Diet-induced obesity mediates a proinflammatory response in pancreatic β cell via toll-like receptor 4

Toll-like receptor 4 has an important role in inflammation and immunity. Whether TLR4 signaling contributes to the link between insulin resistance and islet β cell dysfunction is an unanswered question. Here, we show that in the face of the same high-fat continuous stimulation for 24 weeks, in TLR4-/- HF mice, the weight, fraction of the liver, epididymal fat pad fraction, as well as blood glucose and insulin levels were lower than in the WT HF group. In TLR4-/- HF mice, the O2 consumption, CO2 production and activities were higher than in the WT HF group. Glucose tolerance test, insulin tolerance test and insulin release test suggest that the impaired insulin secretion was significantly improved in TLR4-/- HF mice, compared with the WT HF group. In TLR4-/- HF mice, islet β cell ultrastructure was not damaged in the face of the same high-fat continuous stimulation, compared to that in the WT HF group. By detecting glucose-stimulated insulin secretion in the primary islet, insulin secretion of TLR4-/- HF mice was better than that of the WT HF group, and in the TLR4-/- HF group, at the mRNA level, islet interleukin 6 (IL-6), tumor necrosis factor α (TNF-α), and monocyte chemotactic protein 1 (MCP-1) were significantly lower than in the WT HF group. There was the islet macrophage infiltration in the WT HF group, but no significant macrophage infiltration in the TLR4-/- HF group. These data suggest that the damaged islet functions of the high fat diet-induced obesity mice may be linked to the TLR4 expression level, and the recruitment of macrophages into the islets.