Therapeutic targeting of vascular malformation in a zebrafish model of hereditary haemorrhagic telangiectasia.

Hereditary Haemorrhagic Telangiectasia (HHT) causes arteriovenous malformations (AVMs) in multiple organs to cause bleeding, neurological and other complications. HHT is caused by mutations in the BMP co-receptor endoglin. We characterised a range of vascular phenotypes in embryonic and adult endoglin mutant zebrafish and the effect of inhibiting different pathways downstream of VEGF signalling. Adult endoglin mutant zebrafish developed skin AVMs, retinal vascular abnormalities, and cardiac enlargement. Embryonic endoglin mutants develop an enlarged basilar artery (similar to the previously described enlarged aorta and cardinal vein) and larger numbers of endothelial membrane cysts (kugeln) on cerebral vessels. VEGF inhibition prevented these embryonic phenotypes, leading us to investigate specific VEGF-signalling pathways. Inhibiting TOR or MEK pathways prevented abnormal trunk and cerebral vasculature phenotypes, while inhibiting NOS or MAPK pathways had no effect. Combined subtherapeutic TOR and MEK inhibition prevented vascular abnormalities, confirming synergy between these pathways in HHT. These results indicate the HHT-like phenotype in zebrafish endoglin mutants can be mitigated through modulation of VEGF signalling. Combined low dose MEK and TOR pathway inhibition may represent a novel therapeutic strategy in HHT.