TGF-beta Modulates the Integrity of the Blood Brain Barrier in Vitro, and is Associated with Metabolic Alterations in Pericytes

The blood-brain barrier (BBB) is a selectively permeable boundary that separates the circulating blood from the extracellular fluid of the brain and is an essential component for brain homeostasis. In glioblastoma (GBM), the BBB of peritumoral vessels is often disrupted. Pericytes, being important to maintain the BBB integrity, can be functionally modified by GBM cells by inducing proliferation and cell motility via the TGF-β-mediated induction of central epithelial to mesenchymal transition (EMT) factors., We demonstrate that pericytes strengthen the integrity of the BBB in primary endothelial cell/pericyte co-cultures as in vitro BBB model, using TEER measurement of the barrier integrity. In contrast, this effect was abrogated by TGF-β or conditioned medium from TGF-β secreting GBM cells, finally leading to the disruption of a so far intact and tight BBB. TGF-β dramatically changed the metabolic behavior of pericytes, such as shutting down the TCA cycle, driving energy generation from oxidative phosphorylation towards glycolysis, and by shifting the cells towards the activation of pathways that are necessary to produce molecules used for proliferation and cell division. Furthermore, combined metabolomics and RNASeq analyses indicated that the observed functional changes of TGF-β-treated pericytes are closely connected with their behavior.