3D bioprinting of tissue-specific osteoblasts and endothelial cells to model the human jawbone

Jawbone differs from other bones in many aspects, including its developmental origin and the occurrence of jawbone-specific diseases like MRONJ (medication-related osteonecrosis of the jaw). Although there is a strong need, adequate in vitro models of this unique environment are sparse to date. While previous approaches are reliant e.g. on scaffolds or spheroid culture, 3D bioprinting enables free-form fabrication of complex living tissue structures. In the present work, production of human jawbone models was realised via projection-based stereolithography. Constructs were bioprinted containing primary jawbone-derived osteoblasts and vasculature-like channel structures optionally harbouring primary endothelial cells. After 28 days of cultivation in growth medium or osteogenic medium, expression of cell type-specific markers was confirmed on both the RNA and protein level, while prints maintained their overall structure. Survival of endothelial cells in the printed channels, co-cultured with osteoblasts in medium without supplementation of endothelial growth factors, was demonstrated. Constructs showed not only mineralisation, being one of the characteristics of osteoblasts, but also hinted at differentiation to an osteocyte phenotype. These results indicate the successful biofabrication of an in vitro model of the human jawbone, which presents key features of this special bone entity and hence appears promising for application in jawbone-specific research.

Inspired by the human placenta: a novel 3D bioprinted membrane system to create barrier models

Barrier organ models need a scaffold structure to create a two compartment culture. Technical filter membranes used most often as scaffolds may impact cell behaviour and present a barrier themselves, ultimately limiting transferability of test results. In this work we present an alternative for technical filter membrane systems: a 3D bioprinted biological membrane in 24 well format. The biological membrane, based on extracellular matrix (ECM), is highly permeable and presents a natural 3D environment for cell culture. Inspired by the human placenta we established a coculture of a trophoblast-derived cell line (BeWo b30), together with primary placental fibroblasts within the biological membrane (simulating villous stroma) and primary human placental endothelial cells-representing three cellular components of the human placental villus. All cell types maintained their cell type specific marker expression after two weeks of coculture on the biological membrane. In permeability assays the trophoblast layer developed a barrier on the biological membrane, which was even more pronounced when cocultured with fibroblasts. In this work we present a filter membrane free scaffold, we characterize its properties and assess its suitability for cell culture and barrier models. Further we show a novel placenta inspired model in a complex bioprinted coculture. In the absence of an artificial filter membrane, we demonstrate barrier architecture and functionality.

CXCR4 prevents dispersion of granule neuron precursors in the adult dentate gyrus

Neurogenesis in the adult dentate gyrus (DG) generates new granule neurons that differentiate in the inner one-third of the granule cell layer (GCL). The migrating precursors of these neurons arise from neural stem cells (NSCs) in the subgranular zone (SGZ). Although it is established that pathological conditions, including epilepsy and stroke, cause dispersion of granule neuron precursors, little is known about the factors that regulate their normal placement. Based on the high expression of the chemokine CXCL12 in the adult GCL and its role in guiding neuronal migration in development, we addressed the function of the CXCL12 receptor CXCR4 in adult neurogenesis. Using transgenic reporter mice, we detected Cxcr4-GFP expression in NSCs, neuronal-committed progenitors, and immature neurons of adult and aged mice. Analyses of hippocampal NSC cultures and hippocampal tissue by immunoblot and immunohistochemistry provided evidence for CXCL12-promoted phosphorylation/activation of CXCR4 receptors in NSCs in vivo and in vitro. Cxcr4 deletion in NSCs of the postnatal or mature DG using Cre technology reduced neurogenesis. Fifty days after Cxcr4 ablation in the mature DG, the SGZ showed a severe reduction of Sox2-positive neural stem/early progenitor cells, NeuroD-positive neuronal-committed progenitors, and DCX-positive immature neurons. Many immature neurons were ectopically placed in the hilus and inner molecular layer, and some developed an aberrant dendritic morphology. Only few misplaced cells survived permanently as ectopic neurons. Thus, CXCR4 signaling maintains the NSC pool in the DG and specifies the inner one-third of the GCL as differentiation area for immature granule neurons.