Expression of HNF4alpha in the human and rat choroid plexus – Implications for drug transport across the blood-cerebrospinal-fluid (CSF) barrier

BACKGROUND: The choroid plexus consists of highly differentiated epithelium and functions as a barrier at the interface of the blood-cerebrospinal-fluid (CSF). This tissue may therefore determine the bioavailability and transport of drugs to the brain. Little is known about the expression of drug and xenobiotic metabolizing enzymes (DME) and of drug transporters in the human choroid plexus. Notably, the transcription factor and zinc finger protein HNF4alpha is a master regulator of DMEs and of drug transporters. As of today its activity in the blood-CSF barrier is unknown. Here we report our efforts in determining HNF4alpha activity in the regulation of ABC transporters in the human and rat choroid plexus. RESULTS: We report expression of HNF4alpha by qRT-PCR and by immunohistochemistry and evidence transcript expression of the ATP-binding cassette transporters ABCB1, ABCB4, ABCC1-6 in choroid plexus. Additionally, HNF4alpha DNA binding activity at regulatory sequences of ABCB4 and ABCC1 was determined by EMSA bandshift assays with a specific antibody. We then performed siRNA mediated functional knock down of HNF4alpha in Caco-2 cells and found ABCC1 gene expression to be repressed in cell culture experiments. CONCLUSION: Our study evidences activity of HNF4alpha in human and rat choroid plexus. This transcription factor targets DMEs and drug transporters and may well determine availability of drugs at the blood-CSF barrier.