Long-chain n-3 Polyunsaturated Fatty Acids Mitigate Inflammatory Adipokines Derived from Adipocyte-Macrophage Cross-talk and Ensuing Changes in M1-Macrophage Polarization Markers

Abstract

Macrophages are recruited into obese adipose tissue (AT) and interact with adipocytes to promote further macrophage recruitment and development of chronic AT inflammation, characterized by AT secreted proteins that play a role in development of pathologies, such as insulin resistance. High-fat diet-induced obesity rodent models have shown that the dietary long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFA), eicosapentaenoic acid (EPA) and docoshexaenoic acid (DHA), may prevent excessive AT inflammation. However, the extent to which LC n-3 PUFA modify adipocyte-macrophage cross-talk and whether this occurs through signaling mechanisms involving peroxisome proliferator-activated receptor gamma (PPARγ) or the LC n-3 PUFA upregulated anti-inflammatory adipokine, adiponectin, is not known. In this thesis, it was found that LC n-3 PUFA perturb inflammatory adipokine secretion resulting from adipocyte-macrophage cross-talk in an in vitro co-culture model designed to mimic the ratio of adipocytes:macrophages in obese AT. The addition of a potent PPARγ antagonist to co-cultures with EPA or DHA decreased adipocyte cellular adiponectin without affecting mRNA expression or protein secretion of inflammatory IL-6 and MCP-1 (CCL2). Anti-inflammatory effects of LC n-3 PUFA were also found in an in vitro co-culture model where macrophages were isolated from low or high-fat-fed mice, with or without LC n-3 PUFA, suggesting that dietary LC n-3 PUFA also blunt inflammatory adipocyte-macrophage cross-talk. Additionally, when adiponectin was neutralized in co-cultures there was a partial loss of LC n-3 PUFA-mediated suppression of M1-macrophage polarization and associated cytokine secretion, as well as NLRP3 inflammasome gene expression. Finally, such adiponectin-dependent effects were further observed in an ex vivo model, wherein adiponectin-neutralizing antibody was added to AT conditioned media from LC n-3 PUFA-fed mice prior to incubation with a murine macrophage cell line. Here, neutralizing adiponectin partly reversed LC n-3 PUFA-induced anti-inflammatory effects, including macrophage lipid uptake, mRNA expression of M1-polarization markers and NLRP3 inflammasome genes, as well as secretion of CCL2. Together, the data in this thesis suggest that LC n-3 PUFA mitigate inflammatory adipocyte-macrophage cross-talk partly through an adiponectin-mediated mechanism. Ultimately, this work supports LC n-3 PUFA as a dietary strategy to mitigate obese AT inflammation.