gms | German Medical Science

Objective: Stroke is among the principal causes of long-term disability and death worldwide. Although VEGF has been shown to promote neurovascular remodelling after ischemia, VEGF supplementation after stroke has also been shown to induce blood-brain-barrier (BBB) breakdown along with increased edema as well as new, but dysfunctional vasculature and thus worsened the outcome. Using a bitransgenic mouse model which allows conditional and brain specific VEGF expression, we studied the impact of VEGF on blood vessel integrity as well as neurovascular recovery following middle cerebral artery occlusion (MCAO) in a multimodal and longitudinal manner.

Methods: VEGF gain of function (GOF), VEGF loss of function (LOF) and control animals were exposed to MCAO. GOF and LOF were induced after ischemia. Infarct volume and edema progression were assessed using a 7T MRI. Histological evaluation was performed on day 14 and 28 after MCAO. In addition to histological evaluation, blood-brain-barrier integrity after stroke was studied using extravasation kinetics of fluorescent marker molecules and follow up intravital microscopy (IVM) via a chronic cranial window up to 28 days after ischemia. Vessel morphology was studied using two-Photon microsopy (2PM).

Results: No significant differences in direct lesion volume or edema progression were found between the groups. Immunohistochemistry clearly showed a significant increase in angiogenic proliferation in GOF animals evaluated on day 14 and 28 after MCAO (p<0.005; GOF vs. LOF and control), while no difference was found between LOF and control animals. Stainings for CD31 and Desmin demonstrated high endothelial-pericyte interaction in these newly formed vessels of GOF animals. Follow up functional analysis of the vasculature via IVM revealed a significant increase of total vessel density in GOF animals starting on day 7 after ischemia (p<0.01; GOF vs. LOF and control), No changes in vessel permeability were detectable. 2PMrevealed increased vessel volume and microvascular density along with enhanced vascular complexity (increased bifurcation points) due to induction of VEGF in GOF animals.

Conclusion: Our results clearly show that exposure to brain specific VEGF after experimental stroke does not affect lesion size or edema progression. In contrast we demonstrate in this multimodal and longitudinal study that induction of VEGF leads to a robust pro-angiogenic response characterized by endothelial and pericyte proliferation forming functional vessels with an intact BBB.