The effect of maternal protein restriction during perinatal life on the inflammatory response in pediatric rats.

Fetal growth restriction can affect health outcomes in postnatal life. This study tested the hypothesis that the response to an inflammatory pulmonary insult is altered in pediatric fetal growth restricted rats. Using a low-protein diet during gestation and postnatal life, growth-restricted male and female rats and healthy control rats were exposed to an inflammatory insult via the intratracheal instillation of heat-killed bacteria. After 6 h, animal lungs were examined for lung inflammation and status of the surfactant system. The results showed that in response to an inflammatory insult, neutrophil infiltration was decreased in both male and female rats in the growth-restricted animals compared with the control rats. The amount of surfactant was increased in the growth-restricted animals compared with the control rats, regardless of the inflammatory insult. It is concluded that fetal growth restriction results in increased surfactant and altered neutrophil responses following pulmonary insult.

Comparative efficacy of glucocorticoid receptor agonists on Th2 cell function and attenuation by progesterone.

BACKGROUND: Corticosteroids (CS)s suppress cytokine production and induce apoptosis of inflammatory cells. Prednisone and dexamethasone are oral CSs prescribed for treating asthma exacerbations. While prednisone is more commonly prescribed, dexamethasone is long acting and a more potent glucocorticoid receptor (GR) agonist. It can be administered as a one or two dose regime, unlike the five to seven days required for prednisone, a feature that increases compliance. We compared the relative ability of these two oral CSs to suppress type 2 inflammation. Since progesterone has affinity for the GR and women are more likely to relapse following an asthma exacerbation, we assessed its influence on CS action. RESULTS: Dexamethasone suppressed the level of IL-5 and IL-13 mRNA within Th2 cells with ~ 10-fold higher potency than prednisolone (the active form of prednisone). Dexamethasone induced a higher proportion of apoptotic and dying cells than prednisolone, at all concentrations examined. Addition of progesterone reduced the capacity of both CS to drive cell death, though dexamethasone maintained significantly more killing activity. Progesterone blunted dexamethasone-induction of FKBP5 mRNA, indicating that the mechanism of action was by interference of the CS:GR complex. CONCLUSIONS: Dexamethasone is both more potent and effective than prednisolone in suppressing type 2 cytokine levels and mediating apoptosis. Progesterone attenuated these anti-inflammatory effects, indicating its potential influence on CS responses in vivo. Collectively, our data suggest that when oral CS is required, dexamethasone may be better able to control type 2 inflammation, eliminate Th2 cells and ultimately lead to improved long-term outcomes. Further research in asthmatics is needed.

A role for ATP Citrate Lyase in cell cycle regulation during myeloid differentiation.

Differentiation of myeloid progenitor cells into macrophages is accompanied by increased PU.1 concentration and increasing cell cycle length, culminating in cell cycle arrest. Induction of PU.1 expression in a cultured myeloid cell line expressing low PU.1 concentration results in decreased levels of mRNA encoding ATP-Citrate Lyase (ACL) and cell cycle arrest. ACL is an essential enzyme for generating acetyl-CoA, a key metabolite for the first step in fatty acid synthesis and for histone acetylation. We hypothesized that ACL may play a role in cell cycle regulation in the myeloid lineage. In this study, we found that acetyl-CoA or acetate supplementation was sufficient to rescue cell cycle progression in cultured BN cells treated with an ACL inhibitor or induced for PU.1 expression. Acetyl-CoA supplementation was also sufficient to rescue cell cycle progression in BN cells treated with a fatty acid synthase (FASN) inhibitor. We demonstrated that acetyl-CoA was utilized in both fatty acid synthesis and histone acetylation pathways to promote proliferation. Finally, we found that Acly mRNA transcript levels decrease during normal macrophage differentiation from bone marrow precursors. Our results suggest that regulation of ACL activity is a potentially important point of control for cell cycle regulation in the myeloid lineage.

Activation of Th2 cells downregulates CRTh2 through an NFAT1 mediated mechanism.

CRTh2 (encoded by PTGDR2) is a G-protein coupled receptor expressed by Th2 cells as well as eosinophils, basophils and innate lymphoid cells (ILC)2s. Activation of CRTh2, by its ligand prostaglandin (PG)D2, mediates production of type 2 cytokines (IL-4, IL-5 and IL-13), chemotaxis and inhibition of apoptosis. As such, the PGD2-CRTh2 pathway is considered important to the development and maintenance of allergic inflammation. Expression of CRTh2 is mediated by the transcription factor GATA3 during Th2 cell differentiation and within ILC2s. Other than this, relatively little is known regarding the cellular and molecular mechanisms regulating expression of CRTh2. Here, we show using primary human Th2 cells that activation (24hrs) through TCR crosslinking (αCD3/αCD28) reduced expression of both mRNA and surface levels of CRTh2 assessed by flow cytometry and qRT-PCR. This effect took more than 4 hours and expression was recovered following removal of activation. EMSA analysis revealed that GATA3 and NFAT1 can bind independently to overlapping sites within a CRTh2 promoter probe. NFAT1 over-expression resulted in loss of GATA3-mediated CRTh2 promoter activity, while inhibition of NFAT using a peptide inhibitor (VIVIT) coincided with recovery of CRTh2 expression. Collectively these data indicate that expression of CRTh2 is regulated through the competitive action of GATA3 and NFAT1. Though prolonged activation led to NFAT1-mediated downregulation, CRTh2 was re-expressed when stimulus was removed suggesting this is a dynamic mechanism and may play a role in PGD2-CRTh2 mediated allergic inflammation.

Lenalidomide modulates gene expression in human ABC-DLBCL cells by regulating IKAROS interaction with an intronic control region of SPIB.

Activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL) is associated with a poor prognosis compared with other DLBCL types and therefore represents a top priority for developing novel therapies. Lenalidomide, an immunomodulatory drug in trials for treatment of ABC-DLBCL, targets the transcription factor IKAROS for degradation by the cereblon E3 ubiquitin ligase complex. In this study, we investigated whether the gene encoding the transcription factor SPI-B is a target of IKAROS. Using cultured ABC-DLBCL cell lines, we found that high levels of SPI-B expression conferred resistance to lenalidomide. Lenalidomide treatment of ABC-DLBCL cells resulted in downregulation of SPIB at the level of transcription. SPIB was regulated directly by IKAROS through a binding site located in the first intron of the gene. Inhibition of IKAROS binding using CRISPR/Cas9-mediated transcriptional repression downregulated endogenous SPIB transcription. Finally, ectopic expression of IKAROS protected SPIB from downregulation. These results show that the mechanism of action of lenalidomide in ABC-DLBCL cells involves downregulation of SPIB transcription by cereblon-induced degradation of IKAROS. These results have implications for the design of synthetic lethal therapy for the treatment of ABC-DLBCL.

Coordination of Myeloid Differentiation with Reduced Cell Cycle Progression by PU.1 Induction of MicroRNAs Targeting Cell Cycle Regulators and Lipid Anabolism.

During macrophage development, myeloid progenitor cells undergo terminal differentiation coordinated with reduced cell cycle progression. Differentiation of macrophages from myeloid progenitors is accompanied by increased expression of the E26 transformation-specific transcription factor PU.1. Reduced PU.1 expression leads to increased proliferation and impaired differentiation of myeloid progenitor cells. It is not understood how PU.1 coordinates macrophage differentiation with reduced cell cycle progression. In this study, we utilized cultured PU.1-inducible myeloid cells to perform genome-wide chromatin immunoprecipitation sequencing (ChIP-seq) analysis coupled with gene expression analysis to determine targets of PU.1 that may be involved in regulating cell cycle progression. We found that genes encoding cell cycle regulators and enzymes involved in lipid anabolism were directly and inducibly bound by PU.1 although their steady-state mRNA transcript levels were reduced. Inhibition of lipid anabolism was sufficient to reduce cell cycle progression in these cells. Induction of PU.1 reduced expression of E2f1, an important activator of genes involved in cell cycle and lipid anabolism, indirectly through microRNA 223. Next-generation sequencing identified microRNAs validated as targeting cell cycle and lipid anabolism for downregulation. These results suggest that PU.1 coordinates cell cycle progression with differentiation through induction of microRNAs targeting cell cycle regulators and lipid anabolism.

PU.1 Regulates Ig Light Chain Transcription and Rearrangement in Pre-B Cells during B Cell Development.

B cell development and Ig rearrangement are governed by cell type- and developmental stage-specific transcription factors. PU.1 and Spi-B are E26-transformation-specific transcription factors that are critical for B cell differentiation. To determine whether PU.1 and Spi-B are required for B cell development in the bone marrow, Spi1 (encoding PU.1) was conditionally deleted in B cells by Cre recombinase under control of the Mb1 gene in Spib (encoding Spi-B)-deficient mice. Combined deletion of Spi1 and Spib resulted in a lack of mature B cells in the spleen and a block in B cell development in the bone marrow at the small pre-B cell stage. To determine target genes of PU.1 that could explain this block, we applied a gain-of-function approach using a PU.1/Spi-B-deficient pro-B cell line in which PU.1 can be induced by doxycycline. PU.1-induced genes were identified by integration of chromatin immunoprecipitation-sequencing and RNA-sequencing data. We found that PU.1 interacted with multiple sites in the Igκ locus, including Vκ promoters and regions located downstream of Vκ second exons. Induction of PU.1 induced Igκ transcription and rearrangement. Upregulation of Igκ transcription was impaired in small pre-B cells from PU.1/Spi-B-deficient bone marrow. These studies reveal an important role for PU.1 in the regulation of Igκ transcription and rearrangement and a requirement for PU.1 and Spi-B in B cell development.

Nfkb1 activation by the E26 transformation-specific transcription factors PU.1 and Spi-B promotes Toll-like receptor-mediated splenic B cell proliferation.

Generation of antibodies against T-independent and T-dependent antigens requires Toll-like receptor (TLR) engagement on B cells for efficient responses. However, the regulation of TLR expression and responses in B cells is not well understood. PU.1 and Spi-B (encoded by Sfpi1 and Spib, respectively) are transcription factors of the E26 transformation-specific (ETS) family and are important for B cell development and function. It was found that B cells from mice knocked out for Spi-B and heterozygous for PU.1 (Sfpi1(+/-) Spib(-/-) [PUB] mice) proliferated poorly in response to TLR ligands compared to wild-type (WT) B cells. The NF-κB family member p50 (encoded by Nfkb1) is required for lipopolysaccharide (LPS) responsiveness in mice. PUB B cells expressed reduced Nfkb1 mRNA transcripts and p50 protein. The Nfkb1 promoter was regulated directly by PU.1 and Spi-B, as shown by reporter assays and chromatin immunoprecipitation analysis. Occupancy of the Nfkb1 promoter by PU.1 was reduced in PUB B cells compared to that in WT B cells. Finally, infection of PUB B cells with a retroviral vector encoding p50 substantially restored proliferation in response to LPS. We conclude that Nfkb1 transcriptional activation by PU.1 and Spi-B promotes TLR-mediated B cell proliferation.

Identification of a negative regulatory role for spi-C in the murine B cell lineage.

Spi-C is an E26 transformation-specific family transcription factor that is highly related to PU.1 and Spi-B. Spi-C is expressed in developing B cells, but its function in B cell development and function is not well characterized. To determine whether Spi-C functions as a negative regulator of Spi-B (encoded by Spib), mice were generated that were germline knockout for Spib and heterozygous for Spic (Spib(-/-)Spic(+/-)). Interestingly, loss of one Spic allele substantially rescued B cell frequencies and absolute numbers in Spib(-/-) mouse spleens. Spib(-/-)Spic(+/-) B cells had restored proliferation compared with Spib(-/-) B cells in response to anti-IgM or LPS stimulation. Investigation of a potential mechanism for the Spib(-/-)Spic(+/-) phenotype revealed that steady-state levels of Nfkb1, encoding p50, were elevated in Spib(-/-)Spic(+/-) B cells compared with Spib(-/-) B cells. Spi-B was shown to directly activate the Nfkb1 gene, whereas Spi-C was shown to repress this gene. These results indicate a novel role for Spi-C as a negative regulator of B cell development and function.

Genome-wide comparison of PU.1 and Spi-B binding sites in a mouse B lymphoma cell line.

BACKGROUND: Spi-B and PU.1 are highly related members of the E26-transformation-specific (ETS) family of transcription factors that have similar, but not identical, roles in B cell development. PU.1 and Spi-B are both expressed in B cells, and have been demonstrated to redundantly activate transcription of genes required for B cell differentiation and function. It was hypothesized that Spi-B and PU.1 occupy a similar set of regions within the genome of a B lymphoma cell line. RESULTS: To compare binding regions of Spi-B and PU.1, murine WEHI-279 lymphoma cells were infected with retroviral vectors encoding 3XFLAG-tagged PU.1 or Spi-B. Anti-FLAG chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) was performed. Analysis for high-stringency enriched genomic regions demonstrated that PU.1 occupied 4528 regions and Spi-B occupied 3360 regions. The majority of regions occupied by Spi-B were also occupied by PU.1. Regions bound by Spi-B and PU.1 were frequently located immediately upstream of genes associated with immune response and activation of B cells. Motif-finding revealed that both transcription factors were predominantly located at the ETS core domain (GGAA), however, other unique motifs were identified when examining regions associated with only one of the two factors. Motifs associated with unique PU.1 binding included POU2F2, while unique motifs in the Spi-B regions contained a combined ETS-IRF motif. CONCLUSIONS: Our results suggest that complementary biological functions of PU.1 and Spi-B may be explained by their interaction with a similar set of regions in the genome of B cells. However, sites uniquely occupied by PU.1 or Spi-B provide insight into their unique functions.

PU.1 opposes IL-7-dependent proliferation of developing B cells with involvement of the direct target gene bruton tyrosine kinase.

Deletion of genes encoding the E26 transformation-specific transcription factors PU.1 and Spi-B in B cells (CD19-CreΔPB mice) leads to impaired B cell development, followed by B cell acute lymphoblastic leukemia at 100% incidence and with a median survival of 21 wk. However, little is known about the target genes that explain leukemogenesis in these mice. In this study we found that immature B cells were altered in frequency in the bone marrow of preleukemic CD19-CreΔPB mice. Enriched pro-B cells from CD19-CreΔPB mice induced disease upon transplantation, suggesting that these were leukemia-initiating cells. Bone marrow cells from preleukemic CD19-CreΔPB mice had increased responsiveness to IL-7 and could proliferate indefinitely in response to this cytokine. Bruton tyrosine kinase (BTK), a negative regulator of IL-7 signaling, was reduced in preleukemic and leukemic CD19-CreΔPB cells compared with controls. Induction of PU.1 expression in cultured CD19-CreΔPB pro-B cell lines induced Btk expression, followed by reduced STAT5 phosphorylation and early apoptosis. PU.1 and Spi-B regulated Btk directly as shown by chromatin immunoprecipitation analysis. Ectopic expression of BTK was sufficient to induce apoptosis in cultured pro-B cells. In summary, these results suggest that PU.1 and Spi-B activate Btk to oppose IL-7 responsiveness in developing B cells.

Targeted loss of the ATR-X syndrome protein in the limb mesenchyme of mice causes brachydactyly.

ATR-X syndrome is a rare genetic disorder caused by mutations in the ATRX gene. Affected individuals are cognitively impaired and display a variety of developmental abnormalities, including skeletal deformities. To investigate the function of ATRX during skeletal development, we selectively deleted the gene in the developing forelimb mesenchyme of mice. The absence of ATRX in the limb mesenchyme resulted in shorter digits, or brachydactyly, a defect also observed in a subset of ATR-X patients. This phenotype persisted until adulthood, causing reduced grip strength and altered gait in mutant mice. Examination of the embryonic ATRX-null forelimbs revealed a significant increase in apoptotic cell death, which could explain the reduced digit length. In addition, staining for the DNA damage markers γ-histone 2A family member X (γ-H2AX) and 53BP1 demonstrated a significant increase in the number of cells with DNA damage in the embryonic ATRX-null forepaw. Strikingly, only one large bright DNA damage event was observed per nucleus in proliferating cells. These large γ-H2AX foci were located in close proximity to the nuclear lamina and remained largely unresolved after cell differentiation. In addition, ATRX-depleted forelimb mesenchymal cells did not exhibit hypersensitivity to DNA fork-stalling compounds, suggesting that the nature as well as the response to DNA damage incurred by loss of ATRX in the developing limb fundamentally differs from other tissues. Our data suggest that DNA damage-induced apoptosis is a novel cellular mechanism underlying brachydactyly that might be relevant to additional skeletal syndromes.

Atrx deficiency induces telomere dysfunction, endocrine defects, and reduced life span.

Human ATRX mutations are associated with cognitive deficits, developmental abnormalities, and cancer. We show that the Atrx-null embryonic mouse brain accumulates replicative damage at telomeres and pericentromeric heterochromatin, which is exacerbated by loss of p53 and linked to ATM activation. ATRX-deficient neuroprogenitors exhibited higher incidence of telomere fusions and increased sensitivity to replication stress-inducing drugs. Treatment of Atrx-null neuroprogenitors with the G-quadruplex (G4) ligand telomestatin increased DNA damage, indicating that ATRX likely aids in the replication of telomeric G4-DNA structures. Unexpectedly, mutant mice displayed reduced growth, shortened life span, lordokyphosis, cataracts, heart enlargement, and hypoglycemia, as well as reduction of mineral bone density, trabecular bone content, and subcutaneous fat. We show that a subset of these defects can be attributed to loss of ATRX in the embryonic anterior pituitary that resulted in low circulating levels of thyroxine and IGF-1. Our findings suggest that loss of ATRX increases DNA damage locally in the forebrain and anterior pituitary and causes tissue attrition and other systemic defects similar to those seen in aging.

Loss of ATRX does not confer susceptibility to osteoarthritis.

The chromatin remodelling protein ATRX is associated with the rare genetic disorder ATR-X syndrome. This syndrome includes developmental delay, cognitive impairment, and a variety of skeletal deformities. ATRX plays a role in several basic chromatin-mediated cellular events including DNA replication, telomere stability, gene transcription, and chromosome congression and cohesion during cell division. We have used a loss-of-function approach to directly investigate the role of Atrx in the adult skeleton in three different models of selective Atrx loss. We specifically targeted deletion of Atrx to the forelimb mesenchyme, to cartilage and to bone-forming osteoblasts. We previously demonstrated that loss of ATRX in forelimb mesenchyme causes brachydactyly while deletion in chondrocytes had minimal effects during development. We now show that targeted deletion of Atrx in osteoblasts causes minor dwarfism but does not recapitulate most of the skeletal phenotypes seen in ATR-X syndrome patients. In adult mice from all three models, we find that joints lacking Atrx are not more susceptible to osteoarthritis, as determined by OARSI scoring and immunohistochemistry. These results indicate that while ATRX plays limited roles during early stages of skeletal development, deficiency of the protein in adult tissues does not confer susceptibility to osteoarthritis.

Loss of ATRX in chondrocytes has minimal effects on skeletal development.

BACKGROUND: Mutations in the human ATRX gene cause developmental defects, including skeletal deformities and dwarfism. ATRX encodes a chromatin remodeling protein, however the role of ATRX in skeletal development is currently unknown. METHODOLOGY/PRINCIPAL FINDINGS: We induced Atrx deletion in mouse cartilage using the Cre-loxP system, with Cre expression driven by the collagen II (Col2a1) promoter. Growth rate, body size and weight, and long bone length did not differ in Atrx(Col2cre) mice compared to control littermates. Histological analyses of the growth plate did not reveal any differences between control and mutant mice. Expression patterns of Sox9, a transcription factor required for cartilage morphogenesis, and p57, a marker of cell cycle arrest and hypertrophic chondrocyte differentiation, was unaffected. However, loss of ATRX in cartilage led to a delay in the ossification of the hips in some mice. We also observed hindlimb polydactily in one out of 61 mutants. CONCLUSIONS/SIGNIFICANCE: These findings indicate that ATRX is not directly required for development or growth of cartilage in the mouse, suggesting that the short stature in ATR-X patients is caused by defects in cartilage-extrinsic mechanisms.

Transcriptional regulators of chondrocyte hypertrophy.

Coordinated transition from proliferation to terminal differentiation and hypertrophy of growth plate chondrocytes is required for normal growth of endochondral bones and thus determines final height in humans. Over the last decades, transcription factors of the Sox and Runx families have been shown to be the central regulators of this process. More recently, numerous additional transcription factors have been identified as positive or negative regulators of chondrocyte hypertrophy, such as Shox/Shox2, Dlx5, and MEF2C. These factors do not only control skeletal development and growth, but might also participate in ectopic chondrocyte hypertrophy during the pathogenesis of osteoarthritis. This review focuses on recent advances in our understanding of the transcriptional regulation of chondrocyte hypertrophy, with particular attention to genes that have only recently been implicated in cartilage development or received little attention so far.