ASSESSMENT OF GNAS LOSS OF FUNCTION IN MONOGENIC OBESITY USING THE ZEBRAFISH MODEL

Abstract

GNAS (Guanine Nucleotide-Binding Protein, Alpha Stimulating) is an imprinted gene that encodes the alpha subunit of the stimulatory G protein (Gs), which participates in the signaling of various G protein-coupled receptors. Inactivating genetic and epigenetic alterations in GNAS, leading to Gs deficiency, are associated with severe, early-onset obesity. This study was prompted by our identification of several GNAS variants of uncertain significance (VUSs) in pediatric patients who presented with unexplained, severe, early-onset obesity at Sidra Medicine in Qatar, suspecting monogenic obesity. With the intent of functionally characterizing these variants in the future, we developed, for the first time, a zebrafish model of Gs deficiency, given the numerous advantages of the zebrafish over other model organisms. This was achieved by knockdown of the ortholog, gnas, through microinjection of Morpholino antisense oligonucleotides into the yolks of 1-8-cell-stage zebrafish embryos. The morphant larvae displayed significantly enlarged yolk sacs with substantially increased neutral lipid accumulation at 5 days post-fertilization, in addition to considerably reduced metabolic rates among other developmental abnormalities resembling those seen in humans with Gs deficiency. These results confirm the important role of loss of GNAS function in obesity pathogenesis. This work lays the foundation for the functional characterization of novel or previously reported GNAS VUSs and paves the way for enhancing our understanding of the pathogenesis of monogenic obesity.