Biomedical subjects

Matthias Gebauer

Publications and source records attributed to Matthias Gebauer.

8 recordsLinked to original sources

PubMed2005

Subdental synchondrosis and anatomy of the axis in aging: a histomorphometric study on 30 autopsy cases.

During skeletal development the two ossification centers of the odontoid process are separated from the corpus of the axis by a subdental synchondrosis. This synchondrosis is thought to close and disappear spontaneously in adolescence although this has never been studied in detail. The basis of the dens is of clinical relevance as type II dens fractures are located here. To characterize the morphological architecture of the axis with particular attention to the subdental synchondrosis, the complete axis was harvested from thirty age-matched and gender-matched patients of the three different age groups at autopsy. The subdental synchondrosis and the bone structure of the dens, the basis of the dens and the body of C2 were analyzed by radiography, histology and quantitative histomorphometry. At the macroscopic level the persistency of the subdental synchondrosis in the adult cervical spine was detected in 87% (26 of 30) of the specimens. Histomorphometry revealed a residual disc blastema with an average size of 25.8% of the sagittal depth of the basis of the dens at this level. Bony integration of the synchondrosis was poor throughout all ages. Histologically a cartilaginous matrix composition of the subdental synchondrosis persisted throughout all groups. The trabecular microarchitecture demonstrated a significant reduction of bone volume and trabecular number as well as an increased trabecular separation within the basis of the dens as compared to the corpus or the dens of C2. This histomorphometric data regarding a poor integration of the synchondrosis into the trabecular network and the reduced bone mass within the basis of the dens might offer a previously underestimated explanation for the occurrence of type II dens fractures and their association with pseudoarthrosis, respectively.

Adult↗

PubMed2005

The human chondrosarcoma HCS-2/8 cell line is responsive to BMP-7, but not to IL-1beta.

Cultures of primary chondrocytes as in vitro model systems for studying the cellular behavior of chondrocytes are notoriously difficult to cultivate and propagate. One way to circumvent these problems appears to be the use of immortalized/immortal chondrocytic cell lines. In the present study, we were interested whether the chondrosarcoma derived HCS-2/8 cells are suitable for studying major cellular reaction pattern in response to key anabolic (BMP-7) and catabolic (IL-1beta) factors. Therefore, we used cDNA array and real-time PCR technology in order to evaluate gene expression triggered by stimulation with IL-1beta (0,1-100 ng/ml) and BMP-7 in confluent monolayer cultures. HCS-2/8 cells hardly responded to IL-1beta, but showed good responsiveness to BMP-7. We found 12 genes up- and 17 significantly down-regulated by BMP-7 (out of 340 investigated genes). Besides the expected activation of anabolic genes chondrocytic cells after BMP-stimulation try to neutralize activation of the BMP-signalling cascade by expressing intra- and extracellular BMP-antagonists. Chondrosarcoma derived cell lines are a potential substitute for primary articular chondrocytes promising consistent expression of a differentiated chondrocyte phenotype with sufficient proliferative capacity. However, as shown by this study one needs to carefully select the cell line depending on the effects which one intends to study. In this respect, HCS-2/8 cells are a validated tool for studying BMP-effects on chondrocytes, but not e.g. effects of interleukin-1.

Bone Morphogenetic Protein 7↗

PubMed2005

Mouse models in skeletal physiology and osteoporosis: experiences and data on 14,839 cases from the Hamburg Mouse Archives.

Our understanding of the developmental biology of the skeleton, like that of virtually every other subject in biology, has been transformed by recent advances in human and mouse genetics, but we still know very little, in molecular and genetic terms, about skeletal physiology. Thus, among the many questions that are largely unexplained are the following: why is osteoporosis mainly a women's disease? How is bone mass maintained nearly constant between the end of puberty and the arrest of gonadal functions? Molecular genetics has emerged as a powerful tool to study previously unexplored aspects of the physiology of the skeleton. Among mammals, mice are the most promising animals for this experimental work. The input that transgenic animals can offer to our field depends on our means of phenotypic characterization of the mouse skeleton. In fact, full appreciation of the skeletal characteristics of a given mouse model requires the application of standardized protocols for noninvasive imaging, histology, histomorphometry, biomechanics, and individually adapted in vitro and in vivo analysis. Over the past years we have established a mouse archive that consists of 14,839 cases from more than 120 different mouse models that we have phenotypically characterized in Hamburg. Today, this is one of the biggest databases on the mouse skeleton. This review focuses on one aspect of skeletal physiology, namely skeletal aging, and demonstrates that mouse models can be a valuable tool to gain insights in certain facets of skeletal physiology that have been unexplored previously.

Animals↗

PubMed2004

Increased bone formation in mice lacking apolipoprotein E.

UNLABELLED: ApoE is a plasma protein that plays a major role in lipoprotein metabolism. Here we describe that ApoE expression is strongly induced on mineralization of primary osteoblast cultures. ApoE-deficient mice display an increased bone formation rate compared with wildtype controls, thereby showing that ApoE has a physiologic function in bone remodeling. INTRODUCTION: Apolipoprotein E (ApoE) is a protein component of lipoproteins and facilitates their clearance from the circulation. This is confirmed by the phenotype of ApoE-deficient mice that have high plasma cholesterol levels and spontaneously develop atherosclerotic lesions. The bone phenotype of these mice has not been analyzed to date, although an association between certain ApoE alleles and BMD has been reported. MATERIALS AND METHODS: Primary osteoblasts were isolated from newborn mouse calvariae and mineralized ex vivo. A genome-wide expression analysis was performed during the course of differentiation using the Affymetrix gene chip system. Bones from ApoE-deficient mice and wildtype controls were analyzed using radiography, micro CT imaging, and undecalcified histology. Cellular activities were assessed using dynamic histomorphometry and by measuring urinary collagen degradation products. Lipoprotein uptake assays were performed with (125)I-labeled triglyceride-rich lipoprotein-remnants (TRL-R) using primary osteoblasts from wildtype and ApoE-deficient mice. Serum concentrations of osteocalcin were determined by radioimmunoassay after hydroxyapatite chromatography. RESULTS: ApoE expression is strongly induced on mineralization of primary osteoblast cultures ex vivo. Mice lacking ApoE display a high bone mass phenotype that is caused by an increased bone formation rate, whereas bone resorption is not affected. This phenotype may be explained by a decreased uptake of triglyceride-rich lipoproteins by osteoblasts, resulting in elevated levels of undercarboxylated osteocalcin in the serum of ApoE-deficient mice. CONCLUSION: The specific induction of ApoE gene expression during osteoblast differentiation along with the increased bone formation rate observed in ApoE-deficient mice shows that ApoE has a physiologic role as a regulator of osteoblast function.

Alleles↗

PubMed2004

Resorbability of bone substitute biomaterials by human osteoclasts.

Third generation biomaterials are being designed with the aim that once implanted they will help the body to heal itself. One desirable characteristic of these materials in bone is their ability to be remodeled, i.e. that osteoclasts resorb the material and it is subsequently replaced by newly formed bone through osteoblastic activity. So far the only way to test this biological property of bone substitutes are animal experiments with all their limitations like ethics, costs and limited transferability to man. The present study was designed, to develop a human in vitro assay, allowing to generate human osteoclasts directly on the biomaterial. The assay was validated using calcium phosphate cement and PMMA as biomaterials. Quantification was performed by raster electron microscopy and computer assisted image analysis. Dentin was used as internal standard. Our assay shows iso-bone resorbability of calcium phosphate cement in comparison to unresorbable PMMA cement. Both current clinical orthopedic practice and future skeletal engineering may profit from the availability and use of a test system for the assessment of resorption quality. The assay presented here allows to address this question of resorbability and to select the best materials for the use as bone substitutes in specific patients.

Absorbable Implants↗

PubMed2004

Absence of mouse pleiotrophin does not affect bone formation in vivo.

Pleiotrophin (Ptn) is an extracellular matrix protein that regulates hippocampal synaptic plasticity and learning behavior in vivo. Since the overexpression of Ptn in transgenic mice leads to increased bone formation, we analyzed whether a deficiency in Ptn expression would have a negative effect on bone remodeling. Bones from Ptn-deficient mice and wild-type littermates were analyzed using radiography, muCT imaging and undecalcified histology. Biomechanical stability was determined in a three-point-bending assay. Cellular activities were assessed using dynamic histomorphometry and the determination of urinary collagen degradation products. Skeletons of Ptn-deficient mice have no gross abnormalities, displayed a normal size, and showed no differences in growth plate organization compared to wild-type littermates. There were no obvious differences in bone mass as determined by radiographic and muCT imaging. The absence of a bone remodeling phenotype in Ptn-deficient mice was further confirmed using static histomorphometry and biomechanical testing. Finally, the number, morphology, and function of osteoclasts, osteoblasts, and osteocytes were not altered in Ptn-deficient mice compared to wild-type littermates. The complete skeletal analysis of Ptn-deficient mice presented here demonstrates that the lack of Ptn in mice does not affect bone formation in vivo. Therefore, Ptn does not play a significant role in normal bone physiology.

Animals↗

PubMed2002

3-hydroxy-3-methylglutaryl coenzyme A reductase-independent inhibition of CD40 expression by atorvastatin in human endothelial cells.

OBJECTIVE: 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) exert potent anti-inflammatory effects that are independent of their cholesterol-lowering action. We have investigated the effects of these drugs on cytokine-stimulated CD40 expression in human cultured endothelial cells and monocytes. METHODS AND RESULTS: Reverse transcription-polymerase chain reaction and Western blot analysis revealed that treatment of either cell type with atorvastatin, cerivastatin, or pravastatin (1 to 10 micromol/L) inhibited interferon-gamma plus tumor necrosis factor-alpha-stimulated CD40 expression by approximately 50%, an effect that was not reversed by the HMG-CoA reductase product mevalonic acid (400 micromol/L). In contrast, mevalonic acid prevented the inhibitory effect of atorvastatin on cytokine-stimulated vascular cell adhesion molecule-1 expression and subsequent adhesion of THP-1 monocytes to the cultured endothelial cells. Transcription factor analysis revealed an inhibition by atorvastatin of nuclear factor-kappaB plus signal transducer and activator of transcription-1-dependent de novo synthesis of interferon regulatory factor-1, governing cytokine-stimulated CD40 expression in these cells. One consequence of this statin-dependent downregulation of CD40 expression was a decrease in CD40 ligand-induced endothelial interleukin-12 expression. CONCLUSIONS: By interfering with cytokine-stimulated CD40 expression in vascular cells, statins thus seem capable of attenuating CD40 ligand-induced proinflammatory responses, including atherosclerosis. In addition, they point to the coexistence of HMG-CoA reductase-dependent and -independent effects of statins in the same cell type.

Atorvastatin↗

PubMed2002

Cytokine-inducible CD40 expression in human endothelial cells is mediated by interferon regulatory factor-1.

Given the significance of CD40-CD40 ligand interactions in chronic inflammatory diseases including atherosclerosis, the transcriptional regulation of CD40 expression as a potential therapeutic target was investigated in human umbilical vein cultured endothelial cells. Exposure to interferon-gamma (IFN-gamma) plus tumor necrosis factor-alpha resulted in a marked synergistic de novo expression of CD40, which, according to electrophoretic mobility shift analysis, was attributable to activation of the transcription factors nuclear factor-kappaB (NF-kappaB), signal transducer and activator of transcription-1 (STAT-1), and interferon regulatory factor-1 (IRF-1). Subsequent time-course studies revealed that de novo synthesis of IRF-1 preceded that of CD40. Decoy oligodeoxynucleotide (ODN) neutralization of STAT-1 or IRF-1, but not of NF-kappaB, inhibited cytokine-stimulated CD40 expression by 60% at both the mRNA and protein levels, and this effect was mimicked by antisense ODN blockade of IRF-1 synthesis. In contrast, CD40 expression in response to IFN-gamma stimulation was sensitive to neutralization of STAT-1 only. These findings suggest that depending on the cytokine composition, CD40 expression in human endothelial cells under proinflammatory conditions is governed by STAT-1 either directly or indirectly through de novo synthesis of IRF-1. Moreover, decoy ODN neutralization of these transcription factors may provide a novel therapeutic option for interfering with CD40-CD40 ligand-mediated inflammatory responses in vivo.

Animals↗