Low-dose γ-radiation inhibits IL-1β-induced dedifferentiation and inflammation of articular chondrocytes via blockage of catenin signaling.
Bottom Line: Here, we found that LDR, at doses of 0.5-2 centiGray (cGy), inhibited interleukin (IL)-1β-induced chondrocyte destruction without causing side effects, such as cell death and senescence.LDR also inhibited chondrocyte destruction through the catenin pathway induced by epidermal growth factor, phorbol 12-myristate 13-acetate, and retinoic acid.Collectively, these results identify the molecular mechanisms by which LDR suppresses pathophysiological processes and establish LDR as a potentially valuable therapeutic tool for patients with cytokine- or soluble factors-mediated cartilage disorders.
Affiliation: Division of Radiation Cancer Biology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Department of Chemistry, College of Natural Sciences, Hanyang University, Seoul, Korea.Show MeSH
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Mentions: We next examined whether LDR, at doses of 0–2 cGy, directly modulates the expression of catenin proteins in chondrocytes. Although LDR alone did not alter the expression of catenin proteins (Fig. 5A), both 0.5 and 1 cGy LDR dramatically attenuated IL-1β-induced expression of all catenin proteins (Fig. 5B). Immunofluorescence analyses showed that treatment of chondrocytes with IL-1β significantly increased the levels of all of the tested catenin proteins in both the cytosol and nuclear regions compared to control cells. At a dose of 1 cGy, LDR reduced catenin expression in IL-1β-treated cells to basal levels (Fig. 5C), indicating that LDR inhibits the IL-1β-dependent post-translational stabilization of catenin. Finally, we examined whether LDR reverses the dedifferentiation and inflammatory response induced by overexpression of the above-mentioned α-, β-, and γ-catenin proteins in chondrocytes. Notably, LDR markedly restored the expression of type II collagen and Sox-9 proteins in catenin-overexpressing chondrocytes (Supporting Information Fig. 1B and Fig. 5D), indicating a reduced commitment to dedifferentiation. LDR also inhibited I-κB degradation and COX-2 expression under the same experimental conditions (Supporting Information Fig. 1B and Fig. 5D). Consistent with this, LDR dramatically increased in Sox-9 activity reduced by catenin proteins and decreased in NF-κB activity induced by catenin proteins in chondrocytes; at a dose of 1 cGy, LDR enhanced Sox-9 activity by approximately 2.2-fold, 2.7-fold, and 2.4-fold compared to that in cells transfected with the above-mentioned α-, β-, and γ-catenin constructs, respectively (Supporting Information Fig. 1C and Fig. 5E, left), and reduced NF-κB activity by approximately 74%, 78%, and 75%, respectively (Supporting Information Fig. 1C and Fig. 5E, right), indicating a reduced commitment to inflammation. To further confirm the role of NF-κB signaling in catenin-mediated induction of COX-2 expression, we treated catenin-overexpressing chondrocytes with the NF-κB inhibitor, BAY. Pretreatment with 5 or 10 μM BAY inhibited I-κB degradation in a dose-dependent manner and consistently reduced COX-2 expression compared to IL-1β-treated chondrocytes (Fig. 5F). Degradation of I-κB and induction of COX-2 in cells transfected with the above-mentioned α-, β-, and γ-catenin constructs were also reversed by BAY treatment (Fig. 5G), indicating that NF-κB signaling is downstream of the catenin pathway.
Affiliation: Division of Radiation Cancer Biology, Korea Institute of Radiological & Medical Sciences, Seoul, Korea; Department of Chemistry, College of Natural Sciences, Hanyang University, Seoul, Korea.