Franziska Gröhn

Glycosylation of immunoglobulin G determines osteoclast differentiation and bone loss

Immunglobulin G (IgG) sialylation represents a key checkpoint that determines the engagement of pro- or anti-inflammatory Fcγ receptors (FcγR) and the direction of the immune response. Whether IgG sialylation influences osteoclast differentiation and subsequently bone architecture has not been determined yet, but may represent an important link between immune activation and bone loss. Here we demonstrate that desialylated, but not sialylated, immune complexes enhance osteoclastogenesis in vitro and in vivo. Furthermore, we find that the Fc sialylation state of random IgG and specific IgG autoantibodies determines bone architecture in patients with rheumatoid arthritis. In accordance with these findings, mice treated with the sialic acid precursor N-acetylmannosamine (ManNAc), which results in increased IgG sialylation, are less susceptible to inflammatory bone loss. Taken together, our findings provide a novel mechanism by which immune responses influence the human skeleton and an innovative treatment approach to inhibit immune-mediated bone loss.

Self‐Assembly of Supramolecular Architectures and Polymers by Orthogonal Metal Complexation and Hydrogen‐Bonding Motifs

A modular construction kit with two orthogonal noncovalent binding sites for self-assembly of supramolecular architectures is presented. The heteroditopic building blocks contain a terpyridine (tpy) unit for coordination of metal ions and a Hamilton receptor for multiple H-bonding of cyanuric acid derivatives. The association constants of ligand binding of M(II) complexes (M=Ru, Zn, Fe, and Pt) with a dendritic end cap were determined to be in the range of 10(2) and 10(4) L mol(-1) in chloroform. The capabilities for binding of metal ions were investigated by (1)H NMR and UV/Vis spectroscopy. The Fe complexes are most appropriate for the generation of discrete and high-ordered architectures due to their strong tendency to form FeL(2) complexes. Superstructures are readily formed in a one-pot procedure at room temperature. No mutual interactions between the orthogonal binding motifs were observed, and this demonstrates the highly specific nature of each binding process. Decomplexation experiments were carried out to examine the reversibility of Fe-tpy coordination. Substitution of the terminal end cap with a homoditopic bis-cyanurate linkage leads to formation of an iron-containing supramolecular strand. Formation of coordination polymers was confirmed by viscosity measurements. The supramolecular polymer strands can be reversibly cleaved by addition of a terminating cyanuric acid building block, and this proves the dynamic nature of this noncovalent polymerization process.

Amphiphilic pentaazamacrocyclic manganese superoxide dismutase mimetics.

Five newly functionalized pentaazamacrocyclic manganese complexes, with variable lengths and amounts of the aliphatic groups (three compounds with one linear chain containing 12, 16, and 22 carbon atoms, i.e., MnL1, MnL2, and MnL3, respectively, as well as two compounds containing two C12 and C16 chains, MnL4 and MnL5, respectively) that are derivatives of the known SOD mimetic, Mn(Me2-Pyane), have been synthesized. These amphiphilic complexes were characterized by the ESI mass spectrometry, potentiometric titrations, light scattering, cyclic voltammetry, and direct stopped-flow determination of their SOD activity at pH 8.1 and 7.4 (in phosphate and HEPES buffers). The formation of supramolecular aggregates that predominantly exist in the solution as a defined micellar/nanostructure assembly, with an average 400 nm size, has been demonstrated for MnL1. The biological effects of the selected complexes (MnL1 and MnL2) on the superoxide level in cytosol and mitochondria have been tested, as well as their effects on the prevention of the lipid peroxidation induced by paraquat. Advantages and disadvantages of the lipophilic pentaazamacrocyclic manganese SOD mimetics in comparison to the corresponding nonsubstituted SOD active complex have been discussed.

ZnO nanorods assembled with different porphyrins – size-tunable hybrid particles

We present a fundamental study on ZnO nanorod–porphyrin assembly formation in solution, providing the key to novel tunable hybrid assemblies with potential in solar energy conversion. The combination of 40 nm ZnO nanorods with ionic porphyrins – meso-tetra(4-carboxyphenyl)porphyrin (TCPP) and meso-tetra-(4-sulfonatophenyl)porphyrin (TPPS) – results in the formation of novel well-defined hybrid assemblies which are stable in solution and exhibit an adjustable size up to 500 nm. Structures have been characterized with dynamic light scattering (DLS), transmission electron microscopy (TEM) and absorption and emission spectroscopy. In particular, the combination of both porphyrins with ZnO in a ternary assembly yields a large stability range in terms of the TCPP/ZnO ratio and may be of significance as a hybrid system for solar cells or photocatalysis.

Hydrogen‐Bonded Polymer–Porphyrin Assemblies in Water: Supramolecular Structures for Light Energy Conversion

In this study, a new type of functional, self-assembled nanostructure formed from porphyrins and polyamidoamine dendrimers based on hydrogen bonding in an aqueous solution is presented. As the aggregates formed are promising candidates for solar-energy conversion, their photocatalytic activity is tested using the model reaction of methyl viologen reduction. The self-assembled structures show significantly increased activity as compared to unassociated porphyrins. Details of interaction forces driving the supramolecular structure formation and regulating catalytic efficiency are fundamentally discussed.

Light-Responsive Shape: From Micrometer-Long Nanocylinders to Compact Particles in Electrostatic Self-Assembly

A light-triggered shape change of supramolecular nanostructures is achieved through electrostatically self-assembly of linear polyelectrolytes and oppositely charged dyes in aqueous solution: Upon UV-irradiation, 1-µm-long, flexible cylinders with a cross-section of 10 nm convert into ellipsoids of 400 nm × 40 nm. The nano-object shape is encoded in the molecular dye structure.

Porphyrin microneedles—structure control and catalytic activity

The formation of a novel porphyrin colloidal structure has been investigated—so called microneedles. The porphyrin colloids consist of the tetravalent anionic tetra-(4-sulfonatophenyl)porphyrin (TPPS) and the tetravalent cationic tetra-(N-methyl-4-pyridyl)porphyrin (TMPyP), forming ionic organic solid particles in ethanol. The structure dependence on various influences such as ratio of TMPyP to TPPS, the time of mixing, different solvent mixtures, and the metalation of one porphyrin is investigated with UV-Vis spectroscopy, zeta-potential, light microscopy, and transmission electron microscopy (TEM). The light harvesting potential of the microneedles is demonstrated as a proof of concept by the catalytic degradation of Rose Bengal.

Inducing hetero‐aggregation of different azo dyes through electrostatic self‐assembly

Combining chemically different building blocks in supramolecular nanoparticles is a promising key to tailored structures and functionalities. π-π heterostacks of dye molecules form upon electrostatic self-assembly with a polyelectrolyte, resulting in stable ternary nano-assemblies in aqueous solution. Core-shell spheres, cylinders, and flexible cylinders result, which exhibit new shapes different from the binary systems. Particle shapes can be tuned through the dye composition.

A8.4 Fc-Glycosylation Determines Osteoclastogenic Activity of Immune Complexes

Background and Objectives Autoantibodies recognising citrullinated proteins (ACPA) are highly specific for rheumatoid arthritis (RA), precede the clinical onset of the disease by years and are the strongest known risk factor for bone loss. We have recently shown that ACPA specific for citrullinated vimentin directly interact with osteoclast precursors and induce bone loss. In patients with RA, ACPA-containing immune complexes can be detected in synovial fluid and tissue. We hypothesised that (I) immune complexes directly promote osteoclast maturation and, consecutively, bone loss and that (II) the type of IgG-glycan is important for the interaction with osteoclast precursors, since ACPA have been shown to be hyposialylated. Materials and Methods We differentiated preosteoclasts from human monocytes and stimulated them with artificial immune complexes generated by heat aggregation from pooled human IgG (IVIG). Part of the IgG had been pretreated with neuraminidase or PNGase F to remove sialic acid or the whole Fc glycan, respectively. For in vivo studies we injected murine immune complexes in the knee joints of C57-BL/6 mice. Results Stimulation of preosteoclasts with immune complexes resulted in their dramatically increased maturation to osteoclasts. This effect was even more pronounced with complexes formed from desialylated IgG. Monomeric IgG and fully deglycosylated immune complexes did not alter osteoclast maturation. qPCR and FACS-analyses revealed that all Fcγ receptors (FcγR) are upregulated during osteoclastogenesis with FcγR I and FcγR III being the most prominent ones. Desialylated immune complexes induced the activation of spleen tyrosine kinase (Syk) and phospholipase Cγ (PLCγ) as well as the upregulation of the transcription factor c-fos in preosteoclasts. Injection of murine immune complexes into the knee joints of C57-BL/6 mice caused accumulation of osteoclasts in the vicinity of the site of injection. Conclusions Our data show that IgG immune complexes promote osteoclastogenesis. They upregulate the pro-osteoclastogenic transcription factor c-fos, after binding to activating FcγRs on preosteoclasts. This interaction is highly dependent on the absence of sialic acid in the Fc-glycan of the IgG. Altogether, we propose a novel mechanism by which ACPA promote bone loss independent of inflammation.