Chondrocytes Research Articles

FOXC1 and FOXC2 regulate growth plate chondrocyte maturation towards hypertrophy in the embryonic mouse limb skeleton.

The Forkhead box transcription factors FOXC1 and FOXC2 are expressed in condensing mesenchyme cells at the onset of endochondral ossification. We used the Prx1-cre mouse to ablate Foxc1 and Foxc2 in limb skeletal progenitor cells. Prx1-cre;Foxc1Δ/Δ;Foxc2Δ/Δ limbs were shorter than controls, with worsening phenotypes in distal structures. Cartilage formation and mineralization was severely disrupted in the paws. The radius and tibia were malformed, whereas the fibula and ulna remained unmineralized. Chondrocyte maturation was delayed, with fewer Indian hedgehog-expressing, prehypertrophic chondrocytes forming and a smaller hypertrophic chondrocyte zone. Later, progression out of chondrocyte hypertrophy was slowed, leading to an accumulation of COLX-expressing hypertrophic chondrocytes and formation of a smaller primary ossification center with fewer osteoblast progenitor cells populating this region. Targeting Foxc1 and Foxc2 in hypertrophic chondrocytes with Col10a1-cre also resulted in an expanded hypertrophic chondrocyte zone and smaller primary ossification center. Our findings suggest that FOXC1 and FOXC2 direct chondrocyte maturation towards hypertrophic chondrocyte formation. At later stages, FOXC1 and FOXC2 regulate function in hypertrophic chondrocyte remodeling to allow primary ossification center formation and osteoblast recruitment.

Cartilage-derived cells display heterogeneous pericellular matrix synthesis in agarose microgels

The pericellular matrix (PCM) surrounding chondrocytes is essential for articular cartilage tissue engineering. As the current isolation methods to obtain chondrocytes with their PCM (chondrons) result in a heterogeneous mixture of chondrocytes and chondrons, regenerating the PCM using a tissue engineering approach could prove beneficial. In this study, we aimed to discern the behavior of articular chondrocytes (ACs) in regenerating the PCM in such an approach and whether this would also be true for articular cartilage-derived progenitor cells (ACPCs), as an alternative cell source. Bovine ACs and ACPCs were encapsulated in agarose microgels using droplet-based microfluidics. ACs were stimulated with TGF-β1 and dexamethasone and ACPCs were sequentially stimulated with BMP-9 followed by TGF-β1 and dexamethasone. After 0, 3, 5, and 10 days of culture, PCM components, type-VI collagen and perlecan, and ECM component, type-II collagen, were assessed using flow cytometry and fluorescence microscopy. Both ACs and ACPCs synthesized the PCM before the ECM. It was seen for the first time that synthesis of type-VI collagen always preceded perlecan. While the PCM synthesized by ACs resembled native chondrons after only 5 days of culture, ACPCs often made less well-structured PCMs. Both cell types showed variations between individual cells and donors. On one hand, this was more prominent in ACPCs, but also a subset of ACPCs showed superior PCM and ECM regeneration, suggesting that isolating these cells may potentially improve cartilage repair strategies.

The Effects of Seleno-Methionine in Cadmium-Challenged Human Primary Chondrocytes.

Cadmium (Cd) is a potentially toxic element able to interfere with cellular functions and lead to disease or even death. Cd accumulation has been demonstrated in cartilage, where it can induce damage in joints. The aim of this study was to evaluate the effect of CdCl2 on primary cultures of human chondrocytes and the possible protective effect of seleno-methionine (Se-Met). Human primary articular chondrocytes were cultured and treated as follows: control groups, cells challenged with 7.5 μM and 10 μM CdCl2 alone, and cells pretreated with 10 and 20 μM Se-Met and then challenged with 7.5 μM and 10 μM CdCl2. Twenty-four hours after incubation, cell viability, histological evaluation with hematoxylin-eosin stain, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay were performed. Furthermore, reverse transcription-PCR was carried out to evaluate mRNA levels of BAX, BAK1, CASP-3, and CASP-9. After CdCl2 challenge at both doses, a reduced cell viability and an overexpression of BAX, BAK1, CASP-3, and CASP-9 genes, as well as a high number of TUNEL-positive cells, were demonstrated, all parameters becoming higher as the dose of CdCl2 was increased. The pretreatment with Se-Met lowered the expression of all considered genes, improved cell viability and morphological changes, and reduced the number of TUNEL-positive cells. It was concluded that Se-Met plays a protective role against CdCl2-induced structural and functional changes in chondrocytes in vitro, as it improved cell viability and showed a positive role in the context of the apoptotic pathways. It is therefore suggested that a translational, multifaceted approach, with plant-based diets, bioactive functional foods, nutraceuticals, micronutrients, and drugs, is possibly advisable in situations of environmental pollution caused by potentially toxic elements.

Deletion of Bmal1 in aggrecan-expressing cells leads to mouse temporomandibular joint osteoarthritis.

Articular cartilage is the major affected tissue during the development of osteoarthritis (OA) in temporomandibular joint (TMJ). The core circadian rhythm molecule Bmal1 regulates chondrocyte proliferation, differentiation and apoptosis; however, its roles in condylar cartilage function and in TMJ OA have not been fully elucidated. TMJ OA mouse model was induced by unilateral anterior crossbite (UAC) and Bmal1 protein expression in condylar cartilage were examined by western blot analysis. To determine the role of Bmal1 in TMJ OA, we generated cartilage-specific Bmal1 conditional knockout (cKO) mice (Bmal1Agc1CreER mice) and hematoxylin and eosin staining, toluidine blue and Safranin O/fast green, immunohistochemistry, TUNEL assay, real-time PCR analysis and Western blot assay were followed. Bmal1 expression was reduced in condylar cartilage in a TMJ OA mouse model induced by UAC. The Bmal1 cKO mice displayed decreased cartilage matrix synthesis, reduced chondrocyte proliferation, increased chondrocyte hypertrophy and apoptosis as well as the upregulation of YAP expression in TMJ condylar cartilage. We demonstrated that Bmal1 was essential for TMJ tissue homeostasis and loss-of-function of Bmal1 in chondrocytes leads to the development of TMJ OA.

NS8593 inhibits chondrocyte ferroptosis and alleviates cartilage injury in rat adjuvant arthritis through TRPM7 / HO-1 pathway

Ferroptosis is an emerging target in rheumatoid arthritis (RA). We previously reported that transient receptor potential melastatin 7 (TRPM7) expression is correlated with RA cartilage destruction and demonstrated that TRPM7 mediates ferroptosis in chondrocytes. Here, we further determined the role and mechanism of (R)-N-(Benzimidazol-2-yl)-1,2,3,4-tetrahydro-1-naphthylamine (NS8593), a TRPM7 inhibitor, in chondrocyte ferroptosis of RA. We established in vitro models of ferroptosis in human chondrocytes (C28/I2 cells) by using ferroptosis inducer Erastin. The results showed that NS8593 could protect C28/I2 cells from ferroptosis by inhibiting TRPM7 channel, which was manifested by restoring cell viability, reducing cytotoxicity, affecting the expression of ferroptosis marker protein, and restoring redox balance to alleviate Erastin-induced oxidative stress injury. Mechanistically, the Heme oxygenase-1 (HO-1) axis responded to Erastin stimulation, which resulted in TRPM7-mediated chondrocyte ferroptosis, NS8593 could reduce the expression of HO-1 by inhibiting TRPM7 channel. Moreover, NS8593 alleviated articular cartilage destruction and inhibited chondrocyte ferroptosis in AA rats. In conclusion, NS8593 mitigated articular cartilage damage and chondrocyte ferroptosis through the TRPM7/HO-1 pathway, suggesting that NS8593 may be a potential novel drug for the treatment of RA.

Effects of resveratrol on biochemical and structural outcomes in osteoarthritis: A systematic review and meta-analysis of preclinical studies

Background and objectiveOsteoarthritis (OA) is the most common age-related disease of joints with increasing global prevalence. Persistent inflammation within the joint space is speculated to be the cause of OA. Resveratrol is an anti-inflammatory and antioxidant compound which can influence cartilage metabolism through multiple signalling pathways. This systematic review and meta-analysis aimed to summarize the therapeutic effects of resveratrol in animal models of OA. MethodsA comprehensive literature search was performed using PubMed, Embase, Web of Science, Cochrane Library, China National Knowledge Infrastructure, China Wanfang and VIP databases in May 2023. Studies on the effects of resveratrol in animal models of OA written in English or Mandarin, published from the inception of databases until the date of the search were considered. ResultsFifteen eligibility studies were included and analysed. Resveratrol was shown to inhibit the secretion of interleukin-1β, tumour necrosis factor-α, interleukin-6, nitric oxide, and apoptosis of articular chondrocytes. Joint structure as indicated by Mankin scores was restored with resveratrol in animal OA models. ConclusionResveratrol is a potential therapeutic agent for OA based on animal studies. Further evidence from well-planned human studies would be required to validate its clinical efficacies.

Unveiling the role of hypertrophic chondrocytes in abnormal cartilage calcification: insights into osteoarthritis mechanisms

Unveiling the role of hypertrophic chondrocytes in abnormal cartilage calcification: insights into osteoarthritis mechanisms

Nano-enzyme hydrogels for cartilage repair effectiveness based on ternary strategy therapy.

Designing artificial nano-enzymes for scavenging reactive oxygen species (ROS) in chondrocytes (CHOs) is considered the most feasible pathway for the treatment of osteoarthritis (OA). However, the accumulation of ROS due to the amount of nano-enzymatic catalytic site exposure and insufficient oxygen supply seriously threatens the clinical application of this therapy. Although metal-organic framework (MOF) immobilization of artificial nano-enzymes to enhance active site exposure has been extensively studied, artificial nano-enzymes/MOFs for ROS scavenging in OA treatment are still lacking. In this study, a biocompatible lubricating hydrogel-loaded iron-doped zeolitic imidazolate framework-8 (Fe/ZIF-8/Gel) centrase was engineered to scavenge endogenous overexpressed ROS synergistically generating dissolved oxygen and enhancing sustained lubrication for CHOs as a ternary artificial nano-enzyme. This property enabled the nano-enzymatic hydrogels to mitigate OA hypoxia and inhibit oxidative stress damage successfully. Ternary strategy-based therapies show excellent cartilage repair in vivo. The experimental results suggest that nano-enzyme-enhanced lubricating hydrogels are a potentially effective OA treatment and a novel strategy.

Corrigendum: Electrospun polycaprolactone/silk fibroin nanofiber scaffold with aligned fiber orientation for articular chondrocyte regeneration

Corrigendum: Electrospun polycaprolactone/silk fibroin nanofiber scaffold with aligned fiber orientation for articular chondrocyte regeneration

Cartilage decellularized matrix hydrogel loaded with protocatechualdehyde for targeted epiphycan treatment of osteoarthritis

Osteoarthritis (OA) is a prevalent chronic disease, characterized by chronic inflammation and cartilage degradation. This study aims to deepen the understanding of OA's pathophysiology and to develop novel therapeutic strategies. Our study underscores the pivotal role of Epiphycan (EPYC) and the IL-17 signaling pathway in OA. EPYC, an essential extracellular matrix constituent, has been found to exhibit a positive correlation with the severity of OA. We have discovered that EPYC modulates the activation of the IL-17 signaling pathway within chondrocytes by regulating the interaction between IL-17A and its receptor, IL-17RA. This regulatory mechanism underscores the intricate interplay between the extracellular matrix and immune signaling in the pathogenesis of OA Another finding of our study is the therapeutic effectiveness of protocatechualdehyde (PAH) in OA. PAH significantly reduces chondrocyte hypertrophy and supports cartilage tissue recovery.by targets EPYC. To reduce the side effects of orally administered PAH and maintain its effective drug concentration, we have developed a decellularized matrix hydrogel loaded with PAH for intra-articular injection. This novel drug delivery system is advantageous in minimizing drug-related side effects and ensuring sustained release PAH within the joint cavity.

Bioceramic-mediated chondrocyte hypertrophy promotes calcified cartilage formation for rabbit osteochondral defect repair

Osteochondral tissue is a highly specialized and complex tissue composed of articular cartilage and subchondral bone that are separated by a calcified cartilage interface. Multilayered or gradient scaffolds, often in conjunction with stem cells and growth factors, have been developed to mimic the respective layers for osteochondral defect repair. In this study, we designed a hyaline cartilage-hypertrophic cartilage bilayer graft (RGD/RGDW) with chondrocytes. Previously, we demonstrated that RGD peptide-modified chondroitin sulfate cryogel (RGD group) is chondro-conductive and capable of hyaline cartilage formation. Here, we incorporated whitlockite (WH), a Mg2+-containing calcium phosphate, into RGD cryogel (RGDW group) to induce chondrocyte hypertrophy and form collagen X-rich hypertrophic cartilage. This is the first study to use WH to produce hypertrophic cartilage. Chondrocytes-laden RGDW cryogel exhibited significantly upregulated expression of hypertrophy markers in vitro and formed ectopic hypertrophic cartilage in vivo, which mineralized into calcified cartilage in bone microenvironment. Subsequently, RGD cryogel and RGDW cryogel were combined into bilayer (RGD/RGDW group) and implanted into rabbit osteochondral defect, where RGD layer supports hyaline cartilage regeneration and bioceramic-containing RGDW layer promotes calcified cartilage formation. While the RGD group (monolayer) formed hyaline-like neotissue that extends into the subchondral bone, the RGD/RGDW group (bilayer) regenerated hyaline cartilage tissue confined to its respective layer and promoted osseointegration for integrative defect repair.

Emerging role of hypertrophic chondrocytes in tissue regeneration and fracture healing: a narrative review

Emerging role of hypertrophic chondrocytes in tissue regeneration and fracture healing: a narrative review

A novel mechanism behind irreversible development of cartilage degradation driven articular cartilage defects revealed by rat model: The chain reaction initiated by extracellular vesicles delivered LOC102546541

BackgroundArticular cartilage defects (ACD) are injuries with a diameter greater than 3 mm, resulting from wear and tear on joints. When the diameter of the defect exceeds 6 mm, it can further damage the surrounding joint cartilage, causing osteoarthritis (OA). Try to explain why OA is an irreversible disease, we hypothesize that damaged articular chondrocytes (DAC) may have reduced capacities to repair cartilage because its extracellular vesicle (EVs) that might directly contribute to OA formation. MethodsIn this study, DAC-EVs and AC-EVs were isolated using ultracentrifugation. Next-generation sequencing was employed to screen for a pathogenic long non-coding RNA (lncRNA). After verifying its function in vitro, the corresponding small interfering RNA (siRNA) was constructed and loaded into extracellular vesicles, which were then injected into the knee joint cavities of rats. ResultsThe results revealed that DAC-EVs packaged lncRNA LOC102546541 acts as a competitive endogenous RNA (ceRNA) of MMP13, down-regulating miR-632. Consequently, the function of MMP13 in degrading the extracellular matrix is enhanced, promoting the development of osteoarthritis. ConclusionsThis study uncovered a novel mode of OA pathogenesis using rat models, which DAC deliver pathogenic LOC102546541 packaged EVs to normal articular chondrocytes, amplifying the degradation of the extracellular matrix. Nonetheless, the functions of highly homologous human gene of LOC102546541 need to be verified in the future.

Metabolomic Profiling and Characterization of a Novel 3D Culture System for Studying Chondrocyte Mechanotransduction.

Articular chondrocytes synthesize and maintain the avascular and aneural articular cartilage. In vivo these cells are surrounded by a 3D pericellular matrix (PCM) containing predominantly collagen VI. The PCM protects chondrocytes and facilitates mechanotransduction, and PCM stiffness is critical in transmitting biomechanical signals to chondrocytes. Various culture systems with different hydrogels have been used to encapsulate chondrocytes for 3D culture, but many lack either the PCM or the in vivo stiffness of the cartilage matrix. Here, we demonstrate that primary chondrocytes cultured in alginate will form a pericellular matrix and display a phenotype similar to in vivo conditions. We found that primary human and bovine chondrocytes, when cultured in alginate beads with addition of sodium L-ascorbate for 7 days, had a pronounced PCM, retained their phenotype, and synthesized both collagens VI and II. This novel culture system enables alginate-encapsulated chondrocytes to develop a robust PCM thereby creating a model system to study mechanotransduction. We also observed distinct compression-induced changes in metabolomic profiles between the monolayer-agarose and alginate-released agarose-embedded chondrocytes indicating physiological changes in cell metabolism. Our data suggest that 3D preculture of chondrocytes in alginate before encapsulation in physiologically-stiff agarose leads to a pronounced development of pericellular matrix that is sustained in the presence of ascorbate. This novel model can be useful in studying the mechanism by which chondrocytes respond to cyclical compression and other types of loading simulating in vivo physiological conditions.

Growth deficiency in a mouse model of Kabuki syndrome 2 bears mechanistic similarities to Kabuki syndrome 1.

Growth deficiency is a characteristic feature of both Kabuki syndrome 1 (KS1) and Kabuki syndrome 2 (KS2), Mendelian disorders of the epigenetic machinery with similar phenotypes but distinct genetic etiologies. We previously described skeletal growth deficiency in a mouse model of KS1 and further established that a Kmt2d-/- chondrocyte model of KS1 exhibits precocious differentiation. Here we characterized growth deficiency in a mouse model of KS2, Kdm6atm1d/+. We show that Kdm6atm1d/+ mice have decreased femur and tibia length compared to controls and exhibit abnormalities in cortical and trabecular bone structure. Kdm6atm1d/+ growth plates are also shorter, due to decreases in hypertrophic chondrocyte size and hypertrophic zone height. Given these disturbances in the growth plate, we generated Kdm6a-/- chondrogenic cell lines. Similar to our prior in vitro model of KS1, we found that Kdm6a-/- cells undergo premature, enhanced differentiation towards chondrocytes compared to Kdm6a+/+ controls. RNA-seq showed that Kdm6a-/- cells have a distinct transcriptomic profile that indicates dysregulation of cartilage development. Finally, we performed RNA-seq simultaneously on Kmt2d-/-, Kdm6a-/-, and control lines at Days 7 and 14 of differentiation. This revealed surprising resemblance in gene expression between Kmt2d-/- and Kdm6a-/- at both time points and indicates that the similarity in phenotype between KS1 and KS2 also exists at the transcriptional level.

Growth hormone-receptor disruption in mice reduces osteoarthritis and chondrocyte hypertrophy

Excessive growth hormone (GH) has been shown to promote joint degeneration in both preclinical and clinical studies. Little is known about the effect of disrupted GH or GH receptor (GHR) on joint health. The goal of this study is to investigate joint pathology in mice with either germline (GHR-/-) or adult inducible (iGHR-/-) GHR deficiency. Knee joints from male and female GHR-/- and WT mice at 24 months of age were processed for histological analysis. Also, knee joints from male and female iGHR-/- and WT mice at 22 months of age were scanned by micro-CT (μCT) for subchondral bone changes and characterized via histology for cartilage degeneration. Joint sections were also stained for the chondrocyte hypertrophy marker, COLX, and the cartilage degeneration marker, ADAMTS-5, using immunohistochemistry. Compared to WT mice, GHR-/- mice had remarkably smooth articular joint surfaces and an even distribution of proteoglycan with no signs of degeneration. Quantitatively, GHR-/- mice had lower OARSI and Mankin scores compared to WT controls. By contrast, iGHR-/- mice were only moderately protected from developing aging-associated OA. iGHR-/- mice had a significantly lower Mankin score compared to WT. However, Mankin scores were not significantly different between iGHR-/- and WT when males and females were analyzed separately. OARSI scores did not differ significantly between WT and iGHR-/- in either individual or combined sex analyses. Both GHR-/- and iGHR-/- mice had fewer COLX+ hypertrophic chondrocytes compared to WT, while no significant difference was observed in ADAMTS-5 staining. Compared to WT, a significantly lower trabecular thickness in the subchondral bone was observed in the iGHR-/- male mice but not in the female mice. However, there were no significant differences between WT and iGHR-/- mice in the bone volume to total tissue volume (BV/TV), bone mineral density (BMD), and trabecular number in either sex. This study identified that both germline and adult-induced GHR deficiency protected mice from developing aging-associated OA with more effective protection in GHR-/- mice.

Three‐dimensional bioprinting biphasic multicellular living scaffold facilitates osteochondral defect regeneration

AbstractDue to tissue lineage variances and the anisotropic physiological characteristics, regenerating complex osteochondral tissues (cartilage and subchondral bone) remains a great challenge, which is primarily due to the distinct requirements for cartilage and subchondral bone regeneration. For cartilage regeneration, a significant amount of newly generated chondrocytes is required while maintaining their phenotype. Conversely, bone regeneration necessitates inducing stem cells to differentiate into osteoblasts. Additionally, the construction of the osteochondral interface is crucial. In this study, we fabricated a biphasic multicellular bioprinted scaffold mimicking natural osteochondral tissue employing three‐dimensional (3D) bioprinting technology. Briefly, gelatin‐methacryloyl (GelMA) loaded with articular chondrocytes and bone marrow mesenchymal stem cells (ACs/BMSCs), serving as the cartilage layer, preserved the phenotype of ACs and promoted the differentiation of BMSCs into chondrocytes through the interaction between ACs and BMSCs, thereby facilitating cartilage regeneration. GelMA/strontium‐substituted xonotlite (Sr‐CSH) loaded with BMSCs, serving as the subchondral bone layer, regulated the differentiation of BMSCs into osteoblasts and enhanced the secretion of cartilage matrix by ACs in the cartilage layer through the slow release of bioactive ions from Sr‐CSH. Additionally, GelMA, serving as the matrix material, contributed to the reconstruction of the osteochondral interface. Ultimately, this biphasic multicellular bioprinted scaffold demonstrated satisfactory simultaneous regeneration of osteochondral defects. In this study, a promising strategy for the application of 3D bioprinting technology in complex tissue regeneration was proposed.

FSGT capsule inhibits IL-1β-induced inflammation in chondrocytes and ameliorates osteoarthritis by upregulating LncRNA PACER and downregulating COX2/PGE2.

To explore the efficacy and potential mechanism of Fengshi Gutong capsule (FSGTC) in osteoarthritis (OA) inflammation. The impact of FSGTC on laboratory indicators of OA patients was explored using data mining technology and association rule analysis. Then, the OA cell model was constructed by inducing chondrocytes (CHs) with interleukin-1β (IL-1β). In the presence of FSGTC intervention, the regulatory mechanism of PACER/COX2/PGE2 in OA-CH viability and inflammatory responses was evaluated. Retrospective data mining showed that FSGTC effectively reduced inflammation indexes (ESR, HCRP) of OA patients. Cell experiments showed that LncRNA PACER (PACER) silencing inhibited the proliferation activity of OA-CHs, increased the level of COX2 protein, elevated the levels of PGE2, TNF-α, and IL-1β, and decreased the levels of IL-4 and IL-10 (p < .01). On the contrary, FSGTC-containing serum reversed the effect of PACER silencing on OA-CHs (p < .01). After the addition of COX2 pathway inhibitor, the proliferation activity of OA-CHs was enhanced; the levels of PGE2, TNF-α, and IL-1β were decreased while the levels of IL-4 and IL-10 were increased (p < .01). FSGTC inhibits IL-1β-induced inflammation in CHs and ameliorates OA by upregulating PACER and downregulating COX2/PGE2.

A high throughput cell stretch device for investigating mechanobiology in vitro

Mechanobiology is a rapidly advancing field, with growing evidence that mechanical signaling plays key roles in health and disease. To accelerate mechanobiology-based drug discovery, novel in vitro systems are needed that enable mechanical perturbation of cells in a format amenable to high throughput screening. Here, both a mechanical stretch device and 192-well silicone flexible linear stretch plate were designed and fabricated to meet high throughput technology needs for cell stretch-based applications. To demonstrate the utility of the stretch plate in automation and screening, cell dispensing, liquid handling, high content imaging, and high throughput sequencing platforms were employed. Using this system, an assay was developed as a biological validation and proof-of-concept readout for screening. A mechano-transcriptional stretch response was characterized using focused gene expression profiling measured by RNA-mediated oligonucleotide Annealing, Selection, and Ligation with Next-Gen sequencing. Using articular chondrocytes, a gene expression signature containing stretch responsive genes relevant to cartilage homeostasis and disease was identified. The possibility for integration of other stretch sensitive cell types (e.g., cardiovascular, airway, bladder, gut, and musculoskeletal), in combination with alternative phenotypic readouts (e.g., protein expression, proliferation, or spatial alignment), broadens the scope of high throughput stretch and allows for wider adoption by the research community. This high throughput mechanical stress device fills an unmet need in phenotypic screening technology to support drug discovery in mechanobiology-based disease areas.

Inverse genetics tracing the differentiation pathway of human chondrocytes

ObjectiveMammalian somatic cells can be reprogrammed into induced pluripotent stem cells (iPSCs) via the forced expression of Yamanaka reprogramming factors. However, only a limited population of the cells that pass through a particular pathway can metamorphose into iPSCs, while the others do not. This study aimed to clarify the pathways that chondrocytes follow during the reprogramming process. DesignThe fate of human articular chondrocytes under reprogramming was investigated through a time-coursed single-cell transcriptomic analysis, which we termed an inverse genetic approach. The iPS interference technique was also employed to verify that chondrocytes inversely return to pluripotency following the proper differentiation pathway. ResultsWe confirmed that human chondrocytes could be converted into cells with an iPSC phenotype. Moreover, it was clarified that a limited population that underwent the silencing of SOX9, a master gene for chondrogenesis, at a specific point during the proper transcriptome transition pathway, could eventually become iPSCs. Interestingly, the other cells, which failed to be reprogrammed, followed a distinct pathway toward cells with a surface zone chondrocyte phenotype. The critical involvement of cellular communication network factors (CCNs) in this process was indicated. The idea that chondrocytes, when reprogrammed into iPSCs, follow the differentiation pathway backward was supported by the successful iPS interference using SOX9. ConclusionsThis inverse genetic strategy may be useful for seeking candidates for the master genes for the differentiation of various somatic cells. The utility of CCNs in articular cartilage regeneration is also supported.