Abstract
Rationale Hereditary haemorrhagic telangiectasia (HHT) is an inherited bleeding disorder characterised by arteriovenous malformations (AVMs). Such AVMs affect lungs, liver and brain, whilst telangiectases in mucocutaneous tissues are prone to haemorrhage. HHT type I is caused by loss-of-function endoglin (ENG) mutations. Evidence suggests AVMs result from abnormal responses to VEGF signalling.
Objective We therefore characterised the vascular abnormalities in eng mutant zebrafish and investigated whether these are prevented by inhibiting different pathways downstream of VEGF signalling.
Methods and Results We used light sheet fluorescence microscopy to visualise the vasculature in engmu130 mutant zebrafish. In addition to previously described significantly enlarged dorsal aorta and posterior cardinal vein at 3d post fertilisation, engmu130 embryos had an enlarged basilar artery (BA), and increased formation of endothelial “kugeln” on cerebral vessels. Adult engmu130 fish developed skin AVMs, retinal vascular abnormalities, and an enlarged heart. Tivozanib (AV951), a VEGF receptor tyrosine kinase inhibitor, prevented development of the abnormally enlarged major vessels and normalised the number of kugeln in engmu130 embryos. Inhibiting discrete signalling pathways downstream of VEGFR2 in engmu130 embryos gave further insights. Inhibiting TOR or MEK prevented the abnormal trunk and cerebral vasculature phenotype, whilst targeting NOS and MAPK had no effect. Combining subtherapeutic TOR and MEK inhibition prevented the vascular phenotype, suggesting synergy between TOR and MEK/ERK signalling pathways.
Conclusions These results indicate the HHT-like phenotype in zebrafish endoglin mutants can be mitigated through modulation of VEGF signalling, and implicate combination low dose ERK and TOR pathway inhibitors as a therapeutic strategy in HHT.
Competing Interest Statement
The authors have declared no competing interest.
Non-standard Abbreviations and Acronyms
- (HHT)
- Hereditary haemorrhagic telangiectasia
- (AVMs)
- Arteriovenous malformations
- (ENG)
- Endoglin
- (BA)
- Basilar artery
- (EC)
- Endothelial cell
- (VEGF)
- Vascular endothelial growth factor
- (DA)
- Dorsal aorta
- (PCV)
- Posterior cardinal vein
- (dpf)
- days post fertilisation
- (hpf)
- hours post fertilisation
- (MIP)
- Maximum intensity projection
- (ISVs)
- Intersegmental blood vessels
- (DLAV)
- Dorsal longitudinal anastomotic vessel
- (BMP)
- Beats per minute
- (NO)
- Nitric oxide
- (SMC)
- Smooth muscle cell
- (pERK)
- Phosphorylated ERK