Effect of dietary calcium and 1,25-(OH)2D3 on the expression of calcium transport genes in calbindin-D9k and -D28k double knockout mice.

The phenotypes of calbindin-D9k (CaBP-9k) and -28k (CaBP-28k) single knockout (KO) mice are similar to wild-type (WT) mice due to the compensatory action of other calcium transport proteins. In this study, we generated CaBP-9k/CaBP-28k double knockout (DKO) mice in order to investigate the importance of CaBP-9k and CaBP-28k in active calcium processing. Under normal dietary conditions, DKO mice did not exhibit any changes in phenotype or the expression of active calcium transport genes as compared to WT or CaBP-28k KO mice. Under calcium-deficient dietary conditions, the phenotype and expression of calcium transport genes in CaBP-28k KO mice were similar to WT, whereas in DKO mice, serum calcium levels and bone length were decreased. The intestinal and renal expression of transient receptor potential vanilloid member 6 (TRPV6) mRNA was significantly decreased in DKO mice fed a calcium-deficient diet as compared to CaBP-28k KO or WT mice, and DKO mice died after 4 weeks on a calcium-deficient diet. Body weight, bone mineral density (BMD) and bone length were significantly reduced in all mice fed a calcium and 1,25-(OH)(2)D(3)-deficient diet, as compared to a normal diet, and none of the mice survived more than 4 weeks. These results indicate that deletion of CaBP-28k alone does not affect body calcium homeostasis, but that deletion of CaBP-9k and CaBP-28k has a significant effect on calcium processing under calcium-deficient conditions, confirming the importance of dietary calcium and 1,25-(OH)(2)D(3) during growth and development.

The beneficial effect of the sap of Acer mono in an animal with low-calcium diet-induced osteoporosis-like symptoms.

The sap of Acer mono has been called 'bone-benefit-water' in Korea because of its mineral and sugar content. In particular, the calcium concentration of the sap of A. mono is 37.5 times higher than commercial spring water. In the current study, we examined whether A. mono sap could improve or prevent osteoporosis-like symptoms in a mouse model. Male mice (3 weeks old) were fed a low-calcium diet supplemented with 25, 50 or 100 % A. mono sap, commercial spring water or a high calcium-containing solution as a beverage for 7 weeks. There were no differences in weekly weight gain and food intake among all the groups. Mice that were given a low-calcium diet supplemented with commercial spring water developed osteoporosis-like symptoms. To assess the effect of sap on osteoporosis-like symptoms, we examined serum calcium concentration, and femur density and length, and carried out a histological examination. Serum calcium levels were significantly lower in mice that received a low-calcium diet supplemented with commercial spring water (the negative control group), and in the 25 % sap group compared to mice fed a normal diet, but were normal in the 50 and 100 % sap and high-calcium solution groups. Femur density and length were significantly reduced in the negative control and 25 % sap groups. These results indicate that a 50 % sap solution can mitigate osteoporosis-like symptoms induced by a low-calcium diet. We also examined the regulation of expression of calcium-processing genes in the duodenum and kidney. Duodenal TRPV6 and renal calbindin-D9k were up-regulated dose-dependently by sap, and the levels of these factors were higher than those attained in the spring water-treated control. The results demonstrate that the sap of A. mono ameliorates the low bone density induced by a low-calcium diet, most likely by increasing calcium ion absorption.

Dietary calcium and 1,25-dihydroxyvitamin D3 regulate transcription of calcium transporter genes in calbindin-D9k knockout mice.

The effect(s) of oral calcium and vitamin D(3) were examined on the expression of duodenal and renal active calcium transport genes, i.e., calbindin-D9k (CaBP-9k) and calbindin-D28k (CaBP-28k), transient receptor potential cation channels (TRPV5 and TRPV6), Na(+)/Ca(2+) exchanger 1 (NCX1) and plasma membrane calcium ATPase 1b (PMCA1b), in CaBP-9k KO mice. Wild-type (WT) and KO mice were provided with calcium and vitamin D(3)-deficient diets for 10 weeks. The deficient diet significantly decreased body weights compared with the normal diet groups. The serum calcium concentration of the WT mice was decreased by the deficient diet but was unchanged in the KO mice. The deficient diet significantly increased duodenal transcription of CaBP-9k and TRPV6 in the WT mice, but no alteration was observed in the KO mice. In the kidney, the deficient diet significantly increased renal transcripts of CaBP-9k, TRPV6, PMCA1b, CaBP-28k and TRPV5 in the WT mice but did not alter calcium-relating genes in the KO mice. Two potential mediators of calcium-processing genes, vitamin D receptor (VDR) and parathyroid hormone receptor (PTHR), have been suggested to be useful for elucidating these differential regulations in the calcium-related genes of the KO mice. Expression of VDR was not significantly affected by diet or the KO mutation. Renal PTHR mRNA levels were reduced by the diet, and reduced expression was also seen in the KO mice given the normal diet. Taken together, these results suggest that the active calcium transporting genes in KO mice may have resistance to the deficiency diet of calcium and vitamin D(3).