ETV2 promotes osteogenic differentiation of human dental pulp stem cells through the ERK/MAPK and PI3K-Akt signaling pathways

Human platelet lysate enhances small lipid droplet accumulation of human MSCs through MAPK phosphorylation

BACKGROUND

Human platelet lysate (hPL) has emerged as a promising serum substitute to enhance the self-renewal and multipotency of human mesenchymal stem cells (MSCs). Despite its potential, the specific biological mechanisms by which hPL influences MSC phenotypes remain inadequately understood.

METHODS

We investigated the biological signaling activated by hPL in two common types of human MSCs: bone marrow-derived MSCs (BMSCs) and adipose-derived MSCs (ASCs). Cell adhesion and cell-matrix interaction were assessed through immunofluorescence staining and western blotting. The impact of hPL on lipid droplet formation in MSCs was thoroughly examined using oil red O/BODIPY staining, semi-quantitative analysis, and qRT-PCR. RNA sequencing and intracellular inhibition assays were also performed to elucidate the mechanisms by which hPL modulates MSC behavior.

RESULTS

MSCs cultured in hPL medium demonstrated a reduction in cell size, spreading area, and vinculin puncta,  while enhancing cell proliferation and lipid droplet accumulation compared to those cultured in control media. Notably, the lipid droplets in hPL-treated MSCs were significantly smaller than those in adipocyte-like cells differentiated from MSCs, highlighting hPL's distinctive role in lipid production. Gene and protein expression profiles of hPL-treated MSCs differed from those in adipocyte-like cells. An angiogenic factor array revealed that hPL-MSCs had a distinct angiogenic factor profile compared to FBS-MSCs, with VEGF expression closely linked to HIF-1α expression. RNA-seq data identified approximately 1,900 differentially expressed genes (DEGs) between hPL-MSCs and FBS-MSCs, with enrichment in focal adhesion, ECM-receptor interaction, and PI3K-Akt/MAPK signaling pathways. Inhibition of MAPK phosphorylation significantly hampered lipid formation in hPL-MSCs, underscoring the pivotal role of MAPK signaling in hPL-driven adipogenesis.

CONCLUSION

This study reveals the biological mechanisms by which hPL infleunces MSC behavior and differentiation, offering new insights into its potential application in regenerative medicine and tissue engineering.

Manipulation of signaling pathways in bone tissue engineering and regenerative medicine: Current knowledge, novel strategies, and future directions

During osteogenesis, a large number of bioactive molecules, macromolecules, cells, and cellular signals are activated to induce bone growth and development. The activation of molecular pathways leads to the occurrence of cellular events, ultimately resulting in observable changes. Therefore, in the studies of bone tissue engineering and regenerative medicine, it is essential to target fundamental events to exploit the mechanisms involved in osteogenesis. In this context, signaling pathways are activated during osteogenesis and trigger the activation of numerous other processes involved in osteogenesis. Direct influence of signaling pathways should allow to manipulate the signaling pathways themselves and impact osteogenesis. A combination of sequential cascades takes place to drive the progression of osteogenesis. Also, the occurrence of these processes and, more generally, cellular and molecular processes related to osteogenesis necessitate the presence of transcription factors and their activity. The present review focuses on outlining several signaling pathways and transcription factors influencing the development of osteogenesis, and describes various methods of their manipulation to induce and enhance bone formation.

Adrenomedullin-loaded Gelatin Methacryloyl Hydrogel Promotes Endogenous Dental Pulp Regeneration: An In Vitro and In Vivo Study

INTRODUCTION

To prepare a gelatin methacryloyl (GelMA) hydrogel scaffold embedded with adrenomedullin (ADM) and investigate its impact and underlying mechanisms in endogenous pulp regeneration.

METHODS

ADM was evenly distributed within the GelMA hydrogel through a simple and conventional physical mixing technique. The scaffold underwent characterization via scanning electron microscopy, alongside assessments of swelling, degradation, and release properties. Biocompatibility was evaluated using cytoskeletal and live-dead staining techniques. The hydrogel's influence on dental pulp stem cells' proliferation, migration, and differentiation was assessed with CCK-8 assays, Transwell assays, and alizarin red and alkaline phosphatase staining. Transcriptomics provided insights into potential mechanisms. The angiogenic effects on umbilical vein endothelial cells were examined using scratch and tube formation assays. In vivo, the composite hydrogel's regenerative capacity was tested in a rat model of pulp regeneration. Statistical analysis involved Student's t-test and one-way analysis of variance, with significance set at P < .05.

RESULTS

The ADM-loaded GelMA (GelMA@ADM) hydrogel displayed a porous architecture under electron microscopy conducive to cell adhesion and demonstrated excellent biocompatibility. In vitro experiments showed that GelMA@ADM significantly boosted dental pulp stem cells' migration, proliferation, and differentiation, and enhanced the angiogenic activity of umbilical vein endothelial cells after one week of treatment. Corresponding in vivo experiments revealed that GelMA@ADM facilitated the formation of new vascularized pulp tissue after 2 weeks of treatment.

CONCLUSIONS

The GelMA@ADM hydrogel effectively promotes dental pulp stem cells' proliferation and differentiation, augments vascularization by umbilical vein endothelial cells, and fosters the creation of new vascularized pulp tissue. These findings underscore the potential of GelMA@ADM hydrogel for endogenous pulp regeneration.

Dental pulp stem cells - A basic research and future application in regenerative medicine

Dental pulp is a valuable and accessible source of stem cells (DPSCs) with characteristics similar to mesenchymal stem cells. DPSCs can regenerate a range of tissues and their potential for clinical application in regenerative medicine is promising. DPSCs have been found to express low levels of Class II HLA-DR (MHC) molecules, making them potential candidates for allogeneic transplantation without matching the donor's tissue. Research on the correlation between non-coding RNAs (ncRNAs) and human dental pulp stem cells (DPSCs) provides promising insights into the use of these cells in clinical settings for a wide range of medical conditions. It is possible to use a number of ncRNAs in order to restore the functional role of downregulated ncRNAs that are correlated with osteoblastogenesis, or to suppress the functional role of overexpressed ncRNAs associated with osteoclast differentiation in some cases.

Piezocatalytically-induced controllable mineralization scaffold with bone-like microenvironment to achieve endogenous bone regeneration

Orderly hierarchical structure with balanced mechanical, chemical, and electrical properties is the basis of the natural bone microenvironment. Inspired by nature, we developed a piezocatalytically-induced controlled mineralization strategy using piezoelectric polymer poly-L-lactic acid (PLLA) fibers with ordered micro-nano structures to prepare biomimetic tissue engineering scaffolds with a bone-like microenvironment (pcm-PLLA), in which PLLA-mediated piezoelectric catalysis promoted the in-situ polymerization of dopamine and subsequently regulated the controllable growth of hydroxyapatite crystals on the fiber surface. PLLA fibers, as analogs of mineralized collagen fibers, were arranged in an oriented manner, and ultimately formed a bone-like interconnected pore structure; in addition, they also provided bone-like piezoelectric properties. The uniformly sized HA nanocrystals formed by controlled mineralization provided a bone-like mechanical strength and chemical environment. The pcm-PLLA scaffold could rapidly recruit endogenous stem cells, and promote their osteogenic differentiation by activating cell membrane calcium channels and PI3K signaling pathways through ultrasound-responsive piezoelectric signals. In addition, the scaffold also provided a suitable microenvironment to promote macrophage M2 polarization and angiogenesis, thereby enhancing bone regeneration in skull defects of rats. The proposed piezocatalytically-induced controllable mineralization strategy provides a new idea for the development of tissue engineering scaffolds that can be implemented for multimodal physical stimulation therapy.

ZIF-8-Modified Black Phosphorus Nanosheets Incorporated into Injectable Dual-Component Hydrogels for Enhanced Photothermal Antibacterial and Osteogenic Activities

The development of growth factor-free biomaterials for bone tissue regeneration with anti-infection and anti-inflammatory activities remains challenging. Black phosphorus nanosheets (BPNs), with distinctive attributes, including photothermal conversion and calcium ion chelation, offer potential for use in bone tissue engineering and infection prevention. However, BPNs are prone to oxidation and degradation in aqueous environments, and methods to stabilize BPNs for long-term bone repair remain insufficient. Herein, zeolitic imidazolate framework-8 (ZIF-8) was used to stabilize BPNs via in situ crystallization onto the surface of BPNs (BP@ZIF-8 nanocomposite). A novel injectable dual-component hydrogel comprising gelatin methacryloyl (GelMA) and methacrylate-modified hyaluronic acid (HAMA) was used as a BP@ZIF-8 nanocomposite carrier (GelMA/HAMA/BP@ZIF-8). The BP@ZIF-8 nanocomposite could effectively protect internal BPNs from oxidation and enhance the long-term photothermal performance of the hydrogel in both in vitro and in vivo settings. The GelMA/HAMA/BP@ZIF-8 hydrogel was injectable and exhibited outstanding performance for photothermal conversion, mechanical strength, and biodegradability, as well as excellent photothermal antibacterial activity against Staphylococcus aureus and Escherichia coli in vitro and in an in vivo rat model. The GelMA/HAMA/BP@ZIF-8 hydrogel also provided a microenvironment conducive to osteogenic differentiation, promoting the transformation of M2 macrophages and inhibiting inflammatory responses. Furthermore, the hydrogel promoted bone regeneration and had a synergistic effect with near-infrared irradiation in a rat skull-defect model. Transcriptome sequencing analysis revealed that the PI3K-AKT- and calcium-signaling pathways may be involved in promoting osteogenic differentiation induced by the GH-BZ hydrogel. This study presents an innovative, multifaceted solution to the challenges of bone tissue regeneration with antibacterial and anti-inflammatory effects, providing insights into the design of smart biomaterials with dual therapeutic capabilities.

Mineralised collagen regulated the secretion of adrenomedullin by macrophages to activate the PI3K/AKT signalling pathway to promote bone defect repair

Biomaterials can affect the osteogenic process by regulating the function of macrophages and transforming the bone immune microenvironment. Mineralised collagen (MC) is an artificial bone that is highly consistent to the microstructure of the native osseous matrix. The studies have confirmed that MC can achieve effective regeneration of bone defects, but the potential mechanism of MC regulating osteogenesis is still unclear. This study confirmed that MC regulate the high expression of adrenomedullin (ADM) in macrophages and promote the osteogenic differentiation, proliferation and migration of BMSCs. Moreover, ADM activated the PI3K/Akt pathway, while the inhibition of PI3K/Akt hindered the proliferation, migration and osteogenic differentiation of BMSCs promoted by ADM. Additionally, the rat mandibular defect model confirmed that ADM promote the repair of mandibular defects, and the inhibition of PI3K/Akt pathway hinders the osteogenic effect of ADM. Our study suggests that MC regulates ADM secretion by macrophages, creates an ideal bone immune microenvironment, activates the PI3K/AKT signalling pathway, and promotes osteogenesis.

Multifunctional Prosthesis Surface: Modification of Titanium with Cinnamaldehyde-Loaded Hierarchical Titanium Dioxide Nanotubes

Orthopedic prostheses are the ultimate therapeutic solution for various end-stage orthopedic conditions. However, aseptic loosening and pyogenic infections remain as primary complications associated with these devices. In this study, a hierarchical titanium dioxide (TiO2) nanotube drug delivery system loaded with cinnamaldehyde for the surface modification of titanium implants, is constructed. These specially designed dual-layer TiO2 nanotubes enhance material reactivity and provide an extensive drug-loading platform within a short time. The introduction of cinnamaldehyde enhances the bone integration performance of the scaffold (simultaneously promoting bone formation and inhibiting bone resorption), anti-inflammatory capacity, and antibacterial properties. In vitro experiments have demonstrated that this system promoted osteogenesis by upregulating both Wnt/β-catenin and MAPK signaling pathways. Furthermore, it inhibits osteoclast formation, suppresses macrophage-mediated inflammatory responses, and impedes the proliferation of Staphylococcus aureus and Escherichia coli. In vivo experiments shows that this material enhances bone integration in a rat model of femoral defects. In addition, it effectively enhances the antibacterial and anti-inflammatory properties in a subcutaneous implant in a rat model. This study provides a straightforward and highly effective surface modification strategy for orthopedic Ti implants.

Apoptotic Vesicles Derived from Dental Pulp Stem Cells Promote Bone Formation through the ERK1/2 Signaling Pathway

Osteoporosis is a common degenerative bone disease. The treatment of osteoporosis remains a clinical challenge in light of the increasing aging population. Human dental pulp stem cells (DPSCs), a type of mesenchymal stem cells (MSCs), are easy to obtain and have a high proliferation ability, playing an important role in the treatment of osteoporosis. However, MSCs undergo apoptosis within a short time when used in vivo; therefore, apoptotic vesicles (apoVs) have attracted increasing attention. Currently, the osteogenic effect of DPSC-derived apoVs is unknown; therefore, this study aimed to determine the role of DPSC-derived apoVs and their potential mechanisms in bone regeneration. We found that MSCs could take up DPSC-derived apoVs, which then promoted MSC osteogenesis in vitro. Moreover, apoVs could increase the trabecular bone count and bone mineral density in the mouse osteoporosis model and could promote bone formation in rat cranial defects in vivo. Mechanistically, apoVs promoted MSC osteogenesis by activating the extracellular regulated kinase (ERK)1/2 signaling pathway. Consequently, we propose a novel therapy comprising DPSC-derived apoVs, representing a promising approach to treat bone loss and bone defects.

EID3 inhibits the osteogenic differentiation of periodontal ligament stem cells and mediates the signal transduction of TAZ-EID3-AKT/MTOR/ERK

Exploring the molecular mechanisms of cell behaviors is beneficial for promoting periodontal ligament stem cell (PDLSC)-mediated tissue regeneration. This study intends to explore the regulatory effects of EID3 on cell proliferation, apoptosis, and osteogenic differentiation and to preliminarily explore the regulatory mechanism of EID3. Here, EID3 was overexpressed or knocked down in PDLSCs by recombinant lentivirus. Then, cell proliferation activity was analyzed by colony-forming assay, EdU assay, and cell cycle assay. Cell apoptosis was detected by flow cytometry. The osteo-differentiation potential was analyzed using ALP activity assay, ALP staining, alizarin red staining, and mRNA and protein assay of osteo-differentiation related genes. The results showed that when EID3 was knocked down, the proliferation activity and osteogenic differentiation potential of PDLSCs decreased, while they increased when EID3 was overexpressed. The cell apoptosis rate decreased in PDLSCs with EID3 knockdown but increased in PDLSCs with EID3 overexpression. Moreover, EID3 inhibited the transduction of the AKT/MTOR and ERK signaling pathway. In addition, TAZ negatively regulated the expression of EID3, and the overexpression of EID3 partially reversed the promotive effects of TAZ on the osteogenic differentiation of PDLSCs. Taken together, EID3 inhibits the proliferation and osteogenic differentiation while promoting the apoptosis of PDLSCs. EID3 inhibits the transduction of the AKT/MTOR and ERK signaling pathways and mediates the regulatory effect of TAZ on PDLSC osteogenic differentiation.

Rehabilitation exercise-driven symbiotic electrical stimulation system accelerating bone regeneration

Electrical stimulation can effectively accelerate bone healing. However, the substantial size and weight of electrical stimulation devices result in reduced patient benefits and compliance. It remains a challenge to establish a flexible and lightweight implantable microelectronic stimulator for bone regeneration. Here, we use self-powered technology to develop an electric pulse stimulator without circuits and batteries, which removes the problems of weight, volume, and necessary rigid packaging. The fully implantable bone defect electrical stimulation (BD-ES) system combines a hybrid tribo/piezoelectric nanogenerator to provide biphasic electric pulses in response to rehabilitation exercise with a conductive bioactive hydrogel. BD-ES can enhance multiple osteogenesis-related biological processes, including calcium ion import and osteogenic differentiation. In a rat model of critical-sized femoral defects, the bone defect was reversed by electrical stimulation therapy with BD-ES and subsequent bone mineralization, and the femur completely healed within 6 weeks. This work is expected to advance the development of symbiotic electrical stimulation therapy devices without batteries and circuits.