Hypoxia-induced matrix metalloproteinase-13 expression in astrocytes enhances permeability of brain endothelial cells.

Matrix metalloproteinase-13 (MMP-13) is involved in the degradation of extracellular matrix in many kinds of tissues. Here we found that hypoxia increased MMP-13 protein and mRNA levels in primary rat astrocyte cultures. Hypoxia stimulation also increased the secretion of MMP-13 from astrocytes, as shown by zymographic analysis. In addition, exposure to hypoxia up-regulated the expression of c-Fos and c-Jun time-dependently. Hypoxia-induced MMP-13 overexpression was antagonized by transfection with antisense oligodeoxynucleotides (AS-ODN) of c-Fos or c-Jun. Furthermore, hypoxic-conditioned medium (Hx-CM) collected from astrocytes exposed to hypoxia increased paracellular permeability of adult rat brain endothelial cells (ARBECs). Administration of MMP-13 neutralizing antibody antagonized Hx-CM-induced paracellular permeability of ARBECs. Furthermore, pre-transfection of astrocytes with AS-ODN of c-Fos, c-Jun or MMP-13-shRNA significantly decreased hyperpermeability of ARBECs induced by Hx-CM. The arrangement of tight junction protein (TJP) zonular occludens-1 (ZO-1) of ARBECs disorganized in response to Hx-CM. Administration of Hx-CM to ARBECs also resulted in the production of proteolytic fragments of ZO-1, which was antagonized by transfection of MMP-13-shRNA in primary astrocytes. Administration of MMP-13 recombinant protein to ARBECs led to the disorganization and fragmentation of ZO-1 protein and also increased paracellular permeability. These results suggest that hypoxia-induced MMP-13 expression in astrocytes is regulated by c-Fos and c-Jun. MMP-13 is an important factor leading to the disorganization of ZO-1 and hyperpermeablility of blood-brain barrier in response to hypoxia.