FOXO3A-Short is a Novel Regulator of Non-Oxidative Glucose Metabolism Associated with Human Longevity

Abstract

In humans, intronic polymorphisms in FOXO3A are associated with extreme longevity. Despite many studies reporting this association it is unclear how these polymorphisms alter FOXO3A functionality and human physiology thereby influencing human lifespan. Here, we identify a novel minimally conserved FOXO3A transcriptional isoform, FOXO3A-Short (FOXO3A-S), encoding a major longevity-associated single-nucleotide polymorphism, rs9400239 (C or T), within its 5’ untranslated region. Strikingly, the FOXO3A-S mRNA is highly expressed in skeletal muscle and has very limited expression in other tissues. We find that the rs9400239 variant influences the stability and functionality of the primarily nuclear protein(s) encoded by the FOXO3A-S mRNA. Assessment of the relationship between the FOXO3A-S polymorphism and peripheral glucose clearance during insulin infusion (Rd clamp) in a cohort of Danish twins revealed that longevity T-allele carriers have markedly faster peripheral glucose clearance rates than normal lifespan C-allele carriers. In vitro experiments in human myotube cultures utilizing overexpression of each allele showed that the C-allele repressed glycolysis independently of PI3K signaling while overexpression of the T-allele repressed glycolysis only in a PI3K-inactive background. Supporting this finding inducible knockdown of the FOXO3A-S C-allele in cultured myotubes increased the glycolytic rate. We conclude that the rs9400239 polymorphism acts as a molecular switch which changes the identity of the FOXO3A-S-derived protein(s) which in turn alters the relationship between FOXO3A-S and insulin/PI3K signaling and glycolytic flux in skeletal muscle. This critical difference endows carriers of the FOXO3A-S T-allele with consistently higher insulin-stimulated peripheral glucose clearance rates which may contribute to their longer and healthier lifespans.