Effect of endothelial YAP/TAZ on neuroinflammation and outcome after ischemic stroke in mice

In the acute phase of ischemic stroke, endothelial cell (EC) dysfunction leads to breakdown of the blood-brain barrier with increased vascular permeability, vascular inflammation, and transendothelial migration of leukocytes. ECs are also critical for long-term regenerative processes, such as post-stroke angiogenesis, enabling the transition from brain injury to repair. Yes-associated protein 1 (YAP) and WW domain-containing transcriptional regulator 1 (TAZ) are co-transcriptional regulators of EC proliferation and apoptosis. Several studies showed that YAP/TAZ is essential for developmental angiogenesis. However, the role of YAP/TAZ in adult angiogenesis and particularly in experimental stroke is unknown. Here, we subjected mice with an inducible EC-specific deletion of YAP and TAZ (YT-iKO) to 30-min middle cerebral artery occlusion (MCAo) followed by reperfusion to investigate the effects of endothelial YAP/TAZ on acute and long-term outcome after ischemic stroke. First, we examined mRNA expression of genes related to YAP/TAZ signaling in ischemic brain tissue, such as Id1, Smad6, Ankrd and Ccn2. We found a transient induction with highest expression levels acutely after stroke. Surprisingly, endothelial YAP/TAZ deficiency resulted in reduced lesion volumes 28 days after MCAo, whereas acute lesion size 3 days after stroke did not differ. Moreover, Yap/Taz iEC-KO animals showed no gross differences in vessels morphology 28 days after stroke, and no effect was detected on blood vessel density and EC density. We therefore speculated whether angiogenesis-independent effects of YAP/TAZ might also be associated with improved long-term outcome after stroke. To better understand the underlying mechanisms, we performed RNA sequencing of ECs isolated from ischemic brain tissue of YT-iKO compared with CTRL animals 72h post stroke. Here, we identified differently expressed gene sets involved in inflammatory responses. Therefore, we studied the non-endothelial tissue environment of the brain. We found, that EC YAP/TAZ deletion led to increased expression of anti-inflammatory genes accompanied by increased infiltration of myeloid cells, suggesting a protective phenotype. Besides, acute microglia proliferation was reduced in Y/T-iKO animals. Overall, our results provide new insights into the role of endothelial YAP/TAZ in neuroinflammation after cerebral ischemia. YAP/TAZ may therefore be a potential therapeutic target for the treatment of ischemic stroke.