The role of ovarian aromatase (cyp19a1a) in zebrafish cardiac formation and function

Aromatase, the key enzyme for estrogen biosynthesis, is present in zebrafish as two isoforms: the ovarian form (cyp19a1a; Aromatase A (AroA)) and the brain form (cyp19a1b; Aromatase B (AroB)). Here, we investigated the role of AroA in early cardiac development. RT-PCR and immunostaining demonstrated that only AroA, and not AroB, is expressed in the zebrafish heart, specifically in atrial and ventricular cardiomyocytes and smooth muscle cells of the bulbus arteriosus. Dot blot analysis and whole-mount immunostaining confirmed the reduction of AroA expression in AroA morphants at 2 days post-fertilization (dpf). Phenotypic analysis revealed impaired yolk sac extension and reduced heart size, accompanied by significant downregulation of yolk-associated mRNA expression (vitellogenin 1 (vtg1), ribonuclease-like 2 (rnasel2)) and cardiac development genes (myosin light chain 7 (myl7), natriuretic peptide A (nppa), leucine-rich repeat-containing protein 10 (lrrc10)). Moreover, AroA knockdown suppressed dopamine β-hydroxylase (DBH) protein expression in catecholaminergic cells and significantly reduced heart rate. Morphological assessment using cardiac myosin light chain 2 (cmlc2):GFP and histological staining showed normal cardiac looping but smaller ventricular chambers. Additionally, morphants exhibited reduced end-systolic volume (ESV) and end-diastolic volume (EDV), accompanied by decreases in stroke volume (SV), cardiac output (CO), and ventricular fractional shortening (FS%). Altogether, these findings demonstrate that AroA is an essential regulator of zebrafish heart morphogenesis and function.