title: Systemic circulation and bone recruitment of osteoclast precursors tracked by using fluorescent imaging techniques.
abstract: Osteoclasts are bone-resorbing polykaryons differentiated from monocyte/macrophage-lineage hematopoietic precursors. It remains unclear whether osteoclasts originate from circulating blood monocytes or from bone tissue-resident precursors. To address this question, we combined two different experimental procedures: 1) shared blood circulation "parabiosis" with fluorescently labeled osteoclast precursors, and 2) photoconversion-based cell tracking with a Kikume Green-Red protein (KikGR). In parabiosis, CX(3)CR1-EGFP knock-in mice in which osteoclast precursors were labeled with EGFP were surgically connected with wild-type mice to establish a shared circulation. Mature EGFP(+) osteoclasts were found in the bones of the wild-type mice, indicating the mobilization of EGFP(+) osteoclast precursors into bones from systemic circulation. Receptor activator for NF-κB ligand stimulation increased the number of EGFP(+) osteoclasts in wild-type mice, suggesting that this mobilization depends on the bone resorption state. Additionally, KikGR(+) monocytes (including osteoclast precursors) in the spleen were exposed to violet light, and 2 d later we detected photoconverted "red" KikGR(+) osteoclasts along the bone surfaces. These results indicate that circulating monocytes from the spleen entered the bone spaces and differentiated into mature osteoclasts during a certain period. The current study used fluorescence-based methods clearly to demonstrate that osteoclasts can be generated from circulating monocytes once they home to bone tissues.
authors.affiliation: Laboratory of Cellular Dynamics, World Premier International Research Center Initiative-Immunology Frontier Research Center, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Manato
authors.initials: M
authors.lastname: Kotani
authors.forename: Junichi
authors.initials: J
authors.lastname: Kikuta
authors.forename: Frederick
authors.initials: F
authors.lastname: Klauschen
authors.forename: Takenao
authors.initials: T
authors.lastname: Chino
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Hisataka
authors.initials: H
authors.lastname: Yasuda
authors.forename: Katsuto
authors.initials: K
authors.lastname: Tamai
authors.forename: Atsushi
authors.initials: A
authors.lastname: Miyawaki
authors.forename: Osami
authors.initials: O
authors.lastname: Kanagawa
authors.forename: Michio
authors.initials: M
authors.lastname: Tomura
authors.forename: Masaru
authors.initials: M
authors.lastname: Ishii
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000378:metabolism*; D002465:Cell Movement; D058948:Cell Tracking / Q000379:methods*; D003427:Cross Circulation; D051379:Mice; D008822:Mice, Transgenic; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D010227:Parabiosis; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*