Role of c-Myb in chondrogenesis

Integrated analysis of single-cell and bulk RNA sequencing data identifies the characteristics of ferroptosis in lumbar disc herniation

Lumbar disc herniation (LDH) is the most common condition associated with low back pain, and it adversely impacts individuals' health. Ferroptosis has recently emerged as a novel factor in the pathogenesis of LDH; however, the specific impacts of ferroptosis on LDH have not been fully elucidated. Ferroptosis-related differentially expressed genes (FRDEGs) were identified from the transcriptomic datasets of LDH. Gene set enrichment analysis (GSEA) was conducted to identify biological mechanism and related pathways. LASSO and SVM-RFE algorithms were applied to detect signature genes. Function of the signature gene was confirmed by RT-qPCR. The CIBERSORT algorithm was used to compare immune infiltration between LDH and normal samples. Correlation analysis between MYB and immune cells was analyzed using the Pearson method. Additionally, we used scRNA-seq to dissect cell clusters and cellular interactions. AUCell scoring was used to analyze the ferroptosis scores of different cell types. We found that MYB, a highly expressed ferroptosis-related gene, was associated with LDH By leveraging bioinformatics analysis. In immune infiltration analysis, the abundance of monocytes and macrophages varied significantly between the LDH group and disc spondylolisthesis (DS) group. MYB was correlated with most immune cells. GSEA revealed MYB was significantly enriched in immune-related pathways. Furthermore, scRNA-seq analysis revealed the presence of eight distinct cell types. AUCell analysis showed that macrophages had a high ferroptosis score. Cell trajectory analysis revealed that chondrocyte 1 was at the beginning of the trajectory, while calcification inhibiting chondrocytes and fibrochondrocytes accumulated along the middle and tail end of the trajectory, respectively. Cell-cell communication analysis identified chondrocyte 1 had an extensive communication network with other clusters and interacted with nucleus pulposus through collagen signaling pathway. Our analysis demonstrated that MYB may be a potential therapeutic target for LDH. This study provides a resource for the orthopedics community that will facilitate additional discoveries directedly toward understanding the pathogenesis process of LDH.

Expression dynamics of metalloproteinases during mandibular bone formation: association with Myb transcription factor

As the dentition forms and becomes functional, the alveolar bone is remodelled. Metalloproteinases are known to contribute to this process, but new regulators are emerging and their contextualization is challenging. This applies to Myb, a transcription factor recently reported to be involved in bone development and regeneration. The regulatory effect of Myb on Mmps expression has mostly been investigated in tumorigenesis, where Myb impacted the expression of Mmp1, Mmp2, Mmp7, and Mmp9. The aim of this investigation was to evaluate the regulatory influence of the Myb on Mmps gene expression, impacting osteogenesis and mandibular bone formation. For that purpose, knock-out mouse model was used. Gene expression of bone-related Mmps and the key osteoblastic transcription factors Runx2 and Sp7 was analysed in Myb knock-out mice mandibles at the survival limit. Out of the metalloproteinases under study, Mmp13 was significantly downregulated. The impact of Myb on the expression of Mmp13 was confirmed by the overexpression of Myb in calvarial-derived cells causing upregulation of Mmp13. Expression of Mmp13 in the context of other Mmps during mandibular/alveolar bone development was followed in vivo along with Myb, Sp7 and Runx2. The most significant changes were observed in the expression of Mmp9 and Mmp13. These MMPs and MYB were further localized in situ by immunohistochemistry and were identified in pre/osteoblastic cells as well as in pre/osteocytes. In conclusion, these results provide a comprehensive insight into the expression dynamics of bone related Mmps during mandibular/alveolar bone formation and point to Myb as another potential regulator of Mmp13.

Sex-determining region Y (SRY) attributes to gender differences in RANKL expression and incidence of osteoporosis

Receptor activator of nuclear factor κB ligand (RANKL) plays a crucial role in bone metabolism. RANKL gene misregulation has been implicated in several bone and cancer diseases. Here, we aimed to identify novel transcription regulators of RANKL expression. We discovered that transcription factors, sex-determining region Y (SRY) and c-Myb, regulate RANKL expression. We demonstrated that c-Myb increases and male-specific SRY decreases RANKL expression through direct binding to its 5’-proximal promoter. These results are corroborated by the gene expression in human bone samples. In osteoporotic men, expression of RANKL is 17-fold higher, which correlates with the drastically reduced expression (200-fold) of Sry, suggesting that in osteoporotic men, the upregulation of RANKL is caused by a decrease of Sry. In healthy men, the expression of RANKL is 20% higher than that in healthy women. Our data suggest that gender differences in RANKL expression and bone quality could be due to the sex-specific transcription factor SRY.

A male-specific gene offers clues to diagnosis and treatment of age-related osteoporosis. Osteoporosis was known to be linked to higher expression levels of RANKL, a gene that induces bone resorption, but the details were poorly understood. Nika Lovsin at the University of Ljubljana in Slovenia and co-workers searched for the genetic switches that control RANKL levels. They found that SRY, a gene on the male-specific Y chromosome, was a strong repressor of RANKL. In bone samples from osteoporotic men, expression levels of SRY levels were low and those of RANKL were high, suggesting that in men, when SRY fails to keep the bone-resorbing RANKL in check, osteoporosis results. SRY shows promise as an osteoporosis marker in men, or for development of treatment for both genders. Future research could address what triggers decreased SRY expression in men.

Reactive Oxygen Species Mediate Therapeutic Ultrasound-Induced, Mitogen-Activated Protein Kinase Activation in C28/I2 Chondrocytes

Low-intensity pulsed ultrasound (LIPUS) has been used for the treatment of non-healing fractures because of its therapeutic properties of stimulating enhancing endochondral bone formation. However, its mechanism of action remains unclear. In this study, we hypothesized that LIPUS activates mitogen-activated protein kinases through generation of reactive oxygen species. C28/I2 cells were stimulated with LIPUS for 10 and 20 min, while the control group was treated using a sham LIPUS transducer. Through quantitative reverse transcription polymerase chain reaction and immunoblot analyses, we determined that LIPUS application increased reactive oxygen species generation and cell viability in C28/I2 cells. There were increases in the phosphorylation level of ERK1/2 and in expression of SOX9, COL2 A1 and ACAN genes. These effects were reversed when cells were treated with diphenylene iodonium, which is known to inhibit NADPH oxidase. It was concluded that exposure of chondrocytes to LIPUS led to reactive oxygen species generation, which activated MAPK signaling and further increased chondrocyte-specific gene markers involved in chondrocyte differentiation and extracellular matrix formation.

Osteogenic Potential of the Transcription Factor c-MYB

The transcription factor c-MYB is a well-known marker of undifferentiated cells such as haematopoietic cell precursors, but recently it has also been observed in differentiated cells that produce hard tissues. Our previous findings showed the presence of c-MYB in intramembranous bones and its involvement in the chondrogenic steps of endochondral ossification, where the up-regulation of early chondrogenic markers after c-myb overexpression was observed. Since we previously detected c-MYB in osteoblasts, we aimed to analyse the localisation of c-MYB during later stages of endochondral bone formation and address its function during bone matrix production. c-MYB-positive cells were found in the chondro-osseous junction zone in osteoblasts of trabecular bone as well as deeper in the zone of ossification in cells of spongy bone. To experimentally evaluate the osteogenic potential of c-MYB during endochondral bone formation, micromasses derived from embryonic mouse limb buds were established. Nuclear c-MYB protein expression was observed in long-term micromasses, especially in the areas around nodules. c-myb overexpression induced the expression of osteogenic-related genes such as Bmp2, Comp, Csf2 and Itgb1. Moreover, alizarin red staining and osteocalcin labelling promoted mineralised matrix production in c-myb-overexpressing cultures, whereas downregulation of c-myb by siRNA reduced mineralised matrix production. In conclusion, c-Myb plays a role in the osteogenesis of long bones by inducing osteogenic genes and causing the enhancement of mineral matrix production. This action of the transcription factor c-Myb might be of interest in the future for the establishment of novel approaches to tissue regeneration.

Methionine restriction alters bone morphology and affects osteoblast differentiation

Methionine restriction (MR) extends the lifespan of a wide variety of species, including rodents, drosophila, nematodes, and yeasts. MR has also been demonstrated to affect the overall growth of mice and rats. The objective of this study was to evaluate the effect of MR on bone structure in young and aged male and female C57BL/6J mice. This study indicated that MR affected the growth rates of males and young females, but not aged females. MR reduced volumetric bone mass density (vBMD) and bone mineral content (BMC), while bone microarchitecture parameters were decreased in males and young females, but not in aged females compared to control-fed (CF) mice. However, when adjusted for bodyweight, the effect of MR in reducing vBMD, BMC and microarchitecture measurements was either attenuated or reversed suggesting that the smaller bones in MR mice is appropriate for its body size. In addition, CF and MR mice had similar intrinsic strength properties as measured by nanoindentation. Plasma biomarkers suggested that the low bone mass in MR mice could be due to increased collagen degradation, which may be influenced by leptin, IGF-1, adiponectin and FGF21 hormone levels. Mouse preosteoblast cell line cultured under low sulfur amino acid growth media attenuated gene expression levels of Col1al, Runx2, Bglap, Alpl and Spp1 suggesting delayed collagen formation and bone differentiation. Collectively, our studies revealed that MR altered bone morphology which could be mediated by delays in osteoblast differentiation.

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MR affected the growth rates of males and young females, but not aged females.

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CF and MR mice had similar intrinsic strength properties.

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Low methionine media attenuated bone differentiation genes in MC3T3-E1 preosteoblast cells.

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The lower bone mass in MR mice is appropriate for its smaller body size.