Rapid up-regulation of IRAK-M expression following a second endotoxin challenge in human monocytes and in monocytes isolated from septic patients.
The exposure of human monocytes to the gram-negative endotoxin LPS provokes them to enter a transient state in which they are refractory to further stimulation by LPS. This phenomenon is known as 'endotoxin tolerance' (ET) and it is characterized by a decrease in leukocyte proinflammatory cytokine production in response to LPS. In the present study, we have analyzed the expression of IRAK-M mRNA and protein in a human model of ET using human monocytes isolated from peripheral blood. In these monocyte cultures, IRAK-M mRNA was expressed 6h after stimulation with different doses of LPS. However, endotoxin pretreatment induced a more immediate up-regulation of IRAK-M gene expression, transcripts appearing only one hour after a second LPS-challenge, and the production of high levels of IRAK-M protein in these tolerant monocytes. We also analyzed the response of monocytes isolated from septic patients within a temporal tolerance timeframe when stimulated ex vivo with LPS. In contrast to monocytes from healthy volunteers and patients outside of the tolerance timeframe, monocytes from septic patients rapidly expressed IRAK-M mRNA when stimulated with LPS ex vivo. Moreover, the expression of IRAK-M mRNA was more rapidly induced in the presence of a PI3K inhibitor, suggesting a connection between these two kinases. Thus, our data indicate that IRAK-M could play a pivotal role in the process of ET in human monocytes and provide evidence that PI3K is involved in regulating its expression.
Research Unit, Department of Surgical Research, La Paz Hospital, Madrid 28046, Spain.
Pedro
P
Escoll
Carlos
C
del Fresno
Lourdes
L
García
Gema
G
Vallés
Manuel J
MJ
Lendínez
Francisco
F
Arnalich
Eduardo
E
López-Collazo
D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D004731:Endotoxins / Q000235:genetics / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D053592:Interleukin-1 Receptor-Associated Kinases; D007963:Leukocytes, Mononuclear / Q000187:drug effects* / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008875:Middle Aged; D011494:Protein Kinases / Q000096:biosynthesis* / Q000235:genetics; D018805:Sepsis / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects*
D004731:Endotoxins; D008070:Lipopolysaccharides; D011494:Protein Kinases; C507771:IRAK3 protein, human; D053592:Interleukin-1 Receptor-Associated Kinases