Background: ABC-transporters play an important role in lipid trafficking. Therefore, hepatic expression patterns of ABC-transporters involved in the regulation of cholesterol metabolism were evaluated.
Methods and results: RT-PCR analysis showed that the mRNA expression of 38 ABC-transporters detected in livers of C57Bl/6 mice varied greatly. Although most ABC-transporters were ubiquitously expressed, some members displayed very restricted expression patterns, e.g. ABCA6, A8, B1, B8, B10, B11, C3, D2, and G5/G8 were exclusively (>99%) expressed in parenchymal cells. Interestingly, another 13 ABC-transporters, including ABCA4, A5, A9, A13, B2, B9, C1, C5, D3, D4, F2, G1, and G4 were primarily expressed in Kupffer cells. Although Kupffer cells only contribute to 2.5% of the total liver protein, these 13 genes did contain 9-27% of the total liver expression. Western-type diet feeding (0.25% cholesterol, 15% fat) induced the expression of several primarily Kupffer cell expressed genes, including ABCA5, B9, D3, and D4 (2 to 3-fold higher), whereas the other ABC-transporters were not significantly changed.
Conclusions: Our findings underscore the importance of cellular localization for studying the regulation of key ABC-transporters in liver cholesterol homeostasis. Furthermore, several novel ABC-transporters, including ABCA5, B9, D3, and D4 were identified as putative novel candidates involved in liver macrophage cholesterol homeostasis.