Intercommunications between brain capillary endothelial cells and glial cells increase the transcellular permeability of the blood–brain barrier during ischaemia Julien Brillault, Vincent Berezowski, Rome ´o Cecchelli and Marie-Pierre Dehouck Laboratoire de physiopathologie de la Barrie `re He ´mato-Ence ´phalique, Unite ´ mixte Institut Pasteur de Lille–Universite ´ d’Artois, Faculte ´ Jean Perrin, Lens, France Abstract Increased cerebrovascular permeability is an important factor in the development of cerebral oedema after stroke, implica- ting the blood–brain barrier (BBB). To investigate the effect of hypoxia on the permeability changes, we used a cell culture model of the BBB consisting of a co-culture of brain capillary endothelial cells and glial cells. When endothelial cells from this co-culture model were submitted alone to hypoxic condi- tions, long exposures (48 h) were necessary to result in an increase in endothelial cell monolayer permeability to [ 3 H]in- ulin. When endothelial cells were incubated in presence of glial cells, a huge increase in permeability occurred after 9 h of hypoxic conditions. Oxygen glucose deprivation (OGD) resulted in a much shorter time (i.e. 2 h) required for an increase in permeability. We have demonstrated that this OGD-induced permeability increase involves a transcellular rather than a paracellular pathway. Conditioned medium experiments showed that glial cells secrete soluble permeab- ility factors during OGD. However, endothelial cells have to be made sensitive by OGD in order to respond to these glial soluble factors. This work shows that an early cross-talk between glial and endothelial cells occurs during ischaemic stroke and alters BBB transcellular transport by means of glial factor secretions. Keywords: blood–brain barrier, endothelial cells, glial cells, hypoxia, ischaemia, permeability. J. Neurochem. (2002) 83, 807–817. Neurones and glial cells require a different chemical environmentfromthatfoundinthemainbodycompartment. Inordertoregulateexchangesbetweenbloodandbrainand to maintain homeostasis of the CNS, a blood–brain barrier (BBB)existstoensureproperbrainfunctioning.Mammalian BBBfunctionisduetomicrovascularendothelialcells(ECs) that acquire special properties upon exposure to as yet unknown factors presumably secreted by neighboring glia. The ECs of brain capillaries are sealed together by continu- ous tight junctions and have little transcellular vesicular transport. In addition, a number of proteins are specifically expressedbybrainECswhichmayberequiredformetabolic protection or transport activities at the BBB interface. Both the absence of interruptions between cells and the relative paucity of vesicles reflect the very low non-specific per- meability of the continuous endothelium (Bradbury 1993). Increased cerebrovascular permeability is an important factor in the development of cerebral oedema after stroke, implicating the BBB. Brain oedema accompanies a wide variety of pathological processes and contributes to the morbidity and mortality of many neurological diseases (Lobato et al. 1988). Cerebral oedema can be defined as theexcessiveaccumulationofwaterintheintracellularand/ orextracellularspacesofthebrain.Vasogenicoedemaisone ofthecomponentsofcerebraloedemaandisinitiatedbythe breakdown of the BBB. Disruption of the BBB enables blood-borne substances that are normally excluded, such as metals,kinins,prostaglandinsandproteins,toenterthebrain ResubmittedmanuscriptreceivedJuly19,2002;acceptedJuly22,2002. Address correspondence and reprint requests to Marie-Pierre Dehouck, Laboratoire de physiopathologie de la Barrie `re He ´mato- Ence ´phalique,Unite ´mixteInstitutPasteurdeLille–Universite ´ d’Artois, Faculte ´ Jean Perrin, rue Jean Souvraz, S.P. 18, 62307 Lens cedex, France. E-mail: mpierre.dehouck@univ-artois.fr Abbreviations used: BBB, blood–brain barrier; BBEC, bovine brain endothelial cell; DMEM, Dulbecco’s modified Eagle’s medium, EC, endothelial cell; GFAP, glial fibrillary acidic protein; OGD, oxygen glucose deprivation; PBS, phosphate-buffered saline; TNO, Tris- buffered saline containing ovalbumin; P e , permeability coefficient; VEGF,vascularendothelialgrowthfactor;ZO1,zonulaoccludens1. Journal of Neurochemistry ,2002, 83, 807–817 Ó 2002 International Society for Neurochemistry, Journal of Neurochemistry , 83, 807–817 807