Unknown,Transcriptomics,Genomics,Proteomics

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Distinct mechanisms of inadequate erythropoiesis induced by tumor necrosis factor alpha or malarial pigment

ABSTRACT: The role of infection in erythropoietic dysfunction is poorly understood. In children with P. falciparum malaria, the by-product of hemoglobin digestion in infected red cells (hemozoin) is associated with the severity of anemia which is independent of circulating levels of the inflammatory cytokine tumor necrosis alpha (TNF-alpha). To gain insight into the common and specific effects of TNF-alpha and hemozoin on erythropoiesis, we studied the gene expression profile of purified primary erythroid cultures exposed to either TNF-alpha (10ng/ml) or to hemozoin (12.5microgram/ml heme units) for 24 hours. Perturbed gene function was assessed using co-annotation of associated gene ontologies and expression of selected genes representative of the profile observed was confirmed by real time PCR (rtPCR). The changes in gene expression induced by each agent were largely distinct; many of the genes significantly modulated by TNF-alpha were not affected by hemozoin. The genes modulated by TNF-alpha were significantly enriched for those encoding proteins involved in the control of type 1 interferon signalling and the immune response to viral infection. In contrast, genes induced by hemozoin were significantly enriched for functional roles in regulation of transcription and apoptosis. Further analyses by rtPCR revealed that hemozoin increases expression of transcription factors that form part of the integrated stress response which is accompanied by reduced expression of genes involved in DNA repair. This study confirms that hemozoin induces cellular stress on erythroblasts that is additional to and distinct from responses to inflammatory cytokines and identifies new genes that may be involved in the pathogenesis of severe malarial anemia. More generally the respective transcription profiles highlight the varied mechanisms through which erythropoiesis may be disrupted during infectious disease. Erythroblasts derived from PBMCs were enriched to 97% purity for proerythroblast and intermediate/normoblast phases of differentiation using magnetic bead isolation. There were three treatment groups: media, P.falciparum hemozoin (12.5 microgram /ml hematin units) and tumour necrosis factor alpha(10ng/ml). Total RNA using 7.5 x105 cells per treatment from one donor was extracted using Trizol. Highly significant gene ontological findings (where p> x10^-17 but < x10^-7) were confirmed by quantitative PCR.

ORGANISM(S): Homo sapiens

SUBMITTER: Alison Merryweather-Clarke

PROVIDER: E-GEOD-65577 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Background: Developmental stage-specific globin expression is a complex phenomenon that involves both trans- and cis-acting elements. While functional analyses ensuing recent genome-wide association studies have highlighted the important roles of trans-factors in regulating hemoglobin expression, these factors can not exert their functions without permissive chromatin domains. By transferring thoroughly profiled beta globin locus of undifferentiated human embryonic stem cells (hESCs) or hESC-derived erythroid cells into an adult erythroid transcriptional environment, we studied the influences of histone modifications on the globin expression decision within a fixed transcriptional environment. Shortly after the locus transfer, embryonic epsilon globin was not expressed regardless of original chromatin states, whereas fetal gamma globin was either expressed or not activated depending on original chromatin configurations, and the originally silent adult beta globin either remained silent or became activated depending on the expression status of gamma globin. These data suggest the interplay between transcriptional environment and the chromatin modifications determine the outcome of globin expression. As the ultimate silencing of gamma globin from hESC-derived erythroid cells in the adult transcriptional environment occurred after months-long cell proliferation, our work also has implications on attempts to generate beta globin expressing erythroid cells from hESCs or induced pluripotent stem cells. hESC line H1 (NIH code WA01, WiCell, Madison, WI) and adeno-associated virus (AAV)-targeted lines, were maintained and differentiated as previously described.12 (Details can be found in the supplemental information.) The expression of stem cell markers including SSEA-3, SSEA-4, TRA-1-60, and TRA-1-61 was detected by flow cytometry. To determine whether AAV-targeted lines retained their hematopoietic differentiation potential, confluent hESCs were harvested off the feeder layers and transferred to ultra-low attachment plates to allow for the formation of embryoid bodies (EBs). Day-14 EBs were dissociated into single cells and the expression of surface markers including CD34, CD71, CD45, CD31, CD41 and glycophorin-A was determined by flow cytometry. To induce erythroid differentiation, day-7 EBs were made into single cell suspension and cultured in erythroid-inducing medium for 14 days. Primers for real time PCR analysis of beta locus globin mRNA expression are provided in the supplemental information.

Project description:Understanding the pattern of gene expression and identifying the specific genes expressed during erythropoiesis is crucial for a synthesis of erythroid developmental biology. Here we have isolated four distinct populations of erythroblasts at successive erythropoietin-dependent stages of erythropoiesis including the terminal, pyknotic stage. The transcriptome has been determined using Affymetrix arrays. First, we show that cells sorted by surface expression profile express not only significantly fewer genes than unsorted cells, but also significantly more differences in the expression levels of particular genes between stages than unsorted cells, demonstrating the importance of working with defined cell populations to identify lineage and temporally-specific patterns of gene expression. Second, using standard software and matched filtering we identify eleven differentially regulated genes and one continuously expressed gene previously undetected in erythroid expression studies with unknown roles in erythropoiesis (CA3, CALB1, CTSL2, FKBP1B, GSDMB, ITLN1, LIN7B, RRAD, RUNDC3A, UNQ1887, ZNF805, MYL12B). Finally, using transcription factor binding site analysis we identify potential transcription factors that may regulate gene expression during terminal erythropoiesis. Our stringent lists of differentially regulated and continuously expressed transcripts are a resource for functional studies of erythropoietic protein function and gene regulation. PBMC-derived erythroblasts grown in vitro were harvested at the CFU-E, Pro-E, Int-E and Late-E stages and FACS sorted based on expression of cell surface markers. RNA was extracted from those populations which met rigorous specifications of time cultured in the presence of erythropoietin, morphology and CD36, CD71 and CD235a expression. For each stage, 3 chips were hybridised, each representing a pool of 4 different samples. In addition to these 12 chips, one chip representing a pool of RNA extracted from unsorted cells at each stages was also hybridised.

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Distinct mechanisms of inadequate erythropoiesis induced by tumor necrosis factor alpha or malarial pigment

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