Elin Pauwels

Proof of concept: enthesitis and new bone formation in spondyloarthritis are driven by mechanical strain and stromal cells

Objectives Spondyloarthritides (SpA) are characterised by both peripheral and axial arthritis. The hallmarks of peripheral SpA are the development of enthesitis, most typically of the Achilles tendon and plantar fascia, and new bone formation. This study was undertaken to unravel the mechanisms leading towards enthesitis and new bone formation in preclinical models of SpA. Results First, we demonstrated that TNFΔARE mice show typical inflammatory features highly reminiscent of SpA. The first signs of inflammation were found at the entheses. Importantly, enthesitis occurred equally in the presence or absence of mature T and B cells, underscoring the importance of stromal cells. Hind limb unloading in TNFΔARE mice significantly suppressed inflammation of the Achilles tendon compared with weight bearing controls. Erk1/2 signalling plays a crucial role in mechanotransduction-associated inflammation. Furthermore, new bone formation is strongly promoted at entheseal sites by biomechanical stress and correlates with the degree of inflammation. Conclusions These findings provide a formal proof of the concept that mechanical strain drives both entheseal inflammation and new bone formation in SpA.

An exploratory study of contrast agents for soft tissue visualization by means of high resolution X-ray computed tomography imaging.

High resolution X‐ray computed tomography (CT), or microCT, is a promising and already widely used technique in various scientific fields. Also for histological purposes it has great potential. Although microCT has proven to be a valuable technique for the imaging of bone structures, the visualization of soft tissue structures is still an important challenge due to their low inherent X‐ray contrast. One way to achieve contrast enhancement is to make use of contrast agents. However, contrary to light and electron microscopy, knowledge about contrast agents and staining procedures is limited for X‐ray CT. The purpose of this paper is to identify useful X‐ray contrast agents for soft tissue visualization, which can be applied in a simple way and are also suited for samples larger than (1 cm)3. And 28 chemical substances have been investigated. All chemicals were applied in the form of concentrated aqueous solutions in which the samples were immersed. First, strips of green Bacon were stained to evaluate contrast enhancement between muscle and adipose tissue. Furthermore it was also tested whether the contrast agents remained fixed in the tissue after staining by re‐immersing them in water. Based on the results, 12 contrast agents were selected for further testing on postmortem mice hind legs, containing a variety of different tissues, including muscle, fat, bone, cartilage and tendons. It was evaluated whether the contrast agents allowed a clearer distinction between the different soft tissue structures present. Finally also penetration depth was measured. And 26 chemicals resulted in contrast enhancement between muscle and adipose tissue in the Bacon strips. Mercury(II)chloride (HgCl2), phosphotungstic acid (PTA), phosphomolybdic acid (PMA) and ammonium orthomolybdate ((NH4)2MoO4) remained fixed after re‐immersion in water. The penetration tests showed that potassium iodide (KI) and sodium tungstate can be most efficiently used for large samples of the order of several tens of cm3. PMA, PTA, HgCl2 and also to a lesser extent Na2WO4 and (NH4)2MoO4 allowed a clearer distinction between the different soft tissue structures present.

HECTOR : a 240kV micro-CT setup optimized for research

X-ray micro-CT has become a very powerful and common tool for non-destructive three-dimensional (3D) visualization and analysis of objects. Many systems are commercially available, but they are typically limited in terms of operational freedom both from a mechanical point of view as well as for acquisition routines. HECTOR is the latest system developed by the Ghent University Centre for X-ray Tomography (http://www.ugct.ugent.be) in collaboration with X-Ray Engineering (XRE bvba, Ghent, Belgium). It consists of a mechanical setup with nine motorized axes and a modular acquisition software package and combines a microfocus directional target X-ray source up to 240 kV with a large flat-panel detector. Provisions are made to install a line-detector for a maximal operational range. The system can accommodate samples up to 80 kg, 1 m long and 80 cm in diameter while it is also suited for high resolution (down to 4 μm) tomography. The bi-directional detector tiling is suited for large samples while the variable source-detector distance optimizes the signal to noise ratio (SNR) for every type of sample, even with peripheral equipment such as compression stages or climate chambers. The large vertical travel of 1 m can be used for helical scanning and a vertical detector rotation axis allows laminography experiments. The setup is installed in a large concrete bunker to allow accommodation of peripheral equipment such as pumps, chillers, etc., which can be integrated in the modular acquisition software to obtain a maximal correlation between the environmental control and the CT data taken. The acquisition software does not only allow good coupling with the peripheral equipment but its scripting feature is also particularly interesting for testing new and exotic acquisition routines.

High spectral and spatial resolution X-ray transmission radiography and tomography using a Color X-ray Camera

High resolution X-ray radiography and computed tomography are excellent techniques for non-destructive characterization of an object under investigation at a spatial resolution in the micrometer range. However, as the image contrast depends on both chemical composition and material density, no chemical information is obtained from this data. Furthermore, lab-based measurements are affected by the polychromatic X-ray beam, which results in beam hardening effects. New types of X-ray detectors which provide spectral information on the measured X-ray beam can help to overcome these limitations. In this paper, an energy dispersive CCD detector with high spectral resolution is characterized for use in high resolution radiography and tomography, where a focus is put on the experimental conditions and requirements of both measurement techniques.

Comparison of two single-image phase-retrieval algorithms for in-line x-ray phase-contrast imaging

The attenuation of x-rays in a material forms the basis of x-ray radiography and tomography. By measuring the transmission of the x-rays over a large amount of raypaths, the three-dimensional (3D) distribution of the x-ray linear attenuation coefficient can be reconstructed in a 3D volume. In x-ray microtomography (μCT), however, the x-ray refraction yields a significant signal in the transmission image and the 3D distribution of the refractive index can be reconstructed in a 3D volume. To do so, several methods exist, on both a hardware and software level. In this paper, we compare two similar software methods, the modified Bronnikov algorithm and the simultaneous phase-and-amplitude retrieval. The first method assumes a pure phase object, whereas the latter assumes a homogeneous object. Although these assumptions seem very restrictive, both methods have proven to yield good results on experimental data.

High-resolution imaging of kidney vascular corrosion casts with Nano-CT.

A vascular corrosion cast of an entire mouse kidney was scanned with a modular multiresolution X-ray nanotomography system. Using an isotropic voxel pitch of 0.5 μm, capillary systems such as the vasa recta, peritubular capillaries and glomeruli were clearly resolved. This represents a considerable improvement over corrosion casts scanned with microcomputed tomography systems. The resolving power of this system was clearly demonstrated by the unique observation of a dense, subcapsular mat of capillaries enveloping the entire outer surface of the cortical region. Resolution of glomerular capillaries was comparable to similar models derived from laser scanning confocal microscopy. The high-resolution, large field of view and the three-dimensional nature of the resulting data opens new possibilities for the use of corrosion casting in research.

Frog nuptial pads secrete mating season-specific proteins related to salamander pheromones

SUMMARY Males of many frog species develop spiny nuptial pads with underlying glands on their thumbs during the mating period. We used 3D visualization on the European common frog Rana temporaria to show that the morphology of these glands allows the channelling of secreted molecules to the pads surface during amplexus. Combined transcriptome and proteome analyses show that proteins of the Ly-6/uPAR family, here termed amplexins, are highly expressed in the nuptial glands during the mating season, but are totally absent outside that period. The function of amplexins remains unknown, but it is interesting to note that they share structural similarities with plethodontid modulating factors, proteins that influence courtship duration in salamanders.

X-ray micro-CT reconstruction reveals eight antennomeres in a new fossil taxon that constitutes a sister clade to Dundoxenos and Triozocera (Strepsiptera: Corioxenidae)

Eocenoxenos palintropos gen. nov. et sp.nov., a new fossil strepsipteran taxon from Baltic amber is described. The position of the new genus is based on cladistic analyses of morphological data sets. Most data of the fossil where retrieved with 3D micro-CT scan reconstructions. The new taxon is unambiguously situated as a sister group of the Dundoxenos-Triozocera clade within the Corioxenidae. The eocene taxon combines derived characteristics typical of Corioxenidae with the posession of eight antennomeres with five long flabella, a regained ancestral characteristic.

Functional morphology of the Andean climbing catfishes (Astroblepidae, Siluriformes): Alternative ways of respiration, adhesion, and locomotion using the mouth

Astroblepidae or “climbing catfishes” encompass a single genus of species living in high altitude rivers in the Andes of South America. They are characterized by a specialized head morphology closely resembling their better known, widely radiated sister family Loricariidae, or armored suckermouth catfishes. Existent data show that even though both families share important traits, there are some striking differences as well. Albeit poorly known, Astroblepus species possess a duplicated gill opening, and have the ability to climb vertical rocks or waterfalls. In this study, morphological and kinematic data are combined to yield insights into the functions of the mobile elements of the astroblepid head, and to compare head morphology and biomechanics with those of Loricariidae. We found that, even though there is substantial similarity in head structure of both families, there are major differences in functionally important structures. These include a different lower lip muscle configuration, an alternative oral valve system, and an incurrent gill opening only found in astroblepids. Kinematic analyses confirm that the astroblepid suckermouth, freed from its inhalatory function, offers advantages for climbing in the high‐altitude environment, and is used alternately with the extremely mobile pelvic girdle, in a crawling, nonundulatory motion. J. Morphol. 274:1164–1179, 2013.

EDART, a discrete algebraic reconstructing technique for experimental data obtained with high resolution computed tomography

A novel reconstruction method is presented to improve the image quality of three dimensional (3D) datasets for samples consisting of only one material and surrounding air, obtained with high resolution X-ray Computed Tomography (μCT). It combines discrete tomography with iterative reconstruction algorithms, it is applicable for routine μCT applications and is referred to as the Experimental Discrete Algebraic Reconstruction Technique (EDART). A fast and intuitive method to estimate the attenuation coefficient and segmentation threshold, in case these are unknown, is included. Experimental results illustrate that EDART allows the improvement of the reconstruction quality as compared to standard iterative reconstruction when few projections are available, without significantly increasing the reconstruction time.