Impact of Aging and Sex on the Expression and Function of Xenobiotic Transporters at the Blood-Cerebrospinal Fluid Barrier

Abstract

The blood-cerebrospinal fluid barrier (BCSFB), formed by the choroid plexuses (CP) in the brain ventricles, serves as a critical clearance organ in the brain by mediating bulk-flow CSF clearance and through the active removal of drugs and metabolites by transporters. The choroid plexuses epithelial (CPE) cells are understood to go through morphological and functional changes during aging, leading to a reduction in CSF secretion rate. Emerging evidence also indicate that drug transporter expression can exhibit sex differences in drug disposition organs such as the liver, potentially contributing to differences in drug response. However, currently little is known regarding the impact of aging and sex on transporter expression and function at the BCSFB, which is the focus of this master thesis. The mRNA expression of Slc transporters (Slc22a6, Slc22a8, Slc15a2, Slc29a4, Slco1a1, Slco1a4, Slco1a5, Slco1a6, Slco1c1, Slco3a1) and Abc transporters (Abcb1a, Abcb1b, Abcg2, Abcc1, Abcc4) were analyzed by RT-qPCR in young adult young adult (3 months) and old (20 months) mouse CP tissues. Aquaporin 1 (Aqp1) was used as a marker for CP epithelial cells, and Gapdh and GusB were used as the housekeeping genes. The results showed that while the majority of analyzed genes showed no difference in expression between the two age groups, Abcg2 (Bcrp) mRNA levels increased in aged mice by 70% and 100% in male and female CP tissues, respectively. In contrast, the expression of Slco3a1 (Oatp3a1) was decreased in aged mice by 30% in males and 40% in females. In young adult mice, no significant sex differences were observed for all analyzed transporter genes. However, in old mice, Slc22a8 (Oat3) CP expression in females was 40% lower compared to the male cohort. Using a quantitative real-time imaging method recently developed in our laboratory, the activity of Oatp1a – Mrp1/4 pathway was further investigated and the results showed that the activity of this main pathway for organic anions across the BCSFB is not influenced by aging or sex, consistent with minimal impact of aging on Oatp1a and Mrp1/4 mRNA expression. As BCSFB transporters play a crucial role in removing drugs, toxins, and metabolic wastes from the brain, knowledge gained from this master thesis contributes to understandings of the effect of aging and sex on major BCSFB transporter expression and activity, which may further influence the CSF drug concentrations and the pharmacokinetics of CNS-targeted drugs in geriatric patients and between genders.