Histochemical assessment of osteoclast-like giant cells in Rankl−/− mice

• Published in: Journal of oral biosciences 2023-06, Vol.65 (2), p.175-185
• Main Authors: Miyamoto, Yukina, Hasegawa, Tomoka, Hongo, Hiromi, Yamamoto, Tomomaya, Haraguchi-Kitakamae, Mai, Abe, Miki, Maruoka, Haruhi, Ishizu, Hotaka, Shimizu, Tomohiro, Sasano, Yasuyuki, Udagawa, Nobuyuki, Li, Minqi, Amizuka, Norio
• Format: Article
• Language: English
• Subjects: c-Fos; Osteoblasts; Osteoclasts; RANKL; Siglec-15
• ISSN: 1349-0079
• DOI: 10.1016/j.job.2023.04.003

We examined mice with gene deletion of Receptor activator of nuclear factor-κB (Rank) ligand (Rankl) to histologically clarify whether they contained progenitor cells committed to osteoclastic differentiation up to the stage requiring RANK/RANKL signaling. The tibiae and femora of ten-week-old male wild-type, c-fos−/−, and Rankl−/− mice were used for immunohistochemistry and transmission electron microscopy (TEM). In Rankl−/− mice, we observed osteoclast-like giant cells, albeit in low numbers, with single or two nuclei, engulfing the mineralized extracellular matrix. TEM revealed that these giant cells contained large numbers of mitochondria, vesicles/vacuoles, and clear zone-like structures but no ruffled borders. They often engulfed fragmented bony/cartilaginous components of the extracellular matrix that had been degraded. Additionally, osteoclast-like giant cells exhibited immunoreactivity for vacuolar H+-ATPase, galectin-3, and siglec-15 but not for tartrate-resistant acid phosphatase, cathepsin K, or MMP-9, all of which are classical hallmarks of osteoclasts. Furthermore, osteoclast-like giant cells were ephrinB2-positive as they were near EphB4-positive osteoblasts that are also positive for alkaline phosphatase and Runx2 in Rankl−/− mice. Unlike Rankl−/− mice, c-fos−/− mice lacking osteoclast progenitors and mature osteoclasts had no ephrinB2-positive osteoclast-like cells or alkaline phosphatase-positive/Runx2-reactive osteoblasts. This suggests that similar to authentic osteoclasts, osteoclast-like giant cells might have the potential to activate osteoblasts in Rankl−/− mice. It seems plausible that osteoclast-like giant cells may have acquired some osteoclastic traits and the ability to resorb mineralized matrices even when the absence of RANK/RANKL signaling halted the osteoclastic differentiation cascade.