iPS cell technologies and cartilage regeneration

iPSCs chondrogenic differentiation for personalized regenerative medicine: a literature review

Cartilage, an important connective tissue, provides structural support to other body tissues, and serves as a cushion against impacts throughout the body. Found at the end of the bones, cartilage decreases friction and averts bone-on-bone contact during joint movement. Therefore, defects of cartilage can result from natural wear and tear, or from traumatic events, such as injuries or sudden changes in direction during sports activities. Overtime, these cartilage defects which do not always produce immediate symptoms, could lead to severe clinical pathologies. The emergence of induced pluripotent stem cells (iPSCs) has revolutionized the field of regenerative medicine, providing a promising platform for generating various cell types for therapeutic applications. Thus, chondrocytes differentiated from iPSCs become a promising avenue for non-invasive clinical interventions for cartilage injuries and diseases. In this review, we aim to highlight the current strategies used for in vitro chondrogenic differentiation of iPSCs and to explore their multifaceted applications in disease modeling, drug screening, and personalized regenerative medicine. Achieving abundant functional iPSC-derived chondrocytes requires optimization of culture conditions, incorporating specific growth factors, and precise temporal control. Continual improvements in differentiation methods and integration of emerging genome editing, organoids, and 3D bioprinting technologies will enhance the translational applications of iPSC-derived chondrocytes. Finally, to unlock the benefits for patients suffering from cartilage diseases through iPSCs-derived technologies in chondrogenesis, automatic cell therapy manufacturing systems will not only reduce human intervention and ensure sterile processes within isolator-like platforms to minimize contamination risks, but also provide customized production processes with enhanced scalability and efficiency.

An overview of nasal cartilage bioprinting: from bench to bedside

Nasal cartilage diseases and injuries are known as significant challenges in reconstructive medicine, affecting a substantial number of individuals worldwide. In recent years, the advent of three-dimensional (3D) bioprinting has emerged as a promising approach for nasal cartilage reconstruction, offering potential breakthroughs in the field of regenerative medicine. This paper provides an overview of the methods and challenges associated with 3D bioprinting technologies in the procedure of reconstructing nasal cartilage tissue. The process of 3D bioprinting entails generating a digital 3D model using biomedical imaging techniques and computer-aided design to integrate both internal and external scaffold features. Then, bioinks which consist of biomaterials, cell types, and bioactive chemicals, are applied to facilitate the precise layer-by-layer bioprinting of tissue-engineered scaffolds. After undergoing in vitro and in vivo experiments, this process results in the development of the physiologically functional integrity of the tissue. The advantages of 3D bioprinting encompass the ability to customize scaffold design, enabling the precise incorporation of pore shape, size, and porosity, as well as the utilization of patient-specific cells to enhance compatibility. However, various challenges should be considered, including the optimization of biomaterials, ensuring adequate cell viability and differentiation, achieving seamless integration with the host tissue, and navigating regulatory attention. Although numerous studies have demonstrated the potential of 3D bioprinting in the rebuilding of such soft tissues, this paper covers various aspects of the bioprinted tissues to provide insights for the future development of repair techniques appropriate for clinical use.

Cell Therapy Approaches for Articular Cartilage Regeneration

Articular cartilage is a common cartilage type found in a multitude of joints throughout the human body. However, cartilage is limited in its regenerative capacity. A range of methods have been employed to aid adults under the age of 45 with cartilage defects, but other cartilage pathologies such as osteoarthritis are limited to non-steroidal anti-inflammatory drugs and total joint arthroplasty. Cell therapies and synthetic biology can be utilized to assist not only cartilage defects but have the potential as a therapeutic approach for osteoarthritis as well. In this review, we will cover current cell therapy approaches for cartilage defect regeneration with a focus on autologous chondrocyte implantation and matrix autologous chondrocyte implantation. We will then discuss the potential of stem cells for cartilage repair in osteoarthritis and the use of synthetic biology to genetically engineer cells to promote cartilage regeneration and potentially reverse osteoarthritis.

Cartilage Tissue Engineering in Practice: Preclinical Trials, Clinical Applications, and Prospects

Articular cartilage defects significantly compromise the quality of life in the global population. Although many strategies are needed to repair articular cartilage, including microfracture, autologous osteochondral transplantation, and osteochondral allograft, the therapeutic effects remain suboptimal. In recent years, with the development of cartilage tissue engineering, scientists have continuously improved the formulations of therapeutic cells, biomaterial-based scaffolds, and biological factors, which have opened new avenues for better therapeutics of cartilage lesions. This review focuses on advances in cartilage tissue engineering, particularly in preclinical trials and clinical applications, prospects, and challenges.

Exploring the Role of Enhancer-Mediated Transcriptional Regulation in Precision Biology

The emergence of precision biology has been driven by the development of advanced technologies and techniques in high-resolution biological research systems. Enhancer-mediated transcriptional regulation, a complex network of gene expression and regulation in eukaryotes, has attracted significant attention as a promising avenue for investigating the underlying mechanisms of biological processes and diseases. To address biological problems with precision, large amounts of data, functional information, and research on the mechanisms of action of biological molecules is required to address biological problems with precision. Enhancers, including typical enhancers and super enhancers, play a crucial role in gene expression and regulation within this network. The identification and targeting of disease-associated enhancers hold the potential to advance precision medicine. In this review, we present the concepts, progress, importance, and challenges in precision biology, transcription regulation, and enhancers. Furthermore, we propose a model of transcriptional regulation for multi-enhancers and provide examples of their mechanisms in mammalian cells, thereby enhancing our understanding of how enhancers achieve precise regulation of gene expression in life processes. Precision biology holds promise in providing new tools and platforms for discovering insights into gene expression and disease occurrence, ultimately benefiting individuals and society as a whole.

Induced pluripotent stem cells in companion animals: how can we move the field forward?

Following a one medicine approach, the development of regenerative therapies for human patients leads to innovative treatments for animals, while pre-clinical studies on animals provide knowledge to advance human medicine. Among many different biological products under investigation, stem cells are among the most prominent. Mesenchymal stromal cells (MSCs) are extensively investigated, but they present challenges such as senescence and limited differentiation ability. Embryonic stem cells (ESCs) are pluripotent cells with a virtually unlimited capacity for self-renewal and differentiation, but the use of embryos carries ethical concerns. Induced pluripotent stem cells (iPSCs) can overcome all of these limitations, as they closely resemble ESCs but are derived from adult cells by reprogramming in the laboratory using pluripotency-associated transcription factors. iPSCs hold great potential for applications in therapy, disease modeling, drug screening, and even species preservation strategies. However, iPSC technology is less developed in veterinary species compared to human. This review attempts to address the specific challenges associated with generating and applying iPSCs from companion animals. Firstly, we discuss strategies for the preparation of iPSCs in veterinary species and secondly, we address the potential for different applications of iPSCs in companion animals. Our aim is to provide an overview on the state of the art of iPSCs in companion animals, focusing on equine, canine, and feline species, as well as to identify which aspects need further optimization and, where possible, to provide guidance on future advancements. Following a "step-by-step" approach, we cover the generation of iPSCs in companion animals from the selection of somatic cells and the reprogramming strategies, to the expansion and characterization of iPSCs. Subsequently, we revise the current applications of iPSCs in companion animals, identify the main hurdles, and propose future paths to move the field forward. Transferring the knowledge gained from human iPSCs can increase our understanding in the biology of pluripotent cells in animals, but it is critical to further investigate the differences among species to develop specific approaches for animal iPSCs. This is key for significantly advancing iPSC application in veterinary medicine, which at the same time will also allow gaining pre-clinical knowledge transferable to human medicine.

Differences in the intrinsic chondrogenic potential of human mesenchymal stromal cells and iPSC-derived multipotent cells

BACKGROUND

Human multipotent progenitor cells (hiMPCs) created from induced pluripotent stem cells (iPSCs) represent a new cell source for cartilage regeneration. In most studies, bone morphogenetic proteins (BMPs) are needed to enhance transforming growth factor-β (TGFβ)-induced hiMPC chondrogenesis. In contrast, TGFβ alone is sufficient to result in robust chondrogenesis of human primary mesenchymal stromal cells (hMSCs). Currently, the mechanism underlying this difference between hiMPCs and hMSCs has not been fully understood.

METHODS

In this study, we first tested different growth factors alone or in combination in stimulating hiMPC chondrogenesis, with a special focus on chondrocytic hypertrophy. The reparative capacity of hiMPCs-derived cartilage was assessed in an osteochondral defect model created in rats. hMSCs isolated from bone marrow were included in all studies as the control. Lastly, a mechanistic study was conducted to understand why hiMPCs and hMSCs behave differently in responding to TGFβ.

RESULTS

Chondrogenic medium supplemented with TGFβ3 and BMP6 led to robust in vitro cartilage formation from hiMPCs with minimal hypertrophy. Cartilage tissue generated from this new method was resistant to osteogenic transition upon subcutaneous implantation and resulted in a hyaline cartilage-like regeneration in osteochondral defects in rats. Interestingly, TGFβ3 induced phosphorylation of both Smad2/3 and Smad1/5 in hMSCs, but only activated Smad2/3 in hiMPCs. Supplementing BMP6 activated Smad1/5 and significantly enhanced TGFβ's compacity in inducing hiMPC chondrogenesis. The chondro-promoting function of BMP6 was abolished by the treatment of a BMP pathway inhibitor.

CONCLUSIONS

This study describes a robust method to generate chondrocytes from hiMPCs with low hypertrophy for hyaline cartilage repair, as well as elucidates the difference between hMSCs and hiMPCs in response to TGFβ. Our results also indicated the importance of activating both Smad2/3 and Smad1/5 in the initiation of chondrogenesis.

The role of the immune microenvironment in bone, cartilage, and soft tissue regeneration: from mechanism to therapeutic opportunity

Bone, cartilage, and soft tissue regeneration is a complex spatiotemporal process recruiting a variety of cell types, whose activity and interplay must be precisely mediated for effective healing post-injury. Although extensive strides have been made in the understanding of the immune microenvironment processes governing bone, cartilage, and soft tissue regeneration, effective clinical translation of these mechanisms remains a challenge. Regulation of the immune microenvironment is increasingly becoming a favorable target for bone, cartilage, and soft tissue regeneration; therefore, an in-depth understanding of the communication between immune cells and functional tissue cells would be valuable. Herein, we review the regulatory role of the immune microenvironment in the promotion and maintenance of stem cell states in the context of bone, cartilage, and soft tissue repair and regeneration. We discuss the roles of various immune cell subsets in bone, cartilage, and soft tissue repair and regeneration processes and introduce novel strategies, for example, biomaterial-targeting of immune cell activity, aimed at regulating healing. Understanding the mechanisms of the crosstalk between the immune microenvironment and regeneration pathways may shed light on new therapeutic opportunities for enhancing bone, cartilage, and soft tissue regeneration through regulation of the immune microenvironment.

Advanced injectable hydrogels for cartilage tissue engineering

The rapid development of tissue engineering makes it an effective strategy for repairing cartilage defects. The significant advantages of injectable hydrogels for cartilage injury include the properties of natural extracellular matrix (ECM), good biocompatibility, and strong plasticity to adapt to irregular cartilage defect surfaces. These inherent properties make injectable hydrogels a promising tool for cartilage tissue engineering. This paper reviews the research progress on advanced injectable hydrogels. The cross-linking method and structure of injectable hydrogels are thoroughly discussed. Furthermore, polymers, cells, and stimulators commonly used in the preparation of injectable hydrogels are thoroughly reviewed. Finally, we summarize the research progress of the latest advanced hydrogels for cartilage repair and the future challenges for injectable hydrogels.

Spheroid culture for chondrocytes triggers early stage of endochondral ossification

Endochondral ossification is the process of bone formation derived from growing cartilage during the development of the skeletal system. In previous studies, we have attempted to evoke the osteocyte differentiation of osteoblast precursor cells under a three-dimensional (3D) culture model. In order to recapitulate the endochondral ossification, the present study utilized the self-organized scaffold-free spheroid model reconstructed by pre-chondrocyte cells. Within 2-day cultivation in the absence of the chemically induced chondrogenesis supplements, the chondrocyte marker was greatly expressed in the inner region of the spheroid, whereas the hypertrophic chondrocyte marker was strongly detected in the surface region of the spheroid. Notably, we found out that the gene expression levels of osteocyte markers were also greatly up-regulated compared to the conventional 2D monolayer. Moreover, there was a hypertrophied morphologic change in the pre-chondrocyte spheroid from 4-day to 28-day cultivation. In this study, we highlighted the potentials of the 3D culture method to acquire the hypertrophic chondrocyte differentiation of the pre-chondrocyte cells to recapitulate the early stage of the endochondral ossification. This article is protected by copyright. All rights reserved.

Gene Therapy in Orthopaedics: Progress and Challenges in Pre-Clinical Development and Translation

In orthopaedics, gene-based treatment approaches are being investigated for an array of common -yet medically challenging- pathologic conditions of the skeletal connective tissues and structures (bone, cartilage, ligament, tendon, joints, intervertebral discs etc.). As the skeletal system protects the vital organs and provides weight-bearing structural support, the various tissues are principally composed of dense extracellular matrix (ECM), often with minimal cellularity and vasculature. Due to their functional roles, composition, and distribution throughout the body the skeletal tissues are prone to traumatic injury, and/or structural failure from chronic inflammation and matrix degradation. Due to a mixture of environment and endogenous factors repair processes are often slow and fail to restore the native quality of the ECM and its function. In other cases, large-scale lesions from severe trauma or tumor surgery, exceed the body’s healing and regenerative capacity. Although a wide range of exogenous gene products (proteins and RNAs) have the potential to enhance tissue repair/regeneration and inhibit degenerative disease their clinical use is hindered by the absence of practical methods for safe, effective delivery. Cumulatively, a large body of evidence demonstrates the capacity to transfer coding sequences for biologic agents to cells in the skeletal tissues to achieve prolonged delivery at functional levels to augment local repair or inhibit pathologic processes. With an eye toward clinical translation, we discuss the research progress in the primary injury and disease targets in orthopaedic gene therapy. Technical considerations important to the exploration and pre-clinical development are presented, with an emphasis on vector technologies and delivery strategies whose capacity to generate and sustain functional transgene expression in vivo is well-established.

Material-Assisted Strategies for Osteochondral Defect Repair

The osteochondral (OC) unit plays a pivotal role in joint lubrication and in the transmission of constraints to bones during movement. The OC unit does not spontaneously heal; therefore, OC defects are considered to be one of the major risk factors for developing long-term degenerative joint diseases such as osteoarthritis. Yet, there is currently no curative treatment for OC defects, and OC regeneration remains an unmet medical challenge. In this context, a plethora of tissue engineering strategies have been envisioned over the last two decades, such as combining cells, biological molecules, and/or biomaterials, yet with little evidence of successful clinical transfer to date. This striking observation must be put into perspective with the difficulty in comparing studies to identify overall key elements for success. This systematic review aims to provide a deeper insight into the field of material-assisted strategies for OC regeneration, with particular considerations for the therapeutic potential of the different approaches (with or without cells or biological molecules), and current OC regeneration evaluation methods. After a brief description of the biological complexity of the OC unit, the recent literature is thoroughly analyzed, and the major pitfalls, emerging key elements, and new paths to success are identified and discussed.

A Pilot Study of Seamless Regeneration of Bone and Cartilage in Knee Joint Regeneration Using Honeycomb TCP

The knee joint is a continuous structure of bone and cartilage tissue, making it difficult to regenerate using artificial biomaterials. In a previous study, we succeeded in developing honeycomb tricalcium phosphate (TCP), which has through-and-through holes and is able to provide the optimum microenvironment for hard tissue regeneration. We demonstrated that TCP with 300 μm pore diameters (300TCP) induced vigorous bone formation, and that TCP with 75 μm pore diameters (75TCP) induced cartilage formation. In the present study, we regenerated a knee joint defect using honeycomb TCP. 75TCP and 300TCP were loaded with transforming growth factor (TGF)-β alone or bone morphogenic protein (BMP)-2+TGF-β with or without Matrigel and transplanted into knee joint defect model rabbits. 75TCP showed no bone or cartilage tissue formation in any of the groups with TGF-β alone and BMP-2+TGF-β with/without Matrigel. However, for 300TCP and BMP-2+TGF-β with or without Matrigel, vigorous bone tissue formation was observed in the TCP holes, and cartilage tissue formation in the TCP surface layer was continuous with the existing cartilage. The cartilage area in the TCP surface was larger in the group without Matrigel (with BMP-2+TGF-β) than in the group with Matrigel (with BMP-2+TGF-β). Therefore, honeycomb TCP can induce the seamless regeneration of bone and cartilage in a knee joint.

Methods of Modification of Mesenchymal Stem Cells and Conditions of Their Culturing for Hyaline Cartilage Tissue Engineering

The use of mesenchymal stromal cells (MSCs) for tissue engineering of hyaline cartilage is a topical area of regenerative medicine that has already entered clinical practice. The key stage of this procedure is to create conditions for chondrogenic differentiation of MSCs, increase the synthesis of hyaline cartilage extracellular matrix proteins by these cells and activate their proliferation. The first such works consisted in the indirect modification of cells, namely, in changing the conditions in which they are located, including microfracturing of the subchondral bone and the use of 3D biodegradable scaffolds. The most effective methods for modifying the cell culture of MSCs are protein and physical, which have already been partially introduced into clinical practice. Genetic methods for modifying MSCs, despite their effectiveness, have significant limitations. Techniques have not yet been developed that allow studying the effectiveness of their application even in limited groups of patients. The use of MSC modification methods allows precise regulation of cell culture proliferation, and in combination with the use of a 3D biodegradable scaffold, it allows obtaining a hyaline-like regenerate in the damaged area. This review is devoted to the consideration and comparison of various methods used to modify the cell culture of MSCs for their use in regenerative medicine of cartilage tissue.

Cell-laden injectable microgels: Current status and future prospects for cartilage regeneration

Injectable hydrogels have been employed extensively as versatile materials for cartilage regeneration due to their excellent biocompatibility, tunable structure, and ability to accommodate bioactive factors, as well as their ability to be locally delivered via minimally invasive injection to fill irregular defects. More recently, in vitro and in vivo studies have revealed that processing these materials to produce cell-laden microgels can enhance cell-cell and cell-matrix interactions and boost nutrient and metabolite exchange. Moreover, these studies have demonstrated gene expression profiles and matrix regeneration that are superior compared to conventional injectable bulk hydrogels. As cell-laden microgels and their application in cartilage repair are moving closer to clinical translation, this review aims to present an overview of the recent developments in this field. Here we focus on the currently used biomaterials and crosslinking strategies, the innovative fabrication techniques being used for the production of microgels, the cell sources used, the signals used for induction of chondrogenic differentiation and the resultant biological responses, and the ability to create three-dimensional, functional cartilage tissues. In addition, this review also covers the current clinical approaches for repairing cartilage as well as specific challenges faced when attempting the regeneration of damaged cartilage tissue. New findings related to the macroporous nature of the structures formed by the assembled microgel building blocks and the novel use of microgels in 3D printing for cartilage tissue engineering are also highlighted. Finally, we outline the challenges and future opportunities for employing cell-laden microgels in clinical applications.

Cell Sources for Cartilage Repair-Biological and Clinical Perspective

Cell-based therapy represents a promising treatment strategy for cartilage defects. Alone or in combination with scaffolds/biological signals, these strategies open many new avenues for cartilage tissue engineering. However, the choice of the optimal cell source is not that straightforward. Currently, various types of differentiated cells (articular and nasal chondrocytes) and stem cells (mesenchymal stem cells, induced pluripotent stem cells) are being researched to objectively assess their merits and disadvantages with respect to the ability to repair damaged articular cartilage. In this paper, we focus on the different cell types used in cartilage treatment, first from a biological scientist’s perspective and then from a clinician’s standpoint. We compare and analyze the advantages and disadvantages of these cell types and offer a potential outlook for future research and clinical application.

Bio-3D printing iPSC-derived human chondrocytes for articular cartilage regeneration

Osteoarthritis is a leading cause of pain and joint immobility, the incidence of which is increasing worldwide. Currently, total joint replacement is the only treatment for end-stage disease. Scaffold-based tissue engineering is a promising alternative approach for joint repair but is subject to limitations such as poor cytocompatibility and degradation-associated toxicity. To overcome these limitations, a completely scaffold-free Kenzan method for bio-3D printing was used to fabricate cartilage constructs feasible for repairing large chondral defects. Human induced pluripotent stem cell (iPSC)-derived neural crest cells with high potential to undergo chondrogenesis through mesenchymal stem cell differentiation were used to fabricate the cartilage. Unified, self-sufficient, and functional cartilaginous constructs up to 6 cm²in size were assembled by optimizing fabrication time during chondrogenic induction. Maturation for 3 weeks facilitated the self-organisation of the cells, which improved the construct's mechanical strength (compressive and tensile properties) and induced changes in glycosaminoglycan and type II collagen expression, resulting in improved tissue function. The compressive modulus of the construct reached the native cartilage range of 0.88 MPa in the 5th week of maturation. This paper reports the fabrication of anatomically sized and shaped cartilage constructs, achieved by combining novel iPSCs and bio-3D printers using a Kenzan needle array technology, which may facilitate chondral resurfacing of articular cartilage defects.

Dysregulation of Cells Cycle and Apoptosis in Human Induced Pluripotent Stem Cells Chondrocytes Through p53 Pathway by HT-2 Toxin: An in vitro Study

Kashin–Beck disease (KBD) mainly damages growth plate of adolescents and is susceptible to both gene and gene–environmental risk factors. HT-2 toxin, which is a primary metabolite of T-2 toxin, was regarded as one of the environmental risk factors of KBD. We used successfully generated KBD human induced pluripotent stem cells (hiPSCs) and control hiPSCs, which carry different genetic information. They have potential significance in exploring the effects of HT-2 toxin on hiPSC chondrocytes and interactive genes with HT-2 toxin for the purpose of providing a cellular disease model for KBD. In this study, we gave HT-2 toxin treatment to differentiating hiPSC chondrocytes in order to investigate the different responses of KBD hiPSC chondrocytes and control hiPSC chondrocytes to HT-2 toxin. The morphology of HT-2 toxin-treated hiPSC chondrocytes investigated by transmission electron microscope clearly showed that the ultrastructure of organelles was damaged and type II collagen expression in hiPSC chondrocytes was downregulated by HT-2 treatment. Moreover, dysregulation of cell cycle was observed; and p53, p21, and CKD6 gene expressions were dysregulated in hiPSC chondrocytes after T-2 toxin treatment. Flow cytometry also demonstrated that there were significantly increased amounts of late apoptotic cells in KBD hiPSC chondrocytes and that the mRNA expression level of Fas was upregulated. In addition, KBD hiPSC chondrocytes presented stronger responses to HT-2 toxin than control hiPSC chondrocytes. These findings confirmed that HT-2 is an environmental risk factor of KBD and that p53 pathway interacted with HT-2 toxin, causing damaged ultrastructure of organelles, accelerating cell cycle in G1 phase, and increasing late apoptosis in KBD hiPSC chondrocytes.

The first human induced pluripotent stem cell line of Kashin-Beck disease reveals involvement of heparan sulfate proteoglycan biosynthesis and PPAR pathway

Kashin-Beck disease (KBD) is an endemic osteochondropathy. Due to a lack of suitable animal or cellular disease models, the research progress on KBD has been limited. Our goal was to establish the first disease-specific human induced pluripotent stem cell (hiPSC) cellular disease model of KBD, and to explore its etiology and pathogenesis exploiting transcriptome sequencing. HiPSCs were reprogrammed from dermal fibroblasts of two KBD and one healthy control donor via integration-free vectors. Subsequently, hiPSCs were differentiated into chondrocytes through three-week culture. Gene expression profiles in KBD, normal primary chondrocytes, and hiPSC-derived chondrocytes were defined by RNA sequencing. A Venn diagram was constructed to show the number of shared differentially expressed genes (DEGs) between KBD and normal. Gene oncology and Kyoto Encyclopedia of Genes and Genomes annotations were performed, and six DEGs were further validated in other individuals by RT-qPCR. KBD cellular disease models were successfully established by generation of hiPSC lines. Seventeen consistent and significant DEGs present in all compared groups (KBD and normal) were identified. RT-qPCR validation gave consistent results with the sequencing data. Glycosaminoglycan biosynthesis-heparan sulfate/heparin; PPAR signaling pathway; and cell adhesion molecules (CAMs) were identified to be significantly altered in KBD. Differentiated chondrocytes derived from KBD-origin hiPSCs provide the first cellular disease model for etiological studies of KBD. This study also provides new sights into the pathogenesis and etiology of KBD and is likely to inform the development of targeted therapeutics for its treatment.

Osteochondral Tissue Engineering: The Potential of Electrospinning and Additive Manufacturing

The socioeconomic impact of osteochondral (OC) damage has been increasing steadily over time in the global population, and the promise of tissue engineering in generating biomimetic tissues replicating the physiological OC environment and architecture has been falling short of its projected potential. The most recent advances in OC tissue engineering are summarised in this work, with a focus on electrospun and 3D printed biomaterials combined with stem cells and biochemical stimuli, to identify what is causing this pitfall between the bench and the patients' bedside. Even though significant progress has been achieved in electrospinning, 3D-(bio)printing, and induced pluripotent stem cell (iPSC) technologies, it is still challenging to artificially emulate the OC interface and achieve complete regeneration of bone and cartilage tissues. Their intricate architecture and the need for tight spatiotemporal control of cellular and biochemical cues hinder the attainment of long-term functional integration of tissue-engineered constructs. Moreover, this complexity and the high variability in experimental conditions used in different studies undermine the scalability and reproducibility of prospective regenerative medicine solutions. It is clear that further development of standardised, integrative, and economically viable methods regarding scaffold production, cell selection, and additional biochemical and biomechanical stimulation is likely to be the key to accelerate the clinical translation and fill the gap in OC treatment.

Cartilage Tissue Engineering by Extrusion Bioprinting: Process Analysis, Risk Evaluation, and Mitigation Strategies

Extrusion bioprinting is considered promising in cartilage tissue engineering since it allows the fabrication of complex, customized, and living constructs potentially suitable for clinical applications. However, clinical translation is often complicated by the variability and unknown/unsolved issues related to this technology. The aim of this study was to perform a risk analysis on a research process, consisting in the bioprinting of a stem cell-laden collagen bioink to fabricate constructs with cartilage-like properties. The method utilized was the Failure Mode and Effect Analysis/Failure Mode and Effect Criticality Analysis (FMEA/FMECA) which foresees a mapping of the process to proactively identify related risks and the mitigation actions. This proactive risk analysis allowed the identification of forty-seven possible failure modes, deriving from seventy-one potential causes. Twenty-four failure modes displayed a high-risk level according to the selected evaluation criteria and threshold (RPN > 100). The results highlighted that the main process risks are a relatively low fidelity of the fabricated structures, unsuitable parameters/material properties, the death of encapsulated cells due to the shear stress generated along the nozzle by mechanical extrusion, and possible biological contamination phenomena. The main mitigation actions involved personnel training and the implementation of dedicated procedures, system calibration, printing conditions check, and, most importantly, a thorough knowledge of selected biomaterial and cell properties that could be built either through the provided data/scientific literature or their preliminary assessment through dedicated experimental optimization phase. To conclude, highlighting issues in the early research phase and putting in place all the required actions to mitigate risks will make easier to develop a standardized process to be quickly translated to clinical use.

Use of human induced pluripotent stem cells for cartilage regeneration in vitro and within chondral defect models of knee joint cartilage in vivo: a Preferred Reporting Items for Systematic Reviews and Meta-Analyses systematic literature review

BACKGROUND AIMS

Articular cartilage has limited regenerative ability when damaged through trauma or disease. Failure to treat focal chondral lesions results in changes that inevitably progress to osteoarthritis. Osteoarthritis is a major contributor to disability globally, which results in significant medical costs and lost wages every year. Human induced pluripotent stem cells (hiPSCs) have long been considered a potential autologous therapeutic option for the treatment of focal chondral lesions. Although there are significant advantages to hiPSCs over other stem cell options, such as mesenchymal and embryonic stem cells, there are concerns regarding their ability to form bona fide cartilage and their tumorgenicity in vivo.

METHODS

The authors carried out a systematic literature review on the use of hiPSCs to produce differentiated progeny capable of producing high-quality cartilage in vitro and regenerate cartilage in osteochondral defects in vivo in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Eight studies were included in the review that used hiPSCs or their derived progeny in xenogeneic transplants in animal models to regenerate cartilage in osteochondral defects of the knee joint. The in vitro-differentiated, hiPSC-derived and in vivo defect repair ability of the hiPSC-derived progeny transplants were assessed.

RESULTS

Most studies reported the generation of high-quality cartilage-producing progeny that were able to successfully repair cartilage defects in vivo. No tumorigenicity was observed.

CONCLUSIONS

The authors conclude that hiPSCs offer a valuable source of cartilage-producing progeny that show promise as an effective cell-based therapy in treating focal chondral lesions.

Paracrine Interactions Involved in Human Induced Pluripotent Stem Cells Differentiation into Chondrocytes

Osteoarthritis (OA), as a degenerative joint disease, is the most common form of joint disorder that causes pain, stiffness, and other symptoms associated with OA. Various genetic, biomechanical, and environmental factors have a relevant role in the development of OA. To date, extensive efforts are currently being made to overcome the poor self-healing capacity of articular cartilage. Despite the pivotal role of chondrocytes, their proliferation and repair capacity after tissue injury are limited. Therefore, the development of new strategies to overcome these constraints is urgently needed. Recent advances in regenerative medicine suggest that pluripotent stem cells are promising stem cell sources for cartilage repair. Pluripotent stem cells are undifferentiated cells that have the capacity to differentiate into different types of cells and can self-renew indefinitely. In the past few decades, numerous attempts have been made to regenerate articular cartilage by using induced pluripotent stem cells (iPSCs). The potential applications of patient-specific iPSCs hold great promise for regenerative medicine and OA treatment. However, there are different culture conditions for the preparation and characterization of human iPSCs-derived chondrocytes (hiChondrocytes). Recent biochemical analyses reported that several paracrine factors such as TGFb, BMPs, WNT, Ihh, and Runx have been shown to be involved in cartilage cell proliferation and differentiation from human iPSCs. In this review, we summarize and discuss the paracrine interactions involved in human iPSCs differentiation into chondrocytes in different cell culture media.

Alterations of Glycosphingolipid Glycans and Chondrogenic Markers during Differentiation of Human Induced Pluripotent Stem Cells into Chondrocytes

Due to the limited intrinsic healing potential of cartilage, injury to this tissue may lead to osteoarthritis. Human induced pluripotent stem cells (iPSCs), which can be differentiated into chondrocytes, are a promising source of cells for cartilage regenerative therapy. Currently, however, the methods for evaluating chondrogenic differentiation of iPSCs are very limited; the main techniques are based on the detection of chondrogenic genes and histological analysis of the extracellular matrix. The cell surface is coated with glycocalyx, a layer of glycoconjugates including glycosphingolipids (GSLs) and glycoproteins. The glycans in glycoconjugates play important roles in biological events, and their expression and structure vary widely depending on cell types and conditions. In this study, we performed a quantitative GSL-glycan analysis of human iPSCs, iPSC-derived mesenchymal stem cell like cells (iPS-MSC like cells), iPS-MSC-derived chondrocytes (iPS-MSC-CDs), bone marrow-derived mesenchymal stem cells (BMSCs), and BMSC-derived chondrocytes (BMSC-CDs) using glycoblotting technology. We found that GSL-glycan profiles differed among cell types, and that the GSL-glycome underwent a characteristic alteration during the process of chondrogenic differentiation. Furthermore, we analyzed the GSL-glycome of normal human cartilage and found that it was quite similar to that of iPS-MSC-CDs. This is the first study to evaluate GSL-glycan structures on human iPS-derived cartilaginous particles under micromass culture conditions and those of normal human cartilage. Our results indicate that GSL-glycome analysis is useful for evaluating target cell differentiation and can thus support safe regenerative medicine.

Osteochondral Injury, Management and Tissue Engineering Approaches

Osteochondral lesions (OL) are a common clinical problem for orthopedic surgeons worldwide and are associated with multiple clinical scenarios ranging from trauma to osteonecrosis. OL vary from chondral lesions in that they involve the subchondral bone and chondral surface, making their management more complex than an isolated chondral injury. Subchondral bone involvement allows for a natural healing response from the body as marrow elements are able to come into contact with the defect site. However, this repair is inadequate resulting in fibrous scar tissue. The second differentiating feature of OL is that damage to the subchondral bone has deleterious effects on the mechanical strength and nutritive capabilities to the chondral joint surface. The clinical solution must, therefore, address both the articular cartilage as well as the subchondral bone beneath it to restore and preserve joint health. Both cartilage and subchondral bone have distinctive functional requirements and therefore their physical and biological characteristics are very much dissimilar, yet they must work together as one unit for ideal joint functioning. In the past, the obvious solution was autologous graft transfer, where an osteochondral bone plug was harvested from a non-weight bearing portion of the joint and implanted into the defect site. Allografts have been utilized similarly to eliminate the donor site morbidity associated with autologous techniques and overall results have been good but both techniques have their drawbacks and limitations. Tissue engineering has thus been an attractive option to create multiphasic scaffolds and implants. Biphasic and triphasic implants have been under explored and have both a chondral and subchondral component with an interface between the two to deliver an implant which is biocompatible and emulates the osteochondral unit as a whole. It has been a challenge to develop such implants and many manufacturing techniques have been utilized to bring together two unalike materials and combine them with cellular therapies. We summarize the functions of the osteochondral unit and describe the currently available management techniques under study.

Shaking culture enhances chondrogenic differentiation of mouse induced pluripotent stem cell constructs

Mechanical loading on articular cartilage induces various mechanical stresses and strains. In vitro hydrodynamic forces such as compression, shear and tension impact various cellular properties including chondrogenic differentiation, leading us to hypothesize that shaking culture might affect the chondrogenic induction of induced pluripotent stem cell (iPSC) constructs. Three-dimensional mouse iPSC constructs were fabricated in a day using U-bottom 96-well plates, and were subjected to preliminary chondrogenic induction for 3 days in static condition, followed by chondrogenic induction culture using a see-saw shaker for 17 days. After 21 days, chondrogenically induced iPSC (CI-iPSC) constructs contained chondrocyte-like cells with abundant ECM components. Shaking culture significantly promoted cell aggregation, and induced significantly higher expression of chondrogenic-related marker genes than static culture at day 21. Immunohistochemical analysis also revealed higher chondrogenic protein expression. Furthemore, in the shaking groups, CI-iPSCs showed upregulation of TGF-β and Wnt signaling-related genes, which are known to play an important role in regulating cartilage development. These results suggest that shaking culture activates TGF-β expression and Wnt signaling to promote chondrogenic differentiation in mouse iPSCs in vitro. Shaking culture, a simple and convenient approach, could provide a promising strategy for iPSC-based cartilage bioengineering for study of disease mechanisms and new therapies.

Multiscale mechanics of tissue-engineered cartilage grown from human chondrocytes and human-induced pluripotent stem cells

Tissue-engineered cartilage has shown promising results in the repair of focal cartilage defects. However, current clinical techniques rely on an extra surgical procedure to biopsy healthy cartilage to obtain human chondrocytes. Alternatively, induced pluripotent stem cells (iPSCs) have the ability to differentiate into chondrocytes and produce cartilaginous matrix without the need to biopsy healthy cartilage. However, the mechanical properties of tissue-engineered cartilage with iPSCs are unknown and might be critical to long-term tissue function and health. This study used confined compression, cartilage on glass tribology, and shear testing on a confocal microscope to assess the macroscale and microscale mechanical properties of two constructs seeded with either chondrocyte-derived iPSCs (Ch-iPSCs) or native human chondrocytes. Macroscale properties of Ch-iPSC constructs provided similar or better mechanical properties than chondrocyte constructs. Under compression, Ch-iPSC constructs had an aggregate modulus that was two times larger than chondrocyte constructs and was closer to native tissue. No differences in the shear modulus and friction coefficients were observed between Ch-iPSC and chondrocyte constructs. On the microscale, Ch-iPSC and chondrocyte constructs had different depth-dependent mechanical properties, neither of which matches native tissue. These observed depth-dependent differences may be important to the function of the implant. Overall, this comparison of multiple mechanical properties of Ch-iPSC and chondrocyte constructs shows that using Ch-iPSCs can produce equivalent or better global mechanical properties to chondrocytes. Therefore, iPSC-seeded cartilage constructs could be a promising solution to repair focal cartilage defects. The chondrocyte constructs used in this study have been implanted into humans for clinical trials. Therefore, Ch-iPSC constructs could also be used clinically in place of the current chondrocyte construct.

Culture substrate-associated YAP inactivation underlies chondrogenic differentiation of human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) are a promising cell source for the creation of cartilage to treat articular cartilage damage. The molecular mechanisms that translate culture conditions to the chondrogenic differentiation of hiPSCs remain to be analyzed. To analyze the effects of culture substrates, we chondrogenically differentiated hiPSCs on Matrigel or laminin 511‐E8 while holding the composition of the chondrogenic medium constant. Cartilage was formed from hiPSCs on Matrigel, but not on laminin 511‐E8. On Matrigel, the hiPSCs were round and yes‐associated protein (YAP) was inactive. In contrast, on laminin 511‐E8, the hiPSCs were flat and YAP was active. Treating the laminin 511‐E8 hiPSCs in a bioreactor caused cell aggregates, in which the cells were round and YAP was inactive. Subsequent culture of the aggregates in chondrogenic medium resulted in cartilage formation. Transient knockdown of YAP in hiPSCs around the start of chondrogenic differentiation successfully formed cartilage on laminin 511‐E8, suggesting that the activation of YAP is responsible for the failure of cartilage formation from hiPSCs on laminin 511‐E8. Consistently, the addition of YAP inhibitors to laminin 511‐E8 hiPSCs caused partial cartilage formation. This study contributes to identifying the molecules that mediate the effects of culture substrates on the chondrogenic differentiation of hiPSCs as well as to developing clinically applicable chondrogenic differentiation methods.

RT-qPCR analyses on the osteogenic differentiation from human iPS cells: an investigation of reference genes

Reverse transcription quantitative PCR (RT-qPCR) is used to quantify gene expression and require standardization with reference genes. We sought to identify the reference genes best suited for experiments that induce osteogenic differentiation from human induced pluripotent stem cells. They were cultured in an undifferentiated maintenance medium and after confluence, further cultured in an osteogenic differentiation medium for 28 days. RT-qPCR was performed on undifferentiation markers, osteoblast and osteocyte differentiation markers, and reference gene candidates. The expression stability of each reference gene candidate was ranked using four algorithms. General rankings identified TATA box binding protein in the first place, followed by transferrin receptor, ribosomal protein large P0, and finally, beta-2-microglobulin, which was revealed as the least stable. Interestingly, universally used GAPDH and ACTB were found to be unsuitable. Our findings strongly suggest a need to evaluate the expression stability of reference gene candidates for each experiment.

Visualization of Human Induced Pluripotent Stem Cells-Derived Three-Dimensional Cartilage Tissue by Gelatin Nanospheres

Recently, many studies on the three-dimensional (3D) fabrication of cells have been performed. Under these circumstances, it is indispensable to develop the imaging technologies and methodologies for noninvasive visualization of 3D cells fabricated. The objective of this study is to develop the labeling method of human induced pluripotent stem (iPS) cells-derived 3D cartilage tissue with gelatin nanospheres coincorporating three kinds of quantum dots (QD) and iron oxide nanoparticles (IONP) (GNS_QD+IONP). In this study, two labeling methods were performed. One is that a cartilage tissue was labeled directly by incubating with octaarginine (R8)-treated GNS_QD+IONP (direct labeling method). The other one is a "dissociation and labeling method." First, the cartilage tissue was dissociated to cells in a single dispersed state. Then, the cells were incubated with R8-GNS_QD+IONP in a monolayer culture. Finally, the cells labeled were fabricated to 3D pellets or cell sheets. By the direct labeling method, only cells residing in the surrounding site of cartilage tissue were labeled. On the contrary, the 3D cartilage pellets and the cell sheets were homogenously labeled and maintained fluorescently visualized over 4 weeks. In addition, the cartilage properties were histologically detected even after the process of dissociation and labeling. Homogenous labeling and visualization of human iPS cells-derived 3D cartilage tissue was achieved by the dissociation and labeling method with GNS_QD+IONP. Impact statement The homogenous labeling and visualization of human iPS cells-derived three-dimensional (3D) cartilage tissue was achieved over 4 weeks by the dissociation and labeling method with gelatin nanospheres coincorporating quantum dots (QD) and iron oxide nanoparticles (IONP) (GNS_QD+IONP). The cartilage properties of cells treated were maintained. It is concluded that the dissociation and labeling method with GNS_QD+IONP is a promising to visualize the human iPS cells-derived 3D cartilage tissue.

A lithium-containing biomaterial promotes chondrogenic differentiation of induced pluripotent stem cells with reducing hypertrophy

Background

Induced pluripotent stem cells (iPSCs) exhibit limitless pluripotent plasticity and proliferation capability to provide an abundant cell source for tissue regenerative medicine. Thus, inducing iPSCs toward a specific differentiation direction is an important scientific question. Traditionally, iPSCs have been induced to chondrocytes with the help of some small molecules within 21–36 days. To speed up the differentiation of iPSCs, we supposed to utilize bioactive ceramics to assist chondrogenic-induction process.

Methods

In this study, we applied ionic products (3.125~12.5 mg/mL) of the lithium-containing bioceramic (Li₂Ca₄Si₄O₁₃, L2C4S4) and individual Li⁺ (5.78~23.73 mg/L) in the direct chondrogenic differentiation of human iPSCs.

Results

Compared to pure chondrogenic medium and extracts of tricalcium phosphate (TCP), the extracts of L2C4S4 at a certain concentration range (3.125~12.5 mg/mL) significantly enhanced chondrogenic proteins Type II Collagen (COL II)/Aggrecan/ SRY-Box 9 (SOX9) synthesis and reduced hypertrophic protein type X collagen (COL X)/matrix metallopeptidase 13 (MMP13) production in iPSCs-derived chondrocytes within 14 days, suggesting that these newly generated chondrocytes exhibited favorable chondrocytes characteristics and maintained a low-hypertrophy state. Further studies demonstrated that the individual Li⁺ ions at the concentration range of 5.78~23.73 mg/L also accelerated the chondrogenic differentiation of iPSCs, indicating that Li⁺ ions played a pivotal role in chondrogenic differentiation process.

Conclusions

These findings indicated that lithium-containing bioceramic with bioactive specific ionic components may be used for a promising platform for inducing iPSCs toward chondrogenic differentiation and cartilage regeneration.

Therapeutic "Tool" in Reconstruction and Regeneration of Tissue Engineering for Osteochondral Repair

Repairing osteochondral defects to restore joint function is a major challenge in regenerative medicine. However, with recent advances in tissue engineering, the development of potential treatments is promising. In recent years, in addition to single-layer scaffolds, double-layer or multilayer scaffolds have been prepared to mimic the structure of articular cartilage and subchondral bone for osteochondral repair. Although there are a range of different cells such as umbilical cord stem cells, bone marrow mesenchyml stem cell, and others that can be used, the availability, ease of preparation, and the osteogenic and chondrogenic capacity of these cells are important factors that will influence its selection for tissue engineering. Furthermore, appropriate cell proliferation and differentiation of these cells is also key for the optimal repair of osteochondral defects. The development of bioreactors has enhanced methods to stimulate the proliferation and differentiation of cells. In this review, we summarize the recent advances in tissue engineering, including the development of layered scaffolds, cells, and bioreactors that have changed the approach towards the development of novel treatments for osteochondral repair.

Chondral Differentiation of Induced Pluripotent Stem Cells Without Progression Into the Endochondral Pathway

A major problem with chondrocytes derived in vitro from stem cells is undesired hypertrophic degeneration, to which articular chondrocytes (ACs) are resistant. As progenitors of all adult tissues, induced pluripotent stem cells (iPSCs) are in theory able to form stable articular cartilage. In vitro differentiation of iPSCs into chondrocytes with an AC-phenotype and resistance to hypertrophy has not been demonstrated so far. Here, we present a novel protocol that succeeded in deriving chondrocytes from human iPSCs without using pro-hypertrophic bone-morphogenetic-proteins. IPSC-chondrocytes had a high cartilage formation capacity and deposited two-fold more proteoglycans per cell than adult ACs. Importantly, cartilage engineered from iPSC-chondrocytes had similar marginal expression of hypertrophic markers (COL10A1, PTH1R, IBSP, ALPL mRNAs) like cartilage from ACs. Collagen X was barely detectable in iPSC-cartilage and 30-fold lower than in hypertrophic cartilage derived from mesenchymal stromal cells (MSCs). Moreover, alkaline phosphatase (ALP) activity remained at basal AC-like levels throughout iPSC chondrogenesis, in contrast to a well-known significant upregulation in hypertrophic MSCs. In line, iPSC-cartilage subjected to mineralizing conditions in vitro showed barely any mineralization, while MSC-derived hypertrophic cartilage mineralized strongly. Low expression of Indian hedgehog (IHH) like in ACs but rising BMP7 expression like in MSCs suggested that phenotype stability was linked to the hedgehog rather than the bone morphogenetic protein (BMP) pathway. Taken together, unlimited amounts of AC-like chondrocytes with a high proteoglycan production reminiscent of juvenile chondrocytes and resistance to hypertrophy and mineralization can now be produced from human iPSCs in vitro. This opens new strategies for cartilage regeneration, disease modeling and pharmacological studies.

iPSC Bioprinting: Where are We at?

Here, we present a concise review of current 3D bioprinting technologies applied to induced pluripotent stem cells (iPSC). iPSC have recently received a great deal of attention from the scientific and clinical communities for their unique properties, which include abundant adult cell sources, ability to indefinitely self-renew and differentiate into any tissue of the body. Bioprinting of iPSC and iPSC derived cells combined with natural or synthetic biomaterials to fabricate tissue mimicked constructs, has emerged as a technology that might revolutionize regenerative medicine and patient-specific treatment. This review covers the advantages and disadvantages of bioprinting techniques, influence of bioprinting parameters and printing condition on cell viability, and commonly used iPSC sources, and bioinks. A clear distinction is made for bioprinting techniques used for iPSC at their undifferentiated stage or when used as adult stem cells or terminally differentiated cells. This review presents state of the art data obtained from major searching engines, including Pubmed/MEDLINE, Google Scholar, and Scopus, concerning iPSC generation, undifferentiated iPSC, iPSC bioprinting, bioprinting techniques, cartilage, bone, heart, neural tissue, skin, and hepatic tissue cells derived from iPSC.

Transplantation of Aggregates of Autologous Synovial Mesenchymal Stem Cells for Treatment of Cartilage Defects in the Femoral Condyle and the Femoral Groove in Microminipigs

BACKGROUND

Previous work has demonstrated that patients with cartilage defects of the knee benefit from arthroscopic transplantation of autologous synovial mesenchymal stem cells (MSCs) in terms of magnetic resonance imaging (MRI), qualitative histologic findings, and Lysholm score. However, the effectiveness was limited by the number of cells obtained, so large-sized defects (>500 mm²) were not investigated. The use of MSC aggregates may enable treatment of larger defects by increasing the number of MSCs adhering to the cartilage defect.

PURPOSE

To investigate whether transplantation of aggregates of autologous synovial MSCs with 2-step surgery could promote articular cartilage regeneration in microminipig osteochondral defects.

STUDY DESIGN

Controlled laboratory study.

METHODS

Synovial MSCs derived from a microminipig were examined for in vitro colony-forming and multidifferentiation abilities. An aggregate of 250,000 synovial MSCs was formed with hanging drop culture, and 16 aggregates (for each defect) were implanted on both osteochondral defects (6 × 6 × 1.5 mm) created in the medial femoral condyle and femoral groove (MSC group). The defects in the contralateral knee were left empty (control group). The knee joints were evaluated at 4 and 12 weeks by macroscopic findings and histology. MRI T1rho mapping images were acquired at 12 weeks. For cell tracking, synovial MSCs were labeled with ferucarbotran before aggregate formation and were observed with MRI at 1 week.

RESULTS

Synovial MSCs showed in vitro colony-forming and multidifferentiation abilities. Regenerative cartilage formation was significantly better in the MSC group than in the control group, as indicated by International Cartilage Repair Society score (macro), modified Wakitani score (histology), and T1rho mapping (biochemical MRI) in the medial condyle at 12 weeks. Implanted cells, labeled with ferucarbotran, were observed in the osteochondral defects at 1 week with MRI. No significant difference was noted in the modified Wakitani score at 4 weeks in the medial condyle and at 4 and 12 weeks in the femoral groove.

CONCLUSION

Transplantation of autologous synovial MSC aggregates promoted articular cartilage regeneration at the medial femoral condyle at 12 weeks in microminipigs.

CLINICAL RELEVANCE

Aggregates of autologous synovial MSCs could expand the indications for cartilage repair with synovial MSCs.

One-Step Formation of Chondrocytes through Direct Reprogramming via Polysaccharide-Based Gene Delivery

An innovative strategy for the generation of chondrocytes was thoroughly studied in this paper. Polyetherimide-modified polysaccharides of Porphyra yezoensis (pmPPY) served as a nonviral gene vector and delivered Sox9 plasmid to directly reprogram mouse embryonic fibroblasts into chondrocytes. The gene transfer efficiency was evaluated through ELISA, RT-PCR, and Western blot. The induced chondrocytes were identified through toluidine blue, Safranin O, and the immunostaining. The expression level of collagen II was finally evaluated through western blot. The pSox9/pmPPY nanoparticles (1:50) showed lower cytotoxicity as well as greater gene transfection efficiency than Lipofectamine 2000 and polyetherimide (PEI) (p<0.05). The results of toluidine blue, Safranin O, and the immunostaining of collagen II further showed that the normal MEFs were successfully reprogrammed into chondrocytes. These findings indicate that pmPPY could be a promising gene vector for the generation of chondrocytes via single-gene delivery strategy, which might provide abundant chondrocytes for cartilage repair.

Induced Pluripotent Stem Cells and Their Use in Human Models of Disease and Development

The discovery of somatic cell nuclear transfer proved that somatic cells can carry the same genetic code as the zygote, and that activating parts of this code are sufficient to reprogram the cell to an early developmental state. The discovery of induced pluripotent stem cells (iPSCs) nearly half a century later provided a molecular mechanism for the reprogramming. The initial creation of iPSCs was accomplished by the ectopic expression of four specific genes (OCT4, KLF4, SOX2, and c-Myc; OSKM). iPSCs have since been acquired from a wide range of cell types and a wide range of species, suggesting a universal molecular mechanism. Furthermore, cells have been reprogrammed to iPSCs using a myriad of methods, although OSKM remains the gold standard. The sources for iPSCs are abundant compared with those for other pluripotent stem cells; thus the use of iPSCs to model the development of tissues, organs, and other systems of the body is increasing. iPSCs also, through the reprogramming of patient samples, are being used to model diseases. Moreover, in the 10 years since the first report, human iPSCs are already the basis for new cell therapies and drug discovery that have reached clinical application. In this review, we examine the generation of iPSCs and their application to disease and development.

Direct conversion of pig fibroblasts to chondrocyte-like cells by c-Myc

Unexpectedly, we found that c-Myc-expressing porcine embryonic fibroblasts (PEFs) subcutaneously implanted into nude mice formed cartilage-like tissues in vivo, while previous studies revealed the direct conversion of mouse and human somatic cells into chondrocytes by the combined use of several defined factors, including c-Myc, which prompted us to explore whether PEFs can be reprogrammed to become pig induced chondrocyte-like cells (piCLCs) via ectopic expression of c-Myc alone. In this study, c-Myc-expressing PEFs, designated piCLCs, which exhibited a significantly enhanced proliferation ability in vitro, displayed a chondrogenic phenotypes in vitro, as shown by the cell morphology, toluidine blue staining, alcian blue staining and chondrocyte marker gene expression. Additionally, piCLCs with a polygonal chondrocyte-like morphology were readily and efficiently converted from PEFs by enforced c-Myc expression within 10 days, while piCLCs maintained the chondrocytic phenotype and normal karyotype during long-term subculture. piCLC-derived single clones with a chondrogenic phenotype in vitro exhibited homogeneity in cell morphology and staining intensity compared with mixed piCLCs. Although the mixtures of cartilaginous tissues and tumorous tissues accounted for ~12% (6/51) of all xenografts (51), piCLCs generated stable, homogenous, hyaline cartilage-like tissues without tumour formation at 45 out of the 51 injected sites when subcutaneously injected into nude mice. The hyaline cartilage-like tissues remained for at least 16 weeks. Taken together, these findings demonstrate for the first time the direct induction of chondrocyte-like cells from PEFs with only c-Myc.

Considerations in hiPSC-derived cartilage for articular cartilage repair

Background

A lack of cell or tissue sources hampers regenerative medicine for articular cartilage damage.

Main text

We review and discuss the possible use of pluripotent stem cells as a new source for future clinical use. Human induced pluripotent stem cells (hiPSCs) have several advantages over human embryonic stem cells (hESCs). Methods for the generation of chondrocytes and cartilage from hiPSCs have been developed. To reduce the cost of this regenerative medicine, allogeneic transplantation is preferable. hiPSC-derived cartilage shows low immunogenicity like native cartilage, because the cartilage is avascular and chondrocytes are segregated by the extracellular matrix. In addition, we consider our experience with the aberrant deposition of lipofuscin or melanin on cartilage during the chondrogenic differentiation of hiPSCs.

Short conclusion

Cartilage generated from allogeneic hiPSC-derived cartilage can be used to repair articular cartilage damage.

Bone regeneration strategies: Engineered scaffolds, bioactive molecules and stem cells current stage and future perspectives

Bone fractures are the most common traumatic injuries in humans. The repair of bone fractures is a regenerative process that recapitulates many of the biological events of embryonic skeletal development. Most of the time it leads to successful healing and the recovery of the damaged bone. Unfortunately, about 5-10% of fractures will lead to delayed healing or non-union, more so in the case of co-morbidities such as diabetes. In this article, we review the different strategies to heal bone defects using synthetic bone graft substitutes, biologically active substances and stem cells. The majority of currently available reviews focus on strategies that are still at the early stages of development and use mostly in vitro experiments with cell lines or stem cells. Here, we focus on what is already implemented in the clinics, what is currently in clinical trials, and what has been tested in animal models. Treatment approaches can be classified in three major categories: i) synthetic bone graft substitutes (BGS) whose architecture and surface can be optimized; ii) BGS combined with bioactive molecules such as growth factors, peptides or small molecules targeting bone precursor cells, bone formation and metabolism; iii) cell-based strategies with progenitor cells combined or not with active molecules that can be injected or seeded on BGS for improved delivery. We review the major types of adult stromal cells (bone marrow, adipose and periosteum derived) that have been used and compare their properties. Finally, we discuss the remaining challenges that need to be addressed to significantly improve the healing of bone defects.

Three-Dimensional Bioprinting of Cartilage by the Use of Stem Cells: A Strategy to Improve Regeneration

Cartilage lesions fail to heal spontaneously, leading to the development of chronic conditions which worsen the life quality of patients. Three-dimensional scaffold-based bioprinting holds the potential of tissue regeneration through the creation of organized, living constructs via a "layer-by-layer" deposition of small units of biomaterials and cells. This technique displays important advantages to mimic natural cartilage over traditional methods by allowing a fine control of cell distribution, and the modulation of mechanical and chemical properties. This opens up a number of new perspectives including personalized medicine through the development of complex structures (the osteochondral compartment), different types of cartilage (hyaline, fibrous), and constructs according to a specific patient's needs. However, the choice of the ideal combination of biomaterials and cells for cartilage bioprinting is still a challenge. Stem cells may improve material mimicry ability thanks to their unique properties: the immune-privileged status and the paracrine activity. Here, we review the recent advances in cartilage three-dimensional, scaffold-based bioprinting using stem cells and identify future developments for clinical translation. Database search terms used to write this review were: "articular cartilage", "menisci", "3D bioprinting", "bioinks", "stem cells", and "cartilage tissue engineering".

Building a new strategy for treating heart failure using Induced Pluripotent Stem Cells

Although cell therapy using myoblasts, bone marrow cells, or other stem cells appears to improve functional recovery of the failing heart, mainly by cytokine paracrine effects, its effectiveness in severely damaged myocardium is limited, probably because there are too few residual myocytes to promote cytokine-induced angiogenesis. Recently, cardiogenic stem cells, such as c-kit-positive cells, were reported to generate cardiomyogenic lineages, and basic research experiments showed that implanting these cells, which can differentiate into cardiomyocytes, improves heart function. However, this functional recovery may have also mainly depended on cytokine paracrine effects, because the differentiation to cardiomyocytes in vivo was poor. In contrast, while Induced Pluripotent Stem Cell-derived cardiomyocytes have paracrine effects, they also have the potential to supply newly born myocytes that can function synchronously with the recipient myocardium as "mechanically working cells" in severely damaged myocardium. Thus, they could represent a "true" myocardial regeneration therapy that can actually regenerate severely damaged myocardium. In addition, iPS cells, especially disease-specific iPS cells, have other applications in regenerative medicine such as in drug screening. In this report, we present the state of basic research in the field of cardiac iPS cells.

Repair of Damaged Articular Cartilage: Current Approaches and Future Directions

Articular hyaline cartilage is extensively hydrated, but it is neither innervated nor vascularized, and its low cell density allows only extremely limited self-renewal. Most clinical and research efforts currently focus on the restoration of cartilage damaged in connection with osteoarthritis or trauma. Here, we discuss current clinical approaches for repairing cartilage, as well as research approaches which are currently developing, and those under translation into clinical practice. We also describe potential future directions in this area, including tissue engineering based on scaffolding and/or stem cells as well as a combination of gene and cell therapy. Particular focus is placed on cell-based approaches and the potential of recently characterized chondro-progenitors; progress with induced pluripotent stem cells is also discussed. In this context, we also consider the ability of different types of stem cell to restore hyaline cartilage and the importance of mimicking the environment in vivo during cell expansion and differentiation into mature chondrocytes.

Effect of cellular mass on chondrogenic differentiation during embryoid body formation

One approach to cell differentiation is to use the natural capacity of pluripotent stem cells to form three germ layers via embryoid bodies (EB). However, unification of this process during in vitro culture remains challenging and many microenvironmental factors including the number of cells in the culture can influence differentiation patterns. The number of cells serves a crucial role as it determines access to nutrients, the distribution of oxygen concentration and cellular interactions, all of which influence the fate of the differentiated cells. The influence of EBs derived from human pluripotent cells on the chondrogenic potential of such cells is not well understood. For this reason, the present study sought to determine the effect of varying amounts of cells on the properties of EBs derived from human embryonic stem cells (BG01V cell line). In the present study, 500–2,000 cells per well were cultivated from 5 to 15 days in suspension cell culture. Expression of pluripotency genes and germ layer markers were evaluated in order to determine the EBs with the greatest and least mesodermal properties. Genes associated with pluripotency and chondrogenesis were also evaluated to assess the influence of suspension culture duration and EB size on chondrogenic differentiation. Immunofluorescence staining for pluripotent and chondrocyte-associated proteins confirmed successful differentiation into chondrocyte-like cells. Alcian blue staining confirmed deposition of proteoglycans. These results suggested that EBs formed in 500-cell wells possess the highest mesodermal and prochondrogenic properties. Differentiation of EBs into chondrocytes on day 5 in 500-cell wells was more efficient than in that observed in larger and older EBs.

Repair potential of nonsurgically delivered induced pluripotent stem cell-derived chondrocytes in a rat osteochondral defect model

Human induced pluripotent stem cells (hiPSCs) are thought to be an alternative cell source for future regenerative medicine. hiPSCs may allow unlimited production of cell types that have low turnover rates and are difficult to obtain such as autologous chondrocytes. In this study, we generated hiPSC-derived chondrogenic pellets, and chondrocytes were isolated. To confirm the curative effects, chondrogenic pellets and isolated chondrocytes were transplanted into rat joints with osteochondral defects. Isolated hiPSC-derived chondrocytes were delivered in the defect by a single intra-articular injection. The generated hiPSC-derived chondrogenic pellets had increased chondrogenic marker expression and accumulated extracellular matrix proteins. Chondrocytes were successfully isolated from the pellets. Alcian blue staining and collagen type II were detected in the cells. Chondrogenic marker expression was also increased in the isolated cells. Transplanted chondrogenic pellets and chondrocytes both had curative effects in the osteochondral defect rat model. Detection of human proteins in the joints proved that the cells were successfully delivered into the defect. Chondrogenic pellets or chondrocytes generated from hiPSCs have potential as regenerative medicine for cartilage recovery or regeneration. Chondrocytes isolated from hiPSC-derived chondrogenic pellets had curative effects in damaged cartilage. Injectable hiPSC-derived chondrocytes show the possibility of noninvasive delivery of regenerative medicine for cartilage recovery.

Current Therapeutic Strategies for Stem Cell-Based Cartilage Regeneration

The process of cartilage destruction in the diarthrodial joint is progressive and irreversible. This destruction is extremely difficult to manage and frustrates researchers, clinicians, and patients. Patients often take medication to control their pain. Surgery is usually performed when pain becomes uncontrollable or joint function completely fails. There is an unmet clinical need for a regenerative strategy to treat cartilage defect without surgery due to the lack of a suitable regenerative strategy. Clinicians and scientists have tried to address this using stem cells, which have a regenerative potential in various tissues. Cartilage may be an ideal target for stem cell treatment because it has a notoriously poor regenerative potential. In this review, we describe past, present, and future strategies to regenerate cartilage in patients. Specifically, this review compares a surgical regenerative technique (microfracture) and cell therapy, cell therapy with and without a scaffold, and therapy with nonaggregated and aggregated cells. We also review the chondrogenic potential of cells according to their origin, including autologous chondrocytes, mesenchymal stem cells, and induced pluripotent stem cells.

Plate-Based Phenotypic Screening for Pain Using Human iPSC-Derived Sensory Neurons

Screening against a disease-relevant phenotype to identify compounds that change the outcome of biological pathways, rather than just the activity of specific targets, offers an alternative approach to find modulators of disease characteristics. However, in pain research, use of in vitro phenotypic screens has been impeded by the challenge of sourcing relevant neuronal cell types in sufficient quantity and developing functional end-point measurements with a direct disease link. To overcome these hurdles, we have generated human induced pluripotent stem cell (hiPSC)-derived sensory neurons at a robust production scale using the concept of cryopreserved "near-assay-ready" cells to decouple complex cell production from assay development and screening. hiPSC sensory neurons have then been used for development of a 384-well veratridine-evoked calcium flux assay. This functional assay of neuronal excitability was validated for phenotypic relevance to pain and other hyperexcitability disorders through screening a small targeted validation compound subset. A 2700-compound chemogenomics screen was then conducted to profile the range of target-based mechanisms able to inhibit veratridine-evoked excitability. This report presents the assay development, validation, and screening data. We conclude that high-throughput-compatible pain-relevant phenotypic screening with hiPSC sensory neurons is feasible and ready for application for the identification of new targets, pathways, mechanisms of action, and compounds for modulating neuronal excitability.