gms | German Medical Science

Objective: Cerebral stroke is a major brain injury leading to an increase in vascular permeability and consequently to a brain edema, a serious clinical complication. Its high prevalence poses a serious health burden worldwide. Recent observations show that the stroke also stimulates cell proliferation and angiogenesis, to promote vascular repair and regeneration after ischemia. However vascular repair is slow and the mechanisms involved in repair and remodeling process are not well understood. To improve the understanding of post-stroke vascular repair, we aim in our study to elucidate the role of guidance molecule ephrinB2 in endothelial-pericyte interaction and in repairing blood brain barrier (BBB).

Method: Cerebral infarcts were produced by 30 minutes left middle cerebral artery (MCA) occlusion followed by reperfusion. The success of the vascular occlusion was evaluated by T2-weighted magnetic resonance image (MRI) scans. Retroviral producer cell lines were stereotactically injected into the ischemic hemisphere to overexpress or knockdown the expression EphB4 in the ipsilateral region. The integrity of blood brain barrier was assessed by adminstration of Evans Blue dye.

Results: Our data show post-stroke upregulation of ephrinB2 post-stroke. EphrinB2 expression was 4-fold upregulated after 24 h post-stroke and a gradual decrease was seen towards baseline within 7 days post-stroke. We also present a significant increase in vessel density and angiogenic sprouts from 72 h onwards and stayed significantly increased (p<0.001) even 28 days post-stroke. Furthermore, we show that ephrinB2 participates in angiogenic activity. EphrinB2 activation via EphB4 overexpression increased the pericyte recruitment and the Evan Blue extravasation was significantly decreased from 72 h post-stroke. Quantification of the extravastion area and leaky vessels showed a significantly (p<0.001) improved vessel permeabilty at the site of EphB4wt implanted cells compared to the control empty vector implantation. Additionally, siRNA-mediated EphB4 knockdown increased vessel permeability and slowed down the BBB repair.

Conclusions: Our study reveals that the guidance molecule ephrinB2 plays an important role in angiogenesis and in blood brain barrier recovery. Both the EphB4 overexpression and knockdown experimental approach shows that the early activation of ephrinB2 increases pericyte recruitment leading to reduced vascular permeability, thus to a rapid recovery of the blood brain barrier.