Impaired inflammatory responses to multiple Toll-like receptor ligands in alveolar macrophages of streptozotocin-induced diabetic mice

To investigate the effect of hyperglycemic state on the activation of alveolar macrophages (AMs) mediated via Toll-like receptors (TLRs) typically associated with bacterial infection. AMs obtained from normoglycemic control mice and streptozotocin-induced diabetic mice were stimulated ex vivo with the following: a TLR2 ligand, peptidoglycan (PGN); a TLR4 ligand, lipopolysaccharide (LPS); or a TLR5 ligand, flagellin (FLG). Cytokine production and mRNA expression were measured by ELISA and real-time PCR, respectively. TLR expression was assessed by real-time PCR and flow cytometry. AMs from diabetic mice produced significantly less TNF-alpha after PGN or FLG stimulation, and less IL-6 after FLG stimulation, compared with AMs from control mice. The decrease in the production of these cytokines was associated with reduced mRNA expression of the corresponding cytokines. In contrast, production of TNF-alpha and IL-6 after LPS stimulation did not differ between groups. Furthermore, there was no substantial difference in the expression of TLR2, TLR4, and TLR5 in AMs between the groups. The increased JNK phosphorylation induced by PGN or FLG stimulation was downregulated in AMs from diabetic mice. Hyperglycemic state impairs the reactivity of AMs to multiple TLR ligands. This effect might result from hyperglycemia-induced alteration of intracellular signaling and is unlikely due to the modulation of TLR expression.