Advances and Prospects in Stem Cells for Cartilage Regeneration

The histological features of cartilage call attention to the fact that cartilage has a little capacity to repair itself owing to the lack of a blood supply, Nerven, or lymphangion. Stem cells have emerged as a promising option in the field of cartilage tissue engineering and regenerative medicine and could lead to cartilage repair. Much research has examined cartilage regeneration utilizing stem cells. Jedoch, both the potential and the limitations of this procedure remain controversial. This review presents a summary of emerging trends with regard to using stem cells in cartilage tissue engineering and regenerative medicine. Insbesondere, it focuses on the characterization of cartilage stem cells, the chondrogenic differentiation of stem cells, und die verschiedenen Strategien und Ansätze mit Stammzellen, die bei der Knorpelreparatur und in klinischen Studien verwendet wurden. Basierend auf der Forschung zu Chondrozyten- und Stammzelltechnologien, In diesem Aufsatz werden die Schädigung und Reparatur von Knorpel sowie die klinische Anwendung von Stammzellen erörtert, mit dem Ziel, unser systematisches Verständnis für die Anwendung von Stammzellen bei der Knorpelregeneration zu erweitern; zusätzlich, Es werden mehrere fortgeschrittene Strategien zur Knorpelreparatur besprochen.

1. Einführung
Knorpeldefekte, die häufigste Gelenkerkrankung, kann Schwellungen verursachen, Schmerz, und anschließender Verlust der Gelenkfunktion [1]. Die Fähigkeit zur Selbstreparatur des Knorpels ist aufgrund seiner einzigartigen Struktur begrenzt, da es an Blutversorgung mangelt, Nerven, und Lymphangion; Der Knorpel nimmt Nahrungsergänzungsmittel hauptsächlich aus der Gelenkflüssigkeit auf. daher, traumatische Gelenkknorpelverletzung und frühe Arthrose (OA) Schmerzen verursachen, Arthrose beschleunigen, und schwere Funktionsstörungen verursachen. Eine Meniskusverletzung verursacht beim Patienten Schmerzen, schränkt ihre Bewegung ein, und kann das Auftreten und die Entwicklung von Arthrose beschleunigen. Eine Verletzung des Bandscheibenknorpels ist eine der Hauptursachen für chronische Rückenschmerzen [2].

Knorpelschäden und die daraus resultierende Gewebedegeneration können zu langfristigen chronischen Erkrankungen führen; darüber hinaus, Solche Schäden verbrauchen große Mengen an medizinischen Ressourcen [3]. Jedoch, Der Bereich der regenerativen Medizin hat vielversprechende Entwicklungen bei der Reparatur von Knorpelschäden gezeigt.

Samenzellen sind die Schlüsselkomponenten der regenerativen Medizin, was zur Heilung führt. Autologer Knorpel ist der Goldstandard für Knorpelsamenzellen in der regenerativen Medizin [4]. Autologe Chondrozytenimplantation (ACI) wurde in großem Umfang mit bestätigten klinischen Wirkungen bei der Reparatur von Knorpeldefekten eingesetzt [5, 6]. Da die Spenderquelle für autologe Chondrozyten begrenzt ist, Zellen müssen vor der Implantation in vitro in Monoschichten amplifiziert werden, um die Reparaturanforderungen zu erfüllen. Jedoch, Die Ausdehnung der Monoschichten kann zu einer schnellen Dedifferenzierung der Chondrozyten führen, Dies führt zum Verlust des ursprünglichen Zellphänotyps [7]. Im Vergleich zu normalen Knorpelzellen, Dedifferenzierte Chondrozyten bilden mit größerer Wahrscheinlichkeit Faserknorpel statt hyaliner Knorpel; Letzteres hat bessere biomechanische Eigenschaften und ist langlebiger. Jedoch, Eine autologe Knorpeltransplantation erfordert einen zweiten chirurgischen Eingriff und erhöht das Risiko einer Verletzung des gesunden Knorpels im Spenderbereich. Chondrozyten behalten ihren Phänotyp bei, wenn sie in vivo mit Zytokinen in dreidimensionaler Form kultiviert werden (3D) Kulturen [8, 9]. Jedoch, Die klinische Anwendung der autologen Chondrozytenreparatur ist begrenzt.

Stammzellen haben das Potenzial zur Selbsterneuerung und Differenzierung in mehrere Zelllinien. Stammzellen können in drei Hauptkategorien unterteilt werden: embryonale Stammzellen (ESCs), induzierte pluripotente Stammzellen (iPSCs), und adulte Stammzellen [10]. ESCs werden aus der inneren Zellmasse von Embryonen im Blastozystenstadium gewonnen [11]. iPSCs können durch genetische Reprogrammierung aus somatischen Zellen gewonnen werden [12]. Adulte Stammzellen werden aus verschiedenen adulten Geweben isoliert [13]. ESCs und iPSCs sind pluripotente Zellen, die sich in Zellen aller drei Abstammungslinien differenzieren: Ektoderm, Mesoderm, und Endoderm [14]. Adulte Stammzellen werden in multipotente und unipotente Stammzellen unterteilt; Unipotente Zellen können sich nur in einen Zelltyp differenzieren, wie Satellitenstammzellen oder epidermale Stammzellen. Multipotente Zellen können sich in einer Abstammungslinie in mehrere Zelltypen differenzieren; Zum Beispiel, mesenchymale Stammzellen (MSCs) können sich zu Osteoblasten differenzieren, Chondrozyten, und Fettzellen [13]. Die Fähigkeit zur Selbsterneuerung und das Potenzial zur Mehrfachdifferenzierung von Stammzellen, wie ESCs, iPSCs, und MSCs, wurden im Bereich der Geweberegeneration umfassend untersucht. Außerdem, Studien mit MSCs wurden vollständig im klinischen Umfeld angewendet [15]. In dieser Rezension, Wir konzentrieren uns auf den Knorpelverletzungsmechanismus und Behandlungsstrategien sowie auf Studien an Stammzellen im Bereich der Knorpelregeneration.

2. Charakterisierung von Knorpelstammzellen
Basierend auf der Theorie der kontinuierlichen Schadensreparatur, Dowthwaite et al. waren die ersten, die Knorpelstammzellen beschrieben haben (CSCs) auf der Oberfläche des Gelenkknorpels [16]. Sie entdeckten, dass CSCs und Fibronektin eine enge Wechselbeziehung haben. Außerdem, they showed that CSCs have high colony-forming efficiency and can express Notch 1, which plays an important role in the early steps in notch signaling, inducing chondrogenesis [17].

CSCs also exist in patients with end-stage OA [18], and cells with chondrogenic potential can migrate rapidly into damaged cartilage to downregulate the expression of Runx-2, an osteogenic transcription factor, and enhance the expression of Sox-9, a chondrogenic transcription factor. By regulating Runx-2 and Sox-9 to inhibit osteogenesis in the damaged cartilage, CSCs can facilitate chondrogenesis to improve cartilage self-repair [19]. The matrix synthesis potential of CSCs can be increased without altering their migratory capacity. While cartilage cells usually exist in the surface of cartilage [16, 18], Yu et al. found in 2014 that CSCs also exist in the deep zone of cartilage [20]; one-third of the surface area contains more cartilage stem cells than two-thirds of the deep area.

Different regions have distinct gene expression patterns and specific differentiation potential, and these features may be related to the unique properties of the superficial and deep zone stem cells, thereby participating in articular cartilage homeostasis. Zhou et al. hat das gezeigt, compared with chondrocytes, cartilage stem cells can overexpress chemokines such as interleukin-8 (IL-8) and C-C motif ligand 2 (CCL-2). Jedoch, during pellet cultivation, the content of glycosaminoglycan (GAG) is lower than that in cartilage cells [21]. CSCs overexpress chemokines, which increases immune cells. Außerdem, they mediate inflammation during the processes of cartilage damage and repair. After chondrogenic induction, collagen type II and aggrecan can be detected (but not collagen type X), which differs from bone marrow stem cells (BMSCs) [22]. Jedoch, collagen type X is closely related to cartilage degeneration and aging [23]. Meanwhile, inducing BMSCs and CSCs into chondrocytes in vitro is more likely to lead to cell hypertrophy. Several studies have reported that CSCs have a better effect than synoviocytes in terms of cartilage induction in vitro [21]. These results suggest that CSCs might have a stronger potential than MSCs (BMSCs and synoviocytes) for cartilage induction.

In 2016, Jiang et al. further studied human cartilage-derived stem cells and their potential in the clinical application of cartilage tissue repair [24]. Using in vitro and in vivo experiments, they compared the chondrogenic ability of cartilage stem cells that had been cultured under different conditions. They found that, in the low-density, low-glucose 2-dimensional (2DLL) medium, cartilage stem cells can differentiate into cartilage spontaneously, without being induced, which supports potential for clinical applications. One of the in vivo studies included 15 patients undergoing cartilage repair surgery with cartilage progenitor cells, each of whom had a 6–13 cm2 area of damage. Kürzlich, Huang et al. found stem cells in the meniscus [25]. They compared several characteristics of meniscus-derived stromal cells, autologous BMSCs, and fibrochondrocytes, including their morphology, Proliferation, colony formation, immunocytochemistry, and multidifferentiation. Both meniscus-derived stromal cells and BMSCs have a marker related to stem cells. Zusätzlich, they can differentiate into osteocytes, adipocytes, and chondrocytes in vitro. Compared with BMSCs, Jedoch, more meniscus-derived stromal cells can differentiate into cartilage, which means that they are more effective at chondrogenesis.

Sang et al. isolated nucleus pulposus stem cells (NPSCs) and annulus fibrosus stem cells (AFSCs) from intervertebral discs [26]. Both disk stem cells can form colonies and express stem cell markers during early cell passages, and each type of stem cell has different characteristics that reflect the tissue function that they represent.

There is a gap between the cell phenotype and the potential for regeneration between regular articular cartilage and induced cartilage formed by differentiated cartilage stem cells. This difference affects the ability to form hyaline cartilage of high quality. Jedoch, im Vergleich zu den meisten Stammzellen, Knorpelstammzellen haben ein überlegenes Potenzial für die Knorpelregeneration [27]. Studien zu CSCs befinden sich noch im Anfangsstadium, Weitere Studien sind erforderlich, um ihre Rolle bei der Knorpelregeneration zu verstehen. Autologe Stammzellen stehen vor ähnlichen Problemen wie ACI, wie etwa das Risiko einer Verletzung des gesunden Knorpels, die Notwendigkeit einer zweiten Operation, und eine Reihe von Problemen, die bei der Reparatur von Knorpeldefekten auftreten. Bei der Überwindung von Problemen der zellulären Immunabstoßung oder von Zellen mit geringer Immunogenität, Allogene Knorpelstammzellen stellen einen attraktiven Ansatz für die Reparatur von Knorpeldefekten dar [24].

3. Chondrogene Differenzierung von Stammzellen
Stammzellen haben das Potenzial zur Mehrfachdifferenzierung und Selbstreplikation, Dies macht sie zu einer idealen Wahl für den Einsatz als Saatzellen im Knorpel-Tissue-Engineering. Ein wichtiger Schritt beim Tissue Engineering von Knorpel ist die Induktion von Stammzellen (einschließlich ESCs, iPSCs, und adulte Stammzellen) in Chondrozyten. Durch Tissue Engineering, ESCs können zur Bildung von Chondrozyten angeregt werden, die Knorpelschäden reparieren [54]. Denn undifferenzierte ES haben ein hohes Risiko für Tumorentstehung und Teratome, Es ist wichtig, stabile und effektive Kulturbedingungen zu verwenden, um ESCs zu verstärken und sie zur Differenzierung in eine bestimmte chondrogene Linie zu induzieren [55]. Es wurden viele Strategien angewendet, um die ESC-Differenzierung in eine chondrogene Abstammungslinie zu induzieren [56], einschließlich (1) Bildung embryoider Körper, eine Strategie, die das frühe Stadium der Embryonalentwicklung als Ektoderm nachahmt, Mesoderm, und Ektoderm; (2) Differenzierung in MSCs, a method that takes advantage of the immune exemption features and higher security of MSCs, which facilitates cartilage tissue engineering; Und (3) the use of growth factors and cytokines such as members of the TGF-β family (Z.B., TGF-β1 and TGF-β2), BMP family (Z.B., BMP-2, BMP-4, and BMP-6), PDGF-bb, IGF-1, and sonic hedgehog protein (SHH). Several other strategies have been used that are similar to adult stem cell strategies, such as chondrocyte or fibrocyte coculture, 3D culture to change the cell microenvironment, hypoxia induction, and mechanical stimulation [54].

iPSCs can be derived from somatic cells through genetic reprogramming [57]. ESCs and iPSCs display self-replication and pluripotency, with iPSCs having distinct ethical advantages over ESCs. Originally, four factors—octamer-binding transcription factors 3 Und 4 (3./4. Okt), Kruppel-like factor 4 (Klf4), v-myc avian myelocytomatosis viral oncogene homolog (c-myc), and Sox-2—were identified in a mouse model as being involved in changing fibroblasts into iPSCs [57]. Of the four, Oct3/4 and Sox-2 are transcription factors, while Klf4 and c-myc are genes that are upregulated in tumors [10]. This discovery was a breakthrough in the stem cell field and provided a new tool in gene therapy and tissue engineering. Seitdem, somatic cells, Fibroblasten, and chondrocytes have been reprogrammed successfully to become iPSCs and differentiate into chondrogenic lineage [58]. iPSCs derived from fibroblasts of skin can be induced into chondrocytes. Zusätzlich, based on the HLA phenotype, it is possible to build an iPSC library that can provide allogeneic iPSCs. Cells from the library can be induced into chondrocytes to regenerate cartilage. This strategy is advantageous because it limits costs while offering wide coverage [59]. Compared with other iPSC lines, the iPSC line derived from chondrocytes can express higher quantities of aggrecan gene products [60]. Zusätzlich, the expression of cartilage-related genes does not differ from that of chondrogenic markers. iPSC technology offers a new and safe way to repair cartilage. This process will require optimization of the production process, a better understanding of the biological characteristics, and establishment of a differentiation strategy to achieve a productive and functional chondrocyte-like cell line.

MSCs are considered to be the most promising cells for cartilage regeneration by cell transplantation, and they have been applied clinically [61]. MSCs that differentiate into chondrocytes are induced by molecules, Zytokine (die hauptsächlich Wachstumsfaktoren sind), und die Mikroumgebung in kultivierten Zellen. Die Chondrogenese aus MSCs kann in drei Stadien unterteilt werden [62]. Erste, Die Stammzellen verdichten sich und es kommt zu Zell-Zell-Interaktionen. MSCs beginnen, Adhäsionsmoleküle zu exprimieren, wie N-Cadherin, Tenascin-C, und neuronales Zelladhäsionsmolekül (N-CAM). Die Kondensation von MSCs ist im frühen Stadium der Chondrogenese von entscheidender Bedeutung. Dann, Transkriptionsmediatoren werden aktiviert, wie knochenmorphogenetische Proteine (Schützenpanzer), Sox-9, PTHrP/IHH, und die FGF-Signalwege [63]. Endlich, extrazelluläre Matrix (ECM) und es bilden sich Vorknorpelzellen. Nach der Bildung von Vorknorpel, Die perichondrialen Zellen vermehren sich schnell, mehr ECM absondern, und vollständig differenzieren.

Reife Chondrozyten lokalisieren im Knorpelgewebe. The ability of chondrocytes to maintain their phenotype is closely related to the conditions of their local microenvironment [64], including the type of 3D extracellular matrix, hypoxic conditions, mechanical loading, and specialized morphological structure [65]. Ähnlich, MSCs require specific conditions to differentiate into chondrocytes. The coculture of chondrocytes and MSCs is a new way to culture cells so that chondrocytes can induce MSCs, and MSCs can promote chondrocyte proliferation [66].

4. Cartilage Injury Mechanisms and Treatment
4.1. Articular Cartilage
Articular cartilage damage can occur through violent injury, chronic inflammatory disease such as rheumatoid arthritis (RA), or degenerative joint diseases such as OA. Several important mechanisms related to the occurrence and development of cartilage damage and degeneration include inflammation reactions that change the chondrocyte phenotype, the loss of ECM components, and damage and refactoring of the cartilage-bone unit [67]. Inflammatory cytokines play an important role in the progression of cartilage degeneration, and blocking some inflammatory cytokines can delay cartilage degeneration. Inflammatory cytokines are secreted by mononuclear cells, which induce hyperplasia of the synovial membrane [68]. Studies suggested that inflammatory reactions exist only in the synovial tissue, but recent studies have also confirmed the occurrence of cartilage inflammation. Chondrocytes are separated from the degenerated articular cartilage hypertrophy in vitro [69]. The change in the phenotype of chondrocytes prevents them from producing cartilage ECM components—such as proteoglycan and collagen type II, which are required to maintain the biological characteristics of cartilage cells. Umgekehrt, chondrocytes can reduce the proportion of proteoglycan and produce more collagen type X, which is related to cell senescence [70]. Articular cartilage and subchondral bone form an inseparable organic cartilage-bone unit; in fact, damage and degeneration of articular cartilage are certain to cause subchondral bone destruction [71]. Darüber hinaus, the separation of articular cartilage and subchondral bone causes osteochondritis dissecans (OCD).

Treatment strategies for articular cartilage injuries include palliative treatment strategies, arthroscopic debridement and arthroplasty treatment strategies, and regenerative treatment strategies.

Palliative treatment strategies mainly include physiotherapy (thermal and electrical stimulation, high-intensity ultrasound, pulsed electromagnetic fields, millimeter waves, ultrasound, and low-level laser therapy), weight loss and muscle strengthening programs, und Medikamente (glucosamine and chondroitin are used as treatments for cartilage defects, and although neither drug is used to alleviate the symptoms, they have been proven to reverse or suspend the progression of cartilage degeneration). Injection treatment strategies, compared with surgery, offer convenience and low risk. The injected material can have a direct effect on articular cartilage and remain in the articular cavity for a long time. Due to these characteristics, many different studies on articular cavity injection treatment strategies have been reported, pertaining, Zum Beispiel, to platelet-rich plasma (PRP) [72, 73], drug delivery strategies [74], polyphenol stabilization of cartilage collagen against degradation, action of the IL-1 receptor as an antagonist against lubricin metabolism and cartilage degeneration, the activities of rapamycin [75], alendronate [76], Hyaluronsäure [77], bone morphogenetic protein-7 [78], and lidocaine [79], which reduce live chondrocytes and change the gene expression of COL II and aggrecan, and intra-articular steroid injections [80]. Arthroscopic debridement is used mainly in the middle-late stage of articular cartilage degeneration. Although arthroscopic debridement as a treatment of knee OA has been widely adopted as a surgical option, its efficacy has been controversial [81–83].

Arthroscopic debridement includes articular cavity flushing, meniscus partial nephrectomy, the removal of loose bodies, removal of the synovial membrane, chondroplasty, and osteophyte resection. Studies have shown that arthroscopic debridement can relieve short-term symptoms, especially in patients with OA with acute pain and patients with loose bodies in the articular cavity. Arthroplasty has been used widely in the treatment of late-stage articular cartilage lesions, with replacement usually being of the knee or hip [84].

4.2. Meniscus
The meniscus is composed of lateral fiber and medial transparent chondroid tissues. It disperses the pressure between the tibia platforms and the femoral condyle. Damage to the meniscus is often due to direct violence and can also reflect chronic degeneration [85]. Like cartilage injury, meniscus injury shows limitations in self-repair. Only the lateral fiber, which has a blood supply, can be stitched, but damage to this fiber is quite rare. Apart from causing restricted movement of the knee joint, meniscus injury also changes the mechanical structure of the joint, accelerating cartilage degeneration therein. The most commonly used treatment for meniscus injury is arthroscopic suture or resection. This procedure can provide the best mechanical stability in the meniscus and the strongest binding force in the damaged area. Meniscus injuries that are unable to be sutured are generally treated by meniscus merotomy and meniscus resection [86]. Allograft meniscus transplantation and synthetic materials have been applied clinically and have shown better prevention of knee joint degeneration compared with meniscus resection [87, 88]. Numerous reports describing the use of stem cell-associated tissue engineering to treat meniscal injury have demonstrated advantages in meniscus regeneration, showing promise for future meniscus injury treatments [89, 90].

4.3. Intervertebral Disc
Many patients experience back pain (lifetime prevalence of up to 84%) [91]. Although back pain is a complex disease that can be affected by multiple factors, the majority of back pain in patients is caused by acute injury and degeneration of the intervertebral disc [92]. The intervertebral disc is formed by the inner core of the nucleus pulposus (NP) and the annulus fibrosis, which surrounds the NP. The former consists of chondrocyte-like intervertebral disc cells, unarranged collagen, and gel-like matrix components that are rich in proteoglycans. NP consists of parallel collagen fibers that form a circular arrangement and fibroblast-like cells [93]. Most acute injury due to mechanical force causes the annulus fibrosis to fall apart, and herniated NP oppresses the surrounding tissues, resulting in clinical symptoms. The pathogenesis of intervertebral disc degeneration is unclear; Jedoch, the increased rate of intervertebral disc cell death, loss of the ECM, change of phenotype of the intervertebral disc cells, and excessive inflammatory reaction are thought to play a key role in intervertebral disc degeneration [94].

Acute damage and degeneration of the lumbar joints are treated mainly by conservative or surgical treatments. If conservative treatment fails, surgery can be attempted to relieve the neurothlipsis. Jedoch, these interventions are focused on alleviating symptoms, anstatt eine regenerative Behandlung darzustellen. In den letzten Jahren, Die Einführung und Entwicklung bioregenerativer Therapien hat die Degeneration der Bandscheiben verzögert und eine Gewebereparatur ermöglicht (d.h., ECM-Reparatur und -Regeneration). Zu den bioregenerativen Therapien gehört die Gentherapie, gezielte Behandlung biologischer Faktoren, microRNA (miRNA) Behandlung [95], und Tissue Engineering auf Basis von Stammzellen [2, 61]. Unter diesen bioregenerativen Therapien, Die perkutane Injektion von MSCs wurde klinisch eingesetzt und hatte eine bemerkenswerte Wirkung auf die Verbesserung diskogener Schmerzen [96]. Diese Technologien können den Stoffwechsel in der Mikroumgebung der Bandscheiben verändern und eine Regeneration des Bandscheibengewebes ermöglichen, unter Beibehaltung der ursprünglichen Biomechanik der Wirbelsäule [97]. Obwohl nur wenige klinische Studien die Injektion von MSCs untersucht haben, Sie haben ihre Sicherheit und Eignung zur Linderung diskogener Schmerzen bewiesen. Jedoch, Um diese Vorteile zu belegen, ist weitere klinische Forschung erforderlich [2].

5. Regenerative Medizin bei der Knorpelreparatur
5.1. Mikrofrakturierung
Die Theorie der Mikrofraktur bei der Gelenkknorpelregeneration basiert auf der Annahme, dass pluripotente Stammzellen, Dabei handelt es sich hauptsächlich um BMSCs aus dem Knochenmark, kann durch die Mikrofrakturlücke den beschädigten Bereich erreichen [98]. Am Ende des Verfahrens, Es ist wichtig zu beurteilen, ob Fettkörner aus dem Knochenmark austreten, um die richtige Lochtiefe zu überprüfen. Berichten zufolge funktioniert die Mikrofrakturtechnik am besten, wenn die beschädigte Fläche 2–4 cm2 groß ist [99]. Diese Technologie nutzt die multipotente Fähigkeit von Stammzellen und ermöglicht eine Knorpelreparatur zu geringen Kosten und mit geringem chirurgischen Schaden. Jedoch, the method causes fibrous cartilage formation in the repaired tissue, rather than the hyaline cartilage found in normal articular cartilage, which affects the biological performance [4, 100].

5.2. Mosaicplasty
Mosaicplasty, also known as autologous osteochondral transplantation, employs osteochondral plugs removed from a non-weight-bearing region of the joint to fill the damaged area. First applied in 1997, mosaicplasty is not strictly considered as a regenerative technology, and it also runs the risk of early failure of transplantation. Darüber hinaus, this technology can only repair damaged areas < 4 cm2 [101]. Cartilage that forms in the damaged area by autologous osteochondral transplantation is the same hyaline cartilage as normal cartilage. Mosaicplasty technology gives better results than microfracture repairs, but ACI in turn has more advantages than mosaicplasty [102].

5.3. Scaffold
Durch den Einsatz von Gerüsten kann eine 3D-Mikroumgebung für Knorpelzellen geschaffen werden, Lösung des Problems der Chondrozytendifferenzierung in Monoschichtkulturen. Das Gerüst verhindert den Verlust von Chondrozyten, die in einem orientierten Gerüst wachsen, das die normale Anordnung von Chondrozyten simuliert und so eine bionische Struktur bildet [103]. Durch ihre mechanischen Eigenschaften, Gerüste können Patienten in der Frührehabilitation Vorteile bringen. Gerüste sind eine der wichtigsten Komponenten des Tissue Engineering [104]. Kombiniert mit verschiedenen knorpelbezogenen Zytokinen, Es kann verwendet werden, um autologe Stammzellen zu züchten, um den Zustand der Gewebereparatur in der beschädigten Region abzuschließen, einschließlich Stammzellen aus Blut, Synovialflüssigkeit, Synovialgewebe, und Knorpel. Auf das Gerüst geladene Stammzellen können in vivo unter einer bestimmten Mikroumgebung induziert werden. With the continuous development of material science and the application of 3D printing technology to the field of tissue engineering, cartilage repair combined with scaffold materials offers a promising future direction for articular cartilage, Meniskus, and intervertebral disc repair [105, 106].

5.4. ACI and MACI
First applied in 1994, ACI has been reported widely with its satisfactory long-term, mid-term clinical results and magnetic resonance imaging (MRT) result [5]. Patients receiving ACI are generally <50 Jahre alt, and the area of damage is >1 cm2, and cartilage injury is a type caused by acute trauma [107]. Compared with preliminary stage, ACI has explored much more indications than before. There is quite a challenge that cartilage damage repair has been reported with better clinical effectiveness, such as in patients with failed cartilage repair surgery [108], early stage OA [109], older age [110], complex patellofemoral lesions [111], deep osteochondral lesions, and OCD [112]. Peterson et al. summarized 224 cartilage damage patients who had been treated by ACI in the past 20 Jahre [113]. The subjective scores have a significant increase compared with preoperation time. The report also points out that 74% of the patients feel better or stable and 92% of the patients are satisfied with their treatment. Despite subchondral cysts, osteophytes, bone marrow edema, and other common side effects, ACI still has an excellent clinical result in the long run. Jedoch, this procedure also has several shortcomings, such as a second incision during gaining periosteal patch, hypertrophy in the repair area, and chondrocyte leakage [114]. Es wurde berichtet, dass durch die Verwendung einer Kollagen-I- oder Kollagen-III-Membran anstelle eines Periostpflasters ein zweiter Einschnitt vermieden und die Inzidenzrate von Hypertrophie verringert werden kann. MACI kann das Problem des Zellaustritts durch die 3D-Kultur der Zelle vermeiden. Aber egal ACI oder MACI, Die Aufrechterhaltung des Chondrozyten-Phänotyps ist während der Zellkultur immer noch ein gewaltiges Problem. Im Vergleich zur verlängerten Monoschichtkultur bei ACI, MACI kann eine 3D-Kultur-Mikroumgebung für die Adhäsion von Chondrozyten bereitstellen, Proliferation, und Matrixsekretion zur Aufrechterhaltung des Chondrozyten-Phänotyps [115]. Es wurde berichtet, dass es sich um eine 3D-Kultur-Mikroumgebung handelt [65] und Kokultur [116] Die Verwendung von Stammzellen mit Chondrozyten kann bei der Aufrechterhaltung des Chondrozyten-Phänotyps besser abschneiden, Dies ist der entscheidende Punkt zur Bestimmung der klinischen Auswirkungen von ACI und MACI, was in Zukunft weitere Studien erfordert.

5.5. Stammzellen und die Wirkung von Stammzellen auf die Knorpelreparatur
Im letzten Jahrzehnt, Die stammzellbasierte Behandlung ist weit verbreitet, und die Zahl der Studien zu diesem Thema hat rapide zugenommen. Heute, Eine solche Behandlung ist ein wichtiger Zweig der regenerativen Medizin. Stammzellen haben zwei Wirkungen: Sie haben das Potenzial zur Mehrfachdifferenzierung und verfügen über parakrine und immunmodulatorische Fähigkeiten, Beides sind wichtige Merkmale bei der Knorpelregeneration mithilfe von MSCs [117, 118]. Die Tatsache, dass Stammzellen in Knorpelzellen differenzieren können und dass ein Gerüst für die Zellanheftung genutzt werden kann, macht dieses System für das Knorpelgewebe-Engineering mit Stammzellen in der Klinik zugänglich. Laborstudien und klinische Beweise zeigen, dass Stammzellen eine effiziente Methode zur Behandlung traumatischer Knochen-Knorpel-Verletzungen sind [119]. Although the application of stem cells combined with scaffold materials, by using tissue engineering technology, can achieve a satisfactory repair effect, no studies have shown that the repair effect of stem cells is better than that of chondrocytes. The application of stem cells combined with scaffold, for tissue engineering of traumatic cartilage damage, has a satisfactory effect, but little success has been reported in terms of the repair of OA cartilage degeneration.

This treatment is based on the paracrine and immunomodulatory effects of stem cells. Most stem cell OA treatments involve injections to insert stem cells into the damaged area of the articular cavity. Meniscus injury is treated with articular cavity injection [120, 121], while intervertebral disc damage is treated with local injection [122, 123]. Although the mechanism is not fully understood, the effect is clear, especially for the treatment of OA. Many pathological reports and randomized controlled trials have demonstrated therapeutic effects. Stem cells secrete mediators that promote endogenous growth, stimulate self-proliferation of progenitor cells, and inhibit chondrocyte apoptosis or cartilage degeneration, achieving cartilage regeneration and cartilage protection [124]. Zusätzlich, several studies have shown that the inflammatory response in the injured area inhibits damage repair by endogenous stem cells or progenitor cells (such as cartilage stem cells) [125].

6. Clinical Applications of Stem Cell Therapy in Cartilage Repair
Compared with ESCs and iPSCs, adult stem cells are more secure and are therefore applied first in clinical therapy. MSCs are the most representative adult stem cells and are used widely in clinical cartilage regeneration. MSCs können aus verschiedenen Quellen abgeleitet werden, wie zum Beispiel Knochenmark, fett, Plazenta, Nabelschnurblut, synovial membrane, peripheres Blut, Sehnen, und Knorpel. BMSCs, ADSCs, synovial mesenchymal stem cells (SMSCs), peripheral blood-derived mesenchymal stem cells (PBMSCs), and other stem cells have been applied in clinical cartilage damage repair with satisfactory results (Tisch 1). Tisch 2 summarizes the results of a PubMed database search for clinical trials involving stem cells in cartilage regeneration, published from 2000 until the end of June 2016. Several recent studies have investigated allogeneic BMSCs for treating OA, demonstrating their safety and effectiveness in cartilage repair. Zusätzlich, ADSCs have been studied in recent years in terms of cartilage repair. Compared with BMSCs, ADSCs have certain advantages in the treatment of cartilage damage. Osteoporosis causes a decline in the quantity and quality of BMSCs, but ADSCs can be used to address this condition. The safety of cartilage damage repair is higher when the stroma vascular fraction (SVF) is not cultured in vitro. After liposuction surgery, Fettgewebe, in the form of medical waste, can be reused. The most attractive reason for using PBMSCs is that they are easily acquired and require only one-step surgery for cartilage repair. Few studies have described the use of SMSCs and chondrocyte-derived progenitor cells (CDPCs) to repair cartilage damage, and further clinical tests are required to clarify their advantages and disadvantages. CDPCs originate from cartilage tissue and have a superior ability to differentiate into cartilage. Tissues requiring repair generally include the meniscus of the knee joint and talus cartilage; damage to these regions is limited mainly to cartilage damage or early OA. Cells can be delivered using a variety of methods such as simple direct injection of MSCs, or MSCs mixed with hyaluronic acid (HA), PRP, or glue, as well as MSCs combined with scaffold.

 

Cell type Cell source Location Injury type Cell carrier Cases (N) Follow-up Description Results
CDPCs Autologous, cartilage-derived Knee AC Cartilage defects Collagen type I/III scaffold 15 12 months Compared with BMSCs, the chondrogenic potential was better Ectopic calcification and vascularization were not found in tissue biopsies of four patients. The clinical scores of all patients showed improvement; function improved and pain was relieved. 2016 [24]
BMSCs Autologous Knee AC OA Injection 3 5 years Update of a previous study Long-term follow-up of stem cell injection showed good prognosis for patients with early-stage OA. 2016 [28]
BMSCs Allogenic Knee AC OA Injection BMSCs: 15
HA: 15 12 months RCT Compared to the HA group, the function recovery and quality of regenerated cartilage are meaningfully enhanced in the BMSC group. 2015 [29]
BMSCs Allogenic Knee AC and meniscus OA Injection Low-dose: 18
Hochdosiert: 18
HA: 19 2 years Partial medial meniscectomy RCT Knee joint pain was relieved, and MRI showed meniscus regeneration in the stem cell group. 2014 [30]
BMSCs Autologous Knee AC OA Injection 12 2 years Update of a previous study Pain was relieved after 1 year of treatment, which continued through year 2. MRI showed better quality of cartilage in year 2 compared to year 1. 2014 [31]
BMSCs Autologous Knee AC OA Cartilage defects Injection HA + BMSCs: 28
HA: 28 2 years RCT high tibial osteotomy + microfracture Effectively improving both short-term clinical and cartilage repair tissue scores. 2013 [32]
BMSCs Autologous Ankle Chondral defects Collagen membrane 25 2 years Matrix-associated stem cell transplantation Good clinical scores and no complications. 2013 [33]
BMSCs Autologous Knee AC Cartilage defects Injection periosteal patch Microfracture + BMSCs + HA: 35
BMSCs + patch: 35 2 years   Microfracture + BMSCs + HA are comparable to BMSCs + patch, but minimally invasive. 2012 [34]
SMSCs Autologous Knee AC + meniscus Cartilage defects Arthroscopic transplantation 10 37–80 months 10% autologous human serum used to expand cells MRI scores, Lysholm score, and qualitative histology all show that SMSC transplantation is meaningful. 2015 [35]
ADSCs Autologous Knee AC Cartilage defects Arthroscopic ADSCs + Mikrofraktur + fibrin glue: 40
Mikrofrakturierung: 40 2 years RCT Radiologic and KOOS pain and symptom scores show a more meaningful improvement than that of the control group. 2016 [36]
ADSCs Autologous Knee AC OA Arthroscopic ADSCs + fibrin glue: 20 2 years   Clinical and MRI scores show a significant improvement. 2016 [37]
ADSCs Autologous Knee AC OA Injection SVF: 1,128 12–54 months   No serious side effects, Infektion, or cancer related to SVF. 2015 [38]
ADSCs Autologous Knee AC OA Injection 30 2 Jahre 4.04 × 106 stem cells Effective for elderly patients with OA at the knee. 2015 [39]
ADSCs Autologous Knee AC OA Arthroscopic ADSCs: 37
ADSCs + fibrin glue: 17 24–34 months   Arthroscopic and clinical outcomes were useful for OA in both groups. Jedoch, the ADSC + fibrin glue group had better ICRS scores. 2015 [40]
ADSCs Autologous Knee AC Early OA Arthroscopic ADSCs + fibrin glue: 49 Mean 26.7 months   Patients > 60 years of age or having injury areas < 6 cm2 were not suitable for this treatment. 2015 [41]
ADSCs Autologous Meniscus Meniscal tear Injection ADSCs + PRP + CaCl2 + HA: 1 18 months   Pain was alleviated. MRI at 3 months after treatment showed that the meniscal tear had almost disappeared. 2014 [42]
ADSCs Autologous Knee AC OA Arthroscopic Knee: 37 24–34 months   The factors affecting the repair result were mostly large injury area and high BMI. The second arthroscopic view showed 76% nonregular repair. 2014 [43]
ADSCs Autologous Talus Osteochondral lesions Injection Marrow stimulation: 26
SVF + marrow stimulation: 24 21.9 months   Marrow stimulation with SVF group showed better results than the marrow stimulation alone group. 2014 [44]
ADSCs Autologous Knee AC OA Injection I: low-dose (3), medium-dose (3), hochdosiert (3)
II: hochdosiert (9) 6 months Low dose: 1 × 107 Medium dose: 5 × 107 High dose: 1 × 108 No adverse events. The high-dose group showed better results than the other groups. 2014 [45]
ADSCs Autologous Knee AC OA Injection ADSCs + PRP: 91 30 Monate   Die Sicherheit von autologem SVF und perkutanen lokalen Injektionen wurde durch MRT und telefonische Nachuntersuchung nachgewiesen. 2013 [46]
ADSCs Autologous Knee AC OA Injection SVF + PRP: 18 24–26 Monate   ADSCs des infrapatellaren Fettpolsters waren nützlich zur Linderung von Gelenkschmerzen und zur Verbesserung der Kniegelenkfunktion. 2013 [47]
ADSCs Autologer Talus Osteochondrale Läsionen Injektionsmikrofrakturierung: 30
Mikrofrakturierung + ADSCs: 35 21.8 Monate   Unter den oben genannten Patienten 50 Jahre alt, die Wirkung der Markstimulation + ADSCs waren besser als die Markstimulation allein. >109 Eine Läsionsgröße von mm2 und eine vorhandene subchondrale Zyste zeigten bessere Regenerationsergebnisse. 2013 [48]
ADSCs Autologous Knee AC OA Injection ADSCs + PRP: 25 12 Monate 1.89 × 106 ADSCs, 3 ml-PRP-ADSCs des infrapatellaren Fettpolsters waren nützlich, um Gelenkschmerzen zu lindern und die Funktion des Kniegelenks zu verbessern. 2012 [49]
PBSCs Autologe Knie-AC Chondralläsionen Offene Operation 1 7.5 Jahre Periostlappen + Bei der patellofemoralen Neuausrichtung zeigten CT und MRT bessere Ergebnisse. Eight months after the surgery, the second arthroscopy showed that the new-growth cartilage had a smooth surface. The patient returned to practicing Taekwondo. 2014 [50]
PBSCs Autologous Knee AC Early OA Injection 5 6 months PBSCs + HA + growth factor + microfracture No adverse events and all clinical scores improved. 2013 [51]
PBSCs Autologous Knee AC Chondral defects Arthroscopic Microfracture + HA: 25
PBSCs + Mikrofraktur + HA: 25 2 years RCT PBSC group has a better quality of newborn cartilage than the control group on histological and MRI assessments. 2013 [52]
PBSCs Autologous Knee AC Chondral defects Open surgery 52 6 years Collagen membrane PBSCs are an effective way to repair large cartilage lesions. This method can be used as an alternative to ACI. 2012 [53]
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Tisch 2
Types of stem cells used clinically for cartilage regeneration past and present. This table shows the PubMed database search results for clinical trials involving stem cells in cartilage regeneration, published from 2000 until the end of June 2016 (number of papers).

Year Cell type Total
BMSCs ADSCs PBSCs SDSCs CDPCs
2002 1 0 0 0 0 1
2004 1 0 0 0 0 1
2005 1 0 0 0 0 1
2007 2 0 0 0 0 2
2008 1 0 0 0 0 1
2010 2 0 0 0 0 2
2011 2 1 1 0 0 4
2012 2 1 1 0 0 4
2013 2 2 2 0 0 6
2014 2 4 1 0 0 7
2015 1 4 0 1 0 6
2016 1 2 0 0 1 4
Total 18 14 5 1 1 39

Despite years of research, the use of stem cells in cartilage regeneration has not met expectations. MSCs possess an intrinsic differentiation program for endochondral bone formation [126]. Although researchers seek to avoid the hypertrophic fate of MSCs, they cannot yet create articular hyaline cartilage without the hypertrophic chondrocyte phenotype [69]. This challenge must be overcome to enable better cartilage regeneration using MSC-based tissue engineering. Zusätzlich, the use of stem cells in cartilage regeneration is limited to untreated or multiplication cultured stem cells. Although the feasibility of using stem cells in cartilage regeneration has been proved, few clinical studies have been reported because the induced cells are unstable [127] (d.h., they degenerate readily and lead to tumorigenesis).