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Open AccessArticle

Impact of the Sensory and Sympathetic Nervous System on Fracture Healing in Ovariectomized Mice

1
Department of Orthopaedic Surgery, Experimental Orthopaedics, Centre for Medical Biotechnology (ZMB/Biopark 1), University of Regensburg, 93053 Regensburg, Germany
2
Institute of Pathology, University of Regensburg, 93053 Regensburg, Germany
3
Laboratory of Experimental Rheumatology and Neuroendocrine Immunology, Department of Internal Medicine I, University of Regensburg, 93053 Regensburg, Germany
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2020, 21(2), 405; https://doi.org/10.3390/ijms21020405
Received: 27 November 2019 / Revised: 23 December 2019 / Accepted: 31 December 2019 / Published: 8 January 2020
(This article belongs to the Special Issue Bone Growth and Osteoporosis)
The peripheral nervous system modulates bone repair under physiological and pathophysiological conditions. Previously, we reported an essential role for sensory neuropeptide substance P (SP) and sympathetic nerve fibers (SNF) for proper fracture healing and bone structure in a murine tibial fracture model. A similar distortion of bone microarchitecture has been described for mice lacking the sensory neuropeptide α-calcitonin gene-related peptide (α-CGRP). Here, we hypothesize that loss of SP, α-CGRP, and SNF modulates inflammatory and pain-related processes and also affects bone regeneration during fracture healing under postmenopausal conditions. Intramedullary fixed femoral fractures were set to 28 days after bilateral ovariectomy (OVX) in female wild type (WT), SP-, α-CGRP-deficient, and sympathectomized (SYX) mice. Locomotion, paw withdrawal threshold, fracture callus maturation and numbers of TRAP-, CD4-, CD8-, F4/80-, iNos-, and Arg1-positive cells within the callus were analyzed. Nightly locomotion was reduced in unfractured SP-deficient and SYX mice after fracture. Resistance to pressure was increased for the fractured leg in SP-deficient mice during the later stages of fracture healing, but was decreased in α-CGRP-deficient mice. Hypertrophic cartilage area was increased nine days after fracture in SP-deficient mice. Bony callus maturation was delayed in SYX mice during the later healing stages. In addition, the number of CD 4-positive cells was reduced after five days and the number of CD 8-positive cells was additionally reduced after 21 days in SYX mice. The number of Arg1-positive M2 macrophages was higher in α-CGRP-deficient mice five days after fracture. The alkaline phosphatase level was increased in SYX mice 16 days after fracture. Absence of α-CGRP appears to promote M2 macrophage polarization and reduces the pain threshold, but has no effect on callus tissue maturation. Absence of SP reduces locomotion, increases the pain-threshold, and accelerates hypertrophic callus tissue remodeling. Destruction of SNF reduces locomotion after fracture and influences bony callus tissue remodeling during the later stages of fracture repair, whereas pain-related processes are not affected. View Full-Text
Keywords: fracture; substance P; alpha-CGRP; sympathectomy; sympathetic nerve fibers; ovariectomy; sensory nervous system; bone repair; bone remodeling fracture; substance P; alpha-CGRP; sympathectomy; sympathetic nerve fibers; ovariectomy; sensory nervous system; bone repair; bone remodeling
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Niedermair, T.; Straub, R.H.; Brochhausen, C.; Grässel, S. Impact of the Sensory and Sympathetic Nervous System on Fracture Healing in Ovariectomized Mice. Int. J. Mol. Sci. 2020, 21, 405.

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