DIETARY REGULATION OF FATTY ACID SYNTHASE EXPRESSION

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The de novo lipogenic pathway plays a key role in the maintenance of energy balance in mammals. The rate of lipogenesis is modulated by die in a tissue-specific manner, and the hormone-dependency of the response depends on the type of carbohydrate (glucose or fructose) in the diet. The changes in lipogenic rate are accompanied by changes in the concentration of both the fatty acid synthase (FAS) enzyme and its mRNA in a tissue-specific manner, indicating that FAS is regulated at the level of transcription. The objective of the proposal is to characterize the promoter and enhancer regions of the FAS gene and determine how regulatory elements in these regions interact with trans-acting factors in mediating the response to nutritional status. Changes in the rate of transcription of the FAS gene, in response to carbohydrate-feeding (glucose and fructose), and fasting will be measured in both responsive and non-responsive control tissues. The transcriptional activity of putative promoter and enhancer elements will be assessed by measuring their ability to drive the expression of a coupled reporter gene in vitro. Hepatocyte and adipocyte cell models will be evaluated for their ability to mimic the pattern of FAS regulation observed in vivo and competent cells will be used to study the expression of transfected chimeric FAS/reporter genes. Deletions and mutations will be made in the putative FAS regulatory sequences and the effect on expression of the reporter gene measured. The possible roles of hormones as mediators of diet-induced changes in FAS transcription will be assessed in vitro by monitoring their effects on transcription of both the endogenous FAS gene and the transfected FAS/reporter gene. Candidate regulatory sequences identified in this way will be mapped using protein-DNA binding assays to determine whether specific sequences bind to nuclear proteins present in tissues, obtained from animals subjected to the various dietary regimens, in which the FAS gene is expressed or silent. Finally, the ability of identified promoter and cis-regulatory elements to mediate the die-induced regulation of FAS transcription will be tested in vivo by monitoring the expression of FAS/reporter gene chimeras in transgenic mice in response to changes in nutritional status. Altered expression of FAS and other lipogenic enzymes is observed in disordered states of energy balance such as obesity and cachexia. Obesity is recognized as predisposing to diabetes, hypertension and coronary artery disease. In order to understand how the altered gene expression occurs in obesity it will be necessary first to understand how expression of the genes for lipogenic enzymes is regulated.