Endoglin deficiency elicits hypoxia-driven congestive heart failure in zebrafish

Abstract

Hereditary hemorrhagic Telangiectasia (HHT) also known as Rendu-Osler-Weber syndrome is a rare genetic disease relying on mutations affecting components of TGF-β/BMP signaling pathway in endothelial cells. This disorder is characterized by vascular dysplastic lesions or arterio-venous malformations prone to rupture and ensuing hemorrhages are thought to be responsible for iron deficiency anemia. Along with Activin receptor-like kinase ALK1, Endoglin (CD105) is involved in the vast majority of reported HHT cases. Unlike Type-1 TGF-β Receptor ALK1, Endoglin is not endowed with Ser/Thr kinase activity but serves as an ancillary receptor that modulates TGF-β receptor complex signaling. In this report, we characterized zebrafish endoglin locus and demonstrated that it produces two phylogenetically conserved protein isoforms using a distinctive alternative splicing mechanism. This preliminary work served as a base to the establishment of a Crispr/Cas9 engineered Endoglin mutant line from which functional analysis revealed that Endoglin deficiency results in massive fish death during the course from juvenile stage to adulthood. Endoglin deficient fish develop a cardiomegaly resulting in heart failure and hypochromic anemia which both stem from chronic hypoxia. A combination of histological analysis and confocal imaging evidenced structural alterations of the developing gill and its underlying vascular architecture that tally with respiratory distress and hypoxemia/hypoxia occurrence. Finally, phenylhydrazine treatment demonstrated that lowering hematocrit/blood viscosity constraint strongly alleviates heart failure and enhances survival of Endoglin deficient fish. Altogether our data support the notion that zebrafish Endoglin is crucial for gill proper development and respiratory function and that further studies using zebrafish in general and this endoglin mutant in particular will provide crucial hints of molecular and cellular events altered in HHT for the development of new therapeutic strategies.