Cell density modulates apoptosis in human articular chondrocytes

Live-cell imaging and mathematical analysis of the “community effect” in apoptosis

As a cellular intrinsic mechanism leading to cellular demise, apoptosis was thoroughly characterized from a mechanistic perspective. Nowadays there is an increasing interest in describing the non-cell autonomous or community effects of apoptosis, especially in the context of resistance to cancer treatments. Transitioning from cell-centered to cell population-relevant mechanisms adds a layer of complexity for imaging and analyzing an enormous number of apoptotic events. In addition, the community effect between apoptotic and living cells is difficult to be taken into account for complex analysis. We describe here a robust and easy to implement method to analyze the interactions between cancer cells, while under apoptotic pressure. Using this approach we showed as proof-of-concept that apoptosis is insensitive to cellular density, while the proximity to apoptotic cells increases the probability of a given cell to undergo apoptosis.

Insights on Molecular Mechanisms of Chondrocytes Death in Osteoarthritis

Osteoarthritis (OA) is a joint pathology characterized by progressive cartilage degradation. Medical care is mainly based on alleviating pain symptoms. Compelling studies report the presence of empty lacunae and hypocellularity in cartilage with aging and OA progression, suggesting that chondrocyte cell death occurs and participates to OA development. However, the relative contribution of apoptosis per se in OA pathogenesis appears complex to evaluate. Indeed, depending on technical approaches, OA stages, cartilage layers, animal models, as well as in vivo or in vitro experiments, the percentage of apoptosis and cell death types can vary. Apoptosis, chondroptosis, necrosis, and autophagic cell death are described in this review. The question of cell death causality in OA progression is also addressed, as well as the molecular pathways leading to cell death in response to the following inducers: Fas, Interleukin-1β (IL-1β), Tumor Necrosis factor-α (TNF-α), leptin, nitric oxide (NO) donors, and mechanical stresses. Furthermore, the protective role of autophagy in chondrocytes is highlighted, as well as its decline during OA progression, enhancing chondrocyte cell death; the transition being mainly controlled by HIF-1α/HIF-2α imbalance. Finally, we have considered whether interfering in chondrocyte apoptosis or promoting autophagy could constitute therapeutic strategies to impede OA progression.

Aberrant Expression of proPTPRN2 in Cancer Cells Confers Resistance to Apoptosis

The protein tyrosine phosphatase receptor PTPRN2 is expressed predominantly in endocrine and neuronal cells, where it functions in exocytosis. We found that its immature isoform proPTPRN2 is overexpressed in various cancers, including breast cancer. High proPTPRN2 expression was associated strongly with lymph node-positive breast cancer and poor clinical outcome. Loss of proPTPRN2 in breast cancer cells promoted apoptosis and blocked tumor formation in mice, whereas enforced expression of proPTPRN2 in nontransformed human mammary epithelial cells exerted a converse effect. Mechanistic investigations suggested that ProPTPRN2 elicited these effects through direct interaction with TRAF2, a hub scaffold protein for multiple kinase cascades, including ones that activate NF-κB. Overall, our results suggest PTPRN2 as a novel candidate biomarker and therapeutic target in breast cancer.

Apoptosis in chondrogenesis of human mesenchymal stem cells: effect of serum and medium supplements

Apoptosis is an inevitable process during development and is evident in the formation of articular cartilage and endochondral ossification of growth plate. Mesenchymal stem cells (MSCs) can serve as alternative sources for cell therapy in focal chondral lesions or diffuse osteoarthritis. But there are few, if any, studies investigating apoptosis during chondrogenesis by MSCs. The aim of this study was to find the better condition to prevent apoptosis during chondrogenesis by MSCs. Apoptosis were evaluated in MSCs induced in different chondrogenic media by the use of Annexin V, TUNEL staining, lysosomal labeling with lysotracker and immunostaining of apoptotic markers. We found apparent apoptosis was demonstrated by Annexin V, TUNEL staining and lysosomal labeling during chondrogenesis. Meanwhile, the degree of apoptosis was related to the reagents of the defined chondrogenic medium. Adding serum in medium increased apoptosis, however, TGF-beta1 inhibited apoptosis. The apoptosis was associated with the activation of caspase-3, the increase in the Bax/Bcl-2 ratio, the loss of lysosomal integrity, and the increase of PARP-cleavage. Pro-inflammatory cytokines, IL-1alpha, IL-1beta and TNFalpha did not induce any increase in apoptosis. Interestingly, the inhibition of apoptosis by serum free medium supplemented with ITS was also associated with an increase in the expression of type II collagen, and a decrease in the expression of type X collagen, Runx2, and other osteogenic genes, while TGF-beta1 increased the expression of Sox9, type II and type X collagen and decreased the expression of osteogenic genes. These data suggest apoptosis occurs during chondrogenesis by MSCs by cell death intrinsic pathway activation and this process may be modulated by culture conditions.

The protective effect of sodium hyaluronate on the cartilage of rabbit osteoarthritis by inhibiting peroxisome proliferator-activated receptor-gamma messenger RNA expression

PURPOSE

The purpose of this study was to study the protective effect and influence of sodium hyaluronate (Na-HA) on mRNA expression of peroxisome proliferators-activated receptor gamma (PPAR-gamma) in cartilage of rabbit osteoarthritis (OA) model.

MATERIALS AND METHODS

Forty eight white rabbits were randomly divided into A, B, and C groups. Group A was normal control group, B and C groups underwent unilateral anterior cruciate ligament transection (ACLT). The rabbits in group B were injected normal saline after ACLT; and Group C received intra-articular 1% sodium hyaluronate (HA) injection 5 weeks after surgery, 0.3 mL once a week. At 11th week after surgery, all the rabbits were sacrificed. The cartilage changes on the medial femoral condyles were graded separately. Cartilage sections were stained with safranin-O and HE, and messenger RNA (mRNA) expression of PPAR-gamma was detected by using real time polymerase chain reaction (Real Time-PCR).

RESULTS

Cartilage degeneration in group B was significantly more severe than in A and C injection group. The grey value of Safranin-O of B group was higher than A and C groups. Expression of PPAR-gamma mRNA in group B was higher than group A and C.

CONCLUSION

This study shows that Na-HA has a protective effect on articular cartilage degeneration, and the inhibitory effect on the PPAR-gamma mRNA expression may be one of therapeutic mechanism of Na-HA.

Wnt signaling in cartilage development and degeneration

The Wnt signaling network, which is composed of Wnt ligands, receptors, antagonists, and intracellular signaling molecules, has emerged as a powerful regulator of cell fate, proliferation, and function in multicellular organisms. Over the past two decades, the critical role of Wnt signaling in embryonic cartilage and bone development has been well established, and much has been learnt regarding the role of Wnt signaling in chondrogenesis and cartilage development. However, relatively little is known about the role of Wnt signaling in adult articular cartilage and degenerative cartilage tissue. This review will briefly summarize recent advances in Wnt regulation of chondrogenesis and hypertrophic maturation of chondrocytes, and review data concerning the role of Wnt signaling in the maintenance and degeneration of articular chondrocytes and cartilage.

Different viabilities and toxicity types after 6-OHDA and Ara-C exposure evaluated by four assays in five cell lines

Cell viability studies are useful when screening novel drugs for the diseases that are related to either increased cell death or enhanced cell survival. There are numerous assays but the results that they produce are rarely unanimous. Here we compared the performance of (1) morphological microscopic assay with double DNA staining, (2) propidium iodide-digitonin assay, (3) MTT-assay, and (4) ATP-assay in human neuroblastoma (SH-SY5Y), rat glioma (C6), rabbit smooth muscle (SMC), Chinese hamster ovary (CHO) and monkey fibroblast cells (CV1-P) exposed to cytosine arabinoside (Ara-C) and 6-hydroxydopamine (6-OHDA). We found that neuronal SH-SY5Y cells were most sensitive to both toxins and the results in all viability tests correlated well. All the other cell lines were much more resistant, particularly to Ara-C but also to 6-OHDA. Toxicity of the compounds was best revealed by MTT and ATP assays, measuring the metabolic activity of the cells, and only occasionally by morphological observations or with the propidium iodide-digitonin assay which is based on the cell membrane integrity. In this research, Ara-C induced pure apoptosis whereas the toxicity type of 6-OHDA was dose-dependent. The use of several viability tests and cell lines is recommended when studying cell death, particularly apoptosis, and performance of antiapoptotic compounds.

Combined chondrocyte-copolymer implantation with slow release of basic fibroblast growth factor for tissue engineering an auricular cartilage construct

Basic fibroblast growth factor (b-FGF) may have a role in tissue-engineered chondrogenesis. However, when applied in solution, b-FGF rapidly diffuses from the implant site. In another approach for tissue engineering, poly-lactide-based copolymers have shown promise as scaffolds for chondrocytes used to tissue engineer auricular cartilage in the shape of an ear. This study evaluated the effectiveness of b-FGF impregnated in gelatin microspheres to achieve slow growth factor release for augmenting the in vivo chondrogenic response. Whereas 125I-labeled b-FGF injected in solution showed rapid in vivo clearance from the injection site (only 3% residual after 24 h), when incorporated into gelatin microspheres, 44% and 18% of the b-FGF remained at 3 and 14 days, respectively. Canine chondrocytes were isolated and grown in vitro onto ear-shaped poly-lactide/caprolactone copolymers for 1 week, then implanted into the dorsal subcutaneous tissue of nude mice; implants contained b-FGF either in free solution or in gelatin microspheres. A third group underwent preinjection of b-FGF in gelatin microspheres 4 days before chondrocyte-copolymer implantation. The implants with b-FGF-incorporated microspheres showed the greatest chondrogenic characteristics at 5 and 10 weeks postoperatively: good shape and biomechanical trait retention, strong (histologic) metachromasia, rich vascularization of surrounding tissues, and increased gene expression for type II collagen (cartilage marker) and factor VIII-related antigen (vascular marker). In the case of implant site preadministration with b-FGF-impregnated microspheres, the implant architecture was not maintained as well, and reduced vascularization and metachromasia was also apparent. In conclusion, these findings indicate that a sustained release of b-FGF augments neovascularization and chondrogenesis in a tissue-engineered cartilage construct.

Vitamin D fails to prevent serum starvation- or staurosporine-induced apoptosis in human and rat osteosarcoma-derived cell lines

Previous studies have suggested that 1,25(OH)2D3, the active form of vitamin D3, may increase the survival of bone-forming osteoblasts through an inhibition of apoptosis. On the other hand, vitamin D3 has also been shown to trigger apoptosis in human cancer cells, including osteosarcoma-derived cell lines. In the present study, we show that 1,25(OH)2D3 induces a time- and dose-dependent loss of cell viability in the rat osteosarcoma cell line, UMR-106, and the human osteosarcoma cell line, TE-85. We were unable, however, to detect nuclear condensation, phosphatidylserine externalization, or other typical signs of apoptosis in this model. Moreover, 1,25(OH)2D3 failed to protect against apoptosis induced by serum starvation or incubation with the protein kinase inhibitor, staurosporine. These in vitro findings are thus at variance with several previous reports in the literature and suggest that induction of or protection against apoptosis of bone-derived cells may not be a primary function of vitamin D3.

Identification and characterization of a FasL-like protein and cDNAs encoding the channel catfish death-inducing signaling complex

To elucidate cytolytic mechanisms in the channel catfish, lysates from catfish lymphoid and fibroblast cell lines were screened by Western blot analysis using a panel of antibodies reactive with components of the mammalian apoptotic pathway. Strong reactivity with three proteins (approximate Mr 70,000, 37,000, and 15,000) was seen using an antibody targeted to mammalian Fas ligand (FasL). The sizes of the two smaller proteins are consistent with their tentative designation as membrane-bound (37,000 Mr) and soluble (15,000 Mr) FasL. Treatments known to induce FasL in mammalian systems (e.g., PMA/calcium ionophore, UV-irradiation) induced expression of the 37,000- Mr protein in catfish T-cell lines. Moreover, expression of the 37,000- Mr protein in clonal T cells was up-regulated by increasing cell density. At the nucleotide level, homologues of Fas receptor (FasR), FADD, and caspase 8 were identified and characterized. These gene products likely constitute the teleost equivalent of the death-inducing signaling complex (DISC). FADD was constitutively expressed in all (T, B, macrophage, and fibroblast) cell lines examined as well as in peripheral blood lymphocytes (PBL), whereas FasR and caspase 8 were expressed in all cell lines except CCO, a FasL-positive fibroblast line. In contrast to FasL, expression of FasR and caspase 8 was inversely proportional to cell density. Collectively these studies identified four membrane-proximal proteins involved in the initiation of apoptosis in channel catfish and suggest that mechanisms of cell-mediated cytotoxicity in teleosts are similar to those used by mammals.

Apoptosis in osteoarthritis

Many studies have shown that apoptotic cell death occurs at an increased rate in osteoarthritic cartilage. Whichever type of cell death takes places in articular cartilage, it is important to prevent, because it is detrimental to articular cartilage maintenance. Thus, it is important to characterize events going on during cellular degeneration in more detail. Overall, physicians have reached a reasonable level of understanding of the extent of cell death occurring in the disease process, but they are still at an early stage in the understanding of the mechanisms underlying this process and the means of intervening in this facet of cartilage destruction.

Apoptosis and the loss of chondrocyte survival signals contribute to articular cartilage degradation in osteoarthritis

Apoptotic death of articular chondrocytes has been implicated in the pathogenesis of osteoarthritis (OA). Apoptotic pathways in chondrocytes are multi-faceted, although some cascades appear to play a greater in vivo role than others. Various catabolic processes are linked to apoptosis in OA cartilage, contributing to the reduction in cartilage integrity. Recent studies suggest that beta1-integrin mediated cell-matrix interactions provide survival signals for chondrocytes. The loss of such interactions and the inability to respond to IGF-1 stimulation may be partly responsible for the hypocellularity and matrix degradation that characterises OA. Here we have reviewed the literature in this area of cartilage cell biology in an effort to consolidate the existing information into a plausible hypothesis regarding the involvement of apoptosis in the pathogenesis of OA. Understanding of the interactions that promote chondrocyte apoptosis and cartilage hypocellularity is essential for developing appropriately targeted therapies for inhibition of chondrocyte apoptosis and the treatment of OA.

Role of nitric oxide, reactive oxygen species, and p38 MAP kinase in the regulation of human chondrocyte apoptosis

This study addresses mechanisms by which interleukin-1beta (IL-1beta) regulates human chondrocyte apoptosis induced by a combination of the anti-CD95 antibody CH-11 and the proteasome inhibitor (PSI). The effect of IL-1beta on apoptosis varied among tissue samples. IL-1beta either enhanced (16/22 samples) or inhibited (6/22 samples) DNA fragmentation and caspase-3 processing. The protective effect of IL-1beta was abrogated by the nitric oxide (NO) synthesis inhibitor N-monomethyl-l-arginine (L-NMMA) while apoptosis stimulation was not affected. The NO-donors sodium nitroprusside (SNP) and S-nitroso-N-acetyl penicillamine (SNAP) blocked DNA fragmentation, and this was associated with partial inhibition of caspase-3 processing. Pyrrolidine dithiocarbamate (PDTC), a scavenger of reactive oxygen species (ROS) blocked apoptosis induction by CH-11/PSI as well as the enhancement by IL-1beta. The pro-apoptotic effects of IL-1beta were also abrogated by the p38 inhibitor SB 202190. In conclusion, IL-1beta augments CH-11/PSI induced apoptosis in the majority of chondrocyte samples. The pro-apoptotic effect of IL-1beta is not dependent on NO. In contrast, the anti-apoptotic effect of IL-1beta observed in a minority of samples is partially NO-dependent.

Mechanisms of sodium nitroprusside-induced death in human chondrocytes

The nitric oxide (NO) donor sodium nitroprusside (SNP) has been used to study NO-dependent cell death in human chondrocytes. This study compares SNP-induced chondrocyte death and SNP-activated signaling mechanisms with apoptosis induced by CD95 activation. Sodium nitroprusside increased cell death dose-dependently. Compared to CD95 stimulation, SNP induced only low levels of internucleosomal DNA fragmentation as measured by cell-death enzyme-linked immunosorbent assay (ELISA). However, SNP caused substantial nuclear DNA cleavage, as evidenced by terminal deoxynucleotidyltransferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL). Caspase-3 processing in response to SNP was not detected. The pancaspase inhibitor Z-VAD.FMK partially abrogated the TUNEL signal but did not block cell death or internucleosomal DNA fragmentation. The caspase-3-specific inhibitor Ac-DEVD-CHO did not inhibit the SNP-induced TUNEL signal or internucleosomal DNA fragmentation. DNA degradation was not blocked by the p38 inhibitor SB 202190 but by the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine. The results of this study support the hypothesis that the phenotype and mechanisms of SNP-induced chondrocyte death are distinct from apoptosis induction via CD95.

Expression profile of protein tyrosine kinase genes in human osteoarthritis chondrocytes

OBJECTIVE

To determine the expression profile of protein kinase (PK) and protein tyrosine kinase (PTK) genes in human primary osteoarthritis (OA) chondrocytes and to compare it with that of immortalized human chondrocytes T/C 28a4 with a view to learning whether T/C 28a4 cells can be used for elucidating signal transduction pathways in human chondrocytes.

DESIGN

We used the Atlas Human cDNA Array and a method based on PCR with degenerate primers to analyse the expression profile of protein kinase genes in primary human OA chondrocytes and compared it with that of immortalized human chondrocyte cell line T/C 28a4 using RT-PCR and Western blotting.

RESULTS

A total of 21 PTK genes were identified and several of these have never been shown to be expressed in human OA chondrocytes. Comparative expression analysis of some selected kinase genes showed that the mRNA expression pattern of many protein kinase genes in OA chondrocytes was identical to that of T/C 28a4 cells. However, there were differences in the level of protein expression of selected protein kinases in these cells. For example, mRNA expression of the novel kinase HCK was detected in OA chondrocytes and in the cell lines analysed but by Western blotting HCK protein was not detected in OA chondrocytes. In these studies, we also identified a novel mutant form of the discoidin domain receptor 2 (DDR2) transcript from chondrocyte-like cell line HTB-94.

CONCLUSIONS

Our results provide novel information about protein kinase gene expression in OA chondrocytes and indicate that the transformed chondrocyte cell line T/C 28a4 may be suitable for elucidating signal transduction pathways in chondrocytes and to investigate how they regulate chondrocyte function in inflammatory and degenerative joint diseases.

Regulation of CD95 (Fas/APO-1)-induced apoptosis in human chondrocytes

OBJECTIVE

To examine the role of nuclear factor kappaB (NF-kappaB) and caspases 3, 8, and 9 in CD95-mediated apoptosis of normal chondrocytes.

METHODS

First-passage chondrocytes from normal human knee cartilage were stimulated with CD95 antibody, and cell death was determined by annexin V binding and by an enzyme-linked immunosorbent assay. Activation of caspases 3, 8, and 9 was measured by Western blotting, and their role in death signaling was evaluated using caspase-specific small peptide inhibitors. The influence of NF-kappaB was determined by electrophoretic mobility shift assay (EMSA) and proteasome inhibition-dependent blocking of the degradation of inhibitor of NF-kappaB.

RESULTS

Low levels of NF-kappaB activity were detected by EMSA in unstimulated chondrocytes. NF-kappaB activity was increased in response to agonistic CD95 antibody. CD95 antibody-induced apoptosis was potentiated by the proteasome inhibitors MG-132 and PS1, and this was associated with a reduced nuclear translocation of NF-kappaB. Proteasome inhibitors also caused the induction of DNA fragmentation by tumor necrosis factor alpha. Procaspase 3 processing was enhanced by the proteasome inhibitor MG-132. Procaspase 8 was undetectable by immunoblotting in whole cell lysates of chondrocytes, but caspase 8 messenger RNA was detected by reverse transcription-polymerase chain reaction. Furthermore, apoptosis induced by CD95 stimulation and proteasome inhibitors was blocked by the caspase 8-specific inhibitor Ac-IETD-CHO. Processing of procaspase 9 was not observed, and inhibition of CD95-dependent cell death by the caspase 9 inhibitor Ac-LEHD-CHO was not significant.

CONCLUSION

These results suggest that CD95-dependent cell death is enhanced by NF-kappaB inhibition at and/or downstream of caspase 8 activation and that caspase 9 activation is not involved in CD95-mediated apoptosis in chondrocytes.

Apoptosis may determine the release of skeletal alkaline phosphatase activity from human osteoblast-line cells

Although quantitative measurement of skeletal alkaline phosphatase (sALP) activity in serum can provide an index of the rate of bone formation, the metabolic process that determines the release of sALP - from the surface of osteoblasts, into circulation-is unknown. The current studies were intended to examine the hypothesis that the release of sALP from human osteoblasts is a consequence of apoptotic cell death. We measured the release of sALP activity from human osteosarcoma (SaOS-2) cells and normal human bone cells, under basal conditions and in response to agents that increased apoptosis (TNF-a, okadiac acid) and agents that inhibit apoptosis (IGF-I, calpain, and caspase inhibitors). Apoptosis was determined by the presence of nucleosomes (histone-associated DNA) in the cytoplasm of the cells by using a commercial kit. The results of these studies showed that TNF-a and okadiac acid caused dose- and time-dependent increases in apoptosis in the SaOS-2 cells (r = 0.78 for doses of TNF-a and r = 0.93 for doses of okadiac acid, P <0.005 for each), with associated decreases in cell layer protein (P <0.05 for each) and concomitant increases in the release of sALP activity (e.g., r = 0.89 for TNF-a and r = 0.75 for okadiac acid, P <0.001 for each). In contrast, caspase and calpain inhibitors reduced apoptosis, increased cell layer protein, and decreased the release of sALP activity (P <0.05 for each). Exposure to IGF-I also decreased apoptosis, in a time- and dose-dependent manner (e.g., r = 0.93, P <0.001 for IGF-I doses), with associated proportional effects to increase cell layer protein (P <0.001) and decrease the release of sALP activity (P <0.001). IGF-I also inhibited the actions of TNF-a and okadiac acid to increase apoptosis and sALP release. The associations between apoptosis and sALP release were not unique to osteosarcoma (i.e., SaOS-2) cells, but also seen with osteoblast-line cells derived from normal human bone. Together, these data demonstrate that the release of sALP activity from human osteoblast-line cells in vitro is associated with, and may be a consequence of, apoptotic cell death. These findings are consistent with the general hypothesis that the appearance of sALP activity in serum may reflect the turnover of osteoblast-line cells.

IL-1 beta protects human chondrocytes from CD95-induced apoptosis

This study addresses the effects of IL-1 beta on apoptosis induced by agonistic anti-CD95 (Fas) Ab. IL-1 beta inhibited anti-CD95 Ab-induced apoptosis in all preparations of normal human articular chondrocytes tested. Inhibitors of nitric oxide synthase or cyclooxygenase did not influence the protective effect of IL-1 beta, indicating that nitric oxide and PGs were not involved in the modulation of CD95-induced apoptosis. However, when the IL-1 beta-dependent induction of NF-kappa B was inhibited, the antiapoptotic effect of IL-1 beta was partially reversed, suggesting that NF-kappa B-mediated gene activation is part of the protective mechanism. In addition, IL-1 beta significantly increased the expression of Bcl-2. The protein tyrosine kinase inhibitor herbimycin A completely eliminated the protective effect of IL-1 beta on CD95-induced apoptosis. These findings suggest that IL-1 beta modulates the CD95 death cascade in chondrocytes by mechanisms that involve tyrosine phosphorylation events and NF-kappa B-dependent gene activation.

New developments in the pathogenesis of articular cartilage calcification

Articular cartilage, unlike growth plate cartilage, is specialized to not undergo matrix calcification. However, articular cartilage mineralization, in the form of CPPD (chondrocalcinosis) and hydroxyapatite crystals, frequently accompanies and complicates osteoarthritis and aging. Recent work has demonstrated that certain features of growth cartilage development and mineralization are shared in degenerative cartilage. These include chondrocyte proliferation, hypertrophy and increased apoptosis. Moreover, parathyroid hormone related protein (PTHrP), one of the central mediators of endochondral development, is abundant in osteoarthritic cartilage. Cartilage PPi elaboration and cytosolic transglutaminase activity are markedly increased with aging. Only recently have the molecular identities been defined for the chondrocyte inorganic pyrophosphate (PPi)-generating isozymes of the phosphodiesterase nucleotide pyrophosphatase (PDNP) family (including PC-1 and B10), and for transglutaminase in articular cartilage. This review focuses on the evolving understanding of the potential roles, in articular cartilage calcification, of PTHrP, PDNP family enzymes, PPi metabolism, and transglutaminase activity.