Introduction: Blood brain barrier (BBB) damage resulting from ischemia/reperfusion (I/R) disrupts the neurovascular unit and leads to poor patient outcomes. We recently discovered that caveolin-1-independent subtle structural aberrations of brain microvascular endothelial cells (BMECs), such as abnormal actin polymerization, stress fiber formation and subsequent junctional protein (JP) disassembly, are a novel mechanism for rapid BBB breach after I/R.
Hypothesis: Heat shock protein 27 (HSP27) reduces BBB breakdown after I/R by inhibiting actin polymerization and JP disassembly in BMECs.
Methods: Neuron- or EC-specific HSP27-overexpressing mice were subjected to 1 h MCAO and reperfusion. BBB damage, tissue histology, and neurobehavioral performance were assessed up to 35 d after I/R. I/R-induced BBB damage was also simulated in BMEC cultures, where gene manipulations were achieved using lentiviral vectors. Cell-permeable TAT-HSP27 protein was injected i.v. into mice after I/R to rapidly elevate HSP27 in BMECs.
Results: Targeted overexpression of HSP27 within ECs—but not neurons—was sufficient to reduce early (1-3 h) and late (24 h) BBB damage after I/R (p<0.01). Mechanistically, HSP27 suppressed I/R-induced actin polymerization, stress fibers, and JP disassembly in BMECs, but independent of its anti-cell death properties. Intracerebral infiltration of neutrophils and macrophages was attenuated in EC-HSP27 mice by 35% and 60%, respectively (n=6, p<0.05) at 48 h after I/R. Infarct size was reduced by 35% at 72 h, and sensorimotor functions (p<0.01, cylinder and corner tests) were improved in EC-HSP27 mice up to 21 d. Post-I/R injection of TAT-HSP27 markedly reduced BBB damage and elicited sustained (up to 35 d) protection against neurological deficits.
Conclusions: HSP27 protects against BBB disruption after I/R by inhibiting actin polymerization and JP disassembly in BMECs. HSP27 may be a therapy for ischemic stroke in conjunction with reperfusion.