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Biochemical, Molecular, and Genetic Mechanisms

3T3-L1 Adipocytes and Rat Adipose Tissue Have a High Capacity for Taurine Synthesis by the Cysteine Dioxygenase/Cysteinesulfinate Decarboxylase and Cysteamine Dioxygenase Pathways^1,2

Division of Nutritional Sciences, Cornell University, Ithaca, NY 14853

Taurine is the most abundant free amino acid in the body and is synthesized in mammals by 2 pathways. Taurine is synthesized either from the oxidation of cysteine via cysteine dioxygenase (CDO), which generates cysteinesulfinate that is decarboxylated by cysteinesulfinic acid decarboxylase (CSAD), or from the oxidation of cysteamine by cysteamine (2-aminoethanethiol) dioxygenase (ADO). Both pathways generate hypotaurine, which is oxidized to taurine. To determine whether these pathways for taurine synthesis are present in the adipocyte, we studied 3T3-L1 cells during their adipogenic conversion and fat from rats fed diets with varied sulfur-amino acid content. CDO, CSAD, and ADO protein levels increased during adipogenic differentiation of 3T3-L1 cells and all of these enzymes were significantly increased when cells achieved a mature adipocyte phenotype. Furthermore, these changes were accompanied by an increased hypotaurine and taurine production, particularly when cells were treated with cysteine or cysteamine. CDO mRNA levels also responded robustly to cysteine or cysteamine treatment in adipocytes but not in undifferentiated 3T3-L1 cells. Furthermore, CDO protein and activity were greater in adipose tissue from the rats fed a high protein or cystinesupplemented low protein (LP) diet than in adipose tissue from rats fed a LP diet. Overall, our results demonstrate that CDO is regulated at both the level of enzyme abundance and the level of mRNA in mature adipocytes.

^* To whom correspondence should be addressed. E-mail: mhs6{at}cornell.edu.

Manuscript received 28 August 2008. Initial review completed 1 October 2008. Revision accepted 18 November 2008.