Pathophysiology Aspects of Muscle Atrophy and Osteopenia Induced by Chronic Constriction Injury (CCI) of the Sciatic Nerve in Rat
Authors: Bosco Francesca , Guarnieri Lorenza , Nucera Saverio , Scicchitano Miriam , Ruga Stefano , Cardamone Antonio , Maurotti Samantha , Russo Cristina , Coppoletta Anna Rita , Macrì Roberta , Bava Irene , Scarano Federica , Castagna Fabio , Serra Maria , Caminiti Rosamaria , Maiuolo Jessica , Ilari Sara , Lauro Filomena , Giancotti Luigino Antonio , Muscoli Carolina , Carresi Cristina , Palma Ernesto , Gliozzi Micaela , Musolino Vincenzo , Mollace Vincenzo 
Published: March 2022

Abstract
BackgroundSkeletal muscle atrophy is a condition characterized by a loss of muscle mass and muscle strength. This condition correlates with an imbalance between protein synthesis and protein degradation caused by the hyperactivation of some cellular catabolic pathways. Muscle and bone interact through physical forces and chemical pathways and muscle atrophy is often associated with a loss of bone mass manifesting as osteoporosis. The aim of this study was to evaluate if Chronic Constriction Injury (CCI) of sciatic nerve can be a valid model to study muscle atrophy and consequent osteoporosis.MethodsIn this study the effects of CCI performed on sciatic nerve were tested in rat. Body weight and body composition were assessed at baseline and once per week till the end of the study. Magnetic resonance imaging (MRI) was performed at day zero before ligation and at day 28 before sacrifice. On gastrocnemius muscles catabolic markers were assessed by western blot analysis and a morphological analysis of cross-sectional area of muscle fibers was performed by hematoxylin and eosin staining. After the sacrifice a Micro-Computed Tomography (Micro-CT) on the tibia bone was performed and bone calcium content was determined. Quantitative Real Time PCR was performed on both bone and muscle tissue to quantify expression levels of genes involved in osteopenia and muscle atrophy.ResultsRats underwent to CCI had a lower body weight increase at day 28 compared to the naive group of rats (p < 0.001). The increase in lean body mass and fat mass was also significantly lower in CCI group, compared with the non-operated control rats (p < 0.001). The weights of the skeletal muscle were significantly lower in the ipsilateral hindlimb compared to contralateral muscles; furthermore, the cross-sectional area of muscle fibers decreased significantly in the ipsilateral gastrocnemius. The CCI of the sciatic nerve induced a statistically significant increase of Autophagic and UPS markers protein expression and mRNA expression levels of fbx32 and of TRAF-6 resulted also higher in ipsilateral gastrocnemius. Western blotting analysis showed a statistically significant increase of Pax-7 expression in the ipsilateral GC of rats 28 days after surgery, compared to the contralateral gastrocnemius muscle. Micro-CT showed a statistically significant decrease in the parameters of bone mineral density, bone volume fraction, bone surface density, trabecular number, connectivity density, and bone perimeter of the tibial bone on the ipsilateral hindlimb rather than contralateral tibial bone, whereas the structure model index was significantly higher at 28 days after the surgery. Gene expression levels of TRAF-6 resulted significantly up-regulated in ipsilateral femur.ConclusionsIn this study, chronic nerve constriction appeared to be a valid model for inducing the condition of muscle atrophy causing also changes in bone microstructure and leading to osteoporosis. Therefore, sciatic nerve constriction could be a valid approach to study the muscle-bone crosstalk, and to identify new strategies to prevent osteosarcopenia.