Cardiac function in zebrafish embryos is linked to an androgen receptor-adrenomedullin-proepicardium axis

Abstract

Abstract Background Congenital heart defects (CHDs) comprise the most common congenital malformation affecting nearly 1% of all newborns. In individuals with sex chromosome aneuploidy syndromes, however, the prevalence reaches up to 50% of all livebirths. One commonality to these syndromes is a marked reduction in sex hormones, particularly androgens. Androgen receptor (Ar) insufficiency represents a culprit in the pathophysiology of adult onset cardiovascular disease and arrhythmia, but there are no reports regarding Ar function during heart development. This is surprising as androgens along with its nuclear receptor exist already during early development, even before gonads develop and become functional. Methods We evaluated the role of the Ar during vertebrate heart development by generating loss-of function in zebrafish embryos via pharmacological inhibition, transient CRISPR/Cas9 treatment, or interference of splicing as well as murine cell culture. Results Attenuation of Ar function in zebrafish embryos prevents normal cardiac morphology and physiology as apparent by edema, bradycardia and arrhythmia. Molecularly, we identified increased abundance of adrenomedullin (Adm) 2a as a likely cause for the observed defects. Cellularly, these phenomena may be linked to impaired formation of proepicardial cells, which are reported to intermingle with cells of the conduction system and influence cardiac pacing. Conclusions A disrupted Ar – Adm2 axis possibly contributes to the increased frequency of CHD in individuals suffering from sex chromosome aneuploidy syndrome.Plain english summary Testosterone function is generally mediated by androgen receptors in the nucleus of the cell. Interestingly, the androgen receptor exists already in early embryos, long before sexual maturation will be initiated. This study aimed to investigate the function of the androgen receptor during heart development using zebrafish embryos. Embryos lacking functional androgen receptors display severely impaired heart development resulting in a slower and irregularly beating heart. Consistently, several important structures of the heart including the conduction system necessary for cardiac rhythmicity fail to form and function properly in the absence of androgen receptor function. Loss of androgen receptor function leads to elevated expression of adrenomedullin 2a, which has previously been implicated in heart development and function. Consistent with a study reporting adrenomedullin 2a originating from the proepicardium loss of proepicardial genes could be observed in the absence of the androgen receptor. Taken together, this study identifies a novel role of the androgen receptor during early heart development, most likely independent of the later biological sex.