Activation of WNT signaling restores the facial deficits in a zebrafish with defects in cholesterol metabolism

Abstract

BackgroundInborn errors of cholesterol metabolism occur as a result of mutations in the cholesterol synthesis pathway (CSP). Although mutations in the CSP cause a multiple congenital anomaly syndrome, craniofacial abnormalities are a hallmark phenotype associated with these disorders. Previous studies have established that mutation of the zebrafish hmgcs1 gene (Vu57 allele), which encodes the first enzyme in the CSP, causes defects in craniofacial development and abnormal neural crest cell (NCC) differentiation. However, the molecular mechanisms by which the products of the CSP disrupt NCC differentiation are not completely known. Cholesterol is known to regulate the activity of WNT signaling, an established regulator of NCC differentiation. We hypothesized that defects in cholesterol synthesis reduce WNT signaling, consequently resulting in abnormal craniofacial development.MethodsTo test our hypothesis we performed a combination of pharmaceutical inhibition, gene expression assays, and targeted rescue experiments to understand the function of CSP and WNT signaling during craniofacial development.ResultsWe demonstrate reduced expression of axin2, a WNT downstream target gene in homozygous carriers of the Vu57 allele and in larvae treated with Ro-48-8071, which inhibits the synthesis of cholesterol. Moreover, activation of WNT signaling via treatment with a WNT agonist completely restored the craniofacial defects present in the Vu57 allele.ConclusionsCollectively, these data suggest interplay between the CSP and WNT signaling during craniofacial development.

Regulation of Wnt Signaling Pathways at the Plasma Membrane and Their Misregulation in Cancer

“…Presence of canonical Wnt ligand stimulates enrichment of cholesterol, an essential component of the ordered membrane domains, in the inner membrane leaflet and receptor clustering that is likely aided by other membrane components such as heparin sulfate and phosphatidylinositol-4,5-bisphosphate (PIP2) (Mii et al, 2017;Erazo-Oliveras et al, 2018). Defects in synthesis of cholesterol thus reduces Wnt signaling and results in abnormalities in craniofacial development and neural crest cell differentiation (Sezgin et al, 2017a;Castro et al, 2020). The glycosphingolipid mannosyl glucosylceramide, which assembles with sterols into ordered membrane domains, likewise enhances presynaptic Wnt1/Wingless (Wg) signaling in the lipid rafts and promotes synaptic bouton formation at the Drosophila neuromuscular junction (Huang et al, 2018).…”