Candidate Gene Analysis of Femoral Neck Trabecular and Cortical Volumetric Bone Mineral Density in Older Men

In contrast to conventional dual-energy X-ray absorptiometry, quantitative computed tomography separately measures trabecular and cortical volumetric bone mineral density (vBMD). Little is known about the genetic variants associated with trabecular and cortical vBMD in humans, although both may be important for determining bone strength and osteoporotic risk. In the current analysis, we tested the hypothesis that there are genetic variants associated with trabecular and cortical vBMD at the femoral neck by genotyping 4608 tagging and potentially functional single-nucleotide polymorphisms (SNPs) in 383 bone metabolism candidate genes in 822 Caucasian men aged 65 years or older from the Osteoporotic Fractures in Men Study (MrOS). Promising SNP associations then were tested for replication in an additional 1155 men from the same study. We identified SNPs in five genes (IFNAR2, NFATC1, SMAD1, HOXA, and KLF10) that were robustly associated with cortical vBMD and SNPs in nine genes (APC, ATF2, BMP3, BMP7, FGF18, FLT1, TGFB3, THRB, and RUNX1) that were robustly associated with trabecular vBMD. There was no overlap between genes associated with cortical vBMD and trabecular vBMD. These findings identify novel genetic variants for cortical and trabecular vBMD and raise the possibility that some genetic loci may be unique for each bone compartment. © 2010 American Society for Bone and Mineral Researc

TIEG1/KLF10 Modulates Runx2 Expression and Activity in Osteoblasts

Deletion of TIEG1/KLF10 in mice results in a gender specific osteopenic skeletal phenotype with significant defects in both cortical and trabecular bone, which are observed only in female animals. Calvarial osteoblasts isolated from TIEG1 knockout (KO) mice display reduced expression levels of multiple bone related genes, including Runx2, and exhibit significant delays in their mineralization rates relative to wildtype controls. These data suggest that TIEG1 plays an important role in regulating Runx2 expression in bone and that decreased Runx2 expression in TIEG1 KO mice is in part responsible for the observed osteopenic phenotype. In this manuscript, data is presented demonstrating that over-expression of TIEG1 results in increased expression of Runx2 while repression of TIEG1 results in suppression of Runx2. Transient transfection and chromatin immunoprecipitation assays reveal that TIEG1 directly binds to and activates the Runx2 promoter. The zinc finger containing domain of TIEG1 is necessary for this regulation supporting that activation occurs through direct DNA binding. A role for the ubiquitin/proteasome pathway in fine tuning the regulation of Runx2 expression by TIEG1 is also implicated in this study. Additionally, the regulation of Runx2 expression by cytokines such as TGFβ1 and BMP2 is shown to be inhibited in the absence of TIEG1. Co-immunoprecipitation and co-localization assays indicate that TIEG1 protein associates with Runx2 protein resulting in co-activation of Runx2 transcriptional activity. Lastly, Runx2 adenoviral infection of TIEG1 KO calvarial osteoblasts leads to increased expression of Runx2 and enhancement of their ability to differentiate and mineralize in culture. Taken together, these data implicate an important role for TIEG1 in regulating the expression and activity of Runx2 in osteoblasts and suggest that decreased expression of Runx2 in TIEG1 KO mice contributes to the observed osteopenic bone phenotype

TGF-β Inducible Early Gene 1 Regulates Osteoclast Differentiation and Survival by Mediating the NFATc1, AKT, and MEK/ERK Signaling Pathways

TGF-β Inducible Early Gene-1 (TIEG1) is a Krüppel-like transcription factor (KLF10) that was originally cloned from human osteoblasts as an early response gene to TGF-β treatment. As reported previously, TIEG1−/− mice have decreased cortical bone thickness and vertebral bone volume and have increased spacing between the trabeculae in the femoral head relative to wildtype controls. Here, we have investigated the role of TIEG1 in osteoclasts to further determine their potential role in mediating this phenotype. We have found that TIEG1−/− osteoclast precursors differentiated more slowly compared to wildtype precursors in vitro and high RANKL doses are able to overcome this defect. We also discovered that TIEG1−/− precursors exhibit defective RANKL-induced phosphorylation and accumulation of NFATc1 and the NFATc1 target gene DC-STAMP. Higher RANKL concentrations reversed defective NFATc1 signaling and restored differentiation. After differentiation, wildtype osteoclasts underwent apoptosis more quickly than TIEG1−/− osteoclasts. We observed increased AKT and MEK/ERK signaling pathway activation in TIEG1−/− osteoclasts, consistent with the roles of these kinases in promoting osteoclast survival. Adenoviral delivery of TIEG1 (AdTIEG1) to TIEG1−/− cells reversed the RANKL-induced NFATc1 signaling defect in TIEG1−/− precursors and eliminated the differentiation and apoptosis defects. Suppression of TIEG1 with siRNA in wildtype cells reduced differentiation and NFATc1 activation. Together, these data provide evidence that TIEG1 controls osteoclast differentiation by reducing NFATc1 pathway activation and reduces osteoclast survival by suppressing AKT and MEK/ERK signaling

Passive and active mechanical tests at different scales of the skeletal muscle: a literature review

International audienceHuman skeletal muscle is a complex tissue with a strict and ordered hierarchy (muscle, fiber, myofibril) similar to rodent animal used to study the mechanical properties of healthy and pathological muscles (e.g. mdx mouse to mimic Duchenne disease). Collagen envelopes, actin and titin are the structures implicated in the passive mechanical properties. The active mechanical properties are related to the formation of actin-myosin cross bridges. This article presents the most commonly used mechanical tests to measure in vitro, at different scales, the passive (incremental stepwise extension test, stretch-release test, compressive test, fatigue-recovery test, eccentric contraction test) and active (force-frequency test, tetanus and twitch contraction tests) behaviors of rodent muscles. The next section of this literature review covers the need for in vivo protocols to be as close as possible to physiological conditions, allowing to keep the animal alive and to perform longitudinal mechanical studies, with the presentation of imaging methods (MRI and ultrasound-based elastography) in living rodents. Then the main factors (protocol heterogeneity, aging, etc.) influencing the mechanical properties are presented

Improvements of Liver MR Imaging Clinical Protocols to Simultaneously Quantify Steatosis and Iron Overload

International audiencePurpose : Fat accumulation and iron overload are important cofactors in chronic liver disease. Clinical quantifications of fat fraction and iron are currently assessed using MRI protocols. The purpose is to improve these measurements to simultaneously provide iron and fat maps from a single acquisition. Methods: Ten healthy volunteers and ten patients with steatosis underwent MRI for fat fraction (FF: IDEAL-IQ ®), iron overload concentration (IOC: Gandon, Starmap ®) and viscoelastic characterization (MR-Touch ®). IDEAL-IQ ® data, the clinical FF reference, were compared to the advanced Gandon protocol, post-treated with a 3pt Dixon method. The originality was to use IDEAL-IQ ® fat sequence to quantify iron volu-metrically using the Wood equation. To validate the iron data, the reference Gandon protocol was applied and improved to provide map of IOC. Then, IOC data were also compared to another clinical sequence (Starmap ®) which was also improved (scale, number of ROI). The estimated error associated with each method was evaluated with the coefficient of variation. Results: IDEAL-IQ ® and Gandon protocols were modified to provide simultaneously FF and IOC maps (2D, volume). Healthy FF were in the same range with all protocols (≈3%). For patients with steatosis, Gandon protocols underestimated the FF value (≈7%) compared to IDEAL-IQ ®. Healthy and fibrosis patients were correctly diagnosed (no hemochromatosis) with all the protocols and viscoelastic properties were in the same range. Conclusion: Manufacturer's tools were improved to simultaneously quantify liver markers saving time for the patient and the clinical setting. These parameters are of great value for clinical diagnostics and novel therapeutics to treat liver diseases

Comparison of tendon fiber structures between wild type and TIEG knockout mice using synchrotron microdiffraction

International audienc