RelA/p65 promotes osteoclast differentiation by blocking a RANKL-induced apoptotic JNK pathway in mice
Sergio Vaira, … , Roberta Faccio, Deborah Veis Novack
Sergio Vaira, … , Roberta Faccio, Deborah Veis Novack
Published May 8, 2008
Citation Information: J Clin Invest. 2008;118(6):2088-2097. https://doi.org/10.1172/JCI33392.
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Research Article Bone biology

RelA/p65 promotes osteoclast differentiation by blocking a RANKL-induced apoptotic JNK pathway in mice

Abstract

Osteoclasts (OCs) function to reabsorb bone and are responsible for the bone loss associated with inflammatory arthritis and osteoporosis. OC numbers are elevated in most disorders of accelerated bone destruction, reflecting altered rates of precursor differentiation and apoptosis. Both of these processes are regulated by the JNK family of MAP kinases. In this study, we have demonstrated that the NF-κB subunit RelA/p65 inhibits JNK-mediated apoptosis during a critical period of commitment to the OC phenotype in response to the cytokine RANKL. This RelA/p65-mediated arrest of cell death led to enhanced OC differentiation. Hence, Rela–/– OC precursors displayed prolonged JNK activation in response to RANKL, and this was accompanied by an increase in cell death that prevented efficient differentiation. Although complete blockade of JNK activity inhibits osteoclastogenesis, both short-term blockade in RelA-deficient cultures and suppression of the downstream mediator, Bid rescued apoptosis and differentiation. These antiapoptotic effects were RelA specific, as overexpression of RelA, but not RelB, blocked apoptosis and rescued differentiation in Rela–/– precursors. Thus, RelA blocks a RANKL-induced, apoptotic JNK-Bid pathway, thereby promoting OC differentiation. Consistent with this, mice lacking RelA/p65 in the hematopoietic compartment were shown to have a deficient osteoclastogenic response to RANKL and were protected from arthritis-induced osteolysis.

Authors

Sergio Vaira, Muhammad Alhawagri, Imani Anwisye, Hideki Kitaura, Roberta Faccio, Deborah Veis Novack

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Figure 4

The absence of RelA leads to enhanced JNK activation.

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The absence of RelA leads to enhanced JNK activation. (A) Pre-OCs (B...
(A) Pre-OCs (BMMs cultured for 2 days with M-CSF and RANKL) generated from Rela+/+ (black bars) and Rela–/– (gray bars) mice were then starved of serum and cytokines and restimulated with RANKL for the indicated times prior to RNA extraction and real-time quantitative PCR for xiap, Gadd45b, and Mkp5. Rela–/– pre-OCs show significantly less induction of xiap, Gadd45b and Mkp5. *P < 0.5, **P < 0.01 compared to Rela+/+ at the same time point. (B) Rela+/+ and Rela–/– pre-OCs were starved and restimulated with RANKL for the indicated times, and total lysates were analyzed by immunoblot for pJNK, demonstrating enhanced JNK activation in Rela–/– cultures. A parallel blot with equal loading was used to assess total JNK protein. (C) Rela+/+ and Rela–/– BMMs were cultured in RANKL, with or without the JNK inhibitor SP600125 (1 μm), for 36 hours Apoptosis was then assessed by DNA fragmentation assay. RANKL-mediated apoptosis was abrogated by the JNK inhibitor in Rela–/– cells. The data are representative of 3 independent experiments. †P < 0.05 Rela–/– versus Rela+/+ or Rela–/– with SP600125. (D) Rela+/+ and Rela–/– BMMs were cultured in osteoclastogenic conditions for 8 days, with or without SP600125 for the first 36 hours, showing rescue of differentiation with short-term JNK inhibition. Scale bar: 200 μm.