR1 plays a relevant role in these effects, because cx3cr1GFP/GFP mice recapitulate what found in PLX5622-treated mice. Furthermore, during the light phase, microglia express lower levels of cx3cr1 and a reduction of cx3cr1 expression is also observed when cultured microglial cells are stimulated by ATP, a purinergic molecule released during sleep. Our findings suggest that microglia participate in the regulation of sleep, adapting their cx3cr1 expression in response to the light/dark phase, and modulating synaptic activity in a phase-dependent manner.Bordeaux Region Aquitaine Initiative for Neuroscienc

Rôle des acides gras polyinsaturés dans les processus de myélinisation chez la souris en développement".

Les apports nutritionnels périnataux en acide gras polyinsaturés n-3 et n-6 (AGPI n-3 et n-6), communément appelés oméga-3 et oméga-6, sont essentiels pour le développement cérébral. Ces lipides ne peuvent être synthétisés par notre organisme et doivent donc être apportés par l’alimentation selon un ratio de un AGPI n-3 pour quatre AGPI n-6. Dans les pays occidentaux, la diminution continue des apports en AGPI n-3 depuis des décennies est corrélée significativement à l’incidence croissante des maladies neurodéveloppementales, pathologies dans lesquelles, les processus de myélinisation sont fortement affectés. Cependant, très peu de données étaient disponibles, au commencement de mes travaux de thèse, quant au rôle des AGPI dans la régulation de la fonction des oligodendrocytes et de la myéline.L’objectif principal de ma thèse a été d’étudier le lien potentiel entre une déficience en AGPI n-3 et les altérations du processus de myélinisation ainsi que les mécanismes impliqués, avec une emphase particulière sur les interactions microglie/myéline.Nos travaux montrent que la déficience périnatale en AGPI n-3 entraîne 1) une altération des microglies de la substance blanche et de la maturation des oligodendrocytes au cours du développement cérébral ; 2) une perturbation des fonctions oligodendrocytaires et de l’interaction microglie/myéline; 3) des déficits dans le processus de myélinisation, associé à un amincissement de la gaine de myéline et une altération de son ultra-structure; 4) des déficits d'apprentissage, de sociabilité et l'apparition de comportements anxieux. De plus, favoriser la myélinisation avec des agents pharmacologiques permet de palier les déficits de mémoire des souris déficientes en AGPI n-3.Globalement, le présent travail a précisé certains des mécanismes par lesquels la carence en AGPI n-3 affecte le cerveau en développement en soulignant son effet néfaste sur la microglie et l’oligodendrocyte ainsi que leur fonction plus particulièrement la myélinisation post-natale. Ces résultats sont associés à des anomalies comportementales, similaires à celles observées dans des modèles de troubles du développement neurologique.Perinatal dietary intakes of n-3 and n-6 polyunsaturated fatty acids (n-3 and n-6 PUFAs), commonly known as omega-3 and omega-6, are essential for brain development. These fatty acids cannot be synthesized by our body and must therefore be provided by the diet in a ratio of one n-3 PUFA for four n-6 PUFAs. In Western countries, the continuous decrease in n-3 PUFA intake for decades is significantly correlated with the increasing incidence of neurodevelopmental diseases, pathologies in which myelination processes are strongly affected. However, at the beginning of my thesis work, very little data was available on the role of PUFAs in the regulation of oligodendrocyte and myelin function.The main objective of my thesis was to study the potential link between n-3 PUFA deficiency and alterations in the myelination process and the mechanisms involved, with a particular emphasis on microglia/myelin interactions.Our work shows that perinatal n-3 PUFA deficiency leads to 1) an alteration of white matter associated microglia and oligodendrocyte maturation during brain development; 2) impaired oligodendrocyte functions and microglia/myelin interactions; 3) deficits in the myelination process, associated with thinning of the myelin sheath and ultrastructure alterations; 4) deficits in learning, sociability, and anxious behaviors. Moreover, promoting myelination with pharmacological agents rescued memory deficits in n-3 PUFA deficient mice.Overall, the present work has clarified some of the mechanisms by which n-3 PUFA deficiency affects the developing brain by highlighting its detrimental effect on microglia and oligodendrocyte and their function especially postnatal myelination. These results are associated with behavioral abnormalities, similar to those observed in models of neurodevelopmental disorders

Rôle des acides gras polyinsaturés dans les processus de myélinisation chez la souris en développement".

Les apports nutritionnels périnataux en acide gras polyinsaturés n-3 et n-6 (AGPI n-3 et n-6), communément appelés oméga-3 et oméga-6, sont essentiels pour le développement cérébral. Ces lipides ne peuvent être synthétisés par notre organisme et doivent donc être apportés par l’alimentation selon un ratio de un AGPI n-3 pour quatre AGPI n-6. Dans les pays occidentaux, la diminution continue des apports en AGPI n-3 depuis des décennies est corrélée significativement à l’incidence croissante des maladies neurodéveloppementales, pathologies dans lesquelles, les processus de myélinisation sont fortement affectés. Cependant, très peu de données étaient disponibles, au commencement de mes travaux de thèse, quant au rôle des AGPI dans la régulation de la fonction des oligodendrocytes et de la myéline.L’objectif principal de ma thèse a été d’étudier le lien potentiel entre une déficience en AGPI n-3 et les altérations du processus de myélinisation ainsi que les mécanismes impliqués, avec une emphase particulière sur les interactions microglie/myéline.Nos travaux montrent que la déficience périnatale en AGPI n-3 entraîne 1) une altération des microglies de la substance blanche et de la maturation des oligodendrocytes au cours du développement cérébral ; 2) une perturbation des fonctions oligodendrocytaires et de l’interaction microglie/myéline; 3) des déficits dans le processus de myélinisation, associé à un amincissement de la gaine de myéline et une altération de son ultra-structure; 4) des déficits d'apprentissage, de sociabilité et l'apparition de comportements anxieux. De plus, favoriser la myélinisation avec des agents pharmacologiques permet de palier les déficits de mémoire des souris déficientes en AGPI n-3.Globalement, le présent travail a précisé certains des mécanismes par lesquels la carence en AGPI n-3 affecte le cerveau en développement en soulignant son effet néfaste sur la microglie et l’oligodendrocyte ainsi que leur fonction plus particulièrement la myélinisation post-natale. Ces résultats sont associés à des anomalies comportementales, similaires à celles observées dans des modèles de troubles du développement neurologique.Perinatal dietary intakes of n-3 and n-6 polyunsaturated fatty acids (n-3 and n-6 PUFAs), commonly known as omega-3 and omega-6, are essential for brain development. These fatty acids cannot be synthesized by our body and must therefore be provided by the diet in a ratio of one n-3 PUFA for four n-6 PUFAs. In Western countries, the continuous decrease in n-3 PUFA intake for decades is significantly correlated with the increasing incidence of neurodevelopmental diseases, pathologies in which myelination processes are strongly affected. However, at the beginning of my thesis work, very little data was available on the role of PUFAs in the regulation of oligodendrocyte and myelin function.The main objective of my thesis was to study the potential link between n-3 PUFA deficiency and alterations in the myelination process and the mechanisms involved, with a particular emphasis on microglia/myelin interactions.Our work shows that perinatal n-3 PUFA deficiency leads to 1) an alteration of white matter associated microglia and oligodendrocyte maturation during brain development; 2) impaired oligodendrocyte functions and microglia/myelin interactions; 3) deficits in the myelination process, associated with thinning of the myelin sheath and ultrastructure alterations; 4) deficits in learning, sociability, and anxious behaviors. Moreover, promoting myelination with pharmacological agents rescued memory deficits in n-3 PUFA deficient mice.Overall, the present work has clarified some of the mechanisms by which n-3 PUFA deficiency affects the developing brain by highlighting its detrimental effect on microglia and oligodendrocyte and their function especially postnatal myelination. These results are associated with behavioral abnormalities, similar to those observed in models of neurodevelopmental disorders

Dietary N-3 PUFA deficiency affects sleep-wake activity in basal condition and in response to an inflammatory challenge in mice

Essential polyunsaturated fatty acids (PUFA) from the n-3 and n-6 series constitute the building blocks of brain cell membranes where they regulate most aspects of cell physiology. They are either biosynthesized from their dietary precursors or can be directly sourced from the diet. An overall increase in the dietary n-6/n-3 PUFA ratio, as observed in the Western diet, leads to reduced n-3 PUFAs in tissues that include the brain. Some clinical studies have shown a positive correlation between dietary n-3 PUFA intake and sleep quantity, yet evidence is still sparse. We here used a preclinical model of dietary n-3 PUFA deficiency to assess the precise relationship between dietary PUFA intake and sleep/wake activity. Using electroencephalography (EEG)/electromyography (EMG) recordings on n-3 PUFA deficient or sufficient mice, we showed that dietary PUFA deficiency affects the architecture of sleep-wake activity and the oscillatory activity of cortical neurons during sleep. In a second part of the study, and since PUFAs are a potent modulator of inflammation, we assessed the effect of dietary n-3 PUFA deficiency on the sleep response to an inflammatory stimulus known to modulate sleep/wake activity. We injected mice with the endotoxin lipopolysaccharide (LPS) and quantified the sleep response across the following 12 h. Our results revealed that n-3 PUFA deficiency affects the sleep response in basal condition and after a peripheral immune challenge. More studies are now required aimed at deciphering the molecular mechanisms underlying the intimate relationship between n-3 PUFAs and sleep/wake activity.Program Initiative d’Excellenc

N-3 PUFA Deficiency Affects the Ultrastructural Organization and Density of White Matter Microglia in the Developing Brain of Male Mice

International audienceOver the last century, westernization of dietary habits has led to a dramatic reduction in dietary intake of n-3 polyunsaturated fatty acids (n-3 PUFAs). In particular, low maternal intake of n-3 PUFAs throughout gestation and lactation causes defects in brain myelination. Microglia are recognized for their critical contribution to neurodevelopmental processes, such as myelination. These cells invade the white matter in the first weeks of the post-natal period, where they participate in oligodendrocyte maturation and myelin production. Therefore, we investigated whether an alteration of white matter microglia accompanies the myelination deficits observed in the brain of n-3 PUFA-deficient animals. Macroscopic imaging analysis shows that maternal n-3 PUFA deficiency decreases the density of white matter microglia around post-natal day 10. Microscopic electron microscopy analyses also revealed alterations of microglial ultrastructure, a decrease in the number of contacts between microglia and myelin sheet, and a decreased amount of myelin debris in their cell body. White matter microglia further displayed increased mitochondrial abundance and network area under perinatal n-3 PUFA deficiency. Overall, our data suggest that maternal n-3 PUFA deficiency alters the structure and function of microglial cells located in the white matter of pups early in life, and this could be the key to understand myelination deficits during neurodevelopment. Copyright © 2022 Decoeur, Picard, St-Pierre, Greenhalgh, Delpech, Sere, Layé, Tremblay and Nadjar

Microglial homeostasis disruption modulates non-rapid eye movement sleep duration and neuronal activity in adult female mice.

Sleep is a natural physiological state, tightly regulated through several neuroanatomical and neurochemical systems, which is essential to maintain physical and mental health. Recent studies revealed that the functions of microglia, the resident immune cells of the brain, differ along the sleep-wake cycle. Inflammatory cytokines, such as interleukin-1β and tumor necrosis factor-α, mainly produced by microglia in the brain, are also well-known to promote sleep. However, the contributing role of microglia on sleep regulation remains largely elusive, even more so in females. Given the higher prevalence of various sleep disorders in women, we aimed to determine the role of microglia in regulating the sleep-wake cycle specifically in female mice. Microglia were depleted in adult female mice with inhibitors of the colony-stimulating factor 1 receptor (CSF1R) (PLX3397 or PLX5622), which is required for microglial population maintenance. This led to a 65-73% reduction of the microglial population, as confirmed by immunofluorescence staining against IBA1 (marker of microglia/macrophages) and TMEM119 (microglia-specific marker) in the reticular nucleus of the thalamus and primary motor cortex. The spontaneous sleep-wake cycle was evaluated at steady-state, during microglial homeostasis disruption and after complete microglial repopulation, upon cessation of treatment with the inhibitors of CSF1R, using electroencephalography (EEG) and electromyography (EMG). We found that microglia-depleted female mice spent more time in non-rapid eye movement (NREM) sleep and had an increased number of NREM sleep episodes, which was partially restored after microglial total repopulation. To determine whether microglia could regulate sleep locally by modulating synaptic transmission, we used patch clamp to record spontaneous activity of pyramidal neurons in the primary motor cortex, which showed an increase of excitatory synaptic transmission during the dark phase. These changes in neuronal activity were modulated by microglial depletion in a phase-dependent manner. Altogether, our results indicate that microglia are involved in the sleep regulation of female mice, further strengthening their potential implication in the development and/or progression of sleep disorders. Furthermore, our findings indicate that microglial repopulation can contribute to normalizing sleep alterations caused by their partial depletion

Microglial cannabinoid type 1 receptor regulates brain inflammation in a sex-specific manner

Background: Neuroinflammation is a key feature shared by most, if not all, neuropathologies. It involves complex biological processes that act as a protective mechanism to fight against the injurious stimuli, but it can lead to tissue damage if self-perpetuating. In this context, microglia, the main cellular actor of neuroinflammation in the brain, are seen as a double-edged sword. By phagocyting neuronal debris, these cells can not only provide tissue repair but can also contribute to neuronal damage by releasing harmful substances, including inflammatory cytokines. The mechanisms guiding these apparent opposing actions are poorly known. The endocannabinoid system modulates the release of inflammatory factors such as cytokines and could represent a functional link between microglia and neuroinflammatory processes. According to transcriptomic databases and in vitro studies, microglia, the main source of cytokines in pathological conditions, express the cannabinoid type 1 receptor (CB1R). Methods: We thus developed a conditional mouse model of CB1R deletion specifically in microglia, which was subjected to an immune challenge (peripheral lipopolysaccharide injection). Results: Our results reveal that microglial CB1R differentially controls sickness behavior in males and females. Conclusion: These findings add to the comprehension of neuroinflammatory processes and might be of great interest for future studies aimed at developing therapeutic strategies for brain disorders with higher prevalence in men

Erratum to “N-3 PUFA deficiency disrupts oligodendrocyte maturation and myelin integrity during brain development”

This article corrects the following:N-3 PUFA deficiency disrupts oligodendrocyte maturation and myelin integrity during brain developmentQuentin Leyrolle, Fanny Decoeur, Cyril Dejean, Galadriel Brière, Stephane Leon, Ioannis Bakoyiannis, Emilie Baroux, Tony-Lee Sterley, Clémentine Bosch-Bouju, Lydie Morel, Camille Amadieu, Cynthia Lecours, Marie-Kim St-Pierre, Maude Bordeleau, Helene Roumes, Véronique De Smedt-Peyrusse, Alexandran Séré, Leslie Schwendimann, Stephane Grégoire, Lionel Bretillon, Niyazi Acar, Corinne Joffre, Guillaume Ferreira, Raluca Uricaru, Patricia Thebault, Pierre Gressens, Marie-Eve Tremblay, Sophie Layé, Agnes Nadjar Volume 70Issue 1Glia pages: 50-70 First Published online: September 14, 2021International audienc

N‐3 PUFA deficiency disrupts oligodendrocyte maturation and myelin integrity during brain development

International audienceWesternization of dietary habits has led to a progressive reduction in dietary intake of n-3 polyunsaturated fatty acids (n-3 PUFAs). Low maternal intake of n-3 PUFAs has been linked to neurodevelopmental disorders, conditions in which myelination processes are abnormal, leading to defects in brain functional connectivity. Only little is known about the role of n-3 PUFAs in oligodendrocyte physiology and white matter development. Here, we show that lifelong n-3 PUFA deficiency disrupts oligodendrocytes maturation and myelination processes during the postnatal period in mice. This has long-term deleterious consequences on white matter organization and hippocampus-prefrontal functional connectivity in adults, associated with cognitive and emotional disorders. Promoting developmental myelination with clemastine, a first-generation histamine antagonist and enhancer of oligodendrocyte precursor cell differentiation, rescues memory deficits in n-3 PUFA deficient animals. Our findings identify a novel mechanism through which n-3 PUFA deficiency alters brain functions by disrupting oligodendrocyte maturation and brain myelination during the neurodevelopmental period