Analyses of circRNA Expression throughout the Light-Dark Cycle Reveal a Strong Regulation of Cdr1as, Associated with Light Entrainment in the SCN

Circular RNAs (circRNAs) are a large class of relatively stable RNA molecules that are highly expressed in animal brains. Many circRNAs have been associated with CNS disorders accompanied by an aberrant wake-sleep cycle. However, the regulation of circRNAs in brain homeostasis over daily light-dark (LD) cycles has not been characterized. Here, we aim to quantify the daily expression changes of circRNAs in physiological conditions in healthy adult animals. Using newly generated and public RNA-Seq data, we monitored circRNA expression throughout the 12:12 h LD cycle in various mouse brain regions. We identified that Cdr1as, a conserved circRNA that regulates synaptic transmission, is highly expressed in the suprachiasmatic nucleus (SCN), the master circadian pacemaker. Despite its high stability, Cdr1as has a very dynamic expression in the SCN throughout the LD cycle, as well as a significant regulation in the hippocampus following the entry into the dark phase. Computational integration of different public datasets predicted that Cdr1as is important for regulating light entrainment in the SCN. We hypothesize that the expression changes of Cdr1as in the SCN, particularly during the dark phase, are associated with light-induced phase shifts. Importantly, our work revises the current beliefs about natural circRNA stability and suggests that the time component must be considered when studying circRNA regulation

Glucocorticoid receptor in astrocytes regulates midbrain dopamine neurodegeneration through connexin hemichannel activity

The precise contribution of astrocytes in neuroinflammatory process occurring in Parkinson's disease (PD) is not well characterized. In this study, using GR(Cx30CreERT2) mice that are conditionally inactivated for glucocorticoid receptor (GR) in astrocytes, we have examined the actions of astrocytic GR during dopamine neuron (DN) degeneration triggered by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The results show significantly augmented DN loss in GR(Cx30CreERT2) mutant mice in substantia nigra (SN) compared to controls. Hypertrophy of microglia but not of astrocytes was greatly enhanced in SN of these astrocytic GR mutants intoxicated with MPTP, indicating heightened microglial reactivity compared to similarly-treated control mice. In the SN of GR astrocyte mutants, specific inflammation-associated transcripts ICAM-1, TNF-alpha and Il-1 beta as well as TNF-alpha protein levels were significantly elevated after MPTP neurotoxicity compared to controls. Interestingly, this paralleled increased connexin hemichannel activity and elevated intracellular calcium levels in astrocytes examined in acute midbrain slices from control and mutant mice treated with MPP+. The increased connexin-43 hemichannel activity was found in vivo in MPTP-intoxicated mice. Importantly, treatment of MPTP-injected GR(Cx30CreERT2) mutant mice with TAT-Gap19 peptide, a specific connexin-43 hemichannel blocker, reverted both DN loss and microglial activation; in wild-type mice there was partial but significant survival effect. In the SN of postmortem PD patients, a significant decrease in the number of astrocytes expressing nuclear GR was observed, suggesting the participation of astrocytic GR deregulation of inflammatory process in PD. Overall, these data provide mechanistic insights into GR-modulated processes in vivo, specifically in astrocytes, that contribute to a pro-inflammatory state and dopamine neurodegeneration in PD pathology

Molecular study of chronic inflammation in Parkinson’s Disease

Les corps de Lewy, composés d’agrégats d'α-synucléine (αSyn), sont des inclusions intraneuronales caractéristiques de plusieurs pathologies appelées α-synucléinopathies dont fait partie la maladie de Parkinson (MP). Ces différentes pathologies pourraient reposer sur l’existence de différents assemblages d’αSyn ou « souches ». Dans la MP, la glie chroniquement activée contribue à la perte des neurones dopaminergiques (ND) de la substance noire (SN), une caractéristique majeure de la MP. Le rôle de la glie dans la toxicité induite par différentes souches d’αSyn est inconnu. J’ai pu montrer l’impact différentiel de 2 souches d’αSyn –fibrille et ruban- sur la dégénérescence des ND et sur la réactivité gliale in vivo. Suite à l’injection intrastriatale de ces souches chez la souris, seule les fibrilles induisent une réactivité inflammatoire chronique. In vitro, la clairance et la réactivité microgliale est différente vis à vis des deux souches pouvant participer aux différences pathologiques observées.Les niveaux de glucocorticoïdes (GC), anti-inflammatoires endogènes les plus puissants, sont retrouvés chroniquement élevés chez les patients parkinsoniens. Nous avons pu mettre en évidence une diminution de l'expression du récepteur aux GC (GR) microglial et astrocytaire dans la SN de cerveaux de patients, suggérant un dysfonctionnement du système GC-GR dans la MP. En utilisant des souris dépourvues de GR microglial ou astrocytaire, nous avons pu démontrer l’effet protecteur du GR glial sur la mort des ND induite par l’αSyn ou une toxine, pouvant être expliqué en partie par sa régulation du récepteur immunitaire TLR9 des microglies et de l’activité des hémicanaux astrocytaires.Lewy bodies, composed of α-synuclein (αSyn) aggregates, are intraneuronal inclusions that characterize a group of pathologies called α-synucleinopathies, of which Parkinson's disease (PD) is the most common. It is believed that distinct pathological characteristics of these α-synucleinopathies could arise from existence of different assemblies of αSyn proteins, or "strains". In PD, chronically activated glial cells contribute to the loss dopaminergic neurons (DN) in substantia nigra (SN), a major feature of PD. But the role of glia in the toxicity induced by different strains of αSyn is unknown.During my thesis, I found a differential impact of 2 strains of αSyn-fibril and ribbon-on DN degeneration and glial reactivity in vivo. My results showed greater neurotoxicity of αSyn-fibril strain towards DN, which also maintain a chronic inflammatory state in SN. In primary microglial cells, the 2 strains exhibited differential clearance and inflammatory responses providing further insights into how αSyn strains can participate in different pathological outcomes. Glucocorticoids (GC) is a potent regulator of inflammation acting through its receptor GR. We showed decreased microglial and astrocytic GR expression in the SN of PD, suggesting the dysfunction of GC-GR system could paly a role in chronic inflammation. Using mice lacking GR in microglia or astrocytes, I showed the protective effect of glial GR on αSyn-induced DN death. Two mechanisms of GR dysfunction were identified in these studies: TLR9 activation in microglia and connexin 43 hemichannel activity in astrocytes, both of which regulate DN death in SN

SWI/SNF chromatin remodeler complex within the reward pathway is required for behavioral adaptations to stress

Stress exposure is a cardinal risk factor for most psychiatric diseases. Preclinical and clinical studies point to changes in gene expression involving epigenetic modifications within mesocorticolimbic brain circuits. Brahma (BRM) and Brahma-Related-Gene-1 (BRG1) are ATPase subunits of the SWI/SNF complexes involved in chromatin remodeling, a process essential to enduring plastic changes in gene expression. Here, we show that repeated social defeat induces changes in BRG1 nuclear distribution. The inactivation of the Brg1/Smarca4 gene within dopamine-innervated regions or the constitutive inactivation of the Brm/Smarca2 gene leads to resilience to repeated social defeat and decreases the behavioral responses to cocaine without impacting midbrain dopamine neurons activity. Within striatal medium spiny neurons Brg1 gene inactivation reduces the expression of stress-and cocaine-induced immediate early genes, increases levels of heterochromatin and at a global scale decreases chromatin accessibility. Altogether these data demonstrate the pivotal function of SWI/SNF complexes in behavioral and transcriptional adaptations to salient environmental challenges

SWI/SNF chromatin remodeler complex within the reward pathway is required for behavioral adaptations to stress

International audienceEnduring behavioral changes upon stress exposure involve changes in gene expression sustained by epigenetic modifications in brain circuits, including the mesocorticolimbic pathway. Brahma (BRM) and Brahma Related Gene 1 (BRG1) are ATPase subunits of the SWI/SNF complexes involved in chromatin remodeling, a process essential to enduring plastic changes in gene expression. Here, we show that in mice, social defeat induces changes in BRG1 nuclear distribution. The inactivation of the Brg1/Smarca4 gene within dopamine-innervated regions or the constitutive inactivation of the Brm/Smarca2 gene leads to resilience to repeated social defeat and decreases the behavioral responses to cocaine without impacting midbrain dopamine neurons activity. Within striatal medium spiny neurons, Brg1 gene inactivation reduces the expression of stress-and cocaine-induced immediate early genes, increases levels of heterochromatin and at a global scale decreases chromatin accessibility. Altogether these data demonstrate the pivotal function of SWI/SNF complexes in behavioral and transcriptional adaptations to salient environmental challenges

TLR9 activation via microglial glucocorticoid receptors contributes to degeneration of midbrain dopamine neurons

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Neuro‐immune interactions in health and disease: Insights from FENS‐Hertie 2022 Winter School

Abstract In a great partnership, the Federation of European Neuroscience Societies (FENS) and the Hertie Foundation organized the FENS‐Hertie 2022 Winter School on ‘Neuro‐immune interactions in health and disease’. The school selected 27 PhD students and 13 postdoctoral fellows from 20 countries and involved 14 faculty members experts in the field. The Winter School focused on a rising field of research, the interactions between the nervous and both innate and adaptive immune systems under pathological and physiological conditions. A fine‐tuned neuro‐immune crosstalk is fundamental for healthy development, while disrupted neuro‐immune communication might play a role in neurodegeneration, neuroinflammation and aging. However, much is yet to be understood about the underlying mechanisms of these neuro‐immune interactions in the healthy brain and under pathological scenarios. In addition to new findings in this emerging field, novel methodologies and animal models were presented to foment research on neuro‐immunology. The FENS‐Hertie 2022 Winter School provided an insightful knowledge exchange between students and faculty focusing on the latest discoveries in the biology of neuro‐immune interactions while fostering great academic and professional opportunities for early‐career neuroscientists from around the world