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In a mouse model of ischaemia, mitochondrial particles released from astroctyes are taken up by adjacent neurons, leading to enhanced cell survival signalling; disruption of this release mechanism resulted in worsened neurological outcomes. Neuroprotective effects of neuroglial crosstalk Emerging results suggest that neurons can transfer damaged mitochondria into adjacent astrocytes for disposal and recycling. Here Eng Lo and colleagues identify a transfer of healthy mitochondria in the opposite direction. In a mouse model of ischaemia, the authors demonstrate the release of mitochondrial particles from astrocytes that are taken up by adjacent neurons, leading to enhanced cell survival signalling. Disrupting this transfer led to worsened neurological outcomes. These findings suggest a previously unknown form of crosstalk between glia and damaged neurons, and suggest pathways that may be potentially targeted for improving stroke recovery in the future. Neurons can release damaged mitochondria and transfer them to astrocytes for disposal and recycling 1 . This ability to exchange mitochondria may represent a potential mode of cell-to-cell signalling in the central nervous system. Here we show that astrocytes in mice can also release functional mitochondria that enter neurons. Astrocytic release of extracellular mitochondrial particles was mediated by a calcium-dependent mechanism involving CD38 and cyclic ADP ribose signalling. Transient focal cerebral ischaemia in mice induced entry of astrocytic mitochondria into adjacent neurons, and this entry amplified cell survival signals. Suppression of CD38 signalling by short interfering RNA reduced extracellular mitochondria transfer and worsened neurological outcomes. These findings suggest a new mitochondrial mechanism of neuroglial crosstalk that may contribute to endogenous neuroprotective and neurorecovery mechanisms after stroke.

Acute myocardial infarction (AMI) is serious disease with high morbidity and mortality worldwide. CD38 is an important metabolic enzyme and plays an important role in a variety of diseases. Our previous studies demonstrated that CD38 deficiency significantly reduced Ang-II-induced ventricular hypertrophy and cardiac ischemia-reperfusion injury. However, the roles of cardiomyocytic CD38 in acute myocardial infarction (AMI) remain unknown. Here, we reported that cardiomyocyte-specific CD38 deficiency (CD38 CKO ) significantly improved heart functions in AMI. We observed that CD38 CKO remarkably reduced the fibrosis at the peri-infarct area, and inhibited the apoptosis of cardiomyocytes in infarcted area by elevating the ratio of mitochondrial Bcl2/Bax expression and increased the expressions of the mitochondrial fusion proteins Mfn1 and Mfn2 in the early stage of AMI. Consistently, knockdown of CD38 protected hypoxia-induced apoptosis in cardiomyocytes by increasing the ratio of Bcl2/Bax expression and decreasing cleaved caspase-3. More importantly, 3-TYP, a Sirt3 inhibitor, significantly increased hypoxia-induced apoptosis in CD38-deficient primary cardiomyocytes. In conclusion, our results demonstrated that CD38 CKO suppressed apoptosis of cardiomyocytes in the infracted area of heart via activating NAD + /Sirt3-mediated signaling pathways.

CD38, a transmembrane glycoprotein with ADP-ribosyl cyclase activity, catalyses the formation of Ca 2+ 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 Ca 2+ 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. A niceness protein? An unexpected activity of the transmembrane signalling glycoprotein CD38 suggests that it has a novel role in the regulation of maternal and social behaviours. Found on the surface of many immune cells, CD38 is involved in the fertilization of invertebrate eggs, in HIV infection, cancers and diabetes. The high levels of CD38 in the brain, previously rather puzzling, make more sense now it has been found that it regulates plasma levels of the hormone oxytocin in mice. Mice lacking CD38 show defective nurturing behaviour (in females) and social behaviour (in males). This makes CD38 a possible factor in neurodevelopment disorders.

Cardiac hypertrophy is an early hallmark during the clinical course of heart failure and regulated by various signalling pathways. Recently, we observed that mouse embryonic fibroblasts from CD38 knockout mice were significantly resistant to oxidative stress such as H2O2‐induced injury and hypoxia/reoxygenation‐induced injury. In addition, we also found that CD38 knockout mice protected heart from ischaemia reperfusion injury through activating SIRT1/FOXOs‐mediated antioxidative stress pathway. However, the role of CD38 in cardiac hypertrophy is not explored. Here, we investigated the roles and mechanisms of CD38 in angiotensin II (Ang‐II)‐induced cardiac hypertrophy. Following 14 days of Ang‐II infusion with osmotic mini‐pumps, a comparable hypertension was generated in both of CD38 knockout and wild‐type mice. However, the cardiac hypertrophy and fibrosis were much more severe in wild‐type mice compared with CD38 knockout mice. Consistently, RNAi‐induced knockdown of CD38 decreased the gene expressions of atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) and reactive oxygen species generation in Ang‐II‐stimulated H9c2 cells. In addition, the expression of SIRT3 was elevated in CD38 knockdown H9c2 cells, in which SIRT3 may further activate the FOXO3 antioxidant pathway. The intracellular Ca2+ release induced by Ang‐II markedly decreased in CD38 knockdown H9c2 cells, which might be associated with the decrease of nuclear translocation of NFATc4 and inhibition of ERK/AKT phosphorylation. We concluded that CD38 plays an essential role in cardiac hypertrophy probably via inhibition of SIRT3 expression and activation of Ca2+‐NFAT signalling pathway. Thus, CD38 may be a novel target for treating cardiac hypertrophy.

CD38 is a multifunctional protein widely expressed in cells from the immune system and as a soluble form in biological fluids. CD38 expression is up-regulated by an array of inflammatory mediators, and it is frequently used as a cell activation marker. Studies in animal models indicate that CD38 functional expression confers protection against infection by several bacterial and parasitic pathogens. In addition, infectious complications are associated with anti-CD38 immunotherapy. Although CD38 displays receptor and enzymatic activities that contribute to the establishment of an effective immune response, recent work raises the possibility that CD38 might also enhance the immunosuppressive potential of regulatory leukocytes. This review integrates the current knowledge on the diversity of functions mediated by CD38 in the host defense to infection.

Ischemia/reperfusion (I/R) injury induces irreversible oxidative stress damage to the cardiac muscle. We previously observed that CD38 deficiency remarkably protects mouse embryonic fibroblasts (MEFs) from oxidative stress-induced injury. However, whether CD38 deficiency protects from I/R injury in the heart is not explored. Here, we showed that the hearts of CD38 deficient mice or wild type mice supplied with exogenous NAD were significantly protected from ischemia/reperfusion injury, seen as reduction of the myocardial infarct sizes when the mice were subjected to 30 min ischemia followed by 24 hours of reperfusion. Consistently, the protection of CD38 deficiency on hypoxia/reoxygenation (H/R) injury was confirmed with a CD38 knockdown H9c2 stable cell line. Furthermore, we observed that knockdown of CD38 remarkably inhibited ROS generation and intracellular Ca2+ overloading induced by H/R in H9c2 cells. The FOXO1 and FOXO3 expressions were significantly elevated by H/R injury in CD38 knockdown cells compared with normal H9c2 cells. The cell immunofluorescence assay showed that FOXO1 nuclear translocation was significantly increased in CD38 knockdown H9c2 cells. In addition, we demonstrated that the increase of FOXO1 nuclear translocation was associated with the increased expressions of antioxidant catalase and SOD2 and the attenuated expression of the ROS generation enzyme NOX4. In conclusion, our results provide new evidence that CD38 deficiency protects the heart from I/R injury through activating SIRT1/FOXOs-mediated antioxidative stress pathway.

It has been recently reported that CD38 was highly expressed in adipose tissues from obese people and CD38‐deficient mice were resistant to high‐fat diet (HFD)‐induced obesity. However, the role of CD38 in the regulation of adipogenesis and lipogenesis is unknown. In this study, to explore the roles of CD38 in adipogenesis and lipogenesis in vivo and in vitro, obesity models were generated with male CD38−/− and WT mice fed with HFD. The adipocyte differentiations were induced with MEFs from WT and CD38−/− mice, 3T3‐L1 and C3H10T1/2 cells in vitro. The lipid accumulations and the alternations of CD38 and the genes involved in adipogenesis and lipogenesis were determined with the adipose tissues from the HFD‐fed mice or the MEFs, 3T3‐L1 and C3H10T1/2 cells during induction of adipocyte differentiation. The results showed that CD38−/− male mice were significantly resistant to HFD‐induced obesity. CD38 expressions in adipocytes were significantly increased in WT mice fed with HFD, and the similar results were obtained from WT MEFs, 3T3‐L1 and C3H10T1/2 during induction of adipocyte differentiation. The expressions of PPARγ, AP2 and C/EBPα were markedly attenuated in adipocytes from HFD‐fed CD38−/− mice and CD38−/− MEFs at late stage of adipocyte differentiation. Moreover, the expressions of SREBP1 and FASN were also significantly decreased in CD38−/− MEFs. Finally, the CD38 deficiency‐mediated activations of Sirt1 signalling were up‐regulated or down‐regulated by resveratrol and nicotinamide, respectively. These results suggest that CD38 deficiency impairs adipogenesis and lipogenesis through activating Sirt1/PPARγ‐FASN signalling pathway during the development of obesity.

The disruption in transportation of oxLDL‐derived cholesterol and the subsequent lipid accumulation in macrophages are the hallmark events in atherogenesis. Our recent studies demonstrated that lysosomal Ca2+ messenger of nicotinic acid adenine dinucleotide phosphate (NAADP), an enzymatic product of CD38 ADP‐ribosylcyclase (CD38), promoted lipid endocytic trafficking in human fibroblast cells. The current studies are designed to examine the functional role of CD38/NAADP pathway in the regulation of lysosomal cholesterol efflux in atherosclerosis. Oil red O staining showed that oxLDL concentration‐dependently increased lipid buildup in bone marrow‐derived macrophages from both wild type and CD38−/−, but to a significant higher extent with CD38 gene deletion. Bodipy 493/503 fluorescence staining found that the deposited lipid in macrophages was mainly enclosed in lysosomal organelles and largely enhanced with the blockade of CD38/NAADP pathway. Filipin staining and direct measurement of lysosome fraction further revealed that the free cholesterol constituted a major portion of the total cholesterol segregated in lysosomes. Moreover, in situ assay disclosed that both lysosomal lumen acidity and the acid lipase activity were reduced upon cholesterol buildup in lysosomes. In CD38−/− mice, treatment with Western diet (12 weeks) produced atherosclerotic damage in coronary artery with striking lysosomal cholesterol sequestration in macrophages. These data provide the first experimental evidence that the proper function of CD38/NAADP pathway plays an essential role in promoting free cholesterol efflux from lysosomes and that a defection of this signalling leads to lysosomal cholesterol accumulation in macrophages and results in coronary atherosclerosis in CD38−/− mice.

This study aimed to elucidate the transcriptomic signatures and dysregulated pathways associated with the autoimmune response in Cd38 -/- mice compared to wild-type (WT) mice within the bm12 chronic graft-versus-host disease (cGVHD) lupus model. We conducted bulk RNA sequencing on peritoneal exudate cells (PECs) and spleen cells (SPC) at two and four weeks following adoptive cell transfer. We also analyzed cells from healthy, untreated mice. These analyses revealed a sustained upregulation of a transcriptional profile of purinergic receptors and ectonucleotidases in cGVHD WT PECs, which displayed a coordinated expression with several type I interferon-stimulated genes (ISGs) and with key molecules involved in the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling pathway, two hallmarks in the lupus pathology. A second purinergic receptor transcriptomic profile, which included P2rx7 and P2rx4 , showed a coordinated gene expression of the components of the NLRP3 inflammasome with its potential activators. These processes were transcriptionally less active in cGVHD Cd38 -/- PECs than in WT PECs. We have also shown evidence of a distinct enrichment in pathways signatures that define processes such as Ca 2+ ion homeostasis, cell division, phagosome, autophagy, senescence, cytokine/cytokine receptor interactions, Th17 and Th1/Th2 cell differentiation in Cd38 -/- versus WT samples, which reflected the milder inflammatory and autoimmune response elicited in Cd38 -/- mice relative to WT counterparts in response to the allogeneic challenge. Last, we have shown an intense metabolic reprogramming toward oxidative phosphorylation in PECs and SPC from cGVHD WT mice, which may reflect an increased cellular demand for oxygen consumption, in contrast to PECs and SPC from cGVHD Cd38 -/- mice, which showed a short-lived metabolic effect at the transcriptomic level. Overall, these findings support the pro-inflammatory and immunomodulatory role of CD38 during the development of the cGVHD-lupus disease.

Natural killer (NK) cells are essential for immunosurveillance against transformed cells. Transient receptor potential melastatin 2 (TRPM2) is a Ca 2+ -permeable cation channel gated by ADP-ribose (ADPR). However, the role of TRPM2-mediated Ca 2+ signaling in the antitumor response of NK cells has not been explored. Here, we show that ADPR-mediated Ca 2+ signaling is important for cytolytic granule polarization and degranulation but not involved in target cell recognition by NK cells. The key steps of this pathway are: 1) the activation of intracellular CD38 by protein kinase A following the interaction of the NK cell with a tumor cell results in the production of ADPR, 2) ADPR targets TRPM2 channels on cytolytic granules and 3) TRPM2-mediated Ca 2+ signaling induces cytolytic granule polarization and degranulation, resulting in antitumor activity. NK cells treated with 8-Br-ADPR, an ADPR antagonist, as well as NK cells from Cd38 −/− mice showed reduced tumor-induced granule polarization, degranulation, granzyme B secretion and cytotoxicity of NK cells. Furthermore, TRPM2-deficient NK cells showed an intrinsic defect in tumoricidal activity. These results highlight CD38, ADPR and TRPM2 as key players in the specialized Ca 2+ signaling system involved in the antitumor activity of NK cells.