Fracture repair requires TrkA signaling by skeletal sensory nerves
Zhu Li, Carolyn A. Meyers, Leslie Chang, Seungyong Lee, Zhi Li, Ryan Tomlinson, Ahmet Hoke, Thomas L. Clemens, Aaron W. James
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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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 6

Inhibition of TrkA catalytic activity and its effects on stress fracture healing.

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Inhibition of TrkA catalytic activity and its effects on stress fracture...
(A–F) μCT images of ulnar stress fracture healing in TrkAF592A Thy1-YFP mice treated with 1NMPP1 or vehicle control on (A–C) day 7 and (D–F) day 14 after injury. (A) μCT reconstructions, (B) coronal cross-sectional images, and (C) axial cross-sectional images. (G–I) Quantitative μCT analysis of stress fractures in TrkAF592A Thy1-YFP mice on days 7 and 14 after injury. (G) BV, (H) TV, and (I) BMD of callus. (J–M) Thy1-YFP reporter activity in TrkAF592A Thy1-YFP mice treated with (J and L) vehicle control or (K and M) 1NMPP1, as seen on day 7 after injury. Tile scans and high-magnification images are shown. The thin dashed white line indicates the uppermost boundary of the fracture callus. The thick dashed white line represents the boundary between the fracture callus and the underlying cortex. White arrowheads indicate the fracture site. (N) Quantification of Thy1-YFP reporter activity on days 7 and 14 after injury. (O–R) CD31 immunohistochemical staining of tissue from TrkAF592A Thy1-YFP mice treated with (O and Q) vehicle control or (P and R) 1NMPP1, on day 7 after injury. Tile scans and high-magnification images are shown. (S) Quantification of CD31 immunohistochemical staining, 7 and 14 days after injury. (T and U) High-magnification images of ALP staining of tissue from TrkAF592A Thy1-YFP mice treated with (T) vehicle control or (U) 1NMPP1, on day 7 after injury. (V) Quantification of ALP staining intensity, on day 7 after injury. For all graphs, each dot represents a single sample, with sample numbers indicated below. Scale bars: 500 μm (A and D), 1 mm (B, C, E, and F), 50 μm (J–R), 25 μm (enlarged insets in A–R, T and U). Data are expressed as the mean ± SD. †P < 0.05 versus the vehicle control at the corresponding time point, by 2-tailed Student’s t test.