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The Toll/interleukin-1 receptor (TIR) domain is a canonical component of animal and plant immune systems 1 , 2 . In plants, intracellular pathogen sensing by immune receptors triggers their TIR domains to generate a molecule that is a variant of cyclic ADP-ribose 3 , 4 . This molecule is hypothesized to mediate plant cell death through a pathway that has yet to be resolved 5 . TIR domains have also been shown to be involved in a bacterial anti-phage defence system called Thoeris 6 , but the mechanism of Thoeris defence remained unknown. Here we show that phage infection triggers Thoeris TIR-domain proteins to produce an isomer of cyclic ADP-ribose. This molecular signal activates a second protein, ThsA, which then depletes the cell of the essential molecule nicotinamide adenine dinucleotide (NAD) and leads to abortive infection and cell death. We also show that, similar to eukaryotic innate immune systems, bacterial TIR-domain proteins determine the immunological specificity to the invading pathogen. Our results describe an antiviral signalling pathway in bacteria, and suggest that the generation of intracellular signalling molecules is an ancient immunological function of TIR domains that is conserved in both plant and bacterial immunity. The mechanism of Thoeris—a bacterial anti-phage defence system—is described in detail, revealing that bacterial TIR-domain proteins recognize infection and produce signalling molecules to execute cell death, akin to the roles of these proteins in plants.

Plant nucleotide-binding leucine-rich repeat (NLR) immune receptors activate cell death and confer disease resistance by unknown mechanisms. We demonstrate that plant Toll/interleukin-1 receptor (TIR) domains of NLRs are enzymes capable of degrading nicotinamide adenine dinucleotide in its oxidized form (NAD⁺). Both cell death induction and NAD⁺ cleavage activity of plant TIR domains require known self-association interfaces and a putative catalytic glutamic acid that is conserved in both bacterial TIR NAD⁺-cleaving enzymes (NADases) and the mammalian SARM1 (sterile alpha and TIR motif containing 1) NADase. We identify a variant of cyclic adenosine diphosphate ribose as a biomarker of TIR enzymatic activity. TIR enzymatic activity is induced by pathogen recognition and functions upstream of the genes enhanced disease susceptibility 1 (EDS1) and N requirement gene 1 (NRG1), which encode regulators required for TIR immune function. Thus, plant TIR-NLR receptors require NADase function to transduce recognition of pathogens into a cell death response.

There are eight thermosensitive TRP (transient receptor potential) channels in mammals, and there might be other TRP channels sensitive to temperature stimuli. Here, we demonstrate that TRPM2 can be activated by exposure to warm temperatures (>35°C) apparently via direct heat‐evoked channel gating. β‐NAD + ‐ or ADP‐ribose‐evoked TRPM2 activity is robustly potentiated at elevated temperatures. We also show that, even though cyclic ADP‐ribose (cADPR) does not activate TRPM2 at 25°C, co‐application of heat and intracellular cADPR dramatically potentiates TRPM2 activity. Heat and cADPR evoke similar responses in rat insulinoma RIN‐5F cells, which express TRPM2 endogenously. In pancreatic islets, TRPM2 is coexpressed with insulin, and mild heating of these cells evokes increases in both cytosolic Ca 2+ and insulin release, which is K ATP channel‐independent and protein kinase A‐mediated. Heat‐evoked responses in both RIN‐5F cells and pancreatic islets are significantly diminished by treatment with TRPM2‐specific siRNA. These results identify TRPM2 as a potential molecular target for cADPR, and suggest that TRPM2 regulates Ca 2+ entry into pancreatic β‐cells at body temperature depending on the production of cADPR‐related molecules, thereby regulating insulin secretion.

Sleep apnea syndrome is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia [IH]), and it is a known risk factor for hypertension. The upregulation of the renin-angiotensin system has been reported in IH, and the correlation between renin and CD38 has been noted. We exposed human HEK293 and mouse As4.1 renal cells to experimental IH or normoxia for 24 h and then measured the mRNA levels using a real-time reverse transcription polymerase chain reaction. The mRNA levels of Renin (Ren) and Cd38 were significantly increased by IH, indicating that they could be involved in the CD38-cyclic ADP-ribose signaling pathway. We next investigated the promotor activities of both genes, which were not increased by IH. Yet, a target mRNA search of the microRNA (miRNA) revealed both mRNAs to have a potential target sequence for miR-203. The miR-203 level of the IH-treated cells was significantly decreased when compared with the normoxia-treated cells. The IH-induced upregulation of the genes was abolished by the introduction of the miR-203 mimic, but not the miR-203 mimic NC negative control. These results indicate that IH stress downregulates the miR-203 in renin-producing cells, thereby resulting in increased mRNA levels of Ren and Cd38, which leads to hypertension.

Cyclic adenosine 5′-diphosphate ribose (cADPR) is an emerging Ca 2+ -mobilising second messenger. cADPR analogues have been generated as chemical biology tools via both chemo-enzymatic and total synthetic routes. Both routes rely on the cyclisation of a linear precursor to close an 18-membered macrocyclic ring. We show here that, after cyclisation, there are two possible macrocyclic product conformers that may be formed, depending on whether cyclisation occurs to the “right” or the “left” of the adenine base (as viewed along the H-8 → C-8 base axis). Molecular modelling demonstrates that these two conformers are distinct and cannot interconvert. The two conformers would present a different spatial layout of binding partners to the cADPR receptor/binding site. For chemo-enzymatically generated analogues Aplysia californica ADP-ribosyl cyclase acts as a template to generate solely the “right-handed” conformer and this corresponds to that of the natural messenger, as originally explored using crystallography. However, for a total synthetic analogue it is theoretically possible to generate either product, or a mixture, from a given linear precursor. Cyclisation on either face of the adenine base is broadly illustrated by the first chemical synthesis of the two enantiomers of a “southern” ribose-simplified cIDPR analogue 8-Br- N 9-butyl-cIDPR, a cADPR analogue containing only one chiral sugar in the “northern” ribose, i.e. 8-Br-D- and its mirror image 8-Br-L- N 9-butyl-cIDPR. By replacing the D-ribose with the unnatural L-ribose sugar, cyclisation of the linear precursor with pyrophosphate closure generates a cyclised product spectroscopically identical, but displaying equal and opposite specific rotation. These findings have implications for cADPR analogue design, synthesis and activity.

Herein proteomic profiling of the rat hippocampus from the kindling and pilocarpine models of epilepsy was performed to achieve new potential targets for treating epileptic seizures. A total of 144 differently expressed proteins in both left and right hippocampi by two-dimensional electrophoresis coupled to matrix-assisted laser desorption-mass spectrometry were identified across the rat models of epilepsy. Based on network analysis, the majority of differentially expressed proteins were associated with Ca 2+ homeostasis. Changes in ADP-ribosyl cyclase (ADPRC), lysophosphatidic acid receptor 3 (LPAR3), calreticulin, ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1), synaptosomal nerve-associated protein 25 (SNAP 25) and transgelin 3 proteins were probed by Western blot analysis and validated using immunohistochemistry. Inhibition of calcium influx by 8-Bromo-cADP-Ribose (8-Br-cADPR) and 2-Aminoethyl diphenylborinate (2-APB) which act via the ADPRC and LPAR3, respectively, attenuated epileptic seizures. Considering a wide range of molecular events and effective role of calcium homeostasis in epilepsy, polypharmacy with multiple realistic targets should be further explored to reach the most effective treatments.

A plethora of cellular functions are controlled by calcium signals, that are greatly coordinated by calcium release from intracellular stores, the principal component of which is the sarco/endooplasmic reticulum (S/ER). In 1997 it was generally accepted that activation of various G protein-coupled receptors facilitated inositol-1,4,5-trisphosphate (IP3) production, activation of IP3 receptors and thus calcium release from S/ER. Adding to this, it was evident that S/ER resident ryanodine receptors (RyRs) could support two opposing cellular functions by delivering either highly localised calcium signals, such as calcium sparks, or by carrying propagating, global calcium waves. Coincidentally, it was reported that RyRs in mammalian cardiac myocytes might be regulated by a novel calcium mobilising messenger, cyclic adenosine diphosphate-ribose (cADPR), that had recently been discovered by HC Lee in sea urchin eggs. A reputedly selective and competitive cADPR antagonist, 8-bromo-cADPR, had been developed and was made available to us. We used 8-bromo-cADPR to further explore our observation that S/ER calcium release via RyRs could mediate two opposing functions, namely pulmonary artery dilation and constriction, in a manner seemingly independent of IP3Rs or calcium influx pathways. Importantly, the work of others had shown that, unlike skeletal and cardiac muscles, smooth muscles might express all three RyR subtypes. If this were the case in our experimental system and cADPR played a role, then 8-bromo-cADPR would surely block one of the opposing RyR-dependent functions identified, or the other, but certainly not both. The latter seemingly implausible scenario was confirmed. How could this be, do cells hold multiple, segregated SR stores that incorporate different RyR subtypes in receipt of spatially segregated signals carried by cADPR? The pharmacological profile of 8-bromo-cADPR action supported not only this, but also indicated that intracellular calcium signals were delivered across intracellular junctions formed by the S/ER. Not just one, at least two. This article retraces the steps along this journey, from the curious pharmacological profile of 8-bromo-cADPR to the discovery of the cell-wide web, a diverse network of cytoplasmic nanocourses demarcated by S/ER nanojunctions, which direct site-specific calcium flux and may thus coordinate the full panoply of cellular processes.

The CD38/cyclic ADP-ribose (cADPR) pathway plays a role in various central nervous system diseases and in morphine tolerance, but its role in local anesthetic intoxication is unknown. The aim of this study was to determine the role of the CD38/cADPR pathway in ropivacaine-induced convulsion. Forty male Sprague-Dawley rats were randomly divided into five groups (n = 8 per group): sham group, ropivacaine group, ropivacaine+8-Br-cADPR (5 nmol) group, ropivacaine+8-Br-cADPR (10 nmol) group, and ropivacaine+8-Br-cADPR (20 nmol) group (no rats died). Rats were intracerebroventricularly injected with normal saline or 8-Br-cADPR 30 min before receiving an intraperitoneal injection of ropivacaine. Electroencephalography and convulsion behavior scores were recorded. The hippocampus was harvested from each group and subjected to nicotinamide adenine dinucleotide and cADPR assays, Western blotting analysis, and malondialdehyde (MDA) and superoxide dismutase (SOD) assays. Intraperitoneal injection of ropivacaine (33.8 mg/kg) induced convulsions in rats. CD38 and cADPR levels increased significantly following ropivacaine-induced convulsion (P = 0.031 and 0.020, respectively, compared with the sham group). Intraventricular injection of 8-Br-cADPR (5, 10, and 20 nmol) significantly prolonged convulsion latency (P = 0.037, 0.034, and 0.000, respectively), reduced convulsion duration (P = 0.005, 0.005, and 0.005, respectively), and reduced convulsion behavior scores (P = 0.015, 0.015, and 0.000, respectively). Intraventricular injection of 8-Br-cADPR (10 nmol) also increased the B-cell lymphoma-2 (Bcl-2)/Bcl-2-associated X protein ratio (P = 0.044) and reduced cleaved Caspase 3/Caspase 3 ratio, inducible nitric oxide synthase, MDA and SOD levels (P = 0.014, 0.044, 0.001, and 0.010, respectively) compared with the ropivacaine group. The CD38/cADPR pathway is activated in ropivacaine-induced convulsion. Inhibiting this pathway alleviates ropivacaine-induced convulsion and protects the brain from apoptosis and oxidative stress.

The wrong kind of hormone? Calcium signalling plays an important role in determining the virulence of the human pathogen Toxoplasma gondii , an apicomplexan protozoon. A study of the mechanisms involved has uncovered a surprising agent for this signalling: the plant hormone abscisic acid. Comparative genomics reveals that the pathway for synthesis of the plant hormone was acquired by endosymbiosis. This pathway controls a crucial developmental switch between lytic growth and dormancy, which is a key component of pathogenesis. The plant-like nature of this pathway may be exploited to develop new therapeutics as shown by the ability of a specific inhibitor of abscisic acid biosynthesis to protect mice from lethal infection. Calcium signalling is important for apicomplexan parasite virulence. A newly discovered calcium signalling pathway based on the plant hormone abscisic acid is now reported in Toxoplasma gondii . As this pathway is absent in most animals, it may present a new target for drug intervention. Calcium controls a number of critical events, including motility, secretion, cell invasion and egress by apicomplexan parasites 1 . Compared to animal 2 and plant cells 3 , the molecular mechanisms that govern calcium signalling in parasites are poorly understood. Here we show that the production of the phytohormone abscisic acid (ABA) controls calcium signalling within the apicomplexan parasite Toxoplasma gondii, an opportunistic human pathogen. In plants, ABA controls a number of important events, including environmental stress responses, embryo development and seed dormancy 4 , 5 . ABA induces production of the second-messenger cyclic ADP ribose (cADPR), which controls release of intracellular calcium stores in plants 6 . cADPR also controls intracellular calcium release in the protozoan parasite T. gondii 7 , 8 ; however, previous studies have not revealed the molecular basis of this pathway 9 . We found that addition of exogenous ABA induced formation of cADPR in T. gondii , stimulated calcium-dependent protein secretion, and induced parasite egress from the infected host cell in a density-dependent manner. Production of endogenous ABA within the parasite was confirmed by purification (using high-performance liquid chromatography) and analysis (by gas chromatography-mass spectrometry). Selective disruption of ABA synthesis by the inhibitor fluridone delayed egress and induced development of the slow-growing, dormant cyst stage of the parasite. Thus, ABA-mediated calcium signalling controls the decision between lytic and chronic stage growth, a developmental switch that is central in pathogenesis and transmission. The pathway for ABA production was probably acquired with an algal endosymbiont that was retained as a non-photosynthetic plastid known as the apicoplast. The plant-like nature of this pathway may be exploited therapeutically, as shown by the ability of a specific inhibitor of ABA synthesis to prevent toxoplasmosis in the mouse model.

Herein, we reported on the synthesis of cpIPP, which is a new structurally-reduced analogue of cyclic ADP-ribose (cADPR), a potent Ca2+-releasing secondary messenger that was firstly isolated from sea urchin eggs extracts. To obtain cpIPP the “northern” ribose of cADPR was replaced by a pentyl chain and the pyrophosphate moiety by a phophono-phosphate anhydride. The effect of the presence of the new phosphono-phosphate bridge on the intracellular Ca2+ release induced by cpIPP was assessed in PC12 neuronal cells in comparison with the effect of the pyrophosphate bridge of the structurally related cyclic N1-butylinosine diphosphate analogue (cbIDP), which was previously synthesized in our laboratories, and with that of the linear precursor of cpIPP, which, unexpectedly, revealed to be the only one provided with Ca2+ release properties.