Connexin43 enhances the expression of osteoarthritis-associated genes in synovial fibroblasts in culture

Abstract

BackgroundRecent work has shown that the gap junction protein connexin43 (Cx43) is upregulated in cells of the joint during osteoarthritis (OA). Here we examined if the OA-associated increase in Cx43 expression impacts the function of synovial fibroblasts by contributing to the production of catabolic and inflammatory factors that exacerbate joint destruction in arthritic disease.MethodsUsing rabbit and human synovial fibroblast cell lines, we examined the effects of Cx43 overexpression and Cx43 siRNA-mediated knockdown on the gene expression of OA-associated matrix metalloproteinases (MMP1 and MMP13), aggrecanases (ADAMTS4 and ADAMTS5), and inflammatory factors (IL1, IL6 and PTGS2) by quantitative real time RT-PCR. We examined collagenase activity in conditioned media of cultured synovial cells following Cx43 overexpression. Lastly, we assessed the interplay between Cx43 and the NFκB cascade by western blotting and gene expression studies.ResultsIncreasing Cx43 expression enhanced the gene expression of MMP1, MMP13, ADAMTS4, ADAMTS5, IL1, IL6 and PTGS2 and increased the secretion of collagenases into conditioned media of cultured synovial fibroblasts. Conversely, knockdown of Cx43 decreased expression of many of these catabolic and inflammatory genes. Modulation of Cx43 expression altered the phosphorylation of the NFκB subunit, p65, and inhibition of NFκB with chemical inhibitors blocked the effects of increased Cx43 expression on the mRNA levels of a subset of these catabolic and inflammatory genes.ConclusionsIncreasing or decreasing Cx43 expression alone was sufficient to alter the levels of catabolic and inflammatory genes expressed by synovial cells. The NFκB cascade mediated the effect of Cx43 on the expression of a subset of these OA-associated genes. As such, Cx43 may be involved in joint pathology during OA, and targeting Cx43 expression or function may be a viable therapeutic strategy to attenuate the catabolic and inflammatory environment of the joint during OA.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2474-15-425) contains supplementary material, which is available to authorized users.

Cx43- and Smad-Mediated TGF-β/ BMP Signaling Pathway Promotes Cartilage Differentiation of Bone Marrow Mesenchymal Stem Cells and Inhibits Osteoblast Differentiation

“…The activation of ERK1/2 and small mothers against decapentaplegic homolog (Smad) signaling pathways leads to increased TGF-β1 -induced Cx43 expression, which is required for the differentiation of trophoblast cells [14]. Cx43 is also up-regulated in cells in the joints of patients with osteoarthritis, and targeting Cx43 expression may be a feasible therapeutic strategy to alleviate the inflammatory and catabolic environment of the joint during osteoarthritis [15]. Additionally, BMPs are also known for their importance in the differentiation of osteoblastic lineage and osteogenesis [16].…”

Defective signaling, osteoblastogenesis and bone remodeling in a mouse model of connexin 43 C-terminal truncation

“…The supernatant was used for protein expression analysis by western blotting. For BMSCs, cells were lysed in modified RIPA, as described (Gupta et al, 2014).…”

Expression of Connexin 43 in Synovial Tissue of Patients With Rheumatoid Arthritis

“…Gupta et al 19 reported that increasing Cx43 expression enhanced the gene expression of IL-6, and knockdown of Cx43 decreased expression of IL-6 in osteoarthritis synovium. Therefore, we expected that the expression of Cx43 of synovial tissue was inhibited by tocilizumab which could decrease the expression of IL-6 in synovium.…”