PURPOSE OF REVIEW: The liver plays a central role in whole body lipid metabolism and adapts rapidly to changes in dietary fat composition. This adaption involves changes in the expression of genes involved in glycolysis,de-novo lipogenesis, fatty acid elongation, desaturation and oxidation. This review brings together metabolic and molecular studies that help explain n-3(omega-3) polyunsaturated fatty acid regulation of hepatic gene transcription.
RECENT FINDINGS: Dietary n-3 polyunsaturated fatty acid regulates hepatic gene expression by targeting three major transcriptional regulatory networks: peroxisome proliferator-activated receptor alpha, sterol regulatory element binding protein-1 and the carbohydrate regulatory element binding protein/Max-like factor X heterodimer. 22: 6,n-3, the most prominent n-3 polyunsaturated fatty acid in tissues, is a weak activator of
peroxisome proliferator-activated receptor alpha. Hepatic metabolism of 22:6,n-3, however, generates 20: 5,n-3, a strong peroxisome
proliferator-activated receptor alpha activator. In contrast to peroxisome proliferator-activated receptor alpha, 22: 6,n-3 is the most potent fattyacid regulator of hepatic sterol regulatory element binding protein-1. 22:6,n-3 suppresses sterol regulatory element binding protein-1 gene expression while enhancing degradation of nuclear sterol regulatory element bindingprotein-1 through 26S proteasome and Erk1/2-dependent mechanisms. Both n-3and n-6 polyunsaturated fatty acid suppress carbohydrate regulatory element binding protein and Max-like factor X nuclear abundance and interfere with glucose-regulated hepatic metabolism.
SUMMARY: These studies have revealed unique mechanisms by which specific polyunsaturated fatty acids control peroxisome proliferator activated receptor alpha, sterol regulatory element binding protein-1 and carbohydrate regulatory element binding protein/Max-like factor X function. As such, specific metabolic and signal transduction pathways contribute significantly to the fatty acid regulation of these transcription factors and their corresponding regulatory networks.
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