UbiA prenyltransferase domain containing 1 (UBIAD1) is a novel vitamin K2 biosynthetic enzyme screened and identified from the human genome database. UBIAD1 has recently been shown to catalyse the biosynthesis of Coenzyme Q10 (CoQ10) in zebrafish and human cells. To investigate the function of UBIAD1 in vivo, we attempted to generate mice lacking Ubiad1, a homolog of human UBIAD1, by gene targeting. Ubiad1-deficient (Ubiad1(-/-)) mouse embryos failed to survive beyond embryonic day 7.5, exhibiting small-sized body and gastrulation arrest. Ubiad1(-/-) embryonic stem (ES) cells failed to synthesize vitamin K2 but were able to synthesize CoQ9, similar to wild-type ES cells. Ubiad1(+/-) mice developed normally, exhibiting normal growth and fertility. Vitamin K2 tissue levels and synthesis activity were approximately half of those in the wild-type, whereas CoQ9 tissue levels and synthesis activity were similar to those in the wild-type. Similarly, UBIAD1 expression and vitamin K2 synthesis activity of mouse embryonic fibroblasts prepared from Ubiad1(+/-) E15.5 embryos were approximately half of those in the wild-type, whereas CoQ9 levels and synthesis activity were similar to those in the wild-type. Ubiad1(-/-) mouse embryos failed to be rescued, but their embryonic lifespans were extended to term by oral administration of MK-4 or CoQ10 to pregnant Ubiad1(+/-) mice. These results suggest that UBIAD1 is responsible for vitamin K2 synthesis but may not be responsible for CoQ9 synthesis in mice. We propose that UBIAD1 plays a pivotal role in embryonic development by synthesizing vitamin K2, but may have additional functions beyond the biosynthesis of vitamin K2.
It has been demonstrated that single nucleotide polymorphism (SNP) (R325Q, 974G>A) in the gamma-glutamyl carboxylase (GGCX) gene is associated with the bone mineral density (BMD). In the present study, we investigated the effect of GGCX polymorphism (974G>A) on the correlations among the vitamin K in-take, level of serum vitamin K, and ratio of undercarboxylated osteocalcin (ucOC) to intact osteocalcin (OC) in healthy young Japanese subjects.Healthy young adult subjects (n=189) were genotyped for the poly-morphism, and we measured the levels of serum vitamin K, intact OC, ucOC, and dietary nutrient intakes.Dietary vitamin K intake from vegetables was significantly correlated with the level of serum phylloquinone (PK), and vitamin K intake from fermented beans, natto, was also significantly correlated with the level of serum menaquinone-7 (MK-7). Moreover, the total dietary vitamin K intake showed a significant negative correlation with the ratio of ucOC to intact OC. Interestingly, on grouping by the GGCX genotype, there was a significant interaction between the ratio of ucOC to intact OC with vitamin K intake in homozygotes (GG-type) and heterozygotes (GA-type) (p<0.001). These results suggest that an adequate nutritional strategy is necessary for people with high-risk genotypes (GG- or GA-type).We demonstrated the effects of SNP (974G>A) in the GGCX gene on the correlation between dietary vitamin K intake and gamma-carboxylation of serum OC. Our data may be useful for planning strategies to prevent osteoporosis.前言：γ-麩胺醯羧化酶(GGCX)基因的單核苷酸多型性(SNP)與骨骼礦物質密度 (BMD)之相關性已被證實。本篇研究探討，在日本的健康年輕受試者中，其 GGCX 多型性(974G>A)對於維生素K 攝取、血清中維生素K 濃度和羧化不全骨 鈣素(ucOC)與完整骨鈣素(OC)比值之間關聯性的影響。方法：共有189 位健康 年輕成人進行基因多型性檢測，並測量其血清中維生素K、OC、ucOC 濃度和 飲食中營養素攝取量。結果：飲食中攝取來自蔬菜的維生素K 與血清中維生素 K1(PK；葉綠醌)有顯著相關；而攝取來自發酵豆類-納豆的維生素K 也與血清中 維生素K2(MK-7；甲萘醌-7)有顯著相關。此外，從飲食中攝取的總維生素K 和 ucOC 與OC 比值有顯著負相關。值得注意的是，將GGCX 基因型分組時發現， 同型結合子(GG-type)和異型結合子(GA-type)兩組的ucOC 與OC 比值和維生素 K 攝取有顯著交互作用(p<0.001)。以上結果顯示，適當的營養策略對於具有高 風險基因型(GG-或GA-type)的人是必要的。結論：本研究證實GGCX 基因中的 SNP(974G>A)多型性對於飲食維生素K 攝取與血清骨鈣素γ-羧化相關性之效 應。本資料對於規劃預防骨質疏鬆症之策略也許會有幫助。
To study the adequate intake (AI) for vitamin D in the elderly, we have performed an intervention study with 800 IU/d of vitamin D3 in the institutionalized elderly. Sixty-two institutionalized elderly were randomly assigned to two groups; receiving either supplements of 200 mg calcium plus 800 IU vitamin D3/d (Ca+VD group), or supplements of 200 mg calcium/d (Ca group) for 30 d in October. Serum concentrations of 25-hydroxyvitamin D (25OH-D), parathyroid hormone (PTH), and bone turnover markers were measured before and after intervention. Average dietary vitamin D intake during the intervention period was approximately 300 IU/d in both groups, exceeding the AI in Dietary Reference Intakes for Japanese 2005 of 200 IU/d. In both groups, mean serum 25OH-D level at baseline fell into the hypovitaminosis D range (9.7 ng/mL), despite apparently adequate vitamin D intake. Serum PTH level at baseline was within the reference range. Mean serum 25OH-D concentration significantly increased to 19.3 ng/mL in the Ca+VD group and to 11.1 ng/mL in the Ca group. Post intervention serum 25OH-D level was significantly higher in the Ca+VD group than in the Ca group (p<0.001). In 53 subjects (85.5%) who took more than 80% of their supplements for 30 d, serum PTH level in the Ca+VD group was significantly lower than in the Ca groups (p=0.05). Bone turnover markers were not significantly changed after intervention in either group. Daily supplementation of 800 IU vitamin D3 was considered effective in the institutionalized elderly with minimal chance of sun exposure, but further studies with longer duration are necessary.
Increases of fracture or bedridden and mortality rates associated with fracture are serious social problems in Japan. Therefore, not only the treatment but also the prevention of osteoporosis is important for the benefit of individual QOL and also to reduce the financial burden on society. Vitamin D plays an important role in the regulation of calcium homeostasis and bone metabolism. Among vitamin D metabolites, the serum 25-hydroxyvitamin D (25-D) concentration is the best indicator to assess the vitamin D status. It is known that a mild decrease in the serum 25-D concentration (vitamin D insufficiency) leads to secondary hyperparathyroidism, which has a negative effect on bone metabolism in the elderly. Therefore, vitamin D insufficiency is thought to be one of the risk factors of osteoporosis. Vitamin D insufficiency is common throughout the world. In Japan, we have also confirmed that around half of elderly women show vitamin D insufficiency. Recently, several meta-analyses of vitamin D supplementation to prevent fracture and bone loss in elderly people have been reported. In the present study, current epidemiological studies on the vitamin D status and prevention of osteoporosis, and the requirement of vitamin D to prevent osteoporosis are reviewed.
UbiA prenyltransferase domain-containing protein 1 (UBIAD1) plays a significant role in vitamin K2 (MK-4) synthesis. We investigated the enzymological properties of UBIAD1 using microsomal fractions from Sf9 cells expressing UBIAD1 by analysing MK-4 biosynthetic activity. With regard to UBIAD1 enzyme reaction conditions, highest MK-4 synthetic activity was demonstrated under basic conditions at a pH between 8.5 and 9.0, with a DTT ≥0.1 mM. In addition, we found that geranyl pyrophosphate and farnesyl pyrophosphate were also recognized as a side-chain source and served as a substrate for prenylation. Furthermore, lipophilic statins were found to directly inhibit the enzymatic activity of UBIAD1. We analysed the aminoacid sequences homologies across the menA and UbiA families to identify conserved structural features of UBIAD1 proteins and focused on four highly conserved domains. We prepared protein mutants deficient in the four conserved domains to evaluate enzyme activity. Because no enzyme activity was detected in the mutants deficient in the UBIAD1 conserved domains, these four domains were considered to play an essential role in enzymatic activity. We also measured enzyme activities using point mutants of the highly conserved aminoacids in these domains to elucidate their respective functions. We found that the conserved domain I is a substrate recognition site that undergoes a structural change after substrate binding. The conserved domain II is a redox domain site containing a CxxC motif. The conserved domain III is a hinge region important as a catalytic site for the UBIAD1 enzyme. The conserved domain IV is a binding site for Mg2+/isoprenyl side-chain. In this study, we provide a molecular mapping of the enzymological properties of UBIAD1.
