Age-dependent decline of blood-brain barrier P-glycoprotein expression in the canine brain

The efflux transporter P-glycoprotein serves as a major molecular gatekeeper at the blood-brain barrier. It has been suggested that a reduction of P-glycoprotein activity with aging might enhance exposure of brain tissue to exogenous and endogenous compounds thereby contributing to the development of neurodegenerative diseases. Brain tissue from owner-kept dogs renders an excellent tool to study the impact of aging on the background of variable environmental and genetic influencing factors. Therefore, we determined expression rates of P-glycoprotein in canine post-mortem tissue from 23 non-laboratory dogs. P-glycoprotein expression in the parahippocampal cortex exhibited a negative correlation with age. Analysis of the area labeled for P-glycoprotein in dogs aged >100 months revealed a 72% drop in P-glycoprotein expression as compared to young adults aged 23-36 months. Respective data from the dentate hilus and dentate gyrus indicated an earlier drop with a reduction by 77 and 80% in dogs aged 37-99 months in comparison with younger individuals. In contrast to the decline observed with aging in dogs without plaques, P-glycoprotein expression rates rather tended to increase with further aging in dogs with plaque formation. In conclusion, the thorough analysis of P-glycoprotein expression rates in non-laboratory dogs revealed a significant decline with aging. The data strongly support the concept that age-dependent changes might predispose to neurodegenerative diseases. In the early pathogenesis of Alzheimer's disease which is modelled by diffuse plaques in the canine brain, an up-regulation of P-glycoprotein might act as a compensatory mechanism to enhance Abeta efflux from the brain. Future studies are necessary to further evaluate the correlation between Abeta deposits and P-glycoprotein expression in different phases of the disease.