Role of the N-terminal transmembrane domain in the endo-lysosomal targeting and function of the human ABCB6 protein.

ABCB6 is a homodimeric ATP-binding cassette (ABC) transporter present in the plasma membrane and in intracellular organelles. The intracellular localization of ABCB6 has been a matter of debate, as it has been suggested to reside in the mitochondria and the endo-lysosomal system. Using a variety of imaging modalities including confocal and electron microscopy we confirm the endo-lysosomal localization of ABCB6 and show that the protein is internalized from the plasma membrane through endocytosis, to be distributed to multivesicular bodies and lysosomes. In addition to the canonical nucleotide binding (NBD) and transmembrane domains (TMD), ABCB6 contains a unique N-terminal transmembrane domain (TMD0), which does not show sequence homology to known proteins. We investigated the functional role of these domains through the molecular dissection of ABCB6. We find that the folding, dimerization, membrane insertion and ATP binding/hydrolysis of the core ABCB6 complex devoid of TMD0 is preserved. However, in contrast to the full-length transporter, the core ABCB6 construct is retained at the plasma membrane, and does not appear in Rab5-positive endosomes. TMD0 is directly targeted to the lysosomes, without a passage to the plasma membrane. Collectively, our results reveal that TMD0 represents an independently folding unit, which is dispensable for catalysis, but has a crucial role in the lysosomal targeting of ABCB6

Microstructure and mechanical characterization of cast Mg-Ca-Si alloys

Three different phase fields are predicted and experimentally detected in the Mg rich corner of the Mg-Ca-Si ternary diagram. The present phases are Mg + MgCaSi + Mg2Si in phase field 1, Mg + MgCaSi in phase field 2 and Mg + Mg2Ca + MgCaSi in phase field 3. The focus of this study is on the formation and evolution of the intermetallic phases. The final microstructures have been related with their solidification process and with the alloys mechanical properties. A clear influence of the observed intermetallic phases on the mechanical performance was found. A bigger size and higher amounts of the MgCaSi intermetallic phase increase the alloys strength and make them brittle, while in its fine morphology MgCaSi reduces the strengthening effect and slightly decreases the ductility compared to pure Mg. Mg2Si phase in its needle-like small size morphology contributes to an increase of the hardness and compressive strength. Its presence reduces the alloys ductility making them brittle. Finally, the highest values for compressive strength and hardness are related to the Mg2Ca presence.publisher: Elsevier articletitle: Microstructure and mechanical characterization of cast Mg-Ca-Si alloys journaltitle: Journal of Alloys and Compounds articlelink: http://dx.doi.org/10.1016/j.jallcom.2016.10.059 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved.status: publishe

The Campanian Ignimbrite tephra layer - a regional stratigraphic marker for the MIS 3 loess deposits of Romania

Loess deposits are widespread in Romania and many open profiles are found along the river valleys crossing the southern plains of the country, and these records are important resources for understanding paleoclimate dynamics and the Paleolithic cultural dispersal at the continental scale. However, loess deposits show significant lateral compositional variations, which bring about regional stratigraphic uncertainties, especially when site-to-site correlations still rely mainly on stratigraphic relationships, and only a handful of profiles having been investigated with more precise dating method

Corrosion behaviour of 3 Mg-alloys in one: a high-resolution investigation

Magnesium (Mg) and itsbiodegradable alloys are promising biomaterialsfor bone application. However, their corrosionbehaviour is still poorly understood and theresorption mechanism is still unpredictable in vivo,due to the high complexity of the physiologicalenvironment [1]. Here we report on the in vivodegradation process of 3 Mg alloys as observed onsynchrotron-based micro computed tomography(SRµCT) and on corresponding histologicalsections. SRµCT, thanks to the high contrast-tonoiseratio, enables to clearly detect the changesthat the Mg alloys undergo during corrosion, in anon-destructive way and directly in the bone [2]

Osseointegration of resorbable magnesium screws – A SRμCT Study

The development of resorbable osteofixation materials that degrade upon substitution by regenerated tissue is highly desirable in orthopaedics. Magnesium is promising as implantable material, because of its biocompatibility, osteoconductivity and biodegradation under physiological conditions [1]. Through the selection of alloying elements, the mechanical properties and corrosion behaviour of magnesium can be modulated for application in load-bearing situations. The aim of our research was to investigate the bone integration and the corrosion process of Al-free Mg-alloys in vivo. Our hypothesis was that Mg-based implants stimulate bone growth.METHODS: Mini-screws of two different Mg- alloys, Mg10Gd and Mg-Y-RE (WE43) were manufactured at HZG. The cytocompatibility of the selected alloys was formerly tested and validated in vitro [2, 3]. The mini-screws were implanted in rats after ethical approval. After 1 and 3 months of healing, cylindrical bone-implant blocks were retrieved. Samples were imaged at the P05 Imaging Beamline (IBL) operated by HZG at PETRA III – DESY (Hamburg). We used monochromatic X-rays at 25 keV to take 900 projections and a field of view of 7mm x 1.8 mm, which resulted in 5X magnification with a resolution of ~2.5 μm. 3D data sets were computed using filtered back projection algorithms.RESULTS: The inserted implants healed without any observable adverse effect. On the basis of tomographic data, we were able to compute three- dimensional renderings of dvrscrews and bone with high contrast-to-noise ratios. A qualitative evaluation of the data revealed inhomogeneous surface corrosion of the screws, which maintained their original shape within the study period. New bone formation was observed in all of our samples. We found a considerable increase of implant-bone contact sites with progressing healing time. A quantitative analysis of the tomographic data indicated spatial differences in bone density. In proximity of the implant, newly formed bone matured and became dense after 3 months.Top: Horizontal (left) and vertical (right) sections of a screw after 3 months of healing. Fragments of implants, completely integrated in the bone, are visible. Bar 0.25 mm. Bottom: Orthogonal cut planes (left) and volume rendering (right), showing an implant (gray) into the bone (purple).DISCUSSION & CONCLUSIONS: The SRμCT showed osseointegration of Mg10Gd and WE43. Although the spatial resolution was not sufficient to fully elucidate the alloys microstructure, we observed the distribution of the high absorbing regions in the materials, possibly intermetallic phases and Y or RE oxides. The corrosion of the alloys was slow. Biocompatibility of the tested materials was confirmed by bone growth in intimate contact with the implants.REFERENCES: 1 Witte F,2 et al (2005) Biomaterials 26:3557-3563. Feyerabend F, Fischer J, et al (2010) Acta Biomater. 6:1834-1842. 3Johnson I, et al. H (2011) JBMR-A.ACKNOWLEDGEMENTS: Founding from the People Programme (Marie Curie Actions) Seventh Framework Programme FP7/2007-2013/ under REA grant agreements n° 289163 and n° 312284

Effects of Corroded and Non-Corroded Biodegradable Mg and Mg Alloys on Viability, Morphology and Differentiation of MC3T3-E1 Cells Elicited by Direct Cell/Material Interaction

<div><p>This study investigated the effect of biodegradable Mg and Mg alloys on selected properties of MC3T3-E1 cells elicited by direct cell/material interaction. The chemical composition and morphology of the surface of Mg and Mg based alloys (Mg2Ag and Mg10Gd) were analysed by scanning electron microscopy (SEM) and EDX, following corrosion in cell culture medium for 1, 2, 3 and 8 days. The most pronounced difference in surface morphology, namely crystal formation, was observed when Pure Mg and Mg2Ag were immersed in cell medium for 8 days, and was associated with an increase in atomic % of oxygen and a decrease of surface calcium and phosphorous. Crystal formation on the surface of Mg10Gd was, in contrast, negligible at all time points. Time-dependent changes in oxygen, calcium and phosphorous surface content were furthermore not observed for Mg10Gd. MC3T3-E1 cell viability was reduced by culture on the surfaces of corroded Mg, Mg2Ag and Mg10Gd in a corrosion time-independent manner. Cells did not survive when cultured on 3 day pre-corroded Pure Mg and Mg2Ag, indicating crystal formation to be particular detrimental in this regard. Cell viability was not affected when cells were cultured on non-corroded Mg and Mg alloys for up to 12 days. These results suggest that corrosion associated changes in surface morphology and chemical composition significantly hamper cell viability and, thus, that non-corroded surfaces are more conducive to cell survival. An analysis of the differentiation potential of MC3T3-E1 cells cultured on non-corroded samples based on measurement of Collagen I and Runx2 expression, revealed a down-regulation of these markers within the first 6 days following cell seeding on all samples, despite persistent survival and proliferation. Cells cultured on Mg10Gd, however, exhibited a pronounced upregulation of collagen I and Runx2 between days 8 and 12, indicating an enhancement of osteointegration by this alloy that could be valuable for <i>in vivo</i> orthopedic applications.</p></div