Home About us Contact | |||
Mineral Homeostasis (mineral + homeostasi)
Selected AbstractsEvidence that both 1,,25-dihydroxyvitamin D3 and 24-hydroxylated D3 enhance human osteoblast differentiation and mineralizationJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 3 2006M. van Driel Abstract Vitamin D plays a major role in the regulation of mineral homeostasis and affects bone metabolism. So far, detailed knowledge on the vitamin D endocrine system in human bone cells is limited. Here we investigated the direct effects of 1,,25-(OH)2D3 on osteoblast differentiation and mineralization. Also, we studied the impact of 24-hydroxylation, generally considered as the first step in the degradation pathway of vitamin D, as well as the role of the nuclear and presumed membrane vitamin D receptor (VDR). For this we used a human osteoblast cell line (SV-HFO) that has the potency to differentiate during culture forming a mineralized extracellular matrix in a 3-week period. Transcriptional analyses demonstrated that both 1,,25-(OH)2D3 and the 24-hydroxylated metabolites 24R,25-(OH)2D3 and 1,,24R,25-(OH)3D3 induced gene transcription. All metabolites dose-dependently increased alkaline phosphatase (ALP) activity and osteocalcin (OC) production (protein and RNA), and directly enhanced mineralization. 1,,24R,25-(OH)3D3 stimulated ALP activity and OC production most potently, while for mineralization it was equipotent to 1,,25-(OH)2D3. The nuclear VDR antagonist ZK159222 almost completely blocked the effects of all metabolites. Interestingly, 1,,25-(OH)2D3, an inhibitor of membrane effects of 1,,25-(OH)2D3 in the intestine, induced gene transcription and increased ALP activity, OC expression and mineralization. In conclusion, not only 1,,25-(OH)2D3, but also the presumed 24-hydroxylated "degradation" products stimulate differentiation of human osteoblasts. 1,,25-(OH)2D3 as well as the 24-hydroxylated metabolites directly enhance mineralization, with the nuclear VDR playing a central role. The intestinal antagonist 1,,25-(OH)2D3 acts in bone as an agonist and directly stimulates mineralization in a nuclear VDR-dependent way. J. Cell. Biochem. 99: 922,935, 2006. © 2006 Wiley-Liss, Inc. [source] Vitamin D receptor distribution in intestines of domesticated sheep Ovis ammon f. ariesJOURNAL OF MORPHOLOGY, Issue 2 2008Katharina Riner Abstract The biologically active form of vitamin D, i.e., 1,25-dihydroxycholecalciferol or calcitriol, plays an important role in bone metabolism and calcium homeostasis, which is often disturbed at the onset of lactation in high milk-yielding domestic ruminants. Gene transcription is modulated via vitamin D receptors, but nongenomic effects of vitamin D via membrane receptors have also been described. In the intestines, vitamin D promotes calcium absorption via vitamin D receptors. Vitamin D receptors are of clinical relevance, but have not been systematically assessed within all segments of the intestine in any species. Thus, we present for the first time an immunohistochemical study of the distribution patterns of the vitamin D receptor protein in sheep, which may be the basis for present and future investigations on mineral homeostasis in domestic ruminants. Tissue probes of the intestines were collected from five lambs and five nonlactating and nonpregnant dams, fixed in formalin, embedded in paraffin, and used for the assessment of vitamin D receptor protein. Nuclear vitamin D receptor immunoreaction was scored semiquantitatively and exhibited a segment-specific distribution pattern. Goblet cells always were devoid of any vitamin D receptor immunoreaction. Surface epithelial cells and enterocytes of the crypt openings generally demonstrated only a weak immunoreaction. Basally and/or intermediately located crypt epithelial cells exhibited stronger immunoreactions in duodenum, jejunum, and colon descendens. This basal/intermediate to superficial gradient was most pronounced in the duodenum and less evident in jejunum and colon descendens and not observed in ileum and cecum. There were no age-dependent variations in vitamin D receptor protein expression. Results demonstrate that intestinal vitamin D receptor distribution patterns are segment-specific and strongest immunoreactions correlate with highest intestinal calcium absorptive activities, as reported in literature. Strong expression of vitamin D receptors within the lower half of crypts also suggests a role for calcitriol in epithelial differentiation and cellular homeostasis. J. Morphol., 2008. © 2007 Wiley-Liss, Inc. [source] Genetic analysis identifies quantitative trait loci controlling rosette mineral concentrations in Arabidopsis thaliana under droughtNEW PHYTOLOGIST, Issue 1 2009Artak Ghandilyan Summary ,,Rosettes of 25 Arabidopsis thaliana accessions and an Antwerp-1 (An-1) × Landsberg erecta (Ler) population of recombinant inbred lines (RILs) grown in optimal watering conditions (OWC) and water deficit conditions (WDC) were analysed for mineral concentrations to identify genetic loci involved in adaptation of mineral homeostasis to drought stress. ,,Correlations between mineral concentrations were determined for accessions and a quantitative trait locus (QTL) analysis was performed for the RIL population. ,,Plant growth and rosette mineral contents strongly decreased in WDC compared with OWC. Mineral concentrations also generally decreased, except for phosphorus (P), which remained constant, and potassium (K), which increased. Large variations in mineral concentrations were observed among accessions, mostly correlated with total rosette leaf area. Mineral concentration QTLs were identified in the RIL population, but only a few were common for both conditions. Clusters of mineral concentration QTLs often cosegregated with dry weight QTLs. ,,Water deficit has a strong effect on rosette mineral status. This is genetically determined and seems largely a pleiotropic effect of the reduction in growth. The low number of common mineral concentration QTLs, shared among different RIL populations, tissues and conditions in Arabidopsis, suggests that breeding for robust, mineral biofortified crops will be complex. [source] Nuclear receptors of the enteric tract: guarding the frontierNUTRITION REVIEWS, Issue 2008Daniel R Schmidt In addition to its classical role in mineral homeostasis, the vitamin D receptor has been implicated in diverse physiologic and pathophysiologic processes including immunoregulation and cancer. Interestingly, the vitamin D receptor has been evolutionarily and functionally linked to a select group of nuclear receptors based on a common organism-wide tissue expression profile. These members of the nuclear receptor superfamily, which include the bile acid receptor, xenobiotic receptors, and several orphan nuclear receptors, comprise a transcriptional regulatory network that functions in nutrient uptake, xenobiotic metabolism, and mucosal protection. The major homeostatic functions of the enteric nuclear receptor network are the topic of this review. [source] A comparative view on mechanisms and functions of skeletal remodelling in teleost fish, with special emphasis on osteoclasts and their functionBIOLOGICAL REVIEWS, Issue 2 2009P. Eckhard Witten ABSTRACT Resorption and remodelling of skeletal tissues is required for development and growth, mechanical adaptation, repair, and mineral homeostasis of the vertebrate skeleton. Here we review for the first time the current knowledge about resorption and remodelling of the skeleton in teleost fish, the largest and most diverse group of extant vertebrates. Teleost species are increasingly used in aquaculture and as models in biomedical skeletal research. Thus, detailed knowledge is required to establish the differences and similarities between mammalian and teleost skeletal remodelling, and between distantly related species such as zebrafish (Danio rerio) and medaka (Oryzias latipes). The cellular mechanisms of differentiation and activation of osteoclasts and the functions of teleost skeletal remodelling are described. Several characteristics, related to skeletal remodelling, distinguish teleosts from mammals. These characteristics include (a) the absence of osteocytes in most species; (b) the absence of haematopoietic bone marrow tissue; (c) the abundance of small mononucleated osteoclasts performing non-lacunar (smooth) bone resorption, in addition to or instead of multinucleated osteoclasts; and (d) a phosphorus- rather than calcium-driven mineral homeostasis (mainly affecting the postcranial dermal skeleton). Furthermore, (e) skeletal resorption is often absent from particular sites, due to sparse or lacking endochondral ossification. Based on the mode of skeletal remodelling in early ontogeny of all teleosts and in later stages of development of teleosts with acellular bone we suggest a link between acellular bone and the predominance of mononucleated osteoclasts, on the one hand, and cellular bone and multinucleated osteoclasts on the other. The evolutionary origin of skeletal remodelling is discussed and whether mononucleated osteoclasts represent an ancestral type of resorbing cells. Revealing the differentiation and activation of teleost skeletal resorbing cells, in the absence of several factors that trigger mammalian osteoclast differentiation, is a current challenge. Understanding which characters of teleost bone remodelling are derived and which characters are conserved should enhance our understanding of the process in fish and may provide insights into alternative pathways of bone remodelling in mammals. [source] |