Trans-10, cis-12 conjugated linoleic acid activates the integrated stress response pathway in adipocytes

Trans-10, cis-12 conjugated linoleic acid (t10c12 CLA) causes fat loss in mouse white adipose tissue (WAT) and adipocytes in culture. The early transcriptome changes in treated WAT and 3T3-L1 adipocytes were analyzed using high-density microarrays to better characterize the signaling pathways responding to t10c12 CLA. Gene expression responses between 4 and 24 h after treatment showed a common set of early gene expression changes indicative of an integrated stress response (ISR). The responses of 3T3-L1 preadipocytes treated with t10c12 CLA or adipocytes treated with the cis-9, trans-11 isomer of CLA did not show the ISR, indicating the effect is specific to adipocytes responding to t10c12 CLA. Western blot analysis found increased phosphorylation of eIF2 alpha and increased production of ATF4 confirming at least part of the response to t10c12 CLA is mediated through the ISR pathway. Immunofluorescence microscopy found that the cell type expressing ATF3, an indicator of the ISR, was early stage adipocytes containing oil droplets but lacking the abundant levels of fatty acid binding protein-4 (FABP4) (AP2) found in mature adipocytes. Our data suggests that the ISR precedes and is possibly the cause of the later induction of proinflammatory cytokines observed in t10c12 CLA treated adipocytes. The release of proinflammatory cytokines may explain how the ISR in early stage adipocytes causes lipid loss in mature adipocytes.