Proposal of patient-specific growth plate cartilage xenograft model for FGFR3 chondrodysplasia

High biocompatible polyacrylamide hydrogels fabricated by surface mineralization for subchondral bone tissue engineering

The subchondral bone is an important part of cartilage which contains a large amount of hydroxyapatite. The mineral components of subchondral bone is the key factor which determines the biomechanical strength, and then affects the biological function of articular cartilage. Here, a mineralized polyacrylamide (PAM-Mineralized) hydrogel with good ALP activity, cell adhesion and biocompatibility was fabricated for subchondral bone tissue engineering. The micromorphology, composition and mechanical properties of PAM and PAM-Mineralized hydrogels were studied. The PAM hydrogels showed a porous structure, while the PAM-Mineralized hydrogels had well-distributed layers of hydroxyapatite mineralization on the surface. The XRD results show that the characteristic peak of hydroxyapatite (HA) was measured in PAM-Mineralized, indicating that the main component of the mineralized structure formed on the surface of the hydrogel after mineralization is HA. The formation of HA ectively decreased the rate of equilibrium swelling of the PAM hydrogel, with PAM-M reaching swelling equilibrium at 6 h. Meanwhile, compressive strength of PAM-Mineralized hydrogel (moisture state) reached 290 ± 30 kPa, compressive modulus reached 130 ± 4 kPa. PAM-Mineralized hydrogels did not affect the growth and proliferation of MC3T3-E1 cells. Surface mineralization of PAM hydrogel could significantly improve osteogenic differentiation of MC3T3-E1 cells. These results showed that PAM-Mineralized hydrogel could possess potential application in the field of subchondral bone tissue engineering.

Engraftment of allogeneic iPS cell-derived cartilage organoid in a primate model of articular cartilage defect

Induced pluripotent stem cells (iPSCs) are a promising resource for allogeneic cartilage transplantation to treat articular cartilage defects that do not heal spontaneously and often progress to debilitating conditions, such as osteoarthritis. However, to the best of our knowledge, allogeneic cartilage transplantation into primate models has never been assessed. Here, we show that allogeneic iPSC-derived cartilage organoids survive and integrate as well as are remodeled as articular cartilage in a primate model of chondral defects in the knee joints. Histological analysis revealed that allogeneic iPSC-derived cartilage organoids in chondral defects elicited no immune reaction and directly contributed to tissue repair for at least four months. iPSC-derived cartilage organoids integrated with the host native articular cartilage and prevented degeneration of the surrounding cartilage. Single-cell RNA-sequence analysis indicated that iPSC-derived cartilage organoids differentiated after transplantation, acquiring expression of PRG4 crucial for joint lubrication. Pathway analysis suggested the involvement of SIK3 inactivation. Our study outcomes suggest that allogeneic transplantation of iPSC-derived cartilage organoids may be clinically applicable for the treatment of patients with chondral defects of the articular cartilage; however further assessment of functional recovery long term after load bearing injuries is required.

Developmental principles informing human pluripotent stem cell differentiation to cartilage and bone

Human pluripotent stem cells can differentiate into any cell type given appropriate signals and hence have been used to research early human development of many tissues and diseases. Here, we review the major biological factors that regulate cartilage and bone development through the three main routes of neural crest, lateral plate mesoderm and paraxial mesoderm. We examine how these routes have been used in differentiation protocols that replicate skeletal development using human pluripotent stem cells and how these methods have been refined and improved over time. Finally, we discuss how pluripotent stem cells can be employed to understand human skeletal genetic diseases with a developmental origin and phenotype, and how developmental protocols have been applied to gain a better understanding of these conditions.

The Induced Pluripotent Stem Cells in Articular Cartilage Regeneration and Disease Modelling: Are We Ready for Their Clinical Use?

The development of induced pluripotent stem cells has brought unlimited possibilities to the field of regenerative medicine. This could be ideal for treating osteoarthritis and other skeletal diseases, because the current procedures tend to be short-term solutions. The usage of induced pluripotent stem cells in the cell-based regeneration of cartilage damages could replace or improve on the current techniques. The patient’s specific non-invasive collection of tissue for reprogramming purposes could also create a platform for drug screening and disease modelling for an overview of distinct skeletal abnormalities. In this review, we seek to summarise the latest achievements in the chondrogenic differentiation of pluripotent stem cells for regenerative purposes and disease modelling.

Implantation of Human-Induced Pluripotent Stem Cell-Derived Cartilage in Bone Defects of Mice

Although bone has an innate capacity for repair, clinical situations such as comminuted fracture, open fracture, or the surgical resection of bone tumors produce critical-sized bone defects that exceed the capacity and require external intervention. Initiating endochondral ossification (EO) by the implantation of a cartilaginous template into the bone defect is a relatively new approach to cure critical-sized bone defects. The combination of chondrogenically primed mesenchymal stromal/stem cells and artificial scaffolds has been the most extensively studied approach for inducing endochondral bone formation in bone defects. In this study, we prepared cartilage (human-induced pluripotent stem [hiPS]-Cart) from hiPS cells (hiPSCs) in a scaffoldless manner and implanted hiPS-Cart into 3.5 mm large defects created in the femurs of immunodeficient mice to examine the repair capacity. For the control, nothing was implanted into the defects. The implantation of hiPS-Cart significantly induced more new bone in the defect compared with the control. Culture periods for the chondrogenic differentiation of hiPSCs significantly affected the speed of bone induction, with less time resulting in faster bone formation. Histological analysis revealed that hiPS-Cart induced new bone formation in a manner resembling EO of the secondary ossification center, with the cartilage canal, which extended from the periphery to the center of hiPS-Cart, initially forming in unmineralized cartilage, followed by chondrocyte hypertrophy at the center. In the newly formed bone, the majority of osteocytes, osteoblasts, and adipocytes expressed human nuclear antigen (HNA), suggesting that these types of cells mainly derived from the perichondrium of hiPS-Cart. Osteoclasts and blood vessel cells did not express HNA and thus were mouse. Finally, integration between the newly formed bone and mouse femur was attained substantially. Although hiPS-Cart induced new bone that filled bone defects, the newly formed bone, which is a hybrid of human and mouse, had not remodeled to mature bone within the observation period of this study (28 weeks).

An RNA aptamer restores defective bone growth in FGFR3-related skeletal dysplasia in mice

Achondroplasia is the most prevalent genetic form of dwarfism in humans and is caused by activating mutations in FGFR3 tyrosine kinase. The clinical need for a safe and effective inhibitor of FGFR3 is unmet, leaving achondroplasia currently incurable. Here, we evaluated RBM-007, an RNA aptamer previously developed to neutralize the FGFR3 ligand FGF2, for its activity against FGFR3. In cultured rat chondrocytes or mouse embryonal tibia organ culture, RBM-007 rescued the proliferation arrest, degradation of cartilaginous extracellular matrix, premature senescence, and impaired hypertrophic differentiation induced by FGFR3 signaling. In cartilage xenografts derived from induced pluripotent stem cells from individuals with achondroplasia, RBM-007 rescued impaired chondrocyte differentiation and maturation. When delivered by subcutaneous injection, RBM-007 restored defective skeletal growth in a mouse model of achondroplasia. We thus demonstrate a ligand-trap concept of targeting the cartilage FGFR3 and delineate a potential therapeutic approach for achondroplasia and other FGFR3-related skeletal dysplasias.

Ectopic models recapitulating morphological and functional features of articular cartilage

BACKGROUND

Articular cartilage is an extremely specialized connective tissue which covers all diarthrodial joints. Implantation of chondrogenic cells without or with additional biomaterial scaffolds in ectopic locationsin vivo generates substitutes of cartilage with structural and functional characteristics that are used in fundamental investigations while also serving as a basis for translational studies.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant ectopic models, among which subcutaneous, intramuscular, and kidney capsule transplantation and elaborates on implanted cells and biomaterial scaffolds and on their use to recapitulate morphological and functional features of articular cartilage. Although the absence of a physiological joint environment and biomechanical stimuli is the major limiting factor, ectopic models are an established component for articular cartilage research aiming to generate a bridge between in vitro data and the clinically more relevant translational orthotopic in vivo models when their limitations are considered.

Recent progress of animal transplantation studies for treating articular cartilage damage using pluripotent stem cells

Focal articular cartilage damage can eventually lead to the onset of osteoarthritis with degradation around healthy articular cartilage. Currently, there are no drugs available that effectively repair articular cartilage damage. Several surgical techniques exist and are expected to prevent progression to osteoarthritis, but they do not offer a long-term clinical solution. Recently, regenerative medicine approaches using human pluripotent stem cells (PSCs) have gained attention as new cell sources for therapeutic products. To translate PSCs to clinical application, appropriate cultures that produce large amounts of chondrocytes and hyaline cartilage are needed. So too are assays for the safety and efficacy of the cellular materials in preclinical studies including animal transplantation models. To confirm safety and efficacy, transplantation into the subcutaneous space and articular cartilage defects have been performed in animal models. All but one study we reviewed that transplanted PSC-derived cellular products into articular cartilage defects found safe and effective recovery. However, for most of those studies, the quality of the PSCs was not verified, and the evaluations were done with small animals over short observation periods. Large animals and longer observation times are preferred. We will discuss the recent progress and future direction of the animal transplantation studies for the treatment of focal articular cartilage damages using PSCs.

Evaluation of FGFR inhibitor ASP5878 as a drug candidate for achondroplasia

Achondroplasia is caused by gain-of-function mutations in FGFR3 gene and leads to short-limb dwarfism. A stabilized analogue of C-type natriuretic peptide (CNP) is known to elongate bone by interacting with FGFR3 signals and thus is a promising drug candidate. However, it needs daily administration by percutaneous injection. FGFR inhibitor compounds are other drug candidates for achondroplasia because they directly fix the mutant protein malfunction. Although FGFR inhibitors elongate the bone of model mice, their adverse effects are not well studied. In this study, we found that a new FGFR inhibitor, ASP5878, which was originally developed as an anti-cancer drug, elongated the bone of achondroplasia model male mice at the dose of 300 μg/kg, which confers an AUC of 275 ng·h/ml in juvenile mice. Although ASP5878 was less effective in bone elongation than a CNP analogue, it is advantageous in that ASP5878 can be administered orally. The AUC at which minimal adverse effects were observed (very slight atrophy of the corneal epithelium) was 459 ng·h/ml in juvenile rats. The positive discrepancy between AUCs that brought efficacy and minimal adverse effect suggests the applicability of ASP5878 to achondroplasia in the clinical setting. We also analyzed effects of ASP5878 in a patient-specific induced pluripotent stem cell (iPSC) model for achondroplasia and found the effects on patient chondrocyte equivalents. Nevertheless, cautious consideration is needed when referring to safety data obtained from its application to adult patients with cancer in clinical tests.

FGFR3 Alterations in the Era of Immunotherapy for Urothelial Bladder Cancer

FGFR3 is a prognostic and predictive marker and is a validated therapeutic target in urothelial bladder cancer. Its utility as a marker and target in the context of immunotherapy is incompletely understood. We review the role of FGFR3 in bladder cancer and discuss preclinical and clinical clues of its effectiveness as a patient selection factor and therapeutic target in the era of immunotherapy.

Versatility of Induced Pluripotent Stem Cells (iPSCs) for Improving the Knowledge on Musculoskeletal Diseases

Induced pluripotent stem cells (iPSCs) represent an unlimited source of pluripotent cells capable of differentiating into any cell type of the body. Several studies have demonstrated the valuable use of iPSCs as a tool for studying the molecular and cellular mechanisms underlying disorders affecting bone, cartilage and muscle, as well as their potential for tissue repair. Musculoskeletal diseases are one of the major causes of disability worldwide and impose an important socio-economic burden. To date there is neither cure nor proven approach for effectively treating most of these conditions and therefore new strategies involving the use of cells have been increasingly investigated in the recent years. Nevertheless, some limitations related to the safety and differentiation protocols among others remain, which humpers the translational application of these strategies. Nonetheless, the potential is indisputable and iPSCs are likely to be a source of different types of cells useful in the musculoskeletal field, for either disease modeling or regenerative medicine. In this review, we aim to illustrate the great potential of iPSCs by summarizing and discussing the in vitro tissue regeneration preclinical studies that have been carried out in the musculoskeletal field by using iPSCs.

Understanding paraxial mesoderm development and sclerotome specification for skeletal repair

Pluripotent stem cells (PSCs) are attractive regenerative therapy tools for skeletal tissues. However, a deep understanding of skeletal development is required in order to model this development with PSCs, and for the application of PSCs in clinical settings. Skeletal tissues originate from three types of cell populations: the paraxial mesoderm, lateral plate mesoderm, and neural crest. The paraxial mesoderm gives rise to the sclerotome mainly through somitogenesis. In this process, key developmental processes, including initiation of the segmentation clock, formation of the determination front, and the mesenchymal–epithelial transition, are sequentially coordinated. The sclerotome further forms vertebral columns and contributes to various other tissues, such as tendons, vessels (including the dorsal aorta), and even meninges. To understand the molecular mechanisms underlying these developmental processes, extensive studies have been conducted. These studies have demonstrated that a gradient of activities involving multiple signaling pathways specify the embryonic axis and induce cell-type-specific master transcription factors in a spatiotemporal manner. Moreover, applying the knowledge of mesoderm development, researchers have attempted to recapitulate the in vivo development processes in in vitro settings, using mouse and human PSCs. In this review, we summarize the state-of-the-art understanding of mesoderm development and in vitro modeling of mesoderm development using PSCs. We also discuss future perspectives on the use of PSCs to generate skeletal tissues for basic research and clinical applications.

A deeper understanding of skeletal tissue development and improvements in tissue engineering will help pluripotent stem cell (PSC) therapies to reach their full potential for skeletal repair. The paraxial mesoderm, an embryonic germ layer, is crucial to the formation of healthy axial skeleton. Shoichiro Tani at the University of Tokyo, Japan, and co-workers reviewed current understanding of paraxial mesoderm development and studies involving in vitro PSC skeletal modeling. The formation of the paraxial mesoderm and associated connective tissues comprises multiple stages, and studies in vertebrate embryos have uncovered critical signaling pathways and cellular components important to PSC modeling. Although many individual cellular components can now be modeled, it remains challenging to recreate three-dimensional skeletal tissues. Such an achievement would facilitate a functioning model of bone metabolism, the next step in achieving skeletal regeneration.

The role of the fibroblast growth factor family in bone-related diseases

Fibroblast growth factor (FGF) family members are important regulators of cell growth, proliferation, differentiation, and regeneration. The abnormal expression of certain FGF family members can cause skeletal diseases, including achondroplasia, craniosynostosis syndrome, osteoarthritis, and Kashin-Beck disease. Accumulating evidence shows that FGFs play a crucial role in the growth and proliferation of bone and in the pathogenesis of certain bone-related diseases. Here, we review the involvement of FGFs in bone-related processes and diseases; FGF1 in the differentiation of human bone marrow mesenchymal stem cells and fracture repair; FGF2, FGF9, and FGF18 in osteoarthritis; FGF6 in bone and muscle injury; FGF8 in osteoarthritis and Kashin-Beck disease; and FGF21 and FGF23 on bone regulation. These findings indicate that FGFs are targets for novel therapeutic interventions for bone-related diseases.

Chondrogenic Differentiation of Pluripotent Stem Cells under Controllable Serum-Free Conditions

The repair of damaged articular cartilage using currently available implantation techniques is not sufficient for the full recovery of patients. Pluripotent stem cells (iPSC)-based therapies could bring new perspectives in the treatment of joint diseases. A number of protocols of in vitro differentiation of iPSC in chondrocytes for regenerative purposes have been recently described. However, in order to use these cells in clinics, the elimination of animal serum and feeder cells is essential. In our study, a strictly defined and controllable protocol was designed for the differentiation of pluripotent stem cells (BG01V, ND 41658*H, GPCCi001-A) in chondrocyte-like cells in serum- and a feeder cell-free system, using the embryoid bodies step. The extension of the protocol and culture conditions (monolayer versus 3D culture) was also tested after the initial 21 days of chondrogenic differentiation. Promotion of the chondrogenic differentiation in 3D culture via the elevated expression of genes related to chondrogenesis was achieved. Using immunofluorescence and immunohistochemistry staining techniques, the increased deposition of the specific extracellular matrix was indicated. As a result, chondrocyte-like cells in the early stages of their differentiation using pellet culture under fully controlled and defined conditions were obtained.

Emerging opportunities for induced pluripotent stem cells in orthopaedics

The discovery of induced pluripotent stem cells (iPSCs) has revolutionized biomedicine. Although the potential of iPSCs for tissue regeneration, disease modeling and drug screening has been largely recognized, findings of iPSC research to date are mostly focused on neurology, cardiology and haematology. For orthopaedics, growing interest in the unique cell type has prompted more researchers to get involved in iPSC research. In this article, we introduce the brief history of cellular reprogramming and different reprogramming methods that have been developed, discuss the biology of iPSCs and review previously reported findings of iPSC studies in orthopaedics.

The Translational potential of this article

Stem cell therapies hold great promise for treating orthopaedic diseases, manifested in recent study findings and results of clinical trials. iPSCs are a unique stem cell type derived from a patient’s own cells while still possessing the embryonic stem cell-featured pluripotency for generation of all tissues in the body. The distinctive properties make iPSCs much desirable to fulfill the promise of regenerative medicine for clinical orthopaedics.