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Constitutively active canonical NF-κB pathway induces severe bone loss in mice.

Otero JE, Chen T, Zhang K, Abu-Amer Y - PLoS ONE (2012)

Bottom Line: Mechanistically, we observed that IKK2SSEE induced high expression of not only p65 but also p52 and RelB; the latter two molecules are considered exclusive members of the alternative NF-κB pathway.Furthermore, we found that NF-κB2/p100 is a potent inhibitor of IKK2SSEE-induced osteoclastogenesis.Deletion of p52 enabled more robust osteoclast formation by the active kinase.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopedic Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States of America.

ABSTRACT
Physiologic osteoclastogenesis entails activation of multiple signal transduction pathways distal to the cell membrane receptor RANK. However, atypical osteoclastogenesis driven by pro-inflammatory stimuli has been described. We have reported recently a novel mechanism whereby endogenous mutational activation of the classical NF-κB pathway is sufficient to induce RANKL/RANK-independent osteoclastogenesis. Here we investigate the physiologic relevance of this phenomenon in vivo. Using a knock-in approach, the active form of IKK2, namely IKK2SSEE, was introduced into the myeloid lineage with the aid of CD11b-cre mice. Phenotypic assessment revealed that expression of IKK2SSEE in the myeloid compartment induced significant bone loss in vivo. This observation was supported by a dramatic increase in the number and size of osteoclasts in trabecular regions, elevated levels of circulating TRACP-5b, and reduced bone volume. Mechanistically, we observed that IKK2SSEE induced high expression of not only p65 but also p52 and RelB; the latter two molecules are considered exclusive members of the alternative NF-κB pathway. Intriguingly, RelB and P52 were both required to mediate the osteoclastogenic effect of IKK2SSEE and co-expression of these two proteins was sufficient to recapitulate osteoclastogenesis in the absence of RANKL or IKK2SSEE. Furthermore, we found that NF-κB2/p100 is a potent inhibitor of IKK2SSEE-induced osteoclastogenesis. Deletion of p52 enabled more robust osteoclast formation by the active kinase. In summary, molecular activation of IKK2 may play a role in conditions of pathologic bone destruction, which may be refractory to therapeutic interventions targeting the proximal RANKL/RANK signal.

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Expression levels of IL-1β and OPG are higher in the serum of IKK2SSEEMYELO -tg mice.IL-1β, OPG, RANKL and TNFα levels in the serum of wild type and transgenic mice were measured using commercial ELISA kits. * denotes p<0.05 (IL-1β) and p<0.05 (OPG).
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pone-0038694-g007: Expression levels of IL-1β and OPG are higher in the serum of IKK2SSEEMYELO -tg mice.IL-1β, OPG, RANKL and TNFα levels in the serum of wild type and transgenic mice were measured using commercial ELISA kits. * denotes p<0.05 (IL-1β) and p<0.05 (OPG).

Mentions: To explore the mechanism underlying enhanced osteoclast activity in IKK2SSEEMYELO-tg mice, we measured circulating levels of osteoclastogenic factors (RANKL and OPG) and inflammatory factors (TNFα and IL1β) which function cooperatively with RANKL. Serum level of RANKL and TNFα remain normal, however serum levels of IL1β increased significantly compared to wild type counterparts (fig. 7). Interestingly, serum level of OPG also increased dramatically, probably reflecting compensatory role of OPG in IKK2SSEEMYELO -tg mice. To determine if elevated levels of IL-1β are responsible for the IKK2SSEE osteoclastogenic effect, IKK2SSEE transgenic mice were cross bred with IL-1r knockout mice. However, all parameters of osteoclastogenesis examined in these hybrid mice were similar to those derived from the IKK2SSEEMYELO-tg mice (not shown).


Constitutively active canonical NF-κB pathway induces severe bone loss in mice.

Otero JE, Chen T, Zhang K, Abu-Amer Y - PLoS ONE (2012)

Expression levels of IL-1β and OPG are higher in the serum of IKK2SSEEMYELO -tg mice.IL-1β, OPG, RANKL and TNFα levels in the serum of wild type and transgenic mice were measured using commercial ELISA kits. * denotes p<0.05 (IL-1β) and p<0.05 (OPG).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369901&req=5

pone-0038694-g007: Expression levels of IL-1β and OPG are higher in the serum of IKK2SSEEMYELO -tg mice.IL-1β, OPG, RANKL and TNFα levels in the serum of wild type and transgenic mice were measured using commercial ELISA kits. * denotes p<0.05 (IL-1β) and p<0.05 (OPG).
Mentions: To explore the mechanism underlying enhanced osteoclast activity in IKK2SSEEMYELO-tg mice, we measured circulating levels of osteoclastogenic factors (RANKL and OPG) and inflammatory factors (TNFα and IL1β) which function cooperatively with RANKL. Serum level of RANKL and TNFα remain normal, however serum levels of IL1β increased significantly compared to wild type counterparts (fig. 7). Interestingly, serum level of OPG also increased dramatically, probably reflecting compensatory role of OPG in IKK2SSEEMYELO -tg mice. To determine if elevated levels of IL-1β are responsible for the IKK2SSEE osteoclastogenic effect, IKK2SSEE transgenic mice were cross bred with IL-1r knockout mice. However, all parameters of osteoclastogenesis examined in these hybrid mice were similar to those derived from the IKK2SSEEMYELO-tg mice (not shown).

Bottom Line: Mechanistically, we observed that IKK2SSEE induced high expression of not only p65 but also p52 and RelB; the latter two molecules are considered exclusive members of the alternative NF-κB pathway.Furthermore, we found that NF-κB2/p100 is a potent inhibitor of IKK2SSEE-induced osteoclastogenesis.Deletion of p52 enabled more robust osteoclast formation by the active kinase.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopedic Surgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa, United States of America.

ABSTRACT
Physiologic osteoclastogenesis entails activation of multiple signal transduction pathways distal to the cell membrane receptor RANK. However, atypical osteoclastogenesis driven by pro-inflammatory stimuli has been described. We have reported recently a novel mechanism whereby endogenous mutational activation of the classical NF-κB pathway is sufficient to induce RANKL/RANK-independent osteoclastogenesis. Here we investigate the physiologic relevance of this phenomenon in vivo. Using a knock-in approach, the active form of IKK2, namely IKK2SSEE, was introduced into the myeloid lineage with the aid of CD11b-cre mice. Phenotypic assessment revealed that expression of IKK2SSEE in the myeloid compartment induced significant bone loss in vivo. This observation was supported by a dramatic increase in the number and size of osteoclasts in trabecular regions, elevated levels of circulating TRACP-5b, and reduced bone volume. Mechanistically, we observed that IKK2SSEE induced high expression of not only p65 but also p52 and RelB; the latter two molecules are considered exclusive members of the alternative NF-κB pathway. Intriguingly, RelB and P52 were both required to mediate the osteoclastogenic effect of IKK2SSEE and co-expression of these two proteins was sufficient to recapitulate osteoclastogenesis in the absence of RANKL or IKK2SSEE. Furthermore, we found that NF-κB2/p100 is a potent inhibitor of IKK2SSEE-induced osteoclastogenesis. Deletion of p52 enabled more robust osteoclast formation by the active kinase. In summary, molecular activation of IKK2 may play a role in conditions of pathologic bone destruction, which may be refractory to therapeutic interventions targeting the proximal RANKL/RANK signal.

Show MeSH
Related in: MedlinePlus