Early growth response 2 regulates the survival of thymocytes during positive selection

Transcription factor EGR2 controls homing and pathogenicity of TH17 cells in the central nervous system

CD4+ T helper 17 (TH17) cells protect barrier tissues but also trigger autoimmunity. The mechanisms behind these opposing processes remain unclear. Here, we found that the transcription factor EGR2 controlled the transcriptional program of pathogenic TH17 cells in the central nervous system (CNS) but not that of protective TH17 cells at barrier sites. EGR2 was significantly elevated in myelin-reactive CD4+ T cells from patients with multiple sclerosis and mice with autoimmune neuroinflammation. The EGR2 transcriptional program was intricately woven within the TH17 cell transcriptional regulatory network and showed high interconnectivity with core TH17 cell-specific transcription factors. Mechanistically, EGR2 enhanced TH17 cell differentiation and myeloid cell recruitment to the CNS by upregulating pathogenesis-associated genes and myelomonocytic chemokines. T cell-specific deletion of Egr2 attenuated neuroinflammation without compromising the host's ability to control infections. Our study shows that EGR2 regulates tissue-specific and disease-specific functions in pathogenic TH17 cells in the CNS.

Transcriptional Regulation of Early T-Lymphocyte Development in Thymus

T-lymphocytes play crucial roles for maintaining immune homeostasis by fighting against various pathogenic microorganisms and establishing self-antigen tolerance. They will go through several stages and checkpoints in the thymus from progenitors to mature T cells, from CD4^-CD8^- double negative (DN) cells to CD4⁺CD8⁺ double positive (DP) cells, finally become CD4⁺ or CD8⁺ single positive (SP) cells. The mature SP cells then emigrate out of the thymus and further differentiate into distinct subsets under different environment signals to perform specific functions. Each step is regulated by various transcriptional regulators downstream of T cell receptors (TCRs) that have been extensively studied both in vivo and vitro via multiple mouse models and advanced techniques, such as single cell RNA sequencing (scRNA-seq) and Chromatin Immunoprecipitation sequencing (ChIP-seq). This review will summarize the transcriptional regulators participating in the early stage of T cell development reported in the past decade, trying to figure out cascade networks in each process and provide possible research directions in the future.

Early growth response genes 2 and 3 induced by AP-1 and NF-κB modulate TGF-β1 transcription in NK1.1- CD4+ NKG2D+ T cells

NK1.1^- CD4⁺ NKG2D⁺ T cells are a subpopulation of regulatory T cells that downregulate the functions of CD4⁺ T, CD8⁺ T, natural killer (NK) cells, and macrophages through TGF-β1 production. Early growth response genes 2 (Egr2) and 3 (Egr3) maintain immune homeostasis by modulating T lymphocyte development, inhibiting effector T cell function, and promoting the induction of regulatory T cells. Whether Egr2 and Egr3 directly regulate TGF-β1 transcription in NK1.1^- CD4⁺ NKG2D⁺ T cells remains elusive. The expression levels of Egr2 and Egr3 were higher in NK1.1^- CD4⁺ NKG2D⁺ T cells than in NK1.1^- CD4⁺ NKG2D^- T cells. Egr2 and Egr3 expression were remarkably increased after stimulating NK1.1^- CD4⁺ NKG2D⁺ T cells with sRAE or α-CD3/sRAE. The ectopic expression of Egr2 or Egr3 resulted in the enhancement of TGF-β1 expression, while knockdown of Egr2 or Egr3 led to the decreased expression of TGF-β1 in NK1.1^- CD4⁺ NKG2D⁺ T cells. Egr2 and Egr3 directly bound with the TGF-β1 promoter as demonstrated by the electrophoretic mobility shift assay and dual-luciferase gene reporter assay. Furthermore, the Egr2 and Egr3 expression of NK1.1^- CD4⁺ NKG2D⁺ T cells could be induced by the AP-1 and NF-κB transcriptional factors, but had no involvement with the activation of NF-AT and STAT3. In conclusion, Egr2 and Egr3 induced by AP-1 and NF-κB directly initiate TGF-β1 transcription in NK1.1^- CD4⁺ NKG2D⁺ T cells. This study indicates that manipulating Egr2 and Egr3 expression would potentiate or alleviate the regulatory function of NK1.1^- CD4⁺ NKG2D⁺ T cells and this strategy could be used in the therapy for patients with autoimmune diseases or tumor.

Restricted Expression of the Thymoproteasome Is Required for Thymic Selection and Peripheral Homeostasis of CD8+ T Cells

The thymoproteasome subunit β5t is specifically expressed in cortical thymic epithelial cells (TECs) and generates unique peptides to support positive selection. In this study, using a mouse model ubiquitously expressing β5t, we showed that aberrant expression of self-peptides generated by β5t affects CD8⁺ T cell homeostasis, including thymic selection and maintenance of the peripheral naive pool of CD8⁺ T cells. In mice in which β5t was expressed both in cortical and medullary TECs, the abundance of CD8⁺ lineage thymocytes was reduced, and extra-thymic expression of β5t caused accumulation of CD8⁺ T cells with the memory or exhausted phenotype and induced autoreactive T cell responses. We found that thymoproteasomes are essential for positive selection but that the subsequent change in peptide repertoire in the medulla is also crucial for thymic selection and that β5t-derived peptide must be confined to the thymus to avoid autoimmunity in peripheral tissues.

TRAF3IP3 at the trans-Golgi network regulates NKT2 maturation via the MEK/ERK signaling pathway

Thymic natural killer T (NKT)2 cells are a subset of invariant NKT cells with PLZF^hiGATA3^hiIL-4⁺. The differentiation of NKT2 cells is not fully understood. In the present study, we report an important role of TRAF3-interacting protein 3 (TRAF3IP3) in the functional maturation and expansion of committed NKT2s in thymic medulla. Mice with T-cell-specific deletion of TRAF3IP3 had decreased thymic NKT2 cells, decreased IL-4-producing peripheral iNKTs, and defects in response to α-galactosylceramide. Positive selection and high PLZF expression in CD24⁺CD44^- and CCR7⁺CD44^- immature iNKTs were not affected. Only CD44^hiNK1.1^- iNKTs in Traf3ip3^-/- mice showed reduced expression of Egr2, PLZF, and IL-17RB, decreased proliferation, and reduced IL-4 production upon stimulation. This Egr2 and IL-4 expression was augmented by MEK1/ERK activation in iNKTs, and TRAF3IP3 at the trans-Golgi network recruited MEK1 and facilitated ERK phosphorylation and nuclear translocation. LTβR-regulated bone marrow-derived nonlymphoid cells in the medullary thymic microenvironment were required for MEK/ERK activation and NKT2 maturation. These data demonstrate an important functional maturation process in NKT2 differentiation that is regulated by MEK/ERK signaling at the trans-Golgi network.

ERK Signaling Controls Innate-like CD8+ T Cell Differentiation via the ELK4 (SAP-1) and ELK1 Transcription Factors

In mouse thymocyte development, signaling by the TCR through the ERK pathway is required for positive selection of conventional naive T cells. The Ets transcription factor ELK4 (SAP-1), an ERK-regulated cofactor of the SRF transcription factor, plays an important role in positive selection by activating immediate-early genes such as the Egr transcription factor family. The role of ELK4-SRF signaling in development of other T cell types dependent on ERK signaling has been unclear. In this article, we show that ELK4, and its close relative ELK1, act cell autonomously in the thymus to control the generation of innate-like αβ CD8+ T cells with memory-like characteristics. Mice lacking ELK4 and ELK1 develop increased numbers of innate-like αβ CD8+ T cells, which populate the periphery. These cells develop cell autonomously rather than through expansion of PLZF+ thymocytes and concomitantly increased IL-4 signaling. Their development is associated with reduced TCR-mediated activation of ELK4-SRF target genes and can be partially suppressed by overexpression of the ELK4-SRF target gene EGR2. Consistent with this, partial inhibition of ERK signaling in peripheral CD8+T cells promotes the generation of cells with innate-like characteristics. These data establish that low-level ERK signaling through ELK4 (and ELK1) promotes innate-like αβ CD8+ T cell differentiation, tuning conventional versus innate-like development.

PDCD5 regulates iNKT cell terminal maturation and iNKT1 fate decision

Invariant natural killer T1 (iNKT1) cells are characterized by the preferential expression of T-box transcription factor T-bet (encoded by Tbx21) and the production of cytokine IFN-γ, but the relationship between the developmental process and iNKT1 lineage diversification in the thymus remains elusive. We report in the present study a crucial role of programmed cell death 5 (PDCD5) in iNKT cell terminal maturation and iNKT1 fate determination. Mice with T cell-specific deletion of PDCD5 had decreased numbers of thymic and peripheral iNKT cells with a predominantly immature phenotype and defects in response to α-galactosylceramide. Loss of PDCD5 also selectively abolished the iNKT1 lineage by reducing T-bet expression in iNKT cells at an early thymic developmental stage (before CD44 upregulation). We further demonstrated that TOX2, one of the high mobility group proteins that was highly expressed in iNKT cells at stage 1 and could be stabilized by PDCD5, promoted the permissive histone H3K4me3 modification in the promoter region of Tbx21. These data indicate a pivotal and unique role of PDCD5/TOX2 in iNKT1 lineage determination. They also suggest that the fate of iNKT1 may be programmed at the developmental stage of iNKT cells in the thymus.

Nab2 maintains thymus cellularity with aging and stress

Thymic cellularity is influenced by a variety of biological and environmental factors, such as age and stress; however, little is known about the molecular genetic mechanisms that regulate this process. Immediate early genes of the Early growth response (Egr) family have critical roles in immune function and response to environmental stress. The transcription factors, Egr1, Egr2 and Egr3, play roles in the thymus and in peripheral T-cell activation. Nab2, which binds Egrs 1, 2, and 3 as a co-regulator of transcription, also regulates peripheral T-cell activation. However, a role for Nab2 in the thymus has not been reported. Using Nab2-deficient (KO) mice we found that male Nab2KO mice have reduced thymus size and decreased numbers of thymocytes, compared with age-matched wildtype (WT) mice. Furthermore, the number of thymocytes in Nab2KO males decreases more rapidly with age. This effect is sex-dependent as female Nab2KO mice show neither reduced thymocyte numbers nor accelerated thymocyte loss with age, compared to female WT littermates. Since stress induces expression of Nab2 and the Egrs, we examined whether loss of Nab2 alters stress-induced decrease in thymic cellularity. Restraint stress induced a significant decrease in thymic cellularity in Nab2KO and WT mice, with significant changes in the thymocyte subset populations only in the Nab2KO mice. Stress reduced the percentage of DP cells by half and increased the percentage of CD4SP and CD8SP cells by roughly three-fold in Nab2KO mice. These findings indicate a requirement for Nab2 in maintaining thymocyte number in male mice with age and in response to stress.

Egr2 and Egr3 in regulatory T cells cooperatively control systemic autoimmunity through Ltbp3-mediated TGF-β3 production

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease characterized by multiorgan inflammation induced by autoantibodies. Early growth response gene 2 (Egr2), a transcription factor essential for T-cell anergy induction, controls systemic autoimmunity in mice and humans. We have previously identified a subpopulation of CD4⁺ regulatory T cells, CD4⁺CD25^-LAG3⁺ cells, that characteristically express both Egr2 and LAG3 and control mice model of lupus via TGF-β3 production. However, due to the mild phenotype of lymphocyte-specific Egr2-deficient mice, the presence of an additional regulator has been speculated. Here, we show that Egr2 and Egr3 expressed in T cells cooperatively prevent humoral immune responses by supporting TGF-β3 secretion. T cell-specific Egr2/Egr3 double-deficient (Egr2/3DKO) mice spontaneously developed an early onset lupus-like disease that was more severe than in T cell-specific Egr2-deficient mice. In accordance with the observation that CD4⁺CD25^-LAG3⁺ cells from Egr2/3DKO mice completely lost the capacity to produce TGF-β3, the excessive germinal center reaction in Egr2/3DKO mice was suppressed by the adoptive transfer of WT CD4⁺CD25^-LAG3⁺ cells or treatment with a TGF-β3-expressing vector. Intriguingly, latent TGF-β binding protein (Ltbp)3 expression maintained by Egr2 and Egr3 was required for TGF-β3 production from CD4⁺CD25^-LAG3⁺ cells. Because Egr2 and Egr3 did not demonstrate cell intrinsic suppression of the development of follicular helper T cells, Egr2- and Egr3-dependent TGF-β3 production by CD4⁺CD25^-LAG3⁺ cells is critical for controlling excessive B-cell responses. The unique attributes of Egr2/Egr3 in T cells may provide an opportunity for developing novel therapeutics for autoantibody-mediated diseases including SLE.

Pak2 Controls Acquisition of NKT Cell Fate by Regulating Expression of the Transcription Factors PLZF and Egr2

NKT cells constitute a small population of T cells developed in the thymus that produce large amounts of cytokines and chemokines in response to lipid Ags. Signaling through the Vα14-Jα18 TCR instructs commitment to the NKT cell lineage, but the precise signaling mechanisms that instruct their lineage choice are unclear. In this article, we report that the cytoskeletal remodeling protein, p21-activated kinase 2 (Pak2), was essential for NKT cell development. Loss of Pak2 in T cells reduced stage III NKT cells in the thymus and periphery. Among different NKT cell subsets, Pak2 was necessary for the generation and function of NKT1 and NKT2 cells, but not NKT17 cells. Mechanistically, expression of Egr2 and promyelocytic leukemia zinc finger (PLZF), two key transcription factors for acquiring the NKT cell fate, were markedly diminished in the absence of Pak2. Diminished expression of Egr2 and PLZF were not caused by aberrant TCR signaling, as determined using a Nur77-GFP reporter, but were likely due to impaired induction and maintenance of signaling lymphocyte activation molecule 6 expression, a TCR costimulatory receptor required for NKT cell development. These data suggest that Pak2 controls thymic NKT cell development by providing a signal that links Egr2 to induce PLZF, in part by regulating signaling lymphocyte activation molecule 6 expression.

Triggering receptor expressed on myeloid cells 1 (TREM-1)-mediated Bcl-2 induction prolongs macrophage survival

Triggering receptor expressed on myeloid cells 1 (TREM-1) is a superimmunoglobulin receptor expressed on myeloid cells that plays an important role in the amplification of inflammation. Recent studies suggest a role for TREM-1 in tumor-associated macrophages with relationship to tumor growth and progression. Whether the effects of TREM-1 on inflammation and tumor growth are mediated by an alteration in cell survival signaling is not known. In these studies, we show that TREM-1 knock-out macrophages exhibit an increase in apoptosis of cells in response to lipopolysaccharide (LPS) suggesting a role for TREM-1 in macrophage survival. Specific ligation of TREM-1 with monoclonal TREM-1 (mTREM-1) or overexpression of TREM-1 with adeno-TREM-1 induced B-cell lymphoma-2 (Bcl-2) with depletion of the key executioner caspase-3 prevents the cleavage of poly(ADP-ribose) polymerase. TREM-1 knock-out cells showed lack of induction of Bcl2 with an increase in caspase-3 activation in response to lipopolysaccharide. In addition overexpression of TREM-1 with adeno-TREM-1 led to an increase in mitofusins (MFN1 and MFN2) and knockdown of TREM-1 decreased the expression of mitofusins suggesting that TREM-1 contributes to the maintenance of mitochondrial integrity favoring cell survival. Investigations into potential mechanisms by which TREM-1 alters cell survival showed that TREM-1-induced Bcl-2 in an Egr2-dependent manner. Furthermore, our data shows that expression of Egr2 in response to specific ligation of TREM-1 is ERK mediated. These data for the first time provide novel mechanistic insights into the role of TREM-1 as an anti-apoptotic protein that prolongs macrophage survival.

Zfat-deficiency results in a loss of CD3ζ phosphorylation with dysregulation of ERK and Egr activities leading to impaired positive selection

The human ZFAT gene was originally identified as a susceptibility gene for autoimmune thyroid disease. Mouse Zfat is a critical transcriptional regulator for primitive hematopoiesis and required for peripheral T cell homeostasis. However, its physiological roles in T cell development remain poorly understood. Here, we generated Zfat^f/f-LckCre mice and demonstrated that T cell-specific Zfat-deletion in Zfat^f/f-LckCre mice resulted in a reduction in the number of CD4⁺CD8⁺double-positive (DP) cells, CD4⁺single positive cells and CD8⁺single positive cells. Indeed, in Zfat^f/f-LckCre DP cells, positive selection was severely impaired. Defects of positive selection in Zfat-deficient thymocytes were not restored in the presence of the exogenous TCR by using TCR-transgenic mice. Furthermore, Zfat-deficient DP cells showed a loss of CD3ζ phosphorylation in response to T cell antigen receptor (TCR)-stimulation concomitant with dysregulation of extracellular signal-related kinase (ERK) and early growth response protein (Egr) activities. These results demonstrate that Zfat is required for proper regulation of the TCR-proximal signalings, and is a crucial molecule for positive selection through ERK and Egr activities, thus suggesting that a full understanding of the precise molecular mechanisms of Zfat will provide deeper insight into T cell development and immune regulation.

Egr2 induced during DC development acts as an intrinsic negative regulator of DC immunogenicity

Early growth response gene 2 (Egr2), which encodes a zinc finger transcription factor, is rapidly and transiently induced in various cell types independently of de novo protein synthesis. Although a role for Egr2 is well established in T-cell development, Egr2 expression and its biological function in dendritic cells (DCs) have not yet been described. Here, we demonstrate Egr2 expression during DC development, and its role in DC-mediated immune responses. Egr2 is expressed in the later stage of DC development from BM precursor cells. Even at steady state, Egr2 is highly expressed in mouse splenic DCs. Egr2-knockdown (Egr2-KD) DCs showed increased levels of major histocompatability complex (MHC) class I and II and co-stimulatory molecules, and enhanced antigen uptake and migratory capacities. Furthermore, Egr2-KD abolished SOCS1 expression and signal transducer and activator of transcription 5 (STAT5) activation during DC development, probably resulting in the enhancement of IL-12 expression and Th1 immunogenicity of a DC vaccine. DC-mediated cytotoxic T lymphocyte (CTL) activation and antitumor immunity were significantly enhanced by Egr2-KD, and impaired by Egr2 overexpression in antigen-pulsed DC vaccines. These data suggest that Egr2 acts as an intrinsic negative regulator of DC immunogenicity and can be an attractive molecular target for DC vaccine development.

Early growth response gene-2 controls IL-17 expression and Th17 differentiation by negatively regulating Batf

Early growth response gene (Egr)-2 is important for the maintenance of T cell homeostasis and controls the development of autoimmune disease. However, the underlying mechanisms are unknown. We have now discovered that Egr-2, which is induced by TGF-β and IL-6, negatively regulates the expression of IL-17, but not IL-2 or IFN-γ, in effector T cells. In the absence of Egr-2, CD4 T cells produce high levels of Th17 cytokines, which renders mice susceptible to experimental autoimmune encephalomyelitis induction. T cells lacking Egr-2 show increased propensity for Th17, but not Th1 or Th2, differentiation. Control of IL-17 expression and Th17 differentiation by Egr-2 is due to inhibition of Batf, a transcription factor that regulates IL-17 expression and Th17 differentiation. Egr-2 interacts with Batf in CD4 T cells and suppresses its interaction with DNA sequences derived from the IL-17 promoter, whereas the activation of STAT3 and expression of retinoic acid-related orphan receptor γt are unchanged in Th17 cells in the absence of Egr-2. Thus, Egr-2 plays an important role to intrinsically control Th17 differentiation. We also found that CD4 T cells from multiple sclerosis patients have reduced expression of Egr-2 and increased expression of IL-17 following stimulation with anti-CD3 in vitro. Collectively, our results demonstrate that Egr-2 is an intrinsic regulator that controls Th17 differentiation by inhibiting Batf activation, which may be important for the control of multiple sclerosis development.

Erythropoietin-induced changes in brain gene expression reveal induction of synaptic plasticity genes in experimental stroke

Erythropoietin (EPO) is a neuroprotective cytokine in models of ischemic and nervous system injury, where it reduces neuronal apoptosis and inflammatory cytokines and increases neurogenesis and angiogenesis. EPO also improves cognition in healthy volunteers and schizophrenic patients. We studied the effect of EPO administration on the gene-expression profile in the ischemic cortex of rats after cerebral ischemia at early time points (2 and 6 h). EPO treatment up-regulated genes already increased by ischemia. Hierarchical clustering and analysis of overrepresented functional categories identified genes implicated in synaptic plasticity-Arc, BDNF, Egr1, and Egr2, of which Egr2 was the most significantly regulated. Up-regulation of Arc, BDNF, Dusp5, Egr1, Egr2, Egr4, and Nr4a3 was confirmed by quantitative PCR. We investigated the up-regulation of Egr2/Krox20 further because of its role in neuronal plasticity. Its elevation by EPO was confirmed in an independent in vivo experiment of cerebral ischemia in rats. Using the rat neuroblastoma B104, we found that wild-type cells that do not express EPO receptor (EPOR) do not respond to EPO by inducing Egr2. However, EPOR-expressing B104 cells induce Egr2 early upon incubation with EPO, indicating that Egr2 induction is a direct effect of EPO and that EPOR mediates this effect. Because these changes occur in vivo before decreased inflammatory cytokines or neuronal apoptosis is evident, these findings provide a molecular mechanism for the neuroreparative effects of cytokines and suggest a mechanism of neuroprotection by which promotion of a plastic phenotype results in decreased inflammation and neuronal death.

Age-specific dynamics of human thymus immune cell differentiation

The expression of markers of undifferentiated CD5+ cells, B cells, T-killer/suppressors, and T-helpers was verified by immunohistochemical methods in the thymuses of elderly, senile, and long-lived humans. The counts of CD5+ cells in the thymus progressively decreased with age. Positive correlations between the counts of CD5+ cells and differentiated T cells were detected. The capacity of CD5+ thymocytes to differentiate into T-killer/suppressors decreased with age.

Activation of Elk-1 participates as a neuroprotective compensatory mechanism in models of Huntington's disease

The transcription factor Elk-1 has been revealed as neuroprotective against toxic stimuli. In this study, we explored the neuroprotective capacity of Elk-1 in Huntington's disease. To this aim, we used two exon-1 mutant huntingtin (mhtt) mouse models (R6/1 and R6/2), and a full-length mhtt striatal cell model (STHdh(Q111/Q111) ). Analysis of Elk-1 and pElk-1(Ser383) in the striatum of R6 mice revealed increased levels during the disease progression. Similarly, Elk-1 and pElk-1(Ser383) levels were increased in STHdh(Q111/Q111) cells when compared with wild-type cells. In addition, we observed a predominant nuclear localization of Elk-1 in STHdh(Q111/Q111) cells, and in the striatum of 30-week-old R6/1 mice. Nuclear Elk-1 did not colocalize with mhtt aggregates, suggesting a higher transcriptional activity. In agreement, the knock-down of Elk-1 decreased immediate early genes expression in STHdh(Q111/Q111) cells, but not in wild-type cells. Interestingly, reduction of Elk-1 levels by siRNAs transfection promoted cell death and caspase 3 cleavage in STHdh(Q111/Q111) cells, but not in wild-type cells. In summary, we propose that increased protein levels, phosphorylation and nuclear localization of Elk-1 observed in exon-1 and full-length Huntington's disease models could be a compensatory mechanism activated by striatal cells in response to the presence of mhtt that contributes to neuroprotection.

Elevated and sustained expression of the transcription factors Egr1 and Egr2 controls NKT lineage differentiation in response to TCR signaling

Interactions driven by the T cell antigen receptor (TCR) determine the lineage fate of CD4(+)CD8(+) thymocytes, but the molecular mechanisms that induce the lineage-determining transcription factors are unknown. Here we found that TCR-induced transcription factors Egr2 and Egr1 had higher and more-prolonged expression in precursors of the natural killer T (NKT) than in cells of conventional lineages. Chromatin immunoprecipitation followed by deep sequencing showed that Egr2 directly bound and activated the promoter of Zbtb16, which encodes the NKT lineage-specific transcription factor PLZF. Egr2 also bound the promoter of Il2rb, which encodes the interleukin 2 (IL-2) receptor β-chain, and controlled the responsiveness to IL-15, which signals the terminal differentiation of the NKT lineage. Thus, we propose that persistent higher expression of Egr2 specifies the early and late stages of NKT lineage differentiation, providing a discriminating mechanism that enables TCR signaling to 'instruct' a thymic lineage.

Defective hematopoietic stem cell and lymphoid progenitor development in the Ts65Dn mouse model of Down syndrome: potential role of oxidative stress

AIMS

Down Syndrome (DS), a genetic disease caused by a triplication of chromosome 21, is characterized by increased markers of oxidative stress. In addition to cognitive defects, patients with DS also display hematologic disorders and increased incidence of infections and leukemia. Using the Ts65Dn mouse model of DS, the goal of this study was to examine hematopoietic stem and lymphoid progenitor cell function in DS.

RESULTS

Analysis of hematopoietic progenitor populations showed that Ts65Dn mice possessed fewer functional hematopoietic stem cells and a significantly decreased percentage of bone marrow lymphoid progenitors. Increased reactive oxygen species and markers of oxidative stress were detected in hematopoietic stem cell populations and were associated with a loss of quiescence. Bone marrow progenitor populations expressed diminished levels of the IL-7Rα chain, which was associated with decreased proliferation and increased apoptosis. Modulating oxidative stress in vitro suggested that oxidative stress selectively leads to decreased IL-7Rα expression, and inhibits the survival of IL-7Rα-expressing hematopoietic progenitors, potentially linking increased reactive oxygen species and immunopathology.

INNOVATION

The study results identify a link between oxidative stress and diminished IL-7Rα expression and function. Further, the data suggest that this decrease in IL-7Rα is associated with defective hematopoietic development in Down Syndrome.

CONCLUSION

The data suggest that hematopoietic stem and lymphoid progenitor cell defects underlie immune dysfunction in DS and that increased oxidative stress and reduced cytokine signaling may alter hematologic development in Ts65Dn mice.

Early growth response gene-2 (Egr-2) regulates the development of B and T cells

Background

Understanding of how transcription factors are involved in lymphocyte development still remains a challenge. It has been shown that Egr-2 deficiency results in impaired NKT cell development and defective positive selection of T cells. Here we investigated the development of T, B and NKT cells in Egr-2 transgenic mice and the roles in the regulation of distinct stages of B and T cell development.

Methods and Findings

The expression of Egr1, 2 and 3 were analysed at different stages of T and B cell development by RT-PCT and results showed that the expression was strictly regulated at different stages. Forced expression of Egr-2 in CD2⁺ lymphocytes resulted in a severe reduction of CD4⁺CD8⁺ (DP) cells in thymus and pro-B cells in bone marrow, which was associated with reduced expression of Notch1 in ISP thymocytes and Pax5 in pro-B cells, suggesting that retraction of Egr-2 at the ISP and pro-B cell stages is important for the activation of lineage differentiation programs. In contrast to reduction of DP and pro-B cells, Egr-2 enhanced the maturation of DP cells into single positive (SP) T and NKT cells in thymus, and immature B cells into mature B cells in bone marrow.

Conclusions

Our results demonstrate that Egr-2 expressed in restricted stages of lymphocyte development plays a dynamic, but similar role for the development of T, NKT and B cells.

Chromatin remodeling complex NURF regulates thymocyte maturation

The maturation of T cells requires signaling from both cytokine and T-cell receptors to gene targets in chromatin, but how chromatin architecture influences this process is largely unknown. Here we show that thymocyte maturation post-positive selection is dependent on the nucleosome remodeling factor (NURF). Depletion of Bptf (bromodomain PHD finger transcription factor), the largest NURF subunit, in conditional mouse mutants results in developmental arrest beyond the CD4(+) CD8(int) stage without affecting cellular proliferation, cellular apoptosis, or coreceptor gene expression. In the Bptf mutant, specific subsets of genes important for thymocyte development show aberrant expression. We also observed defects in DNase I-hypersensitive chromatin structures at Egr1, a prototypical Bptf-dependent gene that is required for efficient thymocyte development. Moreover, chromatin binding of the sequence-specific factor Srf (serum response factor) to Egr1 regulatory sites is dependent on Bptf function. Physical interactions between NURF and Srf suggest a model in which Srf recruits NURF to facilitate transcription factor binding at Bptf-dependent genes. These findings provide evidence for causal connections between NURF, transcription factor occupancy, and gene regulation during thymocyte development.

The essential function for serum response factor in T-cell development reflects its specific coupling to extracellular signal-regulated kinase signaling

Serum response factor (SRF) recruits members of two families of signal-regulated coactivators, the extracellular signal-regulated kinase (ERK)-regulated ternary complex factors (TCFs) and the actin-regulated myocardin-related transcription factors (MRTFs), to its target genes through its DNA-binding domain. Whether coactivator association is required for SRF function in vivo and whether particular SRF functions reflect specific coupling to one or the other signal pathway have remained largely unexplored. We show that SRF is essential for thymocyte positive selection and thymic T(reg) and NK T-cell development but dispensable for early thymocyte development and negative selection. Expression of wild-type SRF, or mutants lacking the N-terminal phosphorylation sites or C-terminal transcriptional activation domain, restores positive selection in SRF null thymocytes. In contrast, SRF.V194E, which cannot recruit TCF or MRTF family members, is inactive, although it is recruited to target genes. Fusion of a TCF C-terminal activation domain to SRF.V194E effectively restores ERK-dependent single-positive (SP) thymocyte development. The resulting SP thymocytes exhibit normal surface marker expression and proliferation following T-cell receptor cross-linking. Thus, ERK signaling through the TCF pathway to SRF is necessary and sufficient for SRF function in thymocyte positive selection.

Tenuous paths in unexplored territory: From T cell receptor signaling to effector gene expression during thymocyte selection

During the last step of alphabeta T cell development, thymocytes that have rearranged genes encoding TCR chains and express CD4 and CD8 coreceptors are selected on the basis of their TCR reactivity to escape programmed cell death and become mature CD4 or CD8 T cells. This process is triggered by intrathymic TCR signaling, that activates 'sensor' transcription factors 'constitutively' expressed in DP thymocytes. Eventually, TCR-signaled thymocytes evolve effector transcriptional circuits that control basal metabolism, migration, survival and initiation of lineage-specific gene expression. This review examines how components of the 'sensing' transcription apparatus responds to positive selection signals, and highlights important differences with mature T cell responses. In a second part, we evaluate current observations and hypotheses on the connections between sensing transcription factors and effector circuitries.