Macrophages-bone marrow mesenchymal stem cells crosstalk in bone healing

Multifunctional micro/nano-textured titanium with bactericidal, osteogenic, angiogenic and anti-inflammatory properties: Insights from in vitro and in vivo studies

Titanium (Ti) is widely used as an implantable material for bone repair in orthopedics and dentistry. However, Ti implants are vulnerable to bacterial infections, which can compromise patient recovery and lead to implant failure. While a controlled inflammatory response promotes bone regeneration, chronic inflammation caused by infections can lead to implant failure. Bone repair is a complex process in which inflammation, angiogenesis and osteogenesis are tightly interconnected, requiring cooperation between mesenchymal stem cells (MSC), macrophages and endothelial cells. Here, we fabricated bio-inspired Ti implants with either microstructured (Micro Ti) or nanostructured (Nano Ti) surface textures that exhibit robust mechano-bactericidal properties. In vitro, both textured surfaces improved blood coagulation and osteogenic marker expression compared to smooth Ti surfaces. Additionally, Nano Ti promoted macrophage polarization towards the M2 phenotype and enhanced the paracrine effects of MSCs on angiogenesis, key processes in tissue regeneration. In vivo kinetic analysis of bone reconstruction in a rat calvarial model showed that Nano Ti improved osseointegration, as evidenced by increased bone volume, mineral density, and bone-implant contact. Notably, the Micro Ti surface showed no significant differences from the control implants. These findings highlight the potential of mechano-bactericidal surface nanopatterns to simultaneously prevent infections and enhance osseointegration by modulating protein adsorption, inflammation, angiogenesis and osteogenesis. This study provides new insights into the development of bifunctional Ti implants, offering new perspectives for the next generation of implantable bone-related biomaterials.

Immunomodulatory and bone regenerative properties of copper/procyanidins-modified titanium surfaces

The inflammatory response triggered by the interaction between implants and macrophages is essential for bone regeneration around these implants. This study presents the application of dopamine hydrochloride to develop a copper and procyanidins coating on titanium surfaces to investigate its effects on bacterial inhibition, macrophage polarization, and osteogenic differentiation. The results demonstrated that this copper/procyanidins coating significantly suppressed the growth of Escherichia coli and Staphylococcus aureus. Notably, the initial release of Cu2+ ions promoted macrophage polarization toward a pro-inflammatory phenotype while stimulating the secretion of anti-inflammatory factors. Subsequently, the reduced Cu2+ release combined with procyanidins facilitated the transition from M1 to M2 macrophages-an essential process for bacterial phagocytosis and bone regeneration. Furthermore, this coating enhanced the secretion of osteogenic factors by bone marrow mesenchymal stem cells, enhancing their osteogenic differentiation and integration with bone tissue. These findings highlight the potential of copper/procyanidins coating in developing implant surfaces with immune-modulating and sustained antibacterial properties.

Tenascin-C promotes bone regeneration via inflammatory macrophages

During the early stage of tissue injury, macrophages play important roles in the activation of stem cells for further regeneration. However, the regulation of macrophages during bone regeneration remains unclear. Here, the extracellular matrix (ECM) tenascin-C (TNC) is found to express in the periosteum and recruit inflammatory macrophages. TNC-deficiency in the periosteum delays bone repair. Transplantation of macrophages derived from injured periosteum is able to rescue the decreased skeletal stem cells and impaired bone regeneration caused by TNC deficiency. The cell communication analysis identifies ITGA7 as a TNC receptor contributing to the recruitment of inflammatory macrophages. TNC expression declines in aged mice and the exogenous delivery of TNC significantly promotes bone regeneration after aging through the recruitment of macrophages. Taken together, this study reveals the regulation of macrophage recruitment and its function in the activation of skeletal stem cells after bone injury, providing a strategy to accelerate bone regeneration by TNC delivery.

Advances in computational modeling of cytokine and growth factor dynamics in bone healing: a scoping review

Bone healing is a complex process regulated by intricate biological and mechanical factors and spatially varied regions over time. This scoping review synthesizes current computational models that incorporate cytokines and growth factors, examining their role in bone healing. Through a systematic analysis of 71 studies, this review identifies and categorizes the modeling methodologies used, including mathematical, finite element, agent-based, mechanobiological, pharmacobiological, and hybrid approaches. The findings highlight the predominant use of mathematical models while noting a recent shift toward more sophisticated techniques like finite element and agent-based models. Key cytokines and growth factors, such as TGF-β, RANK-RANKL-OPG, and PTH, are repeatedly used, underscoring their essential roles in regulating cellular processes. This review also analyzes parameter selection and validation strategies, identifying gaps in current practices and emphasizing the need for high-quality experimental validation to improve model reliability. Some bibliometric analyses provide insights into citation networks and keyword co-occurrence, illustrating influential studies in the field and central themes. The findings offer a foundation for future research to enhance model accuracy, aiming toward more predictive and clinically relevant models accounting for biology and mechanics in bone healing.

Polydopamine Nanocomposite Hydrogel for Drug Slow-Release in Bone Defect Repair: A Review of Research Advances

In recent years, hydrogels have emerged as promising candidates for bone defect repair due to their excellent biocompatibility, high porosity, and water-retentive properties. However, conventional hydrogels face significant challenges in clinical translation, including brittleness, low mechanical strength, and poorly controlled drug degradation rates. To address these limitations, as a multifunctional polymer, polydopamine (PDA) has shown great potential in both bone regeneration and drug delivery systems. Its robust adhesive properties, biocompatibility, and responsiveness to photothermal stimulation make it an ideal candidate for enhancing hydrogel performance. Integrating PDA into conventional hydrogels not only improves their mechanical properties but also creates an environment conducive to cell adhesion, proliferation, and differentiation, thereby promoting bone defect repair. Moreover, PDA facilitates controlled drug release, offering a promising approach to optimizing treatment outcomes. This paper first explores the mechanisms through which PDA promotes bone regeneration, laying the foundation for its clinical translation. Additionally, it discusses the application of PDA-based nanocomposite hydrogels as advanced drug delivery systems for bone defect repair, providing valuable insights for both research and clinical translation.

Inhibition of MEK1/2 Signaling Pathway Limits M2 Macrophage Polarization and Interferes in the Dental Socket Repair Process in Mice

Dental socket repair theoretically involves a constructive inflammatory immune response, which evolves from an initial M1 prevalence to a subsequent M2 dominance. In this scenario, the MEK1/2 signaling pathway is allegedly involved in M2 polarization. This study aimed to evaluate the impact of MEK1/2 pharmacological inhibition in the local host response and repair outcome. C57Bl/6-WT 8-week-old male mice were submitted to the extraction of the right upper incisor and treated (or not, control group) with MEK1/2 inhibitor PD0325901 (10 mg/kg/24 h/IP, MEK1/2i group) and analyzed at 0, 3, 7, and 14 days using microcomputed tomography, histomorphometry, birefringence, immunohistochemistry, and PCR array analysis. The results demonstrate that MEK1/2 inhibition limits the development of M2 response over time, being associated with lower expression of M2, MSCs, and bone markers, lower levels of growth and osteogenic factors, along with a higher expression of iNOS, IL-1b, IL-6, and TNF-α, as well inflammatory chemokines, indicating a predominantly M1 pro-inflammatory environment. This modulation of local inflammatory immune response is associated with impaired bone formation as demonstrated by microtomographic and histomorphometric data. The results show that MEK1/2 inhibition delays bone repair after tooth extraction, supporting the concept that M2 macrophages are essential elements for host response regulation and proper repair.

Human macrophage polarisation and regulation of angiogenesis and osteogenesis is dependent on culture extracellular matrix and dimensionality

The immune system plays a crucial role in tissue repair and regeneration. Macrophages have been identified as master regulators of the early immune response and healing outcome, by orchestrating the temporal nature of the initial inflammation phase and coordinating the fate of stem/progenitor cells involved in regeneration. However, traditional in-vitro models for the study of macrophages often fail to fully replicate the complexity of the in-vivo microenvironment, therefore generating models which do not fully capture the extensive spectrum of macrophage behaviour seen in native tissues. To this end, we used a hematoma-mimetic 3D fibrin matrix characteristic of early injured tissues to generate a 3D in-vitro model mirroring the local macrophage microenvironment. Leveraging this framework, we demonstrated significant effects of extracellular matrix and dimensionality on macrophage basal signalling and polarisation, achieving more pronounced regenerative phenotypes upon stimulation with the M2a polarisation factors compared to traditional 2D tissue culture conditions. Moreover, this enhanced physiological macrophage behaviour corresponded to increased coordination of angiogenesis and osteogenesis, better mirroring the healing processes seen in-vivo. Taken together, this study demonstrates the critical importance of integrating tissue composition and 3D architecture when investigating the macrophage behaviour in-vitro, establishing a powerful tool that overcomes known limitations associated with traditional 2D culture on plastic, and can be used to identify and validate novel immunomodulation strategies to enhance tissue regeneration.

Dual-Mode Release of IL-4 and TCP from a PGA-SF Core-Shell Electrospinning Scaffold for Enhanced Bone Regeneration through Synergistic Immunoregulation and Osteogenesis

The successful filling of bone defects remains challenging due to the incongruity between bone graft materials and the dynamic process of bone healing. Developing multifunctional materials matching the dynamic process of bone healing offers a viable solution to the current dilemma. Lines of evidence have shown that engineering osteoimmunomodulatory biomaterials can modulate the function of immune cells and thus promote bone regeneration. Herein, we utilized silk fibroin (SF) and polyglycolic acid (PGA) to create a PGA-SF core-shell fibrous scaffold, incorporating interleukin-4 (IL-4) and tricalcium phosphate (TCP) as a codelivery system (PGA/TCP-SF/IL-4), aiming to achieve an initial rapid release of IL-4 and sustained release of TCP. The PGA/TCP-SF/IL-4 scaffold mimicked the native bone structure and showed superior tenacity in the wetting regime. In vitro studies demonstrated that the PGA/TCP-SF/IL-4 scaffold significantly reduced the inflammatory response by upregulating the M2 macrophages, created a favorable microenvironment for osteogenesis, and facilitated osteogenic differentiation and mineralization. Implantation of the PGA/TCP-SF/IL-4 scaffold into the rat skull defect model notably increased the formation of new bones. IL-4 and TCP acted synergistically in attenuating inflammation and enhancing osteogenic differentiation. Overall, this multifunctional scaffold comprehensively considers the various demands in the bone defect region, which might have a significant potential for application in bone reconstruction.

The Advantages and Shortcomings of Stem Cell Therapy for Enhanced Bone Healing

This review explores the regenerative potential of key progenitor cell types and therapeutic strategies to improve healing of complex fractures and bone defects. We define, summarize, and discuss the differentiation potential of totipotent, pluripotent, and multipotent stem cells, emphasizing the advantages and shortcomings of cell therapy for bone repair and regeneration. The fundamental role of mesenchymal stem cells is highlighted due to their multipotency to differentiate into the key lineage cells including osteoblasts, osteocytes, and chondrocytes, which are crucial for bone formation and remodeling. Hematopoietic stem cells (HSCs) also play a significant role; immune cells such as macrophages and T-cells modulate inflammation and tissue repair. Osteoclasts are multinucleated cells that are important to bone remodeling. Vascular progenitor (VP) cells are critical to oxygen and nutrient supply. The dynamic interplay among these lineages and their microenvironment is essential for effective bone restoration. Therapies involving cells that are more than "minimally manipulated" are controversial and include embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). ESCs, derived from early-stage embryos, possess pluripotent capabilities and have shown promise in preclinical studies for bone healing. iPSCs, reprogrammed from somatic cells, offer personalized medicine applications and can differentiate into various tissue-specific cell lines. Minimally manipulative cell therapy approaches such as the use of bone marrow aspirate concentrate (BMAC), exosomes, and various biomaterials for local delivery are explored for their effectiveness in bone regeneration. BMAC, which contains mostly immune cells but few mesenchymal and VPs, probably improves bone healing by facilitating paracrine-mediated intercellular communication. Exosome isolation harnesses the biological signals and cellular by-products that are a primary source for cell crosstalk and activation. Safe, efficacious, and cost-effective strategies to enhance bone healing using novel cellular therapies are part of a changing paradigm to modulate the inflammatory, repair, and regenerative pathways to achieve earlier more robust tissue healing and improved physical function. Impact Statement Stem cell therapy holds immense potential for bone healing due to its ability to regenerate damaged tissue. Nonmanipulated bone marrow aspirate contains mesenchymal stem cells that promote bone repair and reduce healing time. Induced pluripotent stem cells offer the advantage of creating patient-specific cells that can differentiate into osteoblasts, aiding in bone regeneration. Other delivery methods, such as scaffold-based techniques, enhance stem cell integration and function. Collectively, these approaches can improve treatment outcomes, reduce recovery periods, and advance our understanding of bone healing mechanisms, making them pivotal in orthopedic research and regenerative medicine.

Endochondral Ossification for Spinal Fusion: A Novel Perspective from Biological Mechanisms to Clinical Applications

Degenerative scoliosis (DS), encompassing conditions like spondylolisthesis and spinal stenosis, is a common type of spinal deformity. Lumbar interbody fusion (LIF) stands as a conventional surgical intervention for this ailment, aiming at decompression, restoration of intervertebral height, and stabilization of motion segments. Despite its widespread use, the precise mechanism underlying spinal fusion remains elusive. In this review, our focus lies on endochondral ossification for spinal fusion, a process involving vertebral development and bone healing. Endochondral ossification is the key step for the successful vertebral fusion. Endochondral ossification can persist in hypoxic conditions and promote the parallel development of angiogenesis and osteogenesis, which corresponds to the fusion process of new bone formation in the hypoxic region between the vertebrae. The ideal material for interbody fusion cages should have the following characteristics: (1) Good biocompatibility; (2) Stable chemical properties; (3) Biomechanical properties similar to bone tissue; (4) Promotion of bone fusion; (5) Favorable for imaging observation; (6) Biodegradability. Utilizing cartilage-derived bone-like constructs holds promise in promoting bony fusion post-operation, thus warranting exploration in the context of spinal fusion procedures.

Enhanced osteogenic differentiation in 3D hydrogel scaffold via macrophage mitochondrial transfer

To assess the efficacy of a novel 3D biomimetic hydrogel scaffold with immunomodulatory properties in promoting fracture healing. Immunomodulatory scaffolds were used in cell experiments, osteotomy mice treatment, and single-cell transcriptomic sequencing. In vitro, fluorescence tracing examined macrophage mitochondrial transfer and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Scaffold efficacy was assessed through alkaline phosphatase (ALP), Alizarin Red S (ARS) staining, and in vivo experiments. The scaffold demonstrated excellent biocompatibility and antioxidant-immune regulation. Single-cell sequencing revealed a shift in macrophage distribution towards the M2 phenotype. In vitro experiments showed that macrophage mitochondria promoted BMSCs' osteogenic differentiation. In vivo experiments confirmed accelerated fracture healing. The GAD/Ag-pIO scaffold enhances osteogenic differentiation and fracture healing through immunomodulation and promotion of macrophage mitochondrial transfer.

Systematical Mutational Analysis of FRATtide against Osteoclast Differentiation by Alanine Scanning

Osteoporosis, a global bone disease, results in decreased bone density, mass, and microarchitecture deterioration, increasing fracture risk. In previous research, FRATtide, a peptide derived from a glycogen synthase kinase-3 binding protein, effectively hindered osteoclast differentiation to yield therapeutically potent derivatives via single and double stapling. However, FRATtide's structure-activity relationship remains unclear. This study synthesized 25 FRATtide-derived peptides through systematic alanine scanning and evaluated their activities. Substitutions in Pro2, Leu5, Leu9, Val10, Leu11, Ser12, Asn14, Leu15, Ile16, Glu18, Arg22, Ser25, and Arg26 showed reduced activity, while FRT13 and FRT20 with Gly13 and Arg21 substitutions, respectively, displayed enhanced activities. F-actin binding and bone resorption assays on FRT13 and FRT20 showed better inhibition of osteoclast differentiation and bone resorption compared with FRATtide. This study elucidated FRATtide's structure-activity relationship, thereby facilitating future structural optimization for osteoporosis treatment.

Modulating the phenotype and function of bone marrow-derived macrophages via mandible and femur osteoblasts

Various studies have been investigated the phenotypic and functional distinctions of craniofacial and long bone cells involved in bone regeneration. However, the process of bone tissue regeneration after bone grafting involves complicated interactions between different cell types at the donor-recipient site. Additionally, differences in alterations of the immune microenvironment at the recipient site remained to be explored. Osteoblasts (OBs) and macrophages (MØ) play essential roles in the bone restoration and regeneration processes in the bone and immune systems, respectively. The modulation of MØ on OBs has been extensively explored in the literature, whereas limited research has been conducted on the influence of OBs on the MØ phenotype and function. In the present study, OBs from the mandible and femur (MOBs and FOBs, respectively) promoted cranial defect regeneration in rats, with better outcomes noted in the MOBs-treated group. After MOBs transplantation, a significant inflammatory response was induced, accompanied by an early increase in IL-10 secretion. And then, there was an upregulation in M2-MØ-related cell markers and inflammatory factor expression. Condition media (CM) of OBs mildly inhibited apoptosis in MØ, enhanced their migration and phagocytic functions, and concurrently increased iNOS and Arg1 expression, with MOB-CM demonstrating more pronounced effects compared to FOB-CM. In conclusion, our investigation showed that MOBs and FOBs have the ability to modulate MØ phenotype and function, with MOBs exhibiting a stronger regulatory potential. These findings provide a new direction for improving therapeutic strategies for bone regeneration in autologous bone grafts from the perspective of the immune microenvironment.

Interpenetrating nanofibrillar membrane of self-assembled collagen and antimicrobial peptides for enhanced bone regeneration

Bone regeneration remains a major clinical challenge, especially when infection necessitates prolonged antibiotic treatment. This study presents a membrane composed of self-assembled and interpenetrating GL13K, an antimicrobial peptide (AMP) derived from a salivary protein, in a collagen membrane for antimicrobial activity and enhanced bone regeneration. Commercially available collagen membranes were immersed in GL13K solution, and self-assembly was initiated by raising the solution pH to synthesize the multifunctional membrane called COL-GL. COL-GL was composed of interpenetrating large collagen fibers and short GL13K nanofibrils, which increased hydrophobicity, reduced biodegradation from collagenase, and stiffened the matrix compared to control collagen membranes. Incorporation of GL13K led to antimicrobial and anti-fouling activity against early oral surface colonizer Streptococcus gordonii while not affecting fibroblast cytocompatibility or pre-osteoblast osteogenic differentiation. GL13K in solution also reduced macrophage inflammatory cytokine expression and increased pro-healing cytokine expression. Bone formation in a rat calvarial model was accelerated at eight weeks with COL-GL compared to the gold-standard collagen membrane based on microcomputed tomography and histology. Interpenetration of GL13K within collagen sidesteps challenges with antimicrobial coatings on bone regeneration scaffolds while increasing bone regeneration. This strength makes COL-GL a promising approach to reduce post-surgical infections and aid bone regeneration in dental and orthopedic applications. STATEMENT OF SIGNIFICANCE: The COL-GL membrane, incorporating the antimicrobial peptide GL13K within a collagen membrane, signifies a noteworthy breakthrough in bone regeneration strategies for dental and orthopedic applications. By integrating self-assembled GL13K nanofibers into the membrane, this study successfully addresses the challenges associated with antimicrobial coatings, exhibiting improved antimicrobial and anti-fouling activity while preserving compatibility with fibroblasts and pre-osteoblasts. The accelerated bone formation observed in a rat calvarial model emphasizes the potential of this innovative approach to minimize post-surgical infections and enhance bone regeneration outcomes. As a promising alternative for future therapeutic interventions, this material tackles the clinical challenges of extended antibiotic treatments and antibiotic resistance in bone regeneration scenarios.

Zinc hybrid polyester barrier membrane accelerates guided tissue regeneration

Barrier membranes play a pivotal role in the success of guided periodontal tissue regeneration. The biodegradable barriers predominantly used in clinical practice often lack sufficient barrier strength, antibacterial properties, and bioactivity, frequently leading to suboptimal regeneration outcomes. Although with advantages in mechanical strength, biodegradability and plasticity, bioinert aliphatic polyesters as barrier materials are usually polymerized via toxic catalysts, hard to be functionalized and lack of antibacterial properties. To address these challenges, we propose a new concept that controlled release of bioactive substance on the whole degradation course can give a bioinert aliphatic polyester bioactivity. Thus, a Zn-based catalytic system for polycondensation of dicarboxylic acids and diols is created to prepare zinc covalent hybrid polyester (PBS/ZnO). The atomically-dispersed Zn2+ ions entering main chain of polyester molecules endow PBS/ZnO barrier with antibacterial properties, barrier strength, excellent biocompatibility and histocompatibility. Further studies reveal that relying on long-term controlled release of Zn2+ ions, the PBS/ZnO membrane greatly expedites osteogenetic effect in guided tissue regeneration (GTR) by enhancing the mitochondrial function of macrophages to induce M2 polarization. These findings show a novel preparation strategy of bioactive polyester biomaterials based on long term controlled release of bioactive substance that integrates catalysis, material structures and function customization.

Osteoking promotes bone formation and bone defect repair through ZBP1-STAT1-PKR-MLKL-mediated necroptosis

BACKGROUND

Osteoking has been used for fracture therapy with a satisfying clinical efficacy. However, its therapeutic properties and the underlying mechanisms remain elusive.

METHOD

A bone defect rat model was established to evaluate the pharmacological effects of Osteoking by the dynamic observation of X-ray, micro-CT and histopathologic examination. Transcriptome profiling was performed to identify bone defect-related genes and Osteoking effective targets. Then, a "disease-related gene-drug target" interaction network was constructed and a list of key network targets were screened, which were experimentally verified.

RESULTS

Osteoking effectively promoted bone defect repair in rats by accelerating the repair of cortical bone and the growth of trabeculae. Histopathologically, the bone defect rats displayed lower histopathologic scores in cortical bone, cancellous bone and bone connection than normal controls. In contrast, Osteoking exerted a favorable effect with a dose-dependent manner. The abnormal serum levels of bone turnover markers, bone growth factors and bone metabolism-related biochemical indexes in bone defect rats were also reversed by Osteoking treatment. Following the transcriptome-based network investigation, we hypothesized that osteoking might attenuate the levels of ZBP1-STAT1-PKR-MLKL-mediated necroptosis involved into bone defect. Experimentally, the expression levels of ZBP1, STAT1, PKR and the hallmark inflammatory cytokines for the end of necroptosis were distinctly elevated in bone defect rats, but were all effectively reversed by Osteoking treatment, which were also suppressed the activities of RIPK1, RIPK3 and MLKL in bone tissue supernatants.

CONCLUSIONS

Osteoking may promote bone formation and bone defect repair by regulating ZBP1-STAT1-PKR axis, leading to inhibit RIPK1/RIPK3/MLKL activation-mediated necroptosis.

Advances in the roles of ATF4 in osteoporosis

Osteoporosis (OP) is characterized by reduced bone mass, decreased strength, and enhanced bone fragility fracture risk. Activating transcription factor 4 (ATF4) plays a role in cell differentiation, proliferation, apoptosis, redox balance, amino acid uptake, and glycolipid metabolism. ATF4 induces the differentiation of bone marrow mesenchymal stem cells (BM-MSCs) into osteoblasts, increases osteoblast activity, and inhibits osteoclast formation, promoting bone formation and remodeling. In addition, ATF4 mediates the energy metabolism in osteoblasts and promotes angiogenesis. ATF4 is also involved in the mediation of adipogenesis. ATF4 can selectively accumulate in osteoblasts. ATF4 can directly interact with RUNT-related transcription factor 2 (RUNX2) and up-regulate the expression of osteocalcin (OCN) and osterix (Osx). Several upstream factors, such as Wnt/β-catenin and BMP2/Smad signaling pathways, have been involved in ATF4-mediated osteoblast differentiation. ATF4 promotes osteoclastogenesis by mediating the receptor activator of nuclear factor κ-B (NF-κB) ligand (RANKL) signaling. Several agents, such as parathyroid (PTH), melatonin, and natural compounds, have been reported to regulate ATF4 expression and mediate bone metabolism. In this review, we comprehensively discuss the biological activities of ATF4 in maintaining bone homeostasis and inhibiting OP development. ATF4 has become a therapeutic target for OP treatment.