Docosahexaenoic Acid Enhances Hepatic Serum Amyloid A Expression via Protein Kinase A-dependent Mechanism

Abstract

Serum amyloid A (SAA) reduces fat deposition in adipocytes and hepatoma cells. Human SAA1 mRNA is increased by docosahexaenoic acid (DHA) treatment in human cells. These studies asked whether DHA decreases fat deposition through SAA1 and explored the mechanisms involved. We demonstrated that DHA increased human SAA1 and C/EBP␤ mRNA expression in human hepatoma cells, SK-HEP-1. Utilizing a promoter deletion assay, we found that a CCAAT/enhancer-binding protein ␤ (C/EBP␤)-binding site in the SAA1 promoter region between ؊242 and ؊102 bp was critical for DHA-mediated SAA1 expression. Mutation of the putative C/EBP␤-binding site suppressed the DHA-induced SAA1 promoter activity. The addition of the protein kinase A inhibitor H89 negated the DHA-induced increase in C/EBP␤ protein expression. The up-regulation of SAA1 mRNA and protein by DHA was also inhibited by H89. We also demonstrated that DHA increased protein kinase A (PKA) activities. These data suggest that C/EBP␤ is involved in the DHA-regulated increase in SAA1 expression via PKA-dependent mechanisms. Furthermore, the suppressive effect of DHA on triacylglycerol accumulation was abolished by H89 in SK-HEP-1 cells and adipocytes, indicating that DHA also reduces lipid accumulation via PKA. The observation of increased SAA1 expression coupled with reduced fat accumulation mediated by DHA via PKA suggests that SAA1 is involved in DHA-induced triacylglycerol breakdown. These findings provide new insights into the complicated regulatory network in DHA-mediated lipid metabolism and are useful in developing new approaches to reduce body fat deposition and fatty liver. Serum amyloid A (SAA)3 is a family of apolipoproteins mainly synthesized in mammalian liver. There are constitutive family members (SAA4) and acute-phase members (SAA1 and SAA2) that respond to tissue damage and inflammation. The acute-phase SAA is induced primarily by IL-1, tumor necrosis factor ␣, and IL-6 through the down-regulation of NF-B, CCAAT/enhancer-binding protein (C/EBP) family, and SAA activating factor (SAF) whose binding elements have been located and characterized in the acute-phase SAA promoter region (1). The SAA1 is considered to be a marker for obesity and cardiovascular disease because the expression of SAA1 is correlated well with the degree of obesity (2) and the risk of cardiovascular disease (3). However, the discoveries of the effect of SAA1 in lipid metabolism suggest that SAA1 is a mediator to reduce fat deposition. For example, several lipogenic enzymes, including acetyl-CoA carboxylase 1, lipoprotein lipase, and adipocyte fatty acid-binding protein, are reduced in adipocytes by SAA treatments (4). A glycerol-releasing effect of SAA can also be observed in porcine and human adipocytes (4, 5).The n-3 polyunsaturated fatty acids (PUFA) are beneficial in many chronic diseases, including obesity, coronary heart disease, and fatty livers. A high docosahexaenoic acid/eicosapentaenoic acid diet increases weight loss and decreases fat deposition in mice and humans (6, 7). The inta...

Docosahexaenoic acid suppresses the expression of FoxO and its target genes

“…The effect of n-3 PUFA is likely to be explained by the activation of fatty acid oxidation and PPARγ to reduce plasma levels of FFA and triacylglycerol [52]. Our previous reports indicate that DHA activates protein kinase A to induce hepatic serum amyloid A expression, resulting in increased lipolysis and reduced triacylglycerol accumulation [16,53]. These data imply that fish oil and DHA are beneficial in preventing and treating dyslipidemia in diabetes.…”

“…All participants gave written permission, and the experiment was approved by the ethics committee of National Taiwan University Hospital. Procedures for human and porcine preadipocyte isolation, cell culture and differentiation were described previously [16,17].The SK-HEP-1 cells and differentiated adipocytes were cultured in DMEM and DMEM/F12, respectively, overnight and then treated with or without a fatty acid, palmitic acid (PA), oleic acid (OA) or DHA, bound to 1% fatty acid-free bovine serum albumin (BSA) for 24 h. Total RNA was extracted from tissues and cells by the guanidinium thiocyanatephenol-chloroform extraction method [18]. Genomic DNA was then removed from the RNA samples by the TURBO-DNase free kit (Applied Biosystems, Foster City, CA, USA) followed by reverse transcription into cDNA using the High Capacity cDNA Reverse Transcription kit (Applied Biosystems, Foster City, CA, USA).…”

N-3 polyunsaturated fatty acids regulate lipid metabolism through several inflammation mediators: mechanisms and implications for obesity prevention

“…The elevated TNF-α and IL-6 production induced by n-3 PUFA is inversely related to the PGE 2 concentration [57,69], suggesting that n-3 PUFA increase these pro-inflammatory mediators through regulation of PGE 2 . Recent data show that DHA upregulates the expression of SAA through modulation of C/EBPβ by activating PKA [70]. suggesting another possibility of n-3 PUFAinduced pro-inflammatory response via increased SAA expressions.…”

The n-3 long-chain PUFAs modulate the impact of the GCKR Pro446Leu polymorphism on triglycerides in adolescents

“…LC-PUFAs [mainly DHA ( 32 )] may act by downregulating FAS activation both directly ( 33 ) and by inhibiting sterol regulatory element-binding protein ( 34,35 ) and carbohydrate responsive element-binding protein. Another possible mechanism is that n-3 LC-PUFAs inhibit ACC ( 36 ), whereas the increase in glucose concentration competes to activate ACC ( 37 ). With ACC activation, malonyl-CoA production would lead to inhibition of carnitine palmitoyltransferase 1 and ␤ -oxidation ( 38 ), and thus to an increase in TG production as the oxidative pathway is downregulated.…”