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Identifier |
000416978 |
Title |
Regulation of inflammation in obesity |
Alternative Title |
Μηχανισμοί ρύθμισης της φλεγμονής κατά την παχυσαρκία |
Author
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Λυρώνη, Κωνσταντίνα
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Thesis advisor
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Τσατσάνης, Χρήστος
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Reviewer
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Μαργιωρής, Ανδρέας
Καρδάσης, Δημήτριος
Νότας, Γεώργιος
Ηλιόπουλος, Αριστείδης
Παπακωνσταντή, Ευαγγελία
Βενυχάκη, Μαρία
Μπερτσιάς, Γεώργιος
|
Abstract |
Inflammation underlies a variety of physiological and pathological processes. Over
the years tremendous progress has been made in understanding the cellular and
molecular events that are involved in inflammatory responses. A controlled
inflammatory response is beneficial for the organism in order to maintain
homeostasis, protect from infection and repair tissue damage, but it can also
become detrimental if not regulated appropriately. Different instigators of
inflammation, such as infection and tissue injury, are among the wide spectrum of
adverse conditions that induce inflammation. In chronic inflammatory diseases such
as Rheumatoid Arthritis, Systemic Lupus Erythematosus, Inflammatory Bowel
Diseases and others, pathogenesis occurs due to excessive, inappropriately initiated
inflammatory response. Metabolic diseases such as obesity and type II diabetes are
also characterized by chronic, low-grade inflammation that has led to the concept of
metabolic inflammation (metaflammation). Despite the fact that mechanisms of
inflammatory response have been extensively studied, further elucidating the
molecular controls of inflammation is of crucial importance. Macrophages are key
players in inflammation activated by a wide spectrum of stimuli and acquire a
phenotype that ranges from fully pro-inflammatory (M1) to anti-inflammatory,
mediating resolution of inflammation and tissue repair (M2). Metabolic inflammation
results in changes in macrophage phenotype as well. Inflammed adipose tissue has
an increased number of macrophages and these macrophages are pro-inflammatory
(M1-type). Effective termination of inflammation is as important as controlled
initiation, therefore a plethora of factors exist that act as negative regulators. TLR
signaling contributes to inflammation and metaflammation and is negatively
regulated by the IL-1 Receptor Associated Kinase M (IRAK-M) protein, which acts as
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functional decoy to prevent phosphorylation and further signaling by IRAK-4. The
world-wide epidemic of obesity has led to a dramatic increase in metabolic diseases
associated with metabolic inflammation, hence deciphering the mechanisms
governing processes that establish metaflammation, will allow understanding the
pathogenesis of related conditions. Adipocytes are now acknowledged as more than
cells for lipid storage. They have primary roles in controlling energy homeostasis and
secrete hormones and lipids in order to regulate systemic metabolism. Adipose
tissue is in a state of inflammation in obesity contributing to low grade systemic
inflammation.
Given the established importance of inflammation and metabolism in health and
disease, the present study focused on analyzing the transcriptional and epigenetic
mechanisms of macrophage activation focusing on the mechanisms of regulation of
the intracellular TLR-signaling modulator IRAK-M (a negative regulator of the
TLR4/LPS signaling). The work also aimed to decipher whether adipocytes can
acquire a macrophage-like phenotype in states of inflammation such as obesity and
LPS stimulation and how this is be regulated.
Using high-throughput targeted siRNA knock-down of genes that are known
transcription factors, signaling molecules and epigenetic regulators in macrophages
ones affecting IRAK-M activation by LPS were identified. Molecules that had the
strongest effect in either up-regulating or down-regulating IRAK-M expression were
selected for further validation. The transcription factor C/EBPβ was identified as a
transcriptional activator of the IRAK-M gene upon LPS stimulation of macrophages.
ChIP experiments showed that C/EBPβ is recruited to IRAK-M promoter shortly after
LPS stimulation to activate its transcription. Additional ChIP experiments showed
that NFκΒ/p65 and NFκΒ/RelB were also recruited to IRAK-M promoter shortly after
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C/EBPβ to maintain transcription active. In addition to transcription factors,
epigenetic regulators are also key players in the regulation of gene transcription.
Targeted siRNA knock-down of EZH2, the PRC2 complex methyl-transferase, as
well as stable shRNA expression experiments showed that IRAK-M gene
transcription was regulated by this protein upon LPS activation.
In parallel, we studied inflammatory responses in adipocytes using Mouse
Embryonic Fibroblasts that were differentiated to mature adipocytes as well as
primary adipocytes from lean and obese mice. Cells were activated with LPS and
their phenotype was analyzed. Results showed that adipocytes acquired an
inflammatory phenotype resembling the one observed in macrophages when
activated by LPS. Using gene knock-out animals we found that osteopontin
regulated inflammatory activation of adipocytes. Ablation of OPN resulted in
increased activation of adipocytes since OPN-deficient adipocytes secreted more
TNFα, induced higher levels of iNOS producing more nitrites. This effect was found
to be mediated by PPARγ and probably independent of LPS-TLR4 signaling.
Overall, this study adds to the current knowledge of the regulation of inflammation
and metabolic inflammation by deciphering a mechanism of IRAK-M gene
transcription and by elucidating a new factor that mediates inflammatory response in
adipocytes.
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Language |
English |
Subject |
IRAK-M |
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Macrophages |
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Μακροφάγα |
Issue date |
2018-07-18 |
Collection
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School/Department--School of Medicine--Department of Medicine--Doctoral theses
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Type of Work--Doctoral theses
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Permanent Link |
https://elocus.lib.uoc.gr//dlib/e/e/e/metadata-dlib-1535791403-249237-5501.tkl
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Views |
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