Tianeptine modulates synaptic vesicle dynamics and favors synaptic mitochondria processes in socially isolated rats

Deregulation of synaptic function and neurotransmission has been linked with the development of major depression disorder (MDD). Tianeptine (Tian) has been used as antidepressant with anxiolytic properties and recently as a nootropic to improve cognitive performance, but its mechanism of action is unknown. We conducted a proteomic study on the hippocampal synaptosomal fractions of adult male Wistar rats exposed to chronic social isolation (CSIS, 6 weeks), an animal model of depression and after chronic Tian treatment in controls (nootropic effect) and CSIS-exposed rats (lasting 3 weeks of 6-week CSIS) (therapeutic effect). Increased expression of Syn1 and Camk2-related neurotransmission, vesicle transport and energy processes in Tian-treated controls were found. CSIS led to upregulation of proteins associated with actin cytoskeleton, signaling transduction and glucose metabolism. In CSIS rats, Tian up-regulated proteins involved in mitochondrial energy production, mitochondrial transport and dynamics, antioxidative defense and glutamate clearance, while attenuating the CSIS-increased glycolytic pathway and cytoskeleton organization proteins expression and decreased the expression of proteins involved in V-ATPase and vesicle endocytosis. Our overall findings revealed that synaptic vesicle dynamics, specifically exocytosis, and mitochondria-related energy processes might be key biological pathways modulated by the effective nootropic and antidepressant treatment with Tian and be a potential target for therapeutic efficacy of the stress-related mood disorders.

Caveolin-1 deficiency impairs synaptic transmission in hippocampal neurons

In addition to providing structural support, caveolin-1 (Cav1), a component of lipid rafts, including caveolae, in the plasma membrane, is involved in various cellular mechanisms, including signal transduction. Although pre-synaptic membrane dynamics and trafficking are essential cellular processes during synaptic vesicle exocytosis/synaptic transmission and synaptic vesicle endocytosis/synaptic retrieval, little is known about the involvement of Cav1 in synaptic vesicle dynamics. Here we demonstrate that synaptic vesicle exocytosis is significantly impaired in Cav1–knockdown (Cav1–KD) neurons. Specifically, the size of the synaptic recycled vesicle pool is modestly decreased in Cav1–KD synapses and the kinetics of synaptic vesicle endocytosis are somewhat slowed. Notably, neurons rescued by triple mutants of Cav1 lacking palmitoylation sites mutants show impairments in both synaptic transmission and retrieval. Collectively, our findings implicate Cav1 in activity-driven synaptic vesicle dynamics—both exocytosis and endocytosis—and demonstrate that palmitoylation of Cav1 is important for this activity.

Calcium-vesicles perform active diffusion in the sea urchin embryo during larval biomineralization

ABSTRACTBiomineralization is the process by which organisms use minerals to harden their tissues and provide them with physical support. Biomineralizing cells concentrate the mineral in vesicles that they secret into a dedicated compartment where crystallization occurs. The dynamics of mineral-vesicle motion and the molecular mechanisms that regulate it, are not well understood. Sea urchin larval skeletogenesis provides an excellent platform for the analyses of vesicle kinetics. Here we used calcein labeling and lattice light-sheet microscopy to investigate the three-dimensional (3D) vesicle dynamics in control sea urchin embryos and in Vascular Endothelial Growth Factor Receptor (VEGFR) inhibited embryos, where skeletogenesis is blocked. We developed computational tools for displaying 3D-volumetric movies and for automatically quantifying vesicle dynamics in the different embryonic tissues. Our findings imply that calcium vesicles perform an active diffusion motion in all the cells of the embryo. This mode of diffusion is defined by the mechanical properties of the cells and the dynamic rearrangements of the cytoskeletal network. The diffusion coefficient is larger in the mesenchymal skeletogenic cells compared to the epithelial ectodermal cells, possibly due to the distinct mechanical properties of the two tissues. Vesicle motion is not directed toward the biomineralization compartment, but the vesicles slow down when they approach it, and probably bind for mineral deposition. Under VEGFR inhibition, vesicle volume increases and vesicle speed is reduced but the vesicles continue in their diffusive motion. Overall, our studies provide an unprecedented view of calcium vesicle 3D-dynamics and illuminate possible molecular mechanisms that control vesicle dynamics and deposition.Authors summaryBiomineralization is a widespread, fundamental process by which organisms use minerals to harden their tissues. Mineral bearing vesicles were observed in biomineralizing cells and believed to play an essential role in biomineralization, yet little is known about their three-dimensional (3D) dynamics. Here we quantify 3D-vesicle-dynamics during skeleton formation in sea urchin larvae, using lattice-light-sheet microscopy. We discover that calcium vesicles perform an active diffusive motion in both calcifying and non-calcifying cells of the embryo. The motion of the vesicles in the calcifying skeletogenic cells, is not directed toward the biomineralization compartment and has a diffusion coefficient of ~0.01μm2/sec and average speed of ~0.09μm/sec. The inhibition of Vascular Endothelial Growth Factor Receptor (VEGFR) that blocks skeletogenesis, increases vesicle volume and decreases vesicle speed but doesn’t change the diffusion mode in the embryo cells. Our studies reveal the diffusive motion of mineral bearing vesicles and have implications on basic and translational research.