TIE2 links MEKK3-KLF2/4 and PI3K signaling in cerebral cavernous malformation.

Phospho-TIE2 levels are markedly increased in human and mouse CCM lesions.

• Elevated phospho-TIE2 was observed in human CCM specimens as well as in two mouse models of CCM disease.
• This finding was in contrast to VEGFR2, for which no evidence of augmented signaling was found in CCM lesions.
• The observation was made using human CCM specimens, two mouse models, and primary human endothelial cells.

MEKK3-KLF2/4 signaling drives induction of TIE2 receptor expression in endothelial cells.

• Enhanced MEKK3-KLF2/4 signaling was found to upregulate TIE2 receptor expression.
• This was studied in primary human endothelial cells as well as in mouse CCM models.
• The finding establishes TIE2 as a downstream transcriptional target of the MEKK3-KLF2/4 pathway in the context of CCM.

Genetic or pharmacologic TIE2 blockade resulted in almost complete rescue of CCM formation in mouse models.

• Both genetic and pharmacologic approaches to block TIE2 were tested in mouse CCM models.
• The study reports 'almost complete rescue of CCM formation' following TIE2 blockade.
• This rescue effect was observed across two distinct mouse models of CCM disease.

Neither genetic nor pharmacologic blockade of VEGFR2 reduced CCM formation in mouse models.

• VEGFR2, a major endothelial growth factor receptor, was specifically tested as a candidate mediator of CCM.
• Both genetic and pharmacologic blockade of VEGFR2 were employed in mouse models.
• No reduction in CCM formation was observed with VEGFR2 blockade, and no evidence of augmented VEGFR2 signaling was found in CCM lesions.

TIE2 is identified as the molecular link between the MEKK3-KLF2/4 and PI3K signaling pathways in CCM formation.

• Prior work had established that enhanced MEKK3-KLF2/4 signaling stimulates PI3K signaling in CCM, but the molecular link was undefined.
• This study identifies TIE2 receptor upregulation by MEKK3-KLF2/4 as the mechanism connecting these two pathways.
• The findings suggest TIE2-mediated PI3K activation as a key step in the aggressive growth of CCM lesions following the endothelial two-hit mechanism.

The study examined the roles of VEGFR2 and TIE2 as major endothelial growth factor receptors in CCM using human specimens, two mouse models, and primary human endothelial cells.

• Human CCM specimens were used to assess receptor phosphorylation and expression.
• Two distinct mouse models of CCM disease were employed for genetic and pharmacologic intervention experiments.
• Primary human endothelial cells were used to study receptor signaling mechanisms in vitro.