A missense mutation in the CD38 gene, a novel factor for insulin secretion: association with Type II diabetes mellitus in Japanese subjects and evidence of abnormal function when expressed in vitro

Cluster of differentiation molecules in the metabolic syndrome

Metabolic syndrome (MetS) represents a significant public health concern due to its association with an increased risk of cardiovascular disease, type 2 diabetes, and other serious health conditions. Despite extensive research, the underlying molecular mechanisms contributing to MetS pathogenesis remain elusive. This review aims to provide a comprehensive overview of the molecular mechanisms linking MetS and cluster of differentiation (CD) markers, which play critical roles in immune regulation and cellular signaling. Through an extensive literature review with a systematic approach, we examine the involvement of various CD markers in MetS development and progression, including their roles in adipose tissue inflammation, insulin resistance, dyslipidemia, and hypertension. Additionally, we discuss potential therapeutic strategies targeting CD markers for the management of MetS. By synthesizing current evidence, this review contributes to a deeper understanding of the complex interplay between immune dysregulation and metabolic dysfunction in MetS, paving the way for the development of novel therapeutic interventions.

Downregulation of the Cd38-Cyclic ADP-Ribose Signaling in Cardiomyocytes by Intermittent Hypoxia via Pten Upregulation

Sleep apnea syndrome (SAS) is characterized by recurrent episodes of oxygen desaturation and reoxygenation (intermittent hypoxia, IH), and it is a risk factor for cardiovascular disease (CVD) and insulin resistance/type 2 diabetes. However, the mechanisms linking IH stress and CVD remain elusive. We exposed rat H9c2 and mouse P19.CL6 cardiomyocytes to experimental IH or normoxia for 24 h to analyze the mRNA expression of the components of Cd38-cyclic ADP-ribose (cADPR) signaling. We found that the mRNA levels of cluster of differentiation 38 (Cd38), type 2 ryanodine receptor (Ryr2), and FK506-binding protein 12.6 (Fkbp12.6) in H9c2 and P19.CL6 cardiomyocytes were significantly decreased by IH, whereas the promoter activities of these genes were not decreased. By contrast, the expression of phosphatase and tensin homolog deleted from chromosome 10 (Pten) was upregulated in IH-treated cells. The small interfering RNA for Pten (siPten) and a non-specific control RNA were introduced into the H9c2 cells. The IH-induced downregulation of Cd38, Ryr2, and Fkbp12.6 was abolished by the introduction of the siPten, but not by the control RNA. These results indicate that IH stress upregulated the Pten in cardiomyocytes, resulting in the decreased mRNA levels of Cd38, Ryr2, and Fkbp12.6, leading to the inhibition of cardiomyocyte functions in SAS patients.

CD38–Cyclic ADP-Ribose Signal System in Physiology, Biochemistry, and Pathophysiology

Calcium (Ca²⁺) is a ubiquitous and fundamental signaling component that is utilized by cells to regulate a diverse range of cellular functions, such as insulin secretion from pancreatic β-cells of the islets of Langerhans. Cyclic ADP-ribose (cADPR), synthesized from NAD⁺ by ADP-ribosyl cyclase family proteins, such as the mammalian cluster of differentiation 38 (CD38), is important for intracellular Ca²⁺ mobilization for cell functioning. cADPR induces Ca²⁺ release from endoplasmic reticulum via the ryanodine receptor intracellular Ca²⁺ channel complex, in which the FK506-binding protein 12.6 works as a cADPR-binding regulatory protein. Recently, involvements of the CD38-cADPR signal system in several human diseases and animal models have been reported. This review describes the biochemical and molecular biological basis of the CD38-cADPR signal system and the diseases caused by its abnormalities.

Okamoto model for necrosis and its expansions, CD38-cyclic ADP-ribose signal system for intracellular Ca2+ mobilization and Reg (Regenerating gene protein)-Reg receptor system for cell regeneration

In pancreatic islet cell culture models and animal models, we studied the molecular mechanisms involved in the development of insulin-dependent diabetes. The diabetogenic agents, alloxan and streptozotocin, caused DNA strand breaks, which in turn activated poly(ADP-ribose) polymerase/synthetase (PARP) to deplete NAD+, thereby inhibiting islet β-cell functions such as proinsulin synthesis and ultimately leading to β-cell necrosis. Radical scavengers protected against the formation of DNA strand breaks and inhibition of proinsulin synthesis. Inhibitors of PARP prevented the NAD+ depletion, inhibition of proinsulin synthesis and β-cell death. These findings led to the proposed unifying concept for β-cell damage and its prevention (the Okamoto model). The model met one proof with PARP knockout animals and was further extended by the discovery of cyclic ADP-ribose as the second messenger for Ca2+ mobilization in glucose-induced insulin secretion and by the identification of Reg (Regenerating gene) for β-cell regeneration. Physiological and pathological events found in pancreatic β-cells have been observed in other cells and tissues.

The Circular Life of Human CD38: From Basic Science to Clinics and Back

Monoclonal antibodies (mAbs) were initially considered as a possible “magic bullet” for in vivo elimination of tumor cells. mAbs represented the first step: however, as they were murine in nature (the earliest experience on the field), they were considered unfit for human applications. This prompted the development of techniques for cloning the variable regions of conventional murine antibodies, genetically mounted on human IgG. The last step in this years-long process was the design for the preparation of fully human reagents. The choice of the target molecule was also problematic, since cancer-specific targets are quite limited in number. To overcome this obstacle in the planning phases of antibody-mediated therapy, attention was focused on a set of normal molecules, whose quantitative distribution may balance a tissue-dependent generalized expression. The results and clinical success obtained with anti-CD20 mAbs revived interest in this type of strategy. Using multiple myeloma (MM) as a tumor model was challenging first of all because the plasma cells and their neoplastic counterpart eluded the efforts of the Workshop on Differentiation Antigens to find a target molecule exclusively expressed by these cells. For this reason, attention was turned to surface molecules which fulfill the requisites of being reasonably good targets, even if not specifically restricted to tumor cells. In 2009, we proposed CD38 as a MM target in virtue of its expression: it is absent on early hematological progenitors, has variable but generalized limited expression by normal cells, but is extremely high in plasma cells and in myeloma. Further, regulation of its expression appeared to be dependent on a variety of factors, including exposure to all-trans retinoic acid (ATRA), a potent and highly specific inducer of CD38 expression in human promyelocytic leukemia cells that are now approved for in vivo use. This review discusses the history of human CD38, from its initial characterization to its targeting in antibody-mediated therapy of human myeloma.

Effects of Intermittent Hypoxia on Pulmonary Vascular and Systemic Diseases

Obstructive sleep apnea (OSA) causes many systemic disorders via mechanisms related to sympathetic nerve activation, systemic inflammation, and oxidative stress. OSA typically shows repeated sleep apnea followed by hyperventilation, which results in intermittent hypoxia (IH). IH is associated with an increase in sympathetic activity, which is a well-known pathophysiological mechanism in hypertension and insulin resistance. In this review, we show the basic and clinical significance of IH from the viewpoint of not only systemic regulatory mechanisms focusing on pulmonary circulation, but also cellular mechanisms causing lifestyle-related diseases. First, we demonstrate how IH influences pulmonary circulation to cause pulmonary hypertension during sleep in association with sleep state-specific change in OSA. We also clarify how nocturnal IH activates circulating monocytes to accelerate the infiltration ability to vascular wall in OSA. Finally, the effects of IH on insulin secretion and insulin resistance are elucidated by using an in vitro chamber system that can mimic and manipulate IH. The obtained data implies that glucose-induced insulin secretion (GIS) in pancreatic β cells is significantly attenuated by IH, and that IH increases selenoprotein P, which is one of the hepatokines, as well as TNF-α, CCL-2, and resistin, members of adipokines, to induce insulin resistance via direct cellular mechanisms. Clinical and experimental findings concerning IH give us productive new knowledge of how lifestyle-related diseases and pulmonary hypertension develop during sleep.

From insulin synthesis to secretion: Alternative splicing of type 2 ryanodine receptor gene is essential for insulin secretion in pancreatic β cells

Increases in the intracellular Ca²⁺ concentration in pancreatic islets, resulting from the Ca²⁺ mobilization from the intracellular source through the ryanodine receptor, are essential for insulin secretion by glucose. Cyclic ADP-ribose, a potent Ca²⁺ mobilizing second messenger synthesized from NAD⁺ by CD38, regulates the opening of ryanodine receptor. A novel ryanodine receptor mRNA (the islet-type ryanodine receptor) was found to be generated from the type 2 ryanodine receptor gene by the alternative splicing of exons 4 and 75. The islet-type ryanodine receptor mRNA is expressed in a variety of tissues such as pancreatic islets, cerebrum, cerebellum, and other neuro-endocrine cells, whereas the authentic type 2 ryanodine receptor mRNA (the heart-type ryanodine receptor) was found to be generated using GG/AG splicing of intron 75 and is expressed in the heart and the blood vessel. The islet-type ryanodine receptor caused a greater increase in the Ca²⁺ release by caffeine when expressed in HEK293 cells pre-treated with cyclic ADP-ribose, suggesting that the novel ryanodine receptor is an intracellular target for the CD38-cyclic ADP-ribose signal system in mammalian cells and that the tissue-specific alternative splicing of type 2 ryanodine receptor mRNA plays an important role in the functioning of the cyclic ADP-ribose-sensitive Ca²⁺ release.

Oxytocin system dysfunction as a common mechanism underlying metabolic syndrome and psychiatric symptoms in schizophrenia and bipolar disorders

There is growing interest in using intranasal oxytocin (OT) to treat social dysfunction in schizophrenia and bipolar disorders (i.e., psychotic disorders). While OT treatment results have been mixed, emerging evidence suggests that OT system dysfunction may also play a role in the etiology of metabolic syndrome (MetS), which appears in one-third of individuals with psychotic disorders and associated with increased mortality. Here we examine the evidence for a potential role of the OT system in the shared risk for MetS and psychotic disorders, and its prospects for ameliorating MetS. Using several studies to demonstrate the overlapping neurobiological profiles of metabolic risk factors and psychiatric symptoms, we show that OT system dysfunction may be one common mechanism underlying MetS and psychotic disorders. Given the critical need to better understand metabolic dysregulation in these disorders, future OT trials assessing behavioural and cognitive outcomes should additionally include metabolic risk factor parameters.

The CD38 genotype (rs1800561 (4693C>T): R140W) is associated with an increased risk of admission to the neonatal intensive care unit

BACKGROUNDS

Preterm birth (PTB)/admission to the neonatal intensive care unit (NICU) is a complex disorder associated with significant neonatal mortality and morbidity and long-term adverse health consequences. Multiple lines of evidence suggest that genetic factors play an important role in its etiology.

AIM

Given the role of CD38 in term delivery through oxytocin (OXT) release, we hypothesized that OXT signaling may play a role in the etiology of PTB/admission to the NICU. This study was designed to identify genetic variation in the CD38-oxytocin pathway associated with PTB/admission to the NICU.

METHODS

To identify common genetic variants predisposing individuals to PTB/admission to the NICU, we genotyped two single nucleotide polymorphisms (SNPs) in the CD38-oxytocin pathway in 63 case mothers, 55 control mothers, and 188 female volunteers in Nara Medical University Hospital, Japan.

RESULTS

Maternal genetic effect analysis of the SNP genotype data revealed a significant association between an SNP in CD38 (rs1800561 (4693C>T): R140W), which was reported to be correlated with diabetes and autism, and the risk of NICU admission. On the other hand, an SNP in the oxytocin receptor (OXTR) (rs2254298) showed no correlation with the risk of NICU admission.

CONCLUSION

Our study points to an association between maternal common polymorphisms in the CD38 (rs1800561) gene in Japanese women and susceptibility to PTB/admission to the NICU. Future studies with larger sample sizes are needed to confirm the findings of this study.

Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP) and Endolysosomal Two-pore Channels Modulate Membrane Excitability and Stimulus-Secretion Coupling in Mouse Pancreatic β Cells

Pancreatic β cells are electrically excitable and respond to elevated glucose concentrations with bursts of Ca²⁺ action potentials due to the activation of voltage-dependent Ca²⁺ channels (VDCCs), which leads to the exocytosis of insulin granules. We have examined the possible role of nicotinic acid adenine dinucleotide phosphate (NAADP)-mediated Ca²⁺ release from intracellular stores during stimulus-secretion coupling in primary mouse pancreatic β cells. NAADP-regulated Ca²⁺ release channels, likely two-pore channels (TPCs), have recently been shown to be a major mechanism for mobilizing Ca²⁺ from the endolysosomal system, resulting in localized Ca²⁺ signals. We show here that NAADP-mediated Ca²⁺ release from endolysosomal Ca²⁺ stores activates inward membrane currents and depolarizes the β cell to the threshold for VDCC activation and thereby contributes to glucose-evoked depolarization of the membrane potential during stimulus-response coupling. Selective pharmacological inhibition of NAADP-evoked Ca²⁺ release or genetic ablation of endolysosomal TPC1 or TPC2 channels attenuates glucose- and sulfonylurea-induced membrane currents, depolarization, cytoplasmic Ca²⁺ signals, and insulin secretion. Our findings implicate NAADP-evoked Ca²⁺ release from acidic Ca²⁺ storage organelles in stimulus-secretion coupling in β cells.

A primer of NAADP-mediated Ca(2+) signalling: From sea urchin eggs to mammalian cells

Since the discovery of the Ca(2+) mobilizing effects of the pyridine nucleotide metabolite, nicotinic acid adenine dinucleotide phosphate (NAADP), this molecule has been demonstrated to function as a Ca(2+) mobilizing intracellular messenger in a wide range of cell types. In this review, I will briefly summarize the distinct principles behind NAADP-mediated Ca(2+) signalling before going on to outline the role of this messenger in the physiology of specific cell types. Central to the discussion here is the finding that NAADP principally mobilizes Ca(2+) from acidic organelles such as lysosomes and it is this property that allows NAADP to play a unique role in intracellular Ca(2+) signalling. Lysosomes and related organelles are small Ca(2+) stores but importantly may also initiate a two-way dialogue with other Ca(2+) storage organelles to amplify Ca(2+) release, and may be strategically localized to influence localized Ca(2+) signalling microdomains. The study of NAADP signalling has created a new and fruitful focus on the lysosome and endolysosomal system as major players in calcium signalling and pathophysiology.

CD38 in the nucleus accumbens and oxytocin are related to paternal behavior in mice

Background

Mammalian sires participate in infant care. We previously demonstrated that sires of a strain of nonmonogamous laboratory mice initiate parental retrieval behavior in response to olfactory and auditory signals from the dam during isolation in a new environment. This behavior is rapidly lost in the absence of such signals when the sires are caged alone. The neural circuitry and hormones that control paternal behavior are not well-understood. CD38, a membrane glycoprotein, catalyzes synthesis of cyclic ADP-ribose and facilitates oxytocin (OT) secretion due to cyclic ADP-ribose-dependent increases in cytosolic free calcium concentrations in oxytocinergic neurons in the hypothalamus. In this paper, we studied CD38 in the nucleus accumbens (NAcc) and the role of OT on paternal pup retrieval behavior using CD38 knockout (CD38^−/−) mice of the ICR strain.

Results

CD38^−/− sires failed to retrieve when they were reunited with their pups after isolation together with the mate dams, but not with pup, in a novel cage for 10 min. CD38^−/− sires treated with a single subcutaneous injection of OT exhibited recovery in the retrieval events when caged with CD38^−/− dams treated with OT. We introduced human CD38 in the NAcc of CD38^−/− sires using a lentiviral infection technique and examined the effects of local expression of CD38. Pairs of knockout dams treated with OT and sires expressing CD38 in the NAcc showed more retrieval (83% of wild-type sire levels). Complete recovery of retrieval was obtained in sires with the expression of CD38 in the NAcc in combination with OT administration. Other paternal behaviors, including pup grooming, crouching and huddling, were also more common in CD38^−/− sires with CD38 expression in the NAcc compared with those in CD38^−/− sires without CD38 expression in the NAcc.

Conclusions

CD38 in the NAcc and OT are critical in paternal behavior.

Oxytocin and psychological factors affecting type 2 diabetes mellitus

Background. The aim of this study was to investigate the association of oxytocin with trait and state psychological factors in type 2 diabetic patients. Methods. OXT and psychological variables were analyzed from 86 controlled diabetic patients (glycosylated haemoglobin A1c (HbA1c) < 7%) from 45 uncontrolled diabetic patients (HbA1c ≥ 7). Psychological characteristics were assessed with the Eysenck Personality Questionnaire (EPQ), while state psychological characteristics were measured with the Symptom Checklist 90-R (SCL 90-R). Blood samples were taken for measuring oxytocin in both subgroups during the initial phase of the study. One year later, the uncontrolled diabetic patients were reevaluated with the use of the same psychometric instruments. Results. During the first evaluation of the uncontrolled diabetic patients, a statistically significant positive relationship between the levels of OXT and psychoticism in EPQ rating scale (P < 0.013) was observed. For controlled diabetic patients, a statistically significant negative relationship between oxytocin and somatization (P < 0.030), as well as obsessive-compulsive scores (P < 0.047) in SCL-90 rating scale, was observed. During the second assessment, the values of OXT decreased when the patients managed to control their metabolic profile. Conclusions. The OXT is in association with psychoticism, somatization, and obsessionality may be implicated in T2DM.

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.

Population variability in CD38 activity: correlation with age and significant effect of TNF-α -308G>A and CD38 184C>G SNPs

CD38 (EC 3.2.2.6, NAD(+)-glycohydrolase) is a multifunctional enzyme catalyzing the synthesis and hydrolysis of cyclic ADP-ribose from NAD(+) to ADP-ribose. The loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications. Notably, it has been linked to HIV infection, leukemias, myelomas, solid tumors, Type II Diabetes mellitus, bone metabolism, as well as Autism Spectrum Disorder. Taking into account the crucial role played by CD38 in many diseases and in clinical practice, here we assessed the distribution of CD38 NADase activity in a healthy population (104 sex-matched unrelated individuals, 12-98 years) and determined its main predictors among genetic and physiological factors (age and sex). The mean value of CD38 NADase activity was 0.051±0.023 mU/mg (0.010-0.099 mU/mg), following a normal distribution in the study population (Kolmogorov-Smirnov test P=0.200). The TNF-α -308G>A (rs1800629) resulted the main predictor (β=0.364, P=0.00008), followed by Age (β=0.280, P=0.002) and the CD38 184C>G (rs6449182) (β=0.193, P=0.033). Our study contributes to understanding CD38 enzyme physiological functions, by reporting, for the first time, its activity distribution in healthy individuals and demonstrating a significant positive correlation with age. Moreover, the possible use of TNF-α -308G>A (rs1800629) and the CD38 184C>G (rs6449182) SNPs as predictive genetic markers of CD38 activity, clearly point toward possible pharmacogenomic applications and to a more refined use of CD38 in clinical settings.

Social memory, amnesia, and autism: brain oxytocin secretion is regulated by NAD+ metabolites and single nucleotide polymorphisms of CD38

Previously, we demonstrated that CD38, a transmembrane protein with ADP-ribosyl cyclase activity, plays a critical role in mouse social behavior by regulating the release of oxytocin (OXT), which is essential for mutual recognition. When CD38 was disrupted, social amnesia was observed in Cd38 knockout mice. The autism spectrum disorders (ASDs), characterized by defects in reciprocal social interaction and communication, occur either sporadically or in a familial pattern. However, the etiology of ASDs remains largely unknown. Therefore, the theoretical basis for pharmacological treatments has not been established. Hence, there is a rationale for investigating single nucleotide polymorphisms (SNPs) in the human CD38 gene in ASD subjects. We found several SNPs in this gene. The SNP rs3796863 (C>A) was associated with high-functioning autism (HFA) in American samples from the Autism Gene Resource Exchange. Although this finding was partially confirmed in low-functioning autism subjects in Israel, it has not been replicated in Japanese HFA subjects. The second SNP of interest, rs1800561 (4693C>T), leads to the substitution of an arginine (R) at codon 140 by tryptophan (W; R140W) in CD38. This mutation was found in four probands of ASD and in family members of three pedigrees with variable levels of ASD or ASD traits. The plasma levels of OXT in ASD subjects with the R140W allele were lower than those in ASD subjects lacking this allele. The OXT levels were unchanged in healthy subjects with or without this mutation. One proband with the R140W allele receiving intranasal OXT for approximately 3years showed improvement in areas of social approach, eye contact and communication behaviors, emotion, irritability, and aggression. Five other ASD subjects with mental deficits received nasal OXT for various periods; three subjects showed improved symptoms, while two showed little or no effect. These results suggest that SNPs in CD38 may be possible risk factors for ASD by abrogating OXT function and that some ASD subjects can be treated with OXT in preliminary clinical trials.

Nanospaces between endoplasmic reticulum and mitochondria as control centres of pancreatic β-cell metabolism and survival

Nanometre-scale spaces between organelles represent focused nodes for signal transduction and the control of cellular decisions. The endoplasmic reticulum (ER) and the mitochondria form dynamic quasi-synaptic interaction nanodomains in all cell types examined, but the functional role of these junctions in cellular metabolism and cell survival remains to be fully understood. In this paper, we review recent evidence that ER Ca(2+) channels, such as the RyR and IP(3)R, can signal specifically across this nanodomain to the adjacent mitochondria to pace basal metabolism, with focus on the pancreatic β-cell. Blocking these signals in the basal state leads to a form of programmed cell death associated with reduced ATP and the induction of calpain-10 and hypoxia-inducible factors. On the other hand, the hyperactivity of this signalling domain plays a deleterious role during classical forms of apoptosis. Thus, the nanospace between ER and mitochondria represents a critical rheostat controlling both metabolism and programmed cell death. Many aspects of the mechanisms underlying this control system remain to be uncovered, and new nanotechnologies are required understand these domains at a molecular level.

Attenuation of glucose-induced insulin secretion by intermittent hypoxia via down-regulation of CD38

AIMS

Sleep apnea syndrome (SAS) is characterized by recurrent episodes of oxygen desaturation during sleep, the development of daytime sleepiness, and deterioration in the quality of life. Accumulating evidence suggests the association of intermittent hypoxia (IH), a hallmark of SAS, and type 2 diabetes independently on body mass index and waist circumference. In addition to insulin resistance, the progression to type 2 diabetes is dependent on the impairment of glucose-induced insulin secretion (GIS) from pancreatic β-cells. However, the direct effects of IH on GIS are elusive.

MAIN METHODS

HIT-T15 hamster β-cells and isolated rat islets were exposed to 64 cycles/24 h of IH (5 min hypoxia/10 min normoxia) or normoxia for 24 h. Changes of GIS and gene expression in IH-treated β-cells were analyzed by ELISA and real-time RT-PCR, respectively.

KEY FINDINGS

After IH treatment, GIS both from IH-treated HIT-T15 cells and isolated rat islets were significantly attenuated. The level of insulin mRNA was unchanged by IH. The mRNA levels of glucose transporter 2 (Glut2), glucokinase (GK), sulfonylurea receptor1 (SUR1), and L-type Ca2+channel1.2 (Cav1.2) in IH-treated-islets were similar to those in normoxia-treated islets. In contrast, the mRNA level of CD38 in IH-treated islets was significantly lower than that in normoxia-treated islets. The reporter gene assay revealed that the transcription of CD38 was attenuated by IH, and the transfection of CD38 expression vector recovered the attenuation of GIS by IH.

SIGNIFICANCE

These results indicate that IH stress directly attenuates GIS from β-cells via the down-regulation of CD38.

Low CD38 expression in lymphoblastoid cells and haplotypes are both associated with autism in a family-based study

BACKGROUND

Impairments in social processes characterize one of the core deficits in autism spectrum disorders (ASD) and accumulating evidence suggests that oxytocin neurotransmission is implicated in mediating social adaptation in ASD. Using a mouse model, CD38, a transmembrane protein expressed in immune cells but also in brain, was found to be critical for social behavior via regulation of oxytocin secretion. This prompted us to both examine CD38 expression in human lymphoblastoid cell lines (LBC) as well as to test association between SNPs across the CD38 gene and ASD.

METHODS

LBC’s were derived from 44 ASD lines and 40 "unaffected" parents. Family-based association (UNPHASED) was examined by genotyping 11 tagging SNPs spanning the CD38 gene identified using HapMap data in 170 trios. An additional SNP (rs3796863) associated in a study by Munesue et al. with ASD was also genotyped.

RESULTS

A highly significant reduction in CD38 expression was observed in immortalized lymphocytes derived from ASD subjects compared to their "unaffected" parents (F517.2, P50.00024, df51). Haplotype analysis showed significant association (permutation corrected) between three and seven locus haplotypes and DSM IV ASD in low functioning (IQ < 70) subjects.

CONCLUSIONS

The current report supports a role for CD38 in conferring risk for ASD. Notably, our study shows that this gene is not only associated with low functioning ASD but that CD38 expression is markedly reduced in LBC derived from ASD subjects compared to "unaffected" parents, strengthening the connection between oxytocin and ASD.

CD38 expression, function, and gene resequencing in a human lymphoblastoid cell line-based model system

CD38 is an ecto-enzyme that hydrolyzes NAD. Its expression is a prognostic marker for chronic lymphocytic leukemia. We have characterized individual variation in CD38 expression in lymphoblastoid cell lines from 288 healthy subjects of three ethnicities. Expression varied widely, with significant differences among ethnic groups, and was correlated significantly with CD38 enzymatic activity and protein levels. The CD38 gene was then resequenced using DNA from the same cell lines, with the identification of 53 single nucleotide polymorphisms (SNPs) and one indel, 39 novel. One SNP, rs1130169, was significantly associated with CD38 mRNA expression and explained a portion of the difference in expression among ethnic groups. EMS assay showed nuclear protein binding at or near this SNP. We also determined that variation in CD38 expression in these cell lines was associated with variation in antineoplastic drug sensitivity. These results represent a step toward understanding mechanisms involved in CD38 expression.

CD38 as a molecular compass guiding topographical decisions of chronic lymphocytic leukemia cells

CLL is characterized by a dynamic balance between cells proliferating in the lymphoid organs and circulating cells resisting programmed cell death. Regulating this equilibrium entails complex interactions between tumor and host, modulated by a set of surface molecules expressed by the CLL cell according to environmental conditions. The result is a constantly shifting pattern of resistance, apoptosis and proliferation. The CD38 surface molecule is an independent negative prognostic factor expressed by approximately one-third of CLL patients. Our view is that CD38 is crucial to tumor-host communication and that its signals are detrimental to clinical outcome. CD38(+) CLL cells can proliferate in vitro in the presence of anti-CD38 mAbs and IL-2 and are more sensitive to the effects of the CXCL12 chemokine. Blockage of CD38 signals impairs CLL cell movement from blood to lymphoid organs, as confirmed using animal models. One model to be explored considers CD38 a key component of the CLL invadosome, a still hypothetical membrane domain containing adhesion molecules, chemokine receptors and matrix metalloproteases. Some components of the invadosome are genetically polymorphic, explaining heterogeneity in functional response. The CD38 gene shows genetic differences in the promoter region, some of which represent an independent risk for Richter transformation. In addition to driving the clinical outcome of the disease, CD38 is thus an excellent candidate therapeutic target for a significant subset of CLL patients.

An emerging role for NAADP-mediated Ca2+ signaling in the pancreatic β-cell

Several recent reports, including one in this journal, have reignited the debate about whether the calcium-mobilizing messenger, nicotinic adenine nucleotide diphosphate (NAADP) plays a central role in the regulation of calcium signalling in pancreatic β-cell. These studies have highlighted a role for NAADP-induced Ca(2+) mobilization not only in mediating the effects of the incretin, GLP-1 and the autocrine proliferative effects of insulin, but also possibly a fundamental role in glucose-mediated insulin secretion in the pancreatic β-cell.

TRPM5 regulates glucose-stimulated insulin secretion

Insulin secretion in beta-pancreatic cells due to glucose stimulation requires the coordinated alteration of cellular ion concentrations and a substantial membrane depolarization to enable insulin vesicle fusion with the cellular membrane. The cornerstones of this cascade are well characterized, yet current knowledge argues for the involvement of additional ion channels in this process. TRPM5 is a cation channel expressed in beta-cells and proposed to be involved in coupling intracellular Ca(2+) release to electrical activity and cellular responses. Here, we report that TRPM5 acts as an indispensable regulator of insulin secretion. In vivo glucose tolerance tests showed that Trpm5 (-/-) -mice maintain elevated blood glucose levels for over an hour compared to wild-type littermates, while insulin sensitivity is normal in Trpm5 (-/-) -mice. In pancreatic islets isolated from Trpm5 (-/-) -mice, hyperglycemia as well as arginine-induced insulin secretion was diminished. The presented results describe a major role for TRPM5 in glucose-induced insulin secretion beyond membrane depolarization. Dysfunction of the TRPM5 protein could therefore be an important factor in the etiology of some forms of type 2 diabetes, where disruption of the normal pattern of secretion is observed.

Two genetic variants of CD38 in subjects with autism spectrum disorder and controls

The neurobiological basis of autism spectrum disorder (ASD) remains poorly understood. Given the role of CD38 in social recognition through oxytocin (OT) release, we hypothesized that CD38 may play a role in the etiology of ASD. Here, we first examined the immunohistochemical expression of CD38 in the hypothalamus of post-mortem brains of non-ASD subjects and found that CD38 was colocalized with OT in secretory neurons. In studies of the association between CD38 and autism, we analyzed 10 single nucleotide polymorphisms (SNPs) and mutations of CD38 by re-sequencing DNAs mainly from a case-control study in Japan, and Caucasian cases mainly recruited to the Autism Genetic Resource Exchange (AGRE). The SNPs of CD38, rs6449197 (p<0.040) and rs3796863 (p<0.005) showed significant associations with a subset of ASD (IQ>70; designated as high-functioning autism (HFA)) in the U.S. 104 AGRE family trios, but not with Japanese 188 HFA subjects. A mutation that caused tryptophan to replace arginine at amino acid residue 140 (R140W; (rs1800561, 4693C>T)) was found in 0.6-4.6% of the Japanese population and was associated with ASD in the smaller case-control study. The SNP was clustered in pedigrees in which the fathers and brothers of T-allele-carrier probands had ASD or ASD traits. In this cohort OT plasma levels were lower in subjects with the T allele than in those without. One proband with the T allele who was taking nasal OT spray showed relief of symptoms. The two variant CD38 poloymorphysms tested may be of interest with regard of the pathophysiology of ASD.

TRPM5 regulates glucose-stimulated insulin secretion

Insulin secretion in beta-pancreatic cells due to glucose stimulation requires the coordinated alteration of cellular ion concentrations and a substantial membrane depolarization to enable insulin vesicle fusion with the cellular membrane. The cornerstones of this cascade are well characterized, yet current knowledge argues for the involvement of additional ion channels in this process. TRPM5 is a cation channel expressed in beta-cells and proposed to be involved in coupling intracellular Ca(2+) release to electrical activity and cellular responses. Here, we report that TRPM5 acts as an indispensable regulator of insulin secretion. In vivo glucose tolerance tests showed that Trpm5 (-/-) -mice maintain elevated blood glucose levels for over an hour compared to wild-type littermates, while insulin sensitivity is normal in Trpm5 (-/-) -mice. In pancreatic islets isolated from Trpm5 (-/-) -mice, hyperglycemia as well as arginine-induced insulin secretion was diminished. The presented results describe a major role for TRPM5 in glucose-induced insulin secretion beyond membrane depolarization. Dysfunction of the TRPM5 protein could therefore be an important factor in the etiology of some forms of type 2 diabetes, where disruption of the normal pattern of secretion is observed.

Recent advances in physiological and pathological significance of NAD+ metabolites: roles of poly(ADP-ribose) and cyclic ADP-ribose in insulin secretion and diabetogenesis

Poly(ADP-ribose) synthetase/polymerase (PARP) activation causes NAD+ depletion in pancreatic beta-cells, which results in necrotic cell death. On the other hand, ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase (CD38) synthesizes cyclic ADP-ribose from NAD+, which acts as a second messenger, mobilizing intracellular Ca2+ for insulin secretion in response to glucose in beta-cells. PARP also acts as a regenerating gene (Reg) transcription factor to induce beta-cell regeneration. This provides the new concept that NAD+ metabolism can control the cellular function through gene expression. Clinically, PARP could be one of the most important therapeutic targets; PARP inhibitors prevent cell death, maintain the formation of a second messenger, cyclic ADP-ribose, to achieve cell function, and keep PARP functional as a transcription factor for cell regeneration.

Arginine vasopressin and oxytocin modulate human social behavior

Increasing evidence suggests that two nonapeptides, arginine vasopressin and oxytocin, shape human social behavior in both nonclinical and clinical subjects. Evidence is discussed that in autism spectrum disorders genetic polymorphisms in the vasopressin-oxytocin pathway, notably the arginine vasopressin receptor 1a (AVPR1a), the oxytocin receptor (OXTR), neurophysin I and II, and CD38 (recently shown to be critical for social behavior by mediating oxytocin secretion) contribute to deficits in socialization skills in this group of patients. We also present first evidence that CD38 expression in lymphoblastoid cells derived from subjects diagnosed with autism is correlated with social skill phenotype inventoried by the Vineland Adaptive Behavioral Scales. Additionally, we discuss molecular genetic evidence that in nonclinical subjects both AVPR1a and OXTR genes contribute to prosocial or altruistic behavior inventoried by two experimental paradigms, the dictator game and social values orientation. The role of the AVPR1a is also analyzed in prepulse inhibition. Prepulse inhibition of the startle response to auditory stimuli is a largely autonomic response that resonates with social cognition in both animal models and humans. First results are presented showing that intranasal administration of arginine vasopressin increases salivary cortisol levels in the Trier Social Stress test. To summarize, accumulating studies employing a broad array of cutting-edge tools in psychology, neuroeconomics, molecular genetics, pharmacology, electrophysiology, and brain imaging are beginning to elaborate the intriguing role of oxytocin and arginine vasopressin in human social behavior. We expect that future studies will continue this advance and deepen our understanding of these complex events.

Evolution and function of the ADP ribosyl cyclase/CD38 gene family in physiology and pathology

The membrane proteins CD38 and CD157 belong to an evolutionarily conserved family of enzymes that play crucial roles in human physiology. Expressed in distinct patterns in most tissues, CD38 (and CD157) cleaves NAD(+) and NADP(+), generating cyclic ADP ribose (cADPR), NAADP, and ADPR. These reaction products are essential for the regulation of intracellular Ca(2+), the most ancient and universal cell signaling system. The entire family of enzymes controls complex processes, including egg fertilization, cell activation and proliferation, muscle contraction, hormone secretion, and immune responses. Over the course of evolution, the molecules have developed the ability to interact laterally and frontally with other surface proteins and have acquired receptor-like features. As detailed in this review, the loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications in mice. CD38 is a powerful disease marker for human leukemias and myelomas, is directly involved in the pathogenesis and outcome of human immunodeficiency virus infection and chronic lymphocytic leukemia, and controls insulin release and the development of diabetes. Here, the data concerning diseases are examined in view of potential clinical applications in diagnosis, prognosis, and therapy. The concluding remarks try to frame all of the currently available information within a unified working model that takes into account both the enzymatic and receptorial functions of the molecules.

CD38 is critical for social behaviour by regulating oxytocin secretion

CD38, a transmembrane glycoprotein with ADP-ribosyl cyclase activity, catalyses the formation of Ca2+ signalling molecules, but its role in the neuroendocrine system is unknown. Here we show that adult CD38 knockout (CD38-/-) female and male mice show marked defects in maternal nurturing and social behaviour, respectively, with higher locomotor activity. Consistently, the plasma level of oxytocin (OT), but not vasopressin, was strongly decreased in CD38-/- mice. Replacement of OT by subcutaneous injection or lentiviral-vector-mediated delivery of human CD38 in the hypothalamus rescued social memory and maternal care in CD38-/- mice. Depolarization-induced OT secretion and Ca2+ elevation in oxytocinergic neurohypophysial axon terminals were disrupted in CD38-/- mice; this was mimicked by CD38 metabolite antagonists in CD38+/+ mice. These results reveal that CD38 has a key role in neuropeptide release, thereby critically regulating maternal and social behaviours, and may be an element in neurodevelopmental disorders.

CD38 regulates oxytocin secretion and complex social behavior

The peptide hormone oxytocin plays a critical role in regulating affiliative behaviors including mating, pair-bond formation, maternal/parenting behavior, social recognition, separation distress and other aspects of attachment. Jin and colleagues recently reported intriguing findings that CD38, a transmembrane receptor with ADP-ribosyl cyclase activity, plays a critical role in maternal nurturing behavior and social recognition by regulating oxytocin secretion. This research may have implications for understanding disorders marked by deficits in social cognition and social functioning, including autism, social anxiety disorder, borderline personality disorder and schizophrenia.

Suppressed insulin signaling and increased apoptosis in CD38-null islets

CD38 is a multifunctional enzyme capable of generating metabolites that release Ca2+ from intracellular stores, including nicotinic acid adenine dinucleotide phosphate (NAADP). A number of studies have led to the controversial proposal that CD38 mediates an alternate pathway for glucose-stimulated insulin release and contributes to the pathogenesis of diabetes. It has recently been shown that NAADP mediates Ca2+ mobilization by insulin in human pancreatic beta-cells. In the present study, we report altered Ca2+ homeostasis and reduced responsiveness to insulin, but not glucose, in Cd38-/- beta-cells. In keeping with the antiapoptotic role of insulin signaling, Cd38-/- islets were significantly more susceptible to apoptosis compared with islets isolated from littermate controls. This finding correlated with disrupted islet architecture and reduced beta-cell mass in Cd38-/- mice, both in the context of a normal lab diet and a high-fat diet. Nevertheless, we did not find robust differences in glucose homeostasis in vivo or glucose signaling in vitro in Cd38-/- mice on the C57BL/6 genetic background, in contrast to previous studies by others of Cd38 knockout mice on the ICR background. Thus, our results suggest that CD38 plays a role in novel antiapoptotic signaling pathways but does not directly control glucose signaling in pancreatic beta-cells.

Adenoviral mediated anti-sense CD38 attenuates TNF-alpha-induced changes in calcium homeostasis of human airway smooth muscle cells

CD38 is a membrane-bound protein involved in the synthesis and degradation of cyclic-ADP-ribose (cADPR). cADPR mobilizes calcium from intracellular stores in airway smooth muscle cells. To determine the role of CD38/cADPR signaling in calcium regulation in human airway smooth muscle (HASM) cells, we downregulated CD38 expression using a recombinant replication-defective adenovirus with anti-sense human CD38 (Ad-asCD38). CD38 expression was determined by RT-PCR and real-time quantitative PCR, and ADP-ribosyl cyclase (cyclase) activity was determined by competitive binding assay. In HASM cells infected with Ad-asCD38, TNF-alpha-induced, augmented-CD38 expression and cyclase activity were significantly lower than in TNF-alpha-treated cells. The net intracellular calcium responses to 10 nmol/L bradykinin were measured in HASM cells by fluorescence imaging. In cells infected with Ad-asCD38 in the presence of TNF-alpha, the net intracellular Ca2+ responses were significantly lower than in cells treated with TNF-alpha in the presence of the control vector (p < 0.001). These results provide evidence for the feasibility of using adenoviral vectors for gene transfer to down regulate gene expression, and confirm the role of CD38 in calcium homeostatis in ASM cells.

Anti-CD38 autoimmunity in children with newly diagnosed type 1 diabetes mellitus

AIMS

To test for anti-CD38 autoimmunity in children with newly-diagnosed type 1 diabetes mellitus (DM1).

METHODS

Serum anti-CD38 autoantibodies were detected by Western blot in 270 children (130 girls, 140 boys, mean age 8 +/- 4 years) with newly-diagnosed DM1 and 179 gender- and age-matched non-diabetic children. In 126 diabetic children, another blood sample was obtained 15 +/- 4 months after the diagnosis.

RESULTS

Anti-CD38 autoantibody titers at least 3 SD above the mean value for the control group were found in 4.4% of children with DM1 vs 0.6% of controls (chi2 = 5.8, p <0.016). No statistical differences were observed between anti-CD38 positive and negative patients in terms of phenotype. At follow-up, of six diabetic children who were positive for anti-CD38 antibodies, two were new cases. A positive correlation was found between the antibody titer of diabetic sera at diagnosis and follow up (r = 0.46, p <0.0001).

CONCLUSION

An autoimmune reaction against CD38, a protein expressed in human islets, is associated with newly-diagnosed DM1. In children with DM1, CD38 autoimmunity increases with time and persists.

Characterization and phylogenetic epitope mapping of CD38 ADPR cyclase in the cynomolgus macaque

Background

The CD38 transmembrane glycoprotein is an ADP-ribosyl cyclase that moonlights as a receptor in cells of the immune system. Both functions are independently implicated in numerous areas related to human health. This study originated from an inherent interest in studying CD38 in the cynomolgus monkey (Macaca fascicularis), a species closely related to humans that also represents a cogent animal model for the biomedical analysis of CD38.

Results

A cDNA was isolated from cynomolgus macaque peripheral blood leukocytes and is predicted to encode a type II membrane protein of 301 amino acids with 92% identity to human CD38. Both RT-PCR-mediated cDNA cloning and genomic DNA PCR surveying were possible with heterologous human CD38 primers, demonstrating the striking conservation of CD38 in these primates. Transfection of the cDNA coincided with: (i) surface expression of cynomolgus macaque CD38 by immunofluorescence; (ii) detection of ~42 and 84 kDa proteins by Western blot and (iii) the appearance of ecto-enzymatic activity. Monoclonal antibodies were raised against the cynomolgus CD38 ectodomain and were either species-specific or cross-reactive with human CD38, in which case they were directed against a common disulfide-requiring conformational epitope that was mapped to the C-terminal disulfide loop.

Conclusion

This multi-faceted characterization of CD38 from cynomolgus macaque demonstrates its high genetic and biochemical similarities with human CD38 while the immunological comparison adds new insights into the dominant epitopes of the primate CD38 ectodomain. These results open new prospects for the biomedical and pharmacological investigations of this receptor-enzyme.

CD38 autoimmunity: recent advances and relevance to human diabetes

Human CD38 is a protein which catalyzes the synthesis of nicotinic acid adenine dinucleotide (NAADP+) and the conversion of NAD+ to cADPR. Both cADPR and NAADP+ are powerful intracellular Ca2+ ([Ca2+]i) mobilizers in different cell types. Recently, the presence of CD38 autoantibodies has been found in a significant number (9-15%) of patients with Type 2 or long-standing Type 1 diabetes. These autoantibodies are biologically active, the majority of them (-60%) displaying agonistic properties, i.e., [Ca2+]i mobilization in lymphocytic cell lines and in pancreatic islets. In cultured rat pancreatic islets, the human autoantibodies inhibit glucose-induced insulin release, whereas, in human pancreatic islets CD38 autoantibodies stimulate glucose-mediated insulin secretion. The clinical phenotype of anti-CD38-positive Type 2 diabetes differs from the LADA (latent autoimmune diabetes of adults) phenotype. When accurately matched for age and obesity, only LADA patients with anti-GAD antibodies, but not GAD-negative/ CD38-positive patients, have reduced in vivo beta-cell function in comparison to antibody-negative patients. Transgenic mice overexpressing CD38 show enhanced glucose-induced insulin release, whereas, conversely, CD38 knockout mice display a severe impairment in beta-cell function. Few Japanese diabetic patients carry a missense mutation in the CD38 gene; in Caucasian patients mutations in the CD38 gene have not been found. Collectively, these findings suggest that activation of CD38 represents an alternative signaling pathway for glucose-induced insulin secretion in human beta-cells. More information, however, is necessary to gauge the role of CD38 autoimmunity in the context of the natural history of human Type 1 or Type 2 diabetes.

CD38 polymorphisms in Spanish patients with systemic lupus erythematosus

The ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase (CD38) gene is a positional and functional candidate gene for the susceptibility to systemic lupus erythematosus (SLE) because CD38 gene maps in the described SLE risk region 4p15 and CD38 molecule is a leukocyte activation antigen and ectoenzyme involved in numerous immune functions. The aim of this study was to investigate the possible association of the polymorphisms located at positions 182 of intron 1 (C/G) and 418 (C/T, located in exon 3) of the CD38 gene with the susceptibility and clinical features of SLE. Genotyping of 276 Spanish patients with SLE and 194 controls was performed by polymerase chain reaction amplification-refractory mutation system techniques. No association between the polymorphisms studied and the susceptibility to SLE was found. However, when patients were stratified according to their clinical manifestations, a significant increase of CC individuals and a significant decrease of CG individuals among patients with discoid rash (67.9% vs. 53.1% in controls p = 0.02, pc > 0.05, odds ratio [OR] = 1.87, 95% confidence interval [95% CI] 1.05-3.35; and 23.5% vs. 40.2% in controls, p = 0.008, pc = 0.024, OR = 0.46 95% CI 0.24-0.85) were found. Logistic regression analysis identified CC genotype as an independent risk factor for discoid rash among patients with SLE (p = 0.01, OR = 2.23, 95% CI 1.19-4.18). In conclusion, a slight contribution of the polymorphism located in intron 1 of the CD38 gene in the clinical features of SLE could be postulated.

Insulin constitutively secreted by beta-cells is necessary for glucose-stimulated insulin secretion

Four hypotheses have been posited on the role of insulin in glucose-stimulated insulin secretion; available evidence has supported insulin as being 1) essential, 2) a positive modulator, 3) a negative modulator, or 4) not necessary. Because circulating insulin levels in mice, before or after intraperitoneal glucose injection, are sufficient to elicit insulin responses in insulin-sensitive tissues, it is likely that beta-cell insulin receptors are continuously exposed to stimulating concentrations of insulin. To determine whether constitutively secreted insulin is necessary for glucose-stimulated insulin secretion, CD1 male mouse islets were incubated for 30 min at 4 degrees C in the absence (control) or presence of anti-insulin (1 micro g/ml) or anti-IgG (1 micro g/ml). Then islets were exposed to 3, 11, or 25 mmol/l glucose or to 20 mmol/l arginine. Nontreated islets exhibited first- and second-phase glucose-stimulated insulin secretion. Control and anti-IgG-treated islets, after a 5-min lag phase, increased their insulin secretion in 25 mmol/l glucose. Anti-insulin-treated islets secreted insulin at a basal rate in 3 or 25 mmol/l glucose buffers. Insulin secretion stimulated by 20 mmol/l arginine was the same in islets pretreated with either antibody and showed no lag phase. Taken together, these data suggest that constitutively secreted insulin is required and sufficient for beta-cells to maintain sensitivity to glucose.

CD38/cyclic ADP-ribose-mediated Ca2+ signaling contributes to airway smooth muscle hyper-responsiveness

We previously demonstrated that cyclic ADP-ribose (cADPR) elicits Ca2+ release in airway smooth muscle (ASM) cells through ryanodine receptor channels. CD38 is a cell surface protein that catalyzes the synthesis and degradation of cADPR. In inflammatory diseases such as asthma, augmented Ca2+ responses and Ca2+ sensitivity contribute to increased ASM contractility in response to agonists. In this study, we investigated the regulation of CD38 expression and the role of cADPR-mediated Ca2+ release in airway inflammation. Human ASM cells in culture between the second and fifth passages were exposed to tumor necrosis factor alpha (TNF-alpha), interleukin 1beta, or interferon gamma, or bovine serum albumin (controls). CD38 expression was measured by reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR, and Western blot analysis, and ADP-ribosyl cyclase activity was assayed with nicotinamide guanine dinucleotide as the substrate. Ca2+ responses to acetylcholine, bradykinin, and thrombin were measured in fura-2AM-loaded cells by fluorescence microscopy. Cytokines caused significant augmentation of CD38 expression, ADP-ribosyl cyclase activity, and Ca2+ responses to the agonists, compared with the control. TNF-alpha effects were greater than those of the other two cytokines. The cADPR antagonist 8-bromo-cADPR attenuated the Ca2+ responses to the agonists in control and cytokine-treated cells, with the magnitude of inhibition correlating with the level of CD38. This study provides the first demonstration of a role for CD38-cADPR signaling in a model of inflammatory airway disease.

Recent advances in physiological and pathological significance of tryptophan-NAD+ metabolites: lessons from insulin-producing pancreatic beta-cells

In the early 1980s we found that streptozotocin and alloxan, typical diabetogenic agents, induce pancreatic beta-cell DNA strand breaks through the formation of free radicals. The breaks induce DNA repair involving the activation of poly(ADP-ribose) polymerase (PARP), which uses NAD+ as a substrate. As a result, the intracellular levels of NAD+ fall dramatically. The fall in NAD+ inhibits cellular functions including insulin synthesis and secretion, and thus the beta-cell ultimately dies. We subsequently proposed that maintenance of the NAD+ level is essential for the synthesis and secretion of insulin, and presented a unifying model for beta-cell damage and its prevention (The Okamoto model), in which PARP activation plays an essential role. Recently, the model was reconfirmed by experiments using PARP knockout mice and has been recognized as providing the basis for necrotic death of various cells and tissues. In 1993, we found that cyclic ADP-ribose (cADPR), a metabolite of NAD+, is a second messenger for intracellular Ca2+ mobilization for insulin secretion by glucose, and proposed a novel mechanism of insulin secretion, the CD38-cADPR signal system. Recently, various physiological phenomena from animal to plant cells become understandable in terms of this signal system. In 1984, we demonstrated that the administration of PARP inhibitors to 90% depancreatized rats induces islet regeneration. From the regenerating islet-derived cDNA library we found a novel beta-cell growth factor gene, Reg (Regenerating Gene), and elucidated the mechanism of Reg gene expression in beta-cells, in which PARP acts as a transcription factor for Reg gene expression. PARP bound to the cis-element of Reg promoter and formed the active transcriptional DNA/protein complex. The complex formation was inhibited depending on the autopoly(ADP-ribosyl)ation of PARP in the complex. Thus, PARP inhibitors enhance and stabilize the complex formation for Reg gene transcription. Reg protein acts as an autocrine/paracrine growth factor to induce beta-cell replication via the Reg receptor and ameliorates experimental diabetes.

Recent advances in the Okamoto model: the CD38-cyclic ADP-ribose signal system and the regenerating gene protein (Reg)-Reg receptor system in beta-cells

Twenty years ago, we first proposed our hypothesis on beta-cell damage and its prevention (the Okamoto model), according to which poly(ADP-ribose) synthetase/polymerase (PARP) activation is critically involved in the consumption of NAD(+), leading to energy depletion and cell death by necrosis. Recently, the model was reconfirmed by results using PARP knockout mice and has been recognized as providing the basis for necrotic death of various cells and tissues. Based on the model, we proposed two signal systems in beta-cells: one is the CD38-cyclic ADP-ribose (cADPR) signal system for insulin secretion, and the other is the regenerating gene protein (Reg)-Reg receptor system for beta-cell regeneration. The physiological and pathological significance of the two signal systems in a variety of cells and tissues as well as in pancreatic beta-cells has recently been recognized. Here, we describe the Okamoto model and its descendents, the CD38-cADPR signal system and the Reg-Reg receptor system, focusing on recent advances and how their significance came to light. Because PARP is involved in Reg gene transcription to induce beta-cell regeneration, and the PARP activation reduces the cellular NAD(+) to decrease the formation of cADPR (a second messenger for insulin secretion) and further to cause necrotic beta-cell death, PARP and its inhibitors have key roles in the induction of beta-cell regeneration, the maintenance of insulin secretion, and the prevention of beta-cell death.

cADP-ribose/ryanodine channel/Ca2+-release signal transduction pathway in mesangial cells

Signaling via release of Ca2+ from intracellular stores is mediated by several systems, including the inositol 1,4,5-trisphosphate (IP3) and cADP-ribose (cADPR) pathway. We recently discovered a high capacity for cADPR synthesis in rat glomeruli and cultured mesangial cells (MC). We sought to determine whether 1) cADPR synthesis in MC is regulated by cytokines and hormones, 2) ryanodine receptors (RyRs) are expressed in MC, and 3) Ca2+ is released through RyRs in response to cADPR. We found that ADP-ribosyl cyclase, a CD38-like enzyme that catalyzes cADPR synthesis, is upregulated in MC by tumor necrosis factor-alpha, interleukin-1beta, and all-trans retinoic acid (atRA). [3H]ryanodine binds to microsomal fractions from MC with high affinity in a Ca2+-dependent manner; binding is enhanced by specific RyR agonists and blocked by ruthenium red and cADPR. Western blot analysis confirmed the presence of RyR in MC. Release of 45Ca2+ from MC microsomes was stimulated by cADPR; release was blocked by ruthenium red and 8-bromo-cADPR. ADPR (non-cyclic) was without effect. In MC, TNF-alpha and atRA amplified the increment of cytoplasmic Ca2+ elicited by vasopressin. We conclude that MC possess elements of a novel ADP-ribosyl cyclase-->cADPR-->RyR-->Ca2+-release signaling pathway subject to regulation by proinflammatory cytokines and steroid superfamily hormones.

Significance of ecto-cyclase activity of CD38 in insulin secretion of mouse pancreatic islet cells

Cyclic ADP-ribose (cADPR), a product of CD38, has a second messenger role for in intracellular Ca(2+) mobilization from microsomes of pancreatic islets as well as from a variety of other cells. ADP-ribosylation of CD38 by ecto-mono ADP-ribosyltransferase in activated T cells results in apoptosis as well as inactivation of its activities. We, therefore, examined the effect of ADP-ribosylation of CD38 in mouse pancreatic islet cells. NAD-dependent inactivation and ADP-ribosylation of CD38, intracellular concentrations of cADPR and Ca(2+), and insulin secretion were measured following incubation of mouse pancreatic islet cells with NAD. ADP-ribosylation of CD38 inactivated its ecto-enzyme activities, and abolished glucose-induced increase of cADPR production, intracellular concentration of Ca(2+), and insulin secretion. Taken together, ecto-cyclase activity of CD38 to produce intracellular cADPR seems to be indispensable for insulin secretion.

Autoantibody response to CD38 in Caucasian patients with type 1 and type 2 diabetes: immunological and genetic characterization

Insulin secretion is one of the functions mediated by CD38, a nonlineage pleiotropic cell surface receptor. The molecule is the target of an autoimmune response, because serum autoantibodies (aAbs) to CD38 have been detected in diabetic patients. In the healthy Caucasian population, the CD38 gene is bi-allelic (86% CD38*B and 14% CD38*A), whereas an Arg140Trp mutation has been identified in Japanese diabetic patients. We investigated the relationship between CD38 and diabetes in Caucasian patients by characterizing anti-CD38 aAbs in terms of prevalence and function (agonistic/nonagonistic activity) and by exploring the potential influence of the CD38 genetic background. A novel enzymatic immunoassay, using recombinant soluble CD38 as the target antigen, was developed for the analysis of anti-CD38 aAb titers. Sera from 19.15% of type 1 and 16.67% of type 2 diabetic patients were positive. The majority of anti-CD38 aAbs (57.14%) displayed agonistic properties, i.e., they demonstrated the capability to trigger Ca2+ release in lymphocytic cell lines. In agreement with these functional features, the presence of anti-CD38 aAbs in type 2 diabetic patients was associated with significantly higher levels of fasting plasma C-peptide and insulin, as compared with anti-CD38-counterparts. No diabetic subject carrying the Arg140Trp mutation and no preferential association between diabetes or aAb status and the CD38*A allele was found in the study population. These results show the significance of anti-CD38 aAbs as a new diagnostic marker of beta-cell autoimmunity in diabetes. Moreover, the prevalent agonistic activity of these aAbs suggests that they could mediate relevant effects on target cells by means of Ca2+ mobilization.

Human CD38: a (r)evolutionary story of enzymes and receptors

Human CD38 is the mammalian prototype of a family of proteins which share structural similarities and an ectoenzymatic activity involved in the production of calcium mobilizing compounds. Besides the enzymatic activity, the molecule performs as a receptor, ruling adhesion and signaling in leukocytes. These functions are exerted through the interaction with surface ligands, one of which was identified as CD31. Recently, CD38 has gained attention as a prognostic marker and a pathogenetic agent in leukemias and in other diseases. Together these insights have produced a model of an as yet unique family of molecules, which act independently as receptors and enzymes.

Cyclic ADP ribose as a calcium-mobilizing messenger

This Perspective by Galione and Churchill is one in a series on intracellular calcium release mechanisms. The authors review the evidence for cyclic adenosine diphosphate ribose (cADPR) being a second messenger involved in regulating intracellular calcium. In addition, the physiological stimuli and responses mediated by cADPR are discussed. The Perspective is accompanied by a movie showing a calcium wave triggered by cADPR.

Molecular cloning and functional expression of bovine spleen ecto-NAD+ glycohydrolase: structural identity with human CD38

Bovine spleen ecto-NAD(+) glycohydrolase, an archetypal member of the mammalian membrane-associated NAD(P)(+) glycohydrolase enzyme family (EC 3.2.2.6), displays catalytic features similar to those of CD38, i.e. a protein originally described as a lymphocyte differentiation marker involved in the metabolism of cyclic ADP-ribose and signal transduction. Using amino acid sequence information obtained from NAD(+) glycohydrolase and from a truncated and hydrosoluble form of the enzyme (hNADase) purified to homogeneity, a full-length cDNA clone was obtained. The deduced sequence indicates a protein of 278 residues with a molecular mass of 31.5 kDa. It predicts that bovine ecto-NAD(+) glycohydrolase is a type II transmembrane protein, with a very short intracellular tail. The bulk of the enzyme, which is extracellular and contains two potential N-glycosylation sites, yields the fully catalytically active hNADase which is truncated by 71 residues. Transfection of HeLa cells with the full-length cDNA resulted in the expression of the expected NAD(+) glycohydrolase, ADP-ribosyl cyclase and GDP-ribosyl cyclase activities at the surface of the cells. The bovine enzyme, which is the first 'classical' NAD(P)(+) glycohydrolase whose structure has been established, presents a particularly high sequence identity with CD38, including the presence of 10 strictly conserved cysteine residues in the ectodomain and putative catalytic residues. However, it lacks two otherwise conserved cysteine residues near its C-terminus. Thus hNADase, the truncated protein of 207 amino acids, represents the smallest functional domain endowed with all the catalytic activities of CD38/NAD(+) glycohydrolases so far identified. Altogether, our data strongly suggest that the cloned bovine spleen ecto-NAD(+) glycohydrolase is the bovine equivalent of CD38.

CD38 disruption impairs glucose-induced increases in cyclic ADP-ribose, [Ca2+]i, and insulin secretion

Increases in [Ca2+]i in pancreatic beta cells, resulting from Ca2+ mobilization from intracellular stores as well as Ca2+ influx from extracellular sources, are important in insulin secretion by glucose. Cyclic ADP-ribose (cADPR), accumulated in beta cells by glucose stimulation, has been postulated to serve as a second messenger for intracellular Ca2+ mobilization for insulin secretion, and CD38 is thought to be involved in the cADPR accumulation (Takasawa, S., Tohgo, A., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T., Yonekura, H., and Okamoto, H. (1993) J. Biol. Chem. 268, 26052-26054). Here we created "knockout" (CD38(-/-)) mice by homologous recombination. CD38(-/-) mice developed normally but showed no increase in their glucose-induced production of cADPR in pancreatic islets. The glucose-induced [Ca2+]i rise and insulin secretion were both severely impaired in CD38(-/-) islets, whereas CD38(-/-) islets responded normally to the extracellular Ca2+ influx stimulants tolbutamide and KCl. CD38(-/-) mice showed impaired glucose tolerance, and the serum insulin level was lower than control, and these impaired phenotypes were rescued by beta cell-specific expression of CD38 cDNA. These results indicate that CD38 plays an essential role in intracellular Ca2+ mobilization by cADPR for insulin secretion.