DEL-1 restrains osteoclastogenesis and inhibits inflammatory bone loss in nonhuman primates

DEL-1 (developmental endothelial locus-1) is an endothelial cell-secreted protein that regulates LFA-1 (lymphocyte function-associated antigen-1) integrin-dependent leukocyte recruitment and inflammation in various tissues. We identified a novel regulatory mechanism of DEL-1 in osteoclast biology. Specifically, we showed that DEL-1 is expressed by human and mouse osteoclasts and regulates their differentiation and resorptive function. Mechanistically, DEL-1 inhibited the expression of NFATc1, a master regulator of osteoclastogenesis, in a Mac-1 integrin-dependent manner. In vivo mechanistic analysis has dissociated the anti-inflammatory from the anti-bone-resorptive action of DEL-1 and identified structural components thereof mediating these distinct functions. Locally administered human DEL-1 blocked inflammatory periodontal bone loss in nonhuman primates-a relevant model of human periodontitis. The ability of DEL-1 to regulate both upstream (inflammatory cell recruitment) and downstream (osteoclastogenesis) events that lead to inflammatory bone loss paves the way to a new class of endogenous therapeutics for treating periodontitis and perhaps other inflammatory disorders.

Mammalian target of rapamycin complex 2 regulates invariant NKT cell development and function independent of promyelocytic leukemia zinc-finger

The mammalian target of rapamycin (mTOR) senses and incorporates different environmental cues via the two signaling complexes mTOR complex 1 (mTORC1) and mTORC2. As a result, mTOR controls cell growth and survival, and also shapes different effector functions of the cells including immune cells such as T cells. We demonstrate in this article that invariant NKT (iNKT) cell development is controlled by mTORC2 in a cell-intrinsic manner. In mice deficient in mTORC2 signaling because of the conditional deletion of the Rictor gene, iNKT cell numbers were reduced in the thymus and periphery. This is caused by decreased proliferation of stage 1 iNKT cells and poor development through subsequent stages. Functionally, iNKT cells devoid of mTORC2 signaling showed reduced number of IL-4-expressing cells, which correlated with a decrease in the transcription factor GATA-3-expressing cells. However, promyelocytic leukemia zinc-finger (PLZF), a critical transcription factor for iNKT cell development, is expressed at a similar level in mTORC2-deficient iNKT cells compared with that in the wild type iNKT cells. Furthermore, cellular localization of PLZF was not altered in the absence of mTOR2 signaling. Thus, our study reveals the PLZF-independent mechanisms of the development and function of iNKT cells regulated by mTORC2.

ATRX loss in glioma results in dysregulation of cell-cycle phase transition and ATM inhibitor radio-sensitization

ATRX, a chromatin remodeler protein, is recurrently mutated in H3F3A-mutant pediatric glioblastoma (GBM) and isocitrate dehydrogenase (IDH)-mutant grade 2/3 adult glioma. Previous work has shown that ATRX-deficient GBM cells show enhanced sensitivity to irradiation, but the etiology remains unclear. We find that ATRX binds the regulatory elements of cell-cycle phase transition genes in GBM cells, and there is a marked reduction in Checkpoint Kinase 1 (CHEK1) expression with ATRX loss, leading to the early release of G2/M entry after irradiation. ATRX-deficient cells exhibit enhanced activation of master cell-cycle regulator ATM with irradiation. Addition of the ATM inhibitor AZD0156 doubles median survival in mice intracranially implanted with ATRX-deficient GBM cells, which is not seen in ATRX-wild-type controls. This study demonstrates that ATRX-deficient high-grade gliomas (HGGs) display Chk1-mediated dysregulation of cell-cycle phase transitions, which opens a window for therapies targeting this phenotype.

Influence of electrostatics on the complement regulatory functions of Kaposica, the complement inhibitor of Kaposi's sarcoma-associated herpesvirus

Kaposica, the complement regulator of Kaposi's sarcoma-associated herpesvirus, inhibits complement by supporting factor I-mediated inactivation of the proteolytically activated form of C3 (C3b) and C4 (C4b) (cofactor activity [CFA]) and by accelerating the decay of classical and alternative pathway C3-convertases (decay-accelerating activity [DAA]). Previous data suggested that electrostatic interactions play a critical role in the binding of viral complement regulators to their targets, C3b and C4b. We therefore investigated how electrostatic potential on Kaposica influences its activities. We built a homology structure of Kaposica and calculated the electrostatic potential of the molecule, using the Poisson-Boltzmann equation. Mutants were then designed to alter the overall positive potential of the molecule or of each of its domains and linkers by mutating Lys/Arg to Glu/Gln, and the functional activities of the expressed mutants were analyzed. Our data indicate that 1) positive potential at specific sites and not the overall positive potential on the molecule guides the CFAs and classical pathway DAA; 2) positive potential around the linkers between complement control protein domains (CCPs) 1-2 and 2-3 is more important for DAAs than for CFAs; 3) positive potential in CCP1 is crucial for binding to C3b and C4b, and thereby its functional activities; 4) conversion to negative or enhancement of negative potential for CCPs 2-4 has a marked effect on C3b-linked activities as opposed to C4b-linked activities; and 5) reversal of the electrostatic potential of CCP4 to negative has a differential effect on classical and alternative pathway DAAs. Together, our data provide functional relevance to conservation of positive potential in CCPs 1 and 4 and the linkers of viral complement regulators.

Thymic NF-κB-inducing kinase regulates CD4+ T cell-elicited liver injury and fibrosis in mice

BACKGROUND & AIMS

The liver is an immunologically-privileged organ. Breakdown of liver immune privilege has been reported in chronic liver disease; however, the role of adaptive immunity in liver injury is poorly defined. Nuclear factor-κB-inducing kinase (NIK) is known to regulate immune tissue development, but its role in maintaining liver homeostasis remains unknown. This study aimed to assess the role of NIK, particularly thymic NIK, in regulating liver adaptive immunity.

METHODS

NIK was deleted systemically or conditionally using the Cre/loxp system. Cluster of differentiation [CD]4+ or CD8+ T cells were depleted using anti-CD4 or anti-CD8 antibody. Donor bone marrows or thymi were transferred into recipient mice. Immune cells were assessed by immunohistochemistry and flow cytometry.

RESULTS

Global, but not liver-specific or hematopoietic lineage cell-specific, deletion of NIK induced fatal liver injury, inflammation, and fibrosis. Likewise, adoptive transfer of NIK-null, but not wild-type, thymi into immune-deficient mice induced liver inflammation, injury, and fibrosis in recipients. Liver inflammation was characterized by a massive expansion of T cells, particularly the CD4+ T cell subpopulation. Depletion of CD4+, but not CD8+, T cells fully protected against liver injury, inflammation, and fibrosis in NIK-null mice. NIK deficiency also resulted in inflammation in the lung, kidney, and pancreas, but to a lesser degree relative to the liver.

CONCLUSIONS

Thymic NIK suppresses development of autoreactive T cells against liver antigens, and NIK deficiency in the thymus results in CD4+ T cell-orchestrated autoimmune hepatitis and liver fibrosis. Thus, thymic NIK is essential for the maintenance of liver immune privilege and liver homeostasis.

LAY SUMMARY

We found that global or thymus-specific ablation of the NIK gene results in fatal autoimmune liver disease in mice. NIK-deficient mice develop liver inflammation, injury, and fibrosis. Our findings indicate that thymic NIK is essential for the maintenance of liver integrity and homeostasis.

Keap1-Nrf2 System Plays an Important Role in Invariant Natural Killer T Cell Development and Homeostasis

Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) proteins work in concert to regulate the levels of reactive oxygen species (ROS). The Keap1-Nrf2 antioxidant system also participates in T cell differentiation and inflammation, but its role in innate T cell development and functions remains unclear. We report that T cell-specific deletion of Keap1 results in defective development and reduced numbers of invariant natural killer T (NKT) cells in the thymus and the peripheral organs in a cell-intrinsic manner. The frequency of NKT2 and NKT17 cells increases while NKT1 decreases in these mice. Keap1-deficient NKT cells show increased rates of proliferation and apoptosis, as well as increased glucose uptake and mitochondrial function, but reduced ROS, CD122, and Bcl2 expression. In NKT cells deficient in Nrf2 and Keap1, all these phenotypic and metabolic defects are corrected. Thus, the Keap1-Nrf2 system contributes to NKT cell development and homeostasis by regulating cell metabolism.

Reactive Oxygen Species Regulate the Inflammatory Function of NKT Cells through Promyelocytic Leukemia Zinc Finger

Reactive oxygen species (ROS) are byproducts of aerobic metabolism and contribute to both physiological and pathological conditions as second messengers. ROS are essential for activation of T cells, but how ROS influence NKT cells is unknown. In the present study, we investigated the role of ROS in NKT cell function. We found that NKT cells, but not CD4 or CD8 T cells, have dramatically high ROS in the spleen and liver of mice but not in the thymus or adipose tissues. Accordingly, ROS-high NKT cells exhibited increased susceptibility and apoptotic cell death with oxidative stress. High ROS in the peripheral NKT cells were primarily produced by NADPH oxidases and not mitochondria. We observed that sorted ROS-high NKT cells were enriched in NKT1 and NKT17 cells, whereas NKT2 cells were dominant in ROS-low cells. Furthermore, treatment of NKT cells with antioxidants led to reduced frequencies of IFN-γ- and IL-17-expressing cells, indicating that ROS play a role in regulating the inflammatory function of NKT cells. The transcription factor promyelocytic leukemia zinc finger (PLZF) seemed to control the ROS levels. NKT cells from adipose tissues that do not express PLZF and those from PLZF haplodeficient mice have low ROS. Conversely, ROS were highly elevated in CD4 T cells from mice ectopically expressing PLZF. Thus, our findings demonstrate that PLZF controls ROS levels, which in turn governs the inflammatory function of NKT cells.

Species selectivity in poxviral complement regulators is dictated by the charge reversal in the central complement control protein modules

Variola and vaccinia viruses, the two most important members of the family Poxviridae, are known to encode homologs of the human complement regulators named smallpox inhibitor of complement enzymes (SPICE) and vaccinia virus complement control protein (VCP), respectively, to subvert the host complement system. Intriguingly, consistent with the host tropism of these viruses, SPICE has been shown to be more human complement-specific than VCP, and in this study we show that VCP is more bovine complement-specific than SPICE. Based on mutagenesis and mechanistic studies, we suggest that the major determinant for the switch in species selectivity of SPICE and VCP is the presence of oppositely charged residues in the central complement control modules, which help enhance their interaction with factor I and C3b, the proteolytically cleaved form of C3. Thus, our results provide a molecular basis for the species selectivity in poxviral complement regulators.

Virus–complement interactions: an assiduous struggle for dominance

The complement system is a major component of the innate immune system that recognizes invading pathogens and eliminates them by means of an array of effector mechanisms, in addition to using direct lytic destruction. Viruses, in spite of their small size and simple composition, are also deftly recognized and neutralized by the complement system. In turn, as a result of years of coevolution with the host, viruses have developed multiple mechanisms to evade the host complement. These complex interactions between the complement system and viruses have been an area of focus for over three decades. In this article, we provide a broad overview of the field using key examples and up-to-date information on the complement-evasion strategies of viruses.

β-Catenin is required for the differentiation of iNKT2 and iNKT17 cells that augment IL-25-dependent lung inflammation

Background

Invariant Natural Killer T (iNKT) cells have been implicated in lung inflammation in humans and also shown to be a key cell type in inducing allergic lung inflammation in mouse models. iNKT cells differentiate and acquire functional characteristics during development in the thymus. However, the correlation between development of iNKT cells in the thymus and role in lung inflammation remains unknown. In addition, transcriptional control of differentiation of iNKT cells into iNKT cell effector subsets in the thymus during development is also unclear. In this report we show that β-catenin dependent mechanisms direct differentiation of iNKT2 and iNKT17 subsets but not iNKT1 cells.

Methods

To study the role for β-catenin in lung inflammation we utilize mice with conditional deletion and enforced expression of β-catenin in a well-established mouse model for IL-25-dependen lung inflammation.

Results

Specifically, we demonstrate that conditional deletion of β-catenin permitted development of mature iNKT1 cells while impeding maturation of iNKT2 and 17 cells. A role for β-catenin expression in promoting iNKT2 and iNKT17 subsets was confirmed when we noted that enforced transgenic expression of β-catenin in iNKT cell precursors enhanced the frequency and number of iNKT2 and iNKT17 cells at the cost of iNKT1 cells. This effect of expression of β-catenin in iNKT cell precursors was cell autonomous. Furthermore, iNKT2 cells acquired greater capability to produce type-2 cytokines when β-catenin expression was enhanced.

Discussion

This report shows that β-catenin deficiency resulted in a profound decrease in iNKT2 and iNKT17 subsets of iNKT cells whereas iNKT1 cells developed normally. By contrast, enforced expression of β-catenin promoted the development of iNKT2 and iNKT17 cells. It was important to note that the majority of iNKT cells in the thymus of C57BL/6 mice were iNKT1 cells and enforced expression of β-catenin altered the pattern to iNKT2 and iNKT17 cells suggesting that β-catenin may be a major factor in the distinct pathways that critically direct differentiation of iNKT effector subsets.

Conclusions

Thus, we demonstrate that β-catenin expression in iNKT cell precursors promotes differentiation toward iNKT2 and iNKT17 effector subsets and supports enhanced capacity to produce type 2 and 17 cytokines which in turn augment lung inflammation in mice.

Temporal regulation of Wnt/β-catenin signaling is important for invariant NKT cell development and terminal maturation

The Wnt/β-catenin signaling pathway plays important roles during various cellular functions including survival and proliferation of immune cells. The critical role of this pathway in conventional T cell development is established but little is known about its contributions to innate T cell development. In this study, we found that β-catenin level, an indication of the strength of Wnt/β-catenin signaling, is regulated during invariant NKT (iNKT) cell development. β-catenin levels were greatly increased during iNKT cell selection from double positive thymocytes to Stage 0 of iNKT cell development and during subsequent development to Stage 1. Thereafter, β-catenin levels decrease from Stage 2, which is essential for the terminal maturation of iNKT cells. Failure to dampen Wnt/β-catenin signaling as in mice expressing a stabilized active form of β-catenin (CATtg) resulted in increased Stage 2 and decreased Stage 3 iNKT cells. Inefficient transition from Stage 2 to 3 in CATtg iNKT cells seems to be contributed by poor expression of IL-15R (CD122) and transcription factor T-bet, both of which are necessary for terminal maturation of iNKT cells in the thymus. Consequently, IFN-γ+ iNKT cells were greatly reduced in CATtg mice. Together, our findings reveal that proper regulation of β-catenin and in turn Wnt signaling plays an important role in the terminal maturation and function of iNKT cells.

Beyond Antioxidation: Keap1-Nrf2 in the Development and Effector Functions of Adaptive Immune Cells

Ubiquitously expressed in mammalian cells, the Kelch-like ECH-associated protein 1 (Keap1)-NF erythroid 2-related factor 2 (Nrf2) complex forms the evolutionarily conserved antioxidation system to tackle oxidative stress caused by reactive oxygen species. Reactive oxygen species, generated as byproducts of cellular metabolism, were identified as essential second messengers for T cell signaling, activation, and effector responses. Apart from its traditional role as an antioxidant, a growing body of evidence indicates that Nrf2, tightly regulated by Keap1, modulates immune responses and regulates cellular metabolism. Newer functions of Keap1 and Nrf2 in immune cell activation and function, as well as their role in inflammatory diseases such as sepsis, inflammatory bowel disease, and multiple sclerosis, are emerging. In this review, we highlight recent findings about the influence of Keap1 and Nrf2 in the development and effector functions of adaptive immune cells, that is, T cells and B cells, and discuss the knowledge gaps in our understanding. We also summarize the research potential and targetability of Nrf2 for treating immune pathologies.

Advances in NKT cell Immunotherapy for Glioblastoma

Type I or invariant natural killer T cells belong to a unique lineage of innate T cells, which express markers of both T lymphocytes and NK cells, namely T cell receptor (TCR) and NK1.1 (CD161C), respectively. Thus, apart from direct killing of target cells like NK cells, and they also produce a myriad of cytokines which modulate the adaptive immune responses. Unlike traditional T cells which carry a conventional αβ TCR, NKT cells express semi-invariant TCR - Vα14-Jα18, coupled with Vβ8, Vβ7 and Vβ2 in mice. In humans, the invariant TCR is composed of Vα24-Jα18, coupled with Vβ11.

Stable integrant-specific differences in bimodal HIV-1 expression patterns revealed by high-throughput analysis

HIV-1 gene expression is regulated by host and viral factors that interact with viral motifs and is influenced by proviral integration sites. Here, expression variation among integrants was followed for hundreds of individual proviral clones within polyclonal populations throughout successive rounds of virus and cultured cell replication, with limited findings using CD4+ cells from donor blood consistent with observations in immortalized cells. Tracking clonal behavior by proviral “zip codes” indicated that mutational inactivation during reverse transcription was rare, while clonal expansion and proviral expression states varied widely. By sorting for provirus expression using a GFP reporter in the nef open reading frame, distinct clone-specific variation in on/off proportions were observed that spanned three orders of magnitude. Tracking GFP phenotypes over time revealed that as cells divided, their progeny alternated between HIV transcriptional activity and non-activity. Despite these phenotypic oscillations, the overall GFP+ population within each clone was remarkably stable, with clones maintaining clone-specific equilibrium mixtures of GFP+ and GFP- cells. Integration sites were analyzed for correlations between genomic features and the epigenetic phenomena described here. Integrants inserted in the sense orientation of genes were more frequently found to be GFP negative than those in the antisense orientation, and clones with high GFP+ proportions were more distal to repressive H3K9me3 peaks than low GFP+ clones. Clones with low frequencies of GFP positivity appeared to expand more rapidly than clones for which most cells were GFP+, even though the tested proviruses were Vpr-. Thus, much of the increase in the GFP- population in these polyclonal pools over time reflected differential clonal expansion. Together, these results underscore the temporal and quantitative variability in HIV-1 gene expression among proviral clones that are conferred in the absence of metabolic or cell-type dependent variability, and shed light on cell-intrinsic layers of regulation that affect HIV-1 population dynamics.

Very few HIV-1 infected cells persist in patients for more than a couple days, but those that do pose life-long health risks. Strategies designed to eliminate these cells have been based on assumptions about what viral properties allow infected cell survival. However, such approaches for HIV-1 eradication have not yet shown therapeutic promise, possibly because many assumptions about virus persistence are based on studies involving a limited number of infected cell types, the averaged behavior of cells in diverse populations, or snapshot views. Here, we developed a high-throughput approach to study hundreds of distinct HIV-1 infected cells and their progeny over time in an unbiased way. This revealed that each virus established its own pattern of gene expression that, upon infected cell division, was stably transmitted to all progeny cells. Expression patterns consisted of alternating waves of activity and inactivity, with the extent of activity differing among infected cell families over a 1000-fold range. The dynamics and variability among infected cells and within complex populations that the work here revealed has not previously been evident, and may help establish more accurate correlates of persistent HIV-1 infection.

PLZF-expressing CD4 T cells show the characteristics of terminally differentiated effector memory CD4 T cells in humans

We show the presence of lymphoid tissue-resident PLZF+ CD45RA+ RO+ CD4 T cells in humans. They express HLA-DR, granzyme B, and perforin and are low on CCR7 like terminally differentiated effector memory (Temra) cells and are likely generated from effector T cells (Te) or from central (Tcm) or effector (Tem) memory T (Tcm) cells during immune responses. Tn, Naïve T cells.

Wnt/β-catenin signaling regulates IL-15-mediated terminal maturation and interferon-gamma production of invariant NKT cells

The Wnt/β-catenin signaling pathway is important for various cellular functions including survival and proliferation. The indispensable role of this pathway in conventional T cell development is well established but little is known about its role in innate T cell development. In this study, we investigated the role of the Wnt/β-catenin signaling in the development of invariant natural killer T (NKT) cells using mice that express a constitutively active form of b-catenin (CAT-Tg) or deficient in β-catenin (CAT-KO). Thymic NKT cells were increased in CAT-Tg and decreased in CAT-KO mice compared to their wild type littermates. Thymic NKT cells progress from Stage 0 to Stage 3 as they mature. In the absence of Wnt signaling (CAT-KO), we observed accumulation of Stage 0 NKT cells. In contrast, in CAT-Tg mice, the final maturation was compromised - more Stage 2 but less Stage 3 NKT cells. Thus, stage-specific regulation of Wnt signaling may be critical for the thymic NKT development. Indeed, endogenous β-catenin expression was high in early stages but low in late stages, suggesting that its reduction mounts the stage-2 to -3 NKT transition. The CAT-Tg mice also had lower number of IFN-gamma expressing NKT cells, which, in these cells, correlated with reduced expression of transcription factor Tbet and CD122 (IL-2R & IL-15R subunit), requisites for final maturation and IFN-gamma expression of NKT cells. Further, although PLZF, a master transcription factor for NKT cell development is expressed at high levels in CAT-Tg NKT cells, Wnt signaling-mediated NKT cell maturation was found to be independent of PLZF. Together, our data shows that regulation of Wnt/β-catenin signaling is necessary for terminal maturation and IFN-gamma production of NKT cells.

NKT Cells and Other Innate T Cells: The Immune Cells That Do Not Follow the Rules

This Pillars of Immunology article is a commentary on “A subset of CD4+ thymocytes selected by MHC class I molecules,” a pivotal article by A. Bendelac, N. Killeen, D.R. Littman, and R.H. Schwartz published in Science in 1994, marking the discovery of NKT cells and paving the way for the identification and characterization of other innate T cells. https://doi.org/10.1126/science.7907820.

Keap1-Nrf2 system controls cellular metabolism to govern NKT cell homeostasis and effector functions

Kelch-like ECH-associated protein (Keap1) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) proteins work in concert as anti-oxidant system to regulate reactive oxygen species (ROS) levels. Additionally, Keap1-Nrf2 system has been shown to play a role in T cell-mediated inflammation but its role for maintenance and function of innate T cells is unclear. Using mice with T-cell specific deletion of Keap1 (KO) leading to higher Nrf2 activity, we recently reported that Keap1-Nrf2 system plays an essential role in the development and homeostasis of invariant natural killer T (NKT) cells. At steady state, KO NKT cells show increased rates of proliferation as well as apoptosis together with altered cell metabolism involving higher glucose uptake, glucose transporter-1 expression, mitochondrial mass and mitochondrial potential but lower ROS than WT NKT cells. Interestingly, upon activation with specific ligand a-GalCer, KO NKT cells proliferated lesser than WT NKT cells. Gene expression data indicated higher glycolysis and lower glutaminolysis in activated KO NKT than WT NKT cells. Further, unstimulated WT NKT cells were found to have elevated levels of glutamine and glutamate. NKT cells stimulated in the absence of glutamine survived and proliferated poorly but had no effect on cytokine production suggesting the importance of glutamine metabolism and keeping a check on glycolysis for the homeostasis and proliferation of NKT cells. Overall, our findings indicate that, via Nrf2, Keap1 positively regulates glutaminolysis and negatively regulates glycolysis to maintain NKT cell homeostasis and promote activation-driven proliferation. Here, we report a yet unknown role of Keap1-Nrf2 system in the cell metabolism of T cells.

Regulation of NKT cell metabolism by PLZF

Cellular metabolism and signaling pathways are the key regulators to determine T cell fate, survival and function, particularly during activation. Resting CD4 and CD8 T cells use oxidative phosphorylation as a primary energy source but switches to glycolysis upon activation, which is necessary to produce biomolecules for cell proliferation and function. Failure of this reprogramming is detrimental for T cell mediated immunity. However, little is understood about how NKT cells control their metabolism to survive and function. We found that NKT cells operate distinctly different metabolic programming from CD4 T cells for their survival and function. Supporting evidence includes that, unlike CD4 T cells, oxidative phosphorylation seems to be preferred over glycolysis in NKT cells even after stimulation as revealed by lower level of intracellular lactate produced by NKT cells than CD4 cells after activation. These cells also seem to have high energy as revealed by higher ATP in NKT cells. Although the proper maintenance and functions of stimulated NKT cells need glucose, they are sensitive to the elevated glycolytic potential compared to CD4 T cells resulting in spontaneous cell death accompanied by hyperproliferation. Importantly, PLZF is the essential regulator of NKT cells’ metabolism so that similar changes of glucose metabolism were found in CD4 T cells expressing PLZF. Conversely, NKT cells with haplodeficient PLZF were more tolerant to increased glycolysis, strongly supporting the key role of PLZF in NKT cell metabolism and homeostasis. We are currently investigating the underlying mechanisms by which PLZF controls metabolism in NKT cells using several approaches including metabolomics.

CBIO-03. ATRX LOSS IN GLIOMA RESULTS IN EPIGENETIC DYSREGULATION OF CELL CYCLE PHASE TRANSITION

Gliomas are a leading cause of cancer mortality in children and adults, and new targeted therapies are desperately needed. ATRX is a chromatin remodeling protein that is recurrently mutated in H3F3A-mutant pediatric glioblastoma (GBM) and IDH-mutant grade 2/3 adult glioma. We previously showed that loss of ATRX in glioma results in tumor growth and additional tumor mutations. However, the mechanism driving these phenotypes has not been fully established. We found that in ChIP-Seq/ChIP-qPCR of mouse neuronal precursor cells (NPCs) and GBM cells with isogenic ATRX loss, ATRX binds regulatory elements for cell cycle phase transition gene sets, and ATRX loss subsequently results in reduced expression. Furthermore, human GBM cells with ATRX knock-out demonstrate higher rates of cells in S and G2/M phases, with clusters of cells demonstrating reduced expression of cell cycle regulatory gene sets by single-cell sequencing (scSeq) analysis. In human and mouse GBM in vitro models, ATRX-deficient cells exhibit a seven-fold increase in mitotic index at 16 hours after sub-lethal radiation and enhanced activation of the master cell cycle regulator ATM with radiation. Treatment of ATRX-deficient gliomas with ATM inhibitors results in a selective increase in dysfunctional cell cycling and increased radio-sensitization in ATRX-deficient glioma cells. Using an ATM-luciferase reporter in orthotopically-implanted human GBM cells, both AZD0156 and AZD1390 demonstrate in vivo pathway inhibition. Mice intra-cranially implanted with ATRX-deficient GBM cells demonstrate a doubling of median survival compared to radiated controls (p=0.0018) when treated with AZD0156 combined with radiation; this is not seen in ATRX-sufficient models. This study demonstrates that ATRX-deficient high-grade gliomas display epigenetic dysregulation of cell cycle phase transitions, which opens a new window for therapies targeting this unique phenotype.

Reactive oxygen species regulate the inflammatory function of NKT cells through Promyelocytic Leukaemia Zinc Finger (PLZF) protein

Cellular metabolism controlled by the signaling pathways has a crucial role in dictating the outcome of T cell activation and effector function. Reactive oxygen species (ROS) are byproducts of aerobic metabolism and contribute to both physiological and pathological conditions as a second messenger. In T cells, ROS levels increase upon activation and antigen specific responses of T cells are compromised in the absence of ROS production by mitochondria. However, it is not well understood how NKT cells’ functions are controlled by cell metabolism. In the current study, we investigated the role of ROS in NKT cell function. We found that ROS levels were similar among CD4, CD8 and NKT cell subsets in the thymus but NKT cells showed dramatically increased ROS in the spleen and liver but not in adipose tissues. ROS in the peripheral NKT cells were primarily produced by NADPH oxidases not mitochondria. Accordingly, ROS high NKT cells were susceptible to oxidative stress and underwent apoptotic cell death. Furthermore, ROS play an important role regulating the inflammatory function of NKT cells because antioxidant treatment of NKT cells showed reduced frequencies of IFN-γ+ and IL-17+ cells. In line with this, freshly isolated ROS-high NKT cells had more NKT1 and NKT17 cells but less NKT2 than ROS-low cells. Importantly, these characteristics of NKT cells are regulated by PLZF (Promyelocytic Leukaemia Zinc Finger) protein as evidenced by reduced ROS in NKT cells from adipose tissues that do not express PLZF and also those from PLZF haplodeficient mice. Conversely, ROS were highly elevated in CD4 T cells from mice ectopically expressing PLZF. Together, our study revealed for the first time that ROS regulate NKT cell functions through PLZF.

Nrf2 regulates the activation-driven expansion of CD4 + T-cells by differentially modulating glucose and glutamine metabolism

Upon antigenic stimulation, CD4 + T-cells undergo clonal expansion, elevating their bioenergetic demands and utilization of nutrients like glucose and glutamine. The nuclear factor erythroid 2-related factor 2 (Nrf2) is a well-known regulator of oxidative stress, but its involvement in modulating the metabolism of CD4 + T-cells remains unexplored. Here, we elucidate the role of Nrf2 beyond the traditional antioxidation, in modulating activation-driven expansion of CD4 + T-cells by influencing their nutrient metabolism. T-cell-specific activation of Nrf2 enhances early activation and IL-2 secretion, upregulates TCR-signaling, and increases activation-driven proliferation of CD4 + T-cells. Mechanistically, high Nrf2 inhibits glucose metabolism through glycolysis but promotes glutamine metabolism via glutaminolysis to support increased T-cell proliferation. Further, Nrf2 expression is temporally regulated in activated CD4 + T-cells with elevated expression during the early activation, but decreased expression thereafter. Overall, our findings uncover a novel role of Nrf2 as a metabolic modulator of CD4 + T-cells, thus providing a framework for improving Nrf2-targeting therapies and T-cell immunotherapies.

Viral complement regulators: the expert mimicking swindlers

The complement system is a principal bastion of innate immunity designed to combat a myriad of existing as well as newly emerging pathogens. Since viruses are obligatory intracellular parasites, they are continuously exposed to host complement assault and, therefore, have imbibed various strategies to subvert it. One of them is molecular mimicry of the host complement regulators. Large DNA viruses such as pox and herpesviruses encode proteins that are structurally and functionally similar to human regulators of complement activation (RCA), a family of proteins that regulate complement. In this review, we have presented the structural and functional aspects of virally encoded RCA homologs (vRCA), in particular two highly studied vRCAs, vaccinia virus complement control protein (VCP) and Kaposi's sarcoma-associated herpesvirus complement regulator (kaposica). Importance of these evasion molecules in viral pathogenesis and their role beyond complement regulation are also discussed.