Transient muscle paralysis disrupts bone homeostasis by rapid degradation of bone morphology

Abstract

We have previously shown that transient paralysis of murine hindlimb muscles causes profound degradation of both trabecular and cortical bone in the adjacent skeleton within 3 weeks. Morphologically, the acute loss of bone tissue appeared to arise primarily due to osteoclastic bone resorption. Given that the loss of muscle function in this model is transient, we speculated that the stimulus for osteoclastic activation would be rapid and morphologic evidence of bone resorption would appear before 21 d. We therefore utilized high-resolution in vivo serial micro-CT to assess longitudinal alterations in lower hindlimb muscle volume, proximal tibia trabecular and tibia middiaphysis cortical bone morphology in 16 wk old female C57 mice following transient calf paralysis from a single injection of botulinum toxin A (BtA; 2U/100g body weight). In an acute study, we evaluated muscle and bone alterations at d 0, 3, 5 and 12 following transient calf paralysis. In a chronic study, following d 0 imaging, we assessed the recovery of these tissues following the maximum observed trabecular degradation (d 12) through d 84 post-paralysis. The time course and degree of recovery of muscle, trabecular and cortical bone varied substantially. Significant atrophy of lower limb muscle was evident by d 5 of paralysis, maximal at d 28 (−34.1 ± 0.9%) and partially recovered by d 84. Trabecular degradation within the proximal tibia metaphysis occurred more rapidly, with significant reduction in BV/TV by d 3, maximal loss at d 12 (−76.8 ± 2.9%) with only limited recovery by d 84 (−51.7 ± 5.1% vs. d 0). Significant cortical bone volume degradation at the tibia mid-diaphysis was first identified at d 12, was maximal at d 28 (−9.6 ± 1.2%), but completely recovered by d 84. The timing, magnitude and morphology of the observed bone erosion induced by transient muscle paralysis was consistent with a rapid recruitment and prolific activation of osteoclastic resorption. In a broader context, understanding how brief paralysis of a single muscle group can precipitate such rapid and profound bone resorption in an adjacent bone is likely to provide new insight into how normal muscle function modulates bone homeostasis.

Botulinum Toxin-induced Muscle Paralysis Inhibits Heterotopic Bone Formation

“…Given that current HO treatments such as radiation and nonsteroidal antiinflammatory drugs have potentially severe side effects [5,6,24], transient muscle paralysis and/or focal inhibition of neuromuscular signaling presents an alternative intervention with potential for preventing heterotopic bone after orthopaedic trauma. However, translation of this approach to the clinic will require a better understanding of the cellular mechanisms controlling muscle/bone/nerve interactions so that optimal inhibition of HO can be achieved while the potentially adverse effects of transient neuromuscular inhibition are minimized [2,23].…”

Notch Signaling in Osteocytes Differentially Regulates Cancellous and Cortical Bone Remodeling

“…Expression of NICD from the targeted Rosa26 locus occurs following the excision of the STOP cassette by Cre recombination of loxP sequences (35,36 Muscle Immobilization Protocol-The effect of muscle immobilization on the skeleton was tested in 1-month-old Dmp1-Cre ϩ/Ϫ ;Rosa Notch and littermate control male mice. For this purpose, control and experimental mice were injected with botulinum toxin A (BtxA) (Allergan Inc., Irvine, CA) at a dose of 2 units/100 g of body weight administered in equal amounts in the quadriceps and the triceps surae muscle groups or injected with saline under anesthesia using a ketamine/xylazine mixture intraperitoneally (37)(38)(39)(40). The contralateral limb was used as an internal control.…”

Pulsed focused ultrasound treatment of muscle mitigates paralysis-induced bone loss in the adjacent bone: A study in a mouse model

“…In our previous studies (Poliachik et al 2010), a serial time point design yielded much more consistent results, in which the affected limb was scanned before the experiment and at specific time points thereafter to assess bone changes within the limb. Therefore, the fact that in the present study one of the metrics of bone loss (BS/BV) reached statistical significance between Obtxand FUS-treated groups, and other metrics indicated a trend toward statistical significance, suggests that with a better choice of the control, the results may have reached statistical significance.…”

“…To model appendicular bone loss, we employed a mouse model of disuse using onabotulinumtoxinA (Obtx) to induce paralysis of the calf muscle, which results in rapid degradation of trabecular bone in the proximal tibia (Poliachik et al 2010;Warner et al 2006) This model has been found to reduce, but not remove, ground reaction forces in the affected limb (Manske et al 2011).The resulting maximum trabecular bone loss in this model occurs approximately 12 d after Obtx injection; an average of 77% trabecular bone volume was lost in C57B6 mice. Pulsed focused ultrasound (pFUS) mimicking physiologic muscle contraction rates or LIPUS frequency for fracture healing (1 kHz) (Azuma et al 2001;Leung et al 2004b) was applied to the calf muscle after paralysis in an attempt to mitigate the associated bone loss.…”