Yoshihiro Iwamoto

Macrophage-Adipocyte Interaction: Marked Interleukin-6 Production by Lipopolysaccharide

Objective: Recent studies suggested macrophages were integrated in adipose tissues, interacting with adipocytes, thereby exacerbating inflammatory responses. Persistent low‐grade infection by gram‐negative bacteria appears to promote atherogenesis. We hypothesized a ligand for toll‐like receptor 4 (TLR4), bacterial lipopolysaccharide (LPS), would further exaggerate macrophage‐adipocyte interaction.

DNA microarray analyses of genes expressed differentially in 3T3-L1 adipocytes co-cultured with murine macrophage cell line RAW264.7 in the presence of the toll-like receptor 4 ligand bacterial endotoxin

Recent studies have suggested that macrophages were integrated into adipose tissues to interact with adipocytes, thereby exacerbating inflammatory responses. Furthermore, both adipocytes and macrophages appear to express toll-like receptor-4 (TLR-4), and free fatty acids may stimulate cells through TLR-4. Herein, we analyzed genes differentially expressed in adipocytes when co-cultured with macrophages in the presence of a ligand for TLR-4, bacterial lipopolysaccharide (LPS). RAW264.7, a murine macrophage cell line and differentiated 3T3-L1 adipocytes were co-cultured using a transwell system. Genes differentially expressed in adipocytes were analyzed by the DNA microarray method following 4, 8, 12 and 24 h stimulation with 1 ng ml−1 of Escherichia coli LPS. Randomly selected genes with high expressions were confirmed by quantitative methods at both the gene and the protein level. Co-culture of macrophages and adipocytes with a low LPS concentration (1 ng ml−1) markedly upregulated gene expressions associated with inflammation and/or angiogenesis, such as those of interleukin-6 (IL-6), MCP-1, RANTES and CXCL1/KC, in adipocytes. Furthermore, several genes associated with insulin resistance were differentially expressed. Upregulations of genes encoding MCP-1, RANTES and CXC/KC were confirmed by quantitative methods. These results suggest that ligands for TLR-4 stimulate both adipocytes and macrophages to upregulate the expressions of many genes associated with inflammation and/or angiogenesis.

High glucose up-regulates lipopolysaccharide-stimulated inflammatory cytokine production via c-jun N-terminal kinase in the monocytic cell line THP-1

Diabetic subjects are susceptible to atherosclerosis. It has been postulated that inflammation plays a crucial role in atherogenesis. Since previous studies suggested persistent low-grade infection by Gram-negative bacteria such as Chlamydia spp. and/or periodontal infection is associated with increased atherogenesis among diabetic subjects, we hypothesized that macrophages under hyperglycemia respond to lipopolysaccharide (LPS) challenge in a more exaggerated manner than under normal glucose conditions. Therefore, we examined cytokine productivity and associated signal transduction molecules in LPS-stimulated the monocytic cell line THP-1, under conditions of hyperglycemia. Differentiated THP-1 cells were cultured under normal and high glucose conditions without fetal bovine serum, and were stimulated with Escherichia coli LPS in the presence of LPS binding protein. Following stimulation, activated signal transduction molecules were detected by protein microarray and confirmed thereafter. Results indicated that c-jun N-terminal kinase (JNK) was highly-phosphorylated at high glucose concentrations, and this was confirmed by Western-immunoblotting. Tumor necrosis factor-α and monocyte chemo-attractant protein-1 production were significantly enhanced under these conditions. SP600125, a selective inhibitor of JNK, dose-dependently suppressed the production of these cytokine. Therefore, we suggest that this may be one of the mechanisms by which sub-clinical infection by Gram-negative bacteria promotes atherosclerosis in diabetic subjects.