Fig. 4.

Reaction of pericytes to SAH. Pericytes are in direct communication with ECs, and thus, pericyte contraction in response to SAH can alter BBB integrity. Pericytes are exposed to high concentrations of Hb and other substances such as ET-1, AT2, 20- 20-HETE, TX2, and ATP present in the CSF after SAH that have a predominant constrictor effect. CypA release, caused by Hb, and ROS, can activate CD147, which activates the NF-κB pathway, causing increased expression of MMP-9 and pro-inflammatory cytokines such as IL-6 and TGF-β, as well as upregulation of adhesion molecules (ICAM-1 and VCAM-1). MMP-9 is also upregulated via activation of PAR1/4 by Tb. Upregulation of MMP-9 and elevated cytokines results in the degradation of basal lamina and TJ proteins, thus increasing BBB permeability, allowing leukocyte penetration into the CNS