An O-GlcNAc transferase pathogenic variant that affects pluripotent stem cell self-renewal

Abstract

O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT) is an essential enzyme that modifies proteins with O-GlcNAc. Inborn OGT genetic variants were recently shown to mediate a novel type of Congenital Disorder of Glycosylation (OGT-CDG) which is characterized by X-linked intellectual disability (XLID) and developmental delay. Here, we report an OGTC921Y variant which co-segregates with XLID and epileptic seizures, and results in loss of catalytic activity. Colonies formed by mouse embryonic stem cells carrying OGTC921Y show decreased levels of protein O-GlcNAcylation accompanied by decreased levels of Oct4, Sox2 and extracellular alkaline phosphatase (ALP), implying reduced self-renewal capacity. These data establish a link between OGT-CDG and embryonic stem cell self-renewal, providing a foundation for examining the developmental aetiology of this syndrome.

Rescuable sleep and synaptogenesis phenotypes in aDrosophilamodel of O-GlcNAc transferase intellectual disability

“…Many mutations in OGT causal in intellectual disability modelled previously do not result in a decrease in global O-GlcNAcylation either in embryonic stem cells or patient derived fibroblasts, in many cases due to feedback mechanisms reducing OGA protein levels 3,5,8 . The mutation modelled here is one of only two which has been shown to reduce global O-GlcNAcylation when modelled in mammalian cells 6,22 . Here, we have shown that patient mutations in the catalytic domain of OGT result in decreased O-GlcNAcylation in adult flies, corroborating previous results 5 .…”

“…Expanding upon these results, we have demonstrated that an OGT-CDG catalytic domain mutation can reduce O-GlcNAcylation throughout development, despite a compensatory increase in total DmOGT protein. When modelled in mouse embryonic stem cells, this mutation (C921Y in humans and mice) also results in an increase in OGT protein levels 22 . It is tempting to assert that increased OGT, as opposed to decreased OGA, is a homeostatic mechanism linked specifically to this mutation.…”

“…The catalytic domain fulfils two known functions, the transfer of O-GlcNAc onto serine and threonine residues of nucleocytoplasmic proteins (O-GlcNAcylation) 17,18 , and the proteolytic activation of Host Cell Factor 1 (HCF-1) 19,20 , a known ID-associated protein 21 . While the latter function of OGT potentially contributes to the pathogenicity of some OGT mutations 5 , not all patient mutations have been found to affect HCF-1 processing, neither in vitro nor when modelled in stem cells 7,8,22 . Overall, the role of altered O-GlcNAcylation in OGT-CDG pathogenicity remains an open question, as many of the other functions fulfilled by this protein have the potential to contribute to ID.…”

Intellectual disability and neurogenesis defects associated with increased turnover of an O-GlcNAcase variant

“…Recently, several OGT missense mutations have been identified and characterized in patients affected by a new neurodevelopmental disorder associated with intellectual disability, development delay and dysmorphic features, called OGT-linked Congenital Disorder of Glycosylation (OGT-CDG) (18)(19)(20)(21)(22)(23)(24)(25). While this highlighted an important role of O-GlcNAcylation in neurodevelopment, the molecular mechanisms underlying the disease remain unknown.…”