Angiogenesis by BMP-2-PDLLA-Biohybrids in Co-Culture with Osteoblasts and Endothelia

Adsorbate biohybrids for BMP-2 delivery based on electrospun PDLLA-nanofiber fleeces loaded with 0.6 μg/cm2 rhBMP-2COL (E. coli) strongly induced microvessel- like structures when incubated for 14 days in cocultures of human outgrowth endothelial cells (OEC) together with human primary osteoblasts (pOB). Higher loaded rhBMP-2COL biohybrids (4.6 μg/cm2) were low- to noninductive. Adsorbate biohybrids of rhBMP-2CHO (CHO cells) loaded with 1.0-6.0 μg/cm2 induced only a classic cobblestone- like growth pattern without any microvessels. Concentration- response experiments (7 days) indicate a binding affinity of rhBMP-2COL for microvessel induction in the picomolar range with nanomolar concentrations being non-inductive

Direct comparison of 3D and 2D cultivation reveals higher osteogenic capacity of elderly osteoblasts in 3D

Background The aim of this study was the investigation of the osteogenic potential of human osteoblasts of advanced donor age in 2D and 3D culture. Methods Osteoblasts were induced to osteogenic differentiation and cultivated, using the same polystyrene material in 2D and 3D culture for 2 weeks. Samples were taken to evaluate alkaline phosphatase (ALP) activity, mineralization and gene expression. Results Osteoprotegerin (OPG) levels were significantly increased (8.2-fold) on day 7 in 3D compared to day 0 (p < 0.0001) and 11.6-fold higher in 3D than in 2D (p < 0.0001). Both culture systems showed reduced osteocalcin (OC) levels (2D 85% and 3D 50% of basic value). Collagen type 1 (Col1) expression was elevated in 3D on day 7 (1.4-fold; p = 0.009). Osteopontin (OP) expression showed 6.5-fold higher levels on day 7 (p = 0.002) in 3D than in 2D. Mineralization was significantly higher in 3D on day 14 (p = 0.0002). Conclusion Advanced donor age human primary osteoblasts reveal significantly higher gene expression levels of OPG, Col1 and OP in 3D than in monolayer. Therefore, it seems that a relatively high potential of bone formation in a natural 3D arrangement is presumably still present in osteoblasts of elderly people. Trial registration 5217/11 on the 22nd of Dec. 2011.

A systematic dissection of human primary osteoblasts in vivo at single-cell resolution

Osteoblasts are multifunctional bone cells, which play essential roles in bone formation, angiogenesis regulation, as well as maintenance of hematopoiesis. Although both in vivo and in vitro studies on mice have identified several potential osteoblast subtypes based on their different transition stages or biological responses to external stimuli, the categorization of primary osteoblast subtypes in vivo in humans has not yet been achieved. Here, we used single-cell RNA sequencing (scRNA-seq) to perform a systematic cellular taxonomy dissection of freshly isolated human osteoblasts. Based on the gene expression patterns and cell lineage reconstruction, we identified three distinct cell clusters including preosteoblasts, mature osteoblasts, and an undetermined rare osteoblast subpopulation. This novel subtype was mainly characterized by the nuclear receptor subfamily 4 group A member 1 and 2 (NR4A1 and NR4A2), and its existence was confirmed by immunofluorescence staining. Trajectory inference analysis suggested that the undetermined cluster, together with the preosteoblasts, are involved in the regulation of osteoblastogenesis and also give rise to mature osteoblasts. Investigation of the biological processes and signaling pathways enriched in each subpopulation revealed that in addition to bone formation, preosteoblasts and undetermined osteoblasts may also regulate both angiogenesis and hemopoiesis. Finally, we demonstrated that there are systematic differences between the transcriptional profiles of human osteoblasts in vivo and mouse osteoblasts both in vivo and in vitro, highlighting the necessity for studying bone physiological processes in humans rather than solely relying on mouse models. Our findings provide novel insights into the cellular heterogeneity and potential biological functions of human primary osteoblasts at the single-cell level, which is an important and necessary step to further dissect the biological roles of osteoblasts in bone metabolism under various (patho-) physiological conditions.