Resistance of Foxp3+ regulatory T cells to Nur77-induced apoptosis promotes allograft survival

MicroRNA let-7a mediates posttranscriptional inhibition of Nr4A1 and exacerbates cardiac allograft rejection

BACKGROUND

Acute allograft rejection remains a major obstacle after heart transplantation, and CD4+ T cells play a crucial role in allograft rejection. Upregulation of Nr4A1 could regulate CD4+ T-cell function and alleviate allograft rejection. However, the regulatory mechanism of Nr4A1 in allograft rejection remains elusive.

METHODS

BCLb/c mouse hearts were transplanted into WT C57BL/6 mice, and dynamic detection of the changes in Nr4A1 expression revealed that Nr4A1 was regulated posttranscriptionally after heart transplantation. Potential upstream miRNAs of Nr4A1 were screened, and the transfection of cells with these miRNA mimics/inhibitors and dual-luciferase reporter experiments were performed to clarify the regulatory mechanism of miRNAs on Nr4A1 expression. The miRNA agomiR/antagomiR was applied in vivo to validate the role of the corresponding miRNA in heart transplantation. Finally, Nr4A1 knockout mice and an adoptive T-cell cotransfer model were used to confirm the specific effects of miRNA.

RESULTS

The expression of Nr4A1 protein (rather than mRNA) exhibited a trend of initially increasing and then decreasing rapidly, and this phenomenon could not be reversed by lysosomal or proteasomal inhibitors. The miRNA let-7a directly binds to the Nr4A1 3'UTR and posttranscriptionally regulates Nr4A1 expression. The let-7a antagomiR prolonged allograft survival and regulated CD4+ T-cell function by upregulating Nr4A1 protein expression in CD4+ T cells.

CONCLUSIONS

This study confirmed that let-7a is a potential target for interfering with Nr4A1 expression in CD4+ T cells and preventing the pathological progression of cardiac allograft rejection.

TCR-signals downstream adversely correlate with the survival signals of memory CD8+ T cells under homeostasis

The significance of self-peptide-MHC-I/TCR (SMT) interaction in the survival of CD8⁺ T cells during naïve- and developmental-stages is well documented. However, the same for the memory stage is contentious. Previous studies have attempted to address the issue using MHC-I or TCR deficient systems, but inconsistent findings with memory CD8⁺ T cells of different TCR specificities have complicated the interpretation. Differential presence and/or processing of TCR-signals downstream in memory CD8⁺ T cells of different TCR specificities could be thought of as a reason. In this study, we examined the TCR-signals downstream in memory CD8⁺ T cells and compared them to the presence of survival-related signals (Annexin-V, Bcl-2, and Ki-67). We categorically tracked foreign antigen-experienced memory CD8⁺ T (TM) cells generated after Plasmodium pre-erythrocytic-stage malaria infection in C57BL/6 mice. Interestingly, we found that memory CD8⁺ T cells had more TCR-signals downstream than naive cells. We reasoned and attributed the increased expression of cell adhesion molecules to the enhanced TCR-signaling. TCR-signals downstream correlate more closely with survival signals in naive CD8⁺ T cells than with death signals in TM cells. Further investigation using antigen-specific CD8⁺ T cells and diverse infection systems would aid in conceptualizing the findings.

Nuclear Coregulatory Complexes in Tregs as Targets to Promote Anticancer Immune Responses

T-regulatory (Treg) cells display considerable heterogeneity in their responses to various cancers. The functional differences among this cell type are heavily influenced by multiprotein nuclear complexes that control their gene expression. Many such complexes act mechanistically by altering epigenetic profiles of genes important to Treg function, including the forkhead P3 (Foxp3) transcription factor. Complexes that form with certain members of the histone/protein deacetylase (HDAC) class of enzymes, like HDACs 1, 2, and 3, along with histone methyltransferase complexes, are important in the induction and stabilization of Foxp3 and Treg identity. The functional behavior of both circulating and intratumoral Tregs greatly impacts the antitumor immune response and can be predictive of patient outcome. Thus, targeting these regulatory complexes within Tregs may have therapeutic potential, especially in personalized immunotherapies.

Cytosporone B (Csn-B), an NR4A1 agonist, attenuates acute cardiac allograft rejection by inducing differential apoptosis of CD4+T cells

CD4+T cell-mediated acute rejection remains a major factor that affects the early survival of transplanted organs post-transplantation. Here, we reveal that nuclear receptor subfamily 4 Group A member 1 (Nr4A1) was upregulated during cardiac allograft rejection and that the increased Nr4A1 was primarily localized in intragraft-infiltrating CD4+T cells. Nr4A1 acts as a transcription factor with an important role in CD4+T cell apoptosis, differentiation and T cell dysfunction, which indicates that Nr4A1 may play a critical role in transplant rejection. Cytosporone B (Csn-B) is a naturally occurring agonist of Nr4A1, and the role of Csn-B in the physiological process of cardiac rejection is poorly defined. This study constructed an acute rejection model of abdominal heterotopic cardiac transplantation in mice and investigated whether Csn-B could attenuate acute transplant rejection by modulating the CD4+T lymphocyte response. The results showed that Csn-B prolonged murine cardiac allograft survival and reduced inflammation in allografts. Subsequently, it was confirmed that Csn-B functions by inducing non-Treg apoptosis and promoting Treg cell differentiation. Finally, we also confirmed that Csn-B attenuates acute rejection by directly targeting Nr4A1 in CD4+T cells. Our data suggest that Csn-B is a promising novel therapeutic approach for acute cardiac allograft rejection.

Infectious sporozoite challenge modulates radiation attenuated sporozoite vaccine-induced memory CD8+ T cells for better survival characteristics

Radiation attenuated sporozoite (RAS), a whole parasite vaccine approach provides sterile protection against malaria. However, RAS immunization does not confer protection for long, and that has been correlated with the waning parasite-induced memory CD8⁺ T cell responses. Interestingly, an intermittent infectious (wild-type) sporozoite challenge to the RAS vaccinated mice lengthened the protection period from 6 to 18 months. Herein, we have studied the changes that infectious sporozoite brought in RAS-induced memory CD8⁺ T cells for conferring lengthened protection. We observed that the infectious sporozoite challenge has boosted the frequency of foreign antigen-experienced memory CD8⁺ T cells. In those CD8⁺ T cells, it has reduced the Annexin-V reactivity, raised Bcl-2 expression, and also more cells undergone homeostatic proliferation (Ki-67⁺ ). It has also scaled down the frequency of Nur77 and CX3CR1 high expressing cells in those memory CD8⁺ T cell populations which we further correlated with better survival signals. This article is protected by copyright. All rights reserved.

Post-Translational Regulations of Foxp3 in Treg Cells and Their Therapeutic Applications

Regulatory T (Treg) cells are indispensable for immune homeostasis due to their roles in peripheral tolerance. As the master transcription factor of Treg cells, Forkhead box P3 (Foxp3) strongly regulates Treg function and plasticity. Because of this, considerable research efforts have been directed at elucidating the mechanisms controlling Foxp3 and its co-regulators. Such work is not only advancing our understanding on Treg cell biology, but also uncovering novel targets for clinical manipulation in autoimmune diseases, organ transplantation, and tumor therapies. Recently, many studies have explored the post-translational regulation of Foxp3, which have shown that acetylation, phosphorylation, glycosylation, methylation, and ubiquitination are important for determining Foxp3 function and plasticity. Additionally, some of these targets have been implicated to have great therapeutic values. In this review, we will discuss emerging evidence of post-translational regulations on Foxp3 in Treg cells and their exciting therapeutic applications.

Natural Killer T Lymphocytes Integrate Innate Sensory Information and Relay Context to Effector Immune Responses

It is now appreciated that a group of lymphoid lineage cells, collectively called innate-like effector lymphocytes, have evolved to integrate information relayed by the innate sensory immune system about the state of the local tissue environment and to pass on this context to downstream effector innate and adaptive immune responses. Thereby, innate functions engrained into such innate-like lymphoid lineage cells during development can control the quality and magnitude of an immune response to a tissue-altering pathogen and facilitate the formation of memory engrams within the immune system. These goals are accomplished by the innate lymphoid cells that lack antigen-specific receptors, γδ T cell receptor (TCR)-expressing T cells, and several αβ TCR-expressing T cell subsets-such as natural killer T cells, mucosal-associated invariant T cells, et cetera. Whilst we briefly consider the commonalities in the origins and functions of these diverse lymphoid subsets to provide context, the primary topic of this review is to discuss how the semi-invariant natural killer T cells got this way in evolution through lineage commitment and onward ontogeny. What emerges from this discourse is the question: Has a "limbic immune system" emerged (screaming quietly in plain sight!) out of what has been dubbed "in-betweeners"?

'Nur'turing tumor T cell tolerance and exhaustion: novel function for Nuclear Receptor Nur77 in immunity

The nuclear receptor Nur77 is expressed in a multitude of tissues, regulating cell differentiation and homeostasis. Dysregulation of Nur77 signaling is associated with cancer, cardiovascular disease, and disorders of the CNS. The role of Nur77 in T cells has been studied for almost 30 years now. There is a clear appreciation that Nur77 is crucial for apoptosis of self‐reactive T cells. However, the regulation and function of Nur77 in mature T cells remains largely unclear. In an exciting development, Nur77 has been recently demonstrated to impinge on cancer immunotherapy involving chimeric antigen receptor (CAR) T cells and tumor infiltrating lymphocytes (TILs). These studies indicated that Nur77 deficiency reduced T cell tolerance and exhaustion, thus raising the effectiveness of immune therapy in mice. Based on these novel insights, it may be proposed that regulation of Nur77 activity holds promise for innovative drug development in the field of cellular immunotherapy in cancer. In this review, we therefore summarize the role of Nur77 in T cell selection and maturation; and further develop the idea of targeting its activity in these cells as a potential strategy to augment current cancer immunotherapy treatments.

Nur77 controls tolerance induction, terminal differentiation, and effector functions in semi-invariant natural killer T cells

Semi-invariant natural killer T (iNKT) cells are self-reactive lymphocytes, yet how this lineage attains self-tolerance remains unknown. iNKT cells constitutively express high levels of Nr4a1-encoded Nur77, a transcription factor that integrates signal strength downstream of the T cell receptor (TCR) within activated thymocytes and peripheral T cells. The function of Nur77 in iNKT cells is unknown. Here we report that sustained Nur77 overexpression (Nur77tg) in mouse thymocytes abrogates iNKT cell development. Introgression of a rearranged Vα14-Jα18 TCR-α chain gene into the Nur77tg (Nur77tg;Vα14tg) mouse rescued iNKT cell development up to the early precursor stage, stage 0. iNKT cells in bone marrow chimeras that reconstituted thymic cellularity developed beyond stage 0 precursors and yielded IL-4-producing NKT2 cell subset but not IFN-γ-producing NKT1 cell subset. Nonetheless, the developing thymic iNKT cells that emerged in these chimeras expressed the exhaustion marker PD1 and responded poorly to a strong glycolipid agonist. Thus, Nur77 integrates signals emanating from the TCR to control thymic iNKT cell tolerance induction, terminal differentiation, and effector functions.

Restoring T Cell Tolerance, Exploring the Potential of Histone Deacetylase Inhibitors for the Treatment of Juvenile Idiopathic Arthritis

Juvenile Idiopathic Arthritis (JIA) is characterized by a loss of immune tolerance. Here, the balance between the activity of effector T (Teff) cells and regulatory T (Treg) cells is disturbed resulting in chronic inflammation in the joints. Presently, therapeutic strategies are predominantly aimed at suppressing immune activation and pro-inflammatory effector mechanisms, ignoring the opportunity to also promote tolerance by boosting the regulatory side of the immune balance. Histone deacetylases (HDACs) can deacetylate both histone and non-histone proteins and have been demonstrated to modulate epigenetic regulation as well as cellular signaling in various cell types. Importantly, HDACs are potent regulators of both Teff cell and Treg cell function and can thus be regarded as attractive therapeutic targets in chronic inflammatory arthritis. HDAC inhibitors (HDACi) have proven therapeutic potential in the cancer field, and are presently being explored for their potential in the treatment of autoimmune diseases. Specific HDACi have already been demonstrated to reduce the secretion of pro-inflammatory cytokines by Teff cells, and promote Treg numbers and suppressive capacity in vitro and in vivo. In this review, we outline the role of the different classes of HDACs in both Teff cell and Treg cell function. Furthermore, we will review the effect of different HDACi on T cell tolerance and explore their potential as a therapeutic strategy for the treatment of oligoarticular and polyarticular JIA.

Histone/protein deacetylase inhibitor therapy for enhancement of Foxp3+ T-regulatory cell function posttransplantation

T-regulatory (Treg) cells are like other cells present throughout the body in being subject to biochemical modifications in response to extracellular signals. An important component of these responses involves changes in posttranslational modifications (PTMs) of histones and many nonhistone proteins, including phosphorylation/dephosphorylation, ubiquitination/deubiquitination, and acetylation/deacetylation. Foxp3, the key transcription factor of Tregs, is constantly being rapidly turned over, and a number of these PTMs determine its level of expression and activity. Of interest in the transplant setting, modulation of the acetylation or deacetylation of key lysine residues in Foxp3 can promote the stability and function, leading to increased Treg production and increased Treg suppressive activity. This mini-review focuses on recent data concerning the roles that histone/protein deacetylases (HDACs) play in control of Treg function, and how small molecule HDAC inhibitors can be used to promote Treg-dependent allograft survival in experimental models. These data are discussed in the light of increasing interest in the identification and clinical evaluation of isoform-selective HDAC inhibitors, and their potential application as tools to modulate Foxp3+ Treg cell numbers and function in transplant recipients.

Nr4a1 plays a crucial modulatory role in Th1/Th17 cell responses and CNS autoimmunity

Nuclear receptor4 group A1 (Nr4a1), an orphan nuclear receptor, is down-regulated in peripheral blood mononuclear cells (MNCs) of individuals with multiple sclerosis (MS), and Nr4a1 deficiency results in severe experimental autoimmune encephalomyelitis (EAE), an animal model of MS, caused by increased macrophage infiltration into the central nervous system (CNS). However, the role of Nr4a1 in macrophage phenotype and T cell responses remains poorly understood. In the present study we show that macrophages/microglia of Nr4a1^-/- mice, which exhibited earlier onset and more severe clinical EAE, were polarized to an enhanced type 1 (M1) phenotype and produced higher levels of IL-12 and TNF-α than wild type mice. Significantly increased numbers of CD4⁺ T cells and frequency of CD4⁺IFN-γ⁺ and CD4⁺IL-17⁺ T cells were observed in the CNS and spleen of Nr4a1^-/- mice, with decreased percentages of apoptosis in CD4⁺ T cells. The percentages of CD4⁺Foxp3⁺ Treg cells in the CNS of Nr4a1^-/- mice were also reduced. Furthermore, purified CD4⁺ T cells from naïve Nr4a1^-/- mice exhibited enhanced Th1 and Th17 differentiation capacity, and MOG-reactive Th17 cells from Nr4a1^-/- mice adoptively transferred more severe EAE in recipient mice. Our results, for the first time, demonstrate that Nr4a1 not only induces Type 2 macrophages/microglia phenotype, but is also a critical inhibitory molecule for Th1/Th17 cell differentiation. This finding indicates that Nr4a1-related molecule(s) may have therapeutic potential in MS and likely other autoimmune disorders.

Decitabine inhibits T cell proliferation via a novel TET2-dependent mechanism and exerts potent protective effect in mouse auto- and allo-immunity models

Multiple sclerosis (MS) is an autoimmune disease characterized by the dysregulated immune response including innate and adaptive immune responses. Increasing evidence has proven the importance of epigenetic modification in the progression of MS. Recent studies revealed that low-dose decitabine (Dec, 5-Aza-2'-deoxycytidine), which incorporates into replicating DNA and inhibits DNA methylation, could prevent experimental autoimmune encephalomyelitis (EAE) development by increasing the number of regulatory T cells (Tregs). Here, we showed that higher-dose decitabine relative to previous studies could also distinctly protect mice from EAE and allogeneic cardiac transplantation. Mechanistic studies revealed decitabine suppressed innate responses in EAE mice through inhibiting the activation of microglia and monocyte-derived macrophages that contributed to reduce the severity of EAE. Furthermore, differentiation of naïve CD4+ T cells into Th1 and Th17 cells was significantly suppressed by decitabine in vivo and in vitro. Though in vitro studies showed decitabine could induce Treg differentiation, there was no obvious change in the percentage of Tregs in Dec-treated EAE mice. Most importantly, we found that T cell proliferation was potently inhibited in vivo and in vitro by higher-dose decitabine through increased gene expression of the DNA dioxygenase TET2 which facilitated the expression of several cell cycle inhibitors. Collectively, our study provides novel mechanistic insights of using the epigenetic modifying agents in the management of both allo- and auto-immune responses.

Targeting Sirtuin-1 prolongs murine renal allograft survival and function

Current immunosuppressive medications used after transplantation have significant toxicities. Foxp3(+) T-regulatory cells can prevent allograft rejection without compromising protective host immunity. Interestingly, inhibiting the class III histone/protein deacetylase Sirtuin-1 can augment Foxp3(+) T-regulatory suppressive function through increasing Foxp3 acetylation. Here we determined whether Sirtuin-1 targeting can stabilize biological allograft function. BALB/c kidney allografts were transplanted into C57BL/6 recipients with a CD4-conditional deletion of Sirtuin-1 (Sirt1(fl/fl)CD4(cre)) or mice treated with a Sirtuin-1-specific inhibitor (EX-527), and the native kidneys removed. Blood chemistries and hematocrit were followed weekly. Sirt1(fl/fl)CD4(cre) recipients showed markedly longer survival and improved kidney function. Sirt1(fl/fl)CD4(cre) recipients exhibited donor-specific tolerance, accepted BALB/c, but rejected third-party C3H cardiac allografts. C57BL/6 recipients of BALB/c renal allografts that were treated with EX-527 showed improved survival and renal function at 1, but not 10 mg/kg/day. Pharmacologic inhibition of Sirtuin-1 also improved renal allograft survival and function with dosing effects having relevance to outcome. Thus, inhibiting Sirtuin-1 can be a useful asset in controlling T-cell-mediated rejection. However, effects on non-T cells that could adversely affect allograft survival and function merit consideration.

NR4A orphan nuclear receptors in glucose homeostasis: a minireview

Type 2 diabetes mellitus is a disorder characterized by insulin resistance and a relative deficit in insulin secretion, both of which result in elevated blood glucose. Understanding the molecular mechanisms underlying the pathophysiology of diabetes could lead to the development of new therapeutic approaches. An ever-growing body of evidence suggests that members of the NR4A family of nuclear receptors could play a pivotal role in glucose homeostasis. This review aims to present and discuss advances so far in the evaluation of the potential role of NR4A in the regulation of glucose homeostasis and the development of type 2 diabetes.

HDAC inhibitor therapy in autoimmunity and transplantation

Pharmacological inhibitors of histone/protein deacetylases (HDACi) have considerable therapeutic potential as anti-inflammatory and immunosuppressive drugs. The utility of HDACi as anti-inflammatory agents is dependent upon their proving safe and effective in experimental models. Current pan-HDACi compounds are ill-suited to this role, given the broad distribution of target HDACs and their complex and multifaceted mechanisms of action. By contrast, the development of isoform-selective HDACi may provide important new tools for treatment in autoimmunity and transplantation. This review discusses which HDACs are worthwhile targets in inflammation, and the progress made towards their therapeutic inhibition, including the use of HDAC subclass and isoform-selective HDACi to promote the functions of Foxp3+ T-regulatory cells.

Rationale for HDAC inhibitor therapy in autoimmunity and transplantation

While there are currently more than 70 ongoing clinical trials of inhibitors of so-called classical HDACs (HDACi) as anticancer therapies, given their potency as antiproliferative and angiostatic agents, HDACi also have considerable therapeutic potential as anti-inflammatory and immunosuppressive drugs. The utility of HDACi as anti-inflammatory agents is dependent upon their proving safe and effective in experimental models. Current pan-HDACi compounds are not well suited to this role, given the broad distribution of target HDACs and their complex and multifaceted mechanisms of action. In contrast, the development of isoform-selective HDACi may provide important new tools for therapy in autoimmunity and transplantation. This chapter discusses which HDACs are worthwhile targets in inflammation and progress toward their therapeutic inhibition, including the use of HDAC subclass and isoform-selective HDACi to promote the functions of Foxp3+ T regulatory cells.

Conditional deletion of histone deacetylase 1 in T cells leads to enhanced airway inflammation and increased Th2 cytokine production

Chromatin modifications, such as reversible histone acetylation, play a key role in the regulation of T cell development and function. However, the role of individual histone deacetylases (HDACs) in T cells is less well understood. In this article, we show by conditional gene targeting that T cell-specific loss of HDAC1 led to an increased inflammatory response in an in vivo allergic airway inflammation model. Mice with HDAC1-deficient T cells displayed an increase in all critical parameters in this Th2-type asthma model, such as eosinophil recruitment into the lung, mucus hypersecretion, parenchymal lung inflammation, and enhanced airway resistance. This correlated with enhanced Th2 cytokine production in HDAC1-deficient T cells isolated from diseased mice. In vitro-polarized HDAC1-deficient Th2 cells showed a similar enhancement of IL-4 expression, which was evident already at day 3 of Th2 differentiation cultures and restricted to T cell subsets that underwent several rounds of cell divisions. HDAC1 was recruited to the Il4 gene locus in ex vivo isolated nonstimulated CD4(+) T cells, indicating a direct control of the Il4 gene locus. Our data provide genetic evidence that HDAC1 is an essential HDAC that controls the magnitude of an inflammatory response by modulating cytokine expression in effector T cells.

The regulatory role of dendritic cells in the induction and maintenance of T-cell tolerance

The induction and maintenance of T-cell tolerance to tissue antigens is essential to prevent autoimmunity. Combinations of central and peripheral mechanisms act in parallel to inactivated, eliminated or control autoreactive T cells. Both centrally and peripherally, a key requirement for self-tolerance is the presentation of self-antigens in a correct context. There is now evidence to suggest that dendritic cells (DCs) play a fundamental role in the development of central and peripheral tolerance. In this review, we summarize recent progress toward the definition of the multiple roles of DCs in these processes. We will also discuss the association between defects in the DC compartment and the development of autoimmune responses, with particular reference to DC deregulation in the context of type I diabetes.

Histone/protein deacetylase inhibitors increase suppressive functions of human FOXP3+ Tregs

Histone/protein deacetylases (HDACs) decrease histone and protein acetylation, typically leading to suppression of gene transcription and modulation of various protein functions. We found significant differences in expression of HDAC before and after stimulation of human T regulatory (Treg) and T effector cells, suggesting the potential for future selective targeting of Tregs with HDAC inhibitors (HDACi). Use of various HDACi small molecules enhanced, by up to 4.5-fold (average 2-fold), the suppressive functions of both freshly isolated and expanded human Tregs, consistent with our previous murine data. HDACi use increased Treg expression of CTLA-4, a key negative regulator of immune response, and we found a direct and significant correlation between CTLA-4 expression and Treg suppression. Hence, HDACi compounds are promising pharmacologic tools to increase Treg suppressive functions, and this action may potentially be of use in patients with autoimmunity or post-transplantation.

Microarray analysis identifies altered regulation of nuclear receptor family members in the pre-disease state of multiple sclerosis

Molecular mechanisms that influence susceptibility to multiple sclerosis are poorly understood. We analyzed peripheral blood gene expression profiles in nine healthy subjects up to nine years before the onset of multiple sclerosis in comparison with 11 age-, gender-, and origin-matched healthy subjects who remained multiple sclerosis-free, and 31 subjects during the first clinical episode of multiple sclerosis. Within the 1051 highly variable genes that differentiated between multiple sclerosis-to-be and multiple sclerosis-free subjects, we identified activation of TCR signaling that triggered the Cbl and MAPK cascade in concert with downstream synergic over-expression of NFAT and MEF2B, but failed to augment the expression of the nuclear receptor gene family members NR4A1, NR2F1, VDR and MEF2B, that further resulted in impaired apoptotic machinery. Comparison between multiple sclerosis-to-be and first clinical onset of multiple sclerosis operating module networks demonstrated the evolution of altered regulation of nuclear receptor-dependent apoptosis. Our findings demonstrating a silent multiple sclerosis trait that is associated with suppressed expression of the nuclear receptor network and inhibited apoptosis of activated T-cells support the role of these transcription signals in the evolution of the autoimmune processes that operate in the pre-disease stage of multiple sclerosis.

NGFI-B targets mitochondria and induces cardiomyocyte apoptosis in restraint-stressed rats by mediating energy metabolism disorder

NGFI-B/Nur77/TR3, originally identified as an immediate-early gene rapidly induced by serum and growth factors, is a member of the steroid hormone nuclear receptor superfamily with no identified endogenous ligand. NGFI-B induces apoptosis in a number of cell lineages exposed to proapoptotic stimuli by directly targeting the mitochondria, inducing cytochrome c release. The present study was designed to determine the role of NGFI-B in cardiomyocytes of restraint-stressed rats. The NGFI-B content was increased in mitochondria and reduced in plasma as apoptosis increased. Analysis showed that NGFI-B induces cardiomyocyte apoptosis in restraint-stressed rats by mediating mitochondrial energy metabolism disorder. Several novel mitochondrial proteins, which correlate with NGFI-B, were reported in cardiomyocyte apoptosis of restraint-stressed rats. Five proteins associated with NGFI-B participate directly in mitochondrial energy metabolism. Studies of mitochondrial respiratory efficiency and ATP synthase activity strongly support the findings. These results provide significant information for comprehensively understanding the cellular mechanism of cardiovascular diseases.

Orphan nuclear receptor Nur77 is required for the differentiation of C6 glioma cells induced by cholera toxin

AIM

To investigate a possible regulator gene involved in the cholera toxin-induced differentiation of rat C6 glioma cells.

METHODS

The global changes in the mRNA expression pattern induced by cholera toxin were analyzed using gene chip microarray. The selected gene was then silenced by RNA interference or overexpressed with an ORF plasmid to determine its necessity in this process.

RESULTS

Nur77, a member of the orphan nuclear receptor family (NR4A), was markedly up-regulated during the process of differentiation. Furthermore, RNAi of nur77 attenuated the induction effect of cholera toxin on C6 cells, whereas overexpression of nur77 led to similarly differentiated behavior, including morphologic and biomarker changes, as well as cell cycle arrest.

CONCLUSION

Nur77 participated actively and essentially as an important regulator in the cholera toxin-induced differentiation of C6 cells.