CD38-mediated Inhibition of Bruton's Tyrosine Kinase in Macrophages Prevents Endotoxemic Lung Injury.

TLR4 signaling via endotoxemia in macrophages promotes macrophage transition to the inflammatory phenotype through NLRP3 inflammasome activation. This transition event has the potential to trigger acute lung injury (ALI). However, relatively little is known about the regulation of NLRP3 and its role in the pathogenesis of ALI. Here we interrogated the signaling pathway activated by CD38, an ectoenzyme expressed in macrophages, in preventing ALI through suppressing NLRP3 activation. Wild-type and Cd38-knockout (Cd38-/-) mice were used to assess inflammatory lung injury, and isolated macrophages were used to delineate underlying TLR4 signaling pathway. We showed that CD38 suppressed TLR4 signaling in macrophages by inhibiting Bruton's tyrosine kinase (Btk) through the recruitment of Src homology-2 domain containing protein tyrosine phosphatase-2 (SHP2) and resulting in the dephosphorylation of activated Btk. Cd38-/- mice show enhanced lung polymorphonuclear leukocyte extravasation and severe lung injury. LPS- or polymicrobial sepsis-induced mortality in Cd38-/- mice were markedly augmented compared with wild types. CD38 in macrophages functioned by inhibiting Btk activation through activation of SHP2 and resulting dephosphorylation of Btk, and thereby preventing activation of downstream targets NF-κB and NLRP3. Cd38-/- macrophages displayed markedly increased activation of Btk, NF-κB, and NLRP3, whereas in vivo administration of the Btk inhibitor ibrutinib (a Food and Drug Administration-approved drug) prevented augmented TLR4-induced inflammatory lung injury seen in Cd38-/- mice. Our findings together show upregulation of CD38 activity and inhibition of Btk activation downstream of TLR4 activation as potential strategies to prevent endotoxemic ALI.

CD38 as an immunomodulator in cancer.

CD38 is a transmembrane glycoprotein that is widely expressed in a variety of human tissues and cells, especially those in the immune system. CD38 protein was previously considered as a cell activation marker, and today monoclonal antibodies targeting CD38 have witnessed great achievements in multiple myeloma and promoted researchers to conduct research on other tumors. In this review, we provide a wide-ranging review of the biology and function of the human molecule outside the field of myeloma. We focus mainly on current research findings to summarize and update the findings gathered from diverse areas of study. Based on these findings, we attempt to extend the role of CD38 in the context of therapy of solid tumors and expand the role of the molecule from a simple marker to an immunomodulator.

Daratumumab in Sensitized Kidney Transplantation: Potentials and Limitations of Experimental and Clinical Use.

BACKGROUND: Donor-specific antibodies are associated with increased risk of antibody-mediated rejection and decreased allograft survival. Therefore, reducing the risk of these antibodies remains a clinical need in transplantation. Plasma cells are a logical target of therapy given their critical role in antibody production. METHODS: To target plasma cells, we treated sensitized rhesus macaques with daratumumab (anti-CD38 mAb). Before transplant, we sensitized eight macaques with two sequential skin grafts from MHC-mismatched donors; four of them were also desensitized with daratumumab and plerixafor (anti-CXCR4). We also treated two patients with daratumumab in the context of transplant. RESULTS: The animals treated with daratumumab had significantly reduced donor-specific antibody levels compared with untreated controls (57.9% versus 13% reduction; P<0.05) and prolonged renal graft survival (28.0 days versus 5.2 days; P<0.01). However, the reduction in donor-specific antibodies was not maintained because all recipients demonstrated rapid rebound of antibodies, with profound T cell-mediated rejection. In the two clinical patients, a combined heart and kidney transplant recipient with refractory antibody-mediated rejection and a highly sensitized heart transplant candidate, we also observed a significant decrease in class 1 and 2 donor-specific antibodies that led to clinical improvement of antibody-mediated rejection and to heart graft access. CONCLUSIONS: Targeting CD38 with daratumumab significantly reduced anti-HLA antibodies and anti-HLA donor-specific antibodies in a nonhuman primate model and in two transplant clinical cases before and after transplant. This supports investigation of daratumumab as a potential therapeutic strategy; however, further research is needed regarding its use for both antibody-mediated rejection and desensitization.

Skeletal unloading reduces cluster of differentiation (CD) 38 expression in the bone marrow and osteoblasts of mice.

BACKGROUND: Mechanical unloading induces bone loss in human weight-loaded bones. The findings of recent studies have revealed that cluster of differentiation 38 knockout mice display bone loss similar to that observed in osteoporosis. This study aimed to determine whether the expression of cluster of differentiation 38 is implicated in skeletal unloading and reloading. METHODS: Eight-week-old male C57BL/6J mice were assigned to control, tail-suspension, or reloading after tail-suspension groups. In the tail-suspension group, tail suspension elevated the hind limbs for 1 week. The bilateral femurs and tibias from the groups were evaluated for cluster of differentiation 38 immunocytochemistry, and the cluster of differentiation 38 messenger ribonucleic acid levels and the expression of cluster of differentiation 38 and other cell-surface antigens were evaluated using quantitative real-time polymerase chain reaction and flow cytometric analyses. RESULTS: In the tail-suspension group, the alkaline phosphatase reactivity, cluster of differentiation 38 immunoreactivity in the bone marrow and osteoblasts, and the expression of cluster of differentiation 38 messenger ribonucleic acid and that of other cell-surface antigens were significantly lower than those in the control group. In the reloading after tail-suspension group, the level of cluster of differentiation 38 expression was restored to the same level as that in the control group. CONCLUSIONS: Cluster of differentiation 38 expression declined after skeletal unloading and recovered to normal levels after reloading. In the bone marrow, cluster of differentiation 38 expression plays a crucial role in bone formation in response to mechanical stress.

P2X7 Receptor at the Crossroads of T Cell Fate.

The P2X7 receptor is a ligand-gated, cation-selective channel whose main physiological ligand is ATP. P2X7 receptor activation may also be triggered by ARTC2.2-dependent ADP ribosylation in the presence of extracellular NAD. Upon activation, this receptor induces several responses, including the influx of calcium and sodium ions, phosphatidylserine externalization, the formation of a non-selective membrane pore, and ultimately cell death. P2X7 receptor activation depends on the availability of extracellular nucleotides, whose concentrations are regulated by the action of extracellular nucleotidases such as CD39 and CD38. The P2X7 receptor has been extensively studied in the context of the immune response, and it has been reported to be involved in inflammasome activation, cytokine production, and the migration of different innate immune cells in response to ATP. In adaptive immune responses, the P2X7 receptor has been linked to T cell activation, differentiation, and apoptosis induction. In this review, we will discuss the evidence of the role of the P2X7 receptor on T cell differentiation and in the control of T cell responses in inflammatory conditions.

Protective Role of Autophagy in Nlrp3 Inflammasome Activation and Medial Thickening of Mouse Coronary Arteries.

We hypothesized that autophagy and associated lysosome function serve as a critical modulator during Nod-like receptor family pyrin domain containing 3 (Nlrp3) inflammasome activation on proatherogenic stimuli. We first demonstrated that 7-ketocholesterol stimulated Nlrp3 inflammasome formation and activation as shown by increased colocalization of inflammasome components [Nlrp3 versus apoptosis associated speck-like protein (Asc) or caspase-1] and enhanced cleavage of caspase-1 into active caspase-1 to generate IL-1ß in coronary artery smooth muscle cells. Deletion of the CD38 gene (CD38-/-) that regulates lysosome function and autophagic flux also led to Nlrp3 inflammasome formation and activation. In the presence of rapamycin, the effects of either 7-ketocholesterol treatment or CD38 gene deletion were abolished. The autophagy inhibitor spautin-1 and the lysosome function blocker bafilomycin A1 also enhanced Nlrp3 inflammasome formation and activation. In animal experiments, we found that increased colocalization of Nlrp3 versus Asc or caspase-1 enhanced IL-1ß accumulation and caspase-1 activity in the coronary arterial wall of CD38-/- mice on the Western diet compared with CD38+/+ mice. This increased colocalization was blocked by treatment with rapamycin but enhanced by chloroquine, a water-soluble blocker of autophagic flux. Morphologic examinations confirmed that the media of coronary arteries was significantly thicker in CD38-/- mice on the Western diet than CD38+/+ mice. In conclusion, the deficiency of autophagic flux promotes Nlrp3 inflammasome formation and activation in coronary artery smooth muscle cells on proatherogenic stimulation, leading to medial thickening of the coronary arterial wall.

CD38 targeted treatment for multiple myeloma.

CD38 antigen is highly and uniformly expressed on plasma cells and thus represents an ideal target for the treatment of multiple myeloma (MM) with anti-CD38 monoclonal antibodies (mAbs). Daratumumab is the most advanced anti-CD38 mAb in the clinical development with approval in several indications, nevertheless isatuximab that targets completely different epitope of CD38 molecule is also very promising drug. Anti-CD38 possess pleiotropic mechanism of action that have been described also in other mAbs, but quite specific, novel and very important seems to be the immunomodulatory effect provided by depletion of several CD38+ immunosuppressive immune cell populations. CD38-targeted mAbs induce partial response or better in approximately 30 % of heavily pre-treated myeloma patients as monotherapy. Based on their favourable toxicity profile and distinct mechanism of action, anti-CD38 mAbs represents very attractive partner to back-bone anti-myeloma drugs. Indeed, daratumumab is already approved as a part of three distinct combination regimens in relapsed setting. The combination of daratumumab with lenalidomide and dexamethasone is considered to be the best treatment option in relapsed myeloma with unprecedented prolongation of median PFS, including high rate of good quality responses. CD38 targeted therapy is rapidly moving toward the first line treatment. Anti-CD38 mAbs have been also successfully tested in other plasma cell dyscrasias (such as AL amyloidosis), and they are examined in other hematological malignancies (such as CLL, ALL, AML, etc.) and even in solid oncology as well as in autoimmune disorders. Implementation of CD38 targeted mAbs have been significant milestone in the treatment of MM, similar to that of CD20 targeted mAbs in CLL or non-Hodgkin lymphomas. We believe that this drug may eventually help to reach the cure at least in a subset of MM patients in the near future. Key words: acute myeloid leukemia - CD38 - daratumumab - isatuximab - multiple myeloma.

Impaired function of CD19(+) CD24(hi) CD38(hi) regulatory B cells in patients with pemphigus.

BACKGROUND: Pemphigus is an organ-specific autoimmune bullous disease. OBJECTIVES: To determine the role of regulatory B cells (Bregs) in patients with pemphigus. METHODS: The frequency of the occurrence of CD19(+) CD24(hi) CD38(hi) Bregs was detected from 34 patients with pemphigus and 20 healthy controls. Interleukin (IL)-10 secretion was processed after stimulating B cells. Specific antidesmoglein antibody (Ab) titres and their subclasses were also measured. Ab response and cytokine production from peripheral blood mononuclear cells (PBMCs) with or without Bregs were analysed. RESULTS: The number of Bregs was significantly increased in patients with pemphigus compared with healthy controls (15 ± 7% vs. 9 ± 3%; P < 0·01) and the proportion of Bregs in the active groups (newly diagnosed and chronic active patients) was significantly higher than in remittent individuals (16 ± 7% vs. 13 ± 8%; P = 0·04). The IL-10-producing B cells were significantly increased upon stimulation both in patients and in healthy controls. However, the increase ratio of IL-10-producing B cells between short- and long-term stimulation was significantly lower in patients with pemphigus (1·0-fold vs. 2·6-fold increase in control group; P < 0·01). Strikingly, Bregs from the controls were able to suppress interferon (IFN)-γ expression and T helper cell 1 (Th1) immune response (26% inhibition rate), while the suppressive function of Bregs from patients with pemphigus was significantly decreased (9% inhibition rate). There was no difference in Ab levels from PBMCs with or without Bregs after stimulation. CONCLUSIONS: Bregs in patients with pemphigus are elevated but with defective regulatory function on Th1 cells.

Basal CD38/cyclic ADP-ribose-dependent signaling mediates ATP release and survival of microglia by modulating connexin 43 hemichannels.

It is necessary to investigate the mechanisms underlying ATP release from neural cells, because extracellular ATP plays multiple important biological roles in the brain. CD38 is an ectoenzyme that consumes NAD(+) to produce cyclic ADP-ribose (cADPR), a potent agonist of ryanodine receptors. Our previous study showed that CD38 reductions led to microglial apoptosis. In this study, we used both murine microglial BV2 cells and primary microglial cultures as cellular models to test our hypothesis that basal CD38/cyclic ADP-ribose (CD38/cADPR)-dependent signaling plays a key role in ATP release, which mediates basal survival of microglia. We found that inhibition of CD38/cADPR-dependent signaling by CD38 silencing or 8-Bromo-cADPR, a ryanodine receptor antagonist, produced significant ATP release from BV2 microglia. Cx43 small interfering RNA and Cx43 hemichannel blocker 18-α-glycyrrhetinic acid completely prevented the CD38 silencing or 8-Bromo-cADPR-induced ATP release. Prevention of the ATP release could also be due to P2X7 receptor antagonists. Our study has further suggested a key role of ATP release in the microglial apoptosis induced by decreased CD38/cADPR-dependent signaling. In addition, by using primary microglial cultures, we found that 8-Bromo-cADPR also induced significant ATP release, which could be attenuated by 18-α-glycyrrhetinic acid. 8-Bromo-cADPR was also found to induce death of primary microglial cultures. In conclusion, our results have suggested novel roles of basal activation of CD38/cADPR-dependent signaling in mediating microglial functions and survival: It mediates ATP release from microglia by modulating Cx43 hemichannels, which can significantly affect microglial survival.

Renal vasoconstriction by vasopressin V1a receptors is modulated by nitric oxide, prostanoids, and superoxide but not the ADP ribosyl cyclase CD38.

Renal blood flow (RBF) responses to arginine vasopressin (AVP) were tested in anesthetized wild-type (WT) and CD38(-/-) mice that lack the major calcium-mobilizing second messenger cyclic ADP ribose. AVP (3-25 ng) injected intravenously produced dose-dependent decreases in RBF, reaching a maximum of 25 ± 2% below basal RBF in WT and 27 ± 2% in CD38(-/-) mice with 25 ng of AVP. Renal vascular resistance (RVR) increased 75 ± 6% and 78 ± 6% in WT and CD38(-/-) mice. Inhibition of nitric oxide (NO) synthase with nitro-L-arginine methyl ester (L-NAME) increased the maximum RVR response to AVP to 308 ± 76% in WT and 388 ± 81% in CD38(-/-) (P < 0.001 for both). Cyclooxygenase inhibition with indomethacin increased the maximum RVR response to 125 ± 15% in WT and 120 ± 14% in CD38(-/-) mice (P < 0.001, <0.05). Superoxide suppression with tempol inhibited the maximum RVR response to AVP by 38% in both strains (P < 0.005) but was ineffective when administered after L-NAME. The rate of RBF recovery (relaxation) after AVP was slowed by L-NAME and indomethacin (P < 0.001, <0.005) but was unchanged by tempol. All vascular responses to AVP were abolished by an AVP V1a receptor antagonist. A V2 receptor agonist or antagonist had no effect on AVP-induced renal vasoconstriction. Taken together, the results indicate that renal vasoconstriction by AVP in the mouse is strongly buffered by vasodilatory actions of NO and prostanoids. The vasoconstriction depends on V1a receptor activation without involvement of CD38 or concomitant vasodilatation by V2 receptors. The role of superoxide is to enhance the contractile response to AVP, most likely by reducing the availability of NO rather than directly stimulating intracellular contraction signaling pathways.

Thromboxane-induced renal vasoconstriction is mediated by the ADP-ribosyl cyclase CD38 and superoxide anion.

The present renal hemodynamic study tested the hypothesis that CD38 and superoxide anion (O2(·-)) participate in the vasoconstriction produced by activation of thromboxane prostanoid (TP) receptors in the mouse kidney. CD38 is the major mammalian ADP-ribosyl cyclase contributing to vasomotor tone through the generation of cADP-ribose, a second messenger that activates ryanodine receptors to release Ca(2+) from the sarcoplasmic reticulum in vascular smooth muscle cells. We evaluated whether the stable thromboxane mimetic U-46619 causes less pronounced renal vasoconstriction in CD38-deficient mice and the involvement of O2(·-) in U-46619-induced renal vasoconstriction. Our results indicate that U-46619 activation of TP receptors causes renal vasoconstriction in part by activating cADP-ribose signaling in renal resistance arterioles. Based on maximal renal blood flow and renal vascular resistance responses to bolus injections of U-46619, CD38 contributes 30-40% of the TP receptor-induced vasoconstriction. We also found that the antioxidant SOD mimetic tempol attenuated the magnitude of vasoconstriction by U-46619 in both groups of mice, suggesting mediation by O2(·-). The degree of tempol blockage of U-46619-induced renal vasoconstriction was greater in wild-type mice, attenuating renal vasoconstriction by 40% compared with 30% in CD38-null mice. In other experiments, U-46619 rapidly stimulated O2(·-) production (dihydroethidium fluorescence) in isolated mouse afferent arterioles, an effect abolished by tempol. These observations provide the first in vivo demonstration of CD38 and O2(·-) involvement in the vasoconstrictor effects of TP receptor activation in the kidney and in vitro evidence for TP receptor stimulation of O2(·-) production by the afferent arteriole.

CD38 and chronic lymphocytic leukemia: a decade later.

This review highlights a decade of investigations into the role of CD38 in CLL. CD38 is accepted as a dependable marker of unfavorable prognosis and as an indicator of activation and proliferation of cells when tested. Leukemic clones with higher numbers of CD38(+) cells are more responsive to BCR signaling and are characterized by enhanced migration. In vitro activation through CD38 drives CLL proliferation and chemotaxis via a signaling pathway that includes ZAP-70 and ERK1/2. Finally, CD38 is under a polymorphic transcriptional control after external signals. Consequently, CD38 appears to be a global molecular bridge to the environment, promoting survival/proliferation over apoptosis. Together, this evidence contributes to the current view of CLL as a chronic disease in which the host's microenvironment promotes leukemic cell growth and also controls the sequential acquisition and accumulation of genetic alterations. This view relies on the existence of a set of surface molecules, including CD38, which support proliferation and survival of B cells on their way to and after neoplastic transformation. The second decade of studies on CD38 in CLL will tell if the molecule is an effective target for antibody-mediated therapy in this currently incurable leukemia.

Loss of quiescence and impaired function of CD34(+)/CD38(low) cells one year following autologous stem cell transplantation.

Patients who have undergone autologous stem cell transplantation are subsequently more susceptible to chemotherapy-induced bone marrow toxicity. In the present study, bone marrow primitive progenitor cells were examined one year after autologous stem cell transplantation and compared with normal bone marrow and mobilized peripheral blood stem cells. Post-transplantation bone marrow contained a significantly lower percentage of quiescent cells in the CD34(+)/CD38(low) fraction compared to normal bone marrow. In addition, we observed a strong decrease in stem cell/primitive progenitor frequency in post-transplantation CD34(+) cells as defined by long-term culture assays. Measurement of the levels of reactive oxygen species by flow cytometry revealed comparable levels in post-transplantation and normal bone marrow CD34(+)/CD38(low) cells, while significantly higher levels of reactive oxygen species were observed in CD34(+)/CD38(high) cells following autologous stem cell transplantation compared to normal bone marrow. Moreover, post-transplantation CD34(+) bone marrow cells demonstrated an increased sensitivity to buthionine sulfoximine, a trigger for endogenous production of reactive oxygen species. Gene expression analysis on CD34(+) cells revealed a set of 195 genes, including HMOX1, EGR1, FOS and SIRPA that are persistently down-regulated in mobilized peripheral blood cells and post-transplantation bone marrow compared to normal bone marrow. In conclusion, our data indicate that the diminished regenerative capacity of bone marrow following autologous stem cell transplantation is possibly related to a loss of quiescence and a reduced tolerability to oxidative stress.

Testing the role of P2X7 receptors in the development of type 1 diabetes in nonobese diabetic mice.

Although P2rx7 has been proposed as a type 1 diabetes (T1D) susceptibility gene in NOD mice, its potential pathogenic role has not been directly determined. To test this possibility, we generated a new NOD stock deficient in P2X(7) receptors. T1D development was not altered by P2X(7) ablation. Previous studies found CD38 knockout (KO) NOD mice developed accelerated T1D partly because of a loss of CD4(+) invariant NKT (iNKT) cells and Foxp3(+) regulatory T cells (Tregs). These immunoregulatory T cell populations are highly sensitive to NAD-induced cell death activated by ADP ribosyltransferase-2 (ART2)-mediated ADP ribosylation of P2X(7) receptors. Therefore, we asked whether T1D acceleration was suppressed in a double-KO NOD stock lacking both P2X(7) and CD38 by rescuing CD4(+) iNKT cells and Tregs from NAD-induced cell death. We demonstrated that P2X(7) was required for T1D acceleration induced by CD38 deficiency. The CD38 KO-induced defects in homeostasis of CD4(+) iNKT cells and Tregs were corrected by coablation of P2X(7). T1D acceleration in CD38-deficient NOD mice also requires ART2 expression. If increased ADP ribosylation of P2X(7) in CD38-deficient NOD mice underlies disease acceleration, then a comparable T1D incidence should be induced by coablation of both CD38 and ART2, or CD38 and P2X(7). However, a previously established NOD stock deficient in both CD38 and ART2 expression is T1D resistant. This study demonstrated the presence of a T1D resistance gene closely linked to the ablated Cd38 allele in the previously reported NOD stock also lacking ART2, but not in the newly generated CD38/P2X(7) double-KO line.

Contribution of adenosine-producing ectoenzymes to the mechanisms underlying the mitigation of maternal-fetal conflicts.

The interactions taking place between mother and embryo have been the focus of detailed studies in recent years, where pregnancy is considered as an in vivo transplant. The immune systems of the mother and the embryo together establish a condition of tolerance, which lasts throughout the pregnancy. Alongside immunogenetic components, a contribution is provided by the ectoenzyme network, a chain of surface molecules mainly operating in closed environments and potentially providing inhibitory or activator signals. One of the soluble products of the ectoenzyme network with immunosuppressory potential is adenosine, a purine nucleoside that plays multiple roles in almost all tissues and organs. The hypothesis behind the work was studied in patients with recurrent pregnancy loss (RPL), an event which remains unexplained in over 50 percent of cases. To this aim, we analyzed the expression of CD39 (ectonucleoside triphosphate diphosphohydrolase 1, ENTPD1) and CD73 (ecto-5’-nucleotidase, NT5E), the main pathway for adenosine generation, in samples obtained from women with RPL. The study included the evaluation of the expression of TNF-alpha (a pro-inflammatory cytokine) and of an alternative pathway of adenosine generation run by CD38 (ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase) and PC-1 (ectonucleotide pyrophosphatase/phosphodiesterase 1, ENPP1). The results of this study highlight the existence of a network of surface enzymes expressed at the maternal/fetal interface and addressed to the production of adenosine. Perturbation of this network may induce a rescue pathway driven by CD38 and ENPP1. Ectoenzyme and inflammation may be considered now key elements in orchestrating the events leading to the interruption of pregnancy in the RPL sample analyzed and at the same potentially becoming therapeutic targets.

Catalysis-based inhibitors of the calcium signaling function of CD38.

CD38 is a signaling enzyme responsible for catalyzing the synthesis of cyclic ADP ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate; both are universal Ca(2+) messenger molecules. Ablation of the CD38 gene in mice causes multiple physiological defects, including impaired oxytocin release, that result in altered social behavior. A series of catalysis-based inhibitors of CD38 were designed and synthesized, starting with arabinosyl-2'-fluoro-2'-deoxynicotinamide mononucleotide. Structure-function relationships were analyzed to assess the structural determinants important for inhibiting the NADase activity of CD38. X-ray crystallography was used to reveal the covalent intermediates that were formed with the catalytic residue, Glu226. Metabolically stable analogues that were resistant to inactivation by phosphatase and esterase were synthesized and shown to be effective in inhibiting intracellular cADPR production in human HL-60 cells during induction of differentiation by retinoic acid. The inhibition was species-independent, and the analogues were similarly effective in blocking the cyclization reaction of CD38 in rat ventricular tissue extracts, as well as inhibiting the α-agonist-induced constriction in rat mesentery arteries. These compounds thus represent the first generally applicable and catalysis-based inhibitors of the Ca(2+) signaling function of CD38.

The ΔC splice-variant of TRPM2 is the hypertonicity-induced cation channel in HeLa cells, and the ecto-enzyme CD38 mediates its activation.

Hypertonicity-induced cation channels (HICCs) are key-players in proliferation and apoptosis but their molecular correlate remains obscure. Furthermore, the activation profile of HICCs is not well defined yet. We report here that, in HeLa cells, intracellular adenosine diphosphate ribose (ADPr) and cyclic ADPr (cADPr), as supposed activators of TRPM2, elicited cation currents that were virtually identical to the osmotic activation of HICCs. Silencing of the expression of TRPM2 and of the ecto-enzyme CD38 (as a likely source of ADPr and cADPr) inhibited HICC as well as nucleotide-induced currents and, in parallel, the hypertonic volume response of cells (the regulatory volume increase, RVI) was attenuated. Quantification of intracellular cADPr levels and the systematic application of extra- vs. intracellular nucleotides indicate that the outwardly directed gradient rather than the cellular activity of ADPr and cADPr triggers TRPM2 activation, probably along with a simultaneous biotransformation of nucleotides.Cloning of TRPM2 identified the ΔC-splice variant as the molecular correlate of the HICC, which could be strongly supported by a direct comparison of the respective Ca²âº selectivity. Finally, immunoprecipitation and high-resolution FRET/FLIM imaging revealed the interaction of TRPM2 and CD38 in the native as well as in a heterologous (HEK293T) expression system. We propose transport-related nucleotide export via CD38 as a novel mechanism of TRPM2/HICC activation. With the biotransformation of nucleotides running in parallel, continuous zero trans-conditions are achieved which will render the system infinitely sensitive.

CD38 and its role in oxytocin secretion and social behavior.

Here, we review the functional roles of cyclic ADP-ribose and CD38, a transmembrane protein with ADP-ribosyl cyclase activity, in mouse social behavior via the regulation of oxytocin (OXT) release, an essential component of social cognition. Herein we describe data detailing the molecular mechanism of CD38-dependent OXT secretion in CD38 knockout mice. We also review studies that used OXT, OXT receptor (OXTR), or CD38 knockout mice. Additionally, we compare the behavioral impairments that occur in these knockout mice in relation to the OXT system and CD38. This review also examines autism spectrum disorder (ASD), which is characterized by social and communication impairments, in relation to defects in the OXT system. Two single nucleotide polymorphisms (SNPs) in the human CD38 gene are possible risk factors for ASD via inhibition of OXT function. Further analysis of CD38 in relation to the OXT system may provide a better understanding of the neuroendocrinological roles of OXT and CD38 in the hypothalamus and of the pathophysiology of ASD. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

The contributions of oxytocin and vasopressin pathway genes to human behavior.

Arginine vasopressin (AVP) and oxytocin (OXT) are social hormones and mediate affiliative behaviors in mammals and as recently demonstrated, also in humans. There is intense interest in how these simple nonapeptides mediate normal and abnormal behavior, especially regarding disorders of the social brain such as autism that are characterized by deficits in social communication and social skills. The current review examines in detail the behavioral genetics of the first level of human AVP-OXT pathway genes including arginine vasopressin 1a receptor (AVPR1a), oxytocin receptor (OXTR), AVP (AVP-neurophysin II [NPII]) and OXT (OXT neurophysin I [NPI]), oxytocinase/vasopressinase (LNPEP), ADP-ribosyl cyclase (CD38) and arginine vasopressin 1b receptor (AVPR1b). Wherever possible we discuss evidence from a variety of research tracks including molecular genetics, imaging genomics, pharmacology and endocrinology that support the conclusions drawn from association studies of social phenotypes and detail how common polymorphisms in AVP-OXT pathway genes contribute to the behavioral hard wiring that enables individual Homo sapiens to interact successfully with conspecifics. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Regulating the social brain: a new role for CD38.

Centrally released oxytocin regulates maternal behavior, social memory, and social bonding. A recent paper by Jin et al. published in Nature demonstrates that the transmembrane receptor CD38 plays a critical role in regulating social behaviors by regulating the release of OT from hypothalamic neurons.