Taurine Biosynthesis in a Fish Liver Cell Line (ZFL) Adapted to a Serum-Free Medium

Although taurine has been shown to play multiple important physiological roles in teleosts, little is known about the molecular mechanisms underlying dietary requirements. Cell lines can provide useful tools for deciphering biosynthetic pathways and their regulation. However, culture media and sera contain variable taurine levels. To provide a useful cell line for the investigation of taurine homeostasis, an adult zebrafish liver cell line (ZFL) has been adapted to a taurine-free medium by gradual accommodation to a commercially available synthetic medium, UltraMEM-ITES. Here we show that ZFL cells are able to synthesize taurine and be maintained in medium without taurine. This has allowed for the investigation of the effects of taurine supplementation on cell growth, cellular amino acid pools, as well as the expression of the taurine biosynthetic pathway and taurine transporter genes in a defined fish cell type. After taurine supplementation, cellular taurine levels increase but hypotaurine levels stay constant, suggesting little suppression of taurine biosynthesis. Cellular methionine levels do not change after taurine addition, consistent with maintenance of taurine biosynthesis. The addition of taurine to cells grown in taurine-free medium has little effect on transcript levels of the biosynthetic pathway genes for cysteine dioxygenase (CDO), cysteine sulfinate decarboxylase (CSAD), or cysteamine dioxygenase (ADO). In contrast, supplementation with taurine causes a 30% reduction in transcript levels of the taurine transporter, TauT. This experimental approach can be tailored for the development of cell lines from aquaculture species for the elucidation of their taurine biosynthetic capacity.