Immunophenotypic changes of human articular chondrocytes during monolayer culture reflect bona fide dedifferentiation rather than amplification of progenitor cells

In this study, a time-course comparison of human articular chondrocytes (HAC) and bone marrow-derived mesenchymal stem cells (MSC) immunophenotype was performed in order to determine similarities/differences between both cell types during monolayer culture, and to identify HAC surface markers indicative of dedifferentiation. Our results show that dedifferentiated HAC can be distinguished from MSC by combining CD14, CD90, and CD105 expression, with dedifferentiated HAC being CD14+/CD90bright/CD105dim and MSC being CD14-/CD90dim/CD105bright. Surface markers on MSC showed little variation during the culture, whereas HAC showed upregulation of CD90, CD166, CD49c, CD44, CD10, CD26, CD49e, CD151, CD51/61, and CD81, and downregulation of CD49a, CD54, and CD14. Thus, dedifferentiated HAC appear as a bona fide cell population rather than a small population of MSC amplified during monolayer culture. While most of the HAC surface markers showed major changes at the beginning of the culture period (Passage 1-2), CD26 was upregulated and CD49a downregulated at later stages of the culture (Passage 3-4). To correlate changes in HAC surface markers with changes in extracellular matrix gene expression during monolayer culture, CD14 and CD90 mRNA levels were combined into a new differentiation index and compared with the established differentiation indices based on the ratios of mRNA levels of collagen type II to I (COL2/COL1) and of aggrecan to versican (AGG/VER). A correlation of CD14/CD90 ratio at the mRNA and protein level with the AGG/VER ratio during HAC dedifferentiation in monolayer culture validated CD14/CD90 as a new membrane and mRNA based HAC differentiation index.

FE-Simulation in der klinischen Osteoporoseforschung

Altersbedingte Osteoporose erhöht des Frakturrisiko. Übliche Diagnoseverfahren basieren auf DXA. Leider sind diese ungenau und erklären oft nicht die Effekte von Behandlungen. Eine neue Methode zur Bestimmung der Knochenfestigkeit beginnt derzeit, sich zu etablieren – die Finite-Elemente-Methode (FEM). Diese universelle, im Bereich der Technik weit verbreitete, Methode erlaubt es, die Diagnose und den Behandlungserfolg besser vorauszusagen als DXA. CT-basierende FE-Modelle sind stark von der Bildauflösung abhängig. In diesem Überblicksartikel werden drei unterschiedliche Modelltypen (μCT, HR-pQCT, QCT) vorgestellt und die Ergebnisse von densitometrischen und FE-Analysen verglichen. Dabei waren die FE-Ergebnisse den densitometrischen immer überlegen. Darüber hinaus erlaubt die FEM die Angabe eines biomechanischen Frakturrisikos. Dieser Vorteil der FE-Methode muss jedoch im Licht der höheren Röntgendosen und Betriebskosten der CT-Bildgebung betrachtet werden. Zukünftig wird die FE-Methode klinisch eine weite Verbreitung finden – die Frage ist nur wann und wie!

Comparison of iron isotope variations in modern and Ordovician siliceous Fe oxyhydroxide deposits

Formation pathways of ancient siliceous iron formations and related Fe isotopic fractionation are still not completely understood. Investigating these processes, however, is difficult as good modern analogues to ancient iron formations are scarce. Modern siliceous Fe oxyhydroxide deposits are found at marine hydrothermal vent sites, where they precipitate from diffuse, low temperature fluids along faults and fissures on the seafloor. These deposits exhibit textural and chemical features that are similar to some Phanerozoic iron formations, raising the question as to whether the latter could have precipitated from diffuse hydrothermal fluids rather than from hydrothermal plumes. In this study, we present the first data on modern Fe oxyhydroxide deposits from the Jan Mayen hydrothermal vent fields, Norwegian-Greenland Sea. The samples we investigated exhibited very low δ56Fe values between -2.09‰ and -0.66‰. Due to various degrees of partial oxidation, the Fe oxyhydroxides are with one exception either indistinguishable from low-temperature hydrothermal fluids from which they precipitated (-1.84‰ and -1.53‰ in δ56Fe) or are enriched in the heavy Fe isotopes. In addition, we investigated Fe isotope variations in Ordovician jasper beds from the Løkken ophiolite complex, Norway, which have been interpreted to represent diagenetic products of siliceous ferrihydrite precursors that precipitated in a hydrothermal plume, in order to compare different formation pathways of Fe oxyhydroxide deposits. Iron isotopes in the jasper samples have higher δ56Fe values (-0.38‰ to +0.89‰) relative to modern, high-temperature hydrothermal vent fluids (ca. -0.40‰ on average), supporting the fallout model. However, formation of the Ordovician jaspers by diffuse venting cannot be excluded, due to lithological differences of the subsurface of the two investigated vent systems. Our study shows that reliable interpretation of Fe isotope variations in modern and ancient marine Fe oxyhydroxide deposits depends on comprehensive knowledge of the geological context. Furthermore, we demonstrate that very negative δ56Fe values in such samples might not be the result of microbial dissimilatory iron reduction, but could be caused instead by inorganic reactions.

A Donor-Acceptor Tetrathiafulvalene Ligand Complexed to Iron(II): Synthesis, Electrochemistry, and Spectroscopy of Fe(phen)(2)(TTF-dppz)(PF6)(2)

The synthesis and photophysical properties of the complex Fe(phen)(2)(TTF-dppz)(2+) (TTF-dppz = 4',5'-bis-(propylthio)tetrathiafulvenylidipyrido3,2-a:2',3'-c-phenazine, phen = 1,10-phenanthroline) are described. In this complex, excitation into the metal ligand charge transfer bands results in the population of a high-spin state of iron(II), with a decay lifetime of approximately 1.5 ns, in dichloromethane, at room temperature. An intraligand charge transfer state can also be obtained and has a lifetime of 38 ps. A mechanism for the different states reached is proposed based on transient absorption spectroscopy.