Biology subjects

Roschger, A.

Publications and source records attributed to Roschger, A..

3 recordsLinked to original sources

bioRxiv2023

Twisted plywood-like tissue formation in vitro. Does curvature do the twist?

Little is known about the contribution of 3D surface geometry on the development of multi-layered tissues containing fibrous extracellular matrix components such as those found in bone. Here we elucidate the role of curvature in the formation of chiral, twisted plywood-like structures. Tissues consisting of murine pre-osteoblast cells (MC3T3-E1) were grown on 3D scaffolds with constant mean curvature and negative Gaussian curvature for up to 32 days. Using 3D fluorescence microscopy, the influence of surface curvature on actin stress-fiber alignment and chirality was investigated. To gain mechanistic insights, also MC3T3-E1 cells deficient in nuclear A-type lamins or treated with drugs targeting cytoskeleton proteins were used in our study. We find that wild type cells grow multilayered tissue with fibers predominantly aligned along directions of negative curvature, but where subsequent layers twist in orientation with respect to older tissues with time. Fiber orientation is conserved below the tissue surface thus creating a twisted plywood like material. We further show that this directional organization strongly depends on structural components of the cells (A-type lamins, actin and myosin). Our data indicate the importance of substrate curvature in the formation of 3D tissues and provides new insights into the emergence of chirality. Significance StatementBiological tissues (like compact bone) often consist of multiple fibrous layers which are staggered with a twisting angle relative to each other, thereby improving mechanical performance. The underlying principles of how such tissues are formed and what determines the fiber direction are still debated. Here we report the formation of a twisted plywood-like tissue grown in vitro on constant mean and negative Gaussian curvature substrates and present evidence that for tissue consisting of pre-osteoblast like cells, surface curvature is a main determinant for fiber orientation.

biophysics↗

bioRxiv2020

Three-dimensional interrelationship between osteocyte network and forming mineral during human bone remodeling

During bone remodeling, osteoblasts are known to deposit unmineralized collagenous tissue (osteoid), which mineralizes after some time lag. Some of the osteoblasts differentiate into osteocytes, forming a cell network within the lacunocanalicular network (LCN) of bone. To get more insight into the potential role of osteocytes in the mineralization process of osteoid, sites of bone formation were three-dimensionally imaged in nine forming human osteons using focused ion beam-scanning electron microscopy (FIB-SEM). In agreement with previous observations, the mineral concentration was found to gradually increase from the central Haversian canal towards preexisting mineralized bone. Most interestingly, a similar feature was discovered on a length scale more than 100-times smaller, whereby mineral concentration increased from the LCN, leaving around the canaliculi a zone virtually free of mineral, the size of which decreases with progressing mineralization. This suggests that the LCN controls mineral formation but not just by diffusion of mineralization precursors, which would lead to a continuous decrease of mineral concentration from the LCN. Our observation is, however, compatible with the codiffusion and reaction of precursors and inhibitors from the LCN into the bone matrix.

biophysics↗

bioRxiv2020

Mineral density differences between femoral cortical bone and trabecular bone are not explained by turnover rate alone

Bone mineral density distributions (BMDDs) are a measurable property of bone tissues that depends strongly on bone remodelling and mineralisation processes. These processes can vary significantly in health and disease and across skeletal sites, so there is high interest in analysing these processes from experimental BMDDs. Here, we propose a rigorous hypothesis-testing approach based on a mathematical model of mineral heterogeneity in bone due to remodelling and mineralisation, to help explain differences observed between the BMDD of human femoral cortical bone and the BMDD of human trabecular bone. Recent BMDD measurements show that femoral cortical bone possesses a higher bone mineral density, but a similar mineral heterogeneity around the mean compared to trabecular bone. By combining this data with the mathematical model, we are able to test whether this difference in BMDD can be explained by (i) differences in turnover rate; (ii) differences in osteoclast resorption behaviour; and (iii) differences in mineralisation kinetics between the two bone types. We find that accounting only for differences in turnover rate is inconsistent with the fact that both BMDDs have a similar spread around the mean, and that accounting for differences in osteoclast resorption behaviour leads to biologically inconsistent bone remodelling patterns. We conclude that the kinetics of mineral accumulation in bone matrix must therefore be different in femoral cortical bone and trabecular bone. Although both cortical and trabecular bone are made up of lamellar bone, the different mineralisation kinetics in the two types of bone point towards more profound structural differences than usually assumed.

biophysics↗