Morphological Study for the Osteocytes in Podoplanin-Conditional Knockout Mice

We generated podoplanin-conditional knockout mice where the floxed podoplanin exon3 was deleted by the Dmp1-driven Cre (Dmp1-Cre;PdpnΔ/Δ) and investigated the cell process elongation of podoplanin-deficient mouse osteocyte in vitro and in vivo. The expression of podoplanin is found in odontoblasts while not observed in odontoblasts of Dmp1-Cre;PdpnΔ/Δ mice, indicating that the conditional knockout of podoplanin in Dmp1-expressing cells in Dmp1-Cre;PdpnΔ/Δ mice is successful. There were no differences in the growth of wild-type and Dmp1-Cre;PdpnΔ/Δ mice, and no differences in calcification and alkaline phosphatase activity in cultured calvarial osteoblasts of the wild-type and Dmp1-Cre;PdpnΔ/Δ mice, in total this suggests that the podoplanin-cKO has no effect on generation of the bone. The cell process elongation was suppressed in cultured calvarial osteoblasts of Dmp1-Cre;PdpnΔ/Δ mice compared with wild-type mice. In the electron microscopic study, there were no morphological differences in bone matrix formation and osteocyte distribution in Dmp1-Cre;PdpnΔ/Δ and wild-type mice, whereas the cell process formation was sparser and the network with neighboring cells was more deficient in Dmp1-Cre;PdpnΔ/Δ mice than in wild-type mice. In the quantitative analysis, the number and thickness of the cell processes were significantly smaller and thinner in Dmp1-Cre;PdpnΔ/Δ mice than in wild-type mice. This could suggest that podoplanin plays a role in the formation of the osteocyte network created by the cell process elongation.