Lack of muscle recovery after immobilization in old rats does not result from a defect in normalization of the ubiquitin–proteasome and the caspase‐dependent apoptotic pathways

Abstract

Non-technical summary Immobilization periods increase with age because of decreased mobility and/or because of increased pathological episodes that require bed-rest. Then, sarcopaenia might be partially explained by an impaired recovery of skeletal muscle mass after a catabolic state due to an imbalance of muscle protein metabolism, apoptosis and cellular regeneration. Mechanisms involved during muscle recovery have been little studied and in elderly they remain almost unknown. We show, in rats, that a short immobilization period during ageing initiated muscle atrophy that was indeed not recovered after 40 days. Immobilization was associated with an activation of both the ubiquitin-proteasome and the mitochondria-associated apoptotic pathways and the inflammatory and redox processes, and a decrease of cellular regeneration. We show that the lack of muscle recovery during ageing is not due to a defect in proteolysis or apoptosis down-regulation. These observations lead us to hypothesize that muscle protein synthesis activation after immobilization was altered during ageing.Abstract Immobilization periods increase with age because of decreased mobility and/or increased pathological episodes that require bed-rest. Sarcopaenia might be partially explained by an impaired recovery of skeletal muscle mass after a catabolic state due to an imbalance of muscle protein metabolism, apoptosis and cellular regeneration. Mechanisms involved in muscle recovery have been poorly investigated, and remain almost unknown in the elderly. This study aimed at studying the regulation of the capsase-dependent apoptotic and the ubiquitin-proteasome-dependent proteolytic pathways during immobilization and subsequent recovery during ageing. Old rats (22-24-months old) were subjected to unilateral hindlimb casting for 8 days (I8) and allowed to recover for 10 to 40 days (R10 to R40). Immobilized gastrocnemius muscles atrophied by 21%, and did not recover even at R40. Apoptotic index, amount of polyubiquitinated conjugates, proteasome chymotrypsin-and trypsin-like, apoptosome-linked caspase-9, -3, and -8 activities increased at I8. Conversely, the amount of the myogenic factor myf-5 decreased at I8. These changes paralleled the increase of intramuscular inflammation and oxidative stress. All these parameters normalized as soon as R10. The XIAP/Smac-DIABLO protein ratio decreased by half in immobilized muscles and remained low during recovery. Surprisingly, the non-immobilized leg also atrophied from R20, concomitantly with a decreased XIAP/Smac-DIABLO protein ratio. Altogether, this suggests that the impaired recovery following immobilization in ageing does not result from a lack of normalization of the caspase-dependent * Both authors contributed equally to this work. apoptotic and the ubiquitin-proteasome-dependent pathways, and also that immobilization could induce a general muscle loss and then contribute to the development of sarcopaenia in elderly.(

The worsening of tibialis anterior muscle atrophy during recovery post-immobilization correlates with enhanced connective tissue area, proteolysis, and apoptosis

“…eration processes (12,17,35,46,47). By contrast, the mechanisms responsible for muscle recovery after remobilization are poorly defined.…”

“…Sustained muscle wasting due to immobilization leads to weakening and severe metabolic consequences, which impacts health care costs. This wasting has been investigated thoroughly and results from an imbalance between protein synthesis and breakdown rates but also between apoptotic and regeneration processes (12,17,35,46,47). By contrast, the mechanisms responsible for muscle recovery after remobilization are poorly defined.…”

“…Briefly, in this pathway a poly-Ub chain is covalently attached to the substrate by the Ub conjugation machinery, and the targeted protein is then recognized and degraded by the 26S proteasome (4). This pathway is activated after immobilization or unloading in atrophying muscles from animals (2,25,35,45,46) or humans (23,28,41).…”

“…Briefly, in this pathway a poly-Ub chain is covalently attached to the substrate by the Ub conjugation machinery, and the targeted protein is then recognized and degraded by the 26S proteasome (4). This pathway is activated after immobilization or unloading in atrophying muscles from animals (2,25,35,45,46) or humans (23,28,41).The muscle-specific ubiquitin ligases (E3) muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx)/atrogin-1 play key roles in disuse induced-muscle atrophy (7). In addition, MuRF1 is involved in the ubiquitination of the major contractile proteins such as actin and myosins (13,14,40).…”

Evaluation of Mitochondrial Functions and Dysfunctions in Muscle Biopsy Samples

“…As previously mentioned, subsarcolemmal and intermyofibrillar mitochondria display different susceptibility towards apoptotic stimuli . Mitochondria may therefore be involved in the pathogenesis of muscle atrophy, in obesity and type 2 diabetes or in response to short-term immobilisation in ageing individuals (Kim et al, 2010;Magne et al, 2011).…”