Fracture repair requires TrkA signaling by skeletal sensory nerves
Zhu Li, … , Thomas L. Clemens, Aaron W. James
Zhu Li, … , Thomas L. Clemens, Aaron W. James
Published October 22, 2019
Citation Information: J Clin Invest. 2019;129(12):5137-5150. https://doi.org/10.1172/JCI128428.
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Research Article Bone biology

Fracture repair requires TrkA signaling by skeletal sensory nerves

Abstract

Bone is richly innervated by nerve growth factor–responsive (NGF-responsive) tropomyosin receptor kinase A–expressing (TrKa-expressing) sensory nerve fibers, which are required for osteochondral progenitor expansion during mammalian skeletal development. Aside from pain sensation, little is known regarding the role of sensory innervation in bone repair. Here, we characterized the reinnervation of tissue following experimental ulnar stress fracture and assessed the impact of loss of TrkA signaling in this process. Sequential histological data obtained in reporter mice subjected to fracture demonstrated a marked upregulation of NGF expression in periosteal stromal progenitors and fracture-associated macrophages. Sprouting and arborization of CGRP+TrkA+ sensory nerve fibers within the reactive periosteum in NGF-enriched cellular domains were evident at time points preceding periosteal vascularization, ossification, and mineralization. Temporal inhibition of TrkA catalytic activity by administration of 1NMPP1 to TrkAF592A mice significantly reduced the numbers of sensory fibers, blunted revascularization, and delayed ossification of the fracture callus. We observed similar deficiencies in nerve regrowth and fracture healing in a mouse model of peripheral neuropathy induced by paclitaxel treatment. Together, our studies demonstrate an essential role of TrkA signaling for stress fracture repair and implicate skeletal sensory nerves as an important upstream mediator of this repair process.

Authors

Zhu Li, Carolyn A. Meyers, Leslie Chang, Seungyong Lee, Zhi Li, Ryan Tomlinson, Ahmet Hoke, Thomas L. Clemens, Aaron W. James

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Figure 4

TrkA+CGRP+ sensory nerve sprouting after stress fracture.

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TrkA+CGRP+ sensory nerve sprouting after stress fracture. (A and B) TUBB...
(A and B) TUBB3 whole-mount immunohistochemical staining of the ulnar periosteum before and 6 hours after stress fracture. White dashed lines indicate the fracture site. (C–I) Tile scans and high-magnification images of ulnar fracture calluses in Thy1-YFP reporter animals, with reporter activity shown in green using Imaris surface renderings. (C) Uninjured control. (D–I) Fracture callus on days 3, 7, 14, 28, and 56 after injury. The thin dashed white line represents the uppermost boundary of the periosteum or fracture callus. The thick dashed white line represents the boundary between the periosteum or fracture callus and the underlying cortical bone. White arrowheads indicate the fracture site. (J) Quantification of Thy1-YFP reporter activity from days 1–56 after fracture, indicated as a volumetric measure of YFP reporter activity. (K and L) Representative images of CGRP and TH immunohistochemical detection (yellow) in uninjured periosteum from Thy1-YFP reporter (green) animals. (M and N) CGRP immunohistochemical detection (yellow) and (O) quantification on days 3 and 14 after fracture. (P and Q) TH immunohistochemical detection (yellow) and (R) quantification ons day 3 and 14 after fracture. In the graphs, each dot represents a single sample, with the sample numbers indicated below. Scale bars: 50 μm and 20 μm (insets). Data are expressed as the mean ± SD. ††P < 0.01 versus the uninjured control; ##P < 0.01 versus the day-1 time point, by 1-way ANOVA with post hoc Newman-Keuls test.