Transcriptional regulation by poly(ADP-ribose) polymerase-1 during T cell activation

Poly (ADP-ribose) polymerase-1 regulates HIV-1 replication in human CD4+ T cells

The cellular enzyme poly (ADP-ribose) polymerase-1 (PARP-1) regulates multiple processes that are potentially implicated in HIV-1 infection. However, the role of PARP-1 in HIV-1 infection remains controversial, with reports indicating or excluding that PARP-1 influence early steps of the HIV-1 life cycle. Most of these studies have been conducted with Vesicular Stomatitis virus Glycoprotein G (VSV-G)-pseudotyped, single-round infection HIV-1; limiting our understanding of the role of PARP-1 in HIV-1 replication. Therefore, we evaluated the effect of PARP-1 deficiency or inhibition in HIV-1 replication in human CD4+ T cells. Our data showed that PARP-1 knockout increased viral replication in SUP-T1 cells. Similarly, a PARP-1 inhibitor that targets PARP-1 DNA-binding activity enhanced HIV-1 replication. In contrast, inhibitors affecting the catalytic activity of the enzyme were inactive. In correspondence with the pharmacological studies, mutagenesis analysis indicated that the DNA-binding domain was required for the PARP-1 anti-HIV-1 activity, but the poly-ADP-ribosylation activity was dispensable. Our results also demonstrated that PARP-1 acts at the production phase of the viral life cycle since HIV-1 produced in cells lacking PARP-1 was more infectious than control viruses. The effect of PARP-1 on HIV-1 infectivity required Env, as PARP-1 deficiency or inhibition did not modify the infectivity of Env-deleted, VSV-G-pseudotyped HIV-1. Furthermore, virion-associated Env was more abundant in sucrose cushion-purified virions produced in cells lacking the enzyme. However, PARP-1 did not affect Env expression or processing in the producer cells. In summary, our data indicate that PARP-1 antagonism enhances HIV-1 infectivity and increases levels of virion-associated Env.

Importance

Different cellular processes counteract viral replication. A better understanding of these interfering mechanisms will enhance our ability to control viral infections. We have discovered a novel, antagonist effect of the cellular enzyme poly (ADP-ribose) polymerase-1 (PARP-1) in HIV-1 replication. Our data indicate that PARP-1 deficiency or inhibition augment HIV-1 infectivity in human CD4+ T cells, the main HIV-1 target cell in vivo . Analysis of the mechanism of action suggested that PARP-1 antagonism increases in the virus the amounts of the viral protein mediating viral entry to the target cells. These findings identify for the first time PARP-1 as a host factor that regulates HIV-1 infectivity, and could be relevant to better understand HIV-1 transmission and to facilitate vaccine development.

Identification of Poly(ADP-ribose) Polymerase 9 (PARP9) as a Potent Suppressor for Mycobacterium tuberculosis Infection

ADP-ribosylation is a reversible and dynamic post-translational modification mediated by ADP-ribosyltransferases (ARTs). Poly(ADP-ribose) polymerases (PARPs) are an important family of human ARTs. ADP-ribosylation and PARPs have crucial functions in host-pathogen interaction, especially in viral infections. However, the functions and potential molecular mechanisms of ADP-ribosylation and PARPs in Mycobacterium infection remain unknown. In this study, bioinformatics analysis revealed significantly changed expression levels of several PARPs in tuberculosis patients compared to healthy individuals. Moreover, the expression levels of these PARPs returned to normal following tuberculosis treatment. Then, the changes in the expression levels of PARPs during Mycobacterium infection were validated in Tohoku Hospital Pediatrics-1 (THP1)-induced differentiated macrophages infected with Mycobacterium model strains bacillus Calmette-Guérin (BCG) and in human lung adenocarcinoma A549 cells infected with Mycobacterium smegmatis (Ms), respectively. The mRNA levels of PARP9, PARP10, PARP12, and PARP14 were most significantly increased during infection, with corresponding increases in protein levels, indicating the possible biological functions of these PARPs during Mycobacterium infection. In addition, the biological function of host PARP9 in Mycobacterium infection was further studied. PARP9 deficiency significantly increased the infection efficiency and intracellular proliferation ability of Ms, which was reversed by the reconstruction of PARP9. Collectively, this study updates the understanding of changes in PARP expression during Mycobacterium infection and provides evidence supporting PARP9 as a potent suppressor for Mycobacterium infection.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43657-023-00112-2.

Dual antitumor immunomodulatory effects of PARP inhibitor on the tumor microenvironment: A counterbalance between anti-tumor and pro-tumor

Poly (ADP-ribose)-polymerases (PARPs) play an essential role in the maintenance of genome integrity, DNA repair, and apoptosis. PARP inhibitors (PARPi) exert antitumor effects via synthetic lethality and PARP trapping. PARPi impact the antitumor immune response by modulating the tumor microenvironment, and their effect has dual properties of promoting and inhibiting the antitumor immune response. PARPi promote M1 macrophage polarization, antigen presentation by dendritic cells, infiltration of B and T cells and their killing capacity and inhibit tumor angiogenesis. PARPi can also inhibit the activation and function of immune cells by upregulating PD-L1. In this review, we summarize the dual immunomodulatory effects and possible underlying mechanisms of PARPi, providing a basis for the design of combination regimens for clinical treatment and the identification of populations who may benefit from these therapies.

Role of PARP Inhibitors in Cancer Immunotherapy: Potential Friends to Immune Activating Molecules and Foes to Immune Checkpoints

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) induce cytotoxic effects as single agents in tumors characterized by defective repair of DNA double-strand breaks deriving from BRCA1/2 mutations or other abnormalities in genes associated with homologous recombination. Preclinical studies have shown that PARPi-induced DNA damage may affect the tumor immune microenvironment and immune-mediated anti-tumor response through several mechanisms. In particular, increased DNA damage has been shown to induce the activation of type I interferon pathway and up-regulation of PD-L1 expression in cancer cells, which can both enhance sensitivity to Immune Checkpoint Inhibitors (ICIs). Despite the recent approval of ICIs for a number of advanced cancer types based on their ability to reinvigorate T-cell-mediated antitumor immune responses, a consistent percentage of treated patients fail to respond, strongly encouraging the identification of combination therapies to overcome resistance. In the present review, we analyzed both established and unexplored mechanisms that may be elicited by PARPi, supporting immune reactivation and their potential synergism with currently used ICIs. This analysis may indicate novel and possibly patient-specific immune features that might represent new pharmacological targets of PARPi, potentially leading to the identification of predictive biomarkers of response to their combination with ICIs.

Combining PARP inhibition and immune checkpoint blockade in ovarian cancer patients: a new perspective on the horizon?

Immune checkpoint inhibitors (ICIs) have completely reshaped the treatment of many malignancies, with remarkable improvements in survival outcomes. In ovarian cancer (OC), however, this emerging class of drugs has not yet found a favorable use due to results from phase I and II studies, which have not suggested a substantial antitumoral activity of these agents when administered as monotherapy. Robust preclinical data seem to suggest that the combination ICIs with poly(ADP-ribose) polymerase (PARP) inhibitors (PARPis) may result in a synergistic activity; furthermore, data from phase II clinical studies, evaluating this combination, have shown encouraging outcomes especially for those OC patients not suitable for platinum retreatment. While waiting for ongoing phase III clinical trial results, which will clarify the role of ICIs in combination with PARPis in the newly diagnosed OC, this review aims to summarize the preclinical data and clinical evidence available to date.

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Preclinical data indicate that PARPis exhibit immune modulating properties.

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The combination of PARPi with ICIs displays significant synergistic activity in preclinical models.

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Phase I and II clinical trials showed encouraging results for this combination, especially in platinum-resistant OC.

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Four ongoing phase III trials exploring the combination in first-line setting will delineate the role of immunotherapy in OC.

Therapeutic Potentials of Poly (ADP-Ribose) Polymerase 1 (PARP1) Inhibition in Multiple Sclerosis and Animal Models: Concept Revisiting

Poly (ADP-ribose) polymerase 1 (PARP1) plays a fundamental role in DNA repair and gene expression. Excessive PARP1 hyperactivation, however, has been associated with cell death. PARP1 and/or its activity are dysregulated in the immune and central nervous system of multiple sclerosis (MS) patients and animal models. Pharmacological PARP1 inhibition is shown to be protective against immune activation and disease severity in MS animal models while genetic PARP1 deficiency studies reported discrepant results. The inconsistency suggests that the function of PARP1 and PARP1-mediated PARylation may be complex and context-dependent. The article reviews PARP1 functions, discusses experimental findings and possible interpretations of PARP1 in inflammation, neuronal/axonal degeneration, and oligodendrogliopathy, three major pathological components cooperatively determining MS disease course and neurological progression, and points out future research directions. Cell type specific PARP1 manipulations are necessary for revisiting the role of PARP1 in the three pathological components prior to moving PARP1 inhibition into clinical trials for MS therapy.

Daratumumab Prevents Experimental Xenogeneic Graft-Versus-Host Disease by Skewing Proportions of T Cell Functional Subsets and Inhibiting T Cell Activation and Migration

Graft-versus-host disease (GVHD) remains the major cause of mortality and morbidity in non-relapse patients after allogeneic hematopoietic cell transplantation (allo-HCT). As the number of patients undergoing allo-HCT increases, it will become imperative to determine safe and effective treatment options for patients with GVHD, especially those who become refractory to systemic steroid therapy. Daratumumab (Dara), a humanized IgG1 (ĸ subclass) monoclonal antibody targeting the CD38 epitope, is used for the treatment of multiple myeloma. CD38 is a multifunctional ectoenzyme that behaves either as an enzyme, a cell adhesion molecule or a cell surface receptor involved in cell signaling. CD38 is also expressed on various immune effector and suppressor cells. However, the role of CD38 in the immune response remains elusive. We questioned whether CD38 is a potential therapeutic target against alloreactive T cells in the GVHD pathological process. Here, we investigated the impact of Dara on xenogeneic GVHD (xeno-GVHD) and graft-versus-leukemia (GVL) effects in a humanized murine model of transplantation, where human peripheral blood mononuclear cells were adoptively transplanted into immunocompromised NOD.SCID.gc-null (NSG) mice. Mice receiving Dara treatment experienced less weight loss, longer survival and lower GVHD scores compared with those in the control group. Histological evaluations, flow cytometry, RNA-sequencing and RT-qPCR analysis revealed that Dara efficaciously mitigated GVHD through multiple mechanisms including inhibition of the proliferation, activation and differentiation of CD8⁺ cytotoxic T cells, reduced expression of cytotoxic effector molecules, pro-inflammatory cytokines, chemokines and chemoattractant receptors by T cells and promotion of immunosuppressive T cells. More importantly, Dara preserved the GVL effect in a humanized mouse model of leukemia by metabolic reprograming of T cells to promote the induction of Th17, Th1/17and Tc1/17 cells. Our findings indicate that Dara may be an attractive therapeutic option to separate GVHD from GVL effects in patients with hematopoietic malignancies receiving allo-HCT.

The Role of PARP Inhibitors in the Ovarian Cancer Microenvironment: Moving Forward From Synthetic Lethality

PARP inhibitors (PARPi) have shown promising clinical results and have revolutionized the landscape of ovarian cancer management in the last few years. While the core mechanism of action of these drugs has been largely analyzed, the interaction between PARP inhibitors and the microenvironment has been scarcely researched so far. Recent data shows a variety of mechanism through which PARPi might influence the tumor microenvironment and especially the immune system response, that might even partly be the reason behind PARPi efficacy. One of many pathways that are affected is the cGAS-cGAMP-STING; the upregulation of STING (stimulator of interferon genes), produces more Interferon ϒ and pro inflammatory cytokines, thus increasing intratumoral CD4+ and CD8+ T cells. Upregulation of immune checkpoints such as PD1-PDL1 has also been observed. Another interesting mechanism of interaction between PARPi and microenvironment is the ability of PARPi to kill hypoxic cells, as these cells show an intrinsic reduction in the expression and function of the proteins involved in HR. This process has been defined "contextual synthetic lethality". Despite ovarian cancer having always been considered a poor responder to immune therapy, data is now shedding a new light on the matter. First, OC is much more heterogenous than previously thought, therefore it is fundamental to select predictive biomarkers for target therapies. While single agent therapies have not yielded significant results on the long term, influencing the immune system and the tumor microenvironment via the concomitant use of PARPi and other target therapies might be a more successful approach.

Chrom-Lasso: a lasso regression-based model to detect functional interactions using Hi-C data

Hi-C is a genome-wide assay based on Chromosome Conformation Capture and high-throughput sequencing to decipher 3D chromatin organization in the nucleus. However, computational methods to detect functional interactions utilizing Hi-C data face challenges including the correction for various sources of biases and the identification of functional interactions with low counts of interacting fragments. We present Chrom-Lasso, a lasso linear regression model that removes complex biases assumption-free and identifies functional interacting loci with increased power by combining information of local reads distribution surrounding the area of interest. We showed that interacting regions identified by Chrom-Lasso are more enriched for 5C validated interactions and functional GWAS hits than that of GOTHiC and Fit-Hi-C. To further demonstrate the ability of Chrom-Lasso to detect interactions of functional importance, we performed time-series Hi-C and RNA-seq during T cell activation and exhaustion. We showed that the dynamic changes in gene expression and chromatin interactions identified by Chrom-Lasso were largely concordant with each other. Finally, we experimentally confirmed Chrom-Lasso’s finding that Erbb3 was co-regulated with distinct neighboring genes at different states during T cell activation. Our results highlight Chrom-Lasso’s utility in detecting weak functional interaction between cis-regulatory elements, such as promoters and enhancers.

DNA Damage Response and Immune Defense

DNA damage is the cause of numerous human pathologies including cancer, premature aging, and chronic inflammatory conditions. The DNA damage response (DDR), in turn, coordinates DNA damage checkpoint activation and promotes the removal of DNA lesions. In recent years, several studies have shown how the DDR and the immune system are tightly connected, revealing an important crosstalk between the two of them. This interesting interplay has opened up new perspectives in clinical studies for immunological diseases as well as for cancer treatment. In this review, we provide an overview, from cellular to molecular pathways, on how DDR and the immune system communicate and share the crucial commitment of maintaining the genomic fitness.

The Role of PARP1 in Monocyte and Macrophage Commitment and Specification: Future Perspectives and Limitations for the Treatment of Monocyte and Macrophage Relevant Diseases with PARP Inhibitors

Modulation of PARP1 expression, changes in its enzymatic activity, post-translational modifications, and inflammasome-dependent cleavage play an important role in the development of monocytes and numerous subtypes of highly specialized macrophages. Transcription of PARP1 is governed by the proliferation status of cells at each step of their development. Higher abundance of PARP1 in embryonic stem cells and in hematopoietic precursors supports their self-renewal and pluri-/multipotency, whereas a low level of the enzyme in monocytes determines the pattern of surface receptors and signal transducers that are functionally linked to the NFκB pathway. In macrophages, the involvement of PARP1 in regulation of transcription, signaling, inflammasome activity, metabolism, and redox balance supports macrophage polarization towards the pro-inflammatory phenotype (M1), which drives host defense against pathogens. On the other hand, it seems to limit the development of a variety of subsets of anti-inflammatory myeloid effectors (M2), which help to remove tissue debris and achieve healing. PARP inhibitors, which prevent protein ADP-ribosylation, and PARP1‒DNA traps, which capture the enzyme on chromatin, may allow us to modulate immune responses and the development of particular cell types. They can be also effective in the treatment of monocytic leukemia and other cancers by reverting the anti- to the proinflammatory phenotype in tumor-associated macrophages.

PARP inhibition and immune modulation: scientific rationale and perspectives for the treatment of gynecologic cancers

Poly[adenosine diphosphate (ADP) ribose]polymerase (PARP) has multifaceted roles in the maintenance of genomic integrity, deoxyribonucleic acid (DNA) repair and replication, and the maintenance of immune-system homeostasis. PARP inhibitors are an attractive oncologic therapy, causing direct cancer cell cytotoxicity by propagating DNA damage and indirectly, by various mechanisms of immunostimulation, including activation of the cGAS/STING pathway, paracrine stimulation of dendritic cells, increased T-cell infiltration, and upregulation of death-ligand receptors to increase susceptibility to natural-killer-cell killing. However, these immunostimulatory effects are counterbalanced by PARPi-mediated upregulation of programmed cell-death-ligand 1 (PD-L1), which leads to immunosuppression. Combining PARP inhibition with immune-checkpoint blockade seeks to exploit the immune stimulatory effects of PARP inhibition while negating the immunosuppressive effects of PD-L1 upregulation.

CD38: T Cell Immuno-Metabolic Modulator

Activation and subsequent differentiation of T cells following antigenic stimulation are triggered by highly coordinated signaling events that lead to instilling cells with a discrete metabolic and transcriptional feature. Compelling studies indicate that intracellular nicotinamide adenine dinucleotide (NAD⁺) levels have profound influence on diverse signaling and metabolic pathways of T cells, and hence dictate their functional fate. CD38, a major mammalian NAD⁺ glycohydrolase (NADase), expresses on T cells following activation and appears to be an essential modulator of intracellular NAD⁺ levels. The enzymatic activity of CD38 in the process of generating the second messenger cADPR utilizes intracellular NAD^+, and thus limits its availability to different NAD⁺ consuming enzymes (PARP, ART, and sirtuins) inside the cells. The present review discusses how the CD38-NAD⁺ axis affects T cell activation and differentiation through interfering with their signaling and metabolic processes. We also describe the pivotal role of the CD38-NAD⁺ axis in influencing the chromatin remodeling and rewiring T cell response. Overall, this review emphasizes the crucial contribution of the CD38^-NAD⁺ axis in altering T cell response in various pathophysiological conditions.

Immunomodulatory Roles of PARP-1 and PARP-2: Impact on PARP-Centered Cancer Therapies

Poly(ADP-ribose) polymerase-1 (PARP-1) and PARP-2 are enzymes which post-translationally modify proteins through poly(ADP-ribosyl)ation (PARylation)—the transfer of ADP-ribose chains onto amino acid residues—with a resultant modulation of protein function. Many targets of PARP-1/2-dependent PARylation are involved in the DNA damage response and hence, the loss of these proteins disrupts a wide range of biological processes, from DNA repair and epigenetics to telomere and centromere regulation. The central role of these PARPs in DNA metabolism in cancer cells has led to the development of PARP inhibitors as new cancer therapeutics, both as adjuvant treatment potentiating chemo-, radio-, and immuno-therapies and as monotherapy exploiting cancer-specific defects in DNA repair. However, a cancer is not just made up of cancer cells and the tumor microenvironment also includes multiple other cell types, particularly stromal and immune cells. Interactions between these cells—cancerous and non-cancerous—are known to either favor or limit tumorigenesis. In recent years, an important role of PARP-1 and PARP-2 has been demonstrated in different aspects of the immune response, modulating both the innate and adaptive immune system. It is now emerging that PARP-1 and PARP-2 may not only impact cancer cell biology, but also modulate the anti-tumor immune response. Understanding the immunomodulatory roles of PARP-1 and PARP-2 may provide invaluable clues to the rational development of more selective PARP-centered therapies which target both the cancer and its microenvironment.

The impact of PARPs and ADP-ribosylation on inflammation and host-pathogen interactions

Poly-adenosine diphosphate-ribose polymerases (PARPs) promote ADP-ribosylation, a highly conserved, fundamental posttranslational modification (PTM). PARP catalytic domains transfer the ADP-ribose moiety from NAD⁺ to amino acid residues of target proteins, leading to mono- or poly-ADP-ribosylation (MARylation or PARylation). This PTM regulates various key biological and pathological processes. In this review, we focus on the roles of the PARP family members in inflammation and host-pathogen interactions. Here we give an overview the current understanding of the mechanisms by which PARPs promote or suppress proinflammatory activation of macrophages, and various roles PARPs play in virus infections. We also demonstrate how innovative technologies, such as proteomics and systems biology, help to advance this research field and describe unanswered questions.

Coordinated signals from PARP-1 and PARP-2 are required to establish a proper T cell immune response to breast tumors in mice

Poly(ADP-ribose)-polymerase (PARP)-1 and PARP-2 play an essential role in the DNA damage response. Based on this effect of PARP in the tumor cell itself, PARP inhibitors have emerged as new therapeutic tools both approved and in clinical trials. However, the interactome of multiple other cell types, particularly T cells, within the tumor microenvironment are known to either favor or limit tumorigenesis. Here, we bypassed the embryonic lethality of dually PARP-1/PARP-2-deficient mice by using a PARP-1-deficient mouse with a Cd4-promoter-driven deletion of PARP-2 in T cells to investigate the understudied role of these PARPs in the modulation of T cell responses against AT-3-induced breast tumors. We found that dual PARP-1/PARP-2-deficiency in T cells promotes tumor growth while single deficiency of each protein limited tumor progression. Analysis of tumor-infiltrating cells in dual PARP-1/PARP-2-deficiency host-mice revealed a global change in immunological profile and impaired recruitment and activation of T cells. Conversely, single PARP-1 and PARP-2-deficiency tends to produce an environment with an active and partially upregulated immune response. Our findings pinpoint opposite effects of single and dual PARP-1 and PARP-2-deficiency in modulating the antitumor response with an impact on tumor progression, and will have implications for the development of more selective PARP-centered therapies.

Two may be better than one: PD-1/PD-L1 blockade combination approaches in metastatic breast cancer

Antibodies blocking programmed death 1 (anti-PD-1) or its ligand (anti-PD-L1) are associated with modest response rates as monotherapy in metastatic breast cancer, but are generally well tolerated and capable of generating dramatic and durable benefit in a minority of patients. Anti-PD-1/L1 antibodies are also safe when administered in combination with a variety of systemic therapies (chemotherapy, targeted therapies), as well as with radiotherapy. We summarize preclinical, translational, and preliminary clinical data in support of combination approaches with anti-PD-1/L1 in metastatic breast cancer, focusing on potential mechanisms of synergy, and considerations for clinical practice and future investigation.

Asthma and poly(ADP-ribose) polymerase inhibition: a new therapeutic approach

Asthma is a chronic lung disease affecting people of all ages worldwide, and it frequently begins in childhood. Because of its chronic nature, it is characterized by pathological manifestations, including airway inflammation, remodeling, and goblet cell hyperplasia. Current therapies for asthma, including corticosteroids and beta-2 adrenergic agonists, are directed toward relieving the symptoms of the asthmatic response, with poor effectiveness against the underlying causes of the disease. Asthma initiation and progression depends on the T helper (Th) 2 type immune response carried out by a complex interplay of cytokines, such as interleukin (IL) 4, IL5, and IL13, and the signal transducer and activator of transcription 6. Much of the data resulting from different laboratories support the role of poly(ADP-ribose) polymerase (PARP) 1 and PARP14 activation in asthma. Indeed, PARP enzymes play key roles in the regulation and progression of the inflammatory asthma process because they affect the expression of genes and chemokines involved in the immune response. Consistently, PARP inhibition achievable either upon genetic ablation or by using pharmacological agents has shown a range of therapeutic effects against the disease. Indeed, in the last two decades, several preclinical studies highlighted the protective effects of PARP inhibition in various animal models of asthma. PARP inhibitors showed the ability to reduce the overall lung inflammation acting with a specific effect on immune cell recruitment and through the modulation of asthma-associated cytokines production. PARP inhibition has been shown to affect the Th1–Th2 balance and, at least in some aspects, the airway remodeling. In this review, we summarize and discuss the steps that led PARP inhibition to become a possible future therapeutic strategy against allergic asthma.

Human iPSC-MSC-Derived Xenografts Modulate Immune Responses by Inhibiting the Cleavage of Caspases

Mesenchymal stem cells (MSCs) negatively modulate immune properties. Induced pluripotent stem cells (iPSCs)-derived MSCs are alternative source of MSCs. However, the effects of iPSC-MSCs on T cells phenotypes in vivo remain unclear. We established an iPSC-MSC-transplanted host versus graft reaction mouse model using subcapsular kidney injection. Th1, Th2, regulatory T cells (Treg), and Th17 phenotypes and their cytokines were investigated in vivo and in vitro. The role of caspases and the soluble factors involved in the effects of MSCs were examined. We found that iPSC-MSC grafts led to more cell survival and less infiltration of inflammatory cells in mice. iPSC-MSC transplantation inhibited T cell proliferation, decreased Th1 and Th2 phenotypes and cytokines, upregulated Th17 and Treg subsets. Moreover, iPSC-MSCs inhibited the cleavage of caspases 3 and 8 and inhibition of caspases downregulated Th1, Th2 responses and upregulated Th17, Treg responses. Soluble factors were determined using protein array and TGF-β1/2/3, IL-10, and MCP-1 were found to be highly expressed in iPSC-MSCs. The administration of the soluble factors decreased Th1/2 response, upregulated Treg response and inhibited the cleavage of caspases. Our results demonstrate that iPSC-MSCs regulate T cell responses as a result of a combined action of the above soluble factors secreted by iPSC-MSCs. These factors suppress T cell responses by inhibiting the cleavage of caspases. These data provide a novel immunomodulatory mechanism for the underlying iPSC-MSC-based immunomodulatory effects on T cell responses. Stem Cells 2017;35:1719-1732.

Poly ADP-ribose polymerase-1: Beyond transcription and towards differentiation

Gene regulation mediates the processes of cellular development and differentiation leading to the origin of different cell types each having their own signature gene expression profile. However, the compact chromatin structure and the timely recruitment of molecules involved in various signaling pathways are of prime importance for temporal and spatial gene regulation that eventually contribute towards cell type and specificity. Poly (ADP-ribose) polymerase-1 (PARP-1), a 116-kDa nuclear multitasking protein is involved in modulation of chromatin condensation leading to altered gene expression. In response to activation signals, it adds ADP-ribose units to various target proteins including itself, thus regulating various key cellular processes like DNA repair, cell death, transcription, mRNA splicing etc. This review provides insights into the role of PARP-1 in gene regulation, cell differentiation and multicellular morphogenesis. In addition, the review also explores involvement of PARP-1 in immune cells development and therapeutic possibilities to treat various human diseases.

PARP-1/PARP-2 double deficiency in mouse T cells results in faulty immune responses and T lymphomas

The maintenance of T-cell homeostasis must be tightly regulated. Here, we have identified a coordinated role of Poly(ADP-ribose) polymerase-1 (PARP-1) and PARP-2 in maintaining T-lymphocyte number and function. Mice bearing a T-cell specific deficiency of PARP-2 in a PARP-1-deficient background showed defective thymocyte maturation and diminished numbers of peripheral CD4⁺ and CD8⁺ T-cells. Meanwhile, peripheral T-cell number was not affected in single PARP-1 or PARP-2-deficient mice. T-cell lymphopenia was associated with dampened in vivo immune responses to synthetic T-dependent antigens and virus, increased DNA damage and T-cell death. Moreover, double-deficiency in PARP-1/PARP-2 in T-cells led to highly aggressive T-cell lymphomas with long latency. Our findings establish a coordinated role of PARP-1 and PARP-2 in T-cell homeostasis that might impact on the development of PARP-centred therapies.

Understanding specific functions of PARP-2: new lessons for cancer therapy

Poly(ADP-ribosyl)ation (PARylation) is a widespread and highly conserved post-translational modification catalysed by a large family of enzymes called poly(ADP-ribose) polymerases (PARPs). PARylation plays an essential role in various cardinal processes of cellular physiology and recent approvals and breakthrough therapy designations for PARP inhibitors in cancer therapy have sparked great interest in pharmacological targeting of PARP proteins. Although, many PARP inhibitors have been developed, existing compounds display promiscuous inhibition across the PARP superfamily which could lead to unwanted off-target effects. Thus the prospect of isoform-selective inhibition is being increasingly explored and research is now focusing on understanding specific roles of PARP family members. PARP-2, alongside PARP-1 and PARP-3 are the only known DNA damage-dependent PARPs and play critical roles in the DNA damage response, DNA metabolism and chromatin architecture. However, growing evidence shows that PARP-2 plays specific and diverse regulatory roles in cellular physiology, ranging from genomic stability and epigenetics to proliferative signalling and inflammation. The emerging network of PARP-2 target proteins has uncovered wide-ranging functions of the molecule in many cellular processes commonly dysregulated in carcinogenesis. Here, we review novel PARP-2-specific functions in the hallmarks of cancer and consider the implications for the development of isoform-selective inhibitors in chemotherapy. By considering the roles of PARP-2 through the lens of tumorigenesis, we propose PARP-2-selective inhibition as a potentially multipronged attack on cancer physiology.

STAT6 and PARP Family Members in the Development of T Cell-dependent Allergic Inflammation

Allergic inflammation requires the orchestration of altered gene expression in the target tissue and in the infiltrating immune cells. The transcription factor STAT6 is critical in activating cytokine gene expression and cytokine signaling both in the immune cells and in target tissue cells including airway epithelia, keratinocytes and esophageal epithelial cells. STAT6 is activated by the cytokines IL-4 and IL-13 to mediate the pathogenesis of allergic disorders such as asthma, atopic dermatitis, food allergy and eosinophilic esophagitis (EoE). In this review, we summarize the role of STAT6 in allergic diseases, its interaction with the co-factor PARP14 and the molecular mechanisms by which STAT6 and PARP14 regulate gene transcription.

Synergistic inhibition of PARP-1 and NF-κB signaling downregulates immune response against recombinant AAV2 vectors during hepatic gene therapy

Host immune response remains a key obstacle to widespread application of adeno-associated virus (AAV) based gene therapy. Thus, targeted inhibition of the signaling pathways that trigger such immune responses will be beneficial. Previous studies have reported that DNA damage response proteins such as poly(ADP-ribose) polymerase-1 (PARP-1) negatively affect the integration of AAV in the host genome. However, the role of PARP-1 in regulating AAV transduction and the immune response against these vectors has not been elucidated. In this study, we demonstrate that repression of PARP-1 improves the transduction of single-stranded AAV vectors both in vitro (∼174%) and in vivo (two- to 3.4-fold). Inhibition of PARP-1, also significantly downregulated the expression of several proinflammatory and cytokine markers such as TLRs, ILs, NF-κB subunit proteins associated with the host innate response against self-complementary AAV2 vectors. The suppression of the inflammatory response targeted against these vectors was more effective upon combined inhibition of PARP-1 and NF-κB signaling. This strategy also effectively attenuated the AAV capsid-specific cytotoxic T-cell response, with minimal effect on vector transduction, as demonstrated in normal C57BL/6 and hemophilia B mice. These data suggest that targeting specific host cellular proteins could be useful to attenuate the immune barriers to AAV-mediated gene therapy.

Poly-ADP-ribosyl polymerase-14 promotes T helper 17 and follicular T helper development

Transcription factors are critical determinants of T helper cell fate and require a variety of co-factors to activate gene expression. We previously identified the ADP ribosyl-transferase poly-ADP-ribosyl polymerase 14 (PARP-14) as a co-factor of signal transducer and activator of transcription (STAT) 6 that is important in B-cell and T-cell responses to interleukin-4, particularly in the differentiation of T helper type 2 (Th2) cells. However, whether PARP-14 functions during the development of other T helper subsets is not known. In this report we demonstrate that PARP-14 is highly expressed in Th17 cells, and that PARP-14 deficiency and pharmacological blockade of PARP activity result in diminished Th17 differentiation in vitro and in a model of allergic airway inflammation. We further show that PARP-14 is expressed in T follicular helper (Tfh) cells and Tfh cell development is impaired in PARP-14-deficient mice following immunization with sheep red blood cells or inactivated influenza virus. Decreases in Th17 and Tfh development are correlated with diminished phospho-STAT3 and decreased expression of the interleukin-6 receptor α-chain in T cells. Together, these studies demonstrate that PARP-14 regulates multiple cytokine responses during inflammatory immunity.

PARP is activated in human asthma and its inhibition by olaparib blocks house dust mite-induced disease in mice

The present study establishes poly(ADP-ribose)polymerase's (PARP's) role in chronic asthma, demonstrates that it is activated in human asthma, increases the clinical relevance of targeting PARP for blocking or preventing chronic asthma in humans and presents olaparib as a likely candidate drug.

Our laboratory established a role for poly(ADP-ribose)polymerase (PARP) in asthma. To increase the clinical significance of our studies, it is imperative to demonstrate that PARP is actually activated in human asthma, to examine whether a PARP inhibitor approved for human testing such as olaparib blocks already-established chronic asthma traits in response to house dust mite (HDM), a true human allergen, in mice and to examine whether the drug modulates human cluster of differentiation type 4 (CD4⁺) T-cell function. To conduct the study, human lung specimens and peripheral blood mononuclear cells (PBMCs) and a HDM-based mouse asthma model were used. Our results show that PARP is activated in PBMCs and lung tissues of asthmatics. PARP inhibition by olaparib or gene knockout blocked established asthma-like traits in mice chronically exposed to HDM including airway eosinophilia and hyper-responsiveness. These effects were linked to a marked reduction in T helper 2 (Th2) cytokine production without a prominent effect on interferon (IFN)-γ or interleukin (IL)-10. PARP inhibition prevented HDM-induced increase in overall cellularity, weight and CD4⁺ T-cell population in spleens of treated mice whereas it increased the T-regulatory cell population. In CD3/CD28-stimulated human CD4 ⁺T-cells, olaparib treatment reduced Th2 cytokine production potentially by modulating GATA binding protein-3 (gata-3)/IL-4 expression while moderately affecting T-cell proliferation. PARP inhibition inconsistently increased IL-17 in HDM-exposed mice and CD3/CD28-stimulated CD4⁺ T cells without a concomitant increase in factors that can be influenced by IL-17. In the present study, we provide evidence for the first time that PARP-1 is activated in human asthma and that its inhibition is effective in blocking established asthma in mice.

Enhancing tumor-targeting monoclonal antibodies therapy by PARP inhibitors

Monoclonal antibodies (mAbs) have become a successful therapeutic approach in cancer. However, some patients do not achieve long-term clinical benefit and most mAbs only exert modest effects as monotherapies. Therefore, combinations with chemotherapy are currently being investigated. Emerging studies have shown a synergistic therapeutic effect of PARP inhibitors and mAbs in cancer. PARP enzymes catalytically cleave β-NAD⁺ and transfer the ADP-ribose moiety to acceptor proteins, modifying their function. In here, we update recent data about the therapeutic effect of the combination of PARP inhibitors with mAbs in cancer treatment and discuss the molecular mechanisms involved in this synergy.

The role of poly(ADP-ribose) polymerase-1 inhibitor in carrageenan-induced lung inflammation in mice

Increasing indication is unveiling a role for poly(ADP-ribose) polymerase (PARP)-1 in the regulation of inflammatory/immune responses. The aim of the present study was to determine the potential anti-inflammatory effects of PARP-1 inhibitor 5-aminoisoquinolinone (5-AIQ) to explore the role of PARP-1 inhibitor in a mouse model of carrageenan-induced lung inflammation. A single dose of 5-AIQ (1.5mg/kg) was administered intraperitoneally (i.p.) 1h before λ-carrageenan (Cg) administration. We assessed the effects of 5-AIQ treatment on CD25(+), GITR(+), CD25(+)GITR(+), IL-17(+) and Foxp3(+) cells which were investigated using flowcytometry in pleural exudates and heparinized blood. We also evaluated mRNA expressions of IL-6, TNF-α, IL-1β, IL-10, CD11a, l-selectin (CD62L), ICAM-1, MCP-1, iNOS and COX-2 in the lung tissue. We further examined the effects of 5-AIQ on the key mediators of inflammation, namely COX-2, STAT-3, NF-kB p65, PARP-1, IkB-α and IL-4 protein expression in the lung tissue using western blotting. The results illustrated that the numbers of T cell subsets, IL-17(+) cytokine levels were markedly increased and Foxp3(+) production decreased in the Cg group. Furthermore, Cg-induced up-regulation of adhesion molecules, pro-inflammatory mediators and chemokine expressions. Western blot analysis revealed an increased protein expressions of COX-2, STAT-3 NF-kB p65 and PARP-1 and decreased IkB-α and IL-4 in the Cg group. PARP-1 inhibitor via 5-AIQ treatment reverses the action significantly of all the previously mentioned effects. Moreover, histological examinations revealed anti-inflammatory effects of 5-AIQ, whereas Cg-group aggravated Cg-induced inflammation. Present findings demonstrate the potent anti-inflammatory action of the PARP-1 inhibitor in acute lung injury induced by carrageenan.

Ethanol cytotoxic effect on trophoblast cells

Prenatal ethanol exposure may cause both, altered fetal neurodevelopment and impaired placental function. These disturbances can lead to growth retardation, which is one of the most prevalent features in Fetal Alcohol Syndrome (FAS). It is not known whether there is a specific pattern of cytotoxicity caused by ethanol that can be extrapolated to other cell types. The aim of this study was to determine the cytotoxic effects caused by sustained exposure of trophoblast cells to ethanol. The cytotoxic effect of sustained exposure to standard doses of ethanol on an in vitro human trophoblast cell line, JEG3, was examined. Viable cell count by exclusion method, total protein concentration, lactate dehydrogenase (LDH) activity and activation of apoptotic markers (P-H2AX, caspase-3 and PARP-1) were determined. Sustained exposure to ethanol decreased viable cell count and total protein concentration. LDH activity did not increased in exposed cells but apoptotic markers were detected. In addition, there was a dose-dependent relationship between ethanol concentration and apoptotic pathways activation. Sustained ethanol exposure causes cellular cytotoxicity by apoptotic pathways induction as a result of DNA damage. This apoptotic induction may partially explain the altered function of placental cells and the damage previously detected in other tissues.

Effects of PARP-1 deficiency on Th1 and Th2 cell differentiation

T cell differentiation to effector Th cells such as Th1 and Th2 requires the integration of multiple synergic and antagonist signals. Poly(ADP-ribosy)lation is a posttranslational modification of proteins catalyzed by Poly(ADP-ribose) polymerases (PARPs). Recently, many reports showed that PARP-1, the prototypical member of the PARP family, plays a role in immune/inflammatory responses. Consistently, its enzymatic inhibition confers protection in several models of immune-mediated diseases, mainly through an inhibitory effect on NF-κB (and NFAT) activation. PARP-1 regulates cell functions in many types of immune cells, including dendritic cells, macrophages, and T and B lymphocytes. Our results show that PARP-1KO cells displayed a reduced ability to differentiate in Th2 cells. Under both nonskewing and Th2-polarizing conditions, naïve CD4 cells from PARP-1KO mice generated a reduced frequency of IL-4⁺ cells, produced less IL-5, and expressed GATA-3 at lower levels compared with cells from wild type mice. Conversely, PARP-1 deficiency did not substantially affect differentiation to Th1 cells. Indeed, the frequency of IFN-γ⁺ cells as well as IFN-γ production, in nonskewing and Th1-polarizing conditions, was not affected by PARP-1 gene ablation. These findings demonstrate that PARP-1 plays a relevant role in Th2 cell differentiation and it might be a target to be exploited for the modulation of Th2-dependent immune-mediated diseases.

Beyond DNA repair, the immunological role of PARP-1 and its siblings

ADP-ribosylation is the addition of one or more (up to some hundreds) ADP-ribose moieties to acceptor proteins. There are two major families of enzymes that catalyse this reaction: extracellular ADP-ribosyl-transferases (ARTs), which are bound to the cell membrane by a glycosylphosphatidylinositol anchor or are secreted, and poly(ADP-ribose)-polymerases (PARPs), which are present in the cell nucleus and/or cytoplasm. Recent findings revealed a wide immunological role for ADP-ribosylating enzymes. ARTs, by sensing extracellular NAD concentration, can act as danger detectors. PARP-1, the prototypical representative of the PARP family, known to protect cells from genomic instability, is involved in the development of inflammatory responses and several forms of cell death. PARP-1 also plays a role in adaptive immunity by modulating the ability of dendritic cells to stimulate T cells or by directly affecting the differentiation and functions of T and B cells. Both PARP-1 and PARP-14 (CoaSt6) knockout mice were described to display reduced T helper type 2 cell differentiation and allergic responses. Our recent findings showed that PARP-1 is involved in the differentiation of Foxp3+ regulatory T (Treg) cells, suggesting a role for PARP-1 in tolerance induction. Also ARTs regulate Treg cell homeostasis by promoting Treg cell apoptosis during inflammatory responses. PARP inhibitors ameliorate immune-mediated diseases in several experimental models, including rheumatoid arthritis, colitis, experimental autoimmune encephalomyelitis and allergy. Together these findings show that ADP-ribosylating enzymes, in particular PARP-1, play a pivotal role in the regulation of immune responses and may represent a good target for new therapeutic approaches in immune-mediated diseases.

The guanine-quadruplex structure in the human c-myc gene's promoter is converted into B-DNA form by the human poly(ADP-ribose)polymerase-1

The important regulatory role of the guanine-quadruplex (GQ) structure, present in the nuclease hypersensitive element (NHE) III₁ region of the human c-myc (h c-myc) gene's promoter, in the regulation of the transcription of that gene has been documented. Here we present evidences, that the human nuclear poly(ADP-ribose)polymerase-1 (h PARP-1) protein participates in the regulation of the h c-myc gene expression through its interaction with this GQ structure, characterized by binding assays, fluorescence energy transfer (FRET) experiments and by affinity pull-down experiments in vitro, and by chromatin immunoprecipitation (ChIP)-qPCR analysis and h c-myc-promoter-luciferase reporter determinations in vivo. We surmise that h PARP-1 binds to the GQ structure and participates in the conversion of that structure into the transcriptionally more active B-DNA form. The first Zn-finger structure present in h PARP-1 participates in this interaction. PARP-1 might be a new member of the group of proteins participating in the regulation of transcription through their interactions with GQ structures present in the promoters of different genes.

The interaction between the PARP10 protein and the NS1 protein of H5N1 AIV and its effect on virus replication

Background

During the process that AIV infect hosts, the NS1 protein can act on hosts, change corresponding signal pathways, promote the translation of virus proteins and result in virus replication.

Results

In our study, we found that PARP domain and Glu-rich region of PARP10 interacted with NS1, and the presence of NS1 could induce PARP10 migrate from cytoplasm to nucleus. NS1 high expression could reduce the endogenous PARP10 expression. Cell cycle analysis showed that with inhibited PARP10 expression, NS1 could induce cell arrest in G2-M stage, and the percentage of cells in G2-M stage rise from the previous 10%-45%, consistent with the cell proliferation result. Plague forming unit measurement showed that inhibited PARP10 expression could help virus replication.

Conclusions

In a word, our results showed that NS1 acts on host cells and PARP10 plays a regulating role in virus replication.

Targeting poly(ADP-ribose) polymerase-1 as a promising approach for immunomodulation in multiple sclerosis?

Despite significant advancement in developing therapies for multiple sclerosis (MS), drugs that cure this devastating disorder are an unmet need. Among the remedies showing efficacy in preclinical MS models, inhibitors of poly(ADP-ribose) polymerase (PARP)-1 have gained great momentum. Emerging evidence demonstrates that PARP-1 inhibitors epigenetically regulate gene expression and finely tune transcriptional activation in immune and neural cells. In this review, we present an appraisal of the effects of PARP-1 and its inhibitors on immune activation, with particular emphasis on the processes taking place during the autoimmune attack directed against the central nervous system. One explanation is that drugs inhibiting PARP-1 activity protect from neuroinflammation in MS models via immunomodulation and direct neuroprotection. PARP-1 inhibitors have already reached the clinical arena as cancer treatments, and observations made in treating these patients could help advance treatments for MS.

Absence of poly(ADP-ribose) polymerase 1 delays the onset of Salmonella enterica serovar Typhimurium-induced gut inflammation

The immune system comprises an innate and an adaptive immune response to combat pathogenic agents. The human enteropathogen Salmonella enterica serovar Typhimurium invades the intestinal mucosa and triggers an early innate proinflammatory host gene response, which results in diarrheal disease. Several host factors, including transcription factors and transcription coregulators, are involved in the acute early response to Salmonella infection. We found in a mouse model of enterocolitis induced by S. Typhimurium that the absence of the nuclear protein poly(ADP-ribose) polymerase 1 (PARP1), a previously described cofactor for NF-kappaB-mediated proinflammatory gene expression, is associated with a delayed proinflammatory immune response after Salmonella infection. Our data reveal that PARP1 is expressed in the proliferative zone of cecum crypts, where it is required for the efficient expression of proinflammatory genes, many of which are related to interferon signaling. Consequently, animals lacking PARP1 show impaired infiltration of immune cells into the gut, with severely delayed inflammation.

Review: NAD +: a modulator of immune functions

Latterly, nicotinamide adenine dinucleotide (NAD+) has emerged as a molecule with versatile functions and of enormous impact on the maintenance of cell integrity. Besides playing key roles in almost all major aspects of energy metabolism, there is mounting evidence that NAD+ and its degradation products affect various biological activities including calcium homeostasis, gene transcription, DNA repair, and intercellular communication. This review is aimed at giving a brief insight into the life cycle of NAD+ in the cell, referring to synthesis, action and degradation aspects. With respect to their immunological relevance, the importance and function of the major NAD+ metabolizing enzymes, namely CD38/CD157, ADP-ribosyltransferases (ARTs), poly-ADP-ribose-polymerases (PARPs), and sirtuins are summarized and roles of NAD+ and its main degradation product adenosine 5'-diphosphoribose (ADPR) in cell signaling are discussed. In addition, an outline of the variety of immunological processes depending on the activity of nicotinamide phosphoribosyltransferase (Nampt), the key enzyme of the salvage pathway of NAD+ synthesis, is presented. Taken together, an efficient supply of NAD+ seems to be a crucial need for a multitude of cell functions, underlining the yet only partly revealed potency of this small molecule to influence cell fate.

Increased Foxp3+ regulatory T cells in poly(ADP-Ribose) polymerase-1 deficiency

Growing evidence is unveiling a role for poly(ADP-ribose) polymerase (PARP)-1 in the regulation of inflammatory/immune responses. In the current study, we investigated the effects of PARP-1 deficiency on regulatory T cell differentiation. Increased numbers of regulatory CD4(+)CD25(+)/Foxp3(+) T cells were found in thymus, spleen, and lymph nodes of PARP-1 knockout (KO) mice compared with wild-type (WT) controls. The increased frequency of regulatory T cells in the periphery resulted in impaired CD4 cell proliferation and IL-2 production, which could be restored by CD25(+) cell depletion. Phenotype and inhibitory functions of PARP-1 KO regulatory T cells were similar to WT cells, indicating that PARP-1 affects regulatory T cell differentiation rather than function. Purified naive CD4 cells from PARP-1 KO mice stimulated in vitro expressed forkhead box p3 mRNA at higher levels and generated a greater number of Foxp3(+) cells (inducible regulatory T [iTreg] cells) than the WT counterpart. This finding was due to a higher rate of naive CD4 cell to Foxp3(+) iTreg cell conversion rather than to higher resistance to apoptosis induction. Interestingly, PARP-1 deficiency did not affect retinoid-related orphan receptor-gammat mRNA expression and differentiation of purified naive CD4 cells to Th17 cells. PARP-1 KO iTreg cells showed features similar to WT regulatory T cells, suggesting that modulation of PARP-1 during the immune response might be used to induce greater numbers of functional regulatory T cells. In conclusion, our findings represent the first evidence that PARP-1 can affect regulatory T cell differentiation and open new perspectives on potential targets for modulating immune responses.

PARP-1 deficiency increases the severity of disease in a mouse model of multiple sclerosis

Poly(ADP-ribose) polymerase-1 (PARP-1) has been implicated in the pathogenesis of several central nervous system (CNS) disorders. However, the role of PARP-1 in autoimmune CNS injury remains poorly understood. Therefore, we studied experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis in mice with a targeted deletion of PARP-1. We identified inherent physiological abnormalities in the circulating and splenic immune composition between PARP-1(-/-) and wild type (WT) mice. Upon EAE induction, PARP-1(-/-) mice had an earlier onset and developed a more severe EAE compared with WT cohorts. Splenic response was significantly higher in PARP-1(-/-) mice largely because of B cell expansion. Although formation of Th1 and Th17 effector T lymphocytes was unaffected, PARP-1(-/-) mice had significantly earlier CD4+ T lymphocyte and macrophage infiltration into the CNS during EAE. However, we did not detect significant differences in cytokine profiles between PARP-1(-/-) and WT spinal cords at the peak of EAE. Expression analysis of different PARP isozymes in EAE spinal cords showed that PARP-1 was down-regulated in WT mice and that PARP-3 but not PARP-2 was dramatically up-regulated in both PARP-1(-/-) and WT mice, suggesting that these PARP isozymes could have distinct roles in different CNS pathologies. Together, our results indicate that PARP-1 plays an important role in regulating the physiological immune composition and in immune modulation during EAE; our finding identifies a new aspect of immune regulation by PARPs in autoimmune CNS pathology.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.