Role of the mTOR pathway in LPS-activated monocytes: influence of hypertonic saline.
BACKGROUND
As heightened protein synthesis is the hallmark of many inflammatory syndromes, we hypothesize that the mammalian target of rapamycin (mTOR) pathway, which control the cap-dependent translation initiation phase, was activated by lipopolysaccharide (LPS). In addition, we studied the effect of hypertonic saline solution (HTS) on the mTOR cascade in peripheral blood mononuclear cells (PBMCs).


METHODS
PBMCs were isolated from healthy volunteers and treated with LPS. Cells were pretreated with phosphatidylinositol 3-kinase (PI3K) and mTOR inhibitors, or with HTS. Supernatants were harvested 20 h following LPS treatment, and interleukin-10 (IL-10), interleukin-6 (IL-6) and tumor necrosis alpha (TNFα) were analyzed by ELISA. Immunoblot experiments were performed for components of the PI3K/Akt/mTOR pathway at various time points. RNA was extracted after 90 min for real-time RT-PCR quantification.


RESULTS
The mTOR pathway is activated in PBMCs within 1 h of LPS stimulation. Pretreatment with rapamycin, a specific inhibitor of mTOR, resulted in a significant decrease of IL-10 and IL-6 translation and expression but did not affect the LPS-induced TNFα production. Both the mTOR pathway and the LPS-induced IL-6 production were down-regulated by HTS pretreatment.


CONCLUSIONS
The PI3k/Akt/mTOR cascade modulates LPS-induced cytokines production differentially. IL-10 and IL-6 expression are both up-regulated by activation of the mTOR pathway in response to LPS in PBMCs, while TNFα is not controlled by the mTOR cascade. Meanwhile, pretreatment of PBMCs with a HTS solution suppresses mTOR activity as well as LPS-induced IL-6, suggesting a more central role for mTOR as a regulator of the immuno-inflammatory response.
Schaeffer
Valérie
V
Harborview Medical Center, University of Washington, Seattle, Washington 98109, USA. valschae@u.washington.edu
Arbabi
Saman
S
Garcia
Iris A
IA
Knoll
Megan L
ML
Cuschieri
Joseph
J
Bulger
Eileen M
EM
Maier
Ronald V
RV
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D016753:Interleukin-10 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009000:Monocytes / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012462:Saline Solution, Hypertonic / Q000494:pharmacology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000276:immunology / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D000900:Anti-Bacterial Agents; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D004791:Enzyme Inhibitors; C508609:IL10 protein, human; C508600:IL6 protein, human; D015850:Interleukin-6; D008070:Lipopolysaccharides; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D012462:Saline Solution, Hypertonic; D014409:Tumor Necrosis Factor-alpha; D016753:Interleukin-10; C546842:MTOR protein, human; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus