The Constitutive Expression of Type X Collagen in Mesenchymal Stem Cells from Osteoarthritis Patients Is Reproduced in a Rabbit Model of Osteoarthritis

The expression of type X collagen (COL X), a late-stage chondrocyte hypertrophy marker in human mesenchymal stem cells (MSCs) from osteoarthritis (OA) patients poses a major setback to current cartilage and intervertebral disc tissue engineering efforts. However, it is not yet clear whether COL X is expressed by all human bone marrow stem cells or if it is related to age, gender, site, disease status, or drug therapy. In the current study, we report that COL X expression is upregulated in MSCs from rabbits in a surgical instability model of OA (anterior cruciate ligament transection (ACLT)) when compared to control rabbit MSCs. Thus COL X expression in OA is a common phenomenon that is due to the disease process itself and not to other environmental factors. It is, therefore, critical to understand MSC phenotype in OA patients, as these cells are essential clinically for biological repair of cartilage lesions using autologous stem cells

Differences in third metacarpal trabecular microarchitecture between the parasagittal groove and condyle at birth and in adult racehorses

Background: The aetiology of equine metacarpal condylar fractures is not completely understood and a developmental cause has been postulated. Objectives: To investigate the subchondral bone trabecular microarchitecture of the lateral parasagittal groove and condyle in equine neonates and its adaptation with maturation and athletic activity. Study design: Ex vivo observational study. Methods: Distal metacarpi of neonates, yearlings and adult racehorses (n = 24) were harvested. Dorsal and palmar frontal histological sections, containing the lateral parasagittal groove and condyle, were studied. The sections were digitalised and subchondral trabecular bone quantity and quality parameters and trabecular orientation in the frontal plane were measured. Results: Trabecular spacing and length were greater (P = 0.004 and P = 0.0005 respectively) whereas bone fraction, trabecular number and connectivity were all lower (P = 0.0004, P = 0.0001 and P = 0.001 respectively) in the lateral parasagittal groove compared with the condyle in neonatal foals. Trabecular thickness and bone fraction increased with age in racehorses and trabecular spacing decreased. The predominant trabecular orientation had a consistent pattern in neonates and it changed with maturity and the cumulative effect of racing at all the ROIs except for the palmar lateral parasagittal groove that retained a more 'immature' pattern. Main limitations: Samples were investigated in 2D. 3D processing could have provided more information. Conclusions: Already at birth there are striking differences in the subchondral bone trabecular microarchitecture between the lateral parasagittal groove and condyle in foals. Adaptation of trabeculae is confirmed with maturity in racehorses, with the greatest adaptation measured in bone quantity parameters. The trabecular orientation had a unique and more immature orientation pattern in the lateral palmar parasagittal grooves in adult racehorses and may reflect a weaker structure at this site. © 2018 EVJ Ltd

Differences between foetal and adult meniscus and cartilage revealed by Polarization Second Harmonic Generation Microscopy

International audienc

Maturation of the Meniscal Collagen Structure Revealed by Polarization-Resolved and Directional Second Harmonic Generation Microscopy

International audienceWe report polarization-resolved Second Harmonic Generation (p-SHG) and directional SHG (forward and backward, F/B) measurements of equine foetal and adult collagen in meniscus, over large field-of-views using sample-scanning. Large differences of collagen structure and fibril orientation with maturation are revealed, validating the potential for this novel methodology to track such changes in meniscal structure. The foetal menisci had a non-organized and more random collagen fibrillar structure when compared with adult using P-SHG. For the latter, clusters of homogeneous fibril orientation (inter-fibrillar areas) were revealed, separated by thick fibers. F/B SHG showed numerous different features in adults notably, in thick fibers compared to interfibrillar areas, unlike foetal menisci that showed similar patterns for both directions. This work confirms previous studies and improves the understanding of meniscal collagen structure and its maturation, and makes f/B and p-SHG good candidates for future studies aiming at revealing structural modifications to meniscus due to pathologies. The meniscus is a semilunar fibrocartilaginous structure interposed between the femoral condyle and the tibial plateau in the knee joint. The meniscus is essential for load transmission across the articular surfaces, for femo-rotibial joint stability and for long-term joint health 1. Degradation of the meniscal tissue can increase articular cartilage strain 2 , and may lead to cartilage degeneration and osteoarthritis 3. Knowledge of the complex structure of the meniscal extracellular matrix (ECM) has increased thanks to emerging technologies for in situ imaging of intact specimens, such as Optical Projection Tomography (OPT) 4. In particular the arrangement of meniscal fascicles 4 , its tie-fiber organization 5 , and the menisco-tibial ligament insertion transition have all recently been revealed by investigation of bovine samples 6. SHG microscopy is a recent and powerful technique to image the structure of biological specimens as it provides submicron spatial resolution, has low phototoxicity and a high depth selectivity and penetration. In this respect, SHG imaging is similar to multiphoton-excited fluorescence microscopy 7. However, important differences exist: it is a coherent process sensitive to the phase-matching conditions where the measured signal arises from constructive/destructive interferences, it is also instantaneous and free from photobleaching as the signal conversion is due to a structural arrangement and does not involve electronic transition 8. SHG micros-copy has been used to image fibrillar collagen in specimens including type II collagen in articular cartilage 9-16. Furthermore, because of its coherent nature, the detection of the signal in the direction of propagation (forward-F) provides different imaging features compared to the backward (B) direction 17. The F/B ratio increases with the level of homogeneity of noncentrosymmetric structures within the focal volume and has been related to the size of the collagen fibrils for collagen rich tissues 18,19