Abortive Intussusceptive Angiogenesis Causes Multi-Cavernous Vascular Malformations

Mosaic inactivation of CCM2 in humans causes cerebral cavernous malformations (CCMs) containing adjacent dilated blood-filled multi-cavernous lesions. We used CRISPR-Cas9 mutagenesis to inactivate zebrafish ccm2 resulting in novel lethal multi-cavernous lesions in the embryonic caudal venous plexus (CVP) caused by obstruction of blood flow by intraluminal pillars. These pillars mimic intussusceptive angiogenesis; however, the pillars failed to fuse to split the pre-existing vessel in two. Abortive intussusceptive angiogenesis stemmed from mosaic inactivation of ccm2 leading to patchy klf2a over-expression and resulting aberrant flow signaling. Surviving adult fish manifested histologically-typical hemorrhagic CCM. Formation of mammalian CCM requires flow-regulated transcription factors, KLF2 and KLF4; fish CCM and the embryonic CVP lesion failed to form in klf2a null fish indicating a common pathogenesis with the mammalian lesion. These studies describe the first zebrafish CCM model and establish a mechanism that can explain the formation of characteristic multi-cavernous lesions.