Endocrine Abstracts

Disturbed oestrogen homeostasis is associated with an increased risk of cardiovascular disease. However, the impact of dysregulated oestrogen signalling on vascular development, maintenance and disease is not fully understood. Zebrafish is a well-established model in translational vascular research. In addition, oestrogen receptor expression and oestrogen-responsiveness in endothelial cells (EC) is conserved in zebrafish. Therefore, the aim of this study was to characterise the effect of oestrogen excess in the formation and maintenance of the vascular system using zebrafish as an in vivo model organism.

The effect of oestrogen excess in the forming vasculature was investigated in transgenic Tg(kdrl:eGFP) embryos, which express GFP in EC, after incubation in 8 μM 17β-estradiol (E2) for 48 h. E₂ treatments from early stages of vasculogenesis (16 h post-fertilisation, hpf) induced severe vascular defects including impaired arterio-venous segregation and disconnected/missing intersegmental vessels (ISVs). A similar ISV phenotype and a truncated circulatory loop due to a shorter functional dorsal aorta (DA) was observed when treatments were started from 24 to 26 hpf; after angiogenic sprouting has started, the DA has formed, and arterio-venous segregation has ended. qPCR analyses revealed decreased expression of vegfr2, notch3, the notch ligand gene deltaC, and the arterial marker gene ephrinB2. No overt vascular defects were observed when treatments were initiated after a functional vasculature was formed (48 hpf).

2-methoxyestradiol (2ME2) is an antiangiogenic E₂ metabolite synthesised via two enzymatic steps catalysed by CYP1A1 and catechol-ortho-methyltransferase (COMT). E₂ strongly induced cyp1a expression after 8 and 24 h of treatment. Treatments with 2ME2, however, only recapitulated the E₂-induced ISV phenotype, but not the shortening of the circulatory loop. Similarly, treatments with E₂ and fluoranthene, a CYP1A1 inhibitor, partially rescued the ISV but not the DA phenotype.

Herein, we show that oestrogen excess during vascular development induces severe defects in vasculogenesis, vessel destabilisation and loss of arterial identity. These vascular defects are only partly explained by the conversion of E₂ into 2ME2. Our current studies in oestrogen receptor mutants will bring new insights into the mechanisms linking oestrogen action and vascular disease. Importantly, our data suggest that increased oestrogen signalling during early development due to oestrogen excess or exposure to endocrine disruptors may predispose to vascular malformations.