The impact of pericytes on the blood-brain barrier integrity depends critically on the pericyte differentiation stage

The blood-brain barrier consists of the cerebral microvascular endothelium, pericytes, astrocytes and neurons. In this study we analyzed the differentiation stage dependent influence of primary porcine brain capillary pericytes on the barrier integrity of primary porcine brain capillary endothelial cells. At first, we were able to induce two distinct differentiation stages of the primary pericytes in vitro. TGF beta treated pericytes expressed more alpha-SMA and actin while desmin, vimentin and nestin expression was decreased when compared to bFGF induced cells. Further analysis of alpha-SMA revealed that most of the pericytes differentiated with TGF beta expressed functional alpha-SMA while only few cells expressed functional alpha-SMA in the presence of bFGF. In addition the permeability factors VEGF. MMP-2 and MMP-9 were higher secreted by the alpha-SMA positive phenotype indicating a proangiogenic role of this TGF beta induced pericyte differentiation stage. Higher level of VEGF, MMP-2 and MMP-9 were as well detected in the TGF beta pre-treated pericyte coculture with endothelial cells when compared to the influence of the bFGF pretreated pericytes. The TEER measurement of the barrier integrity of endothelial cells revealed that bFGF induced alpha-SMA negative pericytes stabilize the barrier integrity while alpha-SMA positive pericytes differentiated by TGF beta decrease the barrier integrity. These results together reveal the potential of pericytes to regulate the endothelial barrier integrity in a differentiation stage dependant pathway. (C) 2011 Elsevier Ltd. All rights reserved.