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 4

DAMP/Mincle axis skews metabolic activity of osteoclasts to oxidative phosphorylation and directs osteoclast migration.

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DAMP/Mincle axis skews metabolic activity of osteoclasts to oxidative ph...
(A) Oxygen consumption rate (OCR) profile plot and (B) mitochondrial function parameters analyzed by extracellular flux assay in osteoclasts from WT and Mincle-KO mice, which were supplemented with necrotic osteocyte (Ot) supernatant (1:2) for 24 hours on day 1 of culture, compared with nonsupplemented controls (n = 4/group). A&R, antimycin A and rotenone. (C) Gene expression analysis of metabolic markers Pgk1, Sdha, Sdhb, Sdhc, and Sdhd in osteoclasts from WT and Mincle-KO mice, which were supplemented with necrotic osteocytes (1:2) for 24 hours on day 1 of culture, compared with controls (n = 4/group). (D) Transmission electron microscopy (TEM) images of WT and Mincle-KO osteoclasts, supplemented on day 1 for 24 hours with necrotic osteocytes (1:2), compared with nonsupplemented controls. Yellow arrows show mitochondrial cristae within the cells. Scale bars: 2.6 μm (low-power images, left columns) and 1.21 μm (high-power images, right columns). (E) 3D track plots of the recorded movement of WT and Mincle-KO osteoclasts within 500 minutes (recorded every 5 minutes) after stimulation with necrotic osteocytes. Black arrows show necrotic osteocytes. (F) Percentage of WT and Mincle-KO osteoclasts moving toward necrotic osteocytes in a directed way or moving without direction (n = 15/group). Data are shown as mean ± SD. P values were determined by 2-way ANOVA for multiple comparisons (B and C; interaction P value: 0.7410 for B and <0.0001 for C).