Evidence of vasculature and chondrocyte to osteoblast transdifferentiation in craniofacial synovial joints: Implications for osteoarthritis diagnosis and therapy

Transition of endochondral bone formation at the normal and botulinum-treated mandibular condyle of growing juvenile rat

OBJECTIVE

The aim of this study was to understand the temporal and spatial distribution of canonical endochondral ossification (CEO) and non-canonical endochondral ossification (NCEO) of the normal growing rat condyle, and to evaluate their histomorphological changes following the simultaneous hypotrophy of the unilateral masticatory closing muscles with botulinum toxin (BTX).

DESIGN

46 rats at postnatal 4 weeks were used for the experiment and euthanized at postnatal 4, 8, and 16 weeks. The right masticatory muscles of rats in experimental group were injected with BTX, the left being injected with saline as a control. The samples were evaluated using 3D morphometric, histological, and immunohistochemical analysis with three-dimensional regional mapping of endochondral ossifications.

RESULTS

The results showed that condylar endochondral ossification changed from CEO to NCEO at the main articulating surface during the experimental period and that the BTX-treated condyle presented a retroclined smaller condyle with an anteriorly-shifted narrower articulating surface. This articulating region showed a thinner layer of the endochondral cells, and a compact distribution of flattened cells. These were related to the load concentration, decreased cellular proliferation with thin cellular layers, reduced extracellular matrix, increased cellular differentiation toward the osteoblastic bone formation, and accelerated transition of the ossification types from CEO to NCEO.

CONCLUSION

The results suggest that endochondral ossification under loading tended to show more NCEO, and that masticatory muscular hypofunction by BTX had deleterious effects on endochondral bone formation and changed the condylar growth vector, resulting in a retroclined, smaller, asymmetrical, and deformed condyle with thin cartilage.

Bulk RNA-seq analyses of mandibular condylar cartilage in a post-traumatic TMJ osteoarthritis rabbit model

OBJECTIVE

The temporomandibular joint (TMJ) is anatomically comprised of the mandibular condylar cartilage (CC) lined with fibrocartilaginous superficial zone and is crucial for eating and dental occlusion. TMJ osteoarthritis (OA) leads to pain, joint dysfunction and permanent loss of cartilage tissue. However, there are no drugs clinically available that ameliorate OA and little is known about global profiles of genes that contribute to TMJ OA. Furthermore, animal models that recapitulate the complexity of signalling pathways contributing to OA pathogenesis are crucial for designing novel biologics that thwart OA progression. We have previously developed a New Zealand white rabbit TMJ injury model that demonstrates CC degeneration. Here, we performed genome-wide profiling to identify new signalling pathways critical for cellular functions during OA pathology.

MATERIALS AND METHODS

Temporomandibular joint OA was surgically induced in New Zealand white rabbits. Three months following injury, we performed global gene expression profiling of the TMJ condyle. RNA samples from TMJ condyles were subjected to sequencing. After raw RNA-seq data were mapped to relevant genomes, differential expression was analysed with DESeq2. Gene ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway analysis were conducted.

RESULTS/CONCLUSIONS

Our study revealed multiple pathways altered during TMJ OA induction including the Wnt, Notch and PI3K-Akt signalling pathways. We demonstrate an animal model that recapitulates the complexity of the cues and signals underlying TMJ OA pathogenesis, which is essential for developing and testing novel pharmacologic agents to treat OA.

Temporomandibular joint osteoarthritis: A review of animal models induced by surgical interventions

OBJECTIVES

The pathological mechanism of temporomandibular joint osteoarthritis (TMJOA) is still unclear. Animal models induced by surgical interventions are one of the most ideal tools to imitate human pathological conditions. This review aims to define the similarities and differences of different surgical animal models.

METHODS

Articles of TMJOA surgical animal models were collected including anterior disc displacement, disc perforation, and discectomy. We analyzed their experiments strategies based on comparing preoperative selection, intraoperative methodology, and postoperative manifestations.

RESULTS

No matter which surgical intervention is selected, abnormal stress forces the whole joint to remodel its structure so that it could adapt to functional requirements, resulting in TMJOA eventually. However, anterior disc displacement needs more than 16 weeks to obtain typical manifestations, where the methodology is complicated. The course of perforation and discectomy is around 12-16 weeks, but they could cause excessive damage to the TMJ structure.

CONCLUSIONS

All surgical interventions can cause TMJOA, but the extent of pathology varies from each other. This review will assist future experiments to better understand the pathogenesis of TMJOA and choose the most appropriate model.

Lgr5-expressing secretory cells form a Wnt inhibitory niche in cartilage critical for chondrocyte identity

Osteoarthritis is a degenerative joint disease that causes pain, degradation, and dysfunction. Excessive canonical Wnt signaling in osteoarthritis contributes to chondrocyte phenotypic instability and loss of cartilage homeostasis; however, the regulatory niche is unknown. Using the temporomandibular joint as a model in multiple species, we identify Lgr5-expressing secretory cells as forming a Wnt inhibitory niche that instruct Wnt-inactive chondroprogenitors to form the nascent synovial joint and regulate chondrocyte lineage and identity. Lgr5 ablation or suppression during joint development, aging, or osteoarthritis results in depletion of Wnt-inactive chondroprogenitors and a surge of Wnt-activated, phenotypically unstable chondrocytes with osteoblast-like properties. We recapitulate the cartilage niche and create StemJEL, an injectable hydrogel therapy combining hyaluronic acid and sclerostin. Local delivery of StemJEL to post-traumatic osteoarthritic jaw and knee joints in rabbit, rat, and mini-pig models restores cartilage homeostasis, chondrocyte identity, and joint function. We provide proof of principal that StemJEL preserves the chondrocyte niche and alleviates osteoarthritis.

Evolution and development of the mammalian jaw joint: Making a novel structure

A jaw joint between the squamosal and dentary is a defining feature of mammals and is referred to as the temporomandibular joint (TMJ) in humans. Driven by changes in dentition and jaw musculature, this new joint evolved early in the mammalian ancestral lineage and permitted the transference of the ancestral jaw joint into the middle ear. The fossil record demonstrates the steps in the cynodont lineage that led to the acquisition of the TMJ, including the expansion of the dentary bone, formation of the coronoid process, and initial contact between the dentary and squamosal. From a developmental perspective, the components of the TMJ form through tissue interactions of muscle and skeletal elements, as well as through interaction between the jaw and the cranial base, with the signals involved in these interactions being both biomechanical and biochemical. In this review, we discuss the development of the TMJ in an evolutionary context. We describe the evolution of the TMJ in the fossil record and the development of the TMJ in embryonic development. We address the formation of key elements of the TMJ and how knowledge from developmental biology can inform our understanding of TMJ evolution.

Spheroid culture for chondrocytes triggers early stage of endochondral ossification

Endochondral ossification is the process of bone formation derived from growing cartilage during the development of the skeletal system. In previous studies, we have attempted to evoke the osteocyte differentiation of osteoblast precursor cells under a three-dimensional (3D) culture model. In order to recapitulate the endochondral ossification, the present study utilized the self-organized scaffold-free spheroid model reconstructed by pre-chondrocyte cells. Within 2-day cultivation in the absence of the chemically induced chondrogenesis supplements, the chondrocyte marker was greatly expressed in the inner region of the spheroid, whereas the hypertrophic chondrocyte marker was strongly detected in the surface region of the spheroid. Notably, we found out that the gene expression levels of osteocyte markers were also greatly up-regulated compared to the conventional 2D monolayer. Moreover, there was a hypertrophied morphologic change in the pre-chondrocyte spheroid from 4-day to 28-day cultivation. In this study, we highlighted the potentials of the 3D culture method to acquire the hypertrophic chondrocyte differentiation of the pre-chondrocyte cells to recapitulate the early stage of the endochondral ossification. This article is protected by copyright. All rights reserved.

The Emerging Role of Cell Transdifferentiation in Skeletal Development and Diseases

The vertebrate musculoskeletal system is known to be formed by mesenchymal stem cells condensing into tissue elements, which then differentiate into cartilage, bone, tendon/ligament, and muscle cells. These lineage-committed cells mature into end-stage differentiated cells, like hypertrophic chondrocytes and osteocytes, which are expected to expire and to be replaced by newly differentiated cells arising from the same lineage pathway. However, there is emerging evidence of the role of cell transdifferentiation in bone development and disease. Although the concept of cell transdifferentiation is not new, a breakthrough in cell lineage tracing allowed scientists to trace cell fates in vivo. Using this powerful tool, new theories have been established: (1) hypertrophic chondrocytes can transdifferentiate into bone cells during endochondral bone formation, fracture repair, and some bone diseases, and (2) tendon cells, beyond their conventional role in joint movement, directly participate in normal bone and cartilage formation, and ectopic ossification. The goal of this review is to obtain a better understanding of the key roles of cell transdifferentiation in skeletal development and diseases. We will first review the transdifferentiation of chondrocytes to bone cells during endochondral bone formation. Specifically, we will include the history of the debate on the fate of chondrocytes during bone formation, the key findings obtained in recent years on the critical factors and molecules that regulate this cell fate change, and the role of chondrocyte transdifferentiation in skeletal trauma and diseases. In addition, we will also summarize the latest discoveries on the novel roles of tendon cells and adipocytes on skeletal formation and diseases.

Animal Models of Temporomandibular Joint Osteoarthritis: Classification and Selection

Temporomandibular joint osteoarthritis (TMJOA) is a common degenerative joint disease that can cause severe pain and dysfunction. It has a serious impact on the quality of lives of patients. Since mechanism underlying the pathogenesis of TMJOA is not fully understood, the development of effective tools for early diagnosis and disease-modifying therapies has been hindered. Animal models play a key role in understanding the pathological process of diseases and evaluating new therapeutic interventions. Although some similarities in disease processes between animals and humans are known, no one animal model is sufficient for studying all characteristics of TMJOA, as each model has different translatability to human clinical conditions. For the past 4 decades, TMJOA animal models have been studied by numerous researchers and can be broadly divided into induced, naturally occurring, and genetically modified models. The induced models can be divided into invasive models (intra-articular injection and surgical induction) or non-invasive models (mechanical loading, high-fat diet, and sleep deprivation). Different types of animal models simulate different pathological expressions of TMJOA and have their unique characteristics. Currently, mice, rats, and rabbits are commonly used in the study of TMJOA. This review sought to provide a general description of current experimental models of TMJOA and assist researchers in selecting the most appropriate models for different kinds of research.

An updated view on Temporomandibular Joint degeneration: insights from the cell subsets of mandibular condylar cartilage

The high prevalence of temporomandibular joint osteoarthritis (TMJOA), which causes joint dysfunction, indicates the need for more effective methods for treatment and repair. Mandibular condylar cartilage (MCC), a typical fibrocartilage that experiences degenerative changes during the development of TMJOA, has become a research focus and therapeutic target in recent years. MCC is composed of four zones of cells at various stages of differentiation. The cell subsets in MCC exhibit different physiological and pathological characteristics during development and in TMJOA. Most studies of TMJOA are mainly concerned with gene regulation of pathological changes. The corresponding treatment targets with specific cell subsets in MCC may provide more accurate and reliable results for cartilage repair and TMJOA treatment. In this review, we summarized the current research progress on the cell subsets of MCC from the perspective of MCC development and degeneration. We hope to provide a reference for further exploration of the pathological process of TMJOA and improvement of TMJOA treatment.

A novel in vitro assay to study chondrocyte-to-osteoblast transdifferentiation

PURPOSE

Endochondral ossification, which involves transdifferentiation of chondrocytes into osteoblasts, is an important process involved in the development and postnatal growth of most vertebrate bones as well as in bone fracture healing. To study the basic molecular mechanisms of this process, a robust and easy-to-use in vitro model is desirable. Therefore, we aimed to develop a standardized in vitro assay for the transdifferentiation of chondrogenic cells towards the osteogenic lineage.

METHODS

Murine chondrogenic ATDC5 cells were differentiated into the chondrogenic lineage for seven days and subsequently differentiated towards the osteogenic direction. Gene expression analysis of pluripotency, as well as chondrogenic and osteogenic markers, cell-matrix staining, and immunofluorescent staining, were performed to assess the differentiation. In addition, the effects of Wnt3a and lipopolysaccharides (LPS) on the transdifferentiation were tested by their addition to the osteogenic differentiation medium.

RESULTS

Following osteogenic differentiation, chondrogenically pe-differentiated cells displayed the expression of pluripotency and osteogenic marker genes as well as alkaline phosphatase activity and a mineralized matrix. Co-expression of Col2a1 and Col1a1 after one day of osteogenic differentiation indicated that osteogenic cells had differentiated from chondrogenic cells. Wnt3a increased and LPS decreased transdifferentiation towards the osteogenic lineage.

CONCLUSION

We successfully established a rapid, standardized in vitro assay for the transdifferentiation of chondrogenic cells into osteogenic cells, which is suitable for testing the effects of different compounds on this cellular process.

Diversity of Vascular Niches in Bones and Joints During Homeostasis, Ageing, and Diseases

The bones and joints in the skeletal system are composed of diverse cell types, including vascular niches, bone cells, connective tissue cells and mineral deposits and regulate whole-body homeostasis. The capacity of maintaining strength and generation of blood lineages lies within the skeletal system. Bone harbours blood and immune cells and their progenitors, and vascular cells provide several immune cell type niches. Blood vessels in bone are phenotypically and functionally diverse, with distinct capillary subtypes exhibiting striking changes with age. The bone vasculature has a special impact on osteogenesis and haematopoiesis, and dysregulation of the vasculature is associated with diverse blood and bone diseases. Ageing is associated with perturbed haematopoiesis, loss of osteogenesis, increased adipogenesis and diminished immune response and immune cell production. Endothelial and perivascular cells impact immune cell production and play a crucial role during inflammation. Here, we discuss normal and maladapted vascular niches in bone during development, homeostasis, ageing and bone diseases such as rheumatoid arthritis and osteoarthritis. Further, we discuss the role of vascular niches during bone malignancy.

Involvement of an FTO gene polymorphism in the temporomandibular joint osteoarthritis

Objectives

The FTO gene has been reported as an obesity-associated gene and is also considered a risk gene for osteoarthritis (OA). However, its exact function is unclear, and there is conflicting evidence on the involvement of FTO polymorphisms in OA via obesity. The purpose of this study was to determine the effects of FTO polymorphism rs8044769 alleles on OA in the temporomandibular joint (TMJ), which is minimally affected by body weight.

Materials and methods

A total of 324 TMJs (113 with OA and 211 without OA, serving as controls) from 162 Japanese patients with temporomandibular disorders and undergoing MRI examination were analyzed. Genotyping was conducted, and multivariate analysis was performed after adjusting for the effects of age, sex, body mass index, and TMJ disc abnormalities.

Results

Mean age, BMI, and sex did not differ between the TMJs with OA and the TMJs without OA, but a significant difference was found for positional and dynamic disc abnormalities (P < 0.05). The allele frequency of FTO polymorphisms also differed significantly between the TMJs with OA and the TMJs without OA (P = 0.011). Moreover, logistic regression analysis showed no significant association between BMI (P = 0.581) and the occurrence of TMJOA but also indicated that the CC allele of rs8044769 is a risk factor for TMJOA (P = 0.040).

Conclusions

Our results show that rs8044769 in the FTO gene might be involved in TMJOA.

Clinical relevance

The present study provides a basis for a deeper understanding of the mechanism underlying degenerative skeletal diseases and the more effective selection and development of treatment strategies based on the patients’ genetic characteristics.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00784-021-04278-9.

Tissue engineered autologous cartilage-bone grafts for temporomandibular joint regeneration

Joint disorders can be detrimental to quality of life. There is an unmet need for precise functional reconstruction of native-like cartilage and bone tissues in the craniofacial space and particularly for the temporomandibular joint (TMJ). Current surgical methods suffer from lack of precision and comorbidities and frequently involve multiple operations. Studies have sought to improve craniofacial bone grafts without addressing the cartilage, which is essential to TMJ function. For the human-sized TMJ in the Yucatan minipig model, we engineered autologous, biologically, and anatomically matched cartilage-bone grafts for repairing the ramus-condyle unit (RCU), a geometrically intricate structure subjected to complex loading forces. Using image-guided micromilling, anatomically precise scaffolds were created from decellularized bone matrix and infused with autologous adipose-derived chondrogenic and osteogenic progenitor cells. The resulting constructs were cultured in a dual perfusion bioreactor for 5 weeks before implantation. Six months after implantation, the bioengineered RCUs maintained their predefined anatomical structure and regenerated full-thickness, stratified, and mechanically robust cartilage over the underlying bone, to a greater extent than either autologous bone-only engineered grafts or acellular scaffolds. Tracking of implanted cells and parallel bioreactor studies enabled additional insights into the progression of cartilage and bone regeneration. This study demonstrates the feasibility of TMJ regeneration using anatomically precise, autologous, living cartilage-bone grafts for functional, personalized total joint replacement. Inclusion of the adjacent tissues such as soft connective tissues and the TMJ disc could further extend the functional integration of engineered RCUs with the host.

Osteocyte Dysfunction in Joint Homeostasis and Osteoarthritis

Structural disturbances of the subchondral bone are a hallmark of osteoarthritis (OA), including sclerotic changes, cystic lesions, and osteophyte formation. Osteocytes act as mechanosensory units for the micro-cracks in response to mechanical loading. Once stimulated, osteocytes initiate the reparative process by recruiting bone-resorbing cells and bone-forming cells to maintain bone homeostasis. Osteocyte-expressed sclerostin is known as a negative regulator of bone formation through Wnt signaling and the RANKL pathway. In this review, we will summarize current understandings of osteocytes at the crossroad of allometry and mechanobiology to exploit the relationship between osteocyte morphology and function in the context of joint aging and osteoarthritis. We also aimed to summarize the osteocyte dysfunction and its link with structural and functional disturbances of the osteoarthritic subchondral bone at the molecular level. Compared with normal bones, the osteoarthritic subchondral bone is characterized by a higher bone volume fraction, a larger trabecular bone number in the load-bearing region, and an increase in thickness of pre-existing trabeculae. This may relate to the aberrant expressions of sclerostin, periostin, dentin matrix protein 1, matrix extracellular phosphoglycoprotein, insulin-like growth factor 1, and transforming growth factor-beta, among others. The number of osteocyte lacunae embedded in OA bone is also significantly higher, yet the volume of individual lacuna is relatively smaller, which could suggest abnormal metabolism in association with allometry. The remarkably lower percentage of sclerostin-positive osteocytes, together with clustering of Runx-2 positive pre-osteoblasts, may suggest altered regulation of osteoblast differentiation and osteoblast-osteocyte transformation affected by both signaling molecules and the extracellular matrix. Aberrant osteocyte morphology and function, along with anomalies in molecular signaling mechanisms, might explain in part, if not all, the pre-osteoblast clustering and the uncoupled bone remodeling in OA subchondral bone.

Establishment of Pulp Damage Repair Models in Miniature Pigs Using Diode Lasers

Objective: To establish a controlled pulp damage repair model in miniature pigs by using a diode laser. Background: Laser is a novel kind of controllable energy, and it is widely used in dentistry. Methods: The premolars of four 24- to 28-month-old miniature pigs were divided into three laser groups, according to the output powers of a diode laser, and the nonirradiated first molars acted as controls. The teeth in laser groups were irradiated under three parameters (output powers 1.5, 2.5, 4 W, continuous wave, frequency 50 Hz for 60 sec). The dental and gingival morphology was observed at 0, 7, 14, and 21 days after laser irradiation. The animals were sacrificed for qualitative and quantitative pulp histopathological analysis. Results: The three laser groups present no seriously irreversible dental and gingival damage. In the 1.5-W group, dental pulp exhibited angiectasis and hyperemia with no inflammation, and did not significantly differ with the control groups at 21 days (p > 0.05). In the 2.5-W group, pulpal inflammation was highest at 7 days and then decreased significantly at 21 days, and the tissue repair appeared at 14 days (p < 0.05). In the 4-W group, pulpal inflammation was significantly highest at 7 days, with an increase in the degree of tissue repair (p < 0.05). Conclusions: The output power of 1.5 W developed a reversible pulpitis model; the output powers of 2.5 and 4 W within 7 days led to the development of irreversible pulpitis models, which proceeded as chronic pulpitis with obvious tissue repair.

Effect of Substance P on Differentiation of Bone Marrow Stromal Stem Cells Under Oxidative Stress

Bone marrow stromal stem cells (BMSCs) can be used to treat bone defects but BMSCs are damaged under oxidative stress. The neuropeptide substance P (SP) involves various cellular activities. However, SP’s role in BMSCs differentiation under oxidative stress is unknown. Rat BMSCs were isolated and assigned into control group; oxidative stress group treated with 200 μM H2O2; and SP group, in which 10 mM SP was added under oxidative stress followed by analysis of SP secretion by ELISA, cell proliferation by MTT method, Caspase3 activity, Bax and Bcl-2 level by Real time PCR, ALP activity ROS and SOD content as well as NF-κB level by Western blot. Under oxidative stress, SP secretion was significantly decreased, BMSCs proliferation was inhibited, Caspase3 activity and Bax expression increased, Bcl-2 and ALP activity was decreased along with increased ROS activity and NF-κB level and reduced SOD activity (P <0.05), adding SP to BMSCs under oxidative stress can significantly promote SP secretion and cell proliferation, reduce Caspase3 activity and Bax expression, increase Bcl-2 expression and ALP activity, decreased ROS activity and NF-κB level, and elevated SOD activity (P <0.05). SP secretion from BMSCs cells was reduced under oxidative stress. Up-regulation of SP in BMSCs cells under oxidative stress can inhibit BMSCs apoptosis and promote cell proliferation and osteogenesis by regulating NF-κB.

An Update on Mesenchymal Stem Cell-Centered Therapies in Temporomandibular Joint Osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disease characterized by cartilage degeneration, disrupted subchondral bone remodeling, and synovitis, seriously affecting the quality of life of patients with chronic pain and functional disabilities. Current treatments for TMJOA are mainly symptomatic therapies without reliable long-term efficacy, due to the limited self-renewal capability of the condyle and the poorly elucidated pathogenesis of TMJOA. Recently, there has been increased interest in cellular therapies for osteoarthritis and TMJ regeneration. Mesenchymal stem cells (MSCs), self-renewing and multipotent progenitor cells, play a promising role in TMJOA treatment. Derived from a variety of tissues, MSCs exert therapeutic effects through diverse mechanisms, including chondrogenic differentiation; fibrocartilage regeneration; and trophic, immunomodulatory, and anti-inflammatory effects. Here, we provide an overview of the therapeutic roles of various tissue-specific MSCs in osteoarthritic TMJ or TMJ regenerative tissue engineering, with an additional focus on joint-resident stem cells and other cellular therapies, such as exosomes and adipose-derived stromal vascular fraction (SVF). Additionally, we summarized the updated pathogenesis of TMJOA to provide a better understanding of the pathological mechanisms of cellular therapies. Although limitations exist, MSC-centered therapies still provide novel, innovative approaches for TMJOA treatment.

SOX9 keeps growth plates and articular cartilage healthy by inhibiting chondrocyte dedifferentiation/osteoblastic redifferentiation

Cartilage is essential throughout vertebrate life. It starts developing in embryos when osteochondroprogenitor cells commit to chondrogenesis, activate a pancartilaginous program to form cartilaginous skeletal primordia, and also embrace a growth-plate program to drive skeletal growth or an articular program to build permanent joint cartilage. Various forms of cartilage malformation and degeneration diseases afflict humans, but underlying mechanisms are still incompletely understood and treatment options suboptimal. The transcription factor SOX9 is required for embryonic chondrogenesis, but its postnatal roles remain unclear, despite evidence that it is down-regulated in osteoarthritis and heterozygously inactivated in campomelic dysplasia, a severe skeletal dysplasia characterized postnatally by small stature and kyphoscoliosis. Using conditional knockout mice and high-throughput sequencing assays, we show here that SOX9 is required postnatally to prevent growth-plate closure and preosteoarthritic deterioration of articular cartilage. Its deficiency prompts growth-plate chondrocytes at all stages to swiftly reach a terminal/dedifferentiated stage marked by expression of chondrocyte-specific (Mgp) and progenitor-specific (Nt5e and Sox4) genes. Up-regulation of osteogenic genes (Runx2, Sp7, and Postn) and overt osteoblastogenesis quickly ensue. SOX9 deficiency does not perturb the articular program, except in load-bearing regions, where it also provokes chondrocyte-to-osteoblast conversion via a progenitor stage. Pathway analyses support roles for SOX9 in controlling TGFβ and BMP signaling activities during this cell lineage transition. Altogether, these findings deepen our current understanding of the cellular and molecular mechanisms that specifically ensure lifelong growth-plate and articular cartilage vigor by identifying osteogenic plasticity of growth-plate and articular chondrocytes and a SOX9-countered chondrocyte dedifferentiation/osteoblast redifferentiation process.

DLX5 and HOXC8 enhance the chondrogenic differentiation potential of stem cells from apical papilla via LINC01013

BACKGROUND

Mesenchymal stem cell (MSC)-based cartilage tissue regeneration is a treatment with great potential. How to enhance the MSC chondrogenic differentiation is a key issue involved in cartilage formation. In the present study, we seek to expound the phenotypes and mechanisms of DLX5 in chondrogenic differentiation function in MSCs.

METHODS

Stem cells from apical papilla (SCAPs) were used. The Alcian Blue staining, pellet culture system, and cell transplantation in rabbit knee cartilage defect were used to evaluate the chondrogenic differentiation function of MSCs. Western blot, real-time RT-PCR, and ChIP assays were used to evaluate the molecular mechanisms.

RESULTS

DLX5 and HOXC8 expressions were upregulated during chondrogenic differentiation. In vitro results showed that DLX5 and HOXC8 enhanced the expression of chondrogenic markers including collagen II (COL2), collagen V (COL5), and sex-determining region Y box protein 9 (SOX9) and promoted the chondrogenic differentiation and the formation of cartilage clumps in the pellet culture system. Mechanically, DLX5 and HOXC8 formed protein complexes and negatively regulated the LncRNA, LINC01013, via directly binding its promoter. In vivo transplantation experiment showed that DLX5 and HOXC8 could restore the cartilage defect in the rabbit knee model. In addition, knock-down of LINC01013 enhanced the chondrogenic differentiation of SCAPs.

CONCLUSIONS

In conclusion, DLX5 and HOXC8 enhance the chondrogenic differentiation abilities of SCAPs by negatively regulating LINC01013 in SCAPs, and provided the potential target for promoting cartilage tissue regeneration.