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Defining the Human Brain Proteome Using Transcriptomics and Antibody-Based Profiling with a Focus on the Cerebral Cortex
KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.ORCID iD: 0000-0003-0198-7137
KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.ORCID iD: 0000-0002-0056-1313
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2015 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 6, article id UNSP e0130028Article in journal (Refereed) Published
Abstract [en]

The mammalian brain is a complex organ composed of many specialized cells, harboring sets of both common, widely distributed, as well as specialized and discretely localized proteins. Here we focus on the human brain, utilizing transcriptomics and public available Human Protein Atlas (HPA) data to analyze brain-enriched (frontal cortex) polyadenylated messenger RNA and long non-coding RNA and generate a genome-wide draft of global and cellular expression patterns of the brain. Based on transcriptomics analysis of altogether 27 tissues, we have estimated that approximately 3% (n=571) of all protein coding genes and 13% (n=87) of the long non-coding genes expressed in the human brain are enriched, having at least five times higher expression levels in brain as compared to any of the other analyzed peripheral tissues. Based on gene ontology analysis and detailed annotation using antibody-based tissue micro array analysis of the corresponding proteins, we found the majority of brain-enriched protein coding genes to be expressed in astrocytes, oligodendrocytes or in neurons with molecular properties linked to synaptic transmission and brain development. Detailed analysis of the transcripts and the genetic landscape of brainenriched coding and non-coding genes revealed brain-enriched splice variants. Several clusters of neighboring brain-enriched genes were also identified, suggesting regulation of gene expression on the chromatin level. This multi-angle approach uncovered the brainenriched transcriptome and linked genes to cell types and functions, providing novel insights into the molecular foundation of this highly specialized organ.

Place, publisher, year, edition, pages
2015. Vol. 10, no 6, article id UNSP e0130028
National Category
Medical Biotechnology
Identifiers
URN: urn:nbn:se:kth:diva-170972DOI: 10.1371/journal.pone.0130028ISI: 000356329900125PubMedID: 26076492OAI: oai:DiVA.org:kth-170972DiVA, id: diva2:841435
Note

QC 20150713

Available from: 2015-07-13 Created: 2015-07-13 Last updated: 2018-10-17Bibliographically approved
In thesis
1. Towards a deeper understanding of the human brain
Open this publication in new window or tab >>Towards a deeper understanding of the human brain
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Identifying the proteome variation in different parts of the body provides fundamental molecular details, enabling further findings and mapping of tissue specific proteins. By combining quantitative transcriptomics with qualitative antibody based proteomics, the Human Protein Atlas (HPA) project aims to protein profile each human protein-coding gene. Genes with varying expression levels in the different tissue types are categorized as tissue elevated in one tissue compared to others, thus connecting genes to potential tissue specific functions. This thesis focuses on the most complex organ in the human body, the brain. With its billions of neurons specifically organized and interconnected, the ability of not only controlling the body but also responsible for higher cognitive functions, the brain is still not fully understood.

In my search for brain important proteins, genes were classified at different stages based on expression levels. In Paper I and II the transcriptome of cerebral cortex was compared with peripheral organs to classify genes with elevated expression in the brain. Brain expression information was expanded by including external data (GTEx and FANTOM5) into the analysis, in Paper III. Thereafter, in Paper IV, the three datasets (HPA, GTEx and FANTOM5) were aligned and combined, enabling a consensus classification with an improved representation of the brain complexity. The most recent classification provided whole body gene expression profiles and out of the 19,670 protein-coding genes, 2,501 were expressed at elevated levels in the brain compared to the other tissue types. Twelve individual regions represented the brain as an organ, and were further analyzed and compared for regional classification of gene expression. One thousand genes showed regional variation in expression level, thus classified as regionally elevated within the brain. Interestingly, less than 500 of the genes classified as brain elevated on the whole body level, and were also regionally elevated in the brain. Many genes with regionally variable expression within the brain showed higher expression in a peripheral organ than in the brain when comparing whole body expression. Based on elevated expression in the brain or brain regions, more than 3,000 genes were suggested to be of high importance to the brain.

In addition, this high-throughput approach to combine transcriptomics and protein profiles in tissues and cells further generated new knowledge in several different other aspects: better understanding of uncharacterized and “missing proteins” (Paper III), validation of an antibody improving classification of pituitary adenoma (Paper V) and in Paper VI the possibility to explore cancer specific expression in relation to clinical data and normal tissue expression.

There are multiple diseases of the brain that are poorly understood on both a cellular and molecular level. While my work mainly focused on identifying and understanding the molecular organization of the normal brain, the ultimate goal of mapping and studying the normal expression baseline is to understand the molecular aspects of disease and identify ways to prevent, treat and cure diseases.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 83
Series
TRITA-CBH-FOU ; 50
Keywords
Brain, organization, RNA, classification, mapping, proteins, antibodies
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Research subject
Biotechnology
Identifiers
urn:nbn:se:kth:diva-235670 (URN)978-91-7729-983-7 (ISBN)
Public defence
2018-11-15, Gard aulan, Nobels väg 18, Solna, 10:00 (English)
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Supervisors
Note

QC 20181018

Available from: 2018-10-18 Created: 2018-10-17 Last updated: 2018-10-18Bibliographically approved

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Fagerberg, LinnHäggmark, AnnaUhlén, Mathias

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