Osteocyte necrosis triggers osteoclast-mediated bone loss through macrophage-inducible C-type lectin
Darja Andreev, … , Georg Schett, Aline Bozec
Darja Andreev, … , Georg Schett, Aline Bozec
Published August 10, 2020
Citation Information: J Clin Invest. 2020;130(9):4811-4830. https://doi.org/10.1172/JCI134214.
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Research Article Bone biology Immunology

Osteocyte necrosis triggers osteoclast-mediated bone loss through macrophage-inducible C-type lectin

Abstract

Although the control of bone-resorbing osteoclasts through osteocyte-derived RANKL is well defined, little is known about the regulation of osteoclasts by osteocyte death. Indeed, several skeletal diseases, such as bone fracture, osteonecrosis, and inflammation are characterized by excessive osteocyte death. Herein we show that osteoclasts sense damage-associated molecular patterns (DAMPs) released by necrotic osteocytes via macrophage-inducible C-type lectin (Mincle), which induced their differentiation and triggered bone loss. Osteoclasts showed robust Mincle expression upon exposure to necrotic osteocytes in vitro and in vivo. RNA sequencing and metabolic analyses demonstrated that Mincle activation triggers osteoclastogenesis via ITAM-based calcium signaling pathways, skewing osteoclast metabolism toward oxidative phosphorylation. Deletion of Mincle in vivo effectively blocked the activation of osteoclasts after induction of osteocyte death, improved fracture repair, and attenuated inflammation-mediated bone loss. Furthermore, in patients with osteonecrosis, Mincle was highly expressed at skeletal sites of osteocyte death and correlated with strong osteoclastic activity. Taken together, these data point to what we believe is a novel DAMP-mediated process that allows osteoclast activation and bone loss in the context of osteocyte death.

Authors

Darja Andreev, Mengdan Liu, Daniela Weidner, Katerina Kachler, Maria Faas, Anika Grüneboom, Ursula Schlötzer-Schrehardt, Luis E. Muñoz, Ulrike Steffen, Bettina Grötsch, Barbara Killy, Gerhard Krönke, Andreas M. Luebke, Andreas Niemeier, Falk Wehrhan, Roland Lang, Georg Schett, Aline Bozec

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Figure 6

Mincle-KO mice show improved fracture healing.

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Mincle-KO mice show improved fracture healing. (A) Representative pictur...
(A) Representative pictures of H&E staining of femoral bone 14 days after fracture compared with healthy tibial bone at 14 weeks of age. Scale bars: 200 μm (left) and 100 μm (right). Quantification of filled lacunae (white arrows), dying osteocytes (orange arrows), and empty lacunae (red arrows) (n = 5/group). (B) Immunofluorescence (IF) staining for CD68 (green) and Mincle (red) and DAPI staining (blue) in unaffected tibial bones compared with fractured femoral bones. White arrows indicate Mincle-positive osteoclasts. Scale bar: 50 μm. (C) Quantification of Mincle-positive osteoclasts (OCs) (n = 7/group). (D) Representative μCT images of femoral bones of WT and Mincle-KO mice, 14 days after fracture at 14 weeks of age, showing the dorsal view and the thickness of the fracture callus. Black arrows show the fracture gap. Scale bar: 1 mm. (E) Light-sheet fluorescence microscopy (LSFM) of vascularization (CD31, red) in the callus (autofluorescence, gray) of the aforementioned 2 groups. Scale bar: 1 mm. (F) Quantification of BV/TV in the fracture callus of the aforementioned 2 groups (n = 12–13/group). (G) Representative TRAP staining in the bone callus of WT and Mincle-KO mice. Dark blue arrows indicate the purple-stained osteoclasts. Scale bar: 50 μm. (H) Histomorphometric quantification of Oc.S/BS and Oc.N/B.Pm in the hard callus of Mincle-KO compared with WT mice (n = 11/group). Data are shown as mean ± SD. P values were determined by 2-tailed Student’s t test for single comparisons (C, F, and H).