Vincent Vialou’s research while affiliated with Institut de Biologie Paris-Seine and other places

Brain water homeostasis not only provides a physical protection, but also determines the diffusion of chemical molecules key for information processing and metabolic stability. As a major type of glia in brain parenchyma, astrocytes are the dominant cell type expressing aquaporin water channel. How astrocyte aquaporin contributes to brain water homeostasis in basal physiology remains to be understood. We report that astrocyte aquaporin 4 (AQP4) mediates a tonic water efflux in basal conditions. Acute inhibition of astrocyte AQP4 leads to intracellular water accumulation as optically resolved by fluorescence-translated imaging in acute brain slices, and in vivo by fiber photometry in mobile mice. We then show that aquaporin-mediated constant water efflux maintains astrocyte volume and osmotic equilibrium, astrocyte and neuron Ca ²⁺ signaling, and extracellular space remodeling during optogenetically induced cortical spreading depression. Using diffusion-weighted magnetic resonance imaging (DW-MRI), we observed that in vivo inhibition of AQP4 water efflux heterogeneously disturbs brain water homeostasis in a region-dependent manner. Our data suggest that astrocyte aquaporin, though bidirectional in nature, mediates a tonic water outflow to sustain cellular and environmental equilibrium in brain parenchyma.

Brain water homeostasis not only provides a physical protection, but also determines the diffusion of chemical molecules key for information processing and metabolic stability. As a major type of glia in brain parenchyma, astrocytes are the dominant cell type expressing aquaporin water channel. How astrocyte aquaporin contributes to brain water homeostasis in basal physiology remains to be understood. We report that astrocyte aquaporin 4 (AQP4) mediates a tonic water efflux in basal conditions. Acute inhibition of astrocyte AQP4 leads to intracellular water accumulation as optically resolved by fluorescence-translated imaging in acute brain slices, and in vivo by fiber photometry in mobile mice. We then show that aquaporin-mediated constant water efflux maintains astrocyte volume and osmotic equilibrium, astrocyte and neuron Ca 2+ signaling, and extracellular space remodeling during optogenetically induced cortical spreading depression. Using diffusion-weighted magnetic resonance imaging (DW-MRI), we observed that in vivo inhibition of AQP4 water efflux heterogeneously disturbs brain water homeostasis in a region-dependent manner. Our data suggest that astrocyte aquaporin, though bidirectional in nature, mediates a tonic water outflow to sustain cellular and environmental equilibrium in brain parenchyma.

Comorbidity between psychiatric traits is thought to involve overlapping pleiotropic effects from sets of genes. Notably, substance abuse is a shared comorbid condition among various neurodevelopmental disorders with externalizing symptoms such as autism spectrum disorder and attention-deficit hyperactivity disorder, thus hinting at the nucleus accumbens (NAc) as a site for predisposition underlying convergence of genetic influences in reward-related comorbidity. Here, we identify the autism-related gene encoding the adhesion G protein-coupled receptor (aGPCR) Latrophilin–1/ADGRL1 as an essential transducer of reward mechanisms in the NAc. We found that ADGRL1 mRNA is ubiquitously expressed throughout major NAc neuronal populations in mice. A mouse model of pan-neuronal Adgrl1 deficiency in the NAc displayed cocaine-seeking impairments in adult individuals denoting its role in drug-induced reinforcement and reward. Connecting molecular pathways of cocaine-induced learning, we uncover that ADGRL1 constitutes a functional receptor for autism–related cocaine effector molecule hevin/SPARCL1. Indeed, hevin interacts with membrane-expressed ADGRL1 and induces its internalization while stabilizing its uncleaved fraction. Moreover, hevin alters the formation of intercellular adhesion contacts mediated by ADGRL1 and Neurexin–1. Importantly, the functional constitutive coupling between ADGRL1 and various G protein pathways is selectively modulated by hevin stimulation with a bias toward Gi3, Gs, and G13 proteins. These findings unveil the dual role of ADGRL1 and hevin as genetic risk factors for both psychiatric disorders and substance abuse to define the molecular etiology of comorbidity.

The combination of fluorogenic probes (fluorogens) and self‐labeling protein tags represent a promising tool for imaging biological processes with high specificity but it requires the adequation between the fluorogen and its target to ensure a good activation of its fluorescence. In this work, we report a strategy to develop molecular rotors that specifically target HaloTag with a strong enhancement of their fluorescence. The divergent design facilitates the diversification of the structures to tune the photophysical and cellular properties. Four bright fluorogens with emissions ranging from green to red were identified and applied in wash‐free live cell imaging experiments with good contrast and selectivity. A HaloTag mutant adapted from previous literature reports was also tested and shown to further improve the brightness and reaction rate of the most promising fluorogen of the series both in vitro and in cells. This work opens new possibilities to develop bright chemogenetic reporters with diverse photophysical and biological properties by exploring a potentially large chemical space of simple dipolar fluorophores in combination with protein engineering.

Brain water homeostasis not only provides a physical protection, but also determines the diffusion of chemical molecules key for information processing and metabolic stability. As a major type of glia in brain parenchyma, astrocytes are the dominant cell type expressing aquaporin water channel. How astrocyte aquaporin contributes to brain water homeostasis in basal physiology remains to be understood. We report that astrocyte aquaporin 4 (AQP4) mediates a tonic water efflux in basal conditions. Acute inhibition of astrocyte AQP4 leads to intracellular water accumulation as optically resolved by fluorescence-translated imaging in acute brain slices, and in vivo by fiber photometry in mobile mice. We then show that aquaporin-mediated constant water efflux maintains astrocyte volume and osmotic equilibrium, astrocyte and neuron Ca 2+ signaling, and extracellular space remodeling during optogenetically induced cortical spreading depression. Using diffusion-weighted magnetic resonance imaging (DW-MRI), we observed that in vivo inhibition of AQP4 water efflux heterogeneously disturbs brain water homeostasis in a region-dependent manner. Our data suggest that astrocyte aquaporin, though bidirectional in nature, mediates a tonic water outflow to sustain cellular and environmental equilibrium in brain parenchyma.

Brain water homeostasis provides not only physical protection, but also determines the diffusion of chemical molecules key for information processing and metabolic stability. As a major type of glia in brain parenchyma, astrocytes are the dominant cell type expressing aquaporin water channel. However, how astrocyte aquaporin contributes to brain water homeostasis in basal physiology remains to be understood. We report that astrocyte aquaporin 4 (AQP4) mediates a tonic water efflux in basal conditions. Acute inhibition of astrocyte AQP4 leads to intracellular water accumulation as optically resolved by fluorescence-translated imaging in acute brain slices, and in vivo by fiber photometry in moving mice. We then show that the tonic aquaporin water efflux maintains astrocyte volume equilibrium, astrocyte and neuron Ca 2+ signaling, and extracellular space remodeling during optogenetically induced cortical spreading depression. Using diffusion-weighted magnetic resonance imaging (DW-MRI), we observed that in vivo inhibition of AQP4 water efflux heterogeneously disturbs brain water homeostasis in a region-dependent manner. Our data suggest that astrocyte aquaporin, though bidirectional in nature, mediates a tonic water outflow to sustain cellular and environmental equilibrium in brain parenchyma. Our brain is immersed, thus protected, in a water environment. It ensures intra- and extracellular molecular diffusion, which is vital for brain function and health. Brain water homeostasis is maintained by dynamic water transport between different cell types. Astrocytes are a main type of glial cell widely distributed in brain parenchyma, expressing the bidirectional aquaporin water channel. Here we show that in basal conditions, aquaporin channel mediates a tonic water efflux from astrocytes. This mechanism maintains astrocyte volume stability, activity-gated brain parenchyma remodeling and brain water homeostasis. Our finding sheds light on how astrocytes regulate water states in the brain, and will help to understand brain allostasis in specific life contexts.

Genetically encoded biosensors based on fluorescent proteins are valuable tools for imaging biological processes with high selectivity. In particular, pH-sensitive fluorescent proteins such as the GFP-derived superecliptic pHluorin (SEP) or pHuji allow tracking of protein trafficking through acidic and neutral compartments. Recently, chemogenetic indicators combining synthetic fluorophores with genetically encoded self-labeling protein tags (SLP-tag) offer a versatile alternative that combines the diversity of chemical probes and indicators with the selectivity of the genetic-encoding. Here, we describe a novel fluorogenic and chemogenetic pH sensor consisting of a cell-permeable molecular pH indicator called pHluo-Halo-1 whose fluorescence can be locally activated in cells by reaction with the SLP-tag HaloTag ensuring high signal selectivity in wash-free imaging experiments. pHluo-Halo display a good pH sensitivity and a suitable pKa of 5.9 to monitor biological pH variations. This hybrid chemogenetic pH probe was applied to follow the exocytosis of a CD63-HaloTag fusion proteins enabling the visualization of exosomes released from acidic vesicles into the extracellular media using TIRF microscopy. This chemogenetic platform is expected to be a powerful and versatile tool for elucidating the dynamics and regulatory mechanisms of proteins in living cells.

The combination of fluorogenic probes (fluorogens) and self-labeling protein tags represent a promising tool for imaging biological processes with high specificity but it requires the adequation between the fluorogen and its target to ensure a good activation of its fluorescence. In this work, we report a strategy to develop molecular rotors that specifically target HaloTag with a strong enhancement of their fluorescence. The divergent design facilitates the diversification of the structures to tune the photophysical and cellular properties. Four bright fluorogens with emissions ranging from green to red were identified and applied in wash-free live cell imaging experiments with good contrast and selectivity. A HaloTag mutant adapted from previous literature reports was also tested and shown to further improve the brightness and reaction rate of the most promising fluorogen of the series both in vitro and in cells. This work opens new possibilities to develop bright chemogenetic reporters with diverse photophysical and biological properties by exploring a potentially large chemical space of simple dipolar fluorophores in combination with protein engineering.