Mural cell-derived laminin-5 plays a detrimental role in ischemic stroke

At the blood-brain barrier (BBB), laminin-5 is predominantly synthesized by endothelial cells and mural cells. Endothelial laminin-5 is dispensable for BBB maintenance under homeostatic conditions but inhibits inflammatory cell extravasation in pathological conditions. Whether mural cell-derived laminin-5 is involved in vascular integrity regulation, however, remains unknown. To answer this question, we generated transgenic mice with laminin-5 deficiency in mural cells (5-PKO). Under homeostatic conditions, no defects in BBB integrity and cerebral blood flow (CBF) were observed in 5-PKO mice, suggesting that mural cell-derived laminin-5 is dispensable for BBB maintenance and CBF regulation under homeostatic conditions. After ischemia-reperfusion (MCAO) injury, however, 5-PKO mice displayed less severe neuronal injury, including reduced infarct volume, decreased neuronal death, and improved neurological function. In addition, 5-PKO mice also showed attenuated vascular damage (milder BBB disruption, reduced inflammatory cell infiltration, decreased brain edema, and diminished hemorrhagic transformation). Mechanistic studies revealed less severe tight junction protein (TJP) loss and pericyte coverage reduction in 5-PKO mice after ischemia-reperfusion injury, indicating that the attenuated ischemic injury in 5-PKO mice is possibly due to less severe vascular damage. These findings suggest that mural cell-derived laminin-5 plays a detrimental role in ischemic stroke and that inhibiting its signaling may have a neuroprotective effect.