MICROmanagement of Runx2 Function in Skeletal Cells

Identification of circulating miRNAs as fracture-related biomarkers

Fracture non-unions affect many patients worldwide, however, known risk factors alone do not predict individual risk. The identification of novel biomarkers is crucial for early diagnosis and timely patient treatment. This study focused on the identification of microRNA (miRNA) related to the process of fracture healing. Serum of fracture patients and healthy volunteers was screened by RNA sequencing to identify differentially expressed miRNA at various times after injury. The results were correlated to miRNA in the conditioned medium of human bone marrow mesenchymal stromal cells (BMSCs) during in vitro osteogenic differentiation. hsa-miR-1246, hsa-miR-335-5p, and miR-193a-5p were identified both in vitro and in fracture patients and their functional role in direct BMSC osteogenic differentiation was assessed. The results showed no influence of the downregulation of the three miRNAs during in vitro osteogenesis. However, miR-1246 may be involved in cell proliferation and recruitment of progenitor cells. Further studies should be performed to assess the role of these miRNA in other processes relevant to fracture healing.

Runx2 and Polycystins in Bone Mechanotransduction: Challenges for Therapeutic Opportunities

Bone mechanotransduction is a critical process during skeletal development in embryogenesis and organogenesis. At the same time, the type and level of mechanical loading regulates bone remodeling throughout the adult life. The aberrant mechanosensing of bone cells has been implicated in the development and progression of bone loss disorders, but also in the bone-specific aspect of other clinical entities, such as the tumorigenesis of solid organs. Novel treatment options have come into sight that exploit the mechanosensitivity of osteoblasts, osteocytes, and chondrocytes to achieve efficient bone regeneration. In this regard, runt-related transcription factor 2 (Runx2) has emerged as a chief skeletal-specific molecule of differentiation, which is prominent to induction by mechanical stimuli. Polycystins represent a family of mechanosensitive proteins that interact with Runx2 in mechano-induced signaling cascades and foster the regulation of alternative effectors of mechanotransuction. In the present narrative review, we employed a PubMed search to extract the literature concerning Runx2, polycystins, and their association from 2000 to March 2024. The keywords stated below were used for the article search. We discuss recent advances regarding the implication of Runx2 and polycystins in bone remodeling and regeneration and elaborate on the targeting strategies that may potentially be applied for the treatment of patients with bone loss diseases.

The Role and Mechanism of MicroRNA 21 in Osteogenesis: An Update

MicroRNAs are short, single-stranded ribonucleic acids expressed endogenously in the body to regulate gene expression at the post-translational level, with exogenous microRNA offering an attractive approach to therapy. Among the myriad microRNA candidates involved in controlling bone homeostasis and remodeling, microRNA 21 (miR21) is the most abundant. This paper discusses the studies conducted on the role and mechanism of human miR21 (hsa-miR21) in the regulation of bones and the various pathways mediated by miR21, and explores the feasibility of employing exogenous miR21 as a strategy for promoting osteogenesis. From the literature review, it was clear that miR21 plays a dual role in bone metabolism by regulating both bone formation and bone resorption. There is substantial evidence to date from both in vitro and in vivo studies that exogenous miR21 can successfully accelerate new bone synthesis in the context of bone loss due to injury or osteoporosis. This supports the exploration of applications of exogenous miR21 in bone regenerative therapy in the future.

3D printed biocompatible graphene oxide, attapulgite, and collagen composite scaffolds for bone regeneration

Tissue-engineered bone material is one of the effective methods to repair bone defects, but the application is restricted in clinical because of the lack of excellent scaffolds that can induce bone regeneration as well as the difficulty in making scaffolds with personalized structures. 3D printing is an emerging technology that can fabricate bespoke 3D scaffolds with precise structure. However, it is challenging to develop the scaffold materials with excellent printability, osteogenesis ability, and mechanical strength. In this study, graphene oxide (GO), attapulgite (ATP), type I collagen (Col I) and polyvinyl alcohol were used as raw materials to prepare composite scaffolds via 3D bioprinting. The composite materials showed excellent printability. The microcosmic architecture and properties was characterized by scanning electron microscopy, Fourier transform infrared and thermal gravimetric analyzer, respectively. To verify the biocompatibility of the scaffolds, the viability, proliferation and osteogenic differentiation of Bone Marrow Stromal Cells (BMSCs) on the scaffolds were assessed by CCK-8, Live/Dead staining and Real-time PCR in vitro. The composited scaffolds were then implanted into the skull defects on rat for bone regeneration. Hematoxylin-eosin staining, Masson staining and immunohistochemistry staining were carried out in vivo to evaluate the regeneration of bone tissue.The results showed that GO/ATP/COL scaffolds have been demonstrated to possess controlled porosity, water absorption, biodegradability and good apatite-mineralization ability. The scaffold consisting of 0.5% GO/ATP/COL have excellent biocompatibility and was able to promote the growth, proliferation and osteogenic differentiation of mouse BMSCs in vitro. Furthermore, the 0.5% GO/ATP/COL scaffolds were also able to promote bone regeneration of in rat skull defects. Our results illustrated that the 3D printed GO/ATP/COL composite scaffolds have good mechanical properties, excellent cytocompatibility for enhanced mouse BMSCs adhesion, proliferation, and osteogenic differentiation. All these advantages made it potential as a promising biomaterial for osteogenic reconstruction.

The genetic and epigenetic contributions to the development of nutritional rickets

Nutritional rickets is an important disease in global health. Although nutritional rickets commonly manifests as bony deformities, there is an increased risk of life-threatening seizures secondary to hypocalcaemia. Dietary vitamin D deficiency is associated with the development of nutritional rickets among children and infants. This is especially true in populations of darker skinned individuals in high-latitude environments due to decreased ultraviolet light exposure, and in populations in tropical and subtropical climates due to cultural practices. A growing body of evidence has demonstrated that genetic factors might influence the likelihood of developing nutritional rickets by influencing an individual's susceptibility to develop deficiencies in vitamin D and/or calcium. This evidence has been drawn from a variety of different techniques ranging from traditional twin studies to next generation sequencing techniques. Additionally, the role of the epigenome in the development of rickets, although poorly understood, may be related to the effects of DNA methylation and non-coding RNAs on genes involved in bone metabolism. This review aims to provide an overview of the current evidence that investigates the genetic and epigenetic determinants of nutritional rickets.

Nobiletin promotes osteogenic differentiation of human osteoblastic cell line (MG-63) through activating the BMP-2/RUNX-2 signaling pathway

Nobiletin (NOB) is polymethoxy flavonoids, which plentifully there in Citrus depressa and they demonstrate numerous pharmacological effects. NOB has an anti-proliferative effect, attenuates ovalbumin-treated eosinophilic airway inflammation and Type II collagen treated arthritis. NOB noticeably inhibits bone resorption and renovates bone loss in mice model, but role of NOB in bone metabolism is unclear. Human bone is a important organ that sustains its homeostasis among bone resorpting osteoclasts and bone developing osteoblasts. The balances of among these two kind of cell outcomes are implicated in bone remodeling. The current study designed to explore possessions of NOB on differentiation and proliferation of MG-63 cells and contribution of morphogenetic protein signaling. Cell proliferation was analyzed by MTT, mineralization analysis by alizarin red staining and morphogenetic signaling protein by RT-PCR. No stimulus outcome of NOB on cell proliferation was found at days of 1, 3 and 7. Accumulation of calcium was augmented after that treatment of NOB. The mRNA expression of BMP-2, COL-I, ALP, OCN, RUNX2 and COL1A1 augmented markedly with NOB supplement. Hence, NOB can stimulate osteogenic differentiation of MG-63, almost certainly by promoting RUNX2 and BMP-2 signaling and this result might provide to its action on stimulation of osteoblast development, differentiation and augments of bone mass.

The Signalling Effects of Photobiomodulation on Osteoblast Proliferation, Maturation and Differentiation: A Review

Proliferation of osteoblasts is essential for maturation and mineralization of bone matrix. Ossification, the natural phase of bone-forming and hardening is a carefully regulated phase where deregulation of this process may result in insufficient or excessive bone mineralization or ectopic calcification. Osteoblasts can also be differentiated into osteocytes, populating short interconnecting passages within the bone matrix. Over the past few decades, we have seen a significant improvement in awareness and techniques using photobiomodulation (PBM) to stimulate cell function. One of the applications of PBM is the promotion of osteoblast proliferation and maturation. PBM research results on osteoblasts showed increased mitochondrial ATP production, increased osteoblast activity and proliferation, increased and pro-osteoblast expression in the presence of red and NIR radiation. Osteocyte differentiation was also accomplished using blue and green light, showing that different light parameters have various signalling effects. The current review addresses osteoblast function and control, a new understanding of PBM on osteoblasts and its therapeutic impact using various parameters to optimize osteoblast function that may be clinically important. Graphical Abstract.

Baf45a Mediated Chromatin Remodeling Promotes Transcriptional Activation for Osteogenesis and Odontogenesis

Chromatin remodeling, specifically the tissue-specific regulation in mineralized tissues, is an understudied avenue of gene regulation. Here we show that Baf45a and Baf45d, two Baf45 homologs belong to ATPase-dependent SWI/SNF chromatin remodeling complex, preferentially expressed in osteoblasts and odontoblasts compared to Baf45b and Baf45c. Recently, biochemical studies revealed that BAF45A associates with Polybromo-associated BAF (PBAF) complex. However, the BAF45D subunit belongs to the polymorphic canonical BRG1-associated factor (cBAF) complex. Protein profiles of osteoblast and odontoblast differentiation uncovered a significant increase of BAF45A and PBAF subunits during early osteoblast and odontoblast maturation. Chromatin immunoprecipitation sequencing (ChIP-seq) during the bone marrow stromal cells (BMSCs) differentiation showed higher histone H3K9 and H3K27 acetylation modifications in the promoter of Baf45a and Baf45d and increased binding of bone and tooth specific transcription factor RUNX2. Overexpression of Baf45a in osteoblasts activates genes essential for the progression of osteoblast maturation and mineralization. Furthermore, shRNA-mediated knockdown of Baf45a in odontoblasts leads to markedly altered genes responsible for the proliferation, apoptosis, DNA repair, and modest decrease in dentinogenic marker gene expression. Assay for Transposase-Accessible Chromatin sequencing (ATAC-seq) assay in Baf45a knockout osteoblasts revealed a noticeable reduction in chromatin accessibility of osteoblast and odontoblast specific genes, along with transcription factor Atf4 and Klf4. Craniofacial mesenchyme-specific loss of Baf45a modestly reduced the mineralization of the tooth and mandibular bone. These findings indicated that BAF45A-dependent mineralized tissue-specific chromatin remodeling through PBAF-RUNX2 crosstalk results in transcriptional activation is critical for early differentiation and matrix maturation of mineralized tissues.