Adipose tissue represents an important endocrine organ that secretes a multitude of adipokines known to mediate inflammation, lipid metabolism, and insulin sensitivity in peripheral tissues, such as skeletal muscle. Specifically, adiponectin stimulates skeletal muscle fatty acid oxidation and is associated with improvements in insulin response. Long-chain n-3 polyunsaturated fatty acids (PUFA) are well known for their anti-inflammatory and insulin-sensitizing properties, and their dietary consumption is associated with a more favourable circulating adipokine profile, including increased adiponectin. However, whether n-3 PUFA can directly stimulate adiponectin secretion from human adipocytes, as well as the underlying mechanisms involved, is unknown. In contrast to n-3 PUFA, diets high in saturated fatty acids (SFA) are thought to decrease adiponectin and increase pro-inflammatory adipokines, as well as blunt skeletal muscle response to both adiponectin and insulin, possibly via activation of inflammatory pathways. The role of n-3 PUFA in mediating the communication between adipose tissue and skeletal muscle, as well as preventing SFA-induced impairments in skeletal muscle function, has yet to be examined. In this thesis, it was found that long-chain n-3 PUFA increase adiponectin secretion from human adipocytes via a peroxisome proliferator-activated receptor γ-dependent mechanism. The effects of n-3 PUFA on adiponectin secretion were additive when combined with the thiazolidinedione, rosiglitazone. Second, incorporation of n-3 PUFA into a high SFA diet prevented impairments in adiponectin response and both prevented and restored impairments in insulin response in rodent skeletal muscle. Interestingly, these findings were paralleled by prevention of SFA-induced increases in toll-like receptor 4 expression by n-3 PUFA, suggesting inflammatory changes may be involved. Finally, dietary n-3 PUFA and SFA modulated the secretion of adipose tissue-derived factors from visceral rodent adipose tissue and subsequent exposure of isolated skeletal muscle to such factors induced acute changes in inflammatory gene expression without affecting insulin sensitivity. Together, the findings in this thesis suggest that n-3 PUFA modulate adipokine secretion from adipose tissue and that adipose-derived factors mediate skeletal muscle inflammation and response to adiponectin and insulin. Ultimately, this work highlights the importance of considering n-3 PUFA as a therapeutic strategy in the prevention and treatment of obesity and related pathologies.
Fish Oil-Derived Long-Chain n-3 Polyunsaturated Fatty Acids Reduce Expression of M1-Associated Macrophage Markers in an ex vivo Adipose Tissue Culture Model, in Part through Adiponectin