[Abstract unavailable

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca2؉ -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. Increases in cytosolic Ca2ϩ regulate a myriad of cellular functions including information processing in the central nervous system (1). In many cells, these increases can be driven by mobilization of intracellular Ca 2ϩ stores (2). Much attention has focused on the endoplasmic reticulum as a Ca 2ϩ store (3), but accumulating evidence also implicates acidic organelles such as lysosomes in the control of Ca 2ϩ dynamics (4). In particular, NAADP 2 has emerged as a novel intracellular Ca 2ϩ -mobilizing messenger that links cell surface stimulation to the release of Ca 2ϩ from acidic Ca 2ϩ stores (5). Changes in the concentration of cytosolic Ca 2ϩ in glial cells are key for bidirectional control of neuronal activity (1). Previous studies have shown that extracellular application of NAADP can evoke Ca 2ϩ signals in astrocytes, consistent with a messenger role for NAADP in this cell type, following its internalization (6). Interpretation of these results, however, is clouded by the demonstrated lack of specificity with respect to related nucleotides (6) and by the potential activation by NAADP of cell surface purinergic receptors (7). Whether NAADP acts as an intracellular messenger in astrocytes is therefore unclear.Although the role of inositol trisphosphate and ryanodine receptors is established in mediating Ca 2ϩ release from the ER in response to inositol trisphosphate and cyclic ADP-ribose, respectively (2), the molecular basis for Ca 2ϩ release by NAADP from acidic organelles is less certain (8). In a series of recent studies, however, a novel family of Ca 2ϩ channels, known as the two-pore channels (TPCs), have emerged as likely targets (9). Thus, TPCs localize to endosomes and/or lysosomes through an identified targeting motif and enhance NAADPmediated cytosolic Ca 2ϩ signals when overexpressed (10 -12). Inhibition of TPC expression/function using siRNA (10), TPC knock-out mice (11), or a dominant-negative TPC construct (10) reduces NAADP-evoked Ca 2ϩ signals, and biophysical analyses indicate that TPCs are NAADP-gated Ca 2ϩ -permeable channels (13). Moreover, a functional role for TPCs has been identified in events such ...

Cancer is a leading cause of death worldwide, and its incidence is continually increasing. Although anticancer therapy has improved significantly, it still has limited efficacy for tumor eradication and is highly toxic to healthy cells. Thus, novel therapeutic strategies to improve chemotherapy, radiotherapy and targeted therapy are an important goal in cancer research. Macroautophagy (herein referred to as autophagy) is a conserved lysosomal degradation pathway for the intracellular recycling of macromolecules and clearance of damaged organelles and misfolded proteins to ensure cellular homeostasis. Dysfunctional autophagy contributes to many diseases, including cancer. Autophagy can suppress or promote tumors depending on the developmental stage and tumor type, and modulating autophagy for cancer treatment is an interesting therapeutic approach currently under intense investigation. Nutritional restriction is a promising protocol to modulate autophagy and enhance the efficacy of anticancer therapies while protecting normal cells. Here, the description and role of autophagy in tumorigenesis will be summarized. Moreover, the possibility of using fasting as an adjuvant therapy for cancer treatment, as well as the molecular mechanisms underlying this approach, will be presented.

A better understanding of Ca(2+) signaling and molecular aging alterations is important for preventing apoptosis in age-related diseases. In addition, caloric restriction, resveratrol and autophagy modulation appear to be predominantly cytoprotective, and further studies of this process are promising in age-related disease therapeutics.

Neurodegenerative diseases like Alzheimer’s disease, Parkinson’s disease and Huntington’s disease manifest with the neuronal accumulation of toxic proteins. Since autophagy upregulation enhances the clearance of such proteins and ameliorates their toxicities in animal models, we and others have sought to re-position/re-profile existing compounds used in humans to identify those that may induce autophagy in the brain. A key challenge with this approach is to assess if any hits identified can induce neuronal autophagy at concentrations that would be seen in humans taking the drug for its conventional indication. Here we report that felodipine, an L-type calcium channel blocker and anti-hypertensive drug, induces autophagy and clears diverse aggregate-prone, neurodegenerative disease-associated proteins. Felodipine can clear mutant α-synuclein in mouse brains at plasma concentrations similar to those that would be seen in humans taking the drug. This is associated with neuroprotection in mice, suggesting the promise of this compound for use in neurodegeneration.

No abstract

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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 Ca2+ 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 Ca2+ signalling glutamate-mediated can control the cell metabolism in the central nervous system.