Regulation of the ubiquitin proteasome system in mechanically injured human skeletal muscle

Abstract

Metabolic consequences of direct muscle trauma are insufficiently defined. Their effects on the ubiquitin-proteasome pathway (UPP) of protein degradation in human skeletal muscles are as yet unknown. Thus, we investigated whether the UPP is involved in the metabolic response evoked in directly traumatized human skeletal muscles. Biopsies were obtained from contused muscles after fractures and from normal muscles during elective implant removal (control). As estimated by western blot analyses, concentrations of free ubiquitin and ubiquitin protein conjugates were similar in extracts from injured and uninjured muscles. Ubiquitin protein ligation rates were reduced after injury (1.5+/-0.2 vs. 1.0+/-0.15 fkat/microg; p=0.04). Chymotryptic-, tryptic- and caspase-like proteasome peptidase activities (total activity minus activity in the presence of proteasome inhibitors) increased significantly after trauma (p=0.04 - 0.001). Significant increases in total chymotryptic- and caspase-like activities were attributable to proteasome activation. Our results extend the possible role of the UPP in muscle wasting to direct muscle trauma. They further suggest that the effects of direct mechanical trauma are not limited to the proteasome and imply that ubiquitin protein ligase systems are also involved. Based on the potential role of the UPP in systemic diseases, it might also be a therapeutic target to influence muscle loss in critically ill blunt trauma patients, in which large proportions of muscle are exposed to direct trauma.

Tourniquet-induced ischaemia during total knee arthroplasty results in higher proteolytic activities within vastus medialis cells: a randomized clinical trial

“…The principal findings of the present study were that the proteasome-dependent and proteasome-independent peptidase activities were statistically significantly higher during tourniquet-induced 60-min ischaemia as compared to the non-tourniquet group, suggesting an activation of the molecular cascade of muscle protein degradation, which might explain muscle atrophy after TKA. These results were based on a human model of skeletal muscle ischaemia and did not find to be meaningfully comparable to the previously published data about directly traumatized human [30] and/or rat skeletal muscle [27]. This can mainly be explained due to differences in the study design and experimental setting.…”

“…Mean and standard deviation (SD) were calculated for demographics and standard error of the mean (SEM) for the biochemical data. The power analysis (a priori) was performed based on previously published data [30]. The power analysis (post hoc) considered an effect size of 0.4.…”

“…The present study included irreversible selective proteasome inhibitors such as epoxomicin and ADA. For the purpose of quantification of proteasomedependent/proteasome-independent peptidase activities, the application of epoxomicin and ADA found to be reliable [15,26,27,30]. The high regulation of cytosolic Ub is considered essential for the cell metabolism [1,7,24].…”

“…The exact mechanism of the reduced ubiquitination rate and their clinical significance were not yet defined. However, reduction in the ubiquitination rate assumed to be a regulatory cell response to inflammation in general, aiming to limit protein degradation [30]. While the main scientific interest focused on the ubiquitination process [29], the implication of the deubiquitinating enzymes in skeletal muscles subjected to ischaemia remained unclear.…”

“…Numerous proteolytic systems found to exist and interplay in a sophisticated manner [30]. Ubiquitin proteasome system (UPS) represents one of the main pathways upregulated in catabolic conditions to breakdown muscle proteins promoting muscle loss.…”