Biology subjects

Sommerdijk, N. A. J. M.

Publications and source records attributed to Sommerdijk, N. A. J. M..

3 recordsLinked to original sources

bioRxiv2022

Metabolic acids impact bone mineral maturation

Bone mineral has a complex 3D architecture that is essential to its mechanical properties. It is a complex calcium phosphate phase related to hydroxyapatite that also contains significant quantities of cell respiration metabolites, in particular: carbonate, citrate and lactate. An as-yet unanswered question is what, if any, role do these metabolites collectively play in determining the 3D architecture of bone mineral? Here we synthesize apatitic materials by transformation from precursor mineral phases containing citrate, lactate or carbonate so that the synthesis environment mimics the densely-packed ionic environment within which bone mineral forms in vivo, and so that we can understand the mineral factors that may direct bone mineral 3D architecture. We show that incorporating citrate and lactate leads to complex mineral architectures reminiscent of those in bone mineral, including curvature of the mineral crystals. Our results suggest that metabolic acids may assist the moulding of bone mineral to restricted spaces available for mineral in in vivo bone. We find that the incorporation of lactate creates a softer material and inhibits the transformation towards apatitic structures, which may help to explain why foetal bone - necessarily soft - contains considerable quantities of lactate. High levels of plasma citrate have been previously found to correlate with high bone mineral density. Here we find that citrate incorporation leads to mineral crystal curvature modelling that in in vivo bone mineral suggesting its importance in mineral morphology. We conclude that metabolic anions may play an important role in controlling bone mineral physicochemical properties and 3D architecture.

biophysics↗

bioRxiv2022

Bioinspired Silk Fibroin Mineralization for Advanced In Vitro Bone Remodeling Models

Human in vitro bone models can create the possibility for investigation of physiological bone remodeling while addressing the principle of replacement, reduction and refinement of animal experiments (3R). Current in vitro models lack cell-matrix interactions and their spatiotemporal complexity. To facilitate these analyses, a bone-mimetic template was developed in this study, inspired by bones extracellular matrix composition and organization. Silk fibroin (SF) was used as an organic matrix, poly-aspartic acid (pAsp) was used to mimic the functionality of non-collagenous proteins, and 10x simulated body fluid served as mineralization solution. By using pAsp in the mineralization solution, minerals were guided towards the SF material resulting in mineralization inside and as a coating on top of the SF. After cytocompatibility testing, remodeling experiments were performed in which mineralized scaffold remodeling by osteoclasts and osteoblasts was tracked with non-destructive micro-computed tomography and medium analyses over a period of 42 days. The mineralized scaffolds supported osteoclastic resorption and osteoblastic mineralization, in the physiological bone remodeling specific sequence. This model could therefore facilitate the investigation of cell-matrix interactions and may thus reduce animal experiments and advance in vitro drug testing for bone remodeling pathologies like osteoporosis, where cell-matrix interactions need to be targeted.

bioengineering↗

bioRxiv2020

Nonclassical nucleation of protein mesocrystals via oriented attachment

Self-assembly of proteins holds great promise for the bottom-up design and production of synthetic biomaterials. In conventional approaches, designer proteins are pre-programmed with specific recognition sites that drive the association process towards a desired organized state. Although proven effective, this approach poses restrictions on the complexity and material properties of the end-state. An alternative, hierarchical approach that has found wide adoption for inorganic systems, relies on the production of crystalline nanoparticles which in turn become the building blocks of a next-level assembly process driven by oriented attachment (OA). As it stands, OA has not been observed for proteins. Here we employ cryoEM in the high nucleation rate limit of protein crystals and map the self-assembly route at molecular resolution. We observe the initial formation of facetted nanocrystals that merge lattices by means of OA alignment well before contact is made, satisfying non-trivial symmetry rules in the process. The OA mechanism yields crystal morphologies that are not attainable through conventional crystallization routes. Based on these insights we revisit a system of protein crystallization that has long been classified as non-classical, but our data is in direct conflict with that conclusion supporting a classical mechanism that implicates OA. These observations raise further questions about past conclusions for other proteins and illustrate the importance of maturation stages after primary nucleation has taken place.

biochemistry↗