A stem cell-based approach to cartilage repair

Image-based profiling for drug discovery: due for a machine-learning upgrade?

Image-based profiling is a maturing strategy by which the rich information present in biological images is reduced to a multidimensional profile, a collection of extracted image-based features. These profiles can be mined for relevant patterns, revealing unexpected biological activity that is useful for many steps in the drug discovery process. Such applications include identifying disease-associated screenable phenotypes, understanding disease mechanisms and predicting a drug's activity, toxicity or mechanism of action. Several of these applications have been recently validated and have moved into production mode within academia and the pharmaceutical industry. Some of these have yielded disappointing results in practice but are now of renewed interest due to improved machine-learning strategies that better leverage image-based information. Although challenges remain, novel computational technologies such as deep learning and single-cell methods that better capture the biological information in images hold promise for accelerating drug discovery.

Kartogenin Enhances Chondrogenic Differentiation of MSCs in 3D Tri-Copolymer Scaffolds and the Self-Designed Bioreactor System

Human cartilage has relatively slow metabolism compared to other normal tissues. Cartilage damage is of great clinical consequence since cartilage has limited intrinsic healing potential. Cartilage tissue engineering is a rapidly emerging field that holds great promise for tissue function repair and artificial/engineered tissue substitutes. However, current clinical therapies for cartilage repair are less than satisfactory and rarely recover full function or return the diseased tissue to its native healthy state. Kartogenin (KGN), a small molecule, can promote chondrocyte differentiation both in vitro and in vivo. The purpose of this research is to optimize the chondrogenic process in mesenchymal stem cell (MSC)-based chondrogenic constructs with KGN for potential use in cartilage tissue engineering. In this study, we demonstrate that KGN treatment can promote MSC condensation and cell cluster formation within a tri-copolymer scaffold. Expression of Acan, Sox9, and Col2a1 was significantly up-regulated in three-dimensional (3D) culture conditions. The lacuna-like structure showed active deposition of type II collagen and aggrecan deposition. We expect these results will open new avenues for the use of small molecules in chondrogenic differentiation protocols in combination with scaffolds, which may yield better strategies for cartilage tissue engineering.

Nanotechnology-based drug delivery systems in orthopedics

In recent years, nanotechnology has led to significant scientific and technological advances in diverse fields, specifically within the field of medicine. Owing to the revolutionary implications in drug delivery, nanotechnology-based drug delivery systems have gained an increasing research interest in the current medical field. A variety of nanomaterials with unique physical, chemical and biological properties have been engineered to develop new drug delivery systems for the local, sustained and targeted delivery of drugs with improved therapeutic efficiency and less or no toxicity, representing a very promising approach for the effective management of diseases. The utility of nanotechnology, particularly in the field of orthopedics, is a topic of extensive research. Nanotechnology has a great potential to revolutionize treatment, diagnostics, and research in the field of orthopedics. Nanophase drug delivery has shown great promise in their ability to deliver drugs at nanoscale for a variety of orthopedic applications. In this review, we discuss recent advances in the field of nanostructured drug delivery systems for orthopedic applications.

Recent Advances in Clinical Translation of Intra-Articular Osteoarthritis Drug Delivery Systems

Osteoarthritis (OA) is a degenerative disease of the joints and a leading cause of physical disability in adults. Intra-articular (IA) therapy is a popular treatment strategy for localized, single-joint OA; however, small-molecule drugs such as corticosteroids do not provide prolonged relief. One possible reason for their lack of efficacy is high clearance rates from the joint through constant lymphatic drainage of the synovial tissues and synovial fluid and also by their exchange via the synovial vasculature. Advanced drug delivery strategies for extended release of therapeutic agents in the joint space is a promising approach to improve outcomes for OA patients. Broadly, the basic principle behind this strategy is to encapsulate therapeutic agents in a polymeric drug delivery system (DDS) for diffusion- and/or degradation-controlled release, whereby degradation can occur by hydrolysis or tied to relevant microenvironmental cues such as pH, reactive oxygen species (ROS), and protease activity. In this review, we highlight the development of clinically tested IA therapies for OA and highlight recent systems which have been investigated preclinically. DDS strategies including hydrogels, liposomes, polymeric microparticles (MPs) and nanoparticles (NPs), drug conjugates, and combination systems are introduced and evaluated for clinical translational potential.

SERPINA9 and SERPINB2: Novel Cartilage Lineage Differentiation Markers of Human Mesenchymal Stem Cells with Kartogenin

OBJECTIVE

Human mesenchymal stem cells (hMSCs) are a promising source for regenerative medicine, especially mesodermal lineages. Clinical applications require an understanding of the mechanisms for transcriptional control to maintain the desired cell type. The aim of this study was to identify novel markers for differentiation of hMSCs into bone or cartilage with the use of Kartogenin, by RNA analysis using microarray technology, and explore the role of RhoA-Rho associated protein kinase (ROCK) inhibition in these.

METHODS

Commercial human bone marrow derived primary mesenchymal stem cells were purchased from ATCC. Cells were differentiated in vitro in 2-dimensional cultures using Kartogenin as the main cartilage inducer and bone morphogenetic protein 2 for bone differentiation; cells were cultured with and without ROCK inhibitor Y-27632. After 21 days of culture, whole RNA was extracted and analyzed via Affimetrix microarrays. The most significant hits were validated by quantitative polymerase chain reaction.

RESULTS

We found a total of 1,757 genes that were either up- or downregulated on differentiation, when compared to P1 hMSC (control) at day 0 of differentiation. Two members of the Serpin superfamily, SERPINA9 and SERPINB2, were significantly upregulated in the cartilage groups, whereas they were unchanged in the bone groups with and without ROCK inhibition.

CONCLUSIONS

SERPINA9 and SERPINB2 are novel differentiation markers, and molecular regulator candidates for hMSC lineage commitment toward bone and cartilage, providing a new tool for regenerative medicine. Our study highlights the roles of these 2 genes, with significant upregulation of both in cell cultures stimulated with Kartogenin.

Mouse Models of Osteoarthritis: Surgical Model of Post-traumatic Osteoarthritis Induced by Destabilization of the Medial Meniscus

The surgical model of destabilization of the medial meniscus (DMM) has become a gold standard for studying the onset and progression of post-traumatic osteoarthritis (OA). The DMM model mimics clinical meniscal injury, a known predisposing factor for the development of human OA, and permits the study of structural and biological changes over the course of the disease. In addition, when applied to genetically modified or engineered mouse models, this surgical procedure permits dissection of the relative contribution of a given gene to OA initiation and/or progression. This chapter describes the requirements for the surgical induction of OA in mouse models, and provides guidelines and tools for the subsequent histological, immunohistochemical, and molecular analyses. Methods for the assessment of the contributions of selected genes in genetically modified strains are also provided.

Effects of nanopatterned-surface dishes on chondrocyte growth and cell cycle progression

Discovering and developing ideal cell culture methods is important for cell biology, drug development, and cell therapy. Recent studies have explored and demonstrated the use of nanoscale structures and patterns that influence cell behavior, such as 3D scaffolds. In this study, we analyzed the effects of nanopatterned-surface dishes using chondrocytes as model cells. Chondrocytes grown on nanopatterned dishes exhibited rounded shapes. Interestingly, chondrocytes have a lower COL10 mRNA level when cultured using nanopatterned dishes. The nanopatterned dishes induced G0-/G1-phase cell cycle arrest and reduced the rate of proliferation. Our results suggest that nanoscale structures can directly control cellular behaviors and can be used for chondrocyte cell culture without causing chondrocytes to lose their functions. These results help to elucidate cellular responses and behaviors in native-like environments, and this information can be used to improve human health.

Runx1 up-regulates chondrocyte to osteoblast lineage commitment and promotes bone formation by enhancing both chondrogenesis and osteogenesis

One of the fundamental questions in bone biology is where osteoblasts originate and how osteoblast differentiation is regulated. The mechanism underlying which factors regulate chondrocyte to osteoblast lineage commitment remains unknown. Our data showed that Runt-related transcription factor 1 (Runx1) is expressed at different stages of both chondrocyte and osteoblast differentiation. Runx1 chondrocyte-specific knockout (Runx1f/fCol2α1-cre) mice exhibited impaired cartilage formation, decreased bone density, and an osteoporotic phenotype. The expressions of chondrocyte differentiation regulation genes, including Sox9, Ihh, CyclinD1, PTH1R, and hypertrophic chondrocyte marker genes including Col2α1, Runx2, MMP13, Col10α1 in the growth plate were significantly decreased in Runx1f/fCol2α1-cre mice chondrocytes. Importantly, the expression of osteoblast differentiation regulation genes including Osx, Runx2, ATF4, and osteoblast marker genes including osteocalcin (OCN) and osteopontin (OPN) were significantly decreased in the osteoblasts of Runx1f/fCol2α1-cre mice. Notably, our data showed that osteoblast differentiation regulation genes and marker genes are also expressed in chondrocytes and the expressions of these marker genes were significantly decreased in the chondrocytes of Runx1f/fCol2α1-cre mice. Our data showed that chromatin immunoprecipitation (ChIP) and promoter mapping analysis revealed that Runx1 directly binds to the Indian hedgehog homolog (Ihh) promoter to regulate its expression, indicating that Runx1 directly regulates the transcriptional expression of chondrocyte genes. Collectively, we revealed that Runx1 signals chondrocyte to osteoblast lineage commitment and promotes endochondral bone formation through enhancing both chondrogenesis and osteogenesis genes expressions, indicating Runx1 may be a therapeutic target to enhance endochondral bone formation and prevent osteoporosis fractures.

A Biomimetic Biphasic Osteochondral Scaffold with Layer-Specific Release of Stem Cell Differentiation Inducers for the Reconstruction of Osteochondral Defects

There is a great challenge in regenerating osteochondral defects because they involve lesions of both cartilage and subchondral bone, which have remarkable differences in their chemical compositions and biological lineages. Thus, considering the complicated requirements in osteochondral reconstruction, a biomimetic biphasic osteochondral scaffold (BBOS) with the layer-specific release of stem cell differentiation inducers are developed. The cartilage regeneration layer (cartilage scaffold, CS) in the BBOS contains a hyaluronic acid hydrogel to mimic the composition of cartilage, which is mechanically enhanced by host-guest supramolecular units to control the release of kartogenin (KGN). Additionally, a 3D-printed hydroxyapatite (HAp) scaffold releasing alendronate (ALN) is employed as the bone-regeneration layer (bone scaffold, BS). The two layers are bound by semi-immersion and could regulate the hierarchical targeted differentiation behavior of the stem cells. Compared to the drug-free scaffold, the MSCs in the BBOS could be promoted to differentiate into both chondrocytes and osteoblasts. The in vivo results demonstrate the strong promotion of cartilage or bone regeneration in their respective layers. It is expected that this BBOS with layer-specific inducer release can become a new strategy for osteochondral regeneration.

Current Nanoparticle-Based Technologies for Osteoarthritis Therapy

Osteoarthritis (OA) is a common chronic joint disease that is characterized by joint pain and stiffness, and limitation of motion and the major cause of disability, which reduces life quality of patients and brings a large economic burden to the family and society. Current clinical treatment is mostly limited to symptomatic treatment aimed at pain alleviation and functional improvement, rather than suppressing the progression of OA. Nanotechnology is a promising strategy for the treatment of OA. In this review, we summarize the current experimental progress that focuses on technologies such as liposomes, micelles, dendrimers, polymeric nanoparticles (PNPs), exosomes, and inorganic nanoparticles (NPs) for their potential treatment of OA.

Evidence that TD-198946 enhances the chondrogenic potential of human synovium-derived stem cells through the NOTCH3 signaling pathway

Human synovium-derived stem cells (hSSCs) are an attractive source of cells for cartilage repair. At present, the quality of tissue and techniques used for cartilage regeneration have scope for improvement. A small compound, TD-198946, was reported to enhance chondrogenic induction from hSSCs; however, other applications of TD-198946, such as priming the cell potential of hSSCs, remain unknown. Our study aimed to examine the effect of TD-198946 pretreatment on hSSCs. HSSCs were cultured with or without TD-198946 for 7 days during expansion culture and then converted into a three-dimensional pellet culture supplemented with bone morphogenetic protein-2 (BMP2) and/or transforming growth factor beta-3 (TGFβ3). Chondrogenesis in cultures was assessed based on the GAG content, histology, and expression levels of chondrogenic marker genes. Cell pellets derived from TD-198946-pretreated hSSCs showed enhanced chondrogenic potential when chondrogenesis was induced by both BMP2 and TGFβ3. Moreover, cartilaginous tissue was efficiently generated from TD-198946-pretreated hSSCs using a combination of BMP2 and TGFβ3. Microarray analysis revealed that NOTCH pathway-related genes and their target genes were significantly upregulated in TD-198946-treated hSSCs, although TD-198946 alone did not upregulate chondrogenesis related markers. The administration of the NOTCH signal inhibitor diminished the effect of TD-198946. Thus, TD-198946 enhances the chondrogenic potential of hSSCs via the NOTCH3 signaling pathway. This study is the first to demonstrate the gradual activation of NOTCH3 signaling during chondrogenesis in hSSCs. The priming of NOTCH3 using TD-198946 provides a novel insight regarding the regulation of the differentiation of hSSCs into chondrocytes.

Exosome-mediated delivery of kartogenin for chondrogenesis of synovial fluid-derived mesenchymal stem cells and cartilage regeneration

Transplantation of synovial fluid-derived mesenchymal stem cells (SF-MSCs) is a viable therapy for cartilage degeneration of osteoarthritis (OA). But controlling chondrogenic differentiation of the transplanted SF-MSCs in the joints remains a challenge. Kartogenin (KGN) is a small molecule that has been discovered to induce differentiation of SF-MSCs to chondrocytes both in vitro and in vivo. The clinical application of KGN however is limited by its low water solubility. KGN forms precipitates in the cell, resulting in low effective concentration and thus limiting its chondrogesis-promoting activity. Here we report that targeted delivery of KGN to SF-MSCs by engineered exosomes leads to even dispersion of KGN in the cytosol, increases its effective concentration in the cell, and strongly promotes the chondrogenesis of SF-MSCs in vitro and in vivo. Fusing an MSC-binding peptide E7 with the exosomal membrane protein Lamp 2b yields exosomes with E7 peptide displayed on the surface (E7-Exo) that has SF-MSC targeting capability. KGN delivered by E7-Exo efficiently enters SF-MSCs and induces higher degree of cartilage differentiation than KGN alone or KGN delivered by exosomes without E7. Co-administration of SF-MSCs with E7-Exo/KGN in the knee joints via intra-articular injection also shows more pronounced therapeutic effects in a rat OA model than KGN alone or KGN delivered by exosomes without E7. Altogether, transplantation of SF-MSCs with in situ chondrogenesis enabled by E7-Exo delivered KGN holds promise towards as an advanced stem cell therapy for OA.

A High-Throughput Assay for the Pancreatic Islet Beta-Cell Potassium Channel: Use in the Pharmacological Characterization of Insulin Secretagogues Identified from Phenotypic Screening

Phenotypic screening is a neoclassical approach for drug discovery. We conducted phenotypic screening for insulin secretion enhancing agents using INS-1E insulinoma cells as a model system for pancreatic beta-cells. A principal regulator of insulin secretion in beta-cells is the metabolically regulated potassium channel Kir6.2/SUR1 complex. To characterize hit compounds, we developed an assay to quantify endogenous potassium channel activity in INS-1E cells. We quantified ligand-regulated potassium channel activity in INS-1E cells using fluorescence imaging and thallium flux. Potassium channel activity was metabolically regulated and coupled to insulin secretion. The pharmacology of channel opening agents (diazoxide) and closing agents (sulfonylureas) was used to validate the applicability of the assay. A precise high-throughput assay was enabled, and phenotypic screening hits were triaged to enable a higher likelihood of discovering chemical matter with novel and useful mechanisms of action.

The emerging landscape of nanotheranostic-based diagnosis and therapy for osteoarthritis

Osteoarthritis (OA) is a common degenerative disease involving numerous joint tissues and cells, with a growing rate in prevalence that ultimately results in a negative social impact. Early diagnosis, OA progression monitoring and effective treatment are of significant importance in halting OA process. However, traditional imaging techniques lack sensitivity and specificity, which lead to a delay in timely clinical intervention. Additionally, current treatments only slow the progression of OA but have not meet the largely medical need for disease-modifying therapy. In order to overcome the above-mentioned problems and improve clinical efficacy, nanotheranostics has been proposed on OA remedy, which has confirmed success in animal models. In this review, different imaging targets-based nanoprobe for early and timely OA diagnosis is first discussed. Second, therapeutic strategies delivered by nanosystem are summarized as much as possible. Their advantages and the potential for clinical translation are detailed discussed. Third, nanomedicine simultaneously combined with the imaging for OA treatment is introduced. Nanotheranostics dynamically tracked the OA treatment outcomes to timely and individually adjust therapy. Finally, future prospects and challenges of nanotechnology-based OA diagnosis, imaging and treatment are concluded and predicted. It is believed that nanoprobe and nanomedicine will become prospective in OA therapeutic revolution.

An Injectable Hydrogel Scaffold With Kartogenin-Encapsulated Nanoparticles for Porcine Cartilage Regeneration: A 12-Month Follow-up Study

BACKGROUND

Treatment of cartilage lesions is clinically challenging. A previous study demonstrated that a hyaluronic acid hydrogel (m-HA) with kartogenin (KGN)-loaded PLGA nanoparticles (m-HA+KGN treatment) achieved superior cartilage repair in a rabbit model. However, large animals serve as a bridge to translate animal outcomes into the clinic.

HYPOTHESES

(1) m-HA+KGN treatment could facilitate hyaline cartilage and subchondral bone tissue repair in a porcine model. (2) Defect size and type (full-thickness chondral vs osteochondral) influence the therapeutic efficacy of m-HA+KGN treatment.

STUDY DESIGN

Controlled laboratory study.

METHODS

48 minipigs were randomized into 3 treatment groups: m-HA hydrogel with KGN-loaded PLGA nanoparticles (m-HA+KGN treatment), m-HA hydrogel (m-HA treatment), and untreated (blank treatment). Full-thickness chondral (6.5 mm or 8.5 mm in diameter) or osteochondral (6.5 mm or 8.5 mm in diameter; 5-mm depth) defects were prepared in the medial femoral condyle. At 6 and 12 months postoperatively, defect repair was assessed by macroscopic appearance, magnetic resonance imaging (MRI), micro-computed tomography (µCT), and histologic and biomechanical tests.

RESULTS

The m-HA+KGN group exhibited superior gross and histological healing after evaluation at 6 and 12 months postoperatively. Improved quality of the repaired cartilage demonstrated by MRI and better subchondral bone reconstruction assessed by µCT were observed in the m-HA+KGN group. The m-HA+KGN group showed more hyaline-like cartilage exhibited by histological staining in terms of extracellular matrix, cartilage lacuna, and type II collagen. The biomechanical properties were improved in the m-HA+KGN group. With m-HA+KGN treatment, defects with a diameter of 6.5 mm or full-thickness chondral-type defects possessed significantly higher ICRS macroscopic and histological scores compared with diameter 8.5 mm or osteochondral-type defects.

CONCLUSION

(1) m-HA+KGN treatment facilitated hyaline cartilage and subchondral bone tissue repair in a porcine model at the 12-month follow-up. (2) m-HA+KGN treatment demonstrated better therapeutic efficacy in defects with a diameter of 6.5 mm or full-thickness chondral-type defects.

CLINICAL RELEVANCE

This study verified the efficacy of this innovative KGN release system on cartilage repair. The KGN release system can be injected into defect sites arthroscopically. This convenient and minimally invasive operation holds important prospects for clinical application.

Inhibition of PI3K/Akt/NF-κB signaling by Aloin for ameliorating the progression of osteoarthritis: In vitro and in vivo studies

Osteoarthritis (OA) is a progressive and degenerative joint disease. Aloin is a bitter and yellow-brown-coloured compound from the Aloe plant and is allowed for use in foods as a "natural flavour". In our study, we examined the protective effects of Aloin on the inhibition of OA development as well as its underlying mechanism in both in vitro and vivo experiments. In in-vitro experiments, the protective effect of aloin on the anabolism and catabolism of the extracellular matrix (ECM) induced by IL-1 β in chondrocytes by inhibiting the expression of pro-inflammatory factors, including TNF-α (p = 0.016), IL-6 (p = 0.006), iNOS (p = 0.001) and COX-2 (p = 0.006). Mechanistically, Aloin suppressed the IL-1β-induced activation of the PI3K/Akt/NF-κB signalling pathway cascades. Moreover, molecular docking studies demonstrated that Aloin bound strongly to PI3K. In vivo, Aloin ameliorated the OA process in the destabilization of the medial meniscus (DMM) model. In summary, our findings demonstrate that Aloin ameliorates the progression of OA via the PI3K/Akt/NF-κB signalling pathways, which supports Aloin as a promising therapeutic agent for the treatment of OA.

Biological strategies for osteoarthritis: from early diagnosis to treatment

PURPOSE

To provide an updated review of the literature on the use of orthobiologics as a potential treatment option to alleviate symptoms associated with osteoarthritis (OA), slow the progression of the disease, and aid in cartilage regeneration.

METHODS

A comprehensive review of the literature was performed to identify basic science and clinical studies examining the role of orthobiologics in the diagnosis and management of osteoarthritis.

RESULTS

Certain molecules (such as interleukin-6 (IL-6), interleukin-8 (IL-8), matrix metalloproteinase (MMPs), cartilage oligomeric matrix protein (COMP), and tumor necrosis factor (TNF), microRNAs, growth differentiation factor 11 (GDF-11)) have been recognized as biomarkers that are implicated in the pathogenesis and progression of degenerative joint disease (DJD). These biomarkers have been used to develop newer diagnostic applications and targeted biologic therapies for DJD. Local injection therapy with biologic agents such as platelet-rich plasma or stem cell-based preparations has been associated with significant improvement in joint pain and function in patients with OA and has increased in popularity during the last decade. The combination of PRP with kartogenin or TGF-b3 may also enhance its biologic effect. The mesenchymal stem cell secretome has been recognized as a potential target for the development of OA therapies due to its role in mediating the chondroprotective effects of these cells. Recent experiments have also suggested the modification of gut microbiome as a newer method to prevent OA or alter the progression of the disease.

CONCLUSIONS

The application of orthobiologics for the diagnosis and treatment of DJD is a rapidly evolving field that will continue to expand. The identification of OA-specific and joint-specific biomarker molecules for early diagnosis of OA would be extremely useful for the development of preventive and therapeutic protocols. Local injection therapies with HA, PRP, BMAC, and other stem cell-based preparations are currently being used to improve pain and function in patients with early OA or those with progressed disease who are not surgical candidates. Although the clinical outcomes of these therapies seem to be promising in clinical studies, future research will determine the true role of orthobiologic applications in the field of DJS.

Combination Therapy Using Kartogenin-Based Chondrogenesis and Complex Polymer Scaffold for Cartilage Defect Regeneration

Articular cartilage has a highly organized structure, responsible for supporting tremendous mechanical loads. How to repair defected articular cartilage has become a great challenge as the avascular nature of cartilage limits its regenerative ability. Aiming to facilitate chondrogenic differentiation and cartilage regeneration, we recently explored a novel combination therapy using soluble poly-l-lysine/Kartogenin (L-K) nanoparticles and a poly(lactic-co-glycolic acid) PLGA/methacrylated hyaluronic acid (PLHA) complex scaffold. The potential use for joint cartilage reconstruction was investigated through L-K nanoparticles stimulating adipose-derived stem cells (ADSCs) on PLHA scaffolding, which ultimately differentiated into cartilage in vivo. In this study, on one hand, an effective method was established for obtaining uniform L-K nanoparticles by self-assembly. They were further proved to be biocompatible to ADSCs via cytotoxicity assays in vitro and to accelerate ADSCs secreting type 2 collagen in a dose-dependent manner by immunofluorescence. On the other hand, the porous PLHA scaffold was manufactured by the combination of coprecipitation and ultraviolet (UV) cross-linking. Nanoindentation technology-verified PLHA had an appropriate stiffness close to actual cartilage tissue. Additional microscopic observation confirmed that the PLHA platform supported proliferation and chondrogenesis for ADSCs in vitro. In the presence of ADSCs, a 12-week osteochondral defect regeneration by the combination therapy showed that smooth and intact cartilage tissue successfully regenerated. Furthermore, the results of combination therapy were superior to those of phosphate-buffered saline (PBS) only, KGN, or KGN/PLHA treatment. The results of magnetic resonance imaging (MRI) and histological assessment indicated that the renascent tissue gradually regenerated while the PLHA scaffold degraded. In conclusion, we have developed a novel multidimensional combination therapy of cartilage defect repair that facilitated cartilage regeneration. This strategy has a great clinical translational potential for articular cartilage repair in the near future.

Highly biosafe biomimetic stem cell membrane-disguised nanovehicles for cartilage regeneration

Cartilage injury is very common and results in considerable pain and osteoarthritis. Owing to its low self-renewal capability, cartilage regeneration is still a great challenge for clinicians. Stem cell therapy has been treated as the most promising treatment for cartilage regeneration in recent decades. However, increasing concerns about the potential biosafety of stem cell products such as immune rejection and neoplastic transformation restrict their further application in clinic. Herein, biomimetic stem cell membrane-disguised nanovehicles without biosafety risks are designed and prepared for cartilage regeneration. In this study, based on the disguise of the natural bone marrow mesenchymal stem cell (BMSC) membrane, Kartogenin (KGN) as a drug for cartilage regeneration was encapsulated into Fe3O4 nanoparticles as the core of biomimetic stem cell nanovehicles. In the core-shell structure of biomimetic stem cell nanovehicles, the fabricated KGN-loaded BMSC membrane-disguised Fe3O4 nanoparticles (KGN-MNPs) showed a stable hybrid structure with a uniform size and morphology in the physiological environments. Moreover, the prepared KGN-MNPs exhibited excellent biocompatibility when disguised with the natural membrane of BMSCs and good biosafety by eliminating the nuclei of BMSCs. In a cartilage defect rat model, compared with pure KGN, the intra-articularly injected KGN-MNPs were capable of regenerating an integrated organized structure with a layer of hyaline-like cartilage in a shorter time due to the retained natural activities of the BMSC membrane. In a word, KGN-MNPs as one kind of our designed biomimetic stem cell nanovehicles enable rapid and high quality cartilage regeneration, and provide a novel and standardized strategy for stem cell therapy in the future.

Isolation and Characterization of Human Synovial Fluid-Derived Mesenchymal Stromal Cells from Popliteal Cyst

Mesenchymal stem cells (MSCs) are multipotent progenitor cells in adult tissues. The aim of this study is to isolate and identify synovial fluid-derived mesenchymal stromal cells (SF-MSCs) from the popliteal cyst fluid of pediatric patients. SF-MSCs were collected from the popliteal cyst fluid of pediatric patients during cystectomy surgery. After cyst fluid extraction and adherent culturing, in vitro morphology, growth curve, and cell cycle were observed. The expression of stem cell surface markers was analyzed by flow cytometry, and expression of cell marker protein was detected by immunofluorescence. SF-MSCs were cultured in osteogenic, adipogenic, and chondrogenic differentiation medium. The differentiation potential of SF-MSCs was analyzed by alkaline phosphatase (Alizarin Red), Oil Red O, and Alcian blue. Antibody detection of human angiogenesis-related proteins was performed compared with bone marrow mesenchymal stem cells (BM-MSCs). The results show that SF-MSCs from the popliteal cyst fluid of pediatric patients showed a shuttle appearance and logarithmic growth. Flow cytometry analysis revealed that SF-MSCs were negative for hematopoietic lineage markers (CD34, CD45) and positive for MSC markers (CD44, CD73, CD90, and CD105). Interstitial cell marker (vimentin) and myofibroblast-like cell marker alpha-smooth muscle actin (α-SMA) were positive. These cells could differentiate into osteogenic, adipogenic, and chondrogenic lineages, respectively. Several types of human angiogenesis-related proteins were detected in the cell secretory fluid. These results show that we successfully obtained SF-MSCs from the popliteal cyst fluid of pediatric patients, which have the potential to be a valuable source of MSCs.

Small molecule compounds promote the proliferation of chondrocytes and chondrogenic differentiation of stem cells in cartilage tissue engineering

The application of tissue engineering to generate cartilage is limited because of low proliferative ability and unstable phenotype of chondrocytes. The sources of cartilage seed cells are mainly chondrocytes and stem cells. A variety of methods have been used to obtain large numbers of chondrocytes, including increasing chondrocyte proliferation and stem cell chondrogenic differentiation via cytokines, genes, and proteins. Natural or synthetic small molecule compounds can provide a simple and effective method to promote chondrocyte proliferation, maintain a stable chondrocyte phenotype, and promote stem cell chondrogenic differentiation. Therefore, the study of small molecule compounds is of great importance for cartilage tissue engineering. Herein, we review a series of small molecule compounds and their mechanisms that can promote chondrocyte proliferation, maintain chondrocyte phenotype, or induce stem cell chondrogenesis. The studies in this field represent significant contributions to the research in cartilage tissue engineering and regenerative medicine.

Synovial membrane mesenchymal stem cells: past life, current situation, and application in bone and joint diseases

Mesenchymal stem cells (MSCs) can be isolated from not only bone marrow, but also various adult mesenchymal tissues such as periosteum, skeletal muscle, and adipose tissue. MSCs from different tissue sources have different molecular phenotypes and differentiation potential. Synovial membrane (SM) is an important and highly specific component of synovial joints. Previous studies have suggested that the synovium is a structure with a few cell layers thick and consists mainly of fibroblast-like synoviocytes (FLS), which forms a layer that lining the synovial membrane on the joint cavity and synovial fluid through cell-cell contact. In recent years, studies have found that there are also mesenchymal stem cells in the synovium, and as an important part of the mesenchymal stem cell family, it has strong capabilities of cartilage forming and tissue repairing. This article reviews the sources, surface markers, subtypes, influencing factors, and applications in inflammatory joints of synovial membrane mesenchymal stem cells (SM-MSCs) in recent years, aiming to clarify the research status and existing problems of SM-MSCs.

Naringin and bone marrow mesenchymal stem cells repair articular cartilage defects in rabbit knees through the transforming growth factor-β superfamily signaling pathway

The present study aimed to assess the effect of a combination of naringin and rabbit bone marrow mesenchymal stem cells (BMSCs) on the repair of cartilage defects in rabbit knee joints and to assess possible involvement of the transforming growth factor-β (TGF-β) signaling pathway in this process. After establishing an articular cartilage defect model in rabbit knees, 20 New Zealand rabbits were divided into a sham operation group (Sham), a model group (Mod), a naringin treatment group (Nar), a BMSC group (BMSCs) and a naringin + BMSC group (Nar/BMSCs). At 12 weeks after treatment, the cartilage was evaluated using the International Cartilage Repair Society (ICRS)'s macroscopic evaluation of cartilage repair scale, the ICRS's visual histological assessment scale, the Modified O'Driscoll grading system, histological staining (hematoxylin and eosin staining, toluidine blue staining and safranin O staining) and immunohistochemical staining (type-II collagen, TGF-β3 and SOX-9 immunostaining). Using the above grading systems to quantify the extent of repair, histological quantification and macro quantification of joint tissue repair showed that the Nar/BMSCs group displayed repair after treatment in comparison to the untreated Mod group. Among the injury model groups (Mod, Nar, BMSCs and Nar/BMSCs), the Nar/BMSCs group displayed the highest degree of morphological repair. The results of histological and immunohistochemical staining of the repaired region of the joint defect indicated that the BMSCs had a satisfactory effect on the repair of the joint structure but had a poor effect on the repair of cartilage quality. The Nar/BMSCs group displayed satisfactory therapeutic effects on both repair of the joint structure and cartilage quality. The expression level of type-II collagen was high in the Nar/BMSCs group. Additionally, staining of TGF-β3 and SOX-9 in the Nar/BMSCs group was the strongest compared with that of any other group in the present study. Naringin and/BMSCs together demonstrated a more efficient repair effect on articular cartilage defects in rabbit knees than the use of either treatment alone in terms of joint structure and cartilage quality. One potential mechanism of naringin action may be through activation and continuous regulation of the TGF-β superfamily signaling pathway, which can promote BMSCs to differentiate into chondrocytes.

Kartogenin mediates cartilage regeneration by stimulating the IL-6/Stat3-dependent proliferation of cartilage stem/progenitor cells

A decrease in the number of endogenous stem cells in cartilage is regarded as the cause of cartilage degeneration. Kartogenin (KGN) is known to induce chondrogenesis of cartilage stem/progenitor cells (CSPCs). Using CSPCs isolated from rat cartilage, we analysed changes in the transcriptome after treatment with KGN in vitro. An animal model of destabilization of the medial meniscus (DMM) was then used to identify the effect of intra-articular (IA) KGN injection on CSPC proliferation in vivo. Here, we demonstrated that KGN promoted the proliferation of CSPCs isolated from cartilage. The percentage of G2-M phase cells in the KGN-treated group reached over 10%, nearly twice that in the control group. Transcriptomic profiling of rat CSPCs revealed significant changes in KGN-treated samples compared to control samples. The gene expression levels of IL-6 and its coreceptor Gp130 were much higher in the KGN-treated group than in the control group. Phosphorylation of the IL-6 downstream molecule Stat3 was enhanced via KGN stimulation. The DMM animal model showed increased articular cartilage thickness after IA KGN injection. IHC staining also demonstrated upregulation of Stat3 phosphorylation and enhanced distribution of CD44⁺/CD105⁺ cells in cartilage following IA KGN injection. Thus, our data suggested that KGN promoted cartilage regeneration at least partially by stimulating IL-6/Stat3-dependent proliferation.

Small Molecule Regulation of Stem Cells that Generate Bone, Chondrocyte, and Cardiac Cells

Embryonic stem cells (ESCs) are stem cells (SCs) that can self-renew and differentiate into a myriad of cell types. The process of developing stemness is determined by signaling molecules that drive stem cells to a specific lineage. For example, ESCs can differentiate into mature cells (e.g., cardiomyocytes) and mature cardiomyocytes can be characterized for cell beating, action potential, and ion channel function. A goal of this Perspective is to show how small molecules can be used to differentiate ESCs into cardiomyocytes and how this can reveal novel aspects of SC biology. This approach can also lead to the discovery of new molecules of use in cardiovascular disease. Human induced pluripotent stem cells (hiPSCs) afford the ability to produce unlimited numbers of normal human cells. The creation of patient-specific hiPSCs provides an opportunity to study cell models of human disease. The second goal is to show that small molecules can stimulate hiPSC commitment to cardiomyocytes. How iPSCs can be used in an approach to discover new molecules of use in cardiovascular disease will also be shown in this study. Adult SCs, including mesenchymal stem cells (MSCs), can likewise participate in self-renewal and multilineage differentiation. MSCs are capable of differentiating into osteoblasts, adipocytes or chondrocytes. A third goal of this Perspective is to describe differentiation of MSCs into chondrogenic and osteogenic lineages. Small molecules can stimulate MSCs to specific cell fate both in vitro and in vivo. In this Perspective, some recent examples of applying small molecules for osteogenic and chondrogenic cell fate determination are summarized. Underlying molecular mechanisms and signaling pathways involved are described. Small molecule-based modulation of stem cells shows insight into cell regulation and potential approaches to therapeutic strategies for MSC-related diseases.

Runt-related transcription factor 1 is required for murine osteoblast differentiation and bone formation

Despite years of research investigating osteoblast differentiation, the mechanisms by which transcription factors regulate osteoblast maturation, bone formation, and bone homeostasis is still unclear. It has been reported that runt-related transcription factor 1 (Runx1) is expressed in osteoblast progenitors, pre-osteoblasts, and mature osteoblasts; yet, surprisingly, the exact function of RUNX1 in osteoblast maturation and bone formation remains unknown. Here, we generated and characterized a pre-osteoblast and differentiating chondrocyte-specific Runx1 conditional knockout mouse model to study RUNX1's function in bone formation. Runx1 ablation in osteoblast precursors and differentiating chondrocytes via osterix-Cre (Osx-Cre) resulted in an osteoporotic phenotype and decreased bone density in the long bones and skulls of Runx1f/fOsx-Cre mice compared with Runx1f/f and Osx-Cre mice. RUNX1 deficiency reduced the expression of SRY-box transcription factor 9 (SOX9), Indian hedgehog signaling molecule (IHH), Patched (PTC), and cyclin D1 in the growth plate, and also reduced the expression of osteocalcin (OCN), OSX, activating transcription factor 4 (ATF4), and RUNX2 in osteoblasts. ChIP assays and promoter activity mapping revealed that RUNX1 directly associates with the Runx2 gene promoter and up-regulates Runx2 expression. Furthermore, the ChIP data also showed that RUNX1 associates with the Ocn promoter. In conclusion, RUNX1 up-regulates the expression of Runx2 and multiple bone-specific genes, and plays an indispensable role in bone formation and homeostasis in both trabecular and cortical bone. We propose that stimulating Runx1 activity may be useful in therapeutic approaches for managing some bone diseases such as osteoporosis.

A single cell transcriptional atlas of early synovial joint development

Synovial joint development begins with the formation of the interzone, a region of condensed mesenchymal cells at the site of the prospective joint. Recently, lineage-tracing strategies have revealed that Gdf5-lineage cells native to and from outside the interzone contribute to most, if not all, of the major joint components. However, there is limited knowledge of the specific transcriptional and signaling programs that regulate interzone formation and fate diversification of synovial joint constituents. To address this, we have performed single cell RNA-Seq analysis of 7329 synovial joint progenitor cells from the developing murine knee joint from E12.5 to E15.5. By using a combination of computational analytics, in situ hybridization and in vitro characterization of prospectively isolated populations, we have identified the transcriptional profiles of the major developmental paths for joint progenitors. Our freely available single cell transcriptional atlas will serve as a resource for the community to uncover transcriptional programs and cell interactions that regulate synovial joint development.

Dual functional construct containing kartogenin releasing microtissues and curcumin for cartilage regeneration

BACKGROUND

Regeneration of articular cartilage poses a tremendous challenge due to its limited self-repair capability and inflammation at the damaged site. To generate the desired structures that mimic the structure of native tissue, microtissues with repeated functional units such as cell aggregates have been developed. Multicellular aggregates of mesenchymal stem cells (MSCs) can be used as microscale building blocks of cartilage due to their potential for cell-cell contact, cell proliferation, and differentiation.

METHODS

Chondrogenic microtissues were developed through incorporation of kartogenin-releasing poly (lactic-co-glycolic acid) (PLGA) microparticles (KGN-MP) within the MSC aggregates. The chondrogenic potential of KGN-MP treated MSC aggregates was proven in vitro by studying the chondrogenic markers at the RNA level and histological analysis. In order to address the inflammatory responses at the defect site, the microtissues were delivered in vivo via an injectable, anti-inflammatory hydrogel that contained gelatin methacryloyl (GelMA) loaded with curcumin (Cur).

RESULTS

The KGN-MPs were fabricated to support MSCs during cartilage differentiation. According to real-time RT-PCR analysis, the presence of KGN in the aggregates led to the expression of cartilage markers by the MSCs. Both toluidine blue (TB) and safranin O (SO) staining demonstrated homogeneous glycosaminoglycan production throughout the KGN-MP incorporated MSC aggregates. The curcumin treatment efficiently reduced the expressions of hypertrophy markers by MSCs in vitro. The in vivo results showed that implantation of chondrogenic microtissues (KGN-MP incorporated MSC aggregates) using the curcumin loaded GelMA hydrogel resulted in cartilage tissue regeneration that had characteristic features close to the natural hyaline cartilage according to observational and histological results.

CONCLUSIONS

The use of this novel construct that contained chondrogenic cell blocks and curcumin is highly desired for cartilage regeneration.

Understanding cartilage protection in OA and injury: a spectrum of possibilities

BACKGROUND

Osteoarthritis (OA) is a prevalent musculoskeletal disease resulting in progressive degeneration of the hyaline articular cartilage within synovial joints. Current repair treatments for OA often result in poor quality tissue that is functionally ineffective compared to the hyaline cartilage and demonstrates increased failure rates post-treatment. Complicating efforts to improve clinical outcomes, animal models used in pre-clinical research show significant heterogeneity in their regenerative and degenerative responses associated with their species, age, genetic/epigenetic traits, and context of cartilage injury or disease. These can lead to variable outcomes when testing and validating novel therapeutic approaches for OA. Furthermore, it remains unclear whether protection against OA among different model systems is driven by inhibition of cartilage degeneration, enhancement of cartilage regeneration, or any combination thereof.

MAIN TEXT

Understanding the mechanistic basis underlying this context-dependent duality is essential for the rational design of targeted cartilage repair and OA therapies. Here, we discuss some of the critical variables related to the cross-species paradigm of degenerative and regenerative abilities found in pre-clinical animal models, to highlight that a gradient of regenerative competence within cartilage may exist across species and even in the greater human population, and likely influences clinical outcomes.

CONCLUSIONS

A more complete understanding of the endogenous regenerative potential of cartilage in a species specific context may facilitate the development of effective therapeutic approaches for cartilage injury and/or OA.

Wearable Fixation Device for a Magnetically Controllable Therapeutic Agent Carrier: Application to Cartilage Repair

Recently, significant research efforts have been devoted toward the development of magnetically controllable drug delivery systems, however, drug fixation after targeting remains a challenge hindering long-term therapeutic efficacy. To overcome this issue, we present a wearable therapeutic fixation device for fixing magnetically controllable therapeutic agent carriers (MCTACs) at defect sites and its application to cartilage repair using stem cell therapeutics. The developed device comprises an array of permanent magnets based on the Halbach array principle and a wearable band capable of wrapping the target body. The design of the permanent magnet array, in terms of the number of magnets and array configuration, was determined through univariate search optimization and 3D simulation. The device was fabricated for a given rat model and yielded a strong magnetic flux density (exceeding 40 mT) in the region of interest that was capable of fixing the MCTAC at the desired defect site. Through in-vitro and in-vivo experiments, we successfully demonstrated that MCTACs, both a stem cell spheroid and a micro-scaffold for cartilage repair, could be immobilized at defect sites. This research is expected to advance precise drug delivery technology based on MCTACs, enabling subject-specific routine life therapeutics. Further studies involving the proposed wearable fixation device will be conducted considering prognostics under actual clinical settings.

Anti-Inflammatory and Chondroprotective Effects of Vanillic Acid and Epimedin C in Human Osteoarthritic Chondrocytes

In osteoarthritis (OA), inhibition of excessively expressed pro-inflammatory cytokines in the OA joint and increasing the anabolism for cartilage regeneration are necessary. In this ex-vivo study, we used an inflammatory model of human OA chondrocytes microtissues, consisting of treatment with cytokines (interleukin 1β (IL-1β)/tumor necrosis factor α (TNF-α)) with or without supplementation of six herbal compounds with previously identified chondroprotective effect. The compounds were assessed for their capacity to modulate the key catabolic and anabolic factors using several molecular analyses. We selectively investigated the mechanism of action of the two most potent compounds Vanillic acid (VA) and Epimedin C (Epi C). After identification of the anti-inflammatory and anabolic properties of VA and Epi C, the Ingenuity Pathway Analysis showed that in both treatment groups, osteoarthritic signaling pathways were inhibited. In the treatment group with VA, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling was inhibited by attenuation of the nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκBα) phosphorylation. Epi C showed a significant anabolic effect by increasing the expression of collagenous and non-collagenous matrix proteins. In conclusion, VA, through inhibition of phosphorylation in NF-κB signaling pathway and Epi C, by increasing the expression of extracellular matrix components, showed significant anti-inflammatory and anabolic properties and might be potentially used in combination to treat or prevent joint OA.

The Emerging Role of Exosomal Non-coding RNAs in Musculoskeletal Diseases

Exosomes are phospholipid bilayer-enclosed membrane vesicles derived and constitutively secreted by various metabolically active cells. They are capable of mediating hetero- and homotypic intercellular communication by transferring multiple cargos from donor cells to recipient cells. Nowadays, non-coding RNAs (ncRNAs) have emerged as novel potential biomarkers or disease-targeting agents in a variety of diseases. However, the lack of effective delivery systems may impair their clinical application. Recently, accumulating evidence demonstrated that ncRNAs could be efficiently delivered to recipient cells using exosomes as a carrier, and therefore can exert a critical role in musculoskeletal diseases including osteoarthritis, rheumatoid arthritis, osteoporosis, muscular dystrophies, osteosarcoma and other diseases. Herein, we present an extensive review of biogenesis, physiological relevance and clinical implication of exosome-derived ncRNAs in musculoskeletal diseases.

Synergistic Effects of Kartogenin and Transforming Growth Factor-β3 on Chondrogenesis of Human Umbilical Cord Mesenchymal Stem Cells In Vitro

OBJECTIVE

To explore the effect of kartogenin (KGN) on proliferation and chondrogenic differentiation of human umbilical cord mesenchymal stem cells (hUCMSC) in vitro, and the synergistic effects of KGN and transforming growth factor (TGF)-β3 on hUCMSC.

METHODS

Human umbilical cord mesenchymal stem cells were isolated and cultured. Then the differentiation properties were identified by flow cytometry analysis. HUCMSC were divided into four groups: control group, KGN group, TGF-β3 group, and TK group (with TGF-β3 and KGN added into the medium simultaneously). Cells in all groups were induced for 21 days using the suspension ball culture method. Hematoxylin and eosin, immunofluorescence, and Alcian blue staining were used to analyze chondrogenic differentiation. Real-time reverse transcriptase polymerase chain reaction was performed to investigate genes associated with chondrogenic differentiation.

RESULT

Hematoxylin and eosin staining showed that cells in the TGF-β3 group and the TK group had formed cartilage-like tissue after 21 days of culture. The results of immunofluorescence and Alcian blue staining showed that compared with the control group, cells in the KGN and TGF-β3 groups demonstrated increased secretion of aggrecan after 21 days of culture. In addition, cells in the group combining KGN with TGF-β3 (5.587 ± 0.27, P < 0.01) had more collagen II secretion than cells in the TGF-β3 alone group (2.86 ± 0.141, P < 0.01) or the KGN group (1.203 ± 0.215, P < 0.01). The expression of aggrecan (2.468 ± 0.097, P < 0.05) and SRY-Box 9 (4.08 ± 0.13, P < 0.05) in cells in the group combining KGN with TGF-β3 was significantly higher than those in the TGF-β3 group (2.216 ± 0.09, 3.02 ± 0.132, P < 0.05).'

CONCLUSION

The combination of KGN and TGF-β3 had synergistic effects and induced hUCMSC chondrogenesis. This could represent a new approach for clinical application and studies on cartilage repair and regeneration.

RSK-3 promotes cartilage regeneration via interacting with rpS6 in cartilage stem/progenitor cells

Rationale: Cartilage stem/progenitor cells (CSPC) are a promising cellular source to promote endogenous cartilage regeneration in osteoarthritis (OA). Our previous work indicates that ribosomal s6 kinase 3 (RSK-3) is a target of 4-aminobiphenyl, a chemical enhancing CSPC-mediated cartilage repair in OA. However, the primary function and mechanism of RSK-3 in CSPC-mediated cartilage pathobiology remain undefined.

Methods: We systematically assessed the association of RSK-3 with OA in three mouse strains with varying susceptibility to OA (MRL/MpJ>CBA>STR/Ort), and also RSK-3^-/- mice. Bioinformatic analysis was used to identify the possible mechanism of RSK-3 affecting CSPC, which was further verified in OA mice and CSPC with varying RSK-3 expression induced by chemicals or gene modification.

Results: We demonstrated that the level of RSK-3 in cartilage was positively correlated with cartilage repair capacities in three mouse strains (MRL/MpJ>CBA>STR/Ort). Enhanced RSK-3 expression by 4-aminobiphenyl markedly attenuated cartilage injury in OA mice and inhibition or deficiency of RSK-3 expression, on the other hand, significantly aggravated cartilage damage. Transcriptional profiling of CSPC from mice suggested the potential role of RSK-3 in modulating cell proliferation. It was further shown that the in vivo and in vitro manipulation of the RSK-3 expression indeed affected the CSPC proliferation. Mechanistically, ribosomal protein S6 (rpS6) was activated by RSK-3 to accelerate CSPC growth.

Conclusion: RSK-3 is identified as a key regulator to enhance cartilage repair, at least partly by regulating the functionality of the cartilage-resident stem/progenitor cells.

Transforming growth factor-beta stimulates human bone marrow-derived mesenchymal stem/stromal cell chondrogenesis more so than kartogenin

A previous study identified kartogenin (KGN) as a potent modulator of bone marrow mesenchymal stem/stromal cell (BMSC) chondrogenesis. This initial report did not contrast KGN directly against transforming growth factor-beta 1 (TGF-β1), the most common growth factor used in chondrogenic induction medium. Herein, we directly compared the in vitro chondrogenic potency of TGF-β1 and KGN using a high resolution micropellet model system. Micropellets were cultured for 7–14 days in medium supplemented with TGF-β1, KGN, or both TGF-β1 + KGN. Following 14 days of induction, micropellets exposed to TGF-β1 alone or TGF-β1 + KGN in combination were larger and produced more glycosominoglycan (GAG) than KGN-only cultures. When TGF-β1 + KGN was used, GAG quantities were similar or slightly greater than the TGF-β1-only cultures, depending on the BMSC donor. BMSC micropellet cultures supplemented with KGN alone contracted in size over the culture period and produced minimal GAG. Indicators of hypertrophy were not mitigated in TGF-β1 + KGN cultures, suggesting that KGN does not obstruct BMSC hypertrophy. KGN appears to have weak chondrogenic potency in human BMSC cultures relative to TGF-β1, does not obstruct hypertrophy, and may not be a viable alternative to growth factors in cartilage tissue engineering.

Near-infrared control and real-time detection of osteogenic differentiation in mesenchymal stem cells by multifunctional upconversion nanoparticles

Finding a method to control and detect the differentiation of stem cells in real time remains a challenge for regenerative medicine. Here we developed the multifunctional upconversion nanoparticle (UCNP) approach for both near-infrared (NIR) control and the real-time detection of osteogenic differentiation in mesenchymal stem cells (MSCs). We first synthesized Tm/Er doped core-shell UCNPs (NaYF4:Yb/Tm/Er@NaYF4), and the core-shell UCNPs were coated with mesoporous silica for drug loading and installing photomechanical azobenzene (azo). Then the Arg-Gly-Asp (RGD) peptide and the matrix metalloproteinase 13 (MMP13) sensitive peptide-black hole quencher-3 group (CGPLGVRGK-BHQ-3) were conjugated on the surface of UCNPs for cell targeting and detection of cell differentiation. The final multifunctional UCNPs are called UCNP@mSiO2-azo-peptide-BHQ-3. The drug icariin (ICA), which can induce the osteogenic differentiation of MSCs, was loaded into UCNP@mSiO2-azo-peptide-BHQ-3 to form the UCNP nanocomplexes. ICA could be released from UCNP nanocomplexes in a NIR-controlled manner that is based on the transformation of the trans-isomer of azo into the cis isomer under the upconverted UV and visible light. Meanwhile, UCNP@mSiO2-azo-peptide-BHQ-3 could also be used as a nanoprobe to detect the activity of the MMP13 enzyme by enzyme digestion and UCNP fluorescence recovery. By detecting MMP13, which is produced by osteogenic differentiation, a real-time detection of cell differentiation in living differentiated MSCs could be achieved using UCNP nanoprobes. Thus, the multifunctional UCNPs combined the control of cell differentiation with the real-time detection of cell differentiation in MSCs, which makes them a powerful tool for regulating and detecting the differentiation of MSCs in regenerative medicine.

Ontogeny informs regeneration: explant models to investigate the role of the extracellular matrix in cartilage tissue assembly and development

Osteoarthritis (OA) is typically managed in late stages by replacement of the articular cartilage surface with a prosthesis as an effective, though undesirable outcome. As an alternative, hydrogel implants or growth factor treatments are currently of great interest in the tissue engineering community, and scaffold materials are often designed to emulate the mechanical and chemical composition of mature extracellular matrix (ECM) tissue. However, scaffolds frequently fail to capture the structure and organization of cartilage. Additionally, many current scaffold designs do not mimic processes by which structurally sound cartilage is formed during musculoskeletal development. The objective of this review is to highlight methods that investigate cartilage ontogenesis with native and model systems in the context of regenerative medicine. Specific emphasis is placed on the use of cartilage explant cultures that provide a physiologically relevant microenvironment to study tissue assembly and development. Ex vivo cartilage has proven to be a cost-effective and accessible model system that allows researchers to control the culture conditions and stimuli and perform proteomics and imaging studies that are not easily possible using in vivo experiments, while preserving native cell-matrix interactions. We anticipate our review will promote a developmental biology approach using explanted tissues to guide cartilage tissue engineering and inform new treatment methods for OA and joint damage.

Chitosan modified Fe3O4/KGN self-assembled nanoprobes for osteochondral MR diagnose and regeneration

Chondral and osteochondral defects caused by trauma or pathological changes, commonly progress into total joint degradation, even resulting in disability. The cartilage restoration is a great challenge because of its avascularity and limited proliferative ability. Additionally, precise diagnosis using non-invasive detection techniques is challenging, which increases problems associated with chondral disease treatment. Methods: To achieve a theranostic goal, we used an integrated strategy that relies on exploiting a multifunctional nanoprobe based on chitosan-modified Fe3O4 nanoparticles, which spontaneously self-assemble with the oppositely charged small molecule growth factor, kartogenin (KGN). This nanoprobe was used to obtain distinctively brighter T2-weighted magnetic resonance (MR) imaging, allowing its use as a positive contrast agent, and could be applied to obtain accurate diagnosis and osteochondral regeneration therapy. Results: This nanoprobe was first investigated using adipose tissue-derived stem cells (ADSCs), and was found to be a novel positive contrast agent that also plays a significant role in stimulating ADSCs differentiation into chondrocytes. This self-assembled probe was not only biocompatible both in vitro and in vivo, contributing to cellular internalization, but was also used to successfully make distinction of normal/damaged tissue in T2-weighted MR imaging. This novel combination was systematically shown to be biosafe via the decrement of apparent MR signals and elimination of ferroferric oxide over a 12-week regeneration period. Conclusion: Here, we established a novel method for osteochondral disease diagnosis and reconstruction. Using the Fe3O4-CS/KGN nanoprobe, it is easy to distinguish the defect position, and it could act as a tool for dynamic observation as well as a stem cell-based therapy for directionally chondral differentiation.

A novel elastic and controlled-release poly(ether-ester-urethane)urea scaffold for cartilage regeneration

In the tissue engineering of cartilage, scaffolds with appropriate elasticity and controlled-release properties are essential. Herein, we synthesized a poly(ether-ester-urethane)urea scaffold with a pendant amino group (PEEUUN) through a de-protection process from PEEUU-Boc polymers and grafted kartogenin (KGN) onto the PEEUUN scaffolds (PEEUUN-KGN). Characterization, performance tests, scaffold biocompatibility analysis, and chondrogenesis evaluation both in vitro and in vivo were conducted. The results revealed that the PEEUUN-KGN scaffolds were degradable and three-dimensional (3D) with interconnected pores, and possessed good elasticity, as well as excellent cytocompatibility. Meanwhile, KGN on the PEEUUN-KGN scaffolds underwent stable sustained release for a long time and promoted human umbilical cord mesenchymal stem cells (HUCMSCs) to differentiate into chondrocytes in vitro, thus enhancing cartilage regeneration in vivo. In conclusion, the present PEEUUN-KGN scaffolds would have application potential for cartilage tissue engineering.

Biofunctionalized chondrogenic shape-memory ternary scaffolds for efficient cell-free cartilage regeneration

Cartilage defect repair remains a great clinical challenge due to the limited self-regeneration capacity of cartilage tissue. Surgical treatment of injured cartilage is rather difficult due to the narrow space in the articular cavity and irregular defect area. Herein, we designed and fabricated chondrogenic and physiological-temperature-triggered shape-memory ternary scaffolds for cell-free cartilage repair, where the poly (glycerol sebacate) (PGS) networks ensured elasticity and shape recovery, crystallized poly (1,3-propylene sebacate) (PPS) acted as switchable phase, and immobilized bioactive kartogenin (KGN) endowed the scaffolds with chondrogenic capacity. The resultant scaffolds exhibited shape-memory properties with shape-memory fixed ratio of 98% and recovered ratio of 97% at 37°C for PPS/PGS/KGN-100, indicating a good potential for minimally invasive implantation. The scaffolds gradually degraded in Dulbecco's phosphate-buffered saline and released KGN up to 12 weeks in vitro. In addition, the scaffolds promoted chondrogenic differentiation while inhibiting osteogenic differentiation of bone marrow-derived mesenchymal stem cells in a concentration-dependent manner and cartilage regeneration in full-thickness defects of rat femoropatellar groove for 12 weeks. Consequently, the PPS/PGS/KGN-100 scaffolds stimulated the formation of an overlying layer of neocartilage mimicking the characteristic architecture of native articular cartilage even in the absence of exogenous growth factors and seeded cells. This study provides much inspiration for future research on cartilage tissue engineering. STATEMENT OF SIGNIFICANCE: There are two crucial challenges for cartilage defect repair: the lack of self-regeneration capacity of cartilage tissue and difficult scaffold implantation via traditional open surgery due to space-limited joints. Herein, bioactive body-temperature-responsive shape memory scaffolds are designed to simultaneously address the challenges. The scaffolds can be readily implanted by minimally invasive approach and recover by body-temperature of patient. The integration of kartogenin endows scaffolds the bioactivity, leading to the first example of bulk shape-memory scaffolds for cell-free cartilage repair. These characteristics make the scaffolds advantageous for clinical translation. Moreover, our developed material is easy to be functionalized due to the presence of extensive free hydroxyl groups and provides a versatile platform to design diverse functional shape memory biomaterials.

Kartogenin-loaded coaxial PGS/PCL aligned nanofibers for cartilage tissue engineering

Electrospinning is a valuable technology for cartilage tissue engineering (CTE) due to its ability to produce fibrous scaffolds mimicking the nanoscale and alignment of collagen fibers present within the superficial zone of articular cartilage. Coaxial electrospinning allows the fabrication of core-shell fibers able to incorporate and release bioactive molecules (e.g., drugs or growth factors) in a controlled manner. Herein, we used coaxial electrospinning to produce coaxial poly(glycerol sebacate) (PGS)/poly(caprolactone) (PCL) aligned nanofibers (core:PGS/shell:PCL). The obtained scaffolds were characterized in terms of their structure, chemical composition, thermal properties, mechanical performance and in vitro degradation kinetics, in comparison to monoaxial PCL aligned fibers and respective non-aligned controls. All the electrospun scaffolds produced presented average fiber diameters within the nanometer-scale and the core-shell structure of the composite fibers was clearly confirmed by TEM. Additionally, fiber alignment significantly increased (>2-fold) the elastic modulus of both coaxial and monoxial scaffolds. Kartogenin (KGN), a small molecule known to promote mesenchymal stem/stromal cells (MSC) chondrogenesis, was loaded into the core PGS solution to generate coaxial PGS-KGN/PCL nanofibers. The KGN release kinetics and scaffold biological performance were evaluated in comparison to KGN-loaded monoaxial fibers and respective non-loaded controls. Coaxial PGS-KGN/PCL nanofibers showed a more controlled and sustained KGN release over 21 days than monoaxial PCL-KGN nanofibers. When cultured with human bone marrow MSC in incomplete chondrogenic medium (without TGF-β3), KGN-loaded scaffolds enhanced significantly cell proliferation and chondrogenic differentiation, as suggested by the increased sGAG amounts and chondrogenic markers gene expression levels. Overall, these findings highlight the potential of using coaxial PGS-KGN/PCL aligned nanofibers as a bioactive scaffold for CTE applications.

Injectable double-crosslinked hydrogels with kartogenin-conjugated polyurethane nano-particles and transforming growth factor β3 for in-situ cartilage regeneration

Articular cartilage has a limited ability for self-repair after injury. Implantation of scaffolds functionalized with bioactive molecules that could induce the migration and chondrogenesis of endogenous mesenchymal stem cells (MSCs) provides a convenient alternative for in-situ cartilage regeneration. In this study, we found the synergistic effects of kartogenin (KGN) and transforming growth factor β3 (TGF-β3) on chondrogenesis of MSCs in vitro, indicating that KGN and TGF-β3 are a good match for cartilage regeneration. Furthermore, we confirmed that KGN promoted the chondrogenesis of MSCs through attenuating the degradation of Runx1, which physically interacted with p-Smad3 in nuclei of MSCs. Meanwhile, we designed an injectable double-crosslinked hydrogel with superior mechanical property and longer support for cartilage regeneration by modifying sodium alginate and gelatin. When loaded with KGN conjugated polyurethane nanoparticles (PN-KGN) and TGF-β3, this hydrogel showed biological functions by the release of KGN and TGF-β3, which promoted the MSC migration and cartilage regeneration in one system. In conclusion, the cell-free hydrogel, along with PN-KGN and TGF-β3, provides a promising strategy for cartilage repair by attracting endogenous MSCs and inducing chondrogenesis of recruited cells in a single-step procedure.

Up-Regulation of Superoxide Dismutase 2 in 3D Spheroid Formation Promotes Therapeutic Potency of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells

Umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) are accessible, available in abundance, and have been shown to be a promising source that can regenerate cartilage in patients with osteoarthritis or other orthopedic diseases. Recently, a three-dimensional (3D) cell culture system was developed to mimic the naive tissue microenvironment. However, the efficacy of cells generated from the 3D spheroid culture system has not yet been elucidated. In the present study, we demonstrate the changes in superoxide dismutase 2 (SOD2) gene expression, an indicator of oxidative stress, on 3D spheroid MSCs. Moreover, siRNA transfection and neutralizing antibody investigations were performed to confirm the function of SOD2 and E-cadherin. Overall, we found that SOD2 siRNA transfection in the spheroid form of MSCs increases the expression of apoptotic genes and decreases the clearance of mitochondrial reactive oxygen species (ROS). As a result, we confirm that 3D spheroid formation increases E-cadherin and SOD2 expression, ultimately regulating the phosphoinositide 3-kinase (PI3K/pAkt/pNrf2 and pERK/pNrf2 signaling pathway. Additionally, we show that SOD2 expression on 3D spheroid MSCs affects the regeneration rates of destructive cartilage in an osteoarthritic model. We postulate that the impact of SOD2 expression on 3D spheroid MSCs reduces oxidative stress and apoptosis, and also promotes cartilage regeneration.

Delivering siRNA to control osteogenic differentiation and real-time detection of cell differentiation in human mesenchymal stem cells using multifunctional gold nanoparticles

Schematic representation of the multifunctional gold nanoparticles (AuNP-PEI-peptide-FITC) synthesis and siRNA adsorption to silence the PPARγ gene for controlling osteogenic differentiation and real-time detection of ongoing cell differentiation in hMSCs.

Mesenchymal stem cells for cartilage regeneration

Cartilage injuries are typically caused by trauma, chronic overload, and autoimmune diseases. Owing to the avascular structure and low metabolic activities of chondrocytes, cartilage generally does not self-repair following an injury. Currently, clinical interventions for cartilage injuries include chondrocyte implantation, microfracture, and osteochondral transplantation. However, rather than restoring cartilage integrity, these methods only postpone further cartilage deterioration. Stem cell therapies, especially mesenchymal stem cell (MSCs) therapies, were found to be a feasible strategy in the treatment of cartilage injuries. MSCs can easily be isolated from mesenchymal tissue and be differentiated into chondrocytes with the support of chondrogenic factors or scaffolds to repair damaged cartilage tissue. In this review, we highlighted the full success of cartilage repair using MSCs, or MSCs in combination with chondrogenic factors and scaffolds, and predicted their pros and cons for prospective translation to clinical practice.

Cartilage Extracellular Matrix Scaffold With Kartogenin-Encapsulated PLGA Microspheres for Cartilage Regeneration

Repair of articular cartilage defects is a challenging aspect of clinical treatment. Kartogenin (KGN), a small molecular compound, can induce the differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) into chondrocytes. Here, we constructed a scaffold based on chondrocyte extracellular matrix (CECM) and poly(lactic-co-glycolic acid) (PLGA) microspheres (MP), which can slowly release KGN, thus enhancing its efficiency. Cell adhesion, live/dead staining, and CCK-8 results indicated that the PLGA(KGN)/CECM scaffold exhibited good biocompatibility. Histological staining and quantitative analysis demonstrated the ability of the PLGA(KGN)/CECM composite scaffold to promote the differentiation of BMSCs. Macroscopic observations, histological tests, and specific marker analysis showed that the regenerated tissues possessed characteristics similar to those of normal hyaline cartilage in a rabbit model. Use of the PLGA(KGN)/CECM scaffold may mimic the regenerative microenvironment, thereby promoting chondrogenic differentiation of BMSCs in vitro and in vivo. Therefore, this innovative composite scaffold may represent a promising approach for acellular cartilage tissue engineering.

Multi-arm Avidin nano-construct for intra-cartilage delivery of small molecule drugs

Targeted drug delivery to joint tissues like cartilage remains a challenge that has prevented clinical translation of promising osteoarthritis (OA) drugs. Local intra-articular (IA) injections of drugs suffer from rapid clearance from the joint space and slow diffusive transport through the dense, avascular cartilage matrix comprised of negatively charged glycosaminoglycans (GAGs). Here we apply drug carriers that leverage electrostatic interactions with the tissue's high negative fixed charge density (FCD) for delivering small molecule drugs to cartilage cell and matrix sites. We demonstrate that a multi-arm cationic nano-construct of Avidin (mAv) with 28 sites for covalent drug conjugation can rapidly penetrate through the full thickness of cartilage in high concentration and have long intra-cartilage residence time in both healthy and arthritic cartilage via weak-reversible binding with negatively charged aggrecans. mAv's intra-cartilage mean uptake was found to be 112× and 33× the equilibration bath concentration in healthy and arthritic (50% GAG depleted) cartilage, respectively. mAv was conjugated with Dexamethasone (mAv-Dex), a broad-spectrum glucocorticoid, using a combination of hydrolysable ester linkers derived from succinic anhydride (SA), 3,3-dimethylglutaric anhydride (GA) and phthalic anhydride (PA) in 2:1:1 M ratio that enabled 50% drug release within 38.5 h followed by sustained release in therapeutic doses over 2 weeks. A single 10 μM low dose of controlled release mAv-Dex (2:1:1) effectively suppressed IL-1α-induced GAG loss, cell death and inflammatory response significantly better than unmodified Dex over 2 weeks in cartilage explant culture models of OA. With this multi-arm design, <1 μM Avidin was needed - a concentration which has been shown to be safe, preventing further GAG loss and cytotoxicity. A charge-based cartilage homing drug delivery platform like this can elicit disease modifying effects as well as facilitate long-term symptomatic pain and inflammation relief by enhancing tissue specificity and prolonging intra-cartilage residence time of OA drugs. This nano-construct thus has high translational potential for enabling intra-cartilage delivery of a broad array of small molecule OA drugs and their combinations to chondrocytes, enabling OA treatment with a single injection of low drug doses and eliminating toxicity issues associated with multiple high dose injections.

The combination of microfracture with induction of Wnt / β- Catenin pathway, leads to enhanced cartilage regeneration

INTRODUCTION

Microfracture does not lead to complete healing of full-thickness cartilage defects. The aim of this study was to evaluate the effect of modifying Wnt/β-catenin signaling following microfracture, on the restoration of a full-thickness cartilage defect in a rabbit model. The modification of the canonical Wnt pathway was achieved through per os administration of lithium carbonate, which is an intracellular inhibitor of glycogen synthase kinase 3-β (Gsk3-β) and therefore induces Wnt/β-catenin signaling.

MATERIALS AND METHODS

Full-thickness cartilage defects of 4 mm in diameter were created in the patellar groove of the right femurs of 18 male New Zealand white rabbits. The rabbits were divided into three groups of six (n = 6) based on post-surgery treatment differences, as follows: microfracture only (group 1), microfracture plus lithium carbonate 7 mM in the drinking water for 1 week (group 2), microfracture plus lithium carbonate 7 mM in the drinking water for 4 weeks (group 3). All animals were sacrificed 9 weeks after surgery. The outcome was assessed histologically, by using the International Cartilage Repair Society (ICRS) visual histological scale. Immunohistochemistry for type II collagen was also conducted.

RESULTS

Statistical analysis of the histological ICRS scores showed that group 3 was significantly superior to group 1 in four out of six ICRS categories, while group 2 was superior to 1 in only two out of six.

CONCLUSION

The combination of microfracture and systematic administration of lithium carbonate 7 mM for 4 weeks shows statistically significant superiority in four out of six ICRS categories compared with microfracture only for the treatment of full-thickness cartilage defects in a rabbit experimental model.