Retinol transport and metabolism in transthyretin-"knockout" mice

Mice were made deficient in transthyretin (TTR), the protein that normally transports plasma retinol complexed with retinol-binding protein (RBP), by targeted mutagenesis (TTR-knockout mice). The TTR- mice were healthy and fertile, despite extremely low plasma retinol and RBP levels (6% of wild type). Circulating retinoic acid was 2.3 times that of wild-type controls. Liver levels of RBP were 60% higher in the TTR-mutants compared to wild-type mice, suggesting that lack of TTR may block secretion of RBP-retinol from liver.