Naturally occurring UBIAD1 mutations differentially affect menaquinone biosynthesis and vitamin K‐dependent carboxylation

Abstract

UbiA prenyltransferase domain‐containing protein‐1 (UBIAD1) is responsible for the biosynthesis of menaquinone‐4 (MK‐4), a cofactor for extrahepatic carboxylation of vitamin K‐dependent (VKD) proteins. Genetic variations of UBIAD1 are mainly associated with Schnyder corneal dystrophy (SCD), a disease characterized by abnormal accumulation of cholesterol in the cornea. Results from in vitro studies demonstrate that SCD‐associated UBIAD1 mutations are defective in MK‐4 biosynthesis. However, SCD patients do not exhibit typical phenotypes associated with defects of MK‐4 or VKD carboxylation. Here, we coupled UBIAD1’s biosynthetic activity of MK‐4 with VKD carboxylation in HEK293 cells that stably express a chimeric VKD reporter protein. The endogenous Ubiad1 gene in these cells was knocked out by CRISPR‐Cas9‐mediated genome editing. The effect of UBIAD1 mutations on MK‐4 biosynthesis and VKD carboxylation was evaluated in Ubiad1‐deficient reporter cells by determining the production of MK‐4 or by measuring the efficiency of reporter‐protein carboxylation. Our results show that the hot‐spot mutation N102S has a moderate impact on MK‐4 biosynthesis (retained ˜ 82% activity) but does not affect VKD carboxylation. However, the G186R mutation significantly affected both MK‐4 biosynthesis and VKD carboxylation. Other mutations exhibit varying degrees of effects on MK‐4 biosynthesis and VKD carboxylation. These results are consistent with in vivo results obtained from gene knock‐in mice and SCD patients. Our findings suggest that UBIAD1’s MK‐4 biosynthetic activity does not directly correlate with the phenotypes of SCD patients. The established cell‐based assays in this study provide a powerful tool for the functional studies of UBIAD1 in a cellular milieu.

Vitamin K and the Visual System: A Narrative Review

“…Lending support to these findings and possibly supplying corroboratory data, Chen et al [158], report a HEK293 cell-based model in which they selectively insert and test UBIAD1 mutant variants and independently measure MK4 biosynthesis and VKD protein carboxylation. Comparing p.Asn112Asp to p.Asp102Ser variants, they found an approximate 4.7x difference in VKD carboxylation which is in line with the nearly 4x MGP mRNA induction differences produced by these variants found by Sarosiak et al, thus showing some proportionality in the observed variant effects.…”

Vitamin K and age-related diseases

“…Кроме того, было показано, что концентрация МК-4 в головном мозге крысы положительно коррелирует с концентрацией сфинголипидов, особенно с сульфатидами и сфингомиелином, и как К1, так и МК-4 увеличиваются с потреблением К1. Это согласуется с представлением о том, что МК-4 является результатом конверсии К1 и что церебральный МК-4 возникает в результате приема К1 [34]. Несколько исследований на людях продемонстрировали наличие взаимосвязи между низким уровнем K1 и риском развития болезни Альцгеймера и ухудшением памяти у пожилых людей [26,35].…”

Vascular calcification in chronic kidney disease

“…No further information regarding UBIAD1 is published to date. However, taking into account these previous studies on SCD 69,131,135,136 , we hypothesise that there is a permanent or incorrect binding between HMGCR and UBIAD1, probably caused by the PTM in HMGCR under CKD conditions, that affects and decreases vitamin K2 synthesis. More studies on HMGCR-UBIAD1 binding and vitamin K status would be needed.…”

“…However, to date, there are not enough data available about this dystrophy and the vitamin K status of the patients. Nevertheless, in vitro studies have observed that most of the UBIAD1 mutations, associated with SCD, have a minimal effect on both MK4 biosynthesis and carboxylation of vitamin K-dependent proteins, finding only one mutation directly related to MK4 deficiency 135 . Another study in SCD patients has found increased plasma levels of dp-ucMGP, which would also correlate with low vitamin K status 136 .…”