Current Therapeutic Strategies for Stem Cell-Based Cartilage Regeneration

Cartilage-Specific Gene Expression and Extracellular Matrix Deposition in the Course of Mesenchymal Stromal Cell Chondrogenic Differentiation in 3D Spheroid Culture

Articular cartilage damage still remains a major problem in orthopedical surgery. The development of tissue engineering techniques such as autologous chondrocyte implantation is a promising way to improve clinical outcomes. On the other hand, the clinical application of autologous chondrocytes has considerable limitations. Mesenchymal stromal cells (MSCs) from various tissues have been shown to possess chondrogenic differentiation potential, although to different degrees. In the present study, we assessed the alterations in chondrogenesis-related gene transcription rates and extracellular matrix deposition levels before and after the chondrogenic differentiation of MSCs in a 3D spheroid culture. MSCs were obtained from three different tissues: umbilical cord Wharton's jelly (WJMSC-Wharton's jelly mesenchymal stromal cells), adipose tissue (ATMSC-adipose tissue mesenchymal stromal cells), and the dental pulp of deciduous teeth (SHEDs-stem cells from human exfoliated deciduous teeth). Monolayer MSC cultures served as baseline controls. Newly formed 3D spheroids composed of MSCs previously grown in 2D cultures were precultured for 2 days in growth medium, and then, chondrogenic differentiation was induced by maintaining them in the TGF-β1-containing medium for 21 days. Among the MSC types studied, WJMSCs showed the most similarities with primary chondrocytes in terms of the upregulation of cartilage-specific gene expression. Interestingly, such upregulation occurred to some extent in all 3D spheroids, even prior to the addition of TGF-β1. These results confirm that the potential of Wharton's jelly is on par with adipose tissue as a valuable cell source for cartilage engineering applications as well as for the treatment of osteoarthritis. The 3D spheroid environment on its own acts as a trigger for the chondrogenic differentiation of MSCs.

Case report: Equine metacarpophalangeal joint partial and full thickness defects treated with allogenic equine synovial membrane mesenchymal stem/stromal cell combined with umbilical cord mesenchymal stem/stromal cell conditioned medium

Here, we describe a case of a 5-year-old show-jumping stallion presented with severe lameness, swelling, and pain on palpation of the left metacarpophalangeal joint (MCj). Diagnostic imaging revealed full and partial-thickness articular defects over the lateral condyle of the third metacarpus (MC3) and the dorsolateral aspect of the first phalanx (P1). After the lesion's arthroscopic curettage, the patient was subjected to an innovative regenerative treatment consisting of two intra-articular injections of equine synovial membrane mesenchymal stem/stromal cells (eSM-MSCs) combined with umbilical cord mesenchymal stem/stromal cells conditioned medium (UC-MSC CM), 15 days apart. A 12-week rehabilitation program was accomplished, and lameness, pain, and joint effusion were remarkably reduced; however, magnetic resonance imaging (MRI) and computed tomography (CT) scan presented incomplete healing of the MC3's lesion, prompting a second round of treatment. Subsequently, the horse achieved clinical soundness and returned to a higher level of athletic performance, and imaging exams revealed the absence of lesions at P1, fulfillment of the osteochondral lesion, and cartilage-like tissue formation at MC3's lesion site. The positive outcomes suggest the effectiveness of this combination for treating full and partial cartilage defects in horses. Multipotent mesenchymal stem/stromal cells (MSCs) and their bioactive factors compose a novel therapeutic approach for tissue regeneration and organ function restoration with anti-inflammatory and pro-regenerative impact through paracrine mechanisms.

3D printed osteochondral scaffolds: design strategies, present applications and future perspectives

Articular osteochondral (OC) defects are a global clinical problem characterized by loss of full-thickness articular cartilage with underlying calcified cartilage through to the subchondral bone. While current surgical treatments can relieve pain, none of them can completely repair all components of the OC unit and restore its original function. With the rapid development of three-dimensional (3D) printing technology, admirable progress has been made in bone and cartilage reconstruction, providing new strategies for restoring joint function. 3D printing has the advantages of fast speed, high precision, and personalized customization to meet the requirements of irregular geometry, differentiated composition, and multi-layered boundary layer structures of joint OC scaffolds. This review captures the original published researches on the application of 3D printing technology to the repair of entire OC units and provides a comprehensive summary of the recent advances in 3D printed OC scaffolds. We first introduce the gradient structure and biological properties of articular OC tissue. The considerations for the development of 3D printed OC scaffolds are emphatically summarized, including material types, fabrication techniques, structural design and seed cells. Especially from the perspective of material composition and structural design, the classification, characteristics and latest research progress of discrete gradient scaffolds (biphasic, triphasic and multiphasic scaffolds) and continuous gradient scaffolds (gradient material and/or structure, and gradient interface) are summarized. Finally, we also describe the important progress and application prospect of 3D printing technology in OC interface regeneration. 3D printing technology for OC reconstruction should simulate the gradient structure of subchondral bone and cartilage. Therefore, we must not only strengthen the basic research on OC structure, but also continue to explore the role of 3D printing technology in OC tissue engineering. This will enable better structural and functional bionics of OC scaffolds, ultimately improving the repair of OC defects.

Infra-patellar fat pad-derived mesenchymal stem cells maintain their chondrogenic differentiation potential after arthroscopic harvest with blood-product supplementation

PURPOSE

Mesenchymal stem cells/medicinal signaling cells (MSCs) possess therapeutic potential and are used in regenerative orthopaedics. The infra-patellar fat pad (IFP) is partially resected during knee arthroscopy (KASC) and contains MSCs. Heat, irrigation, and mechanical stress during KASC may decrease MSC's therapeutic potential. This study assessed MSCs' regenerative potential after arthroscopic IFP harvest and potential effects of two blood products (BP) (platelet-rich plasma (PRP), hyperacute serum (HAS)) on MSCs' viability and chondrogenic differentiation capacity.

METHODS

IFP was arthroscopically harvested, isolated, and counted (n = 5). Flow cytometry was used to assess cell viability via staining with annexin V/7-AAD and stemness markers via staining for CD90, CD73, and CD105. MSCs were incubated with blood products, and metabolic activity was determined via an XTT assay. Deposition of cartilage extracellular matrix was determined in histologic sections of chondrogenically differentiated 3D pellet cultures via staining with Alcian Blue. Expression of cartilage-specific genes (SOX9, MMP3/13, ACAN, COL1/2) was analyzed via quantitative PCR.

RESULTS

MSC isolation from IFP yielded 2.66*106 ± 1.49*106 viable cells from 2.7 (0.748) g of tissue. MSC markers (CD 90/105/73) were successfully detected and annexin V staining showed 81.5% viable cells. XTT showed increased metabolic activity. Within the BP groups, this increase was significant (days 0-14, p < 0.05). PCR showed expression of cartilage-specific genes in each group. COL2 (p < 0.01) as well as ACAN (p < 0.001) expression levels were significantly higher in the HAS group. Histology showed successful differentiation.

CONCLUSION

Arthroscopic harvest of IFP-MSCs yields sufficient cells with maintained regenerative potential and viability. Blood products further enhance MSCs' viability.

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.

Exosomes loaded with chondrogenic stimuli agents combined with 3D bioprinting hydrogel in the treatment of osteoarthritis and cartilage degeneration

Osteoarthritis (OA) is a challenging joint inflammatory disease that often leads to disability. Immunoregulatory Exosomes (Exos) have shown promise in OA and cartilage degeneration treatment. Engineering Exos to deliver therapeutic agents like Kartogenin (KGN) has displayed potential for restoring cartilage regeneration. However, challenges include the uneven distribution of Exos at the injury site and the release of Exos cargo out of chondrocytes. Hydrogel-loaded uMSC-Exo has demonstrated significant therapeutic effects in wound healing and tissue regeneration. Recently, a new version of three-dimensional (3D) bioprinting of hydrogel significantly restored cartilage regeneration in OA joints. Combining immune regulatory Exos with 3D bioprinting hydrogel (3D-BPH-Exos) holds the potential for immunomodulating cartilage tissue and treatment of OA. It can reduce intracellular inflammasome formation and the release of inflammatory agents like IL-1β, TNF-α, and INF-γ, while also preventing chondrocyte apoptosis by restoring mitochondrial functions and enhancing chondrogenesis in synovial MSCs, osteoprogenitor cells, and osteoclasts. Loading Exos with chondrogenic stimuli agents in the 3D-BPH-Exos approach may offer a faster and safer strategy for cartilage repair while better inhibiting joint inflammation than high doses of anti-inflammatory drugs and cell-based therapies. This review provides a comprehensive overview of hydrogel bioprinting and exosome-based therapy in OA. It emphasizes the potential of 3D-BPH-Exos loaded with chondrogenic stimuli agents for OA treatment, serving as a basis for further research.

The Dual Role of Small Extracellular Vesicles in Joint Osteoarthritis: Their Global and Non-Coding Regulatory RNA Molecule-Based Pathogenic and Therapeutic Effects

OA is the most common joint disease that affects approximately 7% of the global population. Current treatment methods mainly relieve its symptoms with limited repairing effect on joint destructions, which ultimately contributes to the high morbidity rate of OA. Stem cell treatment is a potential regenerative medical therapy for joint repair in OA, but the uncertainty in differentiation direction and immunogenicity limits its clinical usage. Small extracellular vesicles (sEVs), the by-products secreted by stem cells, show similar efficacy levels but have safer regenerative repair effect without potential adverse outcomes, and have recently drawn attention from the broader research community. A series of research works and reviews have been performed in the last decade, providing references for the application of various exogenous therapeutic sEVs for treating OA. However, the clinical potential of target intervention involving endogenous pathogenic sEVs in the treatment of OA is still under-explored and under-discussed. In this review, and for the first time, we emphasize the dual role of sEVs in OA and explain the effects of sEVs on various joint tissues from both the pathogenic and therapeutic aspects. Our aim is to provide a reference for future research in the field.

Sericin nano-gel agglomerates mimicking the pericellular matrix induce the condensation of mesenchymal stem cells and trigger cartilage micro-tissue formation without exogenous stimulation of growth factors in vitro

Mesenchymal stem cells (MSCs) are excellent seed cells for cartilage tissue engineering and regenerative medicine. Though the condensation of MSCs is the first step of their differentiation into chondrocytes in skeletal development, the process is a challenge in cartilage repairing by MSCs. The pericellular matrix (PCM), a distinct region surrounding the chondrocytes, acts as an extracellular linker among cells and forms the microenvironment of chondrocytes. Inspired by this, sericin nano-gel soft-agglomerates were prepared and used as linkers to induce MSCs to assemble into micro-spheres and differentiate into cartilage-like micro-tissues without exogenous stimulation of growth factors. These sericin nano-gel soft-agglomerates are composed of sericin nano-gels prepared by the chelation of metal ions and sericin protein. The MSCs cultured on 2D culture plates self-assembled into cell-microspheres centered by sericin nano-gel agglomerates. The self-assembly progress of MSCs is superior to the traditional centrifugation to achieve MSC condensation due to its facility, friendliness to MSCs and avoidance of the side-effects of growth factors. The analysis of transcriptomic results suggested that sericin nano-gel agglomerates offered a soft mechanical stimulation to MSCs similar to that of the PCM to chondrocytes and triggered some signaling pathways as associated with MSC chondrogenesis. The strategy of utilizing biomaterials to mimic the PCM as a linker and as a mechanical micro-environment and to induce cell aggregation and trigger the differentiation of MSCs can be employed to drive 3D cellular organization and micro-tissue fabrication in vitro. These cartilage micro-masses reported in this study can be potential candidates for cartilage repairing, cellular building blocks for 3D bio-printing and a model for cartilage development and drug screening.

Fabricating the cartilage: recent achievements

This review aims to describe the most recent achievements and provide an insight into cartilage engineering and strategies to restore the cartilage defects. Here, we discuss cell types, biomaterials, and biochemical factors applied to form cartilage tissue equivalents and update the status of fabrication techniques, which are used at all stages of engineering the cartilage. The actualized concept to improve the cartilage tissue restoration is based on applying personalized products fabricated using a full cycle platform: a bioprinter, a bioink consisted of ECM-embedded autologous cell aggregates, and a bioreactor. Moreover, in situ platforms can help to skip some steps and enable adjusting the newly formed tissue in the place during the operation. Only some achievements described have passed first stages of clinical translation; nevertheless, the number of their preclinical and clinical trials is expected to grow in the nearest future.

Sex-dependent variation in cartilage adaptation: from degeneration to regeneration

Despite acknowledgement in the scientific community of sex-based differences in cartilage biology, the implications for study design remain unclear, with many studies continuing to arbitrarily assign demographics. Clinically, it has been well-established that males and females differ in cartilage degeneration, and accumulating evidence points to the importance of sex differences in the field of cartilage repair. However, a comprehensive review of the mechanisms behind this trend and the influence of sex on cartilage regeneration has not yet been presented. This paper aims to summarize current findings regarding sex-dependent variation in knee anatomy, sex hormones' effect on cartilage, and cartilaginous degeneration and regeneration, with a focus on stem cell therapies. Findings suggest that the stem cells themselves, as well as their surrounding microenvironment, contribute to sex-based differences. Accordingly, this paper underscores the contribution of both stem cell donor and recipient sex to sex-related differences in treatment efficacy. Cartilage regeneration is a field that needs more research to optimize strategies for better clinical results; taking sex into account could be a big factor in developing more effective and personalized treatments. The compilation of this information emphasizes the importance of investing further research in sex differences in cartilage biology.

A Review of Recent Innovations in Cartilage Regeneration Strategies for the Treatment of Primary Osteoarthritis of the Knee: Intra-articular Injections

Background

The pathology of primary osteoarthritis (OA) begins with structural cartilage damage, which initiates a self-propagating inflammatory pathway that further exacerbates cartilage deterioration. Current standard of care for knee primary OA involves treating the inflammatory symptoms to manage pain, which includes intra-articular (IA) injections of cortisone, an anti-inflammatory steroid, followed by a series of joint-cushioning hyaluronic acid gel injections. However, these injections do not delay the progression of primary OA. More focus on the underlying cellular pathology of OA has prompted researchers to develop treatments targeting the biochemical mechanisms of cartilage degradation.

Purpose

Researchers have yet to develop a United States Food and Drug Administration (FDA)-approved injection that has been demonstrated to significantly regenerate damaged articular cartilage. This paper reviews the current research on experimental injections aimed at achieving cellular restoration of the hyaline cartilage tissue of the knee joint.

Study Design

Narrative review.

Methods

The authors conducted a narrative literature review examining studies on primary OA pathogenesis and a systematic review of non-FDA-approved IA injections for the treatment of primary OA of the knee, described as "disease-modifying osteoarthritis drugs" in phase 1, 2, and 3 clinical trials.

Conclusion

New treatment approaches for primary OA investigate the potential of genetic therapies to restore native cartilage. It is clear that the most promising IA injections that could improve treatment of primary OA are bioengineered advanced-delivery steroid-hydrogel preparations, ex vivo expanded allogeneic stem cell injections, genetically engineered chondrocyte injections, recombinant fibroblast growth factor therapy, injections of selective proteinase inhibitors, senolytic therapy via injections, injectable antioxidant therapies, injections of Wnt pathway inhibitors, injections of nuclear factor-kappa β inhibitors, injections of modified human angiopoietin-like-3, various potential viral vector-based genetic therapy approaches, and RNA genetic technology administered via injections.

Hopes and opportunities of stem cells from human exfoliated deciduous teeth (SHED) in cartilage tissue regeneration

Cartilage lesions are common conditions, affecting elderly and non-athletic populations. Despite recent advances, cartilage regeneration remains a major challenge today. The absence of an inflammatory response following damage and the inability of stem cells to penetrate into the healing site due to the absence of blood and lymph vessels are assumed to hinder joint repair. Stem cell-based regeneration and tissue engineering have opened new horizons for treatment. With advances in biological sciences, especially stem cell research, the function of various growth factors in the regulation of cell proliferation and differentiation has been established. Mesenchymal stem cells (MSCs) isolated from different tissues have been shown to increase into therapeutically relevant cell numbers and differentiate into mature chondrocytes. As MSCs can differentiate and become engrafted inside the host, they are considered suitable candidates for cartilage regeneration. Stem cells from human exfoliated deciduous teeth (SHED) provide a novel and non-invasive source of MSCs. Due to their simple isolation, chondrogenic differentiation potential, and minimal immunogenicity, they can be an interesting option for cartilage regeneration. Recent studies have reported that SHED-derived secretome contains biomolecules and compounds that efficiently promote regeneration in damaged tissues, including cartilage. Overall, this review highlighted the advances and challenges of cartilage regeneration using stem cell-based therapies by focusing on SHED.

The Senolytic Drug Fisetin Attenuates Bone Degeneration in the Zmpste24 -/- Progeria Mouse Model

Aging leads to several geriatric conditions including osteoporosis (OP) and associated frailty syndrome. Treatments for these conditions are limited and none target fundamental drivers of pathology, and thus identifying strategies to delay progressive loss of tissue homeostasis and functional reserve will significantly improve quality of life in elderly individuals. A fundamental property of aging is the accumulation of senescent cells. Senescence is a cell state defined by loss of proliferative capacity, resistance to apoptosis, and the release of a proinflammatory and anti-regenerative senescence-associated secretory phenotype (SASP). The accumulation of senescent cells and SASP factors is thought to significantly contribute to systemic aging. Senolytics-compounds which selectively target and kill senescent cells-have been characterized to target and inhibit anti-apoptotic pathways that are upregulated during senescence, which can elicit apoptosis in senescent cells and relieve SASP production. Senescent cells have been linked to several age-related pathologies including bone density loss and osteoarthritis in mice. Previous studies in murine models of OP have demonstrated that targeting senescent cells pharmacologically with senolytic drugs can reduce symptomology of the disease. Here, we demonstrate the efficacy of senolytic drugs (dasatinib, quercetin, and fisetin) to improve age-associated degeneration in bone using the Zmpste24^-/- (Z24^-/-) progeria murine system for Hutchinson-Gilford progeria syndrome (HGPS). We found that the combination of dasatinib plus quercetin could not significantly mitigate trabecular bone loss although fisetin administration could reduce bone density loss in the accelerated aging Z24^-/- model. Furthermore, the overt bone density loss observed in the Z24^-/- model reported herein highlights the Z24 model as a translational model to recapitulate alterations in bone density associated with advanced age. Consistent with the "geroscience hypothesis," these data demonstrate the utility of targeting a fundamental driver of systemic aging (senescent cell accumulation) to alleviate a common condition with age, bone deterioration.

A high-resolution route map reveals distinct stages of chondrocyte dedifferentiation for cartilage regeneration

Articular cartilage damage is a universal health problem. Despite recent progress, chondrocyte dedifferentiation has severely compromised the clinical outcomes of cell-based cartilage regeneration. Loss-of-function changes are frequently observed in chondrocyte expansion and other pathological conditions, but the characteristics and intermediate molecular mechanisms remain unclear. In this study, we demonstrate a time-lapse atlas of chondrocyte dedifferentiation to provide molecular details and informative biomarkers associated with clinical chondrocyte evaluation. We performed various assays, such as single-cell RNA sequencing (scRNA-seq), live-cell metabolic assays, and assays for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq), to develop a biphasic dedifferentiation model consisting of early and late dedifferentiation stages. Early-stage chondrocytes exhibited a glycolytic phenotype with increased expression of genes involved in metabolism and antioxidation, whereas late-stage chondrocytes exhibited ultrastructural changes involving mitochondrial damage and stress-associated chromatin remodeling. Using the chemical inhibitor BTB06584, we revealed that early and late dedifferentiated chondrocytes possessed distinct recovery potentials from functional phenotype loss. Notably, this two-stage transition was also validated in human chondrocytes. An image-based approach was established for clinical use to efficiently predict chondrocyte plasticity using stage-specific biomarkers. Overall, this study lays a foundation to improve the quality of chondrocytes in clinical use and provides deep insights into chondrocyte dedifferentiation.

Lineage Differentiation Potential of Different Sources of Mesenchymal Stem Cells for Osteoarthritis Knee

Tissue engineering and regenerative medicine (TERM) have paved a way for treating musculoskeletal diseases in a minimally invasive manner. The regenerative medicine cocktail involves the usage of mesenchymal stem/stromal cells (MSCs), either uncultured or culture-expanded cells along with growth factors, cytokines, exosomes, and secretomes to provide a better regenerative milieu in degenerative diseases. The successful regeneration of cartilage depends on the selection of the appropriate source of MSCs, the quality, quantity, and frequency of MSCs to be injected, and the selection of the patient at an appropriate stage of the disease. However, confirmation on the most favorable source of MSCs remains uncertain to clinicians. The lack of knowledge in the current cellular treatment is uncertain in terms of how beneficial MSCs are in the long-term or short-term (resolution of pain) and improved quality of life. Whether MSCs treatments have any superiority, exists due to sources of MSCs utilized in their potential to objectively regenerate the cartilage at the target area. Many questions on source and condition remain unanswered. Hence, in this review, we discuss the lineage differentiation potentials of various sources of MSCs used in the management of knee osteoarthritis and emphasize the role of tissue engineering in cartilage regeneration.

Decellularized Avian Cartilage, a Promising Alternative for Human Cartilage Tissue Regeneration

Articular cartilage defects, and subsequent degeneration, are prevalent and account for the poor quality of life of most elderly persons; they are also one of the main predisposing factors to osteoarthritis. Articular cartilage is an avascular tissue and, thus, has limited capacity for healing and self-repair. Damage to the articular cartilage by trauma or pathological causes is irreversible. Many approaches to repair cartilage have been attempted with some potential; however, there is no consensus on any ideal therapy. Tissue engineering holds promise as an approach to regenerate damaged cartilage. Since cell adhesion is a critical step in tissue engineering, providing a 3D microenvironment that recapitulates the cartilage tissue is vital to inducing cartilage regeneration. Decellularized materials have emerged as promising scaffolds for tissue engineering, since this procedure produces scaffolds from native tissues that possess structural and chemical natures that are mimetic of the extracellular matrix (ECM) of the native tissue. In this work, we present, for the first time, a study of decellularized scaffolds, produced from avian articular cartilage (extracted from Gallus Gallus domesticus), reseeded with human chondrocytes, and we demonstrate for the first time that human chondrocytes survived, proliferated and interacted with the scaffolds. Morphological studies of the decellularized scaffolds revealed an interconnected, porous architecture, ideal for cell growth. Mechanical characterization showed that the decellularized scaffolds registered stiffness comparable to the native cartilage tissues. Cell growth inhibition and immunocytochemical analyses showed that the decellularized scaffolds are suitable for cartilage regeneration.

Differentiation of Induced Pluripotent Stem Cells Into Chondrocytes: Methods and Applications for Disease Modeling and Drug Discovery

Induced pluripotent stem cell (iPSC) technology allows pathomechanistic and therapeutic investigation of human heritable disorders affecting tissue types whose collection from patients is difficult or even impossible. Among them are cartilage diseases. Over the past decade, iPSC-chondrocyte disease models have been shown to exhibit several key aspects of known disease mechanisms. Concurrently, an increasing number of protocols to differentiate iPSCs into chondrocytes have been published, each with its respective (dis)advantages. In this review we provide a comprehensive overview of the different differentiation approaches, the hitherto described iPSC-chondrocyte disease models and mechanistic and/or therapeutic insights that have been derived from their investigation, and the current model limitations. Key lessons are that the most appropriate differentiation approach is dependent upon the cartilage disease under investigation and that further optimization is still required to recapitulate the in vivo cartilage. © 2022 American Society for Bone and Mineral Research (ASBMR).

Mesenchymal Stem Cell-Based Therapy as a New Approach for the Treatment of Systemic Sclerosis

Systemic sclerosis (SSc) is an intractable autoimmune disease with unmet medical needs. Conventional immunosuppressive therapies have modest efficacy and obvious side effects. Targeted therapies with small molecules and antibodies remain under investigation in small pilot studies. The major breakthrough was the development of autologous haematopoietic stem cell transplantation (AHSCT) to treat refractory SSc with rapidly progressive internal organ involvement. However, AHSCT is contraindicated in patients with advanced visceral involvement. Mesenchymal stem cells (MSCs) which are characterized by immunosuppressive, antifibrotic and proangiogenic capabilities may be a promising alternative option for the treatment of SSc. Multiple preclinical and clinical studies on the use of MSCs to treat SSc are underway. However, there are several unresolved limitations and safety concerns of MSC transplantation, such as immune rejections and risks of tumour formation, respectively. Since the major therapeutic potential of MSCs has been ascribed to their paracrine signalling, the use of MSC-derived extracellular vesicles (EVs)/secretomes/exosomes as a "cell-free" therapy might be an alternative option to circumvent the limitations of MSC-based therapies. In the present review, we overview the current knowledge regarding the therapeutic efficacy of MSCs in SSc, focusing on progresses reported in preclinical and clinical studies using MSCs, as well as challenges and future directions of MSC transplantation as a treatment option for patients with SSc.

Basic science approaches to common hand surgery problems

The field of hand surgery is constantly evolving to meet challenges of populations with increasing age and higher demands for active living. While our surgical care has improved over the last decades, it seems that future major improvement in outcomes of clinical treatment will come through advances in biologics and the translation of major discoveries in basic science. This article aims to provide an update on where basic science solutions may answer some of the most critical issues in hand surgery, with a focus on augmentation of tissue repair.

Investigation and Comparison of the Effect of TGF-β3, kartogenin and Avocado/Soybean Unsaponifiables on the In-vitro and In-vivo Chondrogenesis of Human Adipose-Derived Stem Cells on Fibrin Scaffold

Due to the lack of suitable therapeutic approaches to cartilage defect, the objective of this study was to determine the effect of Transforming growth factor-β3 (TGF-β3), avocado/soybean (ASU) and Kartogenin (KGN) on chondrogenic differentiation in human adipose-derived stem cells (hADSCs) on fibrin scaffold. hADSCs seeded in fibrin scaffold and cultured in chondrogenic media. These cells were divided into 4 groups (control, TGF-β3, ASU and KGN). Cell viability was estimated by MTT assay. Differentiated cells were evaluated by histological and immunohistochemical (IHC) techniques. Expression genes [sex determining region Y-box 9 (SOX9), Aggrecan (AGG), type II collagen (Coll II) and type X collagen (Coll X)] were assessed by real-time PCR. For a study on an animal model, differentiated cells in fibrin scaffolds were subcutaneously transplanted in rats. Histological and immunohistochemistry were done in the animal model. The results of the real-time PCR indicated that SOX9, AGG and Col II genes expression in TGF-β3, KGN and ASU groups were significantly higher (p < 0.01) compared to the control group, Col X gene expression only in the TGF-β3 group was significantly higher (p< 0.01) compared to the control group. The glycosaminoglycan (GAG) deposition was higher in TGF-β3, KGN and ASU groups compared to the control group. The immunohistological analysis showed the distribution of collagen type X in the extracellular matrix in the fibrin scaffold TGF-β3 group was significantly higher in control, KGN and ASU groups, and (p < 0.001). ASU, particularly KGN, was suitable for successful chondrogenic differentiation of hADSCs and a suppressor of the consequent hypertrophy.

Dental Pulp Stem Cell-Derived Secretome and Its Regenerative Potential

The therapeutic potential of the dental pulp stem (DSC) cell-derived secretome, consisting of various biomolecules, is undergoing intense research. Despite promising in vitro and in vivo studies, most DSC secretome-based therapies have not been implemented in human medicine because the paracrine effect of the bioactive factors secreted by human dental pulp stem cells (hDPSCs) and human exfoliated deciduous teeth (SHEDs) is not completely understood. In this review, we outline the current data on the hDPSC- and SHED-derived secretome as a potential candidate in the regeneration of bone, cartilage, and nerve tissue. Published reports demonstrate that the dental MSC-derived secretome/conditional medium may be effective in treating neurodegenerative diseases, neural injuries, cartilage defects, and repairing bone by regulating neuroprotective, anti-inflammatory, antiapoptotic, and angiogenic processes through secretome paracrine mechanisms. Dental MSC-secretomes, similarly to the bone marrow MSC-secretome activate molecular and cellular mechanisms, which determine the effectiveness of cell-free therapy. Many reports emphasize that dental MSC-derived secretomes have potential application in tissue-regenerating therapy due to their multidirectional paracrine effect observed in the therapy of many different injured tissues.

Enhancement of Chondrogenesis in Hypoxic Precondition Culture: A Systematic Review

BACKGROUND: Cartilage tear has begun to be treated with stem cells. However, stem cell oxygen level culture has not been evaluated for the best environment to enhance chondrogenesis. AIM: The purpose of this review is to focus on the hypoxic oxygen level of stem cells culture as a treatment for cartilage tear. METHODS: A literature search was systemically conducted on PubMed (MEDLINE), OVID, EMBASE, the Cochrane Library, Scopus, Web of Science, Science Direct, Wiley Online Library, Google Scholar, and bibliography of selected articles with the terms (“culture”) AND (“stem cell” OR “mesenchymal stem cell” OR “MSC”) AND (“hypoxic” OR “hypoxia”) AND (“cartilage” OR “chondro*”) as the main keywords. A total of 438 articles were reviewed. Thirty-six articles were considered relevant for this systematic review. RESULTS: The result of this review supports stimulation effects of hypoxic oxygen level stem cell culture in chondrogenesis process. Most studies used 5% oxygen concentration for culture, both of in vivo and in vitro studies. Due to the heterogeneity nature of the included studies, meta-analysis was unable to be conducted. CONCLUSION: Hypoxia state seems to play an important role in chondrocytes proliferation, differentiation, and matrix production.

Review of the Current Trends in Clinical Trials Involving Induced Pluripotent Stem Cells

In 2006, the induced pluripotent stem cell (iPSC) was presented to the world, paving the way for the development of a magnitude of novel therapeutic alternatives, addressing a diverse range of diseases. However, despite the immense cell therapy potential, relatively few clinical trials evaluating iPSC-technology have actually translated into interventional, clinically applied treatment regimens. Herein, our aim was to determine trends in globally conducted clinical trials involving iPSCs. Data were derived both from well-known registries recording clinical trials from across the globe, and databases from individual countries. Comparisons were firstly drawn between observational and interventional studies before the latter was further analyzed in terms of therapeutic and nontherapeutic trials. Our main observations included global distribution, purpose, target size, and types of disorder relevant to evaluated trials. In terms of nontherapeutic trials, the USA conducted the majority, a large average number of participants-187-was included in the trials, and studies on circulatory system disorders comprised a slightly higher proportion of total studies. Conversely, Japan was the frontrunner in terms of conducting therapeutic trials, and the average number of participants was much lower, at roughly 29. Disorders of the circulatory, as well as nervous and visual systems, were all studied in equal measure. This review highlights the impact that iPSC-based cell therapies can have, should development thereof gain more traction. We lastly considered a few companies that are actively utilizing iPSCs in the development of therapies for various diseases, for whom the global trends in clinical trials could become increasingly important.

Perichondrium-inspired permeable nanofibrous tube well promoting differentiation of hiPSC-derived pellet toward hyaline-like cartilage pellet

The pellet formation has been regarded as a golden standard forin vitrochondrogenic differentiation. However, a spatially inhomogeneous chondrogenic microenvironment around a pellet resulted from the use of a traditional impermeable narrow tube, such as the conical tube, undermines the differentiation performance and therapeutic potential of differentiated cartilage pellet in defective articular cartilage treatment. To address this drawback, a perichondrium-inspired permeable nanofibrous tube (PINaT) well with a nanofibrous wall permeable to gas and soluble molecules is proposed. The PINaT well was fabricated with a micro deep drawing process where a flat thin nanofibrous membrane was transformed to a 3.5 mm deep tube well with a ∼50µm thick nanofibrous wall. Similar toin vivoperichondrium, the PINaT well was found to allow oxygen and growth factor diffusion required for chondrogenic differentiation across the entire nanofibrous wall. Analyses of gene expressions (COL2A1, COL10A1, ACAN, and SOX9), proteins (type II and X collagen), and glycosaminoglycans contents were conducted to assess the differentiation performance and clinical efficacy of differentiated cartilage pellet. The regulated spatially homogeneous chondrogenic microenvironment around the human induced pluripotent stem cell-derived pellet (3 × 10⁵cells per pellet) in the PINaT well remarkably improved the quality of the differentiated pellet toward a more hyaline-like cartilage pellet. Furthermore, an accelerated chondrogenic differentiation process of the pellet produced by the PINaT well was achieved for 14 days, demonstrating a hyaline cartilage-specific marker similar to the control pellet differentiated for 20 days. Finally, the enhanced clinical efficacy of the hyaline-like cartilage pellet was confirmed using an osteochondral defect rat model, with the repaired tissue resembling hyaline cartilage rather than fibrous cartilage after 8 weeks of regeneration.

The Use of Infrapatellar Fat Pad-Derived Mesenchymal Stem Cells in Articular Cartilage Regeneration: A Review

Cartilage is frequently damaged with a limited capacity for repair. Current treatment strategies are insufficient as they form fibrocartilage as opposed to hyaline cartilage, and do not prevent the progression of degenerative changes. There is increasing interest in the use of autologous mesenchymal stem cells (MSC) for tissue regeneration. MSCs that are used to treat articular cartilage defects must not only present a robust cartilaginous production capacity, but they also must not cause morbidity at the harvest site. In addition, they should be easy to isolate from the tissue and expand in culture without terminal differentiation. The source of MSCs is one of the most important factors that may affect treatment. The infrapatellar fat pad (IPFP) acts as an important reservoir for MSC and is located in the anterior compartment of the knee joint in the extra-synovial area. The IPFP is a rich source of MSCs, and in this review, we discuss studies that demonstrate that these cells have shown many advantages over other tissues in terms of ease of isolation, expansion, and chondrogenic differentiation. Future studies in articular cartilage repair strategies and suitable extraction as well as cell culture methods will extend the therapeutical application of IPFP-derived MSCs into additional orthopedic fields, such as osteoarthritis. This review provides the latest research concerning the use of IPFP-derived MSCs in the treatment of articular cartilage damage, providing critical information for the field to grow.

Cell Interplay in Osteoarthritis

Osteoarthritis (OA) is a common chronic disease and a significant health concern that needs to be urgently solved. OA affects the cartilage and entire joint tissues, including the subchondral bone, synovium, and infrapatellar fat pads. The physiological and pathological changes in these tissues affect the occurrence and development of OA. Understanding complex crosstalk among different joint tissues and their roles in OA initiation and progression is critical in elucidating the pathogenic mechanism of OA. In this review, we begin with an overview of the role of chondrocytes, synovial cells (synovial fibroblasts and macrophages), mast cells, osteoblasts, osteoclasts, various stem cells, and engineered cells (induced pluripotent stem cells) in OA pathogenesis. Then, we discuss the various mechanisms by which these cells communicate, including paracrine signaling, local microenvironment, co-culture, extracellular vesicles (exosomes), and cell tissue engineering. We particularly focus on the therapeutic potential and clinical applications of stem cell-derived extracellular vesicles, which serve as modulators of cell-to-cell communication, in the field of regenerative medicine, such as cartilage repair. Finally, the challenges and limitations related to exosome-based treatment for OA are discussed. This article provides a comprehensive summary of key cells that might be targets of future therapies for OA.

The effect of sodium metasilicate on the three-dimensional chondrogenesis of mesenchymal stem cells

The benefits of different silicic concentrations on chondrogenesis of mesenchymal stem cell (MSC) are unclear. Here an in vitro scaffoldless model was used to determine the impact of different silicic concentrations on the three-dimensional chondrogenesis of MSCs. Sodium metasilicate solutions were used as the source of silica, and were added in the chondrogenic medium and replenished every 3 days. The thickness and area of cartilage; the expression of collagen II, aggrecan, and the collagen type II/I ratio; the glycosaminoglycan and cell contents; and the tangent modulus of the constructs were all significantly higher in 100 and 200 ng/mL groups compared with those in 0 and 10 ng/mL groups. All the above parameters, as well as several mechanical parameters of cartilage constructs were highest in 200 ng/mL group. Thus, 200 ng/mL sodium metasilicate could promote the chondrogenic differentiation of MSCs and the mechanical and biochemical properties of the cartilage constructs.

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.

Effects of Normal Synovial Fluid and Interferon Gamma on Chondrogenic Capability and Immunomodulatory Potential Respectively on Equine Mesenchymal Stem Cells

Synovial fluid contains cytokines, growth factors and resident mesenchymal stem cells (MSCs). The present study aimed to (1) determine the effects of autologous and allogeneic synovial fluid on viability, proliferation and chondrogenesis of equine bone marrow MSCs (BMMSCs) and (2) compare the immunomodulatory properties of equine synovial fluid MSCs (SFMSCs) and BMMSCs after stimulation with interferon gamma (INF-γ). To meet the first aim of the study, the proliferation and viability of MSCs were evaluated by MTS and calcein AM staining assays. To induce chondrogenesis, MSCs were cultured in a medium containing TGF-β1 or different concentrations of synovial fluid. To meet the second aim, SFMSCs and BMMSCs were stimulated with IFN-γ. The concentration of indoleamine-2,3-dioxygenase (IDO) and nitric oxide (NO) were examined. Our results show that MSCs cultured in autologous or allogeneic synovial fluid could maintain proliferation and viability activities. Synovial fluid affected chondrocyte differentiation significantly, as indicated by increased glycosaminoglycan contents, compared to the chondrogenic medium containing 5 ng/mL TGF-β1. After culturing with IFN-γ, the conditioned media of both BMMSCs and SFMSCs showed increased concentrations of IDO, but not NO. Stimulating MSCs with synovial fluid or IFN-γ could enhance chondrogenesis and anti-inflammatory activity, respectively, suggesting that the joint environment is suitable for chondrogenesis.

Decellularized Porcine Cartilage Scaffold; Validation of Decellularization and Evaluation of Biomarkers of Chondrogenesis

Osteoarthritis is a major concern in the United States and worldwide. Current non-surgical and surgical approaches alleviate pain but show little evidence of cartilage restoration. Cell-based treatments may hold promise for the regeneration of hyaline cartilage-like tissue at the site of injury or wear. Cell-cell and cell-matrix interactions have been shown to drive cell differentiation pathways. Biomaterials for clinically relevant applications can be generated from decellularized porcine auricular cartilage. This material may represent a suitable scaffold on which to seed and grow chondrocytes to create new cartilage. In this study, we used decellularization techniques to create an extracellular matrix scaffold that supports chondrocyte cell attachment and growth in tissue culture conditions. Results presented here evaluate the decellularization process histologically and molecularly. We identified new and novel biomarker profiles that may aid future cartilage decellularization efforts. Additionally, the resulting scaffold was characterized using scanning electron microscopy, fluorescence microscopy, and proteomics. Cellular response to the decellularized scaffold was evaluated by quantitative real-time PCR for gene expression analysis.

Minicircles for Investigating and Treating Arthritic Diseases

Gene delivery systems have become an essential component of research and the development of therapeutics for various diseases. Minicircles are non-viral vectors with promising characteristics for application in a variety of fields. With their minimal size, minicircles exhibit relatively high safety and efficient delivery of genes of interest into cells. Cartilage tissue lacks the natural ability to heal, making it difficult to treat osteoarthritis (OA) and rheumatoid arthritis (RA), which are the two main types of joint-related disease. Although both OA and RA affect the joint, RA is an autoimmune disease, while OA is a degenerative joint condition. Gene transfer using minicircles has also been used in many studies regarding cartilage and its diseased conditions. In this review, we summarize the cartilage-, OA-, and RA-based studies that have used minicircles as the gene delivery system.

Mesenchymal stem/stromal cell-based therapy: mechanism, systemic safety and biodistribution for precision clinical applications

Mesenchymal stem/stromal cells (MSCs) are a promising resource for cell-based therapy because of their high immunomodulation ability, tropism towards inflamed and injured tissues, and their easy access and isolation. Currently, there are more than 1200 registered MSC clinical trials globally. However, a lack of standardized methods to characterize cell safety, efficacy, and biodistribution dramatically hinders the progress of MSC utility in clinical practice. In this review, we summarize the current state of MSC-based cell therapy, focusing on the systemic safety and biodistribution of MSCs. MSC-associated risks of tumor initiation and promotion and the underlying mechanisms of these risks are discussed. In addition, MSC biodistribution methodology and the pharmacokinetics and pharmacodynamics of cell therapies are addressed. Better understanding of the systemic safety and biodistribution of MSCs will facilitate future clinical applications of precision medicine using stem cells.

Ex Vivo Generation and Characterization of Human Hyaline and Elastic Cartilaginous Microtissues for Tissue Engineering Applications

Considering the high prevalence of cartilage-associated pathologies, low self-repair capacity and limitations of current repair techniques, tissue engineering (TE) strategies have emerged as a promising alternative in this field. Three-dimensional culture techniques have gained attention in recent years, showing their ability to provide the most biomimetic environment for the cells under culture conditions, enabling the cells to fabricate natural, 3D functional microtissues (MTs). In this sense, the aim of this study was to generate, characterize and compare scaffold-free human hyaline and elastic cartilage-derived MTs (HC-MTs and EC-MTs, respectively) under expansion (EM) and chondrogenic media (CM). MTs were generated by using agarose microchips and evaluated ex vivo for 28 days. The MTs generated were subjected to morphometric assessment and cell viability, metabolic activity and histological analyses. Results suggest that the use of CM improves the biomimicry of the MTs obtained in terms of morphology, viability and extracellular matrix (ECM) synthesis with respect to the use of EM. Moreover, the overall results indicate a faster and more sensitive response of the EC-derived cells to the use of CM as compared to HC chondrocytes. Finally, future preclinical in vivo studies are still needed to determine the potential clinical usefulness of these novel advanced therapy products.

Preparation and characterization of a soluble eggshell membrane/agarose composite scaffold with possible applications in cartilage regeneration

Articular hyaline cartilage is an extremely hydrated, not vascularized tissue with a low-cell density. The damage of this tissue can occur after injuries or gradual stress and tears (osteoarthritis), minor damages can be self-healed in several weeks, but major injuries may eventually require surgery. In fact, in this case, because of nature of the cartilage (the absence of cells and vascularization) it is difficult to expect its natural regeneration in a reasonable amount of time. In recent years, cell therapy, in which cells are directly transplanted, has attracted attention. In this study, a scaffold for implanting chondrocytes was prepared. The scaffold was made as a sponge using the eggshell membrane and agarose. The eggshell membrane is structurally similar to the extracellular matrix and nontoxic due to its many collagen components and has good biocompatibility and biodegradability. However, scaffolds made of collagen only has poor mechanical properties. For this reason, the disulfide bond of collagen extracted from the insoluble eggshell membrane was cut, converted into water-soluble, and then mixed with agarose to prepare a scaffold. Agarose is capable of controlling mechanical properties, has excellent biocompatibility, and is suitable for forming a hydrogel having a three-dimensional porosity. The scaffold was examined for Fourier-transform infrared, mechanical properties, biodegradability, and biocompatibility. In in vitro experiment, cytotoxicity, cell proliferation, and messenger RNA expression were investigated. The study demonstrated that the agarose/eggshell membrane scaffold can be used for chondrocyte transplantation.

Recent Updates of Diagnosis, Pathophysiology, and Treatment on Osteoarthritis of the Knee

Osteoarthritis (OA) is a degenerative and chronic joint disease characterized by clinical symptoms and distortion of joint tissues. It primarily damages joint cartilage, causing pain, swelling, and stiffness around the joint. It is the major cause of disability and pain. The prevalence of OA is expected to increase gradually with the aging population and increasing prevalence of obesity. Many potential therapeutic advances have been made in recent years due to the improved understanding of the underlying mechanisms, diagnosis, and management of OA. Embryonic stem cells and induced pluripotent stem cells differentiate into chondrocytes or mesenchymal stem cells (MSCs) and can be used as a source of injectable treatments in the OA joint cavity. MSCs are known to be the most studied cell therapy products in cell-based OA therapy owing to their ability to differentiate into chondrocytes and their immunomodulatory properties. They have the potential to improve cartilage recovery and ultimately restore healthy joints. However, despite currently available therapies and advances in research, unfulfilled medical needs persist for OA treatment. In this review, we focused on the contents of non-cellular and cellular therapies for OA, and briefly summarized the results of clinical trials for cell-based OA therapy to lay a solid application basis for clinical research.

Research Progress on Stem Cell Therapies for Articular Cartilage Regeneration

Injury of articular cartilage can cause osteoarthritis and seriously affect the physical and mental health of patients. Unfortunately, current surgical treatment techniques that are commonly used in the clinic cannot regenerate articular cartilage. Regenerative medicine involving stem cells has entered a new stage and is considered the most promising way to regenerate articular cartilage. In terms of theories on the mechanism, it was thought that stem cell-mediated articular cartilage regeneration was achieved through the directional differentiation of stem cells into chondrocytes. However, recent evidence has shown that the stem cell secretome plays an important role in biological processes such as the immune response, inflammation regulation, and drug delivery. At the same time, the stem cell secretome can effectively mediate the process of tissue regeneration. This new theory has attributed the therapeutic effect of stem cells to their paracrine effects. The application of stem cells is not limited to exogenous stem cell transplantation. Endogenous stem cell homing and in situ regeneration strategies have received extensive attention. The application of stem cell derivatives, such as conditioned media, extracellular vesicles, and extracellular matrix, is an extension of stem cell paracrine theory. On the other hand, stem cell pretreatment strategies have also shown promising therapeutic effects. This article will systematically review the latest developments in these areas, summarize challenges in articular cartilage regeneration strategies involving stem cells, and describe prospects for future development.

High-precision, gelatin-based, hybrid, bilayer scaffolds using melt electro-writing to repair cartilage injury

Articular cartilage injury is a common disease in the field of orthopedics. Because cartilage has poor self-repairing ability, medical intervention is needed. Using melt electro-writing (MEW) technology, tissue engineering scaffolds with high porosity and high precision can be prepared. However, ordinary materials, especially natural polymer materials, are difficult to print. In this study, gelatin was mixed with poly (lactic-co-glycolic acid) to prepare high-concentration and high-viscosity printer ink, which had good printability and formability. A composite scaffold with full-layer TGF-β1 loading mixed with hydroxyapatite was prepared, and the scaffold was implanted at the cartilage injury site; microfracture surgery was conducted to induce the mesenchyme in the bone marrow. Quality stem cells thereby promoted the repair of damaged cartilage. In summary, this study developed a novel printing method, explored the molding conditions based on MEW printing ink, and constructed a bioactive cartilage repair scaffold. The scaffold can use autologous bone marrow mesenchymal stem cells and induce their differentiation to promote cartilage repair.

Cartilage Repair by Mesenchymal Stem Cell-Derived Exosomes: Preclinical and Clinical Trial Update and Perspectives

Osteoarthritis (OA) and other degenerative joint diseases are characterized by articular cartilage destruction, synovial inflammation, sclerosis of subchondral bone, and loss of extracellular matrix (ECM). Worldwide, these diseases are major causes of disability. Cell therapies have been considered to be the best therapeutic strategies for long-term treatment of articular cartilage diseases. It has been suggested that the mechanism of stem cell-based therapy is related to paracrine secretion of extracellular vesicles (EVs), which are recognized as the main secretion factors of stem cells. EVs, and in particular the subclass exosomes (Exos), are novel therapeutic approaches for treatment of cartilage lesions and OA. The results of recent studies have shown that EVs isolated from mesenchymal stem cells (MSCs) could inhibit OA progression. EVs isolated from various stem cell sources, such as MSCs, may contribute to tissue regeneration of the limbs, skin, heart, and other tissues. Here, we summarize recent findings of preclinical and clinical studies on different MSC-derived EVs and their effectiveness as a treatment for damaged cartilage. The Exos isolation techniques in OA treatment are also highlighted.

Engineered-extracellular vesicles as an optimistic tool for microRNA delivery for osteoarthritis treatment

Worldwide, osteoarthritis (OA) is one of the most common chronic diseases. In OA, profiling gene expression changes occur and cartilage tissue homeostasis is lost. Suggestions for OA treatment include regulation of gene expressions via the use of microRNAs (miRNAs). However, problems exist with the use of miRNAs, the most important of which is the delivery of sufficient amounts of effective miRNAs to save cartilage tissue. The engineering of extracellular vesicles (EVs) with the use of advanced techniques would be an efficient OA treatment. Therefore, we discuss the importance of miRNAs in terms of cartilage tissue regeneration and review recent advances in production of enriched EVs and miRNA delivery by EVs for future clinical applications.

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.

Examining the Characteristics and Applications of Mesenchymal, Induced Pluripotent, and Embryonic Stem Cells for Tissue Engineering Approaches across the Germ Layers

The field of regenerative medicine utilizes a wide array of technologies and techniques for repairing and restoring function to damaged tissues. Among these, stem cells offer one of the most potent and promising biological tools to facilitate such goals. Implementation of mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs), and embryonic stem cells (ESCs) offer varying advantages based on availability and efficacy in the target tissue. The focus of this review is to discuss characteristics of these three subset stem cell populations and examine their utility in tissue engineering. In particular, the development of therapeutics that utilize cell-based approaches, divided by germinal layer to further assess research targeting specific tissues of the mesoderm, ectoderm, and endoderm. The combinatorial application of MSCs, iPSCs, and ESCs with natural and synthetic scaffold technologies can enhance the reparative capacity and survival of implanted cells. Continued efforts to generate more standardized approaches for these cells may provide improved study-to-study variations on implementation, thereby increasing the clinical translatability of cell-based therapeutics. Coupling clinically translatable research with commercially oriented methods offers the potential to drastically advance medical treatments for multiple diseases and injuries, improving the quality of life for many individuals.

ITGB1 promotes the chondrogenic differentiation of human adipose-derived mesenchymal stem cells by activating the ERK signaling

Adipose-derived mesenchymal stem cell (ADSC) with a high capacity of chondrogenic differentiation was a promising candidate for cartilage defect treatment. This study's objective is to study the roles of integrin β1 (ITGB1) in regulating ADSC chondrogenic differentiations as well as the underlying mechanisms. The identity of ADSC was confirmed by flow cytometry. ITGB1 gene was overexpressed in human ADSC (hADSC) by transfection with LV003-recombinant plasmids. Gene mRNA and protein levels were examined using quantitative RT-PCR and western blotting, respectively. Differentially expressed mRNAs and proteins were characterized by next-generation RNA sequencing and label-free quantitative proteomics, respectively. ERK signaling and AKT signaling in hADSCs were inhibited by treating with SCH772984 and GSK690693, respectively. ITGB1 gene overexpression substantially increased collagen type II alpha 1 chain (COL2A1), aggrecan (ACAN), and SRY-box transcription factor 9 (SOX9) expression but suppressed collagen type I alpha 1 chain (COL1A1) expression in hADSCs. Next-generation RNA sequencing identified a total of 246 genes differentially expressed in hADSCs by ITGB1 overexpression, such as 183 upregulated and 63 downregulated genes. Label-free proteomics characterized 34 proteins differentially expressed in ITGB1-overexpressing hADSCs. Differentially expressed genes and proteins were enriched by different biological processes such as cell adhesion and differentiation and numerous signaling pathways such as the ERK signaling pathway. ERK inhibitor treatment caused substantially enhanced chondrogenic differentiation in ITGB1-overexpressing hADSCs. ITGB1 promoted the chondrogenic differentiation of human ADSCs via the activation of the ERK signaling pathway.

Ultrasound combined with SDF-1α chemotactic microbubbles promotes stem cell homing in an osteoarthritis model

Osteoarthritis (OA) is a common joint disease in the middle and old age group with obvious cartilage damage, and the regeneration of cartilage is the key to alleviating or treating OA. In stem cell therapy, bone marrow stem cell (BMSC) has been confirmed to have cartilage regeneration ability. However, the role of stem cells in promoting articular cartilage regeneration is severely limited by their low homing rate. Stromal cell‐derived factor‐1α (SDF‐1α) plays a vital role in MSC migration and involves activation, mobilization, homing and retention. So, we aim to develop SDF‐1α‐loaded microbubbles MB(SDF‐1α), and to verify the migration of BMSCs with the effect of ultrasound combined with MB(SDF‐1α) in vitro and in vivo. The characteristics of microbubbles and the content of SDF‐1α were examined in vitro. To evaluate the effect of ultrasound combined with chemotactic microbubbles on stem cell migration, BMSCs were injected locally and intravenously into the knee joint of the OA model, and the markers of BMSCs in the cartilage were detected. We successfully prepared MB(SDF‐1α) through covalent bonding with impressive SDF‐1α loading efficacy loading content. In vitro study, ultrasound combined with MB(SDF‐1α) group can promote more stem cell migration with highest migrating cell counts, good cell viability and highest CXCR4 expression. In vivo experiment, more BMSCs surface markers presented in the ultrasound combined with MB(SDF‐1α) group with or without exogenous BMSCs administration. Hence, ultrasound combined with MB(SDF‐1α) could promote the homing of BMSCs to cartilage and provide a novel promising therapeutic approach for OA.

Mesenchymal Stem Cell Therapy in Chondral Defects of Knee: Current Concept Review

PURPOSE

Full-thickness cartilage defects if left alone would increase the risk of osteoarthritis (OA) with severe associated pain and functional disability. Articular cartilage defect may result from direct trauma or chronic degeneration. The capability of the mesenchymal stem cells (MSCs) to repair and regenerate cartilage has been widely investigated. This review describes current trends in MSC biology, the sourcing, expansion, application and role of MSCs in chondral defects of human knees.

METHODS

The studies referencing MSCs and knee osteoarthritis were searched (from1998 to 2020) using PubMed, EMBASE, Cochrane Library, Web of Science and the ClinicalTrials.gov with keywords (MSCs, chondral defects or cartilage degeneration of knee, cartilage regeneration, chondrogenesis, tissue engineering, efficacy and safety). The inclusion criteria were based on use of MSCs for treatment of chondral defects and osteoarthritis of the knee, English language and human studies.

RESULTS

The history of MSC research from the initial discovery of their multipotency to the more recent recognition of their role in cartilage defects of knee is elucidated. Several studies have demonstrated promising results in the clinical application for repair of chondral defects as an adjuvant or independent procedure. Intra-articular MSCs provide improvements in pain and function in knee osteoarthritis at short-term follow-up in many studies. The tendency of MSCs to differentiate into fibrocartilage affecting the outcome is a common issue faced by researchers.

CONCLUSION

Some efficacy has been shown of MSCs for cartilage repair in osteoarthritis; however, the evidence of efficacy of intra-articular MSCs on both clinical outcomes and cartilage repair remains limited. Despite the high quality of evidence to support, MSC therapy has emerged but further refinement of methodology will be necessary to support its routine clinical use.

Three-Dimensional Printing Biologically Inspired DNA-Based Gradient Scaffolds for Cartilage Tissue Regeneration

Cartilage damage caused by aging, repeated overloading, trauma, and diseases can result in chronic pain, inflammation, stiffness, and even disability. Unlike other types of tissues (bone, skin, muscle, etc.), cartilage tissue has an extremely weak regenerative capacity. Currently, the gold standard surgical treatment for repairing cartilage damage includes autografts and allografts. However, these procedures are limited by insufficient donor sources and the potential for immunological rejection. After years of development, engineered tissue now provides a valuable artificial replacement for tissue regeneration purposes. Three-dimensional (3D) bioprinting technologies can print customizable hierarchical structures with cells. The objective of the current work was to prepare a 3D-printed three-layer gradient scaffold with lysine-functionalized rosette nanotubes (RNTK) for improving the chondrogenic differentiation of adipose-derived mesenchymal stem cells (ADSCs). Specifically, biologically inspired RNTKs were utilized in our work because they have unique surface chemistry and biomimetic nanostructure to improve cell adhesion and growth. Different ratios of gelatin methacrylate (GelMA) and poly(ethylene glycol) diacrylate (PEGDA) were printed into a three-layer GelMA-PEGDA gradient scaffold using a stereolithography-based printer, followed by coating with RNTKs. The pores and channels (∼500 μm) were observed in the scaffold. It was found that the population of ADSCs on the GelMA-PEGDA-RNTK scaffold increased by 34% compared to the GelMA-PEGDA scaffold (control). Moreover, after 3 weeks of chondrogenic differentiation, collagen II, glycosaminoglycan, and total collagen synthesis on the GelMA-PEGDA-RNTK scaffold significantly respectively increased by 59%, 71%, and 60%, as compared to the control scaffold. Gene expression of collagen II α1, SOX 9, and aggrecan in the ADSCs growing on the GelMA-PEGDA-RNTK scaffold increased by 79%, 52%, and 47% after 3 weeks, compared to the controls, respectively. These results indicated that RNTKs are a promising type of nanotubes for promoting chondrogenic differentiation, and the present 3D-printed three-layer gradient GelMA-PEGDA-RNTK scaffold shows considerable promise for future cartilage repair and regeneration.

Thickness-wise growth technique for human articular chondrocytes to fabricate three-dimensional cartilage grafts

INTRODUCTION

Cutting the cost of manufacturing is important for extending the use of tissue-engineered therapeutic products. The present study aimed to develop a simple method for fabrication of cartilaginous tissues for regenerative therapy, utilizing the phenomenon where human articular chondrocytes grow thickness-wise and spontaneously form three-dimensionally thick tissues.

METHODS

Normal human articular chondrocytes (NHACs) were cultured with varying concentrations of transforming growth factor beta 1 (TGF-β1) and/or fibroblast growth factor-2 (FGF-2) to optimize the culture condition for thickness-wise growth of chondrocytes. Next, the tissues grown in the optimal condition were subjected to re-differentiation culture in attached and detached states to assess differentiation capacity by evaluating secreted factors, histological analysis, and a gene expression assay.

RESULTS

NHACs grew thickness-wise efficiently in the presence of 1 ng/mL TGF-β1 and 10 ng/mL FGF-2. After two weeks of culture, NHACs grew with 11-fold higher thickness and 16-fold higher cell number compared to cells which were neither treated with TGF-β1 nor with FGF-2. These thickness-wise-grown chondrocytes could be re-differentiated by a differentiation medium according to the increase in melanoma inhibitory activity (MIA) and positive safranin-O staining. Interestingly, the cartilaginous gene expression was considerably different between the attached and detached conditions even in the same culture medium, indicating the necessity of detachment and shrinkage to achieve further differentiation.

CONCLUSIONS

Spontaneous thickness-wise growth might provide a simple tissue-engineering method for manufacturing cartilaginous 3D tissues.

Activation of the SOX-5, SOX-6, and SOX-9 Trio of Transcription Factors Using a Gene-Activated Scaffold Stimulates Mesenchymal Stromal Cell Chondrogenesis and Inhibits Endochondral Ossification

Current treatments for articular cartilage defects relieve symptoms but often only delay cartilage degeneration. Mesenchymal stem cells (MSCs) have shown chondrogenic potential but tend to undergo endochondral ossification when implanted in vivo. Harnessing factors governing joint development to functionalize biomaterial scaffolds, termed developmental engineering, might allow to prime host MSCs to regenerate mature articular cartilage in situ without requiring cell isolation or ex vivo expansion. Therefore, the aim of this study is to develop a gene-activated scaffold capable of delivering developmental cues to host MSCs, thus priming MSCs for articular cartilage differentiation and inhibiting endochondral ossification. It is shown that delivery of the SOX-Trio induced MSCs to over-express COL2A1 and ACAN and deposit a sulfated and collagen type II rich extracellular matrix while hypertrophic gene expression and collagen type X deposition is inhibited. When cell-free SOX-Trio-activated scaffolds are implanted ectopically in vivo, they induced spontaneous chondrogenesis without evidence of hypertrophy. MSCs pre-cultured on SOX-Trio-activated scaffolds prior to implantation differentiate into phenotypically stable chondrocytes as evidenced by a lack of collagen X expression or vascular invasion. This SOX-trio-activated scaffold represents a potent, single treatment, developmentally inspired strategy to prime MSCs in situ for articular cartilage defect repair.

Alterations in characteristics of canine articular chondrocytes in non-passaged long-term monolayer culture: Matter of differentiation, dedifferentiation and redifferentiation

This study investigated the effects of culture time on phenotype stability of canine articular chondrocytes (CACs) in non-passaged long-term monolayer culture. Third passage (P3) CACs isolated from four cartilage samples were seeded at three different initial seeding densities (0.2 × 10⁴, 1.0 × 10⁴ and 5.0 × 10⁴ cells/cm²) and maintained in monolayer condition up to 8 weeks without undergoing subculture after confluence. The characteristic changes of chondrocytes during the culture period were evaluated based on the cell morphology, cell proliferation, glycosaminoglycans (GAGs) content, DNA quantification, mRNA expression and ultrastructure of chondrocytes. Chondrocytes maintained under post-confluence condition exhibited a capability to grow and proliferate up to 4 weeks. Alcian blue staining and Dimethylmethylene blue (DMMB) assay revealed that the extracellular matrix (ECM) synthesis was increased in a time-dependent manner from 2 to 8 weeks. The chondrocyte mRNA expression profile was dramatically affected by prolonged culture time, with a significant downregulation of collagen type I, whereas the expression of collagen type II, aggrecan, Sox9 and matrix metalloproteinase 13 (MMP-13) were significantly upregulated. In addition, transmission electron microscopy (TEM) result indicated dilation of rough endoplasmic reticulum (RER) in these long-term monolayer cultured chondrocytes. These findings demonstrate that the chondrocytes phenotype could be partially redifferentiated through the spontaneous redifferentiation process in long-term cultures using standard culture medium without the addition of chondrogenic supplements or tissue-culture scaffolds.