Clark, A. A. | bioRxiv Science

bioRxiv2026

Cytoglobin regulates ventricular morphogenesis and diastolic function through NO-sGC-cGMP signaling during development.

AimsHypoplastic 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. Methods and ResultsWe 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. ConclusionsThese 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. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=186 HEIGHT=200 SRC="FIGDIR/small/711730v4_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@13a1515org.highwire.dtl.DTLVardef@3e1a6eorg.highwire.dtl.DTLVardef@1394ec2org.highwire.dtl.DTLVardef@161c81c_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2025

Ketogenesis is dispensable for the metabolic adaptations to caloric restriction

Caloric restriction (CR) extends the health and lifespan of diverse species. When fed once daily, CR-treated mice rapidly consume their food and endure a prolonged fast between meals. As fasting is associated with a rise in circulating ketone bodies, we investigated the role of ketogenesis in CR using mice with whole-body ablation of Hmgcs2, the rate-limiting enzyme producing the main ketone body {beta}-hydroxybutyrate ({beta}HB). Here, we report that Hmgcs2 is largely dispensable for many metabolic benefits of CR, including CR-driven changes in adiposity, glycemic control, liver autophagy, and energy balance. Although we observed sex-specific effects of Hmgcs2 on insulin sensitivity, fuel selection, and adipocyte gene expression, the overall physiological response to CR remained robust in mice lacking Hmgcs2. To gain insight into why the deletion of Hmgcs2 does not disrupt CR, we measured fasting {beta}HB levels as mice initiated a CR diet. Surprisingly, as mice adapt to CR, they no longer engage high levels of ketogenesis during the daily fast. Our work suggests that the metabolic benefits of long-term CR are not mediated by ketogenesis.

physiology↗