Mistranslation drives alterations in protein levels and the effects of a synonymous variant at the FGF21 locus

Abstract

Background: Fibroblast growth factor 21 (FGF21) is a liver-derived hormone with pleiotropic beneficial effects on metabolism. Paradoxically, FGF21 levels are elevated in metabolic diseases. Interventions that restore metabolic homeostasis reduce FGF21. Whether abnormalities in FGF21 secretion or resistance in peripheral tissues is the initiating factor in altering FGF21 levels and function in humans is unknown. Methods: I have studied the role of the rs838133 polymorphism in regulating FGF21 protein expression in-vivo and in-vitro. Then, I explored the mechanisms by which this single nucleotide polymorphism (SNP) modulates FGF21 production. I utilized RiboLace methodology to examine FGF21 production associated with the ribosomal translationally active fraction. Next I developed an in-vitro genetic model to help resolve the paradox of FGF21 expression in metabolic disorders. Furthermore, I studied the association between rs838133 and the expression of FGF21 receptors and activity. Finally, I related my findings back to tissue and explored the functional impact of rs838133 on hepatic inflammation. Results: I have shown that the minor (A) allele of the rs838133 polymorphism is associated with higher levels of circulating and hepatic FGF21 and it is not associated with the expression of fibroblast growth factor receptor 1 (FGFR1), Klotho-β (KLB) nor fibroblast activation protein (FAP) and hence and does not alter FGF21 signalling or activity. Then I identified an unanticipated mechanism for the FGF21 levels variation which is a genotype dependant alteration in the translational rate of FGF21. This alteration is most probably the primary event which results in FGF21 levels disturbance. Furthermore, I have demonstrated that codon bias and secondary mRNA structure are pivotal elements of the effect of rs838133 on the FGF21 translation rate. Additionally, I have proposed that ribosomal protein lateral stalk subunit P0 (RPLP0) could be the link between metabolic stress and FGF21 overexpression in metabolic disorders. Finally, I have related my results back to tissue and identified that under metabolic stress, the rs838133 has a deferential inflammatory response in-vivo and in-vitro. Conclusion: My results highlight a dominant role for translation of the FGF21 protein to explain variations in blood levels that is at least partially inherited. These results provide a framework for translational reprogramming of FGF21 to treat metabolic diseases.