Analysis of rat vitamin D-dependent calbindin-D28k gene expression

Influence of feeding and UVB exposition on the absorption mechanisms of calcium in the gastrointestinal tract of veiled chameleons (Chamaeleo calyptratus)

The purpose of this study was to investigate the influence of feeding and UVB exposition on the occurrence and distribution patterns of vitamin D receptors (VDR) and calbindin D28k (Cb-D28k) in the gastrointestinal tract of veiled chameleons. Thus, 56 veiled chameleon hatchlings were divided into six treatment groups: UV (with UVB exposure); No (no supplements, no UVB exposure); CaAUV (with calcium (Ca), vitamin A supplementation, UVB exposure); CaA (with Ca, vitamin A supplementation); CaADUV (with Ca, vitamin A, vitamin D supplementation, UVB exposure); and CaAD (with Ca, vitamin A, vitamin D supplementation). Animals were reared under the suspected conditions for 6 months on locust-based diets. Tissue samples of stomach, duodenum, ileum and colon were taken, and semi-quantitative immunohistochemical methods (IHC) were performed to detect Cb-D28k and VDR. VDR immunoreactions were higher in the luminal epithelium of the duodenum than in that of the ileum. VDR immunoreactions in the luminal epithelium were higher at the base of the villi of the duodenum as compared to the tip. Cb-D28k immunoreactions were mainly observed in the luminal epithelium of the duodenum. The two groups treated with all dietary supplements (CaADUV, CaAD) exhibited a higher Cb-D28k immunoreaction as those with no supplements and UVB exposure only. No immunoreaction for both proteins could be detected in the stomach. This study suggests that the duodenum plays an important role in the active transcellular absorption of Ca in veiled chameleons as shown by the immunohistochemical detection of VDR and Cb-D28k. Expression of Cb-D28k, in particular, appears to be regulated by dietary supplementation of vitamin D and vitamin A. VDRs, however, tended to be upregulated when animals were not supplemented with Ca, vitamin D and vitamin A. This may be due to the decreased Ca concentrations which caused vitamin D activation in the skin without any supplementation, but UVB exposure.

Regulation of tight junction gene expression in the kidney of calbindin-D9k and/or -D28k knockout mice after consumption of a calcium- or a calcium/vitamin D-deficient diet

BACKGROUND

Calciotropic hormones were thought to facilitate calcium transfer through active transcellular or passive paracellular pathway for calcium homeostasis. While calcium transport proteins such as CaBP-28 k, TRPV5, NCX1, PMCA1b are involved in calcium reabsorption of the renal tubule using transcellular transport, tight junction proteins are known as critically related to calcium absorption through paracellular pathway. The regulation of each pathway for calcium transport was well studied but the correlation was not. It is expected that present study will provide new information about the link between transcellular and paracellular pathway within renal tubules.

RESULTS

Transcripts and proteins of tight junction related genes (occludin, ZO-1, and claudins) were examined in CaBP-9 k-and/or-28 k-deficient mice as well as the effect of dietary calcium and/or vitamin D supplementation. With a normal diet, the transcriptional and translational expressions of most tight junction proteins in the kidney was not significantly changed but with a calcium- and vitamin D-deficient diet, and they were significantly increased in the kidney of the CaBP-28 k and CaBP-9 k/28 k double KO (DKO) mice. In these genotypes, the increase of tight junction related transcripts and proteins are referred to as an evidence explaining correlation between transcellular transport and paracellular pathway.

CONCLUSIONS

These findings are particularly interesting in evidences that insufficient transcellular calcium transports are compensated by paracellular pathway in calcium or calcium/vitamin D deficient condition, and that both transcellular and paracellular pathways functionally cooperate for calcium reabsorption in the kidney.

Alteration of tight junction gene expression by calcium- and vitamin D-deficient diet in the duodenum of calbindin-null mice

Calcium absorption is regulated by both active (transcellular) and passive (paracellular) pathways. Although each pathway has been studied, correlations between the two pathways have not been well elucidated. In previous investigations, the critical transcellular proteins, calbindin-D_9k (CaBP-9k) and -D_28k (CaBP-28k), were shown to affect other transcellular pathways by buffering intracellular calcium concentrations. The rate of paracellular calcium transport in the duodenum is generally determined by the expression of tight junction genes. In the present study, the effect of dietary calcium and/or vitamin D supplementation on the expression of tight junction genes (occludin, ZO-1 and claudin 2, 10b, 12 and 15) in the duodenum of CaBP-9k- and/or -28k-deficient mice was examined. With a normal diet, the expression of most tight junction genes in the duodenum was significantly increased in CaBP-9k knockout (KO) mice compared to wild-type (WT) animals. With a calcium- and vitamin D-deficient diet, tight junction gene expression was significantly decreased in the duodenum of the CaBP-9k KO mice. These findings suggest that expression of paracellular tight junction genes is regulated by transcellular CaBP proteins, suggesting that active and passive calcium transport pathways may function cooperatively.

Vitamin D and diabetes: its importance for beta cell and immune function

Experimental evidence indicates that vitamin D may play a role in the defense against type 1 diabetes (T1D) as well as type 2 diabetes (T2D). Epidemiological data have established a link between vitamin D deficiency and an increased incidence of both T1D and T2D, whereas early and long-term vitamin D supplementation may decrease the risk of these disorders. The protective effects of vitamin D are mediated through the regulation of several components such as the immune system and calcium homeostasis. However, an increasing amount of evidence suggests that vitamin D also affects beta cells directly thereby rendering them more resistant to the types of cellular stress encountered during T1D and T2D. This review evaluates the role of vitamin D signaling in the pathogenesis of T1D and T2D with a special emphasis on the direct effects of vitamin D on pancreatic beta cells.

Novel regulation of 25-hydroxyvitamin D3 24-hydroxylase (24(OH)ase) transcription by glucocorticoids: cooperative effects of the glucocorticoid receptor, C/EBP beta, and the Vitamin D receptor in 24(OH)ase transcription

Glucocorticoid-induced bone loss has been proposed to involve direct effects on bone cells as well as alterations in calcium absorption and excretion. Since vitamin D is important for the maintenance of calcium homeostasis, in the present study the effects of glucocorticoids on vitamin D metabolism through the expression of 24(OH)ase, an enzyme involved in the catabolism of 1,25(OH)(2)D(3), were examined. Injection of vitamin D replete mice with dexamethasone (dex) resulted in a significant induction in 24(OH)ase mRNA in kidney, indicating a regulatory effect of glucocorticoids on vitamin D metabolism. Whether glucocorticoids can affect 24(OH)ase transcription is not known. Here we demonstrate for the first time a glucocorticoid receptor (GR) dependent enhancement of 1,25(OH)(2)D(3)-induced 24(OH)ase transcription. Dex treatment of GR and vitamin D receptor (VDR) transfected COS-7 cells and dex treatment of osteoblastic cells (in which VDR and GR are present endogenously) potentiated 1,25(OH)(2)D(3)-induced 24(OH)ase transcription. In addition, GR was found to cooperate with C/EBP beta to enhance VDR-mediated 24(OH)ase transcription. Using the rat 24(OH)ase promoter with the C/EBP site mutated, GR-mediated potentiation of 1,25(OH)(2)D(3)-induced 24(OH)ase transcription was inhibited. Immunoprecipitation indicated that that GR can interact with C/EBP beta and ChIP/re-ChIP analysis showed that C/EBP beta and GR bind simultaneously to the 24(OH)ase promoter. These findings indicate a novel mechanism whereby glucocorticoids can alter VDR-mediated 24(OH)ase transcription through functional cooperation between C/EBP beta and GR that results in an enhanced ability of C/EBP beta to cooperate with VDR in the regulation of 24(OH)ase.

Active intestinal calcium transport in the absence of transient receptor potential vanilloid type 6 and calbindin-D9k

To study the role of the epithelial calcium channel transient receptor potential vanilloid type 6 (TRPV6) and the calcium-binding protein calbindin-D9k in intestinal calcium absorption, TRPV6 knockout (KO), calbindin-D9k KO, and TRPV6/calbindin-D(9k) double-KO (DKO) mice were generated. TRPV6 KO, calbindin-D9k KO, and TRPV6/calbindin-D9k DKO mice have serum calcium levels similar to those of wild-type (WT) mice ( approximately 10 mg Ca2+/dl). In the TRPV6 KO and the DKO mice, however, there is a 1.8-fold increase in serum PTH levels (P < 0.05 compared with WT). Active intestinal calcium transport was measured using the everted gut sac method. Under low dietary calcium conditions there was a 4.1-, 2.9-, and 3.9-fold increase in calcium transport in the duodenum of WT, TRPV6 KO, and calbindin-D9k KO mice, respectively (n = 8-22 per group; P > 0.1, WT vs. calbindin-D9k KO, and P < 0.05, WT vs. TRPV6 KO on the low-calcium diet). Duodenal calcium transport was increased 2.1-fold in the TRPV6/calbindin-D9k DKO mice fed the low-calcium diet (P < 0.05, WT vs. DKO). Active calcium transport was not stimulated by low dietary calcium in the ileum of the WT or KO mice. 1,25-Dihydroxyvitamin D3 administration to vitamin D-deficient null mutant and WT mice also resulted in a significant increase in duodenal calcium transport (1.4- to 2.0-fold, P < 0.05 compared with vitamin D-deficient mice). This study provides evidence for the first time using null mutant mice that significant active intestinal calcium transport occurs in the absence of TRPV6 and calbindin-D9k, thus challenging the dogma that TRPV6 and calbindin-D9k are essential for vitamin D-induced active intestinal calcium transport.

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.

Vitamin D and tissue non-specific alkaline phosphatase in dental cells

Dental epithelium comprises different cell populations, including ameloblasts and stratum intermedium cells. Ameloblasts are vitamin D targets, and at least five proteins undergo specific modulation of their expression following the addition of 1alpha,25(OH)2 vitamin D3[1alpha,25(OH)2D3]. Stratum intermedium cells have not been studied in any great detail regarding vitamin D impact. Interestingly, in these cells, the tissue non-specific alkaline phosphatase (TNAP) is overexpressed. On the other hand, TNAP is a reliable bone marker of vitamin D action, similar to calbindins in kidney and intestine, previously used for studies of vitamin D activity in ameloblasts. Here, TNAP expression and activity were investigated in vivo in the microdissected epithelium and mesenchyme of mandible incisors. Physiological doses of 1alpha,25(OH)2D3 injected in control rats failed to modify TNAP activity in both dental epithelium and mesenchyme. No significant differences were observed in the steady-state levels of TNAP mRNAs of dental tissues from wild-type and vitamin D nuclear receptor (VDRnuc)-deficient mice of the same litters. These data suggest that, in contrast to ameloblasts, stratum intermedium cells are not sensitive to 1alpha,25(OH)2D3. An explanation for such a responsiveness of stratum intermedium cells to 1alpha,25(OH)2D3 is proposed based on the respective expressions of both vitamin D receptors (VDRnuc and 1,25D3-[MARRS]) and the Dlx2 homeobox gene.

Rivastigmine is a potent inhibitor of acetyl- and butyrylcholinesterase in Alzheimer's plaques and tangles

Acetylcholinesterase and butyrylcholinesterase activities emerge in association with plaques and tangles in Alzheimer's disease. These pathological cholinesterases, with altered properties, are suggested to participate in formation of plaques. The present experiment assessed the ability of rivastigmine, a clinically utilized agent that inhibits acetylcholinesterase and butyrylcholinesterase activities, to inhibit cholinesterases in plaques and tangles. Cortical sections from cases of Alzheimer's disease were processed using cholinesterase histochemistry in the presence or absence of rivastigmine. Optical densities of stained sections were utilized as a measure of inhibition. The potency of rivastigmine was compared with those of other specific inhibitors. Optimum staining for cholinesterases in neurons and axons was obtained at pH 8.0. Cholinesterases in plaques, tangles and glia were stained best at pH 6.8. Butyrylcholinesterase-positive plaques were more numerous than acetylcholinesterase-positive plaques. Rivastigmine inhibited acetylcholinesterase in all positive structures in a dose-dependent manner (10(-6)-10(-4) M). However, even at the highest concentration, faint activity remained. In contrast, rivastigmine resulted in complete inhibition of butyrylcholinesterase in all structures at 10(-5) M. Rivastigmine was equipotent to the specific acetylcholinesterase inhibitor BW284C51 and more potent than the butyrylcholinesterase inhibitors iso-OMPA and ethopropazine. In conclusion, rivastigmine is a potent inhibitor of acetylcholinesterase and a more potent inhibitor of butyrylcholinesterase in plaques and tangles. Unlike other cholinesterase inhibitors tested, rivastigmine inhibited cholinesterases in normal and pathological structures with the same potency. Thus, at the therapeutic concentrations used, rivastigmine is likely to result in inhibition of pathological cholinesterases, with the potential of interfering with the disease process.

Functional cooperation between CCAAT/enhancer-binding proteins and the vitamin D receptor in regulation of 25-hydroxyvitamin D3 24-hydroxylase

1,25-Dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] induces the synthesis of 25-hydroxyvitamin D(3) 24-hydroxylase [24(OH)ase], an enzyme involved in its catabolism, thereby regulating its own metabolism. Here we demonstrate that CCAAT enhancer binding protein beta (C/EBPbeta) is induced by 1,25(OH)(2)D(3) in kidney and in osteoblastic cells and is a potent enhancer of vitamin D receptor (VDR)-mediated 24(OH)ase transcription. Transfection studies indicate that 1,25(OH)(2)D(3) induction of 24(OH)ase transcription is enhanced a maximum of 10-fold by C/EBPbeta. Suppression of 1,25(OH)(2)D(3)-induced 24(OH)ase transcription was observed with dominant negative C/EBP or osteoblastic cells from C/EBPbeta(-/-) mice. A C/EBP site was identified at positions -395 to -388 (-395/-388) in the rat 24(OH)ase promoter. Mutation of this site inhibited C/EBPbeta binding and markedly attenuated the transcriptional response to C/EBPbeta. We also report the cooperation of CBP/p300 with C/EBPbeta in regulating VDR-mediated 24(OH)ase transcription. We found that not only 1,25(OH)(2)D(3) but also parathyroid hormone (PTH) can induce C/EBPbeta expression in osteoblastic cells. PTH potentiated the induction of C/EBPbeta and 24(OH)ase expression in response to 1,25(OH)(2)D(3) in osteoblastic cells. Data with the human VDR promoter (which contains two putative C/EBP sites) indicate a role for C/EBPbeta in the protein kinase A-mediated induction of VDR transcription. From this study a fundamental role has been established for the first time for cooperative effects and cross talk between the C/EBP family of transcription factors and VDR in 1,25(OH)(2)D(3)-induced transcription. These findings also indicate a novel role for C/EBPbeta in the cross talk between PTH and 1,25(OH)(2)D(3) that involves the regulation of VDR transcription.

Critical Role of Calbindin-D28k in Calcium Homeostasis Revealed by Mice Lacking Both Vitamin D Receptor and Calbindin-D28k

Calbindin (CaBP)-D28k and CaBP-D9k are cytosolic vitamin D-dependent calcium-binding proteins long thought to play an important role in transepithelial calcium transport. However, recent genetic studies suggest that CaBP-D28k is not essential for calcium metabolism. Genetic ablation of this gene in mice leads to no calcemic abnormalities. Genetic inactivation of the vitamin D receptor (VDR) gene leads to hypocalcemia, secondary hyperparathyroidism, rickets, and osteomalacia, accompanied by 90% reduction in renal CaBP-D9k expression but little change in CaBP-D28k. To address whether the role of CaBP-D28k in calcium homeostasis is compensated by CaBP-D9k, we generated VDR/CaBP-D28k double knockout (KO) mice, which expressed no CaBP-D28k and only 10% of CaBP-D9k in the kidney. On a regular diet, the double KO mice were more growth-retarded and 42% smaller in body weight than VDRKO mice and died prematurely at 2.5-3 months of age. Compared with VDRKO mice, the double KO mice had higher urinary calcium excretion and developed more severe secondary hyperparathyroidism and rachitic skeletal phenotype, which were manifested by larger parathyroid glands, higher serum parathyroid hormone levels, much lower bone mineral density, and more distorted growth plate with more osteoid formation in the trabecular region. On high calcium, high lactose diet, blood-ionized calcium levels were normalized in both VDRKO and the double KO mice; however, in contrast to VDRKO mice, the skeletal abnormalities were not completely corrected in the double KO mice. These results directly demonstrate that CaBP-D28k plays a critical role in maintaining calcium homeostasis and skeletal mineralization and suggest that its calcemic role can be mostly compensated by CaBP-D9k.

Calcium transporter 1 and epithelial calcium channel messenger ribonucleic acid are differentially regulated by 1,25 dihydroxyvitamin D3 in the intestine and kidney of mice

We examined the expression of calcium transporter 1 (CaT1) and epithelial calcium channel (ECaC) mRNA in the duodenum and kidney of mice. Intestinal CaT1 mRNA level increased 30-fold at weaning, coincident with the induction of calbindin-D(9k) expression. In contrast, renal CaT1 and ECaC mRNA expression was equal until weaning when ECaC mRNA is induced and CaT1 mRNA levels fall 70%. Long- and short-term adaptation to changes in dietary calcium (Ca) level and 1,25 dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] injection strongly regulated duodenal calbindin D(9k) and CaT1 mRNA. Following a single dose of 1,25(OH)(2)D(3), induction of CaT1 mRNA occurred rapidly (within 3 h, peak at 6 h of 9.6 +/- 0.8-fold) and preceded the induction of intestinal Ca absorption (significantly increased at 6 h, peak at 9 h). Neither renal CaT1 nor ECaC mRNA were strongly regulated by dietary calcium level or 1,25(OH)(2)D(3) injection. Our data indicate that CaT1 and ECaC mRNA levels are differentially regulated by 1,25(OH)(2)D(3) in kidney and intestine and that there may be a specialized role for CaT1 in kidney in fetal and neonatal development. The rapid induction of intestinal CaT1 mRNA expression by 1,25(OH)(2)D(3), and the marked induction at weaning, suggest that CaT1 is critical for 1,25(OH)(2)D(3)-mediated intestinal Ca absorption.

Immunolocalization of calbindin D28k and vitamin D receptor during root formation of murine molar teeth

Cells in the epithelial rest of Malassez (ERM cells) express calbindin D28k (CB); however, the hormonal regulation of CB in ERM cells remains to be elucidated. We investigated the immunohistochemical localization of CB and 1,25-dihydroxyvitamin D3 receptor (VDR) during root formation of mouse molar teeth in order to clarify whether the expression of CB in ERM cells is dependent on vitamin D. At the early stage of root formation (postnatal (PN) days 10-14), both CB- and VDR-immunoreactive cells were observed intermittently along the root surface. In the apical portion, almost all CB-immunoreactive cells showed VDR immunoreactivity; however, VDR-immunoreactive cells in the most apical portion were immunonegative for CB. In the middle and cervical portions, the distributions of the two proteins were completely different. At the late stage of root formation (PN28d) and in adult animals, CB immunoreactivity was distributed in cells found along the acellular cementum at the bifurcation region, as well as between the dentin and cellular cementum in the apical portion (although these lacked immunoreactivity for VDR). The present results indicate that CB expression in newly disrupted cells from Hertwig's epithelial root sheath occurs in a vitamin-D dependent manner, whereas the expression of CB in mature ERM cells may be independent of vitamin D.

Prolonged unloading of rat soleus muscle causes distinct adaptations of the gene profile

Using commercially available microarray technology, we investigated a series of transcriptional adaptations caused by atrophy of rat m. soleus due to 35 days of hindlimb suspension. We detected 395 out of 1,200 tested transcripts, which reflected 1%-5% of totally expressed genes. From various cellular functional pathways, we detected multiple genes that spanned a 200-fold range of gene expression levels. Statistical analysis combining L1 regression with the sign test based on the conservative Bonferroni correction identified 105 genes that underwent transcriptional adaptations with atrophy. Generally, expressional changes were discrete (<50%) and pointed in the same direction for genes belonging to the same cellular functional units. In particular, a distinct expressional adaptation of genes involved in fiber transformation; that is, metabolism, protein turnover, and cell regulation were noted and matched to corresponding transcriptional changes in nutrient trafficking. Expressional changes of extracellular proteases, and of genes involved in nerve-muscle interaction and excitation-contraction coupling identify previously not recognized adaptations that occur in atrophic m. soleus. Considerations related to technical and statistical aspects of the array approach for profiling the skeletal muscle genome and the impact of observed novel adaptations of the m. soleus transcriptome are put into perspective of the physiological adaptations occurring with muscular atrophy.

Enhancement of VDR-mediated transcription by phosphorylation: correlation with increased interaction between the VDR and DRIP205, a subunit of the VDR-interacting protein coactivator complex

When UMR-106 osteoblastic cells, LLCPK1 kidney cells, and VDR transfected COS-7 cells were transfected with the rat 24-hydroxylase [24(OH)ase] promoter (-1,367/+74) or the mouse osteopontin (OPN) promoter (-777/+79), we found that the response to 1,25dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)] could be significantly enhanced 2- to 5-fold by the protein phosphatase inhibitor, okadaic acid (OA). Enhancement of 1,25-(OH)(2)D(3)-induced transcription by OA was also observed using a synthetic reporter gene containing either the proximal 24(OH)ase vitamin D response element (VDRE) or the OPN VDRE, suggesting that the VDRE is sufficient to mediate this effect. OA also enhanced the 1,25-(OH)(2)D(3)-induced levels of 24(OH)ase and OPN mRNA in UMR osteoblastic cells. The effect of OA was not due to an up-regulation of VDR or to an increase in VDR-RXR interaction with the VDRE. To determine whether phosphorylation regulates VDR-mediated transcription by modulating interactions with protein partners, we examined the effect of phosphorylation on the protein-protein interaction between VDR and DRIP205, a subunit of the vitamin D receptor-interacting protein (DRIP) coactivator complex, using glutathione-S-transferase pull-down assays. Similar to the functional studies, OA treatment was consistently found to enhance the interaction of VDR with DRIP205 3- to 4-fold above the interaction observed in the presence of 1,25-(OH)(2)D(3) alone. In addition, studies were done with the activation function-2 defective VDR mutant, L417S, which is unable to stimulate transcription in response to 1,25-(OH)(2)D(3) or to interact with DRIP205. However, in the presence of OA, the mutant VDR was able to activate 24(OH)ase and OPN transcription and to recruit DRIP205, suggesting that OA treatment may result in a conformational change in the activation function-2 defective mutant that creates an active interaction surface with DRIP205. Taken together, these findings suggest that increased interaction between VDR and coactivators such as DRIP205 may be a major mechanism that couples extracellular signals to vitamin D action.

Effects of vitamin D receptor inactivation on the expression of calbindins and calcium metabolism

Hypocalcemia, rickets, and osteomalacia are major phenotypic abnormalities in vitamin D receptor (VDR)-null mice. In an attempt to understand the abnormal regulation of calcium metabolism in these animals, we examined the expression of calbindins (CaBP) as well as calcium handling in the intestine and kidney of VDR null mice. In adult VDR-null mice, intestinal and renal CaBP-D9k expression was reduced by 50 and 90%, respectively, at both the mRNA and protein levels compared with wild-type littermates, whereas renal CaBP-D28k expression was not significantly changed. Intestinal calcium absorption was measured by the rate of (45)Ca disappearance from the intestine after an oral dose of the isotope. (45)Ca absorption was similar in VDR-null and wild-type mice, but the amount of (45)Ca accumulated in the serum and bone was 3-4 times higher in wild-type mice than in VDR-null mice. Despite the hypocalcemia, the urinary excretion of calcium in VDR-null mice was not different from that in wild-type mice. Moreover, 1 wk of a high-calcium diet treatment that normalized the serum ionized calcium level of VDR-null mice increased the urinary calcium level of these mutant mice to twofold higher than that of wild-type mice on the same diet, suggesting impaired renal calcium conservation in VDR-null mice. These data demonstrate that renal CaBP-D9k, but not CaBP-D28k, is highly regulated by the VDR-mediated action of 1,25-dihydroxyvitamin D(3). Furthermore, the results also suggest that impaired calcium conservation in the kidney may be the most important factor contributing to the development of hypocalcemia in VDR-null mice, and CaBP-D9k may be an important mediator of calcium reabsorption in the kidney.

Interrelationship between signal transduction pathways and 1,25(OH)2D3 in UMR106 osteoblastic cells

In this study, the interrelationship between signal transduction pathways and 1,25-dihydroxyvitamin D(3) [1,25(OH)2D3] action was examined in UMR106 osteoblastic cells. Treatment of these cells with 8-bromo-cAMP (1 mM) resulted in an upregulation of the vitamin D receptor (VDR) and an augmentation in the induction by 1,25(OH)2D3 of 25(OH)D3 24-hydroxylase [24(OH)ase] and osteopontin (OPN) mRNAs as well as gene transcription. Transfection with constructs containing the vitamin D response element devoid of other promoter regulatory elements did not alter the cAMP-mediated potentiation, suggesting that cAMP-enhanced transcription is due, at least in part, to upregulation of VDR. Treatment with phorbol ester [12-O-tetradecanoyl-phorbol-13-acetate (TPA) 100 nM], an activator of protein kinase C, significantly enhanced 1,25(OH)2D3-induced OPN mRNA and transcription but had no effect on VDR or on 24(OH)ase mRNA or transcription. Studies using OPN promoter constructs indicate that TPA-enhanced OPN transcription is mediated by an effect on the OPN promoter separate from an effect on VDR. Thus interactions with signal transduction pathways can enhance 1,25(OH)2D3 induction of 24(OH)ase and OPN gene expression, and, through different mechanisms, changes in cellular phosphorylation may play a significant role in determining the effectiveness of 1,25(OH)2D3 on transcriptional control in cells expressing skeletal phenotypic properties.

Syncollin is differentially expressed in rat proximal small intestine and regulated by feeding behavior

Gradients of gene expression are maintained along the proximal-distal axis of the mammalian small intestine despite a continuously regenerating epithelium. To study the molecular mechanisms responsible for this phenomenon, we utilized a subtractive hybridization strategy to isolate genes differentially expressed in the duodenum but not ileum. We isolated and sequenced 15 clones. The clones were fragments of genes encoding lipases, proteases, and an esterase. A novel clone was characterized and subsequently shown to encode syncollin, a secretory granule protein that binds to syntaxin in a calcium-sensitive manner. RT-PCR and S1 nuclease protection assay were used to clarify the 5'-end of syncollin. Syncollin was expressed in the rat pancreas, spleen, duodenum, and colon. In situ hybridization localized syncollin expression in the pancreas to acinar cells and in the duodenum to villus epithelial cells.

Effect of chronic metabolic acidosis on calbindin expression along the rat distal tubule

Calbindin D28k has been reported to be involved in the transcellular calcium transport along the rat distal tubule. It has also been shown that chronic metabolic acidosis (CMA) induces significant hypercalciuria. The present study investigated whether CMA affects the mRNA and the protein expression of calbindin D28k along isolated distal tubule (DT) of rats. The animals were made acidotic by adding 0.28 mol/L NH4Cl to the drinking water for 7 d. This maneuver was associated with an increase in plasma ionized calcium. Inulin clearance experiments demonstrated that metabolic acidosis did not affect GFR, but it significantly increased both total and fractional urinary calcium excretion. To define the role of calbindin D28k, total RNA was extracted from DT, identified, and microdissected from collagenase-treated kidneys. cDNA was synthesized from RNA using reverse transcriptase and oligo(dT)(12-18) primers. Calbindin D28k mRNA abundance was semiquantified by a competitive reverse transcription-PCR, using an internal standard of cDNA that differed from the wild-type calbindin D28k by a deletion of 86 bp. The reverse transcription-PCR was performed starting from the same amount of total RNA. For each set of experiments, control and acidotic rats were studied in parallel. The identity of the DT was further verified by the presence of the thiazide-sensitive NaCl cotransporter (rTSC1) mRNA. Calbindin D28k mRNA abundance was 0.89 +/- 0.21 amol/ng total RNA in DT of CMA rats (n = 5) compared with 0.30 +/- 0.12 amol/ng total RNA of control rats (n = 5) (P < 0.05). Using specific rabbit polyclonal anti-calbindin D28k antibody, Western blotting was performed starting from thin slices of outer cortex. Densitometric analysis revealed that in acidotic rats (n = 7) there was a 17 +/- 5% (P < 0.05) increase in calbindin D28k protein abundance compared with controls (n = 7). These results indicate that in the rat, ammonium chloride loading induces an increase in filtered ionized calcium load that is associated with a significant upregulation of calbindin D28k both at the mRNA and protein level. These last effects will help to reduce the concomitant hypercalciuria, thus mitigating the consequence of CMA on calcium metabolism.

Selective decrease of mRNAs encoding plasma membrane calcium pump isoforms 2 and 3 in rat kidney

BACKGROUND

Although the existence of multiple isoforms of plasma membrane calcium ATPase (PMCA) is now well documented, their biological functions are not yet known. In this study, we set out to investigate the potential role of PMCA isoforms, previously identified in renal cortical tissue, in tubular reabsorption of calcium (Ca2+).

METHODS

With use of reverse transcription-polymerase chain reaction analysis, we determined levels of mRNAs encoding isoforms of PMCA1 through PMCA4 in renal cortex, liver, and brain of rats with hypercalciuria induced by feeding with a low-phosphate diet (LPD) as compared with Ca2+-retaining rats that were fed a high-phosphate diet (HPD).

RESULTS

We observed that in hypercalciuric LPD-fed rats, the mRNAs encoding isoforms PMCA2b and PMCA3(a + c) are significantly lower (Delta approximately-50%) than in HPD-fed hypocalciuric rats, whereas no changes in mRNAs encoding isoforms PMCA1b and PMCA4 were observed, and mRNA encoding calbindin 28 kDa was increased. On the other hand, the content of mRNAs encoding PMCA2b and PMCA3(a + c) in liver and brain, respectively, was not changed.

CONCLUSION

These findings are evidence that expression of PMCA isoforms in the kidney can be selectively modulated in response to pathophysiologic stimuli. The association of a decrease in mRNA encoding PMCA2b and PMCA3(a + c) with hypercalciuria suggests that the two PMCA isoforms may be operant in tubular reabsorption of Ca2+ and its regulation.

Expression of 25(OH)D3 24-hydroxylase in distal nephron: coordinate regulation by 1,25(OH)2D3 and cAMP or PTH

Previous studies using microdissected nephron segments reported that the exclusive site of renal 25-hydroxyvitamin D3-24-hydroxylase (24OHase) activity is the renal proximal convoluted tubule (PCT). We now report the presence of 24OHase mRNA, protein, and activity in cells that are devoid of markers of proximal tubules but express characteristics highly specific for the distal tubule. 24OHase mRNA was undetectable in vehicle-treated mouse distal convoluted tubule (DCT) cells but was markedly induced when DCT cells were treated with 1,25 dihydroxyvitamin D3 [1,25(OH)2D3]. 24OHase protein and activity were also identified in DCT cells by Western blot analysis and HPLC, respectively. 8-Bromo-cAMP (1 mM) or parathyroid hormone [PTH-(1-34); 10 nM] was found to potentiate the effect of 1, 25(OH)2D3 on 24OHase mRNA. The stimulatory effect of cAMP or PTH on 24OHase expression in DCT cells suggests differential regulation of 24OHase expression in the PCT and DCT. In the presence of cAMP and 1, 25(OH)2D3, a four- to sixfold induction in vitamin D receptor (VDR) mRNA was observed. VDR protein, as determined by Western blot analysis, was also enhanced in the presence of cAMP. Transient transfection analysis in DCT cells with rat 24OHase promoter deletion constructs demonstrated that cAMP enhanced 1, 25(OH)2D3-induced 24OHase transcription but this enhancement was not mediated by cAMP response elements (CREs) in the 24OHase promoter. We conclude that 1) although the PCT is the major site of localization of 24OHase, 24OHase mRNA and activity can also be localized in the distal nephron; 2) both PTH and cAMP modulate the induction of 24OHase expression by 1,25(OH)2D3 in DCT cells in a manner different from that reported in the PCT; and 3) in DCT cells, upregulation of VDR levels by cAMP, and not an effect on CREs in the 24OHase promoter, is one mechanism involved in the cAMP-mediated modulation of 24OHase transcription.

Expression and structure of senescence marker protein-30 (SMP30) and its biological significance

We previously identified a novel protein, the amounts of which are down-regulated in an androgen-independent manner with aging in the rat liver. We designated this protein as senescence marker protein-30 (SMP30). SMP30 is preferentially expressed in cytosol of hepatocytes and renal tubular epithelia, and its expression is maintained at high level throughout the tissue maturing stage as well as young and adult stages, but decreases during senescent stages in both sexes. Subsequently, we cloned cDNAs encoding SMP30 from rat, human and mouse and found that the amino acid sequence of SMP30 is well conserved with remarkable homology among these species. We also determined the genome organization and 5' flanking region of SMP30 in mouse genome. In the meantime, SMP30 turned out to be identical to a Ca2+-binding protein called regucaltin. In order to elucidate the functional significance of SMP30, we have generated Hep G2 cells that stably express large amounts of SMP30 by transfecting human SMP30 cDNA. Cell biological analyses on these SMP30 transfectants suggest that SMP30 regulates Ca2+ homeostasis by enhancing plasma membrane Ca2+-pumping activity in Hep G2 cells. This result implies that the down-regulation of SMP30 may contribute to hepatic deterioration of cellular functions during aging. In this review, we present a overview of SMP30 in its structure, expression and possible physiological roles. We also discuss hypothetical role(s) of SMP30 in aging and Ca2+ homeostasis.

Expression of calbindin-D28k in C6 glial cells stabilizes intracellular calcium levels and protects against apoptosis induced by calcium ionophore and amyloid beta-peptide

The calcium binding protein, calbindin-D28k is normally present in neurons. Recently we reported that brain injury and tumor necrosis factors (TNFs) induce calbindin-D28k in astrocytes. TNF-treated calbindin expressing astrocytes were resistant to acidosis and calcium ionophore toxicity, suggesting that calbindin may have a cytoprotective role in astrocytes in the injured brain (M.P. Mattson, B. Cheng, S.A. Baldwin, V.L. Smith-Swintosky, J. Keller, J. Geddes, Scheff, J.W., Christakos, S., Brain injury and tumor necrosis factors induce calbindin-D28k in astrocytes: evidence for a cytoprotective response, J. Neurosci. Res., 42 (1995) 257). In order to obtain direct evidence for a role of calbindin, using the eukaryotic expression vector pREP4, rat calbindin-D28k was stably expressed in C6 rat astocytoma glial cells. Cytotoxicity in response to calcium ionophore or amyloid beta-peptide (which accumulates in the brain in Alzheimer's disease and has been reported to be neurotoxic) was measured by MTT reduction in vector transfected cells and in calbindin transfected clones. Stably expressed calbindin resulted in increased cell survival in the presence of calcium ionophore (1-10 microM) or amyloid beta-peptide (10-100 microM). In addition, the calcium ionophore or amyloid beta-peptide mediated rise in intracellular calcium in vector transfected cells was significantly attenuated in calbindin expressing cells. Apoptotic cell death was detected by the Hoechst method in vector transfected C6 glial cells treated with calcium ionophore or beta-amyloid (34-36% apoptotic cells/culture). The number of apoptotic nuclei was significantly attenuated in similarly treated calbindin-D28k transfected clones (10-13% apoptotic cells/culture; p<0.01). Our results support the involvement of calcium fluxes in apoptosis and suggest that calbindin-D28k, by buffering calcium, can suppress death in apoptosis susceptible cells in the central nervous system.

Senescence marker protein-30 (SMP30): structure and biological function

Senescence marker protein-30 (SMP30), which we previously identified, is notable for its androgen-independent decrease in the livers of aging rats. Hepatocytes and renal tubular epithelia express large amounts of SMP30 in their cytosol throughout the tissue-maturing process and adulthood, but its level decreases thereafter. Upon cloning cDNAs that encode SMP30 in rats, mice, and humans, we found that the amino acid sequence of SMP30 is well conserved with remarkable homology among these species. However, this gene, which is so strongly conserved in these higher animals, does not appear in yeast. We also determined the genome organization and 5' flanking region of SMP30 in mouse genome. In the meantime, SMP30 turned out be identical to a Ca2+-binding protein called regucalcin (RC). To learn how this protein functions, we transfected Hep G2 cells with human SMP30 cDNA so that these cells stably express large amounts of SMP30. The results suggest that SMP30 regulates Ca2+ homeostasis by enhancing Ca2+-pumping activity in the plasma membranes. Thus, SMP30 seems to play a critical role in the highly differentiated functions of the liver and kidney and to exert a major impact on Ca2+ homeostasis. If so, down-regulation of SMP30 with aging would attribute greatly to the related deterioration of these organs, as indicated in this brief overview of the structure, expression, and function of SMP30.

Evidence for involvement of 17beta-estradiol in intestinal calcium absorption independent of 1,25-dihydroxyvitamin D3 level in the Rat

The sex steroid 17beta-estradiol (17beta-E2) has a broad range of actions, including effects on calcium and bone metabolism. This study with 3-month-old Brown Norway rats was designed to investigate the role of 17beta-E2 in the regulation of calcium homeostasis. Rats were divided in four groups, sham-operated, ovariectomized (OVX), and OVX supplemented with either a 0.025-mg or 0.05-mg 17beta-E2 pellet implanted subcutaneously. After 4 weeks, in none of the groups was serum calcium, phosphate, or parathyroid hormone altered compared with the sham group, while only in the OVX rats was a significant reduction in urinary calcium found. Bone mineral density and osteocalcin were modified, as can be expected after OVX and 17beta-E2 supplementation. OVX resulted in a nonsignificant increase in serum 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Supplementation with either one of the 17beta-E2 dosages resulted in an 80% reduction of 1,25(OH)2D3 and only a 20% reduction in 25-hydroxyvitamin D3 levels. OVX, as well as supplementation with 17beta-E2, did not affect serum levels of vitamin D binding protein. As a consequence, the estimated free 1,25(OH)2D3 levels were also significantly decreased in the 17beta-E2-supplemented group compared with the sham and OVX groups. Next, the consequences for intestinal calcium absorption were analyzed by the in situ intestinal loop technique. Although the 1,25(OH)2D3 serum level was increased, OVX resulted in a significant decrease in intestinal calcium absorption in the duodenum. Despite the strongly reduced 1,25(OH)2D3 levels (18. 1 +/- 2.1 and 16.4 +/- 2.2 pmol/l compared with 143.5 +/- 29 pmol/l for the OVX group), the OVX-induced decrease in calcium absorption could partially be restored by supplementation with either 0.025 mg or 0.05 mg of 17beta-E2. None of the treatments resulted in a significant change in calcium handling in the jejunum, although the trends were similar as those observed in the duodenum. 17beta-E2 did not change the VDR levels in both the intestine and the kidney. In conclusion, the present study demonstrates that 17beta-E2 is positively involved in intestinal calcium absorption, and the data strengthen the assertion that 17beta-E2 exerts this effect independent of 1,25(OH)2D3. In general, 17beta-E2 not only affects bone turnover but also calcium homeostasis via an effect on intestinal calcium absorption. (J Bone Miner Res 1999;14:57-64)

Senescence marker protein-30 (SMP30) rescues cell death by enhancing plasma membrane Ca(2+)-pumping activity in Hep G2 cells

Senescence marker protein-30 (SMP30) has been reported to decrease with aging in the rat liver. SMP30 has been also suggested to play a role as a Ca(2+)-binding protein localized in cytosol of hepatocytes. To elucidate the functional significance of SMP30, we have generated Hep G2 cell lines that stably express large amounts of SMP30 by transfection with human SMP30 cDNA. Using these cell lines, in view of the intracellular Ca2+ homeostasis, we then investigated cytosolic free Ca2+ concentration ([Ca2+]i) and Na(+)-independent Ca2+ efflux from the cells after extracellular ATP stimulation. Although stimulation of cells with ATP caused transient [Ca2+]i increase in both SMP30 and mock transfectants, rate of decrease after peak in [Ca2+]i was enhanced 2-fold by transfection of SMP30. Correspondingly, Ca2+ efflux was significantly increased in SMP30 transfectants compared with mock transfectants. In addition, more SMP30 transfectants survived than mock transfectants when cell death was induced by Ca2+ ionophore treatment. These results suggest that SMP30 regulates [Ca2+]i by modulating plasma membrane Ca(2+)-pumping activity, and thus down-regulation of SMP30 during aging may contribute to deterioration of cellular functions.

Hepatic and renal expression of senescence marker protein-30 and its biological significance

A novel rat hepatic protein was detected and isolated, the amount of which is down-regulated in an androgen-independent manner with ageing. This protein was designated as senescence marker protein-30 (SMP30). Senescence marker protein-30 turned out to be identical to a hepatic calcium-binding protein called regucalcin (RC). This review gives an overview of SMP30 in its structure, expression and possible physiological function(s). A hypothetical role of SMP30 in ageing and calcium homeostasis is also discussed.

Role of retinoic acid in regulation of mRNA expression of CaBP-D28k in the cerebellum of the chicken

In contrast to vitamin D3-dependent gene expression of calbindin (CaBP-D28k) in intestine and kidney, the cerebellar mRNA expression seems independent of vitamin D3. The present study was conducted to elucidate correlation of mRNA expression of CaBP-D28k and vitamin D3 receptor (VDR) in the kidney and cerebellum of the developing chick by Northern blot analysis, localization of CaBP-D28k mRNA within the cerebellum by in situ hybridization, and effect of retinoic acid in ovo on CaBP-D28k mRNA levels. CaBP-D28k mRNA levels were low in the cerebellum until embryonic day 16 (E16) but markedly increased on E18 and reached plateau levels on E20. VDR mRNA levels were low until E16 and significantly increased on E18 but decreased on E20 and remained low on 1 and 7 days after hatching. In the mesonephros, CaBP-D28k mRNA levels were high until E16 but abruptly decreased on E18, while VDR mRNA levels remained relatively constant throughout the examined period between E10 and 20. In situ hybridization analysis clearly demonstrated CaBP-D28k mRNA signals within the Purkinje cells of the cerebellum in the embryo on E12-E18. Although 1.25 dihydroxyvitamin D3 [1.25(OH)2D3, 3 x 10(-10) M injected in ovo on E15 increased CaBP-D28k mRNA levels in the mesonephros on E16 but had no effect on those in the cerebellum. On the contrary, in ovo injection of retinoic acid (10(-10) and 10(-8) M) caused no effect on CaBP-D28k mRNA levels in the mesonephros but significantly increased those in the cerebellum. The results indicate a regulatory role of retinoic acid on mRNA expression of CaBP-D28k in the cerebellar Purkinje cells of the chicken embryo.

Calretinin and calbindin-D28K in male rats during postnatal development

Calcium-binding proteins play potentially important roles in neurogenesis and neuroprotective mechanism(s). Some evidence exists that brain calbindin-D28K (CALB) is regulated by androgens. In the present study, calretinin (CALRET) and CALB patterns were determined by Western analysis in the medial basal hypothalamus (MBH) from male rats along with assaying plasma testosterone levels during postnatal development. Testosterone levels were very low in 7-, 10-, and 30-day-old animals (approximately 0.5 ng/mL), increased in a stair-step fashion to peak levels at 90 days (approximately 3.8 ng/mL), then declined with increasing age to very low levels at 300 days of age (approximately 0.3 ng/mL). At 7 and 10 days, MBH CALRET and CALB levels were low; however, at Day 30 a significant twofold increased was observed. Thereafter, in 60-, 120-, 180-, and 300-day-old animals MBH CALRET and CALB levels were, in general, comparable to 30-day-old values. These findings suggest that there is not a clear correspondence between the androgen status in male rats and the calcium-binding proteins (CALRET & CALB) expressed in the MBH. Therefore, it appears that brain CALRET and CALB are regulated in a developmental fashion with significant increases in expression occurring around the 4th postnatal week.

The effect of 1,25-vitamin D3 on calbindin-D and calcium-metabolic variables in the rat

Intraperitoneal injection of 1,25-(OH)2D3 4 micrograms/kg was given to 84 calcium- and vitamin D-repleted Wistar rats and samples of plasma, duodenal mucosa and renal tissue were taken after 0, 3, 6, 12, 24, 48 and 96 hr (n = 12 at each time interval). Plasma-ionized Ca increased after 6 hr, reached a maximum after 24 hr and returned to the initial values after 96 hr. The concentrations of renal calbindin-D28k and intestinal calbindin-D9k did not increase until 48 hr after injection and remained elevated until 96 hr after. Therefore, significantly elevated concentrations of the cytosolic calbindin-D were found at a time with normal values of plasma Ca. The present data suggest that calbindin-D does not alone increase the transcellular Ca transport and, therefore, supports the view that calbindin-Ds may serve as Ca buffer proteins.

Fetuin expression in the dorsal root ganglia and trigeminal ganglia of perinatal rats

Fetuin, a fetal plasma glycoprotein, has been shown previously to be present in sub-populations of neurons in the developing central and peripheral nervous system. To gain a more complete description of the time course of the appearance of fetuin during neurogenesis we have examined fetuin immunoreactivity, and the presence of fetuin mRNA, in the developing rat trigeminal and dorsal root ganglia. Fetuin immunoreactivity and its mRNA were first seen at embryonic day 15 in the trigeminal ganglia, and at embryonic day 16 in dorsal root ganglia. In both trigeminal and dorsal root ganglion, fetuin appeared to be present up until around the time of birth, and then again between postnatal days 3 and 16. The results suggest that fetuin first appears at around the time that ganglion cell axons reach their central targets, which is also approximately when the cell-death period begins. The proportion of ganglion neurons that were fetuin immunoreactive at different ages was inversely related to the amount of cell death that is known to occur in these populations, thus it seems that fetuin is more likely to be associated not with dying cells, but with those that survive the cell-death period.

A calcium responsive element that regulates expression of two calcium binding proteins in Purkinje cells

Calbindin D28 encodes a calcium binding protein that is expressed in the cerebellum exclusively in Purkinje cells. We have used biolistic transfection of organotypic slices of P12 cerebellum to identify a 40-bp element from the calbindin promoter that is necessary and sufficient for Purkinje cell specific expression in this transient in situ assay. This element (PCE1) is also present in the calmodulin II promoter, which regulates expression of a second Purkinje cell Ca2+ binding protein. Expression of high levels of exogenous calbindin or calretinin decreased transcription mediated by PCE1 in Purkinje cells 2.5- to 3-fold, whereas the presence of 1 microM ionomycin in the extracellular medium increased expression. These results demonstrate that PCE1 is a component of a cell-specific and Ca2+-sensitive transcriptional regulatory mechanism that may play a key role in setting the Ca2+ buffering capacity of Purkinje cells.

Transfection and overexpression of the calcium binding protein calbindin-D28k results in a stimulatory effect on insulin synthesis in a rat beta cell line (RIN 1046-38)

Calbindin-D28k, a calcium binding protein that is thought to act as a facilitator of calcium diffusion in intestine and kidney, is known to be regulated by vitamin D in these tissues. Calbindin-D28k is also present in pancreatic beta cells, but its function in these cells is not known. To determine a role for calbindin-D28k in the beta cell, rat calbindin-D28k was overexpressed in the pancreatic beta cell line RIN 1046-38 by transfection of calbindin in expression vector, and changes in insulin mRNA were examined. Five transfected RIN cell clones were found to overexpress calbindin 6- to 35-fold as determined by radioimmunoassay. Northern blot analysis revealed increases in abundance in calbindin mRNA (>20-fold for most clones). Overexpressed calbindin was functional because it was capable of buffering calcium in response to a rapid calcium influx induced by 1 and 5 microM calcium ionophore. In cells transfected with calbindin, there was a marked increase in the expression of insulin mRNA (>20-fold for most clones compared with vector transfected cells). Besides an increase in insulin mRNA, calbindin overexpression was also associated with an increase in insulin content and release (a 5.8-fold increase in insulin release was noted for clone C10, and a 54-fold increase was noted for clone C2). To begin to address the mechanism whereby overexpression of calbindin results in increased insulin gene expression, calbindin-overexpressing clones were transiently transfected with plasmids incorporating various regions of the rat insulin I (rInsI) promoter linked to the chloramphenicol acetyltransferase coding sequence. Transient transfection with reporter plasmids bearing the regulatory sequences of the rInsI promoter (-345/+1) or five copies of the Far-FLAT minienhancer (-247/-198) from the rInsI promoter suggests that increased insulin mRNA in calbindin transfected cells is due, at least in part, to enhanced insulin gene transcription. These studies provide the first direct evidence (to our knowledge) for a role for calbindin in beta cell function.

Increased sensitivity to 1,25(OH)2D3 in bone from genetic hypercalciuric rats

As a model of human hypercalciuria, we have selectively inbred genetic hypercalciuric stone-forming (GHS) Sprague-Dawley rats whose mean urine calcium excretion is eight to nine times greater than that of controls. A large component of this excess urine calcium excretion is secondary to increased intestinal calcium absorption, which is not due to an elevation in serum 1,25(OH)2D3, but appears to result from an increased number of intestinal 1,25(OH)2D3 receptors (VDR). When GHS rats are fed a low-calcium diet, the hypercalciuria is only partially decreased and urine calcium excretion exceeds intake, suggesting that an additional mechanism contributing to the hypercalciuria is enhanced bone demineralization. To determine if GHS rat bones are more sensitive to exogenous 1,25(OH)2D3, we cultured calvariae from neonatal (2- to 3-day-old) GHS and control rats with or without 1,25(OH)2D3 or parathyroid hormone (PTH) for 48 h at 37 degrees C. There was significant stimulation of calcium efflux from GHS calvariae at 1 and 10 nM 1,25(OH)2D3, whereas control calvariae showed no significant response to 1,25(OH)2D3 at any concentration tested. In contrast, PTH induced similar bone resorption in control and GHS calvariae. Immunoblot analysis demonstrated a fourfold increase in the level of VDR in GHS calvariae compared with control calvariae, similar to the increased intestinal receptors described previously. There was no comparable change in VDR RNA levels as measured by slot blot analysis, suggesting the altered regulation of the VDR occurs posttranscriptionally. That both bone and intestine display an increased amount of VDR suggests that this may be a systemic disorder in the GHS rat and that enhanced bone resorption may be responsible, in part, for the hypercalciuria in the GHS rat.

Gene regulation of senescence marker protein-30 (SMP30): coordinated up-regulation with tissue maturation and gradual down-regulation with aging

Senescence marker protein-30 (SMP30) is a calcium binding protein also called regucalcin. The amounts of SMP30 decrease androgen-independently with aging in the livers of rats. We have studied the expression of SMP30 in livers and kidneys of rats from the embryonic to the senescent stages of life. No transcript was detected in livers or kidneys in day 18 embryos. However, Northern blot analysis showed a marked increase of SMP30 mRNA in livers of neonatal and young rats. The first peak of SMP30 transcript was found in a 5-day-old neonate, in which the amount of mRNA was threefold higher in comparison with 3- to 6.5-month-old adults. The expression of SMP30 protein started to increase from day 7 and rapidly reached a plateau at day 10. The substantial amounts of protein and transcript were maintained in adults up to 3-6.5 months of age. In the kidney, SMP30 mRNA and protein started to increase at day 21 and reached near-maximal levels at day 35. The levels of transcript and protein remained high in adults up to 3 months of age. As the aging process progressed to senescent stages, the levels of transcript and protein decreased significantly in the liver and kidney of aged rats. Therefore, the age-associated decrease of SMP30 in the liver and kidney may be, in a large part, controlled at transcriptional levels. Furthermore, immunohistochemical analysis showed a similar pattern of changes in SMP30 protein expression during neonate, adult and senescent stages in hepatocytes and renal proximal tubular epithelia. The high expression of SMP30 in the tissue-maturing process and adulthood suggests that SMP30 may be required for the maintenance of highly differentiated hepatic and renal functions.

Isolation, characterization and in vivo analysis of the murine calbindin-D28K upstream regulatory region

The genomic locus containing the murine calbindin-D28K gene has been isolated and partially characterized. Genomic cloning revealed an exon/intron chromosomal structure very similar to the avian gene previously described. The ability of the calbindin-D28K upstream region to direct cell-specific expression was tested in vivo. Varying lengths of upstream sequence were used to drive expression of lacZ in transgenic mice. Characterization of 23 transgenic mouse lines revealed that even as much as 3.0 kb of upstream sequence was unable to direct expression independently of integration site effects, suggesting the absence of important elements. Despite the small number of expressing transgenic lines and the great variability, there was a tendency of cell specificity of transgene expression exhibited in distinct brain regions. In the cerebellum, Purkinje cell-specific expression was observed with the shortest (1.0 kb) upstream sequence tested. Specificity of transgene expression in Purkinje cells was abolished with longer portions of upstream sequence. The same observation was made for transgene expression in granule cells of the dentate gyrus, while the opposite effect was observed for expression in CA1 hippocampal cells. The absence of any transgenic lines exhibiting appropriate transgene expression in the kidney suggested that the VDREs described previously for the murine calbindin gene are not sufficient to direct kidney expression in vivo. It is concluded that 3.0 kb of calbindin upstream sequence includes the regulatory elements dictating a portion of cell-specificity in the CNS of transgenic mice, albeit lacking regions that allow expression independently of chromosomal effects.

Alteration in levels of expression of brain calbindin D-28k and calretinin mRNA in genetically epilepsy-prone rats

Variations in the concentration of free calcium in neurons is believed to play a major role in regulating neuronal excitability. Because calcium-binding proteins such as calbindin D-28k and calretinin help to regulate intracellular calcium, we investigated the possibility that the expression of these proteins may be affected in genetically epilepsy-prone rats (GEPRs). The mRNA levels of both proteins were compared across several brain regions using in situ hybridization histochemistry and Northern blot analysis with semiquantitation by optical density measures in autoradiograms from two GEPR strains that differ in the severity of audiogenic seizures (GEPR9 and GEPR3) and from Sprague-Dawley rats. Results revealed a lower level of expression in calbindin D-28k mRNA in the in the caudate putamen-accumbens nuclei in GEPR3 (-30%) and GEPR9 (-60%) relative to controls. The calbindin D-28k mRNA level was also lower in the reuniens nucleus of the thalamus (-41% in GEPR3; -34% in GEPR9). The calretinin mRNA level was lower in the substantia nigra compacta of both GEPR rat strains (-31% in GEPR3 and -34% in GEPR9 relative to controls). No changes in mRNA were detected in other brain regions expressing calbindin D-28k or calretinin mRNA. These results indicate that the expression of these related calcium-binding proteins is altered in the GEPRs before the induction of seizures. This initial defect could alter either the calcium-buffering capacity or regulation of calcium-mediated processes by these proteins and thus play a role in the molecular cascade of events inducing the genetic susceptibility to, and the generalization of, seizures in these rat strains.

The effect of castration on tumor growth rate and cell kinetics in hormone sensitive and hormone insensitive rat prostatic adenocarcinomas

Cell kinetics were measured in vivo in four experimental rat prostatic adenocarcinomas grown in normal or castrated rats. The aim was to investigate the effect of castration on growth rate and cell kinetics in hormone sensitive and hormone insensitive prostatic carcinomas. We used two anaplastic, hormone insensitive, fast growing tumors (Dunning R-3327-AT1 H and E), as well as two well differentiated, hormone sensitive, slow growing tumors (R-3327-H and R-3327-PAP). DNA ploidy, S-phase transit time (Ts), the labeling index (LI) and potential doubling time (Tpot) was determined by dual parameter flow cytometry, after in-vivo labeling, using bromodeoxyuridine (BUdR) and the tumor doubling time (DT) was determined from growth curves. After castration DT in the hormone sensitive H-subline changed from 21.7 days to 82.0 days, and in the PAP-subline from 22.2 days to 33.2 days. No significant changes in Tpot were observed. In the anaplastic tumors no differences in neither DT nor Tpot were seen. The cell loss factor (CLF) was relatively low in the two anaplastic tumors (0.55-0.59) compared to the well differentiated tumors. The CLF was unaffected by castration in the poorly differentiated tumors, whereas it increased significantly (from 0.75 to 0.92, P = 0.005) after castration in the H-tumor, and showed a non-significant increase in the PAP-tumor. This implies that the decrease in tumor growth in the hormone sensitive tumors is due to an increase in cell death, not a decrease in cell proliferation. These data indicate that CLF is the dominating factor in the reduced growth following androgen ablation in an androgen sensitive tumor. This study suggests that Tpot might be an additional predictor of a tumors proliferating rate and it may provide important information of the human prostatic cancer.

Vitamin D3-thyroid hormone receptor heterodimer polarity directs ligand sensitivity of transactivation

The nuclear receptors for 1,25-dihydroxyvitamin D3 (VD) and 3,5,3'-triiodothyronine (T3), that is, VDRs and T3Rs respectively, control aspects of homeostasis, cell growth and differentiation. They activate transcription from response elements consisting of direct repeats, palindromes and inverted palindromes of a variety of hexameric core-binding motifs. VDRs bind preferentially to direct repeats spaced by three nucleotides, whereas T3Rs bind to direct repeats spaced by four nucleotides. VDRs and T3Rs can function as homodimers but heterodimerization with retinoid X or retinoic acid receptors increases their affinity for DNA in vitro and resulting transcriptional activity in vivo. We recently observed the formation of VDR-T3R heterodimers. Here we show that the polarity of the binding of such heterodimers to the VD response element of the rat 9K (relative molecular mass 9,000) calbindin gene promoter was 5'-T3R-VDR-3', whereas on the mouse 28K calbindin VD response element this polarity was reversed to 5'-VDR-T3R-3'. We also show that the ligand for the downstream receptor controls the transcriptional activity of the heterodimeric complex. Thus, polarity seems to be an important regulatory property of heterodimeric nuclear receptor complexes.

The cloning of zebrin II reveals its identity with aldolase C

The sagittal organization of the mammalian cerebellum can be observed at the anatomical, physiological and biochemical level. Previous screening of monoclonal antibodies produced in our laboratory has identified two intracellular antigens, zebrin I and II, that occur exclusively in adult cerebellar Purkinje cells. As their name suggests, the zebrin antibody staining of the Purkinje cell population is not uniform. Rather, zebrin-positive Purkinje cells are organized in stripes or bands that run from anterior to posterior across most of the cerebellum; interposed between the zebrin-positive cells are bands of Purkinje cells that are zebrin-negative. Comparison of the position of the antigenic bands with the anatomy of afferent projections suggests that the bands are congruent with the basic developmental and functional ‘compartments’ of the cerebellum. We report the isolation of cDNA clones of the 36 × 10(3) M(r) antigen, zebrin II, by screening of a mouse cerebellum cDNA expression library. Sequence analysis reveals a 98% identity between our clone and the glycolytic isozyme, aldolase C. In order to more rigorously demonstrate the identity of the two proteins, we stained adult cerebellum with an independent monoclonal antibody raised against aldolase C. Anti-aldolase staining occurs in a previously unreported pattern of sagittal bands of Purkinje cells; the pattern is identical to that revealed by the zebrin II monoclonal. Further, in situ hybridization of antisense aldolase C riboprobe shows that the accumulation of zebrin II/aldolase C mRNA corresponds to the pattern of the zebrin antigen in Purkinje cells. Zebrin II/aldolase C gene expression is thus regulated at the level of transcription (or mRNA stability). In light of previous work that has demonstrated the cell-autonomous and developmentally regimented expression of zebrin II, further studies of the regulation of this gene may lead to insights about the determination of cerebellar compartmentation.

Changes in glutamate receptor and proenkephalin gene expression after kindled seizures

Changes in gene expression after kindled seizures were examined using microdissection of discrete brain areas and Northern and slot blot analyses. Experimental animals were kindled with either of two protocols: (1) a paradigm in which 50 Hz/10 s stimulus trains were delivered every 30 min through hippocampal electrodes (12 stimulations every other day for 4 days) and (2) a traditional approach in which 50 Hz/10 s stimulus trains were given to the hippocampus three times daily for 16 days. Rats were sacrificed 24 h or 30 days after the last kindled seizure. We first examined the possibility that kindling may affect transcription of mRNA for neurotransmitter receptors. We found significant decreases (22-58%) in AMPA/kainate activated glutamate receptor mRNAs (GluR1, -2, -3 mRNAs) in hippocampus, amygdala/entorhinal cortex and in frontoparietal cortex 24 h but not 30 days after rapidly kindled seizures. However, changes in GABA receptor alpha 1, alpha 2, alpha 4 or beta 1 mRNAs were not observed in any brain region 30 days after traditional kindling or 24 h after rapidly kindled seizures. In addition, we tested whether changes in the expression of proenkephalin could be detected after kindling. We found significant increases (1.7-10 fold) in proenkephalin mRNA in the frontoparietal cortex, hippocampus and in the amygdala/entorhinal cortex 24 h but not 30 days after rapidly kindled seizures. Our findings suggest that changes in glutamate receptor and proenkephalin gene expression are robust, acute sequelae to kindled seizures and may be involved in kindling.

Occurrence and localization of calbindin-D28K in kidney and cerebellum of the slider turtle, Trachemys scripta

BACKGROUND

Since its initial discovery in the avian intestine, calbindin-D28K has been reported to occur in various species and tissues. Although calbindin-D28K binds calcium ions in the physiologically relevant range of intracellular calcium, its functional role in the various cell types where it has been localized remains unknown.

METHODS

We examined the occurrence of calbindin-D28K in the brain and kidney of the testudine reptile, Trachemys scripta, by immunoblotting and immunocytochemistry using rabbit anti-sera directed against rat renal calbindin-D28K and chicken intestinal calbindin-D28K.

RESULTS

Immunoblotting revealed the presence of calbindin-D28K in the turtle tissues. A single immunoreactive band in the 28,000 relative molecular mass region was visualized in cerebellar and renal homogenates. Immunocytochemistry revealed reaction product for the presence of calbindin-D28K in the Purkinje cells of the cerebellum, and in the distal tubular cells of the nephron. Processes as well as the perikaryon of the Purkinje cell were immunoreactive.

CONCLUSION

This study describes the occurrence and cellular localization of calbindin-D28K in a reptilian cerebellum, and confirms the phylogenetic distribution of renal calbindin-D28K to the oldest major reptilian group.

Human striatum: chemoarchitecture of the caudate nucleus, putamen and ventral striatum in health and Alzheimer's disease

The morphology and distribution of perikarya positive for choline acetyltransferase, somatostatin, calcium binding protein (calbindin D28K) and nicotinamide adenine dinucleotide phosphate diaphorase were surveyed in the human striatum. Choline acetyltransferase and somatostatin antibodies labeled separate populations of large striatal interneurons. Somatostatin immunoreactivity and nicotinamide adenine dinucleotide phosphate diaphorase (nitric oxide synthase) activity were completely co-localized. Calbindin antibody identified two distinct groups of striatal neurons: (1) numerous medium-sized, lightly stained neurons, probably analogous to striatopallidal projection neurons in the rat, and (2) much less numerous, large, darkly stained neurons. Half of the latter group, but none of the former, were also nicotinamide adenine dinucleotide phosphate diaphorase-positive. Somatostatin-positive and medium-sized, calbindin-positive neurons were more numerous in the caudate nucleus than in the putamen or ventral striatum. By contrast, large calbindin-immunoreactive neurons were more frequently encountered in the putamen. Choline acetyltransferase-positive neurons were evenly distributed across striatal components. In aged control subjects, the size of large, darkly stained calbindin-positive neurons was reduced relative to young subjects. Aging had no effect on somatostatin-, medium-sized calbindin-, or choline acetyltransferase-positive neurons. However, in histologically confirmed cases of Alzheimer's disease, there was a selective, 75% loss of choline acetyltransferase-immunoreactive perikarya from the ventral striatum, but not from the dorsal striatum, compared to aged controls. Furthermore, the remaining cholinergic neurons in the ventral striatum of Alzheimer's disease cases were significantly smaller than similar neurons in controls. These results indicate that various striatal components which have been shown to differ in their anatomical connectivity and functional specialization, also differ in their neurochemical signatures. The specific and marked loss of choline acetyltransferase-positive neurons from the ventral striatum in Alzheimer's disease is consistent with the characteristic cholinergic and 'limbic' pathology in this disease.

Effect of 1,25,28-trihydroxyvitamin D2 and 1,24,25-trihydroxyvitamin D3 on intestinal calbindin-D9K mRNA and protein: is there a correlation with intestinal calcium transport?

Although analogs and metabolites of vitamin D have been tested for their calciotropic activity, very little information has been available concerning the effects of these compounds on gene expression. In this study one analog of vitamin D, 1,25,28-trihydroxyvitamin D2 [1,25,28-(OH)3D2], and one metabolite, 1,24,25-trihydroxyvitamin D3 [1,24,25-(OH)3D3], were tested for their effect on intestinal calbindin-D9K mRNA and protein as well as for their effect on intestinal calcium absorption and bone calcium mobilization. These compounds were also evaluated for their ability to compete for rat intestinal 1,25-(OH)2D3 receptor sites and to induce differentiation of human leukemia (HL-60) cells as indicated by reduction of nitro blue tetrazolium. In vivo studies involved intrajugular injection of 12.5 ng 1,25-(OH)2D3 or test compound to vitamin D-deficient rats and sacrifice after 18 h. 1,25,28-Trihydroxyvitamin D2 had no effect on intestinal calcium absorption, bone calcium mobilization, or intestinal calbindin-D9K protein and mRNA. Competitive binding to 1,25-(OH)2D3 receptors was 0.8% of that observed using 1,25-(OH)2D3. However, 20- and 40-fold higher doses of 1,25,28-(OH)3D2 (250 and 500 ng) resulted in significant inductions in calbindin-D9K protein and mRNA (3.5 to 7.4-fold), although doses as high as 800 ng were found to have no effect on intestinal calcium absorption or bone calcium mobilization.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient expression of calbindin-D28k immunoreactivity in layer V pyramidal neurons during postnatal development of kitten cortical areas

Calbindin-D28k is a 28 kDa calcium binding protein that has been shown to colocalize with a specific subpopulation of gamma-aminobutyric acid inhibitory interneurons in mammalian neocortex. We have examined the ontogeny of calbindin in neonatal kitten cortex in areas 17,18,19,7, medial and lateral suprasylvian visual areas, splenial visual area and cingulate cortex from the day of birth (P0) through maturation of the brain (P101). Transient staining of immature layer V pyramidal cells was seen in kittens six weeks old and younger. This transient staining of pyramidal cells was most intense and the stained neurons were most numerous in cingulate cortex. Apical dendrites of pyramidal cells in cingulate cortex were prominently stained and could be followed to layer I, where they were seen to branch extensively. There were very few calbindin immunoreactive pyramidal cells in primary cortical areas postnatally. Transient staining in extrastriate visual cortical areas disappeared first from the lateral suprasylvian areas, and persisted longest in area 7. Pyramidal neurons in the cingulate gyrus expressed calbindin longest, but calbindin expression by pyramidal neurons ceased by the sixth postnatal week in all areas of the brain.

Increased clearance of 1,25(OH)2D3 and tissue-specific responsiveness to 1,25(OH)2D3 in diabetic rats

The kinetics of 1,25-dihydroxyvitamin D3 [1,25(OH)2-D3] and the in vivo response to 1,25(OH)2D3 (7.5, 15, and 30 ng/100 g body wt), infused or injected subcutaneously for 12-14 days, were studied in male spontaneously diabetic and control BB rats. In control rats, increasing doses of 1,25(OH)2D3 produced parallel increases in plasma 1,25(OH)2D3 and calcium, urinary calcium, duodenal CaBP9K, and renal CaBP28K. 1,25-(OH)2D3 at 30 ng/100 g markedly raised plasma osteocalcin and osteoblast/osteoid surfaces in the tibial metaphysis, but inhibited bone mineralization rate. In diabetic rats, plasma 1,25-(OH)2D3 concentrations were decreased, and the rise of plasma 1,25(OH)2D3 during 1,25(OH)2D3 infusion was blunted, but the free 1,25(OH)2D3 index remained normal or above normal. Diabetic rats had an increased metabolic clearance rate of 1,25-(OH)2D3 (0.38 +/- 0.015 vs. 0.24 +/- 0.007 ml.min-1.kg-1), with no further increase in 1,25(OH)2D3-infused diabetic rats; their relative production rate of 1,25(OH)2D3 was unchanged. The responses of plasma and urinary calcium, duodenal CaBP9K, and renal CaBP28K to infused 1,25(OH)2D3 were normal, as was duodenal calcium absorption in 1,25(OH)2D3-injected diabetic rats. However, the virtual absence of osteoblasts/osteoid in trabecular bone was unaltered in diabetic rats infused with 30 ng/100 g 1,25(OH)2D3, with only minimal increase of their low plasma osteocalcin levels. 1,25(OH)2D3 treatment therefore cannot be expected to reverse diabetic osteopenia.

Gene expression in cells of the central nervous system

This review summarized a part of our studies over a long period of time, relating them to the literature on the same topics. We aimed our research toward an understanding of the genetic origin of brain specific proteins, identified by B. W. Moore and of the high complexity of the nucleotide sequence of brain mRNA, originally investigated by W. E. Hahn, but have not completely achieved the projected goal. According to our studies, the reason for the high complexity in the RNA of brain nuclei might be the high complexity in neuronal nuclear RNA as described in the Introduction. Although one possible explanation is that it results from the summation of RNA complexities of several neuronal types, our saturation hybridization study with RNA from the isolated nuclei of granule cells showed an equally high sequence complexity as that of brain. It is likely that this type of neuron also contains numerous rare proteins and peptides, perhaps as many as 20,000 species which were not detectable even by two-dimensional PAGE. I was possible to gain insight into the reasons for the high sequence complexity of brain RNA by cloning the cDNA and genomic DNA of the brain-specific proteins as described in the previous sections. These data provided evidence for the long 3'-noncoding regions in the cDNA of the brain-specific proteins which caused the mRNA of brain to be larger than that from other tissues. During isolation of such large mRNAs, a molecule might be split into a 3'-poly(A)+RNA and 5'-poly(A)-RNA. In the studies on genomic DNA, genes with multiple transcription initiation sites were found in brain, such as CCK, CNP and MAG, in addition to NSE which was a housekeeping gene, and this may contribute to the high sequence complexity of brain RNA. Our studies also indicated the presence of genes with alternative splicing in brain, such as those for CNP, MAG and NGF, suggesting a further basis for greater RNA nucleotide sequence complexity. It is noteworthy that alternative splicing of the genes for MBP and PLP also produced multiple mRNAs. Such a mechanism may be a general characteristic of the genes for the myelin-specific proteins produced by oligodendrocytes. In considering the high nucleotide sequence complexity, it is interesting that MAG and S-100 beta genes etc. possess two additional sites for poly(A).(ABSTRACT TRUNCATED AT 400 WORDS)