Interleukin-1β mediates macrophage-induced impairment of insulin signaling in human primary adipocytes

PCR array and protein array studies demonstrate that IL-1β (interleukin-1β) stimulates the expression and secretion of multiple cytokines and chemokines in human adipocytes

The role of IL-1β in regulating the expression and secretion of cytokines and chemokines by human adipocytes was examined. Adipocytes were incubated with human IL-1β for 4 or 24 h. The expression of a panel of 84 cytokine/chemokine genes was probed using PCR arrays. IL-1β stimulated the expression of >30 cytokine/chemokine genes on the arrays; 15 showed >100-fold increases in mRNA at 4 or 24 h including CSF3, CXCL1, CXCL2, CXCL12 and IL8. CSF3 exhibited a 10,000-fold increase in mRNA at 4 h. ADIPOQ was among the genes whose expression was inhibited. Protein arrays were used to examine the secretion of cytokines/chemokines from adipocytes. IL-1β stimulated the secretion of multiple cytokines/chemokines including MCP-1, IL-8, IP-10, MIP-1α and MCP-4. The most responsive was IP-10, which exhibited a 5000-fold increase in secretion with IL-1β. IL-1β is likely to play a substantial role in stimulating the inflammatory response in human adipocytes in obesity.

Inflammation and macrophage modulation in adipose tissues

The adipose tissue is an active endocrine organ that harbours not only mature and developing adipocytes but also a wide array of immune cells, including macrophages, a key immune cell in determining metabolic functionality. With adipose tissue expansion, M1 pro-inflammatory macrophage infiltration increases, activates other immune cells, and affects lipid trafficking and metabolism, in part via inhibiting mitochondrial function and increasing reactive oxygen species (ROS). The pro-inflammatory cytokines produced and released interfere with insulin signalling, while inhibiting M1 macrophage activation improves systemic insulin sensitivity. In healthy adipose tissue, M2 alternative macrophages predominate and associate with enhanced lipid handling and mitochondrial function, anti-inflammatory cytokine production, and inhibition of ROS. The sequence of events leading to macrophage infiltration and activation in adipose tissue remains incompletely understood but lipid handling of both macrophages and adipocytes appears to play a major role.