The Proprioceptive System Regulates Morphologic Restoration of Fractured Bones

Publication date: 22 August 2017
Source:Cell Reports, Volume 20, Issue 8
Author(s): Ronen Blecher, Sharon Krief, Tal Galili, Eran Assaraf, Tomer Stern, Yoram Anekstein, Gabriel Agar, Elazar Zelzer
Successful fracture repair requires restoration of bone morphology and mechanical integrity. Recent evidence shows that fractured bones of neonatal mice undergo spontaneous realignment, dubbed "natural reduction." Here, we show that natural reduction is regulated by the proprioceptive system and improves with age. Comparison among mice of different ages revealed, surprisingly, that 3-month-old mice exhibited more rapid and effective natural reduction than newborns. Fractured bones of null mutants for transcription factor Runx3, lacking functional proprioceptors, failed to realign properly. Blocking Runx3 expression in the peripheral nervous system, but not in limb mesenchyme, recapitulated the null phenotype, as did inactivation of muscles flanking the fracture site. Egr3 knockout mice, which lack muscle spindles but not Golgi tendon organs, displayed a less severe phenotype, suggesting that both receptor types, as well as muscle contraction, are required for this regulatory mechanism. These findings uncover a physiological role for proprioception in non-autonomous regulation of skeletal integrity.

Graphical abstract

Teaser

Blecher et al. report that natural reduction, the process whereby fractured bones are realigned, fails in mutant mice lacking functional proprioceptive circuitry. Surprisingly, natural reduction was more rapid and effective in 3-month-old mice than in newborns. These findings suggest a physiological role for proprioception in non-autonomous regulation of skeletal integrity.


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