Docosahexaenoic acid increases cellular adiponectin mRNA and secreted adiponectin protein, as well as PPARγ mRNA, in 3T3-L1 adipocytes

Adiponectin, a protein secreted from adipose tissue, has been shown to have anti-diabetic and anti-inflammatory effects, but its regulation is not completely understood. Long-chain n-3 fatty acids eicosapentaenoic acid (20: 5n-3; EPA) and docosahexaenoic acid (22: 6n-3; DHA) may be involved in adiponectin regulation as they are potential ligands for peroxisome proliferator-activated receptor-gamma (PPAR gamma), a key transcription factor for the adiponectin gene. To examine this, 3T3-L1 adipocytes were incubated with 125 mu mol.L-1 EPA, DHA, palmitic, or oleic acids complexed to albumin, or with albumin alone (control) for 24 h. Adipocytes were also incubated for 24 h with EPA and DHA plus bisphenol-A-diglycidyl ether (BADGE), a PPAR gamma antagonist. Both EPA and DHA increased (p < 0.05) secreted adiponectin concentration compared with the control (44% and 102%, respectively), but did not affect cellular adiponectin protein content. Incubation with BADGE and DHA inhibited increases in secreted adiponectin protein, suggesting that DHA may act through a PPAR gamma-dependent mechanism. However, BADGE had no effect on EPA-induced increases in secreted adiponectin protein. Only DHA enhanced (p < 0.05) PPAR gamma and adiponectin mRNA expression compared wtih the control. Our results demonstrate that DHA increases cellular adiponectin mRNA and secreted adiponectin protein in 3T3-L1 adipocytes, possibly by a mechanism involving PPAR gamma. Moreover, DHA increased adiponectin concentration to a greater extent (40% more, p < 0.05) compared with EPA, emphasizing the need to consider the independent actions of EPA and DHA in adipocytes.