gms | German Medical Science

Objectives: Disorders of central or peripheral nerves can have substantial influence on bone health, repair and regeneration. Previously, we reported impaired biomechanical bone properties and inferior bone matrix quality in tachykinin1 (Tac1)-deficient mice lacking the sensory neuropeptide substance P (SP). Additionally, fracture callus development is affected by the absence of SP indicating a critical effect of sensory nerve fibers on bone health and regeneration. A similar distortion of bone microarchitecture has been described for α-calcitonin gene-related peptide (α-CGRP)-deficient mice. We hypothesize that sensory neuropeptides SP and α-CGRP modulate inflammatory as well as pain-related processes and affect bone regeneration during osteoporotic fracture healing. Therefore, this study investigates the effects of SP and α-CGRP on fracture healing and fracture-related pain processes under conditions of experimental osteoporosis using SP- and α-CGRP-deficient mice and WT controls.

Methods: Ovariectomy was performed in female WT, Tac1-/- and α-CGRP-/- mice (age 8-9 weeks) (all strains are C57Bl/6J), intramedullary fixed femoral fractures were set in the left femora 28 days later. Pain threshold (Dynamic Plantar Aesthesiometer Test for touch sensibility; Ugo Basile) and locomotion (recorded at daylight/night for 1 hour, Software: EthoVision®XT; Noldus Information Technology) were analyzed at 5, 9, 13, 16 and 21 days after fracture. At each time point, fractured femora were fixed, decalcified and embedded in paraffin for histochemical analysis of callus tissue composition (alcian blue/sirius red staining).

Results and conclusion: Pain threshold tends to be higher in Tac1-/- mice 13 and 21 days after fracture compared to WT controls. We did not measure significant differences regarding touch sensibility between α-CGRP-/- mice and WT controls but pain threshold was significantly lower in α-CGRP-/- mice 13 and 16 days after fracture when compared to Tac1-/- mice. Locomotion of Tac1-/- mice during daylight was by trend higher 9 days after fracture and significantly higher 16 days after fracture whereas nightly locomotion is reduced compared to WT mice. Analysis of locomotion during daylight or night revealed no differences between α-CGRP-/- and WT mice. During early fracture healing phase, 5 and 9 days after fracture, transition of mesenchymal to cartilaginous callus tissue seems to be faster in α-CGRP-/- mice compared to WT controls. In contrast, fracture callus tissue composition seems to be similar in Tac1-/- and WT mice.

Our data indicate that sensory neuropeptides SP and α-CGRP exert different effects on fracture healing under conditions of experimental osteoporosis. We found differences in locomotion and fracture-related pain processes in the absence of SP during late phases of osteoporotic fracture healing whereas lack of α-CGRP seems to play a more important role in callus maturation during the early phases of osteoporotic fracture healing.