Thyroid hormone-induced hypertrophy in mesenchymal stem cell chondrogenesis is mediated by bone morphogenetic protein-4

SOX9 haploinsufficiency reveals SOX9-Noggin interaction in BMP-SMAD signaling pathway in chondrogenesis

Campomelic Dysplasia (CD) is a rare congenital disease caused by haploinsufficiency (HI) in SOX9. Patients with CD typically present with skeletal abnormalities and 75% of them have sex reversal. In this study, we use CRISPR/Cas9 to generate a human induced pluripotent stem cell (hiPSC) model from a heathy male donor, based on a previously reported SOX9 splice site mutation in a CD patients. This hiPSCs-derived chondrocytes from heterozygotes (HT) and homozygotes (HM) SOX9 mutation carriers showed significant defects in chondrogenesis. Bulk RNA profiling revealed that the BMP-SMAD signaling pathway, ribosome-related, and chromosome segregation-related gene sets were altered in the HT chondrocytes. The profile also showed significant noggin upregulation in CD chondrocytes, with ChIP-qPCR confirming that SOX9 binds to the distal regulatory element of noggin. This suggests SOX9 plays a feedback role in the BMP signaling pathway by modulating noggin expression rather than acting solely as a downstream regulator. This provides further insights into its dosage sensitivity in chondrogenesis. Overexpression of SOX9 showed promising results with improved sulfated glycosaminoglycans (GAGs) aggregation and COL2A1 expression following differentiation. We hope this finding could provide a better understanding of the dosage-dependent role of SOX9 in chondrogenesis and contribute to the development of improved therapeutic targets for CD patients.

Decellularized Extracellular Matrix Improves Mesenchymal Stromal Cell Spheroid Response to Chondrogenic Stimuli

Cartilage regeneration is hindered due to the low proliferative capacity of chondrocytes and the avascular nature of cartilaginous tissue. Mesenchymal stromal cells (MSCs) are widely studied for cartilage tissue engineering, and the aggregation of MSCs into high-density cell spheroids facilitates chondrogenic differentiation due to increased cell-cell contact. Despite the promise of MSCs, the field would benefit from improved strategies to regulate the chondrogenic potential of MSCs differentiated from induced pluripotent stem cells (iPSCs), which are advantageous for their capacity to yield large numbers of required cells. We previously demonstrated the ability of MSC-secreted extracellular matrix (ECM) to promote MSC chondrogenic differentiation, but the combinatorial effect of iPSC-derived MSC (iMSC) spheroids, iMSC-derived decellularized ECM (idECM), and other stimuli (e.g., oxygen tension and transforming growth factor [TGF]-β) on chondrogenic potential has not been described. Similar to MSCs, iMSCs secreted a collagen-rich ECM. When incorporated into spheroids, idECM increased spheroid diameter and promoted chondrogenic differentiation. The combination of idECM loading, chondrogenic media, and hypoxia enhanced glycosaminoglycan (GAG) content 1.6-fold (40.9 ± 4.6 ng vs. 25.6 ± 3.3 ng, p < 0.05) in iMSC spheroids. Compared with active TGF-β1, the presentation of latent TGF-β1 resulted in greater GAG content (26.6 ± 1.8 ng vs. 41.9 ± 4.3 ng, p < 0.01). Finally, we demonstrated the capacity of individual spheroids to self-assemble into larger constructs and undergo both chondrogenic and hypertrophic differentiation when maintained in lineage-inducing media. These results highlight the potential of idECM to enhance the efficacy of chondrogenic stimuli for improved cartilage regeneration using human MSCs and iMSCs.

TMF suppresses chondrocyte hypertrophy in osteoarthritic cartilage by mediating the FOXO3a/BMPER pathway

Osteoarthritis (OA) is a disease of the joints, characterized by chronic inflammation, cartilage destruction and extracellular matrix (ECM) remodeling. Aberrant chondrocyte hypertrophy promotes cartilage destruction and OA development. Collagen X, the biomarker of chondrocyte hypertrophy, is upregulated by runt-related transcription factor 2 (Runx2), which is mediated by the bone morphogenetic protein 4 (BMP4)/Smad1 signaling pathway. BMP binding endothelial regulator (BMPER), a secreted glycoprotein, acts as an agonist of BMP4. 5,7,3',4'-tetramethoxyflavone (TMF) is a natural flavonoid derived from Murraya exotica L. Results of our previous study demonstrated that TMF exhibits chondroprotective effects against OA development through the activation of Forkhead box protein O3a (FOXO3a) expression. However, whether TMF suppresses chondrocyte hypertrophy through activation of FOXO3a expression and inhibition of BMPER/BMP4/Smad1 signaling remains unknown. Results of the present study revealed that TMF inhibited collagen X and Runx2 expression, inhibited BMPER/BMP4/Smad1 signaling, and activated FOXO3a expression; thus, protecting against chondrocyte hypertrophy and OA development. However, BMPER overexpression and FOXO3a knockdown impacted the protective effects of TMF. Thus, TMF inhibited chondrocyte hypertrophy in OA cartilage through mediating the FOXO3a/BMPER signaling pathway.

Common features of cartilage maturation are not conserved in an amphibian model

BACKGROUND

Mouse, chick, and zebrafish undergo a highly conserved program of cartilage maturation during endochondral ossification (bone formation via a cartilage template). Standard histological and molecular features of cartilage maturation are chondrocyte hypertrophy, downregulation of the chondrogenic markers Sox9 and Col2a1, and upregulation of Col10a1. We tested whether cartilage maturation is conserved in an amphibian, the western clawed frog Xenopus tropicalis, using in situ hybridization for standard markers and a novel laser-capture microdissection RNAseq data set. We also functionally tested whether thyroid hormone drives cartilage maturation in X tropicalis, as it does in other vertebrates.

RESULTS

The developing frog humerus mostly followed the standard progression of cartilage maturation. Chondrocytes gradually became hypertrophic as col2a1 and sox9 were eventually down-regulated, but col10a1 was not up-regulated. However, the expression levels of several genes associated with the early formation of cartilage, such as acan, sox5, and col9a2, remained highly expressed even as humeral chondrocytes matured. Greater deviances were observed in head cartilages, including the ceratohyal, which underwent hypertrophy within hours of becoming cartilaginous, maintained relatively high levels of col2a1 and sox9, and lacked col10a1 expression. Interestingly, treating frog larvae with thyroid hormone antagonists did not specifically reduce head cartilage hypertrophy, resulting rather in a global developmental delay.

CONCLUSION

These data reveal that basic cartilage maturation features in the head, and to a lesser extent in the limb, are not conserved in X tropicalis. Future work revealing how frogs deviate from the standard cartilage maturation program might shed light on both evolutionary and health studies.

Gravity-based patterning of osteogenic factors to preserve bone structure after osteochondral injury in a large animal model

Chondral and osteochondral repair strategies are limited by adverse bony changes that occur after injury. Bone resorption can cause entire scaffolds, engineered tissues, or even endogenous repair tissues to subside below the cartilage surface. To address this translational issue, we fabricated thick-shelled poly(D,L-lactide-co-glycolide) (PLGA) microcapsules containing the pro-osteogenic agents triiodothyronine and ß-glycerophosphate, and delivered these microcapsules in a large animal model of osteochondral injury to preserve bone structure. We demonstrate that the developed microcapsules ruptured in vitro under increasing mechanical loads, and readily sink within a liquid solution, enabling gravity-based patterning along the osteochondral surface. In a large animal, these mechanically-actived microcapsules (MAMCs) were assessed through two different delivery strategies. Intra-articular injection of control MAMCs enabled fluorescent quantification of MAMC rupture and cargo release in a synovial joint setting over time in vivo. This joint-wide injection also confirmed that the MAMCs do not elicit an inflammatory response. In the contralateral hindlimbs, chondral defects were created, MAMCs were patterned in situ, and nanofracture (Nfx), a clinically utilized method to promote cartilage repair, was performed. The NFx holes enabled marrow-derived stromal cells to enter the defect area and served as repeatable bone injury sites to monitor over time. Animals were evaluated 1 and 2 weeks after injection and surgery. Analysis of injected MAMCs showed that bioactive cargo was released in a controlled fashion over 2 weeks. A bone fluorochrome label injected at the time of surgery displayed maintenance of mineral labeling in the therapeutic group, but resorption in both control groups. Alkaline phosphatase (AP) staining at the osteochondral interface revealed higher AP activity in defects treated with therapeutic MAMCs. Overall, this study develops a gravity-based approach to pattern bioactive factors along the osteochondral interface, and applies this novel biofabrication strategy to preserve bone structure after osteochondral injury.

Tetrabromobisphenol A perturbs cell fate decisions via BMP signaling in the early embryonic development of zebrafish

Tetrabromobisphenol A (TBBPA) readily accumulates in the egg yolk of aquatic oviparous animals and is transferred to their embryos. Early embryogenesis is vital for organ formation and subsequent development. The developmental toxicity of TBBPA in aquatic animals has been extensively reported. However, few studies have assessed the toxic effects of TBBPA in the early embryonic development. In this work, we found that TBBPA perturbed cell fate decisions along the dorsal-ventral (DV) axis during gastrulation, further disrupting early organogenesis in the entire embryo. TBBPA exposure increased the number of embryonic cells that acquired a ventral cell fate, which formed epidermis, blood and heart tissues. In return, the number of embryonic cells that acquired a dorsal cell fate was greatly decreased, causing the TBBPA-exposed embryos to develop a small brain and small eyes. We revealed that TBBPA elevated the activity gradient of bone morphogenetic protein (BMP) signaling which is responsible for cell fate specification along the DV axis, with up-regulation of BMP ligands (bmp4, bmp7a) and target genes (szl) and promotion signal transduction through phosphorylation of Smad1/5. As the function of BMP signaling in embryogenesis is highly conserved among many vertebrates, these findings highlight the ecological and health risks of TBBPA.

Thyroid hormone enhances stem cell maintenance and promotes lineage-specific differentiation in human embryonic stem cells

Background

Thyroid hormone triiodothyronine (T3) is essential for embryogenesis and is commonly used during in vitro fertilization to ensure successful implantation. However, the regulatory mechanisms of T3 during early embryogenesis are largely unknown.

Method

To study the impact of T3 on hPSCs, cell survival and growth were evaluated by measurement of cell growth curve, cloning efficiency, survival after passaging, cell apoptosis, and cell cycle status. Pluripotency was evaluated by RT-qPCR, immunostaining and FACS analysis of pluripotency markers. Metabolic status was analyzed using LC–MS/MS and Seahorse XF Cell Mito Stress Test. Global gene expression was analyzed using RNA-seq. To study the impact of T3 on lineage-specific differentiation, cells were subjected to T3 treatment during differentiation, and the outcome was evaluated using RT-qPCR, immunostaining and FACS analysis of lineage-specific markers.

Results

In this report, we use human pluripotent stem cells (hPSCs) to show that T3 is beneficial for stem cell maintenance and promotes trophoblast differentiation. T3 enhances culture consistency by improving cell survival and passaging efficiency. It also modulates cellular metabolism and promotes energy production through oxidative phosphorylation. T3 helps maintain pluripotency by promoting ERK and SMAD2 signaling and reduces FGF2 dependence in chemically defined culture. Under BMP4 induction, T3 significantly enhances trophoblast differentiation.

Conclusion

In summary, our study reveals the impact of T3 on stem cell culture through signal transduction and metabolism and highlights its potential role in improving stem cell applications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02799-y.

Differentiation of Hypertrophic Chondrocytes from Human iPSCs for the In Vitro Modeling of Chondrodysplasias

Chondrodysplasias are hereditary diseases caused by mutations in the components of growth cartilage. Although the unfolded protein response (UPR) has been identified as a key disease mechanism in mouse models, no suitable in vitro system has been reported to analyze the pathology in humans. Here, we developed a three-dimensional culture protocol to differentiate hypertrophic chondrocytes from induced pluripotent stem cells (iPSCs) and examine the phenotype caused by MATN3 and COL10A1 mutations. Intracellular MATN3 or COL10 retention resulted in increased ER stress markers and ER size in most mutants, but activation of the UPR was dependent on the mutation. Transcriptome analysis confirmed a UPR with wide-ranging changes in bone homeostasis, extracellular matrix composition, and lipid metabolism in the MATN3 T120M mutant, which further showed altered cellular morphology in iPSC-derived growth-plate-like structures in vivo. We then applied our in vitro model to drug testing, whereby trimethylamine N-oxide led to a reduction of ER stress and intracellular MATN3.

RASL11B gene enhances hyaluronic acid-mediated chondrogenic differentiation in human amniotic mesenchymal stem cells via the activation of Sox9/ERK/smad signals

This study aimed to elucidate the molecular mechanisms, whereby hyaluronic acid, a main extracellular matrix component of articular cartilage, promotes the chondrogenic differentiation of human amniotic mesenchymal stem cells (hAMSCs). Our previous findings indicated that hyaluronic acid combined with hAMSCs showed a marked therapeutic effect against rat osteoarthritis. In the present study, hyaluronic acid markedly enhanced the expression of chondrocyte-specific markers including Col2α1, Acan, and Sox9 in hAMSCs, with strong synergistic effects on chondrogenic differentiation, in combination with the commonly used inducer, transforming growth factor β3 (TGF-β3). Microarray analysis showed that Ras-like protein family member 11B (RASL11B) played a pivotal role in the process of hyaluronic acid-mediated chondrogenesis of hAMSCs. This directional differentiation was significantly inhibited by RASL11B knockdown, but RASL11B overexpression dramatically promoted the expression of Sox9, a master chondrogenesis transcriptional factor, at the levels of transcription and translation. Increased Sox9 expression subsequently resulted in high expression levels of Col2α1 and Acan and the accumulation of cartilage-specific matrix components, such as type 2 collagen and glycosaminoglycans. Moreover, we observed that RASL11B activated the signal molecules such as ERK1/2, and Smad2/3 in the presence of hyaluronic acid during TGF-β3-induced chondrogenesis of hAMSCs. Taken together, these findings suggest that hyaluronic acid activates the RASL11B gene to potentiate the chondrogenic differentiation of hAMSCs via the activation of Sox9 and ERK/Smad signaling, thus providing a new strategy for cartilage defect repairing by hyaluronic acid-based stem cell therapy.

Matrilin-3-Primed Adipose-Derived Mesenchymal Stromal Cell Spheroids Prevent Mesenchymal Stromal-Cell-Derived Chondrocyte Hypertrophy

Adipose-derived mesenchymal stromal cells (Ad-MSCs) are a promising tool for articular cartilage repair and regeneration. However, the terminal hypertrophic differentiation of Ad-MSC-derived cartilage is a critical barrier during hyaline cartilage regeneration. In this study, we investigated the role of matrilin-3 in preventing Ad-MSC-derived chondrocyte hypertrophy in vitro and in an osteoarthritis (OA) destabilization of the medial meniscus (DMM) model. Methacrylated hyaluron (MAHA) (1%) was used to encapsulate and make scaffolds containing Ad-MSCs and matrilin-3. Subsequently, the encapsulated cells in the scaffolds were differentiated in chondrogenic medium (TGF-β, 1-14 days) and thyroid hormone hypertrophic medium (T3, 15-28 days). The presence of matrilin-3 with Ad-MSCs in the MAHA scaffold significantly increased the chondrogenic marker and decreased the hypertrophy marker mRNA and protein expression. Furthermore, matrilin-3 significantly modified the expression of TGF-β2, BMP-2, and BMP-4. Next, we prepared the OA model and transplanted Ad-MSCs primed with matrilin-3, either as a single-cell suspension or in spheroid form. Safranin-O staining and the OA score suggested that the regenerated cartilage morphology in the matrilin-3-primed Ad-MSC spheroids was similar to the positive control. Furthermore, matrilin-3-primed Ad-MSC spheroids prevented subchondral bone sclerosis in the mouse model. Here, we show that matrilin-3 plays a major role in modulating Ad-MSCs' therapeutic effect on cartilage regeneration and hypertrophy suppression.

Significance of MEF2C and RUNX3 Regulation for Endochondral Differentiation of Human Mesenchymal Progenitor Cells

Guiding progenitor cell development between chondral versus endochondral pathways is still an unachieved task of cartilage neogenesis, and human mesenchymal progenitor cell (MPC) chondrogenesis is considered as a valuable model to better understand hypertrophic development of chondrocytes. Transcription factors Runx2, Runx3, and Mef2c play prominent roles for chondrocyte hypertrophy during mouse development, but little is known on the importance of these key fate-determining factors for endochondral development of human MPCs. The aim of this study was to unravel the regulation of RUNX2, RUNX3, and MEF2C during MPC chondrogenesis, the pathways driving their expression, and the downstream hypertrophic targets affected by their regulation. RUNX2, RUNX3, and MEF2C gene expression was differentially regulated during chondrogenesis of MPCs, but remained low and unregulated when non-hypertrophic articular chondrocytes were differentiated under the same conditions. RUNX3 and MEF2C mRNA and protein levels rose in parallel to hypertrophic marker upregulation, but surprisingly, RUNX2 gene expression changed only by trend and RUNX2 protein remained undetectable. While RUNX3 expression was driven by TGF-β and BMP signaling, MEF2C responded to WNT-, BMP-, and Hedgehog-pathway inhibition. MEF2C but not RUNX3 levels correlated significantly with COL10A1, IHH, and IBSP gene expression when hypertrophy was attenuated. IBSP was a downstream target of RUNX3 and MEF2C but not RUNX2 in SAOS-2 cells, underlining the capacity of RUNX3 and MEF2C to stimulate osteogenic marker expression in human cells. Conclusively, RUNX3 and MEF2C appeared more important than RUNX2 for human endochondral MPC chondrogenesis. Pathways altering the speed of chondrogenesis (FGF, TGF-β, BMP) affected RUNX2 or RUNX3, while pathways changing hypertrophy (WNT, PTHrP/HH) regulated mainly MEF2C. Taken together, reduction of MEF2C levels is a new goal to shift human cartilage neogenesis toward the chondral pathway.

Attenuation of Hypertrophy in Human MSCs via Treatment with a Retinoic Acid Receptor Inverse Agonist

In vitro chondrogenically differentiated mesenchymal stem cells (MSCs) have a tendency to undergo hypertrophy, mirroring the fate of transient "chondrocytes" in the growth plate. As hypertrophy would result in ossification, this fact limits their use in cartilage tissue engineering applications. During limb development, retinoic acid receptor (RAR) signaling exerts an important influence on cell fate of mesenchymal progenitors. While retinoids foster hypertrophy, suppression of RAR signaling seems to be required for chondrogenic differentiation. Therefore, we hypothesized that treatment of chondrogenically differentiating hMSCs with the RAR inverse agonist, BMS204,493 (further named BMS), would attenuate hypertrophy. We induced hypertrophy in chondrogenic precultured MSC pellets by the addition of bone morphogenetic protein 4. Direct activation of the RAR pathway by application of the physiological RAR agonist retinoic acid (RA) further enhanced the hypertrophic phenotype. However, BMS treatment reduced hypertrophic conversion in hMSCs, shown by decreased cell size, number of hypertrophic cells, and collagen type X deposition in histological analyses. BMS effects were dependent on the time point of application and strongest after early treatment during chondrogenic precultivation. The possibility of modifing hypertrophic cartilage via attenuation of RAR signaling by BMS could be helpful in producing stable engineered tissue for cartilage regeneration.

Cytotoxic Properties of HT-2 Toxin in Human Chondrocytes: Could T3 Inhibit Toxicity of HT-2?

Thyroid hormone triiodothyronine (T₃) plays an important role in coordinated endochondral ossification and hypertrophic differentiation of the growth plate, while aberrant thyroid hormone function appears to be related to skeletal malformations, osteoarthritis, and Kashin-Beck disease. The T-2 toxin, present extensively in cereal grains, and one of its main metabolites, HT-2 toxin, are hypothesized to be potential factors associated with hypertrophic chondrocyte-related osteochondropathy, known as the Kashin-Beck disease. In this study, we investigated the effects of T₃ and HT-2 toxin on human chondrocytes. The immortalized human chondrocyte cell line, C-28/I2, was cultured in four different groups: controls, and cultures with T₃, T₃ plus HT-2 and HT-2 alone. Cytotoxicity was assessed using an MTT assay after 24-h-exposure. Quantitative RT-PCR was used to detect gene expression levels of collagen types II and X, aggrecan and runx2, and the differences in runx2 were confirmed with immunoblot analysis. T₃ was only slightly cytotoxic, in contrast to the significant, dose-dependent cytotoxicity of HT-2 alone at concentrations ≥ 50 nM. T₃, together with HT-2, significantly rescued the cytotoxic effect of HT-2. HT-2 induced significant increases in aggrecan and runx2 gene expression, while the hypertrophic differentiation marker, type X collagen, remained unchanged. Thus, T₃ protected against HT-2 induced cytotoxicity, and HT-2 was an inducer of the pre-hypertrophic state of the chondrocytes.

TGF-β Signalling is Suppressed under Pro-Hypertrophic Conditions in MSC Chondrogenesis Due to TGF-β Receptor Downregulation

Background and Objectives

Mesenchymal stem cells (MSCs) become hypertrophic in long term despite chondrogenic differentiation following the pathway of growth plate chondrocytes. This terminal differentiation leads to phenotypically unstable cartilage and was mirrored in vitro by addition of hypertrophy inducing medium. We investigated how intrinsic TGF-β signaling is altered in pro-hypertrophic conditions.

Methods and Results

Human bone marrow derived MSC were chondrogenically differentiated in 3D culture. At day 14 medium conditions were changed to 1. pro-hypertrophic by addition of T3 and withdrawal of TGF-β and dexamethasone 2. pro-hypertrophic by addition of BMP 4 and withdrawal of TGF-β and dexamethasone and 3. kept in prochondrogenic medium conditions. All groups were treated with and without TGFβ-type-1-receptor inhibitor SB431542 from day 14 on. Aggregates were harvested for histo- and immunohistological analysis at d14 and d28, for gene expression analysis (rt-PCR) on d1, d3, d7, d14, d17, d21 and d28 and for Western blot analysis on d21 and d28. Induction of hypertrophy was achieved in the pro-hypertrophic groups while expression of TGFβ-type-1- and 2-receptor and Sox 9 were significantly downregulated compared to pro-chondrogenic conditions. Western blotting showed reduced phosphorylation of Smad 2 and 3 in hypertrophic samples, reduced TGF-β-1 receptor proteins and reduced SOX 9. Addition of SB431542 did not initiate hypertrophy under pro-chondrogenic conditions, but was capable of enhancing hypertrophy when applied simultaneously with BMP-4.

Conclusions

Our results suggest that the enhancement of hypertrophy in this model is a result of both activation of pro-hypertrophic BMP signaling and reduction of anti-hypertrophic TGFβ signaling.

Thyroid Hormone and Skeletal Development

Thyroid hormone (TH) is essential for skeletal development from the late fetal life to the onset of puberty. During this large window of actions, TH has key roles in endochondral and intramembranous ossifications and in the longitudinal bone growth. There is evidence that TH acts directly in skeletal cells but also indirectly, specially via the growth hormone/insulin-like growth factor-1 axis, to control the linear skeletal growth and maturation. The presence of receptors, plasma membrane transporters, and activating and inactivating enzymes of TH in skeletal cells suggests that direct actions of TH in these cells are crucial for skeletal development, which has been confirmed by several in vitro and in vivo studies, including mouse genetic studies, and clinical studies in patients with resistance to thyroid hormone due to dominant-negative mutations in TH receptors. This review examines progress made on understanding the mechanisms by which TH regulates the skeletal development.

Transforming growth factor-beta1 promotes articular cartilage repair through canonical Smad and Hippo pathways in bone mesenchymal stem cells

AIMS

Transforming growth factor-β1 (TGF-β1) is a chondrogenic factor and has been reported to be able to enhance chondrocyte differentiation from bone marrow mesenchymal stem cells (BMSCs). Here we investigate the molecular mechanism through which TGF-β1 chronically promotes the repair of cartilage defect and inhibit chondrocyte hypertrophy.

MAIN METHODS

Animal models of full thickness cartilage defects were divided into three groups: model group, BMSCs group (treated with BMSCs/calcium alginate gel) and BMSCs+TGF-β1 group (treated with Lentivirus-TGF-β1-EGFP transduced BMSCs/calcium alginate gel). 4 and 8weeks after treatment, macroscopic observation, histopathological study and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) were done to analyze phenotypes of the animals. BMSCs were transduced with Lentivirus-TGF-β1-EGFP in vitro and Western blot analysis was performed.

KEY FINDINGS

We found that TGF-β1-expressiing BMSCs improved the repair of the cartilage defect. The impaired cartilage contained higher amount of GAG and type II collagen and was integrated to the surrounding normal cartilage and higher content of GAG and type II collagen. The major events include increased expression of type II collagen following Smad2/3 phosphorylation, and inhibition of cartilage hypertrophy by increasing Yes-associated protein-1 (YAP-1) and inhibiting Runx2 and Col10 after the completion of chondrogenic differentiation.

SIGNIFICANCE

We conclude that TGF-β1 is beneficial to chondrogenic differentiation of BMSCs via canonical Smad pathway to promote early-repairing of cartilage defect. Furthermore, TGF-β1 inhibits chondrocyte hypertrophy by decreasing hypertrophy marker gene expression via Hippo signaling. Long-term rational use of TGF-β1 may be an alternative approach in clinic for cartilage repair and regeneration.

Role of the protease corin in chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) have the potency to differentiate into chondrocytes, osteocytes and adipocytes. Corin is a cardiac protease that activates the natriuretic peptides, thereby regulating blood volume and pressure. In addition to the heart, corin gene upregulation was reported in bone marrow- and adipose tissue-derived MSCs that underwent osteogenic differentiation. To date, the biological significance of corin expression in MSC differentiation remains unknown. In this study we isolated and cultured human bone marrow-derived MSCs that were capable of undergoing chondrogenic, osteogenic and adipogenic lineage differentiation. By reverse transcription polymerase chain reaction (RT-PCR) and immunostaining, we found that corin expression was upregulated when these MSCs underwent chondrogenic, osteogenic and adipogenic differentiation. The upregulation of corin expression was most significant in the cells undergoing chondrogenic lineage differentiation. Silencing corin gene expression by small hairpin RNA in the MSCs inhibited chondrogenic, but not osteogenic and adipogenic, differentiation. These results suggest a novel function of corin in MSC differentiation and chondrocyte development.

Dose-dependent effect of triiodothyronine on the chondrogenic differentiation of mesenchymal stem cells from the bone marrow of female rats

OBJECTIVES

Verify the in-vitro effect of triiodothyronine (T3) on the chondrogenic differentiation of female rat bone marrow mesenchymal stem cells (BMMSCs) over several time periods and at several doses.

METHODS

CD54 + /CD73 + /CD90 +  BMMSCs from Wistar female rats were cultured in chondrogenic medium with or without T3 (0.01; 1; 100; 1000 nm). At seven, 14 and 21 days, the cell morphology, chondrogenic matrix formation and expression of Sox9 and collagen II were evaluated.

KEY FINDINGS

The dose of 100 nm did not alter the parameters evaluated in any of the periods studied. However, the 0.01 nm T3 dose improved the chondrogenic potential by increasing the chondrogenic matrix formation and expression of Sox9 and collagen II in at least one of the evaluated periods; the 1 nm T3 dose also improved the chondrogenic potential by increasing the chondrogenic matrix formation and the expression of collagen II in at least one of the evaluated periods. The 1000 nm T3 dose improved the chondrogenic potential by increasing the chondrogenic matrix formation and Sox9 expression in at least one of the evaluated periods.

CONCLUSIONS

T3 has a dose-dependent effect on the differentiation of BMMSCs from female rats.

Enhanced Chondrogenic Differentiation of Human Umbilical Cord Wharton's Jelly Derived Mesenchymal Stem Cells by GSK-3 Inhibitors

Articular cartilage is an avascular, alymphatic, and aneural system with very low regeneration potential because of its limited capacity for self-repair. Mesenchymal stem cells (MSCs) are the preferred choice for cell-based therapies. Glycogen synthase kinase 3 (GSK-3) inhibitors are compounds that can induce the Wnt signaling pathway, which is involved in chondrogenesis and cartilage development. Here, we investigated the influence of lithium chloride (LiCl) and SB216763 synergistically with TGF-β3 on chondrogenic differentiation in human mesenchymal stem cells derived from Wharton’s jelly tissue (hWJ-MSCs). hWJ-MSCs were cultured and chondrogenic differentiation was induced in monolayer and pellet experiments using chondrogenic medium, chondrogenic medium supplemented with LiCl, or SB216763 for 4 weeks. After in vitro differentiation, cultured cells were examined for the expression of Sox9, ACAN, Col2a1, and β-catenin markers. Glycosaminoglycan (GAG) accumulation was also examined by Alcian blue staining. The results indicated that SB216763 was more effective than LiCl as evidenced by a higher up-regulation of the expression of cartilage-specific markers, including Sox9, ACAN, Col2a1 as well as GAG accumulation. Moreover, collagen type II expression was strongly observed in cells cultured in the chondrogenic medium + SB216763 as evidenced by western blot analysis. Both treatments appeared to mediate the Wnt signaling pathway by up-regulating β-catenin gene expression. Further analyses showed that all treatments suppressed the progression of chondrocyte hypertrophy, determined by decreased expression of Col10a1 and Runx2. These results indicate that LiCl and SB216763 are potential candidates for further in vivo therapeutic trials and would be of great importance for cartilage regeneration.

Differential expression of TGF-β superfamily members and role of Smad1/5/9-signalling in chondral versus endochondral chondrocyte differentiation

Proteins of the transforming-growth-factor-β (TGF-β)-superfamily have a remarkable ability to induce cartilage and bone and the crosstalk of TGF-β - and BMP-signalling pathways appears crucial during chondrocyte development. Aim was to assess the regulation of TGF-β-superfamily members and of Smad2/3- and Smad1/5/9-signalling during endochondral in vitro chondrogenesis of mesenchymal stromal cells (MSC) relative to chondral redifferentiation of articular chondrocytes (AC) to adjust chondrocyte development of MSC towards a less hypertrophic phenotype. While MSC increased BMP4 and BMP7 and reduced TGFBR2 and TGFBR3-expression during chondrogenesis, an opposite regulation was observed during AC-redifferentiation. Antagonists CHRD and CHL2 rose significantly only in AC-cultures. AC showed higher initial BMP4, pSmad1/5/9 and SOX9 protein levels, a faster (re-)differentiation but a similar decline of pSmad2/3- and pSmad1/5/9-signalling versus MSC-cultures. BMP-4/7-stimulation of MSC-pellets enhanced SOX9 and accelerated ALP-induction but did not shift differentiation towards osteogenesis. Inhibition of BMP-signalling by dorsomorphin significantly reduced SOX9, raised RUNX2, maintained collagen-type-II and collagen-type-X lower and kept ALP-activity at levels reached at initiation of treatment. Conclusively, ALK1,2,3,6-signalling was essential for MSC-chondrogenesis and its prochondrogenic rather than prohypertrophic role may explain why inhibition of canonical BMP-signalling could not uncouple cartilage matrix production from hypertrophy as this was achieved with pulsed PTHrP-application.

Expression of BMP and Actin Membrane Bound Inhibitor Is Increased during Terminal Differentiation of MSCs

Chondrogenic differentiating mesenchymal stem cells (MSCs) are mimicking embryonal endochondral ossification and become hypertrophic. BMP (bone morphogenetic protein) and Activin Membrane Bound Inhibitor (BAMBI) is a pseudoreceptor that regulates the activity of transforming growth factor-β (TGF-β) and BMP signalling during chondrogenesis. Both TGF-β and BMP signalling are regulators of chondrogenic cell differentiation. Human bone marrow derived MSCs were chondrogenically predifferentiated in aggregate culture for 14 days. Thereafter, one group was subjected to hypertrophy enhancing media conditions while controls were kept in chondrogenic medium until day 28. Histological evaluation, gene expression by PCR, and Western blot analysis were carried out at days 1, 3, 7, 14, 17, 21, and 28. A subset of cultures was treated with the BMP inhibitor Noggin to test for BMP dependent expression of BAMBI. Hypertrophic differentiated pellets showed larger cells with increased collagen 10 and alkaline phosphatase staining. There was significantly increased expression of BAMBI on gene expression and protein level in hypertrophic cultures compared to the chondrogenic control and increased BMP4 gene expression. Immunohistochemistry showed intense staining of BAMBI in hypertrophic cells. BAMBI expression was dose-dependently downregulated by Noggin. The pseudoreceptor BAMBI is upregulated upon enhancement of hypertrophy in MSC chondrogenic differentiation by a BMP dependent mechanism.

Role of Thyroid Hormones in Skeletal Development and Bone Maintenance

The skeleton is an exquisitely sensitive and archetypal T3-target tissue that demonstrates the critical role for thyroid hormones during development, linear growth, and adult bone turnover and maintenance. Thyrotoxicosis is an established cause of secondary osteoporosis, and abnormal thyroid hormone signaling has recently been identified as a novel risk factor for osteoarthritis. Skeletal phenotypes in genetically modified mice have faithfully reproduced genetic disorders in humans, revealing the complex physiological relationship between centrally regulated thyroid status and the peripheral actions of thyroid hormones. Studies in mutant mice also established the paradigm that T3 exerts anabolic actions during growth and catabolic effects on adult bone. Thus, the skeleton represents an ideal physiological system in which to characterize thyroid hormone transport, metabolism, and action during development and adulthood and in response to injury. Future analysis of T3 action in individual skeletal cell lineages will provide new insights into cell-specific molecular mechanisms and may ultimately identify novel therapeutic targets for chronic degenerative diseases such as osteoporosis and osteoarthritis. This review provides a comprehensive analysis of the current state of the art.

The Regulatory Role of Signaling Crosstalk in Hypertrophy of MSCs and Human Articular Chondrocytes

Hypertrophic differentiation of chondrocytes is a main barrier in application of mesenchymal stem cells (MSCs) for cartilage repair. In addition, hypertrophy occurs occasionally in osteoarthritis (OA). Here we provide a comprehensive review on recent literature describing signal pathways in the hypertrophy of MSCs-derived in vitro differentiated chondrocytes and chondrocytes, with an emphasis on the crosstalk between these pathways. Insight into the exact regulation of hypertrophy by the signaling network is necessary for the efficient application of MSCs for articular cartilage repair and for developing novel strategies for curing OA. We focus on articles describing the role of the main signaling pathways in regulating chondrocyte hypertrophy-like changes. Most studies report hypertrophic differentiation in chondrogenesis of MSCs, in both human OA and experimental OA. Chondrocyte hypertrophy is not under the strict control of a single pathway but appears to be regulated by an intricately regulated network of multiple signaling pathways, such as WNT, Bone morphogenetic protein (BMP)/Transforming growth factor-β (TGFβ), Parathyroid hormone-related peptide (PTHrP), Indian hedgehog (IHH), Fibroblast growth factor (FGF), Insulin like growth factor (IGF) and Hypoxia-inducible factor (HIF). This comprehensive review describes how this intricate signaling network influences tissue-engineering applications of MSCs in articular cartilage (AC) repair, and improves understanding of the disease stages and cellular responses within an OA articular joint.

Molecular basis of imprinting disorders affecting chromosome 14: lessons from murine models

Uniparental inheritance of chromosome 14q32 causes developmental failure during gestation and early postnatal development due to mis-expression of a cluster of imprinted genes under common epigenetic control. Two syndromes associated with chromosome 14q32 abnormalities have been described, Kagami–Ogata and Temple syndromes. Both of these syndromes are characterised by specific impairments of intrauterine development, placentation and early postnatal survival. Such abnormalities arise because the processes of intrauterine growth and postnatal adaptation are critically modulated by the dosage of imprinted genes in the chromosome 14q32 cluster. Much of our understanding of how the imprinted genes in this cluster are regulated, as well as their individual functions in the molecular pathways controlling growth and postnatal adaptation, has come from murine models. Mouse chromosome 12qF1 contains an imprinted region syntenic to human chromosome 14q32, collectively referred to as the Dlk1–Dio3 cluster. In this review, we will summarise the wealth of information derived from animal models of chromosome 12 imprinted gene mis-regulation, and explore the relationship between the functions of individual genes and the phenotypic result of their mis-expression. As there is often a considerable overlap between the functions of genes in the Dlk1–Dio3 cluster, we propose that the expression dosage of these genes is controlled by common regulatory mechanisms to co-ordinate the timing of growth and postnatal adaptation. While the diseases associated with mis-regulated chromosome 14 imprinting are rare, studies carried out in mice on the functions of the affected genes as well as their normal regulatory mechanisms have revealed new mechanistic pathways for the control of growth and survival in early life.

Thyroid hormones enhance the biomechanical functionality of scaffold-free neocartilage

Introduction

The aim of this study was to investigate the effects of thyroid hormones tri-iodothyronine (T3), thyroxine (T4), and parathyroid hormone (PTH) from the parathyroid glands, known to regulate the developing limb and growth plate, on articular cartilage tissue regeneration using a scaffold-free in vitro model.

Methods

In Phase 1, T3, T4, or PTH was applied during weeks 1 or 3 of a 4-week neocartilage culture. Phase 2 employed T3 during week 1, followed by PTH during week 2, 3, or weeks 2 to 4, to further enhance tissue properties. Resultant neotissues were evaluated biochemically, mechanically, and histologically.

Results

In Phase 1, T3 and T4 treatment during week 1 resulted in significantly enhanced collagen production; 1.4- and 1.3-times untreated neocartilage. Compressive and tensile properties were also significantly increased, as compared to untreated and PTH groups. PTH treatment did not result in notable tissue changes. As T3 induces hypertrophy, in Phase 2, PTH (known to suppress hypertrophy) was applied sequentially after T3. Excitingly, sequential treatment with T3 and PTH reduced expression of hypertrophic marker collagen X, while yielding neocartilage with significantly enhanced functional properties. Specifically, in comparison to no hormone application, these hormones increased compressive and tensile moduli 4.0-fold and 3.1-fold, respectively.

Conclusions

This study demonstrated that T3, together with PTH, when applied in a scaffold-free model of cartilage formation, significantly enhanced functional properties. The novel use of these thyroid hormones generates mechanically robust neocartilage via the use of a scaffold-free tissue engineering model.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0541-5) contains supplementary material, which is available to authorized users.

Role of mesenchymal stem cells in cell life and their signaling

Mesenchymal stem cells (MSCs) have various roles in the body and cellular environment, and the cellular phenotypes of MSCs changes in different conditions. MSCs support the maintenance of other cells, and the capacity of MSCs to differentiate into several cell types makes the cells unique and full of possibilities. The involvement of MSCs in the epithelial-mesenchymal transition is an important property of these cells. In this review, the role of MSCs in cell life, including their application in therapy, is first described, and the signaling mechanism of MSCs is investigated for a further understanding of these cells.