Biomedical subjects

Geert Carmeliet

Publications and source records attributed to Geert Carmeliet.

At least 19 recordsLinked to original sources

PubMed2006

Duodenal calcium absorption in dexamethasone-treated mice: functional and molecular aspects.

Reduced intestinal calcium absorption may be part of the pathogenesis of glucocorticoid-induced osteoporosis. 1,25(OH)2D3 is the major regulator of the expression of the active duodenal calcium absorption genes: TRPV6 (influx), calbindin-D9K (intracellular transfer) and PMCA1b (extrusion). We investigated the influence of dexamethasone (5 days: 2 mg/kg bw) on calcium absorption in vivo and on the expression of intestinal and renal calcium transporters in calcium-deprived mice. Total and free 1,25(OH)2D3-concentrations were halved, in line with decreased 25(OH)D3-1-alpha-hydroxylase and increased 24-hydroxylase expression. Nevertheless, no difference in duodenal or renal calcium transporter expression pattern could be detected between vehicle and dexamethasone-treated mice. Accordingly, dexamethasone did not affect in vivo calcium absorption. By contrast, increased calcemia and collagen C-terminal telopeptide levels reflected increased bone resorption. Decreased osteocalcin levels suggested impaired bone formation. Hence, short-term glucocorticoid excess in young animals affected bone metabolism without detectable changes in intestinal or renal calcium handling.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed2006

Vitamin D receptor in chondrocytes promotes osteoclastogenesis and regulates FGF23 production in osteoblasts.

Genomic actions induced by 1alpha25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] are crucial for normal bone metabolism, mainly because they regulate active intestinal calcium transport. To evaluate whether the vitamin D receptor (VDR) has a specific role in growth-plate development and endochondral bone formation, we investigated mice with conditional inactivation of VDR in chondrocytes. Growth-plate chondrocyte development was not affected by the lack of VDR. Yet vascular invasion was impaired, and osteoclast number was reduced in juvenile mice, resulting in increased trabecular bone mass. In vitro experiments confirmed that VDR signaling in chondrocytes directly regulated osteoclastogenesis by inducing receptor activator of NF-kappaB ligand (RANKL) expression. Remarkably, mineral homeostasis was also affected in chondrocyte-specific VDR-null mice, as serum phosphate and 1,25(OH)(2)D levels were increased in young mice, in whom growth-plate activity is important. Both in vivo and in vitro analysis indicated that VDR inactivation in chondrocytes reduced the expression of FGF23 by osteoblasts and consequently led to increased renal expression of 1alpha-hydroxylase and of sodium phosphate cotransporter type IIa. Taken together, our findings provide evidence that VDR signaling in chondrocytes is required for timely osteoclast formation during bone development and for the endocrine action of bone in phosphate homeostasis.

Animals↗

PubMed2006

VDR-dependent regulation of mast cell maturation mediated by 1,25-dihydroxyvitamin D3.

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] is a secosteroid hormone that regulates bone metabolism, controls calcium homeostasis, and possesses immunomodulatory properties. We show here that 1,25(OH)2D3 contributes to the regulation of development and function of mast cells, which play a critical role in several inflammatory disorders. 1,25(OH)2D3 promotes apoptosis and inhibits maturation of mouse bone marrow-derived mast cell precursors. Dose-dependent inhibition of mast cell differentiation by 1,25(OH)2D3 is observed at discrete, intermediate stages of mast cell development, identified by expression of c-kit, FcepsilonRI, and IL-3 receptor-alpha chain, and depends on the expression of the vitamin D receptor (VDR). It is important that mast cell progenitors obtained from VDR-ablated mice undergo an accelerated maturation in vitro and give rise to more responsive mast cells than wild-type. Furthermore, histological analysis of mast cell density in peripheral tissues reveals a moderate increase in the number of mast cells in the skin of VDR-deficient mice compared with wild-type animals. These data support the hypothesis of a physiological role of 1,25(OH)2D3 in mast cell development and suggest novel, therapeutic uses of 1,25(OH)2D3 analogs.

Animals↗

PubMed2006

UVB-induced 1,25(OH)2D3 production and vitamin D activity in intestinal CaCo-2 cells and in THP-1 macrophages pretreated with a sterol Delta7-reductase inhibitor.

Epidermal keratinocytes are able to produce 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and induce vitamin D activity upon UVB irradiation. To find out whether this property is keratinocyte specific, we investigated this characteristic in two other cell types, namely intestinal CaCo-2 cells and the macrophage-like differentiated THP-1 cells. THP-1 macrophages and preconfluent CaCo-2 cells contain the vitamin D receptor (VDR), possess 25-hydroxylase (CYP2R1 and CYP27A1) and 1alpha-hydroxylase (CYP27B1) activity, and survive the low UVB doses essential for vitamin D3 photoproduction. Upon irradiation, 24-hydroxylase (CYP24) mRNA is induced in both cell types pretreated with the sterol Delta7-reductase inhibitor BM15766 whereby the 7-dehydrocholesterol (7-DHC) content was increased. Transfection studies in CaCo-2 cells with a vitamin D response element-containing construct revealed the involvement of the VDR in this UVB-dependent CYP24 induction. The CYP24 inducing activity in BM15766-pretreated UVB-irradiated CaCo-2 cells and THP-1 macrophages was identified as 1,25(OH)2D3 by combined high-performance liquid chromatography radioimmunoassay. Addition of vitamin D binding protein to the CaCo-2 cells attenuated UVB-induced CYP24 induction suggesting the possibility of a paracrine or autocrine role for the photoproduced 1,25(OH)2D3. In conclusion, preconfluent CaCo-2 cells and THP-1 macrophages are able to induce vitamin D activity upon UVB irradiation and hence combine all parts of the vitamin D photoendocrine system, a characteristic which is therefore not keratinocyte specific.

Caco-2 Cells↗

PubMed2006

Placental growth factor mediates mesenchymal cell development, cartilage turnover, and bone remodeling during fracture repair.

Current therapies for delayed- or nonunion bone fractures are still largely ineffective. Previous studies indicated that the VEGF homolog placental growth factor (PlGF) has a more significant role in disease than in health. Therefore we investigated the role of PlGF in a model of semi-stabilized bone fracture healing. Fracture repair in mice lacking PlGF was impaired and characterized by a massive accumulation of cartilage in the callus, reminiscent of delayed- or nonunion fractures. PlGF was required for the early recruitment of inflammatory cells and the vascularization of the fracture wound. Interestingly, however, PlGF also played a role in the subsequent stages of the repair process. Indeed in vivo and in vitro findings indicated that PlGF induced the proliferation and osteogenic differentiation of mesenchymal progenitors and stimulated cartilage turnover by particular MMPs. Later in the process, PlGF was required for the remodeling of the newly formed bone by stimulating osteoclast differentiation. As PlGF expression was increased throughout the process of bone repair and all the important cell types involved expressed its receptor VEGFR-1, the present data suggest that PlGF is required for mediating and coordinating the key aspects of fracture repair. Therefore PlGF may potentially offer therapeutic advantages for fracture repair.

Animals↗

PubMed2006

NuSAP, a mitotic RanGTP target that stabilizes and cross-links microtubules.

Nucleolar and spindle-associated protein (NuSAP) was recently identified as a microtubule- and chromatin-binding protein in vertebrates that is nuclear during interphase. Small interfering RNA-mediated depletion of NuSAP resulted in aberrant spindle formation, missegregation of chromosomes, and ultimately blocked cell proliferation. We show here that NuSAP is enriched on chromatin-proximal microtubules at meiotic spindles in Xenopus oocytes. When added at higher than physiological levels to Xenopus egg extract, NuSAP induces extensive bundling of spindle microtubules and causes bundled microtubules within spindle-like structures to become longer. In vitro reconstitution experiments reveal two direct effects of NuSAP on microtubules: first, it can efficiently stabilize microtubules against depolymerization, and second, it can cross-link large numbers of microtubules into aster-like structures, thick fibers, and networks. With defined components we show that the activity of NuSAP is differentially regulated by Importin (Imp) alpha, Impbeta, and Imp7. While Impalpha and Imp7 appear to block the microtubule-stabilizing activity of NuSAP, Impbeta specifically suppresses aspects of the cross-linking activity of NuSAP. We propose that to achieve full NuSAP functionality at the spindle, all three importins must be dissociated by RanGTP. Once activated, NuSAP may aid to maintain spindle integrity by stabilizing and cross-linking microtubules around chromatin.

Animals↗

PubMed2006

Mathematical modeling of fracture healing in mice: comparison between experimental data and numerical simulation results.

The combined use of experimental and mathematical models can lead to a better understanding of fracture healing. In this study, a mathematical model, which was originally established by Bailón-Plaza and van der Meulen (J Theor Biol 212:191-209, 2001), was applied to an experimental model of a semi-stabilized murine tibial fracture. The mathematical model was implemented in a custom finite volumes code, specialized in dealing with the model's requirements of mass conservation and non-negativity of the variables. A qualitative agreement between the experimentally measured and numerically simulated evolution in the cartilage and bone content was observed. Additionally, an extensive parametric study was conducted to assess the influence of the model parameters on the simulation outcome. Finally, a case of pathological fracture healing and its treatment by administration of growth factors was modeled to demonstrate the potential therapeutic value of this mathematical model.

Animals↗

PubMed2006

Vitamin D resistance.

Vitamin D is a secosteroid of nutritional origin but can also be generated in the skin by ultraviolet light. After two hydroxylations 1,25-(OH)2 vitamin D avidly binds and activates the vitamin D receptor (VDR), a nuclear transcription factor, hereby regulating a large number of genes. The generation of VDR deficient mice has expanded the knowledge on vitamin D from a calcium-regulating hormone to a humoral factor with extensive actions. The effects of the vitamin D system on calcium and bone homeostasis are largely mediated by promoting active intestinal calcium transport via the induction of the epithelial calcium channel TRPV6. Although VDR is redundant in bone, it may regulate the differentiation and function of several bone cells. In skin, VDR expression in keratinocytes is essential in a ligand-independent manner for the maintenance of the normal hair cycle. Therefore, VDR but not vitamin D deficiency results in alopecia. Moreover, 1,25-(OH)2 vitamin D impairs the proliferation not only of keratinocytes but also of many cell types by regulating the expression of cell cycle genes, leading to a G1 cell cycle arrest. In addition, VDR inactivation in mice results in high renin hypertension, cardiac hypertrophy and thrombogenesis. Finally, a dual effect of vitamin D was observed in the immune system where it stimulates the innate immune system while tapering down excessive activation of the acquired immune system. Taken together, the vitamin D endocrine system not only regulates calcium homeostasis but affects several systems mainly by altering gene expression but also by ligand-independent actions.

Animals↗

PubMed2006

Vitamin D and cancer.

1,25-dihydroxy Vitamin D [1,25-(OH)(2)D] exerts its effects via the vitamin D receptor (VDR) that belongs to the steroid/thyroid hormone receptor superfamily leading to gene regulation which results in various biological responses. Within the last two decades, the receptor has been shown to be present not only in classical target tissues such as bone, kidney and intestine but also in many other non-classical tissues. Besides the almost universal presence of VDRs, some cell types (e.g. keratinocytes, monocytes, bone, placenta) are capable of metabolizing 25-hydroxyvitamin D to 1,25(OH)(2)D by the enzyme 1alpha-hydroxylase (CYP27B1). The combined presence of 25(OH)D-1alpha-hydroxylase as well as the specific receptor in several tissues introduced the idea of a paracrine role for 1,25(OH)(2)D. Moreover, it has been demonstrated that 1,25(OH)(2)D can induce differentiation and inhibit proliferation of a wide variety of cell types. The molecular mechanisms behind this antiproliferative action is thoroughly explored but the whole picture is still difficult to understand. Important cell cycle regulators are involved such as cyclins, cyclin dependent kinases and their corresponding inhibitors as well as E2F transcription factors and accompanying pocket proteins. However the precise hierarchical structure of this wide diversity of actions of 1,25(OH)(2)D on genes influencing cell cycle progression is not firmly established nor do we understand which pathways are essential and which redundant. The antiproliferative action makes 1,25-(OH)(2)D and its analogs a possible therapeutic tool to treat hyperproliferative disorders, among which different types of cancer. This review focuses on the effects of 1,25(OH)(2)D and its analogs on cell proliferation, the results in in vivo experiments in Vitamin D deficient or resistant animals to cancer and the current epidemiological and intervention studies linking Vitamin D status or treatment and human cancer.

Animals↗

PubMed2006

Early cellular responses in cortical bone healing around unloaded titanium implants: an animal study.

BACKGROUND: A clear understanding of the early cellular events leading to osseointegration of implants is currently lacking. To gain better insight, titanium implants were inserted in a rabbit model and histologic and histomorphometric analyses were performed at early time points after insertion. METHODS: Thirty-six cylindrical implants were inserted in the tibial diaphysis of six rabbits and left to heal for 1 to 42 days. Samples were processed into paraffin or methylmethacrylate sections, on which the surface of new bone, region of altered nuclear morphology, relative surface of basic multicellular units (BMUs) and blood vessels, and bone-to-implant contact were measured. RESULTS: After coagulum formation, osteoclasts and osteoblasts were observed at the bone surface 1 week after healing. In the preexisting bone, osteocytic lacunae appeared to be devoid of cells. This region of altered nuclear morphology continued to extend for 28 days (P <0.05) after implant insertion. This expansion was accompanied by an invasion of the damaged bone by BMUs that initiated intensive bone remodeling, which reached its maximum after 4 weeks (P <0.05) but was ongoing after 6 weeks of implant insertion. CONCLUSIONS: This study evaluated the early cellular events in cortical bone surrounding titanium implants. The insertion of an implant into bone initiates a series of biologic processes, including the formation of a hematoma, altered nuclear morphology of the osteocytes surrounding the implantation site, intensive bone remodeling, and the formation of new bone, eventually leading to the osseointegration of the implant.

Animals↗

PubMed2004

Molecular pathways involved in the anti-apoptotic effect of 1,25-dihydroxyvitamin D3 in primary human keratinocytes.

We previously reported that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] protects primary human keratinocytes against ultraviolet (UV)B-induced apoptosis. Here, we confirmed the anti-apoptotic effect of 1,25(OH)2D3 in keratinocytes, using cisplatin and doxorubicin as apoptotic triggers. We further showed that 1,25(OH)2D3 activates two survival pathways in keratinocytes: the MEK/extracellular signal regulated kinase (ERK) and the phosphatidylinositol 3-kinase (PI-3K)/Akt pathway. Activation of ERK and Akt by 1,25(OH)2D3 was transient, required a minimal dose of 10(-9) M and could be blocked by actinomycin D and cycloheximide. Moreover, inhibition of Akt or ERK activity with respectively a PI-3K inhibitor (LY294002) or MEK inhibitors (PD98059, UO126), partially or totally suppressed the anti-apoptotic capacity of 1,25(OH)2D3. Finally, 1,25(OH)2D3 changed the expression of different apoptosis regulators belonging to the Bcl-2 family. Indeed, 1,25(OH)2D3 treatment increased levels of the anti-apoptotic protein Bcl-2 and decreased levels of the pro-apoptotic proteins Bax and Bad in a time- and dose-dependent way. Induction of Bcl-2 by 1,25(OH)2D3 was further shown to be mediated by ERK and, to a lesser extent, by Akt. In conclusion, 1,25(OH)2D3 clearly protects keratinocytes against apoptosis (1) by activating the MEK/ERK and the PI-3K/Akt survival pathways and (2) by increasing the Bcl-2 to Bax and Bad ratio.

Antineoplastic Agents↗

PubMed2004

Enhanced osteoclast development in collagen-induced arthritis in interferon-gamma receptor knock-out mice as related to increased splenic CD11b+ myelopoiesis.

Collagen-induced arthritis (CIA) in mice is accompanied by splenomegaly due to the selective expansion of immature CD11b+ myeloblasts. Both disease manifestations are more pronounced in interferon-gamma receptor knock-out (IFN-gammaR KO) mice. We have taken advantage of this difference to test the hypothesis that the expanding CD11b+ splenic cell population constitutes a source from which osteoclast precursors are recruited to the joint synovia. We found larger numbers of osteoclasts and more severe bone destruction in joints of IFN-gammaR KO mice than in joints of wild-type mice. Osteoclast-like multinucleated cells appeared in splenocyte cultures established in the presence of macrophage colony-stimulating factor (M-CSF) and stimulated with the osteoclast-differentiating factor receptor activator of NF-kappaB ligand (RANKL) or with tumour necrosis factor-alpha (TNF-alpha). Significantly larger numbers of such cells could be generated from splenocytes of IFN-gammaR KO mice than from those of wild-type mice. This was not accompanied, as might have been expected, by increased concentrations of the intracellular adaptor protein TRAF6, known to be involved in signalling of RANKL- and TNF-alpha-induced osteoclast formation. Splenocyte cultures of IFN-gammaR KO mice also produced more TNF-alpha and more RANKL than those of wild-type mice. Finally, splenocytes isolated from immunised IFN-gammaR KO mice contained comparatively low levels of pro-interleukin-1beta (pro-IL-1beta) and pro-caspase-1, indicating more extensive conversion of pro-IL-1beta into secreted active IL-1beta. These observations provide evidence that all conditions are fulfilled for the expanding CD11b+ splenocytes to act as a source of osteoclasts and to be indirectly responsible for bone destruction in CIA. They also provide a plausible explanation for the higher susceptibility of IFN-gammaR KO mice to CIA.

Animals↗

PubMed2004

Microarray analysis of 1alpha,25-dihydroxyvitamin D3-treated MC3T3-E1 cells.

The active form of Vitamin D, 1alpha,25-dihydroxyvitamin D(3) [1,25-(OH)(2)D(3)], demonstrates potent antiproliferative actions on normal as well as on malignant cell types by blocking the transition from the G1- to the S-phase of the cell cycle. Key target genes for 1,25-(OH)(2)D(3) in this non-classic effect remain largely unknown. Therefore, this study aims to identify genes that, through changes in expression after 1,25-(OH)(2)D(3) treatment, contribute to the observed antiproliferative effect. cDNA microarrays containing 4600 genes were used to investigate changes in gene expression in MC3T3-E1 mouse osteoblasts at 6 and at 12h after treatment with 1,25-(OH)(2)D(3) (10(-8)M), preceding (6h) or coinciding with (12h) the G1/S block in these cells. Approximately one fifth of the genes that were significantly down-regulated after a 12h incubation period with 1,25-(OH)(2)D(3) were genes involved in the DNA replication process, a basic process for cell growth that starts at the end of G1-phase and continues in S-phase. Down-regulation of these genes by 1,25-(OH)(2)D(3) was confirmed by quantitative RT-PCR in MC3T3-E1. In conclusion, cDNA microarrays revealed that treatment of MC3T3-E1 cells with 1,25-(OH)(2)D(3) resulted in the down-regulation of DNA replication genes in parallel with the observed G1/S-arrest.

3T3 Cells↗

PubMed2004

Soluble VEGF isoforms are essential for establishing epiphyseal vascularization and regulating chondrocyte development and survival.

VEGF is crucial for metaphyseal bone vascularization. In contrast, the angiogenic factors required for vascularization of epiphyseal cartilage are unknown, although this represents a developmentally and clinically important aspect of bone growth. The VEGF gene is alternatively transcribed into VEGF(120), VEGF(164), and VEGF(188) isoforms that differ in matrix association and receptor binding. Their role in bone development was studied in mice expressing single isoforms. Here we report that expression of only VEGF(164) or only VEGF(188) (in VEGF(188/188) mice) was sufficient for metaphyseal development. VEGF(188/188) mice, however, showed dwarfism, disrupted development of growth plates and secondary ossification centers, and knee joint dysplasia. This phenotype was at least partly due to impaired vascularization surrounding the epiphysis, resulting in ectopically increased hypoxia and massive chondrocyte apoptosis in the interior of the epiphyseal cartilage. In addition to the vascular defect, we provide in vitro evidence that the VEGF(188) isoform alone is also insufficient to regulate chondrocyte proliferation and survival responses to hypoxia. Consistent herewith, chondrocytes in or close to the hypoxic zone in VEGF(188/188) mice showed increased proliferation and decreased differentiation. These findings indicate that the insoluble VEGF(188) isoform is insufficient for establishing epiphyseal vascularization and regulating cartilage development during endochondral bone formation.

Angiography↗

PubMed2004

The effects of 1alpha,25-dihydroxyvitamin D3 on the expression of DNA replication genes.

UNLABELLED: To identify key genes in the antiproliferative action of 1,25(OH)2D3, MC3T3-E1 mouse osteoblasts were subjected to cDNA microarray analyses. Eleven E2F-driven DNA replication genes were downregulated by 1,25(OH)2D3. These results were confirmed by quantitative RT-PCR in different cell types, showing the general nature of this action of 1,25(OH)2D3. INTRODUCTION: 1Alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] has a potent antiproliferative action characterized by a blocked transition from the G1- to the S-phase of the cell cycle. This study aims to identify genes whose expression is markedly altered after 1,25(OH)2D3 treatment in parallel with or preceding the observed G1-arrest. MATERIALS AND METHODS: The cDNA microarray technique was used, and the expression of approximately 4600 genes in MC3T3-E1 mouse osteoblasts was studied 6 and 12 h after treatment with 10(-8) M 1,25(OH)2D3. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analyses were performed on MC3T3-E1 cells and on wildtype and vitamin D receptor (VDR) knockout primary murine epidermal keratinocytes (VDRwt MEKs, VDR-/- MEKs) and murine mammary tumor cells (GR) to confirm the microarray data. RESULTS AND CONCLUSIONS: After 12 h of treatment, in parallel with the 1,25(OH)2D3-induced G1 arrest, a particular set of DNA replication genes including a cell division cycle 6 homolog, a DNA polymerase alpha subunit, proliferating cell nuclear antigen, two DNA polymerase delta subunits, and flap-structure specific endonuclease 1, was downregulated at least 2-fold. These genes are known targets of the E2F family of transcription factors, which are probably the central mediators of this action of 1,25(OH)2D3. Indeed, as shown by transfection assays with an E2F reporter construct, 12- and 24-h treatment of MC3T3-E1 cells with 1,25(OH)2D3 reduced E2F activity by 49% and 73%, respectively. Quantitative RT-PCR analyses confirmed the downregulation of these DNA replication genes by 1,25(OH)2D3 in MC3T3-E1, GR, and VDRwt MEKs cells, but not in VDR-/- MEKs cells, showing that this 1,25(OH)2D3-driven antiproliferative action is of a general nature and depends on a functional VDR.

3T3 Cells↗

PubMed2003

NuSAP, a novel microtubule-associated protein involved in mitotic spindle organization.

Here, we report on the identification of nucleolar spindle-associated protein (NuSAP), a novel 55-kD vertebrate protein with selective expression in proliferating cells. Its mRNA and protein levels peak at the transition of G2 to mitosis and abruptly decline after cell division. Microscopic analysis of both fixed and live mammalian cells showed that NuSAP is primarily nucleolar in interphase, and localizes prominently to central spindle microtubules during mitosis. Direct interaction of NuSAP with microtubules was demonstrated in vitro. Overexpression of NuSAP caused profound bundling of cytoplasmic microtubules in interphase cells, and this relied on a COOH-terminal microtubule-binding domain. In contrast, depletion of NuSAP by RNA interference resulted in aberrant mitotic spindles, defective chromosome segregation, and cytokinesis. In addition, many NuSAP-depleted interphase cells had deformed nuclei. Both overexpression and knockdown of NuSAP impaired cell proliferation. These results suggest a crucial role for NuSAP in spindle microtubule organization.

Amino Acid Sequence↗

PubMed2003

Pregnancy in mice lacking the vitamin D receptor: normal maternal skeletal response, but fetal hypomineralization rescued by maternal calcium supplementation.

Fetal mineralization appears to be driven by the pregnancy-induced stimulation of intestinal Ca absorption. We thus hypothesized that mineralization would be impaired in fetuses of mice that lack the vitamin D receptor (VDR). Here we report on the maternal response to pregnancy, and the fetal mineralization, in mice with a homozygous disruption of the VDR gene (VDR-/-) mated with wild-type (wt) males. We found that VDR-/- mice show mild hypocalcemia, clear rickets and osteomalacia on bone histomorphometry, lower cortical bone density on quantitative tomography, and reduced concentrations of calbindin-D9k (CaBP-D9k) in duodenal mucosa and kidney. The skeletal response to pregnancy was comparable in wt and VDR-/- mice; duodenal CaBP-D9k concentrations increased during pregnancy in VDR-/- as in wt mice, but remained 40% lower than in wt mice. We confirmed our hypothesis that mineralization is defective in d18.5 VDR+/- fetuses of VDR-/- mice, both by whole-body Ca determination and histomorphometric evaluation; the number of osteoclastic cells in bone was increased. The fetuses were hypercalcemic and had a 5-fold increase in circulating 1,25(OH)2D3. We then studied pregnancies in VDR-/- females, mated with wt males, fed a high Ca/P/lactose rescue diet during pregnancy. The rescue diet normalized the mineralization, the number of osteoclastic cells, and plasma Ca and 1,25(OH)2D3 concentrations in the fetuses. We interpret the data as evidence that, to ensure normal fetal mineralization, the maternal VDR-dependent intestinal Ca absorption can be substituted by passive Ca absorption entrained by a higher Ca intake. Alternatively or additionally, elevated 1,25(OH)2D3 in utero may disturb bone development.

Animals↗

PubMed2003

VEGF: a modifier of the del22q11 (DiGeorge) syndrome?

Hemizygous deletion of chromosome 22q11 (del22q11) causes thymic, parathyroid, craniofacial and life-threatening cardiovascular birth defects in 1 in 4,000 infants. The del22q11 syndrome is likely caused by haploinsufficiency of TBX1, but its variable expressivity indicates the involvement of additional modifiers. Here, we report that absence of the Vegf164 isoform caused birth defects in mice, reminiscent of those found in del22q11 patients. The close correlation of birth and vascular defects indicated that vascular dysgenesis may pathogenetically contribute to the birth defects. Vegf interacted with Tbx1, as Tbx1 expression was reduced in Vegf164-deficient embryos and knocked-down vegf levels enhanced the pharyngeal arch artery defects induced by tbx1 knockdown in zebrafish. Moreover, initial evidence suggested that a VEGF promoter haplotype was associated with an increased risk for cardiovascular birth defects in del22q11 individuals. These genetic data in mouse, fish and human indicate that VEGF is a modifier of cardiovascular birth defects in the del22q11 syndrome.

Animals↗