Regulatory mechanisms of P-glycoprotein in brain endothelial cells of different species and novel in vivo approaches for the translation of in vitro findings

• Applicant: Professor Dr. Wolfgang Löscher
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Pharmacology ; Cell Biology
• Term: from 2015 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 283795191

In view of the pharmacoresistance of major brain diseases such as epilepsy or depression to common therapies and the potential role of efflux transporters such as P-glycoprotein (Pgp) in the mechanisms underlying drug resistance, it is important to decipher the regulatory mechanisms of Pgp at the blood-brain barrier (BBB), and thereby enable innovative therapeutic interventions. Previous studies focused mainly on transcriptional adjustments (changes in the activity of transcription factors and the expression of Pgp), post-transcriptional modifications (changes in the Pgp protein and regulation of translation of Pgp mRNA by microRNAs), Pgp trafficking mechanisms of already expressed Pgp from intracellular compartments to the apical membrane, as well as Pgp-modulating signal transduction. An entirely new way of looking at Pgp regulation at the BBB is initiated by our observations of cell-to-cell Pgp transfer from cells with high Pgp expression to cells with low Pgp expression. This Pgp-transfer in the brain endothelial cells is mediated via direct cell-cell contact and/or exosomes, in which we have identified Pgp. Another original and surprising finding of our studies is that - in addition to the known drug efflux function of Pgp expressed in the apical plasma membrane of BBB endothelial cells - Pgp can sequester potentially toxic xenobiotics in lysosomes of the endothelial cells. The intracellular lysosomal vesicles traffick by an as yet unknown mechanism to the cell membrane and leave the cell to accumulate on the apical cell membrane and form aciniform vesicle conglomerates (“barrier bodies”) that are phagocytosed by neutrophil granulocytes, thus leading to an effective disposal of the sequestered xenobiotic and an effective protection of brain parenchyma. By the new grant application, we now plan to further characterize the drug-induced formation of barrier bodies in the BBB of different species (human, pig, rat) and decipher the interaction between neutrophils and BBB endothelial cells and its pharmacological modulation in more detail. Furthermore, we will study the impact of barrier body formation for development of drug resistance in response to CNS active drugs (e.g., antiepileptic and antidepressant drugs) and chemotherapeutics. Next, we will try to translate the in vitro findings to the in vivo functioning of the BBB in rodent models. We expect that characterizing the novel regulation mechanisms of Pgp at the BBB will allow developing novel innovative strategies to pharmacologically interact with BBB-mediated resistance mechanisms of brain diseases.

• DFG Programme: Research Grants