Effects of pericytes and various cytokines on integrity of endothelial monolayer originated from blood-nerve barrier: an in vitro study.

In the in vitro blood-brain barrier (BBB) model, astrocytes have been considered to strengthen the barrier function of brain microvascular endothelial cells (BMECs). Because the blood-nerve barrier (BNB) does not comprise cells equivalent to astrocytes, we hypothesized that the integrity of the BNB is supported by endoneurial pericytes, the only cells comprising endoneurial microvessels other than peripheral nerve microvascular endothelial cells (PnMECs). To estimate the barrier function of in vitro BBB/BNB models, we measured the transendothelial electrical resistance (TEER) and permeability for paracellular diffusion of [carboxyl-14C]- inulin across the layers of PnMECs or BMECs co-cultured with pericytes, astrocytes or fibroblasts. When co-cultured with astrocytes, both PnMECs and BMECs showed higher TEER values and significantly lower clearance of inulin. When co-cultured with pericytes, only PnMECs increased the TEER value and lowered the clearance of inulin as effectively as did those co-cultured with astrocytes. Hence, we conclude that endoneurial pericytes may strengthen the BNB function in a PnMEC-specific manner. The TEER values of the PnMEC monolayer challenged by IL-1beta, TNFalpha or VEGF decreased significantly. Based on the present results, the co-culture of PnMECs and pericytes appears to be a useful in vitro BNB model.