RANKL-independent osteoclastogenesis in the SH3BP2 cherubism mice.

Abstract

Even though the receptor activator of the nuclear factor-κB ligand (RANKL) and its receptor RANK have an exclusive role in osteoclastogenesis, the possibility of RANKL/RANK-independent osteoclastogenesis has been the subject of a long-standing debate in bone biology. In contrast, it has been reported that calvarial injection of TNF-ɑ elicits significant osteoclastogenesis in the absence of RANKL/RANK in NF-κB2- and RBP-J-deficient mice, suggesting that inflammatory challenges and secondary gene manipulation are the prerequisites for RANKL/RANK-deficient mice to develop osteoclasts <i>in vivo</i>. Here we report that, even in the absence of RANKL (<i>Rankl</i> ^<i>-/-</i> ), cherubism mice (<i>Sh3bp2</i> ^<i>KI/KI</i> ) harboring the homozygous gain-of-function mutation in SH3-domain binding protein 2 (SH3BP2) develop tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts spontaneously. The <i>Sh3bp2</i> ^<i>KI/KI</i> <i>Rankl</i> ^<i>-/-</i> mice exhibit an increase in tooth exposure and a decrease in bone volume/total volume compared to <i>Sh3bp2</i> ^<i>+/+</i> <i>Rankl</i> ^<i>-/-</i> mice. The multinucleated cells were stained positively for cathepsin K. Osteoclastic marker gene expression in bone and serum TRAP5b levels were elevated in <i>Sh3bp2</i> ^<i>KI/KI</i> <i>Rankl</i> ^<i>-/-</i> mice. Elevation of the serum TNF-ɑ levels suggested that TNF-ɑ is a driver for the RANKL-independent osteoclast formation in <i>Sh3bp2</i> ^<i>KI/KI</i> mice. Our results provide a novel mutant model that develops osteoclasts independent of RANKL and establish that the gain-of-function of SH3BP2 promotes osteoclastogenesis not only in the presence of RANKL but also in the absence of RANKL.