Project description:IL-7 regulates homeostatic mechanisms that maintain the overall size of the T cell pool throughout life. We show that, under steady-state conditions, IL-7 signaling is principally mediated by activation of signal transducers and activators of transcription 5 (STAT5). In contrast, under lymphopenic conditions, there is a modulation of STAT1 expression resulting in an IL-7-dependent STAT1 and STAT5 activation. Consequently, the IL-7-induced transcriptome is altered with enrichment of IFN-stimulated genes (ISGs). Moreover, STAT1 overexpression was associated with reduced survival in CD4+ T cells undergoing lymphopenia-induced proliferation (LIP). We propose a model in which T cells undergoing LIP upregulate STAT1 protein, "switching on" an alternate IL-7-dependent program. This mechanism could be a physiological process to regulate the expansion and size of the CD4+ T cell pool. During HIV infection, the virus could exploit this pathway, leading to the homeostatic dysregulation of the T cell pools observed in these patients.
Project description:IL-7 regulates homeostatic mechanisms that maintain the overall size of the T cell pool throughout life. We show that, under steady-state conditions, IL-7 signaling is principally mediated by activation of signal transducers and activators of transcription 5 (STAT5). In contrast, under lymphopenic conditions, there is a modulation of STAT1 expression resulting in an IL-7-dependent STAT1 and STAT5 activation. Consequently, the IL-7-induced transcriptome is altered with enrichment of IFN-stimulated genes (ISGs). Moreover, STAT1 overexpression was associated with reduced survival in CD4+ T cells undergoing lymphopenia-induced proliferation (LIP). We propose a model in which T cells undergoing LIP upregulate STAT1 protein, "switching on" an alternate IL-7-dependent program. This mechanism could be a physiological process to regulate the expansion and size of the CD4+ T cell pool. During HIV infection, the virus could exploit this pathway, leading to the homeostatic dysregulation of the T cell pools observed in these patients.
Project description:Interleukin-21 (IL-21) is a type 1 cytokine essential for immune cell differentiation and function. Although IL-21 can activate several STAT family transcription factors, previous studies focused mainly on the role of STAT3 in IL-21 signaling. Here, we investigated the role of STAT1 and show that STAT1 and STAT3 have at least partially opposing roles in IL-21 signaling in CD4+ T cells. IL-21 induced STAT1 phosphorylation, and this was augmented in Stat3-deficient CD4+ T cells. RNA-Seq analysis of CD4+ T cells from Stat1- and Stat3-deficient mice revealed that both STAT1 and STAT3 are critical for IL-21-mediated gene regulation. Expression of some genes, including Tbx21 and Ifng, was differentially regulated by STAT1 and STAT3, and interestingly, ChIP-Seq analysis showed that STAT3 binding at Tbx21 and Ifng loci was attenuated in Stat1-deficient cells. Moreover, opposing actions of STAT1 and STAT3 on IFN- expression in CD4+ T cells were demonstrated in vivo during chronic lymphocytic choriomeningitis (LCMV) infection. Finally, IL-21-mediated induction of STAT1 phosphorylation, as well as IFNG and TBX21 expression, were higher in CD4+ T cells from patients with autosomal dominant hyper-IgE syndrome (AD-HIES), which is caused by STAT3 deficiency. These data indicate an interplay between STAT1 and STAT3 in fine-tuning IL-21 actions. Genome-wide transcription factors mapping and binding of STAT3 in mouse CD4+ T cells in both WT and Stat1-deficient mice. RNA-Seq is performed in mouse CD4+ T cells in WT, Stat1-deficient and Stat3-deficient mice.
Project description:SerpinB1 is an endogenous inhibitor of serine proteases recognized for its anti-inflammatory and host-protective properties. Although loss of serpinB1 in mice does not result in gross immune deregulation, serpinb1a(-/-) mice display increased mortality and inflammation-associated morbidity upon challenge with influenza virus. Here, we show that IL-17A(+) ?? and CD4(+) Th17 cells are already expanded in the lungs of serpinb1a(-/-) mice at steady-state. Both ?? and ??(+) CD4(+) CCR6(+) T cells isolated from the lungs of naive serpinb1a(-/-) mice displayed a skewed transcriptional profile relative to WT cells, including increased Th17 signature transcripts [Il17a, l17f, and Rorc (ROR?t)] and decreased Th1 signature transcripts [Ifng, Cxcr3, and Tbx21 (T-bet)] in ?? T cells. In addition to the lung, IL-17A(+) ?? and CD4(+) Th17 cells were increased in the spleen of naive serpinb1a(-/-) mice, despite normal ?? and ?? T cell development in the thymus. Within the ?? T cell compartment, loss of serpinb1a prompted selective expansion of V?4(+) and V?6/V?1(+) cells, which also displayed elevated expression of the proliferating cell nuclear antigen, Ki-67, and IL-17A. Given that serpinb1a is preferentially expressed in WT IL-17A(+) ?? and CD4(+) Th17 cell subsets vis-à-vis other T cell lineages, our findings reveal a novel function of serpinB1 in limiting untoward expansion of lymphocytes with a Th17 phenotype.
Project description:Adult hematopoietic stem cells (HSCs) are predominantly quiescent and can be activated in response to acute stress such as infection or cytotoxic insults. STAT1 is a pivotal mediator of interferon (IFN) signaling and is required for IFN-induced HSC proliferation, but the downstream mechanisms remain unclear and in particular little is known about the role of STAT1 in regulating hematopoietic stem/progenitor cells during homeostasis. Here we show that loss of STAT1 alters the steady state hematopoietic stem and progenitor (HSPC) landscape, impairs HSC function in transplantation assays and delays blood cell regeneration following myeloablation. Under steady state conditions STAT1 was essential for several HSC transcriptional programs including expression of genes involved in virus life cycle, a subset of interferon-stimulated genes, MHC class I genes and genes involved in cell cycle arrest. In addition Stat-1 deficient mice lacked a previously unrecognized quiescent subset of homeostatic HSCs with high levels of MHC II expression (MHC IIhi HSCs). This subset was refractory to 5’-FU induced myeloablation and displayed reduced megakaryocytic potential. Mutant calreticulin, which causes increased megakaryopoiesis in human myeloproliferative neoplasms, gave rise to preferential expansion of MHC IIlo HSCs. These data reveal a STAT1 dependent MHC IIhi quiescent HSC subset and show that STAT1 protects HSCs from proliferative exhaustion.
Project description:Adult hematopoietic stem cells (HSCs) are predominantly quiescent and can be activated in response to acute stress such as infection or cytotoxic insults. STAT1 is a pivotal mediator of interferon (IFN) signaling and is required for IFN-induced HSC proliferation, but the downstream mechanisms remain unclear and in particular little is known about the role of STAT1 in regulating hematopoietic stem/progenitor cells during homeostasis. Here we show that loss of STAT1 alters the steady state hematopoietic stem and progenitor (HSPC) landscape, impairs HSC function in transplantation assays and delays blood cell regeneration following myeloablation. Under steady state conditions STAT1 was essential for several HSC transcriptional programs including expression of genes involved in virus life cycle, a subset of interferon-stimulated genes, MHC class I genes and genes involved in cell cycle arrest. In addition Stat-1 deficient mice lacked a previously unrecognized quiescent subset of homeostatic HSCs with high levels of MHC II expression (MHC IIhi HSCs). This subset was refractory to 5’-FU induced myeloablation and displayed reduced megakaryocytic potential. Mutant calreticulin, which causes increased megakaryopoiesis in human myeloproliferative neoplasms, gave rise to preferential expansion of MHC IIlo HSCs. These data reveal a STAT1 dependent MHC IIhi quiescent HSC subset and show that STAT1 protects HSCs from proliferative exhaustion.
Project description:Interleukin-21 (IL-21) is a type 1 cytokine essential for immune cell differentiation and function. Although IL-21 can activate several STAT family transcription factors, previous studies focused mainly on the role of STAT3 in IL-21 signaling. Here, we investigated the role of STAT1 and show that STAT1 and STAT3 have at least partially opposing roles in IL-21 signaling in CD4+ T cells. IL-21 induced STAT1 phosphorylation, and this was augmented in Stat3-deficient CD4+ T cells. RNA-Seq analysis of CD4+ T cells from Stat1- and Stat3-deficient mice revealed that both STAT1 and STAT3 are critical for IL-21-mediated gene regulation. Expression of some genes, including Tbx21 and Ifng, was differentially regulated by STAT1 and STAT3, and interestingly, ChIP-Seq analysis showed that STAT3 binding at Tbx21 and Ifng loci was attenuated in Stat1-deficient cells. Moreover, opposing actions of STAT1 and STAT3 on IFN- expression in CD4+ T cells were demonstrated in vivo during chronic lymphocytic choriomeningitis (LCMV) infection. Finally, IL-21-mediated induction of STAT1 phosphorylation, as well as IFNG and TBX21 expression, were higher in CD4+ T cells from patients with autosomal dominant hyper-IgE syndrome (AD-HIES), which is caused by STAT3 deficiency. These data indicate an interplay between STAT1 and STAT3 in fine-tuning IL-21 actions.
Project description:To understand the basis behind the defective survival/expansion of Stat1-/- CD4+ T cells in Rag1-/- mice, we analyzed the gene expression of WT and Stat1-/- CD4+ T cells pre- and post-transfer into these mice by RNAseq.
Project description:The main obstacle in curing an established HIV-1 infection is the long-lived reservoir of latently infected CD4+ T cells. This reservoir is maintained by T cell expansion that can be activated by several mechanisms including antigen-driven proliferation and homeostatic proliferation (HSP). Antigen-driven proliferation triggered by T cell receptor (TCR) signaling is a strong physiological inducer of CD4+ T cell expansion. This also reactivates latent HIV-1 and thus, can be the source of viral rebound. Unlike antigen-driven proliferation, HSP allows the expansion of HIV-1-infected CD4+ T cells without activating HIV-1 expression. While this condition strongly activates STAT5 signaling, the mechanisms for HIV-1 containment are unknown. Our previous work using HIV-infected primarily CD4+ T cells maintained under HSP conditions suggested a post-transcriptional block as a cause of the containment (Tsunetsugu-Yokota et al. 2016 Front Microbiol). To decipher the mechanisms that contribute to the HIV-1 refractory state in homeostatic proliferating CD4+ T cells, we analyzed differentially expressed genes in primary CD4 + cells that were cultured either under HSP conditions (culture with IL-7 and IL-15) or after TCR-stimulation (culture with IL-2 after anti-CD3/CD28 activation).
Project description:Hematopoietic stem cells (HSCs) are capable of entering the cell cycle to replenish the blood system in response to inflammatory cues; however, excessive proliferation in response to chronic inflammation can lead to either HSC attrition or expansion. The mechanism(s) that limit HSC proliferation and expansion triggered by inflammatory signals are poorly defined. Here, we show that long-term HSCs (HSCLT) rapidly repress protein synthesis and cell cycle genes following treatment with the proinflammatory cytokine interleukin (IL)-1. This gene program is associated with activation of the transcription factor PU.1 and direct PU.1 binding at repressed target genes. Notably, PU.1 is required to repress cell cycle and protein synthesis genes, and IL-1 exposure triggers aberrant protein synthesis and cell cycle activity in PU.1-deficient HSCs. These features are associated with expansion of phenotypic PU.1-deficient HSCs. Thus, we identify a PU.1-dependent mechanism triggered by innate immune stimulation that limits HSC proliferation and pool size. These findings provide insight into how HSCs maintain homeostasis during inflammatory stress.