Abcb1a and Abcb1b expression in senescence-accelerated mouse (SAM).

It was recently reported that some strains of senescence-accelerated mouse (SAM) including SAMR1 had a spontaneous retroviral insertional mutation in the ATP-binding cassette, sub-family B, member 1A (Abcb1a) gene, while other strains including SAMP8 had not. The Abcb1 gene product, P-glycoprotein, is a representative efflux transporter of cerebral vessels. In this study, using brain samples of SAMR1, Abcb1a gene-mutant mice, and of SAMP8 without that mutation, we examined the gene expression of some representative ATP-binding cassettes, such as Abcb1a, Abcb1b, Abcc, and Abcg2, and the protein expression of P-glycoprotein by real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemical techniques. The gene expression of Abcb1a was decreased in the brain samples of SAMR1 compared with those of SAMP8, while that of Abcb1b was increased in the samples of SAMR1 compared with those of SAMP8. There were no differences in the gene expression of Abcc and Abcg2 between the samples of SAMR1 and SAMP8. The protein expression of P-glycoprotein was decreased in the brain samples of SAMR1 compared with those of SAMP8. Immunosignals of P-glycoprotein were seen in vessels walls, mainly CD34-positive endothelial cells and partially astrocytic cells, in both mice. These findings indicate that SAMR1, Abcb1a-mutant mice, showed decreased expression of Abcb1a gene and P-glycoprotein and increased gene expression of Abcb1b, compared with those of SAMP8 without that mutation, suggesting no clear effect of increased gene expression of Abcb1b on decreased expression of P-glycoprotein. The combination of SAMR1 and SAMP8 may be a good tool to investigate which transporter, Abcb1a or Abcb1b, can be used in drug delivery into the brain.