Traumatic injury elicits JNK-mediated human astrocyte retraction in vitro

Abstract

Brain injury causes dysfunction of the blood–brain barrier (BBB). The BBB is comprised of perivascular astrocytes whose end-feet ensheath brain microvascular endothelial cells. We investigated trauma-induced morphological changes of human astrocytes (HA) and human cerebral microvascular endothelial cells (hCMEC/D3) in vitro, including the potential role of mitogen-activated protein kinase (MAPK) signal-transduction pathways. HA or hCMEC/D3 were grown on flexible culture membranes and subjected to single traumatic injury normalized to 20%, 30% or 55% membrane deformation. Cells were assayed for morphological changes (i.e. retraction) and MAPK phosphorylation and/or expression (c-Jun NH2-terminal kinase (JNK)1/2, extracellular signal-regulated kinase (ERK)1/2, and p38). HA retraction was rapidly elicited with a single traumatic injury (55% membrane deformation; p<0.01). Morphological recovery of HA was observed within 2h (p<0.05). Traumatic injuries increased phospho-JNK1/2 (p<0.05) in HA, indicating MAPK activation. Pre-treatment of HA with structurally distinct JNK inhibitors (25μM), either SP600125 or SU3327, reduced JNK phosphorylation (p<0.05) and trauma-induced HA retraction (P<0.05). In contrast to HA, traumatic injury failed to induce either morphological changes or MAPK activation in hCMEC/D3. In summary, traumatic injury induces JNK-mediated HA retraction in vitro, while sparing morphological changes in cerebral microvascular endothelial cells. Astrocyte retraction from microvascular endothelial cells in vivo may occur after brain trauma, resulting in cellular uncoupling and BBB dysfunction. JNK may represent a potential therapeutic target for traumatic brain injuries.