CXCL12 secreted from adipose tissue recruits macrophages and induces insulin resistance in mice.

Obesity-induced inflammation is initiated by the recruitment of macrophages into adipose tissue. The recruited macrophages, called adipose tissue macrophages, secrete several proinflammatory cytokines that cause low-grade systemic inflammation and insulin resistance. The aim of this study was to find macrophage-recruiting factors that are thought to provide a crucial connection between obesity and insulin resistance. We used chemotaxis assay, reverse phase HPLC and tandem MS analysis to find chemotactic factors from adipocytes. The expression of chemokines and macrophage markers was evaluated by quantitative RT-PCR, immunohistochemistry and FACS analysis. We report our finding that the chemokine (C-X-C motif) ligand 12 (CXCL12, also known as stromal cell-derived factor 1), identified from 3T3-L1 adipocyte conditioned medium, induces monocyte migration via its receptor chemokine (C-X-C motif) receptor 4 (CXCR4). Diet-induced obese mice demonstrated a robust increase of CXCL12 expression in white adipose tissue (WAT). Treatment of obese mice with a CXCR4 antagonist reduced macrophage accumulation and production of proinflammatory cytokines in WAT, and improved systemic insulin sensitivity. In this study we found that CXCL12 is an adipocyte-derived chemotactic factor that recruits macrophages, and that it is a required factor for the establishment of obesity-induced adipose tissue inflammation and systemic insulin resistance.