Normalization of non‐canonical Wnt signalings does not compromise blood‐brain barrier protection conferred by upregulating endothelial Wnt/β‐catenin signaling following ischemic stroke

BACKGROUND: Endothelial canonical (Wnt/β‐catenin) and non‐canonical Wnt signalings (Wnt/PCP and Wnt/Ca(2+)) promote blood‐brain barrier (BBB) development and antagonize each other. However, the effects of ischemic stroke on endothelial canonical and non‐canonical Wnt signalings are unclear. Further, how non‐canonical Wnt signalings are influenced by upregulation of endothelial Wnt/β‐catenin signaling and subsequently affect BBB function following ischemic stroke have not been studied. METHODS: First, we determined the levels of Wnt signaling markers including TCF/LEF1 transcription activity, Axin2 mRNA, phospho‐JNK(Thr183/Tyr185), and NFAT in brain endothelial cells (ECs) with the deletion of Wnt receptor Frizzled (Fzd)4 or Fzd6, the two most abundant Fzds in brain ECs. Next, we observed the effect of ischemia/reperfusion injury on Wnt signalings in brain ECs and adult mice. Last, we assessed the changes of non‐canonical Wnt signalings and BBB injury in the early stage of ischemic stroke in mice with endothelial β‐catenin activation (β‐cat mice). RESULTS: Fzd4 or Fzd6 deletion dampened both Wnt/β‐catenin and Wnt/PCP signalings but enhanced Wnt/Ca(2+) signaling in brain ECs. Both canonical and non‐canonical Wnt signalings in brain ECs were downregulated after ischemia/reperfusion injury in vitro and in vivo. Upregulating endothelial Wnt/β‐catenin signaling in β‐cat mice normalized the downregulated non‐canonical Wnt signalings, which did not compromise its protective effects on BBB integrity and endothelial tight junction following ischemic stroke. CONCLUSIONS: The BBB protection induced by upregulation of endothelial Wnt/β‐catenin signaling may be not interfered by the normalization of non‐canonical Wnt signalings in the early stage of ischemic stroke.