p38/NF‐kB‐dependent expression of COX‐2 during differentiation and inflammatory response of chondrocytes

Abstract

Studying cartilage differentiation, we observed the emergence of inflammation-related proteins suggesting that a common pathway was activated in cartilage differentiation and inflammation. In the present paper, we investigated the expression pathway of the inflammation-related enzyme Cyclooxygenase-2 (COX-2) during differentiation and inflammatory response of the chondrocytic cell line MC615. Cells were cultured either as (i) proliferating prechondrogenic cells expressing type I collagen or (ii) differentiated hyperconfluent cells expressing Sox9 and type II collagen. The p38 and the NF-kB pathways were investigated in standard conditions and after inflammatory agents treatment. NF-kB was constitutively activated in differentiated cells. The activation level of NF-kB in differentiated cells was comparable to the level in proliferating cells treated with the inflammatory agent LPS. In both cases, p65 was bound to the NF-kB consensus sequence of COX-2 promoter. p38, constitutively activated in differentiated cells, was activated in proliferating cells by treatment with LPS or IL-1alpha. In stimulated proliferating cells the two pathways are connected since addition of the p38-specific inhibitor SB203580 inhibited p38 activation, significantly reduced NF-kB activation and repressed COX-2 synthesis indicating that p38 is upstream NF-kB activation and COX-2 synthesis. In differentiated cells, the treatment with the inflammatory agent neither enhance NF-kB activation, nor synthesis of COX-2 while the addition of SB203580 neither repressed activation of p38, nor COX-2 synthesis, suggesting a constitutive activation of a p38/NF-kB/COX2 pathway. Our data indicate that in chondrocytes, COX-2 is expressed via p38 activation/NF-kB recruitment during both differentiation and inflammatory response.

Inhibition of cyclooxygenase-2 impacts chondrocyte hypertrophic differentiation during endochondral ossification

“…These confl icting results may be related to the choice of experimental models: whereas we used chondroprogenitors, PKA/PKC involvement was tested in mature chondrocyte cultures. In relation to this, differentially regulated COX-2 expression during different stages of chondrogenesis was previously suggested (Huh et al, 2003;Ulivi et al, 2008). Importantly, as COX-2 inhibition leads to an indiscriminate shutdown of prostaglandin synthesis, we cannot rule out the possibility that different prostaglandins contribute differently to chondrocyte differentiation.…”

Interleukin-1β Induces Increased Transcriptional Activation of the Transforming Growth Factor-β-activating Integrin Subunit β8 through Altering Chromatin Architecture

“…Interestingly, inhibition of either NFB or p38 completely inhibited IL-1␤-induction of ␤8, indicating that the NFB and p38 pathways are linked in mediating the effects of IL-1␤ on ITGB8 transcription. Interdependence of the NFB and p38 pathways has been well described in multiple cell types, including chondrocytes, astrocytes, and fibroblast derivatives (43)(44)(45). Of the multiple p38 isoforms (␣, ␤, ␦, ␥), the ubiquitously expressed p38␣ isoform has been implicated in the modulation of inflammatory cytokine production (46,47).…”

In Vivo Implanted Bone Marrow-Derived Mesenchymal Stem Cells Trigger a Cascade of Cellular Events Leading to the Formation of an Ectopic Bone Regenerative Niche

“…3B, C). Moreover, IL-1 treatment induced in the MSCs the expression of COX-2 and the downstream enzyme mPGE synthase, whose products play a key role in the inflammatory cascade leading to the acute phase response [11]. It is noteworthy that PGD synthase expression level was unaffected (Fig.…”

“…Western blot analysis was performed as previously described [11]. Briefly, 5 · 10 5 cells were plated, the protein concentration of the lysate was measured using the Bradford method and equal protein amounts were used for western blot.…”