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The impact of cytokines, stress, and the cellular sex on the proteome of cardiac and vascular cell models

  • Cardiovascular diseases are the most common cause of death in industrial nations. The basis of these diseases is a dysfunction in the interaction between the cells the heart is composed of. The main types of cells making up the human heart are cardiomyocytes that build the myocardium and provide the contraction properties, endothelial cells that delimit the blood flowing through the inner chambers and coronary arteries from the myocardial tissue, and fibroblasts, which build the connective tissue. A common process in the development of cardiovascular diseases is the formation of fibrosis due to injury of the endothelium and subsequent infiltration of the cardiac tissue by immune cells, and inflammatory agents like cytokines. Cytokines exert different functions in cardiac cells. Tumor necrosis factor α (TNFα) is an inducer of apoptosis. Transforming growth factor ß (TGFß) is known for activation of proliferation. Other cytokines like C-X-C motif chemokine 11 (CXCL11), interleukin-6 (IL-6), or brain-derived neurotrophic factor (BDNF) have not yet been investigated or their impact on such cells is unknown. Eventually, however, fibrotic scar tissue arises from the transition from fibroblasts to myofibroblasts leading to a stiffening of the cardiac muscle and impaired pump function. In order to prevent the occurrence of these events the balance of proliferation, migration, and differentiation of cardiac cells needs to be controlled very delicately. The mechanisms controlling these interactions are still not well understood, which is why this work aimed at the elucidation of molecular mechanisms within the three main cell types that might play a role in the regulation of cardiac function. A proteomic approach using mass spectrometry was used to identify alterations in protein levels that could provide hints about the involved pathways and find new players as candidates for more detailed investigation. Initially, the proteomic composition of HL-1 cardiomyocytes, L929 fibroblasts, and human umbilical vein endothelial cells (HUVECs) that were cultivated in standard growth conditions without stress was investigated. Half of the total protein intensity was made up by only 42 to 53 proteins, depending on the cell type. More than a third of all proteins were identified in all three cell types, which may be proteins performing common cell functions. Indeed, the proteins displaying the highest abundance seem to be predominantly involved in such common cellular functions as the regulation of glucose metabolism or the cytoskeleton. More specific functions like heart development and muscle contraction were found enriched in cardiomyocytes as were mitochondrial proteins. The proportion of proteins with extracellular localization and function was higher in fibroblasts and endothelial cells. Secondly, the impact of cytokines on the proliferative behavior and the proteomic composition of cardiomyocytes and fibroblasts was analyzed. HL-1 cardiomyocytes and L929 fibroblasts were treated with different concentrations of cytokines with a cytotoxic, proliferative, or yet unknown effect on these cells. While HL-1 cells exhibited no macroscopic reaction to any of the cytokines used, cytotoxic/growth inhibitory (TNFα, CXCL11) and proliferative (TGFß, IL6, BDNF) effects were observed for L929 cells. The latter also showed CXCL11-induced upregulated EIF2 signaling, pointing to a higher need of protein synthesis. The third aim was the examination of proteome adaptations in endothelial cells due to different kinds of stress, as these cells are the first line of defense against inflammatory agents or injury and therefore prone to wounding. The role of the growth factors vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) in wounding and starvation was another object of this study as they are known for their angiogenic and cell survival supporting properties. Additionally, the impact of the cellular sex on the response to stress and growth factors was examined, because a person’s sex plays an important role in susceptibility, risk factors, and outcome of cardiovascular diseases. This has mainly been attributed to the different hormone levels, especially the higher levels of estrogen in premenopausal women, which exerts cardioprotective properties, but also genetic background was reported to play an important role. Only few studies that examined the molecular properties of HUVECs considered the cellular sex and if so, the genetic bias of unrelated samples was not taken into account. This is why Lorenz and colleagues at the Charité in Berlin collected HUVECs from newborn twins of opposite sex, cultivated them without stress in standard growth medium, exposed them to wounding and serum starvation, and investigated the impact of the growth factors and the sex on migrational behavior and metabolic issues. The current work focused on the alterations of not only the intra- but also the extracellular proteome, because paracrine signaling is crucial for intercellular communication in order to cope with stress. General differences between male and female cells were observed for proteins encoded on the X chromosome with higher levels in females (DDX3X, UBA1, EIF1AX, RPS4X, HDHD1), except for one protein with higher levels in male cells (G6PD). A Y-chromosomal protein was, for the first time, identified in endothelial cells (DDX3Y). Wounding, starvation, and growth factor treatment led to alterations and sex-specific different levels in an unexpectedly high number of proteins, with VEGF showing a stronger impact than bFGF. Many proteins with alterations observed without taking the sex into account, were actually only changed in male or female cells. Some proteins were regulated in opposite directions, or growth factors inhibited their secretion in a sex-specific way by unknown mechanisms. Tissue factor pathway inhibitor 2 (TFPI2) should be emphasized as a protein with sex-specific differences, especially in the extracellular space and with increased levels after starvation and VEGF treatment. These observations suggest a temporal lack in TFPI2 synthesis and secretion in male cells, which might explain the enhanced adaptation of females to wounding. The results of this work lay the basis for future investigation by providing a database of intra- and extracellular proteome changes due to different environmental circumstances. It strongly suggests the investigation of male and female HUVECs, and other cells, separately to avoid the impact of the sex observed in this work. Essentially, the observations suggest a number of candidate proteins for more detailed investigations of endothelial and cardiovascular diseases.
  • Das Ziel dieser Arbeit war die Untersuchung der drei kardialen Hauptzelltypen bezüglich molekularer Mechanismen, die eine Rolle bei der Regulation der Herzfunktion spielen könnten. Ein Proteomics-Ansatz mittels Massenspektrometrie wurde angewendet, um (i) die Zusammensetzung des Proteoms von Kardiomyozyten, Fibroblasten und Endothelzellen zu untersuchen, (ii) den Einfluss von Zytokinen auf die Proliferation und die Zusammensetzung des Proteoms von Kardiomyozyten und Fibroblasten zu analysieren, und um (iii) die Veränderung des Proteoms von Endothelzellen aufgrund unterschiedlicher Arten von Stress und den Einfluss des zellulären Geschlechts zu erforschen. Die Beobachtungen in dieser Studie lassen vermuten, dass sich eine Vielzahl zellulärer Mechanismen zwischen den Geschlechtern unterscheidet, wodurch eine getrennte Untersuchung von männlichen und weiblichen Zellen für zukünftige Experimente dringend empfohlen wird. Außerdem wurde mit dieser Arbeit eine umfangreiche Datenbank als Informationsquelle geschaffen, die zukünftige Untersuchungen von Kontrollmechanismen der Endothel-Funktion unterstützen kann.

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Author: Eric Witt
Title Additional (German):Der Einfluss von Zytokinen, Stress, und dem zellulären Geschlecht auf das Proteom kardialer und vaskulärer Zellmodelle
Referee:Prof. Dr. Uwe Völker, Dr. Diana Sommer
Advisor:Dr. Elke Hammer
Document Type:Doctoral Thesis
Year of Completion:2020
Date of first Publication:2020/07/21
Granting Institution:Universität Greifswald, Mathematisch-Naturwissenschaftliche Fakultät
Date of final exam:0020/07/08
Release Date:2020/07/21
Tag:Cell culture, Heart, Mass spectrometry, Molecular biology, Proteome, Twins
GND Keyword:Herz, Massenspektrometrie, Molekularbiologie, Proteom, Zellkultur, Zwilling
Faculties:Mathematisch-Naturwissenschaftliche Fakultät / Interfakultäres Institut für Genetik und Funktionelle Genomforschung
DDC class:500 Naturwissenschaften und Mathematik / 570 Biowissenschaften; Biologie