Molecular Machines Determining the Fate of Endocytosed Synaptic Vesicles in Nerve Terminals

The cycle of a synaptic vesicle (SV) within the nerve terminal is a step-by-step journey with the final goal of ensuring the proper synaptic strength under changing environmental conditions. The SV cycle is a precisely regulated membrane traffic event in cells and, because of this, a plethora of membrane-bound and cytosolic proteins are devoted to assist SVs in each step of the journey. The cycling fate of endocytosed SVs determines both the availability for subsequent rounds of release and the lifetime of SVs in the terminal and is therefore crucial for synaptic function and plasticity. Molecular players that determine the destiny of SVs in nerve terminals after a round of exo-endocytosis are largely unknown. Here we review the functional role in SV fate of phosphorylation/dephosphorylation of SV proteins and of small GTPases acting on membrane trafficking at the synapse, as they are emerging as key molecules in determining the recycling route of SVs within the nerve terminal. In particular, we focus on: (i) the cyclin-dependent kinase-5 (cdk5) and calcineurin (CN) control of the recycling pool of SVs; (ii) the role of small GTPases of the Rab and ADP-ribosylation factor (Arf) families in defining the route followed by SV in their nerve terminal cycle. These regulatory proteins together with their synaptic regulators and effectors, are molecular nanomachines mediating homeostatic responses in synaptic plasticity and potential targets of drugs modulating the efficiency of synaptic transmission

Arf6 regulates the cycling and the readily releasable pool of synaptic vesicles at hippocampal synapse.

Recycling of synaptic vesicles (SVs) is a fundamental step in the process of neurotransmission. Endocytosed SV can travel directly into the recycling pool or recycle through endosomes but little is known about the molecular actors regulating the switch between these SV recycling routes. ADP ribosylation factor 6 (Arf6) is a small GTPase known to participate in constitutive trafficking between plasma membrane and early endosomes. Here, we have morphologically and functionally investigated Arf6-silenced hippocampal synapses and found an activity dependent accumulation of synaptic endosome-like organelles and increased releasecompetent docked SVs. These features were phenocopied by pharmacological blockage of Arf6 activation. The data reveal an unexpected role for this small GTPase in reducing the size of the readily releasable pool of SVs and in channeling retrieved SVs toward direct recycling rather than endosomal sorting. We propose that Arf6 acts at the presynapse to define the fate of an endocytosed SV

Neuronal hyperactivity causes Na+/H+ exchanger-induced extracellular acidification at active synapses

Extracellular pH impacts on neuronal activity, which is in turn an important determinant of extracellular H+ concentration. The aim of this study is to describe the spatio-temporal dynamics of extracellular pH at synaptic sites during neuronal hyperexcitability. To address this issue we created ex.E2GFP, a membrane-targeted extracellular ratiometric pH indicator exquisitely sensitive to acidic shifts. By monitoring ex.E2GFP fluorescence in real time in primary cortical neurons we were able to quantify pH fluctuations during network hyperexcitability induced by convulsant drugs or high frequency electrical stimulation. Sustained hyperactivity caused a pH decrease that was reversible upon silencing of neuronal activity and localized to active synapses. This acidic shift was not attributable to the outflow of synaptic vesicle protons into the cleft nor to the activity of membrane-exposed H+-vATPase, but rather to the activity of the Na+/H+-exchanger. Our data demonstrate that extracellular synaptic pH shifts take place during epileptic-like activity of neural cultures, underlying the strict links existing between synaptic activity and synaptic pH. This evidence may contribute to the understanding of the physio-pathological mechanisms associated with hyperexcitability in the epileptic brain

effects of occupational exposure to glyphosate in winegrowers

Glyphosate is a non-selective systemic herbicide used in agriculture. For almost half a century, the International Agency for Research on Cancer has run a Monographs program, the conclusion in March 2015 that glyphosate is "probably carcinogenic to humans" in addition to being genotoxic and carcinogenic in animals, while the regulatory European Food Safety Authority have asserted that glyphosate poses no public risk. The scientific debate is still lively. We collected detailed socio-demographic, occupational exposures and health surveillance information for 26 winegrowers as aim to investigate exposure to glyphosate and other pesticide. Exposure was assessed through biological monitoring (24-hour urine collection), immune function (IL-4, IL-5, IL-8, IL-12, IL- 17, IL-33, IFN- γ), transcriptional and post transcriptional alterations (miRNA) and genotoxic effects (Comet assay). The exposure conditions in our winegrowers, as referred to the parameters so far analyzed, did not reveal a significant glyphosate absorption nor significant health concerns

Effects of the fermentation process on gas-cell size two-dimensional distribution and rheological characteristics of durum-wheat-based doughs

In this study, the effects of baker's yeast and sourdough fermentation on gas-cell size distribution and height of leavened doughs were evaluated in eight durum-wheat-based doughs of different strengths. Furthermore, the chemical and rheological properties of the doughs were analyzed to determine their effects on the leavening process. The gas-cell size distribution was modeled by a log-normal distribution across the full range of gas-cell sizes (10− 4 to 102 mm2), and by a power-law distribution for the large gas cells. The power law α exponent analysis of variance showed that α distinguished between the two empirical distributions, which indicated that there were more larger cells in the sourdough samples than in the baker's yeast samples. The distribution of the small-to-medium gas cells was the same for the two processes, as indicated by the log-normal parameters. The leavened dough height was generally higher for the baker's yeast dough samples, compared to the sourdough samples, except in the case of samples with very strong and elastic gluten

Identification of Mycobacterium avium subsp. paratuberculosis in Biopsy Specimens from Patients with Crohn's Disease Identified by In Situ Hybridization

Crohn's disease is a chronic inflammatory disease of the gastrointestinal tract of unknown etiology. We report on the presence of cell wall-deficient Mycobacterium avium subsp. paratuberculosis in 35 of 48 paraffin-embedded tissue specimens from 33 patients with Crohn's disease by in situ hybridization with IS900 as a probe

<i>Mycobacterium avium</i> sub. <i>paratuberculosis</i> in tissue samples of Crohn's disease patients

Crohn's disease is a non-specific chronic transmural inflammatory disease. The disease was associated with a frameshit mutation in the NOD2 gene. Nevertheless, other researchers associated the presence of M. paratuberculosis within the intestinal tissues of patients with the disease. An adapted "in situ hybridization" technique was used to detect IS900 M. paratuberculosis DNA in paraffin embedded tissue from Crohns tissue disease samples. We were able to identify M. paratuberculosis DNA in around 69% of the paraffine embedded intestinal samples of Crohn's disease patients analysed. The presence of M. paratuberculosis DNA in the intestinal samples analysed does not necessarily mean that M. paratuberculosis is responsible for Crohn's disease. Our results support the hypothesis that infection may be caused by cell wall defective M. paratuberculosis since no bacteria were detected by Ziehl Neelsen stain