Autism spectrum disorder (ASD) is characterized by early onset of behavioral and cognitive alterations. Low plasma levels of oxytocin (OT) have also been found in ASD patients; recently, a critical role for the enzyme CD38 in the regulation of OT release was demonstrated. CD38 is important in regulating several Ca ²⁺ ‐dependent pathways, but beyond its role in regulating OT secretion, it is not known whether a deficit in CD38 expression leads to functional modifications of the prefrontal cortex (PFC), a structure involved in social behavior. Here, we report that CD38 ^−/− male mice show an abnormal cortex development, an excitation‐inhibition balance shifted toward a higher excitation, and impaired synaptic plasticity in the PFC such as those observed in various mouse models of ASD. We also show that a lack of CD38 alters social behavior and emotional responses. Finally, examining neuromodulators known to control behavioral flexibility, we found elevated monoamine levels in the PFC of CD38 ^−/− adult mice. Overall, our study unveiled major changes in PFC physiologic mechanisms and provides new evidence that the CD38 ^−/− mouse could be a relevant model to study pathophysiological brain mechanisms of mental disorders such as ASD.—Martucci, L. L., Amar, M., Chaussenot, R., Benet, G., Bauer, O., de Zélicourt, A., Nosjean, A., Launay, J.‐M., Callebert, J., Sebrié, C., Galione, A., Edeline, J.‐M., de la Porte, S., Fossier, P., Granon, S., Vaillend, C., Cancela, J.‐M., A multiscale analysis in CD38 ^‐/‐ mice unveils major prefrontal cortex dysfunctions. FASEB J. 33, 5823–5835 (2019). www.fasebj.org

Oxytocin (OT) is a prominent regulator of many aspects of mammalian social behavior and stored in large dense-cored vesicles (LDCVs) in hypothalamic neurons. It is released in response to activity-dependent Ca ²⁺ influx, but is also dependent on Ca ²⁺ release from intracellular stores, which primes LDCVs for exocytosis. Despite its importance, critical aspects of the Ca ²⁺ -dependent mechanisms of its secretion remain to be identified. Here we show that lysosomes surround dendritic LDCVs, and that the direct activation of endolysosomal two-pore channels (TPCs) provides the critical Ca ²⁺ signals to prime OT release by increasing the releasable LDCV pool without directly stimulating exocytosis. We observed a dramatic reduction in plasma OT levels in TPC knockout mice, and impaired secretion of OT from the hypothalamus demonstrating the importance of priming of neuropeptide vesicles for activity-dependent release. Furthermore, we show that activation of type 1 metabotropic glutamate receptors sustains somatodendritic OT release by recruiting TPCs. The priming effect could be mimicked by a direct application of nicotinic acid adenine dinucleotide phosphate, the endogenous messenger regulating TPCs, or a selective TPC2 agonist, TPC2-A1-N, or blocked by the antagonist Ned-19. Mice lacking TPCs exhibit impaired maternal and social behavior, which is restored by direct OT administration. This study demonstrates an unexpected role for lysosomes and TPCs in controlling neuropeptide secretion, and in regulating social behavior.

Ca²⁺ signalling is of prime importance in controlling numerous cell functions in the brain. Endolysosomes are acidic organelles currently emerging as important Ca²⁺ stores in astrocytes, microglia, endothelial cells, and neurons. In neurons, these acidic Ca²⁺ stores are found in axons, soma, dendrites, and axon endings and could provide local sources of Ca²⁺ to control synaptic transmission, neuronal plasticity, and autophagy to name a few. This review will address how acidic Ca²⁺ stores are recruited in response to cell stimulation. We will focus on the role of the endolysosomal two-pore channels (TPCs) and their physiological agonist nicotinic acid adenine dinucleotide phosphate (NAADP) and how they interact with cyclic ADP-ribose and ryanodine receptors from the endoplasmic reticulum. Finally, this review will describe new pharmacological tools and animal mutant models now available to explore acidic Ca²⁺ stores as key elements in brain function and dysfunction.

Cerebral ischemia results in oxygen and glucose deprivation that most commonly occurs after a reduction or interruption in the blood supply to the brain. The consequences of cerebral ischemia are complex and involve the loss of metabolic ATP, excessive K⁺ and glutamate accumulation in the extracellular space, electrolyte imbalance, and brain edema formation. So far, several treatments have been proposed to alleviate ischemic damage, yet few are effective. Here, we focused on the neuroprotective role of lowering the temperature in ischemia mimicked by an episode of oxygen and glucose deprivation (OGD) in mouse cerebellar slices. Our results suggest that lowering the temperature of the extracellular ‘milieu’ delays both the increases in [K⁺]_e and tissue swelling, two dreaded consequences of cerebellar ischemia. Moreover, radial glial cells (Bergmann glia) display morphological changes and membrane depolarizations that are markedly impeded by lowering the temperature. Overall, in this model of cerebellar ischemia, hypothermia reduces the deleterious homeostatic changes regulated by Bergmann glia.

Régulation de la libération d'ocytocine et de vasopressine par les canaux endolysosomaux two-pore channels: L’ocytocine et la vasopressine sont produites et libérées par l’hypothalamus. Chez l’homme et les animaux, ces neurohormones sont d’importants régulateurs comportementaux et, par conséquent, leurs effets sont actuellement largement étudiés dans les maladies neuropsychiatriques pour lesquelles un déficit en ocytocine aggrave le phénotype. Malgré leur importance, les mécanismes régulant la libération d’ocytocine et de vasopressine restent aujourd’hui mal connus. L’enzyme CD38 dont des mutations sont retrouvé dans des formes familiales d’autisme, est un acteur important de la sécrétion d’ocytocine. Cette enzyme, en recrutant le Ca²⁺ du réticulum endoplasmique permet l’exocytose Ca²⁺-dépendante de l’ocytocine. Au cours de ma thèse, j’ai exploré si les souris CD38-/- reproduisent un phénotype autistique et j’ai démontré qu’en plus des défauts d’ocytocine, ces souris présentent des comportements altérés, une macrocéphalie, une excitation corticale plus élevée, et une plasticité altérée dans le cortex préfrontal, l’une des principales structures impliquées dans les comportements sociaux. Ces résultats ont renforcé l’utilisation des souris CD38-/- comme modèle d’étude pour l’autisme. J’ai ensuite exploré les mécanismes par lesquels CD38 contrôle la sécrétion l’ocytocine et de vasopressine. En plus du réticulum, CD38 mobilise le Ca²⁺ à partir des lysosomes en via le canal calcique « two-pore channel » (TPC). J’ai alors démontré que le Ca²⁺ lysosomal était essentiel pour la libération d’ocytocine et de vasopressine hypothalamique mais également dans la réponse Ca²⁺ évoquée par des agonistes dans les neurones hypothalamiques ainsi que dans la plasticité neuronale du cortex préfrontal. Enfin, j’ai proposé un nouveau modèle dans lequel les TPCs sont impliqués dans l’amorçage des vésicules d’ocytocine et de vasopressine à la membrane, un processus physiologique essentiel à la libération de neuropeptide et appelé « priming ». En bref, ces résultats démontrent le rôle crucial des réserves Ca²⁺ endolysosomales qui ont été ignorées jusqu’à présent dans la neurosécrétion et ouvrent la voie à de futures investigations des mécanismes hypothalamique.