Coordinate down-regulation of cartilage matrix gene expression in Bcl-2 deficient chondrocytes is associated with decreased SOX9 expression and decreased mRNA stability

Modulation of apoptosis and Inflammasome activation in chondrocytes: co-regulatory role of Chlorogenic acid

BACKGROUND

The B-cell lymphoma 2 (Bcl-2) protein regulates programmed cell death throughout the disease conditions by upholding apoptotic pathways. However, the mechanism by which it's expressed in chondrocytes still needs to be studied in chondrocyte-related disorders. Additionally, exploring the potential therapeutic role of Chlorogenic acid (CGA) in confluence with Bcl-2 modulation is of significant interest.

METHODS

In vivo and in vitro studies were performed according to our previous methodologies. The chondrocytes were cultured in specific growth media under standard conditions after expression verification of different microRNAs through high-throughput sequencing and verification of Bcl-2 involvement in tibial growth plates. The effect of Bcl-2 expression was investigated by transfecting chondrocytes with miR-460a, siRNA, and their negative controls alone or in combination with CGA. The RNA was extracted and subjected to a reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Western blot analysis and immunofluorescence assays were performed to visualize the intracellular localization of Bcl-2 and associated proteins related to apoptotic and inflammasome pathways. Moreover, apoptosis through flow cytometry was also performed to understand the modulation of concerning pathways.

RESULTS

The suppression of Bcl-2 induced higher apoptosis and mitochondrial dysfunction, leading to IL-1β maturation and affecting the inflammasome during chondrocyte proliferation. Conversely, overexpression attenuated the activation, as evidenced by reduced caspase activity and IL-1β maturation. In parallel, CGA successfully reduced siRNA-induced apoptosis by decreasing Cytochrome C (Cyto C) release from the mitochondria to the cytoplasm, which in turn decreased Caspase-3 and Caspase-7 cleavage with Bcl-2-associated X protein (Bax). Furthermore, siBcl-2 transfection and CGA therapy increased chondrocyte proliferation and survival. The CGA also showed a promising approach to maintaining chondrocyte viability by inhibiting siRNA-induced apoptosis.

CONCLUSIONS

Targeting Bcl-2-mediated regulation might be a possible treatment for chondrocyte-related conditions. Moreover, these results add knowledge of the complicated processes underlying chondrocyte function and the pathophysiology of related diseases, highlighting the significance of target specific therapies. Video Abstract.

Role of Expression of Inflammatory Mediators in Primary and Recurrent Lumbar Disc Herniation

Objective

To assess role of some inflammatory mediators in patients with primary and recurrent lumbar disc herniation. Expression of IL-6, transforming growth factor (TGF)-1, insulin-like growth factor (IGF)-1, and Bcl-2-associated X protein (BAX) have been shown to be more intense in the primary group than the recurrent goup, but this mediators may be important aspects prognostic.

Methods

19 patients underwent primary and revision operations between June 1, 2009 and June 1, 2014, and they were included in this study. The 19 patients’ intervertebral disc specimens obtained from the primary procedures and reoperations were evaluated. Expression of IL-6, TGF-1, IGF-1, and BAX were examined immunohistochemically in the 38 biopsy tissues obtained from the primary and recurrent herniated intervertebral discs during the operation.

Results

For IL-6 expression in the intervertebral disc specimens, there was no difference between the groups. The immunohistochemical study showed that the intervertebral disc specimens in the primary group were stained intensely by TGF-1 compared with the recurrent group. Expression of IGF-1 in the primary group was found moderate. In contrast, in the recurrent group of patients was mild expression of IGF-1. The primary group intervertebral disc specimens were stained moderately by BAX compared with the recurrent group.

Conclusion

The results of our prognostic evaluation of patients in the recurrent group who were operated due to disc herniation suggest that mediators may be important parameters.

Electroacupuncture stimulates remodeling of extracellular matrix by inhibiting apoptosis in a rabbit model of disc degeneration

The present study was designed to determine whether EA stimulates remodeling of extracellular matrix by inhibiting apoptosis in degenerated disc. 40 rabbits were randomly assigned to one of the four groups. Animal model was established by a loading device. Magnetic resonance imaging and Pfirrmann's classification were obtained to evaluate both the model and the EA treatment on disc degeneration. The ultrastructure of discs was observed by TEM. Apoptosis involvement was determined with TUNEL staining and western blot for the protein expression of Bax and Bcl-2. The results indicated that EA intervention decreased the MRI grades. TEM analysis showed an apparent remodeling and rearrangement of disc ECM after EA intervention for 28 days. The number of TUNEL-positive cells in the EA group was significantly lower than that in the compression group. The protein expression demonstrated an antiapoptosis effect mediated by EA. Increased expression of Bcl-2 proteins and reduced Bax protein expression were detected after 28 days treatment. It was concluded that antiapoptosis pathway probably participates in the mechanism of EA stimulating the remodeling of ECM in disc degeneration.

Progression of cartilage degradation, bone resorption and pain in rat temporomandibular joint osteoarthritis induced by injection of iodoacetate

Background

Osteoarthritis (OA) is an important subtype of temporomandibular disorders. A simple and reproducible animal model that mimics the histopathologic changes, both in the cartilage and subchondral bone, and clinical symptoms of temporomandibular joint osteoarthritis (TMJOA) would help in our understanding of its process and underlying mechanism.

Objective

To explore whether injection of monosodium iodoacetate (MIA) into the upper compartment of rat TMJ could induce OA-like lesions.

Methods

Female rats were injected with varied doses of MIA into the upper compartment and observed for up to 12 weeks. Histologic, radiographic, behavioral, and molecular changes in the TMJ were evaluated by light and electron microscopy, MicroCT scanning, head withdrawal threshold test, real-time PCR, immunohistochemistry, and TUNEL assay.

Results

The intermediate zone of the disc loosened by 1 day post-MIA injection and thinned thereafter. Injection of an MIA dose of 0.5 mg or higher induced typical OA-like lesions in the TMJ within 4 weeks. Condylar destruction presented in a time-dependent manner, including chondrocyte apoptosis in the early stages, subsequent cartilage matrix disorganization and subchondral bone erosion, fibrosis, subchondral bone sclerosis, and osteophyte formation in the late stages. Nociceptive responses increased in the early stages, corresponding to severe synovitis. Furthermore, chondrocyte apoptosis and an imbalance between anabolism and catabolism of cartilage and subchondral bone might account for the condylar destruction.

Conclusions

Multi-level data demonstrated a reliable and convenient rat model of TMJOA could be induced by MIA injection into the upper compartment. The model might facilitate TMJOA related researches.

Regulation of cartilage formation and maturation by mitogen-activated protein kinase signaling

The majority of bones comprising the adult vertebrate skeleton are generated from hyaline cartilage templates that form during embryonic development. A process known as endochondral ossification is responsible for the conversion of these transient cartilage anlagen into mature, calcified bone. Endochondral ossification is a highly regulated, multistep cell specification program involving the initial differentiation of prechondrogenic mesenchymal cells into hyaline chondrocytes, terminal differentiation of hyaline chondrocytes into hypertrophic chondrocytes, and finally, apoptosis of hypertrophic chondrocytes followed by bone matrix deposition. Recently, extensive research has been carried out describing roles for the three major mitogen-activated protein kinase (MAPK) signaling pathways, the extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-jun N-terminal kinase (JNK) pathways, in the successive stages of chondrogenic differentiation. In this review, we survey this research examining the involvement of ERK1/2, p38, and JNK pathway signaling in all aspects of the chondrogenic differentiation program from embryonic through postnatal stages of development. In addition, we summarize evidence from in vitro studies examining MAPK function in immortalized chondrogenic cell lines and adult mesenchymal stem cells. We also provide suggestions for future studies that may help ameliorate existing confusion concerning the specific roles of MAPK signaling at different stages of chondrogenesis.

Hypertrophic cardiomyopathy in high-fat diet-induced obesity: role of suppression of forkhead transcription factor and atrophy gene transcription

Cellular hypertrophy is regulated by coordinated pro- and antigrowth machineries. Foxo transcription factors initiate an atrophy-related gene program to counter hypertrophic growth. This study was designed to evaluate the role of Akt, the forkhead transcription factor Foxo3a, and atrophy genes muscle-specific RING finger (MuRF)-1 and atrogin-1 in cardiac hypertrophy and contractile dysfunction associated with high-fat diet-induced obesity. Mice were fed a low- or high-fat diet for 6 mo along with a food-restricted high-fat weight control group. Echocardiography revealed decreased fractional shortening and increased end-systolic diameter and cardiac hypertrophy in high-fat obese but not in weight control mice. Cardiomyocytes from high-fat obese but not from weight control mice displayed contractile and intracellular Ca2+ defects including depressed maximal velocity of shortening/relengthening, prolonged duration of shortening/relengthening, and reduced intracellular Ca2+ rise and clearance. Caspase activities were greater in high-fat obese but not in weight control mouse hearts. Western blot analysis revealed enhanced basal Akt and Foxo3a phosphorylation and reduced insulin-stimulated phosphorylation of Akt and Foxo3a without changes in total protein expression of Akt and Foxo3a in high-fat obese hearts. RT-PCR and immunoblotting results displayed reduced levels of the atrogens atrogin-1 and MuRF-1, the upregulated hypertrophic markers GATA4 and ciliary neurotrophic factor receptor-alpha, as well as the unchanged calcineurin and proteasome ubiquitin in high-fat obese mouse hearts. Transfection of H9C2 myoblast cells with dominant-negative Foxo3a adenovirus mimicked palmitic acid (0.8 mM for 24 h)-induced GATA4 upregulation without an additive effect. Dominant-negative Foxo3a-induced upregulation of pAkt and repression of phosphatase and tensin homologue were abrogated by palmitic acid. These results suggest a cardiac hypertrophic response in high-fat diet-associated obesity at least in part through inactivation of Foxo3a by the Akt pathway.

Apoptosis of human intervertebral discs after trauma compares to degenerated discs involving both receptor-mediated and mitochondrial-dependent pathways

Post-traumatic disc degeneration with consecutive loss of reduction and kyphosis remains a debatable issue within both the operative and nonoperative treatment regimen of thoracolumbar spine fractures. Intervertebral disc (IVD) cell apoptosis has been suggested to play a vital role in promoting the degeneration process. To evaluate and compare apoptosis-regulating signaling mechanisms, IVDs were obtained from patients with thoracolumbar spine fractures (n = 21), patients suffering from symptomatic IVD degeneration (n = 6), and from patients undergoing surgical resection of a primary vertebral tumor (n = 3 used as control samples). All tissues were prospectively analyzed in regards to caspase-3/7, -8, and -9 activity, apoptosis-receptor expression levels, and gene expression of the mitochondria-bound apoptosis-regulating proteins Bax and Bcl-2. Morphologic changes characteristic for apoptotic cell death were confirmed by H&E staining. Statistical significance was designated at p < 0.05 using the Student's t-test. Both traumatic and degenerative IVD demonstrated a significant increase of caspase-3/7 activity with evident apoptosis. Although caspase-3/7 activation was significantly greater in degenerated discs, both showed equally significant activation of the initiator caspases 8 and 9. Traumatic IVD alone demonstrated a significant increase of the Fas receptor (FasR), whereas the TNF receptor I (TNFR I) was equally up-regulated in both morbid IVD groups. Only traumatic IVD showed distinct changes in up-regulated TNF expression, in addition to significantly down-regulated antiapoptotic Bcl-2 protein. Our results suggest that post-traumatic disc changes may be promoted and amplified by both the intrinsic mitochondria-mediated and extrinsic receptor-mediated apoptosis signaling pathways, which could be, in part, one possible explanation for developing subsequent disc degeneration.

Enhanced muscle by myostatin propeptide increases adipose tissue adiponectin, PPAR-alpha, and PPAR-gamma expressions

Muscle tissue utilizes a large portion of metabolic energy for its growth and maintenance. Previously, we demonstrated that transgenic over-expression of myostatin propeptide in mice fed a high-fat diet enhanced muscle mass and circulating adiponectin while the wild-type mice developed obesity and insulin resistance. To understand the effects of enhanced muscle growth on adipose tissue metabolism, we analyzed adiponectin, PPAR-alpha, and PPAR-gamma mRNA expressions in several fat tissues. Results indicated muscled transgenic mice fed a high-fat diet displayed increased epididymal adiponectin mRNA expression by 12 times over wild-type littermates. These transgenic mice fed either a high or normal fat diet also displayed significantly high levels of PPAR-alpha and PPAR-gamma expressions above their wild-type littermates in epididymal fat while their expressions in mesenteric fats were not significantly different between transgenic mice and their littermates. This study demonstrates that enhanced muscle growth has positive effects on fat metabolisms through increasing adiponectin expression and its regulations.

Bcl-2-associated athanogene-1 (BAG-1): a transcriptional regulator mediating chondrocyte survival and differentiation during endochondral ossification

BAG-1, an anti-apoptotic protein, was identified by its ability to bind to BCL-2, HSP70-family molecular chaperones and nuclear hormone receptor family members. Two BAG-1 isoforms, BAG-1L (50 kDa) and BAG-1S (32 kDa) were identified in mouse cells and BAG-1 expression was reported in murine growth plate and articular chondrocytes. The present study aimed to elucidate the role of BAG-1 in the regulation of molecular mechanisms governing chondrocyte differentiation and turnover during endochondral ossification. In long bones of skeletally immature mice, we observed expression of BAG-1 in the perichondrium, osteoblasts, osteocytes in the bone shaft, bone marrow, growth plate and articular chondrocytes. Monolayer cultures of murine chondrocytic ATDC5 cells, which exhibited robust expression of both BAG-1 isoforms and the Bag-1 transcript, were utilized as an in vitro model to delineate the roles of BAG-1. Overexpression of BAG-1L in ATDC5 cells resulted in downregulation of Col2a1 expression, a gene characteristically downregulated at the onset of hypertrophy, and an increase in transcription of Runx-2 and Alkaline phosphatase, genes normally expressed at the onset of chondrocyte hypertrophy and cartilage mineralization in the process of endochondral ossification. We also demonstrated the anti-apoptotic role of BAG-1 in chondrocytes as overexpression of BAG-1 protected ATDC5 cells, which were subjected to heat-shock at 48 degrees C for 30 min, against heat-shock-induced apoptosis. Overexpression of the SOX-9 protein in ATDC5 cells resulted in increased Bag-1 gene expression. To further investigate the regulation of Bag-1 gene expression by SOX-9, CHO cells were co-transfected with the human Bag-1 gene promoter-Luciferase reporter construct and the human pSox-9 expression vector. Activity of the Bag-1 promoter was significantly enhanced by the SOX-9 protein. In conclusion, a novel finding of this study is the role of BAG-1 as a transcriptional regulator of genes involved in chondrocyte hypertrophy and cartilage mineralization during the process of endochondral ossification. Additionally, we have demonstrated for the first time the regulation of Bag-1 gene expression by SOX-9 and the anti-apoptotic role of BAG-1 in chondrocytic cells. Modulation of Bag-1 expression can therefore mediate chondrocyte differentiation and turnover, and offer further insight into the molecular regulation of endochondral ossification.

Metallothionein prevents high-fat diet induced cardiac contractile dysfunction: role of peroxisome proliferator activated receptor gamma coactivator 1alpha and mitochondrial biogenesis

Obesity is associated with oxidative stress and mitochondrial and myocardial dysfunction, although interaction among which remains elusive. This study was designed to evaluate the impact of the free radical scavenger metallothionein on high-fat diet-induced myocardial, intracellular Ca(2+), and mitochondrial dysfunction. FVB and metallothionein transgenic mice were fed a high- or low-fat diet for 5 months to induce obesity. Echocardiography revealed decreased fractional shortening, increased end-systolic diameter, and cardiac hypertrophy in high-fat-fed FVB mice. Cardiomyocytes from high-fat-fed FVB mice displayed enhanced reactive oxygen species (ROS) production, contractile and intracellular Ca(2+) defects including depressed peak shortening and maximal velocity of shortening/relengthening, prolonged duration of relengthening, and reduced intracellular Ca(2+) rise and clearance. Transmission microscopy noted overt mitochondrial damage with reduced mitochondrial density. Western blot analysis revealed enhanced phosphorylation of nuclear factor Foxo3a without changes in Foxo3a, Foxo1a, pFoxo1a, silent information regulator (Sirt), and Akt and pAkt in hearts of high-fat diet-fed FVB mice. The peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), a key regulator of mitochondrial biogenesis, was significantly depressed by high-fat diet feeding and in vitro palmitic acid treatment. RT-PCR further depicted reduced levels of the PGC-1alpha downstream nuclear respiratory factors 1 and 2, mitochondrial transcription factor A, and mitochondrial DNA copy number in hearts of high-fat-fed FVB mice. Intriguingly, the high-fat diet-induced alterations in ROS, myocardial contractile, and mitochondrial and cell signaling were negated by metallothionein, with the exception of pFoxo3a. These data suggest that metallothionein may protect against high-fat diet-induced cardiac dysfunction possibly associated with upregulation of PGC-1alpha and preservation of mitochondrial biogenesis.

Enhanced matrix synthesis in de novo, scaffold free cartilage-like tissue subjected to compression and shear

Production of a de novo cartilage-like tissue construct is a goal for the repair of traumatic chondral defects. We aimed to enhance the matrix synthesis within a scaffold free, de novo cartilage-like tissue construct by way of mechanical load. A novel loading machine that enables the application of shear, as well as compression, was used to subject tissue engineered cartilage-like tissue to mechanical stress. The machine, which applies the load through a roller mechanism, can load up to 20 constructs with four different loading patterns simultaneously. The expression of mRNA encoding matrix products, and subsequent changes in matrix protein content, were analyzed after various loading regimes. The force applied to the immature tissue had a direct bearing on the short-term (first 4 h) response. A load of 0.5 N caused an increase in collagen II and aggrecan mRNA within an hour, with a peak at 2 h. This increased mRNA expression was translated into an increase of up to 60% in the glycosaminoglycan content of the optimally loaded constructs after 4 days of intermittent cyclical loading. Introducing pauses between load cycles reproducibly lead to an increase in GAG/DNA. In contrast, constant cyclical load, with no pause, lead to a decrease in the final glycosaminoglycan content compared with unloaded controls. Our data suggest that a protocol of mechanical stimulation, simulating in vivo conditions and involving shear and compression, may be a useful mechanism to enhance the properties of tissue engineered tissue prior to implantation.

Analysis of human osteoarthritic connective tissue by laser capture microdissection and QRT-PCR

Gene expression levels for type II collagen and aggrecan have been determined as potential measures and disease markers of human osteoarthritis in patients undergoing total knee arthroplasty. In this regard, specimens of affected articular cartilage obtained intraoperatively at the time of surgery were placed in RNAlater(TM) to maintain RNA integrity and subsequently frozen-sectioned. Individual or small numbers of chondrocytes were isolated by laser capture microdissection and their total RNA was extracted and analyzed by quantitative reverse transcription-polymerase chain reaction. Results indicate that type II collagen and aggrecan mRNA expression from specific cells in osteoarthritic tissues are detectable and reproducible using these approaches. Our work is the first to demonstrate successful isolation of RNA limited to chondrocytes comprising small quantities of human osteoarthritic material. The study presents a new avenue by which the disease and its progression may be critically assayed.

Regulation of SOX9 mRNA in human articular chondrocytes involving p38 MAPK activation and mRNA stabilization

Human articular chondrocytes rapidly lose their phenotype in monolayer culture. Recently we have shown that overexpression of the transcription factor SOX9 greatly enhanced re-expression of the phenotype in three-dimensional aggregate cultures. Here we show that endogenous SOX9 mRNA can be rapidly up-regulated in subcultured human articular chondrocytes if grown in alginate, in monolayer with cytochalasin D, or with specific inhibition of the RhoA effector kinases ROCK1 and -2, which all prevent actin stress fiber formation. Disruption of actin stress fibers using any of these redifferentiation stimuli also supported the superinduction of SOX9 by cycloheximide. The superinduction was blocked by inhibitors of the p38 MAPK signaling pathway and involved the stabilization of SOX9 mRNA. Furthermore stimulation of chondrocyte p38 MAPK activity with interleukin-1beta resulted in increased levels of SOX9 mRNA, and this was again dependent on the absence of actin stress fibers in the cells. In this study of chondrocyte redifferentiation we have provided further evidence of the early involvement of SOX9 and have discovered a novel post-transcriptional regulatory mechanism activated by p38 MAPK, which stabilized SOX9 mRNA.

Trauma induces apoptosis in human thoracolumbar intervertebral discs

Background

Vertebral fractures resulting from high energy trauma often comprise the risk of posttraumatic degenerative changes in the affected intervertebral discs (IVD). Particularly in conservatively treated patients, or in cases after implant removal of an exclusively posterior stabilization, consecutive disc degeneration and the associated functional losing of the spinal segment clearly represent detrimental treatment results. In this regard, apoptosis of IVD cells has been suggested to be involved in the critical changes of the extracellular matrix.

Methods

To investigate whether fractures of the vertebrae induce apoptosis in the affected IVD, disc tissue from patients (n = 17) undergoing open reduction and internal fixation of thoracolumbar spine fractures were analysed in regards to caspase activity, apoptosis-receptor expression levels and gene expression of apoptosis-regulating proteins such as Bax and Bcl-2. Healthy IVD tissue (n = 3) obtained from patients undergoing surgical resection of adjacent vertebrae were used as control samples.

Results

In contrast to healthy control IVD tissues, samples from traumatic thoracolumbar IVD showed positive TUNEL staining and a significant increase of caspase-3/7 activity. Interestingly, analyses of the initiator caspase-8 and -9 revealed significantly increased activation levels compared to control values, suggesting the coexistent activation of both the extrinsic (receptor-mediated) and intrinsic (mitochondria-mediated) apoptosis pathway. Accordingly, expression levels of the Fas receptor (FasR) mRNA were significantly increased. Although the TNF receptor I (TNFR I) was only slightly upregulated, corresponding TNFα from trauma IVD presented significantly increased mRNA expression values. Furthermore, traumatic IVD cells demonstrated significantly reduced expression of the mitochondria-bound anti-apoptotic Bcl-2, thereby maintaining baseline transcriptional levels of the pro-apoptotic Bax protein when compared to control IVD cells.

Conclusion

Our data suggest that thoracolumbar fractures induce early caspase-dependent apoptosis in IVD cells of the affected intervertebral disc, in part, by downregulation of the anti-apoptotic protein Bcl-2 (intrinsic apoptosis pathway), as well as signalling via the death receptor complex (TNFR I and FasR).

The zebrafish bcl-2 homologue Nrz controls development during somitogenesis and gastrulation via apoptosis-dependent and -independent mechanisms

Although the role of the b-cell lymphoma (Bcl)-2 family of apoptosis inhibitors is well documented in tumor cells and tissue morphogenesis, their role during the early development of vertebrates is unknown. Here, we characterize Nrz, a new Bcl-2-related inhibitor of apoptosis in zebrafish. Nrz is a mitochondrial protein, antagonizing the death-accelerator Bax. The nrz gene is mainly expressed during gastrulation and somitogenesis. The knockdown of nrz with antisense morpholinos leads to alterations of the somites, correlated with an increase in apoptosis. In addition, earlier during development, in the zebrafish gastrula, nrz knockdown results in an increase of snail-1 expression at the margin and frequent gastrulation arrest at the shield stage, independently of apoptosis. Together these data suggest that Nrz, in addition to its effect on apoptosis, contributes to cell movements during gastrulation by negatively regulating the expression of Snail-1, a transcription factor that controls cell adhesion.

Multiple Signals Induce Endoplasmic Reticulum Stress in Both Primary and Immortalized Chondrocytes Resulting in Loss of Differentiation, Impaired Cell Growth, and Apoptosis

The endoplasmic reticulum is the site of synthesis and folding of secretory proteins and is sensitive to changes in the internal and external environment of the cell. Both physiological and pathological conditions may perturb the function of the endoplasmic reticulum, resulting in endoplasmic reticulum stress. The chondrocyte is the only resident cell found in cartilage and is responsible for synthesis and turnover of the abundant extracellular matrix and may be sensitive to endoplasmic reticulum stress. Here we report that glucose withdrawal, tunicamycin, and thapsigargin induce up-regulation of GADD153 and caspase-12, two markers of endoplasmic reticulum stress, in both primary chondrocytes and a chondrocyte cell line. Other agents such as interleukin-1beta or tumor necrosis factor alpha induced a minimal or no induction of GADD153, respectively. The endoplasmic reticulum stress resulted in decreased chondrocyte growth based on cell counts, up-regulation of p21, and decreased PCNA expression. In addition, perturbation of endoplasmic reticulum function resulted in decreased accumulation of an Alcian Blue positive matrix by chondrocytes and decreased expression of type II collagen at the protein level. Further, quantitative real-time PCR was used to demonstrate a down-regulation of steady state mRNA levels coding for aggrecan, collagen II, and link protein in chondrocytes exposed to endoplasmic reticulum stress-inducing conditions. Ultimately, endoplasmic reticulum stress resulted in chondrocyte apoptosis, as evidenced by DNA fragmentation and annexin V staining. These findings have potentially important implications regarding consequences of endoplasmic reticulum stress in cartilage biology.

Intrajoint comparisons of gene expression patterns in human osteoarthritis suggest a change in chondrocyte phenotype

Osteoarthritis (OA) is a degenerative cartilage disease with varying degrees of severity within a given joint. The purpose of this study was to define a sampling procedure for comparing human minimal and advanced OA cartilage in the same patient and to determine basic patterns of gene expression in these regions. A specific hypothesis under study was that the expression level of Bcl-2 would correlate with Sox9 and aggrecan mRNA expression in vivo as has been demonstrated in vitro. Femoral condylar advanced OA cartilage was located within 1cm of overt lesions, and minimal cartilage was taken from areas with no obvious surface defects. Histological sections were scored for disease severity and chondroitin sulfate and hydroxyproline content was determined. The expression level of nine specific genes (aggrecan, collagen type II, Bcl-2, Sox9, Link protein, osteopontin, and MMP-13, -3, and -9) was determined by quantitative real time PCR. The scores for fibrillation, chondrocyte cloning, and proteoglycan depletion were significantly different between advanced and minimal OA cartilage. The advanced OA cartilage had significantly less chondroitin sulfate than the minimal OA cartilage. Osteopontin mRNA expression showed a 3.6-fold increase in advanced compared to minimal OA cartilage. In contrast, the level of mRNA coding for aggrecan, link protein, Bcl-2, Sox9 and MMP-3, -9, -13 were all decreased in advanced compared to minimal cartilage in the majority of the patients studied. Collagen type II mRNA expression displayed a wide-range of variation. A statistically significant correlation was observed both between Bcl-2 and Sox9 mRNA level, and between Bcl-2 and aggrecan mRNA expression. The patient matched comparison of minimal and advanced OA cartilage revealed differences in cellular and tissue characteristics, and changes in gene expression that may be involved in OA progression. In addition, Bcl-2 may also play a role in regulating the expression of aggrecan through Sox9 in vivo as well as in vitro.

The effects of short-term load duration on anabolic and catabolic gene expression in the rat tail intervertebral disc

The goal of this study was to determine the time-dependent response of the intervertebral disc cells to in vivo dynamic compression. Forty-seven skeletally mature Wistar rats (>12 months old) were instrumented with an Ilizarov-type device spanning caudal disc 8-9. Using a load magnitude (1 MPa) and frequency (1.0 Hz) that were previously shown to significantly alter mRNA levels in the disc, the effects of 0.5 and 4 h of loading were investigated and compared to a sham group and our previous 2 h results. Annulus and nucleus tissue of loaded (c8-9) and internal control discs (c6-7 and c10-11) were separately analyzed by real-time RT-PCR for levels of mRNA coding for various anabolic (collagen-1A1, collagen-2A1, aggrecan) and catabolic (MMP-3, MMP-13, ADAMTs-4) proteins. In the annulus, mRNA levels increased for Collagen types I & II, and MMP 3 & 13 with increasing load duration. In contrast, the nucleus had the largest increases in aggrecan, ADAMTs-4, MMP-3 and MMP-13 after 2 h of loading, with aggrecan and MMP-13 mRNA levels returning to control values after 4 h of loading. Taken in context with our previous studies, we conclude that intervertebral disc cells from the nucleus and annulus have distinct responses to dynamic mechanical compression in vivo with sensitivity to compression magnitude, frequency and duration.

Epigenetic changes to the MDR1 locus in response to chemotherapeutic drugs

The mechanism of action of chemotherapeutic drugs and their ability to induce multidrug resistance (MDR) are of relevance to cancer treatment. Overexpression of P-glycoprotein (Pgp) encoded by the MDR1 gene following chemotherapy can severely limit the efficacy of anticancer agents; however, the manner by which cells acquire high levels of Pgp has not been defined. Herein, we demonstrate that chemotherapeutic drugs induce specific epigenetic modifications at the MDR1 locus, concomitant with MDR1 upregulation mediated by transcriptional activation, and a potential post-transcriptional component. We have established that the mechanisms are not mutually exclusive and are dependent on the methylation state of the MDR1 promoter. MDR1 upregulation did not result in further changes to the CpG methylation profile. However, dramatic changes in the temporal and spatial patterning of histone modifications occurred within the 5' hypomethylated region of MDR1, directly correlating with MDR1 upregulation. Specifically, drug-induced upregulation of MDR1 was associated with increases in H3 acetylation and induction of methylated H3K4 within discrete regions of the MDR1 locus. Our results demonstrate that chemotherapeutic drugs can actively induce epigenetic changes within the MDR1 promoter, and enhance the MDR phenotype.

Bcl-2 positively regulates Sox9-dependent chondrocyte gene expression by suppressing the MEK-ERK1/2 signaling pathway

Bcl-2 is an anti-apoptotic protein that has recently been shown to regulate other cellular functions. We previously reported that Bcl-2 regulates chondrocyte matrix gene expression, independent of its anti-apoptotic function. Here, we further investigate this novel function of Bcl-2 and examine three intracellular signaling pathways likely to be associated with this function. The present study demonstrates that the activity of Sox9, a master transcription factor that regulates the gene expression of chondrocyte matrix proteins, is suppressed by Bcl-2 small interference RNA in the presence of caspase inhibitors. This effect was attenuated by prior exposure of chondrocytes to an adenoviral vector expressing sense Bcl-2. In addition, the down-regulation of Bcl-2, Sox9, and chondrocyte-specific gene expression by serum withdrawal in primary chondrocytes was reversed by expressing Bcl-2. Inhibition of the protein kinase C alpha and NFkappaB pathways had no effect on the maintenance of Sox9-dependent gene expression by Bcl-2. In contrast, whereas the MEK-ERK1/2 pathway negatively regulated the differentiated phenotype in wild type chondrocytes, inhibition of this pathway reversed the loss of differentiation markers and fibroblastic phenotype in Bcl-2-deficient chondrocytes. In conclusion, the present study identifies a specific signaling pathway, namely, MEK-ERK1/2, that is downstream of Bcl-2 in the regulation of Sox9-dependent chondrocyte gene expression and phenotype.

Increased Bcl-2/p53 ratio in human osteoarthritic cartilage: a possible role in regulation of chondrocyte metabolism

OBJECTIVE

To determine whether Bcl-2, p53, and Fas/CD95 help to control cartilage metabolism.

METHODS

Six normal and 14 osteoarthritic (OA) cartilage samples were examined, and two zones from each sample showing the least (Min) and most (Max) anatomical damage were selected. Chondrocytes were isolated by sequential enzymatic digestion and freshly processed. Bcl-2, p53, and Fas/CD95 expression was evaluated by immunofluorescence and FACS analysis; the cell cycle was analysed using propidium iodide, and chondrocyte proliferation assessed by [(3)H]thymidine incorporation.

RESULTS

Intracellular levels of Bcl-2 were significantly higher in Max (27.5%) than in Min (21%, p<0.01) OA or normal chondrocytes (18.5%, p<0.01). Intracellular p53 expression was significantly decreased in Max (25.5%) compared with Min (37%, p<0.01) OA or normal cartilage (41.5%, p<0.05). Fas/CD95 receptor expression on surface chondrocytes did not significantly differ between OA and normal cartilage. Cell cycle analysis showed that the proportion of activated chondrocytes in the S phase was significantly higher in Max (69%) than in Min (49%) OA or normal cartilage (43%). The prevalence of proliferating chondrocytes progressively increased according to the degree of OA damage (mean (SEM) Min 1247 (260), Max 2423 (460), p<0.05). Chondrocyte [(3)H]thymidine uptake correlated positively with Bcl-2 (r(s) = 0.62, p = 0.009) and correlated inversely with p53 levels (r(s) = -0.55, p = 0.02).

CONCLUSIONS

Bcl-2 and p53 play a part in apoptosis, but also help to regulate chondrocyte growth and differentiation. Whereas Bcl-2 promotes cell survival, p53 can arrest cell cycle. The data confirm that chondrocyte activity is enhanced in OA and suggest that the increased Bcl-2/p53 ratio sustains the metabolic boost of chondrocytes.

Anabolic and catabolic mRNA levels of the intervertebral disc vary with the magnitude and frequency of in vivo dynamic compression

The goal of this study was to characterize the anabolic and catabolic mRNA response of the disc to dynamic loading to determine if variations in the magnitude and/or frequency of loading could elicit different cellular responses. Sixty-eight Wistar rats were instrumented with an Ilizarov-type device spanning caudal disc 8-9. Seventy-two hours after surgery, animals were anesthetized and loaded at either 1 or 0.2 MPa at a frequency of 1, 0.2 or 0.01 Hz for 2 h (6 groups). The surgical control (Sham) animals underwent anesthesia with no loading. Loaded (c8-9) and internal-control discs (c6-7 and c10-11) were dissected and annulus and nucleus tissue were separately analyzed by real-time RT-PCR for levels of anabolic (collagen-1A1, collagen-2A1, aggrecan) and catabolic (MMP-3, MMP-13, ADAMTs-4) mRNA. In the nucleus, a frequency-dependent response was seen at 1 MPa with anabolic genes stimulated at 0.01 Hz and catabolic genes at 1 Hz. In the annulus all frequencies resulted in significant up-regulation of catabolic mRNA at 1 MPa loading. In general loading at 0.2 MPa or 0.2 Hz had little effect on gene expression. The results suggest that gene expression of the annulus appears to be more dependent on the magnitude of applied stress, while the nucleus is both magnitude- and frequency-dependent.

Age-related expression patterns of Bag-1 and Bcl-2 in growth plate and articular chondrocytes

Aging cartilage displays increased chondrocyte apoptosis and decreased responsiveness of chondrocytes to growth factors. The molecular mechanisms responsible for these changes have not been identified. Bag-1 is a Bcl-2-binding protein that promotes cell survival, interacts with a diverse group of cellular proteins, and may integrate multiple pathways involved in controlling cell survival, growth, and phenotype. Bcl-2 is important for maintaining chondrocyte phenotype and delaying terminal differentiation and apoptosis of chondrocytes. Comparatively little is known about the role of Bag-1 in cartilage. Here we show that both growth plate and articular chondrocytes in the mouse express the Bag-1 protein. In the growth plate, Bag-1 expression is prominent in the late proliferative and prehypertrophic chondrocytes, displaying a pattern similar to what has been reported for Bcl-2. Further, the expression of both Bcl-2 and Bag-1 declines with age in the articular cartilage. Growth assays demonstrate that knocking down Bag-1 expression causes a decrease in growth rate. These results suggest that Bag-1 is involved in the regulation of chondrocyte phenotype and cartilage aging.