Comparative evaluation of isogenic mesodermal and ectomesodermal chondrocytes from human iPSCs for cartilage regeneration

Musculoskeletal organoids: An emerging toolkit for establishing personalized models of musculoskeletal disorders and developing regenerative therapies

Musculoskeletal (MSK) conditions are the primary cause of physical disability globally. These disorders are physically and mentally debilitating and severely impact the patients' quality of life. As the median age of the world's population increases, there has been an intensifying urgency of developing efficacious therapies for various orthopaedic conditions. Furthermore, the highly heterogeneous nature of MSK conditions calls for a personalized approach to studying disease mechanisms and developing regenerative treatments. Organoids have emerged as an advanced approach to generating functional tissue/organ mimics in vitro, which hold promise in MSK regeneration, disease modeling, and therapeutic development. Herein, we review the preparation, characterization, and application of various MSK organoids. We highlight the potential of patient-specific organoids in the development of personalized medicine and discuss the challenges and opportunities in the future development of MSK organoids. STATEMENT OF SIGNIFICANCE: Despite decades of research, translation of MSK research into clinical applications remains limited, partially attributed to our inadequate understanding of disease mechanisms. To advance therapeutic development, there are critical needs for MSK disease models with higher clinical relevance and predictive power. Additionally, engineered constructs that closely mimic the structural and functional features of native MSK tissues are highly desirable. MSK organoids have emerged as a promising approach to meet the above requirements. To unleash the full potential of MSK organoids necessitates a comprehensive understanding of their categories, construction, development, functions, applications, and challenges. This review aims to fulfill this crucial need, aiming to accelerate the clinical translation of MSK organoid platforms to benefit millions of patients afflicted with MSK conditions.

Fascial Manual Medicine: The Concept of Fascial Continuum

Fascial tissue ubiquitously pervades the body system, becoming the target of many disciplines that use manual techniques for patient treatment. It is a much-debated topic as there is currently no univocal definition among different authors. Due to the non-discontinuity of the fascia, we can speak of a fascial continuum; this principle is the basis of the osteopathic perspective. This vision, which seems banal, is not always applied in manual fascial medicine, where, often, it is conditioned by a reductionist (layers) and mechanistic (compartments) approach, forgetting that the body is not a machine but an organism. This continuity teaches that manual treatment does not only reverberate in the area where the operator's hands rest but creates a series of local and systemic adaptations. This narrative review revises the concept of the fascial continuum by highlighting that fascia is a tissue system (different tissues working in harmony), multi-organ (capable of behaving like an organ), whose macroscopic functional expression (movement) and microscopic (with cellular adaptations) derives from a nanoscopic coherence (electromagnetic behaviors). This means that the body acts as a unit, and makes the manual approach never local but always systemic. The aim of the article is to highlight the fact that the fascial continuum is a single biological entity (solid and fluid), and that manual fascial medicine does not approach a single segment, but the entire person.

Recapitulation of endochondral ossification by hPSC-derived SOX9+ sclerotomal progenitors

Endochondral ossification generates most of the load-bearing bones, recapitulating it in human cells remains a challenge. Here, we report generation of SOX9+ sclerotomal progenitors (scl-progenitors), a mesenchymal precursor at the pre-condensation stage, from human pluripotent stem cells and development of osteochondral induction methods for these cells. Upon lineage-specific induction, SOX9+ scl-progenitors have not only generated articular cartilage but have also undergone spontaneous condensation, cartilaginous anlagen formation, chondrocyte hypertrophy, vascular invasion, and finally bone formation with stroma, thereby recapitulating key stages during endochondral ossification. Moreover, self-organized growth plate-like structures have also been induced using SOX9+ scl-progenitor-derived fusion constructs with chondro- and osteo-spheroids, exhibiting molecular and cellular similarities to the primary growth plates. Furthermore, we have identified ITGA9 as a specific surface marker for reporter-independent isolation of SOX9+ scl-progenitors and established a culture system to support their expansion. Our work highlights SOX9+ scl-progenitors as a promising tool for modeling human skeletal development and bone/cartilage bioengineering.

Autologous iPSC- and MSC-derived chondrocyte implants for cartilage repair in a miniature pig model

BACKGROUND

Induced pluripotent stem cell (iPSC)-derived mesenchymal stem cells (iMSCs) have greater potential for generating chondrocytes without hypertrophic and fibrotic phenotypes compared to bone marrow-derived mesenchymal stem/stromal cells (BMSCs). However, there is a lack of research demonstrating the use of autologous iMSCs for repairing articular chondral lesions in large animal models. In this study, we aimed to evaluate the effectiveness of autologous miniature pig (minipig) iMSC-chondrocyte (iMSC-Ch)-laden implants in comparison to autologous BMSC-chondrocyte (BMSC-Ch)-laden implants for cartilage repair in porcine femoral condyles.

METHODS

iMSCs and BMSCs were seeded into fibrin glue/nanofiber constructs and cultured with chondrogenic induction media for 7 days before implantation. To assess the regenerative capacity of the cells, 19 skeletally mature Yucatan minipigs were randomly divided into microfracture control, acellular scaffold, iMSC, and BMSC subgroups. A cylindrical defect measuring 7 mm in diameter and 0.6 mm in depth was created on the articular cartilage surface without violating the subchondral bone. The defects were then left untreated or treated with acellular or cellular implants.

RESULTS

Both cellular implant-treated groups exhibited enhanced joint repair compared to the microfracture and acellular control groups. Immunofluorescence analysis yielded significant findings, showing that cartilage treated with iMSC-Ch implants exhibited higher expression of COL2A1 and minimal to no expression of COL1A1 and COL10A1, in contrast to the BMSC-Ch-treated group. This indicates that the iMSC-Ch implants generated more hyaline cartilage-like tissue compared to the BMSC-Ch implants.

CONCLUSIONS

Our findings contribute to filling the knowledge gap regarding the use of autologous iPSC derivatives for cartilage repair in a translational animal model. Moreover, these results highlight their potential as a safe and effective therapeutic strategy.

Generation of human expandable limb-bud-like progenitors via chemically induced dedifferentiation

In certain highly regenerative animals, cellular dedifferentiation occurs after injury, allowing specialized cells to become progenitor cells for regeneration. However, this capacity is restricted in human cells due to reduced plasticity. Here, we introduce a chemical-induced dedifferentiation approach that reverts the differentiated cells to a progenitor-like state, conferring the features of human limb bud cells from human adult somatic cells. These chemically induced human limb-bud-like progenitors (hCiLBP cells) show a high degree of transcriptomic similarity to human embryonic limb bud progenitors. Importantly, we established culture conditions that allow hCiLBP cells to undergo extensive expansion while maintaining population homogeneity and long-term self-renewal capacity. Moreover, hCiLBP cells exhibit increased osteochondrogenic differentiation ability, providing an innovative platform for generation of skeletal lineage cell types. These results highlight a potential therapeutic approach for repairing damaged human tissues through reversal of developmental pathways from mature cells to expandable progenitor cells.

Advancing Scaffold-Assisted Modality for In Situ Osteochondral Regeneration: A Shift From Biodegradable to Bioadaptable

Over the decades, the management of osteochondral lesions remains a significant yet unmet medical challenge without curative solutions to date. Owing to the complex nature of osteochondral units with multi-tissues and multicellularity, and inherently divergent cellular turnover capacities, current clinical practices often fall short of robust and satisfactory repair efficacy. Alternative strategies, particularly tissue engineering assisted with biomaterial scaffolds, achieve considerable advances, with the emerging pursuit of a more cost-effective approach of in situ osteochondral regeneration, as evolving toward cell-free modalities. By leveraging endogenous cell sources and innate regenerative potential facilitated with instructive scaffolds, promising results are anticipated and being evidenced. Accordingly, a paradigm shift is occurring in scaffold development, from biodegradable and biocompatible to bioadaptable in spatiotemporal control. Hence, this review summarizes the ongoing progress in deploying bioadaptable criteria for scaffold-based engineering in endogenous osteochondral repair, with emphases on precise control over the scaffolding material, degradation, structure and biomechanics, and surface and biointerfacial characteristics, alongside their distinguished impact on the outcomes. Future outlooks of a highlight on advanced, frontier materials, technologies, and tools tailoring precision medicine and smart healthcare are provided, which potentially paves the path toward the ultimate goal of complete osteochondral regeneration with function restoration.

Advances in cartilage tissue regeneration: a review of stem cell therapies, tissue engineering, biomaterials, and clinical trials

Cartilage tissue, characterized by its limited regenerative capacity, presents significant challenges in clinical therapy. Recent advancements in cartilage regeneration have focused on integrating stem cell therapies, tissue engineering strategies, and advanced modeling techniques to overcome existing limitations. Stem cells, particularly Mesenchymal Stem Cells (MSCs) and induced pluripotent stem cells (iPSCs), hold promise for cartilage repair due to their ability to differentiate into chondrocytes, the key cells responsible for cartilage formation. Tissue engineering approaches, including 3D models, organ-on-a-chip systems, and organoids, offer innovative methods to mimic natural tissue microenvironments and evaluate potential treatments. MSC-based techniques, such as cell sheet tissue engineering, address challenges associated with traditional therapies, including cell availability and culture difficulties. Furthermore, advancements in 3D bioprinting enable the fabrication of complex tissue structures, while organ-on-a-chip systems provide microfluidic platforms for disease modeling and physiological mimicry. Organoids serve as simplified models of organs, capturing some complexity and enabling the monitoring of pathophysiological aspects of cartilage diseases. This comprehensive review underscores the transformative potential of integrating stem cell therapies, tissue engineering strategies, and advanced modeling techniques to improve cartilage regeneration and pave the way for more effective clinical treatments.

Advancements in tissue engineering for articular cartilage regeneration

Articular cartilage injury is a prevalent clinical condition resulting from trauma, tumors, infection, osteoarthritis, and other factors. The intrinsic lack of blood vessels, nerves, and lymphatic vessels within cartilage tissue severely limits its self-regenerative capacity after injury. Current treatment options, such as conservative drug therapy and joint replacement, have inherent limitations. Achieving perfect regeneration and repair of articular cartilage remains an ongoing challenge in the field of regenerative medicine. Tissue engineering has emerged as a key focus in articular cartilage injury research, aiming to utilize cultured and expanded tissue cells combined with suitable scaffold materials to create viable, functional tissues. This review article encompasses the latest advancements in seed cells, scaffolds, and cytokines. Additionally, the role of stimulatory factors including cytokines and growth factors, genetic engineering techniques, biophysical stimulation, and bioreactor systems, as well as the role of scaffolding materials including natural scaffolds, synthetic scaffolds, and nanostructured scaffolds in the regeneration of cartilage tissues are discussed. Finally, we also outline the signaling pathways involved in cartilage regeneration. Our review provides valuable insights for scholars to address the complex problem of cartilage regeneration and repair.

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.

A Review of the Role of Bioreactors for iPSCs-Based Tissue-Engineered Articular Cartilage

BACKGROUND

Osteoarthritis (OA) is the most common degenerative joint disease without an ultimate treatment. In a search for novel approaches, tissue engineering (TE) has shown great potential to be an effective way for hyaline cartilage regeneration and repair in advanced stages of OA. Recently, induced pluripotent stem cells (iPSCs) have been appointed to be essential stem cells for degenerative disease treatment because they allow a personalized medicine approach. For clinical translation, bioreactors in combination with iPSCs-engineerd cartilage could match patients needs, serve as platform for large-scale patient specific cartilage production, and be a tool for patient OA modelling and drug screening. Furthermore, to minimize in vivo experiments and improve cell differentiation and cartilage extracellular matrix (ECM) deposition, TE combines existing approaches with bioreactors.

METHODS

This review summarizes the current understanding of bioreactors and the necessary parameters when they are intended for cartilage TE, focusing on the potential use of iPSCs.

RESULTS

Bioreactors intended for cartilage TE must resemble the joint cavity niche. However, recreating human synovial joints is not trivial because the interactions between various stimuli are not entirely understood.

CONCLUSION

The use of mechanical and electrical stimulation to differentiate iPSCs, and maintain and test chondrocytes are key stimuli influencing hyaline cartilage homeostasis. Incorporating these stimuli to bioreactors can positively impact cartilage TE approaches and their possibility for posterior translation into the clinics.

Hyperplastic Human Macromass Cartilage for Joint Regeneration

Cartilage damage affects millions of people worldwide. Tissue engineering strategies hold the promise to provide off-the-shelf cartilage analogs for tissue transplantation in cartilage repair. However, current strategies hardly generate sufficient grafts, as tissues cannot maintain size growth and cartilaginous phenotypes simultaneously. Herein, a step-wise strategy is developed for fabricating expandable human macromass cartilage (macro-cartilage) in a 3D condition by employing human polydactyly chondrocytes and a screen-defined serum-free customized culture (CC). CC-induced chondrocytes demonstrate improved cell plasticity, expressing chondrogenic biomarkers after a 14.59-times expansion. Crucially, CC-chondrocytes form large-size cartilage tissues with average diameters of 3.25 ± 0.05 mm, exhibiting abundant homogenous matrix and intact structure without a necrotic core. Compared with typical culture, the cell yield in CC increases 2.57 times, and the expression of cartilage marker collagen type II increases 4.70 times. Transcriptomics reveal that this step-wise culture drives a proliferation-to-differentiation process through an intermediate plastic stage, and CC-chondrocytes undergo a chondral lineage-specific differentiation with an activated metabolism. Animal studies show that CC macro-cartilage maintains a hyaline-like cartilage phenotype in vivo and significantly promotes the healing of large cartilage defects. Overall, an efficient expansion of human macro-cartilage with superior regenerative plasticity is achieved, providing a promising strategy for joint regeneration.

Recent development in multizonal scaffolds for osteochondral regeneration

Osteochondral (OC) repair is an extremely challenging topic due to the complex biphasic structure and poor intrinsic regenerative capability of natural osteochondral tissue. In contrast to the current surgical approaches which yield only short-term relief of symptoms, tissue engineering strategy has been shown more promising outcomes in treating OC defects since its emergence in the 1990s. In particular, the use of multizonal scaffolds (MZSs) that mimic the gradient transitions, from cartilage surface to the subchondral bone with either continuous or discontinuous compositions, structures, and properties of natural OC tissue, has been gaining momentum in recent years. Scrutinizing the latest developments in the field, this review offers a comprehensive summary of recent advances, current hurdles, and future perspectives of OC repair, particularly the use of MZSs including bilayered, trilayered, multilayered, and gradient scaffolds, by bringing together onerous demands of architecture designs, material selections, manufacturing techniques as well as the choices of growth factors and cells, each of which possesses its unique challenges and opportunities.

Osteochondrogenesis by TGF-β3, BMP-2 and noggin growth factor combinations in an ex vivo muscle tissue model: Temporal function changes affecting tissue morphogenesis

In the absence of clear molecular insight, the biological mechanism behind the use of growth factors applied in osteochondral regeneration is still unresolved. The present study aimed to resolve whether multiple growth factors applied to muscle tissue in vitro, such as TGF-β3, BMP-2 and Noggin, can lead to appropriate tissue morphogenesis with a specific osteochondrogenic nature, thereby revealing the underlying molecular interaction mechanisms during the differentiation process. Interestingly, although the results showed the typical modulatory effect of BMP-2 and TGF-β3 on the osteochondral process, and Noggin seemingly downregulated specific signals such as BMP-2 activity, we also discovered a synergistic effect between TGF-β3 and Noggin that positively influenced tissue morphogenesis. Noggin was observed to upregulate BMP-2 and OCN at specific time windows of culture in the presence of TGF-β3, suggesting a temporal time switch causing functional changes in the signaling protein. This implies that signals change their functions throughout the process of new tissue formation, which may depend on the presence or absence of specific singular or multiple signaling cues. If this is the case, the signaling cascade is far more intricate and complex than originally believed, warranting intensive future investigations so that regenerative therapies of a critical clinical nature can function properly.

Skeletal dysplasia-causing TRPV4 mutations suppress the hypertrophic differentiation of human iPSC-derived chondrocytes

Mutations in the TRPV4 ion channel can lead to a range of skeletal dysplasias. However, the mechanisms by which TRPV4 mutations lead to distinct disease severity remain unknown. Here, we use CRISPR-Cas9-edited human-induced pluripotent stem cells (hiPSCs) harboring either the mild V620I or lethal T89I mutations to elucidate the differential effects on channel function and chondrogenic differentiation. We found that hiPSC-derived chondrocytes with the V620I mutation exhibited increased basal currents through TRPV4. However, both mutations showed more rapid calcium signaling with a reduced overall magnitude in response to TRPV4 agonist GSK1016790A compared to wildtype (WT). There were no differences in overall cartilaginous matrix production, but the V620I mutation resulted in reduced mechanical properties of cartilage matrix later in chondrogenesis. mRNA sequencing revealed that both mutations up-regulated several anterior HOX genes and down-regulated antioxidant genes CAT and GSTA1 throughout chondrogenesis. BMP4 treatment up-regulated several essential hypertrophic genes in WT chondrocytes; however, this hypertrophic maturation response was inhibited in mutant chondrocytes. These results indicate that the TRPV4 mutations alter BMP signaling in chondrocytes and prevent proper chondrocyte hypertrophy, as a potential mechanism for dysfunctional skeletal development. Our findings provide potential therapeutic targets for developing treatments for TRPV4-mediated skeletal dysplasias.

Regeneration of articular cartilage defects: Therapeutic strategies and perspectives

Articular cartilage (AC), a bone-to-bone protective device made of up to 80% water and populated by only one cell type (i.e. chondrocyte), has limited capacity for regeneration and self-repair after being damaged because of its low cell density, alymphatic and avascular nature. Resulting repair of cartilage defects, such as osteoarthritis (OA), is highly challenging in clinical treatment. Fortunately, the development of tissue engineering provides a promising method for growing cells in cartilage regeneration and repair by using hydrogels or the porous scaffolds. In this paper, we review the therapeutic strategies for AC defects, including current treatment methods, engineering/regenerative strategies, recent advances in biomaterials, and present emphasize on the perspectives of gene regulation and therapy of noncoding RNAs (ncRNAs), such as circular RNA (circRNA) and microRNA (miRNA).

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.

Microcarriers in application for cartilage tissue engineering: Recent progress and challenges

Successful regeneration of cartilage tissue at a clinical scale has been a tremendous challenge in the past decades. Microcarriers (MCs), usually used for cell and drug delivery, have been studied broadly across a wide range of medical fields, especially the cartilage tissue engineering (TE). Notably, microcarrier systems provide an attractive method for regulating cell phenotype and microtissue maturations, they also serve as powerful injectable carriers and are combined with new technologies for cartilage regeneration. In this review, we introduced the typical methods to fabricate various types of microcarriers and discussed the appropriate materials for microcarriers. Furthermore, we highlighted recent progress of applications and general design principle for microcarriers. Finally, we summarized the current challenges and promising prospects of microcarrier-based systems for medical applications. Overall, this review provides comprehensive and systematic guidelines for the rational design and applications of microcarriers in cartilage TE.