Insulin Inhibits LPS-Induced Signaling Pathways in Alveolar Macrophages

Abstract

The systemic inflammatory response syndrome (SIRS) is triggered by lipopolysaccharide (LPS) from Gram-negative bacteria. Insulin was shown to have a protective role in SIRS related to sepsis. Lungs are particularly affected in this condition and provide a second wave of mediators/cytokines which amplifies SIRS. The aim of the present study was to investigate the effect of insulin on the signaling pathways elicited by LPS in alveolar macrophages (AMs) and its consequence in cellular response to LPS measured as production of tumor necrosis factor (TNF). To this purpose, resident AMs from male Wistar rats were obtained by lung lavage and stimulated by LPS (100 ng/mL). Insulin (1 mU/mL) was added 10 min before LPS. Activation (phosphorylation) of signaling molecules by LPS was analyzed by western blot, 30 min after LPS stimulation. TNF was measured in the AMs culture supernatants by bioassay using L-929 tumor cells. Relative to controls, LPS induced a significant increase in the activation of ERK (3.6-fold), p38 (4.4-fold), Tyr-326 Akt (4.7-fold), Ser-473 Akt (6.9-fold), PKCα (4.7-fold) and PKCδ (2.3-fold). Treatment of AMs with insulin before LPS stimulation, significantly reduced the activation of ERK (54%), p38 (48%), Tyr-326 Akt (64%), Ser-473 Akt (41%), PKCα (62%) and PKCδ (39%). LPS induced TNF production in AMs which was also inhibited by insulin (60%). These results show that insulin down-regulates MAPK, PI3K and PKCs and inhibits a downstream effect of LPS, TNF production, in rat AMs stimulated with LPS and suggest that the protective effect of insulin in sepsis could be through modulation of signal transduction pathways elicited by LPS in lung macrophages.

Insulin Influences LPS-Induced TNF-α and IL-6 Release Through Distinct Pathways in Mouse Macrophages from Different Compartments

“…It has recently been discussed extensively by Davies and Taylor [30], and by Perdiguero and Geissmann [31]. By acting on non-diabetic [27] and diabetic mononuclear cells [24], it has been demonstrated that insulin plays additional roles beyond glucose uptake [32] and seems to have important immunomodulatory effects in macrophages. Moreover, insulin binds to its own receptor and has different roles depending on the cell type.…”

“…The cells were treated at a final concentration of 1 mU/mL of insulin from bovine pancreas [27] (Sigma Chemical Co, St. Louis, Mo, USA) concomitantly stimulated with or without LPS (100 ng/mL) from Escherichia coli (serotype 055:B5) (Sigma Chemical Co, St. Louis, Mo, USA) for different time point in different assays. For the inhibition assay, BMDM from diabetic animals were pre-treated with inhibitors for PI3K (10 µM LY294002 and/or 10 nM wortmannin); ERK1/2 (2 µM PD98059) and/or p38 (10 µM SB20190) for 1 h before LPS and/or insulin addition [28].…”

Insulin-induced cytokine production in macrophages causes insulin resistance in hepatocytes

“…Conflicting results about the effect of insulin on cytokine production in macrophages exist. Although insulin inhibited LPS-stimulated kinase activation and TNF␣ production in rat alveolar macrophages (17), it enhanced the LPS-elicited IL-1␣ and IL-1␤ release from whole blood of healthy male volunteers subjected to a hyperinsulinemic euglycemic or hyperinsulinemic hyperglycemic clamp for 6 h prior to blood collection (33). In a different study, the impact on cytokine production of insulin alone was assessed.…”

The Involvement of Cholesterol in Sepsis and Tolerance to Lipopolysaccharide Highlighted by the Transcriptome Analysis of Zebrafish (Danio rerio)

“…This is consistent with reports in mammals because insulin regulates the inflammatory response either directly or indirectly. [65][66][67][68][69][70][71][72] As in the case of the lethal LPS treatment, the lipid metabolism-related genes were affected: the low-density lipoprotein receptor (LDLR) was the most up-modulated gene at 4 dpf. Because LPS can be bound by triglyceride-rich lipoproteins (TRL) that may be internalized through the LDLR pathway, the internalization of lipoprotein bound endotoxin (TRL-LPS) could attenuate the systemic inflammatory response.…”