Aberrantly activated Wnt/β-catenin pathway co-receptors LRP5 and LRP6 regulate osteoblast differentiation in the developing coronal sutures of an Apert syndrome (Fgfr2S252W /+ ) mouse model

Wnt3a-induced LRP6 phosphorylation enhances osteoblast differentiation to alleviate osteoporosis through activation of mTORC1/β-catenin signaling

OBJECTIVE

Osteoporosis (OP) is a common cause of morbidity and mortality in older individuals. The importance of Wnt3a in osteogenic activity and bone tissue homeostasis is well known. Here, we explored the possible molecular mechanism by which Wnt3a mediates the LRP6/mTORC1/β-catenin axis to regulate osteoblast differentiation in OP.

METHODS

OP-related key genes were identified through a bioinformatics analysis. A ROS17/2.8 cell differentiation system for rat osteogenic progenitors and a rat model of senile OP were constructed for in vitro and in vivo mechanism verification.

RESULTS

Bioinformatics analysis revealed that LRP6 was poorly expressed in OP and may play a key role in the occurrence of OP by affecting osteoblast differentiation. LRP6 knockdown inhibited osteoblast differentiation in an in vitro model. In addition, Wnt3a promoted osteoblast differentiation by inducing LRP6 phosphorylation. Moreover, LRP6 promoted mTORC1 expression, which indirectly promoted β-catenin expression, thus promoting osteoblast differentiation. Finally, an in vivo assay revealed that LRP6 inhibition improved OP.

CONCLUSION

Our study provides evidence that Wnt3a induces phosphorylation of LRP6 to activate the mTORC1/β-catenin axis, thus promoting osteoblast differentiation and ultimately improving OP in aged rats.

Targeting LRP6: A new strategy for cancer therapy

Targeting specific molecular drivers of tumor growth is a key approach in cancer therapy. Among these targets, the low-density lipoprotein receptor-related protein 6 (LRP6), a vital component of the Wnt signaling pathway, has emerged as an intriguing candidate. As a cell-surface receptor and vital co-receptor, LRP6 is frequently overexpressed in various cancer types, implicating its pivotal role in driving tumor progression. The pursuit of LRP6 as a target for cancer treatment has gained substantial traction, offering a promising avenue for therapeutic intervention. Here, this comprehensive review explores recent breakthroughs in our understanding of LRP6's functions and underlying molecular mechanisms, providing a profound discussion of its involvement in cancer pathogenesis and drug resistance. Importantly, we go beyond discussing LRP6's role in cancer by discussing diverse potential therapeutic approaches targeting this enigmatic protein. These approaches encompass a wide spectrum, including pharmacological agents, natural compounds, non-coding RNAs, epigenetic factors, proteins, and peptides that modulate LRP6 expression or disrupt its interactions. In addition, also discussed the challenges associated with developing LRP6 inhibitors and their advantages over Wnt inhibitors, as well as the drugs that have entered phase II clinical trials. By shedding light on these innovative strategies, we aim to underscore LRP6's significance as a valuable and multifaceted target for cancer treatment, igniting enthusiasm for further research and facilitating translation into clinical applications.

MAGP2 promotes osteogenic differentiation during fracture healing through its crosstalk with the β-catenin pathway

Osteogenic differentiation is important for fracture healing. Microfibrial-associated glycoprotein 2 (MAGP2) is found to function as a proangiogenic regulator in bone formation; however, its role in osteogenic differentiation during bone repair is not clear. Here, a mouse model of critical-sized femur fracture was constructed, and the adenovirus expressing MAGP2 was delivered into the fracture site. Mice with MAGP2 overexpression exhibited increased bone mineral density and bone volume fraction (BV/TV) at Day 14 postfracture. Within 7 days postfracture, overexpression of MAGP2 increased collagen I and II expression at the fracture callus, with increasing chondrogenesis. MAGP2 inhibited collagen II level but elevated collagen I by 14 days following fracture, accompanied by increased endochondral bone formation. In mouse osteoblast precursor MC3T3-E1 cells, MAGP2 treatment elevated the expression of osteoblastic factors (osterix, BGLAP and collagen I) and enhanced ALP activity and mineralization through activating β-catenin signaling after osteogenic induction. Besides, MAGP2 could interact with lipoprotein receptor-related protein 5 (LRP5) and upregulated its expression. Promotion of osteogenic differentiation and β-catenin activation mediated by MAGP2 was partially reversed by LRP5 knockdown. Interestingly, β-catenin/transcription factor 4 (TCF4) increased MAGP2 expression probably by binding to MAGP2 promoter. These findings suggest that MAGP2 may interact with β-catenin/TCF4 to enhance β-catenin/TCF4's function and activate LRP5-activated β-catenin signaling pathway, thus promoting osteogenic differentiation for fracture repair. mRNA sequencing identified the potential targets of MAGP2, providing novel insights into MAGP2 function and the directions for future research.

Exosome-mediated small interfering RNA delivery inhibits aberrant osteoblast differentiation in Apert syndrome model mice

OBJECTIVE

Apert syndrome, an autosomal dominant congenital disorder characterized by craniosynostosis, is caused by a missense mutation (S252W or P253R) in fibroblast growth factor receptor 2 (FGFR2). Exosomes are naturally occurring carriers that deliver nucleic acids, including small interfering RNA (siRNA), to induce gene silencing. This study aimed to develop siRNA-loaded exosomes (Ex-siRNA^Fgfr2S252W) to silence the Fgfr2^S252W gain-of-function mutation, thereby inhibiting the increased osteoblastic differentiation caused by the constitutive activation of FGFR2 signaling in calvarial osteoblastic cells isolated from Apert syndrome model mice.

DESIGN

Primary calvarial osteoblast-like cells were isolated from the embryonic calvarial sutures of the Apert syndrome model (Fgfr2^S252W/+) and littermate wild-type mice (Ap-Ob and Wt-Ob, respectively). Exosomes were extracted from the serum of wild-type mice, validated using biomarkers, and used to encapsulate siRNAs. After exosome-mediated siRNA transfection, cells were analyzed under a fluorescence microscope to validate the delivery of Ex-siRNA^Fgfr2S252W, followed by western blot and real-time reverse transcription polymerase chain reaction analyses.

RESULTS

After 24 h of Ex-siRNA^Fgfr2S252W delivery in both Ap-Ob and Wt-Ob, siRNA-loaded exosome delivery was validated. Moreover, p44/42 mitogen-activated protein kinase (MAPK) phosphorylation, runt-related transcription factor 2 (Runx2), and collagen type 1 alpha 1 (Col1a1) mRNA expression, and alkaline phosphatase (ALP) activity were significantly increased in Ap-Ob. The levels of phospho-p44/42 protein, Runx2, Col1a1, and ALP were significantly decreased after Ex-siRNA^Fgfr2S252W transfection but did not affect Wt-Ob.

CONCLUSIONS

These results indicate that exosome-mediated delivery of siRNA targeting Fgfr2^S252W is a potential non-invasive treatment for aberrant FGF/FGFR signaling.

FGF signaling in cranial suture development and related diseases

Suture mesenchymal stem cells (SMSCs) are a heterogeneous stem cell population with the ability to self-renew and differentiate into multiple cell lineages. The cranial suture provides a niche for SMSCs to maintain suture patency, allowing for cranial bone repair and regeneration. In addition, the cranial suture functions as an intramembranous bone growth site during craniofacial bone development. Defects in suture development have been implicated in various congenital diseases, such as sutural agenesis and craniosynostosis. However, it remains largely unknown how intricate signaling pathways orchestrate suture and SMSC function in craniofacial bone development, homeostasis, repair and diseases. Studies in patients with syndromic craniosynostosis identified fibroblast growth factor (FGF) signaling as an important signaling pathway that regulates cranial vault development. A series of in vitro and in vivo studies have since revealed the critical roles of FGF signaling in SMSCs, cranial suture and cranial skeleton development, and the pathogenesis of related diseases. Here, we summarize the characteristics of cranial sutures and SMSCs, and the important functions of the FGF signaling pathway in SMSC and cranial suture development as well as diseases caused by suture dysfunction. We also discuss emerging current and future studies of signaling regulation in SMSCs.

mTOR is involved in LRP5-induced osteogenic differentiation of normal and aged periodontal ligament stem cells in vitro

Periodontal ligament stem cells (PDLSCs) plays an important role in tissue engineering. As the age increased, the cell viability and osteogenic differentiation of PDLSCs all decreased. Low density lipoprotein receptor related protein 5 (LRP5) was found to promote bone marrow mesenchymal stem cells osteogenic differentiation. Therefore, our study explored the effect of LRP5 on normal and aged PDLSCs and relative mechanism. Here, we found that the expression of LRP5 in PDLSCs of 24 week-old mice was decreased compared with PDLSCs of 5 week-old mice (n = 5). . LRP5 overexpression in PDLSCs increased the intensity of alkaline phosphatase and alizarin red staining, accompanied with upregulated the levels of RUNX family transcription factor 2, collagen type I, and β-Catenin. LRP5 knockdown displayed the opposite results in PDLSCs in vitro. LRP5 overexpression in aged PDLSCs restored part ability of osteogenic differentiation. Meantime, LRP5 increased the protein expression of phosphorylation of mammalian target of rapamycin (p-mTOR) in normal and aged PDLSCs. Immunofluorescence showed that LRP5 increased the accumulation of p-mTOR nucleus. The effect of LRP5 in promoting osteogenic differentiation of PDLSCs can be antagonized by mTOR inhibitor rapamycin. These findings suggest that LRP5 positively regulate osteogenic differentiation of normal and aged PDLSCs and may be a potential target for enlarging the application of PDLSCs in tissue regeneration.

Craniofacial sutures: Signaling centres integrating mechanosensation, cell signaling, and cell differentiation

Cranial sutures are dynamic structures in which stem cell biology, bone formation, and mechanical forces interface, influencing the shape of the skull throughout development and beyond. Over the past decade, there has been significant progress in understanding mesenchymal stromal cell (MSC) differentiation in the context of suture development and genetic control of suture pathologies, such as craniosynostosis. More recently, the mechanosensory function of sutures and the influence of mechanical signals on craniofacial development have come to the forefront. There is currently a gap in understanding of how mechanical signals integrate with MSC differentiation and ossification to ensure appropriate bone development and mediate postnatal growth surrounding sutures. In this review, we discuss the role of mechanosensation in the context of cranial sutures, and how mechanical stimuli are converted to biochemical signals influencing bone growth, suture patency, and fusion through mediation of cell differentiation. We integrate key knowledge from other paradigms where mechanosensation forms a critical component, such as bone remodeling and orthodontic tooth movement. The current state of the field regarding genetic, cellular, and physiological mechanisms of mechanotransduction will be contextualized within suture biology.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Cyclic Mechanical Strain Regulates Osteoblastic Differentiation of Mesenchymal Stem Cells on TiO2 Nanotubes Through GCN5 and Wnt/β-Catenin

Bone marrow mesenchymal stem cells (BMSCs) play a critical role in bone formation and are extremely sensitive to external mechanical stimuli. Mechanical signals can regulate the biological behavior of cells on the surface of titanium-related prostheses and inducing osteogenic differentiation of BMSCs, which provides the integration of host bone and prosthesis benefits. But the mechanism is still unclear. In this study, BMSCs planted on the surface of TiO₂ nanotubes were subjected to cyclic mechanical stress, and the related mechanisms were explored. The results of alkaline phosphatase staining, real-time PCR, and Western blot showed that cyclic mechanical stress can regulate the expression level of osteogenic differentiation markers in BMSCs on the surface of TiO₂ nanotubes through Wnt/β-catenin. As an important member of the histone acetyltransferase family, GCN5 exerted regulatory effects on receiving mechanical signals. The results of the ChIP assay indicated that GCN5 could activate the Wnt promoter region. Hence, we concluded that the osteogenic differentiation ability of BMSCs on the surface of TiO₂ nanotubes was enhanced under the stimulation of cyclic mechanical stress, and GCN5 mediated this process through Wnt/β-catenin.

[Activation of mir-30a-wnt/β-catenin signaling pathway upregulates cathepsin K expression to promote cementogenic differentiation of periodontal ligament stem cells]

OBJECTIVE

To explore the role of cathepsin K (CTSK) regulated by mir-30a-wnt/β-catenin signaling pathway in cementogenic differentiation of periodontal ligament stem cells (PDLSCs).

METHODS

Human PDLSCs isolated by limiting dilution culture were induced by enamel matrix protein derivative (EMD) for differentiation into cementoblast-like cells. MicroRNA chip technique was employed to screen the differentially expressed microRNAs in the cells during induced differentiation. The effect of inhibiting miR-30a on CTSK expression in the induced cells was examined using RT-PCR and Western blotting. Ceramic scaffolds coated with PDLSCs treated with EMD and transfected with the miR-30a inhibitor or a lentiviral vector for CTSK overexpression were prepared and implanted subcutaneously in nude mice, and 8 weeks later the cellular expressions of cementoblast markers CAP and CEMP-1 were detected with immunohistochemistry to verify whether CTSK participate in cementogenic differentiation of PDLSCs. The role of wnt signaling pathway in miR-30a-mediated regulation of CTSK expression was explored by examining CTSK protein expressions after blocking wnt signaling in PDLSCs.

RESULTS

In PDLSCs with EMD-induced differentiation into cementoblast-like cells, multiple microRNAs exhibited differential expressions; and among them, miR-30a was specifically and significantly up-regulated (P < 0.05). Up-regulation of miR-30a obviously increased the expression of CTSK (P < 0.05) and promoted PDLSCs to form cementum-like tissues with high expressions of CAP and CEMP-1. The regulatory effect of miR-30a on CTSK expression was obviously attenuated after inhibiting wnt/β-catenin signaling pathway.

CONCLUSION

EMD induces cementogenic differentiation of PDLSCs possibly by up-regulating the expression of miR-30a, which further activates the wnt/β-catenin signaling pathway to enhance the expression of CTSK.