Introduction: 

The small ubiquitin related protein "SUMO" modifies target protein functions via post-translational modification and regulates cellular integrity. Sumoylation is triggered in vivo by stressors like oxidative stress but also acute hypoxia. Exercise induced myocellular adaptation requires a complex network of nuclear protein shuttling as well as post-translational modification of proteins and thus may include also the SUMO system as acute modulator of loaded skeletal muscle. Study objectives: It was aimed to investigate whether SUMO-1 is involved in the early response towards exercise in sarcoplasmatic and myonuclear compartments of loaded skeletal muscle myofibers.

Methods: 

6 healthy male subjects (age: 23±4 years; height: 180±8 cm; weight: 79±10 kg) performed 1 single set of 20 maximum eccentric and concentric isokinetic knee extensions. PRE, 15, 30, 60, 240 min and 24h after exercise (EX) muscle biopsies were taken from vastus lateralis muscle. DAB and Fluorescence staining was performed on 7mm cross-sections of skeletal muscle. The density and sub-cellular localization of SUMO-1 in sarcoplasmatic and nuclear compartments of type I and II myofibers were determined via optical densitometry and confocal laser microscopy as well as in whole skeletal muscle lysates by western blotting.

Results: 

Sarcoplasmatic SUMO-1 density was higher in type I than in type II myofibers (p<0.05) PRE exercise, increased 15 to 30 min POST EX significantly (p<0.01) in both fiber types but returning to PRE levels within 60 min. SUMO-1 positive nuclear areas increased significant (p<0.01) from PRE values within 15 min up to 60 min post EX but returning below PRE levels within 24 hours. Confocal microscopy offered a predominant sub cellular localization of SUMO-1 towards the nuclear envelope at baseline and 24h post EX. Western blotting offered substantial changes in the pattern of SUMO-1 positive bands within the first hour POST EX.

Conclusion: 

The present investigation reveals time dependent changes in SUMO-1 density in nuclear and sarcoplasmatic compartments of human skeletal muscle fibers as early response towards high intense resistance exercise. This modulation offers a potential role of the SUMO system in myocellular adaptation towards acute exercise induced stress but also in recurring homeostasis.