Mesenchymal stem cells for cartilage regeneration: Insights into molecular mechanism and therapeutic strategies

The use of mesenchymal stem cells (MSCs) in cartilage regeneration has gained significant attention in regenerative medicine. This paper reviews the molecular mechanisms underlying MSC-based cartilage regeneration and explores various therapeutic strategies to enhance the efficacy of MSCs in this context. MSCs exhibit multipotent capabilities and can differentiate into various cell lineages under specific microenvironmental cues. Chondrogenic differentiation, a complex process involving signaling pathways, transcription factors, and growth factors, plays a pivotal role in the successful regeneration of cartilage tissue. The chondrogenic differentiation of MSCs is tightly regulated by growth factors and signaling pathways such as TGF-β, BMP, Wnt/β-catenin, RhoA/ROCK, NOTCH, and IHH (Indian hedgehog). Understanding the intricate balance between these pathways is crucial for directing lineage-specific differentiation and preventing undesirable chondrocyte hypertrophy. Additionally, paracrine effects of MSCs, mediated by the secretion of bioactive factors, contribute significantly to immunomodulation, recruitment of endogenous stem cells, and maintenance of chondrocyte phenotype. Pre-treatment strategies utilized to potentiate MSCs, such as hypoxic conditions, low-intensity ultrasound, kartogenin treatment, and gene editing, are also discussed for their potential to enhance MSC survival, differentiation, and paracrine effects. In conclusion, this paper provides a comprehensive overview of the molecular mechanisms involved in MSC-based cartilage regeneration and outlines promising therapeutic strategies. The insights presented contribute to the ongoing efforts in optimizing MSC-based therapies for effective cartilage repair.

Ocu-miR-10a-5p promotes the chondrogenic differentiation of rabbit BMSCs by targeting BTRC-mediated Wnt/β-catenin signaling pathway

MicroRNAs (miRNAs) play an important role in articular cartilage damage in osteoarthritis (OA). However, the biological role of miRNAs in the chondrogenic differentiation of bone marrow mesenchymal stem cell (BMSC) remains largely unclear. Rabbit bone marrow mesenchymal stem cells (rBMSCs) were isolated, cultured, and identified. Afterwards, rBMSCs were induced to chondrogenic differentiation, examined by Alcian Blue staining. Differentially expressed miRNAs were identified in rBMSCs between induced and non-induced groups by miRNA sequencing analysis, part of which was validated via PCR assay. Cell viability and apoptosis were assessed by CCK-8 assay and Hoechst staining. Saffron O staining was utilized to assess chondrocyte hyperplasia. The expression of specific chondrogenic markers, including COL2A1, SOX9, Runx2, MMP-13, Aggrecan, and BMP-2, were measured at mRNA and protein levels. The association between beta-transducin repeat containing E3 ubiquitin protein ligase (BTRC) and miR-10a-5p in the miRNA family from rabbit (ocu-miR-10a-5p) was determined by luciferase reporter assay. A total of 76 differentially expressed miRNAs, including 52 downregulated and 24 upregulated miRNAs, were identified in rBMSCs from the induced group. Inhibition of ocu-miR-10a-5p suppressed rBMSC viability and chondrogenic differentiation, as well as downregulated the expression of β-catenin, SOX9, COL2A1, MMP-13, and Runx2. BTRC was predicted and confirmed as a target of ocu-miR-10a-5p. Overexpression of BTRC rescued the promoting impacts of overexpressed ocu-miR-10a-5p on chondrogenic differentiation of rBMSCs and β-catenin expression. Taken together, our data suggested that ocu-miR-10a-5p facilitated rabbit BMSC survival and chondrogenic differentiation by activating Wnt/β-catenin signaling through BTRC.

Suppression of MALAT1 promotes human synovial mesenchymal stem cells enhance chondrogenic differentiation and prevent osteoarthritis of the knee in a rat model via regulating miR-212-5p/MyD88 axis

Osteoarthritis (OA) is one of the most common diseases of the skeleton. Long non-coding RNAs (lncRNAs) are emerging as key players in OA pathogenesis. This work sets out to determine the function of lncRNA MALAT1 in OA and the mechanisms by which it does so. Mesenchymal stem cells isolated from the human synovial membrane are called hSMSCs. The hSMSCs' surface markers were studied using flow cytometry. To determine whether or not hSMSC might differentiate, researchers used a number of different culture settings and labeling techniques. The expression levels of associated genes and proteins were determined using quantitative real-time polymerase chain reaction (RT-qPCR), western blotting (WB), and immunostaining. A dual luciferase reporter experiment and RNA immunoprecipitation (RIP) test demonstrated the direct association between miR-212-5p and MALAT1 or MyD88. MALAT1 was downregulated during the chondrogenic differentiation of hSMSCs, and underexpression of MALAT1 promotes chondrogenesis in hSMSCs. Using dual luciferase reporter and RIP assays facilitated the identification of MALAT1 as a competitive endogenous RNA (ceRNA) that sequesters miR-212-5p. Additionally, the expression of MYD88 was regulated by MALAT1 through direct binding with miR-212-5p. Significantly, the effects of MALAT1 on the chondrogenic differentiation of hSMSCs were counteracted by miR-212-5p/MYD88. Furthermore, our in vivo investigation revealed that the inhibition of MALAT1 mitigated osteoarthritis progression in rat models. In conclusion, the promotion of chondrogenic differentiation in hSMSCs and the protective effect on cartilage tissue in OA can be achieved by suppressing MALAT1, which regulates the miR-212-5p/MyD88 axis.

Electromagnetic field-mediated chitosan/gelatin/nano-hydroxyapatite and bone-derived scaffolds regulate the osteoblastic and chondrogenic phenotypes of adipose-derived stem cells to construct osteochondral tissue engineering niche in vitro

It is critical to explore the effects of electromagnetic field (EMF) on the construction of functional osteochondral tissue, which has shown certain clinical significance for the treatment of osteochondral injury. At present, there are few studies on the effect of the direction of EMF on cells. This study aimed to investigate the effects of EMF coupling on different parameters to control adipose-derived stem cells (ADSCs) proliferation and specific chondrogenic and osteogenic differentiation at 2D level and 3D level. The proliferation and differentiation of EMF-induced ADSCs are jointly regulated by EMF and space structure. In this study, Cs7/Gel3/nHAP scaffolds were prepared with good degradation rate (86.75 ± 4.96 %) and absorb water (1100 %), and the pore size was 195.63 ± 54.72 μm. The bone-derived scaffold with a pore size of 267.17 ± 129.18 μm was obtained and its main component was hydroxyapatite. Cs7/Gel3/nHAP scaffolds and bone-derived scaffolds are suitable as 3D level materials. The optimal EMF intensity was 2 mT for chondrogenic differentiation and proliferation and 1 mT for osteogenic differentiation and proliferation. It is noteworthy that EMF has a negative correlation with ADSCs proliferation in the vertical direction at 2D level, while it has a positive correlation with ADSCs proliferation at 3D level. EMF mediated 3D osteochondral scaffold provide good strategy for osteochondral tissue engineering construction.

Lysine demethylase 3A promotes chondrogenic differentiation of aged human dental pulp stem cells

Background/purpose

Aging severely impairs the beneficial effects of human dental pulp stem cells (hDPSCs) on cartilage regeneration. Lysine demethylase 3A (KDM3A) is involved in regulating mesenchymal stem cells (MSCs) senescence and bone aging. In this study, we investigated the role of KDM3A in hDPSCs aging and whether KDM3A could rejuvenate aged hDPSCs to enhance their chondrogenic differentiation capacity.

Materials and methods

The cellular aging of hDPSCs was evaluated by senescence-associated β-galactosidase (SA-β-gal) staining. Protein levels were determined using Western blot analysis. KDM3A was overexpressed in aged hDPSCs by lentivirus infection. Quantitative reverse-transcription polymerase chain reaction (RT-qPCR) were used to determine the mRNA levels of stemness markers. Toluidine blue staining was used to evaluate the effect of KDM3A overexpression on the chondrogenic differentiation of aged hDPSCs.

Results

hDPSCs at passage 12 or treated with etoposide exhibited augmented cellular senescence as evidenced by increased SA-β-gal activity. KDM3A was significantly increased during senescence of hDPSCs. Overexpression of KDM3A did not affect the stemness properties but significantly promoted the chondrogenic differentiation of aged hDPSCs.

Conclusion

Our findings indicate that KDM3A plays an important role in the maintenance of the chondrogenic differentiation capacity of aged hDPSCs and suggest that therapies targeting KDM3A may be a novel strategy to rejuvenate aged hDPSCs.

Effect of Solanum lycopersicum and Citrus limon-Derived Exosome-Like Vesicles on Chondrogenic Differentiation of Adipose-Derived Stem Cells

Articular cartilage defect treatment is a very important problem because its therapeutic options are not successful enough. Due to the weak self-repairing capacity of the avascular cartilage, even minor damage can progress and cause joint damage leading to osteoarthritis. Although various treatment strategies have been developed to repair damaged cartilage, cell- and exosome-based therapies are promising. Plant extracts have been used for decades, and their effects on cartilage regeneration have been studied. Exosome-like vesicles, which are secreted by all living cells, are involved in cell-to-cell communication and cell homeostasis. The differentiation potential of exosome-like vesicles isolated from S. lycopersicum and C. limon, which are known to have anti-inflammatory and antioxidant properties, was investigated in the differentiation of human adipose-derived mesenchymal stem cells (hASCs) into chondrocytes. In order to obtain tomato-derived exosome-like vesicles (TELVs) and lemon-derived exosome-like vesicles (LELVs) Aquous Two- Phase system was performed. Characterisation of isolated vesicles based on size, shape were achived via Zetasizer, NTA FAME analysis, and SEM techniques. These results showed that TELVs and LELVs increased cell viability and did not show any toxic effects on stem cells. Although TELVs triggered chondrocyte formation, LELVs downregulated. The expression of ACAN, SOX9, and COMP, known as chondrocyte markers, was increased by TELV treatment. In addition, protein expression of the two most important proteins, COL2 and COLXI, found in the extracellular matrix of cartilage, increased. These findings suggest that TELVs can be used for cartilage regeneration, and may be a novel and promising treatment for osteoarthritis.

Selenium Deficiency Can Promote the Expression of VEGF and Inflammatory Factors in Cartilage Differentiation and Mediates Cartilage Injury

Selenium plays a crucial role as a micronutrient, primarily exerting its biological functions through selenoproteins. It has been established that selenium deficiency adversely impacts cartilage development, leading to alterations in chondrocyte function. In regions with low selenium intake, endemic osteochondrosis has been documented, characterized by compromised growth plate and articular cartilage formation. Vascular endothelial growth factor (VEGF) stands out as a pivotal angiogenic factor, with elevated levels contributing significantly to vascular invasion into chondrocytes. This VEGF-mediated invasion serves as a key signal, prompting morphological changes in the growth plate and initiating cartilage remodeling. In animal models, the selenium deficiency group exhibited heightened levels of the cartilage damage marker matrix metalloproteinases 13 (MMP13). This resulted in articular cartilage degeneration, accompanied by a substantial increase in VEGF expression within the growth plate and articular cartilage, as compared to the normal group. In a chondrogenic progenitor cell (CPC) differentiation model, insufficient selenium induced chondrocyte damage and upregulated inflammatory factors such as inducible NO synthase (iNOS) and cyclooxygenase-2 (COX2). The selenium-deficient groups showed elevated expressions of VEGF, VEGFR2, MMP13, Collagen X, and Angiopoietin 1, accelerating the degradation of the extracellular matrix (ECM), which further promoted the development of cartilage-related diseases. Taken together, these findings provide novel insights for a better understanding of the role of low selenium in cartilage degeneration and angiogenesis. They shed light on the intricate influence of low selenium levels on the development of articular cartilage, emphasizing the interconnected pathways and processes involved.

Investigating the Interplay Between Matrix Compliance and Passaging History on Chondrogenic Differentiation of Mesenchymal Stem Cells Encapsulated Within Alginate-Gelatin Hybrid Hydrogels

Mesenchymal stem cells (MSCs) are used widely in tissue engineering and regenerative medicine because of their ease of isolation and their pluripotency. The low survival and retention rate of MSCs at the target site upon implantation can be addressed via encapsulation within hydrogels capable of directing their fate. In this study, the interplay between matrix mechanics and the passage number of MSCs on their chondrogenic differentiation was assessed. Human bone marrow-derived MSCs between passages 4 and 6 were encapsulated within alginate-gelatin hybrid gels. The stiffness of the gels was varied by varying alginate concentrations while maintaining the concentration of gelatin and consequently, the cell adhesion sites, constant. The study revealed that within 4.8 kPa gels, GAG deposition was higher by P4 MSCs compared to P6 MSCs. However, an opposite trend was observed with collagen type 2 deposition. Further, we observed enhanced chondrogenic differentiation upon encapsulation of MSCs within 6.7 kPa hydrogel irrespective of passaging history. However, the effect of matrix compliance was more prominent in the case of higher passaged MSCs suggesting that matrix stiffness can help rescue the reduced differentiation capability of these cells.

Differentiation of Human Induced Pluripotent Stem Cells (iPSCs)-derived Mesenchymal Progenitors into Chondrocytes

Induced pluripotent stem cells (iPSCs) generated from human sources are valuable tools for studying skeletal development and diseases, as well as for potential use in regenerative medicine for skeletal tissues such as articular cartilage. To successfully differentiate human iPSCs into functional chondrocytes, it is essential to establish efficient and reproducible strategies that closely mimic the physiological chondrogenic differentiation process. Here, we describe a simple and efficient protocol for differentiation of human iPSCs into chondrocytes via generation of an intermediate population of mesenchymal progenitors. These methodologies include step-by-step procedures for mesenchymal derivation, induction of chondrogenic differentiation, and evaluation of the chondrogenic marker gene expression. In this protocol, we describe the detailed procedure for successful derivation of mesenchymal progenitor population from human iPSCs, which are then differentiated into chondrocytes using high-density culture conditions by stimulating with bone morphogenetic protein-2 (BMP-2) or transforming growth factor beta-3 (TGFβ-3). The differentiated iPSCs exhibit temporal expression of cartilage genes and accumulation of a cartilaginous extracellular matrix in vitro, indicating successful chondrogenic differentiation. These detailed methodologies help effective differentiation of human iPSCs into the chondrogenic lineage to obtain functional chondrocytes, which hold great promise for modeling skeletal development and disease, as well as for potential use in regenerative medicine for cell-based therapy for cartilage regeneration. Key features • Differentiation of human iPSCs into chondrocytes using 3D culture methods. • Uses mesenchymal progenitors as an intermediate for differentiation into chondrocytes.

Long non-coding RNA MIR22HG suppresses the chondrogenic differentiation of human adipose-derived stem cells by interacting with CTCF to upregulate CRLF1

Improved chondrogenic differentiation of mesenchymal stem cells (MSCs) by genetic regulation is a potential method for regenerating articular cartilage. LncRNA MIR22HG has been proven to accelerate osteogenic differentiation, but the regulation mechanism of chondrogenic differentiation is still unclear. Human adipose-derived stem cells (hADSCs) have been widely utilised for bone tissue engineering applications. The present study aimed to examine the effect of MIR22HG on the chondrogenic differentiation of hADSCs. The results confirmed that MIR22HG was downregulated in the process of chondrogenic differentiation. Subsequently, gain- and loss-of-function of MIR22HG experiments showed that the overexpression of MIR22HG suppressed the deposition of cartilage matrix proteoglycans and decreased the expression of cartilage-related markers (e.g. Sox9, ACAN and Col2A1), whereas the knockdown of MIR22HG had the opposite effect. MIR22HG could bind to CTCF (CCCTC-binding factor), and CTCF could bind to the CRLF1 (cytokine receptor-like factor 1) promoter and upregulate CRLF1 gene expression. Besides, inhibition of CRLF1 can reverse the effect of MIR22HG on cell chondrogenic differentiation of hADSCs. Taken together, our outcomes reveal that MIR22HG suppressed chondrogenic differentiation by interaction with CTCF to stabilise CRLF1.

Human induced pluripotent stem cell line from fibroblasts (HEBHMUi015-A) and chondrogenic differentiation

In this study, fibroblasts were harvested and isolated from a healthy 14-year-old male donor and reprogrammed with four Yamanaka factors containing Oct3/4, Sox2, Klf4 and c-Myc to generate human induced pluripotent stem cell (iPSC) lines. The resulting iPSCs were integration-free, expressed normal karyotype, displayed pluripotency markers, and have been demonstrated to differentiate into cells with three germ layer. And the iPSCs were further differentiated to chondrosphere in vivo. The models could be used to test multiple differentiation protocols and also as a control for screening drugs and studying cartilage related disease.

Primary cilia in skeletal development and disease

Primary cilia are non-motile, microtubule-based sensory organelle present in most vertebrate cells with a fundamental role in the modulation of organismal development, morphogenesis, and repair. Here we focus on the role of primary cilia in embryonic and postnatal skeletal development. We examine evidence supporting its involvement in physiochemical and developmental signaling that regulates proliferation, patterning, differentiation and homeostasis of osteoblasts, chondrocytes, and their progenitor cells in the skeleton. We discuss how signaling effectors in mechanotransduction and bone development, such as Hedgehog, Wnt, Fibroblast growth factor and second messenger pathways operate at least in part at the primary cilium. The relevance of primary cilia in bone formation and maintenance is underscored by a growing list of rare genetic skeletal ciliopathies. We collate these findings and summarize the current understanding of molecular factors and mechanisms governing primary ciliogenesis and ciliary function in skeletal development and disease.

Wedelolactone Promotes the Chondrogenic Differentiation of Mesenchymal Stem Cells by Suppressing EZH2

Background and Objectives

Osteoarthritis (OA) is a degenerative disease that leads to the progressive destruction of articular cartilage. Current clinical therapeutic strategies are moderately effective at relieving OA-associated pain but cannot induce chondrocyte differentiation or achieve cartilage regeneration. We investigated the ability of wedelolactone, a biologically active natural product that occurs in Eclipta alba (false daisy), to promote chondrogenic differentiation.

Methods and Results

Real-time reverse transcription-polymerase chain reaction, immunohistochemical staining, and immunofluorescence staining assays were used to evaluate the effects of wedelolactone on the chondrogenic differentiation of mesenchymal stem cells (MSCs). RNA sequencing, microRNA (miRNA) sequencing, and isobaric tags for relative and absolute quantitation analyses were performed to explore the mechanism by which wedelolactone promotes the chondrogenic differentiation of MSCs. We found that wedelolactone facilitates the chondrogenic differentiation of human induced pluripotent stem cell-derived MSCs and rat bone-marrow MSCs. Moreover, the forkhead box O (FOXO) signaling pathway was upregulated by wedelolactone during chondrogenic differentiation, and a FOXO1 inhibitor attenuated the effect of wedelolactone on chondrocyte differentiation. We determined that wedelolactone reduces enhancer of zeste homolog 2 (EZH2)-mediated histone H3 lysine 27 trimethylation of the promoter region of FOXO1 to upregulate its transcription. Additionally, we found that wedelolactone represses miR-1271-5p expression, and that miR-1271-5p post-transcriptionally suppresses the expression of FOXO1 that is dependent on the binding of miR-1271-5p to the FOXO1 3'-untranscribed region.

Conclusions

These results indicate that wedelolactone suppresses the activity of EZH2 to facilitate the chondrogenic differentiation of MSCs by activating the FOXO1 signaling pathway. Wedelolactone may therefore improve cartilage regeneration in diseases characterized by inflammatory tissue destruction, such as OA.

TNF-α activates RELA expression via TNFRSF1B to upregulate OPA1 expression and inhibit chondrogenic differentiation of human adipose stem cells

BACKGROUND

Tumor necrosis factor-alpha (TNF-α), one of the pro-inflammatory cytokines mediating the local inflammatory process in joints, inhibits cartilage formation and has a detrimental effect on stem cell-based cartilage regeneration for the treatment of osteoarthritis (OA). However, the mechanisms behind this inhibitory effect are still poorly understood. Mitochondrial morphological changes mediated by mitochondrial fusion and fission are highly plastic, are quite sensitive to environmental stimuli and play a crucial role in maintaining cell structure and function. In our study, chondrogenic differentiated human adipose stem cells (hADSCs) were exposed to TNF-α and the effect of TNF-α on the ability of hADSCs to chondrogenic differentiate and on mitochondrial fusion and fission was observed and analyzed. The aim was to investigate the role and mechanisms of mitochondrial fusion and fission regulation in the chondrogenic differentiation of hADSCs under normal conditions and under exposure to TNF-α.

METHODS

We used flow cytometry to identify hADSCs immunophenotypes CD29, CD44, CD34, CD45, and HLA-DR. Alcian blue staining and Sirius red staining were used to observe the formation of proteoglycans and collagen during the chondrogenic differentiation of hADSCs, respectively. The mRNA and protein expression levels of the cartilage formation marker SOX9, type II collagen (COL2A1), and Aggrecan were measured by real-time fluorescent quantitative PCR (RT-qPCR) and western blot, respectively. The fluorescent probes MitoTracker® Red CMXRos and JC-1 were used to visualize mitochondria morphology and detect mitochondrial membrane electricity (MMP). Affymetrix PrimeView™ chips were used for gene expression profiling.

RESULTS

The results showed that the chondrogenic differentiation of hADSCs was inhibited in the presence of TNF-α that optic atrophy 1 (OPA1) expression was significantly upregulated and mitochondria were prolonged and interconnected during this process. Gene microarray and RT-qPCR data showed that the presence of TNF-α led to increased expression of TNFα receptor 2 (TNFRSF1B) and RELA during chondrogenic differentiation of hADSCs.

CONCLUSIONS

TNF-α inhibits chondrogenic differentiation of human adipose stem cells by activating RELA expression through TNFRSF1B upregulating OPA1 expression thereby increasing mitochondrial fusion.

Enhancement of mesenchymal stem cells' chondrogenic potential by type II collagen-based bioscaffolds

BACKGROUND

Osteoarthritis (OA) is a common degenerative chronic disease accounting for physical pain, tissue stiffness and mobility restriction. Current therapeutic approaches fail to prevent the progression of the disease considering the limited knowledge on OA pathobiology. During OA progression, the extracellular matrix (ECM) of the cartilage is aberrantly remodeled by chondrocytes. Chondrocytes, being the main cell population of the cartilage, participate in cartilage regeneration process. To this end, modern tissue engineering strategies involve the recruitment of mesenchymal stem cells (MSCs) due to their regenerative capacity as to promote chondrocyte self-regeneration.

METHODS AND RESULTS

In the present study, we evaluated the role of type II collagen, as the main matrix macromolecule in the cartilage matrix, to promote chondrogenic differentiation in two MSC in vitro culture systems. The chondrogenic differentiation of human Wharton's jelly- and dental pulp-derived MSCs was investigated over a 24-day culture period on type II collagen coating to improve the binding affinity of MSCs. Functional assays, demonstrated that type II collagen promoted chondrogenic differentiation in both MSCs tested, which was confirmed through gene and protein analysis of major chondrogenic markers.

CONCLUSIONS

Our data support that type II collagen contributes as a natural bioscaffold enhancing chondrogenesis in both MSC models, thus enhancing the commitment of MSC-based therapeutic approaches in regenerative medicine to target OA and bring therapy closer to the clinical use.

Stromal cell-derived factor-1α regulates chondrogenic differentiation via activation of the Wnt/β-catenin pathway in mesenchymal stem cells

BACKGROUND

Mesenchymal stem cells (MSCs) have been applied to treat degenerative articular diseases, and stromal cell-derived factor-1α (SDF-1α) may enhance their therapeutic efficacy. However, the regulatory effects of SDF-1α on cartilage differentiation remain largely unknown. Identifying the specific regulatory effects of SDF-1α on MSCs will provide a useful target for the treatment of degenerative articular diseases.

AIM

To explore the role and mechanism of SDF-1α in cartilage differentiation of MSCs and primary chondrocytes.

METHODS

The expression level of C-X-C chemokine receptor 4 (CXCR4) in MSCs was assessed by immunofluorescence. MSCs treated with SDF-1α were stained for alkaline phosphatase (ALP) and with Alcian blue to observe differentiation. Western blot analysis was used to examine the expression of SRY-box transcription factor 9, aggrecan, collagen II, runt-related transcription factor 2, collagen X, and matrix metalloproteinase (MMP)13 in untreated MSCs, of aggrecan, collagen II, collagen X, and MMP13 in SDF-1α-treated primary chondrocytes, of glycogen synthase kinase 3β (GSK3β) p-GSK3β and β-catenin expression in SDF-1α-treated MSCs, and of aggrecan, collagen X, and MMP13 in SDF-1α-treated MSCs in the presence or absence of ICG-001 (SDF-1α inhibitor).

RESULTS

Immunofluorescence showed CXCR4 expression in the membranes of MSCs. ALP stain was intensified in MSCs treated with SDF-1α for 14 d. The SDF-1α treatment promoted expression of collagen X and MMP13 during cartilage differentiation, whereas it had no effect on the expression of collagen II or aggrecan nor on the formation of cartilage matrix in MSCs. Further, those SDF-1α-mediated effects on MSCs were validated in primary chondrocytes. SDF-1α promoted the expression of p-GSK3β and β-catenin in MSCs. And, finally, inhibition of this pathway by ICG-001 (5 µmol/L) neutralized the SDF-1α-mediated up-regulation of collagen X and MMP13 expression in MSCs.

CONCLUSION

SDF-1α may promote hypertrophic cartilage differentiation in MSCs by activating the Wnt/β-catenin pathway. These findings provide further evidence for the use of MSCs and SDF-1α in the treatment of cartilage degeneration and osteoarthritis.

Rps6ka2 enhances iMSC chondrogenic differentiation to attenuate knee osteoarthritis through articular cartilage regeneration in mice

Articular cartilage (AC) is most susceptible to degeneration in knee osteoarthritis (OA); however, the existing treatments for OA do not target the core link of the pathogenesis-"decreased tissue cell function activity and extracellular matrix (ECM) metabolic disorders" for effective intervention. iMSC hold lower heterogeneity and great promise in biological research and clinical applications. Rps6ka2 may play an important role in the iMSC to treat OA. In this study, the CRISPR/Cas9 gene editing Rps6ka2^-/- iMSC were obtained. Effect of Rps6ka2 on iMSC proliferation and chondrogenic differentiation was evaluated in vitro. An OA model was constructed in mice by surgical destabilization of medial meniscus (DMM). The Rps6ka2^-/- iMSC and iMSC were injected into the articular cavity twice-weekly for 8 weeks. In vitro experiments showed that Rps6ka2 could promote iMSC proliferation and chondrogenic differentiation. In vivo results further confirmed that Rps6ka2 could improve iMSC viability to promote ECM production to attenuate OA in mice.

Low-intensity pulsed ultrasound promotes mesenchymal stem cell transplantation-based articular cartilage regeneration via inhibiting the TNF signaling pathway

BACKGROUND

Mesenchymal stem cell (MSC) transplantation therapy is highly investigated for the regenerative repair of cartilage defects. Low-intensity pulsed ultrasound (LIPUS) has the potential to promote chondrogenic differentiation of MSCs. However, its underlying mechanism remains unclear. Here, we investigated the promoting effects and mechanisms underlying LIPUS stimulation on the chondrogenic differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs) and further evaluated its regenerative application value in articular cartilage defects in rats.

METHODS

LIPUS was applied to stimulate cultured hUC-MSCs and C28/I2 cells in vitro. Immunofluorescence staining, qPCR analysis, and transcriptome sequencing were used to detect mature cartilage-related markers of gene and protein expression for a comprehensive evaluation of differentiation. Injured articular cartilage rat models were established for further hUC-MSC transplantation and LIPUS stimulation in vivo. Histopathology and H&E staining were used to evaluate the repair effects of the injured articular cartilage with LIPUS stimulation.

RESULTS

The results showed that LIPUS stimulation with specific parameters effectively promoted the expression of mature cartilage-related genes and proteins, inhibited TNF-α gene expression in hUC-MSCs, and exhibited anti-inflammation in C28/I2 cells. In addition, the articular cartilage defects of rats were significantly repaired after hUC-MSC transplantation and LIPUS stimulation.

CONCLUSIONS

Taken together, LIPUS stimulation could realize articular cartilage regeneration based on hUC-MSC transplantation due to the inhibition of the TNF signaling pathway, which is of clinical value for the relief of osteoarthritis.

3D bioprinting of ultrashort self-assembling peptides to engineer scaffolds with different matrix stiffness for chondrogenesis

62Articular cartilage is a nonvascularized and poorly cellularized tissue with a low self-repair capacity. Therefore, damage to this tissue due to trauma or degenerative joint diseases such as osteoarthritis needs a high-end medical intervention. However, such interventions are costly, have limited healing capacity, and could impair patients' quality of life. In this regard, tissue engineering and three-dimensional (3D) bioprinting hold great potential. However, identifying suitable bioinks that are biocompatible, with the desired mechanical stiffness, and can be used under physiological conditions is still a challenge. In this study, we developed two tetrameric self-assembling ultrashort peptide bioinks that are chemically well-defined and can spontaneously form nanofibrous hydrogels under physiological conditions. The printability of the two ultrashort peptides was demonstrated; different shape constructs were printed with high shape fidelity and stability. Furthermore, the developed ultrashort peptide bioinks gave rise to constructs with different mechanical properties that could be used to guide stem cell differentiation toward specific lineages. Both ultrashort peptide bioinks demonstrated high biocompatibility and supported the chondrogenic differentiation of human mesenchymal stem cells. Additionally, the gene expression analysis of differentiated stem cells with the ultrashort peptide bioinks revealed articular cartilage extracellular matrix formation preference. Based on the different mechanical stiffness of the two ultrashort peptide bioinks, they can be used to fabricate cartilage tissue with different cartilaginous zones, including the articular and calcified cartilage zones, which are essential for engineered tissue integration.

Exosomes from CD133+ human urine-derived stem cells combined adhesive hydrogel facilitate rotator cuff healing by mediating bone marrow mesenchymal stem cells

Background

The inadequate regeneration of natural tissue (mainly fibrocartilage) between tendon and bone during rotator cuff (RC) repair results in an unsatisfactory quality of RC healing. Cell-free therapy based on stem cell exosomes is a safer and more promising approach for tissue regeneration. Here, we investigated the effect of exosomes from human urine-derived stem cells (USCs) and their subpopulations (CD133⁺USCs) on RC healing.

Methods

USCs were isolated from urine and sorted by flow cytometry to obtain CD133⁺ urine-derived stem cells (CD133⁺ USCs). Urine-derived stem cell exosomes (USC-Exos) and CD133⁺ urine-derived stem cell exosomes (CD133⁺ USC-Exos) were subsequently isolated from the cell supernatant and identified by transmission electron microscopy (TEM), particle size analysis, and Western blot. We performed in vitro functional assays to evaluate the effects of USC-Exos and CD133⁺ USC-Exos on human bone marrow mesenchymal stem cells (BMSCs) proliferation, migration, osteogenic differentiation, and chondrogenic differentiation. In vivo experiments were performed by local injection of exosome-hydrogel complexes for the treatment of RC injury. The effects of CD133⁺ USC-Exos and USC-Exos on RC healing were assessed from imaging, histological, and biomechanical tests.

Results

CD133⁺ USCs were positive for CD29, CD44, CD73, CD90, CD133, but negative for CD34 and CD45. Differentiation ability test results showed that both USCs and CD133⁺ USCs had the potential for osteogenic, chondrogenic, and adipogenic differentiation, but CD133⁺ USCs had stronger chondrogenic differentiation ability. CD133⁺ USC-Exos and USC-Exos could be efficiently taken up by BMSCs and promote their migration, osteogenic and chondrogenic differentiation. However, CD133⁺ USC-Exos could promote the chondrogenic differentiation of BMSCs more than USC-Exos. Compared with USC-Exos, CD133⁺ USC-Exos could promote the healing of bone-tendon interface (BTI) more effectively, which might be related to its ability to promote the differentiation of BMSCs into chondroblasts. Although the two exosomes exhibited the same effect in promoting subchondral bone repair in BTI, the CD133⁺ USC-Exos group had higher histological scores and stronger biomechanical properties.

Conclusion

CD133⁺ USC-Exos hydrogel complex may become a promising therapeutic approach for RC healing based on stem cell exosomes.

The translational potential of this article

This is the first study to assess the specific role of CD133⁺ USC-Exos in RC healing which may be related to the activation of BMSCs by CD133⁺ USC-Exos towards chondrogenic differentiation. Further, our study provides a reference for possible future treatment of BTI by applying CD133⁺ USC-Exos hydrogel complex.

CD44 mediates hyaluronan to promote the differentiation of human amniotic mesenchymal stem cells into chondrocytes

OBJECTIVES

CD44 is the major receptor for hyaluronan (HA), but its effect on HA-induced differentiation of human amnion mesenchymal stem cells into chondrocytes is unclear. This study aimed to investigate the effects and mechanisms of CD44 in HA-induced chondrogenesis.

METHODS

Immunocytochemistry and toluidine blue staining were used to assess the secretion of type II collagen and aggrecan, respectively. qRT-PCR and western blotting were performed to evaluate the expression of key genes and proteins.

RESULTS

The expression of aggrecan and type II collagen was downregulated after using the anti-CD44 antibody (A3D8). The transcriptional levels of chondrocytes‑associated genes SRY‑box transcription factor 9, aggrecan, and collagen type II alpha 1 chain were also decreased. Thus, CD44 may mediate HA-induced differentiation of hAMSCs into chondrocytes. Further investigation indicated that expression of phosphorylated (p)‑Erk1/2 and p‑Smad2 decreased following CD44 inhibition. The changes in the expression of p-Erk1/2 and p-Smad2 were consistent after using the ERK1/2 inhibitor (U0126) and agonist (EGF), respectively. After administering the p-Smad2 inhibitor, the expression levels of p-ERK1/2 and p-Smad2 appeared downregulated. The results showed crosstalk between Erk1/2 and Smad2. Moreover, inhibition of p-Erk1/2 and p-Smad2 significantly reduced the accumulation of aggrecan and type II collagen.

CONCLUSION

These data indicate that CD44 mediates HA-induced differentiation of hAMSCs into chondrocytes by regulating Erk1/2 and Smad2 signaling.

Maintenance of methylation profile in imprinting control regions in human induced pluripotent stem cells

BACKGROUND

Parental imprinting is an epigenetic mechanism that leads to monoallelic expression of a subset of genes depending on their parental origin. Imprinting disorders (IDs), caused by disturbances of imprinted genes, are a set of rare congenital diseases that mainly affect growth, metabolism and development. To date, there is no accurate model to study the physiopathology of IDs or test therapeutic strategies. Human induced pluripotent stem cells (iPSCs) are a promising cellular approach to model human diseases and complex genetic disorders. However, aberrant hypermethylation of imprinting control regions (ICRs) may appear during the reprogramming process and subsequent culture of iPSCs. Therefore, we tested various conditions of reprogramming and culture of iPSCs and performed an extensive analysis of methylation marks at the ICRs to develop a cellular model that can be used to study IDs.

RESULTS

We assessed the methylation levels at seven imprinted loci in iPSCs before differentiation, at various passages of cell culture, and during chondrogenic differentiation. Abnormal methylation levels were found, with hypermethylation at 11p15 H19/IGF2:IG-DMR and 14q32 MEG3/DLK1:IG-DMR, independently of the reprogramming method and cells of origin. Hypermethylation at these two loci led to the loss of parental imprinting (LOI), with biallelic expression of the imprinted genes IGF2 and DLK1, respectively. The epiPS™ culture medium combined with culturing of the cells under hypoxic conditions prevented hypermethylation at H19/IGF2:IG-DMR (ICR1) and MEG3/DLK1:IG-DMR, as well as at other imprinted loci, while preserving the proliferation and pluripotency qualities of these iPSCs.

CONCLUSIONS

An extensive and quantitative analysis of methylation levels of ICRs in iPSCs showed hypermethylation of certain ICRs in human iPSCs, especially paternally methylated ICRs, and subsequent LOI of certain imprinted genes. The epiPS™ culture medium and culturing of the cells under hypoxic conditions prevented hypermethylation of ICRs in iPSCs. We demonstrated that the reprogramming and culture in epiPS™ medium allow the generation of control iPSCs lines with a balanced methylation and ID patient iPSCs lines with unbalanced methylation. Human iPSCs are therefore a promising cellular model to study the physiopathology of IDs and test therapies in tissues of interest.

MiR-362-5p inhibits cartilage repair in osteoarthritis via targeting plexin B1

BACKGROUND AND OBJECTIVES

Chondrogenesis of bone marrow mesenchymal stem cells (BMSCs) exerts great function during the pathogenesis of osteoarthritis (OA). Studies have reported the association of plexin B1 (PLXNB1) with OA pathogenesis. In this study, the upstream mechanism and function of PLXNB1 in this disease were explored.

METHODS

Flow cytometry was applied to test BMSC characterization. Chondrogenic differentiation of BMSCs was evaluated by Alcian blue staining. The expression of PLXNB1, miR-362-5p, miR-501-5p, miR-1827, miR-500-5p was measured using RT-qPCR analysis. The protein levels of PLXNB1, Aggrecan, and Silent information regulator factor 2-related enzyme 1 (SIRT1) were determined by western blotting. Binding relationship between miR-362-5p and PLXNB1 was confirmed using bioinformatics analysis and luciferase reporter assay. The in vivo model of OA was established in Sprague-Dawley rats which received medial meniscus instability surgery. For histopathological examination, cartilage tissues in the knee joint of rats were stained with hematoxylin and eosin. Micro-CT analysis was employed to observe the changes of morphometric indices including average trabecular separation, average trabecular thickness, and bone volume fraction.

RESULTS

BMSCs were identified to possess the characteristics of mesenchymal stem cells. PLXNB1 was observed to be highly expressed during chondrogenic differentiation of BMSCs and PLXNB1 overexpression promoted BMSC chondrogenic differentiation. Mechanically, PLXNB1 was targeted by miR-362-5p. In rescue assays, miR-362-5p reversed the effects of PLXNB1 on chondrogenic differentiation of BMSCs. In the in vivo experiments, upregulated PLXNB1 expression alleviated joint injury of OA rats. Additionally, overexpressed miR-362-5p and downregulated PLXNB1 expression levels were detected in OA rats.

CONCLUSION

MiR-362-5p promotes OA progression by suppressing PLXNB1.

Combinatorial Effect of Mesenchymal Stem Cells and Extracellular Vesicles in a Hydrogel on Cartilage Regeneration

BACKGROUND

Mesenchymal stem cells (MSCs) are used for tissue regeneration due to their wide differentiation capacity and anti-inflammatory effects. Extracellular vesicles (EVs) derived from MSCs are also known for their regenerative effects as they contain nucleic acids, proteins, lipids, and cytokines similar to those of parental cells. There are several studies on the use of MSCs or EVs for tissue regeneration. However, the combinatorial effect of human MSCs (hMSCs) and EVs is not clear. In this study, we investigated the combinatorial effect of hMSCs and EVs on cartilage regeneration via co-encapsulation in a hyaluronic-acid (HA)-based hydrogel.

METHODS

A methacrylic-acid-based HA hydrogel was prepared to encapsulate hMSCs and EVs in hydrogels. Through in vitro and in vivo analyses, we investigated the chondrogenic potential of the HA hydrogel-encapsulated with hMSCs and EVs.

RESULTS

Co-encapsulation of hMSCs with EVs in the HA hydrogel increased the chondrogenic differentiation of hMSCs and regeneration of damaged cartilage tissue compared with that of the HA hydrogel loaded with hMSCs only.

CONCLUSION

Co-encapsulation of hMSCs and EVs in the HA hydrogel effectively enhances cartilage tissue regeneration due to the combinatorial therapeutic effect of hMSCs and EVs. Thus, in addition to cartilage tissue regeneration for the treatment of osteoarthritis, this approach would be a useful strategy to improve other types of tissue regeneration.

Tumor necrosis factor-α inhibition restores matrix formation by human adipose-derived stem cells in the late stage of chondrogenic differentiation

BACKGROUND

Cartilage tissue engineering is a promising strategy for treating cartilage damage. Matrix formation by adipose-derived stem cells (ADSCs), which are one type of seed cell used for cartilage tissue engineering, decreases in the late stage of induced chondrogenic differentiation in vitro, which seriously limits research on ADSCs and their application.

AIM

To improve the chondrogenic differentiation efficiency of ADSCs in vitro, and optimize the existing chondrogenic induction protocol.

METHODS

Tumor necrosis factor-alpha (TNF-α) inhibitor was added to chondrogenic culture medium, and then Western blotting, enzyme linked immunosorbent assay, immunofluorescence and toluidine blue staining were used to detect the cartilage matrix secretion and the expression of key proteins of nuclear factor kappa-B (NF-κB) signaling pathway.

RESULTS

In this study, we found that the levels of TNF-α and matrix metalloproteinase 3 were increased during the chondrogenic differentiation of ADSCs. TNF-α then bound to its receptor and activated the NF-κB pathway, leading to a decrease in cartilage matrix synthesis and secretion. Blocking TNF-α with its inhibitors etanercept (1 μg/mL) or infliximab (10 μg/mL) significantly restored matrix formation.

CONCLUSION

Therefore, this study developed a combination of ADSC therapy and targeted anti-inflammatory drugs to optimize the chondrogenesis of ADSCs, and this approach could be very beneficial for translating ADSC-based approaches to treat cartilage damage.

Regulatory of miRNAs in tri-lineage differentiation of C3H10T1/2

MicroRNAs (miRNAs) are non-coding single-stranded RNA molecules encoded by endogenous genes, which play a vital role in cell generation, metabolism, apoptosis and stem cell differentiation. C3H10T1/2, a mesenchymal cell extracted from mouse embryos, is capable of osteogenic differentiation, adipogenic differentiation and chondrogenic differentiation. Extensive studies have shown that not only miRNAs can directly trigger targeted genes to regulate the tri-lineage differentiation of C3H10T1/2, but it also can indirectly regulate the differentiation by triggering different signaling pathways or various downstream molecules. This paper aims to clarify the regulatory roles of different miRNAs on C3H10T1/2 differentiation, and discussing their balance effect among osteogenic differentiation, adipogenic differentiation and chondrogenic differentiation of C3H10T1/2. We also review the biogenesis of miRNAs, Wnt signaling pathways, MAPK signaling pathways and BMP signaling pathways and provide some specific examples of how these signaling pathways act on C3H10T1/2 tri-lineage differentiation. On this basis, we hope that a deeper understanding of the differentiation and regulation mechanism of miRNAs in C3H10T1/2 can provide a promising therapeutic method for the clinical treatment of bone defects, osteoporosis, osteoarthritis and other diseases.

Let-7a-3p Inhibits Chondrogenic Differentiation of Bone Marrow Mesenchymal Stem Cells by Targeting TGF-β3

OBJECTIVE

Chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) plays an important role in osteoarthritis (OA) treatment. Studies have reported the association of transforming growth factor beta-3 (TGF-β3) with chondrogenic differentiation of BMSCs. In this study, the upstream mechanism and functions of TGF-β3 in chondrogenic differentiation of BMSCs were explored.

METHODS AND RESULTS

Flow cytometry was performed for the positive and negative MSC markers. Chondrogenic differentiation of BMSCs was evaluated by Alcian blue staining. Gene expression and protein expression levels were measured by RT-qPCR and western blotting, respectively. Relationship between let-7a-3p and TGF-β3 was confirmed using bioinformatics analysis, luciferase reporter and RNA pulldown assays. Subcellular distributions of TGF-β3 and let-7a-3p were determined by FISH. In this study, BMSCs were identified to possess the characteristics of mesenchymal stem cells. TGF-β3 was found to induce chondrogenic differentiation of BMSCs. Mechanically, TGF-β3 was verified to be targeted by let-7a-3p. In rescue assays, let-7a-3p overexpression reversed the effects of TGF-β3 overexpression on chondrogenic differentiation of BMSCs.

CONCLUSION

Let-7a-3p inhibits chondrogenic differentiation of bone marrow mesenchymal stem cells by targeting TGF-β3.

mTORC1 coordinates NF-κB signaling pathway to promote chondrogenic differentiation of tendon cells in heterotopic ossification

Heterotopic ossification (HO) is a pathological bone formation based on endochondral ossification distinguished by ossification within muscles, tendons, or other soft tissues. There has been growing studies focusing on the treatment with rapamycin to inhibit HO, but the mechanism of mTORC1 on HO remains unclear. Tendon cells (TDs) are the first cells to form during tendon heterotopic ossification. Here, we used an in vivo model of HO and an in vitro model of chondrogenesis induction to elucidate the effect and underlying mechanism of mTORC1 in HO. The current study highlights the effect of rapamycin on murine Achilles tenotomy-induced HO and the role of mTORC1 signaling pathway on TDs. Our result showed that mTORC1 was activation in the early stage of HO, whereas the mTORC1 maintained low expression in the mature ectopic cartilage tissue and the ectopic bone formation sites. The use of mTORC1-specific inhibitor (rapamycin) immediately after Achilles tendon injury could suppress the formation of HO; once ectopic cartilage and bone had formed, treatment with rapamycin could not significantly inhibit the progression of HO. Mechanistically, mTORC1 stimulation by silencing of TSC1 promoted the expression of the chondrogenic markers in TDs. In TDs, treated with mTORC1 stimulation by silencing of TSC1, mTORC1 increased the activation of the NF-κB signaling pathway. NF-κB selective inhibitor BAY11-7082 significantly suppressed the chondrogenesis of TDs that treated with mTORC1 stimulation by silencing of TSC1. Together, our findings demonstrated that mTORC1 promoted HO by regulating TDs chondrogenesis partly through the NF-κB signaling pathway; and rapamycin could be a viable HO therapeutic regimen.

RHOA inhibits chondrogenic differentiation of mesenchymal stem cells in adolescent idiopathic scoliosis

PURPOSE

The etiology of adolescent idiopathic scoliosis (AIS) remains unclear. The chondrogenic differentiation of mesenchymal stem cells (MSCs) is important in AIS, and the Ras homolog gene family member A (RHOA) is associated with chondrogenesis. The purpose of this study was to explore the effect of RHOA on the chondrogenic differentiation of MSCs in AIS.

METHODS

We isolated MSCs from patients with AIS (AIS MSCs) and individuals without AIS (control MSCs). The inhibitor Y27632 was used to inhibit the function of RHOA/ROCK signaling, and plasmid-based overexpression and siRNA-mediated knockdown were used to manipulate RHOA expression. CCK-8 was used to detect cell viability. The phosphorylation levels of LIMK1, MLC2 and cofilin were detected by Western blotting. The mRNA expression of aggrecan, SOX9, and COL2A1 were confirmed using RT-PCR. Immunofluorescence was used to analyze F-actin and collagen II. Alcian blue staining was performed to assess the secretion of glycosaminoglycans (GAGs).

RESULTS

We found that RHOA was significantly upregulated in AIS MSCs, and the phosphorylation levels of LIMK1, MLC2, and cofilin were increased. The mRNA expressions of aggrecan, SOX9, and COL2A1 were notably reduced in AIS MSCs. However, these effects were abolished by Y27632 treatment and RHOA knockdown in AIS MSCs. In addition, RHOA knockdown in AIS MSCs increased the content of collagen II and GAGs. RHOA overexpression in the control MSCs markedly activated the RHOA/ROCK signaling and decreased the expression of aggrecan, SOX9, and COL2A1, F-actin, and GAGs.

CONCLUSION

RHOA regulates the chondrogenic differentiation ability of MSCs in AIS via the RHOA/ROCK signaling pathway and this regulation may involve SOX9.

Fluvastatin promotes chondrogenic differentiation of adipose-derived mesenchymal stem cells by inducing bone morphogenetic protein 2

Background

Adipose-derived mesenchymal stem cells (ADMSCs) are a promising source of material source for medical regeneration of cartilage. Growth factors, including transforming growth factor-β (TGFβ) subfamily members and bone morphogenetic proteins (BMPs), play important roles in inducing and promoting chondrogenic differentiation of MSCs. However, these exogenous growth factors have some drawbacks related to their cost, biological half-life, and safety for clinical application. Several studies have reported that statins, the competitive inhibitors of 3-hydroxy-2-methylglutaryl coenzyme A (HMG-CoA) reductase, induce the expression of BMP2 in multiple cell types as the pleotropic effects. The objective of this study was to investigate the effects of fluvastatin during chondrogenic differentiation of human ADMSCs (hADMSCs).

Methods

The effects of fluvastatin were analyzed during chondrogenic differentiation of hADMSCs in the pellet culture without exogenous growth factors by qRT-PCR and histology. For functional studies, Noggin, an antagonist of BMPs, mevalonic acid (MVA) and geranylgeranyl pyrophosphate (GGPP), metabolites of the mevalonate pathway, ROCK inhibitor (Y27632), or RAC1 inhibitor (NSC23766) were applied to cells during chondrogenic differentiation. Furthermore, RhoA activity was measured by RhoA pulldown assay during chondrogenic differentiation with or without fluvastatin. Statistically significant differences between groups were determined by Student’s t-test or the Tukey–Kramer test.

Results

Fluvastatin-treated cells expressed higher levels of BMP2, SOX9, ACAN, and COL2A1 than control cells, and accumulated higher levels of glycosaminoglycans (GAGs). Noggin significantly inhibited the fluvastatin-mediated upregulation of ACAN and COL2A1. Both MVA and GGPP suppressed the effects of fluvastatin on the expressions of BMP2, SOX9, ACAN, and COL2A1. Furthermore, fluvastatin suppressed the RhoA activity, and inhibition of RhoA–ROCK signaling by Y27632 increased the expressions of BMP2, SOX9, ACAN, and COL2A1, as well as fluvastatin.

Conclusions

Our results suggest that fluvastatin promotes chondrogenic differentiation of hADMSCs by inducing endogenous BMP2, and that one of the mechanisms underlying the effects is inhibition of RhoA–ROCK signaling via suppression of GGPP. Fluvastatin is a safe and low-cost compound that holds promise for use in transplantation of hADMSCs for cartilage regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00600-7.

Irisin enhances chondrogenic differentiation of human mesenchymal stem cells via Rap1/PI3K/AKT axis

Background

Human mesenchymal stem cells (hMSCs) have been proven to have inherent chondrogenic differentiation potential, which appears to be used in cartilage regeneration. Increasing evidence suggests that irisin enhances osteoblast differentiation of MSCs, but little is known about its potential on chondrogenic differentiation.

Methods

In the study, we investigated the effects of irisin on chondrogenic differentiation of hMSCs using a high-density pellet culture system. The cartilage pellets were evaluated by morphology, and the metabolism of cartilage matrix was detected by qPCR, western blot and immunohistochemistry. Next, RNA-seq was performed to explore the underlying mechanism. Furthermore, using the transduction of plasmid, miRNAs mimics and inhibitor, the activation of Rap1/PI3K/AKT axis, the expression level of SIPA1L2, and the functional verification of miR-125b-5p were detected on day 7 of chondrogenic differentiation of hMSCs.

Results

Compared with the controls, we found that irisin treatment could significantly enhance the chondrogenic differentiation of hMSCs, enlarge the induced-cartilage tissue and up-regulate the expression levels of cartilage markers. RNA-seq indicated that irisin activated the Rap1 and PI3K/AKT signaling pathway, and the lower expression level of SIPA1L2 and the higher expression level of miR-125b-5p were found in irisin-treated group. Further, we found that irisin treatment could up-regulate the expression level of miR-125b-5p, targeting SIPA1L2 and consequently activating the Rap1/PI3K/AKT axis on the process of chondrogenic differentiation of hMSCs.

Conclusions

Collectively, our study reveals that irisin can enhance chondrogenic differentiation of hMSCs via the Rap1/PI3K/AKT pathway, suggesting that irisin possesses prospects in cartilage regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03092-8.

Supplementation of articular cartilage-derived chondroprogenitors with bone morphogenic protein-9 enhances chondrogenesis without affecting hypertrophy

INTRODUCTION

Chondroprogenitors (CPCs) have emerged as a promising cellular therapy for cartilage-related pathologies due to their inherent primed chondrogenic potential. Studies report that the addition of growth factors such as parathyroid hormone (PTH) and Bone Morphogenic Protein (BMP) enhance the chondroinducive potential in chondrocytes and mesenchymal stem cells. This study evaluated if supplementation of the standard culture medium for cell expansion with 1-34 PTH and BMP-9 would enhance the chondrogenic potential of CPCs and reduce their hypertrophic tendency.

METHODS

Human chondrocytes were isolated from patients undergoing total knee replacement for osteoarthritis (n = 3). Following fibronectin adhesion assay, passage 1 CPCs were divided and further expanded under three culture conditions (a) control, i.e., cells continued under standard culture conditions, (b) 1-34 PTH group, additional intermittent 6 h exposure with 1-34 PTH and (c) BMP-9 group, additional BMP-9 during culture expansion. All the groups were evaluated for population-doubling, cell cycle analysis, surface marker and gene expression for chondrogenesis, hypertrophy, multilineage differentiation and GAG (glycosaminoglycan)/DNA following chondrogenic differentiation.

RESULTS

Concerning growth kinetics, the BMP-9 group exhibited a significantly lower S-phase and population-doubling when compared to the other two groups. Qualitative analysis for chondrogenic potential (Alcian blue, Safranin O staining and Toluidine blue for GAG) revealed that the BMP-9 group exhibited the highest uptake. The BMP-9 group also showed significantly higher COL2A1 expression than the control group, with no change in the hypertrophy marker expression.

CONCLUSION

BMP-9 can potentially be used as an additive for CPCs expansion, to enhance their chondrogenic potential without affecting their low hypertrophic tendency. The mitigating effects of 1-34PTH on hypertrophy would benefit further investigation when used in combination with BMP-9 to enhance chondrogenesis whilst reducing hypertrophy.

Adaptation of the protein translational apparatus during ATDC5 chondrogenic differentiation

Introduction

Ribosome biogenesis is integrated with many cellular processes including proliferation, differentiation and oncogenic events. Chondrogenic proliferation and differentiation require a high cellular translational capacity to facilitate cartilaginous extracellular matrix production. We here investigated the expression dynamics of factors involved in ribosome biogenesis during in vitro chondrogenic differentiation and determined whether protein translation capacity adapts to different phases of chondrogenic differentiation.

Materials

SnoRNA expression during ATDC5 differentiation was analyzed by RNA sequencing of samples acquired from day 0 (progenitor stage), 7 (chondrogenic stage) and day 14 (hypertrophic stage). RT-qPCR was used to determine expression of fibrillarin, dyskerin, UBF-1, Sox9, Col2a1, Runx2, Col10a1 mRNAs and 18S, 5.8S and 28S rRNAs. Protein expression of fibrillarin, dyskerin and UBF-1 was determined by immunoblotting. Ribosomal RNA content per cell was determined by calculating rRNA RT-qPCR signals relative to DNA content (SYBR Green assay). Total protein translational activity was evaluated with a puromycilation assay and polysome profiling.

Results

As a result of initiation of chondrogenic differentiation (Δt0-t7), 21 snoRNAs were differentially expressed (DE). Hypertrophic differentiation caused DE of 23 snoRNAs (Δt7-t14) and 43 when t0 was compared to t14. DE snoRNAs, amongst others, target nucleotide modifications in the 28S rRNA peptidyl transferase center and the 18S rRNA decoding center. UBF-1, fibrillarin and dyskerin expression increased as function of differentiation and displayed highest fold induction at day 5-6 in differentiation. Ribosomal RNA content per cell was significantly increased at day 7, but not at day 14 in differentiation. Similar dynamics in translational capacity and monosomal ribosome fraction were observed during differentiation.

Conclusion

The expression of a great number of ribosome biogenesis factors is altered during chondrogenic differentiation of ATDC5 cells, which is accompanied by significant changes in cellular translational activity. This elucidation of ribosome biogenesis dynamics in chondrogenic differentiation models enables the further understanding of the role of ribosome biogenesis and activity during chondrocyte cell commitment and their roles in human skeletal development diseases.

Human integrin α10β1-selected mesenchymal stem cells home to cartilage defects in the rabbit knee and assume a chondrocyte-like phenotype

BACKGROUND

Mesenchymal stem cells (MSCs) have shown promising results in stimulating cartilage repair and in the treatment of osteoarthritis (OA). However, the fate of the MSCs after intra-articular injection and their role in cartilage regeneration is not clear. To address these questions, this study investigated (1) homing of labeled human adipose tissue derived integrin α10β1-selected MSCs (integrin α10-MSCs) to a cartilage defect in a rabbit model and (2) the ability of the integrin α10-MSCs to differentiate to chondrocytes and to produce cartilage matrix molecules in vivo.

DESIGN

Integrin α10-MSCs were labeled with superparamagnetic iron oxide nanoparticles (SPIONs) co-conjugated with Rhodamine B to allow visualization by both MRI and fluorescence microscopy. A cartilage defect was created in the articular cartilage of the intertrochlear groove of the femur of rabbits. Seven days post-surgery, labeled integrin α10-MSCs or vehicle were injected into the joint. Migration and distribution of the SPION-labeled integrin α10-MSCs was evaluated by high-field 9.4 T MRI up to 10 days after injection. Tissue sections from the repair tissue in the defects were examined by fluorescence microscopy.

RESULTS

In vitro characterization of the labeled integrin α10-MSCs demonstrated maintained viability, proliferation rate and trilineage differentiation capacity compared to unlabeled MSCs. In vivo MRI analysis detected the labeled integrin α10-MSCs in the cartilage defects at all time points from 12 h after injection until day 10 with a peak concentration between day 1 and 4 after injection. The labeled MSCs were also detected lining the synovial membrane at the early time points. Fluorescence analysis confirmed the presence of the labeled integrin α10-MSCs in all layers of the cartilage repair tissue and showed co-localization between the labeled cells and the specific cartilage molecules aggrecan and collagen type II indicating in vivo differentiation of the MSCs to chondrocyte-like cells. No adverse effects of the α10-MSC treatment were detected during the study period.

CONCLUSION

Our results demonstrated migration and homing of human integrin α10β1-selected MSCs to cartilage defects in the rabbit knee after intra-articular administration as well as chondrogenic differentiation of the MSCs in the regenerated cartilage tissue.

Integrated regulation of chondrogenic differentiation in mesenchymal stem cells and differentiation of cancer cells

Chondrogenesis is the formation of chondrocytes and cartilage tissues and starts with mesenchymal stem cell (MSC) recruitment and migration, condensation of progenitors, chondrocyte differentiation, and maturation. The chondrogenic differentiation of MSCs depends on co-regulation of many exogenous and endogenous factors including specific microenvironmental signals, non-coding RNAs, physical factors existed in culture condition, etc. Cancer stem cells (CSCs) exhibit self-renewal capacity, pluripotency and cellular plasticity, which have the potential to differentiate into post-mitotic and benign cells. Accumulating evidence has shown that CSCs can be induced to differentiate into various benign cells including adipocytes, fibrocytes, osteoblast, and so on. Retinoic acid has been widely used in the treatment of acute promyelocytic leukemia. Previous study confirmed that polyploid giant cancer cells, a type of cancer stem-like cells, could differentiate into adipocytes, osteocytes, and chondrocytes. In this review, we will summarize signaling pathways and cytokines in chondrogenic differentiation of MSCs. Understanding the molecular mechanism of chondrogenic differentiation of CSCs and cancer cells may provide new strategies for cancer treatment.

Distinctive Roles of Wnt Signaling in Chondrogenic Differentiation of BMSCs under Coupling of Pressure and Platelet-Rich Fibrin

BACKGROUND

Although newly formed constructs of feasible pressure-preadjusted bone marrow mesenchymal stem cells (BMSCs) and platelet-rich fibrin (PRF) showed biomechanical flexibility and superior capacity for cartilage regeneration, it is still not very clear how BMSCs and seed cells feel mechanical stimuli and convert them into biological signals, and the difference in signal transduction underlying mechanical and chemical cues is also unclear.

METHODS

To determine whether mechanical stimulation (hydrostatic pressure) and chemical cues (platelet-rich fibrin, PRF) activate canonical or noncanonical Wnt signaling in BMSCs, BMSCs cocultured with PRF were subjected to hydrostatic pressure loading, and the activation of the Wnt signaling molecules and expression of cartilage-associated proteins and genes were determined by western blotting and polymerase chain reaction (PCR). Inhibitors of canonical or noncanonical Wnt signaling, XVX-939 or L690,330, were adopted to investigate the role of Wnt signaling molecules in mechanically promoted chondrogenic differentiation of BMSCs.

RESULTS

Hydrostatic pressure of 120 kPa activated both Wnt/β-catenin signaling and Wnt/Ca²⁺ signaling, with the the maximum promotion effect at 60 min. PRF exerted no synergistic effect on Wnt/β-catenin signaling activation. However, the growth factors released by PRF might reverse the promotion effects of pressure on Wnt/Ca²⁺ signaling. Real-time PCR and Western blotting results showed that pressure could activate the expression of Col-II, Sox9, and aggrecan in BMSCs cocultured with PRF. Blocking experiment found a positive role of Wnt/β-catenin signaling, and a negative role of Wnt/Ca²⁺ signaling in chondrogenic differentiation of the BMSCs. Mutual inhibition exists between canonical and noncanonical Wnt signaling in BMSCs under pressure.

CONCLUSION

Wnt signaling participates in the pressure-promoted chondrogenesis of the BMSCs co-cultured with PRF, with canonical and noncanonical pathways playing distinct roles during the process.

Pre-culture of human mesenchymal stromal cells in spheroids facilitates chondrogenesis at a low total cell count upon embedding in biomaterials to generate cartilage microtissues

Material-assisted cartilage tissue engineering has limited application in cartilage treatment due to hypertrophic tissue formation and high cell counts required. This study aimed at investigating the potential of human mesenchymal stromal cell (hMSC) spheroids embedded in biomaterials to study the effect of biomaterial composition on cell differentiation. Pre-cultured (3 days, chondrogenic differentiation media) spheroids (250 cells/spheroid) were embedded in tyramine-modified hyaluronic acid (THA) and collagen type I (Col) composite hydrogels (four combinations of THA (12.5 vs 16.7 mg/ml) and Col (2.5 vs 1.7 mg/ml) content) at a cell density of 5 × 10⁶ cells/ml (2 × 10⁴ spheroids/ml). Macropellets derived from single hMSCs (2.5 × 10⁵ cells, ScMP) or hMSC spheroids (2.5 × 10⁵ cells, 10³ spheroids, SpMP) served as control. hMSC differentiation was analyzed using glycosaminoglycan (GAG) quantification, gene expression analysis and (immuno-)histology. Embedding of hMSC spheroids in THA-Col induced chondrogenic differentiation marked by upregulation of aggrecan (ACAN) and COL2A1, and the production of GAGs . Lower THA led to more pronounced chondrogenic phenotype compared to higher THA content. Col content had no significant influence on hMSC chondrogenesis. Pellet cultures showed an upregulation in chondrogenic-associated genes and production of GAGs with less upregulation of hypertrophic-associated genes in SpMP culture compared to ScMP group. This study presents hMSC pre-culture in spheroids as promising approach to study chondrogenic differentiation after biomaterial encapsulation at low total cell count (5 × 10⁶/ml) without compromising chondrogenic matrix production. This approach can be applied to assemble microtissues in biomaterials to generate large cartilage construct. STATEMENT OF SIGNIFICANCE: In vitro studies investigating the chondrogenic potential of biomaterials are limited due to the low cell-cell contact of encapsulated single cells. Here, we introduce the use of pre-cultured hMSC spheroids to study chondrogenesis upon encapsulation in a biomaterial. The use of spheroids takes advantage of the high cell-cell contact within each spheroid being critical in the early chondrogenesis of hMSCs. At a low seeding density of 5·10⁶ cells/ml (2 × 10⁴ spheroids/ml) we demonstrated hMSC chondrogenesis and cartilaginous matrix deposition. Our results indicate that the pre-culture might have a beneficial effect on hypertrophic gene expression without compromising chondrogenic differentiation. This approach has shown potential to assemble microtissues (here spheroids) in biomaterials to generate large cartilage constructs and to study the effect of biomaterial composition on cell alignment and migration.

Isolation and Culture of Cranial Neural Crest Cells from the First Branchial Arch of Mice

Craniofacial anomalies (CFA) are a diverse group of deformities, which affect the growth of the head and face. Dysregulation of cranial neural crest cell (NCC) migration, proliferation, differentiation, and/or cell fate specification have been reported to contribute to CFA. Understanding of the mechanisms through which cranial NCCs contribute for craniofacial development may lead to identifying meaningful clinical targets for the prevention and treatment of CFA. Isolation and culture of cranial NCCs in vitro facilitates screening and analyses of molecular cellular mechanisms of cranial NCCs implicated in craniofacial development. Here, we present a method for the isolation and culture of cranial NCCs harvested from the first branchial arch at early embryonic stages. Morphology of isolated cranial NCCs was similar to O9-1 cells, a cell line for neural crest stem cells. Moreover, cranial NCCs isolated from a transgenic mouse line with enhanced bone morphogenetic protein (BMP) signaling in NCCs showed an increase in their chondrogenic differentiation capacity, suggesting maintenance of their in vivo differentiation potentials observed in vitro. Taken together, our established method is useful to visualize cellular behaviors of cranial NCCs.

MiR-539-3p inhibited chondrogenic differentiation in human adipose stem cells by targeting Sox9

Background

Mesenchymal stem cells (MSCs) have emerged as the attractive candidates for cell therapy for cartilage repair in clinical therapy of osteoarthritis (OA). MiR-539-3p was reported to differentially express during chondrogenic differentiation of adipose stem cells (ASCs) by miRNA microarrays. The aim of the study was to investigate the effects and underlying mechanisms of miR-539-3p on chondrogenic differentiation of ASCs.

Methods

Human ASCs (hASCs) were obtained from liposuction and transfected with miR-539-3p mimic or inhibitor. Then, the cells were cultured in chondrogenic differentiation medium including transforming growth factor-β1 (TGF-β1).

Results

Our results found that miR-539-3p was gradually down-regulated during chondrogenic differentiation of hASCs. MiR-539-3p overexpression inhibited TGF-β1-induced chondrogenic differentiation of hASCs, as supported by reducing the gene and protein expression of chondrogenic differentiation markers type II collagen alpha 1 (COL2A1), aggrecan (ACAN), and type II collagen. In contrast, miR-539-3p inhibitor significantly promoted the chondrogenic differentiation of hASCs. Dual luciferase reporter assay demonstrated that Sox9 was a direct target gene of miR-539-3p. The expression of SRY-box transcription factor 9 (Sox9) was up-regulated progressively over time during chondrogenic differentiation of hASCs. Additionally, Sox9 overexpression notably reversed chondrogenic differentiation of hASCs inhibited by miR-539-3p mimic, as demonstrated by the decreased expression of COL2A1, ACAN, and type II collagen.

Conclusions

Altogether, miR-539-3p inhibited chondrogenic differentiation of hASCs by targeting Sox9. MiR-539-3p may have significant clinical applications for use as a targeted therapy of OA.

Next-Generation Sequencing of Circular RNAs Reveals the Molecular Mechanisms of Chondrogenic Differentiation in Human Adipose-derived Stem Cells

Adipose-derived stem cells are one of the potential sources of cells for the treatment of cartilage defects. This study aimed to investigate the molecular mechanisms that account for the chondrogenic differentiation of human adipose-derived stem cells (hADSCs). We employed integrin β1 (ITGB1) overexpression to induce chondrogenic differentiation of hADSCs. Next-generation sequencing was used to determine the mRNAs and circular RNAs (circRNAs) expression profiles in ITGB1-overexpresing and negative control cells. The potential functions of differentially expressed mRNAs were analyzed using the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses. Moreover, differentially expressed circRNAs with the greatest fold change were validated by polymerase chain reaction (PCR), Sanger sequencing, and quantitative real-time PCR (qRT-PCR). These three circRNAs and their downstream microRNAs and mRNAs were used to construct a circRNA-microRNA-mRNA interaction network. The results showed that we identified 713 differentially expressed circRNAs (150 upregulated and 563 downregulated in ITGB1-overexpressing hADSCs versus negative control cells, respectively). Meanwhile, 2383 mRNAs were differentially expressed between two groups (1672 upregulated and 711 downregulated in ITGB1-overexpressing cells compared with the negative control cells). The GO and KEGG analysis results showed that the differentially expressed mRNAs were enriched in biological processes, cellular components, and molecular functions, especially in the phosphatidylinositol 3-kinase (PI3K)-AKT and mitogen-activated protein kinase signaling pathways. Three differentially expressed circRNAs, including hsa_circ_0071127, hsa_circ_0008637, and hsa_circ_0020028, were validated by qRT-PCR. Moreover, the circRNA-microRNA-mRNA network predicted that fibroblast growth factor 2 (FGF2) was a common node regulated by these three circRNAs through several microRNAs, including miR-195-3p, miR-205-3p, and miR-152-3p. We further found that the knockdown of hsa_circ_0020028, but not the two other circRNAs, significantly reduced FGF2 mRNA expression in hADSCs. Furthermore, the knockdown of hsa_circ_0020028 significantly inhibited the protein expression of FGF2, chondrogenic differentiation markers (COL II, aggrecan, and SOX9), and PI3K/AKT signaling in ITGB1-overexpressing hADSCs. This study uncovered the differentially expressed mRNA and circRNA profiles in the chondrogenic differentiation of hADSCs induced by ITGB1 overexpression. Our findings demonstrate that hsa_circ_0020028 regulates the ITGB1 overexpression-mediated chondrogenic differentiation of hADSCs through regulation of FGF2-related signaling pathways.

Comparison of the Infant and Adult Adipose-Derived Mesenchymal Stem Cells in Proliferation, Senescence, Anti-oxidative Ability and Differentiation Potential

BACKGROUND

Infant adipose-derived mesenchymal stem cells (ADSCs) collected from excised polydactyly fat tissue, which was surgical waste, could be cultured and expanded in vitro in this study. In addition, the collecting process would not cause pain in the host. In this study, the proliferation, reduction of senescence, anti-oxidative ability, and differentiation potential in the infant ADSCs were compared with those in the adult ADSCs harvested from thigh liposuction to determine the availability of infant ADSCs.

METHODS

Proliferation was determined by detecting the fold changes in cell numbers and doubling time periods. Senescence was analyzed by investigating the age-related gene expression levels and the replicative stress. The superoxide dismutase (SOD) gene expression, adipogenic, neurogenic, osteogenic, and tenogenic differentiation were compared by RT-qPCR. The chondrogenic differentiation efficiency was also determined using RT-qPCR and immunohistochemical staining.

RESULTS

The proliferation, SOD (SOD1, SOD2 and SOD3) gene expression, the stemness-related gene (c-MYC) and telomerase reverse transcriptase of the infant ADSCs at early passages were enhanced compared with those of the adults'. Cellular senescence related genes, including p16, p21 and p53, and replicative stress were reduced in the infant ADSCs. The adipogenic genes (PPARγ and LPL) and neurogenic genes (MAP2 and NEFH) of the infant ADSC differentiated cells were significantly higher than those of the adults' while the expression of the osteogenic genes (OCN and RUNX) and tenogenic genes (TNC and COL3A1) of both demonstrated opposite results. The chondrogenic markers (SOX9, COL2 and COL10) were enhanced in the infant ADSC differentiated chondrogenic pellets, and the expression levels of SODs were decreased during the differentiation process.

CONCLUSION

Cultured infant ADSCs demonstrate less cellular senescence and replicative stress, higher proliferation rates, better antioxidant defense activity, and higher potential of chondrogenic, adipogenic and neurogenic differentiation.

Folic acid pretreatment and its sustained delivery for chondrogenic differentiation of MSCs

Dietary uptake of folic acid (FA) improves cartilage regeneration. In this work, we discovered that three days of FA treatment is highly effective for promoting chondrogenic differentiation of tonsil-derived mesenchymal stem cells (TMSCs). In a three-dimensional pellet culture, the levels of typical chondrogenic biomarkers, sulfated glycosaminoglycan, proteoglycan, type II collagen (COL II), SRY box transcription factor 9 (SOX 9), cartilage oligomeric matrix protein (COMP), and aggrecan (ACAN) increased significantly in proportion to FA concentration up to 30 μM. At the mRNA expression level, COL II, SOX 9, COMP, and ACAN increased 3.6-6.0-fold with FA treatment at 30 μM compared with the control system that did not receive FA treatment, and the levels with FA treatment were 1.6-2.5 times greater than those in the kartogenin-treated positive control system. FA treatment did not increase type I collagen α1 (COL I α1), an osteogenic biomarker which is a concern with most chondrogenic promoters. At the high FA concentration of 100 μM, significant decreases in chondrogenic biomarkers were observed, which might be related to DNA methylation. A thermogel system incorporating TMSCs and FA provided sustained release of FA over several days, similar to the FA treatment. The thermogel system confirmed the efficacy of FA in promoting chondrogenic promotion of TMSCs. The increased nuclear translocation of core-binding factor β subunit (CBFβ) and the runt-related transcription factor 1 (RUNX1) expression after FA treatment, together with molecular docking studies, suggest that the chondrogenic enhancement mechanism of FA is mediated by CBFβ and RUNX1.

Caspase-9 inhibition decreases expression of Mmp9 during chondrogenesis

Besides cell death, caspase-9 participates in non-apoptotic events, including cell differentiation. To evaluate a possible impact on the expression of chondrogenic/osteogenic factors, a caspase-9 inhibitor was tested in vitro. For this purpose, mouse forelimb-derived micromass cultures, the most common chondrogenic in vitro model, were used. The following analyses were performed based on polymerase chain reaction (PCR) arrays and real-time PCR. The expression of several chondrogenesis-related genes was shown to be altered, some of which may impact chondrogenic differentiation (Bmp4, Bmp7, Sp7, Gli1), mineral deposition (Alp, Itgam) or the remodelling of the extracellular matrix (Col1a2, Mmp9) related to endochondral ossification. From the cluster of genes with altered expression, Mmp9 showed the most significant decrease in expression, of more than 50-fold. Additionally, we determined the possible impact of caspase-9 downregulation on the expression of other Mmp genes. A mild increase in Mmp14 was observed, but there was no change in the expression of other studied Mmp genes (-2, -3, -8, -10, -12, -13). Interestingly, inhibition of Mmp9 in micromasses led to decreased expression of some chondrogenic markers related to caspase-9. These samples also showed a decreased expression of caspase-9 itself, suggesting a bidirectional regulation of these two enzymes. These results indicate a specific impact of caspase-9 inhibition on the expression of Mmp9. The localisation of these two enzymes overlaps in resting, proliferative and pre-hypertrophic chondrocytes during in vivo development, which supports their multiple functions, either apoptotic or non-apoptotic. Notably, a coincidental expression pattern was identified in Pik3cg, a possible candidate for Mmp9 regulation.

Novel nanocomposite scaffold based on gelatin/PLGA-PEG-PLGA hydrogels embedded with TGF-β1 for chondrogenic differentiation of human dental pulp stem cells in vitro

In the current study, a novel nanocomposite hydrogel scaffold comprising of natural-based gelatin and synthetic-based (poly D, L (lactide-co-glycolide) -b- poly (ethylene glycol)-b- poly D, L (lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymer was developed and loaded with transforming growth factor- β1 (TGF-β1). Synthesized scaffolds' chemical structure was examined by ¹H NMR and ATR-FTIR. Scanning electron microscopy (SEM) confirmed particle size and morphology of the prepared nanoparticles as well as the scaffolds. The morphology analysis revealed a porous interconnected structure throughout the scaffold with a pore size dimension of about 202.05 µm. The swelling behavior, in vitro degradation, mechanical properties, density, and porosity were also evaluated. Phalloidin/DAPI staining was utilized for confirming the extended cytoskeleton of the chondrocytes. Alcian blue staining was conducted to determine cartilaginous matrix sulfated glycosaminoglycan (sGAG) synthesis. Eventually, over a period of 21 days, a real-time RT-PCR analysis was applied to measure the mRNA expression of chondrogenic marker genes, type-II collagen, SOX 9, and aggrecan, in hDPSCs cultured for up to 21 days to study the influence of gelatin/PLGA-PEG-PLGA-TGF-β1 hydrogels on hDPSCs. The findings of the cell-encapsulating hydrogels analysis suggested that the adhesion, viability, and chondrogenic differentiation of hDPSCs improved by gelatin/PLGA-PEG-PLGA-TGF-β1 nanocomposite hydrogels. These data supported the conclusion that gelatin/PLGA-PEG-PLGA-TGF-β1 nanocomposite hydrogels render the features that allow thein vitrofunctionality of encapsulated hDPSCs and hence can contribute the basis for new effective strategies for the treatment of cartilage injuries.

Precision 3D printed meniscus scaffolds to facilitate hMSCs proliferation and chondrogenic differentiation for tissue regeneration

Background

The poor regenerative capability and structural complexity make the reconstruction of meniscus particularly challenging in clinic. 3D printing of polymer scaffolds holds the promise of precisely constructing complex tissue architecture, however the resultant scaffolds usually lack of sufficient bioactivity to effectively generate new tissue.

Results

Herein, 3D printing-based strategy via the cryo-printing technology was employed to fabricate customized polyurethane (PU) porous scaffolds that mimic native meniscus. In order to enhance scaffold bioactivity for human mesenchymal stem cells (hMSCs) culture, scaffold surface modification through the physical absorption of collagen I and fibronectin (FN) were investigated by cell live/dead staining and cell viability assays. The results indicated that coating with fibronectin outperformed coating with collagen I in promoting multiple-aspect stem cell functions, and fibronectin favors long-term culture required for chondrogenesis on scaffolds. In situ chondrogenic differentiation of hMSCs resulted in a time-dependent upregulation of SOX9 and extracellular matrix (ECM) assessed by qRT-PCR analysis, and enhanced deposition of collagen II and aggrecan confirmed by immunostaining and western blot analysis. Gene expression data also revealed 3D porous scaffolds coupled with surface functionalization greatly facilitated chondrogenesis of hMSCs. In addition, the subcutaneous implantation of 3D porous PU scaffolds on SD rats did not induce local inflammation and integrated well with surrounding tissues, suggesting good in vivo biocompatibility.

Conclusions

Overall, this study presents an approach to fabricate biocompatible meniscus constructs that not only recapitulate the architecture and mechanical property of native meniscus, but also have desired bioactivity for hMSCs culture and cartilage regeneration. The generated 3D meniscus-mimicking scaffolds incorporated with hMSCs offer great promise in tissue engineering strategies for meniscus regeneration.

Graphical Abstract

Enhancing chondrogenic potential via mesenchymal stem cell sheet multilayering

Advanced tissue engineering approaches for direct articular cartilage replacement in vivo employ mesenchymal stem cell (MSC) sources, exploiting innate chondrogenic potential to fabricate hyaline-like constructs in vitro within three-dimensional (3D) culture conditions. Cell sheet technology represents one such advanced 3D scaffold-free cell culture platform, and previous work has shown that 3D MSC sheets are capable of in vitro hyaline-like chondrogenic differentiation. The present study aims to build upon this understanding and elucidate the effects of an established cell sheet manipulation technique, cell sheet multilayering, on fabrication of MSC-derived hyaline-like cartilage 3D layered constructs in vitro. To achieve this goal, multilayered MSC sheets are prepared and assessed for structural and biochemical transitions throughout chondrogenesis. Results support MSC multilayering as a means of increasing construct thickness and 3D cellular interactions related to in vitro chondrogenesis, including N-cadherin, connexin 43, and integrin β-1. Data indicate that increasing construct thickness from 14 μm (1-layer construct) to 25 μm (2-layer construct) increases these cellular interactions and subsequent in vitro MSC chondrogenesis. However, a clear initial thickness threshold (33 μm - 3-layer construct) is evident that decreases the rate and extent of in vitro chondrogenesis, specifically chondrogenic gene expressions (Sox9, aggrecan, type II collagen) and sulfated proteoglycan accumulation in deposited extracellular matrix (ECM). Together, these data support the utility of cell sheet multilayering as a platform for tailoring construct thickness and subsequent MSC chondrogenesis for future articular cartilage regeneration applications.

Stem cells immortalized by hTERT perform differently from those immortalized by SV40LT in proliferation, differentiation, and reconstruction of matrix microenvironment

Although matrix microenvironment has the potential to improve expanded stem cell proliferation and differentiation capacity, decellularized extracellular matrix (dECM) deposited by senescent cells does not contribute to the rejuvenation of adult stem cells, which has become a barrier to personalized stem cell therapy. Genetic modification is an effective strategy to protect cells from senescence but it carries the increased risk of malignant transformation and genetic instability. In this study, lentivirus carrying either human telomerase reverse transcriptase (hTERT) or simian virus 40 large T antigen (SV40LT) was used to transduce human infrapatellar fat pad-derived stem cells (IPFSCs). We found that virus transduction modified the proliferative, chondrogenic, and adipogenic abilities of IPFSCs. Interestingly, dECM deposited by immortalized cells significantly influenced replicative senescent IPFSCs in proliferation and differentiation preference, the effect of which is hinged on the approach of immortalization using either SV40LT or hTERT. Our findings indicate both dECM expansion and immortalization strategies can be used for replicative senescent adult stem cells' proliferation and lineage-specific differentiation, which benefits future stem cell-based tissue regeneration. This approach may also work for adult stem cells with premature senescence in elderly/aged patients, which needs further investigation. STATEMENT OF SIGNIFICANCE: Adult stem cells are a promising solution for autologous cell-based therapy. Unfortunately, cell senescence due to donor age and/or ex vivo expansion prevents clinical application. Recent progress with decellularized extracellular matrix provides a potential for the rejuvenation of senescent stem cells by improving their proliferation and differentiation capacities. Given the fact that the young matrix can provide a healthy and energetic microenvironment, in this study, two approaches using lentivirus transduction of hTERT and SV40LT were compared. The goal was to immortalize donor cells for deposition of decellularized extracellular matrix. The matrix was demonstrated to contribute diverging effects on the chondrogenic and adipogenic differentiation of expanded stem cells and exhibited proliferation benefits as well. These findings provide an invaluable asset for stem cell-based tissue regeneration.

Tetrahedral framework nucleic acids promote the biological functions and related mechanism of synovium-derived mesenchymal stem cells and show improved articular cartilage regeneration activity in situ

Many recent studies have shown that joint-resident mesenchymal stem cells (MSCs) play a vital role in articular cartilage (AC) in situ regeneration. Specifically, synovium-derived MSCs (SMSCs), which have strong chondrogenic differentiation potential, may be the main driver of cartilage repair. However, both the insufficient number of MSCs and the lack of an ideal regenerative microenvironment in the defect area will seriously affect the regeneration of AC. Tetrahedral framework nucleic acids (tFNAs), notable novel nanomaterials, are considered prospective biological regulators in biomedical engineering. Here, we aimed to explore whether tFNAs have positive effects on AC in situ regeneration and to investigate the related mechanism. The results of in vitro experiments showed that the proliferation and migration of SMSCs were significantly enhanced by tFNAs. In addition, tFNAs, which were added to chondrogenic induction medium, were shown to promote the chondrogenic capacity of SMSCs by increasing the phosphorylation of Smad2/3. In animal models, the injection of tFNAs improved the therapeutic outcome of cartilage defects compared with that of the control treatments without tFNAs. In conclusion, this is the first report to demonstrate that tFNAs can promote the chondrogenic differentiation of SMSCs in vitro and enhance AC regeneration in vivo, indicating that tFNAs may become a promising therapeutic for AC regeneration.

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Tetrahedral framework nucleic acids (tFNAs) can promote SMSCs proliferation by activating the Wnt/β-catenin pathway.

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tFNAs can promote SMSCs migration in vitro and vivo.

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tFNAs can promote SMSCs chondrogenic differentiation by regulating the TGF/Smad2/3 signaling pathway.

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tFNAs show improved articular cartilage in situ regeneration activity in vivo.

Restoration of 5-methoxytryptophan protects against atherosclerotic chondrogenesis and calcification in ApoE-/- mice fed high fat diet

Background

Toll-like receptor-2 (TLR2) promotes vascular smooth muscle cell (VSMC) transdifferentiation to chondrocytes and calcification in a p38 MAPK-dependent manner. Vascular 5-methoxytryptophan (5-MTP) is a newly identified factor with anti-inflammatory actions. As 5-MTP targets p38 MAPK for its actions, we postulated that 5-MTP protects against vascular chondrogenesis and calcification.

Methods

High-fat diet-induced advanced atherosclerosis in mice were performed to investigate the effect of 5-MTP on atherosclerotic lesions and calcification. VSMCs were used to determine the role of 5-MTP in VSMC chondrogenic differentiation and calcification. Alizarin red S and Alcian blue staining were used to measure VSMC calcification and chondrogenic differentiation, respectively.

Results

5-MTP was detected in aortic tissues of ApoE^−/− mice fed control chow. It was reduced in ApoE^−/− mice fed high-fat diet (HFD), but was restored in ApoE^−/−Tlr2^−/− mice, suggesting that HFD reduces vascular 5-MTP production via TLR2. Intraperitoneal injection of 5-MTP or its analog into ApoE^−/− mice fed HFD reduced aortic atherosclerotic lesions and calcification which was accompanied by reduction of chondrogenesis and calcium deposition. Pam3CSK4 (Pam3), ligand of TLR2, induced SMC phenotypic switch to chondrocytes. Pretreatment with 5-MTP preserved SMC contractile proteins and blocked Pam3-induced chondrocyte differentiation and calcification. 5-MTP inhibited HFD-induced p38 MAPK activation in vivo and Pam3-induced p38 MAPK activation in SMCs. 5-MTP suppressed HFD-induced CREB activation in aortic tissues and Pam3-induced CREB and NF-κB activation in SMCs.

Conclusions

These findings suggest that 5-MTP is a vascular arsenal against atherosclerosis and calcification by inhibiting TLR2–mediated SMC phenotypic switch to chondrocytes and the consequent calcification. 5-MTP exerts these effects by blocking p38 MAPK activation and inhibiting CREB and NF-κB transactivation activity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00771-1.

LncRNA NONHSAT030515 promotes the chondrogenic differentiation of human adipose-derived stem cells via regulating the miR-490-5p/BMPR2 axis

BACKGROUND

Chondrogenic differentiation of human adipose-derived stem cells (hADSCs) is important for cartilage generation and degradation. LncRNAs play an essential role in stem cell differentiation. However, the role and mechanism of lncRNA in hADSCs remain unclear. Our previous study showed that miR-490-5p was downregulated during chondrogenic differentiation of hADSCs. In this study, we investigated the effect and mechanism of lncRNA NONHSAT030515 interacting with miR-490-5p on chondrogenic differentiation of hADSCs.

METHODS

Alcian blue staining was used to assess the deposition of chondromatrix proteins following chondrogenic differentiation of human adipose stem cells. Immunohistochemistry was used to evaluate the expression of collagenII. TargetScan, miRTarBase and miRDB database analyses were applied to find the miRNA and target genes of lncRNA NONHSAT030515. A dual luciferase experiment was conducted to identify the direct target of NONHSAT030515. pcDNA3.1- NONHSAT030515 transfection and sh- NONHSAT030515 treatment were conducted to verify the role of lncRNA NONHSAT030515 in chondrogenic differentiation. The levels of Aggrecan, SOX9 and COL2A1 were analyzed by qRT-PCR and Western blot assay.

RESULTS

Alcian blue staining, immunocytochemical, qRT-PCR, and Western blot have determined that lncRNA NONHSAT030515 can promote the chondrogenic differentiation of hADSCs. MiR-490- 5p was the direct target of NONHSAT030515, while BMPR2 was the target gene. This result was confirmed by luciferase reporter assay. Up-regulation of NONHSAT030515 promoted BMPR2 protein expression and promoted chondrogenic differentiation, whereas down-regulation of NONHSAT030515 caused completely opposite results.

CONCLUSION

LncRNA NONHSAT030515 promotes the chondrogenic differentiation of hADSCs through increasing BMPR2 expression by regulating miR-490- 5p.