Review: NAD +: a modulator of immune functions

Effect of the leptin receptor Q223R polymorphism on the host transcriptome following infection with Entamoeba histolytica

Resistance to amebiasis is associated with a polymorphism in the leptin receptor. Previous studies demonstrated that humans with the ancestral Q223 leptin receptor allele were nearly four times less likely to be infected with Entamoeba histolytica than those carrying the mutant R223 allele. We hypothesized that the Q223 allele protected against E. histolytica via STAT3-mediated transcription of genes required for mucosal immunity. To test this, mice containing the humanized LEPR Q or R allele at codon 223 were intracecally infected with E. histolytica. Susceptibility to amebiasis was assessed, and cecal tissues were analyzed for changes in gene expression. By 72 h postchallenge, all Q223 mice had cleared E. histolytica, whereas 39% of 223R mice were infected. Thirty-seven genes were differentially expressed in response to infection at 72 h, including proinflammatory genes (CXCL2, S100A8/9, PLA2G7, ITBG2, and MMP9) and functions pertaining to the movement and activity of immune cells. A comparison at 12 h postchallenge of infected Q223 versus R223 mice identified a subset of differentially expressed genes, many of which were closely linked to leptin signaling. Further analyses indicated that the Q223 gene expression pattern was consistent with a suppressed apoptotic response to infection, while 223R showed increased cellular proliferation and recruitment. These studies are the first to illuminate the downstream effects of leptin receptor polymorphisms on intestinal infection by E. histolytica. As such, they are important for the insight that they provide into this previously uncharacterized mechanism of mucosal immunity.

The innate immune system in demyelinating disease

Demyelinating diseases such as multiple sclerosis are chronic inflammatory autoimmune diseases with a heterogeneous clinical presentation and course. Both the adaptive and the innate immune systems have been suggested to contribute to their pathogenesis and recovery. In this review, we discuss the role of the innate immune system in mediating demyelinating diseases. In particular, we provide an overview of the anti-inflammatory or pro-inflammatory functions of dendritic cells, mast cells, natural killer (NK) cells, NK-T cells, γδ T cells, microglial cells, and astrocytes. We emphasize the interaction of astroctyes with the immune system and how this interaction relates to the demyelinating pathologies. Given the pivotal role of the innate immune system, it is possible that targeting these cells may provide an effective therapeutic approach for demyelinating diseases.

The NAD+-dependent histone deacetylase SIRT6 promotes cytokine production and migration in pancreatic cancer cells by regulating Ca2+ responses

Cytokine secretion by cancer cells contributes to cancer-induced symptoms and angiogenesis. Studies show that the sirtuin SIRT6 promotes inflammation by enhancing TNF expression. Here, we aimed to determine whether SIRT6 is involved in conferring an inflammatory phenotype to cancer cells and to define the mechanisms linking SIRT6 to inflammation. We show that SIRT6 enhances the expression of pro-inflammatory cyto-/chemokines, such as IL8 and TNF, and promotes cell migration in pancreatic cancer cells by enhancing Ca(2+) responses. Via its enzymatic activity, SIRT6 increases the intracellular levels of ADP-ribose, an activator of the Ca(2+) channel TRPM2. In turn, TRPM2 and Ca(2+) are shown to be involved in SIRT6-induced TNF and IL8 expression. SIRT6 increases the nuclear levels of the Ca(2+)-dependent transcription factor, nuclear factor of activated T cells (NFAT), and cyclosporin A, a calcineurin inhibitor that reduces NFAT activity, reduces TNF and IL8 expression in SIRT6-overexpressing cells. These results implicate a role for SIRT6 in the synthesis of Ca(2+)-mobilizing second messengers, in the regulation of Ca(2+)-dependent transcription factors, and in the expression of pro-inflammatory, pro-angiogenic, and chemotactic cytokines. SIRT6 inhibition may help combat cancer-induced inflammation, angiogenesis, and metastasis.

Metabolic sensors and their interplay with cell signalling and transcription

There is an intimate, yet poorly understood, link between cellular metabolic status, cell signalling and transcription. Central metabolic pathways are under the control of signalling pathways and, vice versa, the cellular metabolic profile influences cell signalling through the incorporation of various metabolic sensors into the signalling networks. Thus information about nutrients availability directly and crucially influences crucial cell decisions. In the present review, I summarize our current knowledge of various metabolic sensors and give some examples of the integration of metabolically derived inputs into the signalling system and the regulation of transcription. I also discuss the Warburg effect where the cross-talk between metabolism and signalling is used to orchestrate rapid cell growth and division. It is becoming clear that future research will concentrate on the collection of small-molecule metabolites, whose concentration fluctuates in response to cellular energy levels, searching for their sensors that connect them to the signalling and transcriptional networks.

Immunoregulation through extracellular nucleotides

Extracellular ATP (eATP), the most abundant among nucleotides, can act as a mediator during inflammatory responses by binding to plasmamembrane P2 purinergic receptors, which are widely expressed on cells of the immune system. eATP is generally considered as a classical danger signal, which stimulates immune responses in the presence of tissue damage. Converging evidence from several studies using murine models of chronic inflammation have supported this hypothesis; however, the role of eATP in the regulation of human immune function appears to be more complex. Chronic stimulation with micromolar eATP concentrations inhibits the proliferation of T and NK lymphocytes and enhances the capacity of dendritic cells to promote tolerance. The effect of eATP depends on multiple factors, such as the extent of stimulation, eATP concentration, presence/absence of other mediators in the microenvironment, and pattern of P2 receptor engagement. Small but significant differences in the pattern of P2 receptor expression in mice and humans confer the diverse capacities of ATP in regulating the immune response. Such diversity, which is often overlooked, should therefore be carefully considered when evaluating the role of eATP in human inflammatory and autoimmune diseases.

Nicotinamide, NAD(P)(H), and Methyl-Group Homeostasis Evolved and Became a Determinant of Ageing Diseases: Hypotheses and Lessons from Pellagra

Compartmentalized redox faults are common to ageing diseases. Dietary constituents are catabolized to NAD(H) donating electrons producing proton-based bioenergy in coevolved, cross-species and cross-organ networks. Nicotinamide and NAD deficiency from poor diet or high expenditure causes pellagra, an ageing and dementing disorder with lost robustness to infection and stress. Nicotinamide and stress induce Nicotinamide-N-methyltransferase (NNMT) improving choline retention but consume methyl groups. High NNMT activity is linked to Parkinson's, cancers, and diseases of affluence. Optimising nicotinamide and choline/methyl group availability is important for brain development and increased during our evolution raising metabolic and methylome ceilings through dietary/metabolic symbiotic means but strict energy constraints remain and life-history tradeoffs are the rule. An optimal energy, NAD and methyl group supply, avoiding hypo and hyper-vitaminoses nicotinamide and choline, is important to healthy ageing and avoids utilising double-edged symbionts or uncontrolled autophagy or reversions to fermentation reactions in inflammatory and cancerous tissue that all redistribute NAD(P)(H), but incur high allostatic costs.

Cellular stress responses, hormetic phytochemicals and vitagenes in aging and longevity

Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This paper introduces the emerging role of exogenous molecules in hormetic-based neuroprotection and the mitochondrial redox signaling concept of hormesis and its applications to the field of neuroprotection and longevity. Maintenance of optimal long-term health conditions is accomplished by a complex network of longevity assurance processes that are controlled by vitagenes, a group of genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin and the sirtuin protein systems. Dietary antioxidants, such as polyphenols and L-carnitine/acetyl-L-carnitine, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. Hormesis provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose response relationships, their mechanistic foundations, their relationship to the concept of biological plasticity as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This paper describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways including sirtuin, Nrfs and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. This article is part of a Special Issue entitled: Antioxidants and Antioxidant Treatment in Disease.

SNPs in DNA repair genes associated to meningitis and host immune response

In vitro and in animal models, APE1, OGG1, and PARP-1 have been proposed as being involved with inflammatory response. In this work, we have investigated if the SNPs APE1 Asn148Glu, OGG1 Ser326Cys, and PARP-1 Val762Ala are associated to meningitis. The patient genotypes were investigated by PIRA-PCR or PCR-RFLP. DNA damages were detected in genomic DNA by Fpg treatment. IgG and IgA were measured from plasma and the cytokines and chemokines were measured from cerebrospinal fluid samples using Bio-Plex assays. A higher frequency (P<0.05) of APE1 Glu allele in bacterial meningitis (BM) and aseptic meningitis (AM) patients was observed. The genotypes Asn/Asn in control group and Asn/Glu in BM group was also higher. For the SNP OGG1 Ser326Cys, the genotype Cys/Cys was more frequent (P<0.05) in BM group. The frequency of PARP-1 Val/Val genotype was higher in control group (P<0.05). The occurrence of combined SNPs is significantly higher in BM patients, indicating that these SNPs may be associated to the disease. Increasing in sensitive sites to Fpg was observed in carriers of APE1 Glu allele or OGG1 Cys allele, suggesting that SNPs affect DNA repair activity. Alterations in IgG production were observed in the presence of SNPs APE1 Asn148Glu, OGG1 Ser326Cys or PARP-1 Val762Ala. Moreover, reduction in the levels of IL-6, IL-1Ra, MCP-1/CCL2 and IL-8/CXCL8 was observed in the presence of APE1 Glu allele in BM patients. In conclusion, we obtained indications of an effect of SNPs in DNA repair genes on the regulation of immune response in meningitis.

Flavonoids as inhibitors of human CD38

CD38 is a multifunctional enzyme which is ubiquitously distributed in mammalian tissues. It is involved in the conversion of NAD(P)(+) into cyclic ADP-ribose, NAADP(+) and ADP-ribose and the role of these metabolites in multiple Ca(2+) signaling pathways makes CD38 a novel potential pharmacological target. The dire paucity of CD38 inhibitors, however, renders the search for new molecular tools highly desirable. We report that human CD38 is inhibited at low micromolar concentrations by flavonoids such as luteolinidin, kuromanin and luteolin (IC(50) <10 μM). Docking studies provide some clues on the mode of interaction of these molecules with the active site of CD38.

Ectonucleotidases as regulators of purinergic signaling in thrombosis, inflammation, and immunity

Evolving studies in models of transplant rejection, inflammatory bowel disease, and cancer, among others, have implicated purinergic signaling in clinical manifestations of vascular injury and thrombophilia, inflammation, and immune disturbance. Within the vasculature, spatial and temporal expression of CD39 nucleoside triphosphate diphosphohydrolase (NTPDase) family members together with CD73 ecto-5'-nucleotidase control platelet activation, thrombus size, and stability. This is achieved by closely regulated phosphohydrolytic activities to scavenge extracellular nucleotides, maintain P2-receptor integrity, and coordinate adenosinergic signaling responses. The CD38/CD157 family of extracellular NADases degrades NAD(+) and generates Ca(2+)-active metabolites, including cyclic ADP ribose and ADP ribose. These mediators regulate leukocyte adhesion and chemotaxis. These mechanisms are crucial in vascular homeostasis, hemostasis, thrombogenesis, and during inflammation. There has been recent interest in ectonucleotidase expression by immune cells. CD39 expression identifies Langerhans-type dendritic cells and efficiently distinguishes T regulatory cells from other resting or activated T cells. CD39, together with CD73 in mice, serves as an integral component of the suppressive machinery of T cells. Purinergic responses also impact generation of T helper-type 17 cells. Further, CD38 and changes in NAD(+) availability modulate ADP ribosylation of the cytolytic P2X7 receptor that deletes T regulatory cells. Expression of CD39, CD73, and CD38 ectonucleotidases on either endothelial or immune cells allows for homeostatic integration and control of vascular inflammatory and immune cell reactions at sites of injury. Ongoing development of therapeutic strategies targeting these and other ectonucleotidases offers promise for the management of vascular thrombosis, disordered inflammation, and aberrant immune reactivity.

Sirtuins and inflammation: Friends or foes?

Lysine acetylation/deacetylation has been recognized as an important posttranslational modification regulating numerous cellular processes. Sirtuins represent novel players in these complex regulatory circuits. These NAD-dependent lysine-deacetylases have attracted much interest based on their role in the regulation of lifespan in lower organisms, and their capacity to interfere with cell growth, proliferation and survival in response to stress. Their absolute requirement for NAD suggests that these enzymes may represent an important molecular link between metabolism and several human disorders such as diabetes and cancer. More recently, the identification of several transcription factors known to play a role in the immune system as sirtuin substrates has suggested that this family of enzymes may also play an important role in the regulation of inflammation, a pathological situation with clear links to metabolism and aging in humans. We review herein the possible links between nuclear sirtuins and the regulation of an immune response, and discuss the possible strategies that may lead to the development of novel therapeutic approaches to treat inflammation by targeting sirtuin activity.