Dual function of β-catenin in articular cartilage growth and degeneration at different stages of postnatal cartilage development

Lithium rescues cultured rat metatarsals from dexamethasone-induced growth failure

BACKGROUND

Glucocorticoids are commonly used in children with different chronic diseases. Growth failure represents a so far untreatable undesired side-effect. As lithium chloride (LiCl) is known to induce cell renewal in various tissues, we hypothesized that LiCl may prevent glucocorticoid-induced growth failure.

METHODS

We monitored growth of fetal rat metatarsals cultured ex-vivo with dexamethasone and/or LiCl, while molecular mechanisms were explored through RNA sequencing by implementing the differential gene expression and gene set analysis. Quantification of β-catenin in human growth plate cartilage cultured with dexamethasone and/or LiCl was added for verification.

RESULTS

After 14 days of culture, the length of dexamethasone-treated fetal rat metatarsals increased by 1.4 ± 0.2 mm compared to 2.4 ± 0.3 mm in control bones (p < 0.001). The combination of LiCl and dexamethasone led to bone length increase of 1.9 ± 0.3 mm (p < 0.001 vs. dexamethasone alone). By adding lithium, genes for cell cycle and Wnt/β-catenin, Hedgehog and Notch signaling, were upregulated compared to dexamethasone alone group.

CONCLUSIONS

LiCl has the potential to partially rescue from dexamethasone-induced bone growth impairment in an ex vivo model. Transcriptomics identified cell renewal and proliferation as candidates for the underlying mechanisms. Our observations may open up the development of a new treatment strategy for bone growth disorders.

IMPACT

LiCl is capable to prevent glucocorticoid-induced growth failure in rat metatarsals in vitro. The accompanying drug-induced transcriptomic changes suggested cell renewal and proliferation as candidate underlying mechanisms. Wnt/beta-catenin pathway could be one of those novel mechanisms.

Impact of endoplasmic reticulum stress on chondrocyte apoptosis in rat model of DDH

Developmental dysplasia of the hip (DDH) is a developmental disorder characterized by acetabular dysplasia leading to early osteoarthritis. This study examines the role of endoplasmic reticulum stress (ERS) in chondrocyte apoptosis and cartilage degeneration within a DDH model. In the rat model of DDH, created using a swaddling technique, significant deformities in the femoral head and acetabulum were observed, alongside an upregulation of matrix metalloproteinase-13 in acetabular cartilage. We also noted increased levels of apoptosis and ERS-related factors in the acetabular cartilage of DDH models. Additionally, rat chondrocytes exposed to high-magnitude cyclic tensile strain (CTS, 1 Hz, 10% equibiaxial strain) in vitro exhibited elevated ERS and increased apoptosis. Importantly, treatment with the ERS inhibitor 4-phenylbutyric acid effectively suppressed apoptosis induced by CTS in chondrocytes. Our findings suggest that ERS contributes to the upregulation of apoptosis-related factors in chondrocytes within the DDH model, indicating the potential of ERS modulation as a therapeutic approach for DDH-related cartilage degeneration.

Study on the Role of MicroRNA-214 in the Rehabilitation of Cartilage in Mice with Exercise-Induced Traumatic Osteoarthritis

This study aimed to explore the possible relationship between the expression of Micro RNA-214 (miR-214) and the pathogenesis and recovery in mice with post-traumatic osteoarthritis (PTOA). In this study, 40 male C57BL/6 mice were randomly divided into five groups: model control (MC) group, model (M) group, rehabilitation control (RC) group, model + rehabilitation (M + R) group, and model + convalescent (M + C) group. Four weeks of high-intensity treadmill exercise (HITE) and 4 weeks of moderate-intensity treadmill exercise (MITE) were implemented for PTOA modeling and rehabilitation, respectively. In vitro, 10% elongation mechanical strain was used for IL-1β stimulated chondrocytes. We found that compared with the MC group, there was a significant increase in the aspect of inflammation and catabolism while a dramatic fall in miR-214 expression was observed in the M group. After the 4 weeks of MITE, the level of inflammation and metabolism, as well as miR-214 expression, was partially reversed in the M + R group compared with the M + C group. The expression of miR-214 decreased dramatically after chondrocyte stimulation by IL-1β and then increased significantly after 10% strain was applied to IL-1β-treated cells. These results suggest that a suitable mechanical load can increase the expression of miR-214, and that miR-214 may play a chondroprotective effect in the development of OA.

miR-122 and the WNT/β-catenin pathway inhibit effects of both interleukin-1β and tumor necrosis factor-α in articular chondrocytes in vitro

Interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and WNT/β-catenin signaling cause dysregulation of rat primary articular chondrocytes (rArCs), resulting in cartilage extracellular matrix destruction and osteoarthritis (OA) progression. microRNA (miR) miR-122 represses these effects whereas miR-451 exacerbates IL-1β-stimulated matrix metalloproteinase-13 (MMP-13) and prostaglandin E2 (PGE2) production. The goals of this study were to evaluate crosstalk between these signaling pathways and determine if miR-122 and miR-451 exert their protective/destructive effects through these pathways in an in vitro model of OA. Primary rArCs were treated with IL-1β or TNF-α for 24 h and total DNA, MMP-13, and PGE2, as well as expression levels of miR-122 and miR-451 were measured. After 24-h transfection with miR-122, miR-451, miR-122-inhibitor, or miR-451-inhibitor, rArCs were treated with or without TNF-α for 24 h; total DNA, MMP-13, and PGE2 were measured. Similarly, cells were treated with WNT-agonist lithium chloride (LiCl), WNT-antagonist XAV-939 (XAV), or PKF-118-310 (PKF) with and without IL-1β or TNF-α stimulation. Both IL-1β and TNF-α-stimulation increased MMP-13 and PGE2 production. Transfection with miR-122 prevented TNF-α-stimulated increases in MMP-13 and PGE2 whereas transfection with miR-451 did not change these levels. No differences were found in MMP-13 or PGE2 production with miR-122 or miR-451 inhibitors. LiCl treatment decreased PGE2 production in cultures treated with TNF-α, but not MMP-13. XAV increased TNF-α-stimulated increases in PGE2 but not MMP-13. LiCl reduced IL-1β-stimulated increases in MMP-13 and PGE2. XAV and PKF increased IL-1β-stimulated increases in MMP-13 and PGE2. In this in vitro OA model, miR-122 protects against both IL-1β and TNF-α stimulated increases in MMP-13 and PGE2 production. miR-451 does not act through the TNF-α pathway. The WNT/β-catenin pathway regulates the effects of IL-1β and TNF-α stimulation. This study suggests that miR-122 can be used as a treatment or prevention for OA.

Chronic Circadian Rhythm Disturbance Accelerates Knee Cartilage Degeneration in Rats Accompanied by the Activation of the Canonical Wnt/β-Catenin Signaling Pathway

With the gradual deepening of understanding of systemic health and quality of life, the factors affecting osteoarthritis (OA) are not limited to mechanical injury, metabolic abnormality, age and obesity, etc., but circadian rhythm, which plays a non-negligible role in human daily life. The purpose of this study was to explore the molecular mechanism of chronic circadian rhythm disturbance (CRD) inducing cartilage OA-like degeneration. Rats with the anterior cruciate ligament excision transection (ACLT) were used to establish the early-stage OA model (6-week). The light/dark (LD) cycle shifted 12 h per week for 22 weeks in order to establish a chronic CRD model. BMAL1 knockdown (KD) and Wnt/β-catenin pathway inhibition were performed in chondrocytes. The contents of proinflammatory factors and OA biomarkers in serum and chondrocyte secretions were detected by ELISA. Pathological and immunohistochemical staining of articular cartilage indicated the deterioration of cartilage. WB and qPCR were used to evaluate the relationship between matrix degradation and the activation of Wnt/β-catenin signaling pathway in chondrocytes. We found that chronic CRD could cause OA-like pathological changes in knee cartilage of rats, accelerating cartilage matrix degradation and synovial inflammation. The expression of MMP-3, MMP-13, ADAMTS-4, and β-catenin increased significantly; BMAL1, Aggrecan, and COL2A1 decreased significantly in either LD-shifted cartilage or BMAL1-KD chondrocytes. The expression of β-catenin and p-GSK-3β elevated, while p-β-catenin and GSK-3β diminished. The inhibitor XAV-939 was able to mitigated the increased inflammation produced by transfected siBMAL1. Our study demonstrates that chronic CRD disrupts the balance of matrix synthesis and catabolic metabolism in cartilage and chondrocytes, and it is related to the activation of the canonical Wnt/β-catenin signaling pathway.

β‑catenin signalling inhibits cartilage endplate chondrocyte homeostasis in vitro

Cartilaginous endplate degeneration serves a key role in the process of intervertebral disc (IVD) degeneration, however, effective therapies are hindered by an incomplete understanding of the mechanisms that underlie cartilage endplate (CEP) homeostasis and degeneration. Wnt/β-catenin signalling has been reported as a major factor in regulating biological processes. Whether Wnt/β-catenin signalling engages in CEP homeostasis has not yet been investigated. The present study aimed to assess the function of CEP cells via the activation of Wnt/β-catenin signalling to examine and promote the mechanism of degeneration of CEP in vitro. Rat CEP cells were confirmed to exhibit a chondrocytic phenotype by toluidine blue staining. The increased number of senescence-associated β-galactosidase (SA-β-gal)-positive cells and reduced cellular proliferation were investigated in the presence of a β-catenin inhibitor, and the inhibitor improved the trend of senescence. An increased number of apoptotic cells was detected by lithium chloride treatment, and inhibiting Wnt/β-catenin signalling protected the cells from apoptosis. Expression of the catabolic enzymes, metalloproteinase-13 and a disintegrin and metalloproteinase with thrombospondin motifs-5, and the decreased expression of aggrecan were also observed by Wnt/β-catenin signalling activation, and a Wnt/β-catenin signalling inhibitor decreased the expression of catabolic enzymes and increased the expression of aggrecan induced by Wnt/β-catenin signalling activation. Wnt/β-catenin signalling may provide potential strategies for preventing CEP degeneration.

Expression of pro-apoptotic markers is increased along the osteochondral junction in naturally occurring osteochondrosis

Osteochondrosis (OC) is a naturally occurring disease of the articular-epiphyseal cartilage and subchondral bone layers, leading to pain and decreased mobility. The objective of this study was to characterize gene and protein expression of apoptotic markers in chondrocytes surrounding cartilage canals and along the osteochondral junction of osteochondrosis (OC)-affected and normal cartilage, using naturally occurring disease in horses. Paraffin-embedded osteochondral samples (6 OC, 8 normal controls) and cDNA from chondrocytes captured with laser capture microdissection (4 OC, 6 normal controls) were obtained from the lateral trochlear ridge of femoropatellar joints in 14 immature horses (1–6 months of age). Equine-specific caspase-3, caspase-8, caspase-10, Fas, Bcl-2, BAG-1, TNFα, cytochrome C, thymosin-β10, and 18S mRNA expression levels were evaluated by two-step real-time quantitative PCR. Percentage of cell death was determined using the TUNEL method. Protein expression of caspase-10, Fas, cytochrome C, and thymosin-β10 was determined following immunohistochemistry. Statistical analysis was performed using the Wilcoxon rank sum test or two-sample t-test (p < 0.05). In OC samples, there was significantly increased gene expression of caspase-10, Fas, cytochrome C, and thymosin-β10 in chondrocytes along the osteochondral junction and increased Fas gene expression in chondrocytes adjacent to cartilage canals, compared to controls. In OC samples, higher matrix Fas and cytochrome C protein expression, lower mitochondrial cytochrome C protein expression, and a trend for higher cytoplasmic caspase-10 protein expression were found. Collectively, these results suggest that both extrinsic and intrinsic apoptotic pathways are activated in OC cartilage. Increased apoptosis of osteochondral junction chondrocytes may play a role in OC, based on increased gene expression of several pro-apoptotic markers in this location.

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Pro-apoptotic marker gene expression increased in osteochondrosis cartilage

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Extrinsic and intrinsic apoptotic pathways activated along osteochondral junction

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Higher caspase-10, Fas, cytochrome C, and thymosin-β10 gene expression

Effects of Qi-Fang-Xi-Bi-Granules on Cartilage Morphology and C/ebpα Promoter Methylation in Rats with Knee Osteoarthritis

Objective

To investigate the effects of Qi-Fang-Xi-Bi-Granules (QFXBGs) on cartilage morphology and methylation of C/ebpα (CCAAT/enhancer binding proteinα) at the promoter region.

Methods

Knee osteoarthritis (KOA) modeling was performed in rats in accordance with Hulth's method, and control group received sham operation. Eight weeks after KOA modeling, the rats in the KOA modeling group were further divided into 6 groups. Each group was given the appropriate drug. After 8 weeks, half of the rats were used for Micro-CT scan, HE staining, ABH/OG staining, immunohistochemistry, and TUNNEL staining of the knee joint tissue, and the other half were used to examine C/ebpα promoter methylation.

Results

The three dose groups of QFXBGs all showed lower degrees of surface fissures and flaking, thicker cartilage layer, and restored chondrocyte and subchondral bone morphology, compared with the KOA model group. C/ebpα-22 promoter methylation levels in the high- and low-dose groups were significantly higher than that in the KOA modeling group (p < 0.05), while C/ebpα-2 promoter methylation level in the medium-dose group was significantly higher than that in the KOA modeling group (p < 0.05).

Conclusions

QFXBGs may alleviate articular cartilage degeneration through promoting C/ebpα-2 or C/ebpα-22 methylation at specific promoter sites.

Effects of Wnt/β-catenin signaling on bisphenol A exposure in male mouse reproductive cells

Bisphenol A (BPA) is a chemical used in numerous consumer products that is able to interfere with the mammalian endocrine system. The aim of the present study was to investigate the effects of BPA on male mouse reproductive cells following prenatal to postnatal exposure. In addition, the influence of BPA was detected on the expression levels of β‑catenin and dickkopf WNT signaling pathway inhibitor 1 (DKK‑1) during the differentiation of spermatogenic cells in the mouse testes. β‑catenin and DKK‑1 are two important proteins of the Wnt/β‑catenin signaling pathway. On gestational day 1, pregnant ICR mice were randomly divided into four groups: A dimethyl sulfoxide group, and three groups treated with various concentrations of BPA (0.5, 10, and 50 µg/kg). BPA was administered from gestational day 1 to weaning on postnatal day (PND) 42. The number of murine pups and the male:female ratio was recorded for each group. On PND 42, the male pups were sacrificed and their wet weights and testicular coefficients were measured. Immunohistochemical and western blot analyses were used to detect the protein expression of β‑catenin and DKK‑1 in the testicular tissue samples of the six‑week‑old male mice. The results indicated that the number of murine pups, as well as the testicular viscera coefficient of the male mice, significantly decreased in the BPA‑treated groups, as compared with the control group (P<0.05, P<0.01); however, no significant difference was observed in the male/female ratio in the BPA‑treated groups, as compared with the control group (P>0.05). The results from the immunohistochemical and western blot analyses indicated that the protein expression of β‑catenin and DKK‑1 were significantly increased in the BPA‑treated groups, as compared with the control group, and the distribution of spermospore and Leydig cells also increased in the testes. These results suggest that high expression levels of β‑catenin and DKK‑1 may participate in BPA‑induced pathogenesis in male mouse reproductive cells.

Fibroblast growth factor and canonical WNT/β-catenin signaling cooperate in suppression of chondrocyte differentiation in experimental models of FGFR signaling in cartilage

Aberrant fibroblast growth factor (FGF) signaling disturbs chondrocyte differentiation in skeletal dysplasia, but the mechanisms underlying this process remain unclear. Recently, FGF was found to activate canonical WNT/β-catenin pathway in chondrocytes via Erk MAP kinase-mediated phosphorylation of WNT co-receptor Lrp6. Here, we explore the cellular consequences of such a signaling interaction. WNT enhanced the FGF-mediated suppression of chondrocyte differentiation in mouse limb bud micromass and limb organ cultures, leading to inhibition of cartilage nodule formation in micromass cultures, and suppression of growth in cultured limbs. Simultaneous activation of the FGF and WNT/β-catenin pathways resulted in loss of chondrocyte extracellular matrix, expression of genes typical for mineralized tissues and alteration of cellular shape. WNT enhanced the FGF-mediated downregulation of chondrocyte proteoglycan and collagen extracellular matrix via inhibition of matrix synthesis and induction of proteinases involved in matrix degradation. Expression of genes regulating RhoA GTPase pathway was induced by FGF in cooperation with WNT, and inhibition of the RhoA signaling rescued the FGF/WNT-mediated changes in chondrocyte cellular shape. Our results suggest that aberrant FGF signaling cooperates with WNT/β-catenin in suppression of chondrocyte differentiation.

Age-related differential gene and protein expression in postnatal cartilage canal and osteochondral junction chondrocytes

Wnt/β-catenin, Indian hedgehog (Ihh)/Parathyroid-related peptide (PTHrP) and retinoid signaling pathways regulate cartilage differentiation, growth, and function during development and play a key role in endochondral ossification. The objective of this study was to elucidate the gene and protein expression of signaling molecules of these regulatory pathways in chondrocytes surrounding cartilage canals and the osteochondral junction during neonatal and pre-adolescent development. This study revealed cell-specific and age-related differences in gene and protein expression of signaling molecules of these regulatory pathways. A trend for higher gene expression of PTHrP along the cartilage canals and Ihh along the osteochondral junction suggests the presence of paracrine feedback in articular-epiphyseal cartilage. Differential expression of canonical (β-catenin, Wnt-4, Lrp4, Lrp6) and noncanonical Wnt signaling (Wnt-5b, Wnt-11) and their inhibitors (Dkk1, Axin1, sFRP3, sFRP5, Wif-1) surrounding the cartilage canals and osteochondral junction provides evidence of the complex interactions occurring during endochondral ossification.

Distinct Effect of TCF4 on the NFκB Pathway in Human Primary Chondrocytes and the C20/A4 Chondrocyte Cell Line

OBJECTIVE

Previous studies indicated a difference in crosstalk between canonical WNT pathway and nuclear factor-κB (NFκB) signaling in human and animal chondrocytes. To assess whether the differences found were dependent on cell types used, we tested the effect of WNT modulation on NFκB signaling in human primary articular chondrocytes in comparison with the immortalized human costal chondrocyte cell line C20/A4.

DESIGN

We used gene expression analysis to study the effect of WNT modulation on IL1β-induced matrix metalloproteinase (MMP) expression as well as on WNT and NFκB target gene expression. In addition, we tested the involvement of RelA and TCF4 on activation of the WNT and NFκB pathway by TCF/LEF and NFκB reporter experiments, respectively.

RESULTS

We found an inhibitory effect of both induction and inhibition of WNT signaling on IL1β-induced MMP mRNA expression in primary chondrocytes, whereas WNT modulation did not affect MMP expression in C20/A4 cells. Furthermore, TCF/LEF and NFκB reporter activation and WNT and NFκB target gene expression were regulated differentially by TCF4 and RelA in a cell type-dependent manner. Additionally, we found significantly higher mRNA and protein expression of TCF4 and RelA in C20/A4 cells in comparison with primary chondrocytes.

CONCLUSIONS

We conclude that WNT modulation of NFκB is, at least in part, cell type dependent and that the observed differences are likely because of impaired sensitivity of the NFκB pathway in C20/A4 cells to modulations in WNT signaling. This might be caused by higher basal levels of TCF4 and RelA in C20/A4 cells compared to primary chondrocytes.

Early articular cartilage degeneration in a developmental dislocation of the hip model results from activation of β-catenin

Developmental dislocation or dysplasia of the hip (DDH) is one of the most common deformities in children. Osteoarthritis (OA) is the most frequent long-term complication. The molecular mechanism of early articular cartilage degeneration in DDH is still unclear. It is well known that β-catenin plays a crucial role in articular cartilage degeneration. The objective of this study was to verify the relationship between β-catenin and DDH cartilage degeneration. We used a DDH model that was established by modification of swaddling position in newborn Wistar rats. The hips were isolated from the DDH model rats and untreated control group at the age of 2, 4, 6 and 8 weeks. β-Catenin gene and protein were investigated by quantitative (q)RT-PCR and immunohistochemistry. Collagen X and matrix metalloproteinase (MMP)-13, markers of early cartilage degeneration, were assessed by qRT-PCR. Primary chondrocytes were cultured from cartilage of two groups at the age of 8 weeks. Expression of β-catenin, collagen X and MMP-13 was detected. Continued high expression of β-catenin was observed in cartilage from DDH model rats. mRNA and protein expression of β-catenin was significantly increased in primary chondrocytes of the DDH model compared with the control group. Collagen X and MMP-13 expression was higher in the cartilage and chondrocytes from DDH model rats than the control group. Our findings suggest that early cartilage degeneration in DDH may result from activation of β-catenin signaling.

Looping mediated interaction between the promoter and 3' UTR regulates type II collagen expression in chondrocytes

Type II collagen is the major component of articular cartilage and is mainly synthesized by chondrocytes. Repeated sub-culturing of primary chondrocytes leads to reduction of type II collagen gene (Col2a1) expression, which mimics the process of chondrocyte dedifferentiation. Although the functional importance of Col2a1 expression has been extensively investigated, mechanism of transcriptional regulation during chondrocyte dedifferentiation is still unclear. In this study, we have investigated the crosstalk between cis-acting DNA element and transcription factor on Col2a1 expression in primary chondrocytes. Bioinformatic analysis revealed the potential regulatory regions in the Col2a1 genomic locus. Among them, promoter and 3′ untranslated region (UTR) showed highly accessible chromatin architecture with enriched recruitment of active chromatin markers in primary chondrocytes. 3′ UTR has a potent enhancer function which recruits Lef1 (Lymphoid enhancer binding factor 1) transcription factor, leading to juxtaposition of the 3′ UTR with the promoter through gene looping resulting in up-regulation of Col2a1 gene transcription. Knock-down of endogenous Lef1 level significantly reduced the gene looping and subsequently down-regulated Col2a1 expression. However, these regulatory loci become inaccessible due to condensed chromatin architecture as chondrocytes dedifferentiate which was accompanied by a reduction of gene looping and down-regulation of Col2a1 expression. Our results indicate that Lef1 mediated looping between promoter and 3′ UTR under the permissive chromatin architecture upregulates Col2a1 expression in primary chondrocytes.