Blimp-1 and c-Maf regulate immune gene networks to protect against distinct pathways of pathobiont-induced colitis

Intestinal immune responses to microbes are controlled by the cytokine IL-10 to avoid immune pathology. Here, we use single-cell RNA sequencing of colon lamina propria leukocytes (LPLs) along with RNA-seq and ATAC-seq of purified CD4+ T cells to show that the transcription factors Blimp-1 (encoded by Prdm1) and c-Maf co-dominantly regulate Il10 while negatively regulating proinflammatory cytokines in effector T cells. Double-deficient Prdm1fl/flMaffl/flCd4Cre mice infected with Helicobacter hepaticus developed severe colitis with an increase in TH1/NK/ILC1 effector genes in LPLs, while Prdm1fl/flCd4Cre and Maffl/flCd4Cre mice exhibited moderate pathology and a less-marked type 1 effector response. LPLs from infected Maffl/flCd4Cre mice had increased type 17 responses with increased Il17a and Il22 expression and an increase in granulocytes and myeloid cell numbers, resulting in increased T cell-myeloid-neutrophil interactions. Genes over-expressed in human inflammatory bowel disease showed differential expression in LPLs from infected mice in the absence of Prdm1 or Maf, revealing potential mechanisms of human disease.

Human split hand/foot variants are not as functional as wildtype human PRDM1 in the rescue of craniofacial defects

BACKGROUND

Split hand/foot malformation (SHFM) is a congenital limb disorder presenting with limb anomalies, such as missing, hypoplastic, or fused digits, and often craniofacial defects, including a cleft lip/palate, microdontia, micrognathia, or maxillary hypoplasia. We previously identified three novel variants in the transcription factor, PRDM1, that are associated with SHFM phenotypes. One individual also presented with a high arch palate. Studies in vertebrates indicate that PRDM1 is important for development of the skull; however, prior to our study, human variants in PRDM1 had not been associated with craniofacial anomalies.

METHODS

Using transient mRNA overexpression assays in prdm1a-/- mutant zebrafish, we tested whether the PRDM1 SHFM variants were functional and could lead to a rescue of the craniofacial defects observed in prdm1a-/- mutants. We also mined previously published CUT&RUN and RNA-seq datasets that sorted EGFP-positive cells from a Tg(Mmu:Prx1-EGFP) transgenic line that labels the pectoral fin, pharyngeal arches, and dorsal part of the head to examine Prdm1a binding and the effect of Prdm1a loss on craniofacial genes.

RESULTS

The prdm1a-/- mutants exhibit craniofacial defects including a hypoplastic neurocranium, a loss of posterior ceratobranchial arches, a shorter palatoquadrate, and an inverted ceratohyal. Injection of wildtype (WT) hPRDM1 in prdm1a-/- mutants partially rescues the palatoquadrate phenotype. However, injection of each of the three SHFM variants fails to rescue this skeletal defect. Loss of prdm1a leads to a decreased expression of important craniofacial genes by RNA-seq, including emilin3a, confirmed by hybridization chain reaction expression. Other genes including dlx5a/dlx6a, hand2, sox9b, col2a1a, and hoxb genes are also reduced. Validation by real-time quantitative PCR in the anterior half of zebrafish embryos failed to confirm the expression changes suggesting that the differences are enriched in prx1 expressing cells.

CONCLUSION

These data suggest that the three SHFM variants are likely not functional and may be associated with the craniofacial defects observed in the humans. Finally, they demonstrate how Prdm1a can directly bind and regulate genes involved in craniofacial development.

Human Primordial Germ Cell-Like Cell Induction from Pluripotent Stem Cells by SOX17 and PRDM1 Expression

Human primordial germ cell (PGC) development initiates about 2 weeks after fertilization during embryogenesis. Unique molecular events follow, including epigenetic resetting, to establish functional gametes (egg and sperm). Due to the inaccessibility of human embryos, it is essential to have an amenable experimental platform to investigate the mechanisms and potential dysfunctions of the events. We previously established a PGC-like cell (PGCLC) differentiation method using human pluripotent stem cells (PSCs) via induction of precursor cells followed by stimulation with a cytokine cocktail including BMP. We also revealed that the expression of PGC specifiers, SOX17 and PRDM1, can robustly induce PGCLCs from PSCs without the cytokines. The balance of SOX17 and PRDM1 is critical for germ cell fate since the two factors also regulate endoderm differentiation. Here we describe a detailed procedure for PGCLC differentiation with the balanced induction of SOX17 and PRDM1. The protocol can be used for PGC induction in other mammalian species exhibiting PGCs with SOX17 expression. Together, these studies will advance the understanding of germ cell biology and its applications in reproductive technology and medicine.

T cell receptor signaling strength establishes the chemotactic properties of effector CD8+ T cells that control tissue-residency

Tissue-resident memory (TRM) CD8+ T cells are largely derived from recently activated effector T cells, but the mechanisms that control the extent of TRM differentiation within tissue microenvironments remain unresolved. Here, using an IFNγ-YFP reporter system to identify CD8+ T cells executing antigen-dependent effector functions, we define the transcriptional consequences and functional mechanisms controlled by TCR-signaling strength that occur within the skin during viral infection to promote TRM differentiation. TCR-signaling both enhances CXCR6-mediated migration and suppresses migration toward sphingosine-1-phosphate, indicating the programming of a 'chemotactic switch' following secondary antigen encounter within non-lymphoid tissues. Blimp1 was identified as the critical target of TCR re-stimulation that is necessary to establish this chemotactic switch and for TRM differentiation to efficiently occur. Collectively, our findings show that access to antigen presentation and strength of TCR-signaling required for Blimp1 expression establishes the chemotactic properties of effector CD8+ T cells to promote residency within non-lymphoid tissues.

Blimp1 suppressed CD4+ T cells-induced activation of fibroblast-like synoviocytes by upregulating IL-10 via the rho pathway

BACKGROUND

B lymphocyte-induced maturation protein 1 (Blimp1) is a risk allele for rheumatoid arthritis (RA), but its functional mechanism in RA remains to be further explored.

METHODS

Flow cytometry was performed to detect CD4⁺ T cell differentiation. ELISA was used to measure inflammatory factor secretion. Lentivirus mediated Blimp1 overexpression vector (LV-Blimp1) or short hairpin RNA (sh-Blimp1) were used to infect CD4⁺ T cells stimulated by anti-CD28 and anti-CD3 mAbs. RA fibroblast-like synoviocytes (FLSs) were co-cultured with CD4⁺ T cells or T cell conditioned medium (CD4CM), and cell proliferation, invasion, and expression of adhesion molecules and cytokines in FLSs were evaluated. Mice were injected intradermally with type II collagen to establish a collagen-induced arthritis (CIA) mouse model, and the severity of CIA was evaluated with H&E and Safranin-O staining.

RESULTS

Blimp1 knockdown increased pro-inflammatory factor secretion, but downregulated IL-10 concentration in activated CD4⁺ T cells. Blimp1 overexpression promoted regulatory T cells (Treg) CD4⁺ T cell differentiation and hindered T helper 1 (Th1) and T helper 17 (Th17) CD4⁺ T cell differentiation. Blimp1 overexpression suppressed the expression of pro-inflammatory factors and adhesion molecules in CD4⁺ T cells by upregulating IL-10. Moreover, Blimp1 overexpression impeded the enhanced effect of CD4⁺ T cells/CD4CM on cell adhesion, inflammation, proliferation, invasion and RhoA and Rac1 activities in FLSs by upregulating IL-10. Additionally, administration with LV-Blimp1 alleviated the severity of CIA.

CONCLUSION

Blimp1 restrained CD4⁺ T cells-induced activation of FLSs by promoting the secretion of IL-10 in CD4⁺ T cells via the Rho signaling pathway.

Unkeito Suppresses RANKL-Mediated Osteoclastogenesis via the Blimp1-Bcl6 and NF-κB Signaling Pathways and Enhancing Osteoclast Apoptosis

Osteoporosis is a common bone disease, particularly in menopausal women. Herein, we screened four Kampo medicines (Unkeito (UKT), Kamishoyosan (KSS), Kamikihito (KKT), and Ninjinyoeito (NYT)), frequently used to treat menopausal syndromes, for their effects on receptor activator of nuclear factor-kappaB ligand (RANKL)-induced osteoclast differentiation in RAW 264 cells. Considering that UKT exhibited the most potent effect, we examined its effect on RANKL-induced osteoclastogenesis, the induction of osteoclast apoptosis, and the mechanisms underlying its effects. UKT inhibits RANKL-induced osteoclast differentiation in the early stage and decreases osteoclast-related genes, including tartrate-resistant acid phosphatase (Trap), dendritic cell-specific transmembrane protein (Dcstamp), matrix metalloproteinase-9 (Mmp9), and cathepsin K (Ctsk). Specifically, UKT inhibits the nuclear factor of activated T cells 1 (NFATc1), which is essential for osteoclastogenesis. UKT increases Bcl6, which antagonizes NFATc1 and Dc-stamp, thereby blocking the progression of osteoclasts to maturation. UKT also decreased nuclear translocation by downregulating the activity of p65/NF-κB. In addition, UKT enhances mononuclear osteoclast apoptosis via activation of caspase-3. Herein, we demonstrate that UKT suppresses RANKL-mediated osteoclastogenesis via the Blimp1–Bcl6 and NF-κB signaling pathways and enhances mononuclear osteoclast apoptosis. Furthermore, UKT prevents bone loss in OVX mice. Thus, UKT might be a potential therapeutic agent for postmenopausal osteoporosis.

Super-enhancer hypermutation alters oncogene expression in B cell lymphoma

Diffuse large B cell lymphoma (DLBCL) is the most common B cell non-Hodgkin lymphoma and remains incurable in around 40% of patients. Efforts to sequence the coding genome identified several genes and pathways that are altered in this disease, including potential therapeutic targets1-5. However, the non-coding genome of DLBCL remains largely unexplored. Here we show that active super-enhancers are highly and specifically hypermutated in 92% of samples from individuals with DLBCL, display signatures of activation-induced cytidine deaminase activity, and are linked to genes that encode B cell developmental regulators and oncogenes. As evidence of oncogenic relevance, we show that the hypermutated super-enhancers linked to the BCL6, BCL2 and CXCR4 proto-oncogenes prevent the binding and transcriptional downregulation of the corresponding target gene by transcriptional repressors, including BLIMP1 (targeting BCL6) and the steroid receptor NR3C1 (targeting BCL2 and CXCR4). Genetic correction of selected mutations restored repressor DNA binding, downregulated target gene expression and led to the counter-selection of cells containing corrected alleles, indicating an oncogenic dependency on the super-enhancer mutations. This pervasive super-enhancer mutational mechanism reveals a major set of genetic lesions deregulating gene expression, which expands the involvement of known oncogenes in DLBCL pathogenesis and identifies new deregulated gene targets of therapeutic relevance.

Dependence on Bcl6 and Blimp1 drive distinct differentiation of murine memory and follicular helper CD4+ T cells

During the immune response, CD4+ T cells differentiate into distinct effector subtypes, including follicular helper T (Tfh) cells that help B cells, and into memory cells. Tfh and memory cells are required for long-term immunity; both depend on the transcription factor Bcl6, raising the question whether they differentiate through similar mechanisms. Here, using single-cell RNA and ATAC sequencing, we show that virus-responding CD4+ T cells lacking both Bcl6 and Blimp1 can differentiate into cells with transcriptomic, chromatin accessibility, and functional attributes of memory cells but not of Tfh cells. Thus, Bcl6 promotes memory cell differentiation primarily through its repression of Blimp1. These findings demonstrate that distinct mechanisms underpin the differentiation of memory and Tfh CD4+ cells and define the Bcl6-Blimp1 axis as a potential target for promoting long-term memory T cell differentiation.

Evaluation of MicroRNA-125b-5p and Transcription Factors BLIMP1 and IRF4 Expression in Unsolved Common Variable Immunodeficiency Patients

Common variable immunodeficiency (CVID) is the most prevalent form of symptomatic primary humoral immunodeficiencies characterized by failure in the final differentiation of B lymphocytes. The majority of CVID cases have no identified genetic defect, and epigenetic alteration could be involved in the pathogenesis of CVID. Hence, we aimed to evaluate the expression of hsa-miR-125b-5p -and, B lymphocyte-induced maturation protein-1(BLIMP-1) and interferon regulatory protein-4 (IRF-4) in a group of CVID patients with no definitive genetic diagnosis in comparison with healthy individuals. Ten CVID patients (all known genes excluded) and 10 age and sex-matched healthy controls participated in the study. B lymphocytes were isolated and expression of miR-125b-5p, IRF4, and BLIMP1 were evaluated by real-time polymerase chain reaction (RT-PCR). Moreover, B cell subsets were analyzed by flow cytometry. The results showed that the relative expression of miR-125b-5p in CVID patients was increased while it was decreased for the BLIMP1 and IRF4 transcription factors compared with the healthy controls. Although a reduction was observed in switched and non-switched memory B cells among all high-miR patients, these subsets were decreased in patients with normal miR expression (71.0% and 85.0%, respectively). Our results suggest that overexpression of miR-125b-5p affects the terminal differentiation of B cells in a selected group of CVID patients by downregulating the BLIMP-1 gene and more intensively for the IRF-4 gene expressions.

Heading towards a dead end: The role of DND1 in germ line differentiation of human iPSCs

The DND microRNA-mediated repression inhibitor 1 (DND1) is a conserved RNA binding protein (RBP) that plays important roles in survival and fate maintenance of primordial germ cells (PGCs) and in the development of the male germline in zebrafish and mice. Dead end was shown to be expressed in human pluripotent stem cells (PSCs), PGCs and spermatogonia, but little is known about its specific role concerning pluripotency and human germline development. Here we use CRISPR/Cas mediated knockout and PGC-like cell (PGCLC) differentiation in human iPSCs to determine if DND1 (1) plays a role in maintaining pluripotency and (2) in specification of PGCLCs. We generated several clonal lines carrying biallelic loss of function mutations and analysed their differentiation potential towards PGCLCs and their gene expression on RNA and protein levels via RNA sequencing and mass spectrometry. The generated knockout iPSCs showed no differences in pluripotency gene expression, proliferation, or trilineage differentiation potential, but yielded reduced numbers of PGCLCs as compared with their parental iPSCs. RNAseq analysis of mutated PGCLCs revealed that the overall gene expression remains like non-mutated PGCLCs. However, reduced expression of genes associated with PGC differentiation and maintenance (e.g., NANOS3, PRDM1) was observed. Together, we show that DND1 iPSCs maintain their pluripotency but exhibit a reduced differentiation to PGCLCs. This versatile model will allow further analysis of the specific mechanisms by which DND1 influences PGC differentiation and maintenance.

Adiponectin Enhances B-Cell Proliferation and Differentiation via Activation of Akt1/STAT3 and Exacerbates Collagen-Induced Arthritis

Although B cells have been shown to contribute to the pathogenesis of rheumatoid arthritis (RA), the precise role of B cells in RA needs to be explored further. Our previous studies have revealed that adiponectin (AD) is expressed at high levels in inflamed synovial joint tissues, and its expression is closely correlated with progressive bone erosion in patients with RA. In this study, we investigated the possible role of AD in B cell proliferation and differentiation. We found that AD stimulation could induce B cell proliferation and differentiation in cell culture. Notably, local intraarticular injection of AD promoted B cell expansion in joint tissues and exacerbated arthritis in mice with collagen-induced arthritis (CIA). Mechanistically, AD induced the activation of PI3K/Akt1 and STAT3 and promoted the proliferation and differentiation of B cells. Moreover, STAT3 bound to the promoter of the Blimp-1 gene, upregulated Blimp-1 expression at the transcriptional level, and promoted B cell differentiation. Collectively, we observed that AD exacerbated CIA by enhancing B cell proliferation and differentiation mediated by the PI3K/Akt1/STAT3 axis.

Fatty acid-binding protein 3 regulates differentiation of IgM-producing plasma cells

Plasma cells (PCs), which aim to protect host health, produce various subsets of immunoglobulin (Ig) in response to extracellular pathogens. Blimp-1 (encoded by Prdm1)-a protein that is highly expressed by PCs-is important for PC functions, including the generation of Igs. Fatty acid-binding protein 3 (FABP3) is a carrier protein of polyunsaturated fatty acids (PUFAs) and participates in multiple cellular functions. Although the functions of FABP3 in neurons and cardiac myocytes are well-noted, their roles in immune cells remain to be fully elucidated. In this study, we demonstrate that FABP3 is expressed in activated B cells and that FABP3 promotes PC development and IgM secretion. Moreover, we provide the first evidence that FABP3 is necessary for Blimp-1 expression, by regulating the histone modification of its promoter region. Taken together, our findings reveal that FABP3 acts as a positive regulator of B-cell activation by controlling histone acetylation of the Blimp-1 gene, thereby playing a role in host defense against pathogens.

Mitochondrial stress induced by continuous stimulation under hypoxia rapidly drives T cell exhaustion

Cancer and chronic infections induce T cell exhaustion, a hypofunctional fate carrying distinct epigenetic, transcriptomic and metabolic characteristics. However, drivers of exhaustion remain poorly understood. As intratumoral exhausted T cells experience severe hypoxia, we hypothesized that metabolic stress alters their responses to other signals, specifically, persistent antigenic stimulation. In vitro, although CD8+ T cells experiencing continuous stimulation or hypoxia alone differentiated into functional effectors, the combination rapidly drove T cell dysfunction consistent with exhaustion. Continuous stimulation promoted Blimp-1-mediated repression of PGC-1α-dependent mitochondrial reprogramming, rendering cells poorly responsive to hypoxia. Loss of mitochondrial function generated intolerable levels of reactive oxygen species (ROS), sufficient to promote exhausted-like states, in part through phosphatase inhibition and the consequent activity of nuclear factor of activated T cells. Reducing T cell-intrinsic ROS and lowering tumor hypoxia limited T cell exhaustion, synergizing with immunotherapy. Thus, immunologic and metabolic signaling are intrinsically linked: through mitigation of metabolic stress, T cell differentiation can be altered to promote more functional cellular fates.

Agrimophol suppresses RANKL-mediated osteoclastogenesis through Blimp1-Bcl6 axis and prevents inflammatory bone loss in mice

Excessive activity of osteoclasts causes many bone-related diseases, such as rheumatoid arthritis and osteoporosis. Agrimophol (AGR), a phenolic compound, originated from Agrimonia pilosa Ledeb. In prior studies, AGR is reported to possess schistosomicidal and mycobactericidal activities. However, no reports covered its anti-osteoclastogenesis characteristic. In this study, we found that AGR inhibited RANKL-induced osteoclastogenesis, bone-resorption, F-actin ring formation, and the mRNA expression of osteoclast-associated genes such as CTSK, TRAP, MMP-9, and ATP6v0d2 in vitro. In addition, AGR suppressed RANKL-induced expression of c-Fos and NFATc1. However, AGR treatment did not affect NF-κB activation and MAPKs phosphorylation in RANKL-stimulated BMMs, which implicated that AGR might not influence the initial expression of NFATc1 mediated by NF-κB and MAPKs signaling. Our results further indicated that AGR did not alter phosphorylation levels of GSK3β and the expression of calcineurin, which implicated that AGR treatment might not interfere with phosphorylation and de-phosphorylation of NFATc1 mediated by GSK3β and calcineurin, respectively. B-lymphocyte-induced maturation protein-1 (Blimp1), which was regarded as a transcriptional repressor of negative regulators of osteoclastogenesis, was markedly attenuated in the presence of AGR, leading to the enhanced expression of B-cell lymphoma 6 (Bcl-6). Meanwhile, Blimp1 knockdown in BMMs by siRNA strongly enhanced the expression of Bcl6 and reduced NFATc1 induction by RANKL. These findings suggested that AGR inhibited RANKL-induced osteoclast differentiation through Blimp1-Bcl-6 signaling mediated modulation of NFATc1 and its target genes. Consistent with these in vitro results, AGR exhibited a protective influence in an in vivo mouse model of LPS-induced bone loss by suppressing excessive osteoclast activity and attenuating LPS-induced bone destruction. Hence, these results identified that AGR could be considered as a potential therapeutic agent against bone lysis disease.

Transcription factor NF-κB promotes acute lung injury via microRNA-99b-mediated PRDM1 down-regulation

Acute lung injury (ALI), is a rapidly progressing heterogenous pulmonary disorder that possesses a high risk of mortality. Accumulating evidence has implicated the activation of the p65 subunit of NF-κB [NF-κB(p65)] activation in the pathological process of ALI. microRNAs (miRNAs), a group of small RNA molecules, have emerged as major governors due to their post-transcriptional regulation of gene expression in a wide array of pathological processes, including ALI. The dysregulation of miRNAs and NF-κB activation has been implicated in human diseases. In the current study, we set out to decipher the convergence of miR-99b and p65 NF-κB activation in ALI pathology. We measured the release of pro-inflammatory cytokines (IL-1β, IL-6, and TNFα) in bronchoalveolar lavage fluid using ELISA. MH-S cells were cultured and their viability were detected with cell counting kit 8 (CCK8) assays. The results showed that miR-99b was up-regulated, while PRDM1 was down-regulated in a lipopolysaccharide (LPS)-induced murine model of ALI. Mechanistic investigations showed that NF-κB(p65) was enriched at the miR-99b promoter region, and further promoted its transcriptional activity. Furthermore, miR-99b targeted PRDM1 by binding to its 3'UTR, causing its down-regulation. This in-creased lung injury, as evidenced by increased wet/dry ratio of mouse lung, myeloperoxidase activity and pro-inflammatory cytokine secretion, and enhanced infiltration of inflammatory cells in lung tissues. Together, our findings indicate that NF-κB(p65) promotion of miR-99b can aggravate ALI in mice by down-regulating the expression of PRDM1.

A dichotomy of gene regulatory associations during the activated B-cell to plasmablast transition

The activated B-cell (ABC) to plasmablast transition encompasses the cusp of antibody-secreting cell (ASC) differentiation. We explore this transition with integrated analysis in human cells, focusing on changes that follow removal from CD40-mediated signals. Within hours of input signal loss, cell growth programs shift toward enhanced proliferation, accompanied by ER-stress response, and up-regulation of ASC features. Clustering of genomic occupancy for IRF4, BLIMP1, XBP1, and CTCF with histone marks identifies a dichotomy: XBP1 and IRF4 link to induced but not repressed gene modules in plasmablasts, whereas BLIMP1 links to modules of ABC genes that are repressed, but not to activated genes. Between ABC and plasmablast states, IRF4 shifts away from AP1/IRF composite elements while maintaining occupancy at IRF and ETS/IRF elements. This parallels the loss of BATF expression, which is identified as a potential BLIMP1 target. In plasmablasts, IRF4 acquires an association with CTCF, a feature maintained in plasma cell myeloma lines. Thus, shifting occupancy links IRF4 to both ABC and ASC gene expression, whereas BLIMP1 occupancy links to repression of the activation state.

Loss of prdm1a accelerates melanoma onset and progression

Melanoma is an aggressive, deadly skin cancer derived from melanocytes, a neural crest cell derivative. Melanoma cells mirror the developmental program of neural crest cells in that they exhibit the same gene expression patterns and utilize similar cellular mechanisms, including increased cell proliferation, epithelial-mesenchymal transition, and migration. Here we studied the role of neural crest regulator PRDM1 in melanoma onset and progression. In development, Prdm1a functions to promote neural crest progenitor fate, and in melanoma, we found that PRDM1 has reduced copy number and is recurrently deleted in both zebrafish and humans. When examining expression of neural crest and melanocyte development genes, we show that sox10 progenitor expression is high in prdm1a-/- mutants, while more differentiated melanocyte markers are reduced, suggesting that normally Prdm1a is required for differentiation. Data mining of human melanoma datasets indicates that high PRDM1 expression in human melanoma is correlated with better patient survival and decreased PRDM1 expression is common in metastatic tumors. When one copy of prdm1a is lost in the zebrafish melanoma model Tg(mitfa:BRAFV600E );p53-/- ;prdm1a+/- , melanoma onset occurs more quickly, and the tumors that form have a larger area with increased expression of sox10. These data demonstrate a novel role for PRDM1 as a tumor suppressor in melanoma.

Antibody-secreting cell destiny emerges during the initial stages of B-cell activation

Upon stimulation, B cells assume heterogeneous cell fates, with only a fraction differentiating into antibody-secreting cells (ASC). Here we investigate B cell fate programming and heterogeneity during ASC differentiation using T cell-independent models. We find that maximal ASC induction requires at least eight cell divisions in vivo, with BLIMP-1 being required for differentiation at division eight. Single cell RNA-sequencing of activated B cells and construction of differentiation trajectories reveal an early cell fate bifurcation. The ASC-destined branch requires induction of IRF4, MYC-target genes, and oxidative phosphorylation, with the loss of CD62L expression serving as a potential early marker of ASC fate commitment. Meanwhile, the non-ASC branch expresses an inflammatory signature, and maintains B cell fate programming. Finally, ASC can be further subseted based on their differential responses to ER-stress, indicating multiple development branch points. Our data thus define the cell division kinetics of B cell differentiation in vivo, and identify the molecular trajectories of B cell fate and ASC formation.

Simultaneous deletion of Prdm1 and Vsx2 enhancers in the retina alters photoreceptor and bipolar cell fate specification, yet differs from deleting both genes

The transcription factor OTX2 is required for photoreceptor and bipolar cell formation in the retina. It directly activates the transcription factors Prdm1 and Vsx2 through cell type-specific enhancers. PRDM1 and VSX2 work in opposition, such that PRDM1 promotes photoreceptor fate and VSX2 bipolar cell fate. To determine how OTX2+ cell fates are regulated in mice, we deleted Prdm1 and Vsx2 or their cell type-specific enhancers simultaneously using a CRISPR/Cas9 in vivo retina electroporation strategy. Double gene or enhancer targeting effectively removed PRDM1 and VSX2 protein expression. However, double enhancer targeting favored bipolar fate outcomes, whereas double gene targeting favored photoreceptor fate. Both conditions generated excess amacrine cells. Combined, these fate changes suggest that photoreceptors are a default fate outcome in OTX2+ cells and that VSX2 must be present in a narrow temporal window to drive bipolar cell formation. Prdm1 and Vsx2 also appear to redundantly restrict the competence of OTX2+ cells, preventing amacrine cell formation. By taking a combinatorial deletion approach of both coding sequences and enhancers, our work provides new insights into the complex regulatory mechanisms that control cell fate choice.

Association of circulating SLAMF7+Tfh1 cells with IgG4 levels in patients with IgG4-related disease

BACKGROUND

Follicular helper CD4+ T (Tfh) cells have a critical role in IgG4 production by B cells in IgG4-related disease (IgG4-RD). Recent studies including ours showed that SLAMF7+CD4+ T cells are an important pathological driver of IgG4-RD. In this study, we have sought to elucidate a relationship between helper CD4+ T (Th), particularly Tfh, cells and SLAMF7+ CD4+ T cells in IgG4-RD.

RESULTS

The patients with IgG4-RD enrolled in this study were aged 66 ± 12 years and their titers of serum IgG4 were 372 ± 336 mg/dl. Th1 cells, activated circulating Tfh1 (cTfh1), and activated cTfh2 cells increased in IgG4-RD. SLAMF7 was mainly expressed on Th1 and cTfh1, but not cTfh2, cells in the patients. SLAMF7+ cTfh1 cells were PD-1/CD28 double-positive, whereas SLAMF7+ Th1 cells were CD28 negative. Positive correlations were noted between serum IgG4 levels and the number of activated cTfh2 cells and SLAMF7+ cTfh1 cells, but not SLAMF7+ Th1 cells. Intriguingly, among cTfh1 cells, activated SLAMF7+ cTfh1 cells were high producers of IL-10 along with IL-21. Blimp-1, but not Bcl-6, mRNA was expressed at high levels in activated SLAMF7+ cTfh1 cells. In addition to CD4+ T cells, the frequency of SLAMF7+ fraction was higher in memory B cells than naïve B cells in patients with IgG4RD. Finally, upon stimulation via B-cell receptor and CD40, Tfh1-associated cytokines, IL-21 and IFN-γ, most significantly induced SLAMF7 expression in memory B cells.

CONCLUSIONS

Together, these results suggest that circulating SLAMF7+ Tfh1 cells, along with Tfh2 cells, play a pathologic role in IgG4 production in IgG4-RD.

Heterogenous Populations of Tissue-Resident CD8+ T Cells Are Generated in Response to Infection and Malignancy

Tissue-resident memory CD8+ T cells (Trm) provide host protection through continuous surveillance of non-lymphoid tissues. Using single-cell RNA-sequencing (scRNA-seq) and genetic reporter mice, we identified discrete lineages of intestinal antigen-specific CD8+ T cells, including a Blimp1hiId3lo tissue-resident effector cell population most prominent in the early phase of acute viral and bacterial infections and a molecularly distinct Blimp1loId3hi tissue-resident memory population that subsequently accumulated at later infection time points. These Trm populations exhibited distinct cytokine production, secondary memory potential, and transcriptional programs including differential roles for transcriptional regulators Blimp1, T-bet, Id2, and Id3 in supporting and maintaining intestinal Trm. Extending our analysis to malignant tissue, we also identified discrete populations of effector-like and memory-like CD8+ T cell populations with tissue-resident gene-expression signatures that shared features of terminally exhausted and progenitor-exhausted T cells, respectively. Our findings provide insight into the development and functional heterogeneity of Trm cells, which has implications for enhancing vaccination and immunotherapy approaches.

Multifaceted Role of PRDM Proteins in Human Cancer

The PR/SET domain family (PRDM) comprise a family of genes whose protein products share a conserved N-terminal PR [PRDI-BF1 (positive regulatory domain I-binding factor 1) and RIZ1 (retinoblastoma protein-interacting zinc finger gene 1)] homologous domain structurally and functionally similar to the catalytic SET [Su(var)3-9, enhancer-of-zeste and trithorax] domain of histone methyltransferases (HMTs). These genes are involved in epigenetic regulation of gene expression through their intrinsic HMTase activity or via interactions with other chromatin modifying enzymes. In this way they control a broad spectrum of biological processes, including proliferation and differentiation control, cell cycle progression, and maintenance of immune cell homeostasis. In cancer, tumor-specific dysfunctions of PRDM genes alter their expression by genetic and/or epigenetic modifications. A common characteristic of most PRDM genes is to encode for two main molecular variants with or without the PR domain. They are generated by either alternative splicing or alternative use of different promoters and play opposite roles, particularly in cancer where their imbalance can be often observed. In this scenario, PRDM proteins are involved in cancer onset, invasion, and metastasis and their altered expression is related to poor prognosis and clinical outcome. These functions strongly suggest their potential use in cancer management as diagnostic or prognostic tools and as new targets of therapeutic intervention.

Sex-specific adipose tissue imprinting of regulatory T cells

Adipose tissue is an energy store and a dynamic endocrine organ1,2. In particular, visceral adipose tissue (VAT) is critical for the regulation of systemic metabolism3,4. Impaired VAT function-for example, in obesity-is associated with insulin resistance and type 2 diabetes5,6. Regulatory T (Treg) cells that express the transcription factor FOXP3 are critical for limiting immune responses and suppressing tissue inflammation, including in the VAT7-9. Here we uncover pronounced sexual dimorphism in Treg cells in the VAT. Male VAT was enriched for Treg cells compared with female VAT, and Treg cells from male VAT were markedly different from their female counterparts in phenotype, transcriptional landscape and chromatin accessibility. Heightened inflammation in the male VAT facilitated the recruitment of Treg cells via the CCL2-CCR2 axis. Androgen regulated the differentiation of a unique IL-33-producing stromal cell population specific to the male VAT, which paralleled the local expansion of Treg cells. Sex hormones also regulated VAT inflammation, which shaped the transcriptional landscape of VAT-resident Treg cells in a BLIMP1 transcription factor-dependent manner. Overall, we find that sex-specific differences in Treg cells from VAT are determined by the tissue niche in a sex-hormone-dependent manner to limit adipose tissue inflammation.

Effect of 50-Hz Magnetic Fields on Serum IL-1β and IL-23 and Expression of BLIMP-1, XBP-1, and IRF-4

Investigations demonstrated that magnetic fields (MFs) change cytokine production and expression of some immune system genes. This alteration can affect the immune system function and may lead to some diseases. Therefore, this study investigated two important inflammatory cytokines, i.e., IL-1β and IL-23 at two phases of pre- and post-immunization of the immune system. In addition, the expressions of three important genes in the humoral immunity, i.e., B lymphocyte-induced maturation protein-1 (BLIMP-1), X-box-binding protein-1 (XBP-1), and interferon regulatory factor-4 (IRF-4) were evaluated at post-immunization phase. Eighty adult male rats were divided into four experimental groups and a control. The experimental groups were exposed to 50 -Hz MFs with magnetic flux densities of 1, 100, 500, and 2000 μT, 2 h/day for 2 months. The animals were injected by human serum albumin (100 μg/rat) on days 31, 44, and 58 of exposure. The cytokine levels in serum were measured with enzyme-linked immunosorbent assay (ELISA), and the expression of genes was evaluated with reverse transcription quantitative polymerase chain reaction (RT-qPCR). Serum IL-1β was decreased at pre-immunization phase after exposure to 1 and 100 μT of 50-Hz MFs. In contrast, serum IL-23 was increased at post-immunization phase in 100 μT group. No change was observed in serum IL-1β and IL-23 in each group at pre-immunization phase compared with post-immunization. Furthermore, exposure to 100 μT downregulated expression of BLIMP-1, XBP-1, and IRF-4. In conclusion, exposure to 50-Hz MFs may decrease inflammation at short time and increase it at longer time exposures. In addition, 50-Hz MF exposure may decrease the humoral immune responses. It seems that 50-Hz MFs cause more alteration in immune system function at lower densities (100 μT).

Regulatory T Cells Restrain Interleukin-2- and Blimp-1-Dependent Acquisition of Cytotoxic Function by CD4+ T Cells

In addition to helper and regulatory potential, CD4+ T cells also acquire cytotoxic activity marked by granzyme B (GzmB) expression and the ability to promote rejection of established tumors. Here, we examined the molecular and cellular mechanisms underpinning the differentiation of cytotoxic CD4+ T cells following immunotherapy. CD4+ transfer into lymphodepleted animals or regulatory T (Treg) cell depletion promoted GzmB expression by tumor-infiltrating CD4+, and this was prevented by interleukin-2 (IL-2) neutralization. Transcriptional analysis revealed a polyfunctional helper and cytotoxic phenotype characterized by the expression of the transcription factors T-bet and Blimp-1. While T-bet ablation restricted interferon-γ (IFN-γ) production, loss of Blimp-1 prevented GzmB expression in response to IL-2, suggesting two independent programs required for polyfunctionality of tumor-reactive CD4+ T cells. Our findings underscore the role of Treg cells, IL-2, and Blimp-1 in controlling the differentiation of cytotoxic CD4+ T cells and offer a pathway to enhancement of anti-tumor activity through their manipulation.

Blimp-1 is involved in B cell activation and maturation in Nile tilapia (Oreochromis niloticus)

B lymphocyte-induced maturation protein 1 (Blimp-1), a transcription factor containing zinc finger, is required and sufficient to trigger terminal differentiation of B cells in mammals. The Blimp-1 (OnBlimp-1) from Nile tilapia (Oreochromis niloticus) was identified and characterized its expression pattern during B cell activation and maturation. The cDNA of OnBlimp-1 open reading frame is 2547 bp encoding a protein of 848 amino acids and the predicted molecular weight is 93.36 kDa. OnBlimp-1 contains a SET domain and five ZnF_C2H2 domains, which shares high homology with that of other species. OnBlimp-1 transcription was detected in all examined tissues with high expression in the spleen (SPL). Analysis of sorted lymphocyte populations, including IgM⁺ and IgM^- cells from peripheral blood (PBL), SPL and anterior kidney (AK), indicated that the OnBlimp-1 transcription was highly expressed in the IgM⁺ B cells. Upon LPS stimulation, OnBlimp-1 expression was up-regulated in tissues of PBL, SPL and AK significantly. The expression of OnBlimp-1, as well as the secreted IgM, was significantly up-regulated in the SPL and AK leukocytes stimulated with anti-OnIgM monoclonal antibody and LPS in vitro, respectively. Above results suggest that OnBlimp-1, a cytokine regulating the terminal differentiation of activated B cells to antibody-secreting cells, is likely to play important roles in B cell activation and maturation in Nile tilapia.

Toxoplasma gondii: CD8 T Cells Cry for CD4 Help

Toxoplasma gondii, an apicomplexan parasite, is a pathogenic protozoan that can infect the central nervous system. In pregnant women, infection can result in congenital problems of the fetus, while in immunocompromised individual it can lead to severe neurological consequences. Although CD8 T cells play an important effector role in controlling the chronic infection, their maintenance is dependent on the critical help provided by CD4 T cells. In a recent study, we demonstrated that reactivation of the infection in chronically infected host is a consequence of CD8 T dysfunction caused by CD4 T cell exhaustion. Furthermore, treatment of chronically infected host with antigen-specific non-exhausted CD4 T cells can restore CD8 T cell functionality and prevent reactivation of the latent infection. The exhaustion status of CD4 T cells is mediated by the increased expression of the transcription factor BLIMP-1, and deletion of this molecule led to the restoration of CD4 T cell function, reversal of CD8 exhaustion and prevention of reactivation of the latent infection. In a recent study from our laboratory, we also observed an increased expression of miR146a levels by CD4 T cells from the chronically infected animals. Recent reports have demonstrated that microRNAs (especially miR146a) has a strong impact on the immune system of T. gondii infected host. Whether these molecules have any role in the BLIMP-1 up-regulation and dysfunctionality of these cells needs to be investigated.

Expression of the Plasma Cell Transcriptional Regulator Blimp-1 by Dark Zone Germinal Center B Cells During Periods of Proliferation

Long-lived plasma cells (PCs) develop in germinal centers (GCs) by the differentiation of affinity matured B cells. Antibody affinity maturation involves iterative rounds of somatic hypermutation in dark zones (DZs) and selection in light zones (LZs), however the details of where, when and how PC commitment occurs are not well-understood. Fate bifurcation at the time of selection is one possibility, with the very highest affinity GC B cells differentiating as an alternative to DZ re-entry. However, how this model fits with a need to also retain these clones in the response is not clear. Here, we show that subsets of bona fide DZ cells express the plasma cell master regulator Blimp-1 at low levels during periods of proliferation. Ex vivo culture experiments demonstrate that these cells are not yet committed to plasma cell differentiation but that they may be sensitized to go down that route. Contrary to models in which T cells directly select GC B cells to begin expressing Blimp-1, we found that expression of this transcriptional regulator occurred even when follicular helper T cells were ablated. We speculate that Blimp-1 may be induced during proliferation in the DZ, and that as such single selected cells might give rise to both GC and post-GC progeny.

PR/SET Domain Family and Cancer: Novel Insights from the Cancer Genome Atlas

The PR/SET domain gene family (PRDM) encodes 19 different transcription factors that share a subtype of the SET domain [Su(var)3-9, enhancer-of-zeste and trithorax] known as the PRDF1-RIZ (PR) homology domain. This domain, with its potential methyltransferase activity, is followed by a variable number of zinc-finger motifs, which likely mediate protein⁻protein, protein⁻RNA, or protein⁻DNA interactions. Intriguingly, almost all PRDM family members express different isoforms, which likely play opposite roles in oncogenesis. Remarkably, several studies have described alterations in most of the family members in malignancies. Here, to obtain a pan-cancer overview of the genomic and transcriptomic alterations of PRDM genes, we reanalyzed the Exome- and RNA-Seq public datasets available at The Cancer Genome Atlas portal. Overall, PRDM2, PRDM3/MECOM, PRDM9, PRDM16 and ZFPM2/FOG2 were the most mutated genes with pan-cancer frequencies of protein-affecting mutations higher than 1%. Moreover, we observed heterogeneity in the mutation frequencies of these genes across tumors, with cancer types also reaching a value of about 20% of mutated samples for a specific PRDM gene. Of note, ZFPM1/FOG1 mutations occurred in 50% of adrenocortical carcinoma patients and were localized in a hotspot region. These findings, together with OncodriveCLUST results, suggest it could be putatively considered a cancer driver gene in this malignancy. Finally, transcriptome analysis from RNA-Seq data of paired samples revealed that transcription of PRDMs was significantly altered in several tumors. Specifically, PRDM12 and PRDM13 were largely overexpressed in many cancers whereas PRDM16 and ZFPM2/FOG2 were often downregulated. Some of these findings were also confirmed by real-time-PCR on primary tumors.

A PAX5-OCT4-PRDM1 developmental switch specifies human primordial germ cells

Dysregulation of genetic pathways during human germ cell development leads to infertility. Here, we analysed bona fide human primordial germ cells (hPGCs) to probe the developmental genetics of human germ cell specification and differentiation. We examined the distribution of OCT4 occupancy in hPGCs relative to human embryonic stem cells (hESCs). We demonstrated that development, from pluripotent stem cells to germ cells, is driven by switching partners with OCT4 from SOX2 to PAX5 and PRDM1. Gain- and loss-of-function studies revealed that PAX5 encodes a critical regulator of hPGC development. Moreover, an epistasis analysis indicated that PAX5 acts upstream of OCT4 and PRDM1. The PAX5-OCT4-PRDM1 proteins form a core transcriptional network that activates germline and represses somatic programmes during human germ cell differentiation. These findings illustrate the power of combined genome editing, cell differentiation and engraftment for probing human developmental genetics that have historically been difficult to study.

Aiolos collaborates with Blimp-1 to regulate the survival of multiple myeloma cells

The transcriptional repressor B lymphocyte-induced maturation protein-1 (Blimp-1) has crucial roles in the control of plasma cell differentiation and in maintaining survival of plasma cells. However, how Blimp-1 ensures the survival of plasma cell malignancy, multiple myeloma (MM), has remained elusive. Here we identified Aiolos, an anti-apoptotic transcription factor of MM cells, as a Blimp-1-interacting protein by mass spectrometry. ChIP coupled with DNA microarray was used to profile the global binding of Aiolos and Blimp-1 to endogenous targets in MM cells, which revealed their co-binding to a large number of genes, including apoptosis-related genes. Accordingly, Blimp-1 and Aiolos regulate similar transcriptomes in MM cells. Analysis of the binding motifs for Blimp-1 and Aiolos uncovered a partial motif that was similar across sites for both proteins. Aiolos promotes the binding of Blimp-1 to target genes and thereby enhances Blimp-1-dependent transcriptional repression. Furthermore, treatment with an anti-MM agent, lenalidomide, caused ubiquitination and proteasomal degradation of Blimp-1, leading to the de-repression of a new Blimp-1 direct target, CULLIN 4A (CUL4A), and reduced Aiolos levels. Accordingly, lenalidomide-induced cell death was partially rescued by reintroduction of Blimp-1 or knockdown of CUL4A. Thus, we demonstrated the functional impacts and underlying mechanisms of the interaction between Aiolos and Blimp-1 in maintaining MM cell survival. We also showed that interruption of Blimp-1/Aiolos regulatory pathways contributes to lenalidomide-mediated anti-MM activity.