Abstract
BackgroundObesity increases the risk of developing diabetes mellitus. Clinical studies suggest that risk factors like palmitic acid (PA) and lipopolysaccharide (LPS) exist simultaneously in diabetes with obesity. Combination of PA and LPS even at low concentration can induce strong inflammatory reaction. Monocyte chemoattractant protein-1 (MCP-1) is an important inflammatory chemokine related to insulin resistance and type II diabetes. Our previous study using PCR array revealed that LPS and PA synergistically induce MCP-1 mRNA expression in macrophage cells RAW264.7, while the protein expression of MCP-1 in this case was not investigated. Moreover, the underling mechanism in the synergistic effect of MCP-1 expression or production induced by treatment of LPS and PA combination remains unclear.MethodsProtein secretion of MCP-1 was measured by the enzyme-linked immunosorbent assay (ELISA) and mRNA levels of MCP-1 and Toll-like receptor 4 (TLR4) were measured by real-time PCR. Statistical analysis was conducted using SPSS software.ResultsLPS could increase MCP-1 transcription as well as secretion in RAW264.7, and PA amplified this effect obviously. Meanwhile, combination of LPS with PA increased TLR4 mRNA expression while LPS alone or PA alone could not, TLR4 knockdown inhibited MCP-1 transcription/secretion induced by LPS plus PA. Moreover, not NF-κB inhibitor but inhibitors of mitogen-activated protein kinase (MAPK) signaling pathways, including c-Jun NH2-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38 MAPK were found to block MCP-1 generation stimulated by LPS plus PA.ConclusionLPS and PA synergistically induced MCP-1 secretion in RAW264.7 macrophage cells, in which MCP-1 transcription mediated by MAPK/TLR4 signaling pathways was involved. Combined treatment of PA and LPS in RAW264.7 cells mimics the situation of diabetes with obesity that has higher level of PA and LPS, MAPK/TLR4/ MCP-1 might be potential therapeutic targets for diabetes with obesity.
Highlights
As a chronic metabolic disease, diabetes mellitus as well as its complications impose a great economic burden on individuals worldwide, due to the frequency of diagnosed cases and consequential increases in medical costs [1]
palmitic acid (PA) amplified Monocyte chemoattractant protein-1 (MCP-1) secretion in RAW264.7 macrophage triggered by low-concentration of LPS In order to investigate the synergistic effect on MCP-1 generation mediated by LPS and PA, the secreted protein of MCP-1 in the medium and the MCP-1 mRNA expression in cells were measured
100 μM PA, 1 ng/ml LPS, or 1 ng/ml LPS together with 100 μM PA did not affect cell survival indicating there are no cytotoxicity (Fig. 1e). These data suggested that LPS could stimulate MCP-1 production, the synergistic increase was obvious in case of LPS coupled with PA treatment, but CCR2 was not involved in this synergy
Summary
As a chronic metabolic disease, diabetes mellitus as well as its complications impose a great economic burden on individuals worldwide, due to the frequency of diagnosed cases and consequential increases in medical costs [1]. Low-grade chronic inflammation which was meditated by cytokines and chemokines has been found to be important in diabetes [2, 3]. The serum level of monocyte chemoattractant protein-1 (MCP-1) is significantly increased in mice or patients with type II diabetes [5, 6], and MCP-1 is reported to be a major contributor to the inflammatory process associated with diabetes [7]. MCP-1 has been demonstrated as an important risk factor during the development of insulin resistance and type II diabetes [4]. Obesity increases the risk of developing diabetes mellitus. Clinical studies suggest that risk factors like palmitic acid (PA) and lipopolysaccharide (LPS) exist simultaneously in diabetes with obesity. Monocyte chemoattractant protein-1 (MCP-1) is an important inflammatory chemokine related to insulin resistance and type II diabetes. The underling mechanism in the synergistic effect of MCP-1 expression or production induced by treatment of LPS and PA combination remains unclear
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