BMP9 prevents induction of osteopontin in JNK-inactivated osteoblasts via Hey1-Id4 interaction

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

Histological evaluation of the effects of bone morphogenetic protein 9 and angiopoietin 1 on bone healing

Objectives

Bone healing remains a critical clinical orthopedic problem. Bone, which is a greatly vascularized tissue, depends on the tight temporal and spatial link between blood vessels and bone cells. Thus, angiogenesis is crucial for skeletal growth and bone fracture healing. The purpose of this study was to evaluate the efficacy of the local application of osteogenic and angiogenic factors such as bone morphogenetic protein 9 (BMP9) and angiopoietin 1 (Ang1), respectively, and their combination as an osteoinducer in the process of bone healing.

Methods

Forty-eight male albino rats, weighing 300-400 g and aged 6-8 months, were utilized in this study. The animals underwent surgery on the medial side of the tibia bone. In the control group, an absorbable hemostatic sponge was locally applied to the bone defect, while experimental groups were separated into three groups. In Group I, 1 mg BMP9 was locally applied, Group II was treated with 1 mg Ang1, and Group III was treated with local application of a combination (0.5 mg BMP9 and 0.5 mg Ang1). All experimental groups were fixed with an absorbable hemostatic sponge. The rats were sacrificed on days 14 and 28 after surgery.

Results

Local application of BMP9 alone, Ang1 alone, and their combination to a tibia defect caused osteoid tissue formation and significantly increased the number of bone cells. A gradual decrease in the number of trabecular bone, an increase in trabecular area, and no significant difference in the bone marrow area were noted.

Conclusion

The combination of BMP9 and Ang1 has therapeutic potential in promoting the healing process of bone defects. Osteogenesis and angiogenesis are regulated by BMP9 and Ang1. These factors act together to accelerate bone regeneration more efficiently than either factor alone.

Early induction of Hes1 by bone morphogenetic protein 9 plays a regulatory role in osteoblastic differentiation of a mesenchymal stem cell line

Bone morphogenic protein 9 (BMP9) is one of the most potent inducers of osteogenic differentiation among the 14 BMP members, but its mechanism of action has not been fully demonstrated. Hes1 is a transcriptional regulator with basic helix-loop-helix (bHLH) domain and is a well-known Notch effector. In this study, we investigated the functional roles of early induction of Hes1 by BMP9 in a mouse mesenchymal stem cell line, ST2. Hes1 mRNA was transiently and periodically induced by BMP9 in ST2, which was inhibited by BMP signal inhibitors but not by Notch inhibitor. Interestingly, Hes1 knockdown in ST2 by siRNA increased the expression of osteogenic differentiation markers such as Sp7 and Ibsp and matrix mineralization in comparison with control siRNA transfected ST2. In contrast, forced expression of Hes1 by using the Tet-On system suppressed the expression of osteogenic markers and matrix mineralization by BMP9. We also found that the early induction of Hes1 by BMP9 suppressed the expression of Alk1, an essential receptor for BMP9. In conclusion, BMP9 rapidly induces the expression of Hes1 via the SMAD pathway in ST2 cells, which plays a negative regulatory role in osteogenic differentiation of mesenchymal stem cells induced by BMP9.

Application of BMP in Bone Tissue Engineering

At present, bone nonunion and delayed union are still difficult problems in orthopaedics. Since the discovery of bone morphogenetic protein (BMP), it has been widely used in various studies due to its powerful role in promoting osteogenesis and chondrogenesis. Current results show that BMPs can promote healing of bone defects and reduce the occurrence of complications. However, the mechanism of BMP in vivo still needs to be explored, and application of BMP alone to a bone defect site cannot achieve good therapeutic effects. It is particularly important to modify implants to carry BMP to achieve slow and sustained release effects by taking advantage of the nature of the implant. This review aims to explain the mechanism of BMP action in vivo, its biological function, and how BMP can be applied to orthopaedic implants to effectively stimulate bone healing in the long term. Notably, implantation of a system that allows sustained release of BMP can provide an effective method to treat bone nonunion and delayed bone healing in the clinic.

Blood protein profiles related to preterm birth and retinopathy of prematurity

BACKGROUND

Nearly one in ten children is born preterm. The degree of immaturity is a determinant of the infant's health. Extremely preterm infants have higher morbidity and mortality than term infants. One disease affecting extremely preterm infants is retinopathy of prematurity (ROP), a multifactorial neurovascular disease that can lead to retinal detachment and blindness. The advances in omics technology have opened up possibilities to study protein expressions thoroughly with clinical accuracy, here used to increase the understanding of protein expression in relation to immaturity and ROP.

METHODS

Longitudinal serum protein profiles the first months after birth in 14 extremely preterm infants were integrated with perinatal and ROP data. In total, 448 unique protein targets were analyzed using Proximity Extension Assays.

RESULTS

We found 20 serum proteins associated with gestational age and/or ROP functioning within mainly angiogenesis, hematopoiesis, bone regulation, immune function, and lipid metabolism. Infants with severe ROP had persistent lower levels of several identified proteins during the first postnatal months.

CONCLUSIONS

The study contributes to the understanding of the relationship between longitudinal serum protein levels and immaturity and abnormal retinal neurovascular development. This is essential for understanding pathophysiological mechanisms and to optimize diagnosis, treatment and prevention for ROP.

IMPACT

Longitudinal protein profiles of 14 extremely preterm infants were analyzed using a novel multiplex protein analysis platform combined with perinatal data. Proteins associated with gestational age at birth and the neurovascular disease ROP were identified. Among infants with ROP, longitudinal levels of the identified proteins remained largely unchanged during the first postnatal months. The main functions of the proteins identified were angiogenesis, hematopoiesis, immune function, bone regulation, lipid metabolism, and central nervous system development. The study contributes to the understanding of longitudinal serum protein patterns related to gestational age and their association with abnormal retinal neuro-vascular development.

Bone morphogenetic protein 9 (BMP9) directly induces Notch effector molecule Hes1 through the SMAD signaling pathway in osteoblasts

Bone morphogenetic protein (BMP) 9 is one of the most osteogenic BMPs, but its mechanism of action has not been fully elucidated. Hes1, a transcriptional regulator with a basic helix-loop-helix domain, is a well-known effector of Notch signaling. Here, we find that BMP9 induces periodic increases of Hes1 mRNA and protein expression in osteoblasts, presumably through an autocrine negative feedback mechanism. BMP9-mediated Hes1 induction is significantly inhibited by an ALK inhibitor and overexpression of Smad7, an inhibitory Smad. Luciferase and ChIP assays revealed that two Smad-binding sites in the 5' upstream region of the mouse Hes1 gene are essential for transcriptional activation by BMP9. Thus, our data indicate that BMP9 induces Hes1 expression in osteoblasts via the Smad signaling pathway.