Osteoclasts play a critical role not only in bone homeostasis but also in inflammatory
osteolysis, such as that occurring in inflammatory
arthritis and systemic
inflammation. In both
inflammation conditions, inflammatory
cytokines like
Interleukin (IL)-1,
IL-6 and
tumor necrosis factor (TNF)-α induce RANKL expression in osteoblasts, but the roles of these
cytokines in osteoclast activation remain unclear.
S100A12, an S100 family member, is a low-molecular-weight
calcium-binding protein. Although it has a pro-inflammatory role, its effects on osteoclast differentiation have been unclear. Here we examined the direct effects of
S100A12 on human osteoclasts in vitro.
S100A12 facilitated osteoclast formation in the presence of RANKL, as judged by the cells' morphology and elevated expression of osteoclast-related molecules, including NFATc1, ACP5, CALCR, and ITGβ3. In addition,
S100A12 administration markedly enhanced the osteoclasts'
bone resorption ability, consistent with their increased expression levels of CTSK and CA2. Blocking RAGE and TLR4 cancelled the effects of
S100A12. Our results indicate that
S100A12 is a potential therapeutic target for inflammatory
osteolysis.