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// Gustavo J. S. Pereira 1 , Manuela Antonioli 2, 3 , Hanako Hirata 1 , Rodrigo P. Ureshino 1 , Aline R. Nascimento 1 , Claudia Bincoletto 1 , Tiziana Vescovo 3 , Mauro Piacentini 2, 3 , Gian Maria Fimia 3, 4 , Soraya S. Smaili 1 1 Department of Pharmacology, Federal University of Sao Paulo, (UNIFESP), Sao Paulo, Brazil 2 Department of Biology, University of Rome “Tor Vergata”, Rome, Italy 3 Department of Epidemiology and Preclinical Research, National Institute for Infectious Diseases IRCCS 'Lazzaro Spallanzani', Rome, Italy 4 Department of Biological and Environmental Sciences and Technologies (DiSTeBA), University of Salento, Lecce, Italy Correspondence to: Soraya S. Smaili, email: ssmaili@unifesp.br Gian Maria Fimia, email: gianmaria.fimia@inmi.it Keywords: autophagy, glutamate, NAADP, two-pore channels, AMPK Received: August 20, 2016 Accepted: December 27, 2016 Published: December 31, 2016 ABSTRACT NAADP (nicotinic acid adenine dinucleotide phosphate) has been proposed as a second messenger for glutamate in neuronal and glial cells via the activation of the lysosomal Ca 2+ channels TPC1 and TPC2. However, the activities of glutamate that are mediated by NAADP remain unclear. In this study, we evaluated the effect of glutamate on autophagy in astrocytes at physiological, non-toxic concentration. We found that glutamate induces autophagy at similar extent as NAADP. By contrast, the NAADP antagonist NED-19 or SiRNA-mediated inhibition of TPC1/2 decreases autophagy induced by glutamate, confirming a role for NAADP in this pathway. The involvement of TPC1/2 in glutamate-induced autophagy was also confirmed in SHSY5Y neuroblastoma cells. Finally, we show that glutamate leads to a NAADP-dependent activation of AMPK, which is required for autophagy induction, while mTOR activity is not affected by this treatment. Taken together, our results indicate that glutamate stimulates autophagy via NAADP/TPC/AMPK axis, providing new insights of how Ca 2+ signalling glutamate-mediated can control the cell metabolism in the central nervous system.

Nicotinic acid adenine dinucleotide phosphate (NAADP) has been identified as an important modulator of Ca(2+) release from the endo-lysosomal system in a variety of cells by a new and ubiquitous class of endo-lysosomal ion channels known as the two-pore channels (TPCs). However, the role of TPCs in NAADP action in smooth muscle is not known. In the present work, we investigated the effects of NAADP in gastric smooth muscle cells and its ability to release Ca(2+) by TPCs. We show that Ca(2+) signals mediated by NAADP were inhibited by disrupting Ca(2+) handling by either acidic organelles (using bafilomycin A1) or the Endoplasmic Reticulum (using thapsigargin, ryanodine or 2-APB). Transcripts for endogenous TPC1 and TPC2 were readily detected and recombinant TPCs localized to the endosomes and/or lysosomes. Overexpression of wild-type TPCs but not pore mutants enhanced NAADP-mediated cytosolic Ca(2+) signals. Desensitizing the NAADP pathway inhibited Ca(2+)-responses to extracellular stimulation with carbachol but not ATP. Taken together, these results indicate that NAADP likely induces Ca(2+) release from the endolysosomal system through TPCs which is subsequently amplified via the ER in an agonist-specific manner. Thus, we suggest a second messenger role for NAADP in smooth muscle cells.

Endoplasmic reticulum (ER) and mitochondria are intracellular organelles and their interactions are directly involved in different processes such as Ca(2+) signaling in cell survival and death mechanisms. Bcl-2 is an anti-apoptotic protein intrinsically related to ER and mitochondria, modulating Ca(2+) content in these organelles. We investigated the effects of Bcl-2 overexpression on ER and mitochondrial Ca(2+) dynamics in PC12 cells. Bcl-2 overexpressing and control cells were loaded with Fura 2/AM and stimulated with different drugs. Results showed that in Bcl-2 cells, ACh induced a lower Ca(2+) response compared to control. Ca(2+) release induced by TG was decreased in Bcl-2 cells, however, it was greater in Caff induced Ca(2+) rise. In addition, FCCP induced a higher Ca(2+) release in Bcl-2 cells. These results suggest that Bcl-2 overexpression modulate the ER Ca(2+) pools differently and the release of ER Ca(2+) may increase mitochondrial Ca(2+) accumulation. These alterations of intracellular Ca(2+) stores are important mechanisms for the control of Ca(2+) signaling.

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca(2+)-mobilizing messenger that in many cells releases Ca(2+) from the endolysosomal system. Recent studies have shown that NAADP-induced Ca(2+) mobilization is mediated by the two-pore channels (TPCs). Whether NAADP acts as a messenger in astrocytes is unclear, and downstream functional consequences have yet to be defined. Here, we show that intracellular delivery of NAADP evokes Ca(2+) signals from acidic organelles in rat astrocytes and that these signals are potentiated upon overexpression of TPCs. We also show that NAADP increases acidic vesicular organelle formation and levels of the autophagic markers, LC3II and beclin-1. NAADP-mediated increases in LC3II levels were reduced in cells expressing a dominant-negative TPC2 construct. Our data provide evidence that NAADP-evoked Ca(2+) signals mediated by TPCs regulate autophagy.

Apoptosis is a highly complex form of cell death that can be triggered by alterations in Ca(2+) homeostasis. Members of the Bcl-2 family may regulate apoptosis and modulate Ca(2+) distribution within intracellular compartments. Bax, a proapoptotic member of the family, is constitutively expressed and soluble in the cytosol and, under apoptotic induction, translocates to mitochondrial membranes. However, it is not clear if the intracellular Ca(2+) stores and selective Ca(2+) releases can modulate or control Bax translocation. The aim of this study was to investigate the relation of intracellular Ca(2+) stores with Bax translocation in rat cortical astrocytes. Results show that the classical apoptotic inducer, staurosporine, caused high elevations of cytosolic Ca(2+) that precede Bax translocation. On the other hand, agents that mobilize Ca(2+) from endoplasmic reticulum such as noradrenaline or thapsigargin, induced Bax translocation, while mitochondrial Ca(2+) release evoked by carbonyl cyanide-p-(trifluoromethoxyphenyl) hydrazone was not able to cause Bax punctation. In addition, microinjection of inositol 1,4,5- trisphosphate induced Bax translocation. Taken together, our results show that in Bax overexpressing cortical astrocytes, endoplasmic reticulum-Ca(2+) release may induce Bax transactivation and specifically control apoptosis.

In this study, we investigated agents that increased intracellular calcium levels and their correlation with apoptotic cell death induction. We used rat astrocytes to investigate the increase in cytosolic Ca 2+ (Ca c 2+ ) and apoptosis induction by drugs that mobilize Ca 2+ from different sources. We observed that thapsigargin (Thap), caffeine (Caff) and FCCP which caused similar increases in Ca c 2+ levels (30–40%), also induced similar apoptotic rates (30–35%). On the other hand, antimycin (Anti), staurosporine (STS) and ethanol (Eth) promoted higher increases in Ca c 2+ (55–65 %) and higher apoptotic rates (55–85%). Eth induced cell death in a concentration- and time-dependent manner. After treatment with Eth plus Caff for 6, 12 and 24 h, these effects were strongly potentiated. Results suggest that there might be a correlation between Ca c 2+ increase and the rate of apoptosis. It is possible that Eth induces cell death by activation of more than one pathway and Ca 2+ might be one of the elements involved. The present work indicates that Ca 2+ can potentiate death by ethanol in rat astrocytes.

The influence of castration (30-90 days) on the effects of ATP, noradrenaline (Nor), and carbachol (CCh) were examined in prostatic and epididymal portions of the rat vas deferens. All agonist-induced contractions were greatly increased in the prostatic and suppressed in the epididymal portion of the vas deferens from castrated rats, as compared with those in preparations from normal animals. Responses to Nor showed a typical cumulative dose–effect curve, with an additional twitch at the minimal dose. Responses to CCh were paradoxically changed; the maximum of twitch responses was observed at threshold concentrations (10-7 to 3 · 10-7 M), and decreased at higher concentrations. In the threshold concentration (10-7 M), ATP induced almost maximal responses in a non-cumulative manner. All agonist-induced responses were blocked by isradipine (10-7 M) and increased by pretreatment with reserpine. In normal animals, injection of testosterone insignificantly decreased responses to all agonists. The ratio of the amplitude of high-potassium (80 mM)-induced contractions (mm) to the tissue wet mass (per mg) in preparations from castrated animals also showed oppositely directed modulation of the responses, as compared with that in normal animals. It is suggested that the lack of hormone modifies a negative feedback mechanism of elevation of the intracellular Ca2+ concentration, which exists in normal rats mostly in the prostatic portion and is the reason for regional variation along the vas deferens, to a positive feedback link amplified in castrates.

The inward currents in single smooth muscle cells (SMC) isolated from epididymal part of rat vas deferens have been studied using whole-cell patch-clamp method. Depolarising steps from holding potential -90 mV evoked inward current with fast and slow components. The component with slow activation possessed voltage-dependent and pharmacological properties characteristic for Ca(2+) current carried through L-type calcium channels (I(Ca)). The fast component of inward current was activated at around -40 mV, reached its peak at 0 mV, and disappeared upon removal of Na ions from bath solution. This current was blocked in dose-dependent manner by tetrodotoxin (TTX) with an apparent dissociation constant of 6.7 nM. On the basis of voltage-dependent characteristics, TTX sensitivity of fast component of inward current and its disappearance in Na-free solution it is suggested that this current is TTX-sensitive depolarisation activated sodium current (I(Na)). Cell dialysis with a pipette solution containing no macroergic compounds resulted in significant inhibition of I(Ca) (depression of peak I(Ca) by about 81% was observed by 13 min of dialysis), while I(Na) remained unaffected during 50 min of dialysis. These data draw first evidence for the existence of TTX-sensitive Na(+) current in single SMC isolated from rat vas deferens. These Na(+) channels do not appear to be regulated by a phosphorylation process under resting conditions.

Experiments were performed with rat vas deferens to verify whether agmatine, an endogenous ligand for adrenoceptors and imidazoline receptors, can influence sympathetic neurotransmission, with respect to contractions induced by transmural nerve stimulation, contractions induced by exogenous noradrenaline, and overflow of endogenous noradrenaline. It was shown that agmatine (a) caused a dose-dependent potentiation of electrically induced twitches, up to about 70% in relation to controls, (b) shifted to the right the inhibitory concentration-response curves for clonidine on electrically induced twitches, indicating competitive antagonism at presynaptic α-adrenoceptors, with a pA 2 value of 4.12 ± 0.10, (c) shifted to the right the concentration-response curves for noradrenaline-induced contractions, indicating competitive antagonism at postsynaptic α-adrenoceptors as well, with a pA 2 value of 4.03 ± 0.10, and (d) caused a dose-dependent increase of KCl-induced overflow of noradrenaline, up to about 90% in relation to controls. It is concluded that agmatine has multiple effects on sympathetic neurotransmission in rat vas deferens.