Mild Thermotherapy-Assisted GelMA/HA/MPDA@Roxadustat 3D-Printed Scaffolds with Combined Angiogenesis-Osteogenesis Functions for Bone Regeneration.

Early reconstruction of the vascular network is a prerequisite to the effective treatment of substantial bone defects. Traditional 3D printed tissue engineering scaffolds designed to repair large bone defects do not effectively regenerate the vascular network, and rely only on the porous structure within the scaffold for nutrient transfer and metabolic waste removal. This leads to delayed bone restoration and hence functional recovery. Therefore, strategies for generation scaffolds with the capacity to efficiently regenerate vascularization should be developed. This study loads roxarestat (RD), which can stabilize HIF-1α expression in a normoxic environment, onto the mesopore polydopamine nanoparticles (MPDA@RD) to enhance the reconstruction of vascular network in large bone defects. Subsequently, MPDA@RD is mixed with GelMA/HA hydrogel bioink to fabricate a multifunctional hydrogel scaffold (GHM@RD) through 3D printing. In vitro results show that the GHM@RD scaffolds achieve good angiogenic-osteogenic coupling by activating the PI3K/AKT/HSP90 pathway in BMSCs and the PI3K/AKT/HIF-1α pathway in HUVECs under mild thermotherapy. In vivo experiments reveal that RD and mild hyperthermia synergistically induce early vascularization and bone regeneration of critical bone defects. In conclusion, the designed GHM@RD drug delivery scaffold with mild hyperthermia holds great therapeutic value for future treatment of large bone defects.

Hyperbaric oxygen therapy enhances osteointegration of reimplanted cranial flap by regulating osteogenesis-angiogenesis coupling.

Craniectomy is a lifesaving procedure to alleviate dangerously high intracranial pressure by removing a bone flap from the calvarium. However, the osteointegration of reimplanted bone flap with the existing bone tissue is still a clinical challenge. Hyperbaric oxygen (HBO) therapy has shown efficacy in promoting bone repair and could be a promising treatment for accelerating postoperative recovery. However, the specific cell types that are responsive to HBO treatment are not well understood. In this study, we created a murine model of craniectomy, with reimplantation of the cranial flap after 1 week. The effects of HBO treatment on bone formation and blood vessel formation around reimplanted bone were examined by micro-computed tomography, histological staining, and immunofluorescence staining. Single-cell RNA sequencing (scRNAseq) was utilized to identify key cell subtypes and signaling pathways after HBO treatment. We found that HBO treatment increased bone volume around reimplanted cranial flaps. HBO also increased the volume of Osterix-expressing cells and type H vessels. scRNAseq data showed more mature osteoblasts and endothelial cells, with higher expressions of adhesion and migration-related genes after HBO treatment. Cell-cell interaction analysis revealed a higher expression level of genes between mature osteoblasts and endothelial cells from the angiopoietin 2-integrin α5ß1 pathway. Taken together, HBO therapy promotes the healing process of craniectomy by regulating the crosstalk between vascular endothelial cells and osteogenic cells. These findings provide evidence in a preclinical model that HBO therapy enhances osteointegration by regulating angiogenesis-osteogenesis coupling, providing a scientific basis for utilizing HBO therapy for accelerating postoperative recovery after craniectomy.

ROS-reactive PMS/PC drug delivery system improves new bone formation under diabetic conditions by promoting angiogenesis-osteogenesis coupling via down-regulating NOX2-ROS signalling axis.

Reactive oxygen species (ROS) overproduction and oxidative stress increases bone fragility and fracture risk in long-standing diabetes mellitus cases. In this study, a ROS-reactive drug delivery system was prepared to solve this issue by phenyl sulfide mesoporous silica nanoparticles (PMS) loaded with proanthocyanidin (PC). The effect of PMS/PC on new bone formation under diabetic conditions and the underlying mechanism was investigated in-vitro and in-vivo. The results illustrated that the PC was released from the ROS-reactive PMS/PC triggered by peripheral ROS and then eliminated excessive ROS, which achieved dynamic ROS regulation and reached ROS homeostasis finally. Furthermore, we found PMS/PC promoted osteoblastic differentiation in vitro and increased ossification in vivo by promoting the angiogenesis-osteogenesis coupling via down-regulating the expression of nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) to suppress ROS overproduction, preventing vascular oxidative stress. Therefore, our work has proved a therapeutic potential of ROS-reactive PMS/PC in the treatment of diabetic bone disease and indicates excellent prospects of PMS/PC to depress oxidative stress triggered by excessive ROS which is a key pathological factor in many systematic diseases.

Endothelial cells produce angiocrine factors to regulate bone and cartilage via versatile mechanisms.

Blood vessels are conduits distributed throughout the body, supporting tissue growth and homeostasis by the transport of cells, oxygen and nutrients. Endothelial cells (ECs) form the linings of the blood vessels, and together with pericytes, are essential for organ development and tissue homeostasis through producing paracrine signalling molecules, called angiocrine factors. In the skeletal system, ECs - derived angiocrine factors, combined with bone cells-released angiogenic factors, orchestrate intercellular crosstalk of the bone microenvironment, and the coupling of angiogenesis-to-osteogenesis. Whilst the involvement of angiogenic factors and the blood vessels of the skeleton is relatively well established, the impact of ECs -derived angiocrine factors on bone and cartilage homeostasis is gradually emerging. In this review, we survey ECs - derived angiocrine factors, which are released by endothelial cells of the local microenvironment and by distal organs, and act specifically as regulators of skeletal growth and homeostasis. These may potentially include angiocrine factors with osteogenic property, such as Hedgehog, Notch, WNT, bone morphogenetic protein (BMP), fibroblast growth factor (FGF), insulin-like growth factor (IGF), and platelet-derived growth factor (PDGF). Understanding the versatile mechanisms by which ECs-derived angiocrine factors orchestrate bone and cartilage homeostasis, and pathogenesis, is an important step towards the development of therapeutic potential for skeletal diseases.