Nitric oxide regulates cartilage destruction by causing dedifferentiation and apoptosis of chondrocytes. We investigated the role of the mitogen-activated protein kinase subtypes, extracellular signal-regulated protein kinase (ERK)-1/2, and p38 kinase in NO-induced apoptosis of rabbit articular chondrocytes and their involvement in dedifferentiation. Generation of NO with sodium nitroprusside (SNP) caused dedifferentiation, as indicated by the inhibition of type II collagen expression and proteoglycan synthesis. NO additionally caused apoptosis, accompanied by p53 accumulation and caspase-3 activation. SNP treatment stimulated activation of ERK-1/2 and p38 kinase. Inhibition of ERK-1/2 with PD98059 rescued SNP-induced dedifferentiation but enhanced apoptosis up to 2-fold, whereas inhibition of p38 kinase with SB203580 enhanced dedifferentiation, with significant blockage of apoptosis. The stimulation of apoptosis by ERK inhibition was accompanied by increased p53 accumulation and caspase-3 activity, whereas the inhibitory effect of p38 kinase blockade was associated with reduced p53 accumulation and caspase-3 activity. Our results indicate that NO-induced p38 kinase functions as an induction signal for apoptosis and in the maintenance of chondrocyte phenotype, whereas ERK activity causes dedifferentiation and operates as an anti-apoptotic signal. NO generation is less proapoptotic in chondrocytes that are dedifferentiated by serial monolayer culture or phorbol ester treatment. NO-induced p38 kinase activity is low in dedifferentiated cells compared with that in differentiated chondrocytes, with lower levels of p53 accumulation and caspase-3 activity. Our findings collectively suggest that ERK-1/2 and p38 kinase oppositely regulate NO-induced apoptosis of chondrocytes, in association with p53 accumulation, caspase-3 activation, and differentiation status.

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Nitric oxide (NO) during primary culture of articular chondrocytes causes apoptosis via p38 mitogen-activated protein kinase in association with elevation of p53 protein level, caspase-3 activation, and differentiation status. In this study, we characterized the molecular mechanism by which p38 kinase induces apoptosis through activation of p53. We report here that NO-induced activation of p38 kinase leads to activation of NFB, which in turn induces transcription of the p53 gene. Activated p38 kinase also physically associates and phosphorylates the serine 15 residue of p53, which results in accumulation of p53 protein during NO-induced apoptosis. Ectopic expression of wild-type p53 enhanced NO-induced apoptosis, whereas expression of a dominant negative p53 blocked it, indicating that p53 plays an essential role in NO-induced apoptosis of chondrocytes. The increased accumulation of p53 caused expression of Bax, a pro-apoptotic member of the Bcl-2 family that is known to cause apoptosis via release of cytochrome c and caspase activation. These results suggest that NO-activated p38 kinase activates p53 function in two different ways, transcriptional activation by NFB and direct phosphorylation of p53 protein, leading to apoptosis of articular chondrocytes.

During limb development, epithelial cells in the apical ectodermal ridge keep the underlying mesenchymal cells in a proliferative state preventing differentiation by secreting signaling molecules such as epidermal growth factor (EGF). We investigated the molecular mechanism of the EGF effect on the regulation of micromass culture-induced chondrogenesis of chick limb bud mesenchymal cells as a model system. We found that expression and tyrosine phosphorylation of the EGF receptor was increased transiently during chondrogenesis. Exogenous EGF inhibited chondrogenic differentiation of mesenchymal cells, and this effect was reversed by the EGF receptor inhibitor AG1478. EGF treatment also inhibited the expression and activation of protein kinase C-␣, whereas it activated Erk-1 and inhibited p38 mitogen-activated protein kinase, all of which appeared to be involved in the EGF-induced inhibition of chondrogenesis. Stimulation of the EGF receptor blocked precartilage condensation and altered the expression of cell adhesion molecules such as N-cadherin and integrins ␣ 5 and ␤ 1 . All these EGF effects were reversible by AG1478. The data indicate that EGF negatively regulate chondrogenesis of chick limb bud mesenchymal cells by inhibiting precartilage condensation and by modulating signaling pathways including those of protein kinase C-␣, Erk-1, and p38 mitogen-activated protein kinase.

Background/AimsAlthough indoor air pollution is a well-known risk factor for tuberculosis (TB), the possible link between outdoor air pollution and TB development has not been examined fully. We assessed the impact of outdoor air pollution on TB development in the Seoul metropolitan area, South Korea.MethodsThe mean concentrations of ambient particulate matter (PM) with an aerodynamic diameter ≤ 10 µm (PM10), O3, CO, NO2, and SO2 levels in Seoul, between January 1, 1997 and December 31, 2006, were determined. Furthermore, their association with the risk of developing TB after adjusting for socioeconomic status, between January 1, 2002 and December 31, 2006, was investigated.ResultsBetween January 1, 2002 and December 31, 2006, a total of 41,185 TB cases were reported in Seoul. Concentrations of PM10, O3, CO, and NO2 were not associated with TB incidence in males or females. However, the interquartile increase in SO2 concentration was associated with a 7% increment in TB incidence (relative risk [RR], 1.07; 95% credible interval [CrI], 1.03 to 1.12) in males but not in females (RR, 1.02; 95% CrI, 0.98 to 1.07).ConclusionsLong-term exposure to ambient SO2 increased the risk of TB in males.

BackgroundKorea failed in its risk communication during the early stage of the Middle East Respiratory Syndrome (MERS) outbreak; consequently, it faced difficulties in managing MERS, while disease-related worry increased. Disease-related worry can help disease prevention and management, but can also have a detrimental effect. This study measured the overall level of disease-related worry during the MERS outbreak period in Korea and the influencing factors and levels of disease-related worry during key outbreak periods.MethodsThe cross-sectional survey included 1,000 adults who resided in Korea. An ordinal logistic regression was performed for the overall level of MERS-related worry, and influencing factors of worry were analyzed. A reliability test was performed on the levels of MERS-related worry during key outbreak periods.ResultsThe overall level of MERS-related worry was 2.44. Multivariate analysis revealed that women and respondents w very poor subjective health status had higher levels of worry. Respondents with very high stress in daily life had higher levels of worry than those who reported having little stress. The reliability test results on MERS-related worry scores during key outbreak periods showed consistent scores during each period.ConclusionLevel of worry increased in cases having higher perceived susceptibility and greater trust in informal information, while initial stage of outbreak was closely associated with that at later stages. These findings suggest the importance of managing the level of worry by providing timely and accurate disease-related information during the initial stage of disease outbreak.

Akt is a key downstream effector of the PI3K signaling pathway and plays a role in cell growth and survival. Expression of a myristoylated constitutively active form of Akt (myr-Akt) in PC12 cells could override cell-growth arrest at G2/M phase and apoptosis that were induced by etoposide treatment. On the other hand, inactivation of Akt by expression of its dominant negative mutant form (km-Akt) inhibited cell proliferation by arresting the cells at G2/M phase. Expression of myr-Akt also led to an increase in the protein and mRNA levels of CDK1 and cyclin B1. Furthermore, EMSA data revealed that expression of myr-Akt promoted the binding of NF-Y to the consensus CCAAT promoter sequence, whereas expression of km-Akt almost completely abolished it. Moreover, the Akt activity was minimal in the cells that were arrested at G2/M phase by nocodazole treatment, but reached to a maximal level as the cells progressed to mitosis and G1 phase upon removal of the drug. Treatment with Akt inhibitors, but not with those of MEK or p70S6K, blocked the release of the cells from the nocodazole-induced G2/M arrest, further revealing that the Akt activity is required for G2/M phase transition. These results suggest that Akt facilitate cell-cycle progression at G2/M phase in PC12 cells and this Akt activity is correlated with upregulation of NF-Y DNA-binding activity and cyclin B1/CDK1 gene expression.

In articular chondrocytes, nitric oxide (NO) production triggers dedifferentiation and apoptotic cell death that is regulated by the converse functions of two mitogen-activated protein kinase subtypes, extracellular signal-regulated kinase (ERK) and p38 kinase. Since protein kinase C (PKC) transduces signals that influence differentiation, survival, and apoptosis of various cell types, we investigated the roles and underlying molecular mechanisms of action of PKC isoforms in NO-induced dedifferentiation and apoptosis of articular chondrocytes. We report here that among the expressed isoforms, activities of PKC␣ and -were reduced during NO-induced dedifferentiation and apoptosis. Inhibition of PKC␣ activity was independent of NO-induced activation of ERK or p38 kinase and occurred due to blockage of expression. On the other hand, PKC activity was inhibited as a result of NO-induced p38 kinase activation and was observed prior to proteolytic cleavage by a caspase-mediated process to generate enzymatically inactive fragments. Inhibition of PKC␣ or -activities potentiated NO-induced apoptosis, whereas ectopic expression of these isoforms significantly reduced the number of apoptotic cells and blocked dedifferentiation. Ectopic expression of PKC␣ or -did not affect p38 kinase or ERK but inhibited the p53 accumulation and caspase-3 activation that are required for NO-induced apoptosis of chondrocytes. Therefore, our results collectively indicate that p38 kinase-independent and -dependent inhibition of PKC␣ and -, respectively, regulates NO-induced apoptosis and dedifferentiation of articular chondrocytes.