Cytoglobin-dependent NO-sGC-cGMP signaling regulates ventricular morphogenesis and diastolic function

Hypoplastic left heart syndrome (HLHS) is a severe congenital heart disease characterized by ventricular hypoplasia and impaired cardiac function. Clinically, inhaled nitric oxide (NO) therapy is used to reduce pulmonary vascular resistance and improve cardiopulmonary stability in HLHS patients. However, whether NO signaling contributes to HLHS pathogenesis remains unknown. Cytoglobin (Cygb) is a heme-protein traditionally thought to limit NO bioavailability and downstream activation of the soluble guanylate cyclase (sGC) cyclic guanosine monophosphate (cGMP) signaling pathway. Unexpectedly, our recent work shows that Cygb enhances NO signaling through activation of NO synthase, leading to downstream activation of sGC-cGMP signaling. In zebrafish embryos, Cygb-dependent NO signaling is required for normal cilia motility and the establishment of correct cardiac laterality. Here, our aim was to determine whether Cygb-dependent NO-sGC signaling linked to cilia function regulates cardiac morphogenesis and contributes to ventricular hypoplasia in HLHS.

We found that loss of Cygb ( cygb2 ) in zebrafish disrupts NO-sGC signaling during cardiogenesis, altering cardiac progenitor organization and migration within the anterior lateral plate mesoderm. Disruption of these processes impairs heart tube morphogenesis, thereby producing a compact ventricle wall characterized by increased wall thickness (despite preserved cardiomyocyte number) reduced ventricle size and decreased stroke volume, recapitulating key features of HLHS. Genetic disruption of the sGC ⍺-subunit ( gucy1a1) and pharmacological NO scavenging phenocopy the cygb2 mutant phenotype, resulting in reduced cGMP levels, compact ventricular architecture and decreased stroke volume. Consistently, restoration of NO-sGC signaling in cygb2 mutants rescues early cardiac progenitor patterning, ventricular morphology and stroke volume.

These findings identify Cygb-dependent NO-sGC signaling as a critical developmental pathway for ventricular development and performance, temporally linking cardiac progenitor dynamics to cilia-dependent signaling associated with left-right patterning. This study further suggests that pharmacological activation of sGC may provide a therapeutic strategy for hypoplastic ventricular disease.