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.
Escoll
Pedro
P
Research Unit, Department of Surgical Research, La Paz Hospital, Madrid 28046, Spain.
del Fresno
Carlos
C
García
Lourdes
L
Vallés
Gema
G
Lendínez
Manuel J
MJ
Arnalich
Francisco
F
López-Collazo
Eduardo
E
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