The role of the mitogen-activated protein kinases (MAPKs) in endotoxin tolerance
Year: 2007
Type: dissertation
Abstract: The innate immune response uses pattern recognition receptors, such as TLRs, to recognize \nhighly conserved structures on pathogens. Stimulation of these TLRs induces several signal \ntransduction pathways like NF- B and MAPK signaling pathways. Activation of these \npathways is important to induce the production of pro-inflammatory cytokines and helps to \ninduce the adaptive immune response. In human, there are three well known MAPKs \npathways: ERK1/2, p38 and JNK1/2. They become activated upon phosphorylation on their \nthreonine and tyrosine residues. Termination of these pathways is important to prevent \noverproduction of pro-inflammatory cytokines which can cause septic shock and even death. \nMAPK phosphatases (MKPs) are responsible for dephosphorylating and thereby inactivating \nMAPKs. However, pretreatment with LPS for example, can render immune cells tolerant to a \nsecond exposure with the same endotoxin. This phenomenon is known as endotoxin tolerance \nand has also been observed in septic shock patients. Tolerant cells fail to produce proinflammatory \ncytokines to eliminate the pathogen which caused the endotoxin stimulus; this \nmakes patients more susceptible to a secondary infection which has severe detrimental effects. \nTo investigate the molecular mechanisms of endotoxin tolerance and more precisely the role \nof the MAPKs and MKPs, we started setting up a murine and human in vitro LPS tolerance \nmodel using murine macrophages (RAW 264.7) and human monocyte-derived dendritic cells \n(DCs). The cells were stimulated once for the control condition or twice to induce the \ntolerance state as was reported in the literature. TNF- cytokine production profile was used \nas readout because it is well known that tolerant cells fail to produce this cytokine. Indeed, we \nobserved dramatic decreases of TNF- secretion when the macrophage or DCs were \nchallenged twice with LPS but not when these cells were activated once. In the tolerant cells, \na lower ERK1/2 and p38 phosphorylation was observed compared to non tolerant cells. As \npreviously reported in the literature, we also observed a stabilization of IkB upon two \nsuccessive stimulations with LPS while a nice degradation of this protein was induced 30 min \nafter a single LPS stimulation. Finally, we were able to downregulate by almost 50% MKP-1 \nafter transfection with specific siRNA against MKP-1 in RAW 264.7 cells. However, we were \nnot able to conclude if MKP-1 is involved in the LPS-induced tolerance in RAW 264.7 \nmacrophages.
Author: VOSSIUS, Sofie
Language: English
Subfield: Immunology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2598711539