An Organoid for Woven Bone

Abstract

25 26 ^equal contribution 27 Corresponding authors: anat.akiva@radboudumc.nl ; nico.sommerdijk@radboudumc.nl; 28 s.hofmann@tue.nl 29 Stem cell-based organoids are promising as functional, self-organizing 3D in vitro models for 30 studying the physiology and pathology of various tissues 1 . Bone formation (osteogenesis) is a 31 complex process in which i) cellular differentiation and ii) the generation of a mineralized organic 32 matrix are synchronized to produce a hybrid hierarchical architecture. To study the molecular 33 mechanisms of osteogenesis in health and disease there is great need for organoids that capture 34 both processes in parallel 2 , however, for human bone no such functional model system is yet 35 available 3 . 36 Here, we report the in vitro differentiation of human bone marrow stromal cells into a functional 37 3D self-organizing co-culture of osteoblasts and osteocytes, creating an organoid for early stage 38 bone (woven bone) formation. We demonstrate that the osteocytes form a network showing cell-39 cell communication via the expression of sclerostin, embedded within the collagen matrix that is 40 formed by the osteoblasts and mineralized under biological control. 41

Bioinspired Silk Fibroin Mineralization for Advanced In Vitro Bone Remodeling Models

“…supplied medium or mechanical loading) should therefore be considered for future studies. For example, applying fluid shear stress to the cells to stimulate the osteoid formation and thereby potentially improving osteoblastic control over mineralization [17,50,71,72] .…”

“…Collagen synthesis even tended to decrease in mineralized co-cultured constructs on day 42. This might be explained by a lack of mechanical loading in the system, which is crucial for in vivo bone adaptation and in vitro woven bone formation including collagen synthesis [49,50] . Another explanation might be the excessive mineralization upon osteogenic stimulation in mineralized co-cultured constructs (Figure 6D).…”

Tissue Engineering Through 3D Bioprinting to Recreate and Study Bone Disease

“…Once differentiated, these osteocytes exhibited the normal characteristics of bone as evidenced by the expression of sclerostin and mineralized matrix. The organoid formation of woven bone in this case is very similar to the aberrant bone formation that occurs in osteogenesis imperfecta, right down to the natural co-assembly of collagen fibrils and mineral bone matrix as determined by Raman micro-spectroscopy [ 100 ].…”

“…There are currently seven types of osteogenesis known [ 98 ]. The commonly affected genes in osteogenesis imperfecta include COL1A1, COL1A2, CRTAP, LEPRE1, PPIB, or P3H1 [ 97 , 99 , 100 ]. The drugs used to treat osteogenesis imperfecta include bisphosphonates such as pamidronate, or zoledronic acid, and denosumab [ 98 , 99 ].…”

“…3D organoid models of bone to study osteogenesis have been explored by guiding the differentiation of human bone marrow stromal cells that give rise to both osteoblasts and osteoclasts [ 100 ]. Not only was the scaffold and media culture conditions important in stimulating osteogenesis and mineralized ECM production, but a calibrated level of sheer stress was important in the bone formation.…”