Pierantoni, M. | bioRxiv Science

bioRxiv2022

Heterotopic ossification in intact rat Achilles tendons is characterized by unique mineralized collagen fiber structures

Heterotopic ossification (HO) entails pathological mineral formation inside soft tissues. In human Achilles tendons, HO is often associated with tendinopathies, tendon weakness and pain. One hypothesis is that HO occurs in response to inflammation and by either intramembranous ossification, endochondral ossification, or a combination of both. However, refined details regarding HO deposition and microstructure are still unknown. In this study, we characterize HO in intact rat Achilles tendons through high-resolution phase contrast enhanced synchrotron X-ray tomographic imaging. Furthermore, we test the potential of using a procedure to induce local tissue injury by needling to study the relation between microdamage and formation of HO. The results show that HO occurs in all intact rat tendons occupying up to 1% of the total volume at 16 weeks of age. The HOs are characterized by an elongated ellipsoidal shape and by a distinctive fiber-like internal structure which suggests that some collagen fibers have become mineralized. The data indicates that the deposition along the fibers initiates in the pericellular area, and propagates into the intercellular area. The results also show that multiple HO deposits may merge into bigger structures with time by accession along unmineralized fibers. Furthermore, the presence of unmineralized regions within the deposits may indicate that HOs are not only growing, but mineral resorption can also occur. Additionally, phase contrast enhanced synchrotron X-ray tomography allowed to distinguish microdamage at the fiber level due to needling and it could in the future enable to elucidate the relation between local inflammation, microdamage, and HO deposition.

physiology↗

bioRxiv2020

Cystoliths in Ficus leaves: increasing carbon fixation in saturating light by light scattering off a mineral substrate

The manner in which leaves adapt to different light intensities is key for enabling plants to survive in diverse environments and in constantly changing conditions. Many studies have addressed this subject, but little attention has been given to the effect that mineral deposits in leaves can have on photosynthesis. Here we study 6 species of Ficus and investigate how different cystolith configurations affect photosynthesis in both non-saturating and saturating light. We quantified the effect of light scattering by cystoliths on light absorption by measuring chlorophyll fluorescence intensity using microfluorimetry. We complement this by carbon assimilation measurements to directly estimate how light scattering by cystoliths affects the overall photosynthetic process. We show that light waste is reduced when irradiance is on a cystolith compared to cystolith free tissue. Moreover, light is channeled into the center of the leaf where photosynthesis occurs more efficiently than in the outer layers. This, in turn, leads to more efficient CO2 assimilation. We conclude that cystoliths contribute to photosynthesis optimization under saturating light. Cystoliths reduce the wasted portion of absorbed light under saturating irradiance by scattering light into the light-deprived leaf center. The increased efficiency may well provide important benefits to plants that form mineral scatterers.

plant biology↗