Stage-Dependent Activity and Pro-Chondrogenic Function of PI3K/AKT during Cartilage Neogenesis from Mesenchymal Stromal Cells

Extracellular matrix: Dystroglycan interactions-Roles for the dystrophin-associated glycoprotein complex in skeletal tissue dynamics

Contributions made by the dystrophin-associated glycoprotein complex (DGC) to cell-cell and cell-extracellular matrix (ECM) interactions are vital in development, homeostasis and pathobiology. This review explores how DGC functions may extend to skeletal pathophysiology by appraising the known roles of its major ECM ligands, and likely associated DGC signalling pathways, in regulating cartilage and bone cell behaviour and emergent skeletal phenotypes. These considerations will be contextualised by highlighting the potential of studies into the role of the DGC in isolated chondrocytes, osteoblasts and osteoclasts, and by fuller deliberation of skeletal phenotypes that may emerge in very young mice lacking vital, yet diverse core elements of the DGC. Our review points to roles for individual DGC components-including the glycosylation of dystroglycan itself-beyond the establishment of membrane stability which clearly accounts for severe muscle phenotypes in muscular dystrophy. It implies that the short stature, low bone mineral density, poor bone health and greater fracture risk in these patients, which has been attributed due to primary deficiencies in muscle-evoked skeletal loading, may instead arise due to primary roles for the DGC in controlling skeletal tissue (re)modelling.

ANXA2 promotes chondrocyte differentiation and fracture healing by regulating the phosphorylation of STAT3 and PI3K/AKT signaling pathways

Fractures are common and serious skeletal injuries, and accelerating their healing while alleviating patient suffering remains a clinical challenge. Annexin A2 (ANXA2) is a widely distributed, calcium-dependent, phospholipid-binding protein involved in bone remodeling. However, its role in chondrocyte differentiation and endochondral ossification remains unclear. In this study, we found that ANXA2 is expressed in chondrocytes during growth plate development and fracture healing, as well as during chondrocyte differentiation and maturation in vitro, with its highest expression occurring in the most active differentiation phase. Moreover, ANXA2 knockdown inhibited chondrocyte differentiation, while its overexpression significantly promoted it. We also demonstrated that ANXA2 regulates the chondrogenic and hypertrophic differentiation by mediating the phosphorylation and nuclear translocation of STAT3, as well as activating the PI3K/AKT pathway. Finally, recombinant ANXA2 protein was injected into the tibial fracture sites of mice, verifying its role in promoting endochondral ossification during fracture healing. In conclusion, our study shows that ANXA2 promotes chondrocyte differentiation, partially through the STAT3 and PI3K/AKT pathways. These findings provide insights that could aid in developing new therapies to enhance fracture healing.

Up IGF-I via high-toughness adaptive hydrogels for remodeling growth plate of children

The growth plate is crucial for skeletal growth in children, but research on repairing growth plate damage and restoring growth is limited. Here, a high-toughness adaptive dual-crosslinked hydrogel is designed to mimic the growth plate's structure, supporting regeneration and bone growth. Composed of aldehyde-modified bacterial cellulose (DBNC), methacrylated gelatin (GelMA) and sodium alginate (Alg), the hydrogel is engineered through ionic bonding and Schiff base reactions, creating a macroporous structure. This structure can transform into a denser form by binding with calcium ions. In vitro, the loose macroporous structure of the hydrogels can promote chondrogenic differentiation, and when it forms a dense structure by binding with calcium ions, it also can activate relevant chondrogenic signaling pathways under the influence of insulin-like growth factor I (IGF-1), further inhibiting osteogenesis. In vivo experiments in a rat model of growth plate injury demonstrated that the hydrogel promoted growth plate cartilage regeneration and minimized bone bridge formation by creating a hypoxic microenvironment that activates IGF-1-related pathways. This environment encourages chondrogenic differentiation while preventing the undesired formation of bone tissue within the growth plate area. Overall, the dual-crosslinked hydrogel not only mimics the growth plate's structure but also facilitates localized IGF-1 expression, effectively reshaping the growth plate's function. This approach represents a promising therapeutic strategy for treating growth plate injuries, potentially addressing challenges associated with skeletal growth restoration in pediatric patients.

Angelica sinensis polysaccharide facilitates chondrogenic differentiation of adipose-derived stem cells via MDK-PI3K/AKT signaling cascade

OBJECT

Adipose-derived mesenchymal stem cells (ADSCs) have received significant attention in the field of cartilage tissue repair. Angelica sinensis polysaccharide (ASP) can enhance both the proliferation and differentiation of mesenchymal stem cells. Therefore, we intend to explore the effect of ASP on chondrogenic differentiation of ADSCs in vitro, and elucidate the underlying mechanisms.

METHOD

ADSCs were treated with different concentrations of ASP to determine the optimal concentration. The chondrogenic differentiation of ADSCs was evaluated using Alcian blue staining, qRT-PCR, western blot, and IF staining. Transcriptome sequencing was performed to identify the expression profiles of ADSCs before and after ASP treatment, followed by bioinformatic analyses including differential expression analysis, enrichment analysis, and construction of PPI networks to identify differentially expressed genes (DEGs) associated with ASP and chondrogenic differentiation.

RESULT

Surface markers of isolated rat-derived ADSCs were identified by CD44+CD90+CD45-CD106-, and exhibited the capacity for lipogenic, osteogenic, and chondrogenic differentiation. With increasing concentration of ASP treatment, there was an upregulation in the activity and acidic mucosubstance of ADSCs. The levels of Aggrecan, COL2A1, and Sox9 showed an increase in ADSCs after 28 days of 80 µg/ml ASP treatment. Transcriptome sequencing revealed that ASP-associated DEGs regulate extracellular matrix synthesis, immune response, inflammatory response, and cell cycle, and are involved in the NF-κB, AGE-RAGE, and calcium pathways. Moreover, Edn1, Frzb, Mdk, Nog, and Sulf1 are hub genes in DEGs. Notably, ASP upregulated MDK levels in ADSCs, while knockdown of MDK mitigated ASP-induced elevations in acidic mucosubstance, chondrogenic differentiation-related markers (Aggrecan, COL2A1, and Sox9), and the activity of the PI3K/AKT pathway.

CONCLUSION

ASP enhances the proliferation and chondrogenic differentiation of ADSCs by activating the MDK-mediated PI3K/AKT pathway.

Honeycomb-like biomimetic scaffold by functionalized antibacterial hydrogel and biodegradable porous Mg alloy for osteochondral regeneration

Introduction: Osteochondral repair poses a significant challenge due to its unique pathological mechanisms and complex repair processes, particularly in bacterial tissue conditions resulting from open injuries, infections, and surgical contamination. This study introduces a biomimetic honeycomb-like scaffold (Zn-AlgMA@Mg) designed for osteochondral repair. The scaffold consists of a dicalcium phosphate dihydrate (DCPD)-coated porous magnesium scaffold (DCPD Mg) embedded within a dual crosslinked sodium alginate hydrogel (Zn-AlgMA). This combination aims to synergistically exert antibacterial and osteochondral integrated repair properties. Methods: The Zn-AlgMA@Mg scaffold was fabricated by coating porous magnesium scaffolds with DCPD and embedding them within a dual crosslinked sodium alginate hydrogel. The structural and mechanical properties of the DCPD Mg scaffold were characterized using scanning electron microscopy (SEM) and mechanical testing. The microstructural features and hydrophilicity of Zn-AlgMA were assessed. In vitro studies were conducted to evaluate the controlled release of magnesium and zinc ions, as well as the scaffold's osteogenic, chondrogenic, and antibacterial properties. Proteomic analysis was performed to elucidate the mechanism of osteochondral integrated repair. In vivo efficacy was evaluated using a rabbit full-thickness osteochondral defect model, with micro-CT evaluation, quantitative analysis, and histological staining (hematoxylin-eosin, Safranin-O, and Masson's trichrome). Results: The DCPD Mg scaffold exhibited a uniform porous structure and superior mechanical properties. The Zn-AlgMA hydrogel displayed consistent microstructural features and enhanced hydrophilicity. The Zn-AlgMA@Mg scaffold provided controlled release of magnesium and zinc ions, promoting cell proliferation and vitality. In vitro studies demonstrated significant osteogenic and chondrogenic properties, as well as antibacterial efficacy. Proteomic analysis revealed the underlying mechanism of osteochondral integrated repair facilitated by the scaffold. Micro-CT evaluation and histological analysis confirmed successful osteochondral integration in the rabbit model. Discussion: The biomimetic honeycomb-like scaffold (Zn-AlgMA@Mg) demonstrated promising results for osteochondral repair, effectively addressing the challenges posed by bacterial tissue conditions. The scaffold's ability to release magnesium and zinc ions in a controlled manner contributed to its significant osteogenic, chondrogenic, and antibacterial properties. Proteomic analysis provided insights into the scaffold's mechanism of action, supporting its potential for integrated osteochondral regeneration. The successful in vivo results highlight the scaffold's efficacy, making it a promising biomaterial for future applications in osteochondral repair.

Cause and chondroprotective effects of prostaglandin E2 secretion during mesenchymal stromal cell chondrogenesis

Mesenchymal stromal cells (MSCs) that are promising for cartilage tissue engineering secrete high amounts of prostaglandin E2 (PGE2), an immunoactive mediator involved in endochondral bone development. This study aimed to identify drivers of PGE2 and its role in the inadvertent MSC misdifferentiation into hypertrophic chondrocytes. PGE2 release, which rose in the first three weeks of MSC chondrogenesis, was jointly stimulated by endogenous BMP, WNT, and hedgehog activity that supported the exogenous stimulation by TGF-β1 and insulin to overcome the PGE2 inhibition by dexamethasone. Experiments with PGE2 treatment or the inhibitor celecoxib or specific receptor antagonists demonstrated that PGE2, although driven by prohypertrophic signals, exerted broad autocrine antihypertrophic effects. This chondroprotective effect makes PGE2 not only a promising option for future combinatorial approaches to direct MSC tissue engineering approaches into chondral instead of endochondral development but could potentially have implications for the use of COX-2-selective inhibitors in osteoarthritis pain management.

Induced regeneration of articular cartilage - identification of a dormant regeneration program for a non-regenerative tissue

A mouse organoid culture model was developed to regenerate articular cartilage by sequential treatment with BMP2 and BMP9 (or GDF2) that parallels induced joint regeneration at digit amputation wounds in vivo. BMP9-induced chondrogenesis was used to identify clonal cell lines for articular chondrocyte and hypertrophic chondrocyte progenitor cells from digit fibroblasts. A protocol that includes cell aggregation enhanced by BMP2 followed by BMP9-induced chondrogenesis resulted in the differentiation of organized layers of articular chondrocytes, similar to the organization of middle and deep zones of articular cartilage in situ, and retained a differentiated phenotype following transplantation. In addition, the differentiation of a non-chondrogenic connective tissue layer containing articular chondrocyte progenitor cells demonstrated that progenitor cell sequestration is coupled with articular cartilage differentiation at a clonal level. The studies identify a dormant endogenous regenerative program for a non-regenerative tissue in which fibroblast-derived progenitor cells can be induced to initiate morphogenetic and differentiative programs that include progenitor cell sequestration. The identification of dormant regenerative programs in non-regenerative tissues such as articular cartilage represents a novel strategy that integrates regeneration biology with regenerative medicine.

Tetrahedral framework nucleic acids enhance the chondrogenic potential of human umbilical cord mesenchymal stem cells via the PI3K/AKT axis

The field of regenerative medicine faces a notable challenge in terms of the regeneration of articular cartilage. Without proper treatment, it can lead to osteoarthritis. Based on the research findings, human umbilical cord mesenchymal stem cells (hUMSCs) are considered an excellent choice for regenerating cartilage. However, there is still a lack of suitable biomaterials to control their ability to self-renew and differentiate. To address this issue, in this study using tetrahedral framework nucleic acids (tFNAs) as a new method in an in vitro culture setting to manage the behaviour of hUMSCs was proposed. Then, the influence of tFNAs on hUMSC proliferation, migration and chondrogenic differentiation was explored by combining bioinformatics methods. In addition, a variety of molecular biology techniques have been used to investigate deep molecular mechanisms. Relevant results demonstrated that tFNAs can affect the transcriptome and multiple signalling pathways of hUMSCs, among which the PI3K/Akt pathway is significantly activated. Furthermore, tFNAs can regulate the expression levels of multiple proteins (GSK3β, RhoA and mTOR) downstream of the PI3K-Akt axis to further enhance cell proliferation, migration and hUMSC chondrogenic differentiation. tFNAs provide new insight into enhancing the chondrogenic potential of hUMSCs, which exhibits promising potential for future utilization within the domains of AC regeneration and clinical treatment.

In situ self-assembled organoid for osteochondral tissue regeneration with dual functional units

The regeneration of hierarchical osteochondral units is challenging due to difficulties in inducing spatial, directional and controllable differentiation of mesenchymal stem cells (MSCs) into cartilage and bone compartments. Emerging organoid technology offers new opportunities for osteochondral regeneration. In this study, we developed gelatin-based microcryogels customized using hyaluronic acid (HA) and hydroxyapatite (HYP), respectively for inducing cartilage and bone regeneration (denoted as CH-Microcryogels and OS-Microcryogels) through in vivo self-assembly into osteochondral organoids. The customized microcryogels showed good cytocompatibility and induced chondrogenic and osteogenic differentiation of MSCs, while also demonstrating the ability to self-assemble into osteochondral organoids with no delamination in the biphasic cartilage-bone structure. Analysis by mRNA-seq showed that CH-Microcryogels promoted chondrogenic differentiation and inhibited inflammation, while OS-Microcryogels facilitated osteogenic differentiation and suppressed the immune response, by regulating specific signaling pathways. Finally, the in vivo engraftment of pre-differentiated customized microcryogels into canine osteochondral defects resulted in the spontaneous assembly of an osteochondral unit, inducing simultaneous regeneration of both articular cartilage and subchondral bone. In conclusion, this novel approach for generating self-assembling osteochondral organoids utilizing tailor-made microcryogels presents a highly promising avenue for advancing the field of tissue engineering.