Vitamin D receptor is required for dietary calcium-induced repression of calbindin-D9k expression in mice

Dietary calcium levels regulate calcium transporter gene expression levels in the small intestine of broiler chickens

1. This study investigated the effect of dietary calcium (Ca) levels on growth performance, bone development and Ca transporter gene expression levels in the small intestine of broiler chickens.2. On the day of hatch, 350, Ross 308 male broilers were randomly allotted to one of five treatments with five replicate pens each and 14 birds per pen. Dietary Ca levels in feed were 5.0, 7.0, 9.0, 11.0 and 13.0 g/kg, in which 9.0 g/kg was in the control diet. All diets contained 4.5 g/kg non-phytate phosphorus (NPP).3. The increase in dietary Ca levels from 5.0 to 13.0 g/kg did not affect the growth performance of 1- to 18-day-old broilers (P > 0.05).4. Increasing the Ca levels linearly increased the ash weight and the contents of ash, Ca and phosphorus (P) in the tibia of broilers at 18 days of age (P < 0.05). The contents of ash, Ca and P in broilers fed with 9.0 g/kg Ca were higher than those in birds fed with 5.0 g/kg Ca (P < 0.05).5. Increasing the Ca levels linearly decreased mRNA expression levels of the Ca-binding protein 28-kDa (CaBP-D28k), plasma membrane Ca-transporting ATPase 1b (PMCAlb), sodium (Na)/Ca exchanger 1 (NCX1), nuclear vitamin D receptor (nVDR) and membrane vitamin D receptor (mVDR) in the duodenum of broilers at 18 d of age (P < 0.05). Similar results were seen in the jejunum and ileum. Broilers fed 9.0-13.0 g/kg Ca in feed had lower mRNA expression levels of CaBP-D28k and PMCAlb in the small intestine than birds fed 5.0 g/kg Ca in feed (P < 0.05).6. The data indicated that low levels of dietary Ca stimulated its transporter gene transcription and promoted absorption, but high levels of Ca inhibited transporter gene expression and prevented excessive absorption in the small intestine of broiler chickens.

Potential of Food Hydrolyzed Proteins and Peptides to Chelate Iron or Calcium and Enhance their Absorption

Iron and calcium are two essential micronutrients that have strong effects on nutrition and human health because of their involvement in several biological and redox processes. Iron is responsible for electron and oxygen transport, cell respiration, and gene expression, whereas calcium is responsible for intracellular metabolism, muscle contraction, cardiac function, and cell proliferation. The bioavailability of these nutrients in the body is dependent on enhancers and inhibitors, some of which are found in consumed foods. Hydrolyzed proteins and peptides from food proteins can bind these essential minerals in the body and facilitate their absorption and bioavailability. The binding is also important because excess free iron will increase oxidative stress and the risks of developing chronic diseases. This paper provides an overview of the function of calcium and iron, and strategies to enhance their absorption with an emphasis on hydrolyzed proteins and peptides from foods. It also discusses the relationship between the structure of peptides and their potential to act as transition metal ligands.

High dose vitamin D3 attenuates the hypocalciuric effect of thiazide in hypercalciuric rats

Thiazide is known to decrease urinary calcium excretion. We hypothesized that thiazide shows different hypocalciuric effects depending on the stimuli causing hypercalciuria. The hypocalciuric effect of hydrochlorothiazide (HCTZ) and the expression of transient receptor potential vanilloid 5 (TRPV5), calbindin-D(28K), and several sodium transporters were assessed in hypercalciuric rats induced by high calcium diet and vitamin D(3). Urine calcium excretion and the expression of transporters were measured from 4 groups of Sprague-Dawley rats; control, HCTZ, high calcium-vitamin D, and high calcium-vitamin D with HCTZ groups. HCTZ decreased urinary calcium excretion by 51.4% in the HCTZ group and only 15% in the high calcium-vitamin D with HCTZ group. TRPV5 protein abundance was not changed by HCTZ in the high calcium-vitamin D with HCTZ group compared to the high calcium-vitamin D group. Protein abundance of NHE3, SGLT1, and NKCC2 decreased in the hypercalciuric rats, and only SGLT1 protein abundance was increased by HCTZ in the hypercalciuric rats. The hypocalciuric effect of HCTZ is attenuated in high calcium and vitamin D-induced hypercalciuric rats. This attenuation seems to have resulted from the lack of HCTZ's effect on protein abundance of TRPV5 in severe hypercalciuric condition induced by high calcium and vitamin D.

Gene expression changes in the jejunum of rats during the transient suckling-weaning period

It is well-known that the small intestine of rodents rapidly undergoes differentiation and maturation during the transient suckling-weaning period from postnatal days 13 to 27. In the present study, we examined the gene expression changes in the jejunum of rats during the transient suckling-weaning period by microarray analysis. In the microarray data, we found that the expressions of many genes related to digestion/absorption/excretion of nutrients/ions, such as members of the solute carrier (Slc) family and ATP-binding cassette (Abc) subfamily, were rapidly induced during this period. Furthermore, some transcriptional factors/cofactors (Thrsp, Ppargc1a, Klf15 and Vdr), which are presumably important for the induction of intestinal gene expression after weaning, were rapidly induced during this period. In contrast, genes related to transport of nutrients, such as folate, zinc, fat and phosphate, which are important for early development, were highly expressed in the suckling period and then gradually decreased during weaning. These results indicate that the jejunum matures during the suckling-weaning period accompanied by changes in the expression of many genes related to digestion/absorption/excretion and some genes for transcriptional factors/cofactors.

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).

Vitamin D and human health: lessons from vitamin D receptor null mice

The vitamin D endocrine system is essential for calcium and bone homeostasis. The precise mode of action and the full spectrum of activities of the vitamin D hormone, 1,25-dihydroxyvitamin D [1,25-(OH)(2)D], can now be better evaluated by critical analysis of mice with engineered deletion of the vitamin D receptor (VDR). Absence of a functional VDR or the key activating enzyme, 25-OHD-1alpha-hydroxylase (CYP27B1), in mice creates a bone and growth plate phenotype that mimics humans with the same congenital disease or severe vitamin D deficiency. The intestine is the key target for the VDR because high calcium intake, or selective VDR rescue in the intestine, restores a normal bone and growth plate phenotype. The VDR is nearly ubiquitously expressed, and almost all cells respond to 1,25-(OH)(2)D exposure; about 3% of the mouse or human genome is regulated, directly and/or indirectly, by the vitamin D endocrine system, suggesting a more widespread function. VDR-deficient mice, but not vitamin D- or 1alpha-hydroxylase-deficient mice, and man develop total alopecia, indicating that the function of the VDR and its ligand is not fully overlapping. The immune system of VDR- or vitamin D-deficient mice is grossly normal but shows increased sensitivity to autoimmune diseases such as inflammatory bowel disease or type 1 diabetes after exposure to predisposing factors. VDR-deficient mice do not have a spontaneous increase in cancer but are more prone to oncogene- or chemocarcinogen-induced tumors. They also develop high renin hypertension, cardiac hypertrophy, and increased thrombogenicity. Vitamin D deficiency in humans is associated with increased prevalence of diseases, as predicted by the VDR null phenotype. Prospective vitamin D supplementation studies with multiple noncalcemic endpoints are needed to define the benefits of an optimal vitamin D status.

Relationship of vitamin D with calbindin D9k and D28k expression in ameloblasts

OBJECTIVE

Calbindin D9k (CB9k) and D28k (CB28k) are intracellular soluble calcium-binding proteins, whose expressions are considered to be regulated by vitamin D. However, the amount of CB28k expression in the kidneys of vitamin D receptor-null mice was reported to be similar to that in wild type mice, suggesting no dependence on vitamin D for its expression in kidneys. In the present study, we evaluated the effects of vitamin D on the expressions of CB9k and CB28k during amelogenesis.

DESIGN

Rats fed a vitamin D-deficient diet (VD(-) rats) or a standard diet (VD(+) rats) were subjected to immunohistochemical assays using anti-CB9k and anti-CB28k anti-serum. Further, after culturing in medium containing 1,25(OH)(2)D(3) at various doses, quantitative RT-PCR analyses of CB9k and CB28k mRNA were performed using tooth germs from the lower first molars of ICR mice.

RESULTS

CB9k-immunoreactivity was detected faintly during the secretory stage of ameloblasts in the incisors of VD(+) rats, with increased staining observed during the maturation stage, whereas no such immunoreactivity was detected in those of VD(-) rats. In contrast, the distribution of CB28k in the teeth of VD(-) rats was nearly identical to that in teeth of VD(+) rats, with immunoreactivity detected in both secretory and maturation ameloblasts. Further, quantitative RT-PCR analyses revealed that the amount of CB9k mRNA was increased in a dose-dependent manner, whereas that of CB28k mRNA was not changed.

CONCLUSIONS

Vitamin D has no effect on the expression of CB28k, whereas it has a significant effect on that of CB9k in ameloblasts.

Thalamic calcification in vitamin D receptor knockout mice

Vitamin D is a steroid hormone with many important functions in the brain, mediated through the nuclear vitamin D receptor. Here, we report that aging nuclear vitamin D receptor knockout mice demonstrate a symmetric thalamic calcification with numerous Ca/P-containing laminated bodies. These results are consistent with clinical findings showing brain calcification in patients with vitamin D deficiency. Our results suggest that nuclear vitamin D receptor deficiency leads to brain mineralization in vitamin D receptor knockout mice, which may represent an experimental model of intracranial calcification.

Increased severity of chemically induced seizures in mice with partially deleted Vitamin D receptor gene

Vitamin D is a neuroactive steroid hormone with multiple functions in the brain. Numerous clinical and experimental data link various Vitamin D-related dysfunctions to epilepsy. Here, we study the role of Vitamin D receptors (VDRs) in experimental epilepsy in mice. To examine this problem, we assessed the seizure profiles in VDR knockout mice following a systemic injection of pentylenetetrazole (70 mg/kg). Overall, compared to the wild-type (WT) 129S1 mice (n=10 in each group), the VDR knockout group significantly demonstrated shorter latencies to the onset, higher Racine scores and increased mortality rates. Our findings suggest that VDRs modulate seizure susceptibility in mice, and that the Vitamin D/VDR endocrine system may be involved in the pathogenesis of epilepsy.