Sox9 sustains chondrocyte survival and hypertrophy in part through Pik3ca-Akt pathways

Fluoride Exposure Modulates Skeletal Development and Mineralization in Zebrafish Larvae

The presence of high levels of fluoride (F) in groundwater is a major issue worldwide. Although F is essential for healthy teeth and bones, excessive exposure can cause fluorosis or F toxicity. This condition primarily affects the hard tissues due to their high F retention capacity. F accumulation alters bone formation and resorption mechanisms interfering with mineral homeostasis and eventually manifests as skeletal fluorosis. Albeit the numerous studies on skeletal fluorosis, the effect of F on developmental osteogenesis is inconclusive. In light of this, we studied the effect of F on osteogenic differentiation, bone development, and mineralization in zebrafish. Zebrafish embryos were subjected to a low (25 ppm NaF), and a moderately high (50 ppm NaF) dose, along with a control (E3 medium alone) until 7 days postfertilization (dpf). The F content in the larvae was quantified to reveal a dose-dependent increase in the exposed groups. Alizarin Red and alkaline phosphatase (ALP) staining suggested enhanced mineralization in the F-treated groups. Quantitative analyses of the ALP activity and hydroxyproline (Hyp) content revealed similar results. Alcian blue staining of pharyngeal cartilages showed that F exposure alters the morphology of the major cartilages, indicating a possible craniofacial defect. Moreover, gene expression analyses of the bone markers associated with osteogenic differentiation, early mineralization, and remodeling (runx2a/b, bmp4, ocn, osx, col1a1, alp, rank, rankl, and opg) showed enhanced expression in the low F group. While the 50 ppm F group showed a decline in osteogenic activity, a considerable increase in the expression of mineralization markers was observed. The expression levels of cartilage markers sox9a and sox9b, remained insignificant, indicating the effect of F toxicity on osteogenesis and mineralization. Also, F exposure interferes with bone metabolism through altered osteogenic differentiation, development, and mineralization in zebrafish larvae.

NSAID-mediated cyclooxygenase inhibition disrupts ectodermal derivative formation in axolotl embryos

Embryonic exposures to non-steroidal anti-inflammatory drugs (NSAIDs) have been linked to preterm birth, neural tube closure defects, abnormal enteric innervation, and craniofacial malformations, potentially due to disrupted neural tube or neural crest (NC) cell development. Naproxen (NPX), a common non-steroidal anti-inflammatory drug (NSAID) used to relieve pain and inflammation, exerts its effects through non-selective cyclooxygenase (COX) inhibition. Our lab has identified that the cyclooxygenase (COX-1 and COX-2) isoenzymes are expressed during the early stages of vertebrate embryonic development, and that global inhibition of COX-1 and COX-2 function disrupts NC cell migration and differentiation in Ambystoma mexicanum (axolotl) embryos. NC cells differentiate into various adult tissues including craniofacial cartilage, bone, and neurons in the peripheral and enteric nervous systems. To investigate the specific phenotypic and molecular effects of NPX exposure on NC development and differentiation, and to identify molecular links between COX inhibition and NC derivative anomalies, we exposed late neurula and early tailbud stage axolotl embryos to various concentrations of NPX and performed immunohistochemistry (IHC) for markers of migratory and differentiating NC cells. Our results reveal that NPX exposure impairs the migration of SOX9+ NC cells, leading to abnormal development of craniofacial cartilage structures, including Meckel's cartilage in the jaw. NPX exposure also alters the expression of markers associated with peripheral and central nervous system (PNS and CNS) development, suggesting concurrent neurodevelopmental changes.

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

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

Endoplasmic reticulum stress causes long bone shortening in P4hbC402R/+ mice: A mouse model exhibiting significant features of cole-carpenter syndrome driven by P4HB mutations

Cole-Carpenter syndrome (CCS) is a rare autosomal-dominant genetic disease characterized by craniosynostosis, ocular proptosis, hydrocephalus, distinctive facial features, and bone fragility. Previous cases of CCS are associated with genetic variations in P4HB, which encodes the protein disulfide isomerase (PDI), a key enzyme in protein folding. Patients with CCS caused by P4HB mutations often present with short stature, limb deformities, and abnormal epiphyseal plates. However, the underlying mechanisms are largely unknown. To investigate this, a mouse model expressing the P4hbC402R mutation (corresponding to P4HBC400R in humans) was generated. Although the mouse model did not exhibit craniofacial bone defects or brittle bone phenotypes, it did show significantly shortened long bones-a prominent characteristic of P4HB-induced CCS. This was due to impaired proliferation and delayed hypertrophy of growth plate chondrocytes. Mutant PDI was found to accumulate abnormally in the endoplasmic reticulum (ER), and in vitro experiments revealed defects in both the catalytic and chaperone activities of mutant PDI. In addition, we observed enhanced ER stress and activation of the PKR-like ER kinase (PERK) pathway in P4hbC402R/+ chondrocytes. Inhibition of ER stress mitigated PERK activation, alleviated defective chondrocyte proliferation and differentiation, thereby rescuing bone length. Taken together, enhanced ER stress and the activation of the PERK, potentially initiated by the malfunctioning of PDIC402R or its abnormal accumulation within the ER, or both, lead to compromised chondrocyte proliferation and differentiation in mice, and ultimately stunts mice growth. This provides new insights into the pathogenesis of P4HB-dominated CCS and offers potential therapeutic targets.

Genetics and Epigenetics of Legg-Calvé-Perthes Disease

» Multifactorial Pathogenesis: Legg-Calvé-Perthes disease (LCPD) may result from a complex interplay of genetic, epigenetic, and environmental factors, culminating in avascular necrosis of the femoral head in children aged 4 to 10 years.» Genetic Contributions: Mutations in COL2A1 weaken cartilage integrity, and polymorphisms in IL6 drive inflammatory responses, exacerbating bone resorption and necrosis.» Role of Epigenetics: Epigenetic mechanisms, such as altered DNA methylation and miRNA dysregulation, may modulate disease progression by linking genetic susceptibility to environmental influences.» Environmental Amplifiers: Key environmental risk factors, including maternal smoking, low birth weight, and socioeconomic deprivation, may exacerbate the genetic and epigenetic predisposition to LCPD.» Future Directions: Advancements in genetic screening and epigenetic therapies, such as miRNA modulators and DNA methylation inhibitors, combined with preventive measures like improved prenatal care and reduced smoke exposure, may offer promising avenues for optimizing outcomes in LCPD.

Pain mediator NGF improves chondrocyte extracellular matrix synthesis via PI3K/AKT pathway

OBJECTIVES

Nerve growth factor (NGF) is a key mediator in osteoarthritis pain signaling. Clinical studies revealed that anti-NGF antibodies are often accompanied by progressively worsening cartilage degeneration, although they exhibit significant analgesic effects. However, the relationship between NGF expression and cartilage destruction remains unclear. Our study aimed to investigate the effects of NGF on chondrocytes and to elucidate the underlying mechanisms involved.

METHODS

The ATDC5 cells were induced to differentiate into chondrocytes and stimulated with NGF at different concentrations (0.5-10 ng/mL). The cell counting kit-8 assay (CCK-8) was used to measure the effects of NGF on chondrocyte proliferation. Chondrocytes were subsequently stimulated with varying doses of NGF to identify the expression levels of the extracellular matrix. Chondrocytes were pretreated with GNF5837 (a tropomyosin receptor kinase A inhibitor) or LY294002 (a phosphoinositide 3-kinase inhibitor) before exposure to 5 ng/mL NGF to analyze associated signaling pathways. Western blotting and immunofluorescence staining were employed to analyze expression of related proteins.

RESULTS

Alcian blue, toluidine blue staining, and type II collagen immunofluorescence staining demonstrated that ATDC5 cells differentiated into functional chondrocytes after 14 days of chondrogenic induction. The CCK-8 assay confirmed that cell proliferation was unaffected. NGF (0.5-5 ng/mL) was found to enhance chondrocyte matrix synthesis in a dose-dependent fashion, particularly in the expression of aggrecan, type II collagen, Sox9, and through the activation of the PI3K/AKT signaling pathway. The highest promoting effects were exhibited at 5 ng/mL of NGF. Further analysis indicated that GNF5837 (TRKA inhibitor) or LY294002 (PI3K inhibitor) could reverse the protective effects of NGF on chondrocyte matrix synthesis.

CONCLUSION

Our study identified a potentially beneficial role of NGF at concentrations of 0.5-5 ng/mL in chondrocytes, enhancing extracellular matrix synthesis, with significant involvement of the PI3K/AKT signaling pathway in this process.

NSAID-mediated cyclooxygenase inhibition disrupts ectodermal derivative formation in axolotl embryos

Embryonic exposures to non-stseroidal anti-inflammatory drugs (NSAIDs) have been linked to preterm birth, neural tube closure defects, abnormal enteric innervation, and craniofacial malformations, potentially due to disrupted neural tube or neural crest (NC) cell development. Naproxen (NPX), a common non-steroidal anti-inflammatory drug (NSAID) used to relieve pain and inflammation, exerts its effects through non-selective cyclooxygenase (COX) inhibition. Our lab has identified that the cyclooxygenase (COX-1 and COX-2) isoenzymes are expressed during the early stages of vertebrate embryonic development, and that global inhibition of COX-1 and COX-2 function disrupts NC cell migration and differentiation in Ambystoma mexicanum (axolotl) embryos. NC cells differentiate into various adult tissues including craniofacial cartilage, bone, and neurons in the peripheral and enteric nervous systems. To investigate the specific phenotypic and molecular effects of NPX exposure on NC development and differentiation, and to identify molecular links between COX inhibition and NC derivative anomalies, we exposed late neurula and early tailbud stage axolotl embryos to various concentrations of NPX and performed immunohistochemistry (IHC) for markers of migratory and differentiating NC cells. Our results reveal that NPX exposure impairs the migration of SOX9+ NC cells, leading to abnormal development of craniofacial cartilage structures, including Meckel's cartilage in the jaw. NPX exposure also alters the expression of markers associated with peripheral and central nervous system (PNS and CNS) development, suggesting concurrent neurodevelopmental changes.

RNA Binding Properties of SOX Family Members

SOX proteins are a family of transcription factors (TFs) that play critical functions in sex determination, neurogenesis, and chondrocyte differentiation, as well as cardiac, vascular, and lymphatic development. There are 20 SOX family members in humans, each sharing a 79-residue L-shaped high mobility group (HMG)-box domain that is responsible for DNA binding. SOX2 was recently shown to interact with long non-coding RNA and large-intergenic non-coding RNA to regulate embryonic stem cell and neuronal differentiation. The RNA binding region was shown to reside within the HMG-box domain; however, the structural details of this binding remain unclear. Here, we show that all SOX family members, except group H, interact with RNA. Our mutational experiments demonstrate that the disordered C-terminal region of the HMG-box domain plays an important role in RNA binding. Further, by determining a high-resolution structure of the HMG-box domain of the group H family member SOX30, we show that despite differences in RNA binding ability, SOX30 shares a very similar secondary structure with other SOX protein HMG-box domains. Together, our study provides insight into the interaction of SOX TFs with RNA.

Forkhead box O proteins: steering the course of stem cell fate

Stem cells are pivotal players in the intricate dance of embryonic development, tissue maintenance, and regeneration. Their behavior is delicately balanced between maintaining their pluripotency and differentiating as needed. Disruptions in this balance can lead to a spectrum of diseases, underscoring the importance of unraveling the complex molecular mechanisms that govern stem cell fate. Forkhead box O (FOXO) proteins, a family of transcription factors, are at the heart of this intricate regulation, influencing a myriad of cellular processes such as survival, metabolism, and DNA repair. Their multifaceted role in steering the destiny of stem cells is evident, as they wield influence over self-renewal, quiescence, and lineage-specific differentiation in both embryonic and adult stem cells. This review delves into the structural and regulatory intricacies of FOXO transcription factors, shedding light on their pivotal roles in shaping the fate of stem cells. By providing insights into the specific functions of FOXO in determining stem cell fate, this review aims to pave the way for targeted interventions that could modulate stem cell behavior and potentially revolutionize the treatment and prevention of diseases.

Suppression of Overactive Insulin-Like Growth Factor 1 Attenuates Trauma-Induced Heterotopic Ossification in Mice

Heterotopic ossification (HO) is the ectopic bone formation in soft tissues. Aside from hereditary HO, traumatic HO is common after orthopedic surgery, combat-related injuries, severe burns, or neurologic injuries. Recently, mammalian target of rapamycin (mTOR) was demonstrated to be involved in the chondrogenic and osteogenic processes of HO formation. However, its upstream signaling mechanism remains unknown. The current study used an Achilles tendon puncture-induced HO model to show that overactive insulin-like growth factor 1 (IGF-1) was involved in the progression of HO in mice. Micro-computed tomography imaging showed that IGF-1 not only accelerated the rate of osteogenesis and increased ectopic bone volume but also induced spontaneous ectopic bone formation in undamaged Achilles tendons. Blocking IGF-1 activity with IGF-1 antibody or IGF-1 receptor inhibitor picropodophyllin significantly inhibited HO formation. Mechanistically, IGF-1/IGF-1 receptor activates phosphatidylinositol 3-kinase (PI3K)/Akt signaling to promote the phosphorylation of mTOR, resulting in the chondrogenic and osteogenic differentiation of tendon-derived stem cells into chondrocytes and osteoblasts in vitro and in vivo. Inhibitors of PI3K (LY294002) and mTOR (rapamycin) both suppressed the IGF-1-stimulated mTOR signal and mitigated the formation of ectopic bones significantly. In conclusion, these results indicate that IGF-1 mediated the progression of traumatic HO through PI3K/Akt/mTOR signaling, and suppressing IGF-1 signaling cascades attenuated HO formation, providing a promising therapeutic strategy targeting HO.

Mapk7 deletion in chondrocytes causes vertebral defects by reducing MEF2C/PTEN/AKT signaling

Mutation of the MAPK7 gene was related to human scoliosis. Mapk7 regulated the development of limb bones and skulls in mice. However, the role of MAPK7 in vertebral development is still unclear. In this study, we constructed Col2a1-cre; Mapk7f/f transgenic mouse model to delete Mapk7 in cartilage, which displayed kyphosis and osteopenia. Mechanistically, Mapk7 loss decreased MEF2C expression and thus activated PTEN to oppose PI3K/AKT signaling in vertebral growth plate chondrocytes, which impaired chondrocyte hypertrophy and attenuated vertebral ossification. In vivo, systemic pharmacological activation of AKT rescued impaired chondrocyte hypertrophy and alleviated mouse vertebral defects caused by Mapk7 deficiency. Our study firstly clarified the mechanism by which MAPK7 was involved in vertebral development, which might contribute to understanding the pathology of spinal deformity and provide a basis for the treatment of developmental disorders of the spine.

An Insight into Vital Genes Responsible for β-cell Formation

The regulation of glucose homeostasis and insulin secretion by pancreatic β-cells, when disturbed, will result in diabetes mellitus. Replacement of dysfunctional or lost β-cells with fully functional ones can tackle the problem of β-cell generation in diabetes mellitus. Various pancreatic-specific genes are expressed during different stages of development, which have essential roles in pancreatogenesis and β-cell formation. These factors play a critical role in cellular-based studies like transdifferentiation or de-differentiation of somatic cells to multipotent or pluripotent stem cells and their differentiation into functional β-cells. This work gives an overview of crucial transcription factors expressed during various stages of pancreas development and their role in β-cell specification. In addition, it also provides a perspective on the underlying molecular mechanisms.

Tankyrase: a promising therapeutic target with pleiotropic action

Tankyrase 1 (TNKS1) and tankyrase 2 (TNKS2) enzymes belong to the poly (ADP-ribose) polymerase (PARP) family participates in process of poly-ADP-ribosylation of different target proteins which leads to ubiquitin-mediated proteasomal degradation. Tankyrases are also involved in the pathophysiology of many diseases, especially cancer. Their functions include cell cycle homeostasis (primarily in mitosis), telomere maintenance, Wnt signaling pathway regulation, and insulin signaling (particularly GLUT4 translocation). Studies have implicated that genetic changes, mutations in the tankyrase coding sequence, or up regulation and down regulation of tankyrase are reflected in the numerous disease conditions. Investigations are pursued to develop putative molecules that target tankyrase in various diseases such as cancer, obesity, osteoarthritis, fibrosis, cherubism, and diabetes, thereby providing a new therapeutic treatment option. In the present review, we described the structure and function of tankyrase along with its role in different disease conditions. Furthermore, we also presented cumulative experimental evidences of different drugs acting on tankyrase.

Function and regulation of nuclear factor 1 X-type on chondrocyte proliferation and differentiation

Nuclear factor 1 X-type (Nfix) is a transcription factor related to mental and physical development. However, very few studies have reported the effects of Nfix on cartilage. This study aims to reveal the influence of Nfix on the proliferation and differentiation of chondrocytes, and to explore its potential action mechanism. We isolated primary chondrocytes from the costal cartilage of newborn C57BL/6 mice and with Nfix overexpression or silencing treatment. We used Alcian blue staining and found that Nfix overexpression significantly promoted ECM synthesis in chondrocytes while silencing inhibited ECM synthesis. Using RNA-seq technology to study the expression pattern of Nfix in primary chondrocytes. We found that Nfix overexpression significantly up-regulated genes that are related to chondrocyte proliferation and extracellular matrix (ECM) synthesis and significantly down-regulated genes related to chondrocyte differentiation and ECM degradation. Nfix silencing, however, significantly up-regulated genes associated with cartilage catabolism and significantly down-regulated genes associated with cartilage growth promotion. Furthermore, Nfix exerted a positive regulatory effect on Sox9, and we propose that Nfix may promote chondrocyte proliferation and inhibit differentiation by stimulating Sox9 and its downstream genes. Our findings suggest that Nfix may be a potential target for the regulation of chondrocyte proliferation and differentiation.

Ubiquitin-specific proteases: Vital regulatory molecules in bone and bone-related diseases

Stabilization of bone structure and function involves multiple cell-to-cell and molecular interactions, in which the regulatory functions of post-translational modifications such as ubiquitination and deubiquitination shouldn't be underestimated. As the largest family of deubiquitinating enzymes, the ubiquitin-specific proteases (USPs) participate in the development of bone homeostasis and bone-related diseases through multiple classical osteogenic and osteolytic signaling pathways, such as BMP/TGF-β pathway, NF-κB/p65 pathway, EGFR-MAPK pathway and Wnt/β-catenin pathway. Meanwhile, USPs may also broadly regulate regulate hormone expression level, cell proliferation and differentiation, and may further influence bone homeostasis from gene fusion and nuclear translocation of transcription factors. The number of patients with bone-related diseases is currently enormous, making exploration of their pathogenesis and targeted therapy a hot topic. Pathological increases in the levels of inflammatory mediators such as IL-1β and TNF-α lead to inflammatory bone diseases such as osteoarthritis, rheumatoid arthritis and periodontitis. While impaired body metabolism greatly increases the probability of osteoporosis. Abnormal physiological activity of bone-associated cells results in a variety of bone tumors. The regulatory role of USPs in bone-related disease has received particular attention from academics in recent studies. In this review, we focuse on the roles and mechanisms of USPs in bone homeostasis and bone-related diseases, with the expectation of informing targeted therapies in the clinic.

The Role of the miR-548au-3p/CA12 Axis in Tracheal Chondrogenesis in Congenital Pulmonary Airway Malformations

Background

Literature has identified differentially expressed miRNAs in congenital pulmonary airway malformation (CPAM). However, the functional role of these miRNAs in CPAM remains unclear.

Methods

We obtained diseased lung tissues as well as adjacent normal lung tissue from CPAM patients attending the centre. Hematoxylin and eosin (H&E) and Alcian blue staining were performed. Differentially expressed mRNA expression profile was CPAM tissue, and matched normal tissue specimens were examined by high-throughput RNA sequencing. CCK-8 assay, EdU staining, TUNEL staining, flow cytometry, and the Transwell assay were performed to investigate the effect of miR-548au-3p/CA12 axis on proliferation, apoptosis, and chondrogenic differentiation in rat tracheal chondrocytes. mRNA and protein expression levels were determined using reverse transcription-quantitative PCR and western blot analysis, respectively. The relationship between miR-548au-3p and CA12 was evaluated using the luciferase reporter assay.

Results

The expression level of miR-548au-3p was significantly increased in diseased tissues compared with normal adjacent tissues from patients with CPAM. Our results indicate that miR-548au-3p functions as a positive regulator in rat tracheal chondrocyte proliferation and chondrogenic differentiation. At molecular level, miR-548au-3p promoted N-cadherin, MMP13, and ADAMTS4 expressions and reduced E-cadherin, aggrecan, and Col2A1 expressions. CA12 has been previously reported as a predicted target of miR-548au-3p, and here, we show that overexpression of CA12 in rat tracheal chondrocyte mimics the effects of inhibition of miR-548au-3p. On the other hand, CA12 knockdown reversed the effects of miR-548au-3p on cell proliferation, apoptosis, and chondrogenic differentiation.

Conclusions

In conclusion, the miR-548au-3p/CA12 axis plays a role in the pathogenesis of CPAM and may lead to identification of new approaches for CPAM treatment.

The synergistic effect of physicochemical in vitro microenvironment modulators in human bone marrow stem cell cultures

Modern bioengineering utilises biomimetic cell culture approaches to control cell fate during in vitro expansion. In this spirit, herein we assessed the influence of bidirectional surface topography, substrate rigidity, collagen type I coating and macromolecular crowding (MMC) in human bone marrow stem cell cultures. In the absence of MMC, surface topography was a strong modulator of cell morphology. MMC significantly increased extracellular matrix deposition, albeit in a globular manner, independently of the surface topography, substrate rigidity and collagen type I coating. Collagen type I coating significantly increased cell metabolic activity and none of the assessed parameters affected cell viability. At day 14, in the absence of MMC, none of the assessed genes was affected by surface topography, substrate rigidity and collagen type I coating, whilst in the presence of MMC, in general, collagen type I α1 chain, tenascin C, osteonectin, bone sialoprotein, aggrecan, cartilage oligomeric protein and runt-related transcription factor were downregulated. Interestingly, in the presence of the MMC, the 1000 kPa grooved substrate without collagen type I coating upregulated aggrecan, cartilage oligomeric protein, scleraxis homolog A, tenomodulin and thrombospondin 4, indicative of tenogenic differentiation. This study further supports the notion for multifactorial bioengineering to control cell fate in culture.

Close-to-native bone repair via tissue-engineered endochondral ossification approaches

In order to solve the clinical challenges related to bone grafting, several tissue engineering (TE) strategies have been proposed to repair critical-sized defects. Generally, the classical TE approaches are designed to promote bone repair via intramembranous ossification. Although promising, strategies that direct the osteogenic differentiation of mesenchymal stem/stromal cells are usually characterized by a lack of functional vascular supply, often resulting in necrotic cores. A less explored alternative is engineering bone constructs through a cartilage-mediated approach, resembling the embryological process of endochondral ossification. The remodeling of an intermediary hypertrophic cartilaginous template triggers vascular invasion and bone tissue deposition. Thus, employing this knowledge can be a promising direction for the next generation of bone TE constructs. This review highlights the most recent biomimetic strategies for applying endochondral ossification in bone TE while discussing the plethora of cell types, culture conditions, and biomaterials essential to promote a successful bone regeneration process.

SOX9 in organogenesis: shared and unique transcriptional functions

The transcription factor SOX9 is essential for the development of multiple organs including bone, testis, heart, lung, pancreas, intestine and nervous system. Mutations in the human SOX9 gene led to campomelic dysplasia, a haploinsufficiency disorder with several skeletal malformations frequently accompanied by 46, XY sex reversal. The mechanisms underlying the diverse SOX9 functions during organ development including its post-translational modifications, the availability of binding partners, and tissue-specific accessibility to target gene chromatin. Here we summarize the expression, activities, and downstream target genes of SOX9 in molecular genetic pathways essential for organ development, maintenance, and function. We also provide an insight into understanding the mechanisms that regulate the versatile roles of SOX9 in different organs.

Endostatin in 3D Fibrin Hydrogel Scaffolds Promotes Chondrogenic Differentiation in Swine Neonatal Meniscal Cells

The success of cell-based approaches for the treatment of cartilage or fibro-cartilaginous tissue defects requires an optimal cell source with chondrogenic differentiation ability that maintains its differentiated properties and stability following implantation. For this purpose, the aim of this study was to evaluate the use of endostatin (COL18A1), an anti-angiogenic factor, which is physiologically involved in cell differentiation during meniscus development. Swine neonatal meniscal cells not yet subjected to mechanical stimuli were extracted, cultured in fibrin hydrogel scaffolds, and treated at two different time points (T1 = 9 days and T2 = 21 days) with different concentrations of COL18A1 (10 ng/mL; 100 ng/mL; 200 ng/mL). At the end of the treatments, the scaffolds were examined through biochemical, molecular, and histochemical analyses. The results showed that the higher concentration of COL18A1 promotes a fibro-chondrogenic phenotype and improves cellularity index (DNA content, p < 0.001) and cell efficiency (GAGs/DNA ratio, p < 0.01) after 21 days. These data are supported by the molecular analysis of collagen type I (COL1A1, a marker of fibrous-like tissue, p < 0.001), collagen type II (COL2A1, a marker of cartilaginous-like tissue, p < 0.001) and SRY-Box Transcription Factor 9 (SOX9, an early marker of chondrogenicity, p < 0.001), as well as by histological analysis (Safranin-O staining), laying the foundations for future studies evaluating the involvement of 3D endostatin hydrogel scaffolds in the differentiation of avascular tissues.

Stage-Dependent Activity and Pro-Chondrogenic Function of PI3K/AKT during Cartilage Neogenesis from Mesenchymal Stromal Cells

Differentiating mesenchymal stromal cells (MSCs) into articular chondrocytes (ACs) for application in clinical cartilage regeneration requires a profound understanding of signaling pathways regulating stem cell chondrogenesis and hypertrophic degeneration. Classifying endochondral signals into drivers of chondrogenic speed versus hypertrophy, we here focused on insulin/insulin-like growth factor 1 (IGF1)-induced phosphoinositide 3-kinase (PI3K)/AKT signaling. Aware of its proliferative function during early but not late MSC chondrogenesis, we aimed to unravel the late pro-chondrogenic versus pro-hypertrophic PI3K/AKT role. PI3K/AKT activity in human MSC and AC chondrogenic 3D cultures was assessed via Western blot detection of phosphorylated AKT. The effects of PI3K inhibition with LY294002 on chondrogenesis and hypertrophy were assessed via histology, qPCR, the quantification of proteoglycans, and alkaline phosphatase activity. Being repressed by ACs, PI3K/AKT activity transiently rose in differentiating MSCs independent of TGFβ or endogenous BMP/WNT activity and climaxed around day 21. PI3K/AKT inhibition from day 21 on equally reduced chondrocyte and hypertrophy markers. Proving important for TGFβ-induced SMAD2 phosphorylation and SOX9 accumulation, PI3K/AKT activity was here identified as a required stage-dependent driver of chondrogenic speed but not of hypertrophy. Thus, future attempts to improve MSC chondrogenesis will depend on the adequate stimulation and upregulation of PI3K/AKT activity to generate high-quality cartilage from human MSCs.

Vibration exposure uncovers a critical early developmental window for zebrafish caudal fin development

Mechanical influencers have long been shown to affect mature bone. Bone mechanosensation is a key feature that allows the skeleton to adapt to environmental constraints. In this study, we describe the response of immature, developing bones to a mechanical stimulus. To do so, zebrafish larvae at different stages of development were exposed to whole-body vibration (WBV) at a low frequency of 20 Hz, for up to 4 days. Whole mount Alizarin red and Alcian blue staining revealed age-related and bone type-specific defects. Specifically, the parhypural and hypural 1 caudal fin endoskeletal elements were affected when the exposure to WBV started early during their development. We show that these WBV-induced parhypural and hypural 1 patterning defects are triggered by a Sox9-independent pathway, potentially by reducing the distance separating adjacent chondrogenic condensations in the developing tail skeleton. The remaining hypurals were unaffected by the WBV treatment. Altogether, our results indicate that, upon exposure to vibration, chondrogenic cell progenitors can react to mechanical stimuli early during their development, which ultimately affects the skeletal patterning of the growing zebrafish larvae. These findings open a new research avenue to better understand the cellular processes involved in developing, patterning, and maintaining skeletal tissue.

Reciprocal regulation of Daxx and PIK3CA promotes colorectal cancer cell growth

Upregulation of death-domain-associated protein (Daxx) is strongly associated with diverse cancer types. Among these, the clinicopathological significance and molecular mechanisms of Daxx overexpression in colorectal cancer (CRC) remain unknown. Here, we showed that Daxx expression was increased in both clinical CRC samples and CRC cell lines. Daxx knockdown significantly reduced proliferation activity in CRC cells and tumor growth in a xenograft model. Further studies revealed that Daxx expression could be attenuated by either treatment with the PIK3CA inhibitor PIK-75 or PIK3CA depletion in CRC cells. Conversely, expression of PIK3CA constitutively active mutants could increase Daxx expression. These data suggest that PIK3CA positively regulates Daxx expression. Consistently, the expression levels of PIK3CA and Daxx were positively correlated in sporadic CRC samples. Interestingly, Daxx knockdown or overexpression yielded decreased or increased levels of PIK3CA, respectively, in CRC cells. We further demonstrated that Daxx activates the promoter activity and expression of PIK3CA. Altogether, our results identify a mechanistic pathway of Daxx overexpression in CRC and suggest a reciprocal regulation between Daxx and PIK3CA for CRC cell growth.

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.

Generation and characterization of genome-modified chondrocyte-like cells from the zebra finch cell line immortalized by c-MYC expression

BACKGROUND

Due to their cost effectiveness, ease of use, and unlimited supply, immortalized cell lines are used in place of primary cells for a wide range of research purposes, including gene function studies, CRISPR-based gene editing, drug metabolism tests, and vaccine or therapeutic protein production. Although immortalized cell lines have been established for a range of animal species, there is still a need to develop such cell lines for wild species. The zebra finch, which is used widely as a model species to study the neurobiological basis of human speech disorders, has been employed in several functional studies involving gene knockdown or the introduction of exogenous transgenes in vivo; however, the lack of an immortalized zebra finch cell line has hampered precise genome editing studies.

RESULTS

Here, we established an immortalized cell line by a single genetic event, expression of the c-MYC oncogene, in zebra finch embryonic fibroblasts and examined its potential suitability for gene targeting investigations. Retroviral vector-mediated transduction of c-MYC was used to immortalize zebra finch primary fibroblasts; the transformed cells proliferated stably over several passages, resulting in the expression of chondrocyte-specific genes. The transfection efficiency of the immortalized cells was much higher than that of the primary cells. Targeted knockout of the SOX9 gene, which plays a role in the differentiation of mesenchymal progenitor cells into chondrocytes, was conducted in vitro and both apoptosis and decreased expression levels of chondrogenic marker genes were observed in edited cells.

CONCLUSIONS

The c-MYC induced immortalized chondrocyte-like cell line described here broadens the available options for establishing zebra finch cell lines, paves the way for in-depth biological researches, and provides convenient approaches for biotechnology studies, particularly genomic modification research.

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.

Identification of Transcription Factors Responsible for a Transforming Growth Factor-β-Driven Hypertrophy-like Phenotype in Human Osteoarthritic Chondrocytes

During osteoarthritis (OA), hypertrophy-like chondrocytes contribute to the disease process. TGF-β's signaling pathways can contribute to a hypertrophy(-like) phenotype in chondrocytes, especially at high doses of TGF-β. In this study, we examine which transcription factors (TFs) are activated and involved in TGF-β-dependent induction of a hypertrophy-like phenotype in human OA chondrocytes. We found that TGF-β, at levels found in synovial fluid in OA patients, induces hypertrophic differentiation, as characterized by increased expression of RUNX2, COL10A1, COL1A1, VEGFA and IHH. Using luciferase-based TF activity assays, we observed that the expression of these hypertrophy genes positively correlated to SMAD3:4, STAT3 and AP1 activity. Blocking these TFs using specific inhibitors for ALK-5-induced SMAD signaling (5 µM SB-505124), JAK-STAT signaling (1 µM Tofacitinib) and JNK signaling (10 µM SP-600125) led to the striking observation that only SB-505124 repressed the expression of hypertrophy factors in TGF-β-stimulated chondrocytes. Therefore, we conclude that ALK5 kinase activity is essential for TGF-β-induced expression of crucial hypertrophy factors in chondrocytes.

Spidroin striped micropattern promotes chondrogenic differentiation of human Wharton's jelly mesenchymal stem cells

Cartilage tissue engineering, particularly micropattern, can influence the biophysical properties of mesenchymal stem cells (MSCs) leading to chondrogenesis. In this research, human Wharton’s jelly MSCs (hWJ-MSCs) were grown on a striped micropattern containing spider silk protein (spidroin) from Argiope appensa. This research aims to direct hWJ-MSCs chondrogenesis using micropattern made of spidroin bioink as opposed to fibronectin that often used as the gold standard. Cells were cultured on striped micropattern of 500 µm and 1000 µm width sizes without chondrogenic differentiation medium for 21 days. The immunocytochemistry result showed that spidroin contains RGD sequences and facilitates cell adhesion via integrin β1. Chondrogenesis was observed through the expression of glycosaminoglycan, type II collagen, and SOX9. The result on glycosaminoglycan content proved that 1000 µm was the optimal width to support chondrogenesis. Spidroin micropattern induced significantly higher expression of SOX9 mRNA on day-21 and SOX9 protein was located inside the nucleus starting from day-7. COL2A1 mRNA of spidroin micropattern groups was downregulated on day-21 and collagen type II protein was detected starting from day-14. These results showed that spidroin micropattern enhances chondrogenic markers while maintains long-term upregulation of SOX9, and therefore has the potential as a new method for cartilage tissue engineering.

Calcification and resorption of mouse Meckel's cartilage analyzed by von Kossa and tartrate-resistant acid phosphatase histochemistry and scanning electron microscopy/energy-dispersive X-ray spectrometry

Meckel's cartilage is essential for the normal development of the mandible. The fate of the intermediate portion of Meckel's cartilage is unique as most of it disappears soon after birth except for the part that forms the sphenomandibular ligament. The mechanism of the disappearance of Meckel's cartilage is unknown; therefore, this study was designed to investigate the process of Meckel's cartilage degradation, focusing on cartilage matrix calcification and the appearance of chondroclasts. Developing mouse mandibles at embryonic days 15, 16, 17, and 18, and postnatal day 2 were processed for whole-mount staining with alcian blue and alizarin red. The mandibles on embryonic days 15, 16, 17, and 18 were fixed and embedded in paraffin. Adjacent sections were processed for von Kossa and tartrate-resistant acid phosphatase (TRAP) histochemistry and scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS). Calcification and the element concentrations of calcium, phosphorus, and carbon were examined with von Kossa histochemistry and SEM/EDS. The involvement of chondroclasts was investigated using TRAP histochemistry. The results demonstrated that the intermediate portion of Meckel's cartilage is resorbed by chondroclasts after chondrocyte hypertrophy and cartilage matrix calcification and that the mineral concentration of calcified Meckel's cartilage is comparable to that of the surrounding bone. This study contributes to the understanding of the mechanism of Meckel's cartilage resorption and provides useful insights into the development of the mandible.

Ethanol Alters Phenotype and Synthesis Activity of Rat Neonatal Articular Chondrocytes Grown in 2- and 3-Dimensional Culture

OBJECTIVE

We sought to evaluate the effect of different concentrations of ethanol on phenotype and activity of articular chondrocyte synthesis of neonatal rats in 2-dimensional (2D) and 3-dimensional (3D) culture.

METHODS

Chondrocytes were cultured in chondrogenic medium with different concentrations of ethanol: 0.0% v/v (control); 0.05% v/v (8.6 mM); 0.25% v/v (42.9 mM), and 0.5% v/v (85.7 mM). Chondrocytes under 2D culture were subjected to MTT assay, while chondrocytes under 3D culture were processed for paraffin inclusion and stained by periodic acid Schiff (PAS) to evaluate mean chondrocyte diameter and percentages of cells, nucleus, cytoplasm, well-differentiated matrix, and PAS+ areas. The expression of gene transcripts for aggrecan, Sox9, and type II collagen was evaluated by real-time quantitative polymerase chain reaction.

RESULTS

There was no difference between groups by the MTT assay. PAS staining revealed that chondrocytes treated with 0.5% v/v ethanol had higher percentages of cytoplasm and nuclear areas, but with a reduction in PAS+ matrix area. The mean diameter of chondrocytes was similar between groups. The expression of aggrecan in the group treated with 0.5% v/v ethanol was lower in comparison to that in the control. In the groups treated with 0.25% v/v and 0.5% v/v ethanol, the percentage of differentiated cartilage was lower in comparison with that in the control. The group treated with 0.05% v/v ethanol was similar to the control in all parameters.

CONCLUSIONS

Ethanol acted directly on in vitro cultured articular chondrocytes of newborn rats, altering the chondrocyte phenotype and its synthesis activity, and these effects were dose dependent.

Genome-scale actions of master regulators directing skeletal development

The mammalian skeleton develops through two distinct modes of ossification: intramembranous ossification and endochondral ossification. During the process of skeletal development, SRY-box containing gene 9 (Sox9), runt-related transcription factor 2 (Runx2), and Sp7 work as master transcription factors (TFs) or transcriptional regulators, underlying cell fate specification of the two distinct populations: bone-forming osteoblasts and cartilage-forming chondrocytes. In the past two decades, core transcriptional circuits underlying skeletal development have been identified mainly through mouse genetics and biochemical approaches. Recently emerging next-generation sequencer (NGS)-based studies have provided genome-scale views on the gene regulatory landscape programmed by the master TFs/transcriptional regulators. With particular focus on Sox9, Runx2, and Sp7, this review aims to discuss the gene regulatory landscape in skeletal development, which has been identified by genome-scale data, and provide future perspectives in this field.

Autophagy coordinates chondrocyte development and early joint formation in zebrafish

Autophagy is a catabolic process responsible for the removal of waste and damaged cellular components by lysosomal degradation. It plays a key role in fundamental cell processes, including ER stress mitigation, control of cell metabolism, and cell differentiation and proliferation, all of which are essential for cartilage cell (chondrocyte) development and survival, and for the formation of cartilage. Correspondingly, autophagy dysregulation has been implicated in several skeletal disorders such as osteoarthritis and osteoporosis. To test the requirement for autophagy during skeletal development in zebrafish, we generated an atg13 CRISPR knockout zebrafish line. This line showed a complete loss of atg13 expression, and restricted autophagic activity in vivo. In the absence of autophagy, chondrocyte maturation was accelerated, with chondrocytes exhibiting signs of premature hypertrophy. Focussing on the jaw element, autophagy disruption affected joint articulation causing restricted mouth opening. This gross behavioural phenotype corresponded with a failure to thrive, and death in homozygote atg13 nulls within 17 days. Taken together, our results are consistent with autophagy contributing to the timely regulation of chondrocyte maturation and for extracellular matrix formation.

Nfib promotes chondrocyte proliferation and inhibits differentiation by mildly regulating Sox9 and its downstream genes

BACKGROUND

Chondrocyte proliferation and differentiation play pivotal roles in regulating cartilage formation, endochondral bone formation, and repair. Cartilage damage and underdevelopment may cause severe joint diseases. Various transcription factors regulate cartilage development. Nuclear factor 1 B (Nfib) is a transcription factor that plays a regulatory role in various organs. However, the effect and mechanism of Nfib on the proliferation and differentiation of chondrocytes in cartilage are still largely unknown.

METHODS AND RESULTS

In the present study, we investigated the gene expression patterns in primary chondrocytes with Nfib overexpression or silencing by RNA sequencing (RNA-seq) technology. The results showed that Nfib overexpression significantly up-regulated genes that are related to chondrocyte proliferation and extracellular matrix (ECM) synthesis and significantly down-regulated genes related to chondrocyte differentiation and ECM degradation. However, with Nfib silencing, the genes involved in promoting chondrocyte differentiation were significantly up-regulated, whereas those involved in promoting chondrocyte proliferation were significantly down-regulated. Furthermore, quantitative real-time PCR (qRT-PCR), western blot, alcian blue staining and immunofluorescence staining assays further confirmed that Nfib potentially promotes chondrocyte proliferation and extracellular synthesis but inhibits differentiation.

CONCLUSIONS

The molecular mechanism of Nfib in promoting chondrocyte proliferation and inhibiting differentiation was probably achieved by stimulating Sox9 and its downstream genes. Thus, this study adds new insights regarding the underlying molecular mechanism of transcriptional regulation in cartilage.

In vitro effects of nutraceutical treatment on human osteoarthritic chondrocytes of females of different age and weight groups

The in vitro effects of four nutraceuticals, catechin hydrate, gallic acid, α-tocopherol and ascorbic acid, on the ability of human osteoarthritic chondrocytes of two female obese groups to form articular cartilage (AC) tissues and to reduce inflammation were investigated. Group 1 represented thirteen females in the 50-69 years old range, an average weight of 100 kg and an average body mass index (BMI) of 34⋅06 kg/m2. Group 2 was constituted of three females in the 70-80 years old range, an average weight of 75 kg and an average BMI of 31⋅43 kg/m2. The efficacy of nutraceuticals was assessed in monolayer cultures using histological, colorimetric and mRNA gene expression analyses. AC engineered tissues of group 1 produced less total collagen and COL2A1 (38-fold), and higher COL10A1 (2⋅7-fold), MMP13 (50-fold) and NOS2 (15-fold) mRNA levels than those of group 2. In comparison, engineered tissues of group 1 had a significant decrease in NO levels from day 1 to day 21 (2⋅6-fold), as well as higher mRNA levels of FOXO1 (2-fold) and TNFAIP6 (16-fold) compared to group 2. Catechin hydrate decreased NO levels significantly in group 1 (1⋅5-fold) while increasing NO levels significantly in group 2 (3⋅8-fold). No differences from the negative control were observed in the presence of other nutraceuticals for either group. In conclusion, engineered tissues of the younger but heavier patients responded better to nutraceuticals than those from the older but leaner study participants. Finally, cells of group 2 formed better AC tissues with less inflammation and better extracellular matrix than cells of group 1.

HMGB2 promotes chondrocyte proliferation under negative pressure through the phosphorylation of AKT

Cells in articular cartilage are zonal arranged. Cells in superficial zone cartilage are generally small and proliferative. Appropriate negative pressure stimulation is beneficial to cell survival and tissue repair. Whether negative pressure has promotive impact on the proliferation activity of the superficial zone chondrocytes is of interest. In this study, we isolated superficial chondrocytes from the mandibular condylar cartilage of rats. After negative pressure treatment, the cells were collected for RNA-sequencing, quantitative real-time PCR and western blotting assays, aiming to detect the proliferative responses of chondrocytes to negative pressure and explore the potential molecular mechanisms. Data from RNA-sequencing analysis indicated that the superficial chondrocytes responded to the 4 h -10 kPa treatment by a significant increase in proliferation. In addition, the expression of high-mobility group box 2 (HMGB2) and the phosphorylation of AKT were obviously promoted. Knockdown of HMGB2 decreased AKT phosphorylation and diminished the negative pressure-induced proliferation of chondrocytes, as shown by decreased expression of Ki67 and cyclin-dependent kinase 6 (CDK6). In contrast, overexpression of HMGB2 enhanced AKT phosphorylation and further promoted proliferative activity. Moreover, LY294002, an AKT inhibitor, suppressed the proliferative activity of chondrocytes under negative pressure, while SC79, an activator of AKT phosphorylation, enhanced the proliferation of chondrocytes. Our data demonstrated that HMGB2 exhibits a promotion impact on chondrocyte proliferation under negative pressure via the phosphorylation of AKT. These results provide a new perspective for superficial zone chondrocytes proliferation under negative pressure, which should be benefit for cartilage regeneration.

It is time to crowd your cell culture media - Physicochemical considerations with biological consequences

In vivo, the interior and exterior of cells is populated by various macromolecules that create an extremely crowded milieu. Yet again, in vitro eukaryotic cell culture is conducted in dilute culture media that hardly imitate the native tissue density. Herein, the concept of macromolecular crowding is discussed in both intracellular and extracellular context. Particular emphasis is given on how the physicochemical properties of the crowding molecules govern and determine kinetics, equilibria and mechanism of action of biochemical and biological reactions, processes and functions. It is evidenced that we are still at the beginning of appreciating, let alone effectively implementing, the potential of macromolecular crowding in permanently differentiated and stem cell culture systems.

Linc-ROR promotes mesenchymal stem cells chondrogenesis and cartilage formation via regulating SOX9 expression

OBJECTIVE

The present study is to characterize the role of long intergenic non-coding RNA, regulator of reprogramming (linc-ROR) in bone marrow mesenchymal stem cell (BMSCs) chondrogenesis, cartilage formation and OA development.

METHODS

Linc-ROR expression pattern in articular cartilage tissue sample from OA patients were studied by real-time PCR. Linc-ROR lentivirus mediated BMSCs were constructed. In vitro micromass cultured BMSCs chondrogenesis or in vivo MeHA hydrogel encapsulated BMSCs cartilage formation activity were studied. Linc-ROR associating miRNAs which repressed SOX9 expression were characterized by luciferase assay, real-time PCR and Western blot. Linc-ROR was co-transfected with miRNAs into BMSCs to study its rescue effect on SOX9 expression and chondrogenesis activity.

RESULTS

Linc-ROR was down-regulated in articular cartilage tissue from OA patients and was positively correlated with the expression level of SOX9 (R² = 0.43). Linc-ROR expression was upregulated during BMSCs chondrogenesis. Linc-ROR ectopic expression significantly promoted in vitro BMSCs chondrogenesis and in vivo cartilage formation activities as revealed by safranin O, alcian blue and COL II staining. The mRNA expression level of chondrogenesis markers including COL II, SOX9 and ACAN were increased, and the hypertrophy markers MMP13 and COL X were decreased upon linc-ROR overexpression in BMSCs. Linc-ROR functioned as a miRNA sponge for miR-138 and miR-145. Both miR-138 and miR-145 suppressed BMSCs chondrogenesis activity and SOX9 expression, while co-expression of linc-ROR displayed a rescuing effect.

CONCLUSIONS

Taken together, linc-ROR modulated BMSCs chondrogenesis differentiation and cartilage formation by acting as a competing endogenous RNA for miR-138 and miR-145 and activating SOX9 expression. Linc-ROR could be considered as a new diagnostic and therapeutic target for OA treatment.

Feprazone Ameliorates TNF-α-Induced Loss of Aggrecan via Inhibition of the SOX-4/ADAMTS-5 Signaling Pathway

Background: Arthritis is a cartilage degenerative disease that is mainly induced by the degradation of the cartilage extracellular matrix (ECM), which is found to be regulated by the expression level of a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMT-5), an enzyme degrading Aggrecans in the ECM. Feprazone is a classic nonsteroidal anti-inflammatory drug with promising efficacy in arthritis. The present study aims to investigate the protective effect of Feprazone on the degraded Aggrecan in the human chondrocytes induced with tumor necrosis factor-α (TNF-α) and to clarify the underlying mechanism. Methods: To investigate the effect of Feprazone, the CHON-001 chondrocytes were stimulated with TNF-α (10 ng/mL) in the presence or absence of Feprazone (3, 6 μM) for 24 h. Mitochondrial membrane potential was evaluated using the Rhodamine 123 assay. The gene expressions of interleukin-1β (IL-1β), interleukin-8 (IL-8), monocyte chemotactic protein 1 (MCP-1), and ADAMTS-5 in the treated chondrocytes were detected using real-time quantitative polymerase chain reaction (qRT-PCR), and the protein levels of these targets were determined using enzyme-linked immunosorbent assay (ELISA). SOX-4 was knocked down by transfecting the siRNA into the chondrocytes. Western blot analysis was utilized to evaluate the expression levels of SOX-4, Aggrecan, and protein kinase C (PKCα). Results: First, the reduced mitochondrial membrane potential (ΔΨ_m) and secretion of proinflammatory factors (IL-1β, IL-8, and MCP-1) induced by TNF-α were significantly reversed by treatment with Feprazone. Second, the expression of Aggrecan was significantly decreased by stimulation with TNF-α via upregulation of ADAMTS-5 but was dramatically reversed by the introduction of Feprazone. Third, we found that TNF-α elevated the expression of ADAMTS-5 by upregulating SOX-4, which was observed to be related to the activation of PKCα. Lastly, the elevated expression of SOX-4 induced by TNF-α was significantly reversed by Feprazone. Conclusions: Feprazone might ameliorate TNF-α-induced loss of Aggrecan via the inhibition of the SOX-4/ADAMTS-5 signaling pathway.

Alendronate promotes the gene expression of extracellular matrix mediated by SP-1/SOX-9

BACKGROUND AND PURPOSE

Osteoarthritis (OA) is a disease with significant degenerative changes of articular cartilage, which is reported to be closely related to the integrity of chondrocytes extracellular matrix (ECM). Alendronate belongs to the family of bisphosphonates with promising cartilage repair function. In the present study, the effects of Alendronate on the gene expression of chondrocytes ECM and the potential mechanism will be investigated to explore the potential therapeutic property of Alendronate on OA.

METHODS

Human SW1353 chondrocytes were stimulated with 1 and 2 μM Alendronate for 12 h. The gene expression of Col2α1, COL9α2, and Acan in the treated chondrocytes was determined by qRT-PCR. QRT-PCR and western blot analysis were used to evaluate the expression level of SOX-9 in the treated chondrocytes. The expression level of SP-1 was checked by qRT-PCR and immunostaining. SiRNA against SP-1 was transfected into chondrocytes to knockdown the expression of SP-1. The levels of p-ERK1/2 and total ERK1/2 were examined using western blot analysis. TNF-α was used to induce an OA-like in vitro model in the chondrocytes for therapeutic evaluations.

RESULTS

Treatment with Alendronate increased the levels of ECM related genes (Col2α1, COL9α2, and Acan) in a dose-dependent manner through increasing the expression of SOX-9, a central regulator of ECM genes. Additionally, our findings demonstrate that the effects of Alendronate in the expression of SOX-9 are mediated by SP-1 as silencing of SP-1 abolished these effects. Notably, Alendronate increased the phosphorylation of ERK1/2 and inhibition of ERK1/2 using its specific inhibitor U0126 blocked the expression of SP-1. Finally, we found that treatment with Alendronate could rescue TNF-α-induced reduction of Col2α1, COL9α2, Acan and SOX-9.

CONCLUSION

Our data indicated that Alendronate might promote the gene expression of extracellular matrix through SOX-9 mediated by the ERK1/2/SP1 signaling pathway.

Kindlin-3 mutation in mesenchymal stem cells results in enhanced chondrogenesis

Identifying patient mutations driving skeletal development disorders has driven our understanding of bone development. Integrin adhesion deficiency disease is caused by a Kindlin-3 (fermitin family member 3) mutation, and its inactivation results in bleeding disorders and osteopenia. In this study, we uncover a role for Kindlin-3 in the differentiation of bone marrow mesenchymal stem cells (BMSCs) down the chondrogenic lineage. Kindlin-3 expression increased with chondrogenic differentiation, similar to RUNX2. BMSCs isolated from a Kindlin-3 deficient patient expressed chondrocyte markers, including SOX9, under basal conditions, which were further enhanced with chondrogenic differentiation. Rescue of integrin activation by a constitutively activated β₃ integrin construct increased adhesion to multiple extracellular matrices and reduced SOX9 expression to basal levels. Growth plates from mice expressing a mutated Kindlin-3 with the integrin binding site ablated demonstrated alterations in chondrocyte maturation similar to that seen with the human Kindlin-3 deficient BMSCs. These findings suggest that Kindlin-3 expression mirrors RUNX2 during chondrogenesis.

Tissue Engineering of Cartilage Using a Random Positioning Machine

Articular cartilage is a skeletal tissue of avascular nature and limited self-repair capacity. Cartilage-degenerative diseases, such as osteoarthritis (OA), are difficult to treat and often necessitate joint replacement surgery. Cartilage is a tough but flexible material and relatively easy to damage. It is, therefore, of high interest to develop methods allowing chondrocytes to recolonize, to rebuild the cartilage and to restore joint functionality. Here we studied the in vitro production of cartilage-like tissue using human articular chondrocytes exposed to the Random Positioning Machine (RPM), a device to simulate certain aspects of microgravity on Earth. To screen early adoption reactions of chondrocytes exposed to the RPM, we performed quantitative real-time PCR analyses after 24 h on chondrocytes cultured in DMEM/F-12. A significant up-regulation in the gene expression of IL6, RUNX2, RUNX3, SPP1, SOX6, SOX9, and MMP13 was detected, while the levels of IL8, ACAN, PRG4, ITGB1, TGFB1, COL1A1, COL2A1, COL10A1, SOD3, SOX5, MMP1, and MMP2 mRNAs remained unchanged. The STRING (Search Tool for the Retrieval of Interacting Genes/Proteins) analysis demonstrated among others the importance of these differentially regulated genes for cartilage formation. Chondrocytes grown in DMEM/F-12 medium produced three-dimensional (3D) spheroids after five days without the addition of scaffolds. On day 28, the produced tissue constructs reached up to 2 mm in diameter. Using specific chondrocyte growth medium, similar results were achieved within 14 days. Spheroids from both types of culture media showed the typical cartilage morphology with aggrecan positivity. Intermediate filaments form clusters under RPM conditions as detected by vimentin staining after 7 d and 14 d. Larger meshes appear in the network in 28-day samples. Furthermore, they were able to form a confluent chondrocyte monolayer after being transferred back into cell culture flasks in 1 g conditions showing their suitability for transplantation into joints. Our results demonstrate that the cultivation medium has a direct influence on the velocity of tissue formation and tissue composition. The spheroids show properties that make them interesting candidates for cellular cartilage regeneration approaches in trauma and OA therapy.

G protein subunit β1 is an important mediator of the late stage of endochondral ossification

G protein signaling plays important roles in skeletal development. G protein subunit β1 (GNB1) is a component of the G protein complex and is associated with G protein signaling. In humans, GNB1 mutations cause global developmental and persistent growth delays and severe neurodevelopmental disability. Similarly, Gnb1-knockout (KO) mice display growth retardation with neural tube defects. These genetic studies raise the possibility that GNB1 regulates skeletal development. This study was designed to investigate the role of GNB1 in skeletal development using Gnb1-KO mice. Gnb1-KO mice showed dwarfism, shortening of limbs, and a decreased ossifying zone of long bones. In situ hybridization and RT-qPCR analyses revealed that Col10a1 and Mmp13 expression was reduced in long bones of Gnb1-KO mice, while Runx2, Osterix, Ihh, and Ppr expression levels were similar to those in wild-type littermates. Gnb1-KO-derived osteoblasts maintained calcification abilities and the expression levels of osteoblast marker genes were unaltered, indicating that osteoblast differentiation and function were not affected in Gnb1-KO mice. Taken together, our results show that GNB1 is required for the late stage of endochondral bone formation by regulating Col10a1 and Mmp13 expression.

Remifentanil repairs cartilage damage and reduces the degradation of cartilage matrix in post-traumatic osteoarthritis, and inhibits IL-1β-induced apoptosis of articular chondrocytes via inhibition of PI3K/AKT/NF-κB phosphorylation

Background

Remifentanil (RFT) is an opioid analgesic with a unique pharmacokinetic profile, and plays an important role in the intra- and post-operative periods. Post-traumatic osteoarthritis (PTO) is a particular type of osteoarthritis (OA) that occurs secondary to a traumatic injury. In the present study, we investigated the effects of RFT both in vivo and in vitro.

Methods

In vivo, 50 Sprague Dawley (SD) rats (7 weeks old) were randomly divided into five groups. Four groups of rats received RFT (0.2, 0.5, and 1 µg) or vehicle (PTO group), while the remaining group served as the control. A PTO model in rats was established using the Hulth method. The cartilage damage, articular cartilage formation, and the degradation of cartilage matrix were evaluated. The effects of RFT on cell proliferation, apoptosis, and nuclear factor (NF)-κB phosphorylation were also examined.

Results

The results indicated that RFT improved cartilage damage, enhanced articular cartilage formation, and inhibited the degradation of cartilage matrix in PTO model rats. Compared with the control group, the protein levels of Osterix (OSX), Collagen type I alpha 1 (COL1A1), and osteocalcin (OC) were down-regulated in PTO model rats. RFT also inhibited the interleukin-1β (IL-1β)-induced apoptosis of chondrocytes in vitro. Furthermore, the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/NF-κB pathway was inhibited both in vitro and in vitro.

Conclusions

RFT has significant potential as a therapeutic intervention to ameliorate PTO and provides a foundation for further clinical studies.

LIM domain proteins Pinch1/2 regulate chondrogenesis and bone mass in mice

The LIM domain-containing proteins Pinch1/2 regulate integrin activation and cell–extracellular matrix interaction and adhesion. Here, we report that deleting Pinch1 in limb mesenchymal stem cells (MSCs) and Pinch2 globally (double knockout; dKO) in mice causes severe chondrodysplasia, while single mutant mice do not display marked defects. Pinch deletion decreases chondrocyte proliferation, accelerates cell differentiation and disrupts column formation. Pinch loss drastically reduces Smad2/3 protein expression in proliferative zone (PZ) chondrocytes and increases Runx2 and Col10a1 expression in both PZ and hypertrophic zone (HZ) chondrocytes. Pinch loss increases sclerostin and Rankl expression in HZ chondrocytes, reduces bone formation, and increases bone resorption, leading to low bone mass. In vitro studies revealed that Pinch1 and Smad2/3 colocalize in the nuclei of chondrocytes. Through its C-terminal region, Pinch1 interacts with Smad2/3 proteins. Pinch loss increases Smad2/3 ubiquitination and degradation in primary bone marrow stromal cells (BMSCs). Pinch loss reduces TGF-β-induced Smad2/3 phosphorylation and nuclear localization in primary BMSCs. Interestingly, compared to those from single mutant mice, BMSCs from dKO mice express dramatically lower protein levels of β-catenin and Yap1/Taz and display reduced osteogenic but increased adipogenic differentiation capacity. Finally, ablating Pinch1 in chondrocytes and Pinch2 globally causes severe osteopenia with subtle limb shortening. Collectively, our findings demonstrate critical roles for Pinch1/2 and a functional redundancy of both factors in the control of chondrogenesis and bone mass through distinct mechanisms.

Sox9 promotes renal tubular epithelial‑mesenchymal transition and extracellular matrix aggregation via the PI3K/AKT signaling pathway

Sox9 is important for multiple aspects of development, such as testis, pancreas and heart development. Previous studies have reported that Sox9 induced epithelial‑mesenchymal transition (EMT) and extracellular matrix (ECM) production in organ fibrosis and associated diseases, such as vascular calcification. However, to the best of our knowledge, the role and underlying mechanism of action of Sox9 in renal fibrogenesis remains unknown. The results of the present study revealed that Sox9 expression levels were upregulated in the tubular epithelial cells of a rat model of obstructive nephropathy. Furthermore, the overexpression of Sox9 in NRK‑52E cells was discovered to promote renal tubular EMT and ECM aggregation, and these fibrogenic actions were potentiated by TGF‑β1. Notably, RNA‑sequencing analysis indicated the possible regulatory role of the PI3K/AKT signaling pathway in Sox9‑mediated renal tubular EMT and ECM aggregation. It was further demonstrated that the expression levels of phosphorylated AKT were upregulated in NRK‑52E cells overexpressing Sox9, while the PI3K inhibitors, LY29002 and wortmannin, inhibited the renal tubular EMT and ECM aggregation induced by the overexpression of Sox9 in NEK‑52E cells. In conclusion, the findings of the present study suggested that Sox9 may serve a profibrotic role in the development of renal tubular EMT and ECM aggregation via the PI3K/AKT signaling pathway. Therefore, Sox9 may be considered as a promising target for treating renal fibrosis.

Seaweed polysaccharides as macromolecular crowding agents

Development of mesenchymal stem cell-based tissue engineered implantable devices requires prolonged in vitro culture for the development of a three-dimensional implantable device, which leads to phenotypic drift, thus hindering the clinical translation and commercialisation of such approaches. Macromolecular crowding, a biophysical phenomenon based on the principles of excluded-volume effect, dramatically accelerates and increases extracellular matrix deposition during in vitro culture. However, the optimal macromolecular crowder is still elusive. Herein, we evaluated the biophysical properties of various concentrations of different seaweed in origin sulphated polysaccharides and their effect on human adipose derived stem cell cultures. Carrageenan, possibly due to its high sulphation degree, exhibited the highest negative charge values. No correlation was observed between the different concentrations of the crowders and charge, polydispersity index, hydrodynamic radius and fraction volume occupancy across all crowders. None of the crowders, but arabinogalactan, negatively affected cell viability. Carrageenan, fucoidan, galactofucan and ulvan increased extracellular matrix (especially collagen type I and collagen type V) deposition. Carrageenan induced the highest osteogenic effect and galactofucan and fucoidan demonstrated the highest chondrogenic effect. All crowders were relatively ineffective with respect to adipogenesis. Our data highlight the potential of sulphated seaweed polysaccharides for tissue engineering purposes.

Zebrafish models of skeletal dysplasia induced by cholesterol biosynthesis deficiency

Human disorders of the post-squalene cholesterol biosynthesis pathway frequently result in skeletal abnormalities, yet our understanding of the mechanisms involved is limited. In a forward-genetic approach, we have found that a late-onset skeletal mutant, named kolibernu7 , is the result of a cis-acting regulatory mutation leading to loss of methylsterol monooxygenase 1 (msmo1) expression within pre-hypertrophic chondrocytes. Generated msmo1nu81 knockdown mutation resulted in lethality at larval stage. We demonstrated that this is a result of both cholesterol deprivation and sterol intermediate accumulation by creating a mutation eliminating activity of Lanosterol synthase (Lss). Our results indicate that double lssnu60;msmo1nu81 and single lssnu60 mutants survive significantly longer than msmo1nu81 homozygotes. Liver-specific restoration of either Msmo1 or Lss in corresponding mutant backgrounds suppresses larval lethality. Rescued mutants develop dramatic skeletal abnormalities, with a loss of Msmo1 activity resulting in a more-severe patterning defect of a near-complete loss of hypertrophic chondrocytes marked by col10a1a expression. Our analysis suggests that hypertrophic chondrocytes depend on endogenous cholesterol synthesis, and blocking C4 demethylation exacerbates the cholesterol deficiency phenotype. Our findings offer new insight into the genetic control of bone development and provide new zebrafish models for human disorders of the cholesterol biosynthesis pathway.

Regulation and function of SOX9 during cartilage development and regeneration

Chondrogenesis is a highly coordinated event in embryo development, adult homeostasis, and repair of the vertebrate cartilage. Fate decisions and differentiation of chondrocytes accompany differential expression of genes critical for each step of chondrogenesis. SOX9 is a master transcription factor that participates in sequential events in chondrogenesis by regulating a series of downstream factors in a stage-specific manner. SOX9 either works alone or in combination with downstream SOX transcription factors, SOX5 and SOX6 as chondrogenic SOX Trio. SOX9 is reduced in the articular cartilage of patients with osteoarthritis while highly maintained during tumorigenesis of cartilage and bone. Gene therapy using viral and non-viral vectors accompanied by tissue engineering (scaffolds) is a promising tool to regenerate impaired cartilage. Delivery of SOX9 or chondrogenic SOX Trio into cells produces efficient therapeutic effects on chondrogenesis and this event is facilitated by scaffolds. Non-viral vector-guided delivery systems encapsulated or loaded in mechanically stable solid scaffolds are useful for the regeneration of articular cartilage. Here we review major milestones and most recent studies focusing on regulation and function of chondrogenic SOX Trio, during chondrogenesis and cartilage regeneration, and on the development of advanced technologies in gene delivery with tissue engineering to improve efficiency of cartilage repair process.