Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Investigation of archived formalin-fixed paraffin-embedded (FFPE) pancreatic tissue with whole-genome gene expression microarray.

ABSTRACT: In recent years, the use of FFPE tissue in gene expression microarray (GEM) studies has become a topic of increased interest, because pathology departments worldwide contain an invaluable source of biological disease-specific FFPE- tissue material. Thus far, some published studies on FFPE tissue consider the processed tissue amenable, whereas other studies assert that the tissue is not useful in GEM. In general, pancreatic tissue is known to contain large amounts of nucleases, leading to high turnover rates and degradation of RNA in the tissue. This characteristic, in combination with FFPE processing time and its effect on the tissue, does not make FFPE pancreatic tissue the obvious choice for GEM. The basis for using FFPE pancreatic tissue in RNA-based assays seems suboptimal. Previous GEM studies have used different FFPE tissue types, but GEM studies on FFPE pancreatic tissue have not been published. In most studies, the tissue was specially processed for use with GEMs. Here we demonstrate the usefulness of randomly archived FFPE pancreatic tissues for GEMs. For this purpose we included FFPE pancreatic tissue from patients with congenital hyperinsulinism or insulinoma; In these patients, pancreas resection is performed when medical treatment is not adequate to prevent hyperinsulinemic hypoglycemia or when patients do not respond to medical treatment. Although ribonuclease-rich, we obtained biologically relevant and disease-specific, significant genes; cancer-related genes and genes involved in a) the regulation of insulin secretion and synthesis, b) amino acid metabolism, and c) calcium ion homeostasis. This application may extend the possibilities of gene expression studies to many tissue types, especially in rare diseases, for which fresh frozen tissue is not readily available. A total of 15 samples were included in this study using a 58K chip. 29,134 human 60mer oligonucleotide targets were arrayed on the chips in duplicates. Each chip is hybridized with sample material (labelled with Cy5) from one patient and reference material (labelled with Cy3). Reference material contains pooled RNA from four different cancer cell lines; HeLa (cervical epithelium), SK-BR-3 (mammary gland), HT29 (colon) and A431 (skin) cells. Seven patients with congenital hyperinsulinism (five FFPE and two frozen samples), one patient with insulinoma and five controls were included in the study. Inclusion criteria for controls was that their cause of death was not pancreas-related. Samples were obtained from archived FFPE pancreatic material. The insulinoma sample was included in the study, because the biopsy was originally divided with one part being frozen and the other part being routinely formalin-fixed and paraffin-embedded. In the study we therefore include a frozen insulinoma sample and a FFPE insulinoma sample that was processed in duplicate.

ORGANISM(S): Homo sapiens

SUBMITTER: Nete Michelsen

PROVIDER: E-GEOD-32610 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:For the effectiveness of targeted immunotherapy, which is currently one of the most promising treatments for brain tumors, it is necessary to know specific tumor-associated antigens (TAA). This project aimed to validate the suitability of formalin-fixed and paraffin-embedded (FFPE) material instead of fresh-frozen material for RNA sequencing and downstream TAA identification. Purpose: Detect potential oligodendroglioma-associated antigens using both fresh-frozen and FFPE brain tissues; assess the suitability of the FFPE material for TAA identification. Results: A comparative analysis based on the RNA-seq of canine oligodendroglioma showed that formalin fixation of the samples had a significant effect on the RNA-seq library in terms of quality. Read distribution analysis showed that the FFPE samples contained fewer reads mapping to exonic regions and were enriched with reads mapped to introns and intergenic regions, while the fresh-frozen samples were mostly enriched in reads mapping to exons. Mismatch profile and SNVs calling analyses revealed some substitution artefacts present in the FFPE samples and absent in the corresponding fresh-frozen samples. However, according to the Principal Component Analysis, 36% of the variance between the samples could be explained by the types of conservation, while 43% of the variance could still be attributed to different expression profiles between oligodendroglioma and control conditions. A differential expression analysis of fresh-frozen oligodendroglioma versus fresh-frozen control samples identified 62 potential TAA strongly up-regulated in tumor tissue. The same analysis using the FFPE samples showed 80% of these genes (49/62) also to be differentially expressed. Comparative analysis showed good agreement between FFPE and fresh-frozen RNA-seq libraries in terms of the accuracy of gene expression measurements indicating that archived FFPE tissue can be used for identification of TAA candidates by RNA-seq providing a wealthy source of clinical samples for research. The following 10 genes encoding cell surface proteins have been identified by both approaches as potential TAA candidates based on their strong overexpression in oligodendrogliomas: PDGFRA, NOTCH1, DLL1, GPER1, TNR, IQGAP3, CD44, ERBB3, BCAS1 and ROR2. Future projects still need to investigate their suitability as TAA for targeted immunotherapy. Conclusion: Formalin fixation of the samples had a significant impact on the RNA-seq quality in terms of the accuracy of gene expression measurements, as well as the quality of the nucleotide sequences. Nevertheless, the comparative analysis showed good agreement between FFPE and fresh-frozen RNA-seq libraries.

Dataset Information

Investigation of archived formalin-fixed paraffin-embedded (FFPE) pancreatic tissue with whole-genome gene expression microarray.

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