Autofluorescence of stingray skeletal cartilage: hyperspectral imaging as a tool for histological characterization

Tessellated cartilage is a distinctive composite tissue forming the bulk of the skeleton of cartilaginous fishes (e.g. sharks and rays), built from unmineralized cartilage covered at the surface by a thin layer of mineralized tiles called tesserae. The finescale structure and composition of elasmobranch tessellated cartilage has largely been investigated with electron microscopy, micro-computed tomography and histology, but many aspects of tissue structure and composition remain uncharacterized. In our study, we demonstrate that the tessellated cartilage of a stingray exhibits a strong and diverse autofluorescence, a native property of the tissue which can be harnessed as an effective label-free imaging technique. The autofluorescence signal was excited using a broad range of wavelengths in confocal and light sheet microscopy, comparing several sample preparations (fresh; demineralized and paraffin-embedded; non-demineralized and plastic-embedded) and imaging the tissue at different scales. Autofluorescence varied with sample preparation with the signal in both plastic- and paraffin-embedded samples strong enough to allow visualization of finescale (≥ 1 μm) cellular and matrix structures, such as cell nuclei and current and former mineralization fronts, identifiable by globular mineralized tissue. A defined pericellular matrix (PCM) surrounding chondrocytes was also discernible, described here for the first time in elasmobranchs. The presence of a PCM suggests similarities with mammalian cartilage regarding how chondrocytes interact with their environment, the PCM in mammals acting as a transducer for biomechanical and biochemical signals. A posterior analysis of hyperspectral images by an MCR-ALS unmixing algorithm allowed identification of several distinct fluorescence signatures associated to specific regions in the tissue. Some fluorescence signatures identified could be correlated with collagen type II, the most abundant structural molecule of cartilage. Other fluorescence signatures, however, remained unidentified, spotlighting tissue regions that deserve deeper characterization and suggesting the presence of molecules still unidentified in elasmobranch skeletal cartilage. Our results show that autofluorescence can be a powerful exploratory imaging tool for characterizing less-studied skeletal tissues, such as tessellated cartilage. The images obtained are largely comparable with more commonly used techniques, but without the need for complicated sample preparations or external staining reagents standard in histology and electron microscopy (TEM, SEM)

Bricks, trusses and superstructures: strategies for skeletal reinforcement in batted fishes (rays and skates)

Crushing and eating hard prey (durophagy) is mechanically demanding. The cartilage jaws of durophagous stingrays are known to be reinforced relative to non-durophagous relatives, with a thickened external cortex of mineralized blocks (tesserae), reinforcing struts inside the jaw (trabeculae), and pavement-like dentition. These strategies for skeletal strengthening against durophagy, however, are largely understood only from myliobatiform stingrays, although a hard prey diet has evolved multiple times in batoid fishes (rays, skates, guitarfishes). We perform a quantitative analysis of micro-CT data, describing jaw strengthening mechanisms in Rhina ancylostoma (Bowmouth Guitarfish) and Rhynchobatus australiae (White-spotted Wedgefish), durophagous members of the Rhinopristiformes, the sister taxon to Myliobatiformes. Both species possess trabeculae, more numerous and densely packed in Rhina, albeit simpler structurally than those in stingrays like Aetobatus and Rhinoptera. Rhina and Rhynchobatus exhibit impressively thickened jaw cortices, often involving >10 tesseral layers, most pronounced in regions where dentition is thickest, particularly in Rhynchobatus. Age series of both species illustrate that tesserae increase in size during growth, with enlarged and irregular tesserae associated with the jaws’ oral surface in larger (older) individuals of both species, perhaps a feature of ageing. Unlike the flattened teeth of durophagous myliobatiform stingrays, both rhinopristiform species have oddly undulating dentitions, comprised of pebble-like teeth interlocked to form compound “meta-teeth” (large spheroidal structures involving multiple teeth). This is particularly striking in Rhina, where the upper/lower occlusal surfaces are mirrored undulations, fitting together like rounded woodworking finger-joints. Trabeculae were previously thought to have arisen twice independently in Batoidea; our results show they are more widespread among batoid groups than previously appreciated, albeit apparently absent in the phylogenetically basal Rajiformes. Comparisons with several other durophagous and non-durophagous species illustrate that batoid skeletal reinforcement architectures are modular: trabeculae can be variously oriented and are dominant in some species (e.g. Rhina, Aetobatus), whereas cortical thickening is more significant in others (e.g. Rhynchobatus), or both reinforcing features can be lacking (e.g. Raja, Urobatis). We discuss interactions and implications of character states, framing a classification scheme for exploring cartilage structure evolution in the cartilaginous fishes

Perfil de los pacientes que acuden al médico internista para valoración de osteoporosis: registro OSTEOMED

Producción CientíficaAntecedentes y objetivo: La osteoporosis se considera un trastorno generalizado del esqueleto en el que existe una alteración de la resistencia ósea que predispone a la persona a un mayor riesgo de fractura. Este estudio transversal pretende recoger y presentar las principales características clínicas de los pacientes que acuden a la consulta de los médicos internistas en Espa˜na. Conocer estas características podría facilitar la puesta en marcha de planes de actuación para mejorar la atención de estos pacientes de manera más eficaz y eficiente. Material y métodos: A través del análisis del registro OSTEOMED (Osteoporosis en Medicina Interna), este trabajo presenta las principales características clínicas de los pacientes con osteoporosis que acudieron a las consultas de Medicina Interna en 23 centros hospitalarios espa˜noles entre 2012 y 2017. Se han analizado los motivos de consulta, los valores densitométricos, la presencia de comorbilidades, el tratamiento prescrito y otros factores relacionados con el estilo de vida. Resultados: En total se evaluó a 2.024 pacientes con osteoporosis (89,87% mujeres, 10,13% hombres). La edad media de los pacientes fue de 64,1 ± 12,1 a˜nos (mujeres, 64,7 ± 11,5 a˜nos; hombres, 61,2 ± 14,2 a˜nos). No hubo diferencia entre sexos en la historia de caídas recientes (9,1-6,7%), mientras que sí se apreció en la ingesta diaria de calcio de lácteos (553,8 ± 332,6 mg en mujeres vs. 450,2 ± 303,3 mg en hombres; p < 0,001) y en causas secundarias de osteoporosis(13% de hombres vs. 6,5% de mujeres; p < 0,001). En la muestra se observaron un total de 404fracturas (20%), destacando el número de fracturas vertebrales confirmadas (17,2%, 35,6% enhombres vs. 15,2% de las mujeres; p < 0,001). Una gran parte de los pacientes no recibía eltratamiento indicado y presentaba bajos niveles de actividad física y exposición solar. Un por-centaje importante de pacientes presentó comorbilidades asociadas, siendo las más frecuentesla hipertensión (32%) y la dislipidemia (28%).Conclusiones: Estos resultados definen el perfil del paciente con osteoporosis que acude a laconsulta de Medicina Interna en Espa˜na. Además, ponen de manifiesto el carácter multisistémicode esta entidad que junto con su elevada prevalencia determinan que las consultas específicasde Medicina Interna dedicadas a su manejo son el lugar adecuado para la atención de estos pacientes

Co-aligned chondrocytes : zonal morphological variation and structured arrangement of cell lacunae in tessellated cartilage

In most vertebrates the embryonic cartilaginous skeleton is replaced by bone during development. During this process, cartilage cells (chondrocytes) mineralize the extracellular matrix and undergo apoptosis, giving way to bone cells (osteocytes). In contrast, sharks and rays (elasmobranchs) have cartilaginous skeletons throughout life, where only the surface mineralizes, forming a layer of tiles (tesserae). Elasmobranch chondrocytes, unlike those of other vertebrates, survive cartilage mineralization and are maintained alive in spaces (lacunae) within tesserae. However, the function(s) of the chondrocytes in the mineralized tissue remain unknown. Applying a custom analysis workflow to high-resolution synchrotron microCT scans of tesserae, we characterize the morphologies and arrangements of stingray chondrocyte lacunae, using lacunar morphology as a proxy for chondrocyte morphology. We show that the cell density is comparable in unmineralized and mineralized tissue from our study species and that cells maintain the similar volume even when they have been incorporated into tesserae. This discovery supports previous hypotheses that elasmobranch chondrocytes, unlike those of other taxa, do not proliferate, hypertrophy or undergo apoptosis during mineralization. Tessera lacunae show zonal variation in their shapes—being flatter further from and more spherical closer to the unmineralized cartilage matrix and larger in the center of tesserae— and show pronounced organization into parallel layers and strong orientation toward neighboring tesserae. Tesserae also exhibit local variation in lacunar density, with the density considerably higher near pores passing through the tesseral layer, suggesting pores and cells interact (e.g. that pores contain a nutrient source). We hypothesize that the different lacunar types reflect the stages of the tesserae formation process, while also representing local variation in tissue architecture and cell function. Lacunae are linked by small passages (canaliculi) in the matrix to form elongate series at the tesseral periphery and tight clusters in the center of tesserae, creating a rich connectivity among cells. The network arrangement and the shape variation of chondrocytes in tesserae indicate that cells may interact within and between tesserae and manage mineralization differently from chondrocytes in other vertebrates, perhaps performing analogous roles to osteocytes in bone