Molecular Cloning and Expression Analysis of Bovine Alpha-tocopherol Transfer Protein (α-TTP)

Aims: To understand the mechanisms by which cattle circulate and accumulate vitamin E, we cloned the cDNA for bovine α-tocopherol transfer protein (α-TTP) and examined its expression in different tissues. 

Methodology: A full length α-TTP cDNA was amplified from bovine liver by RT-PCR.  Poly (A)⁺ RNA obtained from bovine tissues was subjected to RT-PCR analysis to examine α-TTP mRNA expression.  Western blot analysis was performed using polyclonal antibody raised against an oligopeptide derived from bovine α-TTP to examine α-TTP protein expression in various bovine tissues.  The localization of α-TTP in bovine lung tissue was examined by immunostaining with anti-bovine α-TTP polyclonal antibody.

Results: The open reading frame consists of 846 nucleotides encoding 282 amino acids with 98% and 83% identities to sheep and rat orthologs, respectively.  Bovine α-TTP mRNA and protein were expressed most strongly in liver and lung, whereas expression of α-TTP mRNA and protein are reported to be very weak or absent in human and rodent lungs.  In the lung, immunostaining suggested that α-TTP is expressed specifically in alveolar walls, which consists of alveolar cells, epithelial cells of small bronchi, and endothelial cells of pulmonary blood vessels. 

Conclusion: These results suggest that, in the lung, α-TTP is involved in supplying vitamin E to alveolar surfactant in order to protect the lung tissue from oxidative stress, and that this role may be more important in bovines than in other mammals.