Abstract 160: The Role of Inhibitor of Differentiation 3 in the Regulation of Monocyte Chemoattractant Protein-1 Within Epididymal Adipose Tissue During Early Stages of Obesity
Background Global deletion of helix-loop-helix (HLH) transcription factor Inhibitor of Differentiation 3 (Id3) attenuates HFD-induced obesity. Specifically, Id3-/- mice have less epididymal adipose tissue (eAT); an effect that may be linked to eAT inflammation. Adipose tissue macrophages play a key role in HFD-induced obesity and are recruited by Monocyte Chemoattractant Protein-1 (MCP-1). MCP-1 is produced by a wide variety of cells. Id3-/- mice have attenuated HFD-induced levels of MCP-1 mRNA and protein in eAT. Consistent with lower levels of MCP-1 in eAT, Id3-/- mice also have decreased numbers of proinflammatory macrophages in eAT after HFD. Id3 is broadly expressed and involved in many disease pathways. It is currently unclear how Id3 is regulating MCP-1 in eAT, or in which MCP-1-producing cell.
Results Id3-/- mice and C57Bl/6 littermate controls were fed HFD (60% fat) for 1 and 4 weeks. Stromavascular fraction (SVF) cells from eAT were cultured with Brefeldin A to inhibit protein secretion. Intracellular levels of MCP-1 were analyzed via flow cytometry. Both 1 and 4 weeks of HFD increased the number of MCP-1+ cells, compared to chow-fed controls. There were two levels of MCP-1 expression. Adipocyte progenitors, identified as CD31-CD45-Ter119-CD34+CD29+Sca-1+, express high levels, and macrophages, identified as CD45+F4/80+CD11b+, express mid levels of MCP-1. MCP-1 high cells increased after 1 week of HFD, and this increase was amplified after 4 weeks of HFD. MCP-1 mid cells did not increase until 4 weeks of HFD. However, in Id3-/- mice, both populations were decreased in number at both stages of HFD. MCP-1+ cells in Id3-/- mice also had lower mean fluorescence intensity (MFI) compared to WT controls, indicating lower levels of MCP-1 per cell.
Conclusion Global deletion of Id3 decreases the number of MCP-1 expressing cells in epididymal adipose tissue, as well as MCP-1 levels per cell. These data suggest that Id3 promotes an immediate response to HFD via an increase in the number of MCP-1 producing cells. There is also evidence that Id3 is directly regulating expression of MCP-1 within adipocyte progenitors. Further studies will elucidate the exact mechanism of regulation of both the number of cells and expression of MCP-1 by Id3.
- © 2013 by American Heart Association, Inc.