The impact of glia-derived extracellular matrices on the barrier function of cerebral endothelial cells: An in vitro study

The blood-brain barrier (BBB) is composed of the cerebral microvascular endothelium, which, together with astrocytes, pericytes, and the extracellular matrix (ECM), contributes to a “neurovascular unit”. It was our objective to clarify the impact of endogenous extracellular matrices on the barrier function of BBB microvascular endothelial cells cultured in vitro. The study was performed in two consecutive steps: (i) The ECM-donating cells (astrocytes, pericytes, endothelial cells) were grown to confluence and then removed from the growth substrate by a protocol that leaves the ECM behind. (ii) Suspensions of cerebral endothelial cells were seeded on the endogenous matrices and barrier formation was followed with time. In order to quantify the tightness of the cell junctions, all experiments were performed on planar gold-film electrodes that can be used to read the electrical resistance of the cell layers as a direct measure for endothelial barrier function (electric cell-substrate impedance sensing, ECIS). We observed that endogenously isolated ECM from both, astrocytes and pericytes, improved the tightness of cerebral endothelial cells significantly compared to ECM that was derived from the endothelial cells themselves as a control. Moreover, when cerebral endothelial cells were grown on extracellular matrices produced by non-brain endothelial cells (aorta), the electrical resistances were markedly reduced. Our observations indicate that glia-derived ECM - as an essential part of the BBB - is required to ensure proper barrier formation of cerebral endothelial cells.