Unknown,Transcriptomics,Genomics,Proteomics

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Gene Expression Profiling of Human Whole Blood Samples with the Illumina WG-DASL Assay

ABSTRACT: Microarray-based gene expression analysis of peripheral whole blood is a common strategy in the development of clinically relevant biomarker panels for a variety of human diseases. However, the results of such an analysis are often plagued by decreased sensitivity and reliability due to the effects of relatively high levels of globin mRNA in whole blood. Globin reduction assays have been shown to overcome such effects, but they require large amounts of total RNA and may induce distinct gene expression profiles. The Illumina whole-genome DASL (WG-DASL) assay can detect gene expression levels using partially degraded RNA samples and has the potential to detect rare transcripts present in highly heterogeneous whole blood samples without the need for globin reduction. We therefore assessed the utility of the WG-DASL assay in the analysis of peripheral whole blood gene expression profiles. We find that gene expression detection is significantly increased with the use of WG-DASL compared to the standard in vitro transcription-based direct hybridization (IVT), while globin-probe-negative WG-DASL did not exhibit significant improvements over globin-probe-positive WG-DASL. Globin reduction increases the detection sensitivity and reliability of both WG-DASL and IVT with little effect on raw intensity correlations: raw intensity correlations between total RNA and globin-reduced RNA were 0.970 for IVT and 0.981 for WG-DASL. Overall, the detection sensitivity of the WG-DASL assay is higher than the IVT-based direct hybridization assay, with or without globin reduction, and should be considered in conjunction with globin reduction methods for future blood-based gene expression studies. Peripheral whole blood samples were collected from eight human donors in PAXGene tubes. RNA was isolated after freezing and storage, and then prepared for gene expression analysis using the Illumina Human-Ref8 v3.0 BeadChip. Alpha and beta globin were reduced from a portion of the total RNA using the GLOBINclear assay (Ambion, Austin, TX, USA). Two methods of microarray target preparation were examined: Illumina IVT-based direct hybridization (IVT) and Illumina Whole-Genome DASL (WG-DASL). Two DASL Assay Oligo pools (DAP) were utilized for DASL target preparation: the DASL Assay Oligo Pool with globin probes (DAP +) and the DASL Asssay Oligo Pool without globin probes (DAP-).

ORGANISM(S): Homo sapiens

SUBMITTER: Mary Winn

PROVIDER: E-GEOD-28064 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Room temperature whole blood mRNA stabilization procedures, such as the PAX gene system, are critical for the application of transcriptional analysis to population-based clinical studies. Global transcriptome analysis of whole blood RNA using microarrays has proven to be challenging due to the high abundance of globin transcripts that constitute 70% of whole blood mRNA in the blood. This is a particular problem in patients with sickle-cell disease, secondary to the high abundance of globin-expressing nucleated red blood cells and reticulocytes in the circulation . In order to more accurately measure the steady state whole blood transcriptome in sickle-cell patients, we evaluated the efficacy of reducing globin transcripts in PAXgene stabilized RNA samples for genome-wide transcriptome analyses using oligonucleotide arrays. We demonstrate here by both microarrays and Q-PCR that the globin mRNA depletion method resulted in 55-65 fold reduction in globin transcripts in whole blood collected from healthy volunteers and sickle-cell disease patients. This led to an improvement in microarray data quality with increased detection rate of expressed genes and improved overlap with the expression signatures of isolated peripheral blood mononuclear (PBMC) preparations. The differentially modulated genes from the globin depleted samples had a higher correlation coefficient to the 112 genes identified to be significantly altered in our previous study on sickle-cell disease using PBMC preparations. Additionally, the analysis of differences between the whole blood transcriptome and PBMC transcriptome reveals important erythrocyte genes that participate in sickle-cell pathogenesis and compensation. The combination of globin mRNA reduction after whole-blood RNA stabilization represents a robust clinical research methodology for the discovery of biomarkers for hematologic diseases and in multicenter clinical trials investigating a wide range of nonhematologic disorders where fractionation of cell types is impracticable. Keywords: Microarrays, PAXgene, globin reduction, whole blood, PBMC

Project description:Whole blood rather than purified peripheral blood mononuclear cells is likely to become the prime tissue using expression microarrays for disease predication or prognosis however excess of globin mRNA may reduce probe detection sensitivity. In our study, we assessed whether whole-blood or globin-reduced RNA gives the most robust and sensitive results to detect small gene expression changes in response to hormone replacement therapy exposure. Each sample (N = 12) were hybridized according to 3 different protocols: no globin reduction (controls), globin reduction using peptid nucleic acids (PNA) and using magnetic beads in the GlobinClear kit from Ambion. Finally, 7 and 4 technical replicates were conducted in no globin reduction and PNA groups, respectively. Both globin reduction approaches were mostly efficient at reducing globin RNA from cRNA. Samples processed by GlobinClear kit gave a very distinct gene expression profiles from the controls while samples processed with PNA gave an intermediary profile closest to the non globin reduction group with a slight increased sensitivity of transcript detection but a loss of reproducibility. Overall, no sign of higher sensitivity in detection of gene expression changes followed by hormone exposure was observed after globin reduction which was therefore judged not beneficial. Keywords: Groups comparaison To assess effect of globin reduction protocols on gene expression from whole-blood, we selected 12 postmenopausal women (6 HRT users and 6 non-HRT users) who were not using other medication than HRT at the time of blood sampling and in order to cover a wide body mass index (BMI) range in both HRT and non HRT users. The samples were also selected to contain the highest concentration of total extracted RNA. Each sample was hybridized according to 3 different protocols: no globin reduction (controls), globin reduction using PNAs, globin reduction using magnetic beads in the GlobinClear™ kit from Ambion. The reproducibility of the globin reduction method compared to the non globin reduction approach was investigated for the PNA method only since this method was the most effective and specific. We planned to conduct 7 technical replicates in each group (i.e. no globin reduction and PNA groups). During amplification process with PNA, 4 samples failed to reverse transcript long fragment of mRNA certainly due to inhibitory contamination and these arrays were therefore excluded from our analyses. One sample (sample 34) was amplified with PNA twice the same day to study technical reproducibility without amplification date effect. Finally, a total of 47 arrays were conducted including 7 and 4 technical replicates in no globin reduction and PNA group, respectively.

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Gene Expression Profiling of Human Whole Blood Samples with the Illumina WG-DASL Assay

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