Sarm1 activation produces cADPR to increase intra-axonal Ca++ and promote axon degeneration in PIPN

Cancer patients frequently develop chemotherapy-induced peripheral neuropathy (CIPN), a painful and long-lasting disorder with profound somatosensory deficits. There are no effective therapies to prevent or treat this disorder. Pathologically, CIPN is characterized by a "dying-back" axonopathy that begins at intra-epidermal nerve terminals of sensory neurons and progresses in a retrograde fashion. Calcium dysregulation constitutes a critical event in CIPN, but it is not known how chemotherapies such as paclitaxel alter intra-axonal calcium and cause degeneration. Here, we demonstrate that paclitaxel triggers Sarm1-dependent cADPR production in distal axons, promoting intra-axonal calcium flux from both intracellular and extracellular calcium stores. Genetic or pharmacologic antagonists of cADPR signaling prevent paclitaxel-induced axon degeneration and allodynia symptoms, without mitigating the anti-neoplastic efficacy of paclitaxel. Our data demonstrate that cADPR is a calcium-modulating factor that promotes paclitaxel-induced axon degeneration and suggest that targeting cADPR signaling provides a potential therapeutic approach for treating paclitaxel-induced peripheral neuropathy (PIPN).

Cyclic ADP-ribose requires CD38 to regulate the release of ATP in visceral smooth muscle

It is well established that the intracellular second messenger cADP-ribose (cADPR) activates Ca(2+) release from the sarcoplasmic reticulum through ryanodine receptors. CD38 is a multifunctional enzyme involved in the formation of cADPR in mammals. CD38 has also been reported to transport cADPR in several cell lines. Here, we demonstrate a role for extracellular cADPR and CD38 in modulating the spontaneous, but not the electrical field stimulation-evoked, release of ATP in visceral smooth muscle. Using a small-volume superfusion assay and an HPLC technique with fluorescence detection, we measured the spontaneous and evoked release of ATP in bladder detrusor smooth muscles isolated from CD38(+/+) and CD38(-/-) mice. cADPR (1 nM) enhanced the spontaneous overflow of ATP in bladders isolated from CD38(+/+) mice. This effect was abolished by the inhibitor of cADPR receptors on sarcoplasmic reticulum 8-bromo-cADPR (80 μM) and by ryanodine (50 μm), but not by the nonselective P2 purinergic receptor antagonist pyridoxal phosphate 6-azophenyl-2',4'-disulfonate (30 μM). cADPR failed to facilitate the spontaneous ATP overflow in bladders isolated from CD38(-/-) mice, indicating that CD38 is crucial for the enhancing effects of extracellular cADPR on spontaneous ATP release. Contractile responses to ATP were potentiated by cADPR, suggesting that the two adenine nucleotides may work in synergy to maintain the resting tone of the bladder. In conclusion, extracellular cADPR enhances the spontaneous release of ATP in the bladder by influx via CD38 and subsequent activation of intracellular cADPR receptors, probably causing an increase in intracellular Ca(2+) in neuronal cells.

Role of cyclic ADP-ribose-Ca2+ signaling in mediating renin production and release in As4.1 cells

The present study was designed to test the hypothesis that cyclic-ADP-ribose (cADPR) serves as a novel second messenger to mediate intracellular Ca(2+) concentration in As4.1 cells, a prototype of renal juxtaglomerular cells, and thereby regulates the renin production and release. Western blot analysis showed that CD38, an enzyme responsible for the production of cADPR, was abundant in As4.1 cells. Using cADPR cycling assay, it was found that NaCl stimulated cADPR production in these cells, which was blocked by inhibition of ADP-ribosyl cyclase with nicotinamide. HPLC analysis showed that the conversion rate of beta-NGD into cGDPR was dramatically increased by NaCl, which was attenuated by nicotinamide. Using fluorescent microscopic imaging analysis, NaCl (100 mM) was demonstrated to stimulate a rapid Ca(2+) increase from the endoplasmic reticulum (ER), which was inhibited by a cADPR antagonist, 8-bromo-cADPR (30 microM), an inhibitor of ADP-ribosyl cyclase, nicotinamide (6 mM), the ryanodine receptors blocker, ryanodine (30 microM), or a Ca(2+)-induced Ca(2+) release inhibitor, tetracaine (10 microM) by 70-90%. Finally, NaCl was found to significantly lower the renin production and release levels in As4.1 cells, which was accompanied by decreases in renin mRNA levels. Pretreatment of these cells with various inhibitors or blockers above significantly blocked the inhibitory effect of NaCl on renin production and release. These results indicate that cADPR-mediated Ca(2+) signaling pathway is present in As4.1 cells and that this signaling pathway may play a contributing role in the regulation of renin production and release.

Vascular physiology of a Ca2+ mobilizing second messenger - cyclic ADP-ribose

Cyclic ADP-ribose (cADPR) is a novel Ca(2+) mobilizing second messenger, which is capable of inducing Ca(2+) release from the sarcoplasmic reticulum (SR) via activation of ryanodine receptors (RyR) in vascular cells. This signaling nucleotide has also been reported to participate in generation or modulation of intracellular Ca(2+) sparks, Ca(2+) waves or oscillations, Ca(2+)- induced Ca(2+) release (CICR) and spontaneous transient outward currents (STOCs) in vascular smooth muscle cells (VSMCs). With respect to the role of cADPR-mediated signaling in mediation of vascular responses to different stimuli, there is accumulating evidence showing that cADPR is importantly involved in the Ca(2+) response of vascular endothelial cells (ECs) and VSMCs to various chemical factors such as vasoactive agonists acetylcholine, oxotremorine, endothelin, and physical stimuli such as stretch, electrical depolarization and sheer stress. This cADPR-RyR-mediated Ca(2+) signaling is now recognized as a fundamental mechanism regulating vascular function. Here we reviewed the literature regarding this cADPR signaling pathway in vascular cells with a major focus on the production of cADPR and its physiological roles in the control of vascular tone and vasomotor response. We also summarized some publish results that unveil the underlying mechanisms mediating the actions of cADPR in vascular cells. Given the importance of Ca(2+) in the regulation of vascular function, the results summarized in this brief review will provide new insights into vascular physiology and circulatory regulation.

Modulation of store-operated Ca2+ entry by cyclic-ADP-ribose

Store-operated Ca2+ entry plays an important role in Ca2+ homeostasis in cells but the mechanisms of control of these channels are not completely understood. We describe an investigation of the role of the CD38-cyclic-ADP-ribose (cADPR)-ryanodine-channel (RyR) signaling pathway in store-operated Ca2+ entry in human smooth muscle. We observed that human myometrial cells have a functional store-operated Ca2+ entry mechanism. Furthermore, we observed the presence of transient receptor potential 1, 3, 4, 5, and 6 ion channels in human myometrial cells. Store-operated Ca2+ transient was inhibited by at least 50-70% by several inhibitors of the RyR, including ryanodine (10 microM), dantrolene (10 microM), and ruthenium red (10 microM). Furthermore, the cell permeable inhibitor of the cADPR-system, 8-Br-cADPR (100 microM), is a potent inhibitor of the store-operated entry, decreasing the store operated entry by 80%. Pre-incubation of cells with 100 microM cADPR and the hydrolysis-resistant cADPR analog 3-deaza-cADPR (50 microM), but not with ADP-ribose (ADPR) leads to a 1.6-fold increase in the store-operated Ca2+ transient. In addition, we observed that nicotinamide (1-10 mM), an inhibitor of cADPR synthesis, also leads to inhibition of the store-operated Ca2+ transient by 50-80%. Finally, we observed that the transient receptor potential channels, RyR, and CD38 can be co-immunoprecipitated, indicating that they interact in vivo. Our observations clearly implicate the CD38-cADPR-ryanodine signaling pathway in the regulation of store-operated Ca2+ entry in human smooth muscle cells.

Evidence that the cADPR signalling pathway controls calcium-mediated microneme secretion in Toxoplasma gondii

The protozoan parasite Toxoplasma gondii relies on calcium-mediated exocytosis to secrete adhesins on to its surface where they can engage host cell receptors. Increases in intracellular calcium occur in response to Ins(1,4,5)P3 and caffeine, an agonist of ryanodine-responsive calcium-release channels. We examined lysates and microsomes of T. gondii and detected evidence of cADPR (cyclic ADP ribose) cyclase and hydrolase activities, the two enzymes that control the second messenger cADPR, which causes calcium release from RyR (ryanodine receptor). We also detected endogenous levels of cADPR in extracts of T. gondii. Furthermore, T. gondii microsomes that were loaded with 45Ca2+ released calcium when treated with cADPR, and the RyR antagonists 8-bromo-cADPR and Ruthenium Red blocked this response. Although T. gondii microsomes also responded to Ins(1,4,5)P3, the inhibition profiles of these calcium-release channels were mutually exclusive. The RyR antagonists 8-bromo-cADPR and dantrolene inhibited protein secretion and motility in live parasites. These results indicate that RyR calcium-release channels that respond to the second-messenger cADPR play an important role in regulating intracellular Ca2+, and hence host cell invasion, in protozoan parasites.

Role of cyclic ADP-ribose in Ca2+-induced Ca2+ release and vasoconstriction in small renal arteries

Cyclic-ADP-ribose (cADPR) has been reported to serve as a second messenger to mobilize intracellular Ca2+ independent of IP3 in a variety of mammalian cells. This cADPR-mediated Ca2+ signaling pathway importantly participates in the regulation of various cell functions. The present study determined the role of endogenous cADPR in mediating ryanodine-sensitive Ca2+-induced Ca2+ release (CICR) in vascular myocytes from small renal arteries and vasomotor response of these arteries. In freshly-isolated renal arterial myocytes, addition of CaCl2 (0.01, 0.1, and 1 mM) into the Ca2+-free bath solution produced a rapid Ca2+ release response from the sarcoplasmic reticulum (SR), with a maximal increase of 237+/-25 nM at 1 mM CaCl2. This CaCl2 response was significantly blocked by a cell-membrane permeant cADPR antagonist, 8-bromo-cADP-ribose (8-br-cADPR) (30 microM) or ryanodine (50 microM). Caffeine, a classical CICR or ryanodine receptor activator was found to stimulate the SR Ca2+ release (Delta[Ca2+]i: 253+/-35 nM), which was also attenuated by 8-br-cADPR or ryanodine. Using isolated and pressurized small renal arteries bathed with Ca2+-free solution, both CaCl2 and caffeine-induced vasoconstrictions were significantly attenuated by either 8-br-cADPR or ryanodine. Biochemical analyses demonstrated that CaCl2 and caffeine did not increase cADPR production in these renal arterial myocytes, but confocal microscopy showed that a dissociation of the accessory protein, FK506 binding protein 12.6 (FKBP12.6) from ryanodine receptors was induced by CaCl2. We conclude that cADPR importantly contributes to CICR and vasomotor responses of small renal arteries through enhanced dissociation of ryanodine receptors from their accessory protein.

Ca release induced by cyclic adenosine diphosphoribose (cADPr) in sea urchin egg homogenates: mechanisms of release and heterogeneity of the Ca compartments

A rapid superfusion system measuring the amounts, kinetics, and Ca dependencies of released 45Ca, was used to examine the effects of ryanodine (RY), caffeine (CF), and cyclic ADP ribose (cADPr) on sea urchin egg homogenates. The RY-sensitive compartment had more than twice the Ca release capacity of the CF-sensitive or cADPr-sensitive compartment. cADPr-stimulated 45Ca release required calcium with half-maximal activation at approximately 0.2 to 0.6 microM [Ca2+]. K(1/2) for cADPr activation was approximately 100 nM, and in spite of the Ca requirement for cADPr-stimulated release, the cADPr affinity was not affected by [Ca2+]. Peak 45Ca release rate with cADPr (3 microM) was greater than with CF (20 mM), yet the release amounts were similar and both were [Ca2+]-dependent. When activated with CF and cADPr simultaneously, 45Ca release was large and, no longer [Ca2+]-dependent. Mg competitively inhibited the Ca activation site(s), yet did not inhibit the activation with CF-plus-cADPr. Pre-release of 45Ca by cADPr with low (approximately 0.1 microM) [Ca2+] right-shifted the [Ca2+] dependence of the remaining cADPr-response. These data suggest that (a) only a portion of RY-sensitive compartments empty when stimulated with cADPr or CF, (b) Ca and cADPr act on non-interacting sites, and (c) cADPr-sensitive compartments represent a heterogeneous population with different [Ca2+] dependencies.

Role of the second-messenger cyclic-adenosine 5'-diphosphate-ribose on adrenocorticotropin secretion from pituitary cells

We examined the role of the second-messenger cyclic-ADP-ribose (cADPR) on the regulation of ACTH secretion using AtT20 corticotroph tumor cell line. We found that the cADPR antagonist, 8-Br-cADPR, substantially diminished the secretion of ACTH induced by CRH and potassium in these cells, whereas xestospongin C, an inositol 1,4,5-triphosphate receptor antagonist, had no effect. In addition, the cADPR agonist, 3-deaza-cADPR, augmented ACTH secretion. The presence of the components of the cADPR system, namely ryanodine receptor, CD38, and cADPR itself, was determined in AtT20 cells. Furthermore, we observed that antagonists of the ryanodine channel and cADPR system can decrease the potassium-induced Ca2+ transients in these cells. These results suggest that cADPR is a second messenger in pituitary cells and regulates ACTH secretion by a mechanism dependent on activation of the ryanodine channel by extracellular Ca2+.

Chemotaxis and calcium responses of phagocytes to formyl peptide receptor ligands is differentially regulated by cyclic ADP ribose

Cyclic ADP ribose (cADPR) is a calcium-mobilizing metabolite that regulates intracellular calcium release and extracellular calcium influx. Although the role of cADPR in modulating calcium mobilization has been extensively examined, its potential role in regulating immunologic responses is less well understood. We previously reported that cADPR, produced by the ADP-ribosyl cyclase, CD38, controls calcium influx and chemotaxis of murine neutrophils responding to fMLF, a peptide agonist for two chemoattractant receptor subtypes, formyl peptide receptor and formyl peptide receptor-like 1. In this study, we examine whether cADPR is required for chemotaxis of human monocytes and neutrophils to a diverse array of chemoattractants. We found that a cADPR antagonist and a CD38 substrate analogue inhibited the chemotaxis of human phagocytic cells to a number of formyl peptide receptor-like 1-specific ligands but had no effect on the chemotactic response of these cells to ligands selective for formyl peptide receptor. In addition, we show that the cADPR antagonist blocks the chemotaxis of human monocytes to CXCR4, CCR1, and CCR5 ligands. In all cases, we found that cADPR modulates intracellular free calcium levels in cells activated by chemokines that induce extracellular calcium influx in the apparent absence of significant intracellular calcium release. Thus, cADPR regulates calcium signaling of a discrete subset of chemoattractant receptors expressed by human leukocytes. Since many of the chemoattractant receptors regulated by cADPR bind to ligands that are associated with clinical pathology, cADPR and CD38 represent novel drug targets with potential application in chronic inflammatory and neurodegenerative disease.

Modulation of calcium signaling by interleukin-13 in human airway smooth muscle: role of CD38/cyclic adenosine diphosphate ribose pathway

CD38/cyclic adenosine diphosphate ribose (cADPR) signaling plays an important role in the regulation of intracellular calcium responses to agonists in a variety of cells, including airway smooth muscle (ASM) cells. The present study was aimed at determining the effect of interleukin (IL)-13, a cytokine implicated in the pathogenesis of asthma, on CD38/cADPR signaling and to ascertain the contribution of CD38/cADPR signaling to IL-13-induced airway hyperresponsiveness. Human ASM cells maintained in culture were exposed to 50 ng/ml IL-13 for 22 h and levels of CD38 expression and intracellular calcium responses to agonists were measured. Treatment of human ASM cells with IL-13 resulted in increased CD38 expression as determined by real-time polymerase chain reaction, Western blot analysis, and indirect immunofluorescence. Increased CD38 expression was reflected as increased ADP-ribosyl cyclase activity in the ASM cell membranes. The net intracellular calcium responses to bradykinin, thrombin, and histamine were significantly (P < or = 0.05) higher in cells treated with IL-13 compared with controls. Furthermore, 8-bromo-cADPR, a cADPR antagonist, attenuated IL-13-induced augmented intracellular calcium responses to agonists in human ASM cells. These findings indicate that the CD38/cADPR-dependent pathway has a major role in IL-13-induced modulation of calcium signaling in human ASM.

The role of cyclic-ADP-ribose-signaling pathway in oxytocin-induced Ca2+ transients in human myometrium cells

Human myometrial contraction plays a fundamental role in labor. Dysfunction of uterine contraction is an important cause of labor progression failure. Although the mechanisms controlling uterine contraction are not completely understood, intracellular Ca2+ mobilization plays an important role during uterine contraction. Several mechanisms of intracellular Ca2+ mobilization are present in smooth muscle, but in the human uterus, only 1,4,5-trisphosphate-induced Ca2+ release has been studied extensively. Ryanodine receptor channels are present in myometrium. We determined the role of the cyclic ADP-ribose (cADPR)-signaling pathway in oxytocin-induced intracellular Ca2+ [(Ca2+)i] transients in human myometrial cells. We found that oxytocin-induced Ca2+ transient is dependent on several sources of Ca2+, including extracellular Ca2+ and intracellular Ca2+ stores. In addition, we found that both the 1,4,5-trisphosphate- and the cADPR-induced Ca2+ releasing systems are important for the induction of [Ca2+]i transients by oxytocin in human myometrial cells. Furthermore, we investigated TNFalpha regulation of oxytocin-induced [Ca2+]i transients, CD38 cyclase activity, and CD38 expression in human myometrial cells. We found that oxytocin-induced [Ca2+]i transients were significantly increased by 50 ng/ml TNF. Similarly, CD38 mRNA levels, CD38 expression, and cyclase activity were increased by TNFalpha, thus increasing cADPR levels. We propose that a complex interaction between multiple signaling pathways is important for the development of intracellular Ca2+ transients induced by oxytocin and that TNFalpha may contribute for the myometrium preparation for labor by regulating the cADPR-signaling pathway. The observation that the cADPR-signaling pathway is important for the development of intracellular Ca2+ transients in human myometrial cells raises the possibility that this signaling pathway could serve as a target for the development of new therapeutic strategies for abnormal myometrial contraction observed during pregnancy.

Cyclic ADP-ribose is a second messenger in the lipopolysaccharide-stimulated proliferation of human peripheral blood mononuclear cells

Cyclic ADP-ribose (cADPR), a universal calcium mobilizer from intracellular stores, was recently demonstrated to stimulate proliferation of various cell types. The role of cADPR in a specific process of monocyte- and plasma-mediated activation of T-lymphocytes by lipopolysaccharide (LPS) was addressed using human mononuclear cells from peripheral blood (PBMCs). Incubation of PBMCs with 0.1 microg/ml of LPS for 24 h provided a doubling in the intracellular levels of cADPR as compared with unstimulated PBMCs. The cADPR increase was abolished either by prior removal of monocytes or by pre-incubating a whole PBMC population with a monoclonal antibody against the monocyte marker CD14. The increased concentrations of intracellular cADPR elicited by LPS stimulation were paralleled by significant increases in NAD+ levels and in the activities of ectocellular and membrane-bound fractions of ADP-ribosyl cyclase/cADPR hydrolase activities. A cytosolic ADP-ribosyl cyclase was also detectable in PBMCs and its activity was comparably enhanced by LPS stimulation. This soluble cyclase is distinguished from the membrane-bound cyclase by both substrate and inhibitor sensitivities. LPS-stimulated PBMCs showed 2-3-fold increases of intracellular calcium ([Ca2+]i), and these changes were prevented completely by the cADPR antagonist 8-Br-cADPR and by ryanodine. Both compounds, and the cyclase inhibitor nicotinamide, significantly inhibited the T-lymphocyte proliferation induced by LPS in PBMCs. These results demonstrate that cADPR plays a role of second messenger in the adaptive immune recognition process of LPS-stimulated proliferation of PBMCs.

Nitric oxide regulates K+ and Cl- channels in guard cells through a subset of abscisic acid-evoked signaling pathways

Abscisic acid (ABA) triggers a complex sequence of signaling events that lead to concerted modulation of ion channels at the plasma membrane of guard cells and solute efflux to drive stomatal closure in plant leaves. Recent work has indicated that nitric oxide (NO) and its synthesis are a prerequisite for ABA signal transduction in Arabidopsis and Vicia guard cells. Its mechanism(s) of action is not well defined in guard cells and, generally, in higher plants. Here we show directly that NO selectively regulates Ca2+-sensitive ion channels of Vicia guard cells by promoting Ca2+ release from intracellular stores to raise cytosolic-free [Ca2+]. NO-sensitive Ca2+ release was blocked by antagonists of guanylate cyclase and cyclic ADP ribose-dependent endomembrane Ca2+ channels, implying an action mediated via a cGMP-dependent cascade. NO did not recapitulate ABA-evoked control of plasma membrane Ca2+ channels and Ca2+-insensitive K+ channels, and NO scavengers failed to block the activation of these K+ channels evoked by ABA. These results place NO action firmly within one branch of the Ca2+-signaling pathways engaged by ABA and define the boundaries of parallel signaling events in the control of guard cell movements.

Functional relation between caffeine- and muscarine-sensitive Ca2+ stores and no Ca2+ releasing action of cyclic adenosine diphosphate-ribose in guinea-pig adrenal chromaffin cells

In voltage-clamped guinea-pig chromaffin cells, muscarine (50 microM) or caffeine (30 mM) produced a transient intracellular Ca(2+) concentration ([Ca(2+)](i)) increase, catecholamine release and an outward K(+) current mediated through Ca(2+) released from internal Ca(2+) stores at a holding potential of -40 mV. Caffeine followed by muscarine failed to evoke these responses, while muscarine followed by caffeine was effective in producing about 30% of [Ca(2+)](i) increase and catecholamine secretion. In cells dialyzed with inositol 1,4,5-trisphosphate (IP(3)), caffeine failed to produce the [Ca(2+)](i) increase. Intracellular application of cyclic adenosine 5'-diphosphate-ribose (cADP-ribose) or 8-bromo cADP-ribose exerted no effect on the resting [Ca(2+)](i) and the caffeine-induced [Ca(2+)](i) increase. These results suggest that IP(3)-sensitive stores are functionally divided into two subpopulations, sensitive and insensitive to caffeine, and it is unlikely that cADP-ribose plays a role as a Ca(2+) releaser in guinea-pig adrenal chromaffin cells.