CD38/cyclic ADP-ribose regulates astrocyte calcium signaling: implications for neuroinflammation and HIV-1-associated dementia

Nampt: a new therapeutic target for modulating NAD+ levels in metabolic, cardiovascular, and neurodegenerative diseases

NAD+ is an important cofactor involved in regulating many biochemical processes in cells. An imbalance in NAD+/NADH ratio is linked to many diseases. NAD+ is depleted in diabetes, cardiovascular and neurodegenerative diseases, and in aging, and is increased in tumor cells. NAD+ is generated in cells via the de novo, Preiss-Handler, and salvage pathways. Most of the cellular NAD+ is generated through Nampt activation, a key rate-limiting enzyme that is involved in the salvage pathway. Restoration of NAD+/NADH balance offers therapeutic advantages for improving tissue homeostasis and function. NAD+ is known to benefit and restore the body's physiological mechanisms, including DNA replication, chromatin and epigenetic modifications, and gene expression. Recent studies elucidate the role of NAD+ in cells utilizing transgenic mouse models. Translational new therapeutics are positioned to utilize the NAD+ restoration strategies for overcoming the drawbacks that exist in the pharmacological toolkit. The present review highlights the significance of Nampt-NAD+ axis as a major player in energy metabolism and provides an overview with insights into future strategies, providing pharmacological advantages to address current and future medical needs.

Pathobiochemistry of Aging and Neurodegeneration: Deregulation of NAD+ Metabolism in Brain Cells

NAD+ plays a pivotal role in energy metabolism and adaptation to external stimuli and stressful conditions. A significant reduction in intracellular NAD+ levels is associated with aging and contributes to the development of chronic cardiovascular, neurodegenerative, and metabolic diseases. It is of particular importance to maintain optimal levels of NAD+ in cells with high energy consumption, particularly in the brain. Maintaining the tissue level of NAD+ with pharmacological tools has the potential to slow down the aging process, to prevent the development of age-related diseases. This review covers key aspects of NAD+ metabolism in terms of brain metabolic plasticity, including NAD+ biosynthesis and degradation in different types of brain cells, as well as its contribution to the development of neurodegeneration and aging, and highlights up-to-date approaches to modulate NAD+ levels in brain cells.

Chrono-Gerontology: Integrating Circadian Rhythms and Aging in Stroke Research

Stroke is a significant public health concern for elderly individuals. However, the majority of pre-clinical studies utilize young and healthy rodents, which may result in failure of candidate therapies in clinical trials. In this brief review/perspective, the complex link between circadian rhythms, aging, innate immunity, and the gut microbiome to ischemic injury onset, progression, and recovery is discussed. Short-chain fatty acids and nicotinamide adenine dinucleotide+ (NAD+ ) production by the gut microbiome are highlighted as key mechanisms with profound rhythmic behavior, and it is suggested to boost them as prophylactic/therapeutic approaches. Integrating aging, its associated comorbidities, and circadian regulation of physiological processes into stroke research may increase the translational value of pre-clinical studies and help to schedule the optimal time window for existing practices to improve stroke outcome and recovery.

Postnatal expression of CD38 in astrocytes regulates synapse formation and adult social memory

Social behavior is essential for health, survival, and reproduction of animals; however, the role of astrocytes in social behavior remains largely unknown. The transmembrane protein CD38, which acts both as a receptor and ADP-ribosyl cyclase to produce cyclic ADP-ribose (cADPR) regulates social behaviors by promoting oxytocin release from hypothalamic neurons. CD38 is also abundantly expressed in astrocytes in the postnatal brain and is important for astroglial development. Here, we demonstrate that the astroglial-expressed CD38 plays an important role in social behavior during development. Selective deletion of CD38 in postnatal astrocytes, but not in adult astrocytes, impairs social memory without any other behavioral abnormalities. Morphological analysis shows that depletion of astroglial CD38 in the postnatal brain interferes with synapse formation in the medial prefrontal cortex (mPFC) and hippocampus. Moreover, astroglial CD38 expression promotes synaptogenesis of excitatory neurons by increasing the level of extracellular SPARCL1 (also known as Hevin), a synaptogenic protein. The release of SPARCL1 from astrocytes is regulated by CD38/cADPR/calcium signaling. These data demonstrate a novel developmental role of astrocytes in neural circuit formation and regulation of social behavior in adults.

Neurodegeneration and inflammation crosstalk: Therapeutic targets and perspectives

Glia, which was formerly considered to exist just to connect neurons, now plays a key function in a wide range of physiological events, including formation of memory, learning, neuroplasticity, synaptic plasticity, energy consumption, and homeostasis of ions. Glial cells regulate the brain's immune responses and confers nutritional and structural aid to neurons, making them an important player in a broad range of neurological disorders. Alzheimer's, ALS, Parkinson's, frontotemporal dementia (FTD), and epilepsy are a few of the neurodegenerative diseases that have been linked to microglia and astroglia cells, in particular. Synapse growth is aided by glial cell activity, and this activity has an effect on neuronal signalling. Each glial malfunction in diverse neurodegenerative diseases is distinct, and we will discuss its significance in the progression of the illness, as well as its potential for future treatment.

Meta-Analysis on Nicotine's Modulation of HIV-Associated Dementia

HIV-Associated Dementia (HAD) is a significant comorbidity that many HIV-patients face. Our study utilized QIAGEN Ingenuity Pathway Analysis (IPA) to identify and analyze molecular profiles and pathways underlying nicotine's impact on HAD pathology. The Qiagen Knowledge Base (QKB) defines HAD as "Dementia associated with acquired immunodeficiency syndrome (disorder)." Although much remains unknown about HAD pathology, the curated research findings from the QKB shows 5 upregulated molecules that are associated with HAD + : CCL2 (Chemokine (C-C motif) ligand 2), L-glutamic acid, GLS (Glutaminase), POLG (DNA polymerase subunit gamma), and POLB (DNA polymerase subunit beta). The current study focused on these 5 HAD pathology molecules as the phenotype of interest. The Pathway Explorer tool of IPA was used to connect nicotine-associated molecules with the 5 HAD associated molecules (HAD pathology molecules) by connecting 29 overlapping molecules (including transcription regulators, cytokines, kinases, and other enzymes/proteins). The Molecule-Activity-Predictor (MAP) tool predicted nicotine-induced activation of the HAD pathology molecules indicating the exacerbation of HAD. However, alternative pathways with more holistic representations of molecular relationships revealed the potential of nicotine as a neuroprotective treatment. It was found that concurrent with nicotine treatment the individual inactivation of several of the intermediary molecules in the holistic pathways caused the downregulation of the HAD pathology molecules. These findings reveal that nicotine may have therapeutic properties for HAD when given alongside specific inhibitory drugs for one or more of the identified intermediary molecules.

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

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

Novel Approaches Used to Examine and Control Neurogenesis in Parkinson's Disease

Neurogenesis is a key mechanism of brain development and plasticity, which is impaired in chronic neurodegeneration, including Parkinson’s disease. The accumulation of aberrant α-synuclein is one of the features of PD. Being secreted, this protein produces a prominent neurotoxic effect, alters synaptic plasticity, deregulates intercellular communication, and supports the development of neuroinflammation, thereby providing propagation of pathological events leading to the establishment of a PD-specific phenotype. Multidirectional and ambiguous effects of α-synuclein on adult neurogenesis suggest that impaired neurogenesis should be considered as a target for the prevention of cell loss and restoration of neurological functions. Thus, stimulation of endogenous neurogenesis or cell-replacement therapy with stem cell-derived differentiated neurons raises new hopes for the development of effective and safe technologies for treating PD neurodegeneration. Given the rapid development of optogenetics, it is not surprising that this method has already been repeatedly tested in manipulating neurogenesis in vivo and in vitro via targeting stem or progenitor cells. However, niche astrocytes could also serve as promising candidates for controlling neuronal differentiation and improving the functional integration of newly formed neurons within the brain tissue. In this review, we mainly focus on current approaches to assess neurogenesis and prospects in the application of optogenetic protocols to restore the neurogenesis in Parkinson’s disease.

Effects of O-GlcNAcylation on functional mitochondrial transfer from astrocytes

Mitochondria may be transferred from cell to cell in the central nervous system and this process may help defend neurons against injury and disease. But how mitochondria maintain their functionality during the process of release into extracellular space remains unknown. Here, we report that mitochondrial protein O-GlcNAcylation is a critical process to support extracellular mitochondrial functionality. Activation of CD38-cADPR signaling in astrocytes robustly induced protein O-GlcNAcylation in mitochondria, while oxygen-glucose deprivation and reoxygenation showed transient and mild protein modification. Blocking the endoplasmic reticulum - Golgi trafficking with Brefeldin A or slc35B4 siRNA reduced O-GlcNAcylation, and resulted in the secretion of mitochondria with decreased membrane potential and mtDNA. Finally, loss-of-function studies verified that O-GlcNAc-modified mitochondria demonstrated higher levels of neuroprotection after astrocyte-to-neuron mitochondrial transfer. Collectively, these findings suggest that post-translational modification by O-GlcNAc may be required for supporting the functionality and neuroprotective properties of mitochondria released from astrocytes.

Blood-Brain Barrier and Neurovascular Unit In Vitro Models for Studying Mitochondria-Driven Molecular Mechanisms of Neurodegeneration

Pathophysiology of chronic neurodegeneration is mainly based on complex mechanisms related to aberrant signal transduction, excitation/inhibition imbalance, excitotoxicity, synaptic dysfunction, oxidative stress, proteotoxicity and protein misfolding, local insulin resistance and metabolic dysfunction, excessive cell death, development of glia-supported neuroinflammation, and failure of neurogenesis. These mechanisms tightly associate with dramatic alterations in the structure and activity of the neurovascular unit (NVU) and the blood-brain barrier (BBB). NVU is an ensemble of brain cells (brain microvessel endothelial cells (BMECs), astrocytes, pericytes, neurons, and microglia) serving for the adjustment of cell-to-cell interactions, metabolic coupling, local microcirculation, and neuronal excitability to the actual needs of the brain. The part of the NVU known as a BBB controls selective access of endogenous and exogenous molecules to the brain tissue and efflux of metabolites to the blood, thereby providing maintenance of brain chemical homeostasis critical for efficient signal transduction and brain plasticity. In Alzheimer's disease, mitochondria are the target organelles for amyloid-induced neurodegeneration and alterations in NVU metabolic coupling or BBB breakdown. In this review we discuss understandings on mitochondria-driven NVU and BBB dysfunction, and how it might be studied in current and prospective NVU/BBB in vitro models for finding new approaches for the efficient pharmacotherapy of Alzheimer's disease.

Protein network exploration prioritizes targets for modulating neuroinflammation in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disease associated with a loss of dopaminergic neurons in the substantia nigra of the brain. Neuroinflammation, another hallmark of the disease, is thought to play an important role in the neurodegenerative process. While mitigating neuroinflammation could prove beneficial for Parkinson's disease, identifying the most relevant biological processes and pharmacological targets as well as drugs to modulate them remains highly challenging. The present study aimed to better understand the protein network behind neuroinflammation in Parkinson's disease and to prioritize possible targets for its pharmacological modulation. We first used text-mining to systematically collect the proteins significantly associated to Parkinson's disease neuroinflammation over the scientific literature. The functional interaction network formed by these proteins was then analyzed by integrating functional enrichment, network topology analysis and drug-protein interaction analysis. We identified 57 proteins significantly associated to neuroinflammation in Parkinson's disease. Toll-like Receptor Cascades as well as Interleukin 4, Interleukin 10 and Interleukin 13 signaling appeared as the most significantly enriched biological processes. Protein network analysis using STRING and CentiScaPe identified 8 proteins with the highest ability to control these biological processes underlying neuroinflammation, namely caspase 1, heme oxygenase 1, interleukin 1beta, interleukin 4, interleukin 6, interleukin 10, tumor necrosis factor alpha and toll-like receptor 4. These key proteins were indexed to be targetable by a total of 38 drugs including 27 small compounds 11 protein-based therapies. In conclusion, our study highlights key proteins in Parkinson's disease neuroinflammation as well as pharmacological compounds acting on them. As such, it may facilitate the prioritization of biomarkers for the development of diagnostic, target-engagement assessment and therapeutic tools against Parkinson's disease.

NAD+ metabolism and its roles in cellular processes during ageing

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme for redox reactions, making it central to energy metabolism. NAD+ is also an essential cofactor for non-redox NAD+-dependent enzymes, including sirtuins, CD38 and poly(ADP-ribose) polymerases. NAD+ can directly and indirectly influence many key cellular functions, including metabolic pathways, DNA repair, chromatin remodelling, cellular senescence and immune cell function. These cellular processes and functions are critical for maintaining tissue and metabolic homeostasis and for healthy ageing. Remarkably, ageing is accompanied by a gradual decline in tissue and cellular NAD+ levels in multiple model organisms, including rodents and humans. This decline in NAD+ levels is linked causally to numerous ageing-associated diseases, including cognitive decline, cancer, metabolic disease, sarcopenia and frailty. Many of these ageing-associated diseases can be slowed down and even reversed by restoring NAD+ levels. Therefore, targeting NAD+ metabolism has emerged as a potential therapeutic approach to ameliorate ageing-related disease, and extend the human healthspan and lifespan. However, much remains to be learnt about how NAD+ influences human health and ageing biology. This includes a deeper understanding of the molecular mechanisms that regulate NAD+ levels, how to effectively restore NAD+ levels during ageing, whether doing so is safe and whether NAD+ repletion will have beneficial effects in ageing humans.

CD38 in Neurodegeneration and Neuroinflammation

Neurodegenerative diseases are characterized by neuronal degeneration as well as neuroinflammation. While CD38 is strongly expressed in brain cells including neurons, astrocytes as well as microglial cells, the role played by CD38 in neurodegeneration and neuroinflammation remains elusive. Yet, CD38 expression increases as a consequence of aging which is otherwise the primary risk associated with neurodegenerative diseases, and several experimental data demonstrated that CD38 knockout mice are protected from neurodegenerative and neuroinflammatory insults. Moreover, nicotinamide adenine dinucleotide, whose levels are tightly controlled by CD38, is a recognized and potent neuroprotective agent, and NAD supplementation was found to be beneficial against neurodegenerative diseases. The aims of this review are to summarize the physiological role played by CD38 in the brain, present the arguments indicating the involvement of CD38 in neurodegeneration and neuroinflammation, and to discuss these observations in light of CD38 complex biology.

SETD7 promotes TNF-α-induced proliferation and migration of airway smooth muscle cells in vitro through enhancing NF-κB/CD38 signaling

The inflammation-induced the excessive proliferation and migration of airway smooth muscle (ASM) cells in the airway wall contribute to airway remodeling in asthma pathogenesis. SET domain-containing lysine methyltransferase 7 (SETD7) has emerged as one of the key regulators of inflammation. Yet, the function of SETD7 in regulating inflammation-induced ASM cell proliferation and invasion remains unclear. In the present study, we aimed to investigate the function of SETD7 in regulating ASM cell proliferation and invasion induced by tumor necrosis factor (TNF)-α in vitro. Our results showed that SETD7 expression was upregulated in ASM cells stimulated with TNF-α. Silencing SETD7 significantly decreased TNF-α-induced ASM cell proliferation and migration, while SETD7 overexpression exhibited the opposite effect. Notably, silencing SETD7 decreased the activation of nuclear factor (NF)-κB and reduced the expression of CD38 induced by TNF-α. Blocking NF-κB activation significantly abrogated the promotional effect of SETD7 overexpression on CD38 expression. Moreover, overexpression of CD38 partially reversed the inhibitory effect of SETD7 silencing on TNF-α-induced ASM cell proliferation and migration. Overall, these results demonstrate that SETD7 regulates TNF-α-induced ASM cell proliferation and migration through modulation of NF-κB/CD38 signaling, suggesting a potential role of SETD7 in asthma airway remodeling.

Friends Turn Foe-Astrocytes Contribute to Neuronal Damage in NeuroAIDS

Astrocytes play a wide variety of roles in the central nervous system (CNS). Various facets of astrocyte-neuron interplay, investigated for the past few decades, have placed these most abundant and important glial cell types to be of supreme importance for the maintenance of the healthy CNS. Interestingly, glial dysfunctions have proven to be the major contributor to neuronal loss in several CNS disorders and pathologies. Specifically, in the field of neuroAIDS, glial dysfunction-mediated neuronal stress is a major factor contributing to the HIV-1 neuropathogenesis. As there is increasing evidence that astrocytes harbor HIV-1 and serve as "safe haven" for the dormant virus in the brain, the indirect pathway of neuronal damage has taken over the direct neuronal damage in its contribution to HIV-1 neuropathogenesis. In this review, we provide a brief insight into the astrocyte functions and dysfunctions in different CNS conditions with an elaborated insight into neuroAIDS. Detailed understanding of the role of astrocytes in neuroAIDS will help in the better therapeutic management of the neurological problems associated with HIV-1 patients.

Minocycline reverses diabetes-associated cognitive impairment in rats

BACKGROUND

Minocycline a tetracycline antibiotic is known for anti-inflammatory and neuroprotective actions. Here we determine the therapeutic potential of minocycline against type 2 diabetes associated cognitive decline in rats.

METHODS

High fat diet (HFD) and low dose streptozotocin (STZ; 25 mg/kg) were used to induce diabetes in Sprague-Dawley rats. Fasting blood glucose and haemoglobin (Hb) A1c were measured in these animals. Cognitive parameters were measured using passive avoidance and elevated plus maze test. Hippocampal Acetylcholine esterase (AchE), reduced glutathione (GSH), cytokines, chemokine levels were measured and histopathological evaluations were conducted. The diabetic animals were then given minocycline (50 mg/kg; 15 days) and the above parameters were reassessed. MTT and Lactate dehydrogenase (LDH) assays were conducted on neuronal cells in the presence of glucose with or without minocycline treatment.

RESULTS

We induced diabetes using HFD and STZ in these animals. Animals showed high fasting blood glucose levels (>245 mg/dl) and HbA1c compared to control animals. Diabetes significantly lowered step down latency and increased transfer latency. Diabetic animals showed significantly higher AchE, Tumor necrosis factor (TNF)-α, Interleukin (IL)-1β and Monocyte chemoattractant protein (MCP)-1 and lower GSH levels and reduced both CA1 and CA3 neuronal density compared to controls. Minocycline treatment partially reversed the above neurobehavioral and biochemical changes and improved hippocampal neuronal density in diabetic animals. Cell line studies showed glucosemediated neuronal death, which was considerably reversed upon minocycline treatment.

CONCLUSIONS

Minocycline, primarily by its anti-inflammatory and antioxidant actions prevented hippocampal neuronal loss thus partially reversing the diabetes-associated cognitive decline in rats.

Inhibiting the CD38/cADPR pathway protected rats against sepsis associated brain injury

BACKGROUND

The CD38/cADPR pathway has been found to play roles in various inflammatory conditions. However, whether CD38 plays a protective or detrimental effect in the central nervous system (CNS) is controversial. The aim of this study was to determine the effect of CD38/cADPR pathway in sepsis associated brain injury.

MATERIALS AND METHODS

Male Sprague-Dawley rats were undergone cecal ligation and puncture (CLP) or sham laparotomies. NAD⁺, cADPR and CD38 were measured in the hippocampus of septic rats at 0, 6, 12, 24, and 48h after CLP surgery. Rats were divided into the sham, CLP group, CLP+ CD38 expression lentivirus (CLP+ CD38 LV), CLP+ CD38 interference lentivirus (CLP+ CD38 Ri), CLP+ negative control lentivirus (CLP+NC) and the CLP+8-Br-cADPR groups. The Western blots of Bcl-2, Bax and iNOS, TUNEL assays, malondialdehyde (MDA) and superoxide dismutase (SOD) assays, transmission electron microscope analysis were performed in the hippocampus of rats.

RESULTS

NAD⁺, cADPR and CD38 levels increased significantly in the hippocampus of septic rats as early as 12-24h after CLP surgery. CD38 knockdown or blocking cADPR with 8-Br-cADPR significantly reduced apoptosis, MDA and SOD activity, iNOS expression and ultrastructural morphology damages in the hippocampus of septic rats.

CONCLUSIONS

In this study, we found that the CD38/cADPR pathway was activated in sepsis associated brain injury. Blocking this pathway protected the hippocampus from apoptosis, oxidative stress and ultrastructural morphology damages in septic rats.

Blocking Cyclic Adenosine Diphosphate Ribose-mediated Calcium Overload Attenuates Sepsis-induced Acute Lung Injury in Rats

Background:

Acute lung injury (ALI) is a common complication of sepsis that is associated with high mortality. Intracellular Ca²⁺ overload plays an important role in the pathophysiology of sepsis-induced ALI, and cyclic adenosine diphosphate ribose (cADPR) is an important regulator of intracellular Ca²⁺ mobilization. The cluster of differentiation 38 (CD38)/cADPR pathway has been found to play roles in multiple inflammatory processes but its role in sepsis-induced ALI is still unknown. This study aimed to investigate whether the CD38/cADPR signaling pathway is activated in sepsis-induced ALI and whether blocking cADPR-mediated calcium overload attenuates ALI.

Methods:

Septic rat models were established by cecal ligation and puncture (CLP). Rats were divided into the sham group, the CLP group, and the CLP+ 8-bromo-cyclic adenosine diphosphate ribose (8-Br-cADPR) group. Nicotinamide adenine dinucleotide (NAD⁺), cADPR, CD38, and intracellular Ca²⁺ levels in the lung tissues were measured at 6, 12, 24, and 48 h after CLP surgery. Lung histologic injury, tumor necrosis factor (TNF)-α, malondialdehyde (MDA) levels, and superoxide dismutase (SOD) activities were measured.

Results:

NAD⁺, cADPR, CD38, and intracellular Ca²⁺ levels in the lungs of septic rats increased significantly at 24 h after CLP surgery. Treatment with 8-Br-cADPR, a specific inhibitor of cADPR, significantly reduced intracellular Ca²⁺ levels (P = 0.007), attenuated lung histological injury (P = 0.023), reduced TNF-α and MDA levels (P < 0.001 and P = 0.002, respectively) and recovered SOD activity (P = 0.031) in the lungs of septic rats.

Conclusions:

The CD38/cADPR pathway is activated in the lungs of septic rats, and blocking cADPR-mediated calcium overload with 8-Br-cADPR protects against sepsis-induced ALI.

CD38 in the pathogenesis of allergic airway disease: Potential therapeutic targets

CD38 is an ectoenzyme that catalyzes the conversion of β-nicotinamide adenine dinucleotide (β-NAD) to cyclic adenosine diphosphoribose (cADPR) and adenosine diphosphoribose (ADPR) and NADP to nicotinic acid adenine dinucleotide phosphate (NAADP) and adenosine diphosphoribose-2'-phosphate (ADPR-P). The metabolites of NAD and NADP have roles in calcium signaling in different cell types including airway smooth muscle (ASM) cells. In ASM cells, inflammatory cytokines augment CD38 expression and to a greater magnitude in cells from asthmatics, indicating a greater capacity for the generation of cADPR and ADPR in ASM from asthmatics. CD38 deficient mice develop attenuated airway responsiveness to inhaled methacholine following allergen sensitization and challenge compared to wild-type mice indicating its potential role in asthma. Regulation of CD38 expression in ASM cells is achieved by mitogen activated protein kinases, specific isoforms of PI3 kinases, the transcription factors NF-κB and AP-1, and post-transcriptionally by microRNAs. This review will focus on the role of CD38 in intracellular calcium regulation in ASM, contribution to airway inflammation and airway hyperresponsiveness in mouse models of allergic airway inflammation, the transcriptional and post-transcriptional mechanisms of regulation of expression, and outline approaches to inhibit its expression and activity.

Endothelial Progenitor Cells Physiology and Metabolic Plasticity in Brain Angiogenesis and Blood-Brain Barrier Modeling

Currently, there is a considerable interest to the assessment of blood-brain barrier (BBB) development as a part of cerebral angiogenesis developmental program. Embryonic and adult angiogenesis in the brain is governed by the coordinated activity of endothelial progenitor cells, brain microvascular endothelial cells, and non-endothelial cells contributing to the establishment of the BBB (pericytes, astrocytes, neurons). Metabolic and functional plasticity of endothelial progenitor cells controls their timely recruitment, precise homing to the brain microvessels, and efficient support of brain angiogenesis. Deciphering endothelial progenitor cells physiology would provide novel engineering approaches to establish adequate microfluidically-supported BBB models and brain microphysiological systems for translational studies.

Blocking NAD(+)/CD38/cADPR/Ca(2+) pathway in sepsis prevents organ damage

BACKGROUND

Although the nicotinamide adenine dinucleotide (NAD(+))/CD38/cyclic ADP ribose (cADPR)/Ca(2+) signaling pathway has been shown to regulate intracellular calcium homeostasis and functions in multiple inflammatory processes, its role in sepsis remains unknown. The aim of this study was to determine whether the NAD(+)/CD38/cADPR/Ca(2+) signaling pathway is activated during sepsis and whether an inhibitor of this pathway, 8-Br-cADPR, protects the organs from sepsis-induced damage.

MATERIALS AND METHODS

Male Sprague-Dawley rats were subjected to cecal ligation and puncture (CLP) or sham laparotomies. NAD(+), cADPR, CD38, and intracellular Ca(2+) levels were measured in the hearts, livers, and kidneys of septic rats at 0, 6, 12, 24, and 48 h after CLP surgery. Rats were also divided into sham, CLP, and CLP+8-Br-cADPR groups, and the hearts, livers, and kidneys were hematoxylin-eosin-stained and assayed for malondialdehyde and superoxide dismutase activities.

RESULTS

NAD(+), cADPR, CD38, and intracellular Ca(2+) levels increased in the hearts, livers, and kidneys of septic rats as early as 6-24 h after CLP surgery. Treatment with 8-Br-cADPR inhibited sepsis-induced intracellular Ca(2+) mobilization, attenuated tissue injury, reduced malondialdehyde levels, and increased superoxide dismutase activity in septic rats.

CONCLUSIONS

The NAD(+)/CD38/cADPR/Ca(2+) signaling pathway was activated during sepsis in the CLP rat model. Blocking this pathway with 8-Br-cADPR protected hearts, livers, and kidneys from sepsis-induced damage.

HIV-1, methamphetamine and astrocytes at neuroinflammatory Crossroads

As a popular psychostimulant, methamphetamine (METH) use leads to long-lasting, strong euphoric effects. While METH abuse is common in the general population, between 10 and 15% of human immunodeficiency virus-1 (HIV-1) patients report having abused METH. METH exacerbates the severity and onset of HIV-1-associated neurocognitive disorders (HAND) through direct and indirect mechanisms. Repetitive METH use impedes adherence to antiretroviral drug regimens, increasing the likelihood of HIV-1 disease progression toward AIDS. METH exposure also directly affects both innate and adaptive immunity, altering lymphocyte numbers and activity, cytokine signaling, phagocytic function and infiltration through the blood brain barrier. Further, METH triggers the dopamine reward pathway and leads to impaired neuronal activity and direct toxicity. Concurrently, METH and HIV-1 alter the neuroimmune balance and induce neuroinflammation, which modulates a wide range of brain functions including neuronal signaling and activity, glial activation, viral infection, oxidative stress, and excitotoxicity. Pathologically, reactive gliosis is a hallmark of both HIV-1- and METH-associated neuroinflammation. Significant commonality exists in the neurotoxic mechanisms for both METH and HAND; however, the pathways dysregulated in astroglia during METH exposure are less clear. Thus, this review highlights alterations in astrocyte intracellular signaling pathways, gene expression and function during METH and HIV-1 comorbidity, with special emphasis on HAND-associated neuroinflammation. Importantly, this review carefully evaluates interventions targeting astrocytes in HAND and METH as potential novel therapeutic approaches. This comprehensive overview indicates, without a doubt, that during HIV-1 infection and METH abuse, a complex dialog between all neural cells is orchestrated through astrocyte regulated neuroinflammation.

Alzheimer's disease pathology is attenuated in a CD38-deficient mouse model

OBJECTIVE

Alzheimer's disease (AD)-associated dementia is due to tissue damage caused by amyloid β (Aβ) deposition within the brain and by accompanying neuroinflammation. The nicotinamide adenine dinucleotide (NAD) glycohydrolase CD38, which is expressed by neurons, astrocytes, and microglial cells, regulates inflammatory and repair processes in the brain and other tissues by degrading NAD and repressing the activity of other NAD-consuming enzymes and by producing NAD-derived metabolites that regulate calcium signaling and migration of inflammatory cells. Given the role of CD38 in neuroinflammation and repair, we examined the effect of CD38 deletion on AD pathology.

METHODS

We crossed APPswePS1ΔE9 (APP.PS) mice with Cd38(-) (/) (-) mice to generate AD-prone CD38-deficient animals (APP.PS.Cd38(-) (/) (-) ) and examined AD-related phenotypes in both groups.

RESULTS

APP.PS.Cd38(-) (/) (-) mice exhibited significant reductions in Aβ plaque load and soluble Aβ levels compared to APP.PS mice, and this correlated with improved spatial learning. Although CD38 deficiency resulted in decreased microglia/macrophage (MM) accumulation, the transcription profile of the Cd38(-) (/) (-) and Cd38(+/) (+) MM was similar, suggesting that the decreased Aβ burden in APP.PS.Cd38(-) (/) (-) mice was not due to alterations in MM activation/function. Instead, APP.PS.Cd38(-) (/) (-) neuronal cultures secreted less Aβ and this reduction was mimicked when APP.PS neuronal cultures were treated with inhibitors that blocked CD38 enzyme activity or the signaling pathways controlled by CD38-derived metabolites. Furthermore, β- and γ-secretase activity was decreased in APP.PS.Cd38(-) (/) (-) mice, which correlated with decreased Aβ production.

INTERPRETATION

CD38 regulates AD pathology in the APP.PS model of AD, suggesting that CD38 may be a novel target for AD treatment.

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.

Mapping NAD(+) metabolism in the brain of ageing Wistar rats: potential targets for influencing brain senescence

Over the last decade, the importance of NAD(+) has expanded beyond its role as an essential cofactor for energy metabolism. NAD(+) has emerged as a major signalling molecule that serves as the sole substrate for several enzymatic reactions including the DNA repair enzyme, poly(ADP-ribose) polymerase (PARP), NAD-dependent protein deacetylases or CD38, and transcriptional factors by a new class of histone deacetylases known as sirtuins. NAD(+) levels are regulated by the metabolic status and cellular stress caused by oxidative stress and DNA damage. Since a detailed study of NAD(+) metabolism in the healthy ageing mammalian brain is nascent, we examined the effect of ageing on intracellular NAD(+) metabolism in different brain regions in female Wistar rats in young (3 months), middle aged (12 months) and older adults (24 months). Our results are the first to show a significant decline in intracellular NAD(+) levels and NAD:NADH ratio with ageing in the CNS, occurring in parallel to an increase in lipid peroxidation and protein oxidation (o- and m-tyrosine) and a decline in total antioxidant capacity. Hyperphosphorylation of H2AX levels was also observed together with increased PARP-1 and PARP-2 expression, and CD38 activity, concomitantly with reduced NAD(+) and ATP levels and SIRT1 function in the cortex, brainstem, hippocampus and cerebellum. Reduced activity of mitochondrial complex I-IV and impaired maximum mitochondrial respiration rate were also observed in the ageing rat brain. Among the multiple physiological pathways associated with NAD(+) catabolism, our discovery of CD38 as the major regulator of cellular NAD(+) levels in rat neurons indicates that CD38 is a promising therapeutic target for the treatment of age-related neurodegenerative diseases.

Src homology-2 domain-containing protein tyrosine phosphatase (SHP) 2 and p38 regulate the expression of chemokine CXCL8 in human astrocytes

CXCL8, one of the first chemokines found in the brain, is upregulated in the brains and cerebrospinal fluid of HIV-1 infected individuals suggesting its potential role in human immune deficiency virus (HIV)-associated neuroinflammation. Astrocytes are known to be the major contributors to the CXCL8 pool. Interleukin (IL)-1β activated astrocytes exhibit significant upregulation of CXCL8. In order to determine the signaling pathways involved in CXCL8 regulation in astrocytes, we employed pharmacological inhibitors for non-receptor Src homology-2 domain-containing protein tyrosine phosphatase (SHP) 2 and mitogen-activated protein kinases (MAPK) pathway and observed reduced expression of CXCL8 following IL-1β stimulation. Overexpression of SHP2 and p38 enzymes in astrocytes led to elevated CXCL8 expression; however, inactivating SHP2 and p38 with dominant negative mutants abrogated CXCL8 induction. Furthermore, SHP2 overexpression resulted in higher SHP2 and p38 enzyme activity whereas p38 overexpression resulted in higher p38 but not SHP2 enzyme activity. Phosphorylation of SHP2 was important for phosphorylation of p38, which in turn was critical for phosphorylation of extracellular signal regulated kinase (ERK). Thus, our findings suggest an important role for SHP2 in CXCL8 expression in astrocytes during inflammation, as SHP2, directly or indirectly, modulates p38 and ERK MAPK in the signaling cascade leading to CXCL8 production. This study provides detailed understanding of the mechanisms involved in CXCL8 production during neuroinflammation.

HIV-1 and IL-1β regulate astrocytic CD38 through mitogen-activated protein kinases and nuclear factor-κB signaling mechanisms

Background

Infection with human immunodeficiency virus type-1 (HIV)-1 leads to some form of HIV-1-associated neurocognitive disorders (HAND) in approximately half of the cases. The mechanisms by which astrocytes contribute to HIV-1-associated dementia (HAD), the most severe form of HAND, still remain unresolved. HIV-1-encephalitis (HIVE), a pathological correlate of HAD, affects an estimated 9-11% of the HIV-1-infected population. Our laboratory has previously demonstrated that HIVE brain tissues show significant upregulation of CD38, an enzyme involved in calcium signaling, in astrocytes. We also reported an increase in CD38 expression in interleukin (IL)-1β-activated astrocytes. In the present investigation, we studied regulatory mechanisms of CD38 gene expression in astrocytes activated with HIV-1-relevant stimuli. We also investigated the role of mitogen-activated protein kinases (MAPKs) and nuclear factor (NF)-κB in astrocyte CD38 regulation.

Methods

Cultured human astrocytes were transfected with HIV-1_YU-2 proviral clone and levels of CD38 mRNA and protein were measured by real-time PCR gene expression assay, western blot analysis and immunostaining. Astrocyte activation by viral transfection was determined by analyzing proinflammatory chemokine levels using ELISA. To evaluate the roles of MAPKs and NF-κB in CD38 regulation, astrocytes were treated with MAPK inhibitors (SB203580, SP600125, U0126), NF-κB interfering peptide (SN50) or transfected with dominant negative IκBα mutant (IκBαM) prior to IL-1β activation. CD38 gene expression and CD38 ADP-ribosyl cyclase activity assays were performed to analyze alterations in CD38 levels and function, respectively.

Results

HIV-1_YU-2-transfection significantly increased CD38 mRNA and protein expression in astrocytes (p < 0.01) in a dose-dependent manner and induced astrocyte activation. IL-β-activation of HIV-1_YU-2-transfected astrocytes significantly increased HIV-1 gene expression (p < 0.001). Treatment with MAPK inhibitors or NF-κB inhibitor SN50 abrogated IL-1β-induced CD38 expression and activity in astrocytes without altering basal CD38 levels (p < 0.001). IκBαM transfection also significantly inhibited IL-1β-mediated increases in CD38 expression and activity in astrocytes (p < 0.001).

Conclusion

The present findings demonstrate a direct involvement of HIV-1 and virus-induced proinflammatory stimuli in regulating astrocyte-CD38 levels. HIV-1_YU-2-transfection effectively induced HIV-1p24 protein expression and activated astrocytes to upregulate CCL2, CXCL8 and CD38. In astrocytes, IL-1β-induced increases in CD38 levels were regulated through the MAPK signaling pathway and by the transcription factor NF-κB. Future studies may be directed towards understanding the role of CD38 in response to infection and thus its role in HAND.

Involvement of cyclic adenosine diphosphoribose receptor activation in ischemic preconditioning induced protection in mouse brain

The present study has been designed to expound the significance of cyclic adenosine diphosphoribose receptor activation in ischemic preconditioning induced reversal of ischemia and reperfusion induced cerebral injury in mice. Bilateral carotid artery occlusion of 17 min followed by reperfusion for 24 h was employed in present study to produce ischemia and reperfusion induced cerebral injury in mice. Cerebral infarct size was measured using triphenyltetrazolium chloride staining. Memory was evaluated using Morris water-maze test. Rota-rod test was employed to assess motor incoordination. Bilateral carotid artery occlusion followed by reperfusion produced cerebral infarction and impaired memory and motor co-ordination. Three preceding episodes of bilateral carotid artery occlusion for 1 min and reperfusion of 1 min (ischemic preconditioning) prevented markedly ischemia-reperfusion-induced cerebral injury measured in terms of infarct size, loss of memory and motor coordination. 8-Bromo-cyclic adenosine diphosphate ribose (2 mg/kg, ip), an antagonist of cyclic ADP-ribose receptor, attenuated the neuroprotective effect of ischemic preconditioning. It is concluded that neuroprotective effect of ischemic preconditioning may be due to the adenosine diphosphoribose receptor activation.

CD38 regulation in activated astrocytes: implications for neuroinflammation and HIV-1 brain infection

Reactive astrogliosis is a key pathological aspect of neuroinflammatory disorders including human immunodeficiency virus type 1 (HIV-1)-associated neurological disease. On the basis of previous data that showedastrocytes activated with interleukin (IL)-1beta induce neuronal injury, we analyzed global gene changes in IL-1beta-activated human astrocytes by gene microarray. Among the up-regulated genes, CD38, a 45-kDa type II single chain transmembrane glycoprotein, was a top candidate, with a 17.24-fold change that was validated by real-time polymerase chain reaction. Key functions of CD38 include enzymatic activities and involvement in adhesion and cell signaling. Importantly, CD38(+)CD8(+) T-cell expression is a clinical correlate for progression of HIV-1 infection and biological marker for immune activation. Thus, CD38 expression in HIV-1 and/or IL-1beta-stimulated human astrocytes and human brain tissues was analyzed. IL-1beta and HIV-1 activation of astrocytes enhanced CD38 mRNA levels. Both CD38 immunoreactivity and adenosine 5'-diphosphate (ADP)-ribosyl cyclase activity were up-regulated in IL-1beta-activated astrocytes. CD38 knockdown using specific siRNAs significantly reduced astrocyte proinflammatory cytokine and chemokine production. However, CD38 mRNA levels were unchanged in IL-1beta knockdown conditions, suggesting that IL-1beta autocrine loop is not implicated in this process. Quantitative immunohistochemical analysis of HIV-seropositive without encephalitis and HIV-1 encephalitis brain tissues showed significant up-regulation of CD38, which colocalized with glial fibrillary acidic protein-positive cells in areas of inflammation. These results suggest an important role of CD38 in the regulation of astrocyte dysfunction during the neuroinflammatory processes involved in neurodegenerative/neuroinflammatory disorders such as HIV-1 encephalitis.