Abstract
Cysteine dioxygenase (CDO) catalyzes the 1st step in the synthesis of taurine from cysteine. Taurine is abundant in tissues and in milk, where concentrations are highest in the first days of lactation. Although most work on CDO has focused on liver, the primary site of expression, we recently noted high levels of CDO mRNA and protein in mammary gland. Since the mammary gland also expresses cysteine sulfinic acid decarboxylase (CSAD), which catalyzes the 2nd step of taurine synthesis, we hypothesized that this tissue may play a role in taurine synthesis during lactation. To assess this possibility, CDO and CSAD mRNA and protein were analyzed in rat mammary gland at various times throughout pregnancy and lactation. Neither CDO nor CSAD expression in mammary gland was positively associated with milk taurine levels. In contrast, plasma and hepatic taurine, and the liver's capacity for taurine synthesis, were elevated at the onset of lactation. Hepatic CSAD mRNA and protein were markedly upregulated with lactation, whereas only a subtle increase in CDO was observed, suggesting that regulation involved partitioning of CSA to taurine vs. pyruvate. We conclude that taurine synthesis in the mammary gland is not specifically regulated in response to the onset of milk secretion, whereas hepatic taurine synthesis appears to be upregulated at this time. This research was supported by NIH DK056649.
Published Version
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