Chondrocyte Maturation Research Articles

Auricular cartilage regeneration using different types of mesenchymal stem cells in rabbits

BackgroundCartilaginous disorders comprise a wide range of diseases that affect normal joint movement, ear and nose shape; and they have great social and economic impact. Mesenchymal stem cells (MSCs) provide a promising regeneration alternative for treatment of degenerative cartilaginous disorders. This study aimed to compare therapeutic potential of different types of laser activated MSCs to promote auricular cartilage regeneration. Twelve adult rabbit allocated equally in four groups, all animals received a surgical mid auricular cartilage defect in one ear; Group I (Positive control) injected sub-perichondrially with phosphate-buffered saline (PBS), Group II (ADMSC-transplanted group) injected adipose-derived MSCs (ADMSCs), Group III (BMMSCs-transplanted group) received bone marrow-derived MSCs (BMMSCs), and Group IV (EMSC-transplanted group) received ear MSCs (EMSCs) in the defected ear. The auricular defect was analyzed morphologically, histopathologically and immunohistochemically after 4 weeks. In addition, a quantitative real-time polymerase chain reaction was used to examine expression of the collagen type II (Col II) and aggrecan as cartilage growth factors.ResultsThe auricles of all treatments appeared completely healed with smooth surfaces and similar tissue color. Histopathologically, defective areas of control positive group, ADMSCs and EMSCs treated groups experienced a small area of immature cartilage. While BMMSCs treated group exhibited typical features of new cartilage formation with mature chondrocytes inside their lacunae and dense extracellular matrix (ECM). In addition, BMMSC treated group showed a positive reaction to Masson’s trichrome and orcein stains. In contrary, control positive, ADMSC and EMSC groups revealed faint staining with Masson’s trichrome and Orcein. Immunohistochemically, there was an intense positive S100 expression in BMMSCs (with a significant increase of area percentage + 21.89 (P < 0.05), a moderate reaction in EMSCs (with an area percentage + 17.97, and a mild reaction in the control group and ADMSCs (area percentages + 8.02 and + 11.37, respectively). The expression of relative col II and aggrecan was substantially highest in BMMSCs (± 0.91 and ± 0.89, respectively). While, Control positive, ADMSCs and EMSCs groups recorded (± 0.41: ± 0.21, ± 0.6: ± 0.44, ± 0.61: ± 0.63) respectively.ConclusionBMMSCs showed the highest chondrogenic potential compared to ADMSCs and EMSCs and should be considered the first choice in treatment of cartilaginous degenerative disorders.

Increased Cellular Expression of Interleukin-6 in Patients With Ossification of the Posterior Longitudinal Ligament.

We performed histologic, immunohistochemical, immunoblot examination and suspension array analyses of cytokine expression in cultured cells derived from human cervical ossification of the posterior longitudinal ligament (OPLL). To determine the roles of interleukin-6 (IL-6) during the maturation of osteoblasts and chondrocytes associated with the development of OPLL. Ectopic OPLL affects ~3% of the general population, with a higher incidence in Asian ethnic groups. Alterations in cytokine profiles may influence osteoblast differentiation, but the mechanisms and signaling pathways associated with the ossification process remain unclear. Samples were collected from 14 patients with OPLL who had undergone spinal surgery and seven with cervical spondylotic myelopathy without OPLL. Tissue sections were used for histologic and immunohistochemical studies, and primary cells from ligamentum samples were used for cytokine array and immunoblotting. A suspension array was used to measure the concentrations of 27 inflammatory cytokines or growth factors. Suspension array and immunoblot analyses revealed significantly elevated levels of IL-6 in OPLL patients. Alterations in IL-6 concentrations were found to alter the expression of the genes Sox9 , Runx2 , and SIRT1 . In addition, immunohistochemical analysis revealed that these factors are present in mesenchymal cells within the degenerative portion of the ligament matrix that is adjacent to the ossification front. IL-6 plays a profound role in the osteoblast differentiation process along with the induction of chondrocyte hypertrophy and cell apoptosis in the early stages of ossification in OPLL. These changes in cytokine profiles are essential factors for regulation of the ectopic ossified plaque in OPLL.

A critical bioenergetic switch is regulated by IGF2 during murine cartilage development

Long bone growth requires the precise control of chondrocyte maturation from proliferation to hypertrophy during endochondral ossification, but the bioenergetic program that ensures normal cartilage development is still largely elusive. We show that chondrocytes have unique glucose metabolism signatures in these stages, and they undergo bioenergetic reprogramming from glycolysis to oxidative phosphorylation during maturation, accompanied by an upregulation of the pentose phosphate pathway. Inhibition of either oxidative phosphorylation or the pentose phosphate pathway in murine chondrocytes and bone organ cultures impaired hypertrophic differentiation, suggesting that the appropriate balance of these pathways is required for cartilage development. Insulin-like growth factor 2 (IGF2) deficiency resulted in a profound increase in oxidative phosphorylation in hypertrophic chondrocytes, suggesting that IGF2 is required to prevent overactive glucose metabolism and maintain a proper balance of metabolic pathways. Our results thus provide critical evidence of preference for a bioenergetic pathway in different stages of chondrocytes and highlight its importance as a fundamental mechanism in skeletal development.

Chondral/Desmal Osteogenesis in 3D Spheroids Sensitized by Psychostimulants.

Attention deficit hyperactivity disorder (ADHD) affects 6.4 million children in the United States of America. Children and adolescents, the main consumers of ADHD medication, are in the bone growth phase, which extends over a period of up to two decades. Thus, impaired proliferation and maturation of chondrocytes and osteoblasts can result in impaired bone formation. The aim of this study is to investigate, for the first time, the effects of the ADHD-medication modafinil, atomoxetine and guanfacine on bone growth and repair in vitro. Using two-dimensional and three-dimensional cell models, we investigated the chondrogenic/osteogenic differentiation, proliferation and viability of human mesenchymal progenitor cells. Real-time cell proliferation was measured by xCELLigence. Live/dead staining and size measurement of hMSC- and MG63 monolayer and spheroids were performed after administration of therapeutic plasma concentrations of modafinil, atomoxetine and guanfacine. Chondrogenic differentiation was quantified by RTqPCR. The chondrogenic and osteogenic differentiation was evaluated by histological cryo-sections. Modafinil, atomoxetine and guanfacine reduced chondrogenic and osteogenic differentiation terms of transcript expression and at the histological level. Cell viability of the MG63- and hMSC monolayer was not impeded by ADHD-medication. Our in vitro results indicate that modafinil, atomoxetine and guanfacine may impair chondrogenic and osteogenic differentiation in a 3D model reflecting the in vivo physiologic condition.

RUNX2 interacts with SCD1 and activates Wnt/β-catenin signaling pathway to promote the progression of clear cell renal cell carcinoma.

Previous studies have demonstrated that Runt-associated transcription factor 2 (RUNX2) serves as the main transcription factor for osteoblast differentiation and chondrocyte maturation. RUNX2 is related to a variety of tumors, particularly tumor invasion and metastasis, while the expression and molecular mechanisms of RUNX2 in clear cell renal cell carcinoma (ccRCC) keep to be determined. Stearyl CoA desaturase 1 (SCD1), an endoplasmic reticulum fatty acid desaturase, transfers saturated fatty acids to monounsaturated fatty acids, is expressed highly in numerous malignancies. The Cancer Genome Atlas (TCGA) datebase and Western blot was used to analyzed the mRNA and protein levels of the target gene in ccRCC tissues and adjacent tissues. The proliferation ability of ccRCC cells was tested by colony forming and EdU assay. The migration ability of cells was detected by transwell assay. Immunoprecipitation was utilized to detect protein-protein interaction. Cycloheximide chase assay was used to measure the half-life of SCD1 protein. In this study, the expressions of RUNX2 and SCD1 are increased in ccRCC tissues as well as ccRCC cell lines. Both RUNX2 and SCD1 could promote proliferation and migration in ccRCC cells. Furthermore, RUNX2 could physically interact with SCD1. In addition, the functional degradation and the inactivation of Wnt/β-catenin signaling pathway triggered by the downregulation of RUNX2 could be partly offset by the overexpression of SCD1. The findings indicate that the RUNX2/SCD1 axis may act as a potential therapeutic target via the Wnt/β-catenin signaling pathway of ccRCC.

Dynamic loading stimulates mandibular condyle remodeling

We and others have reported that low-magnitude high-frequency dynamic loading has an osteogenic effect on alveolar bone. Since chondrocytes and osteoblasts originate from the same progenitor cells, we reasoned that dynamic loading may stimulate a similar response in chondrocytes. A stimulating effect could be beneficial for patients with damaged condylar cartilage or mandibular deficiency. Studies were conducted on growing Sprague-Dawley rats divided into three groups: control, static load, and dynamic load. The dynamic load group received a dynamic load on the lower right molars 5 minutes per day with a 0.3 g acceleration and peak strain of 30 μεregistered by accelerometer and strain gauge. The static load group received an equivalent magnitude of static force (30 με). The control group did not receive any treatment. Samples were collected at days 0, 28, and 56 for reverse transcriptase polymerase chain reaction analysis, microcomputed tomography, and histology and fluorescent microscopy analysis. Our experiments showed that dynamic loading had a striking effect on condylar cartilage, increasing the proliferation and differentiation of mesenchymal cells into chondrocytes, and promoting chondrocyte maturation. This effect was accompanied by increased endochondral bone formation resulting in lengthening of the condylar process. Low-magnitude, high-frequency dynamic loading can have a positive effect on condylar cartilage and endochondral bone formation in vivo. This effect has the potential to be used as a treatment for regenerating condylar cartilage and to enhance the effect of orthopedic appliances on mandibular growth.

Gene Expression and Chondrogenic Potential of Cartilage Cells: Osteoarthritis Grade Differences.

Recent data suggest that cells isolated from osteoarthritic (OA) cartilage express mesenchymal progenitor cell (MPC) markers that have the capacity to form hyaline-like cartilage tissue. Whether or not these cells are influenced by the severity of OA remains unexplored. Therefore, we analyzed MPC marker expression and chondrogenetic potential of cells from mild, moderate and severe OA tissue. Human osteoarthritic tibial plateaus were obtained from 25 patients undergoing total knee replacement. Each sample was classified as mild, moderate or severe OA according to OARSI scoring. mRNA expression levels of MPC markers—CD105, CD166, Notch 1, Sox9; mature chondrocyte markers—Aggrecan (Acan), Col II A1, hypertrophic chondrocyte and osteoarthritis-related markers—Col I A1, MMP-13 and ALPL were measured at the tissue level (day 0), after 2 weeks of in vitro expansion (day 14) and following chondrogenic in vitro re-differentiation (day 35). Pellet matrix composition after in vitro chondrogenesis of different OA-derived cells was tested for proteoglycans, collagen II and I by safranin O and immunofluorescence staining. Multiple MPC markers were found in OA cartilage resident tissue within a single OA joint with no significant difference between grades except for Notch1, which was higher in severe OA tissues. Expression levels of CD105 and Notch 1 were comparable between OA cartilage-derived cells of different disease grades and bone marrow mesenchymal stem cell (BM-MSC) line (healthy control). However, the MPC marker Sox 9 was conserved after in vitro expansion and significantly higher in OA cartilage-derived cells compared to its levels in the BM-MSC. The in vitro expansion of cartilage-derived cells resulted in enrichment while re–differentiation in reduction of MPC markers for all three analyzed grades. However, only moderate OA-derived cells after the in vitro chondrogenesis resulted in the formation of hyaline cartilage-like tissue. The latter tissue samples were also highly positive for collagen II and proteoglycans with no expression of osteoarthritis-related markers (collagen I, ALPL and MMP13). MPC marker expression did not differ between OA grades at the tissue level. Interestingly after in vitro re-differentiation, only moderate OA-derived cells showed the capacity to form hyaline cartilage-like tissue. These findings may have implications for clinical practice to understand the intrinsic repair capacity of articular cartilage in OA tissues and raises the possibility of these progenitor cells as a candidate for articular cartilage repair.

Runx2 regulates chromatin accessibility to direct the osteoblast program at neonatal stages.

SUMMARYThe transcriptional regulator Runx2 (runt-related transcription factor 2) has essential but distinct roles in osteoblasts and chondrocytes in skeletal development. However, Runx2-mediated regulatory mechanisms underlying the distinctive programming of osteoblasts and chondrocytes are not well understood. Here, we perform an integrative analysis to investigate Runx2-DNA binding and chromatin accessibility ex vivo using neonatal osteoblasts and chondrocytes. We find that Runx2 engages with cell-type-distinct chromatin-accessible regions, potentially interacting with different combinations of transcriptional regulators, forming cell-type-specific hotspots, and potentiating chromatin accessibility. Genetic analysis and direct cellular reprogramming studies suggest that Runx2 is essential for establishment of chromatin accessibility in osteoblasts. Functional enhancer studies identify an Sp7 distal enhancer driven by Runx2-dependent binding and osteoblast-specific chromatin accessibility, contributing to normal osteoblast differentiation. Our findings provide a framework for understanding the regulatory landscape encompassing Runx2-mediated and cell-type-distinct enhancer networks that underlie the specification of osteoblasts.

CLEIDOCRANIAL DYSOSTOSIS: A CASE REPORT

Cleidocranial dysplasia is a rare disease caused by a defect in the RUNX2 gene on chromosome 6p21, which represents an essential transition factor for chondrocyte maturation and osteoblast differentiation. The patient affected by the genetic anomaly is 8 years old, and there are similar cases in the maternal family. He is followed up by a geneticist, being classified in ICD q78.8 (other specified osteochondrodysplasias) and ICD q74.0 (other congenital malformations of the upper limbs, including the shoulder girdle). The patient started treatment at the University Dental Service complaining of black, white, and brown spots on his teeth. The oral clinical and panoramic radiography characteristics of this patient include fusion, microdontia, and gyroversion. The treatment consisted of filling and sealant. The patient is under continuous supervision and guidance. The clinical and radiographic characteristics of this anomaly are rarely reported in the scientific literature.

Toxicity mechanisms regulating bone differentiation and development defects following abnormal expressions of miR-30c targeted by triclosan in zebrafish

As a ubiquitous environmental estrogen-disrupting chemical, triclosan (TCS) can induce severe osteotoxicity; however, the underlying molecular mechanisms remain uncertain. Herein, we evaluated the toxic effects of TCS on the development of cartilage and osteogenesis in 5-dpf zebrafish. Under TCS exposure from 62.5 to 250 μg/L, several osteodevelopmental malformations were observed, such as defect of craniofacial cartilage, pharyngeal arch cartilage dysplasia, and impairments on skeletal mineralization. Further, the morphology of mature chondrocytes became swollen and deformed, their number decreased, nucleus displacement occurred, and most immature chondrocytes were crowded at both ends of ceratobranchial. SEM observation of larval caudal fin revealed that, the layer of collagen fibers and the mineralized calcium nodules were significantly decreased, with the collagen fibers becoming shorter upon TCS exposure. The activity of bone-derived alkaline phosphatase significantly reduced, and marker functional genes related to cartilage and osteoblast development were abnormally expressed. RNA-seq and bioinformatics analysis indicated, that changes in marker genes intimately related to the negative regulation of miR-30c-5p overexpression targeted by TCS, and the up-regulation of miR-30c induced bone developmental defects by inhibiting the bone morphogenetic protein (BMP) signaling pathway. These findings were confirmed by artificially intervening the expression of miR-30c and using BMP pathway agonists in vivo. In sum, TCS induced osteototoxicity by targeting miR-30c up-regulation and interfering in the BMP signaling pathway. These findings enhance mechanistic understanding of TCS-induced spontaneous bone disorders and bone metastatic diseases. Further research is necessary to monitor chronic TCS-exposure levels in surrounding environments and develop relevant safety precautions based on TCS environmental risk.

Application of metal and rare earth nanocomposite materials in the repair of cartilage boxing damage

Articular cartilage covers the surface of the joints and is composed of cartilage tissue and its surrounding periosteum. It is an elastic connective tissue that does not ossify for a lifetime. This article aims to study the application of metal and rare earth nanocomposites in the repair of cartilage boxing injuries. In this paper, a numerical solution method for the equation of motion is proposed to study the dynamics of nanocomposites. The dynamics of nanocomposites are studied. The two-phase model algorithm of articular cartilage and the schematic diagram of articular cartilage are used to study the material properties of cartilage. Test the design, then conduct research and analysis on TiO2/Fe/PPy composite materials, conduct exploration experiments to better promote cell differentiation, explore the synthesis of Au–Pt nanoparticles, and analyze the influence of Mn ion on the activity of rBMSC to induce chondrocyte maturation and differentiation Inquiry, etc. The experimental results in this article show that the experimental analysis of nanomaterials and chondrocytes. Finally, this paper selects and uses 19 standard mechanical data sets to investigate and analyze the application of nanocomposite materials to cartilage damage repair, which verifies the accuracy and overall applicability of the method.

Trp53 controls chondrogenesis and endochondral ossification by negative regulation of TAZ activity and stability via β-TrCP-mediated ubiquitination

Transformation-related protein 53 (Trp53) is a critical regulator of cell fate determination by controlling cell proliferation and differentiation. Ablation of Trp53 signaling in osteoblast lineages significantly promotes osteogenesis, bone formation, and bone remodeling. However, how Trp53 regulates chondrogenesis and endochondral bone formation is undefined. In this study, we found that Trp53 expression gradually decreased in tibia growth plates during embryonic development in vivo and during chondrogenesis in vitro. By deleting Trp53 in chondrocyte lineage using Col2-Cre transgenic line, we found that loss of Trp53 in chondrocytes significantly increased growth plate growth and bone formation by increasing chondrocyte proliferation, matrix production and maturation, and bone dynamic formation rate. Mechanistically, our data revealed loss of Trp53 significantly promoted TAZ transcriptional activity through inhibition of TAZ phosphorylation and nuclear translocation, whereas its activity was pronouncedly inhibited after forced expression of Trp53. Furthermore, Co-IP data demonstrated that Trp53 associated with TAZ. Moreover, Trp53 decreased the stability of TAZ protein and promoted its degradation through β-TrCP-mediated ubiquitination. Ablation of TAZ in Col2-Cre;Trp53f/f mice rescued the phenotypes of enhanced chondrogenesis and bone formation caused by Trp53 deletion. Collectively, this study revealed that Trp53 modulates chondrogenesis and endochondral ossification through negative regulation of TAZ activity and stability, suggesting that targeting Trp53 signaling may be a potential strategy for fracture healing, heterotopic ossification, arthritis, and other bone diseases.

Mechanobiological Approaches for Stimulating Chondrogenesis of Stem Cells.

Chondrogenesis is the process of differentiation of stem cells into mature chondrocytes. Such a process consists of chemical, functional, and structural changes which are initiated and mediated by the host environment of the cells. To date, the mechanobiology of chondrogenesis has not been fully elucidated. Hence, experimental activity is focused on recreating specific environmental conditions for stimulating chondrogenesis and to look for a mechanistic interpretation of the mechanobiological response of cells in the cartilaginous tissues. There are a large number of studies on the topic that vary considerably in their experimental protocols used for providing environmental cues to cells for differentiation, making generalizable conclusions difficult to ascertain. The main objective of this contribution is to review the mechanobiological stimulation of stem cell chondrogenesis and methodological approaches utilized to date to promote chondrogenesis of stem cells in vitro. In vivo models will also be explored, but this area is currently limited. An overview of the experimental approaches used by different research groups may help the development of unified testing methods that could be used to overcome existing knowledge gaps, leading to an accelerated translation of experimental findings to clinical practice.

Unilateral Loss of Maxillary Molars in Young Mice Leads to Bilateral Condylar Adaptation and Degenerative Disease.

ABSTRACTThe adaptive response of the mandible and temporomandibular joint (TMJ) to altered occlusion in juvenile patients is presently unclear. To address this question, we established a mouse model in which all molars were extracted from the maxillary right quadrant in prepubertal, 3‐week‐old mice and analyzed morphological, tissue, cellular, and molecular changes in the mandible and condyle 3 weeks later. Unilateral loss of maxillary molars led to significant, robust, bilateral changes, primarily in condylar morphology, including anteroposterior narrowing of the condylar head and neck and increased convexity at the condylar surface, as determined by geometric morphometric analysis. Furthermore, both condyles in experimental mice exhibited a degenerative phenotype, which included decreased bone volume and increased mineral density near the condylar head surface compared to control mice. Changes in condylar morphology and mineralized tissue composition were associated with alterations in the cellular architecture of the mandibular condylar cartilage, including increased expression of markers for mature (Col2a1) and hypertrophic (Col10a1) chondrocytes, suggesting a shift toward differentiating chondrocytes. Our results show significant bilateral condylar morphological changes, alterations in tissue composition, cellular organization, and molecular expression, as well as degenerative disease, in response to the unilateral loss of teeth. Our study provides a relatively simple, tractable mouse tooth extraction system that will be of utility in uncovering the cellular and molecular mechanisms of condylar and mandibular adaptation in response to altered occlusion. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Limb Mesoderm and Head Ectomesenchyme Both Express a Core Transcriptional Program During Chondrocyte Differentiation.

To explain how cartilage appeared in different parts of the vertebrate body at discrete times during evolution, we hypothesize that different embryonic populations co-opted expression of a core gene regulatory network (GRN) driving chondrocyte differentiation. To test this hypothesis, laser-capture microdissection coupled with RNA-seq was used to reveal chondrocyte transcriptomes in the developing chick humerus and ceratobranchial, which are mesoderm- and neural crest-derived, respectively. During endochondral ossification, two general types of chondrocytes differentiate. Immature chondrocytes (IMM) represent the early stages of cartilage differentiation, while mature chondrocytes (MAT) undergo additional stages of differentiation, including hypertrophy and stimulating matrix mineralization and degradation. Venn diagram analyses generally revealed a high degree of conservation between chondrocyte transcriptomes of the limb and head, including SOX9, COL2A1, and ACAN expression. Typical maturation genes, such as COL10A1, IBSP, and SPP1, were upregulated in MAT compared to IMM in both limb and head chondrocytes. Gene co-expression network (GCN) analyses of limb and head chondrocyte transcriptomes estimated the core GRN governing cartilage differentiation. Two discrete portions of the GCN contained genes that were differentially expressed in limb or head chondrocytes, but these genes were enriched for biological processes related to limb/forelimb morphogenesis or neural crest-dependent processes, respectively, perhaps simply reflecting the embryonic origin of the cells. A core GRN driving cartilage differentiation in limb and head was revealed that included typical chondrocyte differentiation and maturation markers, as well as putative novel “chondrocyte” genes. Conservation of a core transcriptional program during chondrocyte differentiation in both the limb and head suggest that the same core GRN was co-opted when cartilage appeared in different regions of the skeleton during vertebrate evolution.

Abstract 932: Conditional p53 loss in chondrocytes leads to osteosarcoma in mice

Abstract Osteosarcoma (OS) is the most common primary malignant bone tumor in children and young adults. Lack of a basic understanding of OS etiology, and lack of a sensitive method to detect pulmonary micro-metastases are major obstacles impeding meaningful therapeutic advancement. Here we report the generation of genetically engineered lineage-tracing mouse OS models, in which p53 expressions were conditionally deleted or mutated in chondrocytes, indicating that OS can originate from chondrocyte-derived osteoblastic-lineage cells. OS incidence peaks during puberty when rapid bone growth occurs. Longitudinal bone growth is achieved through endochondral ossification, a process sustained by growth plates - cartilage discs at the ends of long bones. As bone lengthening, growth plate chondrocytes go through proliferation, differentiation, and maturation in sequential steps to provide a continuous supply of cartilage scaffolds for ossification. Besides, mature chondrocytes residing at chondral-osteo junctions, are themselves an innate source of osteoblasts directly participating in bone formation. Not only there is a close link between OS incidence and growth plate activity, primary OS is most frequently localized at the growing ends of long bones, such as at proximal tibia, distal femurs, and proximal humerus. Given these associations, we hypothesize that mice harboring p53 deletion initiated in mature chondrocytes may develop osteosarcoma, and if so chondrocytes to osteoblasts transformation may be a vulnerable process to genome instability triggers. We generated various chondrocyte-Cre driven lineage-tracing reporter mouse models, in which either Col10a1-Cre or Acn-CreERT2 were Cre drivers to induce p53 deleted, R245W hot spot, and p53 deleted/Rbhet alleles. To date Col10a1-Cre/p53fxfx/Rosa-tomato (Xp53KO) mice developed osteosarcoma with 100% penetrance (n=32). The mean latency in days is 273.3 ± 60.5 (195-330), in a similar range of Osx-cre/p53fxfx mice by CR Walkley, etc. The OS from Xp53KO mice histologically resemble human OS and possessed osteogenic and adipogenic differentiation capacities in vitro. Most notably, the Xp53KO mice developed OS in long bones and spines, no cranium-facial OS was detected. Regarding OS distributions, our Xp53KO OS mice show the closest resemblance to that of humans, compared to previous genetically engineered mouse OS models. Additionally, the transplanted OS from Xp53KO mice showed good response to cyclophosphamide treatment (n=7, 15mg/kg), but not to topotecan (n=7, 0.6mg/kg), vincristine (n=7, 1mg/kg) and rapamycin (n=7, 5mg/kg) treatments, analogous to human OS. With reporter (tomato) expressions, we can trace and isolate the OS ancestry cells from the onsets of deletions to osteosarcoma genesis at any stages, as well as mutant cells in distant sites. Our OS models may unveil critical insights into the development of OS as well as its dissemination. Citation Format: Xin Zhou, Zhaohui Xu, Yizheng Tu, Zhongting Zhang, Richard Gorlick. Conditional p53 loss in chondrocytes leads to osteosarcoma in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 932.

Whole Aspect of Runx2 Functions in Skeletal Development.

Runt-related transcription factor 2 (Runx2) is a fundamental transcription factor for bone development. In endochondral ossification, Runx2 induces chondrocyte maturation, enhances chondrocyte proliferation through Indian hedgehog (Ihh) induction, and induces the expression of vascular endothelial growth factor A (Vegfa), secreted phosphoprotein 1 (Spp1), integrin-binding sialoprotein (Ibsp), and matrix metallopeptidase 13 (Mmp13) in the terminal hypertrophic chondrocytes. Runx2 inhibits the apoptosis of the terminal hypertrophic chondrocytes and induces their transdifferentiation into osteoblasts and osteoblast progenitors. The transdifferentiation is required for trabecular bone formation during embryonic and newborn stages but is dispensable for acquiring normal bone mass in young and adult mice. Runx2 enhances the proliferation of osteoblast progenitors and induces their commitment to osteoblast lineage cells through the direct regulation of the expressions of a hedgehog, fibroblast growth factor (Fgf), Wnt, and parathyroid hormone-like hormone (Pthlh) signaling pathway genes and distal-less homeobox 5 (Dlx5), which all regulate Runx2 expression and/or protein activity. Runx2, Sp7, and Wnt signaling further induce osteoblast differentiation. In immature osteoblasts, Runx2 regulates the expression of bone matrix protein genes, including Col1a1, Col1a2, Spp1, Ibsp, and bone gamma carboxyglutamate protein (Bglap)/Bglap2, and induces osteoblast maturation. Osteocalcin (Bglap/Bglap2) is required for the alignment of apatite crystals parallel to the collagen fibers; however, it does not physiologically work as a hormone that regulates glucose metabolism, testosterone synthesis, or muscle mass. Thus, Runx2 exerts multiple functions essential for skeletal development.

Piezoelectric Effect of Antibacterial Biomimetic Hydrogel Promotes Osteochondral Defect Repair.

The lack of vascular tissue and the low metabolism and biological activity of mature chondrocytes lead to the low regeneration ability of articular cartilage. People try to solve this problem through various methods, but the effect is not very ideal. Inspired by the piezoelectric effect of collagen in cartilage tissue, this work focused on the design of a biomimetic hydrogel by introducing piezoelectric materials and silver nanowires into hydrogel to endow them with piezoelectric and antibacterial properties to promote tissue regeneration. Additionally, the mechanical and swelling properties of the material were adjusted to match natural articular cartilage. Based on bionic principles, a double-layer piezoelectric hydrogel was prepared and applied for the repair of osteochondral defects. An enhanced repair effect of osteochondral defects has been seen, which has demonstrated potential values for future application in bionics principle- and piezoelectric effect-based osteochondral tissue engineering. Furthermore, piezoelectric effect-induced degradation was observed. These results fully indicated the positive effect of the piezoelectric effect on promoting the regeneration of osteochondral tissue and in vivo degradation of materials.

Episodic alcohol exposure attenuates mesenchymal stem cell chondrogenic differentiation during bone fracture callus formation.

During bone fracture repair, mesenchymal stem cells (MSC) differentiate into chondrocytes and osteoblasts to form a fracture callus. Our laboratory previously reported that alcohol-exposed rodents with a surgically created tibia fracture display deficient fracture callus formation and diminished signs of endochondral ossification characterized by the absence of chondrocytes and mature hypertrophic chondrocytes, suggesting that alcohol may inhibit MSC differentiation. These findings led to our hypothesis that alcohol exposure inhibits mesenchymal stem cell chondrogenic differentiation within the developing fracture callus. In the present study, we utilized a lineage-tracing approach to determine which stage(s) of chondrogenic differentiation are affected by alcohol exposure. We utilized lineage-specific reporter mice to determine the effects of alcohol on MSC and early and late chondrogenic cell frequencies within the fracture callus. In addition, serially sectioned slides were stained immunofluorescently and immunohistochemically and quantified to determine the effect of alcohol on cell proliferation and apoptosis, respectively, within the fracture callus of alcohol-administered rodents. Alcohol-administered rodents had a reduced fracture callus area at 4, 6, and 9days postfracture. Alcohol had no effect on apoptosis in the fracture callus at any of the examined timepoints. Alcohol-administered rodents had significantly fewer proliferative cells in the fracture callus at 9days postfracture, but no effect on cell proliferation was observed at earlier fracture callus timepoints. Alcohol-administered rodents had reduced Collagen2a1- and Collagen10a1-expressing cells in the developing fracture callus, suggesting that alcohol inhibits both early chondrogenic differentiation and later chondrocyte maturation during fracture callus development. The data suggest that alcohol could affect normal fracture healing through the mitigation of MSC chondrogenic differentiation at the callus site.

Comparison of clinical outcomes following osteochondral allograft transplantation for osteochondral versus chondral defects in the knee

PurposeOsteochondral allograft (OCA) transplantation is a restorative technique for addressing articular cartilage defects by transferring mature viable chondrocytes with subchondral bone into size-matched lesions. The purpose of this study was to compare differences in clinical and functional outcomes in patients treated with OCA for osteochondral defects compared with isolated chondral pathology.MethodsA retrospective review identified patients who underwent OCA transplantation and grouped them into osteochondral or isolated chondral pathology. Demographic data, surgical history, lesion characteristics, complications, and rate of subsequent surgery were reviewed. The review included 86 patients (24 osteochondral, 62 chondral) with a mean follow-up of 5.4 ± 1.4 years. Outcome measures included the Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS, JR.), International Knee Documentation Committee (IKDC), and Short Form Health Survey (SF-12) physical scores. Failure was defined to include revision OCA, graft removal, conversion to ACI, or conversion to arthroplasty.ResultsThe average age at surgery was 32.3 and 37.3 years for the osteochondral and chondral groups, respectively (P = 0.056). The medial femoral condyle was the most common defect location in both groups. P < 0.05 was considered statistically significant. Patients with osteochondral pathology had significantly greater KOOS JR., IKDC, and SF-12 scores (P < 0.05), and fewer failures were reported in the osteochondral group (8.3% versus 32.3%, P = 0.045). When controlling for age, sex, laterality, BMI, and presence of a concomitant procedure, patients with osteochondral pathology were found to have better KOOS and IKDC scores, but there was no difference in SF12 scores or rates of failure between groups.ConclusionThe findings of this study indicate that patients undergoing OCA for osteochondral defects may have greater functional outcomes and similar failure rates compared with OCA transplantation for isolated chondral pathology.