Inhibition of calpain delays early muscle atrophy after rotator cuff tendon release in sheep.

Severin Ruoss,Sara Abdel-Aziz,Christian Gerber,Linus Oberholzer,Ladina Jungck,Philipp Kindt,Andrea B Rosskopf,Brigitte Von Rechenberg,Karl Wieser,Martin Flück,Karina Klein,Marco Rohner,Daniel Fitze

doi:10.14814/phy2.13833

Abstract

Chronic rotator cuff (RC) tears are characterized by retraction, fat accumulation, and atrophy of the affected muscle. These features pose an intractable problem for surgical repair and subsequent recovery, and their prevention may be easier than reversal. Using an established ovine model, we tested the hypothesis that inhibition of the protease calpain mitigates m. infraspinatus atrophy by preservation of the myofibers’ structural anchors in the sarcolemma (the costameres). Already 2 weeks of distal tendon release led to a reduction in muscle volume (−11.6 ± 9.1 cm3, P = 0.038) and a 8.3% slow‐to‐fast shift of the fiber area (P = 0.046), which were both entirely abolished by chronic local administration of the calpain inhibitor calpeptin alone, and in combination with sildenafil. Calpain inhibition blunted the retraction of the muscle‐tendon unit by 0.8–1.0 cm (P = 0.020) compared with the control group, and prevented cleavage of the costameric protein talin. Calpain 1 and 2 protein levels increased in the medicated groups after 4 weeks, counteracting the efficacy of calpeptin. Hence atrophic changes emerged after 4 weeks despite ongoing treatment. These findings suggest that the early muscular adaptations in the specific case of RC tear in the ovine model are indistinguishable from the atrophy and slow‐to‐fast fiber transformation observed with conventional unloading and can be prevented for 2 weeks. Concluding, calpain is a potential target to extend the temporal window for reconstruction of the ruptured RC tendon before recovery turns impossible.

Highlights

Chronic rotator cuff (RC) tendon tears are among the most frequent causes of shoulder dysfunction (Milgrom et al 1995; Sher et al 1995) leading to various functional deficits including weakness and limited range of motion (Duckworth et al 1999)
30 min, 2, 4, and 6 weeks after tendon release revealed that calpeptin administration prevented muscle atrophy for 2 weeks while muscle volume was lost in the CONTROL group (À11.6 Æ 9.1 cm3, P = 0.038; Fig. 1A)
We found that inhibition of the calcium-activated protease calpain counteracted costamere cleavage and delayed muscle atrophy, retraction, and slow-to-fast phenotype shift until counter-regulation took place by increased calpain 1 + 2 protein levels

Summary

Introduction

Chronic rotator cuff (RC) tendon tears are among the most frequent causes of shoulder dysfunction (Milgrom et al 1995; Sher et al 1995) leading to various functional deficits including weakness and limited range of motion (Duckworth et al 1999). Loss of contractile tissue leads to both radial and longitudinal atrophy, the latter leading to the clinical phenomenon of “myotendinous retraction” which is related to serial removal of sarcomeres from myofibrils (Jamali et al 2000; Ward et al 2010) This process is initiated by specific Ca2+-activated proteases, the calpains, which release sarcomeres by attacking their structural anchors at the Z-disk so that they can be quantitatively degraded by the proteasome (Bullard et al 1990; Alderton and Steinhardt 2000; Tidball and Spencer 2002; Goll et al 2008; Shenkman et al 2015). Inhibition of calpain activity with calpeptin and the NO promoter sildenafil decreases costamere cleavage and muscle atrophy and myotendinous retraction

Ethical approval

Results

Discussion