Rieko Tanabe

Influences of dietary vitamin D restriction on bone strength, body composition and muscle in rats fed a high-fat diet: involvement of mRNA expression of MyoD in skeletal muscle.

Vitamin D insufficiency is associated with a greater risk of osteoporosis and also influences skeletal muscle functions, differentiation and development. The present study investigated the influences of vitamin D restriction on the body composition, bone and skeletal muscle in rats fed a high-fat diet. Sprague-Dawley strain male rats (11weeks old) were divided into four groups and fed experimental diets: a basic control diet (Cont.), a basic control diet with vitamin D restriction (DR), a high-fat diet (F) and a high-fat diet with vitamin D restriction (FDR). At 28days after starting the experimental diets, the visceral fat mass was significantly increased in the F group compared with Cont. group, and the muscle mass tended to decrease in the DR group compared with Cont. group. The total volume of the femur was significantly lower in the DR group compared with Cont. group, and the bone mineral density (BMD) of the femur was significantly lower in the FDR group compared with F group. MyoD is one of the muscle-specific transcription factors. The levels of mRNA expression of MyoD of the gastrocnemius and soleus muscles from the DR group were reduced markedly compared with those from the Cont. group. In conclusion, our findings revealed the influences of a vitamin D-restricted high-fat diet on the bone strength, body composition and muscle. Further studies on vitamin D insufficiency in the regulation of muscle as well as fat and bone metabolism would provide valuable data for the prevention of lifestyle-related disorders, including osteoporosis and sarcopenia.

Spatiotemporal disorder in the axial skeleton development of the Mesp2-null mouse: A model of spondylocostal dysostosis and spondylothoracic dysostosis

Spondylocostal dysostosis (SCDO) is a genetic disorder characterized by severe malformation of the axial skeleton. Mesp2 encodes a basic helix-loop-helix type transcription factor that is required for somite formation. Its human homologue, Mesp2, is a gene affected in patients with SCDO and a related vertebral disorder, spondylothoracic dysostosis (STDO). This work investigated how the loss of Mesp2 affects axial skeleton development and causes the clinical features of SCDO and STDO. We first confirmed, by three-dimensional computed tomography scanning, that Mesp2-null mice exhibited mineralized tissue patterning resembling the radiological features of SCDO and STDO. Histological observations and in situ hybridization probing for extracellular matrix molecules demonstrated that the developing vertebral bodies in Mesp2-null mice were extensively fused with rare insertions of intervertebral tissue. Unexpectedly, the intervertebral tissues were mostly fused longitudinally in the vertebral column, instead of exhibiting extended formation, as was expected based on the caudalized properties of Mesp2-null somite derivatives. Furthermore, the differentiation of vertebral body chondrocytes in Mesp2-null mice was spatially disordered and largely delayed, with an increased cell proliferation rate. The quantitative three-dimensional immunofluorescence image analyses of phospho-Smad2 and -Smad1/5/8 revealed that these chondrogenic phenotypes were associated with spatially disordered inputs of TGF-β and BMP signaling in the Mesp2-null chondrocytes, and also demonstrated an amorphous arrangement of cells with distinct properties. Furthermore, a significant delay in ossification in Mesp2-null vertebrae was observed by peripheral quantitative computed tomography. The current observations of the spatiotemporal disorder of vertebral organogenesis in the Mesp2-null mice provide further insight into the pathogenesis of SCDO and STDO, and the physiological development of the axial skeleton.

Retention of bone strength by feeding of milk and dairy products in ovariectomized rats: involvement of changes in serum levels of 1alpha, 25(OH)2D3 and FGF23

The current study compared the effects of milk, yogurt or whey on the bone strength, body composition and serum biomarkers. Forty 12-week-old female Sprague-Dawley rats were ovariectomized (OVX), and another nine rats received a sham operation (Sham-Cont). After a 1-week recovery period, the OVX rats were divided into four dietary groups: OVX-control group (OVX-Cont), 17% skimmed milk powder diet group (OVX-Milk), 17% powdered fermented milk diet group (OVX-Yogurt) and 12% whey powder and 6% whey protein extract diet group (OVX-Whey) (n=10 in each group). The protein, nitrogen, fat, calcium and phosphorus contents of the experimental diets were adjusted to be similar to the control diet (AIN-93M). Eighty-four days after the beginning of the experimental diet, the total bone mineral density and bone mineral contents of lumbar vertebrae were significantly higher in the OVX-Milk and OVX-Whey groups than in the OVX-Cont group. Furthermore, the level of 1alpha, 25-dihydroxyvitamin D3 [1alpha, 25(OH)2D3] was significantly lower, while the serum level of FGF23 was significantly higher in the OVX-Milk, OVX-Yogurt and OVX-Whey groups than in the OVX-Cont group. These findings suggest that milk and the dairy products could improve bone metabolism in a postmenopausal animal model at least partly through changing the balance between 1alpha, 25(OH)2D3 and FGF23.

Effects of Gamma-Glutamyl Carboxylase Gene Polymorphism (R325Q) on the Association between Dietary Vitamin K Intake and Gamma-Carboxylation of Osteocalcin in Young Adults

INTRODUCTION 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. METHODS 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. RESULTS 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). CONCLUSIONS 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.

Menaquinone-4 (vitamin K2) up-regulates expression of human intestinal alkaline phosphatase in Caco-2 cells.

Alkaline phosphatase (ALP) hydrolyzes several monophosphate esters into inorganic acid and alcohol. In humans, 4 kinds of ALP isozymes have been identified: tissue-nonspecific ALP, intestinal ALP, placental ALP, and germ cell ALP. Intestinal ALP is expressed at a high concentration in the brush border membrane of intestinal epithelial cells and is known to be affected by several kinds of nutrients, such as lipids, but the physiological function of intestinal ALP has remained elusive. Vitamin K is an essential cofactor for the posttranslational carboxylation of glutamate residues into γ-carboxy glutamate. Menaquinone-4 (MK-4) with 4 isoprene units, vitamin K2, has been shown to induce bone-type ALP activity and osteoblastogenesis in human bone marrow cells. In this study, we investigated the effects of MK-4 on the level of ALP activity and expression of ALP messenger RNA in the human colon carcinoma cell line Caco-2, which is known to differentiate into small intestinal epithelial cells in vitro. After treatment with MK-4, there were significant increases in the ALP activities of Caco-2 cells. Inhibitor and thermal inactivation experiments demonstrated that the increased ALP had properties of intestinal-type ALP. Semiquantitative reverse transcription-polymerase chain reaction analysis revealed that expressions of human intestinal ALP and sucrase-isomaltase, which are intestinal differentiation markers, were highly enhanced in Caco-2 cells by MK-4. This is the first report concerning ALP messenger RNA expression induced by vitamin K2 in Caco-2 cells. Further studies on the physiological functions of human intestinal ALP will provide useful data on the novel effects of vitamin K.

Effects of Fok-I Polymorphism in Vitamin D Receptor Gene on Serum 25-Hydroxyvitamin D, Bone-Specific Alkaline Phosphatase and Calcaneal Quantitative Ultrasound Parameters in Young Adults

Several genes have been implicated as genetic determinants of osteoporosis. Vitamin D receptor (VDR) is an intracellular hormone receptor that specifically binds to the biologically active form of vitamin D, 1-alpha, 25- dihydroxyvitamin D3 [1, 25(OH)2D], and mediates its effects. One of the most frequently studied single nucleotide polymorphisms is the restriction fragment length polymorphism (RFLP) Fok-I (rs2228570). The presence of a Fok-I site, designated f, allows protein translation to initiate from the first ATG. An allele lacking the site (ATG>ACG: designated F), initiates from a second ATG site. In the present study, we explored the effect of the VDR Fok-I genotype on associations among serum bone-specific alkaline phosphatase (ALP), 25- hydroxyvitamin D3 [25(OH)D], 1, 25(OH)2D, and the dietary nutrient intake in healthy young Japanese subjects (n=193). Dietary nutrient intakes were calculated based on 3-day food records before the day of blood examinations. Quantitative ultrasound (QUS) parameters at the right calcaneus (heel bone) were measured. The allele frequencies were 0.622 for the F allele and 0.378 for the f allele in all subjects. Grouped by the VDR genotype, a significant positive correlation between the levels of serum bone-specific ALP and 25(OH)D was observed in the FF-type (p=0.005), but not in the ff-type. In addition, there was a significant positive correlation between the level of serum 25(OH)D and osteo-sono assessment index (OSI) in the FF-type (p=0.008), but not in the ff-type. These results suggest that the level of circulating 25(OH)D is an important factor when assessing the VDR Fok-I polymorphism to prevent osteoporosis.

Associations between Serum Bone-Specific Alkaline Phosphatase Activity, Biochemical Parameters, and Functional Polymorphisms of the Tissue-nonspecific Alkaline Phosphatase Gene in a Japanese Population

INTRODUCTION We had demonstrated that single nucleotide polymorphism (787T>C) in the tissue-nonspecific ALP (TNSALP) gene was associated with the bone mineral density (BMD). BMD was the lowest among TNSALP 787T homozygotes (TT-type) and highest among TNSALP 787T>C homozygotes (CC-type) in postmenopausal women. In the present study, we investigated the effects of the TNSALP genotype on associations among serum bonespecific alkaline phosphatase (BAP), serum calcium, and phosphorus in healthy young Japanese subjects. METHODS Young healthy adult subjects (n=193) were genotyped for the polymorphism, and we measured the levels of serum BAP, serum calcium, and phosphorus. Dietary nutrient intakes were calculated based on 3-day food records before the day of blood examinations. RESULTS Grouped by the TNSALP genotype, a significant negative correlation between serum BAP and phosphorus was observed in 787T>C homozygotes (CC-type), but not in heterozygotes (TCtype), nor in 787T homozygotes (TT-type). CONCLUSIONS In the present study, we revealed that the single nucleotide polymorphism 787T>C in the TNSALP gene had effects on the correlation between serum BAP and phosphorus in young adult subjects. These results suggest that variation in TNSALP may be an important determinant of phosphate metabolism. Our data may be useful for planning strategies to prevent osteoporosis.