Tendon-derived cathepsin K–expressing progenitor cells activate Hedgehog signaling to drive heterotopic ossification
Heng Feng, … , Qing Bi, Weiguo Zou
Heng Feng, … , Qing Bi, Weiguo Zou
Published August 27, 2020
Citation Information: J Clin Invest. 2020;130(12):6354-6365. https://doi.org/10.1172/JCI132518.
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Tendon-derived cathepsin K–expressing progenitor cells activate Hedgehog signaling to drive heterotopic ossification

Abstract

Heterotopic ossification (HO) is pathological bone formation characterized by ossification within muscle, tendons, or other soft tissues. However, the cells of origin and mechanisms involved in the pathogenesis of HO remain elusive. Here we show that deletion of suppressor of fused (Sufu) in cathepsin K–Cre–expressing (Ctsk-Cre–expressing) cells resulted in spontaneous and progressive ligament, tendon, and periarticular ossification. Lineage tracing studies and cell functional analysis demonstrated that Ctsk-Cre could label a subpopulation of tendon-derived progenitor cells (TDPCs) marked by the tendon marker Scleraxis (Scx). Ctsk+Scx+ TDPCs are enriched for tendon stem cell markers and show the highest self-renewal capacity and differentiation potential. Sufu deficiency caused enhanced chondrogenic and osteogenic differentiation of Ctsk-Cre–expressing tendon-derived cells via upregulation of Hedgehog (Hh) signaling. Furthermore, pharmacological intervention in Hh signaling using JQ1 suppressed the development of HO. Thus, our results show that Ctsk-Cre labels a subpopulation of TDPCs contributing to HO and that their cell-fate changes are driven by activation of Hh signaling.

Authors

Heng Feng, Wenhui Xing, Yujiao Han, Jun Sun, Mingxiang Kong, Bo Gao, Yang Yang, Zi Yin, Xiao Chen, Yun Zhao, Qing Bi, Weiguo Zou

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Figure 2

Ctsk-Cre–expressing cells in tendons and ligaments contribute to HO.

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Ctsk-Cre–expressing cells in tendons and ligaments contribute to HO. (A...
(A) Schematic of the Ctsk-Cre Rosa26-Ai9 reporter mice. (B) Confocal images of hind limbs from Ctsk-Cre Rosa26-Ai9 mice showing Ctsk expression in the cells of the Achilles tendon, patellar tendon, and quadriceps tendon. Scale bars: 50 μm. (C) Immunofluorescence showing Ctsk+ (Ai9+) cells in the Achilles tendon of 6-week-old Ctsk-CKO Rosa26-Ai9 mice displays the chondrogenic marker COLII (green) and the osteogenic marker OPN (green). Scale bars: 50 μm (left panels); 25 μm (right panels). (D) Quantitative analysis of the percentage of Ctsk+ (Ai9+) cells that express the chondrogenic marker COLII in Achilles tendons. n = 4 per group. (E) Quantitative analysis of the percentage of Ctsk+ (Ai9+) cells that express the osteogenic marker OPN in Achilles tendons. n = 4 per group. (F–I) qRT-PCR analysis of Hh target gene (F), chondrogenic gene (G), osteogenic gene (H), and tendon-related gene (I) expression in sorted Ctsk+ Achilles tendon cells from 6-week-old Ctsk-CKO Rosa26-Ai9 mice compared with Ctsk-Ctrl Rosa26-Ai9 mice. n = 3 per group. (J and K) Immunofluorescence showing Ctsk+Scx+ (orange) cells in the Achilles tendon of 6-week-old Ctsk-CKO Rosa26-Ai9 ScxGFP mice displays the chondrogenic marker COLII and aggrecan (gray). Scale bars: 20 μm. Results are presented as the mean ± SEM; unpaired t test, *P < 0.05, **P < 0.01, ***P < 0.001.