(496a) Demineralized Bone Slices for in Vitro Endosteal Niche Modeling

The trabecular bone implicates clinical significance as a major site for preserving adult stem cells, generating all types of blood cells throughout lifetime, osteoporosis during aging, and in case of cancerous lesion metastasis. In vitro reconstitution of trabecular bone tissue models is imperative to better understand fundamental biology of aforementioned biological processes and explore translational opportunities such as ex vivo expansion of hematopoietic stem cells and drug screening for cancer metastasis and osteoporosis. In this tissue, bone and marrow exist as an integrated organoid. Each tissue represents distinct cellular and extracellular niches that are known as vascular and endosteal niches. While there has been significant progress in modeling vascular niche, in vitro reconstitution of endosteal niche remains premature. The field has focused on bone-forming osteoblasts and bone-resorbing osteoclasts in in vitro bone tissue modeling. However, in reality, the major cell types comprising the endosteal niche is osteocytes and bone lining cells. We have developed a new biomaterial and engineering strategy to faithfully create endosteal bone tissue models. Thin slices of demineralized bone matrix supported osteoblast cell activity and their lining cell differentiation - inactive form of osteoblasts. Further stacking demineralized bone matrix allowed creating lamellar structure of bone, which in turn promoted osteocyte differentiation of osteoblast. We provide evidence that support bone lining and osteocyte differentiation with related gene expression, cellular activities and morphology and secretory profiles. The established endosteal niche model is expected to serve as a foundation for creating better functional trabecular bone tissue models combined with existing vascular niche models.